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Jul 2008

Volume 76, Issue 7, pp. 605-695

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“SO WHAT WILL YOU DO IF STRING THEORY IS WRONG?”

Moataz H. Emam

American Journal of Physics -- July 2008 -- Volume 76, Issue 7, pp. 605 | Cited 1 time

Online Publication Date: Jun 2008

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Abstract Unavailable
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01.70.+w Philosophy of science
10.00.00 THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS

SPEAKING OF LESSONS FROM THE HISTORY OF SCIENCE, DOES THE NAME “HERMANN” RING A BELL?

Caroline L. Herzenberg

American Journal of Physics -- July 2008 -- Volume 76, Issue 7, pp. 606 | Cited 1 time

Online Publication Date: Jun 2008

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01.65.+g History of science

NEVER A DULL MOMENT

R. A. Lewis

American Journal of Physics -- July 2008 -- Volume 76, Issue 7, pp. 607

Online Publication Date: Jun 2008

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Abstract Unavailable
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01.55.+b General physics

GENERAL RELATIVITY FOR ALL COLLEGE STUDENTS

Art Hobson

American Journal of Physics -- July 2008 -- Volume 76, Issue 7, pp. 607

Online Publication Date: Jun 2008

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Abstract Unavailable
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04.00.00 General relativity and gravitation
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Resource Letter GW-2: Global Warming

Michael D. Mastrandrea and Stephen H. Schneider

American Journal of Physics -- July 2008 -- Volume 76, Issue 7, pp. 608 | Cited 1 time

Online Publication Date: Jun 2008

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This Resource Letter provides a guide to the literature on human-induced climate change, also known as global warming [Resource Letter GW-1: Global Warming, John W. Firor, Am. J. Phys. 62, 490–495 (1994)]. After an introductory overview, journal articles, books, and websites are cited for the following topics: the greenhouse effect and radiative forcing, detection and attribution of human-induced climate change, carbon cycle feedbacks, paleoclimate, climate models and modeling uncertainties, projections of future climate change and climate impacts, and mitigation and adaptation policy options.
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01.30.Rr Surveys and tutorial papers; resource letters

Conductors in quasistatic electric fields

Anupam Garg

American Journal of Physics -- July 2008 -- Volume 76, Issue 7, pp. 615

Online Publication Date: Jun 2008

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The problem of determining the electric and magnetic fields in and around a conductor in a quasistatic external electric field is considered. It is shown that there are two frequency regimes corresponding to whether the ratio of the skin depth to the linear size of the conductor is large or small compared to unity. General arguments are made about the magnitudes of the fields, especially their normal and transverse components near the surface of the body. The special case of a spherical conductor is solved explicitly in order to verify the general conclusions about the nature of the fields in these two regimes. Comparison is made with behavior in an external magnetic field.
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41.00.00 Electromagnetism; electron and ion optics

Poynting’s theorem for plane waves at an interface: A scattering matrix approach

V. Domínguez-Rocha, C. Zagoya, and M. Martínez-Mares

American Journal of Physics -- July 2008 -- Volume 76, Issue 7, pp. 621 | Cited 1 time

Online Publication Date: Jun 2008

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We write Poynting’s theorem in a form that allows us to introduce a natural definition of the scattering matrix S. For a dielectric-dielectric interface this balance equation leads to energy flux conservation and the unitarity property of S. For the dielectric-conductor interface the scattering matrix is no longer unitary due to the presence of losses in the conductor, and we denote it by math. The dissipative term in Poynting’s theorem can be interpreted as due to a single parasitic channel or excitation of the absorptive interface. We define an S matrix that includes the parasitic channel, so that S is unitary.
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41.00.00 Electromagnetism; electron and ion optics

Precise measurements of Faraday rotation using ac magnetic fields

V. K. Valev, J. Wouters, and T. Verbiest

American Journal of Physics -- July 2008 -- Volume 76, Issue 7, pp. 626 | Cited 11 times

Online Publication Date: Jun 2008

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We discuss several important issues concerning the use of a lock-in amplifier and the experimental procedure that need to be addressed to obtain accurate measurements of the Faraday rotation using ac magnetic fields. Our study was conducted on BK7 glass. We show that if electronic interference is avoided and the dependence of the signal on the average light intensity is taken into account, an accurate value of the Verdet constant for thin samples can be determined.
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42.00.00 Optics

From laser cooling to aging: A unified Lévy flight description

Eric Bertin and François Bardou

American Journal of Physics -- July 2008 -- Volume 76, Issue 7, pp. 630 | Cited 2 times

Online Publication Date: Jun 2008

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What phenomena such as the subrecoil laser cooling of atoms and aging in glasses have in common is that these systems do not reach steady state during experimental observations, although the observation times are very large compared to microscopic time scales. We discuss some standard models that describe these phenomena and reformulate them in a unified framework in terms of the occupation times of the microscopic states of the system. A universal dynamical mechanism emerges, leading to a generic time-dependent distribution of occupation times, independent of the physical system considered.
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02.50.-r Probability theory, stochastic processes, and statistics
05.00.00 Statistical physics, thermodynamics, and nonlinear dynamical systems

An experiment on the dynamics of thermal diffusion

M. C. Sullivan, B. G. Thompson, and A. P. Williamson

American Journal of Physics -- July 2008 -- Volume 76, Issue 7, pp. 637 | Cited 2 times

Online Publication Date: Jun 2008

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We present an experiment that demonstrates thermal diffusion in metals via a dynamic measurement of the temperature in a metal rod as a function of position and time. From this single measurement and using simple heat flow equations, we can extract the thermal conductivity and the specific heat of the metal to within 5% of the accepted values. This experiment can be extended for advanced students, who can model the heat flow by including heat losses and finite heater models via a numerical solution of a partial differential equation.
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01.50.Pa Laboratory experiments and apparatus
44.00.00 Heat transfer

Explaining irreversibility

Robert H. Swendsen

American Journal of Physics -- July 2008 -- Volume 76, Issue 7, pp. 643 | Cited 2 times

Online Publication Date: Jun 2008

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I describe an approach that helps students understand why the behavior of macroscopic systems distinguishes between past and future, even though the underlying classical or quantum microscopic equations are time-reversal invariant. This approach provides a qualitative understanding of irreversibility by an explicit calculation of irreversible behavior for a simple, time-reversal-invariant model system. The mathematics involved is accessible to upper-level undergraduate students.
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05.00.00 Statistical physics, thermodynamics, and nonlinear dynamical systems

Illustrating Lyapunov’s analysis of asymptotic stability for a heavy particle affected by drag resistance

S. Siboni

American Journal of Physics -- July 2008 -- Volume 76, Issue 7, pp. 649

Online Publication Date: Jun 2008

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The application of Lyapunov’s criterion for the asymptotic stability of equilibrium in mechanical systems is difficult in general because the natural candidate for the role of Lyapunov function, the mechanical energy, is suitable for determining simple stability but not asymptotic stability, unless the energy is modified in a way that is nontrivial, difficult to standardize, and whose physical interpretation is obscure. A simple class of mechanical systems is discussed for which the global asymptotic stability can be checked by means of simple physically reasonable Lyapunov functions. A comparison of alternative Lyapunov functions is also done when possible. The class of systems includes the motion of a heavy body moving through the atmosphere close to the Earth’s surface.
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47.00.00 Fluid dynamics

Quantum simulation of the single-particle Schrödinger equation

Giuliano Benenti and Giuliano Strini

American Journal of Physics -- July 2008 -- Volume 76, Issue 7, pp. 657 | Cited 2 times

Online Publication Date: Jun 2008

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The nature of a quantum computer is described in the concrete context of a quantum simulator of the single-particle Schrödinger equation. We show that a register of 6–10 qubits is sufficient to realize a useful quantum simulator capable of efficiently solving standard quantum mechanical problems.
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03.65.-w Quantum mechanics

Relativistic aberration for accelerating observers

Robert Beig and J. Mark Heinzle

American Journal of Physics -- July 2008 -- Volume 76, Issue 7, pp. 663 | Cited 2 times

Online Publication Date: Jun 2008

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We investigate the effects of the aberration of light for a uniformly accelerating observer. The observer is initially at rest with respect to a luminous spherical object and then starts to move away with constant acceleration. Our main results are the following: (i) The observer sees an initial increase of the apparent size of the object, (ii) the apparent size of the object approaches a nonzero value as the proper time of the observer goes to infinity, and (iii) there exists a critical value of the acceleration such that the apparent size of the object is monotonically increasing when the acceleration is supercritical. Although the first effect is purely nonrelativistic, the others are the result of the relativistic aberration of light and are intimately connected with the Lorentzian geometry of Minkowksi spacetime. The examples we present illustrate that the three effects are more or less negligible in everyday life, but significant in the context of space flight.
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03.30.+p Special relativity

Light cones and repulsive gravity

Giovanni Preti and Fernando de Felice

American Journal of Physics -- July 2008 -- Volume 76, Issue 7, pp. 671 | Cited 5 times

Online Publication Date: Jun 2008

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Contrary to common belief, gravitation can also be repulsive. Examples of repulsive gravity are provided by the naked singularity solutions of the Einstein equations corresponding to the negative mass Schwarzschild, the Reissner–Nordström, and the Kerr spacetimes. We show that their repulsive gravity regions can be identified by a particular behavior of the light cones when use is made of symmetry-adapted coordinate systems.
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04.00.00 General relativity and gravitation
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Integrated approaches in physics education: A graduate level course in physics, pedagogy, and education research

Michael C. Wittmann and John R. Thompson

American Journal of Physics -- July 2008 -- Volume 76, Issue 7, pp. 677 | Cited 1 time

Online Publication Date: Jun 2008

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We describe a course designed to help future educators develop an integrated understanding of different elements of physics education research (PER), including research into student learning, content knowledge from the perspective of how it is learned, and reform-based curricula, together with evidence of their effectiveness. Course elements include equal parts of physics study through proven curricula and discussion of research results in the context of the PER literature. We provide examples of the course content and structure and representative examples of student learning in the class.
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01.40.Fk Research in physics education

Preparing physics graduate students to be educators

Edward Price and Noah Finkelstein

American Journal of Physics -- July 2008 -- Volume 76, Issue 7, pp. 684

Online Publication Date: Jun 2008

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We discuss two efforts that support the preparation of graduate students for their roles as professional physicists, particularly in the areas of teaching and education research. The Preparing Future Physicists program and the Teaching and Learning Physics course are mutually supportive, address broader graduate roles, and support the development of physics education research. Students’ participation in these activities increases their mastery of physics, develops their interest in education and teaching, and engages them in research projects in physics education. We describe these efforts and identify critical features of their successes.
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01.40.Fk Research in physics education
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Relativistic transformation of perpendicular velocity components from the constancy of the speed of light

Ben Yu-Kuang Hu

American Journal of Physics -- July 2008 -- Volume 76, Issue 7, pp. 691 | Cited 1 time

Online Publication Date: Jun 2008

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Mermin has derived the relativistic addition of the parallel components of velocity directly from the constancy of the speed of light. In this note the derivation is extended to the perpendicular components of the velocity.
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03.30.+p Special relativity
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Planets on the table: A laboratory experiment on radiation and planetary effective-temperature concepts

Oleksandr Karabanov, James C. St. John, and William Chameides

American Journal of Physics -- July 2008 -- Volume 76, Issue 7, pp. 692

Online Publication Date: Jun 2008

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A new undergraduate laboratory experiment demonstrates radiation laws and their applications to climatology and environmental science. The experiment emphasizes the planetary energy budget and effective-temperature concepts. A close look at “planets on the table” brings some unanticipated results that challenge students to think critically, to interpret the results of measurements, and to come to valid scientific conclusions.
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01.50.My Demonstration experiments and apparatus
05.00.00 Statistical physics, thermodynamics, and nonlinear dynamical systems
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