Aerodynamic performance of a fan stage utilizing Variable Inlet Guide Vanes (VIGVs) for thrust modulation

An experimental research program was conducted in the Lewis Research Center's 9x15-foot (2.74x4.57 m) low speed wind tunnel to evaluate the aerodynamic performance of an inlet and fan system with variable inlet guide vanes (VIGVs) for use on a subsonic V/STOL aircraft. At high VIGV blade angles (lower weight flow and thrust levels), the fan stage was stalled over a major portion of its radius. In spite of the stall, fan blade stresses only exceeded the limits at the most extreme flow conditions. It was found that inlet flow separation does not necessarily lead to poor inlet performance or adverse fan operating conditions. Generally speaking, separated inlet flow did not adversely affect the fan blade stress levels. There were some cases, however, at high VIGV angles and high inlet angles-of-attack where excessive blade stress levels were encountered. An evaluation term made up of the product of the distortion parameter, K alpha, the weight flow and the fan pressure ratio minus one, was found to correlate quite well with the observed blade stress results

Thrust modulation methods for a subsonic V/STOL aircraft

Low speed wind tunnel tests were conducted to assess four methods for attaining thrust modulation for V/STOL aircraft. The four methods were: (1) fan speed change, (2) fan nozzle exit area change, (3) variable pitch rotor (VPR) fan, and (4) variable inlet guide vanes (VIGV). The interrelationships between inlet and thrust modulation system were also investigated using a double slotted inlet and thick lip inlet. Results can be summarized as: (1) the VPR and VIGV systems were the most promising, (2) changes in blade angle to obtain changes in fan thrust have significant implications for the inlet, and (3) both systems attained required level of thrust with acceptable levels of fan blade stress

Magnitude of nonlinearities in collisionless magnetoplasma waves

Perturbation technique used for approximate solutions to nonlinear hydromagnetic equations of cold collisionless plasm

Effect of variable inlet guide vanes on the operating characteristics of a tilt nacelle inlet/powered fan model

The effects of a variable inlet guide vane (VIGV) assembly on the operating characteristics of a V/STOL inlet and on the performance of a 20-in. (0.508-m) diameter fan engine were investigated. The data indicate that the VIGVs are effective thrust modulators over a wide range of free-stream velocities, nacelle angles of attack, and fan speeds. The thrust modulation ranges, including choking limits, fan stall limits, and inlet separation boundaries are presented. The presence of the VIGV assembly causes significant losses in inlet angle-of-attack capability and generally increases the blade stress levels at all limit conditions except at high angle of attack and high free-stream velocity. Reducing the fan nozzle exit area limited the positive VIGV actuation range and consequently decreased the range of thrust modulation at all limit conditions except at both high free-stream velocity and high angle of attack conditions

Multiple sports concussion in male rugby players: a neurocognitive and neuroimaging study

Abstract Objective: Following a sport related concussion (SRC) visible symptoms generally dissipate in 7-10 days post-injury. However, little is known about the cumulative effects of SRCs both in terms of structural damage to the white matter of the brain and neurocognitive performance. To address this issue, the relationship between the number of SRCs (frequency), axonal white matter (WM) damage and neurocognitive performance was examined. There were three predictions. First, increases in SRC frequency will be associated with decreases in performance on neurocognitive tests. Second, the frequency of SRC will be associated with axonal injury measured three WM tracts: the corpus callosum, the fronto-occipital fasciculus and the inferior longitudinal fasciculus. Third, less accurate and slower performance on a response inhibition task (STOP-IT) will be associated with greater axonal injury. Methods: A cross-sectional correlational design was utilised. Participants were rugby players with a history of SRC, rugby players with no history of SRC and control athletes (N=40) who completed a neurocognitive test battery and had a DTI brain scan. The neurocognitive battery consisted of the following standardised tests: Speed and Capacity of Language Processing Test, CogState Electronic Battery, Stroop Colour and Word Test, Controlled Oral Word Association Test, the Trail Making Test and the experimental test STOP-IT Electronic Test. White matter axonal injury was measured by DTI using fractional anisotropy (FA) and mean diffusivity (MD) metrics. The DTI data was processed using FSL to extract FA and MD DTI metrics in three a-priori regions of interest. Results: Spearman’s correlation analyses did not find significant associations between SRC frequency and neurocognitive performance on the FAS (rs=0.053, 95% CI [-0.27, 0.36]), TMT-A (rs=0.058, 95% CI [-0.26, 0.37]), TMT-B (rs= -0.046, 95% CI [-0.27, 0.36]) and the Stroop Interference (rs= -0.25, 95% CI [-0.07, 0.52]). Similarly, no significant Spearman’s correlations were found between SRC frequency and the computerised neurocognitive tests STOP-IT-SSRT (rs= -0.04, 95% CI [-0.28, 0.35])), STOP-IT–Accuracy (rs= -0.05, 95% CI [-0.27, 0.36]), CogState Detection subtest (rs= -0.15, 95% CI [-0.17, 0.44]), CogState Identification subtest (rs= -0.065, 95% CI [-0.26, 0.37]), CogState One card learning subtest (rs= 0.24, 95% CI [-0.08, 0.52]) or the CogState One back task subtest (rs= 0.06, 95% CI [-0.26, 0.37]). In terms of the DTI data there were no significant associations between SRC frequency and axonal injury measured by FA values in the CC (rs= 0.005, 95% CI [-0.31, 0.32]), ILF (rs= 0.028, 95% CI [-0.29, 0.34]) or FOF (rs= -0.022, 95% CI [-0.30, 0.33]). The same was pattern was found for MD values in the CC (rs= 0.081, 95% CI [-0.24, 0.39]), ILF (rs= -0.16, 95% CI [-0.16, 0.45]) or FOF (rs= -0.15, 95% CI [-0.17, 0.44]) Finally, there were no significant Spearman’s correlations between axonal injury FA values and the STOP-IT SSRT in any of the ROIs: CC (rs= 0.005, 95% CI [-0.31, 0.32]), ILF (rs= 0.028, 95% CI [-0.29, 0.34]) or FOF (rs= -0.022, 95% CI [-0.30, 0.33]). Equally, there were no significant correlations between MD values STOP-IT SSRT in the CC (rs= -0.028, 95% CI [-0.29, 0.34]), ILF (rs= -0.16, 95% CI [-0.16, 0.45]) or FOF (rs= -0.15, 95% CI [-0.17, 0.44]). Likewise, there were no significant Spearman’s correlations between accuracy on the STOP-IT and FA values and in any of the ROIs: CC (rs= 0.19, 95% CI [-0.13, 0.48]), ILF (rs= -0.045, 95% CI [-0.27, 0.35]) and FOF (rs= -0.032, 95% CI [-0.29, 0.34]), or MD values in the CC (rs= -0.11, 95% CI [-0.21, 0.41]), ILF (rs= 0.017, 95% CI [-0.30, 0.33]) or FOF (rs= 0.082, 95% CI [-0.24, 0.39]). This study did not find support for the hypothesis that cumulative SRCs are associated with poorer performance on neurocognitive tests or with axonal injury as measured by FA and MD DTI metrics. Conclusion: The null findings suggest that there are no cumulative effects of SRCs. The current findings are inconsistent with previous cross-sectional research that indicates that there are long-term changes to diffusivity measures present after single SRCs as well as cumulative effects in contact sport athletes. Likewise they are at odds with evidence suggesting that after three SRCs neurocognitive performance can be affected. The study needs to be extended to include a larger sample to ensure the results are not due to low statistical power

Digital image processing and isostatic studies of the regional gravity field of Great Britain and adjacent marine regions

This thesis presents the results of an investigation into the regional gravity field of Great Britain and the adjacent regions. A prerequisite for this study was the development of a computer database designed to store, manipulate and display the information contained within nearly 400,000 gravity and topography point observations for the region. Digital image processing techniques have been applied to the reduction and display of the Bouguer anomaly data. The observed Bouguer anomaly lineaments display a pattern of geological basement structures which correlates closely with those predicted by recent plate tectonic models of the Lower Palaeozoic Caledonian orogeny which assume the convergence of three distinct continental plates. The nature of the isostatic compensation of the topography in the vicinity of the United Kingdom has been investigated using cross spectral analysis of the gravity and topography. The observed cross spectral relationships are compared with those for a theoretical isostatic model which assumes the lithosphere behaves like a thin elastic plate loaded by both surface topography and internal density contrasts overlying an inviscid fluid substratum. For a uniform elastic thickness of the continental lithosphere the best fit between the observed and theoretical relationships is obtained for values of the elastic thickness of the lithosphere of 22.5-24.5 km. A better fit is obtained if the continental lithosphere is assumed to comprise a population of distinct tectonic provinces of equal area with the values of the elastic thickness of the lithosphere for the provinces distributed uniformly between 6-8 km and 86-90 km. Detailed investigations into the structure of the crust beneath the Tertiary igneous complexes of Mull and Skye, northwest Scotland, indicate a possible slight thickening of the crust which is considered to be an important consequence of the mechanism of the emplacement of the complexes

A description of the mental health outcomes of HIV positive adolescents accessing care in Johannesburg

A thesis completed by published work. Submitted to the School of Clinical Medicine, Faculty of Health Sciences, University of the Witwatersrand, in fulfillment of the requirements for the degree of Doctor of Philosophy. johannesburg, South Africa. September, 2017.Background: Adolescents living with HIV are an emerging group in the global HIV/AIDS epidemic. Mental health in this population impacts HIV care, treatment, consequential morbidity and secondary transmission. Perinatally infected HIV positive adolescents (PIA) have high prevalence of mental health disorders; loss and bereavement are particularly pervasive in their lives, however little is known about the mental health of PIA retained in care in South Africa. How PIA beliefs concerning their HIV infection are affected by the cumulative effect of bereavement (particularly of parents), the failure to disclose to them the cause of death and the manner in which they learn their own HIV positive status, is a subject understudied. Similarly, there is a paucity of research on effective ways to manage such bereavement. Resilience, or positive adaptation to challenging situations, may be particularly important for PIA, who are exposed to significant stigma, risks and stressors. However, there is limited research regarding adolescents in South Africa, partly because section 71 of the National Health Act (NHA) requires parental or guardian's consent. This presents a significant barrier to research on HIV infected adolescents aged under 18 years. The aim of this research is to describe the mental health of HIV positive adolescents (13-19 years) accessing care and treatment in Johannesburg and generate evidence to inform mental health policy for this population in South Africa. The study describes the mental health outcomes of this population with a focus on how bereavement and disclosure impacts on mental health, as well as how resilience is manifest in this group. Methods: Prior to commencement of the research, an order was obtained from the High Court in Johannesburg as upper guardian of minor children for the statutory parental or guardian’s consent. For the thesis, data from three studies are presented in five published papers. These studies were conducted using a combination of qualitative and quantitative techniques resulting in a mixed methods study design. For the quantitative study, HIV positive adolescents aged 13-19 years (n=343) accessing five pediatric antiretroviral clinics in Johannesburg were assessed using standardized measures for depression (Children’s Depression Inventory), anxiety (Children’s Manifext Anxiety Scale), post traumatic stress disorder (PTSD) (Child PTSD Checklist) and suicidality (MINI International Psychiatric Interview). In addition to mental health, the survey captured information regarding HIV, sexual reproductive health and coping. Descriptive and bivariate analyses were conducted on all variables using Statistica v13. Two qualitative studies were conducted. The first purposively selected 25 participants from the larger study. The aim was to identify elements of resilience through in-depth interviews in this group of PIA. The second identified the most and least symptomatic participants (n=26) from the larger cohort on scores for mental health (depression, anxiety, post traumatic stress disorder, suicidality). Drawings and written accounts of the loss of a significant attachment figure of participants were assessed and compared by professionals (art therapists, psychologists, social workers and counsellors) in three focus group discussions. The goal of this study was to understand the influence of bereavement on mental health and the use of drawing and writing in expressing the experience of loss. Data were analysed in NVIVO 10 using a thematic approach to coding. The final paper details the process of obtaining ethical approval for research with adolescents in public health facilities through a case study (this PhD). Results: Of the enrolled 343 participants, 27% were symptomatic for depression, anxiety or PTSD; 24% reported suicidality. Results indicated high rates of comorbidity amongst depression, anxiety and PTSD. Females scored significantly higher for depression (p<.001), anxiety (p<.01), and PTSD (p<.001) than males. Those reporting suicidality also reported significantly higher on all three mental health scales suggesting that suicidal individuals are more likely to present with higher levels of depression (p<.001), anxiety (p<.001) and PTSD (p<.001). Almost 90% did not feel that they belonged in the family with which they lived. Peer violence was significantly correlated to all mental health problems, also hunger, being inappropriately touched, being hit and being female. High exposure to violence was evident and not feeling safe at home or in community increased risk for all mental health disorders. Knowing one’s HIV status, however, was protective as was having dreams for the future. The qualitative studies highlighted that despite marked stressors in the lives of these adolescents, a high degree of resilience was described. Characteristics of resilience in this group included a pertinent set of beliefs, including a belief in fate and recognition of personal strength as a consequence of managing adversity. Character traits such as a pragmatic acceptance about one’s life, actively taking responsibility, and a robust self-esteem were evident. Social behaviours included the ability to pursue and access adults and healthcare to meet developmental needs, having a desire to support and help others and challenging HIV related stigma. These characteristics were underscored by the capacity for self-reflection. The studies also revealed that PIA have limited understanding of how they became infected, vertical transmission and potential benefits of PMTCT to their future reproductive needs, despite disclosure. Most participants were experiencing complicated grieving which was impacting negatively on their mental health, ability to accept their HIV status and adhere to treatment. The drawings and written accounts of the qualitative study accentuated contextual deprivation, including high exposure to multiple and consistent losses of significant attachment figures. They also pointed to emotional deprivation and impoverishment, including unresolved complicated grieving. Views from participants emphasized missed opportunities, including failure to address the mental health concerns of this population at risk. The case study suggested that without court intervention, most of the participants, being orphans without guardians, could not have participated in the research because the statutory consent was otherwise impossible. This case study argues for exceptions to the parental consent requirement, by reason of the exclusion of Orphaned and Vulnerable Children and Youth (OVCY) from research. Inconsistent and confusing legal policy that inadvertently silences voices that most need to be heard, as well as law that is inconsistent with principles of justice, inclusiveness and autonomy, are put forward to argue for a change to the National Health Act. Conclusion: HIV positive adolescents accessing care demonstrate high levels of mental health problems that are largely unrecognized and could potentially be addressed within health systems. Recognition of mental health challenges in PIA is crucial to effective HIV care and treatment and providers need to be sufficiently sensitized to this reality. PIA need improved communication regarding vertical transmission and PMTCT to properly understand their HIV status and engage effectively in management. Honest communication about how relatives died and disclosure of HIV status is necessary to reduced stigma, complicated grieving and improve mental health. The impact of unprocessed loss early in life has long-term negative consequences for PIA. Innovative methods are required to address unmet mental health needs of this patient population. The use of non-verbal methods (drawing and writing) by healthcare professionals could be especially valuable to both patient and provider, particularly in the case of managing bereavement. PIA, who face high levels of hardship and change, nevertheless exhibit strong resiliency beliefs, traits, and behaviours. Healthcare environments have the potential to be utilized as powerful resources in fostering resilience in PIA, if characteristics of adolescent resilience are integrated into prevention and intervention programming. Finally, a balance is required between protecting adolescents from exploitation and permitting access to benefits of research. Mandating parental consent for all research does not necessarily give effect to policy. For the vast majority of South African HIV infected adolescents parental consent is not possible. Adolescents are understudied and poorly understood and although these laws are there to protect this vulnerable group, it also makes them and their problems less visible. In order to scale up interventions, careful consideration needs to be placed on how the laws can help researchers benefit adolescents. Section 71 of the National Health Act ought to be amended to facilitate valuable and necessary research concerning HIV infected orphan children and adolescents. Keywords: perinatal HIV infection, HIV positive adolescents, vulnerable youth, mental health, healthcare system, disclosure, violence, orphan, bereavement, complicated grief, drawing, resilience, research, National Health ActLG201