SEARCH · Search NASA
Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
The synthesis of five new U( iv , v ) and U( v , vi ) silicates points toward moderate supercritical synthesis as a new route to the stabilization of mixed-valent uranium compounds.
We investigate the various routes to spatiotemporal chaos in Kerr optical frequency combs, obtained through pumping an ultra-high Q-factor whispering-gallery mode resonator with a continuous-wave laser. The Lugiato–Lefever model is used to build bifurcation diagrams with regards to the parameters that are externally controllable, namely, the frequency and the power of the pumping laser. We show that the spatiotemporal chaos emerging from Turing patterns and solitons display distinctive dynamical features. Experimental spectra of chaotic Kerr combs are also presented for both cases, in excellent agreement with theoretical spectra.
We investigate the use of passive intracavity optical filters for controlling the laser output spectrum of a polarization-mode-locked, ultrafast ytterbium fiber laser. The overall lasing bandwidth is increased or extended by strategic choice of the filter cutoff frequency. Overall laser performance, including pulse compression and intensity noise, is investigated for both shortpass and longpass filters with a range of cutoff frequencies. The intracavity filter not only shapes the output spectra, but also provides a route for overall broader bandwidths and shorter pulses in ytterbium fiber lasers. These results demonstrate that spectral shaping with a passive filter is a useful tool to routinely achieve sub-45 fs pulse durations in ytterbium fiber lasers.
Passive optical elements can play key roles in photonic applications such as plasmonic integrated circuits. Here we experimentally demonstrate passive gap-plasmon focusing and routing in two-dimensions. This is accomplished using a high numerical-aperture metal-dielectric-metal lens incorporated into a planar-waveguide device. Fabrication via metal sputtering, oxide deposition, electron- and focused-ion- beam lithography, and argon ion-milling is reported on in detail. Diffraction-limited focusing is optically characterized by sampling out-coupled light with a microscope. The measured focal distance and full-width-half-maximum spot size agree well with the calculated lens performance. The surface plasmon polariton propagation length is measured by sampling light from multiple out-coupler slits.
Intermediate and high level processing operations are performed on vision data for the organization of images into more meaningful, higher-level topological representations by means of a region-based route planner (RBRP). The RBRP operates in terrain scenarios where some or most of the terrain is occluded, proceeding without a priori maps on the basis of two-dimensional representations and gradient-and-roughness information. Route planning is accomplished by three successive abstractions and yields a detailed point-by-point path by searching only within the boundaries of relatively small regions.
Abstract not provided
Carbon-based materials are the most popular material types in both fundamental research and industrial applications, partly because of their well-controlled nano-morphologies. In the past two decades, we have witnessed a number of breakthroughs in carbon research: fullerenes, carbon nanotubes, and more recently graphene. Nowadays, carbon nanospheres are attracting more and more attention worldwide due to their excellent performance in various fields: drug delivery, heterogeneous catalysis, encapsulation of support and electrode materials. Actually, spherical carbon is an old material, whereas controlling carbon spheres in the nanometer range is a recent story. In the past 5 years, it has become possible to precisely control the particle size, surface area, pore size, chemical composition, and dispersity of carbon nanospheres. Toward this end, a number of synthetic strategies are emerging, such as hydrothermal carbonization of biomass-based resources, extended Stöber synthesis, and organic–organic self-assembly via different binding methods. In this feature article, we summarize recent routes for carbon nanospheres and briefly touch on their applications to shed light on the potential of this field. Throughout this article, a special emphasis is placed on the possible modulation of spherical structures at the nanoscale, and we wish to inspire many more designs and applications of carbon nanostructures in the near future.
This paper presents a linear Integer Programming model for managing air traffic flow in the United States. The decision variables in the model are departure delays and predeparture reroutes of aircraft whose trajectories are predicted to cross weather-impacted regions of the National Airspace System. The model assigns delays to a set of flights while ensuring their trajectories are free of any conflicts with weather. In a deterministic setting, there is no airborne holding due to unexpected weather incursion in a flight s path. The model is applied to solve a large-scale traffic flow management problem with realistic weather data and flight schedules. Experimental results indicate that allowing rerouting can reduce departure delays by nearly 57%, but it is associated with an increase in total airborne time due to longer routes flown by aircraft. The computation times to solve this problem were significantly lower than those reported in the earlier studies.
Mesh networking of wireless sensors implies that individual sensor nodes will be able to communicate with neighboring nodes thereby forming a communication fabric. In the case of traditional wireless sensors, their radio frequency coverage – or RF footprint – is defined by the maximum separation distance between neighboring nodes while still achieving some level of, typically degrading from maximum, information transfer (throughput). Security issues arise in the situations where the sensor nodes are deployed near the physical boundary of an industrial site (edge nodes). In the more general case of the sensors relying on omnidirectional antennas, the edge nodes’ RF footprint may extend beyond the edge of the facility. If the edge nodes perform as routing nodes, then it may be possible for similar sensors/devices outside of the facility boundary to join the network. Here, while various schemes have been implemented to address this security issue, we report on the possibility of using blockchain for security of such edge nodes.
System right-sizing is critical to implementation of wireless power transfer (WPT) for electric vehicles. This study will analyze potential WPT scenarios for the electrification of shuttle buses at Zion National Park utilizing a modelling tool developed by the National Renewable Energy Laboratory called WPTSim. This tool uses second-by-second speed, location, and road grade data from the conventional shuttles in operation to simulate the incorporation of WPT at fine granularity. Vehicle power and state of charge are simulated over the drive cycle to evaluate potential system designs. The required battery capacity is determined based on the rated power at a variable number of charging locations. The outcome of this work is an analysis of the design tradeoffs for the electrification of the shuttle fleet with wireless charging versus conventional overnight charging.
Block copolymers have been extensively studied due to their ability to spontaneously self-organize into a wide variety of morphologies that are valuable in energy-, medical- and conservation-related (nano)technologies. While the phase behavior of bicomponent diblock and triblock copolymers is conventionally governed by temperature and individual block masses, we demonstrate that their phase behavior can alternatively be controlled through the use of blocks with random monomer sequencing. Block random copolymers (BRCs), i.e., diblock copolymers wherein one or both blocks is a random copolymer comprised of A and B repeat units, have been synthesized, and their phase behavior, expressed in terms of the order-disorder transition (ODT), has been investigated. Our results establish that, depending on the block composition contrast and molecular weight, BRCs can microphase-separate. We also report that the predicted ODT can be generated at relatively constant molecular weight and temperature with these new soft materials. This sequence-controlled synthetic strategy is extended to thermoplastic elastomeric triblock copolymers differing in chemistry and possessing a random-copolymer midblock.
Explore the source record for details and available documents.
Not Available
Explore the source record for details and available documents.
Not Available
Not Available