Glossary - Reflexions

Glossary

Vous trouverez dans ce glossaire les définitions de termes présents dans les différents articles, classés de manière alphabétique.

X-ray crystallography

Aa procedure in which X-rays are diffracted by macromolecular crystals. This method allows the arrangement of the atoms in a crystal to be determined.

X-Ray fluorescence

A method for the chemical analysis of matter. It is based on the fact that when matter is bombarded by X-rays, it emits energy in the form of other X-rays (phenomenon of fluorescence). These rays are characteristic of the composition of matter.

X-rays

Discovered in 1895 by Röntgen, x-rays are a form of highly energetic electromagnetic radiation that can travel through matter with a facility relative to the composition of this matter. X-ray technology is very present in our society. In medicine, it allows us to observe fractures or diagnose cancer. It is also found in security systems (metal detectors, etc.) or in instruments used to study the organisation of atoms within matter.

X-rays (in astrophysics)

In light emission, X-rays posess a shorter wavelength and therefore have more energy than UVs which are themselves more energetic than visible light. In astrophysics, the emission of X-rays has been studied since the second half of the twentieth century. They are absorbed by the atmosphere, so it was necessary to wait for the first space observations to detect them. The weak X-ray emissions of the Sun first led to the belief that stars emitted very few of them, but several years later, while preparing for the Apollo emissions, researchers serendipitously observed a strong X-ray emission coming from the Scorpion constellation. Since then, the study of X-rays has become a separate field of astrophysics.

Since 1999, the satellites Chandra (for NASA) and XMM-Newton (for the ESA) are entirely devoted to the emission of X-rays. They have enabled more in-depth studies of massive stars, and the measurement of the rotation of black holes.

xenograft

The transfer of an organ or tissue from one organism to another.

An avant-garde artistic circle founded in Brussels on October 28, 1883, by the lawyer and cultural mainspring Octave Maus (1856-1919), whose members were called ‘twentyists’ and whose painting, aimed at being innovative, privileged light above all else. The XX – the number of members since the departure of James Ensor (1860-1940), Fernand Khnopff (1858-1921) and Van Rysselberghe (1862-1926) – organised annual Salons in the Belgian capital: the first of them opened on February 2, 1884, in the first of the Brussels Palais des Beaux-arts, the future Royal Museum of Ancient Art. A number of artists whom posterity was to recognise joined this association: to restrict ourselves to the most famous, we can cite Félicien Rops (1833-1898), Auguste Rodin (1840-1917) and Georges Minne (1866-1947).

Xylem

Plant tissue made up of cells with thick walls carrying water and mineral salts.