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Dec 1989

Volume 57, Issue 12, pp. 1063-1156

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Errors intentional and otherwise

Robert Weinstock

American Journal of Physics -- December 1989 -- Volume 57, Issue 12, pp. 1063 | Cited 2 times

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01.40.G- Curricula and evaluation
45.05.+x General theory of classical mechanics of discrete systems

About which moving or accelerating points may dynamical moments validly be taken? Errors unintentional

Claude Kacser

American Journal of Physics -- December 1989 -- Volume 57, Issue 12, pp. 1063 | Cited 2 times

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45.05.+x General theory of classical mechanics of discrete systems

The history of demonstration lectures

John L. McKnight and Rolf G. Winter

American Journal of Physics -- December 1989 -- Volume 57, Issue 12, pp. 1063

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01.50.My Demonstration experiments and apparatus
01.65.+g History of science

A comment from a chemist on modernizing the introductory physics texts

Howard R. Leo

American Journal of Physics -- December 1989 -- Volume 57, Issue 12, pp. 1064

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01.30.mp Textbooks for undergraduates

Units for the crew of spaceship Earth

Robert D. Freeman

American Journal of Physics -- December 1989 -- Volume 57, Issue 12, pp. 1064 | Cited 1 time

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06.20.F- Units and standards

The search for gravitational waves—A correction

Massimo Tinto

American Journal of Physics -- December 1989 -- Volume 57, Issue 12, pp. 1065

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04.80.-y Experimental studies of gravity

Is quantum mechanics crazy?

Daniel T. Gillespie

American Journal of Physics -- December 1989 -- Volume 57, Issue 12, pp. 1065

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03.65.Ta Foundations of quantum mechanics; measurement theory
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Editorial: Vote for your favorite AJP papers!

Robert H. Romer

American Journal of Physics -- December 1989 -- Volume 57, Issue 12, pp. 1067

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01.30.-y Physics literature and publications
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Conductance fluctuations in loops of gold

S. Washburn

American Journal of Physics -- December 1989 -- Volume 57, Issue 12, pp. 1069 | Cited 1 time

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The magnetoresistance of small wires and loops is described. At low temperatures, the electrons retain quantum mechanical phase coherence for distances of a micron or so, which is the size scale over which the measurements are made. The random interference of the electron wavefunctions appears as random fluctuations in the magnetoresistance, and in loops, the Aharonov–Bohm effect causes periodic oscillations. The resistance varies randomly with the Fermi energy of the electrons, with the voltage across the sample, and with any transverse voltages applied by external gates. The nonlocal character of the wavefunction leads to resistance fluctuations in configurations where classical physics predicts null results. Throughout the discussion the physics is explained for those new to the field.
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72.15.Gd Galvanomagnetic and other magnetotransport effects
72.15.Qm Scattering mechanisms and Kondo effect

The adiabatic theorem and Berry’s phase

Barry R. Holstein

American Journal of Physics -- December 1989 -- Volume 57, Issue 12, pp. 1079 | Cited 4 times

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A study is presented of Berry’s observation that when a quantum‐mechanical system is transported on a closed adiabatic journey, a topological phase arises in addition to the usual dynamical phase expected from the adiabatic theorem. Consequences are explored in the case of a simple magnetic moment–magnetic field interaction and are shown to lead, among other things, to Dirac’s famous relation between electric and magnetic charges.
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03.65.Ta Foundations of quantum mechanics; measurement theory

Nonradiating sources: The subtle art of changing light into black

Nicole Meyer‐Vernet

American Journal of Physics -- December 1989 -- Volume 57, Issue 12, pp. 1084 | Cited 6 times

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When a point charge accelerates or moves faster than light in a dielectric medium, it radiates. However, sources of finite size can be designed whose peculiar structure ensures that they do not radiate under these conditions. The criterion for absence of radiation of a rigid source in free space is generalized to a dielectric medium, and applied to either oscillating or Čerenkov sources.
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03.50.De Classical electromagnetism, Maxwell equations
41.20.Jb Electromagnetic wave propagation; radiowave propagation

Wobbling, toppling, and forces of contact

Tad McGeer and Leigh Hunt Palmer

American Journal of Physics -- December 1989 -- Volume 57, Issue 12, pp. 1089 | Cited 1 time

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Analyses and experiments are described for two familiar systems that upon close inspection reveal some surprises. The wobbling domino provides a simple model for some important features in the mechanics of walking. It also makes a sensitive level. The toppling pencil calls for careful treatment of friction.
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45.05.+x General theory of classical mechanics of discrete systems

A correction for spring mass in the ubiquitous centripetal force experiment of freshman physics

Robert L. Wildey

American Journal of Physics -- December 1989 -- Volume 57, Issue 12, pp. 1098 | Cited 1 time

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A widely deployed experiment in freshman physics tests the hypothesis that the magnitude of the central force that accomplishes uniform circular motion is mv2/r (equivalently mrω2). This is accomplished by using a spring rotating about one end as the central force applied to a vertically hanging bob of known mass, tracking a circle of measured radius, at a speed deduced by counting revolutions over time. The spring force is independently measured by determining the gravitational force that produces the same degree of extension of the spring. Because the inertia of the spring is unimportant to the latter measurement, but does matter in the dynamical phase of the experiment, an error is introduced. Students have always been admonished to neglect the effects of the mass of the spring; however, typical parameters used in this experiment imply an error greater than 1%, which exceeds the probable error of which the experiment is capable.
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01.50.Pa Laboratory experiments and apparatus
45.05.+x General theory of classical mechanics of discrete systems

Gamow vectors and decaying states

A. Bohm, M. Gadella, and G. Bruce Mainland

American Journal of Physics -- December 1989 -- Volume 57, Issue 12, pp. 1103 | Cited 24 times

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Gamow vectors are generalized eigenvectors of the Hamiltonian with complex eigenvalues that describe exponentially decaying (or growing) states. The energy wavefunctions corresponding to Gamow vectors have a pole immediately below (or above) the real axis in the complex energy plane. Although complex energy values were introduced more than half a century ago for the theory of alpha decay, they have become disreputable and have been banished from quantum mechanics textbooks because of mathematical problems and incorrect physical interpretation. Developments in modern mathematics have now provided a mathematical foundation that has led to the correct physical interpretation. In this article, energy eigenvectors with complex eigenvalues are first introduced by explicitly considering a specific simple decaying system. Then, an elementary account of the properties of Gamow vectors is given. The results from the decaying system provide a motivation for the introduction of Gamow vectors and some of the background information needed to understand their properties.
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03.65.Db Functional analytical methods
03.65.Ge Solutions of wave equations: bound states

A general method for treating the incidence of a plane electromagnetic wave on a plane interface between dielectrics

Joaquin Navasquillo, Vicente Such, and Francisco Pomer

American Journal of Physics -- December 1989 -- Volume 57, Issue 12, pp. 1109 | Cited 1 time

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The fields of the reflected and refracted waves produced when a plane electromagnetic wave impinges on a plane boundary are related to the incident fields by means of a tensorial transformation. This procedure allows a unified treatment of external, internal, and total internal reflection and is suitable for general problems involving transformations of electromagnetic waves. As an application, the transmitted fields for total internal reflection of a bounded electromagnetic beam are obtained.
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03.50.De Classical electromagnetism, Maxwell equations
41.20.Jb Electromagnetic wave propagation; radiowave propagation

New graphical methods for linear regression with errors: Unweighted data

William Lichten

American Journal of Physics -- December 1989 -- Volume 57, Issue 12, pp. 1112

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This article shows that the usual intuitive method for estimating the error in the slope of a graphical, straight‐line fit to a set of data points errs by a factor ∼(N)1/2. For the first time, this article derives from the usual analytical formulas graphical estimates for the errors in the intercept a and slope b for the equation y=a+bx. The result is extended to estimating the error in any derived value y′=a+bx′.
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07.05.Bx Computer systems: hardware, operating systems, computer languages, and utilities
02.60.Ed Interpolation; curve fitting

Statistical treatment of effusion of a dilute gas

Carlo Bernardini

American Journal of Physics -- December 1989 -- Volume 57, Issue 12, pp. 1116

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The problem of effusion of a low‐pressure gas consisting of N molecules through a hole is considered by using simple probability concepts such as Poisson distribution and composition of probabilities. A well‐known partial differential equation, accurate up to the order 1/N, the Fokker–Planck equation, is found and solved by standard techniques. Numerical examples are given concerning characteristic times and the rate of leakage.
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51.10.+y Kinetic and transport theory of gases
05.60.-k Transport processes

A general method for differentiation of vectors in orthogonal systems of coordinates

W. K. Koo and Y. C. Liew

American Journal of Physics -- December 1989 -- Volume 57, Issue 12, pp. 1118

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A general matrix method for differentiating unit vectors in an arbitrary orthogonal system of coordinates is given. The spatial and time derivatives of any vectors can then be obtained by differentiating the vector that has been expressed in terms of a product of a component row matrix and a unit vector column matrix, and then recombining the resultant matrices. Some examples are given to illustrate its use.
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02.40.-k Geometry, differential geometry, and topology

Nonequivalence of a uniformly accelerating reference frame and a frame at rest in a uniform gravitational field

Edward A. Desloge

American Journal of Physics -- December 1989 -- Volume 57, Issue 12, pp. 1121 | Cited 15 times

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A general expression is obtained for the space‐time interval between neighboring events in a one‐dimensional space in which it is possible to set up a rigid reference frame. Particular expressions are then obtained for the interval for the special cases of a rigid frame at rest in a uniform gravitational field and a rigid frame uniformly accelerating in field‐free space. The two expressions are not equivalent and are used to show why, how, and to what extent observations made in a rigid enclosure at rest in a gravitational field are not equivalent to observations made in a rigid enclosure that is uniformly accelerating in field‐free space. Two facts of particular interest that are demonstrated in the course of the analysis are the following: (i) Two spatially separated particles that are simultaneously released from rest and allowed to fall freely in a uniform gravitational field will not remain at rest with respect to one another. (ii) Uniformly accelerating reference frames and inertial frames are the only possible one‐dimensional rigid frames in flat space‐time.
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04.20.Cv Fundamental problems and general formalism

Nonfrictional hysteresis in a rotating U‐tube

Bruce Denardo, Brad Barber, Chris Folley, and William Wright

American Journal of Physics -- December 1989 -- Volume 57, Issue 12, pp. 1126 | Cited 1 time

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The equilibrium states of a liquid in a rotating U‐tube are investigated theoretically for the case where the axis of rotation lies between a vertical arm and the axis of symmetry. Due to the combination of the gravitational, centrifugal, and constraint forces on the liquid, the position can be hysteretic as the angular velocity is varied. Associated with the hysteresis is an instability in which the liquid jumps to a different type of equilibrium state. The behavior is explained qualitatively and derived quantitatively for a square U‐tube. The essential results are generalized to tubes with rounded corners. Finally, there is a brief comment on an experiment in which the hysteresis has been observed.
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47.32.Ef Rotating and swirling flows
47.20.-k Flow instabilities

A one‐dimensional realization of a general model for cluster–cluster aggregation

William J. Titus

American Journal of Physics -- December 1989 -- Volume 57, Issue 12, pp. 1131

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A one‐dimensional realization of a general model for cluster–cluster formation of aggregates is presented and applied to structures with constant geometric growth factors. Such objects exhibit fractal properties, and techniques for analyzing such structures in both direct and reciprocal space are discussed.
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64.60.A- Specific approaches applied to studies of phase transitions

Maximum power point characteristics of heat engines as a general thermodynamic problem

J. M. Gordon

American Journal of Physics -- December 1989 -- Volume 57, Issue 12, pp. 1136 | Cited 13 times

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The average power versus efficiency characteristics of common selected engine cycles and a few irreversibility mechanisms are analyzed toward assessing the universal nature of assorted equations that have been derived recently for efficiency at maximum power point. Most results derived to date are shown to be special cases of one general thermodynamic problem of linearly irreversible heat engines, which explains the unifying basis for seemingly fortuitous similarities in their maximum power point characteristics.
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05.70.Ln Nonequilibrium and irreversible thermodynamics

Simple demonstration of superconductivity in YBa2Cu3O7

G. C. Brown, J. O. Rasure, and W. A. Morrison

American Journal of Physics -- December 1989 -- Volume 57, Issue 12, pp. 1142 | Cited 2 times

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A simple four‐point probe using pressure contacts is used to demonstrate the zero resistivity property of superconducting YBa2Cu3O7 and the superconducting–normal‐state transition as a function of temperature.
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01.50.My Demonstration experiments and apparatus
74.70.-b Superconducting materials other than cuprates

A novel method for solving a class of differential equations

Robert Weinstock

American Journal of Physics -- December 1989 -- Volume 57, Issue 12, pp. 1144 | Cited 1 time

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Application of a previously introduced device is extended so as to effect straightforward solutions of first‐order differential equations of a particular class encountered in the calculus of variations.
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02.30.Hq Ordinary differential equations
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Identification of elements by x‐ray interaction—A laboratory experiment

B. R. Kerur, H. A. Jahagirdar, S. R. Thontadarya, and B. Hanumaiah

American Journal of Physics -- December 1989 -- Volume 57, Issue 12, pp. 1148

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01.50.Pa Laboratory experiments and apparatus
78.70.Dm X-ray absorption spectra

Michelson–Morley analysis

V. S. Soni

American Journal of Physics -- December 1989 -- Volume 57, Issue 12, pp. 1149 | Cited 2 times

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03.30.+p Special relativity

A simple derivation of distribution functions for Bose and Fermi statistics

Helmut Schmidt

American Journal of Physics -- December 1989 -- Volume 57, Issue 12, pp. 1150 | Cited 3 times

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05.30.Fk Fermion systems and electron gas
05.30.Jp Boson systems

Comment on ‘‘General relativistic perihelia precession and the anharmonic oscillator,’’ by M. G. Olsson [Am. J. Phys. 56, 89–91 (1988)]

A. Martin Sánchez, F. Vera Tomé, and C. Miró Rodriguez

American Journal of Physics -- December 1989 -- Volume 57, Issue 12, pp. 1151

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04.20.-q Classical general relativity
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A digital circuit for measuring small flows

A. Arenas, L. Victoria, and T. Luna

American Journal of Physics -- December 1989 -- Volume 57, Issue 12, pp. 1153 | Cited 1 time

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47.80.-v Instrumentation and measurement methods in fluid dynamics
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Models of the Nucleon: From Quarks to Soliton

Rajat K. Bhaduri, Author and Franz Gross

American Journal of Physics -- December 1989 -- Volume 57, Issue 12, pp. 1155

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01.30.mm Textbooks for graduates and researchers
12.39.Ba Bag model
21.60.-n Nuclear structure models and methods
21.30.-x Nuclear forces

Lasers

Peter W. Milonni, Author, Joseph H. Eberly, Author, and Phillip L. Gould

American Journal of Physics -- December 1989 -- Volume 57, Issue 12, pp. 1156

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Abstract Unavailable
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01.30.mp Textbooks for undergraduates
01.30.mm Textbooks for graduates and researchers
42.55.-f Lasers
42.60.-v Laser optical systems: design and operation
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