A process within a refrigeration system during which the primary fluid (the refrigerant) and the secondary fluid (the absorbent) mix after the refrigerant leaves the evaporator.

The circulation of chemical components through the biosphere from, or to, the lithosphere, atmosphere, and hydrosphere: The biogeochemical cycle includes the exchange of elements, like oxygen, carbon, or nitrogen, in the environment between storage pools, such as the atmosphere, biota, oceans, soils, the earth's crust, and human society.

The length of time the reader can be emitting energy.

Regulations in the European Union say readers can be on only ten percent of the time.

The total life of a given fuel in all of its uses and forms, including its extraction or generation, transportation, combustion, air emission, byproduct removal, and waste transportation and disposal.

An evaluation of environment impact that considers the effects of obtaining a fuel; such as, from mining coal or harvesting wood; as well as, the more commonly assessed impacts of burning the fuels for useful heat or electricity.

In Earth science, the successive stages in the circulation and migration of chemical elements among the lithosphere, hydrosphere, and atmosphere during geological changes: The geochemical cycle is the route or the course that chemical elements travel in the surface and crust of the planet Earth.

Theory was developed or formulated by the American geographer and geomorphologist, William Morris Davis (between 1884 and 1934) who modeled the formation of river-eroded landscapes.

This theory suggests that landscapes go through three stages of development (youth, maturity, and old age) and indicates that the rejuvenation of landscapes arises from tectonic uplift of the land.

In the "youthful stage", under the influence of tectonic uplifts, there appears a mountain relief, which is dissected through erosion (the washing out of rocks by rivers) into deep, narrow valleys and sharp-peaked ridges.

With the dissection by streams, the area would reach maturity and, ultimately, would be reduced to an old-age surface called a peneplain (gently undulating, almost featureless plain), with an elevation near sea level.

The model developed by Davis, though important in historical context, is currently considered only a first approximation.

Developments in the sciences of geology and geomorphology, especially the plate tectonics revolution of the 1960s and 1970s, have confirmed the preliminary nature of the model.

The cyclic transfer of water vapor from the earth's surface via evapotranspiration into the atmosphere, from the atmosphere via precipitation back to earth, and through runoff into bodies of water.

A cycle of variation in the magnetic field used for magnetic induction.

The field is periodically reversed until the magnetic induction is a function only of the strength of the field and of its rate of change.

The main periodic cycle in the sun's activity that occurs over about an eleven-year period.

The period is not constant, varying between about 9.5 and 12.5 years.

During the cycle, changes occur in the sun's internal magnetic field and in its surface disturbance level.

1. A thermodynamic combustion cycle consisting of four processes that are used in mechanical engineering:

• An air-fuel mixture is drawn into the cylinder and compressed.
• Heat transfer is added by the spark ignition of the fuel mixture in the cylinder.
• The gases produced by this combustion expand to move the piston downward for the power stroke.
• The burned gases in the cylinder are expelled.

2. A thermodynamic process for the conversion of heat into work; for example, the sequential suction, compression, ignition, and expulsion in a four-stroke engine.

Named after Nikolaus August Otto (1832-1891), a German engineer and inventor.