Subject:
All Disciplines Arts & Humanities Biology & Life Sciences Business & Economics Chemistry & Materials Science Computer Science & Mathematics Engineering Environmental & Earth Sciences Medicine & Pharmacology Physical Sciences Public Health & Healthcare Social Sciences
Sort:
Hottest Latest Alphabetical (A-Z) Alphabetical (Z-A)
Type:
All Topic Review Biography
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.
  • 2.4K
  • 26 Oct 2022
Topic Review
Mercury's Magnetic Field
Mercury's magnetic field is approximately a magnetic dipole (meaning the field has only two magnetic poles) apparently global, on planet Mercury. Data from Mariner 10 led to its discovery in 1974; the spacecraft measured the field's strength as 1.1% that of Earth's magnetic field. The origin of the magnetic field can be explained by dynamo theory. The magnetic field is strong enough near the bow shock to slow the solar wind, which induces a magnetosphere.
  • 2.4K
  • 15 Nov 2022
Topic Review
Municipal Solid Waste Management in Cambodia
Municipal solid waste (MSW) management is one of the utmost challenges for Cambodia’s city and district centers. The unsound management of MSW has detrimentally affected the environment and human health.
  • 2.4K
  • 09 Aug 2022
Topic Review
Second Bulgarian Empire
The Second Bulgarian Empire (Bulgarian: Второ българско царство, Vtorо Bălgarskо Tsarstvo) was a medieval Bulgarian state that existed between 1185 and 1396. A successor to the First Bulgarian Empire, it reached the peak of its power under Tsars Kaloyan and Ivan Asen II before gradually being conquered by the Ottomans in the late 14th and early 15th centuries. It was succeeded by the Principality and later Kingdom of Bulgaria in 1878. Until 1256, the Second Bulgarian Empire was the dominant power in the Balkans, defeating the Byzantine Empire in several major battles. In 1205 Emperor Kaloyan defeated the newly established Latin Empire in the Battle of Adrianople. His nephew Ivan Asen II defeated the Despotate of Epiros and made Bulgaria a regional power again. During his reign, Bulgaria spread from the Adriatic to the Black Sea and the economy flourished. In the late 13th century, however, the Empire declined under constant invasions by Mongols, Byzantines, Hungarians, and Serbs, as well as internal unrest and revolts. The 14th century saw a temporary recovery and stability, but also the peak of Balkan feudalism as central authorities gradually lost power in many regions. Bulgaria was divided into three parts on the eve of the Ottoman invasion. Despite strong Byzantine influence, Bulgarian artists and architects created their own distinctive style. In the 14th century, during the period known as the Second Golden Age of Bulgarian culture, literature, art and architecture flourished. The capital city Tarnovo, which was considered a "New Constantinople", became the country's main cultural hub and the centre of the Eastern Orthodox world for contemporary Bulgarians. After the Ottoman conquest, many Bulgarian clerics and scholars emigrated to Serbia, Wallachia, Moldavia, and Russian principalities, where they introduced Bulgarian culture, books, and hesychastic ideas.
  • 2.4K
  • 10 Oct 2022
Topic Review
Land Administration and Blockchain Technology
Transparency of processes is very crucial across all institutions. In land administration processes, this is particularly important given the multi-stakeholder involvement. This paper argues that transparency of land administration processes involves carrying out and sharing up-to-date information on ownership, value, and the use of land and all of its associated resources among related institutions, right holders and other stakeholders, including third parties, as well as, acting on the information in an open manner. To achieve this in Ghana, blockchain technology has been identified as a complementary tool to the Ghanaian land administration system. Blockchain technology refers to a fully distributed crypto-graphical system that captures and stores a consistent, immutable and linear event log of the transactions between networked actors. The study identifies that given the potentials of blockchain technology which include; decentralization of transaction to all connected stakeholders, the immutability of records, hashing of records that allows for quick access to both historical and current land transactions' data, as well as the blockchain smart contract among others, land administration processes of land tenure, land valuation, land use planning, and land development will benefit from openness, and transparency, and human error elimination. It will also eliminate fraud, and double sales of land among other land challenges identified in the Ghanaian land sector.  The study proposes that for real-time land up-date in land information across all the land sector divisions; land valuation division, land title registration, survey and mapping division, and the public and vested land management division, a permisionless public blockchain architecture be adopted for the Ghanaian land system. This is because, in comparison to the other blockchain architecture types, the permisionless public blockchain allows more transparency, decentralization, openness, integration, and also adheres to privacy and data protection laws. This study and its results are particularly important not only to the Ghanaian land sector and its stakeholders, but to all other land administration systems in the sub-Saharan Africa region given the similarities in land administration across the region. In the Ghanaian context however, the study's findings if implemented will affect the institutional relations and shared authorities between all stakeholders which include government agencies, local chiefs and individual landowners. This is because, land decisions and land data will not become shared responsibility of all stakeholders and not dependent on just some few stakeholders. A successful implementation of blockchain in Ghana's land administration will however depend on negotiations and consensus amongst the different land stakeholder, education of all stakeholders on the technology, and its impacts, as well as standardization in the land administration processes across the different land divisions. This is because, where there is no such standardization, there is a high possibility of inconsistencies and irregularities in the processes which can affect the efficient working of the blockchain system.
  • 2.4K
  • 07 Jun 2021
Topic Review
Heavy Metals and Metalloids
The contamination of soil by heavy metals and metalloids is a worldwide problem due to the accumulation of these compounds in the environment, endangering human health, plants, and animals. Heavy metals and metalloids are normally present in nature, but the rise of industrialization has led to concentrations higher than the admissible ones. They are non-biodegradable and toxic, even at very low concentrations. Several techniques have been developed over the years: - physical remediation (e.g., washing, thermal desorption, solidification), - chemical remediation (e.g., adsorption, catalysis, precipitation/solubilization, electrokinetic methods), - biological remediation (e.g., biodegradation, phytoremediation, bioventing), and combined remediation (e.g., electrokinetic–microbial remediation; washing–microbial degradation).
  • 2.4K
  • 20 May 2021
Topic Review
Degradation of Antibiotics
Antibiotics are the therapeutic option for countless infections treatment; unfortunately, they are the second most common group of drugs in wastewaters worldwide due to failures in industrial waste treatments and their irrational use in humans and animals. Several techniques have been assayed for the degradation and mineralisation of antibiotics to reduce the environmental impact; strategies focused on physical, chemical, biological, and combined process design for degradation.
  • 2.4K
  • 25 Jul 2022
Topic Review
Tropospheric Ozone
Ozone (O3) is a trace gas of the troposphere, with an average concentration of 20–30 parts per billion by volume (ppbv), with close to 100 ppbv in polluted areas. Ozone is also an important constituent of the stratosphere, where the ozone layer exists which is located between 10 and 50 kilometers above the earths surface. The troposphere is the lowest layer of the Earth's atmosphere. It extends from the ground up to a variable height of approximately 14 kilometers above sea level. Ozone is least concentrated in the ground layer (or planetary boundary layer) of the troposphere. Ground level or tropospheric ozone is created by chemical reactions between oxides of nitrogen (NOx gases) and volatile organic compounds (VOCs). The combination of these chemicals in the presence of sunlight form ozone. Its concentration increases as height above sea level increases, with a maximum concentration at the tropopause. About 90% of total ozone in the atmosphere is in the stratosphere, and 10% is in the troposphere. Although tropospheric ozone is less concentrated than stratospheric ozone, it is of concern because of its health effects. Ozone in the troposphere is considered a greenhouse gas, and may contribute to global warming. Photochemical and chemical reactions involving ozone drive many of the chemical processes that occur in the troposphere by day and by night. At abnormally high concentrations (the largest source being emissions from combustion of fossil fuels), it is a pollutant, and a constituent of smog. Its levels have increased significantly since the industrial revolution, as NOx gasses & VOCs are some of the byproducts of combustion. With more heat and sunlight in the summer months, more ozone is formed which is why regions often experience higher levels of pollution in the summer months. Although the same molecule, ground level ozone can be harmful to our health, unlike stratospheric ozone that protects the earth from excess UV radiation. Photolysis of ozone occurs at wavelengths below approximately 310–320 nanometres. This reaction initiates the chain of chemical reactions that remove carbon monoxide, methane, and other hydrocarbons from the atmosphere via oxidation. Therefore, the concentration of tropospheric ozone affects how long these compounds remain in the air. If the oxidation of carbon monoxide or methane occur in the presence of nitrogen monoxide (NO), this chain of reactions has a net product of ozone added to the system.
  • 2.4K
  • 24 Nov 2022
Topic Review
History of Life
The history of life on Earth traces the processes by which living and fossil organisms evolved, from the earliest emergence of life to the present day. Earth formed about 4.5 billion years ago (abbreviated as Ga, for gigaannum) and evidence suggests that life emerged prior to 3.7 Ga. Although there is some evidence of life as early as 4.1 to 4.28 Ga, it remains controversial due to the possible non-biological formation of the purported fossils. The similarities among all known present-day species indicate that they have diverged through the process of evolution from a common ancestor. Only a very small percentage of species have been identified: one estimate claims that Earth may have 1 trillion species. However, only 1.75–1.8 million have been named and 1.8 million documented in a central database. These currently living species represent less than one percent of all species that have ever lived on Earth. The earliest evidence of life comes from biogenic carbon signatures and stromatolite fossils discovered in 3.7 billion-year-old metasedimentary rocks from western Greenland. In 2015, possible "remains of biotic life" were found in 4.1 billion-year-old rocks in Western Australia. In March 2017, putative evidence of possibly the oldest forms of life on Earth was reported in the form of fossilized microorganisms discovered in hydrothermal vent precipitates in the Nuvvuagittuq Belt of Quebec, Canada, that may have lived as early as 4.28 billion years ago, not long after the oceans formed 4.4 billion years ago, and not long after the formation of the Earth 4.54 billion years ago. Microbial mats of coexisting bacteria and archaea were the dominant form of life in the early Archean Epoch and many of the major steps in early evolution are thought to have taken place in this environment. The evolution of photosynthesis, around 3.5 Ga, eventually led to a buildup of its waste product, oxygen, in the atmosphere, leading to the great oxygenation event, beginning around 2.4 Ga. The earliest evidence of eukaryotes (complex cells with organelles) dates from 1.85 Ga, and while they may have been present earlier, their diversification accelerated when they started using oxygen in their metabolism. Later, around 1.7 Ga, multicellular organisms began to appear, with differentiated cells performing specialised functions. Sexual reproduction, which involves the fusion of male and female reproductive cells (gametes) to create a zygote in a process called fertilization is, in contrast to asexual reproduction, the primary method of reproduction for the vast majority of macroscopic organisms, including almost all eukaryotes (which includes animals and plants). However the origin and evolution of sexual reproduction remain a puzzle for biologists though it did evolve from a common ancestor that was a single celled eukaryotic species. Bilateria, animals having a left and a right side that are mirror images of each other, appeared by 555 Ma (million years ago). Algae-like multicellular land plants are dated back even to about 1 billion years ago, although evidence suggests that microorganisms formed the earliest terrestrial ecosystems, at least 2.7 Ga. Microorganisms are thought to have paved the way for the inception of land plants in the Ordovician period. Land plants were so successful that they are thought to have contributed to the Late Devonian extinction event. (The long causal chain implied seems to involve the success of early tree archaeopteris (1) drew down CO2 levels, leading to global cooling and lowered sea levels, (2) roots of archeopteris fostered soil development which increased rock weathering, and the subsequent nutrient run-off may have triggered algal blooms resulting in anoxic events which caused marine-life die-offs. Marine species were the primary victims of the Late Devonian extinction.) Ediacara biota appear during the Ediacaran period, while vertebrates, along with most other modern phyla originated about 525 Ma during the Cambrian explosion. During the Permian period, synapsids, including the ancestors of mammals, dominated the land, but most of this group became extinct in the Permian–Triassic extinction event 252 Ma. During the recovery from this catastrophe, archosaurs became the most abundant land vertebrates; one archosaur group, the dinosaurs, dominated the Jurassic and Cretaceous periods. After the Cretaceous–Paleogene extinction event 66 Ma killed off the non-avian dinosaurs, mammals increased rapidly in size and diversity. Such mass extinctions may have accelerated evolution by providing opportunities for new groups of organisms to diversify.
  • 2.4K
  • 18 Oct 2022
Topic Review
Applications of Chitin in Agricultural Industries
Chitin can play a key role in the agricultural industry due to its water-soluble nature. The different applications of chitin in the agricultural industry have been well documented with even more novel processes still in development. Some of those would include, but are not limited to, being used as fertilizers, soil conditioning agents, plant disease control agents, antitranspirants, fruit retardants, and seed coatings. Furthermore, chitin can increase the natural defense mechanisms in plants by upregulating plant growth regulators, growth stimulants, anti-stress agents, and elicitors for the production of secondary metabolites.
  • 2.3K
  • 24 Dec 2021
  • Page
  • of
  • 271
Featured Entry Collections
>>

Featured Books

>>
Encyclopedia of Social Sciences
Encyclopedia of COVID-19
Encyclopedia of Fungi
Encyclopedia of Digital Society, Industry 5.0 and Smart City
Video Production Service
Feedback