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Topic Review
List of Aircraft (P)
This is a list of aircraft in alphabetical order beginning with 'P'.
  • 5.9K
  • 19 Oct 2022
Topic Review
Surface Passivation
Passivation, in physical chemistry and engineering, refers to coating a material so it becomes "passive", that is, less readily affected or corroded by the environment. Passivation involves creation of an outer layer of shield material that is applied as a microcoating, created by chemical reaction with the base material, or allowed to build by spontaneous oxidation in the air. As a technique, passivation is the use of a light coat of a protective material, such as metal oxide, to create a shield against corrosion. Passivation of silicon is used during fabrication of microelectronic devices. In electrochemical treatment of water, passivation reduces the effectiveness of the treatment by increasing the circuit resistance, and active measures are typically used to overcome this effect, the most common being polarity reversal, which results in limited rejection of the fouling layer.[clarification needed] When exposed to air, many metals naturally form a hard, relatively inert surface layer, usually an oxide (termed the "native oxide layer") or a nitride, that serves as a passivation layer. In the case of silver, the dark tarnish is a passivation layer of silver sulfide formed from reaction with environmental hydrogen sulfide. (In contrast, metals such as iron oxidize readily to form a rough porous coating of rust that adheres loosely and sloughs off readily, allowing further oxidation.) The passivation layer of oxide markedly slows further oxidation and corrosion in room-temperature air for aluminium, beryllium, chromium, zinc, titanium, and silicon (a metalloid). The inert surface layer formed by reaction with air has a thickness of about 1.5 nm for silicon, 1–10 nm for beryllium, and 1 nm initially for titanium, growing to 25 nm after several years. Similarly, for aluminium, it grows to about 5 nm after several years. Surface passivation refers to a common semiconductor device fabrication process critical to modern electronics. It is the process by which a semiconductor surface such as silicon is rendered inert, and does not change semiconductor properties when it interacts with air or other materials. This is typically achieved by thermal oxidation, in which the material is heated and exposed to oxygen. In a silicon semiconductor, this process allows electricity to reliably penetrate to the conducting silicon below the surface, and to overcome the surface states that prevent electricity from reaching the semiconducting layer. Surface passivation by thermal oxidation is one of the key features of silicon technology, and is dominant in microelectronics. The surface passivation process was developed by Mohamed M. Atalla at Bell Labs in the late 1950s. It is commonly used to manufacture MOSFETs (metal-oxide-semiconductor field-effect transistors) and silicon integrated circuit chips (with the planar process), and is critical to the semiconductor industry. Surface passivation is also critical to solar cell and carbon quantum dot technologies.
  • 5.9K
  • 22 Nov 2022
Topic Review
Old Azeri Language
Old Azeri (Persian: آذری‌ باستان‎), also referred to as Azeri or Azari (Persian: آذری‎ Āḏarī [ɑːzæri]), is the extinct Iranian language that was once spoken in Azerbaijan (historic Azerbaijan, also known as Iranian Azerbaijan) before the Turkification of the Azeris. Some linguists believe the southern Tati varieties of Iranian Azerbaijan around Takestan such as the Harzandi and Karingani dialects to be remnants of Azeri. In addition, Old Azeri is known to have strong affinities with Talysh. Azeri was the dominant language in Azerbaijan before it was replaced by Azerbaijani, which is a Turkic language.
  • 5.9K
  • 30 Nov 2022
Topic Review
Landsat 8 and Landsat 9
With the launch of Landsat 9 in September 2021, an optimal opportunity for in-flight cross-calibration occurred when Landsat 9 flew underneath Landsat 8 while being moved into its final orbit. Since the two instruments host nearly identical imaging systems, the underfly event offered ideal cross-calibration conditions. Using the underfly imagery collected by the instruments to estimate cross-calibration parameters for Landsat 9 for a calibration update scheduled at the end of the on-orbit initial verification (OIV) period was studied. Three types of uncertainty were considered: geometric, spectral, and angular (bidirectional reflectance distribution function—BRDF). Differences caused by geometric uncertainty were found to be negligible for this application. 
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  • 01 Jun 2022
Topic Review
Chloramine
Chloramines are derivatives of ammonia by substitution of one, two or three hydrogen atoms with chlorine atoms: monochloramine (chloroamine, NH2Cl), dichloramine (NHCl2), and nitrogen trichloride (NCl3). The term chloramine also refers to a family of organic compounds with the formulas R2NCl and RNCl2 (where R is an organic group). Monochloramine (chloramine) is an inorganic compound with the formula NH2Cl. It is an unstable colorless liquid at its melting point of −66 °C (−87 °F), but it is usually handled as a dilute aqueous solution, in which form it is sometimes used as a disinfectant. Chloramine is too unstable to have its boiling point measured. It is listed as a tumorigen and mutagen. The wholesale cost in the developing world is about 13.80 to 18.41 U.S. dollars per 500 grams.
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  • 16 Nov 2022
Topic Review
Lifestyle (Sociology)
Lifestyle is the interests, opinions, behaviours, and behavioural orientations of an individual, group, or culture. The term was introduced by Austrian psychologist Alfred Adler in his 1929 book, The Case of Miss R., with the meaning of "a person's basic character as established early in childhood". The broader sense of lifestyle as a "way or style of living" has been documented since 1961. Lifestyle is a combination of determining intangible or tangible factors. Tangible factors relate specifically to demographic variables, i.e. an individual's demographic profile, whereas intangible factors concern the psychological aspects of an individual such as personal values, preferences, and outlooks. A rural environment has different lifestyles compared to an urban metropolis. Location is important even within an urban scope. The nature of the neighborhood in which a person resides affects the set of lifestyles available to that person due to differences between various neighborhoods' degrees of affluence and proximity to natural and cultural environments. For example, in areas near the sea, a surf culture or lifestyle can often be present.
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  • 13 Oct 2022
Topic Review
Nanodiamonds Synthesis Techniques
The "state-of-the-art" of the nanodiamonds synthesis techniques is reviewed with emphasis on the more recent one involving pulsed laser ablation. Production of NV centers inside the nanodiamonds and  post-production cleaning processes to remove residual graphite layers are also described.
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  • 27 Oct 2020
Topic Review
History of Purgatory
The idea of purgatory has roots that date back into antiquity. A sort of proto-purgatory called the "celestial Hades" appears in the writings of Plato and Heraclides Ponticus and in many other pagan writers. This concept is distinguished from the Hades of the underworld described in the works of Homer and Hesiod. In contrast, the celestial Hades was understood as an intermediary place where souls spent an undetermined time after death before either moving on to a higher level of existence or being reincarnated back on earth. Its exact location varied from author to author. Heraclides of Pontus thought it was in the Milky Way; the Academicians, the Stoics, Cicero, Virgil, Plutarch, the Hermetical writings situated it between the Moon and the Earth or around the Moon; while Numenius and the Latin Neoplatonists thought it was located between the sphere of the fixed stars and the Earth. Perhaps under the influence of Hellenistic thought, we find another intermediate state entering Jewish religious thought in the last centuries B.C.E. In Maccabees we find the practice of prayer for the dead with a view to their after life purification a practice accepted by some Christians. The same practice appears in other traditions, such as the medieval Chinese Buddhist practice of making offerings on behalf of the dead, who are said to suffer numerous trials. Among other reasons, Catholic belief in purgatory is based on the practice of prayer for the dead. Descriptions and doctrine regarding purgatory developed over the centuries. Those who believe in purgatory interpret extra-biblical passages such as 2 Maccabees 12:41-46 (not accepted as Scripture by Protestants but recognized by Orthodox and Catholics), and biblical passages such as 2 Timothy 1:18, Matthew 12:32, Luke 16:19-16:26, Luke 23:43, 1 Corinthians 3:11-3:15 and Hebrews 12:29 as support for prayer for the dead, an active interim state for the dead prior to the resurrection, and purifying flames after death. The first Christians looked forward to the imminent return of Christ and did not develop detailed beliefs about the interim state. Gradually, Christians, especially in the West, took an interest in circumstances of the interim state between one's death and the future resurrection. Christians both East and West prayed for the dead in this interim state, although theologians in the East refrained from defining it. Augustine of Hippo distinguished between the purifying fire that saves and eternal consuming fire for the unrepentant. Gregory the Great established a connection between earthly penance and purification after death. All Soul's Day, established in the 10th century, turned popular attention to the condition of departed souls. The idea of Purgatory as a physical place (like heaven and hell) was "born" in the late 11th century. Medieval theologians concluded that the purgatorial punishments consisted of material fire. The Western formulation of purgatory proved to be a sticking point in the Great Schism between East and West. The Catholic Church believes that the living can help those whose purification from their sins is not yet completed not only by praying for them but also by gaining indulgences for them as an act of intercession. The later Middle Ages saw the growth of considerable abuses, such as the unrestricted sale of indulgences by professional "pardoners" sent to collect contributions to projects such as the rebuilding of St. Peter's Basilica in Rome. These abuses were one of the factors that led to the Protestant Reformation. Most Protestants rejected the idea of purgatory, as never clearly mentioned in Luther's canon of the Bible, which excludes the Deuterocanonical books. Modern Catholic theologians have softened the punitive aspects of purgatory and stress instead the willingness of the dead to undergo purification as preparation for the happiness of heaven The English Anglican scholar John Henry Newman argued, in a book that he wrote before becoming Catholic, that the essence of the doctrine on purgatory is locatable in ancient tradition, and that the core consistency of such beliefs are evidence that Christianity was "originally given to us from heaven".
  • 5.9K
  • 14 Nov 2022
Topic Review
ATtiny Microcontroller Comparison Chart
ATtiny (also known as TinyAVR) are a subfamily of the popular 8-bit AVR microcontrollers, which typically has fewer features, fewer I/O pins, and less memory than other AVR series chips. The first members of this family were released in 1999 by Atmel (later acquired by Microchip Technology in 2016).
  • 5.9K
  • 03 Nov 2022
Topic Review
Compartmental Models in Epidemiology
Compartmental models are a very general modelling technique. They are often applied to the mathematical modelling of infectious diseases. The population is assigned to compartments with labels – for example, S, I, or R, (Susceptible, Infectious, or Recovered). People may progress between compartments. The order of the labels usually shows the flow patterns between the compartments; for example SEIS means susceptible, exposed, infectious, then susceptible again. The origin of such models is the early 20th century, with important works being that of Ross in 1916, Ross and Hudson in 1917, Kermack and McKendrick in 1927 and Kendall in 1956 The models are most often run with ordinary differential equations (which are deterministic), but can also be used with a stochastic (random) framework, which is more realistic but much more complicated to analyze. Models try to predict things such as how a disease spreads, or the total number infected, or the duration of an epidemic, and to estimate various epidemiological parameters such as the reproductive number. Such models can show how different public health interventions may affect the outcome of the epidemic, e.g., what the most efficient technique is for issuing a limited number of vaccines in a given population.
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  • 02 Dec 2022
Topic Review
Amygdala
The amygdala is one of the areas in the brain involved in the development of PTSD as the starting point for the process of activation of the hypothalamo–pituitary axis and the cascade of physiological responses to acute stress. An appropriate response to acute stress is a vital adaptive mechanism, but its prolongation causes various biopsychosocial (previously, psychosomatic) disorders. Chronic stress leads to higher expression of CRH/CRF in the CE and BLA, which has an anxiogenic effect.
  • 5.9K
  • 13 Jul 2021
Topic Review
Convergent Evolution
Convergent evolution is the independent evolution of similar features in species of different periods or epochs in time. Convergent evolution creates analogous structures that have similar form or function but were not present in the last common ancestor of those groups. The cladistic term for the same phenomenon is homoplasy. The recurrent evolution of flight is a classic example, as flying insects, birds, pterosaurs, and bats have independently evolved the useful capacity of flight. Functionally similar features that have arisen through convergent evolution are analogous, whereas homologous structures or traits have a common origin but can have dissimilar functions. Bird, bat, and pterosaur wings are analogous structures, but their forelimbs are homologous, sharing an ancestral state despite serving different functions. The opposite of convergence is divergent evolution, where related species evolve different traits. Convergent evolution is similar to parallel evolution, which occurs when two independent species evolve in the same direction and thus independently acquire similar characteristics; for instance, gliding frogs have evolved in parallel from multiple types of tree frog. Many instances of convergent evolution are known in plants, including the repeated development of C4 photosynthesis, seed dispersal by fleshy fruits adapted to be eaten by animals, and carnivory.
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  • 24 Oct 2022
Topic Review
Permanent Magnet Linear Synchronous Motor
In high-end testing and manufacturing equipment, a trend exists whereby the traditional servo feed system with a ball screw and rotary motor will gradually be replaced by a direct drive system. The precision motion system driven by a permanent magnet linear synchronous motor (PMLSM) offers several advantages, including high speed, high acceleration, and high positioning accuracy. However, the operating precision of the feed device will be affected by the PMLSM robustness to nonlinear and uncertain disturbances, such as cogging force, friction, thermal effects, residual vibration, and load disturbance.
  • 5.9K
  • 29 Apr 2021
Topic Review
Temporal Envelope and Fine Structure
Temporal envelope (ENV) and temporal fine structure (TFS) are changes in the amplitude and frequency of sound perceived by humans over time. These temporal changes are responsible for several aspects of auditory perception, including loudness, pitch and timbre perception and spatial hearing. Complex sounds such as speech or music are decomposed by the peripheral auditory system of humans into narrow frequency bands. The resulting narrow-band signals convey information at different time scales ranging from less than one millisecond to hundreds of milliseconds. A dichotomy between slow "temporal envelope" cues and faster "temporal fine structure" cues has been proposed to study several aspects of auditory perception (e.g., loudness, pitch and timbre perception, auditory scene analysis, sound localization) at two distinct time scales in each frequency band. Over the last decades, a wealth of psychophysical, electrophysiological and computational studies based on this envelope/fine-structure dichotomy have examined the role of these temporal cues in sound identification and communication, how these temporal cues are processed by the peripheral and central auditory system, and the effects of aging and cochlear damage on temporal auditory processing. Although the envelope/fine-structure dichotomy has been debated and questions remain as to how temporal fine structure cues are actually encoded in the auditory system, these studies have led to a range of applications in various fields including speech and audio processing, clinical audiology and rehabilitation of sensorineural hearing loss via hearing aids or cochlear implants.
  • 5.9K
  • 12 Oct 2022
Topic Review
Football Goalkeeper Injuries
Knowledge and research about football goalkeeper (GK) injuries are scarce, which prevents the development of evidence-based injury prevention programs. Fortunately, progress is evident in injury prevention strategies in outfield football players. However, a GK fulfills a unique role, and an injured GK can substantially impact a team. Thus, there is a need to clarify and summarize current knowledge concerning football goalkeeper pain and injuries.
  • 5.9K
  • 31 May 2021
Topic Review Peer Reviewed
Frederick II of Hohenstaufen (1208–1250)
Frederick II of Hohenstaufen, King of Sicily (1208–1250). Frederick II of Hohenstaufen was the second king of the Swabian dynasty to sit on the throne of Sicily. He was crowned in 1198, but, in consideration of his young age, he only ruled independently from 1208 to 1250 (the year of his death). He not only held the title of King of Sicily but also was the King of Germany (or of the Romans), the King of Jerusalem, and, above all, Emperor of the Holy Roman Empire. His most relevant and innovative iconographic representations were in Southern Italy. For this reason, we focus on the images in this geographical context. In particular, we have nine official (that is, those commissioned directly by him or his entourage) representations of him: the bull (in three main versions), the seal (in three main versions), five coins (four denari and one augustale), the statue of the Capua Gate, and the lost image of the imperial palace in Naples.
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  • 13 Apr 2022
Topic Review
Environmental Protection and Sustainable Development in Madagascar
Located on the East coast of Africa, Madagascar is the world’s fourth-biggest island; Madagascar is host to 12,000 species of vascular plants (96% endemic). Over 90% of all its wildlife is found nowhere else on earth, and 5% of all of the earth’s biodiversity is found in Madagascar. A place where environmental degradation problems have created severe erosion and water quality problems. Despite its biological and cultural diversity, Madagascar is among the poorest countries in the world, with approximately 78% of the population living in extreme poverty with an average income of less than USD 2 per day, and more than three-quarters of the population in rural areas engaged in natural resources dependent livelihood activities. 
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  • 07 Dec 2022
Topic Review
N1 (Rocket)
The N1/L3 (from Ракета-носитель Raketa-nositel', "Carrier Rocket"; Cyrillic: Н1) was a super heavy-lift launch vehicle intended to deliver payloads beyond low Earth orbit. The N1 was the Soviet counterpart to the US Saturn V and was intended to enable crewed travel to the Moon and beyond, with studies beginning as early as 1959. Its first stage, Block A, remains the most powerful rocket stage ever flown. However, all four first stages flown failed mid-flight because a lack of static test firings meant that plumbing issues and other adverse characteristics with the large cluster of thirty engines and its complex fuel and oxidizer feeder system were not revealed earlier in development. The N1-L3 version was designed to compete with the United States Apollo program to land a person on the Moon, using a similar lunar orbit rendezvous method. The basic N1 launch vehicle had three stages, which were to carry the L3 lunar payload into low Earth orbit with two cosmonauts. The L3 contained one stage for trans-lunar injection; another stage used for mid-course corrections, lunar orbit insertion, and the first part of the descent to the lunar surface; a single-pilot LK Lander spacecraft; and a two-pilot Soyuz 7K-LOK lunar orbital spacecraft for return to Earth. The N1-L3 was underfunded and rushed, starting development in October 1965, almost four years after the Saturn V. The project was badly derailed by the death of its chief designer Sergei Korolev in 1966. Each of the four attempts to launch an N1 failed, with the second attempt resulting in the vehicle crashing back onto its launch pad shortly after liftoff. The N1 program was suspended in 1974, and officially canceled in 1976. All details of the Soviet crewed lunar programs were kept secret until the USSR was nearing collapse in 1989.
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  • 30 Nov 2022
Topic Review
Emirate of Ras Al Khaimah
Ras Al Khaimah (RAK) (Arabic: رَأْس ٱلْخَيْمَة; IPA: [raʔs lˈxajma]), also spelled as Ras al Khaimah or Ras al-Khaimah, is one of the seven emirates that make up the United Arab Emirates (UAE). The city of Ras Al Khaimah, sometimes simply abbreviated to RAK City, is the capital of the emirate and home to most of the emirate's residents. It is linked to the medieval trading port of Julfar.[lower-alpha 1] Its name in English means "top of the tent". The emirate borders Oman's exclave of Musandam, and occupies part of the same peninsula. It covers an area of 2,486 km2 (960 sq mi) and has 64 km (40 mi) of beach coastline. As of 2015, the emirate had a population of about 345,000, of which about 31% were Emirati citizens. RAK city has two main areas - the Old Town and Nakheel - on either side of a creek that is home to mangroves and is framed by the North-Western Hajar Mountains. The emirate also consists of several villages and new gated residential developments, such as Al Hamra Village and Mina Al Arab. The emirate is served by Ras Al Khaimah International Airport. Its geography consists of a northern part (where Ras Al Khaimah City and most towns are situated) and a large southerly inland exclave (near the Dubai exclave of Hatta), and a few small islands in the Persian Gulf. Ras Al Khaimah has the most fertile soil in the country, due to a larger share of rainfall and underground water streams from the Hajar.
  • 5.9K
  • 10 Oct 2022
Topic Review
Areca nut
Scientific name:  Areca catechu L. Family: Arecaceae Centre of origin: South-East Asia Common name: kamuhu, adakka, adike, Pinang palm, Betel palm, Areca palm, Supari, Kaunga The generic name is derived from the common name used by the people of the Malabar Coast in southwestern India.
  • 5.9K
  • 16 Feb 2022
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