Prospects for Redshifted 21-cm observations of quasar HII regions

The introduction of low-frequency radio arrays over the coming decade is expected to revolutionize the study of the reionization epoch. Observation of the contrast in redshifted 21cm emission between a large HII region and the surrounding neutral IGM will be the simplest and most easily interpreted signature. We find that an instrument like the planned Mileura Widefield Array Low-Frequency Demonstrator (LFD) will be able to obtain good signal to noise on HII regions around the most luminous quasars, and determine some gross geometric properties, e.g. whether the HII region is spherical or conical. A hypothetical follow-up instrument with 10 times the collecting area of the LFD (MWA-5000) will be capable of mapping the detailed geometry of HII regions, while SKA will be capable of detecting very narrow spectral features as well as the sharpness of the HII region boundary. The MWA-5000 will discover serendipitous HII regions in widefield observations. We estimate the number of HII regions which are expected to be generated by quasars. Assuming a late reionization at z~6 we find that there should be several tens of quasar HII regions larger than 4Mpc at z~6-8 per field of view. Identification of HII regions in forthcoming 21cm surveys can guide a search for bright galaxies in the middle of these regions. Most of the discovered galaxies would be the massive hosts of dormant quasars that left behind fossil HII cavities that persisted long after the quasar emission ended, owing to the long recombination time of intergalactic hydrogen. A snap-shot survey of candidate HII regions selected in redshifted 21cm image cubes may prove to be the most efficient method for finding very high redshift quasars and galaxies.Comment: 14 pages, 8 figures. Submitted to Ap

Transfer of organic carbon through marine water columns to sediments – insights from stable and radiocarbon isotopes of lipid biomarkers

© The Author(s), 2014. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Biogeosciences 11 (2014): 6895-6914, doi:10.5194/bg-11-6895-2014.Compound-specific 13C and 14C compositions of diverse lipid biomarkers (fatty acids, alkenones, hydrocarbons, sterols and fatty alcohols) were measured in sinking particulate matter collected in sediment traps and from underlying surface sediments in the Black Sea, the Arabian Sea and the Ross Sea. The goal was to develop a multiparameter approach to constrain relative inputs of organic carbon (OC) from marine biomass, terrigenous vascular-plant and relict-kerogen sources. Using an isotope mass balance, we calculate that marine biomass in sediment trap material from the Black Sea and Arabian Sea accounted for 66–100% of OC, with lower terrigenous (3–8%) and relict (4–16%) contributions. Marine biomass in sediments constituted lower proportions of OC (66–90%), with consequentially higher proportions of terrigenous and relict carbon (3–17 and 7–13%, respectively). Ross Sea data were insufficient to allow similar mass balance calculations. These results suggest that, whereas particulate organic carbon is overwhelmingly marine in origin, pre-aged allochthonous terrigenous and relict OC become proportionally more important in sediments, consistent with pre-aged OC being better preserved during vertical transport to and burial at the seafloor than the upper-ocean-derived marine OC.Grants OCE-9310364 and OCE-9911678 from the US National Science Foundation (NSF) and the NSF Cooperative Agreement for the Operation of a National Ocean Sciences Accelerator Mass Spectrometry Facility (OCE-0753487 and OCE-123966) supported this research. S. G. Wakeham acknowledges the Hanse Wissenschaftskolleg (Hanse Institute for Advanced Studies), Delmenhorst, Germany, for a fellowship that supported the writing of this manuscript

Acoustic characterization of crack damage evolution in sandstone deformed under conventional and true triaxial loading

We thank the Associate Editor, Michelle Cooke, and the reviewers, Ze'ev Reches and Yves Guéguen, for useful comments which helped to improve the manuscript. We thank J.G. Van Munster for providing access to the true triaxial apparatus at KSEPL and for technical support during the experimental program. We thank R. Pricci for assistance with technical drawings of the apparatus. This work was partly funded by NERC award NE/N002938/1 and by a NERC Doctoral Studentship, which we gratefully acknowledge. Supporting data are included in a supporting information file; any additional data may be obtained from J.B. (e-mail: [email protected]).Peer reviewedPublisher PD

Direct Detection of the Brown Dwarf GJ 802B with Adaptive Optics Masking Interferometry

We have used the Palomar 200" Adaptive Optics (AO) system to directly detect the astrometric brown dwarf GJ 802B reported by Pravdo et al. 2005. This observation is achieved with a novel combination of aperture masking interferometry and AO. The dynamical masses are 0.175$\pm$0.021 M$_\odot$ and 0.064$\pm$0.032 M$_\odot$ for the primary and secondary respectively. The inferred absolute H band magnitude of GJ 802B is M$_H$=12.8 resulting in a model-dependent T$_\mathrm{eff}$ of 1850 $\pm$ 50K and mass range of 0.057--0.074 M$_\odot$.Comment: 4 Pages, 5 figures, emulateapj format, submitted to ApJ

International Workshop on Sustainable Sanitation: Resource Papers

Domestic wastewater reuse is currently not permitted anywhere in Australia but is widely supported by the community, promoted by researchers, and improvised by up to 20% of householders. Its widespread implementation will make an enormous contribution to the sustainability of water resources. Integrated with other strategies in the outdoor living environment of settlements in arid lands great benefit will be derived. This paper describes six options for wastewater reuse under research by the Remote Area Developments Group (RADG) at Murdoch University and case studies are given where productive use is being made for revegetation and food production strategies at household and community scales. Pollution control techniques, public health precautions and maintenance requirements are described. The special case of remote Aboriginal communities is explained where prototype systems have been installed by RADG to generate windbreaks and orchards. New Australian design standards and draft guidelines for domestic greywater reuse produced by the Western Australian state government agencies for mainstream communities are evaluated. It is recommended that dry composting toilets be coupled with domestic greywater reuse and the various types available in Australia are described. For situations where only the flushing toilet will suffice the unique “wet composting” system can be used and this also is described. A vision for household and community-scale on-site application is presented

Higher-Order Topological Insulators

Three-dimensional topological (crystalline) insulators are materials with an insulating bulk, but conducting surface states which are topologically protected by time-reversal (or spatial) symmetries. Here, we extend the notion of three-dimensional topological insulators to systems that host no gapless surface states, but exhibit topologically protected gapless hinge states. Their topological character is protected by spatio-temporal symmetries, of which we present two cases: (1) Chiral higher-order topological insulators protected by the combination of time-reversal and a four-fold rotation symmetry. Their hinge states are chiral modes and the bulk topology is $\mathbb{Z}_2$-classified. (2) Helical higher-order topological insulators protected by time-reversal and mirror symmetries. Their hinge states come in Kramers pairs and the bulk topology is $\mathbb{Z}$-classified. We provide the topological invariants for both cases. Furthermore we show that SnTe as well as surface-modified Bi$_2$TeI, BiSe, and BiTe are helical higher-order topological insulators and propose a realistic experimental setup to detect the hinge states.Comment: 8 pages (4 figures) and 16 pages supplemental material (7 figures

Non-Fermi Liquid Quantum Impurity Physics from non-Abelian Quantum Hall States

We study the physics of electron tunneling between multiple quantum dots and the edge of a quantum Hall state. Our results generalize earlier work [G. A. Fiete, W. Bishara, C. Nayak, Phys. Rev. Lett. 101, 176801 (2008)] in which it was shown that a single quantum dot tunnel coupled to a non-Abelian quantum Hall state can realize a stable multi-channel Kondo fixed point at low-energy. In this work, we investigate the physics of multiple dots and find that a rich set of possible low-energy fixed points arises, including those with non-Fermi liquid properties. Previously unidentified fixed points may also be among the possibilities. We examine both the situation where the dots are spatially separated and where they are in close proximity. We discuss the relation to previous work on two-impurity Kondo models in Fermi liquids and highlight new research directions in multiple quantum impurity problems.Comment: 12 pages, 2 figure

Width and Partial Widths of Unstable Particles in the Light of the Nielsen Identities

Fundamental properties of unstable particles, including mass, width, and partial widths, are examined on the basis of the Nielsen identities (NI) that describe the gauge dependence of Green functions. In particular, we prove that the pole residues and associated definitions of branching ratios and partial widths are gauge independent to all orders. A simpler, previously discussed definition of branching ratios and partial widths is found to be gauge independent through next-to-next-to-leading order. It is then explained how it may be modified in order to extend the gauge independence to all orders. We also show that the physical scattering amplitude is the most general combination of self-energy, vertex, and box contributions that is gauge independent for arbitrary s, discuss the analytical properties of the NI functions, and exhibit explicitly their one-loop expressions in the Z-gamma sector of the Standard Model.Comment: 20 pages (Latex); minor changes included, accepted for publication in Phys. Rev.

On the Solution of Convection-Diffusion Boundary Value Problems Using Equidistributed Grids

The effect of using grid adaptation on the numerical solution of model convection-diffusion equations with a conservation form is studied. The grid adaptation technique studied is based on moving a fixed number of mesh points to equidistribute a generalization of the arc-length of the solution. In particular, a parameter-dependent monitor function is introduced which incorporates fixed meshes, approximate arc-length equidistribution, and equidistribution of the absolute value of the solution, in a single framework. Thus the resulting numerical method is a coupled nonlinear system of equations for the mesh spacings and the nodal values. A class of singularly perturbed problems, including Burgers's equation in the limit of small viscosity, is studied. Singular perturbation and bifurcation techniques are used to analyze the solution of the discretized equations, and numerical results are compared with the results from the analysis. Computation of the bifurcation diagram of the system is performed numerically using a continuation method and the results are used to illustrate the theory. It is shown that equidistribution does not remove spurious solutions present on a fixed mesh and that, furthermore, the spurious solutions can be stable for an appropriate moving mesh method