Stationary Spectra Research Articles

QUADRATURE COMPONENTS FORMING METHOD FOR HOMODYNE ACOUSTO-OPTIC SPECTRUM ANALYZER

Introduction. Among acousto-optic spectrum analyzers with spatial integration, schemes based on optical interferometers provide the largest dynamic range. Nevertheless, they form the signal amplitude spectrum on a certain spatial carrier. Formation of quadrature components can eliminate this spatial carrier. The two-dimensionality of the transformations performed in optical processors provides this elimination by reading of the additional charge of matrix photosensor lines. A renowned method implements this approach using four lines, which in turn determines the estimation time of the signal spectrum.Objective. The objective of the work is to study the possibility of time reduction of the spectrum estimation.Materials and methods. The paper presents the description of two methods of forming the necessary components.The first method uses three photosensor lines, the charge distribution in which has the spatial carrier phaseshifted by 90 ° from line to line. The second method forms the necessary distributions sequentially in three accumulation cycles by means of variation of the initial phase of the reference signal. By the mathematical proof, three distributions with a 90 ° relative phase shift are sufficient to eliminate the spatial carrier.Results. In the first method, reduction of the spectrum estimation time is insignificant, but the parallel distributions formation affords not to impose additional requirements on the signal spectrum. The second method, due to the possibility of using any three sequentially formed distributions for estimation, is potentially three times faster than the first method, but requires the stationary signal spectrum within three accumulation cycles. Researchers can implement this meth-od using a linear photosensor or TDI photosenor. In addition, the method is less demanding to optical scheme parameters.Conclusion. The proposed quadrature components formation methods provide time reduction of the spectrum estimation in interference acousto-optic spectrum analyzers and simplify their design.

Observation of a local maximum in the stationary turbulent spectrum of capillary waves on the surface of liquid hydrogen

The results of experimental studies of wave turbulence in a system of capillary waves formed on the surface of liquid hydrogen at a temperature of 15 K in a cylindrical cell with monochromatic radially symmetric pumping are presented. The local maximum formation with a decrease in the pumping amplitude was observed for the first time in the high-frequency region of the inertial range of the stationary turbulent spectrum at the direct cascade edge. The occurrence of a local maximum can be associated with a significant manifestation of viscous damping in the high-frequency region of the spectrum.

An experimental study of a time-frame implementation of the Speech Transmission Index in fluctuating speech-like noise conditions

Everyday communication takes place in the combined presence of reverberation and background noise, the latter having in some cases fluctuating characteristics and speech-like spectrum. To predict the speech intelligibility for fluctuating maskers, a time-frame implementation of the Speech Transmission Index (STI) in the indirect measurement scheme, named Extended STI (eSTI), has been recently proposed. Stationary speech spectrum noise is used as the probe signal and the a priori knowledge of the impulse response characterizing the transmission chain is required. A key issue of eSTI is the selection of the appropriate time frame for the calculations, whose duration is here assessed by a systematic experimental approach. Listening tests are developed for the scope, using speech-like stationary and fluctuating noises as maskers and rendering sound fields with various reverberation times and over a wide range of signal-to-noise ratios. An interval of frame durations providing equivalent values of eSTI under the two noises is identified. Within the target interval, statistically coincident psychometric curves are obtained for the two noises, thus ensuring that the same eSTI corresponds to the same speech intelligibility.

The focusing problem for the Leith model of turbulence: a self-similar solution of the third kind

Time-dependend evolution of hydrodynamic turbulence corresponding to formation of a thermodynamic state at the large-scale part of the spectrum is studied using the inviscid Leith model. In the wave vector space, the evolution leads to shrinking of the zero-spectrum ‘hole’—the so-called focusing problem. However, in contrast with the typical focusing problem in the nonlinear filtration theory, the focusing time is infinite for the Leith model. Respectively, the evolution is described by a self-similar solution of the third kind (discovered in Nazarenko and Grebenev (2017 J. Phys. A: Math. Theor. 50 035501)), and not the second kind as in the case of the typical filtration problem. Using a phase-plane analysis applied to the dynamical system generated by this type of similarity, we prove the existence of a new self-similar spectrum to this problem. We show that the final stationary spectrum scales as the thermodynamic energy equipartition spectrum, .

Spectral Dynamics of Nitro Derivatives of Xanthione in Solutions.

Nitro derivatives of xanthione, 2,7-dinitro-9 H-xanthene-9-thione and 2,4,7-trinitro-9 H-xanthene-9-thione, have been first synthesized and their stationary and transient spectra have been measured. The stationary spectra show that the attachment of the nitro groups to the xanthione scaffold leads to strong quenching of S2 → S0 fluorescence and the decrease of the oscillator strength of the S2 ← S0 electronic transition. Analysis of the transient absorption spectra uncovers the ultrafast stimulated emission quenching from the second excited state, S2, in the both derivatives. A kinetic scheme has been suggested to rationalize the complex spectral dynamics of the transient absorption signal. The kinetic scheme is deduced from the analysis of the transient spectra and supported by the quantum-chemical calculations, which predict the existence of a dark state and S2 state splitting into two close levels. The ultrafast transitions between S2 state sublevels and the transition into the dark state play a crucial role in spectral dynamics. These new features discovered in the nitro derivatives of xanthione distinguish essentially their spectral dynamics from that observed in xanthione.

Multiple-input multiple-output non-stationary non-Gaussian random vibration control by inverse system method

Abstract This paper investigates the control method for multi-input multi-output non-stationary non-Gaussian random vibration test with the specified references composed of stationary power spectra, moving root mean square distributions and moving kurtosis distributions. The objective of random vibration test is to force the response signals of test structure to satisfy the specified references within tolerances. An inverse system method in time domain is used to guarantee the control of response time-frequency characteristics independently and simultaneously. The evolutionary spectrum theory is utilized to establish the matrix representation of non-stationary non-Gaussian input-output relationships of a linear dynamic system in frequency domain. To analyze a non-stationary non-Gaussian vibration signal, two sets of random numbers named moving root mean square and moving kurtosis are used to modulate a stationary random signal. The transformation process theory is utilized to obtain moving root mean square and moving kurtosis by a moving root mean square distribution and a moving kurtosis distribution respectively. The control algorithms are presented to update the drive signals according to the deviations between responses and references. A numerical example by a cantilever beam and a biaxial vibration test are carried out and the results demonstrate the feasibility and validity of the proposed methods.

Focusing Multireceiver SAS Data Based on the Fourth-Order Legendre Expansion

Using Legendre polynomials and the derivation method of the implicit function, this paper proposes a range-Doppler algorithm for multireceiver synthetic aperture sonar. Based on Legendre polynomials, the two-way slant range is first expanded into a power series with respect to the slow time. Then, the derivation method of the implicit function is exploited to deduce the point of stationary phase and point target reference spectrum (PTRS). Based on this PTRS, the paper presents an imaging algorithm, which uses the range-dependent sub-block processing method to cancel the space-variant coupling between the range and azimuth dimensions. Simulation results and real data processing are presented to validate the proposed method.

Modeling Kinetics of Ultrafast Photoinduced Intramolecular Proton-Coupled Electron Transfer

A model of photoinduced intramolecular proton-coupled electron transfer is derived. The model includes three states as follows: the ground, excited, and product states. The charge transfer is associated with both stages, photoexcitation and product formation. A larger part of the model parameters can be extracted from the stationary absorption and fluorescence spectra of a particular fluorophore. Two different reaction coordinates are associated with the two stages, which are not independent. The angle between the reaction coordinates strongly influences on the kinetics of ultrafast product formation. The stochastic multichannel approach is exploited for simulations of the kinetics. The simulations well reproduce the kinetics of ultrafast intramolecular proton-coupled electron transfer in 2-((2-(2-hydroxyphenyl)benzo[d]oxazol-6-yl)methylene)malononitrile in a few solvents. The transfer is shown to occur totally or partly, depending on the solvent, in the nonequilibrium regime. Analysis of the kinetics of ...

Time-dependent spectra of a three-level atom in the presence of electron shelving

We investigate time-dependent spectra of the intermittent resonance fluorescence of a single, laser-driven, three-level atom due to electron shelving. After a quasi-stationary state of the strong transition, a slow decay due to shelving leads to the steady state of the three-level system. The long-term stationary spectrum consists of a coherent peak, an incoherent Mollow-like structure, and a very narrow incoherent peak at the laser frequency. We find that in the ensemble average dynamics the narrow peak emerges during the slow decay regime, after the Mollow spectrum has stabilized, but well before an average dark time has passed. The coherent peak, being a steady state feature, is absent during the time evolution of the spectrum

How Stochasticity Influences Leading Indicators of Critical Transitions.

Many complex systems exhibit critical transitions. Of considerable interest are bifurcations, small smooth changes in underlying drivers that produce abrupt shifts in system state. Before reaching the bifurcation point, the system gradually loses stability ('critical slowing down'). Signals of critical slowing down may be detected through measurement of summary statistics, but how extrinsic and intrinsic noises influence statistical patterns prior to a transition is unclear. Here, we consider a range of stochastic models that exhibit transcritical, saddle-node and pitchfork bifurcations. Noise was assumed to be either intrinsic or extrinsic. We derived expressions for the stationary variance, autocorrelation and power spectrum for all cases. Trends in summary statistics signaling the approach of each bifurcation depend on the form of noise. For example, models with intrinsic stochasticity may predict an increase in or a decline in variance as the bifurcation parameter changes, whereas models with extrinsic noise applied additively predict an increase in variance. The ability to classify trends of summary statistics for a broad class of models enhances our understanding of how critical slowing down manifests in complex systems approaching a transition.

Spectrum optimization of light-emitting diode insecticide lamp based on partial discharge evaluation

The spectrum distribution of light-emitting diodes (LEDs) is a critical issue in adopting LEDs as an attractant in insect-catching apparatuses via phototaxis effects. Numerous research efforts have attempted to configure the LED spectrum in line with the insect-sensitive spectrum under designed test conditions. Although successful methods have achieved a stationary spectrum configuration, it is less effective when applied directly to an LED insecticide lamp due to the time-variant behaviors of insects in complex environments. Therefore, dynamic optimization for spectrum distribution of the LED insecticide lamp in practical fields remains essential to improve energy efficiency and the control quality of insects. In this paper, an online learning and dynamic control method has been proposed, where dead insects are evaluated by a partial discharge waveform and a cost function derived from the lamp’s safety, efficiency, and effectiveness is optimized using a proposed jumping-predication algorithm. Then, a detailed procedure for developing a smart and effective LED insecticide lamp based on photovoltaic power supply is illustrated, and finally the LED insecticide lamp is validated. The suggested methodology and experimental results shed light on controlling insects and pests using an LED insecticide lamp in green agriculture.

Auditory distraction by speech: Can a babble masker restore working memory performance and subjective perception to baseline?

Background speech has a detrimental impact on employees’ privacy perception and cognitive performance in open-plan offices. Sound masking that covers speech sounds can help to improve the speech privacy and the ability to work undisturbed in open office environments. Recently, non-artificial sounds such as babble or water sounds have been suggested as masking sounds because they may be perceived as more natural and subsequently less annoying. This paper compares the working memory performance and annoyance perception during background speech that was masked by different babble sounds and a waterfall sound to speech that was masked by stationary noise with the frequency spectrum of the distracting background speech signal (target speech). In a first laboratory experiment the effects of different babble sounds were compared with the noise sound at a speech-to-noise ratio of −3 dB. All subjects had to complete a serial short-term memory task and a questionnaire that covered subjective ratings. All sound conditions with masked target speech produced similar error rates and annoyance ratings as unmasked target speech. In a second laboratory experiment, the speech-to-noise ratio of target speech that was masked by babble consisting of 48 target speech signals was varied between −6 and −12 dB in steps of 3 dB. Target based babble resulted in similar error rates as stationary noise at −6 dB speech-to-noise ratio but the findings suggest that target speech that is masked by babble might even be perceived as more annoying than speech that is masked by stationary target spectrum based noise.

Spectrum of Langmuir fluctuations trapped in a cavity of a collisional plasma

The Langmuir fluctuations trapped and enhanced inside a cavity of the electron concentration in a plasma are considered. Stationary fluctuation spectrum is calculated with regard to finite collisional damping of the Langmuir waves and nonequilibrium fluctuation source. It is shown that the fluctuation spectrum obtained exhibits a frequency modulation due to the reflection and superposition of the elementary Langmuir waves in the irregularity. The modulation depth and period as a function of the irregularity size and the electron–ion collision frequency is calculated. These results may help to find from experimental observations such important plasma parameters as the irregularly size and lifetime, as well as the electron collision frequency.

Stationary and time-resolved spectra analysis of pyrazoloquinoline derivatives with pyridyl moiety

Two derivatives of pyrazoloquinoline with pyridyl moiety: 6-N,N-dimethyl-3-phenyl-1-(2-pyridyl)-1H-pyrazolo[3,4-b]quinoline (DMA-1PPhPQ) and 6-N,N-dimethyl-1,3-(di-2-pyridyl)-1H-pyrazolo[3,4-b]quinoline (DMA-1,3PPQ) were synthesized with commercial substrates. The theoretical characterization of both compounds was done. Geometry optimizations give not flat structure with the first absorption band at the wavelength about 390nm for both compounds. Several electro-optical parameters were also calculated. The optical properties of DMA-1PPHPQ and DMA-1,3PPQ were investigated by ultraviolet-visible spectroscopy and stationary as well as time-resolved fluorescence. The fluorescence maximum and fluorescence quantum yield are strongly dependent on solvent polarity function. Results indicate CT fluorescence for both compounds. Because of high emission the investigated pyrazoloquinoline derivatives can be potential candidates for fabrications of electroluminescent devices.

Ringing phenomenon based measurement of weak mode-coupling strength in an optical microresonator

There is always a coupling between the degenerate clockwise (CW) and counter-clockwise (CCW) modes in a whisperinggallery- mode (WGM) optical microresonator, since the surface of the microresonator can not be perfectly smooth. It is important to measure this coupling strength in many applications. When the coupling strength is strong, the conventional method by observing mode splitting in the stationary spectrum can be used to measure its value. However, when the coupling strength is weak, the conventional method will not work. We experimentally demonstrate that the ringing phenomenon can be used to measure weak coupling strength between the CW and CCW modes in a WGM optical microresonator.

Understanding discrete capillary-wave turbulence using a quasi-resonant kinetic equation

Experimental and numerical studies have shown that, with sufficient nonlinearity, the theoretical capillary-wave power-law spectrum derived from the kinetic equation (KE) of weak turbulence theory can be realized. This is despite the fact that the KE is derived assuming an infinite domain with continuous wavenumber, while experiments and numerical simulations are conducted in realistic finite domains with discrete wavenumbers for which the KE theoretically allows no energy transfer. To understand this, we first analyse results from direct simulations of the primitive Euler equations to elucidate the role of nonlinear resonance broadening (NRB) in discrete turbulence. We define a quantitative measure of the NRB, explaining its dependence on the nonlinearity level and its effect on the properties of the obtained stationary power-law spectra. This inspires us to develop a new quasi-resonant kinetic equation (QKE) for discrete turbulence, which incorporates the mechanism of NRB, governed by a single parameter $\unicode[STIX]{x1D705}$ expressing the ratio of NRB and wavenumber discreteness. At $\unicode[STIX]{x1D705}=\unicode[STIX]{x1D705}_{0}\approx 0.02$, the QKE recovers simultaneously the spectral slope $\unicode[STIX]{x1D6FC}_{0}=-17/4$ and the Kolmogorov constant $C_{0}=6.97$ (corrected from the original derivation) of the theoretical continuous spectrum, which physically represents the upper bound of energy cascade capacity for the discrete turbulence. For $\unicode[STIX]{x1D705}<\unicode[STIX]{x1D705}_{0}$, the obtained spectra represent those corresponding to a finite domain with insufficient nonlinearity, resulting in a steeper spectral slope $\unicode[STIX]{x1D6FC}<\unicode[STIX]{x1D6FC}_{0}$ and reduced capacity of energy cascade $C>C_{0}$. The physical insights from the QKE are corroborated by direct simulation results of the Euler equations.

Effects of Hydrostatic Pressure and Electric Field on the Electron-Related Optical Properties in GaAs Multiple Quantum Well.

The properties of the electronic structure of a finite-barrier semiconductor multiple quantum well are investigated taking into account the effects of the application of a static electric field and hydrostatic pressure. With the information of the allowed quasi-stationary energy states, the coefficients of linear and nonlinear optical absorption and of the relative refractive index change associated to transitions between allowed subbands are calculated with the use of a two-level scheme for the density matrix equation of motion and the rotating wave approximation. It is noticed that the hydrostatic pressure enhances the amplitude of the nonlinear contribution to the optical response of the multiple quantum well, whilst the linear one becomes reduced. Besides, the calculated coefficients are blueshifted due to the increasing of the applied electric field, and shows systematically dependence upon the hydrostatic pressure. The comparison of these results with those related with the consideration of a stationary spectrum of states in the heterostructure-obtained by placing infinite confining barriers at a conveniently far distance-shows essential differences in the pressure-induced effects in the sense of resonant frequency shifting as well as in the variation of the amplitudes of the optical responses.

A model of anomalous absorption of laser light on ion acoustic turbulence

Instability of ion acoustic waves due to the return current driven by an electron heat flux is identified as a source of the ion-acoustic turbulence (IAT) in hot, inertial confinement fusion plasmas. Two mechanisms of anomalous absorption are studied, first due to enhanced electron collisionality on ion-acoustic fluctuations and second due to electromagnetic wave conversion into Langmuir waves at the critical density, which is enabled by IAT. An effective absorption coefficient is derived combining the two mechanisms with a stationary IAT spectrum derived from the theory of weak plasma turbulence. Estimates of the return current instability threshold and anomalous absorption are presented for hohlraum plasma in indirect drive fusion experiments. Anomalous absorption is anisotropic due to the angular anisotropy of the IAT spectrum and, according to our theory, can be remarkably effective near the critical density in high Z plasmas. Possible experiments which could identify IAT, and anomalous absorption mechanisms are discussed.

Self-similar formation of the Kolmogorov spectrum in the Leith model of turbulence

The last stage of evolution toward the stationary Kolmogorov spectrum of hydrodynamic turbulence is studied using the Leith model []. This evolution is shown to manifest itself as a reflection wave in the wavenumber space propagating from the largest toward the smallest wavenumbers, and is described by a self-similar solution of a new (third) kind. This stage follows the previously studied stage of an initial explosive propagation of the spectral front from the smallest to the largest wavenumbers reaching arbitrarily large wavenumbers in a finite time, and which was described by a self-similar solution of the second kind [–]. Nonstationary solutions corresponding to ‘warm cascades’ characterised by a thermalised spectrum at large wavenumbers are also obtained.

On the Analysis of Non‐stationary Impedance Spectra

AbstractIn this work we study the possibility to analyze the non‐stationary impedance spectra by employing standard equivalent circuits. For this purpose, the dynamic multi‐frequency analysis (DMFA) is introduced and compared with a set of consecutive stationary impedance spectra. In order to prove the hypothesis, the data are obtained by the simulation in the time domain of the electron transfer process between an electrode and a free‐diffusing redox couple in solution. During the simulation, the system is perturbed with a cyclic voltammetry superimposed to a small multisine perturbation (DMFA) or with a series of stationary impedance spectroscopies. Also, a new fitting algorithm, which takes into account the correlation between consecutive spectra, is proposed and tested. Although the Randles circuit can be used to fit both dynamic and stationary impedance spectra, the values of the fitting parameters are different and depend on the direction of the scan and on the rate. This is related to the influence of the diffusion profile on the fitting parameters.