Half sphere exposure Half sphere exposure Half Sphere Exposure (HSE) is a protein solvent exposure measure that was first introduced by . Like all solvent exposure measures it measures how buried amino acid residues are in a protein. It is found by counting the number of amino acid neighbors within two half spheres of chosen radius around the amino acid. The calculation of HSE is found by dividing a contact number (CN) sphere in two halves by the plane perpendicular to the Cβ-Cα vector. This simple division of the CN sphere results in two strikingly different measures, HSE-up and HSE-down. HSE-up is defined
N-sphere a central point, where the radius may be any positive real number. Thus, the -sphere would be defined by: In particular: An "n"-sphere embedded in an -dimensional Euclidean space is called a hypersphere. The -sphere of unit radius is called the unit -sphere, denoted , often referred to as "the" -sphere. When embedded as described, an -sphere is the surface or boundary of an -dimensional ball. For , the -spheres are the simply connected -dimensional manifolds of constant, positive curvature. The -spheres admit several other topological descriptions: for example, they can be constructed by gluing two -dimensional Euclidean spaces together,