Calcium sulfate an unusual property: when mixed with water at normal (ambient) temperatures, it quickly reverts chemically to the preferred dihydrate form, while physically "setting" to form a rigid and relatively strong gypsum crystal lattice: This reaction is exothermic and is responsible for the ease with which gypsum can be cast into various shapes including sheets (for drywall), sticks (for blackboard chalk), and molds (to immobilize broken bones, or for metal casting). Mixed with polymers, it has been used as a bone repair cement. Small amounts of calcined gypsum are added to earth to create strong structures directly from cast earth, an
Blackboard Learn LLC and were developing a software product that would power online education and be scalable for wider institutional application. At the same time, Matthew Pittinsky and Michael Chasen formed Blackboard LLC and were contracted to help lead the formation of the Educause IMS standards group for online education technology. The two groups merged to form Blackboard Inc., which then developed the Blackboard Learning System. In 2015 the company announced a major upgrade to the user experience, called Ultra. According to company statements, Ultra is to be an optional user interface sitting on top of the existing Learn 9.1 architecture. In