Homofilia por tópicos no espalhamento de memes em redes sociais online

Orientador: André SantanchèDissertação (mestrado) - Universidade Estadual de Campinas, Instituto de ComputaçãoResumo: Um dos problemas centrais na ciência social computacional é entender como a informação se espalha em redes sociais online. Alguns trabalhos afirmam que pessoas que usam estas redes podem não ser capazes de lidar com a quantidade de informação devido às restrições cognitivas, o que resulta em um limite de atenção gasta para ler e compartilhar mensagens. Disso emerge um cenário de competição, em que memes das mensagens visam ser lembrados e compartilhados para que durem mais do que os outros. Esta pesquisa está preocupada em construir uma evidência empírica de que a homofilia desempenha um papel no sucesso de cada meme na competição. A homofilia é um efeito observado quando pessoas preferem interagir com aqueles com os quais se identificam. Coletando dados no Twitter, nós aglomeramos memes em tópicos que são usados para a caracterização da homofilia. Executamos um experimento computacional, baseado num modelo simplificado de memória para adoção de memes, e verificamos que a adoção é influenciada pela homofilia por tópicosAbstract: One of the central problems in the computational social science is to understand how information spreads in online social networks. Some works state that people using these networks may not cope with the amount of information due to cognitive restrictions, resulting in a limit of attention spent reading and sharing messages. A competition scenario emerges, where memes of messages want to be remembered and shared in order to outlast others. This research is concerned with building empirical evidence that homophily plays a role in the success of each meme over the competition. Homophily is an effect observed when people prefer to interact with those they identify with. By gathering data from Twitter, we clustered memes into topics that are used to characterize the homophily. We executed a computational experiment, based on a simplified memory model of meme adoption, and verified that the adoption is influenced by topical homophilyMestradoCiência da ComputaçãoMestre em Ciência da Computação131090/2017-8CNP

PCG and ECG Portable Acquisition System

Heart disease is the leading cause of death in the world, victimizing human beings in all age groups and from different geographic areas. Through the evolution of auscultation technology, the identification and analysis of heartbeats make it possible to prevent and treat heart pathologies with greater success. In this project, a portable, low-power system was developed that allows the acquisition of heart sound signals simultaneously in four different auscultation zones, as well as the acquisition of an electrical signal, subsequently conditioning and processing the different signals. The system also allows the transmission of signals in real-time via Bluetooth Low Energy to a mobile device where they can be recorded for future analysis. The portable system records four phonocardiographs located at four auscultation areas, namely the aortic valve, the mitral valve, the pulmonary valve and the tricuspid valve. These sound signals are converted to analog electrical signals that will be amplified, filtered and converted into digital signals. There is also a two-electrode electrocardiograph in this system, which is also amplified and filtered before being converted to a digital signal and transmitted via wireless communication. The entire system is powered by a battery with a charge voltage of 4.2 V, which allows it to be charged through the USB interface.As doenças cardíacas são a principal causa de morte no mundo, vitimizando seres humanos em todas as faixas etárias e de diferentes àreas geográficas. Através da evolução da tecnologia na auscultação, a identificação e análise dos batimentos cardíacos permitem prevenir e tratar patologias do coração com maior sucesso. Neste projeto foi desenvolvido um sistema portátil de baixa potência que permite a aquisição dos sinais sonoros do coração simultaneamente em quatro diferentes zonas de auscultação, assim como a aquisição de um sinal elétrico, fazendo posteriormente o condicionamento e processamento dos diferentes sinais. O sistema permite ainda a transmissão em tempo-real dos sinais via Bluetooth Low Energy para um dispositivo móvel onde podem gravados para futura análise. O sistema portátil regista quatro fonocardiogramas localizados em quatro áreas de auscultação, nomeadamente na válvula aórtica, na válvula mitral, na válvula pulmónica e na válvula tricúspida. Estes sinais sonoros são convertidos para sinais elétricos analógicos que serão amplificados, filtrados e convertidos de novo para sinais digitais. O sistema regista também o electrocardiograma através de dois elétrodos, que é também amplificado e filtrado antes de ser convertido em sinal digital e transmitido via comunicação sem fios. Todo o sistema é alimentado por uma bateria com tensão de carga 4.2 V, que permite ser carregada através de interface USB

Automata-theoretic and bounded model checking for linear temporal logic

In this work we study methods for model checking the temporal logic LTL. The focus is on the automata-theoretic approach to model checking and bounded model checking. We begin by examining automata-theoretic methods to model check LTL safety properties. The model checking problem can be reduced to checking whether the language of a finite state automaton on finite words is empty. We describe an efficient algorithm for generating small finite state automata for so called non-pathological safety properties. The presented implementation is the first tool able to decide whether a formula is non-pathological. The experimental results show that treating safety properties can benefit model checking at very little cost. In addition, we find supporting evidence for the view that minimising the automaton representing the property does not always lead to a small product state space. A deterministic property automaton can result in a smaller product state space even though it might have a larger number states. Next we investigate modular analysis. Modular analysis is a state space reduction method for modular Petri nets. The method can be used to construct a reduced state space called the synchronisation graph. We devise an on-the-fly automata-theoretic method for model checking the behaviour of a modular Petri net from the synchronisation graph. The solution is based on reducing the model checking problem to an instance of verification with testers. We analyse the tester verification problem and present an efficient on-the-fly algorithm, the first complete solution to tester verification problem, based on generalised nested depth-first search. We have also studied propositional encodings for bounded model checking LTL. A new simple linear sized encoding is developed and experimentally evaluated. The implementation in the NuSMV2 model checker is competitive with previously presented encodings. We show how to generalise the LTL encoding to a more succint logic: LTL with past operators. The generalised encoding compares favourably with previous encodings for LTL with past operators. Links between bounded model checking and the automata-theoretic approach are also explored.reviewe

Enhanced Reinforcement Learning with Attentional Feedback and Temporally Attenuated Distal Rewards

This thesis presents a new reinforcement learning mechanism suitable to be employed in artificial spiking neural networks of leaky integrate-and-fire (LIF) or Izhikevich neurons. The proposed mechanism is upgraded from, and closely built upon the learning algorithm introduced by Florian, in which local synaptic plasticity is based on the relative spike-timing of the pre and post-synaptic neurons (STDP), and is modulated by a global reinforcement signal. This work introduces and deals with multiple challenges identified in existing reinforcement learning schemes, that includes the distal reward problem, the spatial credit assignment problem and the response numbness problem. A number of improvements, that are inspired either from the biological elements or from similar implementations in non-spiking neural networks, are suggested to handle these challenges, and are validated through biologically-inspired experiments. The notion and implementation of attentional feedback that handles the spatial credit assignment problem during synaptic reinforcement are introduced. The effects of attenuated rewards, which gate network learning after satisfactory reinforcement is achieved, are also demonstrated. This aids in the exploration of the agent to discover other rewardable behaviors during learning. A spike-rate based input encoding scheme termed as balanced-pair binary state (BPBS) encoding, and a corresponding methodology for response selection are also introduced to improve network stability and confidence in response selection. The proposed techniques are validated using multiple biologically-inspired single agent as well as multi-agent game-theoretic experimental tasks. The single-agent tasks include exclusive OR (XOR) function reproduction and a bot walking task. The multi-agent interactive and cooperative tasks demonstrated include the general-sum iterated prisoners' dilemma (IPD) game problem and the distributed SensorNetwork problem from the NIPS '05 reinforcement learning benchmarks. The results and findings discussed in this work validate that the proposed improvements to existing implementations of reinforcement learning could, in fact, lead to better brain-like learning and behavior in artificial agents

Slip on ridge transform faults : insights from earthquakes and laboratory experiments

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution June, 2005The relatively simple tectonic environment of mid-ocean ridge transform fault (RTF) seismicity provides a unique opportunity for investigation of earthquake and faulting processes. We develop a scaling model that is complete in that all the seismic parameters are related to the RTF tectonic parameters. Laboratory work on the frictional stability of olivine aggregates shows that the depth extent of oceanic faulting is thermally controlled and limited by the 600°C isotherm. Slip on RTFs is primarily aseismic, only 15% of the tectonic offset is accommodated by earthquakes. Despite extensive fault areas, few large earthquakes occur on RTFs, and few aftershocks follow the large events. Standard models of seismicity, in which all earthquakes result from the same seismic triggering process, do not describe RTF earthquakes. Instead, large earthquakes appear to be preceded by an extended fault preparation process marked by abundant foreshocks within 1 hour and 15 km of the mainshocks. In our experiments normal force vibrations, such as seismic radiation from nearby earthquakes, can weaken and potentially destabilize steadily creeping faults. Integrating the rheology, geology, and seismicity of RTFs, we develop a synoptic model to better understand the spatial distribution of fault strength and stability and provide insight into slip accommodation on RTFs.Funding from the Deep Ocean Earth Institute Fellowship, MIT Presidential Fellowship, NSF Fellowship, and WHOI Academic Programs Office

Photodetachment studies of negative ions at the Cryogenic Storage Ring

In the present work, experimental studies of the photodetachment process of the Si− and Al−4 systems are presented. The measurements were carried out at the Cryogenic Storage Ring (CSR) facility located at the Max Planck Institute for Nuclear Physics in Heidelberg. By storing Si− for up to 2000 s in the T < 10 K CSR environment, making use of the reduced blackbody radiation field inside the CSR, we were able to monitor the decay of long-lived 2D states as well as the weakly bound 2P states. Employing a set of continuous wave and pulsed lasers, the lifetime for the 2P states were found to be τ = (22.5 ± 2.5)s. For the 2D states, a lower limit of τr > 5.7 h (within a confidence level of 90%) was measured. Furthermore, Multi-Configuration Dirac-Hartree-Fock (MCDHF) calculations were performed on the radiatiave lifetimes of the respective states, which show very good agreement with the present measurement. The second part of the studies focuses on the study of spontaneous cooling of stored Al−4 ions at very long time scales. Here, we present measurements that allow us to monitor the cluster cooling rates for up to 30 min and we compare those results to previous measurements at a room temperature device. We find that the cooling time scale is limited by the redistribution of vibrational energy inside the molecule, which we call slow exchange model, and in combination with recurrent fluorescence for energies above the first electronic excited state, they match the observed cooling rates

Photodetachment studies of negative ions at the Cryogenic Storage Ring

In the present work, experimental studies of the photodetachment process of the Si− and Al−4 systems are presented. The measurements were carried out at the CryogenicStorage Ring (CSR) facility located at the Max Planck Institute for Nuclear Physicsin Heidelberg. By storing Si− for up to 2000 s in the T to monitor the decay of long-lived 2D states as well as the weakly bound 2P states. Employing a set of continuous wave and pulsed lasers, the lifetime for the 2P stateswere found to be τ = (22.5 +/- 2.5)s. For the 2D states, a lower limit of τr > 5.7 h (within a confidence level of 90%) was measured. Furthermore, Multi-Configuration Dirac-Hartree-Fock (MCDHF) calculations were performed on the radiatiave lifetimesof the respective states, which show very good agreement with the present measurement.The second part of the studies focuses on the study of spontaneous cooling of stored Al−4 ions at very long time scales. Here, we present measurements that allow us to monitor the cluster cooling rates for up to 30 min and we compare those results to previous measurements at a room temperature device. We find that the cooling time scale is limited by the redistribution of vibrational energy inside the molecule, which we call slow exchange model, and in combination with recurrent fluorescence for energies above the first electronic excited state, they match the observed cooling rates