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[The determination of the maximum permissible noise level for areas and zones incorporating facilities requiring enhanced noise protection].

Noise, a stressogenic factor adversely affecting the body, is subject to monitoring and control, notably, at sites where health considerations impose a more rigorous acoustic regimen. Where systematic and ubiquitous excesses over admissible noise level occur in an urban environment, a special case of health impact is that produced upon an inpatient's course of recovery from illness. This paper presents evidence from a survey of mean excesses over HEI-regulated noise standards for zones enclosing 16 Sofia inpatient facilities. The procedure used to determine and map mean excesses in cities has been made available to the preventive network of local HEIs countrywide; however, it still has not been put into practice everywhere. This renewed presentation, it is hoped, should contribute to recognizing its necessity and making use of the technique. The most frequently encountered excesses over the admissible noise level were within the range 15-20 dB A. For districts incorporating hospital institutions, this acoustic situation may be qualified as not only inadequate to requirements but also as generating a health risk for vulnerable population groups. Clearly, the noise regimen observed in the surveyed zones in an environmental physical hazard hindering the process of recovery from illness--with all health, social, and economic negative effects entailed.

Bulgaria↗

Current noise parameters derived from voltage noise and impedance in embryonic heart cell aggregates.

We have recorded membrane impedance and voltage noise in the pacemaker range of potentials (-70 to -59 mV) from spheroidal aggregates of 7-d embryonic chick ventricle cells made quiescent by exposure to tetrodotoxin in medium containing 4.5 mM K+. The input capacitance is proportional to aggregate volume and therefore to total membrane area. The specific membrane capacitance is 1.24 microF/cm2. The input resistance at constant potential is inversely proportional to aggregate volume and therefore to total membrane area. The specific membrane resistance in 18 k omega . cm2 at -70 mV and increases to 81 k omega . cm2 at -59 mV. The RC time constant is 22 ms at -70 mV and increases to 146 ms at -59 mV. The aggregate transmembrane small-signal impedance can be represented by a parallel RC circuit itself in parallel with an inductive branch consisting of a resistor (rL) and an inductor (L) in series. The time constant of the inductive branch (L/rL) is 340 ms, and is only weakly dependent on potential. Correlation functions of aggregate voltage noise and the impedance data were modeled by a population of channels with simple open-close kinetics. The time constant of a channel (tau s) derived from the noise analysis is 300 ms. The low frequency limit of the pacemaker current noise (SI[0]), derived from the voltage noise and impedance, increases from 10(-20) A2/Hz . cm2 at -67 mV to 10(-19) A2/Hz . cm2 at -61 mV.

Animals↗

Signal-to-noise ratio enhancement based on the whitening transformation of colored structural noise

In the ultrasonic testing and evaluation of highly scattering materials (i.e. non-homogeneous media such as composites, layered and clad materials) structural noise is an important limitation to the visibility of flaw echoes. This noise cannot be reduced by conventional linear filtering or by time-averaging techniques. In order to enhance the defect-to-background noise ratio (SNR), many different algorithms have been developed over the years. This work analyzes three new strategies for SNR enhancement based on the whitening transformation of the colored structural noise. By using this transformation, the small spectral differences between noise and flaw echoes are exploited, thereby allowing an improvement in the visibility of the flaw.

Journal Article↗

Noise in neural networks: thresholds, hysteresis, and neuromodulation of signal-to-noise.

We study a neural-network model including Gaussian noise, higher-order neuronal interactions, and neuromodulation. For a first-order network, there is a threshold in the noise level (phase transition) above which the network displays only disorganized behavior and critical slowing down near the noise threshold. The network can tolerate more noise if it has higher-order feedback interactions, which also lead to hysteresis and multistability in the network dynamics. The signal-to-noise ratio can be adjusted in a biological neural network by neuromodulators such as norepinephrine. Comparisons are made to experimental results and further investigations are suggested to test the effects of hysteresis and neuromodulation in pattern recognition and learning. We propose that norepinephrine may "quench" the neural patterns of activity to enhance the ability to learn details.

Animals↗

Resonant activations for a fluctuating barrier system driven by dichotomous noise and Gaussian white noise.

We consider the escape over a fluctuating barrier in the presence of a dichotomous noise and a Gaussian white noise. It is shown that the mean first passage time (MFPT) over the fluctuating barrier displays two resonant activations. One is the resonant activation of the MFPT as a function of the flipping rate of the fluctuating potential barrier; the other is the resonant activation of the MFPT as a function of the transition rate of the dichotomous noise. In addition, we find that the dichotomous noise can weaken the former resonant activation, but enhance the latter one. By further study, we find that, when the fluctuating potential barrier is driven by two or more dichotomous noises, there are three or more resonant activations.

Journal Article↗

Noise improves three-dimensional perception: stochastic resonance and other impacts of noise to the perception of autostereograms.

Autostereograms can be perceived in different well-defined spatial levels. Therefore they are an excellent tool with which to examine spatiotemporal processes of multistable three-dimensional perception. We study properties of spatial ambiguity such as phase transitions between different spatial levels and hysteresis in perception with and without noise. We show that the perception of physical noise-which is added to the autostereograms in the form of a random dot pattern-is dependent on the perceived spatial level. We demonstrate that noise can be helpful for the perception of depth in some cases. We show that the signal-to-noise ratio of depth perception is enhanced at an intermediate level of noise strength that is the signature of stochastic resonance in depth perception.

Artifacts↗

Examining noise sources at the single-molecule level: 1/f noise of an open maltoporin channel.

We have studied the phenomenological origin of 1/f noise in a solute-specific bacterial ion channel, maltoporin. We show that after excision of small, but resolvable stepwise changes in the recordings of the current through a single open channel, the 1/f noise component disappears and the channel exhibits noise that is "white" below 100 Hz. Combined with results of a recent noise study of several bacterial porins, our observations suggest that 1/f noise is caused by the equilibrium conductance fluctuations related to the conformational flexibility of the channel pore structural constituents.

Artifacts↗

Information-theoretic stochastic resonance in noise-floor limited systems: the case for adding noise

We show that in systems whose output must compete with a noise source, stochastic resonance (maximization of output signal-noise separation as a nonmonotonic function of input noise strength) exists even when measured in terms of fundamental statistical measures and optimal detector performance. This is in contrast to the commonly considered scenario where, without the competing noise, the system (e.g., a driven, overdamped particle moving in a double well potential) is essentially invertible and optimal detector performance monotonically deteriorates with increasing input noise strength.

Journal Article↗

Noise analysis in real-time portal imaging. I. Quantization noise.

The limit at which quantization noise becomes dominant in video-based real-time portal imaging has been studied. Quantization noise due to truncation in integer frame averaging is shown to be dominant over the input analog-to-digital converter (A/D) quantization noise, unless image addition is used in video-based real-time portal imaging systems. Portal images acquired with the Newvicon camera by averaging more than 64 frames are found to be dominated by the quantization noise due to truncation. It has shown that the signal-to-noise ratio (SNR) is limited to 886.8 when using an 8-bit A/D with digital frame averaging, but higher values can be achieved with digital frame addition. It is also shown that digital frame addition together with 16-bit processing can achieve higher contrast resolution than digital frame averaging and 8-bit processing.

Gadolinium↗

[Noise resistance of the dolphin auditory analyzer as a function of the directional angle of the noise].

Masked tonal thresholds by noise in the bottlenose dolphin have been measured as a function of angle of noise direction. Sharp directional selectivity of hearing has been discovered resulting in an abrupt decrease of noise masking with the increase of the angle of noise coming. It has been shown that narrow directional characteristics of hearing is an angle 8 degrees plus or minus 2 degrees for the level of minus 3db. It is one of the main mechanisms supplying the echolocation system of the dolphin with the high level of resistance to noise.

Animals↗

SPECT image noise power: effects of nonstationary projection noise and attenuation compensation.

The effects of nonstationary projection noise and attenuation compensation are included in a theoretic calculation of the radial noise power spectrum (NPS) of single photon emission computed tomographic (SPECT) images. The nonstationary projection noise is shown to cause a relatively large d.c. component in the NPS, especially for small objects; whereas, attenuation compensation increases the total noise variance while only changing the d.c. component slightly. The theoretic calculation agrees well with a radial NPS estimated from 1,250 SPECT images simulated from projections of random Gaussian noise, even though the effects of discrete data collection and reconstruction were not included in the theoretical model.

Computer Simulation↗

Community response to noise: is all noise the same?

There have been nearly a dozen papers published in the last 5 years which compare community response to noise from several different sources such as road and rail traffic. This paper draws on those and other studies to address three questions. First, is the variation in results simply due to random sources or measurement error, such that use of an "average" dose-response curve is appropriate, or is there some identifiable systematic variation? Second, what characteristics of the noise or community might lead to systematic variation, if there is any? Third, under what conditions is it reasonable to use an average function, even if there are systematic variations? Both of the first two questions receive only tentative answers on the basis of available studies. Although the evidence shows different functions for different sources (e.g., rail and road noise), for different types of one source (e.g., air carrier airports and general aviation airports), and even for different studies at the same location (e.g., Heathrow), the evidence is not sufficiently strong to totally reject the idea that all of this is just random variation about an "average" response. As yet, there is no clear identification of what acoustical or community factors explain the differences in response, so it is sensible simply to use the type of source (i.e., road, rail, or air traffic noise) to categorize the differences. The answer to the third question, then, is that an "average" dose-response curve is useful in the face of limited information--that is, when we cannot specify precisely the conditions calling for different functions.

Aircraft↗

Acute effects of noise exposure: an experimental investigation of the effects of noise and task parameters on cognitive vigilance tasks.

Studies of sustained monitoring of sensory information have shown noise-induced impairments only when the level is above 95 dB. Recent results suggest that tasks involving the monitoring of cognitive information may be vulnerable at lower intensities. This last point was confirmed in the present study which used a dual task. Noise reduced the hit-rate on a task involving detection of repeated numbers but had no effect on the average estimate of the relative probabilities of two classes of events. Noise did, however, increase the frequency of very inaccurate estimates. The noise effects were not altered by changes in the priority, difficulty or probability of the two tasks.

Cognition↗

A tentative proposal for classification of audiograms in noise-induced deafness: relationship between audiogram and subjective complaints in noise-exposed workers.

Audiograms obtained from workers exposed to occupational noise were classified into six stages, namely, "normal" and stages I-V of noise-induced deafness, using the audiometric chart and the classification table designed by the authors. Close correlations were observed between the severity of the stage and the degree of hearing in daily life, which support our classification method. On the other hand, the prevalence rate of tinnitus also showed a linear increase in proportion to the severity of the stage, although the mechanism of tinnitus in noise-induced deafness has not yet been elucidated. From the viewpoint of protecting workers from hearing damage due to noise exposure, further investigation is required to make the best use of our classification method in noisy workplaces.

Audiometry↗

Exposure to aircraft noise and risk of psychiatric disorders: the Elmas survey--aircraft noise and psychiatric disorders.

BACKGROUND: Evidence that high levels of aircraft noise lead to psychiatric disorders in the community is contradictory. The aim of the present study was to investigate the frequency of mental disorders in a sample living in the immediate surroundings of an airport compared with those from a sample of residents from the same region who had not been exposed to the risk of aircraft noise. METHODS: Exposed subjects were residents in Giliaquas in the vicinity of Elmas airport (Sardinia, Italy). The control sample was drawn from a database of a large community survey, after matching for sex, age and employment status. All subjects were interviewed using a simplified version of the Composite International Diagnostic Interview. RESULTS: Exposed subjects showed a higher frequency of Generalized Anxiety Disorder and Anxiety Disorder Not Otherwise Specified (NOS). CONCLUSIONS: Previous studies generally suggested that high levels of environmental noise are associated with subsyndromal states (psychiatric symptoms) more than with specific syndromes. The present study shows an increased risk for long-lasting syndromal anxiety states (Generalized Anxiety Disorder and Anxiety Disorder NOS), thus supporting the hypothesis of a sustained central autonomic arousal due to chronic exposure to noise.

Adult↗

Psychophysiological reactions to noise as modified by personal control over noise intensity.

Effects of personal control over noise intensity were studied in experimental situations where subjects performed mental arithmetic under noise exposure. Every other subject was offered a choice between noise intensities, and the next subject, serving as his yoked partner, had to submit to the same noise. Mean measures of catecholamine and cortisol excretion, and of heart rate and subjective effort and discomfort showed that subjects were more aroused in the yoked situation. There were, however, considerable interindividual differences, subjects classified as 'internals' or 'externals' on the basis of the Internal-External Locus of Control Scale responding to the two experimental conditions in congruence with their general beliefs and attitudes with regard to control.

Adult↗

Material from the internal surface of squid axon exhibits excess noise. Implications in modeling membrane noise.

A fluid material from a squid (Loligo pealei) axon was isolated by mechanical application of two types of microcapillary (1-3-mum Diam) to the internal surface of intact and cut-axon preparations. Current noise in the isolated material exceeded thermal levels and power spectra were 1/f in form in the frequency range 1.25-500 Hz with voltage-dependent intensities that were unrelated to specific ion channels. Whether conduction in this material is a significant source of excess noise during axon conduction remains to be determined. Nevertheless, a source of excess noise external to or within an ion channel may not be properly represented solely as an additive term to the spectrum of ion channel noise; a deconvolution of these spectral components may be required for modeling purposes.

Animals↗

Noise, discomfort and mental health. A review of the socio-medical implications of disturbance by noise.

The published work relating to effects of noice on man and animals is reviewed from the standpoint of mental health. Evidence from a number of different disciplines shows that the presence of meaning in the noise is of critical importance in determining the persistence of physical reactions to the noise. The existing evidence linking noise with mental illness is found to be unsatisfactory. The concept of annoyance and the relevance of noise annoyance to mental illness are discussed. Some specific suggestions for further work are put forward.

Adolescent↗