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Nov 2010

Volume 78, Issue 11, pp. 1077-1232

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ENTROPY AND RUST

Daniel F. Styer

American Journal of Physics -- November 2010 -- Volume 78, Issue 11, pp. 1077 | Cited 1 time

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05.70.-a Thermodynamics

A TWENTY YEAR DELAY IN NEWTON’S PUBLISHING?

David Derbes

American Journal of Physics -- November 2010 -- Volume 78, Issue 11, pp. 1077

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01.65.+g History of science

REPLY TO DERBES

Paul J. Nahin

American Journal of Physics -- November 2010 -- Volume 78, Issue 11, pp. 1078

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01.65.+g History of science
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Search for a new editor

Jan Tobochnik

American Journal of Physics -- November 2010 -- Volume 78, Issue 11, pp. 1079

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Abstract Unavailable
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01.10.-m Announcements, news, and organizational activities
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Resource Letter QCD-1: Quantum chromodynamics

Andreas S. Kronfeld and Chris Quigg

American Journal of Physics -- November 2010 -- Volume 78, Issue 11, pp. 1081

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This Resource Letter provides a guide to the literature on quantum chromodynamics (QCD), the relativistic quantum field theory of the strong interactions. Journal articles, books, and other documents are cited for the following topics: Quarks and color, the parton model, Yang–Mills theory, experimental evidence for color, QCD as a color gauge theory, asymptotic freedom, QCD for heavy hadrons, QCD on the lattice, the QCD vacuum, pictures of quark confinement, early and modern applications of perturbative QCD, the determination of the strong coupling and quark masses, QCD and the hadron spectrum, hadron decays, the quark-gluon plasma, the strong nuclear interaction, and QCD’s role in nuclear physics.
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01.30.Rr Surveys and tutorial papers; resource letters
10.00.00 THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS

The magnetic field lines of a helical coil are not simple loops

Martin Lieberherr

American Journal of Physics -- November 2010 -- Volume 78, Issue 11, pp. 1117 | Cited 1 time

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It is shown that the magnetic field lines of a loosely wound helical coil of finite length do not close after one loop. Examples of simple wire shapes that display the same effect are given.
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41.00.00 Electromagnetism; electron and ion optics

Damped oscillations and equilibrium in a mass-spring system subject to sliding friction forces: Integrating experimental and theoretical analyses

P. Onorato, D. Mascoli, and A. DeAmbrosis

American Journal of Physics -- November 2010 -- Volume 78, Issue 11, pp. 1120

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Students have difficulty in understanding friction and its associated phenomena. Introductory university courses usually fail to give the topic the attention it deserves and to emphasize the crucial role of friction in establishing mechanical equilibrium as motion ceases. We present an experimental and a theoretical analysis of the periodic motion of a mass-spring system subject to static and kinetic friction forces. Our analysis takes into account the effects of the static friction force on the final mass position.
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01.50.Pa Laboratory experiments and apparatus
47.00.00 Fluid dynamics

Tracking the stars, Sun, and Moon to connect with the universe

Todd C. McAlpine, Corwin Atwood-Stone, Travis Brown, and John F. Lindner

American Journal of Physics -- November 2010 -- Volume 78, Issue 11, pp. 1128

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We describe the theory, design, and construction of simple electromechanical devices that automatically and continually track celestial objects. As Earth rotates and revolves, a star tracker always points at a star or other objects fixed to the celestial sphere, such as the center of the Milky Way galaxy. A planet tracker can fixate on any celestial object including the planets, the Sun, or the Moon. A sidereal clock mechanism drives the star tracker, and software that encodes astronomical algorithms controls an inexpensive robot that drives the planet tracker. The star tracker acts like a gyroscope, rigidly oriented in space, despite Earth’s motion. Both trackers indicate the passing of time just like clocks and calendars. The resulting lecture, hallway, or museum displays promote awareness of and excitement about our place in the universe.
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01.50.Pa Laboratory experiments and apparatus
95.00.00 Fundamental astronomy and astrophysics; instrumentation, techniques, and astronomical observations

The energy-time uncertainty principle and quantum phenomena

Jack Denur

American Journal of Physics -- November 2010 -- Volume 78, Issue 11, pp. 1132

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We employ the energy-time uncertainty principle to provide heuristic yet helpful insights into tunneling, Unruh radiation, the Schwinger effect, and the ground state of the electromagnetic field. The position-momentum uncertainty principle is employed in auxiliary roles. We also discuss the similarities and differences between quantum and thermal fluctuations.©
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Analytical study of the critical behavior of the nonlinear pendulum

F. M. S. Lima

American Journal of Physics -- November 2010 -- Volume 78, Issue 11, pp. 1146 | Cited 3 times

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The dynamics of a simple pendulum consisting of a small bob and a massless rigid rod has three possible regimes depending on its total energy E: Oscillatory (when E is not enough for the pendulum to reach the top position), “perpetual ascent” when E is exactly the energy needed to reach the top, and nonoscillatory for greater energies. In the latter regime, the pendulum rotates periodically without velocity inversions. In contrast to the oscillatory regime, for which an exact analytic solution is known, the other two regimes are usually studied by solving the equation of motion numerically. By applying conservation of energy, I derive exact analytical solutions to both the perpetual ascent and nonoscillatory regimes and an exact expression for the pendulum period in the nonoscillatory regime. Based on Cromer’s approximation for the large-angle pendulum period, I find a simple approximate expression for the decrease of the period with the initial velocity in the nonoscillatory regime, valid near the critical velocity. This expression is used to study the critical slowing down, which is observed near the transition between the oscillatory and nonoscillatory regimes.
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47.00.00 Fluid dynamics

Visualizing individual microtubules by bright field microscopy

Braulio Gutiérrez-Medina and Steven M. Block

American Journal of Physics -- November 2010 -- Volume 78, Issue 11, pp. 1152

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Microtubules are slender ( ∼ 25 nm diameter), filamentous polymers involved in cellular structure and organization. Individual microtubules have been visualized via fluorescence imaging of dye-labeled tubulin subunits and by video-enhanced, differential interference-contrast microscopy of unlabeled polymers using sensitive CCD cameras. We demonstrate the imaging of unstained microtubules using a microscope with conventional bright field optics in conjunction with a webcam-type camera and a light-emitting diode illuminator. The light scattered by microtubules is image-processed to remove the background, reduce noise, and enhance contrast. The setup is based on a commercial microscope with a minimal set of inexpensive components, suitable for implementation in a student laboratory. We show how this approach can be used in a demonstration motility assay, tracking the gliding motions of microtubules driven by the motor protein kinesin.
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01.50.Pa Laboratory experiments and apparatus
42.00.00 Optics

The response of laser interferometers to a gravitational wave

Adrian Melissinos and Ashok Das

American Journal of Physics -- November 2010 -- Volume 78, Issue 11, pp. 1160

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Laser interferometer detectors are widely used in the extensive effort to detect gravitational waves. The interaction of a gravitational wave with light in the interferometer is usually explained in terms of the motion of the “free” mirrors that form the interferometer arms. It is instructive to show that the same result can be obtained by calculating the propagation of an electromagnetic plane wave between free mirrors in the curved space-time induced by the gravitational wave. We find that the plane wave acquires frequency modulation sidebands at the frequency of the gravitational wave. Such sidebands are equivalent to the time-dependent phase shift imposed on the plane wave, as obtained in the conventional calculation.
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01.50.Pa Laboratory experiments and apparatus
04.00.00 General relativity and gravitation

Stokes’ dream: Measurement of fluid viscosity from the attenuation of capillary waves

F. Behroozi, J. Smith, and W. Even

American Journal of Physics -- November 2010 -- Volume 78, Issue 11, pp. 1165

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The determination of viscosity from the attenuation of capillary waves was first suggested by Stokes more than a century ago. At the time, it was not practical to measure the attenuation of surface waves with the requisite precision to render the method useful. We describe a noncontact method for measuring the wavelength and amplitude of single-frequency capillary waves to obtain reliable values of the surface tension and viscosity. The attenuation data for several glycerin-water mixtures are used to obtain the viscosity as a function of glycerin concentration. For a wide range of viscosity, the method yields results that are in good agreement with the most reliable published data.
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01.50.Pa Laboratory experiments and apparatus
47.00.00 Fluid dynamics

Thermodynamic curvature measures interactions

George Ruppeiner

American Journal of Physics -- November 2010 -- Volume 78, Issue 11, pp. 1170 | Cited 2 times

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Thermodynamic fluctuation theory originated with Einstein, who inverted the relation S = kB ln Ω to express the number of states in terms of entropy: Ω = exp(S/kB). The theory’s Gaussian approximation is discussed in most statistical mechanics texts. I review work showing how to go beyond the Gaussian approximation by adding covariance, conservation, and consistency. This generalization leads to a fundamentally new object: The thermodynamic Riemannian curvature scalar R, a thermodynamic invariant. I argue that |R| is related to the correlation length and suggest that the sign of R corresponds to whether the interparticle interactions are effectively attractive or repulsive.
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04.00.00 General relativity and gravitation
05.70.−a

Maxwell’s equations in a uniformly rotating dielectric medium and the Wilson–Wilson experiment

C. E. S. Canovan and Robin W. Tucker

American Journal of Physics -- November 2010 -- Volume 78, Issue 11, pp. 1181

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We offer a conceptually straightforward and efficient way to formulate and solve problems on the electromagnetics of moving media based on a representation of Maxwell’s equations in terms of differential forms on spacetime together with junction conditions at moving interfaces. This framework is used to address several issues on the theoretical description underlying the interpretation of the Wilson–Wilson experiment.
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03.30.+p Special relativity
41.00.00 Electromagnetism; electron and ion optics

Change of the plane of oscillation of a Foucault pendulum from simple pictures

Thomas F. Jordan and J. Maps

American Journal of Physics -- November 2010 -- Volume 78, Issue 11, pp. 1188

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The change of the plane of oscillation of a Foucault pendulum is calculated without using equations of motion, the Gauss–Bonnet theorem, parallel transport, or assumptions that are difficult to explain.
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47.00.00 Fluid dynamics

Point charge dynamics near a grounded conducting plane

Kevin L. Haglin

American Journal of Physics -- November 2010 -- Volume 78, Issue 11, pp. 1190

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The classic image problem in electromagnetism involves a grounded infinite conducting plane and a point charge. The force of attraction between the point charge and the plane is identified using an equivalent-field picture of an image charge with an opposite sign equidistant behind the plane, resulting in a 1/r2 attractive force between the original charge and the plane. If the point charge is released from rest, it will reach the plane in a time τ, which has not been calculated correctly. The inconsistency is clarified along with an improved solution to the classic image problem. Similar electromagnetism problems are also discussed.
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41.00.00 Electromagnetism; electron and ion optics

Caustics and wavefronts by multiple reflections in a circular surface

Maximino Avendaño-Alejo, Luis Castañeda, and Iván Moreno

American Journal of Physics -- November 2010 -- Volume 78, Issue 11, pp. 1195 | Cited 3 times

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A caustic by reflection at an arbitrary surface is commonly known as a catacaustic. We study the formation of the catacaustic by multiple reflections in a reflecting circular surface by considering a point light source placed at an arbitrary point on the optical axis. The geometrical wavefront associated with multiple reflections for a paraxial approximation occurs for arbitrary locations of the source. Simple relations for the catacaustic and its wavefront are given.
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42.00.00 Optics

Strong coupling, energy splitting, and level crossings: A classical perspective

Lukas Novotny

American Journal of Physics -- November 2010 -- Volume 78, Issue 11, pp. 1199 | Cited 2 times

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Strongly interacting quantum systems are at the heart of many physical processes, ranging from photosynthesis to quantum information. We demonstrate that many characteristic features of strongly coupled systems can be derived classically for a simple coupled harmonic oscillator. This model system is used to derive frequency splittings and to analyze adiabatic and diabatic transitions between the coupled states. A classical analog of the Landau–Zener formula is derived. The classical analysis is intuitive and well suited for introducing students to the basic concepts of strongly interacting systems.
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03.65.−w
47.00.00 Fluid dynamics

Energy flow from a battery to other circuit elements: Role of surface charges

Manoj K. Harbola

American Journal of Physics -- November 2010 -- Volume 78, Issue 11, pp. 1203 | Cited 2 times

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A qualitative description of energy transfer from a battery to a resistor using the Poynting vector was recently published. We make this argument quantitative by considering a long current carrying wire and showing that the energy transferred across a plane perpendicular to the wire is equal to the Joule heating in the wire beyond this plane.
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41.00.00 Electromagnetism; electron and ion optics
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The design and evaluation of an instructional sequence on Ampere’s law

Jenaro Guisasola, José M. Almudí, and Kristina Zuza

American Journal of Physics -- November 2010 -- Volume 78, Issue 11, pp. 1207 | Cited 2 times

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This paper describes the design, implementation, and evaluation of an instructional sequence intended to improve student understanding of Ampere’s law among engineering students taking introductory physics. Participating students performed better on qualitative and quantitative test questions about Ampere’s law than students in a similar class that devoted the same amount of time to the topic but followed traditional instruction. The results suggest that the strategy employed in the sequence can help students to apply and explain the relation between electrical currents and magnetic fields.
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01.40.Fk Research in physics education

A physics department’s role in preparing physics teachers: The Colorado learning assistant model

Valerie Otero, Steven Pollock, and Noah Finkelstein

American Journal of Physics -- November 2010 -- Volume 78, Issue 11, pp. 1218 | Cited 1 time

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In response to substantial evidence that many U.S. students are inadequately prepared in science and mathematics, we have developed an effective and adaptable model that improves the education of all students in introductory physics and increases the numbers of talented physics majors becoming certified to teach physics. We report on the Colorado Learning Assistant model and discuss its effectiveness at a large research university. Since its inception in 2003, we have increased the pool of well-qualified K–12 physics teachers by a factor of approximately three, engaged scientists significantly in the recruiting and preparation of future teachers, and improved the introductory physics sequence so that students’ learning gains are typically double the traditional average.
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01.40.Fk Research in physics education
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Comment on “Some novel delta-function identities” by Charles P. Frahm [Am. J. Phys. 51, 826–829 (1983)]

Jerrold Franklin

American Journal of Physics -- November 2010 -- Volume 78, Issue 11, pp. 1225 | Cited 2 times

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We show that a form for the second partial derivative of 1/r proposed by Frahm and subsequently used by other workers applies only when averaged over smooth functions. We use dyadic notation to derive a more general form without that restriction.
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02.00.00 Mathematical methods in physics

Spreadsheet lock-in amplifier

Richard Wolfson and Darcy Mullen

American Journal of Physics -- November 2010 -- Volume 78, Issue 11, pp. 1227

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Abstract Unavailable
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84.00.00 Electronics; radiowave and microwave technology; direct energy conversion and storage
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Physical Biology of the Cell

Rob Phillips, Jane Kondev, Julie Theriot, Hernan Garcia, and Bernard Chasan, Reviewer, Reviewer

American Journal of Physics -- November 2010 -- Volume 78, Issue 11, pp. 1230

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Abstract Unavailable
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01.30.Vv Book reviews
87.00.00 Biological and medical physics

Street-Fighting Mathematics: The Art of Educated Guessing and Opportunistic Problem Solving

Sanjoy Mahajan and John A. Adam, Reviewer, Reviewer

American Journal of Physics -- November 2010 -- Volume 78, Issue 11, pp. 1230

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Abstract Unavailable

BOOKS RECEIVED

American Journal of Physics -- November 2010 -- Volume 78, Issue 11, pp. 1232

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