Evolution of the structure of amorphous ice - from low-density amorphous (LDA) through high-density amorphous (HDA) to very high-density amorphous (VHDA) ice

We report results of molecular dynamics simulations of amorphous ice for pressures up to 22.5 kbar. The high-density amorphous ice (HDA) as prepared by pressure-induced amorphization of Ih ice at T=80 K is annealed to T=170 K at various pressures to allow for relaxation. Upon increase of pressure, relaxed amorphous ice undergoes a pronounced change of structure, ranging from the low-density amorphous ice (LDA) at p=0, through a continuum of HDA states to the limiting very high-density amorphous ice (VHDA) regime above 10 kbar. The main part of the overall structural change takes place within the HDA megabasin, which includes a variety of structures with quite different local and medium-range order as well as network topology and spans a broad range of densities. The VHDA represents the limit to densification by adapting the hydrogen-bonded network topology, without creating interpenetrating networks. The connection between structure and metastability of various forms upon decompression and heating is studied and discussed. We also discuss the analogy with amorphous and crystalline silica. Finally, some conclusions concerning the relation between amorphous ice and supercooled water are drawn.Comment: 11 pages, 12 postscript figures. To be published in The Journal of Chemical Physic

Results of a 0.03- scale aerodynamic characteristics investigation of Boeing 747 carrier (model no. AX 1319 I-1) mated with a space shuttle orbiter (model 45-0) conducted in the Boeing transonic wind tunnel (CA5), volume 1

The performance, stability, and control characteristics of various carrier aircraft configurations are presented. Aerodynamic characteristics of the carrier mated with the Orbiter, carrier alone, and Orbiter alone were investigated. Carrier support system tare and interference effects were determined. Six-component force and moment data were recorded for the carrier and Orbiter. Buffet onset characteristics of the carrier vertical tail and horizontal tail were recorded. Angles of attack from -3 deg through 26 deg and angles of slideslip between +12 deg and -12 deg were investigated at Mach numbers from 0.15 through 0.70. Photographs are included

Structure and dielectric properties of polar fluids with extended dipoles: results from numerical simulations

The strengths and short-comings of the point-dipole model for polar fluids of spherical molecules are illustrated by considering the physically more relevant case of extended dipoles formed by two opposite charges $\pm q$ separated by a distance $d$ (dipole moment $\mu=q d$). Extensive Molecular Dynamics simulations on a high density dipolar fluid are used to analyse the dependence of the pair structure, dielectric constant \eps and dynamics as a function of the ratio $d/\sigma$ (\sig is the molecular diameter), for a fixed dipole moment $\mu$. The point dipole model is found to agree well with the extended dipole model up to d/\sig \simeq 0.3. Beyond that ratio, \eps shows a non-trivial variation with d/\sig. When d/\sig>0.6, a transition is observed towards a hexagonal columnar phase; the corresponding value of the dipole moment, \mu^2/\sig^3 k T=3, is found to be substantially lower than the value of the point dipole required to drive a similar transition.Comment: 10 pages, 11 figures; Paper submitted to Molecular Physic

Links between boreal forest management, soil fungal communities and below-ground carbon sequestration

1. Forest management has a potential to alter below-ground carbon storage. However, the underlying mechanisms, and the relative importance of carbon input and decomposition in regulation of soil carbon dynamics are poorly understood.2. We examined whether interactive effects of forest fertilization and thinning on carbon stocks in the topsoil of boreal forests were linked to changes in fungal community composition, biomass and enzyme activities, in a long-term fertilization and thinning experiment distributed across 29 Pinus sylvestris forests along a 1,300 km latitudinal transect in Sweden.3. Nitrogen fertilization increased fungal biomass, particularly towards the north and mainly by promoting root-associated Ascomycetes, but the response was moderated by thinning. Fungal biomass correlated positively with carbon stocks in the organic topsoil. However, ectomycorrhizal Cortinarius species were reduced in abundance by fertilization and correlated negatively with carbon stocks.4. Plausibly, increased soil carbon stocks after fertilization are linked to increased input of carbon in the form of root-associated mycelium combined with the loss of ectomycorrhizal decomposers within the genus Cortinarius. These fungal responses to fertilization may mediate a natural climate solution by promoting carbon sequestration in the organic topsoil, but the effect of fertilization may also be undesired from a biodiversity perspective

Metastability of life

The physical idea of the natural origin of diseases and deaths has been presented. The fundamental microscopical reason is the destruction of any metastable state by thermal activation of a nucleus of a nonreversable change. On the basis of this idea the quantitative theory of age dependence of death probability has been constructed. The obtained simple Death Laws are very accurately fulfilled almost for all known diseases.Comment: 3 pages, 4 figure

Manganese availability is negatively associated with carbon storage in northern coniferous forest humus layers

Carbon sequestration below ground depends on organic matter input and decomposition, but regulatory bottlenecks remain unclear. The relative importance of plant production, climate and edaphic factors has to be elucidated to better predict carbon storage in forests. In Swedish forest soil inventory data from across the entire boreal latitudinal range (n = 2378), the concentration of exchangeable manganese was singled out as the strongest predictor (R-2 = 0.26) of carbon storage in the extensive organic horizon (mor layer), which accounts for one third of the total below ground carbon. In comparison, established ecosystem models applied on the same data have failed to predict carbon stocks (R-2 <0.05), and in our study manganese availability overshadowed both litter production and climatic factors. We also identified exchangeable potassium as an additional strong predictor, however strongly correlated with manganese. The negative correlation between manganese and carbon highlights the importance of Mn-peroxidases in oxidative decomposition of recalcitrant organic matter. The results support the idea that the fungus-driven decomposition could be a critical factor regulating humus carbon accumulation in boreal forests, as Mn-peroxidases are specifically produced by basidiomycetes.Peer reviewe

Mycotoxin hazards in the Kenyan food and feed market-a retrospective study

Mycotoxins are toxic fungal metabolites naturally found in food and feed as contaminants. Animal feed and human food samples (n=1818) from three major Kenyan laboratories were categorized as compliant and non-compliant according to Kenya, America (USA) and Europe (EU) mycotoxin regulatory limits. Quantitative risk assessment of dietary aflatoxin intake in maize, wheat, peanut and dairy products in relation to human hepatocellular carcinoma was carried out employing deterministic approach. Non-compliant samples’ proportions were calculated, and logistic regression and chi-square test used to compare different commodities. Animal feed were least compliant, with 64% and 39% having total aflatoxin (AFT) levels above Kenya and USA standards, respectively. Peanuts were the most non-compliant food, with 61% and 47% samples failing Kenya and USA AFT standards respectively, while wheat was least compliant (84%) according to EU threshold for AFT. Half of baby food sampled had AFT level above Kenya and EU standards. High non-compliance rate with Kenya, USA and EU regulatory thresholds with respect to seven different mycotoxins (summarized as “mycotoxins”), and also AFT and aflatoxin M1 alone in edible materials is reported. Significant non-compliance is reported for compound animal feed, peanuts, wheat, baby food, feed ingredients, herbal healthy drink, maize and fodder feed in that order. High levels of aflatoxin residues in animal feed and human food was also observed. Lifetime human consumption of wheat and maize leads to high additional risk for primary liver cancer, human hepatocellular carcinoma (HCC) associated with dietary aflatoxin, wheat and its products causing the highest disease burden. Subsequent implications and limitations of current food safety standards are discussed. Humans and animals in Kenya appear to be chronically exposed to mycotoxin hazards: this calls for surveillance and risk management. There is urgent need for enhanced and consistent surveillance of the dietary mycotoxin hazards observed in this study employing representative sampling plans. Regulation and future research need to focus on reliable analysis techniques, collection of data on toxicological effects of mycotoxins and food consumption pattern, and regulatory limits accordingly set and compliance enforced to protect vulnerable groups such as paediatric, geriatric and sick members of the society to reduce cancer burden in Keny