Oscillation Spectrum Research Articles

Robustness of individualized inferences from longitudinal resting state EEG dynamics.

Tracking how individual human brains change over extended timescales is crucial to clinical scenarios ranging from stroke recovery to healthy aging. The use of resting state (RS) activity for tracking is a promising possibility. However, it is unresolved how a person's RS activity over time can be decoded to distinguish neurophysiological changes from confounding cognitive variability. Here, we develop a method to screen RS activity changes for these confounding effects by formulating it as a problem of change classification. We demonstrate a novel solution to change classification by linking individual-specific change to inter-individual differences. Individual RS-electroencephalography (EEG) was acquired over 5 consecutive days including task states devised to simulate the effects of inter-day cognitive variation. As inter-individual differences are shaped by neurophysiological differences, the inter-individual differences in RS activity on 1 day were analysed (using machine learning) to identify distinctive configurations in each individual's RS activity. Using this configuration as a decision rule, an individual could be re-identified from 2-s samples of the instantaneous oscillatory power spectrum acquired on a different day both from RS and confounded RS with a limited loss in accuracy. Importantly, the low loss in accuracy in cross-day versus same-day classification was achieved with classifiers that combined information from multiple frequency bands at channels across the scalp (with a concentration at characteristic fronto-central and occipital zones). Taken together, these findings support the technical feasibility of screening RS activity for confounding effects and the suitability of longitudinal RS for robust individualized inferences about neurophysiological change in health and disease.

Combustion Characteristics in Scramjet Combustor Operating at Different Inflow Stagnation Pressures

In this study, combustion processes in a cavity-based scramjet combustor are experimentally studied based on the inflow conditions of different stagnation pressures (, 1.3, and 1.6 MPa), which correspond to a Mach 6 flight at trajectories of different dynamic pressures of 0.25, 0.34, 0.43 atm, respectively. Three combustion modes are identified according to flame distribution, flowfield structure, and wall pressure. Cases at the same equivalence ratio and combustion mode with different inflow stagnation pressures are selected to compare flame characteristics. For each inflow condition, flame structure, combustion intensity, and coherence between upstream and downstream flames are analyzed based on CH* chemiluminescence and schlieren imaging measurements. Combustion instability is examined according to statistical results, frequency domain and spatial distribution. It is found that the linearly increased inflow stagnation pressure causes irregularity variance in the combustion oscillation spectra, indicating the quasi-linearly enhanced combustion induces complicated aerodynamic and thermodynamic variances. Chaos of the combustion oscillation is quantitatively evaluated by a classical nonlinear analysis. The dynamic mode decomposition analysis presents that the high-frequency oscillation induced by the self-sustaining shear-layer instability exist mainly in the combustor upper region while the low-frequency oscillation that could be caused by the injector–flame feedback is predominant in the cavity region. In addition, thermo-acoustic couplings, which are in connection with these two kinds of oscillations, have been analyzed. It is further revealed that the variance of the shock waves caused by the backpressure destroys the existing thermo-acoustic feedback related to the high-frequency oscillation, which is the main reason for the chaotic phenomena shown in the transitional state between the scramjet mode and the ramjet mode.

Exciton-Phonon Coupling of Chiral One-Dimensional Lead-Free Hybrid Metal Halides at Room Temperature.

The interaction between organic cations and inorganic metal halide octahedral units strongly affects the properties of organic-inorganic hybrid metal halides. The "soft" property of the lattice provides the possibility of its strong exciton-phonon interaction. Here we report one-dimensional (1D) lead-free chiral organic-inorganic hybrid metal halide single crystals of (R/S)-methylbenzylamine bismuth iodide (R/S-MBA)2Bi2I8, which exhibits a high level of octahedral bond distortion. The introduction of chiral amines leads to a strong chiroptical response in the range of 200-600 nm. The strong exciton-phonon coupling can be observed through the coherent oscillation spectrum of transient absorption dynamics at room temperature. The coherent phonon oscillation frequencies are ∼97 and ∼130 cm-1, corresponding to the symmetrical stretching or bending of the Bi-I octahedron. Our work provides new insights for the study of exciton-phonon coupling in 1D chiral hybrid metal halides.

Multi-cavity gravito-acoustic oscillation modes in stars

Context. Over recent decades, asteroseismology has proven to be a powerful method for probing stellar interiors. Analytical descriptions of the global oscillation modes, in combination with pulsation codes, have provided valuable help in processing and interpreting the large amount of seismic data collected, for instance, by space-borne missions CoRoT, Kepler, and TESS. These prior results have paved the way to more in-depth analyses of the oscillation spectra of stars in order to delve into subtle properties of their interiors. This purpose conversely requires innovative theoretical descriptions of stellar oscillations. Aims. In this paper, we aim to analytically express the resonance condition of the adiabatic oscillation modes of spherical stars in a very general way that is applicable at different evolutionary stages. Methods. In the present formulation, a star is represented as an acoustic interferometer composed of a multitude of resonant cavities where waves can propagate and the short-wavelength JWKB approximation is met. Each cavity is separated from the adjacent ones by barriers, which correspond to regions either where waves are evanescent or where the JWKB approximation fails. Each barrier is associated with a reflection and transmission coefficient. The stationary modes are then computed using two different physical representations: (1) studying the infinite-time reflections and transmissions of a wave energy ray through the ensemble of cavities or (2) solving the linear boundary value problem using the progressive matching of the wave function from one barrier to the adjacent one between the core and surface. Results. Both physical pictures provide the same resonance condition, which ultimately turns out to depend on a number of parameters: the reflection and transmission phase lags introduced by each barrier, the coupling factor associated with each barrier, and the wave number integral over each resonant cavity. Using such a formulation, we can retrieve, in a practical way, the usual forms derived in previous works in the case of mixed modes with two or three cavities coupled though evanescent barriers, low- and large-amplitude glitches, and the simultaneous presence of evanescent regions and glitches. Conclusions. The resonance condition obtained in this work provides a new tool that is useful in predicting the oscillation spectra of stars and interpreting seismic observations at different evolutionary stages in a simple way. Practical applications require more detailed analyses to make the link between the reflection-transmission parameters and the internal structure. These aspects will be the subject of a future paper.

Q-Bursts Generated by the Contact of the Interplanetary Shock Wave with the Magnetosphere

The study presents the results of the global registration of a short-term train of damped oscillations in the frequency range 0,5–30,0 Hz (Q-burst), observed at the initial phase of the preliminary impulse of the sudden onset SC on 09.09.2011. The spatial features of the spectrum of train oscillations are studied. We discovered A spectral-resonance structure of bursts, which is observed globally. It is assumed that bursts are generated as a result of powerful lightning discharges that create red sprites in the ionosphere. The electromagnetic radiation of sprites is captured in the earth-ionosphere waveguide and propagates globally. We assumed that one of the reasons for the increase in the power of the Q-signal is the coincidence of the beginning of its generation with the amplification of the ionospheric current system of the preliminary impulse of the sudden onset of SC.

Investigation of Transverse Instability of a High-Current Relativistic Electron Beam in a Linear Induction Accelerator

The article presents the results of studies on the transverse instability of a high-current relativistic electron beam developing in a linear induction accelerator LIA for 5 MeV electron energy, which is created at the BINP SB RAS together with RFNC VNIITF. These results were obtained using a software package that makes it possible to simulate the dynamics of the instability development, as well as to calculate the increment of this instability averaged over the accelerator length. The package consists of four main parts. The first of them, made on the base of a three-dimensional model of the accelerating module electrodynamic system of the LIA, allows calculating the main characteristics of electromagnetic dipole modes of such a module, the second and third parts are designed to find three-dimensional accelerating electric and focusing magnetic fields, respectively. In the last part of the package, a system of ordinary differential equations is solved that describes both the motion of beam macroparticles in electric and magnetic fields, including the eigenmode fields, and the excitation of the mode fields by the electron beam. The adequacy of the physical models used in the software package was tested by comparing the spectra of field oscillations in the accelerator modules obtained in calculations and recorded in the experiment. On the base of the data obtained, the main regularities of the transverse beam instability development in the frequency range ∆f = 0.3–1.1 GHz were revealed, and possible methods for suppressing this instability in the LIA were proposed.

EXCITATION OF OWN OSCILLATIONS IN SEMICONDUCTOR COMPONENTS OF RADIO PRODUCTS UNDER THE EXPOSURE OF THIRD-PARTY ELECTROMAGNETIC RADIATION

The subject matter is the processes of analysis and mechanisms of interaction of EMP-induced currents and voltages with the processes characterizing the functional purpose of radio products, is usually carried out within the framework of the theory of distributed circuits. The presented approach makes it possible to evaluate the performance criteria in general (for example, to evaluate the critical energy characterizing a thermal breakdown), however, issues related to the determination of various types of electromagnetic interactions that occur directly in the components of a product under the influence of EMR remain open. The aim is the possibility of setting up theoretical and experimental studies based on the proposed calculation model for excitation of natural vibrations of a semiconductor structure (exponential growth of amplitude). The parameters of a third-party pulsed electromagnetic field, induced currents and characteristics of semiconductor devices have been established within which the regime of amplification of natural vibrations of a semiconductor structure is observed. The objectives are: mechanisms of interaction of induced currents with surface vibrations of semiconductor components of a radio product under the influence of pulsed electromagnetic radiation. The methods used are: methods of the theory of small perturbations in determining the spectrum of natural oscillations of the system - currents induced by electromagnetic radiation and natural oscillations of the components of the radio product. The following results are obtained: The mechanisms for the appearance of reversible failures of semiconductor components of radio products under the influence of third-party pulsed electromagnetic fields are determined. It has been established that the presence of a current induced by external radiation leads to the establishment of a mode of amplification of natural oscillations of semiconductor components of a radio product (reversible failures). Conclusion. Quantitative estimates of amplification (generation) modes of oscillations of semiconductor devices, distorting their performance depending on the parameters of external electromagnetic influence, allows developing mechanisms for electromagnetic compatibility of microwave radio products. A comparative analysis of the calculated data obtained in the work can be used in the manufacture of radio devices operating in the millimeter and submillimeter range (amplifiers, generators and frequency converters).

Measuring Frequency and Period Separations in Red-giant Stars Using Machine Learning

Abstract Asteroseismology is used to infer the interior physics of stars. The Kepler and TESS space missions have provided a vast data set of red-giant lightcurves, which may be used for asteroseismic analysis. These data sets are expected to significantly grow with future missions such as PLATO, and efficient methods are therefore required to analyze these data rapidly. Here, we describe a machine-learning algorithm that identifies red giants from the raw oscillation spectra and captures p- and mixed-mode parameters from the red-giant power spectra. We report algorithmic inferences for large frequency separation (Δν), frequency at maximum amplitude ( ν max ), and period separation (ΔΠ) for an ensemble of stars. In addition, we have discovered ∼25 new probable red giants among 151,000 Kepler long-cadence stellar-oscillation spectra analyzed by this method, among which four are binary candidates that appear to possess red-giant counterparts. To validate the results of this method, we selected ∼3000 Kepler stars, at various evolutionary stages ranging from subgiants to red clumps, and compare inferences of Δν, ΔΠ, and ν max with estimates obtained using other techniques. The power of the machine-learning algorithm lies in its speed: It is able to accurately extract seismic parameters from 1000 spectra in ∼5 s on a modern computer (a single core of the Intel® Xeon® Platinum 8280 CPU).

The formation of the mixed anions PAsO7 in solid solutions Mg2P2O7 — Mg2As2O7

The article presents structural features at formation of solid solutions of the isostructural Mg2P2O7 and Mg2As2O7 connections. In these compounds, complex Р2О74-anions, As2O24-, as well as the formation of complex PAsO74 anions, is not natural. The formation of solid solutions is confirmed by the linear dependence of x-ray debaegram and optical refractive indices, depending on the concentration of P/As. In the article, phosphates are involved in energy processes in cells. For the first time, the formation of mixed anions in polyphosphates has been proven. The oscillatory spectra of pyro anions have intervals of localization of terminal and bridging groups of atoms that have no intersection regions. Strip at 662–670 cm-1 (between structures from P: As=0.8:0.2 to 0.1–0.9), located between vsPOP frequency in ᵦ — Mg2P2O7 at 737 cm-1 and the frequencies about 550 cm-1 characteristic of fluctuations of vsAsOAs in alkaline pyroarsenates, is interpreted as a strip of fluctuations of vsPOAs of the mixed PAsO7 ions. In the area, the strip at 925–902 cm-1 is located between frequencies of fluctuations of vasPOP and vasAsOAs. The fluctuations of mastic group P-O found in ranges of infrared absorption allow establishing knowledge of the adjacent anions (PAsO7)4- that it is possible to confirm with quantum-chemical calculations in the subsequent.

Magnetotransport signatures of antiferromagnetism coexisting with charge order in the trilayer cuprate HgBa2Ca2Cu3O8+\u03b4

Multilayered cuprates possess not only the highest superconducting temperature transition but also offer a unique platform to study disorder-free CuO2 planes and the interplay between competing orders with superconductivity. Here, we study the underdoped trilayer cuprate HgBa2Ca2Cu3O8+δ and we report quantum oscillation and Hall effect measurements in magnetic field up to 88 T. A careful analysis of the complex spectra of quantum oscillations strongly supports the coexistence of an antiferromagnetic order in the inner plane and a charge order in the outer planes. The presence of an ordered antiferromagnetic metallic state that extends deep in the superconducting phase is a key ingredient that supports magnetically mediated pairing interaction in cuprates.

Rheological elucidation of the viscoelastic properties and network interaction of mixed high-methoxyl pectin and kappa-carrageenan gels

The interaction between two anionic polysaccharides known for their gelation capability was investigated. Mixtures of high-methoxyl pectin (HMP) and κ-carrageenan (KC) were prepared at different volume fractions. The sample's complex rheological properties and microstructures were investigated by performing linear small amplitude oscillatory shear (SAOS) and nonlinear large amplitude oscillatory shear (LAOS). Pure KC and the HMP/KC mixtures exhibited gel-like properties, whereas pure HMP did not gel at the experimental conditions employed and was characterized as a viscoelastic liquid. Temperature-dependent rheological behavior of HMP/KC mixtures suggested the independent aggregation of KC chains. The viscoelastic properties of the HMP/KC mixtures, such as oscillatory spectrum, and material stiffness, followed that of pure KC, indicating that KC strongly influenced the final gel. The transient behavior of the HMP/KC mixtures in the time sweep and the monotonic decrease of the storage modulus in the linear regime, and the onset of nonlinear rheological behavior in the strain sweep measurements suggested the possibility of the phase-separated network structure of in HMP-rich and KC-rich phases in the mixtures. Based on the rheological data both in the linear and nonlinear regimes, we propose the possibility of a bicontinuous network structure in HMP/KC mixtures, composed of the weak HMP phase in random coil configuration and the dominant KC phase in double helix aggregates.

Analysis of the Oscillations of Stratified Liquid with Elastic Ice

We study the problem of small motions of an ideal stratified liquid with a free surface totally covered by an elastic ice. The elastic ice is modeled by an elastic plate. We reduce the original initial boundary value problem to an equivalent Cauchy problem for a second-order differential equation in a Hilbert space. We obtain conditions under which there exists a strong (with respect to time) solution of the initial boundary value problem describing the evolution of the hydrodynamic system under consideration. We also study the spectrum of normal oscillations, the basic properties of the eigenfunctions.

Impact of charge noise on electron exchange interactions in semiconductors

The electron exchange interaction is a promising medium for the entanglement of single-spin qubits in semiconductors as it results in high-speed two-qubit gates. The quality of such entangling gates is reduced by the presence of noise caused by nearby defects acting as two-level fluctuators. To date, the effect of charge noise has been calculated assuming a Gaussian distribution of exchange interaction frequencies between the qubits equivalent to a linear coupling of charge noise with the exchange interaction. In reality the coupling can differ significantly from this linear-coupling approximation depending on the inter-qubit tunnel coupling, detuning of the qubit system, and the magnitude of charge noise. We derive analytical expressions for the frequency spectra of exchange oscillations that encompasses both linear and non-linear coupling to charge-noise. The resulting decoherence times and decay profiles of the exchange oscillations vary considerably. When compared with recent experiments our model shows that non-linear charge-noise coupling is significant and requires consideration to characterise and optimise exchange-based entangling gates.

On the dynamics of a model wind turbine under passive tower oscillations

Laboratory experiments were carried out to quantify the effect of small-amplitude, passive oscillations of a model wind turbine in the structure of the unsteady motions, wake statistics, and mean power output and associated fluctuations at various yawing β∈[0o,30o] every Δβ=5o. Planar particle image velocimetry was used to characterize the flow statistics, and power output was measured at high temporal resolution. Scenarios with a fixed turbine were included to aid insight into the coupled and separated effects of passive oscillations and yawing. Unsteady pitch motions, dominant of the system dynamics, were more predominant at small but non-zero yaw of β≈5o. The spectral structure of the oscillations showed that the unsteady roll motions contributed substantially under high yawing. Using basic concepts, we derived a formulation for the turbine oscillation spectrum that shows good agreement with measurements; it serves as a base to include other input modulation types. The power output decreased monotonically with β in the fixed and oscillating turbines, which was more distinct for β>15o. Passive oscillations produced higher power for given yaw. A simple yaw-correction of the structure of the power output also showed reasonable agreement with measurements. Finally, mean velocity in the wake of the fixed and oscillating turbines exhibited minor differences for a given yawing. However, the turbulence levels showed distinct changes of turbine motions in the degree of symmetry and magnitude for given yaw.

Technique for Recording and Analysis of the Amplitude Spectrum of the Strength Oscillations of Magnetic and Electric Fields of Combustion Products in a Model Liquid Rocket Engine Fuel Depending on the Combustion Chamber Pressure

Technique for Recording and Analysis of the Amplitude Spectrum of the Strength Oscillations of Magnetic and Electric Fields of Combustion Products in a Model Liquid Rocket Engine Fuel Depending on the Combustion Chamber Pressure

Predictions for Gravity-mode Periods and Surface Abundances in Intermediate-mass Dwarfs from Shear Mixing and Radiative Levitation

Abstract The treatment of chemical mixing in the radiative envelopes of intermediate-mass stars has hardly been calibrated so far. Recent asteroseismic studies demonstrated that a constant diffusion coefficient in the radiative envelope is not able to explain the periods of trapped gravity modes in the oscillation spectra of γ Doradus pulsators. We present a new generation of MESA stellar models with two major improvements. First, we present a new implementation for computing radiative accelerations and Rosseland mean opacities that requires significantly less CPU time. Second, the inclusion of shear mixing based on rotation profiles computed with the 2D stellar structure code ESTER is considered. We show predictions for the mode periods of these models covering stellar masses from 1.4 to 3.0 M ⊙ across the main sequence, computed for different metallicities. The morphology of the chemical mixing profile resulting from shear mixing in combination with atomic diffusion and radiative levitation does allow for mode trapping, while the diffusion coefficient in the outer envelope is large (>106 cm2 s−1). Furthermore, we make predictions for the evolution of surface abundances for which radiative accelerations can be computed. We find that the N/C and C/O abundance ratios correlate with stellar age. We predict that these correlations are observable with precisions ≲ 0.1 dex on these ratios, given that a precise age estimate can be made.

Distributed sensing via the ensemble spectra of uncoupled electronic chaotic oscillators

An electronic chaos generator involving cross-coupled inverter rings with lengths equal to the smallest odd prime numbers is considered, and a spatiotemporally-varying control parameter, hypothetically corresponding to a physical variable to be sensed, is introduced akin to a baseband signal. It is shown that, owing to the fine-grained structure of the spectrogram conveniently generated by this circuit, the control parameter setting and its fluctuations can be accurately estimated from the frequency spectrum, or a portion of it, for instance using a small neural network. Mimicking the effect of a passive receiver listening to a set of such nodes, the effect of summing the partially spectrally-overlapping and largely incoherent signals arising from multiple unsynchronized transmitters is then considered. The possibility of estimating some features of the statistical and topographical distribution of the control parameter from the frequency spectrum of the population ensemble signal(s) is indicated. Physical feasibility is corroborated by experiments involving an integrated circuit prototype realized using 65 nm CMOS technology, through which measurement reproducibility is also assessed. The proposed approach may have advantages for realizing distributed sensing applications because synchronization among the sensor nodes is not required, allowing the use of considerably simpler transmitters rather than mutually-coupled oscillators.

FrosPy: A Modular Python Toolbox for Normal Mode Seismology

Abstract We present free oscillations Python (FrosPy), a modular Python toolbox for normal mode seismology, incorporating several Python core classes that can easily be used and be included in larger Python programs. FrosPy is freely available and open source online. It provides tools to facilitate pre- and postprocessing of seismic normal mode spectra, including editing large time series and plotting spectra in the frequency domain. It also contains a comprehensive database of center frequencies and quality factor (Q) values based on 1D reference model preliminary reference Earth model for all normal modes up to 10 mHz and a collection of published measurements of center frequencies, Q values, and splitting function (or structure) coefficients. FrosPy provides the tools to visualize and convert different formats of splitting function coefficients and plot these as maps. By giving the means of using and comparing normal mode spectra and splitting function measurements, FrosPy also aims to encourage seismologists and geophysicists to learn about normal mode seismology and the study of the Earth’s free oscillation spectra and to incorporate them into their own research or use them for educational purposes.

Magnetoresistance and quantum oscillations in the WTe-=SUB=-2-=/SUB=- semimetal

The discovery of extreme magnetoresistance (XMR) in non-magnetic materials attracted attention to the WTe2 semimetal. We have carried out studies of magnetoresistance in a tungsten ditelluride single crystal in the magnetic field range up to 14 T. Magnetoresistance increased with increasing field following a near quadratic law without saturation. The Shubnikov-de Haas oscillations were observed. Four fundamental frequencies were found in the oscillations spectrum, which correspond to two electron and two hole pockets caused by strong spin-orbit coupling. Keywords: WTe2 semimetal, magnetoresistance, Shubnikov-de Haas oscillations, oscillations spectrum.

Disturbance of potassium iodide solution on nonlinear chemical oscillation system of (NH4)4Ce(SO4)4-NaBrO3-malonic acid

The objective of this paper was to study the effect of potassium iodide solution on nonlinear chemical oscillation system of (NH4)4Ce(SO4)4-NaBrO3-malonic acid in the food safety detection. Taking milk powder and pure water blank samples as tested samples, click the menu to collect data. When oscillation curve went on smoothly to 8 min, potassium iodide solution of different concentration was injected, respectively, and the influence of potassium iodide solution of each concentration on intuitive information and characteristic parameters of the corresponding oscillation spectrum was investigated. The results showed that when the concentration of potassium iodide was higher than 1 × 10-3 mol/L, visual information and some characteristic parameters of nonlinear chemical oscillation spectra of milk powder and pure water blank samples were greatly disturbed, and there was a good linear relationship between oscillatory end time and the concentration of potassium iodide, and correlation coefficient was 0.9902. At the same time, this study provided a reference for the study of disturbance of other components on nonlinear chemical oscillation system in the food safety detection.