The genesis and evolution of karstic conduit systems in the Chalk

2021 ◽  
pp. SP517-2020-126
Author(s):  
Andrew R. Farrant ◽  
Louise Maurice ◽  
Daniel Ballesteros ◽  
Carole Nehme
Keyword(s):  
Landscape Change ◽  
Upper Cretaceous ◽  
Significant Proportion ◽  
Tracer Tests ◽  
Theoretical Models ◽  
Major Influence ◽  
Secondary Porosity ◽  
Conduit Networks ◽  
Conduit Development ◽  
Hydrogeological Data

AbstractThe Upper Cretaceous Chalk Group is renowned as a major aquifer, but the development of secondary porosity due to karstic conduits is poorly understood. Hydrogeological data and evidence from boreholes, sections, and tracer tests indicate that dissolutional conduits occur throughout the Chalk aquifer. Here, we assess the evidence for Chalk karst, and combine it with theoretical models of dissolution and cave formation to produce a conceptual model for the development of karstic conduits. Dissolution due to the mixing of saturated waters of contrasting chemistry along key lithostratigraphical inception horizons form extensive but isolated conduit networks. These form a significant proportion of the secondary porosity and enhance permeability. They prime the aquifer for the development of more integrated conduit networks formed by focussed recharge of unsaturated surface derived water. However, the porous, well-fractured nature of the Chalk means that the time needed to form large integrated cave systems is often longer than timescales of landscape change. Continued landscape evolution and water table lowering halts conduit development before they can enlarge into cave systems except where geological and geomorphological settings are favourable. Groundwater models need to consider the formation of secondary karst permeability as this has a major influence on groundwater flow.

scholarly journals Geophysical Contribution in the Characterization of Deep Water Tables Geometry (Sidi Bouzid, Central Tunisia)

2015 ◽  
Vol 2015 ◽  
pp. 1-16 ◽  
Author(s):  
D. Khazri ◽  
H. Gabtni
Keyword(s):  
Deep Water ◽  
Upper Cretaceous ◽  
Geophysical Data ◽  
Geometrical Analysis ◽  
Groundwater Exploitation ◽  
Sidi Bouzid ◽  
Central Tunisia ◽  
Water Tables ◽  
Hydrogeological Data

Geophysical data combined with geological and hydrogeological data were analyzed to characterize the geometry of Oued El Hajel and Ouled Asker deep water tables (Sidi Bouzid). The obtained results allowed refining the geostructural schema by highlighting the individualization of the NE-SW underground convexity of Ouled Asker and the anticline of axis Es Souda-Hmaeima and Ezaouia on either sides of two hydrogeological thresholds. The geometrical analysis determined the spatial extension of Ouled Asker and Oued El Hajel subbasins. The seismic cartography of semideep and deep reservoirs (Oligo-Miocene; Eocene and upper Cretaceous) associated with the main subbasins contributed to proposing hydrogeological prospect zones for a rationalized groundwater exploitation.

scholarly journals Finger pad friction and its role in grip and touch

2013 ◽  
Vol 10 (80) ◽  
pp. 20120467 ◽  
Author(s):  
Michael J. Adams ◽  
Simon A. Johnson ◽  
Philippe Lefèvre ◽  
Vincent Lévesque ◽  
Vincent Hayward ◽  
...  
Keyword(s):  
Contact Zone ◽  
Coefficient Of Friction ◽  
Normal Load ◽  
Theoretical Models ◽  
Tactile Perception ◽  
Major Influence ◽  
Sliding Velocity ◽  
Stick Slip ◽  
The Coefficient Of Friction ◽  
Finger Pad

Many aspects of both grip function and tactile perception depend on complex frictional interactions occurring in the contact zone of the finger pad, which is the subject of the current review. While it is well established that friction plays a crucial role in grip function, its exact contribution for discriminatory touch involving the sliding of a finger pad is more elusive. For texture discrimination, it is clear that vibrotaction plays an important role in the discriminatory mechanisms. Among other factors, friction impacts the nature of the vibrations generated by the relative movement of the fingertip skin against a probed object. Friction also has a major influence on the perceived tactile pleasantness of a surface. The contact mechanics of a finger pad is governed by the fingerprint ridges and the sweat that is exuded from pores located on these ridges. Counterintuitively, the coefficient of friction can increase by an order of magnitude in a period of tens of seconds when in contact with an impermeably smooth surface, such as glass. In contrast, the value will decrease for a porous surface, such as paper. The increase in friction is attributed to an occlusion mechanism and can be described by first-order kinetics. Surprisingly, the sensitivity of the coefficient of friction to the normal load and sliding velocity is comparatively of second order, yet these dependencies provide the main basis of theoretical models which, to-date, largely ignore the time evolution of the frictional dynamics. One well-known effect on taction is the possibility of inducing stick–slip if the friction decreases with increasing sliding velocity. Moreover, the initial slip of a finger pad occurs by the propagation of an annulus of failure from the perimeter of the contact zone and this phenomenon could be important in tactile perception and grip function.

Comparison Between Numerical and Experimental Dynamic Coefficients of a Hybrid Aerostatic Bearing

2012 ◽  
Vol 134 (12) ◽  
Author(s):  
Mohamed Amine Hassini ◽  
Mihai Arghir ◽  
Manuel Frocot
Keyword(s):  
Experimental Data ◽  
Theoretical Models ◽  
Bulk Flow ◽  
Major Influence ◽  
Aerostatic Bearing ◽  
Complex Flow ◽  
Flow Equations ◽  
Dynamic Coefficients ◽  
Equivalent Area ◽  
Feeding Pressure

Hybrid journal bearings have been considered for many years as a possible replacement for ball bearings in turbopumps used by the aerospace industry. Due to flow regimes dominated by inertia and due to the nature of the lubricant (cryogenic fluids), the prediction of the linearized dynamic coefficients in these bearings must be based on the compressible bulk-flow equations. Theoretical models based on these equations were validated for hybrid bearings working with water or for liquid or gas annular seals. Validations for hybrid compressible bearings are missing. Experimental data obtained for an air lubricated hybrid aerostatic bearing designed with shallow pockets were recently presented; the data consist of linearized dynamic coefficients obtained for rotation speeds up to 50 krpm and up to 7 bars feeding pressure. The present work introduces a consolidated numerical approach for predicting static and linearized dynamic characteristics. Theoretical predictions are based on bulk flow equations in conjunction with CFD analysis. It was found that, for a given feeding pressure, the value of the pressure downstream the orifice has a major influence on all results. Special care was then taken to describe the complex flow in the feeding system and the orifice. Three dimensional CFD was employed because the bulk-flow equations are inappropriate in this part of the bearing. The pressure downstream the orifice stemming from CFD results and the feeding pressure were next imposed in the bulk flow model and the equivalent area of the orifice was obtained from the numerical solution of the steady flow in the bearing. Since the pockets of the hybrid bearing are shallow, this equivalent area is considered as being the harmonic average of the orifice cross section area and of the cylindrical curtain area located between the orifice and the rotor. The comparisons between theoretical dynamic coefficients and experimental data validated this approach of the equivalent area of the orifice.

Comparison Between Numerical and Experimental Dynamic Coefficients of a Hybrid Aerostatic Bearing

2012 ◽  
Author(s):  
Mohamed Amine Hassini ◽  
Mihai Arghir ◽  
Manuel Frocot
Keyword(s):  
Experimental Data ◽  
Theoretical Models ◽  
Bulk Flow ◽  
Major Influence ◽  
Aerostatic Bearing ◽  
Complex Flow ◽  
Flow Equations ◽  
Dynamic Coefficients ◽  
Equivalent Area ◽  
Feeding Pressure

Hybrid journal bearings are considered since many years as a possible replacement for ball bearings in turbo-pumps used by the aerospace industry. Due to flow regimes dominated by inertia and due to the nature of the lubricant (cryogenic fluids), the prediction of the linearized dynamic coefficients in these bearings must be based on the compressible bulk-flow equations. Theoretical models based on these equations were validated for hybrid bearings working with water or for liquid or gas annular seals. Validations for hybrid compressible bearings are missing. Experimental data obtained for an air lubricated hybrid aerostatic bearing designed with shallow pockets were recently presented; the data consist of linearized dynamic coefficients obtained for rotation speeds up to 50 krpm and up to 7 bar feeding pressure. The present work introduces a consolidated numerical approach for predicting static and linearized dynamic characteristics. Theoretical predictions are based on bulk flow equations in conjunction with CFD analysis. It was found that for a given feeding pressure, the value of the pressure downstream the orifice has a major influence on all results. Special care was then taken for describing the complex flow in the feeding system and the orifice. Three dimensional CFD was employed because the bulk-flow equations are inappropriate in this part of the bearing. The pressure downstream the orifice stemming from CFD results and the feeding pressure were next imposed in the bulk flow model and the equivalent area of the orifice was obtained from the numerical solution of the steady flow in the bearing. Since the pockets of the hybrid bearing are shallow, this equivalent area is considered as being the harmonic average of the orifice cross section area and of the cylindrical curtain area located between the orifice and the rotor. The comparisons between theoretical dynamic coefficients and experimental data validated this approach of the equivalent area of the orifice.

Genetic Variation in Political Participation

2008 ◽  
Vol 102 (2) ◽  
pp. 233-248 ◽  
Author(s):  
JAMES H. FOWLER ◽  
LAURA A. BAKER ◽  
CHRISTOPHER T. DAWES
Keyword(s):  
Genetic Variation ◽  
Los Angeles ◽  
Political Participation ◽  
Voter Turnout ◽  
Voting Behavior ◽  
Broad Class ◽  
Large Population ◽  
Significant Proportion ◽  
Theoretical Models ◽  
Individual Level

The decision to vote has puzzled scholars for decades. Theoretical models predict little or no variation in participation in large population elections and empirical models have typically accounted for only a relatively small portion of individual-level variance in turnout behavior. However, these models have not considered the hypothesis that part of the variation in voting behavior can be attributed to genetic effects. Matching public voter turnout records in Los Angeles to a twin registry, we study the heritability of political behavior in monozygotic and dizygotic twins. The results show that a significant proportion of the variation in voting turnout can be accounted for by genes. We also replicate these results with data from the National Longitudinal Study of Adolescent Health and show that they extend to a broad class of acts of political participation. These are the first findings to suggest that humans exhibit genetic variation in their tendency to participate in political activities.

Accurate Heat Transfer Measurements for Condensation on Horizontal, Integral-Fin Tubes

1992 ◽  
Vol 114 (3) ◽  
pp. 719-726 ◽  
Author(s):  
A. Briggs ◽  
X.-L. Wen ◽  
J. W. Rose
Keyword(s):  
Heat Transfer ◽  
Significant Proportion ◽  
Theoretical Models ◽  
Experimental Investigations ◽  
Transfer Coefficients ◽  
Finned Tubes ◽  
Heat Transfer Coefficients ◽  
Tube Wall Temperature ◽  
Overall Resistance ◽  
Fin Tubes

In most earlier experimental investigations of condensation on low-fin tubes, vapor-side heat transfer coefficients have been found from overall (vapor-to-coolant) measurements using either predetermined coolant-side correlations or “Wilson plot” methods. When the outside resistance dominates, or is a significant proportion of the overall resistance, these procedures can give satisfactory accuracy. However, for externally enhanced tubes, and particularly with high-conductivity fluids such as water, significant uncertainties may be present. In order to provide reliable, high-accuracy data, to assist in the development of theoretical models, tests have been conducted using specially constructed plain and finned tubes fitted with thermocouples to measure the tube wall temperature, and hence the vapor-side heat transfer coefficient, directly. The paper describes the technique for manufacturing the tubes and gives results of systematic heat transfer measurements covering the effects of fin height, thickness, and spacing, tube diameter, and vapor velocity. The tests were carried out with steam, ethylene glycol, and R-113, with vertical vapor downflow. The heat flux was measured using an accurately calibrated 10-junction thermopile and paying particular attention to coolant mixing and isothermal immersion of thermocouple junctions. Care was taken to avoid errors due to the presence in the vapor of noncondensing gas and the occurrence of dropwise condensation. Smooth, consistent, and repeatable results were obtained in all cases. The data are presented in easily accessible form and are compared with the results of previous investigations, where indirect methods were used to determine the vapor-side data, and with theory.

STRUCTURE AND DEVELOPMENT OF THE SOUTHERN MARGIN OF AUSTRALIA

1975 ◽  
Vol 15 (1) ◽  
pp. 33 ◽  
Author(s):  
M. G. Boeuf ◽  
H. Doust
Keyword(s):  
Continental Margin ◽  
Seismic Data ◽  
Lower Cretaceous ◽  
Rift Valley ◽  
Upper Cretaceous ◽  
Structural Data ◽  
Theoretical Models ◽  
Palaeomagnetic Data ◽  
Geological Evolution ◽  
Seismic Records

Off the southern coast of Australia, exploration results and deep-water reconnaissance seismic data support the concept of an aseismic Atlantic-type continental margin. Characteristic is a sedimentary wedge which extends from the shelf to the abyssal plains and includes crustal elements of continental and oceanic origin.Oceanward, a continuous level of diffractions ascribed to the top of oceanic crust can be observed on seismic records, steeply dipping beneath the continental rise towards a smooth, flat, often faulted reflector which is correlated with top Precambrian or Palaeozoic continental basement.The sedimentary wedge which overlies the block-faulted and collapsed continental basement is subdivided by unconformities into: (a) a continental Lower Cretaceous unit and a fluviodeltaic unit of Upper Cretaceous-Danian age which are taken to represent rift valley stages of deposition controlled by extensional tectonics and (b) a post-breakup sequence of Tertiary units representing regional collapse and out-building of the shelf. The Upper Cretaceous sequence is missing along much of the continental edge where Tertiary sediments appear to rest directly on the Lower Cretaceous unit.Our interpretation suggests that a prolonged period of uplift took place along the axis of the rift valley prior to continental break-up. On the basis of palaeomagnetic data and biostratigraphic analysis the breakup phase started in the Upper Paleocene.From the continent outward several structural zones can commonly be recognised: (a) a zone of shallow basement with a thin Lower Cretaceous cover normally faulted and overlain by thin gently dipping Tertiary beds, (b) a zone of faulted and landwards tilted basement blocks and Lower Cretaceous sediments overlain (sometimes with clear unconformity) by thick Upper Cretaceous sediments, (c) a zone of thick, moderately deformed Tertiary sediments whose axis of deposition is generally offset to the south of the Upper Cretaceous basinal axis, (d) a zone of rotational faults and associated toe thrusts affecting the Cretaceous sediments and apparently related to the time of margin collapse, (e) an area of little disturbed Cretaceous and Tertiary sediments overlying continental basement. This zone extends into the "magnetic quiet zone" which is therefore believed to be, at least in part, a collapsed portion of the continental margin adjacent to oceanic crust.The interpretation of the geological evolution of the southern Australian margin based on the stratigraphic and structural data presently available can be related to current theoretical models on continental margin development.

scholarly journals Re-assessment of depositional conditions of Cretaceous deposits around the Amfilochia and Arta areas

2019 ◽  
Vol 55 (1) ◽  
pp. 241
Author(s):  
Nikolaos Dimopoulos ◽  
Eleftherios Georgoulas ◽  
Savvas Peridis ◽  
George Iliopoulos ◽  
Nikolina Bourli ◽  
...  
Keyword(s):  
Cross Section ◽  
Upper Cretaceous ◽  
Depositional Environments ◽  
Microfacies Analysis ◽  
Fault Activity ◽  
Carbonate Platforms ◽  
Secondary Porosity ◽  
Strong Deformation ◽  
First Time ◽  
Cretaceous Deposits

Sedimentological studies of the Cretaceous limestones in the central Ionian basin (Amfilochia, Arta as well as Kerasonas areas) indicate that these deposits are composed of calciturbidites interbedded with breccia-microbreccia deposits. In the Amfilochia new cross-section, with a NNW-SSE direction, the lower Cretaceous Vigla limestones and Vigla shales were outcropped for the first time. This section is directed parallel to the paleo Ionian basin axis and the fact of the lateral discontinuity of Vigla limestones and Vigla shales indicate that during the sedimentation of these two Formations there was a restriction along the paleo basin axis, probably due to synsedimentary transfer fault activity. Forty-two (42) samples from Vigla shales were analyzed for their content in CaCO3 and TOC, showed that these sediments present poor to fair hydrocarbon potential. In the Arta new cross-section, with a NE-SW direction, the Upper Cretaceous Senonian deposits showed strong deformation that took place during the compressional regime that affected the Ionian basin after sedimentation. This deformation appears stronger in the western part being close to a major thrust, and thus it is possible that this deformation could be responsible for the high secondary porosity of Upper Cretaceous deposits. Microfacies analysis of these deposits showed in general that deep-sea depositional environments prevailed, nevertheless in a few cases indications for the presence of environments with a shallow character imply the existence of isolated carbonate platforms close to the studied sections. In the studied sections with an E-W direction, no lateral changes were observed in the depositional conditions within the same Formation introducing standard depositional conditions across the paleo basin.

Sign in / Sign up

Export Citation Format

Share Document