Longitudinal inverted compressibility in super-strained metamaterials

We develop a statistical physics theory for solid-solid phase transitions in which a metamaterial undergoes longitudinal contraction in response to increase in external tension. Such transitions, which are forbidden in thermodynamic equilibrium, have recently been shown to be possible during the decay of metastable, super-strained states. We present a first-principles model to predict these transitions and validate it using molecular dynamics simulations. Aside from its immediate mechanical implications, our theory points to a wealth of analogous inverted responses, such as inverted susceptibility or heat-capacity transitions, allowed when considering realistic scales

The value and role of non-invasive prenatal testing in a select South African population

Background. Concerns have been raised about the injudicious use of non-invasive prenatal testing (NIPT) using cell-free DNA (cfDNA), which often leads to inaccuracies in interpretation of the role and value of cfDNA in prenatal screening.Objective. To determine the value and role of NIPT in a select South African (SA) population.Methods. A retrospective review of patients who elected to have NIPT between 1 October 2013 and 30 June 2015 at the Morningside Mediclinic Maternal and Fetal Medicine Centre in Johannesburg, SA. Patients had NIPT after either combined first-trimester screening (CFTS) or a second-trimester ultrasound scan. Data were collected on details of the first- and/or second-trimester screening, results of the NIPT, invasive tests done, decisions made in the event of abnormal results, and pregnancy outcomes.Results. Overall, 3 473 first- and second-trimester fetal assessments were done at the centre during the study period, and 2.3% of patients (n=82) elected to have NIPT. The majority of these individuals elected to have NIPT on the basis of positive findings on CFTS, or markers of aneuploidy detected on a second-trimester ultrasound scan. Of the tests done, 97.6% produced results. Of those with no results, one did not meet quality metrics and the other had a low fetal fraction of cfDNA. There were two abnormal NIPT results, one indicating a high risk of trisomy 13 and the other a triploidy. Patients who screened negative elected not to have an invasive test.Conclusion. The value of NIPT in this study was that it made it possible to avoid a number of invasive tests. NIPT had a role in contingency screening

Angle-resolved photoemission study of the role of nesting and orbital orderings in the antiferromagnetic phase of BaFe2As2

We present a detailed comparison of the electronic structure of BaFe2As2 in its paramagnetic and antiferromagnetic (AFM) phases, through angle-resolved photoemission studies. Using different experimental geometries, we resolve the full elliptic shape of the electron pockets, including parts of dxy symmetry along its major axis that are usually missing. This allows us to define precisely how the hole and electron pockets are nested and how the different orbitals evolve at the transition. We conclude that the imperfect nesting between hole and electron pockets explains rather well the formation of gaps and residual metallic droplets in the AFM phase, provided the relative parity of the different bands is taken into account. Beyond this nesting picture, we observe shifts and splittings of numerous bands at the transition. We show that the splittings are surface sensitive and probably not a reliable signature of the magnetic order. On the other hand, the shifts indicate a significant redistribution of the orbital occupations at the transition, especially within the dxz/dyz system, which we discuss

Cervical length at 23 weeks' gestation - relation to demographic characteristics and previous obstetric history in South African women

Objectives. To determine the distribution of cervical length in a routine population of singleton  pregnancies; to examine the relationship between cervical length, demographic characteristics, and previous obstetric history; and to compare these data with data from a similar study undertaken in the UK.Patients and methods. The study was conducted among women attending routine antenatal clinics at  Coronation, Johannesburg General and Chris Hani Baragwanath hospitals. Cervical length was measured by means of transvaginal ultrasound at 23 weeks' gestation in women with singleton pregnancies attending these clinics, as part of a multicentre randomised trial investigating the value of cerclage in a short cervix. The distribution of cervical length was determined and the significance of differences in median cervical lengths between subgroups was calculated according to maternal age, ethnic origin, maternal body mass index (BMI), cigarette smoking, alcohol intake, and previous obstetric history.Results. Cervical screening was offered to women (N = 2 173) attending clinics for a 23-week scan during the study period (July 1999- September 2002). Most women (N = 1 920) accepted, while 253 declined. Complete outcomes (date and mode of delivery; gestation at delivery, birth weight, Apgar scores,  maternal blood loss, whether the patient was cerclaged or not, and any complications) were obtained for 1 603 women who accepted screening. Cervical length was measured successfully in all cases. Median cervical length was 33.7 mm and in 64 cases (3.3%) the length was 15 mm or less. Significantly shorter cervical lengths were found in those with a history of previous miscarriage, preterm delivery, those aged less than 20 years and those with an abnormal BMI. Cervical length was not significantly shorter in black women than in coloured and white women.Conclusions. At 23 weeks' gestation the median cervical length in a South African population was 33.2 mm. In 3.3% of the population the length was 15 mm. There was an association between cervical length, demographic characteristics and previous obstetric history

How can we reduce the risk of mother-to-child transmission of HIV during invasive obstetric procedures?

Antenatal invasive obstetric procedures may be diagnostic or therapeutic, and are performed at different stages of pregnancy for various indications. The most common indication for an invasive procedure during pregnancy is for fetal karyotyping when a chromosomal abnormality or a genetic defect is suspected, either from the couple’s history or from ultrasound assessment of the fetus. Other less common but equally important indications may be diagnostic (fetoscopy, fetal tissue sampling, estimation of fetal haemoglobin) or therapeutic (aspiration of various fetal cavities, fetal blood transfusion and embryo reductions). In a high HIV prevalence setting like South Africa, a significant proportion of pregnant women in need of invasive procedures will be HIV-infected

Case Report: Delayed presentation and diagnosis of metastatic hepatocellular carcinoma in pregnancy

Hepatocellular carcinoma (HCC) is rare in women of reproductive age. If diagnosed, the underlying cirrhosis is associated with infertility in the majority of cases. There is limited literature on HCC in pregnancy, even more so for cases of metastatic disease. We present a case of delayed presentation and diagnosis of metastatic HCC in pregnancy. A 30-year-old pregnant woman presented at 23 weeks’ gestation and was diagnosed as HIV-infected, with anaemia. She was initiated on an efavirenz-based fixed-dose combination and oral haematinics. She subsequently presented at 32 weeks’ gestation with dyspnoea, and was diagnosed with pre-eclampsia. She was also found to have hepatosplenomegaly and ascites. She went into spontaneous preterm labour at 32 weeks and 4 days. A diagnosis of metastatic HCC was made postpartum, based on the radiological findings and biochemistry. We discuss the challenges of diagnosing metastatic HCC in pregnancy

Cerebral Palsy and Criteria Implicating Intrapartum Hypoxia in Neonatal Encephalopathy – An Obstetric Perspective for the South African Setting

The science surrounding cerebral palsy indicates  that it is a complex medical condition with multiple contributing variables and factors, and causal pathways are often extremely difficult to delineate. The pathophysiological processes are often juxtaposed on antenatal factors, genetics, toxins, fetal priming, failure of neuroscientific autoregulatory mechanisms, abnormal biochemistry and abnormal metabolic pathways. Placing this primed compromised compensated brain through the stresses of an intrapartum process could be the final straw in the pathway  to brain injury and later CP.  It is thus simplistic to base causation of cerebral palsy on only an intrapartum perspective with radiological ‘confirmation’, as is often the practice in medicolegal cases in South African courts. The present modalities (MRI and CTG when available) that retrospectively attempt to determine causation in courts are inadequate when used in isolation. Unless a holistic scientific review of the case including all contributing clinical factors (antepartum, intrapartum and neonatal), fetal heart rate monitoring, neonatal MRI if possible (and preferred) or late MRI, and histology (placental histology if performed) are taken into account, success for plaintiff or defendant currently in a court of law will depend on eloquent legal argument rather than true scientific causality. The 10 criteria set out in this document to implicate acute intrapartum hypoxia in hypoxic ischaemic encephalopathy/neonatal encephalopathy serve as a guideline in the medicolegal setting