更改

{{short description|Destabilising process that occurs in a feedback loop}}

{{short description|Destabilising process that occurs in a feedback loop}}

[[File:Herdwick Stampede.jpg|thumb|right|Alarm or panic can sometimes be spread by positive feedback among a herd of animals to cause a [[stampede]].|链接=Special:FilePath/Herdwick_Stampede.jpg]]

[[File:Herdwick Stampede.jpg|thumb|right|【图1：Alarm or panic can sometimes be spread by positive feedback among a herd of animals to cause a [[stampede.]] 有时，警报或恐慌会通过正反馈在一群动物之间传播，从而引起踩踏事件。】.|链接=Special:FilePath/Herdwick_Stampede.jpg]]

 

 

【图1：Alarm or panic can sometimes be spread by positive feedback among a herd of animals to cause a [[stampede.]] 有时，警报或恐慌会通过正反馈在一群动物之间传播，从而引起踩踏事件。】

 

 

[[File:Stampede loop.png|thumb|[[Causal loop diagram]] that depicts the causes of a stampede as a positive feedback loop.|链接=Special:FilePath/Stampede_loop.png]]

 

 

 

 

[[File:Birmingham Northern Rock bank run 2007.jpg|thumb|right|In sociology a [[network effect]] can quickly create the positive feedback of a [[bank run]]. The above photo is of the [[Nationalisation of Northern Rock#Run on the bank|UK Northern Rock 2007 bank run]].|链接=Special:FilePath/Birmingham_Northern_Rock_bank_run_2007.jpg]]

 

 

'''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.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. In contrast, a system in which the results of a change act to reduce or counteract it has negative feedback.<ref name="theorymodelling" /> Both concepts play an important role in science and engineering, including biology, chemistry, and [[cybernetics]] .

'''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.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. In contrast, a system in which the results of a change act to reduce or counteract it has negative feedback.<ref name="theorymodelling" /> Both concepts play an important role in science and engineering, including biology, chemistry, and [[cybernetics]] .

=== Basic ===

=== Basic 基础===

 

A simple feedback loop is shown in the diagram.  If the loop gain AB is positive, then a condition of ''positive'' or ''regenerative'' feedback exists.

A simple feedback loop is shown in the diagram.  If the loop gain AB is positive, then a condition of ''positive'' or ''regenerative'' feedback exists.

=== Hysteresis ===

=== Hysteresis迟滞 ===

 

{{main|Hysteresis}}

{{main|Hysteresis}}

[[File:Hysteresis sharp curve.svg|thumb|Hysteresis causes the output value to depend on the history of the input|链接=Special:FilePath/Hysteresis_sharp_curve.svg]]

[[File:Hysteresis sharp curve.svg|thumb|【图5 Hysteresis causes the output value to depend on the history of the input 迟滞现象会导致输出值取决于输入的历史记录。】|链接=Special:FilePath/Hysteresis_sharp_curve.svg]]

【图6 In a Schmitt trigger circuit, feedback to the non-inverting input of an amplifier pushes the output directly away from the applied voltage towards the maximum or minimum voltage the amplifier can generate. 在施密特触发器电路中，利用放大器的非反相输入端口产生的反馈，可以直接将电路的输出从原本的外加电压值推向到放大器所能产生的极值电压。】

[[File:Op-Amp Schmitt Trigger.svg|thumb|【图6 In a Schmitt trigger circuit, feedback to the non-inverting input of an amplifier pushes the output directly away from the applied voltage towards the maximum or minimum voltage the amplifier can generate. 在施密特触发器电路中，利用放大器的非反相输入端口产生的反馈，可以直接将电路的输出从原本的外加电压值推向到放大器所能产生的极值电压。】|链接=Special:FilePath/Op-Amp_Schmitt_Trigger.svg]]

 

 

In the real world, positive feedback loops typically do not cause ever-increasing growth, but are modified by limiting effects of some sort. According to [[Donella Meadows]]:

In the real world, positive feedback loops typically do not cause ever-increasing growth, but are modified by limiting effects of some sort. According to [[Donella Meadows]]:

一旦达到极限，它就会稳定下来。但是，如果输入超过极限，那么反馈将改变符号，输出将向相反的方向移动，直到达到相反的极限。因此，该系统表现出<font color="#ff8000"> 双稳态行为bistable behavior</font>。

一旦达到极限，它就会稳定下来。但是，如果输入超过极限，那么反馈将改变符号，输出将向相反的方向移动，直到达到相反的极限。因此，该系统表现出<font color="#ff8000"> 双稳态行为bistable behavior</font>。

== Terminology ==

== Terminology 术语的由来==

 

The terms positive and negative were first applied to feedback before World War II. The idea of positive feedback was already current in the 1920s with the introduction of the regenerative circuit.

The terms positive and negative were first applied to feedback before World War II. The idea of positive feedback was already current in the 1920s with the introduction of the regenerative circuit.

“ ... ... Friis 和 Jensen 对 Black 在对"正反馈 "和 "负反馈 "的区分方法是一样的，都不是基于反馈本身的符号，而是基于它对放大器增益的影响。与之相反的是，当Nyquist和Bode基于Black的工作基础时，将负反馈称为符号相反的反馈。Black难以说服其他人相信他的发明的实用性，有一部分原因是在基本的定义问题上存在混乱。"

“ ... ... Friis 和 Jensen 对 Black 在对"正反馈 "和 "负反馈 "的区分方法是一样的，都不是基于反馈本身的符号，而是基于它对放大器增益的影响。与之相反的是，当Nyquist和Bode基于Black的工作基础时，将负反馈称为符号相反的反馈。Black难以说服其他人相信他的发明的实用性，有一部分原因是在基本的定义问题上存在混乱。"

== Examples and applications ==

== Examples and applications 实例与应用==

 

=== In electronics ===

=== In electronics 在电子领域===

 

 

[[Regenerative circuit]]s were invented and patented in 1914<ref>{{cite patent |inventor-last=Armstrong |inventor-first=E. H. |country-code=US |patent-number=1113149 |title=Wireless receiving system |date=1914}}</ref> for the amplification and reception of very weak radio signals. Carefully controlled positive feedback around a single [[transistor]] amplifier can multiply its [[Gain (electronics)|gain]] by 1,000 or more.<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> 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 circuit]]s were invented and patented in 1914<ref>{{cite patent |inventor-last=Armstrong |inventor-first=E. H. |country-code=US |patent-number=1113149 |title=Wireless receiving system |date=1914}}</ref> for the amplification and reception of very weak radio signals. Carefully controlled positive feedback around a single [[transistor]] amplifier can multiply its [[Gain (electronics)|gain]] by 1,000 or more.<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> 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.

电子系统中发生<font color="#ff8000"> 热失控Thermal runaway</font>的原因是，当电路的某些方面变得更热时，它被允许通过更多的电流，然后它越热，通过的电流就越多，这就使它更热一些，因此它又通过更多的电流。这种现象对有关器件来说通常是灾难性的。如果器件不得不在接近其最大功率处理能力的情况下工作，那么某些条件下就可能出现热失控，这通常可以通过精心设计来改进。

电子系统中发生<font color="#ff8000"> 热失控Thermal runaway</font>的原因是，当电路的某些方面变得更热时，它被允许通过更多的电流，然后它越热，通过的电流就越多，这就使它更热一些，因此它又通过更多的电流。这种现象对有关器件来说通常是灾难性的。如果器件不得不在接近其最大功率处理能力的情况下工作，那么某些条件下就可能出现热失控，这通常可以通过精心设计来改进。

[[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|【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。】|链接=Special:FilePath/Technics_SL-1210MK2.jpg]]

 

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.

音频和视频系统可以表现出正反馈。如果麦克风录入了同一电路中扬声器的放大声音输出，那么就会听到音频反馈的嚎叫和尖叫声（在放大器的最大功率容量下），因为随机噪声被音频系统和房间的特性所过滤后，通过正反馈重新放大。

音频和视频系统可以表现出正反馈。如果麦克风录入了同一电路中扬声器的放大声音输出，那么就会听到音频反馈的嚎叫和尖叫声（在放大器的最大功率容量下），因为随机噪声被音频系统和房间的特性所过滤后，通过正反馈重新放大。

===Audio and live music===

===Audio and live music音频和现场音乐===

 

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.

[[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]]【图12 视频反馈】.|链接=Special:FilePath/Adam_Savage_HOPE.jpg]]

 

===Video===

===Video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 [[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]]''.

=== Switches ===

=== Switches 开关===

 

In [[electrical switch]]es, including [[bimetallic strip]] based thermostats, the switch usually has hysteresis in the switching action. In these cases hysteresis is mechanically achieved via positive feedback within a tipping point mechanism. The positive feedback action minimises the length of time arcing occurs for during the switching and also holds the contacts in an open or closed state.

In [[electrical switch]]es, including [[bimetallic strip]] based thermostats, the switch usually has hysteresis in the switching action. In these cases hysteresis is mechanically achieved via positive feedback within a tipping point mechanism. The positive feedback action minimises the length of time arcing occurs for during the switching and also holds the contacts in an open or closed state.

在电气开关中，包括双金属条型恒温器，开关通常在开关动作中具有滞后性。在这些情况下，滞后是通过一个临界点机构内的正反馈来实现的。正反馈作用可最大限度地减少开关过程中发生电弧的时间，并使触点保持在断开或闭合状态。

在电气开关中，包括双金属条型恒温器，开关通常在开关动作中具有滞后性。在这些情况下，滞后是通过一个临界点机构内的正反馈来实现的。正反馈作用可最大限度地减少开关过程中发生电弧的时间，并使触点保持在断开或闭合状态。

=== In biology ===

=== In biology在生物学中===

[[File:Positive Feedback- Childbirth (1).svg|thumb|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.|链接=Special:FilePath/Positive_Feedback-_Childbirth_(1).svg]]

 

[[File:Positive Feedback- Childbirth (1).svg|thumb|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.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<font color="#ff8000"> 催产素oxytocin</font>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。|链接=Special:FilePath/Positive_Feedback-_Childbirth_(1).svg]]

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.

==== In physiology ====

==== In physiology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]].

==== In gene regulation ====

==== In gene regulation 基因调控====

 

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/>

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/>

==== In evolutionary biology ====

==== In evolutionary biology在进化生物学中 ====

 

[[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.显生宙[[生物多样性]]呈现稳定而非单调的增长，从接近于零一直增长到有几千个属。|链接=Special:FilePath/Phanerozoic_Biodiversity.svg]]

==== Immune system ====

==== Immune system 免疫系统====

 

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>

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 细胞凋亡====

 

[[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>

=== In psychology ===

=== In psychology 在心理学上===

 

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。<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（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。<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/>  

=== In economics ===

=== In economics在经济学中 ===

 

====Markets with social influence====

====Markets with social influence 具有社会影响力的市场====

 

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>

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市场动态====

 

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>

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 系统性风险====

 

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".

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 偏见、社会制度与贫困====

 

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".

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 在气象学中====

 

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.

干旱通过正反馈效应加剧。缺雨会降低土壤湿度，从而杀死植物，使它们通过蒸腾作用释放更少的水分。这两个因素都限制了水蒸气从地表加到大气中的过程，并使吸收水分的干燥灰尘进入大气。水汽少了，既意味着露点温度低，白天的供暖效率也高，减少了大气中湿度导致云的形成的机会。最后，没有云，就不会有雨，这个正反馈循环就形成了。

干旱通过正反馈效应加剧。缺雨会降低土壤湿度，从而杀死植物，使它们通过蒸腾作用释放更少的水分。这两个因素都限制了水蒸气从地表加到大气中的过程，并使吸收水分的干燥灰尘进入大气。水汽少了，既意味着露点温度低，白天的供暖效率也高，减少了大气中湿度导致云的形成的机会。最后，没有云，就不会有雨，这个正反馈循环就形成了。

==== In climatology ====

==== In climatology 在气候学中====

 

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.

政府间气候变化专门委员会(气专委)第四次评估报告指出，"人类活动的变暖可能导致一些突然或不可逆转的影响，这取决于气候变化的速度和程度"。

政府间气候变化专门委员会(气专委)第四次评估报告指出，"人类活动的变暖可能导致一些突然或不可逆转的影响，这取决于气候变化的速度和程度"。

==== In sociology ====

==== In sociology 在社会学中====

 

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.

正反馈的另一个社会学例子是网络效应。当更多的人被鼓励加入一个网络时，这就增加了网络的覆盖面，因此网络扩张得越来越快。病毒视频就是网络效应的一个例子，在这个例子中，一个热门视频的链接被分享和再传播，确保更多的人看到这个视频，然后重新发布链接。这是许多社会现象的基础，包括庞氏骗局和连锁信。在许多情况下，人口量是反馈效应的限制因素。

正反馈的另一个社会学例子是网络效应。当更多的人被鼓励加入一个网络时，这就增加了网络的覆盖面，因此网络扩张得越来越快。病毒视频就是网络效应的一个例子，在这个例子中，一个热门视频的链接被分享和再传播，确保更多的人看到这个视频，然后重新发布链接。这是许多社会现象的基础，包括庞氏骗局和连锁信。在许多情况下，人口量是反馈效应的限制因素。

==== In chemistry ====

==== In chemistry 在化学中====

 

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.

如果化学反应引起热量的释放，而反应本身在较高的温度下发生得更快，那么就很有可能出现正反馈。如果产生的热量没有足够快地从反应物中排除，就会发生热失控，并很快导致化学爆炸。

如果化学反应引起热量的释放，而反应本身在较高的温度下发生得更快，那么就很有可能出现正反馈。如果产生的热量没有足够快地从反应物中排除，就会发生热失控，并很快导致化学爆炸。

==== In conservation ====

==== In conservation 在自然保护中====

 

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.