Dynamic Modeling of the Electric Transportation Network

We introduce a model for the dynamic self-organization of the electric grid. The model is characterized by a conserved magnitude, energy, that can travel following the links of the network to satisfy nodes' load. The load fluctuates in time causing local overloads that drive the dynamic evolution of the network topology. Our model displays a transition from a fully connected network to a configuration with a non-trivial topology and where global failures are suppressed. The most efficient topology is characterized by an exponential degree distribution, in agreement with the topology of the real electric grid. The model intrinsically presents self-induced break-down events, which can be thought as representative of real black-outs.Comment: (e.g. 7 pages, 5 figures

Phototaxis beyond turning: persistent accumulation and response acclimation of the microalga Chlamydomonas reinhardtii

Phototaxis is an important reaction to light displayed by a wide range of motile microorganisms. Flagellated eukaryotic microalgae in particular, like the model organism Chlamydomonas reinhardtii, steer either towards or away from light by a rapid and precisely timed modulation of their flagellar activity. Cell steering, however, is only the beginning of a much longer process which ultimately allows cells to determine their light exposure history. This process is not well understood. Here we present a first quantitative study of the long timescale phototactic motility of Chlamydomonas at both single cell and population levels. Our results reveal that the phototactic strategy adopted by these microorganisms leads to an efficient exposure to light, and that the phototactic response is modulated over typical timescales of tens of seconds. The adaptation dynamics for phototaxis and chlorophyll fluorescence show a striking quantitative agreement, suggesting that photosynthesis controls quantitatively how cells navigate a light field.Comment: Six pages, three figures, plus supplementary materia

Galois-theoretical groups

A group G is called Galois-theoretical if CGCA(H)=H for any subgroup H of G and CACG(B)=B for any subgroup B of A=Aut(G). This paper shows that a group G is Galois-theoretical if and only if G is isomorphic to the trivial group, to the cyclic group of order 3, or to the symmetric group of degree 3

Light control of localized photobioconvection

Microorganismal motility is often characterized by complex responses to environmental physico-chemical stimuli. Although the biological basis of these responses is often not well understood, their exploitation already promises novel avenues to directly control the motion of living active matter at both the individual and collective level. Here we leverage the phototactic ability of the model microalga Chlamydomonas reinhardtii to precisely control the timing and position of localized cell photoaccumulation, leading to the controlled development of isolated bioconvective plumes. This novel form of photobioconvection allows a precise, fast, and reconfigurable control of the spatiotemporal dynamics of the instability and the ensuing global recirculation, which can be activated and stopped in real time. A simple continuum model accounts for the phototactic response of the suspension and demonstrates how the spatiotemporal dynamics of the illumination field can be used as a simple external switch to produce efficient bio mixing

Life Stories in Context: Using the Three-Sphere Context Model To Analyze Amos's Narrative

Despite a wide theoretical consensus among narrative researchers about the importance of referring to context in analyzing narratives, it seems that the various contexts at work in individual life stories and the specific methodological implications of the importance of context are not that clear. In this paper, I will describe a model for context analysis, which refers to three distinct spheres of contexts in which narrators situate their life stories (Zilber, Tuval-Mashiach, & Lieblich, 2008). The first context involves the immediate inter-subjective relationships within and involving which a narrative is produced; the second comprises the collective social field in which a life and story have evolved; and the third surrounds the systems of broad cultural meaning or meta-narratives that underlie and give sense to any particular life story. In the second part of the paper, I will illustrate the three contexts in Amos's story, and claim that viewing his story as it is embedded through these three contexts not only situates it within a more general social framework, but also enables a deeper understanding of his identity and the core themes of his life-story

Runaway electrification of friable self-replicating granular matter

We establish that the nonlinear dynamics of collisions between particles favors the charging of a insulating, friable, self-replicating granular material that undergoes nucleation, growth, and fission processes; we demonstrate with a minimal dynamical model that secondary nucleation produces a positive feedback in an electrification mechanism that leads to runaway charging. We discuss ice as an example of such a self-replicating granular material: We confirm with laboratory experiments in which we grow ice from the vapor phase in situ within an environmental scanning electron microscope that charging causes fast-growing and easily breakable palm-like structures to form, which when broken off may form secondary nuclei. We propose that thunderstorms, both terrestrial and on other planets, and lightning in the solar nebula are instances of such runaway charging arising from this nonlinear dynamics in self-replicating granular matter