ABSTRACT
The gravitational potential ϕ = GM/Rc2 at the surface of the white dwarf G191−B2B is 10 000 times stronger than that at the Earth’s surface. Numerous photospheric absorption features are ...detected, making this a suitable environment to test theories in which the fundamental constants depend on gravity. We have measured the fine-structure constant, α, at the white dwarf surface, used a newly calibrated Hubble Space Telescope (HST) Space Telescope Imaging Spectrograph spectrum of G191−B2B, two new independent sets of laboratory Fe v wavelengths, and new atomic calculations of the sensitivity parameters that quantify Fe v wavelength dependency on α. The two results obtained are: Δα/α0 = (6.36 ± 0.35stat ± 1.84sys) × 10−5 and Δα/α0 = (4.21 ± 0.48stat ± 2.25sys) × 10−5. The measurements hint that the fine-structure constant increases slightly in the presence of strong gravitational fields. A comprehensive search for systematic errors is summarized, including possible effects from line misidentifications, line blending, stratification of the white dwarf atmosphere, the quadratic Zeeman effect and electric field effects, photospheric velocity flows, long-range wavelength distortions in the HST spectrum, and variations in the relative Fe isotopic abundances. None fully account for the observed deviation but the systematic uncertainties are heavily dominated by laboratory wavelength measurement precision.
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•Grazed beef and sheep production has low efficiencies of nitrogen (N) use.•Grassland N use efficiency can be enhanced through sward-inclusion of clover.•Replacing chemical-N ...fertiliser with biological N fixation did not affect yields.•During reseeding grasslands become a carbon source.•After establishment new swards become a carbon sink.
There is currently much debate around the environmental implications of ruminant farming and a need for robust data on nitrogen (N) and carbon (C) fluxes from beef and sheep grazing systems. Here we use data collected from the North Wyke Farm Platform along with the SPACSYS model to examine the N and C budgets and the N use efficiency (NUE) of grassland swards at different stages of establishment. We assessed the transition from permanent pasture (PP) to a high-sugar grass (HSG), and a mixed sward of HSG with white clover (HSGC), identifying data specifically for the reseed (RS) years and the first year following RS (HSG-T and HSGC-T). Dominant fluxes for the N budget were N offtake as cut herbage and via livestock grazing, chemical-N fertiliser and N leaching at 88–280, 15–177, and 36–92 kg N ha−1 a−1, respectively. Net primary productivity, soil respiration and C offtake as cut herbage and via livestock grazing at 1.9–15.9, 1.74–12.5, and 0.34–11.7 t C ha−1 a−1, respectively, were the major C fluxes. No significant differences were found between the productivity of any of the swards apart from in the RS year of establishment. However, NUE of the livestock production system was significantly greater for the HSGC and HSGC-T swards at 32 and 42% compared to all other swards, associated with the low chemical-N fertiliser inputs to these clover-containing swards. Our findings demonstrate opportunities for improving NUE in grazing systems, but also the importance of setting realistic NUE targets for these systems to provide achievable goals for land-managers.
Diffuse water pollution from agriculture (DWPA) is a major environmental concern, with significant adverse impacts on both human and ecosystem health. However, without an appropriate understanding of ...the multiple factors impacting on water, mitigation measures cannot be targeted. Therefore, this paper addresses this gap in understanding, reporting the hydrochemical monitoring evidence collected from the UK Government's Demonstration Test Catchments (DTC) programme including contrasting chalk and clay/mudstone catchments. We use data collected at daily and sub-daily frequency over multiple sites to address: (1) How does the behaviour of the full range of nitrogen (N) species and phosphorus (P) fractions vary? (2) How do N species and P fractions vary inter- and intra-annually? (3) What do these data indicate about the primary pollution sources? And (4) which diffuse pollution mitigation measures are appropriate in our study landscapes?
Key differences in the rates of flux of nutrients were identified, dependent on catchment characteristics. Full N speciation and P fractionation, together with dissolved organic carbon (DOC) enabled identification of the most likely contributing sources in each catchment. Nitrate (NO3-N) was the dominant N fraction in the chalk whereas organic and particulate N comprised the majority of the load in the clay/mudstone catchments. Despite current legislation, orthophosphate (PO4-P) was not found to be the dominant form of P in any of the catchments monitored. The chalk sub-catchments had the largest proportion of inorganic/dissolved organic P (DOP), accompanied by episodic delivery of particulate P (PP). Contrastingly, the clay/mudstone sub-catchments loads were dominated by PP and DOP. Thus, our results show that by monitoring both the inorganic and organic fractions a more complete picture of catchment nutrient fluxes can be determined, and sources of pollution pin-pointed. Ultimately, policy and management to bring nutrient impacts under control will only be successful if a multi-stressor approach is adopted.
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•N speciation and P fractionation analysed for catchments with contrasting character.•Nitrate was the dominant N species in the chalk sub-catchments.•Organic and particulate N comprised the majority of the load in the clay rivers.•Orthophosphate was not found to be the dominant fraction in any of the catchments.•Particulate P was always an important P source, particularly in the clay catchments.
The biogeochemical cycling of carbon, water, energy, aerosols, and trace gases in the Amazon Basin was investigated in the project European Studies on Trace Gases and Atmospheric Chemistry as a ...Contribution to the Large‐Scale Biosphere‐Atmosphere Experiment in Amazonia (LBA‐EUSTACH). We present an overview of the design of the project, the measurement sites and methods, and the meteorological conditions during the experiment. The main results from LBA‐EUSTACH are: Eddy correlation studies in three regions of the Amazon Basin consistently show a large net carbon sink in the undisturbed rain forest. Nitrogen emitted by forest soils is subject to chemical cycling within the canopy space, which results in re‐uptake of a large fraction of soil‐derived NOx by the vegetation. The forest vegetation is both a sink and a source of volatile organic compounds, with net deposition being particularly important for partially oxidized organics. Concentrations of aerosol and cloud condensation nuclei (CCN) are highly seasonal, with a pronounced maximum in the dry (burning) season. High CCN concentrations from biomass burning have a pronounced impact on cloud microphysics, rainfall production mechanisms, and probably on large‐scale climate dynamics.
ABSTRACT
White dwarf (WD) atmospheres are subjected to gravitational potentials around 105 times larger than occur on Earth. They provide a unique environment in which to search for any possible ...variation in fundamental physics in the presence of strong gravitational fields. However, a sufficiently strong magnetic field will alter absorption line profiles and introduce additional uncertainties in measurements of the fine structure constant. Estimating the magnetic field strength is thus essential in this context. Here, we model the absorption profiles of a large number of atomic transitions in the WD photosphere, including first-order Zeeman effects in the line profiles, varying the magnetic field as a free parameter. We apply the method to a high signal-to-noise, high-resolution, far-ultraviolet Hubble Space Telescope/Space Telescope Imaging Spectrograph spectrum of the WD G191−B2B. The method yields a sensitive upper limit on its magnetic field of B < 2300 G at the 3σ level. Using this upper limit, we find that the potential impact of quadratic Zeeman shifts on measurements of the fine structure constant in G191−B2B is 4 orders of magnitude below laboratory wavelength uncertainties.
We examine the velocity structure in the gas associated with H i in the damped Lyα absorption system at redshift z= 1.7764 towards the QSO 1331 + 170 using Arecibo H i 21-cm data, optical spectra ...from the Keck High Resolution Echelle Spectrograph (HIRES) and European Southern Observatory (ESO) Very Large Telescope (VLT) Ultraviolet and Visual Echelle Spectrograph (UVES), and a previously published Hubble Space Telescope (HST) Space Telescope Imaging Spectrograph (STIS) ultraviolet spectrum. From the optical data we find at least two, and possibly three, components showing C i lines. One of these has very narrow lines with Doppler parameter b= 0.55 km s−1, corresponding to a kinetic temperature of 220 K if the broadening is thermal and with a 2σ upper limit of 480 K. We re-examine the H2 analysis undertaken by Cui et al. using the neutral carbon velocity structure, and find a model which is, unlike theirs, consistent with a mixture of collisional and background radiation excitation of the observed H2 rotational levels. Using Voigt profile fits to absorption lines from a range of singly ionized heavy elements we find eight components covering a velocity range of ∼110 km s−1, with a further outlier over 120 km s−1 away from the nearest in the main group. The H i structure is expected to follow some combination of the singly ionized and neutral gas, but the 21-cm absorption profile is considerably different. We suggest, as have others, that this may be because the different extent and brightness distributions of the radio and optical background sources mean that the sightlines are not the same, and so the spin temperature derived by comparing the Lyα and 21-cm line strengths has little physical meaning. The neutral and singly ionized heavy element line profiles also show significant differences, and so the dominant components in each appear to be physically distinct. Attempts to use the range of atomic masses to separate thermal and turbulent components of their Doppler widths were not generally successful, since there are several blended components and the useful mass range (about a factor of 2) is not very large. The velocity structure in all ionization stages up to +3, apart from the neutral heavy elements, is sufficiently complex that it is difficult to separate out the corresponding velocity components for different ionization levels and determine their column densities.
Cycling of low molecular weight dissolved organic nitrogen compounds constitutes an important component of soil organic matter turnover in soils. We determined how rapidly grassland soils can cycle ...urea, compared to the amino acid l-alanine, and the peptide l-trialanine. Using naturally occurring concentrations of 14C-labelled compounds the rates of removal from soil solution and subsequent mineralisation were measured. Biotic removal of all three compounds and subsequent mineralisation to CO2 occurred within minutes. This research has demonstrated, for the first time, the potential for rapid removal of urea at low concentrations by the soil microbial biomass.
•14C-urea cycling was examined in three grassland soils over short-timescales.•The key urea cycling processes examined were biotic removal and mineralisation.•Microbial removal from the soil solution and subsequent mineralisation of urea occurred within minutes.
Innovative solutions are required to provide mental health support at scale in low-resource humanitarian contexts. We aimed to assess the effectiveness of a facilitator-guided, group-based, self-help ...intervention (Self-Help Plus) to reduce psychological distress in female refugees.
We did a cluster randomised trial in rural refugee settlements in northern Uganda. Participants were female South Sudanese refugees with at least moderate levels of psychological distress (cutoff ≥5 on the Kessler 6). The intervention comprised access to usual care and five 2-h audio-recorded stress-management workshops (20–30 refugees) led by briefly trained lay facilitators, accompanied by an illustrated self-help book. Villages were randomly assigned to either intervention (Self-Help Plus or enhanced usual care) on a 1:1 basis. Within 14 villages, randomly selected households were approached. Screening of women in households continued until 20–30 eligible participants were identified per site. The primary outcome was individual psychological distress, assessed using the Kessler 6 symptom checklist 1 week before, 1 week after, and 3 months after intervention, in the intention-to-treat population. All outcomes were measured at the individual (rather than cluster) level. Secondary outcomes included personally identified problems, post-traumatic stress, depression symptoms, feelings of anger, social interactions with other ethnic groups, functional impairment, and subjective wellbeing. Assessors were masked to allocation. This trial was prospectively registered at ISRCTN, number 50148022.
Of 694 eligible participants (331 Self-Help Plus, 363 enhanced usual care), 613 (88%) completed all assessments. Compared with controls, we found stronger improvements for Self-Help Plus on psychological distress 3 months post intervention (β −1·20, 95% CI −2·33 to −0·08; p=0·04; d −0·26). We also found larger improvements for Self-Help Plus 3 months post-intervention for five of eight secondary outcomes (effect size range −0·30 to −0·36). Refugees with different trauma exposure, length of time in settlements, and initial psychological distress benefited similarly. With regard to safety considerations, the independent data safety management board responded to six adverse events, and none were evaluated to be concerns in response to the intervention.
Self-Help Plus is an innovative, facilitator-guided, group-based self-help intervention that can be rapidly deployed to large numbers of participants, and resulted in meaningful reductions in psychological distress at 3 months among South Sudanese female refugees.
Research for Health in Humanitarian Crises (R2HC) Programme.
The hydrological transport of low-molecular weight organic nitrogen (LMWON) compounds has received little attention in the literature, particularly relative to inorganic nitrogen (N), with less ...attention given to the decoupling of the carbon (C) and N cycles following rainfall events. We determined the impacts of the soil biota on the transport of N compounds in a loam soil, using
15
N and
13
C to trace the vertical transport of
15
N
13
C-urea,
15
N
13
C-amino acids,
15
NO
3
, and
15
NH
4
through the soil profile, following simulated rainfall events. This research has demonstrated that biotic assimilation leads to rapid decoupling of the C and N cycles during leaching, with C transport limited to the soil surface (< 2 cm), whereas N which was stored within the soil profile during a single rainfall event could be remobilised and leached (a further 2–6 cm) following an additional rainfall event.
By comparing the widths of absorption lines from O i, Si ii and Fe ii in the redshift z
abs= 2.076 single-component damped Lyα system in the spectrum of Q2206−199 we establish that these absorption ...lines arise in warm neutral medium (WNM) gas at ∼12 000 ± 3000 K. This is consistent with thermal equilibrium model estimates of ∼8000 K for the WNM in galaxies, but not with the presence of a significant cold component. It is also consistent with, but not required by, the absence of C ii fine structure absorption in this system. Some possible implications concerning abundance estimates in narrow-line WNM absorbers are discussed.
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