Properties Of Noise Sources Research Articles

Multitaper Spectrum Analysis of Consonants Produced by Patients With Dentofacial Disharmonies.

This study investigates differences in American English consonants produced by patients who present with various dentofacial disharmonies (DFDs), including severe overbites (Class II), underbites (Class III), and anterior open bites. Previous studies have found that patients with these malocclusion types all produce lingual sibilants and plosives with increased spectral center of gravity and increased spectral variance relative to controls. This result is puzzling since some DFD groups differ from controls in opposite ways, and it is also difficult to interpret because spectral moment measures are affected by a wide range of speech and nonspeech factors. To better understand the articulatory basis of these differences, we apply articulatorily interpretable spectral measures derived from multitaper spectra. We find that all groups of DFD patients produce /s ʃ t tʃ/ with midfrequency spectral peaks that are less prominent than those of the control group, but peak frequency measures are largely the same across all groups. We conclude that the DFD patients differ more in sibilant noise source properties than in front cavity filter properties.

Noise-based ballistic wave passive seismic monitoring. Part 1: body waves

SUMMARY Unveiling the mechanisms of earthquake and volcanic eruption preparation requires improving our ability to monitor the rock mass response to transient stress perturbations at depth. The standard passive monitoring seismic interferometry technique based on coda waves is robust but recovering accurate and properly localized P- and S-wave velocity temporal anomalies at depth is intrinsically limited by the complexity of scattered, diffracted waves. In order to mitigate this limitation, we propose a complementary, novel, passive seismic monitoring approach based on detecting weak temporal changes of velocities of ballistic waves recovered from seismic noise correlations. This new technique requires dense arrays of seismic sensors in order to circumvent the bias linked to the intrinsic high sensitivity of ballistic waves recovered from noise correlations to changes in the noise source properties. In this work we use a dense network of 417 seismometers in the Groningen area of the Netherlands, one of Europe's largest gas fields. Over the course of 1 month our results show a 1.5 per cent apparent velocity increase of the P wave refracted at the basement of the 700-m-thick sedimentary cover. We interpret this unexpected high value of velocity increase for the refracted wave as being induced by a loading effect associated with rainfall activity and possibly canal drainage at surface. We also observe a 0.25 per cent velocity decrease for the direct P-wave travelling in the near-surface sediments and conclude that it might be partially biased by changes in time in the noise source properties even though it appears to be consistent with complementary results based on ballistic surface waves presented in a companion paper and interpreted as a pore pressure diffusion effect following a strong rainfall episode. The perspective of applying this new technique to detect continuous localized variations of seismic velocity perturbations at a few kilometres depth paves the way for improved in situ earthquake, volcano and producing reservoir monitoring.

Markovian nature, completeness, regularity and correlation properties of generalized Poisson-Kac processes

We analyze some basic issues associated with generalized Poisson–Kac (GPK) stochastic processes, starting from the extended notion of the Markovian condition. The extended Markovian nature of GPK processes is established, and the implications of this property derived: the associated adjoint formalism for GPK processes is developed essentially in an analogous way as for the Fokker–Planck operator associated with Langevin equations driven by Wiener processes. Subsequently, the regularity of trajectories is addressed: the occurrence of fractality in the realizations of GPK is a long-term emergent property, and its implication in thermodynamics is discussed. The concept of completeness in the stochastic description of GPK is also introduced. Finally, some observations on the role of correlation properties of noise sources and their influence on the dynamic properties of transport phenomena are addressed, using a Wiener model for comparison.

On the use of the autocorrelation function: the constraint of using frequency band-limited signals for monitoring relative velocity changes

Correlations of seismic noise are commonly used to monitor temporal variations of relative seismic velocity in period ranges from 1 s up to 100 s. Of particular interest is the detection of small changes in the order of 0.01–0.1 % in propagation speeds. Measuring such small differences can, however, be significantly biased by temporal variations in the properties of the noise sources within the corresponding frequency band. Using synthetic data, we show that apparent relative velocity variations might appear only due to changes in the amplitude and frequency content caused by source variations. Removing such unwanted effects by applying narrow bandpass filters in the preprocessing restricts the high-resolution analysis of any signal due to Gabor’s uncertainty limit, i.e., the correlation function suffers a limited resolution to time delay estimates for small correlation times, low-frequency ranges, and in narrow frequency bands. Better understanding of spatiotemporal noise source properties and the theoretical limitations of time–frequency analysis is critical for accurate and reliable passive monitoring.

New developments in ambient noise analysis to characterise the seismic response of landslide-prone slopes

Abstract. We report on new developments in the application of ambient noise analysis applied to investigate the dynamic response of landslide-prone slopes to seismic shaking, with special attention to the directional resonance phenomena recognised in previous studies. These phenomena can be relevant for seismic slope susceptibility, especially when maximum resonance orientation is close to potential sliding directions. Therefore, the implementation of an effective technique for site response directivity detection is of general interest. In this regard methods based on the calculation of horizontal-to-vertical noise spectral ratio (HVNR) are promising. The applicability of such methods is investigated in the area of Caramanico Terme (central Italy), where ongoing accelerometer monitoring of slopes with different characteristics offers the possibility of validation of HVNR analysis. The noise measurements, carried out in different times to test the result repeatability, revealed that sites affected by response directivity persistently show major peaks with a common orientation, consistent with the resonance direction inferred from accelerometer data. In some cases such a directivity turned out parallel to maximum slope direction, but this cannot be considered a systematic feature of slope dynamic response. At sites where directivity is absent, the HVNR peaks do not generally show a preferential orientation, with rare exceptions that could be linked to the presence of temporarily active sources of polarised noise. The observed variations of spectral ratio amplitude can be related to temporal changes in site conditions (e.g. groundwater level/soil water content variations affecting P wave velocity and Poisson's ratio of surficial layer), which can hinder the recognition of main resonance frequencies. Therefore, we recommend conducting simultaneous measurements at nearby sites within the same study area and repeating measurements at different times in order to distinguish significant systematic polarisation caused by site-specific response directivity from polarisation controlled by properties of noise sources. Furthermore, an analysis of persistence in noise recordings of signals with systematic directivity showed that only a portion of recordings contains wave trains having a clear polarisation representative of site directional resonance. Thus a careful selection of signals for HVNR analysis is needed for a correct characterisation of site directional properties.

Spurious velocity changes caused by temporal variations in ambient noise frequency content

Ambient seismic noise cross-correlations are now being used to detect temporal variations of seismic velocity, which are typically on the order of 0.1 per cent. At this small level, temporal variations in the properties of noise sources can cause apparent velocity changes. For example, the spatial distribution and frequency content of ambient noise have seasonal variations due to the seasonal hemispherical shift of storms. Here, we show that if the stretching method is used to measure time-shifts, then the temporal variability of noise frequency content causes apparent velocity changes due to the changes in both amplitude and phase spectra caused by waveform stretching. With realistic seasonal variations of frequency content in the Los Angeles Basin, our numerical tests produce about 0.05 per cent apparent velocity change, comparable to what Meier et al. observed in the Los Angeles Basin. We find that the apparent velocity change from waveform stretching depends on time windows and station-pair distances, and hence it is important to test a range of these parameters to diagnose the stretching bias. Better understanding of spatiotemporal noise source properties is critical for more accurate and reliable passive monitoring.

Noise pollution mapping approach and accuracy on landscape scales

Noise mapping allows the characterization of environmental variables, such as noise pollution or soundscape, depending on the task. Strategic noise mapping (as per Directive 2002/49/EC, 2002) is a tool intended for the assessment of noise pollution at the European level every five years. These maps are based on common methods and procedures intended for human exposure assessment in the European Union that could be also be adapted for assessing environmental noise pollution in natural parks. However, given the size of such areas, there could be an alternative approach to soundscape characterization rather than using human noise exposure procedures. It is possible to optimize the size of the mapping grid used for such work by taking into account the attributes of the area to be studied and the desired outcome. This would then optimize the mapping time and the cost. This type of optimization is important in noise assessment as well as in the study of other environmental variables. This study compares 15 models, using different grid sizes, to assess the accuracy of the noise mapping of the road traffic noise at a landscape scale, with respect to noise and landscape indicators. In a study area located in the Manzanares High River Basin Regional Park in Spain, different accuracy levels (Kappa index values from 0.725 to 0.987) were obtained depending on the terrain and noise source properties. The time taken for the calculations and the noise mapping accuracy results reveal the potential for setting the map resolution in line with decision-makers' criteria and budget considerations.

Energy-based acoustic measurement system for rocket noise

Accurate estimates of the vibroacoustic loading placed on space vehicles and payloads during launch require knowledge of rocket noise source properties and near-field acoustic energy flow characteristics. Without these data, structures may not be designed to handle the correct vibroacoustic loads, which can result in either an over-built, excessively massive structure or an under-designed vibration mitigation system that could result in damage to payloads. These measurements are difficult to perform because of the extreme nature of the acoustic and temperature environments near the rocket plume as well as the large physical size of the rocket noise source. With these design constraints in mind, a field-deployable data acquisition system and energy-based measurement probe have been developed to measure the magnitude, directivity, and spectral content of the rocket source. Initial measurements with various prototypes were conducted during a static test fire at ATK Space Systems Test Services in Promontory, Utah with limited results presented here. [Work sponsored by NASA John C. Stennis Space Center.]

Non-linear stimulus-response behavior of the human stance control system is predicted by optimization of a system with sensory and motor noise

We developed a theory of human stance control that predicted (1) how subjects re-weight their utilization of proprioceptive and graviceptive orientation information in experiments where eyes closed stance was perturbed by surface-tilt stimuli with different amplitudes, (2) the experimentally observed increase in body sway variability (i.e. the “remnant” body sway that could not be attributed to the stimulus) with increasing surface-tilt amplitude, (3) neural controller feedback gains that determine the amount of corrective torque generated in relation to sensory cues signaling body orientation, and (4) the magnitude and structure of spontaneous body sway. Responses to surface-tilt perturbations with different amplitudes were interpreted using a feedback control model to determine control parameters and changes in these parameters with stimulus amplitude. Different combinations of internal sensory and/or motor noise sources were added to the model to identify the properties of noise sources that were able to account for the experimental remnant sway characteristics. Various behavioral criteria were investigated to determine if optimization of these criteria could predict the identified model parameters and amplitude-dependent parameter changes. Robust findings were that remnant sway characteristics were best predicted by models that included both sensory and motor noise, the graviceptive noise magnitude was about ten times larger than the proprioceptive noise, and noise sources with signal-dependent properties provided better explanations of remnant sway. Overall results indicate that humans dynamically weight sensory system contributions to stance control and tune their corrective responses to minimize the energetic effects of sensory noise and external stimuli.

Acoustic source property prediction based on near-field measurements in planar coordinate

Near-field acoustical holography (NAH) can be used to predict the acoustical properties of noise sources by starting from measurements of near-field pressures. In particular, the sound pressure, particle velocity, and intensity can all be estimated on a source plane. In the present work, an equation relating acoustical source properties and the pressure radiated from a source is derived from the Kirchoff–Helmholtz integral equation and is here referred to as the inverse Rayleigh method. The inverse Rayleigh method reduces to the Rayleigh integral when the source is located on an infinite rigid baffle. However, the same equation can also be used to predict the acoustic properties of a source in a more general environment: i.e., without assuming the presence of an infinite rigid baffle. In this article, the inverse Rayleigh method is described and then its relative accuracy is compared with other procedures that can be used to predict source particle velocity from near-field pressure measurements on a planar hologram. By comparing the accuracy of the present NAH method with other procedures in the case of a large hologram, it was found that the inverse Rayleigh method is accurate and computationally efficient for predicting the source particle velocity from near-field pressure measurements both with and without a rigid baffle.

The nature of noise wavefield and its applications for site effects studies: A literature review

The aim of this paper is to discuss the existing scientific literature in order to gather all the available information dealing with the origin and the nature of the ambient seismic noise wavefield. This issue is essential as the use of seismic noise is more and more popular for seismic hazard purposes with a growing number of processing techniques based on the assumption that the noise wavefield is predominantly consisting of fundamental mode Rayleigh waves. This survey reveals an overall agreement about the origin of seismic noise and its frequency dependence. At frequencies higher than 1 Hz, seismic noise systematically exhibits daily and weekly variations linked to human activities, whereas at lower frequencies (between 0.005 and 0.3 Hz) the variation of seismic noise is correlated to natural activities (oceanic, meteorological…). Such a surface origin clearly supports the interpretation of seismic noise wavefield consisting primarily of surface waves. However, the further, very common (though hidden) assumption according which almost all the noise energy would be carried by fundamental mode Rayleigh waves is not supported by the few available data: no “average” number can though be given concerning the actual proportion between surface and body waves, Love and Rayleigh waves (horizontal components), fundamental and higher modes (vertical components), since the few available investigations report a significant variability, which might be related with site conditions and noise source properties.

Creating noise sources for rotorcraft and aircraft noise simulation models

Modern computing power has made noise simulation models, i.e., prediction of actual time histories of sound levels, practical. Switzerland uses its FLULA model for airport noise contours. NASA’s new RNM rotorcraft model uses simulation to address the complexities of rotorcraft noise. The Wyle/USAF NMSIM fixed-wing model has been used to address significant effects associated with complex terrain. A requirement for this type of model is the three-dimensional noise source properties of the aircraft being analyzed. This information is generally extracted from fly-over noise tests. Because noise is needed on a complete sphere (or at least a hemisphere), parts of the noise sphere are associated with long propagation distances and/or grazing incidence to measurement positions. This paper reviews the practical problems associated with turning fly-over measurements into source models. Examples from experience with RNM and NMSIM are presented.

Contraction of information and models in reactor noise analysis

Several methods developed in different fields have been applied to reactor noise analysis: the probability distribution method in the probability theory, the Langevin technique in the statistical physics, the time series analysis in the statistics, and the Kalman filter in the control theory. For reactor diagnosis or reactor safety, it is important to understand relations among them and their merits. To make full use of signals included in reactor noise, the above mentioned methods and techniques are discussed systematically from the physical viewpoint of the contraction of information and the coarse-graining in time and space. Properties of noise sources and spatial dependence of model are also discussed.

A pilot study of context effect of judged annoyance of noise

It has sometime been suggested that the same noise source is judged annoying when it interferes with one's activities, but more often judged not annoying when it is related to one's livelihood or recreational interests. The present report concerns an attempt to determine whether specification of context will correspond to certain judgmental factors of annoyance that are not accounted for by acoustic properties of noise sources. Subjects were asked to recall a specified noise source, then asked to judge whether it would be desirable or undesirable in a certain situation. Tasks were specified which were recreational or occupational. The subject role was described as depending on the noise source, neutral, or interfered with by the noise source. There was no difference between recreational and occupational tasks in terms of the rated desirability of the noise sources. Analysis of variance revealed a significant difference depending on whether the noise source was part of or interfered with the subject's task. The test technique thus agrees with some observations of annoyance factors resulting from environmental noise sources.

Neutron noise monitoring of pressurized water reactor internal vibrations

Analytical and experimental results have shown that the neutron noise signals are typically the sum of a number of different noise sources. These can have significant interactions due to structural coupling and summation effects in the sensor. Analytical techniques have been developed to identify major neutron noise sources and to separate and account for some of the noise source coupling effects. This work has demonstrated the use of various noise source models in neutron noise monitoring applications. Methods of identifying and separating the noise sources have been used to relate changes in the measured spectra to particular noise source properties. The noise source models can then be used to relate noise source properties to physical properties of the system. These techniques are used in routine surveillance applications and have provided proper evaluation of several trends and changes that have been observed in neutron noise monitoring programs. All neutron noise measurements have shown small vibration amplitudes that are in agreement with results from preoperational measurements and analysis. Neutron noise monitoring is being continued on an optional basis in a number of plants as a means of monitoring core clamping and general long-term performance.

Imaging devices using the charge-coupled concept

A unified treatment of the basic electrostatic and dynamic design of charge-coupled devices (CCD's) based on approximate analytical analysis is presented. Clocking methods and tradeoffs are discussed. Driver power dissipation and on-chip power dissipation are analyzed. Properties of noise sources due to charge input and transfer are summarized. Low-noise methods of signal extraction are discussed in detail. The state of the art for linear and area arrays is presented. Tradeoffs in area-array performance from a systems point of view and performance predictions are presented in detail. Time delay and integration (TDI) and the charge-injection device (CID) are discussed. Finally, the uses of the charge-coupled concept in infrared imaging are discussed.