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Glass

Glass is a non-crystalline amorphous solid that is often transparent and has widespread practical, technological, and decorative usage in, for example, window panes, tableware, and optoelectronics. Scientifically, the term "glass" is often defined in a broader sense, encompassing every solid that possesses a non-crystalline (that is, amorphous) structure at the atomic scale and that exhibits a glass transition when heated towards the liquid state.

The most familiar, and historically the oldest, types of glass are based on the chemical compound silica (silicon dioxide), the primary constituent of sand. The term glass, in popular usage, is often used to refer only to this type of material, which is familiar from use as window glass and in glass bottles. Of the many silica-based glasses that exist, ordinary glazing and container glass is formed from a specific type called soda-lime glass, composed of approximately 75% silicon dioxide (SiO₂), sodium oxide (Na₂O) from sodium carbonate (Na₂CO₃), calcium oxide, also called lime (CaO), and several minor additives. A very clear and durable quartz glass can be made from pure silica which is very tough and resistant to thermal shock, being able to survive immersion in water while red hot. However, quartz must be heated to well over 3,000 °F (1,650 °C) (white hot) before it begins to melt, and it has a very narrow glass transition, making glassblowing and hot working difficult. In glasses like soda lime, the other compounds are used to lower the melting temperature and improve the temperature workability of the product at a cost in the toughness, thermal stability, and optical transmittance.

Dog

The domestic dog (Canis lupus familiaris or Canis familiaris) is a domesticated canid which has been selectively bred for millennia for various behaviors, sensory capabilities, and physical attributes.

Although initially thought to have originated as a manmade variant of an extant canid species (variously supposed as being the dhole,golden jackal, or gray wolf), extensive genetic studies undertaken during the 2010s indicate that dogs diverged from an extinct wolf-like canid in Eurasia 40,000 years ago. Being the oldest domesticated animal, their long association with people has allowed dogs to be uniquely attuned to human behavior, as well as thrive on a starch-rich diet which would be inadequate for other canid species.

Dogs perform many roles for people, such as hunting, herding, pulling loads, protection, assisting police and military, companionship, and, more recently, aiding handicapped individuals. This impact on human society has given them the nickname "man's best friend" in the Western world. In some cultures, however, dogs are a source of meat.