Search | Encyclopedia MDPI

Your browser does not fully support modern features. Please upgrade for a smoother experience.

Subject:

Sort by:

Most Viewed Latest Alphabetical (A-Z) Alphabetical (Z-A)

Filter:

All Topic Review Biography Peer Reviewed Entry Video Entry

Topic Review

Refractive Index and Extinction Coefficient of Thin-Film Materials

The derivation of the Forouhi–Bloomer dispersion equations is based on obtaining an expression for k as a function of photon energy, symbolically written as k(E), starting from first principles quantum mechanics and solid state physics. An expression for n as a function of photon energy, symbolically written as n(E), is then determined from the expression for k(E) in accordance to the Kramers–Kronig relations which states that n(E) is the Hilbert Transform of k(E). The Forouhi–Bloomer dispersion equations for n(E) and k(E) of amorphous materials are given as: [math]\displaystyle{ k(E) = \frac{A(E-E_g)^2}{E^2-BE+C} \ }[/math] [math]\displaystyle{ n(E) = n(\infty)+\frac{(B_0 E + C_0 )}{E^2-BE+C} \ }[/math] The five parameters A, B, C, Eg, and n(∞) each have physical significance. Eg is the optical energy band gap of the material. A, B, and C depend on the band structure of the material. They are positive constants such that 4C-B2 > 0. Finally, n(∞), a constant greater than unity, represents the value of n at E = ∞. The parameters B0 and C0 in the equation for n(E) are not independent parameters, but depend on A, B, C, and Eg. They are given by: [math]\displaystyle{ B_0 = \frac{A}{Q} \ \left (\frac{-B^2}{2} \ + E_gB - {E_g}^2 + C \right) }[/math] [math]\displaystyle{ C_0 = \frac{A}{Q} \ \left [({E_g}^2 + C) \frac{B}{2} \ - 2E_g C \right] }[/math] where [math]\displaystyle{ Q = \frac{1}{2} \ (4C - B^2 )^{\frac{1}{2}} }[/math] Thus, for amorphous materials, a total of five parameters are sufficient to fully describe the dependence of both n and k on photon energy, E. For crystalline materials which have multiple peaks in their n and k spectra, the Forouhi–Bloomer dispersion equations can be extended as follows: [math]\displaystyle{ k(E) = \sum_{i=1}^q \left [\frac{A_i(E - E_{g_i})^2}{E^2-B_iE+C_i} \right] }[/math] [math]\displaystyle{ n(E) = n(\infty)+\sum_{i=1}^q \left [\frac{B_{0_i}E+C_{0_i}}{E^2-B_iE+C_i} \right] }[/math] The number of terms in each sum, q, is equal to the number of peaks in the n and k spectra of the material. Every term in the sum has its own values of the parameters A, B, C, Eg, as well as its own values of B0 and C0. Analogous to the amorphous case, the terms all have physical significance.

9.2K
31 Oct 2022

Topic Review

History of Zoology (Through 1859)

The history of zoology before Charles Darwin's 1859 theory of evolution traces the organized study of the animal kingdom from ancient to modern times. Although the concept of zoology as a single coherent field arose much later, systematic study of zoology is seen in the works of Aristotle and Galen in the ancient Greco-Roman world. This work was developed in the Middle Ages by Islamic medicine and scholarship, and in turn their work was extended by European scholars such as Albertus Magnus. During the European Renaissance and early modern period, zoological thought was revolutionized in Europe by a renewed interest in empiricism and the discovery of many novel organisms. Prominent in this movement were the anatomist Vesalius and the physiologist William Harvey, who used experimentation and careful observation, and naturalists such as Carl Linnaeus and Buffon who began to classify the diversity of life and the fossil record, as well as the development and behavior of organisms. Microscopy revealed the previously unknown world of microorganisms, laying the groundwork for cell theory. The growing importance of natural theology, partly a response to the rise of mechanical philosophy, encouraged the growth of natural history (although it entrenched the argument from design). Over the 18th and 19th centuries, zoology became increasingly professional scientific disciplines. Explorer-naturalists such as Alexander von Humboldt investigated the interaction between organisms and their environment, and the ways this relationship depends on geography—laying the foundations for biogeography, ecology and ethology. Naturalists began to reject essentialism and consider the importance of extinction and the mutability of species. Cell theory provided a new perspective on the fundamental basis of life. These developments, as well as the results from embryology and paleontology, were synthesized in Charles Darwin's theory of evolution by natural selection. In 1859, Darwin placed the theory of organic evolution on a new footing, by his discovery of a process by which organic evolution can occur, and provided observational evidence that it had done so.

9.2K
21 Apr 2023

Topic Review

Meat extenders are non-meat substances with high protein contents used to partially substitue (or extend) the meat content in meat products. Initially devised to reduce costs (as meat is the most expensive ingredient in meat products) they can become now a useful strategy to develop more sustainable and healthier meat products.

9.2K
28 Aug 2020

Topic Review

Chinese Polearms

The three most common types of Chinese polearms are the ge (戈), qiang (槍), and ji (戟). They are translated into English as dagger-axe, spear, and halberd. Dagger-axes were originally a short slashing weapon with a 0.9 to 1.8 m long shaft, but around the 4th century BC a spearhead was added to the blade, and it became a halberd. The spear is also sometimes called a mao (矛), which is sometimes used to designate polearms with a wavy snake-like spearhead. There was another polearm weapon known as the pi (鈹), translated into English as either sword-staff or long lance, that was used from ancient times until the Han dynasty. It was essentially a short sword attached to a stick. From the Warring States period onward, the length of Chinese polearms varied from around 2.8 m to 5.5 m, however there is no specific designation for a pike in the traditional Chinese lexicon. A very long spear is just called a long spear.

9.2K
13 Oct 2022

Topic Review

Strategies for Employee Retention in Hospitality Industry

Employee retention is contingent on employee satisfaction, which is comprised of four factors: sustainable positive work environment; sustainable growth opportunities; sustainable & effective communication; and sustainable & effective recruitment and selection practices.

9.2K
17 Jun 2022

Topic Review

Laïcité ([la.i.si.te]), literally "secularity", is a French concept of secularism. It discourages religious involvement in government affairs, especially religious influence in the determination of state policies; it also forbids government involvement in religious affairs, and especially prohibits government influence in the determination of religion. Laïcité does not preclude a right to the free exercise of religion. Dictionaries ordinarily translate laïcité as "secularity" or "secularism" (the latter being the political system), although it is sometimes rendered in English as laicity or laicism by its opponents. While the term was first used with this meaning in 1871 in the dispute over the removal of religious teachers and instruction from elementary schools, the word laïcisme dates to 1842. In its strict and official acceptance, it is the principle of separation of church (or religion) and state. Etymologically, laïcité is a noun formed by adding the suffix -ité (English -ity, Latin -itās) to the Latin adjective lāicus, a loanword from the Greek λᾱϊκός (lāïkós "of the people", "layman"), the adjective from λᾱός (lāós "people"). French secularism has a long history. For the last century, the French government policy has been based on the 1905 French law on the Separation of the Churches and the State.

9.2K
04 Nov 2022

Topic Review

Fleischmann–Pons Experiment

The Fleischmann–Pons experiment was an investigation conducted in the 1980s by Martin Fleischmann of the University of Southampton and Stanley Pons of the University of Utah into whether electrolysis of heavy water on the surface of a palladium (Pd) electrode produces physical effects that defy chemical explanation. Of particular interest was evidence of "excess" (i.e. non-chemical) heat extracted from the deuterium fraction of common surface water which, if true, could have delivered the largest economic shock to the global energy industry since the Pennsylvania oil rush. On March 23, 1989, Fleischmann (then one of the world's leading electrochemists) and Pons reported their work via a press release from the University of Utah (who asserted ownership of the technology) claiming that the table-top apparatus had produced anomalous heat (understood as "excess" heat) of a magnitude they asserted would defy explanation except in terms of nuclear processes, which later came to be referred to as "cold fusion". In addition to the results from calorimetry, they further reported measuring small amounts of nuclear reaction byproducts, including neutrons and tritium. The reported results received wide media attention, and raised hopes of a cheap and abundant source of energy. Many scientists tried to replicate the experiment with the few details available. Hopes faded due to the large number of negative replications, the withdrawal of many reported positive replications, the discovery of flaws and sources of experimental error in the original experiment, and finally the discovery that Fleischmann and Pons had not actually detected nuclear reaction byproducts. By late 1989, most scientists considered cold fusion claims dead.

9.2K
26 Oct 2022

Topic Review

Multijet is Fiat Chrysler Automobiles' term for its current common rail direct injection turbodiesel engine range. Most of the Fiat, Alfa Romeo, Lancia range as well as certain Chrysler, RAM Trucks, Jeep and Maserati vehicles are equipped with Multijet engines. Ownership of some Fiat Multijet designs is shared with General Motors as part of a settlement of the failed merger between the two auto conglomerates. GM Powertrain Torino group in Turin, Italy manages their interest in these engines. Some PSA Peugeot Citroën diesel engines are also rebadged JTD units, and vice versa. Fiat's common rail diesel engine is also known as JTD, an initialism of Jet Turbo Diesel.

9.2K
13 Oct 2022

Topic Review

Mercedes-Benz CLA-Class

The Mercedes-Benz CLA class is a series of luxury compact executive cars manufactured by Mercedes-Benz since 2013. The first generation was a four-door sedan based on the platform of the W176 A-Class and W246 B-Class compact cars, marketed as a four-door coupé. In 2015, Mercedes-Benz expanded the CLA family to include the Shooting Brake, a station wagon configuration. As the V177 A-Class sedan took its place as the budget-conscious sedan, the second generation got longer and wider than the W205 C-Class. The CLA is Mercedes-Benz's first front-wheel drive vehicle offered in the North American market. The CLA range is positioned above the A-Class and it is nearly on the level of the C-Class in the Mercedes model range, and models tend to be less practical than the A-Class it is based on. The CLA first went on sale in Europe in April 2013, and was subsequently introduced in the United States in September 2013. Its largest markets are Western Europe and the United States. Global cumulative CLA sales reached 100,000 during its first year, cited as "our best launch in 20 years" by Mercedes-Benz. Worldwide, Mercedes-Benz sold about 750,000 units of the first generation.

9.2K
28 Oct 2022

Topic Review

Thin-Film Dip-Coating Methods

Coating is the way of incorporating a thin coating of material into a substrate by deposition in either the liquid phase (solution) or the solid phase (powder or nanoparticles), dip-Coating is one of them.

9.2K
10 Aug 2022

Topic Review

Feminist Political Economy

Feminist political economy is a concept from feminist material scholarship. It connects market relations with domestic relations. It examines the roles of women, tensions related to women’s paid and unpaid work, how production and reproduction issues affect women, and the interactions at the micro, meso, and macro level contexts within women's lives.

9.2K
28 Oct 2020

Topic Review

Androcentrism is a cultural and societal phenomenon characterized by the prioritization of male perspectives, experiences, and values over those of women. It manifests in various aspects of society, including language, media representation, and institutional practices, perpetuating gender inequalities and reinforcing patriarchal power structures.

9.2K
08 Feb 2024

Topic Review

Teeth Blackening

Teeth blackening or teeth lacquering is a custom of dyeing one's teeth black. It was most predominantly practiced in Southeast Asian and Oceanic cultures, particularly among Austronesian, Austroasiatic, and Kra-Dai-speaking peoples. It was also practiced in Japan prior to the Meiji era, as well as in India. It was also performed among some groups in the Americas, most notably among the Shuar people of northern Peru and Ecuador. Teeth blackening is usually done during puberty. It was primarily done to preserve the teeth into old age, as it prevents tooth decay similar to the mechanism of modern dental sealants. It was seen as a sign of maturity, beauty, and civilization. A common belief is that blackened teeth differentiated humans from animals. Teeth blackening is often done in conjunction with traditions of tooth sharpening and evulsion, as well as other body modification customs like tattoos. Teeth blackening and filing were regarded with fascination and disapproval by early European explorers and colonists. The practice survives in some isolated ethnic groups in Southeast Asia and Oceania but has mostly disappeared after the introduction of Western beauty standards during the colonial era, and continues among many minority groups in China, Pacific Islands and Southeast Asia. It is mainly prevalent in older women, though the practice is still carried on by some younger women. Sometimes artificial teeth are used to achieve blackened teeth. Teeth blackening is commonly confused with the red-stained teeth from betel chewing. However, betel chewing damages the teeth and gums, while teeth blackening does not.

9.2K
21 Nov 2022

Topic Review

Zipline (Drone Delivery)

Zipline is an American medical product delivery company that is headquartered in South San Francisco, California, and which designs, manufactures, and operates delivery drones. The company operates distribution centers in Rwanda, Ghana, and the US, with signed agreements to begin service in Japan , Nigeria, Cote d'Ivoire, and Kenya. As of December 2021, its drones have made over 225,000 commercial deliveries. The company's drones deliver whole blood, platelets, frozen plasma, and cryoprecipitate along with medical products including vaccines, infusions and routine medical commodities. As of September 2021, more than 75% of blood deliveries in Rwanda outside of Kigali use Zipline drones. In April 2019 in Ghana, the company began using drones to deliver vaccines, blood, and medicines. During the COVID-19 pandemic in 2020, the US Federal Aviation Administration (FAA) granted a Part 107 waiver to Zipline's partner organization Novant Health for the delivery of medical supplies and personal protective equipment (PPE) to medical facilities in North Carolina. Along with nine other drone delivery companies, the FAA selected Zipline to participate in a type certification program for delivery drones.

9.2K
06 Oct 2022

Topic Review

Fruit carving is the art of carving fruit, a very common technique in Europe and Asian countries, and particularly popular in Thailand, China and Japan. There are many fruits that can be used in this process; the most popular one that artists use are watermelons, apples, strawberries, pineapples, and cantaloupes.

9.1K
11 Nov 2022

Topic Review

Non-Hispanic or Latino Whites

Non-Hispanic whites or Non-Latino whites are European Americans, Middle Eastern Americans, and North African Americans as defined by the United States Census Bureau. Americans of European ancestry represent ethnic groups and more than half of the white population are German, Irish, English, Italian and Polish Americans. In the United States , this population was first derived from English (and, to a lesser degree, French) settlement of the Americas, as well as settlement by other Europeans such as the Germans and Dutch that began in the 17th century (see History of the United States). Continued growth since the early 19th century is attributed to sustained very high birth rates alongside relatively low death rates among settlers and natives alike as well as periodically massive immigration from European countries, especially Germany, Ireland, England, Italy, Greece, the Netherlands, France and Wales, as well as Poland, Russia, and many more countries. It typically refers to an English-speaking American in distinction to Spanish speakers in Mexico and the Southwestern states. In some parts of the country, the term Anglo-American is used to refer to non-Hispanic white English speakers as distinct from Spanish speakers although the term is more frequently used to refer to people of British or English descent and might include white people of Hispanic descent who no longer speak Spanish.

9.1K
27 Oct 2022

Topic Review

Nature has two inter-related meanings in philosophy and natural philosophy. On the one hand, it means the set of all things which are natural, or subject to the normal working of the laws of nature. On the other hand, it means the essential properties and causes of individual things. How to understand the meaning and significance of nature has been a consistent theme of discussion within the history of Western Civilization, in the philosophical fields of metaphysics and epistemology, as well as in theology and science. The study of natural things and the regular laws which seem to govern them, as opposed to discussion about what it means to be natural, is the area of natural science. The word "nature" derives from Latin nātūra, a philosophical term derived from the verb for birth, which was used as a translation for the earlier (pre-Socratic) Greek term phusis, derived from the verb for natural growth. Already in classical times, philosophical use of these words combined two related meanings which have in common that they refer to the way in which things happen by themselves, "naturally", without "interference" from human deliberation, divine intervention, or anything outside what is considered normal for the natural things being considered. Understandings of nature depend on the subject and age of the work where they appear. For example, Aristotle's explanation of natural properties differs from what is meant by natural properties in modern philosophical and scientific works, which can also differ from other scientific and conventional usage. Stoicism encourages practitioners to live in accordance with nature. Pyrrhonism encourages practitioners to use the guidance of nature in decision making.

9.1K
09 Oct 2022

Topic Review

Micronutrient Deficiency and Toxicity in Plants

Micronutrients are essential for plants. Their growth, productivity and reproduction are directly influenced by the supply of micronutrients. Currently, there are eight trace elements considered to be essential for higher plants: Fe, Zn, Mn, Cu, Ni, B, Mo, and Cl. Possibly, other essential elements could be discovered because of recent advances in nutrient solution culture techniques and in the commercial availability of highly sensitive analytical instrumentation for elemental analysis.

9.1K
27 Sep 2022

Topic Review

Stall (Fluid Mechanics)

In fluid dynamics, a stall is a reduction in the lift coefficient generated by a foil as angle of attack increases. This occurs when the critical angle of attack of the foil is exceeded. The critical angle of attack is typically about 15 degrees, but it may vary significantly depending on the fluid, foil, and Reynolds number. Stalls in fixed-wing flight are often experienced as a sudden reduction in lift as the pilot increases the wing's angle of attack and exceeds its critical angle of attack (which may be due to slowing down below stall speed in level flight). A stall does not mean that the engine(s) have stopped working, or that the aircraft has stopped moving—the effect is the same even in an unpowered glider aircraft. Vectored thrust in manned and unmanned aircraft is used to surpass the stall limit, thereby giving rise to post-stall technology. Because stalls are most commonly discussed in connection with aviation, this article discusses stalls as they relate mainly to aircraft, in particular fixed-wing aircraft. The principles of stall discussed here translate to foils in other fluids as well.

9.1K
16 Nov 2022

Topic Review

Pigmentary and Structural Coloration in Nature

Most of us get inspired by and interact with the world around us based on visual cues such as the colors and patterns that we see. In nature, coloration takes three primary forms: pigmentary coloration, structural coloration, and bioluminescence. Typically, pigmentary and structural coloration are used by animals and plants for their survival. These forms of coloration are enabled by a variety of intracellular biophotonic structures.

9.1K
09 Jun 2022

Page
of
2727

Featured Entry Collections

>>

Featured Reprints

>>

Encyclopedia of Digital Society, Industry 5.0 and Smart City

Encyclopedia of Digital Society, Industry 5.0 and Smart City
Chief Editor: Sandro Serpa

Encyclopedia of Engineering

Encyclopedia of Social Sciences

Encyclopedia of Social Sciences
Chief Editor: Kum Fai Yuen

Encyclopedia of Medieval Royal Iconography

Encyclopedia of Medieval Royal Iconography
Published Version (2022) >>
Chief Editor: Mirko Vagnoni

Academic Video Service

Feedback

Top