Noise abatement schemes for shielded canyons

Access to quiet areas in cities is important to avoid adverse health effects due to road traffic noise. Most urban areas which are or can become quiet (L_A,eq < 45 dB) are shielded from direct road traffic noise. By transfer paths over roof level, many road traffic noise sources contribute to the level in these shielded areas and noise abatement schemes may be necessary to make these areas quiet. Two real life shielded courtyards in Göteborg have been selected as reference cases for a numerical investigation of noise abatement schemes. The selected areas are modelled as canyons with a road traffic noise source modelled outside the canyon by a finite incoherent line source, which is more realistic than both a coherent and an incoherent line source of infinite length. The equivalent sources method has been used for the calculations. For all studied noise abatement schemes in the shielded canyon, the reductions are largest for the lower canyon observer positions. Façade absorption is the most effective when placed in the upper part of the canyon and can typically yield a reduction of 4 dB(A). Constructing 1 m wide walkways with ceiling absorption reduces the level typically by 3 dB(A). These effects are most effective for narrower canyons. For treatments at the canyon roof, reductions are independent of the canyon observer position and amount to 4 dB(A) for a 1 m tall screen and 2 dB(A) for a grass covering of a saddle roof. Downward refracting conditions increase the levels for the lower canyon observer positions and higher frequencies. For sources located in canyons, abatement schemes therein are more effective for noise reduction in the shielded canyon than similar abatement schemes in the shielded canyon itself, given that all contributing source canyons are treated.     

Annoyance due to single and combined sound exposure from railway and road traffic

Environmental noise is a growing and well recognized health problem. However, in many cases people are exposed not to a single noise source-for example, road, railway, or aircraft noise-but to a combination of noise exposures and there is only limited knowledge of the effects on health of exposure to combined noise sources. A socio-acoustic survey among 1953 persons aged 18-75 years was conducted in residential areas exposed to railway and road traffic noise with sound levels ranging from L(Aeq,24h) 45-72 dB in a municipality east of Gothenburg, Sweden. The objectives were to assess various adverse health effects, including annoyance, and to elucidate the impact of exposure to single and combined noise sources. In areas exposed to both railway and road traffic, the proportion annoyed by the total traffic sound environment (total annoyance) was significantly higher than in areas with one dominant noise source (rail or road traffic) with the same total sound exposure (L(Aeq,24h,tot)). This interaction effect was significant from 59 dB and increased gradually with higher sound levels. Effects of the total sound exposure should be considered in risk assessments and in noise mitigation activities.     

Macroscopic modeling of urban traffic noise - influence of absorption and vehicle flow distribution

Prediction of noise levels at shielded positions in urban areas is more difficult than on exposed positions. At shielded positions, the predictions method must include multiple reflections, and many sources must be taken into account. Using numerical methods that solve the wave equation is possible, but very computationally heavy. Here two methods have been used, a very simplified ray model and a statistical model. The results show that concentrating the traffic and introducing absorption onto building façades will give lower levels at shielded positions.     

Reconstruction of Radio Images of the Sun Obtained by the Siberian Solar Radio Telescope

Reconstruction of radio images of the Sun obtained by the Siberian Solar Radio Telescope (SSRT) encounters two main problems. First, since the solar radio images at a wavelength of 5.2 cm have a high contrast, the amplitude–phase distribution in the antenna–feeder section should be known with a very high accuracy. Second, since such images comprise not only bright compact components but also low-contrast diffuse areas, there is a problem of deconvolution of these diffuse sources, which is inherent to the CLEAN algorithm. To solve the first problem, we determine the amplitude–phase distortions by an iterative analysis of the image itself, in which the opposite sidelobes of the point-source response are compared. To suppress the influence of other sources on the response, we analyze several compact sources. The phase distortions are determined from the asymmetry of the sidelobes, and the amplitude distortions, from sidelobe values. The image is corrected in the spatial-spectrum domain after each iteration. On the one hand, the problems encountered when reconstructing extended sources are related to the fact that the CLEAN algorithm requires significant computer resources. On the other hand, reconstructing images of extended areas requires that the number of cycles of this algorithm should be increased. Another problem consists in the fact that the use of the same clean antenna pattern for reconstructing compact and extended sources results in appearance of high-frequency distortions of the latter sources. If the CLEAN algorithm is applied, then the computer resources are mainly spent to shift the pattern and to find the maximum of the initial image. We decrease the time necessary for shifting the pattern by excluding the points near the zero value from the antenna-pattern data set and by sorting the remaining data points. The time of finding the maximum was decreased by using a local search window. In addition, we use a number of cutoff levels and search the next maximum in the whole image only after reconstructing the windowed image down to the current cut level. To reconstruct bright compact sources, we use the clean antenna pattern close to the ideal pattern. To reconstruct low-contrast diffuse areas, we use the model patterns obtained by convolving the antenna pattern with the images of extended sources.     

Excess attenuation for sound propagation over an urban canyon

Because quiet areas in dense urban environments are important to well-being, the prediction of sound propagation to shielded urban areas is an ongoing research focus. Sound levels in shielded areas, such as canyons between rows of buildings, are strongly influenced by distant sources. Therefore, propagation factors such as metrology, screening, and intermediate canyons—as occur between a source canyon and a receiver canyon—must be addressed in an engineering propagation model. Though current models address many important propagation factors, engineering treatment of a closed urban canyon, subject to multiple internal reflections, remains difficult.A numerical investigation of sound propagation across the open tops of intermediate urban canyons has been performed, using the parabolic equation and equivalent sources methods. Results have been collected for various canyon geometries, and the influences of multiple canyons, canyon/rooftop absorption, variable rooftop height, wind gradient, and correlated versus uncorrelated source models have been investigated. Resulting wideband excess attenuation values ranged from −1 dB to −4 dB per canyon, and were fairly constant with frequency in many useful cases. By characterizing the excess attenuation of canyons intermediate to the source and receiver, the influence of these intermediate canyons could be addressed simply, without the overhead of a detailed numerical calculation.     

Railway noise and vibration annoyance in residential areas

This paper summarizes the results from the 1975 British railway noise study. Noise from railways does cause annoyance and interfere with activities. People in Great Britain appear to find high levels of railway noise to be somewhat less annoying than high levels from other sources. L_eq is as closely related to annoyance as any other index examined. Since annoyance increases steadily with noise level there is no particular “acceptable” railway noise level. Overhead electrified routes appear to be less annoying than diesel routes at the same noise levels. Through train noise, maintenance noise and vibration are the most widely noticed problems associated with railways in residential areas.     

Fission,spallation or fusion-based neutron sources

In this paper the most promising technology for high power neutron sources is briefly discussed. The conclusion is that the route to high power neutron sources in the foreseeable future is spallation — short or long pulse or even CW — all of these sources will have areas in which they excel.      

Biomagnetism

The study of magnetic fields originating in biological systems, particularly the human body, has important implications for diverse areas of biological research, medicine, physiology, psychology and occupational health. This review presents the current status of research in all areas of biomagnetism with special emphasis on the extent to which the results of this research yield information not provided by more conventional techniques. There are three distinct sources of biomagnetic fields: magnetic constituents or contaminants in the body which provide a remanent field, components at the molecular level that respond with either a diamagnetic or paramagnetic susceptibility to an applied field, and electrical currents associated with the movement of ions in body tissue. Diverse techniques for measuring these weak biomagnetic fields are described, with particular attention devoted to those that do not require magnetic shielding. Most early work in this area dealt with fields arising from ion flow in the heart and in the brain, but now research is being directed toward fields known to be produced by current flow in other organs as well. The relationships that have been established between various characteristics of these fields and their electrophysiological sources are summarized.