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Jan 2013

Volume 81, Issue 1, pp. 5-79

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A HIGGS MEMO

Jeremy Bernstein

American Journal of Physics -- January 2013 -- Volume 81, Issue 1, pp. 5

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10.00.00 THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
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Resource Letter PoD-1: The Physics of Dance

Kenneth Laws and Melanie Lott

American Journal of Physics -- January 2013 -- Volume 81, Issue 1, pp. 7

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This Resource Letter provides a guide to the literature on the physics of dance. Journal articles and books are cited for the following topics: General references for dance, physics of dance, research methods in physics of human movement and in biomechanics, using dance in the physics classroom; anatomy and injuries; physics applied to specific dance movements or styles of dance; equipment (dance shoes, flooring, the barre); and dance of physics.
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01.30.Rr Surveys and tutorial papers; resource letters
01.90.+g Other topics of general interest (restricted to new topics in section 01)

Conductance quantization: A laboratory experiment in a senior-level nanoscale science and technology course

R. Tolley, A. Silvidi, C. Little, and K. F. Eid

American Journal of Physics -- January 2013 -- Volume 81, Issue 1, pp. 14

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We describe a simple, inexpensive, and robust undergraduate lab experiment that demonstrates the emergence of quantized conductance as a macroscopic gold wire is broken and unbroken. The experiment utilizes a mechanically controlled break junction and demonstrates how conductance quantization can be used to understand the importance of quantum mechanics at the nanoscale. Such an experiment can be integrated into the curriculum of a course on nanoscale science or contemporary physics at the junior and senior levels.
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01.50.Pa Laboratory experiments and apparatus
03.65.-w Quantum mechanics

Exploring the thermodynamics of a rubber band

David Roundy and Michael Rogers

American Journal of Physics -- January 2013 -- Volume 81, Issue 1, pp. 20

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We describe an upper-division experiment in thermal physics where students measure the tension of a rubber band as a function of temperature and length and use a Maxwell relation to find the change in internal energy and entropy for an isothermal stretch. This allows students to experimentally check the predictions of the entropic spring model for elastomers and observe that the entropy does indeed decrease as a rubber band is stretched.
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01.50.Pa Laboratory experiments and apparatus
05.70.-a Thermodynamics

Reflection of a polarized light cone

Jed Brody, Daniel Weiss, and Keith Berland

American Journal of Physics -- January 2013 -- Volume 81, Issue 1, pp. 24

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We introduce a visually appealing experimental demonstration of Fresnel reflection. In this simple optical experiment, a polarized light beam travels through a high numerical-aperture microscope objective, reflects off a glass slide, and travels back through the same objective lens. The return beam is sampled with a polarizing beam splitter and produces a surprising geometric pattern on an observation screen. Understanding the origin of this pattern requires careful attention to geometry and an understanding of the Fresnel coefficients for S and P polarized light. We demonstrate that in addition to a relatively simple experimental implementation, the shape of the observed pattern can be computed both analytically and by using optical modeling software. The experience of working through complex mathematical computations and demonstrating their agreement with a surprising experimental observation makes this a highly educational experiment for undergraduate optics or advanced-lab courses. It also provides a straightforward yet non-trivial system for teaching students how to use optical modeling software.
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01.50.Pa Laboratory experiments and apparatus
42.00.00 Optics

Energy and momentum entanglement in parametric downconversion

Pablo L. Saldanha and C. H. Monken

American Journal of Physics -- January 2013 -- Volume 81, Issue 1, pp. 28

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We present a simple treatment of the phenomenon of spontaneous parametric downconversion consisting of the coherent scattering of a single pump photon into an entangled photon pair inside a nonlinear crystal. The energy and momentum entanglement of the quantum state of the generated twin photons are seen as a consequence of the fundamental indistinguishability of the time and the position in which the photon pair is created inside the crystal. We also discuss some consequences of photon entanglement.
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03.65.-w Quantum mechanics
42.00.00 Optics

Radiometry and the Friis transmission equation

Joseph A. Shaw

American Journal of Physics -- January 2013 -- Volume 81, Issue 1, pp. 33

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To more effectively tailor courses involving antennas, wireless communications, optics, and applied electromagnetics to a mixed audience of engineering and physics students, the Friis transmission equation—which quantifies the power received in a free-space communication link—is developed from principles of optical radiometry and scalar diffraction. This approach places more emphasis on the physics and conceptual understanding of the Friis equation than is provided by the traditional derivation based on antenna impedance. Specifically, it shows that the wavelength-squared dependence can be attributed to diffraction at the antenna aperture and illustrates the important difference between the throughput (product of area and solid angle) of a single antenna or telescope and the throughput of a transmitter-receiver pair.
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84.00.00 Electronics; radiowave and microwave technology; direct energy conversion and storage

A low voltage “railgun”

Stanley O. Starr, Robert C. Youngquist, and Robert B. Cox

American Journal of Physics -- January 2013 -- Volume 81, Issue 1, pp. 38

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Due to recent advances in solid-state switches and ultra-capacitors, it is now possible to construct a “railgun” that can operate at voltages below 20 V. Railguns typically operate above a thousand volts, generating huge currents for a few milliseconds to provide thousands of g's of acceleration to a small projectile. The low voltage railgun described herein operates for much longer time periods (tenths of seconds to seconds), has far smaller acceleration and speed, but can potentially propel a much larger object. The impetus for this development is to lay the groundwork for a possible ground-based supersonic launch track, but the resulting system may also have applications as a simple linear motor. The system would also be a useful teaching tool, requiring concepts from electrodynamics, mechanics, and electronics for its understanding, and is relatively straightforward to construct.
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41.00.00 Electromagnetism; electron and ion optics

Computational templates for introductory nuclear science using mathcad

D. G. Sarantites and L. G. Sobotka

American Journal of Physics -- January 2013 -- Volume 81, Issue 1, pp. 44

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Computational templates used to teach an introductory course in nuclear chemistry and physics at Washington University in St. Louis are presented in brief. The templates cover both basic and applied topics.
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20.00.00 NUCLEAR PHYSICS

Solution of the quantum initial value problem with transparent boundary conditions

A. Puga and B. N. Miller

American Journal of Physics -- January 2013 -- Volume 81, Issue 1, pp. 50

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Many systems of interest at the forefront of technological development, for example, in quantum computation, consist of weakly interacting elements that obey quantum mechanics. A challenge for modern theoretical physics is to develop a systematic methodology for approaching these “open” quantum systems. In particular, applied mathematicians have formulated the method of transparent boundary conditions (TBCs) to model interacting quantum systems of infinite extent. Here, we consider a particular application of TBCs to the escape of a particle from a one-dimensional infinite well when one of the bounding barriers is extinguished. We analytically obtain the exact time-dependent wave function by a Green's function method and then show that a numerical solution based on the TBC method is in excellent agreement. This work was motivated by an experiment carried out at the University of Texas on escape from a gravitational wedge billiard. Physicists have used billiards to understand and explore both classical and quantum chaos. Although the original experiment was carried out in the classical regime, current work is probing lower temperatures, where a quantum mechanical formulation is required.
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02.70.-c Computational techniques; simulations
03.65.-w Quantum mechanics

Variations on the adiabatic invariance: The Lorentz pendulum

Luis L. Sánchez-Soto and Jesús Zoido

American Journal of Physics -- January 2013 -- Volume 81, Issue 1, pp. 57

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We analyze a simple variant of the Lorentz pendulum in which the length is varied exponentially instead of uniformly as in the standard case. We establish quantitative criteria for the condition of adiabatic changes in both pendula and demonstrate their substantially different physical behavior with regard to adiabatic invariance.
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45.00.00 Classical mechanics of discrete systems

The process of transforming an advanced lab course: Goals, curriculum, and assessments

Benjamin M. Zwickl, Noah Finkelstein, and H. J. Lewandowski

American Journal of Physics -- January 2013 -- Volume 81, Issue 1, pp. 63

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A thoughtful approach to designing and improving labs, particularly at the advanced level, is critical for the effective preparation of physics majors for professional work in industry or graduate school. With that in mind, physics education researchers in partnership with the physics faculty at the University of Colorado Boulder have overhauled the senior-level Advanced Physics Lab course. The transformation followed a three part process of establishing learning goals, designing curricula that align with the goals, and assessment. Similar efforts have been carried out in physics lecture courses at the University of Colorado Boulder, but this is the first systematic research-based revision of one of our laboratory courses. The outcomes of this effort include a set of learning goals, a suite of new lab-skill activities and transformed optics labs, and a set of assessments specifically tailored for a laboratory environment. While the particular selection of advanced lab experiments varies widely between institutions, the overall transformation process, the learning goals, and the assessments are broadly applicable to the instructional lab community.
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01.40.Fk Research in physics education
01.50.Qb Laboratory course design, organization, and evaluation
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Using the Xbox Kinect sensor for positional data acquisition

Jorge Ballester and Chuck Pheatt

American Journal of Physics -- January 2013 -- Volume 81, Issue 1, pp. 71

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The Kinect sensor was introduced in November 2010 by Microsoft for the Xbox 360 video game system. It is designed to be positioned above or below a video display to track player body and hand movements in three dimensions (3D). The sensor contains a red, green, and blue (RGB) camera, a depth sensor, an infrared (IR) light source, a three-axis accelerometer, and a multi-array microphone, as well as hardware required to transmit sensor information to an external receiver. In this article, we evaluate the capabilities of the Kinect sensor as a 3D data-acquisition platform for use in physics experiments. Data obtained for a simple pendulum, a spherical pendulum, projectile motion, and a bouncing basketball are presented. Overall, the Kinect sensor is found to be a useful data-acquisition tool for motion studies in the physics laboratory.
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07.00.00 Instruments, apparatus, and components common to several branches of physics and astronomy
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Chasing Venus: The Race to Measure the Heavens.

Andrea Wulf. and Steve Ruskin, Reviewer, Reviewer

American Journal of Physics -- January 2013 -- Volume 81, Issue 1, pp. 78

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

BOOKS RECEIVED

American Journal of Physics -- January 2013 -- Volume 81, Issue 1, pp. 79

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