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NASA NTRS2016

Nonlinear Wakes Behind a Row of Elongated Roughness Elements

This paper is concerned with the high Reynolds number flow over a spanwise periodic array of roughness elements with inter-element spacing of the order of the local boundary-layer thickness. While earlier work by Goldstein, Sescu, Duck and Choudhari (2010) and Goldstein, Sescu, Duck and Choudhari (2011) was mainly concerned with smaller roughness heights that produced relatively weak distortions of the downstream flow, the focus here is on extending the analysis to larger roughness heights and streamwise elongated planform shapes that together produce a qualitatively different, nonlinear behavior of the downstream wakes. The roughness scale flow now has a novel triple-deck structure that is somewhat different from related studies that have previously appeared in the literature. The resulting flow is formally nonlinear in the intermediate wake region, where the streamwise distance is large compared to the roughness dimensions but small compared to the downstream distance from the leading edge, as well as in the far wake region where the streamwise length scale is of the order of the downstream distance from the leading edge. In contrast, the flow perturbations in both of these wake regions were strictly linear in the earlier work by Goldstein et al (2010, 2011). This is an important difference because the nonlinear wake flow in the present case provides an appropriate basic state for studying the secondary instability and eventual breakdown into turbulence.

Boundary layer control↗

DOE OSTI2024

Ultra-Long Distance BOTDA Sensor System Employing Hybrid Amplification and Advanced Noise Reduction Techniques

Brillouin Optical Time Domain Analysis (BOTDA) sensor systems play a pivotal role in distributed sensing, which enables precise measurements of strain and temperature across extensive fiber lengths. This research offers a comprehensive strategy to extend the sensing range of BOTDA systems beyond tens of kilometers while maintaining high spatial resolutions. Such enhanced sensing is realized through the integration of distributed Raman amplification, inline amplification using erbium-doped fiber amplifiers (EDFA), and advanced noise reduction techniques. Optimizing Raman pump and probe wave profiles ensures the robustness of Brillouin scattering signals, effectively countering attenuation-induced losses. Additionally, enhancing weak Brillouin signals by strategically placing EDFAs at optimal fiber locations keeps sensor sensitivity high. Leveraging inherent redundancy in measured data as a function of frequency and fiber distance, the non-local means (NLM) filter removes noise while preserving essential physical information. In summary, this research has shown a holistic exploration of extending BOTDA’s distance sensing capabilities up to 150 km with spatial resolutions of 8 meters.

Bhatta, Hari↗

DOE OSTI2024

Simulated plant-mediated oxygen input has strong impacts on fine-scale porewater biogeochemistry and weak impacts on integrated methane fluxes in coastal wetlands

Methane (CH 4 ) emissions from wetland ecosystems are controlled by redox conditions in the soil, which are currently underrepresented in Earth system models. Plant-mediated radial oxygen loss (ROL) can increase soil O 2 availability, affect local redox conditions, and cause heterogeneous distribution of redox-sensitive chemical species at the root scale, which would affect CH 4 emissions integrated over larger scales. In this study, we used a subsurface geochemical simulator (PFLOTRAN) to quantify the effects of incorporating either spatially homogeneous ROL or more complex heterogeneous ROL on model predictions of porewater solute concentration depth profiles (dissolved organic carbon, methane, sulfate, sulfide) and column integrated CH 4 fluxes for a tidal coastal wetland. From the heterogeneous ROL simulation, we obtained 18% higher column averaged CH 4 concentration at the rooting zone but 5% lower total CH 4 flux compared to simulations of the homogeneous ROL or without ROL. This difference is because lower CH 4 concentrations occurred in the same rhizosphere volume that was directly connected with plant-mediated transport of CH 4 from the rooting zone to the atmosphere. Sensitivity analysis indicated that the impacts of heterogeneous ROL on model predictions of porewater oxygen and sulfide concentrations will be more important under conditions of higher ROL fluxes or more heterogeneous root distribution (lower root densities). Despite the small impact on predicted CH 4 emissions, the simulated ROL drastically reduced porewater concentrations of sulfide, an effective phytotoxin, indicating that incorporating ROL combined with sulfur cycling into ecosystem models could potentially improve predictions of plant productivity in coastal wetland ecosystems.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2017

Interpretation of Ground Temperature Anomalies in Hydrothermal Discharge Areas

Abstract Researchers have long noted the potential for shallow hydrothermal fluids to perturb near‐surface temperatures. Several investigators have made qualitative or semiquantitative use of elevated surface temperatures; for example, in snowfall calorimetry, or for tracing subsurface flow paths. However, a quantitative framework connecting surface temperature observations with conditions in the subsurface is currently lacking. Here, we model an area of shallow subsurface flow at Burgdorf Hot Springs, a rustic commercial resort in the Payette National Forest, north of McCall, ID, USA. We calibrate the model using shallow (0.2 m depth) ground temperature measurements and overburden thickness estimates from seismic refraction studies. The calibrated model predicts negligible loss of heat energy from the laterally migrating fluids at the Burgdorf site, in spite of the fact that thermal anomalies are observed in the unconsolidated near‐surface alluvium. Although elevated near‐surface ground temperatures are commonly assumed to result from locally high heat flux, this conflicts with the small apparent heat loss during lateral flow inferred at the Burgdorf site. We hypothesize an alternative explanation for near‐surface temperature anomalies that is only weakly dependent on heat flux, and more strongly controlled by the Biot number, a dimensionless parameter that compares the rate at which convection carries heat away from the land surface to the rate at which it is supplied by conduction to the interface.

Price, Adam N.↗

DOE OSTI2017

A derivation and scalable implementation of the synchronous parallel kinetic Monte Carlo method for simulating long-time dynamics

Kinetic Monte Carlo (KMC) simulations are used to study long-time dynamics of a wide variety of systems. Unfortunately, the conventional KMC algorithm is not scalable to larger systems, since its time scale is inversely proportional to the simulated system size. A promising approach to resolving this issue is the synchronous parallel KMC (SPKMC) algorithm, which makes the time scale size-independent. This paper introduces a formal derivation of the SPKMC algorithm based on local transition-state and time-dependent Hartree approximations, as well as its scalable parallel implementation based on a dual linked-list cell method. The resulting algorithm has achieved a weak-scaling parallel efficiency of 0.935 on 1024 Intel Xeon processors for simulating biological electron transfer dynamics in a 4.2 billion-heme system, as well as decent strong-scaling parallel efficiency. The parallel code has been used to simulate a lattice of cytochrome complexes on a bacterial-membrane nanowire, and it is broadly applicable to other problems such as computational synthesis of new materials.

97 MATHEMATICS AND COMPUTING↗

DOE OSTI2021

Seismic Imaging of a Shale Landscape Under Compression Shows Limited Influence of Topography–Induced Fracturing

We used seismic refraction to image the P-wave velocity structure of a shale watershed experiencing regional compression in the Valley and Ridge Province (USA). From estimates showing strong compressional stress, we expected the depth to unweathered bedrock to mirror the hill-valley-hill topography (“bowtie pattern”) by analogy to seismic velocity patterns in crystalline bedrock in the North American Piedmont that also experience compression. Previous researchers used failure potentials calculated for strong compression in the Piedmont to suggest fractures are open deeper under hills than valleys to explain the “bowtie” pattern. Seismic images of the shale watershed, however, show little evidence of such a “bowtie.” Instead, they are consistent with weak (not strong) compression. Here, this contradiction could be explained by the greater importance of infiltration-driven weathering than fracturing in determining seismic velocities in shale compared to crystalline bedrock, or to local perturbations of the regional stress field due to lithology or structures.

58 GEOSCIENCES↗

DOE OSTI2016

Hexadecapolar Colloids

Outermost occupied electron shells of chemical elements can have symmetries resembling that of monopoles, dipoles, quadrupoles and octupoles corresponding to filled s-, p-, d- and forbitals. Theoretically, elements with hexadecapolar outer shells could also exist, but none of the known elements have filled g-orbitals. On the other hand, the research paradigm of ‘colloidal atoms’ displays complexity of particle behaviour exceeding that of atomic counterparts, which is driven by DNA functionalization, geometric shape and topology and weak external stimuli. We describe elastic hexadecapoles formed by polymer microspheres dispersed in a liquid crystal, a nematic fluid of orientationally ordered molecular rods. Because of conically degenerate boundary conditions, the solid microspheres locally perturb the alignment of the nematic host, inducing hexadecapolar distortions that drive anisotropic colloidal interactions. We uncover physical underpinnings of formation of colloidal elastic hexadecapoles and report the ensuing bonding inaccessible to elastic dipoles, quadrupoles and other nematic colloids studied previously.

14 SOLAR ENERGY↗

DOE OSTI2016

Photoconductivity study of acid on Zinc phthalocyanine pyridine thin films

The Metal Phthalocyanine (MPc) have attracted much interest because of chemical and high thermal stability. Molecules forming a crystal of MPc are held together by weak attractive Vander Waals forces. Organic semiconductors have π conjugate bonds which allow electrons to move via π-electron cloud overlaps. Conduction mechanisms for organic semiconductor are mainly through tunneling; hopping between localized states, mobility gaps, and phonon assisted hopping. The photo conductivity of thin films of these complexes changes when exposed to oxidizing and reducing gases. Arrhenius plot is used to find the thermal activation energy in the intrinsic region and impurity scattering region. Arrhenius plotsare used to find the thermal activation energy.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2023

Prospects for annihilating dark matter from M31 and M33 observations with the Cherenkov Telescope Array

M31 and M33 are the closest spiral galaxies and the largest members (together with the Milky Way) of the Local group, which makes them interesting targets for indirect dark matter searches. In this paper we present studies of the expected sensitivity of the Cherenkov Telescope Array (CTA) to an annihilation signal from weakly interacting massive particles from M31 and M33. Here, we show that a 100 h long observation campaign will allow CTA to probe annihilation cross-sections up to <συ> ≈ 5•10 -25 cm 3 s -1 for the τ + τ - annihilation channel (for M31, at a DM mass of 0.3 TeV), improving the current limits derived by HAWC by up to an order of magnitude. We present an estimate of the expected CTA sensitivity, by also taking into account the contributions of the astrophysical background and other possible sources of systematic uncertainty. We also show that CTA might be able to detect the extended emission from the bulge of M31, detected at lower energies by the Fermi /LAT.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS2004

Anomalous Oxygen and Krypton Abundances in Interstellar Gas

The primary objective of this program was to obtain FUSE observations of the interstellar H2 absorption toward a sample of stars observed with the HST STIS spectrograph as part of the ISM SNAP Survey. This Survey was designed to produce a database of high quality, high resolution W spectra from which interstellar gas-phase elemental abundances could be derived for large portions of the Galaxy. In particular, oxygen and krypton were chosen as excellent tracers for measuring the homogeneity of the interstellar gas due to their weak depletion into dust grains. The gas-phase 0 and Kr abundances relative to total hydrogen column density had previously been shown with HST GHRS measurements to be essentially constant in the local Milky Way. One of the main motivations of the ISM SNAP Survey was to determine if this constancy held at greater distances and in denser sightlines (where depletion into dust could be a possibility). The initial ISM SNAP STIS observations indicated a number of sightlines with unusual 0 and Kr abundances relative to the measured H I column densities. Since the appropriate benchmark for accurate abundance comparisons is the total hydrogen column density (H I plus H2), FUSE observations of interstellar H2 were carried out in these sightlines in order to determine if they represent cases of true abundance anomalies.

Meyer, David M.↗

DOE OSTI2020

Quantum Dynamics at Scale: Ultrafast Control of Emergent Functional Materials

Confluence of extreme-scale quantum dynamics simulations (i.e. quantum@scale) and cutting-edge x-ray free-electron laser experiments are revolutionizing materials science. An archetypal example is the exciting concept of using picosecond light pulses to control emergent material properties on demand in atomically-thin layered materials. This paper describes efforts to scale our quantum molecular dynamics engine toward the United States' first exaflop/s computer, under an Aurora Early Science Program project named "Metascalable layered material genome". Key algorithmic and computing techniques incorporated are: (1) globally-scalable and locally-fast solvers within a linear-scaling divide-conquer-recombine algorithmic framework; (2) algebraic `BLASification' of computational kernels; and (3) data alignment and loop restructuring, along with register and cache blocking, for enhanced vectorization and efficient memory access. The resulting weak-scaling parallel efficiency was 0.93 on 131,072 Intel Xeon Phi cores for a 56.6 million atom (or 169 million valence-electron) system, whereas the various code transformations achieved 5-fold speedup. The optimized simulation engine allowed us for the first time to establish a significant effect of substrate on the dynamics of layered material upon electronic excitation.

Algebraic BLASification↗

NASA NTRS1992

Observation of local radio emission associated with type III radio bursts and Langmuir waves

The first clear detection of fundamental and harmonic radiation from the type III radio source region is presented. This radiation is characterized by its lack of frequency drift, its short rise and decay times, its relative weakness compared to the remotely observed radiation and its temporal coincidence with observed Langmuir waves. The observations were made with the radio and plasma frequency (URAP) receivers on the Ulysses spacecraft between about 1 and 2 AU from the Sun.

Reiner, M. J.↗

DOE OSTI2014

Osmoregulation in Methanogens (and Other Interesting Organisms)

Our research has been aimed at (i) identifying, (ii) determining mode of regulation, and (iii) understanding how different classes of compatible solutes (also termed osmolytes) affect macromolecular stability in response to osmotic and thermal stress. For solutes we have identified (e.g., di-inositol-1,1’-phosphate (DIP)), we used NMR to elucidate biosynthetic pathways and then cloned suspected enzymes in the pathway to explore how they are regulated. Compatible solutes are thought to protect proteins from thermal and osmotic stresses by being excluded from the surface, allowing critical water molecules to interact with the protein. This implies there are no specific binding interactions between osmolytes and proteins. However, we and others have often observed very specific solute effects for proteins that suggest a more direct interaction between solute and protein is likely can occur. Measuring such a weak interaction is extremely difficult. We have developed a solution NMR method, high-resolution field cycling relaxometry, that can measure spin-lattice relaxation rates as a function of magnetic field from 11.7 (the field of a 500 MHz spectrometer) to 0.003 T. The methodology is ideal for nuclei in small molecules with moderately long relaxation times at high fields – phosphate groups (31P), enriched carbonyls (13C), or methyl groups (1H). The protein of interest is spin-labeled to introduce a large dipole on it that will dominate the relaxation of nuclei on any small molecules that bind transiently. The key is to measure relaxation below 1-2 T (and extract nuclei-spin label distances in the bound complex) where the small molecule relaxation will be dominated by dipolar mechanisms with a correlation time indicative of the large protein complex. Our explorations of an inositol monophosphatase (the last step in DIP generation) localized four discrete binding sides for the thermoprotectant α-glutamate. This is a novel approach, and while the work did not fully explain how this solute protected the IMPase from thermal denaturation, it did showcase a new and exciting method to monitor weak binding in biological systems.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2016

Recommendations for diagnosing effective radiative forcing from climate models for CMIP6

The usefulness of previous Coupled Model Intercomparison Project (CMIP) exercises has been hampered by a lack of radiative forcing information. This has made it difficult to understand reasons for differences between model responses. Effective radiative forcing (ERF) is easier to diagnose than traditional radiative forcing in global climate models (GCMs) and is more representative of the eventual temperature response. Here we examine the different methods of computing ERF in two GCMs. We find that ERF computed from a fixed sea surface temperature (SST) method (ERF_fSST) has much more certainty than regression based methods. Thirty year integrations are sufficient to reduce the 5–95% confidence interval in global ERF_fSST to 0.1Wm ~2 . For 2xCO2 ERF, 30 year integrations are needed to ensure that the signal is larger than the local confidence interval over more than 90% of the globe. Within the ERF_fSST method there are various options for prescribing SSTs and sea ice. We explore these and find that ERF is only weakly dependent on the methodological choices. Prescribing the monthly averaged seasonally varying model’s preindustrial climatology is recommended for its smaller random error and easier implementation. As part of CMIP6, the Radiative Forcing Model Intercomparison Project (RFMIP) asks models to conduct 30 year ERF_fSST experiments using the model’s own preindustrial climatology of SST and sea ice. The Aerosol and Chemistry Model Intercomparison Project (AerChemMIP) will also mainly use this approach. Lastly, we propose this as a standard method for diagnosing ERF and recommend that it be used across the climate modeling community to aid future comparisons.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2022

A study of degradation mechanisms in PVDF-based photovoltaic backsheets

Abstract Commercial backsheets based on polyvinylidene fluoride (PVDF) can experience premature field failures in the form of outer layer cracking. This work seeks to provide a better understanding of the changes in material properties that lead to crack formation and find appropriate accelerated tests to replicate them. The PVDF-based backsheet outer layer can have a different structure and composition, and is often blended with a poly(methyl methacrylate) (PMMA) polymer. We observed depletion of PMMA upon aging with sequential (MAST) and combined (C-AST) accelerated stress testing. In field-aged samples from Arizona and India, where PVDF crystallizes in its predominant α-phase, the degree of crystallinity greatly increased. MAST and C-AST protocols were, to some extent, able to replicate the increase in crystallinity seen in PVDF after ~ 7 years in the field, but no single-stress test condition (UV, damp heat, thermal cycling) resulted in significant changes in the material properties. The MAST regimen used here was too extreme to produce realistic degradation, but the test was useful in discovering weaknesses of the particular PVDF-based outer layer structure studied. No excessive β-phase formation was observed after aging with any test condition; however, the presence of β-phase was identified locally by Fourier transform infrared spectroscopy (FTIR). We conclude that both MAST and C-AST are relevant tests for screening outdoor failure mechanisms in PVDF backsheets, as they were successful in producing material degradation that led to cracking.

14 SOLAR ENERGY↗

DOE OSTI2015

On the properties of Au2₂P₃ z (z = -1, 0, +1): analysis of geometry, interaction, and electron density

Au₂P₃, the only metastable binary phase of gold phosphide, has been discovered to exhibit remarkable semiconductor properties among metal phosphides. A systematic study on the geometry, the transformation of Au₂P₃ into different valence states and the different interactions among the atoms of the species is performed by using the density functional theory (DFT) method. The global minimum of Au₂P₃- is a 3D structure with C s symmetry. This structure could be distorted from a planar configuration of Au₂P₃ which decreases the steric effect on it and leads to a new stable configuration. An analogous planar configuration, a local minimum rather than a global minimum, is also found in Au₂P₃⁺, due to the electron effect acting on the structure. Natural bond orbital (NBO) analysis reveals the re-distribution progression of the charge within the species. The central located Au atom and another no. 5 positioned P atom play significant roles on the structures. P5, as an electron adjuster, balances the electron distribution at different valence states of the structures. Deformation density analysis supplies information about charge transfer and the bonding type between two adjacent atoms as well. Looking deep into the bonding types, as electron localization function (ELF) suggests, the interaction between two adjacent P atoms (P3 and P4) of Au₂P₃ belongs to a strong covalent bond. The Au–P interactions among the configurations could be classified as weak classical covalent bonds through the atoms in molecules (AIM) dual parameter analysis. And for the first time, the weak interaction between the two adjacent Au atoms (Au1 and Au2) of the charged states of Au₂P₃ (Au₂P₃⁻ and Au₂P₃⁺), are verified and different from the neutral Au₂P₃ through the reduced density gradient (RDG) analysis.

Environmental Molecular Sciences Laboratory↗

DOE OSTI2020

Black hole echoes

In this work, we consider a very simple model for gravitational wave echoes from black hole merger ringdowns which may arise from local Lorentz symmetry violations that modify graviton dispersion relations. If the corrections are sufficiently soft so they do not remove the horizon, the reflection of the infalling waves which trigger the echoes is very weak. As an example, we look at the dispersion relation of a test scalar field corrected by rotonlike operators depending only on spatial momenta, in Gullstrand-Painlevé coordinates. The near-horizon regions of a black hole do become reflective, but only very weakly. The resulting “bounces” of infalling waves can yield repetitive gravity wave emissions but their power is very small. This implies that to see any echoes from black holes we really need an egregious departure from either standard GR or effective field theory, or both. One possibility to realize such strong echoes is the recently proposed classical firewalls which replace black hole horizons with material shells surrounding timelike singularities.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS1985

Martian meteorology and dust storms from Viking observations

Analysis of Viking lander data on atmospheric pressure and temperature variations showed that planning for a manned base will require careful consideration of the effects of local and global dust storms. It is demonstrated that there may be preferred seasons for landing when dust storms are not at maximum strength, as well as preferred latitudes where dust storms are uncharacteristically weak. Viking I data on the diurnal variation in pressure and temperature prior to and during dust storm events are reproduced in graphic form.

Tillman, J. E.↗