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Topic Review
Wind Turbines Vibration Control
The larger wind turbines are facing higher loads, and the imperatives of mass reduction make them more flexible. Size increase of wind turbines results in higher structural vibrations that reduce the lifetime of the components (blades, main shaft, bearings, generator, gearbox, etc.) and might lead to failure or destruction. Different systems to control the vibration of wind turbines are available, acting either on the tower or directly on the blade.
  • 4.0K
  • 06 Jun 2021
Topic Review
Deriving the Schwarzschild Solution
The Schwarzschild solution describes spacetime under the influence of a massive, non-rotating, spherically symmetric object. It is considered by some to be one of the simplest and most useful solutions to the Einstein field equations.
  • 3.9K
  • 18 Oct 2022
Topic Review
Foams and Emulsions
Foams and emulsions are collections of different kinds of bubbles or drops with particular properties. They provide exceptional sensitive bases for measuring low concentrations of molecules down to the level of traces using spectroscopy techniques, thus opening new horizons in microfluidics. The optical and spectral properties of foams and emulsions provide information about their micro-/nanostructures, chemical and time stability, and molecular data of their components. 
  • 3.9K
  • 19 Apr 2022
Topic Review
Ecliptic Coordinate System
The ecliptic coordinate system is a celestial coordinate system commonly used for representing the apparent positions, orbits, and pole orientations of Solar System objects. Because most planets (except Mercury) and many small Solar System bodies have orbits with only slight inclinations to the ecliptic, using it as the fundamental plane is convenient. The system's origin can be the center of either the Sun or Earth, its primary direction is towards the vernal (March) equinox, and it has a right-hand convention. It may be implemented in spherical or rectangular coordinates.
  • 3.9K
  • 19 Oct 2022
Topic Review
Andhaka
In Hindu mythology, Andhaka (Sanskrit: अन्धक, IAST: andhaka, lit. he who darkens) often refer to a malevolent asura who is killed by Shiva for trying to abduct Parvati. His story finds mention in various Hindu texts, including Matsya Purana, Kurma Purana, Linga Purana and Shiva Purana. He is believed to have thousand heads, two thousand eyes, arms and feet.
  • 3.9K
  • 17 Oct 2022
Topic Review
Uniaxial Tensile Test
Tensile testing, also known as tension testing, is a fundamental materials science and engineering test in which a sample is subjected to a controlled tension until failure. Properties that are directly measured via a tensile test are ultimate tensile strength, breaking strength, maximum elongation and reduction in area. From these measurements the following properties can also be determined: Young's modulus, Poisson's ratio, yield strength, and strain-hardening characteristics. Uniaxial tensile testing is the most commonly used for obtaining the mechanical characteristics of isotropic materials. Some materials use biaxial tensile testing. The main difference between these testing machines being how load is applied on the materials.
  • 3.9K
  • 07 Nov 2022
Topic Review
Proton–Proton Chain
The proton–proton chain, also commonly referred to as the p-p chain, is one of two known sets of nuclear fusion reactions by which stars convert hydrogen to helium. It dominates in stars with masses less than or equal to that of the Sun, whereas the CNO cycle, the other known reaction, is suggested by theoretical models to dominate in stars with masses greater than about 1.3 times that of the Sun. In general, proton–proton fusion can occur only if the kinetic energy (i.e. temperature) of the protons is high enough to overcome their mutual electrostatic repulsion. In the Sun, deuterium-producing events are rare. Diprotons are the much more common result of proton–proton reactions within the star, and diprotons almost immediately decay back into two protons. Since the conversion of hydrogen to helium is slow, the complete conversion of the hydrogen initially in the core of the Sun is calculated to take more than ten billion years. Although sometimes called the "proton–proton chain reaction", it is not a chain reaction in the normal sense. In most nuclear reactions, a chain reaction designates a reaction that produces a product, such as neutrons given off during fission, that quickly induces another such reaction. The proton-proton chain is, like a decay chain, a series of reactions. The product of one reaction is the starting material of the next reaction. There are two main chains leading from Hydrogen to Helium in the Sun. One chain has five reactions, the other chain has six.
  • 3.6K
  • 10 Nov 2022
Topic Review
Atomic Mass Unit
The dalton or unified atomic mass unit (SI symbols: Da or u) is a unit of mass widely used in physics and chemistry. . It is approximately the mass of one nucleon (either a proton or neutron). A mass of 1 Da is also referred to as the atomic mass constant and denoted by mu. Several definitions of this unit have been used, implying slightly different values. The current IUPAC endorsed definition is the unified atomic mass unit, denoted by the symbol u. As of 2019, the International System of Units (SI) lists the dalton, symbol Da, as a unit acceptable for use with the SI unit system and secondarily notes that the dalton (Da) and the unified atomic mass unit (u) are alternative names (and symbols) for the same unit. The symbol Da is more widely used in most fields. It is defined precisely as 1/12 of the mass of an unbound neutral atom of carbon-12 in its nuclear and electronic ground state and at rest. Despite being an official abbreviation for a related obsolete unit and not widely used in the scientific literature, the abbreviation "amu" now often refers to the modern unit (Da or u) in many preparatory texts. As of June 2019, the value recommended by the Committee on Data for Science and Technology (CODATA) is 1.66053906660(50)×10−27 kg, or approximately 1.66 yoctograms. This unit is commonly used in physics and chemistry to express the mass of atomic-scale objects, such as atoms, molecules, and elementary particles. For example, an atom of helium has a mass of about 4 Da, and a molecule of acetylsalicylic acid (aspirin), C9H8O4, has a mass of about 180.16 Da. In general, the standard atomic weight of an element is the average weight of its atom as it occurs in nature, expressed in daltons. The molecular masses of proteins, nucleic acids, and other large polymers are often expressed with the units kilodalton (kDa), equal to 1000 daltons, megadalton (MDa), one million daltons, etc. Titin, one of the largest known proteins, has an atomic mass of between 3 and 3.7 megadaltons. The DNA of chromosome 1 in the human genome has about 249 million base pairs, each with an average mass of about 650 Da, or 156 GDa total. The mole is a unit of amount of substance, widely used in chemistry and physics, which was originally defined so that the mass of one mole of a substance, measured in grams, would be numerically equal to the average mass of one of its constituent particles, measured in daltons. That is, the molar mass of a chemical compound was meant to be numerically equal to its average molecular mass. For example, the average mass of one molecule of water is about 18.0153 daltons, and one mole of water is about 18.0153 grams. A protein whose molecule has an average mass of 64 kDa would have a molar mass of 64 kg/mol. However, while this equality can be assumed for almost all practical purposes, it is now only approximate, because of the way the mole was redefined on 20 May 2019. The mass in daltons of an atom is numerically very close to the number of nucleons A in its atomic nucleus. It follows that the molar mass of a compound (grams per mole) is also numerically close to the average number of nucleons per molecule. However, the mass of an atomic-scale object is affected by the binding energy of the nucleons in its atomic nuclei, as well as the mass and binding energy of the electrons. Therefore, this equality holds only for the carbon-12 atom in the stated conditions, and will vary for other substances. For example, the mass of one unbound atom of the common hydrogen isotope (hydrogen-1, protium) is 1.007825032241(94) Da, the mass of one free neutron is 1.008664915823(491) Da, and the mass of one hydrogen-2 (deuterium) atom is 2.014101778114(122) Da. In general, the difference (mass defect) is less than 0.1%; except for hydrogen (about 0.8%), helium-3 (0.5%), lithium (0.25%) and beryllium (0.15%). The atomic mass unit should not be confused with unit of mass in the atomic units systems, which is instead the electron rest mass (me).
  • 3.6K
  • 31 Oct 2022
Topic Review
Bṛhaspati
Bṛhaspati (Sanskrit: बृहस्पति; meaning spati of briha, the spirit of vastness of the universe written as Brihaspati) is an Indian name, and refers to different mythical figures depending on the age of the text. In ancient Hindu literature Brihaspati is a Vedic era sage who counsels the gods, while in some medieval texts the word refers to the largest planet of the solar system, Jupiter. He taught Bhishma the duties of a king which he later taught it to Vidura.
  • 3.6K
  • 18 Oct 2022
Topic Review
Acoustic Properties of Natural-fiber-based Composites
Recent advancement in controlling noise through sound absorption provides an opportunity to investigate various porous materials including fiber-based composites. Natural-fiber-based composites exhibit relatively good sound absorption capability due to their porous structure. Surface modification by alkali treatment can enhance the sound absorption performance. These materials can be used in buildings and interiors for efficient sound insulation. Natural-fiber-based composites have advantages such as high abrasive resistance, low emission of toxic fumes with heat, high specific strength, light weight, low cost, and eco-friendliness. Very rapid growth has been observed in the innovations and use of natural-fiber-based materials and composites for acoustic applications.
  • 3.6K
  • 24 Aug 2021
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