Synchronization in a lattice model of pulse-coupled oscillators

We analyze the collective behavior of a lattice model of pulse-coupled oscillators. By means of computer simulations we find the relation between the intrinsic dynamics of each member of the population and their mutual interactions that ensures, in a general context, the existence of a fully synchronized regime. This condition turns out to be the same as that obtained for the globally coupled population. When the condition is not completely satisfied we find different spatial structures. This also gives some hints about self-organized criticality.

Invaded cluster dynamics for frustrated models

The invaded cluster (IC) dynamics introduced by Machta et al. [Phys. Rev. Lett. 75, 2792 (1995)] is extended to the fully frustrated Ising model on a square lattice. The properties of the dynamics that exhibits numerical evidence of self-organized criticality are studied. The fluctuations in the IC dynamics are shown to be intrinsic of the algorithm and the fluctuation-dissipation theorem is no longer valid. The relaxation time is found to be very short and does not present a critical size dependence.

Nonequilibrium orientational patterns in two-component Langmuir monolayers

A model of a phase-separating two-component Langmuir monolayer in the presence of a photoinduced reaction interconverting two components is formulated. An interplay between phase separation, orientational ordering, and reaction is found to lead to a variety of nonequilibrium self-organized patterns, both stationary and traveling. Examples of the patterns, observed in numerical simulations, include flowing droplets, traveling stripes, wave sources, and vortex defects.

Spatiotemporal order out of noise

Experimental observations of self-organized behavior arising out of noise are also described, and details on the numerical algorithms needed in the computer simulation of these problems are given.

A critical analysis of three psychological research programs of doping behaviour

Objectives To consider the various specific substances-taking activities in sport an examination of three psychological models of doping behaviour utilised by researchers is presented in order to evaluate their real and potential impact, and to improve the relevance and efficiency of anti-doping campaigns. Design Adopting the notion of a "research program" (Lakatos, 1978) from the philosophy of science, a range of studies into the psychology of doping behaviour are classified and critically analysed. Method Theoretical and practical parameters of three research programs are critically evaluated (i) cognitive; (ii) drive; and (iii) situated-dynamic. Results The analysis reveals the diversity of theoretical commitments of the research programs and their practical consequences. The «cognitive program» assumes that athletes are accountable for their acts that reflect the endeavour to attain sporting and non-sporting goals. Attitudes, knowledge and rational decisions are understood to be the basis of doping behaviour. The «drive program» characterises the variety of traces and consequences on psychological and somatic states coming from athlete's experience with sport. Doping behaviour here is conceived of as a solution to reduce unconscious psychological and somatic distress. The «situated-dynamic program» considers a broader context of athletes' doping activity and its evolution during a sport career. Doping is considered as emergent and self-organized behaviour, grounded on temporally critical couplings between athletes' actions and situations and the specific dynamics of their development during the sporting life course. Conclusions These hypothetical, theoretical and methodological considerations offer a more nuanced understanding of doping behaviours, making an effective contribution to anti-doping education and research by enabling researchers and policy personnel to become more critically reflective about their explicit and implicit assumptions regarding models of explanations for doping behaviour.

Deciphering the global organization of clustering in real complex networks

We uncover the global organization of clustering in real complex networks. To this end, we ask whether triangles in real networks organize as in maximally random graphs with given degree and clustering distributions, or as in maximally ordered graph models where triangles are forced into modules. The answer comes by way of exploring m-core landscapes, where the m-core is defined, akin to the k-core, as the maximal subgraph with edges participating in at least m triangles. This property defines a set of nested subgraphs that, contrarily to k-cores, is able to distinguish between hierarchical and modular architectures. We find that the clustering organization in real networks is neither completely random nor ordered although, surprisingly, it is more random than modular. This supports the idea that the structure of real networks may in fact be the outcome of self-organized processes based on local optimization rules, in contrast to global optimization principles.

A Secure and Anonymous Cooperative Sensing Protocol for Cognitive Radio Networks

Spectrum is an essential resource for the provision of mobile services. In order to control and delimit its use, governmental agencies set up regulatory policies. Unfortunately, such policies have led to a deficiency of spectrum as only few frequency bands are left unlicensed, and these are used for the majority of new emerging wireless applications. One promising way to alleviate the spectrum shortage problem is adopting a spectrum sharing paradigm in which frequency bands are used opportunistically. Cognitive radio is the key technology to enable this shift of paradigm.Cognitive radio networks are self-organized systems in which devices cooperate to use those spectrum ranges that are not occupied by licensed users. They carry out spectrum sensing in order to detect vacant channels that can be used for communication. Even though spectrum sensing is an active area of research, an important issue remains unsolved: the secure authentication of sensing reports. Not providing security enables the input of false data in the system thus empowering false results. This paper presents a distributed protocol based on wireless physical layer security, symmetric cryptography and one-way functions that allows determining a final sensing decision from multiple sources in a quick and secure way, as well as it preserves users¿ privacy.

Spektrikuvien tiivistäminen itseorganisoituvan kartan avulla.

Vuosi vuodelta kasvava tietokoneiden prosessointikyky on mahdollistanut harmaataso- ja RGB-värikuvia tarkempien spektrikuvien käsittelyn järjellisessä ajassa ilman suuria kustannuksia. Ongelmana on kuitenkin, ettei talletus- ja tiedonsiirtomedia ole kehittynyt prosessointikyvyn vauhdissa. Ratkaisu tähän ongelmaan on spektrikuvien tiivistäminen talletuksen ja tiedonsiirron ajaksi. Tässä työssä esitellään menetelmä, jossa spektrikuva tiivistetään kahdessa vaiheessa: ensin ryhmittelemällä itseorganisoituvan kartan (SOM) avulla ja toisessa vaiheessa jatketaan tiivistämistä perinteisin menetelmin. Saadut tiivistyssuhteet ovat merkittäviä vääristymän pysyessä siedettävänä. Työ on tehty Lappeenrannan teknillisen korkeakoulun Tietotekniikan osaston Tietojenkäsittelytekniikan tutkimuslaboratoriossa osana laajempaa kuvantiivistyksen tutkimushanketta.

Flocking behaviour: Agent-based simulation and hierarchical leadership.

We have studied how leaders emerge in a group as a consequence of interactions among its members. We propose that leaders can emerge as a consequence of a self-organized process based on local rules of dyadic interactions among individuals. Flocks are an example of self-organized behaviour in a group and properties similar to those observed in flocks might also explain some of the dynamics and organization of human groups. We developed an agent-based model that generated flocks in a virtual world and implemented it in a multi-agent simulation computer program that computed indices at each time step of the simulation to quantify the degree to which a group moved in a coordinated way (index of flocking behaviour) and the degree to which specific individuals led the group (index of hierarchical leadership). We ran several series of simulations in order to test our model and determine how these indices behaved under specific agent and world conditions. We identified the agent, world property, and model parameters that made stable, compact flocks emerge, and explored possible environmental properties that predicted the probability of becoming a leader.

Structural and optical properties of InAs/GaAs quantum structures

The goal of the thesis was to study fundamental structural and optical properties of InAs islands and In(Ga)As quantum rings. The research was carried out at the Department of Micro and Nanosciences of Helsinki University of Technology. A good surface quality can be essential for the potential applications in optoelectronic devices. For such device applications it is usually necessary to control size, density and arrangement of the islands. In order to study the dependence of the structural properties of the islands and the quantum rings on growth conditions, atomic force microscope was used. Obtained results reveal that the size and the density of the In(Ga)As quantum rings strongly depend on the growth temperature, the annealing time and the thickness of the partial capping layer. From obtained results it is possible to conclude that to get round shape islands and high density one has to use growth temperature of 500 ̊C. In the case of formation of In(Ga)As quantum rings the effect of mobility anisotropy is observed that so the shape of the rings is not symmetric. To exclude this effect it is preferable to use a higher annealing temperature of 570 ̊C. Optical properties were characterized by PL spectroscopy. PL emission was observed from buried InAs quantum dots and In(Ga)As quantum rings grown with different annealing time and temperature and covered with a various thickness of the partial capping layer.

Cristais líquidos colestéricos: a quiralidade revela as suas cores

Chirality deeply impacts the macroscopic properties on all scales of the universe from elemental particles through biological structures up to astronomic systems. Specifically, chiral liquid crystals give rise to self-organized macrostructures with unparalleled properties. Here we present easy experiments with a special class of chiral liquid crystals that show temperature-induced selective reflection of light (thermochromic effect). Understanding this thermochromic effect allows undergraduate students better realize important properties of super and supramolecular systems.

A tabela periódica dos elementos químicos prevista por redes neurais artificiais de Kohonen

Although several chemical elements were not known by end of the 18th century, Mendeleyev came up with an astonishing achievement: the periodic table of elements. He was not only able to predict the existence of (then) new elements but also to provide accurate estimates of their chemical and physical properties. This is certainly a relevant example of the human intelligence. Here, we intend to shed some light on the following question: Can an artificial intelligence system yield a classification of the elements that resembles, in some sense, the periodic table? To achieve our goal, we have fed a self-organized map (SOM) with information available at Mendeleyev's time. Our results show that similar elements tend to form individual clusters. Thus, SOM generates clusters of halogens, alkaline metals and transition metals that show a similarity with the periodic table of elements.

Surface Modification of Ceramics

Ceramics are widely used in industrial applications due to their advantageous thermal and mechanical stability. Corrosion of ceramics is a great problem resulting in significant costs. Coating is one method of reducing adversities of corrosion. There are several different thin film deposition processes available such as sol-gel, Physical and Chemical Vapour Deposition (PVD and CVD). One of the CVD processes, called Atomic Layer Deposition (ALD) stands out for its excellent controllability, accuracy and wide process capability. The most commonly mentioned disadvantage of this method is its slowness which is partly compensated by its capability of processing large areas at once. Several factors affect the ALD process. Such factors include temperature, the grade of precursors, pulse-purge times and flux of precursors as well as the substrate used. Wrongly chosen process factors may cause loss of self-limiting growth and thus, non-uniformities in the deposited film. Porous substrates require longer pulse times than flat surfaces. The goal of this thesis was to examine the effects of ALD films on surface properties of a porous ceramic material. The analyses applied were for permeability, bubble point pressure and isoelectric point. In addition, effects of the films on corrosion resistance of the substrate in aqueous environment were investigated. After being exposured to different corrosive media the ceramics and liquid samples collected were analysed both mechanically and chemically. Visual and contentual differences between the exposed and coated ceramics versus the untreated and uncoated ones were analysed by scanning electron microscope. Two ALD film materials, dialuminium trioxide and titanium dioxide were deposited on the ceramic substrate using different pulse times. The results of both film materials indicated that surface properties of the ceramic material can be modified to some extent by the ALD method. The effect of the titanium oxide film on the corrosion resistance of the ceramic samples was observed to be fairly small regardless of the pulse time.

A new avalanche model for solar flares

Thèse numérisée par la Division de la gestion de documents et des archives de l'Université de Montréal

Un modèle à criticalité auto-régulée de la magnétosphère terrestre

Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal