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Topic Review

Principle of Least Action

The principle of least action – or, more accurately, the principle of stationary action – is a variational principle that, when applied to the action of a mechanical system, can be used to obtain the equations of motion for that system. It was historically called "least" because its solution requires finding the path of motion in space that has the least value. The principle can be used to derive Newtonian, Lagrangian and Hamiltonian equations of motion, and even general relativity (see Einstein–Hilbert action). In relativity, a different action must be minimized or maximized. The classical mechanics and electromagnetic expressions are a consequence of quantum mechanics. The stationary action method helped in the development of quantum mechanics. In 1933, the physicist Paul Dirac demonstrated how this principle can be used in quantum calculations by discerning the quantum mechanical underpinning of the principle in the quantum interference of amplitudes. Subsequently Julian Schwinger and Richard Feynman independently applied this principle in quantum electrodynamics. The principle remains central in modern physics and mathematics, being applied in thermodynamics, fluid mechanics, the theory of relativity, quantum mechanics, particle physics, and string theory and is a focus of modern mathematical investigation in Morse theory. Maupertuis' principle and Hamilton's principle exemplify the principle of stationary action. The action principle is preceded by earlier ideas in optics. In Ancient Greece , Euclid wrote in his Catoptrica that, for the path of light reflecting from a mirror, the angle of incidence equals the angle of reflection. Hero of Alexandria later showed that this path was the shortest length and least time. Scholars often credit Pierre Louis Maupertuis for formulating the principle of least action because he wrote about it in 1744 and 1746. However, Leonhard Euler discussed the principle in 1744,[ and evidence shows that Gottfried Leibniz preceded both by 39 years.

4.8K
29 Sep 2022

Topic Review

Integrated Blockchain-Cloud Architecture for Healthcare

Blockchain is a disruptive technology for shaping the next era of a healthcare system striving for efficient and effective patient care. This is thanks to its peer-to-peer, secure, and transparent characteristics. On the other hand, cloud computing made its way into the healthcare system thanks to its elasticity and cost-efficiency nature. However, cloud-based systems fail to provide a secured and private patient-centric cohesive view to multiple healthcare stakeholders. In this situation, blockchain provides solutions to address security and privacy concerns of the cloud because of its decentralization feature combined with data security and privacy, while cloud provides solutions to the blockchain scalability and efficiency challenges. Therefore a novel paradigm of blockchain-cloud integration (BcC) emerges for the domain of healthcare.

4.8K
14 Sep 2021

Topic Review

A myocyte (also known as a muscle cell) is the type of cell found in some types of muscle tissue. Myocytes develop from myoblasts to form muscles in a process known as myogenesis. There are two specialized forms of myocytes with distinct properties: cardiac, and smooth muscle cells. On the other hand, skeletal muscles are formed by morphological units referred to as muscle fibers. Cardiomyocytes are the cells that form the chambers of the heart, and have a single central nucleus. Skeletal muscle fibers help support and move the body and are called syncytia – multinucleated structures formed by fusion of individual myoblasts during embryonic development. Smooth muscle cells control involuntary movements such as the peristalsis contractions in the oesophagus and stomach.

4.8K
25 Oct 2022

Topic Review

Origins of Judaism

The origins of Judaism lie in the Bronze Age amidst polytheistic ancient Semitic religions, specifically Canaanite religion, co-existing with a syncretization with elements of Babylonian religion and of the worship of Yahweh reflected in the early prophetic books of the Hebrew Bible. During the Iron Age I, the Israelite religion became distinct from other Canaanite religions due to the unique monolatristic (proto-monotheistic) worship of Yahweh. During the Babylonian captivity of the 6th and 5th centuries BCE (Iron Age II), certain circles within the exiled Judahites in Babylon refined pre-existing ideas about monotheism, election, divine law and Covenant into a strict monotheistic theology which came to dominate the former Kingdom of Judah in the following centuries. From the 5th century BCE until 70 CE, Israelite religion developed into the various theological schools of Second Temple Judaism, besides Hellenistic Judaism in the diaspora. Second Temple eschatology was significantly influenced by Zoroastrianism. The text of the Hebrew Bible was redacted into its extant form in this period and possibly also canonized as well. Rabbinic Judaism developed during Late Antiquity, during the 3rd to 6th centuries CE; the Masoretic Text of the Hebrew Bible and the Talmud were compiled in this period. The oldest manuscripts of the Masoretic tradition come from the 10th and 11th centuries CE; in the form of the Aleppo Codex of the later portions of the 10th century CE and the Leningrad Codex dated to 1008–1009 CE. Due largely to censoring and the burning of manuscripts in medieval Europe the oldest existing manuscripts of various rabbinical works are quite late. The oldest surviving complete manuscript copy of the Babylonian Talmud is dated to 1342 CE.

4.8K
10 Nov 2022

Topic Review

Recognition Memory

Recognition memory, a subcategory of declarative memory, is the ability to recognize previously encountered events, objects, or people. When the previously experienced event is reexperienced, this environmental content is matched to stored memory representations, eliciting matching signals. As first established by psychology experiments in the 1970s, recognition memory for pictures is quite remarkable: humans can remember thousands of images at high accuracy after seeing each only once and only for a few seconds. Recognition memory can be subdivided into two component processes: recollection and familiarity, sometimes referred to as "remembering" and "knowing", respectively. Recollection is the retrieval of details associated with the previously experienced event. In contrast, familiarity is the feeling that the event was previously experienced, without recollection. Thus, the fundamental distinction between the two processes is that recollection is a slow, controlled search process, whereas familiarity is a fast, automatic process. Mandler's "Butcher-on-the-bus" example: Imagine taking a seat on a crowded bus. You look to your left and notice a man. Immediately, you are overcome with this sense that you've seen this man before, but you cannot remember who he is. This automatically elicited feeling is familiarity. While trying to remember who this man is, you begin retrieving specific details about your previous encounter. For example, you might remember that this man handed you a fine chop of meat in the grocery store. Or perhaps you remember him wearing an apron. This search process is recollection.

4.8K
29 Nov 2022

Topic Review

Control rods are used in nuclear reactors to control the rate of fission of the nuclear fuel – uranium or plutonium. Their compositions include chemical elements such as boron, cadmium, silver, hafnium, or indium, that are capable of absorbing many neutrons without themselves fissioning. These elements have different neutron capture cross sections for neutrons of various energies. Boiling water reactors (BWR), pressurized water reactors (PWR), and heavy-water reactors (HWR) operate with thermal neutrons, while breeder reactors operate with fast neutrons. Each reactor design can use different control rod materials based on the energy spectrum of its neutrons.

4.8K
11 Nov 2022

Topic Review

Pathogenesis and Clinical Presentation of Pott’s Disease

Tuberculosis (TB) prevalence is increasing in developed nations and continuing to cause significant mortality in low- and middle-income countries. As a result of the uptick in cases, there also exists an increased prevalence of extrapulmonary TB. TB is caused by Mycobacterium tuberculosis (M. tb). When M. tb disseminates to the vertebral column, it is called Pott’s disease or spinal TB. The frequency, symptoms, and severity of the disease range by the location of the spine and the region of the affected vertebrae.

4.8K
16 Feb 2023

Topic Review Video

Plastic Waste Governance in Bangladesh

Plastic, an offer of modernity, is presenting a massive threat in altered forms, to our health and environment. Plastic does not only pollute the surface environment, fresh water, and marine ecosystems, but toxic elements released from plastics also percolate down the surface and contaminate groundwater, which we often use as ‘safe’ drinking water. This probable future risk is deeply rooted in the entire governance infrastructure of plastic waste which could potentially lead to contamination of groundwater. A recent study finds 81% of tap water samples collected worldwide contained plastic pollutants, which means that annually we may be ingesting between 3000 and 4000 microparticles of plastic from tap water.

4.8K
04 Mar 2022

Topic Review

Deep Eutectic Solvents

Deep eutectic solvents (DESs), were introduced in 2001 as an alternative to ILs. These showed a stronger ecofriendly profile, with easier and cheaper production, while having similar properties. DESs contain large, asymmetrical ions that have low lattice energy and, thus, low melting points. They are often acquired by the complexation of a quaternary ammonium salt with a metal salt or hydrogen bond donor (HBD). The charge delocalization occurring through hydrogen bonding between, for instance a halide ion and the hydrogen-donor moiety, is responsible for the decrease in the melting point of the mixture, in relation to the melting points of the individual components. Since 2001, many scientists around the globe pursed the utilization of DESs and published a variety of studies. The use of DESs in analytical microextraction techniques is on the rise, due to the many benefits they provide, such as lower cost and easier synthesis than ILs and an environmentally friendly profile, because of the low toxicity reported, although they need further investigation. To this day, the number of HBAs and HBDs is quite limited, so more studies ought to be carried out to present a plethora of DESs available for use. Moreover, DESs are not commercially available yet, substantially affecting and further limiting their usage for routine analyses in industrial or certified laboratories. The extraordinary high relative recoveries, selectivity, low LODs and decent repeatability they offer, render them appropriate for the determination and quantification of lots of compounds in either simple or complex matrices. As seen, most applications regard liquid phase microextractions rather than solid phase microextractions, because of their liquid nature, as it is simpler to use them as supporting solid adsorbents. The fact that the sample preparation of complicated matrices is of high interest makes them ideal for the research. Hopefully, DESs will be available for purchase in the foreseeable future and will replace organic solvents in some analytical methods commonly used nowadays, while more studies are carried out about their properties. Our aim in this review will be towards the use of DESs in analytical extraction and microextraction techniques, while briefly presenting some frequently used DESs, their synthesis methods and their properties. The ever-increasing use of deep eutectic solvents (DES) in microextraction techniques will be discussed, focusing on the reasons needed to replace conventional extraction techniques with greener approaches that follow the principles of green analytical chemistry.

4.8K
10 Feb 2021

Topic Review

The Spemann Organizer

In 1924, to understand the processes involved in developmental biology, Spemann and Mangold transplanted a blastopore lip between different ectodermal regions of amphibian embryos. The transplanted dorsal tissue differentiated mostly into a notochord, while the ectoderm of the host dorsal tissue that was sitting above the transplanted region (blastopore lip) was induced and differentiated to form a Siamese twin containing dorsal tissues such as somites and a neural plate, which would form the central nervous system, forming the bulk of a second axis. The major findings were that the transplant had altered the fate of the overlying cells and that the neural folds were built from recipient cells and not donor cells. Spemann and Mangold discovered the organizing center in the dorsal blastopore lip of amphibians. This center consists of a cluster of cells in the developing embryo that have the ability to interact and instruct morphogenesis in the surrounding cells during gastrulation. When transplanted to the ventral side of the embryo, the center will induce the formation of a secondary axis, promoting the development of the central nervous system, organs, and tissues, as well as the formation of the main body axis. Spemann and Mangold found the first evidence of the organizing center, thereafter called the “Spemann organizer”, and its major role in the development of vertebrates. This discovery also introduced the concept of induction in embryonic development, which refers to the method used by specific cells to affect the fate of other embryonic cells. A major milestone had been achieved for developmental biology.

4.8K
11 Nov 2021

Topic Review

Influence of Technologies on Sustainable Tourism

This study’s objective is to provide an overview on literature state-of-the-art related to sustainable tourism and technological innovations, offering insights for further advancing this domain. We employ a bibliometric analysis and a comprehensive review of 139 articles, collected from Web of Science and Scopus databases, for the purpose of: (i) exploring and discussing the most relevant contributions in the publication network: (ii) highlighting key issues and emerging topics; (iii) uncovering open questions for the future. Our findings reveal contradictory views on the risks and benefits of technology adoption. Artificial intelligence, internet of things, circular economy, big data, augmented and virtual reality emerge as major trends. Five work streams are identified and described, leading to a broader perspective on how technology can shape the future of sustainable tourism. Relevant theoretical and managerial implications are derived. Finally, a research agenda is proposed as guidance for future studies addressing the outcomes of digital disruption on sustainable tourism.

4.8K
29 Nov 2021

Topic Review

Pride is an emotional state deriving positive affect from the perceived value of a person or thing with which the subject has an intimate connection. It may be inwardly or outwardly directed. With a negative connotation pride refers to a foolishly and irrationally corrupt sense of one's personal value, status or accomplishments, used synonymously with hubris. With a positive connotation, pride refers to a content sense of attachment toward one's own or another's choices and actions, or toward a whole group of people, and is a product of praise, independent self-reflection, and a fulfilled feeling of belonging. Philosophers and social psychologists have noted that pride is a complex secondary emotion which requires the development of a sense of self and the mastery of relevant conceptual distinctions (e.g. that pride is distinct from happiness and joy) through language-based interaction with others. Some social psychologists identify the nonverbal expression of pride as a means of sending a functional, automatically perceived signal of high social status. In contrast, pride could also be defined as a lowly disagreement with the truth. One definition of pride comes from St. Augustine: "the love of one's own excellence". A similar definition comes from Meher Baba: "Pride is the specific feeling through which egoism manifests." Pride is sometimes viewed as corrupt or as a vice, sometimes as proper or as a virtue. While some philosophers such as Aristotle (and George Bernard Shaw) consider pride (but not hubris) a profound virtue, some world religions consider pride's fraudulent form a sin, such as is expressed in Proverbs 11:2 of the Hebrew Bible. In Judaism, pride is called the root of all evil. When viewed as a virtue, pride in one's abilities is known as virtuous pride, greatness of soul or magnanimity, but when viewed as a vice it is often known to be self-idolatry, sadistic contempt, vanity or vainglory. Pride can also manifest itself as a high opinion of one's nation (national pride), ethnicity (ethnic pride) and sexual identity.

4.8K
02 Nov 2022

Topic Review

A dugout canoe or simply dugout is a boat made from a hollowed tree. Other names for this type of boat are logboat and monoxylon. Monoxylon (μονόξυλον) (pl: monoxyla) is Greek -- mono- (single) + ξύλον xylon (tree) -- and is mostly used in classic Greek texts. In German, they are called Einbaum ("one tree" in English). Some, but not all, pirogues are also constructed in this manner. Dugouts are the oldest boat type archaeologists have found, dating back about 8,000 years to the Neolithic Stone Age. This is probably because they are made of massive pieces of wood, which tend to preserve better than, e.g., bark canoes. Along with bark canoe and hide kayak, dugout boats were also used by indigenous peoples of the Americas.

4.8K
25 Oct 2022

Topic Review

Economic Disparity in South Korea

Economic disparity in South Korea is the extent by which income, most commonly measured by household or individual, is distributed in an uneven manner in South Korea . According to data during the 2010s, low-income earners[lower-alpha 1] make up to 40% of South Korea's entire labour force. Conversely, the highest income earners[lower-alpha 2] make up only 1–1.3% of the labour force. In general, 98.7% of South Koreans make less than annually. According to 2015 data, more than 63% of workers make less than Template:KRWConvert annually. Many South Koreans especially those of the younger generation feel that they are not benefiting during periods of economic growth, and have criticized the increasingly difficult socioeconomic situation and class stratification in the country, dubbing it as "Hell Joseon" (Korean: 헬조선). They have also described themselves as being a part of the Sampo generation, whereby they have given up on courtship, marriage, and having kids due to the high costs of living and unemployment, and consequently the N-po generation. Moreover, much of the country's income inequality can be attributed to the dominance of chaebols (Korean: 재벌; lit. "rich family"), which has also been seen by many South Koreans as highly corrupt and influential in the political system. Its dominance is also likely to last and engenders the risk of slowing down the transformation of the South Korean economy for the benefit of future generations. The country also has the highest levels of poverty among the elderly in the developed world. In 2018, about half of the country's elderly lived in poverty, three times the OECD average, with many of them homeless. As a result, South Korea regularly claims the highest suicide rate in the OECD and the wider developed world.

4.8K
04 Nov 2022

Topic Review

Meo (Telecommunication Service)

MEO is a mobile and fixed telecommunications service and brand from Altice Portugal (formerly Portugal Telecom), managed by MEO - Serviços de Comunicações e Multimédia. The service was piloted in Lisbon in 2006 and was later extended to Porto and Castelo Branco.

4.8K
03 Nov 2022

Topic Review

Socialist Revolutionary Party

The Socialist Revolutionary Party, or Party of Socialist-Revolutionaries (the SRs or Esers; Russian: Партия социалистов-революционеров, ПСР or эсеры, esery) was a major political party in late Imperial Russia and early Soviet Russia. The SRs were agrarian socialists who obtained a mass following in the years preceding the Russian Revolution by endorsing the overthrow of the Tsar and the redistribution of land to the peasantry. In the elections following the 1905 Revolution, the SRs obtained the majority of the few seats alloted to the peasantry. Following the 1907 coup, the SRs would boycott all subsequent Dumas until the fall of the Tsar in the February Revolution. Controversially, the party leadership would endorse the Russian Provisional Government and participated in multiple coalitions with liberal and moderate socialist parties, while an increasingly vocal minority rejected the Provisional Government's authority and began to align with the Bolsheviks. The pro-government and pro-Soviet factions could not be reconciled and split over the course of the summer of 1917 into the Right and Left SRs respectively. The Left SRs supported the October Revolution and formed a coalition government with the Bolsheviks from November 1917 to July 1918, while the Right SRs denounced what they saw as an illegal coup and boycotted the Congress of Soviets. The SRs obtained a plurality in elections to the Russian Constituent Assembly, with most of the defunct party's seats going to the Right. Citing outdated voter rolls which did not acknowledge the party split and the Assembly's conflicts with the Congress of Soviets, the Bolshevik-Left SR government would dissolve the Constituent Assembly in January 1918. The Left SRs would eventually leave the coalition in July 1918 in protest to the signing of the Treaty of Brest-Litovsk. An abortive uprising by the leadership of the Left SRs resulted in the immediate arrest of most of the party's members. The majority of Left SRs, who opposed the uprising were gradually freed and allowed to keep their government positions, but were unable to organize a new central organ and gradually splintered into multiple pro-Bolshevik parties, all of which would eventually join the Communists by 1921. The Right SRs supported the Whites during the Russian Civil War but were increasingly marginalized by the movement's anti-socialist leadership and ultimately purged. A small Right SR remnant continued to operate in exile from 1923 to 1940 as a member of the Labour and Socialist International.

4.8K
04 Nov 2022

Topic Review Peer Reviewed

Peter IV of Aragon (1336–1387)

Peter IV king of Aragón (1336–1387). He was the seventh king of the Crown of Aragon, and father of Juan I (1387–1396) and Martín I (1396–1410), the last members of the dynasty to take the throne. When Martín died, the Trastámara branch occupied the throne of the kingdom. Peter IV was dazzling in his ability to use art as a tool of authority and sovereignty. With the aim of exalting the dynasty, he patronised various enterprises, among the most important of which was the abbey of Santa Maria de Poblet, which he intended to be a burial place for himself and his successors, a wish that was fulfilled, without exception, down to Juan II, the predecessor of the Catholic Monarchs. A perfectionist and zealot, he endowed important religious events with profound political significance, and promoted works of great symbolism such as the genealogy of the new saló del tinell, or the ordinacions de la casa i cort, to which he added an appendix establishing how the kings of Aragon were to be crowned.

4.8K
13 Apr 2022

Topic Review

Individualist Anarchism in France

Individualist anarchism in France has developed a line of thought that starts from the pioneering activism and writings of Pierre-Joseph Proudhon and Anselme Bellegarrigue in the mid-19th century. In the early 20th century, it produced publications such as L'En-Dehors, L'Anarchie and around its principles it found writers and activists such as Émile Armand, Han Ryner, Henri Zisly, Albert Libertad and Zo d'Axa. In the post-war years, there appeared the publication L'Unique and activist writers such as Charles-Auguste Bontemps. In contemporary times, it has found a new expression in the writings of the prolific philosopher Michel Onfray. Individualist anarchism is a group of several traditions of thought within the anarchist movement that emphasize the individual and his or her will over external determinants such as groups, society, traditions and ideological systems. French individualist anarchism was characterized by an eclectic set of currents of thought and practices which included anti-militarism, freelove, freethought, illegalism and naturism. While most American individualist anarchists advocates mutualism, a libertarian socialist from of market socialism, or a free-market socialist form of classical economics, European individualist anarchists are pluralists who advocate anarchism without adjectives and synthesis anarchism, ranging from anarcho-communist to mutualist economic types.

4.8K
11 Oct 2022

Topic Review

Ultra-Heat Treatment on Milk Proteins

Milk contains approximately 3.5% by weight protein, which is a highly complex system. This milk protein is usually divided into two main fractions based on their solubility nature. Casein proteins are about 75% to 80% of the total protein in the milk and precipitate at pH 4.6 at 20 °C, while 20% of the protein remains in the serum.

4.8K
07 Oct 2021

Topic Review

The Avesta (/əˈvɛstə/) is the primary collection of religious texts of Zoroastrianism, composed in the Avestan language. The Avesta texts fall into several different categories, arranged either by dialect, or by usage. The principal text in the liturgical group is the Yasna, which takes its name from the Yasna ceremony, Zoroastrianism's primary act of worship, and at which the Yasna text is recited. The most important portion of the Yasna texts are the five Gathas, consisting of seventeen hymns attributed to Zoroaster himself. These hymns, together with five other short Old Avestan texts that are also part of the Yasna, are in the Old (or 'Gathic') Avestan language. The remainder of the Yasna's texts are in Younger Avestan, which is not only from a later stage of the language, but also from a different geographic region. Extensions to the Yasna ceremony include the texts of the Vendidad and the Visperad. The Visperad extensions consist mainly of additional invocations of the divinities (yazatas), while the Vendidad is a mixed collection of prose texts mostly dealing with purity laws. Even today, the Vendidad is the only liturgical text that is not recited entirely from memory. Some of the materials of the extended Yasna are from the Yashts, which are hymns to the individual yazatas. Unlike the Yasna, Visperad and Vendidad, the Yashts and the other lesser texts of the Avesta are no longer used liturgically in high rituals. Aside from the Yashts, these other lesser texts include the Nyayesh texts, the Gah texts, the Siroza, and various other fragments. Together, these lesser texts are conventionally called Khordeh Avesta or "Little Avesta" texts. When the first Khordeh Avesta editions were printed in the 19th century, these texts (together with some non-Avestan language prayers) became a book of common prayer for lay people. The term Avesta is from the 9th/10th-century works of Zoroastrian tradition in which the word appears as Zoroastrian Middle Persian abestāg, Book Pahlavi ʾp(y)stʾkʼ. In that context, abestāg texts are portrayed as received knowledge, and are distinguished from the exegetical commentaries (the zand) thereof. The literal meaning of the word abestāg is uncertain; it is generally acknowledged to be a learned borrowing from Avestan, but none of the suggested etymologies have been universally accepted. The widely repeated derivation from *upa-stavaka is from Christian Bartholomae (Altiranisches Wörterbuch, 1904), who interpreted abestāg as a descendant of a hypothetical reconstructed Old Iranian word for "praise-song" (Bartholomae: Lobgesang); but this word is not actually attested in any text.

4.8K
21 Nov 2022

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