Upper Surface (upper + surface)

Distribution by Scientific Domains
Distribution within Life Sciences

Selected Abstracts

Origin and palaeo-environments of calcareous sediments in the Moshaweng dry valley, southeast Botswana

S. Ringrose
Abstract Quaternary sedimentation in the Moshaweng dry valley of southeastern Botswana is evaluated on the basis of geomorphological evolution and sedimentological analyses. Stratigraphic evidence reveals an upper surface (1095 m) containing abundant sil-calcrete, an intermediate surface (1085 m) in which sil-calcrete underlies nodular calcrete and lower (1075 m) surface in which sil-calcrete and nodular calcrete are interbedded. This subdivision is reflected in the geochemical composition of the sediments which show an overall trend of decreasing SiO2 content (and increasing CaCO3 content) with depth from the highest to the lowest surface levels. The calcretes and sil-calcretes represent modifications of pre-existing detrital Kalahari Group sand and basal Kalahari pebbles which thinned over a Karoo bedrock high. Modification took place during wet periods when abundant Ca++ -rich groundwater flowed along the structurally aligned valley system. With the onset of drier conditions, water table fluctuations led to the precipitation of nodular calcretes in the phreatic layer to a depth of about 20 m. A major geochemical change resulted in the preferential silicification of the nodular calcrete deposits. Conditions for silica mobilization may be related to drying-induced salinity and in situ geochemical differentiation brought about by pebble dissociation towards the top of the sediment pile. As calcretization and valley formation progressed to lower levels, silica release took place on a diminishing scale. Thermoluminescence dating infers a mid-Pleistocene age for sil-calcrete formation suggesting that valley evolution and original calcrete precipitation are much older. Late stage dissolution of CaCO3 from pre-existing surface calcretes or sil-calcretes led to the formation of pedogenic case-hardened deposits during a time of reduced flow through the Moshaweng system possibly during the upper or late Pleistocene. Copyright 2002 John Wiley & Sons, Ltd. [source]

Parablastoid holdfasts from the Lower Ordovician of South Wales

John C. W. Cope
Abstract Problematical discoid fossils from the Lower Arenig (Moridunian Stage) of the Llangynog Inlier, South Wales, are interpreted as parablastoid holdfasts. They constitute the first record of holdfasts in this rare echinoderm class. The lower surface has a radial ribbed structure, in contrast to the concentric, reticulate structure of the upper surface. The substrate for attachment was not lithified and may instead have been sediment stabilized by microbial mats. An associated pluricolumnal indicates that the parablastoid column was homeomorphic. Copyright 2005 John Wiley & Sons, Ltd. [source]

Reduced-order controllers for control of flow past an airfoil

S. S. Ravindran
Abstract Reduced-order controller design by means of reduced-order model for control of a wake flow is presented. Reduced-order model is derived by combining the Galerkin projection with proper orthogonal decomposition (POD) or with other related reduced-order approaches such as singular value decomposition or reduced-basis method. In the present investigation, we discuss the applicability of the reduced-order approaches for fast computation of the optimal control for control of vortex shedding behind a thin airfoil through unsteady blowing on the airfoil surface. Accuracy of the reduced-order model is quantified by comparing flow fields obtained from the reduced-order models with those from the full-order simulations under the same free-stream conditions. A control of vortex shedding is demonstrated for Reynolds number 100. It is found that downstream directed blowing on the upper surface of the airfoil near the leading edge is more efficient in mitigating flow separation and suppressing the vortex shedding. Copyright 2005 John Wiley & Sons, Ltd. [source]

Buffeting in transonic flow prediction using time-dependent turbulence model

A. Kourta
Abstract In transonic flow conditions, the shock wave/turbulent boundary layer interaction and flow separations on wing upper surface induce flow instabilities, ,buffet', and then the buffeting (structure vibrations). This phenomenon can greatly influence the aerodynamic performance. These flow excitations are self-sustained and lead to a surface effort due to pressure fluctuations. They can produce enough energy to excite the structure. The objective of the present work is to predict this unsteady phenomenon correctly by using unsteady Navier,Stokes-averaged equations with a time-dependent turbulence model based on the suitable (k,,) turbulent eddy viscosity model. The model used is based on the turbulent viscosity concept where the turbulent viscosity coefficient (C,) is related to local deformation and rotation rates. To validate this model, flow over a flat plate at Mach number of 0.6 is first computed, then the flow around a NACA0012 airfoil. The comparison with the analytical and experimental results shows a good agreement. The ONERA OAT15A transonic airfoil was chosen to describe buffeting phenomena. Numerical simulations are done by using a Navier,Stokes SUPG (streamline upwind Petrov,Galerkin) finite-element solver. Computational results show the ability of the present model to predict physical phenomena of the flow oscillations. The unsteady shock wave/boundary layer interaction is described. Copyright 2005 John Wiley & Sons, Ltd. [source]

Screening Tablets for DOB Using Surface-Enhanced Raman Spectroscopy,

Steven E. J. Bell Ph.D.
Abstract:, 2,5,-Dimethoxy-4-bromoamphetamine (DOB) is of particular interest among the various "ecstasy" variants because there is an unusually long delay between consumption and effect, which dramatically increases the danger of accidental overdose in users. Screening for DOB in tablets is problematic because it is pharmacologically active at 0.2,3 mg, which is c. 50 times less than 3,4-methylenedioxy-N-methylamphetamine (MDMA) and makes it more difficult to detect in seized tablets using conventional spot tests. The normal Raman spectra of seized DOB tablets are dominated by the bands of the excipient with no evidence of the drug component. Here we report the first use of on-tablet surface-enhanced Raman spectroscopy (SERS) to enhance the signal from a low concentration drug. Raman studies (785-nm excitation) were carried on series of model DOB/lactose tablets (total mass c. 400 mg) containing between 1 mg and 15 ,g of DOB and on seized DOB tablets. To generate surface-enhanced spectra, 5 ,L of centrifuged silver colloid was dispensed onto the upper surface of the tablets, followed by 5 ,L of 1.0 mol/dm3 NaCl. The probe laser was directed onto the treated area and spectra accumulated for c. 20 sec (10 sec 2). It was found that the enhancement of the DOB component in the model tablets containing 1 mg DOB/tablet and in the seized tablets tested was so large that their spectra were completely dominated by the vibrational bands of DOB with little or no contribution from the unenhanced lactose excipient. Indeed, the most intense DOB band was visible even in tablets containing just 15 ,g of the drug. On-tablet surface-enhanced Raman spectroscopy is a simple method to distinguish between low dose DOB tablets and those with no active constituent. The fact that unique spectra are obtained allows identification of the drug while the lack of sample preparation and short signal accumulation times mean that the entire test can be carried out in <1 min. [source]

Sequential Monitoring of Burials Containing Large Pig Cadavers Using Ground-Penetrating Radar

John J. Schultz Ph.D.
ABSTRACT: Ground-penetrating radar (GPR) was used to monitor 12 pig burials in Florida, each of which contained a large pig cadaver. Six of the cadavers were buried in sand at a depth of 0.50,0.60 m, and the other six were buried at a depth of 1.00,1.10 m and were in contact with the upper surface of a clay horizon. Control excavations with no pig internment were also constructed as blank graves and monitored with GPR. The burials were monitored with GPR for durations of either 12,13 or 21,21.5 months when they were then excavated to correlate the decomposition state of the cadaver with the GPR imagery. Overall, cadavers in sand were easily detected for the duration of this study at 21.5 months, even when completely skeletonized. Conversely, in clay it became increasingly difficult to image the pig cadavers over the first year of burial, even when they still retained extensive soft tissue structures. [source]

Design and development of a prototype endocavitary probe for high-intensity focused ultrasound delivery with integrated magnetic resonance imaging

Iain P. Wharton MRCS
Abstract Purpose To integrate a high intensity focused ultrasound (HIFU) transducer with an MR receiver coil for endocavitary MR-guided thermal ablation of localized pelvic lesions. Materials and Methods A hollow semicylindrical probe (diameter 3.2 cm) with a rectangular upper surface (7.2 cm 3.2 cm) was designed to house a HIFU transducer and enable acoustic contact with an intraluminal wall. The probe was distally rounded to ease endocavitary insertion and was proximally tapered to a 1.5-cm diameter cylindrical handle through which the irrigation tubes (for transducer cooling) and electrical connections were passed. MR compatibility of piezoceramic and piezocomposite transducers was assessed using gradient-echo (GRE) sequences. The radiofrequency (RF) tuning of identical 6.5 cm 2.5 cm rectangular receiver coils on the upper surface of the probe was adjusted to compensate for the presence of the conductive components of the HIFU transducers. A T1-weighted (T1-W) sliding window dual-echo GRE sequence monitored phase changes in the focal zone of each transducer. High-intensity (2400 W/cm,2), short duration (<1.5 seconds) exposures produced subtherapeutic temperature rises. Results For T1-W images, signal-to-noise ratio (SNR) improved by 40% as a result of quartering the conductive surface of the piezoceramic transducer. A piezocomposite transducer showed a further 28% improvement. SNRs for an endocavitary coil in the focal plane of the HIFU trans-ducer (4 cm from its face) were three times greater than from a phased body array coil. Local shimming improved uniformity of phase images. Phase changes were detected at subtherapeutic exposures. Conclusion We combined a HIFU transducer with an MR receiver coil in an endocavitary probe. SNRs were improved by quartering the conductive surface of the piezoceramic. Further improvement was achieved with a piezocomposite transducer. A phase change was seen on MR images during both subtherapeutic and therapeutic HIFU exposures. J. Magn. Reson. Imaging 2007. 2007 Wiley-Liss, Inc. [source]


Pihiella liagoraciphila gen. et sp. nov. (Rhodophyta) is described for a minute endo/epiphyte that is commonly associated with members of the Liagoraceae ( Nemaliales, Rhodophyta). Algae are discoid or subspherical and grow to a maximum diameter of 400 ,m. Attachment is via isolated elongate rhizoids that penetrate into the loosely filamentous structure of the host or by a pad of several coalesced rhizoids where the host has a more cohesive cortex. Elongate surface hairs are common. Gametophytes are dioecious, the spermatangia arising on surface cells, and carpogonia with elongate trichogynes borne directly on undifferentiated surface supporting cells. Large sporangia form on stalk cells across the upper surface of the plants, these appearing to be either monosporangial or the result of fertilization of the carpogonia and equivalent to undivided zygotosporangia. Carposporophytes and tetrasporangia are unknown. 18S rRNA gene sequence analyses indicate that Pihiella constitutes a clade of long branch length most closely related to the Ahnfeltiales. The unique morphology and reproduction of Pihiella, combined with a substantial genetic divergence from the Ahnfeltiales, suggest that it is sufficiently distinct to warrant placement in a new family and order. We therefore describe the family Pihiellaceae and the order Pihiellales to accommodate the new genus. [source]

A Simple Technique for Purifying Fungal Cultures Contaminated with Bacteria and Mites

S. S. Ko
A simple technique was developed for purifying fungal cultures contaminated with bacteria and mites. It was based on the observation that the growth of bacteria and movement of mites were confined to the upper surface of the agar. A culture contaminated with bacteria and mites was transferred to a piece of clean paper with the upper surface facing down. Small thin pieces (approximately 3 mm 3 mm 0.5 mm) of agar were removed from the exposed surface and transferred to a V-8 agar plate. Colonies that developed from these agar pieces were free from bacteria and mites. [source]

Dual-band circularly polarized antenna with a QUAD-EMC structure

The-Nan Chang
Abstract In this paper, a method for obtaining a single-feed dual-band circularly polarized (CP) antenna with QUAD-EMC structure is presented. The proposed dual-band CP design was achieved by four small patches displayed on the upper surface of a first substrate, and fed electromagnetically by a large patch etched on the lower surface of the same substrate. A second FR4 and a third air substrate were added behind the first substrate to enhance the gain of the antenna. Then, by tuning the sizes of upper and lower patches and truncating patch corners respectively and properly, the proposed antenna can perform dual-band CP radiation using a single probe feed. Prototypes of the proposed antennas designed for RFID operations in the 915-MHz and 2.45-GHz bands are presented and experimentally demonstrated. 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 645,647, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22231 [source]

Infection of Arabidopsis thaliana leaves with Albugo candida (white blister rust) causes a reprogramming of host metabolism

Hsueh-Mei Chou
Albugo candida (Pers.) (O.) Kunze is a biotrophic pathogen which infects the crucifer Arabidopsis thaliana (L.) Heynh forming discrete areas of infection. Eight days after inoculation of leaves, white blisters became visible on the under surface of the leaf although no symptoms were apparent on the upper surface. By day 14, the region of leaf invaded by fungal mycelium had become chlorotic. Recently it has been hypothesized that an accumulation of soluble carbohydrates, following an increase in invertase activity, may trigger sugar signal transduction pathways leading to the repression of photosynthetic gene expression and to the induction of defence proteins. This hypothesis was investigated by quantifying localized changes in carbohydrate and photosynthetic metabolism and the expression of genes encoding photosynthetic and defence proteins. Quantitative imaging of chlorophyll fluorescence revealed that the rate of photosynthesis declined progressively in the invaded regions of the leaf. However, in uninfected regions of the infected leaf the rate of photosynthesis was similar to that measured in the control leaf until late on during the infection cycle when it declined. Images of nonphotochemical fluorescence quenching (NPQ) suggested that the capacity of the Calvin cycle had been reduced in infected regions and that there was a complex metabolic heterogeneity within the infected leaf. A. candida also caused localized changes in the carbohydrate metabolism of the leaf; soluble carbohydrates accumulated in the infected region whereas the amount of starch declined. The reverse was seen in uninfected regions of the infected leaf; carbohydrates did not accumulate until late on during infection and the amount of starch increased as the infection progressed. There was an increase in the activity of invertases which was confined to regions of the leaf invaded by the fungal mycelium. The increase in apoplastic invertase activity was of host origin, as mRNA levels of the AT,FRUCT1 gene (measured by semiquantitative RT-PCR) increased 40-fold in the infected region. The increase in soluble invertase activity resulted from the appearance of a new isoform in the invaded region of the leaf. Current evidence suggests that this was of fungal origin. Northern blot analysis of cab and rbcS showed that photosynthetic gene expression was repressed in the infected leaf from 6 days after inoculation (DAI) when compared to control leaves. In contrast, there was no detectable induction of defence proteins in the infected leaf. These data are discussed in the context of the sugar-sensing hypothesis presented above. [source]

New records of Peyssonnelia armorica and Peyssonnelia harveyana (Rhodophyta, Gigartinales) from Japan

Aki Kato
SUMMARY Two species of the crustose red algal genus Peyssonnelia (Gigartinales, Peyssonneliaceae) are reported from Japanese waters for the first time. These species share the following combination of vegetative and reproductive features: thalli with appressed margins, perithallial filaments arising from the whole upper surface of each hypothallial cell (the Peyssonnelia rubra -type anatomy), unicellular rhizoids, hypobasal calcification and spermatangia that are produced in double chains (the Peyssonnelia harveyana -type spermatangial filament). However, they differ obviously from each other in the hypothallus orientation as seen from below, the perithallus structure in relation to the consistency of the crust, the origin of gonimoblasts and the elevation of the nemathecia. Peyssonnelia armorica is characterized by: (i) hypothallial filaments comprising a polyflabellate layer; (ii) easily separable perithallial filaments in a gelatinous matrix; (iii) gonimoblasts originating exclusively from the auxiliary cell; and (iv) semi-immersed (slightly elevated) nemathecia. Peyssonnelia harveyana is characterized by: (i) hypothallial filaments arranged in parallel rows; (ii) closely packed perithallial filaments in a firm matrix; (iii) gonimoblsts originating from both the auxiliary cell and the connecting filament; and (iv) conspicuously elevated nemathecia. [source]

A new crustose red alga Peyssonnelia rumoiana (Rhodophyta, Gigartinales) from Japan

Aki Kato
SUMMARY The marine red alga Peyssonnelia rumoiana Kato et Masuda, sp. nov. (Peyssonneliaceae, Gigartinales) is described from warm- and cold-temperate regions in Japan. It is principally characterized by having hypo-thallial filaments comprising a polyflabelate layer, proximal perithallial cells arising from the whole upper surface of each hypothallial cell (Peyssonnelia rubra- type anatomy) and closely packed in a firm matrix, the production of two filaments from the proximal perithallial cell, unicellular rhizoids, appressed crust margins and hypobasal calcification. The alga is distinguished from related species by: (i) its conspicuously elevated cystocarpic (100,150 ,m high) and tetrasporangial (80,110 ,m high) nemathecia; (ii) tetrasporangia with or without a unicellular pedicel; and (iii) large (25,45 ,m in diameter by 70,115 ,m in length) tetrasporangia and (iv) the production of double chains of spermatangia (Peyssonnelia harveyana-type spermatangial development). [source]

Phototropic bending of non-elongating and radially growing woody stems results from asymmetrical xylem formation

ABSTRACT Active phototropic bending of non-elongating and radially growing portion of stems (woody stems) has not been previously documented, whereas negative gravitropic bending is well known. We found phototropic bending in woody stems and searched for the underlying mechanism. We inclined 1-year-old Quercus crispula Blume seedlings and unilaterally illuminated them from a horizontal direction perpendicular to (,normal' illumination) or parallel to (,parallel' illumination) the inclination azimuth. With normal illumination, active phototropic bending and xylem formation could be evaluated separately from the negative gravitropic response and vertical deflection resulting from the weight of the seedlings. One-year-old stems with normal illumination bent significantly, with asymmetrical xylem formation towards the illuminated upper surface and side of the stem, whereas those with parallel illumination showed non-significant lateral bending, with asymmetrical xylem formation only on the upper side. A mechanical model was built on the assumption that a bending moment resulted from the asymmetrical xylem formation during phototropic bending of the woody stems. The model fitted the relationship between the observed spatial distributions of the xylem and the observed lateral bending, and thus supported the hypothesis that phototropic bending of woody stems results from asymmetrical xylem formation, as such occurs during gravitropism. [source]

Computational Fluid Dynamics Analysis of Blade Tip Clearances on Hemodynamic Performance and Blood Damage in a Centrifugal Ventricular Assist Device

Jingchun Wu
Abstract An important challenge facing the design of turbodynamic ventricular assist devices (VADs) intended for long-term support is the optimization of the flow path geometry to maximize hydraulic performance while minimizing shear-stress-induced hemolysis and thrombosis. For unshrouded centrifugal, mixed-flow and axial-flow blood pumps, the complex flow patterns within the blade tip clearance between the lengthwise upper surface of the rotating impeller blades and the stationary pump housing have a dramatic effect on both the hydrodynamic performance and the blood damage production. Detailed computational fluid dynamics (CFD) analyses were performed in this study to investigate such flow behavior in blade tip clearance region for a centrifugal blood pump representing a scaled-up version of a prototype pediatric VAD. Nominal flow conditions were analyzed at a flow rate of 2.5 L/min and rotor speed of 3000 rpm with three blade tip clearances of 50, 100, and 200 m. CFD simulations predicted a decrease in the averaged tip leakage flow rate and an increase in pump head and axial thrust with decreasing blade tip clearances from 200 to 50 m. The predicted hemolysis, however, exhibited a unimodal relationship, having a minimum at 100 m compared to 50 m and 200 m. Experimental data corroborate these predictions. Detailed flow patterns observed in this study revealed interesting fluid dynamic features associated with the blade tip clearances, such as the generation and dissipation of tip leakage vortex and its interaction with the primary flow in the blade-blade passages. Quantitative calculations suggested the existence of an optimal blade tip clearance by which hydraulic efficiency can be maximized and hemolysis minimized. [source]

Diversity of host plant relationships and leaf galling behaviours within a small genus of thrips ,Gynaikothrips and Ficus in south east Queensland, Australia

Desley J Tree
Abstract Thrips are well known as gall inducers, yet no field studies have been published on phlaeothripids in the genus Gynaikothrips, which gall Ficus leaves in Australia. A detailed field study was conducted in suburban Brisbane, Australia, on thrips species that induce leaf galls on fig trees. Gynaikothrips ficorum is evidently host specific as it induced leaf galls only on Ficus microcarpa, and did so almost continuously throughout the spring and summer growing season. By contrast, G. australis induced leaf galls on F. macrophylla, F. rubingosa and F. obliqua but only when flushes of new leaves appeared, and this occurred at intervals during spring and summer. Gynaikothrips ficorum feeds on the upper surface of new leaves and this causes the leaf to fold and/or twist into a gall. The life of the gall is about 4 weeks, with the thrips pupating within it. Sometimes, the galls are invaded by a kleptoparasite thrips, Mesothrips jordani. Gynaikothrips australis feeds on the underside of the new leaves and this causes the margins to curl under. The life of the gall is about 6 weeks, with the thrips pupating under the bark of the fig tree branches, and sometimes the galls are shared with an inquiline, G. additamentus. [source]

Numerical models of growth-sediment development above an active monocline

BASIN RESEARCH, Issue 1 2004
Thomas L. Patton
The deposition, erosion and deformation of growth strata associated with an actively growing monocline are modelled using mechanically based numerical experiments. The results demonstrate that the nature of the growth-stratal record depends on (1) the interaction between the base-level rate of change and the rate of change of the accommodation space created due to structural relief across the limbs of the monocline; and (2) the progressive folding of the growth strata. With base-level elevation initially coincident with the upper surface of the pre-tectonic units, constant rates of base-level change create three growth-stratal preservation states. If the base level rises, a growth-sediment wedge covers both limbs of the monocline, with thinner sediment thicknesses on the upthrown limb, forming an on-structure wedge. If the base level falls at a rate less than the rate of accommodation space creation due to structural relief, growth-strata pinch out onto the dipping limb of the monocline, forming an off-structure wedge. If the base level falls at a rate greater than the rate of accommodation space generation due to structural relief, no syntectonic deposition occurs and pre-tectonic units on both sides of the monocline are eroded. Syntectonic unconformities develop within the growth-sediment packages when the rate of accommodation space generation changes during the course of the experiment. The bedding angularity across the unconformities is greatest in the region of the dipping limb of the monocline; off structure, the bedding across the correlative event becomes parallel, forming correlative conformities or disconformities. [source]

Association of rudimentary sacral zygapophyseal facets and accessory and ligamentous articulations: Implications for load transmission at the L5-S1 junction

Niladri Kumar Mahato
Abstract Weight transmitted from the fifth lumbar vertebrae to the sacrum is distributed as three separate components between (a) the vertebral bodies anteriorly, (b) the transverse elements intermediately, and (c) the lumbosacral facet joints, posteriorly. The posterior components of the fifth lumbar vertebra share greater proportion of load in comparison with the posterior elements of the upper lumbar vertebral levels. This study focuses on rudimentary lumbosacral facet articulations and their possible effects on load sharing at this region. Twenty sacra bearing rudimentary articulations were collected for analysis. Sixteen of these sacra presented unilateral rudimentary facets, and the remaining four had facets that were bilaterally rudimentary. Thirteen of the sacra with unilateral rudimentary facets showed an accessory articulating area on the upper surface of the ala on the same side as the rudimentary zygapophyseal facet. The remaining three sacra (out of the 16) showed evidence of strong ligamentous attachments between the L5 and S1 transverse elements on the sides of the rudimentary facets. All the sacra with bilateral rudimentary facets demonstrated bilateral accessory L5,S1 articulations. These observations indicated that load transmission at lumbosacral junctions bearing a rudimentary facet joint is not normal and that their associations with strong L5,S1 lumbosacral ligamentous attachments or accessory articulations at the transverse elements serve a compensatory mechanism for load sharing. Clin. Anat. 23:707,711, 2010. 2010 Wiley-Liss, Inc. [source]

Herbivory in an acid stream

Mark E. Ledger
Summary 1Spatial and temporal variation in the distribution and feeding of non-predatory macroinvertebrates was investigated in a first-order, acid stream in the Ashdown Forest, southern England. 2Stonefly (Nemouridae) and chironomid (Orthocladiinae) larvae were abundant on the upper surfaces of mineral substrata of three sizes (small stones, large stones, bedrock). The density of larvae in each taxonomic group did not vary among substrata of different sizes, although strong seasonal variation existed. 3Nemourids and chironomids (H. marcidus) collected from the upper surfaces of substrata exhibited generalist feeding habits, consuming algae (diatoms, coccoid and filamentous green algae), detritus (biofilm matrix material and fine particulate organic matter (FPOM)) and inorganic debris. 4There was spatial variation in the gut contents of nemourids. The proportion of algae in the guts of larvae often increased with the size of the substratum from which they were collected. Strong temporal variation in the composition of the diet also existed. Nemourids ingested a large quantity of attached algae and biofilm matrix from the biofilm in spring and winter, but consumed loose FPOM and associated microflora in summer and autumn. 5We conclude that, in this acid stream, the trophic linkage between algae and grazers is maintained by ,detritivorous' stonefly and chironomid species. The relationship between the feeding habits of these larvae and other life-history attributes, such as mouthpart morphology and mobility, is discussed. [source]

Characterization and reconstruction of a rock fracture surface by geostatistics

A. Marache
Abstract It is well understood that, in studying the mechanical and hydromechanical behaviour of rock joints, their morphology must be taken into account. A geostatistical approach has been developed for characterizing the morphology of fracture surfaces at a decimetre scale. This allows the analysis of the spatial variability of elevations, and their first and second derivatives, with the intention of producing a model that gives a numerical three-dimensional (3D) representation of the lower and upper surfaces of the fracture. Two samples (I and II) located close together were cored across a natural fracture. The experimental data are the elevations recorded along profiles (using recording steps of 0.5 and 0.02 mm, respectively, for the samples I and II). The goal of this study is to model the surface topography of sample I, so getting estimates for elevations at each node of a square grid whose mesh size will be, for mechanical purposes, no larger than the recording step. Since the fracture surface within the sample core is not strictly horizontal, geostatistical methods are applied to residuals of elevations of sample I. Further, since structural information is necessary at very low scale, theoretical models of variograms of elevations, first and second derivatives are fitted using data of both that sample I and sample II. The geostatistical reconstructions are computed using kriging and conditional simulation methods. In order to validate these reconstructions, variograms and distributions of experimental data are compared with variograms and distributions of the fitted data. Copyright 2002 John Wiley & Sons, Ltd. [source]

Morphologic variability of exposed mass-transport deposits on the eastern slope of Gela Basin (Sicily channel)

BASIN RESEARCH, Issue 2 2007
Daniel Minisini
ABSTRACT The NE portion of Gela Basin in the Sicily Channel is affected by multiple slope failures originated during the late-Quaternary. Basin sequences show evidence of stacked acoustically transparent and/or chaotic units, characterized by irregular upper surfaces, interpreted as mass-transport deposits. The seafloor morphology also shows evidence of both old, partially buried, as well as recent slide products. Two recent slides exposed at seafloor, only 6 km apart (Twin Slides), are similar in geomorphological parameters, age and multistage evolution. Multistage failure of Twin Slides evolved from mud flows, derived from the extensive failure of less consolidated post-glacial units, to localized slides (second stage of failure) affecting older and more consolidated materials. Although Twin Slides are very close to each other and have similar runout and fall height, they produced very dissimilar organization of the displaced masses, likely reflecting the distinct source units affected by failures. Integrating geophysical, sedimentological, structural and palaeontological data, a detailed investigation was conducted to determine the size and internal geometry of this mass-transport complex, to explain the differentiated product and to shed light on its predisposing factors, triggers and timing. [source]

Signature of the Baltic Ice Stream on Funen Island, Denmark during the Weichselian glaciation

BOREAS, Issue 1 2003
Ice streams are major dynamic elements of modern ice sheets, and are believed to have significantly influenced the behaviour of past ice sheets. Funen Island exhibits a number of geomorphological and geological features indicative of a Late Weichselian ice stream, a land-based, terminal branch of the major Baltic Ice Stream that drained the Scandinavian Ice Sheet along the Baltic Sea depression. The ice stream in the study area operated during the Young Baltic Advance. Its track on Funen is characterized by a prominent drumlin field with long, attenuated drumlins consisting of till. The field has an arcuate shape indicating ice-flow deflection around the island's interior. Beneath the drumlin-forming till is a major erosional surface with a boulder pavement, the stones of which have heavily faceted and striated upper surfaces. Ploughing marks are found around the boulders. Exact correspondence of striations, till fabric and drumlin orientation indicates a remarkably consistent flow direction during ice streaming. We infer that fast ice flow was facilitated by basal water pressure elevated to the vicinity of the flotation point. The ice movement was by basal sliding and bed deformation under water pressure at the flotation level or slightly below it, respectively. Subglacial channels and eskers post-dating the drumlins mark a drainage phase that terminated the ice-stream activity close to the deglaciation. Identification of other ice streams in the Peribaltic area is essential for better understanding the dynamics of the land-based part of the Scandinavian Ice Sheet during the last glaciation. [source]