Central heatingA central heating system provides warmth to a number of spaces within a building from one main source of heat. It is a component of heating, ventilation, and air conditioning (short: HVAC) systems, which can both cool and warm interior spaces. A central heating system has a furnace that converts fuel or electricity to heat. The heat is circulated through the building either by fans forcing heated air through ducts, circulation of low-pressure steam to radiators in each heated room, or pumps that circulate hot water through room radiators.
Star formationStar formation is the process by which dense regions within molecular clouds in interstellar space, sometimes referred to as "stellar nurseries" or "star-forming regions", collapse and form stars. As a branch of astronomy, star formation includes the study of the interstellar medium (ISM) and giant molecular clouds (GMC) as precursors to the star formation process, and the study of protostars and young stellar objects as its immediate products. It is closely related to planet formation, another branch of astronomy.
Inversion (meteorology)In meteorology, an inversion is a deviation from the normal change of an atmospheric property with altitude. It almost always refers to an inversion of the air temperature lapse rate, in which case it is called a temperature inversion. Normally, air temperature decreases with an increase in altitude, but during an inversion warmer air is held above cooler air. An inversion traps air pollution, such as smog, close to the ground. An inversion can also suppress convection by acting as a "cap".
Lift (soaring)Lift is a meteorological phenomenon used as an energy source by soaring aircraft and soaring birds. The most common human application of lift is in sport and recreation. The three air sports that use soaring flight are: gliding, hang gliding and paragliding. Energy can be gained by using rising air from four sources: Thermals (where air rises due to heat), Ridge lift, where air is forced upwards by a slope, Wave lift, where a mountain produces a standing wave, Convergence, where two air masses meet In dynamic soaring it is also possible to gain energy, though this uses differences in wind speeds rather than rising air.
Aegean civilizationAegean civilization is a general term for the Bronze Age civilizations of Greece around the Aegean Sea. There are three distinct but communicating and interacting geographic regions covered by this term: Crete, the Cyclades and the Greek mainland. Crete is associated with the Minoan civilization from the Early Bronze Age. The Cycladic civilization converges with the mainland during the Early Helladic ("Minyan") period and with Crete in the Middle Minoan period.
ThermophoresisThermophoresis (also thermomigration, thermodiffusion, the Soret effect, or the Ludwig–Soret effect) is a phenomenon observed in mixtures of mobile particles where the different particle types exhibit different responses to the force of a temperature gradient. This phenomenon tends to move light molecules to hot regions and heavy molecules to cold regions. The term thermophoresis most often applies to aerosol mixtures whose mean free path is comparable to its characteristic length scale , but may also commonly refer to the phenomenon in all phases of matter.
Transitive reductionIn the mathematical field of graph theory, a transitive reduction of a directed graph D is another directed graph with the same vertices and as few edges as possible, such that for all pairs of vertices v, w a (directed) path from v to w in D exists if and only if such a path exists in the reduction. Transitive reductions were introduced by , who provided tight bounds on the computational complexity of constructing them. More technically, the reduction is a directed graph that has the same reachability relation as D.
New Year's DayIn the Gregorian calendar, New Year's Day is the first day of the year; 1 January. Whilst most solar calendars (like the Gregorian and Julian) begin the year regularly at or near the northern winter solstice, cultures that observe a lunisolar or lunar calendar celebrate their Lunar New Year (such as the Chinese New Year and the Islamic New Year) at less fixed points relative to the solar year. In pre-Christian Rome under the Julian calendar, the day was dedicated to Janus, god of gateways and beginnings, for whom January is also named.
ReachabilityIn graph theory, reachability refers to the ability to get from one vertex to another within a graph. A vertex can reach a vertex (and is reachable from ) if there exists a sequence of adjacent vertices (i.e. a walk) which starts with and ends with . In an undirected graph, reachability between all pairs of vertices can be determined by identifying the connected components of the graph. Any pair of vertices in such a graph can reach each other if and only if they belong to the same connected component; therefore, in such a graph, reachability is symmetric ( reaches iff reaches ).
Adriatic SeaThe Adriatic Sea (ˌeɪdriˈætᵻk) is a body of water separating the Italian Peninsula from the Balkan Peninsula. The Adriatic is the northernmost arm of the Mediterranean Sea, extending from the Strait of Otranto (where it connects to the Ionian Sea) to the northwest and the Po Valley. The countries with coasts on the Adriatic are Albania, Bosnia and Herzegovina, Croatia, Italy, Montenegro, and Slovenia. The Adriatic contains more than 1,300 islands, mostly located along the Croatian part of its eastern coast.
