Time-and Frequency Research Articles

Construction of multi-features comprehensive indicator for machinery health state assessment

Health state assessment is critical for mechanical equipment’s smooth and healthy operation. This paper proposes a novel approach for health state assessment based on acoustic signals during the process of machinery running. It consists of multi-domain feature (MF) extraction and comprehensive health indicator (CHI) construction. MF is extracted from various acoustic features, including time and frequency (TF) features, mel-frequency cepstral coefficients, and gammatone frequency cepstral coefficients. The stacked long short-term memory (LSTM) is used to extract the high-level features of the MF, which are then input to the downstream PCA to obtain the LSTM-PCA health indicator (LP-HI). Parallelly, the MF is fed into the self-organizing mapping (SOM) model to calculate the minimum quantization error (MQE) as SOM-MQE health indicator (SM-HI). These two indicators are fused using weighted fusion and nonlinear mapping to calculate CHI. The experimental results on air compressor dataset show a 25.8% reduction in evaluation error compared with SOTA results in this paper. The proposed nonlinear mapping function furthermore reduces fitting error on HI by 38.9%. These demonstrate the effectiveness and superiority of the proposed method in machinery health state assessment.

EEG Emotion Recognition based on Multi scale Self Attention Convolutional Networks

A multi-view self-attention module is proposed and paired with a multi-scale convolutional model to builda multi-view self-attention convolutional network for multi-channel EEG emotion recognition. First, timeand frequency domain characteristics are extracted from multi-channel EEG signals, and a three-dimensionalfeature matrix is built using spatial mapping connections. Then, a multi-scale convolutional network extractsthe high-level abstract features from the feature matrix, and a multi-view self-attention network strengthensthe features. Finally, use the multilayer perceptron for sentiment classification. The experimental results revealthat the multi-view self-attention convolutional network can effectively integrate the time domain, frequencydomain, and spatial domain elements of EEG signals using the DEAP public emotion dataset. The multi-viewself-attention module can eliminate superfluous data, apply attention weight to the network to hasten networkconvergence, and enhance model recognition precision.

POTENTIAL SOLUTIONS, CHALLENGES AND IMPLEMENTATION ISSUES FOR NOMA IN 5G COMMUNICATIONS

Non-Orthogonal Multiple Access (NOMA), a promising radio access technology for 5G and beyond networks, has recently attracted a lot of interest because of its higher spectral efficiency and capacity to serve multiple users simultaneously while maintaining the same time and frequency resources. 5G mobile networks will be able to accommodate at least 100 billion connections between devices, a 1000-fold growth in system capacity, improved coverage, high data rates, and ultra-low energy consumption. A base station (BS) can serve numerous users at the same time, frequency, and code resource thanks to NOMA, which implements multiple access (MA) by utilizing a new dimension - the power domain. One of the fundamental NOMA methods that performs successive interference cancellation (SIC) at the receiver and superposition coding (SC) at the transmitter is the power domain NOMA

Joint Radar and Communications With Multicarrier Chirp-Based Waveform

We consider a multicarrier chirp-based waveform for joint radar and communication (JRC) systems and derive its time discrete periodic ambiguity function (AF). A set of waveform parameters (e.g., chirp rate) can together with the transmit sequence be selected to shape the AF to be thumbtack-like, or to be ridge-like, either along the delay axis or the Doppler axis. We demonstrate how these shapes are applicable for different use cases, e.g., radar target detection or time-and frequency synchronization. The results show that better signal detection performance than OFDM and DFT-s-OFDM can be achieved on channels with large Doppler shift. Furthermore, it is shown how transmit sequences can be selected in order to achieve low peak-to-average-power-ratio (PAPR) of the waveform.

Gearbox faults feature selection and severity classification using machine learning

The most widely used technique for gearbox fault diagnosis is still vibration analysis. The need for gearbox condition monitoring in an automated process is essential and there is still a problem with the selection of features that best describe a fault or its severity level. For this purpose, multiple-domain vibration signals statistic features are extracted through time and frequency domain by postprocessing of raw time signal, time-synchronous average signal, frequency spectra and cepstrum. Five different datasets are considered with different levels of fault analyzing gear chipped and a missing tooth, gear root crack, and gear tooth wear under stable running speed and load. A preliminary experimental study of a single stage test bench gearbox was performed in order to test feature sensitivity to type and level of fault in the process of clustering and classification. Selected features were finally processed using an artificial neural network classifier.

A Non-WSSUS Channel Simulator for V2X Communication Systems

This paper presents a simulator of non-wide sense stationary uncorrelated scattering (non-WSSUS) multipath fading channels for the performance analysis of vehicle-to-everything (V2X) communication systems. The proposed simulator is constructed with the combination of the Monte Carlo and sum-of-cisoids (SOC) principles, and it is suitable for multicarrier transmission schemes such as those defined for dedicated short-range communications (DSRC) and cellular-based V2X (C-V2X) communications. The channel simulator provides an accurate and flexible solution to reproduce the time and frequency (TF) correlation properties of non-WSSUS vehicular channels under arbitrary isotropic and non-isotropic scattering conditions. Furthermore, the proposed simulator allows velocity variations and non-linear trajectories of the mobile stations (MSs). To demonstrate the practical value of the presented simulator, we evaluate the bit error rate (BER) performance of two channel estimation techniques that are considered for IEEE 802.11p transceivers, namely the least squares (LS) estimator and the spectral temporal averaging (STA) technique. The BER performance of both channel estimators was analyzed by considering three propagating scenarios for road safety applications. Our results show that the non-stationary characteristics of the vehicular multipath fading channel have nearly no effects on the LS estimator’s BER performance. In contrast, the performance of the STA estimator is significantly affected by the channel’s non-stationary characteristics. A variation of the original STA technique that applies only a temporal averaging is introduced in this work to improve the system’s BER in non-WSSUS channels.

Effect of Left and Right Nostril Breathing on Heart Rate Variability among Healthy Adult Males: A Cross-sectional Study

The effects of various breathing manoeuvres on autonomic functions, especially those of alternate nostrilbreathing and single nostril breathing have been well documented.1,2,3,4 However, most of the studies haveinvestigated these effects after practiced breathing manoeuvres,5,6,7 and few have looked into the immediateeffects of such types of breathing. The purpose of this study was to determine the immediate effects of asingle session of single nostril breathing, first right nostril and then left nostril, on the various time andfrequency domain parameters of heart rate variability (HRV) and to compare these effects with that of HRVduring normal breathing.Sixty male volunteers (age range, 20 to 40 years) were assessed. Electrocardiography was conducted, usingstandard procedure, under controlled laboratory conditions, for three five-minute periods: during breathingnormally through both nostrils, during the last five minutes of a twenty-minute session of breathing throughthe right nostril only and similarly while breathing through the left nostril only. The R-R intervals obtainedwere analyzed for HRV parameters and further analyzed using different statistical method.When compared to right nostril breathing, a statistically significant increase in mean R-R intervals was notedwith left nostril breathing (p = 0.009). Sympathetic activation with right nostril breathing was also evident,although statistically not found to be significant. A statistically significant higher SDNN with left nostrilbreathing as compared to both nostril breathing (p = 0.004) was also observed. Similarly, NN50 and pNN50were found to be significantly higher with left nostril breathing as compared to both nostril breathing (p =0.003 & 0.007, respectively). However, RMSSD, LF power, HF power, LF norm, HF norm and LF/HF ratiowere not found to be statistically different for the three breathing manoeuvres.Thus our study showed an overall parasympathetic predominance, with an increase in total power of HRVwith left nostril breathing, but the minute variations of HRV were not found to be significantly differentamong the three breathing manoeuvres.

Heart rate variability, the dynamic nature of the retinal microvasculature and cardiac stress: providing insight into the brain-retina-heart link: the SABPA study.

Decreased heart-rate-variability (HRV) indicates increased sympathetic nervous system (SNS) activity and modulation with a shift in the sympatho-vagal balance towards SNS predominance. Increased SNS activity may precede volume-loading hypertension, contribute to increases in cardiac troponin T (cTnT), endothelial dysfunction and small vessel disease. Therefore, we investigated the retinal vasculature, HRV during flicker-light-induced-provocation (FLIP) and systemic cTnT, a marker of cardiac stress, to provide further evidence in support of the brain-retina-heart link. Cross-sectional observations were obtained from a bi-ethnic cohort (N = 264), aged 23-68 years. Fasting serum samples for cTnT were obtained. Retinal vascular calibres were quantified from mydriatic eye fundus images and dynamic retinal vessel calibre responses were determined during FLIP. Time-and frequency domain parameters of HRV were calculated during FLIP for each participant. Africans had wider venules and attenuated time domain parameters during FLIP. In Africans, inverse associations emerged between arteriolar dilation and both cTnT and root-mean squared of the standard deviations of successive RR-intervals (rMSSD) (p = 0.030), and between arteriolar constriction and both low-frequency expressed in normalised units (LFnu) (p = 0.003) and high-frequency expressed in normalised units (p = 0.021). Wider venules inversely associated with standard deviation of the NN intervals (SDNN) as well as LFnu (p = 0.009) in Africans. An opposite profile was observed in Caucasians with both time-and frequency domain parameters of HRV in relation to retinal vessel structure and function. FLIP elicited increased SNS activity and modulation in this bi-ethnic cohort. In Africans, decreased HRV during FLIP accompanied arteriolar and venular responses and elevated systemic levels of cTnT, implying that the SNS exerted a significant effect on the smooth muscle tone of the retinal vasculature. Disrupted retinal autoregulation may imply general autonomic nervous system dysfunction; exemplifying central control by the brain on all systemic regulatory functions, across different vascular beds.

Ocena efektów akustycznych eksploatowanych pojazdów drogowych z wykorzystaniem subiektywnych cech dźwięku

The article proposed an original way to assess the acoustic effects of road vehicles in the environment, with the use of selected methods of sound modeling and simulation. The taken solution presents a way of estimating the acoustic emission to the environment, from the exploited road vehicles, using subjective sound features. In ongoing studies, it is assumed to analyze and evaluate the sound features in the following order: source - propagation way - receiver. The distribution of these features in the time and frequency domains depends on generation, propagation and immission of acoustic energy, by the partial sources of the vehicle. The obtained information in the form of an acoustic signal can be represented by physical and subjective features of the sound. The undertaken research include the use of subjective features of sound in the assessment of acoustic effects of road vehicles exploited in the environment. The developed method was verified using modeling and simulation methods based on recorded acoustic signals in an urbanized environment.

Eigenspace Time Frequency Based Features for Accurate Seizure Detection from EEG Data

BackgroundEpilepsy is a neurological disorder that affects over 2% of the world population. Epilepsy patients suffer from recurring seizures that can be very harmful. The unpredictability of seizures is a major concern for medical practitioners because uncontrollable seizures can lead to sudden death and morbidity. A system that could warn patients and doctors alike about the impending seizure event would dramatically enhance the quality of life for patients. MethodsWhile most previous research works focused on using signal processing tools appropriate for stationary signals, we propose here to use time and frequency (TF) analysis to extract features capable of discriminating normal from abnormal EEG traces (both ictal and interictal). The features are extracted using Singular Value Decomposition (SVD) of the EEG signal Time Frequency matrix. The left singular vectors of the time frequency matrix are used to obtain robust feature vectors. In contrast to existing techniques, the proposed TF-based technique can be used to detect the specific moments of seizure occurrences in time so that this information is used to discriminate interictal from ictal EEG traces. Instead of extracting the features directly from the TF matrix, we transform the left eigenvectors obtained from the SVD of the TF matrix into a feature vector that behaves like to a probability density function. ResultsWe show that almost all classical classification techniques achieve excellent seizure detection results when used with the proposed TF features, irrespective of the classifier used. Contrary to existing works, we test our approach across several real-life scenarios covering 2, 3, and 5 possible classes of data. Our tests provided consistent results across different scenarios. The results, under different scenarios, outperformed existing ones achieving consistently more than 97.3% and up to 99.5% in terms of accuracy, sensitivity, and specificity. ConclusionExperimental results show that the novel features have successfully represented the characteristics of the underlying disease phenomenon from EEG data. Also, we conclude that learning based classifiers are better suited for this application, compared to Bayesian classifiers that have difficulty in adapting to the varying nature of the features' probability distribution function.

근막이완요법(myofascial release)이 Ergometer 운동 후 심박변이도와 대퇴직근 경직도에 미치는 영향

The purpose of the study is to invastigate the effects of myofascaial release on heart rate variability and stiffness of rectus femoris after ergometer exercise. In a cross-over design, 9 young(22.75±1.89years) healthy males performed two incremental 70% HRR cycling bouts, and the neither 10 min of myofascial release or passive rest. The parameters of heart rate variability were obtained from both time-and frequency domain analysis of 5min ECG recording at rest, immediately after exercise and recovery 10min. Standard deviation of the node to node interval(SDNN) and root mean square of successive differences(RMSSD) and the low and high frequency components were calculated as normalized units. In order to measure the mechanical properties like muscle stiffness and elasticity, MyotonPro(Myoton AS ,Tallinn, Estonia) was applied to muscle belly of rectus femoris muscle at rest, immediately after exercise and recovery 10min. From the Myoton measurement, Five indexes (Frequency, Logarithmic Decrement, Dynamic Stiffness, Creep and Mechanical Stress Relaxation) were obtained. The results are as follows: 1. Analysis of HRV revealed a significant increase in sympathetic activity and a significant decrease in parasympathetic activity following ergometer exercise with no significant difference between both groups. 2. The muscle tension and stiffness increased significantly while the elasticity decreased immediately after exercise while no significant effect of myofascial release on mechanical properties indexes was found during recovery period. The results represent that these application of MR technique might influence personal feeling and none-specific recovery from muscle fatigue without any statistically significant change of muscle mechanical properties and heart rate variability.

중정도 평압ㆍ저산소 환경에서의 점진 부하 운동이 심근 자율신경계와 myotonometric 변인에 미치는 영향

The aim of this study is to investigate the effects of normobaric hypoxia exposure on cardiac autonomic system and myotonometric variables during incremental exercise .In a cross-over design, 9 young(23.50±1.77 year) healthy males were asked to perform the incremental cyclic exercise in hypoxia and control(sea level) condition with a week interval. Subjects assigned to the hypoxia condition group breathed hypoxia air corresponding to 2,600m altitude condition for 50minutes through the hypoxic control device(Altrainer, SMTEC Sports & Medical Technologies SA, Nyon, Switzerland). The parameters of heart rate variability were obtained from both time-and frequency domain analysis of 5min ECG recording at rest, post exercise and recovery 15min. Standard deviation of the node to node interval(SDNN) and root mean square of successive differences(RMSSD) and the low and high frequency components were calculated as normalized units. In order to measure the mechanical properties like muscle stiffness and elasticity, MyotonPro(Myoton AS, Tallinn, Estonia) was applied to muscle belly of biceps femoris and gastrocnemius muscle at rest, immediately after exercise and recovery 15min. Arterial oxygen saturation, lactate acid were also measured by pulse oximetry and lactate acid analysis device respectively at rest, immediately after exercise and post 15minute. The result are as follows: 1. Analysis of HRV revealed a significant increase in sympathetic activity and a significant decrease in parasympathetic activity following ergometer exercise. However, no significant difference in parameters of HRV was found between the hypoxia group and the control group. 2. The tension of right biceps femoris · left gastrocnemius measured at rest, immediately after exercise and recovery 15min was significantly higher in hypoxia group than in control group. 3. The stiffness of right biceps femoris and left gastrocnemius measured immediately after exercise and recovery 15min was significantly higher in hypoxia group than in control group. 4. Arterial oxygen saturation of hypoxia group at rest, post exercise and recovery 15min was significantly lower than control group while the lactate acid of hypoxia group was significantly higher.

4650m 상당의 평압·저산소 조건에서 근지구성 운동이 심박변이도에 미치는 영향

The purpose of this study was to investigate the effect of extreme normobaric hypoxia exposure corresponding to 4650m altitude on heart rate variability during muscular endurance exercise. In a cross-over design, 19 young (21.7±2.4years) healthy males were asked to perform the isokinetic leg endurance exercise twice in hypoxia and control(sea level) condition with a week interval. Subjects assigned to the hypoxia condition group was breathed in hypoxia air corresponding to 4,650m altitude condition for 30minutes through the hypoxic control device(Altrainer, SMTEC Sports & Medical Technologies SA, Nyon, Switzerland). Each Subject conducted iso-kinetic knee flexion and extension exercise at 180°/sec, 10bouts, and 10sets using isokinetic dynamometer(Biodex system 4, Medical System Inc, USA). The parameters of heart rate variability were obtained from both time-and frequency domain analysis of 5min EC G recording at rest, post exercise, and post 10min(3 time) after exercise. Mean RR interval and its standard deviation(SDNN), the mean square successive differences(RMSSD), the low and high frequency components were calculated as normalized units. Arterial oxygen saturation was also measured by pulse oximetry at rest, post exercise, and post 10minute. The results were as follows. First, following the hypoxia exposure a significant decrease in arterial oxygen saturation was found(p.05). Second, analysis of HRV revealed a significant increase in sympathetic activity and a significant decrease in parasympathetic activity following muscular endurance exercise both group(p0.1~0.05). Third, no significantly different in parameters of HRV was not found between the hypoxia group and the control group. These findings suggest that the dropped level of arterial oxygen saturation induced by hypoxia exposure may not affect heart rate variability at resting status, during exercise and recovery period. The results also showed that exercise itself rather than status of blood might have more powerful effect on autonomic nerve activities.

일내 시간대별 운동이 심근 자율신경계 반응에 미치는 영향

The acute bout of vigorous exercise has been suggested to incre ase the risk of cardiac events, particularly in morning. The aim of this research was to evaluate the effect of time of day on cardiac autonomic responses to hard exercise, reflected by heart rate variability(HRV). On four occasions, 8 young (20.5±0.7years) healthy males exercised, in random order, on a cycle ergometer at 6:00～7:00, 11:00～12:00, 15:00～16:00, 20:00～21:00h each followed by five min of active recovery. Electrocardiogram data were collected for 5 min periods in the sitting position, at rest before and after each exercise bout. Measures of heart rate variability, obtained from both time-and frequency domain analysis of 5 min ECG recording were as follows: mean RR interval and its standard deviation(SDNN), the root mean square of successive differences(RMSSD), the low and high frequency components which were calculated as normalized units and their ratio(LF/HF ratio). Analysis of heart rate variability revealed a significant increase in sympathetic activity and a significant decrease in parasympathetic activity (P=0.05) following each exercise bout. Although measures of HRV we re not significantly different between exercise trials. HRV variables were associated with higher shifts during the early and morning exercise. These results suggest that exercise when performed in the afternoon and evening periods may be effective in minimizing exercise-induced cardiac sympathovagal dysfunction.

ON THE SENSITIVITY OF CUTTING CONDITIONS ON CUTTING FORCES AND VIBRATION SIGNALS WHEN TURNING WITH TOOL INSERTS WITH INTEGRATED CHIP-BREAKER GEOMETRY

ABSTRACTThis paper is concerned with investigating the effects of cutting conditions on sensorsignals, employing tool inserts with chip breaker geometry and a harder workpiecematerial. Medium double coated carbide grade tool inserts with integral groove chipbreakerwas used to cut EN24T alloy steel. The focus was to investigate andcorroborate the effects of cutting conditions (cutting speed, feed rate and dept of cut)on the cutting forces and vibrations signals during orthogonal turning using coatedchip-breaker geometry indexable tool inserts. Cutting forces and vibration signalswere recorded on-line at the various cutting conditions, and these analysed in timeand frequency modes for features that were sensitive to the variation in the cuttingconditions. Peculiar characteristics in the signal spectrum were identified and thesewere easily associated with changes in the cutting conditions as well as chiplamination.

Parametric modeling of microwave passive components using combined neural networks and transfer functions in the time and frequency

A novel parametric modeling technique is proposed to develop combined neural network and transfer function models for both time and frequency (TF) domain applications of passive components, where the neural network is trained to map geometrical variables to the coefficients of transfer functions. Built on our previous work, a new order-changing module is developed to enforce stability of transfer functions and simultaneously guarantee continuity of coefficients. A constrained optimization strategy is introduced to enforce passivity of transfer functions through a neural network training process. A general equivalent circuit for two-port passive components is generated directly from coefficients of arbitrary-order transfer functions. Once trained, the parametric model can provide accurate and fast prediction of the electromagnetic behavior of passive components with geometrical parameters as variables. Compared to our previous work, the proposed method enables models to work well in the time domain providing good accuracy in challenging modeling applications. Two parametric modeling examples of spiral inductors and interdigital capacitors, and their application in both time and frequency domain simulations of a power amplifier are examined to demonstrate the validity of the proposed technique. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE , 2013.

비만 중년여성의 12주간 운동프로그램 참여가 심박 변이도에 미치는 영향

Obesity is associated with an increased risk of cardiac complications that may be due to abnormal cardiovascular autonomic function reflected by reduced heart rate variability. We investigated the effect of a 12-wk exercise program on heart rate variability in middle-aged obese women. Ten middle-aged obese female volunteers with age 56.2±9.29y, % body fat 35.5±2.72% and BMI 27.1±2.8㎏/㎡. The training period was 12-wk, including 5~6 sessions/wk at an intensity of 40~70% of heart rate reserve(HRR), lasting for 60min/session. Measures of heart rate variability, obtained from both time-and frequency domain analysis of 5min ECG recording were as follows: mean RR interval and its standard deviation(SDNN), the mean square successive differences(rMMSSD), the low and high frequency components which were calculated as normalized units and their ratio(LF/HF). After the exercise program, body mass index and % body fat decreased to 4.8% and 5.5% respectively, which was accompanied by decrease in resting heart rate. Exercise training increased rMSSD by 54%, HFnu by 6.3% and decreased LFnu by 5.7%, LF/HF ratio by 12% significantly. The 12-wk exercise program led to changes in HRV indicative of an improvement in cardiac autonomic modulation in middle-aged women with obesity.

Joint backoff control in time and frequency for multichannel wireless systems and its Markov model for analysis

A new joint random access scheme is proposed to enable effectiveuplink access when users are partially aware of channel conditionsin multichannel wireless systems. The proposed scheme mitigatespacket collisions with joint backoff control in the time andfrequency domains, cooperating with a sensing method that exploitsthe channel conditions. The performance analysis of the joint accessscheme is facilitated by a Markov model that provides a closed-formthroughput expression. Simulation results show that this channelaccess scheme, working together with a simple sensing method, offerssignificant improvements to system throughput.

A Consistency Test of Thickness and Loading Noise Codes Using Ffowcs Williams and Hawkings Equation

The thickness noise predicted by the Ffowcs Williams and Hawkings (FW&H) equation depends on the normal velocity vn which is very sensitive to the meshing size. Isom showed that in far field a monopolar source is equivalent to a dipolar source induced by a uniform distribution of the load on the entire moving surface. The main objective of this paper is to determine a specific expression of Isom′s thickness noise in time and frequency domains for subsonic fans. The scope of the proposed expression of Isom′s thickness noise is to define a benchmark test of consistency for thickness and loading noise codes in both time and frequency domains for subsonic fans when using the free field solution of FW&H′s equation.

Time-resolved magnetization dynamics of cross-tie domain walls in permalloymicrostructures

We report on a picosecond time-resolved x-ray magnetic circular dichroic-photoelectronemission microscopy study of the evolution of the magnetization components of amicrostructured permalloy platelet comprising three cross-tie domain walls. A laser-excitedphotoswitch has been used to apply a triangular 80 Oe, 160 ps magnetic pulse.Micromagnetic calculations agree well with the experimental results, both in time andfrequency, illustrating the large angle precession in the magnetic domains withmagnetization perpendicular to the applied pulse, and showing how the magneticvortices revert their core magnetization while the antivortices remain unaffected.