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Protein folding problem: Is it possible to predict the secondary, tertiary and quaternary structure of a polypeptide sequence based solely on the sequence and environmental information? Inverse protein-folding problem: Is it possible to design a polypeptide sequence which will adopt a given structure under certain environmental conditions?
The crystallographic restriction theorem in its basic form was based on the observation that the rotational symmetries of a crystal are usually limited to 2-fold, 3-fold, 4-fold, and 6-fold. However, quasicrystals can occur with other diffraction pattern symmetries, such as 5-fold; these were not discovered until 1982 by Dan Shechtman .
Structure of iodine heptafluoride, an example of a molecule with the pentagonal-bipyramidal coordination geometry. In chemistry, a pentagonal bipyramid is a molecular geometry with one atom at the centre with seven ligands at the corners of a pentagonal bipyramid. A perfect pentagonal bipyramid belongs to the molecular point group D 5h.
[18]: 1165 Examples of this include the octacyanomolybdate (Mo(CN) 4− 8) and octafluorozirconate (ZrF 4− 8) anions. [18]: 1165 The nonahydridorhenate ion (ReH 2− 9) in potassium nonahydridorhenate is a rare example of a compound with a steric number of 9, which has a tricapped trigonal prismatic geometry. [13]: 254 [18]
A domain wall is the boundary between two neighboring domains. Thus a domain wall is extended in two spatial dimensions and one time dimension. Important examples are: Domain wall (magnetism), an interface separating magnetic domains; Domain wall (optics), for domain walls in optics; Domain wall (string theory), a theoretical 2-dimensional ...
For example, the following would be considered Dirichlet boundary conditions: In mechanical engineering and civil engineering (beam theory), where one end of a beam is held at a fixed position in space. In heat transfer, where a surface is held at a fixed temperature. In electrostatics, where a node of a circuit is held at a fixed voltage.
An antiphase domain (APD) is a type of planar crystallographic defect in which the atoms within a region of a crystal are configured in the opposite order to those in the perfect lattice system. Throughout the entire APD, atoms sit on the sites typically occupied by atoms of a different species.
More generally, any integral domain satisfying the ascending chain condition on principal ideals (ACCP) is an atomic domain. Although the converse is claimed to hold in Cohn's paper, [1] this is known to be false. [2] The term "atomic" is due to P. M. Cohn, who called an irreducible element of an integral domain an "atom".