Railway trackA railway track (British English and UIC terminology) or railroad track (American English), also known as a train track or permanent way, is the structure on a railway or railroad consisting of the , fasteners, railroad ties (sleepers, British English) and ballast (or slab track), plus the underlying subgrade. It enables trains to move by providing a dependable surface for their wheels to roll upon. Early tracks were constructed with wooden or cast iron rails, and wooden or stone sleepers; since the 1870s, rails have almost universally been made from steel.
Track geometryTrack geometry is concerned with the properties and relations of points, lines, curves, and surfaces in the three-dimensional positioning of railroad track. The term is also applied to measurements used in design, construction and maintenance of track. Track geometry involves standards, speed limits and other regulations in the areas of track gauge, alignment, elevation, curvature and track surface. Standards are usually separately expressed for horizontal and vertical layouts although track geometry is three-dimensional.
Continuous trackContinuous track is a system of vehicle propulsion used in tracked vehicles, running on a continuous band of treads or track plates driven by two or more wheels. The large surface area of the tracks distributes the weight of the vehicle better than steel or rubber tyres on an equivalent vehicle, enabling continuous tracked vehicles to traverse soft ground with less likelihood of becoming stuck due to sinking. Modern continuous tracks can be made with soft belts of synthetic rubber, reinforced with steel wires, in the case of lighter agricultural machinery.
Half-trackA half-track is a civilian or military vehicle with regular wheels at the front for steering and continuous tracks at the back to propel the vehicle and carry most of the load. The purpose of this combination is to produce a vehicle with the cross-country capabilities of a tank and the handling of a wheeled vehicle.
Tramway trackTramway track is used on tramways or light rail operations. Grooved rails (or ) are often used to provide a protective flangeway in the trackwork in city streets. Like standard rail tracks, tram tracks consist of two parallel steel rails. Tram rails can be placed on several surfaces, such as with on sleepers like railway tracks, or with grooved rails on concrete sleepers into street surfaces (pavement) for street running. Tram rails in street have the disadvantage that they pose a risk to cyclists.
Color temperatureColor temperature is a parameter describing the color of a visible light source by comparing it to the color of light emitted by an idealized opaque, non-reflective body. The temperature of the ideal emitter that matches the color most closely is defined as the color temperature of the original visible light source. Color temperature is usually measured in kelvins. The color temperature scale describes only the color of light emitted by a light source, which may actually be at a different (and often much lower) temperature.
Track gaugeIn rail transport, track gauge (in American English, alternatively track gage) is the distance between the two rails of a railway track. All vehicles on a rail network must have wheelsets that are compatible with the track gauge. Since many different track gauges exist worldwide, gauge differences often present a barrier to wider operation on railway networks. The term derives from the metal bar, or gauge, that is used to ensure the distance between the rails is correct.
Light pollutionLight pollution is the presence of unwanted, inappropriate, or excessive artificial lighting. In a descriptive sense, the term light pollution refers to the effects of any poorly implemented lighting, during the day or night. Light pollution can be understood not only as a phenomenon resulting from a specific source or kind of pollution, but also as a contributor to the wider, collective impact of various sources of pollution. Although this type of pollution can exist throughout the day, its effects are magnified during the night with the contrast of darkness.
ImageAn image is a visual representation of something. An image can be a two-dimensional (2D) representation, such as a drawing, painting, or photograph, or a three-dimensional (3D) object, such as a carving or sculpture. An image may be displayed through other media, including projection on a surface, activation of electronic signals, or digital displays. Two-dimensional images can be still or animated. Still images can usually be reproduced through mechanical means, such as photography, printmaking or photocopying.
Evaluation strategyIn a programming language, an evaluation strategy is a set of rules for evaluating expressions. The term is often used to refer to the more specific notion of a parameter-passing strategy that defines the kind of value that is passed to the function for each parameter (the binding strategy) and whether to evaluate the parameters of a function call, and if so in what order (the evaluation order). The notion of reduction strategy is distinct, although some authors conflate the two terms and the definition of each term is not widely agreed upon.
