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A (4+3) cycloaddition [1] is a cycloaddition between a four-atom π-system and a three-atom π-system to form a seven-membered ring. Allyl or oxyallyl cations (propenylium-2-olate) are commonly used three-atom π-systems, while a diene (such as butadiene ) plays the role of the four-atom π-system.
For example, in friendly and championship qualifying matches England, when playing the 4–4–2 formation, generally number their players (using the standard right to left system of listing football teams) four defenders – 2, 5, 6, 3; four midfielders – 7, 4, 8, 11; two forwards – 10, 9. This system of numbering can also be adapted to a ...
The two most common formations are the 3–4 defense and the 4–3 defense, where the first number refers to the number of defensive linemen, and the second number refers to the number of linebackers (the number of defensive backs can be inferred, since there must be eleven players on the field). Thus, a 3–4 defense consists of three ...
The quarter formations are run from a 3–1–7 or a 4–0–7 in most instances; the New England Patriots have used an 0–4–7 in some instances with no down linemen. Half dollar defenses are almost always run from a 3–0–8 formation. The eighth defensive back in this case is usually a wide receiver from the offense. The wide receiver can ...
3–4–3 formation. Using a 3–4–3, the midfielders are expected to split their time between attacking and defending. Having only three dedicated defenders means that if the opposing team breaks through the midfield, they will have a greater chance to score than with a more conventional defensive configuration, such as 4–5–1 or 4–4–2.
As the game has developed further, some tactical formations (for example, 4–3–3) have used central midfielders deployed in a wider position to provide width, more defensive protection along the flanks and to help compress play in the opponent's half. They will still support attacking play and sometimes be expected to act as a semi-winger. [51]
The 4-3 defense has 2 tackles and 2 ends; the 3-4 defense has 2 ends and 1 tackle, who is sometimes called a nose tackle (NT) to indicate the 3-4. Tackles line up inside and rely on power to stop the run, while ends line up outside and are faster and more athletic to allow them to pursue the quarterback.
Dimensionless numbers (or characteristic numbers) have an important role in analyzing the behavior of fluids and their flow as well as in other transport phenomena. [1] They include the Reynolds and the Mach numbers, which describe as ratios the relative magnitude of fluid and physical system characteristics, such as density, viscosity, speed of sound, and flow speed.