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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 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
DOE OSTI2012

MAPPING GROWTH AND GRAVITY WITH ROBUST REDSHIFT SPACE DISTORTIONS

Redshift space distortions (RSDs) caused by galaxy peculiar velocities provide a window onto the growth rate of large-scale structure and a method for testing general relativity. We investigate through a comparison of N-body simulations to various extensions of perturbation theory beyond the linear regime, the robustness of cosmological parameter extraction, including the gravitational growth index {gamma}. We find that the Kaiser formula and some perturbation theory approaches bias the growth rate by 1{sigma} or more relative to the fiducial at scales as large as k > 0.07 h Mpc{sup -1}. This bias propagates to estimates of the gravitational growth index as well as {Omega}{sub m} and the equation-of-state parameter and presents a significant challenge to modeling RSDs. We also determine an accurate fitting function for a combination of line-of-sight damping and higher order angular dependence that allows robust modeling of the redshift space power spectrum to substantially higher k.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

Mapping Dense LU Factorization on Multicore Supercomputer Nodes

Dense LU factorization is a prominent benchmark used to rank the performance of supercomputers. Many implementations use block-cyclic distributions of matrix blocks onto a two-dimensional process grid. The process grid dimensions drive a trade-off between communication and computation and are architecture- and implementation-sensitive. The critical panel factorization steps can be made less communication-bound by overlapping asynchronous collectives for pivoting with the computation of rank-k updates. By shifting the computation-communication trade-off, a modified block-cyclic distribution can beneficially exploit more available parallelism on the critical path, and reduce panel factorization's memory hierarchy contention on now-ubiquitous multicore architectures. During active panel factorization, rank-1 updates stream through memory with minimal reuse. In a column-major process grid, the performance of this access pattern degrades as too many streaming processors contend for access to memory. A block-cyclic mapping in the row-major order does not encounter this problem, but consequently sacrifices node and network locality in the critical pivoting steps. We introduce 'striding' to vary between the two extremes of row- and column-major process grids. The maximum available parallelism in the critical path work (active panel factorization, triangular solves, and subsequent broadcasts) is bounded by the length or width of the process grid. Increasing one dimension of the process grid decreases the number of distinct processes and nodes in the other dimension. To increase the harnessed parallelism in both dimensions, we start with a tall process grid. We then apply periodic 'rotation' to this grid to restore exploited parallelism along the row to previous levels. As a test-bed for further mapping experiments, we describe a dense LU implementation that allows a block distribution to be defined as a general function of block to processor. Other mappings can be tested wit...

Computer Science↗
DOE OSTI2015

MASS SUBSTRUCTURE IN ABELL 3128

We perform a detailed two-dimensional weak gravitational lensing analysis of the nearby (z = 0.058) galaxy cluster Abell 3128 using deep ugrz imaging from the Dark Energy Camera (DECam). We have designed a pipeline to remove instrumental artifacts from DECam images and stack multiple dithered observations without inducing a spurious ellipticity signal. We develop a new technique to characterize the spatial variation of the point-spread function that enables us to circularize the field to better than 0.5% and thereby extract the intrinsic galaxy ellipticities. By fitting photometric redshifts to sources in the observation, we are able to select a sample of background galaxies for weak-lensing analysis free from low-redshift contaminants. Photometric redshifts are also used to select a high-redshift galaxy subsample with which we successfully isolate the signal from an interloping z = 0.44 cluster. We estimate the total mass of Abell 3128 by fitting the tangential ellipticity of background galaxies with the weak-lensing shear profile of a Navarro–Frenk–White (NFW) halo and also perform NFW fits to substructures detected in the 2D mass maps of the cluster. This study yields one of the highest resolution mass maps of a low-z cluster to date and is the first step in a larger effort to characterize the redshift evolution of mass substructures in clusters.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

FARADAY ROTATION MEASURE DUE TO THE INTERGALACTIC MAGNETIC FIELD. II. THE COSMOLOGICAL CONTRIBUTION

We investigate the Faraday rotation measure (RM) due to the intergalactic magnetic field (IGMF) through the cosmic web up to cosmological distances, using a model IGMF based on turbulence dynamo in the large-scale structure of the universe. By stacking the IGMF and gas density data up to redshift z = 5 and taking account of the redshift distribution of polarized background radio sources against which the RM is measured, we simulate the sky map of the RM. The contribution from galaxy clusters is subtracted from the map, based on several different criteria of X-ray brightness and temperature. Our findings are as follows. The distribution of RM for radio sources of different redshifts shows that the rms value increases with redshift and saturates for z {approx}> 1. The saturated value is RM{sub rms} {approx} several rad m{sup -2}. The probability distribution function of |RM| follows the lognormal distribution. The power spectrum has a broad plateau over the angular scale of {approx}1{sup 0}-0.{sup 0}1 with a peak around {approx}0.{sup 0}15. The second-order structure function has a flat profile in the angular separation of {approx}> 0.{sup 0}2. Our results could provide useful insights for surveys to explore the IGMF with the Square Kilometer Array (SKA) and upcoming SKA pathfinders.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Development of TDLAS for Water Vapor Concentration Measurement during VHTR Steam Ingress

Very-high-temperature reactors (VHTR) utilize a graphite-moderated, helium-cooled design that provides higher efficiencies and a low-carbon source of process heat (>700 deg. C) for many industrial applications. Safety concerns have led to extensive accident condition investigations. Steam generator heat-exchanger tube rupture accidents (SGTR) can lead to increased reactor core steam density, which causes neutron slowing-down and chemical corrosion of the graphite fuel elements and structural columns. It is important to be able to computationally model the propagation of steam throughout the lower plenum and nuclear reactor core, but experimental data is needed to validate such models. The primary objective of this project is to instrument a scaled down experiment of a VHTR designed by Ohio State University (OSU), with tunable diode laser absorption spectroscopy (TDLAS) diagnostics to measure steam concentration changes and map how water vapor propagates through the test facility's lower plenum and core. The basic principle of absorption spectroscopy is based on a molecular species ability to absorb photons of specific energies. A collimated laser beam of known energy is passed through a test section containing a sample gas. When a transition of the absorbing gas species resonates with the laser frequency, a certain amount of energy will be absorbed based on the rovibrational characteristics of the molecule. The intensity of the transmitted laser light can be measured by a detector after exiting the test section. The Beer-Lambert Law of absorbance is used to recover this information relating beam attenuation to the system dimensions, gas composition, pressure, and temperature. The line-strength is a function of temperature alone and relates the fraction of molecules in a given rovibrational state through the partition function. The partition function describes the statistical properties of a system in thermodynamic equilibrium where the states obey a Boltzmann distribution. Thus, the number density of molecules in a particular state can be determined from the total internal partition function at a particular temperature. The lineshape function of a given absorption transition is derived from the physical interaction between the absorbing species and is dependent on temperature and pressure. Random thermal motion of absorbing molecules result in broadening of the linewidth, called Doppler broadening, which follows a Gaussian distribution. Molecular collisions result in broadening and shifting of the linewidth, called pressure broadening, which follows a Lorentzian distribution. The overall lineshape results in a Voigt profile, which is a convolution of the Gaussian and Lorentzian distributions. The Voigt profile does not have a simple analytical form and is most often calculated numerically or approximated by complex functions. (authors)

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2014

Intensity mapping across cosmic times with the Lyα line

We present a quantitative model of Lyα emission throughout cosmic history and determine the prospects for intensity mapping spatial fluctuations in the Lyα signal. Since (1) our model assumes at z > 6 the minimum star formation required to sustain reionization and (2) is based at z < 6 on a luminosity function (LF) extrapolated from the few observed bright Lyα emitters, this should be considered a lower limit. Mapping the line emission allows probes of reionization, star formation, and large-scale structure (LSS) as a function of redshift. While Lyα emission during reionization has been studied, we also predict the postreionization signal to test predictions of the intensity and motivate future intensity mapping probes of reionization. We include emission from massive dark matter halos and the intergalactic medium (IGM) in our model. We find agreement with current, measured LFs of Lyα emitters at z < 8. However, diffuse IGM emission, not associated with Lyα emitters, dominates the intensity up to z ∼ 10. While our model is applicable for deep-optical or near-infrared observers like the James Webb Space Telescope, only intensity mapping will detect the diffuse IGM emission. We also construct a three-dimensional power spectrum model of the Lyα emission. Finally, we consider the prospects of an intensity mapper for measuring Lyα fluctuations while identifying interloper contamination for removal. Our results suggest that while the reionization signal is challenging, Lyα fluctuations can be an interesting new probe of LSS at late times when used in conjunction with other lines, e.g., Hα, to monitor low-redshift foreground confusion.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Generating log-normal mock catalog of galaxies in redshift space

We present a public code to generate a mock galaxy catalog in redshift space assuming a log-normal probability density function (PDF) of galaxy and matter density fields. We draw galaxies by Poisson-sampling the log-normal field, and calculate the velocity field from the linearised continuity equation of matter fields, assuming zero vorticity. This procedure yields a PDF of the pairwise velocity fields that is qualitatively similar to that of N-body simulations. We check fidelity of the catalog, showing that the measured two-point correlation function and power spectrum in real space agree with the input precisely. We find that a linear bias relation in the power spectrum does not guarantee a linear bias relation in the density contrasts, leading to a cross-correlation coefficient of matter and galaxies deviating from unity on small scales. We also find that linearising the Jacobian of the real-to-redshift space mapping provides a poor model for the two-point statistics in redshift space. That is, non-linear redshift-space distortion is dominated by non-linearity in the Jacobian. The power spectrum in redshift space shows a damping on small scales that is qualitatively similar to that of the well-known Fingers-of-God (FoG) effect due to random velocities, except that the log-normal mock does not include random velocities. This damping is a consequence of non-linearity in the Jacobian, and thus attributing the damping of the power spectrum solely to FoG, as commonly done in the literature, is misleading.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Multicolor photometry of the merging galaxy cluster A2319: Dynamics and star formation properties

Asymmetric X-ray emission and a powerful cluster-scale radio halo indicate that A2319 is a merging cluster of galaxies. This paper presents our multicolor photometry for A2319 with 15 optical intermediate filters in the Beijing-Arizona-Taiwan-Connecticut (BATC) system. There are 142 galaxies with known spectroscopic redshifts within the viewing field of 58' × 58' centered on this rich cluster, including 128 member galaxies (called sample I). A large velocity dispersion in the rest frame, 1622{sub −70}{sup +91} km s{sup –1}, suggests merger dynamics in A2319. The contour map of projected density and localized velocity structure confirm the so-called A2319B substructure, at ∼10' northwest to the main concentration A2319A. The spectral energy distributions (SEDs) of more than 30,000 sources are obtained in our BATC photometry down to V ∼ 20 mag. A u-band (∼3551 Å) image with better seeing and spatial resolution, obtained with the Bok 2.3 m telescope at Kitt Peak, is taken to make star-galaxy separation and distinguish the overlapping contamination in the BATC aperture photometry. With color-color diagrams and photometric redshift technique, 233 galaxies brighter than h {sub BATC} = 19.0 are newly selected as member candidates after an exclusion of false candidates with contaminated BATC SEDs by eyeball-checking the u-band Bok image. The early-type galaxies are found to follow a tight color-magnitude correlation. Based on sample I and the enlarged sample of member galaxies (called sample II), subcluster A2319B is confirmed. The star formation properties of cluster galaxies are derived with the evolutionary synthesis model, PEGASE, assuming a Salpeter initial mass function and an exponentially decreasing star formation rate (SFR). A strong environmental effect on star formation histories is found in the manner that galaxies in the sparse regions have various star formation histories, while galaxies in the dense regions are found to have shorter SFR time scales, older stellar ages, and higher interstellar medium metallicities. For the merging cluster A2319, local surface density is a better environmental indicator rather than the cluster-centric distance. Compared with the well-relaxed cluster A2589, a higher fraction of star-forming galaxies is found in A2319, indicating that the galaxy-scale turbulence stimulated by the subcluster merger might have played a role in triggering the star formation activity.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

Demonstrating the feasibility of line intensity mapping using mock data of galaxy clustering from simulations

Visbal and Loeb (2010) have shown that it is possible to measure the clustering of galaxies by cross correlating the cumulative emission from two different spectral lines which originate at the same redshift. Through this cross correlation, one can study galaxies which are too faint to be individually resolved. This technique, known as intensity mapping, is a promising probe of the global properties of high redshift galaxies. Here, we test the feasibility of such measurements with synthetic data generated from cosmological dark matter simulations. We use a simple prescription for associating galaxies with dark matter halos and create a realization of emitted radiation as a function of angular position and wavelength over a patch of the sky. This is then used to create synthetic data for three different hypothetical instruments, one aboard the Space Infrared Telescope for Cosmology and Astrophysics (SPICA), another consisting of a pair of ground based radio telescopes designed to measure the CO(1-0) and CO(2-1) emission lines, and one on the Cornell Caltech Atacama Telescope (CCAT). We find that the line cross power spectrum can be measured accurately from the synthetic data with errors consistent with the analytical prediction of Visbal and Loeb (2010). Removal of astronomical backgrounds and masking bright line emission from foreground contaminating galaxies do not prevent accurate cross power spectrum measurements.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Prospects for detecting C II emission during the epoch of reionization

We produce simulations of the atomic C ii line emission in large sky fields in order to determine the current and future prospects for mapping this line during the high-redshift epoch of reionization. We calculate the C ii line intensity, redshift evolution, and spatial fluctuations using observational relations between C ii emission and the galaxy star formation rate over the frequency range 200–300 GHz. We estimate an averaged intensity of I{sub C II}=(4±2)×10{sup 2} Jy sr{sup −1} in the redshift range z ∼ 5.3−8.5. Observations of the C ii emission in this frequency range will suffer contamination from emission lines at lower redshifts, in particular CO rotational lines. Using simulations, we estimated the CO contamination to be I{sub CO}≈10{sup 3} Jy sr{sup −1} (originating from galaxies at z < 2.5). Using detailed simulations of the C ii and CO emission across a range of redshifts, we generate maps as a function of angle and frequency, fully taking into account this resolution and light-cone effects. In order to reduce the foreground contamination, we find that we should mask galaxies below redshifts ∼2.5 with a CO(J:2–1) to CO(J:6–5) line flux density higher than 5× 10{sup −22} W m{sup −2} or an AB magnitude lower than m{sub K}=22. We estimate that the additional continuum contamination originating in emission from stars and in dust, free–free, free–bound, and two-photon emission in the interstellar medium is of the order of 10{sup 5} Jy sr{sup −1}, which is well above the expected C ii signal. We also consider the possibility of cross-correlating foreground lines with galaxy surveys in order to probe the intensity of the foregrounds. Finally, we discuss the expected constraints from two experiments capable of measuring the expected C ii power spectrum.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Mapping the influence of ligand electronics on the spectroscopic and 1 O 2 sensitization characteristics of Pd( ii ) biladiene complexes bearing phenyl–alkynyl groups at the 2- and 18-positions

Photodynamic therapy (PDT) is a promising treatment for certain cancers that proceeds via sensitization of ground state 3 O 2 to generate reactive 1 O 2 . Classic macrocyclic tetrapyrrole ligand scaffolds, such as porphyrins and phthalocyanines, have been studied in detail for their 1 O 2 photosensitization capabilities. Despite their compelling photophysics, these systems have been limited in PDT applications because of adverse biological side effects. Conversely, the development of non-traditional oligotetrapyrrole ligands metalated with palladium (Pd[DMBil1]) have established new candidates for PDT that display excellent biocompatibility. Herein, the synthesis, electrochemical, and photophysical characterization of a new family of 2,18-bis(phenylalkynyl)-substituted Pd II 10,10-dimethyl-5,15-bis(pentafluorophenyl)-biladiene (Pd[DMBil2-R]) complexes is presented. These second generation biladienes feature extended conjugation relative to previously characterized Pd II biladiene scaffolds (Pd[DMBil1]). We show that these new derivatives can be prepared in good yield and, that the electronic nature of the phenylalkynyl appendages dramatically influence the Pd II biladiene photophysics. Extending the conjugation of the Pd[DMBil1] core through installation of phenylacetylene resulted in a ~75 nm red-shift of the biladiene absorption spectrum into the phototherapeutic window (600–900 nm), while maintaining the Pd II biladiene's steady-state spectroscopic 1 O 2 sensitization characteristics. Varying the electronics of the phenylalkyne groups via installation of electron donating or withdrawing groups dramatically influences the steady-state spectroscopic and photophysical properties of the resulting Pd[DMBil2-R] family of complexes. The most electron rich variants (Pd[DMBil2-N(CH3)2]) can absorb light as far red as ~700 nm but suffer from significantly reduced ability to sensitize formation of 1 O 2 . By contrast, Pd[DMBil2-R] derivatives bearing electron withdrawing functionalities (Pd[DMBil2-CN] and Pd[DMBil2-CF3]) display 1 O 2 quantum yields above 90%. The collection of results we report suggest that excited state charge transfer from more electron-rich phenyl-alkyne appendages to the electron deficient biladiene core circumvents triplet sensitization. The spectral and redox properties, as well as the triplet sensitization efficiency of each Pd[DMBil2-R] derivative is considered in relation to the Hammett value (σp) for each biladiene's R-group. More broadly, the results reported in this study clearly demonstrate that biladiene redox properties, spectral properties, and photophysics can be perturbed greatly by relatively minor alterations to biladiene structure.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Mesoporous Thin Film Architectures: Addressing Material Demands through Molecular Self-Assembly

Mesoporous thin films spark interest across a wide range of disciplines due to their tunable nanostructures, large internal surface areas, and strong compatibility with planar optical, electronic, and microfluidic devices. While attention in the porous materials community has shifted toward macroporous or disordered nanoporous systems, a resurgence in mesoporous thin film research is underway, driven by new molecular self-assembly methods, advanced materials chemistry, and improved characterization techniques. The integration of high-χN block copolymer design, kinetically persistent micelle templating, and postdeposition processing protocols now allows control over structural parameters such as pore size, wall thickness, porosity, and connectivity. These advances have overcome many of the thermodynamic and processing constraints that previously limited widespread adoption. Rather than serving only as high-surface-area supports, mesoporous thin films are engineered as active interfaces where responsive chemistries and nanoscale confinement act in tandem. Embedding switchable ligands, thermoresponsive polymers, redox mediators, or ion-selective groups directly within the pore walls enables real-time control over transport, optical, and electrochemical properties. These capabilities open up new directions in adaptive coatings, gated membranes, and fast-response biosensors. To further expand their functional scope, mesoporous films are integrated into hierarchical and multicomponent architectures. Techniques such as triblock terpolymer templating, crack-directed assembly, and nanoimprint lithography allow for control over spatial organization on the micron and submicron scale and pore system orientation. This enables programmable anisotropy, enhanced molecular diffusion, and wavelength-selective photonic behavior, essential for next-generation sensing, catalysis, and energy applications. Such structural and functional complexity requires equally sophisticated characterization. Multimodal and in situ techniques can track material dynamics under operational conditions. Recent progress includes extended-range ellipsometric porosimetry (EP) for hierarchical architectures, vacuum EP for interface energetics, time-resolved EP for diffusion kinetics, and correlative AFM-SAXS mapping. The introduction of advanced neutron-based spectroscopies, particularly quasielastic neutron scattering (QENS), promises to provide real-time access to ion transport dynamics and segmental motion under nanoscale confinement, offering a path toward deeper mechanistic understanding of structure-performance correlations in mesoporous systems. This Account reflects the technical advances made and the interdisciplinary collaborations that have shaped our collective vision. The particular dimensions of mesopores enable us to subtly tune interactions at the molecular, interfacial, and mesoscopic levels that permit us to harness nanoconfinement. What emerges is a versatile, modular platform capable of chemical gating, energy transduction, and sensing with a level of tunability unmatched by other porous materials. We highlight critical challenges including the need for more robust large-area processing, a deeper understanding of dynamic behavior under cycling, and better integration with device-level architectures. Our strategies support the transition of mesoporous thin films into active high-performance components in next-generation energy, environmental, and biomedical systems.

oxides↗
DOE OSTI2017

Intensity Mapping of Hα, Hβ, [O II], and [O III] Lines at z < 5

Intensity mapping is becoming a useful tool to study the large-scale structure of the universe through spatial variations in the integrated emission from galaxies and the intergalactic medium. We study intensity mapping of the Hα 6563 A-ring , [O iii] 5007 Å, [O ii] 3727 Å, and Hβ 4861 A-ring lines at 0.8⩽z⩽5.2. The mean intensities of these four emission lines are estimated using the observed luminosity functions (LFs), cosmological simulations, and the star formation rate density (SFRD) derived from observations at z≲5. We calculate the intensity power spectra and consider the foreground contamination of other lines at lower redshifts. We use the proposed NASA small explorer SPHEREx (the Spectro-Photometer for the History of the universe, Epoch of Reionization, and Ices Explorer) as a case study for the detectability of the intensity power spectra of the four emission lines. We also investigate the cross-correlation with the 21 cm line probed by the Canadian Hydrogen Intensity Mapping Experiment (CHIME), Tianlai experiment and the Square Kilometer Array (SKA) at 0.8⩽z⩽2.4. We find both the auto and cross power spectra can be well measured for the Hα, [O iii] and [O ii] lines at z≲3, while it is more challenging for the Hβ line. Finally, we estimate the constraint on the SFRD from intensity mapping, and find we can reach an accuracy higher than 7% at z≲4, which is better than with the usual method of measurements using the LFs of galaxies.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

Use of Neutron Flux Calculated by Shift in a Grizzly Reactor Pressure Vessel Fracture Simulation

The reactor pressure vessel (RPV) plays the critical role of containing the reactor and coolant in a light water reactor nuclear power plant, and must be able to safely perform this function under a variety of normal and off-normal transient loading conditions. The RPV is subjected to harsh environmental conditions (elevated temperature and high neutron flux) whenever the plant is operating, which leads to embrittlement of the steel over time. RPVs contain populations of flaws introduced during the manufacturing process, and the primary safety concern is that during a transient event, a fracture could initiate at the site of one of these flaws and lead to rupture of the RPV. RPVs are very rugged structures, and the probability of this occurring is very low, but as the RPV's steel becomes embrittled over time, its resistance to fracture decreases and this becomes more likely. Assessing the likelihood of RPV fracture during a transient event involves performing a probabilistic fracture mechanics analysis, in which random sampling procedures are used to assess the probability of fracture of a population of flaws. Grizzly offers unique capabilities for modeling the RPV using 1D, 2D, or 3D representations, taking advantage of parallel computing for this type of analysis. One of the important inputs to Grizzly is the spatial distribution of the neutron fluence, which has a large impact on the material embrittlement, and should thus be characterized as accurately as possible. The VERA core simulator developed by the CASL program takes advantage of high performance computing resources to perform high-fidelity multiphysics simulations of reactor physics, including the effects of neutron transport, fuel performance, and thermal hydraulics. Recently a capability was developed to also evaluate neutron fluxes away from the reactor core through the Shift code. This allows for a detailed 3D map of the spatial variation of the fluence in components such as the RPV to be computed, which is ideal for use with Grizzly. This report documents a procedure developed to use the fluences computed in Shift in a Grizzly simulation, which allows for improved realisim in the prediction of the effects of environmental exposure on propensity for reactor pressure vessel fracture. This capability demonstrated on RPVs with multiple types of configurations.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2023

Finding simplicity: unsupervised discovery of features, patterns, and order parameters via shift-invariant variational autoencoders *

Abstract Recent advances in scanning tunneling and transmission electron microscopies (STM and STEM) have allowed routine generation of large volumes of imaging data containing information on the structure and functionality of materials. The experimental data sets contain signatures of long-range phenomena such as physical order parameter fields, polarization, and strain gradients in STEM, or standing electronic waves and carrier-mediated exchange interactions in STM, all superimposed onto scanning system distortions and gradual changes of contrast due to drift and/or mis-tilt effects. Correspondingly, while the human eye can readily identify certain patterns in the images such as lattice periodicities, repeating structural elements, or microstructures, their automatic extraction and classification are highly non-trivial and universal pathways to accomplish such analyses are absent. We pose that the most distinctive elements of the patterns observed in STM and (S)TEM images are similarity and (almost-) periodicity, behaviors stemming directly from the parsimony of elementary atomic structures, superimposed on the gradual changes reflective of order parameter distributions. However, the discovery of these elements via global Fourier methods is non-trivial due to variability and lack of ideal discrete translation symmetry. To address this problem, we explore the shift-invariant variational autoencoders (shift-VAEs) that allow disentangling characteristic repeating features in the images, their variations, and shifts that inevitably occur when randomly sampling the image space. Shift-VAEs balance the uncertainty in the position of the object of interest with the uncertainty in shape reconstruction. This approach is illustrated for model 1D data, and further extended to synthetic and experimental STM and STEM 2D data. We further introduce an approach for training shift-VAEs that allows finding the latent variables that comport to known physical behavior. In this specific case, the condition is that the latent variable maps should be smooth on the length scale of the atomic lattice (as expected for physical order parameters), but other conditions can be imposed. The opportunities and limitations of the shift VAE analysis for pattern discovery are elucidated.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2019

Hole-induced electronic and optical transitions in L a 1 - x S r x Fe O 3 epitaxial thin films

We have investigated the electronic and optical properties of epitaxial La 1-x Sr x FeO 3 for 0 ≤ x ≤ 1 prepared by molecular-beam epitaxy. Core-level and valence-band x-ray photoemission features monotonically shift to lower binding energy with increasing x, indicating downward movement of the Fermi level toward the valence-band maximum. Combining valence-band photoemission and O K -edge x-ray absorption data, we map the evolution of the occupied and unoccupied bands and observe a narrowing of the gap, along with a transfer of state density from just below to just above the Fermi level as a result of hole doping. In-plane transport measurements confirm that the material becomes a p -type semiconductor at lower doping levels and exhibits a conversion from semiconducting to metallic behavior at x = 1. As a result, low-energy optical transitions revealed by spectroscopic ellipsometry are explained based on insight from theoretical densities of states and first-principles calculations of optical absorption spectra.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Discovery of a very large structure at z = 3.78

We report the discovery of a large-scale structure containing multiple protoclusters at z = 3.78 in the Boötes field. The spectroscopic discovery of five galaxies at z = 3.783 ± 0.002 lying within 1 Mpc of one another led us to undertake a deep narrow- and broadband imaging survey of the surrounding field. Within a comoving volume of 72 × 72 × 25 Mpc{sup 3}, we have identified 65 Lyα emitter (LAE) candidates at z = 3.795 ± 0.015, and four additional galaxies at z {sub spec} = 3.730, 3.753, 3.780, 3.835. The galaxy distribution within the field is highly non-uniform, exhibiting three large (≈3-5 ×) overdensities separated by 8-14 Mpc (physical) and possibly connected by filamentary structures traced by LAEs. The observed number of LAEs in the entire field is nearly twice the average expected in field environments based on estimates of the Lyα luminosity function at these redshifts. We estimate that by z = 0 the largest overdensity will grow into a cluster of mass ≈10{sup 15} M {sub ☉}; the two smaller overdensities will grow into clusters of mass (2-6) × 10{sup 14} M {sub ☉}. The highest concentration of galaxies is located at the southern end of the image, suggesting that the current imaging may not map the true extent of the large-scale structure. Finding three large protocluster candidates within a single 0.3 deg{sup 2} field is highly unusual; expectations from theory suggest that such alignments should occur less than 2% of the time. Searching for and characterizing such structures and accurately measuring their volume space density can therefore place constraints on the theory of structure formation. Such regions can also serve as laboratories for the study of galaxy formation in dense environments.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

A weak lensing view of the downsizing of star-forming galaxies

We describe a weak lensing view of the downsizing of star-forming galaxies based on cross-correlating a weak lensing (κ) map with a predicted map constructed from a redshift survey. Moderately deep and high-resolution images with Subaru/Hyper Suprime-Cam covering the 4 deg{sup 2} DLS F2 field provide a κ map with 1 arcmin resolution. A dense complete redshift survey of the F2 field including 12,705 galaxies with R⩽20.6 is the basis for construction of the predicted map. The zero-lag cross-correlation between the κ and predicted maps is significant at the 30σ level. The width of the cross-correlation peak is comparable to the angular scale of rich clusters at z∼0.3, the median depth of the redshift survey. Slices of the predicted map in δz=0.05 redshift bins enable exploration of the impact of structure as a function of redshift. The zero-lag normalized cross-correlation has significant local maxima at redshifts coinciding with known massive X-ray clusters. Even in slices where there are no known massive clusters, there is a significant signal in the cross-correlation originating from lower mass groups that trace the large-scale of the universe. Spectroscopic D{sub n}4000 measurements enable division of the sample into star-forming and quiescent populations. In regions surrounding massive clusters of galaxies, the significance of the cross-correlation with maps based on star-forming galaxies increases with redshift from 5σ at z = 0.3 to 7σ at z=0.5; the fractional contribution of the star-forming population to the total cross-correlation signal also increases with redshift. This weak lensing view is consistent with the downsizing picture of galaxy evolution established from other independent studies.

79 ASTRONOMY AND ASTROPHYSICS↗