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At least 1,513 records · Page 84
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Size, shade, or shape? The contribution of galaxies of different types to the star formation history of the Universe from SDSS-IV MaNGA

ABSTRACT By fitting stellar populations to the fourth generation of the Sloan Digital Sky Survey (SDSS-IV) Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey observations of ∼7000 suitably weighted individual galaxies, we reconstruct the star formation history of the Universe, which we find to be in reasonable agreement with previous studies. Dividing the galaxies by their present-day stellar mass, we demonstrate the downsizing phenomenon, whereby the more massive galaxies hosted the most star formation at earlier times. Further dividing the galaxy sample by colour and morphology, we find that a galaxy’s present-day colour tells us more about its historical contribution to the cosmic star formation history than its current morphology. We show that downsizing effects are greatest among galaxies currently in the blue cloud, but that the level of downsizing in galaxies of different morphologies depends quite sensitively on the morphological classification used, due largely to the difficulty in classifying the smaller low-mass galaxies from their ground-based images. Nevertheless, we find agreement that among galaxies with stellar masses $M_{\star } \gt 6\times 10^{9}\, \mathrm{ M}_{\odot }$, downsizing is most significant in spirals. However, there are complicating factors. For example, for more massive galaxies, we find that colour and morphology are predictors of the past star formation over a longer time-scale than in less massive systems. Presumably this effect is reflecting the longer period of evolution required to alter these larger galaxies’ physical properties, but shows that conclusions based on any single property do not tell the full story.

Peterken, Thomas↗
DOE OSTI2015

Probing star formation in the dense environments of z 1 lensing haloes aligned with dusty star-forming galaxies detected with the South Pole Telescope

We probe star formation in the environments of massive ~1013M⊙ dark matter halos at redshifts of z~1. This star formation is linked to a sub-millimetre clustering signal which we detect in maps of the Planck High Frequency Instrument that are stacked at the positions of a sample of high-redshift (z>2) strongly-lensed dusty star-forming galaxies (DSFGs) selected from the South Pole Telescope (SPT) 2500 deg2 survey. The clustering signal has sub-millimetre colours which are consistent with the mean redshift of the foreground lensing halos (z~1). We report a mean excess of star formation rate (SFR) compared to the field, of (2700±700)M⊙yr-1 from all galaxies contributing to this clustering signal within a radius of 3.5' from the SPT DSFGs. The magnitude of the Planck excess is in broad agreement with predictions of a current model of the cosmic infrared background. The model predicts that 80% of the excess emission measured by Planck originates from galaxies lying in the neighbouring halos of the lensing halo. Using Herschel maps of the same fields, we find a clear excess, relative to the field, of individual sources which contribute to the Planck excess. The mean excess SFR compared to the field is measured to be (370±40)M⊙yr-1 per resolved, clustered source. Our findings suggest that the environments around these massive z~1 lensing halos host intense star formation out to about 2Mpc. The flux enhancement due to clustering should also be considered when measuring flux densities of galaxies in Planck data.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

Suppression of star formation in low-mass galaxies caused by the reionization of their local neighbourhood

Photoheating associated with reionization suppressed star formation in low-mass galaxies. Reionization was inhomogeneous, however, affecting different regions at different times. To establish the causal connection between reionization and suppression, we must take this local variation into account. We analyze the results of CoDa (‘Cosmic Dawn’) I, the first fully coupled radiation-hydrodynamical simulation of reionization and galaxy formation in the Local Universe, in a volume large enough to model reionization globally but with enough resolving power to follow all atomic-cooling galactic halos in that volume. For every halo identified at a given time, we find the redshift at which the surrounding IGM reionized, along with its instantaneous star formation rate (‘SFR’) and baryonic gas-to-dark matter ratio (M gas /M DM ). The average SFR per halo with M < 10 9 M ⊙ was steady in regions not yet reionized, but declined sharply following local reionization. For M > 10 10 M ⊙ , this SFR continued through local reionization, increasing with time, instead. For 10 9 M ⊙ < M < 10 10 M ⊙ , the SFR generally increased modestly through reionization, followed by a modest decline. In general, halo SFRs were higher for regions that reionized earlier. A similar pattern was found for M gas /M DM , which declined sharply following local reionization for M < 10 9 M ⊙ . Local reionization time correlates with local matter overdensity, which determines the local rates of structure formation and ionizing photon consumption. The earliest patches to develop structure and reionize ultimately produced more stars than they needed to finish and maintain their own reionization, exporting their ‘surplus’ starlight to help reionize regions that developed structure later.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

Are galactic star formation and quenching governed by local, global, or environmental phenomena?

ABSTRACT We present an analysis of star formation and quenching in the SDSS-IV MaNGA-DR15, utilizing over 5 million spaxels from ∼3500 local galaxies. We estimate star formation rate surface densities (ΣSFR) via dust corrected H α flux where possible, and via an empirical relationship between specific star formation rate (sSFR) and the strength of the 4000 Å break (D4000) in all other cases. We train a multilayered artificial neural network (ANN) and a random forest (RF) to classify spaxels into ‘star-forming’ and ‘quenched’ categories given various individual (and groups of) parameters. We find that global parameters (pertaining to the galaxy as a whole) perform collectively the best at predicting when spaxels will be quenched, and are substantially superior to local/spatially resolved and environmental parameters. Central velocity dispersion is the best single parameter for predicting quenching in central galaxies. We interpret this observational fact as a probable consequence of the total integrated energy from active galactic neucleus (AGN) feedback being traced by the mass of the black hole, which is well known to correlate strongly with central velocity dispersion. Additionally, we train both an ANN and RF to estimate ΣSFR values directly via regression in star-forming regions. Local/spatially resolved parameters are collectively the most predictive at estimating ΣSFR in these analyses, with stellar mass surface density at the spaxel location (Σ*) being by far the best single parameter. Thus, quenching is fundamentally a global process but star formation is governed locally by processes within each spaxel.

Bluck, Asa F. L.↗
DOE OSTI2017

Suppressed star formation by a merging cluster system

We examine the effects of an impending cluster merger on galaxies in the large scale structure (LSS) RX J0910 at z =1.105. Using multi-wavelength data, including 102 spectral members drawn from the Observations of Redshift Evolution in Large Scale Environments (ORELSE) survey and precise photometric redshifts, we calculate star formation rates and map the specific star formation rate density of the LSS galaxies. These analyses along with an investigation of the color-magnitude properties of LSS galaxies indicate lower levels of star formation activity in the region between the merging clusters relative to the outskirts of the system. We suggest that gravitational tidal forces due to the potential of the merging halos may be the physical mechanism responsible for the observed suppression of star formation in galaxies caught between the merging clusters.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Dynamic Scaling of Colloidal Gel Formation at Intermediate Concentrations

Here, we have examined the formation and dissolution of gels composed of intermediate volume-fraction nanoparticles with temperature-dependent short-range attractions using small-angle x-ray scatter- ing (SAXS), x-ray photon correlation spectroscopy (XPCS), and rheology to obtain nanoscale and macroscale sensitivity to structure and dynamics. Gel formation after temperature quenches to the vicinity of the rheologically-determined gel temperature, T gel , was characterized via the slow-down of dynamics and changes in microstructure observed in the intensity autocorrelation functions and structure factor, respectively, as a function of quench depth (ΔT = T quench - T gel ), wave vector, and formation time (t f ). We find similar patterns in the slow-down of dynamics that maps the wave-vector-dependent dynamics at a particular ΔT and t f to that at other ΔTs and t f s via an effective scaling temperature, Ts. A single Ts applies to a broad range of ΔT and tf but does depend on the particle size. The rate of formation implied by the scaling is a far stronger function of ΔT than that of the attraction strength between colloids. Finally, we interpret this strong temperature de- pendence in terms of changes in cooperative bonding required to form stable, energetically favored, local structures.

42 ENGINEERING↗
DOE OSTI2022

Persistence of negative vacancy and self-interstitial formation energies in atomistic models of amorphous silicon

We use classical potential atomistic modeling to demonstrate that negative vacancy and selfinterstitial formation energies are inherently present in amorphous silicon (a-Si). Our conclusions are based on comprehensive calculations of vacancy and self-interstitial formation energies in nine different models, ranging in size from 1000 to 2744 atoms and formed by quenching liquid Si at rates between 10 10 and 10 12 K/s. We account for a range of possible reference energies corresponding to different choices of reservoirs for atoms inserted into or removed from our models. Moreover, we show that successive addition of either vacancies or self-interstitials does not deplete the number of negative formation energy sites. Instead, it further lowers defect formation energies. Furthermore, these findings lead us to conclude that a-Si is not a structure at or near a local enthalpy minimum nor can it be brought to a local enthalpy minimum through the introduction of constitutional defects.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Extension of the sasCIF format and its applications for data processing and deposition

Recent advances in small-angle scattering (SAS) experimental facilities and data analysis methods have prompted a dramatic increase in the number of users and of projects conducted, causing an upsurge in the number of objects studied, experimental data available and structural models generated. To organize the data and models and make them accessible to the community, the Task Forces on SAS and hybrid methods for the International Union of Crystallography and the Worldwide Protein Data Bank envisage developing a federated approach to SAS data and model archiving. Within the framework of this approach, the existing databases may exchange information and provide independent but synchronized entries to users. At present, ways of exchanging information between the various SAS databases are not established, leading to possible duplication and incompatibility of entries, and limiting the opportunities for data-driven research for SAS users. In this work, a solution is developed to resolve these issues and provide a universal exchange format for the community, based on the use of the widely adopted crystallographic information framework (CIF). The previous version of the sasCIF format, implemented as an extension of the core CIF dictionary, has been available since 2000 to facilitate SAS data exchange between laboratories. The sasCIF format has now been extended to describe comprehensively the necessary experimental information, results and models, including relevant metadata for SAS data analysis and for deposition into a database. Processing tools for these files ( sasCIFtools ) have been developed, and these are available both as standalone open-source programs and integrated into the SAS Biological Data Bank, allowing the export and import of data entries as sasCIF files. Software modules to save the relevant information directly from beamline data-processing pipelines in sasCIF format are also developed. Lastly, this update of sasCIF and the relevant tools are an important step in the standardization of the way SAS data are presented and exchanged, to make the results easily accessible to users and to promote further the application of SAS in the structural biology community.

96 KNOWLEDGE MANAGEMENT AND PRESERVATION↗
DOE OSTI2022

Deep Learning-Assisted Real-Time Forward Modeling of Electromagnetic Logging in Complex Formations

Higher dimensional (i.e., 2-D and 3-D) modeling is indispensable to correctly evaluate the responses of electromagnetic logging tools in complex formation environments. However, limited by the high computational cost of rigorous modeling such as finite difference method and the finite element method, the real-time applications in the well logging industry primarily rely on the 1-D forward solver, which would result in erroneous formation evaluation for complex scenarios. As a result, aiming at realizing fast modeling for electromagnetic logging tools in complex formations, this paper proposes a general framework assisted by deep neural networks (DNNs). The framework consists of three modules: earth model classification, parameter extraction, and surrogate construction. Separate DNNs are trained and tested for different modules. The accuracy and efficiency of the DNN assisted fast modeling are validated by several experiments. Here, this study finds that the fast modeling assisted by DNNs is able to calculate the tool responses and reconstruct the subsurface formations in real-time.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2024

Formation kinetics and thermodynamic stability of the Aurivillius compounds in Bi 4 Ti 3 O 12 –BiFeO 3 system

Abstract The Aurivillius compounds in the Bi 2 O 3 –Fe 2 O 3 –TiO 2 system, combining ferroelectric, semiconducting, and ferromagnetic properties, have attracted particular interest. Formation kinetics and thermodynamic stability are the fundamental knowledge needed for modeling and predicting the temporal microstructure and property evolution during materials processing but have not yet been addressed by quantitative experimental measurement. This article focuses on the Bi n +1 Fe n –3 Ti 3 O 3 n +3 Aurivillius compounds on the Bi 4 Ti 3 O 12 –BiFeO 3 tie‐line to elucidate the mechanisms and thermodynamic controls responsible for phase formation of compounds with various perovskite‐like layers. Five high‐purity Aurivillius compounds Bi 4 Ti 3 O 12 , Bi 5 FeTi 3 O 15 , Bi 6 Fe 2 Ti 3 O 18 , Bi 7 Fe 3 Ti 3 O 21 , and Bi 8 Fe 4 Ti 3 O 24 with integer n = 3–7 values were synthesized and their phase transformation properties and enthalpies of formation were studied by X‐ray diffraction in situ, high temperature differential scanning calorimetry, and high temperature oxide melt solution calorimetry. Thermodynamic stability of the compounds decreases with increasing n , and formation kinetics gradually slow down, demonstrating the inherent difficulty to synthesize pure Aurivillius compounds with n larger than 8. This difficulty was confirmed by an impurity phase coexisting with Bi 9 Fe 5 Ti 3 O 27 .

Gong, Weiping↗
DOE OSTI2018

Study of plasma induced nanostructure formation and surface morphology changes on tungsten and stainless steel at atmospheric pressure

The formation of nanostructures such as “fuzz,” holes, and flakes was observed on tungsten and stainless steel anodes in a 1 atm glow discharge with helium as the feed gas. The structures exhibited morphology similar to the tungsten fuzz growth observed in experiments that simulate wall conditions in fusion reactors, suggesting that similar physics may be present in both scenarios. The anode surface temperature ranged between 1000 and 1300 K with an ion fluence rate of order 10 24 s -1 m -2 . In this work, scanning electron microscope and transmission electron microscope were used to characterize the evolution of nanostructure formation as a function of time. Observed nanostructures were found to vary with the morphology of the discharge plasma attachment. The composition of the structures was found to be predominantly the native metal by using energy dispersive x-ray spectroscopy. This work gives some insight into the formation of nanostructures at atmospheric pressure, which not only has applications for material processing, but also provides potentially another avenue to study fuzz formation processes relevant to fusion plasma-wall interactions.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

Multicomponent new particle formation from sulfuric acid, ammonia, and biogenic vapors

A major fraction of atmospheric aerosol particles, which affect both air quality and climate, form from gaseous precursors in the atmosphere. Highly oxygenated organic molecules (HOMs), formed by oxidation of biogenic volatile organic compounds, are known to participate in particle formation and growth. However, it is not well understood how they interact with atmospheric pollutants, such as nitrogen oxides (NO x ) and sulfur oxides (SO x ) from fossil fuel combustion, as well as ammonia (NH 3 ) from livestock and fertilizers. Here, we show how NO x suppresses particle formation, while HOMs, sulfuric acid, and NH 3 have a synergistic enhancing effect on particle formation. We postulate a novel mechanism, involving HOMs, sulfuric acid, and ammonia, which is able to closely reproduce observations of particle formation and growth in daytime boreal forest and similar environments. The findings elucidate the complex interactions between biogenic and anthropogenic vapors in the atmospheric aerosol system.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2023

LiH formation and its impact on Li batteries revealed by cryogenic electron microscopy

Little is known about how evolved hydrogen affects the cycling of Li batteries. Hypotheses include the formation of LiH in the solid-electrolyte interphase (SEI) and dendritic growth of LiH. Here, we discover that LiH formation in Li batteries likely follows a different pathway: Hydrogen evolved during cycling reacts to nucleate and grow LiH within already deposited Li metal, consuming active Li. We provide the evidence that LiH formed in Li batteries electrically isolates active Li from the current collector that degrades battery capacity. We detect the coexistence of Li metal and LiH also on graphite and silicon anodes, showing that LiH forms in most Li battery anode chemistries. Last, we find that LiH has its own SEI layer that is chemically and structurally distinct from the SEI on Li metal. Our results highlight the formation mechanism and chemical origins of LiH, providing critical insight into how to prevent its formation.

25 ENERGY STORAGE↗
DOE OSTI2020

Astronomical context of Solar System formation from molybdenum isotopes in meteorite inclusions

Calcium-aluminum–rich inclusions (CAIs) in meteorites are the first solids to have formed in the Solar System, defining the epoch of its birth on an absolute time scale. This provides a link between astronomical observations of star formation and cosmochemical studies of Solar System formation. We show that the distinct molybdenum isotopic compositions of CAIs cover almost the entire compositional range of material that formed in the protoplanetary disk. We propose that CAIs formed while the Sun was in transition from the protostellar to pre–main sequence (T Tauri) phase of star formation, placing Solar System formation within an astronomical context. Our results imply that the bulk of the material that formed the Sun and Solar System accreted within the CAI-forming epoch, which lasted less than 200,000 years.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2013

Formation of the structure of gold nanoclusters during crystallization

The structure formation in gold nanoparticles 1.6-5.0 nm in diameter is studied by molecular dynamics simulation using a tight-binding potential. The simulation shows that the initial fcc phase in small Au clusters transforms into other structural modifications as temperature changes. As the cluster size increases, the transition temperature shifts toward the melting temperature of the cluster. The effect of various crystallization conditions on the formation of the internal structure of gold nanoclusters is studied in terms of microcanonical and canonical ensembles. The stability boundaries of various crystalline isomers are analyzed. The obtained dependences are compared with the corresponding data obtained for copper and nickel nanoparticles. The structure formation during crystallization is found to be characterized by a clear effect of the particle size on the stability of a certain isomer modification. Nickel and copper clusters are shown to exhibit common features in the formation of their structural properties, whereas gold clusters demonstrate much more complex behavior.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

The formation of correlated states and optimization of the tunnel effect for low-energy particles under nonmonochromatic and pulsed action on a potential barrier

We consider peculiarities of the formation of a coherent correlated state (CCS) of a low-energy particle under frequency modulation of parameters of a harmonic oscillator that contains this particle by a broadband nonmonochromatic or asymmetric pulsed action. It is shown that in the case of modulation with frequency-normalized intensity, the maximum efficiency of CCS formation corresponds to a narrow-band action, while broadband modulation is optimal for the action with a constant spectral density. As in the case of monochromatic modulation, the maximum correlation coefficient, |r|{sub max}, under the nonmonochromatic action corresponds to parametric resonance at frequency Ω ≈ 2ω{sub 0}. Under a pulsed action, the maximum efficiency of CCS formation and, hence, the maximum probability of the tunnel effect, correspond to pulsed modulation with a short leading edge and a long trailing edge. In particular, under the action of a pulsed magnetic field with an amplitude of 10 kOe and the leading edge duration of 2 × 10{sup –7} s on a gas with deuterium ions, a CCS can be formed with the correlation coefficient |r|{sub max} ≈ 0.9998, for which the tunneling effect probability under the dd interaction at temperature T ≈ 300–500 K increases from D{sub r=0} ≈ 10{sup −80} to D{sub |r|{sub m{sub a{sub x=0.9998}}}}≈0.1. This process can occur in a gas with particle number density n < n{sub cr} ≈ 10{sup 17} cm{sup −3}. The method of CCS formation makes it possible to explain the results of an experiment in which substantial isotope changes were detected when a pulsed electric current and magnetic-field generation occurred.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Peculiarities of Phase Formation in TbBO{sub 3} during Isothermal Annealing

Detailed X-ray studies of changes in the structure of terbium orthoborate TbBO{sub 3} in the course of successive high-temperature isothermal annealing of the initial mixture in the form of an amorphous precursor and in the form of a homogenized mixture of microcrystalline Tb{sub 7}O{sub 12} and B{sub 2}O{sub 3} powders have been carried out. It is shown that the formation of TbBO{sub 3} crystals in both cases occurs through the formation of intermediate two-phase states. Particularly, the triclinic high-temperature ν-TbBO{sub 3} phase is formed already at the first crystallization stages (about 600°C) almost simultaneously with the equilibrium vaterite modification of TbBO{sub 3} (sp. gr. P63/mmc) during low-temperature annealing of an amorphous precursor, which transforms into the vaterite modification at an annealing temperature of 850°C. The phase of monoclinic terbium trioxoborate TbB{sub 3}O{sub 6} is formed at the first stages of phase formation (about 800°C) almost simultaneously with the vaterite phase when the feedstock is annealed in the form of a homogenized mixture of microcrystalline Tb{sub 7}O{sub 12} and B{sub 2}O{sub 3} powders. It also transforms into the vaterite modification at an annealing temperature of 950°, which is preserved up to the highest annealing temperatures in the experiment (1200°C). A hypothetical explanation of the formation of such two-phase states during low-temperature annealing of the feedstock and their disappearance at higher annealing temperatures is proposed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Formation of a Nanophase Wetting Layer and Metal Growth on a Semiconductor

Based on the data on the atomic density of a film and degree of its homogeneity during the formation of the interface between 3d transition metals (Cr, Co, Fe, or Cu) and silicon, a new concept of forming a contact between a reactive metal and a semiconductor has been justified. According to this concept, the low-temperature vapor-phase deposition of a metal onto a semiconductor is accompanied by the formation of a two-dimensional nanophase wetting layer of a metal or its mixture with silicon with a thickness of several monolayers, which significantly affects the interface formation and structure. This concept changes a perspective of forming a contact between a metal and a semiconductor substrate: it is necessary to take into account not only the formation of surface phases and clusters and/or the mixing process, but also the effect of elastic wetting of a substrate by the forming phases.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗