Complex Macroscopic Phenomena Research Articles

Multiscale modeling and analysis of compaction bands in high-porosity sandstones

We present a multiscale investigation on the initiation and development of compaction bands in high-porosity sandstones based on an innovative hierarchical multiscale approach. This approach couples the finite element method and the discrete element method (DEM) to offer direct, rigorous linking of the microscopic origins and mechanisms with complex macroscopic phenomena observed in granular rocks such as strain localization and failure. To simulate compaction band in granular cementitious sandstone, we adopt a bonded contact model with normal and tangential interparticle cohesions in the DEM and propose a dual-porosity structure consisting of macro-pores and interstitial voids for the representative volume element to mimic the typical meso-structure of high-porosity sandstones. In the absence of particle crushing, our multiscale analyses identify debonding and pore collapses as two major contributors to the formation of compaction bands. The critical pressures predicted by our simulations, corresponding to surges of debonding and pore collapse events, agree well with the estimations from field data. The occurrence patterns of compaction band are found closely related to specimen heterogeneity, porosity and confining pressure. Other deformation band patterns, including shear-enhanced compaction bands and compactive shear bands, were also observed under relatively low confining pressure conditions with a rough threshold at $$0.55P^{*}$$ ( $$P^{*}$$ is the critical pressure) on the failure envelop. Key microscopic characteristics attributable to the occurrence of these various deformation patterns, including fabric anisotropy, particle rotation, debonding and pore collapse, are examined. Shear-enhanced compaction bands and pure compaction bands bear many similarities in terms of these microscopic characteristics, whereas both differ substantially from compactive shear bands.

Matching effective few-nucleon theories to QCD

The emergence of complex macroscopic phenomena from a small set of parameters and microscopic concepts demonstrates the power and beauty of physical theories. A theory which relates the wealth of data and peculiarities found in nuclei to the small number of parameters and symmetries of quantum chromodynamics is by that standard of exceptional beauty. Decade-long research on computational physics and on effective field theories facilitate the assessment of the presumption that quark masses and strong and electromagnetic coupling constants suffice to parametrize the nuclear chart. By presenting the current status of that enterprise, this article touches the methodology of predicting nuclei by simulating the constituting quarks and gluons and the development of effective field theories as appropriate representations of the fundamental theory. While the nuclear spectra and electromagnetic responses analyzed computationally so far with lattice QCD are in close resemblance to those which intrigued experimentalists a century ago, they also test the theoretical understanding which was unavailable to guide the nuclear pioneers but developed since then. This understanding is shown to be deficient in terms of correlations amongst nuclear observables and their sensitivity to fundamental parameters. By reviewing the transition from one effective field theory to another, from QCD to pionful chiral theories to pionless and eventually to cluster theories, we identify some of those deficiencies and conceptual problems awaiting a solution before QCD can be identified as the high-energy theory from which the nuclear landscape emerges.

Stochastic but Fine-Tuned: Dualism in Cell Membranes' Organization as Revealed by Computer Simulations

Model lipid bilayers exhibit atomic-scale structural/dynamic properties, which help to understand complex macroscopic phenomena observed in membranes of living cells. These are: local phase separation, clustering, mosaicity of water-lipid interface, water dynamics, ability to bind external molecules (e.g., proteins). Atomistic simulations are invaluable in exploration of such effects, which still resist easy characterization in experiments. We used molecular dynamics simulations to assess physicochemical parameters of a large set of hydrated bilayers composed of lipids with different polar heads and acyl chains. Special attention was given to molecular mechanisms determining dynamic clustering of lipids and fine-tuned interplay of interactions between membrane components [1-3]. Putative relationships between lipid composition and local/integral characteristics of the bilayers were delineated. In particular, anomalous dependence on the lipid composition was observed for mixed bilayers composed of zwitterionic/anionic lipids. Also, the effects of lipid-water environment on membrane peptides and their interactions were investigated [4]. The results permit deciphering of the factors determining microscopic structural and dynamic “portrait” of lipid bilayers and assess he role of heterogeneous and highly fluctuating membrane medium in structural organization and functioning of proteins. This makes possible rational design of lipids with modified properties (e.g., capacity of H-bonding), which could presumably affect local/integral parameters of membranes. Our preliminary data show that such lipids induce significant changes of some crucial properties of model membranes. This opens new avenues in goal-oriented design of artificial membranes with engineered properties.Acknowledgements: Authors thank Russian Science Foundation (14-14-00871), RFBR, RAS MCB Program.[1] D.V. Pyrkova et al., Soft Matter 7 (2011) 2569.[2] N.A. Krylov et al., ACS Nano 7 (2013) 9428.[3] A.O. Chugunov et al., Scientific Reports 4 (2014) 7462.[4] A.A. Polyansky et al., J. Amer. Chem. Soc. 134 (2012) 14390.

Consistent lattice Boltzmann equations for phase transitions.

Unlike conventional computational fluid dynamics methods, the lattice Boltzmann method (LBM) describes the dynamic behavior of fluids in a mesoscopic scale based on discrete forms of kinetic equations. In this scale, complex macroscopic phenomena like the formation and collapse of interfaces can be naturally described as related to source terms incorporated into the kinetic equations. In this context, a novel athermal lattice Boltzmann scheme for the simulation of phase transition is proposed. The continuous kinetic model obtained from the Liouville equation using the mean-field interaction force approach is shown to be consistent with diffuse interface model using the Helmholtz free energy. Density profiles, interface thickness, and surface tension are analytically derived for a plane liquid-vapor interface. A discrete form of the kinetic equation is then obtained by applying the quadrature method based on prescribed abscissas together with a third-order scheme for the discretization of the streaming or advection term in the Boltzmann equation. Spatial derivatives in the source terms are approximated with high-order schemes. The numerical validation of the method is performed by measuring the speed of sound as well as by retrieving the coexistence curve and the interface density profiles. The appearance of spurious currents near the interface is investigated. The simulations are performed with the equations of state of Van der Waals, Redlich-Kwong, Redlich-Kwong-Soave, Peng-Robinson, and Carnahan-Starling.

Heat treatment of concrete and its influence on the mechanical properties

Concrete is used globally for all types of construction. This is mainly due to a market economy that has grown strongly in recent years and the particularities of its own.Despite its good performance at room temperature, concrete can have a critical behavior at high temperature. Analysis of the effects of high temperatures on the microstructure is necessary to understand the complex macroscopic phenomena step because the concrete undergoes physicochemical changes that strongly influence its thermomechanical behavior. Indeed, the strength of concrete can be greatly reduced by damage due to the rise in temperature as it entails the destruction of the constituent hydrates the cement paste by degradation of its mechanical properties such as stiffness, strength …The objective of our work is to study by thermogravimetric and differential thermal analysis (TGA / DTA) and the heated unheated concrete to follow the evolution of solid phases present in the latter when exposed to high temperatures.

Quantum Weirdness? It's All in Your Mind

In this article the author discusses a version of quantum theory that removes the paradoxes of the microscopic world making quantum information a figment of the imagination. Topics include some bizarre paradoxes of quantum mechanics, such as the appearance of particles in two places at the same time, the development of a model in 2001 by a team of physicists that eliminates quantum paradoxes by combining quantum theory with probability theory and reimaging the wave function, called Quantum Bayesianism (QBism), physicists' use of the wave function to calculate the probability that a particle will have a certain property, and some criticisms of QBism, such as its inability to explain complex macroscopic phenomena in microscopic terms.

Altruism: A natural strategy for enhancing survival

We study the influence of altruistic behavior in a prey–predator model permitting the preys to commit suicide by confronting the predators instead of escaping. Surprising, altruistic behavior at microscopic (local) scale, leads to the emergence of new complex macroscopic (global) phenomena characterized by dramatic changes in the dynamic topology of the prey–predator spatiotemporal distribution, yielding spiral patterns. We show that such dynamics enhances the prey's survivability.

EFFECTIVE AVERAGE ACTION IN STATISTICAL PHYSICS AND QUANTUM FIELD THEORY

An exact renormalization group equation describes the dependence of the free energy on an infrared cutoff for the quantum or thermal fluctuations. It interpolates between the microphysical laws and the complex macroscopic phenomena. We present a simple unified description of critical phenomena for O(N)-symmetric scalar models in two, three or four dimensions, including essential scaling for the Kosterlitz-Thouless transition.

An empirical method for modelling and simulating some complex macroscopic phenomena by cellular automata

Novel parallel computing models sometime represent a valid alternative to standard differential equation methods in modelling complex phenomena. In particular, Cellular Automata (CA) provide such an alternative approach for some complex natural systems, whose behaviour can be described in terms of local interactions of their constituent parts. This paper illustrates an empirical method applied with interesting results in modelling and simulating some complex macroscopic phenomena. While classical CA are based upon elementary automata, with few states and a simple transition function, in order to deal with macroscopic phenomena it is often necessary to allow a large number of different states a more complicated transition. The notion of substate is introduced in the macroscopic case for decomposing the state of the cell. The values associated to substates can change in time either due to interactions among substates inside the cell (internal transformations) or to local interactions among neighbouring cells. The internal transformations are treated in a way similar to ordinary difference equations. The local interactions among cells can be often treated according to an algorithm for the minimisation of differences, which describes a tendency of conserved quantities to reach an equilibrium distribution. A large class of complex macroscopic phenomena seem to satisfy the applicability conditions of such an empirical method; some of them are briefly reviewed.

Atomic physics: a renewed vitality

In 1951 I had just accepted a job as assistant professor at New York University. I was at the time a postdoc working in Jerrold Zacharias's atomic‐beams laboratory at MIT. My PhD thesis (at NYU) had been in the field that was then called “gas discharges”, and now has the more dignified appellation of gaseous electronics. I wondered what kind of experiment to set up, upon my return to NYU, that would effectively exploit my rather minimal expertise in two seemingly disparate fields, one involving complex macroscopic phenomena in the gas phase, the other an elegant, though technically challenging field that dealt with atoms one at a time.