Quantum. In physics, a quantum ( pl.: quanta) is the minimum amount of any physical entity ( physical property) involved in an interaction. Quantum is a discrete quantity of energy proportional in magnitude to the frequency of the radiation it represents. The fundamental notion that a property can be "quantized" is referred to as "the ...Quantum Mechanics. Four basic principles of quantum mechanics are: (3.1) Physical States. Every physical system is associated with a Hilbert Space, every unit vector in the space corresponds to a …In this quantum physics introduction for beginners, we will explain quantum physics, also called quantum mechanics, in simple terms. Quantum physics is possibly the most fascinating part of physics that exists. It is the amazing physics that becomes relevant for small particles, where the so-called classical physics is no longer valid.Quantum mechanics is a theory that deals with the most fundamental bits of matter, energy and light and the ways they interact with each other to make up the world. …Quantum physics is the study of matter and energy at its most fundamental level. A central tenet of quantum physics is that energy comes in indivisible packets called quanta. Quanta behave very ... Quantum physics deals with the foundation of our world – the electrons in an atom, the protons inside the nucleus, the quarks that build those protons, and t... Quantum Mechanics: The Theoretical Minimum – Buy Now. Source: Leonard Susskind, Art Friedman/Amazon. Theoretical Minimum is a rare New York Times’ bestseller on quantum mechanics, written by ...In quantum mechanics with complex numbers, the particles Alice and Charlie receive don’t need to be entangled with each other. No real-number description, however, can replicate the pattern of correlations that the three physicists will measure. The new paper shows that treating the system as real requires introducing extra information that ...Quantum mechanics is a branch of physics that explains the behavior of particles at the atomic and subatomic scale. Learn about wave-particle duality, …of his research is in electrodynamics and quantum mechanics. He is the author of over fty arti-cles and four books: Introduction to Electrodynamics (4th edition, Cambridge University Press, 2013), Introduction to Elementary Particles (2nd edition, Wiley-VCH, 2008), Introduction to Quantum Mechanics (2nd edition, Cambridge, 2005), andDecoherence Theory This is not an interpretation, but it is an important element of the modern understanding of quantum mechanics. It expands upon the kind of mathematical analysis that led ...Figure 2.1: In quantum mechanics the right hand side of the Schrödinger equation is written shortly as ˆHΨ(x, t), so (2.2) can be written as. iℏ∂Ψ ( x, t) ∂t = ˆHΨ(x, t) (2.3) This notation has a deeper reason, which is explained here shortly. The operation − ℏ2 2m ∂2Ψ ( x, t) ∂x2 + V(x)Ψ(x, t) can be considered as a ...It introduces some of the important model systems studied in contemporary physics, including two-dimensional electron systems, the fine structure of hydrogen, lasers, and particle scattering. The lectures and lecture notes for this course form the basis of Zwiebach’s textbook Mastering Quantum Mechanics published by MIT Press in April 2022.Page ID. Quantum mechanics explains the aspects of nature at ordinary (macroscopic) scales but extends this description to the small (atomic and subatomic) scales. There are …Subscribe to BBC News www.youtube.com/bbcnewsBritish physicist Brian Cox is challenged by the presenter of Radio 4's 'Life Scientific', Jim Al-Khalili, to ex...Current Weather. 8:54 PM. 71° F. RealFeel® 67°. Air Quality Unhealthy. Wind WNW 12 mph. Wind Gusts 13 mph. Partly cloudy More Details.First published Sun Mar 24, 2002; substantive revision Thu Aug 5, 2021. The Many-Worlds Interpretation (MWI) of quantum mechanics holds that there are many worlds which exist in parallel at the same space and time as our own. The existence of the other worlds makes it possible to remove randomness and action at a distance from quantum theory ...The quantum mind or quantum consciousness is a group of hypotheses proposing that local physical laws and interactions from classical mechanics or connections between neurons alone cannot explain consciousness, positing instead that quantum-mechanical phenomena, such as entanglement and superposition that cause nonlocalized quantum …of his research is in electrodynamics and quantum mechanics. He is the author of over fty arti-cles and four books: Introduction to Electrodynamics (4th edition, Cambridge University Press, 2013), Introduction to Elementary Particles (2nd edition, Wiley-VCH, 2008), Introduction to Quantum Mechanics (2nd edition, Cambridge, 2005), andThe old quantum theory is a collection of results from the years 1900–1925 which predate modern quantum mechanics. The theory was never complete or self-consistent, but was rather a set of heuristic corrections to classical mechanics. The theory is now understood as a semi-classical approximation to modern quantum mechanics.Quantum mechanical laws are usually only found to apply at very low temperatures. Quantum computers, for example, currently operate at around -272°C . At higher temperatures, classical mechanics ...The quantum mind or quantum consciousness is a group of hypotheses proposing that local physical laws and interactions from classical mechanics or connections between neurons alone cannot explain consciousness, positing instead that quantum-mechanical phenomena, such as entanglement and superposition that cause nonlocalized quantum …Quantum mechanics opens the doors for Quantum Engineers to leverage quantum physics to deliver unprecedented solutions to engineering problems. Quantum Engineers specialise in how high-frequency, nanometer-scale electronics can be made to harness quantum nature. When you study Quantum Engineering at UNSW, you'll develop the …10–19: Matrix Mechanics: 10 Matrix Mechanics (PDF - 1.1MB) 11 Eigenvalues, Eigenvectors, and Discrete Variable Representation (PDF - 1.1MB) 12 Matrix Solution of Harmonic Oscillator I (PDF - 1.1MB) 13 Matrix Solution of Harmonic Oscillator II (PDF - 1.3MB) 14 Perturbation Theory I (PDF - 1.2MB) 15 Perturbation Theory II (PDF - 1.2MB) 161.1: Why Quantum Mechanics is Necessary; 1.2: The Schrödinger Equation and Its Components; 1.3: The Born-Oppenheimer Approximation One of the most important approximations relating to applying quantum mechanics to molecules and molecular ions is known as the Born-Oppenheimer (BO) approximation. 1.4: Free Particle Motions in More …Subscribe to BBC News www.youtube.com/bbcnewsBritish physicist Brian Cox is challenged by the presenter of Radio 4's 'Life Scientific', Jim Al-Khalili, to ex... In this quantum physics introduction for beginners, we will explain quantum physics, also called quantum mechanics, in simple terms. Quantum physics is possibly the most fascinating part of physics that exists. It is the amazing physics that becomes relevant for small particles, where the so-called classical physics is no longer valid. Quantum Mechanics Concepts and Applications Second Edition Nouredine Zettili Jacksonville State University, Jacksonville, USA A John Wiley and Sons, Ltd., Publication This 9 week course aims to teach quantum mechanics to anyone with a reasonable college-level understanding of physical science or engineering. Quantum mechanics was once mostly of interest to physicists, chemists and other basic scientists. Now the concepts and techniques of quantum mechanics are essential in many areas of engineering and science such as materials science, nanotechnology ... James Binney. 11 December, 2009. Displaying 1 - 27 of 27 episodes. In this series of physics lectures, Professor J.J. Binney explains how probabilities are obtained from quantum amplitudes, why they give rise to quantum interference, the concept of a complete set of amplitudes and how this defines a "quantum state".Quantum mechanics - Heisenberg, Uncertainty, Principle: The observables discussed so far have had discrete sets of experimental values. For example, the values of the energy of a bound system are always discrete, and angular momentum components have values that take the form mℏ, where m is either an integer or a half-integer, positive or negative. …It turns out that we can just as easily formulate quantum mechanics using the momentum-space wavefunction, ϕ(p, t) ϕ ( p, t), as the real-space wavefunction, ψ(x, t) ψ ( x, t). The former scheme is known as the momentum representation of quantum mechanics. In the momentum representation, wavefunctions are the Fourier …A simple and clear explanation of all the important features of quantum physics that you need to know. Check out this video's sponsor https://brilliant.org/d...Figure 2.1: In quantum mechanics the right hand side of the Schrödinger equation is written shortly as ˆHΨ(x, t), so (2.2) can be written as. iℏ∂Ψ ( x, t) ∂t = ˆHΨ(x, t) (2.3) This notation has a deeper reason, which is explained here shortly. The operation − ℏ2 2m ∂2Ψ ( x, t) ∂x2 + V(x)Ψ(x, t) can be considered as a ...The quantum mind or quantum consciousness is a group of hypotheses proposing that local physical laws and interactions from classical mechanics or connections between neurons alone cannot explain consciousness, positing instead that quantum-mechanical phenomena, such as entanglement and superposition that cause nonlocalized quantum …May 12, 2015 · Leonard Susskind is the Felix Bloch Professor in Theoretical Physics at Stanford University. He is the author of Quantum Mechanics (with Art Friedman) and The Theoretical Minimum (with George Hrabovsky), among other books. He lives in Palo Alto, California. Art Friedman is a data consultant who previously spent fifteen years at Hewlett-Packard ... This is a superposition of waves. Similarly, in quantum science, objects such as electrons and photons have wavelike properties that can combine and become what is called superposed. While waves on the surface of a pond are formed by the movement of water, quantum waves are mathematical. They are expressed as equations that describe the ... Mass defect and binding energy. Nuclear stability and nuclear equations. Half-life plot. Exponential decay and semi-log plots. This unit is part of the Physics library. Browse videos, articles, and exercises by topic. Quantum mechanics is an outrageous departure from our classical, comforting, com-mon sense view of the world. It is more baffling and disturbing than anything dreamt up by science fiction writers. And yet it is undoubtably the correct description of theIn quantum mechanics, the variational method is one way of finding approximations to the lowest energy eigenstate or ground state, and some excited states.This allows calculating approximate wavefunctions such as molecular orbitals. The basis for this method is the variational principle.. The method consists of choosing a "trial wavefunction" depending …The history of quantum mechanics is a fundamental part of the history of modern physics. The major chapters of this history begin with the emergence of quantum ideas to explain individual phenomena—blackbody radiation, the photoelectric effect, solar emission spectra—an era called the Old or Older quantum theories. [1] Quantum mechanics is the branch of physics that deals with the behavior of matter and light on a subatomic and atomic level. It attempts to explain the properties of atoms and molecules and their fundamental particles like protons, neutrons, electrons, gluons, and quarks. The properties of particles include their interactions with each other ... The book Mathematical Foundations of Quantum Mechanics (1932) by John von Neumann is an important early work in the development of quantum theory. Publication history. The book was originally published in German in 1932 by Julius Springer, under the title Mathematische Grundlagen der Quantenmechanik. An ... Lecture 1: An overview of quantum mechanics. Quantum mechanics as a framework. Defining linearity (17:46) Linearity and nonlinear theories. Schrödinger’s equation (10:01) The nature of superposition. Mach-Zehnder interferometer (14:30) Lecture 2: Overview of quantum mechanics (cont.). Interaction-free measurements. Quantum Mechanics. Ph: (02) 4961 1795 97 Denison Street Hamilton, Newcastle NSW 2303 View Map. Courtesy Vehicles. We offer a convenient vehicle loan service. SWAP'N'GO. Simply drop off your car and drive away in Quantum Courtesy Car. It's FREE!! Book Now. Go Green.Jan 10, 2021 · Quantum mechanics is more right, but most of the time classical mechanics is good enough. What I find fascinating is that "good enough" increasingly isn’t. Much of the technology developed in ... Leonard Susskind is the Felix Bloch Professor in Theoretical Physics at Stanford University. He is the author of Quantum Mechanics (with Art Friedman) and The Theoretical Minimum (with George Hrabovsky), among other books. He lives in Palo Alto, California. Art Friedman is a data consultant who previously spent fifteen years at … A simple and clear explanation of all the important features of quantum physics that you need to know. Check out this video's sponsor https://brilliant.org/d... An interpretation of quantum mechanics is an attempt to explain how the mathematical theory of quantum mechanics might correspond to experienced reality. Although quantum mechanics has held up to rigorous and extremely precise tests in an extraordinarily broad range of experiments, there exist a number of contending schools of thought over ... Quantum Mechanics. Argonne maintains a wide-ranging science and technology portfolio that seeks to address complex challenges in interdisciplinary and innovative ways. Below is a list of all articles, highlights, profiles, projects, and organizations related specifically to quantum mechanics. The mysterious world of quantum mechanics has mystified scientists for decades. But this mind-bending theory is the best explanation of reality that we have....There are 3 modules in this course. Course 2 of Statistical Thermodynamics presents an introduction to quantum mechanics at a level appropriate for those with mechanical or aerospace engineering backgrounds. Using a postulatory approach that describes the steps to follow, the Schrodinger wave equation is derived and simple solutions obtained ...In quantum mechanics with complex numbers, the particles Alice and Charlie receive don’t need to be entangled with each other. No real-number description, however, can replicate the pattern of correlations that the three physicists will measure. The new paper shows that treating the system as real requires introducing extra information that ...An interpretation of quantum mechanics is an attempt to explain how the mathematical theory of quantum mechanics might correspond to experienced reality. Although quantum mechanics has held up to rigorous and extremely precise tests in an extraordinarily broad range of experiments, there exist a number of contending schools of thought over ...Quantum mechanics is a hypothesis in material science that gives a depiction of the actual properties of nature at the size of atoms and subatomic particles. It is the foundation of all quantum material science including quantum science, quantum field hypothesis, quantum innovation, and quantum data science.Apr 3, 2024 · MIT researchers observe a hallmark quantum behavior in bouncing droplets. In a study that could help fill some holes in quantum theory, the team recreated a “quantum bomb tester” in a classical droplet test. December 12, 2023. Read full story. The course tries to explain quantum mechanics without a lot of math, specifically without calculus. The professor does this explanation using clever models and short apps with which the students can interact. It is a very effective method and reduces the …David Tong: Lectures on Topics in Quantum Mechanics. This is an advanced course on quantum mechanics. It covers a wide range of topics, including an introduction to atomic physics, quantum foundations and scattering theory. Please do email me if you find any typos or mistakes. PostScript PDF. Content.Quantum physics deals with the foundation of our world – the electrons in an atom, the protons inside the nucleus, the quarks that build those protons, and t...Learn about the history, formalism and applications of quantum mechanics, a branch of physics that describes physical systems with discrete properties and wave-particle duality. Explore examples, …The Principles of Quantum Mechanics is an influential monograph on quantum mechanics written by Paul Dirac and first published by Oxford University Press in 1930. Dirac gives an account of quantum mechanics by "demonstrating how to construct a completely new theoretical framework from scratch"; "problems were tackled top-down, …The phase-space formulation of quantum mechanics places the position and momentum variables on equal footing in phase space. In contrast, the Schrödinger picture uses the position or momentum representations (see also position and momentum space ). The two key features of the phase-space formulation are that the quantum state is described …Quantum mechanics describes how these particles interact with each other and with light, X-rays, gamma rays, and other forms of electromagnetic radiation. One of the great ideas of the 20th century, quantum mechanics continues to be at the forefront of advances in physics in the 21st century. In addition to explaining the structure of atoms and ...of his research is in electrodynamics and quantum mechanics. He is the author of over fty arti-cles and four books: Introduction to Electrodynamics (4th edition, Cambridge University Press, 2013), Introduction to Elementary Particles (2nd edition, Wiley-VCH, 2008), Introduction to Quantum Mechanics (2nd edition, Cambridge, 2005), andIn quantum mechanics with complex numbers, the particles Alice and Charlie receive don’t need to be entangled with each other. No real-number description, however, can replicate the pattern of correlations that the three physicists will measure. The new paper shows that treating the system as real requires introducing extra information that ...These special wavefunctions are called eigenstates, and the multiples are called eigenvalues. Thus, if. Aψa(x) = aψa(x), (3.8.1) (3.8.1) A ψ a ( x) = a ψ a ( x), where a a is a complex number, then ψa ψ a is called an eigenstate of A A corresponding to the eigenvalue a a. Suppose that A A is an Hermitian operator corresponding to some ...Unlike quantum mechanics which has a canonical mathematical framework in terms of von Neumann’s Hilbert space formulation, QFT has no canonical mathematical framework. Even though there is a canonical mathematical framework for quantum mechanics, there are many interpretations of that framework, e.g., many-worlds, GRW, …According to the postulates of quantum mechanics, if the wavefunction defined in Equation \ref{2} is an eigenfunction of this Hamiltonian, every time we measure the total energy of the electron we will measure the corresponding eigenvalue. In other words, if this is true: \(\hat H \psi = a \psi\), then the constant \(a\) is the energy of one ...The phase-space formulation of quantum mechanics places the position and momentum variables on equal footing in phase space. In contrast, the Schrödinger picture uses the position or momentum representations (see also position and momentum space ). The two key features of the phase-space formulation are that the quantum state is described …The old quantum theory is a collection of results from the years 1900–1925 which predate modern quantum mechanics. The theory was never complete or self-consistent, but was rather a set of heuristic corrections to classical mechanics. The theory is now understood as a semi-classical approximation to modern quantum mechanics.Quantum indeterminacy is the apparent necessary incompleteness in the description of a physical system, that has become one of the characteristics of the standard description of quantum physics. Prior to quantum physics, it was thought that. a physical system had a determinate state which uniquely determined all the values of its measurable ...The mysterious world of quantum mechanics has mystified scientists for decades. But this mind-bending theory is the best explanation of reality that we have....Quantum mechanics was once mostly of interest to physicists, chemists and other basic scientists. Now the concepts and techniques of quantum mechanics are essential in many areas of engineering and science such as materials science, nanotechnology, electronic devices, and photonics. This course is a substantial introduction to quantum mechanics ...View full lesson: http://ed.ted.com/lessons/particles-and-waves-the-central-mystery-of-quantum-mechanics-chad-orzelOne of the most amazing facts in physics i...Quantum mechanical laws are usually only found to apply at very low temperatures. Quantum computers, for example, currently operate at around -272°C . At higher temperatures, classical mechanics ...7.2: Wave functions. In quantum mechanics, the state of a physical system is represented by a wave function. In Born’s interpretation, the square of the particle’s wave function represents the probability density of finding the particle around a specific location in space. Wave functions must first be normalized before using them to make ... In this quantum physics introduction for beginners, we will explain quantum physics, also called quantum mechanics, in simple terms. Quantum physics is possibly the most fascinating part of physics that exists. It is the amazing physics that becomes relevant for small particles, where the so-called classical physics is no longer valid. Canonical commutation rule for position q and momentum p variables of a particle, 1927.pq − qp = h/(2πi).Uncertainty principle of Heisenberg, 1927. The uncertainty principle, also known as Heisenberg's indeterminacy principle, is a fundamental concept in quantum mechanics.It states that there is a limit to the precision with which certain pairs of …4.8 stars. 6 ratings. Learn the fundamental notions of quantum mechanics at a level that is accessible to everyone. This course is listed as one of the best online courses of all time by Class Central and was a finalist for the 2018 edX Prize for Exceptional Contributions to Online Teaching and Learning. Play Video. 6 weeks. 7–10 hours per week.The quantum harmonic oscillator is the quantum-mechanical analog of the classical harmonic oscillator. Because an arbitrary smooth potential can usually be approximated as a harmonic potential at the vicinity of a stable equilibrium point, it is one of the most important model systems in quantum mechanics.The latest news on quantum physics, wave particle duality, quantum theory, quantum mechanics, quantum entanglement, quantum teleportation, and quantum computing.Quantum Mechanix Inc. is a creative studio and developer of screen-accurate collectibles and digital apps and games inspired by popular movies and TV shows. 0% Complete Quantum MechanixQuantum mechanical laws are usually only found to apply at very low temperatures. Quantum computers, for example, currently operate at around -272°C. At higher temperatures, classical mechanics ...Quantum mechanical laws are usually only found to apply at very low temperatures. Quantum computers, for example, currently operate at around -272°C . At higher temperatures, classical mechanics ...Feb 20, 2022 · 7.2: Wave functions. In quantum mechanics, the state of a physical system is represented by a wave function. In Born’s interpretation, the square of the particle’s wave function represents the probability density of finding the particle around a specific location in space. Wave functions must first be normalized before using them to make ... This textbook, now in an expanded third edition, emphasizes the importance of advanced quantum mechanics for materials science and all experimental techniques which employ photon absorption, emission, or scattering. Important aspects of introductory quantum mechanics are covered in the first seven chapters to make the subject self-contained …Apr 11, 2024 · Although quantum mechanics is essential to understand microscopic systems, it has little effect on heavier objects. Experiments have now put strict constraints on theories that use gravity to ... His record of successful theoretical research with undergraduate students was recognized in 2011 when he was named as a KITP-Anacapa scholar. AI generated results by. Discover Introduction to Quantum Mechanics, 3rd Edition, David J. Griffiths, HB ISBN: 9781107189638 on Higher Education from Cambridge. David Tong: Lectures on Topics in Quantum Mechanics. This is an advanced course on quantum mechanics. It covers a wide range of topics, including an introduction to atomic physics, quantum foundations and scattering theory. Please do email me if you find any typos or mistakes. PostScript PDF. Content.
The important changes quantum mechanics has undergone in recent years are reflected in this approach for students. A strong narrative and over 300 worked problems lead the student from experiment, through general principles of the theory, to modern applications. Stepping through results allows students to gain a thorough understanding.. Showbox.apk
Quantum mechanics is a hypothesis in material science that gives a depiction of the actual properties of nature at the size of atoms and subatomic particles. It is the foundation of all quantum material science including quantum science, quantum field hypothesis, quantum innovation, and quantum data science.Quantum Mechanics. Ph: (02) 4961 1795 97 Denison Street Hamilton, Newcastle NSW 2303 View Map. Courtesy Vehicles. We offer a convenient vehicle loan service. SWAP'N'GO. Simply drop off your car and drive away in Quantum Courtesy Car. It's FREE!! Book Now. Go Green.An interpretation of quantum mechanics is an attempt to explain how the mathematical theory of quantum mechanics might correspond to experienced reality. Although quantum mechanics has held up to rigorous and extremely precise tests in an extraordinarily broad range of experiments, there exist a number of contending schools of thought over ...Feb 20, 2022 · 7.2: Wave functions. In quantum mechanics, the state of a physical system is represented by a wave function. In Born’s interpretation, the square of the particle’s wave function represents the probability density of finding the particle around a specific location in space. Wave functions must first be normalized before using them to make ... Quantum mechanics opens the doors for Quantum Engineers to leverage quantum physics to deliver unprecedented solutions to engineering problems. Quantum Engineers specialise in how high-frequency, nanometer-scale electronics can be made to harness quantum nature. When you study Quantum Engineering at UNSW, you'll develop the …Mathematically, quantum mechanics can be regarded as a non-classical probability calculus resting upon a non-classical propositional logic. More specifically, in quantum mechanics each probability-bearing proposition of the form “the value of physical quantity \(A\) lies in the range \(B\)” is represented by a projection operator on a Hilbert …David Tong: Lectures on Topics in Quantum Mechanics. This is an advanced course on quantum mechanics. It covers a wide range of topics, including an introduction to atomic physics, quantum foundations and scattering theory. Please do email me if you find any typos or mistakes. PostScript PDF. Content.That theory is known as quantum mechanics, and it is now the basic framework for understanding atomic, nuclear, and subnuclear physics, as well as condensed-matter (or ”solid-state”) physics. The laws of motion (due to Galileo, Newton,...) which preceded quantum theory are referred to as classical mechanics.Quantum mechanics describes how these particles interact with each other and with light, X-rays, gamma rays, and other forms of electromagnetic radiation. One of the great ideas of the 20th century, quantum mechanics continues to be at the forefront of advances in physics in the 21st century. In addition to explaining the structure of atoms and ...In quantum mechanics, the variational method is one way of finding approximations to the lowest energy eigenstate or ground state, and some excited states.This allows calculating approximate wavefunctions such as molecular orbitals. The basis for this method is the variational principle.. The method consists of choosing a "trial wavefunction" depending …Quantum Mechanics. Four basic principles of quantum mechanics are: (3.1) Physical States. Every physical system is associated with a Hilbert Space, every unit vector in the space corresponds to a …Quantum mechanics explains how the universe works with things that are even smaller than atoms. It is also called quantum physics or quantum theory. Mechanics is the part of physics that explains how things move and quantum is the Latin word for 'how much'. A quantum of energy is the least amount possible (or the least extra amount), and ... Quantum Mechanics. In day to day life, we intuitively understand how the world works. Drop a glass and it will smash to the floor. Push a wagon and it will roll along. Walk to a wall and you can't ... Gravity and quantum mechanics tend to stay out of each other's way, but this might change as we devise new experiments to test the applicability of quantum theory to macroscopic systems and larger ...IB Quantum Mechanics. Notes and supplementary material for course taught in 2019-20. first time encounter similar problems and temporary confusions. and aptitudes. The article below discusses some points where. questions. It also gives links to a range of simulation tools. An interpretation of quantum mechanics is an attempt to explain how the mathematical theory of quantum mechanics might correspond to experienced reality. Although quantum mechanics has held up to rigorous and extremely precise tests in an extraordinarily broad range of experiments, there exist a number of contending schools of thought over ... .