Active Brownian particles in random and porous environments

The transport of active particles may occur in complex environments, in which it emerges from the interplay between the mobility of the active components and the quenched disorder of the environment. Here, we explore the structural and dynamical properties of active Brownian particles (ABPs) in random environments composed of fixed obstacles in three dimensions. We consider different arrangements of the obstacles. In particular, we consider two particular situations corresponding to experimentally realizable settings. First, we model pinning particles in (non-overlapping) random positions and, second, in a percolating gel structure and provide an extensive characterization of the structure and dynamics of ABPs in these complex environments. We find that the confinement increases the heterogeneity of the dynamics, with new populations of absorbed and localized particles appearing close to the obstacles. This heterogeneity has a profound impact on the motility induced phase separation exhibited by the particles at high activity, ranging from nucleation and growth in random disorder to a complex phase separation in porous environments.

Gecko-inspired self-adhesive packaging for strain-free temperature sensing based on optical fibre Bragg gratings

The large development of fibre Bragg gratings (FBGs) over decades has made this kind of structures one of the most mature optical fibre sensing technologies existing today, demonstrating key features for a very wide range of applications. FBG sensors are fragile and must be normally protected for real-field applications, although challenging packaging designs are required to mitigate temperature-strain cross-sensitivity issues. Here, a polydimethylsiloxane (PDMS) packaging with a microarray structure that provides gecko-inspired dry adhesion is proposed for strain-free FBG-based temperature sensing. Besides offering protection, the PDMS packaging with an embedded polyamide capillary damps the mechanical strain transferred to the optical fibre, providing FBG-based temperature sensing with a negligible impact of strain. In addition, the microarray structure imprinted on one surface of the packaging provides gecko-inspired dry adhesion based on van der Waals forces. This feature enables the packaged optical fibre sensor to be attached and detached dynamically to nearly any kind of smooth surface, leaving no residuals in the monitored structure. Experimental results verify a fast and accurate temperature response of the sensor with highly mitigated impact of residual strain. The proposed packaged sensor can be used in application where glue is not allowed nor recommendable to be used.

Elastic Moduli: a Tool for Understanding Chemical Bonding and Thermal Transport in Thermoelectric Materials

The elastic behavior of a material can be a powerful tool to decipher thermal transport. In thermoelectrics, measuring the elastic moduli-directly tied to sound velocity-is critical to understand trends in lattice thermal conductivity, as well as study bond anharmonicity and phase transitions, given the sensitivity of elastic moduli to the chemical bonding. In this review, we introduce the basics of elasticity and explain the origin of high-temperature lattice softening from a bonding perspective. We then review elasticity data throughout classes of thermoelectrics, and explore trends in sound velocity, anharmonicity, and thermal conductivity. We reveal how experimental sound velocities can improve the accuracy of common thermal conductivity models and present a critical discussion of Grüneisen parameter estimates from elastic moduli. Readers will be equipped with tools to leverage elasticity measurements or calculations to accurately interpret thermal transport trends.

Multistability, intermittency, and hybrid transitions in social contagion models on hypergraphs

Although ubiquitous, interactions in groups of individuals are not yet thoroughly studied. Frequently, single groups are modeled as critical-mass dynamics, which is a widespread concept used not only by academics but also by politicians and the media. However, less explored questions are how a collection of groups will behave and how their intersection might change the dynamics. Here, we formulate this process as binary-state dynamics on hypergraphs. We showed that our model has a rich behavior beyond discontinuous transitions. Notably, we have multistability and intermittency. We demonstrated that this phenomenology could be associated with community structures, where we might have multistability or intermittency by controlling the number or size of bridges between communities. Furthermore, we provided evidence that the observed transitions are hybrid. Our findings open new paths for research, ranging from physics, on the formal calculation of quantities of interest, to social sciences, where new experiments can be designed.

Gradual transformation of anionic/zwitterionic wormlike micelles from viscous to elastic domains: Unravelling the effect of anionic surfactant chain length

HYPOTHESIS

Ultra-long tailed zwitterionic surfactants often form aqueous wormlike elastic micelles, whereas the shorter ones mainly exhibit spherical viscous micelles. Anionic surfactants are widely used to tune the micellar morphology from spherical into wormlike. Systematic investigations in the molecular level are insightful to understand the viscoelasticity regulative mechanism.

EXPERIMENTS

Anionic/zwitterionic hybrid wormlike micelles are composed of sodium alkylsulfate (SAS) homologues and dodecyl dimethyl amidopropyl hydroxyl sulfobetaine (DHSB). The formation of wormlike micelles was studied by employing rheometer, cryogenic transmission electron microscopy (cryo-TEM) and small angle X-ray scattering (SAXS) techniques. The effects of surfactant concentration, molar ratio, anionic surfactant chain length and temperature were investigated systematically.

FINDINGS

SAS promoted the formation of SAS/DHSB hybrid wormlike micelles. The increase in both chain length and molar ratio (x_SAS) of SAS are advantageous in the enhancement of viscosity. Interestingly, sodium hexadecylsulfate (SHS) endowed elastic wormlike micelles with thermally insensitive viscosity below its Krafft temperature (T_k), which was distinguished from the viscous ones formed by sodium octylsulfate (SOS). SAXS results showed that the size of SAS/DHSB wormlike micelles was primarily determinate by surfactants with longer hydrophobic tails.

Fano interference between collective modes in cuprate high-T(c) superconductors

Cuprate high-T_c superconductors are known for their intertwined interactions and the coexistence of competing orders. Uncovering experimental signatures of these interactions is often the first step in understanding their complex relations. A typical spectroscopic signature of the interaction between a discrete mode and a continuum of excitations is the Fano resonance/interference, characterized by the asymmetric light-scattering amplitude of the discrete mode as a function of the electromagnetic driving frequency. In this study, we report a new type of Fano resonance manifested by the nonlinear terahertz response of cuprate high-T_c superconductors, where we resolve both the amplitude and phase signatures of the Fano resonance. Our extensive hole-doping and magnetic field dependent investigation suggests that the Fano resonance may arise from an interplay between the superconducting fluctuations and the charge density wave fluctuations, prompting future studies to look more closely into their dynamical interactions.

The dynamic nature of percolation on networks with triadic interactions

Percolation establishes the connectivity of complex networks and is one of the most fundamental critical phenomena for the study of complex systems. On simple networks, percolation displays a second-order phase transition; on multiplex networks, the percolation transition can become discontinuous. However, little is known about percolation in networks with higher-order interactions. Here, we show that percolation can be turned into a fully fledged dynamical process when higher-order interactions are taken into account. By introducing signed triadic interactions, in which a node can regulate the interactions between two other nodes, we define triadic percolation. We uncover that in this paradigmatic model the connectivity of the network changes in time and that the order parameter undergoes a period doubling and a route to chaos. We provide a general theory for triadic percolation which accurately predicts the full phase diagram on random graphs as confirmed by extensive numerical simulations. We find that triadic percolation on real network topologies reveals a similar phenomenology. These results radically change our understanding of percolation and may be used to study complex systems in which the functional connectivity is changing in time dynamically and in a non-trivial way, such as in neural and climate networks.

Kibble-Zurek scaling due to environment temperature quench in the transverse field Ising model

The Kibble-Zurek mechanism describes defect production due to non-adiabatic passage through a critical point. Here we study its variant from ramping the environment temperature to a critical point. We find that the defect density scales as [Formula: see text] or [Formula: see text] for thermal or quantum critical points, respectively, in terms of the usual critical exponents and [Formula: see text] the speed of the drive. Both scalings describe reduced defect density compared to conventional Kibble-Zurek mechanism, which stems from the enhanced relaxation due to bath-system interaction. Ramping to the quantum critical point is investigated by studying the Lindblad equation for the transverse field Ising chain in the presence of thermalizing bath, with couplings to environment obeying detailed balance, confirming the predicted scaling. The von-Neumann or the system-bath entanglement entropy follows the same scaling. Our results are generalized to a large class of dissipative systems with power-law energy dependent bath spectral densities as well.

Chiral phonons: circularly polarized Raman spectroscopy and ab initio calculations in a chiral crystal tellurium

Recently, phonons with chirality (chiral phonons) have attracted significant attention. Chiral phonons exhibit angular and pseudoangular momenta. In circularly polarized Raman spectroscopy, the peak split of the Γ 3 $$ {\Gamma}_3 $$ mode is detectable along the principal axis of the chiral crystal in the backscattering configuration. In addition, peak splitting occurs when the pseudoangular momenta of the incident and scattered circularly polarized light are reversed. Until now, chiral phonons in binary crystals have been observed, whereas those in unary crystals have not been observed. Here, we observe chiral phonons in a chiral unary crystal Te. The pseudoangular momentum of the phonon is obtained in Te by an ab initio calculation. From this calculation, we verified the conservation law of pseudoangular momentum in Raman scattering. From this conservation law, we determined the handedness of the chiral crystals. We also evaluated the true chirality of the phonons using a measure with symmetry similar to that of an electric toroidal monopole.

From a microscopic inertial active matter model to the Schrödinger equation

Active field theories, such as the paradigmatic model known as 'active model B+', are simple yet very powerful tools for describing phenomena such as motility-induced phase separation. No comparable theory has been derived yet for the underdamped case. In this work, we introduce active model I+, an extension of active model B+ to particles with inertia. The governing equations of active model I+ are systematically derived from the microscopic Langevin equations. We show that, for underdamped active particles, thermodynamic and mechanical definitions of the velocity field no longer coincide and that the density-dependent swimming speed plays the role of an effective viscosity. Moreover, active model I+ contains an analog of the Schrödinger equation in Madelung form as a limiting case, allowing one to find analoga of the quantum-mechanical tunnel effect and of fuzzy dark matter in active fluids. We investigate the active tunnel effect analytically and via numerical continuation.

Investigation of structural, optical and electrical conductivity of a new organic inorganic bromide: [C12H17N2]2ZnBr4

A new organic-inorganic hybrid, namely the [C₁₂H₁₇N₂]₂ZnBr₄ compound, has been synthesized and studied by single-crystal X-ray diffraction and optical and complex impedance spectroscopy. It crystallized in the centrosymmetric P2₁/n space group at room temperature. The asymmetric unit is constituted by [ZnBr₄]^2- anions, showing slightly distorted tetrahedral geometry, surrounded by four organic (C₁₂H₁₇N₂)⁺ cations. The crystal packing is stabilized by N-H⋯Br and C-H⋯Br hydrogen bonds arranged in a three-dimensional network. The optical absorption measurement confirms the semiconductor nature with a band gap of around 3.94 eV. Additionally, the analysis of Nyquist plots (-Z'' vs. Z') shows that the electrical properties of the material are heavily dependent on frequency and temperature, indicating a relaxation phenomenon and semiconductor-type behavior. Reduction in Z' was observed as a function of temperature and frequency which indicates an increase in ac conductivity and the negative temperature coefficient of resistance. The frequency dependent plots of (-Z'') show that the electrical relaxation is non-Debye in nature. The ac conductivity spectrum obeys Jonscher's universal power law. The Correlated barrier hopping model CBH has been suggested to agree with the conduction mechanism of σ _ac for the [C₁₂H₁₇N₂]₂ZnBr₄ compound.

Ferromagnetic order controlled by the magnetic interface of LaNiO3/La2/3Ca1/3MnO3 superlattices

Interface engineering in complex oxide superlattices is a growing field, enabling manipulation of the exceptional properties of these materials, and also providing access to new phases and emergent physical phenomena. Here we demonstrate how interfacial interactions can induce a complex charge and spin structure in a bulk paramagnetic material. We investigate a superlattice (SLs) consisting of paramagnetic LaNiO₃ (LNO) and highly spin-polarized ferromagnetic La_2/3Ca_1/3MnO₃ (LCMO), grown on SrTiO₃ (001) substrate. We observed emerging magnetism in LNO through an exchange bias mechanism at the interfaces in X-ray resonant magnetic reflectivity. We find non-symmetric interface induced magnetization profiles in LNO and LCMO which we relate to a periodic complex charge and spin superstructure. High resolution scanning transmission electron microscopy images reveal that the upper and lower interfaces exhibit no significant structural variations. The different long range magnetic order emerging in LNO layers demonstrates the enormous potential of interfacial reconstruction as a tool for tailored electronic properties.

Thermodynamic stability of Li-B-C compounds from first principles

Prediction of high-T_c superconductivity in hole-doped Li_xBC two decades ago has brought about an extensive effort to synthesize new materials with honeycomb B-C layers, but the thermodynamic stability of Li-B-C compounds remains largely unexplored. In this study, we use density functional theory to characterize well-established and recently reported Li-B-C phases. Our calculation of the Li chemical potential in Li_xBC helps estimate the (T,P) conditions required for delithiation of the LiBC parent material, while examination of B-C phases helps rationalize the observation of metastable BC₃ polymorphs with honeycomb and diamond-like morphologies. At the same time, we demonstrate that recently reported BC₃, LiBC₃, and Li₂B₂C phases with new crystal structures are both dynamically and thermodynamically unstable. With a combination of evolutionary optimization and rational design, we identify considerably more natural and favorable Li₂B₂C configurations that, nevertheless, remain above the thermodynamic stability threshold.

Phase behavior of medium-length hydrophobically associating PEO-PPO multiblock copolymers in aqueous media

HYPOTHESIS

The micellization of block copolymers of poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO) is driven by the dehydration of PPO at elevated temperatures. At low concentrations, a viscous solution of isolated micelles is obtained, whereas at higher concentrations, crowding of micelles results in an elastic gel. Alternating PEO-PPO multiblock copolymers are expected to exhibit different phase behavior, with altered phase boundaries and thermodynamics, as compared to PEO-PPO-PEO triblock copolymers (Pluronics®) with equal hydrophobicity, thereby proving the pivotal role of copolymer architecture and molecular weight.

EXPERIMENTS

Multiple characterization techniques were used to map the phase behavior as a function of temperature and concentration of PEO-PPO multiblock copolymers (ExpertGel®) in aqueous solution. These techniques include shear rheology, differential and adiabatic scanning calorimetry, isothermal titration calorimetry and light transmittance. The micellar size and topology were studied by dynamic light scattering.

FINDINGS

Multiblocks have lower transition temperatures and higher thermodynamic driving forces for micellization as compared to triblocks due to the presence of more than one PPO block per chain. With increasing concentration, the multiblock copolymers in solution gradually evolve into a viscoelastic network formed by soluble bridges in between micellar nodes, whereas hairy triblock micelles jam into liquid crystalline phases resembling an elastic colloidal crystal.

Influence of Disorder on the Bad Metal Behavior in Polar Amalgams

The two new ternary amalgams K_1-xRb_xHg₁₁ [x = 0.472(7)] and Cs_3-xCa_xHg₂₀ [x = 0.20(3)] represent two different examples of how to create ternary compounds from binaries by statistical atom substitution. K_1-xRb_xHg₁₁ is a Vegard-type mixed crystal of the isostructural binaries KHg₁₁ and RbHg₁₁ [cubic, BaHg₁₁ structure type, space group Pm3̅m, a = 9.69143(3) Å, Rietveld refinement], whereas Cs_3-xCa_xHg₂₀ is a substitution variant of the Rb₃Hg₂₀ structure type [cubic, space group Pm3̅n, a = 10.89553(14) Å, Rietveld refinement] for which a fully substituted isostructural binary Ca phase is unknown. In K_1-xRb_xHg₁₁, the valence electron concentration (VEC) is not changed by the substitution, whereas in Cs_3-xCa_xHg₂₀, the VEC increases with the Ca content. Amalgams of electropositive metals form polar metal bonds and show "bad metal" properties. By thermal analysis, magnetic susceptibility and resistivity measurements, and density functional theory calculations of the electronic structures, we investigate the effect of the structural disorder introduced by creating mixed-atom occupation on the physical properties of the two new polar amalgam systems.

ANi5Bi5.6+δ (A = K, Rb, and Cs): Quasi-One-Dimensional Metals Featuring [Ni5Bi5.6+δ]- Double-Walled Column with Strong Diamagnetism

A new series of compounds, ANi₅Bi_5.6+δ (where A = K, Rb, and Cs) are discovered with a quasi-one-dimensional (Q1D) [Ni₅Bi_5.6+δ]^- double-walled column and a coaxial inner one-dimensional Bi atomic chain. The columns are linked to each other by intercolumn Bi-Bi bonds and separated by an A⁺ cation. Typical metallic behaviors with strong correlation of itinerant electrons and the Sommerfeld coefficient enhanced with the increasing cationic radius were experimentally observed and supported by first-principles calculations. Compared to AMn₆Bi₅ (where A = K, Rb, and Cs), the enhanced intercolumn distances and the substitution of Ni for Mn give rise to strong diamagnetic susceptibilities in ANi₅Bi_5.6+δ. First-principles calculations reveal possible uncharged Ni atoms with even number of electrons in ANi₅Bi_5.6+δ, which may explain the emergence of diamagnetism. ANi₅Bi_5.6+δ, as Q1D diamagnetic metals with strong electron correlation, provide a unique platform to understand exotic magnetism and explore novel quantum effects.

Topological spin texture in the pseudogap phase of a high-Tc superconductor

An outstanding challenge in condensed-matter-physics research over the past three decades has been to understand the pseudogap (PG) phenomenon of the high-transition-temperature (high-T_c) copper oxides. A variety of experiments have indicated a symmetry-broken state below the characteristic temperature T* (refs. ^1-8). Among them, although the optical study⁵ indicated the mesoscopic domains to be small, all these experiments lack nanometre-scale spatial resolution, and the microscopic order parameter has so far remained elusive. Here we report, to our knowledge, the first direct observation of topological spin texture in an underdoped cuprate, YBa₂Cu₃O_6.5, in the PG state, using Lorentz transmission electron microscopy (LTEM). The spin texture features vortex-like magnetization density in the CuO₂ sheets, with a relatively large length scale of about 100 nm. We identify the phase-diagram region in which the topological spin texture exists and demonstrate the ortho-II oxygen order and suitable sample thickness to be crucial for its observation by our technique. We also discuss an intriguing interplay observed among the topological spin texture, PG state, charge order and superconductivity.

Suspended phospholipid bilayers: A new biological membrane mimetic

HYPOTHESIS

The attractive interaction between a cationic surfactant monolayer at the air-water interface and vesicles, incorporating anionic lipids, is sufficient to drive the adsorption and deformation of the vesicles. Osmotic rupture of the vesicles produces a continuous lipid bilayer beneath the monolayer.

EXPERIMENTAL

Specular neutron reflectivity has been measured from the surface of a purpose-built laminar flow trough, which allows for rapid adsorption of vesicles, the changes in salt concentration required for osmotic rupture of the adsorbed vesicles into a bilayer, and for neutron contrast variation of the sub-phase without disturbing the monolayer.

FINDINGS

The neutron reflectivity profiles measured after vesicle addition are consistent with the adsorption and flattening of the vesicles beneath the monolayer. An increase in the buffer salt concentration results in further flattening and fusion of the adsorbed vesicles, which are ruptured by a subsequent decrease in the salt concentration. This process results in a continuous, high coverage, bilayer suspended 11 Åbeneath the monolayer. As the bilayer is not constrained by a solid substrate, this new mimetic is well-suited to studying the structure of lipid bilayers that include transmembrane proteins.

Ä-Coupling Dielectric Functionality with Magnetic Properties in Coordination Metal Complexes

Significant research has been conducted on molecular ferroelectric materials, including pure organic and inorganic compounds; however, studies on ferroelectric materials based on coordination metal complexes are scarce. Ferroelectric materials based on coordination metal complexes have tunable structures and designs, with coexistence or synergy between the ferroelectric behavior and magnetic properties. Compared to inorganic compounds, few coordination metal complexes exhibit coupling between the magnetic and dielectric properties. Coordination metal complexes with strong coupling between the magnetic and dielectric properties exhibit dielectric permittivity variations under external magnetic fields. Therefore, they have attracted substantial interest for their potential use in magnetoelectric devices. In this review, we discuss recent advances in coordination metal complexes, that exhibit coupled magnetic functionalities and ferroelectricity or dielectric properties, including single-molecule magnets, electron delocalization systems, and external stimuli responsive compounds.

Nanomaterials for Fluorescence and Multimodal Bioimaging

Bioconjugated nanomaterials replace molecular probes in bioanalysis and bioimaging in vitro and in vivo. Nanoparticles of silica, metals, semiconductors, polymers, and supramolecular systems, conjugated with contrast agents and drugs for image-guided (MRI, fluorescence, PET, Raman, SPECT, photodynamic, photothermal, and photoacoustic) therapy infiltrate into preclinical and clinical settings. Small bioactive molecules like peptides, proteins, or DNA conjugated to the surfaces of drugs or probes help us to interface them with cells and tissues. Nevertheless, the toxicity and pharmacokinetics of nanodrugs, nanoprobes, and their components become the clinical barriers, underscoring the significance of developing biocompatible next-generation drugs and contrast agents. This account provides state-of-the-art advancements in the preparation and biological applications of bioconjugated nanomaterials and their molecular, cell, and in vivo applications. It focuses on the preparation, bioimaging, and bioanalytical applications of monomodal and multimodal nanoprobes composed of quantum dots, quantum clusters, iron oxide nanoparticles, and a few rare earth metal ion complexes.

The excitable fluid mosaic

The Fluid Mosaic Model by Singer & Nicolson proposes that biological membranes consist of a fluid lipid layer into which integral proteins are embedded. The lipid membrane acts as a two-dimensional liquid in which the proteins can diffuse and interact. Until today, this view seems very reasonable and is the predominant picture in the literature. However, there exist broad melting transitions in biomembranes some 10-20 degrees below physiological temperatures that reach up to body temperature. Since they are found below body temperature, Singer & Nicolson did not pay any further attention to the melting process. But this is a valid view only as long as nothing happens. The transition temperature can be influenced by membrane tension, pH, ionic strength and other variables. Therefore, it is not generally correct that the physiological temperature is above this transition. The control over the membrane state by changing the intensive variables renders the membrane as a whole excitable. One expects phase behavior and domain formation that leads to protein sorting and changes in membrane function. Thus, the lipids become an active ingredient of the biological membrane. The melting transition affects the elastic constants of the membrane. This allows for the generation of propagating pulses in nerves and the formation of ion-channel-like pores in the lipid membranes. Here we show that on top of the fluid mosaic concept there exists a wealth of excitable phenomena that go beyond the original picture of Singer & Nicolson.¹.

DLVO surface forces in liquid films and statistical mechanics of colloidal oscillatory structural forces in dispersion stability

This paper focuses on the theory of the dispersion stability considering two models. In the classical DLVO model of surface forces, the interactions between two particles consist of two terms: the London-van der Waals attractive interaction and the electrostatic repulsive interaction in the frame of the Debye-Hückel theory. The solvent, the aqueous solution of the electrolyte, was considered the continuous phase. The film stability criteria are P_γ > Π and dP_γ/dh > 0. Henderson and Lozada-Cassou (HC) applied the statistical mechanics approach to calculate the film free energy to predict the dispersion stability by considering two large hard spheres as colloidal particles immersed in a fluid of dispersed small particles (the solvent). HC applied the radial distribution function g(r) to calculate the free oscillatory structural energy using W(r) = - kT ln g(r). HC's theoretical approach was also applied to the particle collective interactions in the film and explains the stability of film formed from complex fluids (e.g., micellar and colloidal dispersions). The differences between the solvation oscillatory layering forces and colloidal oscillatory structural forces are discussed. The application of the DLVO model to the dispersion stability is critically reviewed. The role of nanobubbles in the dispersion stability is discussed.

Identifying Steady State in the Network Dynamics of Spiking Neural Networks

Analysis of the dynamics of complex networks can provide valuable information. For example, the dynamics can be used to characterize and differentiate between different network inputs and configurations. However, without quantitatively delineating the network's dynamic regimes, analysis of the network's dynamics is based on heuristics and qualitative signatures of transient or steady-state regimes. This is not ideal because interesting phenomena can occur during the transient regime, steady-state regime, or at the transition between the two dynamic regimes. Moreover, for simulated and observed systems, precise knowledge of the network's dynamical regime is imperative when considering metrics on minimal mathematical descriptions of the dynamics, otherwise either too much or too little data is analyzed. Here, we develop quantitative methods to ascertain the starting point and period of steady-state network activity. Using the precise knowledge of the network's dynamic regimes, we build minimal representations of the network dynamics that form the basis for future work. We show applications of our techniques on idealized signals and on the dynamics of a biologically inspired spiking neural network.

Explosive rigidity percolation in kirigami

Controlling the connectivity and rigidity of kirigami, i.e. the process of cutting paper to deploy it into an articulated system, is critical in the manifestations of kirigami in art, science and technology, as it provides the resulting metamaterial with a range of mechanical and geometric properties. Here, we combine deterministic and stochastic approaches for the control of rigidity in kirigami using the power of k choices, an approach borrowed from the statistical mechanics of explosive percolation transitions. We show that several methods for rigidifying a kirigami system by incrementally changing either the connectivity or the rigidity of individual components allow us to control the nature of the explosive transition by a choice of selection rules. Our results suggest simple lessons for the design of mechanical metamaterials.

Origin of anomalously stabilizing ice layers on methane gas hydrates near rock surface

Gas hydrates (GHs) in water close to freezing temperatures can be stabilised via the formation of ice layers. In a recent work [Boström et al., Astron. Astrophys., A54, 650, 2021], it was found that a surface region with partial gas dilution could be essential for obtaining nano- to micron-sized anomalously stabilizing ice layers. In this paper, it is demonstrated that the Casimir-Lifshitz free energy in multi-layer systems could induce thinner, but more stable, ice layers in cavities than those found for gas hydrates in a large reservoir of cold water. The thickness and stability of such ice layers in a pore filled with cold water could influence the leakage of gas molecules. Additional contributions, e.g. from salt-induced stresses, can also be of importance, and are briefly discussed.

Dispersion of Manganese Dioxide Particles Using Anionic Technol PG and Sodium Cholate in the Preparation for Application as Films on Substrates

Manganese dioxide (MnO2) is widely used in cosmetics and self-cleaning materials because of the high refractive index and photocatalytic activity of this compound. In the present work, the surfaces of MnO2 particles were coated with a commercially available anionic phospholipid mixture, Technol PG, and sodium cholate(SC). These coated particles were readily dispersed in water and subsequently applied as films onto glass substrates by drop-casting.

Emergence of Visible-Light Water Oxidation Upon Hexaniobate-Ligand Entrapment of Quantum-Confined Copper-Oxide Cores

The formation of small 1 to 3 nm organic-ligand free metal-oxide nanocrystals (NCs) is essential to utilization of their attractive size-dependent properties in electronic devices and catalysis. We now report that hexaniobate cluster-anions, [Nb₆ O₁₉ ]^8- , can arrest the growth of metal-oxide NCs and stabilize them as water-soluble complexes. This is exemplified by formation of hexaniobate-complexed 2.4-nm monoclinic-phase CuO NCs (1), whose ca. 350 Cu-atom cores feature quantum-confinement effects that impart an unprecedented ability to catalyze visible-light water oxidation with no added photosensitizers or applied potentials, and at rates exceeding those of hematite NCs. The findings point to polyoxoniobate-ligand entrapment as a potentially general method for harnessing the size-dependent properties of very small semiconductor NCs as the cores of versatile, entirely-inorganic complexes.

The Effect of dry Needling in Chronic Stroke with a complex Network Approach: A Case Study

Background: Dry Needling (DN) has been demonstrated to be effective in improving sensorimotor function and spasticity in patients with chronic stroke. Electroencephalogram (EEG) has been used to analyze if DN has effects on the central nervous system of patients with stroke. There are no studies on how DN works in patients with chronic stroke based on EEG analysis using complex networks. Objective: The aim of this study was to assess how DN works when it is applied in a patient with stroke, using the graph theory. Methods: One session of DN was applied to the spastic brachialis muscle of a 62-year-old man with right hemiplegia after stroke. EEG was used to analyze the effects of DN following metrics that measure the topological configuration: 1) network density, 2) clustering coefficient, 3) average shortest path length, 4) betweenness centrality, and 5) small-worldness. Measurements were taken before and during DN. Results: An improvement of the brain activity was observed in this patient with stroke after the application of DN, which led to variations of local parameters of the brain network in the delta, theta and alpha bands, and inclined towards those of the healthy control bands. Conclusions: This case study showed the positive effects of DN on brain network of a patient with chronic stroke.

Multiple-Intercalation Stages and Universal Tc Enhancement through Polar Organic Species in Electron-Doped 1T-SnSe2

In this work, we report multiple-intercalation stages and universal T_c enhancement of superconductivity in 1T-SnSe₂ through Li and organic molecule co-intercalation. We observe significantly increased lattice parameters of up to 40 Å and a dramatically enlarged interlayer distance of up to ∼11 Å in Li and N,N-dimethylformamide (DMF) co-intercalated SnSe₂. Well-separated co-intercalation stages with different stacking patterns have been discovered by carefully controlled reaction times and concentrations of solutions. These co-intercalation stages are superconductors showing different superconducting signals. In addition, Li and various organic species such as acetone, dimethyl sulfoxide (DMSO), and tetrahydrofuran (THF) have been co-intercalated into SnSe₂ crystals; all of which show an enhanced superconducting T_c compared to solely Li-intercalated SnSe₂. Our findings may provide more insight into effectively tuning the electronic structure of the lamellar structure through organic molecule co-regulation and open a new strategy to engineer the physical properties of these layered materials by controlling their different intercalation stages.

The crucial role of adhesion in the transmigration of active droplets through interstitial orifices

Active fluid droplets are a class of soft materials exhibiting autonomous motion sustained by an energy supply. Such systems have been shown to capture motility regimes typical of biological cells and are ideal candidates as building-block for the fabrication of soft biomimetic materials of interest in pharmacology, tissue engineering and lab on chip devices. While their behavior is well established in unconstrained environments, much less is known about their dynamics under strong confinement. Here, we numerically study the physics of a droplet of active polar fluid migrating within a microchannel hosting a constriction with adhesive properties, and report evidence of a striking variety of dynamic regimes and morphological features, whose properties crucially depend upon droplet speed and elasticity, degree of confinement within the constriction and adhesiveness to the pore. Our results suggest that non-uniform adhesion forces are instrumental in enabling the crossing through narrow orifices, in contrast to larger gaps where a careful balance between speed and elasticity is sufficient to guarantee the transition. These observations may be useful for improving the design of artificial micro-swimmers, of interest in material science and pharmaceutics, and potentially for cell sorting in microfluidic devices.

Fundamental limits to learning closed-form mathematical models from data

Given a finite and noisy dataset generated with a closed-form mathematical model, when is it possible to learn the true generating model from the data alone? This is the question we investigate here. We show that this model-learning problem displays a transition from a low-noise phase in which the true model can be learned, to a phase in which the observation noise is too high for the true model to be learned by any method. Both in the low-noise phase and in the high-noise phase, probabilistic model selection leads to optimal generalization to unseen data. This is in contrast to standard machine learning approaches, including artificial neural networks, which in this particular problem are limited, in the low-noise phase, by their ability to interpolate. In the transition region between the learnable and unlearnable phases, generalization is hard for all approaches including probabilistic model selection.

Phonon-driven intra-exciton Rabi oscillations in CsPbBr(3) halide perovskites

Coupling electromagnetic radiation with matter, e.g., by resonant light fields in external optical cavities, is highly promising for tailoring the optoelectronic properties of functional materials on the nanoscale. Here, we demonstrate that even internal fields induced by coherent lattice motions can be used to control the transient excitonic optical response in CsPbBr₃ halide perovskite crystals. Upon resonant photoexcitation, two-dimensional electronic spectroscopy reveals an excitonic peak structure oscillating persistently with a 100-fs period for up to ~2 ps which does not match the frequency of any phonon modes of the crystals. Only at later times, beyond 2 ps, two low-frequency phonons of the lead-bromide lattice dominate the dynamics. We rationalize these findings by an unusual exciton-phonon coupling inducing off-resonant 100-fs Rabi oscillations between 1s and 2p excitons driven by the low-frequency phonons. As such, prevailing models for the electron-phonon coupling in halide perovskites are insufficient to explain these results. We propose the coupling of characteristic low-frequency phonon fields to intra-excitonic transitions in halide perovskites as the key to control the anharmonic response of these materials in order to establish new routes for enhancing their optoelectronic properties.

Order-disorder charge density wave instability in the kagome metal (Cs,Rb)V3Sb5

The origin of the charge density wave phases in the kagome metal compound AV₃Sb₅ is still under great scrutiny. Here, we combine diffuse and inelastic x-ray scattering to identify a 3-dimensional precursor of the charge order at the L point that condenses into a CDW through a first order phase transition. The quasi-elastic critical scattering indicates that the dominant contribution to the diffuse precursor is the elastic central peak without phonon softening. However, the inelastic spectra show a small broadening of the Einstein-type phonon mode on approaching T_CDW. Our results point to the situation where the Fermi surface instability at the L point is of order-disorder type with critical growth of quasi-static domains. The experimental data indicate that the CDW consists on an alternating Star of David and trihexagonal distortions and its dynamics goes beyond the classical weak-coupling scenario and is discussed within strong-electron phonon coupling and non-adiabatic models.

Emergence of high piezoelectricity from competing local polar order-disorder in relaxor ferroelectrics

Relaxor ferroelectrics are known for outstanding piezoelectric properties, finding a broad range of applications in advanced electromechanical devices. Decoding the origins of the enhanced properties, however, have long been complicated by the heterogeneous local structures. Here, we employ the advanced big-box refinement method by fitting neutron-, X-ray-based total scattering, and X-ray absorption spectrum simultaneously, to extract local atomic polar displacements and construct 3D polar configurations in the classical relaxor ferroelectric Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃. Our results demonstrate that prevailing order-disorder character accompanied by the continuous rotation of local polar displacements commands the composition-driven global structure evolution. The omnidirectional local polar disordering appears as an indication of macroscopic relaxor characteristics. Combined with phase-field simulations, it demonstrates that the competing local polar order-disorder between different states with balanced local polar length and direction randomness leads to a flattening free-energy profile over a wide polar length, thus giving rise to high piezoelectricity. Our work clarifies that the critical structural feature required for high piezoelectricity is the competition states of local polar rather than relaxor.

Small Cellular Particles from European Spruce Needle Homogenate

Small cellular particles (SCPs) are being considered for their role in cell-to-cell communication. We harvested and characterized SCPs from spruce needle homogenate. SCPs were isolated by differential ultracentrifugation. They were imaged by scanning electron microscope (SEM) and cryogenic transmission electron microscope (cryo TEM), assessed for their number density and hydrodynamic diameter by interferometric light microscopy (ILM) and flow cytometry (FCM), total phenolic content (TPC) by UV-vis spectroscopy, and terpene content by gas chromatography-mass spectrometry (GC-MS). The supernatant after ultracentrifugation at 50,000× g contained bilayer-enclosed vesicles whereas in the isolate we observed small particles of other types and only a few vesicles. The number density of cell-sized particles (CSPs) (larger than 2 μm) and meso-sized particles (MSPs) (cca 400 nm-2 µm) was about four orders of magnitude lower than the number density of SCPs (sized below 500 nm). The average hydrodynamic diameter of SCPs measured in 10,029 SCPs was 161 ± 133 nm. TCP decreased considerably due to 5-day aging. Volatile terpenoid content was found in the pellet after 300× g. The above results indicate that spruce needle homogenate is a source of vesicles to be explored for potential delivery use.

Geometrical and magnetic properties of small titanium and chromium clusters on monolayer hexagonal boron nitride

Magnetic clusters on an insulating substrate are potential candidates for spin-based quantum devices. Here we investigate the geometric, electronic, and magnetic structures of small Ti and Cr clusters, from dimers to pentamers, adsorbed on a single-layer hexagonal boron nitride (h-BN) sheet within the framework of density functional theory. The stable adsorption configurations of the Ti clusters and Cr clusters composed of the same number of atoms are found to be totally different from each other. The difference in their bonding mechanisms has been revealed by the density of states and the charge density difference of the corresponding adsorption systems. While chemical bonds are formed between the Ti atoms and the supporting sheet, the Cr clusters are found in the physisorption state on the substrate. In addition, it is shown that the h-BN sheet is energetically favorable for building three-dimensional Ti clusters. These findings support the use of h-BN as a suitable decoupling substrate for manipulation of quantum spin states in small transition metal (TM) clusters and fabrication of devices based on them.

Mutual independence of water and n-nonane nucleation at low temperatures

The interaction of water with different substances in the earth's atmosphere lies at the heart of many processes that influence our climate. However, it is still unclear how different species interact with water on the molecular level and in which ways this interaction contributes to the water vapor phase transition. Here, we report the first measurements of water-nonane binary nucleation in the 50-110 K temperature range, along with unary nucleation data of both. The time-dependent cluster size distribution in a uniform post-nozzle flow was measured by time-of-flight mass spectrometry coupled with single-photon ionization. From these data, we extract experimental rates and rate constants for both nucleation and cluster growth. The observed mass spectra of water/nonane clusters are not or only slightly affected by the introduction of the other vapor, and the formation of mixed clusters was not observed during nucleation of the mixed vapor. Additionally, the nucleation rate of either substance is not much affected by the presence (or absence) of the other species, i.e., the nucleation of water and nonane proceeds independently, indicating that hetero-molecular clusters do not play a role during nucleation. Only at the lowest temperature of our experiment (i.e., 51 K) do the measurements suggest that interspecies interaction slows water cluster growth. The findings here are in contrast to our earlier work in which we showed that vapor components in other mixtures, e.g., CO₂ and toluene/H₂O, can interact to promote nucleation and cluster growth in a similar temperature range.

A maximum entropy approach for the modelling of car-sharing parking dynamics

The science of cities is a relatively new and interdisciplinary topic aimed at studying and characterizing the collective processes that shape the growth and dynamics of urban populations. Amongst other open problems, the forecast of mobility trends in urban spaces is a lively research topic that aims at assisting the design and implementation of efficient transportation policies and inclusive urban planning. To this end, many Machine-Learning models have been put forward to predict mobility patterns. However, most of them are not interpretable -as they build on complex hidden representations of the system configurations- or do not allow for model inspection, thus limiting our understanding of the underlying mechanisms driving the citizen's daily routines. Here, we tackle this problem by building a fully interpretable statistical model that, incorporating only the minimum number of constraints, can predict different phenomena arising in the city. Using data on the movements of car-sharing vehicles in several Italian cities, we infer a model using the Maximum Entropy (MaxEnt) principle. The model allows for an accurate spatio-temporal prediction of car-sharing vehicles' presence in different city areas and, thanks to its simple yet general formulation, to precisely perform anomaly detection (e.g., detect strikes and bad weather conditions from car-sharing data only). We compare the forecasting capabilities of our model with different state-of-the-art models explicitly made for time-series forecasting: SARIMA models and Deep Learning Models. We find that MaxEnt models are highly predictive, outperforming SARIMAs while having similar performances of deep Neural Networks - but with advantages of being more interpretable, more flexibile-i.e., they can be applied to different tasks- and being computationally efficient. Our results show that statistical inference might play a fundamental role in building robust and general models describing urban systems phenomena.

Dissipative Quantum Criticality as a Source of Strange Metal Behavior

The strange metal behavior, usually characterized by a linear-in-temperature (T) resistivity, is a still unsolved mystery in solid-state physics. It is often associated with the proximity to a quantum critical point (a second order transition at temperature T=0, leading to a broken symmetry phase) focusing on the related divergent order parameter correlation length. Here, we propose a paradigmatic shift, focusing on a divergent characteristic time scale due to a divergent dissipation acting on the fluctuating critical modes while their correlation length stays finite. To achieve a divergent dissipation, we propose a mechanism based on the coupling between a local order parameter fluctuation and electron density diffusive modes that accounts both for the linear-in-T resistivity and for the logarithmic specific heat versus temperature ratio CV/T∼log(1/T), down to low temperatures.