Dependent Dispersion Research Articles

Dispersion of dielectric permittivity for composite material based on resistive dipoles

A correspondence has been established between the electrodynamic characteristics of a thin conductive cylindrical dipole and a needle-shaped ellipsoid. A well-known experimental result is theoretically justified, according to which an ellipsoid of the same material inscribed in it corresponds to a dipole. It is shown that, depending on the magnitude of the skin effect, the dispersion dependence of the effective dielectric constant of a dipole-based composite can correspond to both the Lorentz dielectric model and the Debye model. The results of calculating the dielectric constant of the composite according to various mixing formulas are compared with experimental data.

The Phase Structure of Wave Disturbances Excited by a Pulsating Source at the Interface of a Liquid Flow of Finite Depth and an Ice Sheet

The floating ice sheet determines the dynamic interaction between the ocean and the atmosphere, affects the dynamics of the sea surface and subsurface waters, since the ice sheet and the entire mass of liquid under it participate in the general vertical movement. The paper investigates the phase structure of wave fields arising at the interface between ice and a flow of homogeneous liquid of finite thickness when flowing around a localized pulsating source of disturbances. The ice sheet is modeled by a thin elastic plate, the deformations of which are small, and the plate is physically linear. An integral representation of the solution is obtained, and the results of calculations of dispersion dependencies and phase patterns for various parameters of wave generation are presented. It is shown that the main parameters determining the characteristics of the amplitude-phase structure of wave disturbances of the ice sheet surface are ice thickness, flow velocity, and pulsation frequency. Numerical calculations demonstrate that when the flow velocities, ice thickness, and frequency change, there is a noticeable qualitative restructuring of the phase patterns of the excited long-range wave fields at the ice-liquid interface.

Evaluation and modeling of velocity dispersion and frequency-dependent attenuation in gas hydrate-bearing sediments

Wave velocity and attenuation of gas hydrate-bearing samples are often extrapolated from ultrasonic to lower seismic/sonic frequencies, but the impact of measurement frequency on these properties is rarely studied. This study evaluates velocity dispersion and frequency-dependent attenuation in gas hydrate-bearing sediments (GHBS) by comparing vertical seismic profile (VSP) and sonic logging data from the Nankai Trough and Mallik field. We also employ rock physics modeling to simulate the velocity dispersion and frequency-dependent attenuation at both sites. The results show strong velocity dispersion and frequency-dependent attenuation in the Nankai Trough, attributed to thin, low-saturation hydrate intervals. In contrast, the Mallik field exhibits weak dispersion and frequency dependence, likely due to thick, highly saturated hydrate layers. A compilation of global hydrate reservoir attenuations indicates frequency dependence, with a peak in the sonic logging range, likely due to pore-scale hydrate effects. These findings emphasize the necessity of considering the effect of measurement frequency when performing time-to-depth conversion for seismic data based on the sonic velocity at higher frequencies, particularly for thin and lowly saturated hydrate layers, thereby improving the accuracy of hydrate reservoir characterization.

A Gravitational-like Relationship of Dispersion Interactions is Exhibited by 40 Pairs of Molecules and Noble Gas Atoms.

We present computational results of many-body dispersion (MBD) interactions for 40 pairs of molecular and atomic species: hydrocarbons, silanes, corresponding fluorinated derivatives, pairs which have multiple H---H contacts between the molecules, as well as pairs having π-π interactions, and pairs of noble gases. The calculations reveal that the MBD stabilization energy (EDISP,MBD) obeys a global relationship, which is gravitational-like. It is proportional to the product of the masses of the two molecules (M1M2) and inversely proportional to the corresponding distances between the molecular centers-of-mass (RCOM-COM) or the H---H distances of the atoms mediating the interactions of the two molecules (RH-H). This relationship reflects the interactions of instantaneous dipoles, which are formed by the ensemble of bonds/atoms in the interacting molecules. Using the D4-corrected dispersion energy (EDISP,D4), which accounts for three-body interactions, we find that the EDISP,MBD and EDISP,D4 data sets are strongly correlated. Based on valence-bond modeling, the dispersion interactions occur primarily due to the increased contributions of the oscillating-ionic VB structures which maintain favorable electrostatic interactions; the [Sub─C+:H-+H:C-─Sub] and [Sub─C:-+H -H:C+─Sub] structures; Sub symbolizes general residues. This augmented contribution is complemented by simultaneously diminished-weights of the destabilizing pair of structures, [Sub─C+:H--H:C+─Sub] and [Sub─:C- H++H:C-─Sub]. The local charges are propagated to the entire ensemble of bonds/atoms by partially charging the Sub residues, thus bringing about the "gravitational-like" dependence of dispersion.

Poroelastic Response of a Fractured Rock to Hydrostatic Pressure Oscillations

AbstractPoroelastic coupling between fractures and the surrounding rock is important to numerous applications in geosciences. We measure the in‐situ fluid pressure and local strain response of a fractured carbonate sample to hydrostatic pressure oscillations. A linear poroelastic model that represents the rock sample is parameterized using X‐ray imaging and ultrasonic wave transmission measurements. The numerical solution, based on Biot's quasistatic equations, is consistent with the measured frequency dependent dispersion of the apparent bulk modulus of the background matrix and the in‐situ pore pressure response, which is caused by fluid pressure diffusion from the compliant fractures into the stiffer matrix. The observed fluid pressure diffusion is causally related to the numerically quantified intrinsic attenuation at seismic frequencies, which is a major contributor to the dissipation of seismic waves. Our analysis supports the use of a simple approximation of fractures as compliant and planar inclusions in numerical simulations based on linear poroelasticity.

Development of the wave motion induced by near-bottom periodic disturbances in a two-layer shear current

The behavior of wave motion arising in an ideal incompressible homogeneous fluid under switching-on periodic bottom disturbances is studied in the linear approximation for the two-dimensional non-stationary problem. In the undisturbed state, the velocities of two-layer fluid flow are linear functions of the vertical coordinate in each of the layers with different gradients and coincide on the boundary of the layers. The upper boundary of fluid can be either free or bounded by the rigid cover. The dispersion dependences and the group velocities of the appearing wave modes are determined. The vertical displacements of the free surface and the interface between the layers are calculated. A comparison with the solution for a single-layer fluid is carried out.

Piezo-optical properties and infrared spectra of Rb2SO4 crystals

The paper deals with the dispersion dependences of birefringence Δni(λ) of the mechanically free and uniaxially clamped Rb2SO4 crystal along different crystal-physical axes at room temperature. It was found that the crystal has an insignificant normal dispersion d(Δnx)/dλ χ ≤ 0, and uniaxial compressions σm do not change the character, but only the slope of the dependences Δni(λ). Uniaxial loads shift the position of the optical isotropic point both in the short-wavelength (σz) and in the long-wavelength part of the spectrum (σy). The spectral dependences of the combined piezo-optical coefficients πkmo(λ) were calculated and it was found that they have an insignificant dispersion dependence, and the absolute values of the piezo-optical coefficients π31o and π21o are equal to each other in the vicinity of the optical isotropic point at the light wavelength λ = 490 nm. The reflection spectra of Rb2SO4 crystals were measured in the infrared range at room temperature using FT-IR spectrometer and synchrotron radiation and the corresponding ab initio calculations of the phonon partial density of states and the dielectric function were performed.

Assessing abdominal aortic aneurysm growth using radiomic features of perivascular adipose tissue after endovascular repair

ObjectivesThe study aimed to investigate the relationship between the radiomic features of perivascular adipose tissue (PVAT) and abdominal aortic aneurysm (AAA) growth after endovascular aneurysm repair (EVAR).MethodsPatients with sub-renal AAA who underwent regular follow-up after EVAR between March 2014 and March 2024 were retrospectively collected. Two radiologists segmented aneurysms and PVAT. Patients were categorised into growing and non-growing groups based on volumetric changes observed in two follow-up computed tomography examinations. One hundred seven radiomic features were automatically extracted from the PVAT region. Univariable and multivariable logistic regression was performed to analyse radiomic features and clinical characteristics. Furthermore, the performance of the integrated clinico-radiological model was compared with models using only radiomic features or clinical characteristics separately.ResultsA total of 79 patients (68 ± 9 years, 89% men) were enroled in this study, 19 of whom had a growing aneurysm. Compared to the non-growing group, PVAT of growing AAA showed a higher surface area to volume ratio (non-growing vs growing, 0.63 vs 0.70, p = 0.04), and a trend of low dependence and high dispersion manifested by texture features (p < 0.05). The area under the curve of the integrated clinico-radiological model was 0.78 (95% confidence intervals 0.65–0.91), with a specificity of 87%. The integrated model outperformed models using only radiomic or clinical features separately (0.78 vs 0.69 vs 0.69).ConclusionsHigher surface area to volume ratio and more heterogeneous texture presentation of PVAT were associated with aneurysm dilation after EVAR. Radiomic features of PVAT have the potential to predict AAA progression.Clinical relevance statementRadiomic features of PVAT are associated with AAA progression and can be an independent risk factor for aneurysm dilatation to assist clinicians in postoperative patient surveillance and management.Key PointsAfter EVAR for AAA, patients require monitoring for progression.PVAT surrounding growing AAA after EVAR exhibits a more heterogeneous texture.Integrating PVAT-related features and clinical features results in better predictive performance.Graphical

Fault Diagnosis for Rail Profile Data Using Refined Dispersion Entropy and Dependence Measurements

Fault Diagnosis for Rail Profile Data Using Refined Dispersion Entropy and Dependence Measurements

Two-Dimensional Surface Periodic Flows of an Incompressible Fluid in Various Models of the Medium

A comparative analysis of the properties of two-dimensional infinitesimal periodic perturbations propagating over the incompressible fluid surface in various representations of the medium density profiles is carried out. Stratified and homogeneous in density viscous or ideal liquids are considered. Calculations are carried out by methods of the theory of singular perturbations. Dispersion relations and dependences of phase and group velocities for surface waves in physically observed variables are given. The change in the meaning of dispersion relations during the transition from ideal liquids to viscous and from homogeneous to stratified is shown. Taking into account the influence of electric charge does not qualitatively change the nature of two-dimensional dispersion relations. An increase in the surface density of the electric charge leads to a decrease in the wavelength at a fixed frequency and has no noticeable effect on the fine structure of the periodic flow.

Dependence of Structure Variation, Pyrolysis, and Nonlinear Optical Dispersion on the Chemical Etching of Poly Allyl Diglycol Carbonate (PADC) Irradiated with $${\alpha}$$-Particles

Dependence of Structure Variation, Pyrolysis, and Nonlinear Optical Dispersion on the Chemical Etching of Poly Allyl Diglycol Carbonate (PADC) Irradiated with $${\alpha}$$-Particles

Structural, electronic, thermoelectric and optical properties of 2D hexagonal beryllium telluride under DFT investigation

In this study we have investigated structural, electronic, thermoelectric and optical properties of monolayer beryllium telluride compound in the hexagonal lattice phase (h-BeTe) using first principle calculations under density functional theory (DFT) approach. Using the frequency dependent phonon dispersion curves, we have analyzed the stability of the h-BeTe compound. The investigation of structural properties, including density of states (DOS) and band structure, demonstrates that h-BeTe is a direct bandgap semiconductor material with bandgap value of 3.054 eV. The h-BeTe compound exhibits exceptional thermoelectric behavior for a temperature range of 50–800 K, as confirmed by the calculated thermoelectric parameters, including thermal conductivity, electrical conductivity, Seebeck coefficient and figure of merit (ZT). It is vital that h-BeTe exhibits exceptional thermoelectric properties specifically, the figure of merit (ZT > 0.9) provides the efficiency of h-BeTe compound in temperature range of 300–800 K. The optical properties of h-BeTe are investigated for the first time with its interaction in applied external electric field based on various optical parameters such as real and imaginary dielectric constant, refractive index n(ω), extinction coefficient k(ω), absorption coefficient α(ω) and reflectivity R(ω). The optical properties analysis reveals the monolayer hexagonal beryllium telluride to be mostly active in the visible-UV spectrum. These findings have the potential to foster researchers to explore h-BeTe compound experimentally for possible optoelectronic applications.

The band structure of a chain of periodically ordered different quantum dots

The paper introduces a model for a superlattice comprising periodically arranged quantum dots (QDs) and proposes a method for calculating the energy spectrum. This theory was applied to a chain of QDs. The study employed the effective mass approximation and solved the Schrödinger equation using the tight-binding model and nearest neighbor approximation. The energy spectra of electrons were determined as functions of the wave vector, and the theory facilitated the calculation of dispersion dependencies and bandwidths. The presence of different QDs resulted in the subdivision of the mini-zone into upper and lower zones. It was demonstrated and analyzed that the width of the upper zones consistently exceeds that of the lower ones. Furthermore, when the QDs possess identical sizes and materials, no forbidden zone is observed.

Species interactions and eco-evolutionary dynamics of dispersal: the diversity dependence of dispersal.

Dispersal plays a pivotal role in the eco-evolutionary dynamics of spatially structured populations, communities and ecosystems. As an individual-based trait, dispersal is subject to both plasticity and evolution. Its dependence on conditions and context is well understood within single-species metapopulations. However, species do not exist in isolation; they interact locally through various horizontal and vertical interactions. While the significance of species interactions is recognized for species coexistence and food web functioning, our understanding of their influence on regional dynamics, such as their impact on spatial dynamics in metacommunities and meta-food webs, remains limited. Building upon insights from behavioural and community ecology, we aim to elucidate biodiversity as both a driver and an outcome of connectivity. By synthesizing conceptual, theoretical and empirical contributions from global experts in the field, we seek to explore how a more mechanistic understanding of diversity-dispersal relationships influences the distribution of species in spatially and temporally changing environments. Our findings highlight the importance of explicitly considering interspecific interactions as drivers of dispersal, thus reshaping our understanding of fundamental dynamics including species coexistence and the emergent dynamics of metacommunities and meta-ecosystems. We envision that this initiative will pave the way for advanced forecasting approaches to understanding biodiversity dynamics under the pressures of global change. This article is part of the theme issue 'Diversity-dependence of dispersal: interspecific interactions determine spatial dynamics'.

Marginal Fermi liquid behavior at the onset of 2kF density wave order in two-dimensional metals with flat hot spots

We analyze quantum fluctuation effects at the onset of incommensurate 2kF charge- or spin-density-wave order in two-dimensional metals for a model in which the ordering wave vector Q connects a single pair of hot spots on the Fermi surface with a vanishing Fermi surface curvature. The tangential momentum dependence of the bare dispersion near the hot spots is proportional to |kt|α with α&gt;2. We first compute the order parameter susceptibility and the fermion self-energy in a random phase approximation (RPA). Logarithmic divergences are subsequently treated by a renormalization-group analysis. The coupling between the order parameter fluctuations and the fermions vanishes logarithmically in the low-energy limit. As a consequence, the logarithmic divergences found in the RPA do not sum up to anomalous power laws. Instead, only logarithmic corrections to Fermi liquid behavior are obtained. In particular, the quasiparticle weight and the Fermi velocity vanish logarithmically at the hot spots. Published by the American Physical Society 2024

Modeling the Morphology of Fast Radio Bursts and Radio Pulsars with fitburst

We present a framework for modeling astrophysical pulses from radio pulsars and fast radio bursts (FRBs). This framework, called fitburst, generates synthetic representations of dynamic spectra that are functions of several physical and heuristic parameters; the heuristic parameters can nonetheless accommodate a vast range of distributions in spectral energy. fitburst is designed to optimize the modeling of features induced by effects that are intrinsic and extrinsic to the emission mechanism, including the magnitude and frequency dependence of pulse dispersion and scatter broadening. fitburst removes intrachannel smearing through two-dimensional upsampling, and can account for phase-wrapping of “folded” signals that are typically acquired during pulsar-timing observations. We demonstrate the effectiveness of fitburst in modeling data containing pulsars and FRBs observed with the Canadian Hydrogen Intensity Mapping Experiment telescope.

Hole subband dispersions in a cylindrical Ge nanowire: exact results based on the axial Luttinger–Kohn Hamiltonian

Based on the Luttinger–Kohn Hamiltonian in the axial approximation, the transcendental equations determining the hole subband dispersions in a cylindrical Ge nanowire are analytically derived. These equations are more general than that derived using the spherical approximation, and are suitable to study the growth direction dependence of the subband dispersions. The axial approximation almost gives rise to the accurate low-energy subband dispersions for high-symmetry nanowire growth directions [001] and [111]. The perturbation correction from the non-axial term is negligible for these two directions. The lowest two subband dispersions can be regarded as two shifted parabolic curves with an energy gap at kz=0 for both growth directions [001] and [111]. At the position of the energy gap, the eigenstates for growth direction [111] are inverted in comparison with the normal eigenstates for growth direction [001]. A nanowire growth direction where the energy gap closes at kz=0 is predicted to exist between directions [001] and [111].

The crucial role of granular packing structure in marine sediment acoustics

Motivated by the acoustic properties of marine sediments, we study via discrete-element method simulations the frequency dependence of dispersion and attenuation in model marine sediments. By numerically solving for the motion of each grain in a packing, rather than solving a continuum wave equation, we find that the granular packing structure, which is not explicitly considered in existing sediment-acoustics models, plays a crucial role in determining how attenuation and wave speed vary with frequency. Prior work has typically postulated a wave equation that is motivated by grain- scale forces, including viscous effects from the interstitial fluid, without explicitly considering the disordered packing structure of the grains. However, the packing structure is known to produce complex, nonlinear behavior (e.g., during shear or quasistatic compression), and how it affects dispersion and attenuation is not known. We consider linearized forces between particles (i.e., springs and dashpots), and demonstrate that the disordered packing structure leads to emergent scaling laws that do not agree with PDE-based approaches. Our results demonstrate that the granular packing structure must be explicitly considered when constructing theories for the acoustic properties of marine sediments.

Temperature-dependent dispersal and ectotherm species' distributions in a warming world.

Dispersal is a crucial component of species' responses to climate warming. Warming-induced changes in species' distributions are the outcome of how temperature affects dispersal at the individual level. Yet, there is little or no theory that considers the temperature dependence of dispersal when investigating the impacts of warming on species' distributions. Here I take a first step towards filling this key gap in our knowledge. I focus on ectotherms, species whose body temperature depends on the environmental temperature, not least because they constitute the majority of biodiversity on the planet. I develop a mathematical model of spatial population dynamics that explicitly incorporates mechanistic descriptions of ectotherm life history trait responses to temperature. A novel feature of this framework is the explicit temperature dependence of all phases of dispersal: emigration, transfer and settlement. I report three key findings. First, dispersal, regardless of whether it is random or temperature-dependent, allows both tropical and temperate ectotherms to track warming-induced changes in their thermal environments and to expand their distributions beyond the lower and upper thermal limits of their respective climate envelopes. In the absence of dispersal mortality, warming does not alter these new distributional limits. Second, an analysis based solely on trait response data predicts that tropical ectotherms should be able to expand their distributions polewards to a greater degree than temperate ectotherms. Analysis of the dynamical model confirms this prediction. Tropical ectotherms have an advantage when moving to cooler climates because they experience lower within-patch and dispersal mortality, and their higher thermal optima and maximal birth rates allow them to take advantage of the warmer parts of the year. Previous theory has shown that tropical ectotherms are more successful in invading and adapting the temperate climates than vice versa. This study provides the key missing piece, by showing how temperature-dependent dispersal could facilitate both invasion and adaptation. Third, dispersal mortality does not affect the poleward expansion of ectotherm distributions. But, it prevents both tropical and temperate ectotherms from maintaining sink populations in localities that are too warm to be viable in the absence of dispersal. Dispersal mortality also affects species' abundance patterns, causing a larger decline in abundance throughout the range when species disperse randomly rather than in response to thermal habitat suitability. In this way, dispersal mortality can facilitate the evolution of dispersal modes that maximize fitness in warmer thermal environments.

Nonlinear Landau Fan Diagram for Graphene Electrons Exposed to a Moiré Potential.

Due to Landau quantization, the conductance of two-dimensional electrons exposed to a perpendicular magnetic field exhibits oscillations that generate a fan of linear trajectories when plotted in the parameter space spanned by density and field. This fan looks identical, irrespective of the dispersion and field dependence of the Landau level energy. This is no surprise because the position of conductance minima depends solely on the level degeneracy that is linear in flux. The fractal energy spectrum that emerges within each Landau band when electrons are also exposed to a two-dimensional superlattice potential produces numerous additional oscillations, but they also create just linear fans for identical reasons. Here, we report conductance oscillations of graphene electrons exposed to a moiré potential that defy this general rule and form nonlinear trajectories in the density-field plane. We attribute this anomalous behavior to the simultaneous occupation of multiple minibands and magnetic breakdown-induced open orbits.