The strength and stiffness of geocell support packs

In the last couple of decades, geocell reinforced soil systems have been used in challenging new applications. Although the widely different application of cellular confinement systems demand a better understanding of the fundamental behaviour of the functioning of the cellular reinforced soil systems, surprisingly little research on the fundamental behaviour of the structures and the interaction of the components has been done. A research project has been initiated at the University of Pretoria and this thesis constitutes the first step in achieving an understanding in the functioning of geocell reinforced soil systems. This thesis is focused specifically on the geocell support pack I configuration. However, the research output is not limited to this configuration and may find wider application. The support packs were studied at a width to height ratio of 0.5. The fill material used in this study is classified gold tailings from the Witwatersrand Complex and the geocell membranes were manufactured from a thin (nominal thickness of 0.2 mm) High Density Polyethylene (HDPE) sheet. This study provides an understanding of the functioning of the geocell support pack by studying the constitutive behaviour of the fill and membrane material and their interaction, as well as the influence of multiple cells on the composite structures. The behaviour of the classified tailings material is interpreted in terms of Rowe's stress-dilatancy theory and a simple robust constitutive model for the material behaviour is developed. The stress-strain behaviour of the HDPE membranes is strain-rate-dependent and two simple mathematical models for the strain-rate-dependent stress-strain behaviour of the membranes are developed. An analytical calculation procedure for obtaining the stress-strain behaviour of the fill confined with a single geocell is developed with which some of the shortcomings of the previously presented theories are addressed. This procedure uses the models for the fill and membrane behaviour developed as part of this study. The interaction of adjacent cells in a multiple cell geocell structure, influences its behaviour. This thesis shows that, with exception of low axial strain levels, the efficiency of a structure consisting of multiple cells of a certain size is lower than a single cell structure with the same cell size and fill. These results are contrary to previously published opinion. A method for quantifying the efficiency of a multiple cell pack is also developed.Thesis (PhD (Geotechnical Engineering))--University of Pretoria, 2006.Civil Engineeringunrestricte

Thyroid peroxidase antibodies during early gestation and the subsequent risk of first onset postpartum depression:A prospective cohort study

BackgroundDuring the postpartum period, women are at risk for the new onset of both auto-immune thyroid disorders and depression. The presence of thyroid peroxidase antibodies (TPO-ab) during early gestation is predictive for postpartum auto-immune thyroid dysfunction. The aim of this study was to investigate the association between TPO-ab status during early gestation and first-onset postpartum depression.MethodsProspective cohort study (n = 1075) with follow-up during pregnancy up to one year postpartum. Thyroid function and TPO-ab status were measured during early gestation. Depressive symptomatology was assessed during each trimester and at four time points postpartum with the Edinburgh Depression Scale (EDS). Women with antenatal depression were not eligible for inclusion. Self-reported postpartum depression was defined with an EDS cut-off of ≥ 13.ResultsThe cumulative incidence of self-reported first-onset depression in the first postpartum year was 6.3%. A positive TPO-ab status was associated with an increased risk for self-reported first-onset depression at four months postpartum (adjusted OR 3.8; 95% CI 1.3–11.6), but not at other postpartum time points. Prevalence rates of self-reported postpartum depression declined after four months postpartum in the TPO-ab positive group, but remained constant in the TPO-ab negative group.LimitationsDepression was defined with a self-rating questionnaire (EDS).ConclusionsWomen with an increased TPO-ab titer during early gestation are at increased risk for self-reported first-onset depression. The longitudinal pattern of self-reported postpartum depression in the TPO-ab positive group was similar to the typical course of postpartum TPO-ab titers changes. This suggests overlap in the etiology of first-onset postpartum depression and auto-immune thyroid dysfunction. Thyroid function should be evaluated in women with first-onset postpartum depression.<br/

Do stopes contribute to the seismic source?

Parameters such as source location, seismic moment, energy, source size, and stress drop are routinely calculated from mining-induced seismic data. Seismic moment tensors are inverted less routinely because their calculation is more complex and their accuracy depends on the network geometry, among a number of other factors. The models utilized in the source parameter calculations, the most well-known of which is the Brune model, were developed for the global seismicity problem and assume a solid, homogeneous Earth model. However, the tabular orebodies in South African gold and platinum mines are mined extensively and the excavations (stopes) can extend for many kilometres. The seismic source mechanisms on deep-level gold mines are generally compatible with shear failure (Hoffmann et al., 2013), whereas the source mechanisms of events at intermediate-level bord and pillar mines in the platinum district are more compatible with pillar failure and accompanying stope closure (Spottiswoode, Scheepers, and Ledwaba, 2006; Malovichko, van Aswegen, and Clark, 2012). In this paper we investigate the influence of the stope on seismic inversions for the scalar moment, corner frequency/source radius, stress drop through numerical modelling using WAVE3D. The main objective is to determine whether the source parameters calculated from the recorded waveforms are due to a combination of the stope and shearing sources, rather than being related only to a shear source in the host rock. The modelled source is shear rupture in the footwall of a stope. The results show that the stope appears to have an appreciable effect on the seismic inversions. The seismic moment and source radius of the shear source in the stope are larger for the model with a stope compared to the model with no stope. The stress drop for the case with a stope is less than the applied stress drop, which could be an effect of the apparently larger source. This work provides a possible explanation of the second corner frequency often observed in the spectra of seismograms recorded in South Africa platinum mines. This has implications for the accurate determination of source parameters and the assessment of the intensity of shaking in stopes

Dose response relationship between lithium serum levels during pregnancy and birth outcomes

Introduction: Lithium use during pregnancy reduces the risk of mood episodes in the perinatal period for women with bipolar disorder. Some previous studies found deleterious effects of intrauterine lithium exposure on birth outcomes, yet little is known about a dose response relationship. The current study investigated the influence of maternal lithium serum levels on birth outcomes. Methods: This retrospective observational cohort study included women with a bipolar spectrum disorder who were referred to a specialized psychiatric and obstetric outpatient clinic from 2003 to 2019 and used lithium during the entire pregnancy. For 101 pregnancies at least one lithium level during pregnancy was available. A weighted average lithium level was calculated for the entire pregnancy, as well as for each trimester. Detailed information on maternal, obstetric and neonatal outcomes were retrieved from the medical records. Linear and logistic regression models were used to investigate the association between weighted average lithium level and pregnancy duration, birth weight percentiles, preterm birth and large for gestational age births (LGA). In subsequent exploratory analyses, we studied the role of thyroid-stimulating hormone (TSH) and thyroxine (T4) as a mediator in the found associations. Results: The weighted average lithium serum level during pregnancy was negatively associated with pregnancy duration and positively with preterm birth, but not with birth weight percentile or LGA. In exploratory analyses, TSH and T4 did not mediate the association between average lithium serum level and pregnancy duration. Conclusion: The results of this cohort study during pregnancy indicate a dose response relationship between maternal lithium serum levels and pregnancy duration.</p

Fracture banding in caving mines

The Duplancic model of caving is widely accepted in industry and is the framework within which most monitoring and numerical modelling results in caving mines are interpreted. As a result, the damage profile ahead of the cave back is often interpreted as continuously decreasing damage with increasing distance ahead of the cave back. Physical modelling of the caving process performed in a centrifuge did not support this expected behaviour, but instead suggested a discontinuous damage profile ahead of the cave caused by fracture banding. Some support is found in the literature to suggest that the behaviour observed in the models may also be present in the field. This notion is further supported by banding behaviour observed from microseismic monitoring at two block cave mines. Combining the information from the physical models, field observations referred to in the literature, and the microseismic analyses, it is concluded that the Duplancic model needs to be extended to include the phenomenon of fracture banding. It is also reasonable to expect that fracture banding may play a more important role in the caving process than has previously been recognized.http://www.saimm.co.za/journal-papersam2017Civil Engineerin

Adverse Childhood Life Events and Postpartum Psychosis in Bipolar Disorder

Background Women with bipolar disorder are at increased risk of postpartum psychosis. Adverse childhood life events have been associated with depression in the postpartum period, but have been little studied in relation to postpartum psychosis. In this study we investigated whether adverse childhood life events are associated with postpartum psychosis in a large sample of women with bipolar I disorder. Methods Participants were 432 parous women with DSM-IV bipolar I disorder recruited into the Bipolar Disorder Research Network (www.BDRN.org). Diagnoses and lifetime psychopathology, including perinatal episodes, were obtained via a semi-structured interview (Schedules for Clinical Assessment in Neuropsychiatry; Wing et al., 1990) and case-notes. Adverse childhood life events were assessed via self-report and case-notes, and compared between women with postpartum psychosis (n=208) and those without a lifetime history of perinatal mood episodes (n=224). Results There was no significant difference in the rate of any adverse childhood life event, including childhood sexual abuse, or in the total number of adverse childhood life events between women who experienced postpartum psychosis and those without a lifetime history of perinatal mood episodes, even after controlling for demographic and clinical differences between the groups. Limitations Adverse childhood life events were assessed in adulthood and therefore may be subject to recall errors. Conclusions We found no evidence for an association between adverse childhood life events and the occurrence of postpartum psychosis. Our data suggest that, unlike postpartum depression, childhood adversity does not play a significant role in the triggering of postpartum psychosis in women with bipolar disorder

Maternal and infant outcomes associated with lithium use in pregnancy

Background Concerns about teratogenicity and offspring complications limit use of lithium in pregnancy. We aimed to investigate the association between in-utero lithium exposure and risk of pregnancy complications, delivery outcomes, neonatal morbidity and congenital malformations. Methods Meta-analysis of primary data analyzed using a shared protocol. Six study sites participated: Denmark, Canada, Netherlands, Sweden, UK, and US, totaling 727 lithium-exposed pregnancies compared to 21,397 reference pregnancies in mothers with a mood disorder, but unexposed to lithium. Main outcome measures included: (1) pregnancy complications, (2) delivery outcomes, (3) neonatal readmission to hospital within 28 days of birth, and (4) congenital malformations (major malformations and cardiac malformations). Adjusted odds ratios (ORs) and 95% confidence intervals (CIs) were generated using logistic regression models. Site-specific prevalence rates and ORs were pooled using random-effects meta-analytic models. Findings Lithium exposure was not associated with any of the pre-defined pregnancy complications or delivery outcomes. There was an increased risk for neonatal readmission in lithium exposed (27·5%) versus reference group (14·3%) (Pooled aOR1·62; 95% CI: 1·12–2·33). Lithium exposure during first trimester was associated with increased risk of major malformations (7·4% versus 4·3%; pooled aOR 1·71, 95% CI: 1·07–2·72). Similarly, more lithium exposed children had major cardiac malformations, albeit not stasticially significant (2·1% versus 1·6%; pooled aOR 1·54, 95% CI: 0·64–3·70). Limitations in our study include: Serum lithium 5 levels were not available, hence no analyses related to dose-response effects could be performed, and residual confounding from e.g. substance abuse cannot be ruled out. Interpretation Treatment decisions must weigh the potential for increased risks, considering both effct sizes and the precision of the estimates, in particular associated with first-trimester lithium use against its effectiveness at reducing relapse

Predictors of severe relapse in pregnant women with psychotic or bipolar disorders

Pregnancy in women with severe mental illness is associated with adverse outcomes for mother and infant. There are limited data on prevalence and predictors of relapse in pregnancy. A historical cohort study using anonymised comprehensive electronic health records from secondary mental health care linked with national maternity data was carried out. Women with a history of serious mental illness who were pregnant (2007–2011), and in remission at the start of pregnancy, were studied; severe relapse was defined as admission to acute care or self-harm. Predictors of relapse were analysed using random effects logistic regression to account for repeated measures in women with more than one pregnancy in the study period. In 454 pregnancies (389 women) there were 58 (24%) relapses in women with non-affective psychoses and 25 (12%) in women with affective psychotic or bipolar disorders. Independent predictors of relapse included non-affective psychosis (adjusted OR = 2.03; 95% CI = 1.16–3.54), number of recent admissions (1.37; 1.03–1.84), recent self-harm (2.24; 1.15–4.34), substance use (2.15; 1.13–4.08), smoking (2.52; 1.26–5.02) and non-white ethnicity (black ethnicity: 2.37; 1.23,4.57, mixed/other ethnicity: 2.94; 1.32,6.56). Women on no regular medication throughout first trimester were also at greater risk of relapse in pregnancy (1.99; 1.05–3.75). There was no interaction between severity of illness and medication status as relapse predictors. Therefore, women with non-affective psychosis and higher number of recent acute admissions are at significant risk of severe relapse in pregnancy. Continuation of medication in women with severe mental illness who become pregnant may be protective

Lithium exposure during pregnancy increases fetal growth

Background: Lithium is an effective treatment in pregnancy and postpartum for the prevention of relapse in bipolar disorder, but there is a lack of knowledge about the potential adverse impact on fetal development. Aims: To investigate the impact of lithium exposure on early fetal growth. Methods: In this retrospective observational cohort study, we included all singleton pregnancies of women using lithium and referred for advanced fetal ultrasound scanning between 1994 and 2018 to the University Medical Centers in Leiden and Rotterdam, the Netherlands (n=119). The Generation R study, a population-based cohort, served as a non-exposed control population from the same geographic region (n=8184). Fetal head circumference, abdominal circumference, femur length, and transcerebellar diameter were measured by ultrasound at 18–22 weeks of gestation. Results: Lithium use during pregnancy was associated with an average increase in head circumference of 1.77 mm (95% confidence interval: 0.53, 3.01), in abdominal circumference of 5.54 mm (95% confidence interval: 3.95, 7.12) and in femur length of 0.59 mm (95% confidence interval: 0.22, 0.96) at 18–22 weeks gestation. Furthermore, lithium use during pregnancy was associated with an average increase in birth weight of 142.43 grams (95% confidence interval: 58.01, 226.89), whereas it was associated with an average decrease of 1.41 weeks in gestational duration (95% confidence interval: −1.78, −1.05). Conclusions: Lithium use during pregnancy was associated with increased fetal growth parameters at 18–22 weeks gestational age and increased birth weight. Furthe

Postpartum psychiatric disorders

Pregnancy is a complex and vulnerable period that presents a number of challenges to women, including the development of postpartum psychiatric disorders (PPDs). These disorders can include postpartum depression and anxiety, which are relatively common, and the rare but more severe postpartum psychosis. In addition, other PPDs can include obsessive–compulsive disorder, post-traumatic stress disorder and eating disorders. The aetiology of PPDs is a complex interaction of psychological, social and biological factors, in addition to genetic and environmental factors. The goals of treating postpartum mental illness are reducing maternal symptoms and supporting maternal–child and family functioning. Women and their families should receive psychoeducation about the illness, including evidence-based discussions about the risks and benefits of each treatment option. Developing effective strategies in global settings that allow the delivery of targeted therapies to women with different clinical phenotypes and severities of PPDs is essential