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De Memoria et Reminiscentia 1 450a10

Pavel Gregoric

in Aristotle on the Common Sense

This chapter offers an interpretation of the passage in De Memoria et Reminiscentia 1 which aims to show that memory does not belong to the rational capacity of the soul, but rather to what ... More

This chapter offers an interpretation of the passage in De Memoria et Reminiscentia 1 which aims to show that memory does not belong to the rational capacity of the soul, but rather to what Aristotle calls the ‘primary perceptual capacity of the soul’ (proton aisthetikon) and, at one point, the ‘common sense’. The crucial step in the argument relies on the notion of the perception of time, which is investigated in some detail. It is argued that the perception of time requires joint operation of perception and imagination, and is hence the work of the sensory capacity of the soul. In other words, what Aristotle calls the ‘primary perceptual capacity of the soul’ and ‘common sense’ in this passage is the sensory capacity of the soul. This establishes the same reference for the phrase ‘common sense’ in De Partibus Animalium IV.10 and De Memoria et Reminiscentia 1.Less

 Physical Chemistry and Economics: 1933–1937

William Taussig Scott and Martin X. Moleski

in Michael Polanyi: Scientist and Philosopher

In response to the Nazi anti-Jewish policies, Polanyi resigned from the Kaiser Wilhelm Institute and moved to the University of Manchester in 1933. Even as he brought his work in reaction kinetics to ... More

In response to the Nazi anti-Jewish policies, Polanyi resigned from the Kaiser Wilhelm Institute and moved to the University of Manchester in 1933. Even as he brought his work in reaction kinetics to a climax with the publication of Atomic Reactions in 1935, he was deeply immersed in economic studies and philosophical reflection on the nature of a freedom in science and in society, which led in turn to the production of two movies on the economic cycle. Polanyi worked with his colleagues on reaction rates, hydrogen catalysis, proton transfer reactions, ionogenic reactions, pyrolysis, and bond energies.Less

MOLECULAR AND ATOMIC BEAMS

Norman F. Ramsey

in Molecular Beams

A brief history of molecular beams is given along with a detailed description of a typical molecular beam experiment. Schematic diagrams and a photograph are provided. As an illustration the results ... More

A brief history of molecular beams is given along with a detailed description of a typical molecular beam experiment. Schematic diagrams and a photograph are provided. As an illustration the results of an experiment measuring the radio-frequency spectrum of H2 are given. This measurement gives a value of proton magnetic moment, a measurement of the separation of the two protons in the molecule, and a limitation on the possibility of an additional tensor force between two protons. Other very different molecular beam experiments are also described.Less

Hydrogen bonded molecular complexes and compounds

Frank H. Herbstein

in Crystalline Molecular Complexes and Compounds: Structures and Principles

Hydrogen bonding, one of the most important secondary interactions between molecules of the same kind, is no less important among the binary adducts, and most of the same principles apply. Among the ... More

Hydrogen bonding, one of the most important secondary interactions between molecules of the same kind, is no less important among the binary adducts, and most of the same principles apply. Among the most important hydrogen bond donors are -OH, >NH, and -NH2, while >C=O, >O, -Cl, and >S are important acceptors together with charged analogues. The major structural distinction is between ‘Appendage Structures’, where one component forms a framework to which the second component is hydrogen bonded, and ‘Mixed Framework Structures’, where both components form part of an alternating framework. The latter group can have the two components hydrogen bonded in pairs or in larger discrete groupings, the crystals being molecular crystals from a structural point of view, in linear chains, in layers, or in three dimensional frameworks, where many complex arrangements are possible, especially if a third component such as water is present. Finally, the question of the circumstances under which proton transfer takes place (the formation of ions) is considered.Less

Crystal chemistry of mixed-stack π–π* molecular compounds

Frank H. Herbstein

in Crystalline Molecular Complexes and Compounds: Structures and Principles

The room-temperature crystal structures of many mixed stack charge transfer molecular compounds can be grouped into a relatively small number of crystallochemical families. Although the mixed stack ... More

The room-temperature crystal structures of many mixed stack charge transfer molecular compounds can be grouped into a relatively small number of crystallochemical families. Although the mixed stack arrangement predominates, there are structures which deviate to a greater or lesser extent from such an arrangement, for reasons which are often not clear. These maverick structures are reviewed and then the more common mixed stack arrangements are classified into a number of structural groups. Compounds with quinonoid acceptors sometimes have special structural features because of the mode of interaction of the carbonyl groups with aromatic rings. In the quinhydrone family, the (aromatic ring)...carbonyl interaction is supplemented by hydrogen bonding between carbonyl and hydroxyl oxygens, and this leads to considerable structural homogeneity. Many CT compounds where the π-π* interaction is supplemented by hydrogen bonding show special structural features and physical properties different from those with only π-π* interaction. The mixed stack compounds with ionic ground states generally resemble those with neutral ground states in structural terms, but have different physical properties. In the isomeric compounds, the possibility of having both electron and proton transfer leads to variations on the mixed stack theme.Less

GENERALITIES, DEFINITIONS AND PRELIMINARY CLASSIFICATION

Gastone Gilli and Paola Gilli

in The Nature of the Hydrogen Bond: Outline of a Comprehensive Hydrogen Bond Theory

The classical H-bond definitions by Latimer and Rodebush (1920), Pimentel (1960), and Vinogradov and Linnel (1971) are compared in the frame of the Coulson's VB formalism. The H-bond is eventually ... More

The classical H-bond definitions by Latimer and Rodebush (1920), Pimentel (1960), and Vinogradov and Linnel (1971) are compared in the frame of the Coulson's VB formalism. The H-bond is eventually defined as a three-centre-four-electron shared-proton interaction which excludes the three-centre-two electron interactions typical of agostic and borane bonds. Two types of H-bond classifications are considered, the first based on purely chemical criteria (following the previous scheme by Desiraju and Steiner, 1999) and the second on the H-bond physical properties (originally proposed by Jeffrey, 1997). The chemical classification is inclusive of the H-bonds formed by both main-group and metal elements, and pays particular attention to less common bonds and to the accurate classification of strong H-bonds. All classes are separately described with particular concern for geometries and energies of the most typical bonds made.Less

MODELLING THE H-BOND BY THERMODYNAMIC METHODS

Gastone Gilli and Paola Gilli

in The Nature of the Hydrogen Bond: Outline of a Comprehensive Hydrogen Bond Theory

Acid-base parameters of donors (D-H) and acceptors (:A) are crucial in any D-H···:A bond in view of the hypothesis that the difference ΔPA = PA(D-) - PA(:A) or ΔpKa = pKa(D-H) - pKa(A-H+) drive ... More

Acid-base parameters of donors (D-H) and acceptors (:A) are crucial in any D-H···:A bond in view of the hypothesis that the difference ΔPA = PA(D-) - PA(:A) or ΔpKa = pKa(D-H) - pKa(A-H+) drive H-bond strengths, the bond becoming really strong only when this difference tend to zero. This criterion, known as PA/pKa equalization principle, was suggested many years ago but never verified in its generality. This chapter performs a full thermodynamic analysis of the problem showing that it admits general solution by systematic comparisons of PA or pKa values with H-bond solid-state geometries or gas-phase enthalpies, though the combination pKa-geometry has proved to be of more general use. This last method is exploited by compiling extended tables of donor-acceptor pKa values (-14 = pKa = 53), arranging them in an unique bar-chart (the pKa slide rule), and comparing the ΔpKa values computed with the geometries of more than 10,000 crystal structures of X-H···X and N-H···O/O-H···N bonds.Less

Dissecting Matter

Gian Francesco Giudice

in A Zeptospace Odyssey: A Journey into the Physics of the LHC

This chapter recounts the historical process that led to the understanding that matter is not a continuous substance, but comes in lumps. The philosophical concept of atoms, postulated by the Greek ... More

This chapter recounts the historical process that led to the understanding that matter is not a continuous substance, but comes in lumps. The philosophical concept of atoms, postulated by the Greek philosopher Democritus, entered science with the study of chemical reactions and properties of gases. But the first direct evidence for a corpuscular structure of matter came with the discovery of the electron by J. J. Thomson. The next step was Rutherford's discovery of the atomic nucleus, followed by the understanding that the nucleus is made of protons and neutrons. The exploration of the subatomic world led to the development of quantum mechanics, a theory which revolutionized our interpretation of physical reality. The chapter describes also the discovery and the meaning of antimatter.Less

Solid state proton conductors

Rolf Hempelmann

in Quasielastic Neutron Scattering and Solid State Diffusion

Aliovalently doped perovskite-type oxides (e.g., SrCeO3 doped with Yb2O3) contain, for reasons of charge neutrality, oxygen vacancies and become high temperature proton conductors in the presence of ... More

Aliovalently doped perovskite-type oxides (e.g., SrCeO3 doped with Yb2O3) contain, for reasons of charge neutrality, oxygen vacancies and become high temperature proton conductors in the presence of water. Proton conductivity is due to OH- ions on oxygen sites and to proton hopping from oxygen to oxygen according to the Grotthuss mechanism. This chapter examines aliovalently doped perovskites both by QENS and by muon spin rotation. It evaluates the QENS data in terms of the two-state model. Hydrogen bonded systems like CsHSO4 are another class of solid proton conductors. For these compounds, QENS also delivers an atomistic picture of proton diffusion. Another proton carrier is NH3 intercalated in molybdenum bronzes.Less

The other phases of ice

Victor F. Petrenko and Robert W. Whitworth

in Physics of Ice

The water substance exhibits at least 13 crystalline phases. These are denoted by roman numerals such as ice II. Many are stable in particular regions of the pressure — temperature phase diagram ... More

The water substance exhibits at least 13 crystalline phases. These are denoted by roman numerals such as ice II. Many are stable in particular regions of the pressure — temperature phase diagram though some are only metastable. This chapter tabulates the crystal structures and regions of stability of these high-pressure phases. Some phases are proton-ordered forms of others; for example, suitably doped ice Ih orders to ice XI below 72 K. All are formed from distinct water molecules except ice X, which is produced at high pressures above 60 GPa. Ice Ic is the metastable cubic form of ice Ih. Low- and high-density amorphous ices can be produced at low temperatures. All revert via ice Ic to normal ice on warming above about 150 K. The clathrate hydrates are a group of crystalline ice-like compounds in which suitable guest molecules are incorporated in cages of water molecules within the lattice.Less

The atom completed

Maurice Goldhaber

in A Century of Nature: Twenty-One Discoveries that Changed Science and the World

Great discoveries rarely come out of the blue. The neutron has a fascinating prehistory. In the 1920s, common wisdom held that atoms were made from only two constituents: positively charged protons ... More

Great discoveries rarely come out of the blue. The neutron has a fascinating prehistory. In the 1920s, common wisdom held that atoms were made from only two constituents: positively charged protons and negatively charged electrons. When, in 1932, James Chadwick reported the existence of a third, electrically neutral particle—the neutron—it completed the inventory of atomic building blocks and marked the birth of modern nuclear physics. Today, neutrons are used to probe the structure of matter, and neutron physics underpins much of the understanding of astrophysics and cosmology. As befits one of the fundamental building blocks of matter, neutrons have proved to be important in many different fields of science. In astrophysics, neutrons and their reactions are critical to an understanding of events immediately following the Big Bang, and all of the chemical elements heavier than iron are thought to have been formed by neutron capture in supernovae, and in certain types of star.Less

Animated Atom Boy

Nicholas Mee

in The Cosmic Mystery Tour

The concept of the atom dates back to the speculations of Democritus and other Ancient Greek philosophers, but it was only in modern times that atoms were shown to exist and physicists began to ... More

The concept of the atom dates back to the speculations of Democritus and other Ancient Greek philosophers, but it was only in modern times that atoms were shown to exist and physicists began to investigate their structure. Rutherford’s team in Manchester discovered the atomic nucleus and Rutherford proposed that atoms consist of a tiny positively charged nucleus surrounded by negatively charged orbiting electrons. Rutherford and his colleagues went on to discover the nucleus is composed of protons and neutrons. It is now possible to produce pictures of atoms using the scanning tunnelling microscope (STM) invented by Binnig and Rohrer.Less

Stars

Nicholas Manton and Nicholas Mee

in The Physical World: An Inspirational Tour of Fundamental Physics

This chapter gives a concise account of stellar theory. The Sun is presented as a starting point for the study of stars and a test-bed for theories of stellar structure. The Herzsprung–Russell ... More

This chapter gives a concise account of stellar theory. The Sun is presented as a starting point for the study of stars and a test-bed for theories of stellar structure. The Herzsprung–Russell diagram provides the basis for the classification and understanding of stars. The equations of stellar structure are derived and used to describe main sequence stars. Stellar nucleosynthesis and the principal nuclear processes are described, including the proton–proton chain, CNO cycle and triple alpha process. Simple relationships describing stellar properties are derived from the stellar structure functions. These include the mass–radius, mass–temperature and temperature–luminosity relations. The evolution of giant stars beyond the main sequence is discussed, along with their subsequent evolution into white dwarfs or neutron stars. Various types of supernovae and the nuclear processes that occur during such explosions are discussed, along with a detailed account of supernova SN1987A.Less

Beyond Chemistry and Biology

Wolfgang Banzhaf and Lidia Yamamoto

in Artificial Chemistries

Artificial chemistries can be found in fields beyond chemistry and biology. While it is most natural to look at examples from these fields, the self-assembly of entities at different scales can be ... More

Artificial chemistries can be found in fields beyond chemistry and biology. While it is most natural to look at examples from these fields, the self-assembly of entities at different scales can be modeled with ACs. Reactions at smaller scales, like elementary particles or processes in nuclear physics can be similarly modeled from an AC perspective. Even economic and social systems, with interactions based on communication and trade can be modeled with ACs. This chapter will show some examples from the breadth of other fields.Less

Dielectric Relaxation of Water

Udo Kaatze

in Dielectric Relaxation in Biological Systems: Physical Principles, Methods, and Applications

Dielectric relaxation of water as well as ionic and non-ionic aqueous solutions is briefly described as a basic principle of the more complex relaxation characteristics in biological systems. ... More

Dielectric relaxation of water as well as ionic and non-ionic aqueous solutions is briefly described as a basic principle of the more complex relaxation characteristics in biological systems. Proceeding from the architecture of the water molecule the existence of a permanent electric dipole moment, providing the coupling to electromagnetic fields, is demonstrated. Also the unique hydrogen bond network of water, leading to non-instantaneous dipole reorientation and thus relaxation behavior of the dielectric spectrum, is inferred from the molecular structure. Consulting literature data the effect of various solutes on the dielectric relaxation of water is presented and discussed in terms of variations in the molecular interactions. Extrapolated static permittivities of aqueous solutions are presented and related to the effects of dielectric saturation and kinetic depolarization. The discussion involves the difficulty of dipole orientation correlation and appropriate mixture relation for aqueous solutions. Attention is given to the exceedingly high proton mobility.Less

Bayesian reconstruction of particle beam phase space

C Nakhleh, D Higdon, C K Allen, and R Ryne

in Bayesian Theory and Applications

This chapter discusses the application of Bayesian inversion methodology to reconstruct the initial phase space configuration of charged particle beams using a series of one-dimensional projection ... More

This chapter discusses the application of Bayesian inversion methodology to reconstruct the initial phase space configuration of charged particle beams using a series of one-dimensional projection datasets (wirescans). It begins with a brief description of the proton beam produced by the Low Energy Demonstration Accelerator (LEDA) at the Los Alamos National Laboratory. It then describes the modelling approach, which uses process convolutions to represent the initial phase space configurations. This process convolution representation gives a parsimonious representation of the particle density as a function of spatial position and momentum, while ensuring positivity. Next, the chapter describes a Markov chain Monte Carlo (MCMC) scheme for producing posterior draws and a reconstruction for the initial phase space. It also outlines additional sensitivity studies to assess the impact of the prior smoothness on the resulting initial phase space reconstruction.Less

Constructing the Ring, 1968–1972

in Fermilab: Physics, the Frontier, and Megascience

This chapter discusses the history of the construction of the accelerator rings of the National Accelerator Laboratory during the period 1968 to 1972. It explains that while Berkeley designers ... More

This chapter discusses the history of the construction of the accelerator rings of the National Accelerator Laboratory during the period 1968 to 1972. It explains that while Berkeley designers mistrusted Robert R. Wilson's lack of experience in building large proton synchrotrons, his philosophy of taking risks to save money was considered by many in the U.S. as an appropriate, noble, or even patriotic response to the government's call for cost reduction. This chapter suggests that Wilson learned his cost saving strategies from his experience at Ernest Lawrence's laboratory in the 1930s and at Robert Oppenheimer's laboratory in Los Alamos during the 1940s.Less

Hydrogen

Massimo Inguscio and Leonardo Fallani

in Atomic Physics: Precise Measurements and Ultracold Matter

This chapter is devoted to hydrogen, the simplest of the atoms. Spectroscopy of hydrogen represents one of the main methods that allowed physicists to discover the quantum world, since its simple ... More

This chapter is devoted to hydrogen, the simplest of the atoms. Spectroscopy of hydrogen represents one of the main methods that allowed physicists to discover the quantum world, since its simple structure constitutes a primary testing ground for fundamental physical theories, from relativistic quantum mechanics to quantum electrodynamics. The history of hydrogen spectroscopy is used to illustrate fundamental steps in laser spectroscopy, including the development of nonlinear Doppler-free spectroscopy and the possibility of performing direct frequency measurements of light with optical frequency combs. State-of-the-art developments in hydrogen spectroscopy for the determination of fundamental constants (e.g., the Rydberg constant and the proton charge radius) are discussed.Less

The Perplexing Chronicles of Bioenergetics: Making a Living, Now and in the Past

Franklin M. Harold

in In Search of Cell History: The Evolution of Life's Building Blocks

All biological operations require the input of energy. In contemporary organisms, energy is harvested by mechanisms that are essentially electrical. Energy transduction relies on the circulation of ... More

All biological operations require the input of energy. In contemporary organisms, energy is harvested by mechanisms that are essentially electrical. Energy transduction relies on the circulation of ions across membranes (usually protons), and on a sophisticated rotary ATP synthase to capture the energy and conserve it as ATP. This chapter begins with an overview of chemiosmotic energy transduction and then poses the question, How did LUCA make a living? Current thinking questions the traditional notion that that LUCA lived off prebiotic organic molecules, and favors geochemical processes, such as the reduction of CO2 by hydrogen gas. One possible habitat for such organisms would be mineral honeycombs laid down by hydrothermal vents. If there is any truth to this hypothesis, then chemiosmotic energy transduction will have been part of LUCA's endowment, and may have evolved under the special circumstances that prevail in those vents. Subsequent evolution will have led to the liberation of cells from their mineral cradle, and the progressive expansion of energy metabolism by the invention of both photosynthesis and respiration.Less

Characterization of Natural Organic Matter by Nuclear Magnetic Resonance Spectroscopy

Jerry A. Leenheer

in Nuclear Magnetic Resonance Spectroscopy in Environment Chemistry

Natural organic matter (NOM) is a major intermediate in the global carbon, nitrogen, sulfur, and phosphorus cycles. NOM is also the environmental matrix that frequently controls binding, transport, ... More

Natural organic matter (NOM) is a major intermediate in the global carbon, nitrogen, sulfur, and phosphorus cycles. NOM is also the environmental matrix that frequently controls binding, transport, degradation, and toxicity of many organic and inorganic contaminants. Despite its importance, NOM is poorly understood at the structural chemistry level because of its molecular complexity and heterogeniety. Nuclear magnetic resonance (NMR) spectroscopy is one of the most useful spectrometric methods used to investigate NOM structure because qualitative and quantitative organic structure information for certain organic elements can be generated by NMR for NOM in both the solution and solid states under nondegradative conditions. However, NMR spectroscopy is not as sensitive as infrared or ultraviolet-visible spectroscopy; it is not at present applicable to organic oxygen and sulfur, and quantification of NMR spectra is difficult under certain conditions. The purpose of this overview is to present briefly the “state of the art” of NMR characterization of NOM, and to suggest future directions for NMR research into NOM. More comprehensive texts concerning the practice of NMR spectroscopy and its application to NOM in various environments have been produced by Wilson and by Wershaw and Mikita. Carbon, hydrogen, and oxygen are the major elements of NOM; together they comprise about 90% of the mass. The minor elements that constitute the remainder are nitrogen, sulfur, phosphorus, and trace amounts of the various halogen elements. With the exception of coal, in which carbon is the most abundant element, the order of relative abundance in NOM on an atomic basis is H > C > O > N > S > P = halogens. The optimum NMR-active nuclei for these elements are 1H, 13C, 17O, 15N, 33S, 31P, and 19F. The natural abundances and receptivities of these nuclei relative to 1H are given in Table 12.1. Quadrupolar effects for 17O, 33S, and halogen elements other than 19F lead to line broadening that greatly limits resolution in NMR studies of these elements in NOM. Less