Trough Geometry Research Articles

A topographic test for the existence of ground ice in the walls of Coprates Chasma, Mars

Evidence for the former presence of ground ice and its possible role in the erosion of Valles Marineris trough walls is equivocal. This study aims to determine whether variations in the topographic slope angle of the walls of the trough Coprates Chasma are consistent with predicted temperature‐driven differences in the distribution, thermal condition, and strength of ground ice within its walls. Using Mars Orbiter Laser Altimeter topographic data, 247 profiles were made rim to rim across the trough and measurements made of wall slope angle, mean annual surface temperature, and trough geometry (wall height, rim elevation, and trough width). Variations in these parameters along each trough wall, and differences between the two trough walls, were established. The results indicate that the predicted variations along and differences between the walls in the three‐dimensional distribution of ground ice, and in its thermal condition and strength, are unlikely to have caused the measured variations in trough wall slope angle. These observations imply that ground ice has been absent within the trough walls since the age of formation of the spur‐and‐gully wall morphology. The results preclude the spur‐and‐gully morphology having developed by dry mass‐wasting of material above an ice‐rich cryosphere and indicate the action of liquid water to be a more likely origin. The inferred absence of ice within the walls precludes any role of ice in initiating or mobilizing landslides where they have eroded the spur‐and‐gully morphology.

Heterogeneous tectonic inversion of the Mid-Polish Trough related to crustal architecture, sedimentary patterns and structural inheritance

Using a 3-D structural model, we performed a basin-scale analysis of the tectonically inverted Mid-Polish Swell, which developed above the NW–SE-oriented Teisseyre-Tornquist Zone. The later separates the Paleozoic West European Platform from the Precambrian East European Craton. The model permits a comparison between the present depths and sedimentary thicknesses of five layers within the Permian–Mesozoic and Cenozoic successions. The inversion of the NW–SE-trending Mid-Polish Trough during the Late Cretaceous–Paleogene resulted in uplift of a central horst, the Mid-Polish Swell, bounded by two lateral troughs. These structural features are induced by squeezing of a weak crust along the Teisseyre-Tornquist Zone. The swell is characterized by an inherited segmentation which is due to NE–SW transversal faults having crustal roots. From NW to SE, we distinguish the Pomeranian, Kujavian, and Małopolska segments, that are separated by two transversal faults. During the inversion, the Zechstein salt occurring in the Pomeranian and Kujavian segments in the NW acted as decoupling level between the basement and the post-salt cover, leading to disharmonic deformation. Conversely, because no salt occurs in the SE, both basement and cover were jointly deformed. The vertical tectonic uplift at the surface is estimated to amount to 3 km in the Małopolska segment. The structural inheritance of the basement is expressed by the heterogeneous geometry of the swell and tectonic instability during Mesozoic sedimentation. The reasons for the inheritance are seen in the mosaic-type Paleozoic basement SW of the Teisseyre-Tornquist Zone, contrasting the Precambrian East European Craton which acted as a stable buttress in the NE. The horst and trough geometry of Cenozoic sediments blanketing the Mid-Polish swell reveals the ongoing intracontinental compressional stress in Poland.

In vitro and in vivo intrapulmonary distribution of fluorescently labeled surfactant

To determine the distribution of endotracheally administered surfactant at the alveolar level in an animal model of acute respiratory distress syndrome. Prospective, randomized animal study. Research laboratory of a university hospital. Seventy-one male Sprague-Dawley rats, weighing 330-370 g. To measure surfactant distribution in vitro, a glass trough mimicking dichotomic lung anatomy was used to determine the spreading properties of bovine lung surfactant extract supplemented with fluorescent Bodipy-labeled surfactant protein B. To measure surfactant distribution in vivo, rats were anesthetized, and lipopolysaccharide was aerosolized (12 mg/kg body weight) to induce lung injury resembling acute respiratory distress syndrome; in control rats, buffered saline was aerosolized. Twenty-four hours later rats were anesthetized, tracheotomized, and mechanically ventilated (peak airway pressure = 20 mbar; positive end-expiratory pressure = 6 mbar; inspiration time = expiration time = 0.6 sec; Fio2 = 50%). Surfactant (bovine lung surfactant extract, supplemented with fluorescent Bodipy-labeled surfactant protein B; 50 mg/kg body weight) was applied as a bolus; in control rats, saline was administered as a bolus. Rats were ventilated for 5, 15, 30, or 60 mins (n = 8 or 9 for each group). Then, lungs were excised and sliced. Lung slices, divided into aerated (open), underinflated (dystelectatic), or collapsed (atelectatic) alveolar areas, were examined by both light and fluorescence microscopy. In vitro experiments revealed that surfactant spread independent of glass trough geometry and lowered the surface tension to equilibrium values (25 mN/m) within a few seconds. In vivo experiments showed that administered surfactant distributed preferentially into underinflated and aerated alveolar areas. Furthermore, surfactant distribution was not affected by length of mechanical ventilation. When conventional mechanical ventilation was used in lipopolysaccharide-induced lung injury, surfactant preferentially distributed into underinflated and aerated alveolar areas. Because surfactant rarely reached collapsed alveolar areas, methods aiding in alveolar recruitment (e.g., open lung concept or body positioning) should precede surfactant administration.

Segmented Domain Decomposition Multigrid Solutions for Two and Three-Dimensional Viscous Flows

Several viscous incompressible two and three-dimensional flows with strong inviscid interaction and/or axial flow reversal are considered with a segmented domain decomposition multigrid (SDDMG) procedure. Specific examples include the laminar flow recirculation in a trough geometry and in a three-dimensional step channel. For the latter case, there are multiple and three-dimensional recirculation zones. A pressure-based form of flux-vector splitting is applied to the Navier-Stokes equations, which are represented by an implicit, lowest-order reduced Navier-Stokes (RNS) system and a purely diffusive, higher-order, deferred-corrector. A trapezoidal or box-like form of discretization insures that all mass conservation properties are satisfied at interfacial and outflow boundaries, even for this primitive-variable non-staggered grid formulation. The segmented domain strategy is adapted herein for three-dimensional flows and is extended to allow for disjoint subdomains that do not share a common boundary.

A FUNDAMENTAL APPROACH FOR THE RELATIONSHIP BETWEEN THE BOSTWICK MEASUREMENT AND NEWTONIAN FLUID VISCOSITY

ABSTRACTThe Bostwick consistometer is a durable and simple instrument that is widely accepted in industrial practice to evaluate product consistency. Flow observed in the Bostwick consistometer was evaluated as a balance of forces; the resulting expression yields the Bostwick measurement as a function of trough geometry and fluid properties. Experimental measurements for four Newtonian fluids verify the theoretically predicted dependence of the extent of flow on the kinematic viscosity to the – 1/5 power.

Topography and former Scottish tidewater glaciers

Abstract The stillstand positions of many tidewater glaciers in Scottish sea lochs during the Loch Lomond Stadial correspond closely with topographic pinning points in the lochs. These pinning points are locations where the fjord geometry changes significantly, allowing the ablation rates of calving glaciers to alter and restore dynamic equilibrium. Evidence also suggests that water depth may have influenced rates of advance and retreat. Following an initial climatic trigger, the subsequent behaviour of these tidewater glaciers may therefore reflect the influence of trough geometry. The response of calving glaciers to further small‐scale climatic changes can be indirect and variable. This behaviour is analogous to that of contemporary Alaskan tidewater glaciers.

DESIGN OF STATIONARY FINITE LENGTH V-TROUGH SOLAR COLLECTOR

This is a theoretical investigation devoted to optically design a finite length V-trough collector considering multireflections, reflection in space and shading. From the optical analysis the optimum trough geometries were identified for maximum real acceptance. In addition, the thermal performance for a V-trough collector aligned east-west and tilted to any base angle was also studied. The actual solar data for Alexandria (Egypt) was considered as an illustrative example.

Terminal environment, topographic control and fluctuations of West Greenland glaciers

Glaciers are commonly regarded as sensitive indicators of climatic change, but iceberg calving can partially decouple glacier oscillations from climatic forcing. Recent fluctuations (1942–85) of 72 West Greenland outlet glaciers were studied using aerial photographs, and nine of them examined in the field. Despite similar climatic forcing, variable glacier behaviour is apparent. Eighty‐four percent of the land terminating glaciers have been retreating or stable during the period, whereas more than half the tidewater and lake terminating glaciers have been advancing. The calving glaciers exhibit much greater variability in frontal behaviour. Patterns of change suggest that the land‐terminating glaciers are controlled dominantly by variations in summer temperature, but that calving dynamics have caused the tidewater and lake‐calving glaciers to respond to climatic change in non‐linear ways. Dynamic and response contrasts are apparent between freshwater and tidewater glaciers. Trough geometry is of great significance in controlling the nature and magnitude of frontal change of calving glaciers; in particular, topographic ‘pinning points’ represent potentially stable locations within the fjord at which stillstands almost invariably occur, irrespective of climatic change or regional trends.

Convergence properties of high‐Reynolds‐number separated flow calculations

AbstractThe convergence properties of an iterative solution technique for the Reduced Navier–Stokes equations are examined for two‐dimensional steady subsonic flow over bump and trough geometries. Techniques for decreasing the sensitivity to the initial pressure approximation, for fine meshes in particular, are investigated. They are shown to improve the robustness of the relaxation process and to decrease the computational work required to obtain a converged solution. A semi‐coarsening multigrid technique that has previously been found to be particularly advantageous for high‐Reynolds‐number (Re) flows with flow separation and with highly stretched surface‐normal grids is applied herein to further accelerate convergence. Solutions are obtained for the laminar flow over a trough that is more severe than has been considered to date. Sufficient axial grid refinement in this case leads to a shock‐like reattachment and, for sufficiently large Re, to a local ‘divergence’ of the numerical computations. This ‘laminar flow breakdown’ appears to be related to an instability associated with high‐frequency fine‐grid modes that are not resolvable with the present modelling. This behaviour may be indicative of dynamic stall or of incipient transition. The breakdown or instability is shown to be controllable by suitable introduction of transition turbulence models or by laminar flow control, i.e. small amounts of wall suction. This lends further support to the hypothesis that the instability is of a physical rather than numerical character and suggests that full three‐dimensional analysis is required to properly capture the flow behaviour. Another inference drawn from this investigation is that there is a need for careful grid refinement studies in high‐Re flow computations, since coarser grids may yield oscillation‐free solutions that cannot be obtained on finer grids.

Gravity anomalies and flexure of the lithosphere at the Middle Amazon Basin, Brazil

The Middle Amazon Basin is a large Paleozoic sedimentary basin on the Amazonian craton in South America. It contains up to 7 km of mainly shallow water sediments. A chain of Bouguer gravity highs of approximately +40 to +90 mGals transects the basin roughly coincident with the axis of maximum thickness of sediment. The gravity highs are flanked on either side by gravity lows of approximately −40 mGals. The observed gravity anomalies can be explained by a steeply sided zone of high density in the lower crust varying in width from 100 to 200 km wide. Within this region, the continental crust has been intruded/replaced by more dense material to more than half its original thickness of 45–50 km. The much wider sedimentary basin results from regional compensation of the subsurface load and the subsequent load of accumulated sediments by flexure of the lithosphere. The observed geometry of the basin is consistent with an elastic lithosphere model with a mechanical thickness of 15–20 km. Although this value is lower than expected for a stable cratonic region of Early Proterozoic age, it is within the accepted range of effective elastic thicknesses for the earth. Rapid subsidence during the late Paleozoic may be evidence of a second tectonic event or lithospheric relaxation which could lower the effective mechanical thickness of the lithosphere. The high‐density zone in the lower crust, as delineated by gravity and flexural modeling, has a complex sinuous geometry which is narrow and south of the axis of maximum sediment thickness on the east and west margins and wide and offset to the north in the center of the basin. The linear trough geometry of the basin itself is a result of smoothing by regional compensation of the load in the lower crust.

The determination of the propagation constant for the traveling wave in an infinite ground plane

The propagation constant for the travelling wave in a trough in an infinite ground plane is examined. The null-field integral is used to determine the electromagnetic field in the trough structure, and pulse basis functions give the distribution of the aperture fields. From this, the propagation constant is solved for, using the Newton-Raphson iterative scheme. Various sizes of geometries are examined. The far-field patterns are calculated and compared with other solutions, thereby validating the integral formulation which subsequently provided the propagation constant. Measurements of two trough geometries are performed to validate the theoretical results.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Bi-yearly adjusted V-trough concentrators

Previous analyses of V-trough concentrators have resulted in a range of trough geometries and differing concentrator adjustment routines being recommended. While these configurations produce moderate yearly averaged concentration of solar energy, the concentractor performance during the year may vary greatly. It is the intention of the present paper to demonstrate a simple approach for optimizing the trough configuration, in particular to produce uniform monthly-flux-enhancement with minimum adjustment of the concentrator. The method, which is based on reflector characteristics identified from an analysis of single reflector-receiver system, successfully realises configurations that provide satisfactory performance while requiring either the collector tilt or the concentrator to be adjusted only at the equinox. The comparative performance of symmetrical and asymmetrical trough configuration is given and, in addition, the inter-relationship between the trough opening angle, the reflector/cover width ratio, and the frequency of adjustment.