Cellular Grid Research Articles

Three-dimensional hydrofacies assemblages in ice-contact/proximal sediments forming a heterogeneous ‘hybrid’ hydrostratigraphic unit in central Illinois, USA

Three-dimensional (3-D) hydrostratigraphic modelling of glacial sediment assemblages was undertaken as part of a groundwater study in central Illinois, USA. Sediments comprising these assemblages, informally referred to as the Glasford deglacial unit, form discontinuous sand-gravel layers including small aquifer zones, and fine-grained interstratified layers that may impede groundwater movement. This unit is stratigraphically above a regional aquitard overlying the important Mahomet aquifer. The study improves understanding of the internal stratigraphic architecture and hydrostratigraphic character of the unit. Data include descriptions of continuous cores, profiles of near-surface and downhole geophysical logs, and sediment descriptions from water well logs. Discrete bounding surfaces constructed using gOcad represent the main lithofacies assemblages forming a 3-D framework. The framework was further partitioned into a 3-D cellular grid for mapping the spatial distribution of fine- and coarse-grained facies. Hydraulic conductivity (K G) estimates were used to convert these lithofacies into hydrofacies. Medium- to coarse-grained hydrofacies (K G = 1.25 × 10−5 m/s) represent 46 % of the total volume, the remainder being fine-grained hydrofacies (K G = 3.01 × 10−8 m/s). The spatial pattern of these hydrofacies is highly heterogeneous, thus, designating the Glasford deglacial unit as an aquifer or aquitard would be conceptually misleading. The term “hybrid hydrostratigraphic unit” is introduced to better represent conceptually this type of unit in hydrostratigraphic models.

Navier-Stokes Equation and Computational Scheme for Non-Newtonian Debris Flow

This paper proposes a computational approach to debris flow model. In recent years, the theoretical activity on the classical Herschel-Bulkley model (1926) has been very intense, but it was in the early 80s that the opportunity to explore the computational model has enabled considerable progress in identifying the subclasses of applicability of different sets of boundary conditions and their approximations. Here we investigate analytically the problem of the simulation of uniform motion for heterogeneous debris flow laterally confined taking into account mainly the geological data and methodological suggestions derived from simulation with cellular automata and grid systems, in order to propose a computational scheme able to operate a compromise between “global” predictive capacities and computing effort.

A real‐space cellular automaton laboratory

ABSTRACTGeomorphic investigations may benefit from computer modelling approaches that rely entirely on self‐organization principles. In the vast majority of numerical models, instead, points in space are characterized by a variety of physical variables (e.g. sediment transport rate, velocity, temperature) recalculated over time according to some predetermined set of laws. However, there is not always a satisfactory theoretical framework from which we can quantify the overall dynamics of the system. For these reasons, we prefer to concentrate on interaction patterns using a basic cellular automaton modelling framework. Here we present the Real‐Space Cellular Automaton Laboratory (ReSCAL), a powerful and versatile generator of 3D stochastic models. The objective of this software suite, released under a GNU licence, is to develop interdisciplinary research collaboration to investigate the dynamics of complex systems. The models in ReSCAL are essentially constructed from a small number of discrete states distributed on a cellular grid. An elementary cell is a real‐space representation of the physical environment and pairs of nearest‐neighbour cells are called doublets. Each individual physical process is associated with a set of doublet transitions and characteristic transition rates. Using a modular approach, we can simulate and combine a wide range of physical processes. We then describe different ingredients of ReSCAL leading to applications in geomorphology: dune morphodynamics and landscape evolution. We also discuss how ReSCAL can be applied and developed across many disciplines in natural and human sciences. Copyright © 2013 John Wiley & Sons, Ltd.

Cellular grid model based node scheduling algorithm for wireless sensor network

In order to effectively improve the grouping ability of grouping methods for Wireless Sensor Network(WSN),a partition method for sensory field based on the location information of nodes and cellular grid model was proposed,which can divide the whole sensory field into discrete cellular grids.Afterwards,through autonomous cluster head selecting and group assignment of nodes in each cellular grid,a distributed node grouping method was designed.The theoretical analysis and experimental results show that the new node grouping algorithm has good grouping performance.It not only can guarantee 100% global connectivity,but also can guarantee 100% network coverage rate of groups at the same time.

Optimal X-Ray Spectra Selection in Digital Mammography: A Semi-Analytical Study

In this work, a semi-analytical model was developed to determine the contrast-to-noise ratio (CNR) and the normalized average glandular dose (D̅ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">gN</sub> ) in digital mammography, taking into account interactions up to second order. The optimal x-ray spectra were investigated using a Figure of Merit (FOM), for different breast thicknesses (3 cm ≤ L ≤ 7 cm) and glandularities (20% and 50%), anti-scatter grids types, considering a-Se and CsI image receptors. The anode/filter combinations evaluated were: Mo/Mo, Mo/Rh, Rh/Rh, and a W anode combined with k-edge filters (Mo, Ru, Rh, Pd, Ag, Cd, In and Sn), for tube potential between 23 and 35 kVp. Results demonstrate that the W-anode spectra combined with k-edge filters show a superior performance compared to the Mo/Mo combination traditionally employed in mammography, for all conditions analyzed. The optimum general x-ray spectra for 3 cm, 5 cm and 7 cm breasts are, respectively, W/Mo at 23 kVp, W/Pd at 28 kVp and W/Ag at 30 kVp. For the a-Se receptor, the optimum filter atomic number is one unit higher than that obtained for the CsI, while the optimal tube potentials are the same. The optimal tube potential was up to 1-2 kVp greater for a linear grid than that obtained without grid or with a cellular grid. For breast thicker than 7 cm, the optimum filter atomic number also increases by one unit for a linear grid. Compared to standard technique, the performance improvement of a W anode with proper k-edge filters is more noticeable for thicker and denser breasts, for a a-Se receptor and a linear grid. Finally, it was verified that the semi-analytical model implemented provided results of optimum x-ray spectra in a fast and simple way, with a good agreement with those obtained experimentally or by Monte Carlo simulation.

Why Smart Grids?

Summary The transformation to the guide system of renewable energy requires the flexibilization of the energy system where smart grids are the basis for new grid and market functions with close inclusion of customers’ properties. The E-Energy project moma developed a new procedure for a cellular grid operation with automated processes. In this article, the moma system is put in relation to the architecture of the EU-smart grid mandate 490 as well as to moma flexibilization functions.

Grid anisotropy reduction for simulation of growth processes with cellular automaton

Growth processes simulated on a regular cellular automaton grid with simple capture rules are considerably influenced by the structure of the grid. Some of the growth directions are favored over others leading to highly anisotropic or, at least, orientation-dependent growth pattern. A new method is proposed for significant reduction of artificial grid anisotropy in 2D and 3D cellular automata with continuous state variable. The method employs additional diffusion process controlling the growth rate and allows for isotropic or anisotropic growth where the anisotropy is decoupled from the grid structure. Verification of the method is provided in the case of isotropic circular growth, isotropic growth of various shapes in uniform and spatially varying fields, and anisotropic growth with respect to orientation and symmetry of the pattern. Finally, the reduction of grid anisotropy is demonstrated in 2D simulation of dendritic grain growth in pure metal. The shape of the grain is shown to be virtually independent of the orientation. An example growth of a grain with six-fold symmetry is also included.

A Cellular Grid Model to the Repeater Coordination

A Cellular Grid Model to the Repeater Coordination

Stepping robotic system based on cellular grid map

In order to meet the demand of providing varieties of physical services in the intelligent space, this paper designed and implemented a stepping robotic system based on cellular grid map, from both hardware implementation and software algorithm aspects. In the hardware aspect, the paper designed and implemented an omni-directional wheels structure and the mobile platform, stepping robot driving system and sensing detection system. Among them, the designing of the mechanical structure of the entire stepping robot body has greatly improved the effectiveness and reliability of the hardware system. The major innovative work includes analysing and modelling the omni-directional mobile platform with six wheels in mechanics, kinematics and dynamics, the designing and implementation of optical odometer by using FPGA to parse PS/2 protocol, and the laser calibration system. In terms of software algorithms, the paper mainly focused on four contents, consisting of multi-sensor data fusion, creating of a cellular grid map, local path planning and global path planning of the stepping robot based on the map. The main innovative work in the software algorithm includes the achievement of multi-dimensional sensor data fusion algorithm by introducing Mahalanobis distance, six-direction local path planning with the solution of the Dead Angle phenomenon and the Dead Circle phenomenon, as well as extending TSP optimisation problem based on Genetic Algorithm to the state of the cellular grid map. The issues mentioned above have been realised on the simulation platform. In the field test, the precision of the stepping robotic system can reach the millimeter scale.

Natural discretization of pedestrian movement in continuous space

Is there a way to describe pedestrian movement with simple rules, as in a cellular automaton, but without being restricted to a cellular grid? Inspired by the natural stepwise movement of humans, we develop a model that uses local discretization on a circle around virtual pedestrians. This allows for movement in arbitrary directions, only limited by the chosen optimization algorithm and numerical resolution. The radii of the circles correspond to the step lengths of pedestrians and thus are model parameters, which must be derived from empirical observation. Therefore, we conducted a controlled experiment, collected empirical data for step lengths in relation with different speeds, and used the findings in our model. We complement the model with a simple calibration algorithm that allows reproducing known density-velocity relations, which constitutes a proof of concept. Further validation of the model is achieved by reenacting an evacuation scenario from experimental research. The simulated egress times match the values reported for the experiment very well. A new normalized measure for space occupancy serves to visualize the results.

A comparison of image quality and radiation dose between a cellular grid and a linear grid using a mammography phantom

The aim of this study is to establish whether a cellular grid can offer any improvement over a linear grid in terms image quality and radiation dose for a single analogue mammography system.Using a prospective experimental design, a range of exposure factors and Perspex thicknesses were used to simulate conditions found in clinical practice. A Contrast Detail Mammography (CDMAM) test phantom was utilized to produce Image Quality Factor (IQF) and Mean Glandular Dose (MGD) data sets.An identical range of exposure factors/phantom thicknesses were selected for both grids and a direct comparison was made of the calculated IQF and the MGD for each pair of factors.The cellular grid produced a higher IQF for every exposure technique tested, when compared to the linear grid (increase: 1.2% to 35.8%, mean 15.8%, p < 0.005). MGD values with the cellular grid were also minimally increased for the majority of exposure techniques, (increase: −2.4% to 7.9%, mean 3.3%, p < 0.01).In this phantom study, use of the cellular grid resulted in increased IQF with an acceptable increase in MGD under all exposure conditions tested with the largest improvement in IQF seen in the extremes of phantom thickness. This suggests that use of a cellular grid in clinical practice might help improve cancer detection rates, without breaching current radiation dose guidelines for accepted dose levels and be particularly beneficial when examining both very small and very large breasts.

Quantification of scattered radiation in projection mammography: Four practical methods compared

Four different practical methodologies of quantifying scattered radiation for two different digital mammographic systems are compared. The study considered both grid in and grid out geometries for two different antiscatter grid types, a typical linear grid and a cellular grid design. The aim was to find quick and reproducible methods that could be used in place of the beam stop technique. The scatter to primary ratio (SPR) and the scatter fraction (SF) were used to quantify scattered radiation as a function of poly(methyl methacrylate) (PMMA) thickness, grid position, and beam quality. The four scatter estimation methods applied were (1) the beam stop method, (2) a hybrid method that combined measured detector (scatter-free) modulation transfer function (MTF) data and a Monte Carlo simulation of the scatter point spread function, (3) from the low frequency drop data taken from the system MTF, and (4) from the edge spread function (ESF) measured in the presence of PMMA. Repeatability error was assessed for all methods. SPR results acquired with the beam stop method ranged from 0.052 to 0.187 for the system with linear grid and from 0.012 to 0.064 for the cellular grid system, as PMMA thickness was increased from 20 to 80 mm. With the grid removed, beam stop SPR was similar for both systems, ranging between 0.268 and 1.124, for corresponding MTF thicknesses. The direct MTF method had a maximum difference of 24% from the beam stop SPR and SF data for all conditions except the cellular grid in geometry, where maximum difference in SPR was 0.044 (164%). The ESF technique gave large differences from the beam stops for both grid geometries but agreement was within 21% for the grid out geometry. Repeatability error with beam stops was between 1% and 5% for the grid out geometries, while for the grid in cases it was 13% and 87% for the linear and cellular grids, respectively. Repeatability error for the direct MTF method applied to both systems and grid geometries ranged between 3% and 12%. All three alternative methods to the beam stop technique gave reasonable estimates of SPR without grid, with a maximum difference of 24% (mean difference 8%). For the grid in geometry, the direct MTF method gave a maximum difference of 24% for the linear grid system, while maximum percentage difference was 119% (absolute difference of 0.042) for the system with the cellular grid, where SPR values were low. Except for cases where the SPR is very low, the direct MTF method offers a quick and reproducible alternative to the beam stop technique.

A Cellular-rearranging of Population in Genetic Algorithms to Solve Assembly-Line Balancing Problem

Assembly line balancing problem (ALBP) is the allocating of assembly tasks to workstations with consideration of some criteria such as time and the number of workstations. Due to the complexity of ALB, finding the optimum solutions in terms of the number of workstations in the assembly line needs suitable meta-heuristic techniques. Genetic algorithms have been used to a large extent. Due to converging to the local optimal solutions to the most genetic algorithms, the balanced exploration of the new area of search space and exploitation of good solutions by this kind of algorithms as a good way can be sharpened with some meta-heuristic. In this paper, the modified cellular (grid) rearranging-population structure is developed. The individuals of the population are located on cells according to the hamming distance value among individuals as neighbours before regenerations and a family of cellular genetic algorithms (CGAs) is defined. By using the cellular structure and the rearrangements, some of the family members can find better solutions compared with others in the same iterations, and they behave much more reasonably in order to acquire the solution in terms of the number of workstations and the smoothly balanced task assignment on criteria conditions.

A review of alternatives for orthotropic bridge deck panels

Bridge decks are subject to severe loading conditions as they are loaded by large numbers of concentrated axles. In the case of orthotropic bridge decks, it is known that the combination of these loading conditions and the quantity of required welds may not allow for a durable and still cost-effective solution with this type of deck in the future. Nevertheless, still progress is made in the analysis and specifications, but the efforts are large and the profits are moderate. Consequently, a search of alternatives for the future is valuable, and probably even necessary. This paper presents current state of the art regarding alternative solutions for orthotropic decks, including fiber reinforced composites, and then focuses on a steel-concrete sandwich solution, developed by the author. In this solution, a cellular concrete grid is injected between two steel plates, resulting in a non-welded and more isotropic rather than orthotropic deck behaviour. For this purpose, high strength self compacting concrete is to be used. Challenges in the design and manufacture are, in this case, the steel concrete composite (SCC) mix, the steel to concrete adhesion, and the shear capacity, rather than the fatigue design. Theoretical investigations, as well as experimental results, are presented. The results indicate that, although some parameters are still to be optimized, alternative solutions for orthotropic bridge decks panels will be available.

Evaluation of scatter-to-primary ratio, grid performance and normalized average glandular dose in mammography by Monte Carlo simulation including interference and energy broadening effects

In this work, a computational code for the study of imaging systems and dosimetry in conventional and digital mammography through Monte Carlo simulations is described. The developed code includes interference and Doppler energy broadening for simulation of elastic and inelastic photon scattering, respectively. The code estimates the contribution of scattered radiation to image quality through the spatial distribution of the scatter-to-primary ratio (S/P). It allows the inclusion of different designs of anti-scatter grids (linear or cellular), for evaluation of contrast improvement factor (CIF), Bucky factor (BF) and signal difference-to-noise ratio improvement factor (SIF). It also allows the computation of the normalized average glandular dose, . These quantities were studied for different breast thicknesses and compositions, anode/filter combinations and tube potentials. Results showed that the S/P increases linearly with breast thickness, varying slightly with breast composition or the spectrum used. Evaluation of grid performance showed that the cellular grid provides the highest CIF with smaller BF. The SIF was also greater for the cellular grid, although both grids showed SIF < 1 for thin breasts. Results for showed that it increases with the half-value layer (HVL) of the spectrum, decreases considerably with breast thickness and has a small dependence on the anode/filter combination. Inclusion of interference effects of breast tissues affected the values of S/P obtained with the grid up to 25%, while the energy broadening effect produced smaller variations on the evaluated quantities.

A cellular automata model on residential migration in response to neighborhood social dynamics

Residential migration patterns result from complex processes involving households and their neighborhoods. Simulation models assist in understanding this relationship by contextualizing residential mobility within a theoretical framework. The objective of this study is to model these migration patterns created by the interaction between changes in the social structure of households and the positive or negative social attractors in the neighborhood. Specifically, this study links residential mobility to the dynamic interplay between the micro-environment existing within a household and the meso-environment that structures a neighborhood. The cellular automata model developed in this study incorporates transition rules which govern households in their decision to move. The results represented by a cellular grid demonstrate that residential mobility is significantly influenced by density rates, individual household factors and neighborhood attractors. Three contrasting scenarios are presented in this paper to illustrate the impact of occupancy, density, neighborhood social influence, and the effect of a conglomeration of negative social attractors in a neighborhood. Future iterations of this model will incorporate census and crime data in order to test whether the rules governing this model are an accurate reflection of residential mobility in a mid-sized Canadian city.

CA Models for Target Searching Agents

Agents in a cellular grid have the task to move from their start positions to their individual target positions as fast as possible. Four models using agents are proposed that can be applied to the problem. These models are conform to the CA paradigm. The agents have either a moving direction (directed agent) or not (undirected agent). The agents behave either in a deterministic way according to a control automaton inside of each agent or they behave randomly. In order to find the best behaving agents, control automata (“algorithms”) were evolved using a genetic island model. Near optimal algorithms were evolved separately for k = 1 to k = 256 agents in a 32 × 32 environment using 20 random initial configurations for each k . Then these algorithms were ranked using another set of 100 initial configurations for each k . It turned out that the agents behave better with respect to speed and reliability in this order: (1) controlled directed agents, (2) random directed agents, (3) random undirected agents, and (4) controlled undirected agents. Although the controlled directed agents (optimized for each k ) can solve all the given 100 initial configurations in the ranking set, it can not be assured that no deadlocks may occur for other initial configurations.

Advancement through interactive radio

This paper describes the rationale, design and implementation of a system for increasing the status women in developing communities. AIR (Advancement through Interactive Radio) gives female community radio listeners a voice with which to respond to programming and to create programming content. We first describe the cost of excluding women from Information and Communication Technologies (ICT) for development, and explore how community radio represents an opportunity for inclusion. We draw upon feasibility studies and site visits in Southeast Kenya to support the introduction of a mechanism that enables women to "talk back" to the community radio station. Using the principles of Participatory Action Research (PAR), we argue that women will be more likely to benefit from technology-mediated opportunities for development if they themselves produce information that contributes to their advancement, rather than simply consuming information provided by others. Finally, we describe the design and implementation of simple communications device that supports this model for use in communities that are, and will remain for some time, off the electrical and cellular grid. This hand-held device enables women to record voice feedback and news for community radio. This feedback is then routed asynchronously back to the radio station through a probabilistic, delay-tolerant network, where the feedback can inform subsequent broadcasts and facilitate additional discussion. We conclude with a technical summary of the AIR prototype.

Design and Evaluation of a Distributed Clustering Algorithm for Mobile ad hoc Networks

This paper proposes a new clustering algorithm for global positioning system (GPS)-based mobile ad hoc networks that takes into consideration the direction of the overall traffic flow in the network. The proposed cluster leader logic algorithm is motivated by the GPS quorum hybrid routing algorithm, where clusterheads are positioned on the terrain upon a conceptual cellular grid. The proposed distributed clustering algorithm chooses the clusterheads based on the traffic flow patterns, i.e. the nodes best suited to forward and route network traffic are selected. Our approach allows a clusterhead which is overwhelmed with sending packets to identify an additional clusterhead from nodes available in its cell to share its load. Likewise, clusterheads with low load will try to relinquish their role as a clusterhead. We propose a new concept called cell fanning that allows collocated clusterheads in one cell to share routing responsibilities by declaring which cells they are responsible for routing packets to. We conducted extensive simulation experiments with enforced directional traffic patterns. Two important results are presented: power consumption per clusterhead and average queuing delay for each clusterhead. Results in terms of message overheads, number of clusterheads, power consumption, and queuing delay reveal that system performance is enhanced when clusterheads are chosen considering the direction of the traffic flow.

Complexity in a cellular model of river avulsion

We propose a new model of river avulsion that emphasizes simplicity, self-organization, and unprogrammed behavior rather than detailed simulation. The model runs on a fixed cellular grid and tracks two elevations in each cell, a high elevation representing the channel (levee) top and a low one representing the channel bottom. The channel aggrades in place until a superelevation threshold for avulsion is met. After an avulsion is triggered a new flow path is selected by steepest descent based on the low values of elevation. Flow path depends sensitively on floodplain topography, particularly the presence of former abandoned channels. Several behavioral characteristics emerge consistently from this simple model: (1) a tendency of the active flow to switch among a small number of channel paths, which we term the active channel set, over extended periods, leading to clustering and formation of multistory sand bodies in the resulting deposits; (2) a tendency for avulsed channels to return to their previous paths, so that new channel length tends to be generated in relatively short segments; and (3) avulsion-related sediment storage and release, leading to pulsed sediment output even for constant input. Each of these behaviors is consistent with observations from depositional river systems. A single-valued threshold produces a wide variety of avulsion sizes and styles. Larger “nodal” avulsions are rarer because pre-existing floodplain topography acts to steer flow back to the active channel. Channel stacking pattern is very sensitive to floodplain deposition. This work highlights the need to develop models of floodplain evolution at large time and space scales to complement the improving models of river channel evolution.