Resurrection

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Resurrection 

Plaque depicting saints rising from the dead

Resurrection or anastasis is the concept of coming back to life after death. In a number of religions, a dying-and-rising god is a deity which dies and is resurrected. Reincarnation is a similar process hypothesized by other religions, which involves the same person or deity coming back to live in a different body, rather than the same one.

The resurrection of the dead is a standard eschatological belief in the Abrahamic religions. As a religious concept, it is used in two distinct respects: a belief in the resurrection of individual souls that is current and ongoing (Christian idealism, realized eschatology), or else a belief in a singular resurrection of the dead at the end of the world. Some believe the soul is the actual vehicle by which people are resurrected.

The death and resurrection of Jesus is a central focus of Christianity. Christian theological debate ensues with regard to what kind of resurrection is factual – either a spiritual resurrection with a spirit body into Heaven, or a material resurrection with a restored human body. While most Christians believe Jesus' resurrection from the dead and ascension to Heaven was in a material body, some believe it was spiritual.

Like the Abrahamic religions, Hinduism also has a core belief in resurrection and reincarnation. This is known as saṃsāra.

Etymology

Resurrection, from the Latin noun resurrectio -onis, from the verb rego, "to make straight, rule" + preposition sub, "under", altered to subrigo and contracted to surgo, surrexi, surrectum ("to rise", "get up", "stand up") + preposition re-, "again", thus literally "a straightening from under again".

Religion

Ancient religions in the Near East

See also: Dying-and-rising god

The concept of resurrection is found in the writings of some ancient non-Abrahamic religions in the Middle East. A few extant Egyptian and Canaanite writings allude to dying and rising gods such as Osiris and Baal. Sir James Frazer in his book The Golden Bough relates to these dying and rising gods, but many of his examples, according to various scholars, distort the sources. Taking a more positive position, Tryggve Mettinger argues in his recent book that the category of rise and return to life is significant for Ugaritic Baal, Melqart, Adonis, Eshmun, Osiris and Dumuzi.

Ancient Greek religion

In ancient Greek religion a number of men and women became physically immortal as they were resurrected from the dead. Asclepius was killed by Zeus, only to be resurrected and transformed into a major deity. Achilles, after being killed, was snatched from his funeral pyre by his divine mother Thetis and resurrected, brought to an immortal existence in either Leuce, the Elysian plains or the Islands of the Blessed. Memnon, who was killed by Achilles, seems to have received a similar fate. Alcmene, Castor, Heracles, and Melicertes, were also among the figures sometimes considered to have been resurrected to physical immortality. According to Herodotus's Histories, the seventh century BC sage Aristeas of Proconnesus was first found dead, after which his body disappeared from a locked room. Later he found not only to have been resurrected but to have gained immortality.

Many other figures, like a great part of those who fought in the Trojan and Theban wars, Menelaus, and the historical pugilist Cleomedes of Astupalaea, were also believed to have been made physically immortal, but without having died in the first place. Indeed, in Greek religion, immortality originally always included an eternal union of body and soul. As may be witnessed even into the Christian era, not least by the complaints of various philosophers over popular beliefs, traditional Greek believers maintained the conviction that certain individuals were resurrected from the dead and made physically immortal and that for the rest of us, we could only look forward to an existence as disembodied and dead souls.

Greek philosophers generally denied this traditional religious belief in physical immortality. Writing his Lives of Illustrious Men (Parallel Lives) in the first century, the Middle Platonic philosopher Plutarch in his chapter on Romulus gave an account of the mysterious disappearance and subsequent deification of this first king of Rome, comparing it to traditional Greek beliefs such as the resurrection and physical immortalization of Alcmene and Aristeas the Proconnesian, "for they say Aristeas died in a fuller's work-shop, and his friends coming to look for him, found his body vanished; and that some presently after, coming from abroad, said they met him traveling towards Croton". Plutarch openly scorned such beliefs held in traditional ancient Greek religion, writing, "many such improbabilities do your fabulous writers relate, deifying creatures naturally mortal."

Alcestis undergoes resurrection over a three-day period of time, but without achieving immortality.

The parallel between these traditional beliefs and the later resurrection of Jesus was not lost on the early Christians, as Justin Martyr argued: "when we say ... Jesus Christ, our teacher, was crucified and died, and rose again, and ascended into heaven, we propose nothing different from what you believe regarding those whom you consider sons of Zeus." (1 Apol. 21).

Buddhism

Further information: Rebirth (Buddhism)

There are stories in Buddhism where the power of resurrection was allegedly demonstrated in Chan or Zen tradition. One is the legend of Bodhidharma, the Indian master who brought the Ekayana school of India that subsequently became Chan Buddhism to China.

The other is the passing of Chinese Chan master Puhua (Japanese:Jinshu Fuke) and is recounted in the Record of Linji (Japanese: Rinzai Gigen). Puhua was known for his unusual behavior and teaching style so it is no wonder that he is associated with an event that breaks the usual prohibition on displaying such powers. Here is the account from Irmgard Schloegl's "The Zen Teaching of Rinzai".

"One day at the street market Fuke was begging all and sundry to give him a robe. Everybody offered him one, but he did not want any of them. The master [Linji] made the superior buy a coffin, and when Fuke returned, said to him: "There, I had this robe made for you." Fuke shouldered the coffin, and went back to the street market, calling loudly: "Rinzai had this robe made for me! I am off to the East Gate to enter transformation" (to die)." The people of the market crowded after him, eager to look. Fuke said: "No, not today. Tomorrow, I shall go to the South Gate to enter transformation." And so for three days. Nobody believed it any longer. On the fourth day, and now without any spectators, Fuke went alone outside the city walls, and laid himself into the coffin. He asked a traveler who chanced by to nail down the lid.

The news spread at once, and the people of the market rushed there. On opening the coffin, they found that the body had vanished, but from high up in the sky they heard the ring of his hand bell."

Christianity

In Christianity, resurrection most critically concerns the resurrection of Jesus, but also includes the resurrection of Judgment Day known as the resurrection of the dead by those Christians who subscribe to the Nicene Creed (which is the majority or mainstream Christianity), as well as the resurrection miracles done by Jesus and the prophets of the Old Testament.

Resurrection miracles

The Resurrection of Lazarus, painting by Leon Bonnat, France, 1857.

 

Main article: Miracles of Jesus § Resurrection of the dead

In the New Testament, Jesus is said to have raised several persons from death. These resurrections included the daughter of Jairus shortly after death, a young man in the midst of his own funeral procession, and Lazarus of Bethany, who had been buried for four days.

During the Ministry of Jesus on earth, before his death, Jesus commissioned his Twelve Apostles to, among other things, raise the dead.

Similar resurrections are credited to the apostles and Catholic saints. In the Acts of the Apostles, Saint Peter raised a woman named Dorcas (also called Tabitha), and Paul the Apostle revived a man named Eutychus who had fallen asleep and fell from a window to his death. According to the Gospel of Matthew, after Jesus's resurrection, many of those previously dead came out of their tombs and entered Jerusalem, where they appeared to many. Following the Apostolic Age, many saints were said to resurrect the dead, as recorded in Orthodox Christian hagiographies. St Columba supposedly raised a boy from the dead in the land of Picts.

Resurrection of Jesus

Main articles: Life-death-rebirth deity, Resurrection of Jesus, Easter, and Resurrection appearances of Jesus

 

Resurrection of Jesus

Christians regard the resurrection of Jesus as the central doctrine in Christianity. Others take the incarnation of Jesus to be more central; however, it is the miracles – and particularly his resurrection – which provide validation of his incarnation. According to Paul, the entire Christian faith hinges upon the centrality of the resurrection of Jesus and the hope for a life after death. The Apostle Paul wrote in his first letter to the Corinthians:

If only for this life we have hope in Christ, we are to be pitied more than all men. But Christ has indeed been raised from the dead, the first fruits of those who have fallen asleep.

Resurrection of the dead

Main articles: Universal resurrection § Christianity, and Christian eschatology § Resurrection of the dead

Christianity started as a religious movement within 1st-century Judaism (late Second Temple Judaism), and it retains what the New Testament itself claims was the Pharisaic belief in the afterlife and resurrection of the dead. Whereas this belief was only one of many beliefs held about the world to come in Second Temple Judaism, and was notably rejected by the Sadducees, but accepted by the Pharisees (cf. Acts 23:6-8). Belief in the resurrection became dominant within Early Christianity and already in the Gospels of Luke and John, included an insistence on the resurrection of the flesh. Most modern Christian churches continue to uphold the belief that there will be a final resurrection of the dead and world to come.

Belief in the resurrection of the dead, and Jesus' role as judge, is codified in the Apostles' Creed, which is the fundamental creed of Christian baptismal faith. The Book of Revelation also makes many references about the Day of Judgment when the dead will be raised.

The emphasis on the literal resurrection of the flesh remained strong in the medieval ages, and still remains so in Orthodox churches. In modern Western Christianity, especially "from the 17th to the 19th century, the language of popular piety no longer evoked the resurrection of the soul but everlasting life. Although theological textbooks still mentioned resurrection, they dealt with it as a speculative question more than as an existential problem."

Difference from Platonic philosophy

In Platonic philosophy and other Greek philosophical thought, at death the soul was said to leave the inferior body behind. The idea that Jesus was resurrected spiritually rather than physically even gained popularity among some Christian teachers, whom the author of 1 John declared to be antichrists. Similar beliefs appeared in the early church as Gnosticism. However, in Luke 24:39, the resurrected Jesus expressly states "behold my hands and my feet, that it is I myself. Handle me and see, for a spirit does not have flesh and bones as you see, I have."

Hinduism

Further information: Reincarnation

There are folklore, stories, and extractions from certain holy texts that refer to resurrections. One major folklore is that of Savitri saving her husband's life from Yamraj. In the Ramayana, after Ravana was slain by Rama in a great battle between good and evil, Rama requests the king of Devas, Indra, to restore the lives of all the monkeys who died in the great battle. Mahavatar Babaji and Lahiri Mahasaya are also believed to have resurrected themselves.

Islam

Main article: Islamic eschatology

Belief in the Day of Resurrection (yawm al-qiyāmah) is also crucial for Muslims. They believe the time of Qiyāmah is preordained by God but unknown to man. The trials and tribulations preceding and during the Qiyāmah are described in the Quran and the hadith, and also in the commentaries of scholars. The Quran emphasizes bodily resurrection, a break from the pre-Islamic Arabian understanding of death.

According to Nasir Khusraw (d. after 1070), an Ismaili thinker of the Fatimid era, the Resurrection (Qiyāma) will be ushered by the Lord of the Resurrection (Qāʾim al-Qiyāma), an individual symbolizing the purpose and pinnacle of creation from among the progeny of Muhammad and his Imams. Through this individual, the world will come out of darkness and ignorance and “into the light of her Lord” (Quran 39:69). His era, unlike that of the enunciators of the divine revelation (nāṭiqs) before him, is not one where God prescribes the people to work but instead one where God rewards them. Preceding the Lord of the Resurrection (Qāʾim) is his proof (ḥujjat). The Qur’anic verse stating that “the night of power (laylat al-qadr) is better than a thousand months” (Quran 97:3) is said to refer to this proof, whose knowledge is superior to that of a thousand Imams, though their rank, collectively, is one. Hakim Nasir also recognizes the successors of the Lord of the Resurrection to be his deputies (khulafāʾ).

Judaism

Main article: Jewish eschatology

There are three explicit examples in the Hebrew Bible of people being resurrected from the dead:

• The prophet Elijah prays and God raises a young boy from death (1 Kings 17:17-24)
• Elisha raises the son of the Woman of Shunem (2 Kings 4:32-37) whose birth he previously foretold (2 Kings 4:8-16)
• A dead man's body that was thrown into the dead Elisha's tomb is resurrected when the body touches Elisha's bones (2 Kings 13:21)

According to Herbert C. Brichto, writing in Reform Judaism's Hebrew Union College Annual, the family tomb is the central concept in understanding biblical views of the afterlife. Brichto states that it is "not mere sentimental respect for the physical remains that is...the motivation for the practice, but rather an assumed connection between proper sepulture and the condition of happiness of the deceased in the afterlife".

According to Brichto, the early Israelites apparently believed that the graves of family, or tribe, united into one, and that this unified collectivity is to what the Biblical Hebrew term Sheol refers, the common grave of humans. Although not well defined in the Tanakh, Sheol in this view was a subterranean underworld where the souls of the dead went after the body died. The Babylonians had a similar underworld called Aralu, and the ancient Greeks had one known as Hades. According to Brichto, other biblical names for Sheol were Abaddon "ruin", found in Psalm 88:11, Job 28:22 and Proverbs 15:11; Bor "pit", found in Isaiah 14:15, 24:22, Ezekiel 26:20; and Shakhat "corruption", found in Isaiah 38:17, Ezekiel 28:8.

During the Second Temple period, there developed a diversity of beliefs concerning the resurrection. The concept of resurrection of the physical body is found in 2 Maccabees, according to which it will happen through re-creation of the flesh. Resurrection of the dead also appears in detail in the extra-canonical Book of Enoch, 2 Baruch, and 2 Esdras. According to the British scholar in ancient Judaism Philip R. Davies, there is “little or no clear reference … either to immortality or to resurrection from the dead” in the texts of the Dead Sea Scrolls. C.D. Elledge, however, argues that some form of resurrection may be referred to in the Dead Sea texts 4Q521, Pseudo-Ezekiel, and 4QInstruction.

Both Josephus and the New Testament record that the Sadducees did not believe in an afterlife, but the sources vary on the beliefs of the Pharisees. The New Testament claims that the Pharisees believed in the resurrection, but does not specify whether this included the flesh or not. According to Josephus, who himself was a Pharisee, the Pharisees held that only the soul was immortal and the souls of good people will “pass into other bodies,” while “the souls of the wicked will suffer eternal punishment.” Paul the Apostle, who also was a Pharisee, said that at the resurrection what is "sown as a natural body is raised a spiritual body." The Book of Jubilees seems to refer to the resurrection of the soul only, or to a more general idea of an immortal soul.

Anastasis in contemporary philosophy

Anastasis or Ana-stasis is a concept in contemporary philosophy emerging from the works of Jean-Luc Nancy, Divya Dwivedi and Shaj Mohan. Nancy developed the concept through his interpretation of paintings depicting the resurrection of Jesus Christ. Dwivedi and Mohan, referring to Nancy, defined Ana-stasis as coming over stasis, which is a method for philosophy to overcome its end as Martin Heidegger defined. This concept is noted to be linked in the works of Nancy, Dwivedi and Mohan to have a relation to Heidegger's “other beginning of philosophy”. The use of the phrase “anastasis of philosophy” indicates such other beginning.

Technological resurrection

Cryonics is the low-temperature freezing (usually at −196 °C or −320.8 °F or 77.1 K) of a human corpse or severed head, with the speculative hope that resurrection may be possible in the future. Cryonics is regarded with skepticism within the mainstream scientic community. It is generally viewed as a pseudoscience, and has been characterized as quackery.

Russian cosmist Nikolai Fyodorovich Fyodorov advocated resurrection of the dead using scientific methods. Fedorov tried to plan specific actions for scientific research of the possibility of restoring life and making it infinite. His first project is connected with collecting and synthesizing decayed remains of dead based on "knowledge and control over all atoms and molecules of the world". The second method described by Fedorov is genetic-hereditary. The revival could be done successively in the ancestral line: sons and daughters restore their fathers and mothers, they in turn restore their parents and so on. This means restoring the ancestors using the hereditary information that they passed on to their children. Using this genetic method it is only possible to create a genetic twin of the dead person. It is necessary to give back the revived person his old mind, his personality. Fedorov speculates about the idea of "radial images" that may contain the personalities of the people and survive after death. Nevertheless, Fedorov noted that even if a soul is destroyed after death, Man will learn to restore it whole by mastering the forces of decay and fragmentation.

In his 1994 book The Physics of Immortality, American physicist Frank J. Tipler, an expert on the general theory of relativity, presented his Omega Point Theory which outlines how a resurrection of the dead could take place at the end of the cosmos. He posits that humans will evolve into robots which will turn the entire cosmos into a supercomputer which will, shortly before the Big Crunch, perform the resurrection within its cyberspace, reconstructing formerly dead humans (from information captured by the supercomputer from the past light cone of the cosmos) as avatars within its metaverse.

David Deutsch, British physicist and pioneer in the field of quantum computing, formerly agreed with Tipler's Omega Point cosmology and the idea of resurrecting deceased people with the help of quantum computers but he is critical of Tipler's theological views.

Italian physicist and computer scientist Giulio Prisco presents the idea of "quantum archaeology", "reconstructing the life, thoughts, memories, and feelings of any person in the past, up to any desired level of detail, and thus resurrecting the original person via 'copying to the future'".

In his book Mind Children, roboticist Hans Moravec proposed that a future supercomputer might be able to resurrect long-dead minds from the information that still survived. For example, this information can be in the form of memories, filmstrips, medical records, and DNA.

Ray Kurzweil, American inventor and futurist, believes that when his concept of singularity comes to pass, it will be possible to resurrect the dead by digital recreation.

In their science fiction novel The Light of Other Days, Sir Arthur Clarke and Stephen Baxter imagine a future civilization resurrecting the dead of past ages by reaching into the past, through micro wormholes and with nanorobots, to download full snapshots of brain states and memories.

Both the Church of Perpetual Life and the Terasem Movement consider themselves transreligions and advocate for the use of technology to indefinitely extend the human lifespan.

Zombies

Main article: Zombie

A zombie (Haitian French: zombi, Haitian Creole: zonbi) is a fictional undead being created through the reanimation of a human corpse. Zombies are most commonly found in horror and fantasy genre works. The term comes from Haitian folklore, where a zombie is a dead body reanimated through various methods, most commonly magic.

Disappearances (as distinct from resurrection)

See also: Entering heaven alive

As knowledge of different religions has grown, so have claims of bodily disappearance of some religious and mythological figures. In ancient Greek religion, this was a way the gods made some physically immortal, including such figures as Cleitus, Ganymede, Menelaus, and Tithonus. After his death, Cycnus was changed into a swan and vanished. In his chapter on Romulus from Parallel Lives, Plutarch criticises the continuous belief in such disappearances, referring to the allegedly miraculous disappearance of the historical figures Romulus, Cleomedes of Astypalaea, and Croesus. In ancient times, Greek and Roman pagan similarities were explained by the early Christian writers, such as Justin Martyr, as the work of demons, with the intention of leading Christians astray.

In the Buddhist Epic of King Gesar, also spelled as Geser or Kesar, at the end, chants on a mountain top and his clothes fall empty to the ground. The body of the first Guru of the Sikhs, Guru Nanak Dev, is said to have disappeared and flowers left in place of his dead body.

Lord Raglan's Hero Pattern lists many religious figures whose bodies disappear, or have more than one sepulchre. B. Traven, author of The Treasure of the Sierra Madre, wrote that the Inca Virococha arrived at Cusco (in modern-day Peru) and the Pacific seacoast where he walked across the water and vanished. It has been thought that teachings regarding the purity and incorruptibility of the hero's human body are linked to this phenomenon. Perhaps, this is also to deter the practice of disturbing and collecting the hero's remains. They are safely protected if they have disappeared.

The first such case mentioned in the Bible is that of Enoch (son of Jared, great-grandfather of Noah, and father of Methuselah). Enoch is said to have lived a life where he "walked with God", after which "he was not, for God took him" (Genesis 5:1–18). In Deuteronomy (34:6) Moses is secretly buried. Elijah vanishes in a whirlwind 2 Kings (2:11). In the Synoptic Gospels, after hundreds of years these two earlier Biblical heroes suddenly reappear, and are reportedly seen walking with Jesus, then again vanish.^[65] In the Gospel of Luke, the last time Jesus is seen (24:51) he leaves his disciples by ascending into the sky. This ascension of Jesus was a “disappearance” of sorts as recorded by Luke but was after the physical resurrection occurring several days before.

Supramolecular polymer

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Supramolecular_polymer 

The term "polymer" refers to large molecules whose structure is composed of multiple repeating units and the prefix "supra" meaning "beyond the limits of". Supramolecular polymers are a new category of polymers that can potentially be used for material applications beyond the limits of conventional polymers. By definition, supramolecular polymers are polymeric arrays of monomeric units that are connected by reversible and highly directional secondary interactions–that is, non-covalent bonds. These non-covalent interactions include van der Waals interactions, hydrogen bonding, Coulomb or ionic interactions, π-π stacking, metal coordination, halogen bonding, chalcogen bonding, and host–guest interaction. The direction and strength of the interactions are precisely tuned so that the array of molecules behaves as a polymer (that is, it behaves in a way that can be described by the theories of polymer physics) in dilute and concentrated solution, as well as in the bulk.

In conventional polymers, monomeric units are linked by strong covalent bonds and have excellent properties as materials; however, high temperatures and pressures are typically required for processing due to polymer entanglement in the highly viscous melt. Supramolecular polymers combine good material properties with low-viscosity melts that are easy to handle. Additionally, some supramolecular polymers have unique characteristics, such as the ability to self-heal fractures. Although covalent polymers can be recycled, their strong covalent bonds never disintegrate, and go on to negatively affect the environment as plastic wastes. Thus, supramolecular polymers are increasingly getting attention because of their potential for the design of responsive, adaptive, self-healing, and environmentally friendly materials.

History

Monomeric motifs and types of interactions used for the preparation of supramolecular polymers

Modern concept of polymers credited to Hermann Staudinger, who substantiated the existence of covalently linked ultralong molecules in 1920, which he called as macromolecules. The preamble of the field of supramolecular polymers can be considered dye-aggregates and host-guest complexes. In early 19thcentury, scientists working in the field of pigments have noticed certain dye aggregates that may formed via "a special kind of polymerization", however no theory was proposed. After the establishment of the field of supramolecular chemistry and after the award of the Nobel Prize in chemistry in 1987 to Donald J. Cram, Jean-Marie Lehn, and Charles J. Pedersen, chemists started to design and study larger assembled structures from small molecules. In 1988, Takuzo Aida, a Japanese polymer chemist, reported the concept of cofacial assembly wherein the amphiphilic porphyrin monomers are connected via van der Waals interaction forming one-dimensional architectures in solution, which can be considered as a prototype of supramolecular polymers. In the same year 1988, James D. Wuest introduced one-dimensional aggregates based on hydrogen bonding interaction in the crystalline state. With a different strategyusing hydrogen bonds, Jean M. J. Fréchet showed in 1989 that mesogenic molecules with carboxylic acid and pyridyl motifs, upon mixing in bulk, heterotropically dimerize to form a stable liquid crystalline structure. In 1990, Jean-Marie Lehn showed that this strategy can be expanded to form a new category of polymers, which he called "liquid crystalline supramolecular polymer" using complementary triple hydrogen bonding motifs in bulk. In 1993, M. Reza Ghadiri reported a nanotubular supramolecular polymer where a b-sheet-forming macrocyclic peptide monomer assembled together via multiple hydrogen bonding between adjacent macrocycles. In 1994, Anselm. C. Griffin showed an amorphous supramolecular material using a single hydrogen bond between a homotropic molecules having carboxylic acid and pyridine termini. The idea to make mechanically strong polymeric materials by 1D supramolecular association of small molecules requires a high association constant between the repeating building blocks. In 1997, E.W. "Bert" Meijer reported a telechelic monomer with ureidopyrimidinone termini as a "self-complementary" quadruple hydrogen bonding motif and demonstrated that the resulting supramolecular polymer in chloroform shows a temperature-dependent viscoelastic property in solution. This is the first demonstration that supramolecular polymers, when sufficiently mechanically robust, are physically entangled in solution.

Formation mechanisms

Monomers undergoing supramolecular polymerization are considered to be in equilibrium with the growing polymers, and thermodynamic factors therefore dominate the system. However, when the constituent monomers are connected via strong and multivalent interactions, a "metastable" kinetic state can dominate the polymerization. An externally supplied energy, in the form of heat in most cases, can transform the "metastable" state into a thermodynamically stable polymer. A clear understanding of multiple pathways exist in supramolecular polymerization is still under debate, however, the concept of "pathway complexity", introduced by E.W. "Bert" Meijer, shed a light on the kinetic behavior of supramolecular polymerization. Thereafter, many dedicated scientists are expanding the scope of "pathway complexity" because it can produce a variety of interesting assembled structures from the same monomeric units. Along this line of kinetically controlled processes, supramolecular polymers having "stimuli-responsive" and "thermally bisignate" characteristics is also possible.

In conventional covalent polymerization, two models based on step-growth and chain-growth mechanisms are operative. Nowadays, a similar subdivision is acceptable for supramolecular polymerization; isodesmic also known as equal-K model (step-growth mechanism) and cooperative or nucleation-elongation model (chain-growth mechanism). A third category is seeded supramolecular polymerization, which can be considered as a special case of chain-growth mechanism.

Step-growth polymerization

Schematics of "pathway-complexity" and "chain-growth" mechanisms operative in supramolecular polymerization

Supramolecular equivalent of step-growth mechanism is commonly known as isodesmic or equal-K model (K represents the total binding interaction between two neighboring monomers). In isodesmic supramolecular polymerization, no critical temperature or concentration of monomers is required for the polymerization to occur and the association constant between polymer and monomer is independent of the polymer chain length. Instead, the length of the supramolecular polymer chains rises as the concentration of monomers in the solution increases, or as the temperature decreases. In conventional polycondensation, the association constant is usually large that leads to a high degree of polymerization; however, a byproduct is observed. In isodesmic supramolecular polymerization, due to non-covalent bonding, the association between monomeric units is weak, and the degree of polymerization strongly depends on the strength of interaction, i.e. multivalent interaction between monomeric units. For instance, supramolecular polymers consisting of bifunctional monomers having single hydrogen bonding donor/acceptor at their termini usually end up with low degree of polymerization, however those with quadrupole hydrogen bonding, as in the case of ureidopyrimidinone motifs, result in a high degree of polymerization. In ureidopyrimidinone-based supramolecular polymer, the experimentally observed molecular weight at semi-dilute concentrations is in the order of 10⁶ Dalton and the molecular weight of the polymer can be controlled by adding mono-functional chain-cappers.

Chain-growth polymerization

Conventional chain-growth polymerization involves at least two phases; initiation and propagation, while and in some cases termination and chain transfer phases also occur. Chain-growth supramolecular polymerization in a broad sense involves two distinct phases; a less favored nucleation and a favored propagation. In this mechanism, after the formation of a nucleus of a certain size, the association constant is increased, and further monomer addition becomes more favored, at which point the polymer growth is initiated. Long polymer chains will form only above a minimum concentration of monomer and below a certain temperature. However, to realize a covalent analogue of chain-growth supramolecular polymerization, a challenging prerequisite is the design of appropriate monomers that can polymerize only by the action of initiators. Recently one example of chain-growth supramolecular polymerization with "living" characteristics is demonstrated. In this case, a bowl-shaped monomer with amide-appended side chains form a kinetically favored intramolecular hydrogen bonding network and does not spontaneously undergo supramolecular polymerization at ambient temperatures. However, an N-methylated version of the monomer serves as an initiator by opening the intramolecular hydrogen bonding network for the supramolecular polymerization, just like ring-opening covalent polymerization. The chain end in this case remains active for further extension of supramolecular polymer and hence chain-growth mechanism allows for the precise control of supramolecular polymer materials.

Seeded polymerization

This is a special category of chain-growth supramolecular polymerization, where the monomer nucleates only in an early stage of polymerization to generate "seeds" and becomes active for polymer chain elongation upon further addition of a new batch of monomer. A secondary nucleation is suppressed in most of the case and thus possible to realize a narrow polydispersity of the resulting supramolecular polymer. In 2007, Ian Manners and Mitchell A. Winnik introduced this concept using a polyferrocenyldimethylsilane–polyisoprene diblock copolymer as the monomer, which assembles into cylindrical micelles. When a fresh feed of the monomer is added to the micellar "seeds" obtained by sonication, the polymerization starts in a living polymerization manner. They named this method as crystallization-driven self-assembly (CDSA) and is applicable to construct micron-scale supramolecular anisotropic structures in 1D–3D. A conceptually different seeded supramolecular polymerization was shown by Kazunori Sugiyasu in a porphyrin-based monomer bearing amide-appended long alkyl chains. At low temperature, this monomer preferentially forms spherical J-aggregates while fibrous H-aggregates at higher temperature. By adding a sonicated mixture of the J-aggregates ("seeds") into a concentrated solution of the J-aggregate particles, long fibers can be prepared via living seeded supramolecular polymerization. Frank Würthner achieved similar seeded supramolecular polymerization of amide functionalized perylene bisimide as monomer. Importantly, the seeded supramolecular polymerization is also applicable to prepare supramolecular block copolymers.

Examples

Hydrogen bonding interaction

Monomers capable of forming single, double, triple or quadruple hydrogen bonding has been utilized for making supramolecular polymers, and increased association of monomers obviously possible when monomers have maximum number of hydrogen bonding donor/acceptor motifs. For instance, ureidopyrimidinone-based monomer with self-complementary quadruple hydrogen bonding termini polymerized in solution, accordingly with the theory of conventional polymers and displayed a distinct viscoelastic nature at ambient temperatures.

π-π stacking

Monomers with aromatic motifs such as bis(merocyanine), oligo(para-phenylenevinylene) (OPV), perylene bisimide (PBI) dye, cyanine dye, corannulene and nano-graphene derivatives have been employed to prepare supramolecular polymers. In some cases, hydrogen bonding side chains appended onto the core aromatic motif help to hold the monomer strongly in the supramolecular polymer. A notable system in this category is a nanotubular supramolecular polymer formed by the supramolecular polymerization of amphiphilic hexa-peri-hexabenzocoronene (HBC) derivatives. Generally, nanotubes are categorized as 1D objects morphologically, however, their walls adopt a 2D geometry and therefore require a different design strategy. HBC amphiphiles in polar solvents solvophobically assemble into a 2D bilayer membrane, which roles up into a helical tape or a nanotubular polymer. Conceptually similar amphiphilic design based on cyanine dye and zinc chlorin dye also polymerize in water resulting in nanotubular supramolecular polymers.

Host-guest interaction

A variety of supramolecular polymers can be synthesized by using monomers with host-guest complementary binding motifs, such as crown ethers/ammonium ions, cucurbiturils/viologens, calixarene/viologens, cyclodextrins/adamantane derivatives, and pillar arene/imidazolium derivatives [30–33]. When the monomers are "heteroditopic", supramolecular copolymers results, provided the monomers does not homopolymerize. Akira Harada was one of the firstwhorecognize the importance of combining polymers and cyclodextrins. Feihe Huang showed an example of supramolecular alternating copolymer from two heteroditopic monomers carrying both crown ether and ammonium ion termini. Takeharo Haino demonstrated an extreme example of sequence control in supramolecular copolymer, where three heteroditopic monomers are arranged in an ABC sequence along the copolymer chain. The design strategy utilizing three distinct binding interactions; ball-and-socket (calix[5]arene/C60), donor-acceptor (bisporphyrin/trinitrofluorenone), and Hamilton's H-bonding interactions is the key to attain a high orthogonality to form an ABC supramolecular terpolymer.

Chirality

Stereochemical information of a chiral monomer can be expressed in a supramolecular polymer. Helical supramolecular polymer with P-and M-conformation are widely seen, especially those composed of disc-shaped monomers. When the monomers are achiral, both P-and M-helices are formed in equal amounts. When the monomers are chiral, typically due to the presence of one or more stereocenters in the side chains, the diastereomeric relationship between P- and M-helices leads to the preference of one conformation over the other. Typical example is a C₃-symmetric disk-shaped chiral monomer that forms helical supramolecular polymers via the "majority rule". A slight excess of one enantiomer of the chiral monomer resulted in a strong bias to either the right-handed or left-handed helical geometry at the supramolecular polymer level. In this case, a characteristic nonlinear dependence of the anisotropic factor, g, on the enantiomeric excess of a chiral monomer can be generally observed. Like in small molecule based chiral system, chirality of a supramolecular polymer also affected by chiral solvents. Some application such as a catalyst for asymmetric synthesis and circular polarized luminescence are observed in chiral supramolecular polymers too.

Copolymers

A copolymer is formed from more than one monomeric species. Advanced polymerization techniques have been established for the preparation of covalent copolymers, however supramolecular copolymers are still in its infancy and is slowly progressing. In recent years, all plausible category of supramolecular copolymers such as random, alternating, block, blocky, or periodic has been demonstrated in a broad sense.

Properties

In the last 30 years, the field of supramolecular polymers has grown into a very important new branch of polymer science. It has attracted numerous research activities in academia and industrial laboratories worldwide. New dynamic materials with a variety of anomalous properties are added to the field of materials engineering. Many applications in sustainability (easy processing and recycling), electronics, and medicine as well as cosmetics have become available.

Reversibility and dynamicity

One of the important properties of supramolecular polymers is their reversible interactions in the monomeric array. When the interaction between monomers are sufficiently strong, interesting material properties can be expected. The thermodynamic stability of a supramolecular polymer can be described using the association constant, K_ass. When K_ass ≤ 10⁴M⁻¹, the polymeric aggregates are typically small in size and do not show any interesting properties and when K_ass≥ 10¹⁰ M⁻¹, the supramolecular polymer behaves just like covalent polymers due to the lack of dynamics. So, an optimum K_ass = 10⁴–10¹⁰M⁻¹need to be attained for producing functional supramolecular polymers. The dynamics and stability of the supramolecular polymers often affect by the influence of additives (e.g. co-solvent or chain-capper). When a good solvent, for instance chloroform, is added to a supramolecular polymer in a poor solvent, for instance heptane, the polymer disassembles. However, in some cases, cosolvents contribute the stabilization/destabilization of supramolecular polymer. For instance, supramolecular polymerization of a hydrogen bonding porphyrin-based monomer in a hydrocarbon solvent containing a minute amount of a hydrogen bond scavenging alcohol shows distinct pathways, i.e. polymerization favored both by cooling as well as heating, and is known as "thermally bisignate supramolecular polymerization". In another example, minute amounts of molecularly dissolved water molecules in apolar solvents, like methylcyclohexane, become part of the supramolecular polymer at lower temperatures, due to specific hydrogen bonding interaction between the monomer and water.

Self-healing

One of the fascinating properties of supramolecular polymers is its ability to self-heal upon fracture occur. A supramolecular rubber based on vitrimers, introduced by Ludwik Leibler, can self-heal simply by pressing the two broken edges of the material together. In this case, fractures occur when hydrogen bonds between monomers in the material are broken; bringing the edges of the fracture together allows the hydrogen bonds to re-form, sealing up the gap. Impressively, the dynamic behavior of the hydrogen bonds does not compromise the properties of the material. High mechanical strength of a material and self-healing ability is generally mutually exclusive. Thus, a glassy material that can self-heal at room temperature remained a challenge until recently. In an elegant design, Takuzo Aida introduced an innovative polymer glass composed of a supramolecularly polymerized oligomeric ether thiourea, which is mechanically robust (e= 1.4 GPa) but can self-heal, even at room temperature, just by a compression at the fractured surfaces. The invention of self-healable polymer glass updated the preconception that only soft rubbery materials can heal.

Examples of hydrogen-bonding based self-healing 'supramolecular rubber' (a) and 'polymer glass' (b).

Another strategy uses a bivalent poly(isobutylene)s (PIBs) with barbituric acid functionalized at head and tail. Multiple hydrogen bonding existed between the carbonyl group and amide group of barbituric acid enable it to form a supramolecular network. In this case, the snipped small PIBs-based disks can recover itself from mechanical damage after several-hour contact at room temperature.

Covalent polymers containing coordination complexes also have studied for making self-healing materials. Taking advantage of coordination interactions between catechol and ferric ions, researchers developed pH-controlled self-healing supramolecular polymers. The formation of mono-, bis- and triscatehchol-Fe³⁺ complexes can be manipulated by pH, of which the bis- and triscatehchol-Fe³⁺ complexes show elastic moduli as well as self-healing capacity. For example, the triscatehchol-Fe³⁺ can restore its cohesiveness and shape after being torn. Chain-folding polyimide and pyrenyl-end-capped chains give rise to supramolecular networks.

Optoelectronic

To achieve the light-to-charge conversion is the prerequisite step in artificial photosynthesis systems. By incorporating electron donors and electron acceptors into the supramolecular polymers, a number of artificial systems, including photosynthesis system, can be constructed. Owing to the existence of more than one interactions (π-π interaction, hydrogen bonding interaction and the like), electron donor and electron acceptor can be held together in a proper proximity to afford long-lived charge separated states. Then a light-to-charge conversion system with faster photoinduced electron transfer and higher electron-transfer efficiency can be achieved in these artificial polymers.

Biocompatible

It is quite common that biomolecules, such as DNA, protein and the like, come into being through various noncovalent interactions in biological system. Likewise, supramolecular polymers assembles themself via a combination of noncovalent interactions. Such formation manner endows supramolecular polymers with features, being more sensitive to external stimuli and able to render reversibly dynamic changes in structures and functions. By modifying monomeric units of supramolecular polymers with water-soluble pendants, bioactive moieties as well as biomarkers, supramolecular polymers can realize various kinds of functions and applications in biomedical field. At the same time, their reversible and dynamic nature make supramolecular polymers bio-degradable, which surmounts hard-to-degrade issue of covalent polymers and makes supramolecular polymers a promising platform for biomedical applications. Being able to degrade in biological environment lowers potential toxicity of polymers to a great extent and therefore, enhances biocompatibility of supramolecular polymers.

Biomedical applications

With the excellent nature in biodegradation and biocompatibility, supramolecular polymers show great potential in the development of drug delivery, gene transfection and other biomedical applications.

Drug delivery: Multiple cellular stimuli could induce responses in supramolecular polymers. The dynamic molecular skeletons of supramolecular polymers can be depolymerized when exposing to the external stimuli like pH in vivo. On the basis of this property, supramolecular polymers are capable of being a drug carrier. Making use of hydrogen bonding between nucleobases to induce self-assemble into pH-sensitive spherical micelles.

Gene transfection: Effective and low-toxic nonviral cationic vectors are highly desired in the field of gene therapy. On account of the dynamic and stimuli-responsive properties, supramolecular polymers offer a cogent platform to construct vectors for gene transfection. By combining ferrocene dimer with β-cyclodextrin dimer, a redox-control supramolecular polymers system has been proposed as a vector. In COS-7 cells, this supramolecular polymersic vector can release enclosed DNA upon exposing to hydrogen peroxide and achieve gene transfection.

Adjustable mechanical properties

Association and dissociation kinetics for polymer dynamics

1. Basic Principle : Noncovalent interactions between polymer molecules significantly affect the mechanical properties of supramolecular polymers. More interaction between polymers tends to enhance the interaction strength between polymers. The association rate and dissociation rate of interacting groups in polymer molecules determine intermolecular interaction strength. For supramolecular polymers, the dissociation kinetics for dynamic networks plays a critical role in the material design and mechanical properties of the SPNs(supramolecular polymer networks). By changing the dissociation rate of polymer crosslink dynamics, supramolecular polymers have adjustable mechanical properties. With a slow dissociation rate for dynamic networks of supramolecular polymers, glass-like mechanical properties are dominant, on the other hand, rubber-like mechanical properties are dominant for a fast dissociation rate. These properties can be obtained by changing the molecular structure of the crosslink part of the molecule.
2. Experimental examples : One research controlled the molecular design of cucurbit[8]uril, CB[8]. The hydrophobic structure of the second guest of CB-mediated host-guest interaction within its molecular structure can tune the dissociative kinetics of the dynamic crosslinks. To slow the dissociation rate (kd), a stronger enthalpic driving force is needed for the second guest association (ka) to release more of the conformationally restricted water from the CB(8] cavity. In other words, the hydrophobic second guest exhibited the highest Keq and lowest kd values. Therefore, by polymerizing different concentrations of polymer subgroups, different dynamics of the intermolecular network can be designed.For example, mechanical properties like compressive strain can be tuned by this process. Polymerized with different hydrophobic subgroups in CB[B], The compressive strength was found to increase across the series in correlation with a decrease of kd, which could be tuned between 10–100MPa. NVI, is the most hydrophobic subgroup structure of monomer which have two benzene rings, on the other hand, BVI is the least hydrophobic subgroup structure of monomer via control group. Besides, varying concentrations of hydrophobic subgroups in CB[B], polymerized molecules show different compressive properties. Polymers with the highest concentration of hydrophobic subgroups show the highest compressive strain and vice versa.

Biomaterials

Supramolecular polymers with specific, directional, tunable and reversible non-covalent interactions should be advantageous for biomaterials as well as biomedical applications. For instance, the reversible nature of supramolecular polymers can produce biomaterials that can sense and respond to physiological cues, or that mimic the structural and functional aspects of biological signaling. On the basis of their formation mechanisms, supramolecular biomaterials can be broadly classified as: (1) materials prepared from one-dimensional assemblies of molecular stacking motifs as in the case of peptide amphiphiles introduced by Samuel I. Stupp, and (2) materials prepared through chain extension of oligomers or through crosslinking of polymeric precursors by specific supramolecular recognition motifs.

Rationally designed supramolecular polymers-based polymers can simultaneously meet the requirements of aqueous compatibility, bio-degradability, biocompatibility, stimuli-responsiveness and other strict criterion. Consequently, supramolecular polymers can be applied to the biomedical field as a robust system. Other than applications mentioned above, other important and fascinating biomedical applications, like protein delivery, bio-imaging and diagnosis and tissue engineering, are also well developed.

Conceptual expansion

Unconventional monomers

Over the time, methods for supramolecular polymerization has expanded, and the range of its useable monomers has diversified. In addition to plethora of molecular motifs, biomolecules such as DNA, DNA nanostructures and proteins as well as inorganic objects as unconventional monomers has recently been investigated for supramolecular polymerization. In all of these cases, monomers are in much higher size, usually several nanometers, and the non-covalent interactions varies from hydrogen bonding, host-guest and metal coordination. A notable example is Mg^2+-assisted multivalent supramolecular polymerization of ATP-responsive biomolecular machines, chaperonine GroEL, resulting in a highly stable protein nanotube. Importantly, this nanotube shows an ATPase activity and dissociates into short-chain oligomers when treated with ATP because of the opening/closing motions of the constituent GroEL units.

Unconventional media

Supramolecular polymers usually prepared in solution. However anomalous polymeric properties can be expected when these polymers are prepared without a conventional organic or aqueous medium. For instance, liquid crystal media may affect the elementary steps of supramolecular polymerization as demonstrated by Takashi Kato in 1998, in the supramolecular crosslinking polymerization of physical gelators, which form a liquid crystal physical gel. When monomers are designed to be highly affinitive toward the LC media, supramolecular polymerization causes an order-increasing phase transition, resulting in a core-shell columnar LC. Supramolecular polymers can also be prepared in the solid-state, for instance, a nucleobase-appended telechelic oligomer as a monomer, resulted in the formation of 1D fibers upon cooling from its hot melt. As a new class of materials, supramolecular polymers formed at electrode and at the interface also become available.

Labour economics

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Labour_economics 

A "help wanted" sign seeks available workers for jobs.

Labour economics, or labor economics, seeks to understand the functioning and dynamics of the markets for wage labour. Labour is a commodity that is supplied by labourers, usually in exchange for a wage paid by demanding firms. Because these labourers exist as parts of a social, institutional, or political system, labour economics must also account for social, cultural and political variables.

Labour markets or job markets function through the interaction of workers and employers. Labour economics looks at the suppliers of labour services (workers) and the demanders of labour services (employers), and attempts to understand the resulting pattern of wages, employment, and income. These patterns exist because each individual in the market is presumed to make rational choices based on the information that they know regarding wage, desire to provide labour, and desire for leisure. Labour markets are normally geographically bounded, but the rise of the internet has brought about a 'planetary labour market' in some sectors.

Labour is a measure of the work done by human beings. It is conventionally contrasted with other factors of production, such as land and capital. Some theories focus on human capital, or entrepreneurship, (which refers to the skills that workers possess and not necessarily the actual work that they produce). Labour is unique to study because it is a special type of good that cannot be separated from the owner (i.e. the work cannot be separated from the person who does it). A labour market is also different from other markets in that workers are the suppliers and firms are the demanders.

Macro and micro analysis of labour markets

There are two sides to labour economics. Labour economics can generally be seen as the application of microeconomic or macroeconomic techniques to the labour market. Microeconomic techniques study the role of individuals and individual firms in the labour market. Macroeconomic techniques look at the interrelations between the labour market, the goods market, the money market, and the foreign trade market. It looks at how these interactions influence macro variables such as employment levels, participation rates, aggregate income and gross domestic product.

Macroeconomics of labour markets

Job advertisement board in Shenzhen

The labour market in macroeconomic theory shows that the supply of labour exceeds demand, which has been proven by salary growth that lags productivity growth. When labour supply exceeds demand, salary faces downward pressure due to an employer's ability to pick from a labour pool that exceeds the jobs pool. However, if the demand for labour is larger than the supply, salary increases, as employee have more bargaining power while employers have to compete for scarce labour.

The Labour force (LF) is defined as the number of people of working age, who are either employed or actively looking for work (unemployed). The labour force participation rate (LFPR) is the number of people in the labour force divided by the size of the adult civilian noninstitutional population (or by the population of working age that is not institutionalized), LFPR = LF/Population.

The non-labour force includes those who are not looking for work, those who are institutionalized (such as in prisons or psychiatric wards), stay-at-home spouses, children not of working age, and those serving in the military. The unemployment level is defined as the labour force minus the number of people currently employed. The unemployment rate is defined as the level of unemployment divided by the labour force. The employment rate is defined as the number of people currently employed divided by the adult population (or by the population of working age). In these statistics, self-employed people are counted as employed.

The labour market has the ability to create a higher derivative efficiency of labour, especially on a national and international level, compared to simpler forms of labour distribution, leading to a higher financial GDP growth and output. An efficient labor market is important for the private sector as it drives up derivative income through the reduction of relative costs of labour. This presupposes that division of labour is used as a method to attain cost efficiency.

Variables like employment level, unemployment level, labour force, and unfilled vacancies are called stock variables because they measure a quantity at a point in time. They can be contrasted with flow variables which measure a quantity over a duration of time. Changes in the labour force are due to flow variables such as natural population growth, net immigration, new entrants, and retirements. Changes in unemployment depend on inflows (non-employed people starting to look for jobs and employed people who lose their jobs that are looking for new ones) and outflows (people who find new employment and people who stop looking for employment). When looking at the overall macroeconomy, several types of unemployment have been identified, which can be separated into two categories of natural and unnatural unemployment.

Natural Unemployment

• Frictional unemployment – This reflects the fact that it takes time for people to find and settle into new jobs that they feel are appropriate for them and their skill set. Technological advancement often reduces frictional unemployment; for example, internet search engines have reduced the cost and time associated with locating employment or personnel selection.
• Structural unemployment – The number of jobs available in an industry are not sufficient enough to provide jobs to all persons who are interested in working or qualified to work in that industry. This can be due to the changes in industries prevalent in a country or because wages for the industry are too high, causing people to want to supply their labour to that industry.
• Natural rate of unemployment (also known as full employment) – This is the summation of frictional and structural unemployment, that excludes cyclical contributions of unemployment (e.g. recessions) and seasonal unemployment. It is the lowest rate of unemployment that a stable economy can expect to achieve, given that some frictional and structural unemployment is inevitable. Economists do not agree on the level of the natural rate, with estimates ranging from 1% to 5%, or on its meaning – some associate it with "non-accelerating inflation". The estimated rate varies between countries and across time.

Unnatural Unemployment

• Demand deficient unemployment (also known as cyclical unemployment) – In Keynesian economics, any level of unemployment beyond the natural rate is probably due to insufficient goods demand in the overall economy. During a recession, aggregate expenditure is deficient causing the underutilisation of inputs (including labour). Aggregate expenditure (AE) can be increased, according to Keynes, by increasing consumption spending (C), increasing investment spending (I), increasing government spending (G), or increasing the net of exports minus imports (X−M), since AE = C + I + G + (X−M).
• Seasonal unemployment – Unemployment due to seasonal fluctuations of demand for workers across industries, such as in the retail industry after holidays that involve a lot of shopping are over.

Neoclassical microeconomics

Neoclassical economists view the labour market as similar to other markets in that the forces of supply and demand jointly determine the price (in this case the wage rate) and quantity (in this case the number of people employed).

However, the labour market differs from other markets (like the markets for goods or the financial market) in several ways. In particular, the labour market may act as a non-clearing market. While according to neoclassical theory most markets quickly attain a point of equilibrium without excess supply or demand, this may not be true of the labour market: it may have a persistent level of unemployment. Contrasting the labour market to other markets also reveals persistent compensating differentials among similar workers.

Models that assume perfect competition in the labour market, as discussed below, conclude that workers earn their marginal product of labour.

Neoclassical supply

See also: Labour supply

 

The neoclassical model analyzes the trade-off between leisure hours and working hours.

 

Railroad work

Households are suppliers of labour. In microeconomic theory, people are assumed to be rational and seeking to maximize their utility function. In the labour market model, their utility function expresses trade-offs in preference between leisure time and income from time used for labour. However, they are constrained by the hours available to them.

Let w denote the hourly wage, k denote total hours available for labour and leisure, L denote the chosen number of working hours, π denote income from non-labour sources, and A denote leisure hours chosen. The individual's problem is to maximise utility U, which depends on total income available for spending on consumption and also depends on the time spent in leisure, subject to a time constraint, with respect to the choices of labour time and leisure time:

${\displaystyle {\text{maximize}}\quad U(wL+\pi ,A)\quad {\text{subject to}}\quad L+A\leq k.}$

This is shown in the graph below, which illustrates the trade-off between allocating time to leisure activities and allocating it to income-generating activities. The linear constraint indicates that every additional hour of leisure undertaken requires the loss of an hour of labour and thus of the fixed amount of goods that that labour's income could purchase. Individuals must choose how much time to allocate to leisure activities and how much to working. This allocation decision is informed by the indifference curve labelled IC₁. The curve indicates the combinations of leisure and work that will give the individual a specific level of utility. The point where the highest indifference curve is just tangent to the constraint line (point A), illustrates the optimum for this supplier of labour services.

If consumption is measured by the value of income obtained, this diagram can be used to show a variety of interesting effects. This is because the absolute value of the slope of the budget constraint is the wage rate. The point of optimisation (point A) reflects the equivalency between the wage rate and the marginal rate of substitution of leisure for income (the absolute value of the slope of the indifference curve). Because the marginal rate of substitution of leisure for income is also the ratio of the marginal utility of leisure (MU^L) to the marginal utility of income (MU^Y), one can conclude:

${\displaystyle {{MU^{L}} \over {MU^{Y}}}={{dY} \over {dL}},}$

where Y is total income and the right side is the wage rate.

Effects of a wage increase

If the wage rate increases, this individual's constraint line pivots up from X,Y₁ to X,Y₂. He/she can now purchase more goods and services. His/her utility will increase from point A on IC₁ to point B on IC₂. To understand what effect this might have on the decision of how many hours to work, one must look at the income effect and substitution effect.

The wage increase shown in the previous diagram can be decomposed into two separate effects. The pure income effect is shown as the movement from point A to point C in the next diagram. Consumption increases from Y_A to Y_C and – since the diagram assumes that leisure is a normal good – leisure time increases from X_A to X_C. (Employment time decreases by the same amount as leisure increases.)

The Income and Substitution effects of a wage increase

But that is only part of the picture. As the wage rate rises, the worker will substitute away from leisure and into the provision of labour—that is, will work more hours to take advantage of the higher wage rate, or in other words substitute away from leisure because of its higher opportunity cost. This substitution effect is represented by the shift from point C to point B. The net impact of these two effects is shown by the shift from point A to point B. The relative magnitude of the two effects depends on the circumstances. In some cases, such as the one shown, the substitution effect is greater than the income effect (in which case more time will be allocated to working), but in other cases, the income effect will be greater than the substitution effect (in which case less time is allocated to working). The intuition behind this latter case is that the individual decides that the higher earnings on the previous amount of labour can be "spent" by purchasing more leisure.

The Labour Supply curve

If the substitution effect is greater than the income effect, an individual's supply of labour services will increase as the wage rate rises, which is represented by a positive slope in the labour supply curve (as at point E in the adjacent diagram, which exhibits a positive wage elasticity). This positive relationship is increasing until point F, beyond which the income effect dominates the substitution effect and the individual starts to reduce the number of labour hours he supplies (point G) as wage increases; in other words, the wage elasticity is now negative.

The direction of the slope may change more than once for some individuals, and the labour supply curve is different for different individuals.

Other variables that affect the labour supply decision, and can be readily incorporated into the model, include taxation, welfare, work environment, and income as a signal of ability or social contribution.

Neoclassical demand

See also: Labour demand

A firm's labour demand is based on its marginal physical product of labour (MPP_L). This is defined as the additional output (or physical product) that results from an increase of one unit of labour (or from an infinitesimal increase in labour). (See also Production theory basics.)

Labour demand is a derived demand; that is, hiring labour is not desired for its own sake but rather because it aids in producing output, which contributes to an employer's revenue and hence profits. The demand for an additional amount of labour depends on the Marginal Revenue Product (MRP) and the marginal cost (MC) of the worker. With a perfectly competitive goods market, the MRP is calculated by multiplying the price of the end product or service by the Marginal Physical Product of the worker. If the MRP is greater than a firm's Marginal Cost, then the firm will employ the worker since doing so will increase profit. The firm only employs however up to the point where MRP=MC, and not beyond, in neoclassical economic theory.

The MRP of the worker is affected by other inputs to production with which the worker can work (e.g. machinery), often aggregated under the term "capital". It is typical in economic models for greater availability of capital for a firm to increase the MRP of the worker, all else equal. Education and training are counted as "human capital". Since the amount of physical capital affects MRP, and since financial capital flows can affect the amount of physical capital available, MRP and thus wages can be affected by financial capital flows within and between countries, and the degree of capital mobility within and between countries.

According to neoclassical theory, over the relevant range of outputs, the marginal physical product of labour is declining (law of diminishing returns). That is, as more and more units of labour are employed, their additional output begins to decline.

Additionally, although the MRP is a good way of expressing an employer's demand, other factors such as social group formation can the demand, as well as the labour supply. This constantly restructures exactly what a labour market is, and leads way to cause problems for theories of inflation.

Equilibrium

A firm's labour demand in the short run (D) and a horizontal supply curve (S)

The marginal revenue product of labour can be used as the demand for labour curve for this firm in the short run. In competitive markets, a firm faces a perfectly elastic supply of labour which corresponds with the wage rate and the marginal resource cost of labour (W = S_L = MFC_L). In imperfect markets, the diagram would have to be adjusted because MFC_L would then be equal to the wage rate divided by marginal costs. Because optimum resource allocation requires that marginal factor costs equal marginal revenue product, this firm would demand L units of labour as shown in the diagram.

The demand for labour of this firm can be summed with the demand for labour of all other firms in the economy to obtain the aggregate demand for labour. Likewise, the supply curves of all the individual workers (mentioned above) can be summed to obtain the aggregate supply of labour. These supply and demand curves can be analysed in the same way as any other industry demand and supply curves to determine equilibrium wage and employment levels.

Wage differences exist, particularly in mixed and fully/partly flexible labour markets. For example, the wages of a doctor and a port cleaner, both employed by the NHS, differ greatly. There are various factors concerning this phenomenon. This includes the MRP of the worker. A doctor's MRP is far greater than that of the port cleaner. In addition, the barriers to becoming a doctor are far greater than that of becoming a port cleaner. To become a doctor takes a lot of education and training which is costly, and only those who excel in academia can succeed in becoming doctors. The port cleaner, however, requires relatively less training. The supply of doctors is therefore significantly less elastic than that of port cleaners. Demand is also inelastic as there is a high demand for doctors and medical care is a necessity, so the NHS will pay higher wage rates to attract the profession.

Monopsony

Main article: Monopsony

Some labour markets have a single employer and thus do not satisfy the perfect competition assumption of the neoclassical model above. The model of a monopsonistic labour market gives a lower quantity of employment and a lower equilibrium wage rate than does the competitive model.

Asymmetric information

An advertisement for labour from Sabah and Sarawak, seen in Jalan Petaling, Kuala Lumpur

In many real-life situations, the assumption of perfect information is unrealistic. An employer does not necessarily know how hard workers are working or how productive they are. This provides an incentive for workers to shirk from providing their full effort, called moral hazard. Since it is difficult for the employer to identify the hard-working and the shirking employees, there is no incentive to work hard and productivity falls overall, leading to the hiring of more workers and a lower unemployment rate.

One solution that is used to avoid a moral hazard is stock options that grant employees the chance to benefit directly from a firm's success. However, this solution has attracted criticism as executives with large stock-option packages have been suspected of acting to over-inflate share values to the detriment of the long-run welfare of the firm. Another solution, foreshadowed by the rise of temporary workers in Japan and the firing of many of these workers in response to the financial crisis of 2008, is more flexible job- contracts and -terms that encourage employees to work less than full-time by partially compensating for the loss of hours, relying on workers to adapt their working time in response to job requirements and economic conditions instead of the employer trying to determine how much work is needed to complete a given task and overestimating.

Another aspect of uncertainty results from the firm's imperfect knowledge about worker ability. If a firm is unsure about a worker's ability, it pays a wage assuming that the worker's ability is the average of similar workers. This wage under compensates high-ability workers which may drive them away from the labour market as well as at the same time attracting low-ability workers. Such a phenomenon, called adverse selection, can sometimes lead to market collapse.

One way to combat adverse selection, firms will try to use signalling, pioneered by Michael Spence, whereby employers could use various characteristics of applicants differentiate between high-ability or low-ability workers. One common signal used is education, whereby employers assume that high-ability workers will have higher levels of education. Employers can then compensate high-ability workers with higher wages. However, signalling does not always work, and it may appear to an external observer that education has raised the marginal product of labour, without this necessarily being true.

Search models

Main articles: Search theory and Matching theory (macroeconomics)

One of the major research achievements of the 1990–2010 period was the development of a framework with dynamic search, matching, and bargaining.

Personnel economics: hiring and incentives

At the micro level, one sub-discipline eliciting increased attention in recent decades is analysis of internal labour markets, that is, within firms (or other organisations), studied in personnel economics from the perspective of personnel management. By contrast, external labour markets "imply that workers move somewhat fluidly between firms and wages are determined by some aggregate process where firms do not have significant discretion over wage setting." The focus is on "how firms establish, maintain, and end employment relationships and on how firms provide incentives to employees," including models and empirical work on incentive systems and as constrained by economic efficiency and risk/incentive tradeoffs relating to personnel compensation.

Discrimination and inequality

Inequality and discrimination in the workplace can have many effects on workers.

In the context of labour economics, inequality is usually referring to the unequal distribution of earning between households. Inequality is commonly measured by economists using the Gini coefficient. This coefficient does not have a concrete meaning but is more used as a way to compare inequality across regions. The higher the Gini coefficient is calculated to be the larger inequality exists in a region. Over time, inequality has, on average, been increasing. This is due to numerous factors including labour supply and demand shifts as well as institutional changes in the labour market. On the shifts in labour supply and demand, factors include demand for skilled workers going up more than the supply of skilled workers and relative to unskilled workers as well as technological changes that increase productivity; all of these things cause wages to go up for skilled labour while unskilled worker wages stay the same or decline. As for the institutional changes, a decrease in union power and a declining real minimum wage, which both reduce unskilled workers wages, and tax cuts for the wealthy all increase the inequality gap between groups of earners.

As for discrimination, it is the difference in pay that can be attributed to the demographic differences between people, such as gender, race, ethnicity, religion, sexual orientation, etc, even though these factors do not affect the productivity of the worker. Many regions and countries have enacted government policies to combat discrimination, including discrimination in the workplace. Discrimination can be modelled and measured in numerous ways. The Oaxaca decomposition is a common method used to calculate the amount of discrimination that exists when wages differ between groups of people. This decomposition aims to calculate the difference in wages that occurs because of differences in skills versus the returns to those skills. A way of modelling discrimination in the workplace when dealing with wages are Gary Becker's taste models. Using taste models, employer discrimination can be thought of as the employer not hiring the minority worker because of their perceived cost of hiring that worker is higher than that of the cost of hiring a non-minority worker, which causes less hiring of the minority. Another taste model is for employee discrimination, which does not cause a decline in the hiring of minorities, but instead causes a more segregated workforce because the prejudiced worker feels that they should be paid more to work next to the worker they are prejudiced against or that they are not paid an equal amount as the worker they are prejudiced against. One more taste model involves customer discrimination, whereby the employers themselves are not prejudiced but believe that their customers might be, so therefore the employer is less likely to hire the minority worker if they are going to interact with customers that are prejudiced. There are many other taste models other than these that Gary Becker has made to explain discrimination that causes differences in hiring in wages in the labour market.

Criticisms

Many sociologists, political economists, and heterodox economists claim that labour economics tends to lose sight of the complexity of individual employment decisions. These decisions, particularly on the supply side, are often loaded with considerable emotional baggage and a purely numerical analysis can miss important dimensions of the process, such as social benefits of a high income or wage rate regardless of the marginal utility from increased consumption or specific economic goals.

From the perspective of mainstream economics, neoclassical models are not meant to serve as a full description of the psychological and subjective factors that go into a given individual's employment relations, but as a useful approximation of human behaviour in the aggregate, which can be fleshed out further by the use of concepts such as information asymmetry, transaction costs, contract theory etc.

Also missing from most labour market analyses is the role of unpaid labour such as unpaid internships where workers with little or no experience are allowed to work a job without pay so that they can gain experience in a particular profession. Even though this type of labour is unpaid it can nevertheless play an important part in society if not abused by employers. The most dramatic example is child raising. However, over the past 25 years an increasing literature, usually designated as the economics of the family, has sought to study within household decision making, including joint labour supply, fertility, child-raising, as well as other areas of what is generally referred to as home production.

Wage slavery

Main article: Wage slavery

Further information: Economic exploitation and Contemporary slavery

The labour market, as institutionalised under today's market economic systems, has been criticised, especially by both mainstream socialists and anarcho-syndicalists, who utilise the term wage slavery as a pejorative for wage labour. Socialists draw parallels between the trade of labour as a commodity and slavery. Cicero is also known to have suggested such parallels.

According to Noam Chomsky, analysis of the psychological implications of wage slavery goes back to the Enlightenment era. In his 1791 book On the Limits of State Action, classical liberal thinker Wilhelm von Humboldt explained how "whatever does not spring from a man's free choice, or is only the result of instruction and guidance, does not enter into his very nature; he does not perform it with truly human energies, but merely with mechanical exactness" and so when the labourer works under external control, "we may admire what he does, but we despise what he is." Both the Milgram and Stanford experiments have been found useful in the psychological study of wage-based workplace relations.

The American philosopher John Dewey posited that until "industrial feudalism" is replaced by "industrial democracy", politics will be "the shadow cast on society by big business". Thomas Ferguson has postulated in his investment theory of party competition that the undemocratic nature of economic institutions under capitalism causes elections to become occasions when blocs of investors coalesce and compete to control the state.

As per anthropologist David Graeber, the earliest wage labour contracts we know about were in fact contracts for the rental of chattel slaves (usually the owner would receive a share of the money, and the slave, another, with which to maintain his or her living expenses.) Such arrangements, according to Graeber, were quite common in New World slavery as well, whether in the United States or Brazil. C. L. R. James argued that most of the techniques of human organisation employed on factory workers during the industrial revolution were first developed on slave plantations.

Additionally, Marxists posit that labour-as-commodity, which is how they regard wage labour, provides an absolutely fundamental point of attack against capitalism. "It can be persuasively argued", noted one concerned philosopher, "that the conception of the worker's labour as a commodity confirms Marx's stigmatisation of the wage system of private capitalism as 'wage-slavery;' that is, as an instrument of the capitalist's for reducing the worker's condition to that of a slave, if not below it."