Heterogeneous individual motility biases group composition in a model of aggregating cells

Aggregative life cycles are characterized by alternating phases of unicellular growth and multicellular development. Their multiple, independent evolutionary emergence suggests that they may have coopted pervasive properties of single-celled ancestors. Primitive multicellular aggregates, where coordination mechanisms were less efficient than in extant aggregative microbes, must have faced high levels of conflict between different co-aggregating populations. Such conflicts within a multicellular body manifest in the differential reproductive output of cells of different types. Here, we study how heterogeneity in cell motility affects the aggregation process and creates a mismatch between the composition of the population and that of self-organized groups of active adhesive particles. We model cells as self-propelled particles and describe aggregation in a plane starting from a dispersed configuration. Inspired by the life cycle of aggregative model organisms such as Dictyostelium discoideum or Myxococcus xanthus, whose cells interact for a fixed duration before the onset of chimeric multicellular development, we study finite-time configurations for identical particles and in binary mixes. We show that co-aggregation results in three different types of frequency-dependent biases, one of which is associated to evolutionarily stable coexistence of particles with different motility. We propose a heuristic explanation of such observations, based on the competition between delayed aggregation of slower particles and detachment of faster particles. Unexpectedly, despite the complexity and non-linearity of the system, biases can be largely predicted from the behavior of the two corresponding homogenous populations. This model points to differential motility as a possibly important factor in driving the evolutionary emergence of facultatively multicellular life-cycles

Implementação do simulador Siscot para a cidade de Porto Alegre

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Expansão perturbativa em torno do limite atômico para sistemas Kondo e de valência intermediária

Neste trabalho estudamos as propriedades eletrônicas de sistemas compostos de certos elementos de terras raras. Estes sistemas apresentam propriedades físicas anômalas em decorrência da interação entre os elétrons 4f e os elétrons de condução . Eles são conhecidos como sistemas de valência intermediária, sistemas Kondo, ou, quando a baixas temperaturas apresentam massas efetivas eletrônicas muito grandes, como sistemas de férmions pesados. O hamiltoniano modelo para a descrição teórica desses sistemas é o ilamiltoniano Periódico de Anderson. Nossa abordagem ao problema é de tratar perturbativamente a energia cinética dos elétrons de condução no hamiltoniano modelo pelo uso de funções de Green em uma aproximação que desacopla médias de operadores em um dado sítio em produtos de médias de pares de operadores neste sítio. Utilizando esta técnica calculamos a densidade de estados eletrônica, a susceptibilidade estática magnética e o calor especifico eletrônico. Os resultados concordam qualitativamente com os experimentos em sistemas de Ce.In this work we study the electronic properties of systems composed of certain rare-earth elements. These systems present anomalous physical properties due to the interaction between the 4f-electrons and the conduction electrons. They are known as intermediate valence systems, Kondo systems, or heavy-fermion systems, in the case of large electronic effective masses at low temperatures. The model Hamiltonian used in the theoretical description of these systems is the Perioclic Anderson Hamiltonian. Our approach to the problem consists in treating perturbatively the kinetic energy of the conduction electrons in the model Hamiltonian. This is done through the use of Green's functions in an approximation that decouples single site operator averages in products of operator pair averages. With this technique we calculate the electronic density of states, the static magnetic susceptibility and the electronic specific heat. The results agree qualitatively with experiments in Ce systems

Expansão perturbativa em torno do limite atômico para sistemas Kondo e de valência intermediária

Neste trabalho estudamos as propriedades eletrônicas de sistemas compostos de certos elementos de terras raras. Estes sistemas apresentam propriedades físicas anômalas em decorrência da interação entre os elétrons 4f e os elétrons de condução . Eles são conhecidos como sistemas de valência intermediária, sistemas Kondo, ou, quando a baixas temperaturas apresentam massas efetivas eletrônicas muito grandes, como sistemas de férmions pesados. O hamiltoniano modelo para a descrição teórica desses sistemas é o ilamiltoniano Periódico de Anderson. Nossa abordagem ao problema é de tratar perturbativamente a energia cinética dos elétrons de condução no hamiltoniano modelo pelo uso de funções de Green em uma aproximação que desacopla médias de operadores em um dado sítio em produtos de médias de pares de operadores neste sítio. Utilizando esta técnica calculamos a densidade de estados eletrônica, a susceptibilidade estática magnética e o calor especifico eletrônico. Os resultados concordam qualitativamente com os experimentos em sistemas de Ce.In this work we study the electronic properties of systems composed of certain rare-earth elements. These systems present anomalous physical properties due to the interaction between the 4f-electrons and the conduction electrons. They are known as intermediate valence systems, Kondo systems, or heavy-fermion systems, in the case of large electronic effective masses at low temperatures. The model Hamiltonian used in the theoretical description of these systems is the Perioclic Anderson Hamiltonian. Our approach to the problem consists in treating perturbatively the kinetic energy of the conduction electrons in the model Hamiltonian. This is done through the use of Green's functions in an approximation that decouples single site operator averages in products of operator pair averages. With this technique we calculate the electronic density of states, the static magnetic susceptibility and the electronic specific heat. The results agree qualitatively with experiments in Ce systems

Boletín del Servicio Meteorológico Nacional: Epoca 2ª Año X Número 196 - 1961 Julio 15

Neste trabalho estudou-se os efeitos de pressão e temperatura no gradiente de campo elétrico (GCE) presente no sítio do In do composto intermelático AgIn2. As medidas foram feitas através da técnica de correlação angular diferencial perturbada (CADP) da cascata gama 173-247 kev do ¹¹¹Cd, populada pelo decaimento do ¹¹¹In. As medidas do GCE a diferentes pressões mostraram um aumento de vQ e n com pressão e nenhuma indicação de transições de fase até 35 kbar.In this work we studied the effects of pressure and temperature in the Electric Field Gradient (EEG) acting in the In site in AgIn2 intermetallic compund. The measurements were carried out by the time 173-247 keV gamma cascade ¹¹¹Ce, fed by the ¹¹¹In decay. The measurements of the EEG at different pressures, showed an increase of vQ and n with pressure and there is no phase transition up to 35 kbar

Cellular automata on high-dimensional hypercubes

The emergence of nontrivial collective behavior is studied in large families of cellular automata rules implemented on high-dimensional hypercubes. Evidence is found that the region of rule space where such macroscopic dynamics exists is well-defined in the infinite-dimension limit

Cellular automata on high-dimensional hypercubes

The emergence of nontrivial collective behavior is studied in large families of cellular automata rules implemented on high-dimensional hypercubes. Evidence is found that the region of rule space where such macroscopic dynamics exists is well-defined in the infinite-dimension limit