Domain Name System
The addressing system on the Internet generates IP addresses, which are usually indicated by numbers such as 128.201.86.290. Since such numbers are difficult to remember, a user-friendly system has been created known as the Domain Name System (DNS). This system provides the mnemonic equivalent of a numeric IP address and further ensures that every site on the Internet has a unique address. For example, an Internet address might appear as crito.uci.edu. If this address is accessed through a Web browser, it is referred to as a URL (Uniform Resource Locator), and the full URL will appear as http://www.crito.uci.edu.
The Domain Name System divides the Internet into a series of component networks called domains that enable e-mail (and other files) to be sent across the entire Internet. Each site attached to the Internet belongs to one of the domains. Universities, for example, belong to the “edu” domain. Other domains are gov (government), com (commercial organizations), mil (military), net (network service providers), and org (nonprofit organizations).
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A region in a solid within which elementary atomic or molecular magnetic or electric moments are uniformly aligned.
Ferromagnetic domains are regions of parallel-aligned magnetic moments. Each domain may be thought of as a tiny magnet pointing in a certain direction. The relatively thin boundary region between two domains is called a domain wall. Within a wall the magnetic moments rotate from the direction of one of the domains to the direction in the adjacent domain.
A ferromagnet generally consists of a large number of domains. For example, a sample of pure iron at room temperature contains many domains whose directions are distributed randomly, making the sample appear to be unmagnetized as a whole. Iron is called magnetically soft since the domain walls move easily if a magnetic field is applied. In a magnetically hard or permanent magnet material a net macroscopic magnetization is introduced by exposure to a large external magnetic field, but thereafter domain walls are difficult to either form or move, and the material retains its overall magnetization.
Antiferromagnetic domains are regions of antiparallel-aligned magnetic moments. They are associated with the presence of grain boundaries, twinning, and other crystal inhomogeneities.
Ferroelectric domains are electrical analogs of ferromagnetic domains. See also Antiferromagnetism; Ferroelectrics; Ferromagnetism; Magnetic materials; Magnetization; Twinning (crystallography).
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