who came up with the basis of modern atomic theory
Hantaro Nagaoka
12636
the atom's constituent parts might interact with each other. Thomson theorized that multiple electrons revolved in orbit-like rings within a positively charged jelly-like substance, and between the electron's discovery and 1909, this "plum pudding model" was the most widely accepted explanation of atomic structure. Shortly after Thomson's discovery, Hantaro Nagaoka predicted a different model for electronic structure. Unlike the plum pudding model, the positive charge in Nagaoka's "Saturnian Model" was concentrated into a central core, pulling the electrons into circular orbits reminiscent of Saturn's rings. Few people took notice of Nagaoka's work at the time, and Nagaoka himself recognized a
Atomic orbital
19978880
Albert Einstein came up with the theory of relativity. Nuclear physics was a product of New Zealand physicist Ernest Rutherford's work on the atomic nucleus, Danish physicist Niels Bohr's identification of atomic structure and American physicist Carl David Anderson's discovery of the positron. Other advances included English physicist James Chadwick discovering the neutron, while French scientists Irène Joliot-Curie and her husband Frédéric Joliot-Curie studied artificial radioactivity. Further nuclear research was carried out by Enrico Fermi, who transmuted uranium based on Japanese physicist Hantaro Nagaoka's theories on the atom. German scientist Otto Hahn derived barium from uranium, while uranium was split
One World or None
6356933
is a linear combination of these two functions. Coulson and Fischer pointed out that a completely equivalent function is:- as expanding this out gives a linear combination of the covalent and ionic structures. Modern valence bond theory replaces the simple linear combination of the two atomic orbitals with a linear combination of all orbitals in a larger basis set. The two resulting valence bond orbitals look like an atomic orbital on one hydrogen atom slightly distorted towards the other hydrogen atom. Modern valence bond theory is thus an extension of this Coulson–Fischer method. There are a large number of different
Modern valence bond theory
20500529
Klopman-Salem equation The Klopman-Salem equation describes the energetic change that occurs when two chemical species react and their associated molecular orbitals interact with each other. First described independently by Gilles Klopman and Lionel Salem in 1968, this relationship provides a mathematical basis for the key assumptions of frontier molecular orbital theory (i.e., theory of HOMO-LUMO interactions) and hard soft acid base (HSAB) theory. In modern form, the Klopman-Salem equation is commonly given asformula_1,where formula_2 is the electron population in atomic orbital "a",formula_3, formula_4 are the resonance and overlap integrals for the interaction of atomic orbitals "a" and "b",formula_5 is the
Klopman-Salem equation
6356932
co-workers (2002); Song, Mo, Zhang and Wu (2005); and Shaik and Hiberty (2004). In its simplest form the overlapping atomic orbitals are replaced by orbitals which are expanded as linear combinations of the atom-based basis functions, forming linear combinations of atomic orbitals (LCAO). This expansion is optimized to give the lowest energy. This procedure gives good energies without including ionic structures. For example, in the hydrogen molecule, classic valence bond theory uses two 1s atomic orbitals (a and b) on the two hydrogen atoms respectively and then constructs a covalent structure:- and then an ionic structure:- The final wave function
Modern valence bond theory
15946296
Resistance theory in the Early Modern period Resistance theory is an aspect of political thought, discussing the basis on which constituted authority may be resisted, by individuals or groups. In the European context it came to prominence as a consequence of the religious divisions in the early modern period that followed the Protestant Reformation. Resistance theories could justify disobedience on religious grounds to monarchs, and were significant in European national politics and international relations in the century leading up to the Peace of Westphalia of 1648. They can also underpin and justify the concept of revolution as now understood. Resistance
Resistance theory in the Early Modern period
15946310
a controversial literature. These developments broke apart any semblance of unity in Anglican resistance theory. Constantine Phipps defended Sacheverell, and Benjamin Hoadley who was an extreme Whig in his "The Original and Institution of Civil Government Discuss'd" (1710), made opposite and incompatible claims about the treatment of resistance in Richard Hooker, who by now was an iconic figure in Anglican theology. Resistance theory in the Early Modern period Resistance theory is an aspect of political thought, discussing the basis on which constituted authority may be resisted, by individuals or groups. In the European context it came to prominence as a
Resistance theory in the Early Modern period
174962
Hertz's formulations under the assumption of zero adhesion. This DMT theory proved to be rather premature and needed several revisions before it came to be accepted as another material contact theory in addition to the JKR theory. Both the DMT and the JKR theories form the basis of contact mechanics upon which all transition contact models are based and used in material parameter prediction in nanoindentation and atomic force microscopy. So Hertz's research from his days as a lecturer, preceding his great work on electromagnetism, which he himself considered with his characteristic soberness to be trivial, has come down to
Heinrich Hertz
2960342
of each atomic orbital basis. A larger coefficient means that the orbital basis is composed more of that particular contributing atomic orbital—hence, the molecular orbital is best characterized by that type. This method of quantifying orbital contribution as a linear combination of atomic orbitals is used in computational chemistry. An additional unitary transformation can be applied on the system to accelerate the convergence in some computational schemes. Molecular orbital theory was seen as a competitor to valence bond theory in the 1930s, before it was realized that the two methods are closely related and that when extended they become equivalent.
Molecular orbital theory
15289710
resonance" is not needed due to the inclusion of bond-polarity effects in the resonance structures. This is similar to other modern valence bond theory methods. Natural bond orbital In quantum chemistry, a natural bond orbital or NBO is a calculated "bonding orbital" with maximum electron density. The NBOs are one of a sequence of natural localized orbital sets that include "natural atomic orbitals" (NAO), "natural hybrid orbitals" (NHO), "natural bonding orbitals" (NBO) and "natural (semi-)localized molecular orbitals" (NLMO). These natural localized sets are intermediate between basis atomic orbitals (AO) and molecular orbitals (MO): Natural (localized) orbitals are used in computational
Natural bond orbital
101229
far from inert. The theory of the atomists appears to be more nearly aligned with that of modern science than any other theory of antiquity. However, the similarity with modern concepts of science can be confusing when trying to understand where the hypothesis came from. Classical atomists could not have had an empirical basis for modern concepts of atoms and molecules. However, Lucretius, describing atomism in his "De rerum natura", gives very clear and compelling empirical arguments for the original atomist theory. He observes that any material is subject to irreversible decay. Through time, even hard rocks are slowly worn
Democritus
10239824
since they have opposite traits. These are the basis of the two factors that would define temperament in the modern theory. In the last few centuries, various psychologists would begin expressing the four temperaments in terms of pairs of behaviors that were held in common by two temperaments each. Ivan Pavlov (1849–1936), from his work with dogs, came up with the factors of "passivity" (active or passive) and "extremeness" (extreme response or moderate response). His view of the temperaments in dogs was: This theory would also be extended to humans. Alfred Adler (1879–1937) measured "activity" (connected with "energy") against "social
Two-factor models of personality
6768832
of a "new chemistry" and describes the experiments and reasoning that led to his conclusions. Like Newton's "Principia", which was the high point of the Scientific Revolution, Lavoisier's "Traité" can be seen as the culmination of the Chemical Revolution. Lavoisier's work was not immediately accepted and it took several decades for it gain momentum. This transition was aided by the work of Jöns Jakob Berzelius, who came up with a simplified shorthand to describe chemical compounds based on John Dalton's theory of atomic weights. Many people credit Lavoisier and his overthrow of phlogiston theory as the traditional chemical revolution, with
Chemical revolution
74994
semi-empirical atomic orbital calculations were performed. Theoretical chemists became extensive users of the early digital computers. One major advance came with the 1951 paper in Reviews of Modern Physics by Clemens C. J. Roothaan in 1951, largely on the "LCAO MO" approach (Linear Combination of Atomic Orbitals Molecular Orbitals), for many years the second-most cited paper in that journal. A very detailed account of such use in the United Kingdom is given by Smith and Sutcliffe. The first "ab initio" Hartree–Fock method calculations on diatomic molecules were performed in 1956 at MIT, using a basis set of Slater orbitals. For
Computational chemistry
960240
be reduced to mechanistic views. Although he believed in atoms, he did not believe that atomic theories were enough to describe the chemical processes that go on. He believed that atoms could not be isolated individually and that they join together to form elements. He took an empirical approach when establishing his descriptions of chemistry. Stahl used the works of Johann Joachim Becher to help him come up with explanations of chemical phenomena. The main theory that Stahl got from J. J. Becher was the theory of phlogiston. This theory did not have any experimental basis before Stahl. He was
Georg Ernst Stahl
77721
quantum mechanics, two basic theories were proposed to provide a quantum description of chemical bonding: valence bond (VB) theory and molecular orbital (MO) theory. A more recent quantum description is given in terms of atomic contributions to the electronic density of states. In COOP, COHP and BCOOP, evaluation of bond covalency is dependent on the basis set. To overcome this issue, an alternative formulation of the bond covalency can be provided in this way. The center mass of an atomic orbital , with quantum numbers , for atom A is defined as where is the contribution of the atomic orbital
Covalent bond
14955931
Similar models existed in Antiquity, notably the atomic theory associated with Democritus, which was criticized by Aristotle because such a theory entails a vacuum, which Aristotle believed nature abhors. Modern atomic theory traces back to Johannes Kepler and his work on geometric packing problems. Until the twentieth century, graph-like models of crystals focused on the positions of the (atomic) components, and these pre-20th century models were the focus of two controversies in chemistry and materials science. The two controversies were (1) the controversy over Robert Boyle’s corpuscular theory of matter, which held that all material substances were composed of particles,
Periodic graph (crystallography)
545307
such rule was absolutely necessary to any incipient theory, since one needed an assumed molecular formula in order to calculate relative atomic weights. Dalton's "rule of greatest simplicity" caused him to assume that the formula for water was OH and ammonia was NH, quite different from our modern understanding (HO, NH). Despite the uncertainty at the heart of Dalton's atomic theory, the principles of the theory survived. Dalton published his table of relative atomic weights containing six elements, hydrogen, oxygen, nitrogen, carbon, sulfur and phosphorus, with the atom of hydrogen conventionally assumed to weigh 1. Dalton provided no indication in
John Dalton
2754954
basis for Hilbert space was developed from Hilbert's ideas by Erhard Schmidt and Frigyes Riesz. It was almost twenty years later, when quantum mechanics was formulated in terms of the Schrödinger equation, that the connection was made to atomic spectra; a connection with the mathematical physics of vibration had been suspected before, as remarked by Henri Poincaré, but rejected for simple quantitative reasons, absent an explanation of the Balmer series. The later discovery in quantum mechanics that spectral theory could explain features of atomic spectra was therefore fortuitous, rather than being an object of Hilbert's spectral theory. Consider a bounded
Spectral theory
5408822
linear combination of atomic orbitals approach), which is the usual choice within the quantum chemistry community, or plane waves which are typically used within the solid state community. Several types of atomic orbitals can be used: Gaussian-type orbitals, Slater-type orbitals, or numerical atomic orbitals. Out of the three, Gaussian-type orbitals are by far the most often used, as they allow efficient implementations of Post-Hartree–Fock methods. In modern computational chemistry, quantum chemical calculations are performed using a finite set of basis functions. When the finite basis is expanded towards an (infinite) complete set of functions, calculations using such a basis set
Basis set (chemistry)
3296207
may be hybrids. Often, the bonding atomic orbitals have a character of several possible types of orbitals. The methods to get an atomic orbital with the proper character for the bonding is called hybridization. Modern valence bond theory now complements molecular orbital theory, which does not adhere to the valence bond idea that electron pairs are localized between two specific atoms in a molecule but that they are distributed in sets of molecular orbitals which can extend over the entire molecule. Molecular orbital theory can predict magnetic and ionization properties in a straightforward manner, while valence bond theory gives similar
Valence bond theory
12637
fundamental defect in the theory even at its conception, namely that a classical charged object cannot sustain orbital motion because it is accelerating and therefore loses energy due to electromagnetic radiation. Nevertheless, the Saturnian model turned out to have more in common with modern theory than any of its contemporaries. In 1909, Ernest Rutherford discovered that the bulk of the atomic mass was tightly condensed into a nucleus, which was also found to be positively charged. It became clear from his analysis in 1911 that the plum pudding model could not explain atomic structure. In 1913 as Rutherford's post-doctoral student,
Atomic orbital
19141614
Pople diagram A Pople diagram or Pople's Diagram is a diagram which describes the relationship between various calculation methods in computational chemistry. It was initially introduced in January 1965 by Sir John Pople, , during the "Symposium of Atomic and Molecular Quantum Theory" in Florida. The Pople Diagram can be either 2-dimensional or 3-dimensional, with the axes representing ab inito methods, basis sets and treatment of relativity. The diagram attempts to balance calculations by giving all aspects of a computation equal weight. John Pople first introduced the Pople Diagram during the Symposium on Atomic and Molecular Quantum Theory held on
Pople diagram
6901516
usually seen in the context of the Jugendstil, his demand for "the elimination of ornament" joined the slogan "form follows function" as a principle of the architectural so-called Modern Movement that came to dominate the mid-20th century. Walter Gropius, Ludwig Mies van der Rohe and Le Corbusier provided the theoretical basis for the International Style with aims of using industrialised architecture to reshape society. Frank Lloyd Wright, while modern in rejecting historic revivalism, was idiosyncratic in his theory, which he conveyed in copious writing. Wright did not subscribe to the tenets of the International Style, but evolved what he hoped
Architectural theory
5408824
common to use a basis composed of atomic orbitals, centered at each nucleus within the molecule (linear combination of atomic orbitals ansatz). The physically best motivated basis set are Slater-type orbitals (STOs), which are solutions to the Schrödinger equation of hydrogen-like atoms, and decay exponentially far away from the nucleus. While hydrogen-like atoms lack many-electron interactions, it can be shown that the molecular orbitals of Hartree-Fock and density-functional theory also exhibit exponential decay. Furthermore, S-type STOs also satisfy Kato's cusp condition at the nucleus, meaning that they are able to accurately describe electron density near the nucleus. However, calculating integrals
Basis set (chemistry)
78522
used practical, experimental observation to classify materials. In Europe, the Ancient Greek system of Aristotle evolved slightly into the medieval system, which for the first time in Europe became subject to experimental verification in the 1600s, during the Scientific Revolution. Modern science does not support the classical elements as the material basis of the physical world. Atomic theory classifies atoms into more than a hundred chemical elements such as oxygen, iron, and mercury. These elements form chemical compounds and mixtures, and under different temperatures and pressures, these substances can adopt different states of matter. The most commonly observed states of
Classical element
30836
Atomic theory In chemistry and physics, atomic theory is a scientific theory of the nature of matter, which states that matter is composed of discrete units called atoms. It began as a philosophical concept in ancient Greece and entered the scientific mainstream in the early 19th century when discoveries in the field of chemistry showed that matter did indeed behave as if it were made up of atoms. The word "atom" comes from the Ancient Greek adjective "atomos", meaning "indivisible". 19th century chemists began using the term in connection with the growing number of irreducible chemical elements. Around the turn
Atomic theory
6066472
in Rand's work with author Colin Wilson, in "The Atlantis Blueprint" (published in 2002). The second work theorized that Atlantis was to be found in Lesser Antarctica, near the coast of the Ross Ice Shelf. A geological theory known as "Earth Crust Displacement" forms the basis of their work. The Atlantis Blueprint uses both scientific and pseudoscientific (such as mere speculation and assumptions) means to back up the theory. Charles Hapgood came up with the "Earth Crustal Displacement theory". Hapgood's theory suggests that Earth's outer crust is able to move upon the upper mantle layer rapidly up to a distance
Location hypotheses of Atlantis
864834
escape through a small pinhole in a vessel at half the rate of the other (heavier gases diffuse more slowly). A complete theoretical explanation of Graham's law was provided years later by the kinetic theory of gases. Graham's law provides a basis for separating isotopes by diffusion—a method that came to play a crucial role in the development of the atomic bomb. Graham's law is most accurate for molecular effusion which involves the movement of one gas at a time through a hole. It is only approximate for diffusion of one gas in another or in air, as these processes
Graham's law
14398960
back to Pakistan and joined Pakistan Atomic Energy Commission (PAEC). Fayyazuddin joined Pakistan Atomic Energy Commission (PAEC) in 1962 where he worked under Abdus Salam. At the PAEC, he continued his research on the cosmic ray mu mesons. He then published his research journal on the basis of the Bethe-Bloch theory, in which the theory supports the idea of a logarithmic increase of ionization loss for relativistic particles. At the time he published his thesis, there was a controversy between two sets of experiments, Fayyazuddin founded interested to perform the experiment. Fayyazuddin on a post-doctoral research went to United States
Fayyazuddin
13014484
Character orientation Character orientation is how people relate to the world by acquiring and using things (assimilation) and by relating to self and others (socialization), and they can do so either nonproductively or productively. Erich Fromm is a theorist who came up with six different character orientations; Receptive, Exploitative, Hoarding, Necrophilous, Marketing and Productive. German-American psychoanalyst Erich Fromm was influenced by Freudian ideologies when coming up with the theory of character orientation. The basis of character orientation comes from Freud who said that character traits underlie behavior and that they must be inferred from it. These character traits can be
Character orientation
17657192
vortices where he developed what is now called the Gross–Pitaevskii theory of Bose–Einstein condensates, one of the theories more systematically used to describe the physics of ultracold atomic gases nowadays. Another famous paper was written in collaboration with Igor E. Dzyaloshinsky and Evgeny Lifshitz on the van der Waals forces where the theory of the thermal and quantum fluctuations of the electromagnetic field was developed in a systematic way with important implications on modern applications to solid state physics and atomic physics. Lev Pitaevskii started collaborating with the University of Trento at the end of the 1980s through a series
Lev Pitaevskii
9463661
died of the plague in 1637 in Wittenberg. Sennert is notable for his contributions to the development of an early version of atomic theory. Specifically, he forms an intermediate bridge between the works of Geber and the more recognized Corpuscularianists such as Robert Boyle. Corpuscularianism differs from modern atomic theory in a number of significant ways, most noticeably a lack of a mathematical argument for its existence, something Sennert specifically rejected. Sennert is an intermediate step between corpsucular particle theory and Aristotelian forms. The same works that are often sited as demonstrating his early atomist views also emphasize the importance
Daniel Sennert
5408821
Basis set (chemistry) A basis set in theoretical and computational chemistry is a set of functions (called basis functions) that is used to represent the electronic wave function in the Hartree–Fock method or density-functional theory in order to turn the partial differential equations of the model into algebraic equations suitable for efficient implementation on a computer. The use of basis sets is equivalent to the use of an approximate resolution of the identity. The single-particle states (molecular orbitals) are then expressed as linear combinations of the basis functions. The basis set can either be composed of atomic orbitals (yielding the
Basis set (chemistry)
809901
years. He later used the same phrase to describe the Alpher, Herman, and Gamow group. On graduation, he worked on quantum theory in Göttingen, where his research into the atomic nucleus provided the basis for his doctorate. He then worked at the Theoretical Physics Institute of the University of Copenhagen from 1928 to 1931, with a break to work with Ernest Rutherford at the Cavendish Laboratory in Cambridge. He continued to study the atomic nucleus (proposing the "liquid drop" model), but also worked on stellar physics with Robert Atkinson and Fritz Houtermans. In 1931, Gamow was elected a corresponding member
George Gamow
11206629
rise of comparative political theory. The Indian political theorist Aakash Singh Rathore has been attempting to cultivate the discipline with the 2010 book "Indian Political Thought--A Reader" (Routledge), and the 2017 monograph "Indian Political Theory: Laying the Groundwork for Svaraj" (Routledge). All political parties have some ideologies, philosophies and world views. These decide their policy formulation and agenda formation. In modern days, the ideologies of the political parties are similar and thus it is difficult to differentiate them on the basis of their ideologies. The ideologies of some important national parties in India- Groups with different ideologies came together before
Indian political philosophy
13381305
putting out our music."" From this the band members themselves formed Atomic Heart Records, setting up headquarters in New York City, calling their new studio Atomic Heart. Band members Tim and Mark both moved to New York; ""It was a dream of mine, ever since our first American tour in the mid-1990s, to live in New York"", whilst drummer Rick resided in Edinburgh's Craiglockhart, commuting to the New York Studio on a regular basis and working in ""intensive bursts"". The announcement itself of the band's boycott on the album format came at the time of release for Twilight of the
A–Z Series
11776956
atomic model, even though the physical meaning of these oscillators was far from clear. Nevertheless, Bohr and Kramers had two objections to Slater's proposal: As Jammer puts it, this refocussed the theory "to harmonize the physical picture of the continuous electromagnetic field with the physical picture, not as Slater had proposed of light quanta, but of the discontinuous quantum transitions in the atom." Bohr and Kramers hoped to be able to evade the photon hypothesis on the basis of ongoing work by Kramers to describe "dispersion" (in present-day terms inelastic scattering) of light by means of a classical theory of
BKS theory
259574
untenable. There is still something missing." Erwin Schrödinger said "Consciousness cannot be accounted for in physical terms. For consciousness is absolutely fundamental. It cannot be accounted for in terms of anything else". Werner Heisenberg, who came up with the uncertainty principle wrote "The ontology of materialism rested upon the illusion that the kind of existence, the direct ‘actuality’ of the world around us, can be extrapolated into the atomic range. This extrapolation, however, is impossible…Atoms are not things". Some 20th century physicists (such as Eugene Wigner and Henry Stapp) and modern day physicists and science writers—such as Paul Davies and
Materialism
11776953
BKS theory The Bohr–Kramers–Slater theory (BKS theory) was perhaps the final attempt at understanding the interaction of matter and electromagnetic radiation on the basis of the so-called old quantum theory, in which quantum phenomena are treated by imposing quantum restrictions on classically describable behaviour. It was advanced in 1924, and sticks to a "classical" wave description of the electromagnetic field. It was perhaps more a research program than a full physical theory, the ideas that are developed not being worked out in a quantitative way. One aspect, the idea of modelling atomic behaviour under incident electromagnetic radiation using "virtual oscillators"
BKS theory
4465591
be interpreted as wave or particle models. His hypothesis was that an incoming particle would strike the nucleus and create an excited compound nucleus. This formed the basis of his liquid drop model and later provided a theory base for the explanation of nuclear fission. In 1913, Henry Moseley, working from Van den Broek's earlier idea, introduces concept of atomic number to fix inadequacies of Mendeleev's periodic table, which had been based on atomic weight. The peak of Frederick Soddy's career in radiochemistry was in 1913 with his formulation of the concept of isotopes, which stated that certain elements exist
History of chemistry
766374
For many years, most such calculations relied upon the "linear combination of atomic orbitals" (LCAO) approximation, using an ever-larger and more complex basis set of atomic orbitals as the starting point. The last step in such a calculation is the assignment of electrons among the molecular orbitals according to the Aufbau principle. Not all methods in calculational chemistry rely on electron configuration: density functional theory (DFT) is an important example of a method that discards the model. For atoms or molecules with more than one electron, the motion of electrons are correlated and such a picture is no longer exact.
Electron configuration
2824489
principal quantum number "n". The principal quantum number was first created for use in the semiclassical Bohr model of the atom, distinguishing between different energy levels. With the development of modern quantum mechanics, the simple Bohr model was replaced with a more complex theory of atomic orbitals. However, the modern theory still requires the principal quantum number. Apart from the principal quantum number, the other quantum numbers for bound electrons are the azimuthal quantum number ℓ, the magnetic quantum number "m", and the spin quantum number . There is a set of quantum numbers associated with the energy states of
Principal quantum number
1571889
risk on a more scientific basis. Independently of each other, compound interest was studied and probability theory emerged as a well-understood mathematical discipline. Another important advance came in 1662 from a London draper named John Graunt, who showed that there were predictable patterns of longevity and death in a group, or cohort, of people of the same age, despite the uncertainty of the date of death of any one individual. This study became the basis for the original life table. One could now set up an insurance scheme to provide life insurance or pensions for a group of people, and
Actuarial science
297727
not generally considered to be chemical "compounds". For many centuries, Western physicians and chemists believed in vitalism. This was the widespread conception that substances found in organic nature are created from the chemical elements by the action of a "vital force" or "life-force" ("vis vitalis") that only living organisms possess. Vitalism taught that these "organic" compounds were fundamentally different from the "inorganic" compounds that could be obtained from the elements by chemical manipulations. Vitalism survived for a while even after the rise of modern ideas about the atomic theory and chemical elements. It first came under question in 1824, when
Organic compound
17536141
briefly discussing various theories, including quantum theory, Heisenberg discusses the basis for the fundamental concepts of quantum theory. Also by this time Heisenberg has stated, "the interaction between observer and object causes uncontrollable and large changes in the [atomic] system being observed...". In this work Heisenberg also discusses his uncertainty principle or uncertainty relations. The Physical Principles of the Quantum Theory The Physical Principles of the Quantum Theory (German: Physikalische Prinzipien der Quantentheorie) by Nobel laureate (1932) Werner Heisenberg and subsequently translated by Carl Eckart and Frank C. Hoyt. The book was first published in 1930 by University of Chicago
The Physical Principles of the Quantum Theory
3994410
a society, the individual becomes increasingly important, eventually replacing the family or community as the fundamental unit of society. Sociological theories of the late 19th century such as Social Darwinism provided a basis for asking what were the laws of evolution of human society. The current modernization theory originated with the ideas of German sociologist Max Weber (1864–1920) regarding the role of rationality and irrationality in the transition from traditional to modern society. Weber's approach provided the basis for the modernization paradigm as popularized by Harvard sociologist Talcott Parsons (1902–1979), who translated Weber's works into English in the 1930s and
Modernization theory
17755274
court of Rudolph II, to whom he dedicated an edition of "Anversa" in 1584. In Prague, he also met Michiel Coignet and Giordano Bruno, who used the compass to refute Aristotle's hypothesis on the incommensurability of infinitesimals, thus confirming the existence of the "minimum" which was the basis of his atomic theory. Bruno published the dialogues "Mordentius" and "De Mordentii circino" which praised Mordente, but also presented criticisms that raised protests from the mathematician. Mordente replied in 1586 and Bruno responded with the satires "Idiota triumphans" and "De somnii interpretatione." After Mordente gained support in the dispute from the French
Fabrizio Mordente
6066688
Uncleftish Beholding "Uncleftish Beholding" (1989) is a short text written by Poul Anderson. It is written using almost exclusively words of Germanic origin (Anglish), and was intended to illustrate what the English language might look like if it had not received its considerable number of loanwords from other languages, particularly Latin, Greek and French. The text is about basic atomic theory and relies on a number of word coinings, many of which have cognates in modern German, an important scientific language in its own right. The title "Uncleftish beholding" calques "atomic theory". The text begins: It goes on to define
Uncleftish Beholding
1366738
Laurea in physics at the University of Rome La Sapienza in 1929. In 1932, he published a paper in the field of atomic spectroscopy concerning the behaviour of aligned atoms in time-varying magnetic fields. This problem, also studied by I.I. Rabi and others, led to an important sub-branch of atomic physics, that of radio-frequency spectroscopy. In the same year, Majorana published his paper on a relativistic theory of particles with arbitrary intrinsic momentum, in which he developed and applied infinite dimensional representations of the Lorentz group, and gave a theoretical basis for the mass spectrum of elementary particles. Like most
Ettore Majorana
12360696
people who have "a common established law and judicature to appeal to, with authority to decide controversies between them." German philosopher Georg Wilhelm Friedrich Hegel distinguished the "state" from "civil society" ("bürgerliche Gesellschaft") in "Elements of the Philosophy of Right". Hegel believed that civil society and the state were polar opposites, within the scheme of his dialectic theory of history. The modern dipole state–civil society was reproduced in the theories of Alexis de Tocqueville and Karl Marx. Nowadays in post-modern theory civil society is necessarily a source of law, by being the basis from which people form opinions and lobby
Law
262963
the "Linear combination of atomic orbitals molecular orbital method" ansatz. Here, the molecular orbitals are expressed as linear combinations of atomic orbitals. Molecular orbitals were first introduced by Friedrich Hund and Robert S. Mulliken in 1927 and 1928. The linear combination of atomic orbitals or "LCAO" approximation for molecular orbitals was introduced in 1929 by Sir John Lennard-Jones. His ground-breaking paper showed how to derive the electronic structure of the fluorine and oxygen molecules from quantum principles. This qualitative approach to molecular orbital theory is part of the start of modern quantum chemistry. Linear combinations of atomic orbitals (LCAO) can
Molecular orbital
75010
is necessary to include relativistic and spin orbit terms, both of which are far more important for heavy atoms. In all of these approaches, along with choice of method, it is necessary to choose a basis set. This is a set of functions, usually centered on the different atoms in the molecule, which are used to expand the molecular orbitals with the linear combination of atomic orbitals (LCAO) molecular orbital method ansatz. Ab initio methods need to define a level of theory (the method) and a basis set. The Hartree–Fock wave function is a single configuration or determinant. In some
Computational chemistry
3296204
theory: resonance (1928) and orbital hybridization (1930). According to Charles Coulson, author of the noted 1952 book "Valence", this period marks the start of "modern valence bond theory", as contrasted with older valence bond theories, which are essentially electronic theories of valence couched in pre-wave-mechanical terms. Resonance theory was criticized as imperfect by Soviet chemists during the 1950s. According to this theory a covalent bond is formed between the two atoms by the overlap of half filled valence atomic orbitals of each atom containing one unpaired electron. A valence bond structure is similar to a Lewis structure, but where a
Valence bond theory
284524
physicist working at the Institute in Copenhagen, proposed the Bohr–Kramers–Slater theory (BKS). It was more a programme than a full physical theory, as the ideas it developed were not worked out quantitatively. BKS theory became the final attempt at understanding the interaction of matter and electromagnetic radiation on the basis of the old quantum theory, in which quantum phenomena were treated by imposing quantum restrictions on a classical wave description of the electromagnetic field. Modelling atomic behaviour under incident electromagnetic radiation using "virtual oscillators" at the absorption and emission frequencies, rather than the (different) apparent frequencies of the Bohr orbits,
Niels Bohr
4465518
molecules). In 1808, Dalton first published "New System of Chemical Philosophy" (1808-1827), in which he outlined the first modern scientific description of the atomic theory. This work identified chemical elements as a specific type of atom, therefore rejecting Newton's theory of chemical affinities. Instead, Dalton inferred proportions of elements in compounds by taking ratios of the weights of reactants, setting the atomic weight of hydrogen to be identically one. Following Jeremias Benjamin Richter (known for introducing the term "stoichiometry"), he proposed that chemical elements combine in integral ratios. This is known as the law of multiple proportions or Dalton's law,
History of chemistry
2485093
of herring gulls, seeing how they were able to use motionless wings to catch up-currents of air. He measured various birds to see how the centre of gravity compared with the centre of support. As a result of his deliberations, Lanchester, eventually formulated his circulation theory of flight. This is the basis of aerodynamics and the foundation of modern aerofoil theory. In 1894 he tested his theory on a number of models. In 1897 he presented a paper entitled "The soaring of birds and the possibilities of mechanical flight" to the Physical Society, but it was rejected, being too advanced
Frederick W. Lanchester
307808
energy are no longer valid. The two chief theories of modern physics present a different picture of the concepts of space, time, and matter from that presented by classical physics. Classical mechanics approximates nature as continuous, while quantum theory is concerned with the discrete nature of many phenomena at the atomic and subatomic level and with the complementary aspects of particles and waves in the description of such phenomena. The theory of relativity is concerned with the description of phenomena that take place in a frame of reference that is in motion with respect to an observer; the special theory
Physics
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KTH on December 12, 1930. As a KTH professor, Enskog mainly got caught up in teaching duties, and did not do much further research. The fusion of Chapman's and Enskog's theories later became known as the Chapman–Enskog method for solving the Boltzmann equation. In a 1939 book called "The Mathematical Theory of Non-Uniform Gases", written by Chapman and Thomas Cowling and dedicated to David Enskog, the authors expanded this theory under the Chapman-Enskog designation. Further recognition of Enskog's work came in 1945, when the Smyth Report on the US atomic weapons project was published. Chapman and Enskog were mentioned as
David Enskog
307809
of relativity is concerned with motion in the absence of gravitational fields and the general theory of relativity with motion and its connection with gravitation. Both quantum theory and the theory of relativity find applications in all areas of modern physics. While physics aims to discover universal laws, its theories lie in explicit domains of applicability. Loosely speaking, the laws of classical physics accurately describe systems whose important length scales are greater than the atomic scale and whose motions are much slower than the speed of light. Outside of this domain, observations do not match predictions provided by classical mechanics.
Physics
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is located at each center. Importantly, the radius of convergence of this multipole series is sufficiently small that the relevant series will be convergent when describing two molecules in van der Waals contact. The DMA series are derived from ab initio or density functional theory calculations using Gaussian basis sets. If the molecular orbitals are written as linear combinations of atomic basis functions the electron density takes the form of a sum of products of the basis functions, called density matrix elements. Boys (1950) showed that the product of two spherical Gaussian functions, centered at different points, can be expressed
Distributed multipole analysis
5658223
different basis set families may yield drastically different results. These problems can be addressed by modern methods for computing net atomic charges, such as density derived electrostatic and chemical (DDEC) analysis, electrostatic potential analysis, and natural population analysis. Mulliken population analysis Mulliken charges arise from the Mulliken population analysis and provide a means of estimating partial atomic charges from calculations carried out by the methods of computational chemistry, particularly those based on the linear combination of atomic orbitals molecular orbital method, and are routinely used as variables in linear regression (QSAR) procedures. The method was developed by Robert S. Mulliken,
Mulliken population analysis
18365024
Chemistry. John Dalton founded modern Chemistry in 1803 with his atomic theory. William Henry (1774 – 1836) was a Manchester chemist who developed what is known today as Henry's Law. James Joule pioneered the science of thermodynamics in the 1840s while working in Manchester. In the basement of the Royal Manchester Institution a laboratory was installed by Lyon Playfair who worked there briefly as Professor of Chemistry after he left Thomson's of Clitheroe. He was succeeded by Frederick Crace Calvert who made phenol which was used by Joseph Lister as an antiseptic. The teaching of chemistry in Owens College began
School of Chemistry, University of Manchester
319411
Time", a "time policeman" from the Twentieth Century, equipped with information and technologies from much further in the future, is outwitted by a medieval knight and barely escapes with his life. Yet another story, "The Man Who Came Early", features a 20th-century United States Army soldier stationed in Iceland who is transported to the tenth century. Although he is full of ideas, his lack of practical knowledge of how to implement them and his total unfamiliarity with the technology and customs of the period lead to his downfall. Anderson wrote the short essay "Uncleftish Beholding", an introduction to atomic theory,
Poul Anderson
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to the point where he would no longer have any useful moves. In 1952, Fine published the 442-page "The Middle Game in Chess", perhaps the most comprehensive treatment of the subject up until that time. The mid-20th century also saw the publication of "The Middle Game", volumes 1 and 2, by former World Champion Max Euwe and Hans Kramer, and a series of books by the Czechoslovak-German grandmaster Luděk Pachman: three volumes of "Complete Chess Strategy", "Modern Chess Strategy", "Modern Chess Tactics", and "Attack and Defense in Modern Chess Tactics". Another key turning point in middlegame theory came with the
Chess theory
3061320
that became the basis for modern AT; Leont'ev, one of the principal founders of activity theory, both developed and reacted against Vygotsky's work. Leont'ev's formulation of general activity theory is currently the most influential in post-Soviet developments in AT, which have largely been in social-scientific, organizational, and writing-studies rather than psychological research. The second major line of development within activity theory involves Russian scientists, such as P. K. Anokhin and Nikolai Bernstein, more directly concerned with the neurophysiological basis of activity; its foundation is associated with the Soviet philosopher of psychology Sergei Rubinstein. This work was subsequently developed by researchers
Activity theory
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minima of Aristotle. However, the concept of "minima naturalia" continued to shape philosophical thinking even among these mechanistic philosophers in the transitional centuries between the Aristotelianism of the medieval Scholastics and the worked-out atomic theory of modern scientists like Dalton. The mechanist Pierre Gassendi discussed "minima naturalia" in the course of expounding his opposition to Scholastic Aristotelianism, and his own attempted reconciliation between the atomism of Epicurus and the Catholic faith. Aristotle's "mininima naturalia" became "corpuscles" in the alchemical works of Geber and Daniel Sennert, who in turn influenced the corpuscularian alchemist Robert Boyle, one of the founders of modern
Minima naturalia
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important foundational contributions from Catholic scientists include: physics (Galileo) despite his trial and conviction in 1633 for publishing a treatise on his observation that the earth revolves around the sun, which banned his writings and made him spend the remainder of his life under house arrest, acoustics (Mersenne), mineralogy (Agricola), modern chemistry (Lavoisier), modern anatomy (Vesalius), stratigraphy (Steno), bacteriology (Kircher and Pasteur), genetics (Mendel), analytical geometry (Descartes), heliocentric cosmology (Copernicus), atomic theory (Boscovich), and the Big Bang Theory on the origins of the universe (Lemaître). Jesuits devised modern lunar nomenclature and stellar classification and some 35 craters of the moon
Catholic Church and science
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Clerk Maxwell in the 19th century, and remained a deep puzzle for those who advocated an atomic theory of matter. Einstein resolved this problem in 1906 by proposing that atomic motion is quantized. This was the first application of quantum theory to mechanical systems. A short while later, Peter Debye gave a quantitative theory of solid specific heats in terms of quantized oscillators with various frequencies (see Einstein solid and Debye model). One-dimensional problems are easy to solve. At any energy "E", the value of the momentum "p" is found from the conservation equation: which is integrated over all values
Old quantum theory
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Nonbonding MOs: The two theories differ in the order that the electron configuration of the molecule is built up. For valence bond theory, the atomic hybrid orbitals are filled first to produce a full valence configuration of bonding pairs and lone pairs. If several such configurations exist, a weighted superposition of these configurations is then applied. In contrast, for molecular orbital theory a weighted superposition of atomic orbitals is performed first, followed by the filling of the resulting molecular orbitals by the aufbau principle. Either theory has its advantages and uses. As valence bond theory builds the molecular wavefunction out
Chemical bonding model
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"small nut") inside a watery type of fruit (like a peach). In 1844, Michael Faraday used the term to refer to the "central point of an atom". The modern atomic meaning was proposed by Ernest Rutherford in 1912. The adoption of the term "nucleus" to atomic theory, however, was not immediate. In 1916, for example, Gilbert N. Lewis stated, in his famous article "The Atom and the Molecule", that "the atom is composed of the "kernel" and an outer atom or "shell"" The nucleus of an atom consists of neutrons and protons, which in turn are the manifestation of more
Atomic nucleus
3994406
Modernization theory Modernization theory is used to explain the process of modernization within societies. Modernization refers to a model of a progressive transition from a 'pre-modern' or 'traditional' to a 'modern' society. Modernization theory originated from the ideas of German sociologist Max Weber (1864–1920), which provided the basis for the modernization paradigm developed by Harvard sociologist Talcott Parsons (1902–1979). The theory looks at the internal factors of a country while assuming that with assistance, "traditional" countries can be brought to development in the same manner more developed countries have been. Modernization theory was a dominant paradigm in the social sciences
Modernization theory
3994431
a world market economy. Modernization theory Modernization theory is used to explain the process of modernization within societies. Modernization refers to a model of a progressive transition from a 'pre-modern' or 'traditional' to a 'modern' society. Modernization theory originated from the ideas of German sociologist Max Weber (1864–1920), which provided the basis for the modernization paradigm developed by Harvard sociologist Talcott Parsons (1902–1979). The theory looks at the internal factors of a country while assuming that with assistance, "traditional" countries can be brought to development in the same manner more developed countries have been. Modernization theory was a dominant paradigm
Modernization theory
6403354
solids. If we consider the extreme case of isolated atoms, the Wannier function would become an isolated atomic orbital. That limit suggests the choice of an atomic wave function as an approximate form for the Wannier function, the so-called tight binding approximation. Modern explanations of electronic structure like t-J model and Hubbard model are based on tight binding model. Tight binding can be understood by working under a second quantization formalism. Using the atomic orbital as a basis state, the second quantization Hamiltonian operator in the tight binding framework can be written as: Here, hopping integral formula_51 corresponds to the
Tight binding
20339166
fans of the character Devil Dinosaur and had hired Montclare and Reeder to pen the basis for a new series that involved the character ending up in modern day. They came up with the idea of Devil Dinosaur interacting with a girl and fell in love with the idea of working with a hero who wasn't a "regular cape-and-tights superhero". Reeder explains the primary inspiration for the creation of the character: They also viewed the series as a direct sequel to the "Moon-Boy and Devil Dinosaur" series from Jack Kirby hence the first villains that Moon Girl and Devil Dinosaur
Moon Girl (Marvel Comics)
317321
with error, such as in celestial mechanics. The modern predictive approach was pioneered by Bruno de Finetti, with the central idea of exchangeability – that future observations should behave like past observations. This view came to the attention of the Anglophone world with the 1974 translation of de Finetti's book, and has since been propounded by such statisticians as Seymour Geisser. The mathematics of probability can be developed on an entirely axiomatic basis that is independent of any interpretation: see the articles on probability theory and probability axioms for a detailed treatment. Probability interpretations The word probability has been used
Probability interpretations
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and Company, which eventually grew into one of the largest and most successful companies in America. Throughout the 19th century, chemistry was divided between those who followed the atomic theory of John Dalton and those who did not, such as Wilhelm Ostwald and Ernst Mach. Although such proponents of the atomic theory as Amedeo Avogadro and Ludwig Boltzmann made great advances in explaining the behavior of gases, this dispute was not finally settled until Jean Perrin's experimental investigation of Einstein's atomic explanation of Brownian motion in the first decade of the 20th century. Well before the dispute had been settled,
History of chemistry
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was introduced by the Soviet physicists Yakov Frenkel and T. Kontorova. The Frenkel defect became firmly fixed in the physics of solids and liquids. In the 1930s, this research was supplemented with works on the theory of plastic deformation. Their theory, now known as the Frenkel–Kontorova model, is important in the study of dislocations. Tomlinson model The Tomlinson model, also known as the Prandtl–Tomlinson Model, is one of the most popular models in nanotribology widely used as the basis for many investigations of frictional mechanisms on the atomic scale. Essentially, a nanotip is dragged by a spring over a corrugated
Tomlinson model
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as eigenfunctions (wave functions) of the self-consistent field Hamiltonian and it was at this point that molecular orbital theory became fully rigorous and consistent. This rigorous approach is known as the Hartree–Fock method for molecules although it had its origins in calculations on atoms. In calculations on molecules, the molecular orbitals are expanded in terms of an atomic orbital basis set, leading to the Roothaan equations. This led to the development of many ab initio quantum chemistry methods. In parallel, molecular orbital theory was applied in a more approximate manner using some empirically derived parameters in methods now known as
Molecular orbital theory
417182
basis on which the Moon's mean motion should accelerate in response to perturbational changes in the eccentricity of the orbit of Earth around the Sun. Laplace's initial computation accounted for the whole effect, thus seeming to tie up the theory neatly with both modern and ancient observations. However, in 1854, John Couch Adams caused the question to be re-opened by finding an error in Laplace's computations: it turned out that only about half of the Moon's apparent acceleration could be accounted for on Laplace's basis by the change in Earth's orbital eccentricity. Adams's finding provoked a sharp astronomical controversy that
Tidal acceleration
589065
entertainment. One of the earliest steps towards "atomic physics" was the recognition that matter was composed of "atoms", in modern terms the basic unit of a chemical element. This theory was developed by John Dalton in the 18th century. At this stage, it wasn't clear what atoms were - although they could be described and classified by their observable properties in bulk; summarized by the developing periodic table, by John Newlands and Dmitri Mendeleyev around the mid to late 19th century. Later, the connection between atomic physics "and" optical physics became apparent, by the discovery of spectral lines and attempts
Atomic, molecular, and optical physics
1557603
alphabet. As one of the "Physical Review"s reviewers, Bethe saw the manuscript and struck out the words "in absentia". Bethe believed that the atomic nucleus was like a quantum liquid drop. He investigated the nuclear matter problem by considering the work done by Keith Brueckner on perturbation theory. Working with Jeffrey Goldstone, he produced a solution for the case where there was an infinite hard-core potential. Then, working with Baird Brandow and Albert Petschek, he came up with an approximation that converted the scattering equation into an easily solved differential equation. This then led him to the Bethe-Faddeev equation, a
Hans Bethe
30865
An electron can potentially be found at any distance from the nucleus, but, depending on its energy level, exists more frequently in certain regions around the nucleus than others; this pattern is referred to as its atomic orbital. The orbitals come in a variety of shapes-sphere, dumbbell, torus, etc.-with the nucleus in the middle. Atomic theory In chemistry and physics, atomic theory is a scientific theory of the nature of matter, which states that matter is composed of discrete units called atoms. It began as a philosophical concept in ancient Greece and entered the scientific mainstream in the early 19th
Atomic theory
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single 1s atomic orbital for its electron, the bond forms by overlap of these two atomic orbitals. In the figure the two atomic orbitals are depicted on the left and on the right. The vertical axis always represents the orbital energies. Each atomic orbital is singly occupied with an up or down arrow representing an electron. Application of MO theory for dihydrogen results in having both electrons in the bonding MO with electron configuration 1σ. The bond order for dihydrogen is (2-0)/2 = 1. The photoelectron spectrum of dihydrogen shows a single set of multiplets between 16 and 18 eV
Molecular orbital diagram
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Serbian state universities. Physics is taught from Newtonian mechanics, Fluid Dynamics, Waves, Optics, Electricity, Magnetism, to modern physics, usually ending with STR, Relativistic Dynamics, Quantum Theory, Quantum Mechanics, Molecular Physics, Physical Chemistry, Atomic Physics, Solid State Physics, Quantum Optics, Nuclear Physics, Nuclear Engineering, Elementary Particle Physics, and introduction to Astrophysics and Cosmology, General Relativity, and some basic introduction to String Theory, Cosmology, and M-Theory. There are 5 computer labs in Mathematical Gymnasium, with ca. 110 dual core and quad core computers, and one super-computer. The School operates its own wireless network. Students gain knowledge in programming languages (Pascal, Delphi, C,
Mathematical Grammar School
4357780
PLATO used to perform Density Functional Theory, and which still applies to how the Density Functional Tight Binding integral tables are built, is summarized in several papers: The way it now performs tight binding is summarized in the following papers Some examples of its use are listed below. PLATO (computational chemistry) PLATO (Package for Linear-combination of ATomic Orbitals) is a suite of programs for electronic structure calculations. It receives its name from the choice of basis set (numeric atomic orbitals) used to expand the electronic wavefunctions. PLATO is a code, written in C, for the efficient modelling of materials. It
PLATO (computational chemistry)
317332
Eventually, analytical considerations compelled the incorporation of continuous variables into the theory. This culminated in modern probability theory, on foundations laid by Andrey Nikolaevich Kolmogorov. Kolmogorov combined the notion of sample space, introduced by Richard von Mises, and measure theory and presented his axiom system for probability theory in 1933. This became the mostly undisputed axiomatic basis for modern probability theory; but, alternatives exist, such as the adoption of finite rather than countable additivity by Bruno de Finetti. Most introductions to probability theory treat discrete probability distributions and continuous probability distributions separately. The measure theory-based treatment of probability covers the
Probability theory
3304953
to "Y". In contrast, modern portfolio theory is based on a different axiom, called variance aversion, and may recommend to invest into "Y" on the basis that it has lower variance. Maccheroni et al. described choice theory which is the closest possible to the modern portfolio theory, while satisfying monotonicity axiom. Alternatively, mean-deviation analysis is a rational choice theory resulting from replacing variance by an appropriate deviation risk measure. In the 1970s, concepts from MPT found their way into the field of regional science. In a series of seminal works, Michael Conroy modeled the labor force in the economy using
Modern portfolio theory
119433
successful human blood transfusion, the motorised vacuum cleaner, the lawn mower, the seat belt, the hovercraft, the electric motor, steam engines, and theories such as the Darwinian theory of evolution and atomic theory. Newton developed the ideas of universal gravitation, Newtonian mechanics, and calculus, and Robert Hooke his eponymously named law of elasticity. Other inventions include the iron plate railway, the thermosiphon, tarmac, the rubber band, the mousetrap, "cat's eye" road marker, joint development of the light bulb, steam locomotives, the modern seed drill and many modern techniques and technologies used in precision engineering. The Department for Transport is the
England
516837
atomic spectra. Up until that time, attempts to make the old quantum theory of the atom compatible with the theory of relativity, attempts based on discretizing the angular momentum stored in the electron's possibly non-circular orbit of the atomic nucleus, had failed – and the new quantum mechanics of Heisenberg, Pauli, Jordan, Schrödinger, and Dirac himself had not developed sufficiently to treat this problem. Although Dirac's original intentions were satisfied, his equation had far deeper implications for the structure of matter and introduced new mathematical classes of objects that are now essential elements of fundamental physics. The new elements in
Dirac equation
9783296
supporter Steve Fuller, a philosopher, who argues that evolution is the only "scientifically credible basis" for atheism, and anthropologist Jeffrey H. Schwartz, who argues that evolutionary theory cannot account for novelties. He comes to the conclusion that the modern synthetic theory of evolution will be superseded in a future paradigm shift, undermining the arguments of atheists like Dawkins. Liddle also criticizes models of sociocultural evolution such as memetics and interviews skeptics of memetics such as Alister McGrath. In the last quarter of the documentary, Liddle argues against a perceived overreliance on "cold logic" and the amoral scientific method. He focuses
The Trouble with Atheism
30864
exhibit the properties of both a wave and a particle. For example, it can be refracted like a wave, and has mass like a particle. A consequence of describing electrons as waveforms is that it is mathematically impossible to simultaneously derive the position and momentum of an electron. This became known as the Heisenberg uncertainty principle after the theoretical physicist Werner Heisenberg, who first described it and published it in 1927. This invalidated Bohr's model, with its neat, clearly defined circular orbits. The modern model of the atom describes the positions of electrons in an atom in terms of probabilities.
Atomic theory
3296209
when bonds are broken and formed during the course of a chemical reaction. In particular, valence bond theory correctly predicts the dissociation of homonuclear diatomic molecules into separate atoms, while simple molecular orbital theory predicts dissociation into a mixture of atoms and ions. For example, the molecular orbital function for dihydrogen is an equal mixture of the covalent and ionic valence bond structures and so predicts incorrectly that the molecule would dissociate into an equal mixture of hydrogen atoms and hydrogen positive and negative ions. Modern valence bond theory replaces the overlapping atomic orbitals by overlapping valence bond orbitals that
Valence bond theory
8151408
theory only became useful when the atomic conjecture was ignored. Sir Benjamin Collins Brodie in 1866 published the first part of his Calculus of Chemical Operations as a non-atomic alternative to the Atomic Theory. He described atomic theory as a 'Thoroughly materialistic bit of joiners work'. Alexander Williamson used his Presidential Address to the London Chemical Society in 1869 to defend the Atomic Theory against its critics and doubters. This in turn led to further meetings at which the positivists again attacked the supposition that there were atoms. The matter was finally resolved in Dalton's favour in the early 20th
Atomism
1745585
in the late eighteenth century that could explain the phenomenon of heat: the kinetic theory. The two theories were considered to be equivalent at the time, but kinetic theory was the more modern one, as it used a few ideas from atomic theory and could explain both combustion and calorimetry. Quite a number of successful explanations can be, and were, made from these hypotheses alone. We can explain the cooling of a cup of tea in room temperature: caloric is self-repelling, and thus slowly flows from regions dense in caloric (the hot water) to regions less dense in caloric (the
Caloric theory
2175363
nomically, possible if it is permitted by the laws of physics. For example, current theory is thought to allow for there to be an atom with an atomic number of 126, even if there are no such atoms in existence. In contrast, while it is logically possible (i.e. probably via Alcubierre drive or worm holes) to accelerate beyond the speed of light, modern science stipulates that it is not physically possible for material particles or information. Philosophers ponder the properties that objects have independently of those dictated by scientific laws. For example, it might be metaphysically necessary, as some who
Modal logic
240361
fellow Frenchman Claude Louis Berthollet, who argued that the elements could combine in any proportion. The existence of this debate demonstrates that, at the time, the distinction between pure chemical compounds and mixtures had not yet been fully developed. The law of definite proportions contributed to, and was placed on a firm theoretical basis by, the atomic theory that John Dalton promoted beginning in 1803, which explained matter as consisting of discrete atoms, that there was one type of atom for each element, and that the compounds were made of combinations of different types of atoms in fixed proportions. A
Law of definite proportions
74784
Burrau. This work showed that the quantum approach to chemical bonds could be fundamentally and quantitatively correct, but the mathematical methods used could not be extended to molecules containing more than one electron. A more practical, albeit less quantitative, approach was put forward in the same year by Walter Heitler and Fritz London. The Heitler–London method forms the basis of what is now called valence bond theory. In 1929, the linear combination of atomic orbitals molecular orbital method (LCAO) approximation was introduced by Sir John Lennard-Jones, who also suggested methods to derive electronic structures of molecules of F (fluorine) and
Chemical bond
9219629
of Darwinism", scientists proposed various alternative evolutionary mechanisms, which eventually proved untenable. Ronald Fisher, an English statistician, finally united Mendelian genetics with natural selection, in the period between 1918 and his 1930 book "The Genetical Theory of Natural Selection". He gave the theory a mathematical footing and brought broad scientific consensus that natural selection was the basic mechanism of evolution, thus founding the basis for population genetics and the modern evolutionary synthesis, with J.B.S. Haldane and Sewall Wright, which set the frame of reference for modern debates and refinements of the theory. During Darwin's lifetime, many geographical features were given
Charles Darwin
18772869
Heavy metals Heavy metals are generally defined as metals with relatively high densities, atomic weights, or atomic numbers. The criteria used, and whether metalloids are included, vary depending on the author and context. In metallurgy, for example, a heavy metal may be defined on the basis of density, whereas in physics the distinguishing criterion might be atomic number, while a chemist would likely be more concerned with chemical behaviour. More specific definitions have been published, but none of these have been widely accepted. The definitions surveyed in this article encompass up to 96 out of the 118 known chemical elements;
Heavy metals
17457422
The basis of Pakistan were Muslims in South Asia are a separate culture. It was the Two-Nation Theory that lead to the independence of Pakistan." The university curriculum in the country was upgraded by President Zia-ul-Haq, that includes the teaching of Islamic Studies and Arabic languages courses, which were made compulsory for students to get their degrees in arts and social sciences. The Pakistan Studies were made compulsorily for engineering, medical education, commerce, law and nursing education. Extra educational certificates and diplomas were given to people who were "Hafiz". On national priorities, the atomic bomb project was aggressively put forwarded
Conservatism in Pakistan