A rectifier is an electrical device that converts alternating current, which periodically reverses direction, to direct current, which flows in only one direction. The process is known since it "straightens" the direction of current. Physically, rectifiers take a number of forms, including vacuum tube diodes, wet chemical cells, mercury-arc valves, stacks of copper and selenium oxide plates, semiconductor diodes, silicon-controlled rectifiers and other silicon-based semiconductor switches. Synchronous electromechanical switches and motors have been used. Early radio receivers, called crystal radios, used a "cat's whisker" of fine wire pressing on a crystal of galena to serve as a point-contact rectifier or "crystal detector". Rectifiers have many uses, but are found serving as components of DC power supplies and high-voltage direct current power transmission systems. Rectification may serve in roles other than to generate direct current for use as a source of power; as noted, detectors of radio signals serve as rectifiers.

In gas heating systems flame rectification is used to detect presence of a flame. Depending on the type of alternating current supply and the arrangement of the rectifier circuit, the output voltage may require additional smoothing to produce a uniform steady voltage. Many applications of rectifiers, such as power supplies for radio and computer equipment, require a steady constant DC voltage. In these applications the output of the rectifier is smoothed by an electronic filter, which may be a capacitor, choke, or set of capacitors and resistors followed by a voltage regulator to produce a steady voltage. More complex circuitry that performs the opposite function, converting DC to AC, is called an inverter. Before the development of silicon semiconductor rectifiers, vacuum tube thermionic diodes and copper oxide- or selenium-based metal rectifier stacks were used. With the introduction of semiconductor electronics, vacuum tube rectifiers became obsolete, except for some enthusiasts of vacuum tube audio equipment.

For power rectification from low to high current, semiconductor diodes of various types are used. Other devices that have control electrodes as well as acting as unidirectional current valves are used where more than simple rectification is required—e.g. Where variable output voltage is needed. High-power rectifiers, such as those used in high-voltage direct current power transmission, employ silicon semiconductor devices of various types; these are thyristors or other controlled switching solid-state switches, which function as diodes to pass current in only one direction. Rectifier circuits may be multi-phase. Most low power rectifiers for domestic equipment are single-phase, but three-phase rectification is important for industrial applications and for the transmission of energy as DC. In half-wave rectification of a single-phase supply, either the positive or negative half of the AC wave is passed, while the other half is blocked. Mathematically, it is a step function: passing positive corresponds to the ramp function being the identity on positive inputs, blocking negative corresponds to being zero on negative inputs.

Because only one half of the input waveform reaches the output, mean voltage is lower. Half-wave rectification requires a single diode in a single-phase supply, or three in a three-phase supply. Rectifiers yield a pulsating direct current; the no-load output DC voltage of an ideal half-wave rectifier for a sinusoidal input voltage is: V r m s = V p e a k 2 V d c = V p e a k π where: Vdc, Vav – the DC or average output voltage, the peak value of the phase input voltages, the root mean square value of output voltage. A full-wave rectifier converts the whole of the input waveform to one of constant polarity at its output. Mathematically, this corresponds to the absolute value function. Full-wave rectification converts both polarities of the input waveform to pulsating DC, yields a higher average output voltage. Two diodes and a center tapped transformer, or four diodes in a bridge configuration and any AC source, are needed. Single semiconductor diodes, double diodes with common cathode or common anode, four-diode bridges, are manufactured as single components.

For single-phase AC, if the transformer is center-tapped two diodes back-to-back can form a full-wave rectifier. Twice as many turns are required on the transformer secondary to obtain the same output voltage than for a bridge rectifier, but the power rating is unchanged; the average and RMS no-load output voltages of an ideal single-phase full-wave rectifier are: V d

Pavillon de l'eau

The Pavillon de l'eau is a museum devoted to water belonging to the City of Paris and managed by Eau de Paris, the municipal agency in charge of production and distribution of water in Paris. The Pavillon de l’eau offers a permanent exhibition about the water supply history of the city, temporary exhibitions, children's activities and thematic meetings. In 1828, on the ancient road to Versailles, a steam pump was installed in order to pump water from the Seine to supply the municipalities of Auteuil and Passy. By the end of the nineteenth century, the old steam pumps were obsolete; the City Council of Paris voted the construction of a new pumping station to replace the previous one with newer technology. The station consisted of two buildings, the engine room and boiler room, both characterized by a brick structure and large roofs topped by skylights to allow sufficient ventilation and lighting. However, the new pumping station became outdated regarding its coal consumption. So at the end of the First World War a new project was launched to attach a new pump to the previous one, referred to as station B, electrically powered.

In 1955, station A was dismantled and the engine room became used as a garage, as an office for administrative services until 2007, when the Pavillon de l'eau was inaugurated. Alimenter Paris en eau is an exhibition about the water supply of Paris and its history from Roman aqueducts to nowadays. Paris grew up with water. Since the beginning of our times, when Paris was still called Lutetia, the city has experienced four different periods of production and distribution of water; the Roman age, the Middle Ages, the Modern era and the nineteenth century Industrial Revolution. Pavillon de l'eau Eau de Paris official website Paris official website

Upstream (petroleum industry)

The oil and gas industry is divided into three major sectors: upstream and downstream. The upstream sector includes searching for potential underground or underwater crude oil and natural gas fields, drilling exploratory wells, subsequently drilling and operating the wells that recover and bring the crude oil or raw natural gas to the surface. Upstream Industry has traditionally experienced the highest number of Mergers and Divestitures. M&A activity for upstream oil and gas deals in 2012 totaled $254 billion in 679 deals. A large chunk of this M&A, 33% in 2012, was driven by the unconventional/shale boom in the US followed by the Russian Federation and Canada; the aggregate value of Upstream E&P assets available for sale reached a record-high of $135 billion in Q3-2013. The value of Deals in Play doubled from $46 billion in 2009 to $90 billion in 2010. With ongoing M&A activity the level remained the same reaching $85 billion in Dec-2012. However, the first half of 2013 saw $48 billion of net new assets coming on the market.

Remarkably, the total value of Deals in Play in Q3-2013 nearly tripled over 2009 at $46 billion, in less than four years. This categorization comes from value chain concepts before formal development Value Chain Management. Integrated Oil & Gas Company:A company that has upstream as well as downstream operations. Examples include Saudi Aramco, ExxonMobil, BP, Royal Dutch Shell, ChevronTexaco. Independent Oil & Gas Company:A company that has either upstream or downstream operations, but not both. Examples include Anadarko Petroleum, Phillips 66, ConocoPhillips, Murphy Oil. Oil Service Company:A company that provides products and/or services to the oil and gas industry. A combination of labor, and/or other support services. Examples include Schlumberger, Baker Hughes, a GE Company, Halliburton. Oil Equipment Manufacturer:A company that specializes in the sale and distribution of equipment to the oil and gas industry. SecurityMany major security companies take part in securing the industry. Other:Any other oil and gas related business not defined above such as software companies providing necessary IT services for easy execution in the oilfield.

ISO 14224 defines "Upstream" in its definition section as: 3.98 upstream business category of the petroleum industry involving exploration and production. Example: Offshore oil/gas production facilities, Drilling rigs, intervention vessel. List of oil exploration and production companies Upstream innovations