cycle

Date: 1300-1400; Language: French; Origin: Late Latin cyclus, from Greek kyklos 'circle, wheel, cycle'

Cycle or cyclic may refer to:

• Cyclic history, a theory of history
• Cyclical theory, a theory of American political history associated with Arthur Schlesinger, Sr.
• Social cycle, various cycles in social sciences
  • Business cycle, the downward and upward movement of gross domestic product (GDP) around its ostensible, long-term growth trend
• Cycle (music), a set of musical pieces that belong together
  • Cyclic form, a technique of construction involving multiple sections or movements
  • Interval cycle, a collection of pitch classes generated from a sequence of the same interval class
  • Song cycle, individually complete songs designed to be performed in a sequence as a unit
• Menstrual cycle
• Instruction cycle, the time period during which a computer processes a machine language instruction
• Reference cycle, where a software object refers directly or indirectly to itself
• Cycle (geometry) or turn (also: revolution), a unit of plane angle equivalent to 360 degrees
  • Cycles per second, a unit of frequency, the modern equivalent being hertz
• Cycle (graph theory), a nontrivial path in a graph from a node to itself
  • Cycle graph, a graph that is itself a cycle
  • Cycle matroid, a matroid derived from the cycle structure of a graph
• Cycle (sequence), a sequence with repeating values
  • Cycle detection, the algorithmic problem of detecting eventual repetitions in sequences generated by iterated functions
• Cycle, a set equipped with a cyclic order
  • Necklace (combinatorics), equivalence classes of cyclically ordered sequences of symbols modulo certain symmetries
• Charge cycle, charging and discharging a rechargeable battery
• Thermodynamic cycle, a sequence of processes that involve transfer of heat and work into and out of a system
• Cyclic, a primary flight control for helicopters
• Cyclic compound
• Bicycle, Motorcycle, Tricycle, Unicycle

Social cycle theories are among the earliest social theories in sociology. Unlike the theory of social evolutionism, which views the evolution of society and human history as progressing in some new, unique direction(s), sociological cycle theory argues that events and stages of society and history generally repeat themselves in cycles. Such a theory does not necessarily imply that there cannot be any social progress.

The business cycle, also known as the economic cycle or trade cycle, are the fluctuations of gross domestic product (GDP) around its long-term growth trend. The length of a business cycle is the period of time containing a single boom and contraction in sequence. These fluctuations typically involve shifts over time between periods of relatively rapid economic growth (expansions or booms) and periods of relative stagnation or decline (contractions or recessions).

Business cycles are usually measured by considering the growth rate of real gross domestic product. Despite the often-applied term cycles, these fluctuations in economic activity do not exhibit uniform or predictable periodicity. The common or popular usage boom-and-bust cycle refers to fluctuations in which the expansion is rapid and the contraction severe.

A typical helicopter has three flight control inputs—the cyclic stick, the collective lever, and the anti-torque pedals. Depending on the complexity of the helicopter, the cyclic and collective may be linked together by a mixing unit, a mechanical or hydraulic device that combines the inputs from both and then sends along the "mixed" input to the control surfaces to achieve the desired result. The manual throttle may also be considered a flight control because it is needed to maintain rotor speed on smaller helicopters without governors. The governors also help the pilot control the collective pitch on the helicopter's main rotors, to keep a stable, more accurate flight.

The cyclic is used to control the main rotor in order to change the helicopter's direction of movement. In a hover, the cyclic controls the movement of the helicopter forward, back, and laterally. During forward flight, the cyclic control inputs cause flight path changes similar to fixed-wing aircraft flight; left or right inputs cause the helicopter to roll into a turn in the desired direction, and forward and back inputs change the pitch attitude of the helicopter resulting in altitude changes (climbing or descending flight).

A cyclic compound (ring compound) is a term for a compound in the field of chemistry in which one or more series of atoms in the compound is connected to form a ring. Rings may vary in size from three to many atoms, and include examples where all the atoms are carbon (i.e., are carbocycles), none of the atoms are carbon (inorganic cyclic compounds), or where both carbon and non-carbon atoms are present (heterocyclic compounds).

In combinatorics, a branch of mathematics, a matroid /ˈmeitrɔid/ is a structure that abstracts and generalizes the notion of linear independence in vector spaces. There are many equivalent ways to define a matroid axiomatically, the most significant being in terms of: independent sets; bases or circuits; rank functions; closure operators; and closed sets or flats. In the language of partially ordered sets, a finite matroid is equivalent to a geometric lattice.

Matroid theory borrows extensively from the terminology of linear algebra and graph theory, largely because it is the abstraction of various notions of central importance in these fields. Matroids have found applications in geometry, topology, combinatorial optimization, network theory and coding theory. →matrix, asteroid, steroid, thyroid, android, animal

六级/考研单词: upward, gross, construct, multiple, interval, instruct, compute, hardware, geometry, revolve, equivalent, graph, derive, detect, equip, necklace, symmetry, discharge, helicopter, compound, sociology, evolve, implicit, fluctuate, rapid, stagnate, recession, despite, exhibit, usage, collective, lever, pedal, desire, manual, hover, altitude, descend, atom, carbon, mathematics, abstract, rank, finite, algebra, cholesterol