Macquarie University

About: Macquarie University is a education organization based out in Sydney, New South Wales, Australia. It is known for research contribution in the topics: Population & Context (language use). The organization has 14075 authors who have published 47673 publications receiving 1416184 citations. The organization is also known as: Macquarie uni.

A supermassive black hole in an ultra-compact dwarf galaxy

Abstract: Dynamical modelling of the ultra-compact dwarf galaxy M60-UCD1 reveals the presence of a supermassive black hole; this suggests the object is a stripped galaxy nucleus and implies the existence of supermassive black holes in many other ultra-compact dwarf galaxies. The object M60-UCD1 is the brightest ultracompact dwarf galaxy (UCD) currently known and — at about 200 million solar masses — one of the most massive. Anil Seth et al. have used adaptive optics spectra to resolve the kinematics of M60-UCD1. They detect a supermassive black hole of 21 million solar masses at its centre. M60-UCD1 is thus the lowest-mass system known to host a supermassive black hole. The authors suggest that it may once have been at the centre of a larger galaxy that was later tidally torn apart by a massive neighbour. Their analysis also shows that M60-UCD1's stellar mass is consistent with its luminosity, implying that many other ultra-compact dwarf galaxies may contain previously unrecognized supermassive black holes. Ultra-compact dwarf galaxies are among the densest stellar systems in the Universe. These systems have masses of up to 2 × 108 solar masses, but half-light radii of just 3–50 parsecs1. Dynamical mass estimates show that many such dwarfs are more massive than expected from their luminosity2. It remains unclear whether these high dynamical mass estimates arise because of the presence of supermassive black holes or result from a non-standard stellar initial mass function that causes the average stellar mass to be higher than expected3,4. Here we report adaptive optics kinematic data of the ultra-compact dwarf galaxy M60-UCD1 that show a central velocity dispersion peak exceeding 100 kilometres per second and modest rotation. Dynamical modelling of these data reveals the presence of a supermassive black hole with a mass of 2.1 × 107 solar masses. This is 15 per cent of the object’s total mass. The high black hole mass and mass fraction suggest that M60-UCD1 is the stripped nucleus of a galaxy. Our analysis also shows that M60-UCD1’s stellar mass is consistent with its luminosity, implying a large population of previously unrecognized supermassive black holes in other ultra-compact dwarf galaxies2.

Stable recombination hotspots in birds

Abstract: The DNA-binding protein PRDM9 has a critical role in specifying meiotic recombination hotspots in mice and apes, but it appears to be absent from other vertebrate species, including birds. To study the evolution and determinants of recombination in species lacking the gene that encodes PRDM9, we inferred fine-scale genetic maps from population resequencing data for two bird species: the zebra finch, Taeniopygia guttata, and the long-tailed finch, Poephila acuticauda. We found that both species have recombination hotspots, which are enriched near functional genomic elements. Unlike in mice and apes, most hotspots are shared between the two species, and their conservation seems to extend over tens of millions of years. These observations suggest that in the absence of PRDM9, recombination targets functional features that both enable access to the genome and constrain its evolution.

Lanthanide upconversion luminescence at the nanoscale: fundamentals and optical properties

Abstract: Upconversion photoluminescence is a nonlinear effect where multiple lower energy excitation photons produce higher energy emission photons. This fundamentally interesting process has many applications in biomedical imaging, light source and display technology, and solar energy harvesting. In this review we discuss the underlying physical principles and their modelling using rate equations. We discuss how the understanding of photophysical processes enabled a strategic influence over the optical properties of upconversion especially in rationally designed materials. We subsequently present an overview of recent experimental strategies to control and optimize the optical properties of upconversion nanoparticles, focussing on their emission spectral properties and brightness.

Corporate Reporting of Intellectual Capital: Evidence from UK Companies

Abstract: This paper reports the results of an empirical investigation into the intellectual capital reporting (ICR) practices of UK companies in four distinct sectors. It differs from prior ICR studies in that it analyses a wide range of external corporate reporting media for their IC content. It finds major differences between the intellectual capital elements reported in each sector studied, and finds an overall sector effect which is at variance with the expected overall sector effect. The study also finds that a range of corporate media were used for communicating intellectual capital information, and that the annual reports were not a good proxy for the proportion of disclosures across all corporate media.

Dy/Dy*: Variations Arising from Mantle Sources and Petrogenetic Processes

Abstract: Dy/Dy* is the measured value of Dy, a representative middle rare earth element (REE), compared with the value interpolated between La and Yb on a REE plot. It is essentially a measure of the ‘concavity’ of a REE pattern. The use of Dy/Dy* as a proxy for REE pattern shape allows us to compare large amounts of REE data, which can be difficult using standard REE patterns. When Dy/Dy* is combined with Dy/Yb (the slope of the middle-to-heavy REE pattern) REE patterns can effectively be classified by shape. We present a new set of high-quality REE (and other trace element) data for young volcanic rocks from six arcs. When plotted on the Dy/Dy*^Dy/Yb diagram they define a broad negative correlation from LREE-depleted (Tonga^Kermadec) to LREE-enriched (Philippines and Indonesia). This trend corresponds to decreasing Dy/Dy*, reflecting REE patterns varying from concave-down to concave-up respectively. When cogenetic suites from single volcanoes are plotted they define clear trends of decreasing Dy/Yb and Dy/Dy* with differentiation, roughly orthogonal to the general depletion^enrichment trend. The trends for single arc volcanoes are interpreted as most probably reflecting an amphibole control, consistent with the concomitant decreases in Ti/Ti* and increasing SiO2. Available distribution coefficients are, however, also permissive of cpx control on arc REE patterns. Estimated compositions of the continental crust fall along these same trends. In contrast, ocean island basalt (OIB) data all fall to high Dy/Yb, suggesting a significant control by garnet. A global consideration of the data suggests that (1) arc magmas are derived from variably depleted asthenospheric (mid-ocean ridge basalt) mantle sources, (2) arc magma (and continental crust) differentiation is controlled by a mineral phase (or phases) that preferentially partitions MREE and (3) OIB genesis appears to always involve garnet control. We propose that Dy/Dy* is potentially a powerful tool for representing the shapes of REE patterns, especially for large datasets. We also note the importance of using cogenetic rock suites to identify petrogenetic processes rather than regional suites.