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Improved microparticle electrodynamic ion traps for physics teaching
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| Pengarang | : | Kenneth G. Libbrecht |
| Nama Majalah/Jurnal | : | American Journal of Physics |
| Volume / Edisi | : | 86 (No. 7) |
| Halaman | : | 539-558 |
| Abstrak | : | e review the essential physics of microparticle electrodynamic ion traps (MEITs) and suggest several improvements in the design, construction, and application of MEITs in undergraduate physics teaching. Pulling together insights gleaned from a number of disparate sources, we have developed MEITs with better overall performance and reliability in comparison to previous publications. This work builds upon a long history of MEIT advancement over many decades, further lowering the barriers to using these fascinating devices in physics teaching labs and demonstrations. |
Making Fermi estimates by tapping the vast knowledge in our gut
| Pengarang | : | Sanjoy Mahajan |
| Nama Majalah/Jurnal | : | American Journal of Physics |
| Volume / Edisi | : | 86 (No. 7) |
| Halaman | : | 536–538 |
| Abstrak | : | Making Fermi or back-of-the-envelope estimates—for example, the energy E in a typical 9-volt battery—is an ability of which we physicists are proud.1 Yet when even well prepared students try such estimates, they often complain that they have no clue where to start. They are right: My colleague Ben Linder found distressing results when he asked the battery-energy estimate of MIT mechanical-engineering majors.2 I will describe one answer to students' complaint: making a zeroth estimate by talking to our gut (a normal Fermi estimate made before an honest calculation would then be a first estimate). The gut dialogue provides a starting place, improves our intuition for scales in the physical world, and helps us follow, with apologies to Wheeler,3 the first moral principle of estimation: “Never estimate until you can feel the answer.” Talking to our gut, in the sense of “gut feeling,” taps our brain's intuitive knowledge... |
A comparison of student evaluations of instruction vs. students' conceptual learning gains
| Pengarang | : | LaDoris J. Lee |
| Nama Majalah/Jurnal | : | American Journal of Physics |
| Volume / Edisi | : | 86 (No. 7) |
| Halaman | : | 531-535 |
| Abstrak | : | For decades, Student Evaluations of Instruction (or Teaching) have been used to evaluate the quality of teaching at universities and colleges nationwide. Often, student evaluations are the sole measurement of teaching quality in higher education, and as a result have been the subject of extensive study. While many of these investigations make claims about the correlations between student evaluations of instruction and student learning, the validity and reliability of both the methodologies and measurement tools in these studies is not clear. The study reported here uses research-based conceptual inventories, such as the Force Concept Inventory (FCI), to make the more rigorous claim that Student Evaluations of Instruction do not correlate with conceptual learning gains on the FCI. In addition, grading leniency by an instructor (i.e., giving easy A grades) does not correlate with increased student evaluations of instruction. |
Black Box Variational Bayesian Model Averaging
| Pengarang | : | Ag. Prih Adiartanto |
| Nama Majalah/Jurnal | : | The American Statistician |
| Volume / Edisi | : | 77 (No. 1) |
| Halaman | : | 85-96 |
| Abstrak | : | For many decades now, Bayesian Model Averaging (BMA) has been a popular framework to systematically account for model uncertainty that arises in situations when multiple competing models are available to describe the same or similar physical process. The implementation of this framework, however, comes with a multitude of practical challenges including posterior approximation via Markov chain Monte Carlo and numerical integration. We present a Variational Bayesian Inference approach to BMA as a viable alternative to the standard solutions which avoids many of the aforementioned pitfalls. The proposed method is “black box” in the sense that it can be readily applied to many models with little to no model-specific derivation. We illustrate the utility of our variational approach on a suite of examples and discuss all the necessary implementation details. Fully documented Python code with all the examples is provided as well. |
Assignment-Control Plots: A Visual Companion for Causal Inference Study Design
| Pengarang | : | Rachael C. Aikens |
| Nama Majalah/Jurnal | : | The American Statistician |
| Volume / Edisi | : | 77 (No. 1) |
| Halaman | : | 72-84 |
| Abstrak | : | An important step for any causal inference study design is understanding the distribution of the subjects in terms of measured baseline covariates. However, not all baseline variation is equally important. We propose a set of visualizations that reduce the space of measured covariates into two components of baseline variation important to the design of an observational causal inference study: a propensity score summarizing baseline variation associated with treatment assignment and a prognostic score summarizing baseline variation associated with the untreated potential outcome. These assignment-control plots and variations thereof visualize study design tradeoffs and illustrate core methodological concepts in causal inference. As a practical demonstration, we apply assignment-control plots to a hypothetical study of cardiothoracic surgery. To demonstrate how these plots can be used to illustrate nuanced concepts, we use them to visualize unmeasured confounding and to consider the relationship between propensity scores and instrumental variables. While the family of visualization tools for studies of causality is relatively sparse, simple visual tools can be an asset to education, application, and methods development. |
A summary of research-based assessment of students' beliefs about the nature of experimental physics
| Pengarang | : | - |
| Nama Majalah/Jurnal | : | American Journal of Physics |
| Volume / Edisi | : | 86 (No. 3) |
| Halaman | : | 212-219 |
| Abstrak | : | Within the undergraduate physics curriculum, students' primary exposure to experimental physics comes from laboratory courses. Thus, as experimentation is a core component of physics as a discipline, lab courses can be gateways in terms of both recruiting and retaining students within the physics major. Physics lab courses have a wide variety of explicit and/or implicit goals for lab courses, including helping students to develop expert-like beliefs about the nature and importance of experimental physics. To assess students' beliefs, attitudes, and expectations about the nature of experimental physics, there is currently one research-based assessment instrument available—the Colorado Learning Attitudes about Science Survey for Experimental Physics (E-CLASS). Since its development, the E-CLASS has been the subject of multiple research studies aimed at understanding and evaluating the effectiveness of various laboratory learning environments. This paper presents a description of the E-CLASS assessment and a summary of the research that has been done using E-CLASS data with a particular emphasis on the aspects of this work that are most relevant for instructors. |
A Statistical Basis for Reporting Strength of Evidence as Pool Reduction
| Pengarang | : | - |
| Nama Majalah/Jurnal | : | The American Statistician |
| Volume / Edisi | : | 77 (No. 1) |
| Halaman | : | 62-71 |
| Abstrak | : | This article establishes a statistical basis for an evidence-reporting strategy that interprets strength of evidence in terms of a reduction in the size of a pool of relevant conceptual objects. The strategy is motivated by debates in forensic science, wherein the pool would consist of sources of forensic material. An advantage of using the pool-reduction strategy is that it highlights uncertainty that cannot be resolved by empirical considerations. It is shown mathematically to reflect a nonstandard formulation of a Bayes factor, and to extend for use in problems of general quantitative inference. A number of conventions are proposed for full effectiveness of the strategy’s implementation in practice. |
Heat transfer and evaporative cooling in the function of pot-in-pot coolers
| Pengarang | : | Arsène Chemin |
| Nama Majalah/Jurnal | : | American Journal of Physics |
| Volume / Edisi | : | 86 (No. 3) |
| Halaman | : | 206-211 |
| Abstrak | : | A pot-in-pot cooler is an affordable electricity-free refrigerator which uses the latent heat of vaporization of water to maintain a low temperature inside an inner compartment. In this article, we experimentally investigate the influence of the main physical parameters in model pot-in-pot coolers. The effect of the wind on the evaporation rate of the cooling fluid is studied in model experiments while the influence of the fluid properties (thermal conductivity, specific heat, and latent heat) is elucidated using a variety of cooling fluids (water, ethanol, and ether). A model based on a simplified heat conduction equation is proposed and is shown to be in good quantitative agreement with the experimental measurements. |
Twelve years before the quantum no-cloning theorem
| Pengarang | : | - |
| Nama Majalah/Jurnal | : | American Journal of Physics |
| Volume / Edisi | : | 86 (No. 3) |
| Halaman | : | 201-205 |
| Abstrak | : | The celebrated quantum no-cloning theorem establishes the impossibility of making a perfect copy of an unknown quantum state. The discovery of this important theorem for the field of quantum information is currently dated 1982. I show here that an article published in 1970 [J. L. Park, Found. Phys. 1, 23–33 (1970)] contained an explicit mathematical proof of the impossibility of cloning quantum states. I analyze Park's demonstration in the light of published explanations concerning the genesis of the better-known papers on no-cloning. |
Every isochronous potential is shear-equivalent to a harmonic potential
| Pengarang | : | Daniel J. Cross |
| Nama Majalah/Jurnal | : | American Journal of Physics |
| Volume / Edisi | : | 86 (No. 3) |
| Halaman | : | 198-200 |
| Abstrak | : | Harmonic oscillations are isochronous, but so are oscillations in any potential that is shear-equivalent to a harmonic potential. We demonstrate the converse: that every possible isochronous potential is shear-equivalent to a harmonic potential. To do this we show that every potential is shear-equivalent to a unique symmetric potential, and that every isochronous symmetric potential is harmonic. Shearing is thus the only possible period-preserving transformation for potentials with fixed energy. |