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
Sublunary sphere - the idea usually going hand in hand with geocentrism and the concept of a spherical Earth. Avicenna carried forward into the Middle Ages the Aristotelian idea of generation and corruption being limited to the sublunary sphere. Medieval scholastics like Thomas Aquinas - who charted the division between celestial and sublunary spheres in his work "Summa Theologica" - also drew on Cicero and Lucan for an awareness of the great frontier between Nature and Sky, sublunary and aetheric spheres. The result for medieval/Renaissance mentalities was a pervasive awareness of the existence, at the Moon, of what C.S. Lewis called 'this