Macroscopic Regime Research Articles

In Situ Transition of Amorphous Carbon to Graphite-like Structures Using MXene as a Template for Fast and Long-Lasting Macrosuperlubricity.

Achieving fast and long-lasting superlubricity in two-dimensional (2D) materials under high-stress conditions is challenging due to their susceptibility to structural deformations, limited load-bearing capacity, oxidation, and thermal degradation. This study introduces an innovative strategy by utilizing a composite of MXene and H-DLC, where, under high-stress conditions, H-DLC acts as a preferential energy-absorbing phase. MXene serves as a template to rapidly and continuously transform the absorbed energy into graphene-like structures, forming an in situ heterogeneous MXene/graphene-like interface. This process achieves long-lasting macroscopic superlubricity. Friction tests indicate that, under high-stress conditions (∼1.5 GPa Hertz pressure), the coefficient of friction (CoF) of the composite films rapidly decreases to macroscopic superluberic regimes of ∼0.003, with a friction lifespan more than ten times that of the original H-DLC films. In-depth experimental research and tribology-focused molecular dynamics simulations have shown that carbon atoms diffusing from decomposed H-DLC form graphene-like structures under high contact stress, which then evolve into MXene/graphene-like heterostructures. Molecular dynamics simulations reveal that the formation of this heterostructure involves a transition from sp3 to sp2 carbon structures, accompanied by significant energy absorption. Our research presents the lowest CoF achieved by MXene or MXene/H-DLC nanocomposite so far.

From Zipf to Price and beyond

Consider a society comprising n members that are ranked in a decreasing order of their personal wealths. For this society: Zipf’s Law manifests the case in which the members’ ranks and wealths display an inverse power-law relation; and Price’s Law manifests the case in which the n richest members possess, collectively, half of all the wealth. This paper goes from Zipf’s Law to Price’s Law and beyond, and it does so by introducing and exploring a novel Generalized Price’s Law (GPL): a general allometric scaling of the quantiles of rank distributions. Akin to multifractals, the GPL is governed by spectrums of powers. The GPL spectra are investigated, and are shown to be fractal objects: from a socioeconomic perspective, the spectra are power-law Lorenz curves that characterize poor fractality and rich fractality; from a probabilistic perspective, the spectra are characterized by Pareto statistics and by Lindy Laws. The intersection of Zipf’s Law and of the GPL is also investigated, and it is shown to be: (i) the phase transition between the two markedly different fractal regimes of the GPL spectra; (ii) the phase transition between two markedly different macroscopic regimes of Zipf’s Law; (iii) Price’s Law. Metaphorically, this paper establishes navigation directions in the space of rank distributions: how to get from the ‘Zipf street’ to the ‘Price junction’, from there to the new ‘GPL avenue’, and back.

Vacuum levitation and motion control on chip

By isolating from the environment and precisely controlling mesoscopic objects, levitation in vacuum has evolved into a versatile technique that has already benefited diverse scientific directions, from force sensing and thermodynamics to materials science and chemistry. It also holds great promise for advancing the study of quantum mechanics in the unexplored macroscopic regime. However, most current levitation platforms are complex and bulky. Recent efforts in miniaturization of vacuum levitation set-ups have comprised electrostatic and optical traps, but robustness is still a concern for integration into confined settings, such as cryostats or portable devices. Here we show levitation and motion control in high vacuum of a silica nanoparticle at the surface of a hybrid optical–electrostatic chip. By combining fibre-based optical trapping and sensitive position detection with cold damping through planar electrodes, we cool the particle motion to a few hundred phonons. We envisage that our fully integrated platform is the starting point for on-chip devices combining integrated photonics and nanophotonics with precisely engineered electric potentials, enhancing control over the particle motion towards complex state preparation and read-out.

Magnetic resonance insights into the heterogeneous, fractal-like kinetics of chemically recyclable polymers.

Moving toward a circular plastics economy is a vital aspect of global resource management. Chemical recycling of plastics ensures that high-value monomers can be recovered from depolymerized plastic waste, thus enabling circular manufacturing. However, to increase chemical recycling throughput in materials recovery facilities, the present understanding of polymer transport, diffusion, swelling, and heterogeneous deconstruction kinetics must be systematized to allow industrial-scale process design, spanning molecular to macroscopic regimes. To develop a framework for designing depolymerization processes, we examined acidolysis of circular polydiketoenamine elastomers. We used magnetic resonance to monitor spatially resolved observables in situ and then evaluated these data with a fractal method that treats nonlinear depolymerization kinetics. This approach delineated the roles played by network architecture and reaction medium on depolymerization outcomes, yielding parameters that facilitate comparisons between bulk processes. These streamlined methods to investigate polymer hydrolysis kinetics portend a general strategy for implementing chemical recycling on an industrial scale.

A stable and strongly ferromagnetic Fe17O10– cluster with an accordion-like structure

Isolated clusters are ideal systems for tailoring molecule-based magnets and investigating the evolution of magnetic order from microscopic to macroscopic regime. We have prepared pure Fen– (n = 7-31) clusters and observed their gas-collisional reactions with oxygen in a flow tube reactor. Interestingly, only the larger Fen– (n ≥ 15) clusters support the observation of O2-intake, while the smaller clusters Fen– (n = 7-14) are nearly nonreactive. What is more interesting is that Fe17O10– shows up with prominent abundance in the mass spectra indicative of its distinct inertness. In combination with DFT calculations, we unveil the stability of Fe17O10– within an interesting acordion-like structure and elucidate the spin accommodation in such a strongly ferromagnetic iron cluster oxide.

Application of a nanoindentation-based approach for parameter identification to a crystal plasticity model for bcc metals

The application of an inverse method for determining the parameters of a crystal plasticity constitutive law of a body-centered-cubic (BCC) single phase material is presented. Nanoindentation is used as the primary experimental input. An objective function, based on the deviation between the experimentally measured imprint and the simulated one, is minimized by a differential evolution algorithm to obtain the best fitting crystal plasticity parameters. To aid the identification procedure additional experimental data is used: the upper bounds and the ratios of the critical resolved shear stresses of the three slip plane families in BCC are estimated from micropillar compression experiments and used as a constraint in the optimization. The effect of the imposed constraints and the chosen strategy for mapping experimental to simulated displacements is presented and discussed. The validation of the method is done in the macroscopic regime by comparing an experimental tensile test with a simulated one using the obtained crystal plasticity parameters. Accurate results are achieved from two different indents. Therefore, the method is a promising path for determining crystal plasticity parameters in the case where a direct fitting from a macroscopic stress–strain curve is not possible, i.e. in the case of multi-phase materials.

Image-Enhanced Pseudo-Thermal Ghost Imaging with Hybrid Speckle Pattern

In this study, the influence of hybrid speckle patterns on the contrast-to-noise ratio (CNR) and resolution in pseudo-thermal ghost imaging (PGI) was examined based on the object dimensions in the macroscopic and microscopic regimes. This research shows that an enhanced scaling of the ghost image CNR and resolution from that of the hybrid speckle pattern was observed with the increase in speckle size for a macroscopic object, compared with the use of single-size speckle patterns. For microscopic objects, the hybrid speckle pattern also offered the advantage of retrieving ghost images even if the CNR followed the same trend as the resolution. These results were verified using two different slits with the same transmitted area. In addition, the numerical analysis revealed that the interference of the hybrid speckle pattern was the major factor for a better CNR. Based on these findings, the novel hybrid speckle pattern found in this research provides a possible way for future experiments in PGI to regulate hybrid speckle patterns to obtain a better ghost image quality.

Constructive role of shot noise in the collective dynamics of neural networks.

Finite-size effects may significantly influence the collective dynamics of large populations of neurons. Recently, we have shown that in globally coupled networks these effects can be interpreted as additional common noise term, the so-called shot noise, to the macroscopic dynamics unfolding in the thermodynamic limit. Here, we continue to explore the role of the shot noise in the collective dynamics of globally coupled neural networks. Namely, we study the noise-induced switching between different macroscopic regimes. We show that shot noise can turn attractors of the infinitely large network into metastable states whose lifetimes smoothly depend on the system parameters. A surprising effect is that the shot noise modifies the region where a certain macroscopic regime exists compared to the thermodynamic limit. This may be interpreted as a constructive role of the shot noise since a certain macroscopic state appears in a parameter region where it does not exist in an infinite network.

Population spiking and bursting in next-generation neural masses with spike-frequency adaptation.

Spike-frequency adaptation (SFA) is a fundamental neuronal mechanism taking into account the fatigue due to spike emissions and the consequent reduction of the firing activity. We have studied the effect of this adaptation mechanism on the macroscopic dynamics of excitatory and inhibitory networks of quadratic integrate-and-fire (QIF) neurons coupled via exponentially decaying post-synaptic potentials. In particular, we have studied the population activities by employing an exact mean-field reduction, which gives rise to next-generation neural mass models. This low-dimensional reduction allows for the derivation of bifurcation diagrams and the identification of the possible macroscopic regimes emerging both in a single and in two identically coupled neural masses. In single populations SFA favors the emergence of population bursts in excitatory networks, while it hinders tonic population spiking for inhibitory ones. The symmetric coupling of two neural masses, in absence of adaptation, leads to the emergence of macroscopic solutions with broken symmetry, namely, chimera-like solutions in the inhibitory case and antiphase population spikes in the excitatory one. The addition of SFA leads to new collective dynamical regimes exhibiting cross-frequency coupling (CFC) among the fast synaptic timescale and the slow adaptation one, ranging from antiphase slow-fast nested oscillations to symmetric and asymmetric bursting phenomena. The analysis of these CFC rhythms in the θ-γ range has revealed that a reduction of SFA leads to an increase of the θ frequency joined to a decrease of the γ one. This is analogous to what has been reported experimentally for the hippocampus and the olfactory cortex of rodents under cholinergic modulation, which is known to reduce SFA.

Functional central limit theorems for Wigner matrices

We consider the fluctuations of regular functions f of a Wigner matrix W viewed as an entire matrix f(W). Going beyond the well-studied tracial mode, Trf(W), which is equivalent to the customary linear statistics of eigenvalues, we show that Trf(W)A is asymptotically normal for any nontrivial bounded deterministic matrix A. We identify three different and asymptotically independent modes of this fluctuation, corresponding to the tracial part, the traceless diagonal part and the off-diagonal part of f(W) in the entire mesoscopic regime, where we find that the off-diagonal modes fluctuate on a much smaller scale than the tracial mode. As a main motivation to study CLT in such generality on small mesoscopic scales, we determine the fluctuations in the eigenstate thermalization hypothesis (Phys. Rev. A 43 (1991) 2046–2049), that is, prove that the eigenfunction overlaps with any deterministic matrix are asymptotically Gaussian after a small spectral averaging. Finally, in the macroscopic regime our result also generalizes (Zh. Mat. Fiz. Anal. Geom. 9 (2013) 536–581, 611, 615) to complex W and to all crossover ensembles in between. The main technical inputs are the recent multiresolvent local laws with traceless deterministic matrices from the companion paper (Comm. Math. Phys. 388 (2021) 1005–1048).

Odd-Even based asymptotic preserving scheme for a 2D stochastic kinetic–fluid model

A numerical approach to solve a new coupled stochastic kinetic–fluid model is proposed in this paper. The approach yields a stable numerical scheme in the hydrodynamic limit as the Knudsen number goes to zero along the transition from kinetic regime to macroscopic regime. The method is based on the Odd-Even decomposition of the kinetic stochastic chemotaxis–fluid model which leads to an implicit-explicit scheme based on a two steps splitting strategy. The method is numerically validated by various tests in two dimensional space.

Asymptotic shape of isolated magnetic domains

We investigate the energy of an isolated magnetized domainΩ⊂Rnforn=2,3. In non-dimensionalized variables, the energy given byE(Ω)=∫Rn|∇χΩ| dx+∫Rn|∇hΩ|2 dxpenalizes the interfacial area of the domain as well as the energy of the corresponding magnetostatic field. Here, the magnetostatic potentialhΩis determined byΔhΩ=∂1χΩ, corresponding to uniform magnetization within the domain. We consider the macroscopic regime|Ω|→∞, in which we derive compactness andΓ-limit which is formulated in terms of the cross-sectional area of the anisotropically rescaled configuration. We then give the solutions for the limit problems.

On the statistical properties of fluid flows with transitional power-law rheology in heterogeneous porous media

In this work, we study non-Newtonian fluid flow in heterogeneous porous media. We are interested in fluids presenting a specific change in rheology: Newtonian below a certain shear rate and power law above. Since porous media generally exhibit strong spatial heterogeneity at large geological scales, we study the interaction between such inhomogeneity and the nonlinear rheology of the fluid. The coupling between permeability heterogeneity and nonlinear rheology significantly affects the flow. We are particularly in the statistical properties of the velocity field (mean, variance, correlation, etc). Depending on the imposed mean pressure gradient, three macroscopic flow regimes are identified. For a low or high average pressure gradient, the average flow rate increases linearly or according to a power law, respectively. In the latter regime, we observe that the velocity field is more heterogeneous for shear-thinning fluids than for shear-thickening fluids. This is corresponding to a channeling effect of shear-thinning fluids. The intermediate regime corresponds to a progressive and inhomogeneous change of the local rheology. This transient regime is then characterized in terms of pressure gradient range. The flow field is also analyzed statistically. The spatial distribution of the regions above the rheology threshold shows interesting statistical properties. For instance, they exhibit multiscale characteristics (fractal), similar to other critical systems (percolation, avalanches, etc.). If the distribution of their area follows a power-law, the exponent is independent of the disorder. This suggests a kind of “universality” in this problem. More surprisingly, even though some statistical properties are independent of the parameters, an interesting abrupt rotation of the correlations is found for a particular set of parameters. This is explained by using some symmetries of the problem. • The flow of a non-Newtonian fluid in heterogeneous macroscopic porous media is studied. • If the rheology shows a change in behavior, a strong coupling between nonlinear rheology and heterogeneity is observed. • Three macroscopic flow regimes are observed. • The transient flow regime shows multiscale (fractal) properties that are independent of the parameters and the magnitude of the heterogeneity. • An abrupt change in the direction of correlation is also observed for a certain set of parameters.

Extraordinary optical transmission from a thin microcavity by macroscopic quantum effect

The macroscopic quantum effect is revealed to elaborate the extraordinary optical transmission (EOT) from a subwavelength thin microcavity based on the uncertainty property of the transmitted electromagnetic fields after the aperture. A critical radius is found in the thin microcavity under a certain incident electromagnetic wavelength. With the aperture radius varying, the transmitted field can be divided into three regimes: I) the macroscopic quantum regime when the aperture radius is less than the critical radius, in which the field edge effect occurs and the EOT phenomenon is perfectly manifested; II) the wave-particle duality regime in the vicinity of the critical radius, in which the edge effect and diffraction phenomenon exist simultaneously; III) the wave regime when the aperture radius is greater than the critical radius, in which the near-field diffraction emerges. In addition, the influences of incident wavelength and microcavity thickness on EOT are also investigated. Our research has potential applications in advanced optical devices, such as light switch and optical manipulations.

Bipartite Leggett-Garg and macroscopic Bell-inequality violations using cat states: Distinguishing weak and deterministic macroscopic realism

We consider tests of Leggett-Garg's macrorealism and of macroscopic local realism, where for spacelike separated measurements the assumption of macroscopic noninvasive measurability is justified by that of macroscopic Bell locality. We give a mapping between the Bell and Leggett-Garg experiments for microscopic qubits based on spin-$1/2$ eigenstates and gedanken experiments for macroscopic qubits based on two macroscopically distinct coherent states $|\ensuremath{\alpha}\ensuremath{\rangle}$ and $|\ensuremath{-}\ensuremath{\alpha}\ensuremath{\rangle}$ (as $\ensuremath{\alpha}\ensuremath{\rightarrow}\ensuremath{\infty}$). In this mapping, the unitary rotation ${U}_{\ensuremath{\theta}}$ of the Stern-Gerlach analyzer or polarizing beam splitter is realized by a local interaction $H=\mathrm{\ensuremath{\Omega}}{\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{n}}^{4}$ where $\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{n}$ is the number of quanta. By adjusting the time of interaction, one alters the measurement setting $\ensuremath{\theta}$. We thus predict violations of Leggett-Garg and Bell inequalities in a macroscopic regime where coarse-grained measurements $\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{M}$ need only discriminate between two macroscopically distinct coherent states. To interpret the violations, we distinguish between different definitions of macroscopic realism. Deterministic macroscopic local realism (dMR) assumes the system is in a state with a definite outcome ${\ensuremath{\lambda}}_{\ensuremath{\theta}}$ for the measurement $\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{M}$ prior to the unitary rotation ${U}_{\ensuremath{\theta}}$, and is negated by the violations. Weak macroscopic realism (wMR) assumes a definite outcome for systems prepared in a superposition ${\ensuremath{\psi}}_{\text{pointer}}$ of two macroscopically distinct eigenstates of $\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{M}$, after the unitary rotation ${U}_{\ensuremath{\theta}}$. We find that wMR can be viewed consistently with the violations and with the predictions of quantum mechanics for two tests of wMR. A model is presented in which wMR holds and the macroscopic violations emerge over the course of the unitary dynamics occurring at both sites. Implications for the realism of the micro-macro state generated during a quantum measurement are discussed. Finally, we point out an EPR-type paradox, which demonstrates inconsistency between wMR and the completeness of quantum mechanics at a microscopic level.

Dynamical synchronization of two Bosonic Josephson junctions induced by an external driving field in a double-cavity system

In this paper, we investigate the dynamical synchronization of atomic populations in two Bosonic Josephson junctions(BJJs). The two BJJs are placed in two optical cavities, respectively. When there is no coupling between the two optical cavities, the dynamical evolution of the two BJJs is independent, and they can be in macroscopic quantum self-trapping regime or Josephson oscillation regime by controlling the strength of the interatomic interactions, respectively. However, when there is a coupling between the two optical cavities, we can adjust an external driving field to a specific value so that the two BJJs are dynamically synchronized even though the parameters of the two subsystems are different. We also found that it is possible to control the transition of the BJJ from the Josephson oscillation regime to the macroscopic quantum self-trapping regime by controlling the strength of the external driving field.

A reactive transport modeling perspective on the dynamics of interface-coupled dissolution-precipitation

In interface coupled dissolution-precipitation systems, the dynamics of the mineral-fluid interface depends on two intertwining processes: the dissolution of the primary mineral that is needed for subsequent precipitation and the passivation of the dissolution reaction as a result of secondary mineral precipitation. The resulting thickness and texture of the precipitating coating layer will affect the progression of geochemical reactions, flow and transport processes at the macroscopic scale. Understanding the interplay between macroscopic flow regimes and microscopic reaction mechanisms (e.g., nucleation and crystal growth pathways) in controlling the dynamics of the mineral-fluid interface has important implications for predicting natural weathering processes, scaling in the subsurface energy production systems, etc. In this study, we use a micro-continuum pore-scale reactive transport model to investigate the feedback loop between reaction rate and solute transport with explicit consideration of the surface passivation and the diffusion process through the coating layer, as well as the impacts of saturation-dependent nucleation rate on the textures of precipitates that will largely dictate the diffusion properties of the coating layer. Our model results highlight that the drastically different coating behaviors at the macroscopic scale and their dependence on solution supersaturation observed in previous column experiments are primarily controlled by the interplay between mineral reaction rates, advective flow, and diffusion through the dynamically forming coating layer. The diffusion properties of the coating layer also play a secondary but non-negligible role in shaping the evolution of the co-dissolution and precipitation system. The probabilistic nucleation model building on the framework of classical nucleation theory highlights the complex dependence of precipitates’ texture on solution chemistry and substrate properties, which can affect the diffusion process within the precipitates. The modeling observations also underscore the necessity of further investigations to better characterize the properties of the coating layer and to improve modeling descriptions of the nucleation processes.

Enhanced microscopic dynamics in mucus gels under a mechanical load in the linear viscoelastic regime

Mucus is a biological gel covering the surface of several tissues and ensuring key biological functions, including as a protective barrier against dehydration, pathogen penetration, or gastric acids. Mucus biological functioning requires a finely tuned balance between solid-like and fluid-like mechanical response, ensured by reversible bonds between mucins, the glycoproteins that form the gel. In living organisms, mucus is subject to various kinds of mechanical stresses, e.g., due to osmosis, bacterial penetration, coughing, and gastric peristalsis. However, our knowledge of the effects of stress on mucus is still rudimentary and mostly limited to macroscopic rheological measurements, with no insight into the relevant microscopic mechanisms. Here, we run mechanical tests simultaneously to measurements of the microscopic dynamics of pig gastric mucus. Strikingly, we find that a modest shear stress, within the macroscopic rheological linear regime, dramatically enhances mucus reorganization at the microscopic level, as signaled by a transient acceleration of the microscopic dynamics, by up to 2 orders of magnitude. We rationalize these findings by proposing a simple, yet general, model for the dynamics of physical gels under strain and validate its assumptions through numerical simulations of spring networks. These results shed light on the rearrangement dynamics of mucus at the microscopic scale, with potential implications in phenomena ranging from mucus clearance to bacterial and drug penetration.

Bose\u2013Einstein condensate soliton qubit states for metrological applications

We propose a novel platform for quantum metrology based on qubit states of two Bose–Einstein condensate solitons, optically manipulated, trapped in a double-well potential, and coupled through nonlinear Josephson effect. We describe steady-state solutions in different scenarios and perform a phase space analysis in the terms of population imbalance—phase difference variables to demonstrate macroscopic quantum self-trapping regimes. Schrödinger-cat states, maximally path-entangled (N00N) states, and macroscopic soliton qubits are predicted and exploited to distinguish the obtained macroscopic states in the framework of binary (non-orthogonal) state discrimination problem. For an arbitrary frequency estimation we have revealed these macroscopic soliton states have a scaling up to the Heisenberg and super-Heisenberg (SH) limits within linear and nonlinear metrology procedures, respectively. The examples and numerical evaluations illustrate experimental feasibility of estimation with SH accuracy of angular frequency between the ground and first excited macroscopic states of the condensate in the presence of moderate losses, which opens new perspectives for current frequency standard technologies.

Mean-field models of populations of quadratic integrate-and-fire neurons with noise on the basis of the circular cumulant approach.

We develop a circular cumulant representation for the recurrent network of quadratic integrate-and-fire neurons subject to noise. The synaptic coupling is global or macroscopically equivalent to it. We assume a Lorentzian distribution of the parameter controlling whether the isolated individual neuron is periodically spiking or excitable. For the infinite chain of circular cumulant equations, a hierarchy of smallness is identified; on the basis of it, we truncate the chain and suggest several two-cumulant neural mass models. These models allow one to go beyond the Ott-Antonsen Ansatz and describe the effect of noise on hysteretic transitions between macroscopic regimes of a population with inhibitory coupling. The accuracy of two-cumulant models is analyzed in detail.