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Wade Naylor

Publications and source records attributed to Wade Naylor.

At least 19 recordsLinked to original sources

Dominant misconceptions and alluvial flows between Engineering and Physical Science students

In this article we assess the comprehension of physics concepts by Physical Science and Engineering students enrolled in their first semester at the University of Johannesburg (UJ), South Africa ($2022$). We employ different graphical measures to explore similarities and differences using the results of both pre- and post-test data from the Force Concept Inventory assessment tool, from which we calculate dominant misconceptions (DMs) and gains. We also use alluvial diagrams to track the choices made by these two groups of students from pre- to post-test stages. In our analysis, we find that DM results indicate that participating Engineering students outperformed Physical Science students on average, however, the same types of normalised DMs persist at the post-test level. We call these DMs "persistent misconceptions." This is very useful when tracking persistent misconceptions, where when using repeated measures and alluvial diagrams with smaller groups of students, we find that Physical Science students tend to make more chaotic choices.

physics.ed-ph

A three-year comparative study of dominant misconceptions among first-year physics students at a South African university

This article discusses a three-year study (2020 - 2022) of dominant misconceptions (DMs) for a large cohort of first-year physics course students at the University of Johannesburg (UJ), South Africa. Our study considered pre-test scores on the Force Concept Inventory using a graphical method, where we found statistical differences between the mean DM scores for the 2020 cohort, as compared to the 2021 and 2022 cohort; possibly due to the onset of COVID lockdowns. We also compared our data from South Africa with cohorts based in Spain and the Kingdom of Saudi Arabia, where the method of DMs was also applied. From this comparison, we found some differences in the preconception knowledge of the cohorts. Furthermore, we included an analysis of DMs through the `gender lens' for the South African cohort, finding no statistically significant difference between the means for DM scores of students who identify as male or female. Finally, given the diverse language backgrounds and levels of matriculation preparation for university level physics courses, we have also shown how quickly responding to student misconceptions can be efficiently addressed using the method of DMs.

physics.ed-ph

Polarising questions in the Force Concept Inventory

The Force Concept Inventory (FCI) is a well-established physics education assessment tool used to evaluate students' comprehension of elementary mechanics principles. While it can be used to analyse the effectiveness of instruction if deployed as a pre- and post-test, we utilise the FCI here as pre-test only, to extract insights into first-year students' (mis)conceptions of Newtonian mechanics as they enter university. In this preliminary study, we tested 353 students enrolled at the University of Johannesburg in 2021, across six introductory physics courses. We focus on their responses to six "polarising" questions, for which the presence of a correct and a mostly-correct answer allows for a clear demonstration of persistent misconceptions.

physics.ed-ph

Does transitioning to online classes mid-semester affect conceptual understanding?

The Force Concept Inventory (FCI) can be used as an assessment tool to measure conceptual gains in a cohort of students. The FCI uses a conceptions/"misconceptions" lens rather than a context dependent perspective, such as "knowledge-in-pieces". In this study it was given to first year students ($N=256$ students) pre- and post-mechanics lectures, at the University of Johannesburg. From these results we examine the effect of switching mid-semester from traditional classes to online classes, as imposed by the COVID-19 lockdown in South Africa. Overall results indicate no appreciable difference of gain, when bench-marked against previous studies using this assessment tool. When compared with $2019$ grades, the $2020$ semester grades do not appear to be greatly affected. Furthermore, statistical analyses also indicate a gender difference in mean gains in favour of females at the $95\%$ significance level (for paired data, $N=48$).

physics.ed-ph

Gender gap and polarisation of physics on global courses

We extend on previous research on the Force Concept Inventory (FCI) given to first year classical mechanics students (N=66 students, over four years) pre and post score, for students on an international (global) course at Osaka University. In particular, we revisit the notion of "polarisation" in connection with the six polarisation-inducing questions in the FCI and examine its gender aspect. Our data suggest that this phenomenon is not unique to one gender. Furthermore, the extent by which it is exhibited by males may differ from that of females at the beginning (pretest) but the gap closes upon learning more about forces (posttest). These findings are for the most part, complemented by our result for the FCI as a whole. Although the differences in means for males and females suggest a gender gap, statistical analysis shows that there is no gender difference at the 95% confidence level.

physics.ed-ph

Logarithmic divergences in the $k$-inflationary power spectra computed through the uniform approximation

We investigate a calculation method for solving the Mukhanov-Sasaki equation in slow-roll $k$-inflation based on the uniform approximation (UA) in conjunction with an expansion scheme for slow-roll parameters with respect to the number of $e$-folds about the so-called \textit{turning point}. Earlier works on this method has so far gained some promising results derived from the approximating expressions for the power spectra among others, up to second order with respect to the Hubble and sound flow parameters, when compared to other semi-analytical approaches (e.g., Green's function and WKB methods). However, a closer inspection is suggestive that there is a problem when higher-order parts of the power spectra are considered; residual logarithmic divergences may come out that can render the prediction physically inconsistent. Looking at this possibility, we map out up to what order with respect to the mentioned parameters several physical quantities can be calculated before hitting a logarithmically divergent result. It turns out that the power spectra are limited up to second order, the tensor-to-scalar ratio up to third order, and the spectral indices and running converge to all orders. This indicates that the expansion scheme is incompatible with the working equations derived from UA for the power spectra but compatible with that of the spectral indices. For those quantities that involve logarithmically divergent terms in the higher-order parts, existing results in the literature for the convergent lower-order parts calculated in the equivalent fashion should be viewed with some caution; they do not rest on solid mathematical ground.

gr-qc

Adiabatic regularisation of power spectra in $k$-inflation

We look at the question posed by Parker et al. about the effect of UV regularisation on the power spectrum for inflation. Focusing on the slow-roll $k$-inflation, we show that up to second order in the Hubble and sound flow parameters, the adiabatic regularisation of such model leads to no difference in the power spectrum apart from certain cases that violate near scale invariant power spectra. Furthermore, extending to non-minimal $k$-inflation, we establish the equivalence of the subtraction terms in the adiabatic regularisation of the power spectrum in Jordan and Einstein frames.

gr-qc

Vacuum-excited surface plasmon polaritons

We separate Maxwell's equations for background media that allow for both electric and magnetic time-dependence in a generalized Lorenz gauge. In a process analogous to the dynamical Casimir effect (DCE) we discuss how surface plasmon polaritons (SPP)s can be created out of vacuum, via the time-dependent variation of a dielectric and magnetic insulator at a metal interface for TM and TE branches, respectively. We suggest how to extend currently proposed DCE experiments to set up and detect these excitations. Numerical simulations (without any approximation) indicate that vacuum excited SPPs can be of a similar magnitude to the photon creation rate in such experiments. Potential benefits of detecting vacuum excited SPPs, as opposed to DCE photons, are that parametric enhancement does not require a sealed cavity in the axial direction and the detection apparatus might be able to use simple phase matching techniques. For the case of constant permeability, $μ$, TM branch SPPs and photons do not suffer from detuning and attenuation like TE photons.

quant-ph

Gravitino fields in Schwarzschild black hole spacetimes

The analysis of gravitino fields in curved spacetimes is usually carried out using the Newman-Penrose formalism. In this paper we consider a more direct approach with eigenspinor-vectors on spheres, to separate out the angular parts of the fields in a Schwarzschild background. The radial equations of the corresponding gauge invariant variable obtained are shown to be the same as in the Newman-Penrose formalism. These equations are then applied to the evaluation of the quasinormal mode frequencies, as well as the absorption probabilities of the gravitino field scattering in this background.

gr-qc

Polarization of physics on global courses

Since October 2010, the Chemistry-Biology Combined Major Program (CBCMP), an international course taught in English at Osaka University, has been teaching small classes (no more than 20 in size). We present data from the Force Concept Inventory (FCI) given to first year classical mechanics students (N=47 students over three years) pre and post score, for a class that predominantly uses interactive engagement (IE), such as MasteringPhysics. Our findings show a $G$-factor improved score of about $\sim$ 0.18, which is marginally about the average of a traditional based course. Furthermore, we analyse in detail a set of six questions from the FCI, involving the identification of forces acting on a body. We find that student answers tend to cluster about "polarising choices"-a pair of choices containing the correct choice and a wrong choice with the latter corresponding to a superset of forces in the former. Our results are suggestive that students have a good idea of the right set of forces acting on a given system but the inclusion of extra force(s) brings about confusion; something that may be explained by misleading ontological categorisation of forces. In an appendix we also comment on possible correlations between the pre/post score and the level of English ability on entry to the course.

physics.ed-ph

Simulating (p)reheating after inflation via the DCE?

We note some close parallels between preheating/perturbative reheating, (p)reheating, models in post-inflationary cosmology and the dynamical Casimir effect (DCE) in quantum optics. For the plasma-mirror model we show how the effective plasma mass (arising from conduction electrons) behaves like an oscillating inflaton field, while created photons behave like a scalar field coupled quadratically to the inflaton. Furthermore, the effect of spacetime expansion can also be incorporated by varying the dielectric function. We propose an experiment that could mimic (p)reheating for both narrow and broad parametric resonance, by employing technology already being used in attempts to detect DCE photons via plasma-mirrors.

astro-ph.CO

Towards particle creation in a microwave cylindrical cavity

We present for the first time numerical results for the particle (photon) creation rate of Dynamical Casimir effect (DCE) radiation in a resonant cylindrical microwave cavity. Based on recent experimental proposals, we model an irradiated semiconducting diaphragm (SCD) using a time dependent 'plasma sheet' where we show that the number of photons created for the TM_{011} mode is considerably enhanced even for low laser powers (of microjoule order). Conversely to the moving mirror case, we also show that the fundamental TM mode (TM_{010}) is not excited for an irradiated plasma sheet. We show that polarization (arising due to the back reaction of pair created photons with the plasma SCD) implies losses for TM, but not TE modes. However, we argue that these losses can be reduced by lowering the laser power and shortening the relaxation time. The results presented here lead support to the idea that TE and, in particular, TM modes are well suited to the detection of DCE radiation in a cylindrical cavity.

quant-ph

A New Approach to Black Hole Quasinormal Modes: A Review of the Asymptotic Iteration Method

We discuss an approach to obtaining black hole quasinormal modes (QNMs) using the asymptotic iteration method (AIM), initially developed to solve second order ordinary differential equations. We introduce the standard version of this method and present an improvement more suitable for numerical implementation. We demonstrate that the AIM can be used to find radial QNMs for Schwarzschild, Reissner-Nordstrom (RN) and Kerr black holes in a unified way. An advantage of the AIM over the standard continued fraction method (CFM) is that for differential equations with more than three regular singular points Gaussian eliminations are not required. However, the convergence of the AIM depends on the location of the radial or angular position, choosing the best such position in general remains an open problem. This review presents for the first time the spin 0, 1/2 & 2 QNMs of a Kerr black hole and the gravitational and electromagnetic QNMs of the RN black hole calculated via the AIM, and confirms results previously obtained using the CFM. We also presents some new results comparing the AIM to the WKB method. Finally we emphasize that the AIM is well suited to higher dimensional generalizations and we give an example of doubly rotating black holes.

gr-qc

The Conformal Transformation in General Single Field Inflation with Non-Minimal Coupling

The method of a conformal transformation is applied to a general class of single field inflation models with non-minimal coupling to gravity and non-standard kinetic terms, in order to reduce the cosmological perturbative calculation to the conventional minimal coupling case to all orders in perturbation theory. Our analysis is made simple by the fact that all perturbation variables in the comoving gauge are conformally invariant to all orders. The structure of the vacuum, on which cosmological correlation functions are evaluated, is also discussed. We show how quantization in the Jordan frame for non-minimally coupled inflation models can be equivalently implemented in the Einstein frame. It is thereafter argued that the general N-point cosmological correlation functions (of the curvature perturbation) are independent of the conformal frame.

gr-qc

Scalar spheroidal harmonics in five dimensional Kerr-(A)dS

We derive expressions for the general five-dimensional metric for Kerr-(A)dS black holes. The Klein-Gordon equation is explicitly separated and we show that the angular part of the wave equation leads to just one spheroidal wave equation, which is also that for charged five-dimensional Kerr-(A)dS black holes. We present results for the perturbative expansion of the angular eigenvalue in powers of the rotation parameters up to 6th order and compare numerically with the continued fraction method.

gr-qc

Quasi-normal modes for doubly rotating black holes

Based on the work of Chen, Lü and Pope, we derive expressions for the $D\geq 6$ dimensional metric for Kerr-(A)dS black holes with two independent rotation parameters and all others set equal to zero: $a_1\neq 0, a_2\neq0, a_3=a_4=...=0$. The Klein-Gordon equation is then explicitly separated on this background. For $D\geq 6$ this separation results in a radial equation coupled to two generalized spheroidal angular equations. We then develop a full numerical approach that utilizes the Asymptotic Iteration Method (AIM) to find radial Quasi-Normal Modes (QNMs) of doubly rotating flat Myers-Perry black holes for slow rotations. We also develop perturbative expansions for the angular quantum numbers in powers of the rotation parameters up to second order.

hep-th

Black hole quasinormal modes using the asymptotic iteration method

In this article we show that the asymptotic iteration method (AIM) allows one to numerically find the quasinormal modes of Schwarzschild and Schwarzschild de Sitter (SdS) black holes. An added benefit of the method is that it can also be used to calculate the Schwarzschild anti-de Sitter (SAdS) quasinormal modes for the case of spin zero perturbations. We also discuss an improved version of the AIM, more suitable for numerical implementation.

gr-qc