2,360 research outputs found
Cyclic and Long-term Variation of Sunspot Magnetic Fields
Measurements from the Mount Wilson Observatory (MWO) are used to study the
long-term variations of sunspot field strengths from 1920 to 1958. Following a
modified approach similar to that in Pevtsov et al. (2011), for each observing
week we select a single sunspot with the strongest field strength measured that
week and then compute monthly averages of these weekly maximum field strengths.
The data show the solar cycle variation of the peak field strengths with an
amplitude of about 500-700 gauss (G), but no statistically significant
long-term trends. Next, we use the sunspot observations from the Royal
Greenwich Observatory (RGO) to establish a relationship between the sunspot
areas and the sunspot field strengths for Cycles 15-19. This relationship is
then used to create a proxy of peak magnetic field strength based on sunspot
areas from the RGO and the USAF/NOAA network for the period from 1874 to early
2012. Over this interval, the magnetic field proxy shows a clear solar cycle
variation with an amplitude of 500-700 G and a weaker long-term trend. From
1874 to around 1920, the mean value of magnetic field proxy increases by about
300-350 G, and, following a broad maximum in 1920-1960, it decreases by about
300 G. Using the proxy for the magnetic field strength as the reference, we
scale the MWO field measurements to the measurements of the magnetic fields in
Pevtsov et al. (2011) to construct a combined data set of maximum sunspot field
strengths extending from 1920 to early 2012. This combined data set shows
strong solar cycle variations and no significant long-term trend (linear fit to
the data yields a slope of 0.8 G year). On the other hand, the
peak sunspot field strengths observed at the minimum of the solar cycle show a
gradual decline over the last three minima (corresponding to cycles 21-23) with
a mean downward trend of 15 G year
Evidence of a link between the evolution of clusters and their AGN fraction
‘The definitive version is available at www3.interscience.wiley.com .' Copyright Blackwell Publishing / Royal Astronomical Society. DOI: 10.1111/j.1365-2966.2009.14513.xPeer reviewe
On the nature of the short duration GRB 050906
The definitive version is available at www.blackwell-synergy.com. Copyright Blackwell Publishing DOI : 10.1111/j.1365-2966.2007.11953.xPeer reviewe
Modelling spatial and inter-annual variations of nitrous oxide emissions from UK cropland and grasslands using DailyDayCent
This work contributes to the Defra funded projects AC0116: ‘Improving the nitrous oxide inventory’, and AC0114: ‘Data Synthesis, Management and Modelling’. Funding for this work was provided by the UK Department for Environment, Food and Rural Affairs (Defra) AC0116 and AC0114, the Department of Agriculture, Environment and Rural Affairs for Northern Ireland, the Scottish Government and the Welsh Government. Rothamsted Research receives strategic funding from the Biotechnology and Biological Sciences Research Council. This study also contributes to the projects: N-Circle (BB/N013484/1), U-GRASS (NE/M016900/1) and GREENHOUSE (NE/K002589/1).Peer reviewedPublisher PD
Understanding the generation of methanol synthesis and water gas shift activity over copper-based catalysts – A spatially resolved experimental kinetic study using steady and non-steady state operation under CO/CO<sub>2</sub>/H<sub>2</sub> feeds
AbstractUnderstanding the mechanism and generation of activity for methanol synthesis and the water gas shift reactions over copper-based catalysts remains a significant area of study in heterogeneous catalysis. In this work, steady and non-steady state experimental and kinetic modelling methods are presented to demonstrate changes in functionality of a Cu/ZnO/Al2O3 catalyst based on gas composition.Steady-state testing of a Cu/ZnO/Al2O3 catalyst, using experimental spatial discretisation approaches with fixed-bed, integral-operation micro reactors, has generated performance data over a range of PCO/PCO2 ratios (1–10). The data showed a mixture of observations where forward or reverse water gas shift was kinetically favourable, and also where the reaction was significantly limited by thermodynamic equilibrium. A steady state Langmuir–Hinshelwood model based on micro kinetics was most appropriate which includes kinetic descriptions of both directions of the water gas shift reaction. Using this method, the entire dataset could be predicted and an internal consistency within the kinetic model of the key adsorption constants was demonstrated.Non-steady state, ‘reactor start-up’, testing of a Cu/ZnO/Al2O3 catalyst marked a novel approach to further understanding the functionality of the catalyst. Initial changes in surface carbon and oxygen populations were quantified and linked to subsequent dynamic changes in methanol synthesis and water gas shift activity. Cu/ZnO and Cu/Al2O3 formulations were also evaluated and tested using kinetic models, permitting a structural and compositional comparison with Cu/ZnO/Al2O3
Specialised information processing deficits and distinct metabolomics profiles following TM-domain disruption of Nrg1
While there is considerable genetic and pathologic evidence for an association between neuregulin 1 (NRG1) dysregulation and schizophrenia, the underlying molecular and cellular mechanisms remain unclear. Mutant mice containing disruption of the transmembrane (TM) domain of the NRG1 gene constitute a heuristic model for dysregulation of NRG1-ErbB4 signalling in schizophrenia. The present study focused on specialised behavioural and characterisation of hitherto un-characterised information processing phenotypes in this mutant line. Using a mass spectrometry-based metabolomics approach, we also quantified levels of unique metabolites in brain. Across two different sites and protocols, Nrg1 mutants demonstrated deficits in pre-pulse inhibition, a measure of sensorimotor gating that is disrupted in schizophrenia; these deficits were partially reversed by acute treatment with second-, but not first-, generation antipsychotic drugs. However, Nrg1 mutants did not show a specific deficit in latent inhibition, a measure of selective attention that is also disrupted in schizophrenia. In contrast, in the ‘what-where-when’ cognitive paradigm, Nrg1 mutants displayed sex-specific (males only) disruption of ‘what-when’ performance, indicative of impaired episodic memory. Differential metabolomic profiling revealed that these behavioural phenotypes were accompanied, most prominently, by alterations in lipid metabolism pathways. This study is the first to associate these novel physiological mechanisms, previously independently identified as being abnormal in schizophrenia, with disruption of NRG1 function. These data suggest novel mechanisms by which compromised neuregulin function from birth might lead to schizophrenia-relevant behavioural changes in adulthood
Entropy of Anisotropic Universe and Fractional Branes
We obtain the entropy of a homogeneous anisotropic universe applicable, by
assumption, to the fractional branes in the universe in the model of Chowdhury
and Mathur. The entropy for the 3 or 4 charge fractional branes thus obtained
is not of the expected form E^{{3/2}} or E^2. One way the expected form is
realised is if p \to \rho for the transverse directions and if the compact
directions remain constant in size. These conditions are likely to be enforced
by brane decay and annihilation, and by the S, T, U dualities. T duality is
also likely to exclude high entropic cases, found in the examples, which arise
due to the compact space contracting to zero size. Then the 4 charge fractional
branes may indeed provide a detailed realisation of the maximum entropic
principle we proposed recently to determine the number (3 + 1) of large
spacetime dimensions.Comment: Version 2: 21 pages. More discussion and references added. To appear
in General Relativity and Gravitatio
CO temperature-programmed desorption of a hexameric copper hydride nanocluster catalyst supported on functionalized MWCNTs for active site characterization in a low-temperature water-gas shift reaction
A family of novel catalysts was generated using chemically synthesised, atomically precise hexameric copper hydride nanoclusters (Cu6) deposited on carboxyl-pre-functionalized multi-walled carbon nanotubes (MWCNTCOOH). The Cu6/MWCNTCOOH catalysts were synthesized by wet impregnation of MWCNTCOOH with varying copper loading contents (0.5–15 wt%). The study of the interaction between active sites in these materials with CO at low temperatures using CO temperature-programmed desorption in conjunction with the elementary steps in the Langmuir-Hinshelwood mechanism of low-temperature water–gas shift (LTWGS) reaction allowed us to predict the potential catalytic performance of the synthesized catalysts in the LTWGS. The hypothetical activities were correlated with the catalyst surface characterization by CO chemisorption (Cu dispersion, crystallite size and surface area) and characterization of the active phase composition by XRD, showing good agreement. Optimal copper loading was identified to be 1 wt% based on the highest Cu surface area per sample weight and dispersion, and the amount of CO adsorbed per sample weight. The predicted catalytic performance was analysed as a function of support type: MWCNTCOOHcf. non-functionalized MWCNTs and alumina with fixed Cu loading of 1 wt%. The CO reactivity was analysed on Cu2O crystallites as the active phase, with a focus on the most dominant facets: (1 1 0), (1 1 1), (2 0 0) and (2 2 0). A comparison was made with a sample consisting of Cu nanoparticles (CuNP) supported on MWCNTCOOH, and a reference commercial catalyst, 51%CuO/31%ZnO-Al2O3. It is expected that the optimal catalyst, 1%Cu6/MWCNTCOOH, is active for LTWGS reaction from temperatures as low as 120 °C (governed by dew point of water) up to temperatures well below industrial operating temperatures (constrained by temperature rise due to the exothermic reaction that leads to Cu6 sintering)
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