Direct numerical simulation of free-surface and interfacial flow using the VOF method: cavitating bubble clouds and phase change

Direct Numerical Simulation of two-phase ow is used extensively for engineering research and fundamental fluid physics studies. This study is based on the Volume-Of-Fluid (VOF) method, originally created by Hirt and Nicols. This method has gained increased popularity, especially when geometric advection techniques are used coupled with a planar reconstruction of the interface. The focus of the first part of this work is to investigate the hydrodynamics of isothermal cavitation in large bubble clouds, which originated from a larger study of micro-spalling, conducted by the French CEA. A method to deal with volume-changing vapour cavities, or pores, was formulated and implemented in an existing code, PARIS. The ow is idealized by assuming an inviscid liquid, negligible thermal effects and vanishing vapour pressure. A novel investigation of bubble cloud interaction in an expanding liquid using Direct or Detailed Numerical Simulation is presented. The simulation results reveal a pore competition, which is characterised by the Weber number in the ow. In the second part of the study the governing equations are extended to describe incompressible ow with phase change. The description of the work commences with the derivation of the governing equations. Following this, a novel, geometric based, VOF solution method is proposed. In this method a novel way of advecting the VOF function is invented, which treats both mass and energy conservation in conservative form. New techniques include the advection of the interface in a discontinuous velocity field. The proposed algorithms are consistent and elegant, requiring minimal modifications to the existing code. Numerical experiments demonstrate accuracy, robustness and generality. This is viewed as a significant fundamental development in the use of VOF methods to model phase change

Beyond the debate: Exploring the underlying values and assumptions of biodiversity conservation in protected areas

This dissertation examines the current disagreement among scientists and scholars about best practices for biodiversity conservation in protected areas. There is no clear consensus among the scientific community about the most effective approach to conserve biodiversity and several conflicting positions form part of an ongoing debate in the field. Most disagreements and conflicts are based on differences in the underlying values and assumptions of the parties involved in the conflict. The more we know and understand those underlying values, the more constructive the dialog, and the more likely acceptable policy decisions will be developed. This study, presented in three parts, uncovered some of the major discourses and perspectives that exist in the exchanges in literature. I used discourse analysis and Q-methodology, and then applied a policy sciences framework to suggest practical application. The first part of the study is a discourse analysis of eight works representing the breadth of strongly held opinions about biodiversity conservation and the roles of human inhabitants. The results of the discourse analysis identified some dimensions of the conflict that were used in the interpretation of discourses in the subsequent Q-study. The second part of the dissertation explored the underlying values and assumptions in biodiversity conservation using Q-methodology. A total of 275 definitive statements were extracted from a survey of the literature and then categorized according to the dimensions identified in the preceding discourse analysis. Twenty two participants, all actively involved in conservation in protected areas, and some authors of the statements used in the procedure, sorted 48 statements on a scale of -5 (Most unlike my point of view) to +5 (Most like my point of view). Following a Q-methodology analysis of the data, three distinct discourses emerged: a Social Justice perspective that emphasizes the need for a fair and just process, a Concern for Biodiversity perspective based on the need to protect biodiversity from human impacts, and a Biodiversity Across the Landscape perspective based on a need to conserve biodiversity beyond protected areas with a concurrent concern that existing free market mechanisms are not adequate to protecting biodiversity. Though there were clear differences in the underlying assumptions of the three perspectives, there were also some areas of agreement, which raises the potential for dialog and collaboration. The final part of the dissertation was an application of a policy sciences framework to illustrate how the different discourses would lead to different perceptions of problem identification, social processes and decision processes. Some directions for future research based on my findings are both practical (e.g., apply Q-methodology to help understand and resolve biodiversity conservation conflict; develop capacity in negotiation and conflict management) and conceptual (e.g., more research on poverty alleviation; more research to demonstrate the economic value of biodiversity conservation). The results of the Q-study suggest that a dialog among stakeholders involved in conservation efforts, based on common understanding of underlying assumptions uncovered in the Q-study, could lead to advances in developing more effective, innovative and creative conservation approaches

Beyond the debate: Exploring the underlying values and assumptions of biodiversity conservation in protected areas

This dissertation examines the current disagreement among scientists and scholars about best practices for biodiversity conservation in protected areas. There is no clear consensus among the scientific community about the most effective approach to conserve biodiversity and several conflicting positions form part of an ongoing debate in the field. Most disagreements and conflicts are based on differences in the underlying values and assumptions of the parties involved in the conflict. The more we know and understand those underlying values, the more constructive the dialog, and the more likely acceptable policy decisions will be developed. This study, presented in three parts, uncovered some of the major discourses and perspectives that exist in the exchanges in literature. I used discourse analysis and Q-methodology, and then applied a policy sciences framework to suggest practical application. The first part of the study is a discourse analysis of eight works representing the breadth of strongly held opinions about biodiversity conservation and the roles of human inhabitants. The results of the discourse analysis identified some dimensions of the conflict that were used in the interpretation of discourses in the subsequent Q-study. The second part of the dissertation explored the underlying values and assumptions in biodiversity conservation using Q-methodology. A total of 275 definitive statements were extracted from a survey of the literature and then categorized according to the dimensions identified in the preceding discourse analysis. Twenty two participants, all actively involved in conservation in protected areas, and some authors of the statements used in the procedure, sorted 48 statements on a scale of -5 (Most unlike my point of view) to +5 (Most like my point of view). Following a Q-methodology analysis of the data, three distinct discourses emerged: a Social Justice perspective that emphasizes the need for a fair and just process, a Concern for Biodiversity perspective based on the need to protect biodiversity from human impacts, and a Biodiversity Across the Landscape perspective based on a need to conserve biodiversity beyond protected areas with a concurrent concern that existing free market mechanisms are not adequate to protecting biodiversity. Though there were clear differences in the underlying assumptions of the three perspectives, there were also some areas of agreement, which raises the potential for dialog and collaboration. The final part of the dissertation was an application of a policy sciences framework to illustrate how the different discourses would lead to different perceptions of problem identification, social processes and decision processes. Some directions for future research based on my findings are both practical (e.g., apply Q-methodology to help understand and resolve biodiversity conservation conflict; develop capacity in negotiation and conflict management) and conceptual (e.g., more research on poverty alleviation; more research to demonstrate the economic value of biodiversity conservation). The results of the Q-study suggest that a dialog among stakeholders involved in conservation efforts, based on common understanding of underlying assumptions uncovered in the Q-study, could lead to advances in developing more effective, innovative and creative conservation approaches

Leading a College as a Liberal Arts Practice

A common and rather prevalent model for leading and planning in higher education is a contest of wills optimizing local, current matters. In contrast, at Colby-Sawyer College, we are explicit, careful, and collaborative about working together respectfully on qualitative and institutional and long-term matters. We hope that the model for leadership that we have provided below, one that demonstrates how we make our decisions and conduct our business in a style that differs from academic political business as usual, will serve as a model for other institutions

The confession of Belhar : a spirituality of reception in the local church

The General Synod of the Dutch Reformed Church took the following decision during October 2011: 'The General Synod decides to make the Confession of Belhar part of its confessional foundation, that is, in terms of its church ordinances, and commission the Moderamen to prepare the necessary processes regarding ecclesiastical law.' This article deals with the perception of, the reception of and resistance against Belhar as confession in a local congregation, Elardus Park. The research also describes how this obstructs the development of missional focus. The main contribution of this article is to argue that the ecumenical concept's full reception should be assessed within the broader framework of building up a missional local church where a spirituality of reception is fully developed in terms of a missional positioning in Africa.L.E.W. (Nederduitse Gereformeerde Kerk Elardus Park) se M-skripsie ‘Die Opbou van ’n Missionale Gemeente en die Resepsie van die Belydenis van Belhar in die NG Gemeente Elarduspark’ is in 2012 voltooi onder leiding van M.N. (Universiteit van Pretoria).http://www.ve.org.zaam201

Direct Numerical Simulations of pore competition in idealized micro-spall

Cavitation and micro-spall appear when a weakly compressible (or expansible) liquid is suddenly submitted to large negative pressures resulting in volume growth. After the initial phases of uniform expansion and pore opening, a longer-lasting phase of pore growth and competition appears, which is especially difficult to investigate either experimentally or numerically [Signor, PhD, 2008]. Thus this study is among the first of its kind. We present here Direct Numerical Simulations (DNS) of this latter phase for idealized conditions relevant to micro-spall: incompressible inviscid fluid, vanishing vapor pressure in cavities, ballistic uniaxial expansion, perturbed Face-Centered-Cubic arrangement of pores. Under these assumptions, the system is characterized by a single dimensionless group, the Weber number based on the number of pores per unit volume. Volume transfer between pores occurs at low enough Weber numbers, a phenomenon designated as ""pore competition"". The pore competition effect is important as it is the main phenomenon driving the evolution in time of the statistical distribution of pore sizes. Small pores shrink and eventually disappear as their volume is transferred to large pores. Pore statistics and pressure evolution profiles can then be obtained for future modelling purposes. The simulations were performed using the volume of fluid method [Tryygvason, Scardovelli & Zaleski, Cambridge, 2011] with the mixed-Youngs-central scheme for normal vector computation and interface segment reconstruction, lagrangian explicit or ""CIAM"" advection, an original adapted first order extrapolation method in the neighborhood of the free surface, and a ghost fluid method for the pressure boundary condition on the free surface. The pressure used in the boundary condition is computed using Laplace's law, which in turn involves surface tension and curvature. Curvature is computed using the height-function method. The method was tested comparing numerical solutions to solutions of the Rayleigh-Plesset equation for oscillating bubbles. An adapted procedure is used to manage the collapsing cavities. A cavity tagging and Lagrangian tracking algorithm is used to retrieve statistics of cavity sizes

Particularized protection: UNSC mandates and the protection of civilians in armed conflict

The protection of civilians at risk in armed conflict has, since the late 1990s, become institutionalized at the United Nations (UN), gaining acceptance as a normative rationale for UN peacekeeping. However, the bulk of civilians in need of protection in armed conflict are unlikely to attain it. The article develops an argument on ‘particularized protection’ - particularized in that UN Security Council (SC) mandates are formulated and adjusted over time to direct mission protection to specific subsets of civilian populations, that is, those relevant to the UN itself, the host state, other states, NGOs and the media, leaving most local civilians receiving little effective protection. Particularized protection, we argue, is a result of the institutional dynamics involving actors producing mandates - the UNSC - and those providing protection - peacekeeping missions - whereby mandates are specified to direct mission protection to selected, particularized groups. We demonstrate these dynamics in two cases, Côte d’Ivoire and Somalia

Risk Factors Associated with Adverse Fetal Outcomes in Pregnancies Affected by Coronavirus Disease 2019 (COVID-19): A Secondary Analysis of the WAPM study on COVID-19

To evaluate the strength of association between maternal and pregnancy characteristics and the risk of adverse perinatal outcomes in pregnancies with laboratory confirmed COVID-19. Secondary analysis of a multinational, cohort study on all consecutive pregnant women with laboratory-confirmed COVID-19 from February 1, 2020 to April 30, 2020 from 73 centers from 22 different countries. A confirmed case of COVID-19 was defined as a positive result on real-time reverse-transcriptase-polymerase-chain-reaction (RT-PCR) assay of nasal and pharyngeal swab specimens. The primary outcome was a composite adverse fetal outcome, defined as the presence of either abortion (pregnancy loss before 22 weeks of gestations), stillbirth (intrauterine fetal death after 22 weeks of gestation), neonatal death (death of a live-born infant within the first 28 days of life), and perinatal death (either stillbirth or neonatal death). Logistic regression analysis was performed to evaluate parameters independently associated with the primary outcome. Logistic regression was reported as odds ratio (OR) with 95% confidence interval (CI). Mean gestational age at diagnosis was 30.6\ub19.5 weeks, with 8.0% of women being diagnosed in the first, 22.2% in the second and 69.8% in the third trimester of pregnancy. There were six miscarriage (2.3%), six intrauterine device (IUD) (2.3) and 5 (2.0%) neonatal deaths, with an overall rate of perinatal death of 4.2% (11/265), thus resulting into 17 cases experiencing and 226 not experiencing composite adverse fetal outcome. Neither stillbirths nor neonatal deaths had congenital anomalies found at antenatal or postnatal evaluation. Furthermore, none of the cases experiencing IUD had signs of impending demise at arterial or venous Doppler. Neonatal deaths were all considered as prematurity-related adverse events. Of the 250 live-born neonates, one (0.4%) was found positive at RT-PCR pharyngeal swabs performed after delivery. The mother was tested positive during the third trimester of pregnancy. The newborn was asymptomatic and had negative RT-PCR test after 14 days of life. At logistic regression analysis, gestational age at diagnosis (OR: 0.85, 95% CI 0.8-0.9 per week increase; p<0.001), birthweight (OR: 1.17, 95% CI 1.09-1.12.7 per 100 g decrease; p=0.012) and maternal ventilatory support, including either need for oxygen or CPAP (OR: 4.12, 95% CI 2.3-7.9; p=0.001) were independently associated with composite adverse fetal outcome. Early gestational age at infection, maternal ventilatory supports and low birthweight are the main determinants of adverse perinatal outcomes in fetuses with maternal COVID-19 infection. Conversely, the risk of vertical transmission seems negligible

Impact of COVID-19 on cardiovascular testing in the United States versus the rest of the world

Objectives: This study sought to quantify and compare the decline in volumes of cardiovascular procedures between the United States and non-US institutions during the early phase of the coronavirus disease-2019 (COVID-19) pandemic. Background: The COVID-19 pandemic has disrupted the care of many non-COVID-19 illnesses. Reductions in diagnostic cardiovascular testing around the world have led to concerns over the implications of reduced testing for cardiovascular disease (CVD) morbidity and mortality. Methods: Data were submitted to the INCAPS-COVID (International Atomic Energy Agency Non-Invasive Cardiology Protocols Study of COVID-19), a multinational registry comprising 909 institutions in 108 countries (including 155 facilities in 40 U.S. states), assessing the impact of the COVID-19 pandemic on volumes of diagnostic cardiovascular procedures. Data were obtained for April 2020 and compared with volumes of baseline procedures from March 2019. We compared laboratory characteristics, practices, and procedure volumes between U.S. and non-U.S. facilities and between U.S. geographic regions and identified factors associated with volume reduction in the United States. Results: Reductions in the volumes of procedures in the United States were similar to those in non-U.S. facilities (68% vs. 63%, respectively; p = 0.237), although U.S. facilities reported greater reductions in invasive coronary angiography (69% vs. 53%, respectively; p < 0.001). Significantly more U.S. facilities reported increased use of telehealth and patient screening measures than non-U.S. facilities, such as temperature checks, symptom screenings, and COVID-19 testing. Reductions in volumes of procedures differed between U.S. regions, with larger declines observed in the Northeast (76%) and Midwest (74%) than in the South (62%) and West (44%). Prevalence of COVID-19, staff redeployments, outpatient centers, and urban centers were associated with greater reductions in volume in U.S. facilities in a multivariable analysis. Conclusions: We observed marked reductions in U.S. cardiovascular testing in the early phase of the pandemic and significant variability between U.S. regions. The association between reductions of volumes and COVID-19 prevalence in the United States highlighted the need for proactive efforts to maintain access to cardiovascular testing in areas most affected by outbreaks of COVID-19 infection