High sensitivity measurement of 224Ra and 226Ra in water with an improved hydrous titanium oxide technique at the Sudbury Neutrino Observatory

The existing hydrous titanium oxide (HTiO) technique for the measurement of 224Ra and 226Ra in the water at the Sudbury Neutrino Observatory (SNO) has been changed to make it faster and less sensitive to trace impurities in the HTiO eluate. Using HTiO-loaded filters followed by cation exchange adsorption and HTiO co-precipitation, Ra isotopes from 200-450 tonnes of heavy water can be extracted and concentrated into a single sample of a few millilitres with a total chemical efficiency of 50%. Combined with beta-alpha coincidence counting, this method is capable of measuring 2.0x10^3 uBq/kg of 224Ra and 3.7x10^3 uBq/kg of 226Ra from the 232Th and 238U decay chains, respectively, for a 275 tonne D2O assay, which are equivalent to 5x10^16 g Th/g and 3x10^16 g U/g in heavy water.Comment: 8 Pages, 2 figures and 2 table

Deep Eyedentification: Biometric Identification using Micro-Movements of the Eye

We study involuntary micro-movements of the eye for biometric identification. While prior studies extract lower-frequency macro-movements from the output of video-based eye-tracking systems and engineer explicit features of these macro-movements, we develop a deep convolutional architecture that processes the raw eye-tracking signal. Compared to prior work, the network attains a lower error rate by one order of magnitude and is faster by two orders of magnitude: it identifies users accurately within seconds

The Anatomy of a Buried Submarine Hydrothermal System, Clark Volcano, Kermadec Arc, New Zealand

Clark volcano of the Kermadec arc, northeast of New Zealand, is a large stratovolcano comprised of two coalescing volcanic cones; an apparently younger, more coherent, twin-peaked edifice to the northwest and a relatively older, more degraded and tectonized cone to the southeast. High-resolution water column surveys show an active hydrothermal system at the summit of the NW cone largely along a ridge spur connecting the two peaks, with activity also noted at the head of scarps related to sector collapse. Clark is the only known cone volcano along the Kermadec arc to host sulfide mineralization. Volcano-scale gravity and magnetic surveys over Clark show that it is highly magnetized, and that a strong gravity gradient exists between the two edifices. Modeling suggests that a crustal-scale fault lies between these two edifices, with thinner crust beneath the NW cone. Locations of regional earthquake epicenters show a southwest-northeast trend bisecting the two Clark cones, striking northeastward into Tangaroa volcano. Detailed mapping of magnetics above the NW cone summit shows a highly magnetized “ring structure” ~350 m below the summit that is not apparent in the bathymetry; we believe this structure represents the top of a caldera. Oblate zones of low (weak) magnetization caused by hydrothermal fluid upflow, here termed “burn holes,” form a pattern in the regional magnetization resembling Swiss cheese. Presumably older burn holes occupy the inner margin of the ring structure and show no signs of hydrothermal activity, while younger burn holes are coincident with active venting on the summit. A combination of mineralogy, geochemistry, and seafloor mapping of the NW cone shows that hydrothermal activity today is largely manifest by widespread diffuse venting, with temperatures ranging between 56° and 106°C. Numerous, small (≤30 cm high) chimneys populate the summit area, with one site host to the ~7-m-tall “Twin Towers” chimneys with maximum vent fluid temperatures of 221°C (pH 4.9), consistent with δ³⁴S[subscript anhydrite-pyrite] values indicating formation temperatures of ~228° to 249°C. Mineralization is dominated by pyrite-marcasite-barite-anhydrite. Radiometric dating using the ²²⁸Ra/²²⁶Ra and ²²⁶Ra/Ba methods shows active chimneys to be <20 with most <2 years old. However, the chimneys at Clark show evidence for mixing with, and remobilizing of, barite as old as 19,000 years. This is consistent with Nd and Sr isotope compositions of Clark chimney and sulfate crust samples that indicate mixing of ~40% seawater with a vent fluid derived from low K lavas. Similarly, REE data show the hydrothermal fluids have interacted with a plagioclase-rich source rock. A holistic approach to the study of the Clark hydrothermal system has revealed a two-stage process whereby a caldera-forming volcanic event preceded a later cone-building event. This ensured a protracted (at least 20 ka yrs) history of hydrothermal activity and associated mineral deposition. If we assume at least 200-m-high walls for the postulated (buried) caldera, then hydrothermal fluids would have exited the seafloor 20 ka years ago at least 550 m deeper than they do today, with fluid discharge temperatures potentially much hotter (~350°C). Subsequent to caldera infilling, relatively porous volcaniclastic and other units making up the cone acted as large-scale filters, enabling ascending hydrothermal fluids to boil and mix with seawater subseafloor, effectively removing the metals (including remobilized Cu) in solution before they reached the seafloor. This has implications for estimates for the metal inventory of seafloor hydrothermal systems pertaining to arc hydrothermal systems.This is the publisher’s final pdf. The published article is copyrighted by the Society of Economic Geologists and can be found at: http://economicgeology.org

A Motion Illusion Reveals Mechanisms of Perceptual Stabilization

Visual illusions are valuable tools for the scientific examination of the mechanisms underlying perception. In the peripheral drift illusion special drift patterns appear to move although they are static. During fixation small involuntary eye movements generate retinal image slips which need to be suppressed for stable perception. Here we show that the peripheral drift illusion reveals the mechanisms of perceptual stabilization associated with these micromovements. In a series of experiments we found that illusory motion was only observed in the peripheral visual field. The strength of illusory motion varied with the degree of micromovements. However, drift patterns presented in the central (but not the peripheral) visual field modulated the strength of illusory peripheral motion. Moreover, although central drift patterns were not perceived as moving, they elicited illusory motion of neutral peripheral patterns. Central drift patterns modulated illusory peripheral motion even when micromovements remained constant. Interestingly, perceptual stabilization was only affected by static drift patterns, but not by real motion signals. Our findings suggest that perceptual instabilities caused by fixational eye movements are corrected by a mechanism that relies on visual rather than extraretinal (proprioceptive or motor) signals, and that drift patterns systematically bias this compensatory mechanism. These mechanisms may be revealed by utilizing static visual patterns that give rise to the peripheral drift illusion, but remain undetected with other patterns. Accordingly, the peripheral drift illusion is of unique value for examining processes of perceptual stabilization

Microsaccades and preparatory set: a comparison between delayed and immediate, exogenous and endogenous pro- and anti-saccades

When we fixate an object, our eyes are not entirely still, but undergo small displacements such as microsaccades. Here, we investigate whether these microsaccades are sensitive to the preparatory processes involved in programming a saccade. We show that the frequency of microsaccades depends in a specific manner on the intention where to move the eyes (towards a target location or away from it), when to move (immediately after the onset of the target or after a delay), and what type of cue is followed (a peripheral onset or a centrally presented symbolic cue). In particular, in the preparatory interval before and early after target onset, more microsaccades were found when a delayed saccade towards a peripheral target was prepared than when a saccade away was programmed. However, no such difference in the frequency of microsaccades was observed when saccades were initiated immediately after the onset of the target or when the saccades were programmed on the basis of a centrally presented arrow cue. The results are discussed in the context of the neural correlates of response preparation, known as preparatory set.status: publishe

Asia scope and sequence for studies of society and environment: Engaging young Australians with Asia

The purpose of the Asia Scope and Sequence for Studies of Society and Environment is to: articulate key curriculum concepts and content across the compulsory years of schooling (to Year 10); provide advice and support to teachers of Studies of Society and Environment in order to facilitate their efforts to engage young Australians with Asia; point teachers to existing exemplary resources that allow students to engage with Asia in the Studies of Society and Environment classroom; and become the basis of an online schema linking to a repository of curriculum materials that will be extended over time, and that is freely available and accessible to teachers in Australian schools

Primary and secondary teachers' perceptions of salinity curriculum materials

Teachers in Western Australia has been provided with the kit, Salinity in the Classroom: A Resource for Western Australian Schools. We report on the views of teachers' experiences with this kit: a written survey of 63 teachers and interviews with nine teachers. Three themes emerged from the teacher responses: content, pedagogy and distribution of resources. We also reflect on ways that the science education community can contribute to improving such curriculum materials