The role of turbulence during the formation of circumbinary discs

Most stars form in binaries and the evolution of their discs remains poorly understood. To shed light on this subject, we carry out 3D ideal MHD simulations with the AMR code FLASH of binary star formation for separations of $10-20\,\mathrm{AU}$. We run a simulation with no initial turbulence (NT), and two with turbulent Mach numbers of $\mathcal{M} = \sigma_v/c_s = 0.1$ and $0.2$ (T1 and T2) for $5000\,\mathrm{yr}$ after protostar formation. By the end of the simulations the circumbinary discs in NT and T1, if any, have radii of $\lesssim20\,\mathrm{AU}$ with masses $\lesssim0.02\,\mathrm{M}_\odot$, while T2 hosts a circumbinary disc with radius $\sim70-80\,\mathrm{AU}$ and mass $\sim0.12\,\mathrm{M}_\odot$. These circumbinary discs formed from the disruption of circumstellar discs and harden the binary orbit. Our simulated binaries launch large single outflows. We find that NT drives the most massive outflows, and also removes large quantities of linear and angular momentum. T2 produces the least efficient outflows concerning mass, momentum and angular momentum ($\sim$61 per cent, $\sim$71 per cent, $\sim$68 per cent of the respective quantities in NT). We conclude that while turbulence helps to build circumbinary discs which organise magnetic fields for efficient outflow launching, too much turbulence may also disrupt the ordered magnetic field structure required for magneto-centrifugal launching of jets and outflows. We also see evidence for episodic accretion during the binary star evolution. We conclude that the role of turbulence in building large circumbinary discs may explain some observed very old ($>10\,\mathrm{Myr}$) circumbinary discs. The longer lifetime of circumbinary discs may increase the likelihood of planet formation.Comment: Accepted to MNRAS. 17 pages, 11 figures. arXiv admin note: text overlap with arXiv:1705.0815

Effect of Chlorine Dioxide Gas on the Properties of Packaging Materials and Effect of Chlorine Dioxide Gas to Maintain the Quality of Fresh Strawberries

ClO2 as an antimicrobial gas in the headspace of produce package is a relatively novel approach. Gaseous ClO2 is more effective than aqueous ClO2 and can be used in the headspace of fresh food packages. ClO2 gas can diffuse into product surfaces and films. As an oxidizer, it can react with and change polymeric package components, possibly affecting the product’s shelflife. This research studied effects of ClO2 gas treatments on produce packaging materials (APET, two PE types, Nylon). The treatment group (with ClO2) and the control group (without ClO2) of packaging materials were stored at room temperature and at three different relative humidities (49%, 84%, 99%) in sealed chambers. Dart drop, tensile tests, Tg, Tm, Tc, and water vapor transmission rate of materials were performed at six times over a 21-day period. A low dose (2 was a suitable application in these produce packaging materials. This research allows further experimenting with the literature on varying RH’s for the general application (ppm) of ClO2 on each polymer used for common fresh produce applications. This research also studied the use of ClO2 gas sachets to determine the effects on the sensory properties of strawberries. Conditions included typical strawberry storage systems (open pallet system under cold conditions (0-2 0C) and a controlled atmosphere storage system (99% RH, 0-2 0C). Both conditions were tested for 21 days with and without ClO2. ClO2 gas preserved strawberry quality with or without maximum RH. In the absence of 99% RH, ClO2 treated strawberries exhibited better quality than the untreated berries. High RH (99%) alone has significant quality retention of strawberries in a chamber system with or without ClO2. Either ClO2 or high (99%) RH plays a significant role in strawberry preservation in each other’s absence

A BAYESIAN APPROACH FOR BANDWIDTH SELECTION IN KERNEL DENSITY ESTIMATION WITH CENSORED DATA

Estimating an unknown probability density function is a common problem arising frequently in many scientific disciplines. Among many density estimation methods, the kernel density estimators are widely used. However, the classical kernel density estimators suffer from an intrinsic problem as they assign positive values outside the support of the target density. This problem is commonly known as the `Spill over` effect. A modification to the regular kernel estimator is proposed to circumvent this problem. The proposed method uses a lognormal kernel and can be used even in the presence of censoring to estimate any density with a positive support without any spill over at the origin. Strong consistency of this estimator is established under suitable conditions. A Bayesian approach using as inverted gamma prior density is used in the computation of local bandwidths. These bandwidths yield better density estimates. It was shown that these bandwidths converge to zero for suitable choices of prior parameters and as a result the density estimator achieved its asymptotic unbiasedness. A simulation study was carried out to compare the performance of the proposed method with two competing estimators. The proposed estimator was shown to be superior to both competitors under pointwise and global error criteria

Considerations on the Role of Fall-Back Discs in the Final Stages of the Common Envelope Binary Interaction

The common envelope interaction is thought to be the gateway to all evolved compact binaries and mergers. Hydrodynamic simulations of the common envelope interaction between giant stars and their companions are restricted to the dynamical, fast, in-spiral phase. They find that the giant envelope is lifted during this phase, but remains mostly bound to the system. At the same time, the orbital separation is greatly reduced, but in most simulations it levels off? at values larger than measured from observations. We conjectured that during the post-in-spiral phase the bound envelope gas will return to the system. Using hydrodynamic simulations, we generate initial conditions for our simulation that result in a fall-back disk with total mass and angular momentum in line with quantities from the simulations of Passy et al. We find that the simulated fall-back event reduces the orbital separation efficiently, but fails to unbind the gas before the separation levels off once again. We also find that more massive fall-back disks reduce the orbital separation more efficiently, but the efficiency of unbinding remains invariably very low. From these results we deduce that unless a further energy source contributes to unbinding the envelope (such as was recently tested by Nandez et al.), all common envelope interactions would result in mergers. On the other hand, additional energy sources are unlikely to help, on their own, to reduce the orbital separation. We conclude by discussing our dynamical fall-back event in the context of a thermally-regulated post-common envelope phase.Comment: 12 pages, 12 pages, Accepted to MNRA

The role of initial magnetic field structure in the launching of protostellar jets

Magnetic fields are known to play a crucial role in the star formation process, particularly in the formation of jets and outflows from protostellar discs. The magnetic field structure in star-forming regions is not always uniform and ordered, often containing regions of magnetic turbulence. We present grid-based, magnetohydrodynamical simulations of the collapse of a 1M⊙ cloud core, to investigate the influence of complex magnetic field structures on outflow formation, morphology, and efficiency. We compare three cases: a uniform field, a partially turbulent field and a fully turbulent field, with the same magnetic energy in all three cases. We find that collimated jets are produced in the uniform-field case, driven by a magneto-centrifugal mechanism. Outflows also form in the partially turbulent case, although weaker and less collimated, with an asymmetric morphology. The outflows launched from the partially turbulent case carry the same amount of mass as the uniform-field case but at lower speeds, having only have 71 per cent of the momentum of the uniform-field case. In the case of a fully turbulent field, we find no significant outflows at all. Moreover, the turbulent magnetic field initially reduces the accretion rate and later induces fragmentation of the disc, forming multiple protostars. We conclude that a uniform poloidal component of the magnetic field is necessary for the driving of jets.IG would like to thank the Australian National University (ANU) and the Research School and Astronomy and Astrophysics for the opportunity and funding provided as part of the Summer Research Scholarship program. RK thanks the Australian government for the Australian government research training program scholarship stipend. CF acknowledges funding provided by the Australian Research Council’s Discovery Projects (grants DP150104329 and DP170100603), the Future Fellowship scheme (grant FT180100495), and the Australia-Germany Joint Research Cooperation Scheme (UA-DAAD)

Persistence of \u3ci\u3eEscherichia coli\u3c/i\u3e O157:H7 and \u3ci\u3eListeria monocytogenes\u3c/i\u3e on the Exterior of Common Packaging Materials

Acute gastroenteritis (AGE), a major cause of illness, results in 179 million AGE cases every year in the United States. AGE bacteria that have low-infectious dose include E. coli O157:H7 (\u3c10-100 cells) and L. monocytogenes (\u3c1000 cells). Because of their low-infectious dose and high environmental resistance, contaminated surfaces, such as the exterior surface of food packages, could be a source for disease transmission. Our aim was to determine the persistence of E. coli O157:H7 and L. monocytogenes on three packaging materials - oriented polyethylene terephthalate (OPET), oriented polypropylene (OPP), and nylon-6. Coupons (25 cm2) from each material were sterilized under ultraviolet light for 5 minutes. Spot and spread inoculation was done on treatment coupons with ca. 7 log CFU of a 3-strain-mixture of green fluorescent protein (GFP)-labeled E. coli O157:H7. All the coupons were incubated at Technical Association of the Pulp and Paper Industry-TAPPI standards. Surviving E. coliO157:H7 cells on duplicate coupons were recovered in saline at selected time intervals (0, 0.25, 0.5, 1, 2, 3, 5, 7, 14, 15 days). Surviving cells were enumerated on tryptic soy broth supplemented with ampicillin using the 3 tubes most probable number-MPN method described in the Bacteriological Analytical Manual. The experiment was performed in triplicate. The same procedure was carried out for 3-strain-mixture of rifampin-resistant (Rif)-L. monocytogenes using tryptic soy broth supplemented with rifampin for the MPN method. (GFP)-E. coliO157:H7 and (Rif)-L. monocytogenes survived on OPET, OPP, and nylon-6 for 15 days. The survival of E. coli O157:H7 was significantly different (p \u3c 0.05) from the survival of L. monocytogenes between days 0.5-1, 1-2, and 3-5. The survival of both bacteria on all three materials were not significantly different (p \u3e 0.05). E. coli O157:H7 and L. monocytogenes survived for over 2 weeks on OPET, OPP, and nylon 6, suggesting a highly contaminated outer surface of a food package could be a potential fomite for AGE outbreaks

Sustainable infrastructure development - a New Zealand experience

Sustainable Infrastructure has been defined as “…Future friendly, resource efficient …. With pedestrian and public transport oriented systems….”[1] (Back ground paper, UN Expert Group Meeting, 2007) Wide arrays of strategies are available to achieve the above. Creation of transport corridors, higher capacity transport modes, Increased levels of service and future proofing projects are four of them. Using these in an eco efficient manner will provide sustainable transport systems. This paper concentrates on the surface transport strategies adopted in New Zealand. More specifically it wishes to provide an insight to the exclusive busway and buslane operation in New Zealand

Binary star formation and the outflows from their discs

We carry out magnetohydrodynamical simulations with flash of the formation of a single, a tight binary (a ∼ 2.5 au) and a wide binary star (a ∼ 45 au). We study the outflows and jets from these systems to understand the contributions the circumstellar and circumbinary discs have on the efficiency and morphology of the outflow. In the single star and tight binary case, we obtain a single pair of jets launched from the system, while in the wide binary case, two pairs of jets are observed. This implies that in the tight binary case, the contribution of the circumbinary disc on the outflow is greater than that in the wide binary case. We also find that the single star case is the most efficient at transporting mass, linear and angular momentum from the system, while the wide binary case is less efficient ( ∼ 50 per cent, ∼ 33 per cent, ∼ 42 per cent of the respective quantities in the single star case). The tight binary's efficiency falls between the other two cases ( ∼ 71 per cent, ∼66 per cent, ∼87 per cent of the respective quantities in the single star case). By studying the magnetic field structure, we deduce that the outflows in the single star and tight binary star case are magnetocentrifugally driven, whereas in the wide binary star case, the outflows are driven by a magnetic pressure gradient.RK would like to thank the Australian Government and the financial support provided by the Australian Postgraduate Award. CF gratefully acknowledges funding provided by the Australian Research Council’s Discovery Projects (grants DP150104329 and DP170100603)