Dependent Dispersion Research Articles

Laser ablation of titanium in the medium of n-hexane by femtosecond laser pulses at various pressures

The paper presents the results of studies on the synthesis of spherical titanium nanopowders in the medium of n-hexane depending on the pressure of the buffer gas. The dependence of the size dispersion of the obtaining nanopowders on pressure is considered. SEM images of the obtained nanopowders are shown. It has been demonstrated that adjusting the value of the external pressure, it is possible to control the size of the ablation products of laser processing.

Impact of elastic heterogeneity on the propagation of vibrations at finite temperatures in glasses

Some aspects of how sound waves travel through disordered solids are still unclear. Recent work has characterized a feature of disordered solids which seems to influence vibrational excitations at the mesoscales, local elastic heterogeneity. Sound waves propagation has been demonstrated to be strongly affected by inhomogeneous mechanical features of the materials which add to the standard anharmonic couplings, amounting to extremely complex transport properties at finite temperatures. Here, we address these issues for the case of a simple atomic glass former, by Molecular Dynamics computer simulation. In particular, we focus on the transverse components of the vibrational excitations in terms of dynamic structure factors, and characterize the temperature dependence of sound dispersion and attenuation in an extended frequency range. We provide a complete picture of how elastic heterogeneity determines transport of vibrational excitations, also based on a direct comparison of the numerical data with the predictions of the heterogeneous elastic theory.

Analysis of the resonance characteristics of surface plasmon polariton modes at air-metal interfaces in the ultraviolet, visible and infrared regions

Excitation of surface plasmon polariton (SPP) modes results in the appearance of resonance line shapes observed in the attenuated total reflection spectra of layered structures in the Otto or Kretschman configurations. The sensitivity of the resonance characteristics of the propagating modes to changes in optical characteristics of the environment is widely used in sensor devices to determine qualitative and quantitative changes in the environment, as well as low concentrations of substances adsorbed on the surface. In the present work, we analyze the resonance characteristics of SPP modes based on the optical properties of plasmonic materials. Interfaces of metal-dielectric structures support the propagation of SPP modes. Estimation of the dispersion dependences of the propagation constant of the SPP mode, sensitivity to changes in external conditions, enhancement of the near field on the surface is carried out within the electromagnetic theory based on approximations of asymmetric shapes of spectral resonance lines of SPP by Fano formulas in the ultraviolet, visible, and infrared regions.

Orbital dependence of superexchange interaction in charge-ordered manganites

The current investigation is devoted to the theoretical study of orbital structure influence upon magnetic subsystem in half-doped charge-ordered manganites. The main interaction of magnetic subsystem is superexchange interaction. It forms spin-wave dispersion dependencies. Because of charge and orbital ordering, there are a lot of superexchange parameters in these compounds. That makes the dispersion rather complicated. This work clarifies some features of dispersion in terms of orbitally-dependent superexchange interactions.

Magnon-Plasmon Polaritons in the Layered Structure Metal–Ferrite with a Periodic Stripe-Like Structure of Domains

The theory of magnon-plasmon polaritons in the layered structure metal–ferrite–air is presented. It is assumed that the ferrite has an easy-axis anisotropy, and, in the absence of a magnetization field, it is in an unsaturated state with a periodic stripe-like domain structure. A dispersion dependence for magnon-plasmon polaritons and corresponding microwave field distributions in a waveguide structure based on BaFe12O19-type hexaferrite are found. Effects associated with the hybridization of surface plasmon polaritons and domain resonances in the ferrite layer are analyzed. General characteristics of magnon-plasmon-polariton millimeter-wave resonators are discussed.

Calculation of SWR spectra in two- and three-layer magnetic films

In the present work, the calculation and experimental studies of the spin-wave resonance (SWR) spectra in two- and three-layer magnetic films with dissipative or mixed spin pinning mechanisms are carried out. The calculation showed that the SWR spectra for two-layer ferrite-garnet films have approximately twice the number of spin-wave (SW) modes compared to three-layer films on the same field interval, which is confirmed by experiment. An increase in the mismatch of the dispersion dependences is shown for perpendicular and parallel orientations for a three-layer film compared to a two-layer film. The SW-mode linewidth 2ΔHn in three-layer films is approximately twice as wide in two-layer films for identical values of the wave number.

The assessment of power influence of discharge flow from surges under conditions of hydrologically hazardous natural phenomena

Introduction. The analysis of studies on waves of translation and their dynamic effects on water infrastructure facilities indicates the incompleteness of accounting the dispersion component of wave motions in discharge flows. Existing analysis methods for the surge parameters with the dependence of the propagation velocity and wave pressure on the wavelength should be only considered as a rough approximation of the role of dispersion processes accompanying the surge propagation in river flows. The purpose of the research is to increase the accuracy of reliability analyses for equipment and auxiliary mechanisms of hydraulic structures and water facilities in the context of the growth of hydrologically hazardous natural phenomena in the form of surges.
 Materials and methods. The article used an analytical method for calculating the wave motion parameters. It is based on determining the conditions for synchronism of jumps and discontinuities in the parameters of the medium state when passing through front surfaces. An option was suggested for using the frontal characteristics method for integrating equations of unsteady currents in open flows. The paper presented a scheme for solving the differential equations of unsteady motions and continuity of flows in river streams with surges in the presence of resistance forces.
 Results. Analytical design relations were obtained for the velocity and power effects of surges with dispersion dependence on wavelength. An analysis of the obtained solutions is carried out by illustrating the dynamic effects of wave dispersion on water infrastructure facilities.
 Conclusions. The suggested method of the more accurate analysis for the force impact of the discharge flow from surges on the structural elements of hydro-economic and water-transport facilities can be used to determine the reliability of hydraulic structures and water-transport facilities. The obtained analysis relations for determining the kinematic and dynamic characteristics of the dispersion of the surges are advisably recommended to supplement the existing regulatory documents on hydraulic engineering.

Long-range dispersal promotes species persistence in climate extremes.

Anthropogenic global warming in this century can act as a leading factor for large scale species extinctions in the near future. Species, in order to survive, need to develop dispersal strategies depending upon their environmental niche. Based on empirical evidence only a few previous studies have addressed how dispersal can evolve with changing temperature. However, for the analytical tractability, there is a need to develop an explicit model to ask how the temperature-dependent dispersal alters ecological dynamics. We investigate the persistence of species in a spatial ecological model, where dispersal is considered as a function of temperature. Spatial persistence is of major concern and dispersal is reasonably an important factor for extinction risk in the context of promoting synchrony. Our study yields how the temperature influences species decision of dispersal, resulting in either short-range or long-range dispersal. We examine synchronous or asynchronous behavior of species under their thermal dependence of dispersal. Moreover, we also analyze the transients to study the collective behavior of species away from their final or asymptotic dynamics. One of the key findings is at the most unfavorable environmental conditions long-range dispersal works out as the driving force for the persistence of species.

Temperature dependent dispersion models applicable in solid state physics

Abstract Dispersion models are necessary for precise determination of the dielectric response of materials used in optical and microelectronics industry. Although the study of the dielectric response is often limited only to the dependence of the optical constants on frequency, it is also important to consider its dependence on other quantities characterizing the state of the system. One of the most important quantities determining the state of the condensed matter in equilibrium is temperature. Introducing temperature dependence into dispersion models is quite challenging. A physically correct model of dielectric response must respect three fundamental and one supplementary conditions imposed on the dielectric function. The three fundamental conditions are the time-reversal symmetry, Kramers-Kronig consistency and sum rule. These three fundamental conditions are valid for any material in any state. For systems in equilibrium there is also a supplementary dissipative condition. In this contribution it will be shown how these conditions can be applied in the construction of temperature dependent dispersion models. Practical results will be demonstrated on the temperature dependent dispersion model of crystalline silicon.

Effect of thermal lattice and magnetic disorder on phonons in bcc Fe: A first-principles study

We present a first-principles theoretical approach to calculate temperature dependent phonon dispersions in bcc Fe, which captures finite temperature spin-lattice coupling by treating thermal disorder in both the spin and lattice systems simultaneously. With increasing temperature, thermal atomic displacements are found to induce increasingly large fluctuations in local magnetic moment magnitudes. The calculated phonon dispersions of bcc Fe show excellent agreement with measured data over a wide range of temperatures both above and below the magnetic and structural transition temperatures, suggesting the applicability of the developed approach to other magnetic materials.

Autowave Physics of Material Plasticity

The notions of plastic flow localization are outlined in the paper. It is shown that each type of localized plasticity pattern corresponds to a definite stage of deformation hardening. In the course of plastic flow development, a changeover in the types of localization patterns occurs. The types of localization patterns are limited in number: four pattern types are all that can be expected. A correspondence was set up between the emergent localization pattern and the respective flow stage. It is found that the localization patterns are manifestations of the autowave nature of plastic flow localization process, with each pattern type corresponding to a definite mode of autowave. In the course of plastic flow development, the following modes of autowaves will form in the following sequence: switching autowave → phase autowave → stationary dissipative structure → collapse of the autowave. Of particular interest are the phase autowave and the respective pattern observed. Propagation velocity, dispersion, and grain size dependence of wavelength were determined experimentally for the phase autowave. An elastic-plastic strain invariant was also introduced to relate the elastic and plastic properties of the deforming medium. It is found that the autowave characteristics follow directly from this invariant.

Kinematic signatures of cluster formation from cool collapse in the Lagoon Nebula cluster NGC 6530

ABSTRACT We examine the mass dependence of the velocity dispersion of stars in the young cluster NGC 6530 to better understand how it formed. Using a large sample of members we find that the proper motion velocity dispersion increases with stellar mass. While this trend is the opposite of that predicted if the cluster were developing energy equipartition, it is in agreement with recent N-body simulations that find such a trend develops because of the Spitzer instability. In these simulations the massive stars sink to the centre of the cluster and form a self-gravitating system with a higher velocity dispersion. If the cluster has formed by the cool collapse of an initially substructured distribution, then this occurs within 1–2 Myr, in agreement with our observations of NGC 6530. We therefore conclude that NGC 6530 formed from much more extended initial conditions and has since collapsed to form the cluster we see now. This cluster formation model is inconsistent with the idea that all stars form in dense, compact clusters and provides the first dynamical evidence that star clusters can form by hierarchical mergers between subclusters.

Density Dependence of Egg Recruitment and Moth Dispersal in Spruce Budworms

Egg recruitment quantifies the relative importance of realized fecundity and migration rates in the population dynamics of highly mobile insects. We develop here a formal context upon which to base the measurement and interpretation of egg recruitment in population dynamics of eastern and western spruce budworms, two geographically separated species that share a very similar ecology. Under most circumstances, per capita egg recruitment rates in these budworms are higher in low-density populations and lower in high-density populations, relative to the regional mean: Low-density populations are nearly always migration sinks for gravid moths, and dense populations nearly always sources. The slope of this relationship, measured on a log scale, is negatively correlated with migration rate, and ranges between 0 and −1. The steeper the slope, the more marked net migration. Using our western spruce budworm observations, we found strong evidence of density-dependent emigration in budworms, so migration is not simply a random perturbation in the lagged, density-dependent stochastic process leading to budworm outbreaks. It is itself statistically and biologically density-dependent. Therefore, moth migration is a synchronizing factor and a spread mechanism that is essential to understanding the development and expansion of spruce budworm outbreaks at regional scales in the boreal forests of North America.

Enhanced Modal Dispersion Estimation Enabled by Chromatic Dispersion Compensation in Optical Vector Network Analysis

Component characterization is fundamental for understanding the limits of optical devices, sub-systems, and transmission systems. With the introduction of space division multiplexing in optical fiber transmission systems, new impairments, such as mode dependent loss and differential mode dispersion arise. Spatially-diverse optical vector network analyzers are capable of measuring these characteristics in a fast single sweep over a very large bandwidth. As a result of this large bandwidth, these analyzers are sensitive to differential chromatic dispersion within the interferometric measurement setup. This study discusses the influence and compensation of differential chromatic dispersion in such systems. Partial chromatic dispersion compensation is demonstrated to improve the representation and accuracy of impulse response measurements obtained from optical vector network analyzers for fibers and components with large differential chromatic dispersion. Analysis of a 39-core few-mode multi-core fiber is discussed, reporting variances of -2.9-0.1 ps/nm, and 0.6-6.9 ps/nm for the two mode groups, respectively, between the few-mode cores. A correlation with the total impulse response is observed. Furthermore, a maximum propagation skew of 20 ns between cores is observed after 13.6 km.

Metapopulations revisited: the area‐dependence of dispersal matters

The metapopulation concept initiated a paradigm shift in ecology and conservation biology, recognizing the eminent role of dispersal and colonization as fundamental processes contributing to species' long-term persistence. Early models made ad hoc assumptions about a positive area dependency of dispersal (i.e., total number of emigrants), which persisted in the theoretical literature; however, numerous empirical examples of negative area dependencies of dispersal have been reported. Here, we first give a qualitative overview for different area dependencies of dispersal in empirical systems. Then, using a spatially realistic Levins model, we show that extending assumptions on the area dependence of dispersal (ADD) to include all empirically supported parameter space, specifically also negative ADD, alters predictions on several conservation-relevant patterns. Importantly, we find that small patches could be of similar importance as large ones if dispersal decreases inversely with patch area, a result contrasting with previous findings based on a positive ADD. This leads to context-dependent strategies to preserve metapopulations. If dispersal is positively correlated with patch area, efforts should be devoted to preserving large patches and the total habitat area. If dispersal is negatively correlated with patch area, the most efficient strategy is to preserve a high number of patches, including small ones. Our results have direct implications for management decisions in the context of destruction, deterioration, and protection of habitat patches.

A Modulation Format Correction Formula for the Gaussian Noise Model in the Presence of Inter-Channel Stimulated Raman Scattering

A closed-form formula is derived, which corrects for the modulation format dependence of the Gaussian Noise (GN) model in the presence of inter-channel stimulated Raman scattering (ISRS). The analytical result enables a rapid estimate of the nonlinear interference (NLI) for arbitrary modulation formats and avoids the need for complex integral evaluations and split-step simulations. It is shown that the modulation format dependent NLI can be approximated by two contributions, one originating from a single span and one asymptotic contribution for a large number of spans. The asymptotic contribution is solved in closed-form for an arbitrary link function, making the result applicable for generic fiber systems using lumped, distributed or hybrid amplification schemes. The methodology is applied to the ISRS GN model and a modulation format correction formula in closed-form is derived which accounts for an arbitrary number of spans, inter-channel stimulated Raman scattering, arbitrary launch power distributions and wavelength dependent dispersion and attenuation. The proposed formula is validated by numerical simulations over the entire C+L band for multiple fiber types.

Analytical solution for solute transport from a pulse point source along a medium having concave/convex spatial dispersivity within fractal and Euclidean framework

In the present study, analytical solutions of the advection dispersion equation (ADE) with spatially dependent concave and convex dispersivity are obtained within the fractal and the Euclidean frameworks by using the extended Fourier series method. The dispersion coefficient is considered to be proportional to the nth power of a non-homogeneous quadratic spatial function, where the index n is considered to vary between 0 and 1.5 so that the spatial dependence of dispersivity remains within the limit to describe the heterogeneity in the fractal framework. Real values like $$ n = $$ 0.5 and 1.5 are considered to delineate heterogeneity of the aquifer in the fractal framework, whereas integral values like n = 1 represent the same in the Euclidean sense. A concave or convex variation is free from demanding a limiting value as in the case of linear variation, hence it is more appropriate in the ambience of many disciplines in which ADE is used. In this study, concentration at the source site remains uniform until the source is present and becomes zero once it is annihilated forever. The analytical solutions, validated through the respective numerical solutions, are obtained in the form of an extended Fourier series with only first five terms. They are convergent to the desired concentration pattern and are stable with the Peclet number. It has been possible because of the formulation of a new Sturm–Liouville problem with advective information. The analytical solutions obtained in this paper are novel.

Electrical and Optical Properties of Unrelaxed InAs1 –xSbx Heteroepitaxial Structures

The electrical and galvanomagnetic properties of unrelaxed heteroepitaxial InAs1 –xSbx structures (x = 0.43 and 0.38) in a wide temperature range of 5–300 K and magnetic fields up to 8 T are studied. From the thermal-activation dependence of the electrical conductivity, the band gap of the composition InAs0.57Sb0.43 is estimated as 120 meV. The electron concentration in InAs1 –xSbx (6 × 1016 cm–3 for InAs0.62Sb0.38 and 5 × 1016 cm–3 for InAs0.57Sb0.43) determined from the Hall effect agrees well with the electron concentration calculated from the Shubnikov–de-Haas oscillations. We also carry out the spectral ellipsometric studies of unrelaxed heteroepitaxial structures of InAs1 –xSbx (x = 0.43 and 0.38) in the photon energy range of 1–6 eV. The spectral dependences of the imaginary and real parts of the dielectric constant are determined. The dispersion dependences of the refractive index and the extinction coefficient are calculated and presented.

Особливості отримання аерокосмічних зображень, їх оброблення та оцінювання шуму

Зроблено акцент на аерокосмічних зображеннях, методах їх отримання та застосування. Якість отриманих первинних зображень часто не відповідає потребам кінцевих користувачів. Якщо спотворювальним чинником для зображення є шум, то використовуються передусім фільтри, що з різним успіхом усувають різні типи шумів. Виділено групу сучасних систем та засобів програмного забезпечення, що використовують для отримання та оброблення аерокосмічних зображень. Охарактеризовано особливості таких зображень у різних спектральних діапазонах. Подано особливості типових спотворень для такого типу зображень. Окрему увагу при цьому приділено шумам різних типів. Оцінювати рівень шуму можна на базі одного та багатьох зображень. Для цього існують різні методи. Проаналізовано наявні методи оцінювання шуму для графічних зображень, зокрема такі типи методів: визначення функції рівня шуму з єдиного зображення, що використовує залежність дисперсії шуму від інтенсивності зображення і передбачає визначення ділянок однорідності (гомогенності); визначення типу та рівня шуму з гістограми яскравості зображення; оцінка на базі окремого зображення з використанням кусково-гладкої функції попередньої моделі зображень та функції відгуку камер із зарядовим зв'язком; оцінка на базі математичних співвідношень щодо залежності автокореляційної функції зображень від дисперсії адитивного шуму та інші. Експериментальним чином застосовано кілька методів для оцінки шуму для зображення з відкритого датасету DOTA.

Optical characteristics of Gd3Al2Ga3O12 : Ce singlecrystal material

Nowadays new high-energy emission detection technologies with use of materials doped with rare-earth activators appear. There is still a great need for the development of new inorganic scintillators for medical application in particular detection of X-rays and -grays. In this case, the scintillation materials must meet basic requirements: high optical quality, high light output, fast response time and et al. One of these materials is the scintillation crystal Gd3Al2Ga3O12 : Ce (GAGG : Ce) investigated in this work. Analysis of the literature data showed that the optical characteristics of Gd3Al2Ga3O12 : Ce have not been studied enough. Hence the GAGG : Ce optical parameters (spectral transmission and reflection) were measured by optical spectroscopy in the wavelength range 200—750 nm. We calculated values of the absorption and extinction coefficients, refractive indices and the optical band gap of the Gd3Al2Ga3O12 : Ce. We used two spectrophotometric methods to determine the values of the refractive index: Brewster angles (jB) and the reflection coefficients at a small incidence angle of light close to normal (R0). The obtained results were used to build dispersion dependences graphs of the refractive indices.