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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.

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At least 703 records · Page 39
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Computational study of trimer self-assembly and fluid phase behavior

The fluid phase diagram of trimer particles composed of one central attractive bead and two repulsive beads was determined as a function of simple geometric parameters using flat-histogram Monte Carlo methods. A variety of self-assembled structures were obtained including spherical micelle-like clusters, elongated clusters, and densely packed cylinders, depending on both the state conditions and shape of the trimer. Advanced simulation techniques were employed to determine transitions between self-assembled structures and macroscopic phases using thermodynamic and structural definitions. Simple changes in particle geometry yield dramatic changes in phase behavior, ranging from macroscopic fluid phase separation to molecular-scale self-assembly. In special cases, both self-assembled, elongated clusters and bulk fluid phase separation occur simultaneously. Our work suggests that tuning particle shape and interactions can yield superstructures with controlled architecture.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Flame aerosol synthesis of hollow alumina nanoshells for application in thermal insulation

Commercial implementation of hollow nanoshell materials is often limited by difficult scale-up and high cost. Here we present a scalable, continuous, and potentially low-cost route to hollow nanostructured materials using a High Temperature Reducing Jet flame aerosol reactor. The key advantage of this process over traditional flame aerosol synthesis methods is separation of flame chemistry and particle formation, which allows production of hollow nanoshells from an aqueous salt solution without any template or surfactant. We produced amorphous hollow alumina with an average diameter of 181 nm and shell thickness below 10 nm, and demonstrated the generality of the method by also producing hollow SiO 2 , ZrO 2 , Ga 2 O 3 , and Co 2 O 3 . We characterized the morphology, phase transition, thermal stability, and thermal conductivity of the flame-made hollow alumina by electron microscopy, x-ray diffraction, and thermal analysis methods. As a prototypical application, we incorporated hollow alumina into thermal insulation, combining it with common fiberglass insulation to reduce the thermal conductivity by 30% relative to pure fiberglass, to 0.028 W m -1 K -1 while maintaining robust fire-resistance and elasticity.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Insights into the Structure of Ultrasmall Fluorescent Core–Shell Silica Nanoparticles

Ultrasmall fluorescent core–shell nanoparticles (NPs) with a silica core and poly(ethylene glycol) ligand shell are the earliest example of hybrid NPs that have received U.S. investigational new drug FDA approval. They are among only a few inorganic NPs translated to safety, diagnostic, and therapeutic human clinical trials. Despite these achievements, little is known about the exact structure of their 3–4 nm sized silica cores. We report the surprising discovery of a well-defined pentagonal bipyramidal core structure preferentially formed in the aqueous synthesis built from seven primary silica NPs. A combination of reverse-phase high-performance liquid chromatography, cryogenic transmission electron microscopy, and coarse-grained simulations provides fundamental insights into this magic-size cluster formation and its unusual stability. Here, results rationalize the successful NP synthesis scale-up from 1 mL to 50 L, provide clues to the recent discovery of their self-therapeutic properties in oncology via ferroptosis, an iron-dependent cell death mechanism, and promise improved control of particle size distribution via chromatographic separations.

cluster chemistry↗
DOE OSTI2012

THE LONGITUDINAL TRANSPORT OF ENERGETIC IONS FROM IMPULSIVE SOLAR FLARES IN INTERPLANETARY SPACE

We present a study of the longitudinal spread of energetic charged particles from a localized instantaneous compact source on the Sun. Our study utilizes a diffusive-transport model for the propagation of energetic ions in interplanetary space. We show that even for very small values of the ratio of perpendicular to parallel diffusion coefficients-a few percent-the particles spread significantly in longitude. Spatial diffusion and adiabatic energy loss of ions in the interplanetary plasma cause impulsive particle events at Earth's orbit to last a few days. In this time, the combination of transport both along and across the local Parker-spiral magnetic field and the longitudinal motion of the magnetic lines of forces rooted at the Sun as it rotates leads to substantial longitudinal transport of the particles. We show that spacecraft separated by as much as 180 Degree-Sign or more may observe events associated with compact solar sources, such as those from impulsive solar flares. Our results are qualitatively consistent with recent multi-spacecraft observations.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

Evolution of proton shells in 20 ⩽ Z ⩽ 28 and 20 ⩽ N ⩽ 50 nuclei and dispersive optical model

Experimental single-particle proton energies in spherical and nearly spherical 20 ⩽ Z ⩽ 28 medium-mass nuclei and their counterparts evaluated with the aid of data formirror nuclei were analyzed on the basis of the dispersive optical model. The parameters of the dispersive optical potential were extrapolated to the region of unstable nuclei, and the values obtained in this way were then used to predict the single-particle proton energies in the 20 ⩽ N ⩽ 50 nuclei under study. The evolution of the particle-hole energy gap was traced, and features peculiar to single-particle spectra of magic and nonmagic nuclei were revealed by comparing single-particle energies with proton-separation energies.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2018

Prototype Scintillation Detector with Photosensors Based on Silicon Photomultiplier Arrays

A prototype scintillation detector with photosensors based on silicon photomultiplier (SiPM) arrays is described. Such a method of data-taking will make it possible to obtain an image (snapshot) of the event and, thereby, to separate different types of events (particle interactions) in the detector. For this purpose, the characteristics of SiPMs have been studied and a calibration measurement technique developed.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2012

Dynamical crossover between the infinite-volume and empty-lattice limits of ultra-cold fermions in 1D optical lattices

Unlike typical condensed-matter systems, ultra-cold atoms loaded into optical lattices allow separate control of both the particle number and system size. As a consequence, there are two distinct "thermodynamic” limits that can be defined for these systems: i) ’’infinite-volume limit” at constant finite density, and ii) "empty-lattice limit” at constant particle number. To probe the difference between these two limits and their crossover, we consider a partially occupied lattice and study the transport into the unoccupied region of non-interacting fermions and fermions interacting at the mean-field level. In the infinite-volume limit, a finite steady-state current emerges. On the other hand, in the empty-lattice limit there is no finite steady-state current. By changing the initial filling, we find a smooth crossover between the two limits. Our predictions may be verified using available experimental tools and demonstrate a fundamental difference between isolated small systems such as ultra-cold atoms and conventional condensed-matter systems.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2024

A Python Script to Read MCNP6.3 Surface-Source Files

This report provides a Python script to read an MCNP ® surface source file created with the SSW card with SYM = 0 (i.e., the default symmetry treatment). For background: the general format of an MCNP surface-source file is described in; however, that document did not provide coding and/or a tool to interrogate such files. The current format will not be given in this document other than through the record-read statements necessary for the script to function. The reader capability in this report is augmented with the ability to directly write a couple demonstrative outputs: 1. A comma-separated value (CSV) file containing particle phase-space state information and 2. A Matplotlib histogram of the energy distribution of the particles. This report also describes accompanying verification work that shows the script performing as required with MCNP6.2, MCNP6.3, and (expected) MCNP6.4 surface-source files. However, users of the enclosed script must still verify that the script is behaving correctly for their own work.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2016

COMPRESSIBLE RELATIVISTIC MAGNETOHYDRODYNAMIC TURBULENCE IN MAGNETICALLY DOMINATED PLASMAS AND IMPLICATIONS FOR A STRONG-COUPLING REGIME

In this Letter, we report compressible mode effects on relativistic magnetohydrodynamic (RMHD) turbulence in Poynting-dominated plasmas using three-dimensional numerical simulations. We decomposed fluctuations in the turbulence into 3 MHD modes (fast, slow, and Alfvén) following the procedure of mode decomposition in Cho and Lazarian, and analyzed their energy spectra and structure functions separately. We also analyzed the ratio of compressible mode to Alfvén mode energy with respect to its Mach number. We found the ratio of compressible mode increases not only with the Alfvén Mach number, but also with the background magnetization, which indicates a strong coupling between the fast and Alfvén modes. It also signifies the appearance of a new regime of RMHD turbulence in Poynting-dominated plasmas where the fast and Alfvén modes are strongly coupled and, unlike the non-relativistic MHD regime, cannot be treated separately. This finding will affect particle acceleration efficiency obtained by assuming Alfvénic critical-balance turbulence and can change the resulting photon spectra emitted by non-thermal electrons.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1973

Zeta potential control for electrophoresis cells

Zeta potential arises from fact that ions tend to be adsorbed on surface of cell walls. This potential interfaces with electric field sensed by migrating particles and degrades resolution of separation. By regulating sign and magnitude of applied potential induced charge can be used to increase or decrease effective wall zeta potential.

Fogal, G. L.↗
NASA NTRS1977

Surfactant-assisted coal liquefaction

Improved process of coal liquefaction utilizing nonaqueous surfactant has increased oil yield from 50 to about 80%. Asphaltene molecule formation of colloid particles is prevented by surfactant. Separated molecules present more surface area for hydrogenation reaction. Lower requirements for temperature, pressure, and hydrogen lead to reduction in capital and operation costs.

Hsu, G. C.↗
NASA NTRS1980

Indirect microbial detection

Indirect method for detection of microbial growth utilizes flow of charged particles across barrier that physically separated growing cells from electrodes and measures resulting difference in potential between two platinum electrodes. Technique allows simplified noncontact monitoring of all growth in highly infectious cultures or in critical biochemical studies.

Wilkins, J. R.↗
NASA NTRS1985

Ariel 6 measurements of ultra-heavy cosmic ray fluxes in the region 34 or = Z or = 48

The Ariel VI satellite was launched by NASA on a Scout rocket on 3rd June 1979 from Wallops Island, Virginia, USA, into a near circular 625 km orbit inclined at 55 deg. It carried a spherical cosmic ray detector designed by a group from Bristol University. A spherical aluminum vessel of diameter 75 cm contains a gas scintillation mixture and a thin spherical shell of Pilot 425 plastic, and forms a single optical cavity viewed by 16 photomultipliers. Particle tracks through the detector may be characterized by their impact parameter p and by whether or not they pass through the cup of plastic scintillator placed between the sphere and the spacecraft body (referred to below as the Anti-Coincidence Detector or ACD). Individual particle charges are determined by separately measuring the gas scintillation and the Cerenkov emission from the plastic shell. This is possible because of the quite different distribution in time of these emissions.

Fowler, P. H.↗
NASA NTRS1987

A sputtering derived atomic oxygen source for studying fast atom reactions

A technique for the generation of fast atomic oxygen was developed. These atoms are created by ion beam sputtering from metal oxide surfaces. Mass resolved ion beams at energies up to 60 KeV are produced for this purpose using a 150 cm isotope separator. Studies have shown that particles sputtered with 40 KeV Ar(+) on Ta2O5 were dominantly neutral and exclusively atomic. The atomic oxygen also resided exclusively in its 3P ground state. The translational energy distribution for these atoms peaked at ca 7 eV (the metal-oxygen bond energy). Additional measurements on V2O5 yielded a bimodal distribution with the lower energy peak at ca 5 eV coinciding reasonably well with the metal-oxygen bond energy. The 7 eV source was used to investigate fast oxygen atom reactions with the 2-butene stereoisomers. Relative excitation functions for H-abstraction and pi-bond reaction were measured with trans-2-butene. The abstraction channel, although of minor relative importance at thermal energy, becomes comparable to the addition channel at 0.9 eV and dominates the high-energy regime. Structural effects on the specific channels were also found to be important at high energy.

Ferrieri, Richard A.↗
NASA NTRS1988

Multipoint measurements of energetic particles in the magnetosphere

The benefits of energetic-particle measurements in the study of magnetospheric physics are reviewed, including the particles' relative ease of detection, their high rectilinear speed, their range of gyroradii, and their immunity to large-scale electric fields. With such particles, it is possible to observationally separate distinctive plasma regions, uniquely assess field-line topologies, examine connectivity from the magnetospheric equator to the ionosphere, and sense global changes in magnetospheric configuration. Multipoint measurements of energetic particles have contributed substantially to the understanding of the earth magnetopause, the leakage of particles into the upstream region, the effect of sudden storm compressions, the global nature of substorm dynamics, and the location and character of high-energy acceleration processes.

Baker, D. N.↗