Core formation by giant impacts

Ideas about the accretion and early evolution of the Earth and the other terrestrial planets have recently undergone a number of revolutionary changes. It has become clear that giant impacts were far from rare events. In the later stages of accretion any given planetary embryo is liable to be struck several times by other bodies of up to half its own diameter. Such an impact may have the ability to trigger core formation. Traditional accretion models have had great difficulty explaining the formation of the core. If one admits the importance of infrequent large events that may melt an entire hemisphere, the core formation difficulty vanishes. Millimeter-size iron blebs in the melted region will rain out due to their density difference with the silicate melt. Core formation may not require the melting of the entire hemisphere of the planet. The conditions are explored under which impact induced core formation may occur

Identifying unmet training needs for postgraduate research students in the biomedical sciences through audit of examiners' reports

Aim/Purpose: Understanding the educational needs of postgraduate research candidates (PGRs) is essential to facilitate development, support attainment, and maintain graduate quality. Background: The production and effective defence of the research thesis are the summative assessment tools used in postgraduate research education. Examiners’ reports provide a rich source of feedback and indicate the gap between the candidate’s level of performance and that expected for the award. This provides a lens through which to view the unmet training needs of PGR cohorts. Methodology: Following a review of all examiner reports for PGR assessments held over a 12 month period, we explored the quantitative and qualitative dimension data in context in order to identify common training needs for our PGR students. Utilising this theoretical framework and standard thematic analysis, we identified recurring themes and were able to determine key areas for future focus. Contribution: This study utilises independent comment from postgraduate research candidate thesis and oral examination assessment to identify unmet core research training needs. Findings: We recognised seven key areas identified by the examiners for improvement: i) quality of scientific writing, ii) general presentation of thesis, iii) statistics /data analysis, iv) understanding / critical appraisal, v) experimental design, vi) English language and vii) supervision. Academic literacy and numeracy stood out as key areas for future training focus. The results highlight areas for future focus in educational provision and targeted training for PGRs undertaking biomedical and life sciences research within our faculty. Recommendations for Practitioners: Evaluation of postgraduate research programmes should include feedback from a variety of sources and not rely solely on employability and completion rates as measures of success. The examination committees are an important source of feedback on the individual and the programme with regard to attainment of core research skills. Recommendation for Researchers: Regular and wide reaching evaluation of postgraduate research programmes and support available is required to ensure the sector can meet the changing needs of our PGR cohorts. Impact on Society: Doctoral graduates are entering increasingly diverse employment fields. Ensuring the quality of graduates and supporting their journey through candidature ensures the greatest value for society once in the work place. Future Research: This study highlights unmet training needs of PGRs as identified by an inde-pendent expert. The impact of engagement with training and the importance of prior experience are not explored in this study, nor is the student perspective on the process. These will reveal additional dimensions to the evaluation process. </jats:p

Test of a Jastrow-type wavefunction for a trapped few-body system in one dimension

For a system with interacting quantum mechanical particles in a one-dimensional harmonic oscillator, a trial wavefunction with simple structure based on the solution of the corresponding two-particle system is suggested and tested numerically. With the inclusion of a scaling parameter for the distance between particles, at least for the very small systems tested here the ansatz gives a very good estimate of the ground state energy, with the error being of the order of ~1% of the gap to the first excited state

How does the exchange of money impact the therapeutic relationship in private practice? Counsellors’ perspectives: A small scale qualitative study.

Whether we like it or not, money occupies a very important place in the lives of most of us: it symbolises all that we value in society and may even be a metaphor for love. But how does it feel to use it as the medium of exchange in the depth of human interaction we seek to achieve in the therapeutic relationship? This small scale qualitative research used interpretative phenomenological analysis to explore the perspectives on their experience of the impact of the fee transaction of six counsellors in private practice, using semi-structured interviews. Findings suggested that the relationship of the self of the therapist with money played a key part, often leading to a difficulty in reconciling the taking of money with the therapeutic role and this became most apparent in the physical transaction, particularly when it was necessary to ask for money. Participants felt it was important to feel valued, but also that they were providing value for money. The fee represents one of the least well explored elements of the therapeutic alliance. It is barely covered in training programs and therefore the potential comparison between charging for psychotherapy in private practice and prostitution is avoided. It appears that the taboo status that money occupies in society is also to be found in therapy rooms

Homophilic binding of PTP mu, a receptor-type protein tyrosine phosphatase, can mediate cell-cell aggregation

The receptor-like protein tyrosine phosphatase, PTPmu, displays structural similarity to cell-cell adhesion molecules of the immunoglobulin superfamily. We have investigated the ability of human PTPmu to function in such a capacity. Expression of PTPmu, with or without the PTPase domains, by recombinant baculovirus infection of Sf9 cells induced their aggregation. However, neither a chimeric form of PTPmu, containing the extracellular and transmembrane segments of the EGF receptor and the intracellular segment of PTPmu, nor the intracellular segment of PTPmu expressed as a soluble protein induced aggregation. PTPmu mediates aggregation via a homophilic mechanism, as judged by lack of incorporation of uninfected Sf9 cells into aggregates of PTPmu-expressing cells. Homophilic binding has been demonstrated between PTPmu-coated fluorescent beads (Covaspheres) and endogenously expressed PTPmu on MvLu cells. Additionally the PTPmu-coated beads specifically bound to a bacterially expressed glutathione-S-transferase fusion protein containing the extracellular segment of PTPmu (GST/PTPmu) adsorbed to petri dishes. Covaspheres coated with the GST/PTPmu fusion protein aggregated in vitro and also bound to PTPmu expressed endogenously on MvLu cells. These results suggest that the ligand for this transmembrane PTPase is another PTPmu molecule on an adjacent cell. Thus homophilic binding interactions may be an important component of the function of PTPmu in vivo

Reversible adsorption on a random site surface

We examine the reversible adsorption of hard spheres on a random site surface in which the adsorption sites are uniformly and randomly distributed on a plane. Each site can be occupied by one solute provided that the nearest occupied site is at least one diameter away. We use a numerical method to obtain the adsorption isotherm, i.e. the number of adsorbed particles as a function of the bulk activity. The maximum coverage is obtained in the limit of infinite activity and is known exactly in the limits of low and high site density. An approximate theory for the adsorption isotherms, valid at low site density, is developed by using a cluster expansion of the grand canonical partition function. This requires as input the number of clusters of adsorption site of a given size. The theory is accurate for the entire range of activity as long as the site density is less than about 0.3 sites per particle area. We also discuss a connection between this model and the vertex cover problem.Comment: 16 pages, 10 figure

Three-dimensional molecular dynamics simulations of void coalescence during dynamic fracture of ductile metals

Void coalescence and interaction in dynamic fracture of ductile metals have been investigated using three-dimensional strain-controlled multi-million atom molecular dynamics simulations of copper. The correlated growth of two voids during the coalescence process leading to fracture is investigated, both in terms of its onset and the ensuing dynamical interactions. Void interactions are quantified through the rate of reduction of the distance between the voids, through the correlated directional growth of the voids, and through correlated shape evolution of the voids. The critical inter-void ligament distance marking the onset of coalescence is shown to be approximately one void radius based on the quantification measurements used, independent of the initial separation distance between the voids and the strain-rate of the expansion of the system. The interaction of the voids is not reflected in the volumetric asymptotic growth rate of the voids, as demonstrated here. Finally, the practice of using a single void and periodic boundary conditions to study coalescence is examined critically and shown to produce results markedly different than the coalescence of a pair of isolated voids.Comment: Accepted for publication in Physical Review

Control of three species of leafhoppers, on Rubus in British Columbia

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