A compendium of sources of fracture toughness and fatigue crack growth data for metallic alloys, part 3

This Technical Memorandum presents sources of fracture toughness and fatigue crack growth data for metallic alloys. This is Part 3 of a three volume report

The collisional drift mode in a partially ionized plasma

The structure of the drift instability was examined in several density regimes. Let sub e be the total electron mean free path, k sub z the wave-vector component along the magnetic field, and the ratio of perpendicular ion diffusion to parallel electron streaming rates. At low densities (k sub z lambda 1) the drift mode is isothermal and should be treated kineticly. In the finite heat conduction regime square root of m/M k sub z Lambda sub 1) the drift instability threshold is reduced at low densities and increased at high densities as compared to the isothermal threshold. Finally, in the energy transfer limit (k sub z kambda sub e square root of m/M) the drift instability behaves adiabatically in a fully ionized plasma and isothermally in a partially ionized plasma for an ion-neutral to Coulomb collision frequency ratio

The electromagnetic interchange mode in a partially ionized collisional plasma

A collisional electromagnetic dispersion relation is derived from two-fluid theory for the interchange mode coupled to the Alfven, acoustic, drift and entropy modes in a partially ionized plasma. The fundamental electromagnetic nature of the interchange model is noted; coupling to the intermediate Alfven mode is strongly stabilizing for finite k sub z. Both ion viscous and ion-neutral stabilization are included, and it was found that collisions destroy the ion finite Larmor radius cutoff at short perpendicular wavelengths

Investigation of fatigue-crack growth under simple variable-amplitude loading

Fatigue-crack growth under simple variable amplitude loading in aluminum alloy

High density constraint on the entropy instability

The entropy instability squared is a nonisothermal effect which is eliminated by parallel ion pressure at high densities (k sub z lambda sub e 1/2 sq root of m/M), reducing previous growth rate estimates and the range of unstable parameters

Weak double layers in the auroral ionosphere

Previous work on the evolution of weak double layers in a hydrogen plasma was extended to include H(+) and O(+) with relative drift. The relative drift between hydrogen and oxygen ions due to a quasi-static parallel electric field gives rise to a strong linear fluid instability which dominates the ion-acoustic mode at the bottom of the auroral acceleration region. This ion-ion instability can modify ion distributions at lower altitudes and the subsequent nonlinear evolution of weak double layers at higher altitudes in the ion-acoustic regime. Ion hole formation can occur for smaller relative electron-ion drifts than seen in previous simulations, due to the hydrogen-oxygen two-stream instability. This results in local modification of the ion distributions in phase space, and a partial filling of the valley between the hydrogen and oxygen peaks, which would be expected at higher altitudes on auroral field lines. The observed velocity diffusion does not necessarily preclude ion hole and double layer formation in hydrogen in the ion-acoustic regime. These simulation results are consistent with the experimentally measured persistence of separate hydrogen and oxygen peaks, and the observation of weak double layers above an altitude of 3000 km on auroral field lines

Space-based geoengineering: challenges and requirements

The prospect of engineering the Earth's climate (geoengineering) raises a multitude of issues associated with climatology, engineering on macroscopic scales, and indeed the ethics of such ventures. Depending on personal views, such large-scale engineering is either an obvious necessity for the deep future, or yet another example of human conceit. In this article a simple climate model will be used to estimate requirements for engineering the Earth's climate, principally using space-based geoengineering. Active cooling of the climate to mitigate anthropogenic climate change due to a doubling of the carbon dioxide concentration in the Earth's atmosphere is considered. This representative scenario will allow the scale of the engineering challenge to be determined. It will be argued that simple occulting discs at the interior Lagrange point may represent a less complex solution than concepts for highly engineered refracting discs proposed recently. While engineering on macroscopic scales can appear formidable, emerging capabilities may allow such ventures to be seriously considered in the long term. This article is not an exhaustive review of geoengineering, but aims to provide a foretaste of the future opportunities, challenges, and requirements for space-based geoengineering ventures

Gene-history correlation and population structure

Correlation of gene histories in the human genome determines the patterns of genetic variation (haplotype structure) and is crucial to understanding genetic factors in common diseases. We derive closed analytical expressions for the correlation of gene histories in established demographic models for genetic evolution and show how to extend the analysis to more realistic (but more complicated) models of demographic structure. We identify two contributions to the correlation of gene histories in divergent populations: linkage disequilibrium, and differences in the demographic history of individuals in the sample. These two factors contribute to correlations at different length scales: the former at small, and the latter at large scales. We show that recent mixing events in divergent populations limit the range of correlations and compare our findings to empirical results on the correlation of gene histories in the human genome.Comment: Revised and extended version: 26 pages, 5 figures, 1 tabl

Drafting and Implementing an Effective Social Media Policy

Social media is everywhere and used in many business and personal situations. There is no indication that social media use is declining; rather, social media use is constantly expanding into new realms and taking on new forms. Social media launches political campaigns, international pop stars, and new businesses to heightened levels of success or failure with just a few mouse clicks. Because social media information has the ability to spread rapidly, not addressing social media or hoping it will not affect the employer\u27s business is a dangerous practice. Currently, few employers have a Social Media Policy ( Policy ). By not having a Policy, the employer and its business are left vulnerable to the whims of its employees\u27 social media actions and cannot guide employees toward using social media to protect and further the employer\u27s business purpose. A Policy\u27s existence makes the employer proactive rather than reactive. Further, establishing a Policy provides employees with clear expectations about when social media can be used, for what purposes, and what level of privacy an employee should expect regarding personal use. Finally, the employer needs a Policy to promote consistent enforcement among all employees. Inconsistent actions by supervisors for similar employee actions could open the employer up to potential employment discrimination lawsuits. Once the employer understands that it needs a Policy, the next step is deciding what type to implement. The employer must create a Policy that furthers the employer\u27s business purposes. Regardless of whether the employer decides to ban social media or freely allow its use, the employer should always spell it out in a Policy that defines the parameters of social media use. However, before the employer establishes a Policy it should conduct a cost-benefit analysis of social media uses and benefits for the employer versus the cost and resources required to enforce such a Policy. The employer should consider the Policy\u27s monitoring and enforcement costs and the employee productivity costs depending on the level of allowed social media use. Taking into account these considerations, this Article will instruct an employer or employer\u27s counsel on how to best draft an effective Policy that will meet all of the employer\u27s objectives