Time Evolution of Galaxy Scaling Relations in Cosmological Simulations

This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2016 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.We predict the evolution of galaxy scaling relationships from cosmological, hydrodynamical simulations, that reproduce the scaling relations of present-day galaxies. Although we do not assume co-evolution between galaxies and black holes a priori, we are able to reproduce the black hole mass--velocity dispersion relation. This relation does not evolve, and black holes actually grow along the relation from significantly less massive seeds than have previously been used. AGN feedback does not very much affect the chemical evolution of our galaxies. In our predictions, the stellar mass--metallicity relation does not change its shape, but the metallicity significantly increases from $z\sim2$ to $z\sim1$, while the gas-phase mass-metallicity relation does change shape, having a steeper slope at higher redshifts ($z\lesssim3$). Furthermore, AGN feedback is required to reproduce observations of the most massive galaxies at $z\lesssim1$, specifically their positions on the star formation main sequence and galaxy mass--size relation.Peer reviewedFinal Published versio

Biogeochemical couplings among Earth’s ecosystems: a focus on old-growth tropical rainforest

This dissertation explores how physical and biological processes organize the interaction of carbon and nutrient cycles, which underpin life on Earth. In Chapter 2, I establish that ecosystem nitrate accrual exhibits consistent and negative nonlinear correlations with organic carbon availability along a hydrologic continuum from soils, through fresh- water systems and coastal margins, to the open ocean. Across this diversity of environments, we find evidence that resource stoichiometry strongly influences nitrate accumulation by regulating a suite of microbial processes that couple dissolved organic carbon and nitrate cycling. In Chapter 3, I address the climate sensitivity of carbon cycling in old-growth tropical rainforests, which are among Earth&rsquo;s most carbon-rich and productive ecosystems. Collectively they exchange more CO2 with the atmosphere than any other terrestrial biome &ndash; annually, about 16 times more C than the change in atmospheric CO2&nbsp;concentration resulting from fossil fuel use &ndash; thus small imbalances between rainforest carbon uptake and release can influence atmospheric CO2 concentrations. Here, I use meta-analysis of field data to examine the long-term climate sensitivity of rainforest CO2&nbsp;exchange and storage. I found that net primary productivity and biomass carbon peaks in warm, lowland rainforests peaks at the highest rainfall levels, contrasting with a saturating response expected from previous studies in montanae forests. The pattern results from interactions between climatic, edaphic, geographic and biotic controls over carbon accumulations. In Chapter 4, I found that seasonal water availability plays an important role in structuring the tropical nitrogen cycle. Counter to current paradigms that expect tropical lowland rainforests to freely leach bioavailable N, I discovered very low export of bioavailable N from an old-growth tropical watershed. Nitrate loss was closely tied to organic carbon availability for heterotrophic microbes. PON export constituted the largest hydrologic loss pathway for N and was regulated by episodes of intense rainfall that caused surges of sediment yield from erosion. The magnitude of PON loss is larger than measured N inputs, and may constrain N accumulation within the ecosystem over long timescales.</p

Quantifying land surface temperature variability for two Sahelian mesoscale regions during the wet season

Land-atmosphere feedbacks play an important role in the weather and climate of many semi-arid regions. These feedbacks are strongly controlled by how the surface responds to precipitation events, which regulate the return of heat and moisture to the atmosphere. Characteristics of the surface can result in both differing amplitudes and rates of warming following rain. We used spectral analysis to quantify these surface responses to rainfall events using land surface temperature (LST) derived from Earth Observations (EO). We analysed two mesoscale regions in the Sahel and identified distinct differences in the strength of the short-term (< 5–day) spectral variance, notably a shift towards lower frequency variability in forest pixels relative to non-forest areas, and an increase in amplitude with decreasing vegetation cover. Consistent with these spectral signatures, we found that areas of forest, and to a lesser extent grassland regions, warm up more slowly than sparsely vegetated or barren pixels. We applied the same spectral analysis method to simulated LST data from the the Joint UK Land Environment Simulator (JULES) land surface model. We found a reasonable level of agreement with the EO spectral analysis, for two contrasting land surface regions. However JULES shows a significant underestimate in the magnitude of the observed response to rain compared to EO. A sensitivity analysis of the JULES model highlights an unrealistically high level of soil water availability as a key deficiency, which dampens the models response to rainfall events

Screening, intervention and outcome in autism and other developmental disorders: the role of randomized controlled trials

We draw attention to a number of important considerations in the arguments about screening and outcome of intervention in children with autism and other developmental disorders. Autism screening in itself never provides a final clinical diagnosis, but may well identify developmental deviations indicative of autism—or of other developmental disorders—that should lead to referral for further clinical assessment. Decisions regarding population or clinic screening cannot be allowed to be based on the fact that prospective longitudinal RCT designs over decades could never be performed in complex developmental disorders. We propose an alternative approach. Early screening for autism and other developmental disorders is likely to be of high societal importance and should be promoted and rigorously evaluated

Supercritical antisolvent precipitation of amorphous copper–zinc georgeite and acetate precursors for the preparation of ambient‐pressure water‐gas‐shift copper/zinc oxide catalysts

A series of copper-zinc acetate and zincian georgeite precursors have been produced by supercritical CO2 anti-solvent (SAS) precipitation as precursors to Cu/ZnO catalysts for the water gas shift (WGS) reaction. The amorphous materials were prepared by varying the water/ethanol volumetric ratio in the initial metal acetate solutions. Water addition promoted georgeite formation at the expense of mixed metal acetates, which are formed in the absence of the water co-solvent. Optimum SAS precipitation occurs without water to give high surface areas, whilst a high water content gives inferior surface areas and copper-zinc segregation. Calcination of the acetates is exothermic, producing a mixture of metal oxides with high crystallinity. However, thermal decomposition of zincian georgeite resulted in highly dispersed CuO and ZnO crystallites with poor structural order. The georgeite-derived catalysts give superior WGS performance in comparison to the acetate-derived catalysts, which is attributed to enhanced copper-zinc interactions that originate from the precursor

Inhibition of the mechano-enzymatic amyloidogenesis of transthyretin: role of ligand affinity, binding cooperativity and occupancy of the inner channel

Dissociation of the native transthyretin (TTR) tetramer is widely accepted as the critical step in TTR amyloid fibrillogenesis. It is modelled by exposure of the protein to non-physiological low pH in vitro and is inhibited by small molecule compounds, such as the drug tafamidis. We have recently identified a new mechano-enzymatic pathway of TTR fibrillogenesis in vitro, catalysed by selective proteolytic cleavage, which produces a high yield of genuine amyloid fibrils. This pathway is efficiently inhibited only by ligands that occupy both binding sites in TTR. Tolcapone, which is bound with similar high affinity in both TTR binding sites without the usual negative cooperativity, is therefore of interest. Here we show that TTR fibrillogenesis by the mechano-enzymatic pathway is indeed more potently inhibited by tolcapone than by tafamidis but neither, even in large molar excess, completely prevents amyloid fibril formation. In contrast, mds84, the prototype of our previously reported bivalent ligand TTR 'superstabiliser' family, is notably more potent than the monovalent ligands and we show here that this apparently reflects the critical additional interactions of its linker within the TTR central channel. Our findings have major implications for therapeutic approaches in TTR amyloidosis

Kinetic and modeling studies of the reaction of hydroxyl radicals with tetrachloroethylene

Article on kinetic and modeling studies of the reaction of hydroxyl radicals with tetrachloroethylene

Supercritical antisolvent precipitation of amorphous copper–zinc georgeite and acetate precursors for the preparation of ambient-pressure water-gas-shift copper/zinc oxide catalysts

© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim A series of copper–zinc acetate and zincian georgeite precursors have been produced by supercritical CO 2 antisolvent (SAS) precipitation as precursors to Cu/ZnO catalysts for the water gas shift (WGS) reaction. The amorphous materials were prepared by varying the water/ethanol volumetric ratio in the initial metal acetate solutions. Water addition promoted georgeite formation at the expense of mixed metal acetates, which are formed in the absence of the water co-solvent. Optimum SAS precipitation occurs without water to give high surface areas, whereas high water content gives inferior surface areas and copper–zinc segregation. Calcination of the acetates is exothermic, producing a mixture of metal oxides with high crystallinity. However, thermal decomposition of zincian georgeite resulted in highly dispersed CuO and ZnO crystallites with poor structural order. The georgeite-derived catalysts give superior WGS performance to the acetate-derived catalysts, which is attributed to enhanced copper–zinc interactions that originate from the precursor

Enhancement in the rate of nitrate degradation on Au- and Ag-decorated TiO2 photocatalysts

The solar-driven reduction of nitrate to nitrogen has been studied in the presence of a formate hole scavenger, over a series of Au- and Ag-decorated TiO2 catalysts. In this study, the catalyst preparation protocol was found to influence the nitrate transformation in the order: incipient wetness impregnation > stabilizer-free sol immobilization > sol immobilization. However, the sequence of performing specific treatment steps such as drying, calcination and sieving had a less pronounced effect. Low-conversion conditions were utilized to study the photo-degradation of nitrate over a range of monometallic and bimetallic catalysts with metal concentrations in the range M = 0–1 wt% (M: Au, Ag, Pd, AuAg). Our findings demonstrate that selectively degrading nitrate to N2 over these co-catalysts is non-trivial and is metal content dependent. For Au-doped TiO2 catalysts, the highest activity was measured over 0.2 wt% Au/TiO2 while a higher metal loading of 0.4 wt% was required for the Ag/TiO2 photocatalyst. Product selectivity was also demonstrated to be dependent on metal and metal loading: approximately 22% nitrite selectivity was determined over a 0.1 wt% Ag-doped catalysts, however this product was not detected when utilising Au-doped catalysts. Total selectivity to dinitrogen was shown to be possible on both Au and Ag doped catalysts, and again this was dependent on the concentration of the metal (Ag > 0.3 wt%; 0.2 < Au ≥ 0.4 wt%)