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Dec 2008

Volume 76, Issue 12, pp. 1085-I15

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AJP Reviewers

Jan Tobochnik, Editor, John Mallinckrodt, Acting Editor (July 1, 2007–June 30, 2008), and Harvey Gould, Associate Editor

American Journal of Physics -- December 2008 -- Volume 76, Issue 12, pp. 1085

Online Publication Date: Nov 2008

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Below is a list of 802 individuals who have reviewed manuscripts for the American Journal of Physics from July 1, 2007 to August 31, 2008. 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 thank all who have served as reviewers.
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01.10.-m Announcements, news, and organizational activities
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Soap bubbles in paintings: Art and science

F. Behroozi

American Journal of Physics -- December 2008 -- Volume 76, Issue 12, pp. 1087 | Cited 4 times

Online Publication Date: Nov 2008

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Soap bubbles became popular in 17th century paintings and prints primarily as a metaphor for the impermanence and fragility of life. The Dancing Couple (1663) by the Dutch painter Jan Steen is a good example which, among many other symbols, shows a young boy blowing soap bubbles. In the 18th century the French painter Jean-Simeon Chardin used soap bubbles not only as metaphor but also to express a sense of play and wonder. In his most famous painting, Soap Bubbles (1733/1734) a translucent and quavering soap bubble takes center stage. Chardin’s contemporary Charles Van Loo painted his Soap Bubbles (1764) after seeing Chardin’s work. In both paintings the soap bubbles have a hint of color and show two bright reflection spots. We discuss the physics involved and explain how keenly the painters have observed the interaction of light and soap bubbles. We show that the two reflection spots on the soap bubbles are images of the light source, one real and one virtual, formed by the curved surface of the bubble. The faint colors are due to thin film interference effects.
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42.00.00 Optics

Experimental high Reynolds number turbulence with an active grid

Nicolas Mordant

American Journal of Physics -- December 2008 -- Volume 76, Issue 12, pp. 1092

Online Publication Date: Nov 2008

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This article describes the wind tunnel used in the Physics Department of the Ecole Normale Supérieure in Paris for undergraduate laboratory courses. By using an active grid, which consists of a grid of shafts fitted with randomly rotating wings, a fully turbulent flow is observed. The velocity of the air flow is measured with a low cost hot wire probe. The Reynolds number is large enough so that predictions of the 1941 Kolmogorov theory of turbulence can be observed, such as the famous k−5∕3 spectrum, in spite of the small size of the tunnel. Deviations from the Kolmogorov theory are also observed and quantified. The moderate cost and size of the wind tunnel due to the use of the active grid make it a valuable teaching tool for introducing the phenomenology of turbulence to undergraduates.
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01.50.Pa Laboratory experiments and apparatus
47.00.00 Fluid dynamics

A free-electron calculation for quantum size effects in the properties of metallic islands on surfaces

W. A. Atkinson and A. J. Slavin

American Journal of Physics -- December 2008 -- Volume 76, Issue 12, pp. 1099 | Cited 1 time

Online Publication Date: Nov 2008

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A metal film that is only a few atomic layers thick, on an appropriate substrate, creates a quantum well that confines the conduction electrons in the direction perpendicular to the film. As a result, components of the wavevector in the plane of the film are quasicontinuous, but the perpendicular component is discrete. The result is a strong oscillatory dependence of the film properties on film thickness, including the Fermi energy and the density of states. We show that these quantum effects associated with the film thickness can be understood within the free electron theory of metals. Because of its simplicity, the thin-film quantum well is appropriate as a problem for senior undergraduate and graduate students and provides an introduction to quantum size effects.
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73.00.00 Electronic structure and electrical properties of surfaces, interfaces, thin films, and low-dimensional structures

The evolution of free wave packets

Mark Andrews

American Journal of Physics -- December 2008 -- Volume 76, Issue 12, pp. 1102 | Cited 3 times

Online Publication Date: Nov 2008

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We discuss four general features of the force-free evolution of wave packets: (1) The spatial spread of a packet changes with time in a simple way. (2) For sufficiently short durations (related to the spread in the momentum of the packet) the probability distribution will move with uniform speed and little change in shape. (3) After a sufficiently long time (related to the initial spatial spread) the wave function converges to a simple form that is simply related to the momentum distribution of the packet. In this asymptotic regime the shape of the probability distribution no longer changes, and its scale increases linearly with the time. (4) There is an infinite denumerable set of simple wave packets (the Hermite-Gauss packets) that do not change shape at any time during their evolution.
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03.65.-w Quantum mechanics

Semiclassical scattering in two dimensions

Sadhan K. Adhikari and Mahir S. Hussein

American Journal of Physics -- December 2008 -- Volume 76, Issue 12, pp. 1108 | Cited 1 time

Online Publication Date: Nov 2008

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The semiclassical limit of quantum mechanical scattering in two dimensions is developed and the Wentzel–Kramers–Brillouin and eikonal results for two-dimensional scattering is derived. No backward or forward glory scattering is present in two dimensions. Other phenomena, such as rainbows and orbiting, do occur.
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03.65.-w Quantum mechanics

A statistical mechanics model for free-for-all airplane passenger boarding

Jason H. Steffen

American Journal of Physics -- December 2008 -- Volume 76, Issue 12, pp. 1114 | Cited 1 time

Online Publication Date: Nov 2008

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I discuss a model for free-for-all passenger boarding which is employed by some discount air carriers. The model is based on the principles of statistical mechanics, where each seat in the aircraft has an associated energy which reflects the preferences of travelers. As each passenger enters the airplane they select their seats using Boltzmann statistics, proceed to that location, load their luggage, sit down, and the partition function seen by remaining passengers is modified to reflect this fact. I discuss the various model parameters and make qualitative comparisons of this passenger boarding model with those that involve assigned seats. The model can be used to predict the probability that certain seats will be occupied at different times during the boarding process. These results might provide a useful description of this boarding method. The model is a relatively unusual application of undergraduate level physics and describes a situation familiar to many students and faculty.
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05.00.00 Statistical physics, thermodynamics, and nonlinear dynamical systems

A “local observables” method for wave mechanics applied to atomic hydrogen

Peter J. Bowman

American Journal of Physics -- December 2008 -- Volume 76, Issue 12, pp. 1120 | Cited 1 time

Online Publication Date: Nov 2008

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An alternative method of deriving the values of the observables of atomic systems is presented. Rather than using operators and eigenvalues the local variables method uses the continuity equation together with current densities derived from wave functions that are solutions of the Dirac or Pauli equation. The method is applied to atomic hydrogen using the usual language of quantum mechanics rather than that of geometric algebra with which the method is often associated. The picture of the atom that emerges is one in which the electron density as a whole is rotating about a central axis. The results challenge some assumptions of conventional quantum mechanics. Electron spin is shown to be a property of the dynamical motion of the electron and not an intrinsic property of the electron, the ground state of hydrogen is shown to have an orbital angular momentum of ℏ, and excited states are shown to have angular momenta that are different from the eigenvalues of the usual quantum mechanical operators. The uncertainty relations are found not to be applicable to the orthogonal components of the angular momentum. No double electron spin gyromagnetic ratio is required to account for the observed magnetic moments, and the behavior of the atom in a magnetic field is described entirely in kinetic terms.
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03.65.-w Quantum mechanics

Two examples of organic opto-electronic devices: Light emitting diodes and solar cells

J. L. Maldonado, G. Ramos-Ortíz, M. L. Miranda, S. Vázquez-Córdova, M. A. Meneses-Nava, O. Barbosa-García, and M. Ortíz-Gutiérrez

American Journal of Physics -- December 2008 -- Volume 76, Issue 12, pp. 1130 | Cited 4 times

Online Publication Date: Nov 2008

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Organic and polymeric (plastic) opto-electronic devices have been developed over the past decade, and some of them have made the leap from the research laboratory to commercial use. We present a simple and inexpensive method of fabricating organic light emitting diodes and organic photovoltaic cells. The devices are fabricated by the deposition of solid films based on the fluorescent polymer MEH:PPV using the spin-coating technique. The films were sandwiched between electrodes, one of which was made of Bi-Pb-Cd-Sn alloy. An overview of these two devices is also provided.
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01.50.Pa Laboratory experiments and apparatus
42.00.00 Optics

A simple experiment to distinguish between replicated and duplicated compact discs using Fraunhofer diffraction

José Fernández-Dorado, Javier Hernández-Andrés, Eva M. Valero, Juan L. Nieves, and Javier Romero

American Journal of Physics -- December 2008 -- Volume 76, Issue 12, pp. 1137

Online Publication Date: Nov 2008

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Compact discs are a useful tool for studying interference and diffraction. We propose an easy and inexpensive experiment to distinguish between replicated and duplicated compact discs based on Fraunhofer diffraction. The nonvisible differences of the surface of compact discs depend on the way that they have been manufactured and can be seen by using a laser beam in a simple diffraction experiment. The method has been tested on many different brands of CDs and is reliable.
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01.50.My Demonstration experiments and apparatus
42.00.00 Optics

A new constant of motion for an electric charge acted on by a point electric dipole

Sergio Gutiérrez-López, Arnulfo Castellanos-Moreno, and Rodrigo Arturo Rosas-Burgos

American Journal of Physics -- December 2008 -- Volume 76, Issue 12, pp. 1141

Online Publication Date: Nov 2008

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A new constant of the motion is found for an electric charge acted on by an electric dipole. The relation of the constant of the motion to the energy of the particle is found. Some properties of the motion are studied and known results are reproduced more simply. We discuss conditions for the appearance of bounded and unbounded trajectories, motion on a sphere, and on a plane. Small angular oscillations around a stable circular trajectory are also studied.
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41.00.00 Electromagnetism; electron and ion optics

A velocity-dependent potential of a rigid body in a rotating frame

G. A. Moreno and R. O. Barrachina

American Journal of Physics -- December 2008 -- Volume 76, Issue 12, pp. 1146 | Cited 1 time

Online Publication Date: Nov 2008

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We derive a velocity-dependent potential for describing the dynamics of a rigid body in a rotating frame. We show that, as for one-particle systems, the different components of this potential can be associated with electromagnetic analogs. We provide some examples to demonstrate the feasibility of using the potential as an alternative description of rigid body problems.
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47.00.00 Fluid dynamics

Approximations for the period of the simple pendulum based on the arithmetic-geometric mean

Claudio G. Carvalhaes and Patrick Suppes

American Journal of Physics -- December 2008 -- Volume 76, Issue 12, pp. 1150 | Cited 12 times

Online Publication Date: Nov 2008

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We use the arithmetic-geometric mean to derive approximate solutions for the period of the simple pendulum. The fast convergence of the arithmetic-geometric mean yields accurate solutions. We also discuss the invention of the pendulum clock by Christiaan Huygens in 1656–1657.
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47.00.00 Fluid dynamics
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Modeling theory applied: Modeling Instruction in introductory physics

Eric Brewe

American Journal of Physics -- December 2008 -- Volume 76, Issue 12, pp. 1155 | Cited 11 times

Online Publication Date: Nov 2008

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Modeling Instruction is a pedagogical approach which has been widely and successfully employed in high school physics instruction but is not commonly used at the university level. The goal of this paper is to describe the nature of Modeling Instruction at the university level and to clarify the role of models in physics instruction. A university physics class is described as it progresses through a typical modeling cycle, Introduction and Representation, Coordination of Representations, Abstraction and Generalization, and Application and Refinement. The benefits of modeling instruction are discussed.
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01.40.Fk Research in physics education
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Comment on “Feynman’s wobbling plate,” by Slavomir Tuleja, Boris Gazovic, Alexander Tomori, and Jozef Hanc [Am. J. Phys. 75 (3), 240–244 (2007)]

Harry Soodak

American Journal of Physics -- December 2008 -- Volume 76, Issue 12, pp. 1161

Online Publication Date: Nov 2008

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Abstract Unavailable
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47.00.00 Fluid dynamics
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Two experiments in physics based on electrospun polymer nanofibers

Nicholas J. Pinto

American Journal of Physics -- December 2008 -- Volume 76, Issue 12, pp. 1163

Online Publication Date: Nov 2008

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Two experiments related to nanoscience are described. These experiments are currently part of the undergraduate Physics program at the University of Puerto Rico. A simple to build and operate electrospinning apparatus produces conducting polymer nanofibers that are used to fabricate nanoresistors and Schottky nanodiodes. The properties of these devices are straightforward to study. A modification of the sample chamber can convert the nanoresistor experiment into a supersensitive alcohol vapor sensor.
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01.50.Pa Laboratory experiments and apparatus
60.00.00 CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

Inexpensive high-precision capacitance measurements and their applications in undergraduate laboratories

Jeffrey Clayhold and Joseph Priest

American Journal of Physics -- December 2008 -- Volume 76, Issue 12, pp. 1167 | Cited 1 time

Online Publication Date: Nov 2008

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An inexpensive system for precision capacitance measurement is presented. The system is appropriate for undergraduate laboratories is based on a newly available capacitance-to-digital integrated circuit that can measure picofarad capacitances to six significant figures. The circuitry software for controlling the integrated circuit with a personal computer via an I2C interface bus are described. Examples of experiments that make use of the circuitry are discussed, including a novel hydrostatic magnetometer that uses precision capacitance measurement to determine the magnetization of a small sample.
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01.50.Pa Laboratory experiments and apparatus
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Einstein and Oppenheimer: The Meaning of Genius

Silvan S. Schweber and Lewis Pyenson, Reviewer, Reviewer

American Journal of Physics -- December 2008 -- Volume 76, Issue 12, pp. 1172

Online Publication Date: Nov 2008

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Abstract Unavailable
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01.30.Vv Book reviews
01.60.+q Biographies, tributes, personal notes, and obituaries

Energy, Environment, and Climate

Richard Wolfson and Art Hobson, Reviewer, Reviewer

American Journal of Physics -- December 2008 -- Volume 76, Issue 12, pp. 1174

Online Publication Date: Nov 2008

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Abstract Unavailable
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01.30.Vv Book reviews
89.30.-g Fossil fuels and nuclear power

Nuclear Weapons: What You Need to Know

Jeremy Bernstein and Robert E. Welsh, Reviewer, Reviewer

American Journal of Physics -- December 2008 -- Volume 76, Issue 12, pp. 1175

Online Publication Date: Nov 2008

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Abstract Unavailable
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01.30.Vv Book reviews
01.65.+g History of science

BOOKS RECEIVED

American Journal of Physics -- December 2008 -- Volume 76, Issue 12, pp. 1176

Online Publication Date: Nov 2008

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Abstract Unavailable
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Volume 76 Index

American Journal of Physics -- December 2008 -- Volume 76, Issue 12, pp. I1

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Abstract Unavailable
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