Science.gov

Sample records for rainforest boundary dynamics

  1. A tropical rainforest in Colorado 1.4 million years after the Cretaceous-Tertiary boundary.

    PubMed

    Johnson, Kirk R; Ellis, Beth

    2002-06-28

    An extremely diverse lower Paleocene (64.1 million years ago) fossil leaf site from Castle Rock, Colorado, contains fossil litter that is similar to the litter of extant equatorial rainforests. The presence of a high-diversity tropical rainforest is unexpected, because other Paleocene floras are species-poor, a feature generally attributed to the Cretaceous-Tertiary (K-T) extinction. The site occurs on the margin of the Denver Basin in synorogenic sedimentary rocks associated with the rise of the Laramide Front Range. Orographic conditions caused by local topography, combined with equable climate, appear to have allowed for the establishment of rainforests within 1.4 million years of the K-T boundary.

  2. Long-term dynamics of a fragmented rainforest mammal assemblage.

    PubMed

    Laurance, William F; Laurance, Susan G; Hilbert, David W

    2008-10-01

    Habitat fragmentation is a severe threat to tropical biotas, but its long-term effects are poorly understood. We evaluated longer-term changes in the abundance of larger (>1 kg) mammals in fragmented and intact rainforest and in riparian "corridors" in tropical Queensland, with data from 190 spotlighting surveys conducted in 1986-1987 and 2006-2007. In 1986-1987 when most fragments were already 20-50 years old, mammal assemblages differed markedly between fragmented and intact forest. Most vulnerable were lemuroid ringtail possums (Hemibelideus lemuroides), followed by Lumholtz's tree-kangaroos (Dendrolagus lumholtzi) and Herbert River ringtail possums (Pseudocheirus herbertensis). Further changes were evident 20 years later. Mammal species richness fell significantly in fragments, and the abundances of 4 species, coppery brushtail possums (Trichosurus vulpecula johnstoni), green ringtail possums (Pseudochirops archeri), red-legged pademelons (Thylogale stigmatica), and tree-kangaroos, declined significantly. The most surprising finding was that the lemuroid ringtail, a strict rainforest specialist, apparently recolonized one fragment, despite a 99.98% decrease in abundance in fragments and corridors. A combination of factors, including long-term fragmentation effects, shifts in the surrounding matrix vegetation, and recurring cyclone disturbances, appear to underlie these dynamic changes in mammal assemblages.

  3. Open boundary molecular dynamics

    NASA Astrophysics Data System (ADS)

    Delgado-Buscalioni, R.; Sablić, J.; Praprotnik, M.

    2015-09-01

    This contribution analyzes several strategies and combination of methodologies to perform molecular dynamic simulations in open systems. Here, the term open indicates that the total system has boundaries where transfer of mass, momentum and energy can take place. This formalism, which we call Open Boundary Molecular Dynamics (OBMD), can act as interface of different schemes, such as Adaptive Resolution Scheme (AdResS) and Hybrid continuum-particle dynamics to link atomistic, coarse-grained (CG) and continuum (Eulerian) fluid dynamics in the general framework of fluctuating Navier-Stokes equations. The core domain of the simulation box is solved using all-atom descriptions. The CG layer introduced using AdResS is located at the outer part of the open box to make feasible the insertion of large molecules into the system. Communications between the molecular system and the outer world are carried out in the outer layers, called buffers. These coupling preserve momentum and mass conservation laws and can thus be linked with Eulerian hydro- dynamic solvers. In its simpler form, OBMD allows, however, to impose a local pressure tensor and a heat flux across the system's boundaries. For a one component molecular system, the external normal pressure and temperature determine the external chemical potential and thus the independent parameters of a grand-canonical ensemble simulation. Extended ensembles under non-equilibrium stationary states can also be simulated as well as time dependent forcings (e.g. oscillatory rheology). To illustrate the robustness of the combined OBMD-AdResS method, we present simulations of star-polymer melts at equilibrium and in sheared flow.

  4. Tropical Rainforests.

    ERIC Educational Resources Information Center

    Nigh, Ronald B.; Nations, James D.

    1980-01-01

    Presented is a summary of scientific knowledge about the rainforest environment, a tropical ecosystem in danger of extermination. Topics include the current state of tropical rainforests, the causes of rainforest destruction, and alternatives of rainforest destruction. (BT)

  5. Recruitment dynamics in a rainforest seedling community: context-independent impact of a keystone consumer.

    PubMed

    Green, Peter T; O'Dowd, Dennis J; Lake, P S

    2008-05-01

    The influence of keystone consumers on community structure is frequently context-dependent; the same species plays a central organising role in some situations, but not others. On Christmas Island, in the Indian Ocean, a single species of omnivorous land crab, Gecarcoidea natalis, dominates the forest floor across intact rainforest. We hypothesised that this consumer plays a key role in regulating seedling recruitment and in controlling litter dynamics on the island, independent of the type of vegetation in which it occurred. To test this hypothesis, we conducted crab exclusion experiments in two forest types on the island and followed the dynamics of seedling recruitment and litter processing for six years. To determine if these effects were likely to be general across the island, we compared land crab densities and seedling abundance and diversity at ten sites across island rainforest. Surveys across island rainforest showed that seedlings of species susceptible to predation by land crabs are consistently rare. Abundance and diversity of these species were negatively correlated to red crab abundance. Although red land crabs may be important determinants of seedling recruitment to the overstorey, differences in overstorey and seedling composition at the sites suggests that recruitment of vulnerable trees still occurs at a temporal scale exceeding that of this study. These "windows" of recruitment may be related to infrequent events that reduce the effects of land crabs. Our results suggest that unlike the context dependence of most keystone consumers in continental systems, a single consumer, the red land crab, consistently controls the dynamics of seedling recruitment across this island rainforest. PMID:18320231

  6. Recruitment dynamics in a rainforest seedling community: context-independent impact of a keystone consumer.

    PubMed

    Green, Peter T; O'Dowd, Dennis J; Lake, P S

    2008-05-01

    The influence of keystone consumers on community structure is frequently context-dependent; the same species plays a central organising role in some situations, but not others. On Christmas Island, in the Indian Ocean, a single species of omnivorous land crab, Gecarcoidea natalis, dominates the forest floor across intact rainforest. We hypothesised that this consumer plays a key role in regulating seedling recruitment and in controlling litter dynamics on the island, independent of the type of vegetation in which it occurred. To test this hypothesis, we conducted crab exclusion experiments in two forest types on the island and followed the dynamics of seedling recruitment and litter processing for six years. To determine if these effects were likely to be general across the island, we compared land crab densities and seedling abundance and diversity at ten sites across island rainforest. Surveys across island rainforest showed that seedlings of species susceptible to predation by land crabs are consistently rare. Abundance and diversity of these species were negatively correlated to red crab abundance. Although red land crabs may be important determinants of seedling recruitment to the overstorey, differences in overstorey and seedling composition at the sites suggests that recruitment of vulnerable trees still occurs at a temporal scale exceeding that of this study. These "windows" of recruitment may be related to infrequent events that reduce the effects of land crabs. Our results suggest that unlike the context dependence of most keystone consumers in continental systems, a single consumer, the red land crab, consistently controls the dynamics of seedling recruitment across this island rainforest.

  7. Nested and Dynamic Contract Boundaries

    NASA Astrophysics Data System (ADS)

    Strickland, T. Stephen; Felleisen, Matthias

    Previous work on software contracts assumes fixed and statically known boundaries between the parties to a contract. Implementations of contract monitoring systems rely on this assumption to explain the nature of contract violations and to assign blame to violators. In this paper, we explain how to implement arbitrary, nested, and dynamic contract boundaries with two examples. First, we add nestable contract regions to a static, first-order module system. Second, we show that even a dynamic, higher-order, and hierarchical module system can be equipped with software contracts that support precise blame assignment.

  8. Squirmer dynamics near a boundary

    NASA Astrophysics Data System (ADS)

    Ishimoto, Kenta; Gaffney, Eamonn A.

    2013-12-01

    The boundary behavior of axisymmetric microswimming squirmers is theoretically explored within an inertialess Newtonian fluid for a no-slip interface and also a free surface in the small capillary number limit, preventing leading-order surface deformation. Such squirmers are commonly presented as abridged models of ciliates, colonial algae, and Janus particles and we investigate the case of low-mode axisymmetric tangential surface deformations with, in addition, the consideration of a rotlet dipole to represent torque-motor swimmers such as flagellated bacteria. The resulting boundary dynamics reduces to a phase plane in the angle of attack and distance from the boundary, with a simplifying time-reversal duality. Stable swimming adjacent to a no-slip boundary is demonstrated via the presence of stable fixed points and, more generally, all types of fixed points as well as stable and unstable limit cycles occur adjacent to a no-slip boundary with variations in the tangential deformations. Nonetheless, there are constraints on swimmer behavior—for instance, swimmers characterized as pushers are never observed to exhibit stable limit cycles. All such generalities for no-slip boundaries are consistent with observations and more geometrically faithful simulations to date, suggesting the tangential squirmer is a relatively simple framework to enable predications and classifications for the complexities associated with axisymmetric boundary swimming. However, in the presence of a free surface, with asymptotically small capillary number, and thus negligible leading-order surface deformation, no stable surface swimming is predicted across the parameter space considered. While this is in contrast to experimental observations, for example, the free-surface accumulation of sterlet sperm, extensive surfactants are present, most likely invalidating the low capillary number assumption. In turn, this suggests the necessity of surface deformation for stable free-surface three

  9. Simulating drought impacts on energy and water dynamics in Amazonian rainforests

    NASA Astrophysics Data System (ADS)

    Imbuzeiro, H. A.; Costa, M. H.; Galbraith, D.; Christoffersen, B.; Powell, T.; Levine, N. M.; Rowland, L.; Moorcroft, P. R.; Meir, P.; da Costa, A.; Brando, P. M.; Malhi, Y.; Saleska, S. R.; Harper, A. B.

    2011-12-01

    The studies of the interaction between vegetation and climate change in the Amazon Basin indicate that up to half of region's forests may be displaced by savanna vegetation by the end of the century. Additional analyses suggest that complex interactions between land use, fire-frequency, and episodic drought are driving an even more rapid process of forest impoverishment and displacement referred to here as "savannization". But is not clear whether surface/ecosystem models are suitable to analyse extreme events like a drought. A long-term observations of energy and water in a throughfall exclusion experiments have provided unique insights into the energy and water dynamics of Amazonian rainforests during drought conditions. In this study, we evaluate how well the four surface/ecosystem models (CLM-DGVM, ED 2.0, IBIS and JULES) quantify the energy and water dynamics from two Amazonian throughfall exclusion experiments. All models was run for the Tapajos and Caxiuana sites with one baseline year using normal precipitation (i.e. do not impose a drought) and then the drought manipulation was impose for several drought level (10 to 90% rainfall exclusion). To analyse if the models are able to capture dynamics of stress and what is the implications for the energy and water dynamics the sapflow, soil moisture, sensible and latent heat flux are use to compare the models simulations and the throughfall exclusion experiments. We find that models are sensible to drought effects when they simulate the energy fluxes (sensible and latent heat), but the water dynamic is not well capture by the models.

  10. The dynamics of ant mosaics in tropical rainforests characterized using the Self-Organizing Map algorithm.

    PubMed

    Dejean, Alain; Azémar, Frédéric; Céréghino, Régis; Leponce, Maurice; Corbara, Bruno; Orivel, Jérôme; Compin, Arthur

    2016-08-01

    Ants, the most abundant taxa among canopy-dwelling animals in tropical rainforests, are mostly represented by territorially dominant arboreal ants (TDAs) whose territories are distributed in a mosaic pattern (arboreal ant mosaics). Large TDA colonies regulate insect herbivores, with implications for forestry and agronomy. What generates these mosaics in vegetal formations, which are dynamic, still needs to be better understood. So, from empirical research based on 3 Cameroonian tree species (Lophira alata, Ochnaceae; Anthocleista vogelii, Gentianaceae; and Barteria fistulosa, Passifloraceae), we used the Self-Organizing Map (SOM, neural network) to illustrate the succession of TDAs as their host trees grow and age. The SOM separated the trees by species and by size for L. alata, which can reach 60 m in height and live several centuries. An ontogenic succession of TDAs from sapling to mature trees is shown, and some ecological traits are highlighted for certain TDAs. Also, because the SOM permits the analysis of data with many zeroes with no effect of outliers on the overall scatterplot distributions, we obtained ecological information on rare species. Finally, the SOM permitted us to show that functional groups cannot be selected at the genus level as congeneric species can have very different ecological niches, something particularly true for Crematogaster spp., which include a species specifically associated with B. fistulosa, nondominant species and TDAs. Therefore, the SOM permitted the complex relationships between TDAs and their growing host trees to be analyzed, while also providing new information on the ecological traits of the ant species involved.

  11. Increased drought impacts on temperate rainforests from southern South America: results of a process-based, dynamic forest model.

    PubMed

    Gutiérrez, Alvaro G; Armesto, Juan J; Díaz, M Francisca; Huth, Andreas

    2014-01-01

    Increased droughts due to regional shifts in temperature and rainfall regimes are likely to affect forests in temperate regions in the coming decades. To assess their consequences for forest dynamics, we need predictive tools that couple hydrologic processes, soil moisture dynamics and plant productivity. Here, we developed and tested a dynamic forest model that predicts the hydrologic balance of North Patagonian rainforests on Chiloé Island, in temperate South America (42°S). The model incorporates the dynamic linkages between changing rainfall regimes, soil moisture and individual tree growth. Declining rainfall, as predicted for the study area, should mean up to 50% less summer rain by year 2100. We analysed forest responses to increased drought using the model proposed focusing on changes in evapotranspiration, soil moisture and forest structure (above-ground biomass and basal area). We compared the responses of a young stand (YS, ca. 60 years-old) and an old-growth forest (OG, >500 years-old) in the same area. Based on detailed field measurements of water fluxes, the model provides a reliable account of the hydrologic balance of these evergreen, broad-leaved rainforests. We found higher evapotranspiration in OG than YS under current climate. Increasing drought predicted for this century can reduce evapotranspiration by 15% in the OG compared to current values. Drier climate will alter forest structure, leading to decreases in above ground biomass by 27% of the current value in OG. The model presented here can be used to assess the potential impacts of climate change on forest hydrology and other threats of global change on future forests such as fragmentation, introduction of exotic tree species, and changes in fire regimes. Our study expands the applicability of forest dynamics models in remote and hitherto overlooked regions of the world, such as southern temperate rainforests.

  12. Increased Drought Impacts on Temperate Rainforests from Southern South America: Results of a Process-Based, Dynamic Forest Model

    PubMed Central

    Gutiérrez, Alvaro G.; Armesto, Juan J.; Díaz, M. Francisca; Huth, Andreas

    2014-01-01

    Increased droughts due to regional shifts in temperature and rainfall regimes are likely to affect forests in temperate regions in the coming decades. To assess their consequences for forest dynamics, we need predictive tools that couple hydrologic processes, soil moisture dynamics and plant productivity. Here, we developed and tested a dynamic forest model that predicts the hydrologic balance of North Patagonian rainforests on Chiloé Island, in temperate South America (42°S). The model incorporates the dynamic linkages between changing rainfall regimes, soil moisture and individual tree growth. Declining rainfall, as predicted for the study area, should mean up to 50% less summer rain by year 2100. We analysed forest responses to increased drought using the model proposed focusing on changes in evapotranspiration, soil moisture and forest structure (above-ground biomass and basal area). We compared the responses of a young stand (YS, ca. 60 years-old) and an old-growth forest (OG, >500 years-old) in the same area. Based on detailed field measurements of water fluxes, the model provides a reliable account of the hydrologic balance of these evergreen, broad-leaved rainforests. We found higher evapotranspiration in OG than YS under current climate. Increasing drought predicted for this century can reduce evapotranspiration by 15% in the OG compared to current values. Drier climate will alter forest structure, leading to decreases in above ground biomass by 27% of the current value in OG. The model presented here can be used to assess the potential impacts of climate change on forest hydrology and other threats of global change on future forests such as fragmentation, introduction of exotic tree species, and changes in fire regimes. Our study expands the applicability of forest dynamics models in remote and hitherto overlooked regions of the world, such as southern temperate rainforests. PMID:25068869

  13. A Broad Approach to Abrupt Boundaries: Looking Beyond the Boundary at Soil Attributes within and Across Tropical Vegetation Types

    PubMed Central

    Warman, Laura; Bradford, Matt G.; Moles, Angela T.

    2013-01-01

    Most research on boundaries between vegetation types emphasizes the contrasts and similarities between conditions on either side of a boundary, but does not compare boundary to non-boundary vegetation. That is, most previous studies lack suitable controls, and may therefore overlook underlying aspects of landscape variability at a regional scale and underestimate the effects that the vegetation itself has on the soil. We compared 25 soil chemistry variables in rainforest, sclerophyll vegetation and across rainforest-sclerophyll boundaries in north-eastern Queensland, Australia. Like previous studies, we did find some contrasts in soil chemistry across vegetation boundaries. However we did not find greater variation in chemical parameters across boundary transects than in transects set in either rainforest or woodland. We also found that soil on both sides of the boundary is more similar to “rainforest soil” than to “woodland soil”. Transects in wet sclerophyll forests with increasing degrees of rainforest invasion showed that as rainforest invades wet sclerophyll forest, the soil beneath wet sclerophyll forest becomes increasingly similar to rainforest soil. Our results have implications for understanding regional vegetation dynamics. Considering soil-vegetation feedbacks and the differences between soil at boundaries and in non-boundary sites may hold clues to some of the processes that occur across and between vegetation types in a wide range of ecosystems. Finally, we suggest that including appropriate controls should become standard practice for studies of vegetation boundaries and edge effects worldwide. PMID:23593312

  14. Contextualising impacts of logging on tropical rainforest catchment sediment dynamics using the stratigraphic record of in-channel bench deposits

    NASA Astrophysics Data System (ADS)

    Blake, Will; Walsh, Rory; Bidin, Kawi; Annammala, Kogila

    2015-04-01

    It is widely recognised that commercial logging and conversion of tropical rainforest to oil palm plantation leads to enhanced fluvial sediment flux to the coastal zone but the dynamics of delivery and mechanisms that act to retain sediment and nutrients within rainforest ecosystems, e.g. riparian zone and floodplain storage, are poorly understood and underexploited as a management tool. While accretion of lateral in-channel bench deposits in response to forest clearance has been demonstrated in temperate landscapes, their development and value as sedimentary archives of catchment response to human disturbance remains largely unexplored in tropical rainforest river systems. Working within the Segama River basin, Sabah, Malaysian Borneo, this study aimed to test the hypothesis that (1) lateral bench development in tropical rainforest rivers systems is enhanced by upstream catchment disturbance and that (2) the sedimentary record of these deposits can be used to infer changes in sediment provenance and intensification of sediment flux associated with logging activities. Sediment cores were taken from in-channel bench deposits with upstream catchment contributing areas of 721 km2 and 2800 km2 respectively. Accretion rates were determined using fallout 210Pb and 137Cs and the timing of peak accumulation was shown to correspond exactly with the known temporal pattern of logging and associated fluvial sediment response over the period 1980 to present following low pre-logging rates. Major and minor element geochemistry of deposits was used to assess the degree of weathering that deposited sediment had experienced. This was linked to surface (heavily weathered) and subsurface (less weathered) sediment sources relating to initial disturbance by logging and post-logging landsliding responses respectively. A shift in the dominant source of deposited material from surface (i.e. topsoil) to subsurface (i.e. relatively unweathered subsoil close to bedrock) origin was observed

  15. The role of stream water carbon dynamics and export in the carbon balance of a tropical seasonal rainforest, southwest China.

    PubMed

    Zhou, Wen-Jun; Zhang, Yi-Ping; Schaefer, Douglas A; Sha, Li-Qing; Deng, Yun; Deng, Xiao-Bao; Dai, Kai-Jie

    2013-01-01

    A two-year study (2009 ~ 2010) was carried out to investigate the dynamics of different carbon (C) forms, and the role of stream export in the C balance of a 23.4-ha headwater catchment in a tropical seasonal rainforest at Xishuangbanna (XSBN), southwest China. The seasonal volumetric weighted mean (VWM) concentrations of total inorganic C (TIC) and dissolved inorganic C (DIC) were higher, and particulate inorganic C (PIC) and organic C (POC) were lower, in the dry season than the rainy season, while the VWM concentrations of total organic C (TOC) and dissolved organic C (DOC) were similar between seasons. With increased monthly stream discharge and stream water temperature (SWT), only TIC and DIC concentrations decreased significantly. The most important C form in stream export was DIC, accounting for 51.8% of the total C (TC) export; DOC, POC, and PIC accounted for 21.8%, 14.9%, and 11.5% of the TC export, respectively. Dynamics of C flux were closely related to stream discharge, with the greatest export during the rainy season. C export in the headwater stream was 47.1 kg C ha(-1) yr(-1), about 2.85% of the annual net ecosystem exchange. This finding indicates that stream export represented a minor contribution to the C balance in this tropical seasonal rainforest.

  16. The Role of Stream Water Carbon Dynamics and Export in the Carbon Balance of a Tropical Seasonal Rainforest, Southwest China

    PubMed Central

    Zhou, Wen-Jun; Zhang, Yi-Ping; Schaefer, Douglas A.; Sha, Li-Qing; Deng, Yun; Deng, Xiao-Bao; Dai, Kai-Jie

    2013-01-01

    A two-year study (2009 ∼ 2010) was carried out to investigate the dynamics of different carbon (C) forms, and the role of stream export in the C balance of a 23.4-ha headwater catchment in a tropical seasonal rainforest at Xishuangbanna (XSBN), southwest China. The seasonal volumetric weighted mean (VWM) concentrations of total inorganic C (TIC) and dissolved inorganic C (DIC) were higher, and particulate inorganic C (PIC) and organic C (POC) were lower, in the dry season than the rainy season, while the VWM concentrations of total organic C (TOC) and dissolved organic C (DOC) were similar between seasons. With increased monthly stream discharge and stream water temperature (SWT), only TIC and DIC concentrations decreased significantly. The most important C form in stream export was DIC, accounting for 51.8% of the total C (TC) export; DOC, POC, and PIC accounted for 21.8%, 14.9%, and 11.5% of the TC export, respectively. Dynamics of C flux were closely related to stream discharge, with the greatest export during the rainy season. C export in the headwater stream was 47.1 kg C ha−1 yr−1, about 2.85% of the annual net ecosystem exchange. This finding indicates that stream export represented a minor contribution to the C balance in this tropical seasonal rainforest. PMID:23437195

  17. The role of stream water carbon dynamics and export in the carbon balance of a tropical seasonal rainforest, southwest China.

    PubMed

    Zhou, Wen-Jun; Zhang, Yi-Ping; Schaefer, Douglas A; Sha, Li-Qing; Deng, Yun; Deng, Xiao-Bao; Dai, Kai-Jie

    2013-01-01

    A two-year study (2009 ~ 2010) was carried out to investigate the dynamics of different carbon (C) forms, and the role of stream export in the C balance of a 23.4-ha headwater catchment in a tropical seasonal rainforest at Xishuangbanna (XSBN), southwest China. The seasonal volumetric weighted mean (VWM) concentrations of total inorganic C (TIC) and dissolved inorganic C (DIC) were higher, and particulate inorganic C (PIC) and organic C (POC) were lower, in the dry season than the rainy season, while the VWM concentrations of total organic C (TOC) and dissolved organic C (DOC) were similar between seasons. With increased monthly stream discharge and stream water temperature (SWT), only TIC and DIC concentrations decreased significantly. The most important C form in stream export was DIC, accounting for 51.8% of the total C (TC) export; DOC, POC, and PIC accounted for 21.8%, 14.9%, and 11.5% of the TC export, respectively. Dynamics of C flux were closely related to stream discharge, with the greatest export during the rainy season. C export in the headwater stream was 47.1 kg C ha(-1) yr(-1), about 2.85% of the annual net ecosystem exchange. This finding indicates that stream export represented a minor contribution to the C balance in this tropical seasonal rainforest. PMID:23437195

  18. Identification and dynamics of a cryptic suture zone in tropical rainforest

    PubMed Central

    Moritz, C.; Hoskin, C.J.; MacKenzie, J.B.; Phillips, B.L.; Tonione, M.; Silva, N.; VanDerWal, J.; Williams, S.E.; Graham, C.H.

    2009-01-01

    Suture zones, shared regions of secondary contact between long-isolated lineages, are natural laboratories for studying divergence and speciation. For tropical rainforest, the existence of suture zones and their significance for speciation has been controversial. Using comparative phylogeographic evidence, we locate a morphologically cryptic suture zone in the Australian Wet Tropics rainforest. Fourteen out of 18 contacts involve morphologically cryptic phylogeographic lineages, with mtDNA sequence divergences ranging from 2 to 15 per cent. Contact zones are significantly clustered in a suture zone located between two major Quaternary refugia. Within this area, there is a trend for secondary contacts to occur in regions with low environmental suitability relative to both adjacent refugia and, by inference, the parental lineages. The extent and form of reproductive isolation among interacting lineages varies across species, ranging from random admixture to speciation, in one case via reinforcement. Comparative phylogeographic studies, combined with environmental analysis at a fine-scale and across varying climates, can generate new insights into suture zone formation and to diversification processes in species-rich tropical rainforests. As arenas for evolutionary experimentation, suture zones merit special attention for conservation. PMID:19203915

  19. Lithospheric dynamics near plate boundaries

    NASA Technical Reports Server (NTRS)

    Solomon, Sean C.

    1992-01-01

    The progress report on research conducted between 15 Mar. - 14 Sep. 1992 is presented. The focus of the research during the first grant year has been on several problems broadly related to the nature and dynamics of time-dependent deformation and stress along major seismic zones, with an emphasis on western North America but with additional work on seismic zones in oceanic lithosphere as well. The principal findings of our research to date are described in the accompanying papers and abstract. Topics covered include: (1) Global Positioning System measurements of deformations associated with the 1987 Superstition Hills earthquake: evidence for conjugate faulting; (2) Global Positioning System measurements of strain accumulation across the Imperial Valley, California: 1986-1989; (3) present-day crustal deformation in the Salton Trough, southern California; (4) oceanic transform earthquakes with unusual mechanisms or locations: relation to fault geometry and state of stress in the lithosphere; and (5) crustal strain and the 1992 Mojave Desert earthquakes.

  20. Symmetry boundary condition in dissipative particle dynamics

    NASA Astrophysics Data System (ADS)

    Pal, Souvik; Lan, Chuanjin; Li, Zhen; Hirleman, E. Daniel; Ma, Yanbao

    2015-07-01

    Dissipative particle dynamics (DPD) is a coarse-grained particle method for modeling mesoscopic hydrodynamics. Most of the DPD simulations are carried out in 3D requiring remarkable computation time. For symmetric systems, this time can be reduced significantly by simulating only one half or one quarter of the systems. However, such simulations are not yet possible due to a lack of schemes to treat symmetric boundaries in DPD. In this study, we propose a numerical scheme for the implementation of the symmetric boundary condition (SBC) in both dissipative particle dynamics (DPD) and multibody dissipative particle dynamics (MDPD) using a combined ghost particles and specular reflection (CGPSR) method. We validate our scheme in four different configurations. The results demonstrate that our scheme can accurately reproduce the system properties, such as velocity, density and meniscus shapes of a full system with numerical simulations of a subsystem. Using a symmetric boundary condition for one half of the system, we demonstrate about 50% computation time saving in both DPD and MDPD. This approach for symmetric boundary treatment can be also applied to other coarse-grained particle methods such as Brownian and Langevin Dynamics to significantly reduce computation time.

  1. Fractal boundaries in magnetotail particle dynamics

    NASA Technical Reports Server (NTRS)

    Chen, J.; Rexford, J. L.; Lee, Y. C.

    1990-01-01

    It has been recently established that particle dynamics in the magnetotail geometry can be described as a nonintegrable Hamiltonian system with well-defined entry and exit regions through which stochastic orbits can enter and exit the system after repeatedly crossing the equatorial plane. It is shown that the phase space regions occupied by orbits of different numbers of equatorial crossings or different exit modes are separated by fractal boundaries. The fractal boundaries in an entry region for stochastic orbits are examined and the capacity dimension is determined.

  2. Conjoint Seasonal and Intraseasonal Dynamics of Precipitation and NDVI Over The Amazon And The Congo Rainforests

    NASA Astrophysics Data System (ADS)

    Yepes, L. J.; Poveda, G.

    2014-12-01

    We study the conjoint seasonal and intraseasonal variability of precipitation and NDVI over the Amazon and the Congo rainforests, using pentad precipitation from the Tropical Rainfall Measuring Mission (TRMM; 0.25°x0.25°; from 1998 to 2010), as well as from the CPC Merged Analysis of Precipitation (CMAP; 2.5°x2.5°; from 1979 to 2011). NDVI is obtained from NASA (DAAC-EOSDIS) (0.25°x0.25°, from 2000 to 2010). Results for Amazonia show a uni-modal out-phased seasonal cycle of precipitation and NDVI, whereas bi-modal and in-phase over the Congo (Figure 1). Dry months over Amazonia (August-September) correspond with lagged maximum NDVI values in June-July-August (Western-Central-Eastern) and with the second wet season over the Congo, whereas wet-season months over Amazonia (March-April) coincide with the lowest NDVI values, as well as with the first wet season and maximum NDVI over the Congo. A (tropical) transatlantic Empirical Orthogonal Functions (EOF) analysis of pentad precipitation (20-100 day filtered) indicates that EOF No. 1 (52% of variance; Fig. 2a) exhibits a meridional dipole with higher positive loadings over the tropical North Atlantic (5°N-10°N), and higher negative loadings from 5°N to the equator over the Atlantic, and to 15°S over the continents. The Principal Component No. 1 exhibits a predominant 37-day frequency. EOF No. 2 (18% of variance; Fig.2b) exhibits a tripole pattern with positive loadings over southern Amazonia, the tropical North Atlantic, and (south) equatorial Africa, and a transatlantic pattern of negative loadings from 0 to 5°N including both continents, with a 38-day periodicity. EOF No. 3 (8% of variance; Fig. 2c) exhibits a tripole between the Amazon, the Atlantic Ocean and the Congo, with a 19-day frequency. EOF No. 4 (5%; Fig. 2d) shows a dipole between the Amazon and Congo rainforests, with a predominant period of 20 days. The apparent west-to-east patterns identified in the principal EOFs could be associated with

  3. Dynamics of bacterial communities in soils of rainforest fragments under restoration processes

    NASA Astrophysics Data System (ADS)

    Vasconcellos, Rafael; Zucchi, Tiago; Taketani, Rodrigo; Andreote, Fernando; Cardoso, Elke

    2014-05-01

    The Brazilian Atlantic Forest ("Mata Atlântica") has been largely studied due to its valuable and unique biodiversity. Unfortunately, this priceless ecosystem has been widely deforested and only 10% of its original area still remains. Many projects have been successfully implemented to restore its fauna and flora but there is a lack of information on how the soil bacterial communities respond to this process. Thus, our aim was to evaluate the influence of soil attributes and seasonality on soil bacterial communities of rainforest fragments under restoration processes. Soil samples from a native site and two ongoing restoration fragments with different ages of implementation (10 and 20 years) were collected and assayed by using culture-independent approaches. Our findings demonstrate that seasonality barely altered the bacterial distribution whereas soil chemical attributes and plant diversity highly influenced the bacterial community structure during the restoration process. Moreover, the strict relationship observed for two bacterial groups, Solibacteriaceae and Verrucomicrobia, one with the youngest (10 years) and the other with the oldest (native) site suggests their use as bioindicators of soil quality and soil recovery of forest fragments under restoration.

  4. Dynamic professional boundaries in the healthcare workforce.

    PubMed

    Nancarrow, Susan A; Borthwick, Alan M

    2005-11-01

    The healthcare professions have never been static in terms of their own disciplinary boundaries, nor in their role or status in society. Healthcare provision has been defined by changing societal expectations and beliefs, new ways of perceiving health and illness, the introduction of a range of technologies and, more recently, the formal recognition of particular groups through the introduction of education and regulation. It has also been shaped by both inter-professional and profession-state relationships forged over time. A number of factors have converged that place new pressures on workforce boundaries, including an unmet demand for some healthcare services; neo-liberal management philosophies and a greater emphasis on consumer preferences than professional-led services. To date, however, there has been little analysis of the evolution of the workforce as a whole. The discussion of workforce change that has taken place has largely been from the perspective of individual disciplines. Yet the dynamic boundaries of each discipline mean that there is an interrelationship between the components of the workforce that cannot be ignored. The purpose of this paper is to describe four directions in which the existing workforce can change: diversification; specialisation and vertical and horizontal substitution, and to discuss the implications of these changes for the workforce. PMID:16313522

  5. ʻŌhiʻa Lehua rainforest: born among Hawaiian volcanoes, evolved in isolation: the story of a dynamic ecosystem with relevance to forests worldwide

    USGS Publications Warehouse

    Mueller-Dombois, Dieter; Jacobi, James D.; Boehmer, Hans Juergen; Price, Jonathan P.

    2013-01-01

    In the early 1970s, a multidisciplinary team of forest biologists began a study of Hawaiian ecosystems under the International Biological Program (IBP). Research focus was on the intact native ecosystems in and around Hawai'i Volcanoes National Park, in particular the ʻŌhiʻa Lehua rainforest. Patches of dead ʻŌhiʻa stands had been reported from the windward slopes of Mauna Loa and Mauna Kea. Subsequent air photo analyses by a team of US and Hawai'i State foresters discovered rapidly spreading ʻŌhiʻa dieback, also called ʻŌhiʻa forest decline. A killer disease was suspected to destroy the Hawaiian rain forest in the next 15-25 years. Ecological research continued with a focus on the dynamics of the Hawaiian rainforest. This book explains what really happened and why the ʻŌhiʻa rainforest survived in tact as everyone can witness today.

  6. Testing the Pleistocene Tropical Rainforest Refugia Hypothesis: Glacial Tropical Aridity and Vegetation Dynamics in the Amazon Basin

    NASA Astrophysics Data System (ADS)

    Ettwein, V. J.; Maslin, M.; Wagner, T.; Platzman, E.; Zabel, M.; Evershed, R.

    2001-12-01

    The Pleistocene climate and vegetation history of the Amazon Basin is comparatively poorly known. Until now, Amazon Basin aridity has been inferred from highly localised and qualitative indicators of moisture. However, reconstructing glacial Amazon aridity is essential for two main reasons: Firstly it is a key physiological control on the distribution of vegetation and therefore provides a means of testing the Pleistocene tropical refugia hypothesis, which attempts to explain the immense diversity and species endemism of the Amazon Basin. Secondly, Amazonian wetlands represent a major source of atmospheric methane; thus it has been suggested that glacial tropical aridity is the primary control on the reduced levels of atmospheric methane as seen in the ice core records. Deep-sea sediments collected as part of Ocean Drilling Program Leg 155 have enabled past Amazon Basin moisture levels to be quantified for the first time. Maslin and Burns (2000) reconstructed the discharge of the Amazon River using planktonic foraminifera δ 18O, and demonstrated that the discharge of the Amazon was potentially reduced to just 50% of its modern outflow during the Younger Dryas. However, their study covered only the last 14 ka. Here we present the latest results that extend this moisture record back through the Last Glacial Maximum. We also make comparisons with the past vegetation dynamics of the region which have been reconstructed using the δ 13C signature of organic matter (both bulk- and n-alkanes) to differentiate between C3 (rainforest) and C4 (savannah) plants. We also present magnetic characterisation and ICP-ms data, which show the origin of any major variation in the source and quantity of the Amazon River sediment discharge during the last glacial period. Maslin, M.A., and Burns, S.J., Science, 290, 2285 (2000).

  7. Comparative dynamics of small mammal populations in treefall gaps and surrounding understorey within Amazonian rainforest

    USGS Publications Warehouse

    Beck, H.; Gaines, M.S.; Hines, J.E.; Nichols, J.D.

    2004-01-01

    Variation in food resource availability can have profound effects on habitat selection and dynamics of populations. Previous studies reported higher food resource availability and fruit removal in treefall gaps than in the understorey. Therefore, gaps have been considered 'keystone habitat' for Neotropical frugivore birds. Here we test if this prediction would also hold for terrestrial small mammals. In the Amazon, we quantified food resource availability in eleven treefall gaps and paired understorey habitats and used feeding experiments to test if two common terrestrial rodents (Oryzomys megacephalus and Proechimys spp.) would perceive differences between habitats. We live-trapped small mammals in eleven gaps and understorey sites for two years, and compared abundance, fitness components (survival and per capita recruitment) and dispersal of these two rodent species across gaps and understorey and seasons (rainy and dry). Our data indicated no differences in resource availability and consumption rate between habitats. Treefall gaps may represent a sink habitat for Oryzomys where individuals had lower fitness, apparently because of habitat-specific ant predation on early life stages, than in the understorey, the source habitat. Conversely, gaps may be source habitat for Proechimys where individuals had higher fitness, than in the understorey, the sink habitat. Our results suggest the presence of source-sink dynamics in a tropical gap-understorey landscape, where two rodent species perceive habitats differently. This may be a mechanism for their coexistence in a heterogeneous and species-diverse system.

  8. Seasonal dynamics in photosynthesis of woody plants at the northern limit of Asian tropics: potential role of fog in maintaining tropical rainforests and agriculture in Southwest China.

    PubMed

    Zhang, Yong-Jiang; Holbrook, N Michele; Cao, Kun-Fang

    2014-10-01

    The lowland tropical rainforests in Xishuangbanna, Southwest (SW) China, mark the northern limit of Asian tropics. Fog has been hypothesized to play a role in maintaining rainforests and tropical crop production in this region, but the physiological mechanism has not been studied. The goals of this study were to characterize the seasonal dynamics in photosynthesis and to assess the potential for fog to mitigate chilling-induced photodamage for tropical trees and crops in Xishuangbanna. We measured seasonal dynamics in light-saturated net photosynthetic rate (Aa), stomatal conductance (gs), intercellular CO2 concentration, quantum yield of Photosystem II (Fv/Fm) and maximum P700 changes (Pm; indicates the amount of active PSI complex), as well as chilling resistance and fog (light/shading) effects on low temperature-induced decline in Fv/Fm and Pm for native tree and introduced lower latitude tree or woody shrub species grown in a tropical botanical garden. Despite significant decreases in Aa, gs, Pm and Fv/Fm, most species maintained considerably high Aa during the cool season (2.51-14.6 μmol m(-2) s(-1)). Shaded leaves exposed to seasonal low temperatures had higher Fv/Fm than sun-exposed leaves in the cool season. All species could tolerate 1.4 °C in the dark, whereas a combined treatment of low temperature and high light caused a distinctly faster decline in Pm and Fv/Fm compared with low temperature treatment alone. Because fog persistence avoids or shortens the duration of high light condition in the morning when the temperatures are still low, our results provide support for the hypothesis that fog reduces chilling damage to tropical plants in this region and thus plays a role in maintaining tropical rainforests and agriculture in SW China.

  9. Low density gas dynamic wall boundary conditions

    NASA Technical Reports Server (NTRS)

    Collins, F. G.

    1986-01-01

    Low density nozzles or large expansion ratio nozzles used in space experience rarefaction effects near their exit in the form of velocity slip and temperature jump at the walls. In addition, the boundary layers become very thick and there is a very strong viscous/inviscid interaction. For these reasons no existing design technique has been found to accurately predict the nozzle flow properties up to the nozzle exit. The objective of this investigation was to examine the slip boundary conditions and formulate them in a form appropriate for use with a full Navier-Stokes numerical code. The viscous/inviscid interaction would automatically be accounted for by using a compressible Navier-Stokes code. Through examination of the interaction of molecules with solid surfaces, a model for the distribution function of the reflected molecules has been determined and this distribution function has been used to develop a new slip boundary condition that can be shown to yield more realistic surface boundary conditions.

  10. Accurate boundary conditions for exterior problems in gas dynamics

    NASA Technical Reports Server (NTRS)

    Hagstrom, Thomas; Hariharan, S. I.

    1988-01-01

    The numerical solution of exterior problems is typically accomplished by introducing an artificial, far field boundary and solving the equations on a truncated domain. For hyperbolic systems, boundary conditions at this boundary are often derived by imposing a principle of no reflection. However, waves with spherical symmetry in gas dynamics satisfy equations where incoming and outgoing Riemann variables are coupled. This suggests that natural reflections may be important. A reflecting boundary condition is proposed based on an asymptotic solution of the far field equations. Nonlinear energy estimates are obtained for the truncated problem and numerical experiments presented to validate the theory.

  11. Accurate boundary conditions for exterior problems in gas dynamics

    NASA Technical Reports Server (NTRS)

    Hagstrom, Thomas; Hariharan, S. I.

    1988-01-01

    The numerical solution of exterior problems is typically accomplished by introducing an artificial, far-field boundary and solving the equations on a truncated domain. For hyperbolic systems, boundary conditions at this boundary are often derived by imposing a principle of no reflection. However, waves with spherical symmetry in gas dynamics satisfy equations where incoming and outgoing Riemann variables are coupled. This suggests that natural reflections may be important. A reflecting boundary condition is proposed based on an asymptotic solution of the far-field equations. Nonlinear energy estimates are obtained for the truncated problem and numerical experiments presented to validate the theory.

  12. Rapid replacement of riparian rainforest habitat and the impacts on the meandering dynamics of the Kinabatangan River, Borneo

    NASA Astrophysics Data System (ADS)

    Horton, Alexander J.; Constantine, José A.

    2014-05-01

    Meandering rivers are defined by their nature to migrate, remobilising floodplain sediment and constructing new surfaces for riparian vegetation to colonise. The presence of riparian vegetation has long been known to limit the ability of rivers to erode riverbanks, but it has remained unclear the principal means by which vegetation provides this function. As a result, most models that predict meandering behaviour do not fully incorporate vegetation, thereby limiting their utility where forest is rapidly replaced. The problem is particularly acute along the Kinabatangan River of Sabah in Malaysian Borneo, where oil palm plantations are replacing one of the oldest riparian rainforests on the planet. The area of Sabah has seen rapid and extensive land use change in the last 40 years, as virgin rainforest has been systematically cleared for logging, and to make way for oil palm plantations. In the 18 years from 1990 to 2008, Sabah lost half of its intact rainforest, which equates to more than 1.85 million hectares. Using Landsat imagery dating back to 1973, we report here the impacts of this rapid land-use change on rates of meander migration on a 280-km reach of the Kinabatangan River. The river planform has been remarkably stable throughout the time period of study, but individual meanders show a rapid response to large discharge events, migrating over an order of magnitude faster than nearby reaches. Rapidly migrating meanders generally occur along portions of floodplain that have been artificially cleared of riparian vegetation, potentially resulting in significant increases in sediment load and within-channel bar development. A field campaign is planned to investigate the mechanisms by which riparian vegetation effect meander migration in these tropical regions.

  13. Helmdon's First Rainforest

    ERIC Educational Resources Information Center

    Blackburn, Sue

    2003-01-01

    This article describes how Helmdon Primary School is transformed in a memorable learning experience. It started out as a simple idea, a whole-school art exhibition centred on the theme of a tropical rainforest. The focal point was to be a life-sized rainforest created using a variety of media in the school hall. The school wanted the children to…

  14. Fluid-solid boundary conditions for multiparticle collision dynamics.

    PubMed

    Whitmer, Jonathan K; Luijten, Erik

    2010-03-17

    The simulation of colloidal particles suspended in solvent requires an accurate representation of the interactions between the colloids and the solvent molecules. Using the multiparticle collision dynamics method, we examine several proposals for stick boundary conditions, studying their properties in both plane Poiseuille flow (where fluid interacts with the boundary of a stationary macroscopic solid) and particle-based colloid simulations (where the boundaries are thermally affected and in motion). In addition, our simulations compare various collision rules designed to remove spurious slip near solid surfaces, and the effects of these rules on the thermal motion of colloidal particles. Furthermore, we demonstrate that stochastic reflection of the fluid at solid boundaries fails to faithfully represent stick boundary conditions, and conclude that bounce-back conditions should be applied at both mobile and stationary surfaces. Finally, we generalize these ideas to create partial slip boundary conditions at both stationary and mobile surfaces.

  15. Effect of Dynamic Sector Boundary Changes on Air Traffic Controllers

    NASA Technical Reports Server (NTRS)

    Jung, Jaewoo; Lee, Paul; Kessell, Angela; Homola, Jeff; Zelinski, Shannon

    2010-01-01

    The effect of dynamic sector boundary changes on air traffic controller workload was investigated with data from a human-in-the-loop simulation. Multiple boundary changes were made during simulated operations, and controller rating of workload was recorded. Analysis of these data showed an increase of 16.9% in controller workload due to boundary changes. This increased workload was correlated with the number of aircraft handoffs and change in sector volume. There was also a 12.7% increase in average workload due to the changed sector design after boundary changes. This increase was correlated to traffic flow crossing points getting closer to sector boundaries and an increase in the number of flights with short dwell time in a sector. This study has identified some of the factors that affect controller workload when sector boundaries are changed, but more research is needed to better understand their relationships.

  16. Root systems of successional and old-growth forest species and its role on nutrient dynamics within a tropical rainforest in Indonesia

    SciTech Connect

    Soedjito, H.

    1990-01-01

    Most studies of nutrient dynamics in tropical rainforest have focused on the above ground portion of forest trees. However, the aim of this dissertation is to demonstrate the root systems also play an important role in nutrient dynamics. Nutrient dynamics, in general, are likely to differ between successional forest and old-growth forest. To test for differences in nutrient uptake between trees of successional and old-growth forests, the author experimentally compared seedlings of six different species by measuring biomass allocation and nutrient concentrations as well as determining spatial patterns of root distribution and the absorption ability of the root systems by usign the [sup 32]P radiotracer technique. Young saplings of ten species from natural habitats were also examined for the same parameters, and the results to determine whether results of the laboratory experiments were consistent with field results. It was found that as seedlings, roots of successional forest species penetrate deeper into the soil and have longer lateral roots than old-growth forest species. Successional forest species also had greater biomass accumulation rates, higher ability to absorb [sup 32]P, and contained higher levels of nutrients than species of old-growth forest. Mycorrhizal associations are suspected to be responsible for the high nutrient concentrations, primarily of P and N, within successional species. Successional forest tree species had more cases of infection by vesicular arbuscular mycorrhizas (VAM), while old-growth forest species were infected by both VAM and ectomycorrhizas. Therefore, successional seedlings can play an important role in conserving released nutrients after disturbance. At the landscape level, successional species together with old-growth species can maintain sustainable nutrient cycling within tropical rainforests.

  17. Controls on boundary layer ventilation: Boundary layer processes and large-scale dynamics

    NASA Astrophysics Data System (ADS)

    Sinclair, V. A.; Gray, S. L.; Belcher, S. E.

    2010-06-01

    Midlatitude cyclones are important contributors to boundary layer ventilation. However, it is uncertain how efficient such systems are at transporting pollutants out of the boundary layer, and variations between cyclones are unexplained. In this study 15 idealized baroclinic life cycles, with a passive tracer included, are simulated to identify the relative importance of two transport processes: horizontal divergence and convergence within the boundary layer and large-scale advection by the warm conveyor belt. Results show that the amount of ventilation is insensitive to surface drag over a realistic range of values. This indicates that although boundary layer processes are necessary for ventilation they do not control the magnitude of ventilation. A diagnostic for the mass flux out of the boundary layer has been developed to identify the synoptic-scale variables controlling the strength of ascent in the warm conveyor belt. A very high level of correlation (R2 values exceeding 0.98) is found between the diagnostic and the actual mass flux computed from the simulations. This demonstrates that the large-scale dynamics control the amount of ventilation, and the efficiency of midlatitude cyclones to ventilate the boundary layer can be estimated using the new mass flux diagnostic. We conclude that meteorological analyses, such as ERA-40, are sufficient to quantify boundary layer ventilation by the large-scale dynamics.

  18. Deterministic Quantization by Dynamical Boundary Conditions

    SciTech Connect

    Dolce, Donatello

    2010-06-15

    We propose an unexplored quantization method. It is based on the assumption of dynamical space-time intrinsic periodicities for relativistic fields, which in turn can be regarded as dual to extra-dimensional fields. As a consequence we obtain a unified and consistent interpretation of Special Relativity and Quantum Mechanics in terms of Deterministic Geometrodynamics.

  19. Coleman-Gurtin type equations with dynamic boundary conditions

    NASA Astrophysics Data System (ADS)

    Gal, Ciprian G.; Shomberg, Joseph L.

    2015-02-01

    We present a new formulation and generalization of the classical theory of heat conduction with or without fading memory. As a special case, we investigate the well-posedness of systems which consist of Coleman-Gurtin type equations subject to dynamic boundary conditions, also with memory. Nonlinear terms are defined on the interior of the domain and on the boundary and subject to either classical dissipation assumptions, or to a nonlinear balance condition in the sense of Gal (2012). Additionally, we do not assume that the interior and the boundary share the same memory kernel.

  20. People, Parks and Rainforests.

    ERIC Educational Resources Information Center

    Singer, Judith Y.

    1992-01-01

    The MLE Learning Center, a publicly funded day care center and after-school program in Brooklyn, New York, helps children develop awareness of a global community by using local resources to teach the children about the rainforest. (LB)

  1. Detecting dynamical boundaries from kinematic data in biomechanics

    NASA Astrophysics Data System (ADS)

    Ross, Shane D.; Tanaka, Martin L.; Senatore, Carmine

    2010-03-01

    Ridges in the state space distribution of finite-time Lyapunov exponents can be used to locate dynamical boundaries. We describe a method for obtaining dynamical boundaries using only trajectories reconstructed from time series, expanding on the current approach which requires a vector field in the phase space. We analyze problems in musculoskeletal biomechanics, considered as exemplars of a class of experimental systems that contain separatrix features. Particular focus is given to postural control and balance, considering both models and experimental data. Our success in determining the boundary between recovery and failure in human balance activities suggests this approach will provide new robust stability measures, as well as measures of fall risk, that currently are not available and may have benefits for the analysis and prevention of low back pain and falls leading to injury, both of which affect a significant portion of the population.

  2. Detecting dynamical boundaries from kinematic data in biomechanics

    PubMed Central

    Ross, Shane D.; Tanaka, Martin L.; Senatore, Carmine

    2010-01-01

    Ridges in the state space distribution of finite-time Lyapunov exponents can be used to locate dynamical boundaries. We describe a method for obtaining dynamical boundaries using only trajectories reconstructed from time series, expanding on the current approach which requires a vector field in the phase space. We analyze problems in musculoskeletal biomechanics, considered as exemplars of a class of experimental systems that contain separatrix features. Particular focus is given to postural control and balance, considering both models and experimental data. Our success in determining the boundary between recovery and failure in human balance activities suggests this approach will provide new robust stability measures, as well as measures of fall risk, that currently are not available and may have benefits for the analysis and prevention of low back pain and falls leading to injury, both of which affect a significant portion of the population. PMID:20370297

  3. Investigation of Boundary Conditions for Flexible Multibody Spacecraft Dynamics

    NASA Technical Reports Server (NTRS)

    MacLean, John R.; Huynh, An; Quiocho, Leslie J.

    2007-01-01

    In support of both the Space Shuttle and International Space Station programs, a set of generic multibody dynamics algorithms integrated within the Trick simulation environment have addressed the variety of on-orbit manipulator simulation requirements for engineering analysis, procedures development and crew familiarization/training at the NASA Johnson Space Center (JSC). Enhancements to these dynamics algorithms are now being driven by a new set of Constellation program requirements for flexible multibody spacecraft simulation. One particular issue that has been discussed within the NASA community is the assumption of cantilever-type flexible body boundary conditions. This assumption has been commonly utilized within manipulator multibody dynamics formulations as it simplifies the computation of relative motion for articulated flexible topologies. Moreover, its use for modeling of space-based manipulators such as the Shuttle Remote Manipulator System (SRMS) and Space Station Remote Manipulator System (SSRMS) has been extensively validated against flight data. For more general flexible spacecraft applications, however, the assumption of cantilever-type boundary conditions may not be sufficient. This paper describes the boundary condition assumptions that were used in the original formulation, demonstrates that this formulation can be augmented to accommodate systems in which the assumption of cantilever boundary conditions no longer applies, and verifies the approach through comparison with an independent model previously validated against experimental hardware test data from a spacecraft flexible dynamics emulator.

  4. Boundary Dynamics: Implications for Building Parent-School Partnerships

    ERIC Educational Resources Information Center

    Price-Mitchell, Marilyn

    2009-01-01

    This article draws on systems theory, complexity theory, and the organizational sciences to engage boundary dynamics in the creation of parent-school partnerships. These partnerships help children succeed through an emergent process of dialogue and relationship building in the peripheral spaces where parents and schools interact on behalf of…

  5. Rivers as Political Boundaries: Peru and its Dynamic Borders

    NASA Astrophysics Data System (ADS)

    Abad, J. D.; Escobar, C.; Garcia, A. M. P.; Ortals, C.; Frias, C. E.; Vizcarra, J.

    2014-12-01

    Rivers, although inherently dynamic, have been chosen as political boundaries since the beginning of colonization for several reasons. Such divisions were chosen namely for their defensive capabilities and military benefits, and because they were often the first features mapped out by explorers. Furthermore, rivers were indisputable boundaries that did not require boundary pillars or people to guard them. However, it is important to understand the complexities of a river as a boundary. All rivers inevitably change over time through processes such as accretion, deposition, cut-off, or avulsion, rendering a political boundary subject to dispute. Depending upon the flow, size, and surrounding land, a river will migrate differently than others. As these natural features migrate one country loses land while another gains land leading to tension between legal rigidity and fluid dynamism. This in turn can manifest in social disruption due to cultural differences, political upheaval, or conflict risk as a result of scarce water resources. The purpose of this research is to assess the temporal and spatial variability of the political boundaries of Peru that follow rivers. Peru shares borders with Colombia, Brazil, Bolivia, Chile, and Ecuador. A large part of its northern border with Colombia follows the Putumayo River and later the Amazon River. Part of its eastern border with Brazil follows the Yavari River and later the Yaquirana River. These rivers are natural features used as political boundaries yet they differ in how each migrates. By means of a spatial and temporal analysis of satellite images it was possible to obtain erosion and deposition areas for the Putumayo River, the portion of the Amazon River that is part of the Peruvian boundary, the Yavari River, and the Yaquirana River. The erosion and deposition areas were related to land distribution among Peru, Colombia, and Brazil. By examining the Digital Elevation Model one can see how the altitude of the

  6. Viscosity in molecular dynamics with periodic boundary conditions.

    PubMed

    Viscardy, S; Gaspard, P

    2003-10-01

    We report a study of viscosity by the method of Helfand moment in systems with periodic boundary conditions. We propose a new definition of Helfand moment which takes into account the minimum image convention used in molecular dynamics with periodic boundary conditions. Our Helfand-moment method is equivalent to the method based on the Green-Kubo formula and is not affected by ambiguities due to the periodic boundary conditions. Moreover, in hard-ball systems, our method is equivalent to that developed by Alder, Gass, and Wainwright [J. Chem. Phys. 53, 3813 (1970)]. We apply and verify our method in a fluid composed of N> or =2 hard disks in elastic collisions. We show that the viscosity coefficients already take values in good agreement with Enskog's theory for N=2 hard disks in a hexagonal geometry. PMID:14682933

  7. A well posed boundary value problem in transonic gas dynamics

    NASA Technical Reports Server (NTRS)

    Sanz, J. M.

    1978-01-01

    A boundary value problem for the Tricomi equation was studied in connection with transonic gas dynamics. The transformed equation delta u plus 1/3Y u sub Y equals 0 in canonical coordinates was considered in the complex domain of two independent complex variables. A boundary value problem was then set by prescribing the real part of the solution on the boundary of the real unit circle. The Dirichlet problem in the upper unit semicircle with vanishing values of the solution at Y = 0 was solved explicitly in terms of the hypergeometric function for the more general Euler-Poisson-Darboux equation. An explicit representation of the solution was also given for a mixed Dirichlet and Neumann problem for the same equation and domain.

  8. Optimal Control of a Parabolic Equation with Dynamic Boundary Condition

    SciTech Connect

    Hoemberg, D. Krumbiegel, K.; Rehberg, J.

    2013-02-15

    We investigate a control problem for the heat equation. The goal is to find an optimal heat transfer coefficient in the dynamic boundary condition such that a desired temperature distribution at the boundary is adhered. To this end we consider a function space setting in which the heat flux across the boundary is forced to be an L{sup p} function with respect to the surface measure, which in turn implies higher regularity for the time derivative of temperature. We show that the corresponding elliptic operator generates a strongly continuous semigroup of contractions and apply the concept of maximal parabolic regularity. This allows to show the existence of an optimal control and the derivation of necessary and sufficient optimality conditions.

  9. Three dimensional dynamics of rotating structures under mixed boundary conditions

    NASA Astrophysics Data System (ADS)

    Bediz, Bekir; Romero, L. A.; Ozdoganlar, O. Burak

    2015-12-01

    This paper presents the spectral-Tchebychev (ST) technique for solution of three dimensional (3D) dynamics of rotating structures. In particular, structures that exhibit coupled dynamic response require a 3D modeling approach to capture their dynamic behavior. Rotational motions further complicate this behavior, inducing coriolis, centrifugal softening, and (nonlinear) stress-stiffening effects. Therefore, a 3D solution approach is needed to accurately capture the rotational dynamics. The presented 3D-ST technique provides a fast-converging and precise solution approach for rotational dynamics of structures with complex geometries and mixed boundary conditions. Specifically, unlike finite elements techniques, the presented technique uses a series expansion approach considering distributed-parameter system equations: The integral boundary value problem for rotating structures is discretized using the spectral-Tchebychev approach. To simplify the domain of the structures, cross-sectional and rotational transformations are applied to problems with curved cross-section and pretwisted geometry. The nonlinear terms included in the integral boundary value problem are linearized around an equilibrium solution using the quasi-static method. As a result, mass, damping, and stiffness matrices, as well as a forcing vector, are obtained for a given rotating structure. Several case studies are then performed to demonstrate the application and effectiveness of the 3D-ST solution. For each problem, the natural frequencies and modes shapes from the 3D-ST solution are compared to those from the literature (when available) and to those from a commercial finite elements software. The case studies include rotating/spinning parallelepipeds under free and mixed boundary conditions, and a cantilevered pretwisted beam (i.e., rotating blade) with an airfoil geometry rotating on a hub. It is seen that the natural frequencies and mode shapes from the 3D-ST technique differ from those from the

  10. A Poisson-Boltzmann dynamics method with nonperiodic boundary condition

    NASA Astrophysics Data System (ADS)

    Lu, Qiang; Luo, Ray

    2003-12-01

    We have developed a well-behaved and efficient finite difference Poisson-Boltzmann dynamics method with a nonperiodic boundary condition. This is made possible, in part, by a rather fine grid spacing used for the finite difference treatment of the reaction field interaction. The stability is also made possible by a new dielectric model that is smooth both over time and over space, an important issue in the application of implicit solvents. In addition, the electrostatic focusing technique facilitates the use of an accurate yet efficient nonperiodic boundary condition: boundary grid potentials computed by the sum of potentials from individual grid charges. Finally, the particle-particle particle-mesh technique is adopted in the computation of the Coulombic interaction to balance accuracy and efficiency in simulations of large biomolecules. Preliminary testing shows that the nonperiodic Poisson-Boltzmann dynamics method is numerically stable in trajectories at least 4 ns long. The new model is also fairly efficient: it is comparable to that of the pairwise generalized Born solvent model, making it a strong candidate for dynamics simulations of biomolecules in dilute aqueous solutions. Note that the current treatment of total electrostatic interactions is with no cutoff, which is important for simulations of biomolecules. Rigorous treatment of the Debye-Hückel screening is also possible within the Poisson-Boltzmann framework: its importance is demonstrated by a simulation of a highly charged protein.

  11. Dynamic Immersed Boundary Method for Modeling of Turbulent Boundary Layers over Bio-Fouled Surfaces

    NASA Astrophysics Data System (ADS)

    Yang, Xiang; Sadique, Jasim; Mittal, Rajat; Meneveau, Charles

    2013-11-01

    The growth of large organisms on ship surfaces, i.e. macrobiofouling, is a major contributor to drag, and consequently, fuel consumption. The problem of turbulence over biofouled surfaces may be reduced to that of a developing turbulent boundary layer over a surface with a wide range of roughness length scales. Due to the presence of these scales, direct numerical simulation (DNS) or even wall-resolved large-eddy-simulation (LES) is prohibitively expensive. We address this challenge by developing a dynamic immersed boundary method that does not require the flow field nor the roughness to be fully resolved. The effect of unresolved small eddies are included via an LES sub-grid model. The large-scale roughness elements are resolved by a sharp-interface immersed boundary method and the effect of small (unresolved) roughness elements is incorporated through the use of a wall model that assumes a log-law at the grid point closest to the wall. This computationally efficient method is validated against experiments of developing turbulent boundary layer with multiple-scale roughness elements. We present results from this study and provide a discussion of our findings. This work is funded by the Office of Naval Research (ONR) grant N00014-12-1-0582. Fruitful interactions with M. Schultz (USNA), B. Ganapathisubramani and M. Placidi (Southhampton) are also gratefully acknowledged.

  12. Rainforest: Reptiles and Amphibians

    ERIC Educational Resources Information Center

    Olson, Susanna

    2006-01-01

    Rainforest reptiles and amphibians are a vibrantly colored, multimedia art experience. To complete the entire project one may need to dedicate many class periods to production, yet in each aspect of the project a new and important skill, concept, or element is being taught or reinforced. This project incorporates the study of warm and cool color…

  13. Making Rainforests Relevant.

    ERIC Educational Resources Information Center

    Lustbader, Sara

    1995-01-01

    Describes a program for teaching about tropical rainforests in a concrete way using what's outside the door. This activity uses an eastern deciduous hardwood forest as an example. Step-by-step instructions include introductory activities, plus descriptions of stations in the forest to be visited. Resources include books, audio-visual materials,…

  14. [Dynamics of forest landscape boundary at Changbai Mountain].

    PubMed

    Chang, Yu; Bu, Rencang; Hu, Yuanman; Xu, Chonggang; Wang, Qingli

    2004-01-01

    By using Geographic Information System (GIS) and Remote Sensing (RS) technology combined with field investigation and correlation analysis, this study was aimed to explore the dynamics of forest landscape boundary at Changbai Mountain, and to reveal the relationships among landscape fragmentation and changes of landscape boundary indices. The results showed that in the last 20 years or so, tundra decreased by 3694.8 hm2, spruce and fir forest reduced by 130482.03 hm2, and Korean pine-hardwood and mountain birch forest increased by 41610.4 hm2 and 669.78 hm2, respectively. The forest landscapes at Changbai Mountain tended to be more fragmented, and the shape of the landscape boundary became more complicated due to timber harvesting, forest cutting for cropping, and other human activities such as tourism. The changes of landscape shape index (LSI), contrast weighted edge density (CWED), total weighted edge length (TE-WGT) and weighted landscape shape index (LSI-WGT) could be used as good indicators for the degrees of forest landscape fragmentations, which was approved by correlation analysis among landscape fragmentation and changes of landscape boundary indices. The degree of human activities on landscape could be reflected by landscape shape index.

  15. On the relationship between grain-boundary migration and grain-boundary diffusion by molecular-dynamics simulation

    SciTech Connect

    Schoenfelder, B. |; Keblinski, P.; Wolf, D.; Phillpot, S.R.

    1998-07-01

    A molecular-dynamics method for the simulation of the intrinsic migration behavior of individual, flat grain boundaries is presented. A constant driving force for grain-boundary migration is generated by imposing an anisotropic elastic strain on a bicrystal such that the elastic-energy densities in its two halves are different. For the model case of the large-planar-unit-cell, high-angle (001) twist boundary in Cu the authors demonstrate that the drift velocity is proportional to the applied driving force, thus enabling determination of the boundary mobility. The activation energy for grain-boundary migration is found to be distinctly lower than that for grain-boundary self-diffusion. A decrease in the related activation energies with increasing temperature is shown to arise from a crossover in the underlying mechanisms, from solid-like at low temperatures to liquid-like at high-temperatures that is accompanied by an underlying grain-boundary structural transition.

  16. Downward transport of ozone rich air and implications for atmospheric chemistry in the Amazon rainforest

    NASA Astrophysics Data System (ADS)

    Gerken, Tobias; Wei, Dandan; Chase, Randy J.; Fuentes, Jose D.; Schumacher, Courtney; Machado, Luiz A. T.; Andreoli, Rita V.; Chamecki, Marcelo; Ferreira de Souza, Rodrigo A.; Freire, Livia S.; Jardine, Angela B.; Manzi, Antonio O.; Nascimento dos Santos, Rosa M.; von Randow, Celso; dos Santos Costa, Patrícia; Stoy, Paul C.; Tóta, Julio; Trowbridge, Amy M.

    2016-01-01

    From April 2014 to January 2015, ozone (O3) dynamics were investigated as part of GoAmazon 2014/5 project in the central Amazon rainforest of Brazil. Just above the forest canopy, maximum hourly O3 mixing ratios averaged 20 ppbv (parts per billion on a volume basis) during the June-September dry months and 15 ppbv during the wet months. Ozone levels occasionally exceeded 75 ppbv in response to influences from biomass burning and regional air pollution. Individual convective storms transported O3-rich air parcels from the mid-troposphere to the surface and abruptly enhanced the regional atmospheric boundary layer by as much as 25 ppbv. In contrast to the individual storms, days with multiple convective systems produced successive, cumulative ground-level O3 increases. The magnitude of O3 enhancements depended on the vertical distribution of O3 within storm downdrafts and origin of downdrafts in the troposphere. Ozone mixing ratios remained enhanced for > 2 h following the passage of storms, which enhanced chemical processing of rainforest-emitted isoprene and monoterpenes. Reactions of isoprene and monoterpenes with O3 are modeled to generate maximum hydroxyl radical formation rates of 6 × 106 radicals cm-3s-1. Therefore, one key conclusion of the present study is that downdrafts of convective storms are estimated to transport enough O3 to the surface to initiate a series of reactions that reduce the lifetimes of rainforest-emitted hydrocarbons.

  17. Dynamic relaxation of a liquid cavity under amorphous boundary conditions.

    PubMed

    Cavagna, Andrea; Grigera, Tomás S; Verrocchio, Paolo

    2012-05-28

    The growth of cooperatively rearranging regions was invoked long ago by Adam and Gibbs to explain the slowing down of glass-forming liquids. The lack of knowledge about the nature of the growing order, though, complicates the definition of an appropriate correlation function. One option is the point-to-set (PTS) correlation function, which measures the spatial span of the influence of amorphous boundary conditions on a confined system. By using a swap Monte Carlo algorithm we measure the equilibration time of a liquid droplet bounded by amorphous boundary conditions in a model glass-former at low temperature, and we show that the cavity relaxation time increases with the size of the droplet, saturating to the bulk value when the droplet outgrows the point-to-set correlation length. This fact supports the idea that the point-to-set correlation length is the natural size of the cooperatively rearranging regions. On the other hand, the cavity relaxation time computed by a standard, nonswap dynamics, has the opposite behavior, showing a very steep increase when the cavity size is decreased. We try to reconcile this difference by discussing the possible hybridization between mode-coupling theory and activated processes, and by introducing a new kind of amorphous boundary conditions, inspired by the concept of frozen external state as an alternative to the commonly used frozen external configuration. PMID:22667566

  18. Molecular dynamics simulations of He bubble nucleation at grain boundaries

    SciTech Connect

    Yongfeng Zhang; Paul C Millett; Michael Tonks; Liangzhe Zhang; Bulent Biner

    2012-08-01

    The nucleation behavior of He bubbles in nano-grained body-centered-cubic (BCC) Mo is simulated using molecular dynamics (MD) simulations with a bicrystal model, focusing on the effect of grain boundary (GB) structure. Three types of GBs, the (100) twist S29, the ?110? symmetrical tilt (tilt angle of 10.1?), and the (112) twin boundaries, are studied as representatives of random GB, low angle GB with misfit dislocations, and special sigma boundaries. With the same amount of He, more He clusters form in nano-grained Mo with smaller average size compared to that in bulk. The effects of the GB structure originate from the excess volume in GBs. Trapping by excess volume results in reduction in mobility of He atoms, which enhances the nucleation with higher density of bubbles, and impedes the growth of He bubbles by absorption of mobile He atoms. Furthermore, the distribution of excess volume in GBs determines the distribution of He clusters. The effect of GBs becomes less pronounced with increasing vacancy concentration in the matrix.

  19. Rainforests and Rousseau

    ERIC Educational Resources Information Center

    Rohrbach, Marla

    2012-01-01

    One of the fifth-grade art-curriculum objectives is to create a relief print. In this era of budget cuts, the author was looking for a way for her students to meet this objective by making colorful prints without using a lot of expensive printing ink. She knew she wanted to use a rainforest animal theme, as well as share the colorful art of Henri…

  20. Open boundary molecular dynamics of sheared star-polymer melts.

    PubMed

    Sablić, Jurij; Praprotnik, Matej; Delgado-Buscalioni, Rafael

    2016-02-28

    Open boundary molecular dynamics (OBMD) simulations of a sheared star polymer melt under isothermal conditions are performed to study the rheology and molecular structure of the melt under a fixed normal load. Comparison is made with the standard molecular dynamics (MD) in periodic (closed) boxes at a fixed shear rate (using the SLLOD dynamics). The OBMD system exchanges mass and momentum with adjacent reservoirs (buffers) where the external pressure tensor is imposed. Insertion of molecules in the buffers is made feasible by implementing there a low resolution model (blob-molecules with soft effective interactions) and then using the adaptive resolution scheme (AdResS) to connect with the bulk MD. Straining with increasing shear stress induces melt expansion and a significantly different redistribution of pressure compared with the closed case. In the open sample, the shear viscosity is also a bit lowered but more stable against the viscous heating. At a given Weissenberg number, molecular deformations and material properties (recoverable shear strain and normal stress ratio) are found to be similar in both setups. We also study the modelling effect of normal and tangential friction between monomers implemented in a dissipative particle dynamics (DPD) thermostat. Interestingly, the tangential friction substantially enhances the elastic response of the melt due to a reduction of the kinetic stress viscous contribution. PMID:26820315

  1. Holocene Amazon rainforest-savanna dynamics and climatic implications: high-resolution pollen record from Laguna Loma Linda in eastern Colombia

    NASA Astrophysics Data System (ADS)

    Behling, Hermann; Hooghiemstra, Henry

    2000-10-01

    We present a high-resolution pollen record of a 695-cm-long sediment core from Laguna Loma Linda, located at an altitude of 310 m in the transitional zone between the savannas of the Llanos Orientales and the Amazonian rainforest, about 100 km from the Eastern Cordillera. Based on eight AMS 14C ages, the record represents the last 8700 14C yr BP. During the period from 8700 to 6000 14C yr BP the vegetation was dominated by grass savanna with only a few woody taxa, such as Curatella and Byrsonima, present in low abundance. Gallery forest along the drainage system apparently was poorly developed. Compared with today, precipitation must have been significantly lower and seasonality stronger. During the period from 6000 to 3600 14C yr BP, rainforest taxa increased markedly, reflecting an increase in precipitation. Rainforest and gallery forest taxa such as Moraceae/Urticaceae, Melastomataceae, Alchornea, Cecropia and Acalypha, were abundant, whereas Poaceae were reduced in frequency. From 3600 to 2300 14C yr BP rainforest taxa continued to increase; Moraceae/Urticaceae became very frequent, and Myrtaceae and Myrsine became common. Savanna vegetation decreased continuously. We infer that precipitation was still increasing, and that the length of the annual dry period possibly shortened. From 2300 14C yr BP onwards, grass savanna (mainly represented by Poaceae) expanded and Mauritia palms became frequent. This reflects increased human impact on the vegetation.

  2. The Oldest, Slowest Rainforests in the World? Massive Biomass and Slow Carbon Dynamics of Fitzroya cupressoides Temperate Forests in Southern Chile.

    PubMed

    Urrutia-Jalabert, Rocio; Malhi, Yadvinder; Lara, Antonio

    2015-01-01

    Old-growth temperate rainforests are, per unit area, the largest and most long-lived stores of carbon in the terrestrial biosphere, but their carbon dynamics have rarely been described. The endangered Fitzroya cupressoides forests of southern South America include stands that are probably the oldest dense forest stands in the world, with long-lived trees and high standing biomass. We assess and compare aboveground biomass, and provide the first estimates of net primary productivity (NPP), carbon allocation and mean wood residence time in medium-age stands in the Alerce Costero National Park (AC) in the Coastal Range and in old-growth forests in the Alerce Andino National Park (AA) in the Andean Cordillera. Aboveground live biomass was 113-114 Mg C ha(-1) and 448-517 Mg C ha(-1) in AC and AA, respectively. Aboveground productivity was 3.35-3.36 Mg C ha(-1) year(-1) in AC and 2.22-2.54 Mg C ha(-1) year(-1) in AA, values generally lower than others reported for temperate wet forests worldwide, mainly due to the low woody growth of Fitzroya. NPP was 4.21-4.24 and 3.78-4.10 Mg C ha(-1) year(-1) in AC and AA, respectively. Estimated mean wood residence time was a minimum of 539-640 years for the whole forest in the Andes and 1368-1393 years for only Fitzroya in this site. Our biomass estimates for the Andes place these ecosystems among the most massive forests in the world. Differences in biomass production between sites seem mostly apparent as differences in allocation rather than productivity. Residence time estimates for Fitzroya are the highest reported for any species and carbon dynamics in these forests are the slowest reported for wet forests worldwide. Although primary productivity is low in Fitzroya forests, they probably act as ongoing biomass carbon sinks on long-term timescales due to their low mortality rates and exceptionally long residence times that allow biomass to be accumulated for millennia. PMID:26353111

  3. The Oldest, Slowest Rainforests in the World? Massive Biomass and Slow Carbon Dynamics of Fitzroya cupressoides Temperate Forests in Southern Chile.

    PubMed

    Urrutia-Jalabert, Rocio; Malhi, Yadvinder; Lara, Antonio

    2015-01-01

    Old-growth temperate rainforests are, per unit area, the largest and most long-lived stores of carbon in the terrestrial biosphere, but their carbon dynamics have rarely been described. The endangered Fitzroya cupressoides forests of southern South America include stands that are probably the oldest dense forest stands in the world, with long-lived trees and high standing biomass. We assess and compare aboveground biomass, and provide the first estimates of net primary productivity (NPP), carbon allocation and mean wood residence time in medium-age stands in the Alerce Costero National Park (AC) in the Coastal Range and in old-growth forests in the Alerce Andino National Park (AA) in the Andean Cordillera. Aboveground live biomass was 113-114 Mg C ha(-1) and 448-517 Mg C ha(-1) in AC and AA, respectively. Aboveground productivity was 3.35-3.36 Mg C ha(-1) year(-1) in AC and 2.22-2.54 Mg C ha(-1) year(-1) in AA, values generally lower than others reported for temperate wet forests worldwide, mainly due to the low woody growth of Fitzroya. NPP was 4.21-4.24 and 3.78-4.10 Mg C ha(-1) year(-1) in AC and AA, respectively. Estimated mean wood residence time was a minimum of 539-640 years for the whole forest in the Andes and 1368-1393 years for only Fitzroya in this site. Our biomass estimates for the Andes place these ecosystems among the most massive forests in the world. Differences in biomass production between sites seem mostly apparent as differences in allocation rather than productivity. Residence time estimates for Fitzroya are the highest reported for any species and carbon dynamics in these forests are the slowest reported for wet forests worldwide. Although primary productivity is low in Fitzroya forests, they probably act as ongoing biomass carbon sinks on long-term timescales due to their low mortality rates and exceptionally long residence times that allow biomass to be accumulated for millennia.

  4. The Oldest, Slowest Rainforests in the World? Massive Biomass and Slow Carbon Dynamics of Fitzroya cupressoides Temperate Forests in Southern Chile

    PubMed Central

    Urrutia-Jalabert, Rocio; Malhi, Yadvinder; Lara, Antonio

    2015-01-01

    Old-growth temperate rainforests are, per unit area, the largest and most long-lived stores of carbon in the terrestrial biosphere, but their carbon dynamics have rarely been described. The endangered Fitzroya cupressoides forests of southern South America include stands that are probably the oldest dense forest stands in the world, with long-lived trees and high standing biomass. We assess and compare aboveground biomass, and provide the first estimates of net primary productivity (NPP), carbon allocation and mean wood residence time in medium-age stands in the Alerce Costero National Park (AC) in the Coastal Range and in old-growth forests in the Alerce Andino National Park (AA) in the Andean Cordillera. Aboveground live biomass was 113–114 Mg C ha-1 and 448–517 Mg C ha-1 in AC and AA, respectively. Aboveground productivity was 3.35–3.36 Mg C ha-1 year-1 in AC and 2.22–2.54 Mg C ha-1 year-1 in AA, values generally lower than others reported for temperate wet forests worldwide, mainly due to the low woody growth of Fitzroya. NPP was 4.21–4.24 and 3.78–4.10 Mg C ha-1 year-1 in AC and AA, respectively. Estimated mean wood residence time was a minimum of 539–640 years for the whole forest in the Andes and 1368–1393 years for only Fitzroya in this site. Our biomass estimates for the Andes place these ecosystems among the most massive forests in the world. Differences in biomass production between sites seem mostly apparent as differences in allocation rather than productivity. Residence time estimates for Fitzroya are the highest reported for any species and carbon dynamics in these forests are the slowest reported for wet forests worldwide. Although primary productivity is low in Fitzroya forests, they probably act as ongoing biomass carbon sinks on long-term timescales due to their low mortality rates and exceptionally long residence times that allow biomass to be accumulated for millennia. PMID:26353111

  5. Wake Dynamics in the Atmospheric Boundary Layer Over Complex Terrain

    NASA Astrophysics Data System (ADS)

    Markfort, Corey D.

    The goal of this research is to advance our understanding of atmospheric boundary layer processes over heterogeneous landscapes and complex terrain. The atmospheric boundary layer (ABL) is a relatively thin (˜ 1 km) turbulent layer of air near the earth's surface, in which most human activities and engineered systems are concentrated. Its dynamics are crucially important for biosphere-atmosphere couplings and for global atmospheric dynamics, with significant implications on our ability to predict and mitigate adverse impacts of land use and climate change. In models of the ABL, land surface heterogeneity is typically represented, in the context of Monin-Obukhov similarity theory, as changes in aerodynamic roughness length and surface heat and moisture fluxes. However, many real landscapes are more complex, often leading to massive boundary layer separation and wake turbulence, for which standard models fail. Trees, building clusters, and steep topography produce extensive wake regions currently not accounted for in models of the ABL. Wind turbines and wind farms also generate wakes that combine in complex ways to modify the ABL. Wind farms are covering an increasingly significant area of the globe and the effects of large wind farms must be included in regional and global scale models. Research presented in this thesis demonstrates that wakes caused by landscape heterogeneity must be included in flux parameterizations for momentum, heat, and mass (water vapor and trace gases, e.g. CO2 and CH4) in ABL simulation and prediction models in order to accurately represent land-atmosphere interactions. Accurate representation of these processes is crucial for the predictions of weather, air quality, lake processes, and ecosystems response to climate change. Objectives of the research reported in this thesis are: 1) to investigate turbulent boundary layer adjustment, turbulent transport and scalar flux in wind farms of varying configurations and develop an improved

  6. Atmospheric Boundary-Layer Dynamics with Constant Bowen Ratio

    NASA Astrophysics Data System (ADS)

    Porporato, Amilcare

    2009-08-01

    Motivated by the observation that the diurnal evolution of sensible and latent heat fluxes tends to maintain a constant Bowen ratio, we derive approximate solutions of the ordinary differential equations of a simplified atmospheric boundary-layer (ABL) model. Neglecting the early morning transition, the potential temperature and specific humidity of the mixed layer are found to be linearly related to the ABL height. Similar behaviour is followed by the inversion strengths of temperature and humidity at the top of the ABL. The potential temperature of the mixed layer depends on the entrainment parameter and the free-atmosphere temperature lapse rate, while the specific humidity also depends on the free-atmosphere humidity lapse rate and the Bowen ratio. The temporal dynamics appear only implicitly in the evolution of the height of the boundary layer, which in turn depends on the time-integrated surface sensible heat flux. Studying the limiting behaviour of the Bowen ratio for very low and very large values of net available energy, we also show how the tendency to maintain constant Bowen ratio during midday hours stems from its relative insensitivity to the atmospheric conditions for large values of net available energy. The analytical expression for the diurnal evolution of the ABL obtained with constant Bowen ratio is simple and provides a benchmark for the results of more complex models.

  7. Multiscale molecular dynamics using the matched interface and boundary method

    SciTech Connect

    Geng Weihua; Wei, G.W.

    2011-01-20

    The Poisson-Boltzmann (PB) equation is an established multiscale model for electrostatic analysis of biomolecules and other dielectric systems. PB based molecular dynamics (MD) approach has a potential to tackle large biological systems. Obstacles that hinder the current development of PB based MD methods are concerns in accuracy, stability, efficiency and reliability. The presence of complex solvent-solute interface, geometric singularities and charge singularities leads to challenges in the numerical solution of the PB equation and electrostatic force evaluation in PB based MD methods. Recently, the matched interface and boundary (MIB) method has been utilized to develop the first second order accurate PB solver that is numerically stable in dealing with discontinuous dielectric coefficients, complex geometric singularities and singular source charges. The present work develops the PB based MD approach using the MIB method. New formulation of electrostatic forces is derived to allow the use of sharp molecular surfaces. Accurate reaction field forces are obtained by directly differentiating the electrostatic potential. Dielectric boundary forces are evaluated at the solvent-solute interface using an accurate Cartesian-grid surface integration method. The electrostatic forces located at reentrant surfaces are appropriately assigned to related atoms. Extensive numerical tests are carried out to validate the accuracy and stability of the present electrostatic force calculation. The new PB based MD method is implemented in conjunction with the AMBER package. MIB based MD simulations of biomolecules are demonstrated via a few example systems.

  8. MHD Simulations of Plasma Dynamics with Non-Axisymmetric Boundaries

    NASA Astrophysics Data System (ADS)

    Hansen, Chris; Levesque, Jeffrey; Morgan, Kyle; Jarboe, Thomas

    2015-11-01

    The arbitrary geometry, 3D extended MHD code PSI-TET is applied to linear and non-linear simulations of MCF plasmas with non-axisymmetric boundaries. Progress and results from simulations on two experiments will be presented: 1) Detailed validation studies of the HIT-SI experiment with self-consistent modeling of plasma dynamics in the helicity injectors. Results will be compared to experimental data and NIMROD simulations that model the effect of the helicity injectors through boundary conditions on an axisymmetric domain. 2) Linear studies of HBT-EP with different wall configurations focusing on toroidal asymmetries in the adjustable conducting wall. HBT-EP studies the effect of active/passive stabilization with an adjustable ferritic wall. Results from linear verification and benchmark studies of ideal mode growth with and without toroidal asymmetries will be presented and compared to DCON predictions. Simulations of detailed experimental geometries are enabled by use of the PSI-TET code, which employs a high order finite element method on unstructured tetrahedral grids that are generated directly from CAD models. Further development of PSI-TET will also be presented including work to support resistive wall regions within extended MHD simulations. Work supported by DoE.

  9. Rainforest Depiction in Children's Resources

    ERIC Educational Resources Information Center

    Dove, Jane

    2011-01-01

    This article analyses how rainforests are portrayed in children's resources. Twenty books and 12 websites on rainforests, designed for pupils aged between 9 and 14 years, were examined to determine the types and range of animals depicted and how plant life in general is portrayed. The most commonly depicted animal was the orang-utan and other…

  10. Discovering the Ancient Temperate Rainforest.

    ERIC Educational Resources Information Center

    Lindsay, Anne

    1997-01-01

    Two activities for grades 3 through 8 explore species adaptation and forestry issues in the North American rainforests. In one activity, students create imaginary species of plants or animals that are adapted for life in an ancient temperate rainforest. In the second activity, students role play groups affected by plans to log an area of the…

  11. Dynamics of Nanoscale Grain-Boundary Decohesion in Aluminum by Molecular-Dynamics Simulation

    NASA Technical Reports Server (NTRS)

    Yamakov, V.; Saether, E.; Phillips, D. R.; Glaessegen, E. H.

    2007-01-01

    The dynamics and energetics of intergranular crack growth along a flat grain boundary in aluminum is studied by a molecular-dynamics simulation model for crack propagation under steady-state conditions. Using the ability of the molecular-dynamics simulation to identify atoms involved in different atomistic mechanisms, it was possible to identify the energy contribution of different processes taking place during crack growth. The energy contributions were divided as: elastic energy, defined as the potential energy of the atoms in fcc crystallographic state; and plastically stored energy, the energy of stacking faults and twin boundaries; grain-boundary and surface energy. In addition, monitoring the amount of heat exchange with the molecular-dynamics thermostat gives the energy dissipated as heat in the system. The energetic analysis indicates that the majority of energy in a fast growing crack is dissipated as heat. This dissipation increases linearly at low speed, and faster than linear at speeds approaching 1/3 the Rayleigh wave speed when the crack tip becomes dynamically unstable producing periodic dislocation bursts until the crack is blunted.

  12. Numerical analysis of palynological data from Neogene fluvial sediments as evidence for rainforest dynamics in western Amazonia

    NASA Astrophysics Data System (ADS)

    Salamanca, Sonia; van Manen, Milan; Hoorn, Carina

    2014-05-01

    Deep-time records that give an insight into the composition and dynamics of the ancestral Amazon rain forest are rare. Yet to understand the modern biodiversity patterns it is important to untangle the long-term evolution of this forest. Sampling Neogene strata requires drilling operations or complex fieldwork along the rivers where outcrops generally are small. In the nineties an exceptionally good exposure of fluvial sediments of early Miocene age (17.7-16.1 Ma) was documented near the island of Mariñame (Caquetá River, Colombian Amazonia) (Hoorn, 1994). This 60 m sediment succession consists of quartz-rich sands with a circa 10 m black, sandy clay intercalation. Palynomorphs are well preserved in these organic-rich clays and palynological analysis indicated high pollen diversity and changes in composition following changes in the sedimentary environment and water composition (see van Soelen et al., this session). A numerical analysis in R (2013) of the existing data, using a number of multivariate and other statistical techniques now shows a gradient of change in the composition of the Miocene palynological assemblages. Non-metric-multidimensional scaling using distance matrixes (Oksanen, 2012) and their visualizations in correlograms (Friendly, 2002) indicate that the regional (palm) swamp forests of Mauritiides franciscoi (Mauritia), frequently found together with other palms such as Psilamonocolpites amazonicus (Euterpe?) and Psilamonocolpites rinconii, were affected by a marine incursion. The latter is suggested by the change of composition and the presence of estuarine elements such as Zonocostites ramonae (Rhizophora), foraminifer linings and dinoflagellate cysts, which became common during the marine event. In the older part of the section, and at the top, Rhoipites guianensis (Sterculiaceae/Tiliaceae) is quite abundant, in contrast with the relatively low abundance of M. franciscoi. The numerical analysis allowed us to: a) group the pollen data into 3

  13. Computation of dynamic stress intensity factors using the boundary element method based on Laplace transform and regularized boundary integral equations

    NASA Astrophysics Data System (ADS)

    Tanaka, Masataka; Nakamura, Masayuki; Aoki, Kazuhiko; Matsumoto, Toshiro

    1993-07-01

    This paper presents a computational method of dynamic stress intensity factors (DSIF) in two-dimensional problems. In order to obtain accurate numerical results of DSIF, the boundary element method based on the Laplace transform and regularized boundary integral equations is applied to the computation of transient elastodynamic responses. A computer program is newly developed for two-dimensional elastodynamics. Numerical computation of DSIF is carried out for a rectangular plate with a center crack under impact tension. Accuracy of the results is investigated from the viewpoint of computational conditions such as the number of sampling points of the inverse Laplace transform and the number of boundary elements.

  14. Characterising coarse PBA dynamics in real-time above and below a tropical rainforest canopy using a dual channel UV fluorescence aerosol spectrometer.

    NASA Astrophysics Data System (ADS)

    Gabey, A.; Gallagher, M. W.; Burgess, R.; Coe, H.; McFiggans, G.,; Kaye, P. H.; Stanley, W. R.; Davies, F.; Foot, V. E.

    2009-04-01

    single-particle dual channel UV fluorescence spectrometer (Kaye et al., 2008) capable of detecting PBA by inducing fluorescence in two so-called biofluorophores - one present during metabolism and the other an amino acid - in the particle size range 1 m < Dp < 20 m. Real-time PBA measurements were performed above and below the canopy of a tropical rainforest in Borneo, Malaysia as part of the Oxidant and Particle Photochemical Processes (OP3) and the Aerosol Coupling in the Earth System (ACES) projects. PBA were found to dominate the coarse loading at Dp > 2 m. In qualitative agreement with measurements of culturable airborne material in a tropical forest's understory (Gilbert, 2005) a diurnal cycle of PBA number concentration is present, reaching a maximum of ~4000 l-1 at local midnight and falling to ~100 l-1 around midday. The role of the planetary boundary layer's collapse and re-establishment in dictating this variation in is also investigated using LIDAR data. Transient PBA concentration spikes lasting several minutes are superposed on the smooth underlying diurnal variation and occur at similar times each day. Nucleopore filter samples were also taken in-situ and analysed under an Environmental scanning electron microscope (ESEM) in Manchester. The images obtained showed the PBA fraction to be dominated by fungal spores of diameter 2-5 m, from various species including ABM. Since such species tend to release spores in bursts at regular times this appears to account for the PBA concentration spikes.

  15. Dynamics of transport under random fluxes on the boundary

    NASA Astrophysics Data System (ADS)

    Boñgolan-Walsh, Vena Pearl; Duan, Jinqiao; Özgökmen, Tamay

    2008-10-01

    The impact of boundary noise on the dynamical evolution of the scalar transport equation in shear flows is studied, taking off from earlier studies in shear-flow dispersion in internal waves, a mechanism for horizontal mixing in the ocean. In particular, we model a gravity current evolving under an assumed shear-flow. The transport equation is deterministic, with a noise term at the inlet boundary. This was motivated by observed seasonal fluctuations in some known sources of salty, dense water in the oceans, like the Red Sea overflow, as well as observed thermal and saline anomalies in the thermohaline circulation. The noises used were: Wiener white, Wiener colored, Lévy white, and Lévy colored noise. Lévy processes form a more general class of processes which are generally non-Gaussian in distribution, and may have infinitely many jumps in finite time. They have been used to model pollutant point-sources, the flight time of particles in vortices, and linear and nonlinear anomalous diffusion. The major finding was that white noises (Wiener and Lévy ) and colored Wiener noise all have the effect of impeding the diffusion process, by as much as 33%. However, colored Lévy noise (non-Gaussian, time-correlated) does not have this effect on diffusion. This would suggest that time-correlation is more important in distinguishing noises than the distribution of the process that produced the noise. This also explains why Lévy colored noise showed great sensitivity to the stability parameter α, while Lévy white noise is unaffected by its stability parameter.

  16. Neural dynamics in Parkinsonian brain: The boundary between synchronized and nonsynchronized dynamics

    NASA Astrophysics Data System (ADS)

    Park, Choongseok; Worth, Robert M.; Rubchinsky, Leonid L.

    2011-04-01

    Synchronous oscillatory dynamics is frequently observed in the human brain. We analyze the fine temporal structure of phase-locking in a realistic network model and match it with the experimental data from Parkinsonian patients. We show that the experimentally observed intermittent synchrony can be generated just by moderately increased coupling strength in the basal ganglia circuits due to the lack of dopamine. Comparison of the experimental and modeling data suggest that brain activity in Parkinson's disease resides in the large boundary region between synchronized and nonsynchronized dynamics. Being on the edge of synchrony may allow for easy formation of transient neuronal assemblies.

  17. Molecular dynamics simulations of He bubble nucleation at grain boundaries.

    PubMed

    Zhang, Yongfeng; Millett, Paul C; Tonks, Michael; Zhang, Liangzhe; Biner, Bulent

    2012-08-01

    The nucleation behavior of He bubbles in single-crystal (sc) and nano-grain body-centered-cubic (bcc) Mo is simulated using molecular dynamics (MD) simulations, focusing on the effects of the grain boundary (GB) structure. In sc Mo, the nucleation behavior of He bubbles depends on irradiation conditions. He bubbles nucleate by either clustering of He atoms with pre-existing vacancies or self-interstitial-atom (SIA) punching without initial vacancies. In nano-grain Mo, strong precipitation of He at the GBs is observed, and the density, size and spatial distribution of He bubbles vary with the GB structure. The corresponding He bubble density is higher in nano-grain Mo than that in sc Mo and the average bubble size is smaller. In the GB plane, He bubbles distribute along the dislocation cores for GBs consisting of GB dislocations and randomly for those without distinguishable dislocation structures. The simulation results in nano-grain Mo are in agreement with previous experiments in metal nano-layers, and they are further explained by the effect of excess volume associated with the GBs.

  18. Effects of the Basal Boundary on Debris-flow Dynamics

    NASA Astrophysics Data System (ADS)

    Iverson, R. M.; Logan, M.; Lahusen, R. G.; Berti, M.

    2006-12-01

    Data aggregated from 37 large-scale experiments reveal some counterintuitive effects of bed roughness on debris-flow dynamics. In each experiment 10 m3 of water-saturated sand and gravel, mixed with 1 to 12% silt and clay by dry weight, was abruptly released from a gate at the head of a 2-m wide, 1.2-m deep, 82.5-m long rectangular flume inclined 31° throughout most of its length and adjoined to a gently sloping, planar runout surface at its toe. The flume's basal boundary consisted of either a smooth, planar concrete surface or a concrete surface roughened with a grid of conical bumps. Tilt-table tests with dry debris-flow sediment showed that this roughness imparted a basal friction angle of 38°, comparable to the sediment's internal friction angle of 38-42°, whereas the smooth-bed friction angle was 28°. About 20 electronic sensors installed in the flume yielded data on flow speeds and depths as well as basal stresses and pore pressures. Behavior observed in all experiments included development of steep, unsaturated, coarse-grained debris-flow snouts and tapering, liquefied, fine-grained tails. Flows on the rough bed were typically about 50% thicker and 20% slower than flows on the smooth bed, although the rough bed caused snout steepening that enabled flow fronts to move faster than expected, given the increased bed friction. Moreover, flows on rough beds ran out further than flows on smooth beds owing to enhanced grain-size segregation and lateral levee formation. With the rough bed, measured basal stresses and pore pressures differed little from values expected from static gravitational loading of partially liquefied debris. With the smooth bed, however, measured basal stresses and pore pressures were nearly twice as large as expected values. This anomaly resulted from flow disturbance at the upstream lips of steel plates in which sensors were mounted. The lips produced barely visible ripples in otherwise smooth flow surfaces, yet sufficed to generate

  19. Historical distribution of Sundaland's Dipterocarp rainforests at Quaternary glacial maxima.

    PubMed

    Raes, Niels; Cannon, Charles H; Hijmans, Robert J; Piessens, Thomas; Saw, Leng Guan; van Welzen, Peter C; Slik, J W Ferry

    2014-11-25

    The extent of Dipterocarp rainforests on the emergent Sundaland landmass in Southeast Asia during Quaternary glaciations remains a key question. A better understanding of the biogeographic history of Sundaland could help explain current patterns of biodiversity and support the development of effective forest conservation strategies. Dipterocarpaceae trees dominate the rainforests of Sundaland, and their distributions serve as a proxy for rainforest extent. We used species distribution models (SDMs) of 317 Dipterocarp species to estimate the geographic extent of appropriate climatic conditions for rainforest on Sundaland at the last glacial maximum (LGM). The SDMs suggest that the climate of central Sundaland at the LGM was suitable to sustain Dipterocarp rainforest, and that the presence of a previously suggested transequatorial savannah corridor at that time is unlikely. Our findings are supported by palynologic evidence, dynamic vegetation models, extant mammal and termite communities, vascular plant fatty acid stable isotopic compositions, and stable carbon isotopic compositions of cave guano profiles. Although Dipterocarp species richness was generally lower at the LGM, areas of high species richness were mostly found off the current islands and on the emergent Sunda Shelf, indicating substantial species migration and mixing during the transitions between the Quaternary glacial maxima and warm periods such as the present.

  20. Boundary layer effects in optical measurements in gas dynamics.

    PubMed

    Small, R D; Weihs, D

    1976-06-01

    A method for including three-dimensional boundary corrections in the analysis of interferograms of two-dimensional flows is described. An effective optical pathlength is calculated using a displacement thickness concept. Expressions and methods for determining the correction to the optical pathlength are given for laminar and turbulent boundary layers in isoenergetic or diabatic flow. An exact expression is derived for the turbulent case and results given showing the correction to be of the order of 10%.

  1. Boundary-induced dynamics in one-dimensional topological systems and memory effects of edge modes

    NASA Astrophysics Data System (ADS)

    He, Yan; Chien, Chih-Chun

    2016-07-01

    Dynamics induced by a change of boundary conditions reveals rate-dependent signatures associated with topological properties in one-dimensional Kitaev chain and SSH model. While the perturbation from a change of the boundary propagates into the bulk, the density of topological edge modes in the case of transforming to open boundary condition reaches steady states. The steady-state density depends on the transformation rate of the boundary and serves as an illustration of quantum memory effects in topological systems. Moreover, while a link is physically broken as the boundary condition changes, some correlation functions can remain finite across the broken link and keep a record of the initial condition. By testing those phenomena in the nontopological regimes of the two models, none of the interesting signatures of memory effects can be observed. Our results thus contrast the importance of topological properties in boundary-induced dynamics.

  2. Dynamics of turbulent western-boundary currents at low latitude in a shallow-water model

    NASA Astrophysics Data System (ADS)

    Akuetevi, C. Q. C.; Wirth, A.

    2015-06-01

    The dynamics of low latitude turbulent western-boundary currents (WBCs) crossing the Equator are considered using numerical results from integrations of a reduced-gravity shallow-water model. For viscosity values of 1000 m2 s-1 and greater, the boundary layer dynamics compares well to the analytical Munk-layer solution. When the viscosity is reduced, the boundary layer becomes turbulent and coherent structures in the form of anticyclonic eddies, bursts (violent detachments of the viscous sub-layer, VSL) and dipoles appear. Three distinct boundary layers emerge, the VSL, the advective boundary layer and the extended boundary layer. The first is characterized by a dominant vorticity balance between the viscous transport and the advective transport of vorticity; the second by a balance between the advection of planetary vorticity and the advective transport of relative vorticity. The extended boundary layer is the area to which turbulent motion from the boundary extends. The scaling of the three boundary layer thicknesses with viscosity is evaluated. Characteristic scales of the dynamics and dissipation are determined. A pragmatic approach to determine the eddy viscosity diagnostically for coarse-resolution numerical models is proposed.

  3. Dynamics of turbulent western boundary currents at low latitude in a shallow water model

    NASA Astrophysics Data System (ADS)

    Akuetevi, C. Q. C.; Wirth, A.

    2014-11-01

    The dynamics of low latitude turbulent western boundary currents crossing the equator is considered using numerical results from integrations of a reduced gravity shallow-water model. For viscosity values of 1000 m2 s-1 and more, the boundary layer dynamics compares well to the analytical Munk-layer solution. When the viscosity is reduced, the boundary layer becomes turbulent and coherent structures in form of anticyclonic eddies, bursts (violent detachments of the viscous sub-layer) and dipoles appear. Three distinct boundary layers emerge, the viscous sub-layer, the advective boundary layer and the extended boundary layer. The first is characterized by a dominant vorticity balance between the viscous transport and the advective transport of vorticity. The second by a balance between the advection of planetary vorticity and the advective transport of relative vorticity. The extended boundary layer is the area to which turbulent motion from the boundary extends. The scaling of the three boundary layer thicknesses with viscosity is evaluated. Characteristic scales of the dynamics and dissipation are determined. A pragmatic approach to determine the eddy viscosity diagnostically for coarse resolution numerical models is proposed.

  4. Dynamics of turbulent western boundary currents at low latitude in a shallow water model

    NASA Astrophysics Data System (ADS)

    Akuetevi, C. Q. C.; Wirth, A.

    2014-03-01

    The dynamics of low latitude turbulent western boundary currents, subject to two different types of idealized wind forcing, Monsoon Wind and Trade Wind, is considered using numerical results from integrations of a reduced gravity shallow-water model. For viscosity values of 1000 m2 s-1 and above, the boundary layer dynamics compares well to the analytical solutions of the Munk-layer and the inertial-layer, derived from quasigeostrophic theory. Modifications due to variations in the layer thickness (vortex stretching) are only important close to the boundary. When the viscosity is reduced the boundary layer becomes turbulent and coherent structures in form of anticyclonic eddies, bursts (violent detachments of the viscous sub-layer) and dipoles appear. Three distinct boundary layers emerge, the viscous sub-layer, the advective boundary layer and the extended boundary layer. The first is characterized by a dominant vorticity balance between the viscous transport and the advective transport of vorticity. The second by a balance between the advection of planetary vorticity and the advective transport of relative vorticity. The extended boundary layer is the area to which turbulent motion from the boundary extends. The scaling of the three boundary layer thicknesses with viscosity is evaluated. A pragmatic approach to determine the eddy viscosity diagnostically for coarse resolution numerical models is proposed.

  5. Simulation of dynamic interface fracture using spectral boundary integral method

    NASA Astrophysics Data System (ADS)

    Harish, Ajay Bangalore

    Simulation of three-dimensional dynamic fracture events constitutes one of the most challenging topics in the field of computational mechanics. Spontaneous dynamic fracture along the interface of two elastic solids is of great importance and interest to a number of disciplines in engineering and science. Applications include dynamic fractures in aircraft structures, earthquakes, thermal shocks in nuclear containment vessels and delamination in layered composite materials.

  6. Contrasting Strategies of Tree Function in a Seasonal Amazon Rainforest

    NASA Astrophysics Data System (ADS)

    Ivanov, V. Y.; Oliveira, R.; Agee, E.; Brum, M., Jr.; Saleska, S. R.; Fatichi, S.; Ewing, G.

    2015-12-01

    The increased frequency and severity of drought conditions in the Amazon Basin region have emphasized the question of rainforest vulnerability and resilience to heat and drought-induced stresses. However, what emerges from much research is that the impacts of droughts, essential controlling factors of the rainforest function, and variability of tree-scale strategies are yet to be fully understood. We present here a preliminary analysis of hydraulic relations of a seasonal Amazon rainforest using a set of ecohydrologic data collected through the GoAmazon project over dry and wet seasons. Expressions of different hydraulic strategies are identified that convey different implications for tree resilience during short- (diurnal) and longer-term (seasonal) stress periods. These hydraulic strategies appear to be inter-related with the tree growth and non-structural carbohydrate dynamics, contributing to the understanding of trait coordination at the whole-plant scale. Integration of individual responses is conducted over a range of wood density and exposure conditions. The results of this research thus shed light on the implication of variations in the rainforest function for future stresses, vital for predictive models of ecosystem dynamics of next generation.

  7. High junction and twin boundary densities in driven dynamical systems.

    PubMed

    Ding, X; Zhao, Z; Lookman, T; Saxena, A; Salje, E K H

    2012-10-01

    A novel mechanism for the generation of device materials with very high domain boundary densities is described: we shear the sample in a computer experiment and achieve higher twin densities than in rapid quench. These domain patterns are very stable. Elastically soft materials (image with 6.4$ \\times $10(5) atoms) has greater twin densities than hard materials, even for nano-crystals.

  8. Coupling the dynamics of boundary layers and evolutionary dunes

    NASA Astrophysics Data System (ADS)

    Ortiz, Pablo; Smolarkiewicz, Piotr K.

    2009-04-01

    A theoretical formulation and corresponding numerical solutions are presented for fluid flow and sediment transport past evolutionary sand dunes. Time-dependent curvilinear coordinates are employed to fully couple flow aloft with the developing landform. The differential conservation law that defines shape of the lower boundary depends on details of local surface stress, thereby favoring the large eddy simulation of the boundary layer. To shrink the gap between the time scales characteristic of planetary boundary layer flows O(103)s and sand dune evolution O(106)s , a hypothetical “severe-wind scenario” is adopted with the saltation flux amplified up to 3 orders of magnitude. While the results are largely insensitive to the rescaling, the efficacy of computations is greatly improved. The flux-form partial differential equation for the interface profile—via saltation and sand avalanches—is formulated as an advection-diffusion equation, to facilitate discrete integrations. Numerical experiments verify the adopted theoretical framework by reproducing scaling results reported in the literature. The versatility of the approach is illustrated with evolution of a sandhole—an example of application likely never addressed in the literature, yet realizable in nature.

  9. Tropical Rainforest Education. ERIC Digest.

    ERIC Educational Resources Information Center

    Rillero, Peter

    This digest provides four guideposts for tropical rainforest education: (1) structure; (2) location and climate; (3) importance; and (4) conservation of resources. Research is cited and background information provided about the layers of life and the adaptations of life within the tropical rain forest. Aspects of life within and near rain forests…

  10. Dynamic light use and protection from excess light in upper canopy and coppice leaves of Nothofagus cunninghamii in an old growth, cool temperate rainforest in Victoria, Australia.

    PubMed

    Tausz, Michael; Warren, Charles R; Adams, Mark A

    2005-01-01

    Responses to simulated sunflecks were examined in upper canopy and coppice leaves of Nothofagus cunninghamii growing in an old-growth rainforest gully in Victoria, Australia. Shaded leaves were exposed to a sudden increase in irradiance from 20 to 1500 micromol m(-2) s(-1). Gas exchange and chlorophyll fluorescence were measured during a 10 min simulated sunfleck and, in the ensuing dark treatment, we examined the recovery of PS II efficiency and the conversion state of xanthophyll cycle pigments. Photosynthetic induction was rapid compared with tropical and northern hemisphere species. Stomatal conductance was relatively high in the shade and stomata did not directly control photosynthetic induction under these conditions. During simulated sunflecks, zeaxanthin was formed rapidly and photochemical efficiency was reduced. These processes were reversed within 30 min in coppice leaves, but this took longer in upper canopy leaves. Poor drought tolerance and achieving a positive carbon balance in a shaded canopy may be functionally related to high stomatal conductance in the shade in N. cunninghamii. The more persistent reduction in photochemical efficiency of upper canopy leaves, which means less efficient light use in subsequent shade periods, but stronger protection from high light, may be related to the generally higher irradiance and longer duration of sunflecks in the upper canopy, but potentially reduces carbon gain during shade periods by 30%.

  11. Planetary Boundary Layer Dynamics over Reno, Nevada in Summer

    NASA Astrophysics Data System (ADS)

    Liming, A.; Sumlin, B.; Loria Salazar, S. M.; Holmes, H.; Arnott, W. P.

    2014-12-01

    Quantifying the height of the planetary boundary layer (PBL) is important to understand the transport behavior, mixing, and surface concentrations of air pollutants. In Reno, NV, located in complex, mountainous terrain with high desert climate, the daytime boundary layer can rise to an estimated 3km or more on a summer day due to surface heating and convection. The nocturnal boundary layer, conversely, tends to be much lower and highly stable due to radiative cooling from the surface at night and downslope flow of cool air from nearby mountains. With limited availability of radiosonde data, current estimates of the PBL height at any given time or location are potentially over or underestimated. To better quantify the height and characterize the PBL physics, we developed portable, lightweight sensors that measure CO2 concentrations, temperature, pressure, and humidity every 5 seconds. Four of these sensors are used on a tethered balloon system to monitor CO2 concentrations from the surface up to 300m. We will combine this data with Radio Acoustic Sounding System (RASS) data that measures vertical profiles of wind speed, temperature, and humidity from 40m to 400m. This experiment will characterize the diurnal evolution of CO2 concentrations at multiple heights in the PBL, provide insight into PBL physics during stability transition periods at sunrise and sunset, and estimate the nighttime PBL depth during August in Reno. Further, we expect to gain a better understanding of the impact of mixing volume changes (i.e., PBL height) on air quality and pollution concentrations in Reno. The custom portable sensor design will also be presented. It is expected that these instruments can be used for indoor or outdoor air quality studies, where lightness, small size, and battery operation can be of benefit.

  12. Dynamics of lee waves on the boundary layer inversion

    NASA Astrophysics Data System (ADS)

    Sachsperger, Johannes; Serafin, Stefano; Grubišić, Vanda

    2016-04-01

    Lee waves are horizontally propagating non-hydrostatic internal gravity waves that may be generated when stratified flow is lifted over a mountain. Depending on the upstream conditions, two types of lee waves can be distinguished. First, resonant lee waves, which are often explored in the context of Scorer's theory of wave trapping in a two-layer atmosphere, where a discontinuity in the Scorer parameter - with evanescent conditions in the upper layer - gives rise to trapped waves. Second, interfacial lee waves, which may form along a density discontinuity, e.g. a temperature inversion, similar to surface waves on a free water surface. While resonant lee waves have been studied extensively, interfacial lee waves were only rarely discussed in meteorological literature so far. For example, observational studies as well as systematic studies on the wavelength dependencies still seem to be lacking. In this work, we modify Scorer's wave trapping theory by applying a boundary condition that accounts for a density jump between the two fluid layers. In this case, wave resonance is possible along the density discontinuity even if the lower layer is neutrally stratified. The resulting linear theory can be applied for instance to atmospheric boundary layer flows over complex terrain, where part of the mountain wave energy can be trapped along the inversion that caps the boundary layer. We validate this model with observations taken in the area of Vienna and highlight the lee wavelength dependence on the flow parameters by systematically varying the upstream conditions. Since interfacial waves have transcendental frequency dispersion relationships that cannot be solved analytically, we also discuss the implications of the shallow- and deep-water approximations on the wavelength of the resonant mode.

  13. Considerations of blood properties, outlet boundary conditions and energy loss approaches in computational fluid dynamics modeling.

    PubMed

    Moon, Ji Young; Suh, Dae Chul; Lee, Yong Sang; Kim, Young Woo; Lee, Joon Sang

    2014-02-01

    Despite recent development of computational fluid dynamics (CFD) research, analysis of computational fluid dynamics of cerebral vessels has several limitations. Although blood is a non-Newtonian fluid, velocity and pressure fields were computed under the assumptions of incompressible, laminar, steady-state flows and Newtonian fluid dynamics. The pulsatile nature of blood flow is not properly applied in inlet and outlet boundaries. Therefore, we present these technical limitations and discuss the possible solution by comparing the theoretical and computational studies. PMID:24642855

  14. Dynamic behaviour of thin composite plates for different boundary conditions

    SciTech Connect

    Sprintu, Iuliana E-mail: rotaruconstantin@yahoo.com; Rotaru, Constantin E-mail: rotaruconstantin@yahoo.com

    2014-12-10

    In the context of composite materials technology, which is increasingly present in industry, this article covers a topic of great interest and theoretical and practical importance. Given the complex design of fiber-reinforced materials and their heterogeneous nature, mathematical modeling of the mechanical response under different external stresses is very difficult to address in the absence of simplifying assumptions. In most structural applications, composite structures can be idealized as beams, plates, or shells. The analysis is reduced from a three-dimensional elasticity problem to a oneor two-dimensional problem, based on certain simplifying assumptions that can be made because the structure is thin. This paper aims to validate a mathematical model illustrating how thin rectangular orthotropic plates respond to the actual load. Thus, from the theory of thin plates, new analytical solutions are proposed corresponding to orthotropic rectangular plates having different boundary conditions. The proposed analytical solutions are considered both for solving equation orthotropic rectangular plates and for modal analysis.

  15. Impact of Compound Hydrate Dynamics on Phase Boundary Changes

    NASA Astrophysics Data System (ADS)

    Osegovic, J. P.; Max, M. D.

    2006-12-01

    Compound hydrate reactions are affected by the local concentration of hydrate forming materials (HFM). The relationship between HFM composition and the phase boundary is as significant as temperature and pressure. Selective uptake and sequestration of preferred hydrate formers (PF) has wide ranging implications for the state and potential use of natural hydrate formation, including impact on climate. Rising mineralizing fluids of hydrate formers (such as those that occur on Earth and are postulated to exist elsewhere in the solar system) will sequester PF before methane, resulting in a positive relationship between depth and BTU content as ethane and propane are removed before methane. In industrial settings the role of preferred formers can separate gases. When depressurizing gas hydrate to release the stored gas, the hydrate initial composition will set the decomposition phase boundary because the supporting solution takes on the composition of the hydrate phase. In other settings where hydrate is formed, transported, and then dissociated, similar effects can control the process. The behavior of compound hydrate systems can primarily fit into three categories: 1) In classically closed systems, all the material that can form hydrate is isolated, such as in a sealed laboratory vessel. In such systems, formation and decomposition are reversible processes with observed hysteresis related to mass or heat transfer limitations, or the order and magnitude in which individual hydrate forming gases are taken up from the mixture and subsequently released. 2) Kinetically closed systems are exposed to a solution mass flow across a hydrate mass. These systems can have multiple P-T phase boundaries based on the local conditions at each face of the hydrate mass. A portion of hydrate that is exposed to fresh mineralizing solution will contain more preferred hydrate formers than another portion that is exposed to a partially depleted solution. Examples of kinetically closed

  16. Asymmetric exclusion process with a dynamic roadblock and open boundaries

    NASA Astrophysics Data System (ADS)

    Sahoo, Mamata; Klumpp, Stefan

    2016-08-01

    Motivated by complex transport processes occurring in nature, we study a totally asymmetric simple exclusion process (TASEP) with a dynamic ‘roadblock’ particle. The roadblock particle blocks the traffic of moving particles while bound to the lattice, but can stochastically unbind or switch off, thus enabling the traffic to pass. We use simulations to study the dependence of the particle flux on the on/off switching dynamics of the roadblock, which exhibits a surprisingly rich dynamic behaviour. In particular, unlike in other studied TASEP variants with defects, here we observe that the particle flux is affected by the roadblock even in the initiation-limited or low density phase if the roadblock dynamics is slow. Rapid switching off the roadblock results in the typical behaviour of a TASEP with a defect/pause with reduced maximal current, but no effect of the roadblock on the flux in the initiation-limited phase. Moreover, in an intermediate range of roadblock rates, the particle current is found to be system-size dependent.

  17. Dynamical effects of suction/heating on turbulent boundary layers

    NASA Astrophysics Data System (ADS)

    Blackwelder, Ron

    1992-01-01

    The main emphasis of this quarter has been to test the effects of suction in a controlled environment with the emulated wall eddy structure. A study of the curved working wall of the test section in the Goertler Wind Tunnel showed that there were sufficient stresses within the plexiglas that cutting elongated slits for suction would probably cause the surface to develop step-type roughnesses. Thus several individual holes were initially drilled along the streamline direction in a spanwise region between two vortices. Air was withdrawn through this series of holes to provide a semi-continuous region of suction. Differing rates of suction through these holes were used to explore the effects upon the eddy structure. These preliminary results were obtained using visualization; i.e., smoke as introduced via a smoke wire into the boundary layer. Images were captured using a video camera and analyzed to determine the best suction rates. The preliminary results showed that suction has a large effect upon individual streaks of low speed fluid. Without the suction, the low speed region lying in the upwelling zone between two streamwise vortices was broken down by a secondary instability. This instability typically caused the low speed fluid marked with the smoke to oscillate from side to side in a manifestation of an inflectional instability in the spanwise direction as found and reported earlier in this research. With increasing distance downstream, the oscillation amplitude grew very rapidly until it broke down into complete turbulence.

  18. [Dynamics and influence width of dry valley landscape boundary in upper reaches of Minjiang River].

    PubMed

    Yang, Zhao-Ping; Chang, Yu; Yang, Meng; Hu, Yuan-Man; Bu, Ren-Cang; He, Xing-Yuan

    2007-09-01

    Based on RS and GIS techniques, the distribution extent of the dry valley in upper reaches of Minjiang River was determined, with the dynamics and influence width of its landscape boundary analyzed. The results indicated that the dry valley had a gradually expanded distribution, and the total length of its boundary was increased. The boundary complexity increased from 1974 to 1995 but decreased from 1995 to 2000, and the upper boundary of the dry valley ascended rapidly along mountain slope. The uppermost elevation of the dry valley boundary was 3128 m in 1974, 3167 m in 1995, and 3181 m in 2000. In the last 26 years, the upper boundary of the dry valley ascended 53 m in total, being about 2 m per year. The influence width of the dry valley boundary was 800 m, which could be regarded as a buffer zone to disturbances. The area between 800-1200 m from the dry valley boundary to exterior was a transition zone intensely influenced by the dry valley and its surrounding landscape, which should be addressed in the restoration of the dry valley. PMID:18062298

  19. New Reasons to Preserve the Amazon Rainforest

    NASA Astrophysics Data System (ADS)

    Costa, M. H.

    2014-12-01

    Historically, preservation of the rainforest was justified in terms of conservation of biodiversity, protection of indigenous people habitats and maintenance of carbon stocks. Most of these arguments are based on the direct effect of rainforest removal, and ignore second order effects of the presence of the rainforest, such as modulation of regional climate patterns. The rainforest helps define the regional climate of the region, in particular the regional temperature and precipitation patterns. Of course, any activity that depends on the local climate may be affected by changes in the rainforest. Recent evidence in the literature presented enough arguments to believe that the widespread removal of the rainforest will have economic consequences at least in agriculture output and hydroelectric power generation. Economic impacts may affect not only the agriculture and energy sectors, but also several other economic activities that are related to climate. As a country, we are counting with the climate of Amazonia as fixed, but if the present climate needs the presence of the rainforest, we need to quantify the economic value of the climate regulation service provided by the rainforest. Important questions to be answered: How much of the rainforest is needed to conserve the present climate? Where it should stand for best climate regulation? Answer to these questions may affect Brazil´s large-scale policy on land use.

  20. Vertical distribution of HOx concentrations driven by boundary layer dynamics

    NASA Astrophysics Data System (ADS)

    Gomm, Sebastian; Broch, Sebastian; Fuchs, Hendrik; Hofzumahaus, Andreas; Holland, Frank; Bohn, Birger; Häseler, Rolf; Jäger, Julia; Kaiser, Jennifer; Keutsch, Frank; Li, Xin; Lu, Keding; Lohse, Insa; Rohrer, Franz; Tillmann, Ralf; Wegener, Robert; Wolfe, Glenn; Mentel, Thomas F.; Kiendler-Scharr, Astrid; Wahner, Andreas

    2014-05-01

    The hydroxyl (OH) and hydroperoxy (HO2) radicals are key compounds for the degradation of pollutants in the atmosphere. Therefore, accurate and precise measurements of HOx radicals (= OH + HO2) at different altitudes and in different regions are necessary to test our understanding of atmospheric chemical processes. The planetary boundary layer (PBL) is of special interest as it is chemically the most active part of the atmosphere. Until today, there is a general lack of measurements investigating the distribution of radicals, trace gases, and aerosols in the PBL with high spatial resolution. Here, we present results of measurements performed in June/July 2012 in the Po valley region in Italy as part of the Pan-European Gas-AeroSOls-climate interaction Study (PEGASOS). A Zeppelin NT was used as an airborne platform for measurements of HOx radical concentrations and total OH reactivity (kOH) applying a remotely controlled Laser Induced Fluorescence (LIF) instrument. In addition a comprehensive set of other trace gases (O3, CO, NO, NO2, HCHO, HONO, VOCs), photolysis frequencies, particle number concentration, and meteorological parameters were measured. During the morning hours, a layered atmospheric structure with vertical gradients in trace gas concentrations was observed. In altitudes larger than 600 m above ground, air masses with low trace gas concentrations (NOx < 500 ppt, kOH < 3 s-1) were probed, whereas air masses in altitudes below 100 m above ground were influenced by ground emissions resulting in higher trace gas concentrations (NOx > 6 ppb, kOH > 6 s-1). The airship Zeppelin NT was used to perform localized height profiles between 75 and 900 m above ground in order to investigate the influence of these trace gas gradients on HOx radical concentrations. Due to changing chemical conditions, the measured OH concentration shows a variability with height up to a factor of 2.5 and for the measured HO2 concentration up to a factor of 5. Additionally, we present

  1. Assimilation of Thermodynamic and Dynamic Boundary Layer Profiler Data

    NASA Astrophysics Data System (ADS)

    Crowell, S.; Turner, D. D.; Otkin, J.

    2012-12-01

    In 2009, the National Research Council issued a report stating that a fundamental limitation to our understanding of mesoscale meteorological phenomena is the absence of adequate observations in the atmospheric boundary layer. In Otkin et al (2011) and Hartung et al (2011), an Observing Systems Simulation Experiment was described that concluded that the inclusion of thermodynamic retrievals from instruments like the Atmospheric Emitted Radiance Interferometer, together with wind observations from a Doppler lidar, could improve precipitation forecast skill scores using an ensemble Kalman filter (DART) together with the Weather Research and Forecasting Model (WRF). Here we discuss a second set of experiments in which the density of the proposed profiler network was doubled. Surprisingly, the results were only marginally better, and in some cases were degraded. This can be seen to be an effect of decreasing spread in the location of the strongest atmospheric gradients. An alternate set of experiments was performed with the 3D Variational framework, with the background error correlation length scales being tuned to match the EnKF localization as closely as possible. Interestingly, the 3DVar solutions exhibit qualitatively different responses to the assimilation of the observations than the EnKF solutions, with the placement and magnitude of the precipitation being improved, as determined by examining model precipitation on transects passing orthogonal to the front. A second case study will also be presented, in which we explore the relative importance of model error and observations for a springtime convective cased modeled on the May 24, 2011 tornado outbreak that passed through Texas, Oklahoma and Kansas. The sensitivity of convective processes to subgrid physics parameterizations can be seen to be a challenging problem for a data assimilation system, regardless of the quality of the observations being assimilated. Rather than using precipitation as the metric for

  2. Molecular dynamics simulation of temperature profile in partially hydrogenated graphene and graphene with grain boundary.

    PubMed

    Lotfi, Erfan; Neek-Amal, M; Elahi, M

    2015-11-01

    Temperature profile in graphene, graphene with grain boundary and vacancy defects and hydrogenated graphene with different percentage of H-atoms are determined using molecular dynamics simulation. We also obtained the temperature profile in a graphene nanoribbon containing two types of grain boundaries with different misorientation angles, θ=21.8° and θ=32.2°. We found that a temperature gap appears in the temperature profile of a graphene nanoribbon with a grain boundary at the middle. Moreover, we found that the temperature profile in the partially hydrogenated graphene varies with the percentage of hydrogens, i.e. the C:H ratio. Our results show that a grain boundary line in the graphene sheet can change the thermal transport through the system which might be useful for controlling thermal flow in nanostructured graphene.

  3. Dynamic recrystallization and grain boundary migration in B2 FeAl

    NASA Technical Reports Server (NTRS)

    Baker, I.; Gaydosh, D. J.

    1987-01-01

    Transmission electron microscopy and optical microscopy were used to examine polycrystalline specimens of the B2-structured alloy FeAl strained under tension to fracture at elevated temperature. Strain-induced grain boundary migration was observed above 900 K and dynamic recrystallization was found at 1000 K and 1100 K. Little evidence of dynamic recovery was evident but some networks were formed at 1100 K.

  4. A molecular dynamics based investigation of thermally vibrating graphene under different boundary conditions

    NASA Astrophysics Data System (ADS)

    Rahman, R.; Foster, J. T.

    2015-08-01

    In this paper we have investigated the ripples in graphenes under thermal agitation. It is known that as temperature increases ripples originate in the flat landscape of a graphene sheet which is responsible for changing its properties. Among a limited number of works available in literature the role of length scales and temperature on the characteristics of the ripples has been investigated. However it is important to include the boundary conditions with other parameters in order to get a broader picture. In this work graphenes with three different sizes (2 nm, 10 nm and 50 nm) were considered under both simply supported and free-opposite-sides boundary conditions at different temperatures (e.g. 10 K, 100 K and 500 K) using molecular dynamics simulations. The variation in natural frequencies and their dependency on the boundary condition, length scale and temperature was thoroughly studied. Change in the boundary condition can introduce new modes of vibrations in graphenes. A combined effect of length scale, boundary condition and temperature was shown to be responsible for developing the geometrical patterns in the ripples. With free-opposite-sides boundary conditions the ripples are more harmonic in larger graphene than other cases. It was also noticed that the probability distribution for the off-plane displacements of the carbon atoms in graphene is typically non-stationary at small length scales. Variation in boundary conditions and length scales may affect the kurtosis of the distribution. The results showed adequate agreement with available data in the literature.

  5. Numerical approximation of boundary conditions with applications to inviscid equations of gas dynamics

    NASA Technical Reports Server (NTRS)

    Yee, H. C.

    1981-01-01

    A comprehensive overview of the state of the art of well-posedness and stability analysis of difference approximations for initial boundary value problems of the hyperbolic type is presented. The applicability of recent theoretical development to practical calculations for nonlinear gas dynamics is examined. The one dimensional inviscid gas dynamics equations in conservation law form are selected for numerical experiments. The class of implicit schemes developed from linear multistep methods in ordinary differential equations is chosen and the use of linear extrapolation as an explicit or implicit boundary scheme is emphasized. Specification of boundary data in the primitive variables and computation in terms of the conservative variables in the interior is discussed. Some numerical examples for the quasi-one-dimensional nozzle are given.

  6. Dynamics of Helium-Loaded Grain Boundaries under Shear Deformation in alpha-Fe

    SciTech Connect

    Gao, Fei; Yang, Li; Heinisch, Howard L.; Kurtz, Richard J.

    2014-03-01

    To simulate the motion and behavior of helium-loaded grain boundaries (GBs) in bcc Fe under shear deformation using the molecular dynamics simulation method. Here, we report preliminary results on the effects of helium on coupled migration and relative translation of a sigma3 GB at 300 K.

  7. Development of an immersed boundary-phase field-lattice Boltzmann method for Neumann boundary condition to study contact line dynamics

    NASA Astrophysics Data System (ADS)

    Shao, J. Y.; Shu, C.; Chew, Y. T.

    2013-02-01

    The implementation of Neumann boundary condition in the framework of immersed boundary method (IBM) is presented in this paper to simulate contact line dynamics using a phase field-lattice Boltzmann method. Immersed boundary method [10] is known as an efficient algorithm for modelling fluid-solid interaction. Abundance of prominent works have been devoted to refine IBM [1,11,12]. However, they are mainly restricted to problems with Dirichlet boundary condition. Research that implements the Neumann boundary condition in IBM is very limited to the best of our knowledge. This deficiency significantly limits the application of IBM in computational fluid dynamics (CFD) since physical phenomena associated with Neumann boundary conditions are extremely diverse. The difficulty is attributed to the fact that implementation of Neumann boundary condition is much more complex than that of Dirichlet boundary condition. In the present work, we initiate the first endeavour to implement Neumann boundary condition in IBM with assistance of its physical interpretation rather than simple mathematical manipulation. Concretely speaking, rooted from physical conservation law, the Neumann boundary condition is considered as contribution of flux from the boundary to its relevant physical parameter in a control volume. Moreover, the link between the flux and its corresponding flow field variable is directly manipulated through the immersed boundary concept. In this way, the Neumann boundary conditions can be implemented in IBM. The developed method is applied together with phase field-lattice Boltzmann method to study contact line dynamics. The phase field method [27,39], which becomes increasingly popular in multiphase flow simulation, can efficiently capture complex interface topology and naturally resolve the contact line singularity. Meanwhile, the lattice Boltzmann method is known as an alternative to model fluid dynamics and holds good prospect to simulate multiphase flows with

  8. The Origins of Tropical Rainforest Hyperdiversity.

    PubMed

    Pennington, R Toby; Hughes, Mark; Moonlight, Peter W

    2015-11-01

    Traditional models for tropical species richness contrast rainforests as "museums" of old species or "cradles" of recent speciation. High plant species diversity in rainforests may be more likely to reflect high episodic evolutionary turnover of species--a scenario implicating high rates of both speciation and extinction through geological time.

  9. Automated boundary extraction of the spinal canal in MRI based on dynamic programming.

    PubMed

    Koh, Jaehan; Chaudhary, Vipin; Dhillon, Gurmeet

    2012-01-01

    The spinal cord is the only communication link between the brain and the body. The abnormalities in it can lead to severe pain and sometimes to paralysis. Due to the growing gap between the number of available radiologists and the number of required radiologists, the need for computer-aided diagnosis and characterization is increasing. To ease this gap, we have developed a computer-aided diagnosis and characterization framework in lumbar spine that includes the spinal cord, vertebrae, and intervertebral discs. In this paper, we propose two spinal cord boundary extraction methods that fit into our framework based on dynamic programming in lumbar spine MRI. Our method incorporates the intensity of the image and the gradient of the image into a dynamic programming scheme and works in a fully-automatic fashion. The boundaries generated by our method is compared against reference boundaries in terms of Fréchet distance which is known to be a metric for shape analysis. The experimental results from 65 clinical data show that our method finds the spinal canal boundary correctly achieving a mean Fréchet distance of 13.5 pixels. For almost all data, the extracted boundary falls within the spinal cord. So, it can be used as a landmark when marking background regions and finding regions of interest.

  10. Combined effects of surface conditions, boundary layer dynamics and chemistry on diurnal SOA evolution

    NASA Astrophysics Data System (ADS)

    Janssen, R. H. H.; Vilà-Guerau de Arellano, J.; Ganzeveld, L. N.; Kabat, P.; Jimenez, J. L.; Farmer, D. K.; van Heerwaarden, C. C.; Mammarella, I.

    2012-08-01

    We study the combined effects of land surface conditions, atmospheric boundary layer dynamics and chemistry on the diurnal evolution of biogenic secondary organic aerosol in the atmospheric boundary layer, using a model that contains the essentials of all these components. First, we evaluate the model for a case study in Hyytiälä, Finland, and find that it is able to satisfactorily reproduce the observed dynamics and gas-phase chemistry. We show that the exchange of organic aerosol between the free troposphere and the boundary layer (entrainment) must be taken into account in order to explain the observed diurnal cycle in organic aerosol (OA) concentration. An examination of the budgets of organic aerosol and terpene concentrations show that the former is dominated by entrainment, while the latter is mainly driven by emission and chemical transformation. We systematically investigate the role of the land surface, which governs both the surface energy balance partitioning and terpene emissions, and the large-scale atmospheric process of vertical subsidence. Entrainment is especially important for the dilution of organic aerosol concentrations under conditions of dry soils and low terpene emissions. Subsidence suppresses boundary layer growth while enhancing entrainment. Therefore, it influences the relationship between organic aerosol and terpene concentrations. Our findings indicate that the diurnal evolution of secondary organic aerosols (SOA) in the boundary layer is the result of coupled effects of the land surface, dynamics of the atmospheric boundary layer, chemistry, and free troposphere conditions. This has potentially some consequences for the design of both field campaigns and large-scale modeling studies.

  11. Molecular dynamics studies of material property effects on thermal boundary conductance.

    PubMed

    Zhou, X W; Jones, R E; Duda, J C; Hopkins, P E

    2013-07-14

    Thermal boundary resistance (inverse of conductance) between different material layers can dominate the overall thermal resistance in nanostructures and therefore impact the performance of the thermal property limiting nano devices. Because relationships between material properties and thermal boundary conductance have not been fully understood, optimum devices cannot be developed through a rational selection of materials. Here we develop generic interatomic potentials to enable material properties to be continuously varied in extremely large molecular dynamics simulations to explore the dependence of thermal boundary conductance on the characteristic properties of materials such as atomic mass, stiffness, and interfacial crystallography. To ensure that our study is not biased to a particular model, we employ different types of interatomic potentials. In particular, both a Stillinger-Weber potential and a hybrid embedded-atom-method + Stillinger-Weber potential are used to study metal-on-semiconductor compound interfaces, and the results are analyzed considering previous work based upon a Lennard-Jones (LJ) potential. These studies, therefore, reliably provide new understanding of interfacial transport phenomena particularly in terms of effects of material properties on thermal boundary conductance. Our most important finding is that thermal boundary conductance increases with the overlap of the vibrational spectra between metal modes and the acoustic modes of the semiconductor compound, and increasing the metal stiffness causes a continuous shift of the metal modes. As a result, the maximum thermal boundary conductance occurs at an intermediate metal stiffness (best matched to the semiconductor stiffness) that maximizes the overlap of the vibrational modes.

  12. Molecular dynamics study of grain boundary structure and properties at high temperatures

    NASA Astrophysics Data System (ADS)

    Fensin, Saryu Jindal

    This thesis reports research involving the development and application of atomistic simulation methods to study the effects of high homologous temperatures on the structural, thermodynamic, kinetic and mechanical properties of grain boundaries in metals. Our interest in these properties is due to the role they play in governing the evolution of microstructure and deformation of metals during solidification processing. The interest in developing more predictive models for the formation of solidification defects highlights a need to better understand the thermodynamic driving forces underlying grain-boundary premelting and the mobility and shear strength of these interfaces at high temperatures. In this work we study two different elemental systems, namely Ni and Cu, and consider a variety of grain boundary structures characterized by different misorientation angles, twist/tilt character and zero-temperature energies. A method to calculate the disjoining potential from molecular dynamics (MD) is developed and applied to grain boundaries in Ni. The disjoining potential characterizes the variation in grain-boundary free energy as a function of the width of a premelted interfacial layer. The MD method for the calculation of this property is applied to grain boundaries that display continuous premelting transitions, as well as a boundary characterized by a disordered atomic structure displaying a finite interfacial width at the melting temperature. The disjoining potential represents an important input property to larger scale models of solidification and grain coalescence. We further develop analysis methods to characterize the change in the atomic structure of an asymmetric tilt grain boundary in elemental Cu as a function of temperature. This boundary is characterized by a potential-energy surface with multiple minima as a function of the relative translation of the grains parallel to the interface plane. The more complex structure of this boundary, relative to the

  13. Dynamics of place, boundary and object encoding in rat anterior claustrum

    PubMed Central

    Jankowski, Maciej M.; O’Mara, Shane M.

    2015-01-01

    Discrete populations of brain cells signal differing types of spatial information. These “spatial cells” are largely confined to a closely-connected network of sites. We describe here, for the first time, cells in the anterior claustrum of the freely-moving rat encoding place, boundary and object information. This novel claustral spatial signal potentially directly modulates a wide variety of anterior cortical regions. We hypothesize that one of the functions of the claustrum is to provide information about body position, boundaries and landmark information, enabling dynamic control of behavior. PMID:26557060

  14. Boundary Conditions for Dislocation Dynamics Simulations and Stage 0 of BCC Metals at Low Temperature

    SciTech Connect

    Tang, M; Kubin, L P

    2001-05-01

    In order to study the dislocation density evolution of body centered cubic (bcc) crystals at low temperature by dislocation dynamics (DD) simulations, we investigated carefully three different boundary conditions (BC) for DD, i.e., the quasi-free surface BC, the flux-balanced BC, and the periodic BC. The latter two BCs can account for the dislocation loss from the boundary of the finite simulation box. PBC can also eliminate the influence of surfaces and improve the line connectivity. We have found that the PBC provides a convenient and effective boundary condition for DD simulations and have applied it to the study of dislocation density evolution of bcc metals during stage 0 deformation at low temperature.

  15. Wall Boundary Layer Measurements for the NASA Langley Transonic Dynamics Tunnel

    NASA Technical Reports Server (NTRS)

    Wieseman, Carol D.; Bennett, Robert M.

    2007-01-01

    Measurements of the boundary layer parameters in the NASA Langley Transonic Dynamics tunnel were conducted during extensive calibration activities following the facility conversion from a Freon-12 heavy-gas test medium to R-134a. Boundary-layer rakes were mounted on the wind-tunnel walls, ceiling, and floor. Measurements were made over the range of tunnel operation envelope in both heavy gas and air and without a model in the test section at three tunnel stations. Configuration variables included open and closed east sidewall wall slots, for air and R134a test media, reentry flap settings, and stagnation pressures over the full range of tunnel operation. The boundary layer thickness varied considerably for the six rakes. The thickness for the east wall was considerably larger that the other rakes and was also larger than previously reported. There generally was some reduction in thickness at supersonic Mach numbers, but the effect of stagnation pressure, and test medium were not extensive.

  16. Tropical rainforest ecology. (Latest citations from the Life Sciences Collection database). Published Search

    SciTech Connect

    Not Available

    1993-09-01

    The bibliography contains citations concerning ecological studies of tropical rainforests. Topics include plant community structure and development, nutrient dynamics, rainfall characteristics and water budgets, forest dynamics, and descriptive studies performed in specific forest areas. Effects of human activities and factors affecting forest depletion and rejuvination are also considered. (Contains 250 citations and includes a subject term index and title list.)

  17. Rainforests: Conservation and resource management. (Latest citations from the Biobusiness database). Published Search

    SciTech Connect

    Not Available

    1994-12-01

    The bibliography contains citations concerning conservation of rainforest ecology and management of natural resources. Topics include plant community structure and development, nutrient dynamics, rainfall characteristics and water budgets, and forest dynamics. Studies performed in specific forest areas are included. Effects of human activities are also considered. (Contains a minimum of 154 citations and includes a subject term index and title list.)

  18. Dynamical Generation of a Bumpy Layer at the Core-Mantle-Boundary

    NASA Astrophysics Data System (ADS)

    Hansen, U.; Stemmer, K.

    2006-12-01

    Convection in the Earth's mantle is largely influenced by the strong dependence of the viscosity of the mantle material on temperature. A temperature difference of several orders of magnitude leads to a pronounced asymmetry between the upper- and lower boundary of the convecting system. While different scenarios for the upper boundary have been explored (stagnant lid plate-like behavior), the effects on the the lower boundary are less clear. In view of the dynamical formation of structures at the Core-mantle boundary, we apply fully three dimensional models in cartesian and in spherical geometry, in order to study the evolving patterns at the lower boundary in convection with strongly temperature-dependent viscosity at high Rayleigh number. We apply viscosity contrasts of six orders of magnitude. Rayleigh numbers are chosen to ensure that convection is vigorous (Nusselt numbers between 30 and 50 are reached). Under this circumstances the flow typically develops a complex system of channels at the bottom which connect the several existing plumes. Material flows channels, creating a 'bumpy' layer at the Core-mantle boundary (CMB). In order to determine the dynamically induced topography at the CMB, the pressure field will be analyzed.. Additional pressure- dependence of the viscosity has been speculated to prevent plumes from the CMB. We will demonstrate that pressure dependence can enhance, rather than reduce the strength of plumes. Finally we present a new relation between Nusselt- and Rayleigh number for convection with strongly temperature dependent viscosity, based on an extensive data-set from 3D models. This will allow to better estimate the thermal history of the Earth and other planets.

  19. Thermal stability of interface voids in Cu grain boundaries with molecular dynamic simulations

    NASA Astrophysics Data System (ADS)

    Xydou, A.; Parviainen, S.; Aicheler, M.; Djurabekova, F.

    2016-09-01

    By means of molecular dynamic simulations, the stability of cylindrical voids is examined with respect to the diffusion bonding procedure. To do this, the effect of grain boundaries between the grains of different crystallographic orientations on the void closing time was studied at high temperatures from 0.7 up to 0.94 of the bulk melting temperature ({{T}\\text{m}} ). The diameter of the voids varied from 3.5 to 6.5 nm. A thermal instability occurring at high temperatures at the surface of the void placed in a grain boundary triggered the eventual closure of the void at all examined temperatures. The closing time has an exponential dependence on the examined temperature values. A model based on the defect diffusion theory is developed to predict the closing time for voids of macroscopic size. The diffusion coefficient within the grain boundaries is found to be overall higher than the diffusion coefficient in the region around the void surface. The activation energy for the diffusion in the grain boundary is calculated based on molecular dynamic simulations. This value agrees well with the experimental given in the Ashby maps for the creep in copper via Coble GB diffusion.

  20. Testing thermal gradient driving force for grain boundary migration using molecular dynamics simulations

    SciTech Connect

    Bai, Xian-Ming; Zhang, Yongfeng; Tonks, Michael R.

    2015-02-01

    Strong thermal gradients in low-thermal-conductivity ceramics may drive extended defects, such as grain boundaries and voids, to migrate in preferential directions. In this work, molecular dynamics simulations are conducted to study thermal gradient driven grain boundary migration and to verify a previously proposed thermal gradient driving force equation, using uranium dioxide as a model system. It is found that a thermal gradient drives grain boundaries to migrate up the gradient and the migration velocity increases under a constant gradient owing to the increase in mobility with temperature. Different grain boundaries migrate at very different rates due to their different intrinsic mobilities. The extracted mobilities from the thermal gradient driven simulations are compared with those calculated from two other well-established methods and good agreement between the three different methods is found, demonstrating that the theoretical equation of the thermal gradient driving force is valid, although a correction of one input parameter should be made. The discrepancy in the grain boundary mobilities between modeling and experiments is also discussed.

  1. Natural disturbance reduces disease risk in endangered rainforest frog populations.

    PubMed

    Roznik, Elizabeth A; Sapsford, Sarah J; Pike, David A; Schwarzkopf, Lin; Alford, Ross A

    2015-01-01

    Natural disturbances can drive disease dynamics in animal populations by altering the microclimates experienced by hosts and their pathogens. Many pathogens are highly sensitive to temperature and moisture, and therefore small changes in habitat structure can alter the microclimate in ways that increase or decrease infection prevalence and intensity in host populations. Here we show that a reduction of rainforest canopy cover caused by a severe tropical cyclone decreased the risk of endangered rainforest frogs (Litoria rheocola) becoming infected by a fungal pathogen (Batrachochytrium dendrobatidis). Reductions in canopy cover increased the temperatures and rates of evaporative water loss in frog microhabitats, which reduced B. dendrobatidis infection risk in frogs by an average of 11-28% in cyclone-damaged areas, relative to unaffected areas. Natural disturbances to the rainforest canopy can therefore provide an immediate benefit to frogs by altering the microclimate in ways that reduce infection risk. This could increase host survival and reduce the probability of epidemic disease outbreaks. For amphibian populations under immediate threat from this pathogen, targeted manipulation of canopy cover could increase the availability of warmer, drier microclimates and therefore tip the balance from host extinction to coexistence. PMID:26294048

  2. Implications of global warming for the climate of African rainforests.

    PubMed

    James, Rachel; Washington, Richard; Rowell, David P

    2013-01-01

    African rainforests are likely to be vulnerable to changes in temperature and precipitation, yet there has been relatively little research to suggest how the regional climate might respond to global warming. This study presents projections of temperature and precipitation indices of relevance to African rainforests, using global climate model experiments to identify local change as a function of global temperature increase. A multi-model ensemble and two perturbed physics ensembles are used, one with over 100 members. In the east of the Congo Basin, most models (92%) show a wet signal, whereas in west equatorial Africa, the majority (73%) project an increase in dry season water deficits. This drying is amplified as global temperature increases, and in over half of coupled models by greater than 3% per °C of global warming. Analysis of atmospheric dynamics in a subset of models suggests that this could be partly because of a rearrangement of zonal circulation, with enhanced convection in the Indian Ocean and anomalous subsidence over west equatorial Africa, the Atlantic Ocean and, in some seasons, the Amazon Basin. Further research to assess the plausibility of this and other mechanisms is important, given the potential implications of drying in these rainforest regions.

  3. Natural disturbance reduces disease risk in endangered rainforest frog populations

    PubMed Central

    Roznik, Elizabeth A.; Sapsford, Sarah J.; Pike, David A.; Schwarzkopf, Lin; Alford, Ross A.

    2015-01-01

    Natural disturbances can drive disease dynamics in animal populations by altering the microclimates experienced by hosts and their pathogens. Many pathogens are highly sensitive to temperature and moisture, and therefore small changes in habitat structure can alter the microclimate in ways that increase or decrease infection prevalence and intensity in host populations. Here we show that a reduction of rainforest canopy cover caused by a severe tropical cyclone decreased the risk of endangered rainforest frogs (Litoria rheocola) becoming infected by a fungal pathogen (Batrachochytrium dendrobatidis). Reductions in canopy cover increased the temperatures and rates of evaporative water loss in frog microhabitats, which reduced B. dendrobatidis infection risk in frogs by an average of 11–28% in cyclone-damaged areas, relative to unaffected areas. Natural disturbances to the rainforest canopy can therefore provide an immediate benefit to frogs by altering the microclimate in ways that reduce infection risk. This could increase host survival and reduce the probability of epidemic disease outbreaks. For amphibian populations under immediate threat from this pathogen, targeted manipulation of canopy cover could increase the availability of warmer, drier microclimates and therefore tip the balance from host extinction to coexistence. PMID:26294048

  4. Implications of global warming for the climate of African rainforests.

    PubMed

    James, Rachel; Washington, Richard; Rowell, David P

    2013-01-01

    African rainforests are likely to be vulnerable to changes in temperature and precipitation, yet there has been relatively little research to suggest how the regional climate might respond to global warming. This study presents projections of temperature and precipitation indices of relevance to African rainforests, using global climate model experiments to identify local change as a function of global temperature increase. A multi-model ensemble and two perturbed physics ensembles are used, one with over 100 members. In the east of the Congo Basin, most models (92%) show a wet signal, whereas in west equatorial Africa, the majority (73%) project an increase in dry season water deficits. This drying is amplified as global temperature increases, and in over half of coupled models by greater than 3% per °C of global warming. Analysis of atmospheric dynamics in a subset of models suggests that this could be partly because of a rearrangement of zonal circulation, with enhanced convection in the Indian Ocean and anomalous subsidence over west equatorial Africa, the Atlantic Ocean and, in some seasons, the Amazon Basin. Further research to assess the plausibility of this and other mechanisms is important, given the potential implications of drying in these rainforest regions. PMID:23878329

  5. Natural disturbance reduces disease risk in endangered rainforest frog populations.

    PubMed

    Roznik, Elizabeth A; Sapsford, Sarah J; Pike, David A; Schwarzkopf, Lin; Alford, Ross A

    2015-08-21

    Natural disturbances can drive disease dynamics in animal populations by altering the microclimates experienced by hosts and their pathogens. Many pathogens are highly sensitive to temperature and moisture, and therefore small changes in habitat structure can alter the microclimate in ways that increase or decrease infection prevalence and intensity in host populations. Here we show that a reduction of rainforest canopy cover caused by a severe tropical cyclone decreased the risk of endangered rainforest frogs (Litoria rheocola) becoming infected by a fungal pathogen (Batrachochytrium dendrobatidis). Reductions in canopy cover increased the temperatures and rates of evaporative water loss in frog microhabitats, which reduced B. dendrobatidis infection risk in frogs by an average of 11-28% in cyclone-damaged areas, relative to unaffected areas. Natural disturbances to the rainforest canopy can therefore provide an immediate benefit to frogs by altering the microclimate in ways that reduce infection risk. This could increase host survival and reduce the probability of epidemic disease outbreaks. For amphibian populations under immediate threat from this pathogen, targeted manipulation of canopy cover could increase the availability of warmer, drier microclimates and therefore tip the balance from host extinction to coexistence.

  6. Application of a boundary element method to the study of dynamical torsion of beams

    NASA Technical Reports Server (NTRS)

    Czekajski, C.; Laroze, S.; Gay, D.

    1982-01-01

    During dynamic torsion of beam elements, consideration of nonuniform warping effects involves a more general technical formulation then that of Saint-Venant. Nonclassical torsion constants appear in addition to the well known torsional rigidity. The adaptation of the boundary integral element method to the calculation of these constants for general section shapes is described. The suitability of the formulation is investigated with some examples of thick as well as thin walled cross sections.

  7. Amorphization in the vicinity of a grain boundary: A molecular-dynamics approach

    NASA Astrophysics Data System (ADS)

    Gutiérrez, Gonzalo; Kiwi, Miguel; Ramírez, Ricardo

    1996-10-01

    The dynamics of the melting process of a binary system (such as the one formed by Co and Zr) that contains a grain boundary is investigated by means of molecular dynamics using Lennard-Jones-type interatomic potentials. The evolution of the disordering sequence, as the temperature is increased, is quantitatively studied and graphically illustrated. It is found that the presence of the defect acts like a seed for the disordering, with the genesis of an intermediate amorphous phase. The latter is properly identified and characterized and constitutes an intermediate stage before the proper melting process sets in.

  8. Thermal and Chemical Structures at the Core-Mantle Boundary: Implications for the Mantle Dynamics

    NASA Astrophysics Data System (ADS)

    Stein, C.; Mertens, M.; Hansen, U.

    2013-12-01

    The core-mantle boundary (CMB) represents the lower boundary layer of the actively convecting Earth's mantle and is structurally very complex. For example, large low shear wave velocity provinces (LLSVPs) but also small-scale ultra-low velocity zones (ULVZs) have been detected seismically. Thermal and chemical structures such as thermal plumes and thermochemical piles have been considered to explain the complexities. Both affect the dynamics of the Earth's mantle and its temporal evolution. But also the surface plates are an essential aspect of mantle convection that strongly influence the dynamics of the interior. Cold subducting slabs penetrating the lower boundary layer will also affect the CMB topography. To study the structure and dynamics of the lower mantle we use numerical thermochemical models of mantle convection with a complex rheological approach, including a strong temperature-, stress- and pressure-dependent viscosity. This allows for the investigation of thermal plumes and thermochemical piles in combination with plate-like surface motion and deep subduction. In thermochemical convection dense material is viscously trapped by the flow and piled beneath plumes. The presence of the dense layer reduces the mobility of the surface plates but during plate evolution we find a variety of plume classes (plumes, thermals, line-plumes) leaving a complex structure in the CMB topography.

  9. Single-File System with Absorbing Boundary: Tracer Dynamics and First-Passage Properties

    NASA Astrophysics Data System (ADS)

    Ryabov, Artem

    2015-03-01

    In this paper, we review the tagged particle dynamics in a semi-infinite system with an absorbing boundary. The emphasis is on an interplay between the hard-core interparticle interaction and the absorption process. The exact probability density function for the position of a tagged particle is derived by means of probabilistic arguments. First, the initially homogeneous system with constant density of particles is studied. In this setting, the dynamics of the tracer conditioned on nonabsorption becomes subdiffusive, the generalized diffusion coefficient being different from that reported for the system without absorbing boundary. Second, the case when the initial number of particles is finite is discussed. In this case, in the long time limit the tracer diffusion is normal and the hard-core interaction manifests itself through the renormalization of the tracer diffusion coefficient. The Gaussian distribution derived for infinite single-file systems is, in the present semi-infinite setting, replaced by the Rayleigh distribution. Special Issue Comments: This article presents results on the dynamics of a tagged particle in open systems, where the number of particles is not conserved in time. This article is related to the Special Issue articles about advanced statistical properties in single file dynamics,1 the calculation of correlations,2 files with force3 and the zig-zag patterns in files.4

  10. Tracer dynamics in a single-file system with absorbing boundary.

    PubMed

    Ryabov, Artem; Chvosta, Petr

    2014-02-01

    The paper addresses the single-file diffusion in the presence of an absorbing boundary. The emphasis is on an interplay between the hard-core interparticle interaction and the absorption process. The resulting dynamics exhibits several qualitatively new features. First, starting with the exact probability density function for a given particle (a tracer), we study the long-time asymptotics of its moments. Both the mean position and the mean-square displacement are controlled by dynamical exponents which depend on the initial order of the particle in the file. Second, conditioning on nonabsorption, we study the distribution of long-living particles. In the conditioned framework, the dynamical exponents are the same for all particles, however, a given particle possesses an effective diffusion coefficient which depends on its initial order. After performing the thermodynamic limit, the conditioned dynamics of the tracer is subdiffusive, the generalized diffusion coefficient D(1/2) being different from that reported for the system without absorbing boundary.

  11. Tracer dynamics in a single-file system with absorbing boundary

    NASA Astrophysics Data System (ADS)

    Ryabov, Artem; Chvosta, Petr

    2014-02-01

    The paper addresses the single-file diffusion in the presence of an absorbing boundary. The emphasis is on an interplay between the hard-core interparticle interaction and the absorption process. The resulting dynamics exhibits several qualitatively new features. First, starting with the exact probability density function for a given particle (a tracer), we study the long-time asymptotics of its moments. Both the mean position and the mean-square displacement are controlled by dynamical exponents which depend on the initial order of the particle in the file. Second, conditioning on nonabsorption, we study the distribution of long-living particles. In the conditioned framework, the dynamical exponents are the same for all particles, however, a given particle possesses an effective diffusion coefficient which depends on its initial order. After performing the thermodynamic limit, the conditioned dynamics of the tracer is subdiffusive, the generalized diffusion coefficient D1/2 being different from that reported for the system without absorbing boundary.

  12. High Latitude Outer Radiation Belt Boundary Dynamics In Comparison With the Ovation Model

    NASA Astrophysics Data System (ADS)

    Barinova, Vera; Kalegaev, Vladimir; Myagkova, Irina; Riazantseva, Maria; Dolenko, Sergey; Shirokii, Vladimir

    2016-04-01

    The geometry and the dynamics of the Earth's outer radiation belt polar boundary is described at the altitudes between 500 and 1000 km from the Earth surface in dependence on universal time and geomagnetic activity level expressed by the Dst-index. The quantitative model which was built earlier for the Northern hemisphere in quiet conditions using the Coronas-Photon data measured during extremely quiet 2009 epoch is generalized for both quiet and disturbed conditions using Meteor-M 1 and Meteor-M 2 data obtained from 2009 till now. Both hemispheres are studied. Observations of different satellites were mapped to the single altitude using A2000 magnetospheric magnetic field model. The outer radiation belt boundary is compared with equatorward auroral oval boundary represented by Patrick Newel's Ovation Model at NOAA Web-site for the period from July till December 2015. Prediction of the Earth's outer radiation belt polar boundary for one hour is provided based on the Dst forecasting model. Real-time prediction model was implemented into the set of space weather applications of Space Monitoring Data Center of Moscow State University.

  13. Temporal Dynamics of Bacterial and Fungal Community Composition in the Atmospheric Boundary Layer

    NASA Astrophysics Data System (ADS)

    Emerson, J. B.; Perring, A. E.; Schwarz, J. P.; Fahey, D. W.; Fierer, N.

    2014-12-01

    There is increasing evidence for significant microbial influences on atmospheric chemistry, cloud condensation, and ice nuclei concentrations, with known health impacts, yet we have a limited understanding of the types, abundances, and spatiotemporal dynamics of bacteria and fungi in the atmosphere. Here we use culture-independent molecular approaches, including targeted gene sequencing and quantitative PCR, to characterize bacterial and fungal community composition and abundance in the atmospheric boundary layer. We present results from 32 air samples, collected via vacuum filtration at 10 m and 250 m on the Boulder Atmospheric Observatory tower (Erie, CO) between November 2013 and April 2014. Samples were collected at night, and each sample was integrated over consecutive nights for approximately two weeks. Significant temporal shifts in bacterial and fungal community composition were observed over the course of the study, corresponding to changing bacterial and fungal concentrations. Within the same sampling time periods, bacterial and fungal communities from the near-surface atmosphere (10 m) were generally similar to those aloft (250 m), although coupled temporal and altitudinal effects were observed in some cases, particularly for fungi. Overall, our results indicate that bacterial and fungal communities exhibit minimal vertical stratification throughout the nocturnal atmospheric boundary layer but show a high degree of variability on two-week timescales. This study paves the way for further research into the connections between boundary layer microbiology, atmospheric dynamics, emissions, and local meteorology.

  14. The dynamics of inner dead-zone boundaries in protoplanetary discs

    NASA Astrophysics Data System (ADS)

    Latter, Henrik N.; Balbus, Steven

    2012-08-01

    In protoplanetary discs, the inner radial boundary between the MRI turbulent ('active') and MRI quiescent ('dead') zones plays an important role in models of the disc evolution and in some planet formation scenarios. In reality, this boundary is not well-defined: thermal heating from the star in a passive disc yields a transition radius close to the star (<0.1 au), whereas if the disc is already MRI active, it can self-consistently maintain the requisite temperatures out to a transition radius of roughly 1 au. Moreover, the interface may not be static; it may be highly fluctuating or else unstable. In this paper, we study a reduced model of the dynamics of the active/dead zone interface that mimics several important aspects of a real disc system. We find that MRI-transition fronts propagate inwards (a 'dead front' suppressing the MRI) if they are initially at the larger transition radius, or propagate outwards (an 'active front' igniting the MRI) if starting from the smaller transition radius. In both cases, the front stalls at a well-defined intermediate radius, where it remains in a quasi-static equilibrium. We propose that it is this new, intermediate stalling radius that functions as the true boundary between the active and dead zones in protoplanetary discs. These dynamics are likely implicated in observations of variable accretion, such as FU Ori outbursts, as well as in those planet formation theories that require the accumulation of solid material at the dead/active interface.

  15. The dynamic nature of the reconsolidation process and its boundary conditions: Evidence based on human tests.

    PubMed

    Fernández, Rodrigo S; Bavassi, Luz; Forcato, Cecilia; Pedreira, María E

    2016-04-01

    The reconsolidation process is the mechanism by which the strength and/or content of consolidated memories are updated. This process is triggered by the presentation of a reminder (training cues). It is not always possible to trigger the reconsolidation process. For example, memory age and strength are boundary conditions for the reconsolidation process. Here, we investigated the dynamic changes in these conditions. We propose that the boundary conditions of the reconsolidation process are not fixed and vary as a consequence of the interaction between memory features and reminder characteristics. To modify memory properties, participants received a threatening social protocol that improves memory acquisition or a control condition (fake, without social interaction) prior to learning pairs of meaningless syllables. To determine whether a strong young or old declarative memory undergoes the reconsolidation process, we used an interference task (a second list of pairs of meaningless syllables) to disrupt memory re-stabilization. To assess whether the older memory could be strengthened, we repeated the triggering of reconsolidation. Strong young or old memories modulated by a threatening experience could be interfered during reconsolidation and updated (strengthened) by reconsolidation. Rather than being fixed, boundary conditions vary according to the memory features (strong memory), which indicates the dynamic nature of the reconsolidation process. Our findings demonstrate that it is possible to modify these limits by recruiting the reconsolidation process and making it functionally operative again. This novel scenario opens the possibility to new therapeutically approaches that take into account the reconsolidation process.

  16. Effect of Large Finite-Size Wind Farms and Their Wakes on Atmospheric Boundary Layer Dynamics

    NASA Astrophysics Data System (ADS)

    Wu, Ka Ling; Porté-Agel, Fernando

    2016-04-01

    Through the use of large-eddy simulation, the effect of large finite-size wind farms and their wakes on conventionally-neutral atmospheric boundary layer (ABL) dynamics and power extraction is investigated. Specifically, this study focuses on a wind farm that comprises 25 rows of wind turbines, spanning a distance of 10 km. It is shown that large wind farms have a significant effect on internal boundary layer growth both inside and downwind of the wind farms. If the wind farm is large enough, the internal boundary layer interacts with the thermally-stratified free atmosphere above, leading to a modification of the ABL height and power extraction. In addition, it is shown that large wind farms create extensive wakes, which could have an effect on potential downwind wind farms. Specifically, for the case considered here, a power deficit as large as 8% is found at a distance of 10 km downwind from the wind farm. Furthermore, this study compares the wind farm wake dynamics for cases in which the conventionally neutral ABLs are driven by a unidirectional pressure gradient and Coriolis forces.

  17. Linear and nonlinear dynamic analysis by boundary element method. Ph.D. Thesis, 1986 Final Report

    NASA Technical Reports Server (NTRS)

    Ahmad, Shahid

    1991-01-01

    An advanced implementation of the direct boundary element method (BEM) applicable to free-vibration, periodic (steady-state) vibration and linear and nonlinear transient dynamic problems involving two and three-dimensional isotropic solids of arbitrary shape is presented. Interior, exterior, and half-space problems can all be solved by the present formulation. For the free-vibration analysis, a new real variable BEM formulation is presented which solves the free-vibration problem in the form of algebraic equations (formed from the static kernels) and needs only surface discretization. In the area of time-domain transient analysis, the BEM is well suited because it gives an implicit formulation. Although the integral formulations are elegant, because of the complexity of the formulation it has never been implemented in exact form. In the present work, linear and nonlinear time domain transient analysis for three-dimensional solids has been implemented in a general and complete manner. The formulation and implementation of the nonlinear, transient, dynamic analysis presented here is the first ever in the field of boundary element analysis. Almost all the existing formulation of BEM in dynamics use the constant variation of the variables in space and time which is very unrealistic for engineering problems and, in some cases, it leads to unacceptably inaccurate results. In the present work, linear and quadratic isoparametric boundary elements are used for discretization of geometry and functional variations in space. In addition, higher order variations in time are used. These methods of analysis are applicable to piecewise-homogeneous materials, such that not only problems of the layered media and the soil-structure interaction can be analyzed but also a large problem can be solved by the usual sub-structuring technique. The analyses have been incorporated in a versatile, general-purpose computer program. Some numerical problems are solved and, through comparisons

  18. The impact of anthropogenic emissions on the otherwise pristine Amazonian rainforest: Insights on aerosol dynamics as observed during GoAmazon2014/5

    NASA Astrophysics Data System (ADS)

    Carbone, S.; Ferreira De Brito, J.; Cirino, G. G.; Rizzo, L. V.; Holanda, B. A.; Barbosa, H. M.; Ditas, F.; Pöhlker, C.; Chi, X.; Krüger, M. L.; Moran, D.; Saturno, J.; Andreae, M. O.; de Sá, S. S.; Liu, Y.; Martin, S. T.; Souza, R. A. F. D.; Wang, J.; Palm, B. B.; Jimenez, J. L.; Artaxo, P.

    2015-12-01

    The Amazon Basin during the wet season has one of the lowest aerosol concentrations worldwide, with air masses with negligible human impact covering thousands of kilometers of pristine forest. The natural environment is strongly modified near urbanized areas, in particular Manaus, a city of nearly two million people. This unique location provides the ideal laboratory to study isolated urban emissions as well the pristine environment by perturbing it in a relatively known fashion. The GoAmazon2014/5 experiment was designed with these questions in mind, combining remote sensing, in situ, and airborne measurements. This manuscript describes the measurements taken at the T0 site, upwind of Manaus, (the Amazonian Tall Tower Observatory, ATTO site), at the T2 site, near Manaus, frequently impacted by relatively fresh emissions from the city and at T3, 60 km downwind of Manaus. This work relates the aerosol dynamics of the mixture of anthropogenic emissions from Manaus and the biogenic air masses, and how it evolves from T2 to T3 under different atmospheric conditions. Focus is on the aerosol size distribution, supported by aerosol mass spectrometry and gas-phase composition, in particular at the T2 site. At T0, the aerosol number concentration has been observed to increase from an average of 380 cm-3 to 1750 cm-3 from the wet to the dry season. The mean geometric diameter increased as well, from 95 nm to 145 nm. Interestingly, at the T2 site no significant difference was observed in number concentration between wet and dry seasons (approximately 4300 cm-3) with an average diameter of 60 nm during the former and 97 nm in the latter. Such measurements provide a unique dataset to understand the aerosol life cycle and the impact of urban emissions in the heart of the Amazon Forest.

  19. Plant traits demonstrate that temperate and tropical giant eucalypt forests are ecologically convergent with rainforest not savanna.

    PubMed

    Tng, David Y P; Jordan, Greg J; Bowman, David M J S

    2013-01-01

    Ecological theory differentiates rainforest and open vegetation in many regions as functionally divergent alternative stable states with transitional (ecotonal) vegetation between the two forming transient unstable states. This transitional vegetation is of considerable significance, not only as a test case for theories of vegetation dynamics, but also because this type of vegetation is of major economic importance, and is home to a suite of species of conservation significance, including the world's tallest flowering plants. We therefore created predictions of patterns in plant functional traits that would test the alternative stable states model of these systems. We measured functional traits of 128 trees and shrubs across tropical and temperate rainforest - open vegetation transitions in Australia, with giant eucalypt forests situated between these vegetation types. We analysed a set of functional traits: leaf carbon isotopes, leaf area, leaf mass per area, leaf slenderness, wood density, maximum height and bark thickness, using univariate and multivariate methods. For most traits, giant eucalypt forest was similar to rainforest, while rainforest, particularly tropical rainforest, was significantly different from the open vegetation. In multivariate analyses, tropical and temperate rainforest diverged functionally, and both segregated from open vegetation. Furthermore, the giant eucalypt forests overlapped in function with their respective rainforests. The two types of giant eucalypt forests also exhibited greater overall functional similarity to each other than to any of the open vegetation types. We conclude that tropical and temperate giant eucalypt forests are ecologically and functionally convergent. The lack of clear functional differentiation from rainforest suggests that giant eucalypt forests are unstable states within the basin of attraction of rainforest. Our results have important implications for giant eucalypt forest management.

  20. Molecular dynamics simulations of elasto-hydrodynamic lubrication and boundary lubrication for automotive tribology

    NASA Astrophysics Data System (ADS)

    Washizu, Hitoshi; Sanda, Shuzo; Hyodo, Shi-aki; Ohmori, Toshihide; Nishino, Noriaki; Suzuki, Atsushi

    2007-11-01

    Friction control of machine elements on a molecular level is a challenging subject in vehicle technology. We describe the molecular dynamics studies of friction in two significant lubrication regimes. As a case of elastohydrodynamic lubrication, we introduce the mechanism of momentum transfer related to the molecular structure of the hydrocarbon fluids, phase transition of the fluids under high pressure, and a submicron thickness simulation of the oil film using a tera-flops computer. For boundary lubrication, the dynamic behavior of water molecules on hydrophilic and hydrophobic silicon surfaces under a shear condition is studied. The dynamic structure of the hydrogen bond network on the hydrophilic surface is related to the low friction of the diamond-like carbon containing silicon (DLC-Si) coating.

  1. Diffusion Coefficients in Liquid and Grain Boundary Predicted by Ab Initio Molecular Dynamics

    SciTech Connect

    Jablonski, P.D.; Liu, Z.; Fang, H.; Wang, B.

    2011-04-01

    Molecular dynamics (MD) is a powerful tool to probe the thermodynamic and kinetic properties of solid, glass and liquid phases. In classical molecular dynamics (CMD), empirical models are used to describe the force by considering bond, bend and dihedral angle contributions with parameters fitted to experimental data or first-principles calculations of small clusters. In the ab initio molecular dynamics (AIMD), the forces are calculated on the fly using the first-principles density functional theory as discussed above. In the present work, we use AIMD simulations to follow the random walk of atoms in the liquid state. Based on the mean square displacements (MSD), the diffusion coefficients are calculated from the Einstein equation. Furthermore, we extend this approach to understand the diffusion in grain boundaries.

  2. MODIS EVI Landscape Phenology across Amazon Rainforest-Cerrado Ecotone

    NASA Astrophysics Data System (ADS)

    Ratana, P.; Huete, A. R.; Restrepo-Coupe, N.; Shimabukuro, Y. E.

    2012-12-01

    There is ongoing attention and controversy placed on the response of tropical rainforests to seasonal and inter-annual drought periods over Amazon basin. Many studies confirm the seasonal greening observed during dry periods and attribute the greening to increased sunlight under conditions of deep soil water access by intact rainforests. There is controversy, however, on the extent and duration of greening during inter-annual drought periods. In this study, we start with the premise that the Amazon basin is not a uniform biome with a single dry-wet seasonal cycle and therefore, drought impacts and greenness seasonality will be quite variable with location, particularly along known climate- vegetation transitions, such as the Amazon forest- cerrado ecotone transition zone. The 10+ years of Moderate Resolution Imaging Spectroradiometer (MODIS) Enhanced Vegetation Index (EVI) time-series data were analyzed for seasonal/ phenology variations across Amazon rainforest-cerrado ecotone. Strong differences in phenology patterns were found in response to shifts in rainfall and sunlight. Greening in the tropical rainforests and more humid areas of the ecotone, were coincident with maximum periods of solar radiation in the dry season, while the phenology profiles of the drier Amazon forests were more strongly coupled with rainfall. Through the remaining portions of the ecotone region, there were mixed, non-synchronized phenology responses to climate with increasing lags in greening into the latter parts of the dry season. This was partially attributed to differences in vegetation composition and plant functional types in the ecotone and their phenology cycles. Phenology profiles in the transition zone were also highly sensitive to forest fragmentation and conversion, with their seasonal dynamics behaving similarly to the cerrado. In contrast to the rainforests, the ecotone region has received much less attention and is generally ignored in climate-biosphere models, yet is

  3. Piecewise Smooth Dynamical Systems Theory: The Case of the Missing Boundary Equilibrium Bifurcations

    NASA Astrophysics Data System (ADS)

    Hogan, S. J.; Homer, M. E.; Jeffrey, M. R.; Szalai, R.

    2016-10-01

    We present two codimension-one bifurcations that occur when an equilibrium collides with a discontinuity in a piecewise smooth dynamical system. These simple cases appear to have escaped recent classifications. We present them here to highlight some of the powerful results from Filippov's book Differential Equations with Discontinuous Righthand Sides (Kluwer, 1988). Filippov classified the so-called boundary equilibrium collisions without providing their unfolding. We show the complete unfolding here, for the first time, in the particularly interesting case of a node changing its stability as it collides with a discontinuity. We provide a prototypical model that can be used to generate all codimension-one boundary equilibrium collisions, and summarize the elements of Filippov's work that are important in achieving a full classification.

  4. Improved three-dimensional bubble dynamics model based on boundary element method

    NASA Astrophysics Data System (ADS)

    Zhang, A. M.; Liu, Y. L.

    2015-08-01

    Some new theoretical and numerical techniques are adopted in an improved 3D bubble dynamics model based on Boundary Element Method. Firstly, a numerical model under the incompressible potential assumption is established for 3D bubble dynamics, and the traditional technique for the vortex ring induced potential at the reference point in axisymmetric model is extended to arbitrary location in 3D model. Then, to homogenize the boundaries' mesh density, new Density Potential Method is put forward inspired by the Elastic Mesh Technique. It's combined together with the topology optimization based on edge swapping procedure to maintain a desirable mesh for the large deformation problem. Through the verification and the comparison by simulating a benchmark case, the improved model demonstrates good accuracy and stability. Particularly, more toroidal bubble evolution detailed features are captured which are in accordance with the axisymmetric model. Finally, bubble dynamics under different circumstances are simulated with the improved 3D numerical model presented in this paper, which shows that the improved model is also robust.

  5. Approaching the asymptotic regime of rapidly rotating convection: boundary layers versus interior dynamics.

    PubMed

    Stellmach, S; Lischper, M; Julien, K; Vasil, G; Cheng, J S; Ribeiro, A; King, E M; Aurnou, J M

    2014-12-19

    Rapidly rotating Rayleigh-Bénard convection is studied by combining results from direct numerical simulations (DNS), laboratory experiments, and asymptotic modeling. The asymptotic theory is shown to provide a good description of the bulk dynamics at low, but finite Rossby number. However, large deviations from the asymptotically predicted heat transfer scaling are found, with laboratory experiments and DNS consistently yielding much larger Nusselt numbers than expected. These deviations are traced down to dynamically active Ekman boundary layers, which are shown to play an integral part in controlling heat transfer even for Ekman numbers as small as 10^{-7}. By adding an analytical parametrization of the Ekman transport to simulations using stress-free boundary conditions, we demonstrate that the heat transfer jumps from values broadly compatible with the asymptotic theory to states of strongly increased heat transfer, in good quantitative agreement with no-slip DNS and compatible with the experimental data. Finally, similarly to nonrotating convection, we find no single scaling behavior, but instead that multiple well-defined dynamical regimes exist in rapidly rotating convection systems.

  6. Dynamic programming in parallel boundary detection with application to ultrasound intima-media segmentation.

    PubMed

    Zhou, Yuan; Cheng, Xinyao; Xu, Xiangyang; Song, Enmin

    2013-12-01

    Segmentation of carotid artery intima-media in longitudinal ultrasound images for measuring its thickness to predict cardiovascular diseases can be simplified as detecting two nearly parallel boundaries within a certain distance range, when plaque with irregular shapes is not considered. In this paper, we improve the implementation of two dynamic programming (DP) based approaches to parallel boundary detection, dual dynamic programming (DDP) and piecewise linear dual dynamic programming (PL-DDP). Then, a novel DP based approach, dual line detection (DLD), which translates the original 2-D curve position to a 4-D parameter space representing two line segments in a local image segment, is proposed to solve the problem while maintaining efficiency and rotation invariance. To apply the DLD to ultrasound intima-media segmentation, it is imbedded in a framework that employs an edge map obtained from multiplication of the responses of two edge detectors with different scales and a coupled snake model that simultaneously deforms the two contours for maintaining parallelism. The experimental results on synthetic images and carotid arteries of clinical ultrasound images indicate improved performance of the proposed DLD compared to DDP and PL-DDP, with respect to accuracy and efficiency.

  7. Historical distribution of Sundaland’s Dipterocarp rainforests at Quaternary glacial maxima

    PubMed Central

    Cannon, Charles H.; Hijmans, Robert J.; Piessens, Thomas; Saw, Leng Guan; van Welzen, Peter C.; Slik, J. W. Ferry

    2014-01-01

    The extent of Dipterocarp rainforests on the emergent Sundaland landmass in Southeast Asia during Quaternary glaciations remains a key question. A better understanding of the biogeographic history of Sundaland could help explain current patterns of biodiversity and support the development of effective forest conservation strategies. Dipterocarpaceae trees dominate the rainforests of Sundaland, and their distributions serve as a proxy for rainforest extent. We used species distribution models (SDMs) of 317 Dipterocarp species to estimate the geographic extent of appropriate climatic conditions for rainforest on Sundaland at the last glacial maximum (LGM). The SDMs suggest that the climate of central Sundaland at the LGM was suitable to sustain Dipterocarp rainforest, and that the presence of a previously suggested transequatorial savannah corridor at that time is unlikely. Our findings are supported by palynologic evidence, dynamic vegetation models, extant mammal and termite communities, vascular plant fatty acid stable isotopic compositions, and stable carbon isotopic compositions of cave guano profiles. Although Dipterocarp species richness was generally lower at the LGM, areas of high species richness were mostly found off the current islands and on the emergent Sunda Shelf, indicating substantial species migration and mixing during the transitions between the Quaternary glacial maxima and warm periods such as the present. PMID:25385612

  8. Air Flow Path Dynamics In The Vadose Zone Under Various Land Surface Climate Boundary Conditions

    NASA Astrophysics Data System (ADS)

    Illangasekare, T. H.; Sakaki, T.; Schulte, P. E.; Cihan, A.; Christ, J.

    2010-12-01

    land surface dynamically affects the vapor transport pathways. A two-dimensional soil tank 2.4 m long and 1.2 m in height was used in the experimental investigation. The tank was packed using four test sands to represent a heterogeneous configuration. Constant temperature boundary conditions were created at the soil surface using thermostatically controlled heaters. A rain-making device controlled the water flux boundary conditions. The tank was instrumented with dielectric soil moisture sensors to measure soil moisture distribution and hydrophobic tensiometers to record transient air pressures. The data generated were then used to obtain a qualitative understanding of how the heat and water flux boundary conditions control the development of preferential air pathways, and to validate a two-phase flow numerical tool developed based on COMSOL multiphysics simulator.

  9. Stable boundary approximations for a class of implicit schemes for the one-dimensional inviscid equations of gas dynamics

    NASA Technical Reports Server (NTRS)

    Yee, H. C.; Beam, R. M.; Warming, R. F.

    1981-01-01

    The applicability to practical calculations of recent theoretical developments in the stability analysis of difference approximations for initial-boundary-value problems of the hyperbolic type. For the numerical experiments, select the one-dimensional inviscid gas-dynamic equations in conservation-law form is selected. A class of implicit schemes based on linear multistep methods for ordinary differential equations is chosen and the use of space or space-time extrapolations as implicit or explicit boundary schemes is emphasized. Some numerical examples with various inflow-outflow conditions highlight the commonly discussed issues: explicit versus implicit boundary schemes, unconditionally stable schemes, and underspecification or overspecification of boundary conditions.

  10. Dislocation mechanism of void growth at twin boundary of nanotwinned nickel based on molecular dynamics simulation

    NASA Astrophysics Data System (ADS)

    Zhang, Yanqiu; Jiang, Shuyong; Zhu, Xiaoming; Zhao, Yanan

    2016-08-01

    Molecular dynamics simulation was performed to investigate dislocation mechanism of void growth at twin boundary (TB) of nanotwinned nickel. Simulation results show that the deformation of nanotwinned nickel containing a void at TB is dominated by the slip involving both leading and trailing partials, where the trailing partials are the dissociation products of stair-rod dislocations formed by the leading partials. The growth of a void at TB is attributed to the successive emission of the leading partials followed by trailing partials as well as the escape of these partial dislocations from the void surface.

  11. Dynamic Stability Optimization of Laminated Composite Plates under Combined Boundary Loading

    NASA Astrophysics Data System (ADS)

    Shafei, Erfan; Kabir, Mohammad Zaman

    2011-12-01

    Dynamic stability and design optimization of laminated simply supported plates under planar conservative boundary loads are investigated in current study. Examples can be found in internal connecting elements of spacecraft and aerospace structures subjected to edge axial and shear loads. Designation of such elements is function of layup configuration, plate aspect ratio, loading combinations, and layup thickness. An optimum design aims maximum stability load satisfying a predefined stable vibration frequency. The interaction between compound loading and layup angle parameter affects the order of merging vibration modes and may stabilize the dynamic response. Laminated plates are assumed to be angle-plies symmetric to mid-plane surface. Dynamic equilibrium PDE has been solved using kernel integral transformation for modal frequency values and eigenvalue-based orthogonal functions for critical stability loads. The dictating dynamic stability mode is shown to be controlled by geometric stiffness distributions of composite plates. Solution of presented design optimization problem has been done using analytical approach combined with interior penalty multiplier algorithm. The results are verified by FEA approach and stability zones of original and optimized plates are stated as final data. Presented method can help designers to stabilize the dynamic response of composite plates by selecting an optimized layup orientation and thickness for prescribed design circumstances.

  12. Using immersed boundary methods to couple a dynamical ocean model to a dynamical ice sheet/ice shelf model

    NASA Astrophysics Data System (ADS)

    Asay-Davis, Xylar; Lipscomb, William; Price, Steven

    2010-05-01

    The melting of the West Antarctic Ice Sheet (WAIS), the world's largest marine ice sheet, would mean a ~5 meter sea level rise worldwide. About a third of the WAIS lies in the Amundsen Sea Embayment, where small ice shelves provide buttressing for outlet glaciers. Warming oceans may melt the supporting ice shelves leading to accelerated flow of the outlet glaciers. Perhaps more importantly, warming oceans may mean that warm circumpolar deep water can more easily reach the ice sheet grounding line, where it can melt grounded ice directly and force retreat. Previous theoretical work suggests that ice sheets, such as the WAIS, with seabeds that deepen inland may be unstable to grounding line retreat. We present simulations from a coupled dynamical ocean model (based on POP) and dynamical ice sheet/ice shelf model (Glimmer-CISM). This work is a stepping stone toward a global scale simulation of the southern ocean (using CCSM) together with the full Antarctic ice sheet (using Glimmer-CISM). The ocean model uses an immersed boundary method (IBM) to represent the complex, time-evolving geometry of the ice shelf. The IBM allows for accurate representation of the boundary conditions at the ocean/ice interface without the need for a modeling grid that conforms to the boundary or that changes in time. Using simplified seabed and ice shelf geometries, our simulations explore the effects of varying the seabed slope on the stability of ice sheets. We also investigate the melt rates that result from varying levels of seawater warming beneath the ice shelves.

  13. Traction–separation relationships for hydrogen induced grain boundary embrittlement in nickel via molecular dynamics simulations

    DOE PAGESBeta

    Barrows, Wesley; Dingreville, Rémi; Spearot, Douglas

    2015-10-19

    A statistical approach combined with molecular dynamics simulations is used to study the influence of hydrogen on intergranular decohesion. This methodology is applied to a Ni Σ3(112)[11¯0] symmetric tilt grain boundary. Hydrogenated grain boundaries with different H concentrations are constructed using an energy minimization technique with initial H atom positions guided by Monte Carlo simulation results. Decohesion behavior is assessed through extraction of a traction–separation relationship during steady-state crack propagation in a statistically meaningful approach, building upon prior work employing atomistic cohesive zone volume elements (CZVEs). A sensitivity analysis is performed on the numerical approach used to extract the traction–separationmore » relationships, clarifying the role of CZVE size, threshold parameters necessary to differentiate elastic and decohesion responses, and the numerical averaging technique. Results show that increasing H coverage at the Ni Σ3(112)[11¯0] grain boundary asymmetrically influences the crack tip velocity during propagation, leads to a general decrease in the work of separation required for crack propagation, and provides a reduction in the peak stress in the extracted traction–separation relationship. Furthermore the present framework offers a meaningful vehicle to pass atomistically derived interfacial behavior to higher length scale formulations for intergranular fracture.« less

  14. Equilibrium Limit of Boundary Scattering in Carbon Nanostructures: Molecular Dynamics Calculations of Thermal Transport

    NASA Technical Reports Server (NTRS)

    Haskins, Justin; Kinaci, Alper; Sevik, Cem; Cagin, Tahir

    2012-01-01

    It is widely known that graphene and many of its derivative nanostructures have exceedingly high reported thermal conductivities (up to 4000 W/mK at 300 K). Such attractive thermal properties beg the use of these structures in practical devices; however, to implement these materials while preserving transport quality, the influence of structure on thermal conductivity should be thoroughly understood. For graphene nanostructures, having average phonon mean free paths on the order of one micron, a primary concern is how size influences the potential for heat conduction. To investigate this, we employ a novel technique to evaluate the lattice thermal conductivity from the Green-Kubo relations and equilibrium molecular dynamics in systems where phonon-boundary scattering dominates heat flow. Specifically, the thermal conductivities of graphene nanoribbons and carbon nanotubes are calculated in sizes up to 3 microns, and the relative influence of boundary scattering on thermal transport is determined to be dominant at sizes less than 1 micron, after which the thermal transport largely depends on the quality of the nanostructure interface. The method is also extended to carbon nanostructures (fullerenes) where phonon confinement, as opposed to boundary scattering, dominates, and general trends related to the influence of curvature on thermal transport in these materials are discussed.

  15. Periodic boundary conditions for long-time nonequilibrium molecular dynamics simulations of incompressible flows

    NASA Astrophysics Data System (ADS)

    Dobson, Matthew

    2014-11-01

    This work presents a generalization of the Kraynik-Reinelt (KR) boundary conditions for nonequilibrium molecular dynamics simulations. In the simulation of steady, homogeneous flows with periodic boundary conditions, the simulation box deforms with the flow, and it is possible for image particles to become arbitrarily close, causing a breakdown in the simulation. The KR boundary conditions avoid this problem for planar elongational flow and general planar mixed flow [T. A. Hunt, S. Bernardi, and B. D. Todd, J. Chem. Phys. 133, 154116 (2010)] through careful choice of the initial simulation box and by periodically remapping the simulation box in a way that conserves image locations. In this work, the ideas are extended to a large class of three-dimensional flows by using multiple remappings for the simulation box. The simulation box geometry is no longer time-periodic (which was shown to be impossible for uniaxial and biaxial stretching flows in the original work by Kraynik and Reinelt [Int. J. Multiphase Flow 18, 1045 (1992)]. The presented algorithm applies to all flows with nondefective flow matrices, and in particular, to uniaxial and biaxial flows.

  16. An Alternative Frictional Boundary Condition for Computational Fluid Dynamics Simulation of Friction Stir Welding

    NASA Astrophysics Data System (ADS)

    Chen, Gaoqiang; Feng, Zhili; Zhu, Yucan; Shi, Qingyu

    2016-07-01

    For better application of numerical simulation in optimization and design of friction stir welding (FSW), this paper presents a new frictional boundary condition at the tool/workpiece interface for computational fluid dynamics (CFD) modeling of FSW. The proposed boundary condition is based on an implementation of the Coulomb friction model. Using the new boundary condition, the CFD simulation yields non-uniform distribution of contact state over the tool/workpiece interface, as validated by the experimental weld macrostructure. It is found that interfacial sticking state is present over large area at the tool-workpiece interface, while significant interfacial sliding occurs at the shoulder periphery, the lower part of pin side, and the periphery of pin bottom. Due to the interfacial sticking, a rotating flow zone is found under the shoulder, in which fast circular motion occurs. The diameter of the rotating flow zone is smaller than the shoulder diameter, which is attributed to the presence of the interfacial sliding at the shoulder periphery. For the simulated welding condition, the heat generation due to friction and plastic deformation makes up 54.4 and 45.6% of the total heat generation rate, respectively. The simulated temperature field is validated by the good agreement to the experimental measurements.

  17. Convection and reaction in a diffusive boundary layer in a porous medium: Nonlinear dynamics

    NASA Astrophysics Data System (ADS)

    Andres, Jeanne Therese H.; Cardoso, Silvana S. S.

    2012-09-01

    We study numerically the nonlinear interactions between chemical reaction and convective fingering in a diffusive boundary layer in a porous medium. The reaction enhances stability by consuming a solute that is unstably distributed in a gravitational field. We show that chemical reaction profoundly changes the dynamics of the system, by introducing a steady state, shortening the evolution time, and altering the spatial patterns of velocity and concentration of solute. In the presence of weak reaction, finger growth and merger occur effectively, driving strong convective currents in a thick layer of solute. However, as the reaction becomes stronger, finger growth is inhibited, tip-splitting is enhanced and the layer of solute becomes much thinner. Convection enhances the mass flux of solute consumed by reaction in the boundary layer but has a diminishing effect as reaction strength increases. This nonlinear behavior has striking differences to the density fingering of traveling reaction fronts, for which stronger chemical kinetics result in more effective finger merger owing to an increase in the speed of the front. In a boundary layer, a strong stabilizing effect of reaction can maintain a long-term state of convection in isolated fingers of wavelength comparable to that at onset of instability.

  18. An Alternative Frictional Boundary Condition for Computational Fluid Dynamics Simulation of Friction Stir Welding

    NASA Astrophysics Data System (ADS)

    Chen, Gaoqiang; Feng, Zhili; Zhu, Yucan; Shi, Qingyu

    2016-09-01

    For better application of numerical simulation in optimization and design of friction stir welding (FSW), this paper presents a new frictional boundary condition at the tool/workpiece interface for computational fluid dynamics (CFD) modeling of FSW. The proposed boundary condition is based on an implementation of the Coulomb friction model. Using the new boundary condition, the CFD simulation yields non-uniform distribution of contact state over the tool/workpiece interface, as validated by the experimental weld macrostructure. It is found that interfacial sticking state is present over large area at the tool-workpiece interface, while significant interfacial sliding occurs at the shoulder periphery, the lower part of pin side, and the periphery of pin bottom. Due to the interfacial sticking, a rotating flow zone is found under the shoulder, in which fast circular motion occurs. The diameter of the rotating flow zone is smaller than the shoulder diameter, which is attributed to the presence of the interfacial sliding at the shoulder periphery. For the simulated welding condition, the heat generation due to friction and plastic deformation makes up 54.4 and 45.6% of the total heat generation rate, respectively. The simulated temperature field is validated by the good agreement to the experimental measurements.

  19. Traction–separation relationships for hydrogen induced grain boundary embrittlement in nickel via molecular dynamics simulations

    SciTech Connect

    Barrows, Wesley; Dingreville, Rémi; Spearot, Douglas

    2015-10-19

    A statistical approach combined with molecular dynamics simulations is used to study the influence of hydrogen on intergranular decohesion. This methodology is applied to a Ni Σ3(112)[11¯0] symmetric tilt grain boundary. Hydrogenated grain boundaries with different H concentrations are constructed using an energy minimization technique with initial H atom positions guided by Monte Carlo simulation results. Decohesion behavior is assessed through extraction of a traction–separation relationship during steady-state crack propagation in a statistically meaningful approach, building upon prior work employing atomistic cohesive zone volume elements (CZVEs). A sensitivity analysis is performed on the numerical approach used to extract the traction–separation relationships, clarifying the role of CZVE size, threshold parameters necessary to differentiate elastic and decohesion responses, and the numerical averaging technique. Results show that increasing H coverage at the Ni Σ3(112)[11¯0] grain boundary asymmetrically influences the crack tip velocity during propagation, leads to a general decrease in the work of separation required for crack propagation, and provides a reduction in the peak stress in the extracted traction–separation relationship. Furthermore the present framework offers a meaningful vehicle to pass atomistically derived interfacial behavior to higher length scale formulations for intergranular fracture.

  20. Mg2SiO4 Forsterite Grain Boundary Structures and Self-diffusion from Classical Molecular Dynamics Simulations

    NASA Astrophysics Data System (ADS)

    Wagner, J.; Adjaoud, O.; Marquardt, K.; Jahn, S.

    2015-12-01

    It is well understood that grain boundaries influence many key physicochemical properties of crystalline materials and earth materials are no exception to this. Grain boundaries in the mineral olivine have reshaped our understanding of geophysical processes in the earth's mantle, e.g. in form of enhanced element transport through grain boundary diffusion. Investigations of the relation between transport rate, energy and geometry of individual grain boundaries is compulsory to understand transport in aggregates with a lattice preferred orientation (LPO) that favours the presence and or alignment of specific grain boundaries over random grain boundaries in an undeformed rock. In this contribution, we perform classical molecular dynamics simulations of a series of symmetric and one asymmetric tilt grain boundaries of Mg2SiO4 (forsterite), ranging from 9.58° to 90° in misorientation and varying surface termination (see 1). Our emphasis lies on unravelling structural characteristics of high and low angle grain boundaries and how these influence grain boundary energy and self-diffusion processes. To obtain diffusion rates for different grain boundary geometries, we equilibrate the respective grain boundary systems at ambient pressure and temperatures from 1900-2200K and trace their evolution for run durations of more than100 ps. Subsequently, we track the mean square displacement of the different atomic species within the grain boundary layer over time to estimate self-diffusion constants for each grain boundary geometry and temperature. First results suggest that diffusion rates decrease with increasing grain boundary energy. We will discuss these results in the light of recent experimental data and show strength and limitations of the method applied. 1. Adjaoud, O., Marquardt, K., Jahn, S., Phys Chem Miner 39, 749-760 (2012)

  1. Hotspots of boundary accumulation: dynamics and statistics of micro-swimmers in flowing films.

    PubMed

    Mathijssen, Arnold J T M; Doostmohammadi, Amin; Yeomans, Julia M; Shendruk, Tyler N

    2016-02-01

    Biological flows over surfaces and interfaces can result in accumulation hotspots or depleted voids of microorganisms in natural environments. Apprehending the mechanisms that lead to such distributions is essential for understanding biofilm initiation. Using a systematic framework, we resolve the dynamics and statistics of swimming microbes within flowing films, considering the impact of confinement through steric and hydrodynamic interactions, flow and motility, along with Brownian and run-tumble fluctuations. Micro-swimmers can be peeled off the solid wall above a critical flow strength. However, the interplay of flow and fluctuations causes organisms to migrate back towards the wall above a secondary critical value. Hence, faster flows may not always be the most efficacious strategy to discourage biofilm initiation. Moreover, we find run-tumble dynamics commonly used by flagellated microbes to be an intrinsically more successful strategy to escape from boundaries than equivalent levels of enhanced Brownian noise in ciliated organisms.

  2. Roughness Effects on Wind-Turbine Wake Dynamics in a Boundary-Layer Wind Tunnel

    NASA Astrophysics Data System (ADS)

    Barlas, E.; Buckingham, S.; van Beeck, J.

    2016-01-01

    Increasing demand in wind energy has resulted in increasingly clustered wind farms, and raised the interest in wake research dramatically in the last couple of years. To this end, the present work employs an experimental approach with scaled three-bladed wind-turbine models in a large boundary-layer wind-tunnel. Time-resolved measurements are carried out with a three-component hot-wire anemometer in the mid-vertical plane of the wake up to a downstream distance of eleven turbine diameters. The major issue addressed is the wake dynamics i.e. the flow and turbulence characteristics as well as spectral content under two different neutral boundary-layer inflow conditions. The wind tunnel is arranged with and without roughened surfaces in order to mimic moderately rough and smooth conditions. The inflow characterization is carried out by using all three velocity components, while the rest of the study is focused on the streamwise component's evolution. The results show an earlier wake recovery, i.e. the velocity deficit due to the turbine is less persistent for the rough case due to higher incoming turbulence levels. This paves the way for enhanced mixing from higher momentum regions of the boundary layer towards the centre of the wake. The investigation on the turbulent shear stresses is in line with this observation as well. Moreover, common as well as distinguishing features of the turbulent-scales evolution are detected for rough and smooth inflow boundary-layer conditions. Wake meandering disappears for rough inflow conditions but persists for smooth case with a Strouhal number similar to that of a solid disk wake.

  3. Fluid Dynamics of Biomimetic Pectoral Fin Propulsion Using Immersed Boundary Method.

    PubMed

    Li, Ningyu; Su, Yumin

    2016-01-01

    Numerical simulations are carried out to study the fluid dynamics of a complex-shaped low-aspect-ratio pectoral fin that performs the labriform swimming. Simulations of flow around the fin are achieved by a developed immersed boundary (IB) method, in which we have proposed an efficient local flow reconstruction algorithm with enough robustness and a new numerical strategy with excellent adaptability to deal with complex moving boundaries involved in bionic flow simulations. The prescribed fin kinematics in each period consists of the power stroke and the recovery stroke, and the simulations indicate that the former is mainly used to provide the thrust while the latter is mainly used to provide the lift. The fin wake is dominated by a three-dimensional dual-ring vortex wake structure where the partial power-stroke vortex ring is linked to the recovery-stroke ring vertically. Moreover, the connection of force production with the fin kinematics and vortex dynamics is discussed in detail to explore the propulsion mechanism. We also conduct a parametric study to understand how the vortex topology and hydrodynamic characteristics change with key parameters. The results show that there is an optimal phase angle and Strouhal number for this complicated fin. Furthermore, the implications for the design of a bioinspired pectoral fin are discussed based on the quantitative hydrodynamic analysis. PMID:27478363

  4. A dynamic slip boundary condition for wall-modeled large-eddy simulation

    NASA Astrophysics Data System (ADS)

    Bose, S. T.; Moin, P.

    2014-01-01

    Wall models for large-eddy simulation (LES) are a necessity to remove the prohibitive resolution requirements of near-wall turbulence in high Reynolds turbulent flows. Traditional wall models often rely on assumptions about the local state of the boundary layer (e.g., logarithmic velocity profiles) and require a priori prescription of tunable model coefficients. In the present study, a slip velocity boundary condition for the filtered velocity field is obtained from the derivation of the LES equations using a differential filter. A dynamic procedure for the local slip length is additionally formulated making the slip velocity wall model free of any a priori specified coefficients. The accuracy of the dynamic slip velocity wall model is tested in a series of turbulent channel flows at varying Reynolds numbers and in the LES of a National Advisory Committee for Aeronautics (NACA) 4412 airfoil at near-stall conditions. The wall-modeled simulations are able to accurately predict mean flow characteristics, including the formation of a trailing-edge separation bubble in NACA 4412 configuration. The validation cases demonstrate the effectiveness of this wall-modeling approach in both attached and separated flow regimes.

  5. Fluid Dynamics of Biomimetic Pectoral Fin Propulsion Using Immersed Boundary Method

    PubMed Central

    Li, Ningyu; Su, Yumin

    2016-01-01

    Numerical simulations are carried out to study the fluid dynamics of a complex-shaped low-aspect-ratio pectoral fin that performs the labriform swimming. Simulations of flow around the fin are achieved by a developed immersed boundary (IB) method, in which we have proposed an efficient local flow reconstruction algorithm with enough robustness and a new numerical strategy with excellent adaptability to deal with complex moving boundaries involved in bionic flow simulations. The prescribed fin kinematics in each period consists of the power stroke and the recovery stroke, and the simulations indicate that the former is mainly used to provide the thrust while the latter is mainly used to provide the lift. The fin wake is dominated by a three-dimensional dual-ring vortex wake structure where the partial power-stroke vortex ring is linked to the recovery-stroke ring vertically. Moreover, the connection of force production with the fin kinematics and vortex dynamics is discussed in detail to explore the propulsion mechanism. We also conduct a parametric study to understand how the vortex topology and hydrodynamic characteristics change with key parameters. The results show that there is an optimal phase angle and Strouhal number for this complicated fin. Furthermore, the implications for the design of a bioinspired pectoral fin are discussed based on the quantitative hydrodynamic analysis. PMID:27478363

  6. Fluid Dynamics of Biomimetic Pectoral Fin Propulsion Using Immersed Boundary Method.

    PubMed

    Li, Ningyu; Su, Yumin

    2016-01-01

    Numerical simulations are carried out to study the fluid dynamics of a complex-shaped low-aspect-ratio pectoral fin that performs the labriform swimming. Simulations of flow around the fin are achieved by a developed immersed boundary (IB) method, in which we have proposed an efficient local flow reconstruction algorithm with enough robustness and a new numerical strategy with excellent adaptability to deal with complex moving boundaries involved in bionic flow simulations. The prescribed fin kinematics in each period consists of the power stroke and the recovery stroke, and the simulations indicate that the former is mainly used to provide the thrust while the latter is mainly used to provide the lift. The fin wake is dominated by a three-dimensional dual-ring vortex wake structure where the partial power-stroke vortex ring is linked to the recovery-stroke ring vertically. Moreover, the connection of force production with the fin kinematics and vortex dynamics is discussed in detail to explore the propulsion mechanism. We also conduct a parametric study to understand how the vortex topology and hydrodynamic characteristics change with key parameters. The results show that there is an optimal phase angle and Strouhal number for this complicated fin. Furthermore, the implications for the design of a bioinspired pectoral fin are discussed based on the quantitative hydrodynamic analysis.

  7. Hybrid state vector methods for structural dynamic and aeroelastic boundary value problems

    NASA Technical Reports Server (NTRS)

    Lehman, L. L.

    1982-01-01

    A computational technique is developed that is suitable for performing preliminary design aeroelastic and structural dynamic analyses of large aspect ratio lifting surfaces. The method proves to be quite general and can be adapted to solving various two point boundary value problems. The solution method, which is applicable to both fixed and rotating wing configurations, is based upon a formulation of the structural equilibrium equations in terms of a hybrid state vector containing generalized force and displacement variables. A mixed variational formulation is presented that conveniently yields a useful form for these state vector differential equations. Solutions to these equations are obtained by employing an integrating matrix method. The application of an integrating matrix provides a discretization of the differential equations that only requires solutions of standard linear matrix systems. It is demonstrated that matrix partitioning can be used to reduce the order of the required solutions. Results are presented for several example problems in structural dynamics and aeroelasticity to verify the technique and to demonstrate its use. These problems examine various types of loading and boundary conditions and include aeroelastic analyses of lifting surfaces constructed from anisotropic composite materials.

  8. Strongly Coupled Fluid-Body Dynamics in the Immersed Boundary Projection Method

    NASA Astrophysics Data System (ADS)

    Wang, Chengjie; Eldredge, Jeff D.

    2014-11-01

    A computational algorithm is developed to simulate dynamically coupled interaction between fluid and rigid bodies. The basic computational framework is built upon a multi-domain immersed boundary method library, whirl, developed in previous work. In this library, the Navier-Stokes equations for incompressible flow are solved on a uniform Cartesian grid by the vorticity-based immersed boundary projection method of Colonius and Taira. A solver for the dynamics of rigid-body systems is also included. The fluid and rigid-body solvers are strongly coupled with an iterative approach based on the block Gauss-Seidel method. Interfacial force, with its intimate connection with the Lagrange multipliers used in the fluid solver, is used as the primary iteration variable. Relaxation, developed from a stability analysis of the iterative scheme, is used to achieve convergence in only 2-4 iterations per time step. Several two- and three-dimensional numerical tests are conducted to validate and demonstrate the method, including flapping of flexible wings, self-excited oscillations of a system of linked plates and three-dimensional propulsion of flexible fluked tail. This work has been supported by AFOSR, under Award FA9550-11-1-0098.

  9. Vortex dynamics of in-line twin synthetic jets in a laminar boundary layer

    NASA Astrophysics Data System (ADS)

    Wen, Xin; Tang, Hui; Duan, Fei

    2015-08-01

    An experimental investigation is conducted on the vortices induced by twin synthetic jets (SJs) in line with a laminar boundary layer flow over a flat plate. The twin SJs operating at four different phase differences, i.e., Δϕ = 0°, 90°, 180°, and 270°, are visualized using a stereoscopic color dye visualization system and measured using a two-dimensional particle image velocimetry (PIV) system. It is found that depending on the phase difference of twin SJs, three types of vortex structures are produced. At Δϕ = 90°, the two hairpin vortices interact in a very constructive way in terms of the vortex size, strength, and celerity, forming one combined vortex. At Δϕ = 270°, the two individual hairpin vortices do not have much interaction, forming two completely separated hairpin vortices that behave like doubling the frequency of the single SJ case. At Δϕ = 0° and 180°, the two hairpin vortices produced by the twin SJ actuators are close enough, with the head of one hairpin vortex coupled with the legs of the other, forming partially interacting vortex structures. Quantitative analysis of the twin SJs is conducted, including the time histories of vortex circulation in the mid-span plane as well as a selected spanwise-wall-normal plane, and the influence of the twin SJs on the boundary layer flow filed. In addition, dynamic mode decomposition analysis of the PIV data is conducted to extract representative coherent structures. Through this study, a better understanding in the vortex dynamics associated with the interaction of in-line twin SJs in laminar boundary layers is achieved, which provides useful information for future SJ-array applications.

  10. Polymer Chain Dynamics at Interfaces: Role of Boundary Conditions at Solid Interface

    SciTech Connect

    Tapan G. Desai; Pawel Keblinski; Sanat K. Kumar

    2008-01-01

    Using classical molecular dynamics simulations, we study dynamical properties of a single polymer chain dissolved in an explicit solvent and strongly adsorbed at solid-liquid interface. To circumvent a serious challenge posed by finite size effects due to long-range hydrodynamic effects, we developed a correction procedure that substantially limits the finite size effects. Concurrently, we provide an analysis of distinctly different size effects in the directions, transverse and normal to the interface. We find that on analytically smooth interfaces, corresponding to the slip boundary condition, the motions of the polymer chain and the surrounding solvent are hydrodynamically coupled. This leads to the chain diffusion coefficient, D, scaling with the chain degree of polymerization, N, as D ~ N–3/4, consistent with the Zimm dynamics for strongly adsorbed chains. Introduction of transverse forces at the interface results in loss of correlation between the motion of the polymer chain and the solvent. Consequently, D ~ N–1, which is a characteristic of the Rouse dynamics.

  11. Dynamic substructuring by the boundary flexibility vector method of component mode synthesis. Ph.D. Thesis

    NASA Technical Reports Server (NTRS)

    Abdallah, Ayman Ahmed

    1990-01-01

    Component mode synthesis (CMS) is a method of dynamic analysis, for structures having a large number of degrees of freedom (DOF). These structures often required lengthy computer CPU time and large computer memory resources, if solved directly by the finite-element method (FEM). In CMS, the structure is divided into independent components in which the DOF are defined by a set of generalized coordinates defined by displacement shapes. The number of the generalized coordinates are much less than the original number of physical DOF, in the component. The displacement shapes are used to transform the component property matrices and any applied external loads, to a reduced system of coordinates. Reduced system property matrices are assembled, and any type of dynamic analysis is carried out in the reduced coordinate system. Any obtained results are back transformed to the original component coordinate systems. In all conventional methods of CMS, the mode shapes used for components are dynamic mode shapes, supplemented by static deflected shapes. Historically, all the dynamic mode shapes used in conventional CMS are the natural modes (eigenvectors) of components. A new method of CMS, namely the boundary flexibility vector method of CMS, is presented. The method provides for the incorporation of a set of static Ritz vectors, referred to as boundary flexibility vectors, as a replacement and/or supplement to conventional eigenvectors, as displacement shapes for components. The generation of these vectors does not require the solution of a costly eigenvalue problem, as in the case of natural modes in conventional CMS, and hence a substantial saving in CPU time can be achieved. The boundary flexibility vectors are generated from flexibility (or stiffness) properties of components. The formulation presented is for both free and fixed-interface components, and for both the free and forced vibration problems. Free and forced vibration numerical examples are presented to verify

  12. Regional Impacts of Climate Change on the Amazon Rainforest: 2080-2100

    NASA Astrophysics Data System (ADS)

    Cook, K. H.; Vizy, E. K.

    2006-12-01

    A regional climate model with resolution of 60 km is coupled with a potential vegetation model to simulate future climate over South America. The following steps are taken to effectively communicate the results across disciplines and to make them useful to the policy and impacts communities: the simulation is aimed at a particular time period (2081-2100), the climate change results are translated into changes in vegetation distribution, and the results are reported on regional space scales relative to political boundaries. In addition, the model validation in clearly presented to provide perspective on uncertainty for the prognosis. The model reproduces today's climate and vegetation over tropical and subtropical South America accurately. In simulations of the future, the model is forced by the IPCC's A2 scenario of future emissions, which assumes that CO2 emissions continue to grow at essentially today's rate throughout the 21st century, reaching 757 ppmv averaged over 2081-2100. The model is constrained on its lateral boundaries by atmospheric conditions simulated by a global climate model, applied as anomalies to present day conditions, and predicted changes in sea surface temperatures. The extent of the Amazon rainforest is reduced by about 70 per cent in the simulation, and the shrubland (caatinga) vegetation of Brazil's Nordeste region spreads westward and southward well into the continental interior. Bolivia, Paraguay, and Argentina lose all of their rainforest vegetation, and Brazil and Peru lose most of it. The surviving rain forest is concentrated near the equator. Columbia's rainforest survives largely intact and, along the northern coast, Venezuela and French Guiana suffer relatively small reductions. The loss in Guyana and Surinam is 30-50 per cent. Much of the rainforest in the central Amazon north of about 15S is replaced by savanna vegetation, but in southern Bolivia, northern Paraguay, and southern Brazil, grasslands take the place of the

  13. Dynamics of Sulfur Dioxide in the Marine Boundary During Trace P

    NASA Astrophysics Data System (ADS)

    Thornton, D. C.; Tu, F.; Bandy, A. R.; Kim, M.; Thornhill, L.; Barrick, J. D.; Anderson, B.

    2002-12-01

    An atmospheric pressure ionization mass spectrometer (APIMS) was employed to obtain 25 Hz sulfur dioxide (SO2) meausrements during the NASA Trace P field experiment. The APIMS was deployed on the NASA Wallops P-3B, which was equiped with the total air motion measurement system (TAMMS). The APIMS SO2 signal was recorded on the TAMMS data system to insure that the data was recorded on the same time base to allow processing of the data for eddy correlation measurements of SO2 with the vertical wind velocity from TAMMS. A preliminary estimate of the SO2 deposition velocity will be presented. At the high data sampling rates the dynamics of boundary layer could be studied for the effects on the SO2 distribution in conjunction with high data rate water vapor and temperature data from TAMMS. The turbulence data showed that the well mixed layer (within the planetary boundary layer) often was approximately 500 m with an intermittently turbulent layer above. The vertical distribution of SO2 was often constrained by the dynamics of these layers. In some cases the highest SO2 concentrations were in the well mixed layer and at other times the highest SO2 concentrations were in the less well mixed layer above. This partitioning could also be seen for water vapor and sometimes for carbon monoxide. In some cases it appeared that the continental boundary layer air had overrun the marine mixed layer during frontal progress through the experiment area. This partitioning can greatly affect the loss rates and mechanisms of SO2 in the absence of convection. When SO2 is predominantly above the well mixed layer, SO2 loss to the sea surface is primarily controlled by entraiment into the well mixed layer, which is a relatively slow process. When the SO2 is primarily in the well mixed layer its lifetime during transport can be much shorter than during transport aloft unless convection through the boundary layer occurs. The transport of SO2 in and around clouds was also observed during Trace P

  14. New planetary boundary layer parametrization in ECHAM5-HAM: Dynamical refinement of the vertical resolution

    NASA Astrophysics Data System (ADS)

    Siegenthaler-Le Drian, C.; Spichtinger, P.; Lohmann, U.

    2010-09-01

    Marine stratocumulus-capped boundary layers exhibit a strong net cooling impact on the Earth-Atmosphere system. Moreover, they are highly persistent over subtropical oceans. Therefore climate models need to represent them well in order to make reliable projections of future climate. One of the reasons for the absence of stratocumuli in the general circulation model ECHAM5-HAM (Roeckner et al., 2003; Stier et al., 2005) is due to the limited vertical resolution. In the current model version, no vertical sub-grid scale variability of clouds is taken into account, such that clouds occupy the full vertical layer. Around the inversion on top of the planetary boundary layer (PBL), conserved variables often have a steep gradient, which in a GCM may produce large discretization errors (Bretherton and Park, 2009). This inversion has a large diurnal cycle and varies with location around the globe, which is difficult to represent in a classical, coarse Eulerian approach. Furthermore, Lenderink and Holtslag (2000) and Lock (2001) showed that an inconsistent numerical representation between the entrainment parametrization and the other schemes, particularly with the vertical advection can lead to the occurrence of 'numerical entrainment'. The problem can be resolved by introducing a dynamical inversion as introduced by Grenier and Bretherton (2001) and Lock (2001). As these features can be seen in our version of ECHAM5-HAM, our implementation is aimed to reduce the numerical entrainment and to better represent stratocumuli in ECHAM5-HAM. To better resolve stratocumulus clouds, their inversion and the interaction between the turbulent diffusion and the vertical advection, the vertical grid is dynamically refined. The new grid is based on the reconstruction of the profiles of variables experiencing a sharp gradient (temperature, mixing ratio) applying the method presented in Grenier and Bretherton (2001). In typical stratocumulus regions, an additional grid level is thus

  15. Dynamic Multiscale Boundary Conditions for 4D CT of Healthy and Emphysematous Rats

    PubMed Central

    Jacob, Richard E.; Carson, James P.; Thomas, Mathew; Einstein, Daniel R.

    2013-01-01

    Changes in the shape of the lung during breathing determine the movement of airways and alveoli, and thus impact airflow dynamics. Modeling airflow dynamics in health and disease is a key goal for predictive multiscale models of respiration. Past efforts to model changes in lung shape during breathing have measured shape at multiple breath-holds. However, breath-holds do not capture hysteretic differences between inspiration and expiration resulting from the additional energy required for inspiration. Alternatively, imaging dynamically – without breath-holds – allows measurement of hysteretic differences. In this study, we acquire multiple micro-CT images per breath (4DCT) in live rats, and from these images we develop, for the first time, dynamic volume maps. These maps show changes in local volume across the entire lung throughout the breathing cycle and accurately predict the global pressure-volume (PV) hysteresis. Male Sprague-Dawley rats were given either a full- or partial-lung dose of elastase or saline as a control. After three weeks, 4DCT images of the mechanically ventilated rats under anesthesia were acquired dynamically over the breathing cycle (11 time points, ≤100 ms temporal resolution, 8 cmH2O peak pressure). Non-rigid image registration was applied to determine the deformation gradient – a numerical description of changes to lung shape – at each time point. The registration accuracy was evaluated by landmark identification. Of 67 landmarks, one was determined misregistered by all three observers, and 11 were determined misregistered by two observers. Volume change maps were calculated on a voxel-by-voxel basis at all time points using both the Jacobian of the deformation gradient and the inhaled air fraction. The calculated lung PV hysteresis agrees with pressure-volume curves measured by the ventilator. Volume maps in diseased rats show increased compliance and ventilation heterogeneity. Future predictive multiscale models of rodent

  16. Dynamics of flow control in an emulated boundary layer-ingesting offset diffuser

    NASA Astrophysics Data System (ADS)

    Gissen, A. N.; Vukasinovic, B.; Glezer, A.

    2014-08-01

    Dynamics of flow control comprised of arrays of active (synthetic jets) and passive (vanes) control elements , and its effectiveness for suppression of total-pressure distortion is investigated experimentally in an offset diffuser, in the absence of internal flow separation. The experiments are conducted in a wind tunnel inlet model at speeds up to M = 0.55 using approach flow conditioning that mimics boundary layer ingestion on a Blended-Wing-Body platform. Time-dependent distortion of the dynamic total-pressure field at the `engine face' is measured using an array of forty total-pressure probes, and the control-induced distortion changes are analyzed using triple decomposition and proper orthogonal decomposition (POD). These data indicate that an array of the flow control small-scale synthetic jet vortices merge into two large-scale, counter-rotating streamwise vortices that exert significant changes in the flow distortion. The two most energetic POD modes appear to govern the distortion dynamics in either active or hybrid flow control approaches. Finally, it is shown that the present control approach is sufficiently robust to reduce distortion with different inlet conditions of the baseline flow.

  17. Modeling coupled aerodynamics and vocal fold dynamics using immersed boundary methods.

    PubMed

    Duncan, Comer; Zhai, Guangnian; Scherer, Ronald

    2006-11-01

    The penalty immersed boundary (PIB) method, originally introduced by Peskin (1972) to model the function of the mammalian heart, is tested as a fluid-structure interaction model of the closely coupled dynamics of the vocal folds and aerodynamics in phonation. Two-dimensional vocal folds are simulated with material properties chosen to result in self-oscillation and volume flows in physiological frequency ranges. Properties of the glottal flow field, including vorticity, are studied in conjunction with the dynamic vocal fold motion. The results of using the PIB method to model self-oscillating vocal folds for the case of 8 cm H20 as the transglottal pressure gradient are described. The volume flow at 8 cm H20, the transglottal pressure, and vortex dynamics associated with the self-oscillating model are shown. Volume flow is also given for 2, 4, and 12 cm H2O, illustrating the robustness of the model to a range of transglottal pressures. The results indicate that the PIB method applied to modeling phonation has good potential for the study of the interdependence of aerodynamics and vocal fold motion.

  18. Atmospheric Boundary-Layer Dynamics and the Constancy of the Bowen Ratio (Invited)

    NASA Astrophysics Data System (ADS)

    Porporato, A.

    2009-12-01

    The diurnal evolution of sensible and latent heat fluxes tends to maintain a constant Bowen ratio, at least for the central part of the day. Using the solutions of the ordinary differential equations of a simplified atmospheric boundary-layer (ABL) model, we find that neglecting the early morning transition the potential temperature and specific humidity of the mixed layer tend to be linearly related to the ABL height. Similar behavior is followed by the inversion strengths of temperature and humidity at the top of the ABL. The potential temperature of the mixed layer depends on the entrainment parameter and the free-atmosphere temperature lapse rate, while the specific humidity also depends on the free-atmosphere humidity lapse rate and the Bowen ratio. The temporal dynamics appear only implicitly in the evolution of the height of the boundary layer, which in turn depends on the time-integrated surface sensible heat flux. Studying the limiting behavior of the Bowen ratio for very low and very large values of net available energy, we also show how the tendency to maintain constant Bowen ratio during midday hours stems from its relative insensitivity to the atmospheric conditions for large values of net available energy. The analytical expression for the diurnal evolution of the ABL obtained with constant Bowen ratio is simple and provides a benchmark for the results of more complex models.

  19. An immersed boundary method for simulating vesicle dynamics in three dimensions

    NASA Astrophysics Data System (ADS)

    Seol, Yunchang; Hu, Wei-Fan; Kim, Yongsam; Lai, Ming-Chih

    2016-10-01

    We extend our previous immersed boundary (IB) method for 3D axisymmetric inextensible vesicle in Navier-Stokes flows (Hu et al., 2014 [17]) to general three dimensions. Despite a similar spirit in numerical algorithms to the axisymmetric case, the fully 3D numerical implementation is much more complicated and is far from straightforward. A vesicle membrane surface is known to be incompressible and exhibits bending resistance. As in 3D axisymmetric case, instead of keeping the vesicle locally incompressible, we adopt a modified elastic tension energy to make the vesicle surface patch nearly incompressible so that solving the unknown tension (Lagrange multiplier for the incompressible constraint) can be avoided. Nevertheless, the new elastic force derived from the modified tension energy has exactly the same mathematical form as the original one except the different definitions of tension. The vesicle surface is discretized on a triangular mesh where the elastic tension and bending force are calculated on each vertex (Lagrangian marker in the IB method) of the triangulation. A series of numerical tests on the present scheme are conducted to illustrate the robustness and applicability of the method. We perform the convergence study for the immersed boundary forces and the fluid velocity field. We then study the vesicle dynamics in various flows such as quiescent, simple shear, and gravitational flows. Our numerical results show good agreements with those obtained in previous theoretical, experimental and numerical studies.

  20. Molecular dynamic simulation of grain boundary diffusivities and vacancy behavior in Al

    NASA Astrophysics Data System (ADS)

    Shinzawa, Tsutomu

    1999-11-01

    The embedded atom method (EAM), where a highly accurate empirical inter-atomic potential calculation is possible in comparison with the two-body pair potential, is used for the molecular dynamics (MD) simulation. Parameters are fitted for Al and Cu so as to reproduce the metal properties such as elastic constants (C11, C12, and C44) and single vacancy formation energy. Micro-void motion in an Al crystal is simulated using the MD simulator for the EAM and the Morse potentials. The velocity of the micro-void under the EAM potential is less than that under the Morse potential. This discrepancy results from the difference in the surface adsorption energies of these potentials. To compare the accuracy of the Morse and the EAM potentials, surface adsorption energies are calculated. The calculated surface adsorption energy for EAM potential was 90% of the ab initio calculation and the one for the Morse potential was 16%, which implies accuracy of the EAM's energy evaluation is higher than that of the Morse potential. The grain boundary diffusion for Al has been characterized by using the MD simulation with the EAM potential. Diffusivity and activation energy for several grain boundaries are calculated for several conditions. These simulation results are effective to find a way to improve the electromigration failure.

  1. Molecular dynamics simulations of shock waves using the absorbing boundary condition: A case study of methane

    NASA Astrophysics Data System (ADS)

    Bolesta, Alexey V.; Zheng, Lianqing; Thompson, Donald L.; Sewell, Thomas D.

    2007-12-01

    We report a method that enables long-time molecular dynamics (MD) simulations of shock wave loading. The goal is to mitigate the severe interference effects that arise at interfaces or free boundaries when using standard nonequilibrium MD shock wave approaches. The essence of the method is to capture between two fixed pistons the material state at the precise instant in time when the shock front, initiated by a piston with velocity up at one end of the target sample, traverses the contiguous boundary between the target and a second, stationary piston located at the opposite end of the sample, at which point the second piston is also assigned velocity up and the simulation is continued. Thus, the target material is captured in the energy-volume Hugoniot state resulting from the initial shock wave, and can be propagated forward in time to monitor any subsequent chemistry, plastic deformation, or other time-dependent phenomena compatible with the spatial scale of the simulation. For demonstration purposes, we apply the method to shock-induced chemistry in methane based on the adaptive intermolecular reactive empirical bond order force field [S. J. Stuart , J. Chem. Phys. 112, 6472 (2000)].

  2. Thermal boundary conductance between Al films and GaN nanowires investigated with molecular dynamics.

    PubMed

    Zhou, Xiao-Wang; Jones, Reese E; Hopkins, Patrick E; Beechem, Thomas E

    2014-05-28

    GaN nanowires are being pursued for optoelectronic and high-power applications. In either use, increases in operating temperature reduce both performance and reliability making it imperative to minimize thermal resistances. Since interfaces significantly influence the thermal response of nanosystems, the thermal boundary resistance between GaN nanowires and metal contacts has major significance. In response, we have performed systematic molecular dynamics simulations to study the thermal boundary conductance between GaN nanowires and Al films as a function of nanowire dimensions, packing density, and the depth the nanowire is embedded into the metal contact. At low packing densities, the apparent Kapitza conductance between GaN nanowires and an aluminum film is shown to be larger than when contact is made between films of these same materials. This enhancement decreases toward the film-film limit, however, as the packing density increases. For densely packed nanowires, maximizing the Kapitza conductance can be achieved by embedding the nanowires into the films, as the conductance is found to be proportional to the total contact area.

  3. A smooth dissipative particle dynamics method for domains with arbitrary-geometry solid boundaries

    NASA Astrophysics Data System (ADS)

    Gatsonis, Nikolaos A.; Potami, Raffaele; Yang, Jun

    2014-01-01

    A smooth dissipative particle dynamics method with dynamic virtual particle allocation (SDPD-DV) for modeling and simulation of mesoscopic fluids in wall-bounded domains is presented. The physical domain in SDPD-DV may contain external and internal solid boundaries of arbitrary geometries, periodic inlets and outlets, and the fluid region. The SDPD-DV method is realized with fluid particles, boundary particles, and dynamically allocated virtual particles. The internal or external solid boundaries of the domain can be of arbitrary geometry and are discretized with a surface grid. These boundaries are represented by boundary particles with assigned properties. The fluid domain is discretized with fluid particles of constant mass and variable volume. Conservative and dissipative force models due to virtual particles exerted on a fluid particle in the proximity of a solid boundary supplement the original SDPD formulation. The dynamic virtual particle allocation approach provides the density and the forces due to virtual particles. The integration of the SDPD equations is accomplished with a velocity-Verlet algorithm for the momentum and a Runge-Kutta for the entropy equation. The velocity integrator is supplemented by a bounce-forward algorithm in cases where the virtual particle force model is not able to prevent particle penetration. For the incompressible isothermal systems considered in this work, the pressure of a fluid particle is obtained by an artificial compressibility formulation for liquids and the ideal gas law for gases. The self-diffusion coefficient is obtained by an implementation of the generalized Einstein and the Green-Kubo relations. Field properties are obtained by sampling SDPD-DV outputs on a post-processing grid that allows harnessing the particle information on desired spatiotemporal scales. The SDPD-DV method is verified and validated with simulations in bounded and periodic domains that cover the hydrodynamic and mesoscopic regimes for

  4. Escape dynamics and fractal basin boundaries in the planar Earth-Moon system

    NASA Astrophysics Data System (ADS)

    de Assis, Sheila C.; Terra, Maisa O.

    2014-10-01

    The escape of trajectories of a spacecraft, or comet or asteroid in the presence of the Earth-Moon system is investigated in detail in the context of the planar circular restricted three-body problem, in a scattering region around the Moon. The escape through the necks around the collinear points and as well as the leaking produced by considering collisions with the Moon surface, taking the lunar mean radius into account, were considered. Given that different transport channels are available as a function of the Jacobi constant, four distinct escape regimes are analyzed. Besides the calculation of exit basins and of the spatial distribution of escape time, the qualitative dynamical investigation through Poincaré sections is performed in order to elucidate the escape process. Our analyses reveal the dependence of the properties of the considered escape basins with the energy, with a remarkable presence of fractal basin boundaries along all the escape regimes. Finally, we observe the plentiful presence of stickiness motion near stability islands which plays a remarkable role in the longest escape time behavior. The application of this analysis is important both in space mission design and study of natural systems, given that fractal boundaries are related with high sensitivity to initial conditions, implying in uncertainty between safe and unsafe solutions, as well as between escaping solutions that evolve to different phase space regions.

  5. A cut-cell immersed boundary technique for fire dynamics simulation

    NASA Astrophysics Data System (ADS)

    Vanella, Marcos; McDermott, Randall; Forney, Glenn

    2015-11-01

    Fire simulation around complex geometry is gaining increasing attention in performance based design of fire protection systems, fire-structure interaction and pollutant transport in complex terrains, among others. This presentation will focus on our present effort in improving the capability of FDS (Fire Dynamics Simulator, developed at the Fire Research Division, NIST. https://github.com/firemodels/fds-smv) to represent fire scenarios around complex bodies. Velocities in the vicinity of the bodies are reconstructed using a classical immersed boundary scheme (Fadlun and co-workers, J. Comput. Phys., 161:35-60, 2000). Also, a conservative treatment of scalar transport equations (i.e. for chemical species) will be presented. In our method, discrete conservation and no penetration of species across solid boundaries are enforced using a cut-cell finite volume scheme. The small cell problem inherent to the method is tackled using explicit-implicit domain decomposition for scalar, within the FDS time integration scheme. Some details on the derivation, implementation and numerical tests of this numerical scheme will be discussed.

  6. Boundaries of the Peruvian oxygen minimum zone shaped by coherent mesoscale dynamics

    NASA Astrophysics Data System (ADS)

    Bettencourt, João H.; López, Cristóbal; Hernández-García, Emilio; Montes, Ivonne; Sudre, Joël; Dewitte, Boris; Paulmier, Aurélien; Garçon, Véronique

    2015-12-01

    Dissolved oxygen in sea water affects marine habitats and biogeochemical cycles. Oceanic zones with oxygen deficits represent 7% of the volume and 8% of the area of the oceans, and are thought to be expanding. One of the most pronounced lies in the region off Peru, where mesoscale activity in the form of fronts and eddies is strong. Here, we study the dynamics of the Peruvian oxygen minimum zone in a Lagrangian framework, using a coupled physical-biogeochemical numerical model and finite-size Lyapunov exponent fields, to evaluate the role of mesoscale activity. We find that, at depths between 380 and 600 m, mesoscale structures have two distinct roles. First, their mean positions and paths delimit and maintain the oxygen minimum zone boundaries. Second, their high-frequency fluctuations inject oxygen across the oxygen minimum zone boundaries and eddy fluxes are one order of magnitude higher than mean oxygen fluxes. We conclude that these eddy fluxes contribute to the ventilation of the Peruvian oxygen minimum zone.

  7. A smooth dissipative particle dynamics method for domains with arbitrary-geometry solid boundaries

    NASA Astrophysics Data System (ADS)

    Gatsonis, Nikolaos A.; Potami, Raffaele; Yang, Jun

    2014-01-01

    A smooth dissipative particle dynamics method with dynamic virtual particle allocation (SDPD-DV) for modeling and simulation of mesoscopic fluids in wall-bounded domains is presented. The physical domain in SDPD-DV may contain external and internal solid boundaries of arbitrary geometries, periodic inlets and outlets, and the fluid region. The SDPD-DV method is realized with fluid particles, boundary particles, and dynamically allocated virtual particles. The internal or external solid boundaries of the domain can be of arbitrary geometry and are discretized with a surface grid. These boundaries are represented by boundary particles with assigned properties. The fluid domain is discretized with fluid particles of constant mass and variable volume. Conservative and dissipative force models due to virtual particles exerted on a fluid particle in the proximity of a solid boundary supplement the original SDPD formulation. The dynamic virtual particle allocation approach provides the density and the forces due to virtual particles. The integration of the SDPD equations is accomplished with a velocity-Verlet algorithm for the momentum and a Runge-Kutta for the entropy equation. The velocity integrator is supplemented by a bounce-forward algorithm in cases where the virtual particle force model is not able to prevent particle penetration. For the incompressible isothermal systems considered in this work, the pressure of a fluid particle is obtained by an artificial compressibility formulation for liquids and the ideal gas law for gases. The self-diffusion coefficient is obtained by an implementation of the generalized Einstein and the Green-Kubo relations. Field properties are obtained by sampling SDPD-DV outputs on a post-processing grid that allows harnessing the particle information on desired spatiotemporal scales. The SDPD-DV method is verified and validated with simulations in bounded and periodic domains that cover the hydrodynamic and mesoscopic regimes for

  8. The fracture behaviors of monolayer phosphorene with grain boundaries under tension: a molecular dynamics study.

    PubMed

    Guo, Yangyang; Qiao, Chong; Wang, Aihua; Zhang, Jinping; Wang, Songyou; Su, Wan-Sheng; Jia, Yu

    2016-07-27

    The fracture behaviors of monolayer phosphorene (MP) with and without a grain boundary (GB) have been explored by molecular dynamics (MD) simulations. Firstly, in the case of perfect MP, fracture mostly happens on the bond in the zigzag direction when suffering random loading. With the existence of a GB, the crack propagates perpendicular to the GB in different ways under parallel tension to the GB, whereas it propagates along the GB under perpendicular tension to the GB. Then, we found that both the fracture strength and strain decrease with increasing temperature making fracture more likely at relatively high temperatures. Finally, we also found that, similar to graphene, the effect of strain rate on both the fracture strength and strain is not significant, demonstrating that MP is a typical brittle 2D material. Overall, our findings present a useful insight into utilizing phosphorene for mechanical design in electronic devices.

  9. Numerical investigations of solute transport in bimodal porous media under dynamic boundary conditions

    NASA Astrophysics Data System (ADS)

    Cremer, Clemens; Neuweiler, Insa; Bechtold, Michel; Vanderborght, Jan

    2016-04-01

    Quantification of flow and solute transport in the shallow subsurface adjacent to the atmosphere is decisive to prevent groundwater pollution and conserve groundwater quality, to develop successful remediation strategies and to understand nutrient cycling. In nature, due to erratic precipitation-evaporation patterns, soil moisture content and related hydraulic conductivity in the vadose zone are not only variable in space but also in time. Flow directions and flow paths locally change between precipitation and evaporation periods. This makes the identification and description of solute transport processes in the vadose zone a complex problem. Recent studies (Lehmann and Or, 2009; Bechtold et al., 2011a) focused on the investigation of upward transport of solutes during evaporation in heterogeneous soil columns, where heterogeneity was introduced by a sharp vertical material interface between two types of sand. Lateral solute transport through the interface in both (lateral) directions was observed at different depths of the investigated soil columns. Following recent approaches, we conduct two-dimensional numerical simulations in a similar setup which is composed of two sands with a sharp vertical material interface. The investigation is broadened from the sole evaporation to combined precipitation-evaporation cycles in order to quantify transport processes resulting from the combined effects of heterogeneous soil structure and dynamic flow conditions. Simulations are performed with a coupled finite volume and random walk particle tracking algorithm (Ippisch et al., 2006; Bechtold et al., 2011b). By comparing scenarios with cyclic boundary conditions and stationary counterparts with the same net flow rate, we found that duration and intensity of precipitation and evaporation periods potentially have an influence on lateral redistribution of solutes and thus leaching rates. Whether or not dynamic boundary conditions lead to significant deviations in the transport

  10. Atomic structures and oxygen dynamics of CeO2 grain boundaries

    NASA Astrophysics Data System (ADS)

    Feng, Bin; Sugiyama, Issei; Hojo, Hajime; Ohta, Hiromichi; Shibata, Naoya; Ikuhara, Yuichi

    2016-02-01

    Material performance is significantly governed by grain boundaries (GBs), a typical crystal defects inside, which often exhibit unique properties due to the structural and chemical inhomogeneity. Here, it is reported direct atomic scale evidence that oxygen vacancies formed in the GBs can modify the local surface oxygen dynamics in CeO2, a key material for fuel cells. The atomic structures and oxygen vacancy concentrations in individual GBs are obtained by electron microscopy and theoretical calculations at atomic scale. Meanwhile, local GB oxygen reduction reactivity is measured by electrochemical strain microscopy. By combining these techniques, it is demonstrated that the GB electrochemical activities are affected by the oxygen vacancy concentrations, which is, on the other hand, determined by the local structural distortions at the GB core region. These results provide critical understanding of GB properties down to atomic scale, and new perspectives on the development strategies of high performance electrochemical devices for solid oxide fuel cells.

  11. Atomic structures and oxygen dynamics of CeO2 grain boundaries

    PubMed Central

    Feng, Bin; Sugiyama, Issei; Hojo, Hajime; Ohta, Hiromichi; Shibata, Naoya; Ikuhara, Yuichi

    2016-01-01

    Material performance is significantly governed by grain boundaries (GBs), a typical crystal defects inside, which often exhibit unique properties due to the structural and chemical inhomogeneity. Here, it is reported direct atomic scale evidence that oxygen vacancies formed in the GBs can modify the local surface oxygen dynamics in CeO2, a key material for fuel cells. The atomic structures and oxygen vacancy concentrations in individual GBs are obtained by electron microscopy and theoretical calculations at atomic scale. Meanwhile, local GB oxygen reduction reactivity is measured by electrochemical strain microscopy. By combining these techniques, it is demonstrated that the GB electrochemical activities are affected by the oxygen vacancy concentrations, which is, on the other hand, determined by the local structural distortions at the GB core region. These results provide critical understanding of GB properties down to atomic scale, and new perspectives on the development strategies of high performance electrochemical devices for solid oxide fuel cells. PMID:26838958

  12. Assessment of Computational Fluid Dynamics (CFD) Models for Shock Boundary-Layer Interaction

    NASA Technical Reports Server (NTRS)

    DeBonis, James R.; Oberkampf, William L.; Wolf, Richard T.; Orkwis, Paul D.; Turner, Mark G.; Babinsky, Holger

    2011-01-01

    A workshop on the computational fluid dynamics (CFD) prediction of shock boundary-layer interactions (SBLIs) was held at the 48th AIAA Aerospace Sciences Meeting. As part of the workshop numerous CFD analysts submitted solutions to four experimentally measured SBLIs. This paper describes the assessment of the CFD predictions. The assessment includes an uncertainty analysis of the experimental data, the definition of an error metric and the application of that metric to the CFD solutions. The CFD solutions provided very similar levels of error and in general it was difficult to discern clear trends in the data. For the Reynolds Averaged Navier-Stokes methods the choice of turbulence model appeared to be the largest factor in solution accuracy. Large-eddy simulation methods produced error levels similar to RANS methods but provided superior predictions of normal stresses.

  13. The fracture behaviors of monolayer phosphorene with grain boundaries under tension: a molecular dynamics study.

    PubMed

    Guo, Yangyang; Qiao, Chong; Wang, Aihua; Zhang, Jinping; Wang, Songyou; Su, Wan-Sheng; Jia, Yu

    2016-07-27

    The fracture behaviors of monolayer phosphorene (MP) with and without a grain boundary (GB) have been explored by molecular dynamics (MD) simulations. Firstly, in the case of perfect MP, fracture mostly happens on the bond in the zigzag direction when suffering random loading. With the existence of a GB, the crack propagates perpendicular to the GB in different ways under parallel tension to the GB, whereas it propagates along the GB under perpendicular tension to the GB. Then, we found that both the fracture strength and strain decrease with increasing temperature making fracture more likely at relatively high temperatures. Finally, we also found that, similar to graphene, the effect of strain rate on both the fracture strength and strain is not significant, demonstrating that MP is a typical brittle 2D material. Overall, our findings present a useful insight into utilizing phosphorene for mechanical design in electronic devices. PMID:27405397

  14. Stick or Slip? Slippery Questions of Boundary Question in Fluid Dynamics

    NASA Astrophysics Data System (ADS)

    Granick, Steve

    2005-11-01

    Fluid dynamics within small channels draws great interest due to its fundamental interest on the one hand, and the development of microfluidic devices on the practical side, yet detailed knowledge about flow immediately at a solid surface remains too vague. Some experiments were previously performed in which hydrodynamic flow was compared to predictions using the classical stick boundary condition point to a certain amount of slip, but those measurements (from our own laboratory as well as others) suffered from the deficiency that the slip is inferred indirectly. Seeking to remedy this deficiency, this laboratory has undertaken experiments to measure the near-surface flow rate from direct measurement. Previous attempts to measure surface flow rate were limited to a resolution of the optical wavelength. Here, using fluorescence resonance energy transfer (FRET) and fluorescence quenching approaches, we improve the resolution by 1-2 orders of magnitude. Two different flow systems, hydrodynamic flow and electrokinetic flow, were investigated using this novel technique.

  15. The dynamics of the plasmasphere boundary layer as determined by ground magnetometers, satellite observations, and modeling

    NASA Astrophysics Data System (ADS)

    Zesta, E.; Boudouridis, A.; Yizengaw, E.; Jorgensen, A. M.; Carranza-fulmer, T. L.; Moldwin, M.; Mann, I. R.; Chi, P. J.

    2013-12-01

    The plasmasphere boundary layer (PBL) separates the cold and dense plasmaspheric plasma from the more tenuous and hot plasma sheet plasma and organizes the spatial distribution of ULF and VLF waves that can contribute to acceleration or loss processes of radiation belt particles through wave-particle interactions. The PBL has been traditionally determined by in situ observations and can be given by empirical models. Recent work has shown that a mid-latitude chain of well-spaced ground magnetometers can also determine the PBL location. Spectral properties, like the cross-phase reversal in the standard field-line resonance (FLR) determination between two stations closely aligned in latitude, have been shown to indicate the presence of a sharp PBL. We merge data from many ground magnetometer pairs from the SAMBA (South American Meridional B-field Array), McMAC (Mid continent Magnetoseismic Chain), and CARISMA (Canadian Array for Realtime Investigations of Magnetic Activity) chains to provide the best available spatial coverage in L values spanning the plasmasphere and PBL, for a range of dynamic states (L=1.6 to greater than 5). The PBL location is identified as the L value of the station pair for which a reverse phase difference is observed in the standard FLR determination. We compare the FLR determined PBL with the trough boundary determined by GPS Total Electron Content (TEC) analysis and with model PBL. Initial results demonstrate that the PBL as identified by the reverse phase differences is in general agreement with TEC identifications and reasonable agreement with models. Reverse Phase Differences are regularly observed at the L range of 2.7 to 3.7 and are highly correlated with Dst and Kp, as determined by daily correlations. We further examine the more detailed time sequence of the PBL dynamics by focusing on key periods around storms preceded by quiet periods, and by using the full L range of the ground magnetometer pairs.

  16. Phthalate pollution in an Amazonian rainforest.

    PubMed

    Lenoir, Alain; Boulay, Raphaël; Dejean, Alain; Touchard, Axel; Cuvillier-Hot, Virginie

    2016-08-01

    Phthalates are ubiquitous contaminants and endocrine-disrupting chemicals that can become trapped in the cuticles of insects, including ants which were recognized as good bioindicators for such pollution. Because phthalates have been noted in developed countries and because they also have been found in the Arctic, a region isolated from direct anthropogenic influence, we hypothesized that they are widespread. So, we looked for their presence on the cuticle of ants gathered from isolated areas of the Amazonian rainforest and along an anthropogenic gradient of pollution (rainforest vs. road sides vs. cities in French Guiana). Phthalate pollution (mainly di(2-ethylhexyl) phthalate (DEHP)) was higher on ants gathered in cities and along road sides than on those collected in the pristine rainforest, indicating that it follows a human-mediated gradient of disturbance related to the use of plastics and many other products that contain phthalates in urban zones. Their presence varied with the ant species; the cuticle of Solenopsis saevissima traps higher amount of phthalates than that of compared species. However, the presence of phthalates in isolated areas of pristine rainforests suggests that they are associated both with atmospheric particles and in gaseous form and are transported over long distances by wind, resulting in a worldwide diffusion. These findings suggest that there is no such thing as a "pristine" zone. PMID:27372101

  17. African rainforests: past, present and future

    PubMed Central

    Malhi, Yadvinder; Adu-Bredu, Stephen; Asare, Rebecca A.; Lewis, Simon L.; Mayaux, Philippe

    2013-01-01

    The rainforests are the great green heart of Africa, and present a unique combination of ecological, climatic and human interactions. In this synthesis paper, we review the past and present state processes of change in African rainforests, and explore the challenges and opportunities for maintaining a viable future for these biomes. We draw in particular on the insights and new analyses emerging from the Theme Issue on ‘African rainforests: past, present and future’ of Philosophical Transactions of the Royal Society B. A combination of features characterize the African rainforest biome, including a history of climate variation; forest expansion and retreat; a long history of human interaction with the biome; a relatively low plant species diversity but large tree biomass; a historically exceptionally high animal biomass that is now being severely hunted down; the dominance of selective logging; small-scale farming and bushmeat hunting as the major forms of direct human pressure; and, in Central Africa, the particular context of mineral- and oil-driven economies that have resulted in unusually low rates of deforestation and agricultural activity. We conclude by discussing how this combination of factors influences the prospects for African forests in the twenty-first century. PMID:23878339

  18. African rainforests: past, present and future.

    PubMed

    Malhi, Yadvinder; Adu-Bredu, Stephen; Asare, Rebecca A; Lewis, Simon L; Mayaux, Philippe

    2013-01-01

    The rainforests are the great green heart of Africa, and present a unique combination of ecological, climatic and human interactions. In this synthesis paper, we review the past and present state processes of change in African rainforests, and explore the challenges and opportunities for maintaining a viable future for these biomes. We draw in particular on the insights and new analyses emerging from the Theme Issue on 'African rainforests: past, present and future' of Philosophical Transactions of the Royal Society B. A combination of features characterize the African rainforest biome, including a history of climate variation; forest expansion and retreat; a long history of human interaction with the biome; a relatively low plant species diversity but large tree biomass; a historically exceptionally high animal biomass that is now being severely hunted down; the dominance of selective logging; small-scale farming and bushmeat hunting as the major forms of direct human pressure; and, in Central Africa, the particular context of mineral- and oil-driven economies that have resulted in unusually low rates of deforestation and agricultural activity. We conclude by discussing how this combination of factors influences the prospects for African forests in the twenty-first century. PMID:23878339

  19. South-East Asia's Trembling Rainforests.

    ERIC Educational Resources Information Center

    Laird, John

    1991-01-01

    This discussion focuses on potential solutions to the degradation of rainforests in Southeast Asia caused by indiscriminate logging, inappropriate road-construction techniques, forest fires, and the encroachment upon watersheds by both agricultural concerns and peasant farmers. Vignettes illustrate the impact of this degradation upon the animals,…

  20. Ecotourism: The Santa Elena Rainforest Project.

    ERIC Educational Resources Information Center

    Wearing, Stephen

    1993-01-01

    Describes an ecotourism project in which the community of Santa Elena, Costa Rica, are developing a rainforest reserve on government land leased permanently to the local high school. Discusses the impact of the project on the community's economy and environment. (Contains 30 references.) (MDH)

  1. Boundary-layer turbulence modeling and vorticity dynamics: I. A kangaroo-process mixing model of boundary-layer turbulence

    NASA Astrophysics Data System (ADS)

    Dekker, H.; de Leeuw, G.; van den Brink, A. Maassen

    A nonlocal turbulence transport theory is presented by means of a novel analysis of the Reynolds stress, inter alia involving the construct of a sample path space and a stochastic hypothesis. An analytical sampling rate model (satisfying exchange) and a nonlinear scaling relation (mapping the path space onto the boundary layer) lead to an integro-differential equation for the mixing of scalar densities, which represents fully-developed boundary-layer turbulence as a nondiffusive (Kubo-Anderson or kangaroo) type stochastic process. The underlying near-wall behavior (i.e. for y +→0) of fluctuating velocities fully agrees with recent direct numerical simulations. The model involves a scaling exponent ɛ, with ɛ→∞ in the diffusion limit. For the (partly analytical) solution for the mean velocity profile, excellent agreement with the experimental data yields ɛ≈0.58. The significance of ɛ as a turbulence Cantor set dimension (in the logarithmic profile region, i.e. for y +→∞) is discussed.

  2. Hydrography and bottom boundary layer dynamics: Influence on inner shelf sediment mobility, Long Bay, North Carolina

    USGS Publications Warehouse

    Davis, L.A.; Leonard, L.A.; Snedden, G.A.

    2008-01-01

    This study examined the hydrography and bottom boundary-layer dynamics of two typical storm events affecting coastal North Carolina (NC); a hurricane and the passages of two small consecutive extratropical storms during November 2005. Two upward-looking 1200-kHz Acoustic Doppler Current Profilers (ADCP) were deployed on the inner shelf in northern Long Bay, NC at water depths of less than 15 m. Both instruments profiled the overlying water column in 0.35 in bins beginning at a height of 1.35 in above the bottom (mab). Simultaneous measurements of wind speed and direction, wave and current parameters, and acoustic backscatter were coupled with output from a bottom boundary layer (bbl) model to describe the hydrography and boundary layer conditions during each event. The bbl model also was used to quantify sediment transport in the boundary layer during each storm. Both study sites exhibited similar temporal variations in wave and current magnitude, however, wave heights during the November event were higher than waves associated with the hurricane. Near-bottom mean and subtidal currents, however, were of greater magnitude during the hurricane. Peak depth-integrated suspended sediment transport during the November event exceeded transport associated with the hurricane by 25-70%. Substantial spatial variations in sediment transport existed throughout both events. During both events, along-shelf sediment transport exceeded across-shelf transport and was related to the magnitude and direction of subtidal currents. Given the variations in sediment type across the bay, complex shoreline configuration, and local bathymetry, the sediment transport rates reported here are very site specific. However, the general hydrography associated with the two storms is representative of conditions across northern Long Bay. Since the beaches in the study area undergo frequent renourishment to counter the effects of beach erosion, the results of this study also are relevant to coastal

  3. Evaluation of the boundary layer dynamics of the TM5 model over Europe

    NASA Astrophysics Data System (ADS)

    Koffi, E. N.; Bergamaschi, P.; Karstens, U.; Krol, M.; Segers, A.; Schmidt, M.; Levin, I.; Vermeulen, A. T.; Fisher, R. E.; Kazan, V.; Klein Baltink, H.; Lowry, D.; Manca, G.; Meijer, H. A. J.; Moncrieff, J.; Pal, S.; Ramonet, M.; Scheeren, H. A.; Williams, A. G.

    2016-09-01

    We evaluate the capability of the global atmospheric transport model TM5 to simulate the boundary layer dynamics and associated variability of trace gases close to the surface, using radon (222Rn). Focusing on the European scale, we compare the boundary layer height (BLH) in the TM5 model with observations from the National Oceanic and Atmospheric Admnistration (NOAA) Integrated Global Radiosonde Archive (IGRA) and also with ceilometer and lidar (light detection and ranging) BLH retrievals at two stations. Furthermore, we compare TM5 simulations of 222Rn activity concentrations, using a novel, process-based 222Rn flux map over Europe (Karstens et al., 2015), with harmonised 222Rn measurements at 10 stations. The TM5 model reproduces relatively well the daytime BLH (within 10-20 % for most of the stations), except for coastal sites, for which differences are usually larger due to model representation errors. During night, however, TM5 overestimates the shallow nocturnal BLHs, especially for the very low observed BLHs (< 100 m) during summer. The 222Rn activity concentration simulations based on the new 222Rn flux map show significant improvements especially regarding the average seasonal variability, compared to simulations using constant 222Rn fluxes. Nevertheless, the (relative) differences between simulated and observed daytime minimum 222Rn activity concentrations are larger for several stations (on the order of 50 %) than the (relative) differences between simulated and observed BLH at noon. Although the nocturnal BLH is often higher in the model than observed, simulated 222Rn nighttime maxima are actually larger at several continental stations. This counterintuitive behaviour points to potential deficiencies of TM5 to correctly simulate the vertical gradients within the nocturnal boundary layer, limitations of the 222Rn flux map, or issues related to the definition of the nocturnal BLH. At several stations the simulated decrease of 222Rn activity

  4. Dynamic modeling of beams with non-material, deformation-dependent boundary conditions

    NASA Astrophysics Data System (ADS)

    Humer, Alexander

    2013-02-01

    In conventional problems of structural mechanics, both kinematic boundary conditions and external forces are prescribed at fixed material points that are known in advance. If, however, a structure may move relative to its supports, the position of the imposed constraint relations generally changes in the course of motion. A class of problems which inherently exhibits this particular type of non-material boundary conditions is that of axially moving continua. Despite varying in time, the positions of the supports relative to the material points of the body have usually assumed to be known a priori throughout the deformation process in previous investigations. This requirement is abandoned in the present paper, where the dynamic behavior of a structure is studied, which may move freely relative to one of its supports. As a consequence, the position of such a non-material boundary relative to the structure does not only change in time but also depends on the current state of deformation of the body. The variational formulation of the equilibrium relations of a slender beam that may undergo large deformations is presented. To this end, a theory based on Reissner's geometrically exact relations for the plane deformation of beams is adopted, in which shear deformation is neglected for the sake of brevity. Before a finite element scheme is developed, a deformation-dependent transformation of the beam's material coordinate is introduced, by which the varying positions of the constraint relations are mapped onto fixed points with respect to the new non-material coordinate. By means of this transformation, additional convective terms emerge from the virtual work of the inertia forces, whose symmetry properties turn out to be different from what has previously been presented in the literature. In order to obtain approximate solutions, a finite element discretization utilizing absolute nodal displacements as coordinates is subsequently used in characteristic numerical examples

  5. Strongly coupled dynamics of fluids and rigid-body systems with the immersed boundary projection method

    NASA Astrophysics Data System (ADS)

    Wang, Chengjie; Eldredge, Jeff D.

    2015-08-01

    A strong coupling algorithm is presented for simulating the dynamic interactions between incompressible viscous flows and rigid-body systems in both two- and three-dimensional problems. In this work, the Navier-Stokes equations for incompressible flow are solved on a uniform Cartesian grid by the vorticity-based immersed boundary projection method of Colonius and Taira. Dynamical equations for arbitrary rigid-body systems are also developed. The proposed coupling method attempts to unify the treatment of constraints in the fluid and structure-the incompressibility of the fluid, the linkages in the rigid-body system, and the conditions at the interface-through the use of Lagrange multipliers. The resulting partitioned system of equations is solved with a simple relaxation scheme, based on an identification of virtual inertia from the fluid. The scheme achieves convergence in only 2 to 5 iterations per time step for a wide variety of mass ratios. The formulation requires that only a subset of the discrete fluid equations be solved in each iteration. Several two- and three-dimensional numerical tests are conducted to validate and demonstrate the method, including a falling cylinder, flapping of flexible wings, self-excited oscillations of a system of many linked plates in a free stream, and passive pivoting of a finite aspect ratio plate under the influence of gravity in a free stream. The results from the current method are compared with previous experimental and numerical results and good agreement is achieved.

  6. Soft-spring wall based non-periodic boundary conditions for non-equilibrium molecular dynamics of dense fluids

    SciTech Connect

    Ghatage, Dhairyashil; Tomar, Gaurav Shukla, Ratnesh K.

    2015-03-28

    Non-equilibrium molecular dynamics (MD) simulations require imposition of non-periodic boundary conditions (NPBCs) that seamlessly account for the effect of the truncated bulk region on the simulated MD region. Standard implementation of specular boundary conditions in such simulations results in spurious density and force fluctuations near the domain boundary and is therefore inappropriate for coupled atomistic-continuum calculations. In this work, we present a novel NPBC model that relies on boundary atoms attached to a simple cubic lattice with soft springs to account for interactions from particles which would have been present in an untruncated full domain treatment. We show that the proposed model suppresses the unphysical fluctuations in the density to less than 1% of the mean while simultaneously eliminating spurious oscillations in both mean and boundary forces. The model allows for an effective coupling of atomistic and continuum solvers as demonstrated through multiscale simulation of boundary driven singular flow in a cavity. The geometric flexibility of the model enables straightforward extension to nonplanar complex domains without any adverse effects on dynamic properties such as the diffusion coefficient.

  7. How quickly, how deeply, and how strongly can dynamical outer boundary conditions impact Van Allen radiation belt morphology?

    NASA Astrophysics Data System (ADS)

    Mann, Ian R.; Ozeke, Louis G.

    2016-06-01

    Here we examine the speed, strength, and depth of the coupling between dynamical variations of ultrarelativistic electron flux at the outer boundary and that in the heart of the outer radiation belt. Using ULF wave radial diffusion as an exemplar, we show how changing boundary conditions can completely change belt morphology even under conditions of identical wave power. In the case of ULF wave radial diffusion, the temporal dynamics of a new source population or a sink of electron flux at the outer plasma sheet boundary can generate a completely opposite response which reaches deep into the belt under identical ULF wave conditions. Very significantly, here we show that such coupling can occur on timescales much faster than previously thought. We show that even on timescales ~1 h, changes in the outer boundary electron population can dramatically alter the radiation belt flux in the heart of the belt. Importantly, these flux changes can at times occur on timescales much faster than the L shell revisit time obtained from elliptically orbiting satellites such as the Van Allen Probes. We underline the importance of such boundary condition effects when seeking to identify the physical processes which explain the dominant behavior of the Van Allen belts. Overall, we argue in general that the importance of temporal changes in the boundary conditions is sometimes overlooked in comparison to the pursuit of (ever) increasingly accurate estimates of wave power and other wave properties used in empirical representations of wave transport and diffusion rates.

  8. Large-Scale Dynamics of the Magnetospheric Boundary: Comparisons between Global MHD Simulation Results and ISTP Observations

    NASA Technical Reports Server (NTRS)

    Berchem, J.; Raeder, J.; Ashour-Abdalla, M.; Frank, L. A.; Paterson, W. R.; Ackerson, K. L.; Kokubun, S.; Yamamoto, T.; Lepping, R. P.

    1998-01-01

    Understanding the large-scale dynamics of the magnetospheric boundary is an important step towards achieving the ISTP mission's broad objective of assessing the global transport of plasma and energy through the geospace environment. Our approach is based on three-dimensional global magnetohydrodynamic (MHD) simulations of the solar wind-magnetosphere- ionosphere system, and consists of using interplanetary magnetic field (IMF) and plasma parameters measured by solar wind monitors upstream of the bow shock as input to the simulations for predicting the large-scale dynamics of the magnetospheric boundary. The validity of these predictions is tested by comparing local data streams with time series measured by downstream spacecraft crossing the magnetospheric boundary. In this paper, we review results from several case studies which confirm that our MHD model reproduces very well the large-scale motion of the magnetospheric boundary. The first case illustrates the complexity of the magnetic field topology that can occur at the dayside magnetospheric boundary for periods of northward IMF with strong Bx and By components. The second comparison reviewed combines dynamic and topological aspects in an investigation of the evolution of the distant tail at 200 R(sub E) from the Earth.

  9. The Ndynamics package—Numerical analysis of dynamical systems and the fractal dimension of boundaries

    NASA Astrophysics Data System (ADS)

    Avellar, J.; Duarte, L. G. S.; da Mota, L. A. C. P.; de Melo, N.; Skea, J. E. F.

    2012-09-01

    A set of Maple routines is presented, fully compatible with the new releases of Maple (14 and higher). The package deals with the numerical evolution of dynamical systems and provide flexible plotting of the results. The package also brings an initial conditions generator, a numerical solver manager, and a focusing set of routines that allow for better analysis of the graphical display of the results. The novelty that the package presents an optional C interface is maintained. This allows for fast numerical integration, even for the totally inexperienced Maple user, without any C expertise being required. Finally, the package provides the routines to calculate the fractal dimension of boundaries (via box counting). New version program summary Program Title: Ndynamics Catalogue identifier: %Leave blank, supplied by Elsevier. Licensing provisions: no. Programming language: Maple, C. Computer: Intel(R) Core(TM) i3 CPU M330 @ 2.13 GHz. Operating system: Windows 7. RAM: 3.0 GB Keywords: Dynamical systems, Box counting, Fractal dimension, Symbolic computation, Differential equations, Maple. Classification: 4.3. Catalogue identifier of previous version: ADKH_v1_0. Journal reference of previous version: Comput. Phys. Commun. 119 (1999) 256. Does the new version supersede the previous version?: Yes. Nature of problem Computation and plotting of numerical solutions of dynamical systems and the determination of the fractal dimension of the boundaries. Solution method The default method of integration is a fifth-order Runge-Kutta scheme, but any method of integration present on the Maple system is available via an argument when calling the routine. A box counting [1] method is used to calculate the fractal dimension [2] of the boundaries. Reasons for the new version The Ndynamics package met a demand of our research community for a flexible and friendly environment for analyzing dynamical systems. All the user has to do is create his/her own Maple session, with the system to

  10. Ecological and socio-economic functions across tropical land use systems after rainforest conversion.

    PubMed

    Drescher, Jochen; Rembold, Katja; Allen, Kara; Beckschäfer, Philip; Buchori, Damayanti; Clough, Yann; Faust, Heiko; Fauzi, Anas M; Gunawan, Dodo; Hertel, Dietrich; Irawan, Bambang; Jaya, I Nengah S; Klarner, Bernhard; Kleinn, Christoph; Knohl, Alexander; Kotowska, Martyna M; Krashevska, Valentyna; Krishna, Vijesh; Leuschner, Christoph; Lorenz, Wolfram; Meijide, Ana; Melati, Dian; Nomura, Miki; Pérez-Cruzado, César; Qaim, Matin; Siregar, Iskandar Z; Steinebach, Stefanie; Tjoa, Aiyen; Tscharntke, Teja; Wick, Barbara; Wiegand, Kerstin; Kreft, Holger; Scheu, Stefan

    2016-05-19

    Tropical lowland rainforests are increasingly threatened by the expansion of agriculture and the extraction of natural resources. In Jambi Province, Indonesia, the interdisciplinary EFForTS project focuses on the ecological and socio-economic dimensions of rainforest conversion to jungle rubber agroforests and monoculture plantations of rubber and oil palm. Our data confirm that rainforest transformation and land use intensification lead to substantial losses in biodiversity and related ecosystem functions, such as decreased above- and below-ground carbon stocks. Owing to rapid step-wise transformation from forests to agroforests to monoculture plantations and renewal of each plantation type every few decades, the converted land use systems are continuously dynamic, thus hampering the adaptation of animal and plant communities. On the other hand, agricultural rainforest transformation systems provide increased income and access to education, especially for migrant smallholders. Jungle rubber and rubber monocultures are associated with higher financial land productivity but lower financial labour productivity compared to oil palm, which influences crop choice: smallholders that are labour-scarce would prefer oil palm while land-scarce smallholders would prefer rubber. Collecting long-term data in an interdisciplinary context enables us to provide decision-makers and stakeholders with scientific insights to facilitate the reconciliation between economic interests and ecological sustainability in tropical agricultural landscapes. PMID:27114577

  11. Response of an old-growth tropical rainforest to transient high temperature and drought.

    PubMed

    Silva, Carlos E; Kellner, James R; Clark, David B; Clark, Deborah A

    2013-11-01

    Tropical rainforests have experienced episodes of severe heat and drought in recent decades, and climate models project a warmer and potentially drier tropical climate over this century. However, likely responses of tropical rainforests are poorly understood due to a lack of frequent long-term measurements of forest structure and dynamics. We analyzed a 12-year record (1999-2010) of 47 817 annual measurements of canopy height to characterize the response of an old-growth Neotropical rainforest to the severe heat and drought associated with the 1997-1998 El Niño. Well-drained soils on slopes and plateaus experienced a threefold increase in the fraction of the landscape in gaps (≤2 m) and a reduction in the fraction in high canopy (>15 m) causing distributions of canopy height to depart from equilibrium for a period of 2-3 years. In contrast, forests on low-lying alluvial terraces remained in equilibrium and were nearly half as likely to experience upper canopy (>15 m) disturbance over the 12 years of observation. Variation in forest response across topographic positions suggests that tropical rainforests are more sensitive to moisture deficits than high temperature and that topography likely structures landscape-level variation in the severity of drought impacts.

  12. Ecological and socio-economic functions across tropical land use systems after rainforest conversion.

    PubMed

    Drescher, Jochen; Rembold, Katja; Allen, Kara; Beckschäfer, Philip; Buchori, Damayanti; Clough, Yann; Faust, Heiko; Fauzi, Anas M; Gunawan, Dodo; Hertel, Dietrich; Irawan, Bambang; Jaya, I Nengah S; Klarner, Bernhard; Kleinn, Christoph; Knohl, Alexander; Kotowska, Martyna M; Krashevska, Valentyna; Krishna, Vijesh; Leuschner, Christoph; Lorenz, Wolfram; Meijide, Ana; Melati, Dian; Nomura, Miki; Pérez-Cruzado, César; Qaim, Matin; Siregar, Iskandar Z; Steinebach, Stefanie; Tjoa, Aiyen; Tscharntke, Teja; Wick, Barbara; Wiegand, Kerstin; Kreft, Holger; Scheu, Stefan

    2016-05-19

    Tropical lowland rainforests are increasingly threatened by the expansion of agriculture and the extraction of natural resources. In Jambi Province, Indonesia, the interdisciplinary EFForTS project focuses on the ecological and socio-economic dimensions of rainforest conversion to jungle rubber agroforests and monoculture plantations of rubber and oil palm. Our data confirm that rainforest transformation and land use intensification lead to substantial losses in biodiversity and related ecosystem functions, such as decreased above- and below-ground carbon stocks. Owing to rapid step-wise transformation from forests to agroforests to monoculture plantations and renewal of each plantation type every few decades, the converted land use systems are continuously dynamic, thus hampering the adaptation of animal and plant communities. On the other hand, agricultural rainforest transformation systems provide increased income and access to education, especially for migrant smallholders. Jungle rubber and rubber monocultures are associated with higher financial land productivity but lower financial labour productivity compared to oil palm, which influences crop choice: smallholders that are labour-scarce would prefer oil palm while land-scarce smallholders would prefer rubber. Collecting long-term data in an interdisciplinary context enables us to provide decision-makers and stakeholders with scientific insights to facilitate the reconciliation between economic interests and ecological sustainability in tropical agricultural landscapes.

  13. Ecological and socio-economic functions across tropical land use systems after rainforest conversion

    PubMed Central

    Rembold, Katja; Allen, Kara; Beckschäfer, Philip; Buchori, Damayanti; Clough, Yann; Faust, Heiko; Fauzi, Anas M.; Gunawan, Dodo; Hertel, Dietrich; Irawan, Bambang; Jaya, I. Nengah S.; Klarner, Bernhard; Kleinn, Christoph; Knohl, Alexander; Kotowska, Martyna M.; Krashevska, Valentyna; Krishna, Vijesh; Leuschner, Christoph; Lorenz, Wolfram; Meijide, Ana; Melati, Dian; Nomura, Miki; Pérez-Cruzado, César; Qaim, Matin; Siregar, Iskandar Z.; Steinebach, Stefanie; Tjoa, Aiyen; Tscharntke, Teja; Wick, Barbara; Wiegand, Kerstin; Kreft, Holger; Scheu, Stefan

    2016-01-01

    Tropical lowland rainforests are increasingly threatened by the expansion of agriculture and the extraction of natural resources. In Jambi Province, Indonesia, the interdisciplinary EFForTS project focuses on the ecological and socio-economic dimensions of rainforest conversion to jungle rubber agroforests and monoculture plantations of rubber and oil palm. Our data confirm that rainforest transformation and land use intensification lead to substantial losses in biodiversity and related ecosystem functions, such as decreased above- and below-ground carbon stocks. Owing to rapid step-wise transformation from forests to agroforests to monoculture plantations and renewal of each plantation type every few decades, the converted land use systems are continuously dynamic, thus hampering the adaptation of animal and plant communities. On the other hand, agricultural rainforest transformation systems provide increased income and access to education, especially for migrant smallholders. Jungle rubber and rubber monocultures are associated with higher financial land productivity but lower financial labour productivity compared to oil palm, which influences crop choice: smallholders that are labour-scarce would prefer oil palm while land-scarce smallholders would prefer rubber. Collecting long-term data in an interdisciplinary context enables us to provide decision-makers and stakeholders with scientific insights to facilitate the reconciliation between economic interests and ecological sustainability in tropical agricultural landscapes. PMID:27114577

  14. Interaction of run-in edge dislocations with twist grain boundaries in Al-a molecular dynamics study

    NASA Astrophysics Data System (ADS)

    Chandra, S.; Naveen Kumar, N.; Samal, M. K.; Chavan, V. M.; Patel, R. J.

    2016-06-01

    Grain boundaries play an important role in outlining the mechanical properties of crystalline materials. They act as sites for absorption/nucleation of dislocations, which are the main carriers of plastic deformation. In view of this, the interactions between edge dislocations and twist grain boundaries-dislocation pileup, dislocation absorption and dislocation emission were explored by performing molecular dynamics simulations in face-centered cubic Al using embedded atom method. The ?1 1 0? twist grain boundaries with various misorientation angles were selected for this purpose. It was found that the misorientation angle of boundary and stress anomalies arising from repeated dislocation absorption at the grain boundaries are the important parameters in determining the ability of the boundary to emit dislocations. Complex network of dislocations results in later stages of deformation, which may have a significant effect on the mechanical properties of the material. The peculiarities of dislocation nucleation, their emission from twist grain boundaries and the ramifications of this study towards development of higher length scale material models are discussed.

  15. Internal Dynamics and Boundary Forcing Characteristics Associated with Interannual Variability of the Asian Summer Monsoon

    NASA Technical Reports Server (NTRS)

    Lau, K.- M.; Kim, K.-M.; Yang, S.

    1998-01-01

    In this paper, we present a description of the internal dynamics and boundary forcing characteristics of two major components of the Asian summer monsoon (ASM), i.e., the South Asian (SAM) and the Southeast-East Asian monsoon (SEAM). The description is based on a new monsoon-climate paradigm in which the variability of ASM is considered as the outcome of the interplay of a "fast" and an "intermediate" monsoon subsystem, under the influenced of the "slow" varying external forcings. Two sets of regional monsoon indices derived from dynamically consistent rainfall and wind data are used in this study. For SAM, the internal dynamics is represented by that of a "classical" monsoon system where the anomalous circulation is governed by Rossby-wave dynamics, i.e., generation of anomalous vorticity induced by an off-equatorial heat source is balanced by planetary vorticity advection. On the other hand, the internal dynamics of SEAM is characterized by a "hybrid" monsoon system featuring multi-cellular meridional circulation over the East Asian section, extending from the deep tropics to midlatitudes. These meridional-cells link tropical heating to extratropical circulation system via the East Asian jetstream, and are responsible for the characteristic occurrences of zonally oriented anomalous rainfall patterns over East Asian and the subtropical western Pacific. In the extratropical regions, the major upper level vorticity balance is by anomalous vorticity advection and generation by the anomalous divergent circulation. A consequence of this is that compared to SAM, the SEAM is associated with stronger teleconnection patterns to regions outside the ASM. A strong SAM is linked to basin-scale sea surface temperature (SST) fluctuation with significant signal in the equatorial eastern Pacific. During the boreal spring SST warming in the Arabian Sea and the subtropical western Pacific may lead to a strong SAM. For SEAM, interannual variability is tied to SSTA over the Sea of

  16. Depth distribution for boundary of crust-upper mantle and deep dynamical process in eastern Asian

    NASA Astrophysics Data System (ADS)

    Teng, J.; Yan, Y.; Wang, G.; Zheng, H.; Sun, Y.

    2003-04-01

    The continent of China is located in the eastern Asia. The studied region (5°N-55°N, 60°E-150°E) in this work included most of he eastern Asian continent, continental margin and its southeast ocean, it is a key region for studying the global tectonics and continental dynamics. Since the 1970s of last century, deep seismic sounding profiles with the total length of 50,000 km (including seismic reflection profile over 2,000 km length) have been carried out by the Chinese Academy of Sciences, Chinese Seismological Bureau and the Ministry of the Land and Resources of China. This data (up to the year of 2001) provide an important base for overall recognition of Moho undulation and new discoveries in this study. With the results of interpretation of deep seismic sounding profiles acquired in the past 30 years in the continent of China and its adjacent countries and ocean regions, such as Russia Kazakhstan, Japan, India, Pakistan, Philippine, Philippine ocean basin, Pacific and Indian Ocean we complied a 2D Moho distribution map for the continent and its adjacent areas of eastern Asia. From the features of depth distribution and undulation of Moho, it is suggested that the eastern Asian region can be divided into 18gradient belts with different sizes and 18 crustal blocks. The depth of Moho varies smoothly in each block, while the boundary (separating different blocks) delineates the abrupt variation of Moho depth. Then, some subjects, such as orogen, fault system and rift, plate boundary, ocean-continent coupling and geodynamical effect, are discussed based on the distribution gradient belts and block partition features of Moho depth in the eastern Asian and its adjacent regions.

  17. Nanoscale Chemical Imaging of a Dynamic Molecular Phase Boundary with Ultrahigh Vacuum Tip-Enhanced Raman Spectroscopy.

    PubMed

    Jiang, Nan; Chiang, Naihao; Madison, Lindsey R; Pozzi, Eric A; Wasielewski, Michael R; Seideman, Tamar; Ratner, Mark A; Hersam, Mark C; Schatz, George C; Van Duyne, Richard P

    2016-06-01

    Nanoscale chemical imaging of a dynamic molecular phase boundary has broad implications for a range of problems in catalysis, surface science, and molecular electronics. While scanning probe microscopy (SPM) is commonly used to study molecular phase boundaries, its information content can be severely compromised by surface diffusion, irregular packing, or three-dimensional adsorbate geometry. Here, we demonstrate the simultaneous chemical and structural analysis of N-N'-bis(2,6-diisopropylphenyl)-1,7-(4'-t-butylphenoxy)perylene-3,4:9,10-bis(dicarboximide) (PPDI) molecules by UHV tip-enhanced Raman spectroscopy. Both condensed and diffusing domains of PPDI coexist on Ag(100) at room temperature. Through comparison with time-dependent density functional theory simulations, we unravel the orientation of PPDI molecules at the dynamic molecular domain boundary with unprecedented ∼4 nm spatial resolution. PMID:27183322

  18. Simulating carbon, water and energy fluxes of a rainforest and an oil palm plantation using the Community Land Model (CLM4.5)

    NASA Astrophysics Data System (ADS)

    Fan, Yuanchao; Bernoux, Martial; Roupsard, Olivier; Panferov, Oleg; Le Maire, Guerric; Tölle, Merja; Knohl, Alexander

    2014-05-01

    Deforestation and forest degradation driven by the expansion of oil palm (Elaeis guineensis) plantations has become the major source of GHG emission in Indonesia. Changes of land surface properties (e.g. vegetation composition, soil property, surface albedo) associated with rainforest to oil palm conversion might alter the patterns of land-atmosphere energy, water and carbon cycles and therefore affect local or regional climate. Land surface modeling has been widely used to characterize the two-way interactions between climate and human disturbances on land surface. The Community Land Model (CLM) is a third-generation land model that simulates a wide range of biogeophysical and biogeochemical processes. This project utilizes the land-cover/land-use change (LCLUC) capability of the latest CLM versions 4/4.5 to characterize quantitatively how anthropogenic land surface dynamics in Indonesia affect land-atmosphere carbon, water and energy fluxes. Before simulating land use changes, the first objective is to parameterize and validate the CLM model at local rainforest and oil palm plantation sites through separate point simulations. This entails creation and parameterization of a new plant functional type (PFT) for oil palm, as well as sensitivity analysis and adaptation of model parameters for the rainforest PFTs. CLM modelled fluxes for the selected sites are to be compared with field observations from eddy covariance (EC) flux towers (e.g. a rainforest site in Bariri, Sulawesi; an oil palm site in Jambi, Sumatra). After validation, the project will proceed to parameterize land-use transformation system using remote sensing data and to simulate the impacts of historical LUCs on carbon, water and energy fluxes. Last but not least, the effects of future LUCs in Indonesia on the fluxes and carbon sequestration capacity will be investigated through scenario study. Historical land cover changes, especially oil palm coverage, are retrieved from Landsat or MODIS archival

  19. Impact of the lateral boundary conditions resolution on dynamical downscaling of precipitation in mediterranean spain

    NASA Astrophysics Data System (ADS)

    Kim, Do Wan; Liu, Wing Kam; Yoon, Young-Cheol; Belytschko, Ted; Lee, Sang-Ho

    2007-10-01

    Conclusions on the General Circulation Models (GCMs) horizontal and temporal optimum resolution for dynamical downscaling of rainfall in Mediterranean Spain are derived based on the statistical analysis of mesoscale simulations of past events. These events correspond to the 165 heavy rainfall days during 1984 1993, which are simulated with the HIRLAM mesoscale model. The model is nested within the European Centre for Medium-Range Weather Forecasts atmospheric grid analyses. We represent the spectrum of GCMs resolutions currently applied in climate change research by using varying horizontal and temporal resolutions of these analyses. Three sets of simulations are designed using input data with 1°, 2° and 3° horizontal resolutions (available at 6 h intervals), and three additional sets are designed using 1° horizontal resolution with less frequent boundary conditions updated every 12, 24 and 48 h. The quality of the daily rainfall forecasts is verified against rain-gauge observations using correlation and root mean square error analysis as well as Relative Operating Characteristic curves. Spatial distribution of average precipitation fields are also computed and verified against observations. For the whole Mediterranean Spain, model skill is not appreciably improved when using enhanced spatial input data, suggesting that there is no clear benefit in using high resolution data from General Circulation Model for the regional downscaling of precipitation under the conditions tested. However, significant differences are found in verification scores when boundary conditions are interpolated less frequently than 12 h apart. The analysis is particularized for six major rain bearing flow regimes that affect the region, and differences in model performance are found among the flow types, with slightly better forecasts for Atlantic and cold front passage flows. A remarkable spatial variability in forecast quality is found in the domain, with an overall tendency for higher

  20. Vertical Wellbore Flow Monitoring for Assessing Spatial and Temporal Flow Relationships with a Dynamic River Boundary

    SciTech Connect

    Newcomer, Darrell R.; Bjornstad, Bruce N.; Vermeul, Vincent R.

    2010-10-01

    A useful tool for identifying the temporal and spatial ambient wellbore flow relationships near a dynamic river boundary is to continuously monitor ambient vertical wellbore flow with an electromagnetic borehole flowmeter (EBF). This is important because the presence of the wellbore can result in significant mixing or exchange of groundwater vertically across the aquifer. Mixing or exchanging groundwater within the well-screen section can have significant impacts on the distribution of contaminants within the aquifer and adverse effects on the representativeness of groundwater samples collected from the monitoring well. EBF monitoring data collected from long, fully screened wells at Hanford’s 300-Area Integrated Field Research Challenge (IFRC) site, located ~260 to 290 m from the Columbia River, demonstrate that ambient vertical wellbore flow exhibits both a positive (direct) and inverse temporal relationship with periodic river-stage fluctuations over short distances. The ambient flow monitoring wells fully penetrate a highly transmissive unconfined aquifer that consists of unconsolidated coarse sediments of the Hanford formation. The spatial distribution of ambient vertical wellbore flows across the IFRC’s ~2,200 m2 well-field size indicates two general regions of inverse ambient wellbore flow behavior. The western region of the IFRC site is characterized by ambient vertical wellbore flows that are positively related to river-stage fluctuations. In contrast, the eastern region of the site exhibits ambient wellbore flows that are inversely related to river-stage fluctuations. The cause of this opposite relationship between ambient wellbore flows and river-stage changes is not completely understood; however, the positive relationships appear to be associated with high-energy Hanford formation flood deposits. These flood deposits have a well-defined northwest-southeast trend and are believed to coincide with a local paleochannel. This local paleochannel bisects

  1. Simulation of dynamic behavior of surfactants on a hydrophobic surface using periodic-shell boundary molecular dynamics.

    PubMed

    Minami, Daiki; Horikoshi, Satoshi; Sakai, Kenichi; Sakai, Hideki; Abe, Masahiko

    2011-01-01

    The adsorption and aggregation behaviors of sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTAB) on a hydrophobic graphite surface were examined using a novel molecular dynamics (MD) simulation with the periodic-shell boundary condition (PSBC). Differences in the adsorption behavior of SDS and CTAB molecules were clearly shown on the hydrophobic surface. Unexpectedly, the SDS molecules approached the graphite surface with their hydrophilic head groups. This unexpected approach mode was thought to be due to the aqueous layer on the graphite surface. The hydrophobic moiety of SDS molecules repeatedly adsorbed and desorbed on the graphite surface. In addition, SDS molecules kept moving on the graphite surface; thus, they did not form a stable adsorption layer. In contrast to SDS, the hydrophobic moiety of CTAB molecules approached the graphite surface at the primary step of adsorption. The hydrophobic moieties of CTAB molecules came close to each other, whereas the hydrophilic groups separated from one another. This result suggests that the CTAB molecules form molecular assemblies with a curved structure. The simulation results were consistent with the experimental observations. A clear difference between the adsorption behavior of SDS and CTAB molecules was revealed by MD simulations with PSBC.

  2. The shear response of copper bicrystals with Σ11 symmetric and asymmetric tilt grain boundaries by molecular dynamics simulation

    NASA Astrophysics Data System (ADS)

    Zhang, Liang; Lu, Cheng; Tieu, Kiet; Zhao, Xing; Pei, Linqing

    2015-04-01

    Grain boundaries (GBs) are important microstructure features and can significantly affect the properties of nanocrystalline materials. Molecular dynamics simulation was carried out in this study to investigate the shear response and deformation mechanisms of symmetric and asymmetric Σ11<1 1 0> tilt GBs in copper bicrystals. Different deformation mechanisms were reported, depending on GB inclination angles and equilibrium GB structures, including GB migration coupled to shear deformation, GB sliding caused by local atomic shuffling, and dislocation nucleation from GB. The simulation showed that migrating Σ11(1 1 3) GB under shear can be regarded as sliding of GB dislocations and their combination along the boundary plane. A non-planar structure with dissociated intrinsic stacking faults was prevalent in Σ11 asymmetric GBs of Cu. This type of structure can significantly increase the ductility of bicrystal models under shear deformation. A grain boundary can be a source of dislocation and migrate itself at different stress levels. The intrinsic free volume involved in the grain boundary area was correlated with dislocation nucleation and GB sliding, while the dislocation nucleation mechanism can be different for a grain boundary due to its different equilibrium structures.Grain boundaries (GBs) are important microstructure features and can significantly affect the properties of nanocrystalline materials. Molecular dynamics simulation was carried out in this study to investigate the shear response and deformation mechanisms of symmetric and asymmetric Σ11<1 1 0> tilt GBs in copper bicrystals. Different deformation mechanisms were reported, depending on GB inclination angles and equilibrium GB structures, including GB migration coupled to shear deformation, GB sliding caused by local atomic shuffling, and dislocation nucleation from GB. The simulation showed that migrating Σ11(1 1 3) GB under shear can be regarded as sliding of GB dislocations and their combination

  3. Evaluating the impact of built environment characteristics on urban boundary layer dynamics using an advanced stochastic approach

    NASA Astrophysics Data System (ADS)

    Song, Jiyun; Wang, Zhi-Hua

    2016-05-01

    Urban land-atmosphere interactions can be captured by numerical modeling framework with coupled land surface and atmospheric processes, while the model performance depends largely on accurate input parameters. In this study, we use an advanced stochastic approach to quantify parameter uncertainty and model sensitivity of a coupled numerical framework for urban land-atmosphere interactions. It is found that the development of urban boundary layer is highly sensitive to surface characteristics of built terrains. Changes of both urban land use and geometry impose significant impact on the overlying urban boundary layer dynamics through modification on bottom boundary conditions, i.e., by altering surface energy partitioning and surface aerodynamic resistance, respectively. Hydrothermal properties of conventional and green roofs have different impacts on atmospheric dynamics due to different surface energy partitioning mechanisms. Urban geometry (represented by the canyon aspect ratio), however, has a significant nonlinear impact on boundary layer structure and temperature. Besides, managing rooftop roughness provides an alternative option to change the boundary layer thermal state through modification of the vertical turbulent transport. The sensitivity analysis deepens our insight into the fundamental physics of urban land-atmosphere interactions and provides useful guidance for urban planning under challenges of changing climate and continuous global urbanization.

  4. Molecular dynamics study on the effect of boundary heating rate on the phase change characteristics of thin film liquid

    NASA Astrophysics Data System (ADS)

    Hasan, Mohammad Nasim; Morshed, A. K. M. Monjur; Rabbi, Kazi Fazle; Haque, Mominul

    2016-07-01

    In this study, theoretical investigation of thin film liquid phase change phenomena under different boundary heating rates has been conducted with the help of molecular dynamics simulation. To do this, the case of argon boiling over a platinum surface has been considered. The study has been conducted to get a better understanding of the nano-scale physics of evaporation/boiling for a three phase system with particular emphasis on the effect of boundary heating rate. The simulation domain consisted of liquid and vapor argon atoms placed over a platinum wall. Initially the whole system was brought to an equilibrium state at 90K with the help of equilibrium molecular dynamics and then the temperature of the bottom wall was increased to a higher temperature (250K/130K) over a finite heating period. Depending on the heating period, the boundary heating rate has been varied in the range of 1600×109 K/s to 8×109 K/s. The variations of argon region temperature, pressure, net evaporation number with respect to time under different boundary heating rates have been determined and discussed. The heat fluxes normal to platinum wall for different cases were also calculated and compared with theoretical upper limit of maximum possible heat transfer to elucidate the effect of boundary heating rate.

  5. The Tertiary dynamics of the northern Eastern Alps (Austria): changing palaeostresses in a collisional plate boundary

    NASA Astrophysics Data System (ADS)

    Peresson, Herwig; Decker, Kurt

    1997-05-01

    Six Tertiary deviatoric palaeostress tensor groups from 165 stations in the Calcareous Alps describe the upper crustal dynamics of the leading edge of the Adriatic plate during protracted continental collision with the European lower plate. Palaeostress changes are correlated to the kinematic evolution of the plate boundary and to independently derived plate kinematic data of the Alpine-Carpathian-Pannonian area. Each palaeostress direction is defined by 32 to 89 individual tensors which constrain: (1) Late Eocene to ?Oligocene NW-directed compression during thrusting and dextral shearing on WNW-striking faults; NW-directed compression along the northern margin of the Adriatic plate is correlated to its N-directed translation combined with a counterclockwise rotation. (2a) ?Late Eocene to Early Miocene N-directed compression during N-directed thrusting of Penninic and Helvetic units and the Molasse; (2b) Early to Middle Miocene N-directed strike-slip compression during the onset of eastward lateral extrusion; the change from NW- to N-directed compression is interpreted to result from strain partitioning at the Periadriatic fault which has formed the new Adriatic plate boundary since the Oligocene. Dextral shearing on this fault accommodated continued anticlockwise rotation and decoupled the northern Eastern Alps from the rotational component. N-directed compression in the Calcareous Alps paralleled the N-directed translation of the Adriatic plate. (3) Middle Miocene NE-directed compression of thrust- and strike-slip type during lateral extrusion; NE-directed compression in the Calcareous Alps resulted from the drag of the eastward extruding central Eastern Alps. Sinistral shear stress was transmitted across the ENE-trending Salzach-Ennstal fault. NE-oriented σ1-axes include 45° with the E-W-striking zone of distributed sinistral shear in the Calcareous Alps. (4) Middle Miocene E-directed extension associated with orogen-parallel normal faulting of the central

  6. Tracer diffusion in a polymer gel: simulations of static and dynamic 3D networks using spherical boundary conditions

    NASA Astrophysics Data System (ADS)

    Kamerlin, Natasha; Elvingson, Christer

    2016-11-01

    We have investigated an alternative to the standard periodic boundary conditions for simulating the diffusion of tracer particles in a polymer gel by performing Brownian dynamics simulations using spherical boundary conditions. The gel network is constructed by randomly distributing tetravalent cross-linking nodes and connecting nearest pairs. The final gel structure is characterised by the radial distribution functions, chain lengths and end-to-end distances, and the pore size distribution. We have looked at the diffusion of tracer particles with a wide range of sizes, diffusing in both static and dynamic networks of two different volume fractions. It is quantitatively shown that the dynamical effect of the network becomes more important in facilitating the diffusional transport for larger particle sizes, and that one obtains a finite diffusion also for particle sizes well above the maximum in the pore size distribution.

  7. Tracer diffusion in a polymer gel: simulations of static and dynamic 3D networks using spherical boundary conditions.

    PubMed

    Kamerlin, Natasha; Elvingson, Christer

    2016-11-30

    We have investigated an alternative to the standard periodic boundary conditions for simulating the diffusion of tracer particles in a polymer gel by performing Brownian dynamics simulations using spherical boundary conditions. The gel network is constructed by randomly distributing tetravalent cross-linking nodes and connecting nearest pairs. The final gel structure is characterised by the radial distribution functions, chain lengths and end-to-end distances, and the pore size distribution. We have looked at the diffusion of tracer particles with a wide range of sizes, diffusing in both static and dynamic networks of two different volume fractions. It is quantitatively shown that the dynamical effect of the network becomes more important in facilitating the diffusional transport for larger particle sizes, and that one obtains a finite diffusion also for particle sizes well above the maximum in the pore size distribution. PMID:27662260

  8. Vortex dynamics of collapsing bubbles: Impact on the boundary layer measured by chronoamperometry.

    PubMed

    Reuter, Fabian; Cairós, Carlos; Mettin, Robert

    2016-11-01

    Cavitation bubbles collapsing in the vicinity to a solid substrate induce intense micro-convection at the solid. Here we study the transient near-wall flows generated by single collapsing bubbles by chronoamperometric measurements synchronously coupled with high-speed imaging. The individual bubbles are created at confined positions by a focused laser pulse. They reach a maximum expansion radius of approximately 425μm. Several stand-off distances to the flat solid boundary are investigated and all distances are chosen sufficiently large that no gas phase of the expanding and collapsing bubble touches the solid directly. With a microelectrode embedded into the substrate, the time-resolved perturbations in the liquid shear layer are probed by means of a chronoamperometric technique. The measurements of electric current are synchronized with high-speed imaging of the bubble dynamics. The perturbations of the near-wall layer are found to result mainly from ring vortices created by the jetting bubble. Other bubble induced flows, such as the jet and flows following the radial bubble oscillations are perceptible with this technique, but show a minor influence at the stand-off distances investigated. PMID:27245968

  9. Molecular dynamics studies on the dislocation gliding near a tilt boundary

    NASA Astrophysics Data System (ADS)

    Zhiying, Chen

    1996-02-01

    The gliding behavior of edge dislocation near a grain boundary (GB) in copper under pure shear stresses is simulated by using molecular dynamics(MD) method. Many-body potential incorporating the embedded atom method (EAM) is used. The critical shear stresses for a single disocation to pass across GB surface are obtained at values of σ c =23MPa ˜ 68 MPa and 137MPa˜274 MPa for Ω=165 small angle tilt GB at 300K and 20K, respectively. The first result agrees with the experimental yield stress σ y (=42MPa) quite well. It suggests that there might be one of the reasons of initial plastic yielding caused by single dislocation gliding across GB. In addition, there might be possibility to obtain yield strength from microscopic analysis. Moreover, the experimental value of σ y at low temperature is generally higher than that at room temperature. So, these results are in conformity qualitatively with experimental fact. On the other hand, the Ω=25 GB is too strong an obstacle to the dislocation. In this case, a dislocation is able to pass across GB under relatively low stress only when it is driven by other dislocations. This is taken to mean that dislocation pile-up must be built up in front of this kind of GB, if this GB may take effect on the process of plastic deformation.

  10. Thermal boundary conductance enhancement using experimentally achievable nanostructured interfaces - analytical study combined with molecular dynamics simulation.

    PubMed

    Lee, Eungkyu; Zhang, Teng; Hu, Ming; Luo, Tengfei

    2016-06-22

    Interfacial thermal resistance presents great challenges to the thermal management of modern electronics. In this work, we perform an analytical study to enhance the thermal boundary conductance (TBC) of nanostructured interfaces with square-shape pillar arrays, extendable to the characteristic lengths that can be fabricated in practice. As a representative system, we investigate a SiC substrate with the square-shape pillar array combined with epitaxial GaN as the nanostructured interface. By applying a first-order ray tracing method and molecular dynamics simulations to analyze phonon incidence and transmission at the nanostructured interface, we systematically study the impact of the characteristic dimensions of the pillar array on the TBC. Based on the multi-scale analysis we provide a general guideline to optimize the nanostructured interfaces to achieve higher TBC, demonstrating that the optimized TBC value of the nanostructured SiC/GaN interfaces can be 42% higher than that of the planar SiC/GaN interfaces without nanostructures. The model used and results obtained in this study will guide the further experimental realization of nanostructured interfaces for better thermal management in microelectronics. PMID:27275647

  11. Escape dynamics and fractal basins boundaries in the three-dimensional Earth-Moon system

    NASA Astrophysics Data System (ADS)

    Zotos, Euaggelos E.

    2016-03-01

    The orbital dynamics of a spacecraft, or a comet, or an asteroid in the Earth-Moon system in a scattering region around the Moon using the three dimensional version of the circular restricted three-body problem is numerically investigated. The test particle can move in bounded orbits around the Moon or escape through the openings around the Lagrange points L1 and L2 or even collide with the surface of the Moon. We explore in detail the first four of the five possible Hill's regions configurations depending on the value of the Jacobi constant which is of course related with the total orbital energy. We conduct a thorough numerical analysis on the phase space mixing by classifying initial conditions of orbits in several two-dimensional types of planes and distinguishing between four types of motion: (i) ordered bounded, (ii) trapped chaotic, (iii) escaping and (iv) collisional. In particular, we locate the different basins and we relate them with the corresponding spatial distributions of the escape and collision times. Our outcomes reveal the high complexity of this planetary system. Furthermore, the numerical analysis suggests a strong dependence of the properties of the considered basins with both the total orbital energy and the initial value of the z coordinate, with a remarkable presence of fractal basin boundaries along all the regimes. Our results are compared with earlier ones regarding the planar version of the Earth-Moon system.

  12. Vortex dynamics of collapsing bubbles: Impact on the boundary layer measured by chronoamperometry.

    PubMed

    Reuter, Fabian; Cairós, Carlos; Mettin, Robert

    2016-11-01

    Cavitation bubbles collapsing in the vicinity to a solid substrate induce intense micro-convection at the solid. Here we study the transient near-wall flows generated by single collapsing bubbles by chronoamperometric measurements synchronously coupled with high-speed imaging. The individual bubbles are created at confined positions by a focused laser pulse. They reach a maximum expansion radius of approximately 425μm. Several stand-off distances to the flat solid boundary are investigated and all distances are chosen sufficiently large that no gas phase of the expanding and collapsing bubble touches the solid directly. With a microelectrode embedded into the substrate, the time-resolved perturbations in the liquid shear layer are probed by means of a chronoamperometric technique. The measurements of electric current are synchronized with high-speed imaging of the bubble dynamics. The perturbations of the near-wall layer are found to result mainly from ring vortices created by the jetting bubble. Other bubble induced flows, such as the jet and flows following the radial bubble oscillations are perceptible with this technique, but show a minor influence at the stand-off distances investigated.

  13. Effects of land use on surface–atmosphere exchanges of trace gases and energy in Borneo: comparing fluxes over oil palm plantations and a rainforest

    PubMed Central

    Fowler, David; Nemitz, Eiko; Misztal, Pawel; Di Marco, Chiara; Skiba, Ute; Ryder, James; Helfter, Carole; Cape, J. Neil; Owen, Sue; Dorsey, James; Gallagher, Martin W.; Coyle, Mhairi; Phillips, Gavin; Davison, Brian; Langford, Ben; MacKenzie, Rob; Muller, Jennifer; Siong, Jambery; Dari-Salisburgo, Cesare; Di Carlo, Piero; Aruffo, Eleonora; Giammaria, Franco; Pyle, John A.; Hewitt, C. Nicholas

    2011-01-01

    This paper reports measurements of land–atmosphere fluxes of sensible and latent heat, momentum, CO2, volatile organic compounds (VOCs), NO, NO2, N2O and O3 over a 30 m high rainforest canopy and a 12 m high oil palm plantation in the same region of Sabah in Borneo between April and July 2008. The daytime maximum CO2 flux to the two canopies differs by approximately a factor of 2, 1200 mg C m−2 h−1 for the oil palm and 700 mg C m−2 h−1 for the rainforest, with the oil palm plantation showing a substantially greater quantum efficiency. Total VOC emissions are also larger over the oil palm than over the rainforest by a factor of 3. Emissions of isoprene from the oil palm canopy represented 80 per cent of the VOC emissions and exceeded those over the rainforest in similar light and temperature conditions by on average a factor of 5. Substantial emissions of estragole (1-allyl-4-methoxybenzene) from the oil palm plantation were detected and no trace of this VOC was detected in or above the rainforest. Deposition velocities for O3 to the rainforest were a factor of 2 larger than over oil palm. Emissions of nitrous oxide were larger from the soils of the oil palm plantation than from the soils of the rainforest by approximately 25 per cent. It is clear from the measurements that the large change in the species composition generated by replacing rainforest with oil palm leads to profound changes in the net exchange of most of the trace gases measured, and thus on the chemical composition of the boundary layer over these surfaces. PMID:22006962

  14. Effects of land use on surface-atmosphere exchanges of trace gases and energy in Borneo: comparing fluxes over oil palm plantations and a rainforest.

    PubMed

    Fowler, David; Nemitz, Eiko; Misztal, Pawel; Di Marco, Chiara; Skiba, Ute; Ryder, James; Helfter, Carole; Cape, J Neil; Owen, Sue; Dorsey, James; Gallagher, Martin W; Coyle, Mhairi; Phillips, Gavin; Davison, Brian; Langford, Ben; MacKenzie, Rob; Muller, Jennifer; Siong, Jambery; Dari-Salisburgo, Cesare; Di Carlo, Piero; Aruffo, Eleonora; Giammaria, Franco; Pyle, John A; Hewitt, C Nicholas

    2011-11-27

    This paper reports measurements of land-atmosphere fluxes of sensible and latent heat, momentum, CO(2), volatile organic compounds (VOCs), NO, NO(2), N(2)O and O(3) over a 30 m high rainforest canopy and a 12 m high oil palm plantation in the same region of Sabah in Borneo between April and July 2008. The daytime maximum CO(2) flux to the two canopies differs by approximately a factor of 2, 1200 mg C m(-2) h(-1) for the oil palm and 700 mg C m(-2) h(-1) for the rainforest, with the oil palm plantation showing a substantially greater quantum efficiency. Total VOC emissions are also larger over the oil palm than over the rainforest by a factor of 3. Emissions of isoprene from the oil palm canopy represented 80 per cent of the VOC emissions and exceeded those over the rainforest in similar light and temperature conditions by on average a factor of 5. Substantial emissions of estragole (1-allyl-4-methoxybenzene) from the oil palm plantation were detected and no trace of this VOC was detected in or above the rainforest. Deposition velocities for O(3) to the rainforest were a factor of 2 larger than over oil palm. Emissions of nitrous oxide were larger from the soils of the oil palm plantation than from the soils of the rainforest by approximately 25 per cent. It is clear from the measurements that the large change in the species composition generated by replacing rainforest with oil palm leads to profound changes in the net exchange of most of the trace gases measured, and thus on the chemical composition of the boundary layer over these surfaces.

  15. The dynamics of the tundra-taiga boundary: an overview and suggested coordinated and integrated approach to research.

    PubMed

    Callaghan, Terry V; Crawford, Robert M M; Eronen, Matti; Hofgaard, Annika; Payette, Serge; Rees, W Gareth; Skre, Oddvar; Sveinbjörnsson, Bjartmar; Vlassova, Tatiana K; Werkman, Ben R

    2002-08-01

    The tundra-taiga boundary stretches for more than 13,400 km around the Northern Hemisphere and is probably the Earth's greatest vegetation transition. The trees that define the boundary have been sensitive to climate changes in the past and models of future vegetation distribution suggest a rapid and dramatic invasion of the tundra by the taiga. Such changes would generate both positive and negative feedbacks to the climate system and the balance could result in a net warming effect. However, the boundary is becoming increasingly affected by human activities that remove trees and degrade forest-tundra into tundra-like areas. Because of the vastness and remoteness of the tundra-taiga boundary, and of methodological problems such as problematic definitions and lack of standardized methods to record the location and characteristics of the ecotone, a project group has been established under the auspices of the International Arctic Science Committee (IASC). This paper summarizes the initial output of the group and focuses on our uncertainties in understanding the current processes at the tundra-taiga boundary and the conflicts between model predictions of changes in the location of the boundary and contrasting recently observed changes due to human activities. Finally, we present recommendations for a coordinated international approach to the problem and invite the international community to join us in reducing the uncertainties about the dynamics of the ecotone and their consequences.

  16. Litter mercury deposition in the Amazonian rainforest.

    PubMed

    Fostier, Anne Hélène; Melendez-Perez, José Javier; Richter, Larissa

    2015-11-01

    The objective of this work was to assess the flux of atmospheric mercury transferred to the soil of the Amazonian rainforest by litterfall. Calculations were based on a large survey of published and unpublished data on litterfall and Hg concentrations in litterfall samples from the Amazonian region. Litterfall based on 65 sites located in the Amazon rainforest averaged 8.15 ± 2.25 Mg ha(-1) y(-1). Average Hg concentrations were calculated from nine datasets for fresh tree leaves and ten datasets for litter, and a median concentration of 60.5 ng Hg g(-1) was considered for Hg deposition in litterfall, which averaged 49 ± 14 μg m(-2) yr(-1). This value was used to estimate that in the Amazonian rainforest, litterfall would be responsible for the annual removing of 268 ± 77 Mg of Hg, approximately 8% of the total atmospheric Hg deposition to land. The impact of the Amazon deforestation on the Hg biogeochemical cycle is also discussed.

  17. The Green's matrix and the boundary integral equations for analysis of time-harmonic dynamics of elastic helical springs.

    PubMed

    Sorokin, Sergey V

    2011-03-01

    Helical springs serve as vibration isolators in virtually any suspension system. Various exact and approximate methods may be employed to determine the eigenfrequencies of vibrations of these structural elements and their dynamic transfer functions. The method of boundary integral equations is a meaningful alternative to obtain exact solutions of problems of the time-harmonic dynamics of elastic springs in the framework of Bernoulli-Euler beam theory. In this paper, the derivations of the Green's matrix, of the Somigliana's identities, and of the boundary integral equations are presented. The vibrational power transmission in an infinitely long spring is analyzed by means of the Green's matrix. The eigenfrequencies and the dynamic transfer functions are found by solving the boundary integral equations. In the course of analysis, the essential features and advantages of the method of boundary integral equations are highlighted. The reported analytical results may be used to study the time-harmonic motion in any wave guide governed by a system of linear differential equations in a single spatial coordinate along its axis.

  18. Bubble dynamics in a compressible liquid in contact with a rigid boundary

    PubMed Central

    Wang, Qianxi; Liu, Wenke; Zhang, A. M.; Sui, Yi

    2015-01-01

    A bubble initiated near a rigid boundary may be almost in contact with the boundary because of its expansion and migration to the boundary, where a thin layer of water forms between the bubble and the boundary thereafter. This phenomenon is modelled using the weakly compressible theory coupled with the boundary integral method. The wall effects are modelled using the imaging method. The numerical instabilities caused by the near contact of the bubble surface with the boundary are handled by removing a thin layer of water between them and joining the bubble surface with its image to the boundary. Our computations correlate well with experiments for both the first and second cycles of oscillation. The time history of the energy of a bubble system follows a step function, reducing rapidly and significantly because of emission of shock waves at inception of a bubble and at the end of collapse but remaining approximately constant for the rest of the time. The bubble starts being in near contact with the boundary during the first cycle of oscillation when the dimensionless stand-off distance γ = s/Rm < 1, where s is the distance of the initial bubble centre from the boundary and Rm is the maximum bubble radius. This leads to (i) the direct impact of a high-speed liquid jet on the boundary once it penetrates through the bubble, (ii) the direct contact of the bubble at high temperature and high pressure with the boundary, and (iii) the direct impingement of shock waves on the boundary once emitted. These phenomena have clear potential to damage the boundary, which are believed to be part of the mechanisms of cavitation damage. PMID:26442148

  19. Mapping Deforestation and Land Use in Amazon Rainforest Using SAR-C Imagery

    NASA Technical Reports Server (NTRS)

    Saatchi, Sasan S.; Soares, Joao Vianei; Alves, Diogenes Salas

    1996-01-01

    Land use changes and deforestation in tropical rainforests are among the major factors affecting the overall function of the global environment. To routinely assess the spatial extend and temporal dynamics of these changes has become an important challenge in several scientific disciplines such as climate and environmental studies. In this paper, the feasibility of using polarimetric spaceborne SAR data in mapping land cover types in the Amazon is studied.

  20. A study of the convective boundary-layer dynamics using single Doppler radar measurements

    SciTech Connect

    Xu, M.; Gal-Chen, T. )

    1993-11-01

    The kinematic and dynamical properties of the convective planetary boundary layer (CBL) with shear are studied using single Doppler radar measurements. The data were collected using single K-band (0.87 cm) Doppler radar operated by the National Oceanic and Atmospheric Administration Wave Propagation Laboratory. An analysis technique has been developed and tested that is an extension of the velocity azimuth display (VAD). The technique and its associated error analysis are described in detail. Profiles of the mean wind, vertical velocity, associated momentum fluxes, and variances are estimated. In agreement with the classical picture of the CBL, the profile of the vertical velocity variance achieves a relative maximum magnitude in the lower part of the mixed layer. Large magnitudes of vertical flux of horizontal momentum are found at the top of the mixed layer, while countergradient momentum fluxes are found in part of the CBL. The second moment of the Doppler spectrum is utilized, so that the momentum transport by eddies smaller than radar resolution volume is included. In most cases and contrary to most large eddy simulations studies, the effects of the subresolution momentum fluxes on the mixed layer are not negligible. The longitudinal power spectrum on the horizontal velocity near the surface has also been calculated using the Fourier transform techniques. Traditional k[sup [minus]5/3] spectra at the inertial subrange are obtained from which, using standard techniques, the turbulent kinetic energy dissipation rate has been estimated. To test the validity of the single Doppler analysis techniques, the derived turbulence statistics are compared with the results from other measurements. 33 refs., 30 figs, 3 tabs.

  1. Boundary layer charge dynamics in ionic liquid-ionic polymer transducers

    NASA Astrophysics Data System (ADS)

    Davidson, Jacob D.; Goulbourne, N. C.

    2011-01-01

    Ionic polymer transducers (IPTs), also known as ionic polymer-metal composites, are soft sensors and actuators which operate through a coupling of microscale chemical, electrical, and mechanical interactions. The use of an ionic liquid as solvent for an IPT has been shown to dramatically increase transducer lifetime in free-air use, while also allowing for higher applied voltages without electrolysis. In this work, we apply Nernst-Planck/Poisson theory to model charge transport in an ionic liquid IPT by considering a certain fraction of the ionic liquid ions as mobile charge carriers, a phenomenon which is unique to ionic liquid IPTs compared to their water-based counterparts. Numerical simulations are performed using the finite element method to examine how the introduction of another pair of mobile ions affects boundary layer charge dynamics, concentration, and charge density distributions in the electric double layer, and the overall charge transferred and current response of the IPT. Due to interactions with the Nafion ionomer, not all of the ionic liquid ions will function as mobile charge carriers; only a certain fraction will exist as "free" ions. The presence of mobile ionic liquid ions in the transducer will increase the overall charge transferred when a voltage is applied, and cause the current in the transducer to decay more slowly. The additional mobile ions also cause the ionic concentration profiles to exhibit a nonlinear dynamic response, characterized by nonmonotonic ionic concentration profiles in space and time. Although the presence of mobile ionic liquid ions increases the overall amount of charge transferred, this additional charge transfer occurs in a somewhat symmetric manner. Therefore, the additional charge transferred due to the ionic liquid ions does not greatly increase the net bending moment of the transducer; in fact, it is possible that ionic liquid ion movement actually decreases the observed bending response. This suggests that an

  2. Human impacts flatten rainforest-savanna gradient and reduce adaptive diversity in a rainforest bird.

    PubMed

    Freedman, Adam H; Buermann, Wolfgang; Mitchard, Edward T A; Defries, Ruth S; Smith, Thomas B

    2010-09-30

    Ecological gradients have long been recognized as important regions for diversification and speciation. However, little attention has been paid to the evolutionary consequences or conservation implications of human activities that fundamentally change the environmental features of such gradients. Here we show that recent deforestation in West Africa has homogenized the rainforest-savanna gradient, causing a loss of adaptive phenotypic diversity in a common rainforest bird, the little greenbul (Andropadus virens). Previously, this species was shown to exhibit morphological and song divergence along this gradient in Central Africa. Using satellite-based estimates of forest cover, recent morphological data, and historical data from museum specimens collected prior to widespread deforestation, we show that the gradient has become shallower in West Africa and that A. virens populations there have lost morphological variation in traits important to fitness. In contrast, we find no loss of morphological variation in Central Africa where there has been less deforestation and gradients have remained more intact. While rainforest deforestation is a leading cause of species extinction, the potential of deforestation to flatten gradients and inhibit rainforest diversification has not been previously recognized. More deforestation will likely lead to further flattening of the gradient and loss of diversity, and may limit the ability of species to persist under future environmental conditions.

  3. Boundary Layer Dynamics and Sub-Adiabaticity in Convecting Planetary Mantles

    NASA Astrophysics Data System (ADS)

    Moore, W. B.

    2007-05-01

    A broad range of phenomena are influenced by the behavior of thermal boundary layers in planetary mantles including plume temperatures, lithospheric stresses, resistance to plate motions, and the temperature structure of the mantle as a whole. The textbook picture of the temperature profile in a convecting layer consists of two boundary layers separated by a well-mixed, adiabatic interior. The sum of the temperature drops across the upper and lower boundary layers is equal to super-adiabatic temperature drop across the entire layer. This picture does not accurately describe, however, the horizontally averaged temperature structure derived from numerical solutions of the equations of infinite Prandtl number, Boussinesq convection. The sum of the average temperature drops across the boundary layers in such models is always greater than the super-adiabatic drop across the whole layer, with the result that some portions of the interior are sub-adiabatic. The excess average temperature drop across each boundary layer is due to the arrival of material from the other boundary layer which has not equilibrated with the well-mixed interior. It is this material which transfers heat conductively across the boundary and thus controls the heat transport of the layer. Internal heating breaks the symmetry of the boundary layers (as does temperature dependence of viscosity), and it is the interaction between the two boundary layers that sets the equilibrium temperature drops. The scaling of the temperature drop across each boundary layer is controlled by two competing factors which depend on the Rayleigh number in different ways: the scale of boundary layer instabilities and the velocity of plumes (hot and cold). Furthermore, these scalings change as the system becomes time-dependent at moderate Rayleigh number. At very high Rayleigh number, beyond that of most planetary mantles, the plumes do equilibrate with the interior and the textbook picture applies. A scaling theory for the

  4. Dynamical effects on the core-mantle boundary from depth-dependent thermodynamical properties of the lower mantle

    NASA Technical Reports Server (NTRS)

    Zhang, Shuxia; Yuen, David A.

    1988-01-01

    A common assumption in modeling dynamical processes in the lower mantle is that both the thermal expansivity and thermal conductivity are reasonably constant. Recent work from seismic equation of state leads to substantially higher values for the thermal conductivity and much lower thermal expansivity values in the deep mantle. The dynamical consequences of incorporating depth-dependent thermodynamic properties on the thermal-mechanical state of the lower mantle are examined with the spherical-shell mean-field equations. It is found that the thermal structure of the seismically resolved anomalous zone at the base of the mantle is strongly influenced by these variable properties and, in particular, that the convective distortion of the core-mantle boundary (CMB) is reduced with the decreasing thermal expansivity. Such a reduction of the dynamically induced topography from pure thermal convection would suggest that some other dynamical mechanism must be operating at the CMB.

  5. Numerical modeling of the 3D dynamics of ultrasound contrast agent microbubbles using the boundary integral method

    NASA Astrophysics Data System (ADS)

    Wang, Qianxi; Manmi, Kawa; Calvisi, Michael L.

    2015-02-01

    Ultrasound contrast agents (UCAs) are microbubbles stabilized with a shell typically of lipid, polymer, or protein and are emerging as a unique tool for noninvasive therapies ranging from gene delivery to tumor ablation. While various models have been developed to describe the spherical oscillations of contrast agents, the treatment of nonspherical behavior has received less attention. However, the nonspherical dynamics of contrast agents are thought to play an important role in therapeutic applications, for example, enhancing the uptake of therapeutic agents across cell membranes and tissue interfaces, and causing tissue ablation. In this paper, a model for nonspherical contrast agent dynamics based on the boundary integral method is described. The effects of the encapsulating shell are approximated by adapting Hoff's model for thin-shell, spherical contrast agents. A high-quality mesh of the bubble surface is maintained by implementing a hybrid approach of the Lagrangian method and elastic mesh technique. The numerical model agrees well with a modified Rayleigh-Plesset equation for encapsulated spherical bubbles. Numerical analyses of the dynamics of UCAs in an infinite liquid and near a rigid wall are performed in parameter regimes of clinical relevance. The oscillation amplitude and period decrease significantly due to the coating. A bubble jet forms when the amplitude of ultrasound is sufficiently large, as occurs for bubbles without a coating; however, the threshold amplitude required to incite jetting increases due to the coating. When a UCA is near a rigid boundary subject to acoustic forcing, the jet is directed towards the wall if the acoustic wave propagates perpendicular to the boundary. When the acoustic wave propagates parallel to the rigid boundary, the jet direction has components both along the wave direction and towards the boundary that depend mainly on the dimensionless standoff distance of the bubble from the boundary. In all cases, the jet

  6. Dynamic boundary estimation of human heart within a complete cardiac cycle using electrical impedance tomography

    NASA Astrophysics Data System (ADS)

    Rashid, A.; Kim, B. S.; Khambampati, A. K.; Liu, Dong; Kim, S.; Kim, K. Y.

    2010-04-01

    This paper presents an EKF based boundary estimation algorithm to estimate the shape and size of human heart ventricle during a complete cardiac cycle. First-order kinematic model is used as a state evolution model. The boundary of the heart is expressed as coefficients of truncated Fourier series and the conductivity distribution inside the thorax region is assumed to be known a priori. The proposed method is tested with the use of a realistic chest shape FEM mesh.

  7. Volume of fluid (VOF) method for the dynamics of free boundaries

    SciTech Connect

    Hirt, C.W.; Nichols, B.D.

    1981-01-01

    Several methods have been previously used to approximate free boundaries in finite-difference numerical simulations. A simple, but powerful, method is described that is based on the concept of a fractional volume of fluid (VOF). This method is shown to be more flexible and efficient than other methods for treating complicated free boundary configurations. To illustrate the method, a description is given for an incompressible hydrodynamics code, SOLA-VOF, that uses the VOF technique to track free fluid surfaces.

  8. The role of boundary layer dynamics on the diurnal evolution of isoprene and the hydroxyl radical over tropical forests

    NASA Astrophysics Data System (ADS)

    Vilã-Guerau de Arellano, Jordi; Patton, Edward G.; Karl, Thomas; van den Dries, Kees; Barth, Mary C.; Orlando, John J.

    2011-04-01

    We investigate diurnal variability of isoprene and related chemical species in the Amazonian region. The dynamics and chemistry of an atmospheric boundary layer are studied with a large-eddy simulation code and a mixed-layer model which are guided by observations available for the same area. The main features of isoprene and related species are reproduced well, but their evolution raises questions regarding the physical and chemical processes responsible for the observed diurnal behaviors. To address these questions, we systematically examine the role of (1) the exchange of chemical species between the free troposphere and the atmospheric boundary layer (entrainment), (2) surface isoprene and nitric oxide emissions, and (3) new chemical pathways to recycle the hydroxyl radical. The entrainment flux of isoprene is shown to be equally important as surface isoprene emissions in determining the isoprene temporal evolution. Varying the relationship between the initial isoprene mixing ratio in the boundary layer and that in the overlying free troposphere in the early morning results in an 50% increase/decrease in isoprene mixing ratio or more within the atmospheric boundary layer at noon. Entrainment of free tropospheric nitrogen oxides creates changes of similar magnitude to the boundary layer isoprene mixing ratio. These effects of entrainment and surface emissions on isoprene are found for two different chemical regimes. The introduction of an OH recycling pathway in the chemical mechanism increases midday OH. Our findings show that atmospheric dynamics and chemistry are equally important for interpreting the diurnal observation of reactants and for including in regional-scale modeling efforts where turbulence is parameterized.

  9. Recently evolved diversity and convergent radiations of rainforest mahoganies (Meliaceae) shed new light on the origins of rainforest hyperdiversity.

    PubMed

    Koenen, Erik J M; Clarkson, James J; Pennington, Terence D; Chatrou, Lars W

    2015-07-01

    Tropical rainforest hyperdiversity is often suggested to have evolved over a long time-span (the 'museum' model), but there is also evidence for recent rainforest radiations. The mahoganies (Meliaceae) are a prominent plant group in lowland tropical rainforests world-wide but also occur in all other tropical ecosystems. We investigated whether rainforest diversity in Meliaceae has accumulated over a long time or has more recently evolved. We inferred the largest time-calibrated phylogeny for the family to date, reconstructed ancestral states for habitat and deciduousness, estimated diversification rates and modeled potential shifts in macro-evolutionary processes using a recently developed Bayesian method. The ancestral Meliaceae is reconstructed as a deciduous species that inhabited seasonal habitats. Rainforest clades have diversified from the Late Oligocene or Early Miocene onwards. Two contemporaneous Amazonian clades have converged on similar ecologies and high speciation rates. Most species-level diversity of Meliaceae in rainforest is recent. Other studies have found steady accumulation of lineages, but the large majority of plant species diversity in rainforests is recent, suggesting (episodic) species turnover. Rainforest hyperdiversity may best be explained by recent radiations from a large stock of higher level taxa.

  10. Characterising primary productivity measurements across a dynamic western boundary current region

    NASA Astrophysics Data System (ADS)

    Everett, Jason D.; Doblin, Martina A.

    2015-06-01

    Determining the magnitude of primary production (PP) in a changing ocean is a major research challenge. Thousands of estimates of marine PP exist globally, but there remain significant gaps in data availability, particularly in the Southern Hemisphere. In situ PP estimates are generally single-point measurements and therefore we rely on satellite models of PP in order to scale up over time and space. To reduce the uncertainty around the model output, these models need to be assessed against in situ measurements before use. This study examined the vertically-integrated productivity in four water-masses associated with the East Australian Current (EAC), the major western boundary current (WBC) of the South Pacific. We calculated vertically integrated PP from shipboard 14C PP estimates and then compared them to estimates from four commonly used satellite models (ESQRT, VGPM, VGPM-Eppley, VGPM-Kameda) to assess their utility for this region. Vertical profiles of the water-column show each water-mass had distinct temperature-salinity signatures. The depth of the fluorescence-maximum (fmax) increased from onshore (river plume) to offshore (EAC) as light penetration increased. Depth integrated PP was highest in river plumes (792±181 mg C m-2 d-1) followed by the EAC (534±116 mg C m-2 d-1), continental shelf (140±47 mg C m-2 d-1) and cyclonic eddy waters (121±4 mg C m-2 d-1). Surface carbon assimilation efficiency was greatest in the EAC (301±145 mg C (mg Chl-a)-1 d-1) compared to other water masses. All satellite primary production models tested underestimated EAC PP and overestimated continental shelf PP. The ESQRT model had the highest skill and lowest bias of the tested models, providing the best first-order estimates of PP on the continental shelf, including at a coastal time-series station, Port Hacking, which showed considerable inter-annual variability (155-2957 mg C m-2 d-1). This work provides the first estimates of depth integrated PP associated with the

  11. Dynamics of a Thermal-Chemical-Phase Boundary Layer Above the Core-Mantle Boundary and its Influence on the Evolution of the Mantle and Core

    NASA Astrophysics Data System (ADS)

    Tackley, P. J.; Nakagawa, T.; Hernlund, J. W.

    2006-12-01

    It has long been thought that seismic heterogeneities in the D" region might be caused by both thermal and chemical variations; now the post-perovskite transition also appears to be important. Here, dynamical issues associated with a mixed thermal-chemical-phase boundary layer are reviewed. If recent mineral physics data on the density of MORB are correct, a significant fraction of subducted MORB segregates into a layer above the CMB. A layer formed in this way is very heterogeneous and lacks a sharp, clean boundary, unlike layers inserted a priori into calculations. A layer may be global or in the form of intermittent 'piles' and has a large effect on both the mean value and the lateral variation of core heat flux. The post-perovskite transition has a destabilizing influence due to its positive Clapeyron slope, although this is partly offset by latent heat effects. Post-perovskite may occur in localized patches, or in a global, strongly undulating layer, depending on whether the CMB temperature is hot enough to be in the perovskite stability field. Regions containing a thick layer of post-perovskite are anticorrelated with regions containing thick accumulations of chemically-dense material. Post-perovskite regions may have near-vertical sharp edges, perhaps accounting for some seismic observations; in any case lateral variations in the occurrence of post-perovskite can cause seismic velocity variations larger than those caused by thermal or chemical variations. Heat flux across the CMB, as well as lateral variations in this heat flux, are strongly influenced by the presence of global or local chemical layering, but only mildly influenced by post-perovskite, and can be constrained by seismological observations of the post-perovskite boundary. Coupled models of core-mantle evolution taking into account these effects predict that radioactive potassium is needed in the core, in order to simultaneously allow the extraction of enough heat to drive the geodynamo while

  12. Classical molecular dynamics investigation of microstructure evolution and grain boundary diffusion in nano-polycrystalline UO2

    NASA Astrophysics Data System (ADS)

    Govers, K.; Verwerft, M.

    2013-07-01

    The High Burnup Structure (HBS) observed at pellet periphery in conventional Light Water Reactor nuclear fuels and around spots presenting high plutonium content in mixed (U, Pu) oxide fuel - MOX fuel - consists of a restructuration of the original grains into smaller ones. The process is often postulated to occur because of the accumulation of irradiation damage and the retention of fission products in the matrix. The computing power nowadays available enables for simulating larger systems at the atomic scale up to the point that nano-polycrystalline material can now be investigated by empirical potential molecular dynamics. Simulations of nano-polycrystalline UO2 structures have been carried out at various temperatures to investigate atom mobility close to grain boundaries. The variation of Arrhénius parameters for the diffusion coefficient of oxygen, uranium and xenon as a function of the distance from a grain boundary was studied, leading to the distinction of three zones: the grain boundary layers (up to 1 nm depth) presenting enhanced diffusion, an intermediate zone (1 to roughly 2 nm depth) with intermediate diffusion values and the bulk of the grains. The following Arrhénius relations for grain boundary diffusion were derived:

  13. Molecular dynamics study on evaporation and reflection of monatomic molecules to construct kinetic boundary condition in vapor-liquid equilibria

    NASA Astrophysics Data System (ADS)

    Kobayashi, Kazumichi; Hori, Kazumasa; Kon, Misaki; Sasaki, Kiyofumi; Watanabe, Masao

    2016-09-01

    Using molecular dynamics simulations, the present study investigates the precise characteristics of evaporating and reflecting monatomic molecules (argon) composing a kinetic boundary condition (KBC) in a vapor-liquid equilibria. We counted the evaporating and reflecting molecules utilizing two boundaries (vapor and liquid boundaries) proposed by the previous studies (Meland et al. in Phys Fluids 16:223-243, 2004; Gu et al. in Fluid Phase Equilib 297:77-89, 2010). In the present study, we improved the method using the two boundaries incorporating the concept of the spontaneously evaporating molecular mass flux. The present method allows us to count the evaporating and reflecting molecules easily, to investigate the detail motion of the evaporating and reflecting molecules, and also to evaluate the velocity distribution function of the KBC at the vapor-liquid interface, appropriately. From the results, we confirm that the evaporating and reflecting molecules in the normal direction to the interface have slightly faster and significantly slower average velocities than that of the Maxwell distribution at the liquid temperature, respectively. Also, the stall time of the reflecting molecules at the interphase that is the region in the vicinity of the vapor-liquid interface is much shorter than those of the evaporating molecules. Furthermore, we discuss our method for constructing the KBC that incorporates condensation and evaporation coefficients. Based on these results, we suggest that the proposed method is appropriate for investigating KBC in various nonequilibrium states or multi-component systems.

  14. Renewable resource development in the Ecuadorian rainforest

    SciTech Connect

    Hutton, W.C.; Skaggs, M.M. Jr.

    1995-12-31

    This paper discusses the planning and execution of a multi-million dollar, heavy oil renewable resource development project in the Amazon Basin of Ecuador. The project work is authorized under a risk service contract with PETROECUADOR and employs new technology in order to minimize environmental and cultural impacts on the environment and the inhabitants of the areas. During the peak of the project, over 3,000 workers were employed and managed in the rainforest under special guidelines, in order to avoid damages to the environment. The project guidelines are spelled out in a model Environmental Management Plan (EMP) which employs innovative well pad, road and pipeline construction and platform drilling methods to limit deforestation. Reforestation methods are reviewed; scientific baseline and archaeological pre and post construction methods were followed, and methods to control colonization pressures are executed as a part of the EMP described in this paper. In addition, the EMP covers methods used to minimize the disruption of the indigenous population of the area including medical, educational and other programs employed to reduce disease among the indigenous population of the area. Conventional aspects of the EMP include spill control techniques for remote areas of the rainforest, solid waste recycling programs, drilling and construction waste management, landfarming methods, pipeline construction and underground river crossing methods. All of these methods are employed to minimize the environmental and cultural impact of the project on the environment and its inhabitants.

  15. Dynamics and propulsion of a rotating flexible helical rod near a no-slip rigid boundary

    NASA Astrophysics Data System (ADS)

    Jawed, Mohammad; Karimi, Hussain; Reis, Pedro

    We study the effect of a no-slip rigid boundary on the locomotion of uni-flagellar bacteria in a viscous fluid at low Reynolds number conditions, through a combination of computer simulations and experiments. In our analogue model experiments, we exploit the prominence of geometry in this class of problems to rescale the original micron-scale system onto the desktop-scale. We manufacture elastomeric filaments with fully customizable geometric and material properties, and rotate them in a glycerin bath at a finite distance away from a rigid boundary. The experimental results are compared against numerical simulations that combine the Discrete Elastic Rods method in conjunction with Lighthill Slender Body Theory. The no-slip boundary condition on the wall is implemented by the method of images. We first show that the filament buckles above a critical rotation frequency due to fluid loading, and then quantify the dependence of this critical threshold on the distance from the boundary. Excellent agreement is found between experiments and simulations, with no fitting parameters. Moreover, we find that the generated propulsion force is strongly affected by the presence of a nearby boundary.

  16. Marine boundary layer dynamics during the first Lagrangian of the ASTEX experiment

    SciTech Connect

    Duynkerke, P.G.; Zhang, H.; Roode, S.R. de

    1994-12-31

    The authors present measurements of boundary layer properties during the first Lagrangian observation period of the Atlantic Stratocumulus Transition Experiment (ASTEX), June 1992. In this experiment a column of air was tracked for 48 hours as it moved south-westward over water with increasing sea surface temperatures. The authors use the NCAR Electra and MRF C-130 aircraft data to study the cloud evolution during this Lagrangian. From the aircraft data the authors analyzed the turbulence, radiation and micro-physical processes in this cloud-topped atmospheric boundary layer. The authors use initialized analysis fields of the ECMWF to obtain the large scale flow structure: flow fields, temperature, subsidence, etc.

  17. Scaling the fractional advective-dispersive equation for numerical evaluation of microbial dynamics in confined geometries with sticky boundaries

    SciTech Connect

    Parashar, R.; Cushman, J.H.

    2008-06-20

    Microbial motility is often characterized by 'run and tumble' behavior which consists of bacteria making sequences of runs followed by tumbles (random changes in direction). As a superset of Brownian motion, Levy motion seems to describe such a motility pattern. The Eulerian (Fokker-Planck) equation describing these motions is similar to the classical advection-diffusion equation except that the order of highest derivative is fractional, {alpha} element of (0, 2]. The Lagrangian equation, driven by a Levy measure with drift, is stochastic and employed to numerically explore the dynamics of microbes in a flow cell with sticky boundaries. The Eulerian equation is used to non-dimensionalize parameters. The amount of sorbed time on the boundaries is modeled as a random variable that can vary over a wide range of values. Salient features of first passage time are studied with respect to scaled parameters.

  18. South American palaeobotany and the origins of neotropical rainforests.

    PubMed Central

    Burnham, Robyn J; Johnson, Kirk R

    2004-01-01

    Extant neotropical rainforest biomes are characterized by a high diversity and abundance of angiosperm trees and vines, high proportions of entire-margined leaves, high proportions of large leaves (larger than 4500 mm2), high abundance of drip tips and a suite of characteristic dominant families: Sapotaceae, Lauraceae, Leguminosae (Fabaceae), Melastomataceae and Palmae (Arecaceae). Our aim is to define parameters of extant rainforests that will allow their recognition in the fossil record of South America and to evaluate all known South American plant fossil assemblages for first evidence and continued presence of those parameters. We ask when did these critical rainforest characters arise? When did vegetative parameters reach the level of abundance that we see in neotropical forests? Also, when do specific lineages become common in neotropical forests? Our review indicates that evidence of neotropical rainforest is exceedingly rare and equivocal before the Palaeocene. Even in the Palaeocene, the only evidence for tropical rainforest in South America is the appearance of moderately high pollen diversity. By contrast, North American sites provide evidence that rainforest leaf physiognomy was established early in the Palaeocene. By the Eocene in South America, several lines of evidence suggest that neotropical rainforests were diverse, physiognomically recognizable as rainforest and taxonomically allied to modern neotropical rainforests. A mismatch of evidence regarding the age of origin between sites of palaeobotanical high diversity and sites of predicted tropical climates should be reconciled with intensified collecting efforts in South America. We identify several lines of promising research that will help to coalesce previously disparate approaches to the origin, longevity and maintenance of high diversity floras of South America. PMID:15519975

  19. On the dynamic behavior of composite panels under turbulent boundary layer excitations

    NASA Astrophysics Data System (ADS)

    Ciappi, E.; De Rosa, S.; Franco, F.; Vitiello, P.; Miozzi, M.

    2016-03-01

    In this work high Mach number aerodynamic and structural measurements acquired in the CIRA (Italian Aerospace Research Center) transonic wind tunnel and the models used to analyze the response of composite panels to turbulent boundary layer excitation are presented. The two investigated panels are CFRP (Carbon Fiber-Reinforced Polymer) composite plates and their lay-up is similar to configurations used in aeronautical structures. They differ only for the presence of an embedded viscoelastic layer. The experimental set-up has been designed to reproduce a pressure fluctuations field beneath a turbulent boundary layer as close as possible to those in flight. A tripping system, specifically conceived to this aim for this facility, has been used to generate thick turbulent boundary layers at Mach number values ranging between 0.4 and 0.8. It is shown that the designed setup provides a realistic representation of full scale size pressure spectra in the frequency range of interest for the noise component inside the fuselage, generated by turbulent boundary layer. The significant role of the viscoelastic layer at reducing panel's response is detailed and discussed. Finally, it is demonstrated that at high Mach number the aeroelastic effect cannot be neglected when analyzing the panel response, especially when composite materials are considered.

  20. Predictability of time averages. I - Dynamical predictability of monthly means. II - The influence of the boundary forcings. [for weather forecasting

    NASA Technical Reports Server (NTRS)

    Shukla, J.

    1984-01-01

    The physical basis for the dynamic prediction of monthly means in weather parameters is examined in two papers. In the first paper, an attempt is made to determine the theoretical upper limit of dynamical predictability of monthly means for prescribed nonfluctuating external forcings. In the second paper, the physical mechanisms through which changes in the boundary forcings of SST, soil moisture, albedo, and snow influence atmospheric circulation are discussed. On the basis of both studies, the essential requirements for establishing the physical basis for dynamical prediction of monthly means are to show that: (1) fluctuations of monthly means are larger than can be expected due to sampling of day-to-day weather changes; (2) there are low frequency planetary scale components of circulation which remain predictable beyond the limits of synoptic scale predictability; and (3) the influences of the slowly varying boundary conditions of SST, soil moisture, snow, sea ice are large enough to produce significant and detectable changes in the monthly mean circulations. Observational and numerical evidence which support these requirements are presented.

  1. Influence of the added mass effect and boundary conditions on the dynamic response of submerged and confined structures

    NASA Astrophysics Data System (ADS)

    Valentín, D.; Presas, A.; Egusquiza, E.; Valero, C.

    2014-03-01

    The dynamic response of submerged and confined disk-like structures is of interest in the flied of hydraulic machinery, especially in hydraulic turbine runners. This response is difficult to be estimated with accuracy due to the strong influence of the boundary conditions. Small radial gaps as well as short axial distances to rigid surfaces greatly modify the dynamic response because the fact of the added mass and damping effects. Moreover, the effect of the shaft coupling is also important for certain mode-shapes of the structure. In the present study, the influence of the added mass effect and boundary conditions on the dynamic behavior of a submerged disk attached to a shaft is evaluated through experimental tests and structural- acoustic coupling numerical simulations. For the experimentation, a test rig has been developed. It consists of a confined disk attached to a shaft inside a cylindrical container full of water. The disk can be fixed at different axial positions along the shaft. Piezoelectric patches are used to excite the disk and the response is measured with submersible accelerometers. For each configuration tested, the natural frequencies of the disk and the shaft are studied. Numerical results have been compared with experimental results.

  2. Bushmeat hunting changes regeneration of African rainforests.

    PubMed

    Effiom, Edu O; Nuñez-Iturri, Gabriela; Smith, Henrik G; Ottosson, Ulf; Olsson, Ola

    2013-05-22

    To assess ecological consequences of bushmeat hunting in African lowland rainforests, we compared paired sites, with high and low hunting pressure, in three areas of southeastern Nigeria. In hunted sites, populations of important seed dispersers-both small and large primates (including the Cross River gorilla, Gorilla gorilla diehli)-were drastically reduced. Large rodents were more abundant in hunted sites, even though they are hunted. Hunted and protected sites had similar mature tree communities dominated by primate-dispersed species. In protected sites, seedling communities were similar in composition to the mature trees, but in hunted sites species with other dispersal modes dominated among seedlings. Seedlings emerging 1 year after clearing of all vegetation in experimental plots showed a similar pattern to the standing seedlings. This study thus verifies the transforming effects of bushmeat hunting on plant communities of tropical forests and is one of the first studies to do so for the African continent. PMID:23516245

  3. Bushmeat hunting changes regeneration of African rainforests.

    PubMed

    Effiom, Edu O; Nuñez-Iturri, Gabriela; Smith, Henrik G; Ottosson, Ulf; Olsson, Ola

    2013-05-22

    To assess ecological consequences of bushmeat hunting in African lowland rainforests, we compared paired sites, with high and low hunting pressure, in three areas of southeastern Nigeria. In hunted sites, populations of important seed dispersers-both small and large primates (including the Cross River gorilla, Gorilla gorilla diehli)-were drastically reduced. Large rodents were more abundant in hunted sites, even though they are hunted. Hunted and protected sites had similar mature tree communities dominated by primate-dispersed species. In protected sites, seedling communities were similar in composition to the mature trees, but in hunted sites species with other dispersal modes dominated among seedlings. Seedlings emerging 1 year after clearing of all vegetation in experimental plots showed a similar pattern to the standing seedlings. This study thus verifies the transforming effects of bushmeat hunting on plant communities of tropical forests and is one of the first studies to do so for the African continent.

  4. Stability boundaries for aircraft with unstable lateral-directional dynamics and control saturation

    NASA Technical Reports Server (NTRS)

    Shrivastava, Prakash C.; Stengel, Robert F.

    1989-01-01

    Aircraft that do not possess inherent (aerodynamic) stability must rely on closed-loop control systems for stable operation. Because there are limits on the deflections of an aircraft's control surfaces, the region of stable operation also is bounded. These boundaries are investigated for a lateral-directional example in which vertical fin size is inadequate to provide directional stability and where aileron and rudder deflections are subject to saturation. Fourth-order models are used in this study, with flight control logic based on minimum-control-energy linear-quadratic-regulatory theory. It is found that the stability boundaries can be described by unstable limit cycles surrounding stable equilibrium points. Variations in regions of stability with gain levels and command inputs are illustrated. Current results suggest guidelines for permissible limits on the open-loop instability of an aircraft's lateral-directional modes.

  5. Does Diversity Matter In Modeling? Testing A New Version Of The FORMIX3 Growth Model For Madagascar Rainforests

    NASA Astrophysics Data System (ADS)

    Armstrong, A. H.; Fischer, R.; Shugart, H. H.; Huth, A.

    2012-12-01

    Ecological forecasting has become an essential tool used by ecologists to understand the dynamics of growth and disturbance response in threatened ecosystems such as the rainforests of Madagascar. In the species rich tropics, forest conservation is often eclipsed by anthropogenic factors, resulting in a heightened need for accurate assessment of biomass before these ecosystems disappear. The objective of this study was to test a new Madagascar rainforest specific version of the FORMIX3 growth model (Huth and Ditzer, 2000; Huth et al 1998) to assess how accurately biomass can be simulated in high biodiversity forests using a method of functional type aggregation in an individual-based model framework. Rainforest survey data collected over three growing seasons, including 265 tree species, was aggregated into 12 plant functional types based on size and light requirements. Findings indicated that the forest study site compared best when the simulated forest reached mature successional status. Multiple level comparisons between model simulation data and survey plot data found that though some features, such as the dominance of canopy emergent species and relative absence of small woody treelets are captured by the model, other forest attributes were not well reflected. Overall, the ability to accurately simulate the Madagascar rainforest was slightly diminished by the aggregation of tree species into size and light requirement functional type groupings.

  6. Culture or climate? The relative influences of past processes on the composition of the lowland Congo rainforest.

    PubMed

    Brncic, Terry M; Willis, Katherine J; Harris, David J; Washington, Richard

    2007-02-28

    This paper presents the results from a palaeoecological study to establish the impact of prehistoric human activity and climate change on the vegetation and soils of the Goualougo area of the Nouabalé-Ndoki National Park, in the Republic of Congo (Congo-Brazzaville). This is a region that is known from previous work (through evidence of pottery, furnaces and charcoal layers beneath the present day rainforest vegetation) to have had prehistoric settlement dating back to at least 2000 calibrated years before present. In addition, there is climatic evidence to suggest that significant variations in precipitation have occurred in central Africa over the last few millennia. Presently, the region is covered in uninhabited moist semi-evergreen rainforest. Key research questions addressed in this paper include the extent to which the present-day composition of rainforest in this region is as a result of processes of the past (climate change and/or human activity), and the resilience of the rainforest to these perturbations. Statistical analyses of pollen, microscopic charcoal and geochemical data are used to determine the relationship over time between vegetation dynamics and climate change, anthropogenic burning and metal smelting. Significant changes in forest composition are linked to burning and climate change but not metallurgy. The strongest influence on the present day composition appears to be related to the increased anthropogenic burning that started approximately 1000 years ago. Results from this study are discussed in terms of their implications for the present and future management of this globally important forested region.

  7. Influence of boundary-layer dynamics on pollen dispersion and viability

    NASA Astrophysics Data System (ADS)

    Arritt, Raymond W.; Viner, Brian J.; Westgate, Mark E.

    2013-04-01

    Adoption of genetically modified (GM) crops has raised concerns that GM traits can accidentally cross into conventional crops or wild relatives through the transport of wind-borne pollen. In order to evaluate this risk it is necessary to account both for dispersion of the pollen grains and environmental influences on pollen viability. The Lagrangian approach is suited to this problem because it allows tracking the environmental temperature and moisture that pollen grains experience as they travel. Taking advantage of this capability we have combined a high-resolution version of the WRF meteorological model with a Lagrangian particle dispersion model to predict maize pollen dispersion and viability. WRF is used to obtain fields of wind, turbulence kinetic energy, temperature, and humidity which are then used as input to the Lagrangian dispersion model. The dispersion model in turn predicts transport of a statistical sample of a pollen cloud from source plants to receptors. We also use the three-dimensional temperature and moisture fields from WRF to diagnose changes in moisture content of the pollen grains and consequent loss of viability. Results show that turbulent motions in the convective boundary layer counteract the large terminal velocity of maize pollen grains and lift them to heights of several hundred meters, so that they can be transported long distances before settling to the ground. We also found that pollen lifted into the upper part of the boundary layer remains more viable than has been inferred using surface observations of temperature and humidity. This is attributed to the thermal and moisture structure that typifies the daytime atmospheric boundary layer, producing an environment of low vapor pressure deficit in the upper boundary layer which helps maintain pollen viability.

  8. Vibrational properties of a Σ5( 3 1 0 )[ 0 0 1 ] NiO grain boundary: a local analysis by molecular dynamics simulation

    NASA Astrophysics Data System (ADS)

    Karakasidis, Theodoros E.

    2002-08-01

    Using molecular dynamics and a rigid ion potential we studied the vibrational properties of a Σ5(3 1 0)[0 0 1] tilt grain boundary in NiO. We calculated the local density of states and the mean square displacement (MSD) of the cation and ion sublattice for a wide temperature range. We examined their behaviour in the directions parallel and normal to the boundary as a function from the grain boundary plane. We found that the local phonon density of states of the sites of the boundary are altered with comparison to the bulk presenting in general a shift towards lower frequencies in the direction normal to the boundary and toward higher frequencies in the direction parallel to the grain boundary. This anisotropy, which is conformed by the results of the MSDs, is maintained up to high temperatures. We have also observed that the increase of temperature leads to the gradual loosening of the binding of atoms.

  9. Towards Understanding the Mechanism of Receptivity and Bypass Dynamics in Laminar Boundary Layers

    NASA Technical Reports Server (NTRS)

    Lasseigne, D. G.; Criminale, W. O.; Joslin, R. D.; Jackson, T. L.

    1999-01-01

    Three problems concerning laminar-turbulent transition are addressed by solving a series of initial value problems. The first problem is the calculation of resonance within the continuous spectrum of the Blasius boundary layer. The second is calculation of the growth of Tollmien-Schlichting waves that are a direct result of disturbances that only lie outside of the boundary layer. And, the third problem is the calculation of non-parallel effects. Together, these problems represent a unified approach to the study of freestream disturbance effects that could lead to transition. Solutions to the temporal, initial-value problem with an inhomogeneous forcing term imposed upon the flow is sought. By solving a series of problems, it is shown that: A transient disturbance lying completely outside of the boundary layer can lead to the growth of an unstable Tollmien-Schlichting wave. A resonance with the continuous spectrum leads to strong amplification that may provide a mechanism for bypass transition once nonlinear effects are considered. A disturbance with a very weak unstable Tollmien-Schlichting wave can lead to a much stronger Tollmien-Schlichting wave downstream, if the original disturbance has a significant portion of its energy in the continuum modes.

  10. Lidar Applications in Atmospheric Dynamics: Measurements of Wind, Moisture and Boundary Layer Evolution

    NASA Technical Reports Server (NTRS)

    Demoz, Belay; Whiteman, David; Gentry, Bruce; Schwemmer, Geary; Evans, Keith; DiGirolamo, Paolo; Comer, Joseph

    2005-01-01

    A large array of state-of-the-art ground-based and airborne remote and in-situ sensors were deployed during the International H2O Project (THOP), a field experiment that took place over the Southern Great Plains (SGP) of the United States from 13 May to 30 June 2002. These instruments provided extensive measurements of water vapor mixing ratio in order to better understand the influence of its variability on convection and on the skill of quantitative precipitation prediction (Weckwerth et all, 2004). Among the instrument deployed were ground based lidars from NASA/GSFC that included the Scanning Raman Lidar (SRL), the Goddard Laboratory for Observing Winds (GLOW), and the Holographic Airborne Rotating Lidar Instrument Experiment (HARLIE). A brief description of the three lidars is given below. This study presents ground-based measurements of wind, boundary layer structure and water vapor mixing ratio measurements observed by three co-located lidars during MOP at the MOP ground profiling site in the Oklahoma Panhandle (hereafter referred as Homestead). This presentation will focus on the evolution and variability of moisture and wind in the boundary layer when frontal and/or convergence boundaries (e.g. bores, dry lines, thunderstorm outflows etc) were observed.

  11. Entropic lattice Boltzmann model for gas dynamics: Theory, boundary conditions, and implementation.

    PubMed

    Frapolli, N; Chikatamarla, S S; Karlin, I V

    2016-06-01

    We present in detail the recently introduced entropic lattice Boltzmann model for compressible flows [N. Frapolli et al., Phys. Rev. E 92, 061301(R) (2015)PLEEE81539-375510.1103/PhysRevE.92.061301]. The model is capable of simulating a wide range of laminar and turbulent flows, from thermal and weakly compressible flows to transonic and supersonic flows. The theory behind the construction of the model is laid out and its thermohydrodynamic limit is discussed. Based on this theory and the hydrodynamic limit thereof, we also construct the boundary conditions necessary for the simulation of solid walls. We present the inlet and outlet boundary conditions as well as no-slip and free-slip boundary conditions. Details necessary for the implementation of the compressible lattice Boltzmann model are also reported. Finally, simulations of compressible flows are presented, including two-dimensional supersonic and transonic flows around a diamond and a NACA airfoil, the simulation of the Schardin problem, and the three-dimensional simulation of the supersonic flow around a conical geometry. PMID:27415382

  12. Entropic lattice Boltzmann model for gas dynamics: Theory, boundary conditions, and implementation

    NASA Astrophysics Data System (ADS)

    Frapolli, N.; Chikatamarla, S. S.; Karlin, I. V.

    2016-06-01

    We present in detail the recently introduced entropic lattice Boltzmann model for compressible flows [N. Frapolli et al., Phys. Rev. E 92, 061301(R) (2015), 10.1103/PhysRevE.92.061301]. The model is capable of simulating a wide range of laminar and turbulent flows, from thermal and weakly compressible flows to transonic and supersonic flows. The theory behind the construction of the model is laid out and its thermohydrodynamic limit is discussed. Based on this theory and the hydrodynamic limit thereof, we also construct the boundary conditions necessary for the simulation of solid walls. We present the inlet and outlet boundary conditions as well as no-slip and free-slip boundary conditions. Details necessary for the implementation of the compressible lattice Boltzmann model are also reported. Finally, simulations of compressible flows are presented, including two-dimensional supersonic and transonic flows around a diamond and a NACA airfoil, the simulation of the Schardin problem, and the three-dimensional simulation of the supersonic flow around a conical geometry.

  13. Boundary condition identification for a grid model by experimental and numerical dynamic analysis

    NASA Astrophysics Data System (ADS)

    Mao, Qiang; Devitis, John; Mazzotti, Matteo; Bartoli, Ivan; Moon, Franklin; Sjoblom, Kurt; Aktan, Emin

    2015-04-01

    There is a growing need to characterize unknown foundations and assess substructures in existing bridges. It is becoming an important issue for the serviceability and safety of bridges as well as for the possibility of partial reuse of existing infrastructures. Within this broader contest, this paper investigates the possibility of identifying, locating and quantifying changes of boundary conditions, by leveraging a simply supported grid structure with a composite deck. Multi-reference impact tests are operated for the grid model and modification of one supporting bearing is done by replacing a steel cylindrical roller with a roller of compliant material. Impact based modal analysis provide global modal parameters such as damped natural frequencies, mode shapes and flexibility matrix that are used as indicators of boundary condition changes. An updating process combining a hybrid optimization algorithm and the finite element software suit ABAQUS is presented in this paper. The updated ABAQUS model of the grid that simulates the supporting bearing with springs is used to detect and quantify the change of the boundary conditions.

  14. Entropic lattice Boltzmann model for gas dynamics: Theory, boundary conditions, and implementation.

    PubMed

    Frapolli, N; Chikatamarla, S S; Karlin, I V

    2016-06-01

    We present in detail the recently introduced entropic lattice Boltzmann model for compressible flows [N. Frapolli et al., Phys. Rev. E 92, 061301(R) (2015)PLEEE81539-375510.1103/PhysRevE.92.061301]. The model is capable of simulating a wide range of laminar and turbulent flows, from thermal and weakly compressible flows to transonic and supersonic flows. The theory behind the construction of the model is laid out and its thermohydrodynamic limit is discussed. Based on this theory and the hydrodynamic limit thereof, we also construct the boundary conditions necessary for the simulation of solid walls. We present the inlet and outlet boundary conditions as well as no-slip and free-slip boundary conditions. Details necessary for the implementation of the compressible lattice Boltzmann model are also reported. Finally, simulations of compressible flows are presented, including two-dimensional supersonic and transonic flows around a diamond and a NACA airfoil, the simulation of the Schardin problem, and the three-dimensional simulation of the supersonic flow around a conical geometry.

  15. Thalamocortical dynamics of the McCollough effect: boundary-surface alignment through perceptual learning.

    PubMed

    Grossberg, Stephen; Hwang, Seungwoo; Mingolla, Ennio

    2002-05-01

    This article further develops the FACADE neural model of 3-D vision and figure-ground perception to quantitatively explain properties of the McCollough effect (ME). The model proposes that many ME data result from visual system mechanisms whose primary function is to adaptively align, through learning, boundary and surface representations that are positionally shifted due to the process of binocular fusion. For example, binocular boundary representations are shifted by binocular fusion relative to monocular surface representations, yet the boundaries must become positionally aligned with the surfaces to control binocular surface capture and filling-in. The model also includes perceptual reset mechanisms that use habituative transmitters in opponent processing circuits. Thus the model shows how ME data may arise from a combination of mechanisms that have a clear functional role in biological vision. Simulation results with a single set of parameters quantitatively fit data from 13 experiments that probe the nature of achromatic/chromatic and monocular/binocular interactions during induction of the ME. The model proposes how perceptual learning, opponent processing, and habituation at both monocular and binocular surface representations are involved, including early thalamocortical sites. In particular, it explains the anomalous ME utilizing these multiple processing sites. Alternative models of the ME are also summarized and compared with the present model.

  16. Cold-air outbreak during GALE - Lidar observations and modeling of boundary layer dynamics

    NASA Technical Reports Server (NTRS)

    Boers, Reinout; Melfi, S. H.; Palm, Stephen P.

    1991-01-01

    Two cold-air outbreaks were studied during the Genesis of Atlantic Lows Experiment. A lidar system was operated to observe the boundary layer evolution and the development of clouds. On the first day (January 30, 1986) boundary layer rise was less than 50 percent of the value for the second day (March 2, 1986). On the first day only a thin broken cloud cover formed, while on the second day a thick solid cloud deck formed - although the average moisture content was 60 percent of that on the first day. A trajectory slab model was employed to simulate the evolution of the layer over the ocean near the east Atlantic shore. The model allows for vertical gradients in conservative variables under neutrally buoyant conditions. The primary effect of these assumptions, which are based on observed thermodynamic profiles, is to reduce cloudiness to be more in line with observations. Boundary-layer depth was reasonably well predicted as was sensible and latent heat flux.

  17. Simulating drought impacts on energy balance in an Amazonian rainforest

    NASA Astrophysics Data System (ADS)

    Imbuzeiro, H. A.; Costa, M. H.; Galbraith, D.; Christoffersen, B. O.; Powell, T.; Harper, A. B.; Levine, N. M.; Rowland, L.; Moorcroft, P. R.; Benezoli, V. H.; Meir, P.; da Costa, A. C. L.; Brando, P. M.; Malhi, Y.; Saleska, S. R.; Williams, M. D.

    2014-12-01

    The studies of the interaction between vegetation and climate change in the Amazon Basin indicate that up to half of the region's forests may be displaced by savanna vegetation by the end of the century. Additional analyses suggest that complex interactions among land use, fire-frequency, and episodic drought are driving an even more rapid process of the forest impoverishment and displacement referred here as "savannization". But it is not clear whether surface/ecosystem models are suitable to analyze extreme events like a drought. Long-term simulations of throughfall exclusion experiments has provided unique insights into the energy dynamics of Amazonian rainforests during drought conditions. In this study, we evaluate how well six surface/ecosystem models quantify the energy dynamics from two Amazonian throughfall exclusion experiments. All models were run for the Tapajós and Caxiuanã sites with one control plot using normal precipitation (i.e. do not impose a drought) and then the drought manipulation was imposed for several drought treatments (10 to 90% rainfall exclusion). The sap flow, net radiation (Rn), sensible (H), latent (LE) and ground (G) heat flux are used to analyze if the models are able to capture the dynamics of water stress and what the implications for the energy dynamics are. With respect to the model validation, when we compare the sap flow observed and transpiration simulated, models are more accurate to simulate control plots than drought treatments (50% rainfall exclusion). The results show that the models overestimate the sap flow data during the drought conditions, but they were able to capture the changes in the main energy balance components for different drought treatments. The Rn and LE decreased and H increased with more intensity of drought. The models sensitivity analysis indicate that models are more sensitive to drought when rainfall is excluded for more than 60% and when this reduction occurs during the dry season.

  18. Dynamic deformation of volcanic ejecta from the Toba caldera: possible relevance to Cretaceous/Tertiary boundary phenomena

    SciTech Connect

    Carter, N.L.; Officer, C.B.; Chesner, C.A.; Rose, W.I.

    1986-05-01

    Plagioclase and biotite phenocrysts in ignimbrites erupted from the Toba caldera, Sumatra, show microstructures and textures indicative of shock stress levels higher than 10 GPa. Strong dynamic deformation has resulted in intense kinking in biotite and, with increasing shock intensity, the development of plagioclase of planar features, shock mosaicism, incipient recrystallization, and possible partial melting. Microstructures in quartz indicative of strong shock deformation are rare, however, and many shock lamellae, if formed, may have healed during post-shock residence in the hot ignimbrite; they might be preserved in ash falls. Peak shock stresses from explosive silicic volcanism and other endogenous processes may be high and if so would obviate the need for extraterrestrial impacts to produce all dynamically deformed structures, possibly including shock features observed near the Cretaceous/Tertiary boundary. 38 references, 3 figures.

  19. Tear film dynamics with evaporation, wetting, and time-dependent flux boundary condition on an eye-shaped domain

    PubMed Central

    Li, Longfei; Braun, R. J.; Maki, K. L.; Henshaw, W. D.; King-Smith, P. E.

    2014-01-01

    We study tear film dynamics with evaporation on a wettable eye-shaped ocular surface using a lubrication model. The mathematical model has a time-dependent flux boundary condition that models the cycles of tear fluid supply and drainage; it mimics blinks on a stationary eye-shaped domain. We generate computational grids and solve the nonlinear governing equations using the OVERTURE computational framework. In vivo experimental results using fluorescent imaging are used to visualize the influx and redistribution of tears for an open eye. Results from the numerical simulations are compared with the experiment. The model captures the flow around the meniscus and other dynamic features of human tear film observed in vivo. PMID:24926191

  20. Dynamics and energetics of the cloudy boundary layer in simulations of off-ice flow in the marginal ice zone

    NASA Astrophysics Data System (ADS)

    Olsson, Peter Q.; Harrington, Jerry Y.

    2000-05-01

    The case under consideration occurred on March 4, 1993, and was observed as part of the Radiation and Eddy Flux Experiment (REFLEX II) 1993 observational campaign northwest of Spitsbergen. The off-ice flow on this day brought very cold surface air temperatures (-35°C) over a relatively warm ocean surface. The resultant latent and sensible surface heat fluxes produced intense convection and a thermal internal boundary layer (TIBL) which deepened with distance from the ice edge. Two-dimensional cloud-resolving model (CRM) simulations were performed to determine the impact of various cloud parameterizations on the structure and evolution of the TIBL. The model was able to reproduce the observed thermal structure of the boundary layer to within the acknowledged limitations of the CRM approach. Sensitivity studies of cloud type showed that inclusion of mixed-phase microphysics had a large impact of BL depth and structure. Radiative heating of the cloud near cloud base and cooling near cloud top along with latent heat release were found to be significant sources of turbulence kinetic energy even in the present case where very strong surface heat fluxes occur. Ice-phase precipitation processes rapidly depleted the BL of condensate, weakening the radiative thermal forcing. A further consequence of condensate depletion in the mixed-phase cloud was a less humid boundary layer that was able to maintain a larger surface latent heat flux and continuously extract heat through condensation and deposition. Not surprisingly, the presence of clouds had a profound impact on the radiative budget at the surface, with the cloudy BL reducing surface radiative losses more that 60% over clear-sky values. Inclusion of the ice phase significantly affected the radiative budget as compared to purely liquid clouds, illustrating the importance of ice-phase-radiative couplings for accurate simulations of arctic clouds and boundary layer dynamics.

  1. Analysis of temporal variability in land-atmosphere interactions, boundary layer dynamics and chemistry during the 2012 PEGASOS field campaigns

    NASA Astrophysics Data System (ADS)

    Ganzeveld, Laurens; Krol, Maarten; Bosveld, Fred; Hofzumahaus, Andreas; Kiendler-Scharr, Astrid; Rohrer, Franz; Wahner, Andreas; Descari, Stefano

    2014-05-01

    Surface and airborne measurements collected during the 2012 PEGASOS intensive field campaign over the Netherlands and the Po valley, Italy, offer an optimal source of information to further improve our knowledge on the role boundary layer exchange processes in atmospheric chemistry. The use of a zeppelin, sampling close to the surface ( ~50m) up to ~600m altitude and measuring in the early morning, provided detailed measurements of vertical gradients as well as the temporal evolution in chemical composition and relevant meteorological parameters. This allows more detailed analysis of the role of the morning transition and entrainment of residual air masses previously being identified to be essential to daytime chemical processing in the boundary layer. Analysis of these measurements is supported by the use of a number of modelling systems including a selection of 1-D model approaches. In addition, these 1-D models are applied to directly link the observations to the representation of these processes in the 3-D atmospheric chemistry models used to address the overall PEGASOS research goals. In this presentation, results of simulations with an 1-D chemistry-climate model system covering the full measurement period will be presented. Assimilation of meteorological and chemical composition re-analysis data as well as a detailed representation of atmosphere-biosphere and boundary layer exchange processes in this 1-D system allow to assess the role of local scale land-atmosphere interactions versus long-range transport during the PESOSAS field campaigns. In this presentation we will focus on an assessment to what extent daytime boundary layer dynamics and chemistry depends on the short- and more long-term history of the system, e.g., residual layer processing and the role of changes in soil moisture status on land-atmosphere interactions.

  2. Tree topkill, not mortality, governs the dynamics of savanna-forest boundaries under frequent fire in central Brazil.

    PubMed

    Hoffmann, William A; Adasme, Ryan; Haridasan, M; de Carvalho, Marina T; Geiger, Erika L; Pereira, Mireia A B; Gotsch, Sybil G; Franco, Augusto C

    2009-05-01

    Tropical savanna and forest are recognized to represent alternate stable states, primarily determined by feedbacks with fire. Vegetation-fire dynamics in each of these vegetation types are largely determined by the influence of the vegetation on fire behavior, as well as the effects of fire behavior on tree mortality, topkill (defined here as complete death of the aerial biomass, regardless of whether the plant recovers by resprouting), and rate of growth of resprouts. We studied the effect of fire on three savanna-forest boundaries in central Brazil. Fire intensity was greater in savanna than forest, as inferred by a twofold greater height of stem charring. Despite lower fire intensity, forest tree species exhibited higher rates of topkill, which was best explained by their thinner bark, relative to savanna species. Following topkill, there was no tendency for sprouts of savanna trees to grow faster than those of forest species, contrary to expectations, nor was whole-plant mortality higher in forest than in savanna. This contrasts with observations of high rates of postburn mortality in many other tropical forests. The low tree mortality in these transitional forests suggests that the dynamic of these natural savanna-forest boundaries is fundamentally different from that of forest boundaries originating from deforestation in the humid tropics. The forests studied here appear to be much more resilient to occasional incursion of fire from the savanna, despite being unable to invade frequently burned savanna. The thin bark of forest species makes them particularly susceptible to the "fire trap," whereby repeated topkill of small trees prevents recruitment into adult size classes. Rapid growth will be particularly important for forest species to escape the fire trap, so we predict that, where fire is frequent, forests should be restricted to high-resource sites. Here, Mg2+ and Ca2+ concentrations had particularly strong effects on postburn growth rates, suggesting

  3. Dynamic Multiscale Boundary Conditions for 4D CT Images of Healthy and Emphysematous Rat

    SciTech Connect

    Jacob, Rick E.; Carson, James P.; Thomas, Mathew; Einstein, Daniel R.

    2013-06-14

    Changes in the shape of the lung during breathing determine the movement of airways and alveoli, and thus impact airflow dynamics. Modeling airflow dynamics in health and disease is a key goal for predictive multiscale models of respiration. Past efforts to model changes in lung shape during breathing have measured shape at multiple breath-holds. However, breath-holds do not capture hysteretic differences between inspiration and expiration resulting from the additional energy required for inspiration. Alternatively, imaging dynamically – without breath-holds – allows measurement of hysteretic differences. In this study, we acquire multiple micro-CT images per breath (4DCT) in live rats, and from these images we develop, for the first time, dynamic volume maps. These maps show changes in local volume across the entire lung throughout the breathing cycle and accurately predict the global pressure-volume (PV) hysteresis.

  4. The turbulent bottom boundary layer and its influence on local dynamics over the continental shelf

    NASA Astrophysics Data System (ADS)

    Dewey, Richard D.; Leblond, Paul H.; Crawford, William R.

    1988-11-01

    We report on measurements of the structure of the bottom boundary layer on the continental shelf off Vancouver Island. A time series of vertical profiles obtained with the microstructure profiler FLY II revealed large temporal variations in the dissipation rate and in the density structure. The near-bottom current structure was simultaneously measured at fixed heights with conventional current meters. The data reveal the association between the predominantly diurnal tide and the variations in the structure of the bottom boundary layer. A clear distinction appears between the turbulent bottom boundary layer (8-40 m deep in a total water depth of 138 m) and the well-mixed layer (20-40 m deep). The two layers vary independently, with horizontal advection dominating the fluctuations in the thickness of the well-mixed layer while local dissipation is more closely related to the thickness of the turbulent layer. Variations in the density structure of the bottom layer are related to the strength and direction of the vertical shear and to the regional distribution of isopycnals. Current veering is commonly concentrated above the well-mixed layer. The evolution of the characteristics of the bottom layers is followed through a tidal cycle and related to local dissipation and other variables. Microstructure measurements from six locations over the southern portion of the Vancouver Island continental shelf are used to estimate the influence of turbulent energy dissipation on regional-scale flows. That fraction of the dissipation taking place in the bottom boundary layer is attributed to barotropic tidal flows, while that occurring above it is associated with nearly geostrophic baroclinic flows. Results give a lower limit of ˜ 1070 km for the length scale of shelf wave decay, in good agreement with current models; the estimates of tidal friction based on our dissipation measurements are however much lower than required by astronomical observations. An estimate of 230 h is

  5. Transient spatio-temporal dynamics of a diffusive plant-herbivore system with Neumann boundary conditions.

    PubMed

    Yu, Fang; Wang, Lin; Watmough, James

    2016-12-01

    In many existing predator-prey or plant-herbivore models, the numerical response is assumed to be proportional to the functional response. In this paper, without such an assumption, we consider a diffusive plant-herbivore system with Neumann boundary conditions. Besides stability of spatially homogeneous steady states, we also derive conditions for the occurrence of Hopf bifurcation and steady-state bifurcation and provide geometrical methods to locate the bifurcation values. We numerically explore the complex transient spatio-temporal behaviours induced by these bifurcations. A large variety of different types of transient behaviours including oscillations in one or both of space and time are observed. PMID:27572052

  6. On solvability of boundary value problem of magnetic gas dynamics with cylindric and spherical symmetries

    NASA Astrophysics Data System (ADS)

    Koshanov, Bakytbek D.; Smatova, Gulzhazira D.

    2016-08-01

    In this paper initial-boundary value problems for movement equation of viscous heat-conducting gas considering magnetic field are investigated. Besides, a transition from the main three-dimensional equation to an Eulerian variable and a subsequent Lagrangian coordinate is shown. For equations of the heat-conducting gas in the magnetic field, a unique solvability is proved in a case when a flow domain does not include an axis (point) of symmetry. The movements with cylindric and spherical waves are considered simultaneously.

  7. Flowfield dynamics in blunt fin-induced shock wave/turbulent boundary layer interactions

    NASA Technical Reports Server (NTRS)

    Dolling, David S.; Brusniak, Leon

    1994-01-01

    Fluctuating wall pressure measurements have been made on centerline upstream of a blunt fin in a Mach 5 turbulent boundary layer. By examining the ensemble averaged wall pressure distributions for different separation shock foot positions, it has been shown that local fluctuating wall pressure measurements are due to a distinct pressure distribution, Rho(sub i), which undergoes a stretching and flattening effect as its upstream boundary translates aperiodically between the upstream influence and separation lines. The locations of the maxima and minima in the wall pressure standard deviation can be accurately predicted using this distribution, providing quantitative confirmation of the model. This model also explains the observed cross-correlations and ensemble average measurements within the interaction. Using the Rho(sub i) model, wall pressure signals from under the separated flow region were used to reproduce the position-time history of the separation shock foot. Further, the negative time delay peak in the cross-correlation between the predicted and actual shock foot histories suggests that the separated region fluctuations precede shock foot motion. The unsteady behavior of the primary horseshoe vortex and its relation to the unsteady separation shock are described.

  8. Structure and dynamics of turbulent boundary layer flow over healthy and algae-covered corals

    NASA Astrophysics Data System (ADS)

    Stocking, Jonathan B.; Rippe, John P.; Reidenbach, Matthew A.

    2016-09-01

    Fine-scale velocity measurements over healthy and algae-covered corals were collected in situ to characterize combined wave-current boundary layer flow and the effects of algal canopies on turbulence hydrodynamics. Data were collected using acoustic Doppler velocimetry and particle image velocimetry. Flow over healthy corals is well described by traditional wall-bounded shear layers, distinguished by a logarithmic velocity profile, a local balance of turbulence production and dissipation, and high levels of bed shear stress. Healthy corals exhibit significant spatial heterogeneity in boundary layer flow structure resulting from variations in large-scale coral topography. By contrast, the turbulence structure of algae-covered corals is best represented by a plane mixing layer, with a sharp inflection point in mean velocity at the canopy top, a large imbalance of turbulence production and dissipation, and strongly damped flow and shear stresses within the canopy. The presence of an algal canopy increases turbulent kinetic energy within the roughness sublayer by ~2.5 times compared to healthy corals while simultaneously reducing bed shear stress by nearly an order of magnitude. Reduced bed shear at the coral surface and within-canopy turbulent stresses imply reduced mass transfer of necessary metabolites (e.g., oxygen, nutrients), leading to negative impacts on coral health.

  9. Non-steady dynamics of atmospheric turbulence interaction with wind turbine loadings through blade-boundary-layer-resolved CFD

    NASA Astrophysics Data System (ADS)

    Vijayakumar, Ganesh

    Modern commercial megawatt-scale wind turbines occupy the lower 15-20% of the atmospheric boundary layer (ABL), the atmospheric surface layer (ASL). The current trend of increasing wind turbine diameter and hub height increases the interaction of the wind turbines with the upper ASL which contains spatio-temporal velocity variations over a wide range of length and time scales. Our interest is the interaction of the wind turbine with the energetic integral-scale eddies, since these cause the largest temporal variations in blade loadings. The rotation of a wind turbine blade through the ABL causes fluctuations in the local velocity magnitude and angle of attack at different sections along the blade. The blade boundary layer responds to these fluctuations and in turn causes temporal transients in local sectional loads and integrated blade and shaft bending moments. While the integral scales of the atmospheric boundary layer are ˜ O(10--100m) in the horizontal with advection time scales of order tens of seconds, the viscous surface layer of the blade boundary layer is ˜ O(10 -- 100 mum) with time scales of order milliseconds. Thus, the response of wind turbine blade loadings to atmospheric turbulence is the result of the interaction between two turbulence dynamical systems at extremely disparate ranges of length and time scales. A deeper understanding of this interaction can impact future approaches to improve the reliability of wind turbines in wind farms, and can underlie future improvements. My thesis centers on the development of a computational framework to simulate the interaction between the atmospheric and wind turbine blade turbulence dynamical systems using a two step one-way coupled approach. Pseudo-spectral large eddy simulation (LES) is used to generate a true (equilibrium) atmospheric boundary layer over a flat land with specified surface roughness and heating consistent with the stability state of the daytime lower troposphere. Using the data from the

  10. First-order control of surface roughness at three scales: boundary layer dynamics, tracer dispersion and pebble abrasion

    NASA Astrophysics Data System (ADS)

    Jerolmack, D. J.; Litwin, K. L.; Phillips, C. B.; Martin, R. L.

    2012-12-01

    In many situations it may be appropriate to treat surfaces as smooth and particles as spherical, however here we focus on scenarios in which the roughness of the surface exerts a first-order control on flow and transport dynamics. We describe three vignettes at three different scales: (1) roughness transitions and resulting sediment transport dynamics over ~10-km distance in a desert dune field; (2) reach-scale river bed roughness and its influence on dispersion of tracer particles in bed load; and (3) the control of particle surface roughness on the nature and rate of pebble abrasion. For (1), we show how the abrupt transition from a flat surface to a dune field may be treated as a step increase in the aerodynamic roughness parameter - so long as the spatial scale considered is significantly larger than that of an individual dune. This increase causes a spatial decline in the boundary stress downwind that may be understood using simple boundary layer theory, resulting in a factor of three decrease in the sand flux over a distance of kilometers. For (2), laboratory and field studies of tracer particles in bed load indicate that they undergo short flights separated by long rest periods having a power-law tail - even in steady flows. We hypothesize that for near-threshold transport - which predominates is coarse-grained rivers - particles become trapped in 'wells' produced by surface roughness, and their rest time is controlled by the time for the surface to scour down and release them. Laboratory observations support this hypothesis, while comparison to non-geophysical 'flows' indicates that these dynamics are generic to transport in disordered systems. Finally, for (3) we report laboratory experiments by our group and others showing how abrasion rate decreases with decreasing particle roughness. Geometric models quantitatively support the intuition that locations of high positive curvature on pebble surfaces are more susceptible to abrasion; as they are

  11. Crustal dynamics project: The interpretation of crustal dynamics data in terms of plate motions and regional deformation near plate boundaries

    NASA Technical Reports Server (NTRS)

    Solomon, Sean C.

    1990-01-01

    The focus of the research was in two broad areas: (1) the nature and dynamics of time-dependent deformation and stress along major seismic zones, and (2) the nature of long-wavelength oceanic geoid anomalies in terms of lateral variations in upper mantle temperature and composition. The principal findings are described in the appendices.

  12. Defining the boundaries of bedside pulse contour analysis: dynamic arterial elastance.

    PubMed

    Pinsky, Michael R

    2011-01-01

    Assessment of vasomotor tone is essential in defining appropriate resuscitation strategies for the hypotensive patient. Although changes in mean arterial pressure to cardiac output define arterial resistance, resistance is only one component of vasomotor tone. Compliance is the other component. The reciprocal of compliance is arterial elastance (Ea). Importantly, dynamic Ea can be estimated by the pulse pressure variation to stroke volume variation relation. Dynamic Ea is only one component of vasomotor tone, however, and increases in pulse pressure may not be proportional to increases in mean arterial pressure. Also, devices that use the arterial pressure pulse to calculate the stroke volume have an inherent bias that is different amongst devices based on their transfer function algorithms. The use of dynamic Ea for clinical decision-making thus needs to be validated separately for different devices and types of patients. PMID:21345250

  13. Note: Local thermal conductivities from boundary driven non-equilibrium molecular dynamics simulations

    SciTech Connect

    Bresme, F.; Armstrong, J.

    2014-01-07

    We report non-equilibrium molecular dynamics simulations of heat transport in models of molecular fluids. We show that the “local” thermal conductivities obtained from non-equilibrium molecular dynamics simulations agree within numerical accuracy with equilibrium Green-Kubo computations. Our results support the local equilibrium hypothesis for transport properties. We show how to use the local dependence of the thermal gradients to quantify the thermal conductivity of molecular fluids for a wide range of thermodynamic states using a single simulation.

  14. Fluid-dynamic computations on a connection machine - Preliminary timings and complex boundary conditions

    NASA Astrophysics Data System (ADS)

    Oran, Elaine S.; Boris, Jay P.; Brown, Eugene F.

    1990-01-01

    This paper describes the conversion and application of the explicit, time-dependent, fourth-order, phase-accurate, variable-grid flux-corrected transport module, LCPFCT, to the Connection Machine, a fine-grained SIMD parallel processor. Models developed are as similar to the production Cray codes as possible and include a variety of different realistic boundary conditions. Timing comparisons show that a 16K-processor Connection Machine allows computations at speeds up to a factor of seven faster than obtained on a Cray YMP for a functionally equivalent optimized, three-dimensional code. Test calculations of a two-dimensional exploding shock and a three-dimensional helically perturbed jet are described and discussed briefly.

  15. Boundary layer dynamics in a small shallow valley near the Alps (ScaleX campaign)

    NASA Astrophysics Data System (ADS)

    Zeeman, Matthias; Adler, Bianca; Banerjee, Tirtha; Brugger, Peter; De Roo, Frederik; Emeis, Stefan; Matthias, Mauder; Schäfer, Klaus; Wolf, Benjamin; Schmid, Hans Peter

    2016-04-01

    Mountainous terrain presents a challenge for the experimental determination of exchange processes. The Alps modulate synoptic flow and introduce circulation systems that reach into the forelands. In addition, the Prealpine landscape is heterogeneous itself, dominated by patches of forestry on the slopes and agriculture on flat areas. That combined complexity is manifest in atmospheric circulations at multiple scales. We investigated the diurnal evolution of the atmospheric boundary layer with focus on the connection between surface exchange processes and atmospheric circulations at the regional to local scale. The experiment is part of an ongoing, multi-disciplinary study on scale dependencies in the distribution of energy and matter (ScaleX) at the TERENO Prealpine observatory in Germany. We observed vertical profiles of wind speed and air temperature up to 1000 m above ground during June and July 2015 in a small shallow Prealpine valley in Bavaria, Germany. Wind vectors and temperature were observed using ground-based optical, acoustic and radiometric remote sensing techniques. Spatial patterns in wind speed and direction were determined using eddy covariance systems, 3D Doppler LIDAR and acoustic sounding (RASS). Three Doppler LIDAR units were configured to form a virtual tower at the beam intersect. Temperature profiles were observed using radio-acoustic sounding (RASS) and a microwave radiometer (HATPRO). The temporal and spatial resolutions of the resulting vertical profiles were between 1-15 min and between 3-100 m, respectively. The observed variability in wind vectors and stability shows evidence of the link between flow phenomena at micro- to mesoscale and local biosphere-atmosphere exchange processes. We present first results and discuss the predictability of the impact of local and regional (alpine) landscape features on flow and structures in the atmospheric boundary layer.

  16. Boundary layer dynamics in a small shallow valley near the Alps (ScaleX campaign)

    NASA Astrophysics Data System (ADS)

    Mauder, M.; Zeeman, M. J.; Adler, B.; Banerjee, T.; Brugger, P.; De Roo, F.; Emeis, S.; Schäfer, K.; Schmid, H. P. E.; Wolf, B.

    2015-12-01

    Mountainous terrain presents a challenge for the experimental determination of exchange processes. The Alps modulate synoptic flow and introduce circulation systems that reach into the forelands. In addition, the Prealpine landscape is heterogeneous itself, dominated by patches of forestry on the slopes and agriculture on flat areas. That combined complexity is manifest in atmospheric circulations at multiple scales. We investigated the diurnal evolution of the atmospheric boundary layer with focus on the connection between surface exchange processes and atmospheric circulations at the regional to local scale. The experiment is part of an ongoing, multi-disciplinary study on scale dependencies in the distribution of energy and matter (ScaleX) at the TERENO Prealpine observatory in Germany. We observed vertical profiles of wind speed and air temperature up to 1000 m above ground during June and July 2015 in a small shallow Prealpine valley in Bavaria, Germany. Wind vectors and temperature were observed using ground-based optical, acoustic and radiometric remote sensing techniques. Spatial patterns in wind speed and direction were determined using eddy covariance systems, 3D Doppler LIDAR and acoustic sounding (RASS). Three Doppler LIDAR units were configured to form a virtual tower at the beam intersect. Temperature profiles were observed using radio-acoustic sounding (RASS) and a microwave radiometer (HATPRO). The temporal and spatial resolutions of the resulting vertical profiles were between 1-15 min and between 3-100 m, respectively. The observed variability in wind vectors and stability shows evidence of the link between flow phenomena at micro- to mesoscale and local biosphere-atmosphere exchange processes. We present first results and discuss the predictability of the impact of local and regional (alpine) landscape features on flow and structures in the atmospheric boundary layer.

  17. Dynamical Model Simulation of the Morning Boundary Layer Development in Deep Mountain Valleys.

    NASA Astrophysics Data System (ADS)

    Bader, David C.; McKee, Thomas B.

    1983-03-01

    A dry, two-dimensional version of the Colorado State University Multi-dimensional Cloud/Mesoscale Model was used to study the cross-valley evolution of the wind and temperature structures in an idealized east-west oriented mountain valley. Two simulations were performed, one in which the valley was heated symmetrically and a second in which a mid-latitude heating distribution was imposed. Both runs were initiated identically with a stable layer filling the valley to ridgetop and a neutral layer above the ridge. A specified sinusoidal surface potential temperature flux function approximating the diurnal cycle forced the model at the lower boundary.The results of the two simulations were remarkably similar. The model realistically reproduced the gross features found in actual valleys in both structure and timing. The simulated inversions were destroyed three and one-half hours after sunrise as a result of a neutral layer growing up from the surface meeting a descending inversion top. Slope winds with speeds of 3-5 m s1 developed over both sidewalls two and one-half hours after sunrise. Both cases revealed the development of strongly stable pockets of air over the sidewalls which form when cold air advected upslope loses its buoyancy at higher elevations. These stable pockets temporarily block the slope flow and force transient cross-valley circulations to form which act to destabilize the valley boundary layer. Cross-valley mixing and gravity waves rapidly redistribute heat across the valley to prevent large potential temperature gradients from forming. As a result, oven large differences in heating rates between opposing sidewalls do not result in significant cross-valley potential temperature differences. Organized cross-valley circulations and eddy motions enhance lateral mixing in the stable layer as well.

  18. Diffusion behavior of helium in titanium and the effect of grain boundaries revealed by molecular dynamics simulation

    NASA Astrophysics Data System (ADS)

    Gui-Jun, Cheng; Bao-Qin, Fu; Qing, Hou; Xiao-Song, Zhou; Jun, Wang

    2016-07-01

    The microstructures of titanium (Ti), an attractive tritium (T) storage material, will affect the evolution process of the retained helium (He). Understanding the diffusion behavior of He at the atomic scale is crucial for the mechanism of material degradation. The novel diffusion behavior of He has been reported by molecular dynamics (MD) simulation for the bulk hcp-Ti system and the system with grain boundary (GB). It is observed that the diffusion of He in the bulk hcp-Ti is significantly anisotropic (the diffusion coefficient of the [0001] direction is higher than that of the basal plane), as represented by the different migration energies. Different from convention, the GB accelerates the diffusion of He in one direction but not in the other. It is observed that a twin boundary (TB) can serve as an effective trapped region for He. The TB accelerates diffusion of He in the direction perpendicular to the twinning direction (TD), while it decelerates the diffusion in the TD. This finding is attributable to the change of diffusion path caused by the distortion of the local favorable site for He and the change of its number in the TB region. Project supported by the National Natural Science Foundation of China (Grant No. 51501119), the Scientific Research Starting Foundation for Younger Teachers of Sichuan University, China (Grant No. 2015SCU11058), the National Magnetic Confinement Fusion Science Program of China (Grant No. 2013GB109002), and the Cooperative Research Project “Research of Diffusion Behaviour of He in Grain Boundary of HCP-Titanium”, China.

  19. A molecular dynamics study of tilt grain boundary resistance to slip and heat transfer in nanocrystalline silicon

    SciTech Connect

    Chen, Xiang; Chen, Youping; Xiong, Liming; Chernatynskiy, Aleksandr

    2014-12-28

    We present a molecular dynamics study of grain boundary (GB) resistance to dislocation-mediated slip transfer and phonon-mediated heat transfer in nanocrystalline silicon bicrystal. Three most stable 〈110〉 tilt GBs in silicon are investigated. Under mechanical loading, the nucleation and growth of hexagonal-shaped shuffle dislocation loops are reproduced. The resistances of different GBs to slip transfer are quantified through their constitutive responses. Results show that the Σ3 coherent twin boundary (CTB) in silicon exhibits significantly higher resistance to dislocation motion than the Σ9 GB in glide symmetry and the Σ19 GB in mirror symmetry. The distinct GB strengths are explained by the atomistic details of the dislocation-GB interaction. Under thermal loading, based on a thermostat-induced heat pulse model, the resistances of the GBs to transient heat conduction in ballistic-diffusive regime are characterized. In contrast to the trend found in the dislocation-GB interaction in bicrystal models with different GBs, the resistances of the same three GBs to heat transfer are strikingly different. The strongest dislocation barrier Σ3 CTB is almost transparent to heat conduction, while the dislocation-permeable Σ9 and Σ19 GBs exhibit larger resistance to heat transfer. In addition, simulation results suggest that the GB thermal resistance not only depends on the GB energy but also on the detailed atomic structure along the GBs.

  20. Conformational and adsorptive characteristics of albumin affect interfacial protein boundary lubrication: from experimental to molecular dynamics simulation approaches.

    PubMed

    Fang, Hsu-Wei; Hsieh, Man-Ching; Huang, Huei-Ting; Tsai, Cheng-Yen; Chang, Min-Hui

    2009-02-01

    The lifetime of artificial joints is mainly determined by their biotribological properties. Synovial fluid which consists of various biological molecules acts as the lubricant. Among the compositions of synovial fluid, albumin is the most abundant protein. Under high load and low sliding speed articulation of artificial joint, it is believed the lubricants form protective layers on the sliding surfaces under the boundary lubrication mechanism. The protective molecular layer keeps two surfaces from direct collision and thus decreases the possibility of wear damage. However, the lubricating ability of the molecular layer may vary due to the conformational change of albumin in the process. In this study, we investigated the influence of albumin conformation on the adsorption behaviors on the articulating surfaces and discuss the relationship between adsorbed albumin and its tribological behaviors. We performed the friction tests to study the effects of albumin unfolding on the frictional behaviors. The novelty of this research is to further carry out molecular dynamics simulation, and protein adsorption experiments to investigate the mechanisms of the albumin-mediated boundary lubrication of arthroplastic materials. It was observed that the thermal processes induce the loss of secondary structure of albumin. The compactness of the unfolded structure leads to a higher adsorption rate onto the articulating material surface and results in the increase of friction coefficient.

  1. Computational fluid dynamics analysis of cyclist aerodynamics: performance of different turbulence-modelling and boundary-layer modelling approaches.

    PubMed

    Defraeye, Thijs; Blocken, Bert; Koninckx, Erwin; Hespel, Peter; Carmeliet, Jan

    2010-08-26

    This study aims at assessing the accuracy of computational fluid dynamics (CFD) for applications in sports aerodynamics, for example for drag predictions of swimmers, cyclists or skiers, by evaluating the applied numerical modelling techniques by means of detailed validation experiments. In this study, a wind-tunnel experiment on a scale model of a cyclist (scale 1:2) is presented. Apart from three-component forces and moments, also high-resolution surface pressure measurements on the scale model's surface, i.e. at 115 locations, are performed to provide detailed information on the flow field. These data are used to compare the performance of different turbulence-modelling techniques, such as steady Reynolds-averaged Navier-Stokes (RANS), with several k-epsilon and k-omega turbulence models, and unsteady large-eddy simulation (LES), and also boundary-layer modelling techniques, namely wall functions and low-Reynolds number modelling (LRNM). The commercial CFD code Fluent 6.3 is used for the simulations. The RANS shear-stress transport (SST) k-omega model shows the best overall performance, followed by the more computationally expensive LES. Furthermore, LRNM is clearly preferred over wall functions to model the boundary layer. This study showed that there are more accurate alternatives for evaluating flow around bluff bodies with CFD than the standard k-epsilon model combined with wall functions, which is often used in CFD studies in sports.

  2. Asymptotic Dynamics of Self-driven Vehicles in a Closed Boundary

    NASA Astrophysics Data System (ADS)

    Lee, Chi-Lun; Huang, Chia-Ling

    2011-08-01

    We study the asymptotic dynamics of self-driven vehicles in a loop using a car-following model with the consideration of volume exclusions. In particular, we derive the dynamical steady states for the single-cluster case and obtain the corresponding fundamental diagrams, exhibiting two branches representative of entering and leaving the jam, respectively. By simulations we find that the speed average over all vehicles eventually reaches the same value, regardless of final clustering states. The autocorrelation functions for overall speed average and single-vehicle speed are studied, each revealing a unique time scale. We also discuss the role of noises in vehicular accelerations. Based on our observations we give trial definitions about the degree of chaoticity for general self-driven many-body systems.

  3. Patents on periphery of the Amazon rainforest.

    PubMed

    de Moura, Emanoel G; Araújo, José R G; Monroe, Paulo H M; de O Nascimento, Ivaneide; Aguiar, Alana C F

    2009-06-01

    In the humid tropics, on the edges of the Amazon forest, the technological challenges to establishing and maintaining productive and sustainable agricultural systems have yet to be overcome. The groups involved in agriculture in the north of Brazil still engage in the practice of slash and burn in order to prepare and fertilize the soil. This produces negative effects for the local and global environment, without the counter-effect of providing social benefits to rural communities. Whether this process continues is of fundamental importance to many countries because it means that slash and burn agriculture is advancing on the Amazon rainforest, with a negative effect on every dimension of national policy. Beyond social political problems the biggest challenge for researchers in the field of tropical agriculture is to offer technological alternatives that can sustain agriculture in soils derived from sedimentary rocks that have been subjected to a high degree of weathering. In this article patented information is also discussed. Experiments undertaken in this region recommend taking advantage of the rapid growth of plants in the tropics. We aimed at proposing a suitable alternative system for a sustainable soil management in the particular conditions of humid tropics, named as "no-till in alley cropping using tree leguminous mulch." This system offers the advantages of: bringing together, in the same space and at the same time, the processes of cultivation and the regeneration of soil fertility. PMID:20653534

  4. Patents on periphery of the Amazon rainforest.

    PubMed

    de Moura, Emanoel G; Araújo, José R G; Monroe, Paulo H M; de O Nascimento, Ivaneide; Aguiar, Alana C F

    2009-06-01

    In the humid tropics, on the edges of the Amazon forest, the technological challenges to establishing and maintaining productive and sustainable agricultural systems have yet to be overcome. The groups involved in agriculture in the north of Brazil still engage in the practice of slash and burn in order to prepare and fertilize the soil. This produces negative effects for the local and global environment, without the counter-effect of providing social benefits to rural communities. Whether this process continues is of fundamental importance to many countries because it means that slash and burn agriculture is advancing on the Amazon rainforest, with a negative effect on every dimension of national policy. Beyond social political problems the biggest challenge for researchers in the field of tropical agriculture is to offer technological alternatives that can sustain agriculture in soils derived from sedimentary rocks that have been subjected to a high degree of weathering. In this article patented information is also discussed. Experiments undertaken in this region recommend taking advantage of the rapid growth of plants in the tropics. We aimed at proposing a suitable alternative system for a sustainable soil management in the particular conditions of humid tropics, named as "no-till in alley cropping using tree leguminous mulch." This system offers the advantages of: bringing together, in the same space and at the same time, the processes of cultivation and the regeneration of soil fertility.

  5. The dynamics and energetics of midlatitude western boundary currents: A comparison of the Kuroshio Extension and the Gulf Stream

    NASA Technical Reports Server (NTRS)

    Mitchell, James L.; Hallock, Z. R.; Hurlburt, H. E.; Johnson, D. R.; Kindle, J. C.; Teague, W. J.; Thompson, J. D.; Schmitz, W. J.

    1991-01-01

    We will use TOPEX/POSEIDON altimetry in combination with ongoing and planned efforts, including data from the European Remote Sensing satellite (ERS-1), in situ measurements designed specifically to complement satellite altimetry, and assimilation of these several data types into eddy-resolving numerical models in order to understand the dynamics and energetics of midlatitude western boundary currents (specifically, the Gulf Stream and the Kuroshio Extension). A better understanding of the recirculation of midlatitude gyres can best be undertaken in the format of such regional, eddy-resolving experiments. Such regional programs will enhance and be enhanced by the larger scale circulation studies of the World Ocean Circulation Experiment (WOCE) as well as by global-scale eddy-resolving models that we will develop prior to the TOPEX/POSEIDON mission. This effort includes participation on the TOPEDX/POSEIDON Science Team.

  6. Boundary conditions in the vicinity of a dynamic contact line: experimental investigation of viscous drops sliding down an inclined plane.

    PubMed

    Rio, E; Daerr, A; Andreotti, B; Limat, L

    2005-01-21

    To probe the microscopic balance of forces close to a moving contact line, the boundary conditions around viscous drops sliding down an inclined plane are investigated. At first, the variation of the contact angle as a function of the scale of analysis is discussed. The dynamic contact angle is measured at a scale of 6 mum all around sliding drops for different volumes and speeds. We show that it depends only on the capillary number based on the local liquid velocity, measured by particle tracking. This velocity turns out to be normal to the contact line everywhere. It indirectly proves that, in comparison with the divergence involved in the normal direction, the viscous stress is not balanced by intermolecular forces in the direction tangential to the contact line, so that any motion in this last direction gets damped.

  7. [Dynamics of colonies of the speckled ground squirrel (Spermophilus suslicus Guld., 1770) on the northern boundary of the habitat].

    PubMed

    Shilova, S A; Neronov, V V; Shekarova, O N; Savinetskaia, L E

    2010-01-01

    Results of studies in 1999-2009 of the dynamics of five isolated colonies of the speckled ground squirrel (Spermophilus suslicus) at the northern boundary of the habitat of this species (Zaraiskii area, Moscow oblast) are given. An abrupt decrease in the number of this species in colonies was established, as was a multifold decrease (up to 70-90%) in suitable habitats due to the plowing of meadows and build-up of the area. The fragmentation of the optimum habitat of ground squirrels reached a stage where colonies can no longer exist as a stable autonomous system. The process of their extinction unfolds quickly: the number of animals in some colonies decreased five-six times over the last ten years. To preserve this species, it is necessary to create areas of steppefied meadows with regulated agricultural use.

  8. Sharpening our Understanding but Blurring the Boundaries: Dynamic Observations of Surface Reconstruction

    SciTech Connect

    Baer, Donald R.

    2003-08-20

    Every now and then, reading a specific paper stimulates--in my mind at least--a variety of associations and connections that highlight advances that have been made and suggests links between areas that I may not have previously connected. The recent series of papers by McCarty and Bartelt (and co-workers) using low energy electron microscopy (LEEM) to study the dynamics of surface reconstruction of TiO2 , and NiAl sent my thinking in a variety loosely connected directions. Paraphrasing the response of one of my colleagues - the work causes us to think dynamically where we have often thought statically about what happens when surfaces reconstruct. The measurements also highlight the importance of newer techniques to help us visualize and understand phenomena that may have puzzled us for years. The dynamic interactions between surface structure and both the defect structure (and history) of the substrate and the nature of the environment of the specimen highlight an aspect of phenomena that drive surface reconstruction not normally considered and suggests additional and delightful challenges we face in understanding the bulk stability and surface structures of nano-sized objects. Since the physical arrangement of the atoms controls every aspect of the physics and chemistry of a surface or interface, the atomic geometry is a fundamental defining characteristic of a surface. , Details of the structure of a surface, including altered atomic positions, the presence of steps and various types of defects can significantly change the chemistry of a surface and impact processes ranging from the formation of interfaces in electronic components to the efficiency of a catalyst. Because of its importance there has been considerable effort devoted to understanding and predicting surface structures. However, dynamical aspects of surface reconstruction and the significance of material defects in the process have not been part of the standard picture.

  9. A railway track dynamics model based on modal substructuring and a cyclic boundary condition

    NASA Astrophysics Data System (ADS)

    Baeza, Luis; Ouyang, Huajiang

    2011-01-01

    This article presents a technique for modelling the coupled dynamics of a railway vehicle and the track. The method is especially useful for simulating the dynamics of high speed trains running on nonlinear tracks. The main hypothesis is a cyclic system: an infinite track on which there is an infinite set of identical vehicles spaced at a regular interval of distance. Thus the main problems of the finite-length track models (e.g. the waves that reflect at the end of the track and interact with the vehicle; and the time interval of integration must be shorter than the track length divided by the velocity) are avoided. The flexibility of the method can be observed from the case studies presented in the present work: a vehicle passing over a hanging sleeper, and the vehicle-track dynamics for different ballast compaction cases. The results show the influence of the hanging sleeper gap on the wheel-rail contact forces, and the bending moment at the sleeper for different ballast compaction cases.

  10. Thermal adaptation generates a diversity of thermal limits in a rainforest ant community.

    PubMed

    Kaspari, Michael; Clay, Natalie A; Lucas, Jane; Yanoviak, Stephen P; Kay, Adam

    2015-03-01

    The Thermal Adaptation Hypothesis posits that the warmer, aseasonal tropics generates populations with higher and narrower thermal limits. It has largely been tested among populations across latitudes. However, considerable thermal heterogeneity exists within ecosystems: across 31 trees in a Panama rainforest, surfaces exposed to sun were 8 °C warmer and varied more in temperature than surfaces in the litter below. Tiny ectotherms are confined to surfaces and are variously submerged in these superheated boundary layer environments. We quantified the surface CTmin and CTmax s (surface temperatures at which individuals grew torpid and lost motor control, respectively) of 88 ant species from this forest; they ranged in average mass from 0.01 to 57 mg. Larger ants had broader thermal tolerances. Then, for 26 of these species we again tested body CTmax s using a thermal dry bath to eliminate boundary layer effects: body size correlations observed previously disappeared. In both experiments, consistent with Thermal Adaptation, CTmax s of canopy ants averaged 3.5-5 °C higher than populations that nested in the shade of the understory. We impaled thermocouples in taxidermy mounts to further quantify the factors shaping operative temperatures for four ant species representing the top third (1-30 mg) of the size distribution. Extrapolations suggest the smallest 2/3rds of species reach thermal equilibrium in <10s. Moreover, the large ants that walk above the convective superheated surface air also showed more net heating by solar radiation, with operative temperatures up to 4 °C higher than surrounding air. The thermal environments of this Panama rainforest generate a range of CTmax subsuming 74% of those previously recorded for ant populations worldwide. The Thermal Adaptation Hypothesis can be a powerful tool in predicting diversity of thermal limits within communities. Boundary layer temperatures are likely key to predicting the future of Earth's tiny terrestrial

  11. Linking mantle dynamics, plate tectonics and surface processes in the active plate boundary zones of eastern New Guinea (Invited)

    NASA Astrophysics Data System (ADS)

    Baldwin, S.; Moucha, R.; Fitzgerald, P. G.; Hoke, G. D.; Bermudez, M. A.; Webb, L. E.; Braun, J.; Rowley, D. B.; Insel, N.; Abers, G. A.; Wallace, L. M.; Vervoort, J. D.

    2013-12-01

    Eastern New Guinea lies within the rapidly obliquely converging Australian (AUS)- Pacific (PAC) plate boundary zone and is characterized by transient plate boundaries, rapidly rotating microplates and a globally significant geoid high. As the AUS plate moved northward in the Cenozoic, its leading edge has been a zone of subduction and arc accretion. The variety of tectonic settings in this region permits assessment of the complex interplay among mantle dynamics, plate tectonics, and surface processes. Importantly, the timescale of tectonic events (e.g., subduction, (U)HP exhumation, seafloor spreading) are within the valid bounds of mantle convection models. A record of changes in bathymetry and topography are preserved in high standing mountain belts, exhumed extensional gneiss domes and core complexes, uplifted coral terraces, and marine sedimentary basins. Global seismic tomography models indicate accumulation of subducted slabs beneath eastern New Guinea at the bottom of the upper mantle (i.e., <660km depth). Some of the deeply subducted material may indeed be buoyant subducted AUS continental margin (to depths of ~250-300 km), as well as subducted continental material that has reached the point of no return (i.e., > 250-300 km). Preliminary global-scale backward advected mantle convection models, driven by density inferred from joint seismic-geodynamic tomography models, exhibit large-scale flow associated with these subducted slab remnants and predict the timing and magnitude (up to 1500 m) of dynamic topography change (both subsidence and uplift) since the Oligocene. In this talk we will explore the effects of large-scale background mantle flow and plate tectonics on the evolution of topography and bathymetry in eastern New Guinea, and discuss possible mechanisms to explain basin subsidence and surface uplift in the region.

  12. Green Leaf Volatile Emissions during High Temperature and Drought Stress in a Central Amazon Rainforest

    PubMed Central

    Jardine, Kolby J.; Chambers, Jeffrey Q.; Holm, Jennifer; Jardine, Angela B.; Fontes, Clarissa G.; Zorzanelli, Raquel F.; Meyers, Kimberly T.; de Souza, Vinicius Fernadez; Garcia, Sabrina; Gimenez, Bruno O.; de O. Piva, Luani R.; Higuchi, Niro; Artaxo, Paulo; Martin, Scot; Manzi, Antônio O.

    2015-01-01

    Prolonged drought stress combined with high leaf temperatures can induce programmed leaf senescence involving lipid peroxidation, and the loss of net carbon assimilation during early stages of tree mortality. Periodic droughts are known to induce widespread tree mortality in the Amazon rainforest, but little is known about the role of lipid peroxidation during drought-induced leaf senescence. In this study, we present observations of green leaf volatile (GLV) emissions during membrane peroxidation processes associated with the combined effects of high leaf temperatures and drought-induced leaf senescence from individual detached leaves and a rainforest ecosystem in the central Amazon. Temperature-dependent leaf emissions of volatile terpenoids were observed during the morning, and together with transpiration and net photosynthesis, showed a post-midday depression. This post-midday depression was associated with a stimulation of C5 and C6 GLV emissions, which continued to increase throughout the late afternoon in a temperature-independent fashion. During the 2010 drought in the Amazon Basin, which resulted in widespread tree mortality, green leaf volatile emissions (C6 GLVs) were observed to build up within the forest canopy atmosphere, likely associated with high leaf temperatures and enhanced drought-induced leaf senescence processes. The results suggest that observations of GLVs in the tropical boundary layer could be used as a chemical sensor of reduced ecosystem productivity associated with drought stress. PMID:27135346

  13. Green Leaf Volatile Emissions during High Temperature and Drought Stress in a Central Amazon Rainforest.

    PubMed

    Jardine, Kolby J; Chambers, Jeffrey Q; Holm, Jennifer; Jardine, Angela B; Fontes, Clarissa G; Zorzanelli, Raquel F; Meyers, Kimberly T; de Souza, Vinicius Fernadez; Garcia, Sabrina; Gimenez, Bruno O; Piva, Luani R de O; Higuchi, Niro; Artaxo, Paulo; Martin, Scot; Manzi, Antônio O

    2015-09-15

    Prolonged drought stress combined with high leaf temperatures can induce programmed leaf senescence involving lipid peroxidation, and the loss of net carbon assimilation during early stages of tree mortality. Periodic droughts are known to induce widespread tree mortality in the Amazon rainforest, but little is known about the role of lipid peroxidation during drought-induced leaf senescence. In this study, we present observations of green leaf volatile (GLV) emissions during membrane peroxidation processes associated with the combined effects of high leaf temperatures and drought-induced leaf senescence from individual detached leaves and a rainforest ecosystem in the central Amazon. Temperature-dependent leaf emissions of volatile terpenoids were observed during the morning, and together with transpiration and net photosynthesis, showed a post-midday depression. This post-midday depression was associated with a stimulation of C₅ and C₆ GLV emissions, which continued to increase throughout the late afternoon in a temperature-independent fashion. During the 2010 drought in the Amazon Basin, which resulted in widespread tree mortality, green leaf volatile emissions (C₆ GLVs) were observed to build up within the forest canopy atmosphere, likely associated with high leaf temperatures and enhanced drought-induced leaf senescence processes. The results suggest that observations of GLVs in the tropical boundary layer could be used as a chemical sensor of reduced ecosystem productivity associated with drought stress.

  14. Direct numerical simulation of bedload transport using a local, dynamic boundary condition

    USGS Publications Warehouse

    Schmeeckle, M.W.; Nelson, J.M.

    2003-01-01

    Temporally and spatially averaged models of bedload transport are inadequate to describe the highly variable nature of particle motion at low transport stages. The primary sources of this variability are the resisting forces to downstream motion resulting from the geometrical relation (pocket friction angle) of a bed grain to the grains that it rests upon, variability of the near-bed turbulent velocity field and the local modification of this velocity field by upstream, protruding grains. A model of bedload transport is presented that captures these sources of variability by directly integrating the equations of motion of each particle of a simulated mixed grain-size sediment bed. Experimental data from the velocity field downstream and below the tops of upstream, protruding grains are presented. From these data, an empirical relation for the velocity modification resulting from upstream grains is provided to the bedload model. The temporal variability of near-bed turbulence is provided by a measured near-bed time series of velocity over a gravel bed. The distribution of pocket friction angles results as a consequence of directly calculating the initiation and cessation of motion of each particle as a result of the combination of fluid forcing and interaction with other particles. Calculations of bedload flux in a uniform boundary and simulated pocket friction angles agree favourably with previous studies.

  15. Vortex dynamics of a fluid near a boundary with a circular cavity

    NASA Astrophysics Data System (ADS)

    Ryzhov, E. A.; Izrailsky, Yu. G.; Koshel, K. V.

    2014-07-01

    The motion of a point vortex along a rectilinear boundary with a circle cavity, which models the coastline of a bay, and associated fluid particle advection are studied within a model of barotropic inviscid fluid. Using an analytical expression for the complex potential through which the velocity field is determined, we show that fluid particles start moving irregularly when the vortex is passing the cavity due to the nonstationarity of the velocity field generated by the vortex. Some of the fluid particles which were initially inside the vortex atmosphere leave it due to the irregularity and remain within the cavity vicinity. Depending on the initial position of the vortex and a parameter that determines the cavity size, the fraction of these fluid particles can differ significantly from fluid particles initially uniformly distributed within the vortex atmosphere. The escape of fluid particles from the vortex atmosphere is shown to be most efficient in the case of a relatively closed cavity under the condition that the initial vortex atmosphere area should be significantly smaller than the cavity area.

  16. Aerosol dynamics in the equatorial Pacific Marine boundary layer: Microphysics, diurnal cycles and entertainment

    SciTech Connect

    Clarke, A D; Litchy, M; Li, Z

    1996-04-01

    During July-August of 1994 the authors measured the size resolved physiochemical properties of aerosol particles at Christmas Island in the equatorial Pacific. In spite of rapid diurnal conversion of dimethylsulfide (DMS) to sulfur dioxide (SO{sub 2}) the authors found no evidence for new particle production in the marine boundary layer (MBL) and more than 95% of all particles were consistently larger than 0.02{mu}m diameter, indicating an aged aerosol number (size-distribution) was bimodal with peaks near 0.05{mu}m and 0.2{mu}m particle diameter (D{sub p}) and had a cloud-processed intermode minimum at about 0.09{mu}m that varied in phase with diurnal changes in ozone concentration. This suggests that the number distribution for condensation nuclei (CN) and cloud condensation (CCN) was maintained by a quasiequilibrium between entrainment (estimated to be 0.6{+-}0.2 cm s{sup {minus}1}) from sources aloft and processes in the MBL. This implies a replenishment timescale for nuclei of about 2 and 4 days for this region. The stability of the distribution and the 0.09{mu}m cloud processed minima suggests trade winds cumulus supersaturations near 0.35% and updrafts near 1 m s{sup {minus}1}. 17 refs., 4 fig., 1 tab.

  17. The dynamic coupling of a third-generation wave model and a 3D hydrodynamic model through boundary layers

    NASA Astrophysics Data System (ADS)

    Zhang, M. Y.; Li, Y. S.

    1997-08-01

    A third-generation wind wave model based on the energy balance equation taking into account the effects of time-varying currents and coupled dynamically with a semi-implicit three-dimensional hydrodynamic model incorporating the influences of time- and space-varying vertical eddy viscosity, bottom topography and wave-current interactions is presented in this paper. The wave model is synchronously coupled with the three-dimensional hydrodynamic model through the surface atmospheric turbulent boundary layer and the bottom boundary layer. The theory of Janssen (1991) (in Journal of Physical Oceanography21, 1631-1642) is used to incorporate the effects of waves on the surface boundary layer, while the theory of Grant and Maddsen (1979) [in Journal of Geophysical Research (Oceans)84, 1797-1808], which was used by Signell et al. (1990) (in Journal of Geophysical Research95, 9671-9678) on the bottom boundary layer for constant waves, is modified for the inclusion of time-varying waves. The mutual influences between waves and currents are investigated through an idealized continental shelf case and hindcastings of storm events in the sea area adjacent to Hong Kong in the northern South China Sea. Calculations are compared with other computed results and observations. Calculations show that the wave-dependent surface stress incorporated in the three-dimensional hydrodynamic model has significant impact on water surface velocities and surface elevations (over 10% higher). The inclusion of wave-dependent bottom stress also shows some effects; however, in the presence of the wave-dependent surface stress, its effect on surge levels becomes negligible. The effect of currents on waves amounts to the reduction of the significant wave height by about 8% and less for wave mean periods. However, the inclusion of the wave-dependent bottom stress in the three-dimensional hydrodynamic model has little effect on wave characteristics whether or not the wave-dependent surface stress is

  18. Carbon allocation in a Bornean tropical rainforest without dry seasons.

    PubMed

    Katayama, Ayumi; Kume, Tomonori; Komatsu, Hikaru; Saitoh, Taku M; Ohashi, Mizue; Nakagawa, Michiko; Suzuki, Masakazu; Otsuki, Kyoichi; Kumagai, Tomo'omi

    2013-07-01

    To clarify characteristics of carbon (C) allocation in a Bornean tropical rainforest without dry seasons, gross primary production (GPP) and C allocation, i.e., above-ground net primary production (ANPP), aboveground plant respiration (APR), and total below-ground carbon flux (TBCF) for the forest were examined and compared with those from Amazonian tropical rainforests with dry seasons. GPP (30.61 MgC ha(-1) year(-1), eddy covariance measurements; 34.40 MgC ha(-1) year(-1), biometric measurements) was comparable to those for Amazonian rainforests. ANPP (6.76 MgC ha(-1) year(-1)) was comparable to, and APR (8.01 MgC ha(-1) year(-1)) was slightly lower than, their respective values for Amazonian rainforests, even though aboveground biomass was greater at our site. TBCF (19.63 MgC ha(-1) year(-1)) was higher than those for Amazonian forests. The comparable ANPP and higher TBCF were unexpected, since higher water availability would suggest less fine root competition for water, giving higher ANPP and lower TBCF to GPP. Low nutrient availability may explain the comparable ANPP and higher TBCF. These data show that there are variations in C allocation patterns among mature tropical rainforests, and the variations cannot be explained solely by differences in soil water availability.

  19. Assessment of Urban Planetary Boundary Layer Dynamics using Lidar, Microwave Radiometer and Ceilometer Observations over New York City Area

    NASA Astrophysics Data System (ADS)

    Gan, C.; Wu, Y.; Gross, B.; Moshary, F.

    2010-12-01

    Planetary Boundary Layer (PBL) dynamics is crucial in providing accurate air quality forecasts and is very useful in assessing air-transport models. In particular, incorrect determination of PBL dynamics can lead to imprecise surface particulate matter (PM) monitoring since aerosols are usually well mixed within the PBL during the convective heating period. However, PBL dynamics is strongly driven by surface flux measurements which are strongly influenced on the complexities of the urban surface including surface albedo and roughness parameters. Therefore direct assessment of the PBL height dynamics using active sensors is desired to assess the different urban parameterizations. This paper presents long term statistical data comparing the convective PBL growth obtained from lidar based measurements with different Weather Research and Forecast (WRF) parameterizations as well as an urbanized high resolution (uWRF) method based on 3 level urban structure parameterizations. We find that the operational bulk parameterizations used by WRF generally overestimate both the initiation and magnitude of the mixing layer height. This can be explained as an underestimate of the urban surface roughness that tends to reduce the surface buoyant flux. However, we find that comparisons with uWRF tend to overcorrect the convective growth. In support of these efforts, we develop an improved method to separate the convective layer from residual layer and clouds within the lidar signal. Further model assessments include water vapor and temperature from a passive Microwave radiometer. In particular, we find that the differential temperature between air and surface temperature is generally overestimated in the standard WRF models which is consistent with PBL height observations. Estimate PBL (black dash line) and Lidar Measurements on July 2, 2010

  20. Including local rainfall dynamics and uncertain boundary conditions into a 2-D regional-local flood modelling cascade

    NASA Astrophysics Data System (ADS)

    Bermúdez, María; Neal, Jeffrey C.; Bates, Paul D.; Coxon, Gemma; Freer, Jim E.; Cea, Luis; Puertas, Jerónimo

    2016-04-01

    Flood inundation models require appropriate boundary conditions to be specified at the limits of the domain, which commonly consist of upstream flow rate and downstream water level. These data are usually acquired from gauging stations on the river network where measured water levels are converted to discharge via a rating curve. Derived streamflow estimates are therefore subject to uncertainties in this rating curve, including extrapolating beyond the maximum observed ratings magnitude. In addition, the limited number of gauges in reach-scale studies often requires flow to be routed from the nearest upstream gauge to the boundary of the model domain. This introduces additional uncertainty, derived not only from the flow routing method used, but also from the additional lateral rainfall-runoff contributions downstream of the gauging point. Although generally assumed to have a minor impact on discharge in fluvial flood modeling, this local hydrological input may become important in a sparse gauge network or in events with significant local rainfall. In this study, a method to incorporate rating curve uncertainty and the local rainfall-runoff dynamics into the predictions of a reach-scale flood inundation model is proposed. Discharge uncertainty bounds are generated by applying a non-parametric local weighted regression approach to stage-discharge measurements for two gauging stations, while measured rainfall downstream from these locations is cascaded into a hydrological model to quantify additional inflows along the main channel. A regional simplified-physics hydraulic model is then applied to combine these inputs and generate an ensemble of discharge and water elevation time series at the boundaries of a local-scale high complexity hydraulic model. Finally, the effect of these rainfall dynamics and uncertain boundary conditions are evaluated on the local-scale model. Improvements in model performance when incorporating these processes are quantified using observed

  1. Impact of the lateral boundary conditions resolution on dynamical downscaling of precipitation in mediterranean spain

    NASA Astrophysics Data System (ADS)

    Amengual, A.; Romero, R.; Homar, V.; Ramis, C.; Alonso, S.

    2007-08-01

    Studies using transparent, polymeric witness plates consisting of polydimethlysiloxane (PDMS) have been conducted to measure the output of exploding bridge wire (EBW) detonators and exploding foil initiators (EFI). Polymeric witness plates are utilized to alleviate particle response issues that arise in gaseous flow fields containing shock waves and to allow measurements of shock-induced material velocities to be made using particle image velocimetry (PIV). Quantitative comparisons of velocity profiles across the shock waves in air and in PDMS demonstrate the improved response achieved by the dynamic witness plate method. Schlieren photographs complement the analysis through direct visualization of detonator-induced shock waves in the witness plates.

  2. Singularities in Axisymmetric Free Boundaries for ElectroHydroDynamic Equations

    NASA Astrophysics Data System (ADS)

    Garcia, Mariana Smit Vega; Vărvărucă, Eugen; Weiss, Georg S.

    2016-11-01

    We consider singularities in the ElectroHydroDynamic equations. In a regime where we are allowed to neglect surface tension, and assuming that the free surface is given by an injective curve and that either the fluid velocity or the electric field satisfies a certain non-degeneracy condition, we prove that either the fluid region or the gas region is asymptotically a cusp. Our proofs depend on a combination of monotonicity formulas and a non-vanishing result by Caffarelli and Friedman. As a by-product of our analysis we also obtain a special solution with convex conical air-phase which we believe to be new.

  3. Influence of urban morphometric modification on regional boundary-layer dynamics

    NASA Astrophysics Data System (ADS)

    Chan, Allen; Fung, Jimmy C. H.; Lau, Alexis K. H.

    2013-04-01

    Fidelity in simulating urban boundary-layer (UBL) physics is recognized to prescribe the prognostic skill of subsequent regional air pollutant transport modeling. Conventional mesoscale meteorological models (MMM) deployed over the South China coast among urban locales have often yielded positive bias in surface wind speed. This bias has been hypothetically attributed to model parameterizations that yield inaccurate meteorological predictions due to underrepresentation of urban aerodynamic roughness. Chemical transport model (CTM) simulations that are forced by the overestimated UBL wind field may undergo excessive advection which results in negative bias in predicted pollutant concentration. This study aimed to corroborate the proposed causality between parameterized urban morphometry and UBL meteorology. Focus was placed on the urban meteorological adjustments induced by urban morphometry modifications rather than prediction improvements attributable to urban canopy parameterization (UCP). Case studies were devised to assess the sensitivity of an urban-meteorology model to a pervasive, region-wide urban morphometry modification. Performance of a UCP scheme was evaluated for the Pearl River Delta (PRD) region, a meso- β-scale subtropical coastal megalopolis. To benchmark the limits of UBL adjustments that were predominantly attributable to urban morphometric transformation, numerical experiments were conducted against two urban fabrics of vastly dissimilar morphometric compositions, each occupying identical topographic tracts. Differences in the diurnal evolution of UBL structure and in the mean and turbulent flow characteristics were analyzed. This UCP sensitivity study suggests that improved urban morphological realism is able to reduce positive wind speed bias observed in conventional mesoscale meteorological models when applied to the PRD region.

  4. Effect of solid boundaries on swimming dynamics of microorganisms in a viscoelastic fluid

    PubMed Central

    Li, G. -J.; Karimi, A.

    2015-01-01

    We numerically study the effect of solid boundaries on the swimming behavior of a motile microorganism in viscoelastic media. Understanding the swimmer-wall hydrodynamic interactions is crucial to elucidate the adhesion of bacterial cells to nearby substrates which is precursor to the formation of the microbial biofilms. The microorganism is simulated using a squirmer model that captures the major swimming mechanisms of potential, extensile, and contractile types of swimmers, while neglecting the biological complexities. A Giesekus constitutive equation is utilized to describe both viscoelasticity and shear-thinning behavior of the background fluid. We found that the viscoelasticity strongly affects the near-wall motion of a squirmer by generating an opposing polymeric torque which impedes the rotation of the swimmer away from the wall. In particular, the time a neutral squirmer spends at the close proximity of the wall is shown to increase with polymer relaxation time and reaches a maximum at Weissenberg number of unity. The shear-thinning effect is found to weaken the solvent stress and therefore, increases the swimmer-wall contact time. For a puller swimmer, the polymer stretching mainly occurs around its lateral sides, leading to reduced elastic resistance against its locomotion. The neutral and puller swimmers eventually escape the wall attraction effect due to a releasing force generated by the Newtonian viscous stress. In contrast, the pusher is found to be perpetually trapped near the wall as a result of the formation of a highly stretched region behind its body. It is shown that the shear-thinning property of the fluid weakens the wall-trapping effect for the pusher squirmer. PMID:26855446

  5. Refined BCF-type boundary conditions for mesoscale surface step dynamics

    SciTech Connect

    Zhao, Renjie; Ackerman, David M.; Evans, James W.

    2015-06-24

    Deposition on a vicinal surface with alternating rough and smooth steps is described by a solid-on-solid model with anisotropic interactions. Kinetic Monte Carlo (KMC) simulations of the model reveal step pairing in the absence of any additional step attachment barriers. We explore the description of this behavior within an analytic Burton-Cabrera-Frank (BCF)-type step dynamics treatment. Without attachment barriers, conventional kinetic coefficients for the rough and smooth steps are identical, as are the predicted step velocities for a vicinal surface with equal terrace widths. However, we determine refined kinetic coefficients from a two-dimensional discrete deposition-diffusion equation formalism which accounts for step structure. These coefficients are generally higher for rough steps than for smooth steps, reflecting a higher propensity for capture of diffusing terrace adatoms due to a higher kink density. Such refined coefficients also depend on the local environment of the step and can even become negative (corresponding to net detachment despite an excess adatom density) for a smooth step in close proximity to a rough step. Incorporation of these refined kinetic coefficients into a BCF-type step dynamics treatment recovers quantitatively the mesoscale step-pairing behavior observed in the KMC simulations.

  6. Refined BCF-type boundary conditions for mesoscale surface step dynamics

    DOE PAGESBeta

    Zhao, Renjie; Ackerman, David M.; Evans, James W.

    2015-06-24

    Deposition on a vicinal surface with alternating rough and smooth steps is described by a solid-on-solid model with anisotropic interactions. Kinetic Monte Carlo (KMC) simulations of the model reveal step pairing in the absence of any additional step attachment barriers. We explore the description of this behavior within an analytic Burton-Cabrera-Frank (BCF)-type step dynamics treatment. Without attachment barriers, conventional kinetic coefficients for the rough and smooth steps are identical, as are the predicted step velocities for a vicinal surface with equal terrace widths. However, we determine refined kinetic coefficients from a two-dimensional discrete deposition-diffusion equation formalism which accounts for stepmore » structure. These coefficients are generally higher for rough steps than for smooth steps, reflecting a higher propensity for capture of diffusing terrace adatoms due to a higher kink density. Such refined coefficients also depend on the local environment of the step and can even become negative (corresponding to net detachment despite an excess adatom density) for a smooth step in close proximity to a rough step. Incorporation of these refined kinetic coefficients into a BCF-type step dynamics treatment recovers quantitatively the mesoscale step-pairing behavior observed in the KMC simulations.« less

  7. Refined BCF-type boundary conditions for mesoscale surface step dynamics

    NASA Astrophysics Data System (ADS)

    Zhao, Renjie; Ackerman, David M.; Evans, James W.

    2015-06-01

    Deposition on a vicinal surface with alternating rough and smooth steps is described by a solid-on-solid model with anisotropic interactions. Kinetic Monte Carlo (KMC) simulations of the model reveal step pairing in the absence of any additional step attachment barriers. We explore the description of this behavior within an analytic Burton-Cabrera-Frank (BCF)-type step dynamics treatment. Without attachment barriers, conventional kinetic coefficients for the rough and smooth steps are identical, as are the predicted step velocities for a vicinal surface with equal terrace widths. However, we determine refined kinetic coefficients from a two-dimensional discrete deposition-diffusion equation formalism which accounts for step structure. These coefficients are generally higher for rough steps than for smooth steps, reflecting a higher propensity for capture of diffusing terrace adatoms due to a higher kink density. Such refined coefficients also depend on the local environment of the step and can even become negative (corresponding to net detachment despite an excess adatom density) for a smooth step in close proximity to a rough step. Our key observation is that incorporation of these refined kinetic coefficients into a BCF-type step dynamics treatment recovers quantitatively the mesoscale step-pairing behavior observed in the KMC simulations.

  8. Application of a lattice Boltzmann-immersed boundary method for fluid-filament dynamics and flow sensing.

    PubMed

    O׳Connor, Joseph; Revell, Alistair; Mandal, Parthasarathi; Day, Philip

    2016-07-26

    Complex fluid-structure interactions between elastic filaments, or cilia, immersed in viscous flows are commonplace in nature and bear important roles. Some biological systems have evolved to interpret flow-induced motion into signals for the purpose of feedback response. Given the challenges associated with extracting meaningful experimental data at this scale, there has been particular focus on the numerical study of these effects. Porous models have proven useful where cilia arrangements are relatively dense, but for more sparse configurations the dynamic interactions of individual structures play a greater role and direct modelling becomes increasingly necessary. The present study reports efforts towards explicit modelling of regularly spaced wall-mounted cilia using a lattice Boltzmann-immersed boundary method. Both steady and forced unsteady 2D channel flows at different Reynolds numbers are investigated, with and without the presence of a periodic array of elastic inextensible filaments. It is demonstrated that the structure response depends significantly on Reynolds number. For low Reynolds flow, the recirculation vortex aft of successive filaments is small relative to the cilia spacing and does not fully bridge the gap, in which case the structure lags the flow. At higher Reynolds number, when this gap is fully bridged the structure and flow move in phase. The trapping of vortices between cilia is associated with relatively lower wall shear stress. At low to intermediate Reynolds, vortex bridging is incomplete and large deflection is still possible, which is reflected in the tip dynamics and wall shear stress profiles. PMID:26718062

  9. The role of mechanical boundary conditions in the soft mode dynamics of PbTiO3

    NASA Astrophysics Data System (ADS)

    McCash, Kevin; Mani, B. K.; Chang, C.-M.; Ponomareva, I.

    2014-10-01

    The role of different mechanical boundary conditions in the soft mode dynamics of ferroelectric PbTiO3 is systematically investigated using first-principles-based simulations and analytical model. The change in the soft mode dynamics due to hydrostatic pressure, uniaxial and biaxial stresses and biaxial strains is studied in a wide temperature range. Our computations predict: (i) the existence of Curie-Weiss laws that relate the soft mode frequency to the stress or strain; (ii) a non-trivial temperature evolution of the associated Curie-Weiss constants; (iii) a qualitative difference between the soft mode response to stresses/strains and hydrostatic pressure. The latter finding implies that the Curie-Weiss pressure law commonly used for residual stress estimation may not apply for the cases of uniaxial and biaxial stresses and strains. On the other hand, our systematic study offers a way to eliminate this difficulty through the establishment of Curie-Weiss stress and strain laws. Implications of our predictions for some available experimental data are discussed.

  10. Phonon coupling to dynamic short-range polar order in a relaxor ferroelectric near the morphotropic phase boundary

    SciTech Connect

    John A. Schneeloch; Xu, Zhijun; Winn, B.; Stock, C.; Gehring, P. M.; Birgeneau, R. J.; Xu, Guangyong

    2015-12-28

    We report neutron inelastic scattering experiments on single-crystal PbMg1/3Nb2/3O3 doped with 32% PbTiO3, a relaxor ferroelectric that lies close to the morphotropic phase boundary. When cooled under an electric field E∥ [001] into tetragonal and monoclinic phases, the scattering cross section from transverse acoustic (TA) phonons polarized parallel to E weakens and shifts to higher energy relative to that under zero-field-cooled conditions. Likewise, the scattering cross section from transverse optic (TO) phonons polarized parallel to E weakens for energy transfers 4 ≤ ℏω ≤ 9 meV. However, TA and TO phonons polarized perpendicular to E show no change. This anisotropic field response is similar to that of the diffuse scattering cross section, which, as previously reported, is suppressed when polarized parallel to E but not when polarized perpendicular to E. Lastly, our findings suggest that the lattice dynamics and dynamic short-range polar correlations that give rise to the diffuse scattering are coupled.

  11. Phonon coupling to dynamic short-range polar order in a relaxor ferroelectric near the morphotropic phase boundary

    DOE PAGESBeta

    John A. Schneeloch; Xu, Zhijun; Winn, B.; Stock, C.; Gehring, P. M.; Birgeneau, R. J.; Xu, Guangyong

    2015-12-28

    We report neutron inelastic scattering experiments on single-crystal PbMg1/3Nb2/3O3 doped with 32% PbTiO3, a relaxor ferroelectric that lies close to the morphotropic phase boundary. When cooled under an electric field E∥ [001] into tetragonal and monoclinic phases, the scattering cross section from transverse acoustic (TA) phonons polarized parallel to E weakens and shifts to higher energy relative to that under zero-field-cooled conditions. Likewise, the scattering cross section from transverse optic (TO) phonons polarized parallel to E weakens for energy transfers 4 ≤ ℏω ≤ 9 meV. However, TA and TO phonons polarized perpendicular to E show no change. This anisotropicmore » field response is similar to that of the diffuse scattering cross section, which, as previously reported, is suppressed when polarized parallel to E but not when polarized perpendicular to E. Lastly, our findings suggest that the lattice dynamics and dynamic short-range polar correlations that give rise to the diffuse scattering are coupled.« less

  12. Evaluation of the influence of inlet boundary conditions on computational fluid dynamics for intracranial aneurysms: a virtual experiment.

    PubMed

    Pereira, V M; Brina, O; Marcos Gonzales, A; Narata, A P; Bijlenga, P; Schaller, K; Lovblad, K O; Ouared, R

    2013-05-31

    Inlet boundary conditions (BCs) are important inputs of computational fluid dynamics (CFD) in intracranial aneurysms (IAs). We performed sensibility analysis of CFD to different inlet BCs applied to illustrative patient-specific aneurysm-vessel geometry. BCs corresponding to generic and patient-specific pulsatile flow curves were applied to three vascular geometry models of carotid ophthalmic aneurysm-vessel geometry, in which the inlet lengths were different. CFD outcomes were compared to high frame rate Digital Subtraction Angiography (DSA) sequences. The streamlines were found to match contrast agent (CA) motion pattern in the case where the non-truncated inlet vessel model was coupled to generic Womersley BC solution. Even though dynamic pressure loss (55%) was equal for all models and different BCs, the minimum distance to wall of the fastest velocity fields for the non-truncated model was significantly larger (p=0.002) and mean vorticity sign was different. Significant difference in spatial distributions of wall shear stress (WSS) and oscillating shear stress index (OSI) was found in aneurysm between Womersley and Plugflow BC conditions, only. Reliable CFD for carotid ophthalmic aneurysm would require avoiding truncation of the inlet vessel to be independent of the solution applied to generate CFD. PMID:23602597

  13. Combining the Fluctuating Charge Method, Non-Periodic Boundary Conditions and Meta-Dynamics: Aqua Ions as case studies

    PubMed Central

    Mancini, Giordano; Brancato, Giuseppe; Barone, Vincenzo

    2015-01-01

    We present the current status of development of our code for performing Molecular Dynamics (MD) simulations exploiting a polarizable force field based on the Fluctuating Charge (FQ) method and non-Periodic Boundary Conditions (NPBC). Continuing on the path set in a previous work, we increased the capabilities of the code by implementing a number of new features, including: a non-iterative algorithm for rigid trigonal molecule simulations; two additional temperature coupling schemes; a meta-dynamics based approach for effective free energy evaluations. Although these are well known algorithms, each present in one or more widely used MD packages, they have now been tested, for the first time, in the context of the FQ model coupled with NPBC. As case studies, we considered three aqueous ions of increasing charge, namely Na+, Ca2+ and La3+, at infinite dilution. In particular, by exploiting a computational approach recently proposed by our group and based on the metadynamics technique, we focused on the important role played by solvent polarization on ionic hydration structures, also investigating the free energy landscapes of ion coordination and the water exchange rates. Such an approach, previously tested with standard non-polarizable models, was applied here to evaluate the effects of explicit polarization on water exchange barriers between different solvent coordination structures. Moreover, we have analyzed and discussed in some detail non-linear electrostatic effects arising from solvent polarization while going from a mono- to a di- and trivalent ion. PMID:26543440

  14. Coinciding Features in a Turbulent Boundary Layer via Lagrangian Coherent Structures, Dynamic Mode Decomposition and Proper Orthogonal Decomposition

    NASA Astrophysics Data System (ADS)

    Ali, Naseem; Tutkun, Murat; Cal, Rau'l.

    2015-11-01

    Low order decompositions and Lagrangian coherent structures are used to identify structures in a high-Reynolds-number turbulent boundary layer flow. Data are collected in Laboratoire de Mécanique de Lille (LML) wind tunnel using time resolved stereo particle image velocimetry. Low-order descriptors are based on proper orthogonal decomposition (POD) and dynamic mode decomposition (DMD) frameworks to obtain energy content and frequency information of the flow, respectively. Repelling and attracting Lagrangian coherent structures (LCS)s reveal complex patterns within the flow field containing a hyperbolic behavior and the shapes of the attracting and repelling vary with advection time as result of the temporal coherence. The attracting and repelling LCSs are matched with POD and DMD modes to understand the relationship between the frameworks and respective representations. The POD is used as a low pass filtering of kinetic energy and then mode-dependent velocity reconstructions provide, firstly, the most coherent features of the flow and second are employed to generate new mode-based LCSs. This representations then provide clarity as to the organization of the LCS based on the energy contained in them and the dynamic coherence.

  15. Logging cuts the functional importance of invertebrates in tropical rainforest.

    PubMed

    Ewers, Robert M; Boyle, Michael J W; Gleave, Rosalind A; Plowman, Nichola S; Benedick, Suzan; Bernard, Henry; Bishop, Tom R; Bakhtiar, Effendi Y; Chey, Vun Khen; Chung, Arthur Y C; Davies, Richard G; Edwards, David P; Eggleton, Paul; Fayle, Tom M; Hardwick, Stephen R; Homathevi, Rahman; Kitching, Roger L; Khoo, Min Sheng; Luke, Sarah H; March, Joshua J; Nilus, Reuben; Pfeifer, Marion; Rao, Sri V; Sharp, Adam C; Snaddon, Jake L; Stork, Nigel E; Struebig, Matthew J; Wearn, Oliver R; Yusah, Kalsum M; Turner, Edgar C

    2015-04-13

    Invertebrates are dominant species in primary tropical rainforests, where their abundance and diversity contributes to the functioning and resilience of these globally important ecosystems. However, more than one-third of tropical forests have been logged, with dramatic impacts on rainforest biodiversity that may disrupt key ecosystem processes. We find that the contribution of invertebrates to three ecosystem processes operating at three trophic levels (litter decomposition, seed predation and removal, and invertebrate predation) is reduced by up to one-half following logging. These changes are associated with decreased abundance of key functional groups of termites, ants, beetles and earthworms, and an increase in the abundance of small mammals, amphibians and insectivorous birds in logged relative to primary forest. Our results suggest that ecosystem processes themselves have considerable resilience to logging, but the consistent decline of invertebrate functional importance is indicative of a human-induced shift in how these ecological processes operate in tropical rainforests.

  16. Logging cuts the functional importance of invertebrates in tropical rainforest.

    PubMed

    Ewers, Robert M; Boyle, Michael J W; Gleave, Rosalind A; Plowman, Nichola S; Benedick, Suzan; Bernard, Henry; Bishop, Tom R; Bakhtiar, Effendi Y; Chey, Vun Khen; Chung, Arthur Y C; Davies, Richard G; Edwards, David P; Eggleton, Paul; Fayle, Tom M; Hardwick, Stephen R; Homathevi, Rahman; Kitching, Roger L; Khoo, Min Sheng; Luke, Sarah H; March, Joshua J; Nilus, Reuben; Pfeifer, Marion; Rao, Sri V; Sharp, Adam C; Snaddon, Jake L; Stork, Nigel E; Struebig, Matthew J; Wearn, Oliver R; Yusah, Kalsum M; Turner, Edgar C

    2015-01-01

    Invertebrates are dominant species in primary tropical rainforests, where their abundance and diversity contributes to the functioning and resilience of these globally important ecosystems. However, more than one-third of tropical forests have been logged, with dramatic impacts on rainforest biodiversity that may disrupt key ecosystem processes. We find that the contribution of invertebrates to three ecosystem processes operating at three trophic levels (litter decomposition, seed predation and removal, and invertebrate predation) is reduced by up to one-half following logging. These changes are associated with decreased abundance of key functional groups of termites, ants, beetles and earthworms, and an increase in the abundance of small mammals, amphibians and insectivorous birds in logged relative to primary forest. Our results suggest that ecosystem processes themselves have considerable resilience to logging, but the consistent decline of invertebrate functional importance is indicative of a human-induced shift in how these ecological processes operate in tropical rainforests. PMID:25865801

  17. Logging cuts the functional importance of invertebrates in tropical rainforest

    PubMed Central

    Ewers, Robert M.; Boyle, Michael J. W.; Gleave, Rosalind A.; Plowman, Nichola S.; Benedick, Suzan; Bernard, Henry; Bishop, Tom R.; Bakhtiar, Effendi Y.; Chey, Vun Khen; Chung, Arthur Y. C.; Davies, Richard G.; Edwards, David P.; Eggleton, Paul; Fayle, Tom M.; Hardwick, Stephen R.; Homathevi, Rahman; Kitching, Roger L.; Khoo, Min Sheng; Luke, Sarah H.; March, Joshua J.; Nilus, Reuben; Pfeifer, Marion; Rao, Sri V.; Sharp, Adam C.; Snaddon, Jake L.; Stork, Nigel E.; Struebig, Matthew J.; Wearn, Oliver R.; Yusah, Kalsum M.; Turner, Edgar C.

    2015-01-01

    Invertebrates are dominant species in primary tropical rainforests, where their abundance and diversity contributes to the functioning and resilience of these globally important ecosystems. However, more than one-third of tropical forests have been logged, with dramatic impacts on rainforest biodiversity that may disrupt key ecosystem processes. We find that the contribution of invertebrates to three ecosystem processes operating at three trophic levels (litter decomposition, seed predation and removal, and invertebrate predation) is reduced by up to one-half following logging. These changes are associated with decreased abundance of key functional groups of termites, ants, beetles and earthworms, and an increase in the abundance of small mammals, amphibians and insectivorous birds in logged relative to primary forest. Our results suggest that ecosystem processes themselves have considerable resilience to logging, but the consistent decline of invertebrate functional importance is indicative of a human-induced shift in how these ecological processes operate in tropical rainforests. PMID:25865801

  18. Turbulent Boundary Layer Dynamics and its Relationship to Shallow Cumulus Convection over the Central Equatorial Pacific

    NASA Astrophysics Data System (ADS)

    Faloona, I. C.; Conley, S. A.; Lenschow, D. H.; Bandy, A. R.

    2011-12-01

    Eleven research flights of the National Center for Atmospheric Research (NCAR) C-130 aircraft are analyzed in the vicinity of Christmas Island (2°N, 157°W) during August/September 2007 as part of the Pacific Atmospheric Sulfur Experiment (PASE). In addition to sulfur gases DMS and SO2, and other chemical scalars (O3 and CCN), standard meteorological variables such as temperature, moisture, and winds were measured in-situ at high rate. The nocturnal and daytime flights of PASE were focused on turbulent flux profiles below the trade wind inversion (observed at a mean altitude of 1350m asl). Vertical profiles and long, level legs from near the surface to the lower free troposphere were used to characterize the mean vertical structure of the marine boundary layer (MBL, typically located up to near cloud base at ~550m asl) and the buffer layer (BuL, the intermittently turbulent and occasionally cloudy layer above.) A budget of turbulent kinetic energy (TKE) exhibited evenly distributed shear production throughout the MBL along with the expected linear profile of buoyancy production. Two loci of approximately equal parts shear production, transport, and buoyancy production sustain TKE in the BuL at levels of ~70% that within the MBL. A mean cloud fraction profile from the experiment evinces a bimodal distribution of trade wind cumuli with a major peak at the top and a secondary peak in the lower third of the BuL, consistent with the picture of shallow convection supplying the bulk of the TKE to this layer, but not uniformly in the vertical. On eight of the eleven flights a low level jet was observed either within or just above the BuL, and contributes significantly to turbulent activity in the BuL. Moreover, observations of the mean profiles of various reactive scalars provide a unique constraint on average BuL mixing time scales. During the four week mission, sea surface temperatures over the region decreased by 1.5K as the advancing cold tongue brought cooler water

  19. Attribution of precipitation changes in African rainforest

    NASA Astrophysics Data System (ADS)

    Otto, F. E. L.; Allen, M. R.; Bowery, A.; Imbers, J.; Jones, R.; Massey, N.; Miller, J.; Rosier, S.; Rye, C.; Thurston, M.; Wilson, S.; Yamazaki, H.

    2012-04-01

    Global climate change is almost certainly affecting the magnitude and frequency of extreme weather and hydrological events. However, whether and to what extend the occurrence of such an event can be attributed to climate change remains a challenge that relies on good observations as well as climate modelling. A number of recent studies have attempted to quantify the role of human influence on climate in observed weather events as e.g. the 2010 Russian heat wave (Dole et al, 2011; Rahmstorf and Coumou, 2011; Otto et al, 2012). The overall approach is to simulate, with as realistic a model as possible and accounting as far as possible for modelling uncertainties, both the statistics of observed weather and the statistics of the weather that would have obtained had specific external drivers of climate change been absent. This approach requires a large ensemble size to provide results from which the statistical significance and the shape of the distribution of key variables can be assessed. Also, a sufficiently long period of time must be simulated to evaluate model bias and whether the model captures the observed distribution. The weatherathome.net within the climateprediction.net projects provides such an ensemble with many hundred ensemble members per year via volunteer distributed computing. Most previous attribution studies have been about European extreme weather events but the most vulnerable regions to climate change are in Asia and Africa. One of the most complex hydrological systems is the tropical rainforest, which is expected to react highly sensible to a changing climate. Analysing the weatherathome.net results we find that conditions which are too dry for rainforests to sustain without damages occurred more frequently and more severe in recent years. Furthermore the changes in precipitation in that region can be linked to El Nino/ La Nina events. Linking extreme weather events to large-scale teleconnections helps to understand the occurrence of this

  20. Isoprene photochemistry over the Amazon rainforest.

    PubMed

    Liu, Yingjun; Brito, Joel; Dorris, Matthew R; Rivera-Rios, Jean C; Seco, Roger; Bates, Kelvin H; Artaxo, Paulo; Duvoisin, Sergio; Keutsch, Frank N; Kim, Saewung; Goldstein, Allen H; Guenther, Alex B; Manzi, Antonio O; Souza, Rodrigo A F; Springston, Stephen R; Watson, Thomas B; McKinney, Karena A; Martin, Scot T

    2016-05-31

    Isoprene photooxidation is a major driver of atmospheric chemistry over forested regions. Isoprene reacts with hydroxyl radicals (OH) and molecular oxygen to produce isoprene peroxy radicals (ISOPOO). These radicals can react with hydroperoxyl radicals (HO2) to dominantly produce hydroxyhydroperoxides (ISOPOOH). They can also react with nitric oxide (NO) to largely produce methyl vinyl ketone (MVK) and methacrolein (MACR). Unimolecular isomerization and bimolecular reactions with organic peroxy radicals are also possible. There is uncertainty about the relative importance of each of these pathways in the atmosphere and possible changes because of anthropogenic pollution. Herein, measurements of ISOPOOH and MVK + MACR concentrations are reported over the central region of the Amazon basin during the wet season. The research site, downwind of an urban region, intercepted both background and polluted air masses during the GoAmazon2014/5 Experiment. Under background conditions, the confidence interval for the ratio of the ISOPOOH concentration to that of MVK + MACR spanned 0.4-0.6. This result implies a ratio of the reaction rate of ISOPOO with HO2 to that with NO of approximately unity. A value of unity is significantly smaller than simulated at present by global chemical transport models for this important, nominally low-NO, forested region of Earth. Under polluted conditions, when the concentrations of reactive nitrogen compounds were high (>1 ppb), ISOPOOH concentrations dropped below the instrumental detection limit (<60 ppt). This abrupt shift in isoprene photooxidation, sparked by human activities, speaks to ongoing and possible future changes in the photochemistry active over the Amazon rainforest. PMID:27185928

  1. Isoprene photochemistry over the Amazon rainforest.

    PubMed

    Liu, Yingjun; Brito, Joel; Dorris, Matthew R; Rivera-Rios, Jean C; Seco, Roger; Bates, Kelvin H; Artaxo, Paulo; Duvoisin, Sergio; Keutsch, Frank N; Kim, Saewung; Goldstein, Allen H; Guenther, Alex B; Manzi, Antonio O; Souza, Rodrigo A F; Springston, Stephen R; Watson, Thomas B; McKinney, Karena A; Martin, Scot T

    2016-05-31

    Isoprene photooxidation is a major driver of atmospheric chemistry over forested regions. Isoprene reacts with hydroxyl radicals (OH) and molecular oxygen to produce isoprene peroxy radicals (ISOPOO). These radicals can react with hydroperoxyl radicals (HO2) to dominantly produce hydroxyhydroperoxides (ISOPOOH). They can also react with nitric oxide (NO) to largely produce methyl vinyl ketone (MVK) and methacrolein (MACR). Unimolecular isomerization and bimolecular reactions with organic peroxy radicals are also possible. There is uncertainty about the relative importance of each of these pathways in the atmosphere and possible changes because of anthropogenic pollution. Herein, measurements of ISOPOOH and MVK + MACR concentrations are reported over the central region of the Amazon basin during the wet season. The research site, downwind of an urban region, intercepted both background and polluted air masses during the GoAmazon2014/5 Experiment. Under background conditions, the confidence interval for the ratio of the ISOPOOH concentration to that of MVK + MACR spanned 0.4-0.6. This result implies a ratio of the reaction rate of ISOPOO with HO2 to that with NO of approximately unity. A value of unity is significantly smaller than simulated at present by global chemical transport models for this important, nominally low-NO, forested region of Earth. Under polluted conditions, when the concentrations of reactive nitrogen compounds were high (>1 ppb), ISOPOOH concentrations dropped below the instrumental detection limit (<60 ppt). This abrupt shift in isoprene photooxidation, sparked by human activities, speaks to ongoing and possible future changes in the photochemistry active over the Amazon rainforest.

  2. Isoprene photochemistry over the Amazon rainforest

    NASA Astrophysics Data System (ADS)

    Liu, Yingjun; Brito, Joel; Dorris, Matthew R.; Rivera-Rios, Jean C.; Seco, Roger; Bates, Kelvin H.; Artaxo, Paulo; Duvoisin, Sergio; Keutsch, Frank N.; Kim, Saewung; Goldstein, Allen H.; Guenther, Alex B.; Manzi, Antonio O.; Souza, Rodrigo A. F.; Springston, Stephen R.; Watson, Thomas B.; McKinney, Karena A.; Martin, Scot T.

    2016-05-01

    Isoprene photooxidation is a major driver of atmospheric chemistry over forested regions. Isoprene reacts with hydroxyl radicals (OH) and molecular oxygen to produce isoprene peroxy radicals (ISOPOO). These radicals can react with hydroperoxyl radicals (HO2) to dominantly produce hydroxyhydroperoxides (ISOPOOH). They can also react with nitric oxide (NO) to largely produce methyl vinyl ketone (MVK) and methacrolein (MACR). Unimolecular isomerization and bimolecular reactions with organic peroxy radicals are also possible. There is uncertainty about the relative importance of each of these pathways in the atmosphere and possible changes because of anthropogenic pollution. Herein, measurements of ISOPOOH and MVK + MACR concentrations are reported over the central region of the Amazon basin during the wet season. The research site, downwind of an urban region, intercepted both background and polluted air masses during the GoAmazon2014/5 Experiment. Under background conditions, the confidence interval for the ratio of the ISOPOOH concentration to that of MVK + MACR spanned 0.4–0.6. This result implies a ratio of the reaction rate of ISOPOO with HO2 to that with NO of approximately unity. A value of unity is significantly smaller than simulated at present by global chemical transport models for this important, nominally low-NO, forested region of Earth. Under polluted conditions, when the concentrations of reactive nitrogen compounds were high (>1 ppb), ISOPOOH concentrations dropped below the instrumental detection limit (<60 ppt). This abrupt shift in isoprene photooxidation, sparked by human activities, speaks to ongoing and possible future changes in the photochemistry active over the Amazon rainforest.

  3. Isoprene photochemistry over the Amazon rainforest

    NASA Astrophysics Data System (ADS)

    Liu, Yingjun; Brito, Joel; Dorris, Matthew R.; Rivera-Rios, Jean C.; Seco, Roger; Bates, Kelvin H.; Artaxo, Paulo; Duvoisin, Sergio; Keutsch, Frank N.; Kim, Saewung; Goldstein, Allen H.; Guenther, Alex B.; Manzi, Antonio O.; Souza, Rodrigo A. F.; Springston, Stephen R.; Watson, Thomas B.; McKinney, Karena A.; Martin, Scot T.

    2016-05-01

    Isoprene photooxidation is a major driver of atmospheric chemistry over forested regions. Isoprene reacts with hydroxyl radicals (OH) and molecular oxygen to produce isoprene peroxy radicals (ISOPOO). These radicals can react with hydroperoxyl radicals (HO2) to dominantly produce hydroxyhydroperoxides (ISOPOOH). They can also react with nitric oxide (NO) to largely produce methyl vinyl ketone (MVK) and methacrolein (MACR). Unimolecular isomerization and bimolecular reactions with organic peroxy radicals are also possible. There is uncertainty about the relative importance of each of these pathways in the atmosphere and possible changes because of anthropogenic pollution. Herein, measurements of ISOPOOH and MVK + MACR concentrations are reported over the central region of the Amazon basin during the wet season. The research site, downwind of an urban region, intercepted both background and polluted air masses during the GoAmazon2014/5 Experiment. Under background conditions, the confidence interval for the ratio of the ISOPOOH concentration to that of MVK + MACR spanned 0.4-0.6. This result implies a ratio of the reaction rate of ISOPOO with HO2 to that with NO of approximately unity. A value of unity is significantly smaller than simulated at present by global chemical transport models for this important, nominally low-NO, forested region of Earth. Under polluted conditions, when the concentrations of reactive nitrogen compounds were high (>1 ppb), ISOPOOH concentrations dropped below the instrumental detection limit (<60 ppt). This abrupt shift in isoprene photooxidation, sparked by human activities, speaks to ongoing and possible future changes in the photochemistry active over the Amazon rainforest.

  4. Nematode Spatial and Ecological Patterns from Tropical and Temperate Rainforests

    PubMed Central

    Porazinska, Dorota L.; Giblin-Davis, Robin M.; Powers, Thomas O.; Thomas, W. Kelley

    2012-01-01

    Large scale diversity patterns are well established for terrestrial macrobiota (e.g. plants and vertebrates), but not for microscopic organisms (e.g. nematodes). Due to small size, high abundance, and extensive dispersal, microbiota are assumed to exhibit cosmopolitan distributions with no biogeographical patterns. This assumption has been extrapolated from local spatial scale studies of a few taxonomic groups utilizing morphological approaches. Recent molecularly-based studies, however, suggest something quite opposite. Nematodes are the most abundant metazoans on earth, but their diversity patterns are largely unknown. We conducted a survey of nematode diversity within three vertical strata (soil, litter, and canopy) of rainforests at two contrasting latitudes in the North American meridian (temperate: the Olympic National Forest, WA, U.S.A and tropical: La Selva Biological Station, Costa Rica) using standardized sampling designs and sample processing protocols. To describe nematode diversity, we applied an ecometagenetic approach using 454 pyrosequencing. We observed that: 1) nematode communities were unique without even a single common species between the two rainforests, 2) nematode communities were unique among habitats in both rainforests, 3) total species richness was 300% more in the tropical than in the temperate rainforest, 4) 80% of the species in the temperate rainforest resided in the soil, whereas only 20% in the tropics, 5) more than 90% of identified species were novel. Overall, our data provided no support for cosmopolitanism at both local (habitats) and large (rainforests) spatial scales. In addition, our data indicated that biogeographical patterns typical of macrobiota also exist for microbiota. PMID:22984536

  5. Physics of Canopy Boundary Layer Resistance for Better Quantification of Sensitivity of Deforestation Scenarios

    NASA Astrophysics Data System (ADS)

    Ragi, K. B.; Patel, R.

    2015-12-01

    A great deal of studies focused on deforestation scenarios in the tropical rainforests. Though all these efforts are useful in the understanding of its response to climate, the systematic understanding of uncertainties in representation of physical processes related to vegetation through sensitivity studies is imperative antecedently to understand the real role of vegetation in changing the climate. It is understood that the dense vegetation fluxes energy and moisture to the atmosphere. But, how much a specific process/a group of processes in the surface conditions of a specific area helps flux energy, moisture and tracers is unknown due to lack of process sensitivity studies and uncertain due to malfunctioning of processes. In this presentation, we have found a faulty parameterization, through process sensitivity studies, that would abet in energy and moisture fluxes to the atmosphere. The model we have employed is the Common Land Model2014. The area we have chosen is the Congolese rainforest. We have discovered the flaw in the leaf boundary layer resistance (LBLR), through sensitivity studies in the LSMs, especially in the dense forest regions. This LBLR is over-parameterized with constant heat transfer coefficient and characteristic dimension of leaves; and friction velocity. However, it is too scant because of overlooking of significant complex physics of turbulence and canopy roughness boundary layer to function it realistically. Our sensitivity results show the deficiency of this process and we have formulated canopy boundary layer resistance, instead of LBLR, with depending variables such as LAI, roughness length, vegetation temperature using appropriate thermo-fluid dynamical principles. We are running the sensitivity experiments with new formulations for setting the parameter values for the data not available so far. This effort would lead to better physics for the land-use change studies and demand for the retrieval of new parameters from satellite

  6. Aboveground vs. Belowground Carbon Stocks in African Tropical Lowland Rainforest: Drivers and Implications

    PubMed Central

    Bauters, Marijn; Hufkens, Koen; Lisingo, Janvier; Baert, Geert; Verbeeck, Hans; Boeckx, Pascal

    2015-01-01

    Background African tropical rainforests are one of the most important hotspots to look for changes in the upcoming decades when it comes to C storage and release. The focus of studying C dynamics in these systems lies traditionally on living aboveground biomass. Belowground soil organic carbon stocks have received little attention and estimates of the size, controls and distribution of soil organic carbon stocks are highly uncertain. In our study on lowland rainforest in the central Congo basin, we combine both an assessment of the aboveground C stock with an assessment of the belowground C stock and analyze the latter in terms of functional pools and controlling factors. Principal Findings Our study shows that despite similar vegetation, soil and climatic conditions, soil organic carbon stocks in an area with greater tree height (= larger aboveground carbon stock) were only half compared to an area with lower tree height (= smaller aboveground carbon stock). This suggests that substantial variability in the aboveground vs. belowground C allocation strategy and/or C turnover in two similar tropical forest systems can lead to significant differences in total soil organic C content and C fractions with important consequences for the assessment of the total C stock of the system. Conclusions/Significance We suggest nutrient limitation, especially potassium, as the driver for aboveground versus belowground C allocation. However, other drivers such as C turnover, tree functional traits or demographic considerations cannot be excluded. We argue that large and unaccounted variability in C stocks is to be expected in African tropical rain-forests. Currently, these differences in aboveground and belowground C stocks are not adequately verified and implemented mechanistically into Earth System Models. This will, hence, introduce additional uncertainty to models and predictions of the response of C storage of the Congo basin forest to climate change and its contribution to

  7. Functional variation among frugivorous birds: implications for rainforest seed dispersal in a fragmented subtropical landscape.

    PubMed

    Moran, C; Catterall, C P; Green, R J; Olsen, M F

    2004-12-01

    Seed dispersal plays a critical role in rainforest regeneration patterns, hence loss of avian seed dispersers in fragmented landscapes may disrupt forest regeneration dynamics. To predict whether or not a plant will be dispersed in fragmented forests, it is necessary to have information about frugivorous bird distribution and dietary composition. However, specific dietary information for frugivorous birds is often limited. In such cases, information on the seed-crushing behaviour, gape width and relative dietary dominance by fruit may be used to describe functional groups of bird species with respect to their potential to disperse similar seeds. We used this information to assess differences in the seed dispersal potential of frugivorous bird assemblages in a fragmented rainforest landscape of southeast Queensland, Australia. The relative abundance of frugivorous birds was surveyed in extensive, remnant and regrowth rainforest sites (16 replicates of each). Large-gaped birds with mixed diets and medium-gaped birds with fruit-dominated diets were usually less abundant in remnants and regrowth than in continuous forest. Small-gaped birds with mixed diets and birds with fruit as a minor dietary component were most abundant in regrowth. We recorded a similar number of seed-crushing birds and large-gaped birds with fruit-dominated diets across site types. Bird species that may have the greatest potential to disperse a large volume and wide variety of plants, including large-seeded plants, tended to be less abundant outside of extensive forests, although one species, the figbird Sphecotheres viridis, was much more abundant in these areas. The results suggest that the dispersal of certain plant taxa would be limited in this fragmented landscape, although the potential for the dispersal of large-seeded plants may remain, despite the loss of several large-gaped disperser species.

  8. Anthropogenic disturbances jeopardize biodiversity conservation within tropical rainforest reserves.

    PubMed

    Martínez-Ramos, Miguel; Ortiz-Rodríguez, Iván A; Piñero, Daniel; Dirzo, Rodolfo; Sarukhán, José

    2016-05-10

    Anthropogenic disturbances affecting tropical forest reserves have been documented, but their ecological long-term cumulative effects are poorly understood. Habitat fragmentation and defaunation are two major anthropogenic threats to the integrity of tropical reserves. Based on a long-term (four decades) study, we document how these disturbances synergistically disrupt ecological processes and imperil biodiversity conservation and ecosystem functioning at Los Tuxtlas, the northernmost tropical rainforest reserve in the Americas. Deforestation around this reserve has reduced the reserve to a medium-sized fragment (640 ha), leading to an increased frequency of canopy-gap formation. In addition, hunting and habitat loss have caused the decline or local extinction of medium and large herbivores. Combining empirical, experimental, and modeling approaches, we support the hypothesis that such disturbances produced a demographic explosion of the long-lived (≈120 y old, maximum height of 7 m) understory palm Astrocaryum mexicanum, whose population has increased from 1,243-4,058 adult individuals per hectare in only 39 y (annual growth rate of ca 3%). Faster gap formation increased understory light availability, enhancing seed production and the growth of immature palms, whereas release from mammalian herbivory and trampling increased survival of seedlings and juveniles. In turn, the palm's demographic explosion was followed by a reduction of tree species diversity, changing forest composition, altering the relative contribution of trees to forest biomass, and disrupting litterfall dynamics. We highlight how indirect anthropogenic disturbances (e.g., palm proliferation) on otherwise protected areas threaten tropical conservation, a phenomenon that is currently eroding the planet's richest repositories of biodiversity.

  9. Widespread decline of Congo rainforest greenness in the past decade.

    PubMed

    Zhou, Liming; Tian, Yuhong; Myneni, Ranga B; Ciais, Philippe; Saatchi, Sassan; Liu, Yi Y; Piao, Shilong; Chen, Haishan; Vermote, Eric F; Song, Conghe; Hwang, Taehee

    2014-05-01

    Tropical forests are global epicentres of biodiversity and important modulators of climate change, and are mainly constrained by rainfall patterns. The severe short-term droughts that occurred recently in Amazonia have drawn attention to the vulnerability of tropical forests to climatic disturbances. The central African rainforests, the second-largest on Earth, have experienced a long-term drying trend whose impacts on vegetation dynamics remain mostly unknown because in situ observations are very limited. The Congolese forest, with its drier conditions and higher percentage of semi-evergreen trees, may be more tolerant to short-term rainfall reduction than are wetter tropical forests, but for a long-term drought there may be critical thresholds of water availability below which higher-biomass, closed-canopy forests transition to more open, lower-biomass forests. Here we present observational evidence for a widespread decline in forest greenness over the past decade based on analyses of satellite data (optical, thermal, microwave and gravity) from several independent sensors over the Congo basin. This decline in vegetation greenness, particularly in the northern Congolese forest, is generally consistent with decreases in rainfall, terrestrial water storage, water content in aboveground woody and leaf biomass, and the canopy backscatter anomaly caused by changes in structure and moisture in upper forest layers. It is also consistent with increases in photosynthetically active radiation and land surface temperature. These multiple lines of evidence indicate that this large-scale vegetation browning, or loss of photosynthetic capacity, may be partially attributable to the long-term drying trend. Our results suggest that a continued gradual decline of photosynthetic capacity and moisture content driven by the persistent drying trend could alter the composition and structure of the Congolese forest to favour the spread of drought-tolerant species. PMID:24759324

  10. Widespread decline of Congo rainforest greenness in the past decade.

    PubMed

    Zhou, Liming; Tian, Yuhong; Myneni, Ranga B; Ciais, Philippe; Saatchi, Sassan; Liu, Yi Y; Piao, Shilong; Chen, Haishan; Vermote, Eric F; Song, Conghe; Hwang, Taehee

    2014-05-01

    Tropical forests are global epicentres of biodiversity and important modulators of climate change, and are mainly constrained by rainfall patterns. The severe short-term droughts that occurred recently in Amazonia have drawn attention to the vulnerability of tropical forests to climatic disturbances. The central African rainforests, the second-largest on Earth, have experienced a long-term drying trend whose impacts on vegetation dynamics remain mostly unknown because in situ observations are very limited. The Congolese forest, with its drier conditions and higher percentage of semi-evergreen trees, may be more tolerant to short-term rainfall reduction than are wetter tropical forests, but for a long-term drought there may be critical thresholds of water availability below which higher-biomass, closed-canopy forests transition to more open, lower-biomass forests. Here we present observational evidence for a widespread decline in forest greenness over the past decade based on analyses of satellite data (optical, thermal, microwave and gravity) from several independent sensors over the Congo basin. This decline in vegetation greenness, particularly in the northern Congolese forest, is generally consistent with decreases in rainfall, terrestrial water storage, water content in aboveground woody and leaf biomass, and the canopy backscatter anomaly caused by changes in structure and moisture in upper forest layers. It is also consistent with increases in photosynthetically active radiation and land surface temperature. These multiple lines of evidence indicate that this large-scale vegetation browning, or loss of photosynthetic capacity, may be partially attributable to the long-term drying trend. Our results suggest that a continued gradual decline of photosynthetic capacity and moisture content driven by the persistent drying trend could alter the composition and structure of the Congolese forest to favour the spread of drought-tolerant species.

  11. Atomic structure of the ultrathin alumina on NiAl(110) and its antiphase domain boundaries as seen by frequency modulation dynamic force microscopy

    NASA Astrophysics Data System (ADS)

    Simon, G. H.; König, T.; Rust, H.-P.; Heyde, M.; Freund, H.-J.

    2009-09-01

    Atomically resolved frequency modulation dynamic force microscopy (FM-DFM) images of the ultrathin alumina film on NiAl(110) are presented. Images show in detail the surface unit cell, both types of antiphase domain boundaries (translation-related domain boundaries) and lateral displacements within these types of boundaries. Due to the loss of translational symmetry at the boundary, structures of even increased complexity are revealed. Lateral models for these local arrangements have been created on the basis of adjusted unit cell structures. FM-DFM produces on this surface a contrast of extraordinarily high surface sensitivity. It matches the topmost oxygen layer even with respect to topographic height, which adds the third dimension to the analysis. With this the antiphase domain boundaries are shown to be shallow depressions. Furthermore, new symmetry aspects have been found in the topography of these boundaries. The local structure of the film surface shows evidence of substrate influence in its topography and the domain boundary network shows indications that its growth behaviour is affected by this interaction in its very details beyond sheer appearance. Presented results can be linked to the relation between growth and structure of an emerging class of structurally related ultrathin alumina films.

  12. Dynamic recycling of gaseous elemental mercury in the boundary layer of the Antarctic Plateau

    NASA Astrophysics Data System (ADS)

    Dommergue, A.; Barret, M.; Courteaud, J.; Cristofanelli, P.; Ferrari, C. P.; Gallée, H.

    2012-07-01

    Gaseous elemental mercury (Hg(0)) was investigated in the troposphere and in the interstitial air extracted from the snow at Dome Concordia station (alt. 3320 m) on the Antarctic Plateau during January 2009. Measurements showed evidence of a very dynamic and daily cycling of Hg(0) inside the mixing layer with a range of values from 0.2 ng m-3 up to 2.3 ng m-3. During low solar irradiation periods, fast Hg(0) oxidation processes in a confined layer were observed leading to an enrichment of the upper snow layers in divalent Hg. Unexpectedly high Hg(0) concentrations for such a remote place were measured under higher solar irradiation due to the reemission of Hg(0) by the snowpack via photochemical reactions. Hg(0) concentrations showed a negative correlation with ozone mixing ratios, which contrasts with atmospheric mercury depletion events observed during the Arctic spring. It remains unclear whether halogens are involved in Hg(0) oxidation. We suggest that snow surfaces may play a role in promoting the heterogeneous oxidation of Hg(0). The cycling of other oxidants should be investigated together with Hg in order to clarify the complex reactivity on the Antarctic Plateau.

  13. Evidence of impurity and boundary effects on magnetic monopole dynamics in spin ice

    NASA Astrophysics Data System (ADS)

    Revell, H. M.; Yaraskavitch, L. R.; Mason, J. D.; Ross, K. A.; Noad, H. M. L.; Dabkowska, H. A.; Gaulin, B. D.; Henelius, P.; Kycia, J. B.

    2013-01-01

    Electrical resistance is a crucial and well-understood property of systems ranging from computer microchips to nerve impulse propagation in the human body. Here we study the motion of magnetic charges in spin ice and find that extra spins inserted in Dy2Ti2O7 trap magnetic monopole excitations and provide the first example of how defects in a spin-ice material obstruct the flow of monopoles--a magnetic version of residual resistance. We measure the time-dependent magnetic relaxation in Dy2Ti2O7 and show that it decays with a stretched exponential followed by a very slow long-time tail. In a Monte Carlo simulation governed by Metropolis dynamics we show that surface effects and a very low level of stuffed spins (0.30%)--magnetic Dy ions substituted for non-magnetic Ti ions--cause these signatures in the relaxation. In addition, we find evidence that the rapidly diverging experimental timescale is due to a temperature-dependent attempt rate proportional to the monopole density.

  14. Silver and cesium diffusion dynamics at the β-SiC Σ5 grain boundary investigated with density functional theory molecular dynamics and metadynamics.

    PubMed

    Rabone, Jeremy; López-Honorato, Eddie; Van Uffelen, Paul

    2014-02-01

    The diffusion and release of silver-110m, a strong γ-radiation emitter, through silicon carbide in coated nuclear fuel particles has remained an unsolved topic since it was first observed 40 years ago. The challenge remains to explain why, contrary to other elements, silver is capable of escaping the ceramic diffusion barriers. The current work investigates the underlying differences in the diffusion of silver and cesium along a symmetric tilt Σ5 grain boundary of β-SiC through accelerated density functional theory molecular dynamics simulations. The energy barriers extracted from the simulations give diffusion coefficients that are in reasonable agreement with experiment for silver (2.19 × 10(-19) to 1.05 × 10(-17) m(2) s(-1)), but for cesium the equivalent calculated coefficients for this mechanism are much smaller (3.85 × 10(-23) to 2.15 × 10(-21) m(2) s(-1)) than those found experimentally. Analysis of the simulated structures and electron densities and comparisons with the calculations of other researchers suggest that diffusion of silver and cesium in β-SiC proceeds via different mechanisms. The mechanisms of cesium diffusion appear to be dominated by its relatively large size and repulsive interactions with the silicon and carbon atoms; β-SiC grain boundaries still offer higher energy barriers to diffusion. Silver, on the other hand, is not only smaller in size but, as we show for the first time, can also participate in weak bonding interactions with the host atoms where favorable geometries allow, thus reducing the energy barrier and enhancing the rate of diffusion. PMID:24422635

  15. Pruritis and palpable purpura from leeches in the Australian Rainforest

    PubMed Central

    Seiverling, Elizabeth V.; Khalsa, Amrit; Ahrns, Hadjh T.

    2014-01-01

    Leeches are prevalent in the Australian Rainforest. We report two cases of leech bites resulting in pruritis and palpable purpura. The dermatologic sequelae of leech bites, differential diagnosis of pruritic palpable purpura, leech bite treatment, prevention, and complications are reviewed. PMID:26839767

  16. Landscape Variation in Plant Defense Syndromes across a Tropical Rainforest

    NASA Astrophysics Data System (ADS)

    McManus, K. M.; Asner, G. P.; Martin, R.; Field, C. B.

    2014-12-01

    Plant defenses against herbivores shape tropical rainforest biodiversity, yet community- and landscape-scale patterns of plant defense and the phylogenetic and environmental factors that may shape them are poorly known. We measured foliar defense, growth, and longevity traits for 345 canopy trees across 84 species in a tropical rainforest and examined whether patterns of trait co-variation indicated the existence of plant defense syndromes. Using a DNA-barcode phylogeny and remote sensing and land-use data, we investigated how phylogeny and topo-edaphic properties influenced the distribution of syndromes. We found evidence for three distinct defense syndromes, characterized by rapid growth, growth compensated by defense, or limited palatability/low nutrition. Phylogenetic signal was generally lower for defense traits than traits related to growth or longevity. Individual defense syndromes were organized at different taxonomic levels and responded to different spatial-environmental gradients. The results suggest that a diverse set of tropical canopy trees converge on a limited number of strategies to secure resources and mitigate fitness losses due to herbivory, with patterns of distribution mediated by evolutionary histories and local habitat associations. Plant defense syndromes are multidimensional plant strategies, and thus are a useful means of discerning ecologically-relevant variation in highly diverse tropical rainforest communities. Scaling this approach to the landscape level, if plant defense syndromes can be distinguished in remotely-sensed data, they may yield new insights into the role of plant defense in structuring diverse tropical rainforest communities.

  17. Ultrafast carrier dynamics and the role of grain boundaries in polycrystalline silicon thin films grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Titova, Lyubov V.; Cocker, Tyler L.; Xu, Sijia; Baribeau, Jean-Marc; Wu, Xiaohua; Lockwood, David J.; Hegmann, Frank A.

    2016-10-01

    We have used time-resolved terahertz spectroscopy to study microscopic photoconductivity and ultrafast photoexcited carrier dynamics in thin, pure, non-hydrogenated silicon films grown by molecular beam epitaxy on quartz substrates at temperatures ranging from 335 °C to 572 °C. By controlling the growth temperature, thin silicon films ranging from completely amorphous to polycrystalline with minimal amorphous phase can be achieved. Film morphology, in turn, determines its photoconductive properties: in the amorphous phase, carriers are trapped in bandtail states on sub-picosecond time scales, while the carriers excited in crystalline grains remain free for tens of picoseconds. We also find that in polycrystalline silicon the photoexcited carrier mobility is carrier-density-dependent, with higher carrier densities mitigating the effects of grain boundaries on inter-grain transport. In a film grown at the highest temperature of 572 °C, the morphology changes along the growth direction from polycrystalline with needles of single crystals in the bulk of the film to small crystallites interspersed with amorphous silicon at the top of the film. Depth profiling using different excitation wavelengths shows corresponding differences in the photoconductivity: the photoexcited carrier lifetime and mobility are higher in the first 100-150 nm from the substrate, suggesting that thinner, low-temperature grown polycrystalline silicon films are preferable for photovoltaic applications.

  18. Revisiting kinetic boundary conditions at the surface of fuel droplet hydrocarbons: An atomistic computational fluid dynamics simulation.

    PubMed

    Nasiri, Rasoul

    2016-01-01

    The role of boundary conditions at the interface for both Boltzmann equation and the set of Navier-Stokes equations have been suggested to be important for studying of multiphase flows such as evaporation/condensation process which doesn't always obey the equilibrium conditions. Here we present aspects of transition-state theory (TST) alongside with kinetic gas theory (KGT) relevant to the study of quasi-equilibrium interfacial phenomena and the equilibrium gas phase processes, respectively. A two-state mathematical model for long-chain hydrocarbons which have multi-structural specifications is introduced to clarify how kinetics and thermodynamics affect evaporation/condensation process at the surface of fuel droplet, liquid and gas phases and then show how experimental observations for a number of n-alkane may be reproduced using a hybrid framework TST and KGT with physically reasonable parameters controlling the interface, gas and liquid phases. The importance of internal activation dynamics at the surface of n-alkane droplets is established during the evaporation/condensation process. PMID:27215897

  19. Revisiting kinetic boundary conditions at the surface of fuel droplet hydrocarbons: An atomistic computational fluid dynamics simulation

    PubMed Central

    Nasiri, Rasoul

    2016-01-01

    The role of boundary conditions at the interface for both Boltzmann equation and the set of Navier-Stokes equations have been suggested to be important for studying of multiphase flows such as evaporation/condensation process which doesn’t always obey the equilibrium conditions. Here we present aspects of transition-state theory (TST) alongside with kinetic gas theory (KGT) relevant to the study of quasi-equilibrium interfacial phenomena and the equilibrium gas phase processes, respectively. A two-state mathematical model for long-chain hydrocarbons which have multi-structural specifications is introduced to clarify how kinetics and thermodynamics affect evaporation/condensation process at the surface of fuel droplet, liquid and gas phases and then show how experimental observations for a number of n-alkane may be reproduced using a hybrid framework TST and KGT with physically reasonable parameters controlling the interface, gas and liquid phases. The importance of internal activation dynamics at the surface of n-alkane droplets is established during the evaporation/condensation process. PMID:27215897

  20. Revisiting kinetic boundary conditions at the surface of fuel droplet hydrocarbons: An atomistic computational fluid dynamics simulation

    NASA Astrophysics Data System (ADS)

    Nasiri, Rasoul

    2016-05-01

    The role of boundary conditions at the interface for both Boltzmann equation and the set of Navier-Stokes equations have been suggested to be important for studying of multiphase flows such as evaporation/condensation process which doesn’t always obey the equilibrium conditions. Here we present aspects of transition-state theory (TST) alongside with kinetic gas theory (KGT) relevant to the study of quasi-equilibrium interfacial phenomena and the equilibrium gas phase processes, respectively. A two-state mathematical model for long-chain hydrocarbons which have multi-structural specifications is introduced to clarify how kinetics and thermodynamics affect evaporation/condensation process at the surface of fuel droplet, liquid and gas phases and then show how experimental observations for a number of n-alkane may be reproduced using a hybrid framework TST and KGT with physically reasonable parameters controlling the interface, gas and liquid phases. The importance of internal activation dynamics at the surface of n-alkane droplets is established during the evaporation/condensation process.

  1. Waste management with recourse: an inexact dynamic programming model containing fuzzy boundary intervals in objectives and constraints.

    PubMed

    Tan, Q; Huang, G H; Cai, Y P

    2010-09-01

    The existing inexact optimization methods based on interval-parameter linear programming can hardly address problems where coefficients in objective functions are subject to dual uncertainties. In this study, a superiority-inferiority-based inexact fuzzy two-stage mixed-integer linear programming (SI-IFTMILP) model was developed for supporting municipal solid waste management under uncertainty. The developed SI-IFTMILP approach is capable of tackling dual uncertainties presented as fuzzy boundary intervals (FuBIs) in not only constraints, but also objective functions. Uncertainties expressed as a combination of intervals and random variables could also be explicitly reflected. An algorithm with high computational efficiency was provided to solve SI-IFTMILP. SI-IFTMILP was then applied to a long-term waste management case to demonstrate its applicability. Useful interval solutions were obtained. SI-IFTMILP could help generate dynamic facility-expansion and waste-allocation plans, as well as provide corrective actions when anticipated waste management plans are violated. It could also greatly reduce system-violation risk and enhance system robustness through examining two sets of penalties resulting from variations in fuzziness and randomness. Moreover, four possible alternative models were formulated to solve the same problem; solutions from them were then compared with those from SI-IFTMILP. The results indicate that SI-IFTMILP could provide more reliable solutions than the alternatives. PMID:20580864

  2. Waste management with recourse: an inexact dynamic programming model containing fuzzy boundary intervals in objectives and constraints.

    PubMed

    Tan, Q; Huang, G H; Cai, Y P

    2010-09-01

    The existing inexact optimization methods based on interval-parameter linear programming can hardly address problems where coefficients in objective functions are subject to dual uncertainties. In this study, a superiority-inferiority-based inexact fuzzy two-stage mixed-integer linear programming (SI-IFTMILP) model was developed for supporting municipal solid waste management under uncertainty. The developed SI-IFTMILP approach is capable of tackling dual uncertainties presented as fuzzy boundary intervals (FuBIs) in not only constraints, but also objective functions. Uncertainties expressed as a combination of intervals and random variables could also be explicitly reflected. An algorithm with high computational efficiency was provided to solve SI-IFTMILP. SI-IFTMILP was then applied to a long-term waste management case to demonstrate its applicability. Useful interval solutions were obtained. SI-IFTMILP could help generate dynamic facility-expansion and waste-allocation plans, as well as provide corrective actions when anticipated waste management plans are violated. It could also greatly reduce system-violation risk and enhance system robustness through examining two sets of penalties resulting from variations in fuzziness and randomness. Moreover, four possible alternative models were formulated to solve the same problem; solutions from them were then compared with those from SI-IFTMILP. The results indicate that SI-IFTMILP could provide more reliable solutions than the alternatives.

  3. The Evolution of Deformation-Induced Grain-Boundary Porosity and Dynamic Permeability in Crustal Fault Zones: Insights From the Alpine Fault, New Zealand

    NASA Astrophysics Data System (ADS)

    Sauer, K. M.; Toy, V.

    2015-12-01

    Fluids and minor phases have an important influence on the bulk rheology of a deforming rock mass, but they are not uniformly distributed at any scale within fault zones. Additionally, exhumed ductile shear zones show little interconnected porosity or static permeability, requiring a dynamic process at depth to allow fluids to access the deforming rock mass. It was recently recognized that reactive fluids interact with high-strain sites to generate cavities on quartz grain boundaries, increasing the grain-scale porosity and dynamic permeability of the rock and allowing for additional fluids to infiltrate the shear zone along interlinking cavities, stimulating further reaction and cavitation. Grain-boundary cavities and fine-grained secondary phases impede grain-boundary mobility and cause a transition in deformation mechanisms from grain-size insensitive dislocation creep to grain-size sensitive creep, which is recognized as a weakening mechanism that promotes strain localisation. At present, it is unclear how the distribution of grain-boundary pores within fault rocks reflects the bulk mineralogy and phase arrangement, which is a function of shear strain. We have used micro-computed x-ray tomography (μ-CT), SEM imaging, and EDS analyses to examine how the distribution of grain-boundary pores varies in relation to the arrangement of secondary phases in exhumed protomylonites, mylonites, and ultramylonites within the actively-deforming Alpine Fault zone, and in samples acquired from the Deep Fault Drilling Project (DFDP). Additionally, EBSD is coupled with µ-CT and EDS analyses to characterise the evolution of microstructures in three dimensions across a finite strain gradient. Here we examine the relationship and competition between grain-boundary cavitation and microstructural processes during deformation in a high-strain shear zone, and discuss the implications of these grain-scale deformation processes on strain localisation and continental fault zone dynamics.

  4. From ratites to rats: the size of fleshy fruits shapes species' distributions and continental rainforest assembly.

    PubMed

    Rossetto, Maurizio; Kooyman, Robert; Yap, Jia-Yee S; Laffan, Shawn W

    2015-12-01

    Seed dispersal is a key process in plant spatial dynamics. However, consistently applicable generalizations about dispersal across scales are mostly absent because of the constraints on measuring propagule dispersal distances for many species. Here, we focus on fleshy-fruited taxa, specifically taxa with large fleshy fruits and their dispersers across an entire continental rainforest biome. We compare species-level results of whole-chloroplast DNA analyses in sister taxa with large and small fruits, to regional plot-based samples (310 plots), and whole-continent patterns for the distribution of woody species with either large (more than 30 mm) or smaller fleshy fruits (1093 taxa). The pairwise genomic comparison found higher genetic distances between populations and between regions in the large-fruited species (Endiandra globosa), but higher overall diversity within the small-fruited species (Endiandra discolor). Floristic comparisons among plots confirmed lower numbers of large-fruited species in areas where more extreme rainforest contraction occurred, and re-colonization by small-fruited species readily dispersed by the available fauna. Species' distribution patterns showed that larger-fruited species had smaller geographical ranges than smaller-fruited species and locations with stable refugia (and high endemism) aligned with concentrations of large fleshy-fruited taxa, making them a potentially valuable conservation-planning indicator. PMID:26645199

  5. From ratites to rats: the size of fleshy fruits shapes species' distributions and continental rainforest assembly.

    PubMed

    Rossetto, Maurizio; Kooyman, Robert; Yap, Jia-Yee S; Laffan, Shawn W

    2015-12-01

    Seed dispersal is a key process in plant spatial dynamics. However, consistently applicable generalizations about dispersal across scales are mostly absent because of the constraints on measuring propagule dispersal distances for many species. Here, we focus on fleshy-fruited taxa, specifically taxa with large fleshy fruits and their dispersers across an entire continental rainforest biome. We compare species-level results of whole-chloroplast DNA analyses in sister taxa with large and small fruits, to regional plot-based samples (310 plots), and whole-continent patterns for the distribution of woody species with either large (more than 30 mm) or smaller fleshy fruits (1093 taxa). The pairwise genomic comparison found higher genetic distances between populations and between regions in the large-fruited species (Endiandra globosa), but higher overall diversity within the small-fruited species (Endiandra discolor). Floristic comparisons among plots confirmed lower numbers of large-fruited species in areas where more extreme rainforest contraction occurred, and re-colonization by small-fruited species readily dispersed by the available fauna. Species' distribution patterns showed that larger-fruited species had smaller geographical ranges than smaller-fruited species and locations with stable refugia (and high endemism) aligned with concentrations of large fleshy-fruited taxa, making them a potentially valuable conservation-planning indicator.

  6. Bark harvesting systems of Drimys brasiliensis Miers in the Brazilian Atlantic rainforest.

    PubMed

    Mariot, Alexandre; Mantovani, Adelar; Reis, Maurício S dos

    2014-09-01

    Drimys brasiliensis Miers, locally known as cataia or casca-de-anta, is a native tree species of the Atlantic Rainforest. Its bark is harvested from natural populations. This study examined the recovery capacity of the bark of D. brasiliensis under different bark harvesting methods, as well as the influence of these approaches on its population dynamics and reproductive biology. While none of these treatments resulted in changes in phenological behavior or the rate of increase of diameter at breast height and tree height, the removal of wider bark strips resulted in lower rates of bark recovery and higher rates of insect attack and diseases. Accordingly, the results recommend using strips of bark 2 cm wide and 2 m long, with 4 cm between strips, for effective rates of bark regrowth and for lower susceptibility to insect attack and diseases. From these studies, we concluded that D. brasiliensis has a high potential for sustainable management of its natural populations, demonstrating the possibility of generating an important supplementary income for farmers and contributing to the use and conservation of the Atlantic Rainforest. PMID:25119732

  7. Analysis of dynamic stall using unsteady boundary-layer theory. [effect of pitch rate on the delay in forward movement of the rear flow reversal point

    NASA Technical Reports Server (NTRS)

    Scruggs, R. M.; Nash, J. F.; Singleton, R. E.

    1974-01-01

    The unsteady turbulent boundary layer and potential flow about a pitching airfoil are analyzed using numerical methods to determine the effect of pitch rate on the delay in forward movement of the rear flow reversal point. An explicit finite difference scheme is used to integrate the unsteady boundary layer equations, which are coupled at each instant of time to a fully unsteady and nonlinear potential flow analysis. A substantial delay in forward movement of the reversal point is demonstrated with increasing pitch rate, and it is shown that the delay results partly from the alleviation of the gradients in the potential flow, and partly from the effects of unsteadiness in the boundary layer itself. The predicted delay in flow-reversal onset, and its variation with pitch rate, are shown to be in reasonable agreement with experimental data relating to the delay in dynamic stall. From the comparisons it can be concluded (a) that the effects of time-dependence are sufficient to explain the failure of the boundary layer to separate during the dynamic overshoot, and (b) that there may be some link between forward movement of the reversal point and dynamic stall.

  8. The energy-release rate and “self-force” of dynamically expanding spherical and plane inclusion boundaries with dilatational eigenstrain

    NASA Astrophysics Data System (ADS)

    Markenscoff, Xanthippi; Ni, Luqun

    2010-01-01

    In the context of the linear theory of elasticity with eigenstrains, the radiated field including inertia effects of a spherical inclusion with dilatational eigenstrain radially expanding is obtained on the basis of the dynamic Green's function, and one of the half-space inclusion boundary (with dilatational eigenstrain) moving from rest in general subsonic motion is obtained by a limiting process from the spherically expanding inclusion as the radius tends to infinity while the eigenstrain remains constrained, and this is the minimum energy solution. The global energy-release rate required to move the plane inclusion boundary and to create an incremental region of eigenstrain is defined analogously to the one for moving cracks and dislocations and represents the mechanical rate of work needed to be provide for the expansion of the inclusion. The calculated value, which is the "self-force" of the expanding inclusion, has a static component plus a dynamic one depending only on the current value of the velocity, while in the case of the spherical boundary, there is an additional contribution accounting for the jump in the strain at the farthest part at the back of the inclusion having the time to reach the front boundary, thus making the dynamic "self-force" history dependent.

  9. Lineage Range Estimation Method Reveals Fine-Scale Endemism Linked to Pleistocene Stability in Australian Rainforest Herpetofauna

    PubMed Central

    Rosauer, Dan F.; Catullo, Renee A.; VanDerWal, Jeremy; Moussalli, Adnan; Moritz, Craig

    2015-01-01

    Areas of suitable habitat for species and communities have arisen, shifted, and disappeared with Pleistocene climate cycles, and through this shifting landscape, current biodiversity has found paths to the present. Evolutionary refugia, areas of relative habitat stability in this shifting landscape, support persistence of lineages through time, and are thus crucial to the accumulation and maintenance of biodiversity. Areas of endemism are indicative of refugial areas where diversity has persisted, and endemism of intraspecific lineages in particular is strongly associated with late-Pleistocene habitat stability. However, it remains a challenge to consistently estimate the geographic ranges of intraspecific lineages and thus infer phylogeographic endemism, because spatial sampling for genetic analyses is typically sparse relative to species records. We present a novel technique to model the geographic distribution of intraspecific lineages, which is informed by the ecological niche of a species and known locations of its constituent lineages. Our approach allows for the effects of isolation by unsuitable habitat, and captures uncertainty in the extent of lineage ranges. Applying this method to the arc of rainforest areas spanning 3500 km in eastern Australia, we estimated lineage endemism for 53 species of rainforest dependent herpetofauna with available phylogeographic data. We related endemism to the stability of rainforest habitat over the past 120,000 years and identified distinct concentrations of lineage endemism that can be considered putative refugia. These areas of lineage endemism are strongly related to historical stability of rainforest habitat, after controlling for the effects of current environment. In fact, a dynamic stability model that allows movement to track suitable habitat over time was the most important factor in explaining current patterns of endemism. The techniques presented here provide an objective, practical method for estimating

  10. Lineage range estimation method reveals fine-scale endemism linked to Pleistocene stability in Australian rainforest herpetofauna.

    PubMed

    Rosauer, Dan F; Catullo, Renee A; VanDerWal, Jeremy; Moussalli, Adnan; Moritz, Craig

    2015-01-01

    Areas of suitable habitat for species and communities have arisen, shifted, and disappeared with Pleistocene climate cycles, and through this shifting landscape, current biodiversity has found paths to the present. Evolutionary refugia, areas of relative habitat stability in this shifting landscape, support persistence of lineages through time, and are thus crucial to the accumulation and maintenance of biodiversity. Areas of endemism are indicative of refugial areas where diversity has persisted, and endemism of intraspecific lineages in particular is strongly associated with late-Pleistocene habitat stability. However, it remains a challenge to consistently estimate the geographic ranges of intraspecific lineages and thus infer phylogeographic endemism, because spatial sampling for genetic analyses is typically sparse relative to species records. We present a novel technique to model the geographic distribution of intraspecific lineages, which is informed by the ecological niche of a species and known locations of its constituent lineages. Our approach allows for the effects of isolation by unsuitable habitat, and captures uncertainty in the extent of lineage ranges. Applying this method to the arc of rainforest areas spanning 3500 km in eastern Australia, we estimated lineage endemism for 53 species of rainforest dependent herpetofauna with available phylogeographic data. We related endemism to the stability of rainforest habitat over the past 120,000 years and identified distinct concentrations of lineage endemism that can be considered putative refugia. These areas of lineage endemism are strongly related to historical stability of rainforest habitat, after controlling for the effects of current environment. In fact, a dynamic stability model that allows movement to track suitable habitat over time was the most important factor in explaining current patterns of endemism. The techniques presented here provide an objective, practical method for estimating

  11. Calibration of Nitrogen Stable Isotopes and N-dynamics in a Western Boundary Current System (Brazil) during the Holocene

    NASA Astrophysics Data System (ADS)

    Albuquerque, A. L.; Fontana, L.

    2015-12-01

    This research documents changes in relative nitrate utilization and sources based on δ15N of nitrate and sinking particles in an oligotrophic Western Boundary to improve the efficience of the δ15N to provide an understanding of the N-dynamic during the Holocene from sediment records. The Continental Shelf of Southeastern Brazil is dominated by the oligotrophic Brazil Current, whose instabilities promote an untypical western boundary upwelling of South Atlantic Central Water (SACW) and consequently increases of primary productivity. The inorganic nitrogen concentration and the δ15N­nitrate and δ15N of sinking particles was characterized for each water masses present on the shelf (SACW, Tropical Water and Coastal Water). Cross­shelf gradients of nitrogen concentration and stable isotopes were observed. The SACW showed δ15N­nitrate signature around 5­6‰ characterizing the inner and mid­shelf conditions, where the input of new nitrate from upwelling is rapidly used by organisms in the euphotic zone without any fractionation. On the other hands, the dominance of N­ limited TW on the outer shelf provided a δ15N­nitrate and δ15N­sinking particles signals (­2.0 to 3.0‰) lower than the SACW average indicating N­fixation as a dominant source of nitrogen. The δ15N fractionation during upwelling events are also identified, but in smaller scale. The information of preliminary δ15N results from Holocene sediment record along a cross-shelf gradient showed values ranging from 3 to 8 ‰. In general, the tendency of low values recorded in middle Holocene indicates low availability of N during these low productivity stages. These results agreed pretty well with the δ13C records. In contrast, during late Holocene the values were heavy, probably indicating another processes (e.g. complete use of N-pool), which are still under investigation in association with another proxies (e.g. degraded pigments, opal, CaCO3).

  12. Vegetation-climate feedback causes reduced precipitation and tropical rainforest cover in CMIP5 regional Earth system model simulation over Africa

    NASA Astrophysics Data System (ADS)

    Wu, M.; Smith, B.; Samuelsson, P.; Rummukainen, M.; Schurgers, G.

    2012-12-01

    We applied a coupled regional climate-vegetation model, RCA-GUESS (Smith et al. 2011), over the CORDEX Africa domain, forced by boundary conditions from a CanESM2 CMIP5 simulation under the RCP8.5 future climate scenario. The simulations were from 1961 to 2100 and covered the African continent at a horizontal grid spacing of 0.44°. RCA-GUESS simulates changes in the phenology, productivity, relative cover and population structure of up to eight plant function types (PFTs) in response to forcing from the climate part of the model. These vegetation changes feed back to simulated climate through dynamic adjustments in surface energy fluxes and surface properties. Changes in the net ecosystem-atmosphere carbon flux and its components net primary production (NPP), heterotrophic respiration and emissions from biomass burning were also simulated but do not feed back to climate in our model. Constant land cover was assumed. We compared simulations with and without vegetation feedback switched "on" to assess the influence of vegetation-climate feedback on simulated climate, vegetation and ecosystem carbon cycling. Both positive and negative warming feedbacks were identified in different parts of Africa. In the Sahel savannah zone near 15°N, reduced vegetation cover and productivity, and mortality caused by a deterioration of soil water conditions led to a positive warming feedback mediated by decreased evapotranspiration and increased sensible heat flux between vegetation and the atmosphere. In the equatorial rainforest stronghold region of central Africa, a feedback syndrome characterised by reduced plant production and LAI, a dominance shift from tropical trees to grasses, reduced soil water and reduced rainfall was identified. The likely underlying mechanism was a decline in evaporative water recycling associated with sparser vegetation cover, reminiscent of Earth system model studies in which a similar feedback mechanism was simulated to force dieback of tropical

  13. A large-eddy simulation study of the impact of different land-atmosphere coupling schemes on the dynamics of the nocturnal boundary layer (Invited)

    NASA Astrophysics Data System (ADS)

    Stoll, J. R.; Shingleton, N. D.; Bosveld, F.

    2010-12-01

    Accurately reproducing the dynamic two-way interaction between the land surface and the atmosphere in the stable boundary layer (SBL) requires detailed treatment of the governing physical processes. Increasingly, large-eddy simulation (LES) is used for this purpose. In many studies, the dominant treatment of surface boundary conditions is to specify a known state or flux. This results in one-way or weak two-way coupling between the land surface and the boundary layer. The impact of how this coupling is modeled on atmospheric boundary layer (ABL) dynamics is still not fully understood, especially under transitional and weakly turbulent conditions. Here, LES that is fully coupled to a land-surface model (LSM) is used to investigate the nocturnal and the transitional periods of the diurnal cycle. The LSM explicitly solves for the transport of heat and water in a one-dimensional column of the upper soil and is coupled to the atmosphere through a surface energy budget. The fully coupled LES-LSM is used to simulate the third GEWEX (Global Energy and Water Cycle Experiment) ABL (GABLS3) LES intercomparison case. Turbulent boundary layer profiles and surface fluxes are compared to field data and results from simulations using three different levels of physical description as lower boundary conditions. These include simulations with prescribed temperature and moisture state, with a LSM that uses a bare-soil approximation and a LSM that include a skin layer. Overall, simulations with all three types of boundary conditions compare fairly well with the general trends observed in the field data for surface fluxes and boundary layer turbulence statistical profiles during the intercomparison time period (night to early morning) with a few differences. The LES-LSM model under-predicts the latent heat flux during the night and over-predicts the ground heat and moisture fluxes. The addition of a skin layer improves flux predictions during the night and early morning. Surface fluxes

  14. Exploring the likelihood and mechanism of a climate-change-induced dieback of the Amazon rainforest.

    PubMed

    Malhi, Yadvinder; Aragão, Luiz E O C; Galbraith, David; Huntingford, Chris; Fisher, Rosie; Zelazowski, Przemyslaw; Sitch, Stephen; McSweeney, Carol; Meir, Patrick

    2009-12-01

    We examine the evidence for the possibility that 21st-century climate change may cause a large-scale "dieback" or degradation of Amazonian rainforest. We employ a new framework for evaluating the rainfall regime of tropical forests and from this deduce precipitation-based boundaries for current forest viability. We then examine climate simulations by 19 global climate models (GCMs) in this context and find that most tend to underestimate current rainfall. GCMs also vary greatly in their projections of future climate change in Amazonia. We attempt to take into account the differences between GCM-simulated and observed rainfall regimes in the 20th century. Our analysis suggests that dry-season water stress is likely to increase in E. Amazonia over the 21st century, but the region tends toward a climate more appropriate to seasonal forest than to savanna. These seasonal forests may be resilient to seasonal drought but are likely to face intensified water stress caused by higher temperatures and to be vulnerable to fires, which are at present naturally rare in much of Amazonia. The spread of fire ignition associated with advancing deforestation, logging, and fragmentation may act as nucleation points that trigger the transition of these seasonal forests into fire-dominated, low biomass forests. Conversely, deliberate limitation of deforestation and fire may be an effective intervention to maintain Amazonian forest resilience in the face of imposed 21st-century climate change. Such intervention may be enough to navigate E. Amazonia away from a possible "tipping point," beyond which extensive rainforest would become unsustainable.

  15. Mechanisms and tempo of evolution in the African Guineo-Congolian rainforest.

    PubMed Central

    Plana, Vanessa

    2004-01-01

    This paper reviews how and when African rainforest diversity arose, presenting evidence from both plant and animal studies. Preliminary investigations show that these African forests are an assemblage of species of varying age. Phylogenetic evidence, from both African rainforest angiosperms and vertebrates, suggest a Tertiary origin for the major lineages in some of these groups. In groups where savannah species are well represented and rainforest species are a minority, the latter appear to be relics of a Mid-Tertiary rainforest. By contrast, species that are primarily adapted to rainforest have arisen in the past 10 Myr with the main morphological innovations dating from the Late Miocene, and Quaternary speciation dominating in large, morphologically homogeneous groups. The small number of species-level phylogenies for African rainforest plants hinders a more incisive and detailed study into the historical assembly of these continental forests. PMID:15519974

  16. Direct evidence for human reliance on rainforest resources in late Pleistocene Sri Lanka.

    PubMed

    Roberts, Patrick; Perera, Nimal; Wedage, Oshan; Deraniyagala, Siran; Perera, Jude; Eregama, Saman; Gledhill, Andrew; Petraglia, Michael D; Lee-Thorp, Julia A

    2015-03-13

    Human occupation of tropical rainforest habitats is thought to be a mainly Holocene phenomenon. Although archaeological and paleoenvironmental data have hinted at pre-Holocene rainforest foraging, earlier human reliance on rainforest resources has not been shown directly. We applied stable carbon and oxygen isotope analysis to human and faunal tooth enamel from four late Pleistocene-to-Holocene archaeological sites in Sri Lanka. The results show that human foragers relied primarily on rainforest resources from at least ~20,000 years ago, with a distinct preference for semi-open rainforest and rain forest edges. Homo sapiens' relationship with the tropical rainforests of South Asia is therefore long-standing, a conclusion that indicates the time-depth of anthropogenic reliance and influence on these habitats.

  17. Tropical rainforest response to marine sky brightening climate engineering

    NASA Astrophysics Data System (ADS)

    Muri, Helene; Niemeier, Ulrike; Kristjánsson, Jón Egill

    2015-04-01

    Tropical forests represent a major atmospheric carbon dioxide sink. Here the gross primary productivity (GPP) response of tropical rainforests to climate engineering via marine sky brightening under a future scenario is investigated in three Earth system models. The model response is diverse, and in two of the three models, the tropical GPP shows a decrease from the marine sky brightening climate engineering. Partial correlation analysis indicates precipitation to be important in one of those models, while precipitation and temperature are limiting factors in the other. One model experiences a reversal of its Amazon dieback under marine sky brightening. There, the strongest partial correlation of GPP is to temperature and incoming solar radiation at the surface. Carbon fertilization provides a higher future tropical rainforest GPP overall, both with and without climate engineering. Salt damage to plants and soils could be an important aspect of marine sky brightening.

  18. In Brief: Evolution teacher survey; Effects of drought on rainforest

    NASA Astrophysics Data System (ADS)

    Showstack, Randy

    2005-05-01

    More than 30% of teachers responding to an informal survey indicated that they feel pressured to include creationism, intelligent design, or other nonscientific alternatives to evolution in their science classrooms. An experiment to simulate the effects of climate change and severe drought on a parcel of rainforest in the Brazilian Amazon has found that some parts of the affected forest tolerated the dry condition by absorbing water from deeper in the soil.

  19. Hillslope hydrology in tropical rainforest steeplands in Brunei

    NASA Astrophysics Data System (ADS)

    Dykes, A. P.; Thornes, J. B.

    2000-02-01

    Many remaining areas of tropical rainforest in south-east Asia are located on landscapes dominated by deep valleys and very steep slopes. Now that logging activities are extending into these steeplands, it is essential to understand how the natural rainforest system behaves if any kind of realistic assessment of the effects of such disturbance is to be made. This paper examines the hydrological behaviour of an undisturbed rainforest system on steep topography in the Temburong District of Brunei, north-west Borneo. The physical and hydrological properties of the regolith material are generally typical of tropical residual soils. The regolith has a clay texture and a low dry bulk density beneath a superficial litter/organic horizon. The infiltration capacity of the surface soil was several hundred mm h-1. That of the exposed mineral subsoil was an order of magnitude less, similar to the saturated hydraulic conductivity (Ksat) of around 180 mm h-1 at a depth of 150 cm. There was no indication that Ksat reduced with depth except very near the bedrock interface.Soil tensions were measured using a two-dimensional array of tensiometers on a 30° slope. During dry season conditions, infiltrating rain-water contributes to soil moisture, and drying of the soil is dominated by transpiration losses. During wet season conditions, perched water tables quickly develop during heavy rainfall, giving rise to the rapid production of return flow in ephemeral channels. No infiltration excess or saturation overland flow was observed on hillslopes away from channel margins. Subsurface storm flow combined with return flow produce stream flow hydrographs with high peak discharges and very short lag times. Storm event runoff coefficients are estimated to be as high as 40%. It is concluded that the most distinctive feature of the hydrology of this steepland rainforest is the extremely flashy nature of the catchment runoff regime produced by the combination of thin but very permeable regolith

  20. Rainforest conservation as a strategy of climate policy.

    PubMed

    Cansier, Dieter

    2011-11-01

    Tropical forest conservation in developing countries has repeatedly been highlighted as a new element in international climate policy. However, no clear ideas yet exist as to what shape such a conservation strategy might take. In the present paper, we would like to make some observations to this end. It is shown how projects in order to reduce CO(2)-emissions resulting from deforestation and degradation (REDD) can be integrated into a system of tradable emission rights in an industrialised country and which requirements ought to be fulfilled. Instruments are emission credits and emission allowances. Driving actors interested in emission rights through forest projects may be private investors or the rainforest state itself. The efficiency of the system depends on a great extent on a binding reference path for the tolerable emissions from deforestation, which has been agreed upon and adhered to by the rainforest country by means of a forest law aimed at limiting deforestation. Our considerations lead us to conclude that the national baseline approach with an appropriate contribution by the rainforest country coupled with a decentralised system with private investors seems the most viable option. Since additional burdens are imposed on the rainforest country to some extent, a compromise could consist of agreeing on a moderate deforestation path, which is harmonised with the benefits from the forest projects. Combining both programmes (offset credits and emission allowances) is particularly attractive because all participants, and especially the industrialised country, benefit from it. The industrialised country can expand its climate conservation programme without any additional costs to a certain degree. PMID:22162964

  1. Dynamical behavior caused by numerical dynamo simulations in a rotating spherical shell with the heterogeneous outer boundary

    NASA Astrophysics Data System (ADS)

    Nakagawa, T.; Aubert, J.

    2013-12-01

    We use numerical dynamo simulations in a rotating spherical shell to investigate the thermal structure in the core influenced by the heterogeneous top boundary. The experimental study in a rotating hemispherical shell with huge anomalous heterogeneous outer boundary suggested that the ';front' structure caused by huge amplitude of thermal anomalies at the top boundary but not checked in the various dynamo regimes [Sumita and Olson, 2002], which predicted that the major physical mechanism for the ';front' structure could be understood by the thermal wind balance. Aurnou and Aubert [2011] suggested that there would be several regimes when the heterogeneous condition at the top boundary was imposed in numerical dynamo simulations but not investigated thermal structure in the core to check the experimental consequences as well as the regime transition between convective and boundary modulated dynamo regimes. Here we use two Ekman number (10^-4 and 3x10^-5) and fixed magnetic and thermal Prandtl number (the unity) with varying various Rayleigh number defined the amplitude of lateral variation of heat flux across the top boundary. The pattern of heterogeneous boundary condition is used as (l,m)=(2,2). The two or more ';fronts' are found in imposed heterogeneous boundary at least. These fronts are very small time-dependence for their positions with large lateral temperature variations near fronts. This means that the ';front' structure could be found in the MHD dynamo system as well as non-magnetic cases shown in Sumita and Olson [2002] because the Lorentz force contribution to thermal wind balance seems to be very weak compared to the buoyancy flux to balance the Coriolis effect. More information will be provided in the presentation.

  2. Linking biogenic hydrocarbons to biogenic aerosol in the Borneo rainforest

    NASA Astrophysics Data System (ADS)

    Hamilton, J. F.; Alfarra, M. R.; Robinson, N.; Ward, M. W.; Lewis, A. C.; McFiggans, G. B.; Coe, H.; Allan, J. D.

    2013-11-01

    Emissions of biogenic volatile organic compounds are though to contribute significantly to secondary organic aerosol formation in the tropics, but understanding these transformation processes has proved difficult, due to the complexity of the chemistry involved and very low concentrations. Aerosols from above a Southeast Asian tropical rainforest in Borneo were characterised using liquid chromatography-ion trap mass spectrometry, high-resolution aerosol mass spectrometry and Fourier transform ion cyclotron resonance mass spectrometry (FTICRMS) techniques. Oxygenated compounds were identified in ambient organic aerosol that could be directly traced back to isoprene, monoterpenes and sesquiterpene emissions, by combining field data on chemical structures with mass spectral data generated from synthetically produced products created in a simulation chamber. Eighteen oxygenated species of biogenic origin were identified in the rainforest aerosol from the precursors isoprene, α-pinene, limonene, α-terpinene and β-caryophyllene. The observations provide the unambiguous field detection of monoterpene and sesquiterpene oxidation products in SOA above a pristine tropical rainforest. The presence of 2-methyl tetrol organosulfates and an associated sulfated dimer provides direct evidence that isoprene in the presence of sulfate aerosol can make a contribution to biogenic organic aerosol above tropical forests. High-resolution mass spectrometry indicates that sulfur can also be incorporated into oxidation products arising from monoterpene precursors in tropical aerosol.

  3. Linking biogenic hydrocarbons to biogenic aerosol in the Borneo rainforest

    NASA Astrophysics Data System (ADS)

    Hamilton, J. F.; Alfarra, M. R.; Robinson, N.; Ward, M. W.; Lewis, A. C.; McFiggans, G. B.; Coe, H.; Allan, J. D.

    2013-07-01

    Emissions of biogenic volatile organic compounds are though to contribute significantly to secondary organic aerosol formation in the tropics, but understanding the process of these transformations has proved difficult, due to the complexity of the chemistry involved and very low concentrations. Aerosols from above a South East Asian tropical rainforest in Borneo were characterised using liquid chromatography-ion trap mass spectrometry, high resolution aerosol mass spectrometry and fourier transform ion cyclotron resonance mass spectrometry (FTICRMS) techniques. Oxygenated compounds were identified in ambient organic aerosol that could be directly traced back to isoprene, monoterpenes and sesquiterpene emissions, by combining field data on chemical structures with mass spectral data generated from synthetically produced products created in a simulation chamber. Eighteen oxygenated species of biogenic origin were identified in the rainforest aerosol from the precursors isoprene, α-pinene, limonene, α-terpinene and β-caryophyllene. The observations provide the unambiguous field detection of monoterpene and sesquiterpene oxidation products in SOA above a pristine tropical rainforest. The presence of 2-methyltetrol organosulfates and an associated sulfated dimer provides direct evidence that isoprene in the presence of sulfate aerosol can make a contribution to biogenic organic aerosol above tropical forests. High-resolution mass spectrometry indicates that sulfur can also be incorporated into oxidation products arising from monoterpene precursors in tropical aerosol.

  4. [Relationship between antophyte foliar morphology and abiotic factors in the main rainforests of Eastern Cuba].

    PubMed

    Quesada, Eddy Martínez

    2009-01-01

    Relationship between antophyte foliar morphology and abiotic factors in the main rainforests of Eastern Cuba. The foliar morphology of representative antophytes in four rainforest types of Eastern Cuba was studied in relation to the main abiotic factors. Although there are several leaf types in these forests, the microphyll type is the most important among endemic species in the ophiolites complex and the Montane rainforest. At the Lowland rainforest (metamorphic complex) the mesophyll leaf was the most important. Most foliar epidermis had structures normally found in mesomorphic plants, but xeromorphic and higromorphic morphologies were also present. PMID:19637704

  5. A Theoretical and Experimental Investigation of Energy-Containing Scales in the Dynamic Sublayer of Boundary-Layer Flows

    NASA Astrophysics Data System (ADS)

    Katul, Gabriel; Chu, Chia-Ren

    The existence of universal power laws at low wavenumbers (K) in the energy spectrum (Eu) of the turbulent longitudinal velocity (u) is examined theoretically and experimentally for the near-neutral atmospheric surface layer. Newly derived power-law solutions to Tchen's approximate integral spectral budget equation are tested for strong- and weak-interaction cases between the mean flow and turbulent vorticity fields. To verify whether these solutions reproduce the measured Eu at low wavenumbers, velocity measurements were collected in the dynamic sublayer of the atmosphere at three sites and in the inner region of a laboratory open channel. The atmospheric surface layer measurements were carried out using triaxial sonic anemometers over tall corn, short grass, and smooth desert-like sandy soil. The open channel measurements were performed using a two-dimensional boundary-layer probe above a smooth stainless steel bed. Comparisons between the proposed analytical solution for Eu, the dimensional analysis by Kader and Yaglom, and the measured Haar wavelet Eu spectra are presented. It is shown that when strong interaction between the mean flow and turbulent vorticity field occurs, wavelet spectra measurements, predictions by the analytical solution, and predictions by the dimensional analysis of Kader-Yaglom (KY) are all in good agreement and confirm the existence of a -1 power law in Eu(= Cuuu2 * K-1, where Cuu is a constant and u* is the friction velocity). The normalized upper wavenumber limit of the -1 power law (Kz = 1, where z is the height above the zero-plane displacement) is estimated using two separate approaches and compared to the open channel and atmospheric surface-layer measurements. It is demonstrated that the measured upper wavenumber limit is consistent with Tchen's budget but not with the KY assumptions. The constraints as to whether the mean flow and turbulent vorticity strongly interact are considered using a proposed analysis by Panchev. It is

  6. A phase-field approach to no-slip boundary conditions in dissipative particle dynamics and other particle models for fluid flow in geometrically complex confined systems.

    PubMed

    Xu, Zhijie; Meakin, Paul

    2009-06-21

    Dissipative particle dynamics (DPD) is an effective mesoscopic particle model with a lower computational cost than molecular dynamics because of the soft potentials that it employs. However, the soft potential is not strong enough to prevent the DPD particles that are used to represent the fluid from penetrating solid boundaries represented by stationary DPD particles. A phase-field variable, phi(x,t), is used to indicate the phase at point x and time t, with a smooth transition from -1 (phase 1) to +1 (phase 2) across the interface. We describe an efficient implementation of no-slip boundary conditions in DPD models that combines solid-liquid particle-particle interactions with reflection at a sharp boundary located with subgrid scale accuracy using the phase field. This approach can be used for arbitrarily complex flow geometries and other similar particle models (such as smoothed particle hydrodynamics), and the validity of the model is demonstrated by DPD simulations of flow in confined systems with various geometries.

  7. The current refugial rainforests of Sundaland are unrepresentative of their biogeographic past and highly vulnerable to disturbance

    PubMed Central

    Cannon, Charles H.; Morley, Robert J.; Bush, Andrew B. G.

    2009-01-01

    Understanding the historical dynamics of forest communities is a critical element for accurate prediction of their response to future change. Here, we examine evergreen rainforest distribution in the Sunda Shelf region at the last glacial maximum (LGM), using a spatially explicit model incorporating geographic, paleoclimatic, and geologic evidence. Results indicate that at the LGM, Sundaland rainforests covered a substantially larger area than currently present. Extrapolation of the model over the past million years demonstrates that the current “island archipelago” setting in Sundaland is extremely unusual given the majority of its history and the dramatic biogeographic transitions caused by global deglaciation were rapid and brief. Compared with dominant glacial conditions, lowland forests were probably reduced from approximately 1.3 to 0.8 × 106 km2 while upland forests were probably reduced by half, from approximately 2.0 to 1.0 × 105 km2. Coastal mangrove and swamp forests experienced the most dramatic change during deglaciations, going through a complete and major biogeographic relocation. The Sundaland forest dynamics of fragmentation and contraction and subsequent expansion, driven by glacial cycles, occur in the opposite phase as those in the northern hemisphere and equatorial Africa, indicating that Sundaland evergreen rainforest communities are currently in a refugial stage. Widespread human-mediated reduction and conversion of these forests in their refugial stage, when most species are passing through significant population bottlenecks, strongly emphasizes the urgency of conservation and management efforts. Further research into the natural process of fragmentation and contraction during deglaciation is necessary to understand the long-term effect of human activity on forest species. PMID:19549829

  8. Comparison of carbon uptake estimates from forest inventory and Eddy-Covariance for a montane rainforest in central Sulawesi

    NASA Astrophysics Data System (ADS)

    Heimsch, Florian; Kreilein, Heiner; Rauf, Abdul; Knohl, Alexander

    2016-04-01

    Rainforests in general and montane rainforests in particular have rarely been studied over longer time periods. We aim to provide baseline information of a montane tropical forest's carbon uptake over time in order to quantify possible losses through land-use change. Thus we conducted a re-inventory of 22 10-year old forest inventory plots, giving us a rare opportunity to quantify carbon uptake over such a long time period by traditional methods. We discuss shortfalls of such techniques and why our estimate of 1.5 Mg/ha/a should be considered as the lower boundary and not the mean carbon uptake per year. At the same location as the inventory, CO2 fluxes were measured with the Eddy-Covariance technique. Measurements were conducted at 48m height with an LI 7500 open-path infrared gas analyser. We will compare carbon uptake estimates from these measurements to those of the more conventional inventory method and discuss, which factors are probably responsible for differences.

  9. A Deep Quench Approach to the Optimal Control of an Allen–Cahn Equation with Dynamic Boundary Conditions and Double Obstacles

    SciTech Connect

    Colli, Pierluigi; Farshbaf-Shaker, M. Hassan Sprekels, Jürgen

    2015-02-15

    In this paper, we investigate optimal control problems for Allen-Cahn variational inequalities with a dynamic boundary condition involving double obstacle potentials and the Laplace-Beltrami operator. The approach covers both the cases of distributed controls and of boundary controls. The cost functional is of standard tracking type, and box constraints for the controls are prescribed. We prove existence of optimal controls and derive first-order necessary conditions of optimality. The general strategy is the following: we use the results that were recently established by two of the authors for the case of (differentiable) logarithmic potentials and perform a so-called “deep quench limit”. Using compactness and monotonicity arguments, it is shown that this strategy leads to the desired first-order necessary optimality conditions for the case of (non-differentiable) double obstacle potentials.

  10. Individual Species-Area Relationship of Woody Plant Communities in a Heterogeneous Subtropical Monsoon Rainforest

    PubMed Central

    Tsai, Cheng-Han; Lin, Yi-Ching; Wiegand, Thorsten; Nakazawa, Takefumi; Su, Sheng-Hsin

    2015-01-01

    The spatial structure of species richness is often characterized by the species-area relationship (SAR). However, the SAR approach rarely considers the spatial variability of individual plants that arises from species interactions and species’ habitat associations. Here, we explored how the interactions of individual plants of target species influence SAR patterns at a range of neighborhood distances. We analyzed the data of 113,988 woody plants of 110 species from the Fushan Forest Dynamics Plot (25 ha), northern Taiwan, which is a subtropical rainforest heavily influenced by typhoons. We classified 34 dominant species into 3 species types (i.e., accumulator, repeller, or no effect) by testing how the individual species-area relationship (i.e., statistics describing how neighborhood species richness changes around individuals) of target species departs (i.e., positively, negatively, or with no obvious trend) from a null model that accounts for habitat association. Deviation from the null model suggests that the net effect of species’ interactions increases (accumulate) or decreases (repel) neighborhood species richness. We found that (i) accumulators were dominant at small interaction distances (<10–30 m); (ii) the detection of accumulator species was lower at large interaction distances (>30 m); (iii) repellers were rarely detected; and (iv) large-sized and abundant species tended to be accumulators. The findings suggest that positive species interactions have the potential to accumulate neighborhood species richness, particularly through size- and density-dependent mechanisms. We hypothesized that the frequently disturbed environment of this subtropical rainforest (e.g., typhoon-driven natural disturbances such as landslides, soil erosion, flooding, and windthrow) might create the spatial heterogeneity of species richness and promote positive species interactions. PMID:25884405

  11. Individual species-area relationship of woody plant communities in a heterogeneous subtropical monsoon rainforest.

    PubMed

    Tsai, Cheng-Han; Lin, Yi-Ching; Wiegand, Thorsten; Nakazawa, Takefumi; Su, Sheng-Hsin; Hsieh, Chih-Hao; Ding, Tzung-Su

    2015-01-01

    The spatial structure of species richness is often characterized by the species-area relationship (SAR). However, the SAR approach rarely considers the spatial variability of individual plants that arises from species interactions and species' habitat associations. Here, we explored how the interactions of individual plants of target species influence SAR patterns at a range of neighborhood distances. We analyzed the data of 113,988 woody plants of 110 species from the Fushan Forest Dynamics Plot (25 ha), northern Taiwan, which is a subtropical rainforest heavily influenced by typhoons. We classified 34 dominant species into 3 species types (i.e., accumulator, repeller, or no effect) by testing how the individual species-area relationship (i.e., statistics describing how neighborhood species richness changes around individuals) of target species departs (i.e., positively, negatively, or with no obvious trend) from a null model that accounts for habitat association. Deviation from the null model suggests that the net effect of species' interactions increases (accumulate) or decreases (repel) neighborhood species richness. We found that (i) accumulators were dominant at small interaction distances (<10-30 m); (ii) the detection of accumulator species was lower at large interaction distances (>30 m); (iii) repellers were rarely detected; and (iv) large-sized and abundant species tended to be accumulators. The findings suggest that positive species interactions have the potential to accumulate neighborhood species richness, particularly through size- and density-dependent mechanisms. We hypothesized that the frequently disturbed environment of this subtropical rainforest (e.g., typhoon-driven natural disturbances such as landslides, soil erosion, flooding, and windthrow) might create the spatial heterogeneity of species richness and promote positive species interactions.

  12. Individual species-area relationship of woody plant communities in a heterogeneous subtropical monsoon rainforest.

    PubMed

    Tsai, Cheng-Han; Lin, Yi-Ching; Wiegand, Thorsten; Nakazawa, Takefumi; Su, Sheng-Hsin; Hsieh, Chih-Hao; Ding, Tzung-Su

    2015-01-01

    The spatial structure of species richness is often characterized by the species-area relationship (SAR). However, the SAR approach rarely considers the spatial variability of individual plants that arises from species interactions and species' habitat associations. Here, we explored how the interactions of individual plants of target species influence SAR patterns at a range of neighborhood distances. We analyzed the data of 113,988 woody plants of 110 species from the Fushan Forest Dynamics Plot (25 ha), northern Taiwan, which is a subtropical rainforest heavily influenced by typhoons. We classified 34 dominant species into 3 species types (i.e., accumulator, repeller, or no effect) by testing how the individual species-area relationship (i.e., statistics describing how neighborhood species richness changes around individuals) of target species departs (i.e., positively, negatively, or with no obvious trend) from a null model that accounts for habitat association. Deviation from the null model suggests that the net effect of species' interactions increases (accumulate) or decreases (repel) neighborhood species richness. We found that (i) accumulators were dominant at small interaction distances (<10-30 m); (ii) the detection of accumulator species was lower at large interaction distances (>30 m); (iii) repellers were rarely detected; and (iv) large-sized and abundant species tended to be accumulators. The findings suggest that positive species interactions have the potential to accumulate neighborhood species richness, particularly through size- and density-dependent mechanisms. We hypothesized that the frequently disturbed environment of this subtropical rainforest (e.g., typhoon-driven natural disturbances such as landslides, soil erosion, flooding, and windthrow) might create the spatial heterogeneity of species richness and promote positive species interactions. PMID:25884405

  13. Influence of Dynamics and Chemistry on the Diurnal Variation of VOCs in the Planetary Boundary Layer above a Mixed Forest Canopy in the Southeastern United States

    NASA Astrophysics Data System (ADS)

    Guenther, A. B.; Su, L.; Patton, E. G.; Vila-Guerau Arellano, J.; Mak, J. E.

    2014-12-01

    The planetary boundary layer (PBL) is a region of inherent interest because reactive VOCs emitted from the forest canopy are mixed with the residual and free tropospheric air masses, oxidized, and/or otherwise removed in this region. The characterization of diurnal variation of VOCs in the PBL is limited due to the lack of appropriate sampling platforms that are able to probe all the regions of interest: from the surface to the entrainment zone. Here we present the application of the Whole Air Sample Profiler (WASP) system during the 2013 Southeast Atmosphere Study (SAS) campaign. A total of 41 research flights (RFs) were carried out during the 2013 SAS campaign between June 1 and June 14 over the Alabama Aquatic Biodiversity Center (AABC) site and the SEARCH site. During each RF, ambient air sampling started from 50-100 m above the canopy top and stopped at ~1200 m above the mean sea level (a.m.s.l). The air samples were subsequently analyzed by using a proton-transfer-reaction time-of-flight mass spectrometry (PTR-TOF-MS). Here we analyze the vertical profiles and averaged diurnal variation of the mixing ratios of several reactive VOC species, including isoprene, the sum of monoterpenes, and first generation oxidation products of isoprene: methyl vinyl ketone and methacrolein (MVK+MACR). A MiXed Layer Chemistry (MXLCH) model, guided by the meteorological and chemical observations during the SAS campaign, is used to study the influence of boundary layer dynamics and new isoprene oxidation mechanism on the diurnal variation of major biogenic VOCs emitted from the forest canopy. The new scheme includes OH recycling through two pathways under low-NOx regime: (1) hydroxyl peroxy radicals (HOC5H8OO•; ISOPO2) unimolecular isomerization, and (2) ISOPO2+HO2. The model is able to reproduce the evolution of the boundary layer dynamics (including potential temperature, and boundary layer height) during the selected simulation dates. Based on the model results, budget

  14. Boundary Crossing and Boundary Objects

    ERIC Educational Resources Information Center

    Akkerman, Sanne F.; Bakker, Arthur

    2011-01-01

    Diversity and mobility in education and work present a paramount challenge that needs better conceptualization in educational theory. This challenge has been addressed by educational scholars with the notion of "boundaries", particularly by the concepts of "boundary crossing" and "boundary objects". Although studies on boundary crossing and…

  15. Biodiversity and Peace: Where Technology and Montessori Come Together in the Children's Eternal Rainforest, Costa Rica

    ERIC Educational Resources Information Center

    Norris, Jeff

    2016-01-01

    Jeff Norris, initially shocked by the Montessorians who are calling technology into question, states that technology can offer a means of development for the child who is concurrently supporting and learning from the rich and overpowering biodiversity of the rainforest. He speaks for the Children's Eternal Rainforest citizen's science as well as…

  16. Bacillus spp. from rainforest soil promote plant growth under limited nitrogen conditions

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Aims: The aim of this study was to evaluate effects of PGPR (Plant Growth Promoting Rhizobacteria) isolated from rainforest on different plants under limited nitrogen conditions. Methods and Results: Bacterial isolates from a Peruvian rainforest soil were screened for plant growth promoting effects...

  17. Computer simulation model of ecological succession in Australian subtropical rainforest. Environmental Sciences Division Publication No. 1407

    SciTech Connect

    Shugart, H.H.; Mortlock, A.T.; Hopkins, M.S.; Burgess, I.P.

    1980-04-01

    KIAMBRAM, a detailed simulation model for ecological succession in an Australian subtropical humid rainforest is documented in respect to model structure. Model parameters for 125 rainforest tree species are provided. A listing of the KIAMBRAM model and a sample of output from the model is included.

  18. (En)Countering Social and Environmental Messages in the Rainforest Cafe [sic], Children's Picturebooks, and Other Visual Culture Sites

    ERIC Educational Resources Information Center

    Reisberg, Mira; Han, Sandrine

    2009-01-01

    Our study critically examines social and environmental messages in a range of visual sites educating about rainforest environments. We focus primarily on the Rainforest Cafe, an international series of rainforest-themed edutainment restaurant/stores, whose inherent contradictions between consumption and conservation are quite disturbing when…

  19. Tropical Rainforests: A Case Study of UK, 13-Year-Olds' Knowledge and Understanding of These Environments

    ERIC Educational Resources Information Center

    Dove, Jane

    2012-01-01

    Tropical rainforests are biologically rich ecosystems, which are threatened by a variety of different human activities. This study focuses on students' knowledge and understanding of rainforest locations, their reasons for protecting these environments and their familiarity with selected concepts about rainforest vegetation and soil. These…

  20. Replicated throughfall exclusion experiment in an Indonesian perhumid rainforest: wood production, litter fall and fine root growth under simulated drought.

    PubMed

    Moser, Gerald; Schuldt, Bernhard; Hertel, Dietrich; Horna, Viviana; Coners, Heinz; Barus, Henry; Leuschner, Christoph

    2014-05-01

    Climate change scenarios predict increases in the frequency and duration of ENSO-related droughts for parts of South-East Asia until the end of this century exposing the remaining rainforests to increasing drought risk. A pan-tropical review of recorded drought-related tree mortalities in more than 100 monitoring plots before, during and after drought events suggested a higher drought-vulnerability of trees in South-East Asian than in Amazonian forests. Here, we present the results of a replicated (n = 3 plots) throughfall exclusion experiment in a perhumid tropical rainforest in Sulawesi, Indonesia. In this first large-scale roof experiment outside semihumid eastern Amazonia, 60% of the throughfall was displaced during the first 8 months and 80% during the subsequent 17 months, exposing the forest to severe soil desiccation for about 17 months. In the experiment's second year, wood production decreased on average by 40% with largely different responses of the tree families (ranging from -100 to +100% change). Most sensitive were trees with high radial growth rates under moist conditions. In contrast, tree height was only a secondary factor and wood specific gravity had no influence on growth sensitivity. Fine root biomass was reduced by 35% after 25 months of soil desiccation while fine root necromass increased by 250% indicating elevated fine root mortality. Cumulative aboveground litter production was not significantly reduced in this period. The trees from this Indonesian perhumid rainforest revealed similar responses of wood and litter production and root dynamics as those in two semihumid Amazonian forests subjected to experimental drought. We conclude that trees from paleo- or neotropical forests growing in semihumid or perhumid climates may not differ systematically in their growth sensitivity and vitality under sublethal drought stress. Drought vulnerability may depend more on stem cambial activity in moist periods than on tree height or wood

  1. Replicated throughfall exclusion experiment in an Indonesian perhumid rainforest: wood production, litter fall and fine root growth under simulated drought.

    PubMed

    Moser, Gerald; Schuldt, Bernhard; Hertel, Dietrich; Horna, Viviana; Coners, Heinz; Barus, Henry; Leuschner, Christoph

    2014-05-01

    Climate change scenarios predict increases in the frequency and duration of ENSO-related droughts for parts of South-East Asia until the end of this century exposing the remaining rainforests to increasing drought risk. A pan-tropical review of recorded drought-related tree mortalities in more than 100 monitoring plots before, during and after drought events suggested a higher drought-vulnerability of trees in South-East Asian than in Amazonian forests. Here, we present the results of a replicated (n = 3 plots) throughfall exclusion experiment in a perhumid tropical rainforest in Sulawesi, Indonesia. In this first large-scale roof experiment outside semihumid eastern Amazonia, 60% of the throughfall was displaced during the first 8 months and 80% during the subsequent 17 months, exposing the forest to severe soil desiccation for about 17 months. In the experiment's second year, wood production decreased on average by 40% with largely different responses of the tree families (ranging from -100 to +100% change). Most sensitive were trees with high radial growth rates under moist conditions. In contrast, tree height was only a secondary factor and wood specific gravity had no influence on growth sensitivity. Fine root biomass was reduced by 35% after 25 months of soil desiccation while fine root necromass increased by 250% indicating elevated fine root mortality. Cumulative aboveground litter production was not significantly reduced in this period. The trees from this Indonesian perhumid rainforest revealed similar responses of wood and litter production and root dynamics as those in two semihumid Amazonian forests subjected to experimental drought. We conclude that trees from paleo- or neotropical forests growing in semihumid or perhumid climates may not differ systematically in their growth sensitivity and vitality under sublethal drought stress. Drought vulnerability may depend more on stem cambial activity in moist periods than on tree height or wood

  2. Mapping Biodiversity and Setting Conservation Priorities for SE Queensland’s Rainforests Using DNA Barcoding

    PubMed Central

    Shapcott, Alison; Forster, Paul I.; Guymer, Gordon P.; McDonald, William J. F.; Faith, Daniel P.; Erickson, David; Kress, W. John

    2015-01-01

    Australian rainforests have been fragmented due to past climatic changes and more recently landscape change as a result of clearing for agriculture and urban spread. The subtropical rainforests of South Eastern Queensland are significantly more fragmented than the tropical World Heritage listed northern rainforests and are subject to much greater human population pressures. The Australian rainforest flora is relatively taxonomically rich at the family level, but less so at the species level. Current methods to assess biodiversity based on species numbers fail to adequately capture this richness at higher taxonomic levels. We developed a DNA barcode library for the SE Queensland rainforest flora to support a methodology for biodiversity assessment that incorporates both taxonomic diversity and phylogenetic relationships. We placed our SE Queensland phylogeny based on a three marker DNA barcode within a larger international rainforest barcode library and used this to calculate phylogenetic diversity (PD). We compared phylo- diversity measures, species composition and richness and ecosystem diversity of the SE Queensland rainforest estate to identify which bio subregions contain the greatest rainforest biodiversity, subregion relationships and their level of protection. We identified areas of highest conservation priority. Diversity was not correlated with rainforest area in SE Queensland subregions but PD was correlated with both the percent of the subregion occupied by rainforest and the diversity of regional ecosystems (RE) present. The patterns of species diversity and phylogenetic diversity suggest a strong influence of historical biogeography. Some subregions contain significantly more PD than expected by chance, consistent with the concept of refugia, while others were significantly phylogenetically clustered, consistent with recent range expansions. PMID:25803607

  3. Late Holocene and recent rainforest cultural landscapes of North Queensland, Australia

    NASA Astrophysics Data System (ADS)

    Steinberger, L. M.; Moss, P. T.; Haberle, S.; Cosgrove, R.; Ferrier

    2011-12-01

    The tropical rainforests of North Queensland, Australia, have been environments of significant human activity for several thousand years. Palaeoecological research has highlighted the long-term effects of Quaternary climate change on these environments at a broad spatial scale, including the expansion of tropical rainforest across the region following the termination of the Last Glacial Maximum. However, identifying the effects of a hunter-gatherer Aboriginal population has been more difficult. Palaeoecological suggestions of Pleistocene Aboriginal burning, based on pollen and charcoal records, have relied on coincident timing with a general narrative of colonisation rather than direct links with archaeological evidence. Current research is explicitly examining the environmental consequences of human activity in North Queensland rainforests by producing local palaeoecological data directly linked to sites and periods of human occupation. Pollen, macrocharcoal and phytolith records have been produced from sites of human activity within the rainforest. Late Holocene Aboriginal occupation of the rainforest is demonstrated to have had significant cultural links to patches of open vegetation that existed within the rainforest. While these patches are likely to have originated as edaphically controlled remnants of Pleistocene vegetation, their expansion and maintenance in the late Holocene is associated with increasing intensity of Aboriginal occupation of the rainforest. Late Holocene Aboriginal rainforest occupation is also contrasted with the historical European colonisation of the rainforest in the late 19th century, which resulted in the most significant environmental changes in the region since the early Holocene. Historical and ethnographic records provide important cultural context for understanding the transition between Aboriginal and European cultural landscapes of the rainforest.

  4. Thermo-fluid-dynamics of turbulent boundary layer over a moving continuous flat sheet in a parallel free stream

    NASA Astrophysics Data System (ADS)

    Afzal, Bushra; Noor Afzal Team; Bushra Afzal Team

    2014-11-01

    The momentum and thermal turbulent boundary layers over a continuous moving sheet subjected to a free stream have been analyzed in two layers (inner wall and outer wake) theory at large Reynolds number. The present work is based on open Reynolds equations of momentum and heat transfer without any closure model say, like eddy viscosity or mixing length etc. The matching of inner and outer layers has been carried out by Izakson-Millikan-Kolmogorov hypothesis. The matching for velocity and temperature profiles yields the logarithmic laws and power laws in overlap region of inner and outer layers, along with friction factor and heat transfer laws. The uniformly valid solution for velocity, Reynolds shear stress, temperature and thermal Reynolds heat flux have been proposed by introducing the outer wake functions due to momentum and thermal boundary layers. The comparison with experimental data for velocity profile, temperature profile, skin friction and heat transfer are presented. In outer non-linear layers, the lowest order momentum and thermal boundary layer equations have also been analyses by using eddy viscosity closure model, and results are compared with experimental data. Retired Professor, Embassy Hotel, Rasal Ganj, Aligarh 202001 India.

  5. Molecular dynamics simulations of ion solvation by flexible-boundary QM/MM: on-the-fly partial charge transfer between QM and MM subsystems.

    PubMed

    Pezeshki, Soroosh; Lin, Hai

    2014-09-15

    The flexible-boundary (FB) quantum mechanical/molecular mechanical (QM/MM) scheme accounts for partial charge transfer between the QM and MM subsystems. Previous calculations have demonstrated excellent performance of FB-QM/MM in geometry optimizations. This article reports an implementation to extend FB-QM/MM to molecular dynamics simulations. To prevent atoms from getting unreasonably close, which can lead to polarization catastrophe, empirical correcting functions are introduced to provide additive penalty energies for the involved atom pairs and to improve the descriptions of the repulsive exchange forces in FB-QM/MM calculations. Test calculations are carried out for chloride, lithium, sodium, and ammonium ions solvated in water. Comparisons with conventional QM/MM calculations suggest that the FB treatment provides reasonably good results for the charge distributions of the atoms in the QM subsystems and for the solvation shell structural properties, albeit smaller QM subsystems have been used in the FB-QM/MM dynamics simulations.

  6. Topology of sustainable management of dynamical systems with desirable states: from defining planetary boundaries to safe operating spaces in the Earth System

    NASA Astrophysics Data System (ADS)

    Heitzig, Jobst; Kittel, Tim; Donges, Jonathan; Molkenthin, Nora

    2016-04-01

    To keep the Earth System in a desirable region of its state space, such as defined by the recently suggested "tolerable environment and development window", "guardrails", "planetary boundaries", or "safe (and just) operating space for humanity", one not only needs to understand the quantitative internal dynamics of the system and the available options for influencing it (management), but also the structure of the system's state space with regard to certain qualitative differences. Important questions are: Which state space regions can be reached from which others with or without leaving the desirable region? Which regions are in a variety of senses "safe" to stay in when management options might break away, and which qualitative decision problems may occur as a consequence of this topological structure? In this work, we develop a mathematical theory of the qualitative topology of the state space of a dynamical system with management options and desirable states, as a complement to the existing literature on optimal control which is more focussed on quantitative optimization and is much applied in both the engineering and the integrated assessment literature. We suggest a certain terminology for the various resulting regions of the state space and perform a detailed formal classification of the possible states with respect to the possibility of avoiding or leaving the undesired region. Our results indicate that before performing some form of quantitative optimization such as of indicators of human well-being for achieving certain sustainable development goals, a sustainable and resilient management of the Earth System may require decisions of a more discrete type that come in the form of several dilemmas, e.g., choosing between eventual safety and uninterrupted desirability, or between uninterrupted safety and larger flexibility. We illustrate the concepts and dilemmas drawing on conceptual models from climate science, ecology, coevolutionary Earth System modeling

  7. A molecular dynamics study of the effect of thermal boundary conductance on thermal transport of ideal crystal of n-alkanes with different number of carbon atoms

    NASA Astrophysics Data System (ADS)

    Rastgarkafshgarkolaei, Rouzbeh; Zeng, Yi; Khodadadi, J. M.

    2016-05-01

    Phase change materials such as n-alkanes that exhibit desirable characteristics such as high latent heat, chemical stability, and negligible supercooling are widely used in thermal energy storage applications. However, n-alkanes have the drawback of low thermal conductivity values. The low thermal conductivity of n-alkanes is linked to formation of randomly oriented nano-domains of molecules in their solid structure that is responsible for excessive phonon scattering at the grain boundaries. Thus, understanding the thermal boundary conductance at the grain boundaries can be crucial for improving the effectiveness of thermal storage systems. The concept of the ideal crystal is proposed in this paper, which describes a simplified model such that all the nano-domains of long-chain n-alkanes are artificially aligned perfectly in one direction. In order to study thermal transport of the ideal crystal of long-chain n-alkanes, four (4) systems (C20H42, C24H50, C26H54, and C30H62) are investigated by the molecular dynamics simulations. Thermal boundary conductance between the layers of ideal crystals is determined using both non-equilibrium molecular dynamics (NEMD) and equilibrium molecular dynamics (EMD) simulations. Both NEMD and EMD simulations exhibit no significant change in thermal conductance with the molecular length. However, the values obtained from the EMD simulations are less than the values from NEMD simulations with the ratio being nearly three (3) in most cases. This difference is due to the nature of EMD simulations where all the phonons are assumed to be in equilibrium at the interface. Thermal conductivity of the n-alkanes in three structures including liquid, solid, and ideal crystal is investigated utilizing NEMD simulations. Our results exhibit a very slight rise in thermal conductivity values as the number of carbon atoms of the chain increases. The key understanding is that thermal transport can be significantly altered by how the molecules and the

  8. Observations of a two-layer soil moisture influence on surface energy dynamics and planetary boundary layer characteristics in a semiarid shrubland

    NASA Astrophysics Data System (ADS)

    Sanchez-Mejia, Zulia Mayari; Papuga, Shirley A.

    2014-01-01

    We present an observational analysis examining soil moisture control on surface energy dynamics and planetary boundary layer characteristics. Understanding soil moisture control on land-atmosphere interactions will become increasingly important as climate change continues to alter water availability. In this study, we analyzed 4 years of data from the Santa Rita Creosote Ameriflux site. We categorized our data independently in two ways: (1) wet or dry seasons and (2) one of the four cases within a two-layer soil moisture framework for the root zone based on the presence or absence of moisture in shallow (0-20 cm) and deep (20-60 cm) soil layers. Using these categorizations, we quantified the soil moisture control on surface energy dynamics and planetary boundary layer characteristics using both average responses and linear regression. Our results highlight the importance of deep soil moisture in land-atmosphere interactions. The presence of deep soil moisture decreased albedo by about 10%, and significant differences were observed in evaporative fraction even in the absence of shallow moisture. The planetary boundary layer height (PBLh) was largest when the whole soil profile was dry, decreasing by about 1 km when the whole profile was wet. Even when shallow moisture was absent but deep moisture was present the PBLh was significantly lower than when the entire profile was dry. The importance of deep moisture is likely site-specific and modulated through vegetation. Therefore, understanding these relationships also provides important insights into feedbacks between vegetation and the hydrologic cycle and their consequent influence on the climate system.

  9. Bacterial selection by mycospheres of Atlantic Rainforest mushrooms.

    PubMed

    Halsey, Joshua Andrew; de Cássia Pereira E Silva, Michele; Andreote, Fernando Dini

    2016-10-01

    This study focuses on the selection exerted on bacterial communities in the mycospheres of mushrooms collected in the Brazilian Atlantic Rainforest. A total of 24 paired samples (bulk soil vs. mycosphere) were assessed to investigate potential interactions between fungi and bacteria present in fungal mycospheres. Prevalent fungal families were identified as Marasmiaceae and Lepiotaceae (both Basidiomycota) based on ITS partial sequencing. We used culture-independent techniques to analyze bacterial DNA from soil and mycosphere samples. Bacterial communities in the samples were distinguished based on overall bacterial, alphaproteobacterial, and betaproteobacterial PCR-DGGE patterns, which were different in fungi belonging to different taxa. These results were confirmed by pyrosequencing the V4 region of the 16S rRNA gene (based on five bulk soil vs. mycosphere pairs), which revealed the most responsive bacterial families in the different conditions generated beneath the mushrooms, identified as Bradyrhizobiaceae, Burkholderiaceae, and Pseudomonadaceae. The bacterial families Acetobacteraceae, Chrhoniobacteraceae, Planctomycetaceae, Conexibacteraceae, and Burkholderiaceae were found in all mycosphere samples, composing the core mycosphere microbiome. Similarly, some bacterial groups identified as Koribacteriaceae, Acidobacteria (Solibacteriaceae) and an unclassified group of Acidobacteria were preferentially present in the bulk soil samples (found in all of them). In this study we depict the mycosphere effect exerted by mushrooms inhabiting the Brazilian Atlantic Rainforest, and identify the bacteria with highest response to such a specific niche, possibly indicating the role bacteria play in mushroom development and dissemination within this yet-unexplored environment. PMID:27411813

  10. Climate change in Australian tropical rainforests: an impending environmental catastrophe.

    PubMed

    Williams, Stephen E; Bolitho, Elizabeth E; Fox, Samantha

    2003-09-22

    It is now widely accepted that global climate change is affecting many ecosystems around the globe and that its impact is increasing rapidly. Many studies predict that impacts will consist largely of shifts in latitudinal and altitudinal distributions. However, we demonstrate that the impacts of global climate change in the tropical rainforests of northeastern Australia have the potential to result in many extinctions. We develop bioclimatic models of spatial distribution for the regionally endemic rainforest vertebrates and use these models to predict the effects of climate warming on species distributions. Increasing temperature is predicted to result in significant reduction or complete loss of the core environment of all regionally endemic vertebrates. Extinction rates caused by the complete loss of core environments are likely to be severe, nonlinear, with losses increasing rapidly beyond an increase of 2 degrees C, and compounded by other climate-related impacts. Mountain ecosystems around the world, such as the Australian Wet Tropics bioregion, are very diverse, often with high levels of restricted endemism, and are therefore important areas of biodiversity. The results presented here suggest that these systems are severely threatened by climate change.

  11. Cloudiness over the Amazon rainforest: Meteorology and thermodynamics

    NASA Astrophysics Data System (ADS)

    Collow, Allison B. Marquardt; Miller, Mark A.; Trabachino, Lynne C.

    2016-07-01

    Comprehensive meteorological observations collected during GOAmazon2014/15 using the Atmospheric Radiation Measurement Mobile Facility no. 1 and assimilated observations from the Modern-Era Retrospective Analysis for Research and Applications, Version 2 are used to document the seasonal cycle of cloudiness, thermodynamics, and precipitation above the Amazon rainforest. The reversal of synoptic-scale vertical motions modulates the transition between the wet and dry seasons. Ascending moist air during the wet season originates near the surface of the Atlantic Ocean and is advected into the Amazon rainforest, where it experiences convergence and, ultimately, precipitates. The dry season is characterized by weaker winds and synoptic-scale subsidence with little or no moisture convergence accompanying moisture advection. This combination results in the drying of the midtroposphere during June through October as indicated by a decrease in liquid water path, integrated water, and the vertical profile of water vapor mixing ratio. The vertical profile of cloud fraction exhibits a relatively consistent decline in cloud fraction from the lifting condensation level (LCL) to the freezing level where a minimum is observed, unlike many other tropical regions. Coefficients of determination between the LCL and cloud fractional coverage suggest a relatively robust relationship between the LCL and cloudiness beneath 5 km during the dry season (R2 = 0.42) but a weak relationship during the wet season (0.12).

  12. Mantle dynamics and generation of a geochemical mantle boundary along the East Pacific Rise - Pacific/Antarctic ridge

    NASA Astrophysics Data System (ADS)

    Zhang, Guo-Liang; Chen, Li-Hui; Li, Shi-Zhen

    2013-12-01

    A large-scale mantle compositional discontinuity was identified along the East Pacific Rise (EPR) and the Pacific-Antarctic Ridge (PAR) with an inferred transition located at the EPR 23°S-32°S. Because of the EPR-Easter hotspot interactions in this area, the nature of this geochemical discontinuity remains unclear. IODP Sites U1367 and U1368 drilled into the ocean crust that was accreted at ∼33.5 Ma and ∼13.5 Ma, respectively, between 28°S and 30°S on the EPR. We use lavas from Sites U1367 and U1368 to track this mantle discontinuity away from the EPR. The mantle sources for basalts at Sites U1367 and U1368 represent, respectively, northern and southern Pacific mantle sub-domains in terms of Sr-Nd-Pb-Hf isotopes. The significant isotopic differences between the two IODP sites are consistent with addition of ancient subduction-processed ocean crust to the south Pacific mantle sub-domain. Our modeling result shows that a trace element pattern similar to that of U1368 E-MORB can be formed by melting a subduction-processed typical N-MORB. The trace element and isotope compositions for Site U1368 MORBs can be formed by mixing a HIMU mantle end-member with Site U1367 MORBs. Comparison of our data with those from the EPR-PAR shows a geochemical mantle boundary near the Easter microplate that separates the Pacific upper mantle into northern and southern sub-domains. On the basis of reconstruction of initial locations of the ocean crust at the two sites, we find that the mantle boundary has moved northward to the Easter microplate since before 33.5 Ma. A model, in which along-axis asthenospheric flow to where asthenosphere consumption is strongest, explains the movement of the apparent mantle boundary.

  13. Building positive nature awareness in pupils using the "Rainforest of the Austrians" in Costa Rica.

    NASA Astrophysics Data System (ADS)

    Aubrecht, Margit; Hölzl, Irmgard; Huber, Werner; Weissenhofer, Anton

    2013-04-01

    20 years ago, Michael Schnitzler founded the NGO "Rainforest of the Austrians" to help save one of the most diverse rainforests in Central America, the Esquinas rainforest on the Pacific coast of SW Costa Rica, from being destroyed through logging. In this abstract we present an interdisciplinary upper Austrian school project aiming at building positive awareness in pupils towards rainforest conservation by fund-raising to help purchase endangered forest areas. The acquired rainforest was donated to the Costa Rican government and became part of the National Park "Piedras Blancas". In the following, we present a chronology of events and actions of the school project. We started our rainforest project by face-to-face encounters, letting involved persons speak directly to the pupils. Dr. Huber, coordinator of the tropical rainforest station La Gamba in Costa Rica (www.lagamba.at), together with Dr. Weissenhofer, presented an introductory slide show about the "Rainforest of the Austrians". With rainforest images and sounds in their mind the pupils wrote "trips of a lifetime" stories, thus creating idyllic images of rainforest habitats. Following up on that, we visited the exhibition "Heliconia and Hummingbirds" at the Biology Center in Linz. Reports about the slide show and the exhibition followed. Tropical sites were compared by producing climate graphs of La Gamba, Costa Rica, and Manaus in Brazil. The global distribution and the decrease of rainforests were also analyzed. In biology lessons the symbiosis between plants and animals of the rainforest were worked out by searching the Internet. Flyers with profiles of rainforest animals were produced. We also discussed the ecotourism project "RICANCIE" in Ecuador using fact sheets. "RICANCIE" is a Spanish acronym standing for "Indigenous Community Network of the Upper Napo for Intercultural Exchange and Ecotourism". It was founded in 1993 aiming to improve the quality of life for some 200 indigenous Kichwa families

  14. Long-term trends in nitrogen isotope composition and nitrogen concentration in brazilian rainforest trees suggest changes in nitrogen cycle.

    PubMed

    Hietz, Peter; Dünisch, Oliver; Wanek, Wolfgang

    2010-02-15

    Direct or indirect anthropogenic effects on ecosystem nitrogen cycles are important components of global change. Recent research has shown that N isotopes in tree rings reflect changes in ecosystem nitrogen sources or cycles and can be used to study past changes. We analyzed trends in two tree species from a remote and pristine tropical rainforest in Brazil, using trees of different ages to distinguish between the effect of tree age and long-term trends. Because sapwood differed from heartwood in delta(15)N and N concentration and N can be translocated between living sapwood cells, long-term trends are best seen in dead heartwood. Heartwood delta(15)N in Spanish cedar (Cedrela odorata) and big-leaf mahogany (Swietenia macrophylla) increased with tree age, and N concentrations increased with age in Cedrela. Controlling for tree age, delta(15)N increased significantly during the past century even when analyzing only heartwood and after removing labile N compounds. In contrast to northern temperate and boreal forests where wood delta(15)N often decreased, the delta(15)N increase in a remote rainforest is unlikely to be a direct signal of changed N deposition. More plausibly, the change in N isotopic composition indicates a more open N cycle, i.e., higher N losses relative to internal N cycling in the forest, which could be the result of changed forest dynamics.

  15. Strategies of a Bornean tropical rainforest water use as a function of rainfall regime: anisohydric or isohydric?

    NASA Astrophysics Data System (ADS)

    Kumagai, T.; Porporato, A. M.

    2010-12-01

    Although Bornean tropical rainforest are among the moistest biome of the world, they sporadically experience periods of water stress. The observations indicate that these tropical rainforest ecosystems tend to have little regulation of forest water use despite such episodes of severe soil drying. This strategy of water use is often referred to as anisohydric behavior, as opposed to isohydric plants (IHP) that have a wide range of stomatal regulation to prevent hydraulic failure. Although it is generally thought that such an anisohydric behavior is an adaptation to more drought-prone habitats, we show that anisohydric plants (AHP) are also more favored than isohydric plants (IHP) under very moist environments, where there is little risk of hydraulic failure. Thus, we examined the advantages of AHP and IHP as a function of the hydroclimatic environment using stochastic model of soil moisture and carbon assimilation dynamics parameterized by field observations. The results show that under very moist conditions, despite almost the same drought-induced mortality of AHP and IHP, AHP have higher productivity. As precipitation amount increases, the mortality of AHP drastically increases with that of IHP being relatively constant low and IHP surpasses AHP in the productivity.

  16. High variation in foliage and leaf litter chemistry among 45 tree species of a neotropical rainforest community.

    PubMed

    Hättenschwiler, Stephan; Aeschlimann, Beat; Coûteaux, Marie-Madeleine; Roy, Jacques; Bonal, Damien

    2008-01-01

    Distinct ecosystem level carbon : nitrogen : phosphorus (C : N : P) stoichiometries in forest foliage have been suggested to reflect ecosystem-scale selection for physiological strategies in plant nutrient use. Here, this hypothesis was explored in a nutrient-poor lowland rainforest in French Guiana. Variation in C, N and P concentrations was evaluated in leaf litter and foliage from neighbour trees of 45 different species, and the litter concentrations of major C fractions were also measured. Litter C ranged from 45.3 to 52.4%, litter N varied threefold (0.68-2.01%), and litter P varied seven-fold (0.009-0.062%) among species. Compared with foliage, mean litter N and P concentrations decreased by 30% and 65%, respectively. Accordingly, the range in mass-based N : P shifted from 14 to 55 in foliage to 26 to 105 in litter. Resorption proficiencies indicated maximum P withdrawal in most species, but with a substantial increase in variation in litter P compared with foliage. These data suggest that constrained ecosystem-level C : N : P ratios do not preclude the evolution of highly diversified strategies of nutrient use and conservation among tropical rainforest tree species. The resulting large variation in litter quality will influence stoichiometric constraints within the decomposer food web, with potentially far-ranging consequences on nutrient dynamics and plant-soil feedbacks.

  17. Response of CO2 and H2O fluxes in a mountainous tropical rainforest in equatorial Indonesia to El Niño events

    NASA Astrophysics Data System (ADS)

    Olchev, A.; Ibrom, A.; Panferov, O.; Gushchina, D.; Kreilein, H.; Popov, V.; Propastin, P.; June, T.; Rauf, A.; Gravenhorst, G.; Knohl, A.

    2015-11-01

    The possible impact of El Niño-Southern Oscillation (ENSO) events on the main components of CO2 and H2O fluxes between the tropical rainforest and the atmosphere is investigated. The fluxes were continuously measured in an old-growth mountainous tropical rainforest in Central Sulawesi in Indonesia using the eddy covariance method for the period from January 2004 to June 2008. During this period, two episodes of El Niño and one episode of La Niña were observed. All these ENSO episodes had moderate intensity and were of the central Pacific type. The temporal variability analysis of the main meteorological parameters and components of CO2 and H2O exchange showed a high sensitivity of evapotranspiration (ET) and gross primary production (GPP) of the tropical rainforest to meteorological variations caused by both El Niño and La Niña episodes. Incoming solar radiation is the main governing factor that is responsible for ET and GPP variability. Ecosystem respiration (RE) dynamics depend mainly on the air temperature changes and are almost insensitive to ENSO. Changes in precipitation due to moderate ENSO events did not have any notable effect on ET and GPP, mainly because of sufficient soil moisture conditions even in periods of an anomalous reduction in precipitation in the region.

  18. Simulating drought impacts on energy and water balance in an Amazonian rainforest

    NASA Astrophysics Data System (ADS)

    Imbuzeiro, H. A.; Costa, M. H.; Galbraith, D.; Christoffersen, B. J.; Powell, T.; Harper, A. B.; Levine, N. M.; Rowland, L.; Moorcroft, P. R.; Meir, P.; da Costa, A. L.; Brando, P. M.; Wang, J.; Bras, R. L.; Malhi, Y.; Saleska, S. R.; Williams, M. D.

    2013-05-01

    The studies of the interaction between vegetation and climate change in the Amazon Basin indicate that up to half of the region's forests may be displaced by savanna vegetation by the end of the century. Additional analyses suggest that complex interactions among land use, fire-frequency, and episodic drought are driving an even more rapid process of the forest impoverishment and displacement referred here as "savannization". But it is not clear whether surface/ecosystem models are suitable to analyze extreme events like a drought. A long-term observation of energy and water in throughfall exclusion experiments has provided unique insights into the energy and water dynamics of Amazonian rainforests during drought conditions. In this study, we will evaluate how well the six surface/ecosystem models (CLM-DGVM, ED 2.0, IBIS, JULES, SiB and SPA) quantify the energy and water dynamics from two Amazonian throughfall exclusion experiments. All models were run for the Tapajós and Caixuana sites with one baseline year using normal precipitation (i.e. do not impose a drought) and then the drought manipulation was imposed for several drought levels (10 to 90% rainfall exclusion). The sap flow, soil moisture, sensible and latent heat flux will be used to analyze if the models are able to capture dynamics of stress and what the implications for the energy and water dynamics are. We find that models are sensible to drought effects when they simulate the energy fluxes (sensible and latent heat), but the water dynamic is not well capture by the models.

  19. Le Chatelier Principle for Out-of-Equilibrium and Boundary-Driven Systems: Application to Dynamical Phase Transitions

    NASA Astrophysics Data System (ADS)

    Shpielberg, O.; Akkermans, E.

    2016-06-01

    A stability analysis is presented for boundary-driven and out-of-equilibrium systems in the framework of the hydrodynamic macroscopic fluctuation theory. A Hamiltonian description is proposed which allows us to thermodynamically interpret the additivity principle. A necessary and sufficient condition for the validity of the additivity principle is obtained as an extension of the Le Chatelier principle. These stability conditions result from a diagonal quadratic form obtained using the cumulant generating function. This approach allows us to provide a proof for the stability of the weakly asymmetric exclusion process and to reduce the search for stability to the solution of two coupled linear ordinary differential equations instead of nonlinear partial differential equations. Additional potential applications of these results are discussed in the realm of classical and quantum systems.

  20. Computational Fluid Dynamics (CFD) Design of a Blended Wing Body (BWB) with Boundary Layer Ingestion (BLI) Nacelles

    NASA Technical Reports Server (NTRS)

    Morehouse, Melissa B.

    2001-01-01

    A study is being conducted to improve the propulsion/airframe integration for the Blended Wing-Body (BWB) configuration with boundary layer ingestion nacelles. TWO unstructured grid flow solvers, USM3D and FUN3D, have been coupled with different design methods and are being used to redesign the aft wing region and the nacelles to reduce drag and flow separation. An initial study comparing analyses from these two flow solvers against data from a wind tunnel test as well as predictions from the OVERFLOW structured grid code for a BWB without nacelles has been completed. Results indicate that the unstructured grid codes are sufficiently accurate for use in design. Results from the BWB design study will be presented.

  1. Estimating Amazonian rainforest stability and the likelihood for large-scale forest dieback

    NASA Astrophysics Data System (ADS)

    Rammig, Anja; Thonicke, Kirsten; Jupp, Tim; Ostberg, Sebastian; Heinke, Jens; Lucht, Wolfgang; Cramer, Wolfgang; Cox, Peter

    2010-05-01

    Annually, tropical forests process approximately 18 Pg of carbon through respiration and photosynthesis - more than twice the rate of anthropogenic fossil fuel emissions. Current climate change may be transforming this carbon sink into a carbon source by changing forest structure and dynamics. Increasing temperatures and potentially decreasing precipitation and thus prolonged drought stress may lead to increasing physiological stress and reduced productivity for trees. Resulting decreases in evapotranspiration and therefore convective precipitation could further accelerate drought conditions and destabilize the tropical ecosystem as a whole and lead to an 'Amazon forest dieback'. The projected direction and intensity of climate change vary widely within the region and between different scenarios from climate models (GCMs). In the scope of a World Bank-funded study, we assessed the 24 General Circulation Models (GCMs) evaluated in the 4th Assessment Report of the Intergovernmental Panel on Climate Change (IPCC-AR4) with respect to their capability to reproduce present-day climate in the Amazon basin using a Bayesian approach. With this approach, greater weight is assigned to the models that simulate well the annual cycle of rainfall. We then use the resulting weightings to create probability density functions (PDFs) for future forest biomass changes as simulated by the Lund-Potsdam-Jena Dynamic Global Vegetation Model (LPJmL) to estimate the risk of potential Amazon rainforest dieback. Our results show contrasting changes in forest biomass throughout five regions of northern South America: If photosynthetic capacity and water use efficiency is enhanced by CO2, biomass increases across all five regions. However, if CO2-fertilisation is assumed to be absent or less important, then substantial dieback occurs in some scenarios and thus, the risk of forest dieback is considerably higher. Particularly affected are regions in the central Amazon basin. The range of

  2. The interpretation of crustal dynamics data in terms of plate motions and regional deformation near plate boundaries

    NASA Technical Reports Server (NTRS)

    Solomon, Sean C.

    1987-01-01

    The nature and dynamics of time-dependent deformation along major seismic zones including the influence of irregularities in fault geometry on the earthquake cycle, and the processes contributing to the state of stress and rates of strain in plate interior regions were studied. The principle findings of the research are discussed.

  3. The interpretation of crustal dynamics data in terms of plate motions and regional deformation near plate boundaries

    NASA Technical Reports Server (NTRS)

    Soloman, Sean C.

    1991-01-01

    The focus was in two broad areas during the most recent 6-month period: (1) the nature and dynamics of time dependent deformation and stress along major seismic zones; and (2) the nature of long-wavelength oceanic geoid anomalies in terms of lateral variations in upper mantle temperature and composition. The principle findings are described in the accompanying appendices.

  4. Localized solution structure refinement of an F45W variant of ubiquitin using stochastic boundary molecular dynamics and NMR distance restraints.

    PubMed

    Laub, P B; Khorasanizadeh, S; Roder, H

    1995-05-01

    The local structure within an 8-A radius around residue 45 of a recombinant F45W variant of human ubiquitin has been determined using 67 interproton distance restraints measured by two-dimensional proton NMR. Proton chemical shift evidence indicates that structural perturbations due to the F45W mutation are minimal and limited to the immediate vicinity of the site of mutation. Simulated annealing implemented with stochastic boundary molecular dynamics was applied to refine the structure of Trp 45 and 10 neighboring residues. The stochastic boundary method allowed the entire protein to be reassembled from the refined coordinates and the outlying unrefined coordinates with little distortion at the boundary. Refinement began with four low-energy indole ring orientations of F45W-substituted wild-type (WT) ubiquitin crystal coordinates. Distance restraints were derived from mostly long-range NOE cross peaks with 51 restraints involving the Trp 45 indole ring. Tandem refinements of 64 structures were done using either (1) upper and lower bounds derived from qualitative inspection of NOE crosspeak intensities or (2) quantitative analysis of cross-peak heights using the program MARDIGRAS. Though similar to those based on qualitative restraint, structures obtained using quantitative NOE analysis were superior in terms of precision and accuracy as measured by back-calculated sixth-root R factors. The six-membered portion of the indole ring is nearly coincident with the phenyl ring of the WT and the indole NH is exposed to solvent. Accommodation of the larger ring is accompanied by small perturbations in the backbone and a 120 degrees rotation of the chi 2 dihedral angle of Leu 50.

  5. Ethnobotany and the identification of therapeutic agents from the rainforest.

    PubMed

    Balick, M J

    1990-01-01

    Many rainforest plant species, including trees and herbaceous plants, are employed as medicines by indigenous people. In much of the American tropics, locally harvested herbal medicines are used for a significant portion of the primary health care, in both rural and urban areas. An experienced curandero or herbal healer is familiar with those species with marked biological activity, which are often classified as 'powerful plants'. Examples are given from studies in progress since 1987 in Belize, Central America. The Institute of Economic Botany of The New York Botanical Garden is collaborating with the National Cancer Institute in Bethesda, Maryland (USA) in the search for higher plants with anti-AIDS and anticancer activity. Several strategies are cited for identification of promising leads from among the circa 110,000 species of higher plants that are present in the neotropics, the focus of this search. Recommendations are offered for the design of future efforts to identify plant leads for pharmaceutical testing. PMID:2086039

  6. Tyrosine kinase inhibitors from the rainforest tree Polyscias murrayi.

    PubMed

    Buchanan, Malcolm S; Carroll, Anthony R; Edser, Annette; Parisot, John; Addepalli, Rama; Quinn, Ronald J

    2005-02-01

    A series of 3-(4-hydroxyphenyl) propanoic acid derivatives, which inhibit Itk (interleukin-2 inducible T-cell kinase), a Th2-cell target, were isolated from the Australian rainforest tree Polyscias murrayi. The new compound 3-(4-hydroxyphenyl) propionyl choline and a 2:1 mixture of the new compounds 3,4-di-O-3-(4-hydroxyphenyl) propionyl-1,5-dihydroxycyclohexanecarboxylic acid and 3,5-di-O-3-(4-hydroxyphenyl) propionyl-1,4-dihydroxycyclohexanecarboxylic acid were isolated along with two known compounds 3-(4-hydroxyphenyl) propanoic acid and 3-(3,4-hydroxyphenyl) propanoic acid. Their structures were determined by 1D and 2D NMR spectroscopy. The assay results suggest that both the 3-(4-hydroxyphenyl) propanoate and carboxyl moieties contribute to Itk activity of the compounds.

  7. Attribution of changes in precipitation patterns in African rainforests

    NASA Astrophysics Data System (ADS)

    Otto, F. E.; Jones, R. G.; Halladay, K.; Allen, M. R.

    2013-12-01

    The effects of projected future global and regional climate change on the water cycle and thus on global water security are amongst the most economically and politically important challenges that society faces in the 21st century. The provision of secure access to water resources and the protection of communities from water-related risks have emerged as top priorities amongst policymakers within the public and private sectors alike. Investment decisions on water infrastructure rely heavily on quantitative assessments of risks and uncertainties associated with future changes in water-related threats. Especially with the introduction of loss and damages on the agenda of the UNFCCC additionally the attribution of such changes to anthropogenic climate change and other external climate drivers is crucial. Probabilistic event attribution (PEA) provides a method of evaluating the extent to which human-induced climate change is affecting localised weather events and impacts of such events that relies on good observations as well as climate modelling. The overall approach is to simulate both, the statistics of observed weather, and the statistics of the weather that would have occurred had specific external drivers of climate change been absent. The majority of studies applying PEA have focused on quantifying attributable risk, with changes in risk depending on an assumption of 'all other things being equal', including natural drivers of climate change and vulnerability. Most previous attribution studies have focused on European extreme weather events, but the most vulnerable regions to climate change are in Asia and Africa. One of the most complex hydrological systems is the tropical rainforest, with the rainforests in tropical Africa being some of the most under-researched regions in the world. Research in the Amazonian rainforest suggests potential vulnerability to climate change. We will present results from using the large ensemble of atmosphere-only general

  8. Global Warming and Neotropical Rainforests: A Historical Perspective

    NASA Astrophysics Data System (ADS)

    Jaramillo, Carlos; Cárdenas, Andrés

    2013-05-01

    There is concern over the future of the tropical rainforest (TRF) in the face of global warming. Will TRFs collapse? The fossil record can inform us about that. Our compilation of 5,998 empirical estimates of temperature over the past 120 Ma indicates that tropics have warmed as much as 7°C during both the mid-Cretaceous and the Paleogene. We analyzed the paleobotanical record of South America during the Paleogene and found that the TRF did not expand toward temperate latitudes during global warm events, even though temperatures were appropriate for doing so, suggesting that solar insolation can be a constraint on the distribution of the tropical biome. Rather, a novel biome, adapted to temperate latitudes with warm winters, developed south of the tropical zone. The TRF did not collapse during past warmings; on the contrary, its diversity increased. The increase in temperature seems to be a major driver in promoting diversity.

  9. Boundary conditions of patient-specific fluid dynamics modelling of cavopulmonary connections: possible adaptation of pulmonary resistances results in a critical issue for a virtual surgical planning

    PubMed Central

    Pennati, Giancarlo; Corsini, Chiara; Cosentino, Daria; Hsia, Tain-Yen; Luisi, Vincenzo S.; Dubini, Gabriele; Migliavacca, Francesco

    2011-01-01

    Cavopulmonary connections are surgical procedures used to treat a variety of complex congenital cardiac defects. Virtual pre-operative planning based on in silico patient-specific modelling might become a powerful tool in the surgical decision-making process. For this purpose, three-dimensional models can be easily developed from medical imaging data to investigate individual haemodynamics. However, the definition of patient-specific boundary conditions is still a crucial issue. The present study describes an approach to evaluate the vascular impedance of the right and left lungs on the basis of pre-operative clinical data and numerical simulations. Computational fluid dynamics techniques are applied to a patient with a bidirectional cavopulmonary anastomosis, who later underwent a total cavopulmonary connection (TCPC). Multi-scale models describing the surgical region and the lungs are adopted, while the flow rates measured in the venae cavae are used at the model inlets. Pre-operative and post-operative conditions are investigated; namely, TCPC haemodynamics, which are predicted using patient-specific pre-operative boundary conditions, indicates that the pre-operative balanced lung resistances are not compatible with the TCPC measured flows, suggesting that the pulmonary vascular impedances changed individually after the surgery. These modifications might be the consequence of adaptation to the altered pulmonary blood flows. PMID:22670201

  10. The interpretation of crustal dynamics data in terms of plate motions and regional deformation near plate boundaries

    NASA Technical Reports Server (NTRS)

    Solomon, Sean C.

    1987-01-01

    The focus of the research was in two broad areas during the most recent 6 month period: the nature and dynamics of time-dependent deformation along major seismic zones, including the influence of irregularities in fault geometry on the earthquake cycles, and the processes contributing to the state of stress and rates of strain in plate interior regions. The principal findings of the research to date are described.

  11. A classification of ecological boundaries

    USGS Publications Warehouse

    Strayer, D.L.; Power, M.E.; Fagan, W.F.; Pickett, S.T.A.; Belnap, J.

    2003-01-01

    Ecologists use the term boundary to refer to a wide range of real and conceptual structures. Because imprecise terminology may impede the search for general patterns and theories about ecological boundaries, we present a classification of the attributes of ecological boundaries to aid in communication and theory development. Ecological boundaries may differ in their origin and maintenance, their spatial structure, their function, and their temporal dynamics. A classification system based on these attributes should help ecologists determine whether boundaries are truly comparable. This system can be applied when comparing empirical studies, comparing theories, and testing theoretical predictions against empirical results.

  12. An Insect Nidovirus Emerging from a Primary Tropical Rainforest

    PubMed Central

    Zirkel, Florian; Kurth, Andreas; Quan, Phenix-Lan; Briese, Thomas; Ellerbrok, Heinz; Pauli, Georg; Leendertz, Fabian H.; Lipkin, W. Ian; Ziebuhr, John; Drosten, Christian; Junglen, Sandra

    2011-01-01

    ABSTRACT Tropical rainforests show the highest level of terrestrial biodiversity and may be an important contributor to microbial diversity. Exploitation of these ecosystems may foster the emergence of novel pathogens. We report the discovery of the first insect-associated nidovirus, tentatively named Cavally virus (CAVV). CAVV was found with a prevalence of 9.3% during a survey of mosquito-associated viruses along an anthropogenic disturbance gradient in Côte d’Ivoire. Analysis of habitat-specific virus diversity and ancestral state reconstruction demonstrated an origin of CAVV in a pristine rainforest with subsequent spread into agriculture and human settlements. Virus extension from the forest was associated with a decrease in virus diversity (P < 0.01) and an increase in virus prevalence (P < 0.00001). CAVV is an enveloped virus with large surface projections. The RNA genome comprises 20,108 nucleotides with seven major open reading frames (ORFs). ORF1a and -1b encode two large proteins that share essential features with phylogenetically higher representatives of the order Nidovirales, including the families Coronavirinae and Torovirinae, but also with families in a basal phylogenetic relationship, including the families Roniviridae and Arteriviridae. Genetic markers uniquely conserved in nidoviruses, such as an endoribonuclease- and helicase-associated zinc-binding domain, are conserved in CAVV. ORF2a and -2b are predicted to code for structural proteins S and N, respectively, while ORF3a and -3b encode proteins with membrane-spanning regions. CAVV produces three subgenomic mRNAs with 5′ leader sequences (of different lengths) derived from the 5′ end of the genome. This novel cluster of mosquito-associated nidoviruses is likely to represent a novel family within the order Nidovirales. PMID:21673192

  13. Sensitivity of the Amazon rainforest to convective storms

    NASA Astrophysics Data System (ADS)

    Negron Juarez, R. I.; Chambers, J. Q.; Rifai, S. W.; Urquiza Munoz, J. D.; Tello, R.; Alegria Munoz, W.; Marra, D.; Ribeiro, G.; Higuchi, N.

    2012-12-01

    The Amazon rainforest is the largest contiguous continental tropical forest in the world and is a world center of carbon storage, biodiversity, biogeochemical cycles and biogeophysical processes that affect the Earth climate system. Yet anthropogenic activities have produced changes in the forest-climate system. Consequently, an increase in rainfall in both the Western and Central Amazon and a decrease in the Eastern Amazon are expected due to these anthropogenic activities. While the projected decrease in rainfall has been discussed under the context of drought, deforestation, and fires, the effect of an increase in rainfall, and associated convective processes, on forest ecosystems has been overlooked. Across the Amazon rainforest, Western Amazonia has the highest precipitation rates, wood productivity, soil fertility, recruitment and mortality rates. Yet our field-measured tree mortality data from blowdowns that occurred in Western and Central Amazonia do not show a statistical difference in tree mortality between these regions. However, downburst velocities associated with these disturbances were calculated to be lower in Western Amazonia than in the Central Amazon. This suggests the Western Amazon is more highly sensitive to intense convective systems. This result is particularly relevant given the expected increase in rainfall in the Western and Central Amazon. The increase in rainfall is associated with more intense convective systems that in turn imply an increase in low level jet stream (LLJ) intensity east of the Andes. The presence of the LLJ is the main cause of squall lines and an increase in LLJ intensity will therefore cause increased propagation of squall lines into the Amazon basin. More frequent and active squall lines have the potential to increase the intensity and frequency of downbursts responsible for large forest blowdowns that will affect the biogeophysical feedbacks on the forest ecosystem and carbon budget.

  14. Kinematics to dynamics in the New Zealand Plate boundary zone: implications for the strength of the lithosphere

    NASA Astrophysics Data System (ADS)

    Lamb, Simon

    2015-05-01

    New Zealand straddles the boundary between the Australian and Pacific Plate. Cenozoic relative plate motion has resulted in a complex pattern of faulting and block rotation in a zone of continental lithosphere up to 250 km wide. I investigate the implications of the short-term kinematics for the strength of the deforming lithosphere. I use a compilation of seismic reflection/refraction studies and high quality receiver function analyses to determine both the regional structure of the crust, which ranges from 20 to 50 km thick, and fields of buoyancy stress (or GPE per unit volume). Deformation over thousands of years is quantified in terms of velocity and strain rate fields, based on an inversion of neotectonic fault slip and palaeomagnetic data, in the context of the short-term relative plate motions. Forces on the subduction megathrust, as well as deviatoric stresses in the behind subduction region, are calculated from simple 2-D force balances across the Hikurangi Margin, given negligible deviatoric stresses at the along-strike transition between backarc extension and compression. Average megathrust shear stresses are in the range 6-15 MPa, and average lithospheric stresses <20 MPa in the overriding plate. The regional lithospheric strength of the plate boundary zone, assuming a viscous rheology (Newtonian or power law), is determined from an inversion of the field of gradients of buoyancy stress (averaged over either the top 25 km of the crust, or 100-km-thick lithosphere) and strain rate, using the thin sheet stress balance equations, calibrated with the subduction force balance analysis. Effective viscosities for the deforming lithosphere and/or crust are in the range 0.1-5 × 1021 Pa s, with marked weakening in zones of high strain rate, and an abrupt transition to viscosities >1022 Pa s at the margins of the rigid plates. If lateral variations in effective viscosity are only due to non-Newtonian behaviour, these data indicate a bulk power law rheology, with

  15. Microbial Community Dynamics from Permafrost Across the Pleistocene-Holocene Boundary and Response to Abrupt Climate Change

    NASA Astrophysics Data System (ADS)

    Hammad, A.; Mahony, M.; Froese, D. G.; Lanoil, B. D.

    2014-12-01

    Earth is currently undergoing rapid warming similar to that observed about 10,000 years ago at the end of the Pleistocene. We know a considerable amount about the adaptations and extinctions of mammals and plants at the Pleistocene/Holocene (P/H) boundary, but relatively little about changes at the microbial level. Due to permafrost soils' freezing anoxic conditions, they act as microbial diversity archives allowing us to determine how microbial communities adapted to the abrupt warming at the end of P. Since microbial community composition only helps differentiate viable and extant microorganisms in frozen permafrost, microbial activity in thawing permafrost must be investigated to provide a clear understanding of microbial response to climate change. Current increased temperatures will result in warming and potential thaw of permafrost and release of stored organic carbon, freeing it for microbial utilization; turning permafrost into a carbon source. Studying permafrost viable microbial communities' diversity and activity will provide a better understanding of how these microorganisms respond to soil edaphic variability due to climate change across the P/H boundary, providing insight into the changes that the soil community is currently undergoing in this modern era of rapid climate change. Modern soil, H and P permafrost cores were collected from Lucky Lady II site outside Dawson City, Yukon. 16S rRNA high throughput sequencing of permafrost DNA showed the same trends for total and viable community richness and diversity with both decreasing with permafrost depth and only the richness increasing in mid and early P. The modern, H and P soils had 50.9, 33.9, and 27.3% unique viable species and only 14% of the total number of viable species were shared by all soils. Gas flux measurements of thawed permafrost showed metabolic activity in modern and permafrost soils, aerobic CH­­4 consumption in modern, some H and P soils, and anaerobic CH­­4 production in one H

  16. Quantifying the Boundary-Layer Dynamics of Carbon Dioxide from A Built Environment Using A Coupled Urban Land-Atmospheric Model

    NASA Astrophysics Data System (ADS)

    Song, J.; Wang, Z.

    2015-12-01

    Urban areas are significant carbon contributors in the global carbon cycle due to intense carbon emissions from traffic and other human activities and lack of vegetation for carbon absorption. A better understanding on urban carbon variations is important to quantify urban contributions to regional and global carbon budgets under the challenge of climate changes. In this study, we applied a coupled urban land-atmospheric model to simulate the diurnal and seasonal variations of carbon dioxide (CO2) fluxes in the urban boundary layer (UBL) for the Phoenix Metropolitan area, Arizona. The lower boundary conditions of this model are provided by the CO2 fluxes measured using an eddy covariance tower. By analyzing the tower measurements in the urban canopy layer, the highest concentrations of CO2 in a typical weekday coincide with the busiest traffic. Besides, there are more CO2 emissions in winter than in summer possibly due to additional natural gas consumptions for heating. Based on the coupled model, we simulated the diurnal and seasonal evolutions of the mean CO2 concentration as well as the vertical profiles of CO2 concentration in the UBL. It was found that the anthropogenic CO2 sources in a built terrain effectively altered the carbon dynamics in the overlying atmosphere in contrast to its rural surroundings. We also changed the urban landscape characteristics including vegetation fraction, surface roughness, and building density to study their impacts on the CO2 dynamics in the UBL. Overall, the coupled urban land-atmospheric model provides a useful stand-alone tool for quantifying the urban carbon cycle, and can be extended to more general applications such as urban air quality problems.

  17. Topology of sustainable management of dynamical systems with desirable states: from defining planetary boundaries to safe operating spaces in the Earth system

    NASA Astrophysics Data System (ADS)

    Heitzig, J.; Kittel, T.; Donges, J. F.; Molkenthin, N.

    2016-01-01

    To keep the Earth system in a desirable region of its state space, such as defined by the recently suggested "tolerable environment and development window", "guardrails", "planetary boundaries", or "safe (and just) operating space for humanity", one needs to understand not only the quantitative internal dynamics of the system and the available options for influencing it (management) but also the structure of the system's state space with regard to certain qualitative differences. Important questions are, which state space regions can be reached from which others with or without leaving the desirable region, which regions are in a variety of senses "safe" to stay in when management options might break away, and which qualitative decision problems may occur as a consequence of this topological structure? In this article, we develop a mathematical theory of the qualitative topology of the state space of a dynamical system with management options and desirable states, as a complement to the existing literature on optimal control which is more focussed on quantitative optimization and is much applied in both the engineering and the integrated assessment literature. We suggest a certain terminology for the various resulting regions of the state space and perform a detailed formal classification of the possible states with respect to the possibility of avoiding or leaving the undesired region. Our results indicate that, before performing some form of quantitative optimization such as of indicators of human well-being for achieving certain sustainable development goals, a sustainable and resilient management of the Earth system may require decisions of a more discrete type that come in the form of several dilemmas, e.g. choosing between eventual safety and uninterrupted desirability, or between uninterrupted safety and larger flexibility. We illustrate the concepts and dilemmas drawing on conceptual models from climate science, ecology, coevolutionary Earth system

  18. Evolutionary dynamics of a rapidly receding southern range boundary in the threatened California red-legged frog (Rana draytonii)

    USGS Publications Warehouse

    Richmond, Jonathan Q.; Barr, Kelly R.; Backlin, Adam R.; Vandergast, Amy G.; Fisher, Robert N.

    2013-01-01

    Populations forming the edge of a species range are often imperiled by isolation and low genetic diversity, with proximity to human population centers being a major determinant of edge stability in modern landscapes. Since the 1960s, the California red-legged frog (Rana draytonii) has undergone extensive declines in heavily urbanized southern California, where the range edge has rapidly contracted northward while shifting its cardinal orientation to an east-west trending axis. We studied the genetic structure and diversity of these frontline populations, tested for signatures of contemporary disturbance, specifically fire, and attempted to disentangle these signals from demographic events extending deeper into the past. Consistent with the genetic expectations of the ‘abundant-center’ model, we found that diversity, admixture, and opportunity for random mating increases in populations sampled successively further away from the range boundary. Demographic simulations indicate that bottlenecks in peripheral isolates are associated with processes extending tens to a few hundred generations in the past, despite the demographic collapse of some due to recent fire-flood events. While the effects of recent disturbance have left little genetic imprint on these populations, they likely contribute to an extinction debt that will lead to continued range contraction unless management intervenes to stall or reverse the process.

  19. Zeppelin NT - Measurement Platform for the Exploration of Atmospheric Chemistry and Dynamics in the Planetary Boundary Layer

    NASA Astrophysics Data System (ADS)

    Hofzumahaus, Andreas; Holland, Frank; Oebel, Andreas; Rohrer, Franz; Mentel, Thomas; Kiendler-Scharr, Astrid; Wahner, Andreas; Brauchle, Artur; Steinlein, Klaus; Gritzbach, Robert

    2014-05-01

    The planetary boundary layer (PBL) is the chemically most active and complex part of the atmosphere where freshly emitted reactive trace gases, tropospheric radicals, atmospheric oxidation products and aerosols exhibit a large variability and spatial gradients. In order to investigate the chemical degradation of trace gases and the formation of secondary pollutants in the PBL, a commercial Zeppelin NT was modified to be used as an airborne measurement platform for chemical and physical observations with high spatial resolution. The Zeppelin NT was developed by Zeppelin Luftschifftechnik (ZLT) and is operated by Deutsche Zeppelin Reederei (DZR) in Friedrichshafen, Germany. The modification was performed in cooperation between Forschungszentrum Jülich and ZLT. The airship has a length of 75 m, can lift about 1 ton of scientific payload and can be manoeuvered with high precision by propeller engines. The modified Zeppelin can carry measurement instruments mounted on a platform on top of the Zeppelin, or inside the gondola beneath the airship. Three different instrument packages were developed to investigate a. gas-phase oxidation processes involving free radicals (OH, HO2) b. formation of secondary organic aerosols (SOA) c. new particle formation (nucleation) The presentation will describe the modified airship and provide an overview of its technical performance. Examples of its application during the recent PEGASOS flight campaigns in Europe will be given.

  20. Responses of seed-dispersing birds to amount of rainforest in the landscape around fragments.

    PubMed

    Moran, Cath; Catterall, Carla P

    2014-04-01

    Habitat loss and fragmentation alter the composition of bird assemblages in rainforest. Because birds are major seed dispersers in rainforests, fragmentation-induced changes to frugivorous bird assemblages are also likely to alter the ecological processes of seed dispersal and forest regeneration, but the specific nature of these changes is poorly understood. We assessed the influence of fragment size and landscape forest cover on the abundance, species composition, and functional properties of the avian seed disperser community in an extensively cleared, former rainforest landscape of subtropical Australia. Bird surveys of fixed time and area in 25 rainforest fragments (1-139 ha in size across a 1800 km(2) region) provided bird assemblage data which were coupled with prior knowledge of bird species' particular roles in seed dispersal to give measurements of seven different attributes of the seed disperser assemblage. We used multimodel regression to assess how patch size and surrounding forest cover (within 200 m, 1000 m, and 5000 m radii) influenced variation in the abundance of individual bird species and of functional groups based on bird species' responses to fragmentation and their roles in seed dispersal. Surrounding forest cover, specifically rainforest cover, generally had a greater effect on frugivorous bird assemblages than fragment size. Amount of rainforest cover within 200 m of fragments was the main factor positively associated with abundances of frugivorous birds that are both fragmentation sensitive and important seed dispersers. Our results suggest a high proportion of local rainforest cover is required for the persistence of seed-dispersing birds and the maintenance of seed dispersal processes. Thus, even small rainforest fragments can function as important parts of habitat networks for seed-dispersing birds, whether or not they are physically connected by vegetation. PMID:24548306

  1. Responses of seed-dispersing birds to amount of rainforest in the landscape around fragments.

    PubMed

    Moran, Cath; Catterall, Carla P

    2014-04-01

    Habitat loss and fragmentation alter the composition of bird assemblages in rainforest. Because birds are major seed dispersers in rainforests, fragmentation-induced changes to frugivorous bird assemblages are also likely to alter the ecological processes of seed dispersal and forest regeneration, but the specific nature of these changes is poorly understood. We assessed the influence of fragment size and landscape forest cover on the abundance, species composition, and functional properties of the avian seed disperser community in an extensively cleared, former rainforest landscape of subtropical Australia. Bird surveys of fixed time and area in 25 rainforest fragments (1-139 ha in size across a 1800 km(2) region) provided bird assemblage data which were coupled with prior knowledge of bird species' particular roles in seed dispersal to give measurements of seven different attributes of the seed disperser assemblage. We used multimodel regression to assess how patch size and surrounding forest cover (within 200 m, 1000 m, and 5000 m radii) influenced variation in the abundance of individual bird species and of functional groups based on bird species' responses to fragmentation and their roles in seed dispersal. Surrounding forest cover, specifically rainforest cover, generally had a greater effect on frugivorous bird assemblages than fragment size. Amount of rainforest cover within 200 m of fragments was the main factor positively associated with abundances of frugivorous birds that are both fragmentation sensitive and important seed dispersers. Our results suggest a high proportion of local rainforest cover is required for the persistence of seed-dispersing birds and the maintenance of seed dispersal processes. Thus, even small rainforest fragments can function as important parts of habitat networks for seed-dispersing birds, whether or not they are physically connected by vegetation.

  2. Polyglutamine Amyloid Core Boundaries and Flanking Domain Dynamics in Huntingtin Fragment Fibrils Determined by Solid-State Nuclear Magnetic Resonance

    PubMed Central

    2015-01-01

    In Huntington’s disease, expansion of a polyglutamine (polyQ) domain in the huntingtin (htt) protein leads to misfolding and aggregation. There is much interest in the molecular features that distinguish monomeric, oligomeric, and fibrillar species that populate the aggregation pathway and likely differ in cytotoxicity. The mechanism and rate of aggregation are greatly affected by the domains flanking the polyQ segment within exon 1 of htt. A “protective” C-terminal proline-rich flanking domain inhibits aggregation by inducing polyproline II structure (PPII) within an extended portion of polyQ. The N-terminal flanking segment (httNT) adopts an α-helical structure as it drives aggregation, helps stabilize oligomers and fibrils, and is seemingly integral to their supramolecular assembly. Via solid-state nuclear magnetic resonance (ssNMR), we probe how, in the mature fibrils, the htt flanking domains impact the polyQ domain and in particular the localization of the β-structured amyloid core. Using residue-specific and uniformly labeled samples, we find that the amyloid core occupies most of the polyQ domain but ends just prior to the prolines. We probe the structural and dynamical features of the remarkably abrupt β-sheet to PPII transition and discuss the potential connections to certain htt-binding proteins. We also examine the httNT α-helix outside the polyQ amyloid core. Despite its presumed structural and demonstrated stabilizing roles in the fibrils, quantitative ssNMR measurements of residue-specific dynamics show that it undergoes distinct solvent-coupled motion. This dynamical feature seems reminiscent of molten-globule-like α-helix-rich features attributed to the nonfibrillar oligomeric species of various amyloidogenic proteins. PMID:25280367

  3. Spatial and seasonal patterns of fine-scale to mesoscale upper ocean dynamics in an Eastern Boundary Current System

    NASA Astrophysics Data System (ADS)

    Grados, Daniel; Bertrand, Arnaud; Colas, François; Echevin, Vincent; Chaigneau, Alexis; Gutiérrez, Dimitri; Vargas, Gary; Fablet, Ronan

    2016-03-01

    The physical forcing of the ocean surface includes a variety of energetic processes, ranging from internal wave (IW) to submesoscale and mesoscale, associated with characteristic horizontal scales. While the description of mesoscale ocean dynamics has greatly benefited from the availability of satellite data, observations of finer scale patterns remain scarce. Recent studies showed that the vertical displacements of the oxycline depth, which separates the well-mixed oxygenated surface layer from the less oxygenated deeper ocean, estimated by acoustics, provide a robust proxy of isopycnal displacements over a wide range of horizontal scales. Using a high-resolution and wide-range acoustic data set in the Northern Humboldt Current System (NHCS) off Peru, the spatial and temporal patterns of fine-scale-to-mesoscale upper ocean dynamics are investigated. The spectral content of oxycline/pycnocline profiles presents patterns characteristic of turbulent flows, from the mesoscale to the fine scale, and an energization at the IW scale (2 km-200 m). On the basis of a typology performed on 35,000 structures we characterized six classes of physical structures according to their shape and scale range. The analysis reveals the existence of distinct features for the fine-scale range below ∼2-3 km, and clearly indicates the existence of intense IW and submesoscale activity over the entire NHCS region. Structures at scales smaller than ∼2 km were more numerous and energetic in spring than in summer. Their spatiotemporal variability supports the interpretation that these processes likely relate to IW generation by interactions between tidal flows, stratification and the continental slope. Given the impact of the physical forcing on the biogeochemical and ecological dynamics in EBUS, these processes should be further considered in future ecosystem studies based on observations and models. The intensification of upper ocean stratification resulting from climate change makes such

  4. The interpretation of crustal dynamics data in terms of plate motions and regional deformation near plate boundaries

    NASA Technical Reports Server (NTRS)

    Soloman, Sean C.

    1991-01-01

    The focus of the research was in two broad areas: (1) the nature and dynamics of time dependent deformation and stress along major seismic zones; and (2) the nature of long wavelength oceanic geoid anomalies in terms of lateral variations in upper mantle temperature and composition. The principle findings of the research are described in the accompanying appendices. The first two and the fourth appendices are reprints of papers recently submitted for publication, and the third is the abstract of a recently completed thesis supported by this project.

  5. Application of wave mechanics theory to fluid dynamics problems: Boundary layer on a circular cylinder including turbulence

    NASA Technical Reports Server (NTRS)

    Krzywoblocki, M. Z. V.

    1974-01-01

    The application of the elements of quantum (wave) mechanics to some special problems in the field of macroscopic fluid dynamics is discussed. Emphasis is placed on the flow of a viscous, incompressible fluid around a circular cylinder. The following subjects are considered: (1) the flow of a nonviscous fluid around a circular cylinder, (2) the restrictions imposed the stream function by the number of dimensions of space, and (3) the flow past three dimensional bodies in a viscous fluid, particularly past a circular cylinder in the symmetrical case.

  6. A new skink (Scincidae: Carlia) from the rainforest uplands of Cape Melville, north-east Australia.

    PubMed

    Hoskin, Conrad J

    2014-01-01

    Carlia skinks are widespread in New Guinea, Wallacea, and northern and eastern Australia. Most Australian species occur in dry woodlands and savannas or marginal rainforest habitats associated with these. There are two rainforest species, parapatrically distributed in coastal mid-eastern Queensland (C. rhomboidalis) and the Wet Tropics of north-eastern Queensland (C. rubrigularis). These two sister species share a diagnostic morphological trait in having the interparietal scale fused to the frontoparietal. Here I describe a third species in this group, Carlia wundalthini sp. nov., from rainforest uplands of the Melville Range, a rainforest isolate 170 km north of the Wet Tropics. This species is diagnosable on male breeding colouration, morphometrics and scalation. The description of C. wundalthini sp. nov. brings the number of vertebrate species known to be endemic to the rainforest and boulder-fields of Cape Melville to seven. Carlia wundalthini sp. nov. is distinct among these endemics in being the only one that does not appear to be directly associated with rock, being found in rainforest leaf-litter.  PMID:25283915

  7. Two new skinks (Scincidae: Glaphyromorphus) from rainforest habitats in north-eastern Australia.

    PubMed

    Hoskin, Conrad J; Couper, Patrick J

    2014-09-29

    Tropical rainforest is largely restricted in Australia to the fairly continuous Wet Tropics region and disconnected patches to the north on Cape York. The Wet Tropics is relatively well explored and studied, whereas the rainforests of Cape York have received less attention due to their remoteness. Here we describe two new species of Glaphyromorphus skinks from rainforest areas on Cape York. The two new species are most similar to each other and to G. fuscicaudis and G. nigricaudis, but both are readily diagnosed on numerous traits. Glaphyromorphus othelarrni sp. nov. is diagnosed from all similar species by its supralabial count (typically 8 vs 7), high number of subdigital lamellae beneath the 4th finger (14-15 vs < 14), and its relatively longer limbs. Glaphyromorphus nyanchupinta sp. nov. is diagnosed from all similar species by its small body size (max SVL = ~ 54 mm vs > 85 mm) and slender body shape, low number of subdigital lamellae beneath the 4th toe (17-20 vs generally 20 or more), and head and body pattern. Both species also differ from each other and similar congeners in other aspects of body shape, scalation and colour pattern. Glaphyromorphus othelarrni sp. nov. is restricted to boulder-strewn rainforest of the Melville Range, whilst Glaphyromorphus nyanchupinta sp. nov. is known only from upland rainforest in the McIlwraith Range. We discuss patterns of rainforest vertebrate endemism on Cape York, and the importance of lithorefugia in generating these.

  8. A new skink (Scincidae: Saproscincus) from rocky rainforest habitat on Cape Melville, north-east Australia.

    PubMed

    Hoskin, Conrad J

    2013-01-01

    Saproscincus skinks are restricted to wet forest habitats of eastern Australia. Eleven species have previously been described, with most having small distributions in disjunct areas of subtropical and tropical rainforest. The localized distributions and specific habitat requirements of Saproscincus have made them a key group for understanding the biogeographic history of Australia's rainforests. Here I describe a new species of Saproscincus from the Melville Range on Cape Melville, north-east Australia. The Melville Range is composed of boulder-fields and areas of rainforest in the uplands, and is highly isolated from other areas of elevated rainforest. All individuals of the new species were found on a moist ridgeline, active on boulders under a rainforest canopy or on boulder-field immediately adjacent to rainforest. Saproscincus saltus sp. nov. is highly distinct in morphology and colour pattern. Of particular interest are its long limbs and digits compared to congeners, which in conjunction with the observed ecology, suggest a long history of association with rock. The discovery of S. saltus sp. nov. extends the distribution of the genus over 100 km north from the nearest congeners in the Wet Tropics region. This species brings the number of vertebrates known to be endemic to the Melville Range to six, which is remarkable for such a small area.

  9. A new skink (Scincidae: Carlia) from the rainforest uplands of Cape Melville, north-east Australia.

    PubMed

    Hoskin, Conrad J

    2014-10-01

    Carlia skinks are widespread in New Guinea, Wallacea, and northern and eastern Australia. Most Australian species occur in dry woodlands and savannas or marginal rainforest habitats associated with these. There are two rainforest species, parapatrically distributed in coastal mid-eastern Queensland (C. rhomboidalis) and the Wet Tropics of north-eastern Queensland (C. rubrigularis). These two sister species share a diagnostic morphological trait in having the interparietal scale fused to the frontoparietal. Here I describe a third species in this group, Carlia wundalthini sp. nov., from rainforest uplands of the Melville Range, a rainforest isolate 170 km north of the Wet Tropics. This species is diagnosable on male breeding colouration, morphometrics and scalation. The description of C. wundalthini sp. nov. brings the number of vertebrate species known to be endemic to the rainforest and boulder-fields of Cape Melville to seven. Carlia wundalthini sp. nov. is distinct among these endemics in being the only one that does not appear to be directly associated with rock, being found in rainforest leaf-litter. 

  10. Probing the boundary between star clusters and dwarf galaxies: A MUSE view on the dynamics of Crater/Laevens I

    NASA Astrophysics Data System (ADS)

    Voggel, Karina; Hilker, Michael; Baumgardt, Holger; Collins, Michelle L. M.; Grebel, Eva K.; Husemann, Bernd; Richtler, Tom; Frank, Matthias J.

    2016-08-01

    We present MUSE observations of the debated ultrafaint stellar system Crater. We spectroscopically confirm 26 member stars of this system via radial velocity measurements. We derive the systematic instrumental velocity uncertainty of MUSE spectra to be 2.27 km s- 1. This new data set increases the confirmed member stars of Crater by a factor of 3. One out of three bright blue stars and a fainter blue star just above the main-sequence turn-off are also found to be likely members of the system. The observations reveal that Crater has a systemic radial velocity of v_sys=148.18^+1.08_-1.15 km s^{-1}, whereas the most likely velocity dispersion of this system is σ _v=2.04^+2.19_-1.06 km s^{-1}. The total dynamical mass of the system, assuming dynamical equilibrium is then M_tot=1.50^{+4.9}_{-1.2}× 10^5 M_{⊙} implying a mass-to-light ratio of M/LV = 8.52^{+28.0}_{-6.5} M_{⊙}/L_{⊙}, which is consistent with a purely baryonic stellar population within its errors and no significant evidence for the presence of dark matter was found. We also find evidence for a velocity gradient in the radial velocity distribution. We conclude that our findings strongly support that Crater is a faint intermediate-age outer halo globular cluster and not a dwarf galaxy.

  11. Elevated mobility of persistent organic pollutants in the soil of a tropical rainforest.

    PubMed

    Zheng, Qian; Nizzetto, Luca; Liu, Xiang; Borgå, Katrine; Starrfelt, Jostein; Li, Jun; Jiang, Yishan; Liu, Xin; Jones, Kevin C; Zhang, Gan

    2015-04-01

    Semivolatile persistent organic pollutants (POP) are bioaccumulative and toxic contaminants. Their global distribution depends on source distribution, atmospheric transport, degradation, and the exchange with ocean and land surfaces. Forests are crucial terrestrial reservoirs due to the commonly envisaged high capacity of their surface soils to store and immobilize airborne contaminants bound to soil organic matter. Our results show that POPs can be unexpectedly mobile in the soil of a tropical rainforest due to fast litter turnover (leading to rapid POP transfer to the subsoil) and leaching rates exceeding degradation rates especially for more hydrophobic congeners. Co-transport in association with leaching fine particulate and dissolved organic matter appears as a relevant driver of this PCB export. A markedly different distribution pattern is displayed in this soil in comparison to soils of colder environments with lower overall storage capacity. These findings show that biogeochemistry of organic matter degradation and weathering can influence POP soil fate. Because tropical forests represent 60% of the global terrestrial productivity, the highlighted dynamics might have an implication for the general distribution of these contaminants.

  12. Mammalian gastrointestinal parasites in rainforest remnants of Anamalai Hills, Western Ghats, India.

    PubMed

    Chakraborty, Debapriyo; Hussain, Shaik; Reddy, D Mahendar; Raut, Sachin; Tiwari, Sunil; Kumar, Vinod; Umapathy, Govindhaswamy

    2015-06-01

    Habitat fragmentation is postulated to be a major factor influencing infectious disease dynamics in wildlife populations and may also be responsible, at least in part, for the recent spurt in the emergence, or re-emergence, of infectious diseases in humans. The mechanism behind these relationships are poorly understood due to the lack of insights into the interacting local factors and insufficient baseline data in ecological parasitology of wildlife. Here, we studied the gastrointestinal parasites of nonhuman mammalian hosts living in 10 rainforest patches of the Anamalai Tiger Reserve, India. We examined 349 faecal samples of 17 mammalian species and successfully identified 24 gastrointestinal parasite taxa including 1 protozoan, 2 trematode, 3 cestode and 18 nematode taxa. Twenty of these parasites are known parasites of humans. We also found that as much as 73% of all infected samples were infected by multiple parasites. In addition, the smallest and most fragmented forest patches recorded the highest parasite richness; the pattern across fragments, however, seemed to be less straightforward, suggesting potential interplay of local factors.

  13. Boundary Layer

    NASA Technical Reports Server (NTRS)

    Loitsianskii. L. G.

    1956-01-01

    The fundamental, practically the most important branch of the modern mechanics of a viscous fluid or a gas, is that branch which concerns itself with the study of the boundary layer. The presence of a boundary layer accounts for the origin of the resistance and lift force, the breakdown of the smooth flow about bodies, and other phenomena that are associated with the motion of a body in a real fluid. The concept of boundary layer was clearly formulated by the founder of aerodynamics, N. E. Joukowsky, in his well-known work "On the Form of Ships" published as early as 1890. In his book "Theoretical Foundations of Air Navigation," Joukowsky gave an account of the most important properties of the boundary layer and pointed out the part played by it in the production of the resistance of bodies to motion. The fundamental differential equations of the motion of a fluid in a laminar boundary layer were given by Prandtl in 1904; the first solutions of these equations date from 1907 to 1910. As regards the turbulent boundary layer, there does not exist even to this day any rigorous formulation of this problem because there is no closed system of equations for the turbulent motion of a fluid. Soviet scientists have done much toward developing a general theory of the boundary layer, and in that branch of the theory which is of greatest practical importance at the present time, namely the study of the boundary layer at large velocities of the body in a compressed gas, the efforts of the scientists of our country have borne fruit in the creation of a new theory which leaves far behind all that has been done previously in this direction. We shall herein enumerate the most important results by Soviet scientists in the development of the theory of the boundary layer.

  14. Grain boundaries

    SciTech Connect

    Balluffi, R.W.; Bristowe, P.D.

    1991-01-01

    The present document is a progress report describing the work accomplished to date during the second year of our four-year grant (February 15, 1990--February 14, 1994) to study grain boundaries. The research was focused on the following three major efforts: Study of the atomic structure of grain boundaries by means of x-ray diffraction, transmission electron microscopy and computer modeling; study of short-circuit diffusion along grain boundaries; and development of a Thin-film Deposition/Bonding Apparatus for the manufacture of high purity bicrystals.

  15. Molecular dynamics simulations of ion solvation by flexible-boundary QM/MM: on-the-fly partial charge transfer between QM and MM subsystems.

    PubMed

    Pezeshki, Soroosh; Lin, Hai

    2014-09-15

    The flexible-boundary (FB) quantum mechanical/molecular mechanical (QM/MM) scheme accounts for partial charge transfer between the QM and MM subsystems. Previous calculations have demonstrated excellent performance of FB-QM/MM in geometry optimizations. This article reports an implementation to extend FB-QM/MM to molecular dynamics simulations. To prevent atoms from getting unreasonably close, which can lead to polarization catastrophe, empirical correcting functions are introduced to provide additive penalty energies for the involved atom pairs and to improve the descriptions of the repulsive exchange forces in FB-QM/MM calculations. Test calculations are carried out for chloride, lithium, sodium, and ammonium ions solvated in water. Comparisons with conventional QM/MM calculations suggest that the FB treatment provides reasonably good results for the charge distributions of the atoms in the QM subsystems and for the solvation shell structural properties, albeit smaller QM subsystems have been used in the FB-QM/MM dynamics simulations. PMID:25056247

  16. Object-oriented design and implementation of CFDLab: a computer-assisted learning tool for fluid dynamics using dual reciprocity boundary element methodology

    NASA Astrophysics Data System (ADS)

    Friedrich, J.

    1999-08-01

    As lecturers, our main concern and goal is to develop more attractive and efficient ways of communicating up-to-date scientific knowledge to our students and facilitate an in-depth understanding of physical phenomena. Computer-based instruction is very promising to help both teachers and learners in their difficult task, which involves complex cognitive psychological processes. This complexity is reflected in high demands on the design and implementation methods used to create computer-assisted learning (CAL) programs. Due to their concepts, flexibility, maintainability and extended library resources, object-oriented modeling techniques are very suitable to produce this type of pedagogical tool. Computational fluid dynamics (CFD) enjoys not only a growing importance in today's research, but is also very powerful for teaching and learning fluid dynamics. For this purpose, an educational PC program for university level called 'CFDLab 1.1' for Windows™ was developed with an interactive graphical user interface (GUI) for multitasking and point-and-click operations. It uses the dual reciprocity boundary element method as a versatile numerical scheme, allowing to handle a variety of relevant governing equations in two dimensions on personal computers due to its simple pre- and postprocessing including 2D Laplace, Poisson, diffusion, transient convection-diffusion.

  17. Dynamic finite-strain modelling of the human left ventricle in health and disease using an immersed boundary-finite element method

    PubMed Central

    Gao, Hao; Carrick, David; Berry, Colin; Griffith, Boyce E.; Luo, Xiaoyu

    2016-01-01

    Detailed models of the biomechanics of the heart are important both for developing improved interventions for patients with heart disease and also for patient risk stratification and treatment planning. For instance, stress distributions in the heart affect cardiac remodelling, but such distributions are not presently accessible in patients. Biomechanical models of the heart offer detailed three-dimensional deformation, stress and strain fields that can supplement conventional clinical data. In this work, we introduce dynamic computational models of the human left ventricle (LV) that are derived from clinical imaging data obtained from a healthy subject and from a patient with a myocardial infarction (MI). Both models incorporate a detailed invariant-based orthotropic description of the passive elasticity of the ventricular myocardium along with a detailed biophysical model of active tension generation in the ventricular muscle. These constitutive models are employed within a dynamic simulation framework that accounts for the inertia of the ventricular muscle and the blood that is based on an immersed boundary (IB) method with a finite element description of the structural mechanics. The geometry of the models is based on data obtained non-invasively by cardiac magnetic resonance (CMR). CMR imaging data are also used to estimate the parameters of the passive and active constitutive models, which are determined so that the simulated end-diastolic and end-systolic volumes agree with the corresponding volumes determined from the CMR imaging studies. Using these models, we simulate LV dynamics from enddiastole to end-systole. The results of our simulations are shown to be in good agreement with subject-specific CMR-derived strain measurements and also with earlier clinical studies on human LV strain distributions. PMID:27041786

  18. Climate change implications in the northern coastal temperate rainforest of North America

    USGS Publications Warehouse

    Shanley, Colin S.; Pyare, Sanjay; Goldstein, Michael I.; Alaback, Paul B.; Albert, David M.; Beier, Colin M.; Brinkman, Todd J.; Edwards, Rick T.; Hood, Eran; MacKinnon, Andy; McPhee, Megan V.; Patterson, Trista; Suring, Lowell H.; Tallmon, David; Wipfli, Mark S.

    2015-01-01

    We synthesized an expert review of climate change implications for hydroecological and terrestrial ecological systems in the northern coastal temperate rainforest of North America. Our synthesis is based on an analysis of projected temperature, precipitation, and snowfall stratified by eight biogeoclimatic provinces and three vegetation zones. Five IPCC CMIP5 global climate models (GCMs) and two representative concentration pathways (RCPs) are the basis for projections of mean annual temperature increasing from a current average (1961–1990) of 3.2 °C to 4.9–6.9 °C (5 GCM range; RCP4.5 scenario) or 6.4–8.7 °C (RCP8.5), mean annual precipitation increasing from 3130 mm to 3210–3400 mm (3–9 % increase) or 3320–3690 mm (6–18 % increase), and total precipitation as snow decreasing from 1200 mm to 940–720 mm (22–40 % decrease) or 720–500 mm (40–58 % decrease) by the 2080s (2071–2100; 30-year normal period). These projected changes are anticipated to result in a cascade of ecosystem-level effects including: increased frequency of flooding and rain-on-snow events; an elevated snowline and reduced snowpack; changes in the timing and magnitude of stream flow, freshwater thermal regimes, and riverine nutrient exports; shrinking alpine habitats; altitudinal and latitudinal expansion of lowland and subalpine forest types; shifts in suitable habitat boundaries for vegetation and wildlife communities; adverse effects on species with rare ecological niches or limited dispersibility; and shifts in anadromous salmon distribution and productivity. Our collaborative synthesis of potential impacts highlights the coupling of social and ecological systems that characterize the region as well as a number of major information gaps to help guide assessments of future conditions and adaptive capacity.

  19. Soil moisture variation and dynamics across a wildfire burn boundary in a loblolly pine (Pinus taeda) forest

    NASA Astrophysics Data System (ADS)

    Cardenas, M. Bayani; Kanarek, Michael R.

    2014-11-01

    A year after the most destructive wildfire in Texas (USA) history which occurred in and around Bastrop State Park, we established a 165 m-long study transect, bridging burned and unburned areas, to study post-wildfire soil moisture dynamics. Soil moisture content (θ) was monitored indirectly approximately monthly for half a year using a variety of methods with different measurement scales including: 2D electrical resistivity (ER) imaging and surface and vertical profiles using probes which measure soil dielectric properties. The burned section, where the majority of loblolly pine trees were killed, had higher θ and lower ER whereas the unburned end which is still populated by live pine trees had lower θ and higher ER. This pattern persisted from the ground surface and down to ∼2 m and through the study period even after a rainfall event which made the whole transect generally wetter but with the burned end showing a much stronger wetting response to the storm. The differences in θ cannot be explained by differences in soil texture with the burned end with sand soil and the unburned end with less permeable loamy sand. The differing results may be explained by loss of canopy cover and by reduced transpiration at the burned end where the dead roots may also potentially serve as macropores. Thus, after fires and until new vegetation cover has grown, the burned areas will store and transmit more water which could lead to increased groundwater recharge and promote the recovery or invasion of certain types of vegetation.

  20. Surface layer ozone and nitric oxides in the Arctic: The inuence of boundary layer dynamics, snowpack chemistry, surface exchanges, and seasonality

    NASA Astrophysics Data System (ADS)

    Van Dam, Brie A.

    The snowpack is a region of active chemistry. Aqueous chemistry in a quasi-liquid layer on snow grains and gas-phase chemical reactions in snow interstitial air can lead to the production or destruction of important trace gases. Physical transport parameters such as wind pumping and diffusion affect the vertical distribution of gases within the snowpack. The resulting emission or uptake of trace gases at the atmosphere-snowpack interface can have significant in uence on the chemistry of the lower atmosphere. In this work the dynamic interactions between the snowpack and atmosphere are examined from multiple perspectives. The primary focus is on ozone (O3) and nitrogen oxides (NOx) in the Arctic, a region undergoing widespread environmental change. To investigate an ice-sheet location with year round snow cover, data from a two-year campaign at Summit, Greenland are implemented. At Summit this study examines (1) the processes contributing to vigorous chemistry in snow interstitial air, and (2) the role of the boundary layer over snow in determining surface layer NOx. Physical and chemical processes are shown to contribute to distinct seasonal and diurnal cycles of O3, NO, and NO2 in the snowpack. Boundary layer depths estimated from sonic anemometer turbulence quantities are used alongside sodar-derived values to show that the depth of the stable to weakly stable boundary layer at Summit was not a primary factor in determining NO x in early summer. Motivated by observations of an increase in the length of the snow-free season in the Arctic in recent decades, data from a one-year experiment at the seasonally-snow covered location of Toolik Lake, AK are also incorporated. This study shows the first observations of springtime ozone depletion events at a location over 200 km from the coast in the Arctic. FLEXPART analysis is used to illustrate that these inland events are linked to transport conditions. Lastly at this location, eddy-covariance O3 uxes were calculated to

  1. Vertical stratification of the termite assemblage in a neotropical rainforest.

    PubMed

    Roisin, Yves; Dejean, Alain; Corbara, Bruno; Orivel, Jerôme; Samaniego, Mirna; Leponce, Maurice

    2006-08-01

    The importance of termites as decomposers in tropical forests has long been recognized. Studies on the richness and diversity of termite species and their ecological function have flourished in more recent times, but these have been mostly conducted in a thin stratum within a standing man's reach. Our aims were to evaluate the specific richness and composition of the termite assemblage in the canopy of a tropical rainforest and to determine its originality with respect to the sympatric ground-level fauna. We conducted systematic searches for canopy termites, together with conventional sampling of the sympatric ground-level fauna, in the San Lorenzo forest, Panama. We hypothesized that (1) the canopy accommodates two categories of wood-feeding termites (long-distance foragers and small-colony "one-piece" species) and possibly soil-feeders in suspended soil-like habitats; (2) due to the abundance of soil-feeders, the overall diversity of the ground fauna is higher than that of the canopy; (3) differences in microclimate and resource accessibility favour vertical stratification among wood-feeders. Sixty-three canopy samples yielded ten species of termites, all wood-feeders. Five of these were not found at ground level, although a total of 243 ground samples were collected, representing 29 species. In addition to long-distance foragers (Microcerotermes and Nasutitermes spp.) and small-colony termites (mostly Kalotermitidae), the canopy fauna included Termes hispaniolae, a wood-feeding Termitidae from an allegedly soil-feeding genus, living in large dead branches. Soil-feeders were absent from the canopy, probably because large epiphytes were scarce. As predicted, the ground fauna was much richer than that of the canopy, but the species richness of both habitats was similar when only wood-feeders were considered. Vertical stratification was strongly marked among wood-feeders, as all common species, apart from the arboreal-nesting Microcerotermes arboreus, could

  2. Vertical stratification of the termite assemblage in a neotropical rainforest.

    PubMed

    Roisin, Yves; Dejean, Alain; Corbara, Bruno; Orivel, Jerôme; Samaniego, Mirna; Leponce, Maurice

    2006-08-01

    The importance of termites as decomposers in tropical forests has long been recognized. Studies on the richness and diversity of termite species and their ecological function have flourished in more recent times, but these have been mostly conducted in a thin stratum within a standing man's reach. Our aims were to evaluate the specific richness and composition of the termite assemblage in the canopy of a tropical rainforest and to determine its originality with respect to the sympatric ground-level fauna. We conducted systematic searches for canopy termites, together with conventional sampling of the sympatric ground-level fauna, in the San Lorenzo forest, Panama. We hypothesized that (1) the canopy accommodates two categories of wood-feeding termites (long-distance foragers and small-colony "one-piece" species) and possibly soil-feeders in suspended soil-like habitats; (2) due to the abundance of soil-feeders, the overall diversity of the ground fauna is higher than that of the canopy; (3) differences in microclimate and resource accessibility favour vertical stratification among wood-feeders. Sixty-three canopy samples yielded ten species of termites, all wood-feeders. Five of these were not found at ground level, although a total of 243 ground samples were collected, representing 29 species. In addition to long-distance foragers (Microcerotermes and Nasutitermes spp.) and small-colony termites (mostly Kalotermitidae), the canopy fauna included Termes hispaniolae, a wood-feeding Termitidae from an allegedly soil-feeding genus, living in large dead branches. Soil-feeders were absent from the canopy, probably because large epiphytes were scarce. As predicted, the ground fauna was much richer than that of the canopy, but the species richness of both habitats was similar when only wood-feeders were considered. Vertical stratification was strongly marked among wood-feeders, as all common species, apart from the arboreal-nesting Microcerotermes arboreus, could

  3. Soil respiration flux in northern coastal temperate rainforest ecosystems

    NASA Astrophysics Data System (ADS)

    D'Amore, D. V.; Nay, S. M.; Edwards, R.; Valentine, D. W.; Hood, E. W.

    2009-12-01

    Forest carbon budgets are of increasing concern because of their linkages with changing climate. The potential source strength of northern forested ecosystems is of great interest due to the large carbon stock of these systems, especially the extensive peatlands. Where very few long-term measurements of soil carbon cycles have been made, such as the North Pacific coastal temperate margin, peatlands have potentially large but largely unknown source strengths, particularly through soil respiration. The easily and widely measured factors that influence the metabolism of plants and microorganisms in soils, such as temperature, moisture and substrate quality, must be coupled with a network of plot-scale measurements of soil respiration fluxes in this region in order to produce reasonable models of soil respiration flux across gradients of climate, vegetation and soil types. We designed a study to address this issue and measured soil respiration across a hydrologic gradient to quantify the influence of soil temperature and moisture on the magnitude and seasonality of carbon fluxes in the coastal temperate rainforest biome. Replicated study sites were established in three common ecosystem types (peatlands, forested wetlands, and upland forest) within three coastal watersheds. In total, nine sites of the three ecosystem types were measured at monthly intervals during the snow-free period between May and November for two years. Soil respiration fluxes during the six-month measurement period were used to construct a respiration flux model for each landscape type. Soil respiration fluxes followed the seasonal temperature pattern in all ecosystem types and also varied with soil saturation as well in uplands. Temperature dependent models of soil respiration flux were best fit to intermediate drainage conditions in forested wetlands and explained up to 85% of the variation in this ecosystem type. Modeled soil respiration estimates were better at low temperatures with high water

  4. Soil respiration flux in northern coastal temperate rainforest ecosystems

    NASA Astrophysics Data System (ADS)

    D'Amore, David; Nay, S. Mark; Edwards, Richard; Valentine, David; Hood, Eran

    2010-05-01

    Forest carbon budgets are of increasing concern because of their linkages with changing climate. The potential source strength of northern forested ecosystems is of great interest due to the large carbon stock of these systems, especially the extensive peatlands. Where very few long-term measurements of soil carbon cycles have been made, such as the North Pacific coastal temperate margin, peatlands have potentially large but largely unknown source strengths, particularly through soil respiration. The easily and widely measured factors that influence the metabolism of plants and microorganisms in soils, such as temperature, moisture and substrate quality, must be coupled with a network of plot-scale measurements of soil respiration fluxes in this region in order to produce reasonable models of soil respiration flux across gradients of climate, vegetation and soil types. We designed a study to address this issue and measured soil respiration across a hydrologic gradient to quantify the influence of soil temperature and moisture on the magnitude and seasonality of carbon fluxes in the coastal temperate rainforest biome. Replicated study sites were established in three common ecosystem types (peatlands, forested wetlands, and upland forest) within three coastal watersheds. In total, nine sites of the three ecosystem types were measured at monthly intervals during the snow-free period between May and November for two years. Soil respiration fluxes during the six-month measurement period were used to construct a respiration flux model for each landscape type. Soil respiration fluxes followed the seasonal temperature pattern in all ecosystem types and also varied with soil saturation as well in uplands. Temperature dependent models of soil respiration flux were best fit to intermediate drainage conditions in forested wetlands and explained up to 85% of the variation in this ecosystem type. Modeled soil respiration estimates were better at low temperatures with high water

  5. Characterising the effect of a variety of surface roughness on boundary layer wind and dynamics within the scanning Doppler lidar network in Finland

    NASA Astrophysics Data System (ADS)

    Hirsikko, Anne; O'Connor, Ewan J.; Wood, Curtis R.; Vakkari, Ville

    2013-04-01

    Aerosol particle and trace gas atmospheric content is controlled by natural and anthropological emissions. However, further dispersion in the atmosphere is driven by wind and dynamic mixing. Atmospheric surface and boundary layer dynamics have direct and indirect effects on weather, air quality and processes affecting climate (e.g. gas exchange between ecosystem and atmosphere). In addition to the amount of solar energy and prevailing meteorological condition, the surface topography has a strong influence on the close to surface wind field and turbulence, particularly in urban areas (e.g. Barlow and Coceal, 2009). In order to characterise the effect of forest, urban and coastal surfaces on boundary layer wind and mixing, we have utilised the Finnish Doppler lidar network (Hirsikko et al., 2013). The network consists of five 1.5 μm Doppler lidars (HALO Photonics, Pearson et al., 2009), of which four are capable of full hemispheric scanning and are located at Helsinki (60.12°N, 25.58°E, 45 m asl.), Utö island (59.47°N, 21.23°E, 8 m asl.), SMEAR II at Hyytiälä (61.50°N, 24.17°E, 181 m asl.) and Kuopio (62.44°N, 27.32°E, 190 m asl.). The fifth lidar at Sodankylä (67.37°N, 26.63°E, 171 m asl.) is a new model designed for the Arctic environment with no external moving parts, but still retains limited scan capability. Investigation of boundary layer wind and mixing condition can now be extended beyond vertical profiles of horizontal wind, and dissipation rate of turbulent kinetic energy (O'Connor et al., 2010) throughout the boundary layer. We have applied custom designed scanning routines for 3D-observation of the wind fields and simultaneous aerosol particle distribution continuously for over one year at Helsinki and Utö, and began similar scanning routines at Kuopio and Hyytiälä in spring 2013. In this long term project, our aims are to 1) characterise the effect of the land-sea interface and the urban environment on the wind and its turbulent nature

  6. The interpretation of crustal dynamics data in terms of plate motions and regional deformation near plate boundaries

    NASA Astrophysics Data System (ADS)

    Solomon, Sean C.

    During our participation in the NASA Crustal Dynamics Project under NASA contract NAS-27339 and grant NAG5-814 for the period 1982-1991, we published or submitted for publication 30 research papers and 52 abstracts of presentations at scientific meetings. In addition, five M.I.T. Ph.D. students (Eric Bergman, Steven Bratt, Dan Davis, Jeanne Sauber, Anne Sheehan) were supported wholly or in part by this project during their thesis research. Highlights of our research progress during this period include the following: application of geodetic data to determine rates of strain in the Mojave block and in central California and to clarify the relation of such strain to the San Andreas fault and Pacific-North American plate motions; application of geodetic data to infer post seismic deformation associated with large earthquakes in the Imperial Valley, Hebgen Lake, Argentina, and Chile; determination of the state of stress in oceanic lithosphere from a systematic study of the centroid depths and source mechanisms of oceanic intraplate earthquakes; development of models for the state of stress in young oceanic regions arising from the differential cooling of the lithosphere; determination of the depth extent and rupture characteristics of oceanic transform earthquakes; improved determination of earthquake slip vectors in the Gulf of California, an important data set for the estimation of Pacific-North American plate motions; development of models for the state of stress and mechanics of fold-and-thrust belts and accretionary wedges; development of procedures to invert geoid height, residual bathymetry, and differential body wave travel time residuals for lateral variations in the characteristic temperature and bulk composition of the oceanic upper mantle; and initial GPS measurements of crustal deformation associated with the Imperial-Cerro Prieto fault system in southern California and northern Mexico. Full descriptions of the research conducted on these topics may be

  7. The interpretation of crustal dynamics data in terms of plate motions and regional deformation near plate boundaries

    NASA Technical Reports Server (NTRS)

    Solomon, Sean C.

    1991-01-01

    During our participation in the NASA Crustal Dynamics Project under NASA contract NAS-27339 and grant NAG5-814 for the period 1982-1991, we published or submitted for publication 30 research papers and 52 abstracts of presentations at scientific meetings. In addition, five M.I.T. Ph.D. students (Eric Bergman, Steven Bratt, Dan Davis, Jeanne Sauber, Anne Sheehan) were supported wholly or in part by this project during their thesis research. Highlights of our research progress during this period include the following: application of geodetic data to determine rates of strain in the Mojave block and in central California and to clarify the relation of such strain to the San Andreas fault and Pacific-North American plate motions; application of geodetic data to infer post seismic deformation associated with large earthquakes in the Imperial Valley, Hebgen Lake, Argentina, and Chile; determination of the state of stress in oceanic lithosphere from a systematic study of the centroid depths and source mechanisms of oceanic intraplate earthquakes; development of models for the state of stress in young oceanic regions arising from the differential cooling of the lithosphere; determination of the depth extent and rupture characteristics of oceanic transform earthquakes; improved determination of earthquake slip vectors in the Gulf of California, an important data set for the estimation of Pacific-North American plate motions; development of models for the state of stress and mechanics of fold-and-thrust belts and accretionary wedges; development of procedures to invert geoid height, residual bathymetry, and differential body wave travel time residuals for lateral variations in the characteristic temperature and bulk composition of the oceanic upper mantle; and initial GPS measurements of crustal deformation associated with the Imperial-Cerro Prieto fault system in southern California and northern Mexico. Full descriptions of the research conducted on these topics may be

  8. Dynamics of convergent plate boundaries: Insights from subduction-related serpentinite melanges from the northern edge of the Caribbean plate

    NASA Astrophysics Data System (ADS)

    García-Casco, A.

    2012-04-01

    MORB-derived eclogite) incorporated late in the convergent history when oceanic subduction was completed. Hence, incorporation of tectonic slices of the subduction channel into the shallow (low-P, low-T) melanges and subducted/accreted continental margins occur when collision-related dynamics imposed by subduction of buoyant continental or oceanic lithosphere affected the plate margin. Aqueous fluid, sourced from both subducted sediment and metamafic/ultramafic material, was available in large quantity in the subduction environment, as indicated by massive antigoritite, rinds of metasomatic rocks around included HP metamafic rocks, retrogressed eclogite, jadeitite and hydrothermal veins within antigoritite. Such a vigorous hydrology (fluid-flow) deep in the subduction environment point to the development of wide subduction channels and explain the abundance of accreted blocks. It can also explain the scarcity of large scale (>km) slices of the subducted oceanic lithosphere in the belt, for these are likely the result of focalized distribution of deformation occurring when forearc peridotite is barely hydrated (Agard et al., Long-term coupling along the subduction plate interface: Insights from exhumed rocks and models. This session, EGU 2012). Alternatively, these large tectonic slices may have been formed by the collision dynamics caused by late-stage subduction/accretion of the continental margin (or buoyant -thick- oceanic crust). Except maturation (cooling) of the subduction zone with time at orogenic belt-scale, no other simple generalization can be reached on the thermal state of the subducting plate and the exhumation process of the subduction channel. P-T-t paths of HP rocks indicate that slab fragments ranging from cold to hot coexisted during relatively short time intervals (ca. 10 Myr), and some fragments of the subduction channel were exhumed shortly after formation while others lasted several tens of Myr to arrive to the near-surface forearc

  9. Landscape Patterns in Rainforest Phylogenetic Signal: Isolated Islands of Refugia or Structured Continental Distributions?

    PubMed Central

    Kooyman, Robert M.; Rossetto, Maurizio; Sauquet, Hervé; Laffan, Shawn W.

    2013-01-01

    Objectives Identify patterns of change in species distributions, diversity, concentrations of evolutionary history, and assembly of Australian rainforests. Methods We used the distribution records of all known rainforest woody species in Australia across their full continental extent. These were analysed using measures of species richness, phylogenetic diversity (PD), phylogenetic endemism (PE) and phylogenetic structure (net relatedness index; NRI). Phylogenetic structure was assessed using both continental and regional species pools. To test the influence of growth-form, freestanding and climbing plants were analysed independently, and in combination. Results Species richness decreased along two generally orthogonal continental axes, corresponding with wet to seasonally dry and tropical to temperate habitats. The PE analyses identified four main areas of substantially restricted phylogenetic diversity, including parts of Cape York, Wet Tropics, Border Ranges, and Tasmania. The continental pool NRI results showed evenness (species less related than expected by chance) in groups of grid cells in coastally aligned areas of species rich tropical and sub-tropical rainforest, and in low diversity moist forest areas in the south-east of the Great Dividing Range and in Tasmania. Monsoon and drier vine forests, and moist forests inland from upland refugia showed phylogenetic clustering, reflecting lower diversity and more relatedness. Signals for evenness in Tasmania and clustering in northern monsoon forests weakened in analyses using regional species pools. For climbing plants, values for NRI by grid cell showed strong spatial structuring, with high diversity and PE concentrated in moist tropical and subtropical regions. Conclusions/Significance Concentrations of rainforest evolutionary history (phylo-diversity) were patchily distributed within a continuum of species distributions. Contrasting with previous concepts of rainforest community distribution, our findings of

  10. Giant eucalypts - globally unique fire-adapted rain-forest trees?

    PubMed

    Tng, D Y P; Williamson, G J; Jordan, G J; Bowman, D M J S

    2012-11-01

    CONTENTS: Summary    1 I. Introduction    1 II. Giant eucalypts in a global context    2 III. Giant eucalypts - taxonomy and distribution    4 IV. Growth of giant eucalypts    6 V. Fire and regeneration of giant eucalypts    8 VI. Are giant eucalypts different from other rain-forest trees?    9 VII. Conclusions 10 Acknowledgements 11 References 11 SUMMARY: Tree species exceeding 70 m in height are rare globally. Giant gymnosperms are concentrated near the Pacific coast of the USA, while the tallest angiosperms are eucalypts (Eucalyptus spp.) in southern and eastern Australia. Giant eucalypts co-occur with rain-forest trees in eastern Australia, creating unique vegetation communities comprising fire-dependent trees above fire-intolerant rain-forest. However, giant eucalypts can also tower over shrubby understoreys (e.g. in Western Australia). The local abundance of giant eucalypts is controlled by interactions between fire activity and landscape setting. Giant eucalypts have features that increase flammability (e.g. oil-rich foliage and open crowns) relative to other rain-forest trees but it is debatable if these features are adaptations. Probable drivers of eucalypt gigantism are intense intra-specific competition following severe fires, and inter-specific competition among adult trees. However, we suggest that this was made possible by a general capacity of eucalypts for 'hyper-emergence'. We argue that, because giant eucalypts occur in rain-forest climates and share traits with rain-forest pioneers, they should be regarded as long-lived rain-forest pioneers, albeit with a particular dependence on fire for regeneration. These unique ecosystems are of high conservation value, following substantial clearing and logging over 150 yr.

  11. Giant eucalypts - globally unique fire-adapted rain-forest trees?

    PubMed

    Tng, D Y P; Williamson, G J; Jordan, G J; Bowman, D M J S

    2012-11-01

    CONTENTS: Summary    1 I. Introduction    1 II. Giant eucalypts in a global context    2 III. Giant eucalypts - taxonomy and distribution    4 IV. Growth of giant eucalypts    6 V. Fire and regeneration of giant eucalypts    8 VI. Are giant eucalypts different from other rain-forest trees?    9 VII. Conclusions 10 Acknowledgements 11 References 11 SUMMARY: Tree species exceeding 70 m in height are rare globally. Giant gymnosperms are concentrated near the Pacific coast of the USA, while the tallest angiosperms are eucalypts (Eucalyptus spp.) in southern and eastern Australia. Giant eucalypts co-occur with rain-forest trees in eastern Australia, creating unique vegetation communities comprising fire-dependent trees above fire-intolerant rain-forest. However, giant eucalypts can also tower over shrubby understoreys (e.g. in Western Australia). The local abundance of giant eucalypts is controlled by interactions between fire activity and landscape setting. Giant eucalypts have features that increase flammability (e.g. oil-rich foliage and open crowns) relative to other rain-forest trees but it is debatable if these features are adaptations. Probable drivers of eucalypt gigantism are intense intra-specific competition following severe fires, and inter-specific competition among adult trees. However, we suggest that this was made possible by a general capacity of eucalypts for 'hyper-emergence'. We argue that, because giant eucalypts occur in rain-forest climates and share traits with rain-forest pioneers, they should be regarded as long-lived rain-forest pioneers, albeit with a particular dependence on fire for regeneration. These unique ecosystems are of high conservation value, following substantial clearing and logging over 150 yr. PMID:23121314

  12. Impact of Lowland Rainforest Transformation on Diversity and Composition of Soil Prokaryotic Communities in Sumatra (Indonesia).

    PubMed

    Schneider, Dominik; Engelhaupt, Martin; Allen, Kara; Kurniawan, Syahrul; Krashevska, Valentyna; Heinemann, Melanie; Nacke, Heiko; Wijayanti, Marini; Meryandini, Anja; Corre, Marife D; Scheu, Stefan; Daniel, Rolf

    2015-01-01

    Prokaryotes are the most abundant and diverse group of microorganisms in soil and mediate virtually all biogeochemical cycles in terrestrial ecosystems. Thereby, they influence aboveground plant productivity and diversity. In this study, the impact of rainforest transformation to intensively managed cash crop systems on soil prokaryotic communities was investigated. The studied managed land use systems comprised rubber agroforests (jungle rubber), rubber plantations and oil palm plantations within two Indonesian landscapes Bukit Duabelas and Harapan. Soil prokaryotic community composition and diversity were assessed by pyrotag sequencing of bacterial and archaeal 16S rRNA genes. The curated dataset contained 16,413 bacterial and 1679 archaeal operational taxonomic units at species level (97% genetic identity). Analysis revealed changes in indigenous taxon-specific patterns of soil prokaryotic communities accompanying lowland rainforest transformation to jungle rubber, and intensively managed rubber and oil palm plantations. Distinct clustering of the rainforest soil communities indicated that these are different from the communities in the studied managed land use systems. The predominant bacterial taxa in all investigated soils were Acidobacteria, Actinobacteria, Alphaproteobacteria, Betaproteobacteria, and Gammaproteobacteria. Overall, the bacterial community shifted from proteobacterial groups in rainforest soils to Acidobacteria in managed soils. The archaeal soil communities were mainly represented by Thaumarchaeota and Euryarchaeota. Members of the Terrestrial Group and South African Gold Mine Group 1 (Thaumarchaeota) dominated in the rainforest and members of Thermoplasmata in the managed land use systems. The alpha and beta diversity of the soil prokaryotic communities was higher in managed land use systems than in rainforest. In the case of bacteria, this was related to soil characteristics such as pH value, exchangeable Ca and Fe content, C to N ratio

  13. Impact of Lowland Rainforest Transformation on Diversity and Composition of Soil Prokaryotic Communities in Sumatra (Indonesia).

    PubMed

    Schneider, Dominik; Engelhaupt, Martin; Allen, Kara; Kurniawan, Syahrul; Krashevska, Valentyna; Heinemann, Melanie; Nacke, Heiko; Wijayanti, Marini; Meryandini, Anja; Corre, Marife D; Scheu, Stefan; Daniel, Rolf

    2015-01-01

    Prokaryotes are the most abundant and diverse group of microorganisms in soil and mediate virtually all biogeochemical cycles in terrestrial ecosystems. Thereby, they influence aboveground plant productivity and diversity. In this study, the impact of rainforest transformation to intensively managed cash crop systems on soil prokaryotic communities was investigated. The studied managed land use systems comprised rubber agroforests (jungle rubber), rubber plantations and oil palm plantations within two Indonesian landscapes Bukit Duabelas and Harapan. Soil prokaryotic community composition and diversity were assessed by pyrotag sequencing of bacterial and archaeal 16S rRNA genes. The curated dataset contained 16,413 bacterial and 1679 archaeal operational taxonomic units at species level (97% genetic identity). Analysis revealed changes in indigenous taxon-specific patterns of soil prokaryotic communities accompanying lowland rainforest transformation to jungle rubber, and intensively managed rubber and oil palm plantations. Distinct clustering of the rainforest soil communities indicated that these are different from the communities in the studied managed land use systems. The predominant bacterial taxa in all investigated soils were Acidobacteria, Actinobacteria, Alphaproteobacteria, Betaproteobacteria, and Gammaproteobacteria. Overall, the bacterial community shifted from proteobacterial groups in rainforest soils to Acidobacteria in managed soils. The archaeal soil communities were mainly represented by Thaumarchaeota and Euryarchaeota. Members of the Terrestrial Group and South African Gold Mine Group 1 (Thaumarchaeota) dominated in the rainforest and members of Thermoplasmata in the managed land use systems. The alpha and beta diversity of the soil prokaryotic