Letteratura scientifica selezionata sul tema "POWER SPECTRUM CONDITION"
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Articoli di riviste sul tema "POWER SPECTRUM CONDITION"
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Bhattarai, Shishir, e Prem Nath Maskey. "Effect of Linear Soil Condition on Seismic Inputs". Technical Journal 2, n. 1 (10 novembre 2020): 48–55. http://dx.doi.org/10.3126/tj.v2i1.32829.
Testo completoAbstract (sommario):
Seismic inputs to structures in terms of risk consistent response spectrum and seismic hazard curves are developed at bedrock level considering ten independent seismic source zone in the vicinity of the Kathmandu valley. The seismic hazard curve is derived by assuming temporal occurrence of earthquakes to follow Poisson model. Response spectrum is developed using an empirical relationship of spectral ordinates with magnitude of earthquakes and epicentral distance. The seismic risk factor is introduced in response spectrum using conditional probabilities. Power spectral density function consistent with response spectrum is derived and ground acceleration time histories are derived from power spectral density function using Monte Carlo technique. To obtain free field hazard curves and ground motion parameters, one dimensional wave propagation analysis is used for two different underlying soil conditions.
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Su, J. K., e B. Girod. "Power-spectrum condition for energy-efficient watermarking". IEEE Transactions on Multimedia 4, n. 4 (dicembre 2002): 551–60. http://dx.doi.org/10.1109/tmm.2002.806535.
Testo completo
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Chandra, Rajorshi Sushovan, e Tarun Souradeep. "Primordial Power Spectrum reconstruction from CMB Weak Lensing Power Spectrum". Journal of Cosmology and Astroparticle Physics 2021, n. 10 (1 ottobre 2021): 081. http://dx.doi.org/10.1088/1475-7516/2021/10/081.
Testo completoAbstract (sommario):
Abstract We use the modified and improved Richardson-Lucy (IRL) deconvolution algorithm to reconstruct the Primordial Power Spectrum (PPS) from the Weak Lensing Power Spectrum CL ϕϕ reconstructed from CMB anisotropies. This provides an independent window to observe and constrain the PPS PR (k) along different k scales as compared to CMB Temperature Power Spectrum. The Weak Lensing Power Spectrum does not contain secondary variations in power and hence is cleaner, unlike the Temperature Power Spectrum which suffers from lensing which must be addressed during PPS reconstructions. We demonstrate that the physical behaviour of the weak lensing kernel is unique and reconstructs broad features over k. We provide an in-depth analysis of the error propagation using simulated data and Monte-Carlo sampling, using Planck best-fit cosmological parameters to simulate the data with cosmic variance limited error bars. The error and initial condition analyses provide a clear picture of the optimal reconstruction region for the estimator while providing a detailed statistical insight of the results. We also provide an algorithm for PR (k) sampling sparsity to be used based on the given data and errors, to optimize statistical significance. Eventually we plan to use this method on actual mission data and provide a cross reference to PPS reconstructed from other sectors and any possible features in them.
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Zhang, Yu, Tong Zhu e Jing Zhou. "Understanding Power Spectrum Density Transmissibility". Shock and Vibration 2016 (2016): 1–9. http://dx.doi.org/10.1155/2016/8479721.
Testo completoAbstract (sommario):
Power spectrum density transmissibility (PSDT) is a type of complex frequency domain function proposed recently. It describes the relation between cross-spectra of system outputs. Since PSDTs with same local-reference degree of freedom (DOF) combination but with different transferring output DOFs cross each other at the system’s poles under certain load condition, the functions have been used as the primary data in operational modal analysis (OMA) to extract modal parameters, and such technique is named as PSDT-based OMA (PSDTOMA). Because PSDT is a concept that appears recently, researches on which, especially, in-depth discussions aim at the essence and properties of PSDT are very rare. For appropriate application of PSDTOMA, it is necessary to perform further study on such problem obviously. In this paper, two paths to get PSDT, which, respectively, are referred to as PSDT estimator and PSDT syntheticism, are given firstly; some properties about PSDT are explored based on the PSDT syntheticism, and the relation between PSDT and single reference transmissibility function (STF) is analyzed. Finally, the above conclusions are verified with numerical values and experimental data.
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Kunz, Torben, e Richard J. Greatbatch. "Effect of the Kinematic Lower Boundary Condition on the Spectral and Autocorrelation Structure of Annular Variability in the Troposphere". Journal of the Atmospheric Sciences 71, n. 6 (30 maggio 2014): 2264–79. http://dx.doi.org/10.1175/jas-d-13-0104.1.
Testo completoAbstract (sommario):
Abstract The dynamical origin of the spectral and autocorrelation structure of annular variability in the troposphere is investigated by a deductive approach. Specifically, the structure of the power spectrum and autocorrelation function of the zonal-mean geopotential is analyzed for the case of a quasigeostrophic spherical atmosphere subject to a white noise mechanical forcing applied in a single Hough mode and concentrated at a particular level in the vertical, with vertically uniform Newtonian cooling and Rayleigh drag concentrated at a rigid lower boundary. Analytic expressions for the power spectrum are presented together with expressions for an approximate red noise (i.e., a Lorentzian-shaped) power spectrum. It is found that for an infinitely deep atmosphere the power spectrum can be well approximated by a red noise process for the first few Hough modes (associated with large Rossby heights), provided the distance from the forcing is not larger than about one Rossby height. When a frictional rigid lower boundary is included, however, the approximation is generally bad. The high-frequency part of the power spectrum exhibits near-exponential behavior and the autocorrelation function shows a transition from a rapid decay at short lags to a much slower decay at longer lags, if the thermal and mechanical damping time scales are sufficiently well separated. Since observed annular variability exhibits the same characteristics, the above results lead to the hypothesis that these characteristics may, to some extent, be intrinsic to the linear zonal-mean response problem—although the need for an additional contribution from eddy feedbacks is also implied by the results.
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Liu, Yunjuan, e Dongsheng Chen. "An analysis on EEG power spectrum under pressure of girdle". International Journal of Clothing Science and Technology 27, n. 4 (3 agosto 2015): 495–505. http://dx.doi.org/10.1108/ijcst-05-2014-0065.
Testo completoAbstract (sommario):
Purpose – The pressure exerted on the body by clothes is one important factor affecting the comfort of clothing, it is an effective method to evaluate pressure comfort by physiology and psychology. The purpose of this paper is to measure, electroencephalography (EEG), an index of brain activity in order to examine the effect on brain activity conditions caused by oppression exerted by clothing on the body. Design/methodology/approach – EEG power spectrum analysis was conduct to verify the electrophysiological characteristic of brain caused by pressure on the body by girdle. Findings – Experimental results showed that the intensity of α waves in the pressure condition is decreased compared to the non-pressure condition, and the somatosensory activated by pressure of girdle mainly in occipital, frontal and parietal region of brain. Originality/value – It was clarified that it is impossible to evaluate the clothes pressure by physiological technique of EEG, this study has enriched methods of evaluation pressure comfort.
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Mnif, M., N. Smaoui, L. Triki, J. Donia, R. Feki, I. Gassara, S. Omri et al. "EEG power spectrum analysis for Tunisian schizophrenic patients". European Psychiatry 66, S1 (marzo 2023): S1075. http://dx.doi.org/10.1192/j.eurpsy.2023.2283.
Testo completoAbstract (sommario):
IntroductionSchizophrenia (SCZ) is a common and disabling psychiatric condition. Its diagnosis is entirely clinical. Many researchers have looked into electroencephalogram (EEG) power spectrum analysis for SCZ to find specific abnormalities.Objectives The objective of this study was to analyze the EEG of patients with SCZ using power spectral density and to compare them with those of healthy controls, in order to look for specificities.Methods This was a cross-sectional, descriptive, and analytical case-control study conducted with patients followed for SCZ in the psychiatry "C" department at the Hedi Chaker hospital in Sfax. Healthy controls were included. Patients were assessed by the Positive and Negative schizophrenia scale (PANSS). All participants benefited from an EEG at rest condition at the service of the functional exploration at the Habib Bourguiba hospital in Sfax. We have measured the powers of each band using Welch power spectral density method called absolute power (AP). Statistical analyses were carried out.ResultsFifteen schizophrenics and 15 controls, all male, were included. The average age of schizophrenics and healthy controls was 40 years ±12.72 years and 47.93 ± 15.61 years respectively. There were no significant differences in age between patients and controls. Schizophrenics had a mean PANSS of 64.6±22.7.At the quantitative EEG, differences appeared to be insignificant. There was an overall decrease in AP for the alpha band particularly in the parietal and occipital lobes in schizophrenics (53,16 ± 48,83 μV2 and 75,17 ± 56,28 μV2 respectively) compared to controls (335,15 ± 994,73 μV2 and 400,24 ± 1109,95 μV2 respectively). There was also an overall decrease in AP for the different frequency bands in schizophrenics compared to controls. However, values persisted high in the temporal lobe for all frequency bands.ConclusionsIn conclusion, this decrease in AP for the alpha band in the parietal and occipital lobes in schizophrenics can be a sensitive biomarker for diagnosing SCZ.Disclosure of InterestNone Declared
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Bouissou, P., P. Y. Estrade, F. Goubel, C. Y. Guezennec e B. Serrurier. "Surface EMG power spectrum and intramuscular pH in human vastus lateralis muscle during dynamic exercise". Journal of Applied Physiology 67, n. 3 (1 settembre 1989): 1245–49. http://dx.doi.org/10.1152/jappl.1989.67.3.1245.
Testo completoAbstract (sommario):
The relationship between intramuscular pH and the frequency components of the surface electromyographic (EMG) power spectrum from the vastus lateralis muscle was studied in eight healthy male subjects during brief dynamic exercise. The studies were carried out in placebo control and metabolic alkalosis induced by oral administration of NaHCO3. At the onset of exercise, blood pH was 0.08 units higher in alkalosis compared with placebo. Muscle lactate accumulation during exercise was higher in alkalosis (32 +/- 5 mmol/kg wet wt) than in placebo (17 +/- 4 mmol/kg wet wt), but no difference in intramuscular pH was found between the two conditions. The EMG power spectrum was shifted toward lower frequencies during fatigue in the control condition (10.1 +/- 0.9%), and these spectral shifts, evaluated from changes in the mean power frequency (MPF) of the EMG power spectrum, were further accentuated in alkalosis (19 +/- 2%). Although the changes in frequency components of EMG correlated with muscle lactate accumulation (r = 0.68, P less than 0.01), no direct relationship with muscle pH was observed. We conclude that alkalosis results in a greater reduction in MPF associated with a higher muscle lactate accumulation. However, the good correlation observed between the two variables is not likely causative, and a dissociation between intramuscular pH and the increase in the low-frequency content of EMG power spectrum appears during muscle fatigue.
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Kornatowski, Eugeniusz. "Mechanical-Condition Assessment of Power Transformer Using Vibroacoustic Analysis". Key Engineering Materials 500 (gennaio 2012): 40–44. http://dx.doi.org/10.4028/www.scientific.net/kem.500.40.
Testo completoAbstract (sommario):
This paper presents a method for vibroacoustic analysis of a transformer in the steady state. The standard approach to this problem has been based on analysis of the vibration frequency spectrum recorded with an accelerometer mounted on the transformer’s tank. To improve legibility of measurement results, the paper suggests the analysis method for the relative coefficient of harmonic frequency contents hnorm(f). The conducted experiment showed that high values of hnorm within a wide frequency range testify to deformation of windings and degradation of solid insulation.
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Eastham, M. S. P., e K. M. Schmidt. "Absence of high-energy spectral concentration for Dirac systems with divergent potentials". Proceedings of the Royal Society of Edinburgh: Section A Mathematics 135, n. 4 (agosto 2005): 689–702. http://dx.doi.org/10.1017/s0308210500004078.
Testo completoAbstract (sommario):
It is known that one-dimensional Dirac systems with potentials q which tend to −∞ (or ∞) at infinity, such that 1/q is of bounded variation, have a purely absolutely continuous spectrum covering the whole real line. We show that, for the system on a half-line, there are no local maxima of the spectral density (points of spectral concentration) above some value of the spectral parameter if q satisfies certain additional regularity conditions. These conditions admit thrice-differentiable potentials of power or exponential growth. The eventual sign of the derivative of the spectral density depends on the boundary condition imposed at the regular end-point.
Tesi sul tema "POWER SPECTRUM CONDITION"
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Lindsay, Tara Reeves. "Applying Adaptive Prognostics to Rolling Element Bearings". Thesis, Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/7568.
Testo completoAbstract (sommario):
Rolling element bearing failure can cause problems for industries ranging from mild inconveniences such as simple replacement to catastrophic damage such as large production-line equipment failure. Rolling element bearing failure has plagued industries for many years. Bearings are currently monitored to determine whether or not there is a defect in the bearing, but the remaining lifetime of the bearing remains unknown. This research estimates the bearings remaining lifetime through digital signal processing in conjunction with a modified version of Pariss equationa fatigue-failure equation well known in rotating machinery prognostics.
An energy quantity, coined the Power Spectrum Value (PSV), is the maximum amplitude of the frequencies within a relatively small band around the resonant frequency of the system. The current PSV is estimated and updated using a chronologically weighted least squares algorithm. It is this PSV which is implemented in the modified Paris equation to determine the remaining lifetime of the bearing. This research presents a non-intrusive method of determining the lifetime of the bearing so that the bearings utility is maximized and reactive maintenance procedures are minimized.
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Rylands, Naasef. "Condition monitoring of induction motors in the nuclear power station environment". Master's thesis, University of Cape Town, 2018. http://hdl.handle.net/11427/29686.
Testo completoAbstract (sommario):
The induction motor is a highly utilised electrical machine in industry, with the nuclear industry being no exception. A typical nuclear power station usually contains more than 1000 motors, where they are used in safety and non-safety application. The efficient and fault-free operation of this machine is critical to the safe and economical operation of any plant, including nuclear power stations. A comprehensive literature review was conducted that covered the functioning of the induction machine, its common faults and methods of detecting these faults. The Condition Based Maintenance framework was introduced in which condition monitoring of induction machines is an essential component. The main condition monitoring methods were explained with the main focus being on Motor Current Signature Analysis (MCSA) and the various methods associated with it. Three analysis methods were selected for further study, namely, Current Signature Analysis, Instantaneous Power Signature Analysis (IPSA) and Motor Square Current Signature Analysis (MSCSA). Essentially, the methodology used in this dissertation was to study the three common motor faults (bearings, stator and rotor cage) in isolation and compare the results to that of the healthy motor of the same type. The test loads as well as fault severity were varied where possible to investigate its effect on the fault detection scheme. The data was processed using an FFT based algorithm programed in MATLAB. The results of the study of the three spectral analysis techniques showed that no single technique is able to detect motor faults under all tested circumstances. The MCSA technique proved the most capable of the three techniques as it was able to detect faults under most conditions, but generally suffered poor results in inverter driven motor applications. The IPSA and MSCSA techniques performed selectively when compared to MCSA and were relatively successful when detecting the mechanical faults. The fact that the former techniques produce results at unique points in the spectrum would suggest that they are more suitable for verifying results. As part of a comprehensive condition monitoring scheme, as required by a large population of the motors on a nuclear power station, the three techniques presented in this study could readily be incorporated into the Condition Based Maintenance framework where the strengths of each could be exploited.
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Braglia, Matteo. "Initial conditions for cosmological perturbations in scalar-tensor dark-energy models". Master's thesis, Alma Mater Studiorum - Università di Bologna, 2017. http://amslaurea.unibo.it/13860/.
Testo completoAbstract (sommario):
We discuss the evolution and imprints of isocurvature initial conditions for the scalar field in scalar tensor extensions of Einstein gravity. We consider the simplest models of scalar tensor theories, as Induced gravity (IG, which can be recasted in form of Jordan-Brans-Dicke theory by a redefinition of the scalar field) or non-minimally coupled (NMC) scalar fields in which the acceleration of the Universe is connected to a variation of the effective Planck mass. After introducing the fundamental ideas of cosmological perturbation theory and scalar tensor theories of gravity, we give the evolution equations for matter, metric and scalar field fluctuations in synchronous gauge. We use this set of equations for both the IG and the NMC models to find a new isocurvature solution in which the scalar field fluctuations compensate for the relativistic components respectively. We also show how we can generalize the well known isocurvature modes in Einstein GR to these models. We show the different evolution of cosmological fluctuations for these isocurvature initial conditions compared to the standard adiabatic one. After that, we compute the CMB angular power spectrum for these solutions in the IG model, with the help of a modified Einstein-Boltzmann CLASS code. In particular the CMB power spectrum is computed separately for adiabatic and isocurvature initial conditions, i.e. for totally uncorrelated modes, and with arbitrary correlations leading to an interesting explanation of the lack of power in the low multipoles region of the CMB temperature power spectrum. Finally we show how a simple model of double inflation in IG could explain the generation of the new isocurvature mode.
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Ahnesjö, Henrik. "Fault detection of planetary gearboxes in BLDC-motors using vibration and acoustic noise analysis". Thesis, Uppsala universitet, Institutionen för elektroteknik, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-425966.
Testo completoAbstract (sommario):
This thesis aims to use vibration and acoustic noise analysis to help a production line of a certain motor type to ensure good quality. Noise from the gearbox is sometimes present and the way it is detected is with a human listening to it. This type of error detection is subjective, and it is possible for human error to be present. Therefore, an automatic test that pass or fail the produced Brush Less Direct Current (BLDC)-motors is wanted. Two measurement setups were used. One was based on an accelerometer which was used for vibration measurements, and the other based on a microphone for acoustic sound measurements. The acquisition and analysis of the measurements were implemented using the data acquisition device, compactDAQ NI 9171, and the graphical programming software, NI LabVIEW. Two methods, i.e., power spectrum analysis and machine learning, were used for the analyzing of vibration and acoustic signals, and identifying faults in the gearbox. The first method based on the Fast Fourier transform (FFT) was used to the recorded sound from the BLDC-motor with the integrated planetary gearbox to identify the peaks of the sound signals. The source of the acoustic sound is from a faulty planet gear, in which a flank of a tooth had an indentation. Which could be measured and analyzed. It sounded like noise, which can be used as the indications of faults in gears. The second method was based on the BLDC-motors vibration characteristics and uses supervised machine learning to separate healthy motors from the faulty ones. Support Vector Machine (SVM) is the suggested machine learning algorithm and 23 different features are used. The best performing model was a Coarse Gaussian SVM, with an overall accuracy of 92.25 % on the validation data.
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Arnqvist, Johan. "Mean Wind and Turbulence Conditions in the Boundary Layer above Forests". Doctoral thesis, Uppsala universitet, Luft-, vatten och landskapslära, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-237764.
Testo completoAbstract (sommario):
As wind turbines have grown, new installation areas become possible. Placing wind turbines in forested landscapes introduce uncertainties to the wind resource estimation. Even though close-to-canopy processes have been studied intensively during the last thirty years, the focus has mostly been on exchange processes and the height span of the studies has been below the rotor of a modern wind turbine. This thesis contains analysis of new measurements from a 138 m high tower in a forested landscape. The previous knowledge of near-canopy processes is extended to the region above the roughness sublayer. It is shown that above the roughness sublayer, the surface layer behaves as over low vegetation, and Monin-Obukhov similarity is shown to hold for several variables. However, in stable stratification, effects that could be linked to the boundary layer depth are shown to be present in the measurements. These include wind turning with height, the behaviour of the turbulence length scale and the curvature of the wind profile. Two new analytical models are presented in the thesis. One is a flux-profile expression in the roughness sublayer, which allows for analytical integration of the wind gradient. The model suggests that the roughness-sublayer effect depends on stratification and that the aerodynamic roughness length changes with stability. A decrease of roughness length in stable stratification is confirmed with a new method to determine the roughness length using measurements from the 138 m tower. The other model determines the spectral tensor in stable stratification using analytical solution to the rapid distortion equations for stratified shear flow, with homogeneous stratification and shear. By using a formulation for the integration time of the distortions of an isotropic spectrum, a model is derived which provides the cross spectra of velocity and temperature at any two given points in space. Finally the existence of waves in the wind over forests is investigated and it is concluded that the Kelvin-Helmholtz instability can create waves which are coherent in time and exist over the entire height span of wind turbine rotors. Linear wave theory is shown to be able to explain certain features of the waves.Vindforsk III, Wind power in forests
Vindforsk IV, Forest wind
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Kerbal, Sofiane. "Development of new criteria for train detection and evaluation in critical conditions". Thesis, KTH, Skolan för elektroteknik och datavetenskap (EECS), 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-253201.
Testo completoAbstract (sommario):
Railway signaling is of paramount importance to ensure traffic management andsafety on the rail network. The main lines are divided into sections called ‘blocks’,which are governed by a fixed signal installation. To prevent trains from colliding,each block allows one train at once. In France (and most European countries),train detection is performed by an electrical device called track circuit that consistsof a transmitter and a receiver installed at the track-side, and connected via therails. In the absence of a train, an electrical signal flows from the transmitter tothe receiver through the rails. As a train enters a track circuit, its axles shuntthe rails, provoking a short circuit (also called ‘shunt’): the signal transmitted tothe receiver drops. The detection of that signal drop results in the detection of atrain. This method rarely fails throughout the network, but there can be criticalcases where it may be inefficient. In this Master’s Thesis, new detection criteriaproposed in previous studies have been tested on signals measured in poor shuntingconditions. Three approaches have been tested: one in the time domain and two inthe frequency domain. The time approach compares the short-term and long-termstatistics of the received signals. The observation of a change in the spectra of thereceived signals around the 3rd order harmonic (3OH) has led to the implementationof two frequency criteria: the estimation of the band power around the 3OH andthe detection of the 3OH peaks. The obtained results show that better detection isachieved when the new criteria and the existing one are combined.Tågsignalsystem är väsentliga för att garantera trafikstyrning och säkerhet i tågnätet.Spåren är indelade i sektioner, s.k. block, som övervakas med fasta signalinstallationer.För att hindra tåg från att krocka, tillåts bara ett tåg i taget per block. IFrankrike (och de flesta andra europeiska länder), detekteras tågen med en elektriskspårkrets som består av en sändare och en mottagare som är installerad bredvidspåret och ansluten till rälsen. När inget tåg finns på spåret, flyter en elektrisk signalfrån sändaren till mottagaren via spåret. När ett tåg anländer, kortsluts kretsenav hjulaxeln och signalen försvinner från mottagaren. Minskningen i signalstyrkaanvänds för att detektera tåget. Denna metod sällan misslyckas i tågnätet, men iovanliga fall kan det uppstå farliga situationer. I detta examensarbete utvärderasnya detektionsmetoder, som har föreslagits i tidigare studier, på signaler som haruppmätts under förhållanden med dålig kontakt mellan hjul och spår. Tre olika metoderhar testats, en i tidsdomänen och två i frekvensdomänen. Tidsdomänsmetodenjämför kortvarig och långvarig statistik för den mottagna signalen. I spektrum förden mottagna signalen, har man observerat en förändring runt den tredje övertonen,samt detektering av frekvenstoppar vid tredje övertonen. De erhållna resultatenvisar på förbättrad detektering när de nya och existerande kriterierna kombineras.
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Sendrowski, Janek. "Feigenbaum Scaling". Thesis, Linnéuniversitetet, Institutionen för matematik (MA), 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-96635.
Testo completoAbstract (sommario):
In this thesis I hope to provide a clear and concise introduction to Feigenbaum scaling accessible to undergraduate students. This is accompanied by a description of how to obtain numerical results by various means. A more intricate approach drawing from renormalization theory as well as a short consideration of some of the topological properties will also be presented. I was furthermore trying to put great emphasis on diagrams throughout the text to make the contents more comprehensible and intuitive.
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Martineau, Killian. "Quelques aspects de cosmologie et de physique des trous noirs en gravitation quantique à boucles Detailed investigation of the duration of inflation in loop quantum cosmology for a Bianchi I universe with different inflaton potentials and initial conditions Some clarifications on the duration of inflation in loop quantum cosmology A first step towards the inflationary trans-Planckian problem treatment in loop quantum cosmology Scalar spectra of primordial perturbations in loop quantum cosmology Phenomenology of quantum reduced loop gravity in the isotropic cosmological sector Primordial Power Spectra from an Emergent Universe: Basic Results and Clarifications Fast radio bursts and the stochastic lifetime of black holes in quantum gravity Quantum fields in the background spacetime of a polymeric loop black hole Quasinormal modes of black holes in a toy-model for cumulative quantum gravity Seeing through the cosmological bounce: Footprints of the contracting phase and luminosity distance in bouncing models Dark matter as Planck relics without too exotic hypotheses A Status Report on the Phenomenology of Black Holes in Loop Quantum Gravity: Evaporation, Tunneling to White Holes, Dark Matter and Gravitational Waves". Thesis, Université Grenoble Alpes (ComUE), 2019. http://www.theses.fr/2019GREAY044.
Testo completoAbstract (sommario):
Cantonnée à la physique mathématique depuis des décennies, la gravitation quantique entre désormais dans le giron de la science expérimentale. Suivant cette mouvance nous considérons dans cette thèse trois cadres d’application de la gravitation quantique à boucles (LQG) : le système Univers, les trous noirs et les astroparticules. Le troisième n’est qu’esquissé tandis que les deux premiers sont présentés plus en détails.Le secteur cosmologique étant l’un des domaines les plus prometteurs pour tester et contraindre des théories de gravité quantique, le développement de différents modèles tentant d’appliquer les idées de la LQG à l’Univers primordial ne s’est pas fait attendre. Les travaux que nous présentons portent sur la phénoménologie associée à ces modèles; tant dans le secteur homogène (où nous nous focalisons notamment sur la durée de la phase d’inflation), que dans le secteur inhomogène (nous étudions ce coup-ci le devenir des spectres de puissance primordiaux). Ces études combinées nous permettent alors de préciser dans quelle mesure des effets de gravité quantique (à boucles) peuvent être observés dans les anisotropies du fond diffus cosmologique.D’autre part les trous noirs, non contents de faire partie des objets les plus étranges et les plus fascinants de l’Univers, constituent également des sondes privilégiées pour tester des théories de gravitation. Nous développons la phénoménologie associée à différents traitements des trous noirs en gravitation quantique à boucles. Celle-ci intervient sur une grande variété de fronts : de l’évaporation de Hawking aux ondes gravitationnelles, en passant par la matière noire. C’est sans nul doute un domaine riche et vaste.Finalement, l’existence d’une échelle de longueur minimale, prédite par la majorité des théories de gravité quantique, suggère une généralisation du principe d’incertitude de Heisenberg. Partant de ce constat nous présentons également dans ce manuscrit une méthodologie permettant de calculer une nouvelle relation de dispersion de la lumière à partir du principe d’incertitude généralisé le plus couramment répanduAfter decades of being confined to mathematical physics, quantum gravity now enters the field of experimental science. Following this trend, we consider throughout this thesis three implementation frameworks of Loop Quantum Gravity (LQG): the Universe as a system, black holes and astroparticles. The last one is only outlined while the first two are presented in more detail.Since the cosmological sector is one of the most promising areas for testing and constraining quantum gravity theories, it was not long before the development of different models attempting to apply the ideas of the LQG to the primordial Universe. The work we present deals with the phenomenology associated with these models; both in the homogeneous sector (where we focus particularly on the duration of the inflation phase), as in the inhomogeneous sector (where this time, we study the fate of the primordial power spectra). These combined studies then allow us to specify to what extent effects of (loop) quantum gravity can be observed in the anisotropies of the cosmic microwave background.On the other hand black holes, not content to be among the strangest and most fascinating objects of the Universe, are also prominent probes to test the theories of gravitation. We develop the phenomenology associated with different treatments of black holes in the loop quantum gravity framework, which intervenes on multiple levels: from the evaporation of Hawking to gravitational waves, including dark matter. This is undoubtedly a rich and vast area.Finally, the existence of a minimal length scale, predicted by the majority of quantum gravity theories, suggests a generalization of the Heisenberg uncertainty principle. On the basis of this observation, we also present in this manuscript a methodology to derive a new relation dispersion of light from the most widely used generalized uncertainty principle
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GARG, PRINCE. "AN IMAGE WATERMARKING TECHNIQUE USING POWER SPECTRUM CONDITION". Thesis, 2017. http://dspace.dtu.ac.in:8080/jspui/handle/repository/16270.
Testo completoAbstract (sommario):
In this project, the energy efficient watermarking scheme is explored. The energy efficient watermark has the power spectrum which is same as the power spectrum of the original signal, So, the watermark signal has high resemblance with original signal. In order to be energy efficient, the watermark must satisfy the power spectrum condition according to which the power spectrum of watermark signal is directly proportional to power spectrum of original signal. The watermarks which follow the criteria of power spectrum are more robust as compared to the watermarks which do not fulfill the criteria of power spectrum condition. The watermark which do not satisfy the power spectrum condition are vulnerable to Wiener attacks whereas the watermark which are PSC complaint are highly resist to wiener attacks and the watermark can be recovered with very high perceptibility.
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"An Online Monitoring and Fault Location Methodology for Underground Power Cables". Master's thesis, 2016. http://hdl.handle.net/2286/R.I.38467.
Testo completoAbstract (sommario):
abstract: With the growing importance of underground power systems and the need for greater reliability of the power supply, cable monitoring and accurate fault location detection has become an increasingly important issue. The presence of inherent random fluctuations in power system signals can be used to extract valuable information about the condition of system equipment. One such component is the power cable, which is the primary focus of this research.
This thesis investigates a unique methodology that allows online monitoring of an underground power cable. The methodology analyzes conventional power signals in the frequency domain to monitor the condition of a power cable.
First, the proposed approach is analyzed theoretically with the help of mathematical computations. Frequency domain analysis techniques are then used to compute the power spectral density (PSD) of the system signals. The importance of inherent noise in the system, a key requirement of this methodology, is also explained. The behavior of resonant frequencies, which are unique to every system, are then analyzed under different system conditions with the help of mathematical expressions.
Another important aspect of this methodology is its ability to accurately estimate cable fault location. The process is online and hence does not require the system to be disconnected from the grid. A single line to ground fault case is considered and the trend followed by the resonant frequencies for different fault positions is observed.
The approach is initially explained using theoretical calculations followed by simulations in MATLAB/Simulink. The validity of this technique is proved by comparing the results obtained from theory and simulation to actual measurement data.Dissertation/Thesis
Masters Thesis Electrical Engineering 2016
Libri sul tema "POWER SPECTRUM CONDITION"
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Noback, R. The generation of equal probability design load conditions, using P.S.D.-techniques. Amsterdam: National Aerospace Laboratory NLR, 1985.
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Burundi: Une gouvernance fortement marquée par le spectre des élections de 2010 : rapport d'observation du premier semestre, 2009. Bujumbura: Observatoire de l'action gouvernementale, 2009.
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Maggiore, Michele. Evolution of cosmological perturbations. Oxford University Press, 2018. http://dx.doi.org/10.1093/oso/9780198570899.003.0010.
Testo completoAbstract (sommario):
Evolutions equations for cosmological perturbations. Single-component and multi-component fluids. Super-horizon and sub-horizon limits. Adiabatic and isocurvature initial conditions. Analytic and numerical solutions. Power spectra and transfer functions for scalar and tensor perturbations. GW damping from neutrino free-streaming.
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Tiwari, Sandip. Electromechanics and its devices. Oxford University Press, 2017. http://dx.doi.org/10.1093/oso/9780198759874.003.0005.
Testo completoAbstract (sommario):
Electromechanics—coupling of mechanical forces with others—exhibits a continuum-to-discrete spectrum of properties. In this chapter, classical and newer analysis techniques are developed for devices ranging from inertial sensors to scanning probes to quantify limits and sensitivities. Mechanical response, energy storage, transduction and dynamic characteristics of various devices are analyzed. The Lagrangian approach is developed for multidomain analysis and to bring out nonlinearity. The approach is extended to nanoscale fluidic systems where nonlinearities, fluctuation effects and the classical-quantum boundary is quite central. This leads to the study of measurement limits using power spectrum and, correlations with slow and fast forces. After a diversion to acoustic waves and piezoelectric phenomena, nonlinearities are explored in depth: homogeneous and forced conditions of excitation, chaos, bifurcations and other consequences, Melnikov analysis and the classic phase portaiture. The chapter ends with comments on multiphysics such as of nanotube-based systems and electromechanobiological biomotor systems.
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Grabe, Shelly. Transnational Feminism in Psychology: Women’s Human Rights, Liberation, and Social Justice. A cura di Phillip L. Hammack. Oxford University Press, 2016. http://dx.doi.org/10.1093/oxfordhb/9780199938735.013.20.
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The paradigm of transnational feminism emerged in response to the economic and social dislocation that has disproportionately exacerbated women’s rights violations since the neoliberal restructuring of the global economy in the 1980s and 1990s. This chapter proposes that to have a better understanding of women’s rights and justice, contributions from a social justice-oriented psychology that integrates feminist scholarship and empirical findings based on women’s grassroots resistance and activism are necessary. It proposes a transnational feminist liberation psychology whereby researchers (1) work from the grassroots by fostering meaningful alliances with others working outside the academy in a joint pursuit of liberation, (2) use methodology that investigates sites of resistance, bringing visibility to a fuller spectrum of women’s lived experience, and (3) recognize how dimensions of power and inequality impact research. Given the persistent violations of women’s rights globally, it is imperative to understand the psychosocial conditions that lead to justice.
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Mellette, Justin. Peculiar Whiteness. University Press of Mississippi, 2021. http://dx.doi.org/10.14325/mississippi/9781496832535.001.0001.
Testo completoAbstract (sommario):
Peculiar Whiteness argues for deeper consideration of the complexities surrounding the disparate treatment of poor whites throughout southern literature and attests to how broad such experiences have been. While the history of prejudice against this group is not the same as the legacy of violence perpetrated against people of color in America, individuals regarded as ‘white trash’ have suffered a dehumanizing process in the writings of various white authors. Poor white characters are frequently maligned as grotesque and anxiety-inducing, especially when they are aligned in close proximity to blacks or with other troubling conditions such as physical difference. Thus, as a symbol, much has been asked of poor whites, and various iterations of the label (e.g., ‘white trash,’ tenant farmers, or even people with a little less money than average) have been subject to a broad spectrum of judgment, pity, compassion, fear, and anxiety. Peculiar Whiteness engages key issues in contemporary critical race studies, whiteness studies, and southern studies, both literary and historical. Through discussions of authors including Charles Chesnutt, Thomas Dixon, Erskine Caldwell, William Faulkner, and Flannery O’Connor, the book analyzes how we see how whites in a position of power work to maintain their status, often by finding ways to re-categorize and marginalize people who might not otherwise have seemed to fall under the auspices or boundaries of ‘white trash.’
Capitoli di libri sul tema "POWER SPECTRUM CONDITION"
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Hassan, Mohamed A., Michael R. Habib e Abdel M. Bayoumi. "Detection and Classification of Helicopter Drive Shaft Faults Using Neuro-Fuzzy Based on Wavelet Power Spectrum Algorithm". In Advances in Asset Management and Condition Monitoring, 437–50. Cham: Springer International Publishing, 2020. http://dx.doi.org/10.1007/978-3-030-57745-2_37.
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Czifra, Árpád. "Sensitivity of Power Spectral Density (PSD) Analysis for Measuring Conditions". In Studies in Computational Intelligence, 505–17. Berlin, Heidelberg: Springer Berlin Heidelberg, 2009. http://dx.doi.org/10.1007/978-3-642-03737-5_36.
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Xu, Lang, Steven Chatterton e Paolo Pennacchi. "Condition Monitoring of Rolling Element Bearing Based on Moving Average Cross-Correlation of Power Spectral Density". In Advances in Mechanism and Machine Science, 3411–18. Cham: Springer International Publishing, 2019. http://dx.doi.org/10.1007/978-3-030-20131-9_336.
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Ripoll Servent, Ariadna. "When Words Do Not Follow Deeds: An Analysis of Party Competition Between Centre-Right and Eurosceptic Radical-Right Parties in the European Parliament". In Palgrave Studies in European Union Politics, 123–46. Cham: Springer International Publishing, 2022. http://dx.doi.org/10.1007/978-3-030-94012-6_6.
Testo completoAbstract (sommario):
AbstractThe rise in Eurosceptic and populist parties has put pressure on mainstream centre-right parties and often leads to difficult choices between staying in the centre and moving farther to the right. Given the second-order nature of European Parliament (EP) elections, these shifts have direct consequences for the balance of power on the right of the political spectrum. Increased levels of polarisation in the past legislative periods have put the European People’s Party (EPP) under pressure and led to more ideological diversity. With a content analysis of legislative amendments from two files—the Eurodac Regulation (2016/0132/COD) and the Qualifications Regulation (2016/0223/COD)—the chapter examines whether and under which conditions the positions of the EPP can be clearly delimited from those of far-right Eurosceptic and populist parties. These two files compare dynamics of cooperation and competition in the area of migration, a classical bone of contention between radical- and centre-right parties.
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Beggel, Sebastian, Joachim Pander e Jürgen Geist. "Ecological Indicators for Surface Water Quality - Methodological Approaches to Fish Community Assessments in China and Germany". In Terrestrial Environmental Sciences, 47–67. Cham: Springer International Publishing, 2021. http://dx.doi.org/10.1007/978-3-030-80234-9_2.
Testo completoAbstract (sommario):
AbstractAssessments of aquatic ecosystem health rely increasingly on biological indicators such as fish community structure, but national approaches differ. To use bioindicators efficiently and to allow cross-country comparisons, standardized tools and methods are required. Within this study, currently applied procedures for stream ecosystem assessment in China and Germany are summarized and active and passive fish sampling methodologies used in both countries are investigated. The methodological comparison was based on the results of a joint Chinese German workshops within the SINOWATER project in 2016. A joint sampling campaign was then conducted in 2017 at 6 representative sites within 70 km of the Fan River, a tributary to the Liao River System in Liaoning province, China. Active methods comprised single-pass electrofishing methods as typically applied in Germany and China as well as seining. As passive methods, common minnow traps, gill-netting and longline-fishing were used. To allow the comparability between methods, a standardized sampling design comprising several replicates at each site was chosen, covering a range of different ecological stream conditions. By comparison of the different fishing methodologies, electrofishing yielded the best overall results to assess fish biodiversity in terms of species abundance, richness and catch per unit effort. Differences in the effectiveness of the different electrofishing approaches mostly depended on the power source used. To cover the full spectrum of the fish community and to detect very rare species, a combination of different active and passive methods was most useful. If electrofishing is the method of choice, it is very important to adjust the gear power to river specific conditions such as flow, size and depth. The results of this joint Chinese-German study may aid in the selection of suitable sampling methods for fish community assessments in the future.
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Liu, Mingxuan, Xinyang Fan, Danrong Song, Bin Zheng e Meng Zhang. "Fatigue Analysis Method of Steel Containment of Floating Nuclear Power Plant". In Springer Proceedings in Physics, 1046–59. Singapore: Springer Nature Singapore, 2023. http://dx.doi.org/10.1007/978-981-99-1023-6_88.
Testo completoAbstract (sommario):
AbstractFloating nuclear power plant (FNPP) is a movable nuclear power plant built on the floating platform, which can provide clean and stable power for remote coastal areas, and are currently a hot research topic in the field of nuclear power. The steel containment is located in the reactor compartment of the FNPP and it is an important safety guarantee structure. Fatigue and fracture have been an important issue for ship and offshore structures for a long time. Fatigue failure of containment will have serious consequences.In order to research the fatigue life analysis method of steel containment of the first FNPP in China, the paper adopts miner linear cumulative damage theory and spectral analysis method, based on the American Society of Mechanical Engineers (ASME) standards and relevant standards of China Classification Society (CCS), and uses AQWA to analyze Wave load of FNPP. The hydrodynamic calculation results are imported into finite element model to analyze the structural response of each point of containment, and calibrate the transfer function data of each key point by using the linear system theory and regular wave periodic evaluation method. The fatigue analysis of each point is carried out according to the transfer function and the wave dispersion diagram drawn by the forty years monitoring sea conditions of the working sea area of the FNPP. The result shows that the fatigue life of steel containment is superior and meets the service requirements.
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Yesilyurt, Isa, e A. D. Ball. "Detection and Location of Tooth Defect in a Two-Stage Helical Gearbox Using the Smoothed Instantaneous Power Spectrum". In Condition Monitoring and Diagnostic Engineering Management, 465–72. Elsevier, 2001. http://dx.doi.org/10.1016/b978-008044036-1/50054-8.
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Maurya, Rakesh Kumar, e Akhil Nekkanti. "Combustion Instability Analysis Using Wavelets in Conventional Diesel Engine". In Mathematical Concepts and Applications in Mechanical Engineering and Mechatronics, 390–413. IGI Global, 2017. http://dx.doi.org/10.4018/978-1-5225-1639-2.ch019.
Testo completoAbstract (sommario):
Combustion instability affects the drivability, power, engine performance and efficiency. Elimination of combustion instabilities leads to increase in power for the same fuel economy. Effective controller can reduce combustion instabilities by understanding patterns in the cyclic variations. In this study, cyclic variations of combustion parameters were analyzed in a diesel engine using wavelet analysis. The experiments were conducted at varying loads and compression ratios at 1500 rpm. At steady state condition, cylinder pressure data of 2000 consecutive combustion cycles was measured. Continuous Wavelet Transform was used to capture non-stationary or transient features that might not have been detected using other transforms. Wavelet Power Spectrum (WPS) and Global Wavelet Spectrum were further used to determine the relationship between fluctuations in combustion parameters. Contour Plots were plotted based on WPS for visualizing the intensity and frequency of cyclic Variations. It was found that cyclic variability decreases with increase in engine load and compression ratio.
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Selvaraju, Vinothini, P. A. Karthick e Ramakrishnan Swaminathan. "Analysis of Frequency Bands of Uterine Electromyography Signals for the Detection of Preterm Birth". In Studies in Health Technology and Informatics. IOS Press, 2021. http://dx.doi.org/10.3233/shti210165.
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In this work, an attempt has been made to analyze the influence of the frequencies bands in uterine electromyography (uEMG) signals on the detection of preterm birth. The signals recorded from the women’s abdomen during pregnancy are considered in this study. The signals are subjected to preprocessing using digital bandpass Butterworth filter and decomposed into different frequency bands namely, 0.3-1.0 Hz (F1), 1.0-2.0 Hz (F2) and 2.0-3.0Hz (F3). Spectral features namely, peak magnitude, peak frequency, mean frequency and median frequency are extracted from the power spectrum. Classification models namely, k-nearest neighbor, support vector machine and random forest are employed to distinguish the term and preterm conditions. The results show that the features extracted from these frequency bands are able to differentiate term and preterm condition. Particularly, the frequency band F3 performs better than other frequency bands. The features associated with these frequencies along with random forest classification model achieves a maximum accuracy of 75.2%. Thus, these measures could be used to accurately detect the preterm birth well in advance.
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Livingston, Lucy A., e Francesca Happé. "Understanding Atypical Social Behaviour Using Social Cognitive Theory". In The Cognitive Basis of Social Interaction Across the Lifespan, 147–76. Oxford University Press, 2021. http://dx.doi.org/10.1093/oso/9780198843290.003.0007.
Testo completoAbstract (sommario):
Autism spectrum disorder (ASD) is often proposed to be the condition of atypical social cognition, because the social behaviours observed in ASD can be attributed to a range of atypicalities in underlying social cognitive processing. This chapter presents and critiques the most prominent social cognitive theories. We suggest that the ‘Theory of Mind’ theory of autism—which proposes that autistic social atypicalities are best explained by difficulties in inferring the mental states of other people—continues to be the most compelling social cognitive theory, with the greatest explanatory power. We also reflect upon ongoing issues that stymy our understanding of the social cognitive underpinnings of ASD, including heterogeneity, co-occurring conditions, and compensatory ability. Finally, the chapter touches on ongoing debates in the field and suggests avenues for future research required to facilitate knowledge of autistic social behaviour and cognition across the whole lifespan.
Atti di convegni sul tema "POWER SPECTRUM CONDITION"
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Su, Jonathan K., e Bernd Girod. "Fundamental performance limits of power-spectrum condition-compliant watermarks". In Electronic Imaging, a cura di Ping W. Wong e Edward J. Delp III. SPIE, 2000. http://dx.doi.org/10.1117/12.384986.
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Rahman, Ananna, Niloy Sikder e Abdullah-Al Nahid. "Heart Condition Monitoring Using Ensemble Technique Based on ECG Signals’ Power Spectrum". In 2019 International Conference on Computer, Communication, Chemical, Materials and Electronic Engineering (IC4ME2). IEEE, 2019. http://dx.doi.org/10.1109/ic4me247184.2019.9036493.
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De Koker, E., e E. Van Rooyen. "Optimal apodization of acoustooptic power spectrum analyzers". In OSA Annual Meeting. Washington, D.C.: Optica Publishing Group, 1989. http://dx.doi.org/10.1364/oam.1989.mg7.
Testo completoAbstract (sommario):
Interferometric spectrum analyzers offer improved performance over power spectrum analyzers but not without a substantial increase in complexity. In this paper a technique for improving the performance of power spectrum analyzers is presented. The intensity profile of the input light beam controls the level of the sidelobes in the detection plane as well as the resolution of the analyzer. This profile, together with acoustic attenuation also controls the instantaneous dynamic range by suppressing acoustic nonlinearities. The most common criterion used for determining the resolution of an acoustooptic spectrum analyzer is the Rayleigh criterion. The application of this criterion requires two signals of the same power, a condition which rarely occurs in practice. A condition more likely to occur is that the signal powers vary extensively and require a large dynamic range. It is for this reason that the use of the Rayleigh criterion in spectrum analysis is not recommended. A different criterion is suggested and shown to be more appropriate. The most general weighting function used is Gaussian. This function is evaluated by using the suggested criterion for resolution shown not to be optimal. An optimal weighting function is determined incorporating the effect of acoustic attention and acoustic nonlinearities. This is shown to exert an appreciable influence on system specifications and design.
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Xing, Yu-Jin, Zhang Qu e Wen-Bin Shangguan. "Identification of Vehicle Noise Based on Transfer Path and Condition Power Spectrum Analysis". In WCX SAE World Congress Experience. 400 Commonwealth Drive, Warrendale, PA, United States: SAE International, 2022. http://dx.doi.org/10.4271/2022-01-0306.
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Azimirad, M., A. R. M. Gharabaghi e M. R. Chenaghlou. "Deterministic-Spectral Fatigue Analysis of a Typical Jacket Platform (SPD1) Using Directional Wave Spectrum". In ASME 2007 26th International Conference on Offshore Mechanics and Arctic Engineering. ASMEDC, 2007. http://dx.doi.org/10.1115/omae2007-29418.
Testo completoAbstract (sommario):
Fixed offshore platforms or Jacket type platforms are the most common offshore structures used for oil & gas Exploration & Production industry in Persian Gulf, because water depth is such that the shallow water condition is dominant. Sea waves as dominant environmental loading are cyclic and have random nature. The applied cyclic sea wave forces will lead to fatigue damages in jacket’s joints. There are different methods to investigate the fatigue life of jackets such as deterministic method, simplified method, spectral method and transient method. Spectral method is a suitable method, which can consider the random nature of sea waves in fatigue analysis. Deterministic-spectral method developed by Bishop et al. is used to estimate the fatigue life of shallow water jacket platforms. However, in this method the frequency spectrum of waves is used in the analysis, but generally sea waves are propagating in different directions with different frequencies, so directional wave spectrum can consider wave randomness more properly. In this paper, frequency domain spectral method using Deterministic-Spectral approach has been used to estimate the fatigue life of a typical jacket platform (SPD1 at South Pars Field - Persian Gulf). Base wave cases were chosen from joint histogram of height & period that is calculated based on scatter diagrams of South Pars Field. First the jacket was modeled by ANSYS software, then by applying base wave cases to it and analyzing the critical TT joint under internal cyclic forces, hot spot stress transfer functions at 8 nodes around the intersection of joint were obtained. Using JONSWAP standard spectrum and the spreading function proposed by Goda, sea state’s Power Spectral Densities (PSD) and directional spectrums are multiplied to obtain stress spectra. The fatigue damage and fatigue life then are calculated. Results indicate that the fatigue life based on frequency spectrum is less than the fatigue life based on directional spectrum.
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Mauricio, Alexandre, Shuangwen Sheng e Konstantinos Gryllias. "Condition Monitoring of Wind Turbine Planetary Gearboxes Under Different Operating Conditions". In ASME Turbo Expo 2019: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/gt2019-91136.
Testo completoAbstract (sommario):
Abstract Digitally enhanced services for wind power could reduce Operations and Maintenance (O&M) costs as well as the Levelised Cost Of Energy (LCOE). Therefore, there is a continuous need for advanced monitoring techniques which can exploit the opportunities of Internet of Things (IoT) and Big Data Analytics, revolutionizing the future of the energy sector. The heart of wind turbines is a rather complex epicyclic gearbox. Among others, extremely critical gearbox components which are often responsible for machinery stops are the rolling element bearings. The vibration signatures of bearings are rather weak compared to other components, such as gears, and as a result an extended number of signal processing techniques and tools have been proposed during the last decades, focusing towards accurate, early, and on time bearing fault detection with limited false alarms and missed detections. Envelope Analysis is one of the most important methodologies, where an envelope of the vibration signal is estimated usually after filtering around a frequency band excited by impacts due to the bearing faults. Different tools, such as Kurtogram, have been proposed in order to accurately select the optimum filter parameters (center frequency and bandwidth). Cyclic Spectral Correlation and Cyclic Spectral Coherence, based on Cyclostationary Analysis, have been proved as very powerful tools for condition monitoring. The monitoring techniques seem to have reached a mature level in case a machinery operates under steady speed and load. On the other hand, in case the operating conditions change, it is still unclear whether the change of the monitoring indicators is due to the change of the health of the machinery or due to the change of the operating parameters. Recently, the authors have proposed a new tool called IESFOgram, which is based on Cyclic Spectral Coherence and can automatically select the filtering band. Furthermore, the Cyclic Spectral Coherence is integrated along the selected frequency band leading to an Improved Envelope Spectrum. In this paper, the performance of the tool is evaluated and further extended on cases operating under different speeds and different loads. The effectiveness of the methodology is tested and validated on the National Renewable Energy Laboratory (NREL) wind turbine gearbox vibration condition monitoring benchmarking data set which includes various faults with different levels of diagnostic complexity as well as various speed and load operating conditions.
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Malagon-Carvajal, Gabriel, Jeisson Bello-Pena, Gabriel Ordonez-Plata e Cesar Duarte. "A discussion of an improved method based on a modified DFT for spectrum estimation under Asynchronous Sampling Condition". In 2016 Clemson University Power Systems Conference (PSC). IEEE, 2016. http://dx.doi.org/10.1109/psc.2016.7462825.
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Mittelstein, Michael, David Mehuys, Amnon Yariv, Rona Sarfaty e Jeffery E. Ungar. "Broadband Tunability of Gain-Flattened Quantum Well Semiconductor Lasers with an External Grating". In OSA Annual Meeting. Washington, D.C.: Optica Publishing Group, 1988. http://dx.doi.org/10.1364/oam.1988.pdp6.
Testo completoAbstract (sommario):
The spectral tunability of quantum well semiconductor lasers is found to approach the range of dye lasers. Gain spectra calculations predict, for a particular pumping condition, a wide spectral range of nearly flat gain from quantum well lasers. This flattening results from contributions to the gain, at high pumping current, from electron-hole transitions in the second (n = 2) quantized state. In addition, the gain spectrum is stretched out to shorter wavelengths. Consequently, properly designed quantum well lasers can have an effective tuning range 2 to 3 times that of conventional semiconductor lasers. This flat gain spectrum enabled us to tune broad area, single quantum well lasers over a spectral width of 90 nm with an external grating. No antireflection coating of the lasers was required. Rather, the condition of broad, flattened gain was achieved by optimizing the length of the lasers to near 200 μm. Power output from the free side of the tuned lasers exceeded 200 mW (pulsed) in a single longitudinal mode over most of the spectrum. The 11% tuning range achieved is the largest published value for a semiconductor laser. This work was supported in part by the National Science Foundation and the Office of Naval Research, and M. Mittelstein acknowledges support from a Newport Research Award.
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Hassan, Mohammed A., David Coats, Yong-June Shin e Abdel E. Bayoumi. "Quadratic-nonlinearity power-index spectrum and its application in condition based maintenance (CBM) of helicopter drive trains". In 2012 IEEE International Instrumentation and Measurement Technology Conference (I2MTC). IEEE, 2012. http://dx.doi.org/10.1109/i2mtc.2012.6229264.
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Mohammed, Sufyan A., Nouby M. Ghazaly e Jamil Abdo. "Gearbox Vibration Analysis Using a Spectrogram and Power Spectrum Approach". In ASME 2022 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2022. http://dx.doi.org/10.1115/imece2022-95218.
Testo completoAbstract (sommario):
Abstract Vibration analysis is essential in rotating machinery fault diagnosis. As a vibration contains the dynamic information of a machine, improvement based on analysis has an effective role in predictive and preventive maintenance. In the present paper, the short Fourier transform is applied to determine the frequency variation of a gearbox signal with time due to different loads and driver speeds. In addition, the power spectral density (PSD) is used to represent the randomness of the signal since many frequencies occur simultaneously. The gearbox health condition is measured, and signal fault is simulated as tooth breakage for five cases: 0% (healthy), 25%, 50%, 75%, and 100% (complete tooth breakage). The obtained results proved that it is more powerful to use both spectrograms and PSD for gearbox fault diagnosis. This method is also improved with the ability to distinguish gearbox vibration signals for anomaly detection.
Rapporti di organizzazioni sul tema "POWER SPECTRUM CONDITION"
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Olsson, Olle. Industrial decarbonization done right: identifying success factors for well-functioning permitting processes. Stockholm Environment Institute, novembre 2021. http://dx.doi.org/10.51414/sei2021.034.
Testo completoAbstract (sommario):
1 Introduction 1.1 The urgency of industrial decarbonization The last few years have seen several of the world’s largest carbon dioxide-emitting countries and leading heavy industry companies committing to mid-century net-zero targets (Buckley 2021; Denyer and Kashiwagi 2020; McCurry 2020; Myers 2020). Consequently, the discussion on economy-wide transition to net-zero is accelerating, with focus shifting from “if” to “when” and “how”, even for heavy industry sectors like steel, cement and chemicals. This makes it increasingly urgent to analyse not just whether it is technologically feasible to decarbonize heavy industry, but also investigate issues more directly related to practical implementation. This includes site-specific planning, infrastructure availability, and consultation with local authorities and other stakeholders. Many of the latter considerations are formalized as part of the permitting processes that are an essential vehicle to ensure that industrial interests are balanced against interests of society at large. However, doing this balancing act can turn out to be very complicated and associated with uncertainties as to their outcome, as well as being demanding in resources and time. At the same time, to ensure broad buy-in and support from society, the investments needed must be implemented in a way that takes a broad spectrum of sustainability concerns into account, not just climate change mitigation. A key question is if and how permitting processes can run more smoothly and efficiently while still ensuring inclusive consultations, fair procedures and adherence to legal certainty. This policy brief discusses this question from the starting point of Swedish conditions, but many of the points raised will be relevant for a broader international discussion on taking industrial decarbonization to implementation. 1.2 Industrial transition and permitting processes in Sweden Decarbonization of the industrial sector in Sweden essentially entails a relatively small number of investment projects in the cement, steel, petrochemical and refinery sectors, where the vast majority of carbon emissions are concentrated (Karltorp et al. 2019; Nykvist et al. 2020). However, while few in number, the size of these investments means that their implementation will by necessity become relevant to many other parts of society. In connection with the increasing focus on how to implement industrial decarbonization in Sweden, discussions about permitting processes have been brought higher up on the agenda. While there has been an active discussion on permitting processes in Sweden for quite some time, it has primarily been focused on aspects related to mining and wind power (Larsen et al. 2017; Raitio et al. 2020). The last few years have, however, focused increasingly on industrial projects, in particular related to a proposed – though eventually cancelled – expansion of an oil refinery in the southwestern part of the country (Blad 2020). In terms of political discussions, both the governmental initiative Fossil-free Sweden (2020) and the Swedish Climate Policy Council (2020) emphasize that permitting processes need to become faster in order for Sweden’s industrial transition to be implemented in line with the time plan set by the 2017 Swedish Climate Act. Business representatives and organizations are also voicing concerns about the slow speed of permitting (Balanskommissionen 2019; Jacke 2018). At the same time, criticism has been raised that much of the environmental damage done in Sweden comes from activities conducted within limits set by environmental permits, which could be a flaw in the system (Malmaeus and Lindblom 2019). Finally, recent public inquiries have also discussed permitting processes.