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"...'feedback' exists between two parts when each affects the other."[1](p53, §4/11) A feedback loop where all outputs of a process are available as causal inputs to that process "Simple causal reasoning about a feedback system is difficult because the first system influences the second and second system influences the first, leading to a circular argument. In this context, the term "feedback" has also been used as an abbreviation for: Feedback signal – the conveyance of information fed back from an output, or measurement, to an input, or effector, that affects the system.Feedback loop – the closed path made up of the system itself and the path that transmits the feedback about the system from its origin (for example, a sensor) to its destination (for example, an actuator).Negative feedback – the case where the fed-back information acts to control or regulate a system by opposing changes in the output or measurement. History[edit] Types[edit] Positive and negative feedback[edit] Biology[edit]

Related:  System Theory

State-space representation In control engineering, a state-space representation is a mathematical model of a physical system as a set of input, output and state variables related by first-order differential equations. "State space" refers to the space whose axes are the state variables. The state of the system can be represented as a vector within that space. Jamming avoidance response Two neighboring Eigenmannia perform the jamming avoidance response: When one fish with an electric discharge of 400 Hz encounters a second fish with the same frequency, one fish shifts its frequency upward and the other shifts its frequency downward. The jamming avoidance response or JAR is a behavior performed by some species of weakly electric fish. The JAR occurs when two electric fish with wave discharges meet – if their discharge frequencies are very similar, each fish will shift its discharge frequency to increase the difference between the two fish's discharge frequencies. By doing this, both fish prevent jamming of their sense of electroreception. The behavior has been most intensively studied in the South American species Eigenmannia virescens (order Gymnotiformes).

Inverted pendulum Balancing cart, a simple robotics system 1976. A second type of inverted pendulum is a tiltmeter for tall structures, which consists of a wire anchored to the bottom of the foundation and attached to a float in a pool of oil at the top of the structure that has devices for measuring movement of the neutral position of the float away from its original position. Overview[edit] Another way that an inverted pendulum may be stabilized, without any feedback or control mechanism, is by oscillating the support rapidly up and down. This is called Kapitza's pendulum. If the oscillation is sufficiently strong (in terms of its acceleration and amplitude) then the inverted pendulum can recover from perturbations in a strikingly counterintuitive manner.

Dynamical system The Lorenz attractor arises in the study of the Lorenz Oscillator, a dynamical system. Overview[edit] Before the advent of computers, finding an orbit required sophisticated mathematical techniques and could be accomplished only for a small class of dynamical systems. Numerical methods implemented on electronic computing machines have simplified the task of determining the orbits of a dynamical system. Metcalfe's law Two telephones can make only one connection, five can make 10 connections, and twelve can make 66 connections. Metcalfe's law states that the value of a telecommunications network is proportional to the square of the number of connected users of the system (n2). First formulated in this form by George Gilder in 1993,[1] and attributed to Robert Metcalfe in regard to Ethernet, Metcalfe's law was originally presented, circa 1980, not in terms of users, but rather of "compatible communicating devices" (for example, fax machines, telephones, etc.)[2] Only more recently with the launch of the Internet did this law carry over to users and networks as its original intent was to describe Ethernet purchases and connections.[3] The law is also very much related to economics and business management, especially with competitive companies looking to merge with one another. Network effects[edit]

Piezoelectric motor Insides of a slip-stick piezoelectric motor. Two piezoelectric crystals are visible that provide the mechanical torque. A piezoelectric motor or piezo motor is a type of electric motor based upon the change in shape of a piezoelectric material when an electric field is applied. Piezoelectric motors make use of the converse piezoelectric effect whereby the material produces acoustic or ultrasonic vibrations in order to produce a linear or rotary motion. In one mechanism, the elongation in a single plane is used to make a series of stretches and position holds, similar to the way a caterpillar moves. [1] Current designs[edit]

Calculus History[edit] Modern calculus was developed in 17th century Europe by Isaac Newton and Gottfried Wilhelm Leibniz (see the Leibniz–Newton calculus controversy), but elements of it have appeared in ancient Greece, China, medieval Europe, India, and the Middle East. Ancient[edit] Personal identity What does it take for individuals to persist from moment to moment—or in other words, for the same individual to exist at different moments? Generally, it is the unique numerical identity of persons through time.[3][4] That is to say, the necessary and sufficient conditions under which a person at one time and a person at another time can be said to be the same person, persisting through time.[note 5] In the modern philosophy of mind, this concept of personal identity is sometimes referred to as the diachronic problem[note 6] of personal identity.[5] The synchronic problem[note 7] is grounded in the question of what features or traits characterize a given person at one time. Identity is an issue for both continental philosophy and analytic philosophy. A question in continental philosophy is in what sense can the contemporary conception of identity be maintained, while many prior propositions, postulates, and presuppositions about the world are different.[6][7]

Gyroscope A gyroscope Gyroscopes based on other operating principles also exist, such as the electronic, microchip-packaged MEMS gyroscope devices found in consumer electronic devices, solid-state ring lasers, fibre optic gyroscopes, and the extremely sensitive quantum gyroscope. Applications of gyroscopes include inertial navigation systems where magnetic compasses would not work (as in the Hubble telescope) or would not be precise enough (as in ICBMs), or for the stabilization of flying vehicles like radio-controlled helicopters or unmanned aerial vehicles. Due to their precision, gyroscopes are also used in gyrotheodolites to maintain direction in tunnel mining.[2] Conceptual model A conceptual model is a model made of the composition of concepts, which are used to help people know, understand, or simulate a subject the model represents. Some models are physical objects; for example, a toy model which may be assembled, and may be made to work like the object it represents. The term conceptual model may be used to refer to models which are formed after a conceptualization (generalization)[1] process in the mind. Conceptual models represent human intentions or semantics[citation needed][dubious ].

Illusion of control The illusion of control is the tendency for people to overestimate their ability to control events, for instance to feel that they control outcomes that they demonstrably have no influence over.[1] The effect was named by psychologist Ellen Langer and has been replicated in many different contexts.[2] It is thought to influence gambling behavior and belief in the paranormal.[3] Along with illusory superiority and optimism bias, the illusion of control is one of the positive illusions. Although, the idea of illusion of control has been studied prior to Langer. Psychological theorists have consistently emphasized the importance of perceptions of control over life events. One of the earliest instances of this is when Adler[who?] argued that people strive for proficiency in their lives. Heider[who?]