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Dec 2011

Volume 79, Issue 12, pp. 1189-1279

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AJP Reviewers

David P. Jackson, Editor and Harvey Gould, Associate Editor

American Journal of Physics -- December 2011 -- Volume 79, Issue 12, pp. 1189

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Below is a list of 825 individuals who have reviewed manuscripts for the American Journal of Physics from September 1, 2010 to August 31, 2011. If you reviewed for AJP during this time and are not on the list, we apologize and hope that you will let us know so that we can correct our records. The thoughtful and expert advice provided by our reviewers is essential for maintaining the quality of the journal and insuring that it fulfills its educational mission. On behalf of all AJP authors and readers, we sincerely thank all who have served as reviewers.
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01.10.-m Announcements, news, and organizational activities
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2011 AAPT Award Citations at the Summer Meeting, Omaha Nebraska

American Journal of Physics -- December 2011 -- Volume 79, Issue 12, pp. 1191

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Abstract Unavailable
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01.10.-m Announcements, news, and organizational activities
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Probability, geometry, and dynamics in the toss of a thick coin

Ee Hou Yong and L. Mahadevan

American Journal of Physics -- December 2011 -- Volume 79, Issue 12, pp. 1195

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When a thick cylindrical coin is tossed in the air and lands without bouncing on an inelastic substrate, it ends up on its face or its side. We account for the rigid body dynamics of spin and precession and calculate the probability distribution of heads, tails, and sides for a thick coin as a function of its dimensions and the distribution of its initial conditions. Our theory yields a simple expression for the aspect ratio of homogeneous coins with a prescribed frequency of heads or tails compared to sides, which we validate using data from the results of tossing coins of different aspect ratios.

The added mass of a spherical projectile

J. Pantaleone and J. Messer

American Journal of Physics -- December 2011 -- Volume 79, Issue 12, pp. 1202

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When a ball moves through the air, the air exerts a force on the ball. For a sphere moving at constant velocity with respect to the air, this force is called the drag force and it has been well measured. If the sphere moves with a nonconstant velocity there are additional forces. These “unsteady” forces depend on the sphere’s acceleration and, in principle, also on higher derivatives of the motion. The force equal to a constant times the acceleration is called the “added mass” because it increases the effective inertia of the sphere moving through the fluid. We measure the unsteady forces on a sphere by observing the one- and two-dimensional projectile motion of light spheres around the highest point. The one-dimensional motion is well described by just the usual buoyant force and the added mass as calculated in the ideal fluid model. This measurement is an excellent experiment for introductory physics students. For spheres in two-dimensional projectile motion the downward vertical acceleration at the highest point increases with the horizontal velocity. This effect can be described by an additional force proportional to the speed times the acceleration.
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05.70.-a Thermodynamics
47.00.00 Fluid dynamics

Measurement of sub-natural linewidth AC Stark shifts in cold atoms: An experiment for an advanced undergraduate laboratory

J. D. Kleykamp, A. J. Hachtel, D. G. Kane, M. D. Marshall, N. J. Souther, P. K. Harnish, and S. Bali

American Journal of Physics -- December 2011 -- Volume 79, Issue 12, pp. 1211

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We measure sub-MHz AC Stark shifts, also known as light shifts, in an undergraduate laboratory setting using Raman pump-probe spectroscopy to observe sub-natural linewidth spectral features in the transmission spectrum of a weak probe beam passing through a sample of cold 85Rb atoms confined in a magneto-optical trap. To make this observation a pair of inexpensive fast photodiodes and acousto-optic modulators is needed, in addition to equipment commonly found in advanced undergraduate optics labs with laser cooling and atom trapping setups. A theoretical description of light shifts accessible to junior and senior-level physics majors is provided.
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01.50.Pa Laboratory experiments and apparatus
30.00.00 ATOMIC AND MOLECULAR PHYSICS
42.00.00 Optics

Paradoxical reflection in quantum mechanics

Pedro L. Garrido, Sheldon Goldstein, Jani Lukkarinen, and Roderich Tumulka

American Journal of Physics -- December 2011 -- Volume 79, Issue 12, pp. 1218

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We discuss a phenomenon of elementary quantum mechanics that is counterintuitive, non-classical, and apparently not widely known: the reflection of a particle at a downward potential step. In contrast, classically, particles are reflected only at upward steps. The conditions for this effect are that the wavelength is much greater than the width of the potential step and the kinetic energy of the particle is much smaller than the depth of the potential step. The phenomenon is suggested by non-normalizable solutions to the time-independent Schrödinger equation. We present numerical and mathematical evidence that it is also predicted by the time-dependent Schrödinger equation. The paradoxical reflection effect suggests and we confirm mathematically that a particle can be trapped for a long time (though not indefinitely) in a region surrounded by downward potential steps, that is, on a plateau.
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03.65.-w Quantum mechanics

Teaching solar cell I-V characteristics using SPICE

Archana Devasia and Santosh K. Kurinec

American Journal of Physics -- December 2011 -- Volume 79, Issue 12, pp. 1232

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The basic equivalent circuit of a p-n junction solar cell is most commonly represented as consisting of a current source in parallel with two diodes and two parasitic resistances. The output of a solar cell is measured by obtaining the current-voltage (I–V) characteristics for different illumination intensities, and various parameters are extracted from these characteristics. Because the nature of the information derived from these characteristics is not obvious to the beginning students in photovoltaics, a simulation using SPICE was utilized to explain three solar cell I–V characteristics—dark I–V, illuminated I–V, and open circuit voltage versus the short circuit current (illumination intensity). Students can construct a solar cell and study the effect of the diode and parasitic parameters on the three output I–V characteristics. Series and parallel combinations of solar cells for arrays and modules using bypass diodes are demonstrated using SPICE as educational tools for understanding the role of bypass diodes.
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84.00.00 Electronics; radiowave and microwave technology; direct energy conversion and storage

A low cost remote sensing system using PC and stereo equipment

Joel F. Campbell, Michael A. Flood, Narasimha S. Prasad, and Wade D. Hodson

American Journal of Physics -- December 2011 -- Volume 79, Issue 12, pp. 1240

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A system using a personal computer, speaker, and a microphone is used to detect objects, and make crude measurements using a carrier modulated by a pseudorandom noise (PN) code. This system can be constructed using a personal computer and audio equipment commonly found in the laboratory or at home, or more sophisticated equipment that can be purchased at a reasonable cost. We demonstrate its value as an instructional tool for teaching concepts of remote sensing and digital signal processing.
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01.50.Pa Laboratory experiments and apparatus
43.00.00 Acoustics

Orbits of the Kepler problem via polar reciprocals

E. D. Davis

American Journal of Physics -- December 2011 -- Volume 79, Issue 12, pp. 1246

Online Publication Date: Nov 2011

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Polar reciprocals of trajectories are an elegant alternative to hodographs for motion in a central force field. Their principal advantage is that the transformation from a trajectory to its polar reciprocal is its own inverse. The form of the polar reciprocals of Kepler orbits is established, and a geometrical construction is presented for the orbits of the Kepler problem starting from their polar reciprocals. No obscure knowledge of conics is required to demonstrate the validity of the method. Unlike a graphical procedure suggested by Feynman and extended by Derbes, the method based on polar reciprocals works without changes for elliptical, parabolic, and hyperbolic trajectories.
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45.00.00 Classical mechanics of discrete systems

Unraveling a classical mechanics brain twister

Norman Paris and Michael L. Broide

American Journal of Physics -- December 2011 -- Volume 79, Issue 12, pp. 1250

Online Publication Date: Nov 2011

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We present a comprehensive analysis of an intriguing classical mechanics problem involving the coupled motion of two blocks. The problem illustrates fundamental physics concepts and theoretical techniques. We solve the equations of motion numerically and gain insight into common misconceptions about this system. The problem provides rich opportunities for student investigations using analytical and numerical methods.
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45.00.00 Classical mechanics of discrete systems

Nonlinear ordinary differential equations in fluid dynamics

John D. Ramshaw

American Journal of Physics -- December 2011 -- Volume 79, Issue 12, pp. 1255

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The equivalence between nonlinear ordinary differential equations (ODEs) and linear partial differential equations (PDEs) was recently revisited by Smith, who used the equivalence to transform the ODEs of Newtonian dynamics into equivalent PDEs, from which analytical solutions to several simple dynamical problems were derived. We show how this equivalence can be used to derive a variety of exact solutions to the PDEs describing advection in fluid dynamics in terms of solutions to the equivalent ODEs for the trajectories of Lagrangian fluid particles. The PDEs that we consider describe the time evolution of non-diffusive scalars, conserved densities, and Lagrangian surfaces advected by an arbitrary compressible fluid velocity field u(x, t). By virtue of their arbitrary initial conditions, the analytical solutions are asymmetric and three-dimensional even when the velocity field is one-dimensional or symmetrical. Such solutions are useful for verifying multidimensional numerical algorithms and computer codes for simulating advection and interfacial dynamics in fluids. Illustrative examples are discussed.

John S. Bell’s concept of local causality

Travis Norsen

American Journal of Physics -- December 2011 -- Volume 79, Issue 12, pp. 1261

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John Stewart Bell’s famous theorem is widely regarded as one of the most important developments in the foundations of physics. Yet even as we approach the 50th anniversary of Bell’s discovery, its meaning and implications remain controversial. Many workers assert that Bell’s theorem refutes the possibility suggested by Einstein, Podolsky, and Rosen (EPR) of supplementing ordinary quantum theory with “hidden” variables that might restore determinism and/or some notion of an observer-independent reality. But Bell himself interpreted the theorem very differently—as establishing an “essential conflict” between the well-tested empirical predictions of quantum theory and relativistic local causality. Our goal is to make Bell’s own views more widely known and to explain Bell’s little-known formulation of the concept of relativistic local causality on which his theorem rests. We also show precisely how Bell’s formulation of local causality can be used to derive an empirically testable Bell-type inequality and to recapitulate the EPR argument.
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01.70.+w Philosophy of science
03.65.-w Quantum mechanics
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An Indispensable Truth: How Fusion Power Can Save the Planet.

Francis F. Chen and Gary J. Weisel, Reviewer, Reviewer

American Journal of Physics -- December 2011 -- Volume 79, Issue 12, pp. 1276

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Abstract Unavailable

Relativity for the Questioning Mind.

Daniel F. Styer and Stephen Boughn, Reviewer, Reviewer

American Journal of Physics -- December 2011 -- Volume 79, Issue 12, pp. 1277

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Abstract Unavailable

BOOKS RECEIVED

American Journal of Physics -- December 2011 -- Volume 79, Issue 12, pp. 1279

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