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Topic Review
Fire-vegetation Feedbacks and Alternative Stable States
The relationship between fire, vegetation, and climate create what is known as a fire regime. Within a fire regime, fire ecologists study the relationship between diverse ecosystems and fire; not only how fire affects vegetation, but also how vegetation affects the behavior of fire. The study of neighboring vegetations types that may be highly flammable and less flammable has provided insight into how these vegetation types can exist side by side, and are maintained by the presence or absence of fire events. Ecologists have studied these boundaries between different vegetation types, such as a closed canopy forest and a grassland, and hypothesized how climate, and soil fertility create these boundaries in vegetation types. Research in the field of pyrogeography shows how fire also plays an important role in the maintenance of dominant vegetation types, and how different vegetation types with distinct relationships to fire can exist side by side in the same climate conditions. These relationships can be described in conceptual models called fire-vegetation feedbacks, and alternative stable states.
  • 567
  • 29 Sep 2022
Topic Review
Firestorm
A firestorm is a conflagration which attains such intensity that it creates and sustains its own wind system. It is most commonly a natural phenomenon, created during some of the largest bushfires and wildfires. Although the term has been used to describe certain large fires, the phenomenon's determining characteristic is a fire with its own storm-force winds from every point of the compass. The Black Saturday bushfires and the Great Peshtigo Fire are possible examples of forest fires with some portion of combustion due to a firestorm, as is the Great Hinckley Fire. Firestorms have also occurred in cities, usually due to targeted explosives, such as in the aerial firebombings of Hamburg, Dresden, and Tokyo, and the atomic bombings of Hiroshima and Nagasaki.
  • 528
  • 19 Oct 2022
Topic Review
First Bulgarian Empire
The First Bulgarian Empire (Old Bulgarian: ц︢рьство бл︢гарское, ts'rstvo bl'garskoe) was a medieval Bulgarian state that existed in Southeastern Europe between the 7th and 11th centuries AD. It was founded in 681 when Bulgar tribes led by Asparuh moved to the northeastern Balkans. There they secured Byzantine recognition of their right to settle south of the Danube by defeating – possibly with the help of local South Slavic tribes – the Byzantine army led by Constantine IV. At the height of its power, Bulgaria spread from the Danube Bend to the Black Sea and from the Dnieper River to the Adriatic Sea. As the state solidified its position in the Balkans, it entered into a centuries-long interaction, sometimes friendly and sometimes hostile, with the Byzantine Empire. Bulgaria emerged as Byzantium's chief antagonist to its north, resulting in several wars. The two powers also enjoyed periods of peace and alliance, most notably during the Second Arab siege of Constantinople, where the Bulgarian army broke the siege and destroyed the Arab army, thus preventing an Arab invasion of Southeastern Europe. Byzantium had a strong cultural influence on Bulgaria, which also led to the eventual adoption of Christianity in 864. After the disintegration of the Avar Khaganate, the country expanded its territory northwest to the Pannonian Plain. Later the Bulgarians confronted the advance of the Pechenegs and Cumans, and achieved a decisive victory over the Magyars, forcing them to establish themselves permanently in Pannonia. During the late 9th and early 10th centuries, Simeon I achieved a string of victories over the Byzantines. Thereafter, he was recognized with the title of Emperor, and proceeded to expand the state to its greatest extent. After the annihilation of the Byzantine army in the battle of Anchialus in 917, the Bulgarians laid siege to Constantinople in 923 and 924. The Byzantines, however, eventually recovered, and in 1014, under Basil II, inflicted a crushing defeat on the Bulgarians at the Battle of Kleidion. By 1018, the last Bulgarian strongholds had surrendered to the Byzantine Empire, and the First Bulgarian Empire had ceased to exist. It was succeeded by the Second Bulgarian Empire in 1185. After the adoption of Christianity, Bulgaria became the cultural center of Slavic Europe. Its leading cultural position was further consolidated with the invention of the Glagolitic and Early Cyrillic alphabets shortly after in the capital Preslav, and literature produced in Old Bulgarian soon began spreading north. Old Bulgarian became the lingua franca of much of Eastern Europe and it came to be known as Old Church Slavonic. In 927, the fully independent Bulgarian Patriarchate was officially recognized. The ruling Bulgars and other non-Slavic tribes in the empire gradually mixed and adopted the prevailing Slavic language, thus gradually forming the Bulgarian nation from the 7th century to the 9th century. Since the late 9th century, the names Bulgarians and Bulgarian gained prevalence and became permanent designations for the local population, both in literature and in common parlance. The development of Old Church Slavonic literacy had the effect of preventing the assimilation of the South Slavs into neighbouring cultures, while stimulating the formation of a distinct Bulgarian identity.
  • 3.8K
  • 25 Oct 2022
Topic Review
First Grinnell Expedition
The First Grinnell Expedition of 1850 was the first American effort, financed by Henry Grinnell, to determine the fate of the lost Franklin Polar Expedition. Led by Lieutenant Edwin De Haven, the team explored the accessible areas along Franklin's proposed route. In coordination with British expeditions, they identified the remains of Franklin's Beechy Island winter camp, providing the first solid clues to Franklin's activities during the winter of 1845 before becoming icebound themselves.
  • 267
  • 02 Dec 2022
Topic Review
First United Nations Report on Problems of Human-Environment
The 1969 UN Report “Problems of the Human Environment” was a seminal work that first highlighted environmental problems at a global scale. This report underpinned a series of subsequent international summits and conventions of the 1992 Rio Earth Summit and the subsequent three global conventions on Biodiversity, Climate Change and Desertification. Many issues of that day have declined in importance or been superseded, and several major environmental problems (including climate change and plastic pollution) were not foreseen. Most of the report’s predictions proved to be much more conservative than proved by reality (a criticism that has also been levelled at contemporary IPCC reports).
  • 821
  • 06 Sep 2022
Topic Review
Fissure Ridges
Fissure ridges consist of elongated travertine masses with an apical fissure that follows the long axis of the body. Two symmetrical or asymmetrical walls made up of bedded travertine are typically dipping away from the central fissure. The internal part of the fissure is often cut by a network of sealed fractures, almost parallel to the long axis of the ridge, normally filled by banded Ca-carbonate (i.e., calcite and/or aragonite), almost parallel to the vein-walls (the so called “banded travertine” in). These veins developed within the fault zone and represent conduits along which geothermal fluids move towards the surface. Therefore, their analysis, in terms of geometry, age (using U/Th, U/Pb, and 14C geochronology), and geochemical properties, provides information about the structural features and timing of the fault system, and on the fluid path from depth to surface. Furthermore, travertine deposited in a fissure ridge is characterized by distinct petrographic and geochemical features preserving information on the parent fluids and ancient depositional conditions. The shape of the fissure ridge body depends on the flow rate, carbonate precipitation rate, and surface topography upon which deposition took place.
  • 1.0K
  • 13 Jul 2021
Topic Review Video
Fixed and Floating Offshore Structures
Diverse forms of offshore oil and gas structures are utilized for a wide range of purposes and in varying water depths. They are designed for unique environments and water depths around the world. The applications of these offshore structures require different activities for proper equipment selection, design of platform types, and drilling/production methods. There are advances made in ocean engineering which include a variety of innovative offshore structure designs, ranging from fixed platforms to floating platforms. Some of these structures include the deep-water semisubmersible platforms, jack-up rigs, floating offshore wind turbines (FOWTs), FPS (floating production systems) units.
  • 8.4K
  • 19 Aug 2022
Topic Review
Flag Clouds in Mt.Everest
Flag clouds refer to flag-shaped stationary clouds that appear on the windward side of isolated snow-covered peaks under specific terrain conditions. By observing it, we can forecast the local weather.
  • 308
  • 22 Jan 2024
Topic Review
Flashline Mars Arctic Research Station
The Flashline Mars Arctic Research Station (FMARS) is the first of two simulated Mars habitats (or Mars Analog Research Stations) established and maintained by the Mars Society.
  • 688
  • 10 Oct 2022
Topic Review
Floating Island
A floating island is a mass of floating aquatic plants, mud, and peat ranging in thickness from several centimeters to a few meters. Floating islands are a common natural phenomenon that are found in many parts of the world. They exist less commonly as an artificial phenomenon. Floating islands are generally found on marshlands, lakes, and similar wetland locations, and can be many hectares in size.
  • 3.6K
  • 21 Oct 2022
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