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At least 1,369 records · Page 76
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Simultaneously upgrading CO 2 and light alkanes into value-added products

We will discuss recent results from our group in reacting CO 2 and light alkanes to produce syngas, olefins, aromatics, and oxygenates. We will mainly use the simultaneous upgrading of CO 2 and ethane (SU-CO 2 Et) as examples to demonstrate the feasibility and reaction pathways of these processes. We will briefly discuss synthesis methods and essential structural characterization techniques that can be applied to SU-CO 2 Et catalysts. We will then illustrate how to identify and apply distinct active sites for different upgrading processes, using a combination of kinetic studies, in situ characterization, and density functional theory (DFT) calculations. We will conclude the Perspective by pointing out challenges and potential directions in catalyst design and synthesis, as well as structural characterization and mechanistic investigations, to further advance the simultaneous upgrading of CO 2 and light alkanes.

03 NATURAL GAS↗
DOE OSTI2019

Supply and value chain analysis of mixed biomass feedstock supply system for lignocellulosic sugar production

Here the sustainable supply of high-quality, low-cost biomass feedstock to cellulosic biorefineries is still a challenge. Utilizing corn stover as the single feedstock to a biorefinery also poses a source of risk to seasonal feedstock availability, affordability, and sustainability. Implementing a year-round feedstock switching strategy or utilizing an optimal mixture of corn stover, miscanthus, and switchgrass is demonstrated to diminish these concerns while reducing the cost of sugar production by as much as 3.8% and 13.6%, respectively, when compared to a baseline sugar price of 441.9 $ metric ton-1 (t) attributed to a fixed corn stover feedstock basis. This study determines that a mixing ratio of corn stover, miscanthus, and switchgrass of 36%, 50%, and 14%, respectively, minimizes the selling price of sugar. If miscanthus is sufficiently available in the future, its fraction could be further increased to 70% by reducing the fraction of corn stover. We find that the mixed feedstock considered in this study reduces the nutrient replacement and feedstock transportation costs and improves the quality of feedstock (determined by total carbohydrates and ash) relative to corn stover alone. Results suggest that a high-quality feedstock with a high carbohydrate content is an important metric for consideration, beyond strictly the feedstock cost, to reduce the selling price of sugar and its uncertainties. In the future this may be supported by the increased availability of higher carbohydrate feedstocks such as miscanthus.

09 BIOMASS FUELS↗
DOE OSTI2017

The potential value of early (1939-1967) upper-air data in atmospheric climate reanalysis

In recent years a number of reanalysis datasets have been published that cover the past century or more, including the ‘Twentieth Century Reanalysis’ 20CRv2 and the European Reanalysis of the twentieth century ERA-20C. These datasets are widely used, showing the need for, and possible benefit of, reanalysis data products designed for climate applications.The twentieth-century reanalyses so far have assimilated only surface observations, and rely on independent estimates of monthly averaged sea-surface temperatures and sea ice concentrations as boundary conditions. While 20CRv2 uses only observations of surface and sea-level pressure, ERA-20C additionally assimilates marine winds.Here we describe an experimental reanalysis, referred to as ERA-PreSAT, which covers the period 1939–1967 and also assimilates historical upper-air data. Assessments of this dataset including comparisons with independent data show that (i) temperature biases in the Northern Hemisphere are largely reduced compared to reanalyses that assimilate surface data only, (ii) concentration of 1940s upper-air data in the northern extra tropics created a strong interhemispheric asymmetry which is likely not realistic, (iii) the forecast skill in the Northern Hemisphere has increased substantially compared to reanalyses that assimilate surface data only, (iv) day-to-day and (in the northern extratropics) month-to-month correlations with independent observations (of total column ozone, upper-air data) increase over time, (v) interannual variability is well captured in the reanalysis, (vi) a signature of the stratospheric Quasi-Biennial Oscillation is present as far back as the 1940s,and (vii) tropical cyclones are not well represented. Furthermore, the generally encouraging results from the experimental ERA-PreSAT reanalysis underline that early upper-air data greatly contribute to our knowledge on the troposphere and lower stratosphere over the twentieth century.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2018

Bioconversion of Methane for Value-Added Products

This chapter will briefly summarize the background of methane production from natural gas and biogas together with an introduction to the biomolecular basis of methanotrophy and the actual and potential commercial applications. This chapter also discusses the safety considerations for using methane in laboratory and safe development of methane-based bioprocesses. In the end, this chapter will focus on the process development for biological conversion of methane into desired products with attention to the enhancement of mass transfer efficiency and the development of bioreactor designs.

09 BIOMASS FUELS↗
DOE OSTI2024

BPS fivebrane stars. Part I. Expectation values of observables

We study ensembles of 1/2-BPS bound states of fundamental strings and NS-fivebranes (NS5-F1 states) in the AdS decoupling limit. We revisit a solution corresponding to an ensemble average of these bound states, and find that the appropriate duality frame for describing the near-source structure is the T-dual NS5-P frame, where the bound state is a collection of momentum waves on the fivebranes. We find that the fivebranes are generically well-separated; this property results in the applicability of perturbative string theory. The geometry sourced by the typical microstate is not close to that of an extremal non-rotating black hole; instead the fivebranes occupy a ball whose radius is parametrically much larger than the “stretched horizon” scale of the corresponding black hole. These microstates are thus better characterized as BPS fivebrane stars than as small black holes.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2019

Real-Time US-{sup 18}FDG-PET/CT Image Fusion for Guidance of Thermal Ablation of {sup 18}FDG-PET-Positive Liver Metastases: The Added Value of Contrast Enhancement

Purpose: To assess the feasibility of US-{sup 18}FDG-PET/CT fusion-guided microwave ablation of liver metastases either poorly visible or totally undetectable with US, CEUS and CT, but visualized by PET imaging. Materials and Methods: Twenty-three patients with 58 liver metastases underwent microwave ablation guided by image fusion system that combines US with {sup 18}FDG-PET/CT images. In 28/58 tumors, {sup 18}FDG-PET/CT with contrast medium (PET/CECT) was used. The registration technical feasibility, registration time, rates of correct targeting, technical success at 24 h, final result at 1 year and complications were analyzed and compared between the PET/CT and PET/CECT groups. Results: Registration was successfully performed in all cases with a mean time of 7.8 + 1.7 min (mean + standard deviation), (4.6 + 1.5 min for PET/CECT group versus 10.9 + 1.8 min for PET/CT group, P < 0.01). In total, 46/58 (79.3%) tumors were correctly targeted, while 3/28 (10.7%) and 9/30 (30%) were incorrectly targeted in PET/CT and PET/CECT group, respectively (P < 0.05). Complete ablation was obtained at 24 h in 70.0% of cases (n = 40 tumors), 23/28 (82.1%) in the PET/CECT group and 17/30 (56.7%) in the PET/CT group (P < 0.037). Fourteen tumors underwent local retreatment (11 ablations, 2 with resection and 1 with stereotactic body radiation therapy), while 4 tumors could not be retreated because of distant disease progression and underwent systemic therapy. Finally, 54/58 (93.1%) tumors were completely treated at 1 year. One major complication occurred, a gastrointestinal hemorrhage which required surgical repair. Conclusions: Percutaneous ablation of {sup 18}FDG-PET-positive liver metastases using fusion imaging of real-time US and pre-acquired {sup 18}FDG-PET/CT images is feasible, safe and effective. Contrast-enhanced PET/CT improves overall ablation accuracy and shortens procedural duration time.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2019

Endovascular Treatment of Post-thrombotic Venous Ilio-Femoral Occlusions: Prognostic Value of Venous Lesions Caudal to the Common Femoral Vein

Objectives: To propose a scale of severity for post-thrombotic venous lesions (PTVLs) after ilio-femoral deep venous thrombosis and to compare the grade with the results of endovascular treatment of ilio-femoral PTVLs. Methods: In this retrospective monocentric observational study, we included 95 patients treated for ilio-femoral PTVLs. We proposed a four-grade scale evaluating the severity of PTVLS caudal to the common femoral vein based on CT phlebography and per-operative phlebography. For most patients, venous patency was assessed with color duplex ultrasonography and the clinical efficacy of the intervention using the Villalta and CIVIQ scores. Results: Recanalization was successful in 100% of patients with a morbidity rate of 4%. After a mean follow-up of 21 months, the overall primary patency was 75%, the assisted primary patency 82%, and the secondary patency 93%. Secondary patency was 100% for grade 0–1, 90% for grade 2, and 63% for grade 3 (p < 0.002). There was no correlation between the extension of stenting caudally of the common femoral vein and venous patency. The mean improvements in the Villalta and CIVIQ-20 scores were, respectively, 4.6 (p < 0.0001) and 18 (p < 0.0001); scores were not correlated with the grade of PTVLs in the thigh. Conclusion: Venous patency after endovascular treatment of ilio-femoral PTVLs was strongly linked to the severity of PTVLs caudal to the common femoral vein but not to the extent of stenting.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2018

Diagnosing added value of convection-permitting regional models using precipitation event identification and tracking

Dynamical downscaling with high-resolution regional climate models may offer the possibility of realistically reproducing precipitation and weather events in climate simulations. As resolutions fall to order kilometers, the use of explicit rather than parametrized convection may offer even greater fidelity. However, these increased resolutions both allow and require increasingly complex diagnostics for evaluating model fidelity. Here we focus on precipitation evaluation and analyze five 2-month-long dynamically downscaled model runs over the continental United States that employ different convective and microphysics parameterizations, including one high-resolution convection-permitting simulation. All model runs use the Weather Research and Forecasting Model driven by National Center for Environmental Prediction reanalysis data. We show that employing a novel rainstorm identification and tracking algorithm that allocates essentially all rainfall to individual precipitation events allows new insights into model biases. Results include that, at least in these runs, model wet bias is driven by excessive areal extent of individual precipitating events, and that the effect is time-dependent, producing excessive diurnal cycle amplitude. This amplified cycle is driven not by new production of events but by excessive daytime enlargement of long-lived precipitation events. Here, we further show that in the domain average, precipitation biases appear best represented as additive offsets. Of all model configurations evaluated, convection-permitting simulations most consistently reduced biases in precipitation event characteristics.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2025

Combining biotechnology with sustainability: feasibility of bioenergy sorghum in generating high-value bioproducts

Biofuels generated through fermentation of plant-derived lignocellulosic biomass are currently not competitive with fossil fuels. Here, a framework is described for the engineering of valuable coproducts to improve the economic feasibility of biofuel production. To accomplish this goal, the desirable traits of the bioenergy crop Sorghum bicolor are harnessed via modern engineering approaches. A robust analysis is provided to highlight the scientific basis, costs, regulatory challenges, and lucrative nature of coproduct development. Sustainable biofuel production could also have far-reaching societal impacts, especially in the context of our rapidly changing global climate. This perspective suggests that the path to profitable biofuel production is attainable and encourages consideration of similar approaches by the biotechnology industry.

09 BIOMASS FUELS↗
DOE OSTI2019

Spread of Values of a Cantor-Type Fractal Continuous Nonmonotone Function

By using the Q{sub 5}{sup ∗}-representation of numbers[0,1]∋x=β{sub α{sub 1(x)1}}+∑{sub k=2}{sup ∞}(β{sub α{sub k(x)k}}∏{sub j=1}{sup k−1}q{sub α{sub j(x)j}})=Δ{sub α{sub 1(x)α{sub 2(x)…α{sub k(x)…}{sup Q{sub 5}{sup ∗}}}}} determined by the quinary alphabet A{sub 5} ≡ {0, 1, 2, 3, 4} and an infinite stochastic matrix ‖q{sub ik}‖, i ∈ A{sub 5}, k ∈ N, with positive elements (q{sub 0k} + q{sub 1k} + q{sub 2k} + q{sub 3k} + q{sub 4k} = 1) such that ∏{sub k=1}{sup ∞}max{sub i}{q_i_k}=0 and β{sub 0k} = 0, β{sub i + 1, k} = β{sub ik} + q{sub ik}, i= (0,4)-bar , we define a continuous Cantor-type function by the equalityf(Δ{sub α{sub 1…α{sub k…}{sup Q{sub 5}{sup ∗}}}})=δ{sub α{sub 1(x)1}}+∑{sub k=2}{sup ∞}(δ{sub α{sub k(x)k}}∑{sub j=1}{sup k−1}g{sub α{sub j(x)j}})≡Δ{sub α{sub 1(x)…α{sub k(x)…}{sup G}}}, where δ{sub 0n} = 0, δ{sub 1n}=((2+ε{sub n})/4), δ{sub 2n}=(2/4)=δ{sub 3n}, and δ{sub 4n}=((2−ε{sub n})/4), i.e., δ{sub i + 1, n} = δ{sub in} + g{sub in}, n ∈ N, and (ε{sub n}) is a given sequence of real numbers such that 0 ≤ ε{sub n} ≤ 1. We prove that this function is well defined and continuous. Moreover, it does not have intervals of monotonicity, except the intervals where it is constant. A criterion of bounded variation of the function is also established. We are especially interested in the problem of level sets of the function and in the topological and metric properties of the images of Cantor-type sets.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2018

An Eco-Friendly System for the Production of Value-Added Materials from Dairy Manure

A technoeconomic model has been developed to explore the viability of a two-stage anaerobic digester (AD) coupled with additional processes to increase the economic attractiveness of a new manure treatment system. The addition of a polyhydroxyalkanoate (PHA) reactor, algae cultivation system (ACS), and a biomass treatment system, such as, fast-pyrolysis or hydrothermal liquefaction (HTL) would further sequester carbon and nutrients, as well as add valuable products that can be sold or used on-site to mitigate costs. The Decision-support for Digester-Algae IntegRation for Improved Environmental and Economic Sustainability (DAIRIEES) model is used to evaluate the effectiveness and viability of this system to achieve economic and environmental sustainability by the dairy industry. The DAIRIEES model was used to evaluate the effectiveness and viability of this system to achieve economic viability and environmental sustainability by the dairy industry. A base case with mass flows and economics for a 10,000 herd dairy is considered. The integrated manure treatment system can reduce the amount of nitrogen released from the manure by 61.7%. If the ACS is not incorporated into the system, the nitrogen reduction drops to 19%. Similarly, the amount of phosphorus available for release to the environment is reduced by 37.4% with the full system, and by 26% for the system without the ACS. The results of the economic analysis indicate a net loss for the integrated system with algae cultivation. Without algae cultivation, the manure treatment system is profitable with a payback period of less than five years.

09 BIOMASS FUELS↗
DOE OSTI2019

Prognostic value of left ventricular dyssynchrony evaluated by gated myocardial perfusion imaging in patients with chronic kidney disease and normal perfusion defect scores

Background: This study aimed to investigate whether indices of left ventricular (LV) dyssynchrony by gated myocardial perfusion SPECT (GMPS) could be useful to predict prognosis in chronic kidney disease (CKD) patients with normal perfusion defect scores. Methods: One hundred and sixty-seven CKD patients with normal perfusion defect scores on adenosine-stress {sup 201}Tl GMPS and no previous history of overt heart diseases were enrolled. Phase standard deviation (PSD) and bandwidth (BW) were automatically calculated from GMPS. The major adverse cardiac events (MACEs) for a mean of 560 days were defined as sudden cardiac death, fatal arrhythmias, and acute coronary syndrome requiring urgent coronary revascularization. Patients were divided into two groups according to the presence or absence of MACEs. Results: The MACEs occurred in 12 patients (7.1%). Patients who experienced MACEs showed significantly higher PSD and wider BW than those who did not. In the Kaplan-Meier event-free survival analysis, cardiac event rate was significantly higher in the high-PSD and wide-BW group (n = 81) than in the low-PSD and narrow-BW group (n = 71) (P = .002). The multivariate regression analysis revealed that the PSD was associated with MACEs (odds ratio 1.33, 95% confidence interval 1.05-1.69, P = .01). Conclusion: The LV dyssynchrony indices from GMPS may be novel prognostic predictors in CKD patients with normal perfusion defect scores.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2019

The prognostic value of heart rate response during vasodilator stress myocardial perfusion imaging in patients with end-stage renal disease undergoing renal transplantation

Background: In asymptomatic end-stage renal disease (ESRD) patients undergoing vasodilator stress myocardial perfusion imaging (MPI) prior to renal transplantation (RT), the impact of pre-transplant heart rate response (HRR) to vasodilator stress on post-RT outcomes is unknown. Methods: We analyzed a retrospective cohort of asymptomatic patients with ESRD who underwent a vasodilator stress SPECT-MPI and subsequently received RT. Blunted HRR was defined as HRR <28% for regadenoson stress and <20% for adenosine stress. The primary endpoint was major adverse cardiac events (MACE), defined as cardiac death or myocardial infarction. Clinical risk was assessed using the sum of risk factors set forth by the AHA/ACCF consensus statement on the assessment of RT candidates. Results: Among 352 subjects, 140 had an abnormal pre-transplant HRR. During a mean follow-up of 3.2 ± 2.0 years, 85 (24%) MACEs were observed. Blunted HRR was associated with increased MACE risk (hazard ratio 1.72; 95% confidence interval 1.12-2.63, P = 0.013), and remained significant after adjustment for gender, sum of AHA/ACCF risk factors, summed stress score, baseline heart rate, and β-blocker use. HRR was predictive of MACE in patients with normal MPI and irrespective of clinical risk. Blunted HRR was associated with a significant increase in post-operative (30-day) MACE risk (17.9% vs 8.5%; P = 0.009). Conclusion: In asymptomatic ESRD patients being evaluated for RT, a blunted pre-transplant HRR was predictive of post-RT MACE. HRR may be a valuable tool in the risk assessment of RT candidates.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2019

Diagnostic value of stress thallium-201/rest technetium-99m-sestamibi sequential dual isotope high-speed myocardial perfusion imaging for the detection of haemodynamically relevant coronary artery stenosis

Background: The aim of this study was to determine the diagnostic accuracy of stress thallium-201/rest technetium-99m-sestamibi sequential dual-isotope high-speed myocardial perfusion imaging (DI-HS-MPI) against invasively determined fractional flow reserve (FFR). Methods: Fifty-four consecutive patients prospectively underwent DI-HS-MPI before invasive coronary angiography. Perfusion was scored visually by summed stress score on a patient and coronary territory basis. Significant coronary artery disease (CAD) was defined by the presence of ≥ 90% stenosis/occlusion or fractional flow reserve ≤ 0.80 for coronary stenosis ≥ 50%. Results: FFR was measured in 69 of 162 coronary vessels, with 1.28 ± 0.56 vessels assessed/patient. Sensitivity, specificity, and diagnostic accuracy of MPI for the detection of significant CAD were 92.8%, 69.2%, and 81.4%, on a patient basis, and 83.7%, 90.4%, and 88.8% by coronary territory. Conclusions: DI-HS-MPI accurately detects functionally significant CAD as defined by using FFR.

62 RADIOLOGY AND NUCLEAR MEDICINE↗