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At least 433 records · Page 24
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Establishment of a Nationwide Plasma Science and Fusion Energy Certification and Apprenticeship Programs

Here we propose the establishment of a national Plasma Science and Fusion Energy training program that will combine professional development certification courses with hands-on apprenticeship opportunities. The program should be developed by a collaboration of stakeholders (academia, national laboratories, and industry) and should offer pathways for students from community colleges (CCs), minority-serving institutions (MSIs), high school graduates, and veterans. We argue that certification courses offer fast and flexible discipline-specific education that can be rapidly translated into marketable skills through hands-on apprenticeship opportunities. Furthermore, we first list major findings and recommendations related to the fusion workforce and discuss how to address them through the establishment of the proposed training program. We then highlight the appropriateness of this format for engagement with CCs, MSIs, high schools, and veteran employment services. In the final section, we provide a strategy for the establishment of the program, along with a tentative timeline and projected costs.

Certification↗
DOE OSTI2012

MOLECULAR LINE OBSERVATIONS OF MCLD 123.5+24.9 IN THE POLARIS CIRRUS

In this paper, we present results of millimeter-wave observations with various molecular lines made toward MCLD 123.5+24.9 in the Polaris cirrus using the 45 m telescope at Nobeyama Radio Observatory. MCLD 123.5+24.9 is one of the rare dense cores forming in diffuse cirrus clouds where star formation may rarely take place. In order to investigate the structure, dynamics, the evolutionary stage of MCLD 123.5+24.9, we observed this core in 17 emission lines from 13 different molecular species. Emission lines of CS, CCS, and HC{sub 3}N are strongly detected all over the core, while those of SO and N{sub 2}H{sup +} are weak or remain undetected, indicating that MCLD 123.5+24.9 is in an early stage of core evolution in terms of chemical composition. Based on comparison of the fractional abundances of CCS and HC{sub 3}N, which are considered indicators of chemical age, with those of other cores with and without star formation as well as with model calculations in the literature, we suggest that MCLD 123.5+24.9 is in a phase prior to star formation. From the C{sup 18}O data obtained, we derived the total molecular mass of MCLD 123.5+24.9 to be {approx}3 M{sub Sun} at an assumed distance of 150 pc. There are three subcores in MCLD 123.5+24.9, called CS-A, CS-B, and CS-C. We derived their masses to be 0.2-0.6 M{sub Sun }. We also investigated the dynamical stability of MCLD 123.5+24.9 and the subcores by applying the virial theorem to find that MCLD 123.5+24.9 is not gravitationally bound as a whole, while the individual subcores are in the virial equilibrium and can collapse with a small increase of external pressure imposed on their surfaces.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

CHEMISTRY IN DISKS. VII. FIRST DETECTION OF HC{sub 3}N IN PROTOPLANETARY DISKS

Molecular line emission from protoplanetary disks is a powerful tool to constrain their physical and chemical structure. Nevertheless, only a few molecules have been detected in disks so far. We take advantage of the enhanced capabilities of the IRAM 30 m telescope by using the new broadband correlator (fast Fourier Transform Spectrometer) to search for so far undetected molecules in the protoplanetary disks surrounding the T Tauri stars DM Tau, GO Tau, LkCa 15, and the Herbig Ae star MWC 480. We report the first detection of HC{sub 3}N at 5{sigma} in the GO Tau and MWC 480 disks with the IRAM 30 m, and in the LkCa 15 disk (5{sigma}), using the IRAM array, with derived column densities of the order of 10{sup 12} cm{sup -2}. We also obtain stringent upper limits on CCS (N < 1.5 Multiplication-Sign 10{sup 12} cm{sup -3}). We discuss the observational results by comparing them to column densities derived from existing chemical disk models (computed using the chemical code Nautilus) and based on previous nitrogen- and sulfur-bearing molecule observations. The observed column densities of HC{sub 3}N are typically two orders of magnitude lower than the existing predictions and appear to be lower in the presence of strong UV flux, suggesting that the molecular chemistry is sensitive to the UV penetration through the disk. The CCS upper limits reinforce our model with low elemental abundance of sulfur derived from other sulfur-bearing molecules (CS, H{sub 2}S, and SO).

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

ON THE ROAD TO MORE REALISTIC GALAXY CLUSTER SIMULATIONS: THE EFFECTS OF RADIATIVE COOLING AND THERMAL FEEDBACK PRESCRIPTIONS ON THE OBSERVATIONAL PROPERTIES OF SIMULATED GALAXY CLUSTERS

Flux-limited X-ray surveys of galaxy clusters show that clusters come in two roughly equally proportioned varieties: 'cool core' clusters (CCs) and non-'cool core' clusters (NCCs). In previous work, we have demonstrated using cosmological N-body + Eulerian hydrodynamic simulations that NCCs are often consistent with early major merger events that destroy embryonic CCs. In this paper we extend those results and conduct a series of simulations using different methods of gas cooling and of energy and metal feedback from supernovae, where we attempt to produce a population of clusters with realistic central cooling times, entropies, and temperatures. We find that the use of metallicity-dependent gas cooling is essential to prevent early overcooling, and that adjusting the amount of energy and metal feedback can have a significant impact on observable X-ray quantities of the gas. We are able to produce clusters with more realistic central observable quantities than have previously been attained. However, there are still significant discrepancies between the simulated clusters and observations, which indicates that a different approach to simulating galaxies in clusters is needed. We conclude by looking toward a promising subgrid method of modeling galaxy feedback in clusters that may help to ameliorate the discrepancies between simulations and observations.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

A BAYESIAN METHOD FOR THE ANALYSIS OF THE DUST EMISSION IN THE FAR-INFRARED AND SUBMILLIMETER

We present a method, based on Bayesian statistics, to fit the dust emission parameters in the far-infrared and submillimeter wavelengths. The method estimates the dust temperature and spectral emissivity index, plus their relationship, properly taking into account the statistical and systematic uncertainties. We test it on three sets of simulated sources detectable by the Herschel Space Observatory in the PACS and SPIRE spectral bands (70-500 {mu}m), spanning over a wide range of dust temperatures. The simulated observations are a one-component interstellar medium and two two-component sources, both warm (H II regions) and cold (cold clumps (CCs)). We first define a procedure to identify the better model, then we recover the parameters of the model and measure their physical correlations by means of a Markov Chain Monte Carlo algorithm adopting multi-variate Gaussian priors. In this process, we assess the reliability of the model recovery and of parameter estimation. We conclude that the model and parameters are properly recovered only under certain circumstances and that false models may be derived in some cases. We applied the method to a set of 91 starless CCs in an interarm region of the Galactic plane with low star formation activity, observed by Herschel in the Hi-GAL survey. Our results are consistent with a temperature-independent spectral index.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Influence of superconductor film composition on adhesion strength of coated conductors

The effect of high temperature superconductor (HTS) film composition on the adhesion strength of rare- earth barium copper oxide coated conductors (CCs) has been studied. It has been found that the mechanical integrity of the superconductor layer is very susceptible to the defects especially those along the ab plane, probably due to the weak interfaces between the defects and the matrix. Gd and Y in the standard composition were substituted with Sm and the number of in-plane defects was drastically reduced. Consequently, a four-fold increase in adhesion or peeling strength in Sm-based CCs was achieved compared to the standard GdYBCO samples.

Kesgin, Ibrahim↗
DOE OSTI2016

Feasibility and electromagnetic analysis of a REBCO superconducting undulator

Recent advances in second-generation (2G) high temperature superconducting (HTS) coated conductors (CCs) have made them very attractive for new applications such as undulators. In this study, we have, for the first time, experimentally evaluated a design to validate applicability of 2G-HTS tapes for next generation undulator magnetic structures. A two-period undulator magnetic core was fabricated and 2G-HTS CCs were successfully wound onto the undulator core. The performance of the undulator magnetic structure was investigated and the highest engineering current density, J e , in such configuration reported yet was obtained. A new U-slit tape configuration was used to reduce the number of resistive joints and it was shown that with this new technique affordable levels of resistance values can be achieved for short length undulators. The ferromagnetic core was designed such as to accommodate winding the U-slit tapes. Finally, test results indicated that the winding and the soldering procedures are successful and do not deteriorate the performance of the 2G-HTS tapes.

2G-HTS↗
DOE OSTI2015

Measurement of fluid rotation, dilation, and displacement in particle image velocimetry using a Fourier–Mellin cross-correlation

Traditional particle image velocimetry (PIV) uses discrete Cartesian cross correlations (CCs) to estimate the displacements of groups of tracer particles within small subregions of sequentially captured images. However, these CCs fail in regions with large velocity gradients or high rates of rotation. In this paper, we propose a new PIV correlation method based on the Fourier–Mellin transformation (FMT) that enables direct measurement of the rotation and dilation of particle image patterns. In previously unresolvable regions of large rotation, our algorithm significantly improves the velocity estimates compared to traditional correlations by aligning the rotated and stretched particle patterns prior to performing Cartesian correlations to estimate their displacements. Furthermore, our algorithm, which we term Fourier–Mellin correlation (FMC), reliably measures particle pattern displacement between pairs of interrogation regions with up to ±180° of angular misalignment, compared to 6–8° for traditional correlations, and dilation/compression factors of 0.5–2.0, compared to 0.9–1.1 for a single iteration of traditional correlations.

42 ENGINEERING↗
DOE OSTI2026

Variation in supercurrent connectivity and vortex pinning of state-of-the-art pulsed laser deposited RE Ba 2 Cu 3 O 7- x coated conductors

REBa 2 Cu 3 O 7-x (REBCO, RE: rare earth) coated conductors (CCs) suffer from great critical current I c differences between different manufacturers, I c variations within individual manufacturers, and often significant lengthwise fluctuations. The understanding of such variations is complicated by the lack of a direct correlation between I c and the critical current density J c . In fact, although J c is the fundamental property determined by the local vortex pinning landscape, I c is often limited by variable current blocking mechanisms. An important practical complexity is commercial practices of performing J c and I c evaluations based on I c at 77 K and self-field (sf), where connectivity variation dominates over vortex pinning variations. However, at higher fields and lower temperatures, vortex pinning becomes more complex and highly variable, making predictions of I c and J c at arbitrary temperature T, magnetic field H, and field orientation θ, quite uncertain. To address some aspects of this problem, we conducted detailed spool-to-spool performance characterization on recently manufactured REBCO CCs. Despite J c (77 K, sf) varies by only ∼11%, J c (77 K, 1 T) of its minimum and maximum (for H//ab-plane) show variations of ∼21% and ∼32%, respectively. This emphasizes the shortcoming in using J c (77 K, sf) as parameter for evaluating even the low field performance. An even more remarkable spool-to-spool J c variation of ∼68% was observed at 20 K and 15 T for H//ab-plane. To identify the origin of such lack of reproducibility we performed microstructural characterizations, which revealed, within the REBCO layer, large variation in the density of copper oxide (CuO x ) particles ranging from 0.1 to 2 μm in size. We believe that they play a decisive role in reducing the effective cross-section of the REBCO layer by not simply blocking current themselves, but also by nucleating off-axis REBCO grains, whose misoriented grain boundaries adversely impact REBCO grain-to-grain connectivity. The REBCO growth associated with high density CuO x particles also leads to the more disordered spatial arrangement of BaHfO 3 precipitate arrays, which, when self-aligning along the ab-planes, generate stronger pinning enhancing J c (H//ab) at all temperatures. In this way, we established that variations of both connectivity and vortex pinning are thus directly coupled. Our results also explain why the so-called ‘lift-factor’, typically defined by the ratio between I c (T, H) and I c (77 K, sf), frequently turns out to be unreliable.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Climate and carbon budget implications of linked future changes in CO 2 and non-CO 2 forcing

The approximate proportional relationship between cumulative carbon emissions and instantaneous global temperature rise (the carbon budget approximation) has proven to be a useful concept to translate policy-relevant temperature objectives into CO 2 emissions pathways. However, when non-CO 2 forcing is changing along with CO 2 forcing, errors in the approximation increases. Using the GCAM model to produce an ensemble of ~3000 scenarios, we show that linked changes in CO 2 forcing, aerosol forcing, and non-CO 2 greenhouse gas (GHG) forcing lead to an increase in total non-CO 2 forcing over the 21st century across mitigation scenarios. This increase causes the relationship between instantaneous temperature and cumulative CO 2 emissions to become more complex than the proportional approximation often assumed, particularly for low temperature objectives such as 1.5 °C. The same linked changes in emissions also contribute to a near-term increase in aerosol forcing that effectively places a limit on how low peak temperature could be constrained through GHG mitigation alone. In particular, we find that 23% of scenarios that include CCS (but only 1% of scenarios that do not include CCS) achieve a temperature objective of 1.5 °C without temperature overshoot.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2011

OPTICAL LINE EMISSION IN BRIGHTEST CLUSTER GALAXIES AT 0 < z < 0.6: EVIDENCE FOR A LACK OF STRONG COOL CORES 3.5 Gyr AGO?

In recent years the number of known galaxy clusters beyond z {approx}> 0.2 has increased drastically with the release of multiple catalogs containing >30,000 optically detected galaxy clusters over the range 0 < z < 0.6. Combining these catalogs with the availability of optical spectroscopy of the brightest cluster galaxy (BCG) from the Sloan Digital Sky Survey allows for the evolution of optical emission-line nebulae in cluster cores to be quantified. For the first time, the continuous evolution of optical line emission in BCGs over the range 0 < z < 0.6 is determined. A minimum in the fraction of BCGs with optical line emission is found at z {approx} 0.3, suggesting that complex, filamentary emission in systems such as Perseus A is a recent phenomenon. Evidence for an upturn in the number of strongly emitting systems is reported beyond z > 0.3, hinting at an earlier epoch of strong cooling. We compare the evolution of emission-line nebulae to the X-ray-derived cool core (CC) fraction from the literature over the same redshift range and find overall agreement, with the exception that an upturn in the strong CC fraction is not observed at z > 0.3. The overall agreement between the evolution of CCs and optical line emission at low redshift suggests that emission-line surveys of galaxy clusters may provide an efficient method of indirectly probing the evolution of CCs and thus provide insights into the balance of heating and cooling processes at early cosmic times.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

The impact of regional resources and technology availability on carbon dioxide removal potential in the United States

To achieve net zero carbon emissions by mid-century, the United States may need to rely on carbon dioxide removal (CDR) to offset emissions from difficult-to-decarbonize sectors and/or shortfalls in near-term mitigation efforts. CDR can be delivered using many approaches with different requirements for land, water, geologic carbon storage capacity, energy, and other resources. The availability of these resources varies by region in the U.S. suggesting that CDR deployment will be uneven across the country. Using the global change analysis model for the United States (GCAM-USA), we modeled six classes of CDR and explored their potential using four scenarios: a scenario where all the CDR pathways are available (Full Portfolio), a scenario with restricted carbon capture and storage (Low CCS), a scenario where the availability of bio-based CDR options is limited (Low Bio), and a scenario with constraints on enhanced rock weathering (ERW) capabilities (Low ERW). We find that by employing a diverse set of CDR approaches, the U.S. could remove between 1 and 1.9 GtCO 2 /yr by midcentury. In the Full Portfolio scenario, direct air carbon capture and storage (DACCS) predominates, delivering approximately 50% of CO 2 removal, with bioenergy with carbon capture and storage contributing 25%, and ERW delivering 11.5%. Texas and the agricultural Midwest lead in CDR deployment due to their abundant agricultural land and geological storage availability. In the Low CCS scenario, reliance on DACCS decreases, easing pressure on energy systems but increasing pressure on the land. In all cases CDR deployment was found to drive important impacts on energy, land, or materials supply chains (to supply ERW, for example) and these effects were generally more pronounced when fewer CDR technologies were available.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2012

Enhancement of satellite precipitation estimation via unsupervised dimensionality reduction

A methodology to enhance Satellite Precipitation Estimation (SPE) using unsupervised dimensionality reduction (UDR) techniques is developed. This enhanced technique is an extension to the Precipitation Estimation from Remotely Sensed Imagery using an Artificial Neural Network (PERSIANN) and Cloud Classification System (CCS) method (PERSIANN-CCS) enriched using wavelet features combined with dimensionality reduction. Cloud-top brightness temperature measurements from Geostationary Operational Environmental Satellite (GOES-12) are used for precipitation estimation at 4 km 4 km spatial resolutions every 30 min. The study area in the continental United States covers parts of Louisiana, Arkansas, Kansas, Tennessee, Mississippi, and Alabama. Based on quantitative measures, root mean square error (RMSE) and Heidke skill score (HSS), the results show that the UDR techniques can improve the precipitation estimation accuracy. In addition, ICA is shown to have better performance than other UDR techniques; and in some cases, it achieves 10% improvement in the HSS.

Mahrooghy, Majid↗
DOE OSTI2014

Double-sided reel-to-reel metal-organic chemical vapor deposition system of YBa{sub 2}Cu{sub 3}O{sub 7-δ} thin films

Two-micrometer thick YBa{sub 2}Cu{sub 3}O{sub 7-δ} (YBCO) films have been successfully deposited on both sides of LaAlO{sub 3} single crystalline substrates by using a home-made reel-to-reel metal-organic chemical vapor deposition (MOCVD) system, which has two opposite symmetrical shower heads and a special-designed heater. This technique can simultaneously fabricate double-sided films with high deposition rate up to 500 nm/min, and lead to doubling current carrying capability of YBCO, especially for coated conductors (CCs). X-ray diffraction analysis showed that YBCO films were well crystallized and highly epitaxial with the full width at half maximum values of 0.2° ∼ 0.3° for the rocking curves of (005) YBCO and 1.0° for Φ-scans of (103) YBCO. Scanning electron microscope revealed dense, crack-free, slightly rough surface with Ba-Cu-O precipitates. The films showed critical current density (J{sub c}, 77 K, 0 T) of about 1 MA/cm{sup 2}, and overall critical current of 400 A/cm, ascribed to the double-sided structure. Our results also demonstrated that the temperature and composition in the deposition zone were uniform, which made MOCVD preparation of low cost and high performance double-sided YBCO CCs more promising for industrialization.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

SU-G-BRB-05: Automation of the Photon Dosimetric Quality Assurance Program of a Linear Accelerator

Purpose: To develop an automated method to calculate a linear accelerator (LINAC) photon radiation field size, flatness, symmetry, output and beam quality in a single delivery for flattened (FF) and flattening-filter-free (FFF) beams using an ionization chamber array. Methods: The proposed method consists of three control points that deliver 30×30, 10×10 and 5×5cm{sup 2} fields (FF or FFF) in a step-and-shoot sequence where the number of monitor units is weighted for each field size. The IC Profiler (Sun Nuclear Inc.) with 5mm detector spacing was used for this study. The corrected counts (CCs) were calculated and the locations of the maxima and minima values of the first-order gradient determined data of each sub field. Then, all CCs for each field size are summed in order to obtain the final profiles. For each profile, the radiation field size, symmetry, flatness, output factor and beam quality were calculated. For field size calculation, a parameterized gradient method was used. For method validation, profiles were collected in the detector array both, individually and as part of the step-and-shoot plan, with 9.9cm buildup for FF and FFF beams at 90cm source-to-surface distance. The same data were collected with the device (plus buildup) placed on a movable platform to achieve a 1mm resolution. Results: The differences between the dosimetric quantities calculated from both deliveries, individually and step-and-shoot, were within 0.31±0.20% and 0.04±0.02mm. The differences between the calculated field sizes with 5mm and 1mm resolution were ±0.1mm. Conclusion: The proposed single delivery method proved to be simple and efficient in automating the photon dosimetric monthly and annual quality assurance.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2016

Technical Note: Robust measurement of the slice-sensitivity profile in breast tomosynthesis

Purpose: The purpose of this work is to improve the repeatability of the measurement of the slice-sensitivity profile (SSP) in reconstructed breast tomosynthesis volumes. Methods: A grid of aluminum ball-bearings (BBs) within a PMMA phantom was imaged on breast tomosynthesis systems from three different manufacturers. The full-width half-maximum (FWHM) values were measured for the SSPs of the BBs in the reconstructed volumes. The effect of transforming the volumes from a Cartesian coordinate system (CCS) to a cone-beam coordinate system (CBCS) on the variability in the FWHM values was assessed. Results: Transforming the volumes from a CCS to a CBCS before measuring the SSPs reduced the coefficient of variation (COV) in the measurements of FWHM in repeated measurements by 56% and reduced the dependence of the FWHM values on the location of the BBs within the reconstructed volume by 76%. Conclusions: Measuring the SSP in the volumes in a CBCS improves the robustness of the measurement.

60 APPLIED LIFE SCIENCES↗