Chemical substance

A chemical substance is a form of matter that has constant chemical composition and characteristic properties. It cannot be separated into components by physical separation methods, i.e., without breaking chemical bonds. Chemical substances can be chemical elements, chemical compounds, ions or alloys.

Chemical substances are often called 'pure' to set them apart from mixtures. A common example of a chemical substance is pure water; it has the same properties and the same ratio of hydrogen to oxygen whether it is isolated from a river or made in a laboratory. Other chemical substances commonly encountered in pure form are diamond (carbon), gold, table salt (sodium chloride) and refined sugar (sucrose). However, in practice, no substance is entirely pure, and chemical purity is specified according to the intended use of the chemical.

Chemical substances exist as solids, liquids, gases or plasma, and may change between these phases of matter with changes in temperature or pressure. Chemical reactions convert one chemical substance into another.

Chemistry

Chemistry is a branch of physical science that studies the composition, structure, properties and change of matter. Chemistry includes topics such as the properties of individual atoms, how atoms form chemical bonds to create chemical compounds, the interactions of substances through intermolecular forces that give matter its general properties, and the interactions between substances through chemical reactions to form different substances.

Chemistry is sometimes called the central science because it bridges other natural sciences, including physics, geology and biology. For the differences between chemistry and physics see Comparison of chemistry and physics.

Scholars disagree about the etymology of the word chemistry. The history of chemistry can be traced to alchemy, which had been practiced for several millennia in various parts of the world.

Etymology

The word chemistry comes from the word alchemy which was an earlier set of practices that encompassed elements of chemistry, metallurgy, philosophy, astrology, astronomy, mysticism and medicine. It is often seen as linked to the quest to turn lead or another common starting material into gold. Alchemy, which was practiced around 330, is the study of the composition of waters, movement, growth, embodying, disembodying, drawing the spirits from bodies and bonding the spirits within bodies (Zosimos). An alchemist was called a 'chemist' in popular speech, and later the suffix "-ry" was added to this to describe the art of the chemist as "chemistry".

Drug

A drug is any substance other than food, that when inhaled, injected, smoked, consumed, absorbed via a patch on the skin or dissolved under the tongue causes a physiological change in the body.

In pharmacology, a pharmaceutical drug or medicine, is a chemical substance used to treat, cure, prevent, diagnose a disease or promote well-being. Traditionally drugs were obtained through extraction from medicinal plants, but more recently also by organic synthesis. Pharmaceutical drugs may be used for a limited duration, or on a regular basis for chronic disorders.

Pharmaceutical drugs are often classified into drug classes—groups of related drugs that have similar chemical structures, the same mechanism of action (binding to the same biological target), a related mode of action, and that are used to treat the same disease. The Anatomical Therapeutic Chemical Classification System (ATC), the most widely used drug classification system, assigns drugs a unique ATC code, which is an alphanumeric code that assigns it to specific drug classes within the ATC system. Another major classification system is the Biopharmaceutics Classification System. This classifies drugs according to their solubility and permeability or absorption properties.

Software

Computer software also called a program or simply software is any set of instructions that directs a computer to perform specific tasks or operations. Computer software consists of computer programs, libraries and related non-executable data (such as online documentation or digital media). Computer software is non-tangible, contrasted with computer hardware, which is the physical component of computers. Computer hardware and software require each other and neither can be realistically used without the other.

At the lowest level, executable code consists of machine language instructions specific to an individual processor—typically a central processing unit (CPU). A machine language consists of groups of binary values signifying processor instructions that change the state of the computer from its preceding state. For example, an instruction may change the value stored in a particular storage location in the computer—an effect that is not directly observable to the user. An instruction may also (indirectly) cause something to appear on a display of the computer system—a state change which should be visible to the user. The processor carries out the instructions in the order they are provided, unless it is instructed to "jump" to a different instruction, or interrupted.

Software (novel)

Software is a 1982 cyberpunk science fiction novel written by Rudy Rucker. It won the first Philip K. Dick Award in 1983. The novel is the first book in Rucker's Ware Tetralogy, and was followed by a sequel, Wetware, in 1988.

Plot summary

Software introduces Cobb Anderson as a retired computer scientist who was once tried for treason for figuring out how to give robots artificial intelligence and free will, creating the race of boppers. By 2020, they have created a complex society on the Moon, where the boppers developed because they depend on super-cooled superconducting circuits. In that year, Anderson is a pheezer — a freaky geezer, Rucker's depiction of elderly Baby Boomers — living in poverty in Florida and terrified because he lacks the money to buy a new artificial heart to replace his failing, secondhand one.

As the story begins, Anderson is approached by a robot duplicate of himself who invites him to the Moon to be given immortality. Meanwhile, the series' other main character, Sta-Hi Mooney the 1st — born Stanley Hilary Mooney Jr. — a 25-year-old cab driver and "brainsurfer", is kidnapped by a gang of serial killers known as the Little Kidders who almost eat his brain. When Anderson and Mooney travel to the Moon together at the boppers' expense, they find that these events are closely related: the "immortality" given to Anderson turns out to be having his mind transferred into software via the same brain-destroying technique used by the Little Kidders.

Software (development cooperation)

See also

Further reading