Lattice Of Particles Research Articles

Topological transport of a classical droplet in a lattice of time

AbstractThouless charge pumps are quantum mechanical devices whose operation relies on topology. They provide the means for transporting quantum matter in space lattices with a single quantum precision. Contrasting space crystals that spontaneously break a continuous spatial translation symmetry and form crystals in space, time crystals have emerged as novel states of matter that organise into time lattices and spontaneously break a discrete time translation symmetry. The utility of Thouless pumps that enable topologically protected quantised transport of electrons and neutral atoms in spatial superlattices leads to the question if corresponding devices exist for time crystals. Here we show that topological pumps can be realised for time solids by transporting droplets of a liquid forward and backward in time lattices and we measure the topological index that characterises such pumping processes. By exploiting a synthetic time dimension, classical time crystals can circumvent the quantum tunnelling that underpins Thouless charge pumps. Our results establish topological pumping through time instead of space and pave the way for applications of time crystals.Key Points Periodically driven fluid droplets can be made to bounce persistently in a gravitational field and may undergo spontaneous time translation symmetry breaking forming classical time crystals. These classical time crystals can be pumped from one time site to another, and this pumping process is characterised by a topological index. Our observations establish a classical temporal counterpart to Thouless pumping of quantum particles in space lattices.

Formulation and dermal delivery of a new active pharmaceutical ingredient in an in vitro wound model for the treatment of chronic ulcers

The aim of this study was to investigate dermal delivery of the new active pharmaceutical ingredient (API) TOP-N53 into diabetic foot ulcer using an in vitro wound model consisting of pig ear dermis and elucidate the impact of drug formulation and wound dressing taking into consideration clinical relevance in the home care setting and possible bacterial infection. Different formulation approaches for the poorly water-soluble API including colloidal solubilization, drug micro-suspension and cosolvent addition were investigated; moreover, the effect of (micro-)viscosity of hydrogels used as primary wound dressing on delivery was assessed. Addition of Transcutol® P as cosolvent to water improved solubility and was significantly superior to all other approaches providing a sustained three-day delivery that reached therapeutic drug levels in the tissue. Solubilization in micelles or liposomes, on the contrary, did not boost delivery while micro-suspensions exhibited sedimentation on the tissue surface. Microbial contamination was responsible for considerable metabolism of the drug leading to tissue penetration of metabolites which may be relevant for therapeutic effect. Use of hydrogels under semi-occlusive conditions significantly reduced drug delivery in a viscosity-dependent fashion. Micro-rheologic analysis of the gels using diffusive wave spectroscopy confirmed the restricted diffusion of drug particles in the gel lattice which correlated with the obtained tissue delivery results. Hence, the advantages of hydrogel dressings from the applicatory characteristic point of view must be weighed against their adverse effect on drug delivery. The employed in vitro wound model was useful for the assessment of drug delivery and the development of a drug therapy concept for chronic diabetic foot ulcer. Mechanistic insights about formulation and dressing performance may be applied to drug delivery in other skin conditions such as digital ulcer.

Suppression of scattering from slow to fast subsystems and application to resonantly Floquet-driven impurities in strongly interacting systems

We study solutions to the Lippmann-Schwinger equation in systems where a slow subsystem is coupled to a fast subsystem via an impurity. Such situations appear when a high-frequency Floquet-driven impurity is introduced into a low-energy system, but the driving frequency is at resonance with a high-energy band. In contrast to the case of resonant bulk driving, where the particles in the low-energy system are excited into the high-energy band, we surprisingly find that these excitations are suppressed for resonantly driven impurities. Still, the transmission through the impurity is strongly affected by the presence of the high-energy band in a universal way that does not depend on the details of the high-energy band. We apply our general result to two examples and show the suppression of excitations from the low-energy band into the high-energy band: a) bound pairs in a Fermi-Hubbard chain scattering at a driven impurity, which is at resonance with the Hubbard interaction and b) particles in a deep optical lattice described by the tight-binding approximation, which scatter at a driven impurity, whose driving frequency equals the band gap between the two lowest energy bands.

Thermo-Mechanical and Mechano-Thermal Effects in Liquids Explained by Means of the Dual Model of Liquids

We pursue to illustrate the capabilities of the Dual Model of Liquids (DML) showing that it may explain crossed effects notable in Non-Equilibrium Thermodynamics (NET). The aim of the paper is to demonstrate that the DML may correctly model the thermodiffusion, in particular getting formal expressions for positive and negative Soret coefficient, and another “unexpected” mechano-thermal effect recently discovered in liquids submitted to shear strain, for which the first-ever theoretical interpretation is provided. Both applications of the DML are supported by the comparison with experimental data. The phenomenology of liquids, either pure or mixtures, submitted to external force fields is characterized by coupled effects, for instance mechano-thermal and thermo-mechanical effects, depending on whether the application of a mechanical force field generates a coupled thermal effect in the liquid sample or vice-versa. Although these phenomena have been studied since their discoveries, dating back to the XIX century, no firm theoretical interpretation exists yet. Very recently the mesoscopic model of liquids DML has been proposed and its validity and applicability demonstrated in several cases. According to DML, liquids are arranged on a mesoscopic scale by means of aggregates of molecules, or liquid particles. These structures share the liquid world with a population of lattice particles, i.e., elastic waves that interact with the liquid particles by means of an inertial force, allowing the mutual exchange of energy and momentum between the two populations. The hit particle relaxes the acquired energy and momentum due to the interaction, giving them back to the system a step forward and a time-lapse later, alike in a tunnel effect.

Visualizing Ultrasound Sources Using Signal Time Reversal in the Particle Dynamics Model

A method is proposed for solving the inverse problem of reconstructing acoustic wave sources from field measurements on some surface using wavefront reversal in the particle dynamics method. In this method, the studied medium is represented as a set of interacting particles (material points or solid bodies), for which classical equations of motion are written. The paper considers the representation of a medium as a set of particles in a body-centered cubic crystal lattice. The case of a linear dependence of the force of attraction of particles on distance is considered. The advantage of this approach is the ability to take into account wave propagation in arbitrarily inhomogeneous media using a single numerical model. The possibility of visualizing two spherical acoustic wave sources in water behind an obstacle has been demonstrated numerically and experimentally, despite the presence of transverse waves in the considered model of a solid body; their influence is negligible in this case. The method was tested experimentally on a soundproof screen with an aperture simulating a sound-emitting object of complex shape. A wave from a point source of short pulses passes through the aperture. Using a receiving acoustic sensor mounted on a two-dimensional scanner, the spatiotemporal distribution of sound vibrations on the water surface was measured. By processing the datausing wavefront reversal in the particle model, the image of the aperture in the soundproof screen was reconstructed.

How Does Heat Propagate in Liquids?

In this paper, we proceed to illustrate the consequences and implications of the Dual Model of Liquids (DML) by applying it to the heat propagation. Within the frame of the DML, propagation of thermal (elastic) energy in liquids is due to wave-packet propagation and to the wave-packets’ interaction with the material particles of the liquid, meant in the DML as aggregates of molecules swimming in an ocean of amorphous liquid. The liquid particles interact with the lattice particles, a population of elastic wave-packets, by means of an inertial force, exchanging energy and momentum with them. The hit particle relaxes at the end of the interaction, releasing the energy and momentum back to the system a step forward and a time lapse later, like in a tunnel effect. The tunnel effect and the duality of liquids are the new elements that suggest on a physical basis for the first time, using a hyperbolic equation to describe the propagation of energy associated to the dynamics of wave-packet interaction with liquid particles. Although quantitatively relevant only in the transient phase, the additional term characterizing the hyperbolic equation, usually named the “memory term”, is physically present also once the stationary state is attained; it is responsible for dissipation in liquids and provides a finite propagation velocity for wave-packet avalanches responsible in the DML for the heat conduction. The consequences of this physical interpretation of the “memory” term added to the Fourier law for the phononic contribution are discussed and compiled with numerical prediction for the value of the memory term and with the conclusions of other works on the same topic.

Effects of long-range inter-particle interactions and isolated defect on quantum walks of two hard-core bosons in one-dimensional lattices

The quantum walk of two hard-core bosons in one-dimensional lattice under the effect of long-range inter-particle interaction is studied in detail. We also simulate the influence of an isolated defect that may exist in the lattice on the quantum walk of two particles by adding an additional potential energy to a certain lattice site. Using exact diagonalization method, the continuous-time quantum walk is directly simulated. The numerical simulations show that the range of interaction (long-range or short-range), the strength of the inter-particle interaction, the initial state of the two particles and the presence of the isolated defect have great influences on the quantum walk. Under the effect of strong long-range interaction, the particles initially located on the non-adjacent lattice sites have a co-walking behavior, while under the short-range interactions (nearest-neighbor interactions) only two particles initially located on the neighboring lattice sites can exhibit co-walking. After introducing the isolated defect into the system with strong interaction, two particles residing on the same side of the isolated defect keep co-walking, while two particles located on either sides of the isolated defect or one particle located on the isolated defect and the other particle staying on the side of the isolated defect, the two particles keep stationary or co-walking near the defect, displaying the characteristics of localization. By using the second-order perturbation theory of degenerate quantum system, a comprehensive theoretical analysis of the above numerical results is given. The theoretical analysis reveals the underlying physical law of quantum walks of two particles in one-dimensional lattice under the effects of strong long-range interaction and isolated defect in the lattice.

Thermodynamic mechanism and its geological significance in the transformation of albite under inorganic acid environments based on the total dissolution model

Feldspar of lithosphere undergoes transformation in an acidic fluid environment. This process significantly influences the transformation of sandstone reservoirs in sedimentary basins. Currently, there is debate on the transformation mechanism, which has led to debates in predictions of favorable reservoirs in deep sedimentary basins, in terms of their origin, type, and distribution. In this study, the transformation process of feldspar is determined based on the total dissolution model, and thermodynamics is used in the calculation process. Firstly, the precipitation order of the minerals and the reaction path during the transformation process are determined. Secondly, the obtained results are compared with the results of weathered feldspar samples, laboratory-based physical simulation samples, and sandstone samples from a sedimentary basin. Finally, the changes of sandstone reservoirs which is caused by feldspar transformation processes are discussed. Based on those results, it can be deduced that the release of inter-granular particles (Na/K/Ca) in feldspar does not conform to the total dissolution model, whereas the release of lattice particles (Si and Al) conforms to the model. The total dissolution model can deduce the genetic mechanism and occurrence of authigenic kaolinite in sandstone reservoirs. When the temperature is below 120 °C, authigenic kaolinites are directly precipitated from the pore fluids or via the reaction of Al(OH)3(s) with H4SiO4(aq). The kaolinite aggregates are worm-like, with a pure chemical composition. When the temperature is above 120 °C, the feldspar particles react with Al(OH)3(s) and transformed to kaolinites. The kaolinite aggregates are particle-like, containing heteroatoms. The differences in the genetic mechanism of kaolinite lead to evident differences for type and distribution of secondary pores formed during feldspar transformation.

Ordered domains in sheared dense suspensions: The link to viscosity and the disruptive effect of friction

Monodisperse suspensions of Brownian colloidal spheres crystallize at high densities, and ordering under shear has been observed at densities below the crystallization threshold. We perform large-scale simulations of a model suspension containing over 105 particles to quantitatively study the ordering under shear and to investigate its link to the rheological properties of the suspension. We find that at high rates, for Pe>1, the shear flow induces an ordering transition that significantly decreases the measured viscosity. This ordering is analyzed in terms of the development of layering and planar order, and we determine that particles are packed into hexagonal crystal layers (with numerous defects) that slide past each other. By computing local ψ6 and ψ4 order parameters, we determine that the defects correspond to chains of particles in a squarelike lattice. We compute the individual particle contributions to the stress tensor and discover that the largest contributors to the shear stress are primarily located in these lower density, defect regions. The defect structure enables the formation of compressed chains of particles to resist the shear, but these chains are transient and short-lived. The inclusion of a contact friction force allows the stress-bearing structures to grow into a system-spanning network, thereby disrupting the order and drastically increasing the suspension viscosity.

Non-linear optical characteristics of sand glass

In this work the nonlinear optical characteristics of sand glass which is the origin of quartz crystal were evaluated, sand glass particles from mining site waste were prepared by washing, drying, magnetic separation and sieving. The particles are soaked in sulphonic acid H2 SO4 acidic solution with 30% concentration for 100 hours, the new compound with optical characteristics was formed at different volume fractions of sandglass such as 20%,40%,60%, and 80% respectively. The new machine was developed for manufacturing the new compound from sand glass. The optical nonlinear absorption coefficient of the sand glass-ceramics material was investigated using the Z-scan technique, provided with nanosecond pulses of second harmonic (green Nd:YAG laser with 532nm wavelength). The effect of lattice structure and particles concentration on the non-linear optical properties were also discussed. The conclusions and recommendations for the best material and concertation for nonlinear optical material were mentioned. The research end with conclusions and recommendation for the development of new optical materials based on micro and nanoparticles from natural resources.

Controllable three-dimensional electrostatic lattices for manipulation of cold polar molecules

Engineering many-body systems of particles in lattices has attracted intense interest in the last few decades, thanks to their promising applications such as in quantum computation or topological matter. While lattices of different dimensions have been demonstrated with magnetic and/or optical fields, little work has been done upon three-dimensional (3D) electrostatic lattices to tame polar molecules. Here, we propose a 3D electrostatic lattice consisting of periodically distributed square-patterned electrodes in space, whose potentials reach tens of millikelvin and can be controlled easily. Detailed analysis and Monte Carlo simulations indicate that ${\mathrm{ND}}_{3}$ molecules in its $|J,KM\ensuremath{\rangle}=|1,\ensuremath{-}1\ensuremath{\rangle}$ state can be effectively trapped and evaporatively cooled. In addition, replacing the electrodes with different patterns enables realizing 3D electric lattices with new topological geometry (e.g., honeycomb or kagome). As a natural extension of the 3D optical and magnetic lattices, the 3D electrostatic lattice offers intriguing perspectives for cold chemistry, quantum simulation, and precision metrology.

Refrigeration using magnetocaloric and electrocaloric effects in a Fermi–Hubbard optical dimer exposed to a heat bath

We consider a Fermi–Hubbard dimer exposed to external electromagnetic fields and a Fermi gas bath under the assumptions of a repulsive two-particle interaction and the half-filling condition. Using the exact diagonalization method, it was found that the entropy and heat capacity rapidly rise within distinct localized regions of the magnetic and electric fields at low temperatures. The behavior of the magnetic (electric) Grüneisen ratio denotes that the direction of the external field determines the magnetization or demagnetization (polarization or depolarization) due to the magnetocaloric (electrocaloric) effect among the lattice particles at a given temperature. At the same time, the isothermal entropic change as a function of the temperature indicates that refrigeration is optimized when the electric field along the line joining the two sites of the optical lattice is assisted by a transverse magnetic field.

Magnetic Bloch oscillations and domain wall dynamics in a near-Ising ferromagnetic chain

When charged particles in periodic lattices are subjected to a constant electric field, they respond by oscillating. Here we demonstrate that the magnetic analogue of these Bloch oscillations are realised in a ferromagnetic easy axis chain. In this case, the “particles” undergoing oscillatory motion in the presence of a magnetic field are domain walls. Inelastic neutron scattering reveals three distinct components of the low energy spin-dynamics including a signature Bloch oscillation mode. Using parameter-free theoretical calculations, we are able to account for all features in the excitation spectrum, thus providing detailed insights into the complex dynamics in spin-anisotropic chains.

Continuous Limit, Rational Solutions, and Asymptotic State Analysis for the Generalized Toda Lattice Equation Associated with 3 × 3 Lax Pair

Discrete integrable nonlinear differential difference equations (NDDEs) have various mathematical structures and properties, such as Lax pair, infinitely many conservation laws, Hamiltonian structure, and different kinds of symmetries, including Lie point symmetry, generalized Lie bäcklund symmetry, and master symmetry. Symmetry is one of the very effective methods used to study the exact solutions and integrability of NDDEs. The Toda lattice equation is a famous example of NDDEs, which may be used to simulate the motions of particles in lattices. In this paper, we investigated the generalized Toda lattice equation related to 3×3 matrix linear spectral problem. This discrete equation is related to continuous linear and nonlinear partial differential equations under the continuous limit. Based on the known 3×3 Lax pair of this equation, the discrete generalized (m,3N−m)-fold Darboux transformation was constructed for the first time and extended from the 2×2 Lax pair to the 3×3 Lax pair to give its rational solutions. Furthermore, the limit states of such rational solutions are discussed via the asymptotic analysis technique. Finally, the exponential–rational mixed solutions of the generalized Toda lattice equation are obtained in the form of determinants.

Pseudospin-one particles in the time-periodic dice lattice: a new approach to transport control

The controlling of the transmission in the pseudospin-one Dirac–Weyl systems offers a rich tool to study new concepts of massive Dirac electron tunneling by means of a time-dependent potential. The time-periodic potential is one of the experimental techniques to have more control over the tunneling effect. In this paper, we study the transmission coefficient for different sidebands to obtain total transmission. We show how the super Klein tunneling under special conditions is independent of the incidence angle, oscillation amplitude, frequency, and barrier width. We consider a band gap opening with different locations of the flat band and modulate the resonances by tuning free parameters in our system.

Interplay of orientational order and roughness in simulated thin film growth of anisotropically interacting particles.

Roughness and orientational order in thin films of anisotropic particles are investigated using kinetic Monte Carlo simulations on a cubic lattice. Anisotropic next-neighbor interactions between the lattice particles were chosen to mimic the effects of shape anisotropy in the interactions of disk- or rodlike molecules with van der Waals attractions. Increasing anisotropy leads first to a preferred orientation in the film (which is close to the corresponding equilibrium transition) while the qualitative mode of roughness evolution (known from isotropic systems) does not change. At strong anisotropies, an effective step-edge (Ehrlich-Schwoebel) barrier appears and a nonequilibrium roughening effect is found, accompanied by reordering in the film which can be interpreted as the nucleation and growth of domains of lying-down disks or rods. The information on order and roughness is combined into a diagram of dynamic growth modes.

A Relativistic Toda Lattice Hierarchy, Discrete Generalized (m,2N−m)-Fold Darboux Transformation and Diverse Exact Solutions

This paper investigates a relativistic Toda lattice system with an arbitrary parameter that is a very remarkable generalization of the usual Toda lattice system, which may describe the motions of particles in lattices. Firstly, we study some integrable properties for this system such as Hamiltonian structures, Liouville integrability and conservation laws. Secondly, we construct a discrete generalized (m,2N−m)-fold Darboux transformation based on its known Lax pair. Thirdly, we obtain some exact solutions including soliton, rational and semi-rational solutions with arbitrary controllable parameters and hybrid solutions by using the resulting Darboux transformation. Finally, in order to understand the properties of such solutions, we investigate the limit states of the diverse exact solutions by using graphic and asymptotic analysis. In particular, we discuss the asymptotic states of rational solutions and exponential-and-rational hybrid solutions graphically for the first time, which might be useful for understanding the motions of particles in lattices. Numerical simulations are used to discuss the dynamics of some soliton solutions. The results and properties provided in this paper may enrich the understanding of nonlinear lattice dynamics.

Energy spreading, equipartition, and chaos in lattices with non-central forces

We numerically study a one-dimensional, nonlinear lattice model which in the linear limit is relevant to the study of bending (flexural) waves. In contrast with the classic one-dimensional mass-spring system, the linear dispersion relation of the considered model has different characteristics in the low frequency limit. By introducing disorder in the masses of the lattice particles, we investigate how different nonlinearities in the potential (cubic, quadratic, and their combination) lead to energy delocalization, equipartition, and chaotic dynamics. We excite the lattice using single site initial momentum excitations corresponding to a strongly localized linear mode and increase the initial energy of excitation. Beyond a certain energy threshold, when the cubic nonlinearity is present, the system is found to reach energy equipartition and total delocalization. On the other hand, when only the quartic nonlinearity is activated, the system remains localized and away from equipartition at least for the energies and evolution times considered here. However, for large enough energies for all types of nonlinearities we observe chaos. This chaotic behavior is combined with energy delocalization when cubic nonlinearities are present, while the appearance of only quadratic nonlinearity leads to energy localization. Our results reveal a rich dynamical behavior and show differences with the relevant Fermi–Pasta–Ulam–Tsingou model. Our findings pave the way for the study of models relevant to bending (flexural) waves in the presence of nonlinearity and disorder, anticipating different energy transport behaviors.

Tunable exciton-polaritons emerging from WS2 monolayer excitons in a photonic lattice at room temperature

Engineering non-linear hybrid light-matter states in tailored lattices is a central research strategy for the simulation of complex Hamiltonians. Excitons in atomically thin crystals are an ideal active medium for such purposes, since they couple strongly with light and bear the potential to harness giant non-linearities and interactions while presenting a simple sample-processing and room temperature operability. We demonstrate lattice polaritons, based on an open, high-quality optical cavity, with an imprinted photonic lattice strongly coupled to excitons in a WS2 monolayer. We experimentally observe the emergence of the canonical band-structure of particles in a one-dimensional lattice at room temperature, and demonstrate frequency reconfigurability over a spectral window exceeding 85 meV, as well as the systematic variation of the nearest-neighbour coupling, reflected by a tunability in the bandwidth of the p-band polaritons by 7 meV. The technology presented in this work is a critical demonstration towards reconfigurable photonic emulators operated with non-linear photonic fluids, offering a simple experimental implementation and working at ambient conditions.

Scattering of two particles in a one-dimensional lattice

This study concerns the two-body scattering of particles in a one-dimensional periodic potential. A convenient ansatz allows for the separation of center-of-mass and relative motion, leading to a discrete Schr\"odinger equation in the relative motion that resembles a tight-binding model. A lattice Green's function is used to develop the Lippmann-Schwinger equation, and ultimately derive a multiband scattering $K$ matrix which is described in detail in the two-band approximation. Two distinct scattering lengths are defined according to the limits of zero relative quasimomentum at the top and bottom edges of the two-body collision band. Scattering resonances occur in the collision band when the energy is coincident with a bound state attached to another higher or lower band. Notably, repulsive on-site interactions in an energetically closed lower band lead to collision resonances in an excited band.