Group velocityThe group velocity of a wave is the velocity with which the overall envelope shape of the wave's amplitudes—known as the modulation or envelope of the wave—propagates through space. For example, if a stone is thrown into the middle of a very still pond, a circular pattern of waves with a quiescent center appears in the water, also known as a capillary wave. The expanding ring of waves is the wave group or wave packet, within which one can discern individual waves that travel faster than the group as a whole.
ArtèreUne (du grec ἀρτηρία, artêria) est un vaisseau sanguin qui conduit le sang du cœur aux autres tissus de l'organisme. La quasi-totalité des artères conduisent le sang oxygéné vers les organes (par opposition aux veines), sauf pour les artères pulmonaires qui conduisent un sang pauvre en oxygène vers les poumons. Une artère est constituée de plusieurs couches concentriques : l'intima (au contact direct du sang) constituée d'un endothélium (composé de cellules épithéliales pavimenteuses) et d'une couche sous-endothéliale qui correspond à un tissu conjonctif lâche.
Signal velocityThe signal velocity is the speed at which a wave carries information. It describes how quickly a message can be communicated (using any particular method) between two separated parties. No signal velocity can exceed the speed of a light pulse in a vacuum (by Special Relativity). Signal velocity is usually equal to group velocity (the speed of a short "pulse" or of a wave-packet's middle or "envelope"). However, in a few special cases (e.g.
Coronary catheterizationA coronary catheterization is a minimally invasive procedure to access the coronary circulation and blood filled chambers of the heart using a catheter. It is performed for both diagnostic and interventional (treatment) purposes. Coronary catheterization is one of the several cardiology diagnostic tests and procedures. Specifically, through the injection of a liquid radiocontrast agent and illumination with X-rays, angiocardiography allows the recognition of occlusion, stenosis, restenosis, thrombosis or aneurysmal enlargement of the coronary artery lumens; heart chamber size; heart muscle contraction performance; and some aspects of heart valve function.
BarotraumatismeUn barotraumatisme est un accident touchant les tissus d'un organisme vivant. Il est causé par un changement de pression des gaz dans le corps. Concrètement, un barotraumatisme survient lorsqu'il y a une difficulté d'adaptation entre la pression à l'intérieur d'une cavité du corps et la pression externe. Ces variations de pression peuvent survenir lors d'activités comme la plongée sous-marine, la plongée en apnée ou lors de voyages en avion. La variation des pressions est énoncée par la loi de Boyle-Mariotte.
