The role of the “Casimir force analogue” at the microscopic processes of crystallization and melting

Melting (crystallization), a phase transition from a crystalline solid to a liquid state, is a common phenomenon in nature. We suggest a new factor, “the Casimir force analogue”, to describe mechanisms of melting and crystallization. The Casimir force analogue is a force occurring between the surfaces of solid and liquid phases of metals caused by different energy density of phonons of these phases. It explains abrupt changes in geometry and thermodynamic parameters at a melting point. “The Casimir force analogue” helps to estimate latent melting heat and to gain an insight into a solid–liquid transition problem.     

Econophysical visualization of Adam Smith’s invisible hand

Consider a complex system whose macrostate is statistically observable, but yet whose operating mechanism is an unknown black-box. In this paper we address the problem of inferring, from the system’s macrostate statistics, the system’s intrinsic force yielding the observed statistics. The inference is established via two diametrically opposite approaches which result in the very same intrinsic force: a top-down approach based on the notion of entropy, and a bottom-up approach based on the notion of Langevin dynamics. The general results established are applied to the problem of visualizing the intrinsic socioeconomic force–Adam Smith’s invisible hand–shaping the distribution of wealth in human societies. Our analysis yields quantitative econophysical representations of figurative socioeconomic forces, quantitative definitions of “poor” and “rich”, and a quantitative characterization of the “poor-get-poorer” and the “rich-get-richer” phenomena.     

Community detection based on the “clumpiness” matrix in complex networks

The “clumpiness” matrix of a network is used to develop a method to identify its community structure. A “projection space” is constructed from the eigenvectors of the clumpiness matrix and a border line is defined using some kind of angular distance in this space. The community structure of the network is identified using this borderline and/or hierarchical clustering methods. The performance of our algorithm is tested on some computer-generated and real-world networks. The accuracy of the results is checked using normalized mutual information. The effect of community size heterogeneity on the accuracy of the method is also discussed.     

Structural modal excitation using travelling impulses—force frequency shifting

A review of existing hardware and methods for vibration testing of large structures is given by Koss and has shown that the size of inertial vibration shakers, to achieve a specific displacement, has to increase, as a structure becomes larger. In previous papers the concept of “force frequency shifting (ffs) for structural excitation”, was introduced to develop a more compact structural vibration exciter than is presently available for low frequencies. An ffs shaker operates at a frequency much greater than the natural frequency of the structure under test but generates a modal force at the lower frequency of the structure. This effect is accomplished by moving a vibrating force back and forth across the structure while the force is applied normally to its surface. For example, the generalized force generated by an ffs shaker at the fundamental structural frequency for a simply supported beam is given by 1.65Pr/l where P is the high frequency out of balance force, r is the throw amplitude and l is the beam length. The term that reduces the efficiency of force transfer from high to low frequencies is “r/l” as, usually, the length of a structure is much greater than the throw of the force. This paper introduces another force frequency shifting approach that allows r/l to be large. This is accomplished by placing force exciters along a structure-spatial array, spaced a distance ΔX apart, and each force exciter is activated for a short period of time to simulate a travelling force traversing the structure forwards and backwards. The “force throw r “can thus be made large. Results of simulations and experiments verify that force frequency shifting can be accomplished using travelling impulses and modal identification can be achieved.     

Saturation field direction dependence of domain structures in NiFe elements

The domain structures in NiFe elements were studied by magnetic force microscopy measurement and micromagnetic modeling. The remanent states in the elements were dependent on the direction of the saturation field. The “S” and “U” states were observed at remanence by applying the saturation field at different directions. The “S” and “U” states are metastable: magnetic force microscopy tip field-induced switching from the “S” and “U” states to the flux closure configuration was observed.     

“Antiferromagnetism” in social relations and Bonabeau model

We here present a fixed agents version of an original model of the emergence of hierarchies among social agents first introduced by Bonabeau et al. Having interactions occurring on a social network rather than among “walkers” does not drastically alter the dynamics. But it makes social structures more stable and give a clearer picture of the social organisation in a “mixed” regime, where finite ordered domains appear.     

AN INTELLIGENT TAP TEST AS AN INSPECTION TOOL FOR CORROSION IN CHEQUER PLATE FLOORS

The “coin-tap” test has the ability to indicate damage in a structural element due to a localized change of stiffness or damping. The change in vibration signature may be detected by ear or more precisely by measurement of the dynamic contact force. A method for discriminating between measurements made on sound and damaged structures is presented. An unsupervised neural network algorithm is used for recognizing the differences between contact force patterns. The method is used for non-destructive inspection of corrosion damage to steel chequer plate floors in industrial buildings. It is shown that the intelligent tap test is a useful and practical diagnostic tool for detecting localized damage in structures.     

Statistical dynamics of religion evolutions

A religion affiliation can be considered as a “degree of freedom” of an agent on the human genre network. A brief review is given on the state of the art in data analysis and modelization of religious “questions” in order to suggest and if possible initiate further research, after using a “statistical physics filter”. We present a discussion of the evolution of 18 so-called religions, as measured through their number of adherents between 1900 and 2000. Some emphasis is made on a few cases presenting a minimum or a maximum in the investigated time range—thereby suggesting a competitive ingredient to be considered, besides the well accepted “at birth” attachment effect. The importance of the “external field” is still stressed through an Avrami late stage crystal growth-like parameter. The observed features and some intuitive interpretations point to opinion based models with vector, rather than scalar, like agents.     

Comment on ‘An optimal algorithm for counting networks motifs’ [Physica A 381 (2007) 482-490]

Network motifs in a given network are small connected subnetworks that occur at significantly higher frequencies than would be expected for a random network. In their 2007 article “An optimal algorithm for counting network motifs”, Itzhack, Mogilevski, and Louzoun present an algorithm for detecting network motifs. Based on an experimental comparison with a motif detection software called FANMOD, they claim that their algorithm is “more than a thousand times faster” than any previous motif detection algorithm. We show that this claim is not correct and based on a significant flaw in the experimental setup. Once the experimental data of Itzhack et al. is corrected for this flaw, the implementation of their algorithm actually turns out to be a little slower than FANMOD for random Erd?s-Rényi graphs. For random scale-free networks, the implementation of Itzhack et al. is faster only by a factor of ∼1.5, not the orders of magnitude claimed by Itzhack et al.     

The multi-agent Parrondo’s model based on the network evolution

A multi-agent Parrondo’s model is proposed in the paper. The model includes link A based on the rewiring mechanism (the network evolution) + game B (dependent on the spatial neighbors). Moreover, to produce the paradoxical effect and analyze the “agitating” effect of the network evolution, the dynamic processes of the network evolution + game B are studied. The simulation results and the theoretical analysis both show that the network evolution can make game B which is losing produce the winning paradoxical effect. Furthermore, we obtain the parameter space where the strong or weak Parrondo’s paradox occurs. Each size of the region of the parameter space is larger than the one in the available multi-agent Parrondo’s model of game A + game B. This result shows that the “agitating” effect of rewiring based on the network evolution is better than that of the zero-sum game between individuals.     

Formation mechanism of “memory” phenomenon of microchannel plate image intensifier

A discrete resistance capacitance dynodes chain of channel multiplication model worked in a continuous variable dynode number described here is an attempt to explain the formation mechanism of “memory” phenomenon of microchannel plate image intensifier, wherein it was concluded conclusion that “memory” phenomenon of image intensifiers were the results of a silicon-rich layer, which existed between emission layer and conduction layer of channel inner wall of microchannel plate, having much higher resistance as compared with the conduction layer, and there are two distinct appearance ways of “negative memory” and “positive memory” only due to a difference in illumination and duration of the image intensifier suffered, and a strictly controlled MCP manufacture process would make considerable reduction of “memory” phenomenon occurrence ratio.     

A comment on the paper “Stochastic feedback, nonlinear families of Markov processes, and nonlinear Fokker-Planck equations” by T.D. Frank

The purpose of this comment is to correct mistaken assumptions and claims made in the paper “Stochastic feedback, nonlinear families of Markov processes, and nonlinear Fokker-Planck equations” by T. D. Frank [T.D. Frank, Stochastic feedback, non-linear families of Markov processes, and nonlinear Fokker-Planck equations, Physica A 331 (2004) 391]. Our comment centers on the claims of a “non-linear Markov process” and a “non-linear Fokker-Planck equation.” First, memory in transition densities is misidentified as a Markov process. Second, the paper assumes that one can derive a Fokker-Planck equation from a Chapman-Kolmogorov equation, but no proof was offered that a Chapman-Kolmogorov equation exists for the memory-dependent processes considered. A “non-linear Markov process” is claimed on the basis of a non-linear diffusion pde for a 1-point probability density. We show that, regardless of which initial value problem one may solve for the 1-point density, the resulting stochastic process, defined necessarily by the conditional probabilities (the transition probabilities), is either an ordinary linearly generated Markovian one, or else is a linearly generated non-Markovian process with memory. We provide explicit examples of diffusion coefficients that reflect both the Markovian and the memory-dependent cases. So there is neither a “non-linear Markov process”, nor a “non-linear Fokker-Planck equation” for a conditional probability density. The confusion rampant in the literature arises in part from labeling a non-linear diffusion equation for a 1-point probability density as “non-linear Fokker-Planck,” whereas neither a 1-point density nor an equation of motion for a 1-point density can define a stochastic process. In a closely related context, we point out that Borland misidentified a translation invariant 1-point probability density derived from a non-linear diffusion equation as a conditional probability density. Finally, in the Appendix A we present the theory of Fokker-Planck pdes and Chapman-Kolmogorov equations for stochastic processes with finite memory.     

A network of two-Chinese-character compound words in the Japanese language

Some statistical properties of a network of two-Chinese-character compound words in the Japanese language are reported. In this network, a node represents a Chinese character and an edge represents a two-Chinese-character compound word. It is found that this network has properties of being “small-world” and “scale-free”. A network formed by only Chinese characters for common use (joyo-kanji in Japanese), which is regarded as a subclass of the original network, also has the small-world property. However, a degree distribution of the network exhibits no clear power law. In order to reproduce the disappearance of the power-law property, a model for a selecting process of the Chinese characters for common use is proposed.     

In situ Video-STM study of the potential-induced (1 × 1) → “hex” transition on Au(1 0 0) electrode surfaces in Cl containing solution

The potential-induced (1 × 1) → “hex” transition on Au(1 0 0) electrodes in 0.01 M Na₂SO₄ + 1 mM HCl was studied by in situ scanning tunneling microscopy at high time resolution (Video-STM). According to these observations the elementary units of the “hex” surface reconstruction, hexagonally-ordered strings in the Au surface layer, are highly dynamic nanoscale objects. Isolated “hex” strings exhibit dynamic fluctuations in structure and position on the millisecond timescale. These fluctuations exceed the mobility of multistring “hex” domains by several orders of magnitude and can be explained by collective dynamic processes within the strings. Furthermore, the observations reveal a novel 1D mass transport mechanism along the strings, details on the nucleation and growth of “hex” strings and complex string restructuring processes, facilitating “hex” domain ripening.     

A planar electromagnetic “black hole” based on graphene

Graphene can be used as a platform for transformation-optics devices due to its tunability of conductivity. Besides conductivity, we show that the loss of graphene can also be controlled. Using this priority and taking the advantage of transformation optics, we realize the concept of electromagnetic “black hole” by using of a single-layer graphene. Numerical simulations demonstrate that the surface plasmon polariton waves incident to the “black hole” are bent towards the central area and absorbed by the inner core. The advantages of graphene-based “black hole” are its planar, isotropic, and nonmagnetic characteristics.     

Rich-club and page-club coefficients for directed graphs

Rich-club and page-club coefficients and their null models are introduced for directed graphs. Null models allow for a quantitative discussion of the rich-club and page-club phenomena. These coefficients are computed for four directed real-world networks: Arxiv High Energy Physics paper citation network, Web network (released from Google), Citation network among US Patents, and email network from a EU research institution. The results show a high correlation between rich-club and page-club ordering. For journal paper citation network, we identify both rich-club and page-club ordering, showing that “elite” papers are cited by other “elite” papers. Google web network shows partial rich-club and page-club ordering up to some point and then a narrow declining of the corresponding normalized coefficients, indicating the lack of rich-club ordering and the lack of page-club ordering, i.e. high in-degree (PageRank) pages purposely avoid sharing links with other high in-degree (PageRank) pages. For UC patents citation network, we identify page-club and rich-club ordering providing a conclusion that “elite” patents are cited by other “elite” patents. Finally, for email communication network we show lack of both rich-club and page-club ordering. We construct an example of synthetic network showing page-club ordering and the lack of rich-club ordering.     

Fronts and bumps in spatially extended Kuramoto networks

We consider moving fronts and stationary “bumps” in networks of non-locally coupled phase oscillators. Fronts connect regions of high local synchrony with regions of complete asynchrony, while bumps consist of spatially-localised regions of partially-synchronous oscillators surrounded by complete asynchrony. Using the Ott-Antonsen ansatz we derive non-local differential equations which describe the network dynamics in the continuum limit. Front and bump solutions of these equations are studied by either “freezing” them in a travelling coordinate frame or analysing them as homoclinic or heteroclinic orbits. Numerical continuation is used to determine parameter regions in which such solutions exist and are stable.     

Cat & Celeste: Gamma astronomy at thémis

Two independent sampling arrays, THEMISTOCLE and ASGAT, were installed in 1988 on the site of a former power solar, “Thémis”, in the french Pyrenees. Shortly after the discovery of the TeV gamma-ray emission from the Crab Nebula by the imaging telescope of the Whipple Observatory, the “Thémis” arrays confirmed these observations and extended them to higher energies. They are now interconnected with a new imaging telescope whose expected energy threshold is about 200 GeV. This last device is under commissioning at the time of this Symposium. The complete setup is named “CAT” for “Cherenkov Array at Thémis”. Furthermore, the overall Thémis solar plant will soon be reactivated as a γ-ray detector, most of its heliostats back to operation, a large secondary mirror taking the place of the solar furnace. This approved CELESTE project will represent a further step towards low energies, hopefully closing the gap between space and ground-based observations.     

Kohn’s theorem, Larmor’s equivalence principle and the Newton–Hooke group

We consider non-relativistic electrons, each of the same charge to mass ratio, moving in an external magnetic field with an interaction potential depending only on the mutual separations, possibly confined by a harmonic trapping potential. We show that the system admits a “relativity group” which is a one-parameter family of deformations of the standard Galilei group to the Newton–Hooke group which is a Wigner–?nönü contraction of the de Sitter group. This allows a group-theoretic interpretation of Kohn’s theorem and related results. Larmor’s theorem is used to show that the one-parameter family of deformations are all isomorphic. We study the “Eisenhart” or “lightlike” lift of the system, exhibiting it as a pp-wave. In the planar case, the Eisenhart lift is the Brdi?ka–Eardley–Nappi–Witten pp-wave solution of Einstein–Maxwell theory, which may also be regarded as a bi-invariant metric on the Cangemi–Jackiw group.