Modelling diffusion in crystals under high internal stress gradients

Diffusion of vacancies and impurities in metals is important in many processes occurring in structural materials. This diffusion often takes place in the presence of spatially rapidly varying stresses. Diffusion under stress is frequently modelled by local approximations to the vacancy formation and diffusion activation enthalpies which are linear in the stress, in order to account for its dependence on the local stress state and its gradient. Here, more accurate local approximations to the vacancy formation and diffusion activation enthalpies, and the simulation methods needed to implement them, are introduced. The accuracy of both these approximations and the linear approximations are assessed via comparison to full atomistic studies for the problem of vacancies around a Lomer dislocation in Aluminium. Results show that the local and linear approximations for the vacancy formation enthalpy and diffusion activation enthalpy are accurate to within 0.05 eV outside a radius of about 13 Å (local) and 17 Å (linear) from the centre of the dislocation core or, more generally, for a strain gradient of roughly up to 6 × 10^6 m^-1 and 3 × 10^6 m^-1, respectively. These results provide a basis for the development of multiscale models of diffusion under highly non-uniform stress

Seeking Peace in the Niger Delta: Oil, Natural Gas, and Other Vital Resources

Nigeria’s oil-rich Niger Delta region has seen little benefit from the billions of dollars earned from oil over the last four decades, prompting a growing but disorganized insurgency across the region. Irresponsible oil companies and government officials have reduced the Niger Delta to one of the most polluted environments on earth. Corrupt local and national politicians, many of whom came to power through rigged elections, have colluded to manipulate ethnic divisions amid poverty to loot the region’s wealth. Consequently, the people of the Niger Delta have no formal political voice in Nigeria’s nascent democratic system, increasing the appeal of militias as alternatives for political influence and economic sustenance. A new Nigerian president takes office in May 2007, and he will likely have a brief window of opportunity to undertake measures to reverse the governance crisis in the Niger Delta. This article originally appeared in a 2007 issue of the New England Journal of Public Policy (Volume 21, Issue 2): http://scholarworks.umb.edu/nejpp/vol21/iss2. For this reprint, the authors have prepared an update, which is included after the conclusion of the original article

Oil. Seeking Peace in the Niger Delta: Oil, Natural Gas, and Other Vital Resources

Nigeria’s oil-rich Niger Delta region has seen little benefit from the billions of dollars earned from oil over the last four decades, prompting a growing but disorganized insurgency across the region. Irresponsible oil companies and government officials have reduced the Niger Delta to one of the most polluted environments on earth. Corrupt local and national politicians, many of whom came to power through rigged elections, have colluded to manipulate ethnic divisions amid poverty to loot the region’s wealth. Consequently, the people of the Niger Delta have no formal political voice in Nigeria’s nascent democratic system, increasing the appeal of militias as alternatives for political influence and economic sustenance. A new Nigerian president takes office in May 2007, and he will likely have a brief window of opportunity to undertake measures to reverse the governance crisis in the Niger Delta

High-efficiency receptor-mediated delivery of small and large (48 kilobase gene constructs using the endosome-disruption activity of defective or chemically inactivated adenovirus particles.

One limit to successful receptor-mediated gene delivery is the exit of the endocytosed material from the endosome. We demonstrate here the delivery of marker genes to tissue culture cells using a modification of the receptor-mediated gene delivery technique that exploits the endosomolytic activity of defective adenovirus particles. In particular, greater than 90% of the transfected-cell population is found to express a beta-galactosidase gene, and, most importantly, this high level of expression can be obtained with psoralen-inactivated virus particles. Furthermore, because the delivered gene is not carried within the genome of the adenovirus particle, the size constraints are relieved, and we can, therefore, show the delivery of a 48-kilobase cosmid DNA molecule

Slow light with integrated gain and large pulse delay

We demonstrate slow and stored light in Rb vapor with a combination of desirable features: minimal loss and distortion of the pulse shape, and large fractional delay (> 10). This behavior is enabled by: (i) a group index that can be controllably varied during light pulse propagation; and (ii) controllable gain integrated into the medium to compensate for pulse loss. Any medium with the above two characteristics should be able to realize similarly high-performance slow light.Comment: 5 pages, 4 figures; abstract is shortened, some typo correcte

The Pitfalls of Aid

The United States must not be dissuaded from restoring the promotion of freedom and democracy as a core principle of U.S. foreign policy. Democracy assistance is both a reflection of American values and in America's strategic interests. America's next president will be challenged to revitalize the democracy agenda — and get it right. What's needed to address the challenges of the 21st century is a more versatile approach based on the requirements of each country and tailored to the characteristics of different regime types — authoritarian regimes, illiberal democracies, free-wheeling kleptocracies and post-conflict countries

A \u27New\u27 Hybrid Minnow

The specimen of a hybrid between the minnows Chrosomus erythrogaster and Dionda nubila is described. Taken in southeastern Minnesota near the known northernmost distributional limits of both parent species, this hybrid is between the parental extremes in most of the anatomical features examined

Production of 21 Ne in depth-profiled olivine from a 54 Ma basalt sequence, Eastern Highlands (37° S), Australia

In this study we investigate the cosmogenic neon component in olivine samples from a vertical profile in order to quantify muogenic 21Ne production in this mineral. Samples were collected from an 11 m thick Eocene basalt profile in the Eastern Highlands of southeastern Australia. An eruption age of 54.15 ± 0.36 Ma (2σ) was determined from 40Ar/39Ar step-heating experiments (n = 6) on three whole-rock samples. A 36Cl profile on the section indicated an apparent steady state erosion rate of 4.7 ± 0.5 m Ma−1. The eruption age was used to calculate in situ produced radiogenic 4He and nucleogenic 3He and 21Ne concentrations in olivine. Olivine mineral separates (n = 4), extracted from the upper two metres of the studied profile, reveal cosmogenic 21Ne concentrations that attenuate exponentially with depth. However, olivine (Fo68) extracted from below 2 m does not contain discernible 21Ne aside from magmatic and nucleogenic components, with the exception of one sample that apparently contained equal proportions of nucleogenic and muogenic neon. Modelling results suggest a muogenic neon sea-level high-latitude production rate of 0.02 ± 0.04 to 0.9 ± 1.3 atoms g−1 a−1 (1σ), or <2.5% of spallogenic cosmogenic 21Ne production at Earth’s surface. These data support a key implicit assumption in the literature that accumulation of muogenic 21Ne in olivine in surface samples is likely to be negligible/minimal compared to spallogenic 21Ne