Topic
Physical quantity
About: Physical quantity is a research topic. Over the lifetime, 1744 publications have been published within this topic receiving 17749 citations.
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Papers
TL;DR: In this paper, a series of papers dealing with many-particle systems from a unified, nonperturbative point of view is presented, which includes derivations and discussions of various field-theoretical techniques which will be applied in subsequent papers.
Abstract: This is the first of a series of papers dealing with many-particle systems from a unified, nonperturbative point of view. It contains derivations and discussions of various field-theoretical techniques which will be applied in subsequent papers. In a short introduction the general method of approach is summarized, and its relationship to other field-theoretic problems indicated. In the second section the macroscopic properties of the spectra of many-particle systems are described. Asymptotic evaluations are performed which characterize these macroscopic features in terms of intensive parameters, and the relationship of these parameters to thermodynamics is discussed. The special characteristics of the ground state are shown to follow as a limiting case of the asymptotic evaluations. The third section is devoted to the time-dependent field correlation functions, or Green's functions, which describe the microscopic behavior of a multiparticle system. These functions are defined, and related to intensive macroscopic variables when the energy and number of particles are large. Spectral representations and other properties of various one-particle Green's functions are derived. In the fourth section the treatment of non-equilibrium processes is considered. As a particular example, the electromagnetic properties of a system are expressed in terms of the special two-particle Green's function which describes current correlation. The discussion yields specifically a fluctuation-dissipation theorem, a sum rule for conductivity, and certain dispersion relations. The fifth section deals with the differential equations which determine the Green's functions. The boundary conditions that characterize the Green's function equations are exhibited without reference to adiabatic decoupling. A method for solving the equations approximately, by treating the correlations among successively larger numbers of particles, is considered. The first approximation in this sequence is shown to yield a generalized Hartree-like equation. A related, but rigorous, identity for the single-particle Green's function is then derived. A second approximation, which takes certain two-particle correlations into account, is shown to produce various additional effects: The interaction between particles is altered in a manner characterized by the intensive macroscopic parameters, and the modification and spread of the energy-momentum relation come into play. In the final section compact formal expressions for the Green's functions and other physical quantities are derived. Alternative equations and systematic approximations for the Green's functions are obtained.
1,334 citations
Book•
27 Aug 1993
TL;DR: In this article, the authors introduce physical quantities and units, definitions and symbols for units, fundamental physical constants conversion of units, Greek alphabet index of symbols, pressure conversion factors and energy conversion factors.
Abstract: Historical introduction Physical quantities and units Tables of physical quantities Definitions and symbols for units Recommended mathematical symbols Fundamental physical constants Conversion of units References Greek alphabet Index of symbols Pressure conversion factors Energy conversion factors.
1,232 citations
Book•
6 Feb 1991
TL;DR: In this article, Figliola and Beasley first discuss the basics of measurement, analogue and digital data acquisition systems and signal processing, the statistics of measurement and the analysis of error and uncertainty.
Abstract: The assignment of numerical values to physical quantities underlies all quantitative statements in engineering and the physical sciences. This assignment is achieved by the process of measurement. The physical quantity being measured and the precision required in the numerical value determines the instrumentation to be used. The design of a measurement system therefore involves the analysis of the attribute to be measured, the means available for its detection and the verification that the measurement system performs as intended and can achieve the desired accuracy and precision. In this book Figliola and Beasley first discuss in general terms the basics of measurement, analogue and digital data acquisition systems and signal processing, the statistics of measurement and the analysis of error and uncertainty. In successive chapters they concentrate on the instruments and their physical basis in the areas of electricity, temperature, fluid flow, elastic strain and mechanics (displacement, motion, force and power). The coverage is directed towards measurements in various branches of engineering, with numerous worked examples and problems for students (approximately 30 to 40) at the end of each chapter. Since it is an American engineering text, the book uses both SI and English units. Unfortunately, the text is flawed by numerous errors. Some of the more egregious are that in chapter 1, `dimension' is used in place of `unit', the definitions given for the ampere and the ohm are in terms of `international' units that were abandoned in 1948 and derived units are expressed, for example, as `' in place of the standard forms (SI, ISO, ANSI) of `' or `'. There are furthermore numerous minor numerical errors and inconsistencies. One of the more serious flaws is the failure to distinguish between bias errors and uncertainty due to bias in the discussion of chapter 5. There is also a misuse of the student in the evaluation of uncertainty (although this error is not exclusively Figliola and Beasley's, since it occurs in ANSI documents on fluid flow measurement). Given the estimate for variance, with degrees of freedom, an uncertainty interval at confidence level p is properly , while the uncertainty for a combined quantity is where is evaluated from the Welch - Satterthwaite expression In spite of its shortcomings, the book collects a great deal of material in one place and, in the hands of a careful instructor who is aware of its flaws, could be useful as a supplementary text on measurement. E Richard Cohen
944 citations
1 Jan 1984
TL;DR: The fundamental equations of the electrodynamics of continuous media are obtained by averaging the equations for the electromagnetic field in a vacuum as discussed by the authors, and the form of the equations and significance of the quantities appearing in them depend on the physical nature of the medium and on the way in which the field varies with time.
Abstract: Macroscopic electrodynamics is concerned with the study of electromagnetic fields in space that is occupied by matter. Electrodynamics deals with physical quantities averaged over elements of volume that are physically infinitesimal and ignore the microscopic variations of the quantities that result from the molecular structure of matter. The fundamental equations of the electrodynamics of continuous media are obtained by averaging the equations for the electromagnetic field in a vacuum. The form of the equations of macroscopic electrodynamics and the significance of the quantities appearing in them depend on the physical nature of the medium and on the way in which the field varies with time. Charges present in a conductor must be located on its surface. The presence of charges inside a conductor would cause an electric field in it. These charges can be distributed on its surface, however, in such a way that the fields that they produce in its interior are mutually balanced. The mean field in the vacuum is almost the same as the actual field. The two fields differ only in the immediate neighborhood of the body, where the effect of the irregular molecular fields is noticeable, and this difference does not affect the averaged field equations.
767 citations
01 Jul 1988-Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment
TL;DR: In this paper, the authors describe how to combine correlated estimates in order to provide the best single answer, and also how to check whether the correlated estimates are mutually consistent, and illustrate its application by using it for a specific experiment which measured the lifetime of charmed particles.
Abstract: Experiments to measure a single physical quantity often produce several estimates based on the same data, and which are hence correlated. We describe how to combine these correlated estimates in order to provide the best single answer, and also how to check whether the correlated estimates are mutually consistent.
We discuss the properties of our technique, and illustrate its application by using it for a specific experiment which measured the lifetime of charmed particles.
537 citations
Related Topics (5)
Performance Metrics
| Year | Papers |
|---|---|
| 2021 | 40 |
| 2020 | 52 |
| 2019 | 65 |
| 2018 | 75 |
| 2017 | 62 |
| 2016 | 81 |