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Topic Review
Kya (Unit)
A year is the orbital period of a planetary body, for example, the Earth, moving in its orbit around the Sun. Due to the Earth's axial tilt, the course of a year sees the passing of the seasons, marked by change in weather, the hours of daylight, and, consequently, vegetation and soil fertility. In temperate and subpolar regions around the planet, four seasons are generally recognized: spring, summer, autumn and winter. In tropical and subtropical regions, several geographical sectors do not present defined seasons; but in the seasonal tropics, the annual wet and dry seasons are recognized and tracked. A calendar year is an approximation of the number of days of the Earth's orbital period, as counted in a given calendar. The Gregorian calendar, or modern calendar, presents its calendar year to be either a common year of 365 days or a leap year of 366 days, as do the Julian calendars; see below. For the Gregorian calendar, the average length of the calendar year (the mean year) across the complete leap cycle of 400 years is 365.2425 days. The ISO standard ISO 80000-3, Annex C, supports the symbol a (for Latin annus) to represent a year of either 365 or 366 days. In English, the abbreviations y and yr are commonly used. In astronomy, the Julian year is a unit of time; it is defined as 365.25 days of exactly 86,400 seconds (SI base unit), totalling exactly 31,557,600 seconds in the Julian astronomical year. The word year is also used for periods loosely associated with, but not identical to, the calendar or astronomical year, such as the seasonal year, the fiscal year, the academic year, etc. Similarly, year can mean the orbital period of any planet; for example, a Martian year and a Venusian year are examples of the time a planet takes to transit one complete orbit. The term can also be used in reference to any long period or cycle, such as the Great Year.
  • 3.1K
  • 14 Nov 2022
Topic Review
Polyenes
Polyenes were, after griseofulvin, the first fungal-specific antibiotics on the market and ever since, more than 200 polyene antifungals have been discovered, of which amphotericin B, nystatin and natamycin are most commonly used in antifungal therapy .
  • 3.1K
  • 12 Jan 2021
Topic Review
Species Problem
The species problem is the set of questions that arises when biologists attempt to define what a species is. Such a definition is called a species concept; there are at least 26 recognized species concepts. A species concept that works well for sexually reproducing organisms such as birds is useless for species that reproduce asexually, such as bacteria. The scientific study of the species problem has been called microtaxonomy. One common, but sometimes difficult, question is how best to decide which species an organism belongs to, because reproductively isolated groups may not be readily recognizable, and cryptic species may be present. There is a continuum from reproductive isolation with no interbreeding, to panmixis, unlimited interbreeding. Populations can move forward or backwards along this continuum, at any point meeting the criteria for one or another species concept, and failing others. Many of the debates on species touch on philosophical issues, such as nominalism and realism, and on issues of language and cognition. The current meaning of the phrase "species problem" is quite different from what Charles Darwin and others meant by it during the 19th and early 20th centuries. For Darwin, the species problem was the question of how new species arose. Darwin was however one of the first people to question how well-defined species are, given that they constantly change.
  • 3.1K
  • 02 Nov 2022
Topic Review
List of Peaks by Prominence
This is a list of mountain peaks ordered by their topographic prominence.
  • 3.1K
  • 18 Oct 2022
Topic Review
Lipid Peroxidation
Lipid peroxidation refers to the process in which lipids are oxidized to generate lipid peroxides as a primary product. Cellular lipid peroxidation can occur through different reactions, but they can be categorized into enzyme and non-enzyme dependent reactions. The primary substrates in lipid peroxidation reactions are polyunsaturated lipids since carbon-carbon double bonds are susceptible to reactive oxygen species, such as the hydroxyl radical (HO•), which is a key radical that participates in peroxidation reactions.
  • 3.1K
  • 14 Dec 2020
Topic Review
Single Cell Protein
Single cell protein (SCP) is the first product of the fermentation process and has proven to be a good protein alternative. Food competition is becoming more intense as the world’s population continues to grow. Soon, SCP may be able to compensate for a protein deficit. Various global businesses are focusing on SCP production, and the scope of its application is expanding as time and knowledge increases.
  • 3.1K
  • 30 Aug 2021
Topic Review
Electrocommunication
Electrocommunication is the communication method used by weakly-electric fish. Weakly-electric fish are a group of animals that utilize a communicating channel that is "invisible" to most other animals: electric signaling. Electric fish communicate by generating an electric field that a second individual receives with its electroreceptors. The fish interprets the message using the signal's frequencies, waveforms, delay, etc. The best studied species are two freshwater lineages- the African Mormyridae and the South American Gymnotiformes. While weakly-electric fish are the only group that have been identified to carry out both generation and reception of electric fields, other species either generate signals or receive them, but not both. Animals that either generate or receive electric fields are found only in wet or aquatic environments due to water's relatively low electrical resistance, compared to other substances (e.g. air). So far, communication between electric fish has been identified mainly to serve the purpose of conveying information such as: species courtship and biological sex motivational status (e.g. attack warning, submission, etc.) environmental conditions
  • 3.1K
  • 31 Oct 2022
Topic Review
Hongdu L-15
The Hongdu L-15 Falcon (猎鹰) is a supersonic advanced training and light combat aircraft being developed by Nanchang-based Hongdu Aviation Industry Corporation (HAIC) to meet the Chinese People's Liberation Army Air Force (PLAAF) and People's Liberation Army Naval Air Force (PLANAF) lead-in fighter trainer (LIFT) requirements, as well as next-generation training and light combat needs for foreign customers.
  • 3.1K
  • 28 Nov 2022
Topic Review
The Epididymis
The epididymis is a convoluted, crescent-shaped structure that connects the testis to the vas deferens and has four main anatomical regions each with unique characteristics and functions: the initial segment, caput (head), corpus (body) and cauda (tail).
  • 3.1K
  • 05 Nov 2020
Topic Review
Microneedles
Microneedles (MNs) represent micron-sized structures, consisting of a variety of materials, that have been recently emerged as physical enhances for a painless and safe transdermal delivery of drugs through the skin.
  • 3.1K
  • 02 Dec 2020
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