Theory of interfacial charge-transfer complex photophysics in π\pi-conjugated polymer-fullerene blends

We present a theory of the electronic structure and photophysics of 1:1 blends of derivatives of polyparaphenylenevinylene and fullerenes. Within the same Coulomb-correlated Hamiltonian applied previously to interacting chains of single-component $\pi$-conjugated polymers, we find an exciplex state that occurs below the polymer's optical exciton. Weak absorption from the ground state occurs to the exciplex. We explain transient photoinduced absorptions in the blend, observed for both above-gap and below-gap photoexcitations, within our theory. Photoinduced absorptions for above-gap photoexcitation are from the optical exciton as well as the exciplex, while for below-gap photoexcitation induced absorptions are from the exciplex alone. In neither case are free polarons generated in the time scale of the experiment. Importantly, the photophysics of films of single-component $\pi$-conjugated polymers and blends can both be understood by extending Mulliken's theory of ground-state charge transfer to the case of excited-state charge transfer.Comment: 9 pages, 8 figure

Correlated-electron description of the photophysics of thin films of π\pi-conjugated polymers

We extend Mulliken's theory of ground state charge transfer in a donor-acceptor complex to excited state charge transfer between pairs of identical $\pi$-conjugated oligomers, one of which is in the optically excited state and the other in the ground state, leading to the formation of a charge-transfer exciton. Within our theory, optical absorptions from the charge-transfer exciton should include a low energy intermolecular charge-transfer excitation, as well as distinct intramolecular excitations from both the neutral delocalized exciton component and the Coulombically bound polaron-pair component of the charge-transfer exciton. We report high order configuration-interaction calculations for pairs of oligomers of poly-paraphenylenevinylene (PPV) that go beyond our previous single configuration-interaction calculation and find all five excited state absorptions predicted using heuristic arguments based on the Mulliken concept. Our calculated excited state absorption spectrum exhibits strong qualitative agreement with the complete wavelength-dependent ultrafast photoinduced absorption in films of PPV derivatives, suggesting that a significant fraction of the photoinduced absorption here is from the charge-transfer exciton. We make detailed comparisons to experiments, and a testable experimental prediction

A view of paediatric outcomes research

No Abstract. South African Medical Journal Vol. 95(10) 2005: 785-78

Private-sector caesarean sections in perspective

No Abstract

Is registrarship a different experience for women?

Objective. To detennine differences between male and female registrars in their subjective perceptions and experience of a paediatrics registrar training programme.Design. Cross-sectional survey.Setting. University-affiliated teaching hospitals.Participants. Thirty-nine paediatrics registrars.Results. Of the 39 respondents, 18 (46%) were women. Men were older than women (30A v. 29.1 years, p = 0.049). There were no gender differences in the number of hours worked per week (65.7 v. 67.8 hours, P = 0.384) or participation in the training programme. Success rates in postgraduate paediatrics examinations were also similar for the two groups (85% v. 76%, P = 0.486). Male registrars were more likely to have 'moonlighted' (43% v. 6%, P =0.011). FIfty-nine per cent of female registrars believed that they had been disadvantaged in their careers because of their gender, 28% felt that more was expected of a woman registrar and 22% of the female trainees claimed to have been subjected to sexual harassment. The majority (82%) of women registrars contemplated taking time off from practising clinical paediatrics in the Mure (postregistrarship), mainly for child-bearing purposes. Female respondents criticised both the academic department and the hospital authorities for discriminatory practices, such as the awarding of home loans to men and women who were breadwinners only. The findings suggest that women registrars do feel disadvantaged and discriminated against, and highlight the need for flexible, creative programmes that recognise the needs and aspirations of female registrars and, indeed, all women in academic medicine

Energy expenditure in office workers with identified health risks

Objective. To measure the daily energy expenditure in employees previously identified as having ≥2 risk factors for chronic disease, and to identify potential risk-reducing interventions for implementation within or outside the workplace. Design. A total of 122 employees with ≥2 risk factors for chronic disease identified in an in-house screening programme were invited to participate in a 6-month health management programme. Physical assessments included anthropometric measurements, blood pressure, blood glucose and cholesterol estimations, and bicycle ergometry. Participants were invited to wear a ‘metabolic armband' (Body Media SenseWear Pro Armband®) for 6 days. Metabolic measures included active and total energy expenditure (AEE, TEE), and daily MET levels (metabolic equivalents expressed as kcal/kg/hour). Differences were explored between genders, and relationships sought between energy expenditure, lifestyle and anthropometric data. Setting. A corporate working environment. All measures and assessments were carried out in the in-house fitness facility. Interventions. The health management programme involved physical assessments and personalised weight and activity management plans. Main outcome measures. TEE per day, duration and quantification of physical activity, METS, AEE, number of steps per day and body position recording. Relationships were explored between the latter and anthropometric measures such as body mass index (BMI) and percentage body fat. Result. Altogether 53 (43%) of the eligible subjects volunteered for the 6-month programme and 49 enrolled for the metabolic armband study. The males were more active than the females, but both had BMI and body fat estimates that categorised them as overweight to obese. METS and AEE were positively correlated with duration of exercise rather than intensity, and negatively correlated with BMI. In a stepwise regression analysis for the total group 77% of the variance in MET levels was accounted for by per cent body fat and steps per day. Multivariate analysis by gender (with per cent body fat as the dependent variable) suggested that males would have to increase the duration of vigorous exercise in order to reduce body fat, while females would benefit from sitting less, sleeping more, and increasing the duration of moderate exercise. Conclusion and clinical relevance. In a self-selected sample involving motivated individuals, the SenseWear® armband provided information that would be useful in directing further research in women, focusing on sleeping pattern and moderately increasing activity levels. South African Journal of Sports Medicine Vol. 20 (2) 2008: pp. 40-4

Globular Cluster Systems in Brightest Cluster Galaxies. III: Beyond Bimodality

We present new deep photometry of the rich globular cluster (GC) systems around the Brightest Cluster Galaxies UGC 9799 (Abell 2052) and UGC 10143 (Abell 2147), obtained with the HST ACS and WFC3 cameras. For comparison, we also present new reductions of similar HST/ACS data for the Coma supergiants NGC 4874 and 4889. All four of these galaxies have huge cluster populations (to the radial limits of our data, comprising from 12000 to 23000 clusters per galaxy). The metallicity distribution functions (MDFs) of the GCs can still be matched by a bimodal-Gaussian form where the metal-rich and metal-poor modes are separated by ~0.8 dex, but the internal dispersions of each mode are so large that the total MDF becomes very broad and nearly continuous from [Fe/H] = -2.4 to Solar. There are, however, significant differences between galaxies in the relative numbers of \emph{metal-rich} clusters, suggesting that they underwent significantly different histories of mergers with massive, gas-rich halos. Lastly, the proportion of metal-poor GCs rises especially rapidly outside projected radii R > 4 R_eff, suggesting the importance of accreted dwarf satellites in the outer halo. Comprehensive models for the formation of GCs as part of the hierarchical formation of their parent galaxies will be needed to trace the systematic change in structure of the MDF with galaxy mass, from the distinctly bimodal form in smaller galaxies up to the broad continuum that we see in the very largest systems.Comment: In press for Astrophysical Journa

A review of selection criteria used by medical scheme advisers to approve or deny procedures with a cosmetic component

Objective. To review and apply statistical tests to the selection criteria used by two medical advisers to approve or deny applications for three common cosmetic or reconstructive procedures within a large group of medical schemes.Design. A retrospective descriptive study which applied multiple regression analysis, frequency analysis, comparison of means and simple correlations to the data sets for three procedures.Setting. Administrative records from the clinical files of medical advisers and the administrator's claims database.Subjects. Data were reviewed for 1 143 members who, between January and December 1996, submitted applications for breast reduction, excimer laser refractive surgery, or otoplasty.Main outcome measures. The primary outcome measure was the statistical relationship between medical advisers' selection criteria and final decision. In addition, the financial implications of these cosmetic/reconstructive procedures were assessed.Results. For the three procedures reviewed there was a statistically significant relationship behveen 5 of 13 preoperative criteria requested and the medical advisers' opinion. Excimer laser surgery was generally approved on the basis of the refractive error (myopia> -3.00; astigmatism > -1.5 dioptres); otoplasty was generally approved for children aged :≤ 12.years; and breast reduction was usually covered for women with a sternal-nipple distance > 29.0 cm and with a cup size ≥ DD. The other data submitted were similarly distributed between the approved and denied groups.Conclusions. Review of medical advisers' decisions is important in an era of protocols, guidelines and 'standard operating procedures'. Selection criteria for approval of applications for medically necesssary cosmetic/reconstructive surgery must be reviewed and revised to provide a reliable, reproducible and statistically valid process