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Artykuły w czasopismach na temat "Impulsive noise due to plasma"
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Oh, Hyungkook, Dongho Seo i Haewoon Nam. "Design of a Test for Detecting the Presence of Impulsive Noise". Sensors 20, nr 24 (12.12.2020): 7135. http://dx.doi.org/10.3390/s20247135.
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This paper proposes a new test method of detecting the presence of impulsive noise based on a complementary cumulative density function (CCDF). Impulsive noise severely degrades performance of communication systems and the conventional Kolmogorov–Smirnov (K–S) test may not perform well, because the test does not consider the characteristics of impulsive noise. In order to detect the presence of impulsive noise reliably, the CCDF of measurement samples is analyzed and compared with the CCDF of additive white Gaussian noise to find the difference between those CCDFs. Due to the nature of heavy-tails in impulsive noise, only the maximum difference may not be sufficient for the accurate detection of impulsive noise. Therefore, the proposed method applies the test hypothesis using the weighted sum of all the differences between those CCDFs. Simulation results justify that the proposed test is more robust and provides lower miss detection probability than the K–S test in the presence of impulsive noise.
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Lee, Sang Kwon, i Jung Soo Lee. "Design of Adaptive Filter for Health Monitoring on a Gearbox". Key Engineering Materials 321-323 (październik 2006): 1237–40. http://dx.doi.org/10.4028/www.scientific.net/kem.321-323.1237.
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Impulsive vibration signals in gearbox are often associated with faults, which lead to due to irregular impacting. Thus these impulsive vibration signals can be used as indicators of machinery faults. However it is often difficult to make objective measurement of impulsive signals because of background noise signals. In order to ease the measurement of impulsive signal embedded in background noise, we enhance the impulsive signals using adaptive signal processing and then analyze them in time and frequency domain by using time-frequency representation. This technique is applied to the diagnosis of faults within laboratory gearbox.
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Dai, Jiang’an, Tianshuang Qiu, Shengyang Luan, Quan Tian i Jiacheng Zhang. "An Improved Toeplitz Approximation Method for Coherent DOA Estimation in Impulsive Noise Environments". Entropy 25, nr 6 (20.06.2023): 960. http://dx.doi.org/10.3390/e25060960.
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Direction of arrival (DOA) estimation is an important research topic in array signal processing and widely applied in practical engineering. However, when signal sources are highly correlated or coherent, conventional subspace-based DOA estimation algorithms will perform poorly due to the rank deficiency in the received data covariance matrix. Moreover, conventional DOA estimation algorithms are usually developed under Gaussian-distributed background noise, which will deteriorate significantly in impulsive noise environments. In this paper, a novel method is presented to estimate the DOA of coherent signals in impulsive noise environments. A novel correntropy-based generalized covariance (CEGC) operator is defined and proof of boundedness is given to ensure the effectiveness of the proposed method in impulsive noise environments. Furthermore, an improved Toeplitz approximation method combined CEGC operator is proposed to estimate the DOA of coherent sources. Compared to other existing algorithms, the proposed method can avoid array aperture loss and perform more effectively, even in cases of intense impulsive noise and low snapshot numbers. Finally, comprehensive Monte-Carlo simulations are performed to verify the superiority of the proposed method under various impulsive noise conditions.
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Karakuş, Oktay, Ercan E. Kuruoğlu i Mustafa A. Altınkaya. "Modelling impulsive noise in indoor powerline communication systems". Signal, Image and Video Processing 14, nr 8 (4.06.2020): 1655–61. http://dx.doi.org/10.1007/s11760-020-01708-1.
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Abstract Powerline communication (PLC) is an emerging technology that has an important role in smart grid systems. Due to making use of existing transmission lines for communication purposes, PLC systems are subject to various noise effects. Among those, the most challenging one is the impulsive noise compared to the background and narrowband noise. In this paper, we present a comparative study on modelling the impulsive noise amplitude in indoor PLC systems by utilising several impulsive distributions. In particular, as candidate distributions, we use the symmetric $$\alpha $$ α -Stable (S$$\alpha $$ α S), generalised Gaussian, Bernoulli Gaussian and Student’s t distribution families as well as the Middleton Class A distribution, which dominates the literature as the impulsive noise model for PLC systems. Real indoor PLC system noise measurements are investigated for the simulation studies, which show that the S$$\alpha $$ α S distribution achieves the best modelling success when compared to the other families in terms of the statistical error criteria, especially for the tail characteristics of the measured data sets.
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Wang, Houyou, Yong Guo i Lidong Yang. "Parameter Estimation of LFM Signals Based on FOTD-CFRFT under Impulsive Noise". Fractal and Fractional 7, nr 11 (15.11.2023): 822. http://dx.doi.org/10.3390/fractalfract7110822.
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Due to the short duration and high amplitude characteristics of impulsive noise, these parameter estimation methods based on Gaussian assumptions are ineffective in the presence of impulsive noise. To address this issue, a LFM signal parameter estimation method is proposed based on FOTD and CFRFT. Firstly, the mathematical expression of FOTD is presented and its tracking performance is verified. Secondly, the tracked signal is subjected to discrete time CFRFT, and a mathematical optimization model for LFM signal parameter estimation is established on the fractional spectrum characteristic. Finally, a correction method for non-standard SαS distributed noise is proposed, and the performance of parameter estimation under both standard and non-standard SαS distributions are analyzed. The simulation results show that this method not only effectively suppresses the impact of impulsive noise on the fractional spectrum of LFM signal, but also has better parameter estimation accuracy and stability in the low GSNR. The proposed method is particularly effective under the measured noise environment, as it successfully suppresses the impact of impulsive noise and achieves high-precision parameter estimation.
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Shafieipour, Mohammad, Heng-Siong Lim i Teong-Chee Chuah. "Decoding of Turbo Codes in Symmetric Alpha-Stable Noise". ISRN Signal Processing 2011 (29.03.2011): 1–7. http://dx.doi.org/10.5402/2011/683972.
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This paper investigates the decoding of turbo codes in impulsive symmetric α-stable (SαS) noise. Due to the nonexistence of a closed-form expression for the probability density function (pdf) of α-stable processes, numerical-based SαS pdf is used to derive branch transition probability (btp) for the maximum a posteriori turbo decoder. Results show that in Gaussian noise, the turbo decoder achieves similar performance using both the conventional and the proposed btps, but in impulsive channels, the turbo decoder with the proposed btp substantially outperforms the turbo decoder utilizing the conventional btp. Results also confirm that the turbo decoder incorporating the proposed btp outperforms the existing Cauchy-based turbo decoder in non-Cauchy impulsive noise, while the two decoders accomplish similar performance in Cauchy noise.
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Tian, Tian, Kunde Yang, Fei-Yun Wu i Ying Zhang. "Channel Estimation for Underwater Acoustic Communications in Impulsive Noise Environments: A Sparse, Robust, and Efficient Alternating Direction Method of Multipliers-Based Approach". Remote Sensing 16, nr 8 (13.04.2024): 1380. http://dx.doi.org/10.3390/rs16081380.
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Channel estimation in Underwater Acoustic Communication (UAC) faces significant challenges due to the non-Gaussian, impulsive noise in ocean environments and the inherent high dimensionality of the estimation task. This paper introduces a robust channel estimation algorithm by solving an l1−l1 optimization problem via the Alternating Direction Method of Multipliers (ADMM), effectively exploiting channel sparsity and addressing impulsive noise outliers. A non-monotone backtracking line search strategy is also developed to improve the convergence behavior. The proposed algorithm is low in complexity and has robust performance. Simulation results show that it exhibits a small performance deterioration of less than 1 dB for Channel Impulse Response (CIR) estimation in impulsive noise environments, nearly matching its performance under Additive White Gaussian Noise (AWGN) conditions. For Delay-Doppler (DD) doubly spread channel estimation, it maintains Bit Error Rate (BER) performance comparable to using ground truth channel information in both AWGN and impulsive noise environments. At-sea experimental validations for channel estimation in Orthogonal Frequency Division Multiplexing (OFDM) systems further underscore the fast convergence speed and high estimation accuracy of the proposed method.
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Enguix, Ivan Felis, Marta Sánchez Egea, Antonio Guerrero González i David Arenas. "Acoustic Characterization of Impulsive Underwater Noise Present in Port Facilities: Practical Case in the Port of Cartagena". Proceedings 4, nr 1 (14.11.2018): 57. http://dx.doi.org/10.3390/ecsa-5-05755.
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The data recording of underwater noise is a key aspect for the prevention and improvement of management systems of maritime spaces. Thus, due to the presence of activities potentially generating impulsive noise, ports deserve special attention. This article describes and shows the results of the spatial monitoring of both the basal noise and impulsive noise sources present in port facilities. A vessel was equipped with a smart digital hydrophone with a working frequency range between 10 and 200 kHz and an RVR (Received Voltage Response) of, approximately, −170 dB @ 1 V/µPa. Coupling the acoustic data together with the GPS coordinates of the vessel, a GIS map with spatiotemporal distribution of the basal sound pressure levels was made, identifying the sources of impulsive noise of interest and its temporal characteristics. This is a preliminary step for the development of future studies on underwater noise pollution and its potential impact on biodiversity in the environment of port facilities, with the maximum guarantees possible.
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Lee, Sang Kwon, Jinhoi Gu i Byung-Og Cho. "Damage Identification of an Automotive Engine Based on Detection of Impact Vibration Using an Adaptive Filter". Key Engineering Materials 306-308 (marzec 2006): 229–34. http://dx.doi.org/10.4028/www.scientific.net/kem.306-308.229.
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In an automotive engine, faults induce impulsive vibrations and thereby degrade engine performance, making it important for an automotive engineer to detect and analyze impulsive vibration signals for fault diagnosis. However, detecting and identifying impulsive signals is often difficult because of interfering signals such as those due to engine firing, harmonics of crankshaft speed and broadband noise components. These interferences hinder early fault detection. To overcome this difficulty we present a two-stage ALEF (Adaptive Line Enhancer Filter) that is capable of enhancing impulsive signals embedded in background noise. This method is used to pre-process signals prior to time-frequency analysis via higher order methods such as the combined higher order time-frequency.
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Dou, Yuzi, i Sen Li. "Kernel Function-Based Ambiguity Function and Its Application on DOA Estimation in Impulsive Noise". Sensors 22, nr 18 (15.09.2022): 6996. http://dx.doi.org/10.3390/s22186996.
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To solve the problem that the traditional ambiguity function cannot well reflect the time-frequency distribution characteristics of linear frequency modulated (LFM) signals due to the presence of impulsive noise, two robust ambiguity functions: correntropy-based ambiguity function (CRAF) and fractional lower order correntropy-based ambiguity function (FLOCRAF) are defined based on the feature that correntropy kernel function can effectively suppress impulsive noise. Then these two robust ambiguity functions are used to estimate the direction of arrival (DOA) of narrowband LFM signal under an impulsive noise environment. Instead of the covariance matrix used in the ESPRIT algorithm by the spatial CRAF matrix and FLOCRAF matrix, the CRAF-ESPRIT and FLOCRAF-ESPRIT algorithms are proposed. Computer simulation results show that compared with the algorithms only using ambiguity function and the algorithms only using the correntropy kernel function-based correlation, the proposed algorithms using ambiguity function based on correntropy kernel function have good performance in terms of probability of resolution and estimation accuracy under various circumstances. Especially, the performance of the FLOCRAF-ESPRIT algorithm is better than the CRAF-ESPRIT algorithm in the environment of low generalized signal-to-noise ratio and strong impulsive noise.
Rozprawy doktorskie na temat "Impulsive noise due to plasma"
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Kazemzadeh, Osgoei Bentolhoda. "Conception d’un système de transmission haut débit dans un canal doublement sélectif : système de TransPod". Electronic Thesis or Diss., Limoges, 2024. http://www.theses.fr/2024LIMO0055.
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Cette thèse explore la modélisation des canaux et la conception de la couche physique pour améliorer les communications à haut débit dans les canaux sans fil à haute mobilité, en se concentrant spécifiquement sur le système TransPod. Le travail commence par une revue complète des canaux sans fil, en se focalisant sur les canaux doublement sélectifs, leurs dégradations, et les techniques de modulation telles que OFDM et OTFS. Nous caractérisons ensuite le canal de transmission du guide TransPod, en examinant à la fois les caractéristiques à grande échelle et à petite échelle, et en traitant le bruit provenant du système de transmission de puissance basé sur le plasma. Un système de communication à double liaison est proposé pour atténuer les déconnexions fréquentes. Nous proposons une nouvelle technique d’estimation de canal basée sur des pilotes pour les systèmes OTFS dans le domaine retard-Doppler, et introduisons une méthode d’estimation du canal Doppler fractionnaire basée sur l’apprentissage automatique utilisant les deep neural networkThis thesis explores channel modeling and physical layer design to enhance high data rate communications in high mobility wireless channels, with a specific focus on the TransPod system. The work begins with a comprehensive review of wireless channels, focusing on doubly selective channels, their impairments, and modulation techniques such as OFDM and OTFS. We then characterize the TransPod guideway transmission channel, examining both large-scale and small-scale characteristics, and addressing noise from the plasma-based power transmission system. A dual-link communication system is proposed to mitigate frequent disconnectivity. We propose a novel sequence-pilot-based channel estimation technique for OTFS systems in delay-Doppler domain and introduce a machine learning-based method for fractional Doppler channel estimation using deep neural network
Części książek na temat "Impulsive noise due to plasma"
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Kazemzadeh, Bentolhoda, Ryan Janzen, Hamid Meghdadi, Vahid Meghdadi i Abbas Bradai. "Modeling of Noise due to a Plasma-Based Contactless Power Transmission System for Ultra-High-Speed Transportation". W Ubiquitous Networking, 149–59. Cham: Springer Nature Switzerland, 2024. http://dx.doi.org/10.1007/978-3-031-62488-9_12.
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Nandedkar, Deepak. "Further Studies on D.C. Noise in Plasma Due to Electron-Ion Collisions". W Recent Advances in Properties of ‘Physics/Electrical Engineering’ Materials, 181–201. Book Publisher International (a part of SCIENCEDOMAIN International), 2022. http://dx.doi.org/10.9734/bpi/mono/978-93-5547-658-6/ch7.
Pełny tekst źródłaStreszczenia konferencji na temat "Impulsive noise due to plasma"
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Zhu, Zheng, i QiJun Zhao. "Numerical Optimization for Rotor Blade-tip Planform with Low HSI Noise Characteristics in Forward Flight". W Vertical Flight Society 71st Annual Forum & Technology Display, 1–9. The Vertical Flight Society, 2015. http://dx.doi.org/10.4050/f-0071-2015-10070.
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Based on CFD/FW-H_pds methods and hybrid optimization technique, an optimization design procedure for rotor planform with low HSI noise characteristics is established. In this solver, based on the moving-embedded grid methodology, a CFD simulation method for the aerodynamic characteristics of rotor is developed by solving the compressible Reynolds-averaged Navier-Stokes (RANS) equations. Among the optimization process, the high-qualified blade grids are generated by a high-efficient parameterized method. Additionally, the high-speed impulsive (HSI) noise characteristics generated by transonic helicopter rotor are analyzed through a robust prediction method based on FW-H_pds equations (Ffowcs Williams-Hawkings equations with penetrable data surface). Aiming at the minimization of the noise level in forward flight, optimization analyses based on the rotor blade with double-swept and tapered tip have been accomplished with the aerodynamic performance as constraints. The genetic algorithm and surrogated model based on Latin Hypercube Sampling (LHS) design and Radial Basis Function (RBF) are combined as a hybrid optimization technique. Compared with rectangular blades, it shows that the noise level of rotor with optimized blade-tip shape can be decreased obviously at the present calculating condition. For the rotor with optimized blade-tip, the HSI noise level can be reduced effectively due to its weaker transonic "delocalization" phenomenon in the region of blade-tip.
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Legg, Matthew W., Alec J. Duncan, Anthony Zaknich i Michael V. Greening. "Analysis of impulsive biological noise due to snapping shrimp as a point process in time". W OCEANS 2007 - Europe. IEEE, 2007. http://dx.doi.org/10.1109/oceanse.2007.4302279.
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Lee, Sang-Kwon, i Paul R. White. "Fault Identification for Rotating Machinery Using Adaptive Signal Processing and Time-Frequency Analysis". W ASME 1997 Design Engineering Technical Conferences. American Society of Mechanical Engineers, 1997. http://dx.doi.org/10.1115/detc97/vib-4236.
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Abstract Impulsive sound and vibration signals in rotating machinery are often associated with faults which lead to due to irregular impacting. Thus these impulsive sound and vibration signals can be used as indicators of machinery faults. However it is often difficult to make objective measurement of impulsive signals because of background noise signals. In order to ease the measurement of impulsive sounds embedded in background noise, we enhance the impulsive signals using adaptive signal processing and then analyze them in time and frequency domain by using time-frequency representation. This technique is applied to the diagnosis of faults within internal combustion engine and industrial gear.
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Samimy, Mo, Jin-Hwa Kim i Martin Kearney-Fischer. "Active Control of Noise in Supersonic Jets Using Plasma Actuators". W ASME Turbo Expo 2009: Power for Land, Sea, and Air. ASMEDC, 2009. http://dx.doi.org/10.1115/gt2009-59456.
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Noise mitigation has been in the forefront of research and development since the advent of jet engines. Supersonic commercial and especially supersonic military aircraft cannot take the advantages offered by large bypass ratio engines due to significant drag penalty and performance degradation. Therefore, other control techniques must be utilized to reduce noise and satisfy the more recent and looming future stringent noise regulations. A class of plasma actuators has recently been developed at the Ohio State University that offers a significant promise. These actuators possess a wide bandwidth and can provide large amplitude perturbations enabling manipulation of various instabilities in high Reynolds number subsonic and supersonic jets for noise mitigation as well as mixing enhancement. A brief overview of the actuators and some results are presented in perfectly-expanded Mach 1.3 axisymmetric unheated and heated jets.
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Rachaprolu, Joel Sundar, i Eric Greenwood. "Helicopter Noise Source Separation Using an Order Tracking Filter". W Vertical Flight Society 78th Annual Forum & Technology Display. The Vertical Flight Society, 2022. http://dx.doi.org/10.4050/f-0078-2022-17433.
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Due to the importance of understanding the aeroacoustics of rotorcraft with continually changing noise sources, this paper presents a new technique for source separation from ground-based acoustic measurements. The source separation process is based on combining a time-domain de-Dopplerization method with the Vold-Kalman (VK) order tracking filter approach. This process can extract rotor harmonic noise even when the sources are continuously changing with time, including impulsive events such as Blade Vortex Interaction (BVI) noise. The advantage of this approach over traditional methods such as harmonic averaging is that the phase and amplitude relationship of acoustic signals is preserved throughout the extraction process. The approach is applied to the measured acoustic data from a Bell 430 helicopter. The measured data were separated into main rotor harmonic, tail rotor harmonic, and broadband residual components. For steady-state conditions, the extracted components could be de-propagated to form acoustic spheres showing the directivity of the separated main and tail rotor components. The source separation process was also applied to a maneuvering flight condition. Each component has different pulse shapes and directivity trends, consistent with aeroacoustic theory.
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Lemire, Se´bastien, i Huu Duc Vo. "Reduction of Fan and Compressor Wake Defect Using Plasma Actuation for Tonal Noise Reduction". W ASME Turbo Expo 2008: Power for Land, Sea, and Air. ASMEDC, 2008. http://dx.doi.org/10.1115/gt2008-50821.
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This paper proposes a new technique to reduce the noise generated by rotor-stator interaction (tonal noise) in fans and compressors. The method involves the use of single dielectric barrier discharge (plasma) actuators near the blade trailing edge to reduce blade wakes. Plasma actuators are a new and simple type of active flow control device consisting of two parallel and offset electrodes separated by a layer of dielectric material. The application of a high AC voltage at high frequency to the electrodes generates a body force on the flow in the vicinity of the electrodes to inject momentum without mass addition. A preliminary assessment of the proposed concept is performed with a computational study on a modern low-speed compressor rotor geometry. A plasma actuator model is implemented in an established turbomachinery CFD code. Simulations are carried out to evaluate the effect of the actuator strength, location and actuation method (continuous versus pulsed) on the rotor wake. Results show that plasma actuators operated in continuous mode near the trailing edge can significantly influence the wake of the rotor with relatively little power consumption. The effectiveness of the actuation is proportional to actuator strength (induced body force). The exact position of the actuator in the trailing edge region has little effect on the effectiveness of the actuation. The results from simulations for pulsed actuation show very low time-averaged influence on the wake and are not fully conclusive, due possibly to the frequencies simulated and the limitations of the RANS CFD tool.
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Zhang, Weiming, i Tomio Koyama. "A Study on Noise in Synchronous Belt Drives: Experimental and Theoretical Analysis of Impact Sound". W ASME 2000 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. American Society of Mechanical Engineers, 2000. http://dx.doi.org/10.1115/detc2000/ptg-14409.
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Abstract There are two kinds of noise in synchronous belt drives. One is steady sound caused by transverse vibration of belt, and another is impact sound radiating from meshing point of belt and pulley. Recently, it has been reported that the impact sound is due to the sound occurring in an air pipe built up between pulley groove and belt because the frequency of impact sound coincides with the fundamental natural frequency of an open ended pipe whose length equals width of the belt. However, this conclusion is obtained experimentally, there has no theoretical analysis provided. In this study, an analysis of the impact sound is provided to prove its generation mechanism and discuss factors that influence the level of sound theoretically. Sound field in an open ended pipe subjected to an impulsive sound source is analyzed. Comparison between experimental and analytical results is carried out. It is concluded that the level of impact sound is in proportion to the width of belt, and the acoustic energy of impact sound is in proportion to the cube of the width of belt.
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Rodrigues, F. F., J. C. Pascoa i M. Trancossi. "Experimental Thermal Characterization of DBD Plasma Actuators". W ASME 2017 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/imece2017-70541.
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DBD plasma actuators have several applications within the field of active flow control. Separation control, wake control, aircraft noise reduction, modification of velocity fluctuations or boundary layer control are just some examples of their applications. They present several attractive features such as, their simple construction, very low mass, fast response, low power consumption and robustness. Besides their aerodynamic applications, these devices have also possible applications within the field of heat transfer, for example film cooling applications. However, due to the extremely high electric fields in the plasma region and consequent impossibility of applying intrusive techniques, there is a relative lack of information about DBDs thermal characteristics. In an attempt to contradict this scenario, this work describes the thermal behaviour of DBD plasma actuators. The total power consumed, the fraction of power that is dissipated as heat energy and the dielectric temperature variation due to the plasma operation are some parameters with great interest in any plasma actuator applications. Thus, these parameters were quantified and the results were presented and discussed. Infra-red thermography measurements were performed in order to obtain the temperature distribution of the dielectric layer. During this work we analysed DBD plasma actuators with different dielectric thicknesses and also with different dielectric materials, whose thermal behaviour was not reported in the literature yet. Conclusions were taken in order to extend the fundamental knowledge on the thermal aspects of the DBD plasma actuators.
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Backhaus, Claus, i Simon Siebers. "Work-related noise exposure in a neonatal intensive care unit". W 13th International Conference on Applied Human Factors and Ergonomics (AHFE 2022). AHFE International, 2022. http://dx.doi.org/10.54941/ahfe1002129.
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Premature infants are children born before the 37th week of gestation. They often need to be cared for in neonatal intensive care units (NICUs) after birth, where they are continuously exposed to noise that can affect sleep patterns and lead to growth and developmental delays. To date, there are no unified limits for the prevention of noise exposure in NICUs. Recommendations for maximal continuous sound levels vary - depending on the professional society - between 35 and 60 dB(A) for daytime values and 20 to 60 dB(A) for nighttime values. They span a range from quiet whispering to normal road traffic noise. Existing studies of noise measurements in NICUs indicate that these recommendations are generally not met. A limitation of previous work is their short time periods that noise measurements were made for, usually one or two hours. As a result, it is not possible to make statements about the diurnal cyclic change in noise exposure, which may have an influence on the circadian rhythm of premature infants, for example. The present work aims to determine the intensity and diurnal cyclic differences of noise exposure in a NICU. In addition, particularly noisy work activities are identified in order to derive suggestions for prevention.For this purpose, the continuous sound levels are recorded for 22 work shifts in a German level 1 perinatal center. Measurements are made in the patient room and the inside of an infant incubator. The mean daily noise exposure levels (LEX,8h) of the early, late and night shifts are calculated and the peak sound level (LpCpeak) is recorded. To test for a day-night rhythm, these are compared using one-factor ANOVA. Using the Contextual Inquiry method, work analyses are performed for 12 work shifts and the early, late and night shifts with the highest equivalent continuous sound level (LAeq) are examined for noise-intensive work activities as examples. The measurement results in LEX,8h and LpCpeak values of up to 49.7 dB(A) and 124.4 dB(C) inside the infant incubator and 55.4 dB(A) and 110.3 dB(C) in the patient room. A day-night rhythm of noise exposure could not be demonstrated. The most noise-intensive work activities included the suctioning of patients and the conversations conducted in the process, with an LAeq of 63 dB(A). In addition, numerous very high impulsive noise events are identified which contribute to the noise exposure of premature infants. The presented study proves that the noise exposure is too high, which is very likely to affect the sleep behavior of premature infants. The results correspond with the statements of comparable studies. It is remarkable that especially the high peak noise levels are mainly due to trivial causes, which can be avoided by simple preventive measures.
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Kim, Jin-Hwa, Martin Kearney-Fischer, Mo Samimy i Sivaram Gogineni. "Far-Field Noise Control in Supersonic Jets From Conical and Contoured Nozzles". W ASME Turbo Expo 2010: Power for Land, Sea, and Air. ASMEDC, 2010. http://dx.doi.org/10.1115/gt2010-22377.
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Plasma actuators are used to control far-field noise in Mach 1.65 jets from contoured and conical supersonic axisymmetric nozzles (henceforth contoured and conical jets, respectively). The contoured nozzle is designed using the method of characteristics for shock-free jet. The conical nozzle has converging and diverging conical sections with a sharp throat. Eight plasma actuators, distributed uniformly around the nozzle exit, are used and the jet is forced with azimuthal modes (m) 0–3, and ±4 and forcing Strouhal numbers ranging from 0.09 to 4.0. The far-field acoustic noise is measured by a linear microphone array covering polar angles from 25 to 80° relative to the jet axis. In both jets, the lower forcing azimuthal modes (m = 0 and 1) are less effective than the higher modes (m = 2, 3, and ±4), which have similar levels of overall sound pressure level (OASPL) reduction. At shallow angles relative to the jet axis, the reduction in OASPL is about 1.6–1.8 dB at low forcing Strouhal numbers in both jets at the most effective forcing mode of m = 3. However, the OASPL in the sideline direction is only slightly increased (about 1 dB) for both the contoured and conical jets at m = 3. The reduction at shallow polar angles is related to the decrease in the peak mixing noise level in both jets. The range of forcing Strouhal numbers providing significant noise reduction and the range of polar angles over which the noise is reduced, are both much larger in the conical jet compared to the contoured jet. The screech tones are also reduced or suppressed most likely due to weakening of naturally occurring structures by forcing.
Raporty organizacyjne na temat "Impulsive noise due to plasma"
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ESA, ESA EOP-SM, i NASA SMD NASA. Exploring Earth’s Interface with Space – The Scientific Case for a Satellite Mission to the Lower Thermosphere-Ionosphere Transition Region. ESA, lipiec 2024. http://dx.doi.org/10.5270/esa-nasa.lti-sc.2024-07-v1.0.
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Exploring Earth’s Interface with Space – The Scientific Case for a Satellite Mission to the Lower Thermosphere-Ionosphere Transition Region SUMMARY This report describes the scientific case for a mission concept to study the Earth’s Lower Thermosphere-Ionosphere – the LTI – which is the interface region between our atmosphere and space. The LTI is situated at altitudes between 100-200 km and is uniquely characterized by complex interactions between the co-existing neutral and ionized gases. The LTI receives and dissipates hundreds of gigajoules of energy every second from above due to solar wind interactions with our planet’s magnetosphere. Simultaneously, this region continuously receives energy and momentum input from below in the form of tides and gravity waves originating in the lower and middle atmosphere as well as impulsive input from thunderstorms, volcanoes, and earthquakes, whose energy content rivals that provided by the magnetosphere. The LTI responds dramatically to all of these driving forces producing large variations in many key properties, such as neutral and plasma number densities, motions, temperatures, and composition, as well as electric fields, conductivity, and currents. Importantly, the LTI also acts as a critical interface that subsequently regulates this energy transfer from the magnetosphere above and from the neutral atmosphere below.