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At least 1,099 records · Page 61
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Linear downscaling from MODIS to landsat: connecting landscape composition with ecosystem functions

The open and free access to Landsat and MODIS products have greatly promoted scientific investigations on spatiotemporal change in land mosaics and ecosystem functions at landscape to regional scales. Unfortunately, there is a major mismatch in spatial resolution between MODIS products at coarser resolution (≥ 250 m) and landscape structure based on classified Landsat scenes at finer resolution (30 m). Based on practical needs for downscaling popular MODIS products at 500 m resolution to match classified land cover at Landsat 30 m resolution, we proposed an innovative modelling approach so that landscape structure and ecosystem functions can be directly studied for their interconnections. As a proof-of-concept of our downscaling approach, we selected the watershed of the Kalamazoo River in southwestern Michigan, USA as the testbed. MODIS products for three fundamental variables of ecosystem function are downscaled to ensure the approach can be extrapolated to multiple functional measurements. They are blue-sky albedo (0–1), evapotranspiration (ET, mm), and gross primary production (GPP, Mg C ha -1 year -1 ). An object-oriented classification of Landsat images in 2011 was processed to generate a land cover map for landscape structure. The downscaling model was tested for the five Level IV ecoregions within the watershed. We achieved satisfactory downscaling models for albedo, ET, and GPP for all five ecoregions. The adjusted R2 was > 0.995 for albedo, 0.915–0.997 for ET, and 0.902–0.962 for GPP. The estimated albedo, ET, and GPP values appear different in the region. The estimated albedo was the lowest for water (0.076–0.107) and the highest for cropland (0.166–0.172). Estimated ET was the highest for the built-up cover type (525.6–687.1 mm) and the lowest for forest (209.7–459.7 mm). The estimated GPP was the highest for the build-up cover type (8.65–9.85 Mg C ha -1 year -1 ) and the lowest for forest. Estimated values for albedo, ET, and GPP appear reasonable for their ranges in the Kalamazoo River region and are consistent with values reported in the literature. Despite these promising results, the downscaling approach relies on strong assumptions and can carry substantial uncertainty. Finally, it is only valid at a spatial scale where similar climate, soil, and landforms exist (i.e., values in isolated patches of the same cover type are similar). Plausibly, the uncertainties associated with each estimation, as well as the model residuals, can be explored for other pattern-process relationships within the landscape.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2021

Accounting for connectivity alters the apparent roles of spatial and environmental processes on metacommunity assembly

Understanding the relative contributions of spatial and environmental processes on community assembly is a central question in ecology. Despite this long-standing interest, our understanding of how landscape structure may drive spatial processes of community assembly remains poorly understood in part because of the challenge of tracking community assembly across landscapes and quantifying key aspects of landscapes that may impact assembly processes. Here, we examined the roles of spatial and environmental processes on structuring assemblies of ants in 72 cleared patches embedded within a forested landscape.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2026

Ecological connectivity and habitat loss shape patterns of genetic diversity in a threatened salamander

Context The maintenance of genetic diversity is essential for preserving adaptive potential in populations, yet it is increasingly threatened by landscape alteration. The field of landscape genetics offers a framework for assessing how patch-level landscape conditions, modeled at multiple scales, influence genetic diversity. Objectives We sought to assess how local environmental features and connectivity influence genetic diversity across 74 four-toed salamander (Hemidactylium scutatum) breeding wetlands in the southeastern United States. Methods Using next-generation sequencing data and hierarchical Bayesian models, we examined genome-wide heterozygosity in relation to local landscape features and ecological connectivity. We also assessed the scale of effect of landscape features and tested for temporal lag effects. Results Genetic diversity was lower in wetlands with higher levels of historic deforestation and lower connectivity. An interaction between deforestation and connectivity indicated that deforestation had stronger negative effects in isolated wetlands but weaker effects in well-connected wetlands. Accounting for scale of effect and temporal lags was critical for detecting these relationships. Conclusions Our analyses highlight the importance of assessing the spatial scale (scale of effect) and temporal lag of landscape features to detect key drivers of genetic diversity. In line with population genetic theory, our results indicate that the genetic consequences of habitat loss do not affect populations uniformly and are most severe in isolated populations where gene flow cannot buffer against loss of diversity. Altogether, we highlight the importance of considering the interaction of habitat loss and connectivity in conservation genetic management.

Hemidactylium scutatum↗
DOE OSTI2019

Design of a wideband microstrip nanoantenna array

This paper presents the design of a logarithmic array of microstrip nano-antennas at terahertz frequencies. For applications in which small antennas are required, microstrip antennas are preferred. However, they have a narrow bandwidth. To overcome this problem in microstrip antennas, a log-periodic nanoantenna design is presented which exhibits a wide bandwidth and ultra-compact design. This antenna is smaller in size compared to log-periodic antennas in microwave bands and comparable and better radiation characteristics. The proposed Log-periodic microstrip nanoantenna array consists of seven patch elements on a dielectric layer and are fed directly by a feed line through the branch lines connected to each of the elements. Scaling factor, τ = 0.95 is considered for this design and inset feed is used. In this structure, the substrate has a relative dielectric constant of ε{sub r} = 4.4 and a thickness of h = 800 nm. For good performance at high frequencies, gold is used for the design of the antenna. The considered operating frequency is 3.3 THz corresponding to a wavelength of 91 µm. Good impedance matching and a wide bandwidth of 800 GHz is obtained.

42 ENGINEERING↗
DOE OSTI2019

Channel capacity enhancement by adjustable graphene-based MIMO antenna in THz band

This paper offers the design of a graphene-based MIMO antenna with an adjustable radiation pattern for THz communications. To make the radiation pattern adjustable a superstrate layer of graphene based patch, is added to the designed MIMO antenna which increases Channel Capacity. In addition to adjustable radiation pattern, the gain of antenna in the main lobe is also increased. The losses of THz channel is investigated and the angle of the main lobe of the designed antenna is set to the angle with the lowest loss. The channel capacity is evaluated and compared with the antenna without the superstrate layer. It is shown that channel capacity is significantly enhanced.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2024

Identification and characterization of the low molecular mass ferredoxins involved in central metabolism in Heliomicrobium modesticaldum

The homodimeric Type I reaction center (RC) from Heliomicrobium modesticaldum lacks the PsaC subunit found in Photosystem I and instead uses the interpolypeptide [4Fe–4S] cluster F X as the terminal electron acceptor. Our goal was to identify which of the small mobile dicluster ferredoxins encoded by the H. modesticaldum genome are capable of accepting electrons from the heliobacterial RC (HbRC) and pyruvate:ferredoxin oxidoreductase (PFOR), a key metabolic enzyme. Analysis of the genome revealed seven candidates: HM1_1462 (PshB1), HM1_1461 (PshB2), HM1_2505 (Fdx3), HM1_0869 (FdxB), HM1_1043, HM1_0357, and HM1_2767. Heterologous expression in Escherichia coli and studies using time-resolved optical spectroscopy revealed that only PshB1, PshB2, and Fdx3 are capable of accepting electrons from the HbRC and PFOR. Modeling studies using AlphaFold show that only PshB1, PshB2, and Fdx3 should be capable of docking on PFOR at a positively charged patch that overlays a surface-proximal [4Fe–4S] cluster. Proteomic analysis of wild-type and gene deletion strains ΔpshB1, ΔpshB2, ΔpshB1pshB2, and Δfdx3 grown under nitrogen-replete conditions revealed that Fdx3 is undetectable in the wild-type, ΔpshB1, and Δfdx3 strains, but it is present in the ΔpshB2 and ΔpshB1pshB2 strains, implying that Fdx3 may substitute for PshB2. When grown under nitrogen-deplete conditions, Fdx3 is present in the wild-type and all deletion strains except for Δfdx3. None of the knockout strains demonstrated significant impairment during chemotrophic dark growth on pyruvate, photoheterotrophic light growth on pyruvate, or phototrophic growth on acetate+CO 2 , indicating a high degree of redundancy among these three electron transfer proteins. As a result, loss of both PshB1 and PshB2, but not FdxB, resulted in poor growth under N 2 -fixing conditions.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2026

Reactive Transport Modeling with Physics-Informed Machine Learning for Critical Minerals Applications

This study presents a physics-informed neural network (PINN) framework for reactive transport modeling for simulating fast bimolecular reactions in porous media. Accurate characterization of cAhemical interactions and product formation in surface and subsurface environments is essential for advancing critical mineral extraction and related geoscience applications. The proposed methodology sequentially addresses the flow and diffusion–reaction subproblems. The flow field is computed using a mixed formulation, while the diffusion–reaction system is modeled via two uncoupled tensorial diffusion equations reformulated in terms of chemical invariants. PINNs are employed to solve the governing equations, enabling data-efficient, mesh-free prediction of chemical concentration fields. The framework is validated through a series of benchmark problems involving flow in heterogeneous porous media. Initial verification is conducted using patch tests for the flow field, followed by validation of the transport problem with emphasis on preserving non-negativity of concentrations. The complete fast bimolecular reaction scenario is then solved, yielding spatial distributions of reactants and product species. Results demonstrate that the PINNs-based approach effectively captures sharp, mixing-limited reaction fronts and dispersive mixing behavior, offering reliable predictions of reactive plume evolution. These capabilities are crucial for evaluating long-term subsurface behavior in applications such as fluid storage, energy extraction, and efficient extraction of critical minerals.

42 ENGINEERING↗
DOE OSTI2018

Effects of Reoxidation of Liquid Steel and Slag Composition on the Chemistry Evolution of Inclusions During Electroslag Remelting

Electroslag remelting (ESR) is increasingly used to produce some varieties of special steels and alloys, mainly because of its ability to provide extreme cleanliness and an excellent solidification structure simultaneously. In the present study, the combined effects of varying SiO{sub 2} contents in slag and reoxidation of liquid steel on the chemistry evolution of inclusions and the alloying element content in steel during ESR were investigated. The inclusions in the steel before ESR refining were found to be oxysulfides of patch-type (Ca,Mn)S adhering to a CaO-Al{sub 2}O{sub 3}-SiO{sub 2}-MgO inclusion. The oxide inclusions in both the liquid metal pool and remelted ingots are CaO-Al{sub 2}O{sub 3}-MgO and MgAl{sub 2}O{sub 4} together with CaO-Al{sub 2}O{sub 3}-SiO{sub 2}-MgO inclusions (slightly less than 30 pct of the total inclusions), which were confirmed to originate from the reduction of SiO{sub 2} from the original oxide inclusions by dissolved Al in liquid steel during ESR. CaO-Al{sub 2}O{sub 3}-MgO and MgAl{sub 2}O{sub 4} are newly formed inclusions resulting from the reactions taking place inside liquid steel in the liquid metal pool caused by reoxidation of liquid steel during ESR. Increasing the SiO{sub 2} content in slag not only considerably reduced aluminum pickup in parallel with silicon loss during ESR, but also suppressed the decrease in SiO{sub 2} content in oxide inclusions. (Ca,Mn)S inclusions were fully removed before liquid metal droplets collected in the liquid metal pool.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Evolution of Oxide–Sulfide Complex Inclusions and Its Correlation with Steel Cleanliness During Electroslag Rapid Remelting (ESRR) of Tool Steel

The evolution of CaO-Al{sub 2}O{sub 3}-MgO-(SiO{sub 2}) inclusions associated with CaS during electroslag rapid remelting (ESRR) of the tool steel with ultra low oxygen (8 ppm) under protective atmosphere was investigated. Thermodynamic calculation was performed to evaluate the oxygen level of liquid steel and the inclusion evolution during ESRR with the help of FactSage software (CON2 database). The results demonstrated that the reoxidation of liquid steel took place during industrial ESRR, resulting in the oxygen pickup of approximately double content. The oxygen level in the steel was determined by [Al]-[O] equilibrium during ESRR, whereas FeO in the slag transferred oxygen into the liquid steel, as indicated by the significant oxygen pickup. The inclusions in the steel electrode are oxide–sulfide type of CaO-Al{sub 2}O{sub 3}-MgO partially wrapped with CaS. The original oxide inclusions that had not been removed in ESRR process were transformed to liquid CaO-Al{sub 2}O{sub 3}-SiO{sub 2}-MgO inclusions through reacting with the dissolved oxygen supplied from the reoxidation of liquid steel and concerned elements in liquid steel during ESRR. These CaO-Al{sub 2}O{sub 3}-SiO{sub 2}-MgO inclusions were invariably associated with patch-type or shell-type CaS, which hold different formation mechanisms. The inclusions ranging from 2 to 4 µm take up a dominant proportion (a little more than 50 pct of the total inclusions) in the remelted ingots, and those larger than 8 µm account for about 3 pct. Melting rates of ESRR not only exerted a negligible effect on the steel cleanliness and the removal efficiency of oxide inclusions, but also on the inclusion size distribution.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Orientation Relationships of Pure Tin on Single Crystal Germanium Substrates

The limited number of independent β-Sn grain orientations resulting from the difficulty in nucleating β-Sn during solidification of Sn-based solders has a large effect on the resulting β-Sn grain size and, hence, on overall solder joint performance and reliability. This study analyzes the efficacy of Ge as a heterogeneous nucleation agent for β-Sn by observing the morphologies and orientation relationships of as-deposited, solid-state annealed, and liquid-state annealed pure Sn films on single crystal Ge (100), (110), and (111) substrates. Here, the results from scanning electron microscopy and electron backscatter diffraction showed that the as-deposited Sn films all deposited with a Sn (001)|| z-axis texture, regardless of the underlying Ge substrate orientation. Solid-state annealing at 150 °C for 5 min did not result in significant dewetting of the Sn films, and the films maintained their as-deposited texture of Sn (001)|| z-axis, regardless of the underlying Ge substrate orientation. Liquid-state annealing at 235 °C for 1 min resulted is large-scale dewetting of the Sn films and re-orientation of the Sn films on the various Ge substrates. After solidification, the Ge (100) and (110) single crystal substrates produced patches of dewetted grains of the same orientation but there were no consistent Sn grain textures after liquid-state annealing, suggesting no single orientation relationship. In contrast, solidification on Ge (111) single crystal substrates resulted in isolated grains with a single Sn film texture and an orientation relationship of (100) Sn ∥(111) Ge and [100] Sn ∥[110] Ge . Density Functional Theory simulations of the experimentally observed Ge (111) sample orientation relationship and the Ge/Sn cube-on-cube orientation relationship suggest favorable relative interfacial binding energies for both interface orientations.

36 MATERIALS SCIENCE↗
DOE OSTI2014

The method of imbedded Lagrangian element to estimate wave power absorption by some submerged devices

A simple approach is described to estimate the wave power absorption potential of submerged devices known to cause wave focusing and flow enhancement. In particular, the presence of a flow-through power take-off (PTO) system, such as low-head turbines, can be accounted for. The wave radiation characteristics of an appropriately selected Lagrangian element (LE) in the fluid domain are first determined. In the limit of a vanishing mass, the LE reduces to a patch of distributed normal dipoles. Here, the hydrodynamic coefficients of this virtual object are then input in a standard equation of motion where the effect of the PTO can be represented, for example, as a dashpot damping term. The process is illustrated for a class of devices recently proposed by Carter and Ertekin (2011), although in a simplified form. Favorable wave power absorption is shown for large ratios of the LE wave radiation coefficient over the LE added mass coefficient. Under optimal conditions, the relative flow reduction from the PTO theoretically lies between 0.50 and 1/√2≈ 0.71, with lower values corresponding to better configurations. Wave power capture widths, the sensitivity of results to PTO damping and sample spectral calculations at a typical site in Hawaiian waters are proposed to further illustrate the versatility of the method.

16 TIDAL AND WAVE POWER↗
DOE OSTI2024

ESM data downscaling: a comparison of super-resolution deep learning models

Abstract Climate projections at fine spatial resolutions are required to conduct accurate risk assessment for critical infrastructure and design adaptation planning. Generating these projections using advanced Earth system models (ESM) requires significant computational resources. To address this issue, various statistical downscaling techniques have been introduced to generate fine-resolution data from coarse-resolution simulations. In this study, we evaluate and compare five deep learning-based downscaling techniques, namely, super-resolution convolutional neural networks, fast super-resolution convolutional neural network ESM, efficient sub-pixel convolutional neural network, enhanced deep residual network (EDRN), and super-resolution generative adversarial network (SRGAN). These techniques are applied to a dataset generated by the Energy Exascale Earth System Model (E3SM), focusing on key surface variables such as surface temperature, shortwave heat flux, and longwave heat flux. Models are trained and validated using paired fine-resolution (0.25 $$^{\circ }$$ ∘ ) and coarse-resolution (1 $$^{\circ }$$ ∘ ) monthly data obtained from a 9-year simulation. Next, blind testing is performed using monthly data obtained from two different years outside of the training and validation set. To evaluate the efficiency of each technique, different statistical metrics are used, including mean squared error (MSE), peak signal-to-noise ratio (PSNR), structural similarity index measure (SSIM), and learned perceptual image patch similarity (LPIPS). The results show that EDRN outperforms other algorithms in terms of PSNR, SSIM, and MSE, but struggles to capture fine-scale features in the data. In contrast, SRGAN, a generative model that uses perceptual loss, excels in capturing fine details at boundaries and internal structures, resulting in lower LPIPS than other methods.

Pawar, Nikhil M. (ORCID:0000000211613289)↗
DOE OSTI2018

Minimum fuel trajectories for round trip lunar missions

In this work, a study about minimum fuel trajectories in a round trip journey to the Moon is presented. It is assumed that the velocity changes are instantaneous, that is, the propulsion system is capable of delivering impulses such that the fuel consumption is represented by the total velocity increment applied to the space vehicle. It is also assumed that the velocity increments are applied tangentially to the terminal orbits, and, the outgoing trip and the return trip are analyzed separately such that the whole mission is performed with four impulses (two impulses in each trip). The mathematical models used to describe the motion of the space vehicle are three: the lunar patched-conic approximation; the classic planar circular restricted three-body problem, and, the planar bi-circular restricted four-body problem (PBR4BP). For computing the optimal trajectories, the Sequential Gradient-Restoration Algorithm with constraints is used. The influence of the Sun on round trip lunar missions is analyzed through the PBR4BP model. For all models, the trajectories studied are direct ascent maneuvers, and, both the outgoing and return trips are considered. The results obtained through the different models are compared with each other. The optimal results for the PBR4BP model show that a small reduction of the fuel consumption can be achieved if the initial phase angle of the Sun is chosen properly.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Batch Active Learning for Multispectral and Hyperspectral Image Segmentation Using Similarity Graphs

Abstract Graph learning, when used as a semi-supervised learning (SSL) method, performs well for classification tasks with a low label rate. We provide a graph-based batch active learning pipeline for pixel/patch neighborhood multi- or hyperspectral image segmentation. Our batch active learning approach selects a collection of unlabeled pixels that satisfy a graph local maximum constraint for the active learning acquisition function that determines the relative importance of each pixel to the classification. This work builds on recent advances in the design of novel active learning acquisition functions (e.g., the Model Change approach in arXiv:2110.07739) while adding important further developments including patch-neighborhood image analysis and batch active learning methods to further increase the accuracy and greatly increase the computational efficiency of these methods. In addition to improvements in the accuracy, our approach can greatly reduce the number of labeled pixels needed to achieve the same level of the accuracy based on randomly selected labeled pixels.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2021

How to create an artificial magnetosphere for Mars

If humanity is ever to consider substantial, long-term colonization of Mars, the resources needed are going to be extensive. For a long-term human presence on Mars to be established, serious thought would need to be given to terraforming the planet. One major requirement for such terraforming is having the protection of a planetary magnetic field - which Mars currently does not have. Here, the Earth's magnetosphere helps protect the planet from the potential sterilizing effects of cosmic rays and also helps retain the atmosphere, which would otherwise by stripped by large solar storms as they pass over the planet. Mars does have small patches of remnant surface magnetic field, but these are localized in the southern hemisphere and are not of sufficient size or magnitude to protect the planet or a colony.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Coarsening of complex microstructures following spinodal decomposition

Coarsening plays a pivotal role in materials engineering, but our understanding of the dynamics of coarsening in morphologically complex systems is still limited. In this paper, we examine the correlations between the interfacial velocity and interfacial morphologies, and then predict the evolution of mean curvature based on the correlations. Three simulated structures with varying volume fractions, two bicontinuous and one nonbicontinuous, are generated using the Cahn-Hilliard equation. We find general correlations between interfacial velocity and mean curvature, as well as between interfacial velocity and the surface Laplacian of the mean curvature. Furthermore, we find that the probability of finding a patch of interface with a given normal velocity and the same local principal curvatures is described well by a Gaussian distribution, independent of the principal curvature values and the volume fractions of the structures. We also find that average interfacial velocity is described by a polynomial of the mean curvature and the net curvature. Based on this finding, we develop a semi-analytical approach to predicting the rate of change of the mean curvature, which determines the morphological evolution of complex microstructures.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Atomistic modeling of interface strengthening in Al-Si eutectic alloys

Al-Si cast alloys are usually composed of α-Al and Al-Si eutectic. Si flakes and Al matrix generally hold cube-on-cube orientation relationship with the primary interface (111) Al ∥(111) Si . Extensive experimental studies demonstrated that Si flakes cannot significantly improve mechanical properties of Al-Si cast alloys. We hypothesize that the weak strengthening effect associated with Si flakes might be attributed to thermomechanical properties of Al-Si interfaces besides their morphologies. To characterize Al-Si interfaces with a large lattice mismatch (> 30%), we proposed the quasi-coincident site lattice (Q-CSL) as reference lattice, and demonstrated that the Q-CSL Al-Si coherent interface has three characteristic coherent structures, one stable and low energy structure and two metastable and high energy structures. The translation vectors for the same type of coherent Q-CSL structures are consistent with three displacement shift complete (DSC) vectors. The two metastable structures can be obtained by shifting the low energy structure with three partial DSC vectors. Semi-coherent interface is composed of the low energy Q-CSL patches and three sets of interface misfit dislocations with Burgers vectors same as the DSC vectors. Atomistic simulations revealed that Al-Si interface exhibits low shear resistance. Ideal shear strength of the Q-CSL coherent interface is 110 MPa and semi-coherent interface is 20 MPa. The low shear resistance is attributed to the glide of interface misfit dislocations. Al-Si interface also exhibits low formation and migration energies of point defects. Owing to low shear strength and low formation and migration energies of point defects, interface sliding or shear readily happen under mechanical loading or during dislocation-interface interactions. Lattice dislocations can cross slip onto or climb along Al-Si interfaces. These reactions decrease the number of accumulated dislocation loops around Si flakes and promote nucleation and emission of lattice dislocations from Al-Si interfaces to matrix, consequently reduce the repulsive force on approaching dislocations and weaken Si flakes strengthening effect. In situ tension and compression tests in a scanning electron microscope reveal relatively weak strengthening effect due to Si flakes, consistent with the computed dislocation interaction with interfaces and shear behavior of interfaces.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Gas pore correlations in laser powder bed fusion of Al6061

Additive manufacturing (AM) of metal materials based on powder bed fusion technology is widely used now in many industries. A known limitation of this type of manufacturing is the formation of gas pores in the bulk material. Here we present a combined X-ray imaging and mid-infrared pyrometry study of pore formation in side-by-side tracks of Al6061 for different processing conditions using both in-situ and post-processing analysis. By carefully quantifying the distributions and correlations of pore positions, we show that an existing pore in one track often catalyzes the formation of another pore in an adjacent track. In a raster scan strategy commonly used to construct bulk material, this phenomenon has the result of forming subsurface perforations, or lines of pores transverse to the scanning direction in a rastered patch. If controlled, this effect can be eliminated to improve the yield strength of the build, or exploited to create programmable failures for specific purposes.

36 MATERIALS SCIENCE↗