Anisotropic-Isotropic Transition of Cages at the Glass Transition.

Characterizing the local structural evolution is an essential step in understanding the nature of glass transition. In this work, we probe the evolution of Voronoi cell geometry in simple glass models by simulations and colloid experiments, and find that the individual particle cages deform anisotropically in supercooled liquid and isotropically in glass. We introduce an anisotropy parameter k for each Voronoi cell, whose mean value exhibits a sharp change at the mode-coupling glass transition ϕ_{c}. Moreover, a power law of packing fraction ϕ∝q_{1}^{d} is discovered in the supercooled liquid regime with d>D, in contrast to d=D in the glass regime, where q_{1} is the first peak position of structure factor, and D is the space dimension. This power law is qualitatively explained by the change of k. The active motions in supercooled liquid are spatially correlated with long axes rather than short axes of Voronoi cells. In addition, the dynamic slowing down approaching the glass transition can be well characterized through a modified free-volume model based on k. These findings reveal that the structural parameter k is effective in identifying the structure-dynamics correlations and the glass transition in these systems.

Chiral active particles are sensitive reporters to environmental geometry.

Chiral active particles (CAPs) are self-propelling particles that break time-reversal symmetry by orbiting or spinning, leading to intriguing behaviors. Here, we examined the dynamics of CAPs moving in 2D lattices of disk obstacles through active Brownian dynamics simulations and granular experiments with grass seeds. We find that the effective diffusivity of the CAPs is sensitive to the structure of the obstacle lattice, a feature absent in achiral active particles. We further studied the transport of CAPs in obstacle arrays under an external field and found a reentrant directional locking effect, which can be used to sort CAPs with different activities. Finally, we demonstrated that parallelogram lattices of obstacles without mirror symmetry can separate clockwise and counter-clockwise CAPs. The mechanisms of the above three novel phenomena are qualitatively explained. As such, our work provides a basis for designing chirality-based tools for single-cell diagnosis and separation, and active particle-based environmental sensors.

Depressive disorder benefits of cities: Evidence from the China.

BACKGROUND: Rapid urbanization is a major trend in global population migration. There is growing debate about whether this urban-rural disparity exacerbate depression at the individual level. This study aims to investigate how urban living has a beneficial impact on individual mental health. METHODS: Based on the data of 15,764 participants in the 2018 China Health and Retirement Longitudinal Study (CHARLS), we perform analysis of variance to identify the gap in depression levels between urban and rural areas. Extensive comparisons and detailed statistical analyses are carried out to demonstrate the differences in social participation between urban and rural residents. Finally, we conduct a series of mediation and moderation analyses to reveal the underlying mechanisms of depressive disorder benefits of cities. RESULTS: The results indicate that those who lived in urban areas were less likely to suffer from depression (ß = -1.461, 95 % CI = [-1.691, -1.235], p < 0.001). Social engagement is found to mediate the relationship between residence type (ß = 0.164, 95 % CI = [0.136, 0.193], p < 0.001) and individual depression (ß = -0.462, 95 % CI = [-0.587, -0.337], p < 0.001). City size plays a moderating role in the association between urban living and social engagement. LIMITATIONS: The mechanism is conducted through cross-sectional data. Self-reported depression status is accessed in this study, which could lead to measurement error. CONCLUSION: This study demonstrates the beneficial effects of urban living on individual depression, and reveals the mechanism by which urbanization at different scales affects the prevalence of depression.

Two modes of motions for a single disk on the vibration stage.

The motion of a single granular particle is important for understanding their collective motions on vibration stage, but it remains poorly studied for simple shaped particles, such as a disk. Here, we systematically measure the motions of a single disk with different vibration amplitudesAat a fixed vibration frequencyfor a fixed accelerationa. The distributions, time-correlations, and power spectra of displacements per step, mean squared displacements and couplings for translational and rotational motions are measured. These analyses reveal that the motions randomly switch between active and inactive modes. Bothaandfare important to particle's motions and the fraction of active mode. The translational and rotational kinetic energy deviates from Boltzmann distribution and violates the equipartition theorem in each mode. We find three types of motion: rolling, lying flat, and fluttering, which give rise to active and inactive modes. The translational and rotational mean squared displacements, autocorrelations, and power spectra at differentacollapse in active modes, because the disk rolls along its rim with a fixed inclination angle though our system is under vibration and confinement. The nonzero cross-correlations between particle's translational and rotational motions indicate that only translational motions are insufficient for understanding dense particle systems.

In situ observation of coalescence of nuclei in colloidal crystal-crystal transitions.

Coalescence of nuclei in phase transitions significantly influences the transition rate and the properties of product materials, but these processes occur rapidly and are difficult to observe at the microscopic scale. Here, we directly image the coalescence of nuclei with single particle resolution during the crystal-crystal transition from a multilayer square to triangular lattices. The coalescence process exhibits three similar stages across a variety of scenarios: coupled growth of two nuclei, their attachment, and relaxation of the coalesced nucleus. The kinetics vary with nucleus size, interface, and lattice orientation; the kinetics include acceleration of nucleus growth, small nucleus liquefaction, and generation/annihilation of defects. Related mechanisms, such as strain induced by nucleus growth and the lower energy of liquid-crystal versus crystal-crystal interfaces, appear to be common to both atomic and colloidal crystals.

Economic development, weak ties, and depression: Evidence from China.

OBJECTIVES: Weak ties are becoming mainstream in daily relationships and play an essential role in the improvement of individuals' mental health. Despite growing concerns on depression, inclusion of weak ties is limited. To address the gap, this study empirically shed light on the role of weak ties on individual depression in the context of economic development. METHOD: A cross-sectional study was conducted based on 2018 China Health and Retirement Longitudinal Study (CHARLS) with a sample of 16,545 individuals. A moderated mediation model is constructed to evaluate the impact of economic development (GDP) on the degrees of depression, the mediating effect of weak ties, and the moderating effect of residents' residence types (living in urban or rural areas). RESULTS: Economic development exerts a significant direct impact on depression (ß=-1.027, p<0.001). Weak ties are significantly negatively correlated with depression (ß=-0.574, p<0.001), and act as a mediator between economic development and local individual depression. In addition, the residence type plays a moderating role between economic development and weak ties (ß=0.193, p<0.001). That is, living in urban areas would introduce the higher the level of weak ties. CONCLUSIONS: Higher economic development is largely conducive to alleviating the degrees of depression, weak ties play a mediating role between economic development and depression, and residence types exert a positive moderating effect on the economic development and weak ties.

Surface premelting and melting of colloidal glasses.

The nature of liquid-to-glass transition is a major puzzle in science. A similar challenge exists in glass-to-liquid transition, i.e., glass melting, especially for the poorly investigated surface effects. Here, we assemble colloidal glasses by vapor deposition and melt them by tuning particle attractions. The structural and dynamic parameters saturate at different depths, which define a surface liquid layer and an intermediate glassy layer. The power-law growth of both layers and melting front behaviors at different heating rates are similar to crystal premelting and melting, suggesting that premelting and melting can be generalized to amorphous solids. The measured single-particle kinetics reveal various features and confirm theoretical predictions for glass surface layer.

A dataset on corporate sustainability disclosure.

Enterprises, as key emitters, play a vital role in promoting sustainable development. Corporate sustainability disclosure provides a key channel for stakeholders to gain insights into a company's sustainability progress. However, few studies have been conducted to measure sustainability disclosure at the firm level. In this study, we apply the machine learning techniques to listed companies' management discussion and analysis (MD&A) documents and construct a dataset on corporate sustainability disclosure, including the Corporate Sustainability Disclosure Index (CSDI), CSDI_Economic Dimension (CSDI_ECO), CSDI_Environmental Dimension (CSDI_ENV), and CSDI_Social Dimension (CSDI_SOCI). The dataset will be updated annually. To the best of our knowledge, this is the first sustainability disclosure dataset constructed at the firm level. Our dataset reflects corporate managements' sustainability attitudes and promotes the implementation of corporate sustainability strategies and subsequent sustainable economic and social outcomes.

Morphologies and dynamics of free surfaces of crystals composed of active particles.

Active matter exhibits various collective motions and nonequilibrium phases, such as crystals; however, their surface properties have been poorly explored. Here, we use Brownian dynamics simulations to investigate the surface morphology and dynamics of two-dimensional active crystals during and after growth. For crystal growth on a substrate, the position and roughness of the crystal surface reach steady states at different times. In the steady state, the surface exhibits superdiffusive behaviour at the short time, and the roughness is insensitive to the roughening process and particle activity. We observe two-stage and three-stage surface roughening at different Péclet numbers. The result of dynamic scaling analysis shows that the surface is similar to anomalous roughening, which is distinct from the normal roughening typically found in conventional passive systems. Capillary wave theory for a thermal equilibrium system can describe the active surface fluctuations only in the long-wavelength regime, indicating that active particles mainly drive the surface out of equilibrium locally. These similarities and differences between the active and passive crystal surfaces are essential for understanding active crystals and interfaces.

Association between periprocedural myocardial injury and long-term all-cause mortality in patients undergoing transcatheter aortic valve replacement: a systematic review and meta-analysis.

Objective. The purpose of this meta-analysis was to investigate the effect of periprocedural myocardial injury (PPMI) on long-term all-cause mortality in patients undergoing transcatheter aortic valve replacement (TAVR) and to explore potential factors associated with mortality risk. Design. The PubMed, Embase, and Cochrane Library databases were searched up to April 2022. Studies reporting the effect of PPMI on the risk of long-term all-cause mortality were included. The summary odds ratio (OR) was calculated using a random effects model. Additionally, meta-regression and subgroup analyses were conducted according to specific research characteristics to explore sources of heterogeneity. Results. Fourteen studies involving 6,415 patients who underwent TAVR showed that the occurrence of PPMI was associated with a higher risk of long-term mortality. Subgroup analysis showed that in the group of aged ≥82 years, men accounted for less than 50%, coronary artery disease patients accounted for more than 50%, and the proportion of patients with chronic kidney disease accounted for more than 60%, the proportion of patients with atria fibrillation accounted for less than 30%, and the Society of Thoracic Surgeons predicted risk of mortality score was >8 points, patients with PPMI had higher long-term all-cause mortality than those without PPMI. Conclusions. Among the patients who underwent TAVR, those who developed PPMI had higher long-term all-cause mortality.

Internal-stress-induced solid-solid transition involving orientational domains of anisotropic particles.

Colloidal particles with anisotropic interaction, such as Janus particles, are important model systems for anisotropic atoms and molecules. Janus particles in a single crystal can rotate collectively and form polycrystalline orientational domains as the temperature increases, while the lattice structure in the translational degree of freedom is preserved. Such an unusual solid-solid transition preserves the long-range translational order but loses the orientational order, and its mechanism is unclear. We find that the transition is induced by internal strains and the orientation-position coupling plays an essential role in the transition. We explain the mechanism using the anisotropic elasticity theory and derive the transition condition and the directions of the domain boundaries by analyzing the strain energy and the stress. The results of the molecular dynamics simulation are consistent with the theoretical analysis. Such a transition mechanism can exist in other anisotropic particle systems.

Morphologies and dynamics of the interfaces between active and passive phases.

Active matters exhibit interesting collective behaviors and novel phases, which provide an important platform for the study of nonequilibrium physics. Mixtures of active and passive particles have been intensively studied in motility-induced phase separation, but the morphology of the active-passive interface has been poorly explored. In this work, we investigate the interface morphology in two-dimensional mixtures of active and passive particles using Brownian dynamics simulations. By systematically changing the Péclet number (Pe) and area fraction (ρ), we obtain the phase diagram of the active-passive interface, including rough sharp, rough invasive and flat interdiffusive interfaces. For a sharp interface, dynamic scaling analysis in the propagation stage shows that the roughness exponent α, the growth exponent ß, the time exponent κ, and the dynamic exponent z satisfy z = α/(ß - κ). Such anomalous scaling indicates that the roughening behavior does not belong to the conventional universality classes with Family-Vicsek scaling for the growth of passive interfaces. On the other hand, the interface in the middle-wavelength regime during the morphology relaxation stage can be described by capillary wave theory. The mean interface position propagates with time as t1/2, which is robust at different ρ and Pe values in the propagation stage and exhibits superdiffusion in the morphology relaxation stage. These similarities and differences between the active-inactive interfaces and passive interfaces cast light on the interfacial growth of active matter.

Mean-field model of melting in superheated crystals based on a single experimentally measurable order parameter.

Melting is one of the most studied phase transitions important for atomic, molecular, colloidal, and protein systems. However, there is currently no microscopic experimentally accessible criteria that can be used to reliably track a system evolution across the transition, while providing insights into melting nucleation and melting front evolution. To address this, we developed a theoretical mean-field framework with the normalised mean-square displacement between particles in neighbouring Voronoi cells serving as the local order parameter, measurable experimentally. We tested the framework in a number of colloidal and in silico particle-resolved experiments against systems with significantly different (Brownian and Newtonian) dynamic regimes and found that it provides excellent description of system evolution across melting point. This new approach suggests a broad scope for application in diverse areas of science from materials through to biology and beyond. Consequently, the results of this work provide a new guidance for nucleation theory of melting and are of broad interest in condensed matter, chemical physics, physical chemistry, materials science, and soft matter.

Dynamics of a vibration-driven single disk.

Granular particles exhibit rich collective behaviors on vibration beds, but the motion of an isolated particle is not well understood even for uniform particles with a simple shape such as disks or spheres. Here we measured the motion of a single disk confined to a quasi-two-dimensional horizontal box on a vertically vibrating stage. The translational displacements obey compressed exponential distributions whose exponent [Formula: see text] increases with the frequency, while the rotational displacements exhibit unimodal distributions at low frequencies and bimodal distributions at high frequencies. During short time intervals, the translational displacements are subdiffusive and negatively correlated, while the rotational displacements are superdiffusive and positively correlated. After prolonged periods, the rotational displacements become diffusive and their correlations decay to zero. Both the rotational and the translational displacements exhibit white noise at low frequencies, and blue noise for translational motions and Brownian noise for rotational motions at high frequencies. The translational kinetic energy obeys Boltzmann distribution while the rotational kinetic energy deviates from it. Most energy is distributed in translational motions at low frequencies and in rotational motions at high frequencies, which violates the equipartition theorem. Translational and rotational motions are not correlated. These experimental results show that the random diffusion of such driven particles is distinct from thermal motion in both the translational and rotational degrees of freedom, which poses new challenges to theory. The results cast new light on the motion of individual particles and the collective motion of driven granular particles.

Translational and rotational critical-like behaviors in the glass transition of colloidal ellipsoid monolayers.

Critical-like behaviors have been found in translational degrees of freedom near the glass transition of spherical particle systems mainly with local polycrystalline structures, but it is not clear if criticality exists in more general glassy systems composed of nonspherical particles without crystalline structures. Here, through experiments and simulations, we show critical-like behaviors in both translational and rotational degrees of freedom in monolayers of monodisperse colloidal ellipsoids in the absence of crystalline orders. We find rich features of the Ising-like criticality in structure and slow dynamics at the ideal glass transition point ϕ0, showing the thermodynamic nature of glass transition at ϕ0 A dynamic criticality is found at the mode-coupling critical point ϕc for the fast-moving clusters whose critical exponents increase linearly with fragility, reflecting a dynamic glass transition. These results cast light on the glass transition and explain the mystery that the dynamic correlation lengths diverge at two different temperatures.

Surface roughening, premelting and melting of monolayer and bilayer crystals.

Dimensionality often strongly affects material properties and phase transition behaviors, but its effects on crystal surfaces, such as roughening and premelting, have been poorly studied. Our simulation revealed that these surface behaviors are distinct in monolayer and multilayer Lennard-Jones (LJ) crystals. Solid surfaces fluctuate as capillary waves during the roughening process, but complete roughening is preempted by premelting. As the melting temperature is approached, the thickness of the premelted liquid layer approaches a constant (i.e., blocked premelting) for monolayer crystals, but diverges as a power law (i.e., complete premelting) for bilayer and trilayer crystals. The surface liquids of monolayer crystals contain crystalline patches and exhibits rough liquid-vapour and liquid-crystal interfaces, in contrast to the normal surface liquids of bilayer and trilayer crystals. Monolayer crystals melt heterogeneously from the surface without forming a hexatic phase and produce many vacancies.

Shear-assisted grain coarsening in colloidal polycrystals.

Grain growth under shear annealing is crucial for controlling the properties of polycrystalline materials. However, their microscopic kinetics are not well understood because individual atomic trajectories are difficult to track. Here, we study grain growth with single-particle kinetics in colloidal polycrystals using video microscopy. Rich grain-growth phenomena are revealed in three shear regimes, including the normal grain growth (NGG) in weak shear melting-recrystallization process in strong shear. For intermediate shear, early stage NGG is arrested by built-up stress and eventually gives way to dynamic abnormal grain growth (DAGG). We find that DAGG occurs via a melting-recrystallization process, which naturally explains the puzzling stress drop at the onset of DAGG in metals. Moreover, we visualize that grain boundary (GB) migration is coupled with shear via disconnection gliding. The disconnection-gliding dynamics and the collective motions of ambient particles are resolved. We also observed that grain rotation can violate the conventional relation [Formula: see text] (R is the grain radius, and θ is the misorientation angle between two grains) by emission and annihilation of dislocations across the grain, resulting in a step-by-step rotation. Besides grain growth, we discover a result in shear-induced melting: The melting volume fraction varies sinusoidally on the angle mismatch between the triangular lattice orientation of the grain and the shear direction. These discoveries hold potential to inform microstructure engineering of polycrystalline materials.

Power laws in pressure-induced structural change of glasses.

Many glasses exhibit fractional power law (FPL) between the mean atomic volume va and the first diffraction peak position q1, i.e. [Formula: see text] with d ≃ 2.5 deviating from the space dimension D = 3, under compression or composition change. What structural change causes such FPL and whether the FPL and d are universal remain controversial. Here our simulations show that the FPL holds in both two- and three-dimensional glasses under compression when the particle interaction has two length scales which can induce nonuniform local deformations. The exponent d is not universal, but varies linearly with the deformable part of soft particles. In particular, we reveal an unexpected crossover regime with d > D from crystal behavior (d = D) to glass behavior (d < D). The results are explained by two types of bond deformation. We further discover FPLs in real space from the radial distribution functions, which correspond to the FPLs in reciprocal space.

Melting and solid-solid transitions of two-dimensional crystals composed of Janus spheres.

Colloidal model systems have been extensively used in the studies of various phase transitions, but melting and solid-solid transitions have rarely been explored in monolayer colloidal crystals with anisotropic attractions. Patchy colloidal particles have served as important model systems of atoms and molecules with anisotropic interactions. In this work, we study the melting and solid-solid transitions of two-dimensional crystals composed of Janus colloidal spheres using Langevin dynamics simulation. We discovered a first-order solid-solid transition from a single crystal with uniform stripes to a novel crystal with polycrystalline domains of stripes. The centers of masses of the particles maintain the morphology of a single crystal with long-range translational and bond-orientational orders, but particle orientations form polycrystalline domains of stripes. The stripe domains form by a strain-induced nucleation process via the collective rotation of particles. In addition to this solid-solid transition, the melting transition at a higher temperature follows a two-step Kosterlitz-Thouless-Halperin-Nelson-Young (KTHNY) scenario, similar to most isotropic particle systems.