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Environmental Noise
Published in Wayne T. Davis, Joshua S. Fu, Thad Godish, Air Quality, 2021
Wayne T. Davis, Joshua S. Fu, Thad Godish
Sound is a form of energy produced by vibrating objects or aerodynamic disturbances. The former includes our vocal cords and operating motors, automobiles, and airplanes; the latter, thunder, sonic booms, and air movement.
Radiation Hazards
Published in Dag K. Brune, Christer Edling, Occupational Hazards in the Health Professions, 2020
Humans can hear sound within a frequency range of 20 to 20,000 Hz. It is, however, possible to have a hearing sensation below 20 Hz, although without tonal characteristics. The hearing threshold at the frequency of 20 Hz is about 74 dB, while at 4 Hz the threshold is as high as 130 dB. One starts to experience tickling and unpleasant pressure in the ears at 140 dB.
Gases: comparison with experiment
Published in Michael de Podesta, Understanding the Properties of Matter, 2020
Sound travels considerably slower through gases than through solids or liquids. As shown in Table 5.14, the maximum speed at 0°C is approximately 1000 ms−1 for the gases with the lightest molecules, helium and hydrogen. This may be compared with the values for solids (Table 7.6) and liquids (Table 9.5) which are typically of the order of 3000 ms−1.
Textile dye effluent treatment using advanced sono-electrocoagulation techniques: A Taguchi and particle swarm optimization modeling approach
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2023
Numerous technologies reported for treating textile wastewater-like coagulation, flocculation, adsorption, membrane filtration, biological methods, advanced oxidation, and reduction process, etc. (Singh et al. 2019). Electrochemical wastewater technologies such as electrocoagulation, electro-oxidation, and electro-flotation are efficient wastewater technologies which do not require any chemicals. The electrocoagulation techniques have several advantages over the traditional coagulation process such as smaller operation time, maximum removal efficiency, minimum sludge generation, and compatibility (Safwat 2020). Sound is mechanical energy that can travel through solid, liquid, and gas media. In sonication, ultrasound wave with a frequency of 20,000 Hz or higher is applied. Depending on the insolation power and frequency, ultrasound generates localized high-energy molecules in a medium (Maha Lakshmi and Sivashanmugam 2013). When the negative pressure is strong enough to disrupt the distance between the molecules of a liquid, cavitation bubbles form (Dizge et al. 2018). Sono-electrochemistry has several advantages, including the ability to reduce the thickness of the diffusion layer, clean the electrodes, and accelerate the adsorption process (Yang et al. 2016).
Influential variables impacting the reliability of building occupancy sensor systems: A systematic review and expert survey
Published in Science and Technology for the Built Environment, 2022
Yiyi Chu, Debrudra Mitra, Zheng O’neill, Kristen Cetin
There are two main types of sound-wave-based sensors, including acoustical sensors and ultrasonic sensors. Acoustic wave sensors are so named because their detection mechanism is a mechanical or acoustic wave using a piezoelectric material. For this application such sensors detect only human-audible sound with a frequency of 20 Hz–20 kHz (Launer, Zakis, and Moore 2016). Ultrasonic sensors measure distances based on transmitting and receiving ultrasonic signals, which detect these sounds that are inaudible to humans. An ultrasonic sensor is generally made up of piezoelectric material, where the ultrasonic transmitter transmits an ultrasonic wave, which then travels through a medium of air until it is intersected by a material. The wave is reflected back when it detects a person, which can then be detected by the ultrasonic receiver. By analyzing the time and distance at which the reflected ultrasonic wave is received, one can infer whether there is a person in the space. Compared to other sensors, the main advantages of the use of sound-wave-based sensor technologies is that they can include an increased range of sensitivity for minor movement. However, the disadvantage would be that certain materials, such as cloth or foam, absorb sound waves, causing problems when a person is covered in multiple layers of clothing so the sensor would not detect motion consistently, and they are highly sensitive to reflective materials such as glass or plastic (Yavari, Lee, et al. 2014).
The automated driver as a new road user
Published in Transport Reviews, 2021
Ane Dalsnes Storsæter, Kelly Pitera, Edward D. McCormack
Auditory feedback in vehicles provides information on the engine, transmission, tyres and aerodynamics (Walker et al., 2006) as well as warnings of disruptive events such as the proximity of emergency vehicles (Macadam, 2003). Whether a sound is audible to humans depends both on the power of the sound, measured in decibels (dB), and the frequency of the vibration (Hz). Humans hear above 0 dB and feel discomfort from 110 dB and up (Institute for Quality and Efficiency in Health, 2008). Normal hearing detects frequencies of sound between 20 and 20,000 Hz (Bagai, 2006). Humans are excellent at localising the sources of sounds, i.e. determining the range, elevation and azimuth angles of a sound’s source (Duraiswami & Raykar, 2005). Hearing is also used to determine the movement of objects that are not immediately in view, and it is therefore vital for safe and effective orientation (Gatehouse & Noble, 2004). The distance range of hearing is dependent on the loudness of the sound (Pasnau, 1999) as well as environmental factors including temperature and humidity (Harris, 1966).