The Effect of Initial Void Configuration on the Morphological Evolution Under the Action of Normalized Electron Wind Forces

2001 ◽  
Vol 714 ◽  
Author(s):  
Ersin Emre Oren ◽  
Tarik Omer Ogurtani
Keyword(s):  
Morphological Evolution ◽  
Strong Dependence ◽  
Thermodynamic Formalism ◽  
Time Step ◽  
Euler’S Method ◽  
Morphological Variations ◽  
Comprehensive Picture ◽  
Void Shape ◽  
Evolution Dynamics ◽  
Electron Wind

ABSTRACTIn these studies a comprehensive picture of void shape evolution dynamics and its strong dependence on the initial configuration has been thoroughly investigated by utilizing hypocycloid algebra to generate four different shapes of main interest. Our mathematical model on the isotropic diffusion and mass accumulation on void surfaces, under the action of applied electrostatic potential and capillary effects, follows a novel irreversible but discrete thermodynamic formalism of interphases and surfaces.As a result during the intragranual motion, in addition to the crescent-like slit formation, very rich and also unusual void morphological variations such as fragmentations into the daughter voids or inner island generation have been observed under the severe (normalized) electron wind intensities or very long exposure times. In these numerical experiments, the Euler's method of finite differences with an automatic time step self-adjustment has been utilized in combination with a rather powerful and fast indirect boundary element method (IBEM) for the solution of the Laplace equation.

scholarly journals Effects of spatial discretization in ice-sheet modelling using the shallow-ice approximation

2006 ◽  
Vol 52 (176) ◽  
pp. 89-98 ◽  
Author(s):  
J. Van Den Berg ◽  
R.S.W. Van De Wal ◽  
J. Oerlemans
Keyword(s):  
Initial Conditions ◽  
Strong Dependence ◽  
Ice Sheet ◽  
Model Parameters ◽  
Time Step ◽  
Numerical Errors ◽  
Surface Gradient ◽  
Dimension Analysis ◽  
Sloping Bed ◽  
Ice Model

AbstractThis paper assesses a two-dimensional, vertically integrated ice model for its numerical properties in the calculation of ice-sheet evolution on a sloping bed using the shallow-ice approximation. We discuss the influence of initial conditions and individual model parameters on the model’s numerical behaviour, with emphasis on varying spatial discretizations. The modelling results suffer badly from numerical problems. They show a strong dependence on gridcell size and we conclude that the widely used gridcell spacing of 20 km is too coarse. The numerical errors are small in each single time-step, but increase non-linearly over time and with volume change, as a result of feedback of the mass balance with height. We propose a new method for the calculation of the surface gradient near the margin, which improves the results significantly. Furthermore, we show that we may use dimension analysis as a tool to explain in which situations numerical problems are to be expected.

scholarly journals Parameter sensitivity of a watershed-scale flood forecasting model as a function of modelling time-step

2012 ◽  
Vol 44 (2) ◽  
pp. 334-350 ◽  
Author(s):  
Fiachra O'Loughlin ◽  
Michael Bruen ◽  
Thorsten Wagener
Keyword(s):  
Sensitivity Analysis ◽  
Strong Dependence ◽  
Flow Regimes ◽  
Flood Forecasting ◽  
Parameter Sensitivity ◽  
Hydrograph Separation ◽  
Time Step ◽  
Soil Moisture Accounting ◽  
Distributed Modelling ◽  
Sensitivity Indices

Although ongoing technological advances have alleviated data restrictions and most of the computational barriers to distributed modelling, lumped, parsimonious, conceptual and rainfall-runoff models are still widely used for flood forecasting. However both optimum parameter values and the fluxes of water through individual model components change significantly with the time-step used. Thus, such models should be used with caution in applications such as hydrograph separation or water quality studies that require the fluxes through individual flow routes through the model or which try to relate parameters to physical features of the catchment. To demonstrate this time-scale limitation, a parameter sensitivity analysis was performed on the lumped conceptual Soil Moisture Accounting and Routing with Groundwater component (SMARG) model for a 182 km2 rural catchment in Ireland for a number of time-steps, flow regimes and evaluation metrics. A global sensitivity analysis method (Higher Dimensional Model Representation) showed that sensitivity indices vary greatly with time-step and evaluation metric. The sensitivity of parameters also varied for different flow regimes. Certain parameters' sensitivities remain fairly constant across both flow regimes and time-step, while others are very much regime or time-step dependent. Care should be taken in using internal information from conceptual models because of this strong dependence on time-step.

scholarly journals An Accurate and Practical Explicit Hybrid Method for the Chan–Vese Image Segmentation Model

Mathematics ◽  
2020 ◽  
Vol 8 (7) ◽  
pp. 1173
Author(s):  
Darae Jeong ◽  
Sangkwon Kim ◽  
Chaeyoung Lee ◽  
Junseok Kim
Keyword(s):  
Image Segmentation ◽  
Governing Equation ◽  
Hybrid Method ◽  
Operator Splitting ◽  
Splitting Method ◽  
Phase Field Model ◽  
Gradient Flow ◽  
Time Step ◽  
Euler’S Method ◽  
Operator Splitting Method

In this paper, we propose a computationally fast and accurate explicit hybrid method for image segmentation. By using a gradient flow, the governing equation is derived from a phase-field model to minimize the Chan–Vese functional for image segmentation. The resulting governing equation is the Allen–Cahn equation with a nonlinear fidelity term. We numerically solve the equation by employing an operator splitting method. We use two closed-form solutions and one explicit Euler’s method, which has a mild time step constraint. However, the proposed scheme has the merits of simplicity and versatility for arbitrary computational domains. We present computational experiments demonstrating the efficiency of the proposed method on real and synthetic images.

Tectonic Evolution, Geology, and Geomorphology

2005 ◽  
Author(s):  
Alain Demoulin
Keyword(s):  
Stress Field ◽  
Western Europe ◽  
Morphological Evolution ◽  
Molasse Basin ◽  
North West ◽  
The North ◽  
Comprehensive Picture ◽  
History Of ◽  
Mid Atlantic Ridge ◽  
West European

The present-day major relief features of western Europe are to a great extent determined by the underlying geological structures, either passively or actively. To get a comprehensive picture of their morphological evolution and interrelations, this chapter provides an overview of the spatial and temporal characteristics of the larg-escale tectonic framework of the continent. After having described the west European landscape at the end of the Palaeozoic, to which time the oldest preserved landforms date back, an outline of the Mesozoic and Cenozoic history of the major tectonic domains follows. Finally, some denudation estimates highlighting the relationship between tectonics, erosion, and the resulting relief, will be discussed. The three main influences on the present-day topographic patterns are those of the Alpine orogeny, the Cenozoic West European rifting, and the imprint of Variscan structures. They combine within a regional stress field determined by the Africa–Eurasia collision and the Alpine push as well as the mid-Atlantic ridge push. Since the end of the Miocene, this stress field is characterized by a fan-shaped distribution of SHmax along the northern border of the Alpine arc. This gives way to a more consistent NW–SE to NNW–SSE direction of compression further from the chain (Bergerat 1987; Müller et al. 1992). Topographically, western Europe may be roughly divided into a series of belts parallel to the Alpine chain. The Alpine chain culminates in a number of peaks exceeding 4,000 m in elevation (4,810 m at Mont Blanc) but the average altitude is in the order of 2,000 m. To the north, the mountainous Alps are bordered by the Molasse foredeep basin whose surface makes an inclined plane descending northwards from c.1,000 m to c.300 m near the Donau River in the Regensburg-Passau area. To the north-west, the Molasse basin narrows between the Alps and the Jura Mountains and is occupied by several extended lakes inherited from Quaternary glacial activity. Next to the Molasse basin in the north and west is a wide belt of recently more or less uplifted areas between 200 and 1,000 m in elevation (and locally in excess of 1,000 m in the French Massif Central and the Bohemian massif).

scholarly journals 3D Physical Modeling of an Artificial Beach Nourishment: Laboratory Procedures and Nourishment Performance

2021 ◽  
Vol 9 (6) ◽  
pp. 613
Author(s):  
André Guimarães ◽  
Carlos Coelho ◽  
Fernando Veloso-Gomes ◽  
Paulo A. Silva
Keyword(s):  
Sediment Transport ◽  
Physical Modeling ◽  
Morphological Evolution ◽  
Beach Nourishment ◽  
Sediment Concentration ◽  
Morphological Variations ◽  
Coastal Defense ◽  
Local Wave ◽  
Laboratory Procedures ◽  
Movable Bed

Beach nourishment represents a type of coastal defense intervention, keeping the beach as a natural coastal defense system. Altering the cross-shore profile geometry, due to the introduction of new sediments, induces a non-equilibrium situation regarding the local wave dynamics. This work aims to increase our knowledge concerning 3D movable bed physical modeling and beach nourishment impacts on the hydrodynamics, sediment transport, and morphodynamics. A set of experiments with an artificial beach nourishment movable bed model was prepared. Hydrodynamic, sediment transport, and morphological variations and impacts due to the presence of the nourishment were monitored with specific equipment. Special attention was given to the number and positioning of the monitoring equipment and the inherent constraints of 3D movable beds laboratory tests. The nourishment induced changes in the beach dynamics, leading to an increase in the flow velocities range and suspended sediment concentration, and effectively increasing the emerged beach width. Predicting and anticipating the morphological evolution of the modeled beach has a major impact on data accuracy, since it might influence the monitoring equipment’s correct position. Laboratory results and constraints were characterized to help better define future laboratory procedures and strategies for increasing movable bed models’ accuracy and performance.

scholarly journals Beach Monitoring and Morphological Response in the Presence of Coastal Defense Strategies at Riccione (Italy)

2021 ◽  
Vol 9 (8) ◽  
pp. 851
Author(s):  
Claudia Romagnoli ◽  
Flavia Sistilli ◽  
Luigi Cantelli ◽  
Margherita Aguzzi ◽  
Nunzio De Nigris ◽  
...  
Keyword(s):  
Climate Change ◽  
Morphological Evolution ◽  
Anthropogenic Activities ◽  
Future Climate Change ◽  
Defense Strategies ◽  
Morphological Variations ◽  
Natural Processes ◽  
Management Actions ◽  
Sediment Redistribution ◽  
Coastal Defense

The coastal area at Riccione, in the southern Emilia-Romagna littoral region, is exposed to erosive processes, which are expected to be enhanced by climate change. The beach, mostly composed of fine sand, is maintained through various defense strategies, including frequent nourishment interventions for balancing the sediment deficit and other experimental solutions for reducing coastal erosion. Artificial reshaping of the beach and “common practices” in the sediment management redefine the beach morphology and the sediment redistribution almost continuously. These activities overlap each other and with the coastal dynamics, and this makes it very difficult to evaluate their effectiveness, as well as the role of natural processes on the beach morphological evolution. Topo-bathymetric and sedimentological monitoring of the beach has been carried out on a regular basis since 2000 by the Regional Agency for Prevention, Environment and Energy of Emilia-Romagna (Arpae). Further monitoring of the emerged and submerged beach has been carried out in 2019–2021 in the framework of the research project STIMARE, focusing on innovative strategies for coastal monitoring in relation with erosion risk. The aim of this study is to assess the coastal behavior at the interannual/seasonal scale in the southern coastal stretch of Riccione, where the adopted coastal defense strategies and management actions mostly control the morphological variations in the emerged and submerged beach besides the wave and current regime. The topo-bathymetric variations and erosion/accretion patterns provided by multitemporal monitoring have been related to natural processes and to anthropogenic activities. The morphological variations have been also assessed in volumetric terms in the different subzones of the beach, with the aim of better understanding the onshore/offshore sediment exchange in relation with nourishments and in the presence of protection structures. The effectiveness of the adopted interventions to combat erosion, and to cope with future climate change-related impacts, appears not fully successful in the presence of an overall sediment deficit at the coast. This demonstrates the need for repeated monitoring of the emerged and submerged beach in such a critical setting.

Void Evolution via Coupled Creep and Electromigration in Confined Small Scale Interconnects

2006 ◽  
Author(s):  
Wei Lu ◽  
Dongchoul Kim
Keyword(s):  
High Efficiency ◽  
Three Dimensional ◽  
Small Scale ◽  
Creep Flow ◽  
Void Evolution ◽  
Void Shape ◽  
Kinetics Of ◽  
Electron Wind ◽  
Biconjugate Gradient Method ◽  
Biconjugate Gradient

This paper proposes a three dimensional electromigration model for void evolution in small scale interconnects. Concurrent kinetics of creep flow and surface diffusion as well as the effect of surrounding material are considered to provide better understanding of the evolution process. The multiple kinetics and energetics are incorporated into a diffusive interface model. A semi-implicit Fourier spectral method and the preconditioned biconjugate-gradient method are proposed in the computations to achieve high efficiency and numerical stability. We systematically studied kinetic processes from diffusion dominated to creep dominated. Which process dominates, as revealed by the analysis, is determined by a combination of viscosity, mobility, interconnect thickness, and void radius. Previous studies on electromigration suggest that the void shape evolution is determined by the competition between the electron wind force and the surface energy. There exists a critical initial void shape, which determines whether a void evolves into a slit or not. However, our simulations show that in the same situation a creep dominated process can lead to a quite different morphology. A spherical void can evolve into a bowl shape, and further split into two smaller voids. It is also shown that the interconnect geometry has an important effect.

CBED analysis of impurity distributions in AlN

1990 ◽  
Vol 48 (4) ◽  
pp. 214-215
Author(s):  
Daniel Callahan ◽  
G. Thomas
Keyword(s):  
Aluminum Nitride ◽  
Bulk Material ◽  
Strong Dependence ◽  
Lattice Parameter ◽  
Promising Technique ◽  
Nitride Ceramics ◽  
Surface Phases ◽  
Convergent Beam ◽  
Oxygen Impurities

Oxygen impurities may significantly influence the properties of nitride ceramics with a strong dependence on the microstructural distribution of the impurity. For example, amorphous oxygen-rich grain boundary phases are well-known to cause high-temperature mechanical strength degradation in silicon nitride whereas solutionized oxygen is known to decrease the thermal conductivity of aluminum nitride. Microanalytical characterization of these impurities by spectral methods in the AEM is complicated by reactions which form oxygen-rich surface phases not representative of the bulk material. Furthermore, the impurity concentrations found in higher quality ceramics may be too low to measure by EDS or PEELS. Consequently an alternate method for the characterization of impurities in these ceramics has been investigated.Convergent beam electron diffraction (CBED) is a promising technique for the study of impurity distributions in aluminum nitride ceramics. Oxygen is known to enter into stoichiometric solutions with AIN with a consequent decrease in lattice parameter.

Toward a neuroscope: An application of high-performance computing for real-time evaluation of brain function using MRI

1994 ◽  
Vol 52 ◽  
pp. 922-923
Author(s):  
C. S. Potter ◽  
C. D. Gregory ◽  
H. D. Morris ◽  
Z.-P. Liang ◽  
P. C. Lauterbur
Keyword(s):  
Human Brain ◽  
Brain Function ◽  
High Performance ◽  
Complex Signal ◽  
Time Step ◽  
Brain Organization ◽  
Cognitive Studies ◽  
Positron Emission ◽  
Imaging And Spectroscopy ◽  
3D Anatomy

Over the past few years, several laboratories have demonstrated that changes in local neuronal activity associated with human brain function can be detected by magnetic resonance imaging and spectroscopy. Using these methods, the effects of sensory and motor stimulation have been observed and cognitive studies have begun. These new methods promise to make possible even more rapid and extensive studies of brain organization and responses than those now in use, such as positron emission tomography.Human brain studies are enormously complex. Signal changes on the order of a few percent must be detected against the background of the complex 3D anatomy of the human brain. Today, most functional MR experiments are performed using several 2D slice images acquired at each time step or stimulation condition of the experimental protocol. It is generally believed that true 3D experiments must be performed for many cognitive experiments. To provide adequate resolution, this requires that data must be acquired faster and/or more efficiently to support 3D functional analysis.

A quantitative image analysis method for the determination of cocontinuity in polymer blends

1993 ◽  
Vol 51 ◽  
pp. 894-895
Author(s):  
William A. Heeschen
Keyword(s):  
Image Analysis ◽  
Polymer Blends ◽  
Quantitative Measurement ◽  
Morphological Evolution ◽  
Phase Ratio ◽  
Irregular Shapes ◽  
Quantitative Image ◽  
Discrete Domains ◽  
A Domains

Two new morphological measurements based on digital image analysis, CoContinuity and CoContinuity Balance, have been developed and implemented for quantitative measurement of morphology in polymer blends. The morphology of polymer blends varies with phase ratio, composition and processing. A typical morphological evolution for increasing phase ratio of polymer A to polymer B starts with discrete domains of A in a matrix of B (A/B < 1), moves through a cocontinuous distribution of A and B (A/B ≈ 1) and finishes with discrete domains of B in a matrix of A (A/B > 1). For low phase ratios, A is often seen as solid convex particles embedded in the continuous B phase. As the ratio increases, A domains begin to evolve into irregular shapes, though still recognizable as separate domains. Further increase in the phase ratio leads to A domains which extend into and surround the B phase while the B phase simultaneously extends into and surrounds the A phase.

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