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Telescopes for Inner Space: Fiber Optics and Endoscopes
Published in Suzanne Amador Kane, Boris A. Gelman, Introduction to Physics in Modern Medicine, 2020
Suzanne Amador Kane, Boris A. Gelman
It is an experimental fact that the speed of light varies from medium to medium. In a vacuum, light moves at the extremely high speed of about 3.00 × 108 meters per second (3.00 × 108 m/s or 186,000 miles/s); this value is represented by the letter c. However, whenever light travels through a medium other than a vacuum, its interactions with the material result in a lower speed. This is because the light is repeatedly absorbed and re-emitted by atoms and molecules as it travels through the medium. The interaction between light and matter results in the reduction of speed of the transmission of light by a factor characteristic of a given medium.
Basic Mathematics and Systems of Measurement Units
Published in Muhammad H. Rashid, Ahmad Hemami, Electricity and Electronics for Renewable Energy Technology, 2017
Among all the entities that we measure, some can be considered principal, from which other items can be derived. We have already seen examples of this in the measurement of length: If the unit for measuring length is feet (ft), then for area we can use ft2 and for volume ft3 may be employed. In the metric system we have meter (m) for length, and m2 and m3 for area and volume, respectively. Another example is the unit for measuring speed of something moving. If meter (foot) is the unit for measuring length (or distance) and second is the unit for measuring time, then meters per second (m/sec) or feet per second (ft/s) can be used for the unit of speed.
Sound waves
Published in Michael Talbot-Smith, Sound Engineering Explained, 2012
In the air, under normal conditions, sound waves travel at about 340 metres per second (m/s). This is close to 760 miles/hour, or about 1120 feet/second. The velocity varies slightly with air temperature, which is why players of wind instruments need, literally, to warm up their instruments, as the pitch depends on the speed with which sound waves oscillate within the instrument. For most practical purposes, apart from the instance just quoted, the variation in sound wave velocity with temperature is unimportant. Details are given in Part 2 of this chapter. The symbol for sound wave velocity is, in this book, v.
Bone quality in young adults with intellectual disability involved in adapted competitive football
Published in European Journal of Sport Science, 2019
Vicente Lizondo, Jordi Caplliure-Llopis, Dolores Escrivá, Jose Enrique De La Rubia, Carlos Barrios
The quantitative ultrasound (QUS) measurement was part of a broad physical assessment conducted by specially trained medical assistants. Bone mass parameters were measured by QUS evaluation using the Lunar Achilles Insight device (GE Healthcare, Little Chalfont, Great Britain). The QUS technique was chosen based on its ability to estimate bone quality in adolescents and young adults with a short examination time, the ease of implementation in routine activities, and the absence of adverse effects. The Lunar Achilles Insight device is a portable device that allows a quick estimation of 2 basic parameters: broadband ultrasound attenuation (BUA) and speed of sound (SOS). The BUA refers to the absorption of energy by bone and soft tissue when sound waves travel through them. Its unit is dB/MHz. Increase in BUA correlates to increased bone trabecula content. The SOS refers to the division of the length of the body part studied by the sound wave transmission time. Its unit of measurement is metre per second (m/s). Increase in SOS correlates to reduced bone mineral content (Chin & Ima-Nirwana, 2013). Both ultrasonographic measurements constitute a clinical variable called the stiffness index which has been used to determine the risk of osteoporotic fractures and is comparable to BMD which is measured by DXA (Trimpou, Bosaeus, Bengtsson, & Landin-Wilhelmsen, 2010; Xu, Guo, Gong, Xu, & Bai, 2014).