Smoothed Particle Magnetohydrodynamics III. Multidimensional tests and the div B = 0 constraint

In two previous papers (Price & Monaghan 2004a,b) (papers I,II) we have described an algorithm for solving the equations of Magnetohydrodynamics (MHD) using the Smoothed Particle Hydrodynamics (SPH) method. The algorithm uses dissipative terms in order to capture shocks and has been tested on a wide range of one dimensional problems in both adiabatic and isothermal MHD. In this paper we investigate multidimensional aspects of the algorithm, refining many of the aspects considered in papers I and II and paying particular attention to the code's ability to maintain the div B = 0 constraint associated with the magnetic field. In particular we implement a hyperbolic divergence cleaning method recently proposed by Dedner et al. (2002) in combination with the consistent formulation of the MHD equations in the presence of non-zero magnetic divergence derived in papers I and II. Various projection methods for maintaining the divergence-free condition are also examined. Finally the algorithm is tested against a wide range of multidimensional problems used to test recent grid-based MHD codes. A particular finding of these tests is that in SPMHD the magnitude of the divergence error is dependent on the number of neighbours used to calculate a particle's properties and only weakly dependent on the total number of particles. Whilst many improvements could still be made to the algorithm, our results suggest that the method is ripe for application to problems of current theoretical interest, such as that of star formation.Comment: Here is the latest offering in my quest for a decent SPMHD algorithm. 26 pages, 15 figures, accepted for publication in MNRAS. Version with high res figures available from http://www.astro.ex.ac.uk/people/dprice/pubs/spmhd/spmhdpaper3.pd

Methanol Masers as Tracers of Circumstellar Disks

We show that in many methanol maser sources the masers are located in lines, with a velocity gradient along them which suggests that the masers are situated in edge-on circumstellar, or protoplanetary, disks. We present VLBI observations of the methanol maser source G309.92+0.48, in the 12.2 GHz transition, which confirm previous observations that the masers in this source lie along a line. We show that such sources are not only linear in space but, in many cases, also have a linear velocity gradient. We then model these and other data in both the 6.7 GHz and the 12.2 GHz transition from a number of star formation regions, and show that the observed spatial and velocity distribution of methanol masers, and the derived Keplerian masses, are consistent with a circumstellar disk rotating around an OB star. We consider this and other hypotheses, and conclude that about half of these methanol masers are probably located in edge-on circumstellar disks around young stars. This is of particular significance for studies of circumstellar disks because of the detailed velocity information available from the masers.Comment: 38 pages, 13 figures accepted by Ap

Smoothed Particle Hydrodynamics and Magnetohydrodynamics

This paper presents an overview and introduction to Smoothed Particle Hydrodynamics and Magnetohydrodynamics in theory and in practice. Firstly, we give a basic grounding in the fundamentals of SPH, showing how the equations of motion and energy can be self-consistently derived from the density estimate. We then show how to interpret these equations using the basic SPH interpolation formulae and highlight the subtle difference in approach between SPH and other particle methods. In doing so, we also critique several `urban myths' regarding SPH, in particular the idea that one can simply increase the `neighbour number' more slowly than the total number of particles in order to obtain convergence. We also discuss the origin of numerical instabilities such as the pairing and tensile instabilities. Finally, we give practical advice on how to resolve three of the main issues with SPMHD: removing the tensile instability, formulating dissipative terms for MHD shocks and enforcing the divergence constraint on the particles, and we give the current status of developments in this area. Accompanying the paper is the first public release of the NDSPMHD SPH code, a 1, 2 and 3 dimensional code designed as a testbed for SPH/SPMHD algorithms that can be used to test many of the ideas and used to run all of the numerical examples contained in the paper.Comment: 44 pages, 14 figures, accepted to special edition of J. Comp. Phys. on "Computational Plasma Physics". The ndspmhd code is available for download from http://users.monash.edu.au/~dprice/ndspmhd

Indigenous microbial surrogates in wastewater used to understand public health risk expressed in the Disability-Adjusted Life Year (DALY) metric

In any wastewater recycling scheme, the protection of public health is of primary importance. In Australia, the public health requirements applying to the treatment of recycled water are stringent. They use the Disability-Adjusted Life Year (DALY) metric to set a level of negligible public health risk. The target maximum risk of 10-6 DALY per person per year has been adopted in Australian water recycling guidelines since 2006. A key benefit of the DALY approach is its ability to standardise the understanding of risk across disparate areas of public health. To address the key challenge of translating the results of monitoring of microorganisms in the recycled water into this quantitative public health metric, we have developed a novel method. This paper summarises an approach where microbial surrogate organisms indigenous to wastewater are used to measure the efficiency of water recycling treatment processes and estimate public health risk. An example of recent implementation in the Greater Sydney region of Australia is provided

Metallurgical and Mechanical Assessment of Hybrid Additively-Manufactured Maraging Tool Steels via Selective Laser Melting

A complete metallurgical and mechanical assessment of additively manufactured maraging tool steels has been undertaken, beginning with the initial powder and ending at hybrid builds. The effect of powder recycling on powder characteristics is investigated using flowability, size distribution, and density measurements. Virgin and re-used powder have similar characteristics in terms of size distribution and chemical and phase homogeneity, but no flowability. A microstructural characterization of the as-built and heat-treated samples is undertaken, showing the phase evolution, and the formation of porosity between build layers. The age-hardening response of the alloy at 490˚C and 650˚C is demonstrated to be similar to the material in the wrought condition. Finally, hybrid build scenarios are examined – maraging steel powder deposited onto C300 maraging steel, as well as H13 tool steel substrates – using digital image correlation. In both cases, the interface remains coherent without any sign of de-bonding during tensile deformation. In the case of the maraging steel powder / C300 substrate, the deformation is homogeneous throughout until failure localizes away from the interface. In the case of the maraging steel powder / H13 substrate, the deformation is predominantly within the substrate until failure localizes at the interface. A heat treatment strategy for the maraging steel powder / H13 tool steel substrate is proposed.Natural Sciences and Engineering Council of Canada, Exco Engineering Ltd

Human resources issues and Australian Disaster Medical Assistance Teams: results of a national survey of team members

Background: Calls for disaster medical assistance teams (DMATs) are likely to continue in response to international disasters. As part of a national survey, this study was designed to evaluate Australian DMAT experience in relation to the human resources issues associated with deployment.\ud \ud Methods: Data was collected via an anonymous mailed survey distributed via State and Territory representatives on the Australian Health Protection Committee, who identified team members associated with Australian DMAT deployments from the 2004 South East Asian Tsunami disaster.\ud \ud Results: The response rate for this survey was 50% (59/118). Most personnel had deployed to the Asian Tsunami affected areas with DMAT members having significant clinical and international experience. While all except one respondent stated they received a full orientation prior to deployment, only 34% of respondents (20/59) felt their role was clearly defined pre deployment. Approximately 56% (33/59) felt their actual role matched their intended role and that their clinical background was well suited to their tasks. Most respondents were prepared to be available for deployment for 1 month (34%, 20/59). The most common period of notice needed to deploy was 6–12 hours for 29% (17/59) followed by 12–24 hours for 24% (14/59). The preferred period of overseas deployment was 14–21 days (46%, 27/59) followed by 1 month (25%, 15/59) and the optimum shift period was felt to be 12 hours by 66% (39/59). The majority felt that there was both adequate pay (71%, 42/59) and adequate indemnity (66%, 39/59). Almost half (49%, 29/59) stated it was better to work with people from the same hospital and, while most felt their deployment could be easily covered by staff from their workplace (56%, 33/59) and caused an inconvenience to their colleagues (51%, 30/59), it was less likely to interrupt service delivery in their workplace (10%, 6/59) or cause an inconvenience to patients (9%, 5/59). Deployment was felt to benefit the affected community by nearly all (95%, 56/59) while less (42%, 25/59) felt that there was a benefit for their own local community. Nearly all felt their role was recognised on return (93%, 55/59) and an identical number (93%, 55/59) enjoyed the experience. All stated they would volunteer again, with 88% strongly agreeing with this statement.\ud \ud Conclusions: This study of Australian DMAT members provides significant insights into a number of human resources issues and should help guide future deployments. The preferred 'on call' arrangements, notice to deploy, period of overseas deployment and shift length are all identified. This extended period of operations needs to be supported by planning and provision of rest cycles, food, temporary accommodation and rest areas for staff. The study also suggests that more emphasis should be placed on team selection and clarification of roles. While the majority felt that there was both adequate pay and adequate indemnity, further work clarifying this, based on national conditions of service should be, and are, being explored currently by the state based teams in Australia. Importantly, the deployment was viewed positively by team members who all stated they would volunteer again, which allows the development of an experienced cohort of team members

Water safety plans by utilities: a review of research on implementation

Water supply is essential to public health, quality of life, environmental protection, economic activity, and sustainable development. In this context, it is imperative to assure the continuous improvement of all processes and practices conducive to guarantee water quality and safety. Water Safety Plans (WSPs) by water utilities are an important public policy tool to accomplish these goals. This manuscript reviews the international evidence of the adoption and implementation of water safety planning and reports the current situation in Portugal, as part of the necessary adjustment of the national legal framework to the publication of the Directive (EU) 2015/1787, October 6th, on water quality for human consumption. The aim is to draw lessons from several successful WSP experiments around the world and extract lessons from these cases when drafting new legislation in Portugal and elsewhere. Findings suggest there are four critical dimensions and key elements of success in developing and implementing WSPs: leadership commitment, technical knowledge, governance, and interagency collaboration.This research is partially supported by the “Programa Operacional da Região Norte”, NORTE2020, in the context of project NORTE-01-0145-FEDER-000037 (SmartEGOV) and by the Portuguese Science and Technology Foundation (Fundação para a Ciência e Tecnologia) [Grant No. PEst-OE/CJP/UI0758/2014]

Logistic support provided to Australian disaster medical assistance teams: results of a national survey of team members

Background: It is likely that calls for disaster medical assistance teams (DMATs) continue in response to international disasters. As part of a national survey, the present study was designed to evaluate the Australian DMAT experience and the need for logistic support.\ud \ud Methods: Data were collected via an anonymous mailed survey distributed via State and Territory representatives on the Australian Health Protection Committee, who identified team members associated with Australian DMAT deployments from the 2004 Asian Tsunami disaster.\ud \ud Results: The response rate for this survey was 50% (59/118). Most of the personnel had deployed to the South East Asian Tsunami affected areas. The DMAT members had significant clinical and international experience. There was unanimous support for dedicated logistic support with 80% (47/59) strongly agreeing. Only one respondent (2%) disagreed with teams being self sufficient for a minimum of 72 hours. Most felt that transport around the site was not a problem (59%; 35/59), however, 34% (20/59) felt that transport to the site itself was problematic. Only 37% (22/59) felt that pre-deployment information was accurate. Communication with local health providers and other agencies was felt to be adequate by 53% (31/59) and 47% (28/59) respectively, while only 28% (17/59) felt that documentation methods were easy to use and reliable. Less than half (47%; 28/59) felt that equipment could be moved easily between areas by team members and 37% (22/59) that packaging enabled materials to be found easily. The maximum safe container weight was felt to be between 20 and 40 kg by 58% (34/59).\ud \ud Conclusions: This study emphasises the importance of dedicated logistic support for DMAT and the need for teams to be self sufficient for a minimum period of 72 hours. There is a need for accurate pre deployment information to guide resource prioritisation with clearly labelled pre packaging to assist access on site. Container weights should be restricted to between 20 and 40 kg, which would assist transport around the site, while transport to the site was seen as problematic. There was also support for training of all team members in use of basic equipment such as communications equipment, tents and shelters and water purification systems