Anomalous Fluctuations Research Articles

Persistent pre-seismic signature detected by means of Na-K-Mg geothermometry records in a saline spring of Vrancea area (Romania)

Abstract. A six year-long hydrochemical monitoring operation was conducted in Vrancea seismic zone (Romania), addressing a saline spring that proved to be suitable for Na-K-Mg geothermometry diagnosis. During the considered time-interval (2003–2009), only one important earthquake (mb=5.8) occurred in Vrancea region, this circumstance providing an unambiguous reference-moment between pre-seismic and post-seismic periods. On occurrence of that earthquake, an anomalous fluctuation of the Na-K temperature was detected – a result largely similar to previous ones recorded worldwide (California, southwest Egypt, northeast India). Yet such fluctuations may not necessarily be induced by earthquake-associated processes: they can occur also "routinely", possibly reflecting some environmental, meteorologically-induced "noise". It was therefore important to examine whether the variations observed in the data values could be plausibly related to a seismogenesis process. By additionally investigating (in a "scattterplot" diagram) the correlation between the Na-K temperatures and the values of a so-called "maturity index", a specific pattern emerged, with pre-seismic data-points plotting in a distinct domain of the diagram; moreover, those data-points appeared to describe a "drift away" pathway with respect to the remaining data-points "cluster", recorded during the subsequent 4 years of post-seismic monitoring. The "drift away" pattern persistently evolved for at least 18 months, ending just before the mb=5.8 earthquake and consequently suggesting the existence of some kind of long-term precursory phenomenon.

Stochastic Relaxation of the Contact Line of a Water Drop on a Solid Substrate Subjected to White Noise Vibration: Roles of Hysteresis

Relaxation of the three phase contact line of a sessile drop of water on a low energy surface is studied by subjecting it to a white noise vibration. While a spring force acts on the contact line whenever the contact angle deviates from its equilibrium value, it is opposed by hysteresis. The drop, therefore, remains pinned at a metastable state. With an appropriate amount of vibration, the drop can reach a global equilibrium state irrespective of its initial state, be it advanced or retreated. While the end state is free of hysteresis, the current study sheds light on the dynamics of relaxation that is analyzed in conjunction with a modified Langevin equation. Instead of exhibiting a smooth relaxation as predicted by the Langevin equation with a smooth background potential, stepwise relaxation is observed in most cases. These stepwise relaxations can be explained if the background potential is made slightly corrugated that signifies the existence of metastable states of a drop on a surface. The fluctuation of the displacement of the contact line is highly non-Gaussian. It is shown that an exponential distribution of the displacement fluctuation arises due to the nonlinear hysteresis term in the Langevin equation. The observations of stick-slip motion, the large time of relaxation, and the anomalous displacement fluctuation suggest that hysteresis is present during the relaxation process of the drop even though the final state reached by the drop is free of hysteresis. Finally, we compare the displacement fluctuations of the contact line on two different surfaces: a silicone rubber and a fluorocarbon monolayer. Although the displacement fluctuation is exponential in both cases, the later surface exhibits a greater variance of the distribution than the former plausibly due to differences in hysteresis. This result indicates that the fluctuation of displacement may be used as a tool to study the surface property of a low energy substrate.

Active Re-Modelling of Cortical Actin Regulates Spatiotemporal Organization of Molecules on a Living Cell Surface

Cell surface proteins such as lipid-tethered GPI-anchored proteins, Ras-proteins and several glycoproteins, are distributed as monomers and nanoclusters on the surface of living cells. The spatial distribution and dynamics of formation and breakup of these nanoclusters is unusual and controlled by the active remodeling dynamics of the underlying cortical actin (CA). To explain these results, we propose a novel mechanism of nanoclustering, based on the active hydrodynamics of the CA and its coupling to local membrane composition. In addition, our theory makes a falsifiable prediction -- GPI-APs must exhibit anomalous concentration fluctuations resembling those at criticality; we confirm this using a fluorescence-based assay. Our work addresses a central issue in cell biology, namely the nature of molecular organization and its spatiotemporal regulation on the plasma membrane.

Triplet Cooper pairing by spin fluctuations peculiar to non-centrosymmetric system

We study a mechanism of superconductivity in non-centrosymmetric systems like CePt3Si, where the spin-triplet superconducting state coexists with the spin-singlet one in principle, because of the lack of inversion symmetry. In the non-centrosymmetric system, anomalous spin fluctuations like spin fluctuation of off-diagonal spin indices also remain in addition to usual spin fluctuations. It is found that superconductivity appears around the magnetic phase, where the usual spin fluctuations induce spin-singlet superconductivity, while the anomalous spin fluctuations make spin-triplet one develop to stabilize the superconducting state.

Triplet Cooper Pair Formation by Anomalous Spin Fluctuations in Non-centrosymmetric Superconductors

A microscopic theory for the spin triplet Cooper pairing in non-centrosymmetric superconductors like CePt_3Si and CeTSi_3 (T=Rh, Ir) is presented. The lack of inversion symmetry leads to new anomalous spin fluctuations which stabilize the triplet part in addition to the singlet part originating from the centrosymmetric spin fluctuations. It is shown that both parts have similar nontrivial momentum dependence of A_1 type. Therefore the mixed singlet-triplet gap function has accidental line nodes on both Fermi surface sheets which are stable as function of temperature. This gap function explains the salient features of CePt_3Si and CeTSi_3 superconductors.

Anomalous fluctuation properties

We complement and extend our work on fluctuations arising in nonequilibrium systems in steady states driven by Lévy noise [H. Touchette and E. G. D. Cohen, Phys. Rev. E 76, 020101(R) (2007)]. As a concrete example, we consider a particle subjected to a drag force and a Lévy white noise with tail index mu epsilon (0,2), and calculate the probability distribution of the work done on the particle by the drag force, as well as the probability distribution of the work dissipated by the dragged particle in a nonequilibrium steady state. For 0<mu<2, both distributions satisfy what we call an anomalous fluctuation property characterized by positive and negative fluctuations that asymptotically have the same probability. For mu=2, by contrast, the work and dissipated work distributions satisfy the known conventional and extended fluctuation relations, respectively, which are both characterized by positive fluctuations that are exponentially more probable than negative fluctuations. The difference between these different fluctuation behaviors is discussed in the context of large deviation theory. Experiments that could probe or reveal an anomalous fluctuation property are also discussed.

Towards first-principles understanding of the metal–insulator transition in fluid alkalimetals

By treating the electron–ion interaction as a perturbation in the first-principles Hamiltonian, wehave calculated the density response functions of a fluid alkali metal to find an interesting chargeinstability due to anomalous electronic density fluctuations occurring at some finite wavevectorQ in a dilute fluid phase above the liquid–gas critical point. Since|Q| is smaller than the diameter of the Fermi surface, this instability necessarily impedes theelectric conduction, implying its close relevance to the metal–insulator transition in fluidalkali metals.

Effects of Tobin taxes in minority game markets

We show that the introduction of Tobin taxes in agent-based models of currency markets can lead to a reduction of both speculative trading and the magnitude of exchange rate fluctuations at intermediate tax rates. In this regime revenues obtained from speculators are maximal for the institutions acting as market makers. We here focus on minority game models of markets, which are accessible by exact techniques from statistical mechanics. Results are supported by computer simulations. Our findings suggest that at finite systems sizes the effect is most pronounced in a critical region around the phase transition of the infinite system, but much weaker if the market is operating far from criticality and does not exhibit anomalous fluctuations.

Study of self potential anomalous fluctuations in a seismic active zone of Lucano Apennine (southern Italy): recent results

Abstract. Geoelectrical fluctuations measured in seismic areas have been attributed to stress and strain changes, associated with earthquakes. The complex nature of this problem has suggested the development of monitoring stations in order to perform geophysical monitoring for a long time period and with a high sample rate. In this paper, anomalous geoelectrical fluctuations of SP signals recorded in the S. Loja basin, Lucano Apennine chain by Tito and Picerno stations, and linked with seismic activity, are analyzed and discussed.

Extreme events in bimodal systems

The extreme value statistics of systems possessing a two-hump probability density of the relevant variable, in which the left peak is more pronounced than the right one, is studied. It is shown that systems of this type display a nontrivial transient behavior in the form of anomalous fluctuations around the mean, for certain (finite) ranges of observational time windows. The results are illustrated on independent identically distributed random variables, systems possessing two locally stable states and subjected to additive white noise, and dynamical systems in the regime of deterministic chaos.

Weakly Non-Ergodic Statistical Physics

We find a general formula for the distribution of time averaged observables for weakly non-ergodic systems. Such type of ergodicity breaking is known to describe certain systems which exhibit anomalous fluctuations, e.g. blinking quantum dots and the sub-diffusive continuous time random walk model. When the fluctuations become normal we recover usual ergodic statistical mechanics. Examples of a particle undergoing fractional dynamics in a binding force field are worked out in detail. We briefly discuss possible physical applications in single particle experiments.

Properties of nonadiabatic quantum fluctuations of the strongly coupled electron-phonon systems

A new variational-ansatz of states of electrons and phonons was proposed on the basis of the Holstein model in strongly coupled electron-phonon systems for studying the influence of nonadiabatic phonon fluctuation, arising from the motion and density fluctuation of electrons, on the properties of ground state, uncertainty relation, stability of polarons, charge density wave (CDW) and phonon staggered ordering. The new ansatz represents the correlation among the displacement and squeezing states of phonons and polaron’s state of electrons as well as the squeezing-antisqueezing effect. The correlation and squeezing-antisqueezing effect result in the decrease of ground state energy, enhancement of stability of the systems, increase of binding energy of the polarons, weakening of the growing speed of polaron narrowing of the electron band, increase of the charge density wave order and suppression of the increased tendency of anomalous quantum fluctuation of the phonons in such a case, when compared with the uncorrelated case in the systems. The results obtained show that the ground state determined by the new state ansatz is most stable, thus the new ansatz describing the properties of the coupled electron phonon systems is very relevant and available, especially in strongly coupled and largely squeezed cases.

Backscattering enhancement analysis for targets in continuous random media based on wave polarization

Owing to the double passage effect, the phenomenon of backscattering enhancement arises in which the radar cross-section (RCS) in a random medium is twice that in free space. In a previous study, it was proved that the enhancement in radar cross-section (ERCS) deviates from two and has large and anomalous fluctuations, sometimes as a result of the wave polarization and other parameters, especially for targets in strong random media. Linear, including horizontal and vertical, polarizations were considered. In this paper, a numerical analysis is presented to show that the fluctuations can be reduced and make ERCS dependent almost only on the double passage effect under certain conditions. Therefore, we will have a better detection technique of targets of large sizes in continuous random media. In doing that, the linear and circular polarizations of incident waves are considered. We assume the case where a directly incident wave is produced by a line source in the far field distributed uniformly along the axis parallel to the conducting cylinder (target) axis.

Anomalous Fluctuations in Sliding Motion of Cytoskeletal Filaments Driven by Molecular Motors: Model Simulations

It has been found in in vitro experiments that cytoskeletal filaments driven by molecular motors show finite diffusion in sliding motion even in the long filament limit [Imafuku, Y. et al. Biophys. J. 1996, 70, 878-886. Noda, N. et al. Biophysics 2005, 1, 45-53]. This anomalous fluctuation can be evidence for cooperativity among the motors in action because fluctuation should be averaged out for a long filament if the action of each motor is independent. In order to understand the nature of the fluctuation in molecular motors, we perform numerical simulations and analyze velocity correlation in three existing models that are known to show some kind of cooperativity and/or large diffusion coefficient, i.e., the Sekimoto-Tawada model [Sekimoto, K.; Tawada, K. Phys. Rev. Lett. 1995, 75, 180], the Prost model [Prost, J. et al. Phys. Rev. Lett. 1994, 72, 2652], and the Duke model [Duke, T. Proc. Natl. Acad. Sci. U.S.A. 1999, 96, 2770]. It is shown that the Prost model and the Duke model do not give a finite diffusion in the long filament limit, in spite of the collective action of motors. On the other hand, the Sekimoto-Tawada model has been shown to give a diffusion coefficient that is independent of filament length, but it comes from the long time correlation whose time scale is proportional to filament length, and our simulations show that such a long correlation time conflicts with the experimental time scales. We conclude that none of the three models represent experimental findings. In order to explain the observed anomalous diffusion, we have to search for a mechanism that will allow both the amplitude and the time scale of the velocity correlation to be independent of the filament length.

On the correlation structure of some random point processes on the line

The correlation structure of some remarkable point processes on the one-dimensional real line is investigated. More specifically, focus is on translation invariant determinantal, permanental and/or renewal point processes. In some cases, anomalous (non-Poissonian) fluctuations for the number of points in a large window can be observed. This may be read from the total correlation function of the point process. We try to understand when and why this occurs and what are the anomalous behaviors to be expected. From examples, it is shown that determinantal (fermion) point processes can be super-homogeneous (the number variance grows slower than the number mean) and even hyper-uniform (when variance growth saturates). Renewal point processes with bounded spacings variance are essentially Poissonian (the number variance grows like the number mean as in Poisson models). Under certain conditions, permanental (boson) point processes can be sub-homogeneous or critical (in the sense that the number variance grows faster than the number mean). We give several detailed examples illustrating these properties of interest together with unexpected behaviors.

Mechanisms for the Interannual Variability in the Tropical Indian Ocean. Part I: The Role of Remote Forcing from the Tropical Pacific

Abstract A series of experiments are conducted using a coupled ocean–atmosphere general circulation model in regional coupled mode, which permits active air–sea interaction only within the Indian Ocean to the north of 30°S, with sea surface temperatures (SSTs) prescribed over the rest of the world oceans. In this paper, an ensemble of nine simulations has been analyzed with the observed SST anomalies for 1950–98 prescribed over the uncoupled region. The purpose of this study is to determine the major patterns of interannual variability in the tropical Indian Ocean that could be related to the global low-frequency fluctuations and to understand the physical links between the remote forcing and the regional coupled variations. The ensemble coupled simulations with prescribed SST outside the Indian Ocean are able to reproduce a considerable amount of observed variability in the tropical Indian Ocean during 1950–98. The first EOF modes of the simulated upper-ocean heat content and SST anomalies show structures that are quite consistent with those from the historical upper oceanic temperature and SST analyses. The dominant pattern of response is associated with an oceanic dynamical adjustment of the thermocline depth in the southwestern Indian Ocean. In general, a deepening of the thermocline in the southwest is usually accompanied by the enhanced upwelling and thermocline shoaling centered near the Sumatra coast. Further analysis shows that the leading external forcing is from the El Niño–Southern Oscillation (ENSO), which induces an anomalous fluctuation of the atmospheric anticyclones on both sides of the equator over the Indian Ocean, starting from the evolving stage of an El Niño event in boreal summer. Apart from weakening the Indian monsoon, the surface equatorial easterly anomalies associated with this circulation pattern first induce equatorial and coastal upwelling anomalies near the Sumatra coast from summer to fall, which enhance the equatorial zonal SST gradient and stimulate intense air–sea feedback in the equatorial ocean. Moreover, the persistent anticyclonic wind curl over the southern tropical Indian Ocean, reinforced by the equatorial air–sea coupling, forces substantial thermocline change centered at the thermocline ridge in the southwestern Indian Ocean for seasons. The significant thermocline change has profound and long-lasting influences on the SST fluctuations in the Indian Ocean. It should be noted that the ENSO forcing is not the only way that this kind of basinwide Indian Ocean fluctuations can be generated. As will be shown in the second part of this study, similar low-frequency fluctuations can also be generated by processes within the Indian and western Pacific region without ENSO influence. The unique feature of the ENSO influence is that, because of the high persistence of the atmospheric remote forcing from boreal summer to winter, the life span of the thermocline anomalies in the southwestern Indian Ocean is generally longer than that generated by regional coupled processes.

NMR studies of the partially disordered state in a triangular antiferromagnetUNi4B

A triangular antiferromagnet UNi4B experiences a partially disordered state, in which two-thirds of U 5f moments order in a vertex-likestructure and one-third of U 5f moments remain paramagnetic. Magnetization and NMR measurementsof UNi4B have been performed to study the dynamical properties of U magnetic momentsin the partially disordered state. The value of the effective moment aboveTN derived from the fitting of the Curie–Weiss law suggests a significant crystal fieldsplitting and the Kondo effect. The Weiss temperature was also estimated to be−28 K, which suggests that the exchange interaction is antiferromagnetic.Furthermore, the exchange interaction estimated from the relaxation rateT1−1 above 50 K is 18 K, which is close to the Weiss temperature. These results suggest that the dominantinteractions between U moments are antiferromagnetic in the basal plane. The relaxation rateT1−1 decreasesabruptly below TN down to 15 K and is almost constant between 10 and 15 K. In the sametemperature range, the magnetic susceptibility still increases withdecreasing temperature. However, the effective moment estimated belowTN is almost the sameas that above TN. This shows that there are anomalous fluctuations belowTN which cannot be explained by the simple model.

Nonlinear electronic transport and anomalous resistance fluctuations in the stripe state ofLa2NiO4.14

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THE ROLE OF GEOGRAPHY AND TRAFFIC IN THE STRUCTURE OF COMPLEX NETWORKS

We report a study of the correlations among topological, weighted and spatial properties of large infrastructure networks. We review the empirical results obtained for the air-transportation infrastructure that motivates a network modeling approach which integrates the various attributes of this network. In particular, we describe a class of models which include a weight-topology coupling and the introduction of geographical attributes during the network evolution. The inclusion of spatial features is able to capture the appearance of non-trivial correlations between the traffic flows, the connectivity pattern and the actual distances of vertices. The anomalous fluctuations in the betweenness-degree correlation function observed in empirical studies are also recovered in the model. The presented results suggest that the interplay between topology, weights and geographical constraints is a key ingredient in order to understand the structure and evolution of many real-world networks.

Magnetic Potassium Clusters in a Nanographite Host System

The magnetism and structure for potassium clusters physisorbed in nanographite-based nanoporous host are investigated. Potassium clusters are subjected to a slight charge transfer to a host nanographite and modify the magnetism of the edge-state spins of nanographite. The localized spins of 4s electrons in the potassium cluster interact with each other through a strong antiferromagnetic interaction. Finite size effect and structural disorder around the cluster surface are responsible for anomalous spin fluctuations in the magnetism.