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Topic Review
Types of Adsorbents
There are two types of adsorbents, namely, natural and synthetic adsorbents. Several examples of natural adsorbents include clay and zeolite (abundant and cheap). On the other hand, researchers can produce synthetic adsorbents (activated carbon) via agricultural waste, industrial waste, and household waste.
  • 7.8K
  • 27 Oct 2022
Topic Review
Structure of the Earth
The internal structure of the Earth is layered in spherical shells: an outer silicate solid crust, a highly viscous asthenosphere and mantle, a liquid outer core that is much less viscous than the mantle, and a solid inner core. Scientific understanding of the internal structure of the Earth is based on observations of topography and bathymetry, observations of rock in outcrop, samples brought to the surface from greater depths by volcanoes or volcanic activity, analysis of the seismic waves that pass through the Earth, measurements of the gravitational and magnetic fields of the Earth, and experiments with crystalline solids at pressures and temperatures characteristic of the Earth's deep interior.
  • 1.5K
  • 26 Oct 2022
Topic Review
List of Selected Stars for Navigation
Fifty-eight selected navigational stars are given a special status in the field of celestial navigation. Of the approximately 6,000 stars visible to the naked eye under optimal conditions, the selected stars are among the brightest and span 38 constellations of the celestial sphere from the declination of −70° to +89°. Many of the selected stars were named in antiquity by the Babylonians, Greeks, Romans, and Arabs. The star Polaris, often called the "North Star", is treated specially due to its proximity to the north celestial pole. When navigating in the Northern Hemisphere, special techniques can be used with Polaris to determine latitude or gyrocompass error. The other 57 selected stars have daily positions given in nautical almanacs, aiding the navigator in efficiently performing observations on them. A second group of 115 "tabulated stars" can also be used for celestial navigation, but are often less familiar to the navigator and require extra calculations. For purposes of identification, the positions of navigational stars — expressed as declination and sidereal hour angle — are often rounded to the nearest degree. In addition to tables, star charts provide an aid to the navigator in identifying the navigational stars, showing constellations, relative positions, and brightness.
  • 2.5K
  • 26 Oct 2022
Topic Review
Muslim World
The terms Muslim world and Islamic world commonly refer to the Islamic community, which is also known as the Ummah. This consists of all those who adhere to the religions beliefs and laws of Islam, or to societies where Islam is practiced. In a modern geopolitical sense, these terms refer to countries where Islam is widespread, although there are no agreed criteria for inclusion. The term Muslim-majority countries is an alternative often used for the latter sense. The history of the Muslim world spans about 1,400 years and includes a variety of socio-political developments, as well as advances in the arts, science, philosophy, and technology, particularly during the Islamic Golden Age. All Muslims look for guidance to the Quran and believe in the prophetic mission of the Islamic prophet Muhammad, but disagreements on other matters have led to the appearance of different religious schools of thought and sects within Islam. In the modern era, most of the Muslim world came under European colonial domination. The nation states that emerged in the post-colonial era have adopted a variety of political and economic models, and they have been affected by secular and as well as religious trends. (As of 2013), the combined GDP (nominal) of 49 Muslim majority countries was US$5.7 trillion, (As of 2016), they contributed 8% of the world's total. As of 2015, 1.8 billion or about 24.1% of the world population are Muslims. By the percentage of the total population in a region considering themselves Muslim, 91% in the Middle East-North Africa (MENA), 89% in Central Asia, 40% in Southeast Asia, 31% in South Asia, 30% in Sub-Saharan Africa, 25% in Asia–Oceania, around 6% in Europe, and 1% in the Americas. Most Muslims are of one of two denominations: Sunni Islam (85-90%) and Shia (10-15%), However, other denominations exist in pockets, such as Ibadi (primarily in Oman). About 13% of Muslims live in Indonesia, the largest Muslim-majority country; 31% of Muslims live in South Asia, the largest population of Muslims in the world; 20% in the Middle East–North Africa, where it is the dominant religion; and 15% in Sub-Saharan Africa and West Africa. Muslims are the overwhelming majority in Central Asia, the majority in the Caucasus and widespread in Southeast Asia. India is the country with the largest Muslim population outside Muslim-majority countries. Sizeable Muslim communities are also found in the Americas, China, and Europe. Islam is the fastest-growing major religion in the world.
  • 4.1K
  • 26 Oct 2022
Topic Review
Geography and Cartography in Medieval Islam
Medieval Islamic geography and cartography refer to the study of geography and cartography in the Muslim world during the Islamic Golden Age (variously dated between the 8th century and 16th century). Muslim scholars made advances to the mapmaking traditions of earlier cultures, particularly the Hellenistic geographers Ptolemy and Marinus of Tyre,:193 combined with what explorers and merchants learned in their travels across the Old World (Afro-Eurasia). Islamic geography had three major fields: exploration and navigation, physical geography, and cartography and mathematical geography. Islamic geography reached its apex with Muhammad al-Idrisi in the 12th century.
  • 2.4K
  • 26 Oct 2022
Topic Review
Outer Space
Outer space, or simply space, is the expanse that exists beyond the Earth and between celestial bodies. Outer space is not completely empty—it is a hard vacuum containing a low density of particles, predominantly a plasma of hydrogen and helium, as well as electromagnetic radiation, magnetic fields, neutrinos, dust, and cosmic rays. The baseline temperature of outer space, as set by the background radiation from the Big Bang, is 2.7 kelvins (−270.45 °C; −454.81 °F). The plasma between galaxies accounts for about half of the baryonic (ordinary) matter in the universe; it has a number density of less than one hydrogen atom per cubic metre and a temperature of millions of kelvins. Local concentrations of matter have condensed into stars and galaxies. Studies indicate that 90% of the mass in most galaxies is in an unknown form, called dark matter, which interacts with other matter through gravitational but not electromagnetic forces. Observations suggest that the majority of the mass-energy in the observable universe is dark energy, a type of vacuum energy that is poorly understood. Intergalactic space takes up most of the volume of the universe, but even galaxies and star systems consist almost entirely of empty space. Outer space does not begin at a definite altitude above the Earth's surface. However, the Kármán line, an altitude of 100 km (62 mi) above sea level, is conventionally used as the start of outer space in space treaties and for aerospace records keeping. The framework for international space law was established by the Outer Space Treaty, which entered into force on 10 October 1967. This treaty precludes any claims of national sovereignty and permits all states to freely explore outer space. Despite the drafting of UN resolutions for the peaceful uses of outer space, anti-satellite weapons have been tested in Earth orbit. Humans began the physical exploration of space during the 20th century with the advent of high-altitude balloon flights. This was followed by manned rocket flights and, then, manned Earth orbit, first achieved by Yuri Gagarin of the Soviet Union in 1961. Due to the high cost of getting into space, manned spaceflight has been limited to low Earth orbit and the Moon. On the other hand, unmanned spacecraft have reached all of the known planets in the Solar System. Outer space represents a challenging environment for human exploration because of the hazards of vacuum and radiation. Microgravity also has a negative effect on human physiology that causes both muscle atrophy and bone loss. In addition to these health and environmental issues, the economic cost of putting objects, including humans, into space is very high.
  • 7.4K
  • 26 Oct 2022
Topic Review
Rainfall Threshold
Sediment-related disaster is one of the most significant natural disasters, from the perspective of magnitude, damage and loss to human life and infrastructure, and disruption to socio-economic activities. The rainfall threshold is the condition or amount of rainfall that is likely to initiate sediment-related disasters, it is agreed that the rainfall threshold is the most significant tool to predict impending occurrences.
  • 1.5K
  • 26 Oct 2022
Topic Review
Korla
Korla (sometimes as Kurla, or Kurle) is the second largest city in Xinjiang, and is, administratively, a county-level city and the seat of the Bayingolin Mongol Autonomous Prefecture, which is larger than Great Britain and is the largest Chinese prefecture. Korla is also known for its "fragrant" pears.
  • 680
  • 26 Oct 2022
Topic Review
Climate-Alliance Germany
Climate-Alliance Germany (German: Klima-Allianz Deutschland) is a network of more than 120 civil society organizations, including environment groups, development groups, churches, organisations from the fields of youth, education, culture and health, as well as trade unions, and consumer associations. Founded in 2007, the aim of the Alliance is to provide a common front to apply pressure to German decision-makers to adopt climate protection measures. Prominent members include WWF, BUND (or Friends of the Earth Germany), and the trade union ver.di. A key issue for the Alliance is the prevention of new coal-fired power plants (the Anti-Coal Campaign). The Alliance wants the German government to phase-out coal (Kohleausstieg) and promote renewable energy.
  • 274
  • 25 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.
  • 3.6K
  • 25 Oct 2022
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