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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 685 records · Page 38
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Star formation properties in barred galaxies. III. Statistical study of bar-driven secular evolution using a sample of nearby barred spirals

Stellar bars are important internal drivers of secular evolution in disk galaxies. Using a sample of nearby spiral galaxies with weak and strong bars, we explore the relationships between the star formation feature and stellar bars in galaxies. We find that galaxies with weak bars tend coincide with low concentrical star formation activity, while those with strong bars show a large scatter in the distribution of star formation activity. We find enhanced star formation activity in bulges toward stronger bars, although not predominantly, consistent with previous studies. Our results suggest that different stages of the secular process and many other factors may contribute to the complexity of the secular evolution. In addition, barred galaxies with intense star formation in bars tend to have active star formation in their bulges and disks, and bulges have higher star formation densities than bars and disks, indicating the evolutionary effects of bars. We then derived a possible criterion to quantify the different stages of the bar-driven physical process, while future work is needed because of the uncertainties.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

LoCuSS: THE STEADY DECLINE AND SLOW QUENCHING OF STAR FORMATION IN CLUSTER GALAXIES OVER THE LAST FOUR BILLION YEARS

We present an analysis of the levels and evolution of star formation activity in a representative sample of 30 massive galaxy clusters at 0.15 < z < 0.30 from the Local Cluster Substructure Survey, combining wide-field Spitzer/MIPS 24 μm data with extensive spectroscopy of cluster members. The specific SFRs of massive (M > or approx. 10{sup 10} M{sub ☉}) star-forming cluster galaxies within r{sub 200} are found to be systematically ∼28% lower than their counterparts in the field at fixed stellar mass and redshift, a difference significant at the 8.7σ level. This is the unambiguous signature of star formation in most (and possibly all) massive star-forming galaxies being slowly quenched upon accretion into massive clusters, their star formation rates (SFRs) declining exponentially on quenching timescales in the range 0.7-2.0 Gyr. We measure the mid-infrared Butcher-Oemler effect over the redshift range 0.0-0.4, finding rapid evolution in the fraction (f{sub SF}) of massive (M{sub K} < – 23.1) cluster galaxies within r{sub 200} with SFRs > 3 M{sub ☉} yr{sup –1}, of the form f{sub SF}∝(1 + z){sup 7.6±1.1}. We dissect the origins of the Butcher-Oemler effect, revealing it to be due to the combination of a ∼3 × decline in the mean specific SFRs of star-forming cluster galaxies since z ∼ 0.3 with a ∼1.5 × decrease in number density. Two-thirds of this reduction in the specific SFRs of star-forming cluster galaxies is due to the steady cosmic decline in the specific SFRs among those field galaxies accreted into the clusters. The remaining one-third reflects an accelerated decline in the star formation activity of galaxies within clusters. The slow quenching of star formation in cluster galaxies is consistent with a gradual shut down of star formation in infalling spiral galaxies as they interact with the intracluster medium via ram-pressure stripping or starvation mechanisms. The observed sharp decline in star formation activity among cluster galaxies since z ∼ 0.4 likely reflects the increased susceptibility of low-redshift spiral galaxies to gas removal mechanisms as their gas surface densities decrease with time. We find no evidence for the build-up of cluster S0 bulges via major nuclear starburst episodes.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

The era of star formation in galaxy clusters

We analyze the star formation properties of 16 infrared-selected, spectroscopically confirmed galaxy clusters at 1 < z < 1.5 from the Spitzer/IRAC Shallow Cluster Survey (ISCS). We present new spectroscopic confirmation for six of these high-redshift clusters, five of which are at z > 1.35. Using infrared luminosities measured with deep Spitzer/Multiband Imaging Photometer for Spitzer observations at 24 μm, along with robust optical + IRAC photometric redshifts and spectral-energy-distribution-fitted stellar masses, we present the dust-obscured star-forming fractions, star formation rates, and specific star formation rates in these clusters as functions of redshift and projected clustercentric radius. We find that z ∼ 1.4 represents a transition redshift for the ISCS sample, with clear evidence of an unquenched era of cluster star formation at earlier times. Beyond this redshift, the fraction of star-forming cluster members increases monotonically toward the cluster centers. Indeed, the specific star formation rate in the cores of these distant clusters is consistent with field values at similar redshifts, indicating that at z > 1.4 environment-dependent quenching had not yet been established in ISCS clusters. By combining these observations with complementary studies showing a rapid increase in the active galactic nucleus (AGN) fraction, a stochastic star formation history, and a major merging episode at the same epoch in this cluster sample, we suggest that the starburst activity is likely merger-driven and that the subsequent quenching is due to feedback from merger-fueled AGNs. The totality of the evidence suggests we are witnessing the final quenching period that brings an end to the era of star formation in galaxy clusters and initiates the era of passive evolution.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

The effects of flow-inhomogeneities on molecular cloud formation: Local versus global collapse

Observational evidence from local star-forming regions mandates that star formation occurs shortly after, or even during, molecular cloud formation. Models of molecular cloud formation in large-scale converging flows have identified the physical mechanisms driving the necessary rapid fragmentation. They also point to global gravitational collapse driving supersonic turbulence in molecular clouds. Previous cloud formation models have focused on turbulence generation, gravitational collapse, magnetic fields, and feedback. Here, we explore the effect of structure in the flow on the resulting clouds and the ensuing gravitational collapse. We compare two extreme cases, one with a collision between two smooth streams, and one with streams containing small clumps. We find that structured converging flows lead to a delay of local gravitational collapse ({sup c}ore formation{sup )}. Hence, the cloud has more time to accumulate mass, eventually leading to a strong global collapse, and thus to a high core formation rate. Uniform converging flows fragment hydrodynamically early on, leading to the rapid onset of local gravitational collapse and an overall low core formation rate. This is also mirrored in the core mass distribution: the uniform initial conditions lead to more low-mass cores than the clumpy initial conditions. Kinetic (E{sub k} ) and gravitational energy (E{sub g} ) budgets suggest that collapse is only prevented for E{sub k} >> E{sub g} , which occurs for large scales in the smooth flow, and for small scales for the clumpy flow. Whenever E{sub k} ≈ E{sub g} , we observe gravitational collapse on those scales. Signatures of chemical abundance variations evolve differently for the gas phase and for the stellar population. For smooth flows, the forming cloud is well mixed, while its stellar population retains more information about the initial metallicities. For clumpy flows, the gas phase is less well mixed, while the stellar population has lost most of the information about its origin.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Resolved star formation on sub-galactic scales in a merger at z = 1.7

We present a detailed analysis of Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) G141 grism spectroscopy for seven star-forming regions of the highly magnified lensed starburst galaxy RCSGA 032727-132609 at z = 1.704. We measure the spatial variations of the extinction in RCS0327 through the observed Hγ/Hβ emission line ratios, finding a constant average extinction of E(B – V){sub gas} = 0.40 ± 0.07. We infer that the star formation is enhanced as a result of an ongoing interaction, with measured star formation rates derived from demagnified, extinction-corrected Hβ line fluxes for the individual star-forming clumps falling >1-2 dex above the star formation sequence. When combining the HST/WFC3 [O III] λ5007/Hβ emission line ratio measurements with [N II]/Hα line ratios from Wuyts et al., we find that the majority of the individual star-forming regions fall along the local 'normal' abundance sequence. With the first detections of the He I λ5876 and He II λ4686 recombination lines in a distant galaxy, we probe the massive-star content of the star-forming regions in RCS0327. The majority of the star-forming regions have a He I λ5876 to Hβ ratio consistent with the saturated maximum value, which is only possible if they still contain hot O-stars. Two regions have lower ratios, implying that their last burst of new star formation ended ∼5 Myr ago. Together, the He I λ5876 and He II λ4686 to Hβ line ratios provide indirect evidence for the order in which star formation is stopping in individual star-forming knots of this high-redshift merger. We place the spatial variations of the extinction, star formation rate and ionization conditions in the context of the star formation history of RCS0327.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Kiloparsec-scale simulations of star formation in disk galaxies. III. Structure and dynamics of filaments and clumps in giant molecular clouds

We present hydrodynamic simulations of self-gravitating dense gas in a galactic disk, exploring scales ranging from 1 kpc down to ∼0.1 pc. Our primary goal is to understand how dense filaments form in giant molecular clouds (GMCs). These structures, often observed as infrared dark clouds (IRDCs) in the Galactic plane, are thought to be the precursors to massive stars and star clusters, so their formation may be the rate-limiting step controlling global star formation rates in galactic systems as described by the Kennicutt–Schmidt relation. Our study follows on from Van Loo et al., which carried out simulations to 0.5 pc resolution and examined global aspects of the formation of dense gas clumps and the resulting star formation rate. Here, using our higher resolution, we examine the detailed structural, kinematic, and dynamical properties of dense filaments and clumps, including mass surface density (Σ) probability distribution functions, filament mass per unit length and its dispersion, lateral Σ profiles, filament fragmentation, filament velocity gradients and infall, and degree of filament and clump virialization. Where possible, these properties are compared to observations of IRDCs. By many metrics, especially too large mass fractions of high Σ>1 g cm{sup −2} material, too high mass per unit length dispersion due to dense clump formation, too high velocity gradients, and too high velocity dispersion for a given mass per unit length, the simulated filaments differ from observed IRDCs. We thus conclude that IRDCs do not form from global fast collapse of GMCs. Rather, we expect that IRDC formation and collapse are slowed significantly by the influence of dynamically important magnetic fields, which may thus play a crucial role in regulating galactic star formation rates.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Intermittent self-sustaining star formation in massive, low-redshift galaxies exhibiting a peak metallicity plateau

The decline of star formation in massive low-redshift galaxies, often referred to as “quenching,” has been attributed to a variety of factors. Some proposals suggest that erupting active galactic nuclei may strip galaxies of their interstellar medium (ISM), and thus the ability to form stars. Here, we note that, whereas star formation is universal in small, low-redshift galaxies, the fractional duty cycles Φ of star formation steadily decline in galaxies of increasing mass, although star formation may not cease entirely. We show that when the infall of gas from extragalactic space ceases, galaxies of high stellar mass M{sub *} appear to sustain star formation with gas liberated in mass loss from evolved low- and intermediate-mass stars admixed with occasional SN II ejecta. This model quantitatively accounts for the universal limiting metallicity plateau at a ratio of oxygen to hydrogen atoms, Z{sub O}=n{sub O}/n{sub H}∼1.3×10{sup −3}, characterizing high-mass, intermittently star-forming galaxies. We show that when duty cycles Φ are specifically taken into account, the star formation rates of galaxies on this plateau correspond to mass loss rates from evolving stars of the order of M-dot ∼10{sup −11} M{sub ∗} yr{sup −1}, in rough agreement with observed estimates. Far-infrared continuum and fine-structure line observations, as well as molecular data, may soon be able to resolve whether or not low levels of sporadic star formation can be sustained indefinitely in massive galaxies.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

THE MILKY WAY AS A HIGH-REDSHIFT GALAXY: THE IMPORTANCE OF THICK DISK FORMATION IN GALAXIES

We compare the star formation history and dynamics of the Milky Way (MW) with the properties of distant disk galaxies. During the first ∼4 Gyr of its evolution, the MW formed stars with a high star formation intensity (SFI), Σ{sub SFR} ≈ 0.6 M {sub ☉} yr{sup –1} kpc{sup –2} and as a result, generated outflows and high turbulence in its interstellar medium (ISM). This intense phase of star formation corresponds to the formation of the thick disk. The formation of the thick disk is a crucial phase that enables the MW to have formed approximately half of its total stellar mass by z ∼ 1 which is similar to ''MW progenitor galaxies'' selected by abundance matching. This agreement suggests that the formation of the thick disk may be a generic evolutionary phase in disk galaxies. Using a simple energy injection-kinetic energy relationship between the one-dimensional velocity dispersion and SFI, we can reproduce the average perpendicular dispersion in stellar velocities of the MW with age. This relationship, its inferred evolution, and required efficiency are consistent with observations of galaxies from z ≈ 0-3. The high turbulence generated by intense star formation naturally resulted in a thick disk, a chemically well-mixed ISM, and is the mechanism that links the evolution of MW to the observed characteristics of distant disk galaxies.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

An Adaptable Seismic Data Format

We present ASDF, the Adaptable Seismic Data Format, a modern and practical data format for all branches of seismology and beyond. The growing volume of freely available data coupled with ever expanding computational power opens avenues to tackle larger and more complex problems. Current bottlenecks include inefficient resource usage and insufficient data organization. Properly scaling a problem requires the resolution of both these challenges, and existing data formats are no longer up to the task. ASDF stores any number of synthetic, processed or unaltered waveforms in a single file. A key improvement compared to existing formats is the inclusion of comprehensive meta information, such as event or station information, in the same file. Additionally, it is also usable for any non-waveform data, for example, cross-correlations, adjoint sources or receiver functions. Last but not least, full provenance information can be stored alongside each item of data, thereby enhancing reproducibility and accountability. Any data set in our proposed format is self-describing and can be readily exchanged with others, facilitating collaboration. The utilization of the HDF5 container format grants efficient and parallel I/O operations, integrated compression algorithms and check sums to guard against data corruption. To not reinvent the wheel and to build upon past developments, we use existing standards like QuakeML, StationXML, W3C PROV and HDF5 wherever feasible. Usability and tool support are crucial for any new format to gain acceptance. We developed mature C/Fortran and Python based APIs coupling ASDF to the widely used SPECFEM3D_GLOBE and ObsPy toolkits.

58 GEOSCIENCES↗
DOE OSTI2020

The age–chemical abundance structure of the Galactic disc – II. α -dichotomy and thick disc formation

ABSTRACT We extend our previous work on the age–chemical abundance structure of the Galactic outer disc to the inner disc (4 < r < 8 kpc) based on the SDSS/APOGEE survey. Different from the outer disc, the inner disc stars exhibit a clear bimodal distribution in the [Mg/Fe]–[Fe/H] plane. While a number of scenarios have been proposed in the literature, it remains challenging to recover this bimodal distribution with theoretical models. To this end, we present a chemical evolution model embedding a complex multiphase inner disc formation scenario that matches the observed bimodal [Mg/Fe]–[Fe/H] distribution. In this scenario, the formation of the inner disc is dominated by two main starburst episodes $6\,$Gyr apart with secular, low-level star formation activity in between. In our model, the first starburst occurs at early cosmic times ($t\sim 1\,$ Gyr) and the second one $6\,$ Gyr later at a cosmic time of $t\sim 7\,$ Gyr. Both these starburst episodes are associated with gas accretion events in our model, and are quenched rapidly. The first starburst leads to the formation of the high-α sequence, and the second starburst leads to the formation of the metal-poor low-α sequence. The metal-rich low-α stars, instead, form during the secular evolution phase between the two bursts. Our model shows that the α-dichotomy originates from the rapid suppression of star formation after the first starburst. The two starburst episodes are likely to be responsible for the formation of the geometric thick disc (z >1 kpc), with the old inner thick disc and the young outer thick disc forming during the first and the second starbursts, respectively.

Lian, Jianhui↗
DOE OSTI2019

Widespread star formation inside galactic outflows

Abstract Several models have predicted that stars could form inside galactic outflows and that this would be a new major mode of galaxy evolution. Observations of galactic outflows have revealed that they host large amounts of dense and clumpy molecular gas, which provide conditions suitable for star formation. We have investigated the properties of the outflows in a large sample of galaxies by exploiting the integral field spectroscopic data of the large MaNGA-SDSS4 galaxy survey. We find evidence for prominent star formation occurring inside at least 30 per cent of the galactic outflows in our sample, whilst signs of star formation are seen in up to half of the outflows. We also show that even if star formation is prominent inside many other galactic outflows, this may have not been revealed as the diagnostics are easily dominated by the presence of even faint active galactic nucleus and shocks. If very massive outflows typical of distant galaxies and quasars follow the same scaling relations observed locally, then the star formation inside high-z outflows can be up to several 100 $\rm M_{\odot }~yr^{-1}$ and could contribute substantially to the early formation of the spheroidal component of galaxies. Star formation in outflows can also potentially contribute to establishing the scaling relations between black holes and their host spheroids. Moreover, supernovae exploding on large orbits can chemically enrich in situ and heat the circumgalactic and intergalactic medium. Finally, young stars ejected on large orbits may also contribute to the reionization of the Universe.

Gallagher, R.↗
DOE OSTI2024

Bridging the Gap Between LLMs and LNS with Dynamic Data Format and Architecture Codesign

Deep neural networks (DNNs) have achieved tremendous success in the past few years. However, their training and inference demand exceptional computational and memory resources. Quantization has been shown as an effective approach to mitigate the cost, with the mainstream data types reduced from FP32 to FP16/BF16 and recently FP8 in the latest NVIDIA H100 GPUs. With increasingly aggressive quantization, however, the conventional floating-point formats suffer from limited precision in representing numbers around zero. Recently, NVIDIA demonstrated the potential of using a Logarithmic Number System (LNS) for the next generation of tensor cores. While LNS mitigates the hurdles in representing small numbers, in this work we observed a mismatch between LNS and the emerging Large Language Models (LLM), where LLM exhibits significant outliers when directly adopting the LNS format. In this paper, we present a data-format/architecture codesign to bright this gap. On the format side, we propose a dynamic LNS format to flexibly represent outliers at a higher precision, by exploiting asymmetry in the LNS representation and identifying outliers through a per-vector basis. On the architecture side, for demonstration, we realize the dynamic LNS format in a systolic array, which can handle the irregularity of the outliers at runtime. We implement our approach on an Alveo U280 FPGA as a prototype. Experimental results show that our design can effectively handle the outliers and resolve the mismatch between LNS and LLM, contributing to an accuracy improvement of 15.4% and 16% over the floating-point and the original LNS baselines, using four state-of-the-art LLM models. Our observation and design lay a solid foundation for the large-scale adoption of the LNS format in the next-generation deep learning hardware.

Haghi, Pouya↗
DOE OSTI2020

Formate dependent heterodisulfide reduction in a Methanomicrobiales archaeon

Hydrogenotrophic methanogens produce CH 4 using H 2 as an electron donor to reduce CO 2 . In the absence of H 2 , many are able to use formate or alcohols as alternate electron donors. Methanogens from the order Methanomicrobiales are capable of growth with H 2 , but many lack genes encoding hydrogenases that are typically found in other hydrogenotrophic methanogens. In an effort to better understand electron flow in methanogens from the Methanomicrobiales, we undertook a genetic and biochemical study of heterodisulfide reductase (Hdr) in Methanoculleus thermophilus. Hdr catalyzes an essential reaction by coupling the first and last steps of methanogenesis through flavin-based electron bifurcation. Hdr from M. thermophilus co-purified with formate dehydrogenase (Fdh) and only displayed activity when formate was supplied as an electron donor. We found no evidence of an Hdr associated hydrogenase, and H 2 could not function as an electron donor, even with Hdr purified from cells grown on H 2 . Here, we found that cells catalyze a formate hydrogenlyase activity that is likely essential for generating the formate needed for the Hdr reaction. Together, these results highlight the importance of formate as an electron donor for methanogenesis and suggest the ability to use formate is closely integrated into the methanogenic pathway in organisms from the order Methanomicrobiales.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2018

Low-Moisture Switchgrass Bulk-Format Logistics Costs Based on Engineering Data

Abstract. Logistics costs that spanned harvest, transport, storage, preprocessing, and year-round delivery of 371,870 dMg year -1 of milled, low-moisture switchgrass (SG) to a local biorefinery were determined for bulk-format versus round-bale systems. Separate spreadsheet analyses were conducted for three diesel fuel prices ($0.53 L -1 , $0.92 L -1 , and $1.32 L -1 ) because of the wide range of fuel prices during the project. A detailed analysis scenario identified a common harvest period, equipment annual use, other equipment uses, and protected SG storage on gravel pad, along with equipment performances based on previously published tests primarily for commercially available equipment. The bulk-format system used a depot equipped with stacker/reclaimer technology for storage, whereas the round-bale system used field-side bale stacks for storage, with both systems assuming 6% losses, primarily attributed to storage. Results indicated total costs for bulk-format versus round-bale systems of $54.63 per dry Mg (dMg -1 ), $60.41 dMg -1 , and $66.21 dMg -1 versus $54.59 dMg -1 , $62.10 dMg -1 , and $67.93 dMg -1 corresponding with diesel fuel costs of $0.53 L -1 , $0.92 L -1 , and $1.32 L -1 , respectively. The most significant bulk-format system total cost of $22.79 dMg -1 was associated with a stacker/reclaimer, conveyance, and dust collection at the depot, which was 42% of total costs at a diesel fuel cost of $0.53 L -1 . For the round-bale system, bale chopping total costs was highest and represented an average of 27% of total costs, with costs ranging from $14.63 dMg -1 to $19.08 dMg -1 for diesel fuel input costs ranging from $0.53 L -1 to $1.32 L -1 , respectively. For comparison, the forage harvester provided harvesting and chopping in the bulk-format system at total costs ranging from $6.47 dMg -1 to $8.80 dMg -1 across the same range of diesel fuel input cost. The forage harvester provided an economic advantage in size reduction compared to tub grinding. Truck hauling for both the bulk-format and round-bale systems represented significant expenses at all selected fuel costs. In addition, the multiple times that round bales were handled represented accumulating costs that were sensitive to diesel fuel costs. Keywords: Bales, Bioenergy, Bulk format, Densification, Field chop, Logistics, Transportation.

Agriculture↗
DOE OSTI2022

ESS-DIVE Reporting Format for Location Metadata

The ESS-DIVE location metadata reporting format provides instructions and templates for reporting a minimum set of metadata for discrete point locations in geographic space represented by x, y, and z coordinates. This format was created based on a need for earth and environmental science researchers to more consistently provide metadata about locations where they conduct studies. To create the format, we incorporated elements from ESS-DIVE’s community reporting formats as well as 12 additional data standards or other data resources (e.g., databases, data systems, or repositories). In the template, we ask researchers to indicate unique locations using Location IDs and indicate hierarchies of locations through parent location IDs. We also provide additional optional fields for researchers to indicate how they measured the point location and the date and time that the location was first used as a research siteThis dataset contains support documentation for the reporting format (README.md and instructions.md), a terminology guide (guide.md), a crosswalk indicating how this reporting format relates to existing standards and data resources (Location_metadata_crosswalk.csv), a data dictionary (dd.csv), file-level metadata (flmd.csv), and the location metadata templates in both CSV (Location_metadata_template.csv) and Excel formats (Location_metadata_template.xlsx).

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2025

Analcime-wairakite formation during experimental cement-bentonite alteration at 200–300 °C

Engineered barrier system materials in nuclear waste repositories may undergo hydrothermal alteration in response to groundwater saturation and heating events over their long operational timescales. Hydrothermal interactions between engineered materials (e.g., bentonite buffers, cements, waste canister materials) and the host rock environment may drive alteration processes that affect the advantageous properties of some barrier materials. However, such alteration will also promote the formation of zeolites, hydrothermally formed minerals that may themselves act to isolate radionuclides. Understanding the environmental conditions that control radionuclide-sorbing properties of zeolites, such as Si/Al ratio or Na content, will be valuable for assessing the changing properties of engineered barrier materials in the case of an in situ heating event. Here, we present experimental work characterizing the formation of zeolites during hydrothermal interactions between generic clay and cement barrier materials, with a focus on the analcime-wairakite zeolite series, which has known radionuclide sorption and exchange properties. We present the results of hydrothermal experiments combining uncured ordinary Portland cement powder with steel and Wyoming bentonite in the presence of Opalinus clay and a synthesized Opalinus clay groundwater to simulate water-saturated conditions in an argillaceous rock repository. The experiments were conducted isothermally at 200 or 300 °C for 8 to 24 weeks. In contrast to analogous studies that did not include cement reactants, we observed the formation of analcime-group minerals in all experiments. The addition of cement resulted in lower Si/Al ratios in the zeolites compared to similar studies that did not include cement. The presence of cement as a reactant was interpreted to promote analcime formation at 200 °C. At 300 °C, we observed higher calcium and silica concentrations in the aqueous solutions as well as increased wairakite formation and decreased analcime formation compared to the experiments at 200 °C. These results show a fully realized analcime-wairakite solid solution that falls between Si/Al = 2 (ideal) and a trend of analcime minerals that have increasing Si/Al ratios with increasing Na/(Na+Ca). Our results show predictable relationships between the Si/Al ratio and the analcime-wairakite content under hydrothermal conditions and illustrate that repository material interactions may promote the formation of zeolites in the analcime-wairakite solid-solution series during heating events in the subsurface.

58 GEOSCIENCES↗
DOE OSTI2017

File format for normalizing radiological concentration exposure rate and dose rate data for the effects of radioactive decay and weathering processes

This report specifies the electronic file format that was agreed upon to be used as the file format for normalized radiological data produced by the software tool developed under this TI project. The NA-84 Technology Integration (TI) Program project (SNL17-CM-635, Normalizing Radiological Data for Analysis and Integration into Models) investigators held a teleconference on December 7, 2017 to discuss the tasks to be completed under the TI program project. During this teleconference, the TI project investigators determined that the comma-separated values (CSV) file format is the most suitable file format for the normalized radiological data that will be outputted from the normalizing tool developed under this TI project. The CSV file format was selected because it provides the requisite flexibility to manage different types of radiological data (i.e., activity concentration, exposure rate, dose rate) from other sources [e.g., Radiological Assessment and Monitoring System (RAMS), Aerial Measuring System (AMS), Monitoring and Sampling). The CSV file format also is suitable for the file format of the normalized radiological data because this normalized data can then be ingested by other software [e.g., RAMS, Visual Sampling Plan (VSP)] used by the NA-84’s Consequence Management Program.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2020

Insights into cosmological structure formation with machine learning.

Our modern understanding of cosmological structure formation posits that small matter density fluctuations present in the early Universe, as traced by the cosmic microwave background, grow via gravitational instability to form extended haloes of dark matter. A theoretical understanding of the structure, evolution and formation of dark matter haloes is an essential step towards unravelling the intricate connection between halo and galaxy formation, needed to test our cosmological model against data from upcoming galaxy surveys. Physical understanding of the process of dark matter halo formation is made difficult by the highly non-linear nature of the haloes' evolution. I describe a new approach to gain physical insight into cosmological structure formation based on machine learning. This approach combines the ability of machine learning algorithms to learn non-linear relationships, with techniques that enable us to physically interpret the learnt mapping. I describe applicatio ns of th e method, with the aim of investigating which aspects of the early universe density field impact the later formation of dark matter haloes. First I present a case where the process of halo formation is turned into a binary classification problem; the algorithm predicts whether or not dark matter `particles' in the initial conditions of a simulation will collapse into haloes of a given mass range. Second, I present its generalization to regression, where the algorithm infers the final mass of the halo to which each particle will later belong. I show that the initial tidal shear does not play a significant role compared to the initial density field in establishing final halo masses. Finally, I demonstrate that extending the framework to deep learning algorithms such as convolutional neural networks allows us to explore connections between the early universe and late time haloes beyond those studied by existing analytic approximations of halo collapse.

79 ASTRONOMY AND ASTROPHYSICS↗