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The first virtual worlds presented on the Internet were communities and chat rooms, some of which evolved into MUDs and MUSHes. The first MUD, known as MUD1, was released in 1978. The acronym originally stood for Multi-User Dungeon, but later also came to mean Multi-User Dimension and Multi-User Domain.

 

"The Perfect Filler Between Real World Flying" Imagine "Real Life" Flying At The Comfort Of Your Home... With 120+ Aircraft to Master, From the 1903 Wright Flyer to the Latest Military Fighter Jets. 20,000+ Real Airports With changeable Weather and NASA Flight Models. Realistic Worldwide Terrain Based On US Defense Mapping Agency + Lifetime F.R.E.E updates/upgrades. sed On Television Episodes & Professional Flight Schools - The Most Realistic Flight Sim To Date... Meet up online with other ProFlightSimulator Users to fly in formation, put on an air show or just to have fun. You can easily locate other pilots or yourself with Google Map integration - Multiplayer map server shows all the active pilots superimposed on top of a Google map. Enjoy Real-Life Flying >>Today...        Heartwood formation is a genetically programmed process that occurs spontaneously. Some uncertainty exists as to whether the wood dies during heartwood formation, as it can still chemically react to decay organisms, but only once. Heartwood is often visually distinct from the living sapwood, and can be distinguished in a cross-section where the boundary will tend to follow the growth rings. For example, it is sometimes much darker. However, other processes such as decay or insect invasion can also discolor wood, even in woody plants that do not form heartwood, which may lead to confusion. Sapwood (or alburnum) is the younger, outermost wood; in the growing tree it is living wood, and its principal functions are to conduct water from the roots to the leaves and to store up and give back according to the season the reserves prepared in the leaves. However, by the time they become competent to conduct water, all xylem tracheids and vessels have lost their cytoplasm and the cells are therefore functionally dead. All wood in a tree is first formed as sapwood. The more leaves a tree bears and the more vigorous its growth, the larger the volume of sapwood required. Hence trees making rapid growth in the open have thicker sapwood for their size than trees of the same species growing in dense forests. Sometimes trees (of species that do form heartwood) grown in the open may become of considerable size, 30 cm (12 in) or more in diameter, before any heartwood begins to form, for example, in second-growth hickory, or open-grown pines. The term heartwood derives solely from its position and not from any vital importance to the tree. This is evidenced by the fact that a tree can thrive with its heart completely decayed. Some species begin to form heartwood very early in life, so having only a thin layer of live sapwood, while in others the change comes slowly. Thin sapwood is characteristic of such species as chestnut, black locust, mulberry, osage-orange, and sassafras, while in maple, ash, hickory, hackberry, beech, and pine, thick sapwood is the rule. Others never form heartwood. .