Planar laser-plasma interaction (LPI) experiments at the National Ignition Facility (NIF) have allowed access for the first time to regimes of electron density scale length (∼500 to 700 μm), ...electron temperature (∼3 to 5 keV), and laser intensity (6 to 16×10^{14} W/cm^{2}) that are relevant to direct-drive inertial confinement fusion ignition. Unlike in shorter-scale-length plasmas on OMEGA, scattered-light data on the NIF show that the near-quarter-critical LPI physics is dominated by stimulated Raman scattering (SRS) rather than by two-plasmon decay (TPD). This difference in regime is explained based on absolute SRS and TPD threshold considerations. SRS sidescatter tangential to density contours and other SRS mechanisms are observed. The fraction of laser energy converted to hot electrons is ∼0.7% to 2.9%, consistent with observed levels of SRS. The intensity threshold for hot-electron production is assessed, and the use of a Si ablator slightly increases this threshold from ∼4×10^{14} to ∼6×10^{14} W/cm^{2}. These results have significant implications for mitigation of LPI hot-electron preheat in direct-drive ignition designs.
Improved understanding of the interactive relationships of plant material decomposition kinetics to biochemical characteristics and nitrogen availability is required for terrestrial C accounting and ...sustainable land management. In this study, 15 typical and/or native Australian plant materials were finely ground and incubated with a sandy soil at 25
°C and 55% water holding capacity without nitrogen (−N) or with nitrogen (+N) addition (77
mg N
kg
−1 soil as KNO
3). The C mineralisation dynamics were monitored for 356 days and the initial biochemical characteristics of the plant materials were determined by NMR and wet-chemical analyses.
Under the −N treatment, C mineralisation rates of the plant materials were positively correlated with their initial N contents during the first several weeks, and then negatively correlated with lignin and polyphenols contents during the late stages of incubation. Thus the ratios of lignin/N, polyphenols/N and (lignin+polyphenols)/N had more consistent correlation with the cumulative amounts of C mineralised throughout the incubation than did any single component. In terms of the C types determined by NMR analysis, the C mineralisation rates were initially related positively to carbonyl C contents, and then negatively to aryl and
O-aryl C contents from day 3 onwards.
Addition of NO
3
−–N accelerated C mineralisation during the early stages, but resulted in lower cumulative C mineralisation at the end of the incubation for most plant materials. Under the +N treatment, the decomposition rates were correlated with the contents of lignin and the sum of cellulose+acid detergent-extractable non-phenolic compounds, or with aryl,
O-aryl and
N-alkyl+methoxyl C contents. Regardless of the N treatment, the ratios of aryl/carbonyl,
O-aryl/carbonyl and (aryl+
O-aryl)/carbonyl C had the closest and most consistent correlations with the cumulative C mineralisation among all biochemical indices examined.
A double exponential model with defined mineralisation rate constants for the active and slow pools was used to describe the C mineralisation dynamics. The biological meanings of the kinetically estimated active and slow pool sizes are interpreted and their relationships to the initial chemical/biochemical composition of the plant materials are explored.
The roles of microbial biomass (MBC) and substrate supply as well as their interaction with clay content in determining soil respiration rate were studied using a range of soils with contrasting ...properties. Total organic C (TOC), water-soluble organic carbon, 0.5
M K
2SO
4-extractable organic C and 33.3
mM KMnO
4-oxidisable organic carbon were determined as C availability indices. For air-dried soils, these indices showed close relationship with flush of CO
2 production following rewetting of the soils. In comparison, MBC determined with the chloroform fumigation–extraction technique had relatively weaker correlation with soil respiration rate. After 7
d pre-incubation, soil respiration was still closely correlated with the C availability indices in the pre-incubated soils, but poorly correlated with MBC determined with three different techniques—chloroform fumigation extraction, substrate-induced respiration, and chloroform fumigation–incubation methods. Results of multiple regression analyses, together with the above observations, suggested that soil respiration under favourable temperature and moisture conditions was principally determined by substrate supply rather than by the pool size of MBC. The specific respiratory activity of microorganisms (CO
2-C/MBC) following rewetting of air-dried soils or after 7
d pre-incubation was positively correlated with substrate availability, but negatively correlated with microbial pool size. Clay content had no significant effect on CO
2 production rate, relative C mineralization rate (CO
2-C/TOC) and specific respiratory activity of MBC during the first week incubation of rewetted dry soils. However, significant protective effect of clay on C mineralization was shown for the pre-incubated soils. These results suggested that the protective effect of clay on soil organic matter decomposition became significant as the substrate supply and microbial demand approached to an equilibrium state. Thereafter, soil respiration would be dependent on the replenishment of the labile substrate from the bulk organic C pool.
Climatic conditions and cultural practices in the sub-tropical and tropical high-rainfall regions in which sugarcane is grown in Australia are conducive to rapid carbon and nitrogen cycling. Previous ...research has identified substantial exchanges of methane (CH
4) and nitrous oxide (N
2O) between sugarcane soils and the atmosphere. However, that research has been mostly short-term. This paper describes recent work aimed at quantifying exchanges of CH
4 and N
2O from fertilised sugarcane soils over whole growing seasons. Micrometeorological and chamber techniques provided continuous measurements of gas emissions in whole-of-season studies in a burnt-cane crop on an acid sulfate soil (ASS) that was fertilised with 160
kg nitrogen (N)
ha
−1 as urea in the south of the sugarcane belt (Site 1), and in a crop on a more representative trash-blanketed soil fertilised with 150
kg urea-N
ha
−1 in the north (Site 2). Site 1 was a strong source of CH
4 with a seasonal emission (over 342 days) of 19.9
kg CH
4
ha
−1. That rate corresponds to 0.5–5% of those expected from rice and wetlands. The many drains in the region appear to be the main source. The net annual emission of CH
4 at Site 2 over 292 days was essentially zero, which contradicts predictions that trash-blankets on the soil are net CH
4 sinks. Emissions of N
2O from the ASS at Site 1 were extraordinarily large and prolonged, totalling 72.1
kg
N
2O
ha
−1 (45.9
kg
N
ha
−1) and persisting at substantial rates for 5 months. The high porosity and frequent wetting with consequent high water filled pore space and the high carbon content of the soil appear to be important drivers of N
2O production. At Site 2, emissions were much smaller, totalling 7.4
kg
N
2O
ha
−1 (4.7
kg
N
ha
−1), most of which was emitted in less than 3 months. The emission factors for N
2O (the proportion of fertiliser nitrogen emitted as N
2O–N) were 21% at Site 1 and 2.8% at Site 2. Both factors exceed the default national inventory value of 1.25%. Calculations suggest that annual N
2O production from Australian sugarcane soils is around 3.8
kt
N
2O, which is about one-half a previous estimate based on short-term measurements, and although ASS constitute only about 4% of Australia's sugarcane soils, they could contribute about 25% of soil emissions of N
2O from sugarcane. The uptake of 50–94
t
CO
2
ha
−1 from the atmosphere by the crops at both sites was offset by emissions of CH
4 and N
2O to the atmosphere amounting to 22
t
CO
2-e
ha
−1 at Site 1 and 2
t
CO
2-e
ha
−1 at Site 2.
We present the first results from a reverberation-mapping campaign undertaken during the first half of 2012, with additional data on one active galactic nucleus (AGN) (NGC 3227) from a 2014 campaign. ...Our main goals are (1) to determine the black hole masses from continuum-Hβ reverberation signatures, and (2) to look for velocity-dependent time delays that might be indicators of the gross kinematics of the broad-line region. We successfully measure Hβ time delays and black hole masses for five AGNs, four of which have previous reverberation mass measurements. The values measured here are in agreement with earlier estimates, though there is some intrinsic scatter beyond the formal measurement errors. We observe velocity-dependent Hβ lags in each case, and find that the patterns have changed in the intervening five years for three AGNs that were also observed in 2007.
Blazars are active galactic nuclei, which are powerful sources of radiation whose central engine is located in the core of the host galaxy. Blazar emission is dominated by non-thermal radiation from ...a jet that moves relativistically towards us, and therefore undergoes Doppler beaming. This beaming causes flux enhancement and contraction of the variability timescales, so that most blazars appear as luminous sources characterized by noticeable and fast changes in brightness at all frequencies. The mechanism that produces this unpredictable variability is under debate, but proposed mechanisms include injection, acceleration and cooling of particles, with possible intervention of shock waves or turbulence. Changes in the viewing angle of the observed emitting knots or jet regions have also been suggested as an explanation of flaring events and can also explain specific properties of blazar emission, such as intra-day variability, quasi-periodicity and the delay of radio flux variations relative to optical changes. Such a geometric interpretation, however, is not universally accepted because alternative explanations based on changes in physical conditions-such as the size and speed of the emitting zone, the magnetic field, the number of emitting particles and their energy distribution-can explain snapshots of the spectral behaviour of blazars in many cases. Here we report the results of optical-to-radio-wavelength monitoring of the blazar CTA 102 and show that the observed long-term trends of the flux and spectral variability are best explained by an inhomogeneous, curved jet that undergoes changes in orientation over time. We propose that magnetohydrodynamic instabilities or rotation of the twisted jet cause different jet regions to change their orientation and hence their relative Doppler factors. In particular, the extreme optical outburst of 2016-2017 (brightness increase of six magnitudes) occurred when the corresponding emitting region had a small viewing angle. The agreement between observations and theoretical predictions can be seen as further validation of the relativistic beaming theory.
There is a significant discrepancy between the values of the proton electric form factor, G(E)(p), extracted using unpolarized and polarized electron scattering. Calculations predict that small ...two-photon exchange (TPE) contributions can significantly affect the extraction of G(E)(p) from the unpolarized electron-proton cross sections. We determined the TPE contribution by measuring the ratio of positron-proton to electron-proton elastic scattering cross sections using a simultaneous, tertiary electron-positron beam incident on a liquid hydrogen target and detecting the scattered particles in the Jefferson Lab CLAS detector. This novel technique allowed us to cover a wide range in virtual photon polarization (ϵ) and momentum transfer (Q(2)) simultaneously, as well as to cancel luminosity-related systematic errors. The cross section ratio increases with decreasing ϵ at Q(2)=1.45 GeV(2). This measurement is consistent with the size of the form factor discrepancy at Q(2)≈1.75 GeV(2) and with hadronic calculations including nucleon and Δ intermediate states, which have been shown to resolve the discrepancy up to 2-3 GeV(2).
ABSTRACT
We present a multiwavelength study of the flat-spectrum radio quasar CTA 102 during 2013–2017. We use radio-to-optical data obtained by the Whole Earth Blazar Telescope, 15 GHz data from the ...Owens Valley Radio Observatory, 91 and 103 GHz data from the Atacama Large Millimeter Array, near-infrared data from the Rapid Eye Monitor telescope, as well as data from the Swift (optical-UV and X-rays) and Fermi (γ-rays) satellites to study flux and spectral variability and the correlation between flux changes at different wavelengths. Unprecedented γ-ray flaring activity was observed during 2016 November–2017 February, with four major outbursts. A peak flux of (2158 ± 63) × 10−8 ph cm−2 s−1, corresponding to a luminosity of (2.2 ± 0.1) × 1050 erg s−1, was reached on 2016 December 28. These four γ-ray outbursts have corresponding events in the near-infrared, optical, and UV bands, with the peaks observed at the same time. A general agreement between X-ray and γ-ray activity is found. The γ-ray flux variations show a general, strong correlation with the optical ones with no time lag between the two bands and a comparable variability amplitude. This γ-ray/optical relationship is in agreement with the geometrical model that has successfully explained the low-energy flux and spectral behaviour, suggesting that the long-term flux variations are mainly due to changes in the Doppler factor produced by variations of the viewing angle of the emitting regions. The difference in behaviour between radio and higher energy emission would be ascribed to different viewing angles of the jet regions producing their emission.
Youth mental health is a major concern both in Australia and internationally. Identifying at-risk young people is a core service priority. This report describes a “Youth Social Inclusion Program” ...developed in Australia to assist young people identified as having social difficulties that prevent them linking into formal mental health services. This report describes the Australian service context and uses the “program explication” methodology to document: the program activities, therapeutic processes, and underpinning evidence for the benefits of this service. Program explication is a consulting method designed to assist services to identify and review implicit program logic assumptions against evaluation literature. We demonstrate the application of this method in exploring the assumptions and evidence for the Youth Social Inclusion Program, targeting outreach to socially anxious young people in Australia. The Youth Social Inclusion Program involved seven logically consistent activities. Our literature search revealed moderate evidence for the expected benefits of the activities. This practice-based design drew on several theoretical perspectives. Given that the program logic has been established, we outline a proposal for further evaluation.
•Youth Social Inclusion Program targets socially anxious and isolated young people.•Program explication reviews program logic against evaluation literature.•Evidence-informed activities designed to outreach to at-risk young people.
Abstract
We report on long-term multiwavelength monitoring of blazar Mrk 421 by the GLAST-AGILE Support Program of the Whole Earth Blazar Telescope (GASP-WEBT) collaboration and Steward Observatory, ...and by the Swift and Fermi satellites. We study the source behaviour in the period 2007–2015, characterized by several extreme flares. The ratio between the optical, X-ray and γ-ray fluxes is very variable. The γ-ray flux variations show a fair correlation with the optical ones starting from 2012. We analyse spectropolarimetric data and find wavelength-dependence of the polarization degree (P), which is compatible with the presence of the host galaxy, and no wavelength dependence of the electric vector polarization angle (EVPA). Optical polarimetry shows a lack of simple correlation between P and flux and wide rotations of the EVPA. We build broad-band spectral energy distributions with simultaneous near-infrared and optical data from the GASP-WEBT and ultraviolet and X-ray data from the Swift satellite. They show strong variability in both flux and X-ray spectral shape and suggest a shift of the synchrotron peak up to a factor of ∼50 in frequency. The interpretation of the flux and spectral variability is compatible with jet models including at least two emitting regions that can change their orientation with respect to the line of sight.
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