Minimum Noise Level Research Articles

Evaluation of Noise Levels in Intensive Care Units in Two Large Teaching Hospitals – A Prospective Observational Study

Critically ill patients do not sleep well. One of the major environmental factors influencing sleep is noise. We prospectively measured noise levels and their relation to the time of day and location in different parts of two separate intensive care units (ICUs). Maximum, minimum and average noise levels were collected over 24 hour periods on five random days in both ICUs using digital sound meters, measured by the A-weighted decibel scale (dB (A)). The World Health Organisation (WHO) recommends that the average background noise in hospitals should not exceed 35 dB (A), and that peaks during the night should be less than 40 dB (A). The measured noise levels in both ICUs were well above the WHO standards. We recommend that various aspects, including staff education and modification of ICU design, must be carefully considered to provide an optimum environment for critically ill patients.

Ruído em hospital universitário: impacto na qualidade de vida

OBJETIVO: Aferir os níveis de ruído em distintos ambientes de um hospital universitário e investigar o impacto dessa exposição na qualidade de vida dos profissionais que atuam nesses ambientes. MÉTODOS: O ruído foi aferido por meio de medidor de pressão sonora em três períodos do dia: manhã, tarde e noite, durante uma semana, em diferentes dependências de um hospital, a saber: UTI neonatal, nutrição, anfiteatros, gráfica, lavanderia, marcenaria e serralheria. Para cinco trabalhadores de cada setor, foi solicitado o preenchimento dos questionários de hábitos auditivos e de Qualidade de vida (WHOQOL-Bref), adaptado para o Português Brasileiro. Para cada questão do WHOQOL-Bref atribuiu-se de 0 a 5 pontos, sendo que, ao final, quanto maior a pontuação, melhor qualidade de vida o indivíduo considera ter. RESULTADOS: Houve diferença significativa entre os ambientes, para os valores mínimos e máximos de pressão sonora, independentemente do período do dia em que foi realizada a aferição. Todos os ambientes puderam ser considerados prejudiciais. Nos escores apresentados nas questões de qualidade de vida geral e nos domínios do WHOQOL-Bref (Qualidade de Vida, Físico, Psicológico, Relações Sociais e Meio Ambiente), observou-se que não houve diferença entre os setores. CONCLUSÃO: Os níveis mínimos e máximos de ruído em todos os setores, com exceção da UTI neonatal, excedem os previstos para ambiente hospitalar; a variação dos níveis de ruído caracteriza ambientes com ruídos intermitentes que colocam em risco a saúde auditiva dos funcionários; os níveis de ruído aferidos evidenciam a necessidade de implementação de Programa de Conservação Auditiva, com medidas coletivas e individuais.

SU-E-I-02: Effects of Projection View Sampling On CT Numbers and Noise Level in Cone Beam Breast CT

Purpose: To investigate and optimize the effects of the number of projection views for minimal noise level in cone bream breast CT. Methods: An Anrad flat panel detector was used on a bench top experimental CBCT system with fixed exposure. A wax phantom simulating a breast was used to study the reconstruction artifacts. A Lucite phantom with uniform structure was used to study the variation of the noise level with the number of views. The phantoms were scanned with 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1200 and 1400 evenly spaced projection views over 360° while keeping the total exposure at a level corresponding to a mean glandular dose (MGD) of 7.2 mGys. Each image set was reconstructed with Feldkamp's backprojection algorithm using a ramp filter. Two regions of interest (ROIs) were selected in the reconstructed images, one at the center and the other near the edge. Mean values and standard variations were measured in ROIs and plotted as the function of the number of projection views. Results: The mean values for the wax phantom were found to peak at 300 projection views. The standard variation was lowest with 400 projection views for both Lucite and wax phantoms. Conclusion: For the detector and exposure level used, 400 projection views resulted in lowest noise level, indicating optimal combination of reconstruction artifacts from projection view sampling and image noises, which tend to decrease and increase with the number of projection views, respectively. This work was supported in part by grants CA139830, CA138502 and CA124585 from the NIH‐NCI.

Sensitivity estimate of magnetic field sensors based on high-temperature superconducting yttrium cuprate

Experimental studies of the interaction of variable and constant magnetic fields with supercon-ducting YBa2Cu3O7 − x ceramics are presented. A technique for estimating the minimal noise level of magnetic field sensors based on superconducting yttrium cuprate is suggested. Ways to reach the ultimate sensitivity of such devices are considered.

The association between road traffic noise exposure and blood pressure among children in Germany: The GINIplus and LISAplus studies

Studies examining the association between road traffic noise and blood pressure in children are scarce. Nighttime noise levels and window orientations have not been considered in most previous studies. Investigate the association between road traffic noise exposure and blood pressure among children, and investigate the impact of bedroom window direction on this association. We measured blood pressure in 605 children aged 10 years from two Munich cohorts. Demographic and health information was collected by parent completed questionnaires. Road traffic noise levels were assessed by day-evening-night noise indicator "Lden" and night noise indicator "Lnight". Minimum and maximum levels within a 50 m buffer around child's home address were derived. Generalized additive models were applied to explore effect of noise levels on systolic and diastolic blood pressure (SBP and DBP). The orientation of child's bedroom window was considered in sensitivity analyses. DBP was significantly associated with the minimum level of noise during 24 h (Lden_min) and nightime (Lnight_min). Specifically, DBP increased by 0.67 and 0.89 mmHg for every 5 A-weighted decibels increase in Lden_min and Lnight_min. After adjusting for Lden_min (Lnight_min), DBP of children whose bedroom window faced the street was 1.37 (1.28) mmHg higher than those whose bedroom window did not, these children showed statistically significant increased SBP for Lden_min (3.05 mmHg) and Lnight_min (3.27 mmHg) compared to children whose bedroom window did not face the street. Higher minimum levels of weighted day-evening-night noise and nighttime noise around the home residence may increase a child's blood pressure.

The learning advantage: bird species that learn their song show a tighter adjustment of song to noisy environments than those that do not learn

Song learning has evolved within several avian groups. Although its evolutionary advantage is not clear, it has been proposed that song learning may be advantageous in allowing birds to adapt their songs to the local acoustic environment. To test this hypothesis, we analysed patterns of song adjustment to noisy environments and explored their possible link to song learning. Bird vocalizations can be masked by low-frequency noise, and birds respond to this by singing higher-pitched songs. Most reports of this strategy involve oscines, a group of birds with learning-based song variability, and it is doubtful whether species that lack song learning (e.g. suboscines) can adjust their songs to noisy environments. We address this question by comparing the degree of song adjustment to noise in a large sample of oscines (17 populations, 14 species) and suboscines (11 populations, 7 species), recorded in Brazil (Manaus, Brasilia and Curitiba) and Mexico City. We found a significantly stronger association between minimum song frequency and noise levels (effect size) in oscines than in suboscines, suggesting a tighter match in oscines between song transmission capacity and ambient acoustics. Suboscines may be more vulnerable to acoustic pollution than oscines and thus less capable of colonizing cities or acoustically novel habitats. Additionally, we found that species whose song frequency was more divergent between populations showed tighter noise-song frequency associations. Our results suggest that song learning and/or song plasticity allows adaptation to new habitats and that this selective advantage may be linked to the evolution of song learning and plasticity.

Assessment of Work Zone Noise Levels at a Cement Factory in Tanga, Tanzania

Noise of machines in cement industries was found to be one of the major occupational hazards for the workers of industrial sector. The objectives of this study were to measure the noise levels in various production sections at a cement factory in Tanga, Tanzania and assess attitudes of workers towards noise health hazards. Noise levels were measured using a digital sound level meter at three appropriate locations of the working zone of the workers. Questionnaires were provided to each worker in selected production section and field under close supervision to avoid influence of one’s results by other subject. The results showed maximum noise level at the power plant section with 104.82 dBA and minimum noise level was 50 dBA observed in offices. The maximum and average noise levels measured in most production sections exceeded the allowed limit value of 85 dBA as recommended by Tanzania Bureau of Standards (TBS). Subjective responses indicated that 47.5% of workers are exposure to noise for more than 5 years whereas, 82.5% of workers indicated that there could be health effects caused by the noise from machines. The study suggests that, though most workers ever use protective gears during working hours, health checkups for noise related effects should be carried out regularly.Keywords: Noise levels, Noise exposure, Cement factory, Survey, Tanzania

Far-Field Sound Radiation Due to an Installed Open Rotor

Future single rotation propeller and contra-rotating advanced open rotor concepts promise a significant fuel efficiency advantage over current generation turbofan engines. The development of rotors which produce a minimum level of noise is a critical technical issue which needs to be resolved in order for these concepts to become viable aircraft propulsors. Noise and emissions are subject to stringent legislative requirements, thus accurate models are required in order to predict the noise radiated from aircraft engines. In this article, the development of a theoretical model to predict noise levels of an installed open rotor is reported. First a canonical problem is examined: how to predict the pressure field produced by a rotating ring of point sources adjacent to a rigid cylinder. Analytic expressions for the far-field pressure from a rotating ring of single-frequency monopole and dipole point sources, located near an infinitely long rigid cylinder, immersed in a constant axial mean flow, are explicitly formulated. Illustrative results show how the far-field pressure is affected by varying the source rotational direction, source location and source radius. Next the solution of the canonical problem is utilized to formulate a more advanced model to predict the noise due to an installed open rotor. In this model, the rotor noise sources are represented by a distribution of rotating sources. The adjacent aircraft fuselage is modeled by the rigid cylinder, and the effect of the fuselage boundary layer and other steady distortions are neglected. Also neglected is the scattering from other surfaces such as the pylon, wing and centerbody. This distributed source model can be used to calculate the effect of scattering of open rotor noise by an adjacent cylindrical fuselage. The model can be used to calculate both rotor-alone tones and tones produced by periodic unsteady loading on the rotor blades. Practical examples are provided which show how the effect of blade rotational direction and propeller location relative to the fuselage affect the sound produced by the interaction of a pylon wake with a rotor in a pusher configuration.

Astrophysical foregrounds and primordial tensor-to-scalar ratio constraints from cosmic microwave backgroundB-mode polarization observations

We study the effects of astrophysical foregrounds on the ability of CMB B-mode polarization experiments to constrain the primordial tensor-to-scalar ratio, r. To clean the foreground contributions we use parametric, maximum likelihood component separation technique, and consider experimental setups optimized to render a minimal level of the foreground residuals in the recovered CMB map. We consider nearly full-sky observations, include two diffuse foreground components, dust and synchrotron, and study cases with and without calibration errors, spatial variability of the foreground properties, and partial or complete B-mode lensing signal removal. In all these cases we find that in the limit of very low noise level and in the absence of the intrumental or modeling systematic effects, the foreground residuals do not lead to a limit on the lowest detectable value of r. But the need to control the foreground residuals will play a major role in determining the minimal noise levels necessary to permit a robust detection of r < 0.1 and therefore in optimizing and forecasting the performance of the future missions. For current and proposed experiments noise levels, the foreground residuals are found non-negligible and potentially can affect our ability to set constraints on r. We also show how the constraints can be significantly improved on by restricting the post component separation processing to a smaller sky area. This procedure applied to a case of a COrE-like satellite mission is shown to result potentially in over an order of magnitude improvement in the detectable value of r. With sufficient knowledge of the experimental bandpasses as well as foreground component scaling laws, our conclusions are found to be independent on the assumed overall normalization of the foregrounds and only quantitatively depend on specific parametrizations assumed for the foreground components.

The accuracy of parameter estimation by curve fitting in the presence of noise

Curve fitting of a spectrum or intensity line by chi-square minimization to obtain estimates of parameters is commonly used in fields ranging from (Raman) spectroscopy to position detection. The error or noise in the parameters such as peak position, obtained by the fitting procedure, depends on three error sources in the original data. The limited number of counts in the signal, a systematic error due to binning the data (e.g., to detector pixels), and background noise are identified as the main contributors to the inaccuracy of the estimated parameters after the fitting procedure has been completed. An analysis using analytical calculations and Monte Carlo simulations shows that the effects of limited signal counts and binning both favor a spread of the signal over as many bins as possible, while the background noise has least influence if the signal is concentrated in very few bins. These conflicting demands define a minimum attainable noise level. Hence an optimal situation can be identified where the signal is spread over a definite amount of bins to obtain minimal noise in the extracted parameters such as peak position. A good strategy is presented to obtain this optimum spread of the signal over the bins. This is very relevant to all scientific fields that make use of curve fitting, as it enables a thorough assessment and minimization of the uncertainty in the values obtained.

On the Computing of the Minimum Distance of Linear Block Codes by Heuristic Methods

The evaluation of the minimum distance of linear block codes remains an open problem in coding theory, and it is not easy to determine its true value by classical methods, for this reason the problem has been solved in the literature with heuristic techniques such as genetic algorithms and local search algorithms. In this paper we propose two approaches to attack the hardness of this problem. The first approach is based on genetic algorithms and it yield to good results comparing to another work based also on genetic algorithms. The second approach is based on a new randomized algorithm which we call "Multiple Impulse Method (MIM)", where the principle is to search codewords locally around the all-zero codeword perturbed by a minimum level of noise, anticipating that the resultant nearest nonzero codewords will most likely contain the minimum Hamming-weight codeword whose Hamming weight is equal to the minimum distance of the linear code.

Virtual monochromatic imaging in dual‐source dual‐energy CT: Radiation dose and image quality

To evaluate the image quality of virtual monochromatic images synthesized from dual-source dual-energy computed tomography (CT) in comparison with conventional polychromatic single-energy CT for the same radiation dose. In dual-energy CT, besides the material-specific information, one may also synthesize monochromatic images at different energies, which can be used for routine diagnosis similar to conventional polychromatic single-energy images. In this work, the authors assessed whether virtual monochromatic images generated from dual-source CT scanners had an image quality similar to that of polychromatic single-energy images for the same radiation dose. First, the authors provided a theoretical analysis of the optimal monochromatic energy for either the minimum noise level or the highest iodine contrast to noise ratio (CNR) for a given patient size and dose partitioning between the low- and high-energy scans. Second, the authors performed an experimental study on a dual-source CT scanner to evaluate the noise and iodine CNR in monochromatic images. A thoracic phantom with three sizes of attenuating rings was used to represent four adult sizes. For each phantom size, three dose partitionings between the low-energy (80 kV) and the high-energy (140 kV) scans were used in the dual-energy scan. Monochromatic images at eight energies (40 to 110 keV) were generated for each scan. Phantoms were also scanned at each of the four polychromatic single energy (80, 100, 120, and 140 kV) with the same radiation dose. The optimal virtual monochromatic energy depends on several factors: phantom size, partitioning of the radiation dose between low- and high-energy scans, and the image quality metrics to be optimized. With the increase of phantom size, the optimal monochromatic energy increased. With the increased percentage of radiation dose on the low energy scan, the optimal monochromatic energy decreased. When maximizing the iodine CNR in monochromatic images, the optimal energy was lower than that when minimizing noise level. When the total radiation dose was equally distributed between low and high energy in dual-energy scans, for minimum noise, the optimal energies were 68, 71, 74, and 77 keV for small, medium, large, and extra-large (xlarge) phantoms, respectively; for maximum iodine CNR, the optimal energies were 66, 68, 70, 72 keV. With the optimal monochromatic energy, the noise level was similar to and the CNR was better than that in a single-energy scan at 120 kV for the same radiation dose. Compared to an 80 kV scan, however, the iodine CNR in monochromatic images was lower for the small, medium, and large phantoms. In dual-source dual-energy CT, optimal virtual monochromatic energy depends on patient size, dose partitioning, and the image quality metric optimized. With the optimal monochromatic energy, the noise level was similar to and the iodine CNR was better than that in 120 kV images for the same radiation dose. Compared to single-energy 80 kV images, the iodine CNR in virtual monochromatic images was lower for small to large phantom sizes.

Determination of pharmaceutically related compounds by suppressed ion chromatography: I. Effects of organic solvent on suppressor performance

This overall study aims to investigate gradient elution ion-exchange chromatography of pharmaceutically relevant compounds using universal nebulisation detectors, such as evaporative light scattering detection (ELSD). Addition of organic solvents to the eluent is necessary to minimise hydrophobic adsorption on the polymeric stationary phase and improve solubility of analytes. It is also necessary to de-salt the eluent prior to detection, and in this work, ion chromatography suppressors were used for this step. Such suppressors have been designed for aqueous eluents, so the purpose of the present study was to investigate the effects of methanol and acetonitrile on suppressor performance. Chemical and electrolytic suppressors were evaluated for baseline drift, noise and efficiency of suppression using aqueous/organic eluents containing up to 40% (v/v) methanol or acetonitrile. Chemical suppression of aqueous/organic eluents showed minimal noise levels, uniform low baseline and low gradient drift. Electrolytic suppression gave good performance, but with higher baseline conductivity levels and baseline drift than chemical suppression. The elevated baseline was found not to be caused by incomplete suppression of the eluent, but was attributed to chemical reactions involving the organic solvents and facilitated by high electric currents and heat generation. It was demonstrated that suppressed ion-exchange separation using a complex KOH elution profile could be coupled with ELSD, with the suppressor effectively de-salting the eluent, producing a stable baseline. Finally, complementary separation selectivity was demonstrated using a set of pharmaceutically related organic acids separated by reversed-phase and ion-exchange methods.

Effects of urban morphology on the traffic noise distribution through noise mapping: A comparative study between UK and China

Due to the rapid urban development and massive population increase in many eastern cities, the difference in urban density and morphology between typical western and eastern cities is becoming significant. This consequently makes the noise distribution in the eastern cities rather different from typical low density European cities. In this research, two representative cities with different urban densities, Greater Manchester in the UK and Wuhan in China, were selected, which have low and high average urban density respectively, and also have considerable differences in building form and traffic pattern. In the mean time, these two cities have similar urban scale and traffic amount. In each city, based on the urban morphological analyses considering urban land-use, building and road density, and noise source distribution, a number of typical urban areas, 500 * 500 m 2 each, were sampled. A noise-mapping software package was then used to generate generic noise maps, based on existing digital vector maps for terrain and building, and traffic data obtained by on-site measurements. The comparison results show that the average and minimum noise level in Greater Manchester samples is generally higher than that in Wuhan samples, while the maximum noise level in Wuhan samples is mostly higher. By developing a Matlab program, correlations have been analysed between noise distributions and the urban characteristics relating to urban density, such as the road and building coverage ratio. Overall, comparisons between these two typical cities have shown significant effects of urban morphology on the traffic noise distribution.

Assessment of (Ld) day time average noise level at major crossings of Jammu city, J&amp;K

The present study has been carried to assess (Ld) Day Time Average Noise level (7.00 A.M. to 9.00 P.M) at eleven major crossings of Jammu City. The minimum and maximum noise levels were recorded to be 39.9 dB (A) and 109.2 dB (A) respectively. The (Ld) values at all the sites were observed to be above permissible limits prescribed by CPCB. The calculated value of Ld at all the sites were observed to be statistically significant at 0.05 (5%) level of significance (p=0.000-0.004). &#x0D;

Assessment of noise pollution in Haridwar city of Uttarakhand State, India during Kumbh Mela 2010 and its impact on human health

The present study was carried to investigate the noise level at four different locations of Haridwar viz. Singh Dwar, Rishikul, Chandi ghat and Har Ki Pauri during Kumbh Mela 2010. During normal days maximum noise levels were recorded at Chandi ghat i.e. 87.11±0.45 dB (A) in the evening hours and minimum noise levels were recorded at Har Ki Pauri i.e. 60.8±0.89 dB (A) in the morning hours. While during festival days maximum noise levels were at Har Ki Pauri i.e. 88.4 ± 1.65 dB (A) in the evening respectively and Rishikul the least being 54.93±0.53 dB (A) in the morning hours. Noise levels in all the areas were found to be above the ambient noise standard. These high noise levels may have induced headache, annoyance, lack of concentration and other varied effects on human health.

The variability of naturally occurring magnetic field levels: 10 Hz to 8 kHz

The variability of naturally occurring magnetic fields in the frequency range from [Formula: see text] over a period of one year was studied. Contour plots for the [Formula: see text], [Formula: see text], and [Formula: see text] components and for frequencies of 10, 100, 1000, 2000, and 8000 Hz were produced. Average, minimum, maximum, and the standard deviations of these fields were also calculated for 12 distinctive time intervals. In the 1– to 8–kHz frequency range, the noise levels are typically higher at night. In the 10- to 100-Hz frequency range, the noise levels are typically higher during the day. During mid- to late-summer, there is frequent thunderstorm activity, known in the southwest United States as the monsoon season. The magnetic field levels are often very high during this time period. These variability ranges can be used to estimate the lowest levels of noise that may be encountered during field surveys, which iswhat the authors are looking for when running controlled-source electrical method surveys. These variability ranges can also be used to estimate the highest levels that may be encountered, which is what the authors are looking for when running natural-source electrical methods surveys, such as audio frequency magnetotelluric (AMT) surveys. These measurements of magnetic field strength variability show that better data for controlled-source electrical measurements can be obtained using the minimum noise level measurements, as opposed to using signal integration or signal averaging with all of the data. The minimum noise level is found by using frequency bins adjacent to the signal-frequency bin. Likewise, if one is interested in measuring the naturally occurring magnetic field data, using the maximum values during each time interval makes AMT measurements possible when the natural signal level is very low, particularly in the AMT dead zone around [Formula: see text].

Wide area real time kinematic decimetre positioning with multiple carrier GNSS signals

This paper presents the technical basis for wide area real time decimetre positioning services using multiple carrier signals transmitted by future GNSS such as modernized GPS and Compass systems. The first step is to form two ionosphere-reduced extra-widelanes (EWL) that have the minimal total noise levels in cycles, considering the effects of the ionospheric and tropospheric delays, orbital error, and phase noise terms in various observational environments. The proposed three carrier ambiguity resolution approach can determine the integer ambiguities of the selected EWL signals with geometry-free and geometry-based estimations respectively over the distances of typically hundreds of kilometres. With two ambiguity-fixed EWL signals, the kinematic positioning solutions can be achieved in decimetre level accuracy. A semi-simulation method is employed to generate three frequency Compass data to demonstrate the above expected performance for decimetre positioning services. Both theoretical and experimental results have demonstrated the overall 3D root mean square accuracy of better than 15 cm obtained through with a phase smoothing process over 120 epochs. The dominating error factor in this positioning result is the residual tropospheric biases, which would become less correlated as the baselines grow beyond hundreds of kilometres. With respect to dual-frequency based precise point positioning and wide area differential positioning solutions, a major advantage of using the third frequency signals is the convergence time being shorten from tens of minutes to a few minutes. In addition, due to the instant ambiguity resolution capability, phase breaks or cycle slips no longer affect the continuity of the solutions. This reliable decimetre positioning capability introduces a significant improvement to safety-of-life, liability-critical and professional applications.

Evolution of barrier-resistance noise in CoFeB/MgO/CoFeB tunnel junctions during annealing

The low-frequency resistance noise in sputtered-deposited magnetic tunnel junctions with MgO barriers has been measured as a function of annealing time at different annealing temperatures. The noise has a 1/f spectrum and it is quantified by a Hooge-like parameter α given in units of μm2. Unannealed devices have the highest noise levels and their α parameters exhibit a pronounced dependence on the voltage bias across the junction. A significant increase in tunneling magnetoresistance (TMR) is observed for short annealing times (on the order of minutes) at high temperatures and it is correlated with a large reduction in noise and in its bias dependence. The maximum TMR and minimum noise levels are reached at a later time that depends on temperature, being shorter at higher annealing temperatures. Devices annealed at 380 and at 430 °C exhibit the same minimum noise levels, α≈2×10−10 μm2. The origin of the resistance noise, its annealing time evolution, and its bias dependence are discussed and they are attributed to vacancy defects in the MgO barriers.

Deep ocean noise measurements in the Philippine Sea.

In the spring of 2009, a newly developed distributed vertical line array (DVLA) receiver made up of two, 1000‐m‐long subarrays with 30 hydrophones each was deployed for approximately 1 month in the northern Philippine Sea. One subarray spanned the sound‐channel axis, and the second subarray spanned the surface conjugate depth (about 4200 m). Twenty of the 30 hydrophones in the deep subarray were spaced 5 m apart (half‐lambda at 150 Hz), allowing the vertical directionality of the ambient noise below the surface conjugate depth to be determined. The minimum omnidirectional ambient noise levels decreased significantly below the surface conjugate depth at frequencies from 50 to 500 Hz, similar to behavior previously observed in the central North Pacific Ocean. The minimum noise levels presumably correspond to times when wind speeds are low and surface conditions are calm so that there is little locally generated, low‐frequency noise.