Sudden Rearrangement Research Articles

Nonlinear dynamics, avalanches, and noise for driven Wigner crystals

We consider the driven dynamics of Wigner crystals interacting with random disorder. Using numerical simulations, we find a rich variety of transport phenomena as a function of charge density, drive, and pinning strength. For weak pinning, the system forms a defect free crystal that depins elastically. When the pinning is stronger, a pinned glass phase appears that depins into a filamentary flow state, transitions at higher drives into a disordered flow phase, and finally forms a moving smectic. Within the filamentary flow phase, the conduction curves can show switching dynamics as well as negative differential conductivity in which switching events cause some flow channels to be blocked. The velocity noise in the filamentary flow regime exhibits narrow band characteristics due to the one-dimensional nature of the motion, while the moving smectic has narrow band velocity noise with a washboard frequency. In the disordered flow state, the noise power reaches a peak value and the noise has a $1/f$ character. Our transport results are consistent with recent experimental transport studies in systems where Wigner crystal states are believed to be occurring. Below the conduction threshold, we find that avalanches with a power law size distribution appear when there are sudden local rearrangements of charges from one pinned configuration to another.

Collisions of nonlinear waves in flexible mechanical metamaterials

Flexible mechanical metamaterials are compliant structures designed to achieve desired mechanical properties via large deformation or rotation of their components. While their static properties (such as Poisson’s ratio) have been studied extensively, much less work has been done on their dynamic properties, especially nonlinear dynamic properties induced by large movement of internal components. Here, we examine the nonlinear dynamic response arising from impact loading of mechanical materials that consist of 1D and 2D arrangements of rotating squares, which leads to formation of solitons. Permanent magnets are added to the squares, which causes the metamaterial to become multistable. Rotations of the squares can thereby lead to sudden rearrangements of squares into new phases. We experimentally and numerically characterize the collisions of solitons in these flexible mechanical metamaterials, which, depending on their amplitude and chirality, can induce a variety of responses, including phase transitions.

Revealing meso-structure dynamics in additive manufacturing of energy storage via operando coherent X-ray scattering

3D printing is an emerging technology for the fabrication of energy storage devices, offering advantages over traditional manufacturing methods. However, optimization and design of such devices requires an understanding of the meso‑structure formation during the 3D printing process. This study utilizes operando coherent X-ray scattering, X-ray Photon Correlation Spectroscopy (XPCS), to study the spatiotemporally-resolved far-from-equilibrium dynamics during direct ink writing 3D printing. Lithium Titanate (LTO) based ink is prepared and rheologically tested for its shear-thinning properties. Two-time intensity-intensity functions are calculated to be used in subsequent quantitative analysis, which allows for an overall characterization of the dynamics, description of an initial fast decorrelation and identification of sudden rearrangements of subdomains of the sample. The results show the dynamics to be anisotropic, spatiotemporally heterogenous and marked by distinct rearrangement events, all of which impact the electrochemical performance of energy storage devices. The studied 3D printing ink is used to fabricate electrodes which are then electrochemically tested, showing good performance in cycling and retaining structural integrity. This work furthers the understanding of the far-from-equilibrium material dynamics during 3D printing, giving quantitative characterization of this process, and highlights aspects of structure formation relevant to the electrochemical performance of the resultant energy storage device.

Oblique plate collision and orogenic translation of the Southern Apennines revealed by post-Messinian interregional unconformities in the Bradano Basin (Ionian Sea - Central Mediterranean)

The Bradano Basin is a foreland basin along the Africa/Eurasia plate boundary. Due to its location and physiography, between Southern Apennines (SA) and Calabrian Arc (CA), it represents a natural recorder of Plio-Pleistocene tectonic processes. Integrated analysis of seismic reflection data, exploration well logs and seafloor bathymetry allowed us to unravel the basin architecture and the interplay between tectonics and sedimentation, providing stratigraphic and structural evidences on deep processes and shallow morpho-structural development. It results, that the post-Messinian tectonic evolution on this area is marked by two major tectonic events, whose effects are recorded in four sedimentary sequences bounded by interregional unconformities. During Pliocene times, an obliquely convergent margin led to collision between SA and CA, associated with shelf to deep marine turbiditic deposits. Around the Pliocene-Pleistocene boundary (2.58 Ma), a sudden and widespread rearrangement took place. The SA front, along with portions of the earlier obliquely collisional margin, started to move toward the NE, along progressively deeper detachments involving the lower Apulia plate. During this phase, a fast (3.8–8.3 cm/yr) ~50 km translation of the orogenic wedge was followed by uplift and slow-rate shortening (1.9 mm/year), associated with seafloor folding. This second phase is marked by deep marine deposits in the central part of the basin, and clinoforms in shallower western and northern sectors. Our data suggest that no oceanic crust is presently subducting below the Bradano Basin, although we cannot exclude that a narrow sliver of oceanic lithosphere was subducted before and/or during Pliocene times. The complex deformation pattern observed, represents the response to the interaction of (small-) plates, which is still active and important to be considered in neotectonics and paleoseismological reconstructions.

How does static granular matter re-arrange for different isotropic strain rate?

The question of how soft granular matter, or dense amorphous systems, re-arrange their microstructure under isotropic compression and de-compression, at different strain rates, will be answered by particle simulations of frictionless model systems in a periodic three-dimensional cuboid. Starting compression below jamming, the systems experience the well known jamming transition, with characteristic evolutions of the state variables elastic energy, elastic stress, coordination number, and elastic moduli. For large strain rates, kinetic energy comes into play and the evolution is more dynamic. In contrast, at extremely slow deformation, the system relaxes to hyper-elastic states, with well-defined elastic moduli, in static equilibrium between irreversible (plastic) re-arrangement events, discrete in time. Small, finite strains explore those reversible (elastic) states, before larger strains push the system into new states, by irreversible, sudden re-arrangements of the micro-structure.

The effect of energy dissipation on the dynamic response of reinforced concrete structure

Solving problems associated with protecting buildings from progressive collapse and minimizing resources is becoming increasingly important. In many countries, ensuring such protection is set in accordance with the requirements of national regulatory documents and, therefore, researches aimed at developing effective ways to protect constructive systems from progressive collapse under special actions are relevant. In this regard, the present work presents studies of the influence of energy dissipation in constructive reinforced concrete elements during their sudden structural rearrangement caused by the removal of one of the supporting elements. The hysteretic dispersion accompanying the nonlinear load-unload cycle of the cross-section during crack formation is taken into account. The damping mechanism of reinforced concrete elements of the constructive system is described by the equivalent viscous damping model, based on the hypothesis of proportionality of the damping force and the oscillation velocity. Approbation of the calculated model is carried out in relation to the reinforced concrete frame structures, the physical models of which were tested under the considered loading regime. A comparison of the experimental and calculated parameters shows the effectiveness of the proposed model for assessing the dynamic response of reinforced concrete structures with cracks under the static-dynamic loading regime.

Organic acids under pressure: elastic properties, negative mechanical phenomena and pressure induced phase transitions in the lactic, maleic, succinic and citric acids

The behavior under pressure of the lactic, maleic, succinic and citric acids is studied using first principles methods. The four acids exhibit NLC effects due to the onset of pressure induced phase transitions or sudden structural rearrangements.

Avalanches driven by pressure gradients in a magnetized plasma

The results are presented for a basic heat transport experiment involving an off-axis heat source in which avalanche events occur. The configuration consists of a long, hollow, cylindrical region of elevated electron temperature embedded in a colder plasma, and far from the device walls [Van Compernolle et al. Phys. Rev. E 91, 031102(R) (2015)]. The avalanche events are identified as sudden rearrangements of the pressure profile following the growth of fluctuations from ambient noise. The intermittent collapses of the plasma pressure profile are associated with unstable drift-Alfvén waves and exhibit both radial and poloidal dynamics. After each collapse, the plasma enters a quiescent phase in which the pressure profile slowly recovers and steepens until a threshold is exceeded, and the process repeats. The use of reference probes as time markers allows for the visualization of the 2D spatio-temporal evolution of the avalanche events. Avalanches are observed only for a limited combination of heating powers and magnetic fields. At higher heating powers, the system transits from the avalanche regime into a regime dominated by sustained drift-Alfvén wave activity. This manuscript focuses on new results that illustrate the individual contributions to the avalanche process from density and temperature gradients in the presence of zero-order, sheared flows.

Analysis of Reaction Processes On the Basis of the Evolution of Dynamic Orbital Forces: Examples of Cycloadditions, SN2 Substitution, Nucleophilic Addition, and Hydrogen Transposition

The derivative of the energy of a canonical molecular orbital (MO) [or dynamical orbital forces (DOFs)] with respect to a bond length provides a reliable index of the bonding/antibonding character of this MO on this bond. The DOFs of selected MOs as a function of the reaction coordinate were computed for a panel of model reaction mechanisms: [2+4] (Diels-Alder) cycloaddition, [2+2] cycloaddition, second-order nucleophilic substitution (SN 2), nucleophilic addition to a carbonyl group, and [1,2] hydrogen transposition. The results highlight the nature of the reorganization of the main MOs and the stage of the reaction coordinate (RC) at which it occurs. For instance, in the Diels-Alder reaction, one can identify a part of the reaction that is dominated by repulsive four-electron interactions and another part dominated by attractive two-electron interactions. Also, the shape of the DOF as a function of the reaction coordinate reveals the existence of avoided MO crossings and their location on the RC. Even for spontaneous reactions with monotonic variation in the potential energy, extrema of the MO energy and sudden electron rearrangements can be put into evidence. This study provides quantitative support to classical MO analyses of reactivity such as correlation diagrams and frontier approximation.

High-gamma oscillations in the motor cortex during visuo-motor coordination: A tACS interferential study.

While the role of beta (∼20Hz), theta (∼5Hz) and alpha (∼10Hz) oscillations in the motor areas have been repeatedly associated with defined properties of motor performance, the investigation of gamma (∼40-90Hz) oscillatory activity is a more recent and still not fully understood component of motor control physiology, despite its potential clinical relevance for motor disorders. We have implemented an online neuromodulation paradigm based on transcranial alternating current stimulation (tACS) of the dominant motor cortex during a visuo-motor coordination task. This approach would allow a better understanding of the role of gamma activity, as well as that of other oscillatory bands, and their chronometry throughout the task. We tested the effects of 5Hz, 20Hz, 60Hz (mid-gamma) 80Hz (high-gamma) and sham tACS on the performance of a sample of right-handed healthy volunteers, during a custom-made unimanual tracking task addressing several randomly occurring components of visuo-motor coordination (i.e., constant velocity or acceleration pursuits, turns, loops). Data showed a significant enhancement of motor performance during high-gamma stimulation - as well as a trending effect for mid-gamma - with the effect being prominent between 200 and 500ms after rapid changes in tracking trajectory. No other effects during acceleration or steady pursuit were found. Our findings posit a role for high-frequency motor cortex gamma oscillations during complex visuo-motor tasks involving the sudden rearrangement of motor plan/execution. Such a "prokinetic" effect of high-gamma stimulation might be worth to be tested in motor disorders, like Parkinson's disease, where the switching between different motor programs is impaired.

Rapid ice flow rearrangement induced by subglacial drainage in West Antarctica

AbstractIce streams are corridors of rapid ice flow draining the ice sheets. They can exhibit astonishing spatial variability on annual to centennial time scales. We propose that changes in the subglacial drainage of meltwater could induce these sudden rearrangements of ice streams. We develop a two‐dimensional, thermomechanical model representing an ice stream cross section and couple it to a plastically deforming bed with spatially variable meltwater influx. We find that where ice flows over deformable sediments and lacks significant topographic control, the efficiency of subglacial water drainage exerts direct control on the velocity, location, and width of ice streams. This implies that meltwater percolation at the meter scale could have a significant effect on the short‐term variability in ice loss from a continental‐scale ice sheet. We verify our model against previous analytical results and validate it against surface observations from the Siple Coast of West Antarctica.

The Tangled Nature Model for organizational ecology

The Tangled Nature Model--a biologically inspired model of evolutionary ecology--is described, simulated, and analyzed to show its applicability in organization science and organizational ecology. It serves as a conceptual framework for understanding the dynamics in populations of organizations. A salient dynamical feature of this model is the spontaneous generation of a symbiotic group of core organizations. This core, consisting of several dominating species, introduces a mesoscopic level between that of the individual and the whole system. Despite prolonged periods of stability, this core is disrupted at random by parasitic interactions causing sudden core rearrangements. The size distribution of the core organizations is log-normal as predicted by theory and supported by empirical findings. As a simple application of the model, we study the adaptation of organizations to changes in resource availability in terms of population size, population diversity, and ecological efficiency. We find evidence that a temporary reduction in resources forces a consolidation resulting in a sustained increase in overall efficiency, suggesting that such reductions can be applied strategically to drive incremental improvements.

Whole-body hierarchical motion and force control for humanoid robots

Robots acting in human environments usually need to perform multiple motion and force tasks while respecting a set of constraints. When a physical contact with the environment is established, the newly activated force task or contact constraint may interfere with other tasks. The objective of this paper is to provide a control framework that can achieve real-time control of humanoid robots performing both strict and non strict prioritized motion and force tasks. It is a torque-based quasi-static control framework, which handles a dynamically changing task hierarchy with simultaneous priority transitions as well as activation or deactivation of tasks. A quadratic programming problem is solved to maintain desired task hierarchies, subject to constraints. A generalized projector is used to quantitatively regulate how much a task can influence or be influenced by other tasks through the modulation of a priority matrix. By the smooth variations of the priority matrix, sudden hierarchy rearrangements can be avoided to reduce the risk of instability. The effectiveness of this approach is demonstrated on both a simulated and a real humanoid robot.

The Tangled Nature Model for Organizational Ecology

The Tangled Nature Model, a biologically inspired model of evolutionary ecology, is described, simulated and analyzed to show its applicability in organization science and organizational ecology, both as a conceptual framework and as a tool for qualitative prediction about real organizations. We find that a symbiotic group of core organizations is generated, with the core disrupted at random by parasitic interactions causing sudden core rearrangements. This core is a spontaneously generated mesoscopic level of structure between the individual and whole system level. As a simple application of the model, we study the adaptation of organizations to changes in resource availability in terms of population size, population diversity, and ecological efficiency. We find evidence that a temporary reduction in resources forces a consolidation resulting in a sustained increase in overall efficiency, suggesting that such reductions can be applied strategically to drive incremental improvements.

Developing a model for neutron star oscillations following starquakes

Glitches -- sudden increases in spin rate -- are observed in many pulsars. One mechanism advanced to explain glitches in the youngest pulsars is that they are caused by a starquake, a sudden rearrangement of the crust of the neutron star. Starquakes have the potential to excite some of the oscillation modes of the neutron star, which means that they are of interest as a source of gravitational waves. These oscillations could also have an impact on radio emission. In this paper we make upper estimates of the amplitude of the oscillations produced by a starquake, and the corresponding gravitational wave emission. We then develop a more detailed framework for calculating the oscillations excited by the starquake, using a toy model of a solid, incompressible star where all strain is lost instantaneously from the star at the glitch. For this toy model, we give plots of the amplitudes of the modes excited, as the shear modulus and rotation rate of the star are varied. We find that for our specific model, the largest excitation is generally of a mode similar to the $f$-mode of an incompressible fluid star, but that other modes of the star are excited to a significant degree over small parameter ranges of the rotation rate.

Liquefaction of immersed granular media under isotropic compression

We report an observation of the spontaneous liquefaction of glass beads immersed in water and compacted by external isotropic stress. We show that during compression, loose granular samples exhibit a series of sudden rearrangements accompanied by a transient overpressure of interstitial fluid. Ultimately, spontaneous liquefaction with large deformation of the sample is observed. By contrast, denser samples do not show a liquefaction by maintaining its shape integrity. We then discuss the potential mechanisms which could explain this unexpected liquefaction.

Recent searches for gravitational-wave bursts associated with magnetar flares with LIGO, GEO, and Virgo

Energetic electromagnetic flares from magnetars - highly magnetized neutron stars - are associated with sudden rearrangements of the mechanical and/or magnetic configurations of the star, which can give rise to mechanical oscillations, some of which may be strong radiators of gravitational waves. General arguments have indicated that gravitational-wave bursts associated temporally with (giant) flares from galactic magnetars may be observable with ground-based gravitational wave detectors. After discussing the expectations based on the astrophysical models, we present results from several campaigns to search for such bursts using the first generation of LIGO, GEO, and Virgo detectors over the period 2005-2009, emphasizing the most recent results. No detections have been made, and we present astrophysically informed limits. Finally, we discuss prospects for progress.

Arctic Warming is Not Greenhouse Warming

After two thousand years of slow cooling Arctic, warming suddenly began more than a century ago. It has continued, with a break in the middle, until this day. The rapid start of this warming rules out the greenhouse effect as its cause. Apparently the time scale of the accumulation of CO2 in the air and the Arctic warming does not match. It is likely that the cause of this warming was a relatively sudden rearrangement of the North Atlantic current system at the turn of the century that directed warm currents into the Arctic Ocean. All observations of Arctic warming can be accounted for as consequences of these flows of warm water to the Arctic. This explains why all attempts to model Arctic warming have failed: Models set up for greenhouse warming are the wrong models for non-greenhouse warming. It turns out that satellites which have been measuring global temperature for the last 31 years cannot see any sign of current warming that supposedly started in the late seventies. This absence of warming in the satellite record is in accord with the observations of Ferenc Miskolczi on IR absorption by the atmosphere. What warming satellites do see is only a short spurt that began with the super El Nino of 1998, raised global temperature by a third of a degree in four years, and then stopped. It was of oceanic origin.

Polymer surfactant kinetics using surface plasmon resonance spectroscopy dodecyltrimethylammonium chloride/polyacrylic acid system

Kinetics of polymer surfactant interactions and the effect of surfactant binding on the conformational dynamics of the polymer were explored in this work using surface plasmon resonance spectroscopy. Polyacrylic acid was modified with thiol to varying degrees so as to force the polymer to form different loop sizes upon adsorption on the gold SPR sensor surface. Dodecyltrimethylammonium chloride in solution was flowed over the polymer-coated sensor surface and the binding was followed in real time. It was found that control of the loop size of the polymer on the solid surface enabled in turn the control of surfactant binding, with the largest loop allowing the maximum amount of surfactant to bind and vice versa. The kinetic plot of the binding showed three distinct segments. The first segment followed convective–diffusive kinetics. The second and third segments followed first-order kinetics with the second rate being significantly faster than the first one. Careful analysis of the second segment showed that it is possible to divide it into two different segments, each following a first-order kinetics, with the second rate being slightly slower than the first one suggesting a gradual slow down of the reaction due to convolution from the polymer conformational changes. Mechanistically, the sudden increase in the rate for the third segment of surfactant binding implies that the polymer matrix is opening up so as to incorporate more surfactant molecules. This was attributed to the formation of charged double surfactant species the repulsive interaction of which prevented the polymer network from imploding. Studies using unmodified polymers suggested the possibility of sudden conformational rearrangement in the polymer network, with progress in surfactant binding. Furthermore, the reflectance of the SPR spectrum was found to increase upon surfactant binding, implying that there is a decreased efficiency of coupling of the incident radiation into the surface plasmon mode of the metal, which suggests that the surfactant actually penetrated the polymer matrix.

Coronal holes and the solar polar field reversal

The relationship between the solar polar magnetic field reversal and coronal hole evolution is investigated for the time interval from 1996 to 2001. The distribution of coronal holes shows some evolutionary changes in relation to the polarity reversals, and these changes appear to be coordinated with changes in the global magnetic field structure, suggesting that the polar reversal originates from global processes. There are periods when the character of the coronal hole distribution on the solar disk changes significantly, indicating that the magnetic field structure changes. These can be interpreted as periods of rearrangement of the multipole magnetic field structure. It is found that the evolution of the geometric structure of the photospheric magnetic field during these periods is not characterized by a continuous transition from one dominant structure to another, but by relatively sudden rearrangement of the dominant geometrical structure of the magnetic field. These coronal holes and photospheric magnetic field rearrangements coincide with the polar photospheric magnetic field strength variations. The minimum phase of the solar cycle is dominated by the dipole component of the global solar magnetic field. The zonal magnetic field structure and zonal non-polar coronal hole distribution existed at that time. The sectorial magnetic field structure appears when the polar field strength reaches 0.7 of its maximum value in the corresponding hemisphere. This structure was established at dierent times in each hemisphere. In the north hemisphere it has existed since November 1998 and in the south hemisphere it has existed since October 1997. The rearrangement from one configuration to another occurs during a short time period, about 1 2 solar rotations. The coronal hole number and area evolution indicates a redistribution of positive-polarity and negative-polarity photospheric magnetic fields inside these longitudinal sectors, which reflects the solar polar field reversal.