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At least 955 records · Page 53
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Physical and Chemical Morphology of Passively Sampled Environmental Films

Environmental surface films are important mediators in the fate and transport of persistent organic pollutants (POP) via largely uncharacterized mechanisms. This work presents the first analysis of the physical and chemical morphology of passively sampled environmental films. The films are developed in urban, sub-urban, and metropolitan locations for timescales ranging from 1 to 52 weeks by exposing polished silicon wafers to collect passively deposited tropospheric particulate matter. The time-dependent spatial morphology of the films is analyzed by bright-field, scanning electron, and atomic force microscopies. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) imaging data are analyzed to report the film’s chemical morphology and speciation. We find that the film matrix presents an extremely complex physical and chemical system. Deposited PM sizes span six orders of magnitude (millimeter to nanometer regimes), and surface coverages range from ca. 5 % for one week films and ca. 98 % for 52 week films. We observe significant amounts of mineral dust, biogenic organics, and occasional indications of flora growth (i.e., spores). The films exhibit nanoscale surface features indicative of small particulate depositions as well as films of (semi)volatile molecules. SIMS imaging reveals diverse and sometimes segregated chemical domains of hydrocarbons, inorganics, metals, and proteinaceous macromolecules. This work presents the first spatially resolved physical and chemical surface characterization of native environmental films, beginning a study of mechanisms by which these films form, persist, and mature in the environment.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Effect of the size of nanoparticles on their dissolution within metal-glass nanocomposites under sustained irradiation

We investigate the dissolution law of metallic nanoparticles (NPs) under sustained irradiation. The system is composed of isolated spherical gold NPs (4–100 nm) embedded in an amorphous silica host matrix. Samples are irradiated at room temperature in the nuclear stopping power regime with 4 MeV Au ions for fluences up to 8 × 10{sup 16 }cm{sup −2}. Experimentally, the dependence of the dissolution kinetics on the irradiation fluence is linear for large NPs (45–100 nm) and exponential for small NPs (4–25 nm). A lattice-based kinetic Monte Carlo (KMC) code, which includes atomic diffusion and ballistic displacement events, is used to simulate the dynamical competition between irradiation effects and thermal healing. The KMC simulations allow for a qualitative description of the NP dissolution in two main stages, in good agreement with the experiment. Moreover, the perfect correlation obtained between the evolution of the simulated flux of ejected atoms and the dissolution rate in two stages implies that there exists an effect of the size of NPs on their dissolution and a critical size for the transition between the two stages. The Frost-Russell model providing an analytical solution for the dissolution rate, accounts well for the first dissolution stage but fails in reproducing the data for the second stage. An improved model obtained by including a size-dependent recoil generation rate permits fully describing the dissolution for any NP size. This proves, in particular, that the size effect on the generation rate is the principal reason for the existence of two regimes. Finally, our results also demonstrate that it is justified to use a unidirectional approximation to describe the dissolution of the NP under irradiation, because the solute concentration is particularly low in metal-glass nanocomposites.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

Characterization of white poplar and eucalyptus after ionic liquid pretreatment as a function of biomass loading using X-ray diffraction and small angle neutron scattering

A systematic study was done to understand interactions among biomass loading during ionic liquid (IL) pretreatment, biomass type and biomass structures. White poplar and eucalyptus samples were pretreated using 1-ethyl-3-methylimidazolium acetate (EmimOAc) at 110 °C for 3 h at biomass loadings of 5, 10, 15, 20 and 25 wt%. All of the samples were chemically characterized and tested for enzymatic hydrolysis. Physical structures including biomass crystallinity and porosity were measured by X-ray diffraction (XRD) and small angle neutron scattering (SANS), respectively. SANS detected pores of radii ranging from ~25 to 625 Å, enabling assessment of contributions of pores with different sizes to increased porosity after pretreatment. Contrasting dependences of sugar conversion on white poplar and eucalyptus as a function of biomass loading were observed and cellulose crystalline structure was found to play an important role.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2022

Neutron capture of UO 2 targets prepared by spin-coating assisted combustion synthesis

Two uranium dioxide (UO 2 ) targets of (414 ± 23) nm and (1092 ± 93) nm thicknesses were prepared on 6061 aluminum alloy and puratronic grade aluminum backing materials. The targets were deposited with a novel method combining spin coating and solution combustion synthesis (SCS). The target layers consisted of small (3–7 nm) UO 2 grains and uniformly distributed ultra-small (1–3 nm) pores. The prepared targets were tested at the Los Alamos National Laboratory’s LANSCE facility for neutron irradiation damage and suitability for neutron capture experiments. The samples showed no signs of target material loss after the irradiation. However, irradiation caused a significant increase in the grain size (4–10 nm), as well as upward mass diffusion and coalescence of the pores due to the thermal spikes. The magnesium in the aluminum 6061 alloy backing also diffused into the UO 2 layer during neutron irradiation. The structural changes in the target after the irradiation do not affect the data from neutron capture. As a result, the new method can be used more broadly to prepare other actinide targets for nuclear physics experiments.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2024

Crystal structure and shape selection in the growth of 3D metallic crystallites on layered materials: Fe on MoS 2

Nucleation and growth of supported 3D metal clusters or crystallites during deposition on MoS 2 , or on other weakly-adhering layered materials, can potentially produce diverse growth shapes, and even crystal structures differing from the bulk metal. For Fe deposition on MoS 2 , SEM and AFM observations reveal three distinct crystallite shapes. By comparison with atomistic structure models incorporating realistic Fe-MoS 2 interface structures, here we conclude that these are: triangular fcc(111) pyramids with sloped {100} side facets; bcc(110) A-frame tents with sloped {100} side facets; and bcc(110) mesas with vertical {100} and {110} side facets. The following picture is proposed for the competitive formation of clusters and crystallites with different structures: (i) small nanoclusters formed at the onset of deposition exhibit facile fluxional dynamics allowing sampling of different crystal structures and shapes; (ii) sufficient fluxionality implies a Boltzmann distribution of sampled structures, and thus coexistence of different structures follows from the demonstrated similar energies for those structures; (iii) growing clusters reach a threshold size above which the characteristic time scale for restructuring exceeds that for cluster growth. Thereafter, clusters are locked-in to a specific crystal structure and shape as revealed by imaging of larger crystallites. Despite a penalty for fcc(111) over bcc(111) pyramids based on bulk energetics, favorable surface and interface energies makes them preferable for smaller sizes.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Structure Dominates Localization of Tracers within Aging Nanoparticle Glasses

We investigate the transport and localization of tracer probes in a glassy matrix as a function of relative size using dynamic X-ray scattering experiments and molecular dynamics simulations. The quiescent relaxations of tracer particles evolve with increasing waiting time, t w . The corresponding relaxation times increase exponentially at small t w and then transition to a power-law behavior at longer t w . As tracer size decreases, the aging behavior weakens and the particles become less localized within the matrix until they delocalize at a critical size ratio δ o ≈ 0.38. In conclusion, localization does not vary with sample age even as the relaxations slow by approximately an order of magnitude, suggesting that matrix structure controls tracer localization.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

A Combined SAXS/SANS Study for the in Situ Characterization of Ligand Shells on Small Nanoparticles: The Case of ZnO

ZnO nanoparticles (NPs) have great potential for their use in, e.g., thin film solar cells due to their electro-optical properties adjustable on the nanoscale. Therefore, the production of well-defined NPs is of major interest. For a targeted production process, the knowledge of the stabilization layer of the NPs during and after their formation is of particular importance. For the study of the stabilizer layer of ZnO NPs prepared in a wet chemical synthesis from zinc acetate, only ex situ studies have been performed so far. An acetate layer bound to the surface of the dried NPs was found; however, an in situ study which addresses the stabilizing layer surrounding the NPs in a native dispersion was missing. By the combination of small angle scattering with neutrons and X-rays (SANS and SAXS) for the same sample, we are now able to observe the acetate shell in situ for the first time. In addition, the changes of this shell could be followed during the ripening process for different temperatures. With increasing size of the ZnO core (d core ) the surrounding shell (d shell ) becomes larger, and the acetate concentration within the shell is reduced. For all samples, the shell thickness was found to be larger than the maximum extension of an acetate molecule with acetate concentrations within the shell below 50 vol %. Furthermore, there is not a monolayer of acetate molecules that covers the NPs but rather a swollen shell of acetate ions. This shell is assumed to hinder the growth of the NPs to larger macrostructures. In addition, we found that the partition coefficient μ between acetate in the shell surrounding the NPs and the total amount of acetate in the solution is about 10% which is in good agreement with ex situ data determined by thermogravimetric analysis.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Machine Learning Framework for Characterizing Processing–Structure Relationship in Block Copolymer Thin Films

The morphology of block copolymers (BCPs) critically influences material properties and applications. This work introduces a machine learning (ML)-enabled, high-throughput framework for analyzing grazing incidence small-angle X-ray scattering (GISAXS) data and atomic force microscopy (AFM) images to characterize BCP thin film morphology. A convolutional neural network was trained to classify AFM images by surface features, achieving 97% testing accuracy. Classified images were then analyzed to extract 2D grain size measurements from the samples in a high-throughput manner. ML models were trained to predict domain orientation based on processing parameters such as solvent ratio, additive type, and additive ratio. GISAXS-based properties were predicted with strong performances (R 2 > 0.75), while AFM-based property predictions were less accurate (R 2 < 0.60), likely due to the localized nature of AFM measurements compared to the bulk information captured by GISAXS. Beyond model performance, interpretability was addressed using SHapley Additive exPlanations (SHAP). SHAP analysis revealed that the additive ratio had the largest impact on morphological predictions, where additive provides the BCP chains with increased volume to rearrange into thermodynamically favorable morphologies. This interpretability helps validate model predictions and offers insight into parameter importance. Altogether, the presented framework combining high-throughput characterization and interpretable ML offers an approach to exploring and optimizing BCP thin film morphology across a broad processing landscape.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Using refractive lenses to provide a variable spot size for Kirkpatrick–Baez mirrors

For many X-ray microprobe experiments it is desirable to be able to vary the beam size: using large beams for survey scans and a small beam for the final measurements. Beryllium refractive lenses were found to be a simple and controllable method for enlarging the focus in a Kirkpatrick–Baez-based microprobe. They can provide variable spot size, can be quickly inserted or removed and do not move the beam center on the sample.

47 OTHER INSTRUMENTATION↗
DOE OSTI2016

Zinc-Nucleated D 2 and H 2 Crystal Formation from Their Liquids

Calorimetric measurements at University of Rochester Laboratory for Laser Energetics of D 2 crystallization from the melt indicate that zinc can act as a heterogeneous nucleation seed with suppressed supercooling. We further studied in this paper this effect for a variety of zinc substrates using the optical-access cryogenic sample cell at Lawrence Livermore National Laboratory. Small supercoolings are observed, some as low as 5 mK, but results depend on the zinc history and sample preparation. In general, thin samples prepared by physical vapor deposition were not effective in nucleating crystal formation. Larger (several-millimeter) granules showed greater supercooling suppression, depending on surface modification and granule size. Surfaces of these granules are morphologically varied and not uniform. Scanning electron microscope images were not able to correlate any particular surface feature with enhanced nucleation. Finally, application of classical nucleation theory to the observed variation of supercooling level with granule size is consistent with nucleation features with sizes <100 nm and with wetting angles of a few degrees.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Characterization of porosity in sulfide ore minerals: A USANS/SANS study

Porosity plays a key role in the formation and alteration of sulfide ore minerals, yet our knowledge of the nature and formation of the residual pores is very limited. Herein, we report the application of ultra-small-angle neutron scattering and small-angle neutron scattering (USANS/SANS) to assess the porosity in five natural sulfide minerals (violarite, marcasite, pyrite, chalcopyrite, and bornite) possibly formed by hydrothermal mineral replacement reactions and two synthetic sulfide minerals (violarite and marcasite) prepared experimentally by mimicking natural hydrothermal conditions. USANS/SANS data showed very different pore size distributions for these minerals. Natural violarite and marcasite tend to possess less pores in the small size range (<100 nm) compared with their synthetic counterparts. This phenomenon is consistent with a higher degree of pore healing or diagenetic compaction experienced by the natural violarite and marcasite. Surprisingly, nanometer-sized (<20 nm) pores were revealed for a natural pyrite cube from La Rioga, Spain, and the sample has a pore volume fraction of ~7.7%. Both chalcopyrite and bornite from the massive sulfide assemblage of the Olympic Dam deposit in Roxby Downs, South Australia, were found to be porous with a similar pore volume fraction (~15%), but chalcopyrite tends to have a higher proportion of nanometer-size pores centered at ~4 nm while bornite tends to have a broader pore size distribution. The specific surface area is generally low for these minerals ranging from 0.94 to 6.28 m2/g, and the surfaces are generally rough as surface fractal behavior was observed for all these minerals. This investigation has demonstrated that USANS/SANS is a very useful tool for analyzing porosity in ore minerals. We believe that with this quantified porosity information a deeper understanding of the complex fluid flow behavior within the porous minerals can be expected.

mineral replacement reactions↗
DOE OSTI2019

New X-Ray Spectrometer Developed

X-ray absorption spectroscopy (XAS) and X-ray emission spectroscopy (XES) are useful tools for characterizing numerous properties of a given material. They can give elemental composition, metal oxidation states, spin state, orbital occupancy, and more. A drawback is that these types of measurements have historically needed synchrotron light sources to generate high flux X-ray beams and high-resolution monochromators to provide a monoenergetic excitation source. Synchrotrons are building-sized facilities (often operated in the U.S. by the DOE) and have the scheduling complexities and logistical issues that accompany any large-scale research facility. There are added challenges for scientists wishing to analyze radioactive samples such as plutonium or other actinides. These limitations are now mitigated by a small, “portable” X-ray emission and absorption spectrometers developed by Los Alamos scientists and the University of Washington.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
NASA NTRS1972

Multiple asteroid flyby opportunities in the 1970's and 1980's.

Trajectory characteristics are described for several representative multiple asteroid flyby (MAF) missions possible in the 1970's and early 1980's, many of which are constrained to include a flyby of Ceres, the largest asteroid. It is shown that flybys of three or four asteroids are possible with spacecraft having a delta-V capability of less than 1 km per sec. The major technical problems associated with MAF missions are due to the small size and poorly known orbits of aster oids. These factors make acquisition, guidance, and science measurements difficult, especially for the very small asteroids. Yet, MAF missions are expected to provide a significant increase in knowledge of basic properties of asteroids and to lay the groundwork for more sophisticated rendezvous and sample return missions.

Brooks, D. R.↗
NASA NTRS1975

Mobile data buoy system

The Mobile Data Buoy System was conceived to serve the users requirement for obtaining water quality parameters from two separate watershed systems. In view of the cost constraints of the ERTS program it was obvious that the network of 10 sampling stations required could not be of the fixed installation type; therefore, it was decided to go to a system of battery powered buoys of a size that could be used in one watershed system for a period of time and then moved to another by use of a relatively small 6.7 m (22 foot) boat. The basic idea of the water quality measurement program was to establish the water quality pattern of change from the headwaters of the watersheds to and through the Mobile Bay. This would allow the investigator to develop a good picture of the state's major water resources and the pressures from pollution that are being imposed. At this point in deployment of this mobile system of buoys, it is too early to put a quantitative value on the system, however it appears less expensive than known fixed installations as to first cost. It has a basic advantage in that it can be moved, at very little expense, to alternate sites where it is desired to obtain water quality data. It is to be noted this buoy system which covers a 80 Km (50 mile) stretch of the Black Warrior River and then skips down 483 Km (300 miles) to Mobile Bay for the next measurements would not be feasible unless there is a satellite to collect and relay the data.

Morton, R. A.↗
NASA NTRS2011

2014/2219 Tri-Point Crack Analysis

Friction stir welding (FSW) is a solid state welding process with potential advantages for aerospace and automotive industries dealing with light alloys. Self-reacting friction stir welding (SR-FSW) is one variation of the FSW process being developed at the National Aeronautics and Space Administration (NASA) for use in the fabrication of propellant tanks. Friction plug welding is used to seal the exit hole that remains in a circumferential SR-FSW. The objective of this study was to evaluate the deformation response at the tips of cracks located in the heat affected zone of friction plug welds and to study the fracture behavior of welds with defects in the form of fatigue cracks. The study used existing 2014-T6 to 2219-T87 self-reacting friction stir weld panels with 2219-T87 friction plug welds. Electro-discharge machined (EDM) notches were machined into the heat affected zone of the plug at the plug-to-base metal interface. Samples were then cycled to generate a fatigue crack emanating from the notch. After the fatigue crack reached a pre-defined length, a speckle pattern was applied and the ARAMIS system (a three dimensional imaging correlation system) was used to measure the deformations at the crack tip under a sequence of loads. Testing was conducted at ambient laboratory conditions. Fracture data from the testing was analyzed to evaluate residual strength capability of the panel as a function of flaw size. ARAMIS strain data was evaluated to examine strain and deformation patterns that develop around the crack tip and at the plug/weld interfaces. Four samples were used in this study, with three samples in a post-weld heat treated condition. Three samples contained large diameter plugs (M5) and one sample contained a small diameter plug (M3). Two samples were 4 inches in width and two samples were 8.5 inches in width. All samples failed through the precrack with residual strengths ranging from 37 ksi to 42 ksi.

Horton, Karla Renee↗
NASA NTRS2020

Thermal system and environmental testing of the Mars Helicopter

The Mars Helicopter will be a technology demonstration conducted during the Mars 2020 mission. The primary mission objective is to achieve several 90-second flights demonstrating the feasibility of heavier than air flight on Mars and capture visible light images via forward and nadir mounted cameras. These flights could possibly provide reconnaissance data for sampling site selection for other Mars surface missions. A solar array and batteries for flight operations, imaging, communications, and survival heating power the Helicopter. The thermal design is driven by minimizing survival heater energy while maintaining compliance with allowable flight temperatures in a variable thermal environment. Due to the small size of the Helicopter and its complex geometries, along with the fact that it operates with very low power and small margins in the extreme Mars environment, additional care had to be paid while planning thermal tests and designing the thermal system. The first section of the paper describes the evolution of the thermal system of the Mars Helicopter. After the first thermal vacuum test of the engineering model, the thermal team has conducted a partial effect analysis on the thermal design components that had a major impact on the system performance. Several design choices derived by analysis and test have been made to meet the energy allocation and the temperature requirements. These changes included increased gas gaps to reduce gas conduction, low emissivity coatings for internal components, blanket implementation, optimization of wire routing and fine-tuning of surface operations to optimize waste heat recovery. The second part of the paper describes the flight model thermal vacuum test and the subsequent thermal model correlation necessary to confirm the fidelity of the analysis results.

Pauken, Michael↗
DOE OSTI2015

Large Scale Sequencing of Dothideomycetes Provides Insights into Genome Evolution and Adaptation

Dothideomycetes is the largest and most diverse class of ascomycete fungi with 23 orders 110 families, 1300 genera and over 19,000 known species. We present comparative analysis of 70 Dothideomycete genomes including over 50 that we sequenced and are as yet unpublished. This extensive sampling has almost quadrupled the previous study of 18 species and uncovered a 10 fold range of genome sizes. We were able to clarify the phylogenetic positions of several species whose origins were unclear in previous morphological and sequence comparison studies. We analyzed selected gene families including proteases, transporters and small secreted proteins and show that major differences in gene content is influenced by speciation.

Haridas, Sajeet↗
DOE OSTI2016

A universal density structure for circumgalactic gas

We develop a new method to constrain the physical conditions in the cool (∼10{sup 4} K) circumgalactic medium (CGM) from measurements of ionic column densities by assuming that the cool CGM spans a large range of gas densities and that small high-density clouds are hierarchically embedded in large low-density clouds. The new method combines the information available from different sightlines during the photoionization modeling, thus yielding tighter constraints on CGM properties compared to traditional methods that model each sightline individually. Applying this new technique to the COS Halos survey of low-redshift ∼L* galaxies, we find that we can reproduce all observed ion columns in all 44 galaxies in the sample, from the low ions to O VI, with a single universal density structure for the cool CGM. The gas densities span the range 50≲ρ/ ρ-bar {sub b}≲5×10{sup 5} ( ρ-bar {sub b} is the cosmic mean), while the physical size of individual clouds scales as ∼ρ {sup −1}, from ≈35 kpc for the low-density O VI clouds to ≈6 pc for the highest-density low-ion clouds. The deduced cloud sizes are too small for this density structure to be driven by self-gravity; thus, its physical origin is unclear. The implied cool CGM mass within the virial radius is (1.3 ± 0.4) × 10{sup 10} M{sub ⊙} (∼1% of the halo mass), distributed rather uniformly over the 4 decades in density. The mean cool gas density profile scales as R{sup −1.0±0.3}, where R is the distance from the galaxy center. We construct a 3D model of the cool CGM based on our results, which we argue provides a benchmark for the CGM structure in hydrodynamic simulations. Our results can be tested by measuring the coherence scales of different ions.

79 ASTRONOMY AND ASTROPHYSICS↗