April 27th, 2021

лошадь, диаграмма, Фейнман


Хорошее введение, все аккуратно собрано в кучку.

Predicting outcomes of electric dipole and magnetic moment experiments: https://arxiv.org/abs/2104.12230
V. G. Baryshevsky, P. I. Porshnev
The anomalous magnetic and electric dipole moments in spin motion equation acquire pseudoscalar corrections if the T(CP)-noninvariance is admitted. It allows to explain the discrepancy between experimental and theoretical values of muon (g−2) factor under assumption that the pseudoscalar correction is the dominant source of this discrepancy.
лошадь, диаграмма, Фейнман

Капельная модель и нейтронные звезды в аудитории

Кажется, первая часть у меня уже где-то была, но пусть тут будут обе. Интересно, моделировать в Excel - это новая мода такая?

From nuclei to neutron stars: simple binding energy computer modelling in the classroom (Part 1): https://arxiv.org/abs/2007.06872

A. Pastore, A. M. Romero, C. Diget, A. Rios, K. Leech, P. Stokoe
We present a simple activity based on the liquid-drop model which allows secondary school students to explore the uses of mathematical models and gain an intuitive understanding of the concept of binding energy, and in particular the significance of positive binding energy. Using spreadsheets provided as Supplementary Material, students can perform simple manipulations on the different coefficients of the model to understand the role of each of its five terms. Students can use the spreadsheets to determine model parameters by optimising the agreement with real atomic mass data. %This will subsequently be used to predict the limit of existence of the Segré chart and to find the minimum mass of a neutron star. This activity can be used as the starting point of a discussion about theoretical models, their validation when it comes to describing experimental data and their predictive power towards unexplored regimes.
Comments: Published Physics Education 56 (3), 035012

From nuclei to neutron stars: simple binding energy computer modelling in the classroom (part 2): https://arxiv.org/abs/2104.12449
A. Rios, A. Pastore, C. Diget, A. M. Romero, K. Leech, P. Stokoe
We introduce two simple online activities to explore the physics of neutron stars. These provide an introduction to the basic properties of compact objects, like their masses and radii, for secondary school students. The first activity explores the idea of the minimum mass of a neutron star. It is directly linked to the concept of binding energy and follows on from our previous activities. The second activity focuses on the maximum mass of neutron stars using a solvable model of the neutron star interior. The activities are based on spreadsheets, provided as Supplementary Material, and can be easily adapted to different levels, age groups and discussion topics. In particular, these activities can naturally lead towards discussions on extrapolations and limits of theoretical models.
Comments: This submission is a follow-up of Part 1 in arXiv:2007.06872, published as A Pastore et al 2021 Phys. Educ. 56 035012 in this https URL. Worksheet attached in Excel file
лошадь, диаграмма, Фейнман

Кажется, что-то забавное по численным методам

A class of new stable, explicit methods to solve the non-stationary heat equation: https://arxiv.org/abs/2104.12530
Endre Kovács
We present a class of new explicit and stable numerical algorithms to solve the spatially discretized linear heat or diffusion equation. After discretizing the space and the time variables like conventional finite difference methods, we do not approximate the time derivatives by finite differences, but use constant neighbor and linear neighbour approximations to decouple the ordinary differential equations and solve them analytically. During this process, the timestep-size appears not in polynomial, but in exponential form with negative exponents, which guarantees stability. We compare the performance of the new methods with analytical and numerical solutions. According to our results, the methods are first and second order in time and can be much faster than the commonly used explicit or implicit methods, especially in the case of extremely large stiff systems.
Comments: 21 pages
Subjects: Numerical Analysis (math.NA); Mathematical Physics (math-ph); Computational Physics (physics.comp-ph)
Journal reference: Numerical Methods for Partial Differential Equation, Volume 37, Issue 3, May 2021, Pages 2469-2489
лошадь, диаграмма, Фейнман

Сжатые состояния на учебном уровне

Making squeezed-coherent states concrete by determining their wavefunction: https://arxiv.org/abs/2104.11350
Eduardo Munguia-Gonzalez, Sheldon Rego, J. K. Freericks
With the successes of the Laser Interferometer Gravitational-wave Observatory, we anticipate increased interest in working with squeezed states in the undergraduate and graduate quantum-mechanics classroom. Because squeezed-coherent states are minimum uncertainty states, their wavefunctions in position and momentum space must be Gaussians. But this result is rarely discussed in treatments of squeezed states in quantum textbooks or quantum optics textbooks. In this work, we show three different ways to construct the wavefunction for squeezed-coherent states: (i) a differential equation-based approach; (ii) an approach that uses an expansion in terms of the simple-harmonic oscillator wavefunctions; and (iii) a fully operator-based approach. We do this to illustrate that the concept of the wavefunction can be introduced no matter what methodology an instructor wishes to use. We hope that working with the wavefunction will help demystify the concept of a squeezed-coherent state.
Comments: (27 pages, 1 figure, accepted for publication in Am. J. Phys.)
лошадь, диаграмма, Фейнман

Бесконечность - это насколько далеко?

How far away is infinity? An electromagnetic exercise to develop intuition regarding models: https://arxiv.org/abs/2104.12728
Alvaro Suarez, Martin Monteiro, Mateo Dutra, Arturo C. Marti
The estimation of the electric field in simple situations provides an opportunity to develop intuition about the models used in physics. We propose an activity aimed at university students of General Physics where the electric field of a finite line of charge is compared, analytically or numerically, with the fields of an infinite line and of a point charge. Contrary to intuition, it is not necessary to get very close for the line charge to be considered infinite, nor to move very far away for the finite line field to resemble that of a point charge. We conducted this activity with a group of students and found that many of them have not yet developed an adequate intuition about the approximations used in electromagnetism.
Comments: 5 pages, 2 figures