Inhomogeneous Structure Research Articles

Scattering of surface waves by inhomogeneities in crystalline structures

In current scientific and technological scenarios, studies of transmittance of surface waves across structured interfaces have gained some wind amidst applications to metasurfaces, electronic edge-waves, crystal grain boundaries, etc. The results presented in the present article shed a light on the influence of material inhomogeneities on propagation of surface waves. Within the framework of classical mechanics, an analogue of the Gurtin–Murdoch model is employed where elastic properties on surface are assumed to be distinct from bulk. Restricting to scalar waves on prototype square lattice half-plane, particles on considered structured surface have piecewise-constant mass and surface force-constants across an interfacial point. Particles in bulk lattice interact with nearest neighbours in a way that involves unequal force-constants parallel to surface versus normal to it. A surface wave band exists for such lattice structure wherein the waveform decays exponentially inside the half-plane. A formula for surface wave transmittance is given based on an exact solution on half-plane, and, thus, previous work (Sharma & Eremeyev 2019 Int. J. Eng. Sci. 143 , 33–38 ( doi:10.1016/j.ijengsci.2019.06.007 )) is extended. An explicit expression for fraction of energy influx leaked via bulk waves is a highlight. Included are graphical results for several illustrative values of surface structure parameters.

Evolution of the magnetic field in spatially inhomogeneous axion structures

Evolution of the magnetic field in spatially inhomogeneous axion structures

On the local aspect of valley magnetic moments

Valley magnetic moments play a crucial role in valleytronics in 2D hexagonal materials. Traditionally, insights drawn from the study of quantum states in homogeneous bulks have led to a widespread belief that only materials with broken structural inversion symmetry can exhibit nonvanishing valley magnetic moments. This belief, however, limits the scope of relevant applications, especially for materials with inversion symmetry, such as gapless monolayer graphene, despite its advantage in routine growth and production. This work revisits valley-derived magnetic moments in a broad context covering inhomogeneous structures as well. It generalizes the notion of a valley magnetic moment for a state from an integrated quantity to the local field called the “local valley magnetic moment” with space-varying distribution. It explores the local magnetic moment analytically both within the Dirac model and through a symmetry argument. Numerical investigations are conducted within the tight-binding model. Overall, we demonstrate that the breaking of inversion symmetry in the electron probability distribution leads to nonvanishing local magnetic moments. This probability-based breaking can occur in both structural inversion symmetric and symmetry-broken structures. In suitable inversion-symmetric structures with inhomogeneity, e.g., zigzag nanoribbons of gapless monolayer graphene, it is shown that the local moment of a state can be nonvanishing while the corresponding integrated moment is subject to the broken symmetry constraint. Moreover, it is demonstrated that the local moment can interact with space-dependent magnetic fields, resulting in field effects such as valley Zeeman splitting. Such effects can be exploited for local valley control as a conduit for the implementation of valleytronics.

The Dimorphos ejecta plume properties revealed by LICIACube.

The Double Asteroid Redirection Test (DART) had an impact with Dimorphos (a satellite of the asteroid Didymos) on 26 September 20221. Ground-based observations showed that the Didymos system brightened by a factor of 8.3 after the impact because of ejecta, returning to the pre-impact brightness 23.7 days afterwards2. Hubble Space Telescope observations made from 15 minutes after impact to 18.5 days after, with a spatial resolution of 2.1 kilometres per pixel, showed a complex evolution of the ejecta3, consistent with other asteroid impact events. The momentum enhancement factor, determined using the measured binary period change4, ranges between 2.2 and 4.9, depending on the assumptions about the mass and density of Dimorphos5. Here we report observations from the LUKE and LEIA instruments on the LICIACube cube satellite, which was deployed 15 days in advance of the impact of DART. Data were taken from 71 seconds before the impact until 320 seconds afterwards. The ejecta plume was a cone with an aperture angle of 140 ± 4degrees. The inner region of the plume was blue, becoming redder with increasing distance from Dimorphos. The ejecta plume exhibited a complex and inhomogeneous structure, characterized by filaments, dust grains and single or clustered boulders. The ejecta velocities ranged from a few tens ofmetres per second to about 500 metres per second.

Evolution of the magnetic field in spatially inhomogeneous axion structures

Изучается временна́я эволюция магнитных полей в различных конфигурациях пространственно-неоднородных псевдоскалярных полей, представляющих собой когерентную суперпозицию аксионов. Для таких систем выводится новое уравнение индукции для магнитного поля, в котором учитывается эта неоднородность. На основе этого уравнения исследуется эволюция пары волн Черна-Саймонса, взаимодействующих с линейно убывающим псевдоскалярным полем. Ненулевой градиент псевдоскалярного поля приводит к смешиванию этих волн. Затем рассматривается задача в компактной области, когда исходная волна Черна-Саймонса зеркально-симметрична. В этой ситуации неоднородность псевдоскалярного поля приводит к эффективному изменению $\alpha$-параметра динамо. Таким образом, влияние пространственно-неоднородного псевдоскалярного поля на эволюцию магнитного поля сильно зависит от геометрии системы.

Non‐Invasive Super‐Resolution Imaging Through Scattering Media Using Object Fluctuation

AbstractIntroducing super‐resolution techniques to imaging through scattering media potentially revolutionizes the technical analysis for many exotic applications, such as cell structures behind biological tissues. The main challenge is scattering media's inhomogeneous structures, which scramble the light path and create noise‐like speckle patterns, hindering object's visualization even at a low‐resolution level. Here, a computational method is proposed relying on the object's spatial and temporal fluctuation to visualize nanoscale objects through scattering media non‐invasively. Taking advantage of the optical memory effect and multiple frames, the point spreading function (PSF) of scattering media is estimated. Multiple images of fluctuating objects are obtained by deconvolution; then, the super‐resolution image is achieved by computing the higher‐order cumulants. Non‐linearity of high order cumulant significantly suppresses artifacts in the resulting images and enhances resolution by a factor of , where N is the cumulant order. The proof‐of‐concept demonstrates a resolution of 266 nm at the 6th‐order cumulant with numerical aperture (NA) of 0.42, breaking the diffraction limit by a factor of 2.45. An adaptive approach is also demonstrated for imaging through dynamic scattering media. The non‐invasive super‐resolution speckle fluctuation imaging (NISFFI) presents a nanoscopy technique with straightforward imaging hardware configuration to visualize samples behind scattering media.

DETERMINATION OF THE AMOUNT OF LOAD ON PROTECTIVE STRUCTURES OF CIVIL DEFENSE AGAINST THE INFLUENCE OF A SHOCK WAVE ACCORDING TO DBN V.2.2-5:2023

The main types of explosions and their differences between each other are considered, as well as the difference in excess pressure in the air shock wave is shown. The definition of the calculated load on various load-bearing elements depending on the type of building, its location and structural inhomogeneities of building structures according to DBN B.2.2-5:20023 [1] is given. One of the extreme effects, the danger of which must be taken into account when designing protective structures of civil protection, is an external explosion, which can be caused by both man-made and military factors. The explosion generates a whole complex of loads and impacts. The pressure at the front of the air shock wave, as well as the duration of the compression and rarefaction phases, depend on the amount of explosives and the distance to the center of the explosion or cloud boundary. In general, a detonation explosion is characterized by the possibility of significant pressure on the front of the air shock wave and the short duration of the action (tenths and even hundredths of a second). The air shock wave, when interacting with the structure, affects its above-ground and underground parts. This process is complex: at the beginning of the interaction process, the air shock wave affects the external structures of the above-ground part of the building and the surface of the soil in front of the building, causing a compression wave in it, which, in turn, affects the front outer face of the underground part. Further, the air shock wave, passing through the structural inhomogeneities of building structures in the form of window and door openings, affects the internal load-bearing and non-load-bearing structures of the building, as well as the covering of the underground part. At the same time, compression waves in the soil affect the side and rear walls of the underground part.

A Catalyst-Like System Enables Efficient Perovskite Solar Cells.

High-quality perovskite films are essential for achieving high performance of optoelectronic devices; However, solution-processed perovskite films are known to suffer from compositional and structural inhomogeneity due to lack of systematic control over the kinetics during the formation. Here, the microscopic homogeneity of perovskite films is successfully enhanced by modulating the conversion reaction kinetics using a catalyst-like system generated by a foaming agent. The chemical and structural evolution during this catalytic conversion is revealed by a multimodal synchrotron toolkit with spatial resolutions spanning many length scales. Combining these insights with computational investigations, a cyclic conversion pathway model is developed that yields exceptional perovskite homogeneity due to enhanced conversion, having a power conversion efficiency of 24.51% for photovoltaic devices. This work establishes a systematic link between processing of precursor and homogeneity of the perovskite films.

High temperature magneto-dielectric response and dielectric relaxations in PrIG

A high temperature MD effect has been observed in Pr3Fe5O12 (PrIG) which is a new member of rare earth iron garnets (RIG) family. Research indicates that this material has two dielectric relaxations in the temperature range from 370 K to 565 K and a dielectric anomaly around 580 K. The first dielectric relaxation is attributed to the conduction for the similar activation energy with conduction. The other dielectric relaxation in the higher temperature range originated from the inhomogeneous structure. And, the coupling between the ferrimagnetic phase transition and the dielectric response was observed at 1 kHz 0.35 T 580K.

Reversible Molecular Conformation Transitions of Smectic Liquid Crystals for Light/Bias-Gated Transistor Memory.

In recent years, organic photonic field-effect transistors have made remarkable progress with the rapid development of conjugated polycrystalline materials. Liquid crystals, with their smooth surface, defined layer thickness, and crystalline structures, are commonly used for these advantages. In this work, a series of smectic liquid crystalline molecules, 2,9-didecyl-dinaphtho-thienothiophene (C10-DNTT), 2,7-didecyl-benzothieno-benzothiopene (C10-BTBT), 3,9-didecyl-dinaphtho-thiophene (C10-DNT), and didecyl-sexithiophene (C10-6T), have been used in photonic transistor memory, functioning as both hole-transport channels and electron traps to investigate systematically the reasons and mechanisms behind the memory behavior of smectic liquid crystals. After thermal annealing, C10-BTBT and C10-6T/C10-DNTT are homeotropically aligned from the smectic A and smectic X phases, respectively. The 3D-ordered structure of these smectic-aligned crystals contributed to efficient photowriting and electrical erasing processes. Among them, the device performance of C10-BTBT was particularly significant, with a memory window of 21 V. The memory ratio could reach 1.5 × 106 and maintain a memory ratio of over 3 orders after 10,000 s, contributing to its smectic A structure. Through the research, we confirmed the memory and light/bias-gated behaviors of these smectic liquid crystalline molecules, attributing them to reversible molecular conformation transitions and the inherent structural inhomogeneity inside the polycrystalline channel layer.

Three-dimensional flow velocity determination using laser-induced fluorescence method with asymmetric optical vortex beams

Laser-induced fluorescence (LIF) Doppler spectroscopy using an optical vortex beam with an asymmetric intensity distribution, referred to as aOVLIF, is proposed as a new method to measure plasma flow velocity. LIF spectra were calculated numerically using typical laboratory low-temperature plasma parameters, and it was revealed that an ion flow across the beam produces a frequency shift of the spectra. This method also has the capability of temperature measurements. The propagation effects of asymmetric optical vortex beams are discussed assuming an actual experiment, and it is found that the sensitivity to the transverse flow velocity is approximately unchanged. The aOVLIF method, which exploits the inhomogeneous phase structure of optical vortices, can be applied to the determination of three-dimensional velocity vectors and promises to enhance the usefulness of conventional LIF spectroscopy using plane waves.

Changes in the structure of the amorphous phase under heat treatment and deformation

The influence of heat treatment and deformation on the change in the structure of amorphous alloys Co67Fe7Si12B9Nb5, Al87Ni8Y5, Al88Ni6Y6, Al87Ni8Gd5, Al87Ni8La5, Zr50Cu15Ti16Ni19 obtained by melt quen-ching has been studied. It has been established that both heat treatment and deformation lead to the for-mation of a heterogeneous structure, while structure inhomogeneities can be due to formation the regions both with different concentrations of components (during heat treatment) or/and with different density (free volume concentration). At the early stages of crystallization, the phase composition of the emerging struc-ture depends on the type of impact on the amorphous structure and processing parameters (temperature, type and degree of deformation). The sizes of nanocrystals and the fraction of the nanocrystalline component depend on the prehistory of the sample.

Lattice dynamics and elastic waves scattering by surrogate atoms in quasi-one dimensional atomic assemblies

An analytical and numerical formalism is developed to study the influence of the various positions of substitution atoms B on the scattering and transmission vibration modes in quasi-1D monatomic structures A. The matching technique is employed to calculate the dynamical properties and transmittance spectra of two substituted atomic sites. The theoretical formalism gives a complete description of the lattice dynamics and the vibration-waves propagation in the presence of the impurity sites. Numerical calculations are performed for three different positions of the two substituted atoms B in the low-dimensional structure consisting of double monatomic parallel chains. First, we examine the position where the two B atoms are adjacent in the y-direction, afterwards, we place the two sites side by side in the x-direction. Lastly, the two sites are placed in oblique configuration. The obtained results show that phonons associated to the inhomogeneous structures are strongly dependent on the scattering frequency, elastic force parameters and the position of the atomic substituted sites. In the three considered positions, the presence of the B atoms gives rise to localized vibration effects. The fluctuations observed in the vibration spectra are related to resonances due to the coherent coupling between travelling phonons and the localized vibration modes in the neighborhood of the impurity sites.

Effect of inhomogeneous structure on the water desalination performance of graphitic carbon nitride nanochannels: A molecular dynamics study

The transport behaviors of aqueous solution in two-dimensional (2D) nanomaterial-based separation membranes are correlated with the structure of the nanoconfined geometry. However, little is known about the impact of asymmetric structures on the transport behavior of aqueous solutions in membranes. In this work, we use molecular dynamics (MD) simulations to investigate the transport behaviors of aqueous solution in non-parallel stacked graphitic carbon nitride (g-C3N4) nanochannels. Interestingly, the non-parallel stacking of g-C3N4 could lead to the local aggregation of water, resulting in an inhomogeneous density distribution within the nanochannel. The high-density region in g-C3N4 nanochannel significantly disrupted the continuum fluid of water. Moreover, the inhomogeneous density distribution of water could impede ion transport in the non-parallel g-C3N4 nanochannel. It was found that ions cannot maintain compact hydration structures in the high-density region. This work reveals the unique properties of slightly tilted membrane structures, providing novel perspective for the design of next-generation nanofluidic devices.

Single-crystalline oligomer-based conductors modeling the doped poly(3,4-ethylenedioxythiophene) family.

Conductive polymers with highly conjugated systems, such as the doped poly(3,4-ethylenedioxythiophene) (PEDOT) family, are commonly used in organic electronics. However, their structural inhomogeneity with various chain lengths makes it difficult to control their conductivities and structural details. On the other hand, low-molecular-weight materials have well-defined structures but relatively narrow conjugate areas with a limited range of Coulomb repulsion between carriers (Ueff), which hamper the flexible control of conductivities. To bridge this gap, we developed oligomer-based conductors, which are intermediate materials between polymers and low-molecular-weight materials. Using a library of single-crystal charge-transfer salts of oligo(3,4-ethylenedioxythiophene) (oligoEDOT) analogs that model the doped PEDOT family, we have investigated the structure-determining factors affecting their conductivities, such as counter anion variations, lengths of oligomer donor, and band fillings. Through the screening study, we developed oligoEDOT analogs with tunable room temperature conductivities by several orders of magnitude, including a metallic state above room temperature. In this study, we consistently evaluated the electronic structural insights by first-principles calculations and revealed that Ueff is the dominant factor that determines the relationship between the structures and conductivities. The unique features of oligoEDOT conductor systems with widely variable Ueff can differentiate these systems from strongly electron-correlated systems.

Effect of Decompression Hole Structure Design on Stress Inhomogeneity of Stainless Steel Base Force Transducers

In order to reduce the stress inhomogeneity of the stainless steel base force transducer, the force transducer structure with decompression holes of different depths and different hole morphologies is designed in this paper and compared with the traditional force transducer structure without decompression hole design. According to the finite element analysis theory, the stress inhomogeneity level under different pressures and different structures is tested using a simulation platform. When a flat-bottomed hole is used and the depth of the decompression hole is 7 mm, the stress inhomogeneity of the inner ring of the force measurement structure is 32.77% of the original scheme, and the stress inhomogeneity of the outer ring is 90.12% of the original scheme. The simulation results show that the use of a suitable decompression hole structure can help to reduce the stress inhomogeneity of the force measurement structure. This work provides a new idea in the field of sensor optimization.

Influence of the coagulation bath on the nanostructure of cellulose films regenerated from an ionic liquid solution.

Cellulose membranes were prepared from an EMIMAc ionic liquid solution by nonsolvent-induced phase separation (NIPS) in coagulation baths of water-acetone mixtures, ethanol-water mixtures and water at different temperatures. High water volume fractions in the coagulation bath result in a highly reproducible gel-like structure with inhomogeneities observed by small-angle neutron scattering (SANS). A structural transition of cellulose takes place in water-acetone baths at very low water volume fractions, while a higher water bath temperature increases the size of inhomogeneities in the gel-like structure. These findings demonstrate the value of SANS for characterising and understanding the structure of regenerated cellulose films in their wet state. Such insights can improve the engineering and structural tuning of cellulose membranes, either for direct use or as precursors for carbon molecular sieve membranes.

3D Polarisation of a Structured Laser Beam and Prospects for its Application to Charged Particle Acceleration

A Structured Laser Beam (SLB) is a type of optical beam with spatially inhomogeneous 3D polarisation structures. Generating SLBs from vector beams allows the creation of Hollow Structured Laser Beams (HSLB) with a dark central core. In this way, atypical electric and magnetic field vectors, which are purely longitudinally polarized in the dark zones of the beam, are obtained. The SLB spatial distribution can also include regions with both the electric and magnetic fields longitudinally polarized and oriented in the same or opposite directions. The SLB has a transverse distribution similar to that of a Bessel beam but can theoretically propagate to infinity, therefore giving the potential to generate strong, longitudinally oriented electric fields over long distances, which could possibly allow the acceleration of charged particles. The results of the study of this phenomenon, including simulations of the spatial distribution of the electromagnetic field components, are presented in this paper.

Determination of interaction parameters in a bottom-up approach employed in reactive dissipative particle dynamics simulations for thermosetting polymers.

The limitations in previous dissipative particle dynamics (DPD) studies confined simulations to a narrow resin range. This study refines DPD parameter calculation methodology, extending its application to diverse polymer materials. Using a bottom-up approach with molecular dynamics (MD) simulations, we evaluated solubility parameters and bead number density governing nonbonded interactions via the Flory-Huggins parameter and covalent-bonded interactions. Two solubility parameter methods, Hildebrand and Krevelen-Hoftyzer, were compared for DPD simulations. The Hildebrand method, utilizing MD simulations, demonstrates higher consistency and broader applicability in determining solubility parameters for all DPD particles. The DPD/MD curing reaction process was examined in three epoxy systems: DGEBA/4,4'-DDS, DGEBA/MPDA and DGEBA/DETA. Calculations for the curing profile, gelation point, radial distribution function and branch ratio were performed. Compared to MD data for DGEBA/4,4'-DDS, the maximum deviation in secondary reactions between epoxy and amine groups according to DPD simulations with Krevelen-Hoftyzer was 14.8%, while with the Hildebrand method, it was 1.7%. The accuracy of the DPD curing reaction in reproducing the structural properties verifies its expanded application to general polymeric material simulations. The proposed curing DPD simulations, with a short run time and minimal computational resources, contributes to high-throughput screening for optimal resins and investigates mesoscopic inhomogeneous structures in large resin systems.

On modeling radiation-induced charge effects in objects of complex geometry

Algorithms for supercomputer modeling of the radiation-induced charge effects in materials of a complex multimodal structure are constructed. A geometric model of an object is created using Stilinger-Lubachevsky algorithms for objects of complex geometry. The model includes a system of detectors for statistical evaluation of functionals on the space of solutions of the photon-electron cascade transport equations. Visualization of simulation results is carried out using the three-dimensional approximation based on the neural network technology. The thechnique of mathematical simulating the generation and development of a photon-electronic cascade in a medium is used. The examples of results of calculations of the charge effects in a fragment of a bimodal material are presented. The results of the calculations show that the spatial distribution of the radiation-induced charges has a sharply inhomogeneous structure caused by the presence of boundaries of materials with different radiation properties.