1.
Prague
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Prague is the capital and largest city of the Czech Republic. It is the 14th largest city in the European Union and it is also the historical capital of Bohemia. Situated in the north-west of the country on the Vltava river, the city has a temperate climate, with warm summers and chilly winters. Prague has been a political, cultural, and economic centre of central Europe with waxing and waning fortunes during its history and it was an important city to the Habsburg Monarchy and its Austro-Hungarian Empire. Prague is home to a number of cultural attractions, many of which survived the violence. Main attractions include the Prague Castle, the Charles Bridge, Old Town Square with the Prague astronomical clock, since 1992, the extensive historic centre of Prague has been included in the UNESCO list of World Heritage Sites. The city has more than ten major museums, along with theatres, galleries, cinemas. An extensive modern public transportation system connects the city, also, it is home to a wide range of public and private schools, including Charles University in Prague, the oldest university in Central Europe. Prague is classified as an Alpha- global city according to GaWC studies, Prague ranked sixth in the Tripadvisor world list of best destinations in 2016. Its rich history makes it a popular tourist destination, and the city more than 6.4 million international visitors annually. Prague is the fifth most visited European city after London, Paris, Istanbul, the region was settled as early as the Paleolithic age. In the last century BC, the Celts were slowly driven away by Germanic tribes, around the area where present-day Prague stands, the 2nd century map of Ptolemaios mentioned a Germanic city called Casurgis. In the following century, the Czech tribes built several fortified settlements in the area, most notably in Levý Hradec, Butovice and in the Šárka valley. The construction of what came to be known as the Prague Castle began near the end of the 9th century, the first masonry under Prague Castle dates from the year 885 at the latest. The other prominent Prague fort, the Přemyslid fort Vyšehrad, was founded in the 10th century, Prague Castle is dominated by the cathedral, which was founded in 1344, but completed in the 20th century. The legendary origins of Prague attribute its foundation to the 8th century Czech duchess and prophetess Libuše and her husband, Přemysl, legend says that Libuše came out on a rocky cliff high above the Vltava and prophesied, I see a great city whose glory will touch the stars. She ordered a castle and a town called Praha to be built on the site, a 17th century Jewish chronicler David Solomon Ganz, citing Cyriacus Spangenberg, claimed that the city was founded as Boihaem in c.1306 BC by an ancient king, Boyya. The region became the seat of the dukes, and later kings of Bohemia, under Roman Emperor Otto II the area became a bishopric in 973
2.
District heating
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District heating is a system for distributing heat generated in a centralized location for residential and commercial heating requirements such as space heating and water heating. District heating plants can provide higher efficiencies and better control than localized boilers. A combination of CHP and centralized heat pumps are used in the Stockholm multi energy system, the core element of many district heating systems is a heat-only boiler station. Additionally a cogeneration plant is added in parallel with the boilers. Both have in common that they are based on combustion of primary energy carriers. In the case of a fossil fueled cogeneration plant, the output is typically sized to meet half of the peak heat load. The boiler capacity will be able to meet the entire heat demand unaided and it is not economic to size the cogeneration plant alone to be able to meet the full heat load. In the New York City steam system, that is around 2.5 GW, Germany has the largest amount of CHP in Europe. The combination of cogeneration and district heating is very energy efficient, a simple thermal power station can be 20–35% efficient, whereas a more advanced facility with the ability to recover waste heat can reach total energy efficiency of nearly 80%. Some may exceed 100% based on the heating value by condensing the flue gas as well. Waste heat from nuclear plants is sometimes used for district heating. The principles for a combination of cogeneration and district heating applies the same for nuclear as it does for a thermal power station. Russia has several cogeneration nuclear plants which together provided 11.4 PJ of district heat in 2005, Russian nuclear district heating is planned to nearly triple within a decade as new plants are built. Other nuclear-powered heating from cogeneration plants are in Ukraine, the Czech Republic, Slovakia, Hungary, Bulgaria, one use of nuclear heat generation was with the Ågesta Nuclear Power Plant in Sweden closed in 1974. In Switzerland, the Beznau Nuclear Power Plant provides heat to about 20,000 people, history Geothermal district heating was used in Pompeii, and in Chaudes-Aigues since the 14th Century. In 1890, the first wells were drilled to access a hot water resource outside of Boise, in 1892, after routing the water to homes and businesses in the area via a wooden pipeline, the first geothermal district heating system was created. As of a 2007 study, there were 22 geothermal district heating systems in the United States, as of 2010, two of those systems have shut down. The table below describes the 20 GDHS currently operational in America, use of solar heat for district heating has been increasing in Denmark and Germany in recent years
3.
Optical fiber
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An optical fiber or optical fibre is a flexible, transparent fiber made by drawing glass or plastic to a diameter slightly thicker than that of a human hair. Fibers are also used for illumination, and are wrapped in bundles so that they may be used to carry images, thus allowing viewing in confined spaces, as in the case of a fiberscope. Specially designed fibers are used for a variety of other applications, some of them being fiber optic sensors. Optical fibers typically include a transparent core surrounded by a transparent cladding material with an index of refraction. Light is kept in the core by the phenomenon of internal reflection which causes the fiber to act as a waveguide. Fibers that support many propagation paths or transverse modes are called multi-mode fibers, multi-mode fibers generally have a wider core diameter and are used for short-distance communication links and for applications where high power must be transmitted. Single-mode fibers are used for most communication links longer than 1,000 meters, being able to join optical fibers with low loss is important in fiber optic communication. This is more complex than joining electrical wire or cable and involves careful cleaving of the fibers, precise alignment of the cores. For applications that demand a permanent connection a fusion splice is common, in this technique, an electric arc is used to melt the ends of the fibers together. Another common technique is a splice, where the ends of the fibers are held in contact by mechanical force. Temporary or semi-permanent connections are made by means of specialized optical fiber connectors, the field of applied science and engineering concerned with the design and application of optical fibers is known as fiber optics. The term was coined by Indian physicist Narinder Singh Kapany who is acknowledged as the father of fiber optics. Guiding of light by refraction, the principle that makes fiber optics possible, was first demonstrated by Daniel Colladon, John Tyndall included a demonstration of it in his public lectures in London,12 years later. When the ray passes from water to air it is bent from the perpendicular. If the angle which the ray in water encloses with the perpendicular to the surface be greater than 48 degrees, the angle which marks the limit where total reflection begins is called the limiting angle of the medium. For water this angle is 48°27′, for flint glass it is 38°41′, unpigmented human hairs have also been shown to act as an optical fiber. Practical applications, such as close internal illumination during dentistry, appeared early in the twentieth century, image transmission through tubes was demonstrated independently by the radio experimenter Clarence Hansell and the television pioneer John Logie Baird in the 1920s. The principle was first used for medical examinations by Heinrich Lamm in the following decade
4.
Cable television
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This contrasts with broadcast television, in which the television signal is transmitted over the air by radio waves and received by a television antenna attached to the television. FM radio programming, high-speed Internet, telephone services, and similar non-television services may also be provided through these cables, analog television was standard in the 20th century, but since the 2000s, cable systems have been upgraded to digital cable operation. A cable channel is a television network available via cable television, alternative terms include non-broadcast channel or programming service, the latter being mainly used in legal contexts. Examples of cable/satellite channels/cable networks available in many countries are HBO, MTV, Cartoon Network, E. Eurosport, the abbreviation CATV is often used for cable television. It originally stood for Community Access Television or Community Antenna Television, in areas where over-the-air TV reception was limited by distance from transmitters or mountainous terrain, large community antennas were constructed, and cable was run from them to individual homes. The origins of cable broadcasting for radio are even older as radio programming was distributed by cable in some European cities as far back as 1924, Cable television has gone through a series of steps of evolution in the United States and Canada. Particularly in Canada, communities with their own signals were fertile cable markets, as viewers wanted to receive American signals. Early systems carried only a maximum of seven channels, using 2,4,5 or 6,7,9,11 and 13, as the equipment was unable to confine the signal discreetly within the assigned channel bandwidth. The reason 4 and 5 along with 6 and 7 could be used together was because of the 4 MHz gap between 4 and 5 and the nearly 90 MHz gap between 6 and 7. Even though eight channels are listed, in systems that maximized 7 channels. As equipment improved, all channels could be utilized, except where a local VHF television station broadcast. Local broadcast channels were not usable for signals deemed to be priority, later, the cable operators began to carry FM radio stations, and encouraged subscribers to connect their FM stereo sets to cable. Before stereo and bilingual TV sound became common, Pay-TV channel sound was added to the FM stereo cable line-ups, about this time, operators expanded beyond the 12-channel dial to use the midband and superband VHF channels adjacent to the high band 7-13 of North American television frequencies. Some operators as in Cornwall, Ontario, used a dual distribution network with Channels 2-13 on each of the two cables, during the 1980s, United States regulations not unlike public, educational, and government access created the beginning of cable-originated live television programming. These stations evolved partially into todays over-the-air digital subchannels, where a main broadcast TV station e. g, many live local programs with local interests were subsequently created all over the United States in most major television markets in the early 1980s. This evolved into todays many cable-only broadcasts of diverse programming, including cable-only produced television movies and miniseries, Cable specialty channels, starting with channels oriented to show movies and large sporting or performance events, diversified further, and narrowcasting became common. By the late 1980s, cable-only signals outnumbered broadcast signals on cable systems, by the mid-1980s in Canada, cable operators were allowed by the regulator to enter into distribution contracts with cable networks on their own. By the 1990s, tiers became common, with customers able to subscribe to different tiers to obtain different selections of additional channels above the basic selection, by subscribing to additional tiers, customers could get specialty channels, movie channels, and foreign channels
5.
Telephone
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A telephone, or phone, is a telecommunications device that permits two or more users to conduct a conversation when they are too far apart to be heard directly. In 1876, Scottish emigrant Alexander Graham Bell was the first to be granted a United States patent for a device that produced clearly intelligible replication of the human voice and this instrument was further developed by many others. The telephone was the first device in history that people to talk directly with each other across large distances. Telephones rapidly became indispensable to businesses, government, and households, the essential elements of a telephone are a microphone to speak into and an earphone which reproduces the voice in a distant location. Until approximately the 1970s most telephones used a dial, which was superseded by the modern DTMF push-button dial. The receiver and transmitter are usually built into a handset which is held up to the ear, the dial may be located either on the handset, or on a base unit to which the handset is connected. The transmitter converts the sound waves to electrical signals which are sent through the network to the receiving phone. The receiving telephone converts the signals into audible sound in the receiver, telephones permit duplex communication, meaning they allow the people on both ends to talk simultaneously. The first telephones were connected to each other from one customers office or residence to another customers location. Being impractical beyond just a few customers, these systems were replaced by manually operated centrally located switchboards. For greater mobility, various systems were developed for transmission between mobile stations on ships and automobiles in the middle 20th century. Hand-held mobile phone]s was introduced for personal service starting in 1973, by the late 1970s several mobile telephone networks operated around the world. In 1983, the Advanced Mobile Phone System was launched, offering a standardized technology providing portability for users far beyond the residence or office. These analog cellular system evolved into digital networks with better security, greater capacity, better regional coverage, the public switched telephone network, with its hierarchical system of many switching centers, interconnects telephones around the world for communication with each other. With the standardized international numbering system, E.164, each line has an identifying telephone number. Although originally designed for voice communications, convergence has enabled most modern cell phones to have many additional capabilities. Since 1999, the trend for mobile phones is smartphones that integrate all mobile communication, a traditional landline telephone system, also known as plain old telephone service, commonly carries both control and audio signals on the same twisted pair of insulated wires, the telephone line. The control and signaling equipment consists of three components, the ringer, the hookswitch, and a dial, the ringer, or beeper, light or other device, alerts the user to incoming calls
6.
Direct-buried cable
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Most direct-buried cable is built to specific tolerances to heat, moisture, conductivity, and soil acidity. DBC is preferable in some areas since it is resistant to being the focus of lightning discharges. Most cable of this kind is coaxial or bundled fiber-optic in nature, direct-buried cable is cheaper and easier to lay than other kinds of cable that require protection from the earth. However, DBC is also cut during digging or other excavations. As a result, most direct-buried cable is found on side roads, some power cabling is also direct-buried. This kind of cabling must follow strict regulatory procedures regarding installation and this is usually used for undergrounding in areas where overhead cabling is impractical or dangerous. Guide to direct buried cabling procedures
7.
Alaska
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Alaska is a U. S. state located in the northwest extremity of North America. To the north are the Chukchi and Beaufort seas–the southern parts of the Arctic Ocean, the Pacific Ocean lies to the south and southwest. Alaska is the largest state in the United States by area, the 3rd least populous, approximately half of Alaskas residents live within the Anchorage metropolitan area. Alaskas economy is dominated by the fishing, natural gas, military bases and tourism are also a significant part of the economy. The United States purchased Alaska from the Russian Empire on March 30,1867, the area went through several administrative changes before becoming organized as a territory on May 11,1912. It was admitted as the 49th state of the U. S. on January 3,1959, the name Alaska was introduced in the Russian colonial period when it was used to refer to the peninsula. It was derived from an Aleut, or Unangam idiom, which refers to the mainland of Alaska. Literally, it means object to which the action of the sea is directed, Alaska is the northernmost and westernmost state in the United States and has the most easterly longitude in the United States because the Aleutian Islands extend into the Eastern Hemisphere. Alaska is the only non-contiguous U. S. state on continental North America and it is technically part of the continental U. S. but is sometimes not included in colloquial use, Alaska is not part of the contiguous U. S. often called the Lower 48. The capital city, Juneau, is situated on the mainland of the North American continent but is not connected by road to the rest of the North American highway system. Alaskas territorial waters touch Russias territorial waters in the Bering Strait, as the Russian Big Diomede Island, Alaska has a longer coastline than all the other U. S. states combined. Alaska is the largest state in the United States by total area at 663,268 square miles, over twice the size of Texas, Alaska is larger than all but 18 sovereign countries. Counting territorial waters, Alaska is larger than the area of the next three largest states, Texas, California, and Montana. It is also larger than the area of the 22 smallest U. S. states. Also referred to as the Panhandle or Inside Passage, this is the region of Alaska closest to the rest of the United States, as such, this was where most of the initial non-indigenous settlement occurred in the years following the Alaska Purchase. The region is dominated by the Alexander Archipelago as well as the Tongass National Forest and it contains the state capital Juneau, the former capital Sitka, and Ketchikan, at one time Alaskas largest city. The Alaska Marine Highway provides a vital transportation link throughout the area. The Interior is the largest region of Alaska, much of it is uninhabited wilderness, Fairbanks is the only large city in the region
8.
Permafrost
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In geology, permafrost is ground, including rock or soil, at or below the freezing point of water 0 °C for two or more years. Most permafrost is located in high latitudes, but alpine permafrost may exist at altitudes in much lower latitudes. Ground ice is not always present, as may be in the case of nonporous bedrock, Permafrost accounts for 0. 022% of total water on earth and exists in 24% of exposed land in the Northern Hemisphere. It also occurs subsea on the shelves of the continents surrounding the Arctic Ocean, portions of which were exposed during the last glacial period. A global temperature rise of 1.5 °C above current levels would be enough to start the thawing of permafrost in Siberia, Permafrost is soil, rock or sediment that is frozen for more than two consecutive years. In areas not overlain by ice, it exists beneath a layer of soil, rock or sediment, in practice, this means that permafrost occurs at an average air temperature of -2 °C or colder. Active layer thickness varies with the season, but is 0.3 to 4 meters thick, in the Northern Hemisphere, 24% of the ice-free land area, equivalent to 19 million square kilometers, is more or less influenced by permafrost. Most of this area is found in Siberia, northern Canada, Alaska, beneath the active layer annual temperature swings of permafrost become smaller with depth. The deepest depth of permafrost occurs where geothermal heat maintains a temperature above freezing, above that bottom limit there may be permafrost, whose temperature doesnt change annually—isothermal permafrost. The extent of permafrost varies with the climate, today, a considerable area of the Arctic is covered by permafrost. Overlying permafrost is an active layer that seasonally thaws during the summer. Plant life can be supported only within the active layer since growth can occur only in soil that is fully thawed for some part of the year, thickness of the active layer varies by year and location, but is typically 0. 6–4 m thick. In areas of continuous permafrost and harsh winters, the depth of the permafrost can exceed 1,400 m, Permafrost can also store carbon, both as peat and as methane. Work investigating the permafrost carbon pool size estimates that 1400–1700 Gt of carbon is stored in the northern circumpolar permafrost region, while a recent study that includes stores of the Tibetan Plateau, estimates total carbon pools in the permafrost of the Northern Hemisphere to be 1832 Gt. This large carbon pool represents more carbon than currently exists in all living things, Permafrost typically forms in any climate where the mean annual air temperature is less than the freezing point of water. Exceptions are found in moist-wintered forest climates, such as in Northern Scandinavia and the North-Eastern part of European Russia west of the Urals, fossil cold anomalies in the Geothermal gradient in areas where deep permafrost developed during the Pleistocene persist down to several hundred metres. This is evident from temperature measurements in boreholes in North America, typically, the below-ground temperature varies less from season to season than the air temperature, with mean annual temperatures tending to increase with depth. Thus, if the annual air temperature is only slightly below 0 °C
9.
Water table
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The water table is the upper surface of the zone of saturation. The zone of saturation is where the pores and fractures of the ground are saturated with water, the water table is the surface where the water pressure head is equal to the atmospheric pressure. It may be visualized as the surface of the materials that are saturated with groundwater in a given vicinity. The groundwater may be from precipitation or from groundwater flowing into the aquifer, in areas with sufficient precipitation, water infiltrates through pore spaces in the soil, passing through the unsaturated zone. At increasing depths water fills in more of the spaces in the soils. Below the water table, in the zone, layers of permeable rock that yield groundwater are called aquifers. In less permeable soils, such as tight bedrock formations and historic lakebed deposits, the water table should not be confused with the water level in a deeper well. The elevation of the water in this well is dependent upon the pressure in the deeper aquifer and is referred to as the potentiometric surface. The water table may vary due to changes such as precipitation and evapotranspiration. Springs, rivers, lakes and oases occur when the table reaches the surface. Springs commonly form on hillsides, where the Earths slanting surface may intersect with the water table, Groundwater entering rivers and lakes accounts for the base-flow water levels in water bodies. Within an aquifer, the table is rarely horizontal, but reflects the surface relief due to the capillary effect in soils, sediments. In the aquifer, groundwater flows from points of pressure to points of lower pressure. The slope of the table is known as the hydraulic gradient, which depends on the rate at which water is added to and removed from the aquifer. This occurs when there is a layer of rock or sediment or relatively impermeable layer above the main water table/aquifer. If a perched aquifers flow intersects the Earths dry surface, at a wall for example. On low-lying oceanic islands with porous soil, freshwater tends to collect in lenticular pools on top of the denser seawater intruding from the sides of the islands, such an islands freshwater lens, and thus the water table, rises and falls with the tides. In some regions, for example, Great Britain or California, winter precipitation is higher than summer precipitation
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