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Cable maintenance is important for cable structures such as cable-stayed and Nielsen-Lohse bridges. In the current maintenance practice, cable tension is estimated from the lower mode natural frequencies of the cable. It is theoretically possible to estimate the bending stiffness of the cable and the parameters of the dampers installed on the cable if the higher mode natural frequencies, damping factors, and mode shapes are available. Conventionally, the natural vibration characteristics of the cables are estimated manually from the acceleration Fourier spectrum. The estimation accuracy of the lower mode natural frequencies is high. However, the estimation accuracy of the higher mode natural frequencies is not high, and the estimation accuracy of damping factors and mode shapes is low irrespective of modal order. In this paper, the N4SID, one of the subspace methods, is adopted to estimate the natural vibration characteristics of the cables. The N4SID is applied to numerical and experimental results of bridge cables to investigate the estimation accuracy. The numerical investigation found that the accuracy of the natural frequencies and damping factors is high, the accuracy of mode shape is high in the cable without a damper, and the accuracy of mode shape is only high for the limited low modes and low for the other mode in the cable with a damper. The experimental investigation found that the N4SID has better accuracy than the conventional estimation method. [ABSTRACT FROM AUTHOR]

Afghanistan is situated close to the area where the Indian, Arabian, and Eurasian tectonic plates converge. The consequent seismic hazard causes the region to be repeatedly struck by major earthquakes. However, there is a lack of seismic instrumentation in the region, and only limited historical ground motions are available thus presenting a challenge for structural designers. Due to the absence of information and a database of ground motions, buildings in the region are often built without guidance from seismic codes. Consequently, the earthquakes in the region continue to cause enormous destruction to the built environment of the region. On 22 June 2022, the southeastern region of the country was struck by a major Mw 6.2 earthquake having a maximum modified Mercalli intensity of IX. In this study, synthetic ground motions are obtained using the modified stochastic finite fault methodology for Khost and Kabul cities in the region. The results from simulations obtained in the current study are observed to compare well with the available records of the earthquake. The obtained findings are reported as simulated accelerograms, acceleration response spectra, and Fourier response spectra, which will be immensely beneficial in understanding the behavior of the built environment of the region. [ABSTRACT FROM AUTHOR]

Type or paste your abstract here as prescribed by the journal's instructions for authors. Type or paste your abstract here as prescribed by the journal's instructions for authors. Type or paste your abstract here as prescribed by the journal's instructions for authors. Type or paste your abstract here. This paper deals with dynamics of incommensurate superstructure at the moment of its formation. Lyapunov exponent value spectra, phase portraits, incommensurate modulation wave vector behavior, Fourier spectra and maps of incommensurate phase dynamic modes under changed parameters of long-range interaction (Т) and anisotropic interaction (K) in interval 0.0 ÷ 1.0 were analyzed. The calculations were made in Python environment applying Skipy, JiTCODE libraries. Under low values of Т and K parameters (0.0015 ÷ 0.03) a chaotic state occurs in this system. It is determined by the interaction between different spatial areas of the correlated motion of tetrahedral groups. The interaction of spatial areas of the correlated motion of tetrahedral groups violates the modulation pattern of tetrahedral group motion causing the superstructure chaotic state. The study of Fourier spectra has shown that interaction of spatial areas of tetrahedral group correlated motion of causes the chaotic state that is non-stable and is destroyed by long-range interaction. The impact of surface energy on the interaction of spatial areas of tetrahedral group correlated motion is determined by decreased amplitude of vibrations of tetrahedral groups causing the disappearance of the chaotic state. [ABSTRACT FROM AUTHOR]

The aim of the study is to extend the list of spectral lines of atomic and single ionized holmium (Ho) into the near infrared wavelength range up to 1750 nm. Spectra of a Ho hollow cathode discharge lamp with neon or argon as buffer gases have been measured with a Fourier Transform spectrometer in different spectral ranges. In total, the range from 700 nm to 1750 nm i.e. from 5 710 cm − 1 to 14 280 cm − 1 has been covered. A total of almost 800 spectral lines were detected. Based on the known energy levels of atom and ion Ho, 589 lines could be classified as Ho I transitions and 31 lines as Ho II transitions. The remaining 171 lines could mostly be classified as different Ho I or Ho II, based on different signal-to-noise ratios in spectra measured with different buffer gases. In the wavelength range from 1200 nm to 1750 nm, a list of Ho lines is presented for the first time. In the wavelength range from 700 nm to 1200 nm 216 lines had not been listed in literature up to now. [Display omitted] • FT spectra of Holmium in the near infrared (700 nm to 1750 nm). • 791 spectral lines identified by comparing spectra with different discharge conditions. • 515 spectral lines published for the first time. • Simulation of hyperfine structure ⇒ 620 spectral lines classified, 203 for the first time. [ABSTRACT FROM AUTHOR]

The paper presents and analyzes the Fourier spectra of the complete waveforms of the P and S waves measured on the drilling core samples in the laboratory. Measurements were performed on sandstone and aluminum samples at 12 different pressures. For measurements on an aluminum sample, the spectra show significantly higher amplitude values at all pressures and at all frequencies than for sandstone sample. In the case of sandstone sample, the energy of the P wave is concentrated in the frequency band between 100,000 Hz and 300,000 Hz, while the energy of the S wave is predominantly in the frequency band between 300,000 Hz and 800,000 Hz. Based on acoustic measurements, it can also be stated that the maximum of the energy spectrum of the P wave measured on the same sample is significantly higher than that of the S wave. [ABSTRACT FROM AUTHOR]

Inversions of empirical data and ground-motion models to find Fourier spectral parameters can result in parameter combinations that produce over-saturation of short-period response spectral ordinates. While some evidence for over-saturation in empirical data exists, most ground-motion modellers do not permit this scaling within their models. Host-to-target adjustments that are made to published ground-motion models for use in site-specific seismic hazard analyses frequently require the identification of an equivalent set of Fourier spectral parameters. In this context, when inverting response spectral models that do not exhibit over-saturation effects, it is desirable to impose constraints upon the Fourier parameters to match the scaling of the host-region model. The key parameters that determine whether over-saturation arises are the geometric spreading rate (γ) and the exponential rate within near-source saturation models (hβ). The article presents the derivation of simple nonlinear constraints that can be imposed to prevent over-saturation when undertaking Fourier spectral inversions. [ABSTRACT FROM AUTHOR]

Typical seismic ground-motion models predict the response spectral ordinates (GMM-SA), which are the damped responses of a suite of single-degree-of-freedom oscillators. Response spectra represent the response of an idealized structure to input ground-motion, but not the physics of the actual ground-motion. To complement the regionally adaptable GMM-SA of Kotha et al. (2020), we introduce a model capable of predicting Fourier amplitudes (GMM-FA); developed from the Engineering Strong Motion (ESM) dataset for pan-Europe. This GMM-FA reveals the very high variability of high frequency ground-motions, which are completely masked in a GMM-SA. By maintaining the development strategies of GMM-FA identical to that of the GMM-SA, we are able to evaluate the physical meaning of the spatial variability of anelastic attenuation and source characteristics. We find that a fully data-driven geospatial index, Activity Index (AIx), correlates well with the spatial variability of these physical effects. AIx is a fuzzy combination of seismicity and crustal parameters, and can be used to adapt the attenuation and source non-ergodicity of the GMM-FA to regions and tectonic localities sparsely sampled in ESM. While AIx, and a few other parameters we touch upon, may help understand the spatial variability of high frequency attenuation and source effects, the high frequency site-response variability—dominating the overall aleatory variance—is yet unresolvable. With the rapid increase in quantity and quality of ground-motion datasets, our work demonstrates the need to upgrade regionalization techniques, site-characterisation, and a paradigm shift towards Fourier ground-motion models to complement the traditional response spectra prediction models. [ABSTRACT FROM AUTHOR]

Simulation of the coherent excitation of molecules by laser radiation is carried out. It is based on simple models, i.e., quantum systems with N + 1 energy level. The exact solution of differential equations describing the process in terms of the simplest semi-classical Rabi model is obtained without integration of differential equations but using discrete mathematics with Fourier transform and discrete orthogonal polynomials. The Fourier transform realizes the transition from continuum t-space with time-dependent probability amplitudes an(t) of a quantum system to discrete Fourier space where Fourier spectra Fn(ω) are spectral images of an(t). The spectra are shown to be described by some discrete orthogonal polynomial sequence corresponding to the quantum system. The example shows how using specially constructed polynomials one can calculate the Fourier spectra and find the probability amplitudes an(t) describing the excitation of a quantum system. The established one-to-one correspondence between the polynomial characteristics and the coefficients of differential equations allows us to calculate all the characteristics of quantum systems whose excitation is described by the solution. Thus, the transition from functions an(t) to their spectral space allows one to solve some dynamic equations without integration reducing the problem to calculating the finite sum from 0 to N. [ABSTRACT FROM AUTHOR]

The one-dimensional nonlinear dynamical wave interactions in a system of quasineutral two-fluid plasma in a constant magnetic field are investigated. The existence of the travelling wave solutions is discussed. The modulation stability of linear waves and the modulation instability of weakly nonlinear waves are presented. Both suggest that the Korteweg-de Vries (KdV) system is modulationally stable. Besides, the wave interactions including the periodic wave interaction and the solitary wave interaction are captured and presented. It is shown that these interacting waves alternately exchange their energy during propagation. The Fourier spectrum analysis is used to depict the energy transformation between the primary and harmonic waves. It is known that the wave interactions in magnetized plasma play an important role in various processes of heating and energy transportation in space and astrophysical plasma. However, few researchers have considered such magnetohydrodynamic (MHD) wave interactions in plasma. It is expected that this work can provide additional insight into understanding of behaviors of MHD wave interactions. [ABSTRACT FROM AUTHOR]

Potential change in the hydrological cycles may lead to changes in extreme events such as drought due to the changes in intensity, frequency, and seasonality of precipitation and evaporative demand. In this study, projected drought scenarios and associated uncertainties in the late 21st century over the Continental United States are analysed based on seven regional climate models (RCMs) contributing to the Coordinated Regional Climate Downscaling Experiment. Meteorological drought scenarios are analysed based on standardized precipitation evapotranspiration index (SPEI). Here, we propose a new multimodel ensemble approach based on the similarity of spectral power of different frequency components of the SPEI time series. The approach combines output from different RCMs based on their ability to produce the observed power spectra as well as convergence towards the average spectra from all participating RCMs in the future climate. Furthermore, to understand the SPEI variability associated with climate teleconnection, continuous wavelet transform‐based spectral coherency between the SPEI and two climate indices: the El Niño–Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO) is analysed. Results show that among‐model uncertainty is the dominant source of uncertainties in the projected drought scenarios with contributions as large as 97% to the total uncertainty. Fifteen to 20% more frequent droughts are projected in future climate due to a decrease in mean SPEI as well as an increase in the variability of SPEI. Observed SPEI variability is strongly associated with ENSO variability while PDO modulates the strength of correlation between the SPEI and the ENSO. Spectral analysis of future SPEI shows that the increase in the SPEI variability is due to an increase in interannual variability as well as an enhanced ENSO teleconnection over the study area. The results show the increased role of climatic variability and hence the enhanced predictability of drought scenarios in the future climate. [ABSTRACT FROM AUTHOR]

The hypothesis is explored that the high‐frequency magnetic spectral power of the solar wind is associated with the spatial profiles of strong current sheets (directional discontinuities) in the solar wind plasma. This hypothesis is based on previous findings about current sheets and the solar wind's magnetic power spectra (1) that the amplitude distribution and waiting time distribution of strong current sheets determines the amplituic composition and the electron strade and spectral slope of the "inertial range" of frequencies and (2) that the thicknesses of strong current sheets in the solar wind determine the breakpoint frequency that ends the inertial range. Solar wind current sheets are collected from the WIND 0.09375‐s and MMS 7.8 × 10−3‐s magnetic data sets, and the current sheets are individually Fourier transformed. At frequencies above the solar wind breakpoint (1) the shape of the magnetic power spectra of the current sheets resembles the shape of the magnetic power spectra of the solar wind and (2) the current sheets occur frequently enough to account for the magnetic power of the solar wind above the breakpoint. This has implications for the physics underlying the high‐frequency magnetic power spectral density of the solar wind, supplementing the energy‐cascade description of the high‐frequency spectrum. Key Points: The high‐frequency breakpoint in the solar wind's magnetic power spectral density and the power above the breakpoint are of interestThe power spectrum of individual solar wind current sheets has the same shape as the power spectrum of the solar wind above the breakpointThe density of current sheets in the solar wind is sufficient to account for the spectral power of the solar wind above the breakpoint [ABSTRACT FROM AUTHOR]

The Beeler–Reuter model is one of the oldest models of the cardiac ventricular cell. This model is used in many scientific studies that investigate the propagation of the action potential. In this paper, dynamical properties of Beeler–Reuter model with respect to the frequency and amplitude of the stimulus pulse with the shape of the half-sine period are being investigated. For this purpose bifurcation diagrams, the Fourier spectra, and the 0–1 test for chaos was applied. [ABSTRACT FROM AUTHOR]

The present work develops the mathematical base of ill-posed inverse problems in optics, as well as a method of processing and reconstructing scenes from incomplete information of their Fourier spectra. This problem is a part of the general problem of the eliminating the influence atmospheric and optical distortion when finding and registering an object at large distances under bad atmospheric conditions. The designed programmed methods are also used to process medical images.

The emergence of biometric-based authentication using modern sensors on electronic devices has led to an escalated use of face recognition technologies. While these technologies may seem intriguing, they are accompanied by numerous implicit drawbacks. In this paper, we look into the problem of face anti-spoofing (FAS) on a frame level in an attempt to ameliorate the risks of face-spoofed attacks in biometric authentication processes. We employed a bi-directional feature pyramid network (BiFPN) that is used for convolutional multi-scaled feature extraction on the EfficientDet detection architecture, which is novel to the task of FAS. We further use these convolutional multi-scaled features in order to perform deep pixel-wise supervision. For all of our experiments, we performed evaluations across all major datasets and attained competitive results for the majority of the cases. Additionally, we showed that introducing an auxiliary self-supervision branch tasked with reconstructing the inputs in the frequency domain demonstrates an average classification error rate (ACER) of 2.92% on Protocol IV of the OULU-NPU dataset, which is significantly better than the currently available published works on pixel-wise face anti-spoofing. Moreover, following the procedures of prior works, we performed inter-dataset testing, which further consolidated the generalizability of the proposed models, as they showed optimum results across various sensors without any fine-tuning procedures.

The effects of natural disasters such as earthquakes on our environment lead to different earthquake analysis. Seismic site response analysis is one of these analyses, which can be done using different methods. The seismic response analysis carried out in this research was based on Equivalent linear and Nonlinear method. Two seismically active regions which are part of Kohat Platue (Shakardarra) and Hazara Kashmir Syntaxes (Muzaffarabad) were selected. The sites were tested for vertical component input ground motions of magnitude 7.0ML (PGA= 0.07g) and 4.9mb (PGA= 0.018g). The soil profiles for both sites were prepared on the average results of five geotechnical (SPT) upholes data at Muzaffarabad (MUZ) site and twenty seismic upholes data at Shakardarra (SHD). The soil samples collected at MUZ site were sandy gravel, sand and clay and at SHD sandy gravel, sand, clayey sand and clay, for which were tested for damping ratio of 5% using site response analysis programs (NERA and EERA). The stress-strain models, strain energy models, response models (amplification models, Fourier response models and spectral response models) were constructed for each type of soil sample on the basis of input motions data using NERA and EERA, which were then compared. According to comparison, the soils at sites were under great stresses and these exhibited negligible amount of strains, the PGA values calculated were interpreted as incompatible for intermediate to high man-made buildings. [ABSTRACT FROM AUTHOR]

The present work develops the mathematical base of ill-posed inverse problems in optics, as well as a method of processing and reconstructing scenes from incomplete information of their Fourier spectra. This problem is a part of the general problem of the eliminating the influence atmospheric and optical distortion when finding and registering an object at large distances under bad atmospheric conditions. The designed programmed methods are also used to process medical images. [ABSTRACT FROM AUTHOR]

The main aim of this paper is to study the evolution of the transmembrane potential on the cardiac cell under different rates and amplitudes of stimulation. For modeling this potential, the modification of the Fenton‐Karma model was applied. It is a phenomenological model with 3 degrees of freedom that corresponds to nondimensional transmembrane potential and gating variables for regulation of inward and outward ion currents that can better reproduce the shape of the transmembrane potential than the original Fenton‐Karma model. The model was newly forced by stimulus with the shape of the half‐sine period. As the main goal of the paper is to show that this model is showing regular as well as irregular motion; periodic and chaotic patterns are detected using bifurcation diagrams, the Fourier spectra, Poincaré sections, and 0‐1 test for chaos. [ABSTRACT FROM AUTHOR]

Featured Application: This work can be used for fast characterizing the phase modulation of the spatial light modulator (SLM) and shows the applications in coherent imaging by using the SLM. Although digital holography is used widely at present, the information contained in the digital hologram is still underutilized. For example, the phase values of the Fourier spectra of the hologram are seldom used directly. In this paper, we take full advantage of them for characterizing the phase modulation of a spatial light modulator (SLM). Incident plane light beam is divided into two beams, one of which passes the SLM and interferes with the other one. If an image with a single grey scale loads on the SLM, theoretical analysis proves that the phase of the Fourier spectra of the obtained hologram contains the added phase and a constant part relative to the optical distance. By subtracting the phase for the image with the grey scale of 0 from that for the image with other grey scales, the phase modulation can be characterized. Simulative and experimental results validate that the method is effective. The SLM after characterization is successfully used for coherent imaging, which reconfirms that this method is exact in practice. When compared to the traditional method, the new method is much faster and more convenient. [ABSTRACT FROM AUTHOR]

Chaotic dynamics of microbeams made of functionally graded materials (FGMs) is investigated in this paper based on the modified couple stress theory and von Kármán geometric nonlinearity. We assume that the beam properties are graded along the thickness direction. The influence of size-dependent and functionally graded coefficients on the vibration characteristics, scenarios of transition from regular to chaotic vibrations as well as a series of static problems with an emphasis put on the load-deflection behavior are studied. Our theoretical/numerical analysis is supported by methods of nonlinear dynamics and the qualitative theory of differential equations supplemented by Fourier and wavelet spectra, phase portraits, and Lyapunov exponents spectra estimated by different algorithms, including Wolf’s, Rosenstein’s, Kantz’s, and neural networks. We have also detected and numerically validated a general scenario governing transition into chaotic vibrations, which follows the classical Ruelle-Takens-Newhouse scenario for the considered values of the size-dependent and grading parameters. [ABSTRACT FROM AUTHOR]

Although digital holography is used widely at present, the information contained in the digital hologram is still underutilized. For example, the phase values of the Fourier spectra of the hologram are seldom used directly. In this paper, we take full advantage of them for characterizing the phase modulation of a spatial light modulator (SLM). Incident plane light beam is divided into two beams, one of which passes the SLM and interferes with the other one. If an image with a single grey scale loads on the SLM, theoretical analysis proves that the phase of the Fourier spectra of the obtained hologram contains the added phase and a constant part relative to the optical distance. By subtracting the phase for the image with the grey scale of 0 from that for the image with other grey scales, the phase modulation can be characterized. Simulative and experimental results validate that the method is effective. The SLM after characterization is successfully used for coherent imaging, which reconfirms that this method is exact in practice. When compared to the traditional method, the new method is much faster and more convenient.

The high frequency decay parameter, kappa and its variations in distance is evaluated using 114 three component strong motion records from two strong events in Northwestern Iran. We show that in classical method of estimating kappa, the results are very sensitive to the choices of (where spectrum starts to fall) and (where spectrum reaches the noise floor) and automated procedures for estimating kappa are likely to lead to a biased estimation. For the present database, we found an obvious concavity in dependency of kappa on distance. The kappa values in distance were regressed to a trilinear shape for which the first line has a zero slope. Based on this trilinear shape the zero distance kappa are 0.043 and 0.026 for horizontal and vertical components, respectively. [ABSTRACT FROM AUTHOR]

Transformation of square pulse signals by the multilayer Rosen type piezoelectric transformer (PT) is investigated with the goals to preserve the signal waveform and achieve maximum efficiency for power electronics and LED lighting applications. The voltage gain of the transformer is calculated from equations of linear piezoelectricity and motion for a broad frequency range that includes multiple resonant frequencies of PT. The transformation of the square pulse is simulated numerically by applying the voltage gain function to the Fourier spectrum of the input signal, and then, restoring the time-domain output signal from its spectrum. A half-bridge MOSFET amplifier is built to drive the PT in the experimental setup. The measurements of the input and output waveforms and their Fourier spectra verify the calculations. It is shown that the components of the spectrum and the waveform of the square pulse signal can be preserved in the output signal by using multiple resonant frequencies of the transformer. With the accurate match between the signal harmonics and the resonant frequencies of the transformer voltage gain, the square pulse signal provides higher output power than a sine or a square wave, provided that the dominant harmonics of all signals have the same amplitude. [ABSTRACT FROM AUTHOR]

The spectral representation method (SRM) is widely used when simulating spatially variable ground motions. It has mainly two formulas, i.e., the random amplitudes and the random phases formulas. There exist three methods for decomposing the cross spectral density matrix: Cholesky decomposition, eigen decomposition, and root decomposition. Therefore, there are six forms with respect to the different combinations of the simulation formulas and the decomposition methods. To provide researchers and engineers with the guidance on choosing simulation method, the six forms are systematically investigated from five aspects: the power intensity, response spectra, and stochastic error of auto/cross spectral density, Fourier spectra, and difference indexes for Fourier amplitudes and phases. Finally, we give the following advice: the characteristics of the ground motions simulated by the random amplitudes formula are independent of the decomposition method, while the characteristics of the ground motions simulated by random phases formula are dependent of the decomposition method. Furthermore, the root decomposition is strongly recommended when utilizing the random phases formula. [ABSTRACT FROM PUBLISHER]

In a social environment, various types of stress can be overwhelming. Humans frequently encounter these stressful situations in social life. Stress is divided into physical stress and mental stress; the latter is induced by heavy mental workloads and has become a huge social problem, leading to mental disorders and possibly suicide in the worst scenario. Investigations into monitoring mental stress and reducing stressful conditions are, therefore, important for its prevention. In the present study, we focused on autonomous sensory meridian response (ASMR) sound, which is known to improve the human mental condition through its comforting and relaxing effects. We investigated the effect of ASMR on the mental workload induced by mental tasks by the evaluation of EEG activation patterns in normal subjects. Our results showed a significant decrease in alpha-band activity and a significant increase in gamma (high beta)-band activity under the induction of mental workload by mental tasks compared to the resting condition. When applying ASMR sound, alpha- and gamma-band activity under the induction of mental workload by mental tasks was restored to the level of the resting condition. In conclusion, these results indicate that ASMR sound reduces the mental stress induced by mental workload.

Periodograms and Fourier spectra of different experimental time series are calculated. The efficiency of the methods applied to study different signals is considered. The periodogram method often makes it possible to identify periodicities which are hardly identifiable by the Fourier analysis. First of all, it concerns the quasiperiodic processes with a considerable variability in amplitude and form of the rhythmical component, but almost constant period or very weak stable rhythm with a nonsinusoidal form. One more advantage of the periodograms is their low sensitivity to pauses and omissions in the time series. However, data preprocessing is often needed, for instance, filtration of high frequency noise, rarer data interrogation, and analysis of the rhythmical component form. The rhythms revealed by the periodogram method are commonly studied additionally to confirm their significance and to describe their properties. The low computational effectiveness, even relative to the classical Fourier transformation, is one more disadvantage of the periodogram method. [ABSTRACT FROM AUTHOR]

The article presents a study which uses the Fourier-based FOTO method of canopy texture analysis to Google Earth's very-high-resolution images at the wet evergreen forests in the Western Ghats of India. The main objective of the study include assessing the predictive power of the method on aboveground biomass of tropical forests and to test the merits of free Google Earth images relative to their native commercial IKONOS counterparts.

Three methods for calculating the periodograms of superimposed epochs, designed for revealing and investigating periodic components with nonharmonic signal forms are described. Examples of periodograms and Fourier spectra calculated for model time series with known properties are presented. Comparative efficiency of the methods for signals of different forms is discussed. The results of analysis of different experimental signals will be compared in a separate paper that will be a sequel to this work on the optimized choice of methods for analysis of periodic processes. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, on the basis of the theories and methods of ecology and ordinary differential equation, a food web system with impulsive perturbations and distributed time delay is established. By using the theories of impulsive equation, small amplitude perturbation skills and comparison technique, we get the condition which guarantees the global asymptotical stability of the prey and intermediate predator eradication periodic solution. On this basis, we get that the food web system is permanent if some parameters are satisfied with certain conditions. In order to show that these conditions are effective, the influences of impulsive perturbations on the inherent oscillation and distributed time delay are studied numerically; these show rich dynamics, such as period-halving bifurcation, chaotic band, narrow or wide periodic window, chaotic crises. Moreover, the computation of the largest Lyapunov exponent shows the chaotic dynamic behavior of the model. Meanwhile, we investigate the qualitative nature of strange attractor by using Fourier spectra. All of these results may be useful in the study of the dynamic complexity of ecosystems. [Copyright &y& Elsevier]

Abstract: In this paper, by using the theories and methods of ecology and ordinary differential equation, an ecological model consisting of two preys and one predator with impulsive control strategy is established. By using the theories of impulsive equation, small amplitude perturbation skills and comparison technique, we get the condition which guarantees the global asymptotical stability of the prey-eradication periodic solution. It is proved that the system is permanent. Further, influences of the impulsive perturbation on the inherent oscillation are studied numerically, which shows rich dynamics, such as period-doubling bifurcation, period-halving bifurcation, chaotic band, narrow or wide periodic window, chaotic crises,etc. Moreover, the computation of the largest Lyapunov exponent demonstrates the chaotic dynamic behavior of the model. At the same time, we investigate the qualitative nature of the strange attractor by using Fourier spectra. All these results may be useful for the study of the dynamic complexity of ecosystems. [Copyright &y& Elsevier]

Previous studies have demonstrated that human contrast sensitivity curves have marked extremes [4]. This phenomenon has not yet been investigated. The present report describes studies of plots of frequency-contrast characteristics obtained using gratings with orientations of 0°, 90°, and 135°. The results showed that: 1) periodically located extremes were marked on the averaged curve obtained using gratings with an orientation of 0°, while use of gratings with orientations of 90° and 135° gave weak peaks; 2) on repeat testing, the amplitudes of extremes decreased sharply, to the level of disappearance by day 5 of testing. These data lead to the suggestion that the phenomenon of local extremes is not associated with random errors by the subjects but reflects the specific characteristics of information processing by the visual system. [ABSTRACT FROM AUTHOR]

Abstract: Free vibration of soils happens frequently during some large earthquakes, perhaps seeming like a paradox. This happens because the energy released from seismic sources in some cases is not stationary in time, allowing relaxation intervals in between without important seismic wave arrivals in which free soil vibration happens. Two techniques to estimate the natural period of the free vibration from accelerograms are presented: autocorrelograms and Fourier spectra. Both techniques sometimes allow measuring higher mode frequencies of the soil for the three first modes as well as modal damping. Free vibration modal periods satisfy the classic 1D equation S-wave theory. The presence of free vibrations corresponds to shear wave soil energy radiation episodes rather than to energy amplification of incoming stationary seismic shear waves suggested by the dynamic soil amplification. These results explain the discrepancies observed between the theoretical soil dynamic amplification and the accelerographic measurement. Observation of free vibration of soils is not always possible, it depends on the duration of the time windows without important seismic waves arrivals compared to the natural period and damping of the soil. [Copyright &y& Elsevier]

We measured ultraweak emissions of the Xenopus laevis eggs and embryos during normal development and under the influence of stress factors in a spectral range of 250 to 800 nm using a photomultiplier. The registered emissions were analyzed by several basic characteristics: mean intensity, histograms, kurtosis, linear trends, and Fourier spectra. We followed relationships between these parameters and developmental stage, as well as the number of individuals in optic contact with each other. The ultraweak emissions did not differ from the background at all developmental stages according to the mean intensity. But Fourier analysis revealed the reliable presence of a number of spectral lines of ultraweak emission, predominantly in the range of 10−2–50 Hz, in the embryos at developmental stages 2 to 11. The intensity of ultraweak emissions reliably decreased within the first 10 min after egg activation and fertilization, as well as in the case of optic interaction between groups of embryos. Sharp cooling, increase in osmotic medium pressure, and transfer in a Ca2+ and Mg2+-free medium induced a short term (∼1–5 min) increase in the mean intensity of ultraweak emission. We studied specific features of ultraweak emissions from different parts of the embryo. The intensity of emission from the animal part of early blastula exceeded those from the vegetal area and entire embryo. Separated fragments of the lateral ectoderm at the neurula stage had higher mean intensities of ultraweak emission than intact embryos at the same developmental stages. [ABSTRACT FROM AUTHOR]

In recent papers by Brackx, Delanghe and Sommen, some fundamental higher dimensional distributions have been reconsidered in the framework of Clifford analysis, eventually leading to the introduction of four broad classes of new distributions in Euclidean space. In the current paper we continue the in-depth study of these distributions, more specifically the study of their behaviour in frequency space, thus extending classical results of harmonic analysis. [ABSTRACT FROM AUTHOR]

We compared the characteristics of ultraweak emissions from groups of loach embryos of different ages in the presence or absence of optic interaction. The percentage of zero values of emission gradually increased during the first hour of optic interaction. The number and height of rare big pulses estimated by the value of kurtosis increased in parallel. In addition, the correlation between the Fourier spectra of optically interacting samples decreased at a higher rate than in the absence of optical contact. Just after the 1-hour optic interaction was terminated, the number of high pulses decreased in a younger interacting group and increased in the older one and the farther away the partner groups were in developmental stages, the more pronounced these differences were. Measurements of the Fourier spectra after long-term (12–22-hour) optic interactions have shown that an “exchange” of autocorrelation characteristics of the spectra took place among the samples: the sums of autocorrelation coefficients were inverted in the vast majority of cases, often with an “overshoot” or, at least, were smoothed over with reference to the control samples. We conclude that the previously described effects of optic interactions between groups of loach embryos of different ages could be due to changes in the frequency spectra of their ultraweak emissions. [ABSTRACT FROM AUTHOR]

Any reactions of the living systems are to a great extent context-dependent. Meanwhile, the biological essence of a “context” remains to be obscure. We suggest that it may be based upon an ensemble of molecular–supramolecular oscillators, which have different characteristic times. For testing this hypothesis, we applied the Fourier statistics to the time series of the records of an ultraweak photon emission (UWPE) registered from fish eggs and embryos and from cell cultures. We detected the regular changes of the UWPE Fourier spectra (FS) during embryonic development and physiological reactions of cell cultures. In many cases, such changes were going on in a holistic manner, i.e. involving broad spectral areas rather than single frequency maxims. FS of the earlier developmental stages showed greater instability and the presence of a short-range order only. On the contrary, at the advanced developmental stages a long-range order has emerged within the spectra. Another distinction of the highly organized biological samples (developing embryos, confluent fibroblasts cultures) from non-biological controls and “poorly organized” samples (non-fertilized eggs, non-confluent, poorly spread cell cultures) was the UWPE correlation dynamics which was more cooperative in highly organized samples. A non-invasive technique of UWPE registration may be useful for exploring a fluctuated oscillatory background of the developmental and physiological states of biological samples. [Copyright &y& Elsevier]

A time division multiplex (TDM)communication system for base band analog signals is described. The constant amplitude pulse width modulation scheme utilizes small pulse width deviations for short-haul optical, fiber applications. An enhanced signal-to-noise ratio (S / N) for low-frequency information (< 1000 Hz) may be secured by detecting a high-order Fourier signal component of the sampling frequency. [ABSTRACT FROM AUTHOR]