Total internal reflectionIn physics, total internal reflection (TIR) is the phenomenon in which waves arriving at the interface (boundary) from one medium to another (e.g., from water to air) are not refracted into the second ("external") medium, but completely reflected back into the first ("internal") medium. It occurs when the second medium has a higher wave speed (i.e., lower refractive index) than the first, and the waves are incident at a sufficiently oblique angle on the interface.
Reflection (physics)Reflection is the change in direction of a wavefront at an interface between two different media so that the wavefront returns into the medium from which it originated. Common examples include the reflection of light, sound and water waves. The law of reflection says that for specular reflection (for example at a mirror) the angle at which the wave is incident on the surface equals the angle at which it is reflected. In acoustics, reflection causes echoes and is used in sonar. In geology, it is important in the study of seismic waves.
Norwegian cyclone modelThe older of the models of extratropical cyclone development is known as the Norwegian cyclone model, developed during and shortly after World War I within the Bergen School of Meteorology. In this theory, cyclones develop as they move up and along a frontal boundary, eventually occluding and reaching a barotropically cold environment. It was developed completely from surface-based weather observations, including descriptions of clouds found near frontal boundaries.
Syphilitic aortitisSyphilitic aortitis is inflammation of the aorta associated with the tertiary stage of syphilis infection. SA begins as inflammation of the outermost layer of the blood vessel, including the blood vessels that supply the aorta itself with blood, the vasa vasorum. As SA worsens, the vasa vasorum undergo hyperplastic thickening of their walls thereby restricting blood flow and causing ischemia of the outer two-thirds of the aortic wall. Starved for oxygen and nutrients, elastic fibers become patchy and smooth muscle cells die.
Transcranial DopplerTranscranial Doppler (TCD) and transcranial color Doppler (TCCD) are types of Doppler ultrasonography that measure the velocity of blood flow through the brain's blood vessels by measuring the echoes of ultrasound waves moving transcranially (through the cranium). These modes of medical imaging conduct a spectral analysis of the acoustic signals they receive and can therefore be classified as methods of active acoustocerebrography.
GautengGauteng (xaʊˈtɛŋ , Sotho-Tswana for 'place of gold'; eGoli or iGoli îːˈgóːlì) is one of the nine provinces of South Africa. Situated on the Highveld, Gauteng is the smallest province by land area in South Africa. Although Gauteng accounts for only 1.5% of the country's land area, it is home to more than a quarter of its population (26%). Highly urbanised, the province contains the country's largest city, Johannesburg, which is also one of the largest cities in the world.
ApartheidApartheid (əˈpɑːrt(h)aɪt, especially South African English: əˈpɑːrt(h)eɪt, aˈpartɦɛit; , aparthood) was a system of institutionalised racial segregation that existed in South Africa and South West Africa (now Namibia) from 1948 to the early 1990s. Apartheid was characterised by an authoritarian political culture based on baasskap ( 'boss-hood' or 'boss-ship'), which ensured that South Africa was dominated politically, socially, and economically through minoritarianism by the nation's dominant minority white population.
