Sand ripple volume generator for underwater acoustic models, a cellular automaton Monte-Carlo approach

Cellular automata have been successfully used to model the sand dynamics of aeolian dunes and ripples. The cellular automata Monte-Carlo model proposed in this paper expands the capabilities of cellular automata models to under water ripple formation introducing not a two dimensional matrix but two three dimensional volumes, being a sand volume and a water volume. The proposed model has the capability to generate optimal environmental data to input in other mathematical models in need of environmental data. The following enhancements were implemented: optional abstraction levels of the hydrodynamic behavior, morphological formation of underwater ripples under unilateral currents in any direction as well as morphological formation of underwater ripples under wave current interaction, grain size distribution of the sand in every time step in the entire volume and compaction distribution in every time step in the entire sediment volume. The proposed cellular automata model is a closed toroidal system. The toroidal approach of the model enables to build up infinite rippled surfaces by using the generated sediment volumes as tiles; this solves boundary problems in for example acoustic models. Using the fractal properties of the sand ripples, infinite surfaces containing rippled dunes can be generated

Lattice gas cellular automata model for rippling and aggregation in myxobacteria

A lattice-gas cellular automaton (LGCA) model is used to simulate rippling and aggregation in myxobacteria. An efficient way of representing cells of different cell size, shape and orientation is presented that may be easily extended to model later stages of fruiting body formation. This LGCA model is designed to investigate whether a refractory period, a minimum response time, a maximum oscillation period and non-linear dependence of reversals of cells on C-factor are necessary assumptions for rippling. It is shown that a refractory period of 2-3 minutes, a minimum response time of up to 1 minute and no maximum oscillation period best reproduce rippling in the experiments of {\it Myxoccoccus xanthus}. Non-linear dependence of reversals on C-factor is critical at high cell density. Quantitative simulations demonstrate that the increase in wavelength of ripples when a culture is diluted with non-signaling cells can be explained entirely by the decreased density of C-signaling cells. This result further supports the hypothesis that levels of C-signaling quantitatively depend on and modulate cell density. Analysis of the interpenetrating high density waves shows the presence of a phase shift analogous to the phase shift of interpenetrating solitons. Finally, a model for swarming, aggregation and early fruiting body formation is presented

Epidemic modelling by ripple-spreading network and genetic algorithm

Mathematical analysis and modelling is central to infectious disease epidemiology. This paper, inspired by the natural ripple-spreading phenomenon, proposes a novel ripple-spreading network model for the study of infectious disease transmission. The new epidemic model naturally has good potential for capturing many spatial and temporal features observed in the outbreak of plagues. In particular, using a stochastic ripple-spreading process simulates the effect of random contacts and movements of individuals on the probability of infection well, which is usually a challenging issue in epidemic modeling. Some ripple-spreading related parameters such as threshold and amplifying factor of nodes are ideal to describe the importance of individuals’ physical fitness and immunity. The new model is rich in parameters to incorporate many real factors such as public health service and policies, and it is highly flexible to modifications. A genetic algorithm is used to tune the parameters of the model by referring to historic data of an epidemic. The well-tuned model can then be used for analyzing and forecasting purposes. The effectiveness of the proposed method is illustrated by simulation results

Nonlinear Dynamics of Aeolian Sand Ripples

We study the initial instability of flat sand surface and further nonlinear dynamics of wind ripples. The proposed continuous model of ripple formation allowed us to simulate the development of a typical asymmetric ripple shape and the evolution of sand ripple pattern. We suggest that this evolution occurs via ripple merger preceded by several soliton-like interaction of ripples.Comment: 6 pages, 3 figures, corrected 2 typo

Optimal Pedestrian Path Planning in Evacuation Scenario

Simulation of evacuation plans is a relatively complex problem. It is necessary to simulate a number of separate processes which interact in the result. Namely, they are pedestrian-pedestrian interactions, pedestrian-static object (e.g. wall) interactions and pedestrian-environment (fire, smoke, etc.) interactions. In this case, the evacuation simulation is controled on the microscopic level. Microscopic level considers each individual separately and pedestrian is planning his/her path to the exit with regard to the above-mentioned interactions. In this article we focus on path planning during evacuation and describe algorithms applied in this area. At the end we propose a method of the space evaluation with linear time complexity and planned path compared with commercial software tools

Understanding morphogenesis in myxobacteria from a theoretical and experimental perspective

Several species of bacteria exhibit multicellular behaviour, with individuals cells cooperatively working together within a colony. Often this has communal benefit since multiple cells acting in unison can accomplish far more than an individual cell can and the rewards can be shared by many cells. Myxobacteria are one of the most complex of the multicellular bacteria, exhibiting a number of different spatial phenotypes. Colonies engage in multiple emergent behaviours in response to starvation culminating in the formation of massive, multicellular fruiting bodies. In this thesis, experimental work and theoretical modelling are used to investigate emergent behaviour in myxobacteria. Computational models were created using FABCell, an open source software modelling tool developed as part of the research to facilitate modelling large biological systems. The research described here provides novel insights into emergent behaviour and suggests potential mechanisms for allowing myxobacterial cells to go from a vegetative state into a fruiting body. A differential equation model of the Frz signalling pathway, a key component in the regulation of cell motility, is developed. This is combined with a three-dimensional model describing the physical characteristics of cells using Monte Carlo methods, which allows thousands of cells to be simulated. The unified model explains how cells can ripple, stream, aggregate and form fruiting bodies. Importantly, the model copes with the transition between stages showing it is possible for the important myxobacteria control systems to adapt and display multiple behaviours

Emerging Technologies - NanoMagnets Logic (NML)

In the last decades CMOS technology has ruled the electronic scenario thanks to the constant scaling of transistor sizes. With the reduction of transistor sizes circuit area decreases, clock frequency increases and power consumption decreases accordingly. However CMOS scaling is now approaching its physical limits and many believe that CMOS technology will not be able to reach the end of the Roadmap. This is mainly due to increasing difficulties in the fabrication process, that is becoming very expensive, and to the unavoidable impact of leakage losses, particularly thanks to gate tunnel current. In this scenario many alternative technologies are studied to overcome the limitations of CMOS transistors. Among these possibilities, magnetic based technologies, like NanoMagnet Logic (NML) are among the most interesting. The reason of this interest lies in their magnetic nature, that opens up entire new possibilities in the design of logic circuits, like the possibility to mix logic and memory in the same device. Moreover they have no standby power consumption and potentially a much lower power consumption of CMOS transistors. In literature NML logic is well studied and theoretical and experimental proofs of concept were already found. However two important points are not enough considered in the analysis approach followed by most of the work in literature. First of all, no complex circuits are analyzed. NML logic is very different from CMOS technologies, so to completely understand the potential of this technology it is mandatory to investigate complex architectures. Secondly, most of the solutions proposed do not take into account the constraints derived from fabrication process, making them unrealistic and difficult to be fabricated experimentally. This thesis focuses therefore on NML logic keeping into account these two important limitations in the research approach followed in literature. The aim is to obtain a complete and accurate overview of NML logic, finding realistic circuital solutions and trying to improve at the same time their performance. After a brief and complete introduction (Chapter 1), the thesis is divided in two parts, which cover the two fundamental points followed in this three years of research: A circuits architecture analysis and a technological analysis. In the architecture analysis first an innovative VHDL model is described in Chapter 2. This model is extensively used in the analysis because it allows fast simulation of complex circuits, with, at the same time, the possibility to estimate circuit per- formance, like area and power consumption. In Chapter 3 the problem of signals synchronization in complex NML circuits is analyzed and solved, using as benchmark a simple but complete NML microprocessor. Different solutions based on asynchronous logic are studied and a new asynchronous solution, specifically designed to exploit the potential of NML logic, is developed. In Chapter 4 the layout of NML circuits is studied on a more physical level, considering the limitations of fabrication processes. The layout of NML circuits is therefore changed accordingly to these constraints. Secondly CMOS circuits architectures are compared to more simple architectures, evaluating therefore which one is more suited for NML logic. Finally the problem of interconnections in NML technology is analyzed and solutions to improve it are found. In Chapter 5 the problem of feedback signals in heavy pipelined technologies, like NML, is studied. Solutions to improve performances and synchronize signals are developed. Systolic arrays are then analyzed as possible candidate to exploit NML potential. Finally in Chapter 6 ToPoliNano, a simulator dedicated to NML and other emerging technologies, that we are developing, is described. This simulator allows to follow the same top-down approach followed for CMOS technology. The layout generator and the simulation engine are detailed described. In the first chapter of the technological analysis (Chapter 7), the performance of NML logic is explored throughout low level simulations. The aim is to understand if these circuits can be fabricated with optical lithography, allowing therefore the commercial development of NML logic. Basic logic gates and the clock system are there analyzed from a low level perspective. In Chapter 8 an innovative electric clock system for NML technology is shown and the first experimental results are reported. This clock system allows to achieve true low power for NML technology, obtaining a reduction of power consumption of 20 times considering the best CMOS transistors available. This power consumption takes into account all the losses, also the clock system losses. Moreover the solution presented can be fabricated with current technological processes. The research work behind this thesis represents an important breakthrough in NML logic. The solutions here presented allow the design and fabrication of complex NML circuits, considering the particular characteristics of this technology and considerably improving the performance. Moreover the technological solutions here presented allow the design and fabrication of circuits with available fabrication process with a considerable advantage over CMOS in terms of power consumption. This thesis represents therefore a considerable step froward in the study and development of NML technolog