Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session Q15: General Topics in Statistical and Nonlinear Physics and Applications to Social Systems |
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Sponsoring Units: GSNP Chair: Sid Redner, Boston University Room: 316 |
Wednesday, March 18, 2009 11:15AM - 11:27AM |
Q15.00001: Phase transitions by means of information theory E.E. Vogel, G. Saravia, F. Bachmann, B. Fierro, J. Fischer Sequential files for observables show different compression capabilities depending on the temperature T at which the simulation is done. Compressed files reach maximum size at a T coinciding with the critical temperature TC; these TCs can be independently determined by well of established methods (Binder cumulants or time autocorrelation functions). This behavior can be explained by information theory: near the critical temperature values for the observable span a large universe and the sequence is chaotic; under TC the system is trapped within few states yielding monotonous sequences of values; over TC values tend to the corresponding thermal noise. Compression is maximal in presence of repeated information which is to be found away from TC. This new method to obtain TC is successfully applied to the Edwards-Anderson model where a ferromagnetic 2D Ising system is progressively changed by randomly introducing antiferromagnetic interactions in concentration x. Analysis is done for classical Monte Carlo simulations on square lattice of different sizes, increasing x, varying T. Possible extensions of this treatment are discussed. [Preview Abstract] |
Wednesday, March 18, 2009 11:27AM - 11:39AM |
Q15.00002: An Efficient Numerical Approach for Nonlinear Fokker-Planck equations Dustin Otten, Prakash Vedula Fokker-Planck equations which are nonlinear with respect to their probability densities that occur in many nonequilibrium systems relevant to mean field interaction models, plasmas, classical fermions and bosons can be challenging to solve numerically. To address some underlying challenges in obtaining numerical solutions, we propose a quadrature based moment method for efficient and accurate determination of transient (and stationary) solutions of nonlinear Fokker-Planck equations. In this approach the distribution function is represented as a collection of Dirac delta functions with corresponding quadrature weights and locations, that are in turn determined from constraints based on evolution of generalized moments. Properties of the distribution function can be obtained by solution of transport equations for quadrature weights and locations. We will apply this computational approach to study a wide range of problems, including the Desai-Zwanzig Model (for nonlinear muscular contraction) and multivariate nonlinear Fokker-Planck equations describing classical fermions and bosons, and will also demonstrate good agreement with results obtained from Monte Carlo and other standard numerical methods. [Preview Abstract] |
Wednesday, March 18, 2009 11:39AM - 11:51AM |
Q15.00003: Universal formulation of Casimir forces for static objects with arbitrary shapes and susceptibilities Sahand Rahi We have derived a general formula for the Casimir energy of any number of objects with arbitrary but linear electric permittivities and magnetic permeabilities. The formula is more general than existing ones since it applies to more than two objects and allows arbitrary shapes. It even allows for objects to be inside of one another and thus enables the study of the Casimir force between one object and a cavity. It requires as input the T-matrix of each individual object. The formula is applied to the geometry of two infinite cylinders, two cylinders opposite one or two metallic plates, and a dielectric sphere and dielectric plate. [Preview Abstract] |
Wednesday, March 18, 2009 11:51AM - 12:03PM |
Q15.00004: Triggering and control of stick-slip friction Shmuel M. Rubinstein, Gil Cohen, Jay Fineberg Even regular stick slip frictional sliding always has some stochasticity associated to it. This stochasticity appears as uncertainty in the period between consecutive slip events. We show that once harmonic perturbations are introduced to the shear loading this picture changes significantly. Even relatively small perturbations can trigger the slip instability causing it to occur at a specific phase of the perturbation. This triggering either eliminates the stochastic element completely, or constrains it so that the stick-slip periods differ by discrete multiples of the period perturbation. [Preview Abstract] |
Wednesday, March 18, 2009 12:03PM - 12:15PM |
Q15.00005: Topological order and topological memories at finite temperature Alioscia Hamma, Claudio Castelnovo, Claudio Chamon We discuss the notion of topological order and topological memories at finite temperature. We argue that topological order is given by a long range pattern of entanglement and relaxation times that scale with the size of the system. We obtain the behavior of topological entropy in 3D for the toric code and similar models, showing that half of it is completely washed out in the thermodynamic limit at any finite temperature. This corresponds to the fact that quantum memory is spoiled at any finite temperature and relaxation times are independent of the size of the system. We also study the possibility of obtaining long lived metastable states by confining defects by means of effective long ranged interactions. We discuss the implications for the existence of topological order and stable quantum memories at temperatures different from zero. [Preview Abstract] |
Wednesday, March 18, 2009 12:15PM - 12:27PM |
Q15.00006: ABSTRACT WITHDRAWN |
Wednesday, March 18, 2009 12:27PM - 12:39PM |
Q15.00007: Extended Universality in Potts Models on Square and Triangular Lattices Mikael Wood, Carlos Wexler It has been recently discovered [1] that some families of systems exhibit universal behavior both near and away from any critical point. Specifically, it has been shown that all thermodynamic observables of the p-state Potts model on a square lattice collapse to the values of the 2-D planar XY model above a certain ``extended universality'' temperature $T_{eu}$ [1]. We have extended these results to the Potts model on triangular and honeycomb lattices. We hypothesize that such sharp transition between discrete and continuous behavior of the observables is due to a Nyquist-Shannon type theorem for statistical mechanics. We present evidence for this interpretation and discuss its relevance to emergent systems. \\[4pt] [1] {\em Universality away from critical points in two-dimensional phase transitions}; C.M. Lapilli, P. Pfeifer, and C. Wexler; Phys. Rev. Lett. {\bf 96}, 140603 (2006). [Preview Abstract] |
Wednesday, March 18, 2009 12:39PM - 12:51PM |
Q15.00008: Enhanced Transition Matrix Methods David Yevick, Michael Reimer Recently we have adapted the transition matrix Monte-Carlo method to general communication systems [IEEE Photon.Technol. Lett. 1529 (2007), IEEE Communications Letters, 755 (2008)]. In these studies we compared and integrated different multicanonical and transition-matrix methods. We determined that the standard multicanonical method can be reformulated more simply and accurately by constructing the intermediate probability density function (density of states) after a small number of Markov transitions from the ratios of the elements of the transition matrix between adjacent states. Further, we considered an algorithmically more simple procedure in which transitions only occur from a given state to another state that has previously been less frequently sampled. Here we found that while substantial errors often result if the perturbation that links adjacent Markov states is small, numerical accuracy can be restored by restricting the Markov chain to within a single histogram bin for a certain number of transitions before allowing transitions to other bins. We finally summarize our application of these procedures to several problems in optical and wireless communication theory. [Preview Abstract] |
Wednesday, March 18, 2009 12:51PM - 1:03PM |
Q15.00009: $S$-index: Measuring significant, not average, citation performance Manolis Antonoyiannakis We recently [1] introduced the ``citation density curve'' (or cumulative impact factor curve) that captures the full citation performance of a journal: its size, impact factor, the maximum number of citations per paper, the relative size of the different-cited portions of the journal, etc. The citation density curve displays a universal behavior across journals. We exploit this universality to extract a simple metric (the ``$S$-index'') to characterize the citation impact of ``significant'' papers in each journal. In doing so, we go beyond the journal impact factor, which only measures the impact of the average paper. The conventional wisdom of ranking journals according to their impact factors is thus challenged. Having shown the utility and robustness of the $S$-index in comparing and ranking journals of different sizes but within the same field, we explore the concept further, going beyond a single field, and beyond journals. Can we compare different scientific fields, departments, or universities? And how should one generalize the citation density curve and the $S$-index to address these questions? [1] M. Antonoyiannakis and S. Mitra, ``Is PRL too large to have an `impact'?'', Editorial, Physical Review Letters, December 2008. [Preview Abstract] |
Wednesday, March 18, 2009 1:03PM - 1:15PM |
Q15.00010: ABSTRACT WITHDRAWN |
Wednesday, March 18, 2009 1:15PM - 1:27PM |
Q15.00011: Statistical laws for career longevity Alexander Petersen, Woo-Sung Jung, Jae-Suk Yang, H. Eugene Stanley Career length distinguishes successful long tenures from unsuccessful short stints, and partially reflects the contributions of an employee to the goals of the employer. In some professions, there are well-defined metrics that quantify career longevity, prowess, and productivity, which together contribute to the overall success rating for an individual employee. In this talk, I motivate a stochastic model for career development that relies on two key ingredients, random progress within the career and random stopping times terminating the career. This model is exactly solvable, predicting the probability density function (pdf) of career longevity, characterized by two parameters, $\alpha$ and $x_{c}$. The parameter $\alpha$ quantifies the power-law scaling of the pdf, which is terminated by an exponential cutoff after a crossover value $x_{c}$, representing the mean career lifetime. We test the model with the large quantity of empirical data available for several professional sports leagues, American baseball, Korean baseball, American basketball, and English soccer, finding excellent agreement with the model's predictions. In all, the generality of the model suggests that there may be common stochastic forces that underly progress, success, and longevity in various professions. [Preview Abstract] |
Wednesday, March 18, 2009 1:27PM - 1:39PM |
Q15.00012: Battles: Intelligent Army versus Insurgency Linda Shanahan, Surajit Sen A ``simple'' battle can be thought of as a conflict between two parties, each with finite reserves, and typically fought on one side’s territory. Modern battles are often strategic, based largely on the speed of information processing and decision making and are mission oriented rather than to annex new territory. Here, we analyze such battles using a simple model in which the ``blue'' army fights a {\bf strategic} battle against a ``red'' army that is well matched in combat power and in red’s territory. We assume that the blue army attacks strategically while the red army attempts to neutralize the enemy when in close enough proximity, implemented here as ``on- site,'' with randomly varying force levels to potentially confuse and drive the blue's strategies. The temporal evolution of the model battles incorporate randomness in the deployment of the reds and hence possess attendant history dependence. We show that minimizing risk exposure and making strategic moves based on local intelligence are often the deciding factors that determine the outcome of battles among well matched adversaries. [Preview Abstract] |
Wednesday, March 18, 2009 1:39PM - 1:51PM |
Q15.00013: Complete trails of social network evolution: The past 10 years of complex network research Deokjae Lee, Kwang-Il Goh, Byungnam Kahng, Doochul Kim During the last 10 years since the publication of pioneering papers on small-world and scale-free networks, more than 5,500 distinct researchers produced more than 4,000 research papers on complex networks, setting an unprecedented example in the history of science. Based on the dataset of published papers on complex networks during the years 1998--2007, here we study the complete evolution of the co-authorship network in network science. This dataset allows us to study the complete trail of social network evolution from the inception, in particular in the early transient stage, which has not been addressed empirically in previous studies. We find that distinct patterns in network topology emerge during the evolution: A fractal, tree-like giant cluster forms in the early stage through the cluster aggregation process, akin to the pattern near the percolation point, then followed by the entanglement process due to appearance of large-scale loops in later times. This evolution pattern is also observed in the co-authorship network on string theory. The giant cluster is found to be dynamic yet robust upon removal of obsolete inactive links, providing the core part underneath the further developed network. Finally, based on the empirical observations, we introduce a network evolution model, successfully reproducing the observed patterns. [Preview Abstract] |
Wednesday, March 18, 2009 1:51PM - 2:03PM |
Q15.00014: Statistical mechanics of image processing by digital halftoning Jun-ichi Inoue, Wataru Norimatsu, Yohei Saika, Masato Okada We consider the problem of digital halftoning (DH). The DH is an image processing representing each grayscale in images in terms of black and white dots, and it is achieved by making use of the threshold dither mask, namely, each pixel is determined as {\it black} if the grayscale pixel is greater than or equal to the mask value and as {\it white} vice versa. To determine the mask for a given grayscale image, we assume that human-eyes might recognize the BW dots as the corresponding grayscale by linear filters. Then, the Hamiltonian is constructed as a distance between the original and recognized images which is written in terms of the mask. Finding the ground state of the Hamiltonian via deterministic annealing, we obtain the optimal mask and the BW dots simultaneously. From the spectrum analysis, we find that the BW dots are desirable from the view point of human-eyes modulation properties. We also show that the lower bound of the mean square error for the inverse process of the DH is minimized on the Nishimori line which is well-known in the research field of spin glasses. [Preview Abstract] |
Wednesday, March 18, 2009 2:03PM - 2:15PM |
Q15.00015: Molecular Kinetic Analysis of a Finite-Time Carnot Heat Engine Yuki Izumida, Koji Okuda We show the first derivation of the efficiency at the maximum power for a finite-time Carnot heat engine of a weakly interacting gas which we can regard as a nearly ideal gas. Using this simple model, we check the celebrated Curzon-Ahlborn (CA) efficiency by performing the event-driven MD simulation as a numerical experiment for the first time[1,2]. This numerical experiment reveals that the CA efficiency is realized only in the limit of the small temperature difference $T_{\mathrm{c}}$ $\rightarrow$ $T_{\mathrm{h}}$ where $T_{\mathrm{h}}$ and $T_{\mathrm{c}}$ are the temperatures of the hot and cold heat reservoirs, respectively. Our molecular kinetic analysis can explain the numerical results theoretically. \newline[1] F. Curzon and B. Ahlborn, Am. J. Phys. \textbf{43}, 22 (1975). \newline[2] Y. Izumida and K. Okuda, Europhys. Lett. \textbf{83}, 60003 (2008). [Preview Abstract] |
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