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110-435: A hole is an opening in or through a particular medium, usually a solid body . Holes occur through natural and artificial processes, and may be useful for various purposes, or may represent a problem needing to be addressed in many fields of engineering . Depending on the material and the placement, a hole may be an indentation in a surface (such as a hole in the ground), or may pass completely through that surface (such as

220-438: A cloud chamber – a particle detector in which moving electrons (or positrons) leave behind trails as they move through the gas. The electric charge-to-mass ratio of a particle can be measured by observing the radius of curling of its cloud-chamber track in a magnetic field . Positrons, because of the direction that their paths curled, were at first mistaken for electrons travelling in the opposite direction. Positron paths in

330-426: A dimer , it can embed itself in cellular bilayer membranes and form a hole through which water molecules can pass. In engineering , machining , and tooling , a hole may be a blind hole or a through hole (also called a thru-hole or clearance hole ). A blind hole is a hole that is reamed , drilled , or milled to a specified depth without breaking through to the other side of the workpiece. A through hole

440-526: A positron can form an antihydrogen atom , which is believed to have the same properties as a hydrogen atom. This leads to the question of why the formation of matter after the Big Bang resulted in a universe consisting almost entirely of matter, rather than being a half-and-half mixture of matter and antimatter . The discovery of charge parity violation helped to shed light on this problem by showing that this symmetry, originally thought to be perfect,

550-515: A rock sample is a random aggregate of minerals and/or mineraloids , and has no specific chemical composition. The vast majority of the rocks of the Earth's crust consist of quartz (crystalline SiO 2 ), feldspar, mica, chlorite , kaolin , calcite, epidote , olivine , augite , hornblende , magnetite , hematite , limonite and a few other minerals. Some minerals, like quartz , mica or feldspar are common, while others have been found in only

660-590: A biological revulsion that associates trypophobic shapes with danger or disease, and may therefore have an evolutionary basis. An example of the use of holes in popular culture can be found in the Beatles lyric from the song, " A Day in the Life ", from their 1967 album Sgt. Pepper's Lonely Hearts Club Band : I read the news today, oh boy: Four thousand holes in Blackburn Lancashire. And though

770-496: A cloud-chamber trace the same helical path as an electron but rotate in the opposite direction with respect to the magnetic field direction due to their having the same magnitude of charge-to-mass ratio but with opposite charge and, therefore, opposite signed charge-to-mass ratios. The antiproton and antineutron were found by Emilio Segrè and Owen Chamberlain in 1955 at the University of California, Berkeley . Since then,

880-541: A composite made up of a thermoplastic matrix such as acrylonitrile butadiene styrene (ABS) in which calcium carbonate chalk, talc , glass fibers or carbon fibers have been added for strength, bulk, or electro-static dispersion. These additions may be referred to as reinforcing fibers, or dispersants, depending on their purpose. Thus, the matrix material surrounds and supports the reinforcement materials by maintaining their relative positions. The reinforcements impart their special mechanical and physical properties to enhance

990-1043: A few locations worldwide. The largest group of minerals by far is the silicates (most rocks are ≥95% silicates), which are composed largely of silicon and oxygen , with the addition of ions of aluminium, magnesium , iron, calcium and other metals. Ceramic solids are composed of inorganic compounds, usually oxides of chemical elements. They are chemically inert, and often are capable of withstanding chemical erosion that occurs in an acidic or caustic environment. Ceramics generally can withstand high temperatures ranging from 1,000 to 1,600 °C (1,830 to 2,910 °F). Exceptions include non-oxide inorganic materials, such as nitrides , borides and carbides . Traditional ceramic raw materials include clay minerals such as kaolinite , more recent materials include aluminium oxide ( alumina ). The modern ceramic materials, which are classified as advanced ceramics, include silicon carbide and tungsten carbide . Both are valued for their abrasion resistance, and hence find use in such applications as

1100-425: A hole created by a hole puncher in a piece of paper). Holes can occur for a number of reasons, including natural processes and intentional actions by humans or animals. Holes in the ground that are made intentionally, such as holes made while searching for food, for replanting trees, or postholes made for securing an object, are usually made through the process of digging . Unintentional holes in an object are often

1210-468: A hole is a supermassive black hole , an astronomical object which can be billions of times more massive than Earth's sun . The deepest hole on Earth is the man-made Kola Superdeep Borehole , with a true vertical drill-depth of more than 7.5 miles (12 kilometers), which is only a fraction of the nearly 4,000 mile (6,400 kilometer) distance to the center of the Earth. In mathematics , holes are examined in

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1320-580: A material can absorb before mechanical failure, while fracture toughness (denoted K Ic ) describes the ability of a material with inherent microstructural flaws to resist fracture via crack growth and propagation. If a material has a large value of fracture toughness , the basic principles of fracture mechanics suggest that it will most likely undergo ductile fracture. Brittle fracture is very characteristic of most ceramic and glass-ceramic materials that typically exhibit low (and inconsistent) values of K Ic . For an example of applications of ceramics,

1430-558: A material that indicates its ability to conduct heat . Solids also have a specific heat capacity , which is the capacity of a material to store energy in the form of heat (or thermal lattice vibrations). Electrical properties include both electrical resistivity and conductivity , dielectric strength , electromagnetic permeability , and permittivity . Electrical conductors such as metals and alloys are contrasted with electrical insulators such as glasses and ceramics. Semiconductors behave somewhere in between. Whereas conductivity in metals

1540-440: A meltdown of the metallic parts. Work is also being done in developing ceramic parts for gas turbine engines . Turbine engines made with ceramics could operate more efficiently, giving aircraft greater range and payload for a set amount of fuel. Such engines are not in production, however, because the manufacturing of ceramic parts in the sufficient precision and durability is difficult and costly. Processing methods often result in

1650-578: A metallic conductor, current is carried by the flow of electrons, but in semiconductors, current can be carried either by electrons or by the positively charged " holes " in the electronic band structure of the material. Common semiconductor materials include silicon, germanium and gallium arsenide . Many traditional solids exhibit different properties when they shrink to nanometer sizes. For example, nanoparticles of usually yellow gold and gray silicon are red in color; gold nanoparticles melt at much lower temperatures (~300 °C for 2.5 nm size) than

1760-422: A non-crystalline intergranular phase. Glass-ceramics are used to make cookware (originally known by the brand name CorningWare ) and stovetops that have high resistance to thermal shock and extremely low permeability to liquids. The negative coefficient of thermal expansion of the crystalline ceramic phase can be balanced with the positive coefficient of the glassy phase. At a certain point (~70% crystalline)

1870-430: A number of ways. One of these is in homology , which is a general way of associating certain algebraic objects to other mathematical objects such as topological spaces . Homology groups were originally defined in algebraic topology , and homology was originally a rigorous mathematical method for defining and categorizing holes in a mathematical object called a manifold . The initial motivation for defining homology groups

1980-519: A particle and antiparticle are in the appropriate quantum states, then they can annihilate each other and produce other particles. Reactions such as e  +  e  →  γ γ (the two-photon annihilation of an electron-positron pair) are an example. The single-photon annihilation of an electron-positron pair, e  +  e  →  γ , cannot occur in free space because it

2090-455: A particle propagating either backward or forward in time. In Feynman diagrams, anti-particles are shown traveling backwards in time relative to normal matter, and vice versa. This technique is the most widespread method of computing amplitudes in quantum field theory today. Since this picture was first developed by Stückelberg, and acquired its modern form in Feynman's work, it is called

2200-529: A periodic lattice. Mathematically, the potential of the ion cores can be treated by various models, the simplest being the nearly free electron model . Minerals are naturally occurring solids formed through various geological processes under high pressures. To be classified as a true mineral, a substance must have a crystal structure with uniform physical properties throughout. Minerals range in composition from pure elements and simple salts to very complex silicates with thousands of known forms. In contrast,

2310-443: A person who provides an account of an event that lacks important details can be said to have "holes in their story", and a fictional work with unexplained narrative elements can be said to have plot holes . A person who has suffered loss is often referred to as having a "hole in their heart". The concept of a "God-shaped hole" occurs in religious discourse: [H]umans are commonly said to have “a God-shaped hole” in our souls. If you are

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2420-506: A physical object is taken to its logical extreme in the fictional concept of a portable hole , exemplified in role-playing games and characterized as a "hole" that a person can carry with them, keep things in, and enter themselves as needed. In art holes are sometimes referred to as negative space , as in the case of the Japanese concept of Ma . Holes can also be referenced metaphorically as existing in non-tangible things. For example,

2530-405: A pictorial understanding of the fact that the particle and antiparticle have equal mass m and spin J but opposite charges q . This allowed him to rewrite perturbation theory precisely in the form of diagrams. Richard Feynman later gave an independent systematic derivation of these diagrams from a particle formalism, and they are now called Feynman diagrams . Each line of a diagram represents

2640-455: A piezoelectric response several times larger than the traditional piezoelectric material quartz (crystalline SiO 2 ). The deformation (~0.1%) lends itself to useful technical applications such as high-voltage sources, loudspeakers, lasers, as well as chemical, biological, and acousto-optic sensors and/or transducers. Anti-particle Onia In particle physics , every type of particle of "ordinary" matter (as opposed to antimatter )

2750-454: A proton annihilate to give two photons. Robert Oppenheimer and Igor Tamm , however, proved that this would cause ordinary matter to disappear too fast. A year later, in 1931, Dirac modified his theory and postulated the positron , a new particle of the same mass as the electron. The discovery of this particle the next year removed the last two objections to his theory. Within Dirac's theory,

2860-428: A real scalar field , then one finds that there is only one kind of annihilation operator; therefore, real scalar fields describe neutral bosons. Since complex scalar fields admit two different kinds of annihilation operators, which are related by conjugation, such fields describe charged bosons. By considering the propagation of the negative energy modes of the electron field backward in time, Ernst Stückelberg reached

2970-643: A religious person, you can explain the hole by saying that God put it there in order to make it easier for us to receive Him. If you are a naturalist or an atheist, you believe the God-shaped hole is in our minds, not our souls. You then look for reasons that the concept of God might have evolved in our species. The Unicode symbol for HOLE, U+1F573, was approved in 2014 as part of the Miscellaneous Symbols and Pictographs chart in Unicode 7.0, and

3080-499: A resin during processing, which is then shaped into a final form. Polymers that have been around, and that are in current widespread use, include carbon-based polyethylene , polypropylene , polyvinyl chloride , polystyrene , nylons, polyesters , acrylics , polyurethane , and polycarbonates , and silicon-based silicones . Plastics are generally classified as "commodity", "specialty" and "engineering" plastics. Composite materials contain two or more macroscopic phases, one of which

3190-455: A reversed charge. These holes were interpreted as "negative-energy electrons" by Paul Dirac and mistakenly identified with protons in his 1930 paper A Theory of Electrons and Protons However, these "negative-energy electrons" turned out to be positrons , and not protons . This picture implied an infinite negative charge for the universe – a problem of which Dirac was aware. Dirac tried to argue that we would perceive this as

3300-426: A sign of damage . Potholes and sinkholes can damage human settlements. Holes can occur in a wide variety of materials, and at a wide range of scales. The smallest holes observable by humans include pinholes and perforations , but the smallest phenomenon described as a hole is an electron hole , which is a position in an atom or atomic lattice where an electron is missing. The largest phenomenon described as

3410-442: A significant portion of the fields of solid-state chemistry, physics, materials science and engineering. Metallic solids are held together by a high density of shared, delocalized electrons, known as " metallic bonding ". In a metal, atoms readily lose their outermost ("valence") electrons , forming positive ions . The free electrons are spread over the entire solid, which is held together firmly by electrostatic interactions between

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3520-420: A single hole serves all of these purposes. The formation of holes is a significant event in the development of an animal: All animals start out in development with one hole, the blastopore . If there are two holes, the second hole forms later. The blastopore can arise at the top or the bottom of the embryo. Gramicidin A , a polypeptide with a helical shape, has been described as a portable hole. When it forms

3630-692: A way that the strain is directly proportional to the stress ( Hooke's law ). The coefficient of the proportion is called the modulus of elasticity or Young's modulus . This region of deformation is known as the linearly elastic region. Three models can describe how a solid responds to an applied stress: Many materials become weaker at high temperatures. Materials that retain their strength at high temperatures, called refractory materials , are useful for many purposes. For example, glass-ceramics have become extremely useful for countertop cooking, as they exhibit excellent mechanical properties and can sustain repeated and quick temperature changes up to 1000 °C. In

3740-471: A wide distribution of microscopic flaws that frequently play a detrimental role in the sintering process, resulting in the proliferation of cracks, and ultimate mechanical failure. Glass-ceramic materials share many properties with both non-crystalline glasses and crystalline ceramics . They are formed as a glass, and then partially crystallized by heat treatment, producing both amorphous and crystalline phases so that crystalline grains are embedded within

3850-414: A wide variety of polymers and plastics . Wood is a natural organic material consisting primarily of cellulose fibers embedded in a matrix of lignin . Regarding mechanical properties, the fibers are strong in tension, and the lignin matrix resists compression. Thus wood has been an important construction material since humans began building shelters and using boats. Wood to be used for construction work

3960-415: Is a hole that is made to go completely through the material of an object. In other words, a through hole is a hole that goes all the way through something. Taps used for through holes are generally tapered since it will tap faster and the chips will be released when the tap exits the hole. The etymology of the blind hole is that it is not possible to see through it. It may also refer to any feature that

4070-474: Is a natural organic material consisting primarily of cellulose fibers embedded in a matrix of organic lignin . In materials science, composites of more than one constituent material can be designed to have desired properties. The forces between the atoms in a solid can take a variety of forms. For example, a crystal of sodium chloride (common salt) is made up of ionic sodium and chlorine , which are held together by ionic bonds . In diamond or silicon,

4180-686: Is also a fundamental feature of many biological materials and the manner by which the structures are assembled from the molecular level up. Thus, self-assembly is emerging as a new strategy in the chemical synthesis of high performance biomaterials. Physical properties of elements and compounds that provide conclusive evidence of chemical composition include odor, color, volume, density (mass per unit volume), melting point, boiling point, heat capacity, physical form and shape at room temperature (solid, liquid or gas; cubic, trigonal crystals, etc.), hardness, porosity, index of refraction and many others. This section discusses some physical properties of materials in

4290-459: Is also true: the antiparticle of the positron is the electron. Some particles, such as the photon , are their own antiparticle. Otherwise, for each pair of antiparticle partners, one is designated as the normal particle (the one that occurs in matter usually interacted with in daily life). The other (usually given the prefix "anti-") is designated the antiparticle . Particle–antiparticle pairs can annihilate each other, producing photons ; since

4400-431: Is antilinear and antiunitary, ⟨ Ψ | T Φ ⟩ = ⟨ Φ | T − 1 Ψ ⟩ {\displaystyle \langle \Psi |T\,\Phi \rangle =\langle \Phi |T^{-1}\,\Psi \rangle } . If | p , σ , n ⟩ {\displaystyle |p,\sigma ,n\rangle } denotes

4510-399: Is associated with an antiparticle with the same mass but with opposite physical charges (such as electric charge ). For example, the antiparticle of the electron is the positron (also known as an antielectron). While the electron has a negative electric charge, the positron has a positive electric charge, and is produced naturally in certain types of radioactive decay . The opposite

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4620-469: Is caused by electrons, both electrons and holes contribute to current in semiconductors. Alternatively, ions support electric current in ionic conductors . Many materials also exhibit superconductivity at low temperatures; they include metallic elements such as tin and aluminium, various metallic alloys, some heavily doped semiconductors, and certain ceramics. The electrical resistivity of most electrical (metallic) conductors generally decreases gradually as

4730-416: Is commonly known as lumber or timber . In construction, wood is not only a structural material, but is also used to form the mould for concrete. Wood-based materials are also extensively used for packaging (e.g. cardboard) and paper, which are both created from the refined pulp. The chemical pulping processes use a combination of high temperature and alkaline (kraft) or acidic (sulfite) chemicals to break

4840-470: Is impossible to conserve energy and momentum together in this process. However, in the Coulomb field of a nucleus the translational invariance is broken and single-photon annihilation may occur. The reverse reaction (in free space, without an atomic nucleus) is also impossible for this reason. In quantum field theory, this process is allowed only as an intermediate quantum state for times short enough that

4950-411: Is no long-range order in the position of the atoms. These solids are known as amorphous solids ; examples include polystyrene and glass. Whether a solid is crystalline or amorphous depends on the material involved, and the conditions in which it was formed. Solids that are formed by slow cooling will tend to be crystalline, while solids that are frozen rapidly are more likely to be amorphous. Likewise,

5060-464: Is often ceramic. For example, a continuous matrix, and a dispersed phase of ceramic particles or fibers. Applications of composite materials range from structural elements such as steel-reinforced concrete, to the thermally insulative tiles that play a key and integral role in NASA's Space Shuttle thermal protection system , which is used to protect the surface of the shuttle from the heat of re-entry into

5170-499: Is taken to a specific depth, more specifically referring to internally threaded hole (tapped holes). Not considering the drill point, the depth of the blind hole, conventionally, may be slightly deeper than that of the threaded depth. There are three accepted methods of threading blind holes: At least two U.S. tool manufacturers have manufactured tools for thread milling in blind holes: Ingersoll Cutting Tools of Rockford, Illinois, and Tooling Systems of Houston, Texas, who introduced

5280-409: Is the ability of crystals to generate a voltage in response to an applied mechanical stress. The piezoelectric effect is reversible in that piezoelectric crystals, when subjected to an externally applied voltage, can change shape by a small amount. Polymer materials like rubber, wool, hair, wood fiber, and silk often behave as electrets . For example, the polymer polyvinylidene fluoride (PVDF) exhibits

5390-421: Is the notion of homotopy group : these are invariants of a topological space that, when non-trivial (one also says in this case that the space is not k-connected ), detect the presence of "holes" in the sense that the space contains a sphere that cannot be contracted to a point. The term of hole is often used informally when discussing these objects. For surfaces a notion closer to the intuitive meaning exists:

5500-400: Is the study of the behavior of solid matter under external actions such as external forces and temperature changes. A solid does not exhibit macroscopic flow, as fluids do. Any degree of departure from its original shape is called deformation . The proportion of deformation to original size is called strain. If the applied stress is sufficiently low, almost all solid materials behave in such

5610-479: Is used in pinhole cameras to form an image without the use of a lens . Pinholes on produce packaging have been used to control the atmosphere and relative humidity within the packaging. In many fields, pinholes are a harmful side effect of manufacturing processes. For example, in the assembly of microcircuits , pinholes in the dielectric insulator layer coating the circuit can cause the circuit to fail. Therefore, "[t]o avoid pinholes that might protrude through

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5720-483: Is used in capacitors. A capacitor is an electrical device that can store energy in the electric field between a pair of closely spaced conductors (called 'plates'). When voltage is applied to the capacitor, electric charges of equal magnitude, but opposite polarity, build up on each plate. Capacitors are used in electrical circuits as energy-storage devices, as well as in electronic filters to differentiate between high-frequency and low-frequency signals. Piezoelectricity

5830-451: The Dirac equation contain negative energy quantum states. As a result, an electron could always radiate energy and fall into a negative energy state. Even worse, it could keep radiating infinite amounts of energy because there were infinitely many negative energy states available. To prevent this unphysical situation from happening, Dirac proposed that a "sea" of negative-energy electrons fills

5940-461: The Hamiltonian then one sees immediately that the expectation value of H need not be positive. This is because E(k) can have any sign whatsoever, and the combination of creation and annihilation operators has expectation value 1 or 0. So one has to introduce the charge conjugate antiparticle field, with its own creation and annihilation operators satisfying the relations where k has

6050-462: The genus of a connected, orientable surface is an integer representing the maximum number of cuttings along non-intersecting closed simple curves without rendering the resultant manifold disconnected. In layman's terms, it is exactly the number of "holes" the surface has, when represented as a submanifold in 3-space. In physics, antimatter is pervasively described as a hole, a location that, when brought together with ordinary matter to fill

6160-513: The periodic table moving diagonally downward right from boron . They separate the electrical conductors (or metals, to the left) from the insulators (to the right). Devices made from semiconductor materials are the foundation of modern electronics, including radio, computers, telephones, etc. Semiconductor devices include the transistor , solar cells , diodes and integrated circuits . Solar photovoltaic panels are large semiconductor devices that directly convert light into electrical energy. In

6270-428: The physical and chemical properties of solids. Solid-state chemistry is especially concerned with the synthesis of novel materials, as well as the science of identification and chemical composition . The atoms, molecules or ions that make up solids may be arranged in an orderly repeating pattern, or irregularly. Materials whose constituents are arranged in a regular pattern are known as crystals . In some cases,

6380-405: The Earth's atmosphere. One example is Reinforced Carbon-Carbon (RCC), the light gray material that withstands reentry temperatures up to 1,510 °C (2,750 °F) and protects the nose cap and leading edges of Space Shuttle's wings. RCC is a laminated composite material made from graphite rayon cloth and impregnated with a phenolic resin . After curing at high temperature in an autoclave,

6490-549: The Thread Mill in 1977, a device that milled large internal threads in the blind holes of oil well blowout preventers . Today many CNC milling machines can run such a thread milling cycle (see a video of such a cut in the "External links" section). One use of through holes in electronics is with through-hole technology , a mounting scheme involving the use of leads on the components that are inserted into holes drilled in printed circuit boards (PCB) and soldered to pads on

6600-427: The aerospace industry, high performance materials used in the design of aircraft and/or spacecraft exteriors must have a high resistance to thermal shock. Thus, synthetic fibers spun out of organic polymers and polymer/ceramic/metal composite materials and fiber-reinforced polymers are now being designed with this purpose in mind. Because solids have thermal energy , their atoms vibrate about fixed mean positions within

6710-400: The annihilation and creation operators by writing where we use the symbol k to denote the quantum numbers p and σ of the previous section and the sign of the energy, E(k) , and a k denotes the corresponding annihilation operators. Of course, since we are dealing with fermions , we have to have the operators satisfy canonical anti-commutation relations. However, if one now writes down

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6820-494: The antiparticle and the particle coincide: pairs of photons , Z  bosons , π   mesons , and hypothetical gravitons and some hypothetical WIMPs all self-annihilate. However, electrically neutral particles need not be identical to their antiparticles: for example, the neutron and antineutron are distinct. In 1932, soon after the prediction of positrons by Paul Dirac , Carl D. Anderson found that cosmic-ray collisions produced these particles in

6930-493: The antiparticle. In particular a massive particle and its antiparticle transform under the same irreducible representation of the Poincaré group which means the antiparticle has the same mass and the same spin. If C {\displaystyle C} , P {\displaystyle P} and T {\displaystyle T} can be defined separately on the particles and antiparticles, then where

7040-441: The antiparticles of many other subatomic particles have been created in particle accelerator experiments. In recent years, complete atoms of antimatter have been assembled out of antiprotons and positrons, collected in electromagnetic traps. ... the development of quantum field theory made the interpretation of antiparticles as holes unnecessary, even though it lingers on in many textbooks. Steven Weinberg Solutions of

7150-493: The atoms share electrons and form covalent bonds . In metals, electrons are shared in metallic bonding . Some solids, particularly most organic compounds, are held together with van der Waals forces resulting from the polarization of the electronic charge cloud on each molecule. The dissimilarities between the types of solid result from the differences between their bonding. Metals typically are strong, dense, and good conductors of both electricity and heat . The bulk of

7260-567: The brief stated: "There are 4,000 holes in the road in Blackburn, Lancashire, or one twenty-sixth of a hole per person, according to a council survey. If Blackburn is typical, there are two million holes in Britain's roads and 300,000 in London". Holes have also been described as ontological parasites because they can only exist as aspects of another object. The psychological concept of a hole as

7370-543: The case when antiparticles are produced naturally via beta decay or the collision of cosmic rays with Earth's atmosphere), or by the simultaneous creation of both a particle and its antiparticle (pair production), which can occur in particle accelerators such as the Large Hadron Collider at CERN . Particles and their antiparticles have equal and opposite charges, so that an uncharged particle also gives rise to an uncharged antiparticle. In many cases,

7480-411: The charges of the particle and antiparticle are opposite, total charge is conserved. For example, the positrons produced in natural radioactive decay quickly annihilate themselves with electrons, producing pairs of gamma rays , a process exploited in positron emission tomography . The laws of nature are very nearly symmetrical with respect to particles and antiparticles. For example, an antiproton and

7590-663: The chemical bonds of the lignin before burning it out. One important property of carbon in organic chemistry is that it can form certain compounds, the individual molecules of which are capable of attaching themselves to one another, thereby forming a chain or a network. The process is called polymerization and the chains or networks polymers, while the source compound is a monomer. Two main groups of polymers exist: those artificially manufactured are referred to as industrial polymers or synthetic polymers (plastics) and those naturally occurring as biopolymers. Monomers can have various chemical substituents, or functional groups, which can affect

7700-467: The chemical properties of organic compounds, such as solubility and chemical reactivity, as well as the physical properties, such as hardness, density, mechanical or tensile strength, abrasion resistance, heat resistance, transparency, color, etc.. In proteins, these differences give the polymer the ability to adopt a biologically active conformation in preference to others (see self-assembly ). People have been using natural organic polymers for centuries in

7810-411: The early 1980s, Toyota researched production of an adiabatic ceramic engine with an operating temperature of over 6,000 °F (3,320 °C). Ceramic engines do not require a cooling system and hence allow a major weight reduction and therefore greater fuel efficiency. In a conventional metallic engine, much of the energy released from the fuel must be dissipated as waste heat in order to prevent

7920-543: The elements in the periodic table , those to the left of a diagonal line drawn from boron to polonium , are metals. Mixtures of two or more elements in which the major component is a metal are known as alloys . People have been using metals for a variety of purposes since prehistoric times. The strength and reliability of metals has led to their widespread use in construction of buildings and other structures, as well as in most vehicles, many appliances and tools, pipes, road signs and railroad tracks. Iron and aluminium are

8030-405: The energy of the vacuum is exactly E 0 . Since all energies are measured relative to the vacuum, H is positive definite. Analysis of the properties of a k and b k shows that one is the annihilation operator for particles and the other for antiparticles. This is the case of a fermion . This approach is due to Vladimir Fock , Wendell Furry and Robert Oppenheimer . If one quantizes

8140-435: The entire thickness of the dielectric layer, it is a common practice to screen several layers of dielectric with drying and firing after each screening", thereby preventing the pinholes from becoming continuous. It has been noted that holes occupy an unusual ontological position in philosophy, as people tend to refer to them as tangible and countable objects, when in fact they are the absence of something in another object. In

8250-578: The extreme hardness of zirconia is utilized in the manufacture of knife blades, as well as other industrial cutting tools. Ceramics such as alumina , boron carbide and silicon carbide have been used in bulletproof vests to repel large-caliber rifle fire. Silicon nitride parts are used in ceramic ball bearings, where their high hardness makes them wear resistant. In general, ceramics are also chemically resistant and can be used in wet environments where steel bearings would be susceptible to oxidation (or rust). As another example of ceramic applications, in

8360-433: The form of waxes and shellac , which is classified as a thermoplastic polymer. A plant polymer named cellulose provided the tensile strength for natural fibers and ropes, and by the early 19th century natural rubber was in widespread use. Polymers are the raw materials (the resins) used to make what are commonly called plastics. Plastics are the final product, created after one or more polymers or additives have been added to

8470-535: The glass-ceramic has a net coefficient of thermal expansion close to zero. This type of glass-ceramic exhibits excellent mechanical properties and can sustain repeated and quick temperature changes up to 1000 °C. Glass ceramics may also occur naturally when lightning strikes the crystalline (e.g. quartz) grains found in most beach sand . In this case, the extreme and immediate heat of the lightning (~2500 °C) creates hollow, branching rootlike structures called fulgurite via fusion . Organic chemistry studies

8580-673: The gold slabs (1064 °C); and metallic nanowires are much stronger than the corresponding bulk metals. The high surface area of nanoparticles makes them extremely attractive for certain applications in the field of energy. For example, platinum metals may provide improvements as automotive fuel catalysts , as well as proton exchange membrane (PEM) fuel cells. Also, ceramic oxides (or cermets) of lanthanum , cerium , manganese and nickel are now being developed as solid oxide fuel cells (SOFC). Lithium, lithium-titanate and tantalum nanoparticles are being applied in lithium-ion batteries. Silicon nanoparticles have been shown to dramatically expand

8690-436: The hole, results in both the hole and the matter cancelling each-other out. This is analogous to patching a pothole with asphalt, or filling a bubble below the surface of water with an equal amount of water to cancel it out. The most direct example is the electron hole ; a fairly general theoretical description is provided by the Dirac sea , which treats positrons (or anti-particles in general) as holes. Holes provide one of

8800-517: The holes were rather small, They had to count them all, Now they know how many holes it takes to fill the Albert Hall. The reference to 4,000 holes was written by John Lennon , and inspired by a Far & Near news brief from the same 17 January edition of the Daily Mail , which had also provided inspiration for previous verses of the song. Under the headline "The holes in our roads",

8910-556: The incoming light prior to capture. Here again, surface area of the nanoparticles (and thin films) plays a critical role in maximizing the amount of absorbed radiation. Many natural (or biological) materials are complex composites with remarkable mechanical properties. These complex structures, which have risen from hundreds of million years of evolution, are inspiring materials scientists in the design of novel materials. Their defining characteristics include structural hierarchy, multifunctionality and self-healing capability. Self-organization

9020-448: The ions and the electron cloud. The large number of free electrons gives metals their high values of electrical and thermal conductivity. The free electrons also prevent transmission of visible light, making metals opaque, shiny and lustrous . More advanced models of metal properties consider the effect of the positive ions cores on the delocalised electrons. As most metals have crystalline structure, those ions are usually arranged into

9130-499: The laminate is pyrolized to convert the resin to carbon, impregnated with furfural alcohol in a vacuum chamber, and cured/pyrolized to convert the furfural alcohol to carbon. In order to provide oxidation resistance for reuse capability, the outer layers of the RCC are converted to silicon carbide. Domestic examples of composites can be seen in the "plastic" casings of television sets, cell-phones and so on. These plastic casings are usually

9240-418: The matrix properties. A synergism produces material properties unavailable from the individual constituent materials, while the wide variety of matrix and strengthening materials provides the designer with the choice of an optimum combination. Semiconductors are materials that have an electrical resistivity (and conductivity) between that of metallic conductors and non-metallic insulators. They can be found in

9350-488: The normal state of zero charge. Another difficulty was the difference in masses of the electron and the proton. Dirac tried to argue that this was due to the electromagnetic interactions with the sea, until Hermann Weyl proved that hole theory was completely symmetric between negative and positive charges. Dirac also predicted a reaction e  +  p  →  γ  +  γ , where an electron and

9460-535: The one pictured here, which is a complicated example of mass renormalization . Quantum states of a particle and an antiparticle are interchanged by the combined application of charge conjugation C {\displaystyle C} , parity P {\displaystyle P} and time reversal T {\displaystyle T} . C {\displaystyle C} and P {\displaystyle P} are linear, unitary operators, T {\displaystyle T}

9570-518: The opposite side either by manual assembly (hand placement) or by the use of automated insertion mount machines. A pinhole is a small hole, usually made by pressing a thin, pointed object such as a pin through an easily penetrated material such as a fabric or a very thin layer of metal . Similar holes made by other means are also often called pinholes. Pinholes may be intentionally made for various reasons. For example, in optics pinholes are used as apertures to select certain rays of light. This

9680-409: The ordered (or disordered) lattice. The spectrum of lattice vibrations in a crystalline or glassy network provides the foundation for the kinetic theory of solids . This motion occurs at the atomic level, and thus cannot be observed or detected without highly specialized equipment, such as that used in spectroscopy . Thermal properties of solids include thermal conductivity , which is the property of

9790-409: The perception of a figure rather than a hole. There is a debate on whether holes are special and whether they are perceived as having their own shape. They may be special in some cases, but not in the ownership of the contours. Some people have an aversion to the sight of irregular patterns or clusters of small holes, a condition called trypophobia . Researchers hypothesize that this is the result of

9900-528: The problem of infinite charge of the universe remains. Some bosons also have antiparticles, but since bosons do not obey the Pauli exclusion principle (only fermions do), hole theory does not work for them. A unified interpretation of antiparticles is now available in quantum field theory , which solves both these problems by describing antimatter as negative energy states of the same underlying matter field, i.e. particles moving backwards in time. ( e ) If

10010-499: The production of polycrystalline transparent ceramics such as transparent alumina and alumina compounds for such applications as high-power lasers. Advanced ceramics are also used in the medicine, electrical and electronics industries. Ceramic engineering is the science and technology of creating solid-state ceramic materials, parts and devices. This is done either by the action of heat, or, at lower temperatures, using precipitation reactions from chemical solutions. The term includes

10120-427: The proportionality sign indicates that there might be a phase on the right hand side. As C P T {\displaystyle CPT} anticommutes with the charges, C P T Q = − Q C P T {\displaystyle CPT\,Q=-Q\,CPT} , particle and antiparticle have opposite electric charges q and -q. One may try to quantize an electron field without mixing

10230-439: The purification of raw materials, the study and production of the chemical compounds concerned, their formation into components, and the study of their structure, composition and properties. Mechanically speaking, ceramic materials are brittle, hard, strong in compression and weak in shearing and tension. Brittle materials may exhibit significant tensile strength by supporting a static load. Toughness indicates how much energy

10340-421: The quantum state of a particle n {\displaystyle n} with momentum p {\displaystyle p} and spin J {\displaystyle J} whose component in the z-direction is σ {\displaystyle \sigma } , then one has where n c {\displaystyle n^{c}} denotes the charge conjugate state, that is,

10450-507: The regular ordering can continue unbroken over a large scale, for example diamonds, where each diamond is a single crystal . Solid objects that are large enough to see and handle are rarely composed of a single crystal, but instead are made of a large number of single crystals, known as crystallites , whose size can vary from a few nanometers to several meters. Such materials are called polycrystalline . Almost all common metals, and many ceramics , are polycrystalline. In other materials, there

10560-583: The same p , and opposite σ and sign of the energy. Then one can rewrite the field in the form where the first sum is over positive energy states and the second over those of negative energy. The energy becomes where E 0 is an infinite negative constant. The vacuum state is defined as the state with no particle or antiparticle, i.e. , a k | 0 ⟩ = 0 {\displaystyle a_{k}|0\rangle =0} and b k | 0 ⟩ = 0 {\displaystyle b_{k}|0\rangle =0} . Then

10670-527: The solid state. The mechanical properties of materials describe characteristics such as their strength and resistance to deformation. For example, steel beams are used in construction because of their high strength, meaning that they neither break nor bend significantly under the applied load. Mechanical properties include elasticity , plasticity , tensile strength , compressive strength , shear strength , fracture toughness , ductility (low in brittle materials) and indentation hardness . Solid mechanics

10780-447: The specific crystal structure adopted by a crystalline solid depends on the material involved and on how it was formed. While many common objects, such as an ice cube or a coin, are chemically identical throughout, many other common materials comprise a number of different substances packed together. For example, a typical rock is an aggregate of several different minerals and mineraloids , with no specific chemical composition. Wood

10890-479: The storage capacity of lithium-ion batteries during the expansion/contraction cycle. Silicon nanowires cycle without significant degradation and present the potential for use in batteries with greatly expanded storage times. Silicon nanoparticles are also being used in new forms of solar energy cells. Thin film deposition of silicon quantum dots on the polycrystalline silicon substrate of a photovoltaic (solar) cell increases voltage output as much as 60% by fluorescing

11000-442: The structure, properties, composition, reactions, and preparation by synthesis (or other means) of chemical compounds of carbon and hydrogen , which may contain any number of other elements such as nitrogen , oxygen and the halogens: fluorine , chlorine , bromine and iodine . Some organic compounds may also contain the elements phosphorus or sulfur . Examples of organic solids include wood, paraffin wax , naphthalene and

11110-416: The study of visual perception, a hole is a special case of figure-ground , because the ground region is entirely surrounded by the figure. For a region to be perceived as a visual hole three factors are important: depth factors indicating that the enclosed region lies behind; grouping between the enclosed region and the surround; and figural factors (for example symmetry, convexity, or familiarity) that lead to

11220-508: The temperature is lowered, but remains finite. In a superconductor, however, the resistance drops abruptly to zero when the material is cooled below its critical temperature. An electric current flowing in a loop of superconducting wire can persist indefinitely with no power source. A dielectric , or electrical insulator, is a substance that is highly resistant to the flow of electric current. A dielectric, such as plastic, tends to concentrate an applied electric field within itself, which property

11330-794: The two most commonly used structural metals. They are also the most abundant metals in the Earth's crust . Iron is most commonly used in the form of an alloy, steel, which contains up to 2.1% carbon , making it much harder than pure iron. Because metals are good conductors of electricity, they are valuable in electrical appliances and for carrying an electric current over long distances with little energy loss or dissipation. Thus, electrical power grids rely on metal cables to distribute electricity. Home electrical systems, for example, are wired with copper for its good conducting properties and easy machinability. The high thermal conductivity of most metals also makes them useful for stovetop cooking utensils. The study of metallic elements and their alloys makes up

11440-483: The two primary forms of conduction in a semi-conductor , that is, the material from which transistors are made; without holes, current could not flow, and transistors turn on and off by enabling or disabling the creation of holes. Animal bodies tend to contain specialized holes which serve various biological functions, such as the intake of oxygen or food, the excretion of waste, and the intake or expulsion of other fluids for reproductive purposes. In some simple animals,

11550-414: The universe, already occupying all of the lower-energy states so that, due to the Pauli exclusion principle , no other electron could fall into them. Sometimes, however, one of these negative-energy particles could be lifted out of this Dirac sea to become a positive-energy particle. But, when lifted out, it would leave behind a hole in the sea that would act exactly like a positive-energy electron with

11660-418: The violation of energy conservation can be accommodated by the uncertainty principle . This opens the way for virtual pair production or annihilation in which a one particle quantum state may fluctuate into a two particle state and back. These processes are important in the vacuum state and renormalization of a quantum field theory. It also opens the way for neutral particle mixing through processes such as

11770-464: The wear plates of crushing equipment in mining operations. Most ceramic materials, such as alumina and its compounds, are formed from fine powders, yielding a fine grained polycrystalline microstructure that is filled with light-scattering centers comparable to the wavelength of visible light . Thus, they are generally opaque materials, as opposed to transparent materials . Recent nanoscale (e.g. sol-gel ) technology has, however, made possible

11880-400: Was only approximate. The question about how the formation of matter after the Big Bang resulted in a universe consisting almost entirely of matter remains an unanswered one, and explanations so far are not truly satisfactory, overall. Because charge is conserved , it is not possible to create an antiparticle without either destroying another particle of the same charge (as is for instance

11990-411: Was part of Emoji 1.0, published in 2015. As pictorial representations for emoji are platform-dependent, Emojipedia shows images of the hole symbol as depicted on various platforms. Solid The branch of physics that deals with solids is called solid-state physics , and is the main branch of condensed matter physics (which also includes liquids). Materials science is primarily concerned with

12100-445: Was the observation that two shapes can be distinguished by examining their holes. For instance, a circle is not a disk because the circle has a hole through it while the disk is solid, and the ordinary sphere is not a circle because the sphere encloses a two-dimensional hole while the circle encloses a one-dimensional hole. Because a hole is immaterial, it is not immediately obvious how to define one or distinguish it from others. Another

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