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12 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

lasy v0.1

Lasy is a Python library that facilitates numerical simulations of the interaction of complex laser pulses with plasmas. More specifically, lasy offers many ways to define complex laser pulses (e.g. from commonly-known analytical formulas, from experimental measurements, etc.) and then computes and saves the corresponding laser field in a standardized file. This file can then be read by external plasma simulation codes, that will then simulate the interaction between the complex laser pulse and a plasma. Lasy is useful for instance for numerical simulations of plasma-based particle accelerators, plasma-based laser amplification, etc. Lasy avoids having to duplicate the code that defines complex laser pulses in each plasma simulation codes, and instead provides a trusted, centralized implementation.

Lehe, Remi↗
DOE OSTI2024

Fe-carbide/Fe-oxide-based nanocomposites synthesized as magnetic nanomaterials via laser ablation synthesis in solution (LASiS)

Magnetic nanostructured materials (MNMs) have gained prominence in materials technology developments owing to their potential biomedical applications for hyperthermia cancer treatment, and transplant organ cryopreservation. Herein, we report the facile and cost-effective synthesis of Fe-based composite MNMs, comprising both Fe@Fe 2 O 3 and Fe 3 C@C core-shell nanoparticles (NPs), via Laser Ablation Synthesis in Solution (LASiS) using Fe targets ablated under acetone and toluene. Detailed materials characterizations using electron microscopy-based imaging, diffraction studies, and spectroscopic analyses - including Raman and Mössbauer spectroscopy - relate the structure-composition properties for different Fe-oxide/carbide phases in the aforesaid MNMs to their respective magnetic responses. Specifically, we confirm the presence of ultra-small (2–10 nm) amorphous Fe-oxide NPs, as well as Fe@Fe 2 O 3 core-shell NPs (20–40 nm) in the samples synthesized by ablating Fe under acetone. In contrast, samples synthesized under toluene indicate a higher concentration of Fe 3 C@C core-shell NPs (20–40 nm) with a relatively low concentration of Fe 2 O 3 NPs (2–10 nm). Furthermore, the crystallinity of the metallic phases and carbonaceous shell coatings are systematically increased by carrying out LASiS under heated toluene (up to ~95 °C). Importantly, mössbauer spectroscopy results indicate that the elevation in toluene temperature leads to an increase in the concentrations of Fe 3 C@C NPs from ~40 % to ~53 % (at.).

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on LaSi by Materials Project

LaSi crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. La is bonded in a 7-coordinate geometry to seven equivalent Si atoms. There are a spread of La–Si bond distances ranging from 3.15–3.30 Å. Si is bonded in a 9-coordinate geometry to seven equivalent La and two equivalent Si atoms. Both Si–Si bond lengths are 2.52 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on LaSi by Materials Project

LaSi crystallizes in the orthorhombic Cmcm space group. The structure is three-dimensional. there are two inequivalent La sites. In the first La site, La is bonded in a 6-coordinate geometry to six equivalent Si atoms. There are four shorter (3.17 Å) and two longer (3.22 Å) La–Si bond lengths. In the second La site, La is bonded in a 8-coordinate geometry to eight equivalent Si atoms. There are four shorter (3.14 Å) and four longer (3.24 Å) La–Si bond lengths. Si is bonded in a 9-coordinate geometry to seven La and two equivalent Si atoms. There are one shorter (2.49 Å) and one longer (2.59 Å) Si–Si bond lengths.

36 MATERIALS SCIENCE↗
NASA NTRS1976

Description of a landing site indicator (LASI) for light aircraft operation

An experimental cockpit mounted head-up type display system was developed and evaluated by LaRC pilots during the landing phase of light aircraft operations. The Landing Site Indicator (LASI) system display consists of angle of attack, angle of sideslip, and indicated airspeed images superimposed on the pilot's view through the windshield. The information is made visible to the pilot by means of a partially reflective viewing screen which is suspended directly in frot of the pilot's eyes. Synchro transmitters are operated by vanes, located at the left wing tip, which sense angle of attack and sideslip angle. Information is presented near the center of the display in the form of a moving index on a fixed grid. The airspeed is sensed by a pitot-static pressure transducer and is presented in numerical form at the top center of the display.

Fuller, H. V.↗
NASA NTRS1978

Simulation and flight evaluation of a head-up landing aid for general aviation

A head-up general aviation landing aid called a landing site indicator (LASI) was tested in a fixed-base, visual simulator and in an airplane to determine the effectiveness of the LASI. The display, which had a simplified format and method of implementation, presented to the pilot in his line of sight through the windshield a graphic representation of the airplane's velocity vector. In each testing model (simulation of flight), each of 4 pilots made 20 landing approaches with the LASI and 20 approaches without it. The standard deviations of approach and touchdown parameters were considered an indication of pilot consistency. Use of the LASI improved consistency and also reduced elevator, aileron, and rudder control activity. Pilots' comments indicated that the LASI reduced work load. An appendix is included with a discussion of the simulator effectiveness for visual flight tasks.

Harris, R. L., Sr.↗
NASA NTRS1974

Simulation and flight evaluation of a heads-up display for general aviation

A landing-site indicator (LASI) has been devised as a relatively simple heads-up display to show the pilot the magnitude and direction of the aircraft's velocity vector superimposed on the pilot's view of the landing area. A total of 160 landings were performed in a fixed-base simulation program by four pilots with and without the LASI display. These tests showed the display to be of beneficial use in making the approaches more consistent. Some inferences were also made that the physical workload would also be less with its use. The pilots generally agreed that the LASI, as represented in the simulation was a useful landing aid. Additional pilot comments from preliminary flight tests of a breadboard LASI display unit tend to confirm the simulator results.

Harris, R. L., Sr.↗
NASA NTRS1973

An exploratory simulation study of a head-up display for general aviation lightplanes

The concept of a simplified head-up display referred to as a landing-site indicator (LASI) for use in lightplanes is discussed. Results of a fixed-base simulation study exploring the feasibility of the LASI concept are presented in terms of measurements of pilot performance, control-activity parameters, and subjective comments of four test subjects. These subjects, all of whom had various degrees of piloting experience in this type aircraft, performed a series of simulated landings both with and without the LASI starting from different initial conditions in the final approach leg of the landing maneuver.

Harris, R. L., Sr.↗
DOE OSTI2024

Titanium Dioxide Nanomaterial Ink Production Through Laser Ablation Synthesis in Solution for Printed Electronics Applications

Flexible and printed electronics have become increasingly popular as they make possible the production of flexible, low-cost, multifunction devices that are unachievable through traditional manufacturing methods. The printed films are significantly impacted and thus limited by the existing ink production process. Herein, an alternate technique of generating high-quality titanium dioxide (TiO 2 ) nanoparticle ink compatible with aerosol jet printing using laser ablation synthesis in solution (LASiS) is showcased. Dynamic light scattering data and transmission electron microscopy confirm the particle size distribution. UV–vis measurements are performed, and the Beer–Lambert relationship is used to determine the concentration of the generated ink. The inks generated at two different repetition rates are compared: 200 kHz and 1 MHz. X-Ray diffraction analysis of the aerosol jet printed thin film post-thermal sintering confirms the grain size and phase purity of the printed thin films. This work demonstrates the effectiveness of the LASiS technique in producing printable nanoparticle inks with little-to-no postprocessing.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Laser-Induced Trapping of Metastable Amorphous AlO x /C (2.5 < x ≤ 3.5) Nanocomposites: Implications for Use as Solid Phase Gas Generators

The synthesis of kinetically "frozen" metastable nanostructures remains elusive. This limitation has severely restricted the current paradigms in materials discovery. We overcame this challenge by phase-stabilizing unusually hyperoxidized and metastable amorphous aluminum oxide (a-AlO x ; 2.5 < x ≤ 3.5) nanostructures. Specifically, we employed laser ablation synthesis in solution (LASiS) as a one-pot nonequilibrium technique to achieve this pivotal advancement. Structural and compositional characterizations of the as-synthesized material reveal highly disordered a-AlO x nanoparticles that are remarkably stabilized by interfacial monolayers of ordered carbon atoms. Both structure and chemical composition were confirmed with disparate characterization methods at different length scales. The nanoparticles of sizes less than10 nm were stable even at elevated temperatures. Only at temperatures higher than 750 °C do the a-AlO x structures undergo a solid-solid phase transition that culminates in the formation of stable α-Al 2 O 3 while releasing excess trapped gases. In conclusion, such disruptive materials can find applications in emerging technologies seeking metastable phase-change materials for solid phase gas generators, batteries, neuromorphic computing, and energetic additives.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Kinetic analyses for solid-state phase transition of metastable amorphous-AlO x (2.5 < x ≤ 3.0) nanostructures into crystalline alumina polymorphs

Solid-solid phase change materials (SS-PCMs) hold promise for energy storage/dissipation in batteries and energetic materials. Yet, phase change kinetics for SS-PCMs undergoing metastable to semi-stable/stable phase transformations remain relatively ill-studied because trapping metastable phases remain challenging. Recently, we demonstrated the kinetic entrapment and stabilization of a highly disordered and amorphous Al-oxide phase m-AlO x @C (x~2.5-3.0) via laser ablation synthesis in solution (LASiS). We report here, to our knowledge, the first chemical kinetics analysis for S-S phase transition of the m-AlO 3 @C nanocomposites (< 5–8 nm sizes) into semi-stable equilibrium alumina phases (θ/γ-Al 2 O 3 ) via disproportionation reaction, while releasing excess trapped gases. Our results indicate the atomic density of the AlO 3 structures to be ~5–10 times less than that of the final Al 2 O 3 phases, which led to the hypothesis of a volume shrinkage process during their phase transition. Temperature-dependent X-ray diffraction studies reveal the high-temperature phase transition for m-AlO 3 → θ/γ-Al 2 O 3 to follow contracting volume kinetics model, thereby validating our earlier hypothesis. Using the geometric volume contraction model, reaction kinetics analyses from Arrhenius plots reveal the activation energy barrier for the phase transition to be ~270±11 kJ/mol. This makes the activation energy barrier nearly identical to the oxidation of micron-sized Al particles.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1999

Lightning First Pulses Used in the "Last" (Time-of-Arrival) and "Atlas" (Single Station) Total Lightning Mapping Systems

The first RF pulse from "total lightning' discharges (cloud and ground flashes) has been used in different ways to locate the origin of flashes in two new types of lightning detection systems. The multisensor LASI time-of-arrival (TOA) system uses GPS timing of the first pulse. The ATLAS single sensor system uses the amplitude of the first pulse, which is invariant in magnitude and polarization for all lightning discharges, to determine distance from the sensor. It is significantly more accurate than past single sensor lightning mapping systems. The polarity of the first pulse generally identifies lightning type (IC or CG). Both systems utilize only the first pulse which makes signal processing much simpler than with previous lightning locating systems. Knowing the position where lightning begins (maximum electric fields, mixed phase hydrometeors and updrafts) is valuable for identifying convective cells producing the hazardous meteorological conditions caused by thunderstorms. It is also important for research studying thunderstorm electrification and associated microphysical problems.

Markson, Ralph↗