ARC (file format)

ARC is a lossless data compression and archival format by System Enhancement Associates (SEA). It was very popular during the early days of networked dial-up BBS. The file format and the program were both called ARC. The ARC program made obsolete the previous use of a combination of the SQ program to compress files and the LU program to create .LBR archives, by combining both compression and archiving functions into a single program. Unlike ZIP, ARC is incapable of compressing entire directory trees. The format was subject to controversy in the 1980s—an important event in debates over what would later be known as open formats.

The .arc file extension is often used for several file archive-like file types. For example, the Internet Archive uses its own ARC format to store multiple web resources into a single file. The FreeArc archiver also uses .arc extension, but uses a completely different file format.

Nintendo uses an unrelated 'ARC' format for resources, such as MIDI, voice samples, or text, in GameCube and Wii games. Several unofficial extractors exist for this type of ARC file.

Arc (projective geometry)

A (simple) arc in finite projective geometry is a set of points which satisfies, in an intuitive way, a feature of curved figures in continuous geometries. Loosely speaking, they are sets of points that are far from "line-like" in a plane or far from "plane-like" in a three-dimensional space. In this finite setting it is typical to include the number of points in the set in the name, so these simple arcs are called k-arcs. An important generalization of the k-arc concept, also referred to as arcs in the literature, are the (k, d)-arcs.

k-arcs in a projective plane

In a finite projective plane π (not necessarily Desarguesian) a set A of k (k ≥ 3) points such that no three points of A are collinear (on a line) is called a k - arc. If the plane π has order q then k ≤ q + 2, however the maximum value of k can only be achieved if q is even. In a plane of order q, a (q + 1)-arc is called an oval and, if q is even, a (q + 2)-arc is called a hyperoval.

Every conic in the Desarguesian projective plane PG(2,q), i.e., the set of zeros of an irreducible homogeneous quadratic equation, is an oval. A celebrated result of Beniamino Segre states that when q is odd, every (q + 1)-arc in PG(2,q) is a conic. This is one of the pioneering results in finite geometry.

Directed graph

In mathematics, and more specifically in graph theory, a directed graph (or digraph) is a graph, or set of vertices connected by edges, where the edges have a direction associated with them. In formal terms, a directed graph is an ordered pair G = (V, A) (sometimes G = (V, E)) where

It differs from an ordinary or undirected graph, in that the latter is defined in terms of unordered pairs of vertices, which are usually called edges, arcs, or lines.

A directed graph is called a simple digraph if it has no multiple arrows (two or more edges that connect the same two vertices in the same direction) and no loops (edges that connect vertices to themselves). A directed graph is called a directed multigraph or multidigraph if it may have multiple arrows (and sometimes loops). In the latter case the arrow set forms a multiset, rather than a set, of ordered pairs of vertices.

Airó

Airó is a Portuguese parish, located in the municipality of Barcelos. The population in 2011 was 913, in an area of 3.02 km².

References

Air (classical element)

Air (also sometimes called Wind) is often seen as a universal power or pure substance. Its fundamental importance to life can be seen in words such as aspire, inspire, perspire and spirit, all derived from the Latin spirare.

Greek and Roman tradition

Air is one of the four classical elements in ancient Greek philosophy and science. According to Plato, it is associated with the octahedron; air is considered to be both hot and wet. The ancient Greeks used two words for air: aer meant the dim lower atmosphere, and aether meant the bright upper atmosphere above the clouds.Plato, for instance writes that "So it is with air: there is the brightest variety which we call aether, the muddiest which we call mist and darkness, and other kinds for which we have no name...." Among the early Greek Pre-Socratic philosophers, Anaximenes (mid-6th century BCE) named air as the arche. A similar belief was attributed by some ancient sources to Diogenes Apolloniates (late 5th century BCE), who also linked air with intelligence and soul (psyche), but other sources claim that his arche was a substance between air and fire.Aristophanes parodied such teachings in his play The Clouds by putting a prayer to air in the mouth of Socrates.

Air (painting)

Air ...is a painting created by Flemish painter Jan van Kessel (1626-1679) and was painted around the year 1647. It is a part of the permanent collection at the Flint Institute of Arts.

Description

The four elements - earth, air, fire and water - were popular subjects with 17th century painters. In this painting, air is represented by a wide variety of creatures of flight, mythological figures and atmospheric conditions. A multitude of birds, including peacocks, turkeys, parrots, owls and an ostrich are shown in the painting. Several bats also appear in the painting, including one in the upper right that devours a bird while in flight. In the center of the painting, Apollo drives his chariot across the sky. Beneath him, Urania, the Muse of Astronomy, sits on a cloud, and in her left hand she holds an armillary sphere. Another of her attributes, the compass, appears on the ground next to her along with an astrolabe, a quadrant, and a cross staff, which are all instruments used for measuring the position of the planets and stars. All of this takes place in a landscape characterized by a dark, stormy sky on the left, complete with a bolt of lightning. On the right, the sky brightens over a vast expanse of trees and mountains.