In physics, a state of matter is one of the distinct forms in which matter can exist. Four states of matter are observable in everyday life: solid, liquid, gas, and plasma. Many other states are known to exist, such as glass or liquid crystal, and some only exist under extreme conditions, such as Bose–Einstein condensates,  neutron-degenerate matter, and quark-gluon plasma, which only occur, respectively, in situations of extreme cold, extreme density, and extremely high-energy. Some other states are believed to be possible but remain theoretical for now.  For a complete list of all exotic states of matter, see the list of states of matter.
Historically, the distinction is made based on qualitative differences in properties. Matter in the solid state maintains a fixed volume and shape, with component particles (atoms, molecules or ions) close together and fixed into place. Matter in the liquid state maintains a fixed volume, but has a variable shape that adapts to fit its container. Its particles are still close together but move freely. Matter in the gaseous state has both variable volume and shape, adapting both to fit its container. Its particles are neither close together nor fixed in place. Matter in the plasma state has variable volume and shape, but as well as neutral atoms, it contains a significant number of ions and electrons, both of which can move around freely.
The term phase is sometimes used as a synonym for state of matter, but a system can contain several immiscible phases of the same state of matter.
The four fundamental states
Solid

In a solid, constituent particles (ions, atoms, or molecules) are closely packed together. The forces between particles are so strong that the particles cannot move freely but can only vibrate. As a result, a solid has a stable, definite shape, and a definite volume. Solids can only change their shape by force, as when broken or cut.
In crystalline solids, the particles (atoms, molecules, or ions) are packed in a regularly ordered, repeating pattern. There are various different crystal structures, and the same substance can have more than one structure (or solid phase). For example, iron has a body-centred cubic structure at temperatures below 912°C, and a face-centred cubic structure between 912 and 1394°C. Ice has fifteen known crystal structures, or fifteen solid phases, which exist at various temperatures and pressures.[1]
Glasses and other non-crystalline, amorphous solids without long-range order are not thermal equilibrium ground states; therefore they are described below as nonclassical states of matter.
Solids can be transformed into liquids by melting, and liquids can be transformed into solids by freezing. Solids can also change directly into gases through the process of sublimation, and gases can likewise change directly into solids through deposition.
Liquid

A liquid is a nearly incompressible fluid that conforms to the shape of its container but retains a (nearly) constant volume independent of pressure. The volume is definite if the temperature and pressure are constant. When a solid is heated above its melting point, it becomes liquid, given that the pressure is higher than the triple point of the substance. Intermolecular (or interatomic or interionic) forces are still important, but the molecules have enough energy to move relative to each other and the structure is mobile. This means that the shape of a liquid is not definite but is determined by its container. The volume is usually greater than that of the corresponding solid, the best known exception being water, H2O. The highest temperature at which a given liquid can exist is its critical temperature.[2]
Gas

A gas is a compressible fluid. Not only will a gas conform to the shape of its container but it will also expand to fill the container.
In a gas, the molecules have enough kinetic energy so that the effect of intermolecular forces is small (or zero for an ideal gas), and the typical distance between neighboring molecules is much greater than the molecular size. A gas has no definite shape or volume, but occupies the entire container in which it is confined. A liquid may be converted to a gas by heating at constant pressure to the boiling point, or else by reducing the pressure at constant temperature.
At temperatures below its critical temperature, a gas is also called a vapor, and can be liquefied by compression alone without cooling. A vapor can exist in equilibrium with a liquid (or solid), in which case the gas pressure equals the vapor pressure of the liquid (or solid).
A supercritical fluid (SCF) is a gas whose temperature and pressure are above the critical temperature and critical pressure respectively. In this state, the distinction between liquid and gas disappears. A supercritical fluid has the physical properties of a gas, but its high density confers solvent properties in some cases, which leads to useful applications. For example, supercritical carbon dioxide is used to extract caffeine in the manufacture of decaffeinated coffee.[3]
Plasma

Like a gas, plasma does not have definite shape or volume. Unlike gases, plasmas are electrically conductive, produce magnetic fields and electric currents, and respond strongly to electromagnetic forces. Positively charged nuclei swim in a "sea" of freely-moving disassociated electrons, similar to the way such charges exist in conductive metal, where this electron "sea"  allows matter in the plasma state to conduct electricity.
A gas is usually converted to a plasma in one of two ways. e.g. Either from a huge voltage difference between two points, or by exposing it to extremely high temperatures. Heating matter to high temperatures causes electrons to leave the atoms, resulting in the presence of free electrons. This creates a so-called partially ionised plasma. At very high temperatures, such as those present in stars, it is assumed that essentially all electrons are "free", and that a very high-energy plasma is essentially bare nuclei swimming in a sea of electrons. This forms the so-called fully ionised plasma.
The plasma state is often misunderstood, and although not freely existing under normal conditions on Earth, it is quite commonly generated by either lightning, electric sparks, fluorescent lights, neon lights or in plasma televisions. The Sun's corona, some types of flame, and stars are all examples of illuminated matter in the plasma state.
Phase transitions

A state of matter is also characterized by phase transitions. A phase transition indicates a change in structure and can be recognized by an abrupt change in properties. A distinct state of matter can be defined as any set of states distinguished from any other set of states by a phase transition. Water can be said to have several distinct solid states.[4] The appearance of superconductivity is associated with a phase transition, so there are superconductive states. Likewise, ferromagnetic states are demarcated by phase transitions and have distinctive properties.
When the change of state occurs in stages the intermediate steps are called mesophases. Such phases have been exploited by the introduction of liquid crystal technology.[5][6]
The state or phase of a given set of matter can change depending on pressure and temperature conditions, transitioning to other phases as these conditions change to favor their existence; for example, solid transitions to liquid with an increase in temperature. Near absolute zero, a substance exists as a solid. As heat is added to this substance it melts into a liquid at its melting point, boils into a gas at its boiling point, and if heated high enough would enter a plasma state in which the electrons are so energized that they leave their parent atoms.
Forms of matter that are not composed of molecules and are organized by different forces can also be considered different states of matter. Superfluids (like Fermionic condensate) and the quark–gluon plasma are examples.
In a chemical equation, the state of matter of the chemicals may be shown as (s) for solid, (l) for liquid, and (g) for gas. An aqueous solution is denoted (aq). Matter in the plasma state is seldom used (if at all) in chemical equations, so there is no standard symbol to denote it. In the rare equations that plasma is used in plasma is symbolized as (p).
Non-classical states
Glass

Glass is a non-crystalline or amorphous solid material that exhibits a glass transition when heated towards the liquid state. Glasses can be made of quite different classes of materials: inorganic networks (such as window glass, made of silicate plus additives), metallic alloys, ionic melts, aqueous solutions, molecular liquids, and polymers.
Thermodynamically, a glass is in a metastable state with respect to its crystalline counterpart. The conversion rate, however, is practically zero.
Crystals with some degree of disorder
A plastic crystal is a molecular solid with long-range positional order but with constituent molecules retaining rotational freedom; in an orientational glass this degree of freedom is frozen in a quenched disordered state.
Similarly, in a spin glass magnetic disorder is frozen.
Liquid crystal states

Liquid crystal states have properties intermediate between mobile liquids and ordered solids. Generally, they are able to flow like a liquid, but exhibiting long-range order. For example, the nematic phase consists of long rod-like molecules such as para-azoxyanisole, which is nematic in the temperature range 118–136°C.[7] In this state the molecules flow as in a liquid, but they all point in the same direction (within each domain) and cannot rotate freely. Like a crystalline solid, but unlike a liquid, liquid crystals react to polarized light.
Other types of liquid crystals are described in the main article on these states. Several types have technological importance, for example, in liquid crystal displays.
Magnetically ordered
Transition metal atoms often have magnetic moments due to the net spin of electrons that remain unpaired and do not form chemical bonds. In some solids the magnetic moments on different atoms are ordered and can form a ferromagnet, an antiferromagnet or a ferrimagnet.
In a ferromagnet—for instance, solid iron—the magnetic moment on each atom is aligned in the same direction (within a magnetic domain). If the domains are also aligned, the solid is a permanent magnet, which is magnetic even in the absence of an external magnetic field. The magnetization disappears when the magnet is heated to the Curie point, which for iron is 768°C.
An antiferromagnet has two networks of equal and opposite magnetic moments, which cancel each other out so that the net magnetization is zero. For example, in nickel(II) oxide (NiO), half the nickel atoms have moments aligned in one direction and half in the opposite direction.
In a ferrimagnet, the two networks of magnetic moments are opposite but unequal, so that cancellation is incomplete and there is a non-zero net magnetization. An example is magnetite (Fe3O4), which contains Fe2+ and Fe3+ ions with different magnetic moments.
A quantum spin liquid (QSL) is a disordered state in a system of interacting quantum spins which preserves its disorder to very low temperatures, unlike other disordered states. It is not a liquid in physical sense, but a solid whose magnetic order is inherently disordered. The name "liquid" is due to an analogy with the molecular disorder in a conventional liquid. A QSL is neither a ferromagnet, where magnetic domains are parallel, nor an antiferromagnet, where the magnetic domains are antiparallel; instead, the magnetic domains are randomly oriented. This can be realized e.g. by geometrically frustrated magnetic moments that cannot point uniformly parallel or antiparallel. When cooling down and settling to a state, the domain must "choose" an orientation, but if the possible states are similar in energy, one will be chosen randomly. Consequently, despite strong short-range order, there is no long-range magnetic order.
Microphase-separated

 Copolymers can undergo microphase separation to form a diverse array of periodic nanostructures, as shown in the example of the styrene-butadiene-styrene block copolymer shown at right. Microphase separation can be understood by analogy to the phase separation between oil and water. Due to chemical incompatibility between the blocks, block copolymers undergo a similar phase separation. However, because the blocks are covalently bonded to each other, they cannot demix macroscopically as water and oil can, and so instead the blocks form nanometer-sized structures. Depending on the relative lengths of each block and the overall block topology of the polymer, many morphologies can be obtained, each its own phase of matter.
Ionic liquids also display microphase separation. The anion and cation are not necessarily compatible and would demix otherwise, but electric charge attraction prevents them from separating. Their anions and cations appear to diffuse within compartmentalized layers or micelles instead of freely as in a uniform liquid.[8]
Low-temperature states
Superfluid

Close to absolute zero, some liquids form a second liquid state described as superfluid because it has zero viscosity (or infinite fluidity; i.e., flowing without friction). This was discovered in 1937 for helium, which forms a superfluid below the lambda temperature of 2.17 K. In this state it will attempt to "climb" out of its container.[9] It also has infinite thermal conductivity so that no temperature gradient can form in a superfluid. Placing a superfluid in a spinning container will result in quantized vortices.
These properties are explained by the theory that the common isotope helium-4 forms a Bose–Einstein condensate (see next section) in the superfluid state. More recently, Fermionic condensate superfluids have been formed at even lower temperatures by the rare isotope helium-3 and by lithium-6.[10]
Bose–Einstein condensate

In 1924, Albert Einstein and Satyendra Nath Bose predicted the "Bose–Einstein condensate" (BEC), sometimes referred to as the fifth state of matter. In a BEC, matter stops behaving as independent particles, and collapses into a single quantum state that can be described with a single, uniform wavefunction.
In the gas phase, the Bose–Einstein condensate remained an unverified theoretical prediction for many years. In 1995, the research groups of Eric Cornell and Carl Wieman, of JILA at the University of Colorado at Boulder, produced the first such condensate experimentally. A Bose–Einstein condensate is "colder" than a solid. It may occur when atoms have very similar (or the same) quantum levels, at temperatures very close to absolute zero (−273.15°C).
Fermionic condensate

A fermionic condensate is similar to the Bose–Einstein condensate but composed of fermions. The Pauli exclusion principle prevents fermions from entering the same quantum state, but a pair of fermions can behave as a boson, and multiple such pairs can then enter the same quantum state without restriction.
Rydberg molecule
One of the metastable states of strongly non-ideal plasma is Rydberg matter, which forms upon condensation of excited atoms. These atoms can also turn into ions and electrons if they reach a certain temperature. In April 2009, Nature reported the creation of Rydberg molecules from a Rydberg atom and a ground state atom,[11] confirming that such a state of matter could exist.[12] The experiment was performed using ultracold rubidium atoms.
Quantum Hall state

A quantum Hall state gives rise to quantized Hall voltage measured in the direction perpendicular to the current flow. A quantum spin Hall state is a theoretical phase that may pave the way for the development of electronic devices that dissipate less energy and generate less heat. This is a derivation of the Quantum Hall state of matter.
Photonic matter

Photonic matter is a phenomenon where photons interacting with a gas develop apparent mass, and can interact with each other, even forming photonic "molecules". The source of mass is the gas, which is massive. This is in contrast to photons moving in empty space, which have no rest mass, and cannot interact.
Dropleton

A "quantum fog" of electrons and holes that flow around each other and even ripple like a liquid, rather than existing as discrete pairs.[13]
High-energy states
Degenerate matter

Under extremely high pressure, as in the cores of dead stars, ordinary matter undergoes a transition to a series of exotic states of matter collectively known as degenerate matter, which are supported mainly by quantum mechanical effects. In physics, "degenerate" refers to two states that have the same energy and are thus interchangeable. Degenerate matter is supported by the Pauli exclusion principle, which prevents two fermionic particles from occupying the same quantum state. Unlike regular plasma, degenerate plasma expands little when heated, because there are simply no momentum states left. Consequently, degenerate stars collapse into very high densities. More massive degenerate stars are smaller, because the gravitational force increases, but pressure does not increase proportionally.
Electron-degenerate matter is found inside white dwarf stars. Electrons remain bound to atoms but are able to transfer to adjacent atoms. Neutron-degenerate matter is found in neutron stars. Vast gravitational pressure compresses atoms so strongly that the electrons are forced to combine with protons via inverse beta-decay, resulting in a superdense conglomeration of neutrons. Normally free neutrons outside an atomic nucleus will decay with a half life of just under 15 minutes, but in a neutron star, the decay is overtaken by inverse decay. Cold degenerate matter is also present in planets such as Jupiter and in the even more massive brown dwarfs, which are expected to have a core with metallic hydrogen. Because of the degeneracy, more massive brown dwarfs are not significantly larger. In metals, the electrons can be modeled as a degenerate gas moving in a lattice of non-degenerate positive ions.
Quark matter

In regular cold matter, quarks, fundamental particles of nuclear matter, are confined by the strong force into hadrons that consist of 2–4 quarks, such as protons and neutrons. Quark matter or quantum chromodynanamical (QCD) matter is a group of phases where the strong force is overcome and quarks are deconfined and free to move. Quark matter phases occur at extremely high densities or temperatures, and there are no known ways to produce them in equilibrium in the laboratory; in ordinary conditions, any quark matter formed immediately undergoes radioactive decay.
Strange matter is a type of quark matter that is suspected to exist inside some neutron stars close to the Tolman–Oppenheimer–Volkoff limit (approximately 2–3 solar masses), although there is no direct evidence of its existence. In strange matter, part of the energy available manifests as strange quarks, a heavier analogue of the common down quark. It may be stable at lower energy states once formed, although this is not known.
Quark–gluon plasma is a very high-temperature phase in which quarks become free and able to move independently, rather than being perpetually bound into particles, in a sea of gluons, subatomic particles that transmit the strong force that binds quarks together. This is analogous to the liberation of electrons from atoms in a plasma. This state is briefly attainable in extremely high-energy heavy ion collisions in particle accelerators, and allows scientists to observe the properties of individual quarks, and not just theorize. Quark–gluon plasma was discovered at CERN in 2000. Unlike plasma, which flows like a gas, interactions within QGP are strong and it flows like a liquid.
At high densities but relatively low temperatures, quarks are theorized to form a quark liquid whose nature is presently unknown. It forms a distinct color-flavor locked (CFL) phase at even higher densities. This phase is superconductive for color charge. These phases may occur in neutron stars but they are presently theoretical.
Color-glass condensate

Color-glass condensate is a type of matter theorized to exist in atomic nuclei traveling near the speed of light. According to Einstein's theory of relativity, a high-energy nucleus appears length contracted, or compressed, along its direction of motion. As a result, the gluons inside the nucleus appear to a stationary observer as a "gluonic wall" traveling near the speed of light. At very high energies, the density of the gluons in this wall is seen to increase greatly. Unlike the quark–gluon plasma produced in the collision of such walls, the color-glass condensate describes the walls themselves, and is an intrinsic property of the particles that can only be observed under high-energy conditions such as those at RHIC and possibly at the Large Hadron Collider as well.
Very high energy states
Various theories predict new states of matter at very high energies. An unknown state has created the baryon asymmetry in the universe, but little is known about it. In string theory, a Hagedorn temperature is predicted for superstrings at about 1030 K, where superstrings are copiously produced. At Planck temperature (1032 K), gravity becomes a significant force between individual particles. No current theory can describe these states and they cannot be produced with any foreseeable experiment. However, these states are important in cosmology because the universe may have passed through these states in the Big Bang.
The gravitational singularity predicted by general relativity to exist at the center of a black hole is not a phase of matter; it is not a material object at all (although the mass-energy of matter contributed to its creation) but rather a property of spacetime at a location. It could be argued, of course, that all particles are properties of spacetime at a location,[14] leaving a half-note of controversy on the subject.
Other proposed states
Supersolid

A supersolid is a spatially ordered material (that is, a solid or crystal) with superfluid properties. Similar to a superfluid, a supersolid is able to move without friction but retains a rigid shape. Although a supersolid is a solid, it exhibits so many characteristic properties different from other solids that many argue it is another state of matter.[15]
String-net liquid

In a string-net liquid, atoms have apparently unstable arrangement, like a liquid, but are still consistent in overall pattern, like a solid. When in a normal solid state, the atoms of matter align themselves in a grid pattern, so that the spin of any electron is the opposite of the spin of all electrons touching it. But in a string-net liquid, atoms are arranged in some pattern that requires some electrons to have neighbors with the same spin. This gives rise to curious properties, as well as supporting some unusual proposals about the fundamental conditions of the universe itself.
Superglass

A superglass is a phase of matter characterized, at the same time, by superfluidity and a frozen amorphous structure.
Dark matter

While dark matter is estimated to comprise 83% of the mass of matter in the universe, most of its properties remain a mystery due to the fact that it neither absorbs nor emits electromagnetic radiation, and there are many competing theories regarding what dark matter is actually made of. Thus, while it is hypothesized to exist and comprise the vast majority of matter in the universe, almost all of its properties are unknown and a matter of speculation, because it has only been observed through its gravitational effects.[16][17]
See also
Hidden states of matter
Classical element
Condensed matter physics
Cooling curve
Phase (matter)
Supercooling
Superheating

Notes and references

 Citat: "...They have become the first to create a new type of matter, a gas of atoms that shows high-temperature superfluidity."

 Citat: "...We apparently have observed, for the first time, a solid material with the characteristics of a superfluid...but because all its particles are in the identical quantum state, it remains a solid even though its component particles are continually flowing..."


Stem cells are cells that can differentiate into other types of cells, and can also divide in self-renewal to produce more of the same type of stem cells.
In mammals, there are two broad types of stem cells: embryonic stem cells, which are isolated from the inner cell mass of blastocysts, and adult stem cells, which are found in various tissues. In adult organisms, stem cells and progenitor cells act as a repair system for the body, replenishing adult tissues. In a developing embryo, stem cells can differentiate into all the specialized cells—ectoderm, endoderm and mesoderm (see induced pluripotent stem cells)—but also maintain the normal turnover of regenerative organs, such as blood, skin, or intestinal tissues.
There are three known accessible sources of autologous adult stem cells in humans:
bone marrow, adipose tissue, and blood. Stem cells can also be taken from umbilical cord blood just after birth. Of all stem cell types, autologous harvesting involves the least risk. By definition, autologous cells are obtained from one's own body, just as one may bank his or her own blood for elective surgical procedures.
Adult stem cells are frequently used in various medical therapies (e.g., bone marrow transplantation). Stem cells can now be artificially grown and transformed (differentiated) into specialized cell types with characteristics consistent with cells of various tissues such as muscles or nerves. Embryonic cell lines and autologous embryonic stem cells generated through somatic cell nuclear transfer or dedifferentiation have also been proposed as promising candidates for future therapies.[1] Research into stem cells grew out of findings by Ernest A. McCulloch and James E. Till at the University of Toronto in the 1960s.[2][3]
Properties
The classical definition of a stem cell requires that it possesses two properties:
Self-renewal: the ability to go through numerous cycles of cell division while maintaining the undifferentiated state.
Potency: the capacity to differentiate into specialized cell types. In the strictest sense, this requires stem cells to be either totipotent or pluripotent—to be able to give rise to any mature cell type, although multipotent or unipotent progenitor cells are sometimes referred to as stem cells. Apart from this it is said that stem cell function is regulated in a feed back mechanism.
Self-renewal
Two mechanisms exist to ensure that a stem cell population is maintained:
1. Obligatory asymmetric replication: a stem cell divides into one mother cell that is identical to the original stem cell, and another daughter cell that is differentiated.
When a stem cell self-renews it divides and does not disrupt the undifferentiated state. This self-renewal demands control of cell cycle as well as upkeep of multipotency or pluripotency, which all depends on the stem cell.[4]
2. Stochastic differentiation: when one stem cell develops into two differentiated daughter cells, another stem cell undergoes mitosis and produces two stem cells identical to the original.
Potency meaning

Potency specifies the differentiation potential (the potential to differentiate into different cell types) of the stem cell.[5]
Totipotent (a.k.a. omnipotent) stem cells can differentiate into embryonic and extraembryonic cell types. Such cells can construct a complete, viable organism.[5] These cells are produced from the fusion of an egg and sperm cell. Cells produced by the first few divisions of the fertilized egg are also totipotent.[6]
Pluripotent stem cells are the descendants of totipotent cells and can differentiate into nearly all cells,[5] i.e. cells derived from any of the three germ layers.[7]
Multipotent stem cells can differentiate into a number of cell types, but only those of a closely related family of cells.[5]
Oligopotent stem cells can differentiate into only a few cell types, such as lymphoid or myeloid stem cells.[5]
Unipotent cells can produce only one cell type, their own,[5] but have the property of self-renewal, which distinguishes them from non-stem cells (e.g. progenitor cells, which cannot self-renew).
Identification
In practice, stem cells are identified by whether they can regenerate tissue. For example, the defining test for bone marrow or hematopoietic stem cells (HSCs) is the ability to transplant the cells and save an individual without HSCs. This demonstrates that the cells can produce new blood cells over a long term. It should also be possible to isolate stem cells from the transplanted individual, which can themselves be transplanted into another individual without HSCs, demonstrating that the stem cell was able to self-renew.
Properties of stem cells can be illustrated in vitro, using methods such as clonogenic assays, in which single cells are assessed for their ability to differentiate and self-renew.[8][9] Stem cells can also be isolated by their possession of a distinctive set of cell surface markers. However, in vitro culture conditions can alter the behavior of cells, making it unclear whether the cells shall behave in a similar manner in vivo. There is considerable debate as to whether some proposed adult cell populations are truly stem cells.[10]
Embryonic

Embryonic stem cells (ESCs) are the cells of the inner cell mass of a blastocyst, formed prior to implantation in the uterus.[11] In human embryonic development the blastocyst stage is reached 4–5 days after fertilization, at which time it consists of 50–150 cells. ESCs are pluripotent and give rise during development to all derivatives of the three  germ layers: ectoderm, endoderm and mesoderm. In other words, they can develop into each of the more than 200 cell types of the adult body when given sufficient and necessary stimulation for a specific cell type. They do not contribute to the extraembryonic membranes or to the placenta.
During embryonic development the cells of the inner cell mass continuously divide and become more specialized.  For example, a portion of the ectoderm in the dorsal part of the embryo specializes as 'neurectoderm', which will become the future central nervous system.[12] Later in development, neurulation causes the neurectoderm to form the neural tube.  At the neural tube stage, the anterior portion undergoes encephalization to generate or 'pattern' the basic form of the brain.  At this stage of development, the principal cell type of the CNS is considered a neural stem cell.
The neural stem cells self-renew and at some point transition into radial glial progenitor cells. Early-formed RGPs self-renew by symmetrical division to form a reservoir group of progenitor cells. These cells transition to a neurogenic state and start to divide asymmetrically to produce a large diversity of many different neuron types, each with unique gene expression, morphological, and functional characteristics. The process of generating neurons from radial glial cells is called neurogenesis. The radial glial cell, has a distinctive bipolar morphology with highly elongated processes spanning the thickness of the neural tube wall. It shares some glial characteristics, most notably the expression of glial fibrillary acidic protein (GFAP).[13][14]  The radial glial cell is the primary neural stem cell of the developing vertebrate CNS, and its cell body resides in the ventricular zone, adjacent to the developing ventricular system.  Neural stem cells are committed to the neuronal lineages (neurons, astrocytes, and oligodendrocytes), and thus their potency is restricted.[12]
Nearly all research to date has made use of mouse embryonic stem cells (mES) or human embryonic stem cells (hES) derived from the early inner cell mass.  Both have the essential stem cell characteristics, yet they require very different environments in order to maintain an undifferentiated state. Mouse ES cells are grown on a layer of gelatin as an extracellular matrix (for support) and require the presence of leukemia inhibitory factor (LIF) in serum media. A drug cocktail containing inhibitors to GSK3B and the MAPK/ERK pathway, called 2i, has also been shown to maintain pluripotency in stem cell culture.[15] Human ESCs are grown on a feeder layer of mouse embryonic fibroblasts and require the presence of basic fibroblast growth factor (bFGF or FGF-2).[16] Without optimal culture conditions or genetic manipulation,[17] embryonic stem cells will rapidly differentiate.
A human embryonic stem cell is also defined by the expression of several transcription factors and cell surface proteins. The transcription factors Oct-4, Nanog, and Sox2 form the core regulatory network that ensures the suppression of genes that lead to differentiation and the maintenance of pluripotency.[18]  The cell surface antigens most commonly used to identify hES cells are the glycolipids stage specific embryonic antigen 3 and 4 and the keratan sulfate antigens Tra-1-60 and Tra-1-81. By using human embryonic stem cells to produce specialized cells like nerve cells or heart cells in the lab, scientists can gain access to adult human cells without taking tissue from patients. They can then study these specialized adult cells in detail to try and catch complications of diseases, or to study cells reactions to potentially new drugs.  The molecular definition of a stem cell includes many more proteins and continues to be a topic of research.[19]
There are currently no approved treatments using embryonic stem cells. The first human trial was approved by the US Food and Drug Administration in January 2009.[20] However, the human trial was not initiated until October 13, 2010 in Atlanta for spinal cord injury research. On November 14, 2011 the company conducting the trial (Geron Corporation) announced that it will discontinue further development of its stem cell programs.[21] ES cells, being pluripotent cells, require specific signals for correct differentiation—if injected directly into another body, ES cells will differentiate into many different types of cells, causing a teratoma. Differentiating ES cells into usable cells while avoiding transplant rejection are just a few of the hurdles that embryonic stem cell researchers still face.[22] Due to ethical considerations, many nations currently have moratoria or limitations on either human ES cell research or the production of new human ES cell lines. Because of their combined abilities of unlimited expansion and pluripotency, embryonic stem cells remain a theoretically potential source for regenerative medicine and tissue replacement after injury or disease.[23]

 Mouse embryonic stem cells with fluorescent marker
 Human embryonic stem cell colony on mouse embryonic fibroblast feeder layer

Fetal
The primitive stem cells located in the organs of fetuses are referred to as fetal stem cells.[24]
There are two types of fetal stem cells:
Fetal proper stem cells come from the tissue of the fetus proper, and are generally obtained after an abortion. These stem cells are not immortal but have a high level of division and are multipotent.
Extraembryonic fetal stem cells come from extraembryonic membranes, and are generally not distinguished from adult stem cells. These stem cells are acquired after birth, they are not immortal but have a high level of cell division, and are pluripotent.[25]
Adult

Adult stem cells, also called somatic (from Greek σωματικóς, "of the body") stem cells, are stem cells which maintain and repair the tissue in which they are found.[26] They can be found in children, as well as adults.[27]
There are three known accessible sources of autologous adult stem cells in humans:
Bone marrow, which requires extraction by harvesting, that is, drilling into bone (typically the femur or iliac crest).
Adipose tissue (fat cells), which requires extraction by liposuction.[28]
Blood, which requires extraction through apheresis, wherein blood is drawn from the donor (similar to a blood donation), and passed through a machine that extracts the stem cells and returns other portions of the blood to the donor.
Stem cells can also be taken from umbilical cord blood just after birth. Of all stem cell types, autologous harvesting involves the least risk. By definition, autologous cells are obtained from one's own body, just as one may bank his or her own blood for elective surgical procedures.
Pluripotent adult stem cells are rare and generally small in number, but they can be found in umbilical cord blood and other tissues.[29] Bone marrow is a rich source of adult stem cells,[30] which have been used in treating several conditions including liver cirrhosis,[31] chronic limb ischemia [32] and endstage heart failure.[33] The quantity of bone marrow stem cells declines with age and is greater in males than females during reproductive years.[34] Much adult stem cell research to date has aimed to characterize their potency and self-renewal capabilities.[35]   DNA damage accumulates with age in both stem cells and the cells that comprise the stem cell environment.  This accumulation is considered to be responsible, at least in part, for increasing stem cell dysfunction with aging (see DNA damage theory of aging).[36]
Most adult stem cells are lineage-restricted (multipotent) and are generally referred to by their tissue origin (mesenchymal stem cell, adipose-derived stem cell, endothelial stem cell, dental pulp stem cell, etc.).[37][38] Muse cells (multi-lineage differentiating stress enduring cells) are a recently discovered pluripotent stem cell type found in multiple adult tissues, including adipose, dermal fibroblasts, and bone marrow. While rare, muse cells are identifiable by their expression of SSEA-3, a marker for undifferentiated stem cells, and general mesenchymal stem cells markers such as CD105. When subjected to single cell suspension culture, the cells will generate clusters that are similar to embryoid bodies in morphology as well as gene expression, including canonical pluripotency markers Oct4, Sox2, and Nanog.[39]
Adult stem cell treatments have been successfully used for many years to treat leukemia and related bone/blood cancers through bone marrow transplants.[40]  Adult stem cells are also used in veterinary medicine to treat tendon and ligament injuries in horses.[41]
The use of adult stem cells in research and therapy is not as controversial as the use of embryonic stem cells, because the production of adult stem cells does not require the destruction of an embryo. Additionally, in instances where adult stem cells are obtained from the intended recipient (an autograft), the risk of rejection is essentially non-existent. Consequently, more US government funding is being provided for adult stem cell research.[42]
With the increasing demand of human adult stem cells for both research and clinical purposes (typically 1–5 million cells per kg of body weight are required per treatment) it becomes of utmost importance to bridge the gap between the need to expand the cells in vitro and the capability of harnessing the factors underlying replicative senescence. Adult stem cells are known to have a limited lifespan in vitro and to enter replicative senescence almost undetectably upon starting in vitro culturing.[43]

Amniotic
Multipotent stem cells are also found in amniotic fluid. These stem cells are very active, expand extensively without feeders and are not tumorigenic. Amniotic stem cells are multipotent and can differentiate in cells of adipogenic, osteogenic, myogenic, endothelial, hepatic and also neuronal lines.[44]
Amniotic stem cells are a topic of active research.
Use of stem cells from amniotic fluid overcomes the ethical objections to using human embryos as a source of cells.  Roman Catholic teaching forbids the use of embryonic stem cells in experimentation; accordingly, the Vatican newspaper "Osservatore Romano" called amniotic stem cells "the future of medicine".[45]
It is possible to collect amniotic stem cells for donors or for autologuous use: the first US amniotic stem cells bank [46][47] was opened in 2009 in Medford, MA, by Biocell Center Corporation[48][49][50] and collaborates with various hospitals and universities all over the world.[51]
Induced pluripotent

Adult stem cells have limitations with their potency; unlike embryonic stem cells (ESCs), they are not able to differentiate into cells from all three germ layers. As such, they are deemed multipotent.
However, reprogramming allows for the creation of pluripotent cells, induced pluripotent stem cells (iPSCs), from adult cells. These are not adult stem cells, but adult cells (e.g. epithelial cells) reprogrammed to give rise to cells with pluripotent capabilities. Using genetic reprogramming with protein transcription factors, pluripotent stem cells with ESC-like capabilities have been derived.[52][53][54] The first demonstration of induced pluripotent stem cells was conducted by Shinya Yamanaka and his colleagues at Kyoto University.[55] They used the transcription factors Oct3/4, Sox2, c-Myc, and Klf4 to reprogram mouse fibroblast cells into pluripotent cells.[52][56] Subsequent work used these factors to induce pluripotency in human fibroblast cells.[57] Junying Yu, James Thomson, and their colleagues at the University of Wisconsin–Madison used a different set of factors, Oct4, Sox2, Nanog and Lin28, and carried out their experiments using cells from human foreskin.[52][58] However, they were able to replicate Yamanaka's finding that inducing pluripotency in human cells was possible.
Induced pluripotent stem cells differ from embryonic stem cells. They share many similar properties, such as pluripotency and differentiation potential, the expression of pluripotency genes, epigenetic patterns, embryoid body and teratoma formation, and viable chimera formation,[55][56] but there are many differences within these properties. The chromatin of iPSCs appears to be more "closed" or methylated than that of ESCs.[55][56] Similarly, the gene expression pattern between ESCs and iPSCs, or even iPSCs sourced from different origins.[55] There are thus questions about the "completeness" of reprogramming and the somatic memory of induced pluripotent stem cells. Despite this, inducing adult cells to be pluripotent appears to be viable.
As a result of the success of these experiments, Ian Wilmut, who helped create the first cloned animal Dolly the Sheep, has announced that he will abandon somatic cell nuclear transfer as an avenue of research.[59]
Furthermore, induced pluripotent stem cells provide several therapeutic advantages. Like ESCs, they are pluripotent. They thus have great differentiation potential; theoretically, they could produce any cell within the human body (if reprogramming to pluripotency was "complete").[55] Moreover, unlike ESCs, they potentially could allow doctors to create a pluripotent stem cell line for each individual patient.[60] Frozen blood samples can be used as a valuable source of induced pluripotent stem cells.[61] Patient specific stem cells allow for the screening for side effects before drug treatment, as well as the reduced risk of transplantation rejection.[60] Despite their current limited use therapeutically, iPSCs hold create potential for future use in medical treatment and research.
Lineage

To ensure self-renewal, stem cells undergo two types of cell division (see Stem cell division and differentiation diagram). Symmetric division gives rise to two identical daughter cells both endowed with stem cell properties. Asymmetric division, on the other hand, produces only one stem cell and a progenitor cell with limited self-renewal potential. Progenitors can go through several rounds of cell division before terminally differentiating into a mature cell. It is possible that the molecular distinction between symmetric and asymmetric divisions lies in differential segregation of cell membrane proteins (such as receptors) between the daughter cells.[62]
An alternative theory is that stem cells remain undifferentiated due to environmental cues in their particular niche. Stem cells differentiate when they leave that niche or no longer receive those signals. Studies in Drosophila germarium have identified the signals decapentaplegic and adherens junctions that prevent germarium stem cells from differentiating.[63][64]
Treatments

Stem cell therapy is the use of stem cells to treat or prevent a disease or condition.  Bone marrow transplant is a form of stem cell therapy that has been used for many years without controversy.[65][66]
Advantages
Stem cell treatments may lower symptoms of the disease or condition that is being treated. The lowering of symptoms may allow patients to reduce the drug intake of the disease or condition. Stem cell treatment may also provide knowledge for society to further stem cell understanding and future treatments.[67]
Disadvantages
Stem cell treatments may require immunosuppression because of a requirement for radiation before the transplant to remove the person's previous cells, or because the patient's immune system may target the stem cells. One approach to avoid the second possibility is to use stem cells from the same patient who is being treated.
Pluripotency in certain stem cells could also make it difficult to obtain a specific cell type. It is also difficult to obtain the exact cell type needed, because not all cells in a population differentiate uniformly. Undifferentiated cells can create tissues other than desired types.[68]
Some stem cells form tumors after transplantation;[69] pluripotency is linked to tumor formation especially in embryonic stem cells, fetal proper stem cells, induced pluripotent stem cells. Fetal proper stem cells form tumors despite multipotency.[70]
Research

Some of the fundamental patents covering human embryonic stem cells are owned by the Wisconsin Alumni Research Foundation (WARF) – they are patents 5,843,780, 6,200,806, and 7,029,913 invented by James A. Thomson. WARF does not enforce these patents against academic scientists, but does enforce them against companies.[71]
In 2006, a request for the US Patent and Trademark Office (USPTO) to re-examine the three patents was filed by the Public Patent Foundation on behalf of its client, the non-profit patent-watchdog group Consumer Watchdog (formerly the Foundation for Taxpayer and Consumer Rights).[71]   In the re-examination process, which involves several rounds of discussion between the USPTO and the parties, the USPTO initially agreed with Consumer Watchdog and rejected all the claims in all three patents,[72] however in response, WARF amended the claims of all three patents to make them more narrow, and in 2008 the USPTO found the amended claims in all three patents to be patentable. The decision on one of the patents (7,029,913) was appealable, while the decisions on the other two were not.[73][74] Consumer Watchdog appealed the granting of the '913 patent to the USPTO's Board of Patent Appeals and Interferences (BPAI) which granted the appeal, and in 2010 the BPAI decided that the amended claims of the '913 patent were not patentable.[75]  However, WARF was able to re-open prosecution of the case and did so, amending the claims of the '913 patent again to make them more narrow, and in January 2013 the amended claims were allowed.[76]
In July 2013, Consumer Watchdog announced that it would appeal the decision to allow the claims of the '913 patent to the US Court of Appeals for the Federal Circuit (CAFC), the federal appeals court that hears patent cases.[77]  At a hearing in December 2013, the CAFC raised the question of whether Consumer Watchdog had legal standing to appeal; the case could not proceed until that issue was resolved.[78]
Treatment

Diseases and conditions where stem cell treatment is being investigated include:
Diabetes[79]
Rheumatoid arthritis[79]
Parkinson's disease[79]
Alzheimer's disease[79]
Osteoarthritis[79]
Stroke and traumatic brain injury repair[80]
Learning disability due to congenital disorder [81]
Spinal cord injury repair [82]
Heart infarction [83]
Anti-cancer treatments [84]
Baldness reversal[85]
Replace missing teeth [86]
Repair hearing [87]
Restore vision [88] and repair damage to the cornea[89]
Amyotrophic lateral sclerosis [90]
Crohn's disease [91]
Wound healing [92]
Male infertility due to absence of spermatogonial stem cells. [93] In recent studies, scientist have found a way to solve this problem by reprogramming a cell and turning it into a spermatozoon. Other studies have proven the restoration of spermatogenesis by introducing human iPSC cells in mice testicles. This could mean the end of azoospermia.[94]
Female infertility: oocytes made from embrionic stem cells. Recently, scientists have found the ovarian stem cells, a rare type of cells (0,014%) found in the ovary. It is not clear their existence yet, but the impact it could have are limitless. It could be used as a treatment not only for infertility, but also for premature ovarian insufficiency.[95]
Research is underway to develop various sources for stem cells, and to apply stem cell treatments for neurodegenerative diseases and conditions, diabetes, heart disease, and other conditions.[96] Research is also underway in generating organoids using stem cells, which would allow for further understanding of human development, organogenesis, and modeling of human diseases.[97]
In more recent years, with the ability of scientists to isolate and culture embryonic stem cells, and with scientists' growing ability to create stem cells using somatic cell nuclear transfer and techniques to create induced pluripotent stem cells, controversy has crept in, both related to abortion politics and to human cloning.
Hepatotoxicity and drug-induced liver injury account for a substantial number of failures of new drugs in development and market withdrawal, highlighting the need for screening assays such as stem cell-derived hepatocyte-like cells, that are capable of detecting toxicity early in the drug development process.[98]
See also

Cell bank
Human genome
Meristem
Mesenchymal stem cell
Partial cloning
Plant stem cell
Stem cell controversy
Stem cell marker
Shinya Yamanaka

Library resources about
 Main Page


Part of a series on theMajor League Baseball postseason
Wild Card
ALWCG
NLWCG
Division Series
ALDS
NLDS
League Championship Series
ALCS (Winners list)
NLCS (Winners list)
World Series
List of World Series champions
Commissioner's Trophy
Teams
Appearances
Series
Streaks
Droughtsvt
The World Series is the annual championship series of Major League Baseball (MLB) and concludes the MLB postseason. First played in 1903,[1] the World Series championship is determined through a best-of-seven playoff and is a contest between the champions of baseball's National League (NL) and American League (AL).[2] Often referred to as the "Fall Classic",[3] the modern World Series has been played every year since 1903 with two exceptions: in 1904, when the NL champion New York Giants declined to play the AL champion Boston Americans; and in 1994, when the series was canceled due to the players' strike.[1][2][4][5]
The best-of-seven style has been the format of all World Series except in 1903, 1919, 1920, and 1921, when the winner was determined through a best-of-nine playoff.[1][2] Although the large majority of contests have been played entirely during the month of October, a small number of Series have also had games played during September and November. The Series-winning team is awarded the Commissioner's Trophy.[6] Players, coaches, and others associated with the team are generally given World Series rings to commemorate their victory; however, they have received other items such as pocket watches and medallions in the past.[7] The winning team is traditionally invited to the White House to meet the President of the United States.
A total of 114 Series have been contested, with the NL champion winning 48 and the AL champion winning 66. The New York Yankees of the AL have played in 40 World Series through 2018—winning 27—the most Series appearances and most victories of any Major League Baseball franchise. The Los Angeles Dodgers of the NL have the most losses with 14. The St. Louis Cardinals have represented the NL 19 times, and won 11 championships, second-most among all teams and most among NL clubs.[3] Both the Giants and the Los Angeles Dodgers have appeared in more World Series, with 20 each.
The Seattle Mariners and the Washington Nationals (formerly Montreal Expos) are the only current Major League Baseball franchises to have never appeared in a World Series; the San Diego Padres, Colorado Rockies, Texas Rangers (formerly the 1961–1971 version of the Washington Senators), Tampa Bay Rays, and Milwaukee Brewers (formerly Seattle Pilots) have all played in the Series but have never won. The Toronto Blue Jays are the only franchise from outside the United States to appear in a World Series, winning in 1992 and 1993. The Houston Astros have represented both the NL (2005) and the AL (2017), winning the Series in 2017. The current World Series champions are the Boston Red Sox.
Winners
Numbers in parentheses in the table are World Series appearances as of the date of that World Series, and are used as follows:
Winning team and losing team columns indicate the number of times that team has appeared in a World Series as well as each respective teams' World Series record to date.
National League team
American League team

Series appearances by club
Appearances by club

Years of appearance
In the sortable table below, teams are ordered first by number of appearances, then by number of wins, and finally by year of first appearance. In the "Season(s)" column, bold years indicate winning World Series appearances.

Frequent matchups
The following are the 20 matchups of teams that have occurred two or more times in the World Series. All teams which have participated in these were "Classic Eight" members of either the American or National League; no expansion team (created in 1961 or later) has faced an opponent more than once in a World Series.

Notes
 The 1907, 1912, and 1922 World Series each included one tied game.
 The 1903, 1919, 1920, and 1921 World Series were in a best-of-nine format (carried by the first team to win five games).
 Indicates a team which made the playoffs as a wild card team (rather than by winning a division).[1]
 The Brewers were in the American League from 1969–1997, after which they switched to the National League.[122]
 The Astros were in the National League from 1962–2012, after which they switched to the American League.
See also

List of National League pennant winners
List of American League pennant winners
List of Major League Baseball franchise postseason streaks
List of Major League Baseball franchise postseason droughts
List of pre-World Series baseball champions

 – official website

Who played in the baseball world series?


History of the People's
Republic of China (PRC)
1949–1976
Mao era

Revolution
Korean War

Killings of landlords
Zhen Fan
Three-anti and Five-anti Campaigns
New Democracy
Hundred Flowers Campaign
Anti-Rightist Campaign
Great Leap Forward
(Great Chinese Famine)
Cultural Revolution (Lin BiaoGang of FourTiananmen Incident)
1976–1989
Restructuring

Economic reform
Sino-Vietnamese War
Beijing Spring
Anti-Spiritual Pollution Campaign
Tiananmen Square protests

1989–2002
Rising power
One country, two systems (Hong KongMacau)
Chinese unification
2002–present
Recent history

Sichuan earthquake
Beijing Olympics
Shanghai 2010 Expo
Wang Lijun incident
2015 China Victory Day Parade
Anti-corruption campaign
 after the 18th Party Congress

History of

China
PRC constitution
Beijing
Shanghai

Generations of leadership

1.Mao
2.Deng
3.Jiang
4.Hu
5.Xi

Culture
Economy
Education
Geography
Politics

 Chinaportalvt

 History of ChinaANCIENTNeolithic c. 8500 – c. 2070 BCEXia c. 2070 – c. 1600 BCEShang c. 1600 – c. 1046 BCEZhou c. 1046 – 256 BCEWestern ZhouEastern ZhouSpring and AutumnWarring StatesIMPERIALQin 221–207 BCEHan 202 BCE – 220 CE Western Han Xin Eastern HanThree Kingdoms 220–280 Wei, Shu and WuJin 266–420 Western Jin Eastern JinSixteen KingdomsNorthern and Southern dynasties
 420–589Sui 581–618Tang 618–907 (Wu Zhou 690–705)Five Dynasties and
Ten Kingdoms
 907–979Liao 916–1125Song 960–1279 Northern SongWestern Xia Southern SongJinYuan 1271–1368Ming 1368–1644Qing 1636–1912MODERNRepublic of China 1912–1949People's Republic of China 1949–presentRelated articles
Chinese historiography
Timeline of Chinese history
Dynasties in Chinese history
Linguistic history
Art history
Economic history
Education history
Science and technology history
Legal history
Media history
Military history
Naval history
viewtalk
The history of the People's Republic of China details the history of mainland China since October 1, 1949, when, after a near complete victory by the Communist Party of China (CPC) in the Chinese Civil War, Mao Zedong proclaimed the People's Republic of China (PRC) from atop Tiananmen.  The PRC has for several decades been synonymous with China, but it is only the most recent political entity to govern mainland China, preceded by the Republic of China (ROC) and thousands of years of imperial dynasties.
1949–1976: Socialist transformation under Mao Zedong

Following the Chinese Civil War and victory of Mao Zedong's Communist forces over the Kuomintang forces of Generalissimo Chiang Kai-shek, who fled to Taiwan, Mao declared the founding of the People's Republic of China on October 1, 1949. Mao's first goal was a total overhaul of the land ownership system, and extensive land reforms. China's old system of gentry landlord ownership of farmland and tenant peasants was replaced with a distribution system in favor of poor/landless peasants which significantly reduced economic inequality. Over a million landlords were executed.[1] In Zhangzhuangcun, in the more thoroughly reformed north of the country, most "landlords" and "rich peasants" had lost all their land and often their lives or had fled. All formerly landless workers had received land, which eliminated this category altogether. As a result, "middling peasants," who now accounted for 90 percent of the village population, owned 90.8 percent of the land.[2] Mao laid heavy theoretical emphasis on class struggle, and in 1953 began various campaigns to persecute former landlords and merchants, including the execution of more powerful landlords. Drug trafficking in the country as well as foreign investment were largely wiped out.
Mao believed that socialism would eventually triumph over all other ideologies, and following the First Five-Year Plan based on a Soviet-style centrally controlled economy, Mao took on the ambitious project of the Great Leap Forward in 1958, beginning an unprecedented process of collectivization in rural areas. Mao urged the use of communally organized iron smelters to increase steel production, pulling workers off of agricultural labor to the point that large amounts of crops rotted unharvested. Mao decided to continue to advocate these smelters despite a visit to a factory steel mill which proved to him that high quality steel could only be produced in a factory. He thought that ending the program would dampen peasant enthusiasm for his political mobilization, the Great Leap Forward.
The implementation of Maoist thought in China may have been responsible for over 40–70 million deaths including famine during peacetime[3], with the Great Leap Forward,  Anti-Rightist Campaign of 1957–1958,[4] and the Cultural Revolution. Millions died from both executions and forced labour.
Because of Mao's land reforms during the Great Leap Forward, which resulted in massive famines, thirty million perished between 1958 and 1961.  By the end of 1961 the birth rate was nearly cut in half because of malnutrition.[5] Active campaigns, including party purges and "reeducation" resulted in the imprisonment or execution of those deemed to hold views contrary to Maoist ideals.[6]
Mao's failure with the Leap reduced his power in government, whose administrative duties fell to Liu Shaoqi and Deng Xiaoping.
To impose socialist orthodoxy and rid China of "old elements", and at the same time serving certain political goals, Mao began the Cultural Revolution in May 1966. The campaign was far reaching into all aspects of Chinese life. Red Guards terrorized the streets as many ordinary citizens were deemed counter-revolutionaries. Education and public transportation came to a nearly complete halt. Daily life involved shouting slogans and reciting Mao quotations. Many prominent political leaders, including Liu and Deng, were purged and deemed "capitalist-roaders". The campaign would not come to a complete end until the death of Mao in 1976.
Supporters of the Maoist Era claim that under Mao, China's unity and sovereignty was assured for the first time in a century, and there was development of infrastructure, industry, healthcare, education (only 20% of the population could read in 1949, compared to 65.5% thirty years later)[7], which raised standard of living for the average Chinese. They also claimed that campaigns such as the Great Leap Forward – an example of the concept New Democracy – and the Cultural Revolution were essential in jumpstarting China's development and "purifying" its culture. Others[8] claim that though the consequences of both these campaigns were economically and humanly disastrous, they left behind a "clean slate" on which later economic progress could be built. Supporters often also doubt statistics or accounts given for death tolls or other damages incurred by Mao's campaigns, attributing the high death toll to natural disasters, famine, or other consequences of political chaos during the rule of Chiang Kai-shek.
1976–1989: Rise of Deng Xiaoping and economic reforms

Mao Zedong's death was followed by a power struggle between the Gang of Four, Hua Guofeng, and eventually Deng Xiaoping. Deng would maneuver himself to the top of China's leadership by 1980. At the Third Plenum of the Eleventh National Party Congress Central Committee, Deng embarked China on the road to Economic Reforms and Openness (改革开放 Gaige Kaifang), policies that began with the de-collectivization of the countryside, followed with industrial reforms aimed at decentralizing government controls in the industrial sector. A major document presented at the September 1979 Fourth Plenum, gave a "preliminary assessment" of the entire 30-year period of Communist rule. At the plenum, party Vice Chairman Ye Jianying declared the Cultural Revolution "an appalling catastrophe" and "the most severe setback to [the] socialist cause since [1949]."[9] The Chinese government's condemnation of the Cultural Revolution culminated in the Resolution on Certain Questions in the History of Our Party Since the Founding of the People's Republic of China, adopted by the Sixth Plenary Session of the Eleventh Central Committee of the Communist Party of China. This stated that "Comrade Mao Zedong was a great Marxist and a great proletarian revolutionary, strategist and theorist. It is true that he made gross mistakes during the "cultural revolution", but, if we judge his activities as a whole, his contributions to the Chinese revolution far outweigh his mistakes. His merits are primary and his errors secondary."[10]
On the subject of Mao's legacy Deng coined the famous phrase "7 parts good, 3 parts bad" and avoided denouncing Mao altogether. Deng championed the idea of Special Economic Zones (SEZs), areas where foreign investment would be allowed to pour in without strict government restraint and regulations, running on a basically capitalist system. Deng laid emphasis on light industry as a stepping stone to the development of heavy industries.
Supporters of the economic reforms point to the rapid development of the consumer and export sectors of the economy, the creation of an urban middle class that now constitutes 15% of the population, higher living standards (which is shown via dramatic increases in GDP per capita, consumer spending, life expectancy, literacy rate, and total grain output) and a much wider range of personal rights and freedoms for average Chinese as evidence of the success of the reforms.
Although standards of living improved significantly in the 1980s, Deng's reforms were not without criticism. Hard-liners asserted that Deng opened China once again to various social evils, and an overall increase in materialistic thinking, while liberals attacked Deng's unrelenting stance on political reform. Liberal forces began gathering in different forms to protest against the Party's authoritarian leadership. In 1989, the death of Hu Yaobang, a liberal figure, triggered weeks of spontaneous protests in the Tiananmen Square. The government imposed martial law and sent in tanks and soldiers to suppress the demonstrations. Western countries and multilateral organizations briefly suspended their formal ties with China's government under Premier Li Peng's leadership, which was directly responsible for the military curfew and bloody crackdown.
Critics of the economic reforms, both in China and abroad, claim that the reforms have caused wealth disparity, environmental pollution, rampant corruption, widespread unemployment associated with layoffs at inefficient state-owned enterprises, and has introduced often unwelcome cultural influences. Consequently, they believe that China's culture has been corrupted, the poor have been reduced to a hopeless abject underclass, and that the social stability is threatened. They are also of the opinion that various political reforms, such as moves towards popular elections, have been unfairly nipped in the bud.  Regardless of either view, today, the public perception of Mao has improved at least superficially; images of Mao and Mao related objects have become fashionable, commonly used on novelty items and even as talismans. However, the path of modernization and market-oriented economic reforms that China started since the early 1980s appears to be fundamentally unchallenged. Even critics of China's market reforms do not wish to see a backtrack of these two decades of reforms, but rather propose corrective measures to offset some of the social issues caused by existing reforms.
In 1979, the Chinese government instituted a one child policy to try to control its rapidly increasing population.  The controversial policy resulted in a dramatic decrease in child poverty. The law currently applies to about a third of mainland Chinese, with plans in place to ease it to a two-child limit.[11][12]
The achievements of Lee Kuan Yew to create an economic superpower in Singapore had a profound effect on the Communist leadership in China. They made a major effort, especially under Deng Xiaoping, to emulate his policies of economic growth, entrepreneurship, and subtle suppression of dissent. Over 22,000 Chinese officials were sent to Singapore to study its methods.[13]
1989–2002: Economic growth under the third generation

After the events at Tiananmen, Deng Xiaoping retired from public view. While keeping ultimate control, power was passed onto the third generation of leadership led by Jiang Zemin, who was hailed as its "core". Economic growth, despite foreign trade embargoes, returned to a fast pace by the mid-1990s. Jiang's macroeconomic reforms furthered Deng's vision for "Socialism with Chinese Characteristics". At the same time, Jiang's period saw a continued rise in social corruption in all areas of life.  Unemployment skyrocketed as unprofitable SOE's were closed to make way for more competitive ventures, internally and abroad. The ill-equipped social welfare system was put on a serious test. Jiang also laid heavy emphasis on scientific and technological advancement in areas such as space exploration. To sustain vast human consumption, the Three Gorges Dam was built, attracting supporters and widespread criticism. Environmental pollution became a very serious problem as Beijing was frequently hit by sandstorms as a result of desertification.
The 1990s saw two foreign colonies returned to China, Hong Kong from Britain in 1997, and Macau from Portugal in 1999. Hong Kong and Macau mostly continued their own governance, retaining independence in their economic, social, and judicial systems.
Jiang and President Clinton exchanged state visits, but Sino-American relations took very sour turns at the end of the decade. On May 7, 1999, during the Kosovo War, US aircraft bombed the Chinese embassy in Belgrade. The U.S. government claimed the strike was due to bad intelligence and false target identification.
Inside the US, the Cox Report stated that China had been stealing various top US military secrets.
In 2001, a US surveillance plane collided with a Chinese fighter jet over international waters near Hainan, inciting further outrage with the Chinese public, already dissatisfied with the US.
On the political agenda, China was once again put on the spotlight for the banning of public Falun Gong activity in 1999. Silent protesters from the spiritual movement sat outside of Zhongnanhai, asking for dialogue with China's leaders. Jiang saw it as threatening to the political situation and outlawed the group altogether, while using the mass media to denounce it as an evil cult.
Conversely, Premier Zhu Rongji's economic policies held China's economy strong during the Asian Financial Crisis. Economic growth averaged at 8% annually, pushed back by the 1998 Yangtze River Floods. After a decade of talks, China was finally admitted into the World Trade Organization.  Standards of living improved significantly, although a wide urban-rural wealth gap was opened, as China saw the reappearance of the middle class. Wealth disparity between East and the Western hinterlands continued to widen by the day, prompting government programs to "develop the West", taking on such ambitious projects such as the Qinghai-Tibet Railway. The burden of education was greater than ever.  Rampant corruption continued despite Premier Zhu's anti-corruption campaign that executed many officials.
2002–present

The first major issue faced by China in the 21st century as a new generation of leaders led by Hu Jintao after assuming power was the public health crisis involving SARS, an illness that seemed to have originated out of Guangdong province. China's position in the war on terror drew the country closer diplomatically to the United States. The economy continues to grow in double-digit numbers as the development of rural areas became the major focus of government policy. In gradual steps to consolidate his power, Hu Jintao removed Shanghai Party Chief Chen Liangyu and other potential political opponents amidst the fight against corruption, and the ongoing struggle against once powerful Shanghai clique. The assertion of the Scientific Perspective to create a Socialist Harmonious Society is the focus of the Hu-Wen administration, as some Jiang-era excesses are slowly reversed. In the years after Hu's rise to power, respect of basic human rights in China continue to be a source of concern.
The political status and future of Taiwan remain uncertain, but steps have been taken to improving relations between the Communist Party and several of Taiwan's parties that hold a less antagonistic view towards China, notably former rival Kuomintang.
The continued economic growth of the country as well as its sporting power status gained China the right to host the 2008 Summer Olympics. However, this also put Hu's administration under intense spotlight.  While the 2008 Olympic was commonly understood to be a come-out party for People's Republic of China, in light of the March 2008 Tibet protests, the government received heavy scrutiny. The Olympic torch was met with protest en route. Within the country these reactions were met with a fervent wave of nationalism with accusations of Western bias against China.
In May 2008, a massive earthquake registering 8.0 on the Richter scale hit Sichuan province of China, exacting a death toll officially estimated at approximately 70,000.  The government responded more quickly than it did with previous events, and has allowed foreign media access to the regions that were hit the hardest.  The adequacy of the government response was generally praised, and the relief efforts extended to every corner of Chinese life.
In May and June 2008, heavy rains in southern China caused severe flooding in the provinces of Anhui, Hunan, Jiangxi, Fujian and Guangdong, with dozens of fatalities and over a million people forced to evacuate. As of 2009 China has increased its internet monitoring capabilities by adding hundreds of new monitoring stations.

See also

History of China
History of the Republic of China
History of Hong Kong
History of Macau
Dynasties in Chinese History
Economic History of China
Historiography of China
History of Chinese Art
History of Education in China
History of Science and Technology in China
Legal History of China
Linguistic History of China
Military history of China
Naval History of China
Timeline of Chinese history

Further reading
Lynch, Michael. Access to History: Mao's China 1936–97 (3rd ed. Hachette UK, 2015)
Historiography
Eben V. Racknitz, Ines. "Repositioning History for the Future – Recent Academic Debates in China" History Compass (2014) 12#6 pp. 465–472.
Finnane, Antonia. "Reinventing Modern China: Imagination and Authenticity in Chinese Historical Writing." Asian Studies Review 39#1 (2015): 163–164.
Longxi, Zhang. "Re-conceptualizing China in our Time: From a Chinese Perspective." European Review 23#2 (2015): 193–209.
Unger, Jonathan. Using the Past to Serve the Present: Historiography and Politics in Contemporary China (Routledge, 2015)

 by Yiching Wu
 by P.M. Calabrese
 by Gerhard K. Heilig
 – 2006 PBS documentary. KQED Public Television and Granada Television for PBS, Granada International and the BBC.

When was the People's Republic of China founded?


A number of large diamonds have gained fame, both as examples of the beautiful nature of diamonds and because of the famous people who wore, bought, and sold them. A partial list of famous diamonds in history follows.

See also

List of largest rough diamonds

 – Several full text books and article of many famous diamonds. Non Commercial.