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Positive Feedback
Positive feedback (exacerbating feedback, self-reinforcing feedback) is a process that occurs in a feedback loop which exacerbates the effects of a small disturbance. That is, the effects of a perturbation on a system include an increase in the magnitude of the perturbation. That is, ''A produces more of B which in turn produces more of A''.Keesing, R.M. (1981). Cultural anthropology: A contemporary perspective (2nd ed.) p.149. Sydney: Holt, Rinehard & Winston, Inc. In contrast, a system in which the results of a change act to reduce or counteract it has negative feedback. Both concepts play an important role in science and engineering, including biology, chemistry, and cybernetics. Mathematically, positive feedback is defined as a positive loop gain around a closed loop of cause and effect. That is, positive feedback is in phase with the input, in the sense that it adds to make the input larger. Positive feedback tends to cause system instability. When the loop gain is pos ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Stampede Loop
A stampede () is a situation in which a group of large animals suddenly start running in the same direction, especially because they are excited or frightened. Non-human species associated with stampede behavior include zebras, cattle, elephants, reindeer, sheep, pigs, goats, blue wildebeests, walruses, wild horses, and rhinoceroses. Some media sources refer to situations in which people were injured or have died due to compression in very dense crowds as a "stampede", but this is a misnomer; the more appropriate term would be crush, or crowd collapse. Cattle stampedes 
Anything unusual may start a stampede among cattle. Especially at night, things such as lighting a match, someone ju ...
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Thermal Runaway
Thermal runaway describes a process that is accelerated by increased temperature, in turn releasing energy that further increases temperature. Thermal runaway occurs in situations where an increase in temperature changes the conditions in a way that causes a further increase in temperature, often leading to a destructive result. It is a kind of uncontrolled positive feedback. In chemistry (and chemical engineering), thermal runaway is associated with strongly exothermic reactions that are accelerated by temperature rise. In electrical engineering, thermal runaway is typically associated with increased current flow and power dissipation. Thermal runaway can occur in civil engineering, notably when the heat released by large amounts of curing concrete is not controlled. In astrophysics, runaway nuclear fusion reactions in stars can lead to nova and several types of supernova explosions, and also occur as a less dramatic event in the normal evolution of solar-mass stars, the "he ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Value Judgement
A value judgment (or value judgement) is a judgment of the rightness or wrongness of something or someone, or of the usefulness of something or someone, based on a comparison or other relativity. As a generalization, a value judgment can refer to a judgment based upon a particular set of values or on a particular value system. A related meaning of value judgment is an expedient evaluation based upon limited information at hand, where said evaluation was undertaken because a decision had to be made on short notice. Explanation A ''value judgment'' is a thought about something based on what it “ought” or “should” be given an opinion about what counts as “good” or “bad” — contrast from a thought based on what the facts are. E.g. “The government should improve access to education” is a value judgement (that education is good). “People will buy less of our products if our price goes up” is not a value judgement because it is based on the fact that people tend ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gain (electronics)
In electronics, gain is a measure of the ability of a two-port circuit (often an amplifier) to increase the power or amplitude of a signal from the input to the output port by adding energy converted from some power supply to the signal. It is usually defined as the mean ratio of the signal amplitude or power at the output port to the amplitude or power at the input port. It is often expressed using the logarithmic decibel (dB) units ("dB gain"). A gain greater than one (greater than zero dB), that is amplification, is the defining property of an active component or circuit, while a passive circuit will have a gain of less than one. The term ''gain'' alone is ambiguous, and can refer to the ratio of output to input voltage (''voltage gain''), current (''current gain'') or electric power (''power gain''). In the field of audio and general purpose amplifiers, especially operational amplifiers, the term usually refers to voltage gain, but in radio frequency amplifiers ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Positive Feedback Diagram (2)
Positive is a property of positivity and may refer to: Mathematics and science * Positive formula, a logical formula not containing negation * Positive number, a number that is greater than 0 * Plus sign, the sign "+" used to indicate a positive number * Positive operator, a type of linear operator in mathematics * Positive result, a result that has been found significant in statistical hypothesis testing * Positive test, a diagnostic test result that indicates some parameter being evaluated was present * Positive charge, one of the two types of electrical charge * Positive (electrical polarity), in electrical circuits * Positive lens, in optics * Positive (photography), a positive image, in which the color and luminance correlates directly with that in the depicted scene * Positive sense, said of an RNA sequence that codes for a protein Philosophy and humanities * Affirmative (policy debate), the team which affirms the resolution * Negative and positive rights, concern ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Public Address
A public address system (or PA system) is an electronic system comprising microphones, amplifiers, loudspeakers, and related equipment. It increases the apparent volume (loudness) of a human voice, musical instrument, or other acoustic sound source or recorded sound or music. PA systems are used in any public venue that requires that an announcer, performer, etc. be sufficiently audible at a distance or over a large area. Typical applications include sports stadiums, public transportation vehicles and facilities, and live or recorded music venues and events. A PA system may include multiple microphones or other sound sources, a mixing console to combine and modify multiple sources, and multiple amplifiers and loudspeakers for louder volume or wider distribution. Simple PA systems are often used in small venues such as school auditoriums, churches, and small bars. PA systems with many speakers are widely used to make announcements in public, institutional and commercial buildings ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Audio Feedback
Audio feedback (also known as acoustic feedback, simply as feedback) is a positive feedback situation which may occur when an acoustic path exists between an audio input (for example, a microphone or guitar pickup) and an audio output (for example, a loudspeaker). In this example, a signal received by the microphone is amplified and passed out of the loudspeaker. The sound from the loudspeaker can then be received by the microphone again, amplified further, and then passed out through the loudspeaker again. The frequency of the resulting howl is determined by resonance frequencies in the microphone, amplifier, and loudspeaker, the acoustics of the room, the directional pick-up and emission patterns of the microphone and loudspeaker, and the distance between them. The principles of audio feedback were first discovered by Danish scientist Søren Absalon Larsen, hence it is also known as the Larsen effect. Feedback is almost always considered undesirable when it occurs with a s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Business Cycle
Business cycles are intervals of expansion followed by recession in economic activity. These changes have implications for the welfare of the broad population as well as for private institutions. Typically business cycles are measured by examining trends in a broad economic indicator such as Real Gross Domestic Production. Business cycle fluctuations are usually characterized by general upswings and downturns in a span of macroeconomic variables. The individual episodes of expansion/recession occur with changing duration and intensity over time. Typically their periodicity has a wide range from around 2 to 10 years (the technical phrase "stochastic cycle" is often used in statistics to describe this kind of process.) As in arvey, Trimbur, and van Dijk, 2007, ''Journal of Econometrics'' such flexible knowledge about the frequency of business cycles can actually be included in their mathematical study, using a Bayesian statistical paradigm. There are numerous sources of busines ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tacoma Narrows Bridge (1940)
The 1940 Tacoma Narrows Bridge, the first Tacoma Narrows Bridge, was a suspension bridge in the U.S. state of Washington that spanned the Tacoma Narrows strait of Puget Sound between Tacoma and the Kitsap Peninsula. It opened to traffic on July 1, 1940, and dramatically collapsed into Puget Sound on November 7 of the same year. The bridge's collapse has been described as "spectacular" and in subsequent decades "has attracted the attention of engineers, physicists, and mathematicians". Throughout its short existence, it was the world's third-longest suspension bridge by main span, behind the Golden Gate Bridge and the George Washington Bridge. Construction began in September 1938. From the time the deck was built, it began to move vertically in windy conditions, so construction workers nicknamed the bridge Galloping Gertie. The motion continued after the bridge opened to the public, despite several damping measures. The bridge's main span finally collapsed in winds on t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Locking Pliers
Locking pliers (also called Vise-Grips, a vice grip, Mole wrench or mole grips) are pliers that can be locked into position, using an "over-center" cam action. Locking pliers are available with many different jaw styles, such as needle-nose pliers, wrenches, clamps and various shapes to fix metal parts for welding. They also come in many sizes. History The first locking pliers, with the trade name Vise-Grip, were invented by William S. Petersen in De Witt, Nebraska, United States in 1924. Later, in 1955, in the United Kingdom, M K Mole and Son, a hand tool manufacturing company, under the managing direction of Thomas Coughtrie, began making nearly identical pliers. Etymology In the United States, the brand name "''Vise Grips''" is close to a generic name for this type of pliers. The same is true in the United Kingdom of the brand name "''Mole Wrench''". The spelling "''vise''" is mentioned in Samuel Johnson's 1755 dictionary. This spelling is orthodox in the United St ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Miniature Snap-action Switch
A miniature snap-action switch, also trademarked and frequently known as a micro switch, is an electric switch that is actuated by very little physical force, through the use of a tipping-point mechanism, sometimes called an "over-center" mechanism. Switching happens reliably at specific and repeatable positions of the actuator, which is not necessarily true of other mechanisms. They are very common due to their low cost but high durability, greater than 1 million cycles, and up to 10 million cycles for heavy-duty models. This durability is a natural consequence of the design. The defining feature of micro switches is that a relatively small movement at the actuator button produces a relatively large movement at the electrical contacts, which occurs at high speed (regardless of the speed of actuation). Most successful designs also exhibit hysteresis, meaning that a small reversal of the actuator is insufficient to reverse the contacts; there must be a significant movement in th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tipping Point (physics)
Hysteresis is the dependence of the state of a system on its history. For example, a magnet may have more than one possible magnetic moment in a given magnetic field, depending on how the field changed in the past. Plots of a single component of the moment often form a loop or hysteresis curve, where there are different values of one variable depending on the direction of change of another variable. This history dependence is the basis of memory in a hard disk drive and the remanence that retains a record of the Earth's magnetic field magnitude in the past. Hysteresis occurs in ferromagnetic and ferroelectric materials, as well as in the deformation of rubber bands and shape-memory alloys and many other natural phenomena. In natural systems it is often associated with irreversible thermodynamic change such as phase transitions and with internal friction; and dissipation is a common side effect. Hysteresis can be found in physics, chemistry, engineering, biology, and econom ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
