Quantitative determination of stratospheric aerosol characteristics

There are no author-identified significant results in this report

Testing Theoretical Evolutionary Models with AB Dor C and the Initial Mass Function

We assess the constraints on the evolutionary models of young low-mass objects that are provided by the measurements of the companion AB Dor C by Close and coworkers and by a new comparison of model-derived IMFs of star-forming regions to the well-calibrated IMF of the solar neighborhood. After performing an independent analysis of Close's imaging and spectroscopic data for AB Dor C, we find that AB Dor C is not detected at a significant level (SN 1.2) in the SDI images when one narrow-band image is subtracted from another, but that it does appear in the individual SDI frames as well as the images at JHK. Using the age of 75-150 Myr for AB Dor from Luhman, Stauffer, & Mamajek, the luminosity predicted by the models of Chabrier & Baraffe is consistent with the value that we estimate. We measure a spectral type of M6+/-1 from the K-band spectrum of AB Dor C, which is earlier than the value of M8+/-1 from Close and is consistent with the model predictions when a dwarf temperature scale is adopted. In a test of these models at much younger ages, we show that the low-mass IMFs that they produce for star-forming regions are similar to the IMF of the solar neighborhood. If the masses of the low-mass stars and brown dwarfs in these IMFs of star-forming regions were underestimated by a factor of two as suggested by Close, then the IMF characterizing the current generation of Galactic star formation would have to be radically different from the IMF of the solar neighborhood.Comment: 15 pages, accepted to the Astrophysical Journa

Alteration and Oxidiation of an Olivine Lamprophyre Dike from Southern Utah, USA: An Analog for Mars

We report on oxidized basaltic dike intrusions on the Colorado Plateau as analog for Martian basalt oxidation

Quantum spin liquids and the metal-insulator transition in doped semiconductors

We describe a new possible route to the metal-insulator transition in doped semiconductors such as Si:P or Si:B. We explore the possibility that the loss of metallic transport occurs through Mott localization of electrons into a quantum spin liquid state with diffusive charge neutral "spinon" excitations. Such a quantum spin liquid state can appear as an intermediate phase between the metal and the Anderson-Mott insulator. An immediate testable consequence is the presence of metallic thermal conductivity at low temperature in the electrical insulator near the metal-insulator transition. Further we show that though the transition is second order the zero temperature residual electrical conductivity will jump as the transition is approached from the metallic side. However the electrical conductivity will have a non-monotonic temperature dependence that may complicate the extrapolation to zero temperature. Signatures in other experiments and some comparisons with existing data are made.Comment: 4 pages text + 3 pages Appendices, 3 Figures; v2 - References Adde

Making intelligent systems team players: Case studies and design issues. Volume 1: Human-computer interaction design

Initial results are reported from a multi-year, interdisciplinary effort to provide guidance and assistance for designers of intelligent systems and their user interfaces. The objective is to achieve more effective human-computer interaction (HCI) for systems with real time fault management capabilities. Intelligent fault management systems within the NASA were evaluated for insight into the design of systems with complex HCI. Preliminary results include: (1) a description of real time fault management in aerospace domains; (2) recommendations and examples for improving intelligent systems design and user interface design; (3) identification of issues requiring further research; and (4) recommendations for a development methodology integrating HCI design into intelligent system design

Multiple closed loop recycling of carbon fibre composites with the HiPerDiF (High Performance Discontinuous Fibre) method

AbstractThe aim of this article is to apply the concept of Circular Economy, where end-of-life products and production wastes are recycled into reusable materials, to carbon fibre reinforced plastics. This not only reduces the amount of material disposed into landfills, but also enables manufacturers to achieve significant savings. While current research focuses on the performance of recycled carbon fibre reinforced composites after one recycling process, this paper aims to investigate the performance of composites remanufactured from short carbon fibres that have undergone multiple recycling loops with the High Performance Discontinuous Fibre (HiPerDiF) method. The HiPerDiF method enables the production of aligned short fibre composites with exceptional mechanical properties. In addition, using short fibres makes the composite material intrinsically easy to recycle. Short virgin carbon fibres underwent two loops of fibre reclamation and remanufacturing. A correlation between the composites’ mechanical properties and the nature of the fibres, i.e. reduction in fibre lengths, as well as the residual matrix accumulation from the reclaiming process over a number of recycling loops, was established

Using AI/expert system technology to automate planning and replanning for the HST servicing missions

This paper describes a knowledge-based system that has been developed to automate planning and scheduling for the Hubble Space Telescope (HST) Servicing Missions. This new system is the Servicing Mission Planning and Replanning Tool (SM/PART). SM/PART has been delivered to the HST Flight Operations Team (FOT) at Goddard Space Flight Center (GSFC) where it is being used to build integrated time lines and command plans to control the activities of the HST, Shuttle, Crew and ground systems for the next HST Servicing Mission. SM/PART reuses and extends AI/expert system technology from Interactive Experimenter Planning System (IEPS) systems to build or rebuild time lines and command plans more rapidly than was possible for previous missions where they were built manually. This capability provides an important safety factor for the HST, Shuttle and Crew in case unexpected events occur during the mission

Rabi oscillations under ultrafast excitation of graphene

We study coherent nonlinear dynamics of carriers under ultrafast interband excitation of an intrinsic graphene. The Rabi oscillations of response appear with increasing of pumping intensity. The photoexcited distribution is calculated versus time and energy taking into account the effects of energy relaxation and dephasing. Spectral and temporal dependencies of the response on a probe radiation (transmission and reflection coefficients) are considered for different pumping intensities and the Rabi oscillations versus time and intensity are analyzed.Comment: 6 pages, 6 figure