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Resource Letter MP-4: The Manhattan Project and related nuclear research
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| Pengarang | : | B. Cameron Reed |
| Nama Majalah/Jurnal | : | American Journal of Physics |
| Volume / Edisi | : | 91 (No. 7) |
| Halaman | : | 495-509 |
| Abstrak | : | This fourth Resource Letter on the Manhattan Project comprises over 140 new sources to complement the 390 listed in the first three on this topic. Books, review papers, and journal articles are cited for the categories of general works; specific topics within the Manhattan Project; technical and historical works; biographies and autobiographies; international wartime programs, allied intelligence, and the use of the bombs; postwar developments; and educational materials. A separate section lists videos and websites. |
Conditional probability as found in nature: Facilitated diffusion
| Pengarang | : | Ori Hachmo |
| Nama Majalah/Jurnal | : | American Journal of Physics |
| Volume / Edisi | : | 91 (No. 8) |
| Halaman | : | 653-658 |
| Abstrak | : | Search processes are ubiquitous in physical and biological phenomena, often involving the random motion of molecules. In particular, transcription factors (TFs) are proteins that regulate gene expression and need to find their DNA targets quickly—which is difficult to achieve with random motion alone. Nature came up with a remarkable solution known as facilitated diffusion, combining 1D diffusion along the DNA and “excursions” of diffusion in 3D that help the TF to quickly arrive at distant parts of the DNA. In this paper, we show that this process can be analyzed naturally using the concept of conditional probability, providing an alternative intuition to the effectiveness of this mechanism. |
Cosmological horizons
| Pengarang | : | Michele Re Fiorentin |
| Nama Majalah/Jurnal | : | American Journal of Physics |
| Volume / Edisi | : | 91 (No. 8) |
| Halaman | : | 644-652 |
| Abstrak | : | The recently unveiled deep-field images from the James Webb Space Telescope have renewed interest in what we can and cannot see of the universe. Answering these questions requires understanding the so-called “cosmological horizons” and the “Hubble sphere.” Here, we review the topic of cosmological horizons in a form that university physics teachers can use in their lessons, using the latest data about the so-called standard “Lambda cold dark matter” (ΛCDM) model. Graphical representations are plotted in terms of both conformal and proper coordinates as an aid to understand the propagation of light in the expanding universe at various epochs. |
The nuclear optical model and its optical-scattering analog: Mie scattering
| Pengarang | : | Don C. Colladay |
| Nama Majalah/Jurnal | : | American Journal of Physics |
| Volume / Edisi | : | 91 (No. 8) |
| Halaman | : | 637-643 |
| Abstrak | : | The methods devised by Gustav Mie in 1908 to explain the scattering of electromagnetic waves have a close analogy with quantum-mechanical models developed many years later to describe nuclear scattering. In particular, these models use either a complex index of refraction or a complex nuclear scattering potential to account for attenuation caused by non-elastic scattering. We briefly outline the historical development of these models and give examples illustrating the close analogy between them, their parameters, and the resulting scattering. In both models, the ratio of the incident wavelength to the object size, λ/D, can be determined from the scattering characteristics, allowing the extraction of microscopic particle dimensions. This close analogy allows students to simulate accelerator-based nuclear scattering experiments with table-top optical-scattering experiments. |
Introducing corrugated surfaces in electrostatic problems via a perturbative approach
| Pengarang | : | Alexandre P. Costa |
| Nama Majalah/Jurnal | : | American Journal of Physics |
| Volume / Edisi | : | 91 (No. 8) |
| Halaman | : | 629-636 |
| Abstrak | : | In electromagnetism courses, students often solve Poisson's equation for a point charge in the presence of an infinitely large perfectly conducting planar surface, usually by the method of images. However, no surface is perfectly flat; so at some level, corrugations must be introduced to model the real world. Clinton et al. [Phys. Rev. B 31, 7540 (1985)] solved the problem, including corrugations, using a perturbative calculation of the corresponding Green's function. We provide a detailed pedagogical review of this calculation and extend it in order to solve for the electrostatic potential of a corrugated neutral conducting cylinder in the presence of a uniform electric field. These calculations can be used as pedagogical examples of this perturbative approach in electromagnetism course |
Self-inductance and magnetic flux
| Pengarang | : | Dwi Asmianto |
| Nama Majalah/Jurnal | : | American Journal of Physics |
| Volume / Edisi | : | 91 (No. 8) |
| Halaman | : | 622-628 |
| Abstrak | : | The canonical equation for self-inductance involving magnetic flux is examined, and a more general form is presented that can be applied to continuous current distributions. We attempt to clarify and extend the use of the standard equation by recasting it in its more versatile form. |
Modeling the induced voltage of a disk magnet in free fall
| Pengarang | : | - |
| Nama Majalah/Jurnal | : | American Journal of Physics |
| Volume / Edisi | : | 91 (No. 8) |
| Halaman | : | 617-621 |
| Abstrak | : | We drop a circular disk magnet through a thin coil of wire, record the induced voltage, and compare the results to an analytic model based on the dipole approximation and Faraday's law, which predicts that the difference between the voltage peak magnitudes corresponding to the entry and exit of the magnet should be in proportion to ?, where z0 is the initial height of the magnet above the center of the coil. Agreement between the model and experimental data is excellent. This easily reproduced experiment provides an opportunity for students at a range of levels to quantitatively explore the effects of magnetic induction. |
Helping students apply superposition principle in problems involving spherical, cylindrical, and planar charge distributions
| Pengarang | : | Jing Li |
| Nama Majalah/Jurnal | : | American Journal of Physics |
| Volume / Edisi | : | 91 (No. 8) |
| Halaman | : | 613-616 |
| Abstrak | : | We describe student difficulties in applying the superposition principle in combination with Gauss's law. We addressed these difficulties by developing a tutorial that uses guided inquiry. Students who used this tutorial following lecture-based instruction performed significantly better on these topics than those who did not. Instructors can assign the tutorial as classwork or homework. |
Infinite-fold energy degeneracy in 2D square lattices of magnetic spheres
| Pengarang | : | Kyongwan Kim |
| Nama Majalah/Jurnal | : | American Journal of Physics |
| Volume / Edisi | : | 91 (No. 8) |
| Halaman | : | 603-612 |
| Abstrak | : | We show that a two-dimensional square lattice of magnets can be studied by placing small cylindrical neodymium magnets inside plastic spherical shells and floating them on water, leaving their magnetic moments free to re-orient within the plane. Experimentally, anti-correlated dipole orientations between nearest neighbors appear to be favored energetically. This motivates the construction of a simplified single-variable energy function for a 2D square lattice of magnetic dipoles. For odd numbers of spheres, this ansatz yields a continuum of dipole configurations with the same energies, matching the observed behavior that the orientation of the dipoles in these lattices can be rotated freely. The behavior of square lattices with even numbers of spheres is strikingly different, showing strongly preferred orientations. While the energy calculated in this simplified model is larger than that of the actual ground state for finite size clusters, its asymptotic value in the limit where the number of spheres goes to infinity is in good agreement with the literature value. Additionally, rectangular arrangements of magnetic spheres with and without a defect are analyzed within the class of the single variable energy function. Simple experimental demonstrations qualitatively reproduce several interesting results obtained from all these analyses. |
Rendezvous revisited: The search for fast-intercept solutions
| Pengarang | : | T. A. Engstrom |
| Nama Majalah/Jurnal | : | American Journal of Physics |
| Volume / Edisi | : | 91 (No. 8) |
| Halaman | : | 595-602 |
| Abstrak | : | Orbital interception scenarios typically involve a chaser that is actively maneuvered to encounter an inertial target and may be undertaken for a variety of purposes, including docking spacecraft or colliding with an asteroid for planetary defense studies. Viable intercept trajectories are constrained by the free-fall path of the target and by auxiliary conditions such as the available time or fuel budget. Whereas a constraint on the time to intercept is central to the (extensively studied) Lambert problem, a less common but more visually compelling constraint is that of the available fuel for intercept. This was the basis of a recent study [E. M. Edlund, Am. J. Phys. 89, 559–566 (2021)], which analyzed one of the two families of possible intercept solutions that were identified. The second family, studied in more detail here, describes intercepts at all points in the orbit and has the interesting property that it admits fast-intercept solutions. This work concludes the analysis of this problem; it develops a general condition that describes both families of intercepts, presents representative solutions, and considers the sensitivity of these solutions to errors in the control parameters. |