Quasigroup

In mathematics, especially in abstract algebra, a quasigroup is an algebraic structure resembling a group in the sense that "division" is always possible. Quasigroups differ from groups mainly in that they need not be associative.

A quasigroup with an identity element is called a loop.

Definitions

There are at least two equivalent formal definitions of quasigroup. One defines a quasigroup as a set with one binary operation, and the other, from universal algebra, defines a quasigroup as having three primitive operations. We begin with the first definition.

A quasigroup (Q, ∗) is a set, Q, with a binary operation, ∗, (that is, a magma), obeying the Latin square property. This states that, for each a and b in Q, there exist unique elements x and y in Q such that both

hold. (In other words: Each element of the set occurs exactly once in each row and exactly once in each column of the quasigroup's multiplication table, or Cayley table. This property ensures that the Cayley table of a finite quasigroup is a Latin square.)

Loop (knot)

In reference to knots, loop may refer to:

References

Turn (biochemistry)

A turn is an element of secondary structure in proteins where the polypeptide chain reverses its overall direction. For beta turns go to Beta turn.

Definition

According to one definition, a turn is a structural motif where the C^α atoms of two residues separated by few (usually 1 to 5) peptide bonds are close (< 7 Å), while the residues do not form a secondary structure element such as an alpha helix or beta sheet with regularly repeating backbone dihedral angles. Although the proximity of the terminal C^α atoms usually correlates with formation of a hydrogen bond between the corresponding residues, a hydrogen bond is not a requirement in this turn definition. That said, in many cases the H-bonding and C^α-distance definitions are equivalent.

Types of turns

Turns are classified according to the separation between the two end residues:

In an α-turn the end residues are separated by four peptide bonds ().

In a β-turn (the most common form), by three bonds ().

In a γ-turn, by two bonds ().

Iguana (disambiguation)

Iguana may refer to:

See also

RG-34

The RG-34 (formerly denoted as Iguana FV4) is a South African MRAP. Specially designed to be mine-resistant, it has been produced in multiple variants, equipped for troop or cargo transport, command, and fire support.

Development

Development of the Iguana was initiated under contract by Industrial & Automotive South Africa (IADSA) for a Belgian firm, Sabiex; the first prototype being completed in early 2002. By June 2009, BAE Land Systems had obtained necessary rights to develop and manufacture the vehicle. The RG-34 was initially displayed with a potent weapons system for an MRAP, in the form of an overlarge turret fitted with a 90mm (3.5 in.) gun. This has since been replaced by a more ergonomic tactical remote turret (TRT) boasting a 25mm M242 autocannon and a co-axial 7.62mm machine gun.

Design

RG-34's cross-country performance is attributed to its unique suspension, a multi-link hydro-pneumatic structure mounted on a very rigid chassis. This affords optimal performance on road surfaces, a superior turning radius, and clearance over rugged terrain. When deployed in the reconnaissance role long-range fuel tanks give the vehicle an extended operating range of 1,000 kilometres.