November 2017 Issue, Volume 85, No. 11
Confining rigid balls by mimicking quadrupole ion trapping
The rotating saddle not only is an interesting system that is able to trap a ball near its saddle point, but can also intuitively illustrate the operating principles of quadrupole ion traps in modern physics. Unlike the conventional models based on the mass-point approximation, we study the stability of a ball in a rotating-saddle trap using rigid-body dynamics. The stabilization condition of the system is theoretically derived and subsequently verified by experiments. The results are compared with the previous mass-point model, giving large discrepancy as the curvature of the ball is comparable to that of the saddle. We also point out that the spin angular velocity of the ball is analogous to the cyclotron frequency of ions in an external magnetic field utilized in many prevailing ion-trapping schemes.
Guest Editorial
Guest Editorial: Truth, beauty, and supergravity by Stanley Deser. DOI: 10.1119/1.4994807
Papers
Entanglement isn't just for spin by Daniel V. Schroeder. DOI: 10.1119/1.5003808
Confining rigid balls by mimicking quadrupole ion trapping by Wenkai Fan, Li Du, Sihui Wang, and Huijun Zhou. DOI: 10.1119/1.5005927
Dielectric media considered as vacuum with sources by Hans Olaf Hågenvik, Kjell Bløtekjær, and Johannes Skaar. DOI: 10.1119/1.5003810
Variational approach to the soft-Coulomb potential in low-dimensional quantum systems by Federico Grasselli. DOI: 10.1119/1.4994809
Cosmic ray topography by Matthew Bressler, Lydia Goodwin, and Abaz Kryemadhi. DOI: 10.1119/1.4996874
An acoustic demonstration of an avoided crossing by William Newman, Alexandria Skinner, and Shawn A. Hilbert. DOI: 10.1119/1.4996871
PHYSICS EDUCATION RESEARCH
Personalized instructor responses to guided student reflections: Analysis of two instructors' perspectives and practices by Daniel L. Reinholz, and Dimitri R. Dounas-Frazer. DOI: 10.1119/1.5002683
NOTES AND DISCUSSIONS
Comment on “Not all counterclockwise thermodynamic cycles are refrigerators” [Am. J. Phys. 84, 413–418 (2016)] by João P. S. Bizarro. DOI: 10.1119/1.5005928
Reply to “Comment on ‘Not all counterclockwise thermodynamic cycles are refrigerators’” [Am. J. Phys. 85, 861–863 (2017)] by R. H. Dickerson, and J. Mottmann. DOI: 10.1119/1.5005929
Three new roads to the Planck scale by Valerio Faraoni. DOI: 10.1119/1.4994804
Comment on “Magnetic field calculation for arbitrarily shaped planar wires” [Am. J. Phys. 68(3), 254–258 (2000)] by S. Gratkowski. DOI: 10.1119/1.5005528
A demonstration of decoherence for beginners by L. Lerner. DOI: 10.1119/1.5005526
APPARATUS AND DEMONSTRATION NOTES
A compact grism spectrometer for small optical telescopes by Dominic A. Ludovici, and Robert L. Mutel. DOI: 10.1119/1.5000801
BOOK REVIEWS
John Stewart Bell and Twentieth-Century Physics: Vision and Integrity by Michael Nauenberg. DOI: 10.1119/1.4983117
Rays, Waves, and Scattering: Topics in Classical Mathematical Physics by James A. Lock. DOI: 10.1119/1.5005527
Drawing Physics: 2,600 Years of Discovery from Thales to Higgs by Dwight E. Neuenschwander. DOI: 10.1119/1.5002679
BOOKS RECEIVED
American Journal of Physics 85, 883 (2017); http://doi.org/10.1119/1.5005825
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