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Aim: Timbre in piano performance plays a critical role in enhancing musical expression. However, timbre control in current piano performance education relies mostly on descriptive characterization, which involves large variations of interpretation. The current study aimed to mitigate the limitations by identifying quantitative indices with adequate precision to characterize piano timbre. Methods: A total of 24 sounds of G6 were recorded from 3 grand pianos, by 2 performers, and with 4 repetitions. The sounds were processed and analyzed with audio software for the frequencies and volumes of harmonic series in the spectrum curves. Ten quantitative timbre indices were calculated. Precision validation with statistical gage R&R analysis was conducted to gage the repeatability (between repetitions) and reproducibility (between performers) of the indices. The resultant percentage study variation (%SV) of an index must be ≤10% to be considered acceptable for characterizing piano timbre with enough precision. Results: Out of the 10 indices, 4 indices had acceptable precision in characterizing piano timbre with %SV ≤10%, including the square sum of relative volume (4.40%), the frequency-weighted arithmetic mean of relative volume (4.29%), the sum of relative volume (3.11%), and the frequency-weighted sum of relative volume (2.09%). The novel indices identified in the current research will provide valuable tools to advance the measurement and communication of timbre and advance music performance education. [ABSTRACT FROM AUTHOR]

Few-shot learning, especially few-shot image classification (FSIC), endeavors to recognize new categories using only a handful of labeled images by transferring knowledge from a model trained on base categories. Despite numerous efforts to address the challenge of deficient transferability caused by the distribution shift between the base and new classes, the fundamental principles remain a subject of debate. In this paper, we elucidate why a decline in performance occurs and what information is transferred during the testing phase, examining it from a frequency spectrum perspective. Specifically, we adopt causality on the frequency space for FSIC. With our causal assumption, non-causal frequencies (e.g., background knowledge) act as confounders between causal frequencies (e.g., object information) and predictions. Our experimental results reveal that different frequency components represent distinct semantics, and non-causal frequencies adversely affect transferability, resulting in suboptimal performance. Subsequently, we suggest a straightforward but potent approach, namely the Frequency Spectrum Mask (FRSM), to weight the frequency and mitigate the impact of non-causal frequencies. Extensive experiments demonstrate that the proposed FRSM method significantly enhanced the transferability of the FSIC model across nine testing datasets. [ABSTRACT FROM AUTHOR]

High Impedance Fault (HIF) detection in distribution networks is challenging for protection engineers, mainly because HIFs possess unique characteristics, including non-linearity, asymmetry, randomness, and relatively low fault current levels compared to the feeder load current. In this regard, the study proposes an approach to detect HIFs in a radial distribution feeder based on the spectrum analysis of current signals at the substation bus. The proposed method comprises two stages: signal decomposition and feature extraction. Fast Fourier Transform (FFT) is utilized for signal decomposition, followed by feature extraction. These features are subsequently used as input to an artificial neural network (ANN) to distinguish HIF from non-HIF events, such as linear and non-linear load switching, capacitor bank switching, and transformer energization. The proposed method's efficacy is rigorously evaluated under various dynamic conditions, demonstrating that the method can detect and differentiate HIFs from non-fault events with a high detection rate and high accuracy of 99.3%, irrespective of the HIF location and fault resistance. [ABSTRACT FROM AUTHOR]

The increasing demand for high-speed machine tools has elicited the widespread adoption of specially designed spindles that incorporate built-in motors and ball bearings. To ensure the durability and reliability of these spindles during high-speed operations, various sensors and control devices are employed to actively regulate their dynamic characteristics. However, the direct measurement of internal heat generation or high-frequency bearing vibrations poses substantial challenges, hindering the reliable diagnosis of failure signals. Herein, we propose a data mining technology to predict failures in high-speed ball spindles by leveraging a comparative analysis of dynamic responses with reference patterns based on specific failure types. For this purpose, dynamic signals combined with various failure responses are rigorously analyzed and characterized in the frequency domain. Thereafter, the resulting individual failure responses are subjected to data mining analysis wherein four feature identification scores are evaluated within six reference frequency ranges. The entire lifetime of the spindle is categorized into four distinct degradation stages, namely the initial, propagation, developed, and deterioration stages. This categorization enables efficient and reliable estimation of spindle-failure progression by precisely measuring and analyzing the dynamic responses of the high-speed ball spindle. The proposed data mining technology enhances the ability to predict and diagnose failures in high-speed ball spindles, thereby facilitating timely maintenance and reducing downtime in manufacturing processes. [ABSTRACT FROM AUTHOR]

Introduction: The ankle joint is one of the most vulnerable joints in the body due to weight bearing. Pronated foot is one of the most common complications of the lower limbs. Therefore, the aim of the present study was to investigate the effect of training in water and training with thera-band on the frequency spectrum of electrical activity of lower limb muscles in people with pronated foot during walking. Methods: The present research was a clinical trial study that was conducted in a semi-experimental and laboratory. The statistical sample of the present study included 45 students of University of Mohaghegh Ardabili who had pronated foot, were selected purposefully and were randomly and equally placed in three groups: TheraBand, exercise in water, and control. The training protocol used for the water training group was based on the sports prescription guidelines of the American College of Sports Medicine (ACSM), and for the training group with the thera-band, it was performed using an orange thera-band in three sets with repetitions of 14 movements. To measure the frequency spectrum of the electrical activity of the lower limb muscles, it was recorded using a wireless surface electromyography device. Likewise, analysis of variance with repeated measurements and Bonferroni post hoc test were used to analyze the data at a significance level of P≤0.05. Results: The results showed that the interactive effect of time and group on the middle frequency spectrum of electromyography of the vastus medialis muscle in the exercises of the thera-band group during walking had a significant decrease (P=0.02). Other variables from the pre-test stage to the post-test did not show statistically significant differences (P

The songs of seven grasshopper species of subfamily Gomphocerinae from Russia, Ukraine, Georgia, and Kazakhstan were studied. We analysed not only the sound, but also the stridulatory movements of the hind legs to more entirely describe the songs. In Mesasippus kozhevnikovi, Chorthippus macrocerus, and C. hammarstroemi, the legs are moved in a relatively simple pattern; four other species, Myrmeleotettix palpalis, Stenobothrus newskii, C. pullus, and Megaulacobothrus aethalinus demonstrate more complex leg movements. In six of the seven species studied, the courtship songs contain more sound elements than the calling songs. The highest number of courtship sound elements was found in M. palpalis and M. aethalinus. The different parts of a remarkably long stridulatory file in M. aethalinus are thought to participate in the production of different sound elements. The songs in S. newskii are shown for the first time. This species produces sound not only by common stridulation but also by wing beats. A relationship of S. newskii to some other species of the genus Stenobothrus, which are able to crepitate, is discussed. We also analyse the frequency spectra of the songs. A maximum energy of the song power spectra in six species studied lies in ultrasound range (higher than 20 kHz). In only M. aethalinus, the main peaks in the song power spectra lie lower than 20 kHz. The courtship behaviour in M. palpalis, C. macrocerus, and C. hammarstroemi was shown to include conspicuous visual display (movements of antennae, palps and the whole body). [ABSTRACT FROM AUTHOR]

Background and Aims This study aimed to compare the frequency spectrum of ground reaction forces in blind and healthy participants with open and closed eyes during walking. Methods This study was quasi-experimental. The statistic samples comprised 15 blind men with a mean age of 25.22±6.33 years and 15 healthy men with a mean age of 27.22±5.31 years. They were selected by available sampling. A foot scan (RS Scan International, Belgium) device was used to measure the foot pressure values while walking. Variables of foot pressure were recorded at a sampling frequency of 300 Hz. For data analysis, we used the paired t test to compare the within-group means and the independent t test to compare the between-group means in SPSS software, version 24. Results The results showed that the frequency content with 99.5% power was greater in the blind group than in the healthy group with open eyes in the vertical direction, first metatarsal, and lateral and medial heel parts (P<0.05). Also, the frequency content with 99.5% power was greater in the healthy group with closed eyes than those healthy ones with open eyes (P<0.05). The frequency content with 99.5% power (P=0.004) and numbers of essential harmonics (P=0.003) in the vertical direction in the blind group were respectively 9.84% and 13.51% less than the healthy group with closed eyes. The number of essential harmonics (P=0.002) in the vertical direction in the healthy group with closed eyes was 20.61% greater than those healthy ones with open eyes. The frequency content with 99.5% power in the vertical direction in the blind group was less than that of the healthy group with closed eyes (P=0.023). Conclusion Considering the increase in frequency with 99.5% power and the number of essential harmonics in different areas of the soles of the foot in the blind group and healthy group with closed eye, it is recommended that physiotherapists, motion analysts, and rehabilitation specialists design a special rehabilitation protocol for blind people and those who lost their vision due to an accident. [ABSTRACT FROM AUTHOR]

An accurate model is needed to simulate the electromagnetic fields induced by short-period ocean waves to study the influence of the induced fields on the data set of marine magnetotelluric (mMT), marine controlled source electromagnetic (mCSEM), and marine airborne (low altitude) magnetic anomaly detection (MAD). By using a three-dimensional (3-D) linear wave model and directly solving linear equations derived from Maxwell’s equations and boundary conditions of a horizontal layered seabed, we obtained analytical solutions of the six components of the electromagnetic fields induced by three components of the velocity of ocean waves and three components of geomagnetic fields. In addition to horizontal currents induced by the horizontal velocity and vertical geomagnetic field, the contributions from the horizontal current induced by the vertical velocity and horizontal geomagnetic field and vertical current were considered in the governing equations. On the basis of the solutions, we studied how the geomagnetic field and wind fields affect the relationship between the two horizontal components and between the horizontal and vertical components of the electromagnetic fields at the sea surface. We simulated the influence of water depth and wind fields on the distribution of the spectrum and time series of the induced fields by using a typical wave spectrum and directional spectrum. Finally, the possibility of detecting seafloor conductivity structures by using the electromagnetic response of short ocean waves was also discussed.

Gas turbine vibration data may exhibit considerable differences under time-varying conditions, which poses challenges for neural network anomaly detection. We first propose a framework for a gas turbine vibration frequency spectra process under time-varying operation conditions, assisting neural networks' ability to capture weak information. The framework involves scaling spectra for aligning all frequency components related to rotational speed and normalizing frequency amplitude in a self-adaptive way. Degressive beta variational autoencoder is employed for learning spectra characteristics and anomaly detection, while a multi-category anomaly index is proposed to accommodate various operating conditions. Finally, a dataset of blade Foreign Object Damage (FOD) fault occurring under time-varying operating conditions was used to validate the framework and anomaly detection. The results demonstrate that the proposed method can effectively reduce the spectra differences under time-varying conditions, and also detect FOD fault during operation, which are challenging to identify using conventional methods. [ABSTRACT FROM AUTHOR]

This paper investigates the possibility of improving the vibration isolation of a tractor cab by changing the stiffness of its rubber-metal supports. A spectral analysis of the vibration isolation properties of these supports is presented. The research was conducted on a BELARUS 1221 tractor at idling, at the maximum engine speed, with no load. The cab was mounted on rubber-metal vibration absorbers of serial design with different rubber hardness. Measurements were made with a first class certified Oktava 101VM instrument with registration of RMS acceleration values, expressed in dB, in the frequency range of 8-1000 Hz. The instrument was set in "local vibration" mode. The AR2082M probe was attached to the respective measurement points using adhesive. Mathematical relationships are given to optimize the work on the development of a new and upgraded design of the rubber-metal supports in use. It is shown that varying the stiffness of the rubber-metal supports has different effects in the low and high frequencies of the spectrum. A stiff support is effective in damping low-frequency vibrations but degrades the support's properties in damping high-frequency vibrations, and vice versa. A soft support is more effective at higher frequencies and reduces the effectiveness of the support at lower frequencies. [ABSTRACT FROM AUTHOR]

It is shown that fine and rough structures can be differentiated in the radiation spectrum of a powerful laser diode. The relationship between the spectrum's characteristics and the internal parameters of the laser's structure is established and verified experimentally during degradation of the device. The effect of losses in the resonator and the coherence of laser radiation on both fine and rough structures of the radiation spectrum is shown. [ABSTRACT FROM AUTHOR]

Numerous studies highlight the analysis and modeling of the characteristics of the musical timbre of violins, obtained on the basis of the acoustic perception of the experienced subjects, the acoustic quality of the violins being interpreted on the basis of the statistical analysis of the psycho-acoustic impressions. Also, there are studies on the structural behavior of the violin to determine signature modes. However, the analysis of the radiated frequency response in three overlapping regions, as described in the literature, have been less studied. In this sense, the paper presents the study of the behavior of a historical violin, on the entire audio range, examining the frequency response function. The acoustic signal is produced by the excitation of the strings by the violinist, and the recording of the acoustic signals was made both in a concert hall and in an anechoic chamber. The results in the form of acoustic spectrograms, frequency spectrum, magnitude, and power spectrum density for each receiver were analyzed comparatively between the two acoustic spaces, the sounds emitted by the violins are amplified or dampened. [ABSTRACT FROM AUTHOR]

A mathematical model is developed that describes the process of defocusing images for the case of an incoherent optical system and non-monochromatic light. The proposed model can be used as a method of preliminary preparation of images (interferograms) in computer systems for processing complex interferograms without the use of optical defocusing devices. The defocusing method can be quite effectively used in two cases: a) as a low-pass filter, which, with an appropriate choice of the defocus parameter, reduces the impact of the high-frequency components of the complex interference pattern and more clearly distinguishes the moire pattern. b) as a way to select informative fragments of images, by which it is possible, if necessary, to synthesize the original image. This method of preprocessing of images makes it possible to drastically reduce the amount of input data during their computer processing, classification and decoding of interferograms. [ABSTRACT FROM AUTHOR]

A broadband antenna can transmit and receive radio signals across a broad frequency spectrum. The use of broadband millimeter-wave (mmWave) band antennas has garnered significant interest in wireless communication research. As a result, this type of antenna finds applications in television, radio broadcasting, and radar communication. The millimeterwave broadband antenna covers an extensive range of frequencies, leading to distinct design methodologies for such structures. The primary focus of this manuscript is to present a comprehensive overview of the recent developments in millimeter-wave antenna design, encompassing an in-depth analysis of the working principles of broadband antennas and their associated design characteristics. This review aims to shed light on the challenging path for antenna researchers and the potential enhancements achievable through broadband antenna technologies. Various applications, including enhanced wireless communication, high-definition and ultra-high-definition multimedia, and security signal intelligence, necessitate high data rates and significantly greater bandwidth. Consequently, a substantial demand for millimeter-wave broadband antennas can cater to these requirements. [ABSTRACT FROM AUTHOR]

Background. The relevance of the topic is determined by the increasingly widespread use of accelerometry data in the field of medicine, as well as in everyday life. The work raises the problem of automated determination of the type of human physical activity based on data collected using a wrist three-axis accelerometer. Materials and methods. To solve the problem, the method of analyzing the frequency spectrum of the signal was used. The accelerometer built into the smart watch was used as a source of initial data. To develop the data analysis program, the Scilab package of applied mathematical programs was used. Results. In order to analyze indicators of human physical activity, a program was developed that allows one to process and study data obtained from a three-axis accelerometer. For data analysis, a sliding window function has been implemented that shifts graphs at the touch of a button. Conclusions. A comparative analysis of graphs of frequency spectra and spectral differences showed that, along with the type of physical activity, the results are influenced by individual characteristics, which can complicate the identification of activities.

In-band emission represents a critical metric for assessing the reliability of a mobile communication network and ensuring quality of service (QoS) for end users. In the 5G network deployment, due to the limited availability of frequency spectrum, mobile users and internet-of-things (IoT) devices will transmit on the same frequency bands, necessitating more stringent in-band interference management to facilitate interference-free communication. In order to ensure that high-power user equipment (UEs) accessing the shared 5G uplink channel are able to communicate without disruption and without interfering with low-power devices, it is imperative to undertake in-band emissions analysis and control. This paper explores the issue of in-band emission interference, which pertains to the interference that arises in unallocated sub-bands within a specific bandwidth. Specifically, this investigation delves into the modeling approach and regulated in-band emissions within a non-standalone (NSA) 5G network. To verify compliance with 3GPP requirements for in-band emissions regulations, an over-the-air (OTA) testing system is employed to examine in-band emissions in the physical uplink shared channel (PUSCH). The study employs various resource block distributions, offsets, and modulation techniques within the specified NR channel bandwidth. All simulations are based on 3GPP specifications. [ABSTRACT FROM AUTHOR]

Trace fossils record the interactions between organisms and their surroundings, and can therefore provide unique insights into the coevolution of trace makers and the environment. However, identifying the producers of trace fossils is challenging because different animals can create very similar traces and many ichnotaxa can therefore only be attributed to broad morphological grades. For example, simple horizontal traces like Gordia are generally suggested to have been produced by vermiform organisms, potentially encompassing a range of animal phyla. This uncertainty makes it difficult to decipher their palaeobiological significance through major evolutionary events and episodes of environmental change. We have developed new mathematical approaches for identifying previously unrecognized signatures left by the trace makers of simple marine locomotory traces. We calculated the deviation angle series of self‐crossing traces made by extant isopods, polychaetes, gastropods and nematodes, computing the frequency spectrum and autocorrelation function in each case. The results reveal that each of these taxa left unique markers during the trace‐making process, reflecting differences in their anatomy and locomotory behaviour. We were able to identify the possible trace makers of several early Palaeozoic Gordia specimens, demonstrating that ichnospecies within the same ichnogenus can be created by distantly related animals with very different morphologies and/or behaviours. This novel mathematical framework has great potential for identifying the possible producers of diverse trace fossils through deep time, helping to uncover the earliest evidence of certain animals or behaviours. It also has great potential for quantifying ichnotaxonomy, consolidating the link between ichnology and palaeobiology. [ABSTRACT FROM AUTHOR]

Wind loads have become one of the key influencing factors for the running safety of vehicles and comfort of passengers. The investigation of the wind speed spectrum characteristics of a moving vehicle under turbulent crosswinds is of great importance. Expressions of the wind speed spectrum of a moving vehicle were obtained from the von Kármán spectrum, based on Taylor's frozen flow hypothesis. The influencing factors, including the ratio of the vehicle speed to the wind speed and wind yaw angles, were analyzed. The change rules of the wind speed spectrum peak and its corresponding frequency were also studied. The results show that the wind speed spectrum peak values of the moving vehicle were larger than those of the static vehicle. The wind speed spectrum peak values corresponding to the moving vehicle were first increased and then decreased, as the wind yaw angles increased. Some of the frequencies corresponding to the longitudinal wind speed spectrum values of the moving vehicle were smaller than those of the static vehicle. Therefore, the energy had been transferred to the lower frequency. For the moving vehicle, the frequency values corresponding to the longitudinal wind speed spectrum peak were first increased and then decreased, as the ratio of the vehicle speed to the wind speed and the wind yaw angle increased. [ABSTRACT FROM AUTHOR]

Sound elements were studied for a six strings sape, a traditional instrument. The frequency was evaluated using a frequency spectrum and a time frequency plane. PicoScope oscilloscopes and Adobe Audition version 3 were used to record the acoustic spectra. Fast Fourier Transform (FFT) analysis was used for the Fourier spectra (using PicoScope) and time frequency analysis (TFA) spectrograms (using Adobe Audition). The Fourier spectra identified the partial frequencies up to 10th overtone. The sape have an acoustic spectrum pattern with a constant harmonic overtone. Open strings 1 through 6 have notes F3, F3, A3, Bb3, G3, and C4, respectively. String 1 has 17 frets. Strings 2 through 6 are for drone purposes with no fret. The open string 1 and frets 1 through 17 have notes F3, G3, A3, Bb3, C4, D4, E4, F4, G4, A4, Bb4, C5, D5, E5, F5, G5, A5, and C6. String 1 has 2 octaves in the F major key with a jumping note in the third octave, which consists of F5, G5, A5, and C6 only. [ABSTRACT FROM AUTHOR]

The paper considers the problem of determining the natural frequencies and eigenwaves of transverse vibrations for the Bernoulli–Euler equation with variable coefficients. Such problems arise both in the case of complex geometry of a vibrating solid and in the case of functionally graded materials or the accumulation of damage in a classical elastic material. Solutions of boundary value problems are constructed using the expansion in Peano series. Under broad assumptions, the uniform convergence of Peano series is shown and estimates of the residual terms are obtained. Examples of the numerical implementation of the proposed procedure are given for bending vibrations of a rod with certain parameters of a variable cross section (geometric heterogeneity) and elastic modulus distribution (physical heterogeneity). Numerical examples are focused on assessing the geometric and elastic properties of samples in an experimental study of the fatigue strength of alloys during high-frequency cyclic tests based on the general principle of point resonant loading. The method proposed for solving problems of resonant vibrations for the Bernoulli–Euler equation can be used in the design of new promising cyclic test schemes and mathematical modeling of fatigue failure processes under high-frequency resonant vibrations. [ABSTRACT FROM AUTHOR]

In radiological imaging, the acquisition of the required diagnostic image quality under optimized conditions is important. Although techniques based on structural similarity (SSIM) have been investigated, concerns have been raised regarding their application to medical images. This study aims to clarify the properties of SSIM as an image quality index in medical images, focusing on digital radiography and verifying the correspondence between the evaluation results obtained by SSIM and the frequency spectrum. The analysis target was chest X-ray images of a human-body phantom. Various types of processing were applied to the images, and several regions of interest (ROIs) were used in local areas for analysis. The SSIM was measured using unprocessed data as a reference while changing the calculation parameters, and the spatial frequency spectrum of each local region was analyzed. Thus, a significant effect of ROI size was observed when calculating the SSIM. This indicates that larger the ROI size leads to SSIM values closer to 1 for all analysis conditions. In addition, a relationship between the size of the ROI in the analysis and the frequency components is demonstrated. It was shown that careful attention should be paid to the structures included in the ROI, and parameter settings should be reconsidered. Furthermore, when using SSIM to assess medical images, a multiscale SSIM method obtained by changing the ROI size would be useful. [ABSTRACT FROM AUTHOR]

In order to obtain the fundamental information for the measurement of thin oil film thickness adhered on lubrication surface using ultrasonic method, the ultrasonic calculation considering the scattering attenuation at each interface and the influence of frequency spectrum of ultrasonic waves were performed. The echo ratio of the wave reflected from the adhered film is hardly affected by the roughness on general lubrication surfaces with Rq≦1μm. On the other hand, the echo ratio is strongly affected by the frequency spectrum, and the relationship between the adhered film thickness and the echo ratio (calibration curve) calculated assuming the center frequency and frequency spectrum of the measured wave almost agrees with the experimental results. Based on the echo ratio distribution measured by the cylinder sliding type oil film thickness observation device, adhered film thickness distribution of the engine cylinder was plotted. Adhered oil film thickness increases and decreases symmetrically on the inlet and outlet sides of the piston ring when the oil supply is sufficient. However, the thickness of the adhered oil film becomes thin and its distribution is flattened throughout the stroke when the oil flow rate is reduced. On the other hand, the relationship between the film thicknesses LA on the cylinder and the film thickness LR on the piston ring for a sufficient oil flow rate is close to the shape of infinity (∞), and adhered film thicknesses of the lower side of top ring (LAT) and of the upper side of second ring (LAS) show a negative correlation. Therefore, these correlations of film thickness behavior have a potential to be one of the indicators of deterioration of lubrication conditions.

Sound elements were studied for a six strings sape, a traditional instrument. The frequency was evaluated using a frequency spectrum and a time frequency plane. PicoScope oscilloscopes and Adobe Audition version 3 were used to record the acoustic spectra. Fast Fourier Transform (FFT) analysis was used for the Fourier spectra (using PicoScope) and time frequency analysis (TFA) spectrograms (using Adobe Audition). The Fourier spectra identified the partial frequencies up to 10th overtone. The sape have an acoustic spectrum pattern with a constant harmonic overtone. Open strings 1 through 6 have notes F3, F3, A3, Bb3, G3, and C4, respectively. String 1 has 17 frets. Strings 2 through 6 are for drone purposes with no fret. The open string 1 and frets 1 through 17 have notes F3, G3, A3, Bb3, C4, D4, E4, F4, G4, A4, Bb4, C5, D5, E5, F5, G5, A5, and C6. String 1 has 2 octaves in the F major key with a jumping note in the third octave, which consists of F5, G5, A5, and C6 only.

Background. Due to the special structure of the knee joint in genu valgus individuals, neuromuscular characteristics of muscles can be disturbed and this may change postural control. This study aimed to investigate the effect of 8 weeks of training with an elastic band on the frequency spectrum of lower limb muscles in genu valgum patients during running. Methods. This study was a clinical trial in which 24 male students (20-30 years old) were randomly divided into control and experimental groups. Corrective exercises were performed for 8 weeks using an elastic band for the experimental group. The electrical activity of selected muscles was recorded by an electromyography system. Statistical analysis was performed using repeated measures ANOVA test at the significant level of 0.05. Results. Findings showed a significant increase in the frequency spectrum of rectus femoris (P=0.026; d=1.669) after training. Conclusion. Quadriceps muscles increase knee joint stability along with balance during movements. Therefore, increasing the median frequency of knee joint muscles improve balance. Practical Implications. The results of this study showed that exercises with elastic bands are useful for people with Genu valgum, and in particular, the use of these exercises leads to improved balance and performance.

Few-shot learning, especially few-shot image classification (FSIC), endeavors to recognize new categories using only a handful of labeled images by transferring knowledge from a model trained on base categories. Despite numerous efforts to address the challenge of deficient transferability caused by the distribution shift between the base and new classes, the fundamental principles remain a subject of debate. In this paper, we elucidate why a decline in performance occurs and what information is transferred during the testing phase, examining it from a frequency spectrum perspective. Specifically, we adopt causality on the frequency space for FSIC. With our causal assumption, non-causal frequencies (e.g., background knowledge) act as confounders between causal frequencies (e.g., object information) and predictions. Our experimental results reveal that different frequency components represent distinct semantics, and non-causal frequencies adversely affect transferability, resulting in suboptimal performance. Subsequently, we suggest a straightforward but potent approach, namely the Frequency Spectrum Mask (FRSM), to weight the frequency and mitigate the impact of non-causal frequencies. Extensive experiments demonstrate that the proposed FRSM method significantly enhanced the transferability of the FSIC model across nine testing datasets.

Monitoring a person’s physical activity has a wide range of applications in both sports and medicine. With the advancement of technology for measuring human movement, it is possible to monitor the performed activity without a need for an expert to directly overlook the trainee. While the initial interest focused mainly on aerobic exercises, research has recently begun to focus on strength exercises. The goal is to achieve the highest possible accuracy in tracking movement while maintaining the low cost and energy autonomy of the monitoring device. In this paper, an algorithm for the segmentation and classification of repetitive movements during workouts based on 3-axis accelerometer data from a wearable device is presented. The accelerometer signals were recorded continuously during the workout session which consisted typically of 9 strength exercises, where 8 default movements were repeated in three sets. Segmentation of the acceleration signals recorded during the workout was done using the frequency spectrum of the acceleration magnitude with an accuracy of 99.4%, while the classification of the segmented movements was done using the Dynamic Time Warping (DTW) algorithm with an accuracy of 85.7%.

Arc radiation-induced polymer nozzle ablation plays a crucial role in the operation of self-blast circuit breakers. Up to now, there is no study specifically on the spectral distribution of radiated power from a switching arc towards the nozzle surface and its implication to nozzle ablation. Three-dimensional radiation transfer calculation has been performed in this study for arcs burning in the mixture of C 4 F 7 N + C O 2 + PTFE , a gaseous environment that is under significant focus in the development of SF6 free switching technology to aim net-zero by the middle of this century. Results show that photons from infrared to extreme ultraviolet (UV, up to 5 × 1015 Hz) are emitted from the core of high current arcs. However, the high-frequency photons are mostly absorbed within the arc column, especially at the arc edge, and only photons up to 1.7 × 10 15 Hz (far UV, 7 eV) can penetrate the arc edge and cold gas and reach the nozzle surface. The spectral distribution of the radiative energy at different instantaneous currents (15 kA, 28 kA and 60 kA peak) and different locations of the nozzle is presented and compared in detail. The location of the radiation absorption zone at the arc edge and the radiative power reaching the nozzle wall as a function of the instantaneous current is, in particular, purposely considered. [ABSTRACT FROM AUTHOR]

In response to the problems of high cost and operation difficulties in extracting centrifugal pump speed data, and large errors of the obtained priori parameters, a completely data-driven centrifugal pump speed identification method was proposed. Firstly, the complex spectrum of vibration signals was obtained through fast Fourier transform(FFT) calculation, and then the equivalent speed spectrum was calculated by using the spectrum in the effective frequency band. After that, the difference between the spectral peak of the velocity spectrum and the background energy was calculated to obtain the maximum value of difference and compare it with the current background energy. If the condition was satisfied, the corresponding frequency was the rotational frequency of the centrifugal pump. The envelope spectrum was obtained by demodating the original vibration signal, and the fault frequency with obvious harmonic characteristics was searched in the envelope spectrum, and the sideband characteristics around the fault frequency were analyzed. Combining with the fault frequency and sideband characteristics, the fault diagnosis of the centrifugal pump could be analyzed. Finally, the accuracy of the above algorithm model was verified by the actual centrifugal pump vibration data obtained from the experiment. The experimental results show that for the impact signal of the centrifugal pump with obvious inner ring fault characteristics, the rotation frequency is accurately identified as 43.58 Hz, and in the envelope spectrum, the obvious fault feature frequency is 214.8 Hz and the fault feature coefficient is 4.93, which is in line with the fault signal characteristics of the bearing inner ring and is consistent with the actual centrifugal pump fault. The results show that the method of calculating the difference between the spectral peak of the velocity spectrum and the background energy can effectively eliminate noise interference, accurately identify the equipment speed, and provide technical support for equipment fault diagnosis in actual engineering. [ABSTRACT FROM AUTHOR]

Vibrations and waves are investigated in periodic systems that consist of identical subsystems having an arbitrary structure. Spectral regularities are found for such systems. Their dispersion curves are shown to consist of branches, each of which corresponds to its own mode shape of elastic vibrations of the subsystem. The presence of band gaps in such systems, in which a harmonic signal cannot be transmitted, was revealed, and their boundaries were determined. The mode shapes of vibrations in various frequency ranges are obtained. Modulated waves are shown to arise in the system due to modulation by lower frequencies, which correspond to system vibrations without taking into account the elastic properties of the constituent subsystems. [ABSTRACT FROM AUTHOR]

Background. Due to the special structure of the knee joint in genu valgus individuals, neuromuscular characteristics of muscles can be disturbed and this may change postural control. This study aimed to investigate the effect of 8 weeks of training with an elastic band on the frequency spectrum of lower limb muscles in genu valgum patients during running. Methods. This study was a clinical trial in which 24 male students (20-30 years old) were randomly divided into control and experimental groups. Corrective exercises were performed for 8 weeks using an elastic band for the experimental group. The electrical activity of selected muscles was recorded by an electromyography system. Statistical analysis was performed using repeated measures ANOVA test at the significant level of 0.05. Results. Findings showed a significant increase in the frequency spectrum of rectus femoris (P=0.026; d=1.669) after training. Conclusion. Quadriceps muscles increase knee joint stability along with balance during movements. Therefore, increasing the median frequency of knee joint muscles improve balance. Practical Implications. The results of this study showed that exercises with elastic bands are useful for people with Genu valgum, and in particular, the use of these exercises leads to improved balance and performance. [ABSTRACT FROM AUTHOR]

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The sound field of a harmonically radiating monopole moving along arbitrary trajectories in three-dimensional space is studied in the frequency range and represented as a convolution integral in Cartesian coordinates. The observation time of the motion of the source can be finite or infinite. This convolution integral is referred to as the "Cartesian Convolution Integral " and is applied to point sources moving on special orbits described by circular and conical helices. For such helical orbits, an alternative approach in cylindrical or spherical coordinates leads to closed form expressions in the form of infinite series for the frequency spectra. The comparison of the results of the Cartesian Convolution Integral with those of the series expansion shows a very good agreement. Finally, the Cartesian Convolution Integral is used to calculate the spectral sound field of a source moving along an elliptical helix. [ABSTRACT FROM AUTHOR]

Radio frequency interference (RFI) comprises undesirable distortions from other frequency bands overlapping the specified band of operation. RFI contributes to increased detected power and temperature of the baseband processing units, resulting in considerable discrepancies in the received measurements. RFI mitigation techniques have been proposed to tackle this problem. However, the cost of implementing most RFI removal algorithms can be highly prohibitive. Removing such unwanted signals would involve removing a portion of the desired intelligence, leading to a potential loss of valuable information. The requirement for experimental frequency scans to detect, and mitigate RFI becomes important. Field measurements were conducted across three microwave links located in urban environments. The spectrum analyzer and a 0.6-meter antenna dish were used for the frequency scans at 6–8 GHz in horizontal and vertical polarizations. The availability of the desired frequencies, which is key to frequency planning is presented. The cumulative distribution functions, histogram and probability density functions of the measured data, which are crucial to determining the impact of interference on the microwave links, are presented. The statistical characteristics of the measured data are highlighted. Overall, the RFI data would provide insights on RFI detection and mitigation, leading to a high quality of service for the benefit of mobile subscribers.

Gas turbine vibration data may exhibit considerable differences under time-varying conditions, which poses challenges for neural network anomaly detection. We first propose a framework for a gas turbine vibration frequency spectra process under time-varying operation conditions, assisting neural networks’ ability to capture weak information. The framework involves scaling spectra for aligning all frequency components related to rotational speed and normalizing frequency amplitude in a self-adaptive way. Degressive beta variational autoencoder is employed for learning spectra characteristics and anomaly detection, while a multi-category anomaly index is proposed to accommodate various operating conditions. Finally, a dataset of blade Foreign Object Damage (FOD) fault occurring under time-varying operating conditions was used to validate the framework and anomaly detection. The results demonstrate that the proposed method can effectively reduce the spectra differences under time-varying conditions, and also detect FOD fault during operation, which are challenging to identify using conventional methods.

At 12.8 MHz center frequency, the advanced miniaturized polymerbased planar high quality factor (Q) passive elements embedded bandpass filter works in the L-band. Because most of the demands operate inside the spectrum, the wideband or high-speed operation necessary to enhance must be acquired in microwave frequency ranges. The channel has a quiet, high-performance microfilter with wideband rejection. Capacitors and inductors are used in the high quality factor (Q) passive components, and related networks are incorporated in the filter. Embedded layers are concatenated using Three-Dimensional Integrated Circuit (3D-IC) integration, parasitics are removed, and interconnection losses are negotiated using de-embedding methods. A wireless application-based Liquid Crystalline Polymer (LCP) viewpoint is employed as a substrate material in this work. The polymer processes, their properties, and the incorporated high-Q Band Pass Filter Framework. The suggested filter model is computed and manufactured utilizing the L-band frequency spectrum, decreasing total physical length by 31% while increasing bandwidth by 45%. [ABSTRACT FROM AUTHOR]

The signal of acoustic emission (AE) captured during the sandstone shear failure is the key information to ascertain the damage degree (DD) of rock. To reveal the frequency spectrum and damage characteristics of saturated-and-dry red sandstone, the AE parameters of saturated-and-dry red sandstone such as cumulative energy, cumulative ring counts, the dominant and secondary frequencies (DSF) were analyzed during shear test by using AE monitoring technique. Results show that the shear damage stress of red sandstone is determined according to the cumulative energy and cumulative ring counts curves. The DD is expressed via cumulative ring counts and the relationship between DD and shear strain is established. DSF of red sandstone in saturated-and-dry state decrease when normal stress increases. The conclusion obtained in this study is of very important theoretical significance to determine shear DD of red sandstone. [ABSTRACT FROM AUTHOR]

The turn-on change rate of drain current diDS(on)/dt is an electrical parameter that is suitable for the online monitoring of junction temperature in SiC MOSFETs. In practical applications, the change of an external circuit changes the temperature-sensitive characteristic of diDS(on)/dt. In this paper, a SiC MOSFET in a Buck converter is taken as the research object. First, it is theoretically derived and experimentally verified that the power loop inductance and drive loop resistance are parasitic parameters that affect the temperature-sensitive characteristic of diDS(on)/dt. Second, according to the spectrum peak characteristics caused by the drain–source turn-off oscillation voltage of the SiC MOSFET, the theoretical relationship between the diDS(on)/dt temperature-sensitive characteristic and the peak of the drain–source turn-off oscillation voltage is studied. It is concluded that the spectrum peak can reflect the change of the diDS(on)/dt temperature-sensitive characteristic caused by the change of the parasitic parameters. Based on the above research, a model of a modified diDS(on)/dt temperature-sensitive characteristic considering parasitic effect is established in this paper. Through experimental verification, this model can largely eliminate the junction temperature monitoring error caused by the change of the external circuit. [ABSTRACT FROM AUTHOR]

Monitoring a person's physical activity has a wide range of applications in both sports and medicine. With the advancement of technology for measuring human movement, it is possible to monitor the performed activity without a need for an expert to directly overlook the trainee. While the initial interest focused mainly on aerobic exercises, research has recently begun to focus on strength exercises. The goal is to achieve the highest possible accuracy in tracking movement while maintaining the low cost and energy autonomy of the monitoring device. In this paper, an algorithm for the segmentation and classification of repetitive movements during workouts based on 3-axis accelerometer data from a wearable device is presented. The accelerometer signals were recorded continuously during the workout session which consisted typically of 9 strength exercises, where 8 default movements were repeated in three sets. Segmentation of the acceleration signals recorded during the workout was done using the frequency spectrum of the acceleration magnitude with an accuracy of 99.4%, while the classification of the segmented movements was done using the Dynamic Time Warping (DTW) algorithm with an accuracy of 85.7%. [ABSTRACT FROM AUTHOR]

Introduction: Depression is a serious psychiatric disorder characterized by prolonged sadness, loss of interest or pleasure. The dominant alpha peak activity in resting-state EEG is suggested to be an intrinsic neural marker for diagnosis of mental disorders. Methods: To investigate an association between alpha peak activity and depression severity, the present study recorded resting-state EEG (EGI 128 channels, off-line average reference, source reconstruction by a distributed inverse method with the sLORETA normalization, parcellation of 68 Desikan- Killiany regions) from 155 patients with depression (42 males, mean age 35 years) and acquired patients' scores of Self-Rating Depression Scales. We measured both the alpha peak amplitude that is more related to synchronous neural discharging and the alpha peak frequency that is more associated with brain metabolism. Results: The results showed that over widely distributed brain regions, individual patients' alpha peak amplitudes were negatively correlated with their depressive scores, and individual patients' alpha peak frequencies were positively correlated with their depressive scores. Discussion: These results reveal that alpha peak amplitude and frequency are associated with self-rating depressive score in different manners, and the finding suggests the potential of alpha peak activity in resting-state EEG acting as an important neural factor in evaluation of depression severity in supplement to diagnosis. [ABSTRACT FROM AUTHOR]

Abstract Time varying mass engineering structure is the type of structure where the total mass of the structure changes rapidly, and the loads generated are dependent on the properties of the structure, discharge rate and the properties of the materials inside the structure. A discharging silo is a typical time varying mass civil engineering structure where the total mass of the entire structure changes during the discharge of the stored materials. This paper presents a novel combinatory approach using Hilbert Transform and Variational Mode Decomposition methods to analyse nonlinear and non-stationary signals collected from the experimental silo filled with iron ore and one filled with sand. In particular, the silo filled with sand was producing loud foghorn like sound during discharge. The results revealed the existence of a frequency spectrum that can be developed further to assess the structural integrity of a time varying mass civil engineering structure such as a silo without the impacting silo operation and throughput. The obtained frequency spectrum shows that there is a noticeable difference between the spectra for the silo filled with iron ore and the silo filled with sand.

With continuing increase in the production of machines, decrease in the batch size, and expansion of the product range, metal-cutting equipment must meet high reliability standards. The operational time of the equipment as a whole will be decreased in the event of sudden component failure and loss of the expected working life between scheduled maintenance sessions. In that context, it is prudent to determine the actual closeness of machine parts to their expected expiration date. For diagnostics, it is expedient to use information regarding the spectral composition of the vibrational frequencies in the operation of metal-cutting equipment. From the overall frequency spectrum, those segments characteristic of specific components must be identified. To that end, characteristic combinations for individual states of the machine parts are determined experimentally. [ABSTRACT FROM AUTHOR]

Gate oxide degradation, which considerably affects turn-on/-off dynamics of the switch, embraces a large percentage of chip-related failure modes both in silicon and silicon carbide power MOSFETs. The gate oxide layer is thinner in silicon carbide power MOSFETs in comparison to their silicon-based counterparts. Consequently, the problem of gate oxide degradation has become a more crucial impediment in achieving reliable performance in silicon carbide power MOSFETs. This problem is even more severe in high-frequency applications due to higher EMI signature and complicated and costly measurement. In this article, a reliable fully analog cost-effective gate oxide degradation condition monitoring technique is proposed and validated. High-order harmonics magnitudes of drain–source voltage are used to produce a dc signal as the aging precursor of the gate oxide region. Using a dedicated degradation setup, the credibility of the developed condition monitoring technique was examined at different rates of gate oxide degradation for 650-V/22-A silicon carbide discrete MOSFET. In 200-kHz, 217-V switch operation, the proposed precursor showed 68% change in comparison to its initial value. This brings a high-resolution assessment on the reliability level of the switch gate oxide region. [ABSTRACT FROM AUTHOR]

In this work, a procedure to obtain an accurate value of the critical speed of a cracked shaft is presented. The method is based on the transversal displacements of the cracked section when the shaft is rotating at submultiples of the critical speed. The SERR (Strain Energy Ralease Rate) theory and the CCL (Crack Closure Line) approach are used to analyse the proposed methodology for considering the behaviour of the crack. In order to obtain the best information and to define the procedure, the orbits and the frequency spectra at different subcritical rotational speed intervals are analyzed by means of the Fast Fourier Transform. The comparison of the maximum values of the FFT peaks within the intervals allows the subcritical speed to be determined, along with the value of the critical speed. When verified, the proposed procedure is applied to shafts with the same geometry and material and with cracks of increasing depth. The results show that the critical speed diminishes with the severity of the crack, as expected. A comparison is made between the critical speed obtained using the vertical and the horizontal displacements, finding no remarkable differences, meaning that in practical applications only one sensor for one of the displacements (in the vertical or horizontal direction) is needed to determine the critical speed. This is one of the main contributions of the paper, as it means that the orbits of the shaft are not needed. Finally, after this study we can conclude that the best results are achieved when the critical speed is obtained using data displacement in only one direction within the intervals around 1 2 or 1 3 of the critical speed. [ABSTRACT FROM AUTHOR]