China 
Africa 
Explore chapters and articles related to this topic
Consolidation and skills development
Published in Andrew Norton, Dynamic Fields and Waves, 2019
The Doppler effect describes the change in frequency which occurs when there is motion of either the wave source or the observer. For sound waves, motion of either the source or the observer, relative to the air through which the wave propagates, leads to such a frequency shift, as derived in Chapter 2. The speed of light c arises naturally in Maxwell’s equations, leading to the nineteenth-century idea that light propagates with speed c through a hypothetical medium called the ether. The Michelson-Morley experiment tried to measure the motion of the Earth relative to this ether, and arrived instead at the conclusion that there is no stationary ether through which light propagates. Contrary to nineteenth-century expectations, the speed of light is a fundamental constant: all observers will always measure the speed of light in a vacuum to have the value c = 3.00 × 108 m s−1.
What Is Light?
Published in Travis S. Taylor, Introduction to Laser Science and Engineering, 2019
Another major point discussed by Huygens in his Treatise on Light was the observation by Ole Romer (1644–1710), a Danish astronomer shown in Figure 1.23, who through observations of Jupiter’s moon Io calculated the speed of light for the first time. Romer calculated light speed to be about 220,000 km/s, which is close to the now more accurate measurement of 299,792 km/s. While Romer’s measurement was off by about 26% the major impact on physics of the time was proving that the speed of light was finite and not instantaneous. To this point in history, the speed of light was still conjecture and finally the conjecture was over. The speed of light was finite!
The Nature of Light
Published in Abdul Al-Azzawi, Light and Optics, 2018
In 1675, the first successful estimate of the speed of light was made by the Danish astronomer Ole Roemer (1644–1710). His method involved astronomical observations of one of the moons of Jupiter, called Io. At that time, four of Jupiter’s 14 moons had been discovered, and the periods of their orbits were known. Io, the innermost moon, has a period of about 42.5 h. This was measured by observing the eclipse of Io as it passed behind Jupiter, as shown in Figure 1.1. The period of Jupiter is about 12 years, so as the Earth moves through 180° around the sun, Jupiter revolves through only 15°.
Development of a wireless passive capacitively coupled contactless conductivity detection (WPC4D) for fluidic flow detection utilizing 3D printing and PCB technologies
Published in Instrumentation Science & Technology, 2023
Bao-Anh Hoang, Van-Anh Bui, Kien Do Trung, Hang Bui Thu, Trinh Chu Duc, Tung Thanh Bui, Loc Do Quang
In this work, we focus on the sensing performance of the WPC4D system. The influence of fluidic flows such as fluid type, fluid velocity, and peristaltic period will be considered elsewhere. Besides, to simplify the 3D model calculation process, only the RF module was employed to analyze the sensing performance by evaluating the reflection coefficient S11 of the system. The simulation considered there was no influence of the fluidic flow’s factors. The most common approach for modeling RF, microwave, and millimeter wave devices is to solve the wave equation based on the electric field variables described by:[35] where is the relative permeability, is the angular frequency, and is the complex relative permittivity. The wavenumber of free space is defined to be: where is the speed of light in a vacuum and is the permittivity of the vacuum.
The limits of Riemann solutions to the relativistic van der Waals fluid
Published in Applicable Analysis, 2021
Thus, the first goal of this paper is to solve the Riemann problem for the relativistic van der Waals fluid (1), (2). According to the principle of special relativity, the velocity of relativistic fluid should be less than c, the speed of light. Thus, the physically relevant region of solution to the relativistic van der Waals fluid (1) and (2) in this paper is which is obviously quite different from that of the isothermal and polytropic gas. In the region , we consider the following Riemann initial data for (1) and (2), where and are arbitrary constants. In fact, the study of Riemann problem for relativistic flow plays a vital role in the field of mathematics and physics as well as in engineering. By means of the Lorentz transformation, the specific expression of the shock wave is formulated and the geometric properties of rarefaction wave and shock wave curves are analyzed. Then, by the method of analyzing in the phase plane, we establish the existence and uniqueness of Riemann solutions with five different structures. See Section 3 below.
Modelling of a variable optical switch based on the parametric amplification in a photonic crystal fibre
Published in Journal of Modern Optics, 2018
Hassan Pakarzadeh, Mostafa Sharifian
where c is the speed of light in the vacuum, is the ZDW of the fibre, and and are the wavelengths of the pump and the signal, respectively. Moreover, S0 is the dispersion slope of the fibre calculated at the ZDW. The FOPA gain calculated in decibel (dB) units is defined as: