Topographic Domains Research Articles

Phosphorite occurrences on the western continental margin of India: An update

Marine phosphorites are well known from the tropical upwelling zones along the west coast of North America, South America, and African continents. Despite having similar oceanographic and topographic set-ups, comparable scales of phosphorite occurrences have not been reported from the western margin of the Indian subcontinent. However, Seabed surveys carried out by the Geological Survey of India during the last decade unearthed phosphatic crusts and nodules from several elevated topographic domains off the west coast of India. These new findings necessitate an update to the phosphorite zone map of the present-day Ocean. On the seamounts and spurs off the west coast of India, ferruginous and non-ferruginous phosphorites occur in the form of crusts and nodules within the water depth range of 300 to 800 m. Geochemical evidence and concurrent occurrences of varied types of phosphorites within the same topographic domain point to the prevalence of multiple episodes of short-duration phosphogenesis along the western margin of India.

Accuracy of Finite Fault Slip Estimates in Subduction Zone Regions With Topographic Green's Functions and Seafloor Geodesy

AbstractUntil recently, the lack of seafloor geodetic instrumentation and the use of unrealistically simple, half‐space based forward models have resulted in poor resolution of near‐trench slip in subduction zone settings. Here, we use a synthetic framework to investigate the impact of topography and geodetic data distribution on coseismic slip estimates in various subduction zone settings. We calculate surface displacements in two synthetic topographic domains that have topography similar to that of Chile and Japan, respectively. We then attempt to image target slip distributions by using a Bayesian approach to solve for slip with two sets of Green's functions—one that accounts for topography and one that does not—and five sets of 50 or more observation points selected from the synthetic surface displacements. Three of these sets of observation points are entirely onland, and two include 5–10 seafloor geodetic sites. We find that the use of topographic Green's functions always improves inferred slip models, and with seafloor geodetic data, it enables an almost perfect recovery of a target slip model, even in the near‐trench region. Critically, our results demonstrate that it would be impossible for non‐topographic Green's functions to properly recover the true slip distribution, particularly in the near‐trench region. We also perform a parameter study with approximately 4,000 slip models estimated using a least‐square approach, and find that topographic Green's functions yield significantly more accurate slip models in cases where good data (well distributed and reasonably dense) are available, even in the absence of seafloor geodetic sites.

A connectivity-constrained computational account of topographic organization in primate high-level visual cortex

Inferotemporal (IT) cortex in humans and other primates is topographically organized, containing multiple hierarchically organized areas selective for particular domains, such as faces and scenes. This organization is commonly viewed in terms of evolved domain-specific visual mechanisms. Here, we develop an alternative, domain-general and developmental account of IT cortical organization. The account is instantiated in interactive topographic networks (ITNs), a class of computational models in which a hierarchy of model IT areas, subject to biologically plausible connectivity-based constraints, learns high-level visual representations optimized for multiple domains. We find that minimizing a wiring cost on spatially organized feedforward and lateral connections, alongside realistic constraints on the sign of neuronal connectivity within model IT, results in a hierarchical, topographic organization. This organization replicates a number of key properties of primate IT cortex, including the presence of domain-selective spatial clusters preferentially involved in the representation of faces, objects, and scenes; columnar responses across separate excitatory and inhibitory units; and generic spatial organization whereby the response correlation of pairs of units falls off with their distance. We thus argue that topographic domain selectivity is an emergent property of a visual system optimized to maximize behavioral performance under generic connectivity-based constraints.

Developing topographic visual domain organization in a recurrent neural network with biological constraints

Developing topographic visual domain organization in a recurrent neural network with biological constraints

Terrain units, land use and land cover, and gross primary productivity of the largest fluvial basin in the Brazilian Amazonia/Cerrado ecotone: The Araguaia River basin

Integrity of most of tropical wetlands is threatened because they are often considered freely available resources of land and water. The Bananal, in the Araguaia River Basin, and the Pantanal in the Paraguai River Basin, are the two largest Brazilian wetlands influenced by the tropical seasonal floods. The purpose of this study is to integrate landscape structural and functional factors with the GPP dynamics over different terrain units present in the Araguaia River Basin. The study was conducted through the integration of different databases, including the topographic domains, protected areas and indigenous lands; land use and land cover map (year 2016); time series of GPP derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) sensor (period of 2000–2015); Shuttle Radar Topography Mission (SRTM) digital elevation models (DEM); and precipitation data produced by the WorldClim version 2 dataset. GPP time series were processed using statistical methods of time series decomposition. The results show that, in the alluvial domains, we find grasslands (mostly), alluvial forests with the highest levels of GPP, and the largest legally protected areas. Spatial distribution of pasturelands across the entire basin is broad while croplands are concentrated mainly in geologically old and high plateaus. The time series analysis revealed the presence of intra- and inter-annual vegetation patterns and a continuous increase of GPP over time. The results contribute to the understanding of the linkages between land use changes and global carbon cycles by considering land use as a response of how the landscape is organized. The results may provide subsidies for public policies for the carbon budget equilibrium, conservation of biodiversity, and rational use of natural resources.

Geomorphological Analysis of ExoMars Candidate Landing Site Oxia Planum

The article is devoted to a detailed photogeological and topographic analysis of the surface in the region of Oxia Planum, which is the most likely landing site for the rover of the ExoMars mission. The landing site consists of two topographic domains (highlands and lowlands) separated by a sharp regional slope. The highland domain accounts for approximately 25% of the landing site. The main unit of this domain is lava plains with an absolute model age of 3.65 Ga. These plains extend to the west and cover almost the entire surface of the lowlands, where they are overlain by a relatively thin (first tens of meters) layer of material removed from the highlands during the period of fluvial activity. The age of its final phase is estimated at 3.53 Ga. The material to be tested by the ExoMars rover is mainly associated with the final accumulation phase and is represented by deposits of dark and light smooth plains within the lowlands. The material of the dark plains mainly consists of a more coarse-grained fraction of the highland lava plains redeposited near the topographic boundary separating the highlands and lowlands. Deposits of the light plains are dominant at the landing site and are represented by a finer fraction of the material of the lava plains and light mantle material, in which clay minerals are likely predominant.

Effects of topographic domain and land use on spatial variability of deep soil moisture in the semi-arid Loess Plateau of China

AbstractDeep soil moisture is fundamental to hydrological cycle and ecosystem sustainability in arid and semi-arid regions. This study examined the combined effects of topographic domain and land use on the spatial variability of deep soil moisture (0–5 m) on the semi-arid Loess Plateau of China. Our results showed that deep soil moisture was generally temporally stable due to the thick loess soil in the plateau region. The depth-averaged soil moisture was slightly lower in the gully domain compared to the hillslope domain but was dependent on the soil depths. Soil moisture variability was clearly larger in the gully domain when compared with that in the hillslope domain in the 0–5 m profile. The mean soil moisture contents in comparable soil depths were lower in forestland than in grassland (and farmland), particularly in the hillslope domain. Land uses had similar vertical distribution characteristics of deep soil moisture for each topographic domain. Soil moisture showed highly significant positive correlations with slope aspect in the hillslope domain and with profile curvature in the gully domain.

Identifying a Suitable Model for Low-Flow Simulation in Watersheds of South-Central Chile: A Study Based on a Sensitivity Analysis

Choosing a model that suitably represents the characteristics of a watershed to simulate low flows is crucial, especially in watersheds whose main source of baseflow generation depends on groundwater storage and release. The goal of this investigation is to study the performance and representativeness of storage-release process modeling, considering aspects such as the topography and geology of the modeled watershed through regional sensitivity analysis, in order to improve low-flow prediction. To this end, four groundwater storage-release structures in various watersheds with different geological (fractured and sedimentary rock) and topographic domains (steep and gentle slopes) were analyzed. The results suggest that the two-reservoir structure with three runoff responses is suitable (better) for simulating low flows in watersheds with fractured geological characteristics and rugged or steep topography. The results also indicate that a one-reservoir model can be adequate for predicting low flows in watersheds with a sedimentary influence or flat topography.

Soil moisture variations at different topographic domains and land use types in the semi-arid Loess Plateau, China

Soil moisture plays a fundamental role in eco-hydrological processes in the semi-arid Loess Plateau. Catchments on the Loess Plateau can be generally divided into the hillslope domain and gully domain. However, the soil moisture variations linked to topographic domains and land use types remain poorly understood. Therefore, in this study, differences in soil moisture among three typical land use types (forestland, native grassland, and farmland) were investigated and compared between the spatial domains of hillslope and gully in the Jiegou catchment on the semi-arid Loess Plateau of China. Additionally, the spatial variations in the soil moisture of the 0–100 cm layers were explored in both wet and dry periods to evaluate the seasonal effects of different spatial domains and land use types. The results showed that including gully soil moisture weakly increased the spatially averaged soil moisture in the catchment but obviously increased the variability during wet periods. In contrast, the spatial means decreased weakly while the variability obviously decreased during dry periods. Soil moisture in forestland was lower than that in native grassland and farmland at all spatial domains during both wet and dry periods. The results also indicated that surface soil moisture (0–10 cm) differs between spatial domains but not land use types, which mainly due to the differences of evapotranspiration on the two topographic domains. In contrast, deep soil moisture (80–100 cm) differs among land use types but not spatial domains, which because of the differences of root water uptake among land use types. In addition, slope aspect played a more important role than slope gradient and elevation in the distribution of soil moisture at the hillslope domain. This was because the slope aspect affected the ground temperature by receiving different solar radiation, and further affected the soil evaporation and vegetation transpiration. Therefore, the results of this study indicates that both topographic domains and land use types should be considered when attempting to characterize soil moisture variability or modelling surface hydrological processes at catchment scale in heavily gullied regions.

Improved quantification of CO2 emission at Campi Flegrei by combined Lagrangian Stochastic and Eulerian dispersion modelling

This study investigates fumarolic CO2 emissions at Campi Flegrei (Southern Italy) and their dispersion in the lowest atmospheric boundary layer. We innovatively utilize a Lagrangian Stochastic dispersion model (WindTrax) combined with an Eulerian model (DISGAS) to diagnose the dispersion of diluted gas plumes over large and complex topographic domains. New measurements of CO2 concentrations acquired in February and October 2014 in the area of Pisciarelli and Solfatara, the two major fumarolic fields of Campi Flegrei caldera, and simultaneous measurements of meteorological parameters are used to: 1) test the ability of WindTrax to calculate the fumarolic CO2 flux from the investigated sources, and 2) perform predictive numerical simulations to resolve the mutual interference between the CO2 emissions of the two adjacent areas. This novel approach allows us to a) better quantify the CO2 emission of the fumarolic source, b) discriminate “true” CO2 contributions for each source, and c) understand the potential impact of the composite CO2 plume (Pisciarelli “plus” Solfatara) on the highly populated areas inside the Campi Flegrei caldera.

Mechanisms Responsible for the Observed Thermodynamic Structure in a Convective Boundary Layer Over the Hudson Valley of New York State

We examine cases of a regional elevated mixed layer (EML) observed during the Hudson Valley Ambient Meteorology Study (HVAMS) conducted in New York State, USA in 2003. Previously observed EMLs referred to topographic domains on scales of 10\(^{5}\)–10\(^{6}\) km\(^{2}\). Here, we present observational evidence of the mechanisms responsible for the development and maintenance of regional EMLs overlying a valley-based convective boundary layer (CBL) on much smaller spatial scales (<5000 km\(^{2})\). Using observations from aircraft-based, balloon-based, and surface-based platforms deployed during the HVAMS, we show that cross-valley horizontal advection, along-valley channelling, and fog-induced cold-air pooling are responsible for the formation and maintenance of the EML and valley-CBL coupling over New York State’s Hudson Valley. The upper layer stability of the overlying EML constrains growth of the valley CBL, and this has important implications for air dispersion, aviation interests, and fog forecasting.

Drainage reorganization during mountain building in the river system of the Eastern Cordillera of the Colombian Andes

The Eastern Cordillera of Colombia is a thick-skinned thrust-fold belt that is characterized by two topographic domains: (1) the axial zone, a high altitude plateau (the Sabana de Bogotá, 2500masl) with low local relief and dominated by longitudinal rivers, and (2) the Cordillera flanks, where local relief exceeds 1000m and transverse rivers dominate. On the basis of an analysis of digital topography and river parameters combined with a review of paleodrainage data, we show that the accumulation of shortening and crustal thickening during the Andean orogeny triggered a process of fluvial reorganization in the Cordillera. Owing to a progressive increase of the regional slope, the drainage network evolves from longitudinal to transverse-dominated, a process that is still active at present. This study provides the idea of progressive divide migration toward the inner part of the mountain belt, by which the area of the Sabana de Bogotá plateau is decreasing, the flanks increase in area, and ultimately transverse rivers will probably dominate the drainage of the Cordillera.

Seismic constraints on dynamic links between geomorphic processes and routing of sediment in a steep mountain catchment

Abstract. Landscape dynamics are determined by interactions amongst geomorphic processes. These interactions allow the effects of tectonic, climatic and seismic perturbations to propagate across topographic domains, and permit the impacts of geomorphic process events to radiate from their point of origin. Visual remote sensing and in situ observations do not fully resolve the spatiotemporal patterns of surface processes in a landscape. As a result, the mechanisms and scales of geomorphic connectivity are poorly understood. Because many surface processes emit seismic signals, seismology can determine their type, location and timing with a resolution that reveals the operation of integral landscapes. Using seismic records, we show how hillslopes and channels in an Alpine catchment are interconnected to produce evolving, sediment-laden flows. This is done for a convective storm, which triggered a sequence of hillslope processes and debris flows. We observe the evolution of these process events and explore the operation of two-way links between mass wasting and channel processes, which are fundamental to the dynamics of most erosional landscapes. We also track the characteristics and propagation of flows along the debris flow channel, relating changes of observed energy to the deposition/mobilization of sediments, and using the spectral content of debris flow seismic signals to qualitatively infer sediment characteristics and channel abrasion potential. This seismological approach can help to test theoretical concepts of landscape dynamics and yield understanding of the nature and efficiency of links between individual geomorphic processes, which is required to accurately model landscape dynamics under changing tectonic or climatic conditions and to anticipate the natural hazard risk associated with specific meteorological events.

Formation and analysis of topographical domains between lipid membranes tethered by DNA hybrids of different lengths.

We recently described a strategy to prepare DNA-tethered lipid membranes either to fixed DNA on a surface or to DNA displayed on a supported bilayer [Boxer et al., J. Struct. Biol., 2009, 168, 190; Boxer et al., Langmuir, 2011, 27, 5492]. With the latter system, the DNA hybrids are laterally mobile; when orthogonal sense-antisense pairs of different lengths are used, the DNA hybrids segregate by height and the tethered membrane deforms to accommodate the height difference. This architecture is particularly useful for modelling interactions between membranes mediated by molecular recognition and resembles cell-to-cell junctions. The length, affinity and population of the DNA hybrids between the membranes are completely controllable. Interesting patterns of height segregation are observed by fluorescence interference contrast microscopy. Diverse behavior is observed in the segregation and pattern forming process and possible mechanisms are discussed. This model system captures some of the essential physics of synapse formation and is a step towards understanding lipid membrane behaviour in cell-to-cell junctions.

Spontaneous strain of conductive strontium titanate Sr1− x La x TiO3 measured by using X-ray topographic domain contrast

We have measured the spontaneous strain c/a − 1 of the antiferrodistortive phase transition in the conductive strontium titanates Sr1− x La x TiO3 with x = 0, 0.005, 0.010, and 0.050 by using X-ray topographic domain contrast. We have found that the substitution of a small amount of La3+ ions into SrTiO3 leads to the large increase of the phase transition temperature T a, the saturated spontaneous strain (c/a − 1)s, and the saturated order parameter ϕ s. The values of T a and (c/a − 1)s of Sr0.95La0.05TiO3 are twice as large as those of SrTiO3. These findings indicate that the large increase of T a, (c/a − 1)s and ϕ s are not caused by the doped conduction electrons, but by the crystal structure change, due to the substitution of La3+ ions into Sr2+ sites.

Phosphatidylserine Membrane Translocation in Human Spermatozoa: Topography in Membrane Domains and Relation to Cell Vitality

The complex structure of the human spermatozoa membrane comprises five topographic domains. Transmembrane asymmetry of the distribution of phospholipids including phosphatidylserine (PS) is considered a marker of cell activity. The objective of the study was to determine which cytomembrane domains of human spermatozoa are involved in PS membrane translocation and to identify the possible relationship of PS translocation with spermatozoa morphology and vitality. In normozoospermic semen of 35 donors, annexin-V labeling with fluorescein determined PS translocation. Propidium iodide staining distinguished between vital and dead spermatozoa. Three types of PS membrane translocation have been distinguished: (1) in the midpiece, (2) in the acrosomal part and (3) simultaneously in the midpiece and acrosomal part. In morphologically normal vital spermatozoa, PS translocation occurred in the midpiece but never in the equatorial region. In dead spermatozoa, simultaneous PS translocation in the midpiece and acrosomal part was most often observed. The difference between proportions of, respectively, vital and dead spermatozoa presenting PS translocation located in different domains was significant (P < 0.0001). In vital cells, there was no difference in PS translocation prevalence between morphologically normal and abnormal spermatozoa (P > 0.05). The strict relation of PS translocation to specific membrane domains indicates functional specificity. It seems doubtful to include this phenomenon in physiological mechanisms of elimination of abnormal spermatozoa.

Structural insights into a unique cellulase fold and mechanism of cellulose hydrolysis.

Clostridium thermocellum is a well-characterized cellulose-degrading microorganism. The genome sequence of C. thermocellum encodes a number of proteins that contain type I dockerin domains, which implies that they are components of the cellulose-degrading apparatus, but display no significant sequence similarity to known plant cell wall-degrading enzymes. Here, we report the biochemical properties and crystal structure of one of these proteins, designated CtCel124. The protein was shown to be an endo-acting cellulase that displays a single displacement mechanism and acts in synergy with Cel48S, the major cellulosomal exo-cellulase. The crystal structure of CtCel124 in complex with two cellotriose molecules, determined to 1.5 Å, displays a superhelical fold in which a constellation of α-helices encircle a central helix that houses the catalytic apparatus. The catalytic acid, Glu96, is located at the C-terminus of the central helix, but there is no candidate catalytic base. The substrate-binding cleft can be divided into two discrete topographical domains in which the bound cellotriose molecules display twisted and linear conformations, respectively, suggesting that the enzyme may target the interface between crystalline and disordered regions of cellulose.

Vertebral artery hypoplasia may contribute to abnormal vestibular evoked myogenic potentials.

Congenital vertebral artery hypoplasia (VAH) is an uncommon embryonic variation of the posterior circulation. The clinical relevance and hemodynamic impact of VAH have been under debate. We tried to localize the topographic domain of vertebral artery hypoplasia with vestibular evoked myogenic potential (VEMP) studies. From January 2005 to October 2005, we reviewed the magnetic resonance angiographic records of 250 health check-up outpatients (108 men and 142 women; mean age, 30.8 +/- 14.0 years; range, 25 to 55 years). There were 26 subjects with a hypoplasic VA. We performed a case-control study by recruiting another 26 healthy subjects without hypoplastic VA as a control group. VEMP testing was performed in each subject for comparison. The results revealed that 88.47% of the healthy subjects with a VAH demonstrated abnormal VEMPs either unilaterally or bilaterally, which was statistically higher than control group without a VAH (p=0.019). Given that hypoplasic VA was exclusively right-sided in these patients, the majority of whom had an ipsilateral delayed response or absence of VEMP. We therefore hypothesize that VA hypoplasia might contribute to brain stem lesion or interruption of sacculo-collic reflex.

Heterotypic interaction of fibroblasts and endothelial cells on restricted area

The polysaccharide hyaluronic acid (Hyal) was photoimmobilized on glass surfaces to obtain a pattern with squares and rectangles of different dimensions and chemistry. The microstructured surfaces were characterized by Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), Attenuated Total Reflection Infrared Spectroscopy (ATR FT-IR), and Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS). Surface analysis revealed the presence of a pattern consisting of alternating glass and Hyal microstructures whose dimensions decreased from the center to the edge of the sample. The behavior of Human Coronary Artery Endothelial Cells (HCAEC) and human tumoral dermal fibroblasts (C54) was studied on these micropatterned surfaces. Neither HCAEC nor C54 adhered to the immobilized Hyal but both adapted their shape to the different sizes of the glass squares and rectangles. The number of adherent HCAEC and C54 depended on the dimensions of both the glass domains and the nuclei of the cells. Co-cultured C54 on HCAEC patterned surfaces showed a heterotypic cell-cell interaction in the same chemical and topographic domain for the first time. In comparison to other techniques for patterning two different cell types, our approach was non cytotoxic and allowed arbitrary geometric patterns to form on different biocompatible substrata.

Eddy Formation near the West Coast of Greenland

Abstract This paper extends A. Bracco and J. Pedlosky’s investigation of the eddy-formation mechanism in the eastern Labrador Sea by including a more realistic depiction of the boundary current. The quasigeostrophic model consists of a meridional, coastally trapped current with three vertical layers. The current configuration and topographic domain are chosen to match, as closely as possible, the observations of the boundary current and the varying topographic slope along the West Greenland coast. The role played by the bottom-intensified component of the boundary current on the formation of the Labrador Sea Irminger Rings is explored. Consistent with the earlier study, a short, localized bottom-trapped wave is responsible for most of the perturbation energy growth. However, for the instability to occur in the three-layer model, the deepest component of the boundary current must be sufficiently strong, highlighting the importance of the near-bottom flow. The model is able to reproduce important features of the observed vortices in the eastern Labrador Sea, including the polarity, radius, rate of formation, and vertical structure. At the time of formation, the eddies have a surface signature as well as a strong circulation at depth, possibly allowing for the transport of both surface and near-bottom water from the boundary current into the interior basin. This work also supports the idea that changes in the current structure could be responsible for the observed interannual variability in the number of Irminger Rings formed.