Measuring the extent of convective cores in low-mass stars using Kepler data: towards a calibration of core overshooting

Our poor understanding of the boundaries of convective cores generates large uncertainties on the extent of these cores and thus on stellar ages. Our aim is to use asteroseismology to consistently measure the extent of convective cores in a sample of main-sequence stars whose masses lie around the mass-limit for having a convective core. We first test and validate a seismic diagnostic that was proposed to probe in a model-dependent way the extent of convective cores using the so-called $r_{010}$ ratios, which are built with $l=0$ and $l=1$ modes. We apply this procedure to 24 low-mass stars chosen among Kepler targets to optimize the efficiency of this diagnostic. For this purpose, we compute grids of stellar models with both the CESAM2k and MESA evolution codes, where the extensions of convective cores are modeled either by an instantaneous mixing or as a diffusion process. Among the selected targets, we are able to unambiguously detect convective cores in eight stars and we obtain seismic measurements of the extent of the mixed core in these targets with a good agreement between the CESAM2k and MESA codes. By performing optimizations using the Levenberg-Marquardt algorithm, we then obtain estimates of the amount of extra-mixing beyond the core that is required in CESAM2k to reproduce seismic observations for these eight stars and we show that this can be used to propose a calibration of this quantity. This calibration depends on the prescription chosen for the extra-mixing, but we find that it should be valid also for the code MESA, provided the same prescription is used. This study constitutes a first step towards the calibration of the extension of convective cores in low-mass stars, which will help reduce the uncertainties on the ages of these stars.Comment: 27 pages, 15 figures, accepted in A&

An analysis of neonates with surgical diagnoses admitted to the neonatal intensive care unit at Charlotte Maxeke Johannesburg Academic Hospital, South Africa

Background. The burden of neonatal surgical conditions is not well documented in low- to middle-income countries (LMICs). These conditions are thought to be relatively common, with a considerable proportion of neonates admitted to the neonatal intensive care unit (NICU) requiring surgical intervention.Objectives. To review neonates with surgical conditions admitted to the NICU in our hospital setting.Methods. This was a retrospective, descriptive study of neonates with surgical conditions admitted to the NICU at Charlotte Maxeke Johannesburg Academic Hospital (CMJAH), South Africa, between 1 January 2013 and 31 December 2015. The characteristics and survival of these neonates were described using univariate analysis. The NICU at CMJAH is combined with a paediatric intensive care unit, to a total of 15 beds, and serves as a referral unit.Results. Of 923 neonates admitted to the NICU, 319 (34.6%) had primarily surgical conditions. Of these 319 neonates, 205 survived (64.3%). There were 125/319 neonates (39.2%) with necrotising enterocolitis (NEC), 55 of whom survived (55/125; 44.0%), making the presence of NEC significantly associated with poor outcome (p<0.001). Other significant predictors of poor outcome were the patient being outborn (p=0.029); the presence of late-onset sepsis (p<0.001), with Gram-negative organisms (p=0.005); and lesser gestational age (p=0.001) and lower birth weight (p<0.001). Major birth defects were present in 166/319 neonates (52.0%). The abdomen was the most prevalent site of surgery, with 216/258 procedures (83.7%) being abdominal, resulting in a mortality rate of 76/216 (35.2%).Conclusions. Neonates with major surgical conditions accounted for one-third of NICU admissions in the present study. The study highlights the considerable burden placed on paediatric surgical services at a large referral hospital in SA. Paediatric surgical services, with early referral and improvement of neonatal transport systems, must be a priority in planned healthcare interventions to reduce neonatal mortality in LMICs

Developmental outcome of very low birth weight infants in a developing country

Background: Advances in neonatal care allow survival of extremely premature infants, who are at risk of handicap. Neurodevelopmental follow up of these infants is an essential part of ongoing evaluation of neonatal care. The neonatal care in resource limited developing countries is very different to that in first world settings. Follow up data from developing countries is essential; it is not appropriate to extrapolate data from units in developed countries. This study provides follow up data on a population of very low birth weight (VLBW) infants in Johannesburg, South Africa. Methods: The study sample included all VLBW infants born between 01/06/2006 and 28/02/2007 and discharged from the neonatal unit at Charlotte Maxeke Johannesburg Academic Hospital (CMJAH). Bayley Scales of Infant and Toddler Development Version 111 (BSID) 111 were done to assess development. Regression analysis was done to determine factors associated with poor outcome. Results: 178 infants were discharged, 26 were not available for follow up, 9 of the remaining 152 (5.9%) died before an assessment was done; 106 of the remaining 143 (74.1%) had a BSID 111 assessment. These 106 patients form the study sample; mean birth weight and mean gestational age was 1182 grams (SD: 197.78) and 30.81 weeks (SD: 2.67) respectively. The BSID (111) was done at a median age of 16.48 months. The mean cognitive subscale was 88.6 (95% CI: 85.69-91.59), 9 (8.5%) were < 70, mean language subscale was 87.71 (95% CI: 84.85-90.56), 10 (9.4%) < 70, and mean motor subscale was 90.05 (95% CI: 87.0-93.11), 8 (7.6%) < 70. Approximately one third of infants were identified as being at risk (score between 70 and 85) on each subscale. Cerebral palsy was diagnosed in 4 (3.7%) of babies. Factors associated with poor outcome included cystic periventricular leukomalacia (PVL), resuscitation at birth, maternal parity, prolonged hospitalisation and duration of supplemental oxygen. PVL was associated with poor outcome on all three subscales. Birth weight and gestational age were not predictive of neurodevelopmental outcome. Conclusion: Although the neurodevelopmental outcome of this group of VLBW infants was within the normal range, with a low incidence of cerebral palsy, these results may reflect the low survival of babies with a birth weight below 900 grams. In addition, mean subscale scores were low and one third of the babies were identified as "at risk", indicating that this group of babies warrants long-term follow up into school going age

Serum procalcitonin as an early marker of neonatal sepsis

Background. It has recently been suggested that procalcitonin (PCT) is of value in the diagnosis of neonatal sepsis, with varying results. This study was to evaluate the role of PCT as a single early marker of neonatal sepsis. Setting. Neonatal Unit, Johannesburg Hospital, and Microbiology Laboratory, National Health Laboratory Service (NHLS), South Africa. Subjects and methods. Neonates undergoing evaluation for sepsis between April and August 2002 were eligible for inclusion. Patients were categorised into ‘no infection', ‘possible infection' and ‘definite infection' on the basis of C-reactive protein (CRP), white cell count (WCC), platelet count and blood culture results. PCT was correlated with infection categories. Results. One hundred and eighty-three neonates were enrolled. One hundred and eighteen had no infection, 52 possible infection and 13 definite infection. PCT differed significantly among infection categories (p < 0.0001) and correlated significantly with CRP at presentation (correlation coefficient 0.404, p < 0.001) and CRP at 24 hours (correlation coefficient 0.343, p < 0.001). PCT predicted 89.5% of definite infection. Receiver operating characteristic (ROC) analysis for PCT to predict definite infection showed odds ratio (OR) 1.145 (95% confidence interval (CI): 1.05 - 1.25) with an area under the curve of 0.778. PCT had a negative predictive value of 0.95 (95% CI: 0.915 - 0.988) for definite infection. Conclusions. Although PCT was significantly related to the category of infection, it is not sufficiently reliable to be the sole marker of neonatal sepsis. PCT would be useful as part of a full sepsis evaluation, but is relatively expensive. A negative PCT on presentation may rule out sepsis, but this needs to be evaluated further. S Afr Med J 2004; 94: 851-854

Seismic detection of acoustic sharp features in the CoRoT target HD49933

The technique of determining the acoustic location of layers of sharp changes in the sound speed inside a star from the oscillatory signal in its frequencies is applied on a solar-type star, the CoRoT target, HD49933. We are able to determine the acoustic depth of the second helium ionisation zone of HD49933 to be 794 +55/-68 seconds. The acoustic depth of the base of the convective zone is found to be 1855 +173/-412 seconds where the large error bars reflect the ambiguity in the result, which is difficult to determine with present precision on the frequencies because of the intrinsically weak nature of the signal. The positions of both these layers are consistent with those in a representative stellar model of HD49933.Comment: Accepted for publication in Astronomy & Astrophysic

Developmental outcome of very low birth weight infants in a developing country

BACKGROUND: Advances in neonatal care allow survival of extremely premature infants, who are at risk of handicap. Neurodevelopmental follow up of these infants is an essential part of ongoing evaluation of neonatal care. The neonatal care in resource limited developing countries is very different to that in first world settings. Follow up data from developing countries is essential; it is not appropriate to extrapolate data from units in developed countries. This study provides follow up data on a population of very low birth weight (VLBW) infants in Johannesburg, South Africa. METHODS: The study sample included all VLBW infants born between 01/06/2006 and 28/02/2007 and discharged from the neonatal unit at Charlotte Maxeke Johannesburg Academic Hospital (CMJAH). Bayley Scales of Infant and Toddler Development Version 111 (BSID) 111 were done to assess development. Regression analysis was done to determine factors associated with poor outcome. RESULTS: 178 infants were discharged, 26 were not available for follow up, 9 of the remaining 152 (5.9%) died before an assessment was done; 106 of the remaining 143 (74.1%) had a BSID 111 assessment. These 106 patients form the study sample; mean birth weight and mean gestational age was 1182 grams (SD: 197.78) and 30.81 weeks (SD: 2.67) respectively. The BSID (111) was done at a median age of 16.48 months. The mean cognitive subscale was 88.6 (95% CI: 85.69 - 91.59), 9 (8.5%) were < 70, mean language subscale was 87.71 (95% CI: 84.85 - 90.56), 10 (9.4%) < 70, and mean motor subscale was 90.05 (95% CI: 87.0 - 93.11), 8 (7.6%) < 70. Approximately one third of infants were identified as being at risk (score between 70 and 85) on each subscale. Cerebral palsy was diagnosed in 4 (3.7%) of babies. Factors associated with poor outcome included cystic periventricular leukomalacia (PVL), resuscitation at birth, maternal parity, prolonged hospitalisation and duration of supplemental oxygen. PVL was associated with poor outcome on all three subscales. Birth weight and gestational age were not predictive of neurodevelopmental outcome. CONCLUSION: Although the neurodevelopmental outcome of this group of VLBW infants was within the normal range, with a low incidence of cerebral palsy, these results may reflect the low survival of babies with a birth weight below 900 grams. In addition, mean subscale scores were low and one third of the babies were identified as "at risk", indicating that this group of babies warrants long-term follow up into school going age

Solar-like oscillations with low amplitude in the CoRoT target HD 181906

Context: The F8 star HD 181906 (effective temperature ~6300K) was observed for 156 days by the CoRoT satellite during the first long run in the centre direction. Analysis of the data reveals a spectrum of solar-like acoustic oscillations. However, the faintness of the target (m_v=7.65) means the signal-to-noise (S/N) in the acoustic modes is quite low, and this low S/N leads to complications in the analysis. Aims: To extract global variables of the star as well as key parameters of the p modes observed in the power spectrum of the lightcurve. Methods: The power spectrum of the lightcurve, a wavelet transform and spot fitting have been used to obtain the average rotation rate of the star and its inclination angle. Then, the autocorrelation of the power spectrum and the power spectrum of the power spectrum were used to properly determine the large separation. Finally, estimations of the mode parameters have been done by maximizing the likelihood of a global fit, where several modes were fit simultaneously. Results: We have been able to infer the mean surface rotation rate of the star (~4 microHz) with indications of the presence of surface differential rotation, the large separation of the p modes (~87 microHz), and therefore also the ridges corresponding to overtones of the acoustic modes.Comment: Paper Accepted to be published in A&A. 10 Pages, 12 figure

Electromagnetic transition form factors of negative parity nucleon resonances

We have calculated the transition form factors for the electromagnetic excitation of the negative parity resonances of the nucleon using different models previously proposed and we discuss their results and limits by comparison with experimental data.Comment: 13 pages, 6 figures, to be published on Journal of Physics

A prospective observational study of developmental outcomes in survivors of neonatal hypoxic ischaemic encephalopathy in South Africa

Background. Neonatal hypoxic ischaemic encephalopathy (NHIE) is an important cause of long-term handicap in survivors. There is limited information on the burden of handicap from NHIE in sub-Saharan Africa.Objectives. To determine the developmental outcomes in survivors of NHIE in South Africa (SA).Methods. In this prospective observational study, the developmental outcomes in 84 infants who had survived hypoxic ischaemic encephalopathy (the NHIE group) were compared with those in 64 unaffected infants (the control group). The Bayley Scales of Infant Development version III were used for assessment of developmental outcomes.Results. Significant differences were found between the developmental outcomes of the two groups, with a significantly lower composite language score and higher proportions with language, motor and cognitive developmental delays in the NHIE group than in the control group. Cerebral palsy (CP) was present in 13 of the infants with NHIE (15.5%) and none in the control group (p&lt;0.001). CP was associated with developmental delay, and also with the severity of NHIE. Therapeutic hypothermia (TH) was administered in 58.3% of the study group, but although it was associated with lower rates of CP and developmental delay than in the group without TH, the only significant difference was for delay on the language subscale.Conclusions. Survivors of NHIE in SA are at risk of poor developmental outcomes.