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Topic Review

SpaceX Dragon 2

The SpaceX Dragon 2 is a class of reusable spacecraft developed and manufactured by American aerospace manufacturer SpaceX as the successor to the Dragon cargo spacecraft. It has two variants: Crew Dragon, a human-rated capsule capable of ferrying up to seven astronauts, and Cargo Dragon, an updated replacement for the original Dragon spacecraft. The spacecraft launches atop a Falcon 9 Block 5 rocket and returns to Earth via an ocean splashdown. Unlike its predecessor, the spacecraft can dock itself to the ISS instead of being berthed. Crew Dragon is equipped with an integrated launch escape system (LES) capable of accelerating the vehicle away from the rocket in an emergency at 11.8 m/s2, accomplished by using a set of four side-mounted thruster pods with two SuperDraco engines each. The spacecraft features redesigned solar arrays and a modified outer mold line compared to the original Dragon, and possess new flight computers and avionics. As of March 2020, four Dragon 2 spacecraft have been manufactured (not counting structural test articles that were never airborne). Crew Dragon serves as one of two spacecraft that is expected to transport crews to and from the International Space Station (ISS) under NASA's Commercial Crew Program, the other being the Boeing CST-100 Starliner. It is also expected to be used in flights by American space tourism company Space Adventures and to shuttle tourists to and from Axiom Space's planned space station. Crew Dragon's first non-piloted test flight occurred in March 2019, and its first crewed flight – with astronauts Robert Behnken and Douglas Hurley – occurred in May 2020. This test flight marked the first time a private company launched a crewed orbital spacecraft. Cargo Dragon is expected to supply cargo to the ISS under a Commercial Resupply Services-2 contract with NASA, along with Northrop Grumman Innovation Systems' Cygnus spacecraft and Sierra Nevada Corporation's Dream Chaser spacecraft. The first flight of the Cargo Dragon is planned to launch in October 2020.

8.1K
26 Oct 2022

Topic Review

Left-Wing Market Anarchism

Left-wing market anarchism is a strand of free-market anarchism and an individualist anarchist, left-libertarian and libertarian socialist political philosophy and market socialist economic theory stressing the value of radically free markets, termed freed markets to distinguish them from the common conception which these libertarians believe to be riddled with statist and capitalist privileges. Proponents of this approach distinguish themselves from right-libertarians and strongly affirm the classical liberal ideas of self-ownership and free markets while maintaining that taken to their logical conclusions these ideas support anti-capitalist, anti-corporatist, anti-hierarchical and pro-labor positions in economics; anti-imperialism in foreign policy; and thoroughly radical views regarding socio-cultural issues. Key theorists in this area include contemporary scholars such as Kevin Carson, Gary Chartier, Charles W. Johnson, Roderick T. Long, Chris Matthew Sciabarra, Ryan Neugebauer, Sheldon Richman and Brad Spangler. The genealogy of left-wing market anarchism, sometimes labeled market-oriented or free-market left-libertarianism, overlaps to a significant degree with that of Steiner–Vallentyne left-libertarianism as the roots of that tradition are sketched in the book The Origins of Left-Libertarianism. Carson–Long-style left-libertarianism is rooted in 19th-century mutualism and in the work of figures such as Thomas Hodgskin, French Liberal School thinkers such as Gustave de Molinari and American individualist anarchists such as Benjamin Tucker and Lysander Spooner, among others. Several left-wing market anarchists who come from the left-Rothbardian school or tradition cite Murray Rothbard's homestead principle with approval to support worker cooperatives. While with notable exceptions libertarians in the United States after the heyday of individualist anarchism tended to ally with the political right, relationships between such libertarians and the New Left thrived in the 1960s, laying the groundwork for modern left-wing market anarchism. Left-wing market anarchism identifies with left-libertarianism, a position which names several related yet distinct approaches to politics, society, culture and political and social theory, stressing both individual freedom and social justice. Unlike right-libertarians, left-libertarians believe that neither claiming nor mixing one's labor with natural resources is enough to generate full private property rights and maintain that all natural resources such as land, oil and gold ought to be held in some egalitarian manner, either unowned or owned collectively. Those left-libertarians who support private property do so under different property norms and theories, or under the condition that recompense is offered to the local or global community.

8.1K
30 Nov 2022

Topic Review

Green Monopropellants

Green propellants are usually defined as low-hazard, low-toxicity, environmentally friendly propellants that are considered safe during various phases of spacecraft development, launch, and operations. Such propellants provide safe handling and storability when compared to conventional toxic propellants such as hydrazine and its derivatives that require special handling protocols and adhering to strict safety measurements that, in addition to others, include using Self-Contained Atmospheric Protective Ensemble (SCAPE) suits. Due to their favorable characteristics, green propellants demonstrate higher commercial value by being able to cut costs related to transportation, storage, handling, and further reduces ground operations time. Recently, a more specified definition has been noted by Mayer et al. (2018) [3], based on the Acute Toxicity Classification (ATC) by the Global Harmonized System of classification and labeling of chemicals (GHS) [6], which denotes that propellants possessing ATC levels of three and safer are considered as green propellants. ATC levels are typically categorized on a 1:5 scale where level one denotes the most toxic class and level five is considered the least toxic class. Moreover, a controversial topic arises when referring to some modern green propellants, whether to address them by the term “monopropellants” or by more specific terms including (premixed propellants, fuel blends, or mixtures). Monopropellants are fundamentally defined as propellants consisting of chemical compounds (for example N2H4), which release energy through exothermic chemical decomposition. Since the evolution of liquid gun propellants based on HAN compound and other nitrate salts aqueous solutions, the term “monopropellants” was used to describe such premixed formulations. As widely used in literature and industry, some modern green propellants, for instance the Energetic Ionic Liquids (EILs), are undoubtedly classified and described as “monopropellants.” Basically, it can be interpreted from the previous that a "green monopropellant" may be defined as: "A low-hazard, low-toxicity, and safe-to handle propellant that is stored in a single tank and is able to decompose from its storage state by the help of a catalyst or other ignition method, such as thermal or electric ignition, can be considered a “green monopropellant” as long as it does not require another separately stored propellant for decomposition."

8.1K
28 Sep 2021

Topic Review

Red Supergiant Star

Red supergiants (RSGs) are stars with a supergiant luminosity class (Yerkes class I) of spectral type K or M. They are the largest stars in the universe in terms of volume, although they are not the most massive or luminous. Betelgeuse and Antares are the brightest and best known red supergiants (RSGs), indeed the only first magnitude red supergiant stars.

8.1K
18 Nov 2022

Topic Review

Video Game Live Streaming

Video game live streaming is a kind of real-time video social media that integrates traditional broadcasting and online gaming. Real-time, sociability and suspense are the main features of video game live streaming. Video game live streaming can meet user demands in social integration, personal integration, tension release, affection, and cognition. In order to have a more comprehensive understanding of video game live streaming, the following text summarizes the background from the live streaming industry and research status. After that, the definition, users, features and community classification of video game live streaming are introduced in detail.

8.1K
02 Nov 2020

Topic Review

List of Folk Heroes

This is a list of folk heroes.

8.1K
17 Oct 2022

Topic Review

Factors Affecting Hair Health

Hair health is associated with personal distress and psychological well-being. Even though hair loss (alopecia) does not affect humans’ biological health, it affects an individual’s social well-being. So, treatment for hair problems and improving hair health are obligatory.

8.1K
07 Feb 2023

Topic Review

Foreign Influences on Pompeii

Several non-native societies had an influence on Ancient Pompeian culture. Historians’ interpretation of artefacts, preserved by the Eruption of Mount Vesuvius in 79, identify that such foreign influences came largely from Ancient Greece and Hellenistic cultures of the Eastern Mediterranean, including Egypt. Greek influences were transmitted to Pompeii via the Greek colonies in Magna Graecia (Southern Italy), which were formed in the 8th century BC. Hellenistic influences originated from Roman commerce, and later conquest of Egypt from the 2nd century BC. Specifically, these cultures contributed to the development of Pompeii’s art, architecture and religious spheres. For instance, Greek influences can be identified in the Alexander Mosaic, horse-shoe shaped theatres and Pompeii’s adoption of the Greek pantheon of gods. Examples of Egyptian influences can be found in the Nile Mosaic, garden art in the Villa of Julia Felix and the Cult of Isis.

8.1K
11 Oct 2022

Topic Review

Hauran (Arabic: حوران / ALA-LC: Ḥawrān), also spelled Hawran, Houran and Horan, known to the Ancient Greeks and Romans as Auranitis, is a volcanic plateau, a geographic area and a people located in southwestern Syria and extending into the northwestern corner of Jordan, it’s known to be the birth place of the dabke dance which is the most popular dance in all of the Levant.

8.1K
10 Nov 2022

Topic Review

Social control refers to the mechanisms, norms, and practices through which societies regulate individual behavior and maintain order. It encompasses both formal institutions such as laws and regulations, as well as informal social norms and expectations. Social control mechanisms serve to reinforce conformity to societal norms, values, and expectations, while also deterring deviant behavior through sanctions and rewards.

8.1K
26 Jan 2024

Topic Review

Frogs in Culture

Frogs play a variety of roles in culture, appearing in folklore and fairy tales such as the Brothers Grimm story of The Frog Prince. In ancient Egypt and Mesopotamia, frogs symbolized fertility, while in classical antiquity, the Greeks and Romans associated frogs with fertility, harmony, and licentiousness. Frogs are the subjects of fables attributed to Aesop, of proverbs in various cultures, and of art. Frog characters such as Kermit the frog and Pepe the Frog feature in popular culture. They are eaten in some parts of the world including France. In Australia, a fondant dessert is known as frog cake.

8.1K
27 Nov 2022

Topic Review

Silicon photonics has drawn increasing attention since recent decades and is promising to act as a key technology for future daily applications due to its various merits including ultra-low cost, high integration density owing to the high refractive index of silicon and compatibility with current semiconductor fabrication process. Optical interconnects is an important issue in silicon photonic integrated circuits to transmit light and fiber-to-chip optical interconnects is vital in application scenarios like data centers and optical transmission systems. There are mainly two categories of fiber-to-chip optical coupling, that is off-plane coupling and in-plane coupling. Grating couplers work under the former category while edge couplers function as in-plane coupling. In this paper, we mainly focus on edge couplers in silicon photonic integrated circuits. We deliver an introduction to the research background, operation mechanism and design principles of silicon photonic edge couplers. The state-of-the-art of edge couplers is reviewed according to different configurations as to the device structure, identifying the performance, fabrication feasibility and applications. In addition, a brief comparison between edge couplers and grating couplers is conducted. Packaging issue is also discussed and several prospective techniques for further improvements of edge couplers are proposed.

8.1K
27 Oct 2020

Topic Review

Application of RAP in Asphalt Concrete Pavements

The use of recycled asphalt pavement (RAP) materials in asphalt concrete pavements (ACP) brings significant cost and environmental benefits. In practice, however, the amount of RAP readily available far exceeds the amount being utilized in ACPs, which still leaves the problem of excess RAP in the environment partially solved. Additionally, ACPs containing RAP materials (i.e., RAP-ACPs) can still be landfilled after they have reached the end of their useful life, which may restore the original environmental waste problem. To address these, researchers have demonstrated different ways to maximize the application of RAP in ACPs. Among them, the use of RAP in pavement preventive maintenance (PPM) treatments and the repeated recycling of RAP-ACPs (i.e., RnAP) are specifically discussed herein. It is envisaged that, by promoting these two practices, the application and benefits of RAP can be further maximized to improve sustainability.

8.1K
25 Nov 2022

Topic Review

The PSA XUD is a Diesel engine designed and built by PSA - Peugeot and Citroën. It is an Indirect injection (IDI) engine, that uses a version of the Ricardo Consulting Engineers Ricardo Comet V prechamber cylinder head design. The engine comes in 1.8 L (1,769 cc) N/A, 1.8 Turbo, 1.9 L (1,905 cc) N/A, Turbo, 2.1 12 valve N/A and Turbo and was the predecessor to the HDI range of engines. Early HDi Engines were a PSA design, later 16 valve engines were jointly developed with Ford.

8.1K
28 Oct 2022

Topic Review

Social Complexity

Social complexity refers to the intricate and interconnected nature of social systems, where various elements such as institutions, individuals, and cultural dynamics interact in non-linear and unpredictable ways. It involves the recognition that social phenomena often exhibit emergent properties that cannot be fully understood by analyzing individual components in isolation, emphasizing the need for interdisciplinary approaches to grasp the complexity of social structures and behaviors.

8.1K
26 Jan 2024

Topic Review

Collective Consciousness

Collective consciousness, a concept introduced by sociologist Emile Durkheim, refers to the shared beliefs, values, norms, and symbols that unite members of a society and shape their collective identity. It represents the collective understanding of social reality, guiding individuals' behaviors, interactions, and perceptions within a community. Collective consciousness fosters social cohesion, solidarity, and integration by providing a common framework for interpreting the world and coordinating social action.

8.1K
08 Feb 2024

Topic Review

Traditional Fermented Foods in Korea

Fermented foods are loved and enjoyed worldwide and are part of a tradition in several regions of the world. Koreans have traditionally had a healthy diet since people in this region have followed a fermented-foods diet for at least 5000 years. Fermented-product footprints are evolving beyond boundaries and taking the lead in the world of food. Fermented foods, such as jang (fermented soybean products), kimchi (fermented vegetables), jeotgal (fermented fish), and vinegar (liquor with grain and fruit fermentation), are prominent fermented foods in the Korean culture.

8.1K
09 Dec 2022

Topic Review

Matthews Correlation Coefficient

The Matthews correlation coefficient (MCC) or phi coefficient is used in machine learning as a measure of the quality of binary (two-class) classifications, introduced by biochemist Brian W. Matthews in 1975. The MCC is defined identically to Pearson's phi coefficient, introduced by Karl Pearson, also known as the Yule phi coefficient from its introduction by Udny Yule in 1912. Despite these antecedents which predate Matthews's use by several decades, the term MCC is widely used in the field of bioinformatics and machine learning. The coefficient takes into account true and false positives and negatives and is generally regarded as a balanced measure which can be used even if the classes are of very different sizes. The MCC is in essence a correlation coefficient between the observed and predicted binary classifications; it returns a value between −1 and +1. A coefficient of +1 represents a perfect prediction, 0 no better than random prediction and −1 indicates total disagreement between prediction and observation. However, if MCC equals neither −1, 0, or +1, it is not a reliable indicator of how similar a predictor is to random guessing because MCC is dependent on the dataset. MCC is closely related to the chi-square statistic for a 2×2 contingency table where n is the total number of observations. While there is no perfect way of describing the confusion matrix of true and false positives and negatives by a single number, the Matthews correlation coefficient is generally regarded as being one of the best such measures. Other measures, such as the proportion of correct predictions (also termed accuracy), are not useful when the two classes are of very different sizes. For example, assigning every object to the larger set achieves a high proportion of correct predictions, but is not generally a useful classification. The MCC can be calculated directly from the confusion matrix using the formula: In this equation, TP is the number of true positives, TN the number of true negatives, FP the number of false positives and FN the number of false negatives. If any of the four sums in the denominator is zero, the denominator can be arbitrarily set to one; this results in a Matthews correlation coefficient of zero, which can be shown to be the correct limiting value. The MCC can be calculated with the formula: using the positive predictive value, the true positive rate, the true negative rate, the negative predictive value, the false discovery rate, the false negative rate, the false positive rate, and the false omission rate. The original formula as given by Matthews was: This is equal to the formula given above. As a correlation coefficient, the Matthews correlation coefficient is the geometric mean of the regression coefficients of the problem and its dual. The component regression coefficients of the Matthews correlation coefficient are Markedness (Δp) and Youden's J statistic (Informedness or Δp'). Markedness and Informedness correspond to different directions of information flow and generalize Youden's J statistic, the [math]\displaystyle{ \delta }[/math]p statistics and (as their geometric mean) the Matthews Correlation Coefficient to more than two classes. Some scientists claim the Matthews correlation coefficient to be the most informative single score to establish the quality of a binary classifier prediction in a confusion matrix context.

8.0K
18 Nov 2022

Topic Review

Triceratops (/traɪˈsɛrəˌtɒps/ trahy-ser-uh-tops; lit. three-horned face) is a genus of herbivorous chasmosaurine ceratopsid dinosaur that first appeared during the late Maastrichtian stage of the Late Cretaceous period, about 68 million years ago in what is now North America. It is one of the last-known non-avian dinosaur genera, and became extinct in the Cretaceous–Paleogene extinction event 66 million years ago. The name Triceratops, which literally means 'three-horned face', is derived from the Greek words trí- (τρί-) meaning 'three', kéras (κέρας) meaning 'horn', and ṓps (ὤψ) meaning 'face'. Bearing a large bony frill, three horns on the skull, and a large four-legged body, exhibiting convergent evolution with rhinoceroses and bovines, Triceratops is one of the most recognizable of all dinosaurs and the most well-known ceratopsid. It was also one of the largest, up to 8–9 metres (26–30 ft) long and 5–9 metric tons (5.5–9.9 short tons) in body mass. It shared the landscape with and was most likely preyed upon by Tyrannosaurus, though it is less certain that two adults did battle in the fanciful manner often depicted in museum displays and popular images. The functions of the frills and three distinctive facial horns on its head have long inspired debate. Traditionally, these have been viewed as defensive weapons against predators. More recent interpretations find it probable that these features were primarily used in species identification, courtship, and dominance display, much like the antlers and horns of modern ungulates. Triceratops was traditionally placed within the "short-frilled" ceratopsids, but modern cladistic studies show it to be a member of the Chasmosaurinae which usually have long frills. Two species, T. horridus and T. prorsus, are considered valid today, from the seventeen species that have ever been named. Research published in 2010 concluded that the contemporaneous Torosaurus, a ceratopsid long regarded as a separate genus, represents Triceratops in its mature form. This view has been disputed; further data is needed to settle the debate. Triceratops has been documented by numerous remains collected since the genus was first described in 1889 by American paleontologist Othniel Charles Marsh. Specimens representing life stages from hatchling to adult have been found. As the archetypal ceratopsid, Triceratops is one of the most popular dinosaurs, and has been featured in film, postal stamps, and many other types of media.

8.0K
01 Nov 2022

Topic Review

The Processor Technology VDM-1, for Video Display Module, was the first video card for S-100 bus computers. Created in 1975, it allows an S-100 machine to produce its own display, and when paired with a keyboard and their 3P+S card, it eliminates the need for a separate video terminal. Using a 7 x 9 dot matrix and ASCII characters, it produces a 64-column by 16-row text display. The VDM-1 is a complex card and was soon replaced by an increasing number of similar products from other companies. An early competitor was the Solid State Music VB-1, which offers an identical display from a much simpler card. Later cards using LSI chips have enough room to include the keyboard controller as well.

8.0K
08 Oct 2022

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