A Medley of Potpourri

Wednesday, August 9, 2023

Electrosynthesis

From Wikipedia, the free encyclopedia
https://en.wikipedia.org/wiki/Electrosynthesis

In electrochemistry, electrosynthesis is the synthesis of chemical compounds in an electrochemical cell. Compared to ordinary redox reactions, electrosynthesis sometimes offers improved selectivity and yields. Electrosynthesis is actively studied as a science and also has industrial applications. Electrooxidation has potential for wastewater treatment as well.

Experimental setup

The basic setup in electrosynthesis is a galvanic cell, a potentiostat and two electrodes. Typical solvent and electrolyte combinations minimizes electrical resistance. Protic conditions often use alcohol-water or dioxane-water solvent mixtures with an electrolyte such as a soluble salt, acid or base. Aprotic conditions often use an organic solvent such as acetonitrile or dichloromethane with electrolytes such as lithium perchlorate or tetrabutylammonium salts. The choice of electrodes with respect to their composition and surface area can be decisive. For example, in aqueous conditions the competing reactions in the cell are the formation of oxygen at the anode and hydrogen at the cathode. In this case a graphite anode and lead cathode could be used effectively because of their high overpotentials for oxygen and hydrogen formation respectively. Many other materials can be used as electrodes. Other examples include platinum, magnesium, mercury (as a liquid pool in the reactor), stainless steel or reticulated vitreous carbon. Some reactions use a sacrificial electrode that is consumed during the reaction like zinc or lead. Cell designs can be undivided cell or divided cell type. In divided cells the cathode and anode chambers are separated with a semiporous membrane. Common membrane materials include sintered glass, porous porcelain, polytetrafluoroethene or polypropylene. The purpose of the divided cell is to permit the diffusion of ions while restricting the flow of the products and reactants. This separation simplifies workup. An example of a reaction requiring a divided cell is the reduction of nitrobenzene to phenylhydroxylamine, where the latter chemical is susceptible to oxidation at the anode.

Reactions

Organic oxidations take place at the anode. Compounds are reduced at the cathode. Radical intermediates are often invoked. The initial reaction takes place at the surface of the electrode and then the intermediates diffuse into the solution where they participate in secondary reactions.

The yield of an electrosynthesis is expressed both in terms of the chemical yield and current efficiency. Current efficiency is the ratio of Coulombs consumed in forming the products to the total number of Coulombs passed through the cell. Side reactions decrease the current efficiency.

The potential drop between the electrodes determines the rate constant of the reaction. Electrosynthesis is carried out with either constant potential or constant current. The reason one chooses one over the other is due to a trade-off of ease of experimental conditions versus current efficiency. Constant potential uses current more efficiently because the current in the cell decreases with time due to the depletion of the substrate around the working electrode (stirring is usually necessary to decrease the diffusion layer around the electrode). This is not the case under constant current conditions, however. Instead, as the substrate's concentration decreases the potential across the cell increases in order to maintain the fixed reaction rate. This consumes current in side reactions produced outside the target voltage.

Anodic oxidations

A well-known electrosynthesis is the Kolbe electrolysis, in which two carboxylic acids decarboxylate, and the remaining structures bond together:

A variation is called the non-Kolbe reaction when a heteroatom (nitrogen or oxygen) is present at the α-position. The intermediate oxonium ion is trapped by a nucleophile, usually solvent.

Anodic electrosynthesis oxidize primary aliphatic amine to nitrile.
Amides can be oxidized to N-acyliminium ions, which can be captured by various nucleophiles, for example:

This reaction type is called a Shono oxidation. An example is the α-methoxylation of N-carbomethoxypyrrolidine

Oxidation of a carbanion can lead to a coupling reaction for instance in the electrosynthesis of the tetramethyl ester of ethanetetracarboxylic acid from the corresponding malonate ester
α-amino acids form nitriles and carbon dioxide via oxidative decarboxylation at AgO anodes (the latter is formed in-situ by oxidation of Ag₂O):

Cyanoacetic acid from cathodic reduction of carbon dioxide and anodic oxidation of acetonitrile.
Propiolic acid is prepared commercially by oxidizing propargyl alcohol at a lead electrode.

Cathodic reductions

In the Markó–Lam deoxygenation, an alcohol could be almost instantaneously deoxygenated by electroreducing its toluate ester.

In concept, adiponitrile is prepared from dimerizing acrylonitrile:

2 CH₂=CHCN + 2 e⁻ + 2 H⁺ → NC(CH₂)₄CN

In practice,the cathodic hydrodimerization of activated olefins is applied industrially in the synthesis of adiponitrile from two equivalents of acrylonitrile :

The cathodic reduction of arene compounds to the 1,4-dihydro derivatives is similar to a Birch reduction. Examples from industry are the reduction of phthalic acid:

and the reduction of 2-methoxynaphthalene:

The Tafel rearrangement, named for Julius Tafel, was at one time an important method for the synthesis of certain hydrocarbons from alkylated ethyl acetoacetate, a reaction accompanied by the rearrangement reaction of the alkyl group:

The cathodic reduction of a nitrile to a primary amine in a divided cell; the cathodic reduction of benzyl cyanide to phenethylamine is shown:

Cathodic reduction of a nitroalkene can give the oxime in good yield. At higher negative reduction potentials, the nitroalkene can be reduced further, giving the primary amine but with lower yield.

Azobenzene is prepared in industrial electrosynthesis using nitrobenzene.
An electrochemical carboxylation of a para-isobutyl benzyl chloride to Ibuprofen is promoted under supercritical carbon dioxide.
Cathodic reduction of a carboxylic acid (oxalic acid) to an aldehyde (glyoxylic acid, shows as the rare aldehyde form) in a divided cell:

Originally phenylpropanoic acid could be prepared from reduction of cinnamic acid by electrolysis.
An electrocatalysis by a copper complex helps reduce carbon dioxide to oxalic acid; this conversion uses carbon dioxide as a feedstock to generate oxalic acid.
It has been reported that formate can be formed by the electrochemical reduction of CO₂ (in the form of bicarbonate) at a lead cathode at pH 8.6:

HCO−3 + H₂O + 2e⁻ → HCO−2 + 2OH⁻

CO₂ + H₂O + 2e⁻ → HCO−2 + OH⁻

If the feed is CO₂ and oxygen is evolved at the anode, the total reaction is:

CO₂ + OH⁻ → HCO−2 + ¹/₂ O₂

Redox reactions

Cathodic reduction of carbon dioxide and anodic oxidation of acetonitrile afford cyanoacetic acid.
An electrosynthesis employing alternating current prepares phenol at both the cathode and the anode.

Electrofluorination

In organofluorine chemistry, many perfluorinated compounds are prepared by electrochemical synthesis, which is conducted in liquid HF at voltages near 5–6 V using Ni anodes. The method was invented in the 1930s. Amines, alcohols, carboxylic acids, and sulfonic acids are converted to perfluorinated derivatives using this technology. A solution or suspension of the hydrocarbon in hydrogen fluoride is electrolyzed at 5–6 V to produce high yields of the perfluorinated product.

Effective radiated power

From Wikipedia, the free encyclopedia
https://en.wikipedia.org/wiki/Effective_radiated_power

Effective radiated power (ERP), synonymous with equivalent radiated power, is an IEEE standardized definition of directional radio frequency (RF) power, such as that emitted by a radio transmitter. It is the total power in watts that would have to be radiated by a half-wave dipole antenna to give the same radiation intensity (signal strength or power flux density in watts per square meter) as the actual source antenna at a distant receiver located in the direction of the antenna's strongest beam (main lobe). ERP measures the combination of the power emitted by the transmitter and the ability of the antenna to direct that power in a given direction. It is equal to the input power to the antenna multiplied by the gain of the antenna. It is used in electronics and telecommunications, particularly in broadcasting to quantify the apparent power of a broadcasting station experienced by listeners in its reception area.

An alternate parameter that measures the same thing is effective isotropic radiated power (EIRP). Effective isotropic radiated power is the hypothetical power that would have to be radiated by an isotropic antenna to give the same ("equivalent") signal strength as the actual source antenna in the direction of the antenna's strongest beam. The difference between EIRP and ERP is that ERP compares the actual antenna to a half-wave dipole antenna, while EIRP compares it to a theoretical isotropic antenna. Since a half-wave dipole antenna has a gain of 1.64 (or 2.15 dB) compared to an isotropic radiator, if ERP and EIRP are expressed in watts their relation is

E I R P (W) = 1.64 \cdot E R P (W)

If they are expressed in decibels

E I R P (d B) = E R P (d B) + 2.15

Definitions

Effective radiated power and effective isotropic radiated power both measure the power density a radio transmitter and antenna (or other source of electromagnetic waves) radiates in a specific direction: in the direction of maximum signal strength (the "main lobe") of its radiation pattern. This apparent power is dependent on two factors: the total power output and the radiation pattern of the antenna – how much of that power is radiated in the desired direction. The latter factor is quantified by the antenna gain, which is the ratio of the signal strength radiated by an antenna in its direction of maximum radiation to that radiated by a standard antenna. For example, a 1,000-watt transmitter feeding an antenna with a gain of 4 (6 dBi) will have the same signal strength in the direction of its main lobe, and thus the same ERP and EIRP, as a 4,000-watt transmitter feeding an antenna with a gain of 1 (0 dBi). So ERP and EIRP are measures of radiated power that can compare different combinations of transmitters and antennas on an equal basis.

In spite of the names, ERP and EIRP do not measure transmitter power, or total power radiated by the antenna, they are just a measure of signal strength along the main lobe. They give no information about power radiated in other directions, or total power. ERP and EIRP are always greater than the actual total power radiated by the antenna.

The difference between ERP and EIRP is that antenna gain has traditionally been measured in two different units, comparing the antenna to two different standard antennas; an isotropic antenna and a half-wave dipole antenna:

Isotropic gain is the ratio of the power density $S_{max}$ (signal strength in watts per square meter) received at a point far from the antenna (in the far field) in the direction of its maximum radiation (main lobe), to the power $S_{max,isotropic}$ received at the same point from a hypothetical lossless isotropic antenna, which radiates equal power in all directions $G_{i} = \frac{S_{max}}{S_{max,isotropic}}$ Gain is often expressed in logarithmic units of decibels (dB). The decibel gain relative to an isotropic antenna (dBi) is given by $G (dBi) = 10 \log \frac{S_{max}}{S_{max,isotropic}}$
Dipole gain is the ratio of the power density received from the antenna in the direction of its maximum radiation to the power density $S_{max,dipole}$ received from a lossless half-wave dipole antenna in the direction of its maximum radiation $G_{d} = \frac{S_{max}}{S_{max,dipole}}$ The decibel gain relative to a dipole (dBd) is given by $G (dBd) = 10 \log \frac{S_{max}}{S_{max,dipole}}$

In contrast to an isotropic antenna, the dipole has a "donut-shaped" radiation pattern, its radiated power is maximum in directions perpendicular to the antenna, declining to zero on the antenna axis. Since the radiation of the dipole is concentrated in horizontal directions, the gain of a half-wave dipole is greater than that of an isotropic antenna. The isotropic gain of a half-wave dipole is 1.64, or in decibels 10 log 1.64 = 2.15 dBi, so

G_{i} = 1.64 G_{d}

In decibels

G (dBi) = G (dBd) + 2.15

The two measures EIRP and ERP are based on the two different standard antennas above:

EIRP is defined as the RMS power input in watts required to a lossless isotropic antenna to give the same maximum power density far from the antenna as the actual transmitter. It is equal to the power input to the transmitter's antenna multiplied by the isotropic antenna gain $E I R P = G_{i} P_{in}$ The ERP and EIRP are also often expressed in decibels (dB). The input power in decibels is usually calculated with comparison to a reference level of one watt (W): $P_{in} (d B W) = 10 \log P_{in}$ . Since multiplication of two factors is equivalent to addition of their decibel values $E I R P (d B W) = G (dBi) + P_{in} (d B W)$
ERP is defined as the RMS power input in watts required to a lossless half-wave dipole antenna to give the same maximum power density far from the antenna as the actual transmitter. It is equal to the power input to the transmitter's antenna multiplied by the antenna gain relative to a half-wave dipole $E R P = G_{d} P_{in}$ In decibels $E R P (d B W) = G (dBd) + P_{in} (d B W)$

Since the two definitions of gain only differ by a constant factor, so do ERP and EIRP

E I R P (W) = 1.64 \cdot E R P (W)

In decibels

E I R P (d B W) = E R P (dBW) + 2.15

Relation to transmitter output power

The transmitter is usually connected to the antenna through a transmission line and impedance matching network. Since these components may have significant losses $L$ , the power applied to the antenna is usually less than the output power of the transmitter $P_{TX}$ . The relation of ERP and EIRP to transmitter output power is

E I R P (d B W) = P_{TX} (d B W) - L (d B) + G (dBi)

E R P (d B W) = P_{TX} (d B W) - L (d B) + G (dBi) - 2.15

Losses in the antenna itself are included in the gain.

Relation to signal strength

If the signal path is in free space (line-of-sight propagation with no multipath) the signal strength (power flux density in watts per square meter) $S$ of the radio signal on the main lobe axis at any particular distance $r$ from the antenna can be calculated from the EIRP or ERP. Since an isotropic antenna radiates equal power flux density over a sphere centered on the antenna, and the area of a sphere with radius $r$ is $A = 4 π r^{2}$ then

S (r) = \frac{E I R P}{4 π r^{2}}

Since

E I R P = E R P \times 1.64

S (r) = \frac{0.41 \times E R P}{π r^{2}}

However if the radio waves travel by ground wave as is typical for medium or longwave broadcasting, skywave, or indirect paths play a part in transmission, the waves will suffer additional attenuation which depends on the terrain between the antennas, so these formulas are not valid.

Dipole vs. isotropic radiators

Because ERP is calculated as antenna gain (in a given direction) as compared with the maximum directivity of a half-wave dipole antenna, it creates a mathematically virtual effective dipole antenna oriented in the direction of the receiver. In other words, a notional receiver in a given direction from the transmitter would receive the same power if the source were replaced with an ideal dipole oriented with maximum directivity and matched polarization towards the receiver and with an antenna input power equal to the ERP. The receiver would not be able to determine a difference. Maximum directivity of an ideal half-wave dipole is a constant, i.e., 0 dBd = 2.15 dBi. Therefore, ERP is always 2.15 dB less than EIRP. The ideal dipole antenna could be further replaced by an isotropic radiator (a purely mathematical device which cannot exist in the real world), and the receiver cannot know the difference so long as the input power is increased by 2.15 dB.

The distinction between dBd and dBi is often left unstated and the reader is sometimes forced to infer which was used. For example, a Yagi–Uda antenna is constructed from several dipoles arranged at precise intervals to create better energy focusing (directivity) than a simple dipole. Since it is constructed from dipoles, often its antenna gain is expressed in dBd, but listed only as dB. This ambiguity is undesirable with respect to engineering specifications. A Yagi–Uda antenna's maximum directivity is 8.77 dBd = 10.92 dBi. Its gain necessarily must be less than this by the factor η, which must be negative in units of dB. Neither ERP nor EIRP can be calculated without knowledge of the power accepted by the antenna, i.e., it is not correct to use units of dBd or dBi with ERP and EIRP. Let us assume a 100-watt (20 dBW) transmitter with losses of 6 dB prior to the antenna. ERP < 22.77dBW and EIRP < 24.92dBW, both less than ideal by η in dB. Assuming that the receiver is in the first side-lobe of the transmitting antenna, and each value is further reduced by 7.2 dB, which is the decrease in directivity from the main to side-lobe of a Yagi-Uda. Therefore, anywhere along the side-lobe direction from this transmitter, a blind receiver could not tell the difference if a Yagi-Uda was replaced with either an ideal dipole (oriented towards the receiver) or an isotropic radiator with antenna input power increased by 1.57 dB.

Polarization

Polarization has not been taken into account so far, but it must be properly clarified. When considering the dipole radiator previously we assumed that it was perfectly aligned with the receiver. Now assume, however, that the receiving antenna is circularly polarized, and there will be a minimum 3 dB polarization loss regardless of antenna orientation. If the receiver is also a dipole, it is possible to align it orthogonally to the transmitter such that theoretically zero energy is received. However, this polarization loss is not accounted for in the calculation of ERP or EIRP. Rather, the receiving system designer must account for this loss as appropriate. For example, a cellular telephone tower has a fixed linear polarization, but the mobile handset must function well at any arbitrary orientation. Therefore, a handset design might provide dual polarization receive on the handset so that captured energy is maximized regardless of orientation, or the designer might use a circularly polarized antenna and account for the extra 3 dB of loss with amplification.

FM example

For example, an FM radio station which advertises that it has 100,000 watts of power actually has 100,000 watts ERP, and not an actual 100,000-watt transmitter. The transmitter power output (TPO) of such a station typically may be 10,000 to 20,000 watts, with a gain factor of 5 to 10 (5× to 10×, or 7 to 10 dB). In most antenna designs, gain is realized primarily by concentrating power toward the horizontal plane and suppressing it at upward and downward angles, through the use of phased arrays of antenna elements. The distribution of power versus elevation angle is known as the vertical pattern. When an antenna is also directional horizontally, gain and ERP will vary with azimuth (compass direction). Rather than the average power over all directions, it is the apparent power in the direction of the antenna's main lobe that is quoted as a station's ERP (this statement is just another way of stating the definition of ERP). This is particularly applicable to the huge ERPs reported for shortwave broadcasting stations, which use very narrow beam widths to get their signals across continents and oceans.

United States regulatory usage

ERP for FM radio in the United States is always relative to a theoretical reference half-wave dipole antenna. (That is, when calculating ERP, the most direct approach is to work with antenna gain in dBd). To deal with antenna polarization, the Federal Communications Commission (FCC) lists ERP in both the horizontal and vertical measurements for FM and TV. Horizontal is the standard for both, but if the vertical ERP is larger it will be used instead.

The maximum ERP for US FM broadcasting is usually 100,000 watts (FM Zone II) or 50,000 watts (in the generally more densely populated Zones I and I-A), though exact restrictions vary depending on the class of license and the antenna height above average terrain (HAAT). Some stations have been grandfathered in or, very infrequently, been given a waiver, and can exceed normal restrictions.

Microwave band issues

For most microwave systems, a completely non-directional isotropic antenna (one which radiates equally and perfectly well in every direction – a physical impossibility) is used as a reference antenna, and then one speaks of EIRP (effective isotropic radiated power) rather than ERP. This includes satellite transponders, radar, and other systems which use microwave dishes and reflectors rather than dipole-style antennas.

Lower-frequency issues

In the case of medium wave (AM) stations in the United States, power limits are set to the actual transmitter power output, and ERP is not used in normal calculations. Omnidirectional antennas used by a number of stations radiate the signal equally in all directions. Directional arrays are used to protect co- or adjacent channel stations, usually at night, but some run directionally 24 hours. While antenna efficiency and ground conductivity are taken into account when designing such an array, the FCC database shows the station's transmitter power output, not ERP.

Related terms

According to the Institution of Electrical Engineers (UK), ERP is often used as a general reference term for radiated power, but strictly speaking should only be used when the antenna is a half-wave dipole, and is used when referring to FM transmission.

EMRP

Effective monopole radiated power (EMRP) may be used in Europe, particularly in relation to medium wave broadcasting antennas. This is the same as ERP, except that a short vertical antenna (i.e. a short monopole) is used as the reference antenna instead of a half-wave dipole.

CMF

Cymomotive force (CMF) is an alternative term used for expressing radiation intensity in volts, particularly at the lower frequencies. It is used in Australian legislation regulating AM broadcasting services, which describes it as: "for a transmitter, [it] means the product, expressed in volts, of: (a) the electric field strength at a given point in space, due to the operation of the transmitter; and (b) the distance of that point from the transmitter's antenna".

It relates to AM broadcasting only, and expresses the field strength in "microvolts per metre at a distance of 1 kilometre from the transmitting antenna".

HAAT

The height above average terrain for VHF and higher frequencies is extremely important when considering ERP, as the signal coverage (broadcast range) produced by a given ERP dramatically increases with antenna height. Because of this, it is possible for a station of only a few hundred watts ERP to cover more area than a station of a few thousand watts ERP, if its signal travels above obstructions on the ground.

Ringworld

From Wikipedia, the free encyclopedia

Ringworld
Paperback first edition
Author	Larry Niven
Illustrator	Dean Ellis
Country	United States
Language	English
Series	Ringworld storyline from Known Space
Genre	Science fiction
Publisher	Ballantine Books
Publication date	October 1970
Media type	Print (hardcover, paperback), audiobook
Pages	342 pages
Awards	Locus Award for Best Novel (1971)
ISBN	0-345-02046-4
Followed by	The Ringworld Engineers, 1979

Ringworld is a 1970 science fiction novel by Larry Niven, set in his Known Space universe and considered a classic of science fiction literature. Ringworld tells the story of Louis Wu and his companions on a mission to the Ringworld, a rotating wheel artificial world, an alien construct in space 186 million miles (299 million kilometres) in diameter. Niven later added three sequel novels and then cowrote, with Edward M. Lerner, four prequels and a final sequel; the five latter novels constitute the Fleet of Worlds series. All the novels in the Ringworld series tie into numerous other books set in Known Space. Ringworld won the Nebula Award in 1970, as well as both the Hugo Award and Locus Award in 1971.

Plot summary

On planet Earth in 2850 AD, Louis Gridley Wu is celebrating his 200th birthday. Despite his age, Louis is in perfect physical condition due to the longevity drug boosterspice. He meets Nessus, a Pierson's puppeteer, who offers him a mysterious job. Intrigued, Louis eventually accepts. Speaker-to-Animals (Speaker), who is a Kzin, and Teela Brown, a young human woman who becomes Louis's lover, also join the crew.

On the puppeteer home world, they are told that the expedition's goal is to investigate the Ringworld, a gigantic artificial ring, to see if it poses any threat. The Ringworld is about one million miles (1.6 million km) wide and approximately the diameter of Earth's orbit (which makes it about 584.3 million miles or 940.4 million km in circumference), encircling a sunlike star. It rotates to provide artificial gravity 99.2% as strong as Earth's from centrifugal force. The Ringworld has a habitable, flat inner surface (equivalent in area to approximately three million Earths), a breathable atmosphere and a temperature optimal for humans. Night is provided by an inner ring of shadow squares which are connected to each other by thin, ultra-strong wire. When the crew completes their mission, they will be given the starship in which they travelled to the puppeteer home world; it is orders of magnitude faster than any possessed by humans or Kzinti.

When they reach the vicinity of the Ringworld, they are unable to contact anyone, and their ship, the Lying Bastard, is disabled by the Ringworld's automated meteoroid-defense system. The severely damaged vessel collides with a strand of shadow-square wire and crash-lands near a huge mountain, "Fist-of-God". As the fusion drive is destroyed, they are unable to launch back into space where they could use the undamaged faster-than-light hyperdrive to return home. They set out to find a way to get the Lying Bastard off the Ringworld.

Using their flycycles (similar to antigravity motorcycles), they try to reach the rim of the ring, where they hope to find some technology that will help them. It will take them months to cross the vast distance. When Teela develops "Plateau trance" (a kind of highway hypnosis), they are forced to land. On the ground, they encounter apparently primitive human natives who live in the crumbling ruins of a once-advanced city and think that the crew are the engineers who created the ring, and whom they revere as gods. The crew is attacked when they commit what the natives consider blasphemy (the misuse of certain technologies).

They continue their journey, during which Nessus reveals some Puppeteer secrets: they have conducted experiments on both humans (breeding for luck via Birthright Lotteries: all of Teela's ancestors for six generations were born from winning the lottery) and Kzinti (breeding for reduced aggression via the Man-Kzin wars, which the Kzinti always lost). Speaker's outrage forces Nessus to flee and follow them from a safe distance.

In a floating building over the ruins of a city, they find a map of the Ringworld and videos of its past civilization.

While flying through a giant storm caused by air escaping through a hole in the Ring floor due to a meteoroid impact, Teela becomes separated from the others. While Louis and Speaker search for her, their flycycles are caught by an automated police trap designed to catch traffic offenders. They are trapped in the basement of a floating police station. Nessus enters the station to try to help them.

In the station, they meet Halrloprillalar Hotrufan ("Prill"), a former crew member of a trading spaceship that collected plants and animals that couldn't adapt to the Ringworld. When her ship returned to the Ringworld the last time, they found that civilization had collapsed. The crew managed to enter the Ringworld, but some of them were killed and others suffered brain damage when the device that let them pass through the Ringworld floor failed. From her account, they learn that a mold was brought back from one of the original planets of the engineers by a spaceship like Prill's; it broke down the superconductors vital to the Ringworld civilization, dooming it.

Teela reaches the police station, accompanied by her new lover, a native "hero" called Seeker who helped her survive. Based on an insight gained from studying an ancient Ringworld map, Louis comes up with a plan to get home. Teela chooses to remain on the Ringworld with Seeker. Louis, formerly skeptical about breeding for luck, now wonders if the entire mission was caused by Teela's luck, to unite her with her true love and help her mature.

The party collects one end of the shadow-square wire that was snapped when the ship crashed. They travel back to their crashed ship in the floating police station, dragging the wire behind them. Louis threads it through the ship to tether it to the police station. He then takes the police station up to the summit of "Fist-of-God", the enormous mountain near their crash site. The mountain had not appeared on the Ringworld map, leading Louis to conclude that it is in fact the result of a meteoroid impact with the underside of the ring, which pushed the "mountain" up from the ring's floor and broke through. The top of the mountain, above the atmosphere, is therefore just a hole in the Ringworld floor. Louis drives the police station over the edge, dragging the Lying Bastard along with it. The Ringworld spins very quickly, so once the ship drops through the hole and clears the ring, they can use the ship's hyperdrive to get home. The book concludes with Louis and Speaker discussing returning to the Ringworld.

Reception

Algis Budrys found Ringworld to be "excellent and entertaining ... woven together very skillfully and proceed[ing] at a pretty smooth pace." While praising the novel generally, he faulted Niven for relying on inconsistencies regarding evolution in his extrapolations to support his fictional premises.

Sam Jordison described Ringworld as "arguably one of the most influential science fiction novels of the past 50 years.

Concepts reused

In addition to the two aliens, Niven includes a number of concepts from his other Known Space stories:

The puppeteers' General Products hulls, which are impervious to any known force except visible light and gravity, and for a long time thought indestructible by anything except antimatter. The Fleet of Worlds prequels reveal two other ways that the hulls can be destroyed.
The Slaver stasis field, which causes time in the enclosed volume to stand still; since time has for all intents and purposes ceased for an object in stasis, no harm can come to anything within the field.
The idea that luck is a genetic trait that can be strengthened by selective breeding.
The tasp, a device that remotely stimulates the pleasure center of the brain; it temporarily incapacitates its target and is extremely psychologically addictive. If the subject cannot, for whatever reason, get access to the device, intense depression can result, often to the point of madness or suicide. To use a tasp on someone from hiding, relieving them of their anger or depression, is called "making their day".
Boosterspice, a drug that restores or indefinitely preserves youth.
Scrith, the metal-like substance of which the Ringworld is built (and presumably the shadow squares and wires too), that has a tensile strength nearly equal in magnitude to the strong nuclear force making it similar to the concept of nuclear matter. This makes it an example of unobtainium. This is similar to the Pak Protector's "twing" used in other Larry Niven stories.
Impact armor, a flexible form of clothing that hardens instantly into a rigid form stronger than steel when rapidly deformed, similar to certain types of bulletproof vests.
The hyperspace shunt, an engine for faster-than-light travel, but slow enough (1 light-year per 3 days, ~122 c) to keep the galaxy vast and unknown; the new "quantum II hyperspace shunt", developed by the Puppeteers but not yet released to humans, can cross a light-year in just 1.25 minutes (~421 000 c).
Point-to-point teleportation at the speed of light is possible with transfer booths (on Earth) and stepping disks (on the Puppeteer homeworld); on Earth, people's sense of place and global position has been lost due to instantaneous travel; cities and cultures have blended together.
A theme well covered in the novel is that of cultures suffering technological breakdowns who then proceed to revert to belief systems along religious lines. Most Ringworld societies have forgotten that they live on an artificial structure, and now attribute the phenomena and origin of their world to divine power.

Errors

The opening chapter of the original paperback edition of Ringworld featured Louis Wu teleporting eastward around the Earth in order to extend his birthday. Moving in this direction would, in fact, make local time later rather than earlier, so that Wu would soon arrive in the early morning of the next calendar day. Niven was "endlessly teased" about this error, which he corrected in subsequent printings to show Wu teleporting westward. In his dedication to The Ringworld Engineers, Niven wrote, "If you own a first paperback edition of Ringworld, it's the one with the mistakes in it. It's worth money."

After the publication of Ringworld, many fans identified numerous engineering problems in the Ringworld as described in the novel. One major one was that the Ringworld, being a rigid structure, was not actually in orbit around the star it encircled and would eventually drift, ultimately colliding with its sun and disintegrating. This led MIT students attending the 1971 Worldcon to chant, "The Ringworld is unstable!" Niven wrote the 1980 sequel The Ringworld Engineers in part to address these engineering issues. In it, the ring is found to have a system of attitude jets atop the rim walls, but the Ringworld has become gravely endangered because most of the jets have been removed by the natives, to power their interstellar ships. (The natives had forgotten the original purpose of the jets.)

The second chapter refers to standard Earth gravity as 9.98 m/s² (or even gives the unit as m/s [sic]), while standard Earth gravity is 9.81 m/s². The fifth chapter refers to Nereid as Neptune's largest moon; the planet's largest moon is Triton.

Influence

"Ringworld", has become a generic term for such a structure, which is an example of what science fiction fans call a "Big Dumb Object", or more formally a megastructure. Other science fiction authors have devised their own variants of Niven's Ringworld, notably Iain M. Banks' Culture Orbitals, best described as miniature Ringworlds, and the titular ring-shaped Halo structures of the video game series Halo. Such a mini-Ringworld appears in Star Wars: The Book of Boba Fett, Season 1, Episode 5.

Adaptations

Games

In 1984, a role-playing game based on this setting was produced by Chaosium named The Ringworld Roleplaying Game. Information from the RPG, along with notes composed by RPG author John Hewitt with Niven, was later used to form the "Bible" given to authors writing in the Man-Kzin Wars series. Niven himself recommended that Hewitt write one of the stories for the original two MKW books, although this never came to pass.

Tsunami Games released two adventure games based on Ringworld. Ringworld: Revenge of the Patriarch was released in 1992 and Return to Ringworld in 1994. A third game, Ringworld: Within ARM's Reach, was also planned, but never completed.

The video game franchise Halo, created by Bungie, took inspiration from the book in the creation and development of its story around the eponymous rings, called Halos. These are physically similar to the Ringworld, however they are much smaller and do not encircle the star, instead orbiting stars or planets.

The open source video game Endless Sky features an alien species that creates ringworlds.

In 2017 Paradox Interactive added a DLC called "Utopia" to their game Stellaris, allowing the player to restore or build ringworlds.

In 2021 Mobius Digital added a DLC called "Echoes of the Eye" to their game Outer Wilds, which allows the player to explore a hidden, abandoned ringworld and determine what happened to its inhabitants.

On screen

There have been many aborted attempts to adapt the novel to the screen.

In 2001, Larry Niven reported that a movie deal had been signed and was in the early planning stages.

In 2004, the Sci-Fi Channel reported that it was developing a Ringworld miniseries. The series never came to fruition.

In 2013, it was again announced by the channel, now rebranded as Syfy, that a miniseries of the novel was in development. This proposed 4-hour miniseries was being written by Michael R. Perry and would have been a co-production between MGM Television and Universal Cable Productions.

In 2017, Amazon announced that Ringworld was one of three science fiction series it was developing for its streaming service. MGM were again listed as a co-producer.

OEL manga

Tor/Seven Seas (same joint venture of Macmillan's Tor Books and Seven Seas Entertainment who also published the English-language translation of Afro Samurai) published a two-part original English-language manga adaptation of Ringworld, with the script written by Robert Mandell and the artwork by Sean Lam. Ringworld: The Graphic Novel, Part One, covering the events of the novel up to the sunflower attack on Speaker, was released on July 8, 2014. Part Two was released on November 10, 2015.

In other works

Terry Pratchett intended his 1981 novel Strata to be a "piss-take/homage/satire" of Ringworld. Niven took it in good humor and enjoyed the work.
The plot of the first-person shooter Halo: Combat Evolved for the Xbox, Windows, and Mac OS X also takes place on an artificial ring structure. Similarities to Ringworld have been noted in the game, and Niven was asked (but declined) to write the first novel based on the series.
"All in Fun" by Jerry Oltion, in Fantasy & Science Fiction, January 2009, mentions a faithful big-budget movie adaptation of Ringworld.
In Ernest Cline's 2011 novel Ready Player One, one of the sectors of the OASIS, the worldwide virtual reality network that is the novel's primary setting, is mentioned as being an adaptation of Ringworld.
The 1987 novel The Alexandrian Ring by William R. Forstchen takes place on a ring much like Niven's.
Episode 5 of The Book of Boba Fett features a station called Glavis that is shaped like a ring and features sun shades in much the same way that Niven's does.

Books in series

Ringworld (1970)
The Ringworld Engineers (1980)
The Ringworld Throne (1996)
Ringworld's Children (2004)

Fate of Worlds: Return from the Ringworld (2012)