Marta Becker Villamil

Towards an integrated system for planning and assisting maxillofacial orthognathic surgery

Computer-assisted maxillofacial orthognathic surgery is an emerging and interdisciplinary field linking orthognathic surgery, remote signal engineering and three-dimensional (3D) medical imaging. Most of the computational solutions already developed make use of different specialized systems which introduce difficulties both in the information transfer from one stage to the others and in the use of such systems by surgeons. Trying to address such issue, in this work we present a common computer-based system that integrates proposed modules for planning and assisting the maxillofacial surgery. With that we propose to replace the current standard orthognathic preoperative planning, and to bring information from a virtual planning to the real operative field. The system prototype, including three-dimensional cephalometric analysis, static and dynamic virtual orthognathic planning, and mixed reality transfer of information to the operation room, is described and the first results obtained are presented.

A Model for Generating and Animating Groups of Virtual Agents

This paper presents a model to generate and animate groups which emerge as a function of interaction among virtual agents. The agents are characterized through the following parameters: sociability, communication, comfort, perception and memory. The emergent groups are characterized through the cohesion parameter which describes the homogeneity of ideas of the group members. In this work we are mainly interested in investigating the formation of groups (membership and time for grouping), the groups characterization (cohesion parameter) and their visual representation (group formation). The overall results suggest that the interaction among agents contributes to larger groups and higher crowd cohesion values.

Simulation of the human TMJ behavior based on interdependent joints topology

The temporomandibular joint (TMJ) is one of the most important and complex joints of the body and its pathologies affect a great percentage of the human population. The simulation of the TMJ behavior during opening, closing and chewing movements can be very useful to the understanding of this articulation by physicians, helping them to prevent or fix problems due to accidents or diseases. This work proposes a model to simulate the human TMJ behavior based on the concept of two interdependent joints. The model was conceived using multimodal information acquired from CT and MRI images of a live person, as well as motion data acquired from this same person with a magnetic motion capture device. Simulation of movement of other TMJs, based on different morphology of bones and teeth, is obtained by adapting the regular captured motion data through collision detection and treatment methods. The proposed model was evaluated through image registration techniques by comparing our simulated results with real, captured motion data. We also validate the model showing how it can be used to predict TMJ behavior in the presence of different--normal or abnormal--bones and teeth morphologies.

A model to simulate the mastication motion at the temporomandibular joint

The understanding of the mastication system motion is essential to maxillofacial surgeons and dentists in the procedures concerning jaw and teeth corrections. The temporomandibular joint (TMJ), despite its complexity, is one of the most frequently used joints of the human body. The incidence of a great number of injuries in this joint is influenced not only by its regular use during the mastication, but also by the strong forces applied by the muscles and the wide range of movements it is capable to perform. In this work, we propose the development of a jaw simulator capable of reproducing the complete mastication movement. Our jaw simulator is basically composed by three triangle meshes representing the 3D model of the cranium, mandible and teeth; and an anatomically-based joint model conceived to represent the TMJ motion. The polygonal meshes describing the bones and teeth are obtained from CT images and the jaw motion is simulated using the joint model guided by a 3D motion curve obtained from the composition of the standard 2D curves available in the medical literature. The scale, height and width of these original curves are modified to simulate different kind and size of food and to represent the movements’ variability depending on patient morphology (teeth, bones, joints and muscles). The evaluation of preliminary results involved the comparison of a dynamic MRI of a healthy person with the respective simulation.

GUGA: A tool for participatory cities

Participatory cities are those that allow the participation of citizens in the construction and improvement of their common daily life. In this work we present a tool for that participation, allowing the citizens to register the occurrences as well as take knowledge about the global geographic status of their city in on a variety of contexts (security, transit, etc.). However, a tool like that, fed by the people, certainly will deal with a large amount of information, distributed geographically. To accomplish that, a precise criterion for visualizing the resultant density distribution of occurrences must be used. In this paper, we also propose an automatic method for that visualization based on Voronoi Diagrams. The Voronoi polygons divide the region according to the concentration of occurrences. In this scheme, the area of each Voronoi polygon defines the density of the occurrences of the specific categories which are shown in the city map in color and transparency intensities for visualization. This can easily reveal the space distribution of important issues, in a variety of contexts such as criminality, commercial and industrial activities, drugs traffic, illumination concerns, and others.

Modeling and Simulation of Masticatory Muscles

Abstract Medical simulators play an important role in helping the development of prototype prostheses, pre-surgical planning and in a better understanding of the mechanical phenomena involved in muscular activity. This article focuses in modeling and simulating the activity of the jaw muscular system. The model involves the use of three-dimensional bone models and muscle modeling based on Hill type actuators. Ligament restrictions to mandible movement were taken into account in our model. Data collected from patients were used to partially parameterize our model so that it could be used in medical applications. In addition, the simulation of muscles employed a new methodology based on insertion curves, with many lines of action for each group of muscles. A simulator was developed, which allowed real time visualization of individual muscle activation under each correspondent simulation time. The model derived trajectory was then compared to the assembled data, remaining mostly within the convex hull of the mandible motion curves captured. Furthermore, the model accurately described the desired border movements.

Modelling consumers decision-making process about excluding products as a result of mutual influence

We present a model for the evolution of opinion distribution in a society with respect to two excluding concepts or choices A and B. It is considered a situation where two excluding concepts are on a dispute for exclusivity, through the consecutive interactions among the consumers, one trying to persuade the other of their position. The strength of influence of each consumer over those it relates with, depends on its social status as well as the enthusiasm (extremism degree) it defends its side. Here we propose a model taking these factors into consideration using an approach based on agents. Each agent is equipped with a fixed social status, as well as a variable position with respect to the two concepts. They are put to interact among themselves, following a rule such that the change an agent imposes to the other is proportional to the persuader status and its degree of decision (opinion) for one or other concept. This makes the position of the interacting agents to vary in time. We then analyse the tendencies of consumers opinion as a whole as time passes, for a variety of initial configurations, to see what the final stationary results and how fast they are attained. We found that extremism was always the final state of society opinion, that is, with all consumers opting for the same product, with an extreme (maximum) degree of decision. Also, we conclude that the most important factor for deciding which choice wins, and how fast, is the ratio between the status averages of both groups, the one of those more convinced of A and the one of those more convinced of B. In fact, the group with the larger social status average wins the other even in significant initial disadvantages in number of individuals or in average degree of conviction.

Visualization and analysis of interacting occurences in a smart city

New information and communication technologies enable a better management of the available resources in a smart city. Leaders need tools to analyze data for better decisions, anticipate problems and resolve them proactively. In this context, this article proposes a simulation tool to analyze the interaction of typical cities occurrences like criminal and police. The information of both occurrences, including their densities, are inserted and visualized on a city map. Each record is marked on the GPS point where it happened. From these inputs data, the interactions are modeled by Voronoi Diagrams. The occurrences change their position according to the size area of the opposite event. In this way, crimes runway from police and police catch crimes occurrences. As results, we show that a large increase of police actions will not influence quantitatively in the reduction of criminal occurrences out of a critical zone.

Modeling and Visualization Individual and Collective Opinions towards Extremism in a Society

Abstract The present work is an attempt to approach the modeling and visualization of individual opinion towards extremism in a society. We consider a scenario where two opposite concepts are on a dispute for exclusivity, via the effort of the individuals to convince each other of their own oppinion/decision. The power of convincement of each individual over the community depends on its influence, its communicability and on the enthusiasm (extremism) it defends its side. Here we propose a model taking these three factors into consideration. We analyze the system changes in real time by following the agents extremism parameter of the society, representing its distribution in a graphical fashion and present realizations of the proposed model for a variety of initial configurations (input parameter sets). The results analysis suggest that the most important factor is influence more then the number of individuals defending a position. Moreover, communicability has small or no relevance. Visualization schemes for following individuals interactions are also included.

Opinion dynamics: A study of the relation between status and communicability

A remarkable characteristic of human beings is their tendency to form societies. That put themselves in a social position, where they interact with the environment and try to convince others of their own convictions. This study proposes a model for interactions among individuals of a society, accompanying the evolution of their opinions over time. We consider a situation where the individuals are subordinated to choose between two mutually exclusive options, A and B. Each one of the individuals is gifted with status, opinion and communicability, forming groups according to their degree of conviction to A or B. In this analysis we tried to identify which initial parameters of the groups - average opinion, average status and number of individuals - could cause the greatest impact on the dynamics outcome. When communicability is independent of status, an equilibrium between initial parameters was noticed, showing that none of them is more relevant than the other. However, when communicability is an increasing status function, status presented the major importance. We conclude that status must be associated to communicability to have a prominent role in the dynamics. According to this study, in usual situations where the status shows to be more relevant, it must be somehow associated to communicability.