Randomly connected cellular automata: A search for critical connectivities

I study the Chate-Manneville cellular automata rules on randomly connected lattices. The periodic and quasi-periodic macroscopic behaviours associated with these rules on finite-dimensional lattices persist on an infinite-dimensional lattice with finite connectivity and symmetric bonds. The lower critical connectivity for these models is at C=4 and the mean-field connectivity, if finite, is not smaller than C=100. Autocorrelations are found to decay as a power-law with a connectivity independent exponent approx. equal to -2.5. A new intermitten chaotic phase is also discussed.Comment: 9 pages, 5 figures, compressed with uufiles. One figure (too large) missing, available via e-mail ([email protected]) To appear in Europhys. Let

The Democratic Peace Unraveled: It’s the Economy

Recent research indicates that the democratic peace—the observation that democratic nations rarely fight each other—is spurious: that advanced capitalism accounts for both democracy and the democratic peace (Mousseau 2009). This is not a trivial prospect: if economic conditions explain the democratic peace, then a great deal of research on governing institutions and foreign policy is probably obsolete. This study addresses all the recent defenses of the democratic peace and reports new results using a new measure that directly gauges the causal mechanism of contract flows dependent on third-party enforcement. Analyses of most nations from 1961 to 2001 show contract-intensive "impersonal" economy to be the second most powerful variable in international conflict—following only contiguity—and, once considered, there is no evidence of causation from democracy to peace. It is impersonal economy, not democracy or unfettered markets, which appears to explain the democratic peace..

Urban Poverty and Support for Islamist Terror: Survey Results of Muslims in Fourteen Countries

Survey respondents in fourteen countries representing 62% of the world’s Muslim population indicate that approval of Islamist terror is not associated with religiosity, lack of education, poverty, or income dissatisfaction. Instead, it is associated with urban poverty. These results are consistent with the thesis that Islamist terrorists obtain support and recruits from the urban poor, who pursue their economic interests off the market in politics in collective groups. These groups compete over state rents, so a gain for one group is a loss for another, making terrorism of members of out-groups rational. The rise of militant Islam can be attributed to high rates of urbanization in many Muslim countries in recent decades, which fosters violence as rising groups seek to dislodge prior groups entrenched in power. Rising group leaders also compete over new urban followers, so they promote fears of out-groups and package in-group identities in ways that ring true for the urban poor. Because many of the urban poor are migrants from the countryside, popular packages are those which identify with traditional rural values and distinguish enemies as those associated with urban modernity and the secular groups already in power. Imams have an incentive to preach want audiences want to hear, so a mutated in-group version of Islam—Islamism—struck a chord in several large cities around the globe at the same time. With globalization of the media, in many developing countries the West is widely (albeit wrongly) perceived as an inimical out-group associated with urban modernity. The best political strategy to limit support and recruits for Islamist terrorist groups is to enhance the economic opportunities available for the urban poor, and to provide them the needed services, such as access to health care and education, that many currently obtain from Islamist groups.

The role of surface charge in the interaction of nanoparticles with model pulmonary surfactants

Inhaled nanoparticles traveling through the airways are able to reach the respiratory zone of the lungs. In such event, the incoming particles first enter in contact with the liquid lining the alveolar epithelium, the pulmonary surfactant. The pulmonary surfactant is composed of lipids and proteins that are assembled into large vesicular structures. The question of the nature of the biophysicochemical interaction with the pulmonary surfactant is central to understand how the nanoparticles can cross the air-blood barrier. Here we explore the phase behavior of sub-100 nm particles and surfactant substitutes in controlled conditions. Three types of surfactant mimetics, including the exogenous substitute Curosurf, a drug administred to infants with respiratory distress syndrome are tested together with aluminum oxide (Al2O3), silicon dioxide (SiO2) and polymer (latex) nanoparticles. The main result here is the observation of the spontaneous nanoparticle-vesicle aggregation induced by Coulombic attraction. The role of the surface charges is clearly established. We also evaluate the supported lipid bilayer formation recently predicted and find that in the cases studied these structures do not occur. Pertaining to the aggregate internal structure, fluorescence microscopy ascertains that the vesicles and particles are intermixed at the nano- to microscale. With particles acting as stickers between vesicles, it is anticipated that the presence of inhaled nanomaterials in the alveolar spaces could significantly modify the interfacial and bulk properties of the pulmonary surfactant and interfere with the lung physiology.Comment: 20 pages, 6 figure

Numerical studies of the vibrational isocoordinate rule in chalcogenide glasses

Many properties of alloyed chalcogenide glasses can be closely correlated with the average coordination of these compounds. This is the case, for example, of the ultrasonic constants, dilatometric softening temperature and the vibrational densities of states. What is striking, however, is that these properties are nevertheless almost independent of the composition at given average coordination. Here, we report on some numerical verification of this experimental rule as applied to vibrational density of states.Comment: 7 pages, including 3 figure

Identification of relaxation and diffusion mechanisms in amorphous silicon

The dynamics of amorphous silicon at low temperatures can be characterized by a sequence of discrete activated events, through which the topological network is locally reorganized. Using the activation-relaxation technique, we create more than 8000 events, providing an extensive database of relaxation and diffusion mechanisms. The generic properties of these events - size, number of atoms involved, activation energy, etc. - are discussed and found to be compatible with experimental data. We introduce a complete and unique classification of defects based on their topological properties and apply it to study of events involving only four-fold coordinated atoms. For these events, we identify and present in detail three dominant mechanisms.Comment: 4 pages, three figures, submitted to PR

Tight-binding molecular-dynamics studies of defects and disorder in covalently-bonded materials

Tight-binding (TB) molecular dynamics (MD) has emerged as a powerful method for investigating the atomic-scale structure of materials --- in particular the interplay between structural and electronic properties --- bridging the gap between empirical methods which, while fast and efficient, lack transferability, and ab initio approaches which, because of excessive computational workload, suffer from limitations in size and run times. In this short review article, we examine several recent applications of TBMD in the area of defects in covalently-bonded semiconductors and the amorphous phases of these materials.Comment: Invited review article for Comput. Mater. Sci. (38 pages incl. 18 fig.