This clinical methods comparison study describes the difference between light levels measured at the wrist (Actiwatch-L) and at the eye (Daysimeter) in a postoperative in-patient population. The mean ...difference between the two devices was less than 10 lux at light levels less than 5000 lux. Agreement between the devices was found to decrease as eye-level light exposure increased. Measurements at eye level of 5000 lux or more corresponded to a difference between the devices of greater than 100 lux. Agreement between the eye- and wrist-level light measurements also appears to be influenced by time of day. During the day, the measurement differences were on average 50 lux higher at eye level, whereas at night they were on average 50 lux lower. Although the wrist-level monitor was found to underestimate light exposure at higher light levels, it was well tolerated by participants in the clinical setting. In contrast, the eye-level monitor was cumbersome and uncomfortable for the patients to wear. This study provides light-exposure data on patients in real conditions in the clinical environment. The results show that wrist-level monitoring provides an adequate estimate of light exposure for in-hospital circadian studies. (Author correspondence: g.warman@auckland.ac.nz)
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A first-ever demonstration of controlling power and torque injection through time evolution of neutral beam energy has been achieved in recent experiments at the DIII-D tokamak (Luxon 2002 Nucl. ...Fusion 42 614). Pre-programmed waveforms for the neutral beam energy produce power and torque inputs that can be separately and continuously controlled. Previously, these inputs were tailored using on/off modulation of neutral beams resulting in large perturbations (e.g. power swings of over 1 MW). The new method includes, importantly for experiments, the ability to maintain a fixed injected power while varying the torque. In another case, different beam energy waveforms (in the same plasma conditions) produce significant changes in the observed spectrum of beam ion-driven instabilities. Measurements of beam ion loss show that one energy waveform results in the complete avoidance of coherent losses due to Alfvénic instabilities. This new method of neutral beam operation is intended for further application in a variety of DIII-D experiments including those concerned with high-performance steady state scenarios, fast particle effects, and transport in the low torque regime. Developing this capability would provide similar benefits and improved plasma control for other magnetic confinement fusion facilities.
Zircon grains in rocks from the Yilgarn Craton record crust formation dating back to shortly after the formation of the Earth. However, much of the evidence is cryptic and not apparent in the mapped ...geology. New Lu-Hf isotopic results, combined with existing Lu-Hf and Sm-Nd isotopic data, indicate five model-age probability peaks in the central and eastern Yilgarn Craton: at ca 4200, ca 3500, ca 3100, ca 2800 Ma and ca 2700 Ma. The ca 3100 Ma, ca 2800 Ma and ca 2700 Ma model-age peaks likely correspond to crust formation events. Evidence of the earlier peaks is not seen directly in the rock record, although zircon crystals in rocks of the Southern Cross Domain of the Youanmi Terrane show a long history of reworking pointing back to mantle extraction more than 4200 million years ago. The earliest peak is not recorded in the Eastern Goldfields Superterrane, indicating that crust formation in this region post-dated the earliest development of the Yilgarn Craton. Subsequent, broadly contemporaneous, episodes of mantle extraction and crustal reworking are indicated by the datasets for both the Eastern Goldfields Superterrane and the Southern Cross Domain. Magmas in the Eastern Goldfields Superterrane had a substantial juvenile input whereas those in the Southern Cross Domain recorded major reworking of older crust. The rock records for both the Eastern Goldfields Superterrane and the Southern Cross Domain share common elements of history after ca 2960 Ma. Both regions appear to have been subjected to major heating at ca 3100 Ma and ca 2800 Ma that resulted in the generation of juvenile crust in the east and reworking of older crust in the west. The ca 3500 Ma event is not readily evident in the rock record and may reflect a mixed age. However, the ca 3100 Ma and ca 2800 Ma events are recorded by both granite suites and greenstone successions across the craton. The ca 2700 Ma event is most evident in rocks from the Eastern Goldfields Superterrane.
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New geological mapping and geochronology in the northeast Yilgarn Craton has changed our geological understanding of this region. The Yilgarn Craton had previously been divided into a series of ...terranes, with the easternmost Eastern Goldfields Superterrane separated from the Youanmi Terrane, which forms the core of the protocraton, by the Ida Fault zone. The Eastern Goldfields Superterrane was subdivided into the western Kalgoorlie, central Kurnalpi, and eastern Burtville terranes, with the latter, easternmost terrane the focus of the new field mapping and geochronology. Four main episodes of greenstone crustal growth have been recognised in the northeast Yilgarn Craton: ca 2970-2910 Ma, ca 2815-2800 Ma, 2775-2735 Ma, and ca 2715-2630 Ma. Rather than a single Burtville Terrane, as previously proposed, the distribution of greenstone magmatism reveals a previously unrecognised young (<2720 Ma) Yamarna Terrane in the northeast corner of the craton. The Yamarna Terrane is separated from the older (>2735 Ma) redefined Burtville Terrane by the Yamarna Shear Zone, which is now regarded as a terrane boundary. The correlation of lithologies and ages of magmatism in the northeast Yilgarn Craton with the rest of the craton indicates that the Burtville Terrane has affinities with the Youanmi Terrane that forms the nucleus of the craton, whereas the Yamarna Terrane has affinities with the Kalgoorlie Terrane in the west of the Eastern Goldfields Superterrane. The Burtville and Youanmi terranes shared a common history from ca 2970 Ma until ca 2720 Ma, when regional extension accommodated deposition of the Kambalda Sequence in the Kalgoorlie Terrane. It appears that extension also occurred along the Yamarna Shear Zone after ca 2720 Ma, accommodating the deposition of greenstones in the Yamarna Terrane. Like the Kalgoorlie and Kurnalpi Terranes, the Yamarna Terrane contains inherited zircon and local older rocks. This suggests that the ca 2720 Ma extension did not result in widespread rifting and the formation of extensive oceanic crust. Rather, there was thinning of older crust that extended right across the current Yilgarn Craton.
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Helicon current drive, also called fast wave current drive in the lower hybrid range of frequencies, has long been regarded as a promising current drive tool for reactor grade plasmas. A newly ...installed MW-level system at DIII-D will be the first test of this technology in reactor-relevant plasmas, in the sense that full single-pass absorption is expected. A 30-module traveling wave antenna has been installed and optimized in-vessel in early 2020. The linear electromagnetic characteristics of the unloaded module array have been extensively tested both on the bench and in the vessel at instrumentation power levels. Excellent performance has been achieved, ~2% reflected power and ~1.5% dissipated power per module in air, in a 10 MHz band around 476 MHz. Stripline feeds on both ends of the antenna allow either co or counter current drive. The installation of a 1.2 MW klystron and associated high-power electronics was completed in Fall 2020. Commissioning of the antenna is ongoing. An important goal of this experiment is to validate the helicon current drive physics basis using an extensive set of new and upgraded diagnostics.
We report measurements and ab initio calculations of a large
negative nonlinear refractive index in xenon for linearly-polarized KrF laser light, and describe a simple experiment that demonstrates ...xenon compensation of both self-focusing and self-phase modulation. This effect arises because KrF laser frequencies lie just above a two-photon resonance with the Xe
6p
1
2
0
state at 249.6 nm. The negative nonlinear index resulted in self-defocusing of 10 ps linearly-polarized 248.4 nm pulses in a 4.6 m cell at Xe pressures up to 1000 Torr. Numerical simulations of this defocusing at pressures up to 266 Torr yield a nonlinear index
n
2 = − (2.06 ± 0.14) × 10
−14 esu for 760 Torr and 300 K, but the simulations fail to adequately reproduce the shapes of the measured profiles at pressures significantly above 266 Torr. In the compensation experiment, the cell was first filled up to 1260 Torr with pure carbon dioxide, whose large positive
n
2 resulted in self-focusing of the beam. A small amount of Xe was then added to the cell and allowed to mix with the CO
2. Less than 130 Torr of Xe completely compensated the 1260 Torr of CO
2, allowing both the spectrum and beam profile to be recovered. Numerical simulations of the self-focusing measurements yield a nonlinear index of (1.60 ± 0.07) × 10
−15 esu for CO
2, and the compensation experiment gives
n
2(Xe) = − (1.82 ± 0.08) × 10
−14esu at 760 Torr, 300 K, and 248.4 nm. The combined defocusing and compensation measurements give
n
2(Xe)=−(1.97±0.23)×10
−14 esu, in good agreement with our ab initio calculation of − (1.54 ± 0.30) × 10
−14 esu.
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•A stratigraphic, geochemical and geochronological study of the Agnew Greenstone Belt.•Nine conformable subaqueous lavas and comagmatic intrusions erupted over ∼30Ma.•Two cycles identified, each ...starting with komatiite and becoming more evolved and contaminated.•∼2720–2705Ma Kalgoorlie Terrane volcanism forms two groups separated by Bardoc Fault.•∼2705–2690Ma Kalgoorlie Terrane volcanism is widespread, correlating over 100skm.
The thick package of ∼2.7Ga mafic and ultramafic lavas and intrusions preserved among the Neoarchean of the Kalgoorlie Terrene in Western Australia provides valuable insight into geological processes controlling the most prodigious episode of growth and preservation of juvenile continental crust in Earth's history. Limited exposure of these rocks results in uncertainty about their age, physical and chemical characteristics, and stratigraphic relationships. This in turn prevents confident correlation of regional occurrences of mafic and ultramafic successions (both intrusive and extrusive) and hinders the interpretation of tectonic setting and magmatic evolution. A recent stratigraphic drilling program of the Neoarchean stratigraphy of the Agnew Greenstone Belt in Western Australia has provided continuous exposures through a c. 7km thick sequence of mafic and ultramafic units. In this study, we present a volcanological, lithogeochemical and chronological study of the Agnew Greenstone Belt, and provide the first pre-2690Ma regional correlation across the Kalgoorlie Terrane. The Agnew Greenstone Belt records ∼30m.y. of episodic ultramafic–mafic magmatism that includes two cycles, each defined by a komatiite that is overlain by units that become more evolved and contaminated with time. The sequence is divided into nine conformable packages, each consisting of stacked subaqueous lava flows and comagmatic intrusions, as well as two sills without associated extrusions. Lavas, with the exception of intercalations between two units, form a layer-cake stratigraphy and were likely erupted from a system of fissures tapping the same magma source. The komatiites are not contaminated by continental crust (La/SmPM∼0.7) and are of the Al-undepleted Munro-type. Crustal contamination is evident in many units (Songvang Basalt, Never Can Tell Basalt, Redeemer Basalt, and Turrett Dolerite), as judged by La/Sm>1, negative Nb and Ti anomalies, and geochemical mixing trends towards felsic contaminants. Crystal fractionation was also significant, with early olivine and chromite (Mg#>65) followed by plagioclase and clinopyroxene removal (Mg<65), and in the most evolved case, titanomagnetite accumulation. Three new TIMS dates on granophyric zones of mafic sills and one ICP-MS date from an interflow felsic tuff are presented and used for regional stratigraphic correlation. Cycle I magmatism began at ∼2720Ma and ended ∼2705Ma, whereas cycle II began ∼2705Ma and ended at 2690.7±1.2Ma. Regional correlations indicate the western Kalgoorlie Terrane consists of a remarkably similar stratigraphy that can be recognised at Agnew, Ora Banda and Coolgardie, whereas the eastern part of the terrane (e.g., Kambalda Domain) does not include cycle I, but correlates well with cycle II. This research supports an autochthonous model of greenstone formation, in which one large igneous province, represented by two complete cycles, is constructed on sialic crust. New stratigraphic correlations for the Kalgoorlie Terrane indicate that many units can be traced over distances >100km, which has implications for exploration targeting for stratigraphically hosted ultramafic Ni and VMS deposits.
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