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

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

Do global value chains spread knowledge and pollution? evidence from EU regions

In this paper we investigate the relationship between participation in global value chains and the environment from a spatial perspective. By drawing on an original dataset on global value chain participation, emissions of nitrogen oxides and sulphur oxides, and green patents for European regions, we present novel evidence about the relationship between global value chains, green technologies and air pollution at the regional level. Our findings suggest that although participation in global value chains may lead to lower polluting emissions, this effect largely depends on the capacity of regions to exploit the green knowledge deriving from participation and on the specific form of participation. When European regions are integrated with backward linkages (i.e., importing inputs to produce exports) they record lower levels of air pollution; conversely, participation through forward linkages (i.e., exporting inputs for other places' exports) leads to an increase in air pollution. Backward participation also come out to support the development of green technologies that mediate the effects of global value chains on the environment posited by the "Pollution Haven" hypothesis. Overall, the relationship between global value chains participation and air pollution will depend on the type of participation and on the capacity of territories to profit it for the development of green technologies

High Altitude Long Endurance Air Vehicle Analysis of Alternatives and Technology Requirements Development

The objective of this study was to develop a variety of High Altitude Long Endurance (HALE) Unmanned Aerial Vehicle (UAV) conceptual designs for two operationally useful missions (hurricane science and communications relay) and compare their performance and cost characteristics. Sixteen potential HALE UAV configurations were initially developed, including heavier-than-air (HTA) and lighter-than-air (LTA) concepts with both consumable fuel and solar regenerative (SR) propulsion systems. Through an Analysis of Alternatives (AoA) down select process, the two leading consumable fuel configurations (one each from the HTA and LTA alternatives) and an HTA SR configuration were selected for further analysis. Cost effectiveness analysis of the consumable fuel configurations revealed that simply maximizing vehicle endurance can lead to a sub-optimum system solution. An LTA concept with a hybrid propulsion system (solar arrays and a hydrogen-air proton exchange membrane fuel cell) was found to have the best mission performance; however, an HTA diesel-fueled wing-body-tail configuration emerged as the preferred consumable fuel concept because of the large size and technical risk of the LTA concept. The baseline missions could not be performed by even the best HTA SR concept. Mission and SR technology trade studies were conducted to enhance understanding of the potential capabilities of such a vehicle. With near-term technology SR-powered HTA vehicles are limited to operation in favorable solar conditions, such as the long days and short nights of summer at higher latitudes. Energy storage system specific energy and solar cell efficiency were found to be the key technology areas for enhancing HTA SR performance

LEO to GEO (and Beyond) Transfers Using High Power Solar Electric Propulsion (HP-SEP)

Rideshare, or Multi-Payload launch configurations, are becoming more and more commonplace but access to space is only one part of the overall mission needs. The ability for payloads to achieve their target orbits or destinations can still be difficult and potentially not feasible with on-board propulsion limitations. The High Power Solar Electric Propulsion (HP-SEP) Orbital Maneuvering Vehicle (OMV) provides transfer capabilities for both large and small payload in excess of what is possible with chemical propulsion. Leveraging existing secondary payload adapter technology like the ESPA provides a platform to support Multi-Payload launch and missions. When coupled with HP-SEP, meaning greater than 30 kW system power, very large delta-V maneuvers can be accomplished. The HP-SEP OMV concept is designed to perform a Low Earth Orbit to Geosynchronous Orbit (LEO-GEO) transfer of up to six payloads each with 300kg mass. The OMV has enough capability to perform this 6 kms maneuver and have residual capacity to extend an additional transfer from GEO to Lunar orbit. This high deltaV capability is achieved using state of the art 12.5kW Hall Effect Thrusters (HET) coupled with high power roll up solar arrays. The HP-SEP OMV also provides a demonstration platform for other SEP technologies such as advanced Power Processing Units (PPU), Xenon Feed Systems (XFS), and other HET technologies. The HP-SEP OMV platform can be leveraged for other missions as well such as interplanetary science missions and applications for resilient space architectures

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