Impact of Simulated 1/f Noise for HI Intensity Mapping Experiments

Cosmology has entered an era where the experimental limitations are not due to instrumental sensitivity but instead due to inherent systematic uncertainties in the instrumentation and data analysis methods. The field of HI intensity mapping (IM) is still maturing, however early attempts are already systematics limited. One such systematic limitation is 1/f noise, which largely originates within the instrumentation and manifests as multiplicative gain fluctuations. To date there has been little discussion about the possible impact of 1/f noise on upcoming single-dish HI IM experiments such as BINGO, FAST or SKA. Presented in this work are Monte-Carlo end-to-end simulations of a 30 day HI IM survey using the SKA-MID array covering a bandwidth of 950 and 1410 MHz. These simulations extend 1/f noise models to include not just temporal fluctuations but also correlated gain fluctuations across the receiver bandpass. The power spectral density of the spectral gain fluctuations are modelled as a power-law, and characterised by a parameter $\beta$. It is found that the degree of 1/f noise frequency correlation will be critical to the success of HI IM experiments. Small values of $\beta$ ($\beta$ < 0.25) or high correlation is preferred as this is more easily removed using current component separation techniques. The spectral index of temporal fluctuations ($\alpha$) is also found to have a large impact on signal-to-noise. Telescope slew speed has a smaller impact, and a scan speed of 1 deg s$^{-1}$ should be sufficient for a HI IM survey with the SKA.Comment: 22 pages, 15 figures, 2 table

Evaluating weaknesses of "perceptual-cognitive training" and "brain training" methods in sport: An ecological dynamics critique

The recent upsurge in "brain training and perceptual-cognitive training," proposing to improve isolated processes, such as brain function, visual perception, and decision-making, has created significant interest in elite sports practitioners, seeking to create an "edge" for athletes. The claims of these related "performance-enhancing industries" can be considered together as part of a process training approach proposing enhanced cognitive and perceptual skills and brain capacity to support performance in everyday life activities, including sport. For example, the "process training industry" promotes the idea that playing games not only makes you a better player but also makes you smarter, more alert, and a faster learner. In this position paper, we critically evaluate the effectiveness of both types of process training programmes in generalizing transfer to sport performance. These issues are addressed in three stages. First, we evaluate empirical evidence in support of perceptual-cognitive process training and its application to enhancing sport performance. Second, we critically review putative modularized mechanisms underpinning this kind of training, addressing limitations and subsequent problems. Specifically, we consider merits of this highly specific form of training, which focuses on training of isolated processes such as cognitive processes (attention, memory, thinking) and visual perception processes, separately from performance behaviors and actions. We conclude that these approaches may, at best, provide some "general transfer" of underlying processes to specific sport environments, but lack "specificity of transfer" to contextualize actual performance behaviors. A major weakness of process training methods is their focus on enhancing the performance in body "modules" (e.g., eye, brain, memory, anticipatory sub-systems). What is lacking is evidence on how these isolated components are modified and subsequently interact with other process "modules," which are considered to underlie sport performance. Finally, we propose how an ecological dynamics approach, aligned with an embodied framework of cognition undermines the rationale that modularized processes can enhance performance in competitive sport. An ecological dynamics perspective proposes that the body is a complex adaptive system, interacting with performance environments in a functionally integrated manner, emphasizing that the inter-relation between motor processes, cognitive and perceptual functions, and the constraints of a sport task is best understood at the performer-environment scale of analysis

Synthesis of Liquid Core−Shell Particles and Solid Patchy Multicomponent Particles by Shearing Liquids Into Complex Particles (SLICE)

We report a simple method that uses (i) emulsion shearing with oxidation to make core–shell particles, and (ii) emulsion shearing with surface-tension driven phase segregation to synthesize particles with complex surface compositions and morphologies. Subjecting eutectic gallium–indium, a liquid metal, to shear in an acidic carrier fluid we synthesized smooth liquid core–shell particles 6.4 nm to over 10 μm in diameter. Aggregates of these liquid particles can be reconfigured into larger structures using a focused ion beam. Using Field’s metal melts we synthesized homogeneous nanoparticles and solid microparticles with different surface roughness and/or composition through shearing and phase separation. This extension of droplet emulsion technique, SLICE, applies fluidic shear to create micro- and nanoparticles in a tunable, green, and low-cost approach

Supernova feedback and the energy deposition in molecular clouds

This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2020 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved. Final published version available at: https://doi.org/10.1093/mnras/staa451.Feedback from supernovae is often invoked as an important process in limiting star formation, removing gas from galaxies and, hence, as a determining process in galaxy formation. Here, we report on numerical simulations, investigating the interaction between supernova explosions and the natal molecular cloud. We also consider the cases with and without previous feedback from the high-mass star in the form of ionizing radiation and stellar winds. The supernova is able to find weak points in the cloud and creates channels through which it can escape, leaving much of the well-shielded cloud largely unaffected. This effect is increased when the channels are preexisting due to the effects of previous stellar feedback. The expanding supernova deposits its energy in the gas that is in these exposed channels, and, hence, sweeps up less mass when feedback has already occurred, resulting in faster outflows with less radiative losses. The full impact of the supernova explosion is then able to impact the larger scale of the galaxy in which it abides. We conclude that supernova explosions have only moderate effects on their dense natal environments but that with preexisting feedback, the energetic effects of the supernova are able to escape and affect the wider scale medium of the galaxy.Peer reviewe

Supersonic Propulsion: Inlet Shock Wave/Boundary Layer Interaction in a Diffuser

Using a finite-volume approach and ANSYS/FLUENT, supersonic flow over a 2-D ramp of varying angles is modeled. The computational results from this model will be used to further explore the design of supersonic diffusers used on military aircraft. Using grid capturing features and inflation layers, shockwave and boundary layer interactions will be observed as well as wave-associated pressure changes in supersonic turbulent flow. The Spalart-Allmaras single-equation model of turbulent flow will be used in all simulations to more accurately represent the phenomena that occur in such high-speed environments. The size of upstream zones and recirculation zones will be obtained through this model where applicable. Downstream zones of influence will be represented in terms of skin friction coefficient. Single-ramp data will be compared with double-ramp data to better understand how diffusers are modeled in industry for supersonic aircraft. This data will be the basis for the latter simulations representing internal compression and spike inlets. Inlet geometries are compared based on their stagnation pressure losses

Can the removal of molecular cloud envelopes by external feedback affect the efficiency of star formation?

The authors thank Paul Clark for his contribution towards the original concept of this paper and the anonymous referee for their helpful comments. Our column density plots were produced using Daniel Price’s SPLASH software (Price 2007). The authors gratefully acknowledge support from the ECOGAL project, grant agreement 291227, funded by the European Research Council under ERC-2011-ADG. This work used the compute resources of the St Andrews MHD Cluster. This work used the DiRAC Complexity system, operated by the University of Leicester IT Services, which forms part of the STFC DiRAC HPC Facility (www.dirac.ac.uk). This equipment is funded by BIS National E-Infrastructure capital grant ST/K000373/1 and STFC DiRAC Operations grant ST/K0003259/1. DiRAC is part of the National E-Infrastructure.We investigate how star formation efficiency can be significantly decreased by the removal of a molecular cloud’s envelope by feedback from an external source. Feedback from star formation has difficulties halting the process in dense gas but can easily remove the less dense and warmer envelopes where star formation does not occur. However, the envelopes can play an important role keeping their host clouds bound by deepening the gravitational potential and providing a constraining pressure boundary. We use numerical simulations to show that removal of the cloud envelopes results in all cases in a fall in the star formation efficiency (SFE). At 1.38 free-fall times our 4 pc cloud simulation experienced a drop in the SFE from 16 to six percent, while our 5 pc cloud fell from 27 to 16 per cent. At the same time, our 3 pc cloud (the least bound) fell from an SFE of 5.67 per cent to zero when the envelope was lost. The star formation efficiency per free-fall time varied from zero to ≈0.25 according to α, defined to be the ratio of the kinetic plus thermal to gravitational energy, and irrespective of the absolute star forming mass available. Furthermore the fall in SFE associated with the loss of the envelope is found to even occur at later times. We conclude that the SFE will always fall should a star forming cloud lose its envelope due to stellar feedback, with less bound clouds suffering the greatest decrease.PostprintPeer reviewe

Clinical quality and performance measurement in the prehospital emergency medical services in the low-to- middle-income country setting

Thesis (PhD)--Stellenbosch University, 2021.ENGLISH SUMMARY : Background: Measuring quality and safety in any healthcare setting however is highly contextual, and depends on the manner in which quality is defined or viewed within that setting. It is this contextual nature that has provoked significant debate and hindered efforts at developing formal standards or criteria for measuring quality and safety in healthcare, regardless of setting. Historically, performance within the Emergency Medical Services (EMS) delivering prehospital emergency care has been assessed primarily based on response times. While easy to measure and valued by the public, overall, response time targets are a poor predictor of quality of care and clinical outcomes. Aim: The overall aim of the research was to develop a framework for clinical quality and performance-based assessment of prehospital emergency care for use in the South African EMS. Method: The research was divided amongst four studies, with each study constituting one of the overall research objectives. Study I was a sequential explanatory mixed methods study with the aim of understanding the knowledge, attitudes and practices of clinical quality and performance assessment amongst South African EMS personnel. Part 1 consisted of a webbased cross-sectional survey, and Part 2 consisted of semi-structured telephonic interviews of select participants from Part 1 to explore the results of the survey. Descriptive statistics were carried out to summarise and present all survey items, and conventional content analysis employed to analyse the interview data. Study II utilised a three round modified Delphi study to identify, refine and review a list of appropriate quality indicators for potential use in the South African EMS setting. For Study III a novel quality indicator appraisal protocol was developed consisting of two categorical-based appraisal methods, combined with the qualitative analysis of their consensus application, and tested against the outcomes of Study II. Descriptive statistics were utilised to describe and summarize the categorical based appraisal data. Inter-rater reliability was calculated using percentage agreement and Gwet’s AC1. Correlation between the individual methods and the protocol was calculated using Spearman’s rank Correlation and z-test. Conventional content analysis was utilised to analyse the group discussions. Study IV utilised a multiple exploratory case study design to evaluate the current state of quality systems in the South African EMS. A formative assessment was conducted on the quality systems of four provincial EMS and one national private EMS, following which semi-structured interviews were conducted to further explore the results obtained from the formative assessment, supported by multiple secondary data sources. Descriptive statistics were utilised to describe and summarize the formative assessment. Conventional content analysis was utilised to analyse the interview data and document analysis utilised to sort and analyse the supporting data. Results: Despite relatively poor knowledge of organisational-specific quality systems, understanding of the core components and importance of quality systems was demonstrated. The role of these systems in the Low to Middle Income Country setting (LMICs) was supported by participants, where the importance of context, system transparency, reliability and validity were essential towards achieving ongoing success and utilisation. The role of leadership and communication towards the effective facilitation of such a system was equally identified. Participating services generally scored higher for structure and planning. Measurement and improvement were found to be more dependent on utilisation and perceived mandate. There was a relatively strong focus on clinical quality assessment within the private service, whereas in the provincial systems, measures were exclusively restricted to call times with little focus on clinical care. Staff engagement and programme evaluation were generally among the lowest scores. A multitude of contextual factors were identified that affected the effectiveness of quality systems, centred around leadership, vision and mission, and quality system infrastructure and capacity, guided by the need for comprehensive yet pragmatic strategic policies and standards. A total, 104 quality indicators reached consensus agreement including, 90 clinical QIs, across 15 subcategories, and 14 non-clinical QIs across two subcategories. Amongst the clinical category, airway management (n=13 QIs; 14%); out-of-hospital cardiac arrest (n=13 QIs; 14%); and acute coronary syndromes (n=11 QIs; 12%) made up the majority. Within the non-clinical category, adverse events made up the significant majority with nine QIs (64%). There was mixed inter-rater reliability of the individual methods. There was similarly poor to moderate correlation of the results obtained between the individual methods (Spearman’s rank correlation=0.42,p<0.001). From a series of 104 QIs, 11 were identified that were shared between the individual methods. A further 19 QIs were identified and not shared by each method, highlighting the benefits of a multimethod approach. Conclusion: For the purposes of this study we focused on the technical competence aspect of quality, in developing our measurement framework. Towards this, we identified a significant number of QIs assessed to be valid and feasible for the South African prehospital emergency care setting. The majority of which are centred around clinically focused processes of care, measures that are lacking in current performance assessment in EMS in South Africa. However, we also discovered the importance and influencing role of the individual practitioners and quality system in which the QIs will be implemented, a point highlighted across all the methodologies and studies. Given the potential magnitude of this influence, it is of the utmost importance that any measurement framework examining technical quality, have equal in-depth understanding of these factors in order to be successful.AFRIKAANSE OPSOMMING : Geen opsomming beskikbaar.Doctora

X-ray translucent reaction cell for simulation of carbon mineral storage reservoir environments

Understanding how in-situ mineralization of CO2 affects the porosity, permeability, and pore network of the host rock is critical to assessing the viability of basalt reservoirs as carbon dioxide repositories. Here, we present an x-ray translucent environmental cell which allows carbon mineralization, and other fluid–rock reactions to be studied in real time and on the grain scale under simulated geological reservoir conditions using microtomographic imaging. The cell operates autonomously from a CT instrument and is periodically quenched and relocated for scanning, enabling long duration operando experiments. Samples are reacted under controlled conditions of chemistry, temperature, and fluid pressure. Porosity and permeability changes are tracked through digital image analysis of successive CT scans. Samples are fully recoverable, allowing for a suite of post-mortem analyses. The cell design uses readily available materials, can sustain long-term operating temperatures of up to 200 °C, and is reproducible at low cost with a centre lathe and a mill using a conveniently equipped mechanical workshop