Vecteur vitesseLe vecteur vitesse, nommé parfois vélocité, est une notion de physique qui à la différence de la vitesse comprend un déplacement vers un point. Par exemple, une voiture a une vitesse de 60 km/h mais a une vélocité de 60 km/h vers le nord, le nord étant un point de référence ou de destination pour la voiture. Le terme vélocité est tiré des mots latins velocitas et velox signifiant respectivement rapidité, vitesse, et rapide, prompt, véloce, mots ayant eux-mêmes une origine obscure, mais supposé étant lié à la racine proto-indo-européenne wegh- signifiant "aller, bouger," et "transport dans un véhicule".
Convection–diffusion equationThe convection–diffusion equation is a combination of the diffusion and convection (advection) equations, and describes physical phenomena where particles, energy, or other physical quantities are transferred inside a physical system due to two processes: diffusion and convection. Depending on context, the same equation can be called the advection–diffusion equation, drift–diffusion equation, or (generic) scalar transport equation.
Soil steam sterilizationSoil steam sterilization (soil steaming) is a farming technique that sterilizes soil with steam in open fields or greenhouses. Pests of plant cultures such as weeds, bacteria, fungi and viruses are killed through induced hot steam which causes vital cellular proteins to unfold. Biologically, the method is considered a partial disinfection. Important heat-resistant, spore-forming bacteria can survive and revitalize the soil after cooling down. Soil fatigue can be cured through the release of nutritive substances blocked within the soil.
Local systemIn mathematics, a local system (or a system of local coefficients) on a topological space X is a tool from algebraic topology which interpolates between cohomology with coefficients in a fixed abelian group A, and general sheaf cohomology in which coefficients vary from point to point. Local coefficient systems were introduced by Norman Steenrod in 1943. The category of perverse sheaves on a manifold is equivalent to the category of local systems on the manifold. Let X be a topological space.
Étoilevignette|Le Soleil, l’étoile la plus proche de la Terre, vu lors d'une éruption en ultraviolets avec de fausses couleurs. Une étoile est un corps céleste plasmatique qui rayonne sa propre lumière par réactions de fusion nucléaire, ou des corps qui ont été dans cet état à un stade de leur cycle de vie, comme les naines blanches ou les étoiles à neutrons. Cela signifie qu'ils doivent posséder une masse minimale pour que les conditions de température et de pression au sein de la région centrale permettent l'amorce et le maintien de ces réactions nucléaires, seuil en deçà duquel on parle d'objets substellaires.
Groundwater modelGroundwater models are computer models of groundwater flow systems, and are used by hydrologists and hydrogeologists. Groundwater models are used to simulate and predict aquifer conditions. An unambiguous definition of "groundwater model" is difficult to give, but there are many common characteristics. A groundwater model may be a scale model or an electric model of a groundwater situation or aquifer. Groundwater models are used to represent the natural groundwater flow in the environment.
Analogie électro-hydrauliquevignette|Analogie entre un circuit hydraulique (à gauche) et un circuit électronique (à droite). L'analogie électro-hydraulique est une apparence de similitude entre les grandeurs électriques et hydraulique. Comme le courant électrique est invisible et que les processus en jeu dans l'électronique sont souvent difficiles à démontrer, les différents composants électroniques peuvent être représentés par des équivalents hydrauliques.
Electrical resistivity and conductivityElectrical resistivity (also called volume resistivity or specific electrical resistance) is a fundamental specific property of a material that measures its electrical resistance or how strongly it resists electric current. A low resistivity indicates a material that readily allows electric current. Resistivity is commonly represented by the Greek letter ρ (rho). The SI unit of electrical resistivity is the ohm-metre (Ω⋅m).
Stratified squamous epitheliumA stratified squamous epithelium consists of squamous (flattened) epithelial cells arranged in layers upon a basal membrane. Only one layer is in contact with the basement membrane; the other layers adhere to one another to maintain structural integrity. Although this epithelium is referred to as squamous, many cells within the layers may not be flattened; this is due to the convention of naming epithelia according to the cell type at the surface. In the deeper layers, the cells may be columnar or cuboidal.
Parent materialParent material is the underlying geological material (generally bedrock or a superficial or drift deposit) in which soil horizons form. Soils typically inherit a great deal of structure and minerals from their parent material, and, as such, are often classified based upon their contents of consolidated or unconsolidated mineral material that has undergone some degree of physical or chemical weathering and the mode by which the materials were most recently transported.
