Search

For the linear wave and Schrödinger equations we show how observability can be deduced from the observability of solutions localized in frequency with a dyadic scale. [ABSTRACT FROM AUTHOR]

Optically transparent dual‐band frequency‐selective surfaces (FSSs) are promising candidates to address the specific design challenges of the Internet of Things. This paper demonstrates their potential by discussing different configurations of the two single‐layer FSS designs on an innovative optically transparent polyvinyl chloride surface material. First, FSS cells consist of two cross dipoles placed forming angles of ±45∘ $\pm 4{5}^{\circ }$, where each rotated dipole structure parallel to the other. Then, in the second design, each one of the two cells is mirrored to enable polarization control for each band. As a proof‐of‐concept, five prototypes of each design having a unit cell size of 0.43λ0×0.43λ0 $0.43{\lambda }_{0}\times 0.43{\lambda }_{0}$ are fabricated through a combination of cost‐effective printing and shearing. The manufactured prototypes yield more than 93% transparency and robust dual‐band performance. Moreover, more than 20 and 40 dB isolation for lower‐ and upper‐frequency bands are achieved from the fabricated prototypes. High‐transparency, cost‐effectiveness, and robust high performance in terms of suppression make both structures suitable for sub‐6‐GHz fifth generation applications. [ABSTRACT FROM AUTHOR]

Objectives. In recent years, there has been growing scientific interest in the creation of intelligent interfaces for computer control based on biometric data, such as electromyography signals (EMGs), which can be used to classify human hand gestures to form the basis for organizing an intuitive human-computer interface. However, problems arising when using EMG signals for this purpose include the presence of nonlinear noise in the signal and the significant influence of individual human characteristics. The aim of the present study is to investigate the possibility of using neural networks to filter individual components of the EMG signal.Methods. Mathematical signal processing techniques are used along with machine learning methods.Results. The overview of the literature on the topic of EMG signal processing is carried out. The concept of intelligent processing of biological signals is proposed. The signal filtering model using a convolutional neural network structure based on Python 3, TensorFlow and Keras technologies was developed. Results of an experiment carried out on an EMG data set to filter individual signal components are presented and discussed.Conclusions. The possibility of using artificial neural networks to identify and suppress individual human characteristics in biological signals is demonstrated. When training the network, the main emphasis was placed on individual features by testing the network on data received from subjects not involved in the learning process. The achieved average 5% reduction in individual noise will help to avoid retraining of the network when classifying EMG signals, as well as improving the accuracy of gesture classification for new users.

Abstract Background Physical activity (PA) during childhood is important for preventing future metabolic syndrome (MetS). To examine the relationship between PA and MetS in more detail, accurate measures of PA are needed. Previous studies have only utilized a small part of the information available from accelerometer measured PA. This study investigated the association between measured PA and MetS in children with a new method for data processing and analyses that enable more detailed interpretation of PA intensity level. Methods The association between PA pattern and risk factors related to MetS was investigated in a cross- sectional sample of children (n = 2592, mean age 10.9 years, 49.4% male) participating in the European multicenter I. Family study. The risk factors examined include body mass index, blood pressure, high-density lipoprotein cholesterol, insulin resistance and a combined risk factor score (MetS score). PA was measured by triaxial accelerometers and raw data was processed using the 10 Hz frequency extended method (FEM). The PA output was divided into an intensity spectrum and the association with MetS risk factors was analyzed by partial least squares regression. Results PA patterns differed between the European countries investigated, with Swedish children being most active and Italian children least active. Moderate intensity physical activity was associated with lower insulin resistance (R 2 = 2.8%), while vigorous intensity physical activity was associated with lower body mass index (R 2 = 3.6%), MetS score (R 2 = 3.1%) and higher high-density lipoprotein cholesterol (R 2 = 2.3%). PA of all intensities was associated with lower systolic- and diastolic blood pressure, although the associations were weaker than for the other risk factors (R 2 = 1.5% and R 2 = 1.4%). However, the multivariate analysis implies that the entire PA pattern must be considered. The main difference in PA was observed between normal weight and overweight children. Conclusions The present study suggests a greater importance of more PA corresponding to an intensity of at least brisk walking with inclusion of high-intense exercise, rather than a limited time spent sedentary, in the association to metabolic health in children. The methods of data processing and statistical analysis enabled accurate analysis and interpretation of the health benefits of high intensity PA that have not been shown previously.

In order to analyze the impact of multisource vibration on the imaging quality of aerospace optical payload during camera scanning, a dynamic imaging quality degradation model fused with satellite vibration filter templates is established. Firstly, according to the motion scanning process of the TDI camera, a filter template combining the amplitude and frequency of the vibration source is designed; Secondly, a piecewise function of satellite vibration with a frequency range of 1 Hz to 1000 Hz is obtained by curve fitting, and the amplitudes of different frequency ranges are brought into the image filter template to simulate the output image affected by the vibration. Finally, the output degraded image is analyzed through structural similarity and mean square error. The simulation results show that during the imaging process of the aerospace scanning mirror, the line frequency of the camera changes regularly with the scanning speed. When platform vibration frequency is similar to the camera’s exposure frequency, it will have a large impact on image quality. Therefore, when the camera’s exposure frequency is 110 Hz, vibration at a frequency of 110 Hz will further degrade the image quality. This article is expected to provide guidance for spatial vibration suppression and image quality degradation assessment in the imaging process of aerospace scanning mirrors.

Noise is always present in offshore seismic data, as there isn't a single method that could eliminate all the forms of noise. In this study, noise removal techniques were applied to attenuate different noises in 2D shallow-marine seismic data from the Baltic Sea area. Amplitude recovery should be applied before the noise attenuation stage as a preconditioning process for showing all noises in the deeper part of the seismic data. Frequency filters (notch filter and low-cut filter), frequency-wavenumber (FK) filter, and swell noise attenuation (Deswell) were applied as robust noise attenuation techniques. The method of directly modifying the amplitude spectrum of the seismic data is known as frequency filtering. A notch filter can be used to remove the harmonic noise of the power line harmonic noise (monofrequency noise). A low-cut filter can be used to remove the lowfrequency noises due to the influence of hydrostatic pressure variations. The linearly correlated events, such as tail-buoy and operational noise, were removed using the FK filter. Incoherent noise, such as swell noise, can be attenuated by swell noise attenuation (Deswell). The seismic results are displayed before and after the applied noise attenuation techniques to prove the validity of the applied filters. This study aimed to show the importance of shallow offshore seismic data processing in removing different types of noise, as it increases the value of data for seismic data interpretation and marine geohazard assessment. [ABSTRACT FROM AUTHOR]

Abstract A hybrid image allows multiple image interpretations to be modulated by the viewing distance. Originally, it can be constructed by combining the low and high spatial frequencies of two different images. The original hybrid image synthesis was limited to similar shapes of source images that were aligned in the edges, e.g., faces with a different expression, to produce an effective double image interpretation. In our previous work, we proposed a noise-inserted method for synthesizing a hybrid image from dissimilar shape images or unaligned images. In this work, we propose a novel method for adding an image to be seen from a middle viewing distance. The middle-frequency (MF) image is extracted by a special bandpass filter, which generates ringing while extracting only specified frequency bands. With this method, the middle frequency should be perceived as a meaningless pattern when viewed from a far distance and close up. A parameter tuning experiment was performed to determine the suitable cutoff frequencies for designing the filter for the MF image. We found that ringings of a suitable size could be used to make the middle frequency less noticeable when seen from far away.

Background: Physical activity (PA) during childhood is important for preventing future metabolic syndrome (MetS). To examine the relationship between PA and MetS in more detail, accurate measures of PA are needed. Previous studies have only utilized a small part of the information available from accelerometer measured PA. This study investigated the association between measured PA and MetS in children with a new method for data processing and analyses that enable more detailed interpretation of PA intensity level. Methods: The association between PA pattern and risk factors related to MetS was investigated in a cross- sectional sample of children (n = 2592, mean age 10.9 years, 49.4% male) participating in the European multicenter I. Family study. The risk factors examined include body mass index, blood pressure, high-density lipoprotein cholesterol, insulin resistance and a combined risk factor score (MetS score). PA was measured by triaxial accelerometers and raw data was processed using the 10 Hz frequency extended method (FEM). The PA output was divided into an intensity spectrum and the association with MetS risk factors was analyzed by partial least squares regression. Results: PA patterns differed between the European countries investigated, with Swedish children being most active and Italian children least active. Moderate intensity physical activity was associated with lower insulin resistance (R2 = 2.8%), while vigorous intensity physical activity was associated with lower body mass index (R2 = 3.6%), MetS score (R2 = 3.1%) and higher high-density lipoprotein cholesterol (R2 = 2.3%). PA of all intensities was associated with lower systolic- and diastolic blood pressure, although the associations were weaker than for the other risk factors (R2 = 1.5% and R2 = 1.4%). However, the multivariate analysis implies that the entire PA pattern must be considered. The main difference in PA was observed between normal weight and overweight children. Conclusions: The present study suggests a greater importance of more PA corresponding to an intensity of at least brisk walking with inclusion of high-intense exercise, rather than a limited time spent sedentary, in the association to metabolic health in children. The methods of data processing and statistical analysis enabled accurate analysis and interpretation of the health benefits of high intensity PA that have not been shown previously. [ABSTRACT FROM AUTHOR]

Magnonics rely on the wave nature of the magnetic excitations to process information, an approach that is common to many fields such as photonics, phononics, and plasmonics. Nevertheless, magnons, the quanta of spin-wave excitations, have the unique advantage to be at frequencies that are lying between a few GHz to tens of GHz, that is, in the technologically relevant radio-frequency bands for 4G and 5G telecommunications. Furthermore, their typical wavelengths are compatible with on-chip integration. Here, we demonstrate radio-frequency signal filtering by a micron-scale magnonic crystal (MC) based on a nanopatterned 20 nm-thick film of yttrium iron garnet with a minimum feature size of 100 nm where the Bragg vector is set to be kB = 2.1 μm–1. We map the intensity and the phase of spin waves (SWs) propagating in the periodic magnetic structure using phase-resolved microfocus Brillouin light-scattering spectroscopy. Based on these maps, we obtain the SW dispersion and the attenuation characteristics. Efficient filtering is obtained with a frequency selectivity of 20 MHz at an operating frequency of 4.9 GHz. The results are analyzed by performing time- and frequency-resolved full-scale micromagnetic simulations of the MC that reproduce quantitatively the complexity of the harmonic response across the magnonic band gap and allow the identification of the relevant SW-quantized modes, thereby providing an in-depth insight into the physics of SW propagation in periodically modulated nanoscale structures. [ABSTRACT FROM AUTHOR]

Ground roll is a common coherent noise in land seismic acquisition, which is usually characterized by high amplitudes, low frequencies, and low propagation velocities. Removing ground roll is a key procedure in seismic data processing. In this letter, we develop a novel ground roll suppression approach termed f-x variational mode decomposition (VMD), which has the characteristic of a frequency-dependent, high-wavenumber filter. This new algorithm first applies VMD on constant frequency slices in the frequency-offset domain within the frequency range of ground roll in order to extract the ground roll, and then the denoised data can be obtained by subtracting them adaptively from the original data. A synthetic example is given to demonstrate that the proposed method is able to suppress ground roll well and preserve seismic reflections effectively compared with other conventional techniques such as frequency filtering and f-k filtering. Application of the method on field data further demonstrates the potential of the f-x VMD algorithm in industrial applications. [ABSTRACT FROM AUTHOR]

A hybrid image allows multiple image interpretations to be modulated by the viewing distance. Originally, it can be constructed by combining the low and high spatial frequencies of two different images. The original hybrid image synthesis was limited to similar shapes of source images that were aligned in the edges, e.g., faces with a different expression, to produce an effective double image interpretation. In our previous work, we proposed a noise-inserted method for synthesizing a hybrid image from dissimilar shape images or unaligned images. In this work, we propose a novel method for adding an image to be seen from a middle viewing distance. The middle-frequency (MF) image is extracted by a special bandpass filter, which generates ringing while extracting only specified frequency bands. With this method, the middle frequency should be perceived as a meaningless pattern when viewed from a far distance and close up. A parameter tuning experiment was performed to determine the suitable cutoff frequencies for designing the filter for the MF image. We found that ringings of a suitable size could be used to make the middle frequency less noticeable when seen from far away. [ABSTRACT FROM AUTHOR]

Machine learning applied to computer vision and signal processing is achieving results comparable to the human brain due to the great improvements brought by deep neural networks (DNN). The majority of state-of-the-art architectures are DNN-related, but only a few explicitly explore the frequency domain to extract useful information and improve the results. This paper presents a new approach for exploring the Fourier transform of the input images, which is composed of trainable frequency filters that boost discriminative components in the spectrum. Additionally, we propose a cropping procedure to allow the network to learn both global and local spectral features of the image blocks. The proposed method proved to be competitive concerning well-known DNN architectures in the selected experiments, which involved texture classification, cataract detection, and retina image analysis, where there is a noticeable appeal for the frequency domain, with the advantage of being a lightweight model. • A new architecture for neural networks exploring the frequency domain is proposed. • Trainable frequency filters retrieve image discriminative features. • A block division scheme allows extracting local and global spectral features. • A frequency pooling technique reduces the model parameters and training time. • The proposed model reaches competitive results when compared to modern ConvNets. [ABSTRACT FROM AUTHOR]

• A design of all silicon dielectric metamaterial (SDM) is presented. • Shifting ranges of resonances are 0.36 THz in TE mode and 0.27 THz in TM mode. • There are two linear trends for the polarization switching function at 1.60 THz and 2.10 THz. • Correction coefficients are 0.99608 and 0.99726 for the resonance at 1.60 THz and 2.10 THz, respectively. • Modulation depths are 74 % and 74.5 % for the resonance at 1.60 THz and 2.10 THz, respectively. All silicon dielectric metamaterial (SDM) composed of two outer symmetric semi-circular rings and two inner symmetric split-ring resonators (SRRs) is presented. The electromagnetic responses of SDM device with different structure heights in transverse electrical (TE) and transverse magnetic (TM) modes are studied by numerical simulations and experiments. By increasing structure height of SDM device, the resonances of the SDM devices exhibit red-shift and the resonant intensities become stronger. The shifting ranges of resonances are 0.36 THz in TE mode and 0.27 THz in TM mode. Furthermore, the SDM device with structure height of 100 μm demonstrates great resonant intensity, and two extra resonances are generated at 1.60 THz and 2.26 THz in TM mode. By further investigating the polarization characteristics of SDM device with structure height of 100 μm, there are two linear trends for the polarization switching function at 1.60 THz and 2.10 THz. The corresponding correction coefficients are 0.99608 and 0.99726 and the modulation depths are 74 % and 74.5 % for the resonance at 1.60 THz and 2.10 THz, respectively. This SDM design paves the way to the strategy of the development of frequency filtering, polarization switching, and resonance modulation characteristics in the THz-wave applications. All-dielectric THz metamaterial composed of two outer symmetric semi-circular rings and two inner symmetric split-ring resonators with highly linear polarization switching characteristic [Display omitted] [ABSTRACT FROM AUTHOR]

In this paper an algorithm is proposed for determining the source of excitation of electromagnetic waves emitted by the Ground - penetrating radar (GPR) device as a function of time. A mathematical model for solving this problem was constructed and tested on model data. We have built an algorithm for constructing a source function based on real georadar data. For this purpose, the results of experimental studies conducted in field conditions using the Loza-V GPR. Experiments were carried out in the medium: air - sand. The received signal of the response of the medium was processed from interference and noise. For this purpose, we use frequency filtering, signal averaging, amplitude correction for processing radarograms. In the future, the obtained table form of the disturbance signal will be used by us to study inhomogeneous media, including the study of localized objects. The series of calculations for the considered problems are given.

This review re‐examines the use of accelerometer and oxygen uptake data for the assessment of activity intensity. Accelerometers capture mechanical work, while oxygen uptake captures the energy cost of this work. Frequency filtering needs to be considered when processing acceleration data. A too restrictive filter attenuates the acceleration signal for walking and, to a higher degree, for running. This measurement error affects shorter (children) more than taller (adults) individuals due to their higher movement frequency. Less restrictive filtering includes more movement‐related signals and provides measures that better capture mechanical work, but may include more noise. An optimal filter cut‐point is determined where most relevant acceleration signals are included. Further, accelerometer placement affects what part of mechanical work being captured. While the waist placement captures total mechanical work and therefore contributes to measures of activity intensity equivalent by age and stature, the thigh and wrist placements capture more internal work and do not provide equivalent measures. Value calibration of accelerometer measures is usually performed using measured oxygen uptake with the metabolic equivalent of task (MET) as reference measure of activity intensity. However, the use of MET is not stringent and is not a measure of activity intensity equivalent by age and stature. A candidate measure is the mass‐specific net oxygen uptake, VO2net (VO2tot − VO2stand). To improve measurement of physical activity intensity using accelerometers, research developments are suggested concerning the processing of accelerometer data, use of energy expenditure as reference for activity intensity, and calibration procedure with absolute versus relative intensity. [ABSTRACT FROM AUTHOR]

We discuss the possibility that the contours or details of images can be obtained by using the low-spatial-frequency or high-spatial-frequency parts of the reference beam in ghost imaging. The influence of the threshold selection which is used to divide the reference pattern into low-frequency and high-frequency parts is quite different. With the increase of the threshold, the signal-to-noise ratio (SNR) of low-frequency ghost imaging increases firstly and then decreases, while SNR of high-frequency ghost imaging decreases gradually. Under a suitable threshold, the results are compared with those by directly filtering ghost-image from the traditional ghost imaging. It is shown that better imaging quality can be obtained by using our scheme. To further improve imaging quality, the method of subtracting background before correlation calculation is also presented. [ABSTRACT FROM AUTHOR]

To study the effect of the passband of a digital filter on the nature of the attenuation of the amplitude of an acoustic emission (AE) pulse and on the change in the group velocity of a wave packet in the near zone of up to 300 mm from the radiation source, studies were conducted on a multilayered polymer-composite-material (PCM) panel and an AMG-2 aluminum alloy plate with a thickness of 6 mm. In the course of the experiments, it has been established that narrowing the passband of the digital filter from 30–500 to 100–200 kHz can significantly affect the accuracy of the coordinate location of AE-event radiation sources situated near AE transducers, at a distance of less than 100 mm. As the passband of the digital filter narrows and the low- and high-frequency components of the spectrum are cut off, the wave front of the recorded pulse becomes more gently sloping, resulting in an increase in the difference of arrival times (DAT) of pulses to the AE transducers and in a decrease in the calculated group velocity of the wave packet. The error arising in this case is greater than the passband of the filter applied. [ABSTRACT FROM AUTHOR]

An improved method of physical activity accelerometer data processing, involving a wider frequency filter than the most commonly used ActiGraph filter, has been shown to better capture variations in physical activity intensity in a lab setting. The aim of the study was to investigate how this improved measure of physical activity affected the relationship with markers of cardiometabolic health. Accelerometer data and markers of cardiometabolic health from 725 adults from two samples, LIV 2013 and SCAPIS pilot, were analyzed. The accelerometer data was processed using both the original ActiGraph method with a low-pass cut-off at 1.6 Hz and the improved method with a low-pass cut-off at 10 Hz. The relationship between the physical activity intensity spectrum and a cardiometabolic health composite score was investigated using partial least squares regression. The strongest association between physical activity and cardiometabolic health was shifted towards higher intensities with the 10 Hz output compared to the ActiGraph method. In addition, the total explained variance was higher with the improved method. The 10 Hz output enables correctly measuring and interpreting high intensity physical activity and shows that physical activity at this intensity is stronger related to cardiometabolic health compared to the most commonly used ActiGraph method.

We review our recent progress on the realisation of pulse shaping in passively-mode-locked fibre lasers by inclusion of an amplitude and/or phase spectral filter into the laser cavity. We numerically show that depending on the amplitude transfer function of the in-cavity filter, various regimes of advanced waveform generation can be achieved, including ones featuring parabolic-, flat-top- and triangular-profiled pulses. An application of this approach using a flat-top spectral filter is shown to achieve the direct generation of high-quality sinc-shaped optical Nyquist pulses with a widely tunable bandwidth from the laser oscillator. We also present the operation of an ultrafast fibre laser in which conventional soliton, dispersion-managed soliton (stretched-pulse) and dissipative soliton mode-locking regimes can be selectively and reliably targeted by adaptively changing the dispersion profile and bandwidth programmed on an in-cavity programmable filter. The results demonstrate the strong potential of an in-cavity spectral pulse shaper for achieving a high degree of control over the dynamics and output of mode-locked fibre lasers.

Abstract We report a 1 × N hybrid radio frequency (RF) photonic splitter with arbitrary phase shift and amplitude ratio using a dual-polarization dual-parallel Mach Zehnder modulator (DP-DPMZM). The DP-DPMZM is properly set to generate an orthogonally polarized single-sideband (SSB) modulated optical signal. By controlling a polarization controller (PC) and a polarizer (Pol.) that cascaded behind the modulator, an RF photonic splitter with arbitrary phase and amplitude ratio can be realized. Compared with previous reported works, the proposed RF splitter can be operated in a wide bandwidth since no optical or electrical filters are involved. The proposed scheme is theoretically analyzed and experimentally verified. [ABSTRACT FROM AUTHOR]

A new type of optical in-line holographic three-dimensional (3-D) video display system with omnidirectional viewing zones by using a center-symmetric multi-sideband filtering method is proposed. The frequency spectrum of the complex hologram is center-symmetrically divided into even numbers of multi-sidebands and partitioned into two groups by being alternately selected along the angular direction. One group corresponding to the conjugate image is filtered out in both of the digital-recording and optical-reconstruction processes with their specific filter masks. Then, from the other group, the real image, which can be viewed from almost all directions with a set of angularly-subdivided viewing zones, is reconstructed on the optical 4- f lens system without a conjugate image. Fourier-optical analysis and experiments with 3-D objects in motion confirm the feasibility of the proposed system. [ABSTRACT FROM AUTHOR]

High and low CO2 partial pressure (Pco2) levels can induce consequences to the internal system of a karstic cave. This then can further affect the state of the cave. Subsequently, speleothem growths and the walls with prehistorical paintings and engravings will be affected with either calcite dissolution or precipitation. Thus, pinpointing the major components of Pco2 is found indispensable. In this paper, a method is proposed in order to (1) identify the major components of the Pco2 and (2) quantify each specific contribution to the Pco2. Pco2, air temperature, air pressure, and water flow were measured from 2008 to 2010 in Lascaux Cave (Southwest of France). Pco2 varied from 0.62% (6200 ppm) in summer to 0.04% (400 ppm) in winter. We identified three major components: (1) seasonal: component A; (2) low frequency: component B; and (3) high frequency: component C. The method is applied to estimate the contribution of each component. Component A was modelled with a sinusoid curve fitted to the Pco2 measures. This component was subtracted from the measured Pco2. Then, from the remaining value of Pco2, Fourier transform, frequency filtering, and inverse Fourier transform were applied to separate high- and low-frequency components. As a result, the seasonal component A contributes 77% of the measured Pco2, while components B and C supply 13 and 11%, respectively. The three identified components have links with environmental parameters such as temperature, water flow, and atmospheric pressure. Hypotheses were proposed to describe these links. Knowledge on these aspects can help in cave management and protection specifically in answering the question: which parameter should be given more attention.Separation and quantification of the major components of CO2 signal in Lascaux Cave [ABSTRACT FROM AUTHOR]

We have experimentally demonstrated a world record of transmitting 60-GHz radio frequency signals over 200-km standard single-mode fiber (SSMF) through a novel end-to-end fiber-wireless integration and transport scheme using a low-cost directly modulated laser without requiring expensive optical dispersion compensation component and an external modulator. We designed a special dual-stage single-sideband (SSB) modulation and power-detection scheme to overcome the power fading caused by severe chromatic dispersion. The SSB signals are generated by the operations in both optical and electrical domains to avoid any possible beating between the two sidebands. In the experiment, QPSK wireless signals at 14 Gb/s are successfully transmitted through a 200-km SSMF and 1-m 60-GHz wireless channel with a bit error rate less than $3.8\times 10^{-3}$. The proposed dual-stage SSB modulation and power-detection scheme are free of expensive devices, such as microwave sources, dispersion compensation components, narrow-linewidth laser sources, or external optical modulators. [ABSTRACT FROM AUTHOR]

n order to realize the application of active surface filtering technology in an optical window, an optically controlled active surface filtering technology is proposed. Photoelectrically conductive thin-film photovoltaic effect is used to control the dimensional change of the metal frequency-selective surface (FSS), thereby achieving active control of surface filtering. Starting from the theory, the principle of active surface filtering technology is described. CST software is used to simulate the FSS characteristics of two types of metal FSSs, “cross” bandpass type and “Jerusalem” band-stop type, under light irradiation conditions. The results show that the filter center frequency is changed from 23 and 13 GHz to 27.6 and 9.8 GHz, respectively, with the change of the structure size. In this experiment, the cross bandpass type and Jerusalem band-stop type optically controlled active FSS are, respectively, fabricated by coating, etching, and electron beam evaporation techniques. With annealing temperature of 750°C and the annealing time of 300 s, it gets the best optoelectronic performance. The experimental results are that the sensitive wavelength of photoconductive thin film is 0.6  μm and the optimal illumination power is 150  mW  /  cm2. The sample filter center frequency is changed from 23.8 and 13.5 GHz to 28 and 10.5 GHz, respectively, which is basically consistent with the simulation results. This paper concludes that the use of light control can realize active control of surface filtering [ABSTRACT FROM AUTHOR]

To stably operate the power grid under a mass introduction of photovoltaic systems, a method to estimate the areal photovoltaic power in real time is necessary. The estimation method proposed in this paper achieves high accuracy by separately estimating the high- and low-frequency components of photovoltaic power. The high-frequency component is estimated using power flow at the distribution substation, whereas the low-frequency component is estimated using solar irradiance, ambient temperature, power flow, and if available 30-min integrated values of the electric load measured by smart meters. To evaluate the proposed method, simulations using measured data were performed. These were performed under four scenarios depending on the acceptance of a 15-min delay and the availability of smart meter data. In the best-case scenario, where 15-min delays to estimate the areal photovoltaic power is accepted and smart meter data are available, the estimation was performed with yearly root-mean-square error of approximately 2.2% of the total system capacity. Even in the worst-case scenario, where 15-min delays were unaccepted and smart meters not installed, the estimation was performed with yearly root-mean-square error of approximately 3.7% of the system capacity. [ABSTRACT FROM PUBLISHER]

Copyright of Hydrographic Surveying & Charting / Haiyang Cehui is the property of Hydrographic Surveying & Charting Editorial Board and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Current learning-based dehazing methods simply rely on the paired synthetic datasets and physical models, which can hardly describe the complicated degradation for practical applications. These methods still struggle to achieve haze removal, color distortion, and detail restoration instantly, and they ignore the frequency characteristic differences and prior knowledge importance. To address these problems, we propose an unpaired stage-wise framework integrating frequency-guided filtering and progressive physics learning in an adversarial dehazing network, called FPD-Net. To be specific, a guided filter based on frequency information is employed to decompose the high and low frequency components for better feature extraction. We further merge the prior and physical knowledge to form progressive physics learning, which produces pleasing haze-free outputs with high visibility and reality. For better atmospheric light estimation, the variational auto-encoder and Kullback–Leibler loss are included to represent the illumination message. Extensive experiments on both synthetic and real datasets prove that our designed FPD-Net achieves better performance visually and quantitatively than the comparison dehazing models. [ABSTRACT FROM AUTHOR]

We propose and numerically demonstrate a novel simple method to produce optical Nyquist pulses based on pulse shaping in a passively mode-locked fiber laser with an in-cavity flat-top spectral filter. The proposed scheme takes advantage of the nonlinear in-cavity dynamics of the laser and offers the possibility to generate high-quality sinc-shaped pulses with widely tunable bandwidth directly from the laser oscillator. We also show that the use of a filter with a corrective convex profile relaxes the need for large nonlinear phase accumulation in the cavity by offsetting the concavity of the nonlinearly broadened pulse spectrum.

A widely tunable single-passband microwave photonic filter (MPF) based on a distributed-feedback semiconductor optical amplifier (DFB-SOA) is proposed and experimentally demonstrated in this paper. The fundamental principle is to recover the suppressed optical carrier from a passband optical filter by the wavelength-selective amplification via a DFB-SOA. A microwave signal is then generated by beating the recovered optical carrier with the phase-modulated lower sideband, and thus, an MPF is achieved with the shape of the passband optical filter that is mapped from the optical domain to the electrical domain. By tuning the central wavelength of the passband optical filter, a single-passband MPF with a frequency tuning range from 5 to 35 GHz is obtained. The 3-dB bandwidth and the out-of-band suppression ratio are measured to be 4 GHz and 20 dB, respectively. In addition, the tunability of the MPF that is dependent on the driven current of the DFB-SOA is also experimentally investigated.

Summary Several cell types experience repetitive mechanical stimuli, including vein endothelial cells during pulsating blood flow, inner ear hair cells upon sound exposure, and skin cells and their innervating dorsal root ganglion (DRG) neurons when sweeping across a textured surface or touching a vibrating object. While mechanosensitive Piezo ion channels have been clearly implicated in sensing static touch, their roles in transducing repetitive stimulations are less clear. Here, we perform electrophysiological recordings of heterologously expressed mouse Piezo1 and Piezo2 responding to repetitive mechanical stimulations. We find that both channels function as pronounced frequency filters whose transduction efficiencies vary with stimulus frequency, waveform, and duration. We then use numerical simulations and human disease-related point mutations to demonstrate that channel inactivation is the molecular mechanism underlying frequency filtering and further show that frequency filtering is conserved in rapidly adapting mouse DRG neurons. Our results give insight into the potential contributions of Piezos in transducing repetitive mechanical stimuli. [ABSTRACT FROM AUTHOR]

Based on zero-padding and frequency-domain self-filtering, a robust and effective spectrum centroid carrier-removal method for carrier interferogram analysis is proposed. The interferogram is first spatial zero padded to increase the frequency resolution, and then the frequency domain self-filtering is carried out to suppress the noise and enhance the carrier component. Finally, the carrier frequencies are estimated by calculating the spectral centroid of the upside lobe. The simulations and experiments are carried out to testify the feasibility of this method. In addition, some factors, such as the carrier frequency values, the level of random noise, and the window size of the spectral filter, are analyzed and discussed. Compared with existing carrier-removal methods, the proposed method is effective and accurate for suppressing the carrier-removal error [ABSTRACT FROM AUTHOR]

Low-frequency information is crucial for recovering background velocity, but the lack of low-frequency information in field data makes inversion impractical without accurate initial models. Laplace-Fourier domain waveform inversion can recover a smooth model from real data without low-frequency information, which can be used for subsequent inversion as an ideal starting model. In general, it also starts with low frequencies and includes higher frequencies at later inversion stages, while the difference is that its ultralow frequency information comes from the Laplace-Fourier domain. Meanwhile, a direct implementation of the Laplace-transformed wavefield using frequency domain inversion is also very convenient. However, because broad frequency bands are often used in the pure time domain waveform inversion, it is difficult to extract the wavefields dominated by low frequencies in this case. In this paper, low-frequency components are constructed by introducing time attenuation into the recorded residuals, and the rest of the method is identical to the traditional time domain inversion. Time windowing and frequency filtering are also applied to mitigate the ambiguity of the inverse problem. Therefore, we can start at low frequencies and to move to higher frequencies. The experiment shows that the proposed method can achieve a good inversion result in the presence of a linear initial model and records without low-frequency information. [ABSTRACT FROM AUTHOR]

A novel ultra-narrow dual-passband microwave photonic filter (MPF) with wide tunability based on stimulated Brillouin scattering (SBS) is presented. The proposed dual-passband MPF is implemented via the usage of carrier suppressed modulation of an electrooptic modulator (EOM). The passband separation of the dual-passband filter is determined by the oscillation radio frequency (RF) that is applied onto the EOM, where the frequency change of the RF oscillator results in two times the bandpass frequency shift with a central frequency that is symmetric with respect to the SBS frequency shift. A complete theoretical model based on the combined effects of the Brillouin gain and loss in a dual-wavelength Brillouin pump structure is presented to characterize the filter RF responses. Experimental results show a widely tunable dual-passband MPF that has an ultra-narrow bandwidth of 20.1MHz with over 35 dB out-of-band rejection ratio and a 20–3-dB bandwidth shape factor of 2.5. [ABSTRACT FROM PUBLISHER]

Bessel illumination is an established method in optical imaging and manipulation to achieve an extended depth of field without compromising the lateral resolution. When broadband or multicolour imaging is required, wavelength-dependent changes in the radial profile of the Bessel illumination can complicate further image processing and analysis. We present a solution for engineering a multicolour Bessel beam that is easy to implement and promises to be particularly useful for broadband imaging applications. A phase-only spatial light modulator (SLM) in the image plane and an iterative Fourier Transformation algorithm (IFTA) are used to create an annular light distribution in the back focal plane of a lens. The 2D Fourier transformation of such a light ring yields a Bessel beam with a constant radial profile for different wavelength. [ABSTRACT FROM AUTHOR]

All-fiber filters with multiple narrow, flat-top channels are designed and fabricated, by incorporating both the phase sampling technique and multiple π phase shifts into a fiber Bragg gratings. The phase sampling yields multiple reflection bands with high uniformity, while the combination of multiple phase shifts allows a narrow, flat-top transmission channel in each reflection band identically, leading to multiple narrow, flattop channels. Such filters with nine channels are then fabricated and characterized with excellent comprehensive specifications, including a 3-dB bandwidth less than 800 MHz, a rectangular shape factor close to 2.5, an insertion loss less than 1 dB, and an out-of-band rejection greater than 25 dB. [ABSTRACT FROM AUTHOR]

Filtering of non-stationary noisy seismic signals using the fixed basis functions (sine and cosine) generates artifacts in the final output and thereby leads to wrong interpretation. In order to circumvent the problem, we propose here, a new Weighted Eigen Spectrogram (WES) based robust time domain Singular Spectrum Analysis (SSA) frequency filtering algorithm. The new WES is used to simplify the Eigen triplet grouping procedure in SSA. We tested the robustness of the algorithm on synthetic seismic data assorted with field-simulated noise. Then we applied the method to filter the high-resolution seismic reflection field data. The band pass filtering of noisy seismic records suggests that the underlying algorithm is efficient for improving the signal to noise ratio (S/N) and also it is user-friendly. [ABSTRACT FROM AUTHOR]

In this work, a low-pass plasmonic filter based on spoof surface plasmon polaritons (SSPPs) is reported by etching the two grounds of coplanar waveguide with periodic grooves. The cutoff frequency of the filter coincides with the asymptotic frequency of the SSPPs that are supported by the periodic grooves, which can be tuned by the depth of the grooves at will. In addition, a T-shaped groove is designed to increase the equivalent depth of the groove so as to realize the miniaturization of the proposed filter by decreasing the equivalent cutoff frequency of the SSPPs. Measured S-parameters of the two proposed low-pass plasmonic filters agree well with the simulated ones, which validates our ideas and designs. This simple low-pass plasmonic filter can find potential applications in plasmonic circuits and systems. [ABSTRACT FROM AUTHOR]

SUMMARY Time-resolved reflection measurement using broadband, short terahertz pulses can provide cross-sectional images of dielectric materials at different depths. Low-frequency components which have responses over a wide time range may result in inclusion of spurious signals which arise from strong reflections at other depths. Model calculations showed that such spurious signals can be suppressed by application of a frequency filter of an appropriate center frequency. The effect of frequency filtering was investigated in cross-sectional imaging of an IC card. Cross-sectional images were obtained at depth intervals of 0.18 mm, which provided images at five different depth intervals. As a result of frequency filtering, spurious signals resulting from strong reflections at different depths could be reduced in intensity, which resulted in improvement of the measurement resolution of the depth distribution. [ABSTRACT FROM AUTHOR]

We present a tapped tunable delay line filter for radiofrequency (RF) photonic filtering applications, capable of rapid tunability over a wide RF bandwidth limited only by the optical components’ losses, while maintaining independence from polarization state. Multiple fiber taps with contrasting dispersion slopes are used in intensity-modulated direct detection microwave photonic links. A temporal delay is generated between the signals within each arm of the link. Once a signal is received using balanced differential detection, nulls are generated as a function of the laser's operating wavelength. Tuning of the laser allows for a rapid shifting of the nulls in the RF spectrum to dynamically mitigate co-site interference. Through this method we demonstrate the potential for rapid tunability over the RF spectrum by the variation of the operating wavelength of the optical carrier. [ABSTRACT FROM PUBLISHER]

We review our recent progress on the realisation of pulse shaping in passively-mode-locked fibre lasers by inclusion of an amplitude and/or phase spectral filter into the laser cavity. We numerically show that depending on the amplitude transfer function of the in-cavity filter, various regimes of advanced waveform generation can be achieved, including ones featuring parabolic-, flat-top- and triangular-profiled pulses. An application of this approach using a flat-top spectral filter is shown to achieve the direct generation of high-quality sinc-shaped optical Nyquist pulses with a widely tunable bandwidth from the laser oscillator. We also present the operation of an ultrafast fibre laser in which conventional soliton, dispersion-managed soliton (stretched-pulse) and dissipative soliton mode-locking regimes can be selectively and reliably targeted by adaptively changing the dispersion profile and bandwidth programmed on an in-cavity programmable filter. The results demonstrate the strong potential of an in-cavity spectral pulse shaper for achieving a high degree of control over the dynamics and output of mode-locked fibre lasers. [ABSTRACT FROM AUTHOR]

Long-term synaptic depression (LTD) in cortico-striatal circuits is initiated by depolarization of striatal medium spiny neurons through a convergent cortical glutamatergic input. This produces retrograde endocannabinoid signaling to presynaptic cortical terminals and eventually results in long term (>30 min) decreases in glutamate release. These same circuits can also undergo short-term depression (STD) through a less well-defined process in which the magnitude of postsynaptic responses returns to baseline levels within 10 min. Additionally, the cortico-striatal circuit shows characteristics of a GABA A receptor-dependent low-pass filter, which results in significant attenuation of high frequency cortical inputs. The majority of in vitro studies of LTD have used a 100-Hz induction paradigm and it is unclear whether other frequencies, which may also have physiological relevance, have equivalent ability to induce this form of plasticity. Here we have investigated the effectiveness of a range of induction paradigms in producing LTD in cortico-striatal circuits, and demonstrate that some lower frequency paradigms, with perhaps more physiological relevance, are more effective at inducing LTD. We also show that GABA A receptor-dependent frequency filtering in this circuit is altered following the induction of LTD and STD suggesting an important role for synaptic depression in signal processing in these circuits. [ABSTRACT FROM AUTHOR]

A new technique is presented to reconfigure the dispersion-induced RF fading in a spectrum-sliced microwave photonic filter to an arbitrary spectral shape, including the flat-top response with rectangular shape and operating frequencies beyond conventional baseband. The technique is based on the Fourier transform of the modified optical source power spectrum, which is realized by applying a designed optical amplitude and phase manipulation using a diffraction-based spectral pulse shaper to the ports of a dual-output Mach–Zehnder electro-optic modulator in combination with a broadband light source. This scheme is fundamentally different from earlier finite-impulse-response-based spectrum-sliced microwave-photonic filters that require specific slicing elements for optical taps, but offers the same flexibility in realizing various filter passband characteristics with the added benefit of widely shape-invariant tuning and a single passband response. Experimental results verify the technique and demonstrate a continuously tunable dispersion-induced RF fading up to 20 GHz, exhibiting shape invariance and a flat-top response. [ABSTRACT FROM PUBLISHER]

The features of the processing of an electrocardiograph signal using band-pass frequency filtering on a background of distorting interference and noise of different kinds are analyzed. An approach to choosing the optimum passband and type of bandpass filter is proposed, based on the criterion of maximizing the signal-to-noise ratio at the filter output and minimizing the signal distortions, taking into account the variability of the heart rhythm. Two versions of such a bandpass filter are considered, namely, an analog active 2nd order filter and a digital 8th order filter. [ABSTRACT FROM AUTHOR]

A quadratic polar coordinate transform technique is proposed to improve the demodulation accuracy of the circular carrier interferogram. Through the quadratic coordinate transform, the circular carrier interferogram is converted to the linear carrier interferogram with uniform spatial frequency, whose signal spectrum is significantly separated from the unwanted ones. Thus, the phase under test can be accurately retrieved by the conventional Fourier transform technique. Both the simulant and experimental results demonstrate that the proposed technique can be used for precise demodulation of the phase distribution of a circular carrier interferogram. [ABSTRACT FROM AUTHOR]