更改

Regenerative circuits were invented and patented in 1914 for the amplification and reception of very weak radio signals. Carefully controlled positive feedback around a single transistor amplifier can multiply its gain by 1,000 or more. Therefore, a signal can be amplified 20,000 or even 100,000 times in one stage, that would normally have a gain of only 20 to 50. The problem with regenerative amplifiers working at these very high gains is that they easily become unstable and start to oscillate. The radio operator has to be prepared to tweak the amount of feedback fairly continuously for good reception. Modern radio receivers use the superheterodyne design, with many more amplification stages, but much more stable operation and no positive feedback.

Regenerative circuits were invented and patented in 1914 for the amplification and reception of very weak radio signals. Carefully controlled positive feedback around a single transistor amplifier can multiply its gain by 1,000 or more. Therefore, a signal can be amplified 20,000 or even 100,000 times in one stage, that would normally have a gain of only 20 to 50. The problem with regenerative amplifiers working at these very high gains is that they easily become unstable and start to oscillate. The radio operator has to be prepared to tweak the amount of feedback fairly continuously for good reception. Modern radio receivers use the superheterodyne design, with many more amplification stages, but much more stable operation and no positive feedback.

再生电路于1914年被发明并获得专利<ref>{{cite patent |inventor-last=Armstrong |inventor-first=E. H. |country-code=US |patent-number=1113149 |title=Wireless receiving system |date=1914}}</ref>，用于放大和接收非常微弱的无线电信号。通过仔细控制单晶体管放大器周围的正反馈，可以使其增益增加1000倍或更多<ref>{{cite web|last=Kitchin|first=Charles|title=A Short Wave Regenerative Receiver Project|url=http://www.electronics-tutorials.com/receivers/regen-radio-receiver.htm|accessdate=23 September 2010|url-status=live|archiveurl=https://web.archive.org/web/20100710100031/http://www.electronics-tutorials.com/receivers/regen-radio-receiver.htm|archivedate=10 July 2010}}</ref> 。因此，一个信号可以在一个阶段被放大20000甚至100000倍，而在通常只有20到50的增益。而再生放大器在如此高的增益下工作带来的问题则是信号很容易变得不稳定，开始振荡。无线电操作员必须不断地调整反馈量，以获得良好的接收效果。而现代无线电接收机采用超异构设计，多了许多放大级，去掉了正反馈并使其工作更稳定。

再生电路于1914年被发明并获得专利<ref>{{cite patent |inventor-last=Armstrong |inventor-first=E. H. |country-code=US |patent-number=1113149 |title=Wireless receiving system |date=1914}}</ref>，用于放大和接收非常微弱的无线电信号。通过仔细控制单晶体管放大器周围的正反馈，可以使其增益增加1000倍或更多<ref>{{cite web|last=Kitchin|first=Charles|title=A Short Wave Regenerative Receiver Project|url=http://www.electronics-tutorials.com/receivers/regen-radio-receiver.htm|accessdate=23 September 2010|url-status=live|archiveurl=https://web.archive.org/web/20100710100031/http://www.electronics-tutorials.com/receivers/regen-radio-receiver.htm|archivedate=10 July 2010}}</ref> 。因此，一个信号可以在一个阶段被放大20000甚至100000倍，而在通常只有20到50的增益。在如此高的增益下工作带来的问题则是信号很容易变得不稳定，开始振荡。无线电操作员必须不断地调整反馈量，以获得良好的接收效果。而现代无线电接收机采用超异构设计，多了许多放大级，去掉了正反馈并使其工作更稳定。

Many electronic circuits, especially amplifiers, incorporate negative feedback. This reduces their gain, but improves their linearity, input impedance, output impedance, and bandwidth, and stabilises all of these parameters, including the closed-loop gain. These parameters also become less dependent on the details of the amplifying device itself, and more dependent on the feedback components, which are less likely to vary with manufacturing tolerance, age and temperature. The difference between positive and negative feedback for AC signals is one of phase: if the signal is fed back out of phase, the feedback is negative and if it is in phase the feedback is positive. One problem for amplifier designers who use negative feedback is that some of the components of the circuit will introduce phase shift in the feedback path. If there is a frequency (usually a high frequency) where the phase shift reaches 180°, then the designer must ensure that the amplifier gain at that frequency is very low (usually by low-pass filtering). If the loop gain (the product of the amplifier gain and the extent of the positive feedback) at any frequency is greater than one, then the amplifier will oscillate at that frequency (Barkhausen stability criterion). Such oscillations are sometimes called parasitic oscillations. An amplifier that is stable in one set of conditions can break into parasitic oscillation in another. This may be due to changes in temperature, supply voltage, adjustment of front-panel controls, or even the proximity of a person or other conductive item.

Many electronic circuits, especially amplifiers, incorporate negative feedback. This reduces their gain, but improves their linearity, input impedance, output impedance, and bandwidth, and stabilises all of these parameters, including the closed-loop gain. These parameters also become less dependent on the details of the amplifying device itself, and more dependent on the feedback components, which are less likely to vary with manufacturing tolerance, age and temperature. The difference between positive and negative feedback for AC signals is one of phase: if the signal is fed back out of phase, the feedback is negative and if it is in phase the feedback is positive. One problem for amplifier designers who use negative feedback is that some of the components of the circuit will introduce phase shift in the feedback path. If there is a frequency (usually a high frequency) where the phase shift reaches 180°, then the designer must ensure that the amplifier gain at that frequency is very low (usually by low-pass filtering). If the loop gain (the product of the amplifier gain and the extent of the positive feedback) at any frequency is greater than one, then the amplifier will oscillate at that frequency (Barkhausen stability criterion). Such oscillations are sometimes called parasitic oscillations. An amplifier that is stable in one set of conditions can break into parasitic oscillation in another. This may be due to changes in temperature, supply voltage, adjustment of front-panel controls, or even the proximity of a person or other conductive item.

许多电子电路，特别是放大器，都采用了负反馈。这降低了它们的增益，但改善了它们的线性度、输入阻抗、输出阻抗和带宽，并稳定了所有这些参数，包括闭环增益。这些参数也变得不那么依赖于放大器件本身的细节，而更多地依赖于反馈元件，因为反馈元件不太可能随着制造公差、使用年限和温度而变化。交流信号的正反馈和负反馈的区别在于相位问题：如果信号反馈失相，则反馈为负，如果相位一致，则反馈为正。对于使用负反馈的放大器设计者来说，有一个问题是，电路中的一些元件会在反馈路径中引入相移。如果有一个频率(通常是高频)的相移达到180°，那么设计者必须确保该频率的放大器增益非常低(通常通过低通滤波)。如果任何频率下的环增益（放大器增益与正反馈程度的乘积）大于1，那么放大器将在该频率下发生振荡（巴克豪森稳定性准则）。这种振荡有时被称为寄生振荡。在一组条件下稳定的放大器在另一组条件下可能会发生寄生振荡。这可能是由于温度、电源电压的变化，前面板控制的调整，甚至是人或其他导电物品的接近。

许多电子电路，特别是放大器，都采用了负反馈。这降低了放大器的信号增益，但改善了它的线性度、输入阻抗、输出阻抗和带宽，并稳定了包括闭环增益等参数。同时，这些参数也变得不那么依赖于放大器件本身的细节，而更多地依赖于反馈元件，因为反馈元件一般随着制造公差、使用年限和温度而变化。交流信号的正反馈和负反馈的区别在于相位问题：如果信号反馈失相，则反馈为负，如果相位一致，则反馈为正。对于需要使用负反馈放大器的设计者来说，有一个问题是，电路中的一些元件会在反馈路径中引入相移。如果有一个频率(通常是高频)的相移达到180°，那么设计者必须确保该频率的放大器增益非常低（通常通过低通滤波）。如果任何频率下的环增益（放大器增益与正反馈程度的乘积）大于1，那么放大器将在该频率下发生振荡（巴克豪森稳定性准则）。这种振荡有时被称为寄生振荡：在一组条件下稳定的放大器在另一组条件下可能会发生寄生振荡。这可能是由于温度、电源电压的变化，前板（用户界面）的变化，甚至是由于人或其他导电物品的接近。

Amplifiers may oscillate gently in ways that are hard to detect without an oscilloscope, or the oscillations may be so extensive that only a very distorted or no required signal at all gets through, or that damage occurs. Low frequency parasitic oscillations have been called 'motorboating' due to the similarity to the sound of a low-revving exhaust note.

Amplifiers may oscillate gently in ways that are hard to detect without an oscilloscope, or the oscillations may be so extensive that only a very distorted or no required signal at all gets through, or that damage occurs. Low frequency parasitic oscillations have been called 'motorboating' due to the similarity to the sound of a low-revving exhaust note.

放大器可能会以没有示波器很难检测到的方式轻轻振荡，或者振荡的范围很广，只有一个非常失真或根本不需要的信号通过，或者发生损坏。由于低频寄生振荡与低转速排气音符的声音相似，因此被称为 "汽艇"。

放大器可能会以示波器很难检测到的方式轻轻振荡，或者振荡可能非常大，只有非常扭曲或根本没有真正的信号，或者振荡会引起损坏发生。由于低频寄生振荡与低转速排气音符的声音相似，因此被称为 "汽艇"。

The effect of using a Schmitt trigger (B) instead of a comparator (A)

【图8 The effect of using a Schmitt trigger (B) instead of a comparator (A) 使用施密特触发器(b)代替比较器(a)的效果】

 

使用施密特触发器(b)代替比较器(a)的效果

Many common digital electronic circuits employ positive feedback. While normal simple boolean logic gates usually rely simply on gain to push digital signal voltages away from intermediate values to the values that are meant to represent boolean '0' and '1', but many more complex gates use feedback. When an input voltage is expected to vary in an analogue way, but sharp thresholds are required for later digital processing, the Schmitt trigger circuit uses positive feedback to ensure that if the input voltage creeps gently above the threshold, the output is forced smartly and rapidly from one logic state to the other. One of the corollaries of the Schmitt trigger's use of positive feedback is that, should the input voltage move gently down again past the same threshold, the positive feedback will hold the output in the same state with no change. This effect is called hysteresis: the input voltage has to drop past a different, lower threshold to 'un-latch' the output and reset it to its original digital value. By reducing the extent of the positive feedback, the hysteresis-width can be reduced, but it can not entirely be eradicated. The Schmitt trigger is, to some extent, a latching circuit.

Many common digital electronic circuits employ positive feedback. While normal simple boolean logic gates usually rely simply on gain to push digital signal voltages away from intermediate values to the values that are meant to represent boolean '0' and '1', but many more complex gates use feedback. When an input voltage is expected to vary in an analogue way, but sharp thresholds are required for later digital processing, the Schmitt trigger circuit uses positive feedback to ensure that if the input voltage creeps gently above the threshold, the output is forced smartly and rapidly from one logic state to the other. One of the corollaries of the Schmitt trigger's use of positive feedback is that, should the input voltage move gently down again past the same threshold, the positive feedback will hold the output in the same state with no change. This effect is called hysteresis: the input voltage has to drop past a different, lower threshold to 'un-latch' the output and reset it to its original digital value. By reducing the extent of the positive feedback, the hysteresis-width can be reduced, but it can not entirely be eradicated. The Schmitt trigger is, to some extent, a latching circuit.

许多常见的数字电路都采用正反馈。一般简单的布尔逻辑门通常只是依靠增益将数字信号电压从中间值推到代表布尔值0和1的值上，但许多更复杂的门都采用了反馈。当输入电压以模拟方式发生变化，但后期数字处理需要尖锐的阈值时，施密特触发电路使用正反馈，以确保当输入电压轻微超过阈值时，输出被巧妙而迅速地从一个逻辑状态转移到另一个逻辑状态。施密特触发器使用正反馈的一个必然结果是，如果输入电压再次缓慢下降，超过相同的阈值，正反馈将使输出保持在相同的状态而不改变。这种效应被称为滞后: 输入电压必须降到一个不同的、较低的阈值，才能“解锁”输出，并将其重置为原始数字。通过减小正反馈的程度，可以减小滞后宽度，但不能完全消除。施密特触发器在某种程度上是一个闭锁电路。

许多常见的数字电路都采用正反馈。一般简单的布尔逻辑门通常只是依靠增益将数字信号电压从中间值推到代表布尔值0和1的值上，但许多更复杂的门都采用了反馈。当输入的模拟电压发生变化，但后期数字处理需要尖锐阈值时，施密特触发电路通过正反馈机制确保当输入电压轻微超过阈值时，输出电压可以巧妙而迅速地从一个逻辑状态转移到另一个逻辑状态。施密特触发器使用正反馈的一个必然结果是，如果输入电压再次缓慢下降，超过了相同的阈值，由于正反馈的机制，输出电压将保持在相同的逻辑状态而不改变。这种效应被称为滞后: 输入电压必须降到一个不同的、较低的阈值，才能“解锁”输出，并将其重置为原始数字。通过减小正反馈的程度，可以减小滞后宽度，但宽度不能被完全消除。施密特触发器在某种程度上是一个闭锁电路。

Positive feedback is a mechanism by which an output is enhanced, such as protein levels. However, in order to avoid any fluctuation in the protein level, the mechanism is inhibited stochastically (I), therefore when the concentration of the activated protein (A) is past the threshold ([I]), the loop mechanism is activated and the concentration of A increases exponentially if d[A]=k [A]

【图9 Positive feedback is a mechanism by which an output is enhanced, such as protein levels. However, in order to avoid any fluctuation in the protein level, the mechanism is inhibited stochastically (I), therefore when the concentration of the activated protein (A) is past the threshold ([I]), the loop mechanism is activated and the concentration of A increases exponentially if d[A]=k [A] 正反馈是一种增强输出的机制，如蛋白质水平。但为了避免蛋白质水平的波动，该机制是随机抑制的（I），因此只有当激活的蛋白质（A）浓度超过阈值（[I]）时，循环机制被激活，如果d[A]=k[A]，A的浓度就会成倍增加。】

Illustration of an R-S ('reset-set') flip-flop made from two digital nor gates with positive feedback. Red and black mean logical '1' and '0', respectively.

【图10 Illustration of an R-S ('reset-set') flip-flop made from two digital nor gates with positive feedback. Red and black mean logical '1' and '0', respectively. R-S("复位-设置")触发器的说明，由两个带正反馈的数字诺尔门组成。红色和黑色分别表示逻辑上的 "1 "和 "0"。】

An electronic flip-flop, or "latch", or "bistable multivibrator", is a circuit that due to high positive feedback is not stable in a balanced or intermediate state. Such a bistable circuit is the basis of one bit of electronic memory.  The flip-flop uses a pair of amplifiers, transistors, or  logic gates connected to each other so that positive feedback maintains the state of the circuit in one of two unbalanced stable states after the input signal has been removed, until a suitable alternative signal is applied to change the state. Computer random access memory (RAM) can be made in this way, with one latching circuit for each bit of memory.

An electronic flip-flop, or "latch", or "bistable multivibrator", is a circuit that due to high positive feedback is not stable in a balanced or intermediate state. Such a bistable circuit is the basis of one bit of electronic memory.  The flip-flop uses a pair of amplifiers, transistors, or  logic gates connected to each other so that positive feedback maintains the state of the circuit in one of two unbalanced stable states after the input signal has been removed, until a suitable alternative signal is applied to change the state. Computer random access memory (RAM) can be made in this way, with one latching circuit for each bit of memory.

电子触发器，或“锁存器” ，或“双稳态多谐振荡器” ，是一种由于高正反馈而不稳定的平衡或中间状态的电路。这样的双稳态电路是一位电子存储器的基础。 触发器使用一对放大器、晶体管或逻辑门相互连接，使正反馈在输入信号被移除后，电路的状态维持在两种非平衡稳定状态中的一种，直到施加一个合适的替代信号来改变状态。计算机随机存取存储器(RAM)可以用这种方法制作，每位存储器有一个锁存电路。

电子触发器，或“锁存器” ，或“双稳态多谐振荡器” ，是一种由于高正反馈而不稳定于平衡或中间状态的电路。这样的双稳态电路是一位电子存储器的基础。 触发器使用一对放大器、晶体管或逻辑门相互连接，正反馈机制使得输入信号被去除后，电路可以维持在两种非平衡稳定状态中的一种，直到一个合适的替代信号重新作为输入，以改变电路状态。计算机随机存取存储器(RAM)可以用这种方式运作，每位存储器有一个锁存电路。

}}</ref>

}}</ref>

Thermal runaway occurs in electronic systems because some aspect of a circuit is allowed to pass more current when it gets hotter, then the hotter it gets, the more current it passes, which heats it some more and so it passes yet more current. The effects are usually catastrophic for the device in question. If devices have to be used near to their maximum power-handling capacity, and thermal runaway is possible or likely under certain conditions, improvements can usually be achieved by careful design.

Thermal runaway occurs in electronic systems because some aspect of a circuit is allowed to pass more current when it gets hotter, then the hotter it gets, the more current it passes, which heats it some more and so it passes yet more current. The effects are usually catastrophic for the device in question. If devices have to be used near to their maximum power-handling capacity, and thermal runaway is possible or likely under certain conditions, improvements can usually be achieved by careful design.

[[File:Technics SL-1210MK2.jpg|thumb|left|A phonograph turntable is prone to acoustic feedback.|链接=Special:FilePath/Technics_SL-1210MK2.jpg]]

[[File:Technics SL-1210MK2.jpg|thumb|left|A phonograph turntable is prone to acoustic feedback.|链接=Special:FilePath/Technics_SL-1210MK2.jpg]]

A phonograph turntable is prone to acoustic feedback.

【图11 A phonograph turntable is prone to acoustic feedback. 留声机转盘容易受到声反馈的影响。】

 

Audio and video systems can demonstrate positive feedback. If a microphone picks up the amplified sound output of loudspeakers in the same circuit, then howling and screeching sounds of audio feedback (at up to the maximum power capacity of the amplifier) will be heard, as random noise is re-amplified by positive feedback and filtered by the characteristics of the audio system and the room.

Audio and video systems can demonstrate positive feedback. If a microphone picks up the amplified sound output of loudspeakers in the same circuit, then howling and screeching sounds of audio feedback (at up to the maximum power capacity of the amplifier) will be heard, as random noise is re-amplified by positive feedback and filtered by the characteristics of the audio system and the room.

===Audio and live music===

===Audio and live music===

Audio feedback (also known as acoustic feedback, simply as feedback, or the Larsen effect) is a special kind of positive feedback which occurs when a sound loop exists between an audio input (for example, a microphone or guitar pickup) and an audio output (for example, a loudly-amplified 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 sound 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. For small PA systems the sound is readily recognized as a loud squeal or screech.

Audio feedback (also known as acoustic feedback, simply as feedback, or the Larsen effect) is a special kind of positive feedback which occurs when a sound loop exists between an audio input (for example, a microphone or guitar pickup) and an audio output (for example, a loudly-amplified 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 sound 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. For small PA systems the sound is readily recognized as a loud squeal or screech.

音频反馈（也称为声反馈，简称反馈，或拉森效应）是一种特殊的正反馈，当音频输入（例如，麦克风或吉他拾音器）和音频输出（例如，大声放大的扬声器）之间存在声音回路时，就会出现这种反馈。在这个例子中，麦克风接收到的信号被放大并从扬声器传出。然后，来自扬声器的声音可以再次被麦克风接收，进一步放大，然后再次通过扬声器传递出去。 所产生的声音的频率由传声器、放大器和扬声器的共振频率、房间的声学特性、传声器和扬声器的定向拾音和发射模式以及它们之间的距离决定。对于小型的扩声系统来说，这种声音很容易被识别为响亮的吱吱声或尖叫声。

音频反馈（也称为声反馈，简称反馈，或拉森效应）是一种特殊的正反馈，当音频输入（例如，麦克风或吉他拾音器）和音频输出（例如，大声放大的扬声器）之间存在声音回路时，就会出现这种反馈。在这个例子中，麦克风接收到的信号被放大并从扬声器传出。然后，来自扬声器的声音可以再次被麦克风接收，进一步放大，然后再次通过扬声器传递出去。 所产生的声音的频率由传声器、放大器和扬声器的共振频率、房间的声学特性、传声器和扬声器的定向拾音和发射模式以及它们之间的距离决定。对于小型的扩声系统来说，这种声音很容易的体现的响亮的吱吱声或尖叫声。

Feedback is almost always considered undesirable when it occurs with a singer's or public speaker's microphone at an event using a sound reinforcement system or PA system. Audio engineers use various electronic devices, such as equalizers and, since the 1990s, automatic feedback detection devices to prevent these unwanted squeals or screeching sounds, which detract from the audience's enjoyment of the event. On the other hand, since the 1960s, electric guitar players in rock music bands using loud guitar amplifiers and distortion effects have intentionally created guitar feedback to create a desirable musical effect.  "I Feel Fine" by the Beatles marks one of the earliest examples of the use of feedback as a recording effect in popular music. It starts with a single, percussive feedback note produced by plucking the A string on Lennon's guitar. Artists such as the Kinks and the Who had already used feedback live, but Lennon remained proud of the fact that the Beatles were perhaps the first group to deliberately put it on vinyl. In one of his last interviews, he said, "I defy anybody to find a record—unless it's some old blues record in 1922—that uses feedback that way."

Feedback is almost always considered undesirable when it occurs with a singer's or public speaker's microphone at an event using a sound reinforcement system or PA system. Audio engineers use various electronic devices, such as equalizers and, since the 1990s, automatic feedback detection devices to prevent these unwanted squeals or screeching sounds, which detract from the audience's enjoyment of the event. On the other hand, since the 1960s, electric guitar players in rock music bands using loud guitar amplifiers and distortion effects have intentionally created guitar feedback to create a desirable musical effect.  "I Feel Fine" by the Beatles marks one of the earliest examples of the use of feedback as a recording effect in popular music. It starts with a single, percussive feedback note produced by plucking the A string on Lennon's guitar. Artists such as the Kinks and the Who had already used feedback live, but Lennon remained proud of the fact that the Beatles were perhaps the first group to deliberately put it on vinyl. In one of his last interviews, he said, "I defy anybody to find a record—unless it's some old blues record in 1922—that uses feedback that way."

在使用扩声系统或扩音系统的活动中，当歌手或公众演讲者的麦克风发生反馈时，几乎总是被认为是不受欢迎的。音频工程师使用各种电子设备，如均衡器，自20世纪90年代以来，自动反馈检测设备，以防止这些不需要的尖叫声或尖叫声，这些声音影响了观众对活动的享受。另一方面，自20世纪60年代以来，摇滚乐队中的电吉他手使用大音量的吉他放大器和失真效果，有意制造吉他反馈，以创造理想的音乐效果。 披头士乐队的 "I Feel Fine "标志着流行音乐中最早使用反馈作为录音效果的例子之一。它的开头是由Lennon拨动吉他上的A弦产生的一个单一的、有冲击力的反馈音。像 Kinks 和 Who 等艺术家已经在现场使用了反馈，但是Lennon仍然为披头士乐队可能是第一个特意把它放在黑胶唱片上的乐队而感到骄傲。在他最后的一次采访中，他说，“我认为任何人都不可能找到一张唱片——除非它是1922年的一张旧布鲁斯唱片——那样使用反馈。”

在歌手或公众演讲者使用扩声系统或扩音系统的活动中，麦克风发生的正反馈几乎总是被认为是不受欢迎的。自20世纪90年代以来，音频工程师使用各种电子设备，如均衡器或者自动反馈检测设备，来防止这些不受欢迎的尖叫声或尖叫声，这些声音影响了观众对活动的享受。另一方面，自20世纪60年代以来，摇滚乐队中的电吉他手使用大音量的吉他放大器和失真效果，有意制造吉他中的正反馈，以创造理想的音乐效果。 披头士乐队的 "I Feel Fine "是流行音乐中最早使用反馈作为录音效果的例子之一。它的开头是由Lennon拨动吉他上的A弦产生的一个单一的、有冲击力的反馈音。像 Kinks 和 Who 等艺术家已经在现场使用了正反馈，但是Lennon仍然为披头士乐队可能是第一个特意把它放在黑胶唱片上的乐队而感到骄傲。在他最后的一次采访中，他说，“我敢说任何人都找不到这样的唱片，除非是1922年用这种方式录制的老蓝调唱片。”

The principles of audio feedback were first discovered by Danish scientist Søren Absalon Larsen. Microphones are not the only transducers subject to this effect. Record deck pickup cartridges can do the same, usually in the low frequency range below about 100&nbsp;Hz, manifesting as a low rumble. Jimi Hendrix was an innovator in the intentional use of guitar feedback in his guitar solos to create unique sound effects. He helped develop the controlled and musical use of audio feedback in electric guitar playing, and later Brian May was a famous proponent of the technique.

The principles of audio feedback were first discovered by Danish scientist Søren Absalon Larsen. Microphones are not the only transducers subject to this effect. Record deck pickup cartridges can do the same, usually in the low frequency range below about 100&nbsp;Hz, manifesting as a low rumble. Jimi Hendrix was an innovator in the intentional use of guitar feedback in his guitar solos to create unique sound effects. He helped develop the controlled and musical use of audio feedback in electric guitar playing, and later Brian May was a famous proponent of the technique.

音频反馈的原理是由丹麦科学家Søren Absalon Larsen首先发现的。麦克风并不是唯一受此影响的换能器。录音板拾音器也可以做到这一点，通常在100赫兹以下的低频范围内，表现为低沉的轰鸣声。Jimi Hendrix是一个创新者，在他的吉他独奏中有意使用吉他反馈来创造独特的声音效果。他帮助开发了电吉他演奏中音频反馈的可控性和音乐性，后来Brian May也是这种技术的著名支持者。

音频反馈的原理是由丹麦科学家Søren Absalon Larsen首先发现的。麦克风并不是唯一受此影响的传感器。录音板拾音器也会产生正反馈，通常是在100赫兹以下的低频范围内表现出低沉的轰鸣声。Jimi Hendrix是一个创新者，在他的吉他独奏中有意使用吉他正反馈来创造独特的声音效果。他帮助发展了电吉他演奏中音频反馈的可控性和音乐性，后来Brian May也是这种技术的著名支持者。

[[File:Adam Savage HOPE.jpg|thumb|right|220px|[[Video feedback]].|链接=Special:FilePath/Adam_Savage_HOPE.jpg]]

[[File:Adam Savage HOPE.jpg|thumb|right|220px|[[Video feedback]].|链接=Special:FilePath/Adam_Savage_HOPE.jpg]]

视频

视频

Similarly, if a [[video camera]] is pointed at a [[Video monitor|monitor]] screen that is displaying the camera's own signal, then repeating patterns can be formed on the screen by positive feedback. This video feedback effect was used in the opening sequences to the [[Doctor Who (season 1)|first]] [[Doctor Who (season 10)|ten]] series of the television program ''[[Doctor Who]]''.Similarly, if a video camera is pointed at a monitor screen that is displaying the camera's own signal, then repeating patterns can be formed on the screen by positive feedback. This video feedback effect was used in the opening sequences to the first ten series of the television program Doctor Who.

Similarly, if a [[video camera]] is pointed at a [[Video monitor|monitor]] screen that is displaying the camera's own signal, then repeating patterns can be formed on the screen by positive feedback. This video feedback effect was used in the opening sequences to the [[Doctor Who (season 1)|first]] [[Doctor Who (season 10)|ten]] series of the television program ''[[Doctor Who]]''.

 

Similarly, if a video camera is pointed at a monitor screen that is displaying the camera's own signal, then repeating patterns can be formed on the screen by positive feedback. This video feedback effect was used in the opening sequences to the first ten series of the television program Doctor Who.

 

Positive feedback is the amplification of a body's response to a stimulus. For example, in childbirth, when the head of the fetus pushes up against the cervix (1) it stimulates a nerve impulse from the cervix to the brain (2). When the brain is notified, it signals the pituitary gland to release a hormone called oxytocin(3). Oxytocin is then carried via the bloodstream to the uterus(4) causing contractions, pushing the fetus towards the cervix eventually inducing childbirth.

Positive feedback is the amplification of a body's response to a stimulus. For example, in childbirth, when the head of the fetus pushes up against the cervix (1) it stimulates a nerve impulse from the cervix to the brain (2). When the brain is notified, it signals the pituitary gland to release a hormone called oxytocin(3). Oxytocin is then carried via the bloodstream to the uterus(4) causing contractions, pushing the fetus towards the cervix eventually inducing childbirth.

正反馈是指身体对刺激的反应的放大。例如，在分娩过程中，当胎儿的头顶到子宫颈时(1)，会刺激神经冲动从子宫颈到大脑(2)。大脑接到通知后，会向脑垂体发出信号，释放一种叫做催产素的激素(3)。催产素随后通过血液流向子宫(4)，引起宫缩，将胎儿推向子宫颈，最终促使分娩。

生物学中的正反馈是指身体对刺激的反应的放大。例如，在分娩过程中，当胎儿的头顶到子宫颈时(1)，会刺激神经冲动从子宫颈到大脑(2)。大脑接到通知后，会向脑垂体发出信号，释放一种叫做催产素的激素(3)。催产素随后通过血液流向子宫(4)，引起宫缩，将胎儿推向子宫颈，最终促使分娩。

==== In physiology ====

==== In physiology ====

在生理学中

在生理学中

A number of examples of positive feedback systems may be found in [[physiology]].

A number of examples of positive feedback systems may be found in [[physiology]].

* Another example is the process of [[Coagulation|blood clotting]]. The loop is initiated when injured tissue releases signal chemicals that activate platelets in the blood. An activated platelet releases chemicals to activate more platelets, causing a rapid cascade and the formation of a blood clot.<ref name=Guyton1991/>{{rp|pages=392–394}}

* Another example is the process of [[Coagulation|blood clotting]]. The loop is initiated when injured tissue releases signal chemicals that activate platelets in the blood. An activated platelet releases chemicals to activate more platelets, causing a rapid cascade and the formation of a blood clot.<ref name=Guyton1991/>{{rp|pages=392–394}}

* [[Lactation]] also involves positive feedback in that as the baby suckles on the nipple there is a nerve response into the spinal cord and up into the hypothalamus of the brain, which then stimulates the [[pituitary]] gland to produce more [[prolactin]] to produce more milk.<ref name=Guyton1991/>{{rp|page=926}}

* [[Lactation]] also involves positive feedback in that as the baby suckles on the nipple there is a nerve response into the spinal cord and up into the hypothalamus of the brain, which then stimulates the [[pituitary]] gland to produce more [[prolactin]] to produce more milk.<ref name=Guyton1991/>{{rp|page=926}}

* The generation of [[nerve signal]]s is another example, in which the membrane of a nerve fibre causes slight leakage of sodium ions through sodium channels, resulting in a change in the membrane potential, which in turn causes more opening of channels, and so on ([[Hodgkin cycle]]). So a slight initial leakage results in an explosion of sodium leakage which creates the nerve [[action potential]].<ref name=Guyton1991/>{{rp|page=59}}

* The generation of [[nerve signal]]s is another example, in which the membrane of a nerve fibre causes slight leakage of sodium ions through sodium channels, resulting in a change in the membrane potential, which in turn causes more opening of channels, and so on ([[Hodgkin cycle]]). So a slight initial leakage results in an explosion of sodium leakage which creates the nerve [[action potential]].<ref name=Guyton1991/>{{rp|page=59}}

* In [[excitation–contraction coupling]] of the heart, an increase in intracellular calcium ions to the cardiac myocyte is detected by ryanodine receptors in the membrane of the sarcoplasmic reticulum which transport calcium out into the cytosol in a positive feedback physiological response.

* In [[excitation–contraction coupling]] of the heart, an increase in intracellular calcium ions to the cardiac myocyte is detected by ryanodine receptors in the membrane of the sarcoplasmic reticulum which transport calcium out into the cytosol in a positive feedback physiological response.

In most cases, such feedback loops culminate in counter-signals being released that suppress or break the loop. Childbirth contractions stop when the baby is out of the mother's body. Chemicals break down the blood clot. Lactation stops when the baby no longer nurses.<ref name=Guyton1991/>

In most cases, such feedback loops culminate in counter-signals being released that suppress or break the loop. Childbirth contractions stop when the baby is out of the mother's body. Chemicals break down the blood clot. Lactation stops when the baby no longer nurses.<ref name=Guyton1991/>

正反馈是基因调控中研究得很好的一种现象，其中最常见的是与双稳态有关。当一个基因通过双负反馈循环直接或间接激活自身时，就会出现正反馈。遗传工程师已经在细菌中构建并测试了简单的正反馈网络，以证明双稳态的概念。<ref name=Hasty2002/>

正反馈是基因调控中研究得很好的一种现象，其中最常见的是与双稳态有关。当一个基因通过双负反馈循环直接或间接激活自身时，就会出现正反馈。遗传工程师已经在细菌中构建并测试了简单的正反馈网络，以证明双稳态的概念。<ref name=Hasty2002/>

正反馈的一个典型例子是大肠杆菌中的乳糖操纵子。正反馈在细胞分化、发育和癌症进展中起着不可或缺的作用，因此，基因调控中的正反馈可以产生显著的生理后果。分子动力学中的随机运动加上正反馈可以引发有趣的效应，例如从同一母细胞中产生表型不同的细胞群。<ref name=Veening2008/>  

正反馈的一个典型例子是大肠杆菌中的乳糖操纵子。正反馈在细胞分化、发育和癌症进展中起着不可或缺的作用，因此，基因调控中的正反馈可以产生显著的生理结果。分子动力学中的随机运动加上正反馈可以引发有趣的效应，例如从同一母细胞中产生表型不同的细胞群。<ref name=Veening2008/> 这种情况的发生是因为噪声会被正反馈放大。正反馈也可以发生在细胞信号的其他形式中，如酶动力学或代谢途径。<ref name=Christoph2001/>

这种情况的发生是因为噪声会被正反馈放大。正反馈也可以发生在细胞信号的其他形式中，如酶动力学或代谢途径。<ref name=Christoph2001/>

==== In evolutionary biology ====

==== In evolutionary biology ====

Positive feedback loops have been used to describe aspects of the dynamics of change in biological [[evolution]].  For example, beginning at the macro level, [[Alfred J. Lotka]] (1945) argued that the evolution of the species was most essentially a matter of selection that fed back energy flows to capture more and more energy for use by living systems.<ref name=Lotka1945/> At the human level, [[Richard D. Alexander]] (1989) proposed that social competition between and within human groups fed back to the selection of intelligence thus constantly producing more and more refined human intelligence. <ref name=Alexander1989/> [[Bernard Crespi|Crespi]] (2004) discussed several other examples of positive feedback loops in evolution.<ref name=Crespi2004/>  The analogy of [[Evolutionary arms race]]s provide further examples of positive feedback in biological systems.<ref name=Blindwatchmaker/>

Positive feedback loops have been used to describe aspects of the dynamics of change in biological [[evolution]].  For example, beginning at the macro level, [[Alfred J. Lotka]] (1945) argued that the evolution of the species was most essentially a matter of selection that fed back energy flows to capture more and more energy for use by living systems.<ref name=Lotka1945/> At the human level, [[Richard D. Alexander]] (1989) proposed that social competition between and within human groups fed back to the selection of intelligence thus constantly producing more and more refined human intelligence. <ref name=Alexander1989/> [[Bernard Crespi|Crespi]] (2004) discussed several other examples of positive feedback loops in evolution.<ref name=Crespi2004/>  The analogy of [[Evolutionary arms race]]s provide further examples of positive feedback in biological systems.<ref name=Blindwatchmaker/>

正反馈循环被用来描述生物进化中变化动态的各个方面。 例如，在宏观层面，阿尔弗雷德•J•洛特卡Alfred J. Lotka(1945)认为，物种的进化最本质上是一个选择问题，它反馈了能量流，以获取越来越多的能量供生物系统使用。<ref name=Lotka1945/>在人类层面，理查德•D•亚历山大 Richard D. Alexander(1989)提出，人类群体之间和群体内部的社会竞争反馈到智力的选择上，从而不断产生更多、更完善的人类智力。 <ref name=Alexander1989/> Bernard Crespi(2004)讨论了进化中正反馈循环的其他几个例子。进化军备竞赛的类比给生物系统中的正反馈提供了进一步的例子。<ref name=Blindwatchmaker/>

在进化生物学中正反馈循环被用来描述生物进化中变化动态的各个方面。 例如，在宏观层面，Alfred J. Lotka（1945）认为，物种的演变最重要的是选择反馈能量流动以捕获越来越多的能源系统的能量。<ref name=Lotka1945/>在人类层面，Richard D. Alexander(1989)提出，人类群体之间和群体内部的社会竞争会影响智力的选择，从而时不时地会产生更多、更完善的人类智力。 <ref name=Alexander1989/> Bernard Crespi（2004）讨论了进化中正反馈循环的其他几个例子。通过与军备竞赛进行类比，给生物系统中的正反馈提供了进一步的例子。<ref name=Blindwatchmaker/>

[[File:Phanerozoic Biodiversity.svg|300px|right|thumb|During the Phanerozoic the [[biodiversity]] shows a steady but not monotonic increase from near zero to several thousands of genera.|链接=Special:FilePath/Phanerozoic_Biodiversity.svg]]

[[File:Phanerozoic Biodiversity.svg|300px|right|thumb|During the Phanerozoic the [[biodiversity]] shows a steady but not monotonic increase from near zero to several thousands of genera.|链接=Special:FilePath/Phanerozoic_Biodiversity.svg]]

It has been shown that changes in [[biodiversity]] through the [[Phanerozoic]] correlate much better with hyperbolic model (widely used in [[demography]] and [[macrosociology]]) than with [[Exponential growth|exponential]] and [[Logistic function|logistic]] models (traditionally used in [[population biology]] and extensively applied to [[fossil]] [[biodiversity]] as well). The latter models imply that changes in diversity are guided by a first-order positive feedback (more ancestors, more descendants) and/or a [[negative feedback]] arising from resource limitation.  Hyperbolic model implies a second-order positive feedback. The hyperbolic pattern of the [[world population growth]] has been demonstrated (see below) to arise from a second-order positive feedback between the population size and the rate of [[technological growth]]. The hyperbolic character of biodiversity growth can be similarly accounted for by a positive feedback between the diversity and community structure complexity. It has been suggested that the similarity between the curves of [[biodiversity]] and human population probably comes from the fact that both are derived from the interference of the hyperbolic trend (produced by the positive feedback) with cyclical and stochastic dynamics.<ref>Markov A., [[Andrey Korotayev|Korotayev A.]] [https://archive.today/20120630063924/http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B83WC-4N0HJMK-2&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&_docanchor=&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=74a80d7c55ff987c9fc8d9c7963feab9 "Phanerozoic marine biodiversity follows a hyperbolic trend." [[Palaeoworld]]. Volume 16, Issue 4, December 2007, Pages 311-318]</ref><ref>{{cite journal | last1 = Markov | first1 = A. | last2 = Korotayev | first2 = A. | year = 2008 | title = Hyperbolic growth of marine and continental biodiversity through the Phanerozoic and community evolution | url = http://elementy.ru/genbio/abstracts?artid=177 | journal = Journal of General Biology | volume = 69 | issue = 3 | pages = 175–194 | pmid = 18677962 | url-status = live | archiveurl = https://web.archive.org/web/20091225000305/http://elementy.ru/genbio/abstracts?artid=177 | archivedate = 2009-12-25 }}</ref>

It has been shown that changes in [[biodiversity]] through the [[Phanerozoic]] correlate much better with hyperbolic model (widely used in [[demography]] and [[macrosociology]]) than with [[Exponential growth|exponential]] and [[Logistic function|logistic]] models (traditionally used in [[population biology]] and extensively applied to [[fossil]] [[biodiversity]] as well). The latter models imply that changes in diversity are guided by a first-order positive feedback (more ancestors, more descendants) and/or a [[negative feedback]] arising from resource limitation.  Hyperbolic model implies a second-order positive feedback. The hyperbolic pattern of the [[world population growth]] has been demonstrated (see below) to arise from a second-order positive feedback between the population size and the rate of [[technological growth]]. The hyperbolic character of biodiversity growth can be similarly accounted for by a positive feedback between the diversity and community structure complexity. It has been suggested that the similarity between the curves of [[biodiversity]] and human population probably comes from the fact that both are derived from the interference of the hyperbolic trend (produced by the positive feedback) with cyclical and stochastic dynamics.<ref>Markov A., [[Andrey Korotayev|Korotayev A.]] [https://archive.today/20120630063924/http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B83WC-4N0HJMK-2&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&_docanchor=&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=74a80d7c55ff987c9fc8d9c7963feab9 "Phanerozoic marine biodiversity follows a hyperbolic trend." [[Palaeoworld]]. Volume 16, Issue 4, December 2007, Pages 311-318]</ref><ref>{{cite journal | last1 = Markov | first1 = A. | last2 = Korotayev | first2 = A. | year = 2008 | title = Hyperbolic growth of marine and continental biodiversity through the Phanerozoic and community evolution | url = http://elementy.ru/genbio/abstracts?artid=177 | journal = Journal of General Biology | volume = 69 | issue = 3 | pages = 175–194 | pmid = 18677962 | url-status = live | archiveurl = https://web.archive.org/web/20091225000305/http://elementy.ru/genbio/abstracts?artid=177 | archivedate = 2009-12-25 }}</ref>

研究表明，在显生宙，生物多样性的变化与双曲模型（广泛用于人口学和宏观社会学）的相关性要比指数模型和逻辑逻辑斯谛（传统上用于人口生物学，并广泛用于生物多样性化石）的相关性好得多。后者的模型意味着多样性的变化是由一阶正反馈（更多的祖先，更多的后代）和/或资源限制产生的负反馈所引导的。双曲模型意味着二阶正反馈。世界人口增长的双曲线模式已被证明（见下文），源于人口数量与技术增长速度之间的二阶正反馈。生物多样性增长的双曲特征同样可以由多样性与群落结构复杂性之间的正反馈来解释。有人认为，生物多样性和人口曲线之间的相似性可能来自这样一个事实，即两者都是由双曲趋势(由正反馈产生)与周期性和随机性动态的干扰而产生的。

研究表明，在显生宙，生物多样性的变化与双曲模型（广泛用于人口学和宏观社会学）的相关性要比指数模型和逻辑斯特模型（传统上用于人口生物学，并广泛用于生物多样性化石）的相关性好得多。后者的模型意味着多样性的变化是由一阶正反馈（更多的祖先，更多的后代）和资源限制产生的负反馈所引导的。双曲模型意味着二阶正反馈。世界人口增长的双曲线模式已被证明源于人口数量与技术增长速度之间的二阶正反馈。生物多样性增长的双曲特征同样可以由多样性与群落结构复杂性之间的正反馈来解释。有人认为，生物多样性和人口曲线之间的相似性可能来自这样一个事实，即两者都是由双曲趋势(由正反馈产生)与周期性和随机性的动态干扰而产生的。

A [[cytokine storm]], or '''hypercytokinemia''' is a potentially fatal immune reaction consisting of a positive feedback loop between [[cytokine]]s and [[immune cell]]s, with highly elevated levels of various cytokines.<ref name="osterholm">{{cite journal | last = Osterholm | first = Michael T. | author-link = Michael Osterholm |title = Preparing for the Next Pandemic | journal = The New England Journal of Medicine | volume = 352 | issue = 18 | pages = 1839–1842 | date = 2005-05-05 | url = | doi = 10.1056/NEJMp058068  | pmid = 15872196 | citeseerx = 10.1.1.608.6200 }}</ref> In normal immune function, positive feedback loops can be utilized to enhance the action of B lymphocytes. When a B cell binds its antibodies to an antigen and becomes activated, it begins releasing antibodies and secreting a complement protein called C3. Both C3 and a B cell's antibodies can bind to a pathogen, and when a B cell has its antibodies bind to a pathogen with C3, it speeds up that B cell's secretion of more antibodies and more C3, thus creating a positive feedback loop.<ref>{{cite journal|last=Paul|first=William E.|title=Infectious Diseases and the Immune System|journal=Scientific American|volume=269|issue=3|date=September 1993|page=93|bibcode=1993SciAm.269c..90P|doi=10.1038/scientificamerican0993-90|pmid=8211095}}</ref>

A [[cytokine storm]], or '''hypercytokinemia''' is a potentially fatal immune reaction consisting of a positive feedback loop between [[cytokine]]s and [[immune cell]]s, with highly elevated levels of various cytokines.<ref name="osterholm">{{cite journal | last = Osterholm | first = Michael T. | author-link = Michael Osterholm |title = Preparing for the Next Pandemic | journal = The New England Journal of Medicine | volume = 352 | issue = 18 | pages = 1839–1842 | date = 2005-05-05 | url = | doi = 10.1056/NEJMp058068  | pmid = 15872196 | citeseerx = 10.1.1.608.6200 }}</ref> In normal immune function, positive feedback loops can be utilized to enhance the action of B lymphocytes. When a B cell binds its antibodies to an antigen and becomes activated, it begins releasing antibodies and secreting a complement protein called C3. Both C3 and a B cell's antibodies can bind to a pathogen, and when a B cell has its antibodies bind to a pathogen with C3, it speeds up that B cell's secretion of more antibodies and more C3, thus creating a positive feedback loop.<ref>{{cite journal|last=Paul|first=William E.|title=Infectious Diseases and the Immune System|journal=Scientific American|volume=269|issue=3|date=September 1993|page=93|bibcode=1993SciAm.269c..90P|doi=10.1038/scientificamerican0993-90|pmid=8211095}}</ref>

细胞因子风暴，或称高细胞因子血症，是一种潜在的致命性免疫反应，由细胞因子和免疫细胞之间的正反馈环组成，各种细胞因子水平高度升高[36]在正常的免疫功能中，可以利用正反馈环来增强B淋巴细胞的作用。<ref name="osterholm">{{cite journal | last = Osterholm | first = Michael T. | author-link = Michael Osterholm |title = Preparing for the Next Pandemic | journal = The New England Journal of Medicine | volume = 352 | issue = 18 | pages = 1839–1842 | date = 2005-05-05 | url = | doi = 10.1056/NEJMp058068  | pmid = 15872196 | citeseerx = 10.1.1.608.6200 }}</ref>当B细胞将其抗体与抗原结合并被激活后，就开始释放抗体并分泌一种称为C3的补体蛋白。C3和B细胞的抗体都可以与病原体结合，当B细胞的抗体与C3结合后，就会加快该B细胞分泌更多的抗体和更多的C3，从而形成一个正反馈循环。<ref>{{cite journal|last=Paul|first=William E.|title=Infectious Diseases and the Immune System|journal=Scientific American|volume=269|issue=3|date=September 1993|page=93|bibcode=1993SciAm.269c..90P|doi=10.1038/scientificamerican0993-90|pmid=8211095}}</ref>

细胞因子风暴，或称高细胞因子血症，是一种潜在的致命性免疫反应，表现为各种细胞因子水平高度升高，这是由细胞因子和免疫细胞之间的正反馈环组成。[36]在正常的免疫功能中，可以利用正反馈环来增强B淋巴细胞的作用。<ref name="osterholm">{{cite journal | last = Osterholm | first = Michael T. | author-link = Michael Osterholm |title = Preparing for the Next Pandemic | journal = The New England Journal of Medicine | volume = 352 | issue = 18 | pages = 1839–1842 | date = 2005-05-05 | url = | doi = 10.1056/NEJMp058068  | pmid = 15872196 | citeseerx = 10.1.1.608.6200 }}</ref>当B细胞将其抗体与抗原结合并被激活后，就开始释放抗体并分泌一种称为C3的补体蛋白。C3和B细胞的抗体都可以与病原体结合，当B细胞的抗体与C3结合后，就会加快该B细胞分泌更多的抗体和更多的C3蛋白，从而形成一个正反馈循环。<ref>{{cite journal|last=Paul|first=William E.|title=Infectious Diseases and the Immune System|journal=Scientific American|volume=269|issue=3|date=September 1993|page=93|bibcode=1993SciAm.269c..90P|doi=10.1038/scientificamerican0993-90|pmid=8211095}}</ref>

==== Cell death ====

==== Cell death ====

[[Apoptosis]] is a [[caspase]]-mediated process of cellular death, whose aim is the removal of long-lived or damaged cells. A failure of this process has been implicated in prominent conditions such as [[cancer]] or [[Parkinson's disease]]. The very core of the apoptotic process is the auto-activation of caspases, which may be modeled via a positive-feedback loop. This positive feedback exerts an auto-activation of the [[effector caspase]] by means of intermediate caspases. When isolated from the rest of apoptotic pathway, this positive-feedback presents only one stable steady state, regardless of the number of intermediate activation steps of the effector caspase.<ref name="ReferenceA"/> When this core process is complemented with inhibitors and enhancers of caspases effects, this process presents bistability, thereby modeling the alive and dying states of a cell.<ref>{{cite journal|last=Eissing|first=Thomas |doi=10.1074/jbc.M404893200 |title=Bistability analyses of a caspase activation model for receptor-induced apoptosis|journal=Journal of Biological Chemistry|volume=279 |issue=35 |date=2014|pages=36892–36897|pmid=15208304 |doi-access=free}}</ref>

[[Apoptosis]] is a [[caspase]]-mediated process of cellular death, whose aim is the removal of long-lived or damaged cells. A failure of this process has been implicated in prominent conditions such as [[cancer]] or [[Parkinson's disease]]. The very core of the apoptotic process is the auto-activation of caspases, which may be modeled via a positive-feedback loop. This positive feedback exerts an auto-activation of the [[effector caspase]] by means of intermediate caspases. When isolated from the rest of apoptotic pathway, this positive-feedback presents only one stable steady state, regardless of the number of intermediate activation steps of the effector caspase.<ref name="ReferenceA"/> When this core process is complemented with inhibitors and enhancers of caspases effects, this process presents bistability, thereby modeling the alive and dying states of a cell.<ref>{{cite journal|last=Eissing|first=Thomas |doi=10.1074/jbc.M404893200 |title=Bistability analyses of a caspase activation model for receptor-induced apoptosis|journal=Journal of Biological Chemistry|volume=279 |issue=35 |date=2014|pages=36892–36897|pmid=15208304 |doi-access=free}}</ref>

细胞凋亡是一种由酪蛋白酶介导的细胞死亡过程，其目的是清除长寿或受损的细胞。这一过程的失败与癌症或帕金森氏病等著名疾病有关。细胞凋亡过程的核心是半胱氨酸蛋白酶的自动激活，它可以通过一个正反馈循环来建模。这种正反馈通过中间胱天蛋白酶使效应子胱天蛋白酶自动活化。当从凋亡途径的其他部分分离出来时，无论效应子胱天蛋白酶的中间激活步骤的数量如何，这种正反馈仅呈现一种稳定的稳态。<ref name="ReferenceA"/>  

细胞凋亡是一种由酪蛋白酶介导的细胞死亡过程，其目的是清除长寿或受损的细胞。这一过程的失效与癌症或帕金森氏病等著名疾病有关。细胞凋亡过程的核心是半胱氨酸蛋白酶的自动激活，它可以通过一个正反馈循环来建模。这种正反馈通过中间胱天蛋白酶使效应子胱天蛋白酶自动活化。当从凋亡途径的其他部分分离出来时，无论效应子胱天蛋白酶的中间激活步骤数量有多少，这种正反馈仅呈现一种稳定的稳态。<ref name="ReferenceA"/> 当该核心过程与胱天蛋白酶作用的抑制剂和增强剂相辅相成时，该过程呈现双稳态，从而模拟细胞的存活和死亡状态。

当该核心过程与胱天蛋白酶作用的抑制剂和增强剂相辅相成时，该过程呈现双稳态，从而模拟细胞的存活和死亡状态。

Winner (1996) described gifted children as driven by positive feedback loops involving setting their own learning course, this feeding back satisfaction, thus further setting their learning goals to higher levels and so on.<ref name=Winner1996/>  Winner termed this positive feedback loop as a "rage to master."  Vandervert (2009a, 2009b) proposed that the [[child prodigy]] can be explained in terms of a positive feedback loop between the output of thinking/performing in [[working memory]], which then is fed to the [[cerebellum]] where it is streamlined, and then fed back to working memory thus steadily increasing the quantitative and qualitative output of working memory.<ref name=Vandervert2009a/><ref name=Vandervert2009b/>  Vandervert also argued that this working memory/cerebellar positive feedback loop was responsible for [[language]] evolution in working memory.

Winner (1996) described gifted children as driven by positive feedback loops involving setting their own learning course, this feeding back satisfaction, thus further setting their learning goals to higher levels and so on.<ref name=Winner1996/>  Winner termed this positive feedback loop as a "rage to master."  Vandervert (2009a, 2009b) proposed that the [[child prodigy]] can be explained in terms of a positive feedback loop between the output of thinking/performing in [[working memory]], which then is fed to the [[cerebellum]] where it is streamlined, and then fed back to working memory thus steadily increasing the quantitative and qualitative output of working memory.<ref name=Vandervert2009a/><ref name=Vandervert2009b/>  Vandervert also argued that this working memory/cerebellar positive feedback loop was responsible for [[language]] evolution in working memory.

温纳（Winner，1996）将有天赋的孩子描述为受到正反馈循环的驱动，这些反馈循环涉及设置自己的学习课程，反馈自己的满意程度，从而进一步将他们的学习目标提高到更高水平等等。<ref name=Winner1996/>

Winner（1996）将有天赋的孩子描述为受到正反馈循环的驱动，这些反馈循环体现在他们自己的课程学习上，通过反馈自己的满意程度，从而进一步将他们的学习目标提高到更高水平等等。<ref name=Winner1996/>Winner将这种正反馈循环称为 "狂热的掌握"。 Vandervert(2009a，2009b)提出，神童可以用工作记忆中的思维/表现输出之间的正反馈回路来解释，工作记忆中的思维/表现输出被反馈到小脑，在那里被精简，然后再反馈到工作记忆中，从而稳定地增加工作记忆的数量和质量输出。<ref name=Vandervert2009a/><ref name=Vandervert2009b/>  

Winner将这种正反馈循环称为 "愤怒的掌握"。 Vandervert(2009a，2009b)提出，神童可以用工作记忆中的思维/表现的输出之间的正反馈回路来解释，工作记忆中的思维/表现的输出被反馈到小脑，在那里被精简，然后再反馈到工作记忆中，从而稳定地增加工作记忆的数量和质量输出。<ref name=Vandervert2009a/><ref name=Vandervert2009b/>  

=== In economics ===

=== In economics ===

Product recommendations and information about past purchases have been shown to influence consumers choices significantly whether it is for music, movie, book, technological, and other type of products. Social influence often induces a rich-get-richer phenomenon ([[Matthew effect]]) where popular products tend to become even more popular.<ref name="altszyler2017">{{cite journal | title= Transient dynamics in trial-offer markets with social influence: Trade-offs between appeal and quality. | author1= Altszyler, E | author2= Berbeglia, F. | author3= Berbeglia, G. | author4= Van Hentenryck, P. | journal= PLOS ONE | year= 2017 | volume= 12 | issue= 7 | df= | doi=10.1371/journal.pone.0180040 |pmid = 28746334| pmc= 5528888 | page=e0180040| bibcode= 2017PLoSO..1280040A }}</ref>

Product recommendations and information about past purchases have been shown to influence consumers choices significantly whether it is for music, movie, book, technological, and other type of products. Social influence often induces a rich-get-richer phenomenon ([[Matthew effect]]) where popular products tend to become even more popular.<ref name="altszyler2017">{{cite journal | title= Transient dynamics in trial-offer markets with social influence: Trade-offs between appeal and quality. | author1= Altszyler, E | author2= Berbeglia, F. | author3= Berbeglia, G. | author4= Van Hentenryck, P. | journal= PLOS ONE | year= 2017 | volume= 12 | issue= 7 | df= | doi=10.1371/journal.pone.0180040 |pmid = 28746334| pmc= 5528888 | page=e0180040| bibcode= 2017PLoSO..1280040A }}</ref>

事实证明，产品推荐和过去购买的信息对消费者的选择影响很大，无论是音乐、电影、书籍、技术还是其他类型的产品。社会影响往往会诱发一种 "富者越富 "的现象（马太效应），即热门产品往往会变得更加受欢迎。<ref name="altszyler2017">{{cite journal | title= Transient dynamics in trial-offer markets with social influence: Trade-offs between appeal and quality. | author1= Altszyler, E | author2= Berbeglia, F. | author3= Berbeglia, G. | author4= Van Hentenryck, P. | journal= PLOS ONE | year= 2017 | volume= 12 | issue= 7 | df= | doi=10.1371/journal.pone.0180040 |pmid = 28746334| pmc= 5528888 | page=e0180040| bibcode= 2017PLoSO..1280040A }}</ref>

事实证明，产品推荐和消费者先前的购买信息对消费者的选择影响很大，无论是音乐、电影、书籍、电子产品还是其他类型的产品。社会影响往往会诱发一种 "富者越富 "的现象（马太效应），即热门产品往往会变得更加受欢迎。<ref name="altszyler2017">{{cite journal | title= Transient dynamics in trial-offer markets with social influence: Trade-offs between appeal and quality. | author1= Altszyler, E | author2= Berbeglia, F. | author3= Berbeglia, G. | author4= Van Hentenryck, P. | journal= PLOS ONE | year= 2017 | volume= 12 | issue= 7 | df= | doi=10.1371/journal.pone.0180040 |pmid = 28746334| pmc= 5528888 | page=e0180040| bibcode= 2017PLoSO..1280040A }}</ref>

====Market dynamics====

====Market dynamics====

According to the theory of [[reflexivity (social theory)|reflexivity]] advanced by [[George Soros]], price changes are driven by a positive feedback process whereby investors' expectations are influenced by price movements so their behaviour acts to reinforce movement in that direction until it becomes unsustainable, whereupon the feedback drives prices in the opposite direction.<ref>{{citation |title=Behavioural Technical Analysis |first=Paul V. |last=Azzopardi |publisher=Harriman House Limited |year=2010 |page=116 |isbn=9780857190680 |url=https://books.google.com/books?id=04Ay8qviuwgC&pg=PA116&lpg=PA116 |url-status=live |archiveurl=https://web.archive.org/web/20170329103058/https://books.google.com/books?id=04Ay8qviuwgC&pg=PA116&lpg=PA116&source=bl&hl=en&sa=X&f=false |archivedate=2017-03-29 }}</ref>

According to the theory of [[reflexivity (social theory)|reflexivity]] advanced by [[George Soros]], price changes are driven by a positive feedback process whereby investors' expectations are influenced by price movements so their behaviour acts to reinforce movement in that direction until it becomes unsustainable, whereupon the feedback drives prices in the opposite direction.<ref>{{citation |title=Behavioural Technical Analysis |first=Paul V. |last=Azzopardi |publisher=Harriman House Limited |year=2010 |page=116 |isbn=9780857190680 |url=https://books.google.com/books?id=04Ay8qviuwgC&pg=PA116&lpg=PA116 |url-status=live |archiveurl=https://web.archive.org/web/20170329103058/https://books.google.com/books?id=04Ay8qviuwgC&pg=PA116&lpg=PA116&source=bl&hl=en&sa=X&f=false |archivedate=2017-03-29 }}</ref>

根据乔治•索罗斯 George Soros提出的反射性理论，价格变化是由一个正反馈过程驱动的，即投资者的预期受到价格变动的影响，因此他们的行为会强化这个方向的运动，直到它变得不可持续，于是反馈推动价格向相反的方向发展。<ref>{{citation |title=Behavioural Technical Analysis |first=Paul V. |last=Azzopardi |publisher=Harriman House Limited |year=2010 |page=116 |isbn=9780857190680 |url=https://books.google.com/books?id=04Ay8qviuwgC&pg=PA116&lpg=PA116 |url-status=live |archiveurl=https://web.archive.org/web/20170329103058/https://books.google.com/books?id=04Ay8qviuwgC&pg=PA116&lpg=PA116&source=bl&hl=en&sa=X&f=false |archivedate=2017-03-29 }}</ref>

根据George Soros提出的反射性理论，价格变化是由一个正反馈过程驱动的，即投资者的预期受到价格变动的影响，因此他们的行为会强化这个方向的价格变动，直到价格的变化变得不可持续，于是反馈推动价格向相反的方向发展。<ref>{{citation |title=Behavioural Technical Analysis |first=Paul V. |last=Azzopardi |publisher=Harriman House Limited |year=2010 |page=116 |isbn=9780857190680 |url=https://books.google.com/books?id=04Ay8qviuwgC&pg=PA116&lpg=PA116 |url-status=live |archiveurl=https://web.archive.org/web/20170329103058/https://books.google.com/books?id=04Ay8qviuwgC&pg=PA116&lpg=PA116&source=bl&hl=en&sa=X&f=false |archivedate=2017-03-29 }}</ref>

==== Systemic risk ====

==== Systemic risk ====

Systemic risk is the risk that an amplification or leverage or positive feedback process presents to a system. This is usually unknown, and under certain conditions this process can amplify exponentially and rapidly lead to destructive or chaotic behavior.  A Ponzi scheme is a good example of a positive-feedback system: funds from new investors are used to pay out unusually high returns, which in turn attract more new investors, causing rapid growth toward collapse. W. Brian Arthur has also studied and written on positive feedback in the economy (e.g. W. Brian Arthur, 1990). Hyman Minsky proposed a theory that certain credit expansion practices could make a market economy into "a deviation amplifying system" that could suddenly collapse, sometimes called a "Minsky moment".

Systemic risk is the risk that an amplification or leverage or positive feedback process presents to a system. This is usually unknown, and under certain conditions this process can amplify exponentially and rapidly lead to destructive or chaotic behavior.  A Ponzi scheme is a good example of a positive-feedback system: funds from new investors are used to pay out unusually high returns, which in turn attract more new investors, causing rapid growth toward collapse. W. Brian Arthur has also studied and written on positive feedback in the economy (e.g. W. Brian Arthur, 1990). Hyman Minsky proposed a theory that certain credit expansion practices could make a market economy into "a deviation amplifying system" that could suddenly collapse, sometimes called a "Minsky moment".

系统性风险是指一个放大或杠杆或正反馈过程给系统带来的风险。这通常是未知的，在某些条件下，这个过程会成倍放大，并迅速导致破坏性或混乱的行为。 庞氏骗局就是正反馈系统的一个很好的例子：来自新投资者的资金被用来支付异常高的回报，反过来又吸引了更多的新投资者，导致快速增长走向崩溃。W.布赖恩•阿瑟W. Brian Arthur 也对经济中的正反馈进行了研究和著述（如W. Brian Arthur，1990）。海曼•明斯基 Hyman Minsky提出了一个理论，认为某些信用扩张行为会使市场经济变成一个 "偏差放大系统"，从而可能会突然崩溃，有时被称为 "明斯基时刻"。

系统性风险是指放大效应或杠杆或正反馈过程给系统带来的风险。这通常是未知的，在某些条件下，这个过程会成倍放大，并迅速导致破坏性或混乱的行为。 庞氏骗局就是正反馈系统的一个很好的例子：来自新投资者的资金被用来支付异常高的回报，反过来又吸引了更多的新投资者，导致快速增长进而走向崩溃。W. Brian Arthur 也对经济中的正反馈进行了研究和著述（如W. Brian Arthur，1990）。Hyman Minsky提出了一个理论，认为某些信用扩张行为会使市场经济变成一个 "偏差放大系统"，从而可能会突然崩溃，这有时被称为 "明斯基时刻"。

Simple systems that clearly separate the inputs from the outputs are not prone to systemic risk.  This risk is more likely as the complexity of the system increases, because it becomes more difficult to see or analyze all the possible combinations of variables in the system even under careful stress testing conditions.  The more efficient a complex system is, the more likely it is to be prone to systemic risks, because it takes only a small amount of deviation to disrupt the system.  Therefore, well-designed complex systems generally have built-in features to avoid this condition, such as a small amount of friction, or resistance, or inertia, or time delay to decouple the outputs from the inputs within the system. These factors amount to an inefficiency, but they are necessary to avoid instabilities.

Simple systems that clearly separate the inputs from the outputs are not prone to systemic risk.  This risk is more likely as the complexity of the system increases, because it becomes more difficult to see or analyze all the possible combinations of variables in the system even under careful stress testing conditions.  The more efficient a complex system is, the more likely it is to be prone to systemic risks, because it takes only a small amount of deviation to disrupt the system.  Therefore, well-designed complex systems generally have built-in features to avoid this condition, such as a small amount of friction, or resistance, or inertia, or time delay to decouple the outputs from the inputs within the system. These factors amount to an inefficiency, but they are necessary to avoid instabilities.

输入和输出明确分开的简单系统不容易发生系统性风险。 随着系统复杂性的增加，这种风险更容易发生，因为即使在仔细的压力测试条件下，也更难看到或分析系统中所有可能的变量组合。 一个复杂系统的效率越高，就越容易发生系统性风险，因为只需要很小的偏差就可以破坏系统。 因此，设计良好的复杂系统一般都会有一些内在的功能来避免这种情况的发生，比如在系统内有少量的摩擦力，或阻力，或惯性，或时间延迟来使输出与输入脱钩。这些因素相当于一种低效率，但它们是避免不稳定的必要条件。

输入和输出明确分开的简单系统不容易发生系统性风险。 随着系统复杂性的增加，这种风险更容易发生，因为即使在详细的压力测试条件下，也更难看到或分析系统中所有可能的变量组合。 一个复杂系统的效率越高，就越容易发生系统性风险，因为只需要很小的偏差就可以破坏系统。 因此，设计良好的复杂系统一般都会有一些内在的功能来避免这种情况的发生，比如在系统内有少量的摩擦力，或阻力，或惯性，或时间延迟来使输出与输入脱钩。这些因素造成了低效率，但它们是避免不稳定的必要条件。

The 2010 Flash Crash incident was blamed on the practice of high-frequency trading (HFT), although whether HFT really increases systemic risk remains controversial.

The 2010 Flash Crash incident was blamed on the practice of high-frequency trading (HFT), although whether HFT really increases systemic risk remains controversial.

  |title= Human Population and the Environmental Crisis

  |title= Human Population and the Environmental Crisis

人口与环境危机

人口与环境危机

Agriculture and human population can be considered to be in a positive feedback mode, which means that one drives the other with increasing intensity. It is suggested that this positive feedback system will end sometime with a catastrophe, as modern agriculture is using up all of the easily available phosphate and is resorting to highly efficient monocultures which are more susceptible to systemic risk.

Agriculture and human population can be considered to be in a positive feedback mode, which means that one drives the other with increasing intensity. It is suggested that this positive feedback system will end sometime with a catastrophe, as modern agriculture is using up all of the easily available phosphate and is resorting to highly efficient monocultures which are more susceptible to systemic risk.

有人提出，由于人口和技术之间的二阶正反馈，增长速度正在加快。技术增长增加了土地对人的承载能力，从而导致人口增长，而这反过来又推动了技术的进一步增长。

有人提出，由于人口和技术之间的二阶正反馈，增长速度正在加快。技术增长增加了土地对人的承载能力，从而导致人口增长，而这反过来又推动了技术的进一步增长。

Prejudice, social institutions and poverty

==== Prejudice, social institutions and poverty ====

Gunnar Myrdal described a vicious circle of increasing inequalities, and poverty, which is known as "circular cumulative causation".

Gunnar Myrdal described a vicious circle of increasing inequalities, and poverty, which is known as "circular cumulative causation".

贡纳尔 · 缪尔达尔Gunnar Myrdal描述了一个不平等和贫困加剧的恶性循环，这就是所谓的”循环累积因果关系”。

Gunnar Myrdal描述了一个不平等和贫困加剧的恶性循环，这就是所谓的”循环累积因果关系”。

==== In meteorology ====

==== In meteorology ====

Drought intensifies through positive feedback. A lack of rain decreases soil moisture, which kills plants and/or causes them to release less water through transpiration. Both factors limit evapotranspiration, the process by which water vapor is added to the atmosphere from the surface, and add dry dust to the atmosphere, which absorbs water. Less water vapor means both low dew point temperatures and more efficient daytime heating, decreasing the chances of humidity in the atmosphere leading to cloud formation. Lastly, without clouds, there cannot be rain, and the loop is complete.

Drought intensifies through positive feedback. A lack of rain decreases soil moisture, which kills plants and/or causes them to release less water through transpiration. Both factors limit evapotranspiration, the process by which water vapor is added to the atmosphere from the surface, and add dry dust to the atmosphere, which absorbs water. Less water vapor means both low dew point temperatures and more efficient daytime heating, decreasing the chances of humidity in the atmosphere leading to cloud formation. Lastly, without clouds, there cannot be rain, and the loop is complete.

==== In climatology ====

==== In climatology ====

Climate "forcings" may push a climate system in the direction of warming or cooling, for example, increased atmospheric concentrations of greenhouse gases cause warming at the surface. Forcings are external to the climate system and feedbacks are internal processes of the system. Some feedback mechanisms act in relative isolation to the rest of the climate system while others are tightly coupled. Forcings, feedbacks and the dynamics of the climate system determine how much and how fast the climate changes. The main positive feedback in global warming is the tendency of warming to increase the amount of water vapor in the atmosphere, which in turn leads to further warming. The main negative feedback comes from the Stefan–Boltzmann law, the amount of heat radiated from the Earth into space is proportional to the fourth power of the temperature of Earth's surface and atmosphere.

Climate "forcings" may push a climate system in the direction of warming or cooling, for example, increased atmospheric concentrations of greenhouse gases cause warming at the surface. Forcings are external to the climate system and feedbacks are internal processes of the system. Some feedback mechanisms act in relative isolation to the rest of the climate system while others are tightly coupled. Forcings, feedbacks and the dynamics of the climate system determine how much and how fast the climate changes. The main positive feedback in global warming is the tendency of warming to increase the amount of water vapor in the atmosphere, which in turn leads to further warming. The main negative feedback comes from the Stefan–Boltzmann law, the amount of heat radiated from the Earth into space is proportional to the fourth power of the temperature of Earth's surface and atmosphere.

气候 "诱因 "可能会将气候系统推向变暖或变冷的方向，例如，大气中温室气体浓度的增加会导致地表变暖。诱因是气候系统的外部因素，而反馈是系统的内部过程。一些反馈机制与气候系统的其他部分相对孤立地发挥作用，而其他机制则是紧密耦合的。气候系统的作用力、反馈和动态决定了气候变化的程度和速度。全球变暖的主要正反馈是变暖使大气中的水汽量增加的趋势，进而导致进一步变暖。主要的负反馈来自Stefan-Boltzmann定律，从地球辐射到空间的热量与地球表面和大气温度的四次方成正比。

气候 中的"诱因 "可能会将气候系统推向变暖或变冷的方向，例如，大气中温室气体浓度的增加会导致地表变暖。诱因是气候系统的外部因素，而反馈是系统的内部过程。一些反馈机制与气候系统的其他部分相对孤立地发挥作用，而另一些则是紧密耦合的。气候系统的作用力、反馈和动态决定了气候变化的程度和速度。全球变暖中的主要正反馈是变暖使大气中的水汽量增加，进而导致进一步变暖。主要的负反馈来自Stefan-Boltzmann定律，从地球辐射到空间的热量与地球表面和大气温度的四次方成正比。

Other examples of positive feedback subsystems in climatology include:

Other examples of positive feedback subsystems in climatology include:

Methane hydrates can be unstable so that a warming ocean could release more methane, which is also a greenhouse gas.

Methane hydrates can be unstable so that a warming ocean could release more methane, which is also a greenhouse gas.

Peat, occurring naturally in peat bogs, contains carbon. When peat dries it decomposes, and may additionally burn. Peat also releases nitrous oxide.

Peat, occurring naturally in peat bogs, contains carbon. When peat dries it decomposes, and may additionally burn. Peat also releases nitrous oxide.

==== In sociology ====

==== In sociology ====

A self-fulfilling prophecy is a social positive feedback loop between beliefs and behavior: if enough people believe that something is true, their behavior can make it true, and observations of their behavior may in turn increase belief. A classic example is a bank run.

A self-fulfilling prophecy is a social positive feedback loop between beliefs and behavior: if enough people believe that something is true, their behavior can make it true, and observations of their behavior may in turn increase belief. A classic example is a bank run.

Another sociological example of positive feedback is the network effect. When more people are encouraged to join a network this increases the reach of the network therefore the network expands ever more quickly. A viral video is an example of the network effect in which links to a popular video are shared and redistributed, ensuring that more people see the video and then re-publish the links. This is the basis for many social phenomena, including Ponzi schemes and chain letters. In many cases population size is the limiting factor to the feedback effect.

Another sociological example of positive feedback is the network effect. When more people are encouraged to join a network this increases the reach of the network therefore the network expands ever more quickly. A viral video is an example of the network effect in which links to a popular video are shared and redistributed, ensuring that more people see the video and then re-publish the links. This is the basis for many social phenomena, including Ponzi schemes and chain letters. In many cases population size is the limiting factor to the feedback effect.

==== In chemistry ====

==== In chemistry ====

If a chemical reaction causes the release of heat, and the reaction itself happens faster at higher temperatures, then there is a high likelihood of positive feedback. If the heat produced is not removed from the reactants fast enough, thermal runaway can occur and very quickly lead to a chemical explosion.

If a chemical reaction causes the release of heat, and the reaction itself happens faster at higher temperatures, then there is a high likelihood of positive feedback. If the heat produced is not removed from the reactants fast enough, thermal runaway can occur and very quickly lead to a chemical explosion.

==== In conservation ====

==== In conservation ====

Many wildlife are hunted for their parts which can be quite valuable. The closer to extinction that targeted species become, the higher the price there is on their parts. This is an example of positive feedback.

Many wildlife are hunted for their parts which can be quite valuable. The closer to extinction that targeted species become, the higher the price there is on their parts. This is an example of positive feedback.