arXiv subjects

Andrew J. A. James

Publications and source records attributed to Andrew J. A. James.

6 recordsLinked to original sources

arXiv2026

Student responses to a modified Force Concept Inventory: The Newtonian Mechanics Quiz

Even in the era of modern physics, understanding and applying Newton's classical Laws of Motion are key skills for physicists and form a core component of instructional programmes. Students arrive in the classroom with intuitive ideas about force and motion that are often misaligned with Newtonian thinking. Prior research has shown that these incorrect intuitive ideas are remarkably persistent, and can stay with students throughout their education and beyond. Reliable instruments, that can accurately evaluate student understanding of Newtonian mechanics, are required to track student progress and evaluate the efficacy of instructional programmes. The Force Concept Inventory (FCI), a conceptual quiz composed of multiple-choice questions, is a well-established instrument, developed to address these challenges. The FCI, and how students respond to its questions, has been widely investigated and discussed in the literature. Notably, research has shown that: correct responses to questions do not always correspond to correct application of Newtonian concepts; and the limited response options given for multiple-choice questions often do not capture the full range of student thinking. There is therefore a burgeoning need to develop new instruments that probe students' understanding at a deeper level, by interrogating conceptual understanding from multiple perspectives and incorporating different question formats that require students to construct and consider their responses. We introduce the Newtonian Mechanics Quiz (NMQ), a modified version of the FCI that incorporates follow-up questions in a variety of formats, each with different diagnostic functions. This article describes the development and validation of the NMQ instrument, and illustrates several novel analyses enabled by the student response dataset that can offer deep insight into students' conceptual understanding of Newton's Laws.

physics.ed-ph↗

arXiv2026

What do student responses to the car-truck problems tell us? An investigation into two Force Concept Inventory questions

Concept inventories are widely used in Physics Education Research to uncover student misconceptions and measure the effectiveness of instruction. Two questions in the widely used multiple-choice Force Concept Inventory concern a car that is pushing a truck, as the car is accelerating and then when a steady speed has been reached. We investigate the premise that correct answering of these questions is because of good conceptual understanding of Newton's Third Law, by analyzing responses to a modified inventory that randomly offers students multiple-choice or free-text versions of the questions and follows these with questions in which students select the physical principle(s) they used. The results from 674 attempts from students at six universities show a similar pattern of results for multiple-choice and free-text versions, also comparable with Force Concept Inventory results from one of the universities in the preceding five years, but with marked differences relative to early published Force Concept Inventory data. Free-text responses and the law-selection sub-questions can reveal more about conceptual understanding than can be seen in multiple-choice responses alone. For the accelerating system (Question 15), correct responses are usually attributed to Newton's Third Law and incorrect responses are usually attributed to Newton's Second Law. When speed is constant (Question 16), around 90% of responses are correct, but a significant number of these are attributed to Newton's First Law or the Superposition Principle rather than Newton's Third Law, especially pre-instruction. We conclude that students are confusing balanced forces on a single object moving at constant speed with the correct equal-and-opposite interaction pair between two objects, and correct responses to Question 16 may be concealing an underlying misconception.

physics.ed-ph↗

arXiv2019

Signatures of rare states and thermalization in a theory with confinement

There is a dichotomy in the nonequilibrium dynamics of quantum many body systems. In the presence of integrability, expectation values of local operators equilibrate to values described by a generalized Gibbs ensemble, which retains extensive memory about the initial state of the system. On the other hand, in generic systems such expectation values relax to stationary values described by the thermal ensemble, fixed solely by the energy of the state. At the heart of understanding this dichotomy is the eigenstate thermalization hypothesis (ETH): individual eigenstates in nonintegrable systems are thermal, in the sense that expectation values agree with the thermal prediction at a temperature set by the energy of the eigenstate. In systems where ETH is violated, thermalization can be avoided. Thus establishing the range of validity of ETH is crucial in understanding whether a given quantum system thermalizes. Here we study a simple model with confinement, the quantum Ising chain with a longitudinal field, in which ETH is violated. Despite an absence of integrability, there exist rare (nonthermal) states that persist far into the spectrum. These arise as a direct consequence of confinement: pairs of particles are confined, forming new `meson' excitations whose energy can be extensive in the system size. We show that such states are nonthermal in both the continuum and in the low-energy spectrum of the corresponding lattice model. We highlight that the presence of such states within the spectrum has important consequences, with certain quenches leading to an absence of thermalization and local observables evolving anomalously.

cond-mat.str-el↗

arXiv2018

Nonthermal states arising from confinement in one and two dimensions

We show that confinement in the quantum Ising model leads to nonthermal eigenstates, in both continuum and lattice theories, in both one (1D) and two dimensions (2D). In the ordered phase, the presence of a confining longitudinal field leads to a profound restructuring of the excitation spectrum, with the low-energy two-particle continuum being replaced by discrete 'meson' modes (linearly confined pairs of domain walls). These modes exist far into the spectrum and are atypical, in the sense that expectation values in the state with energy $E$ do not agree with the microcanonical (thermal) ensemble prediction. Single meson states persist above the two meson threshold, due to a surprising lack of hybridization with the ($n\geq4$)-domain wall continuum, a result that survives into the thermodynamic limit and that can be understood from analytical calculations. The presence of such states is revealed in anomalous post-quench dynamics, such as the lack of a light cone, the suppression of the growth of entanglement entropy, and the absence of thermalization for some initial states. The nonthermal states are confined to the ordered phase - the disordered (paramagnetic) phase exhibits typical thermalization patterns in both 1D and 2D in the absence of integrability.

cond-mat.stat-mech↗

arXiv2017

Non-perturbative methodologies for low-dimensional strongly-correlated systems: From non-abelian bosonization to truncated spectrum methods

We review two important non-perturbative approaches for extracting the physics of low-dimensional strongly correlated quantum systems. Firstly, we start by providing a comprehensive review of non-Abelian bosonization. This includes an introduction to the basic elements of conformal field theory as applied to systems with a current algebra, and we orient the reader by presenting a number of applications of non-Abelian bosonization to models with large symmetries. We then tie this technique into recent advances in the ability of cold atomic systems to realize complex symmetries. Secondly, we discuss truncated spectrum methods for the numerical study of systems in one and two dimensions. For one-dimensional systems we provide the reader with considerable insight into the methodology by reviewing canonical applications of the technique to the Ising model (and its variants) and the sine-Gordon model. Following this we review recent work on the development of renormalization groups, both numerical and analytical, that alleviate the effects of truncating the spectrum. Using these technologies, we consider a number of applications to one-dimensional systems: properties of carbon nanotubes, quenches in the Lieb-Liniger model, 1+1D quantum chromodynamics, as well as Landau-Ginzburg theories. In the final part we move our attention to consider truncated spectrum methods applied to two-dimensional systems. This involves combining truncated spectrum methods with matrix product state algorithms. We describe applications of this method to two-dimensional systems of free fermions and the quantum Ising model, including their non-equilibrium dynamics.

cond-mat.str-el↗

arXiv2005

Spin dynamics of the quasi two dimensional spin-1/2 quantum magnet Cs_2CuCl_4

We study dynamical properties of the anisotropic triangular quantum antiferromagnet Cs_2CuCl_4. Inelastic neutron scattering measurements have established that the dynamical spin correlations cannot be understood within a linear spin wave analysis. We go beyond linear spin wave theory by taking interactions between magnons into account in a 1/S expansion. We determine the dynamical structure factor and carry out extensive comparisons with experimental data. We find that compared to linear spin wave theory a significant fraction of the scattering intensity is shifted to higher energies and strong scattering continua are present. However, the 1/S expansion fails to account for the experimentally observed large quantum renormalization of the exchange energies.

cond-mat.str-el↗