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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 847 records · Page 47
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Causal Mechanism Graph – A new notation for capturing cause-effect knowledge in software dependability

Understanding cause-effect relations between concepts in software dependability engineering is fundamental to various research or industrial activities. Cognitive maps are traditionally used to elicit and represent such knowledge; however they seem incapable of accurately representing complex causal mechanisms in dependability engineering. Here, this paper proposes a new notation called Causal Mechanism Graph (CMG) to elicit and represent the cause-effect domain knowledge embedded in experts’ minds or described in the literature. CMG contains a new set of symbols elicited from domain experts to capture the recurring interaction mechanisms between multiple concepts in software dependability engineering. Furthermore, compared to major existing graphic methods, CMG is particularly robust and suitable for mental knowledge elicitation: it allows one to represent the full range of cause-effect knowledge, accurately or fuzzily as one sees fit depending on the depth of knowledge he/she has. This feature combined with excellent reliability and validity poses CMG as a promising method that has the potential to be used in various areas, such as software dependability requirement elicitation, software dependability assessment and dependability risk control.

42 ENGINEERING↗
DOE OSTI2018

Moving beyond the van Krevelen diagram: A new stoichiometric approach for compound classification in organisms

van Krevelen diagrams (O:C vs H:C ratios of elemental formulas) have been widely used in studies to obtain an estimation of the main compound categories present in environmental samples. However, the limits defining a specific compound category based solely on O:C and H:C ratios of elemental formulas have never been accurately listed or proposed to classify metabolites in biological samples. Furthermore, while O:C vs. H:C ratios of elemental formulas can provide an overview of the compound categories, such classification is inefficient because of the large overlap among different compound categories along both axes. We propose a more accurate compound classification for biological samples analyzed by high-resolution mass spectrometry-based on an assessment of the C:H:O:N:P stoichiometric ratios of over 130,000 elemental formulas of compounds classified in 6 main categories: lipids, peptides, amino-sugars, carbohydrates, nucleotides and phytochemical compounds (oxy-aromatic compounds). Our multidimensional stoichiometric compound classification (MSCC) constraints showed a highly accurate categorization of elemental formulas to the main compound categories in biological samples with over 98% of accuracy representing a substantial improvement over any classification based on the classic van Krevelen diagram. This method represents a significant step forward in environmental research, especially ecological stoichiometry and eco-metabolomics studies, by providing a novel and robust tool to further our understanding the ecosystem structure and function through the chemical characterization of different biological samples.

Compound Classification, Ecological Stoichiometry,↗
DOE OSTI2015

Azobenzene-based organic salts with ionic liquid and liquid crystalline properties

Two sets of new azobenzene-based bromide salts are synthesized, and their thermal photochromic properties are studied. Both sets are based on the imidazolium cation. The first set (1) features a symmetric biscation where two imidazolium head groups (Im) with different alkyl chains (Cn) are connected to a central azobenzene unit (Azo): [Azo(C1-Im-Cn) 2 ]; n = 6, 8, 10, 12, 14. The other one contains an n-alkyl-imidazolium cation (Cn-Im) bearing a terminal azobenzene unit (C1-Azo) substituted with an alkoxy chain (O-Cm) of either two (2) or six (3) carbon atoms: [C1-Azo-O-Cm-Im-Cn]; m = 2, n = 8, 10, 12 and m = 6, n = 8, 10, 12, 14, 16. For both cation classes, the influence of alkyl chains of varying length on the thermal phase behavior was investigated by differential scanning calorimetry (DSC) and polarizing optical microscopy (POM). For five compounds (Azo(-C1-Im-C12) 2 (1d), Azo(-C1-Im-C12) 2 (1e), C1-Azo-O-C2-Im-C10 (2b), C1-Azo-O-C2-Im-C12 (2c), and C1-Azo-O-C6-Im-C16 (3e)), the formation of a liquid crystalline phase was observed. The biscationic salts (1) are all comparatively high melting organic salts (180–240 °C), and only the two representatives with long alkylchains (C12 and C14) exhibit liquid crystallinity. The monocationic salts with an O–C2 bridge (2) melt between 140 and 170 °C depending on the alkyl chain length, but from an alkyl chain of 10 and more carbon atoms on they form a smectic A liquid crystalline phase. The representatives of the third set with a O–C6 bridge qualify as ionic liquids with melting points less than 100 °C. However, only the representative with a hexadecyl chain forms a liquid crystalline phase. Representative single crystals for all sets of cations could be grown that allowed for single crystal structure analysis. Together with small-angle X-ray scattering experiments they allow for a more detailed understanding of the thermal properties. As a result, through irradiation with UV-light (320–366 nm) all compounds undergo trans–cis isomerization, which reverses under visible light (440 nm).

36 MATERIALS SCIENCE↗
DOE OSTI2026

Microwave-Assisted Plastic Upcycling: Dynamic Data Reconciliation, Parameter Estimation, and Kinetic Modeling

Microwave (MW)-assisted catalytic pyrolysis offers a promising pathway for efficient plastic upcycling. This work develops an integrated modeling framework combining dynamic data reconciliation, a temperature-dependent rate model, and a yield model to represent the time-varying production rate of components in MW-assisted LDPE pyrolysis conducted in a batch reactor. An Arrhenius-type rate model with a temperature-dependent reaction order is developed. A biexponential correlation is proposed for the yield of gaseous products that enables to capture the evolving product formation behavior during conversion. In the yield correlation, one term is used to represent the initial increase in yield, reflecting the rapid formation of intermediate or primary products at the early stages of the reaction when a larger fraction of the reactant remains available. As conversion progresses, the influence of this term gradually diminishes. The other term accounts for the subsequent decrease in the predicted yield, representing secondary reactions such as further cracking or coke formation that reduce the concentration of certain products at higher conversion. The model is found to accurately represent reconciled experimental flow rate profiles from an in-house MW-assisted catalytic batch reactor for major products, including ethylene, ethane, 1-butene, and benzene, across 250−350 °C. Ethylene remains the dominant product but decreases from about 41.95% at 250 °C to 30.14% at 350 °C, while heavier products increase significantly, with 1-butene rising to nearly 8.37% and benzene reaching 2.17% at intermediate temperatures. The model shows that the ethylene production rate can be maximized at around 270 °C. The models developed in this work can be utilized for process optimization, reactor design and scale-up of microwave-assisted plastic conversion technologies, and economic analysis.

Damahe, Harish [West Virginia Univ., Morgantown, W↗
DOE OSTI2023

Selecting Suitable Near-Native Lignins for Research

There are several methods to isolate near-native lignins, including milled-wood lignin, enzymatic lignin, cellulolytic enzyme lignin, and enzymatic mild-acidolysis lignin. Which one is the most representative of the native lignin? Herein, near-native lignins were isolated from different plant groups and structurally analyzed to determine how well these lignins represented their native lignin counterparts. Analytical methods were applied to understand the molecular weight, monomer composition, and distribution of interunit linkages in the structure of the lignins. The results indicated that either enzymatic lignin or cellulolytic enzyme lignin may be used to represent native lignin in softwoods and hardwoods. None of the lignins, however, appeared to represent native lignins in grasses (monocot plants) because of substantial syringyl/guaiacyl differences. Furthermore, complicating the understanding of grass lignin structure, large amounts of hydroxycinnamates acylate their polysaccharides and, when released, are often conflated with actual lignin monomers.

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

Navigating Large Chemical Spaces Using Graph Theory and Integer Programming

Navigating and analyzing large chemical spaces are necessary to accelerate the design and discovery of new molecules and chemical processes. In this work, we introduce a computational framework that integrates graph theory and integer programming to enable the efficient navigation of large chemical spaces. Our framework represents the chemical space as a graph, wherein nodes represent molecules and edges represent the degree of similarity or connectivity based on domain-specific information. Using the graph representation, we identify representative molecules by computing the so-called minimum dominating set (MDS), which in our context is the minimum set of molecules that is connected to all other molecules. We present a suite of solution strategies for the MDS problem including heuristic and rigorous integer programming (IP) approaches. We show that these approaches allow us to capture physicochemical properties and domain-specific logic and constraints, facilitating the identification of molecules with the target properties. We demonstrate the effectiveness of the proposed approach by navigating the chemical space of per- and polyfluoroalkyl substances (PFAS); this comprises approximately 15,000 molecular structures. We compare our framework against traditional dimensionality reduction and clustering methods such as t-SNE and K-means clustering.

Chemical structure↗
DOE OSTI2017

Linking Silica Support Morphology to the Dynamics of Aminopolymers in Composites

A combined computational and experimental approach is used to elucidate the effect of silica support morphology on polymer dynamics and CO 2 adsorption capacities in aminopolymer/silica composites. Furthermore, simulations are based on coarse-grained molecular dynamics simulations of aminopolymer composites where a branched aminopolymer, representing poly(ethylenimine) (PEI), is impregnated into different silica mesoporous supports. The morphology of the mesoporous supports varies from hexagonally packed cylindrical pores representing SBA-15, double gyroids representing KIT-6 and MCM-48, and cagelike structures representing SBA-16. In parallel, composites of PEI and the silica supports SBA-15, KIT-6, MCM-48, and SBA-16 are synthesized and characterized, including measuring their CO 2 uptake. Simulations predict that a 3D pore morphology, such as those of KIT-6, MCM-48, and SBA-16, will have faster segmental mobility and have lower probability of primary amine and surface silanol associations, which should translate to higher CO 2 uptake in comparison to a 2D pore morphology such as that of SBA-15. We found that KIT-6 has higher CO 2 uptake than SBA-15 at equivalent PEI loading, even though both supports have similar surface area and pore volume. But, this is not the case for the MCM-48 support, which has smaller pores, and SBA-16, whose pore structure rapidly degrades after PEI impregnation.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Improving Land Surface Temperature Simulation in CoLM Over the Tibetan Plateau through Fractional Vegetation Cover Derived from a Remotely Sensed Clumping Index and Model-Simulated Leaf Area Index

Parameterizations of fractional vegetation cover (FVC) in land surface models have important effects on simulations of surface energy budget, especially in arid and semiarid regions. This study uses a FVC scheme in which FVC is derived from leaf area index and a remotely sensed clumping index. The performance of the new scheme (SMFVC) is evaluated against Moderate Resolution Imaging Spectroradiometer (MODIS) land surface temperature (LST) and in situ soil temperature observations, together with two other FVC schemes, a general FVC scheme (CTL) based on land cover map and a climatology-based FVC scheme (RSFVC) that uses long-term remotely sensed Normalized Difference Vegetation Index of MODIS. The three FVC schemes were implemented in the Common Land Model (CoLM) and applied in the Tibetan Plateau using the same forcing data and default parameters. Our results demonstrate that FVC schemes have significant influence on the CoLM performance: (1) the RSFVC and SMFVC schemes significantly reduce the LST biases found in CTL, particularly in grassland and during summer; (2) soil temperature evaluation by in situ observations from three networks on the Tibetan Plateau corroborates the LST results; and (3) the improvements are mainly related to representing temporal (seasonal) variability and subgrid heterogeneity of FVC, which improves surface albedo and surface energy balance. In other words, by including more vegetation characteristics, such as using a clumping index, land surface models may better simulate surface vegetation condition and further better represent the land surface energy budget over the Tibetan Plateau.

Li, Chengwei↗
DOE OSTI2021

Effects of organized convection parameterization on the MJO and precipitation in E3SMv1. Part I: Mesoscale heating

Mesoscale organization of convection is typically not represented in global circulation models, and hence its influence on the global circulation is not accounted for. The heating component of a parameterization that represents the dynamical and physical effects of circulations associated with organized convection, referred to as the multiscale coherent structure parameterization (MCSP), is implemented in the Energy Exascale Earth System Model version 1 (E3SMv1). Numerical simulations are conducted to assess its impact on the simulated climate. Besides E3SMv1 simulations, we performed high-resolution (1 km) simulations using the Weather Research and Forecasting (WRF) Model to determine the temperature tendencies induced by mesoscale convective systems embedded in deep convection. We tuned the free parameters of the MCSP based on the WRF simulations. MCSP heating enhances Kevin wave spectra in E3SMv1, improves the representation of the Madden-Julian Oscillation, and impacts on mean precipitation that vary with locations and seasons, including a reduction of biases over the tropical Pacific.

Climate Modeling↗
DOE OSTI2016

Biofilm plasmids with a rhamnose operon are widely distributed determinants of the ‘swim-or-stick’ lifestyle in roseobacters

Alphaproteobacteria of the metabolically versatile Roseobacter group (Rhodobacteraceae) are abundant in marine ecosystems and represent dominant primary colonizers of submerged surfaces. Motility and attachment are the prerequisite for the characteristic ‘swim-or-stick’ lifestyle of many representatives such as Phaeobacter inhibens DSM 17395. It has recently been shown that plasmid curing of its 65-kb RepA-I-type replicon with >20 genes for exopolysaccharide biosynthesis including a rhamnose operon results in nearly complete loss of motility and biofilm formation. The current study is based on the assumption that homologous biofilm plasmids are widely distributed. We analyzed 33 roseobacters that represent the phylogenetic diversity of this lineage and documented attachment as well as swimming motility for 60% of the strains. All strong biofilm formers were also motile, which is in agreement with the proposed mechanism of surface attachment. We established transposon mutants for the four genes of the rhamnose operon from P. inhibens and proved its crucial role in biofilm formation. In the Roseobacter group, two-thirds of the predicted biofilm plasmids represent the RepA-I type and their physiological role was experimentally validated via plasmid curing for four additional strains. Horizontal transfer of these replicons was documented by a comparison of the RepA-I phylogeny with the species tree. A gene content analysis of 35 RepA-I plasmids revealed a core set of genes, including the rhamnose operon and a specific ABC transporter for polysaccharide export. Taken together, our data show that RepA-I-type biofilm plasmids are essential for the sessile mode of life in the majority of cultivated roseobacters.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2022

Natural switches in behaviour rapidly modulate hippocampal coding

Throughout their daily lives, animals and humans often switch between different behaviours. However, neuroscience research typically studies the brain while the animal is performing one behavioural task at a time, and little is known about how brain circuits represent switches between different behaviours. Here we tested this question using an ethological setting: two bats flew together in a long 135 m tunnel, and switched between navigation when flying alone (solo) and collision avoidance as they flew past each other (cross-over). Bats increased their echolocation click rate before each cross-over, indicating attention to the other bat. Hippocampal CA1 neurons represented the bat’s own position when flying alone (place coding). Notably, during cross-overs, neurons switched rapidly to jointly represent the interbat distance by self-position. This neuronal switch was very fast—as fast as 100 ms—which could be revealed owing to the very rapid natural behavioural switch. The neuronal switch correlated with the attention signal, as indexed by echolocation. Interestingly, the different place fields of the same neuron often exhibited very different tuning to interbat distance, creating a complex non-separable coding of position by distance. Theoretical analysis showed that this complex representation yields more efficient coding. Overall, our results suggest that during dynamic natural behaviour, hippocampal neurons can rapidly switch their core computation to represent the relevant behavioural variables, supporting behavioural flexibility.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2013

Cooling rate and size effects on the medium-range structure of multicomponent oxide glasses simulated by molecular dynamics

A set of molecular dynamics simulations were performed to investigate the effect of cooling rate and system size on the medium-range structure of melt-derived multicomponent silicate glasses, represented by the quaternary 45S5 Bioglass composition. Given the significant impact of the glass degradation on applications of these materials in biomedicine and nuclear waste disposal, bulk structural features which directly affect the glass dissolution process are of particular interest. Connectivity of the silicate matrix, ion clustering and nanosegregation, distribution of ring and chain structural patterns represent critical features in this context, which can be directly extracted from the models. A key issue is represented by the effect of the computational approach on the corresponding glass models, especially in light of recent indications questioning the suitability of conventional MD approaches (that is, involving melt-and-quench of systems containing ∼10{sup 3} atoms at cooling rates of 5-10 K/ps) when applied to model these glasses. The analysis presented here compares MD models obtained with conventional and nonconventional cooling rates and system sizes, highlighting the trend and range of convergence of specific structural features in the medium range. The present results show that time-consuming computational approaches involving much lower cooling rates and/or significantly larger system sizes are in most cases not necessary in order to obtain a reliable description of the medium-range structure of multicomponent glasses. We identify the convergence range for specific properties and use them to discuss models of several glass compositions for which a possible influence of cooling-rate or size effects had been previously hypothesized. The trends highlighted here represent an important reference to obtain reliable models of multicomponent glasses and extract converged medium-range structural features which affect the glass degradation and thus their application in different fields. In addition, as a first application of the present findings, the fully converged structure of the 45S5 glass was further analyzed to shed new light on several dissolution-related features whose interpretation has been rather controversial in the past.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Study of movement of the western and central belts of Peninsular Malaysia using GPS data analysis

Since the large earthquakes in Sumatera and Nias, there were some tremors incidents at Bukit Tinggi. Therefore, a study on the earth’s crust movement and the effects of the earthquake in Indonesia on the tectonic blocks of Peninsular Malaysia have been carried out using GPS data analysis. GPS data from five MyRTKnet stations within Peninsular Malaysia have been analyzed to monitor the movement of two major tectonic blocks of Peninsular Malaysia which are the western belt represented by the Behrang (BEHR) and UPM Serdang (UPMS) stations and the central belt represented by Bentong (BENT), Jerantut (JRNT) and Temerloh (TLOH) stations. GPS data recorded from 2005 to 2010 were analysed based on horizontal and vertical displacements of the respective stations by using Trimble Business Centre (TBC) software. Based on the results of accumulated displacements of recorded GPS data from January 2006 to December 2013, it shows that the western belt which represented by UPMS has shifted 0.096m towards northwest with changes of ellipsoidal height of +0.030m while the central belt which represented by TLOH has shifted 0.080m towards northwest with changes of ellipsoidal height of −0.015m. Meanwhile, BENT station which is located on the Bentong-Raub suture zone turns to its original position as well as JRNT station. However, BEHR station which are located in western belt do not show any movements. All of these movements may be due to the influence of reactive faults in the stations area stimulated by several large earthquakes that occurred in 2005 to 2010. Study on using the GPS data analysis and combine with integrated geophysical methods are necessary to understand in detail about the tectonic evolution of Peninsular Malaysia.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

CCSD(T) calculations of stabilities and properties of confined systems

We analyze energies, electron affinities and polarizabilities of small anions exposed to an external confinement. The second electron in free O{sup 2−} and S{sup 2−} anions is unbound. We investigate the stabilizing effect of the spherical harmonic-oscillator confining potential ω. on these anions employing the Hartree-Fock stability analysis as introduced by Čížek and Paldus. With increasing strength of the external harmonic-oscillator confinement potential ω the broken symmetry (BS) solutions are systematically eliminated. For ω larger than 0.1 all BS solutions for O{sup 2−} disappear. For ω larger than 0.13 the CCSD(T) energy of O{sup 2−} becomes more negative than the energy of the singly charged O{sup −} anion. We relate the harmonic-oscillator confining potential to a crystalline environment in which the O{sup 2−} and S{sup 2−} anions are stable. We also present a model allowing calculations of the in-crystal polarizabilities of anions. The model is based on CCSD(T) calculations of static polarizabilities of selected anions exposed to the spherical harmonic-oscillator confining potential ω This artificial confinement potential ω is then related to the ionic radii of the cation in representative crystal lattices. We investigate the polarizability of O{sup 2−} and S{sup 2−} anions in MgO, MgS, CaO, CaS, SrO, SrS, BaO and BaS crystals. We compare our results with alternative models for in-crystal polarizabilities. External confinement also stabilizes the uracil anion U{sup −}, as is shown by calculations with a stepwise micro-hydration of U{sup −}. Upon hydration is the CCSD(T) adiabatic electron affinity (AEA) of uracil enhanced by about 250 up to 570 meV in comparison with AEA of the isolated molecule, depending on the geometry of the hydrated uracil anion complex. We tried to find an analogy of the stabilization effect of the external confinement on the otherwise unstable anions. In uracil and its anion is the external confinement represented by the polarized continuum solvation model with dielectric constant as a variational parameter. The physical behavior of ions exposed to an artificial external, spherical harmonic-oscillator confining potential ω, the environment represented by a crystal structure and the confinement represented by the solvent, all have considerable stabilizing effect on the otherwise unstable free anion.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Highly efficient nonprecious metal catalyst prepared with metal–organic framework in a continuous carbon nanofibrous network

Fuel cell vehicles, the only all-electric technology with a demonstrated >300 miles per fill travel range, use Pt as the electrode catalyst. The high price of Pt creates a major cost barrier for large-scale implementation of polymer electrolyte membrane fuel cells. Nonprecious metal catalysts (NPMCs) represent attractive low-cost alternatives. However, a significantly lower turnover frequency at the individual catalytic site renders the traditional carbon-supported NPMCs inadequate in reaching the desired performance afforded by Pt. Unconventional catalyst design aiming at maximizing the active site density at much improved mass and charge transports is essential for the next-generation NPMC. We report here a method of preparing highly efficient, nanofibrous NPMC for cathodic oxygen reduction reaction by electrospinning a polymer solution containing ferrous organometallics and zeolitic imidazolate framework followed by thermal activation. The catalyst offers a carbon nanonetwork architecture made of microporous nanofibers decorated by uniformly distributed high-density active sites. In a single-cell test, the membrane electrode containing such a catalyst delivered unprecedented volumetric activities of 3.3 A∙cm -3 at 0.9 V or 450 A∙cm -3 extrapolated at 0.8 V, representing the highest reported value in the literature. Improved fuel cell durability was also observed.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2015

Latitudinal and energy dependence of energetic neutral atom spectral indices measured by the Interstellar Boundary Explorer

We investigate the latitudinal and energy dependence of the globally distributed 0.5–6 keV energetic neutral atom (ENA) spectra measured by the Interstellar Boundary Explorer (IBEX) during the first 3 yrs of the mission. Our results are: (1) the ENA spectral indices at the two lowest energies (0.89 and 1.47 keV) exhibit no clear trend with ecliptic latitude θ, while those at ∼2.29 and ∼3.41 keV exhibit a clear latitudinal pattern; flatter spectra occur above 60° latitude and steeper spectra occur ±30° of the equator. (2) The latitudinal dependence of the spectral indices at different energies can be represented by the cosine function γ=a{sub 0}+a{sub 1}cos(a{sub 2}θ) with unique offsets, amplitudes, and phase angles; the higher energy ENA indices transition to successively larger amplitudes within ±45° of the equator. Our results confirm the previously reported latitudinal organization of the ENA spectra and their remarkable similarity to that of the solar wind (SW) speed observed by Ulysses in the inner heliosphere. While earlier studies showed that the ∼0.5–6 keV globally distributed ENA spectral indices could be represented as single power laws over much of the sky, our new results indicate that this is an over-simplification because the spectral indices have an energy and latitude dependence. This dependence is an important factor that must be taken into consideration by models and simulations that seek to map the IBEX ENA observations back to the latitudinal profile of the SW speed structure observed in the inner heliosphere.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

STABILITY OF THE OUTER PLANETS IN MULTIRESONANT CONFIGURATIONS WITH A SELF-GRAVITATING PLANETESIMAL DISK

We study the effect of a massive planetesimal disk on the dynamical stability of the outer planets in a system representing the early solar system assuming, as has been suggested recently, that these planets were initially locked in a compact and multiresonant configuration as a result of gas-driven migration in a protoplanetary disk. The planetesimal disk is represented by an ensemble of 2000 lunar mass bodies for which the gravitational interaction is calculated self-consistently using the Mercury6.5 code. Several initial multiresonant configurations and planetesimal disk models are considered. Under such conditions a strong dynamical instability, manifested as a rapid giant planet migration and planetesimal disk dispersal, develops on a timescale of less than 40 Myr in most cases. Dynamical disk heating due to the gravitational interactions among planetesimals leads to more frequent interactions between the planetesimals and the ice giants, in comparison to models in which planetesimal–planetesimal interactions are neglected. The number of particles used to represent the planetesimal disk has implications for our results, and although our studies represent the first self-consistent calculations of unstable planetesimal-driven migration, our results point toward the need for using more realistic treatments of the planetesimal disk. Finally, in the framework of our model, we discuss the possible implications of our results on the early evolution of the solar system.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

FermI large area telescope third source catalog

We present the third Fermi Large Area Telescope (LAT) source catalog (3FGL) of sources in the 100 MeV–300 GeV range. Based on the first 4 yr of science data from the Fermi Gamma-ray Space Telescope mission, it is the deepest yet in this energy range. Relative to the Second Fermi LAT catalog, the 3FGL catalog incorporates twice as much data, as well as a number of analysis improvements, including improved calibrations at the event reconstruction level, an updated model for Galactic diffuse γ-ray emission, a refined procedure for source detection, and improved methods for associating LAT sources with potential counterparts at other wavelengths. The 3FGL catalog includes 3033 sources above 4σ significance, with source location regions, spectral properties, and monthly light curves for each. Of these, 78 are flagged as potentially being due to imperfections in the model for Galactic diffuse emission. Twenty-five sources are modeled explicitly as spatially extended, and overall 238 sources are considered as identified based on angular extent or correlated variability (periodic or otherwise) observed at other wavelengths. For 1010 sources we have not found plausible counterparts at other wavelengths. More than 1100 of the identified or associated sources are active galaxies of the blazar class; several other classes of non-blazar active galaxies are also represented in the 3FGL. Pulsars represent the largest Galactic source class. From source counts of Galactic sources we estimate that the contribution of unresolved sources to the Galactic diffuse emission is ∼3% at 1 GeV.

79 ASTRONOMY AND ASTROPHYSICS↗