General Dispersion Research Articles

Wavelength manipulation in a grating metasurface loaded Bloch surface wave structure

We report the realization of a wavelength interrogated Bloch surface wave device structure by exploiting the surface properties via introducing a dielectric grating metasurface on top of a photonic crystal slab. A general dispersion relation based on impedance approach is adopted as the guideline to design the proposed structure. The sustained Bloch surface wave mode along the interface between the dielectric grating metasurface and the external medium can be manipulated by properly tuning the structural parameters. Comprehensive theoretical and numerical investigations regarding the effects of the grating metasurface on the surface mode’s properties, including the reflection properties, dispersion relation as well as the enhanced electronic field have been conducted. With these results, the existence of Bloch surface mode in the band-gap can be determined and it is revealed that the structure is capable of tuning the resonance wavelength by satisfying the excitation condition, thus making it a promising candidate for high-sensitive optical sensing.

Защитно-совладающее поведение в подростковом и юношеском возрасте

The article presents data on studying correspondence between psychological defense mechanisms and coping strategies in teenage and adolescent years within the context of a unified system of self-regulation and adaptation. The relevance of research into defensive-coping behavior is conditioned by the need to understand interaction between defense mechanisms and coping strategies in teenage years and adolescence, as well as to solve the practical problem, i.e. to improve adaptive capabilities of adolescents and young men in stressful situations by reducing non-constructive forms of defensive-coping behavior. The purpose of the study is to investigate the interconnection between defense mechanisms and coping strategies as an individual makes a transition from teenage to adolescent years. Supposedly, defense mechanisms and coping strategies can both complement and contradict each other in teenage and adolescent years. The study was carried out on a sample (N = 203) consisting of representatives of teenage (n = 94, aged 12 to 15) and adolescent age groups (n = 109, aged 17 to 19), who attended general education and vocational schools of the town of Lipetsk. We used the following techniques: Life style index (R. Plutchik et al.), SACS test (S. Hobfoll). Based on the factor analysis, we singled out 4 styles of defensive-coping behaviour in teenagers (which explain 56.2% of general dispersion) and 5 styles of defensive-coping behaviour in adolescents (which explain 62.1% of general dispersion). We determined the factorial structure of the defensive-coping behavior of adolescents and young men. The analysis of the variables of the identified factors established the following: 1) problem-oriented coping strategies are in opposition to the defensive mechanism of regression; 2) immature forms of defense mechanisms (regression and substitution) "support" non-constructive coping strategies; 3) in adolescence, problem-oriented coping is used more actively. To ensure positive result in counseling practice with adolescents and young men, it is important to work with both non-constructive coping strategies and immature defenses.

Impact of the Nocturnal Low-Level Jet and Orographic Waves on Turbulent Motions and Energy Fluxes in the Lower Atmospheric Boundary Layer

The nocturnal low-level jet (LLJ) and orographic (gravity) waves play an important role in the generation of turbulence and pollutant dispersion and can affect the energy production by wind turbines. Additionally, gravity waves have an influence on the local mixing and turbulence within the surface layer and the vertical flux of mass into the lower atmosphere. On 25 September 2017, during a field campaign, a persistent easterly LLJ and gravity waves were observed simultaneously in a coastal area in the north of France. We explore the variability of the wind speed, turbulent eddies, and turbulence kinetic energy in the time–frequency and space domain using an ultrasonic anemometer and a scanning wind lidar. The results reveal a significant enhancement of the turbulence-kinetic-energy dissipation (by 50%) due to gravity waves in the LLJ shear layer (below the jet core) during the period of wave propagation. Large magnitudes of zonal and vertical components of the shear stress (approximately 0.4 and 1.5 m2 s−2, respectively) are found during that period. Large eddies (scales of 110 to 280 m) matching the high-wind-speed regime are found to propagate the momentum downwards, which enhances the mass transport from the LLJ shear layer to the roughness layer. Furthermore, these large-scale eddies are associated with the crests while comparatively small-scale eddies are associated with the troughs of the gravity wave.

Coordinatively unsaturated aluminum anchored Ru cluster for catalytic hydrogenation of benzene

The design and synthesis of highly dispersed metal catalyst have attracted increasing attention, and it is still challenging to generate stable metal clusters with high metal loadings. Support plays a crucial role in determining particle morphology and dispersion. Herein, we demonstrate a strategy for synthesizing an amorphous alumina with 62% Al3+penta sites (penta-coordinated Al3+) via solution combustion synthesis. It provides sufficient oxygen defects to anchor Ru species. For benzene hydrogenation reaction, the catalyst displays the high TOF (18833 h−1), which is about 2 times higher than that of catalysts supported on commercial alumina. The DFT calculations also confirm that the high catalytic performance is closely correlated with the special configuration of Ru active sites over coordinatively unsaturated alumina. The penta-coordinated Al3+ was also applied to prepare Pd catalyst with high dispersion. This work provides a superior support which possesses abundant Al3+penta sites and affords a possibility for the generation of high and stable dispersion for the preparation of supported metal catalysts.

Effect of Thermal Conductivity, Compressive Viscosity and Radiative Cooling on the Phase Shift of Propagating Slow Waves with and Without Heating–Cooling Imbalance

We study phase shifts of the propagating slow waves in coronal loops invoking the effects of thermal conductivity, compressive viscosity, radiative losses and heating-cooling imbalance. We derive a general dispersion relation and solve it to determine phase shifts of density and temperature perturbations relative to the velocity and their dependence on equilibrium parameters ($\rho_0$, $T_0$). We estimate phase difference ($\Delta \phi$) between density and temperature perturbations and its dependence on $\rho_0$ and $T_0$. The effect of viscosity on the phase shifts was found negligible. The role of radiative losses along with h/c imbalance for chosen specific heating function ($H(\rho, T) \propto \rho^{-0.5} T^{-3}$) in determining phase shifts, is found to be significant for the high density and low temperature loops. The h/c imbalance can increase the phase difference ($\Delta \phi \approx 140^\circ$) for low temperature loops compared to the constant heating case ($\Delta \phi \approx 30^\circ$). We derive a general expression for the polytropic index. We find that in the presence of thermal conduction alone, the polytropic index remains close to its classical value for all the considered $\rho_0$ and $T_0$. However, it reduces to a value $1.2$ when loop density is decreased by an order of magnitude compared to its normal coronal value. We find that the inclusion of radiative losses, with or without h/c imbalance, cannot explain the observed polytropic index. The thermal ratio ($d$) needs to be enhanced by an order of magnitude, in order to explain its observed value $1.1 \pm 0.02$ in the solar loops. We also explore the role of different heating functions for typical coronal parameters and found that although the polytropic index remains close to its classical value, the phase difference is highly dependent on the form of heating function (The abstract is restructured for arxiv).

General dispersion properties of magnetized plasmas with drifting bi-Kappa distributions. DIS-K: Dispersion Solver for Kappa Plasmas

Space plasmas are known to be out of (local) thermodynamic equilibrium, as observations show direct or indirect evidences of non-thermal velocity distributions of plasma particles. Prominent are the anisotropies relative to the magnetic field, anisotropic temperatures, field-aligned beams or drifting populations, but also, the suprathermal populations enhancing the high-energy tails of the observed distributions. Drifting bi-Kappa distribution functions can provide a good representation of these features and enable for a kinetic fundamental description of the dispersion and stability of these collision-poor plasmas, where particle–particle collisions are rare but wave–particle interactions appear to play a dominant role in the dynamics. In the present paper we derive the full set of components of the dispersion tensor for magnetized plasma populations modelled by drifting bi-Kappa distributions. A new solver called DIS-K (DIspersion Solver for Kappa plasmas) is proposed to solve numerically the dispersion relations of high complexity. The solver is validated by comparing with the damped and unstable wave solutions obtained with other codes, operating in the limits of drifting Maxwellian and non-drifting Kappa models. These new theoretical tools enable more realistic characterizations, both analytical and numerical, of wave fluctuations and instabilities in complex kinetic configurations measured in-situ in space plasmas.

Reaching the Planck scale with muon lifetime measurements

Planck scale modified dispersion relations are one way how to capture the influence of quantum gravity on the propagation of fundamental point particles effectively. We derive the time dilation between an observer's or particle's proper time, given by a Finslerian length measure induced from a modified dispersion relation, and a reference laboratory time. To do so, the Finsler length measure for general first order perturbations of the general relativistic dispersion relation is constructed explicitly. From this we then derive the time dilation formula for the $\kappa$-Poincar\'e dispersion relation in several momentum space bases, as well as for modified dispersion relations considered in the context of string theory and loop quantum gravity. Most interestingly we find that the momentum Lorentz factor in the present and future colliders can, in principle, become large enough to constrain the Finsler realization of the $\kappa$-Poincar\'e dispersion relation in the bicrossproduct basis as well as a string theory inspired modified dispersion relation, at Planck scale sensitivity with the help of the muon's lifetime.

Whitham modulation theory for generalized Whitham equations and a general criterion for modulational instability

AbstractThe Whitham equation was proposed as a model for surface water waves that combines the quadratic flux nonlinearity of the Korteweg–de Vries equation and the full linear dispersion relation of unidirectional gravity water waves in suitably scaled variables. This paper proposes and analyzes a generalization of Whitham's model to unidirectional nonlinear wave equations consisting of a general nonlinear flux function and a general linear dispersion relation . Assuming the existence of periodic traveling wave solutions to this generalized Whitham equation, their slow modulations are studied in the context of Whitham modulation theory. A multiple scales calculation yields the modulation equations, a system of three conservation laws that describe the slow evolution of the periodic traveling wave's wavenumber, amplitude, and mean. In the weakly nonlinear limit, explicit, simple criteria in terms of general and establishing the strict hyperbolicity and genuine nonlinearity of the modulation equations are determined. This result is interpreted as a generalized Lighthill–Whitham criterion for modulational instability.

Rehabilitation after myocardial infarction by using of biofeedback training, controlled by capnometry

Abstract Funding Acknowledgements Type of funding sources: None. The increasing activity of the sympathetic nervous system was shown during myocardial infarction (MI). There are data that bio management application increases the vagal influences on a heart rate for patients with chronic coronary artery disease. The purpose of this study was the assessment of changes of vegetative regulation of heart rate in patients with MI, receiving along with standard methods of treatment and rehabilitation sessions of cardiorespiratory training (KRT). 48 patients with IM in an early period of disease at the age from 40 till 70 years were surveyed. The main group was created from 29 people by whom KRT (5–10 sessions) was carried out. The assessment of efficiency and safety of KRT was carried out on a clinical picture and parameters of heart rate variability (HRV) before, after, and during KRT. The Control group consisted of 19 patients receiving only standard treatment. To exclude hyperventilation syndrome, capnometry was performed before the start of the KRT session to determine the FetCO2 individual norm for the certain patient to control the training process in a particular session. After each active sample, the concentration of carbon dioxide in the air exhaled by the patient was measured, and when it decreased below 95% of the initial value, the depth of breathing was adjusted. The use of capnometry in the study avoided adverse events during the sessions. During carrying out of KRT, and after KRT worsening of the clinical picture at patients of the main group was not observed. HRV analysis at patients of the main group showed that after the end of KRT decrease in an index of tension (p < 0,05), an increase in an indicator of the general dispersion of heart rate (p < 0,05), and also a tendency to increase of vagal part of total power during spectral analysis (р=0,05) was observed. Normalization of heart rate and arterial pressure, growth of cardiorespiratory index, and index of a variation took place, cardiorespiratory synchronization was restored. Persons from the control group had no such changes. Thus, the application of KRT realizing a mode of functional bio management of heart rate, as the instrument of psychophysiological support of standard medicament therapy showed the efficiency of its use in the program of rehabilitation of patients with myocardial infarction. The result of a comprehensive approach is the reduction of sympathetic and increase of vagal influences on heart rate, normalization of the main indicators of the cardiovascular system.

General method for synthesizing dispersive coupling matrix of microwave bandpass filters

AbstractIn this paper, a general method for synthesizing dispersive coupling matrix (DCM) of coupled-resonator bandpass filters with the general dispersion is proposed. Compared to the dispersion-less coupling matrix synthesized by classic approaches, the DCM incorporates the identity of the physical realization and provides an accurate description of the filter. Moreover, the DCM can accurately describe the complex resonators and coupling elements with intentional strong dispersion. A DCM consists of two parts: the frequency-invariant part that corresponds to the coupling matrix at the center frequency and the frequency-variant part that reflects the dispersion of the physical realization. By iteratively adjusting the transmission zeros governed by the given filter topology and ignoring the transmission zeros brought by the dispersion, the synthesis method can directly obtain the frequency-invariant part so that the overall DCM leads to an equal-ripple response. To illustrate the general synthesis method, two design examples are presented, which include a filter with unintentional weak dispersion and a filter with intentional strong dispersion. The examples are validated by EM simulation, demonstrating the effectiveness, accuracy, and generality of the proposed synthesis framework. Key words: dispersive coupling matrix, filter synthesis, microwave bandpass filter

Local analysis of electrostatic modes in a two-fluid E×B plasma

A local study of linear electrostatic modes, applicable to the dynamics perpendicular to the magnetic field in a plasma with crossed electric and magnetic fields, is presented. The analysis is based on a two-fluid model that takes into account the finite-electron-gyroradius effects through a rigorous gyroviscosity tensor and includes a dissipative friction force in the electron momentum equation. A comprehensive dispersion relation, valid for arbitrary electron temperature, is derived, which describes properly all the relevant waves for wavelengths longer than the electron Larmor radius. For a homogeneous and dissipationless plasma, such a fluid dispersion relation agrees with the long-wavelength limit of the kinetic electron–cyclotron-drift instability dispersion relation that extends the results to arbitrary short wavelengths. The general fluid dispersion relation covers different parametric regimes that depend on the relative ion-to-electron drift velocity and on the presence of equilibrium inhomogeneities and/or dissipation. Depending on such conditions, its roots yield as follows: two-stream instabilities, driven solely by the relative drift between species; drift-gradient instabilities, driven by the combination of the relative drift and equilibrium gradients; and drift-dissipative instabilities, driven by the combination of the relative drift and friction. Instability thresholds are determined and some distinctive unstable modes are described analytically.

Modes of propagation and instabilities in finitely conducting neutrino-modified magnetohydrodynamic viscous plasma

Low-frequency wave propagations and instabilities are studied taking into account the finite electrical resistivity and viscosity of the neutrino-coupled plasma. It is assumed that the plasma is permeated by magnetic field. The formulation and analysis of the system including the Fermi weak force due to neutrino plasma coupling is done by neutrino magneto hydrodynamics model. The general dispersion relation is derived from the set of perturbed equations to signify the role of dissipative effects on the growth rate and condition of both neutrino instability and self-gravitational instability. To discuss the influence of resistivity and viscosity on the dynamics of the system, the general dispersion relation is reduced for both perpendicular and parallel mode of propagations. The self-gravitating modes are modified by the presence of neutrinos, viscosity, and resistivity in both perpendicular and parallel modes of propagation, while the gravitational instability criterion is modified only by neutrinos. It is also observed that the number density of neutrinos works against the gravitational instability, while the neutrino beam-free energy supports the self-gravitational instability. In the case of perpendicular propagation, the neutrino beam instability criterion and growth rate are affected by dissipative effects.

The biofeedback training, controlled by capnometry is a successful method of rehabilitation after myocardial infarction

Abstract Funding Acknowledgements Type of funding sources: None. The increasing activity of the sympathetic nervous system was shown during myocardial infarction (MI). There are data that bio management application increases the vagal influences on a heart rate for patients with chronic coronary artery disease. The purpose of this study was the assessment of changes of vegetative regulation of heart rate in patients with MI, receiving along with standard methods of treatment and rehabilitation sessions of cardiorespiratory training (KRT). 48 patients with IM in an early period of disease at the age from 40 till 70 years were surveyed. The main group was created from 29 people by whom KRT (5–10 sessions) was carried out. The assessment of efficiency and safety of KRT was carried out on a clinical picture and parameters of heart rate variability (HRV) before, after, and during KRT. The Control group consisted of 19 patients receiving only standard treatment. To exclude hyperventilation syndrome, capnometry was performed before the start of the KRT session to determine the FetCO2 individual norm for the certain patient to control the training process in a particular session. After each active sample, the concentration of carbon dioxide in the air exhaled by the patient was measured, and when it decreased below 95% of the initial value, the depth of breathing was adjusted. The use of capnometry in the study avoided adverse events during the sessions. During carrying out of KRT, and after KRT worsening of the clinical picture at patients of the main group was not observed. HRV analysis at patients of the main group showed that after the end of KRT decrease in an index of tension (p < 0,05), an increase in an indicator of the general dispersion of heart rate (p < 0,05), and also a tendency to increase of vagal part of total power during spectral analysis (р=0,05) was observed. Normalization of heart rate and arterial pressure, growth of cardiorespiratory index, and index of a variation took place, cardiorespiratory synchronization was restored. Persons from the control group had no such changes. Thus, the application of KRT realizing a mode of functional bio management of heart rate, as the instrument of psychophysiological support of standard medicament therapy showed the efficiency of its use in the program of rehabilitation of patients with myocardial infarction. The result of a comprehensive approach is the reduction of sympathetic and increase of vagal influences on heart rate, normalization of the main indicators of the cardiovascular system.

Influence of the dispersion relation on the Unruh effect according to the relativistic Doppler shift method

We examine the influence of the dispersion relation on the Unruh effect by Lorentz boosting the phase of Minkowski vacuum fluctuations endowed with an arbitrary dispersion relation. We find that, unlike what happens with a linear dispersion relation exhibited by massless fields, thermality is lost for general dispersion relations. We show that thermality emerges with a varying "apparent" Davies-Unruh temperature depending on the acceleration of the observer and on the degree of departure from linearity of the dispersion relation. The approach has the advantage of being intuitive and able to pinpoint why such a loss of thermality occurs and when such a deviation from thermality becomes significant. We discuss the link of our results with the well-known fundamental difference between the thermalization theorem and the concept of Rindler noise. We examine the possible experimental validation of our results based on a successful setup for testing the classical analogue of the Unruh effect recently described in the literature.

Charting the fifth force landscape

Fifth forces arising from hidden sector scalar operator exchange, as probed in a variety of present and planned experiments, can be captured by a general dispersion relation involving one real, positive, spectral density function. Previously considered scalar fifth forces, from tree-level to more exotic loop-level possibilities, are derived in this formalism, without explicitly performing conventional loop calculations. A variety of experimental observables commonly used in fifth force searches are also presented in the same formalism, allowing the straightforward extraction of limits on any specific model. The speculative possibility of probing hidden sector violations of unitarity, causality, or locality, manifested as a breakdown of the positivity of the spectral density, is also discussed.

On-Chip Broadband Mid-Infrared Supercontinuum Generation Based on Highly Nonlinear Chalcogenide Glass Waveguides

On-chip mid-infrared (MIR) supercontinuum generation (SCG) covering the molecular functional spectral region (3–12 μm) offers the advantages of robustness, simplicity, and compactness. Yet, the spectral range still cannot be expanded beyond 10 μm. In this study, on-chip ultrabroadband MIR SCG in a high numerical aperture chalcogenide (ChG) waveguide is numerically investigated. The ChG waveguide with a Ge-As-Se-Te core and Ge-Se upper and lower cladding is designed to optimize the nonlinear coefficients and dispersion profile. Assisted by dispersive wave generation in both short- and long-wavelength range, broadband SCG ranging from 2 to 13 µm is achieved. Besides, a fabrication scheme is proposed to realize precise manipulation of dispersion design. Such results demonstrate that such sources are suitable for compact, chip-integrated molecular spectroscopy applications.

Magnetoinductive waves in attenuating media

The capability of magnetic induction to transmit signals in attenuating environments has recently gained significant research interest. The wave aspect—magnetoinductive (MI) waves—has been proposed for numerous applications in RF-challenging environments, such as underground/underwater wireless networks, body area networks, and in-vivo medical diagnosis and treatment applications, to name but a few, where conventional electromagnetic waves have a number of limitations, most notably losses. To date, the effects of eddy currents inside the dissipative medium have not been characterised analytically. Here we propose a comprehensive circuit model of coupled resonators in a homogeneous dissipative medium, that takes into account all the electromagnetic effects of eddy currents, and, thereby, derive a general dispersion equation for the MI waves. We also report laboratory experiments to confirm our findings. Our work will serve as a fundamental model for design and analysis of every system employing MI waves or more generally, magnetically-coupled circuits in attenuating media.

Study of Pulse Formation in an EDFL Under a Large Dispersion Variation Hybridly Mode-Locked by Graphene and Nonlinear Polarization Rotation

In this work, we present a detailed experimental study of pulse formation mechanism in an EDFL, hybridly mode-locked by use of a CVD monolayer graphene onto a D-shaped optical fiber and nonlinear polarization rotation (NPR), under a large intracavity dispersion influence (up to 100 times) ranging from 12.3 to 1382 m cavity lengths. Analyzing the spectral evolution, temporal and soliton behaviors of the pulse, our results revealed the presence of four laser operating regimes with non-soliton and soliton formation from short to ultralong cavity lengths, all related to graphene/NPR nonlinearities, dispersion and soliton propagation influences.

Dispersion relations for waves in visco-gravitating anisotropic magnetoplasmas

The effect of Braginskii's full viscosity tensor on an infinite non-conducting, gravitating anisotropic plasma in which the medium is trapped in a strong magnetic field is discussed in the context of Braginskii's magnetohydrodynamic model with Chew–Goldberger–Low double adiabatic approximation and finite Larmor radius (FLR) correction. Through linearization of the perturbed equations, the general dispersion relation is derived for the separate compression, shear, and drift viscosity components as well as the FLR corrections. We investigate the stability for parallel and transverse perturbations with respect to the direction of the magnetic field, and both gravitational and fire-hose instabilities are found. The role of each viscous term is to suppress instability, but each component works in different ways. The FLR acts in a way that is very similar to the drift viscosity. The instability threshold is found to be independent of viscosity for compression and shear viscosity, but both the drift viscosity and FLR corrections can change the critical wavenumber for the instability. The compression viscosity is most effective at reducing the growth rate of the gravitational instability, whereas the shear viscosity works to suppress the fire-hose instability. The result of the present study may be useful for the study of large scale compression, shear, and drift plasma flow in and around clusters of galaxies and galactic disks and for the solar and stellar wind.

Magnetorotational Instability in Quantum Dusty Plasma

Abstract Magnetorotational instability (MRI) in complex quantum plasma, which comprises electron, ion, and dust grains, is investigated. Electrons are considered to be degenerate while ions and dust grains are taken as nondegenerate. The general dispersion relation for MRI with the effect of spin magnetization is derived using local approximations. The instability criteria for spin quantum plasma are derived using low-frequency approximations. Due to the complex nature of the dispersion relation, MHD assumptions are used to define the instability criteria. The dust mass plays a significant role in both the dispersion and growth rate of the magnetorotational mode. The complex mass of dust modifies the instability criteria. Spin magnetization force arises due to electron Pauli spin matrices and has an important role in low-temperature and highly dense plasmas that are found mainly in white dwarfs, neutron stars, and in core-collapse supernovae. It is found that spin magnetization influences the criteria for instability and hence the properties of MHD waves in the degenerate plasma.