Frequency Overlap Research Articles

Frequency of clinical signs in patients with Cushing's syndrome and mild autonomous cortisol secretion: overlap is common.

Cushing's syndrome (CS) can be difficult to diagnose. A timely diagnosis, however, is the cornerstone for targeted treatment, to reduce morbidity and mortality. One reason for the difficulties to identify early on patients with CS might be the presence of a mild phenotype. The aim of the study was to classify the phenotypic landscape of CS. We studied patients with overt CS and mild autonomous cortisol secretion (MACS). The study was part of the German Cushing's registry. Patients were prospectively included at time of diagnosis and the number of comorbidities and clinical signs and symptoms were assessed in a standardized fashion. One hundred twenty-nine patients with CS (pituitary CS, n = 85, adrenal CS, n = 32, ectopic CS, n = 12, respectively) and 48 patients with MACS were included. Patients with clinical signs and/or comorbidities typical for CS and at least 2 pathological screening tests were classified as having CS. Patients with a 1 mg low-dose-dexamethasone-suppression test above 1.8 µg/dL without being clinically overt CS were classified as having MACS. On average, patients with CS had 2 comorbidities (range 1-3) at time of diagnosis (pituitary CS: 2 [1-3], adrenal CS: 3 [2-4], ectopic CS: 3 [2-4]). Patients with MACS, however, had 3 comorbidities (range 2-3). Hypertension was the most common comorbidity in all subtypes of CS (78%-92%) and in patients with MACS (87%). Of a total of 11 clinical signs, patients with CS had on average 5 with 28% of patients having between 0 and 3 clinical signs, 50% 4-7 signs, and 22% more than 7 clinical signs. Patients with MACS had on average 2 clinical signs (range 1-3) at time of diagnosis. The phenotypic landscape of CS is quite variable. The frequency of comorbidities is similar between patients with CS and MACS. A relevant number of patients with overt CS have just a few clinical signs. There is also an overlap in frequency of symptoms and clinical signs between patients with CS and MACS. According to the current guidelines, 96% of our patients with MACS fall into the category "consideration of adrenalectomy". This should be kept in mind when making treatment decisions in the latter group of patients.

Fault signature extraction of rolling bearings under variable speed via time–frequency overlap group sparse representation

The high-fidelity extraction of the nonperiodic fault transients of rolling bearings under variable speed is of significant importance, while still a challenge for early-stage fault diagnosis of major equipment such as aero engines and wind turbines. A method termed continuous symmetric Laplace wavelet transform (CSLWT) enhanced time–frequency overlap group sparse (OGS) representation is proposed in this paper. A symmetric Laplace mother wavelet function is proposed which could satisfy the admissibility condition of wavelet decomposition and reconstruction, upon which the CSLWT is fabricated and adopted as the sparse representation dictionary to match the nonperiodic fault transients. Since the decomposition coefficients of nonperiodic fault impulses via the CSLWT exhibit group sparsity on the time–frequency plane with unknown intervals, the time–frequency OGS model is adopted and then solved for extraction of the nonperiodic fault transients. Moreover, a data driven, multi-objective optimization strategy is presented for determining the hyper-parameters of the sparse model. The correlated kurtosis of angular envelope signal (CK-AE) and harmonic-to-noise energy ratio of the order spectrum (HNR-OS) are introduced as the optimization objectives, and the Pareto front is solved based on the NSGA-II algorithm, upon which the acceptable solutions set is chosen from the Pareto front, and the proper hyper-parameters are further determined via proposed normalized solutions distance density sorting of the acceptable solutions set. The performance of the proposed method is validated via processing both simulated and experimental vibration signals, as well as compared with some tradition fault diagnosis methods.

Interpreting the latent space of a Convolutional Variational Autoencoder for semi-automated eye blink artefact detection in EEG signals

Electroencephalography (EEG) allows the investigation of brain activity. However, neural signals often contain artefacts, hindering signal analysis. For example, eye-blink artefacts are particularly challenging due to their frequency overlap with neural signals. Artificial intelligence, particularly Variational Autoencoders (VAE), has shown promise in EEG artefact removal. This research explores the design and application of Convolutional VAEs for automatically detecting and removing eye blinks in EEG signals. The latent space of CVAE, trained on EEG topographic maps, is used to identify latent components that are selective for eye blinks. Receiver Operating Characteristic (ROC) curves and Area Under the Curve (AUC) are employed to evaluate the discriminative performance of each latent component. The most discriminative component, determined by the highest AUC, is modified to eliminate eye blinks. The evaluation of artefact removal involves visual inspection and Pearson correlation index assessment of the original EEG signal and the reconstructed clean version, focusing on the Fp1 and Fp2 channels most affected by eye-blink artefacts. Results indicate that the proposed method effectively removes eye blinks without significant loss of information related to the neural signal, demonstrating Pearson correlation values around 0.60 for each subject. The contribution to the knowledge offered by this research study is the design and application of a novel offline pipeline for automatically detecting and removing eye blinks from multi-variate EEG signals without human intervention.

A 0.055 mm2 Total Area Triple-Loop Wideband Fractional-N All-Digital Phase-Locked Loop Architecture for 1.9–6.1 GHz Frequency Tuning

This paper presents a wideband fractional-N all-digital phase-locked loop (WBPLL) architecture featuring a triple-loop configuration capable of tuning frequencies from 1.9 to 6.1 GHz. The first and second loops, automatic frequency control (AFC) and counter-assisted phase-locked loop (CAPLL), respectively, perform coarse locking, while the third loop employs a digital sub-sampling architecture without a frequency divider for fine locking. In this third loop, fractional-N frequency synthesis is achieved using a delta-sigma modulator (DSM) and digital-to-time converter (DTC). To minimize area, digital modules such as counters, comparators, and differentiators used in the AFC and CAPLL loops are reused. Furthermore, a moving average filter (MAF) is employed to reduce the frequency overlap ratio of the digitally controlled oscillator (DCO) between the second and third loops, ensuring stable loop switching. The total power consumption of the WBPLL varies with the frequency range, consuming between 8.8 mW at the WBPLL minimum output frequency of 1.9 GHz and 12.8 mW at the WBPLL maximum output frequency of 6.1 GHz, all at a 1.0 V supply. Implemented in a 28 nm CMOS process, the WBPLL occupies an area of 0.055 mm2.

Frequency importance functions in simulated bimodal cochlear-implant users with spectral holes.

Frequency importance functions (FIFs) for simulated bimodal hearing were derived using sentence perception scores measured in quiet and noise. Acoustic hearing was simulated using low-pass filtering. Electric hearing was simulated using a six-channel vocoder with three input frequency ranges, resulting in overlap, meet, and gap maps, relative to the acoustic cutoff frequency. Spectral holes present in the speech spectra were created within electric stimulation by setting amplitude(s) of channels to zero. FIFs were significantly different between frequency maps. In quiet, the three FIFs were similar with gradually increasing weights with channels 5 and 6 compared to the first three channels. However, the most and least weighted channels slightly varied depending on the maps. In noise, the patterns of the three FIFs were similar to those in quiet, with steeper increasing weights with channels 5 and 6 compared to the first four channels. Thus, channels 5 and 6 contributed to speech perception the most, while channels 1 and 2 contributed the least, regardless of frequency maps. Results suggest that the contribution of cochlear implant frequency bands for bimodal speech perception depends on the degree of frequency overlap between acoustic and electric stimulation and if noise is absent or present.

Modeling of free vibrations and resonant frequencies of simply-supported submerged horizontal plate.

A theoretical approach was applied to study the vibration of simple-supported submerged horizontal plate. The derived analytical solution was used to determine natural frequencies for a horizontal plate vibrating in fluid. The investigations were conducted for a very wide range of material density and elasticity modulus covering all materials used in engineering practice. Analysis shows that plate vibration frequency decreases with increasing plate width and draft, and decreases with decreasing plate thickness. Moreover, the results show that a substantial effect on vibration of submerged plate has mass of water above plate. The results also show that plate vibration frequency decreases with increasing plate material density and decreases with decreasing elasticity modulus. The dominant factors affecting the vibration of the submerged plate are the plate width, the plate thickness, and elasticity modulus. For moderate and low values of elasticity modulus, vibration frequency is becoming lower than frequency of water waves. This is very important because wave frequencies overlap with the natural plate vibration frequencies, which may lead to resonance and failure of a structure. The problem is that the overlap of plate vibration frequencies and wave frequencies occurs for very wide range of wave and plate parameters. Laboratory experiments confirm theoretical results.

Ambient light immunity of a frequency-modulated continuous-wave (FMCW) LiDAR chip.

The interference between a frequency-modulated continuous-wave (FMCW) light detection and ranging (LiDAR) and other LiDARs or sunlight was theorized, considering the spatial overlap, frequency overlap, and intensity ratio. It has been concluded that the interference probability between LiDARs can be lower than a safety standard value for autonomous vehicles when the number of the resolution points of a single LiDAR is increased sufficiently and that the interference with incoherent sunlight does not occur. Due to the coherent detection of FMCW, such ambient light immunity is much better than time-of-flight LiDAR. The dependence of the interference on the wavelength range, sweep bandwidth, and sweep period was also observed experimentally using a silicon (Si) photonics FMCW LiDAR chip incorporating slow-light grating beam scanners. It was shown that the interference can be suppressed by increasing the number of resolution points and changing their common parameters moderately. Regarding the contamination of sunlight, unwanted beam shift due to heating was observed, although it will be suppressed simply by wavelength filtering.

Coupled bunch mode zero correction within the orbit feedback bandwidth

The fast orbit feedback (FOFB) bandwidth for Advanced photon source upgrade (APS-U) will be DC-1 kHz and the synchrotron frequency will be between 100-560 Hz. This frequency overlap places coupled bunch mode 0 (CBM0) induced horizontal orbit motion inside the orbit feedback bandwidth, potentially affecting our ability to achieve beam stability goals. Longitudinal feedback kicker is not strong enough to damp CBM0 oscillations. We developed new beam-based feedback method to suppress CBM0 oscillations with low level RF phase as actuator. It uses existent FOFB framework with no changes to the feedback algorithm. Effectiveness of this method is verified using present APS operations lattice where synchrotron frequency is outside orbit feedback bandwidth. In the present work, low alpha lattice is created to emulate APS-U setting where synchrotron frequency is inside the orbit feedback bandwidth. Experiments with this lattice successfully demonstrated CBM0 correction within orbit feedback bandwidth. Combined operation of orbit feedback and CBM0 correction is stable, and CBM0 oscillations are damped. We achieved better orbit motion suppression and corrector drive efforts are reduced as well.

Interactions Between Slopes of Residual Hearing and Frequency Maps in Simulated Bimodal and Electric-Acoustic Stimulation Hearing.

The aim of this study was to determine the effects of residual hearing slopes and cochlear implant frequency map settings on bimodal and electric-acoustic stimulation (EAS) benefits in speech perception. Adults with normal hearing were recruited for simulated bimodal and EAS hearing. Sentence perception was measured unilaterally and bilaterally. For the acoustic stimulation, three slopes of high-frequency hearing loss were created using low-pass filters with a cutoff frequency of 500 Hz: steep (96 dB/octave), medium (48 dB/octave), and shallow (24 dB/octave). For the electric stimulation, an eight-channel sinewave vocoder was used with an output frequency range (1000-7938 Hz) with three input frequency ranges to create frequency maps, overlap (188-7938 Hz), meet (500-7938 Hz), and gap (750-7938 Hz), relative to the cutoff frequency in the acoustic stimulation. The largest bimodal/EAS benefit occurred with the shallow slope, and the smallest occurred with the steep slope. The effects of the slopes on bimodal/EAS benefit were greatest with the meet or gap map and the least with the overlap map. EAS benefit was greater than bimodal benefit at higher signal-to-noise ratios regardless of frequency map. The results indicate that correlation between bimodal/EAS benefit and residual hearing could potentially improve if slopes were considered. The optimal frequency map differed with different slopes, suggesting that the slopes of residual hearing should be carefully considered in fitting bimodal and EAS hearing. EAS hearing provided greater benefit over bimodal hearing, suggesting that spectrotemporal integration was better within one ear (i.e., EAS) than across ears (i.e., bimodal).

Широкополосный элемент антенной решетки СВЧ диапазона с управляемой поляризацией

There is an increasing interest with domestic satellite communication and broadband access services [1]. An integral part of such systems are ground terminals, the operating frequencies of which includes centimeter and millimeter bands. These circumstances require timely development of client terminal antennas. The article is devoted to the study of a compact Orthomode transducer combined with radiating element of relatively small electrical size (up to ≈ 1 λ), which can be used as part of an antenna array of a terrestrial satellite communication terminal. The proposed solution will make it possible to create arrays with controlled polarization in a wide frequency range. According to the modeling results, the frequency overlap coefficient of 1.4 is achievable, which corresponds to 93% of the standard waveguide frequency range.

An interconnectivity framework for analyzing and demarcating real-time operations across critical infrastructures and over time

Models and modeling of interconnected critical infrastructures are on the rise. A different framework is provided here for analyzing and distinguishing interconnected operations in real time and over time. Our framework treats interconnected operations as the unit and level of analysis rather than as methodologically distinct operations of conceptually separate infrastructures. We focus on interconnectivity configurations, shifts, connected system control variables, and changing performance standards across important shifts. Implications of the conceptual and methodological refocusing are drawn for policy and management. Our framework allows for a new understanding of reliability in relation to interconnectivity management, including the identification of potential errors in assessing and acting upon interconnectivity shifts. These include failing to recognize when changes in communication patterns need to follow from interconnectivity shifts and neglecting the operational importance of improvisations where system control variables (like electricity frequency or water pressure) overlap or are shared. Larger implications for interinfrastructural and societal safety are drawn throughout.

Analysis and design of K-band low-phase-noise differential DCOs implemented in 22 nm FD-SOI for 76–81 GHz automotive radars

This paper presents two K-band low-phase-noise digitally controlled oscillators (DCOs) with a frequency tuning range (FTR) of more than 20% for 76–81 GHz automotive radars. The proposed triple-bank DCO (T-DCO) relies on the medium-tuning and fine-tuning banks to cover the linear chirp band, thus facing the issues of complex frequency calibration and frequency overlap of more than 15% like conventional DCOs. To address these issues, an original dual-bank DCO (D-DCO) is proposed, which solely relies on the large fine-tuning bank to achieve a fine frequency resolution of 2 MHz and a fine-tuning range of 1.94 GHz by employing a customized MOM capacitor of 973 aF. Moreover, both T-DCO and D-DCO are implemented in a 22 nm FD-SOI process, achieving the best-in-class phase noise lower than −110 dBc/Hz over the entire frequency range at 1 MHz frequency offset, while consuming 24 mW from a 1.2 V supply voltage.

Abstract 212: True2 duplex sequencing reveals a diverse landscape of unique somatic mutations beyond the surgical margins of high- and low-grade diffuse gliomas

Abstract Introduction: High- and low-grade diffuse gliomas commonly recur regardless of therapy. Here, we sought to detect and profile molecular evidence of disease in nearby brain tissue absent of tumor by standard-of-care clinical imaging. Methods: Twenty-two patients presenting to the University of Utah with radiographic evidence of a new high- to low-grade intrinsic brain tumor were enrolled after providing written informed consent. Using intraoperative stereotactic guidance, tissue was acquired from bulky tumor (36 samples) and beyond the surgical margins in peritumoral edema (29 samples). All samples underwent somatic mutation discovery using a custom-designed 114 kb panel (115 genes) and True2 duplex sequencing. True2 is a duplex adapter-based technology developed and empirically validated to achieve >95% sensitivity for an allele frequency ≥0.1% at a false positive rate of <1 per 100 kb panel positions. Results: Somatic mutations were detected in all samples regardless of radiographic location. The mean number of mutations was similar between bulky tumor and peritumoral edema (5.6±2.4 vs. 5.1±2.9 mutations/sample, respectively; P=0.48). Although the mean allele frequency of variants was higher in tumor compared to edema (16.0±21.2% vs. 11.2±17.4%, respectively; P=0.017), there was a strong overlap in the allele frequency ranges (tumor: 0.07% to 90.3% vs. edema: 0.10% to 75.6%). Notably, one-third of all the somatic mutations detected had an allele frequency <0.5%. Common diagnostic mutations specific to each tumor type were present in both tumor and edema - TERT promoter mutations in glioblastoma and oligodendroglioma; IDH1/2 mutations in astrocytoma and oligodendroglioma. In edema, mutations associated with glioblastoma but unique to a single sample occurred in TP53, EGFR, PTEN, NF1, ATRX, SCN9A, and MTOR at an allele frequency ranging from 0.10% to 20.22%. The edema of astrocytomas similarly harbored unique mutations in TP53, PTEN, and NF1, but mutations in EGFR, ATRX, SCN9A, and MTOR were absent. In contrast to both glioblastoma and astrocytoma, oligodendrogliomas exhibited a diverse collection of unique CIC and PAFAH1B3 mutations in edema at an allele frequency between 0.13% and 3.63%. Conclusions: The application of True2 technology to conduct a discovery search for very-low frequency somatic mutations found the molecular burden between tumor and adjacent edema to be remarkably similar. Our findings indicate an extensive tumor presence beyond the surgical margins in diffuse gliomas with unique and abundant somatic mutations that may form the foundation of recurrent lesions. Molecular analysis of adjacent tissue identified as radiographically unaffected by bulky tumor to better characterize the mutational landscape of migratory subclones may directly impact personalized medicine for high- and low-grade diffuse glioma patients. Citation Format: Hunter Underhill, Michael Karsy, Christian Davidson, Sabine Hellwig, Samuel Stevenson, Sydney Vincenti, Charlie Dean, Brion Harrison, Eric Goold, Mary Bronner, Howard Colman, Randy Jensen. True2 duplex sequencing reveals a diverse landscape of unique somatic mutations beyond the surgical margins of high- and low-grade diffuse gliomas [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 212.

When birds sing at the same pitch, they avoid singing at the same time

Birds singing in choruses must contend with the possibility of interfering with each other's songs, but not all species will interfere with each other to the same extent due to signal partitioning. Some evidence suggests that singing birds will avoid temporal overlap only in cases where there is overlap in the frequencies their songs occupy, but the extent to which this behaviour varies according to level of frequency overlap is not yet well understood. We investigated the hypothesis that birds will increasingly avoid heterospecific temporal overlap as their frequency overlap increases by testing for a linear correlation between frequency overlap and temporal avoidance across a community of temperate eastern North American birds. We found that there was a significant correlation across the whole community and within 12 of 15 commonly occurring individual species, which supports our hypothesis and adds to the growing body of evidence that birds adjust the timing of their songs in response to frequency overlap.

Intelligent fault diagnosis of planetary gearboxes under time-varying conditions based on dynamic adversarial balance adaptation with multi-label information confusion

Intelligent diagnosis methods based on big data have been extensively applied in the fault diagnosis of rotating equipment such as planetary gearboxes. Most of these methods usually satisfy the condition of independent identically distribution among the training and diagnosis data. However, the data distribution in the actual diagnosis task struggles to satisfy the above conditions due to the lack of fault data, missing label information and the feature differences within different signals, thus increasing the difficulty of cross-condition fault diagnosis in small sample sets. Therefore, we propose a dynamic adversarial balance adaptation method with multi-label information confusion (MLC-DABA) for diagnosing planetary gearbox faults under time-varying conditions. In the signal preprocessing process, we transform the nonstationary timing signals into two-dimensional time-frequency matrices for the feature learning of networks, which avoids the frequency characteristic mess caused by frequency overlap. Moreover, we adopt a balance adaptation algorithm to dynamically evaluate the feature distribution between source and target tasks through the domain labels and category labels, thus establishing a balanced adaptation relationship between the feature distributions of both tasks. This dynamic adversarial training mechanism can tap more domain-invariant feature information to measure the distribution distance among tasks, thus closing the feature differences in different tasks and increasing the generalization of source tasks to the data distribution in target tasks. The proposed method is verified in planetary gearbox experiments. Experimental analysis results indicate that the diagnostic performance of MLC-DABA outperforms other comparison methods in terms of accuracy and training robustness.

Design Approach for Pattern-Reconfigurable Patch Antenna Without Extra Feeding Networks

In this communication, an efficient approach with multiple loading techniques is proposed to design a low profile, single-fed, pattern reconfigurable patch antenna with broadside and dual-beam radiation patterns. Initially, a transmission-line model is developed to theoretically investigate the resonant frequency of a rectangular patch antenna with radiation efficiency ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\eta _{r}$ </tex-math></inline-formula> ) into consideration as well. It is revealed that the frequency overlap in the two states without significantly sacrificing <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\eta _{r}$ </tex-math></inline-formula> can be achieved by properly loading shorting pins and open-ended stubs. Besides, the two center-loaded elements, i.e., a shunt capacitor and a series inductor, are also studied for demonstration of their unique effects on impedance matching for both states or operating modes. Then, a design guideline is summarized based on the theoretical analysis. Following the developed guideline, two examples working at the same operating frequency of 2.45 GHz are designed, fabricated, and tested. Measured gains of 9.6 (8.7) and 5.6 (5.3 dBi) of antenna example A (example B) are obtained for broadside and dual-beam modes, respectively. The measured and simulated results are observed in good agreement, thereby demonstrating the validity of the proposed scheme. The merits of low profile, high gain, and no need of extra feeding networks make the proposed antennas good candidates for modern communication systems.

Corpus callosum involvement in MOG antibody-associated disease in comparison to AQP4-IgG-seropositive neuromyelitis optica spectrum disorder and multiple sclerosis

Background: Data on corpus callosum involvement in myelin oligodendrocyte glycoprotein antibody-associated disease (MOGAD) are limited. Objective: The objective of the study was to compare callosal lesions in MOGAD, multiple sclerosis (MS), and aquaporin-4-IgG positive neuromyelitis optica spectrum disorder (AQP4+NMOSD). Results: Callosal lesion frequency was similar in MOGAD (38/171 (22%)), MS (24/72 (33%)), and AQP4+NMOSD (18/63 (29%)). Clinical phenotypes included encephalopathy (47%) and focal supratentorial (21%) or infratentorial (45%) deficits. None had callosal-disconnection syndromes. Maximal callosal-T2-lesion diameter (median (range)) in millimeter was similar in MOGAD (21 (4–77)) and AQP4+NMOSD (22 (5–49); p = 0.93) but greater than in MS (10.5 (2–64)). Extracallosal extension (21/38 (55%)) and T2-lesion resolution (19/34 (56%)) favored MOGAD. Conclusions: Despite similar frequency and imaging overlap, larger lesions, sagittal midline involvement, and lesion resolution favored MOGAD.

Automated Discourse Analysis Techniques and Implications for Writing Assessment

Analysing writing development as a function of foreign language competence is important in secondary school children because the developmental patterns are strongest at a young age when successful interventions are needed. Although a number of researchers have explored the degree to which specific textual characteristics in EFL students’ essays are associated with high and low ratings by teachers, the extent to which such characteristics are associated with rater-mediated assessment under standard exam conditions remains relatively unexplored. Motivated by the above void in pertinent literature, the overall aim of the present study was to investigate the relationship between specific discourse features present in the writing scripts of EFL learners sitting for the British Council’s APTIS for TEENS exam and the assigned scores during operational scoring by specially trained raters. A total of 800 international EFL students aged 13 to 15 years old took part in the study, and 800 scored written essays on the same task prompt of the pertinent test produced under standard exam conditions were analysed. The results showed statistically significant differences (p ≤ 0.05) between the linguistic features identified in the essays produced by young EFL learners at different levels of language competence. The main text features that were repeatedly found to make a significant contribution to distinguishing scores assigned to texts both within and across levels were word frequency, word abstractness, lexical diversity, lexical and semantic overlap, all of which could be used to obtain a numerical cut-off point between proficiency levels. These findings support the notion that progress in L2 writing is primarily associated with producing more elaborate texts with more sophisticated words, more complex sentence structure and fewer cohesive features as a function of increased language competence. The findings of the study could provide practical guidance to EFL teachers, material developers and test designers as to the kind of linguistic strategies young EFL learners develop as a function of their level of language competence and suggestions to consider when designing EFL classroom curricula, writing skills textbooks and exam papers on written production.

A MLE-based blind signal separation method for time–frequency overlapped signal using neural network

The blind signal separation (BSS) algorithm obtains each original/source signal from the observed signal collected by the receiving antenna or sensor. Objective/loss/cost function and optimization method are two key parts of BSS algorithm. Modifying the objective function and optimization from the perspective of neural network (NN) is a novel concept in BSS domain. L_2 regularization is adopted as a term of maximum likelihood estimation (MLE)-based objective function like in Liu et al. (Sensors 21(3):973, 2021); however, we modified the probability density function (PDF) term of the objective function and used the kernel density estimation method for time–frequency overlapped digital communication signal. Multiple optimizers are studied in this paper, and we figure out the right optimizer for our application scenario. A varies of comparison experiments—whose separation results will be provided in forms of correlation coefficient and performance index—are carried out, which indicate our method can converge quickly and achieve satisfactory separation results with performance index (PI) lower than 0.02 when signal-to-noise ratio (SNR) no less than 10dB. Additionally, it demonstrates performance of our method is better than that of typical separation—FastICA, especially for the lower SNR environment, and it shows that our method is not sensitive to the frequency overlap level (FOL) of the source signal, even FOL as high as 100%; it still can get high-precision separation results with textrm{PI}<0.02.

Research on the identification of asynchronous vibration parameters of rotating blades based on blade tip timing vibration measurement theory

The identification of rotating blade vibration parameters is crucial for diagnosing the health of the blades. While there are many rotating blade vibration measurement techniques, the tip timing vibration theory is currently used by most for non-contact rotating blade vibration measurements, which presents a number of challenges in its practical implementation. However, the traditional bladetip timing vibration measurement method is less involved in the calculation of vibration displacement and vibration data pre-processing and the frequency mixing problem brought on by undersampling is not fully analyzed. The majority of methods to increase measurement accuracy are studied in depth in data post-processing. The accuracy of identifying the spinning blade vibration parameters is lowered, and even identification error arises, as a result of measuring noise interference and the impact of frequency overlap. This work adjusts the calculation of blade tip vibration displacement based on the theory of blade tip timing vibration measurement and applies the Savitzky-Golay noise filtering technique to increase calculation accuracy. To combat the effect of frequency confusion brought on by undersampling and increase the precision of asynchronous vibration parameter detection of spinning blades, the synthetic phase difference spectrum correction method is adopted. In the experiments described in this work, a revolving blade is excited by an electromagnetic exciter to create vibrations at a single frequency. To determine the blade asynchronous vibration characteristics at various rotation speeds, rotating blade asynchronous vibration tests were carried out on a rotor blade table. The outcomes demonstrate that the blade asynchronous vibration parameters can be accurately identified using the parameter identification method, and the maximum vibration frequency identification error is 7.2%, demonstrating the accuracy of the blade asynchronous vibration parameter identification method.