67,340 research outputs found
Surface and subsurface characterisation of salt pans
No full textThis data collection bundles six datasets about the surface, subsurface and environmental conditions of saltpans that express polygonal patterns in their surface salt crust that are fully described in Lasser et al., 2020 (https://doi.org/10.5194/essd-2020-86). Information stems from 5 field sites at Badwater Basin and 21 field sites at Owens Lake – both in central California, US. All data was recorded during two field campaigns, from between November and December, 2016, and in January 2018. (1) Lasser, J., Goehring, L. (2020a). Grain size distributions of sand samples from Owens Lake and Badwater Basin in central California, collected in 2016 and 2018. PANGAEA - Data Publisher for Earth &amp; Environmental Science. https://doi.org/10.1594/PANGAEA.910996 (2) Lasser, J., Goehring, L. (2020b): Subsurface salt concentration profiles and pore water density measurements from Owens Lake, central California, measured in 2018 (Version 2). PANGAEA, https://doi.org/10.1594/PANGAEA.922264 (3) Lasser, J., Goehring, L., Nield, J. M. (2020). Images and Videos from Owens Lake and Badwater Basin in central California, taken in 2016 and 2018 [Data set]. PANGAEA - Data Publisher for Earth &amp; Environmental Science. https://doi.org/10.1594/PANGAEA.911054 (4) Lasser, J., Karius, V. (2020). Chemical characterization of salt samples from Owens Lake and Badwater Basin, central California, collected in 2016 and 2018. PANGAEA - Data Publisher for Earth &amp; Environmental Science. https://doi.org/10.1594/PANGAEA.911239 (5) Nield, J. M., Lasser, J., Goehring, L. (2020). TLS surface scans from Owens Lake and Badwater Basin, central California, measured in 2016 and 2018 [Data set]. PANGAEA - Data Publisher for Earth &amp; Environmental Science. https://doi.org/10.1594/PANGAEA.911233 (6) Nield, J. M., Lasser, J., Goehring, L. (2020): Temperature and humidity time-series from Owens Lake, central California, measured during one week in November 2016 (Version 2). Max Planck Institute for Dynamics and Self-Organization, PANGAEA, https://doi.org/10.1594/PANGAEA.922231</span
Analysis of single-crystal neutron diffuse scattering from ice Ih
No full textThe single-crystal neutron diffuse scattering from ice contains a great deal of information, not only on the disorder of the hydrogen atoms but also on the instantaneous atomic positions. It is difficult to extract this information, and a series of reverse Monte Carlo (RMC) techniques have been developed for this purpose, with mixed success. The present paper presents new constrained RMC methods used to try and obtain more reliable information on the static and thermal disorder in ice. However it has been found that the RMC results depend strongly on the starting configuration, meaning that some of the conclusions of the earlier paper of Nield and Whitworth (Nield, V. M.; Whitworth, R. W. J. Phys.: Condens. Matter 1995, 7, 8258) are invalid
Evidence for the decay B0→J/ψω and measurement of the relative branching fractions of meson decays to J/ψη and J/ψη′
No full textFirst evidence of the B 0 → J / ψ ω decay is found and the B s 0 → J / ψ η and B s 0 → J / ψ η ′ decays are studied using a dataset corresponding to an integrated luminosity of 1.0 fb -1 collected by the LHCb experiment in proton-proton collisions at a centre-of-mass energy of sqrt(s) = 7 TeV. The branching fractions of these decays are measured relative to that of the B 0 → J / ψ ρ 0 decay:frac(B (B 0 → J / ψ ω), B (B 0 → J / ψ ρ 0)) = 0.89 ± 0.19 (stat) - 0.13 + 0.07 (syst),frac(B (B s 0 → J / ψ η), B (B 0 → J / ψ ρ 0)) = 14.0 ± 1.2 (stat) - 1.5 + 1.1 (syst) - 1.0 + 1.1 (frac(f d, f s)),frac(B (B s 0 → J / ψ η ′), B (B 0 → J / ψ ρ 0)) = 12.7 ± 1.1 (stat) - 1.3 + 0.5 (syst) - 0.9 + 1.0 (frac(f d, f s)), where the last uncertainty is due to the knowledge of f d / f s, the ratio of b-quark hadronization factors that accounts for the different production rate of B 0 and B s 0 mesons. The ratio of the branching fractions of B s 0 → J / ψ η ′ and B s 0 → J / ψ η decays is measured to befrac(B (B s 0 → J / ψ η ′), B (B s 0 → J / ψ η)) = 0.90 ± 0.09 (stat) - 0.02 + 0.06 (syst)
Breakwater morphological modelling: predicting equilibrium morphologies using entropy based techniques
No full textIn order to design suitable breakwaters for beach protection, morphological modelling is required. This modelling can be utilised to determine the effectiveness of different structures and the position that sand is likely to move to when a stable, equilibrium morphology develops. The majority of morphological models currently used are time-step based. They involve the interaction of wave, current, sediment transport and sediment balance modules. Sediment is transported over a small amount of time, after which the modules are updated and sediment transport calculations begin again. In this paper a new method is put forward, where the need to time step is avoided. Different morphologies are compared directly, based on an objective function, where morphologies closer to the desired equilibrium have a smaller net sediment transport. Morphologies are modified using global optimisation techniques. This new method is able to predict sediment deposition in the lee of detached shore parallel breakwaters
Spatial variability of the atmosphere over southern England, and its effect on scene-based atmospheric corrections
No full textEarth observation data acquired in the optical region require atmospheric correction before they can be used quantitatively. Most operational methods of atmospheric correction assume that the atmospheric properties are uniform across the image, but this assumption is unlikely to be valid for large images. This study aims to characterize the spatial variation in atmospheric properties over a typical mid-latitude area (southern England), and to assess the errors that would result from applying a scene-based atmospheric correction to data collected under this variable atmosphere. Two key atmospheric properties – aerosol optical thickness (AOT) and precipitable water content (PWC) – are assessed over two clear days in June 2006, and results show an AOT range of approximately 0.1–0.5 and a PWC range of 1.5–3.0 cm. Radiative transfer modelling shows that errors in reflectance of up to 1.7 percentage points, and up to a 5% change in normalized difference vegetation index, can be caused by AOT variability, but that PWC variability has minimal effects. Sensitivity analyses also show that the high uncertainty of many data sources used to provide AOT values for atmospheric correction may also lead to significant errors in the resulting products. The spatial variability of the atmosphere cannot be ignored, and we are in need of operational, generic methods to perform a spatially variable atmospheric correction
Self-organisation and entropy in the 2-D morphological modelling of an open channel
No full textA robust method has been developed to predict the two-dimensional morphology of sediment in a rectangular channel that contains a constriction, using self-organisation. This method overcomes the need to model the formation of dynamic equilibrium morphologies over time, which can lead to the amplification of small errors in each time step. This method will be of benefit to areas of coastal research such as the prediction of equilibrium formations behind a detached breakwater, and the formation of complex morphology in an estuary. This paper includes a comparison of a number of different methods and objective function formulae and discusses their strengths and weaknesses. It concludes that the self-organisation method compares favourably to a process-based method and a laboratory study, and outperforms extrema hypotheses methods
Structure of a large photosystem II supercomplex from Acaryochloris marina
No full textAcaryochloris marina is a prochlorophyte-like cyanobacterium containing both phycobilins and chlorophyll d as light harvesting pigments. We show that the chlorophyll d light harvesting system, composed of Pcb proteins, functionally associates with the photosystem II (PSII) reaction center (RC) core to form a giant supercomplex. This supercomplex has a molecular mass of about 2300 kDa and dimensions of 385 A x 240 A. It is composed of two PSII-RC core dimers arranged end-to-end, flanked by eight symmetrically related Pcb proteins on each side. Thus each PSII-RC monomer has four Pcb subunits acting as a light harvesting system which increases the absorption cross section of the PSII-RC core by almost 200%.<br/
Letter from Carl Hayden to M. J. Riordan
No full textLetter from Carl Hayden to M. J. Riordan expressing his support for Coconino County in turning over the Bright Angel Trail to the federal government
Iron deficiency induces a chlorophyll d-binding Pcb antenna system around Photosystem I in Acaryochloris marina.
No full textThe prochlorophyte-like cyanobacterium Acaryochloris marina contains two pcb genes, pcbA and pcbC, which encode chlorophyll (Chl) d-binding antenna proteins PcbA and PcbC, respectively. Using real-time reverse transcriptase polymerase chain reaction (RT-PCR), it is shown that when Acaryochloris cells are grown in an iron-deficient medium, the transcription of the pcbC gene is up-regulated compared to that of pcbA. Biochemical and immunological analyses indicated that under the same iron-deficient conditions, the level of Photosystem I (PSI) decreased compared with that of Photosystem II (PSII). Electron microscopy revealed that concomitant with these changes was the formation of Pcb-PSI supercomplexes which, in their largest form, were composed of 18 Pcb subunits forming a ring around the trimeric PSI reaction centre core. Mass spectrometry indicated that the PcbC protein is the main constituent of this outer PSI antenna system. It is therefore concluded that in Acaryochloris, the PcbC protein forms an antenna for PSI when iron levels become limiting and in this way compensates for the drop in the level of PSI relative to PSII which occurs under these conditions
The dynamism of salt crust patterns on playas
No full textPlayas are common in arid environments and can be major sources of mineral dust that can influence global climate. These landforms typically form crusts that limit evaporation and dust emission, modify surface erosivity and erodibility, and can lead to over prediction or under prediction of (1) dust-emission potential and (2) water and heat fluxes in energy balance modeling. Through terrestrial laser scanning measurements of part of the Makgadikgadi Pans of Botswana (a Southern Hemisphere playa that emits significant amounts of dust), we show that over weeks, months, and a year, the shapes of these surfaces change considerably (ridge thrusting of >30 mm/week) and can switch among continuous, ridged, and degraded patterns. Ridged pattern development changes the measured aerodynamic roughness of the surface (as much as 3 mm/week). The dynamic nature of these crusted surfaces must be accounted for in dust entrainment and moisture balance formulae to improve regional and global climate models
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