what is the overall effect of a negative feedback mechanism
negative feedback generally promotes stability
1687924
Negative feedback Negative feedback (or balancing feedback) occurs when some function of the output of a system, process, or mechanism is fed back in a manner that tends to reduce the fluctuations in the output, whether caused by changes in the input or by other disturbances. Whereas positive feedback tends to lead to instability via exponential growth, oscillation or chaotic behavior, negative feedback generally promotes stability. Negative feedback tends to promote a settling to equilibrium, and reduces the effects of perturbations. Negative feedback loops in which just the right amount of correction is applied with optimum timing can be very
Negative feedback
1687924
Negative feedback Negative feedback (or balancing feedback) occurs when some function of the output of a system, process, or mechanism is fed back in a manner that tends to reduce the fluctuations in the output, whether caused by changes in the input or by other disturbances. Whereas positive feedback tends to lead to instability via exponential growth, oscillation or chaotic behavior, negative feedback generally promotes stability. Negative feedback tends to promote a settling to equilibrium, and reduces the effects of perturbations. Negative feedback loops in which just the right amount of correction is applied with optimum timing can be very
Negative feedback
171953
differently to the same hormonal signal. The rate of hormone biosynthesis and secretion is often regulated by a homeostatic negative feedback control mechanism. Such a mechanism depends on factors that influence the metabolism and excretion of hormones. Thus, higher hormone concentration alone cannot trigger the negative feedback mechanism. Negative feedback must be triggered by overproduction of an "effect" of the hormone. Hormone secretion can be stimulated and inhibited by: One special group of hormones is the tropic hormones that stimulate the hormone production of other endocrine glands. For example, thyroid-stimulating hormone (TSH) causes growth and increased activity of another endocrine
Hormone
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masking effect of the human hearing system. After applying moderate amounts of negative feedback (10–15 dB), the low-order harmonics are reduced, but higher-order harmonics are introduced. Since these are not masked as well, the distortion becomes audibly worse even though the overall THD may go down. This has led to a view that negative feedback is detrimental in audio amplifiers, leading audiophile manufacturers to market their amplifiers as "zero feedback" (even if they use local feedback to linearize each stage). However, as the amount of negative feedback is increased further, harmonics are reduced overall but new harmonics are introduced. Increasing
Negative-feedback amplifier
1843947
more estradiol. Eventually, when the follicle has fully matured, a spike in 17α-hydroxyprogesterone production by the follicle inhibits the production of estrogens, leading to a decrease in estrogen-mediated negative feedback of GnRH in the hypothalamus, which then stimulates the release of LH from the anterior pituitary. However another theory of the LH peak is a positive feedback mechanism from estradiol. The levels keep rising through the follicular phase and when they reach an unknown threshold, this results in the peak of the LH. This effect is opposite from the usual negative feedback mechanism presented at lower levels. In other words,
Luteinizing hormone
2148999
Servomechanism In control engineering a servomechanism, sometimes shortened to servo, is an automatic device that uses error-sensing negative feedback to correct the action of a mechanism. It usually includes a built-in encoder or other position feedback mechanism to ensure the output is achieving the desired effect. The term correctly applies only to systems where the feedback or error-correction signals help control mechanical position, speed or other parameters. For example, an automotive power window control is not a servomechanism, as there is no automatic feedback that controls position—the operator does this by observation. By contrast a car's cruise control uses closed-loop
Servomechanism
6120451
published which again suggested the possibility of an "Iris Effect". It also proposed what it called a "plausible physical mechanism for an iris effect." In 2017 a paper was published which found that "tropical anvil cirrus clouds exert a negative climate feedback in strong association with precipitation efficiency". If confirmed then that finding would be highly supportive of the existence of an "Iris Effect". Iris hypothesis The iris hypothesis is a hypothesis proposed by Richard Lindzen et al. in 2001 that suggested increased sea surface temperature in the tropics would result in reduced cirrus clouds and thus more infrared radiation
Iris hypothesis
3937049
enemy territory) leads to greater resources or capabilities, and hence greater scope for further successes (for example further conquests or economic investments). The overall dynamic balance of the game will depend on the comparative strength of positive and negative feedback processes, and therefore decreasing the power of positive feedback processes has the same effect as introducing negative feedbackback processes. Positive feedback processes may be limited by making capabilities some concave function of a measure of raw success. For example: (1) In role paying games using a level structure, the level attained is usually a concave transformation of experience points -
Game balance
14077262
this element leads to its own inhibition through upstream elements, this is canonically negative feedback (red blunt arrow). A negative feedback loop is also known as a balancing loop, and it may be common to see oscillations in which a delayed negative feedback signal is used to maintain homeostatic balance in the system. Feedback loops can be used for amplification (positive) or self-correction (negative). The right combination of positive and negative feedback loops can generate ultrasensitivity and bistability, which in turn can generate decisive transitions and oscillations. Positive and negative feedback loops do not always operate distinctly. In the mechanism
Biochemical switches in the cell cycle
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responses as either positive or negative. The first participant then had an opportunity to review each of their partner’s positive/negative ratings. After a brief distractor test, the first participant was asked to recall as many of their partner’s feedback ratings as possible. Researchers found that when the two partners had a close relationship, mnemic neglect was not demonstrated. When the two partners were strangers, mnemic neglect was maintained. Green, Sedikides, Pinter, and Van Tongeren admit that further research must be conducted to determine the mechanism behind the effect relationships have on mnemic neglect. Feedback from close friends may be more
Mnemic neglect
20569750
experience social rejection. However, it is unclear what effect increased rejection has on one’s experience with depression. Of the ways depression might lead to increased social stressors, negative feedback seeking and reassurance seeking are two of the most explored. Both behaviors involve questioning social partners about oneself in ways that are aversive to others, differing in whether the feedback sought is positive or negative Evidence compatible with reassurance seeking and negative feedback seeking increasing social stress and depression symptoms comes from the frequency of these behaviors among the depressed and the responses of others that often accompany these actions. For
Social Predictors of Depression
15451485
also lead to degradation of IRS-1. Signal transduction is a mechanism in which the cell responds to a signal from the environment by activating several proteins and enzymes that will give a response to the signal. Feedback mechanism might involve negative and positive feedbacks. In the negative feedback, the pathway is inhibited and the final result of the transduction pathway is reduced or limited. In positive feedback, the transduction pathway is promoted and stimulated to produce more products. Insulin secretion results in positive feedback in different ways. Firstly, insulin increases the uptake of glucose from blood by the translocation and
Insulin signal transduction pathway
9770582
effect on its own rate of synthesis, whereas in a simple negative loop, each element has a negative effect on its own rate of synthesis. A simple positive feedback loop results in epigenetic regulation and have multiple steady states and a simple negative feedback loop results in homeostatic regulation. Abstraction: A chain of positive interactions is equivalent to a direct positive interaction between the two extreme elements, and any two negative interactions cancel out each other’s effect. In this way, any simple feedback loop can be abridged to a one-element loop, positive or negative according to the number of negative
Kinetic logic
126783
in most modern amplifiers to improve bandwidth and distortion and control gain. In a negative feedback amplifier part of the output is fed back and added to the input in opposite phase, subtracting from the input. The main effect is to reduce the overall gain of the system. However, any unwanted signals introduced by the amplifier, such as distortion are also fed back. Since they are not part of the original input, they are added to the input in opposite phase, subtracting them from the input. In this way, negative feedback also reduces nonlinearity, distortion and other errors introduced by
Amplifier
12505675
the hypothalamus which release CRH that stimulates the pituitary gland to release ACTH which stimulates the adrenal glands to release cortisol. Cortisol has a negative feedback effect on the pituitary gland and hypothalamus. In people with MDD the often shows increased activation in depressed people, but the mechanism behind this is not yet known. Increased basal cortisol levels and abnormal response to dexamethasone challenges have been observed in people with MDD. Early life stress has been hypothesized as a potential cause of HPA dysfunction. HPA axis regulation may be examined through a dexamethasone suppression tests, which tests the feedback mechanisms.
Biology of depression
111882
can be either activated or inhibited by other molecules. For example, the end product(s) of a metabolic pathway are often inhibitors for one of the first enzymes of the pathway (usually the first irreversible step, called committed step), thus regulating the amount of end product made by the pathways. Such a regulatory mechanism is called a negative feedback mechanism, because the amount of the end product produced is regulated by its own concentration. Negative feedback mechanism can effectively adjust the rate of synthesis of intermediate metabolites according to the demands of the cells. This helps with effective allocations of materials
Enzyme
60379
products act as transcriptional activators for their own expression and for targets downstream of Shh signaling. Simultaneously, the Shh signaling network is controlled by a negative feedback loop wherein the Gli transcription factors activate the enhanced transcription of a repressor (Ptc). This signaling network illustrates the simultaneous positive and negative feedback loops whose exquisite sensitivity helps create a bistable switch. Bistability can only arise in biological and chemical systems if three necessary conditions are fulfilled: positive feedback, a mechanism to filter out small stimuli and a mechanism to prevent increase without bound. Bistable chemical systems have been studied extensively to
Bistability
3260262
effect of an isolated impairment of sex steroid (e.g., DHEA in the adrenal, but also gonadal testosterone and estrogens) synthesis, whereas mineralocorticoid (e.g., aldosterone) and glucocorticoid (e.g., cortisol) levels remain normal. Normal aldosterone level can be attributed to the fact that aldosterone is independent of hypothalamus-pituitary axis feedback system, being mainly controlled by the level of serum potassium. Because of the normal aldosterone level, hypertension is not expected. Normal cortisol level can be explained by the strong negative feedback mechanism of cortisol on hypothalamus-pituitary axis system. That is, in the beginning, 17,20-lyase deficiency will block synthesis of sex steroid hormones,
Congenital adrenal hyperplasia due to 17α-hydroxylase deficiency
4487866
an increase in the core temperature will act as a feedback mechanism that decreases the core power. This attribute is known as a negative temperature coefficient of reactivity. Most LWRs also have negative reactivity coefficients; however, in an IFR, this effect is strong enough to stop the reactor from reaching core damage without external action from operators or safety systems. This was demonstrated in a series of safety tests on the prototype. Pete Planchon, the engineer who conducted the tests for an international audience quipped "Back in 1986, we actually gave a small [20 MWe] prototype advanced fast reactor a
Integral fast reactor
582584
Increasing temperatures in the polar regions is expected in increase the amount of low-level clouds, whose stratification prevents the convection of moisture to upper levels. This feedback would partially cancel the increased surface warming due to the cloudiness. This negative feedback has less effect than the positive feedback. The upper atmosphere more than cancels negative feedback that causes cooling, and therefore the increase of CO is actually exacerbating the positive feedback as more CO enters the system. The Intergovernmental Panel on Climate Change (IPCC) assessment reports contain a summary of the current status of knowledge on the effect of cloud
Cloud feedback
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Entourage effect The entourage effect is a proposed mechanism by which compounds present in cannabis which are largely non-psychoactive by themselves modulate the overall psychoactive effects of the plant (these resulting principally from the action of the main psychoactive component of cannabis, tetrahydrocannabinol (THC)). Cannabidiol (CBD) is believed to be the major modulatory component of cannabis, mitigating some of the negative, psychosis-like effects of THC, and is included in some medicinal formulations alongside THC. CBD co-administration also reduces the negative effects of THC on memory. Myrcene, which is recognized as a sedative component in hops, may be responsible for the
Entourage effect
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by autoreceptors through the rate-limiting enzyme tyrosine hydroxylase, an effect mediated by decreased cyclic AMP-mediated phosphorylation-activation of the enzyme. α receptors also cause decreased intracellular cyclic AMP expression which results in smooth muscle relaxation or decreased secretion. TCAs activate a negative feedback mechanism through their effects on presynaptic receptors. One probable explanation for the effects on decreased neurotransmitter release is that, as the receptors activate, inhibition of neurotransmitter release occurs (including suppression of voltage-gated Ca currents and activation of G protein-coupled receptor-operated K currents). Repeated exposure of agents with this type of mechanism leads to inhibition of neurotransmitter release, but
Serotonin–norepinephrine reuptake inhibitor
3278790
effect to gullibility. The effect has been said to confirm the so-called "Pollyanna principle", which states that individuals tend "to use or accept positive words of feedback more frequently than negative words of feedback". Two factors are important in producing the Forer effect, according to the findings of replication studies. The content of the description offered is important, with specific emphasis on the ratio of positive to negative trait assessments. The other important factor is that the subject trusts the honesty of the person providing feedback. The study was repeated again in 2011 with the statements altered so that they
Barnum effect
9308826
autonomic feedback mechanism, rather than through central chemicals like oxytocin, serotonin, and prolactin. Autonomic feedback is already known to regulate other physiologic systems, such as breathing, blood pressure, and gut motility. This theory suggests that after male ejaculation, decreased wall tension in structures such as the seminal vesicles leads to a change in the fine autonomic signals sent from these organs, effectively creating a negative feedback loop. Such a mechanism is similar to decreased gastric and bowel motility once gastric contents have passed through. Once the feedback loop has been created, the refractory period remains until the loop is broken
Refractory period (sex)
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to operate. However, negative feedback systems can still be subject to oscillations. This is caused by the slight delays around any loop. Due to these delays the feedback signal of some frequencies can arrive one half cycle later which will have a similar effect to positive feedback and these frequencies can reinforce themselves and grow over time. This problem is often dealt with by attenuating or changing the phase of the problematic frequencies. Unless the system naturally has sufficient damping, many negative feedback systems have low pass filters or dampers fitted. There are a large number of different examples of
Negative feedback
15362066
reduces cloud formation. The heating of the atmosphere aloft also leads to a cooling of the surface, resulting in less evaporation of surface water. The effects described here all lead to a reduction in cloud cover i.e. an increase in planetary albedo. The semi-direct effect classified as a climate feedback) by the IPCC due to the interdependence between it and the hydrological cycle. However, it has previously been classified as a negative radiative forcing. Sulfate aerosol has two main effects, direct and indirect. The direct effect, via albedo, is a cooling effect that slows the overall rate of global warming:
Particulates
12945109
a destabilising positive feedback (e.g. warming causing more warming); and if in the opposite direction, it is a stabilising negative feedback (e.g. warming causing a cooling effect). If a sufficiently strong net positive feedback occurs, it is said that a climate tipping point has been passed and the temperature will continue to change until the changed conditions result in negative feedbacks that restabilise the climate on a new, stable equilibrium manifold. An example of a negative feedback is that radiation leaving the Earth increases in proportion to the fourth power of temperature, in accordance with the Stefan-Boltzmann law. This feedback
Runaway climate change
9722675
movement. In order to understand the sedimentary budget of a coastal environment it is important to know the different types of feedback that can determine whether there is stability. When a beach environment is effected by wind, wave and tidal energy it responds with either positive or negative feedback which determines whether the system is balanced and in equilibrium. Negative feedback is a stabilising mechanism acting to oppose changes to coastal morphology and establish equilibrium. A coastal environment in equilibrium is able to dissipate or reflect incoming energy without the occurrence of sediment input or output and change to morphology.
Sedimentary budget
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negative feedback and some are discussed below. One use of feedback is to make a system (say "T") self-regulating to minimize the effect of a disturbance (say "D"). Using a negative feedback loop, a measurement of some variable (for example, a process variable, say "E") is subtracted from a required value (the 'set point') to estimate an operational error in system status, which is then used by a regulator (say "R") to reduce the gap between the measurement and the required value. The regulator modifies the input to the system "T" according to its interpretation of the error in the
Negative feedback
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dampen fluctuations in real GDP. Mainstream economics asserts that the market pricing mechanism operates to match supply and demand, because mismatches between them feed back into the decision-making of suppliers and demanders of goods, altering prices and thereby reducing any discrepancy. However Norbert Wiener wrote in 1948: The notion of economic equilibrium being maintained in this fashion by market forces has also been questioned by numerous heterodox economists such as financier George Soros and leading ecological economist and steady-state theorist Herman Daly, who was with the World Bank in 1988-1994. Negative feedback Negative feedback (or balancing feedback) occurs when some
Negative feedback
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Synaptic scaling In neuroscience, synaptic scaling (or homeostatic scaling) is a form of homeostatic plasticity, in which the brain responds to chronically elevated activity in a neural circuit with negative feedback, allowing individual neurons to reduce their overall action potential firing rate. Where Hebbian plasticity mechanisms modify neural synaptic connections selectively, synaptic scaling normalizes all neural synaptic connections by decreasing the strength of each synapse by the same factor (multiplicative change), so that the relative synaptic weighting of each synapse is preserved. Synaptic scaling is a post-synaptic homeostatic plasticity mechanism that takes place with changes in the quantity of AMPA
Synaptic scaling
16267257
are metabolic, myogenic and neurogenic. Metabolic regulation is driven by difference the between cerebral metabolism (demand) and oxygen delivery through cerebral blood flow (supply) and acts by means of a vasoactive substance. In principle, this is a negative feedback control system that seeks to balance cerebral blood flow to its demand. The effect of transmural blood pressure changes are directly detected by the vascular smooth muscle in arterioles, probably via a stress sensing mechanism. Then, the calibers are adjusted accordingly to keep blood flow constant. The vascular smooth muscle actuators in the resistance arterioles are controlled via sympathetic innervation, receiving
Cerebral autoregulation
2062347
people who participated, 81% voted Nakamichi Shockwafe Ultra 9.2 DTS:X Soundbar for best overall performance and 99% voted it for best overall value. The event was covered by Audioholics. The time alignment of an amplified music signal and its distortion components has a profound effect on perceived sound quality. Nakamichi researchers discovered that the human ear is much more tolerant of harmonic distortion if the distortion components are time-aligned with respect to the primary signal. Nakamichi Harmonic Time Alignment (HTA) amplifiers adopt a wideband, low open-loop gain design. A minimal amount of negative feedback is used, but, more important, it
Nakamichi
18322080
regulation route. Cannabinoid system modulators like "N"-palmitoylethanolamine may be said to exhibit the entourage effect, increasing receptors affinity to enhance endogenous anandamide activity and/or reducing enzymatic anandamide degradation. Entourage effect The entourage effect is a proposed mechanism by which compounds present in cannabis which are largely non-psychoactive by themselves modulate the overall psychoactive effects of the plant (these resulting principally from the action of the main psychoactive component of cannabis, tetrahydrocannabinol (THC)). Cannabidiol (CBD) is believed to be the major modulatory component of cannabis, mitigating some of the negative, psychosis-like effects of THC, and is included in some medicinal formulations
Entourage effect
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and provide a cover over the reinforcement that protects against corrosion. What about concrete spacers with a plastic clip or fixing mechanism? Does the plastic clip or fixing mechanism in the concrete spacer have a negative effect on material integrity? Does it weaken the corrosion protective cover over the reinforcement? The answer is no! The plastic clip or fixing mechanism is hinged from the top of the spacer and does not come into contact with the soffit of the concrete. The plastic clip or fixing mechanism is embedded only 5 mm into the spacer, which maintains the material integrity at
Rebar spacer
2149009
steam engines for use in ship steering. The simplest kind of servos use bang–bang control. More complex control systems use proportional control, PID control, and state space control, which are studied in modern control theory. Servos can be classified by means of their feedback control systems: The servo bandwidth indicates the capability of the servo to follow rapid changes in the commanded input. Servomechanism In control engineering a servomechanism, sometimes shortened to servo, is an automatic device that uses error-sensing negative feedback to correct the action of a mechanism. It usually includes a built-in encoder or other position feedback mechanism
Servomechanism
203614
from increased greenhouse gases might outweigh orbital forcing for as long as intensive use of fossil fuels continues. Each glacial period is subject to positive feedback which makes it more severe, and negative feedback which mitigates and (in all cases so far) eventually ends it. Ice and snow increase Earth's albedo, i.e. they make it reflect more of the sun's energy and absorb less. Hence, when the air temperature decreases, ice and snow fields grow, and this continues until competition with a negative feedback mechanism forces the system to an equilibrium. Also, the reduction in forests caused by the ice's
Ice age
893753
hours. The exact mechanism of these opposite responses of LH levels to estradiol is not well understood. In animals, a gonadotropin-releasing hormone (GnRH) surge has been shown to precede the LH surge, suggesting that estrogen's main effect is on the hypothalamus, which controls GnRH secretion. This may be enabled by the presence of two different estrogen receptors in the hypothalamus: estrogen receptor alpha, which is responsible for the negative feedback estradiol-LH loop, and estrogen receptor beta, which is responsible for the positive estradiol-LH relationship. However, in humans it has been shown that high levels of estradiol can provoke 32 increases
Menstrual cycle
166339
effector molecules of GPCRs (including those involved in negative feedback pathways) are also targeted to lipid rafts, this has the effect of facilitating rapid receptor signaling. GPCRs respond to extracellular signals mediated by a huge diversity of agonists, ranging from proteins to biogenic amines to protons, but all transduce this signal via a mechanism of G-protein coupling. This is made possible by a guanine-nucleotide exchange factor (GEF) domain primarily formed by a combination of IL-2 and IL-3 along with adjacent residues of the associated TM helices. The G protein-coupled receptor is activated by an external signal in the form of
G protein-coupled receptor
13133749
the mutation of the gene was affecting the basic oscillator mechanism. Paul Hardin, Jeffrey Hall, and Michael Rosbash demonstrated that relationship by discovering that within the PERIOD gene, there was a feedback mechanism that controlled the oscillation. The mid-1990s saw an outpouring of discoveries, with CLOCK, CRY, and others being added to the growing list of oscillating genes. The primary molecular mechanism behind an oscillating gene is best described as a transcription/translation feedback loop. This loop contains both positive regulators, which increase gene expression, and negative regulators, which decrease gene expression. The fundamental elements of these loops are found across
Oscillating gene
306815
either input, this is an "open-loop" circuit acting as a comparator. If predictable operation is desired, negative feedback is used, by applying a portion of the output voltage to the inverting input. The "closed-loop" feedback greatly reduces the gain of the circuit. When negative feedback is used, the circuit's overall gain and response becomes determined mostly by the feedback network, rather than by the op-amp characteristics. If the feedback network is made of components with values small relative to the op amp's input impedance, the value of the op-amp's open-loop response "A" does not seriously affect the circuit's performance. The
Operational amplifier
295410
adopt the standard thereby creating greater industry-wide lock-in to the standard. Broadly, there are two kinds of networks effects: Additionally, there are two sources of economic value that are relevant when analyzing products that display network effects: Negative network externalities, in the mathematical sense, are those that have a negative effect compared to normal (positive) network effects. Just as positive network externalities (network effects) cause positive feedback loops and exponential growth, negative network externalities create negative feedback and exponential decay. In nature, negative network externalities are the forces that pull towards equilibrium, are responsible for stability, and are the physical
Network effect
1687937
response. They may even exhibit instability. Harry Nyquist of Bell Laboratories proposed the Nyquist stability criterion and the Nyquist plot that identify stable feedback systems, including amplifiers and control systems. The figure shows a simplified block diagram of a negative feedback amplifier. The feedback sets the overall (closed-loop) amplifier gain at a value: where the approximate value assumes β"A " » 1. This expression shows that a gain greater than one requires β < 1. Because the approximate gain 1/β is independent of the open-loop gain "A", the feedback is said to 'desensitize' the closed-loop gain to variations in "A
Negative feedback
147896
inverted on its way round the control loop, the system is said to have "negative feedback"; otherwise, the feedback is said to be "positive". Negative feedback is often deliberately introduced to increase the stability and accuracy of a system by correcting or reducing the influence of unwanted changes. This scheme can fail if the input changes faster than the system can respond to it. When this happens, the lag in arrival of the correcting signal can result in overcorrection, causing the output to oscillate or "hunt". While often an unwanted consequence of system behaviour, this effect is used deliberately in
Feedback
5119931
most commonly specified measures are the cross-section for thermal neutron absorption, and resonance integral which considers the contribution of absorption peaks at certain neutron energies specific to a particular nuclide, usually above the thermal range, but encountered as neutron moderation slows the neutron down from an original high energy. The thermal energy of the nucleus also has an effect; as temperatures rise, Doppler broadening increases the chance of catching a resonance peak. In particular, the increase in uranium-238's ability to absorb neutrons at higher temperatures (and to do so without fissioning) is a negative feedback mechanism that helps keep nuclear
Neutron capture
13005378
will act as a negative feedback mechanism. The negative feedback mechanisms work to protect against saturation or suppression of the circuit activity as a whole. Axonal modulation is a type of plasticity in which the number, activity, or location of ion channels in the axon changes. This causes the neuron to behave differently when stimulated. The modulation of ion channels is a response to a change in the stimulation frequencies of a neuron. Because it is the summation of the action potentials that eventually results in the threshold polarization being crossed, the temporal relationship of different input signals is very
Nonsynaptic plasticity
4480987
as Clomid) is a selective estrogen receptor modulator (SERM). It is the most widely used fertility drug. It is used as an ovarian stimulator by inhibiting the negative feedback of estrogen at the hypothalamus. As the negative feedback of estrogen is inhibited, the hypothalamus secretes GnRh which in turn stimulates the anterior pituitary to secrete LH and FSH which help in ovulation. Although primarily a breast cancer treatment, aromatase inhibitors can also work as fertility medication, probably through a mechanism similar to clomiphene. Aromatase inhibitors will decrease the amount of testosterone converted to estradiol. Less estradiol circulating in the body
Fertility medication
16151113
feedback experiment indicated that auditory feedback becomes important during speech production even for adults, if the auditory perception pathway is altered. A further well-known effect, which underlines the importance of auditory feedback throughout a person's lifetime, is that the production of sounds such as sibilant fricatives (like /s/) begins to deteriorate in deafened adults. Because auditory feedback needs more than 100 milliseconds before a correction occurs at the production level, it is a slow correction mechanism in comparison with the duration (or production time) of speech sounds (vowels or consonants). Thus auditory feedback is too slow to correct the production
Auditory feedback
147882
a disturbance or the amplitude of an oscillation, and those that lead to a "decrease" of the same. The terms positive and negative feedback are defined in different ways within different disciplines. The two definitions may cause confusion, such as when an incentive (reward) is used to boost poor performance (narrow a gap). Referring to definition 1, some authors use alternative terms, replacing "positive/negative" with "self-reinforcing/self-correcting", "reinforcing/balancing", "discrepancy-enhancing/discrepancy-reducing" or "regenerative/degenerative" respectively. And for definition 2, some authors advocate describing the action or effect as positive/negative "reinforcement" or "punishment" rather than feedback. Yet even within a single discipline an example of
Feedback
1259087
tulip mania (in the mid-1630s) is often considered the first recorded economic bubble. Because it is often difficult to observe intrinsic values in real-life markets, bubbles are often conclusively identified only in retrospect, once a sudden drop in prices has occurred. Such a drop is known as a "crash" or a "bubble burst". Both the boom and the burst phases of the bubble are examples of a positive feedback mechanism, in contrast to the negative feedback mechanism that determines the equilibrium price under normal market circumstances. Prices in an economic bubble can fluctuate erratically, and become impossible to predict from
Economic bubble
3318190
having a limited effect on muscle growth. However, increases in cardiac myostatin can increase its serum concentration, which may cause skeletal muscle atrophy. Pathological states that increase cardiac stress and promote heart failure can induce a rise in both cardiac myostatin mRNA and protein levels within the heart. In ischemic or dilated cardiomyopathy, increased levels of myostatin mRNA have been detected within the left ventricle. As a member of the TGF-β family, myostatin may play a role in post-infarct recovery. It has been hypothesized that hypertrophy of the heart induces an increase in myostatin as a negative feedback mechanism in
Myostatin
14293761
relatively cold upper atmosphere is less than that emitted toward the ground from the lower atmosphere. Thus, the strength of the greenhouse effect depends on the atmosphere's rate of temperature decrease with height. Both theory and climate models indicate that global warming will reduce the rate of temperature decrease with height, producing a negative "lapse rate feedback" that weakens the greenhouse effect. Measurements of the rate of temperature change with height are very sensitive to small errors in observations, making it difficult to establish whether the models agree with observations. Climate change feedback Climate change feedback is important in the
Climate change feedback
124961
of the active device cancels the (positive) internal loss resistance in the resonator, in effect creating a resonator with no damping, which generates spontaneous continuous oscillations at its resonant frequency. The negative-resistance oscillator model is not limited to one-port devices like diodes; feedback oscillator circuits with two-port amplifying devices such as transistors and tubes also have negative resistance. At high frequencies, transistors and FETs do not need a feedback loop, but with certain loads applied to one port can become unstable at the other port and show negative resistance due to internal feedback, causing them to oscillate. So high-frequency oscillators
Electronic oscillator
7425867
mechanism of action. Progestogen negative feedback decreases the pulse frequency of gonadotropin-releasing hormone (GnRH) release by the hypothalamus, which decreases the release of follicle-stimulating hormone (FSH) and greatly decreases the release of luteinizing hormone (LH) by the anterior pituitary. Decreased levels of FSH inhibit follicular development, preventing an increase in estradiol levels. Progestogen negative feedback and the lack of estrogen positive feedback on LH release prevent a mid-cycle LH surge. Inhibition of follicular development and the absence of a LH surge prevent ovulation. Estrogen was originally included in oral contraceptives for better cycle control (to stabilize the endometrium and thereby
Hormonal contraception
14293757
larger greenhouse effect than that due to CO alone. Although this feedback process causes an increase in the absolute moisture content of the air, the relative humidity stays nearly constant or even decreases slightly because the air is warmer. Climate models incorporate this feedback. Water vapor feedback is strongly positive, with most evidence supporting a magnitude of 1.5 to 2.0 W/m/K, sufficient to roughly double the warming that would otherwise occur. Water vapor feedback is considered a faster feedback mechanism. As the temperature of a black body increases, the emission of infrared radiation back into space increases with the fourth
Climate change feedback
12436038
Another protein important in Akt attenuation is Carboxy Terminal Modulator Protein (CTMP). CTMP binds to the regulatory domain of Akt, blocking its phosphorylation and activation. When the pathway is activated by insulin, insulin receptor substrate 1 (IRS-1) transcription is down-regulated, in a negative feedback loop via mTORC1 and S6K1 activation. S6K1 is also able to phosphorylate IRS-1 at multiple serine residues, preventing binding to RTKs. Another negative feedback control mechanism regulating the pathway involves FoxO transcription factors. Activated Akt causes FoxO degradation, so it can no longer inhibit PP2A, thus leading to a decrease in Akt phosphorylation. Once active, Akt
Akt/PKB signaling pathway
14190855
considered only moderately descriptive, less positive, and less important (i.e. modest vs. immodest). Feedback that counteracts a central self-conception is recalled much less frequently than feedback that counteracts a peripheral self-conception. In fact, the recall for feedback on modifiable traits was unaffected by whether the feedback was positive or negative. Sedikides and Green (2004) offered a mechanism by which they believe mnemic neglect occurs. Self-referent information is processed in two stages. The first stage checks the information for compatibility with self-concept. Self-threatening information is confined to this stage because it is found to be incompatible with self-concept. During the second
Mnemic neglect
299439
FSH inhibit follicular development, preventing an increase in estradiol levels. Progestogen negative feedback and the lack of estrogen positive feedback on LH secretion prevent a mid-cycle LH surge. Inhibition of follicular development and the absence of an LH surge prevent ovulation. Estrogen was originally included in oral contraceptives for better cycle control (to stabilize the endometrium and thereby reduce the incidence of breakthrough bleeding), but was also found to inhibit follicular development and help prevent ovulation. Estrogen negative feedback on the anterior pituitary greatly decreases the secretion of FSH, which inhibits follicular development and helps prevent ovulation. Another primary mechanism
Combined oral contraceptive pill
1688047
video feedback effect was used in the opening sequences to the first ten series of the television program "Doctor Who". In electrical switches, 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. A number of examples of positive feedback systems may be found in physiology. In most cases, such feedback loops culminate in counter-signals
Positive feedback
9660939
of chemokines in tissues critically influence immune responses. The molecular mechanism behind neurokinin's role as a chemoattractor is currently unclear. Neurokinin A has an inhibitory effect on the formation of myeloid cells, and appear to be involved in one specific receptor since the effect can be completely abolished by a NK-2 receptor-selective antagonist. The inhibitory effect of neuronkinin A is countered by the excitatory effect of a structurally similar compound: substance P. The opposite effects on myelogenesis by substance P and neurokinin A may represent an important feedback mechanism for maintenance of homeostasis. The binding of neurokinin A to the
Neurokinin A
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also plays a negative role in people's overall psychological well-being. FOMO is believed to trigger negative social and emotional experiences, such as boredom and loneliness, through social media usage. Consistent with earlier research, an empirical study on FOMO in 2013 found that FOMO has a negative effect on people's overall mood and life satisfaction. In terms of the cognitive effects, FOMO could further instill a belief that an interruption is more like a "connection". FOMO may drive someone to constantly look for a better or more interesting connection with others, abandoning current connections to do so, without realizing that what
Fear of missing out
14293731
Climate change feedback Climate change feedback is important in the understanding of global warming because feedback processes may amplify or diminish the effect of each climate forcing, and so play an important part in determining the climate sensitivity and future climate state. Feedback in general is the process in which changing one quantity changes a second quantity, and the change in the second quantity in turn changes the first. Positive feedback amplifies the change in the first quantity while negative feedback reduces it. The term "forcing" means a change which may "push" the climate system in the direction of warming
Climate change feedback
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Positive feedback Positive feedback is a process that occurs in a feedback loop in which the effects of a small disturbance 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. Both concepts play an important role in science and engineering, including biology, chemistry, and cybernetics. Mathematically, positive feedback is defined as a positive loop gain around a closed loop of cause and effect.
Positive feedback
4127337
model, an important macroeconomic model for which the Nobel prize was recently granted to Diamond, Mortensen and Pissarides (DMP). Shimer explained that in the standard DMP model, a shock that raises the value of what firms sell – other things the same – increases their incentive to hire workers by raising profits per worker. The problem, according to Shimer is that this mechanism sets into motion a negative feedback loop which in the end largely cancels firms' incentive to expand employment. In particular, as employment expands, labor market conditions in general begin to improve for workers and this puts them
Paul Milgrom
1448396
other words, smaller distortion/intermodulation). By sacrificing gain, it also has an additional effect of increasing the bandwidth of the amplifier. However, a negative feedback amplifier can be unstable such that it may oscillate. Once the stability problem is solved, the negative feedback amplifier is extremely useful in the field of electronics. Black published a famous paper, "Stabilized feedback amplifiers", in 1934. He was born in Leominster, Massachusetts in 1898. He went to Worcester Polytechnic Institute (WPI) for his first degree. Subsequently, he received a B.S.S. in Electrical Engineering from WPI in 1921 and then joined Western Electric, which was the
Harold Stephen Black
6704910
allowed photodissociation to occur, with lighter hydrogen gas escaping to space and oxygen reacting with surface rocks. This model is supported by the deuterium/hydrogen ratio on Venus which is 150 times greater than the D/H ratio on Earth. Positive feedbacks do not have to lead to a runaway effect, as the gain is not always sufficient. A strong negative feedback always exists (radiation from a planet increases in proportion to the fourth power of temperature, in accordance with the Stefan-Boltzmann law) so the positive feedback effect has to be very strong to cause a runaway effect (see gain). An increase
Runaway greenhouse effect
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high distortion are quoted for guitar amplifiers). Historically, negative feedback in single ended pentode amplifiers was quite common (for example, the Mullard 3-3 design built around EL84). Today negative feedback is less popular with SET amplifiers, with many having no overall feedback loop. Their frequency response, limited by transformer passband, is then modulated by irregularities in loudspeaker impedance. This, and the very low attainable power levels (3 Watts for 2A3 to 20 Watts for 6C33C), requires careful matching of amplifier to speakers; selection is usually limited to high-efficiency loudspeakers with a sensitivity exceeding 90 dB/Watt. Single-ended triode (SET) amplifiers are
Single-ended triode
20105473
that five genes ("per", "tim", "dbt", "Clk", and "cyc") controlled circadian rhythms in "Drosophila". The "per"-"tim" regulation mechanism was known at this time, though "Clk" regulation was not yet known. Hardin and his team conducted a series of experiments to identify the two interlocked feedback loops in the circadian mechanism of "Drosophila". This means that the "per"-"tim" feedback loop connects to the "Clk"-"cyc" feedback loop, so that one loop has an effect on the other, and vice versa. They measured wild-type and mutant "Clk" mRNA levels to identify any changes in transcription levels. They observed that the PER-TIM complex suppresses
Paul Hardin (chronobiologist)
12877490
on electric guitar amplifiers. The first presence control on a Fender amplifier, for example, appeared in 1954 on the Twin. In 1955 it appeared on the 1/15 Pro-Amp, the 3/10 Bandmaster, the 2/10 Super, and the 4/10 Bassman. The original Fender presence control acted upon the amplifier's negative-feedback loop. As the level of "presence" was increased, so more and more of the higher frequencies in the negative-feedback loop were dumped to ground, leaving the low and mid-range frequencies. Increasing the presence resulted in there being less and less negative feedback on high frequencies. The effect varied according to amplitude. Later
Presence (amplification)
14079541
methods and is used as a tool to create and modify networks. Regulatory feedback network Regulatory feedback networks are neural networks that perform inference using Negative feedback. The feedback is not used to find optimal learning or training weights but to find the optimal activation of nodes. In effect this approach is most similar to a non-parametric method but is different from K-nearest neighbors in that it can be shown to mathematically emulate feedforward neural networks. Regulatory feedback networks started as a model to explain brain phenomena found during recognition including network-wide bursting and difficulty with similarity found universally in
Regulatory feedback network
3977094
of the tank. The float is often ball-shaped, hence the name "ballcock". The valve is connected to the incoming water supply, and is opened and closed by the lever which has the float mounted on the end. When the water level rises, the float rises with it; once it rises to a pre-set level, the mechanism forces the lever to close the valve and shut off the water flow. This is an example of negative feedback and of proportional control. When a toilet's handle is turned, a discharge mechanism is activated by means of a rod or chain. The mechanism
Ballcock
14079540
Regulatory feedback network Regulatory feedback networks are neural networks that perform inference using Negative feedback. The feedback is not used to find optimal learning or training weights but to find the optimal activation of nodes. In effect this approach is most similar to a non-parametric method but is different from K-nearest neighbors in that it can be shown to mathematically emulate feedforward neural networks. Regulatory feedback networks started as a model to explain brain phenomena found during recognition including network-wide bursting and difficulty with similarity found universally in sensory recognition. This approach can also perform mathematically equivalent classification as feedforward
Regulatory feedback network
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the op-amp is used in a closed-loop design (negative feedback, where there is a signal path of some sort feeding back from the output to the inverting input). These rules are commonly used as a good first approximation for analyzing or designing op-amp circuits. None of these ideals can be perfectly realized. A real op-amp may be modeled with non-infinite or non-zero parameters using equivalent resistors and capacitors in the op-amp model. The designer can then include these effects into the overall performance of the final circuit. Some parameters may turn out to have negligible effect on the final design
Operational amplifier
147892
assumed to specify "negative feedback". The most common general-purpose controller using a control-loop feedback mechanism is a proportional-integral-derivative (PID) controller. Heuristically, the terms of a PID controller can be interpreted as corresponding to time: the proportional term depends on the "present" error, the integral term on the accumulation of "past" errors, and the derivative term is a prediction of "future" error, based on current rate of change. In ancient times, the float valve was used to regulate the flow of water in Greek and Roman water clocks; similar float valves are used to regulate fuel in a carburettor and also
Feedback
147889
and activator proteins are used to create genetic operons, which were identified by Francois Jacob and Jacques Monod in 1961 as "feedback loops". These feedback loops may be positive (as in the case of the coupling between a sugar molecule and the proteins that import sugar into a bacterial cell), or negative (as is often the case in metabolic consumption). On a larger scale, feedback can have a stabilizing effect on animal populations even when profoundly affected by external changes, although time lags in feedback response can give rise to predator-prey cycles. In zymology, feedback serves as regulation of activity
Feedback
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commonplace circuits (feedback amplifiers, resistive and time-dependent converters, negative impedance converters, etc.). The theorems are useful in 'circuit analysis' especially for analyzing circuits with feedback and certain transistor amplifiers at high frequencies. There is a close relationship between Miller theorem and Miller effect: the theorem may be considered as a generalization of the effect and the effect may be thought as of a special case of the theorem. The Miller theorem establishes that in a linear circuit, if there exists a branch with impedance "Z", connecting two nodes with nodal voltages "V" and "V", we can replace this branch by
Miller theorem
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liquidity disappears, which increases even more the concentration of toxic flow in the overall volume, which triggers a feedback mechanism that forces even more market makers out. This cascading effect has caused hundreds of liquidity-induced crashes in the past, the "flash crash" being one (major) example of it. One hour before the "flash crash", order flow toxicity was the highest in recent history. However, independent studies published in 2013 strongly disputed the last claim. In particular, in 2011 Andersen and Bondarenko conducted a comprehensive investigation of the two main versions of VPIN used by its creators, one based on the
2010 Flash Crash
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phenomenon, known as the Larsen effect, is the result of a positive feedback. In general, every oscillator consists of three main parts. These are the power source or pump, the amplifier and the positive feedback leading to the output. The corresponding parts in a SASER device are the excitation or pumping mechanism, the active (amplifying) medium, and the feedback leading to acoustic radiation. Pumping can be performed, for instance, with an alternating electric field or with some mechanical vibrations of resonators. The active medium should be a material in which sound amplification can be induced. An example of a feedback
Sound amplification by stimulated emission of radiation
2262164
a cell divides, two cells result which, although they contain the same genome in full, can differ in which genes are turned on and making proteins. Sometimes a 'self-sustaining feedback loop' ensures that a cell maintains its identity and passes it on. Less understood is the mechanism of epigenetics by which chromatin modification may provide cellular memory by blocking or allowing transcription. A major feature of multicellular animals is the use of morphogen gradients, which in effect provide a positioning system that tells a cell where in the body it is, and hence what sort of cell to become. A
Gene regulatory network
1530898
feedback will continue to reduce total distortion towards zero provided the system is strictly stable. Negative-feedback amplifier A Negative-feedback amplifier (or feedback amplifier) is an electronic amplifier that subtracts a fraction of its output from its input, so that negative feedback opposes the original signal. The applied negative feedback can improve its performance (gain stability, linearity, frequency response, step response) and reduces sensitivity to parameter variations due to manufacturing or environment. Because of these advantages, many amplifiers and control systems use negative feedback. An idealized negative-feedback amplifier as shown in the diagram is a system of three elements (see Figure
Negative-feedback amplifier
227552
being the only one that has defined its own environment: [The pace of human ecology] is determined by the progress of man's technology (p35)... human ecology (economy) is governed by mechanisms of POSITIVE feedback, defined as a mechanism which tends to encourage behavior rather than to attenuate it (p43). Positive feedback always involves the danger of an 'avalanche' effect... One particular kind of positive feedback occurs when individuals OF THE SAME SPECIES enter into competition among themselves... For many animal species, environmental factors keep... intraspecies selection from [leading to] disaster... But there is no force which exercises this type of
Konrad Lorenz
1530888
no feedforward) where "division" is used because the input connection is "shunt": the feedback two-port is in parallel with the signal source at the input side of the amplifier. A reminder: "A" is the "loaded" open loop gain found above, as modified by the resistors of the feedback network. The impedance seen by the load needs further discussion. The load in Figure 5 is connected to the collector of the output transistor, and therefore is separated from the body of the amplifier by the infinite impedance of the output current source. Therefore, feedback has no effect on the output impedance,
Negative-feedback amplifier
11908722
Delayed density dependence In population ecology delayed density dependence describes a situation where population growth is controlled by negative feedback operating with a time lag. Delayed density dependence has been used by ecologists to explain population cycles. Ecologists have been unable to successfully explain regular population cycles for many decades; delayed density dependence may hold the answer. Here populations are allowed to increase above their normal capacity because there is a time lag until negative feedback mechanisms bring the population back down. This effect has been used to explain the widely fluctuating population cycles of lemmings, forest insects as well
Delayed density dependence
7972374
the surrounding interstitium from luminal fluid. The Tubular fluid is diluted because the cell's walls are water-impermeable and do not lose water as NaCl is actively reabsorbed. Thus, the TAL is an important segment of the TGF system, and its transport properties allow it to act as a key operator of the TGF system. A reduction of GFR occurs as a result of TGF when NaCl concentration at the sensor site is increased within the physiological range of approximately 10 to 60 mM. The TGF mechanism is a negative feedback loop in which the chloride ion concentration is sensed downstream
Tubuloglomerular feedback
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to share positive news, and are emotionally affected by positive news more than twice than by negative news. Positivity effect In psychology and cognitive science, the positivity effect is the ability to constructively analyze a situation where the desired results are not achieved; but still obtain positive feedback that assists our future progression. When a person is considering people they like (including themselves), the person tends to make situational attributions about their negative behaviors and dispositional attributions about their positive behaviors. The reverse may be true for people that the person dislikes. This may well be because of the dissonance
Positivity effect
9152700
designing and selling process. When asked about their thoughts on the overall effect of the fashion blogs, McCollough stated, “Blogs posting things about us, going viral, spreading throughout the internet… it has an extraordinary impact on the business”. They also stated how in the past, they would have to wait three, four days to hear a review on their line, but now the feedback comes almost instant. When asked about how the blogs directly affect their own designs, they explained while they do read numerous blogs daily, they try to take each criticism (positive or negative) with a grain of
Fashion blog
306847
is the comparator with hysteresis, the Schmitt trigger. Some circuits may use "positive" feedback and "negative" feedback around the same amplifier, for example triangle-wave oscillators and active filters. Because of the wide slew range and lack of positive feedback, the response of all the open-loop level detectors described above will be relatively slow. External overall positive feedback may be applied, but (unlike internal positive feedback that may be applied within the latter stages of a purpose-designed comparator) this markedly affects the accuracy of the zero-crossing detection point. Using a general-purpose op-amp, for example, the frequency of "E" for the sine
Operational amplifier
1530858
Negative-feedback amplifier A Negative-feedback amplifier (or feedback amplifier) is an electronic amplifier that subtracts a fraction of its output from its input, so that negative feedback opposes the original signal. The applied negative feedback can improve its performance (gain stability, linearity, frequency response, step response) and reduces sensitivity to parameter variations due to manufacturing or environment. Because of these advantages, many amplifiers and control systems use negative feedback. An idealized negative-feedback amplifier as shown in the diagram is a system of three elements (see Figure 1): Fundamentally, all electronic devices that provide power gain (e.g., vacuum tubes, bipolar transistors, MOS
Negative-feedback amplifier
2499211
leads to a long-term increase in AMPA receptors and thus synaptic strength and plasticity. If the strength of a synapse is only reinforced by stimulation or weakened by its lack, a positive feedback loop will develop, causing some cells never to fire and some to fire too much. But two regulatory forms of plasticity, called scaling and metaplasticity, also exist to provide negative feedback. Synaptic scaling is a primary mechanism by which a neuron is able to stabilize firing rates up or down. Synaptic scaling serves to maintain the strengths of synapses relative to each other, lowering amplitudes of small
Synaptic plasticity
126811
output from an amplifier cannot exceed its input power. The amplifier circuit has an "open loop" performance. This is described by various parameters (gain, slew rate, output impedance, distortion, bandwidth, signal-to-noise ratio, etc.). Many modern amplifiers use negative feedback techniques to hold the gain at the desired value and reduce distortion. Negative loop feedback has the intended effect of lowering the output impedance and thereby increasing electrical damping of loudspeaker motion at and near the resonance frequency of the speaker. When assessing rated amplifier power output, it is useful to consider the applied load, the signal type (e.g., speech or
Amplifier
2662182
feedback on their performance may improve their skills when an experiment provides this feedback for the first time. Research on the demand effect also suggests that people may be motivated to please the experimenter, at least if it does not conflict with any other motive. They may also be suspicious of the purpose of the experimenter. Therefore, Hawthorne effect may only occur when there is usable feedback or a change in motivation. Parsons defines the Hawthorne effect as "the confounding that occurs if experimenters fail to realize how the consequences of subjects' performance affect what subjects do" [i.e. learning effects,
Hawthorne effect
1532965
led researchers investigating Lindzen's theory to conclude that the Iris effect would instead warm the atmosphere. Lindzen disputed this, claiming that the negative feedback from high-level clouds was still larger than the weak positive feedback estimated by Lin et al. Lindzen has expressed his concern over the validity of computer models used to predict future climate change. Lindzen said that predicted warming may be overestimated because of their handling of the climate system's water vapor feedback. The feedback due to water vapor is a major factor in determining how much warming would be expected to occur with increased atmospheric concentrations
Richard Lindzen
582586
global mean CRF is negative). In response to global warming, the cooling effect of clouds on climate might be enhanced or weakened, thereby producing a radiative feedback to climate warming (Randall "et al"., 2006; NRC, 2003; Zhang, 2004; Stephens, 2005; Bony "et al"., 2006). In the most recent, the IPCC Fifth Assessment Report (2013), cloud feedback effects are discussed in the Working Group 1 report, in Chapter 7, "Clouds and Aerosols", with some additional discussion on uncertainties in Chapter 9, "Evaluation of Climate Models". The report states "Cloud feedback studies point to five aspects of the cloud response to climate
Cloud feedback
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levels of FSH inhibit follicular development, preventing an increase in estradiol levels. Progestogen negative feedback and the lack of estrogen positive feedback on LH release prevent a LH surge. Inhibition of follicular development and the absence of a LH surge prevent ovulation. A secondary mechanism of action of all progestogen-containing contraceptives is inhibition of sperm penetration by changes in the cervical mucus. Inhibition of ovarian function during DMPA use causes the endometrium to become thin and atrophic. These changes in the endometrium could, theoretically, prevent implantation. However, because DMPA is highly effective in inhibiting ovulation and sperm penetration, the possibility
Medroxyprogesterone acetate
4772118
added (i.e. by a flywheel) or the system uses feedback to actively counter the effect. Direct drive mechanisms are present in several products: Direct drive mechanism A direct drive mechanism is one that takes the power coming from a motor without any reductions (such as a gearbox). The main disadvantage of the system is that it needs a special motor. Usually motors are built to achieve maximum torque at high rotational speeds, usually 1500 or 3000 rpm. While this is useful for many applications (such as an electric fan), other mechanisms need a relatively high torque at very low speeds,
Direct drive mechanism
7210609
the sudden blue starch colour. But since process A is still acting, this slowly fades back to clear. The eventual resumption of process B is invisible, but can be revealed by the use of a suitable electrode. A negative feedback loop which includes a delay (mediated here by process A) is a general mechanism for producing oscillations in many physical systems, but is very rare in "nonbiological" homogeneous chemical systems. (The BZ oscillating reaction has a somewhat similar feedback loop.) Briggs–Rauscher reaction The Briggs–Rauscher oscillating reaction is one of a small number of known oscillating chemical reactions. It is especially
Briggs–Rauscher reaction
111876
does not follow the Michaelis-Menten equation. An irreversible inhibitor permanently inactivates the enzyme, usually by forming a covalent bond to the protein. Penicillin and aspirin are common drugs that act in this manner. In many organisms, inhibitors may act as part of a feedback mechanism. If an enzyme produces too much of one substance in the organism, that substance may act as an inhibitor for the enzyme at the beginning of the pathway that produces it, causing production of the substance to slow down or stop when there is sufficient amount. This is a form of negative feedback. Major metabolic
Enzyme
2472336
to haem is protoporphyrin IX (PPIX), an effective photosensitiser. Haem itself is not a photosensitiser, due to the coordination of a paramagnetic ion in the centre of the macrocycle, causing significant reduction in excited state lifetimes. The haem molecule is synthesised from glycine and succinyl coenzyme A (succinyl CoA). The rate-limiting step in the biosynthesis pathway is controlled by a tight (negative) feedback mechanism in which the concentration of haem regulates the production of ALA. However, this controlled feedback can be by-passed by artificially adding excess exogenous ALA to cells. The cells respond by producing PPIX (photosensitiser) at a faster
Photodynamic therapy
10977703
can be used to contain and even prevent a liquidity crisis (elaborated below). One of the mechanisms, that can work to amplify the effects of a small negative shock to the economy, is the Balance Sheet Mechanism. Under this mechanism, a negative shock in the financial market lowers asset prices and erodes the financial institution's capital thus worsening its balance sheet. Consequently, two liquidity spirals come into effect, which amplify the impact of the initial negative shock. In an attempt to maintain its leverage ratio, the financial institution must sell its assets, precisely at a time when their price is
Liquidity crisis
2314792
variation in the intensity of solar radiation calculated as the Earth's orbit evolves. If orbital forcing causes climate change, science needs to explain why the observed effect is amplified compared to the theoretical effect. Some climate systems exhibit amplification (positive feedback) and damping responses (negative feedback). An example of amplification would be if, with the land masses around 65° north covered in year-round ice, solar energy were reflected away. Amplification would mean that an ice age induces changes that impede orbital forcing from ending the ice age. The Earth's current orbital inclination is 1.57° (see above). Earth presently moves through
Milankovitch cycles
170358
been discussed in a number of papers Roy Spencer "et al." suggested "a net reduction in radiative input into the ocean-atmosphere system" in tropical intraseasonal oscillations "may potentially support" the idea of an "Iris" effect, although they point out that their work is concerned with much shorter time scales. Other analyses have found that the iris effect is a "positive" feedback rather than the negative feedback proposed by Lindzen. James Hansen's 1984 climate model projections versus observed temperatures are updated each year by Dr Mikako Sato of Columbia University. The RealClimate website provides an annual update comparing both Hansen's 1988
Global warming controversy