Conductance anomalies in quantum wires

We study the conductance threshold of clean nearly straight quantum wires in the magnetic field. As a quantitative example we solve exactly the scattering problem for two-electrons in a wire with planar geometry and a weak bulge. From the scattering matrix we determine conductance via the Landauer-Buettiker formalism. The conductance anomalies found near 0.25(2e^2/h) and 0.75(2e^2/h) are related to a singlet resonance and a triplet resonance, respectively, and survive to temperatures of a few degrees. With increasing in-plane magnetic field the conductance exhibits a plateau at e^2/h, consistent with recent experiments.Comment: Quantum wire with planar geometry; in-plane magnetic fiel

SEI power source alternatives for rovers and other multi-kWe distributed surface applications

To support the Space Exploration Initiative (SEI), a study was performed to investigate power system alternatives for the rover vehicles and servicers that were subsequently generated for each of these rovers and servicers, candidate power sources incorporating various power generation and energy storage technologies were identified. The technologies were those believed most appropriate to the SEI missions, and included solar, electrochemical, and isotope systems. The candidates were characterized with respect to system mass, deployed area, and volume. For each of the missions a preliminary selection was made. Results of this study depict the available power sources in light of mission requirements as they are currently defined

Introduction of Forage Legumes into Pastures of Three Different Grasses

It was evaluated the introduction of a mixture of calopo, galaxia, perennial soybean, guata and stylo broadcsted into marandu, setaria and tanzania half-plots already established in three cafeterias, each one located inside a paddock of each grass. The legumes were seeded in the end of the Spring (12/07/98), after the plots had been cut down and fertilized. The cafeterias were grazed intermittently by buffaloes maintained in the three paddocks. The occurrence of the five legume plants was avaluated by countings (#/m2) effected in the middle of Autumn, Winter and Spring of 1999 and Summer of 2000. Along with this last counting it was evaluated the forage remained after grazing and its N%. Marandu-grass presented the higher amount of forage remained after grazing but the lower presence of legumes along all countings. The contrary happened with Tanzania-grass. Significantly higher N% was found in the mixed grass half-plots compared with them without legumes

Solid State Aircraft Concept Overview

Due to recent advances in polymers, photovoltaics, and batteries a unique type of aircraft may be feasible. This is a solid-state aircraft, with no conventional mechanical moving parts. Airfoil, propulsion, energy production, energy storage and control are combined in an integrated structure. The key material of this concept is an ionic polymeric-metal composite (IPMC) that provides source of control and propulsion. This material has the unique capability of deforming in an electric field and returning to its original shape when the field is removed. Combining the IPMC with thin-film batteries and thin-film photovoltaics provides both energy source and storage in the same structure. The characteristics of the materials enables flapping motion of the wing to be utilized to generate the main propulsive force. Analysis shows that a number of design configurations can be produced to enable flight over a range of latitudes on Earth, Venus and possibly Mars

A paper-based device for glyphosate electrochemical detection in human urine: A case study to demonstrate how the properties of the paper can solve analytical issues

In the ever-growing demand for agricultural production, the use of pesticides and the consequential health risks is an issue that remains in the spotlight. The biomonitoring of pesticides in biological matrices is a mandatory task to point out the adverse effects on those people that are particularly exposed (i.e., occupational exposure) and to customize the use of pesticides for safer and more aware agricultural practices (i.e., precision agriculture). To overcome the bottleneck of costs and long sample treatments, we conceived a paper-based analytical device for the fast and smart detection of glyphosate in human urines, which is still the most widespread pesticide. Importantly, we demonstrate how to face the analytical interference given by uric acid to develop an electrochemical sensor for glyphosate detection using paper as a multifunctional material. To this purpose, a sample treatment was pointed out and integrated into a paper strip to decrease the level of uric acid in urines, finally delivering a ready-to-use device that combines lateral and vertical flow. The effective decrease of uric acid after the paper-integrated treatment is verified by direct oxidation in differential pulse voltammetry, whereas glyphosate detection can be carried out by enzyme inhibition assay in chronoamperometry. The system showed a limit of detection for glyphosate of 75 μg/L and a linear range of 100 - 700 μg/L. Additionally, the sustainability of the paper device was assessed and compared with reference chromatographic methods. Overall, this work provides an example of how to design green sensing solutions for addressing analytical challenges in line with the White Analytical Chemistry principle

Solar-Powered Aircraft: Energy-Optimal Path Planning and Perpetual Endurance

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76439/1/AIAA-40139-801.pd

Tiller Population Stability of Aruana Guineagrass Subjected to Cutting Severities and Fertilized with Nitrogen

Tiller appearance, death and survival rates determine the persistency of each grass species and their herbage accumulation. The balance between these factors may vary with frequency and intensity of grazing and nitrogen (N) fertilization. Separated analysis of data on tiller appearance and survival or death may not indicate if tiller population is stable in a given time, that is, if tiller appearance in relation to tiller survival is large enough to maintain tiller population stable. In order to avoid that, an integrated analysis of tiller appearance and death was used, the tiller population stability index (SI), as defined by Bahmani et al. (2003). Aruana Guineagrass (Panicum maximum Jacques cv. Aruana) is widely used as pasture for sheep, which are extremely susceptible to infestation by larvae of gastrointestinal parasites in tropical pasture-based systems. One way to mitigate this problem, reducing the need for the use of anthelmintics, is by managing pastures with post-grazing height low enough to favor the incidence of sunlight at the base of tussocks, killing and controlling larval development, without jeopardizing canopy regrowth and persistence. Sward targets for grazing Aruana Guineagrass correspond to a pre-grazing height of 30 cm, equivalent to 95% canopy light interception during regrowth, and a post-grazing height of 15 cm (Zanini et al. 2012). The objective of this experiment was to evaluate tiller population stability of Aruana Guineagrass subjected to cutting severities and N fertilization using the stability index

Physical and Quality Seed Traits Observed in New Pigeon Pea (\u3cem\u3eCajanus Cajan\u3c/em\u3e) Hybrids

Pigeon pea seed production may be affected by factors such as % of pure seeds, mean seed weight, incidence of pests and diseases and environmental stresses. Harvested seeds from different cultivars may also vary in germination %, hardseededness and germination speed. Hardseededness (seed coat impermeability to water) commonly occurs in forage legume species (Hopkinson, 1993). There is considerable variation among different entries for seed characters but this is not considered within genetic materials. This research analysed harvested seeds of selected individuals of two segregating F2 pigeon pea populations for the above cited traits and assessed the range of variation for them resulting from the hybridisation process

Thermal Energy for Lunar In Situ Resource Utilization: Technical Challenges and Technology Opportunities

Oxygen production from lunar raw materials is critical for sustaining a manned lunar base but is very power intensive. Solar concentrators are a well-developed technology for harnessing the Sun s energy to heat regolith to high temperatures (over 1375 K). The high temperature and potential material incompatibilities present numerous technical challenges. This study compares and contrasts different solar concentrator designs that have been developed, such as Cassegrains, offset parabolas, compound parabolic concentrators, and secondary concentrators. Differences between concentrators made from lenses and mirrors, and between rigid and flexible concentrators are also discussed. Possible substrate elements for a rigid mirror concentrator are selected and then compared, using the following (target) criteria: (low) coefficient of thermal expansion, (high) modulus of elasticity, and (low) density. Several potential lunar locations for solar concentrators are compared; environmental and processing-related challenges related to dust and optical surfaces are addressed. This brief technology survey examines various sources of thermal energy that can be utilized for materials processing on the lunar surface. These include heat from nuclear or electric sources and solar concentrators. Options for collecting and transporting thermal energy to processing reactors for each source are examined. Overall system requirements for each thermal source are compared and system limitations, such as maximum achievable temperature are discussed