Concept

Air burst

Résumé
An air burst or airburst is the detonation of an explosive device such as an anti-personnel artillery shell or a nuclear weapon in the air instead of on contact with the ground or target. The principal military advantage of an air burst over a ground burst is that the energy from the explosion (as well as any shell fragments) is distributed more evenly over a wider area; however, the peak energy is lower at ground zero. Air burst artillery has a long history. The shrapnel shell was invented by Henry Shrapnel of the British Army in about 1780 to increase the effectiveness of canister shot. It was used in the later Napoleonic wars and stayed in use until superseded in Artillery of World War I. Modern shells, though sometimes called "shrapnel shells", actually produce fragments and splinters, not shrapnel. Air bursts were used in the First World War to shower enemy positions and men with shrapnel balls to kill the largest possible number with a single burst. When infantry moved into deep trenches, shrapnel shells were rendered useless and high-explosive shells were used to attack field fortifications and troops in the open. The time fuses for the shells could be set to function on contact or in the air, or at a certain time after contact. Early anti-aircraft warfare used time fuses to function when they reached the estimated altitude of the target. During World War II a "proximity fuze" was developed for antiaircraft use, controlled by a Doppler radar device within the shell that caused it to explode when near the target. The idea was later adapted for use against ground targets. During the Vietnam War, air bursting shells were used to great effect to defend bases. This tactic was known as "Killer Junior" when referring to 105 mm or 155 mm shells, and "Killer Senior" when employed with larger howitzers. Some anti-personnel bounding mines such as Germany's World War II "Bouncing Betty" fire a grenade into the air, which detonates at waist level, increasing the blast radius and harm inflicted by detonation, shock wave, and flying splinters.
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Puissance des armes nucléaires
La puissance explosive de l'arme nucléaire est la quantité d'énergie libérée lorsqu'une arme nucléaire explose, exprimée habituellement en masse équivalente de trinitrotoluène (TNT), soit en kilotonnes (milliers de tonnes de TNT) ou mégatonnes (millions de tonnes de TNT), ou parfois en térajoules (un kilotonne de TNT vaut ). Comme la quantité précise de l'énergie libérée par la TNT est et a été sujet à des incertitudes de mesure, surtout à l'aube de l'ère nucléaire, la convention couramment admise est qu'un kilotonne de TNT équivaut à .
Effects of nuclear explosions
The effects of a nuclear explosion on its immediate vicinity are typically much more destructive and multifaceted than those caused by conventional explosives. In most cases, the energy released from a nuclear weapon detonated within the lower atmosphere can be approximately divided into four basic categories: the blast and shockwave: 50% of total energy thermal radiation: 35% of total energy ionizing radiation: 5% of total energy (more in a neutron bomb) residual radiation: 5–10% of total energy with the mass of the explosion.
Hypocentre
thumb|Épicentre et hypocentre (ou foyer). Lhypocentre ou foyer est le point de départ de la rupture sismique sur une faille. C'est à ce point que sont émis les trains d'ondes sismiques captées ensuite à leurs arrivées par les sismomètres. C'est donc un point essentiel dont la localisation, qui comprend aussi la profondeur à l'intérieur de la terre, est très importante dans l'analyse des tremblements de terre. La projection de l’hypocentre sur la surface terrestre s'appelle l’épicentre.
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