Preliminary assessment of power-generating tethers in space and of propulsion for their orbit maintenance

The concept of generating power in space by means of a conducting tether deployed from a spacecraft was studied. Using hydrogen and oxygen as the rocket propellant to overcome the drag of such a power-generating tether would yield more benefit than if used in a fuel cell. The mass consumption would be 25 percent less than the reactant consumption of fuel cells. Residual hydrogen and oxygen in the external tank and in the orbiter could be used very effectively for this purpose. Many other materials (such as waste from life support) could be used as the propellant. Electrical propulsion using tether generated power can compensate for the drag of a power-generating tether, half the power going to the useful load and the rest for electric propulsion. In addition, the spacecraft's orbital energy is a large energy reservoir that permits load leveling and a ratio of peak to average power equal to 2. Critical technologies to be explored before a power-generating tether can be used in space are delineated

«Transitional» Texts Across the World – What Are They?

The main argument of this article is that, to some degree, all texts can be called ‘transitional’: they are, necessarily, set within the ongoing or processes of history, thus multiple in nature, flexible, changing, conditional on specific occasions, shaped by their cultural context(s), their medium and, above all, by specific creators and receivers. Similarly, I argue that there does not exist anything necessarily revolutionary about the once touted but now widely questioned “Great Divide” between orality and literacy across which texts had to make a great transition. I also discuss the various different modes and situations in which texts could be said to be, for different users and purposes, in some way ‘transitional’, with particular reference to examples from Africa and the South Pacific. I conclude that all culture, all language, all human action is in a sense transitional and dynamic.Este artículo sostiene que todos los textos, en alguna medida, pueden ser llamados “transicionales”: necesariamente están insertos en la marcha o proceso de la historia, y por tanto son múltiples por naturaleza, flexibles, cambiantes, condicionados por ocasiones específicas, modelados por su(s) contexto(s) cultural(es), su medio y, sobre todo, por los productores y receptores individuales. Igualmente, explico que no existe nada necesariamente revolucionario acerca de la “gran división”, tiempo atrás publicitada pero ahora ampliamente cuestionada, entre oralidad y escritura, a través de la cual los textos tenían que hacer una gran transición. También discuto los diferentes modos y situaciones en los que se puede decir que los textos son, para distintos usuarios y fines, “transicionales” de alguna manera, con particular referencia a ejemplos de África y del Pacífico sur. Concluyo que toda la cultura, todo el lenguaje, toda la actividad humana es, en cierto sentido, transicional y dinámica

Continuous-flow laboratory simulation of stream water quality changes downstream of an untreated wastewater discharge.

In regions of the world with poor provision of wastewater treatment, raw sewage is often discharged directly into surface waters. This paper describes an experimental evaluation of the fate of two organic chemicals under these conditions using an artificial channel cascade fed with a mix of settled sewage and river water at its upstream end and operated under continuous steady-state conditions. The experiments underpin an environmental risk assessment methodology based on the idea of an “impact zone” (IZ) – the zone downstream of wastewater emission in which water quality is severely impaired by high concentrations of unionised ammonia, nitrite and biochemical oxygen demand (BOD). Radiolabelled dodecane-6-benzene sulphonate (DOBS) and aniline hydrochloride were used as the model chemical and reference compound respectively. Rapid changes in 14C counts were observed with flow-time for both these materials. These changes were most likely to be due to complete mineralisation. A dissipation half-life of approximately 7.1 h was observed for the 14C label with DOBS. The end of the IZ was defined as the point at which the concentration of both unionised ammonia and nitrite fell below their respective predicted no-effect concentrations for salmonids. At these points in the cascade, approximately 83 and 90% of the initial concentration of 14C had been removed from the water column, respectively. A simple model of mineral nitrogen transformations based on Michaelis–Menten kinetics was fitted to observed concentrations of NH4, NO2 and NO3. The cascade is intended to provide a confirmatory methodology for assessing the ecological risks of chemicals under direct discharge co

Acclimation responses of Arabidopsis thaliana to sustained phosphite treatments

Phosphite () induces a range of physiological and developmental responses in plants by disturbing the homeostasis of the macronutrient phosphate. Because of its close structural resemblance to phosphate, phosphite impairs the sensing, membrane transport, and subcellular compartmentation of phosphate. In addition, phosphite induces plant defence responses by an as yet unknown mode of action. In this study, the acclimation of Arabidopsis thaliana plants to a sustained phosphite supply in the growth medium was investigated and compared with plants growing under varying phosphate supplies. Unlike phosphate, phosphite did not suppress the formation of lateral roots in several Arabidopsis accessions. In addition, the expression of well-documented phosphate-starvation-induced genes, such as miRNA399d and At4, was not repressed by phosphite accumulation, whilst the induction of PHT1;1 and PAP1 was accentuated. Thus, a mimicking of phosphate by phosphite was not observed for these classical phosphate-starvation responses. Metabolomic analysis of phosphite-treated plants showed changes in several metabolite pools, most prominently those of aspartate, asparagine, glutamate, and serine. These alterations in amino acid pools provide novel insights for the understanding of phosphite-induced pathogen resistance

TiB_2 and ZrB_2 diffusion barriers in GaAs Ohmic contact technology

The transition metal diboride compounds, ZrB_2 and TiB_2, interposed between Ni/Ge/Au Ohmic contact metallization on n‐type GaAs wafers and an overlying thick Au contact layer, have been investigated to evaluate their effectiveness in stabilizing the Ohmic contact by limiting the in‐diffusion of Au. All of the metal layers were e‐beam deposited except the ZrB_2 which was rf‐diode sputtered. The barrier layer thicknesses were 50 and 100 nm for the TiB_2 and the ZrB_2, respectively. Postdeposition alloying of the contacts was performed at 400, 425, or 450 °C. Auger electron spectroscopy depth profiling of the resultant Ohmic contacts demonstrates that the barrier layers effectively preclude penetration of Au to the Ohmic contact structure. Specific contact resistivities for such contacts are in the low 10^(−7) Ω cm^2 range; although some degradation of the contact resistivity is observed after long term annealing, the values of resistivities do not exceed 1.5×10^(−6) Ω cm^2 after 92 h at 350 °C

Arabidopsis PHOSPHATE TRANSPORTER1 genes PHT1;8 and PHT1;9 are involved in root-to-shoot translocation of orthophosphate

In plants, the uptake from soil and intercellular transport of inorganic phosphate (Pi) is mediated by the PHT1 family of membrane-spanning proton : Pi symporters. The Arabidopsis thaliana AtPHT1 gene family comprises nine putative high-affinity Pi transporters. While AtPHT1;1 to AtPHT1;4 are involved in Pi acquisition from the rhizosphere, the role of the remaining transporters is less clear

Marine extinction risk shaped by trait-environment interactions over 500 million years

Perhaps the most pressing issue in predicting biotic responses to present and future global change is understanding how environmental factors shape the relationship between ecological traits and extinction risk. The fossil record provides millions of years of insight into how extinction selectivity (i.e., differential extinction risk) is shaped by interactions between ecological traits and environmental conditions. Numerous paleontological studies have examined trait-based extinction selectivity; however, the extent to which these patterns are shaped by environmental conditions is poorly understood due to a lack of quantitative synthesis across studies. We conducted a meta-analysis of published studies on fossil marine bivalves and gastropods that span 458 million years to uncover how global environmental and geochemical changes covary with trait-based extinction selectivity. We focused on geographic range size and life habit (i.e., infaunal vs. epifaunal), two of the most important and commonly examined predictors of extinction selectivity. We used geochemical proxies related to global climate, as well as indicators of ocean acidification, to infer average global environmental conditions. Life-habit selectivity is weakly dependent on environmental conditions, with infaunal species relatively buffered from extinction during warmer climate states. In contrast, the odds of taxa with broad geographic ranges surviving an extinction ( \u3e 2500km for genera, \u3e 500km for species) are on average three times greater than narrow-ranging taxa (estimate of odds ratio: 2.8, 95% confidence interval=2.3-3.5), regardless of the prevailing global environmental conditions. The environmental independence of geographic range size extinction selectivity emphasizes the critical role of geographic range size in setting conservation priorities

Maintenance of Fertility in the Face of Meiotic Drive

Selfish genetic elements that gain a transmission advantage through the destruction of sperm have grave implications for drive male fertility. In the X-linked meiotic drive system (SR) of a stalk-eyed fly, we found that SR males have greatly enlarged testes and maintain high fertility despite the destruction of half of their sperm, even when challenged with fertilizing large numbers of females. Conversely, we observed reduced allocation of resources to the accessory glands that probably explains the lower mating frequency of SR males. Body size and eye span were also reduced, which are likely to impair viability and precopulatory success. We discuss the potential evolutionary causes of these differences between drive and standard males

Preliminary impact speed and angle criteria for design of a nuclear airplane fission product containment vessel

Studying aircraft accidents to determine impact angle and speed criteria for designing nuclear airplane fission product containment vesse