Retrospective protocols in usability testing: a comparison of Post-session RTA versus Post-task RTA reports

We present the results of a study that compared two placements of the Retrospective Think-aloud (RTA): A Post-session RTA where the think-aloud occurs after all tasks are complete, and a Post-task RTA where the think-aloud is elicited after each task. Data from task performance and verbal measures were collected from 24 participants. The results suggest that in terms of task performance, participants in the Post-session RTA condition performed tasks faster, with fewer errors and fewer clicks than in the Post-task RTA condition. In terms of utterances, participants in the Post-task RTA condition produced significantly more utterances that explained actions, expectations and procedural descriptions than in the Post-session RTA condition

Ethical oversight of student data in learning analytics: a typology derived from a cross-continental, cross-institutional perspective

The growth of learning analytics as a means to improve student learning outcomes means that student data is being collected, analyzed, and applied in previously unforeseen ways. As the use of this data continues to shape academic and support interventions, there is increasing need for ethical reflection on operational approvals for learning analytics research. Though there are clear processes for vetting studies resulting in publication of student-gathered data, there is little comparable oversight of internally generated student-focused research. Increasingly, ethical concerns about the collection and harvesting of student data have been raised, but there is no clear indication how to address or oversee these ethical concerns. In addition, staff members who are not typical researchers may be less familiar with approvals processes and the need to demonstrate potential for harm, etc. If current trends point to a range of individuals harvesting and analyzing student data (mostly without students' informed consent or knowledge), how can the real danger of unethical behavior be curbed to mitigate the risk of unintended consequences? A systematic appraisal of the policy frameworks and processes of ethical review at three research institutions (namely, the University of South Africa, the Open University in the United Kingdom, and Indiana University in the United States) provides an opportunity to compare practices, values, and priorities. From this cross-institutional review, a working typology of ethical approaches is suggested within the scope of determining the moral intersection of internal student data usage and application

Crack Front Waves and the dynamics of a rapidly moving crack

Crack front waves are localized waves that propagate along the leading edge of a crack. They are generated by the interaction of a crack with a localized material inhomogeneity. We show that front waves are nonlinear entities that transport energy, generate surface structure and lead to localized velocity fluctuations. Their existence locally imparts inertia, which is not incorporated in current theories of fracture, to initially "massless" cracks. This, coupled to crack instabilities, yields both inhomogeneity and scaling behavior within fracture surface structure.Comment: Embedded Latex file including 4 figure

Critical examination of cohesive-zone models in the theory of dynamic fracture

We have examined a class of cohesive-zone models of dynamic mode-I fracture, looking both at steady-state crack propagation and its stability against out-of-plane perturbations. Our work is an extension of that of Ching, Langer, and Nakanishi (CLN) (Phys. Rev. E, vol. 53, no. 3, p. 2864 (1996)), who studied a non-dissipative version of this model and reported strong instability at all non-zero crack speeds. We have reformulated the CLN theory and have discovered, surprisingly, that their model is mathematically ill-posed. In an attempt to correct this difficulty and to construct models that might exhibit realistic behavior, we have extended the CLN analysis to include dissipative mechanisms within the cohesive zone. We have succeeded to some extent in finding mathematically well posed systems; and we even have found a class of models for which a transition from stability to instability may occur at a nonzero crack speed via a Hopf bifurcation at a finite wavelength of the applied perturbation. However, our general conclusion is that these cohesive-zone models are inherently unsatisfactory for use in dynamical studies. They are extremely difficult mathematically, and they seem to be highly sensitive to details that ought to be physically unimportant.Comment: 19 pages, REVTeX 3.1, epsf.sty, also available at http://itp.ucsb.edu/~lobkovs

A multiple scales approach to crack front waves

Perturbation of a propagating crack with a straight edge is solved using the method of matched asymptotic expansions (MAE). This provides a simplified analysis in which the inner and outer solutions are governed by distinct mechanics. The inner solution contains the explicit perturbation and is governed by a quasi-static equation. The outer solution determines the radiation of energy away from the tip, and requires solving dynamic equations in the unperturbed configuration. The outer and inner expansions are matched via the small parameter L/l defined by the disparate length scales: the crack perturbation length L and the outer length scale l associated with the loading. The method is first illustrated for a scalar crack model and then applied to the elastodynamic mode I problem. The dispersion relation for crack front waves is found by requiring that the energy release rate is unaltered under perturbation. The wave speed is calculated as a function of the nondimensional parameter kl where k is the crack front wavenumber, and dispersive properties of the crack front wave speed are described for the first time. The example problems considered here demonstrate that the potential of using MAE for moving boundary value problems with multiple scales.Comment: 25 pages, 5 figure

Conceptualisation and psychometric evaluation of positive psychological outcome measures used in adolescents and young adults living with HIV:a mixed scoping and systematic review protocol

Introduction Sub-Saharan Africa bears the greatest burden of HIV. Concomitant mental disorders are common, necessitating the integration of mental healthcare into routine HIV care. Consequently, it is necessary to holistically evaluate the mental health of adolescents and young adults living with HIV (AYALHIV, 10–24 years old) by measuring negative and positive psychological constructs (eg, anxiety and self-acceptance, respectively). There has been a proliferation of positive psychological outcome measures, but the evidence of their psychometric robustness is fragmented. This review, therefore, seeks to (1) identify positive psychological outcomes used in AYALHIV in sub-Saharan Africa and map the constructs onto corresponding measures and (2) critically appraise the psychometrics of the identified outcomes Methods and analysis This mixed review will be done in two parts. First, a scoping review will identify positive psychological outcomes and map them onto corresponding outcome measures. Subsequently, we will systematically evaluate the psychometric properties of the outcomes identified from the scoping review. Independent and blinded reviewers will search articles in PubMed, Scopus, Web of Science, Africa-Wide Information, CINAHL, PsychINFO and Google Scholar from inception through 30 September 2022. Thereafter, separate independent reviewers will screen the retrieved articles. We will apply a narrative synthesis to map the key constructs emerging from the scoping review. For the systematic review, the risk of bias across studies will be evaluated using the COnsensus-based Standards for the selection of health Measurement INstruments (COSMIN) checklist. The quality of the psychometric properties will be rated using the COSMIN checklist and qualitatively synthesised using the modified Grading of Recommendations Assessment, Development and Evaluation checklist. Ethics and dissemination No ethical approvals are needed. The mixed-review outputs will collectively inform the development, implementation and evaluation of bespoke interventions for AYALHIV. Review outcomes will be disseminated in a peer-reviewed journal, on social media and through policy briefs

Energy radiation of moving cracks

The energy radiated by moving cracks in a discrete background is analyzed. The energy flow through a given surface is expressed in terms of a generalized Poynting vector. The velocity of the crack is determined by the radiation by the crack tip. The radiation becomes more isotropic as the crack velocity approaches the instability threshold.Comment: 7 pages, embedded figure

Effects of the Spin-Orbit and Tensor Interactions on the M1M1 and E2E2 Excitations in Light Nuclei

The effects of varying the spin-orbit and tensor components of a realistic interaction on $M1$ excitation rates and $B(E2)'s$ are studied on nuclei in the $0p$ and $1s-0d$ shells. Not only the total $M1$ but also the spin and orbital parts separately are studied. The single-particle energies are first calculated with the same interaction that is used between the valence nucleons. Later this stringent condition is relaxed somewhat and the $1s$ level is raised relative to $0d$. For nuclei up to $^{28}Si$, much better results i.e stronger $B(M1)$ rates are obtained by increasing the strength of the spin-orbit interaction relative to the free value. This is probably also true for $^{32}S$, but $^{36}Ar$ presents some difficulties. The effects of weakening the tensor interaction are also studied. On a more subtle level, the optimum spin-orbit interaction in the lower half of the $s-d$ shell, as far as $M1$ excitations are concerned, is substantially larger than the difference $E(J=3/2^+)_1-E(J=5/2^+)_1=5.2~MeV$ in $^{17}O$. A larger spin-orbit splitting is also needed to destroy the triaxiality in $^{22}Ne$. Also studied are how much $M1$ orbital and spin strength lies in an observable region and how much is buried in the grass at higher energies. It is noted that for many nuclei the sum $B(M1)_{orbital}+B(M1)_{spin}$ is very close to $B(M1)_{total}$, indicating that the summed cross terms are very small.Comment: 39 pages, revtex 3.

Modelling the spread and control of African swine fever in domestic and feral pigs

African swine fever (ASF) represents a significant threat to the Australian pork sector and the economy in general. Estimates of the economic damages from a large multi-state outbreak of ASF in Australia exceed $A2 billion. ASF outbreaks are widespread and increasing in number in Asia and Europe. Although ASF is not present in Australia, detections of ASF viral fragments in undeclared pork products intercepted at the Australian border and the recent spread of the disease to neighbouring Papua New Guinea demonstrate the significance of the threat. The AADIS model (Bradhurst et al., 2015), simulates the spread and control of contagious emergency animal diseases such as foot-and-mouth disease. The ability to evaluate different outbreak scenarios in time and space, and trial various control measures, assists the development of animal health policy. This project expanded the AADIS modelling framework to simulate the potential spread and control of ASF in Queensland domestic and feral pig populations. Of particular interest was the epidemiological interface between domestic and feral pigs and the potential role of ASF-infectious feral pig carcasses in transmission. The upgraded model will provide a useful decision support tool to assist with preparedness and planning for ASF outbreaks. The report provides a literature review on ASF, feral pigs in Australia, and ASF decision support tools. Case studies on the spread and control of ASF in domestic and feral pigs demonstrate the functionality of the new model. Queensland was selected as the test case study area due to the wide distribution and high numbers of feral pigs and the availability of local expertise and data from Biosecurity Queensland, Department of Agriculture and Fisheries, Australian Pork Limited and SunPork Group Pty Ltd. The model was parameterised from the literature review and expert opinion that incorporated local knowledge of Australian production systems and environmental conditions. Note that the model is only parameterised for Queensland and will be scaled up to a national model through Biosecurity Innovation Program project 182021