Trends to equilibrium for a class of relativistic diffusions

We address the question of the trends to equilibrium for a large class C of relativistic diffusions. We show the existence of a spectral gap using the Lyapounov method and deduce the exponential decay of the distance to equilibrium in L2-norm and in total variation. A similar result was obtained recently in arXiv:1009.5086 for a particular process of the class C.Comment: 10 page

Inferring phylogenetic networks with maximum pseudolikelihood under incomplete lineage sorting

Phylogenetic networks are necessary to represent the tree of life expanded by edges to represent events such as horizontal gene transfers, hybridizations or gene flow. Not all species follow the paradigm of vertical inheritance of their genetic material. While a great deal of research has flourished into the inference of phylogenetic trees, statistical methods to infer phylogenetic networks are still limited and under development. The main disadvantage of existing methods is a lack of scalability. Here, we present a statistical method to infer phylogenetic networks from multi-locus genetic data in a pseudolikelihood framework. Our model accounts for incomplete lineage sorting through the coalescent model, and for horizontal inheritance of genes through reticulation nodes in the network. Computation of the pseudolikelihood is fast and simple, and it avoids the burdensome calculation of the full likelihood which can be intractable with many species. Moreover, estimation at the quartet-level has the added computational benefit that it is easily parallelizable. Simulation studies comparing our method to a full likelihood approach show that our pseudolikelihood approach is much faster without compromising accuracy. We applied our method to reconstruct the evolutionary relationships among swordtails and platyfishes ($Xiphophorus$: Poeciliidae), which is characterized by widespread hybridizations

Does trading volume really explain stock returns volatility?

Assuming that the variance of daily price changes and trading volume are both driven by the same latent variable measuring the number of price-relevant information arriving on the market, the Mixture of Distribution Hypothesis (MDH) represents an intuitive and appealing explanation for the empirically observed correlation between volume and volatility of speculative assets. This paper investigates to which extent the temporal dependence of volatility and volume is compatible with a MDH model through a systematic analysis of the long memory properties of power transformations of both series. It is found that the fractional differencing parameter of the volatility series reaches its maximum for a power transformation around and then decreases for other order moments while the differencing parameter of the trading volume remains remarkably unchanged. The volatility process thus exhibits a high degree of intermittence whereas the volume dynamic appears much smoother. The results suggest that volatility and volume may share common short-term movements but that their long-run behavior is fundamentally different.Volatility Persistence, Long Memory, Trading Volume

Economic feasibility of an experimental octopus fishery in South Africa

Octopus vulgaris was identified as a new marine resource to be commercially exploited through an experimental fishery. A recent policy on developing fisheries in South Africa emphasizes the importance of investigating the economic feasibility of a fishery as part of its management framework. The study reported here generated baseline information necessary in the design of the experimental fishery, giving guidelines as to which vessels, fishing gear and markets would be most feasible. The proposed fishery, gear and vessel type, fishing techniques and expected catch rates are described, the results of market research are outlined, and the cost of fishing is estimated. The potential business should consist of small and medium-sized vessels deploying unbaited pots attached to long lines. The longline pot fishery could be economically feasible, provided a 30 percent catch in 6600 pots/month is attained. Only existing, debt-free vessels should be used. The minimum catch per unit effort (CPUE) for various fishing operation scenarios was calculated to determine economic feasibility. This is an estimated minimum CPUE, based on assumptions that cannot be confirmed until the fishery starts. Furthermore, this economic analysis also needs to be assessed by stakeholders with experience of fishery operationsRhodes Centenary issue of: South African Journal of Science

Use of palliative chemotherapy in South Africa: National survey of paediatric oncologists and experience in a single unit

BACKGROUND: Palliative chemotherapy is cancer-directed therapy, which aims at stopping or slowing down the progression of the malignancy even though it may not have any potential for remission or cure. In South Africa, delayed diagnosis of childhood cancer is a common problem for a variety of reasons including lack of health care facilities, transport, information about the disease and delayed presentation due to traditional healer visits or other cultural issues. In patients who present with advanced cancer, or in patients with relapsed cancer without realistic hope of cure, palliative chemotherapy can be offered in an attempt to manage symptoms, improve quality of life and prolong meaningful survival. OBJECTIVES: This research study evaluated South African paediatric oncologists' perspectives and practices regarding the use of chemotherapy in patients with cancer with no realistic hope of cure. The second part of the study described the use of palliative chemotherapy in patients who received treatment at the Steve Biko Academic Hospital Paediatric oncology unit. DESIGN & METHOD: An online survey was conducted among paediatric oncologists in South Africa. The main aims of the questionnaire were to assess paediatric oncologists' considerations around the use of palliative chemotherapy, and then focus on the most recent patients treated with palliative chemotherapy. For the second part of the study, a file review was done of deceased patients who died in the period from January 2012 to December 2018 and who had received palliative chemotherapy as part of their cancer management. We reviewed diagnoses, palliative chemotherapy regimens, timing of initiation and stopping palliative chemotherapy, and whether end of life decisions and discussions were documented. RESULTS: A total of 41 participants completed the survey, giving a response rate of 89%. The majority of the paediatric oncologists were either neutral or agreed that palliative chemotherapy should be considered. The most important treatment aim was to improve quality of life of the patient (92.7% of respondents). The most important considerations when prescribing palliative chemotherapy was to minimise toxicity of the chemotherapy regimen (4.56 mean, SD=0.5 utilising a 5 point scale where 1=not important to 5=very important), and the effectiveness of the chemotherapy (4.37; SD=0.48). Only 19.5% of patients received treatment primarily because parents requested it. According to the oncologists polled, the key considerations were largely achieved in the most recent patient treated with palliative chemotherapy. Individual opinions and preferences concerning recommending palliative chemotherapy differ between paediatric oncologists. Of the 305 patient deaths recorded in the study period, a total of 74 patients had received palliative chemotherapy and were included in the file review. The most common diagnoses were neuroblastoma (18.2%), retinoblastoma (15.6%) and osteosarcoma (14.3%). At the time of diagnosis, the median age of the patients was 6.0 years (range 0.3 to 17.6 years). In 47 patients (63.5%) the disease was deemed incurable at first diagnosis and palliative chemotherapy given from the onset of treatment, while 27 patients (36.5%) were given palliative chemotherapy at relapse. The median time from last palliative chemotherapy to death was 30 days (range 0-742 days). The main documented aim of palliative chemotherapy was to improve symptom control (97.3%) while parents' opinion played an important role in 32.9% of cases. About half of the patients (41 of 74, 55.4%) had documentation of symptomatic improvement. CONCLUSION: Although the overall attitude towards the use of palliative chemotherapy is positive, there is great inter-individual variation between oncologists in opinions and experience. The lack of empirical data to justify recommendations about palliative chemotherapy remains a problem, and the researcher hopes that this study will spark productive discussion and planning towards more structured use of palliative chemotherapy in children with cancer in South Africa. This study shows that many decisions around end of life care and decision-making could be better researched using a quantitative, prospective, interview-based approach. Repeated measurements of the child and family's quality of life and its associations with palliative chemotherapy should be a research priority in future

The life world of a ten-year-old child born with HIV

M.Ed. (Educational Psychology)Please refer to full text to view abstrac