Electron-hole pairs during the adsorption dynamics of O2 on Pd(100) - Exciting or not?

During the exothermic adsorption of molecules at solid surfaces dissipation of the released energy occurs via the excitation of electronic and phononic degrees of freedom. For metallic substrates the role of the nonadiabatic electronic excitation channel has been controversially discussed, as the absence of a band gap could favour an easy coupling to a manifold of electronhole pairs of arbitrarily low energies. We analyse this situation for the highly exothermic showcase system of molecular oxygen dissociating at Pd(100), using time-dependent perturbation theory applied to first-principles electronic-structure calculations. For a range of different trajectories of impinging O2 molecules we compute largely varying electron-hole pair spectra, which underlines the necessity to consider the high-dimensionality of the surface dynamical process when assessing the total energy loss into this dissipation channel. Despite the high Pd density of states at the Fermi level, the concomitant non-adiabatic energy losses nevertheless never exceed about 5% of the available chemisorption energy. While this supports an electronically adiabatic description of the predominant heat dissipation into the phononic system, we critically discuss the non-adiabatic excitations in the context of the O2 spin transition during the dissociation process.Comment: 20 pages including 7 figures; related publications can be found at http://www.fhi-berlin.mpg.de/th/th.html [added two references, changed V_{fsa} to V_{6D}, modified a few formulations in interpretation of spin asymmetry of eh-spectra, added missing equals sign in Eg.(2.10)

Airborne particulate matter accumulation on common green wall plants

© 2019, © 2019 Taylor & Francis Group, LLC. In order to better design greening systems for effective particulate matter (PM) removal, it is important to understand the impact leaf traits have on PM deposition. There are however, inconsistences amongst the leaf traits that have previously been correlated with PM accumulation. The aim of this paper was to identify vegetation characteristics of green wall plants that were associated with the accumulation of particulate matter. To determine patterns associated with different leaf morphologies, eleven common ornamental plant species were sampled across 15 sites, over a 6 month duration. PM deposition was determined gravimetrically and its associated size fractions determined microscopically. Linear mixed models were used to identify statistical patterns relating to differences in PM deposition across plant species. PM deposition and the relative frequencies of particle size fractions were found to be statistically different among species, sites and months. Green wall plants were shown to be effective at PM accumulation as all of the assessed plant species had equivalent PM removal efficiency, with minimal evidence of influential leaf characteristics that could enhance PM removal

Can Green Walls Reduce Outdoor Ambient Particulate Matter, Noise Pollution and Temperature?

Green walls have previously demonstrated the capacity to reduce particulate matter (PM), noise pollution, and temperature conditions in manipulative experiments and computational models. There is, however, minimal evidence that green walls can influence ambient environmental conditions, especially taking into account the variable environmental conditions encountered in situ. The aim of this paper was to determine if green walls have a quantitative effect on ambient air quality in an urban environment. Ambient PM, noise, and temperature were recorded at 12 green wall and adjacent reference wall locations across a dense urban centre, over a 6-month period. The results indicated that PM levels and temperature did not significantly differ between the green wall and reference wall sites. Ambient noise at the green wall sites, however, was significantly lower than at the reference wall locations. It is suggested that mechanically assisted, or 'active' green wall systems may have a higher PM and temperature reduction capacity, and if so, they will be more valuable for installation in situ compared to standard passive systems, although this will require further research

Complex soil contamination severely impacts seed-sown crop viability in Australia

Food security is a critical issue for many global communities. Heavy metal contaminationin soilspresenta majorand ongoingecologicalriskassociated with human activitieswhich may impactthe viability and safety ofseed-sown crops. To better understand the impacts of soil contamination by heavy metals on seed-sown crop viability, we examined germination responses of eight commercially-important fruit and vegetablecropspecies to copper, zinc, andleadcontaminationat levels likely to be foundin contaminated regions inAustralia. We compared the germination attributes of days to first germination, germination period, and total proportion of seeds germinated underconcentrationlimitsof heavy metals detectedat degraded sites andcurrentAustralianNational Environment Protection Measure thresholds for domestic soils (i.e., copper 6,000 mgkg-1, zinc 4,700 mgkg-1, lead 300 mgkg-1). Thecombined heavy metal treatment (i.e. all three metals) significantly inhibited germination for all edible crop species with only carrots able to germinate under complex, multi-metal-contaminatedconditions. Seed viability was significantly decreasedin mulberry (M.alba var.tatarica, M. nigra, and M. rubra) andlettuce(L. sativa),with loweredseed germination in all metalscomparedtocarrot(D. carota),radish(R. sativus), tomato(S. lycopersicum) andcommon bean(P. vulgaris). These results indicate heavy metal contamination is a notable risk to seed-sown crop species, with multi-metal contaminationeventslikely to be severely damagingto lettuce, tomato, radish, common bean, and mulberry crops

Acute cocoa flavanol supplementation improves muscle macro- and microvascular but not anabolic responses to amino acids in older men

The anabolic effects of nutrition on skeletal muscle may depend on adequate skeletal muscle perfusion, which is impaired in older people. Cocoa flavanols have been shown to improve flow-mediated dilation, an established measure of endothelial function. However, their effect on muscle microvascular blood flow is currently unknown. Therefore, the objective of this study was to explore links between the consumption of cocoa flavanols, muscle microvascular blood flow and muscle protein synthesis (MPS) in response to nutrition in older men. To achieve this objective leg blood flow (LBF), muscle microvascular blood volume (MBV) and MPS were measured under postabsorptive and postprandial (I.V glamin, dextrose to sustain glucose ~7.5 mmol·l-1) conditions in 20 older men. Ten of these men were studied with no cocoa flavanol intervention and a further 10 were studied with the addition of 350 mg of cocoa flavanols at the same time as nutrition began. Leg [femoral artery] blood flow was measured by Doppler ultrasound, muscle MBV by contrast-enhanced ultrasound (CEUS) using DefinityTM perflutren contrast agent and MPS using [1, 2-13C2] leucine tracer techniques. Our results show that although older individuals do not show an increase in LBF or MBV in response to feeding, these absent responses are apparent when cocoa flavanols are given acutely with nutrition. However this restoration in vascular responsiveness is not associated with improved MPS responses to nutrition. We conclude that acute cocoa flavanol supplementation improves muscle macro- and microvascular responses to nutrition, independently of modifying muscle protein anabolism

Quantum magnetic oscillations in the absence of closed electron trajectories

Quantum magnetic oscillations in crystals are typically understood in terms of Bohr-Sommerfeld quantisation, the frequency of oscillation is given by the area of a closed electron trajectory. However, since the 1970s, oscillations have been observed with frequencies that do not correspond to closed electron trajectories and this effect has remained not fully understood. Previous theory has focused on explaining the effect using various kinetic mechanisms, however, frequencies without a closed electron orbit have been observed in equilibrium and so a kinetic mechanism cannot be the entire story. In this work we develop a theory which explains these frequencies in equilibrium and can thus be used to understand measurements of both Shubnikov-de Haas and de Haas-van Alphen oscillations. We show, analytically, that these frequencies arise due to multi-electron correlations. We then extend our theory to explain a recent experiment on artificial crystals in GaAs two-dimensional electron gases, which revealed for the first time magnetic oscillations having frequencies that are half of those previously observed. We show that the half-frequencies arise in equilibrium from single-particle dynamics with account of impurities. Our analytic results are reinforced by exact numerics, which we also use clarify prior works on the kinetic regime.Comment: 15 pages, 10 figure