Statistical Mechanics Conference

104th SMC Program
104th List of invited talks and abstracts
104th SMC short talk schedule
SMC 104 presentation of talks

104th Statistical Mechanics Conference Invited Speakers Title & Abstracts

Jayanth Banavar, Pennsylvania State University

"Metabolic efficiency and the shapes of flora and fauna"

Abstract: TBA Kurt Binder, University of Johannes Gutenberg

"Monte carlo methods for estimating interfacial free energies and line tensions"
Abstract? click here

Sang-Wook Cheong, Rutgers University

"Ferroelectric domain patterns and graph theory?"

Abstract: TBA Giovanni Ciccotti, University of Rome, "La Sapienza"

"Free energies for rare events: Temperature accelerated MD & MC"

Abstract: The talk addresses a case of the challenges associated, for MD/MC practitioners, with rare events, events whose statistical properties cannot be computed by brute force simulations. In particular we present a new technique, useful to compute the free energy landscape associated with activated processes, and illustrate it in a simple but instructive case. The technique derives from a procedure, introduced by E. Vanden Eijnden & L. Maragliano (Chem. Phys. Lett. 426, 168 (2006); Single-sweep methods for free energy calculations, J. Chem. Phys., 2008, 128, 184110), called TAMD, which gets the free energy landscape, in few collective variables (CV's) describing the process of interest, by extending the phase space of the system with the addition of the collective variables taken as new, slow, degrees of freedom, coupled to the original system by a suitable biasing potential. The extended system can be let to evolve for the fast, physical, variables at the physical temperature while the slow variables are thermostatted at a much higher temperature. The result is that the system can be shown to evolve sampling the full free energy landscape in spite of the presence of rare events. In the case, frequent in applications, when the CV's cannot be expresses in a analytical form, the procedure can be substituted by a temperature accelerated Monte Carlo (TAMC) since the MC "evolution" needs only the energies and no more the forces associated to the sampling. The new techniques will be demonstrated and, then, illustrated with the characterization of a nucleation process.Nathan Clisby, The University of Melbourne

"Efficient Monte Carlo simulation of polymers"

Joint work with: Yenchao Chua, Brian D. Leahy, Ka Yee C. Lee, and Binhua Lin
Abstract: In this talk I will discuss recent progress in improving the efficiency of Monte Carlo simulations of polymers via a new data structure, and novel choices of Markov chain. The new data structure allows for high quality simulations of self-avoiding walks with up to 270 million steps via the pivot algorithm, and will soon be extended to other polymer models and a larger set of non-local moves. I will then discuss the occurrence of non-obvious length scales in lattice polymer systems which can lead to surprisingly long integrated autocorrelation times if not identified. I will describe the technique used to resolve this problem, which is quite generic, and discuss the relevance of this work to systems such as confined polymers and polymer knotting.
References:

1. Nathan Clisby, "Efficient implementation of the pivot algorithm for self-avoiding walks", J. Stat. Phys. 140:349-392 (2010).
2. Nathan Clisby, "Accurate estimate of the critical exponent $
   u$ for self-avoiding walks via a fast implementation of the pivot algorithm", Phys. Rev. Lett. 104: 055702 (2010).

Susan Coppersmith, University of Wisconsin, Madison

"Incommensurate phases of a compressed nanoparticle film"

Joint work with: Yenchao Chua, Brian D. Leahy, Ka Yee C. Lee, and Binhua Lin
Abstract: TBA Michael W. Deem, Rice University

"The adaptive, heritable bacterial immune system: Heterogeneous diversity of spacers within CRISPR"

Abstract: Clustered regularly interspaced short palindromic repeats (CRISPR) in bacterial and archaeal DNA have recently been shown to be a new type of anti-viral immune system in these organisms. We here study the diversity of spacers in CRISPR under selective pressure. We propose a population dynamics model that explains the biological observation that the leader proximal end of CRISPR is more diversified and the leader-distal end of CRISPR is more conserved. This result is shown to be in agreement with recent experiments. Our results show that the CRISPR spacer structure is influenced by and provides a record of the viral challenges that bacteria face. Charles Doering, University of Michigan

"Demographic stochasticity versus spatial variation in the competition between fast and slow dispersers"

Abstract: Dispersal is an important strategy that allows organisms to locate and exploit favorable habitats. The question arises: given competition in a spatially heterogeneous landscape, what is the optimal rate of dispersal? Continuous population models predict that an otherwise identical species with a lower dispersal rate always drives a competing species to extinction in the presence of spatial variation of resources. However, the introduction of intrinsic demographic stochasticity can reverse this conclusion. We present a simple model in which competition between the exploitation of resources and stochastic fluctuations leads to victory by either the faster or slower of two species depending on the environmental parameters. A simplified limiting case of the model, analyzed by closing the moment and correlation hierarchy, quantitatively predicts which species will win in the complete model under given parameters of spatial variation and average local carrying capacity. This joint work with J.N. Waddell and L.M. Sander was published in Theoretical Population Biology 77, 279-286 (2010).Bill Eaton, National Institute of Health

"An Ising-like model for protein folding"

Abstract: Ayse Erzan,Istanbul Technical University

"Spectral Renormalization Group Theory on Networks"

Abstract: We set up a renormalization group scheme by expanding an arbitrary scalar field living on the nodes of an arbitrary network, in terms of the eigenvectors of the normalized graph Laplacian[1]. The renormalization tranformation involves, as usual[2] the integration over the more ``rapidly varying" components of the field, corresponding to eigenvectors with larger eigenvalues, and then rescaling. The critical exponents depend on the particular graph through the spectral density of the eigenvalues, as is also found for real space renormalization group schemes.[3]

1. F.K.R. Chung, Spectral Graph theory, CBMS Regional Conference Series in Mathematics, 92, Conference Board of the Mathematical Sciences, Washington (1997).
2. K.G. Wilson and J. Kogut, Phys. Rep. , 83, 75 (1974).
3. S.N. Dorogovtsev, A.V. Goltsev, J.F.F. Mendes, Rev. Mod. Phys., 80, 1275 (2008).

Erwin Frey, University of Munich

"Minimal premisses for the evolution and maintenance of cooperation"

Abstract: TBA Marty Golubitsky, Ohio State University

"Phase-shift synchrony and symmetries of periodic solutions in networks"

Abstract: TBA Terry Hwa, University of California, San Diego

"On bacterial growth, drug resistance, and evolution"

Abstract: TBA Jorge Jose, Indiana University

"Non-equilibrium biophysical model of self-organized in-vitro spindle formation"

Abstract: TBA Vladimir Korepin, Stony Brook

"Measures of entanglement in spin chains"

Abstract: Two different measures will be considered: negativity and entropy of a subsystem. Corresponding spin chains are AKLT and XY. Exact analytical results will be presented. Preliminary list of references are: arXiv:1002.2931 , arXiv:1003.2007 Gabi Kotliar, Rutgers University

"The Mystery of the Hidden Order in URu2Si2"

Abstract: In 1986 a sharp second order phase transition was detected in a heavy fermion material URu2Si2. From the point of view of thermodynamical quantities, it resembled an ordinary Neel transtion with an entropy loss of around 1/5 Log(2). However, experimentalits and theorist have been trying to figure out what is the order parameter describing this order without success ever since. Every single experimental probe has been used on this material to infer the nature of the low temperature phase and its order parameter. In the absence of conclusive result, this low temperature phase is called the Hidden Order phase. Elucidating its nature represents one of the most challenging problems in the field of strongly correlated electrons. In this talk I will first introduce the problem, and review key experiments constraining the possible answers. We will then present our recent studies of this problem using state of the art Dynamical Mean Field Theory methods, and a low energy theory inspired by the first principles calculations. This should be a gentle introduction to some statistical-mechanics inspired techniques to treat strong correlation problems. We will identify the order parameter as the formation of an hexadecapolar moment in the f shell. The low energy theory will connect the order parameter of the HO phase, to a conventional antiferromagnetic phase via a U(1) rotation. The conventional antiferromagnetic phase can be reached by applying pressure. We will a discuss the nature of the unusual nature of the Kondo effect in this system, and explore further experimental consequences of our proposal.
References: K. Haule and G. Kotliar : Nature Physics 5, 796 (2009) and Europhysics Letters 89, 57006 (2010). Werner Krauth, ENS, Paris

"Damage spreading and coupling in Markov chains "

Abstract: In this talk, I will relate the coupling of Markov chains, at the basis of perfect sampling methods, with damage spreading, which captures the chaotic nature of stochastic dynamics. For two-dimensional spin glasses and hard spheres, the obstacle to the application of perfect-sampling schemes is posed by damage spreading rather than by the survey problem of the entire configuration space. Dynamical damage-spreading transitions are deeply inside the paramagnetic and liquid phases, and the critical values of the transition temperatures and densities depend on the coupling scheme. I will discuss a classic proof that for arbitrary Monte Carlo algorithms, damage spreading can be avoided through non-Markovian coupling schemes.
Reference: Bernard, Chanal, Krauth, arXiv:1010.1195 Kurt Kremer, Max Planck Institute for Polymer Research

"Adaptive Resolution Simulations: Towards Open Systems Molecular Dynamics Simulations"

Abstract: The relation between atomistic structure, architecture, molecular weight and material properties is a basic concern of modern soft matter science. This longstanding aim by now goes far beyond standard properties of bulk materials. A typical additional focus is on surface interface aspects or the relation between structure and function in nanoscopic molecular assemblies. This all implies a thorough understanding on many length and correspondingly time scales ranging from (sub)-atomic to macroscopic. Traditionally computer simulations have been separated in two main groups, namely simplified models to deal with generic or universal aspects, i.e. critical exponents, of polymers and those employing classical force field simulations with (almost) all atomistic detail, i.e. for the diffusion of small additives in small "sample". To progress further adaptive schemes have to be developed, which allow for a free exchange of particles (atoms, molecules) between the different levels of resolution. First attempts towards this direction will be presented in this lecture. We study model systems, which display a spatially variable resolution with a free exchange of particles between the different regimes, ranging from atomistic resolution to coarse grained and continuum. M. Praprotnik, L. Delle Site, and K. Kremer, Multiscale Simulation of Soft Matter: From Scale Bridging to Adaptive Resolution, Annu. Rev. Phys. Chem. 59, 2008 David Landau,University of Georgia

"Monte Carlo simulations of the HP model: The 'Ising model of protein folding'"

Abstract: TBA Tom Lubensky, University of Pennsylvania

"Isostaticity, Auxetic Response, and Conformal Invariance in Two-dimensional Elastic Networks;"

Abstract: The square and kagome lattice with springs connecting nearest neighbor sites are periodic lattices that are just on the threshold of mechanical stability: they are isostatic. Adding next nearest neighbor spring moves them away from the isostatic limit and converts zero-frequency bulk floppy modes to finite-frequency modes. This talk will interpret the isostatic limit in these systems as a kind of phase transition, reminiscent of the jamming transition of packed soft spheres, with a divergent length and vanishing frequency scale. It will also introduce a twisted version of the kagome lattice. This lattice has a zero bulk modulus, and as a result, its long-wavelength elastic energy is conformally invariant. It is also isotropic auxetic material, i.e., it has a negative Poisson ratio. It has the same coordination number as the untwisted lattice and, therefore, must have the same number of zero modes. These, however, are Rayleigh surface waves rather than bulk phonon modes.Cristina Marchetti, Syracuse University

"Collective dynamics of active systems: on the order of the flocking transition"

Coauthors: Shradha Mishra and Sriram Ramaswamy
Abstract: Bacterial suspensions and extracts of cytoskeletal filaments and motor proteins are examples of assemblies of interacting self-driven units that collectively generate motion or mechanical stress. They form a new variety of complex fluids, known as active fluids, that exhibit fascinating collective behavior, including nonequilibrium phase transitions, pattern formation and novel rheology. An example of this behavior is the self-organization of dense populations of swimming or gliding bacteria into large-scale dynamical structures, such as jets and swirls, characterized by typical velocities much larger than that of individual organisms. This behavior is highly unusual in low-Reynolds number systems and is reminiscent of the onset of turbulence in high Reynolds number flow. In this talk I will describe our work on using nonequilibrium statistical physics to derive a continuum description of active fluids from specific models of single particle dynamics. This work aims at understanding the role of physical interactions, such as steric effects and medium-mediated hydrodynamic couplings, relative to genetically and biochemically-regulated signaling, in controlling the large-scale behavior of these systems. New results on activity-induced thinning and thickening will be presented.
Some References:

1. Enhanced diffusion and ordering of self-propelled rods, Aparna Baskaran and M. Cristina Marchetti, Phys. Rev. Lett. 101, 268101 (2008).
2. Fluctuations and Pattern Formation in Self-Propelled Particles, S. Mishra, A. Baskaran and M. Cristina Marchetti, Phys. Rev. E 81, 061916 (2010).
3. Statistical mechanics and hydrodynamics of Bacterial Suspensions, Aparna Baskaran and M. Cristina Marchetti, Proc. Nat. Acad. Sci. 106, 15567-15572 (2009).
4. Sheared active fluids: thickening, thinning and vanishing viscosity, L.Giomi, T. B. Liverpool and M. Cristina Marchetti, Phys. Rev. E 81, 051908 (2010),

Joaquin Marro, University of Granada

"Networks of excitable units: structure and nonequilibrium phase transitions"

Abstract ?click here A. Middleton, Syracuse University

"Algorithms and chaos and universality for two-dimensional Ising spin glasses"
Coauthors: C. K. Thomas and D. A. Huse
Abstract: Simulating glassy systems by local Monte Carlo generally requires extremely long runs. In the case of the two-dimensional Ising spin glass, efficient algorithms can be used to calculate partition functions and to sample configurations exactly from the Boltzmann distribution. We studied thermodynamic quantities for both bimodal and Gaussian distributions of bond weights, using sizes of up to L=512 and precisions of up to 4096 bits, to provide insight into this glassy model. The length scale at which entropy becomes important and produces "chaos", the extreme sensitivity of the state to temperature, is found to depend on the type of randomness. Although there is a type of universality, some critical exponents depend on the distribution of disorder, including the specific heat exponent.

Sid Nagel, University of Chicago

"Memories"

Abstract: TBA Lawrence Pratt,Tulane University

"Organizing information for the statistical theory of liquid water: Good theories are either Gaussian or everything"

Abstract: TBA Nikolay Prokofiev,University of Massachussetts

"Solution of the dirty Boson problem"

Abstract: I will discuss the theorem of inclusions which makes general rigorous statements about phase transitions in disordered systems such as: (i) transitions between fully gaped and superfluid phases are forbidden and there must exist an intermediate gapless insulating phase; (ii) all transitions between gapfull and gapless phases have to be of the Griffiths type when the vanishing of the gap at the critical point is due to a zero concentration of rare regions with extreme fluctuations of disorder mimicing a regular gapless system. The theorem will be applied to the phase diagram of the disordered Bose-Hubbard model at unity filling which has been controversial for many years. I will also explain the vortex phase mechanism governing the shape of the phase diagram in the vicinity of the diagram tip in d=1,2. A highly non-trivial shape of the phase diagram in d=3 is revealed with the worm algorithm; for example, superfluidity persists in random potentials nearly 50 (!) times larger than the particle half-bandwidth. John Reppy, Cornell University

"Is Supersolid Superfluid?"

Abstract: Thirty-five years lapsed between the early predictions of a supersolid state of solid 4He by Chester (1968), Andreev and Lifshitz (1969), and Leggett (1970) and the surprising discovery of experimental evidence for its existence. Eunsoeng Kim and Moses Chan in 2004 conducted a series of torsional oscillator experiments with solid 4He and discovered an anomalous unexpected decrease in the period of the oscillator at temperatures below 250 mK. They interpreted this decrease in oscillator period as a result of a superfluid-like decoupling of a fraction of the solid helium moment of inertia from the motion of the oscillator. This discovery generated a flurry of experimental and theoretical interest that remains unabated to this day. The aim of the work presented here is to examine the basic nature of the supersolid phenomenon. Is it really a manifestation of a Bose-condensed superfluid-like state of solid 4He or not? The most recent experiments have produced more surprises that require a rethinking of our concept of the supersolid phenomenon in solid 4He. 1) Phys. Rev. Lett. 104, 255301 (2010).Troy Shinbrot - Rutgers University

"Granular Electrostatics"

Abstract: Although electrostatics is in principle a purely linear system of well established equations, in this talk we focus on the surprising fact that the most elementary behaviors of electrostatic charging in a collisional gas remain largely unexplained. As a case in point, it has been known at least since Michael Faraday's time that grains in desert sandstorms spontaneously generate strong electrical charges; likewise volcanic dust plumes produce spectacular lightning displays. Yet the grains involved are essentially identical, and start out in a neutral, grounded state. In this talk, we describe simulations and laboratory experiments that confirm that chemically and mechanically identical particles in a collisional state can build up large charges, and we describe mechanisms and open questions underlying this curious behavior. Some references: T. Shinbrot & HJ Herrmann, "Static in Motion" Nature 451 (2008) 773-4 T. Phätz, HJ Herrmann, T. Shinbrot, "Why do particle clouds generate electric charges?" Nature Physics 6 (2010) 364-8. T. Shinbrot, TS Komatsu & Q. Zhao, "Spontaneous tribocharging of similar materials," Europhysics Letters 83 (2008) 24004 1-4 Alan Sokal, New York University

"Overcoming critical slowing-down: Where do we stand 23 years after Swendsen and Wang?"

Abstract: I begin by reviewing the Swendsen-Wang algorithm for ferromagnetic q-state Potts models -- and its extension to noninteger q due to Chayes and Machta -- and our current state of knowledge about these algorithms' dynamic critical behavior. I then discuss recent results concerning the dynamic critical behavior of Sweeny's local algorithm for the random-cluster model, notably the surprising phenomenon of critical speeding-up. Finally, I discuss similar but more complicated phenomena in the worm algorithm for the ferromagnetic Ising model. Boris Svistunov, University of Massachussets, Amherst

"Diagrammatic Monte Carlo for Fermionic Systems"

Abstract: Monte Carlo sampling of the Feynman diagrammatic series can be used for tackling hard fermionic quantum many-body problems in the thermodynamic limit. I will introduce the technique and present illustrative results for the repulsive Hubbard model in the correlated Fermi liquid regime, as well as the results for the equation of state for the system of resonant fermions in the regime of BCS-BEC crossover. Dave Thirumalai, University of Maryland

"Learning about Molecular Motors Using Polymer models"

Abstract: TBA Henk van beijeren, Institute for Theoretical Physics, Utrecht, The Netherlands

"Multi-species simple exclusion processes with two-way traffic and overtaking"

Abstract? click here Frank Verstraete, University of Vienna

"Variational methods for 1+1 dimensional quantum field theories"

Abstract: TBA Michael Vogelius, Rutgers University

"Electromagnetic Cloaking at all frequencies"

Abstract: TBA David Wilson, Microsoft

"XOR-Ising loops and the Gaussian free field"

Abstract: TBA Ned Wingreen, Princeton University

"Why are chemotaxis receptors clustered but other receptors aren't?"

Abstract: The chemotaxis network of bacteria such as E. coli is remarkable for its sensitivity to minute relative changes in chemical concentrations in the environment. Indeed, E. coli cells can detect concentration changes corresponding to only ~3 molecules in the volume of a cell. Much of this acute sensitivity can be traced to the collective behavior of teams of chemoreceptors on the cell surface. Instead of receptors switching individually between active and inactive configurations, teams of 6-20 receptors switch on and off, and bind or unbind ligand, collectively. Similar to the binding and unbinding of oxygen molecules by tetramers of hemoglobin, the result is a sigmoidal binding curve. Coupled with a system for adaptation that tunes the operating point to the steep region of this sigmoidal curve, the advantage for chemotaxis is gain i.e., small relative changes in chemical concentrations are transduced into large relative changes in signaling activity (specifically, the rate of phosphorylation of the response regulator CheY). However, something is troubling about this simple explanation: in addition to providing gain, the coupling of receptors into teams also increases noise, and the net result is a decrease in the signal-to-noise ratio of the network. Why then are chemoreceptors observed to form cooperative teams? We present a novel hypothesis that the run-and-tumble chemotactic strategy of bacteria leads to a "noise threshold", below which noise does not significantly decrease chemotactic velocity, but above which noise dramatically decreases this velocity.

Schedule of Short talks

SESSION A

A1: Mohammad Maghrebi, MIT

"Finite temperature corrections to the Casimir force"
Coauthors: J Rahi, T Emig, N Graham, R Jaffe, M Kardar
Abstract: While Casimir forces are associated with quantum fluctuations of the electromagnetic field,at finite temperature excitation of real photons also contribute to the interaction energy. In most experimental setups to date, finite temperature contributions have only amounted to smallcorrections that are hard to detect. We find, however, that room temperature modifications of the Casimir force are in fact quite significant for a sharp cone, such as the tip of an atomic force microscope. We provide explicit analytic formulae for the finite temperature Casimir force on a sharp tip, and indicate their relevance to experiments.

A2: M. Krüger, MIT

"Radiative heat transfer to a sphere from a warm wall"
Coauthors: M. Krüger, T. Emig and M. Kardar
Abstract We study radiative heat transfer between small objects at close proximity. If the sizes of the objects and/or their mutual separation are small compared to the thermal wavelength, energy transfer via electromagnetic radiation can be comparatively much larger than for macroscopic objects, where Planck's radiation law holds. We develop a formalism starting from thermal current-fluctuations in warm objects, and employing multiple scattering techniques to compute the heat radiation. As an example, we discuss the case of a cold sphere in front of a warm wall.

A3: D. Volovik, Boston University

"First passage propoerties of bursty random walks"
Abstract: We investigate the first-passage properties of bursty random walks on a finite one-dimensional interval of length L, in which unit-length steps to the left occur with probability close to one, while steps of length b to the right -- "bursts" -- occur with small probability. This stochastic process provides a crude description of the early stages of virus spread in an organism after exposure. The interesting regime arises when b is of the order of but less than 1, where the conditional exit time to reach L, corresponding to an infected state, has a non-monotonic dependence on initial position. Both the exit probability and the infection time exhibit complex dependences on the initial condition due to the interplay between the burst length and interval length.

A4: D. R. Amor, University of Girona

"Effects of punishment in mobile prisoner's dilemma players"
Coauthors: J. Fort
Abstract: Physical and mathematical models of social systems are a very active field of current research. Some models focus on the conditions under which cooperation can spread. Very recently, the effect of the motion of individuals has been analyzed. It has been shown that cooperation can spread only if the motion of prisoner dilemma players is sufficiently slow. We have introduced punishment in such models. Our results show that occasional costly punishment maintains the high cooperation level, even if the temptation to defect is increased up to some threshold. Moreover, cooperation remains successful under higher speeds, and even under soft antisocial punishment.

A5: Shiliyang Xu, Syracuse University

"Semiflexible Polymer Brushes as Vicious Accelerating Walkers"
Coauthors: J. M. Schwarz
Abstract

A6: L. Cao, Syracuse University

"Level spacing statistics for quantum k-core percolation"
Coauthors: L. Cao* and J. M. Schwarz
Abstract:Quantum percolation is the study of hopping transport of a quantum particle on randomly diluted percolation clusters. Quantum k-core percolation is the study of quantum transport on k-core percolation clusters where each occupied bond must have at least k occupied neighboring bonds. Within the random phase approximation, we found a random first-order phase transition for the k-core conduction transition on the Bethe lattice, and p_q, the quantum percolation critical probability, is equal to p_c, the geometric percolation critical probability [Phys. Rev. B 82,104211 (2010)]. To further test this result, we numerically compute the level spacing distribution as a function of occupation probability p and system size. The simulation results provide confirmation for the existence of a discontinuous onset of quantum conduction at p_q=p_c.

A7: S. Vaikuntanathan, University of Maryland, College Park

"Escorted Free Energy Simulations: A strategy to estimate free energy differences efficiently"
Coauthors: C. Jarzynski
Abstract: Nonequilibrium, "fast switching" estimates of equilibrium free energy differences are often plagued by poor convergence due to dissipation. We propose a method to improve these estimates by generating trajectories with reduced dissipation. Introducing an artificial flow field that couples the system coordinates to the external parameter driving the simulation, we derive an identity for the free energy difference in terms of the resulting trajectories. When the flow field effectively escorts the system along a near-equilibrium path, the free energy estimate converges efficiently and accurately.

A8: B. Miller, Texas Christian University

"Cosmology in One Dimension"
Coauthors: J.L. Rouet
Abstract: Concentrations of matter, such as galaxies and galactic clusters,originated as very small density fluctuations in the early universe. The existence of galaxy clusters and super-clusters suggests that a natural scale for the matter distribution may not exist. A point of controversy is whether the distribution is fractal and, if so, over what range of scales. One-dimensional models demonstrate that the important dynamics for cluster formation occur in the position-velocity plane. Here the development of scaling behavior and multifractal geometry is investigated for a family of one-dimensional models for three different, scale-free, initial conditions. The methodology employed includes: 1) The derivation of explicit solutions for the gravitational potential and field for a one-dimensional system with periodic boundary conditions (Ewald sums for one dimension); 2) The development of a procedure for obtaining scale-free initial conditions for the growing mode in phase space for an arbitrary power-law index; 3) The evaluation of power spectra, correlation functions, and generalized fractal dimensions at different stages of the system evolution. It is shown that a simple analytic representation of the power spectra captures the main features of the evolution, including the correct time dependence of the crossover from the linear to nonlinear regime and the transition from regular to fractal geometry. A possible physical mechanism for understanding the self-similar evolution is introduced. It is shown that hierarchical cluster formation depends both on the model and the initial power spectrum. Under special circumstances a simple relation between the power spectrum, correlation function, and correlation dimension in the highly nonlinear regime is confirmed.

A9: L. Blum, Rutgers University

"New result for the critical parameters of the restricted primitive model using the Hypernetted Bridge Approximation"
Abstract: New results from the hyper netted bridge function theory for the critical parameters of the restricted primitive model usting show excellent agreement with computer simulations. The only free parameter is the dimer solvent diameter which is fixed requiring virial-compressibility consitency.

A10: J. Olejarz, Boston University

"Strange relaxation in 3D Ising model"
Coauthors: J. Olejarz*, S. Redner and P. Krapivsky
Abstract: We investigate the long-time properties of the Ising-Glauber model on a periodic cubic lattice after a quench to zero temperature. We find: (i) domains at long time are highly interpenetrating and topologically complex, (ii) the long-time state is almost never static, and (iii) the energy relaxation is extremely slow and has a complex time dependence.

A11: R.K.P. Zia, Virginia Tech.

"Four Species in Cyclic Competition"
Coauthors: C.H. Durney, S. O. Case and M. Pleimling
Abstract: Generalizing the cyclically competing three-species model (Berr, et. al., PRL 102, 048102 (2009)), we consider a system involving four species (with no spatial structure): A+B -> A+A, ..., D+A -> D+D. Unlike the 3 species case, where the weakest tends to survive, no simple general rule applies here. Instead, the four form alliance pairs, much like in the game of Bridge, so that the end states typically consists of coexisting (but non-interacting) pairs: AC or BD. I will describe the stochastic model, the associated master equation, and the mean-field approximation, i.e., a deterministic set of equations of evolution.

A12: C.H. Durney, Virginia Tech.

"Mean Field Theory (MFT) Predictions for Four Species in Cyclic Competition"
Coauthors: S. Case, M. Pleimling, and R.K.P. Zia
Abstract: Studying the deterministic evolution of four species competing cyclically (A+B -> A+A with rate k_a, ..., D+A -> D+D with rate k_d), we find an intuitively understandable combination of the reaction rates, k_a*k_c-k_b*k_d, which controls whether the AC or BD pair survives. When this combination is zero, MFT predicts closed orbits encircling a fixed line. Limitations and implications of MFT will also be discussed.

A13: S. Case, Virginia Tech

"Surprises from Simulations of Four Species in Cyclic Competition"
Coauthors: M. Pleimling, R.K.P. Zia and C.H. Durney
Abstract:Using Monte Carlo techniques, we investigate a stochastic system with N individuals, consisting of four species and competing cyclically. Letting a randomly chosen pair react by A+B -> A+A, etc., N remains a constant while the fractions of each species evolve non-trivially. Unlike the 3 species case, our system typically ends in absorbing states with coexisting pairs: AC or BD. Thus, the number of absorbing state scales with N, instead of being O(1). Simulation results for N00 are presented, showing some rather unexpected behavior, especially for a system with extremely disparate rates.

A14: E.B. Kaufmann, Purdue University

"Critical exponents in the two-species asymmetric diffusion model"
Abstract: We present a study of the two species totally asymmetric diffusion model using the Bethe Ansatz. The Hamiltonian has $U_q(SU(3))$ symmetry. We derive the nested Bethe Ansatz equations and obtain the dynamical critical exponent from the finite--size scaling properties of the eigenvalue with the smallest real part. The dynamical critical exponent is $frac{3}{2}$ which is the exponent corresponding to KPZ growth in the single species asymmetric diffusion model.

A15: S. Henkes, Syracuse University

"Elasticity of a cross-linked active bundle"
Coauthors: T.B. Liverpool, M.C. Marchetti, and A.A. Middleton
Abstract: Understanding the effect of motor proteins, such as myosins, on the elasticity of crosslinked actin networks is essential to our understanding of cell mechanics. Both in vivo and in vitro, these active networks have radically different mechanical properties from their equilibrium counterparts, including contractile behavior and higher elastic moduli. Existing theoretical models do not address the relative role of passive and active crosslinkers in controlling the network contractility and stiffening. We construct a one dimensional lattice model with minimal ingredients, that is, rigid polar filaments, spring-like passive crosslinks and active crosslinks with on/off dynamics implemented through non-equilibrium Monte Carlo solution of the corresponding master equations. We find, consistent with experiments, that the network needs to be percolated through the passive crosslinks to be mechanically stable. Contractile behavior is observed for all concentrations of active crosslinks. We study the mechanical properties of the gel in the phase space of motor processivity, crosslink stiffness, and concentration of active crosslinks.

A16: C. Thomas, Texas A & M Univerity

"The specific heat of the two-dimensional Ising spin glass"
Coauthors: A. Alan Middleton, David A. Huse
Abstract: We examine the behavior of the specific heat in the two-dimensional Ising spin glass. At low temperatures, the specific heat is dominated by contributions from excitations at the smallest length scales with nonzero energy. For continuous disorder distributions, this length scale is O(1), which leads to a specific heat C ~ T. For discrete disorder, the smallest excitations with nonzero energy occur at a temperature-dependent length scale which modifies the specific heat exponent. Due to large finite-size effects, this can be seen numerically only in systems with L > 100. In both cases, these small-length scale effects mask the critical behavior due to the spin glass phase transition at zero temperature.

A17: S. Redner, Boston University

"Can Partisan Voting Lead to the Truth"
Coauthors: N. Masuda
Abstract: We study a voter model in which each agent has an innate preference for one of two states --- truth and falsehood. due to interactions with its neighbors, an agent that prefers truth can be in the "false" state (and therefore discordant with its innate preference) or in the internally condordant "true" state, and vice versa for agents that intrinsically prefer falsehood. We determine when the population can ultimately reach a consensus of the truth or get stuck in a partisan state with no consensus.

SESSION B

B1: S. Ji, Rutgers University

"Distances between RNA trajectories are distributed according to Planck's radiation law or the Gaussian distribution law depending on their metabolic functions"
Coauthors: K. So
Abstract

B2: L. Sperzel, Rutgers University

"Decoding pathway-specific RNA waves of budding yeast undergoing glucose-galactose shift - the sounds of cell language"
Coauthors: S. Ji
Abstract

B3: A. Shekhawat, Cornell University
"Universal Properties of Fuse Network Fracture Strength Distribution"
Coauthors: C. Manzato, S. Zapperi, J.P. Sethna
Abstract: Fuse networks are a paradigmatic example of brittle fracture. In this talk we show that the fracture strength for Duxbury type fuse networks is in the Gumbel universality class. We contrast this with the widely held belief that fracture statistics are always in the Weibull universality class. We emphasize the connection between fracture and extreme value statistics and explain how the universality class effects the scaling behavior at large length scales. We discuss results of large scale 2-D fuse network simulations and mention some interesting open questions.

B4: M. K. Hawkins, University of Maryland

"Relaxation of Terrace Width Distribution of Vicinal (001) with Zigzag [110] Steps - PART II"
Coauthors: M. Hawkins* and T.L. Einstein
Abstract: We discuss dynamical and steady state results of Kinetic Monte Carlo simulations which show the relaxation of zigzag steps on a vicinal (001) surface. Dynamical results show that the standard deviation of terrace widths of zigzag steps saturates faster than that of straight steps, and its higher level moments are larger (more uctuations). The Arrhenius plots of relaxation times show that 2-atom processes are dominant in attaining a steady state conguration for zigzag steps, in contrast to straight steps where 3-atom processes are dominant. In the steady state, step-step cor- relation functions of zigzag steps further re ect the greater uctuations for zigzag steps compared to straight steps. Also, steady state terrace width distributions for the zigzag system show oscillations in the param- eter P(0), which quanties the amount of step touching. This work was supported by NSF-MRSEC at University of Maryland, DMR 0520471.

B5: A. Gabel, Boston University

"A facilitated asymmetric exclusion process"
Coauthors: S. Redner and P. Krapivsky
Abstract:We study a modified form of the Asymmetric Exclusion Process where hopping rates depend on the local particle arrangement. In our model, particles on a 1-D lattice will move only when pushed from behind by a neigbhor. We find a phase transition from active to absorbing final states as well as the presence of a discontinuity in the rarefaction wave that develops from an initial step function density profile.

B6: H. Kim, University of Notre Dame

"Degree-based graph construction and sampling"
Coauthors: Z. Toroczkai, P.L. Erdos, I. Miklos and L.A Szekely, C.I. Del Genio, K. E. Bassler
Abstract: Network representation and modeling has been one of the most comprehensive ways to study complex systems, ranging from social sciences through chemical compounds to biochemical reaction networks in the cell. However, the network describing the system frequently has to be built from incomplete connectivity data, a typical case being degree-based graph construction, when only the sequence of node degrees is available. In this presentation I will introduce problems and results related to the construction of all the possible graphs and sampling from the class of graphs with fixed degree-sequence. Firstly, for graph construction, we will present necessary and sufficient conditions for a sequence of integers to be realized as a simple graph's degree sequence under the condition that a specific set of connections from an arbitrary node are avoided [1]. Secondly, by using this result, we will show how to provide an efficient, polynomial time algorithm that generates graph samples with a given degree sequence. Unlike other existing algorithms, this method always produces statistically independent samples, without back-tracking or rejections. Also, the algorithm provides the weight associated with each sample, allowing graph observables to be measured uniformly over the graph ensemble [2]. Finally, we will show how these theorems and algorithms can be extended to directed graphs [3].
REFERENCES:

1. Hyunju Kim, Zoltan Toroczkai, Peter L Erdos, István Miklos and Laszlo A Szekely. Degree-based graph construction. J. Phys. A: Math. Theor. (Fast Track Communication) 42, 392001 (2009).
2. Charo I. Del Genio, Hyunju Kim, Zoltán Toroczkai, Kevin E. Bassler. Efficient and exact sampling of simple graphs with given arbitrary degree sequence. PLoS ONE, 5(4), e10012, (2010).
3. Hyunju Kim, Charo I. Del Genio, Kevin E. Bassler, and Zoltán Toroczkai. Constructing and sampling directed graphs with given degree sequence. Preprint, to be submitted.

B7: A. Souslov, University of Pennsylvania

"Constructing Lattice Models with Extraordinary Elasticity"
Coauthors: Xiaoming Mao, Kai Sun, and Tom Lubensky
Abstract:Taking inspiration from jammed systems, we develop isostatic lattice models with unusual and highly tunable elastic properties. A two- (three-) dimensional isostatic lattice has four (six) neighbors, exactly enough to constrain local soft modes, though a sub-extensive number of soft modes remain. We can extend these modes into soft deformations, creating families of lattices with the same connectivity, but different particle configurations. We thus deform the two-dimensional square and kagome and the three-dimensional pyrochlore lattices. Through simple arguments we illustrate the role of symmetry on the long-wavelength elasticity of such systems and gain further insight by examining the full phonon spectrum. We find various models exhibiting negative Poisson ratio and floppy surface modes.

B8: N. Thyagu, Rutgers Univerity

"Competitive cluster growth on networks: complex dynamics and survival strategies"
Coauthors:A. Mehta
Abstract: We extend the study of a model of competitive cluster growth [1-4] in an active medium from a regular topology to a complex network topology; this is done by adding nonlocal connections with probability $p$ to sites on a regular lattice, thus enabling one to interpolate between regularity and full randomness. The model on networks demonstrates high sensitivity to small changes in initial configurations, which we characterize using damage spreading. The main focus of this paper is, however, the devising of survival strategies through selective networking, to alter the fate of an arbitrarily chosen cluster: whether this be to revive a dying cluster to life, or to make a weak survivor into a stronger one. Although such goals are typically achieved by networking with relatively small clusters, our results suggest that it ought to be possible also to network successfully with peers and larger clusters. The main indication of this comes from the probability distributions of mass differences between survivors and their immediate neighbours, which show an interesting universality; they suggest strategies for winning against the odds.

1. J. M. Luck, and A. Mehta, Eur. Phys. J. B 44, 79 (2005)
2. A. Mehta, A. S. Majumdar and J. M. Luck, pp. 199-204 in `Econophysics of Wealth Distributions' edited by A. Chatterjee et al, Springer-Verlag Italia (2005).
3. A. S. Majumdar, Phys. Rev. Lett. 90, 031303 (2003).
4. A. S. Majumdar, A. Mehta and J. M. Luck, Phys. Lett. B 607, 219 (2005).

B9: N. Zimbovskaya, University of Puerto Rico at Humacao

"Nanoparticle shape instability by Coulomb interactions"
Abstract: Metal atoms adsorbed on few-layer graphenes condense to form nanometer-size droplets whose growth in size is limited by a competition between the surface tension and repulsive electrostatic interactions from charge transfer between the metal droplet and the graphene. Under certain conditions a growing droplet can be unstable to a family of shape instabilities. This phenomenon was observed for Yb deposited and annealed on few-layer graphenes. A theoretical model to describe it is developed. The model describes the onset of shape instabilities for nanoparticles where their growth is limited by a generic repulsive potential and provides a good account of the experimentally observed structures for Yb on graphene [1].

1. L. A. Somers, N. A. Zimbovskaya, A. T. Johnson, and E. J. Mele, Phys. Rev. B 82, 115430 (2010).

B10: A. Toom, UFPE, Brazil

"Random Monads"
Abstract: A monad (as suggested by V. Arnold) is a pair (S,M), where S is a finite set having n elements called points and M is a map from S to S. We fix some initial point I and define an infinite sequence I, M(I), M(M(I)),... We denote: by Vis (visited) the number of points which enter this sequence; by Rec (recurrent) the number of points which enter this sequence at least twice; Tra (transient) the number of points which enter this sequence only once. We introduce randomness in the simplest way: M(.) are uniformly distributed in S and independent from each other. Thus Vis, Rec and Tra are integer random variables. We estimate their modes, expectations and standard deviations and some other quantities and in all cases obtain approximatedly square root of n with different coefficients.

B11: S. Jolad, Virginia Tech.

"Contact process on static and adaptive networks"
Coauthors: R. Zia, W. Jia and B. Schmittmann
Abstract: We consider epidemic spreading on an adaptive network where individuals have a fluctuating number of connections around some preferred degree $kappa$. Using very simple rules for forming such a network, we find some unusual statistical properties which provide an excellent platform to study adaptive contact processes. For example, by letting $kappa$ depend on the fraction of infected individuals, we can model behavioral changes in response to how the extent of the epidemic is perceived. Specifically, we explore how various simple feedback mechanisms affect transitions between active and inactive states.

B12: Y. Fily, Syracuse University

"Emerging "self propulsion" of a pair of rotors in a viscous liquid"
Coauthors:Y. Fily, A. Baskaran and M.C. Marchetti
Abstract:A particle rotating in a viscous fluid generates an azimuthal flow field felt by other particles present in the fluid. Two such particle of opposite vorticities push each other in the same direction, resulting in a steady motion of the center of mass: the pair becomes self propelled. We study the diffusion of such a "self propelled" pair. As the distance between the two objects varies, the effective self propulsion velocity of the center of mass varies too, leading to non trivial diffusion behavior.

B13: P. Cladis, Advanced LC Tech

"Icosahedral Nematic Liquid Crystal Elastomers"
Coauthors: S. Krause, Y. Yusuf, S.Hashimoto, L. G. Fel, H. Finkelmann, S. Kai, P.E. Cladis
Abstract:A phase transition theory, supported by experiments from a new class of liquid crystal elastomers characterized as a nematic network with smetic C Clusters will be presented.

B14: Y. Liu, Northeastern University

"Controllability of Complex Networks"
Coauthors: J.-J. Slotine, A.-L. Barabasi
Abstract: The ultimate proof of our understanding of natural or technological systems is reflected in our ability to control them. While control theory offers mathematical tools to steer engineered systems towards a desired state, we lack a general framework to control complex self-organized systems, like the regulatory network of a cell or the Internet. Here we develop analytical tools to study the controllability of an arbitrary complex directed network, identifying the set of driver nodes whose time-dependent control can guide the system's dynamics. We apply these tools to real and model networks, finding that sparse inhomogeneous networks, which emerge in many real complex systems, are the most difficult to control. In contrast, dense and homogeneous networks can be controlled via a few driver nodes. Counterintuitively, we find that in both model and real systems the driver nodes tend to avoid the hubs. We show that the robustness of control to link failure is determined by a core percolation problem, helping us understand why many complex systems are relatively insensitive to link deletion. The developed approach offers a framework to address the controllability of an arbitrary network, representing a key step towards the eventual control of complex systems.

SESSION C

C1: Y. Terada, Tohoku University, Japan

"Dynamics and spatial configurations of magnetic colloidal monolayers and chains confined in thin films"
Abstract: We perform extensive Brownian dynamics simulation of dilute magnetic colloidal monolayers and chains confined in thin films. The diffusivity of colloids and chains are controlled by applied external magnetic field, and film thickness. However it is found that all data collapse on a single master curve once the data are rescaled by theoretical singular point. We also discuss the structure of colloidal monolayers and chains.

C2: D. Quint, Syracuse University

"Buckling of Branched Cytoskeletal Filaments "
Coauthors: J.M. Schwartz
Abstract: In vitro experiments of growing dendritic actin networks demonstrate reversible stress-softening at high loads, above some critical load. The transition to the stress-softening regime has been attributed to the elastic buckling of individual actin filaments. To estimate the critical load above which softening should occur, we extend the elastic theory of buckling of individual filaments embedded in a network to include the buckling of branched filaments, a signature trait of growing dendritic actin networks. Under certain assumptions, there will be approximately a seven-fold increase in the classical critical bucking load, when compared to the unbranched filament, which is entirely due to the presence of a branch. Moreover, we go beyond the classical buckling regime to investigate the effect of entropic fluctuations. The result of compressing the filament in this case leads to an increase in these fluctuations and eventually the harmonic approximation breaks down signifying the onset of the buckling transition. We compute corrections to the classical critical buckling load near this breakdown.

C3: M. Vucelja, Courant Institute

"Irreversible Monte Carlo algorithms for efficient sampling"
Abstract: Equilibrium systems evolve according to Detailed Balance (DB). This principle guided the development of Monte Carlo sampling techniques, of which the Metropolis-Hastings(MH) algorithm is the famous representative. It is also known that DB is sufficient but not necessary. We construct irreversible deformation of a given reversible algorithm capable of dramatic improvement of sampling from known distribution. Our transformation modifies transition rates keeping the structure of transitions intact. To illustrate the general scheme we design an Irreversible version of Metropolis-Hastings (IMH) and test it on an example of a spin cluster. Standard MH for the model suffers from critical slowdown, while IMH is free from critical slowdown.

C4:. Szafran, Rutgers University

"Blackbody radiation law-based estimation of the coupling constant between transcriptosomes and degradosomes in budding yeast"
Coauthors: S. Ji
Abstract

C5: J. Qin, Pennsylvania State University

"Entanglement length from polymer knotting statistics"
Coauthors: J. Qin* and S. T. Milner
Abstract: Polymer motions in dense melts are severely constrained by the uncrossability of surrounding molecules. Effectively the polymer chains can be thought as being confined inside a tube-like region. The tube diameter, or the entanglement length, is the key parameter needed to understand the diverse mechanical properties of materials, but the understanding of its origin on the molecule level is still lacking. We simulated entangled polymer rings, whose topological states are well defined, and sampled the topologically distinct states by implementing various molecular rebridging Monte Carlo moves. We identify the topological states by computing the Knot invariant polynomial, and accumulated the knot statistics with aperiodic and 2d periodic boundary conditions. From the ring length dependence of the unknot probability and the information theoretical entropy we extracted the entanglement length.

C6: D. Herzog, University of Arizona

"The Top Lyapunov Exponent in a Model for the Turbulent Dispersion of Heavy Particles"
Coauthors: David P. Herzog*, Krzysztof Gawedzki, Jan Wehr
Abstract: We will discuss a stochastic differential equation that models the particle separation in a turbulent flow. Using control theory and H"{o}rmander's theorem, we show ergodicity of projected versions of the resulting Markov process, allowing us to uncover formulas for the top Lyapunov exponent in the original model. Methods utilized here can be applied to stochastic differential equations in general to help establish ergodicity.

C7: M. Damron, Princeton University

"Non-polygonal limit shapes in i.i.d. first-passage percolation and infinite coexistence in spatial growth models"
Coauthors: M. Hochman
Abstract:We construct an edge-weight distribution for i.i.d. first-passage percolation on Z2 whose limit shape is not a polygon and has extreme points which are arbitrarily dense in the boundary. Consequently, the associated Richardson-type growth model can support coexistence of a countably infinite number of distinct species, and the graph of infection has infinitely many ends.

C8: T. Luchko, Rutgers University

"Three Dimensional Molecular Theory of Solvation for Molecular Mechanics"
Coauthors: Tyler Luchko* and David A. Case
Abstract:We present an overview of the three dimensional molecular theory of solvation (known as 3D-RISM) as implemented in the AmberTools molecular modeling suite. We will give a brief review of the theory as well as a description of strengths and shortcomings of the model relative to other common solvation methods (e.g. explicit solvent and Poisson-Boltzmann).

C9: S. Simonella, University of Rome "Sapienza"

"Borel summability of ?₄⁴ planar theory via multiscale analysis"
Coauthors: Marcello Porta
Abstract

C10: P. Kleban, University of Maine

"Crossing cluster densities in rectangular geometries at 2-D critical points"
Coauthors_for_short_talk: J. J. H. Simmons, U. Chicago, R. M. Ziff and S. Flores, U. Michigan
Abstract: We perform a complete analysis of a certain six-point correlation function, for any critical model indexed by the SLE parameter 2 ? k ? 8. For percolation (k = 6) this quantity specifies the density of critical clusters at a point z conditioned to touch either or both opposite ends of the rectangle, with these ends 'wired', ie constrained to be in a single cluster. By appropriately choosing the (algebraic) prefactor, we find that the conformal blocks are independent of y, and are in fact given by the Appell function F1. Further analysis identifies the solutions corresponding to the various physical conditioning at the ends. We examine consequences of these solutions for factorization behavior.

C11: G. Ramirez-Santiago , University of

"Spatial gradients of phosphoproteins as a cell signaling process"
Abstract: Cells respond to external signals trough phosphorylation and spatial relocation of proteins. The reversible phosphorylation of proteins is crucial to the regulation of many aspects of cellular function. Here we analyze quantitatively the phosphoprotein spatial gradients in a cell of different shapes: planar, cuboidal, spherical and spheroidal. It is found that the magnitude of these gradients increases by several orders of magnitude as the eccentricity of a spheroidal cell approaches that of cell with spherical geometry. We also show that in spite of the smallness of the cell (few micrometers) the length scale of the spatial gradients is sufficiently small to take place inside the cell.

Presentations of Talks Given at the 104th Statistical Mechanics Conference

• J. Banavar, Penn State
"Metabolic efficiency and the shapes of flora and fauna"

• K. Binder, University of Johannes Gutenberg
"Monte carlo methods for estimating interfacial free energies and line tensions"

• G. Ciccotti, University of Rome, "La Sapienza"
"Free energies for rare events: Temperature accelerated MD & MC"

• N. Clisby, University of Melbourne
"Efficient Monte Carlo simulation of polymers"

• C. Doering,University of Michigan
"Demographic stochasticity versus spatial variation in the competition between fast and slow dispersers"

• A. Erzan, Istanbul Technical University
"Spectral renormalization group theory on networks"

• M. Golubitsky, Ohio State University
"Phase-shift synchrony and symmetries of periodic solutions in networks"

• W. Krauth, Ecole Normale Superieure
"Damage speading and coupling in Markov chains"

• K. Kremer, Max Planck Institute for Polymer Research
"Adaptive Resolution Simulations: Towards Open Systems Molecular Dynamics Simulations"

• J. Marro, University of Granada
"Networks of excitable units: structure and nonequilibrium phase transitions"

• L. Pratt, Tulane University
"Organizing information for the statistical theory of liquid water: Good theories are either Gaussian or everything"

• A. Sokal, New York University
"Overcoming Critical Slowing down: Where Do We Stand 23 Years after Swendsen and Wang?"

• F. Verstraete, University of Vienna
"Variational methods for 1+1 dimensional quantum field theories"

• M. Vogelius, Rutgers University
"Electromagnetic Cloaking at all frequencies"