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Topic Review
Bow Shocks in Astrophysics
Bow shocks form the boundary between a magnetosphere and an ambient (or at least surrounding) magnetized medium. This occurs when the magnetic field of an astrophysical object interacts with the nearby flowing ambient plasma. For example, when the solar wind, flowing with a relative speed of order 400 km/s, encounters the magnetic field of Earth, a bow shape boundary forms. For Earth and other magnetized planets, it is the boundary at which the speed of the stellar wind abruptly drops as a result of its approach to the magnetopause. For stars, this boundary is typically the edge of the astrosphere, where the stellar wind meets the interstellar medium.
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  • 27 Oct 2022
Topic Review
The Feynman Lectures on Physics
The Feynman Lectures on Physics is a physics textbook based on some lectures by Richard P. Feynman, a Nobel laureate who has sometimes been called "The Great Explainer". The lectures were presented before undergraduate students at the California Institute of Technology (Caltech), during 1961–1963. The book's co-authors are Feynman, Robert B. Leighton, and Matthew Sands. The Feynman Lectures on Physics is perhaps the most popular physics book ever written. More than 1.5 million English-language copies have been sold; probably even more copies have been sold in a dozen foreign-language editions. A 2013 review in Nature described the book as having "simplicity, beauty, unity ... presented with enthusiasm and insight".
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  • 27 Oct 2022
Topic Review
Electricity Meter
thumb|North American domestic analogue electricity meter. thumb|Electricity meter with transparent plastic case (Israel) thumb|North American domestic electronic electricity meter An electricity meter, electric meter, electrical meter, or energy meter is a device that measures the amount of electric energy consumed by a residence, a business, or an electrically powered device. Electric utilities use electric meters installed at customers' premises for billing and monitoring purposes. They are typically calibrated in billing units, the most common one being the kilowatt hour (kWh). They are usually read once each billing period. When energy savings during certain periods are desired, some meters may measure demand, the maximum use of power in some interval. "Time of day" metering allows electric rates to be changed during a day, to record usage during peak high-cost periods and off-peak, lower-cost, periods. Also, in some areas meters have relays for demand response load shedding during peak load periods.
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Topic Review
Mooning
Mooning is the act of displaying one's bare buttocks by removing clothing, e.g., by lowering the backside of one's trousers and underpants, usually bending over, whether also exposing the genitals or not. Mooning is used in the English-speaking world to express protest, scorn, disrespect, or provocation, or can be done for shock value, fun, or as a form of exhibitionism. Some jurisdictions regard mooning to be indecent exposure, sometimes depending on the context.
  • 7.2K
  • 27 Oct 2022
Topic Review
List of Conjunctions
This is a list of the Solar System's recent and forthcoming planetary conjunctions (in other words, when two planets look close together). In astronomy, a conjunction is an event, defined only when using either an equatorial or an ecliptic celestial coordinate system, in which any two astronomical objects (e.g. asteroids, moons, planets, stars) have the same celestial longitude, normally as when observed from the Earth (geocentric). In the case of a geocentric conjunction of two of the Solar System's planets, since the Solar System's planets appear to travel "along the same line" (the ecliptic), the two planets appear to an Earthbound observer as being near one another in the sky around the time of the conjunction. The list below presents instances during the period 2005–2020 in which two Solar System's planets are in conjunction according to the equatorial coordinate system (in which the celestial longitude is termed right ascension).
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  • 27 Oct 2022
Topic Review
Domestic Refrigerators in Smart Grids
Domestic refrigeration and freezing appliances can be used for electrical load shifting from peak to off-peak demand periods, thus allowing greater penetration of renewable energy sources (RES) and significantly contributing to the reduction of CO2 emissions. The full realization of this potential can be achieved with the synergistic combination of smart grid (SG) technologies and the application of phase-change materials (PCMs). Being permanently online, these ubiquitous appliances are available for the most advanced strategies of demand-side load management (DSLM), including real-time demand response (DR) and direct load control (DLC).
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  • 27 Oct 2022
Topic Review
Bioelectromagnetics
Bioelectromagnetics, also known as bioelectromagnetism, is the study of the interaction between electromagnetic fields and biological entities. Areas of study include electrical or electromagnetic fields produced by living cells, tissues or organisms, including bioluminescent bacteria; for example, the cell membrane potential and the electric currents that flow in nerves and muscles, as a result of action potentials. Others include animal navigation utilizing the geomagnetic field; the effects of man-made sources of electromagnetic fields like mobile phones; and developing new therapies to treat various conditions. The term can also refer to the ability of living cells, tissues, and organisms to produce electrical fields and the response of cells to electromagnetic fields.
  • 468
  • 27 Oct 2022
Topic Review
Resonance
Resonance describes the phenomenon of increased amplitude that occurs when the frequency of an applied periodic force (or a Fourier component of it) is equal or close to a natural frequency of the system on which it acts. When an oscillating force is applied at a resonant frequency of a dynamic system, the system will oscillate at a higher amplitude than when the same force is applied at other, non-resonant frequencies. Frequencies at which the response amplitude is a relative maximum are also known as resonant frequencies or resonance frequencies of the system. Small periodic forces that are near a resonant frequency of the system have the ability to produce large amplitude oscillations in the system due to the storage of vibrational energy. Resonance phenomena occur with all types of vibrations or waves: there is mechanical resonance, Orbital resonance, acoustic resonance, electromagnetic resonance, nuclear magnetic resonance (NMR), electron spin resonance (ESR) and resonance of quantum wave functions. Resonant systems can be used to generate vibrations of a specific frequency (e.g., musical instruments), or pick out specific frequencies from a complex vibration containing many frequencies (e.g., filters). The term resonance (from Latin resonantia, 'echo', from resonare, 'resound') originated from the field of acoustics, particularly the sympathetic resonance observed in musical instruments, e.g., when one string starts to vibrate and produce sound after a different one is struck.
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  • 27 Oct 2022
Topic Review
More Hall Annex
The More Hall Annex, formerly the Nuclear Reactor Building, was a building on the campus of the University of Washington (UW) in Seattle, Washington, United States, that once housed a functional nuclear research reactor. It was inaugurated in 1961 and shut down in 1988, operating at a peak of 100 kilowatts thermal (kWt), and was officially decommissioned in 2007. The reactor was housed in a reinforced concrete building designed in the Brutalist architectural style by UW faculty members. They designed the reactor room with large windows that allowed observation from the outside, in an attempt to demonstrate the safety of nuclear energy. The Nuclear Reactor Building was added to the National Register of Historic Places in 2009, after a campaign led by an architecture student in response to the proposed demolition of the building. A later demolition plan prompted a lawsuit from preservation groups, which ended with a court ruling exempting the building from the city's landmarks-preservation ordinance. While this decision was eventually overturned, the university demolished the building in July 2016 and replaced it with a new computer science building that opened in February 2019.
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Topic Review
Spin
Spin is an intrinsic form of angular momentum carried by elementary particles, and thus by composite particles (hadrons) and atomic nuclei. Spin is one of two types of angular momentum in quantum mechanics, the other being orbital angular momentum. The orbital angular momentum operator is the quantum-mechanical counterpart to the classical angular momentum of orbital revolution and appears when there is periodic structure to its wavefunction as the angle varies. For photons, spin is the quantum-mechanical counterpart of the polarization of light; for electrons, the spin has no classical counterpart. The existence of electron spin angular momentum is inferred from experiments, such as the Stern–Gerlach experiment, in which silver atoms were observed to possess two possible discrete angular momenta despite having no orbital angular momentum. The existence of the electron spin can also be inferred theoretically from the spin–statistics theorem and from the Pauli exclusion principle—and vice versa, given the particular spin of the electron, one may derive the Pauli exclusion principle. Spin is described mathematically as a vector for some particles such as photons, and as spinors and bispinors for other particles such as electrons. Spinors and bispinors behave similarly to vectors: they have definite magnitudes and change under rotations; however, they use an unconventional "direction". All elementary particles of a given kind have the same magnitude of spin angular momentum, though its direction may change. These are indicated by assigning the particle a spin quantum number. The SI unit of spin is the same as classical angular momentum (i.e., N·m·s, J·s, or kg·m2·s−1). In practice, spin is given as a dimensionless spin quantum number by dividing the spin angular momentum by the reduced Planck constant ħ, which has the same dimensions as angular momentum, although this is not the full computation of this value. Very often, the "spin quantum number" is simply called "spin". The fact that it is a quantum number is implicit.
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