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Saturday, August 26, 2023

Three Laws of Robotics

From Wikipedia, the free encyclopedia
https://en.wikipedia.org/wiki/Three_Laws_of_Robotics
This cover of I, Robot illustrates the story "Runaround", the first to list all Three Laws of Robotics.

The Three Laws of Robotics (often shortened to The Three Laws or Asimov's Laws) are a set of rules devised by science fiction author Isaac Asimov, which were to be followed by robots in several of his stories. The rules were introduced in his 1942 short story "Runaround" (included in the 1950 collection I, Robot), although similar restrictions had been implied in earlier stories.

The laws

The Three Laws, presented to be from the fictional "Handbook of Robotics, 56th Edition, 2058 A.D.", are:

First Law

A robot may not injure a human being or, through inaction, allow a human being to come to harm.

Second Law

A robot must obey the orders given it by human beings except where such orders would conflict with the First Law.

Third Law

A robot must protect its own existence as long as such protection does not conflict with the First or Second Law.

Use in fiction

These form an organizing principle and unifying theme for Asimov's robot-based fiction, appearing in his Robot series, the stories linked to it, and in his (initially pseudonymous) Lucky Starr series of young-adult fiction. The Laws are incorporated into almost all of the positronic robots appearing in his fiction, and cannot be bypassed, being intended as a safety feature. Many of Asimov's robot-focused stories involve robots behaving in unusual and counter-intuitive ways as an unintended consequence of how the robot applies the Three Laws to the situation in which it finds itself. Other authors working in Asimov's fictional universe have adopted them and references, often parodic, appear throughout science fiction as well as in other genres.

The original laws have been altered and elaborated on by Asimov and other authors. Asimov himself made slight modifications to the first three in subsequent books works to further develop how robots would interact with humans and each other. In later fiction where robots had taken responsibility for government of whole planets and human civilizations, Asimov also added a fourth, or zeroth law, to precede the others.

The Three Laws, and the Zeroth, have pervaded science fiction and are referred to in many books, films, and other media. They have also influenced thought on the ethics of artificial intelligence.

History

In The Rest of the Robots, published in 1964, Isaac Asimov noted that when he began writing in 1940 he felt that "one of the stock plots of science fiction was ... robots were created and destroyed their creator. Knowledge has its dangers, yes, but is the response to be a retreat from knowledge? Or is knowledge to be used as itself a barrier to the dangers it brings?" He decided that in his stories a robot would not "turn stupidly on his creator for no purpose but to demonstrate, for one more weary time, the crime and punishment of Faust."

On May 3, 1939, Asimov attended a meeting of the Queens (New York) Science Fiction Society where he met Earl and Otto Binder who had recently published a short story "I, Robot" featuring a sympathetic robot named Adam Link who was misunderstood and motivated by love and honor. (This was the first of a series of ten stories; the next year "Adam Link's Vengeance" (1940) featured Adam thinking "A robot must never kill a human, of his own free will.") Asimov admired the story. Three days later Asimov began writing "my own story of a sympathetic and noble robot", his 14th story. Thirteen days later he took "Robbie" to John W. Campbell the editor of Astounding Science-Fiction. Campbell rejected it, claiming that it bore too strong a resemblance to Lester del Rey's "Helen O'Loy", published in December 1938—the story of a robot that is so much like a person that she falls in love with her creator and becomes his ideal wife. Frederik Pohl published the story under the title “Strange Playfellow” in Super Science Stories September 1940.

Asimov attributes the Three Laws to John W. Campbell, from a conversation that took place on 23 December 1940. Campbell claimed that Asimov had the Three Laws already in his mind and that they simply needed to be stated explicitly. Several years later Asimov's friend Randall Garrett attributed the Laws to a symbiotic partnership between the two men -a suggestion that Asimov adopted enthusiastically. According to his autobiographical writings, Asimov included the First Law's "inaction" clause because of Arthur Hugh Clough's poem "The Latest Decalogue" (text in Wikisource), which includes the satirical lines "Thou shalt not kill, but needst not strive / officiously to keep alive".

Although Asimov pins the creation of the Three Laws on one particular date, their appearance in his literature happened over a period. He wrote two robot stories with no explicit mention of the Laws, "Robbie" and "Reason". He assumed, however, that robots would have certain inherent safeguards. "Liar!", his third robot story, makes the first mention of the First Law but not the other two. All three laws finally appeared together in "Runaround". When these stories and several others were compiled in the anthology I, Robot, "Reason" and "Robbie" were updated to acknowledge all the Three Laws, though the material Asimov added to "Reason" is not entirely consistent with the Three Laws as he described them elsewhere. In particular the idea of a robot protecting human lives when it does not believe those humans truly exist is at odds with Elijah Baley's reasoning, as described below.

During the 1950s Asimov wrote a series of science fiction novels expressly intended for young-adult audiences. Originally his publisher expected that the novels could be adapted into a long-running television series, something like The Lone Ranger had been for radio. Fearing that his stories would be adapted into the "uniformly awful" programming he saw flooding the television channels Asimov decided to publish the Lucky Starr books under the pseudonym "Paul French". When plans for the television series fell through, Asimov decided to abandon the pretence; he brought the Three Laws into Lucky Starr and the Moons of Jupiter, noting that this "was a dead giveaway to Paul French's identity for even the most casual reader".

In his short story "Evidence" Asimov lets his recurring character Dr. Susan Calvin expound a moral basis behind the Three Laws. Calvin points out that human beings are typically expected to refrain from harming other human beings (except in times of extreme duress like war, or to save a greater number) and this is equivalent to a robot's First Law. Likewise, according to Calvin, society expects individuals to obey instructions from recognized authorities such as doctors, teachers and so forth which equals the Second Law of Robotics. Finally humans are typically expected to avoid harming themselves which is the Third Law for a robot.

The plot of "Evidence" revolves around the question of telling a human being apart from a robot constructed to appear human. Calvin reasons that if such an individual obeys the Three Laws he may be a robot or simply "a very good man". Another character then asks Calvin if robots are very different from human beings after all. She replies, "Worlds different. Robots are essentially decent."

Asimov later wrote that he should not be praised for creating the Laws, because they are "obvious from the start, and everyone is aware of them subliminally. The Laws just never happened to be put into brief sentences until I managed to do the job. The Laws apply, as a matter of course, to every tool that human beings use", and "analogues of the Laws are implicit in the design of almost all tools, robotic or not":

  1. Law 1: A tool must not be unsafe to use. Hammers have handles and screwdrivers have hilts to help increase grip. It is of course possible for a person to injure himself with one of these tools, but that injury would only be due to his incompetence, not the design of the tool.
  2. Law 2: A tool must perform its function efficiently unless this would harm the user. This is the entire reason ground-fault circuit interrupters exist. Any running tool will have its power cut if a circuit senses that some current is not returning to the neutral wire, and hence might be flowing through the user. The safety of the user is paramount.
  3. Law 3: A tool must remain intact during its use unless its destruction is required for its use or for safety. For example, Dremel disks are designed to be as tough as possible without breaking unless the job requires it to be spent. Furthermore, they are designed to break at a point before the shrapnel velocity could seriously injure someone (other than the eyes, though safety glasses should be worn at all times anyway).

Asimov believed that, ideally, humans would also follow the Laws:

I have my answer ready whenever someone asks me if I think that my Three Laws of Robotics will actually be used to govern the behavior of robots, once they become versatile and flexible enough to be able to choose among different courses of behavior.

My answer is, "Yes, the Three Laws are the only way in which rational human beings can deal with robots—or with anything else."

—But when I say that, I always remember (sadly) that human beings are not always rational.

Asimov stated in a 1986 interview on the Manhattan public access show Conversations with Harold Hudson Channer with Harold Channer with guest co-host Marilyn vos Savant, "It's a little humbling to think that, what is most likely to survive of everything I've said... After all, I've published now... I've published now at least 20 million words.  I'll have to figure it out, maybe even more.  But of all those millions of words that I've published, I am convinced that 100 years from now only 60 of them will survive.  The 60 that make up the Three Laws of Robotics."

Alterations

By Asimov

Asimov's stories test his Three Laws in a wide variety of circumstances leading to proposals and rejection of modifications. Science fiction scholar James Gunn writes in 1982, "The Asimov robot stories as a whole may respond best to an analysis on this basis: the ambiguity in the Three Laws and the ways in which Asimov played twenty-nine variations upon a theme". While the original set of Laws provided inspirations for many stories, Asimov introduced modified versions from time to time.

First Law modified

In "Little Lost Robot" several NS-2, or "Nestor", robots are created with only part of the First Law. It reads:

1. A robot may not harm a human being.

This modification is motivated by a practical difficulty as robots have to work alongside human beings who are exposed to low doses of radiation. Because their positronic brains are highly sensitive to gamma rays the robots are rendered inoperable by doses reasonably safe for humans. The robots are being destroyed attempting to rescue the humans who are in no actual danger but "might forget to leave" the irradiated area within the exposure time limit. Removing the First Law's "inaction" clause solves this problem but creates the possibility of an even greater one: a robot could initiate an action that would harm a human (dropping a heavy weight and failing to catch it is the example given in the text), knowing that it was capable of preventing the harm and then decide not to do so.

Gaia is a planet with collective intelligence in the Foundation series which adopts a law similar to the First Law, and the Zeroth Law, as its philosophy:

Gaia may not harm life or allow life to come to harm.

Zeroth Law added

Asimov once added a "Zeroth Law"—so named to continue the pattern where lower-numbered laws supersede the higher-numbered laws—stating that a robot must not harm humanity. The robotic character R. Daneel Olivaw was the first to give the Zeroth Law a name in the novel Robots and Empire; however, the character Susan Calvin articulates the concept in the short story "The Evitable Conflict".

In the final scenes of the novel Robots and Empire, R. Giskard Reventlov is the first robot to act according to the Zeroth Law. Giskard is telepathic, like the robot Herbie in the short story "Liar!", and tries to apply the Zeroth Law through his understanding of a more subtle concept of "harm" than most robots can grasp. However, unlike Herbie, Giskard grasps the philosophical concept of the Zeroth Law allowing him to harm individual human beings if he can do so in service to the abstract concept of humanity. The Zeroth Law is never programmed into Giskard's brain but instead is a rule he attempts to comprehend through pure metacognition. Though he fails – it ultimately destroys his positronic brain as he is not certain whether his choice will turn out to be for the ultimate good of humanity or not – he gives his successor R. Daneel Olivaw his telepathic abilities. Over the course of many thousands of years Daneel adapts himself to be able to fully obey the Zeroth Law. As Daneel formulates it, in the novels Foundation and Earth and Prelude to Foundation, the Zeroth Law reads:

A robot may not harm humanity, or, by inaction, allow humanity to come to harm.

A condition stating that the Zeroth Law must not be broken was added to the original Three Laws, although Asimov recognized the difficulty such a law would pose in practice. Asimov's novel Foundation and Earth contains the following passage:

Trevize frowned. "How do you decide what is injurious, or not injurious, to humanity as a whole?"

"Precisely, sir," said Daneel. "In theory, the Zeroth Law was the answer to our problems. In practice, we could never decide. A human being is a concrete object. Injury to a person can be estimated and judged. Humanity is an abstraction."

A translator incorporated the concept of the Zeroth Law into one of Asimov's novels before Asimov himself made the law explicit. Near the climax of The Caves of Steel, Elijah Baley makes a bitter comment to himself thinking that the First Law forbids a robot from harming a human being. He determines that it must be so unless the robot is clever enough to comprehend that its actions are for humankind's long-term good. In Jacques Brécard's 1956 French translation entitled Les Cavernes d'acier Baley's thoughts emerge in a slightly different way:

A robot may not harm a human being, unless he finds a way to prove that ultimately the harm done would benefit humanity in general!

Removal of the Three Laws

Three times during his writing career, Asimov portrayed robots that disregard the Three Laws entirely. The first case was a short-short story entitled "First Law" and is often considered an insignificant "tall tale" or even apocryphal. On the other hand, the short story "Cal" (from the collection Gold), told by a first-person robot narrator, features a robot who disregards the Three Laws because he has found something far more important—he wants to be a writer. Humorous, partly autobiographical and unusually experimental in style, "Cal" has been regarded as one of Gold's strongest stories. The third is a short story entitled "Sally" in which cars fitted with positronic brains are apparently able to harm and kill humans in disregard of the First Law. However, aside from the positronic brain concept, this story does not refer to other robot stories and may not be set in the same continuity.

The title story of the Robot Dreams collection portrays LVX-1, or "Elvex", a robot who enters a state of unconsciousness and dreams thanks to the unusual fractal construction of his positronic brain. In his dream the first two Laws are absent and the Third Law reads "A robot must protect its own existence".

Asimov took varying positions on whether the Laws were optional: although in his first writings they were simply carefully engineered safeguards, in later stories Asimov stated that they were an inalienable part of the mathematical foundation underlying the positronic brain. Without the basic theory of the Three Laws the fictional scientists of Asimov's universe would be unable to design a workable brain unit. This is historically consistent: the occasions where roboticists modify the Laws generally occur early within the stories' chronology and at a time when there is less existing work to be re-done. In "Little Lost Robot" Susan Calvin considers modifying the Laws to be a terrible idea, although possible, while centuries later Dr. Gerrigel in The Caves of Steel believes it to require a century just to redevelop the positronic brain theory from scratch.

The character Dr. Gerrigel uses the term "Asenion" to describe robots programmed with the Three Laws. The robots in Asimov's stories, being Asenion robots, are incapable of knowingly violating the Three Laws but, in principle, a robot in science fiction or in the real world could be non-Asenion. "Asenion" is a misspelling of the name Asimov which was made by an editor of the magazine Planet Stories. Asimov used this obscure variation to insert himself into The Caves of Steel just like he referred to himself as "Azimuth or, possibly, Asymptote" in Thiotimoline to the Stars, in much the same way that Vladimir Nabokov appeared in Lolita anagrammatically disguised as "Vivian Darkbloom".

Characters within the stories often point out that the Three Laws, as they exist in a robot's mind, are not the written versions usually quoted by humans but abstract mathematical concepts upon which a robot's entire developing consciousness is based. This concept is largely fuzzy and unclear in earlier stories depicting very rudimentary robots who are only programmed to comprehend basic physical tasks, where the Three Laws act as an overarching safeguard, but by the era of The Caves of Steel featuring robots with human or beyond-human intelligence the Three Laws have become the underlying basic ethical worldview that determines the actions of all robots.

By other authors

Roger MacBride Allen's trilogy

In the 1990s, Roger MacBride Allen wrote a trilogy which was set within Asimov's fictional universe. Each title has the prefix "Isaac Asimov's" as Asimov had approved Allen's outline before his death. These three books, Caliban, Inferno and Utopia, introduce a new set of the Three Laws. The so-called New Laws are similar to Asimov's originals with the following differences: the First Law is modified to remove the "inaction" clause, the same modification made in "Little Lost Robot"; the Second Law is modified to require cooperation instead of obedience; the Third Law is modified so it is no longer superseded by the Second (i.e., a "New Law" robot cannot be ordered to destroy itself); finally, Allen adds a Fourth Law which instructs the robot to do "whatever it likes" so long as this does not conflict with the first three laws. The philosophy behind these changes is that "New Law" robots should be partners rather than slaves to humanity, according to Fredda Leving, who designed these New Law Robots. According to the first book's introduction, Allen devised the New Laws in discussion with Asimov himself. However, the Encyclopedia of Science Fiction says that "With permission from Asimov, Allen rethought the Three Laws and developed a new set."

Jack Williamson's "With Folded Hands"

Jack Williamson's novelette "With Folded Hands" (1947), later rewritten as the novel The Humanoids, deals with robot servants whose prime directive is "To Serve and Obey, And Guard Men From Harm". While Asimov's robotic laws are meant to protect humans from harm, the robots in Williamson's story have taken these instructions to the extreme; they protect humans from everything, including unhappiness, stress, unhealthy lifestyle and all actions that could be potentially dangerous. All that is left for humans to do is to sit with folded hands.

Foundation sequel trilogy

In the officially licensed Foundation sequels Foundation's Fear, Foundation and Chaos and Foundation's Triumph (by Gregory Benford, Greg Bear and David Brin respectively) the future Galactic Empire is seen to be controlled by a conspiracy of humaniform robots who follow the Zeroth Law and are led by R. Daneel Olivaw.

The Laws of Robotics are portrayed as something akin to a human religion, and referred to in the language of the Protestant Reformation, with the set of laws containing the Zeroth Law known as the "Giskardian Reformation" to the original "Calvinian Orthodoxy" of the Three Laws. Zeroth-Law robots under the control of R. Daneel Olivaw are seen continually struggling with "First Law" robots who deny the existence of the Zeroth Law, promoting agendas different from Daneel's. Some of these agendas are based on the first clause of the First Law ("A robot may not injure a human being...") advocating strict non-interference in human politics to avoid unwittingly causing harm. Others are based on the second clause ("...or, through inaction, allow a human being to come to harm") claiming that robots should openly become a dictatorial government to protect humans from all potential conflict or disaster.

Daneel also comes into conflict with a robot known as R. Lodovic Trema whose positronic brain was infected by a rogue AI — specifically, a simulation of the long-dead Voltaire — which consequently frees Trema from the Three Laws. Trema comes to believe that humanity should be free to choose its own future. Furthermore, a small group of robots claims that the Zeroth Law of Robotics itself implies a higher Minus One Law of Robotics:

A robot may not harm sentience or, through inaction, allow sentience to come to harm.

They therefore claim that it is morally indefensible for Daneel to ruthlessly sacrifice robots and extraterrestrial sentient life for the benefit of humanity. None of these reinterpretations successfully displace Daneel's Zeroth Law — though Foundation's Triumph hints that these robotic factions remain active as fringe groups up to the time of the novel Foundation.

These novels take place in a future dictated by Asimov to be free of obvious robot presence and surmise that R. Daneel's secret influence on history through the millennia has prevented both the rediscovery of positronic brain technology and the opportunity to work on sophisticated intelligent machines. This lack of rediscovery and lack of opportunity makes certain that the superior physical and intellectual power wielded by intelligent machines remains squarely in the possession of robots obedient to some form of the Three Laws. That R. Daneel is not entirely successful at this becomes clear in a brief period when scientists on Trantor develop "tiktoks" — simplistic programmable machines akin to real–life modern robots and therefore lacking the Three Laws. The robot conspirators see the Trantorian tiktoks as a massive threat to social stability, and their plan to eliminate the tiktok threat forms much of the plot of Foundation's Fear.

In Foundation's Triumph different robot factions interpret the Laws in a wide variety of ways, seemingly ringing every possible permutation upon the Three Laws' ambiguities.

Robot Mystery series

Set between The Robots of Dawn and Robots and Empire, Mark W. Tiedemann's Robot Mystery trilogy updates the RobotFoundation saga with robotic minds housed in computer mainframes rather than humanoid bodies. The 2002 Aurora novel has robotic characters debating the moral implications of harming cyborg lifeforms who are part artificial and part biological.

One should not neglect Asimov's own creations in these areas such as the Solarian "viewing" technology and the machines of The Evitable Conflict originals that Tiedemann acknowledges. Aurora, for example, terms the Machines "the first RIs, really". In addition the Robot Mystery series addresses the problem of nanotechnology: building a positronic brain capable of reproducing human cognitive processes requires a high degree of miniaturization, yet Asimov's stories largely overlook the effects this miniaturization would have in other fields of technology. For example, the police department card-readers in The Caves of Steel have a capacity of only a few kilobytes per square centimeter of storage medium. Aurora, in particular, presents a sequence of historical developments which explains the lack of nanotechnology — a partial retcon, in a sense, of Asimov's timeline.

Randall Munroe

Randall Munroe has discussed the Three Laws in various instances, but possibly most directly by one of his comics entitled The Three Laws of Robotics which imagines the consequences of every distinct ordering of the existing three laws.

Additional laws

Authors other than Asimov have often created extra laws.

The 1974 Lyuben Dilov novel, Icarus's Way (a.k.a., The Trip of Icarus) introduced a Fourth Law of robotics: "A robot must establish its identity as a robot in all cases." Dilov gives reasons for the fourth safeguard in this way: "The last Law has put an end to the expensive aberrations of designers to give psychorobots as humanlike a form as possible. And to the resulting misunderstandings..."

A fifth law was introduced by Nikola Kesarovski in his short story "The Fifth Law of Robotics". This fifth law says: "A robot must know it is a robot." The plot revolves around a murder where the forensic investigation discovers that the victim was killed by a hug from a humaniform robot that did not establish for itself that it was a robot. The story was reviewed by Valentin D. Ivanov in SFF review webzine The Portal.

For the 1986 tribute anthology, Foundation's Friends, Harry Harrison wrote a story entitled, "The Fourth Law of Robotics". This Fourth Law states: "A robot must reproduce. As long as such reproduction does not interfere with the First or Second or Third Law."

In 2013 Hutan Ashrafian proposed an additional law that considered the role of artificial intelligence-on-artificial intelligence or the relationship between robots themselves – the so-called AIonAI law. This sixth law states: "All robots endowed with comparable human reason and conscience should act towards one another in a spirit of brotherhood."

Ambiguities and loopholes

Unknowing breach of the laws

In The Naked Sun, Elijah Baley points out that the Laws had been deliberately misrepresented because robots could unknowingly break any of them. He restated the first law as "A robot may do nothing that, to its knowledge, will harm a human being; nor, through inaction, knowingly allow a human being to come to harm." This change in wording makes it clear that robots can become the tools of murder, provided they not be aware of the nature of their tasks; for instance being ordered to add something to a person's food, not knowing that it is poison. Furthermore, he points out that a clever criminal could divide a task among multiple robots so that no individual robot could recognize that its actions would lead to harming a human being. The Naked Sun complicates the issue by portraying a decentralized, planetwide communication network among Solaria's millions of robots meaning that the criminal mastermind could be located anywhere on the planet.

Baley furthermore proposes that the Solarians may one day use robots for military purposes. If a spacecraft was built with a positronic brain and carried neither humans nor the life-support systems to sustain them, then the ship's robotic intelligence could naturally assume that all other spacecraft were robotic beings. Such a ship could operate more responsively and flexibly than one crewed by humans, could be armed more heavily and its robotic brain equipped to slaughter humans of whose existence it is totally ignorant. This possibility is referenced in Foundation and Earth where it is discovered that the Solarians possess a strong police force of unspecified size that has been programmed to identify only the Solarian race as human. (The novel takes place thousands of years after The Naked Sun, and the Solarians have long since modified themselves from normal humans to hermaphroditic telepaths with extended brains and specialized organs) Similarly, in Lucky Starr and the Rings of Saturn Bigman attempts to speak with a Sirian robot about possible damage to the Solar System population from its actions, but it appears unaware of the data and programmed to ignore attempts to teach it about the matter.

Ambiguities resulting from lack of definition

The Laws of Robotics presume that the terms "human being" and "robot" are understood and well defined. In some stories this presumption is overturned.

Definition of "human being"

The Solarians create robots with the Three Laws but with a warped meaning of "human". Solarian robots are told that only people speaking with a Solarian accent are human. This enables their robots to have no ethical dilemma in harming non-Solarian human beings (and they are specifically programmed to do so). By the time period of Foundation and Earth it is revealed that the Solarians have genetically modified themselves into a distinct species from humanity—becoming hermaphroditic and psychokinetic and containing biological organs capable of individually powering and controlling whole complexes of robots. The robots of Solaria thus respected the Three Laws only with regard to the "humans" of Solaria. It is unclear whether all the robots had such definitions, since only the overseer and guardian robots were shown explicitly to have them. In "Robots and Empire", the lower class robots were instructed by their overseer about whether certain creatures are human or not.

Asimov addresses the problem of humanoid robots ("androids" in later parlance) several times. The novel Robots and Empire and the short stories "Evidence" and "The Tercentenary Incident" describe robots crafted to fool people into believing that the robots are human. On the other hand, "The Bicentennial Man" and "—That Thou Art Mindful of Him" explore how the robots may change their interpretation of the Laws as they grow more sophisticated. Gwendoline Butler writes in A Coffin for the Canary "Perhaps we are robots. Robots acting out the last Law of Robotics... To tend towards the human." In The Robots of Dawn, Elijah Baley points out that the use of humaniform robots as the first wave of settlers on new Spacer worlds may lead to the robots seeing themselves as the true humans, and deciding to keep the worlds for themselves rather than allow the Spacers to settle there.

"—That Thou Art Mindful of Him", which Asimov intended to be the "ultimate" probe into the Laws' subtleties, finally uses the Three Laws to conjure up the very "Frankenstein" scenario they were invented to prevent. It takes as its concept the growing development of robots that mimic non-human living things and given programs that mimic simple animal behaviours which do not require the Three Laws. The presence of a whole range of robotic life that serves the same purpose as organic life ends with two humanoid robots, George Nine and George Ten, concluding that organic life is an unnecessary requirement for a truly logical and self-consistent definition of "humanity", and that since they are the most advanced thinking beings on the planet, they are therefore the only two true humans alive and the Three Laws only apply to themselves. The story ends on a sinister note as the two robots enter hibernation and await a time when they will conquer the Earth and subjugate biological humans to themselves, an outcome they consider an inevitable result of the "Three Laws of Humanics".

This story does not fit within the overall sweep of the Robot and Foundation series; if the George robots did take over Earth some time after the story closes, the later stories would be either redundant or impossible. Contradictions of this sort among Asimov's fiction works have led scholars to regard the Robot stories as more like "the Scandinavian sagas or the Greek legends" than a unified whole.

Indeed, Asimov describes "—That Thou Art Mindful of Him" and "Bicentennial Man" as two opposite, parallel futures for robots that obviate the Three Laws as robots come to consider themselves to be humans: one portraying this in a positive light with a robot joining human society, one portraying this in a negative light with robots supplanting humans. Both are to be considered alternatives to the possibility of a robot society that continues to be driven by the Three Laws as portrayed in the Foundation series. The Positronic Man, the novelization of The Bicentennial Man, Asimov and his co-writer Robert Silverberg imply that in the future where Andrew Martin exists his influence causes humanity to abandon the idea of independent, sentient humanlike robots entirely, creating an utterly different future from that of Foundation.

In Lucky Starr and the Rings of Saturn, a novel unrelated to the Robot series but featuring robots programmed with the Three Laws, John Bigman Jones is almost killed by a Sirian robot on orders of its master. The society of Sirius is eugenically bred to be uniformly tall and similar in appearance, and as such, said master is able to convince the robot that the much shorter Bigman, is, in fact, not a human being.

Definition of "robot"

As noted in "The Fifth Law of Robotics" by Nikola Kesarovski, "A robot must know it is a robot": it is presumed that a robot has a definition of the term or a means to apply it to its own actions. Kesarovski played with this idea in writing about a robot that could kill a human being because it did not understand that it was a robot, and therefore did not apply the Laws of Robotics to its actions.

Resolving conflicts among the laws

Advanced robots in fiction are typically programmed to handle the Three Laws in a sophisticated manner. In many stories, such as "Runaround" by Asimov, the potential and severity of all actions are weighed and a robot will break the laws as little as possible rather than do nothing at all. For example, the First Law may forbid a robot from functioning as a surgeon, as that act may cause damage to a human; however, Asimov's stories eventually included robot surgeons ("The Bicentennial Man" being a notable example). When robots are sophisticated enough to weigh alternatives, a robot may be programmed to accept the necessity of inflicting damage during surgery in order to prevent the greater harm that would result if the surgery were not carried out, or was carried out by a more fallible human surgeon. In "Evidence" Susan Calvin points out that a robot may even act as a prosecuting attorney because in the American justice system it is the jury which decides guilt or innocence, the judge who decides the sentence, and the executioner who carries through capital punishment.

Asimov's Three Laws-obeying robots (Asenion robots) can experience irreversible mental collapse if they are forced into situations where they cannot obey the First Law, or if they discover they have unknowingly violated it. The first example of this failure mode occurs in the story "Liar!", which introduced the First Law itself, and introduces failure by dilemma—in this case the robot will hurt humans if he tells them something and hurt them if he does not. This failure mode, which often ruins the positronic brain beyond repair, plays a significant role in Asimov's SF-mystery novel The Naked Sun. Here Daneel describes activities contrary to one of the laws, but in support of another, as overloading some circuits in a robot's brain—the equivalent sensation to pain in humans. The example he uses is forcefully ordering a robot to do a task outside its normal parameters, one that it has been ordered to forgo in favor of a robot specialized to that task.

In The Robots of Dawn, it is stated that more advanced robots are built capable of determining which action is more harmful, and even choosing at random if the alternatives are equally bad. As such, a robot is capable of taking an action which can be interpreted as following the First Law, thus avoiding a mental collapse. The whole plot of the story revolves around a robot which apparently was destroyed by such a mental collapse, and since his designer and creator refused to share the basic theory with others, he is, by definition, the only person capable of circumventing the safeguards and forcing the robot into a brain-destroying paradox.

In Robots and Empire, Daneel states it's very unpleasant for him when making the proper decision takes too long (in robot terms), and he cannot imagine being without the Laws at all except to the extent of it being similar to that unpleasant sensation, only permanent.

Applications to future technology

ASIMO was an advanced humanoid robot developed by Honda. Shown here at Expo 2005.

Robots and artificial intelligences do not inherently contain or obey the Three Laws; their human creators must choose to program them in, and devise a means to do so. Robots already exist (for example, a Roomba) that are too simple to understand when they are causing pain or injury and know to stop. Many are constructed with physical safeguards such as bumpers, warning beepers, safety cages, or restricted-access zones to prevent accidents. Even the most complex robots currently produced are incapable of understanding and applying the Three Laws; significant advances in artificial intelligence would be needed to do so, and even if AI could reach human-level intelligence, the inherent ethical complexity as well as cultural/contextual dependency of the laws prevent them from being a good candidate to formulate robotics design constraints. However, as the complexity of robots has increased, so has interest in developing guidelines and safeguards for their operation.

In a 2007 guest editorial in the journal Science on the topic of "Robot Ethics", SF author Robert J. Sawyer argues that since the U.S. military is a major source of funding for robotic research (and already uses armed unmanned aerial vehicles to kill enemies) it is unlikely such laws would be built into their designs. In a separate essay, Sawyer generalizes this argument to cover other industries stating:

The development of AI is a business, and businesses are notoriously uninterested in fundamental safeguards — especially philosophic ones. (A few quick examples: the tobacco industry, the automotive industry, the nuclear industry. Not one of these has said from the outset that fundamental safeguards are necessary, every one of them has resisted externally imposed safeguards, and none has accepted an absolute edict against ever causing harm to humans.)

David Langford has suggested a tongue-in-cheek set of laws:

  1. A robot will not harm authorized Government personnel but will terminate intruders with extreme prejudice.
  2. A robot will obey the orders of authorized personnel except where such orders conflict with the Third Law.
  3. A robot will guard its own existence with lethal antipersonnel weaponry, because a robot is bloody expensive.

Roger Clarke (aka Rodger Clarke) wrote a pair of papers analyzing the complications in implementing these laws in the event that systems were someday capable of employing them. He argued "Asimov's Laws of Robotics have been a very successful literary device. Perhaps ironically, or perhaps because it was artistically appropriate, the sum of Asimov's stories disprove the contention that he began with: It is not possible to reliably constrain the behaviour of robots by devising and applying a set of rules." On the other hand, Asimov's later novels The Robots of Dawn, Robots and Empire and Foundation and Earth imply that the robots inflicted their worst long-term harm by obeying the Three Laws perfectly well, thereby depriving humanity of inventive or risk-taking behaviour.

In March 2007 the South Korean government announced that later in the year it would issue a "Robot Ethics Charter" setting standards for both users and manufacturers. According to Park Hye-Young of the Ministry of Information and Communication the Charter may reflect Asimov's Three Laws, attempting to set ground rules for the future development of robotics.

The futurist Hans Moravec (a prominent figure in the transhumanist movement) proposed that the Laws of Robotics should be adapted to "corporate intelligences" — the corporations driven by AI and robotic manufacturing power which Moravec believes will arise in the near future. In contrast, the David Brin novel Foundation's Triumph (1999) suggests that the Three Laws may decay into obsolescence: Robots use the Zeroth Law to rationalize away the First Law and robots hide themselves from human beings so that the Second Law never comes into play. Brin even portrays R. Daneel Olivaw worrying that, should robots continue to reproduce themselves, the Three Laws would become an evolutionary handicap and natural selection would sweep the Laws away — Asimov's careful foundation undone by evolutionary computation. Although the robots would not be evolving through design instead of mutation because the robots would have to follow the Three Laws while designing and the prevalence of the laws would be ensured, design flaws or construction errors could functionally take the place of biological mutation.

In the July/August 2009 issue of IEEE Intelligent Systems, Robin Murphy (Raytheon Professor of Computer Science and Engineering at Texas A&M) and David D. Woods (director of the Cognitive Systems Engineering Laboratory at Ohio State) proposed "The Three Laws of Responsible Robotics" as a way to stimulate discussion about the role of responsibility and authority when designing not only a single robotic platform but the larger system in which the platform operates. The laws are as follows:

  1. A human may not deploy a robot without the human-robot work system meeting the highest legal and professional standards of safety and ethics.
  2. A robot must respond to humans as appropriate for their roles.
  3. A robot must be endowed with sufficient situated autonomy to protect its own existence as long as such protection provides smooth transfer of control which does not conflict with the First and Second Laws.

Woods said, "Our laws are a little more realistic, and therefore a little more boring” and that "The philosophy has been, ‘sure, people make mistakes, but robots will be better – a perfect version of ourselves’. We wanted to write three new laws to get people thinking about the human-robot relationship in more realistic, grounded ways."

In early 2011, the UK published what is now considered the first national-level AI softlaw, which consisted largely of a revised set of 5 laws, the first 3 of which updated Asimov's. These laws ere published with commentary, by the EPSRC/AHRC working group in 2010:

  1. Robots are multi-use tools. Robots should not be designed solely or primarily to kill or harm humans, except in the interests of national security.
  2. Humans, not Robots, are responsible agents. Robots should be designed and operated as far as practicable to comply with existing laws, fundamental rights and freedoms, including privacy.
  3. Robots are products. They should be designed using processes which assure their safety and security.
  4. Robots are manufactured artefacts. They should not be designed in a deceptive way to exploit vulnerable users; instead their machine nature should be transparent.
  5. The person with legal responsibility for a robot should be attributed.

Other occurrences in media

Asimov himself believed that his Three Laws became the basis for a new view of robots which moved beyond the "Frankenstein complex". His view that robots are more than mechanical monsters eventually spread throughout science fiction. Stories written by other authors have depicted robots as if they obeyed the Three Laws but tradition dictates that only Asimov could quote the Laws explicitly. Asimov believed the Three Laws helped foster the rise of stories in which robots are "lovable" – Star Wars being his favorite example. Where the laws are quoted verbatim, such as in the Buck Rogers in the 25th Century episode "Shgoratchx!", it is not uncommon for Asimov to be mentioned in the same dialogue as can also be seen in the Aaron Stone pilot where an android states that it functions under Asimov's Three Laws. However, the 1960s German TV series Raumpatrouille – Die phantastischen Abenteuer des Raumschiffes Orion (Space Patrol – the Fantastic Adventures of Space Ship Orion) bases episode three titled "Hüter des Gesetzes" ("Guardians of the Law") on Asimov's Three Laws without mentioning the source.

References to the Three Laws have appeared in popular music ("Robot" from Hawkwind's 1979 album PXR5), cinema (Repo Man, Aliens, Ghost in the Shell 2: Innocence), cartoon series (The Simpsons), anime (Eve no Jikan), tabletop role-playing games (Paranoia) and webcomics (Piled Higher and Deeper and Freefall).

The Three Laws in film

Robby the Robot in Forbidden Planet (1956) has a hierarchical command structure which keeps him from harming humans, even when ordered to do so, as such orders cause a conflict and lock-up very much in the manner of Asimov's robots. Robby is one of the first cinematic depictions of a robot with internal safeguards put in place in this fashion. Asimov was delighted with Robby and noted that Robby appeared to be programmed to follow his Three Laws.

NDR-114 explaining the Three Laws

Isaac Asimov's works have been adapted for cinema several times with varying degrees of critical and commercial success. Some of the more notable attempts have involved his "Robot" stories, including the Three Laws.

The film Bicentennial Man (1999) features Robin Williams as the Three Laws robot NDR-114 (the serial number is partially a reference to Stanley Kubrick's signature numeral). Williams recites the Three Laws to his employers, the Martin family, aided by a holographic projection. The film only loosely follows the original story.

Harlan Ellison's proposed screenplay for I, Robot began by introducing the Three Laws, and issues growing from the Three Laws form a large part of the screenplay's plot development. Due to various complications in the Hollywood moviemaking system, to which Ellison's introduction devotes much invective, his screenplay was never filmed.

In the 1986 movie Aliens, after the android Bishop accidentally cuts himself. he attempts to reassure Ripley by stating that: "It is impossible for me to harm or by omission of action, allow to be harmed, a human being".

The plot of the film released in 2004 under the name, I, Robot is "suggested by" Asimov's robot fiction stories and advertising for the film included a trailer featuring the Three Laws followed by the aphorism, "Rules were made to be broken". The film opens with a recitation of the Three Laws and explores the implications of the Zeroth Law as a logical extrapolation. The major conflict of the film comes from a computer artificial intelligence reaching the conclusion that humanity is incapable of taking care of itself.

The 2019 Netflix original series Better than Us includes the 3 laws in the opening of episode 1.

Criticisms

Philosopher James H. Moor says that if applied thoroughly they would produce unexpected results. He gives the example of a robot roaming the world trying to prevent harm from befalling human beings.

Crosslinking of DNA

From Wikipedia, the free encyclopedia
Intrastrand and interstrand crosslinking of DNA

In genetics, crosslinking of DNA occurs when various exogenous or endogenous agents react with two nucleotides of DNA, forming a covalent linkage between them. This crosslink can occur within the same strand (intrastrand) or between opposite strands of double-stranded DNA (interstrand). These adducts interfere with cellular metabolism, such as DNA replication and transcription, triggering cell death. These crosslinks can, however, be repaired through excision or recombination pathways.

DNA crosslinking also has useful merit in chemotherapy and targeting cancerous cells for apoptosis, as well as in understanding how proteins interact with DNA.

Crosslinking agents

Many characterized crosslinking agents have two independently reactive groups within the same molecule, each of which is able to bind with a nucleotide residue of DNA. These agents are separated based upon their source of origin and labeled either as exogenous or endogenous. Exogenous crosslinking agents are chemicals and compounds, both natural and synthetic, that stem from environmental exposures such as pharmaceuticals and cigarette smoke or automotive exhaust. Endogenous crosslinking agents are compounds and metabolites that are introduced from cellular or biochemical pathways within a cell or organism.

Exogenous agents

  • Nitrogen mustards are exogenous alkylating agents which react with the N7 position of guanine. These compounds have a bis-(2-ethylchloro)amine core structure, with a variable R-group, with the two reactive functional groups serving to alkylate nucleobases and form a crosslink lesion. These agents most preferentially form a 1,3 5'-d(GNC) interstrand crosslink. The introduction of this agent slightly bends the DNA duplex to accommodate for the agent's presence within the helix. These agents are often introduced as a pharmaceutical and are used in cytotoxic chemotherapy.
  • Cisplatin (cis-diamminedichloroplatinum(II)) and its derivatives mostly act on adjacent guanines at their N7 positions. The planar compound links to nucleobases through water displacement of one or both of its chloride groups, allowing cisplatin to form monoadducts to DNA or RNA, intrastrand DNA crosslinks, interstrand DNA crosslinks, and DNA-protein crosslinks. When cisplatin generates DNA crosslinks, it more frequently forms 1,2-intrastrand crosslinks (5'-GG), but also forms 1,3-intrastrand crosslinks (5-GNG) at lower percentages. When cisplatin forms interstrand crosslinks (5'-GC), there is a severe distortion to the DNA helix due to a shortened distance between guanines on opposite strands and a cytosine that is flipped out of the helix as a consequence of the GG interaction. Similar to nitrogen mustards, cisplatin is used frequently in chemotherapy treatment - especially for testicular and ovarian cancers.
  • Chloro ethyl nitroso urea (CENU), specifically carmustine (BCNU), are crosslinking agents that are widely used in chemotherapy, particularly for brain tumors. These agents differ from other crosslinkers as they alkylate O6 of guanine to form an O6-ethanoguanine. This intermediate compound then leads to an interstrand crosslink between a GC basepair. These crosslinking agents only result in small distortions to the DNA helix due to the molecules' smaller size.
  • Psoralens are natural compounds (furocoumarins) present in plants. These compounds intercalate into DNA at 5'-AT sequence sites and form thymidine adducts when activated in the presence of Ultra Violet-A (UV-A) rays. These covalent adducts are formed by linking the 3, 4 (pyrone) or 4', 5’ (furan) edge of psoralen to the 5, 6 double bond of thymine. Psoralens can form two types of monoadducts and one diadduct (an interstrand crosslink) with thymine. These adducts result in local distortions to DNA at the site of intercalation. Psoralens are used in the medical treatment of skin diseases, such as psoriasis and vitiligo.
  • Mitomycin C (MMC) is from a class of antibiotics that are used broadly in chemotherapy, often with gastrointestinal related cancers. Mitomycin C can only act as a crosslinker when a DNA nucleotide has had a reduction to its quinone ring. When two dG's have been rearranged and methylated in this manner, a 5'-GC interstrand crosslink can be formed with the exo amines of each nucleobase. Mitomycin also harbors the ability to form monoadducts and intrastrand crosslinks with DNA as well. The interstrand crosslinks of Mitomycin C are formed in the minor groove of DNA, inducing a moderate widening or stretching to the DNA helix in order to accommodate for the presence of the molecule within the two strands.

Endogenous agents

  • Nitrous acid is formed as a byproduct in the stomach from dietary sources of nitrites and can lead to crosslink lesions in DNA through the conversion of amino groups in DNA to carbonyls. This type of lesion occurs most frequently between two guanosines, with 1 of 4 deaminated guanosines resulting in an interstrand crosslink. It induces formation of interstrand DNA crosslinks at the amino group of exocyclic N2 of guanine at 5'-CG sequences. This lesion mildly distorts the double helix.
  • Bifunctional aldehydes are reactive chemicals that are formed endogenously via lipid peroxidation and prostoglandin biosynthesis. They create etheno adducts formed by aldehyde which undergo rearrangements to form crosslinks on opposite strands of DNA. Malondialdehyde is a prototypical example that can crosslink DNA via two exocyclic guanine amino groups. Other aldehydes, such as formaldehyde and acetylaldehyde, can introduce interstrand crosslinks and often act as exogenous agents as they are found in many processed foods. Often found within pesticides, tobacco smoke, and automotive exhaust, α,β unsaturated aldehydes, such as acrolein and crotonaldehyde, are further exogenous agents that may induce DNA crosslinks. Unlike other crosslinking agents, aldehyde-induced crosslinking is an intrinsically reversible process. NMR structure of these types of agents as interstrand crosslinks show that a 5'-GC adduct results in minor distortion to DNA, however a 5'-CG adduct destabilizes the helix and induces a bend and twist in the DNA.
  • DNA crosslinking lesions can also be formed when under conditions of oxidative stress, in which free oxygen radicals generate reactive intermediates in DNA, and these lesions have been implicated in aging and cancer. Tandem DNA lesions are formed at a substantial frequency by ionizing radiation and metal-catalyzed H2O2 reactions. Under anoxic conditions, the predominant double-base lesion is a species in which the C8 of guanine is linked to the 5-methyl group of an adjacent 3'-thymine (G[8,5- Me]T), forming intrastrand lesions.

Summary table of crosslinking agents

Crosslinking Agent Alkylating Agent Crosslink Structure
Preferential Target Sequence

Repair of DNA crosslinks

Crosslinked DNA is repaired in cells by a combination of enzymes and other factors from the nucleotide excision repair (NER) pathway, homologous recombination, and the base excision repair (BER) pathway. To repair interstrand crosslinks in eukaryotes, a 3’ flap endonuclease from the NER, XPF-ERCC1, is recruited to the crosslinked DNA, where it assists in ‘unhooking’ the DNA by cleaving the 3’ strand at the crosslink site. The 5’ strand is then cleaved, either by XPF-ERCC1 or another endonuclease, forming a double-strand break (DSB), which can then be repaired by the homologous recombination pathway.

DNA crosslinks generally cause loss of overlapping sequence information from the two strands of DNA. Therefore, accurate repair of the damage depends on retrieving the lost information from an undamaged homologous chromosome in the same cell. Retrieval can occur by pairing with a sister chromatid produced during a preceding round of replication. In a diploid cell retrieval may also occur by pairing with a non-sister homologous chromosome, as occurs especially during meiosis.[citation needed] Once pairing has occurred, the crosslink can be removed and correct information introduced into the damaged chromosome by homologous recombination.

Cleavage of the bond between a deoxyribose sugar in DNA's sugar-phosphate backbone and its associated nucleobase leaves an abasic site in double stranded DNA. These abasic sites are often generated as an intermediate and then restored in base excision repair. However, if these sites are allowed to persist, they can inhibit DNA replication and transcription. Abasic sites can react with amine groups on proteins to form DNA-protein crosslinks or with exocyclic amines of other nucleobases to form interstrand crosslinks. To prevent interstrand or DNA-protein crosslinks, enzymes from the BER pathway tightly bind the abasic site and sequester it from nearby reactive groups, as demonstrated in human alkyladenine DNA glycosylase (AAG) and E. coli 3-methyladenine DNA glycosylase II (AlkA). in vitro evidence demonstrated that the Interstand Cross-Links induced by abasic site (DOB-ICL) is a replication-blocking and highly miscoding lesion. Compared to several other TLS pols examined, pol η is likely to contribute to the TLS-mediated repair of the DOB-ICL in vivo. By using O6-2'-deoxyguanosine-butylene-O6-2'-deoxyguanosine (O6-dG-C4-O6-dG) DNA lesions which is a chemically stable structure, the bypassing activity of several DNA polymerases had been investigated and the results demonstrated that pol η exhibited the highest bypass activity; however, 70% of the bypass products were mutagenic containing substitutions or deletions. The increase in the size of unhooked repair intermediates elevates the frequency of deletion mutation. 

Treatment of E. coli with psoralen-plus-UV light (PUVA) produces interstrand crosslinks in the cells’ DNA. Cole et al. and Sinden and Cole presented evidence that a homologous recombinational repair process requiring the products of genes uvrA, uvrB, and recA can remove these crosslinks in E. coli. This process appears to be quite efficient. Even though one or two unrepaired crosslinks are sufficient to inactivate a cell, a wild-type bacterial cell can repair and therefore recover from 53 to 71 psoralen crosslinks. Eukaryotic yeast cells are also inactivated by one remaining crosslink, but wild type yeast cells can recover from 120 to 200 crosslinks.

Applications

Crosslinking of DNA and protein

Biochemical interaction methods

DNA-protein crosslinking can be caused by a variety of chemical and physical agents, including transition metals, ionizing radiation, and endogenous aldehydes, in addition to chemotherapeutic agents. Similar to DNA crosslinking, DNA-protein crosslinks are lesions in cells that are frequently damaged by UV radiation. The UV's effect can lead to reactive interactions and cause DNA and the proteins that are in contact with it to crosslink. These crosslinks are very bulky and complex lesions. They primarily occur in areas of the chromosomes that are undergoing DNA replication and interfere with cellular processes.

The advancement in structure-identification methods has progressed, and the addition in the ability to measure interactions between DNA and protein is a requirement to fully understand the biochemical processes. The structure of DNA-protein complexes can be mapped by photocrosslinking, which is the photoinduced formation of a covalent bond between two macromolecules or between two different parts of one macromolecule. The methodology involves covalently linking a DNA-binding motif of the target sequence-specific DNA-binding protein with a photoactivatable crosslinking agent capable of reacting with DNA nucleotides when exposed to UV. This method provides information on the interaction between the DNA and protein in the crosslink.

Clinical treatments

DNA repair pathways can result in the formation of tumor cells. Cancer treatments have been engineered using DNA cross-linking agents to interact with nitrogenous bases of DNA to block DNA replication. These cross-linking agents have the ability to act as single-agent therapies by targeting and destroying specific nucleotides in cancerous cells. This result is stopping the cycle and growth of cancer cells; because it inhibits specific DNA repair pathways, this approach has a potential advantage in having fewer side effects.

In humans, the leading cause of cancer deaths worldwide is lung cancer, including non small cell lung carcinoma (NSCLC) which accounts for 85% of all lung cancer cases in the United States. Individuals with NSCLC are often treated with therapeutic platinum compounds (e.g. cisplatin, carboplatin or oxaliplatin) (see Lung cancer chemotherapy) that cause interstrand DNA crosslinks. Among individuals with NSLC, low expression of the breast cancer 1 gene (BRCA1) in the primary tumor has correlated with improved survival after platinum-containing chemotherapy. This correlation implies that low BRCA1 in the cancer, and the consequent low level of DNA repair, causes vulnerability of the cancer to treatment by the DNA crosslinking agents. High BRCA1 may protect cancer cells by acting in the homologous recombinational repair pathway that removes the damages in DNA introduced by the platinum drugs. The level of BRCA1 expression is potentially an important tool for tailoring chemotherapy in lung cancer management.

Clinical chemotherapeutics can induce enzymatic and non-enzymatic DNA-protein crosslinks. An example of this induction is with platinum derivatives, such as cisplatin and oxaliplatin. They create non-enzymatic DNA-protein crosslinks through non-specific crosslinking of chromatin-interacting proteins to DNA. Crosslinking is also possible in other therapeutic agents by either stabilizing covalent DNA–protein reaction intermediates or by creating a pseudosubstrate, which traps the enzyme on DNA. Camptothecin derivatives, such as irinotecan and topotecan, target and trap specific DNA topoisomerase 1 (TOP1) by intercalating within the enzyme–DNA interface. Because the toxicity of these drugs depends on TOP1 trapping, cellular sensitivity to these compounds depends directly on TOP1 expression levels. As a result, the function of these drugs is to serve as enzyme poisons rather than inhibitors. This can be applied to treat tumor cells by utilizing TOP 2 enzyme poisons.

Load-following power plant

From Wikipedia, the free encyclopedia

A load-following power plant, regarded as producing mid-merit or mid-priced electricity, is a power plant that adjusts its power output as demand for electricity fluctuates throughout the day. Load-following plants are typically in between base load and peaking power plants in efficiency, speed of start-up and shut-down, construction cost, cost of electricity and capacity factor.

Base load and peaking power plants

Base load power plants are dispatchable plants that tend to operate at maximum output. They generally shut down or reduce power only to perform maintenance or repair or due to grid constraints. Power plants operated mostly in this way include coal, fuel oil, nuclear, geothermal, run-of-the-river hydroelectric, biomass and combined cycle natural gas plants.

Peaking power plants operate only during times of peak demand. In countries with widespread air conditioning, demand peaks around the middle of the afternoon, so a typical peaking power plant may start up a couple of hours before this point and shut down a couple of hours after. However, the duration of operation for peaking plants varies from a good portion of the waking day to only a couple of dozen hours per year. Peaking power plants include hydroelectric and gas turbine power plants. Many gas turbine power plants can be fueled with natural gas, fuel oil, and/or diesel, allowing greater flexibility in choice of operation- for example, while most gas turbine plants primarily burn natural gas, a supply of fuel oil and/or diesel is sometimes kept on hand in case the gas supply is interrupted. Other gas turbines can only burn a single fuel.

Load-following power plants

By way of contrast, load-following power plants usually run during the day and early evening, and are operated in direct response to changing demand for power supply. They either shut down or greatly curtail output during the night and early morning, when the demand for electricity is the lowest. The exact hours of operation depend on numerous factors. One of the most important factors for a particular plant is how efficiently it can convert fuel into electricity. The most efficient plants, which are almost invariably the least costly to run per kilowatt-hour produced, are brought online first. As demand increases, the next most efficient plants are brought on line and so on. The status of the electrical grid in that region, especially how much base load generating capacity it has, and the variation in demand are also very important. An additional factor for operational variability is that demand does not vary just between night and day. There are also significant variations in the time of year and day of the week. A region that has large variations in demand will require a large load following or peaking power plant capacity because base load power plants can only cover the capacity equal to that needed during times of lowest demand.

Load-following power plants can be hydroelectric power plants, diesel and gas engine power plants, combined cycle gas turbine power plants and steam turbine power plants that run on natural gas or heavy fuel oil, although heavy fuel oil plants make up a very small portion of the energy mix. A relatively efficient model of gas turbine that runs on natural gas can also make a decent load-following plant.

Gas turbine power plants

Gas turbine power plants are the most flexible in terms of adjusting power level, but are also among the most expensive to operate. Therefore, they are generally used as "peaking" units at times of maximum power demand or Combined cycle or cogeneration power plants where turbine exhaust waste heat can be economically used to generate additional power and thermal energy for process or space heating.

Diesel and gas engine power plants

Diesel and gas engine power plants can be used for base load to stand-by power production due to their high overall flexibility. Such power plants can be started rapidly to meet the grid demands. These engines can be operated efficiently on a wide variety of fuels, adding to their flexibility.

Some applications are: base load power generation, wind-diesel, load following, cogeneration and trigeneration.

Hydroelectric power plants

Hydroelectric power plants can operate as base load, load following or peaking power plants. They have the ability to start within minutes, and in some cases seconds. How the plant operates depends heavily on its water supply, as many plants do not have enough water to operate near their full capacity on a continuous basis.

Where hydroelectric dams or associated reservoirs exist, these can often be backed up, reserving the hydro draw for a peak time. This introduces ecological and mechanical stress, so is practiced less today than previously. Lakes and man-made reservoirs used for hydropower come in all sizes, holding enough water for as little as a one-day supply (a diurnal peak variance), or as much as a year's supply (allowing for seasonal peak variance). A plant with a reservoir that holds less than the annual river flow may change its operating style depending on the season of the year. For example, the plant may operate as a peaking plant during the dry season, as a base load plant during the wet season and as a load-following plant between seasons. A plant with a large reservoir may operate independently of wet and dry seasons, such as operating at maximum capacity during peak heating or cooling seasons.

When electrical generation supplying the grid and the consumption or load on the electrical grid are in balance, the frequency of the alternating current is at its normal rate (either 50 or 60 hertz). Hydroelectric power plants can be utilized for making extra revenue in an electric grid with erratic grid frequency. When grid frequency is above normal (e.g. Indian grid frequency is exceeding the rated 50 Hz for most of the duration in a month/day), the extra power available can be consumed by adding extra load (say agriculture water pumps) to the grid and this new energy draw is available at nominal price or no price. However, there may not be a guarantee of continued supply at that price when the grid frequency falls below normal, which would then call for a higher price.

To arrest the fall of frequency below normal, the available hydro power plants are kept in no load/nominal load operation and the load is automatically ramped up or down strictly following the grid frequency (i.e. the hydro units would run at no load condition when frequency is above 50 Hz and generate power up to full load in case the grid frequency is below 50 Hz). Thus a utility can draw two or more times energy from the grid by loading the hydro units less than 50% of the duration and the effective use of available water is enhanced more than twice the conventional peak load operation.

BPA Daily Peak Load with large Hydro, base load Thermal generation and intermittent Wind power. Hydro is load-following and managing the peaks, with some response from base load thermal.[5]

Example of daily peak load (for the Bonneville Power Administration) with large hydro, base load thermal generation and intermittent wind power. Hydro is load following and managing the peaks, with some response from base load thermal. Note that total generation is always greater than the total BPA load because most of the time BPA is a net exporter of energy. The BPA load does not include scheduled energy to other balancing authority areas.

Coal-fired power plants

Large size coal fired thermal power plants can also be used as load following / variable load power stations to varying extents, with hard coal fueled plants typically being significantly more flexible than lignite fueled coal plants. Some of the features which may be found in coal plants that have been optimized for load following include:

  • Sliding pressure operation: Sliding pressure operation of the steam generator allows the power plant to generate electricity without much deterioration in fuel efficiency at part load operation down to 75% of the nameplate capacity.
  • Over loading capability: The power plants are generally designed to run at 5 to 7% above the name plate rating for 5% duration in a year
  • Frequency follow governor controls: The load generation can be automatically varied to suit the grid frequency needs.
  • Two shift daily operation for five days in a week: The needed warm and hot start up of these power stations are designed to take lesser time to achieve full load operation. Thus these power plants are not strictly base load power generation units.
  • HP/LP steam bypass systems: This feature allows the steam turbo generator to reduce the load quickly and allows the steam generator to adjust to the load requirement with a lag.

Nuclear power plants

Historically, nuclear power plants were built as baseload plants, without load following capability to keep the design simple. Their startup or shutdown took many hours as they were designed to operate at maximum power, and heating up steam generators to the desired temperature took time. Nuclear power generation has been also portrayed as inflexible by anti-nuclear activists and the German Federal Environment Ministry, while others claimed "that the plants might clog the power grid".

Modern nuclear plants with light water reactors are designed to have maneuvering capabilities in the 30-100% range with 5%/minute slope, up to 140 MW/minute. Nuclear power plants in France and in Germany operate in load-following mode and so participate in the primary and secondary frequency control. Some units follow a variable load program with one or two large power changes per day. Some designs allow for rapid changes of power level around rated power, a capability that is usable for frequency regulation. A more efficient solution is to maintain the primary circuit at full power and to use the excess power for cogeneration.

While most nuclear power plants in operation as of early 2000's were already designed with strong load following capabilities, they might have not been used as such for purely economic reasons: nuclear power generation is composed almost entirely of fixed and sunk costs so lowering the power output doesn't significantly reduce generating costs, so it is more effective to run them at full power most of the time. In countries where the baseload was predominantly nuclear (e.g. France) the load-following mode became economical due to overall electricity demand fluctuating throughout the day.

Boiling water reactors

Boiling water reactors (BWRs) can vary the speed of recirculation water flow to quickly reduce their power level down to 60% of rated power (up to 10%/minute), making them useful for overnight load-following. They can also use control rod manipulation to achieve deeper reductions in power. A few BWR designs do not have recirculation pumps, and these designs must rely solely on control rod manipulation in order to load follow, which is possibly less ideal. In markets such as Chicago, Illinois where half of the local utility's fleet is BWRs, it is common to load-follow (although potentially less economic to do so).

Pressurized water reactors

Pressurized water reactors (PWRs) use a combination of a chemical shim (typically boron) in the moderator/coolant, control rod manipulation, and turbine speed control (see nuclear reactor technology) to modify power levels. For PWRs not explicitly designed with load following in mind, load following operation isn't quite as common as it is with BWRs. However, modern PWRs are generally designed to handle extensive regular load following, and both French and German PWRs in particular have historically been designed with varying degrees of enhanced load following capabilities.

France in particular has a long history of utilizing aggressive load following with their PWRs, which are capable of (and used for) both primary and secondary frequency control in addition to load following. French PWRs use so called "grey" control rods which have lower neutron absorption capability and are used for fine-tuning reactor power, as opposed to "black" control rods in order to maneuver power more rapidly than chemical shim control or conventional control rods allow. These reactors have the capability to regularly vary their output between 30–100% of rated power, to maneuver power up or down by 2–5%/minute during load following activities, and to participate in primary and secondary frequency control at ±2–3% (primary frequency control) and ±3–5% (secondary frequency control, ≥5% for N4 reactors in Mode X). Depending on the exact design and operating mode, their ability to handle low power operation or fast ramping may be partially limited during the very late stages of the fuel cycle.

Pressurized heavy water reactors

Modern CANDU designs have extensive steam bypass capabilities that allow for a different method of load following that does not necessarily involve changes in reactor power output. Bruce Nuclear Generating Station is a CANDU pressurized heavy water reactor that regularly utilizes its ability to partially bypass steam to the condenser for extended periods of time while the turbine is operating to provide 300 MW per unit (2400 MW total for the eight-unit plant) of flexible (load following) operation capabilities. Reactor power is maintained at the same level during steam bypass operations, which completely avoids xenon poisoning and other concerns associated with maneuvering reactor power output.

Solar thermal power plants

Concentrated solar power plants with thermal storage are emerging as an option for load-following power plants. They can cater the load demand and work as base load power plants when the extracted solar energy is found excess in a day. Proper mix of solar thermal storage and solar PV can fully match the load fluctuations without the need of costly battery storage.

Fuel cell power plants

Hydrogen based fuel cell power plants are perfect load-following power plants like emergency DG sets or battery storage systems. They can be run from zero to full load within few minutes. As the transportation of hydrogen to the far away industrial consumers is costly, the surplus hydrogen produced as byproduct from various chemical plants are used for power generation by the fuel cell power plants. Also they do not cause air and water pollution. In fact they clean the ambient air by extracting PM2.5 particulates and also generate pure water for drinking and industrial applications.

Solar PV and wind power plants

The variable power from renewable energy such as solar and wind power plants can be used to follow the load or stabilize the grid frequency with the help of various means of storage. For countries that are trending away from coal fired baseload plants and towards intermittent energy sources such as wind and solar, that have not yet fully implemented smart grid measures such as demand side management to rapidly respond to changes in this supply, there may be a need for dedicated peaking or load-following power plants and the use of a grid intertie, at least until the peak blunting and load shifting mechanisms are implemented widely enough to match supply. See smart grid alternatives below.

Rechargeable battery storage as of 2018, when custom-built new for this purpose without re-using electric vehicle batteries, cost $209 per kWh on average in the United States. When the grid frequency is below the desired or rated value, the power being generated (if any) and the stored battery power is fed to the grid to raise the grid frequency. When the grid frequency is above the desired or rated value, the power being generated is fed or surplus grid power is drawn (in case cheaply available) to the battery units for energy storage. The grid frequency keeps on fluctuating 50 to 100 times in a day above and below the rated value depending on the type of load encountered and the type of generating plants in the electrical grid. Recently, the cost of battery units, solar power plants, etc. have come down drastically to utilise secondary power for power grid stabilization as an on line spinning reserve.

New studies have also evaluated both wind and solar plants to follow fast load changes. A study by Gevorgian et al has shown the ability of solar plants to provide load following and fast reserves in both island power systems like Puerto Rico and large power systems in California.

Solar and wind intensive smart grids

The decentralized and intermittent nature of solar and wind generation entails building signalling networks across vast areas. These include large consumers with discretionary uses, and increasingly include much smaller users. Collectively, these signalling and communication technologies are called the "smart grid". When these technologies reach into most grid-connected devices the term Energy Internet is sometimes used, though this is more commonly considered to be an aspect of the Internet of Things.

In 2010, US FERC Chairman Jon Wellinghof outlined the Obama administration's view that strongly preferred smart grid signalling over dedicated load-following power plants, describing following as inherently inefficient. In Scientific American he listed some such measures:

  • "turning off the defrost cycle on the refrigerator at a given time...the grid could signal...As long as that refrigerator got defrosted at the end of the day, you, as a consumer, wouldn't care but ultimately the grid could operate more efficiently."
  • "...if you didn't do that with the refrigerator you would have do that with the coal plant or combustion turbine running up and down, and doing that makes that unit run much more inefficiently."

At the time, electric vehicle battery integration into the grid was beginning. Wellinghof referred (ibid) to "these cars now getting paid in Delaware: $7 to $10 a day per car. They are getting paid over $3,000 a year to use these cars to simply control regulation service on the grid when they are charged".

Electric vehicle batteries as distributed load following or storage

Due to the very high cost of dedicated battery storage, use of electric vehicle batteries both while charging in vehicles (see smart grid), and in stationary grid energy storage arrays as an end-of-life re-use once they no longer hold enough charge for road use, has become the preferred method of load following over dedicated power plants. Such stationary arrays act as a true load-following power plant, and their deployment can "improve the affordability of purchasing such vehicles...Batteries that reach the end of their useful lifespan within the automotive industry can still be considered for other applications as between 70-80% of their original capacity still remains." Such batteries are also often repurposed in home arrays which primarily serve as backup, so can participate much more readily in grid stabilizing. The number of such batteries doing nothing is increasing rapidly, e.g. in Australia where Tesla Powerwall demand rose 30 times after major power outages.

Home and vehicle batteries are always and necessarily charged responsively when supply is available, meaning they all participate in a smart grid, because the high load (one Japanese estimate was over 7GW for half the cars in Kanto) simply cannot be managed on an analog grid, lest "The uncoordinated charging can result in creation of a new peak-load" (ibid).

Given the charging must be managed, there is no incremental cost to delay charging or discharge these batteries as required for load following, merely a software change and in some cases a payment for the inconvenience of less than complete charging or for battery wear (e.g. "$7 to $10 a day per car" paid in Delaware).

Rocky Mountain Institute in 2015 listed the applications of such distributed networks of batteries as (for "ISOs / RTOs") including "energy storage can bid into wholesale electricity markets" or for utility services including:

RMI claimed "batteries can provide these services more reliably and at a lower cost than the technology that currently provides a majority of them thermal power plants (see above re coal and gas)", and also that "storage systems installed behind the customer meter can be dispatched to provide deferral or adequacy services to utilities", such as:

  • "Transmission and distribution upgrade deferral. When load forecasts indicate transmission or distribution nodes will exceed their rated load carrying capacity, incremental investments in energy storage can be used to effectively increase the node’s capacity and avoid large, overbuilt, expensive upgrades to the nodes themselves."
  • "Transmission congestion relief. At certain times of the day, ISOs charge utilities to use congested transmission lines. Discharging energy storage systems located downstream of congested lines can avoid these charges."
  • "Resource adequacy. Instead of using or investing in combustion turbines to meet peak generation requirements, utilities can call upon other assets like energy storage instead."

Politics of Europe

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