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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 451 records · Page 25
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Simultaneous enhancement of the coercivity and remanence at high temperatures in a sintered Nd-Fe-B magnet after grain boundary diffusion with Dy60Co40 alloy

Highlights: • Dy and Co enriched shells were formed on the Nd{sub 2}Fe{sub 14}B grain boundaries. • Coercivity and remanence were increased simultaneously at high temperatures. • Remanence stability was improved with little change of the Curie temperature. - Abstract: The grain boundary diffusion process (GBDP) using Dy{sub 60}Co{sub 40} alloy was applied to a sintered Nd-Fe-B magnet. After GBDP the temperature stability of remanence was improved greatly with the remanence temperature coefficient improving from −0.140%/°C to −0.095%/°C while the Curie temperature increased marginally. Both the coercivity and remanence were increased simultaneously at high temperatures. Microstructure and composition analysis revealed that Dy and Co enriched shells were formed on Nd{sub 2}Fe{sub 14}B grain boundaries after GBDP. The Dy enriched shell increased the coercivity while the Co enriched shell decreased the temperature sensitivity of remanence and then increased the remanence at high temperatures.

36 MATERIALS SCIENCE↗
DOE OSTI2017

The Role of Diffusion in the Transport of Energetic Electrons during Solar Flares

The transport of the energy contained in suprathermal electrons in solar flares plays a key role in our understanding of many aspects of flare physics, from the spatial distributions of hard X-ray emission and energy deposition in the ambient atmosphere to global energetics. Historically the transport of these particles has been largely treated through a deterministic approach, in which first-order secular energy loss to electrons in the ambient target is treated as the dominant effect, with second-order diffusive terms (in both energy and angle) generally being either treated as a small correction or even neglected. Here, we critically analyze this approach, and we show that spatial diffusion through pitch-angle scattering necessarily plays a very significant role in the transport of electrons. We further show that a satisfactory treatment of the diffusion process requires consideration of non-local effects, so that the electron flux depends not just on the local gradient of the electron distribution function but on the value of this gradient within an extended region encompassing a significant fraction of a mean free path. Our analysis applies generally to pitch-angle scattering by a variety of mechanisms, from Coulomb collisions to turbulent scattering. We further show that the spatial transport of electrons along the magnetic field of a flaring loop can be modeled rather effectively as a Continuous Time Random Walk with velocity-dependent probability distribution functions of jump sizes and occurrences, both of which can be expressed in terms of the scattering mean free path.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2008

Spiking Neurons for Analysis of Patterns

Artificial neural networks comprising spiking neurons of a novel type have been conceived as improved pattern-analysis and pattern-recognition computational systems. These neurons are represented by a mathematical model denoted the state-variable model (SVM), which among other things, exploits a computational parallelism inherent in spiking-neuron geometry. Networks of SVM neurons offer advantages of speed and computational efficiency, relative to traditional artificial neural networks. The SVM also overcomes some of the limitations of prior spiking-neuron models. There are numerous potential pattern-recognition, tracking, and data-reduction (data preprocessing) applications for these SVM neural networks on Earth and in exploration of remote planets. Spiking neurons imitate biological neurons more closely than do the neurons of traditional artificial neural networks. A spiking neuron includes a central cell body (soma) surrounded by a tree-like interconnection network (dendrites). Spiking neurons are so named because they generate trains of output pulses (spikes) in response to inputs received from sensors or from other neurons. They gain their speed advantage over traditional neural networks by using the timing of individual spikes for computation, whereas traditional artificial neurons use averages of activity levels over time. Moreover, spiking neurons use the delays inherent in dendritic processing in order to efficiently encode the information content of incoming signals. Because traditional artificial neurons fail to capture this encoding, they have less processing capability, and so it is necessary to use more gates when implementing traditional artificial neurons in electronic circuitry. Such higher-order functions as dynamic tasking are effected by use of pools (collections) of spiking neurons interconnected by spike-transmitting fibers. The SVM includes adaptive thresholds and submodels of transport of ions (in imitation of such transport in biological neurons). These features enable the neurons to adapt their responses to high-rate inputs from sensors, and to adapt their firing thresholds to mitigate noise or effects of potential sensor failure. The mathematical derivation of the SVM starts from a prior model, known in the art as the point soma model, which captures all of the salient properties of neuronal response while keeping the computational cost low. The point-soma latency time is modified to be an exponentially decaying function of the strength of the applied potential. Choosing computational efficiency over biological fidelity, the dendrites surrounding a neuron are represented by simplified compartmental submodels and there are no dendritic spines. Updates to the dendritic potential, calcium-ion concentrations and conductances, and potassium-ion conductances are done by use of equations similar to those of the point soma. Diffusion processes in dendrites are modeled by averaging among nearest-neighbor compartments. Inputs to each of the dendritic compartments come from sensors. Alternatively or in addition, when an affected neuron is part of a pool, inputs can come from other spiking neurons. At present, SVM neural networks are implemented by computational simulation, using algorithms that encode the SVM and its submodels. However, it should be possible to implement these neural networks in hardware: The differential equations for the dendritic and cellular processes in the SVM model of spiking neurons map to equivalent circuits that can be implemented directly in analog very-large-scale integrated (VLSI) circuits.

Huntsberger, Terrance↗
DOE OSTI2015

Characterization of Cr-rich Cr-Sb multilayer films: Syntheses of a new metastable phase using modulated elemental reactants

The new metastable compound Cr{sub 1+x}Sb with x up to 0.6 has been prepared via a thin film approach using modulated elemental reactants and investigated by in-situ X-ray reflectivity, X-ray diffraction, differential scanning calorimetry, energy dispersive X-ray analysis as well as transmission electron microscopy and atomic force microscopy. The new Cr-rich antimonide crystallizes in a structure related to the Ni{sub 2}In-type structure, where the crystallographic position (1/3, 2/3, 3/4) is partially occupied by excess Cr. The elemental layers of the pristine material interdiffused significantly before Cr{sub 1+x}Sb crystallized. A change in the activation energy was observed for the diffusion process when crystal growth starts. First-principles electronic structure calculations provide insight into the structural stability, magnetic properties and resistivity of Cr{sub 1+x}Sb. - Graphical abstract: 1 amorphous multilayered film 2 interdiffused amorphous film 3 metastable crystalline phase 4 thermodynamic stable phase (and by-product). - Highlights: • Interdiffusion of amorphous Cr and Sb occurs before crystallization. • Crystallization of a new metastable phase Cr{sub 1.6}Sb in Ni{sub 2}In-type structure. • The new Cr-rich phase shows half-metallic behavior.

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

Probing the Release and Uptake of Water in α-MnO 2 · x H 2 O

Alpha-MnO 2 is of interest as a cathode material for 3 V lithium batteries and as an electrode/electrocatalyst for higher energy, hybrid Li-ion/Li–O 2 systems. It has a structure with large tunnels that contain stabilizing cations such as Ba 2+ , K + , NH 4 + , and H3O + (or water, H 2 O). When stabilized by H 3 O + /H 2 O, the protons can be ion-exchanged with lithium to produce a Li 2 O-stabilized α-MnO 2 structure. It has been speculated that the electrocatalytic process in Li–O 2 cells may be linked to the removal of lithium and oxygen from the host α-MnO 2 structure during charge, and their reintroduction during discharge. In this investigation, hydrated α-MnO 2 was used, as a first step, to study the release and uptake of oxygen in α-MnO 2 . Temperature-resolved in situ synchrotron X-ray diffraction (XRD) revealed a nonlinear, two-stage, volume change profile, which with the aide of X-ray absorption near-edge spectroscopy (XANES), redox titration, and density functional theory (DFT) calculations, is interpreted as the release of water from the α-MnO 2 tunnels. The two stages correspond to H 2 O release from intercalated H 2 O species at lower temperatures and H 3 O + species at higher temperature. Thermogravimetric analysis confirmed the release of oxygen from α-MnO 2 in several stages during heating–including surface water, occluded water, and structural oxygen–and in situ UV resonance Raman spectroscopy corroborated the uptake and release of tunnel water by revealing small shifts in frequencies during the heating and cooling of α-MnO 2 . Lastly, DFT calculations revealed the likelihood of disordered water species in binding sites in α-MnO 2 tunnels and a facile diffusion process.

36 MATERIALS SCIENCE↗
NASA NTRS2012

Fermi Large Area Telescope Observations of the Supernova Remnant GS.7-0.1

We present a detailed analysis of the GeV gamma-ray emission toward the supernova remnant (SNR) G8.7-0.1 with the Large Area Telescope (LAT) onboard the Fermi Gamma-ray Space Telescope. An investigation of the relationship among G8.7-0.1 and the TeV unidentified source HESS J1804-216 provides us with an important clue on diffusion process of cosmic rays if particle acceleration operates in the SNR. The GeV gamma-ray emission is extended with most of the emission in positional coincidence with the SNR G8.7-0.1 and a lesser part located outside the western boundary of G8.7-0.1. The region of the gamma-ray emission overlaps spatially-connected molecular clouds, implying a physical connection for the gamma-ray structure. The total gamma-ray spectrum measured with LAT from 200 MeV-100 GeV can be described by a broken power-law function with a break of 2.4 +/- 0.6 (stat) +/- 1.2 (sys) GeV, and photon indices of2.10 +/- 0.06 (stat) +/- 0.10 (sys) below the break and 2.70 +/- 0.12 (stat) +/- 0.14 (sys) above the break. Given the spatial association among the gamma rays, the radio emission ofG8.7-0.1, and the molecular clouds, the decay of pions produced by particles accelerated in the SNR and hitting the molecular clouds naturally explains the GeV gamma-ray spectrum. We also find that the GeV morphology is not well represented by the TeV emission from HESS Jl804-2l6 and that the spectrum in the Ge V band is not consistent with the extrapolation of the TeV gamma-ray spectrum. The spectral index of the TeV emission is consistent with the particle spectral index predicted by a theory that assumes energy-dependent diffusion of particles accelerated in an SNR. We discuss the possibility that the TeV-spectrum originates from the interaction of particles accelerated in G8.7-0.l with molecular clouds, and we constrain the diffusion coefficient of the particles.

Ferrara, E. C.↗
NASA NTRS2011

Fermi Large Area Telescope Observations of the Supernova Remnant GS.7-0.1

We present a detailed analysis of the GeV gamma-ray emission toward the supernova remnant (SNR) G8.7-0.1 with the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope. An investigation of the relationship among G8.7-0.l and the TeV unidentified source HESS J1804-216 provides us with an important clue on diffusion process of cosmic rays if particle acceleration operates in the SNR. The GeV gamma-ray emission is extended with most of the emission in positional coincidence with the SNR G8.7-0.l and a lesser part located outside the western boundary of G8.7-0.l. The region of the gamma-ray emission overlaps spatially-connected molecular clouds, implying a physical connection for the gamma-ray structure. The total gamma-ray spectrum measured with LAT from 200 MeV-100 GeV can be described by a broken power-law function with a break of 2.4 +/- 0.6 (stat) +/- 1.2 (sys) GeV, and photon indices of 2.10 +/- 0.06 (stat) +/- 0.10 (sys) below the break and 2.70 +/- 0.12 (stat) +/- 0.l4 (sys) above the break. Given the spatial association among the gamma rays, the radio emission of G8.7-0.1, and the molecular clouds, the decay of 1IoS produced by particles accelerated in the SNR and hitting the molecular clouds naturally explains the GeV gamma-ray spectrum. We also find that the GeV morphology is not well represented by the TeV emission from HESS J1804-216 and that the spectrum in the GeV band is not consistent with the extrapolation of the TeV gamma-ray spectrum. The spectral index of the TeV emission is consistent with the particle spectral index predicted by a theory that assumes energy-dependent diffusion of particles accelerated in an SNR. We discuss the possibility that the TeV spectrum originates from the interaction of particles accelerated in G8.7-0.1 with molecular clouds, and we constrain the diffusion coefficient of the particles.

Ajello, M.↗
DOE OSTI2018

Effects of Calcite Impurities in Bentonite Buffer Systems on Uranium(VI) Solution Speciation and Sorption Behavior

In many nuclear waste disposal scenarios, bentonite is the proposed buffer material surrounding nuclear waste containers. Its main mineralogical component, Na-montmorillonite clay, is expected to limit radionuclide mobility to slow diffusion processes due to the clay’s low porosity and permeability, and the high sorption affinity of clay surface complexation and cation exchange sites for many radionuclides. Given its mineral structure, montmorillonite provides two types of porosities that can be accessible to radioactive contaminants: macropores between clay particles and interlayer spaces within clay particles, which become dominant at increasing degrees of bentonite compaction. Despite the fact that bentonite naturally contains a variety of mineral impurities (e.g., quartz, feldspars and calcite), most previous studies have only focused on radionuclide interactions with pure Na-montmorillonite phases. Hence, in this study, we will investigate the influence of calcite impurities on uranium(VI) (U(VI)) solution speciation and sorption behavior in bentonite systems. In the presence of water, calcite impurities are expected to lead to milli-molar concentrations of dissolved calcium over a wide range of pH conditions. Consequently, Ca 2+ could – at least partially – replace Na + on clay cation exchange sites, with further implications for exchange reactions of cationic U(VI) species. In addition, ternary U(VI)-Ca-carbonate solution species (CaUO 2 (CO 3 ) 3 2- and Ca 2 UO 2 (CO 3 ) 3 ) will largely replace U(VI)-carbonate species (UO 2 (CO 3 ) 3 4- and UO 2 (CO 3 ) 2 2- ) at alkaline pH. These larger, but lower-charged U(VI) species, may show different sorption and diffusion characteristics, e.g. if their access to negatively-charged clay interlayer spaces is different from binary U(VI)-carbonate complexes. In this presentation, we will first demonstrate the impacts of calcite impurities on U(VI) solution speciation based on PHREEQC simulations. We will then discuss first results from U(VI) sorption studies in these systems. This research is being performed using funding received from the DOE Office of Nuclear Energy's Nuclear Energy University Program.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2015

Influence of growth conditions on exchange bias of NiMn-based spin valves

As shown in previous investigations, a correlation between a NiMn-based spin valve's thermal stability and its inherent exchange bias exists, even if the blocking temperature of the antiferromagnet is clearly above the heating temperature and the reason for thermal degradation is mainly diffusion and not the loss of exchange bias. Samples with high exchange bias are thermally more stable than samples with low exchange bias. Those structures promoting a high exchange bias are seemingly the same suppressing thermally induced diffusion processes (A. Wienecke and L. Rissing, “Relationship between thermal stability and layer-stack/structure of NiMn-based GMR systems,” in IEEE Transaction on Magnetic Conference (EMSA 2014)). Many investigations were carried out on the influence of the sputtering parameters as well as the layer thickness on the magnetoresistive effect. The influence of these parameters on the exchange bias and the sample's thermal stability, respectively, was hardly taken into account. The investigation described here concentrates on the last named issue. The focus lies on the influence of the sputtering parameters and layer thickness of the “starting layers” in the stack and the layers forming the (synthetic) antiferromagnet. This paper includes a guideline for the evaluated sputtering conditions and layer thicknesses to realize a high exchange bias and presumably good thermal stability for NiMn-based spin valves with a synthetic antiferromagnet.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Achievement of high coercivity in sintered R-Fe-B magnets based on misch-metal by dual alloy method

The R-Fe-B (R, rare earth) sintered magnets prepared with different ratio of alloys of MM-Fe-B (MM, misch-metal) and Nd-Fe-B by dual alloy method were investigated. As expected, the high ratio of MM-Fe-B alloy degrades the hard magnetic properties heavily with intrinsic coercivity lower than 5 kOe. When the atomic ratio MM/R ≤ 21.5% the magnetic properties can reach a practical level of B{sub r} ≥ 12.1 kGs, H{sub cj} ≥ 10.7 kOe, and (BH){sub max} ≥ 34.0 MGOe. And the effect of H{sub cj} enhancement by the grain boundary diffusion process is obvious when MM/R ≤ 21.5%. It is revealed that the decrement of intrinsic magnetic properties of R{sub 2}Fe{sub 14}B matrix phase is not the main reason of the degradation of the magnets with high MM ratio. The change of deteriorated microstructure together with phase component plays fundamental roles in low H{sub cj}. In high MM ratio magnets, (a) after annealing, Ce atoms inside main phase are inclined to be segregated in the outer layer of the main phase grains; (b) there is no thin layer of Ce-rich phase as an analogue of Nd-rich phase to separate main phase grains; (c) excessive Ce tends to form CeFe{sub 2} grains.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Geometrical effects on the electron residence time in semiconductor nano-particles

We have used random walk (RW) numerical simulations to investigate the influence of the geometry on the statistics of the electron residence time τ{sub r} in a trap-limited diffusion process through semiconductor nano-particles. This is an important parameter in coarse-grained modeling of charge carrier transport in nano-structured semiconductor films. The traps have been distributed randomly on the surface (r{sup 2} model) or through the whole particle (r{sup 3} model) with a specified density. The trap energies have been taken from an exponential distribution and the traps release time is assumed to be a stochastic variable. We have carried out (RW) simulations to study the effect of coordination number, the spatial arrangement of the neighbors and the size of nano-particles on the statistics of τ{sub r}. It has been observed that by increasing the coordination number n, the average value of electron residence time, τ{sup ¯}{sub r} rapidly decreases to an asymptotic value. For a fixed coordination number n, the electron's mean residence time does not depend on the neighbors' spatial arrangement. In other words, τ{sup ¯}{sub r} is a porosity-dependence, local parameter which generally varies remarkably from site to site, unless we are dealing with highly ordered structures. We have also examined the effect of nano-particle size d on the statistical behavior of τ{sup ¯}{sub r}. Our simulations indicate that for volume distribution of traps, τ{sup ¯}{sub r} scales as d{sup 2}. For a surface distribution of traps τ{sup ¯}{sub r} increases almost linearly with d. This leads to the prediction of a linear dependence of the diffusion coefficient D on the particle size d in ordered structures or random structures above the critical concentration which is in accordance with experimental observations.

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

First-principles study of hydrogen-enhanced phosphorus diffusion in silicon

We present a first-principles study on the interstitial-mediated diffusion process of neutral phosphorus (P) atoms in a silicon crystal with the presence of mono-atomic hydrogen (H). By relaxing initial Si structures containing a P atom and an H atom, we derived four low-energy P-H-Si defect complexes whose formation energies are significantly lower than those of P-Si defect complexes. These four defect complexes are classified into two groups. In group A, an H atom is located near a Si atom, whereas in group B, an H atom is close to a P atom. We found that the H atom pairs with P or Si atom and changes the nature bonding between P and Si atoms from out-of-phase conjugation to in-phase conjugation. This fact results in the lower formation energies compare to the cases without H atom. For the migration of defect complexes, we have found that P-H-Si defect complexes can migrate with low barrier energies if an H atom sticks to either P or Si atom. Group B complexes can migrate from one lattice site to another with an H atom staying close to a P atom. Group A complexes cannot migrate from one lattice site to another without a transfer of an H atom from one Si atom to another Si atom. A change in the structure of defect complexes between groups A and B during the migration results in a transfer of an H atom between P and Si atoms. The results for diffusion of group B complexes show that the presence of mono-atomic H significantly reduces the activation energy of P diffusion in a Si crystal, which is considered as a summation of formation energy and migration barrier energy, leading to the enhancement of diffusion of P atoms at low temperatures, which has been suggested by recent experimental studies.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

The origin of the extragalactic gamma-ray background and implications for dark matter annihilation

The origin of the extragalactic γ-ray background (EGB) has been debated for some time. The EGB comprises the γ-ray emission from resolved and unresolved extragalactic sources, such as blazars, star-forming galaxies, and radio galaxies, as well as radiation from truly diffuse processes. This Letter focuses on the blazar source class, the most numerous detected population, and presents an updated luminosity function and spectral energy distribution model consistent with the blazar observations performed by the Fermi-Large Area Telescope (LAT). Additionally, we show that blazars account for 50$_{-11}^{+12}$% of the EGB photons (>0.1 GeV), and that Fermi-LAT has already resolved ~70% of this contribution. Blazars, and in particular hard-spectrum sources such as BL Lacs, are responsible for most of the EGB emission above 100 GeV. We find that the extragalactic background light, which attenuates blazars' high-energy emission, is responsible for the high-energy cutoff observed in the EGB spectrum. Finally, we show that blazars, star-forming galaxies, and radio galaxies can naturally account for the amplitude and spectral shape of the background in the 0.1–820 GeV range, leaving only modest room for other contributions. In conclusion, this allows us to set competitive constraints on the dark matter annihilation cross section.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Elevated Temperature Alpha Spectroscopy with Nickel-Platinum {sup 4}H-SiC Schottky Diodes

In order to protect against the diversion of special nuclear material during pyro-processing of spent nuclear fuel, an online monitoring of the actinide concentrations must be developed. In order to do so, alpha spectroscopy can be employed in order to determine the relative concentrations of various isotopes based on the characteristic alpha spectrum of each isotope of interest. The operating temperatures in the pyro-processing environment are such that high temperature operability of alpha detectors is required. The Idaho National Laboratory (INL) electro-refiner operates at a molten salt temperature of approximately 500 deg. C. The vapor temperature above the molten salt is approximately 100 deg. C. In order to provide reasonably compact online monitoring of the actinide concentrations within the molten salt the detector would be located in this vapor region. The temperature in this location is too high for a commercial silicon detector to operate without serious signal degradation due to thermal noise. As the operating temperature increases, the thermal energy available to the charge carriers within the semiconductor increases. For narrow band-gap semiconductors like silicon, this increase in free charge carriers with increasing temperature leads to unacceptable leakage current at relatively low temperatures when compared with wide band-gap materials. In order to overcome this, a wide band-gap material is employed. An alpha particle sensor utilizing a nickel Schottky barrier {sup 4}HSiC wafer was heated to a temperature of 100 deg. C and an alpha spectrum collected. The performance of the sensor at 100 deg. C was compared to the room temperature performance. Molten salts such as those used in the INL electro-refiner exhibit strong corrosive properties. Any sensor which will be exposed to or submerged in the molten salt must have a ruggedized sensor face capable to withstand the corrosive environment. In the contact design utilized in this paper the Schottky barrier forming metal, nickel, is coated with a thin layer of platinum to serve as a corrosion resistant layer. An additional modification to previous designs was the simplification of the Schottky barrier composition. A Schottky barrier is created when a metal is brought into close physical contact with a semiconductor. To first order, the barrier height of the Schottky barrier is a result of the mismatch between the electron affinity of the semiconductor and the metal work function of the metal. In previous iterations, the high temperature performance of the detectors had been limited by diffusion processes between the various metal layers. In order to reduce the likelihood of such a degradation, the Schottky contact structure was simplified without loss of functionality. By replacing the multiple metal layers with a nickel Schottky forming layer capped with a thin platinum layer, the potential degradation of the Schottky barrier height could be reduced, primarily through the similar Schottky barrier height to nickel formed by platinum with SiC.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
NASA NTRS2011

Observation of Hydrological Processes Using Remote Sensing: Volume 2: The Science of Hydrology - Chapter 2.14

Improving water management can make a significant contribution to achieving most of the Millennium Development Goals established by the UN General Assembly in 2000, especially those related to poverty, hunger, and major diseases. The World Summit on Sustainable Development (WSSD) in 2002 recognized this need. Water and sanitation in particular received great attention from the Summit. The Johannesburg Plan of Implementation recommended to improve water resources management and scientific understanding of the water cycle through joint cooperation and research. For this purpose, it is recommended to promote knowledge sharing, provide capacity building, and facilitate the transfer of technology including remote-sensing (RS) and satellite technologies, especially to developing countries and countries with economies in transition, and to support these countries in their efforts to monitor and assess the quantity and quality of water resources, for example, by establishing and/or further developing national monitoring networks and water resources databases and by developing relevant national indicators. The Johannesburg Plan also adopted integrated water resources management as the overarching concept in addressing and solving water-related issues. As a result of the commitments made in the Johannesburg Plan of Implementation, several global and regional initiatives have emerged. Current international initiatives such as the Global Monitoring for Environment and Security (GMES) program of the European Commission and the European Space Agency (ESA), and the Global Earth Observation System of Systems (GEOSS) 10-Year Implementation Plan, have all identified Earth observation (EO) of the water cycle as the key in helping to solve the world s water problems. The availability of spatial information on water quantity and quality will also enable closure of the water budget at river basin and continental scales to the point where effective water management is essential (e.g., as requested by the European Union s Water Framework Directive (WFD), as well as national policies). Geo-information science and EO are vital in achieving a better understanding of the water cycle and better monitoring, analysis, prediction, and management of the world s water resources. The major components of the water cycle of the Earth system and their possible observations are presented. Such observations are essential to understand the global water cycle and its variability, both spatially and temporally, and can only be achieved consistently by means of EOs. Additionally, such observations are essential to advance our understanding of coupling between the terrestrial, atmospheric, and oceanic branches of the water cycle, and how this coupling may influence climate variability and predictability. Water resources management directly interferes with the natural water cycle in the forms of building dams, reservoirs, water transfer systems, and irrigation systems that divert and redistribute part of the water storages and fluxes on land. The water cycle is mainly driven and coupled to the energy cycle in terms of phase changes of water (changes among liquid, water vapor, and solid phases) and transport of water by winds in addition to gravity and diffusion processes. The water-cycle components can be observed with in situ sensors as well as airborne and satellite sensors in terms of radiative quantities. Processing and conversion of these radiative signals are necessary to retrieve the water-cycle components.

Wilder, Peter↗
DOE OSTI2016

Radiation Effects in Innovative Structural Materials

The extreme radiation environments and demanding structural conditions of next-generation fission and proposed fusion reactors will require high performance materials with very high radiation resistance. Although conventional structural materials such as ferritic/ martensitic steels offer several attractive features, there is value in exploring alternative materials systems that may offer unprecedented radiation stability while also offering good thermomechanical properties. As noted elsewhere, options for designing radiation resistance include (a) the traditional approach of introducing a very high sink strength for recombination of radiation-induced vacancies and interstitials (e.g., Ti-modified stainless steels or 'nano-cluster-strengthened ferritic alloys', (b) utilizing materials with immobile vacancies at the operating temperature (e.g., silicon carbide), and (c) utilizing certain classes of materials that inherently exhibit superior resistance to radiation defect retention and accumulation (e.g., ferritic steels). Three relatively new but promising structural materials systems were selected for investigation, based on their favorable unirradiated mechanical properties and potential for good stability under irradiation: High entropy alloys (HEAs), bulk metallic glass (BMG), and MAX phase ceramics. The high configurational entropy in HEAs might alter point defect (solute and radiation defects) diffusion processes, thus potentially enhancing the recombination of radiation-produced damage. Therefore, HEAs offer the potential of a new class of materials for radiation resistance category (c) mentioned previously. A variety of BMGs such as Zr{sub 52.5}Cu{sub 17.9}Ni{sub 14.6}Al{sub 10}Ti{sub 5} offer good mechanical properties including fracture toughness values that may exceed 100 MPa-m{sup 1/2} and near net shape fabrication potential. The lack of crystallinity in BMGs prohibits the formation of conventional Frenkel pair defects under irradiation and therefore offer the possibility of another new material system for radiation resistance category (c). MAX phase ceramics (e.g., Ti{sub 3}SiC{sub 2}, Ti{sub 3}AlC{sub 2}, Ti{sub 2}AlC) have good mechanical properties and contain a nano-laminate structure that could provide a very high point defect sink strength. Due to their refractory nature, many of the MAX phase ceramics may exhibit negligible vacancy mobility up to high temperatures. Therefore, MAX phase ceramics offer the potential to provide radiation resistance in either categories (a) and (b), depending on the operating temperature. For this study, a novel 27%Fe-27%Mn-28%Ni-18%Cr single phase face centered cubic high entropy alloy was synthesized that exhibited good strength and ductility over a wide temperature range. Zr{sub 52.5}Cu{sub 17.9}Ni{sub 14.6}Al{sub 10}Ti{sub 5} (BAM-11) was selected as a prototypic advanced BMG. Several MAX phase ceramics (e.g., Ti{sub 3}SiC{sub 2}, Ti{sub 3}AlC{sub 2}, Ti{sub 2}AlC) that have good unirradiated thermal and mechanical properties were also investigated. The irradiation damage behaviors of these three novel materials systems have been studied after fission neutron at ∼75 deg. C up to 1 dpa and Ni ion irradiation at 25- 700 deg. C up to 30 dpa (lower temperatures and doses for the BMGs). All three sets of materials generally exhibited good radiation stability within certain temperature regimes. For example, the BMG exhibited only minor (<10%) change in strength that appeared to saturate after a dose of ∼1 dpa. A key shortcoming of current BMGs are that they can not be used at temperatures >>300 deg. C due to glass to crystalline transition at elevated temperature. The MAX phase ceramics irradiated at 400-700 deg. C appeared to be in the 'low temperature' regime where vacancies are immobile and therefore the radiation hardening saturated at relatively low doses. The Ti{sub 3}SiC{sub 2} MAX phase exhibited the best overall radiation stability over a wide temperature range. The HEA exhibited fine scale dislocation loop formation, no observable cavity swelling and reduced amounts of Cr depletion compared to traditional austenitic Fe-Cr-Ni alloys after ion irradiation, which suggests suppressed point defect and solute diffusion behavior. (authors)

36 MATERIALS SCIENCE↗
DOE OSTI2018

Electrochemical Behavior of Sn-9Zn-xTi Lead-Free Solders in Neutral 0.5M NaCl Solution

Electrochemical techniques were employed to study the electrochemical corrosion behavior of Sn-9Zn-xTi (x = 0, 0.05, 0.1, 0.2 wt.%) lead-free solders in neutral 0.5M NaCl solution, aiming to figure out the effect of Ti content on the corrosion properties of Sn-9Zn, providing information for the composition design of Sn-Zn-based lead-free solders from the perspective of corrosion. EIS results reveal that Ti addition was involved in the corrosion product layer and changed electrochemical interface behavior from charge transfer control process to diffusion control process. The trace amount of Ti addition (0.05 wt.%) can refine the microstructure and improve the corrosion resistance of Sn-9Zn solder, evidenced by much lower corrosion current density (i{sub corr}) and much higher total resistance (R{sub t}). Excess Ti addition (over 0.1 wt.%) led to the formation of Ti-containing IMCs, which were confirmed as Sn{sub 3}Ti{sub 2} and Sn{sub 5}Ti{sub 6}, deteriorating the corrosion resistance of Sn-9Zn-xTi solders. The main corrosion products were confirmed as Sn{sub 3}O(OH){sub 2}Cl{sub 2} mixed with small amount of chlorine/oxide Sn compounds.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Expeditious modeling of vapor transport and reactions in polymeric materials

We present a methodology for approximating dynamic adsorption of vapor coupled with diffusion in polymeric materials. In previous publications, the dynamic adsorption was represented by ordinary differential equations (ODEs) and solved in concentration and parameter space. To accelerate the calculation, we have developed a statistical approximation method using computationally cheap surrogate models (e.g., algebraic polynomials) that replace the ODE solutions of adsorption and are coupled with the diffusion equations. Since the polynomial presentation of the adsorption term is obtained in a standard format prior to modeling coupled sorption‐diffusion, the adsorption operator can be expressed as input data in the transport code. Compared to conventional operator‐splitting methods, the polynomial approximation of adsorption offers better computational efficiency. The methodology is demonstrated and validated using a dynamic Langmuir adsorption model that is coupled to diffusion and absorption models and applied to a water vapor sorption‐diffusion process in polydimethylsiloxane polymers. © 2017 American Institute of Chemical Engineers AIChE J , 63: 4079–4089, 2017

Sun, Yunwei↗