Flow field computations for blunt bodies in planetary environments

Numerical analysis on flow distribution around hypersonic blunt body in planetary atmospher

Reactive self-heating model of aluminum spherical nanoparticles

Aluminum-oxygen reaction is important in many highly energetic, high pressure generating systems. Recent experiments with nanostructured thermites suggest that oxidation of aluminum nanoparticles occurs in a few microseconds. Such rapid reaction cannot be explained by a conventional diffusion-based mechanism. We present a rapid oxidation model of a spherical aluminum nanoparticle, using Cabrera-Mott moving boundary mechanism, and taking self-heating into account. In our model, electric potential solves the nonlinear Poisson equation. In contrast with the Coulomb potential, a "double-layer" type solution for the potential and self-heating leads to enhanced oxidation rates. At maximal reaction temperature of 2000 C, our model predicts overall oxidation time scale in microseconds range, in agreement with experimental evidence.Comment: submitte

Analysis of the project fire re-entry package flow field final technical report

Theoretical prediction of state of gas in flow field surrounding Apollo type vehicle in reentry at hypersonic speed

An Entomopathogenic Nematode by Any Other Name

Among the diversity of insect-parasitic nematodes, entomopathogenic nematodes (EPNs) are distinct, cooperating with insect-pathogenic bacteria to kill insect hosts. EPNs have adapted specific mechanisms to associate with and transmit bacteria to insect hosts. New discoveries have expanded this guild of nematodes and refine our understanding of the nature and evolution of insect–nematode associations. Here, we clarify the meaning of “entomopathogenic” in nematology and argue that EPNs must rapidly kill their hosts with the aid of bacterial partners and must pass on the associated bacteria to future generations

Co- variation in soil biodiversity and biogeochemistry in northern and southern Victoria Land, Antarctica

Data from six sites in Victoria Land (72–77°S) investigating co-variation in soil communities (microbial and invertebrate) with biogeochemical properties showthe influence of soil properties on habitat suitability varied among local landscapes as well as across climate gradients. Species richness of metazoan invertebrates (Nematoda, Tardigrada and Rotifera) was similar to previous descriptions in this region, though identification of three cryptic nematode species of Eudorylaimus through DNA analysis contributed to the understanding of controls over habitat preferences for individual species. Denaturing Gradient Gel Electrophoresis profiles revealed unexpectedly high diversity of bacteria. Distribution of distinct bacterial communities was associated with specific sites in northern and southern Victoria Land, as was the distribution of nematode and tardigrade species. Variation in soil metazoan communities was related to differences in soil organic matter, while bacterial diversity and community structure were not strongly correlated with any single soil property. There were no apparent correlations between metazoan and bacterial diversity, suggesting that controls over distribution and habitat suitability are different for bacterial and metazoan communities. Our results imply that top-down controls over bacterial diversity mediated by their metazoan consumers are not significant determinants of bacterial community structure and biomass in these ecosystems

Dipolar Interactions and Origin of Spin Ice in Ising Pyrochlore Magnets

Recent experiments suggest that the Ising pyrochlore magnets ${\rm Ho_{2}Ti_{2}O_{7}}$ and ${\rm Dy_{2}Ti_{2}O_{7}}$ display qualitative properties of the spin ice model proposed by Harris {\it et al.} \prl {\bf 79}, 2554 (1997). We discuss the dipolar energy scale present in both these materials and consider how they can display spin ice behavior {\it despite} the presence of long range interactions. Specifically, we present numerical simulations and a mean field analysis of pyrochlore Ising systems in the presence of nearest neighbor exchange and long range dipolar interactions. We find that two possible phases can occur, a long range ordered antiferromagnetic one and the other dominated by spin ice features. Our quantitative theory is in very good agreement with experimental data on both ${\rm Ho_{2}Ti_{2}O_{7}}$ and ${\rm Dy_{2}Ti_{2}O_{7}}$. We suggest that the nearest neighbor exchange in ${\rm Dy_{2}Ti_{2}O_{7}}$ is {\it antiferromagnetic} and that spin ice behavior is induced by long range dipolar interactions.Comment: 4 postscript figures included. Submitted to Physical Review Letters Contact: [email protected]

Customers as decision-makers: strategic environmental assessment in the private sector

Despite its diversification and global spread, strategic environmental assessment (SEA) remains limited mainly to activities characterised by well-defined planning processes, typically within the public sector. This article explores the possible application of SEA within certain private-sector contexts where higher-level strategy-making itself is inherently weaker and development is often piecemeal and reactive. The possible adaptation of SEA to the preparation of a strategic document by a particular industrial concern in the UK is examined: this draws attention to the multi-actor nature of development processes within the industry. This leads to the suggestion that SEA in this setting should be thought of as a form of environmental advocacy oriented towards industrial customers, who are understood as sharing a decision-making role in infrastructure development.</p