Dynamic Spectral Characteristics Research Articles

Hybrid spectrum sensing enhancement for cognitive radio in 6G radio system

This article highlights the potential advantages of the proposed hybrid algorithm for 6G. The algorithm's adaptability addresses the dynamic spectral characteristics of 6G environments, enabling seamless transition between different spectral conditions. The hybrid approach holds promise for enhancing spectrum utilization, reducing interference, and optimizing overall communication system performance. As 6G technology evolves, the integration of Energy Detection and Cyclostationary Spectrum Sensing through the hybrid algorithm offers a glimpse into innovative techniques that can shape the future of wireless communication, unlocking the potential for enhanced connectivity, efficiency, and user experience. Several parameters such as Probability of detection (Pd), Probability of false alarm (pfa), Biter error rate (BER) and Power spectral density (PSD) are compared and analysed with the conventional spectrum sensing algorithms. It is seen that the proposed hybrid algorithms obtained a substantial detection performance at the low Signal to noise ratio (SNR).

Study on the Dynamic Stability and Spectral Characteristics of a Toppling Dangerous Rock Mass under Seismic Excitation

To evaluate the dynamic stability of dangerous rock masses under seismic excitation more reasonably, a mass viscoelasticity model was adopted to simulate the two main controlling surfaces of a toppling dangerous rock mass. Based on the principles of structural dynamics, a dynamic response analysis model and motion equations were established for toppling dangerous rock masses. The Newmark-β method was utilized to establish a calculation method for the dynamic stability coefficient of a toppling dangerous rock mass. This method was applied to the WY2 dangerous rock mass developed in a steep cliff zone in Luoyi Village, and the dynamic stability coefficient time history was calculated. Subsequently, the acceleration response signals of the dangerous rock mass in different directions were analyzed using wavelet packet transform. The results show that the sum of the energy proportions of the first to third frequency bands in the n1 and s2 directions exceeded 95%. This suggests that the n1 and s2 directions of the WY2 dangerous rock mass suffered the initial damage under bidirectional seismic actions. Finally, the marginal spectra variations of the acceleration response signals in different directions were analyzed based on the HHT. The results show that the seismic energy in the n1 and s2 directions of the dangerous rock mass was found to be the most significant under seismic loading, indicating that the rock mass experienced the most severe damage along these two directions. This reveals that the failure mode of the dangerous rock mass is inclined toppling, consistent with the results of wavelet packet analysis.

An underwater sound event detection algorithm based on Temporal Graph Convolutional Network

Accurate underwater sound event detection (SED) and real-time underwater situation awareness plays an important role in intelligent sonar system. However, little research on underwater SED has been done because underwater acoustics have very complex and dynamic spectral and temporal characteristics which make underwater SED difficult to solve. The goal of SED is to recognize type and time of the input audio signal and most of SED research have been focused on airborne sound so far. To address underwater SED problem, we adopt temporal graph convolutional network (T-GCN), which is originally designed for traffic prediction and is composed of GCN and gated recurrent unit (GRU) To capture spectral and temporal information simultaneously, the GCN is used to learn topological structures to capture spectral correlation and the GRU is used to learn changes of input sound to capture temporal correlation. The proposed model utilizes sound spectrogram and its annotation with temporal information as input and then the GCN and GRU of the model is employed to solve underwater SED problem. Experiments using urban SED dataset and underwater sound dataset, demonstrate that our proposed model expresses connection of spectral and temporal information effectively and shows reliable underwater SED performance accordingly.

Modeling of dynamic and spectral viscoelastic characteristics of composite materials

When designing products made of composite materials intended for use in difficult conditions of inhomogeneous deformations and temperatures, it is important to take into account viscoelastic, including spectral and dynamic, properties of the binder and fillers. The article considers dynamic characteristics (complex modulus, complex malleability, their real and imaginary parts, loss angle tangent) and spectral characteristics of relaxation and creep and their dependence on each other. The abovementioned characteristics were found for all known types of creep kernel and relaxation kernel. To find the spectral characteristics, one of the numerical methods of reversing the Laplace transformation was used - the method of quadrature formulas. Algorithms and computer programs have been compiled to implement this method.

Static and dynamic spectral characteristics of Swedish voiceless fricatives.

Descriptions of the acoustic characteristics of Swedish voiceless fricatives are scarce and are limited to static measures derived from the speech of a small number of speakers. The current study provides an updated acoustic description of the static (spectral, temporal, and intensity) characteristics of word-initial voiceless fricatives in Central Standard Swedish. In addition, temporal variation of spectral centre of gravity is modelled using a generalized additive mixed model. Results show that fricatives were differentiated in terms of spectral properties, duration, and intensity level, such that sibilant fricatives were generally longer and more intense than non-sibilant fricatives. Spectral centre of gravity differentiated between all places of articulation apart from labio-dental /f/. Gender differences were found for centre of gravity in /s/ but overall, sex/gender differences were small. Dynamic analyses revealed differences in curvature as well as overall level of spectral centre of gravity across the duration of the fricative, associated with place of articulation and mediated by vowel context, fricative duration, and speaker specific patterns. The results from the present study are valuable for future cross-linguistic research, and as reference for investigations concerning children's acquisition of Swedish voiceless fricatives.

A novel forecasting method of flutter critical wind speed for the 15 MW wind turbine blade based on aeroelastic wind tunnel test

Flutter is one of the primary challenge that has to be overcome for the development of super-large wind turbine blade. Although the vibration wind tunnel test based on an aeroelastic scale model is the most effective solution, similarity ratio and measuring accuracy of the model cannot be solved accurately by traditional methods. In this study, a novel aerodynamic-stiffness mapping integrated three-dimensional complete aeroelastic scale model design method of super-long flexible blades based on the principle of equivalent stiffness of main beam was proposed for the first time. Later, synchronous full-wind angle wind tunnel tests of vibration and force measurement were carried out using the high-speed photography technology and a high-frequency six-component balance. The nonlinear dynamic response spectral characteristics of NREL-15MW super-long flexible blades were discussed systematically. A comparative analysis of flutter performances and critical instability state of wind turbine blades based on blade tip deflection and blade root reaction force was carried out, which proved the feasibility of forecasting flutter performances according to blade root reaction force. Finally, the blade root reaction force method for flutter instability forecasting of super-long flexible blades was put forward. Results show that the proposed aeroelastic scale model design and experimental method can simulate dynamic performances and flutter behaviors of wind turbine blades accurately and effectively. In the test, it finds that the super-long flexible blades flutter in pitch angle ranges of 93°–96° and 284°–287°. In the flutter ranges, the flutter critical wind speed decreases firstly and then increases with the increase of pitch angle, reaching the valley (5.4 m/s) at 94°. The blade root reaction force and blade tip deflection have consistent divergence and strong correlation. It is suggested that the wind turbine blade enters into the flutter critical state when the flutter index of blade root reaction force is δ ≥ 2%.

Effect of leaching time on phytotoxicity of dissolved organic matter derived from black carbon based on spectroscopy

Black carbon (BC) exports huge amounts of its derived DOM from terrestrial ecosystems annually through a variety of ways (i.e., erosion or runoff migration). The pyrolytic feedstock type and temperature resulted in DOM derived from highly condensed aromatic and non-aromatic BC. However, the behaviors of low aromatic BC-derived DOM at diverse leaching time are poorly understood. In this work, low aromatic BCs were prepared by pyrolysis corn straws at 250 °C, 350 °C and 450 °C. Extraction experiments for four leaching time (6 h, 10 h, 15 h and 21 h) were set up to simulate BC-derived DOM generative process in nature. The phytotoxicity of BC-derived DOM was evaluated via germination index (GI). Spectral characteristics were discussed to analyze the phytotoxicity variations of fluorescence components composition at different time, including the excitation-emission matrix-parallel factor, two-dimensional correlation spectra and Fourier transform infrared spectroscopy. The results suggested that low aromatic BC-derived DOM might contain aromatic phenolic compounds. A longer time contributed to accumulate the complex, hard-to-use organic matters, leading to lower GI. These results would supplement the dynamic spectral characteristics of low aromatic BC-derived DOM and its environmental risks during the leaching process.

Low-power swept-source Raman spectroscopy.

'Molecular fingerprinting' with Raman spectroscopy can address important problems-from ensuring our food safety, detecting dangerous substances, to supporting disease diagnosis and management. However, the broad adoption of Raman spectroscopy demands low-cost, portable instruments that are sensitive and use lasers that are safe for human eye and skin. This is currently not possible with existing Raman spectroscopy approaches. Portability has been achieved with dispersive Raman spectrometers, however, fundamental entropic limits to light collection both limits sensitivity and demands high-power lasers and cooled expensive detectors. Here, we demonstrate a swept-source Raman spectrometer that improves light collection efficiency by up to 1000× compared to portable dispersive spectrometers. We demonstrate high detection sensitivity with only 1.5 mW average excitation power and an uncooled amplified silicon photodiode. The low optical power requirement allowed us to utilize miniature chip-scale MEMS-tunable lasers with close to eye-safe optical powers for excitation. We characterize the dynamic range and spectral characteristics of this Raman spectrometer in detail, and use it for fingerprinting of different molecular species consumed everyday including analgesic tablets, nutrients in vegetables, and contaminated alcohol. By moving the complexity of Raman spectroscopy from bulky spectrometers to chip-scale light sources, and by replacing expensive cooled detectors with low-cost uncooled alternatives, this swept-source Raman spectroscopy technique could make molecular fingerprinting more accessible.

STUDY ON THE SPECTRUM CHARACTERISTICS OF VORTEX-INDUCED VIBRATION OF THREE TANDEM CIRCULAR CYLINDERS

The numerical computation of vortex-induced vibration of three circular cylinders in a tandem arrangement with two degrees of freedom has been carried out. The effects of Reynolds number, natural frequency ratio and reduced velocity on the dynamic response and spectral characteristics of three tandem cylinders were analyzed. The results indicate that the Reynolds number and natural frequency ratio have little influence on the amplitude and fluid force coefficient of the upstream cylinder. The frequency locked region of the midstream cylinder increases with the increasing of Reynolds number. The dynamic response of the midstream cylinder is greatly affected by the wake of the upstream cylinder, whereas the effect of natural frequency ratio is small. Meanwhile, when the reduced velocity is small, Reynolds number and natural frequency ratio have great influence on the fluid force coefficient. In addition, the amplitude and the fluid force coefficient of the downstream cylinder are greatly affected by Reynolds number and natural frequency ratio. Reynolds number, natural frequency ratio and reduced velocity have great influence on the main peak amplitude, spectrum component and fluctuation of fluid force coefficients PSD curve. The fluctuation of the PSD curve becomes intense, giving rise to the movement trajectory of cylinder from 8 shape to irregular shape. As natural frequency ratio increases to 2.0, the P$+$S mode is found in the wake of the upstream cylinder, which leads to the occurrence of asymmetric motion, and the equality of main peaks of the PSD curve of the lift and drag coefficients. Finally, the variation of average power value of excitation load with reduced velocity is similar to that of corresponding structural dynamic response. In the same reduced velocity range, the strength of structural vibration response is directly proportional to the average power value of displacement. When analyzing the power spectral density of lift coefficient in different intervals, the vibration frequency ratio has more influence on the structural vibration response.

Dynamic spectral characteristics of defective sounds pronunciation in students with minimal dysarthric disorders

The article is devoted to the analysis of the spectrographic characteristics of defective sounds pronunciation in children with minimal dysarthric disorders (mild dysarthria). These characteristics were obtained in the process of an experimental-phonetic study. It involved the study of the nature of changes that occur during the transition from one sound to another and also during the pronunciation of a single sound. The article presents the results of the experiment carried out on the basis of a qualitative analysis of dynamic spectrograms of syllables; describes the most permanent signs characterizing the defective sounds pronunciation in syllables of various structures (open, closed). The nature of the mutual influences of sounds in various structures of syllables is revealed. Comparative data were obtained for the acoustic (formant) proximity of various variants of defective pronunciation to the sound standard in children with minimal dysarthric disorders. The contextual phonetic influences at the level of syllables are determined, taking into account the acoustic characteristics of sounds and their defective variants.

Spectral Analysis of the Dynamic Behavior of a Welding Arc During Pulsed Gas Metal Arc Welding of AA5083 Aluminum Alloy With ER5183 Wire

The dynamic behavior of an arc plasma involves the complex heat and mass transfer process in the arc welding process, especially for pulsed gas metal arc welding (P-GMAW). The spectral diagnostics of the arc plasma is essential to both the validation of simulation results and the monitoring and control of the arc welding process. In this article, we studied the dynamic behavior and spatial spectral characteristics of the welding arc during the pulsed gas metal arc welding of the AA5083 aluminum alloy with an ER5183 wire using a high-speed camera and spectrometer. Based on the acquired spectra at different time points of the pulse, we calculated the plasma characteristics using the spectral lines emitted from the shielding gas and the metal vapor. The variation and spectral diagnosis of the arc indicated that the bright region was mainly caused by radiation from the metal vapor, which easily increased at the peak current. The measured arc temperature and electron density were elevated along with the welding current. Moreover, the ratio of metal vapor in the arc plasma also increased due to strengthened evaporation from the electrode. Along the horizontal axis, the arc temperature increased and reached a maximum in the central part of the arc. There was a potential local minimum near the electrode as the current increased. The drop of temperature near the electrode was mainly caused by the rapid evaporation and cooling effects of metal vapor.

Asymmetric discrimination of nonspeech tonal analogues of vowels.

Directional asymmetries reveal a universal bias in vowel perception favoring extreme vocalic articulations, which lead to acoustic vowel signals with dynamic formant trajectories and well-defined spectral prominences because of the convergence of adjacent formants. The present experiments investigated whether this bias reflects speech-specific processes or general properties of spectral processing in the auditory system. Toward this end, we examined whether analogous asymmetries in perception arise with nonspeech tonal analogues that approximate some of the dynamic and static spectral characteristics of naturally produced /u/ vowels executed with more versus less extreme lip gestures. We found a qualitatively similar but weaker directional effect with 2-component tones varying in both the dynamic changes and proximity of their spectral energies. In subsequent experiments, we pinned down the phenomenon using tones that varied in 1 or both of these 2 acoustic characteristics. We found comparable asymmetries with tones that differed exclusively in their spectral dynamics, and no asymmetries with tones that differed exclusively in their spectral proximity or both spectral features. We interpret these findings as evidence that dynamic spectral changes are a critical cue for eliciting asymmetries in nonspeech tone perception, but that the potential contribution of general auditory processes to asymmetries in vowel perception is limited. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Dynamic Response Analysis for NW Planetary Gear Transmission Used in Electric Wheel Hub

Taking the NW planetary gear transmission of an electric wheel hub as the research object, the mesh model was developed to calculate the mesh parameters using Masta. Then the lump parameter method was used to establish the dynamic model of the NW planetary transmission system considering the time-varying mesh stiffness, transmission error and bearing stiffness. The impacts of the torque load on the dynamic characteristics including the dynamic mesh force, center trajectory, offsets and load sharing coefficients were investigated. Results show that the dynamic mesh force waveform and spectral characteristics of each planetary gear at high and low speeds under the rated and maximum torque load are almost identical. Compared to the peak response at speed 485 rpm and 1770 rpm, both the magnitude and location of the third response at relative high speed about 4300 rpm are increased due to the load increasing. The mean and fluctuation range of the offsets in the radial direction are both larger than the tangential direction. As the load increases, the mean value of the radial offset increases and the magnitude decreases significantly. The mean value of the tangential offset decreases significantly, but the magnitude increases first and then decreases. The load sharing characteristics of the low-speed stage of the NW planetary gear is better than the first stage. With the increase of the load, the load sharing performance of a two-stage planetary transmission gets better and the difference in load sharing between the high-speed and low-speed stages also decreases.

Dynamic spectral characteristics of high-resolution simulated equatorial plasma bubbles

Manifestations of severe nighttime equatorial ionospheric disturbances have been observed for decades. It is generally accepted that the phenomena are caused by large depletions, referred to as equatorial plasma bubbles (EPBs), which are initiated on the rising unstable bottom side of the nighttime F layer. Physics-based simulations have enhanced our understanding of the EPB phenomenon. However, until very recently, stochastic structure smaller than ∼ 10 km was not well resolved. Recent high-resolution EPB simulations have extended the resolution to hundreds of meters, which provides a unique opportunity to characterize intermediate-scale EPB structure.This paper presents a summary analysis of simulated high-resolution intermediate-scale EPB structure. Estimation of altitude-dependent power law spectral density function parameters provides an altitude versus time history of the intermediate-scale structure development. Local structure onset is associated with successive bifurcation of rising EPBs. Developed structure characterized by a two-component power law spectral density function ultimately subtends several hundred kilometers in altitude.Two-component inverse power-law structure was first observed in early in situ rocket measurements. It has been observed in diagnostic measurements of beacon-satellite and GPS scintillation data as well as in situ measurements from Atmospheric Explorer and C/NOFS satellites. The EPB simulation data fully support the reported EPB diagnostics as well as a correlation between the turbulent strength and the large-scale spectral index parameter estimates. However, recent analyses have shown that the correlation is an intrinsic property of power-law parameter estimation.

The dynamics of voiceless sibilant fricative production in children between 7 and 13 years old: An ultrasound and acoustic study.

This study reports on dynamic tongue shape and spectral characteristics of sibilant fricatives /s/ and /ʃ/ in Scottish English speaking children aged between 7 and 13 years old. The sequences /əCa/ and /əCi/ were produced by 40 children, with ten participants in each age group, and two-year intervals between successive groups. Productions of the same sequences by ten adults were used for comparison with the children's data. Quantitative dynamic analyses were carried out on spectral information and on ultrasound imaging data on tongue shape. All age groups differentiated between the two consonants in the fricative centroid and in tongue shape. Vowel-on-consonant effects showed consonant-specific patterns across age groups without a consistent increase or decrease in the extent of coarticulation with increasing age. The extent of discriminability between the two fricatives increased with age on both acoustic and articulatory measures. Younger speakers were generally more variable than older speakers. Complementary findings from the centroid and tongue shape measures suggest that age-related differences are due to the ongoing maturation of controlling the tongue in coordination with other articulators, particularly the jaw, throughout childhood.

Photo-bleaching mechanism of the BAC-Si in bismuth/erbium co-doped optical fibers.

Photo-bleaching of the silica-related bismuth active center (BAC-Si) in bismuth/erbium co-doped optical fibers is investigated. By analyzing dynamic spectral characteristics of BAC-Si, the photo-bleaching of the BAC-Si is found to be linked to the escape of an excited electron from the bismuth site in the BAC-Si. This mechanism of BAC-Si bleaching linked to an escaping excited electron is further confirmed with both photo-bleaching experiments by different laser pump wavelengths and a potential energy model describing the loss of an excited electron. Additionally, the temperature effect on the photo-bleaching, which is in good agreement with the above findings, is observed and discussed.

서울 방언 단모음의 소리 변화와 음향 단서 연구: 단일지점 포먼트와 궤적 양상

While acoustic studies in the past decade documented a raised /o/ by showing their lowered first formants (F1) almost overlapped with those of high back vowel /u/, no consensus has been made in terms of how this /o/-raising affects the vowels as a system in Seoul Korean. The current study aimed to investigate the age- and gender-related differences of the relative distance among the vowels to better understand the influence of this on-going sound change on the vowel system. We measured the static and dynamic spectral characteristics (F1 and F2) of the seven Korean monophthong vowels /e a ʌ o u ɨ i/ in the spontaneous speech of Seoul Corpus, and depicted the patterns of 30 individual speakers (10 speakers in each group of teens, 20s and 40s) as a function of age and gender. The static spectral examination showed low F1 values of /o/ in the spontaneous speech corpus confirming the vowel /o/ raising, and also revealed greater F2 values of /u, ɨ/ suggesting their anterior articulations. The tendencies were stronger when the speakers were younger and female. The spectral trajectories further showed that the F1 and F2 between /o/ and /u/ were differentiated throughout the vowel mid-point although the trajectories gradually merged near the vowel mid point in the older male speakers' productions. The acoustic evidence of contrast among /o, u, ɨ/ supports that the raised /o/ is not indicative of a merger with /u/ but rather implying a chain-like vowel shift in the Seoul Korean.

Dynamic spectral characteristics measurement of DFB interband cascade laser under injection current tuning

The dynamic spectral properties of semiconductor lasers during its tuning are very important for frequency modulation-based applications. The spectral properties of a distributed feedback (DFB) interband cascade laser (ICL) under injection current tuning (i.e., slope efficiency, dynamic tuning rate, and instantaneous linewidth) were measured by using short delayed self-heterodyne interferometry combined with time-frequency analysis of the interferometric signal. The relations of these spectral characteristics with the injection current, tuning frequency, and operating temperature of the laser were investigated as well. The dynamic tuning rate of the laser varies from 0.07 nm/mA to 0.16 nm/mA depending on the injection current and tuning frequency, which is considerably below the static tuning rate 0.20 nm/mA. The laser instantaneous linewidth increases within 360 kHz to 760 kHz as the injection current increases or the tuning frequency increases. Unexpectedly, both the dynamic tuning rate and linewidth seem not to be related to the operating temperature of the laser. These results will be very useful for understanding the spectral properties and optimizing the frequency modulation of DFB-ICLs.

Acoustic characteristics of clearly spoken English tense and lax vowels.

Clearly produced vowels exhibit longer duration and more extreme spectral properties than plain, conversational vowels. These features also characterize tense relative to lax vowels. This study explored the interaction of clear-speech and tensity effects by comparing clear and plain productions of three English tense-lax vowel pairs (/i-ɪ/, /ɑ-ʌ/, /u-ʊ/ in /kVd/ words). Both temporal and spectral acoustic features were examined, including vowel duration, vowel-to-word duration ratio, formant frequency, and dynamic spectral characteristics. Results revealed that the tense-lax vowel difference was generally enhanced in clear relative to plain speech, but clear-speech modifications for tense and lax vowels showed a trade-off in the use of temporal and spectral cues. While plain-to-clear vowel lengthening was greater for tense than lax vowels, clear-speech modifications in spectral change were larger for lax than tense vowels. Moreover, peripheral tense vowels showed more consistent clear-speech modifications in the temporal than spectral domain. Presumably, articulatory constraints limit the spectral variation of these extreme vowels, so clear-speech modifications resort to temporal features and reserve the primary spectral features for tensity contrasts. These findings suggest that clear-speech and tensity interactions involve compensatory modifications in different acoustic domains.

Method of images segmentation by dynamic spectral characteristics

In considered method we use basic principles of biometrics and bioradiolocation for solution of the problem of images segmentation. Using dynamic spectral characteristics, obtained by means of wavelet spectrum we extract biometric indicator in form of signal of brightness pixels modification at the face skin part, specified by heartbeat. It is proposed to use quasi-matched wavelet filters for efficient selection of human heartbeat signal and it is shown the possibility of its frequency measurement practically at real-time mode. Obtained results can be used for many medical applications, security systems, object identification, etc.