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1
Eberhard, Monika J. B., Jan-Hendrik Schleimer, Susanne Schreiber, and Bernhard Ronacher. "A temperature rise reduces trial-to-trial variability of locust auditory neuron responses." Journal of Neurophysiology 114, no. 3 (September 2015): 1424–37. http://dx.doi.org/10.1152/jn.00980.2014.
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The neurophysiology of ectothermic animals, such as insects, is affected by environmental temperature, as their body temperature fluctuates with ambient conditions. Changes in temperature alter properties of neurons and, consequently, have an impact on the processing of information. Nevertheless, nervous system function is often maintained over a broad temperature range, exhibiting a surprising robustness to variations in temperature. A special problem arises for acoustically communicating insects, as in these animals mate recognition and mate localization typically rely on the decoding of fast amplitude modulations in calling and courtship songs. In the auditory periphery, however, temporal resolution is constrained by intrinsic neuronal noise. Such noise predominantly arises from the stochasticity of ion channel gating and potentially impairs the processing of sensory signals. On the basis of intracellular recordings of locust auditory neurons, we show that intrinsic neuronal variability on the level of spikes is reduced with increasing temperature. We use a detailed mathematical model including stochastic ion channel gating to shed light on the underlying biophysical mechanisms in auditory receptor neurons: because of a redistribution of channel-induced current noise toward higher frequencies and specifics of the temperature dependence of the membrane impedance, membrane potential noise is indeed reduced at higher temperatures. This finding holds under generic conditions and physiologically plausible assumptions on the temperature dependence of the channels' kinetics and peak conductances. We demonstrate that the identified mechanism also can explain the experimentally observed reduction of spike timing variability at higher temperatures.
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Yu, Gary. "Offset‐amplitude variation and controlled‐amplitude processing." GEOPHYSICS 50, no. 12 (December 1985): 2697–708. http://dx.doi.org/10.1190/1.1441890.
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The partition of plane seismic waves at plane interfaces introduces changes in seismic amplitude which vary with angle of incidence. These amplitude variations are a function of the elastic parameters of rocks on either side of the interface. Controlled‐amplitude processing is designed to obtain the true amplitude information which is geologic in origin. The offset‐amplitude information may be successfully used to predict the fluid type in reservoir sands. Various tests were carried out on a seismic profile from the Gulf Coast. The processing comparison emphasized the effects and pitfalls of trace equalization, coherent noise, offset, and surface‐related problems. Two wells drilled at amplitude anomaly locations confirmed the prediction of hydrocarbons from offset‐amplitude analysis. Furthermore, controlled‐amplitude processing provided clues in evaluating reservoir quality, which was not evident on the conventional relative amplitude data.
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Wilson, Hamish, and Lutz Gross. "Amplitude variation with offset-friendly bootstrapped differential semblance." GEOPHYSICS 82, no. 5 (September 1, 2017): V297—V309. http://dx.doi.org/10.1190/geo2016-0395.1.
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Spectral noise, low resolution, and attenuation of semblance peaks due to amplitude variation with offset (AVO) anomalies hamper the reliability of velocity analysis in the semblance spectrum for seismic data processing. Increasing resolution and reducing noise while accounting for AVO has posed a challenge in various semblance schemes due to a trade-off in resolution and AVO detectability. A new semblance scheme is introduced that aims to remove this trade-off. The new scheme uses the concepts of bootstrapped differential semblance with trend-based AB semblance. Results indicate that the new scheme indeed increases spectral resolution, reduces noise, and accounts for AVO anomalies. These improvements facilitate velocity control for automatic and manual picking methods and, hence, provide a means for more reliable apparent velocity models.
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Cooper, Steven. "Wind Farm Noise—Modulation of the Amplitude." Acoustics 3, no. 2 (June 1, 2021): 364–90. http://dx.doi.org/10.3390/acoustics3020025.
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The operation of a wind turbine results in a series of pulses where there is a significant instantaneous increase in the amplitude of the pressure signal, dependent upon the wind speed at the turbine blades. The variations in the amplitude of the sound being emitted can be significant at receiver locations both as an audible and inaudible sound. The modulation of the A-weighted amplitude of the acoustic signature for wind turbines is often referred to as “amplitude modulation”. Criteria have been proposed in the UK to define “excessive amplitude modulation”. In a technical sense, the general descriptor for wind turbine amplitude modulation is incorrect. The correct term for the variation of the A-weighted level is modulation of the amplitude. The rate of the modulation of the dB(A) level occurs at the blade pass frequency, which is in the infrasound region. Turbines can exhibit amplitude modulation in the low frequency region. The differences between amplitude modulation and modulation of the amplitude occurring at an infrasound rate are discussed in the context for an environmental assessment of a wind farm with respect to permit conditions and a simplified method of assessment with respect to the Modulation Index.
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Chen, Yangkang, Weilin Huang, Yatong Zhou, Wei Liu, and Dong Zhang. "Plane-wave orthogonal polynomial transform for amplitude-preserving noise attenuation." Geophysical Journal International 222, no. 3 (June 20, 2020): 1789–804. http://dx.doi.org/10.1093/gji/ggaa188.
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SUMMARY Amplitude-preserving data processing is an important and challenging topic in many scientific fields. The amplitude-variation details in seismic data are especially important because the amplitude variation is directly related with the subsurface wave impedance and fluid characteristics. We propose a novel seismic noise attenuation approach that is based on local plane-wave assumption of seismic events and the amplitude preserving capability of the orthogonal polynomial transform (OPT). The OPT is a way for representing spatially correlative seismic data as a superposition of polynomial basis functions, by which the random noise is distinguished from the useful energy by the high orthogonal polynomial coefficients. The seismic energy is the most correlative along the structural direction and thus the OPT is optimally performed in a flattened gather. We introduce in detail the flattening operator for creating the flattened dimension, where the OPT can be applied subsequently. The flattening operator is created by deriving a plane-wave trace continuation relation following the plane-wave equation. We demonstrate that both plane-wave trace continuation and OPT can well preserve the strong amplitude variation existing in seismic data. In order to obtain a robust slope estimation performance in the presence of noise, a robust slope estimation approach is introduced to substitute the traditional method. A group of synthetic, pre-stack and post-stack field seismic data are used to demonstrate the potential of the proposed framework in realistic applications.
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Kim, Hack-Yoon. "Speech Enhancement Using Robust MAP Amplitude Spectral Estimator for Arbitrary Noise Variation." Journal of Korean Institute of Information Technology 14, no. 2 (February 29, 2016): 37. http://dx.doi.org/10.14801/jkiit.2016.14.2.37.
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Ojima, Hirotaka, Kazutaka Nonomura, Li Bo Zhou, Jun Shimizu, and Teppei Onuki. "Design of Digital Filters for Si Wafer Surface Profile Measurement - Denoising by Total Variation." Key Engineering Materials 516 (June 2012): 332–36. http://dx.doi.org/10.4028/www.scientific.net/kem.516.332.
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In the semiconductor industry, high resolution and high accuracy measurement is needed for the geometric evaluation of Si wafers. The flatness parameters are important to evaluate the wafer profile and are required to be the same level as the design rule of IC, and the tolerance for flatness is very tight. According to SEMI (Semiconductor Equipment and Materials International) standards, the required wafer flatness will be 22 nanometres by the year 2016. However, to obtain a higher resolution for sensors, the uncertainty becomes very large compared to the resolution and influences the measured data when the noise is increased. High resolution instruments always incorporate a certain degree of noise. In the presence of noise, form parameters are normally biased. Correction and compensation need a large population of measurements to analytically estimate both bias and uncertainty. The estimation is still far from perfect because of the nature of noise. Another approach is to extract a true profile by filtering noise from the measured data. For the purpose of noise reduction, low-pass filters by Gaussian smoothing and Fourier transform are often used. The noise is normally considered to be a component of small deviation (amplitude) with high frequency which also takes a normal distribution around zero. However these conventional filters can remove the noise in the spatial frequency domain only. So, it is essential to design a filter capable of removing the noise both in the spatial frequency domain and the amplitude component. Thus, we have designed and developed new type of digital filter for denoising. We introduce two new digital filters. One is wavelet transform capable of denoising in the spatial frequency domain and amplitude component, and the other is total variation that can be applied to discontinuous signals without introducing artificial Gibbs Effects.
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Nykaza, Edward T., and Dan Valente. "Community and individual variation in response to noise from high amplitude impulsive sounds." Journal of the Acoustical Society of America 132, no. 3 (September 2012): 2086. http://dx.doi.org/10.1121/1.4755703.
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Rutherford, Steven R. "Noise‐discriminating, statistical‐amplitude compensation for AVO analysis." GEOPHYSICS 58, no. 12 (December 1993): 1831–39. http://dx.doi.org/10.1190/1.1443398.
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Statistical amplitude balancing/compensation techniques are widely used in the industry to prepare seismic data for amplitude variation with offset (AVO) processing and analysis. The intent of such statistical techniques is to compensate the data for the average signal decay with offset such that reflectors that are anomalous with respect to this average decay can be detected and analyzed. Statistical amplitude compensation techniques, however, suffer from a serious flaw when applied to data sets having low signal‐to‐noise ratios (S/N) that vary with offset. An artifact of this flaw is often a suppression of the AVO effects one is trying to detect. When S/N is low and decreases with offset, as is usually the case, the rms amplitude measurements that statistical techniques are based upon become increasingly dominated by noise as offset increases. This can lead to a suppression of the far offsets by the balancing scalars responding to a noise level that is increasing with offset. A noise‐discriminating, statistical‐amplitude compensation technique can be designed that counteracts the detrimental effects of noise. This technique is based on the premise that a common‐midpoint (CMP) ensemble average of crosscorrelations of like offset data is proportional to the average signal amplitude corresponding to that offset. The average signal decay with offset can be estimated with this technique and used to amplitude compensate a data set for AVO analysis. The noise‐discriminating statistical technique performs extremely well on synthetic data. When applied to a Gulf of Mexico data set having poor S/N characteristics, the technique also performs well and offers encouragement that it will be useful in actual practice.
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ZHANG, Y. X., C. C. BOON, and K. S. YEO. "DESIGN AND ANALYSIS OF A 2.4 GHz HYBRID TYPE AUTOMATIC AMPLITUDE CONTROL VCO WITH FORWARD NOISE REDUCTION." Journal of Circuits, Systems and Computers 23, no. 04 (April 2014): 1450048. http://dx.doi.org/10.1142/s0218126614500480.
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This paper presents a voltage-controlled oscillator (VCO) with automatic amplitude control (AAC) loop. The proposed AAC VCO employs a hybrid type AAC loop and targets the Industrial, Scientific and Medical (ISM) band applications. The proposed AAC loop can also prevent the AAC from generating extra noise to the VCO and avoid stability problem which is common for conventional AAC loop. Detail transient analysis of this AAC VCO is derived. Based on this analysis, design steps applicable for such type of AAC loop is obtained. Measurement result shows the peak amplitude variation over the operation range of 2.25–2.54 GHz is less than 9 mV (without the AAC loop, amplitude variation can be as large as 40 mV, or 22.2% for 180 mV amplitude). Power consumption of the proposed AAC VCO is 4.5 mW while the power consumed by the loop is 0.8 mW and phase noise is -105 dBc/Hz at 100 kHz offset frequency. Worst case settling time is less than 10.5 μs.
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Bekara, Maïza, and Mirko van der Baan. "High-amplitude noise detection by the expectation-maximization algorithm with application to swell-noise attenuation." GEOPHYSICS 75, no. 3 (May 2010): V39—V49. http://dx.doi.org/10.1190/1.3428749.
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High-amplitude noise is a common problem in seismic data. Current filtering techniques that target this problem first detect the location of the noise and then remove it by damping or interpolation. Detection is done conventionally by comparing individual data amplitudes in a certain domain to a user-controlled local threshold. In practice, the threshold is optimally tuned by trial and error and is often changed to match the varying noise power across the data set. We have developed an automatic method to compute the appropriate threshold for high-amplitude noise detection and attenuation. The main idea is to exploit differences in statistical properties between noise and signal amplitudes to construct a detection criterion. A model that consists of a mixtureof two statistical distributions, representing the signal and the noise, is fitted to the data. Then it is used to estimate the probability (i.e., likelihood) that each sample in the data is noisy by means of an expectation-maximization (EM) algorithm. Only those samples with a likelihood greater than a specific threshold are considered to be noise. The resulting probability threshold is better adapted to the data compared to a conventional amplitude threshold. It offers the user, through the probability threshold value, the possibility to quantify the confidence in whether a large amplitude anomaly is considered as noise. The method is generic; however, our work develops and implements the method for swell-noise attenuation. Initial results are encouraging, showing slightly better performance than an optimized conventional method but with much less parameter testing and variation.
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Sarkar, Debashish, Robert T. Baumel, and Ken L. Larner. "Velocity analysis in the presence of amplitude variation." GEOPHYSICS 67, no. 5 (September 2002): 1664–72. http://dx.doi.org/10.1190/1.1512814.
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Conventional semblance velocity analysis is equivalent to modeling prestack seismic data with events that have hyperbolic moveout but no amplitude variation with offset (AVO). As a result of its assumption that amplitude is independent of offset, this method might be expected to perform poorly for events with strong AVO—especially for events with polarity reversals at large offset, such as reflections from tops of some class 1 and class 2 sands. We find that substantial amplitude variation and even phase change with offset do not compromise the conventional semblance measure greatly. Polarity reversal, however, causes conventional semblance to fail. The semblance method can be extended to take into account data with events that have amplitude variation, expressed by AVO intercept and gradient (i.e., the Shuey approximation). However, because of the extra degrees of freedom introduced in AVO‐sensitive semblance, resolution of the estimated velocities is decreased. This is because the data can be modeled acceptably with a range of combined erroneous velocity and AVO behavior. To address this problem, in addition to using the Shuey equation to describe the amplitude variation, we constrain the AVO parameters (intercept and gradient) to be related linearly within each semblance window. With this constraint we can preserve velocity resolution and improve the quality of velocity analysis in the presence of amplitude and even polarity variation with offset. Results from numerical tests suggest that the modified semblance is accurate in the presence of polarity reversals. Tests also indicate, however, that in the presence of noise, the signal peak in conventional semblance has better standout than does that in the modified semblance measures.
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Tran, Hoai-Nam. "Properties of Neutron Noise Induced by Localized Perturbations in an SFR." Science and Technology of Nuclear Installations 2015 (2015): 1–14. http://dx.doi.org/10.1155/2015/140979.
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Investigation of the properties of neutron noise induced by localized perturbations in a sodium-cooled fast reactor has been performed using a multigroup neutron noise simulator. Three representations of the noise source associated with the perturbations of absorption, fission, and scattering cross sections, respectively, were assumed to be located at the first fuel ring around the central assembly. The energy- and space-dependent noise, that is, the amplitude and the phase, was calculated in a wide range of frequencies, for example, 0.1–100 Hz. The results show that in the important energy range (>1.0 keV) where the noise amplitude is significant the phase is almost constant with energy at the calculated frequencies despite the source types. At low frequencies, the variation of the phase is negligibly small at a large distance from the source. The perturbation in several fast groups has a significant contribution and dominates the amplitude and the phase of the induced noise.
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Liu, Hongxing, Jingye Li, Xiaohong Chen, Bo Hou, and Li Chen. "Amplitude variation with offset inversion using the reflectivity method." GEOPHYSICS 81, no. 4 (July 2016): R185—R195. http://dx.doi.org/10.1190/geo2015-0332.1.
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Most existing amplitude variation with offset (AVO) inversion methods are based on the Zoeppritz’s equation or its approximations. These methods assume that the amplitude of seismic data depends only on the reflection coefficients, which means that the wave-propagation effects, such as geometric spreading, attenuation, transmission loss, and multiples, have been fully corrected or attenuated before inversion. However, these requirements are very strict and can hardly be satisfied. Under a 1D assumption, reflectivity-method-based inversions are able to handle transmission losses and internal multiples. Applications of these inversions, however, are still time-consuming and complex in computation of differential seismograms. We have evaluated an inversion methodology based on the vectorized reflectivity method, in which the differential seismograms can be calculated from analytical expressions. It is computationally efficient. A modification is implemented to transform the inversion from the intercept time and ray-parameter domain to the angle-gather domain. AVO inversion is always an ill-posed problem. Following a Bayesian approach, the inversion is stabilized by including the correlation of the P-wave velocity, S-wave velocity, and density. Comparing reflectivity-method-based inversion with Zoeppritz-based inversion on a synthetic data and a real data set, we have concluded that reflectivity-method-based inversion is more accurate when the propagation effects of transmission losses and internal multiples are not corrected. Model testing has revealed that the method is robust at high noise levels.
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Moura, Daniella Jorge de, Irenilza de Alencar Nääs, Elaine Cangussu de Souza Alves, Thayla Morandi Ridolfi de Carvalho, Marcos Martinez do Vale, and Karla Andrea Oliveira de Lima. "Noise analysis to evaluate chick thermal comfort." Scientia Agricola 65, no. 4 (2008): 438–43. http://dx.doi.org/10.1590/s0103-90162008000400018.
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The relationship between thermal environment and chick performance has widely been evaluated, however the consideration that the assessment of the comfort may be estimated by interpreting both amplitude and frequency of bird vocalization under tropical housing conditions is a new concept. This research had as objective of estimating thermal comfort for chicks during the heating phase using this new concept. An experiment was carried out inside a climate controlled chamber (A) for establishing the behavioral pattern related to environmental temperature limits. Forty five chicks were reared inside a 2.3 m² box. A video camera was placed 2.0 m above the birds and the images were captured and registered in a computer. From the pattern determined in the controlled chamber an evaluation of the results was proceeded in a commercial broiler farm (experiment B) using similar bird density in order to validate the data. Environmental temperature, and both amplitude and frequency of the vocalizations of the chick group reared under heating were continuously recorded in both experiments. A correlation between group behavioral pattern and their vocalization, was found, evaluated not only by the noise amplitude but also by the noise frequency spectrum. When the thermal inertia is maintained by adequate use of curtains the birds vocalized less which is coincident with the low sudden variation of the temperature of the environmental. It was possible to estimate the thermal comfort for chicks at the heating stage by recording the amplitude and the frequency of the noise emitted by the reared group.
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Mayrand, Louis J., and Bernd Milkereit. "Automated editing and true-amplitude stacking of seismic data." Canadian Journal of Earth Sciences 25, no. 11 (November 1, 1988): 1811–23. http://dx.doi.org/10.1139/e88-171.
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Lateral changes in recording conditions often require that trace amplitudes be balanced, with consequent loss of information on the lateral amplitude variation of reflected energy. We present a quality-control and automated editing algorithm that recognizes source and geophone coupling problems and different noise levels along the survey line. Problem traces are discarded, and true-amplitude stacking of the remaining ones is possible with constant scaling factors. Application of the algorithm to one of the Vancouver Island LITHOPROBE profiles gives a nominal signal-to-noise improvement of 15 dB and a better understanding of recording problems in the field. Our analysis shows that the varying strength of a reflection from near the top of the subducting Juan de Fuca plate cannot be explained by changing recording conditions alone. Results suggest that the extra effort involved in the automated optimization of common midpoint stacks of low signal-to-noise deep seismic data is warranted only if lateral amplitude information is to be preserved.
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Liu, Chunyu, Khurram Aslam, and Charles A. Langston. "Directionality of ambient noise in the Mississippi embayment." Geophysical Journal International 223, no. 2 (August 5, 2020): 1100–1117. http://dx.doi.org/10.1093/gji/ggaa366.
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SUMMARY Cross-correlations of ambient seismic noise from 277 broad-band stations within the Mississippi embayment (ME) with at least 1 month of recording time between 1990 and 2018 are used to estimate source locations of primary and secondary microseisms. We investigate source locations by analysing the azimuthal distribution of the signal-to-noise ratios (SNRs) and positive/negative amplitude differences. We use 84 stations with 1 yr of continuous recordings to explore seasonal variations of SNRs and amplitude differences. We also investigate the seasonal ambient noise ground motions using 2-D frequency–wavenumber (FK) analysis of a 50-station array. We observe that: (1) two major azimuths can be identified in the azimuthal distribution of SNRs and amplitude differences. We also observe two minor azimuths in the seasonal variation of SNRs, amplitude differences and 2-D FK power spectra. Monthly 2-D FK power spectra reveal that two energy sources are active in the Northern Hemisphere winter and two relatively weak sources are active in summer. (2) Backprojection suggests that primary microseisms originate along the coasts of Australia or New Zealand, Canada and Alaska, Newfoundland or Greenland and South America. (3) Secondary microseisms are generated in the deep water of the northern and southern Pacific Ocean, along the coasts of Canada and Alaska associated with near-shore reflections and in the deep water of south of Greenland. (4) Weak energy is observed in the third quadrant of the azimuthal distribution of amplitude differences of sedimentary Rayleigh and Love waves in the period band of 1–5 s and correlates with the direction of widening of the basin.
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Hu, Zeng-Zhen, Arun Kumar, Jieshun Zhu, Peitao Peng, and Bohua Huang. "On the Challenge for ENSO Cycle Prediction: An Example from NCEP Climate Forecast System, Version 2." Journal of Climate 32, no. 1 (December 7, 2018): 183–94. http://dx.doi.org/10.1175/jcli-d-18-0285.1.
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Abstract This work demonstrates the influence of the initial amplitude of the sea surface temperature anomaly (SSTA) associated with El Niño–Southern Oscillation (ENSO) following its evolutionary phase on the forecast skill of ENSO in retrospective predictions of the Climate Forecast System, version 2. It is noted that the prediction skill varies with the phase of the ENSO cycle. The averaged skill (linear correlation) of Niño-3.4 index is in a range of 0.15–0.55 for the amplitude of Niño-3.4 index smaller than 0.5°C (e.g., initial phase or neutral condition of ENSO), and 0.74–0.93 for the amplitude larger than 0.5°C (e.g., mature condition of ENSO) for 0–6-month lead predictions. The dependence of the prediction skills of ENSO on its phase is linked to the variation of signal-to-noise ratio (SNR). This variation is found to be mainly due to the changes in the amplitude of the signal (prediction of the ensemble mean) during different phases of the ENSO cycle, as the noise (forecast spread among the ensemble members), both in the Niño-3.4 region and the whole Pacific, does not depend much on the Niño-3.4 amplitude. It is also shown that the spatial pattern of unpredictable noise in the Pacific is similar to the predictable signal. These results imply that skillful prediction of the ENSO cycle, either at the initial time of an event or during the transition phase of the ENSO cycle, when the anomaly signal is weak and the SNR is small, is an inherent challenge.
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Ramig, Lorraine Olson, Ronald C. Scherer, Estelle R. Klasner, Ingo R. Titze, and Yoshiyuki Horii. "Acoustic Analysis of Voice in Amyotrophic Lateral Sclerosis." Journal of Speech and Hearing Disorders 55, no. 1 (February 1990): 2–14. http://dx.doi.org/10.1044/jshd.5501.02.
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Acoustic measures of phonatory instability (coefficient of variation for amplitude, coefficient of variation for frequency, shimmer, jitter, and harmonics-to-noise ratio), phonatory limits (maximum fundamental frequency range and maximum duration of vowel phonation), and the nasal-oral amplitude ratio were measured five times throughout a 6-month period from the phonation of a 69-year-old male patient with amyotrophic lateral sclerosis (ALS), an age- and sex-matched control subject, and on one occasion from a 16-subject control group matched to the patient in age and sex. The patient was free of vocal symptoms at the initiation of the study. When compared to the other recording sessions, the final recording of the ALS patient was characterized by increased coefficient of variation for amplitude, increased coefficient of variation for frequency, increased shimmer, increased jitter, reduced harmonics-to-noise ratio, and reduced maximum vowel duration. These acoustic manifestations of increased phonatory instability and reduced phonatory limits over time were in contrast to the consistency observed in the phonation of the longitudinal control subject and were outside the range of plus or minus one standard deviation on most acoustic variables when compared to the control group. These findings support the potential use of acoustic analysis in reflecting progression of ALS and suggest the need for further studies to investigate the relationship between acoustic analysis of voice and manifestations of neurological disease.
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Zhang, Jiu Peng, Guo Qiang Liu, and Peng Zhi Wang. "Skid-Resistance and Noise-Reducing Characteristics of Exposed-Aggregate Cement Concrete Pavement." Advanced Materials Research 1052 (October 2014): 352–57. http://dx.doi.org/10.4028/www.scientific.net/amr.1052.352.
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EACCP is a new-type cement concrete pavement with better skid-resistance and less traffic noise. In this paper, skid-resistance and noise-reducing performance of EACCP are tested and analyzed by laboratory and outdoor tests. The results indicate that the relationship between BPN and EAD is followed the parabola variation laws. With the increase of EAD, TD decreases. And skid-resistance value exists the extremum. If BPN is targeted as skid-resistance optimization goal for pavement surface features, the optimized EAD is existed and approximately to 40~60. The relationship between BPN and TD is also followed the parabola variation laws which also suggests the existence of the optimized TD scope approximately to 0.8~1.0mm.The relationship between TD and EAD can be simulated by index variation laws. With the increase of EAD, TD decreases, which proves the evident noise-reducing performance of EACCP. And the reduction amplitude of noise increases with vehicular acceleration.
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K. Hameed, Husamuldeen, W. Z. Wan Hasan, Suhaidi Shafie, Siti Anom Ahmad, and Haslina Jaafar. "Amplitude independent versus amplitude dependent muscle activity detection algorithms: a comparative study." Indonesian Journal of Electrical Engineering and Computer Science 17, no. 2 (February 1, 2020): 583. http://dx.doi.org/10.11591/ijeecs.v17.i2.pp583-593.
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<span>The amplitude dependent muscle activity detection algorithms of the surface electromyography (sEMG) signals are very sensitive to the changes in the background noise levels and the performance of these amplitude-based methods is highly deteriorated when the Signal to Noise ratio (SNR) of the sEMG signal is low. sEMG signals of deep and small muscles as well as sEMG signals recorded from patients that have neuromuscular diseases may not meet this SNR requirement which motivates the need for amplitude independent algorithms that can detect weak muscle activities. </span><span lang="EN-GB">Moreover, the sEMG signal amplitude is not constant during the recording time due to the variation in the characteristics of the electrode-skin interface and due to the changes in the ground reference level</span><span>.</span><span lang="EN-GB"> Therefore, the performance of the muscle activity detection algorithms should not be affected by the involuntary amplitude variations of the sEMG signal in order to achieve reliable control of robotic devices intended for disabled people.</span><span lang="EN-GB">To accentuate the importance of the amplitude independent muscle activity detection methods over the amplitude dependent detection methods, a comparative study has been conducted in this paper between the performance of an amplitude independent muscle activity detection algorithm (FLA-MSE algorithm) and three amplitude dependent algorithms with respect to the detection capability of weak muscle activities and with respect to the immunity against false alarms. The results have showed that the performance of the amplitude independent algorithm outperformed the performance of the amplitude dependent algorithms for detecting weak muscle activities and for robustness against false alarms.</span>
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Madsen, Rasmus Bødker, and Thomas Mejer Hansen. "Estimation and accounting for the modeling error in probabilistic linearized amplitude variation with offset inversion." GEOPHYSICS 83, no. 2 (March 1, 2018): N15—N30. http://dx.doi.org/10.1190/geo2017-0404.1.
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A linearized form of Zoeppritz equations combined with the convolution model is widely used in inversion of amplitude variation with offset (AVO) seismic data. This is shown to introduce a “modeling error,” compared with using the full Zoeppritz equations, whose magnitude depends on the degree of subsurface heterogeneity. Then, we evaluate a methodology for quantifying this modeling error through a probability distribution. First, a sample of the unknown probability density describing the modeling error is generated. Then, we determine how this sample can be described by a correlated Gaussian probability distribution. Finally, we develop how such modeling errors affect the linearized AVO inversion results. If not accounted for (which is most often the case), the modeling errors can introduce significant artifacts in the inversion results, if the signal-to-noise ratio is less than 2, as is the case for most AVO data obtained today. However, if accounted for, such artifacts can be avoided. The methodology can easily be adapted and applied to most linear AVO inversion methods, by allowing the use of the inferred modeling error as a correlated Gaussian noise model.
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Avelino, P. P., M. S. Cunha, and W. J. Chaplin. "Modelling stochastic signatures in classical pulsators." Monthly Notices of the Royal Astronomical Society 492, no. 3 (January 15, 2020): 4477–83. http://dx.doi.org/10.1093/mnras/staa125.
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ABSTRACT We consider the impact of stochastic perturbations on otherwise coherent oscillations of classical pulsators. The resulting dynamics are modelled by a driven damped harmonic oscillator subject to either an external or an internal forcing and white noise velocity perturbations. We characterize the phase and relative amplitude variations using analytical and numerical tools. When the forcing is internal the phase variation displays a random walk behaviour and a red noise power spectrum with a ragged erratic appearance. We determine the dependence of the root mean square phase and relative amplitude variations (σΔφ and σΔA/A, respectively) on the amplitude of the stochastic perturbations, the damping constant η, and the total observation time tobs for this case, under the assumption that the relative amplitude variations remain small, showing that σΔφ increases with $t_{\rm obs}^{1/2}$ becoming much larger than σΔA/A for tobs ≫ η−1. In the case of an external forcing the phase and relative amplitude variations remain of the same order, independent of the observing time. In the case of an internal forcing, we find that σΔφ does not depend on η. Hence, the damping time cannot be inferred from fitting the power of the signal, as done for solar-like pulsators, but the amplitude of the stochastic perturbations may be constrained from the observations. Our results imply that, given sufficient time, the variation of the phase associated with the stochastic perturbations in internally driven classical pulsators will become sufficiently large to be probed observationally.
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Chen, Wen Yan, and Hang Tuo. "An Improved FFT Algorithm and its Application in the Measurement of Grounding Resistance." Advanced Materials Research 546-547 (July 2012): 260–65. http://dx.doi.org/10.4028/www.scientific.net/amr.546-547.260.
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For the problems of noise and clutter interference in the measurement of grounding resistance, the article designs a grounding resistance measurement method based on an improved FFT algorithm. We deduce the harmonic amplitude correction formula which can more accurately measure the frequency of the interference signals and the amplitude of the effective signals, and thus improve the measurement accuracy of grounding resistance. This paper also devises a grounding resistance measurement scheme combining the algorithm and the variation-frequency method. The simulation results and the validation of experimental data show that, the algorithm evidently reduces the noise and improves the measurement precision. The algorithm is of high practical value to the grounding resistance measurement.
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Panou, A. A., N. Theodulidis, P. M. Hatzidimitriou, C. B. Papazachos, and K. Stylianidis. "AMBIENT NOISE HORIZONTAL-TO-VERTICAL SPECTRAL RATIO FOR ASSESSING SITE EFFECTS IN URBAN ENVIRONMENTS: THE CASE OF THESSALONIKI CITY ( NORTHERN GREECE )." Bulletin of the Geological Society of Greece 36, no. 3 (January 1, 2004): 1467. http://dx.doi.org/10.12681/bgsg.16536.
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250 ambient noise measurements were performed in a dense grid (about 150mX150m) covering the historical center of the city of Thessaloniki (Northern Greece), that was strongly affected by the 20/6/1978 (M=6.5) damaging earthquake. The data were processed using the method of horizontal- to-vertical (H/V) spectral ratio (Nogoshi and Igarashi, 1971; Nakamura, 1989). In order to evaluate diurnal and seasonal variation (summer - winter) of the ambient noise H/V spectral ratio, systematic measurements were performed in eight sites. The fundamental frequency (fo) and the corresponding H/V amplitude level (Ao) from the ambient noise H/V spectral ratio for each site were calculated. Spatial interpolation of the fundamental frequency (fo) and the corresponding H/V amplitude level (Ao) was attempted between all points and respective contour maps were produced. Diurnal variation of the ambient noise H/V spectral ratio showed that it is preferable to perform measurements during the calm hours of a day, when manmade noise is relatively low. However, no systematic seasonal fluctuation effect on the ambient noise H/V spectral ratio was identified for the city of Thessaloniki. Contour maps of both fundamental frequency (fo) and corresponding H/V amplitude level (Ao) were compared versus the macroseismic data of the 1978 earthquake (Leventakis, 2003), as well as with related geological (IGME, 1978) and geotechnical (Anastasiadis et al., 2001) studies for the same area. Damage distribution due to 20/6/1978 earthquake (Penelis et al., 1985) was also converted to EMS_98 (European Macroseismic Scale, 1998). For seventy buildings, made of reinforced concrete, we have also compared the obtained results with the dynamic amplification of the buildings (Ubuilding) at the fundamental soil frequency (fo). The results encourage the use of ambient noise measurements along with the (H/V) spectral ratio technique as a nonexpensive and fast tool in microzonation studies to be carried out in urban environments.
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GOUGAM, LEILA AIT, MOULOUD TRIBECHE, and FAWZIA MEKIDECHE. "Large-amplitude electrostatic solitary structures in a charge varying dusty plasma with vortex-like ion distribution." Journal of Plasma Physics 73, no. 3 (June 2007): 331–46. http://dx.doi.org/10.1017/s0022377806004661.
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AbstractA numerical investigation is presented to show the existence, formation and possible realization of large-amplitude solitary potentials in a charge varying dusty plasma with trapped ion particles. These nonlinear localized structures are self-consistent solutions of the Vlasov equation representing saturated states of a three-stream unstable collisionless dusty plasma. The saturation is provided by an interplay between ion trapping and dust charging. It is found that under certain conditions the effect of dust charge variation can be quite important. In particular, it may be noted that the dust charge variation leads to an additional enlargement of the nonlinear localized structure. Furthermore, our results show that the dust charge variation provides an alternate physical mechanism causing dissipation and as a consequence causes the wave amplitude to decay and transfer to the so-called noise tail.
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Harben, P. E., and E. Hjortenberg. "Variation in microseism power and direction of approach in northeast Greenland." Bulletin of the Seismological Society of America 83, no. 6 (December 1, 1993): 1939–58. http://dx.doi.org/10.1785/bssa0830061939.
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Abstract Previous work on background noise at seismic stations in Greenland has shown minimum seismic noise in the winter months for frequencies around 1 Hz and maximum seismic noise in the winter months for periods around 6 sec. We have analyzed microseism data from three new digital seismic stations installed during the summer of 1991 in northeast Greenland at Nord, Daneborg, and Scoresbysund. We determined seasonal and station-to-station variations in spectral power density between August and December in the frequency band between 10 sec periods and 5-Hz frequencies. These variations are in agreement with previous studies at periods of 1 and 6 sec. During the summer months, all three stations recorded a minimum for the average spectral power density in the microseism band between 10- and 5-sec periods. From about 3-sec periods to at least 5-Hz frequencies, the average spectral power density is at a maximum during the summer at all three stations. Conversely, the winter months have a maximum in spectral power density between 10- and 5-sec periods and a minimum between about 3-sec periods and at least 5-Hz frequencies at all stations. Station-to-station average-spectral-power-density comparisons show that Nord and Daneborg are roughly comparable over most of the frequency band between 10-sec periods and at least 5-Hz frequencies. Scoresbysund has a systematically higher spectral power density between 8-sec periods and at least 5-Hz frequencies. Overall, Nord had the lowest background seismic noise, at some frequencies approaching the values of a low noise model. We determined average direction of approaches in the 8- to 4-sec period band for each station during the months of August and November; these determinations agreed with previous studies. The predominant average direction of approaches were: southwest for Nord, south for Daneborg, and southeast for Scoresbysund. Although the microseism amplitude is larger and the direction-of-approach scatter is smaller during the winter months at all three stations, the direction-of-approach mean is apparently independent of season. A large number of storms develop around Iceland and typically track northeast, giving rise to large amplitude microseisms at Scoresbysund but relatively small amplitude microseisms at Daneborg and no microseism activity at Nord. This complete lack of microseism energy at Nord (and to a lesser degree Daneborg) from known frequent microseism sources in the Greenland Sea is shown for one 5-day period in August 1991. Other studies have shown that thick sediments in the Atlantic Ocean's continental margins are responsible for the absence of short-period surface waves from mid-ocean ridge earthquakes that have paths traversing such continental margins. Thick sediments act to attenuate, scatter, and disperse short-period surface waves. Indirect evidence indicates that the northeast Greenland shelf has thick and variable sediment layers. Because the paths of surface waves to Nord (and to a lesser extent Daneborg) originating from typical storms in the Greenland Sea have long path lengths traversing the northeast Greenland shelf, we conclude that this is the likely explanation for the lack of southeast directions from Nord (and to a lesser degree Daneborg) in the observed microseism direction of approaches.
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Gardner, D. "Variations in amplitude and time course of inhibitory postsynaptic currents." Journal of Neurophysiology 56, no. 5 (November 1, 1986): 1424–38. http://dx.doi.org/10.1152/jn.1986.56.5.1424.
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In order to examine the relative contributions of changes in amplitude and time course to synaptic plasticity, variations in peak amplitude and time constant of decay have been analyzed from inhibitory postsynaptic currents (PSC) recorded in voltage-clamped Aplysia buccal ganglia neurons. In these cells, synaptic currents with single time constant decay can be recorded with low noise under well-controlled space clamp. Over a population of 36 neurons, duration was more narrowly distributed than amplitude, but each varied. The coefficient of variation (CV) was 0.21 for decay time constant (tau) and 0.87 for peak conductance (g peak). Population variances are larger than can be accounted for by such variables as temperature and noise amplitude, suggesting that functional modifications alter each of these determinants of synaptic effectiveness over the long term. Recordings of up to several hundred PSC in each of 16 neurons show that both PSC amplitude and time course recorded in a single cell can vary independently over short time spans. Decay remained single exponential as time course changed. CV for tau averaged 0.11; CV for g peak was 0.19. Variability of tau was not an artifact of amplitude; CV was relatively uncorrelated with current amplitudes or sample size. Smoothing and adding excess noise to each individual PSC of a set produced only small changes to CV, showing that variability was not an artifact of noise. Several specific manipulations of the presynaptic neuron altered both PSC amplitude and time course. Tetanic stimulation of the presynaptic neuron produced short-term potentiation of both amplitude and time course of subsequent PSCs. Peak amplitude was increased by 80%; tau by 12%. Reducing interspike intervals from 10 to 1 s produced habituation of both amplitude and time course, with g peak decreasing by 35 to 40% and tau by 10%. Conditioning DC depolarization of the presynaptic neuron enhanced PSC amplitude with little effect on decay time constant. Although short-term plastic changes affect PSC amplitude more than duration, each is alterable. Parallel changes in both can synergistically alter synaptic charge transfer, and therefore efficacy. Similar mechanisms may produce larger long-term differences seen between neurons.
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Lampens, P., R. Garrido, L. Parrao, J. H. Peña, T. Arentoft, and Y. Frémat. "Photometry of the δ Scuti Star DG Leo: Preliminary Results." International Astronomical Union Colloquium 191 (August 2004): 73–74. http://dx.doi.org/10.1017/s0252921100008502.
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AbstractNew uvby photoelectric photometry has been acquired for the triple star DG Leo at two different observatories equipped with analogous instrumentation. A preliminary period analysis indicates the presence of at least 3 close δ Scuti frequencies (10-12 c/d, 3-6 mmag) and a slow variation. This slow variation fits quite well with half the orbital period of the spectroscopic binary; the noise level in the amplitude spectrum is only 3–4 mmag (after prewhitening).
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Zhang, Junsheng, Mengchun Pan, Qingfa Du, Jiafei Hu, Kun Sun, Yang Yu, Xinmiao Zhang, and Huihui Luo. "Amplitude Control Method of Magnetic Flux Vertical Modulation Structure for TMR Magnetic Sensor Based on Harmonic Component of Modulated Signal." Micromachines 12, no. 6 (June 19, 2021): 722. http://dx.doi.org/10.3390/mi12060722.
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Magnetic flux vertical modulation method based on piezoelectric resonance can reduce the 1/f noise of tunnel magnetoresistance (TMR) magnetic sensor and significantly improves the low-frequency magnetic field detectivity. However, the amplitude variation of the modulation structure will lead to the instability of the sensor output. In order to improve the amplitude stability of the modulation structure, an amplitude control method based on the amplitude ratio of the first and second harmonic components of the modulated signal was proposed. Compared with the piezoelectric or capacitive feedback method, this method does not require an independent amplitude conversion circuit, and has the advantages of simple structure, high control efficiency and strong anti-interference ability. The experimental results showed that the amplitude and temperature drift of the modulated structure was significantly suppressed, which is of great significance for enhancing the adaptability of the TMR magnetic sensor to the application environments.
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Senior, A., and F. Honary. "Observations of the spatial structure of electron precipitation pulsations using an imaging riometer." Annales Geophysicae 21, no. 4 (April 30, 2003): 997–1003. http://dx.doi.org/10.5194/angeo-21-997-2003.
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Abstract. Electron precipitation can be modulated by geomagnetic pulsation activity. This can be observed as pulsation of cosmic noise absorption as measured by riometers. Observations of such pulsations exhibiting field-line resonance and particle-driven characteristics using an imaging riometer are presented and the capability of the instrument to map their spatial structure is demonstrated. It is shown that for the events studied, the spatial variation of pulsation phase as measured by the riometer agrees with that inferred from ground-based magnetometers, whereas the spatial variation of pulsation amplitude may show a different structure. It is suggested that this is consistent with the mechanism proposed by Coroniti and Kennel (1970) where one would expect a fixed phase relationship between magnetic and absorption pulsations, but where the amplitude of the absorption pulsation can depend on several factors other than the amplitude of the magnetic pulsation.Key words. Ionosphere (ionosphere–magnetosphere interactions; particle precipitation) – Magnetospheric physics (MHD waves and instabilities)
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Nie, Xin, Yangyang Zhu, and Lei Li. "The Flow Noise Characteristics of a Control Valve." Open Mechanical Engineering Journal 8, no. 1 (December 31, 2014): 960–66. http://dx.doi.org/10.2174/1874155x01408010960.
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Using the enterprise’s valve as the research object, the research studied the characteristics of the flow field and noise of the valve. The theory of (LES) LES and Lighthill acoustic analogy is applied to study the flow noise at 100% opening and at 70% opening of valve in the same flow. The result shows that the region of variation of pressure and velocity is in the valve sleeve window. The sound pressure spectrum characteristics of the same group of monitoring points were similar, when they were in low frequency. Acoustic pressure amplitude was observed to be relatively small, when monitoring points were in high frequency. When the valve opening decreased, because of the throttle effect of valve windows, the whole dB SPL of valve became strong. The noise outside the valve exhibited dipole characteristics.
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Araújo, Simone Adad, Marcos Grellet, José Carlos Pereira, and Marcelo Oliveira Rosa. "Normatização de medidas acústicas da voz normal." Revista Brasileira de Otorrinolaringologia 68, no. 4 (August 2002): 540–44. http://dx.doi.org/10.1590/s0034-72992002000400014.
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Introdução: A análise acústica da voz com o avanço da tecnologia digital surge como um exame complementar promissor para aumentar a precisão diagnóstica em laringologia. Objetivo: Normatização das medidas acústicas de freqüência fundamental, perturbação e ruído na voz normal de brasileiros dos sexos masculino e feminino. Forma de estudo: Clínico prospectivo. Material e Método: Pesquisa no período de março a agosto de 1997, no Ambulatório de Otorrinolaringologia do Hospital das Clínicas da Faculdade de Medicina de Ribeirão Preto da Universidade de São Paulo, com 80 voluntários da cidade de Ribeirão Preto e região, sendo 40 do sexo masculino e 40 do feminino, selecionados por meio de triagem, foram realizadas gravações digitais dos fonemas /a/, /e/ e /i/, originando uma amostra de 240 sinais acústicos submetidos ao Programa de Análise Acústica da Voz, desenvolvido na Escola de Engenharia de São Carlos da Universidade de São Paulo com obtenção das medidas acústicas. Resultados: Foram obtidos valores médios em relação a sexo e fonemas das medidas de: Freqüência fundamental, Jitter (Directional Perturbation Factor, Perturbation Variation Index, Jitter Ratio, Jitter Factor, Period Perturbation Quotient), Shimmer (Directional Perturbation Factor, Amplitude Variation Index, Amplitude Perturbation Quotient), Spectral Noise Level, Harmonic-to-noise ratio, Harmonic-to-noise ratio cepstrum, Normalized Noise Energy e Breathiness ratio. Conclusão: A normatização das medidas acústicas é necessária para conhecer melhor a voz normal. Os valores obtidos são compatíveis em sua grande maioria com à literatura existente.
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Scherer, Ronald C., Vernon J. Vail, and Chwen Geng Guo. "Required Number of Tokens to Determine Representative Voice Perturbation Values." Journal of Speech, Language, and Hearing Research 38, no. 6 (December 1995): 1260–69. http://dx.doi.org/10.1044/jshr.3806.1260.
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Acoustic perturbation analyses of prolonged vowels are used in determining phonatory stability characteristics. When a number of tokens are analyzed, the average perturbation values create a stability profile of the voice. How many tokens are needed to obtain a representative perturbation value? In this study, five perturbation measures were considered, namely, jitter, shimmer, harmonics-to-noise ratio, coefficient of variation for amplitude, and coefficient of variation for frequency. Subject groups were chosen on the basis of individual average perturbation values. Results indicate that, except for the harmonics-to-noise ratio, generally, the less stable the voice, the greater is the number of tokens needed to obtain representative averages. For highly stable voices, at least six tokens are suggested; for voices with normal to high levels of instability, at least 15 tokens are recommended. Regardless of vocal stability, at least 10 tokens are suggested for the harmonics-to-noise ratio measure.
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Lumi, Neeme, Ain Ainsaar, and Romi Mankin. "Noise-Induced Transitions in a Population Growth Model Based on Size-Dependent Carrying Capacity." Mathematical Problems in Engineering 2014 (2014): 1–8. http://dx.doi.org/10.1155/2014/120624.
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The stochastic dynamics of a population growth model with size-dependent carrying capacity is considered. The effect of a fluctuating environment on population growth is modeled as a multiplicative dichotomous noise. At intermediate values of population size the deterministic counterpart of the model behaves similarly to the Von Foerster model for human population, but at small and very large values of population size substantial differences occur. In the stochastic case, an exact analytical solution for the stationary probability distribution is found. It is established that variation of noise correlation time can cause noise-induced transitions between three different states of the system characterized by qualitatively different behaviors of the probability distributions of the population size. Also, it is shown that, in some regions of the system parameters, variation of the amplitude of environmental fluctuations can induce single unidirectional abrupt transitions of the mean population size.
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Zhang, Jing Zhi. "A 520MHz Wideband Variable Gain Amplifier." Applied Mechanics and Materials 556-562 (May 2014): 1564–67. http://dx.doi.org/10.4028/www.scientific.net/amm.556-562.1564.
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The design and realization of a wideband variable gain amplifier for RF system is presented. The cascade of LNA and controllable attenuation makes the design have a 0-90dB gain adjustment range. Special care is devoted to the solution of typical problems encountered in the design of the amplifier, such as signal shielding and power supply decoupling. The amplifier uses passive amplitude-frequency equalization, 0.1-460MHz band variation is less than 1dB, the 3dB bandwidth is up to 520MHz. The noise characteristic is low, the total input referred noise is less than 15.5nV⁄√¯Hz.
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Li, Shengjun, Bingyang Liu, Jianhu Gao, and Huaizhen Chen. "Amplitude Variation with Angle Inversion for New Parameterized Porosity and Fluid Bulk Modulus." Geofluids 2021 (January 13, 2021): 1–11. http://dx.doi.org/10.1155/2021/8888118.
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Estimating porosity and fluid bulk modulus is an important goal of reservoir characterization. Based on the model of fluid substitution, we first propose a simplified bulk modulus of a saturated rock as a function of bulk moduli of minerals and fluids, in which we employ an empirical relationship to replace the bulk modulus of dry rock with that of minerals and a new parameterized porosity. Using the simplified bulk modulus, we derive a PP-wave reflection coefficient in terms of the new parameterized porosity and fluid bulk modulus. Focusing on reservoirs embedded in rocks whose lithologies are similar, we further simplify the derived reflection coefficient and present elastic impedance that is related to porosity and fluid bulk modulus. Based on the presented elastic impedance, we establish an approach of employing seismic amplitude variation with offset/angle to estimate density, new parameterized porosity, and fluid bulk modulus. We finally employ noisy synthetic seismic data and real datasets to verify the stability and reliability of the proposed inversion approach. Test on synthetic seismic data illustrates that the proposed inversion approach can produce stable inversion results in the case of signal-to-noise ratio (SNR) of 2, and applying the approach to real datasets, we conclude that reliably results of porosity and fluid bulk modulus are obtained, which is useful for fluid identification and reservoir characterization.
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Duquet, Bertrand, and Kurt J. Marfurt. "Filtering coherent noise during prestack depth migration." GEOPHYSICS 64, no. 4 (July 1999): 1054–66. http://dx.doi.org/10.1190/1.1444613.
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We can often suppress short‐period multiples by predictive deconvolution. We can often suppress coherent noise with significantly different moveout by time‐invariant dip filtering on common‐shot, common‐receiver or NMO-corrected common‐midpoint gathers. Unfortunately, even time variant dip filtering on NMO-corrected data breaks down in the presence of strong lateral velocity variation where the underlying NMO correction breaks down. Underattenuated multiples, converted waves, and diffracted head waves can significantly impede and/or degrade prestack migration‐driven velocity analysis and amplitude variation with offset analysis as well as the quality of the final stacked image. Generalization of time‐variant dip filtering based on conventional NMO corrections of common‐midpoint gathers also breaks down for less conventional data processing situations where we wish to enhance data having nonhyperbolic moveout, such as converted wave energy or long‐offset P-wave reflections in structurally deformed anisotropic media. We present a methodology that defines a depth‐variant velocity filter based on an approximation to the true velocity/depth structure of the earth developed by the interpreter/processor during the normal course of their prestack imaging work flow. Velocity filtering in the depth domain requires the design and calibration of two new least‐squares transforms: a constrained least‐squares common offset Kirchhoff depth migration transform and a transform in residual migration‐velocity moveout space. Each of these new least‐squares transforms can be considered to be generalizations of the well‐known discrete Radon transform commonly used in the oil and gas exploration industry.
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Tyiasning, Stephanie, and Dennis Cooke. "A comparison of competing amplitude variation with offset techniques applied to tight gas sand exploration in the Cooper Basin of Australia." Interpretation 3, no. 3 (August 1, 2015): SZ15—SZ26. http://dx.doi.org/10.1190/int-2014-0262.1.
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We have developed a tight gas amplitude variation with offset (AVO) case history from the Cooper Basin of Australia that addressed the exploration problem of mapping thin fluvial tight gas sand bodies. In the Cooper Basin, Permian Toolachee and Patchawarra sands are difficult to interpret on seismic data due to strong reflections from adjacent Permian coals. This is not the common AVO problem of distinguishing between coal and gas sand, but a more difficult class-I AVO problem of mapping fluvial sands beneath a sheet coal that varies in thickness. We have reviewed local rock properties and concluded that Poisson’s ratio is probably the most appropriate rock property to solve the above exploration problem. We have compared various seismic attributes made using the extended elastic impedance (EEI) technique and a rotation of near and far partial stacks. In a synthetic modeling study that included random noise and tuning, we compared the noise-discrimination abilities of three competing AVO crossplot techniques and “rotated” the attributes made from them. These three crossplots were as follows: intercept versus gradient (I-G), full-stack versus far-minus-near (Full-FmN), and near-stack versus far-stack (N-F). Previous papers on this subject have found that (I-G) crossplots had a spurious correlation in the presence of noise that did not occur with the (Full-FmN) and (N-F) crossplots. We found that for our class-I AVO case, (1) the advantage of the (Full-FmN) and (N-F) crossplots disappeared in the presence of tuning, (2) if tuning was present, the optimal rotation angle was determined by the “tuning angle,” not by the noise angle or some desired EEI angle, and (3) if the three different crossplots were rotated by their respective “tuning” angles, the results were identical.
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Baytok, Sait, Şeref Arzu Aktepe, and Muhlis Ünaldi. "Amplitude variation with offset analysis of time-lapse land seismic data in a gas field, Thrace Basin, Turkey." Interpretation 4, no. 4 (November 1, 2016): T543—T556. http://dx.doi.org/10.1190/int-2015-0186.1.
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The Thrace Basin that is located in northwestern Turkey contains sandstone and carbonate reservoirs of Eocene and Oligocene age. Production and exploration activities are still underway. Mapping undrained sweet spots from seismic data is currently a challenge, so time lapse (4D) seismic is used to reduce the risk for new production and development drilling. We have evaluated the normalization and amplitude variation with offset (AVO) analysis of 3D-4D land seismic data in a gas producing field from which baseline and monitor surveys were acquired in 2002 and 2011, respectively. Through AVO analysis, intercept (A) and gradient (B) analysis was conducted, and fluid factor (FF) attribute maps were generated for the assessment of the remaining potential areas. Synthetic gathers were created for simulation of the AVO response, drained and undrained stages and compared with the corresponding 4D seismic data. The drainage of gas from the reservoir interval is evident from the difference maps between 2002 and 2011 seismic data. Both data sets were processed using an amplitude friendly processing sequence. This parallel processing was followed a mild data conditioning and crossequalization for reliable 4D interpretation. The 4D seismic data, especially land data, has low repeatability and requires conditioning to reduce the 4D noise. The 4D noise can be described as nonrepeatable noise, and any difference outside the reservoir zone is not related to production. A so-called crossequalization was applied to the base and the monitor data to bring out similarities so that they cancel out when differences of seismic data and its attributes indicated only the production results over the reservoir zones. As the available 4D data crossequalization software was implemented for stack data only, we created angle band stacks and crossequalized each angle band stack from the base and the monitor data cubes. Five angle band stacks from the base and the monitor prestack data cubes 0°–55° (0°–15°, 15°–25°, 25°–35°, 35°–45°, and 45°–55°) were crossequalized individually. The crossequalized angle band stacks were used in AVO analysis and AVO inversion to generate pore fill identifiers such as FF to map possible undrained zones after 10 years of production.
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Zong, Zhaoyun, and Lixiang Ji. "Model parameterization and amplitude variation with angle and azimuthal inversion in orthotropic media." GEOPHYSICS 86, no. 1 (December 14, 2020): R1—R14. http://dx.doi.org/10.1190/geo2018-0778.1.
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Horizontal layered formations with a suite of vertical or near-vertical fractures are usually assumed to be an approximate orthotropic medium and are more suitable for estimating fracture properties with wide-azimuth prestack seismic data in shale reservoirs. However, the small contribution of anisotropic parameters to the reflection coefficients highly reduces the stability of anisotropic parameter estimation by using seismic inversion approaches. Therefore, a novel model parameterization approach for the reflectivity and a pragmatic inversion method are proposed to enhance the stability of the inversion for orthotropic media. Previous attempts to characterize orthotropic media properties required using four or five independent parameters. However, we have derived a novel formulation that reduces the number of parameters to three. The inversion process is better conditioned with fewer degrees of freedom. An accuracy comparison of our formula with the previous ones indicates that our approach is sufficiently precise for reasonable parameter estimation. Furthermore, a Bayesian inversion method is developed that uses the amplitude variation with angle and azimuth (AVAZ) of the seismic data. Smooth background constraints reduce the similarity between the inversion result and the initial model, thereby reducing the sensitivity of the initial model to the inversion result. Cauchy and Gaussian probability distributions are used as prior constraints on the model parameters and the likelihood function, respectively. These ensure that the results are within the range of plausibility. Synthetic examples demonstrate that the adopted orthotropic AVAZ inversion method is feasible for estimating the anisotropic parameters even with moderate noise. The field data example illustrates the inversion robustness and stability of the adopted method in a fractured reservoir with a single well control.
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Deoniziak, Krzysztof, and Tomasz S. Osiejuk. "Seasonality and social factors, but not noise pollution, influence the song characteristics of two leaf warbler species." PLOS ONE 16, no. 9 (September 2, 2021): e0257074. http://dx.doi.org/10.1371/journal.pone.0257074.
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Changes in the acoustic signalling of animals occupying urban ecosystems is often associated with the masking effects of noise pollution, but the way in which they respond to noise pollution is not straightforward. An increasing number of studies indicate that responses can be case specific, and some species have been found to respond differently to high levels of natural versus anthropogenic noise, as well as different levels of the latter. While the perception of noise between species may vary with its source, amplitude and temporal features, some species may possess broader environmental tolerance to noise pollution, as they use higher frequency vocalizations that are less masked by low-frequency urban noise. In this study, we explored the song variation of two closely related leaf warblers, the Common Chiffchaff Phylloscopus collybita and the Willow Warbler Phylloscopus trochilus, inhabiting urban green spaces and nonurban forests. The main goal of our study was to evaluate the impact of moderate levels of noise pollution on the songs of species which use higher frequency vocalizations and large frequency bandwidth. Previous studies found that the Common Chiffchaff modified their song in response to intense noise pollution, while no such data is available for the Willow Warbler. However, the majority of urban green spaces, which serve as wildlife hot spots in urban environments are usually polluted with moderate noise levels, which may not mask the acoustic signals of species that communicate with higher frequency. We analysed the spectral and temporal song parameters of both warblers and described the ambient noise present in males’ territories. Additionally, we looked at the social and seasonal aspects of bird song, since there is more than just noise in urban ecosystems which may affect acoustic communication. We found no evidence for noise-related bird song divergence in either species, however, we showed that social factors, time of day and season influence certain Common Chiffchaff and Willow Warbler song characteristics. Lack of noise-related bird song divergence may be due to the relatively low variation in its amplitude or other noise features present within the song frequency range of the studied species. Similar results have previously been shown for a few songbird species inhabiting urban ecosystems. Although in many cases such results remain in the shadow of the positive ones, they all contribute to a better understanding of animal communication in urban ecosystems.
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Li, Yanli, Lala Mei, Ran Li, and Changan Wu. "Using Noise Level to Detect Frame Repetition Forgery in Video Frame Rate Up-Conversion." Future Internet 10, no. 9 (August 24, 2018): 84. http://dx.doi.org/10.3390/fi10090084.
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Frame repetition (FR) is a common temporal-domain tampering operator, which is often used to increase the frame rate of video sequences. Existing methods detect FR forgery by analyzing residual variation or similarity between video frames; however, these methods are easily interfered with by noise, affecting the stability of detection performance. This paper proposes a noise-level based detection method which detects the varying noise level over time to determine whether the video is forged by FR. Wavelet coefficients are first computed for each video frame, and median absolute deviation (MAD) of wavelet coefficients is used to estimate the standard deviation of Gaussian noise mixed in each video frame. Then, fast Fourier transform (FFT) is used to calculate the amplitude spectrum of the standard deviation curve of the video sequence, and to provide the peak-mean ratio (PMR) of the amplitude spectrum. Finally, according to the PMR obtained, a hard threshold decision is taken to determine whether the standard deviation bears periodicity in the temporal domain, in which way FR forgery can be automatically identified. The experimental results show that the proposed method ensures a large PMR for the forged video, and presents a better detection performance when compared with the existing detection methods.
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Marcello, Marco, and Michael R. H. White. "Spatial and temporal information coding and noise in the NF-κB system." Biochemical Society Transactions 38, no. 5 (September 24, 2010): 1247–50. http://dx.doi.org/10.1042/bst0381247.
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NF-κB (nuclear factor κB) regulates cellular stress and the immune responses to infection. Its activation results in oscillations in nuclear NF-κB abundance. We treated cells with repeated short pulses of TNFα (tumour necrosis factor α) at various intervals to mimic pulsatile inflammatory signals. At all pulse intervals analysed, we observed synchronous cycles of NF-κB nuclear translocation. Lower frequency stimulations gave repeated full-amplitude translocations, whereas higher frequency pulses gave translocations with reduced amplitude, indicating that the system failed to reset completely. Deterministic and stochastic mathematical models predicted how negative feedback loops might regulate both system resetting and cellular heterogeneity. Altering the stimulation interval gave different patterns of NF-κB-dependent gene expression, supporting a functional role for oscillation frequency. The causes of cell-to-cell variation and the possible functions of these processes in cells and tissues are discussed. The NF-κB system is just one of a number of known biological oscillators that include calcium signalling, transcription cycles, p53, the segmentation clock, the circadian clock, the cell cycle and seasonal rhythms. The way such cycles are integrated could be part of the answer as to how organisms achieve complexity while retaining the robustness of cellular decision-making processes.
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Querfurth, H. "Transducer action of isolated frog muscle spindle evoked by pseudorandom noise stimuli." Journal of Neurophysiology 55, no. 1 (January 1, 1986): 1–12. http://dx.doi.org/10.1152/jn.1986.55.1.1.
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The dynamic response properties of the isolated frog muscle spindle receptor were investigated by recording the receptor potential evoked by pseudorandom noise (PRN) stimuli. The entire dynamic range of the receptor was determined by measuring the sensory response either at different intensities of the PRN stimulus (sigma = 8-30 microns) around a constant mean length or at the same intensity while varying the mean length from resting length L0 up to L0 + 150 microns. The 3-dB bandwidth of the test signal was 130 Hz. Random stimuli often evoked brief receptor potentials with variable size but characteristic shape. This shape contained a fast depolarization transient of the receptor potential during the stretching phase of the stimulus and a slowly decaying repolarization transient during release of stretch. The depolarization transient rose faster in proportion to the increasing amplitude of the receptor potential, so that larger receptor potentials were more phasic in character than smaller ones. The repolarization transient exhibited two segments of different exponential decay: The first brief repolarization phase lasted for 5 ms; its decline (tau = 2-5 ms) was faster for larger receptor potentials. The second slowly decaying repolarization transient was the same for different receptor potential amplitudes (tau = 47 ms). Consequently, the slow repolarization transients of succeeding receptor potentials displayed temporal summation. Since the amplitude and shape of the receptor potential remained constant during repeated sequences of PRN stimuli, this test stimulus was the most appropriate for the investigation of dynamic response properties under stationary conditions. Long-term stimulation caused a small shift of the mean membrane voltage towards hyperpolarizing values. This finding together with the marked "off effect" after termination of the stimulus indicate the action of an electrogenic pumping mechanism. The dynamic range of the muscle spindle receptor extended from resting length L0 up to L0 + 100 microns. Within this range static prestretches placed a bias upon the transducing site and effectively enhanced the amplitude of the receptor potential. Further prestretch beyond the dynamic region kept the receptor potential constant at its maximum amplitude. The receptor potential amplitude distribution was not symmetrical about the mean but was skewed in favor of depolarization values responding to the stretch trajectories of the PRN stimulus. Variation of the operating point by increasing the static prestretch also shifted the mode of the response distribution towards depolarization.(ABSTRACT TRUNCATED AT 400 WORDS)
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Contreras, Arturo, Andre Gerhardt, Paul Spaans, and Matthew Docherty. "Characterization of fluvio-deltaic gas reservoirs through AVA deterministic, stochastic, and wave-equation-based seismic inversion: A case study from the Carnarvon Basin, Western Australia." Leading Edge 39, no. 2 (February 2020): 92–101. http://dx.doi.org/10.1190/tle39020092.1.
Full textAbstract:
Multiple state-of-the-art inversion methods have been implemented to integrate 3D seismic amplitude data, well logs, geologic information, and spatial variability to produce models of the subsurface. Amplitude variation with angle (AVA) deterministic, stochastic, and wave-equation-based amplitude variation with offset (WEB-AVO) inversion algorithms are used to describe Intra-Triassic Mungaroo gas reservoirs located in the Carnarvon Basin, Western Australia. The interpretation of inverted elastic properties in terms of lithology- and fluid-sensitive attributes from AVA deterministic inversion provides quantitative information about the geomorphology of fluvio-deltaic sediments as well as the delineation of gas reservoirs. AVA stochastic inversion delivers higher resolution realizations than those obtained from standard deterministic methods and allows for uncertainty analysis. Additionally, the cosimulation of petrophysical parameters from elastic properties provides precise 3D models of reservoir properties, such as volume of shale and water saturation, which can be used as part of the static model building process. Internal multiple scattering, transmission effects, and mode conversion (considered as noise in conventional linear inversion) become useful signals in WEB-AVO inversion. WEB-AVO compressibility shows increased sensitivity to residual/live gas discrimination compared to fluid-sensitive attributes obtained with conventional inversions.
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Liang, Yingbo, and Jian Fu. "Watershed Algorithm for Medical Image Segmentation Based on Morphology and Total Variation Model." International Journal of Pattern Recognition and Artificial Intelligence 33, no. 05 (April 8, 2019): 1954019. http://dx.doi.org/10.1142/s0218001419540193.
Full textAbstract:
The traditional watershed algorithm has the limitation of false mark in medical image segmentation, which causes over-segmentation and images to be contaminated by noise possibly during acquisition. In this study, we proposed an improved watershed segmentation algorithm based on morphological processing and total variation model (TV) for medical image segmentation. First of all, morphological gradient preprocessing is performed on MRI images of brain lesions. Secondly, the gradient images are denoised by the all-variational model. While retaining the edge information of MRI images of brain lesions, the image noise is reduced. And then, the internal and external markers are obtained by forced minimum technique, and the gradient amplitude images are corrected by using these markers. Finally, the modified gradient image is subjected to watershed transformation. The experiment of segmentation and simulation of brain lesion MRI image is carried out on MATLAB. And the segmentation results are compared with other watershed algrothims. The experimental results demonstrate that our method obtains the least number of regions, which can extract MRI images of brain lesions effectively. In addition, this method can inhibit over-segmentation, improving the segmentation results of lesions in MRI images of brain lesions.
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Van Cauter, E. "Estimating false-positive and false-negative errors in analyses of hormonal pulsatility." American Journal of Physiology-Endocrinology and Metabolism 254, no. 6 (June 1, 1988): E786—E794. http://dx.doi.org/10.1152/ajpendo.1988.254.6.e786.
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Previous studies evaluating computer algorithms for endocrine pulse detection have estimated the rate of false-positive pulses in series of purely random variations (i.e., “noise”) and have determined pulse-detection criteria associated with low levels of such false-positive rates. The present study investigates the relationship between the false-positive rate and the sizes of the false-positive and false-negative errors on pulse frequency for series including both pulses and noise. The algorithm used (ULTRA) proceeds by eliminating all peaks of concentration for which either the increment or the decrement does not exceed a threshold expressed in multiples of the local intra-assay coefficient of variation. A total of 336 computer-generated series was analyzed using thresholds of two and three coefficients of variation. The effects of noise level, pulse frequency, pulse amplitude, and presence of a base-line variation on the sizes of the false-positive and false-negative errors were evaluated. The false-positive rate in noise series exceeded the false-positive rate by a 4- to 10-fold factor in series including at least 8 pulses/100 samples. When pulse frequency increased, the false-positive error decreased, but the false-negative error increased. In series with more than 8 pulses/100 samples, the use of thresholds aimed at maintaining the false-positive rate in noise series below 1% resulted in a false-negative error in excess of 20%. In conclusion, for hormonal profiles that include 8 or more pulses/100 samples, the use of pulse-detection criteria tailored to minimize the false-positive rate in noise series may result in an underestimation of pulse frequency.
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Contreras, Arturo, Carlos Torres-Verdín, and Tim Fasnacht. "Sensitivity analysis of data-related factors controlling AVA simultaneous inversion of partially stacked seismic amplitude data: Application to deepwater hydrocarbon reservoirs in the central Gulf of Mexico." GEOPHYSICS 72, no. 1 (January 2007): C19—C29. http://dx.doi.org/10.1190/1.2399353.
Full textAbstract:
We consider the inversion of synthetic and recorded seismic amplitude variation with angle AVA data to appraise the influence of several data-related factors that control the vertical resolution and accuracy of the estimated spatial distributions of elastic properties. We use measurements acquired in deepwater hydrocarbon reservoirs in the central Gulf of Mexico to generate synthetic seismic amplitude data and evaluate inversion results with both synthetic and recorded seismic amplitudes. Detailed sensitivity analysis of synthetic amplitude data indicates that, even in the most ideal scenario (perfectly migrated data, isotropic media, noise-free seismic amplitude data, sufficient far-angle coverage, and accurate estimates of angle-dependent wavelets and low-frequency components), input elastic models are not reconstructedaccurately by the inversion of synthetic seismic amplitudes. We attribute this result to the relatively low vertical resolution of the seismic amplitude data. P-wave impedance is the most accurate of the inverted properties, followed by S-impedance and bulk density. Additionally, sufficient far-angle coverage is crucial for the accurate estimation of 1D distributions of S-impedance and bulk density. We show that time alignment of partial-angle stacks for correcting residual NMO effects improves the vertical resolution of the estimated spatial distributions of elastic parameters and consistently decreases the data misfit. Finally, we found that the accuracy of the inverted distributions of elastic parameters is improved substantially by (1) increasing the preserved AVA information via multiple single-angle stacks, (2) correcting the P-wave velocity field used for calculating angles in partial-angle stacking, and (3) excluding far-angle data with low signal-to-noise ratios.
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Lee, Kyunghyun, Jinhwan Oh, Hyukwoo Lee, and Kwanho You. "Earthquake Magnitude Estimation Using a Total Noise Enhanced Optimization Model." Sensors 19, no. 6 (March 25, 2019): 1454. http://dx.doi.org/10.3390/s19061454.
Full textAbstract:
In this paper, a heterodyne laser interferometer, which is used as a sensor for high-precision displacement measurement, is introduced to measure ground vibration and seismic waves as a seismometer. The seismic wave is measured precisely through the displacement variation obtained by the heterodyne laser interferometer. The earthquake magnitude is estimated using only the P-wave magnitudes for the first 3 s through the total noise enhanced optimization (TNEO) model. We use data from southern California to investigate the relationship between peak acceleration amplitude ( P d ) and the earthquake magnitude ( M g ). For precise prediction of the earthquake magnitude using only the P d value, the TNEO model derives the relation equation between P d and the magnitude, considering the noise present in each measured seismic data. The optimal solution is obtained from the TNEO model based objective function. We proved the performance of the proposed method through simulation and experimental results.