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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
NASA NTRS2019

Interplanetary Low-Thrust Design Using Proximal Policy Optimization

This paper aims to demonstrate a reinforcement learning technique for developing complex, decision-making policies capable of planning interplanetary transfers.Using Proximal Policy Optimization (PPO), a neural network agent is trained to produce a closed-loop controller capable of transfers between Earth and Mars.The agent is trained in an environment that utilizes a medium fidelity solar electric propulsion model and a real ephemeris model of the Earth and Mars. The results are compared against those generated by the Evolutionary Mission Trajectory Generator (EMTG) tool.

proximal policy optimization↗
NASA NTRS2024

Demonstration of GaN HEMT MMIC High-Power Amplifier for Lunar Proximity Communications

In this paper, we demonstrate a high efficiency, Ka-band (23.15 to 23.55 GHz) GaN HEMT MMIC based single-ended high power amplifier (HPA). The measured Pout, Gain, PAE, RMS EVM for Offset-QPSK, 8PSK, 16APSK, and 32APSK waveforms, 3rd-order IMD products, noise figure, and phase noise are presented. The results indicate that the saturated output power (P sat ) and the small signal Gain are on the order of 38.8 dBm (7.6 W) and 29.3 dB, respectively. The PAE at Psat is 20.0%. At the 1-dB compression point, the RMS EVM and the out-of-band spectral regrowth are less than 6% and –26 dBc respectively, for all four waveforms. Additionally, the spectrum is in compliance with the NTIA mask requirements for all four waveforms. The output 3rd-order intercept point (OIP3) is on the order of 42 dBm. The noise figure is less than 9.5 dB. The SSB phase noise spectral density is compliant with the envelope defined by the MIL-STD-188-164C. The HPA can enable proximity forward links between the orbiting Gateway/relay satellites and the lunar surface elements and cross links between relay satellites.

Ka-band↗
DOE OSTI2012

Proximate and Ultimate Compositional Changes in Corn Stover during Torrefaction using Thermogravimetric Analyzer and Microwaves

Abstract The world is currently aiming to reduce the dependence on fossil fuels and to achieve a sustainable renewable supply. Renewable energies represent a diversity of energy sources that can help to maintain the equilibrium of different ecosystems. Among the various sources of renewable energy, biomass is considered carbon neutral because the carbon dioxide released during its use is already part of the carbon cycle. Increasing the use of biomass for energy can help to reduce the negative CO2 impact on the environment and help meet the targets established in the Kyoto Protocol. Energy from biomass can be produced from different processes, including thermochemical (direct combustion, gasification, and pyrolysis), biological (anaerobic digestion, fermentation), or chemical (esterification) technologies. There are lot challenges in using biomass for energy applications. To name few low bulk density, high moisture content, irregular size and shape, hydrophilic nature and low calorific value. In commercial scale operation large quantities of biomass are needed and this will create problems associated with storage and transportation. Furthermore, grinding raw biomass with high moisture content is very challenging as there are no specific equipments and can increase the costs and in some cases it becomes highly impossible. All of these drawbacks led to development of some pretreatment techniques to make biomass more suitable for fuel applications. One of the promising techniques is torrefaction. Torrefaction is heating the biomass in an inert environment or reduced environment. During torrefaction biomass losses moisture, becomes more brittle and with increased energy density values. There are different techniques used for torrefaction of biomass. Fixed bed, bubbling sand bed and moving bed are the most common ones used. The use of microwaves for torrefaction purposes has not been explored. In the present study we looked into the torrefaction of biomass using the regular and microwaves and their effect on proximate and ultimate composition. Studies indicated that microwave torrefaction is a good way to torrefy the biomass in short periods of time. A maximum calorific value of 21 MJ/kg is achievable at 6 min residence time compared to 15 min using the dry torrefaction technique. Increasing the residence time increased the carbon content where a maximum carbon content of 52.20 % was achievable at lower residence time. The loss of volatiles is comparatively lower compared to dry torrefaction technique. Moisture content of microwave torrefied samples was in between 2-2.5 % (w.b).

09 BIOMASS FUELS↗
DOE OSTI2019

Microbial communities across a hillslope‐riparian transect shaped by proximity to the stream, groundwater table, and weathered bedrock

Abstract Watersheds are important suppliers of freshwater for human societies. Within mountainous watersheds, microbial communities impact water chemistry and element fluxes as water from precipitation events discharge through soils and underlying weathered rock, yet there is limited information regarding the structure and function of these communities. Within the East River, CO watershed, we conducted a depth‐resolved, hillslope to riparian zone transect study to identify factors that control how microorganisms are distributed and their functions. Metagenomic and geochemical analyses indicate that distance from the East River and proximity to groundwater and underlying weathered shale strongly impact microbial community structure and metabolic potential. Riparian zone microbial communities are compositionally distinct, from the phylum down to the species level, from all hillslope communities. Bacteria from phyla lacking isolated representatives consistently increase in abundance with increasing depth, but only in the riparian zone saturated sediments we found Candidate Phyla Radiation bacteria. Riparian zone microbial communities are functionally differentiated from hillslope communities based on their capacities for carbon and nitrogen fixation and sulfate reduction. Selenium reduction is prominent at depth in weathered shale and saturated riparian zone sediments and could impact water quality. We anticipate that the drivers of community composition and metabolic potential identified throughout the studied transect will predict patterns across the larger watershed hillslope system.

58 GEOSCIENCES↗
DOE OSTI2017

Probing Molecular‐Transport Properties using the Superconducting Proximity Effect

Molecular electronics research focuses on the study and application of molecular building blocks for the fabrication of nanoscale electronic devices, and on utilizing their self‐organization properties to achieve large‐scale electronic circuits. One of the key issues in molecular electronics is to identify the mechanism governing the electrical conductivity along the molecules. More specifically, the problem is to determine whether the junction behaves as a tunnel barrier, or the junction provides electron or hole conduction channels through the molecule. Due to the large energy gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), it is usually assumed in calculations that the molecule may contain only one conducting channel either for electrons or for holes. Experimentally, measurements using a local‐probe tip or a small gap between two metallic leads strongly depend on the nature of the linkage between the molecules and the contacts, which is hard to optimize. Here, a new approach is presented to study the electronic and transport properties of molecules using the superconducting proximity effect. Insight into these properties is gained by monitoring the modifications of the superconducting properties upon linking nanoparticles to a superconductor via the studied molecules.

Katzir, Eran↗
DOE OSTI2022

Proximity Portability and in Transit , M-to-N Data Partitioning and Movement in SENSEI [Book Chapter]

In high-performance parallel in situ processing, the term in transit processing refers to those configurations where data must move from a producer to a consumer that runs on separate resources. In the context of parallel and distributed computing on an HPC platform one of the central challenges is to determine a mapping of data from producer ranks to consumer ranks. This problem is complicated by the heterogeneity that arises in producer-consumer pairs, such as when producer and consumer codes have different levels of concurrency, different scaling characteristics, or different data models. The resulting mapping and movement of data from M producer to N consumer ranks can have a significant impact on aggregate application performance, particularly when the data consumer requires only a subset of the overall data for its task. This chapter focuses on the design considerations that underlie SENSEI’s implementation to this challenging problem. These design considerations extend the core SENSEI architecture and include ideas like the need to accommodate flexibility in the choice of different partitioning methods, the ability for a data consumer to request and receive only the subset of data needed for its particular operation, and the ability to leverage any of several different data transport tools. The idea of proximity portability, being able to use different data transport methods as part of an in transit workflow, is illustrated through the use of three different transport layers where switching from one transport tool to another is accomplished with only a configuration file change. Here, the chapter also includes a performance analysis summary showing the performance gains that are possible in terms of multiple metrics, such as memory footprint, time to solution, and amount of data moved, when using optimized partitioners in an in transit setting, gains that are made possible by the implementation shaped by specific design considerations.

Bethel, E. Wes↗
DOE OSTI2015

Embolisation of a Proximal Type I Endoleak Post-Nellix Aortic Aneurysm Repair Complicated by Reflux of Onyx into the Nellix Endograft Limb

We report the first case of intervention for a proximal type 1 endoleak following Nellix endovascular aneurysm sealing repair of an aortic aneurysm. This was complicated by migration of Onyx into one of the Nellix graft limbs causing significant stenosis. Subsequent placement of a covered stent to affix the Onyx between the stent and the wall of the Nellix endograft successfully restored stent patency.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2016

A Retrospective Comparison of Ultrasound-Assisted Catheter-Directed Thrombolysis and Catheter-Directed Thrombolysis Alone for Treatment of Proximal Deep Vein Thrombosis

BackgroundRecent studies have suggested that catheter-directed thrombolysis (CDT) reduces development of post-thrombotic syndrome (PTS). Ultrasound-assisted CDT (USCDT) might enhance the efficiency of thrombolysis. We aimed to compare USCDT with CDT on efficacy, safety, development of PTS, and quality of life after long-term follow-up.MethodsWe describe a retrospective case series of 94 consecutive patients admitted with iliofemoral or more proximal deep vein thrombosis (DVT) to the University Hospital from 2002 to 2011, treated either with CDT or USCDT. Scheduled follow-up visits took place between April 2013 and January 2014. Venography measured the degree of residual luminal obstruction of the affected veins. Each patient completed the Short Form 36-item health survey assessment and the Venous Insufficiency Epidemiological and Economic Study-Quality of Life/Symptoms questionnaires. PTS was assessed using the Villalta scale.ResultsRisk factors of DVT were equally distributed between groups. In the USCDT group, we observed a significant decline in the duration of thrombolytic treatment (<48 h: 27 vs. 10 %), shortened hospital stay (median 6.0 days (IQR 5.0–9.0) vs. 8.0 (IQR 5.8–12.0)), and less implantation of (intravenous) stents (30 vs. 55 %). There was no difference in patency (76 vs. 79 % fully patent), prevalence of PTS (52 vs. 55 %), or quality of life between groups after long-term follow-up (median 65 months, range: 15–141).ConclusionsIn this observational study, USCDT was associated with shortened treatment duration, shorter hospital stay, and less intravenous stenting, compared to CDT alone without affecting the long-term prevalence of PTS or quality of life.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2019

Two Wire System and Modified Olive Tip to Facilitate Implantation of Fenestrated TEVAR in Patient with Proximal Descending Aortic Pathology: First Two Cases

Introduction: Although Fenestrated TEVAR (F-TEVAR) has been considered to be a more physiologic approach to treat proximal descending aortic pathology, its application is still limited due to availability, cost and technical difficulties. We introduce a new design of fenestrated stent graft with a new delivery system and successfully performed first in human implantation in two patients, one with an aortic aneurysm and one with an acute aortic dissection. Materials and Methods: The design of these two wires fenestrated stent graft include creation of an additional lumen at the side of the olive tip during manufacture, from which an additional wire can be introduced for a side branch passing into the fenestration, running inside the stent graft and exit the delivery sheath through additional hub. The two wires will facilitate delivery and deployment of the stent graft. One patient with descending aortic aneurysm and another with Stanford B aortic dissection is included in this first in human study. Results: The aneurysm and dissection were completely excluded immediately after the TEVAR. Six month follow up CT showed good position of the stent graft and patent LSA in both patients. In the patient with aortic dissection, expansion of the true lumen and partial thrombosis of the false lumen was seen. Conclusions: This is a report of a two wire system in 2 patients with distal aortic arch pathology demonstrating a good technical and clinical success using pre-cannulated fenestrations through a modified nose cone olive. Level of Evidence: Level 4, report of two cases.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2022

A proximal trust-region method for nonsmooth optimization with inexact function and gradient evaluations

Many applications require minimizing the sum of smooth and nonsmooth functions. For example, basis pursuit denoising problems in data science require minimizing a measure of data misfit plus an $\ell^1$-regularizer. Similar problems arise in the optimal control of partial differential equations (PDEs) when sparsity of the control is desired. Here, we develop a novel trust-region method to minimize the sum of a smooth nonconvex function and a nonsmooth convex function. Our method is unique in that it permits and systematically controls the use of inexact objective function and derivative evaluations. When using a quadratic Taylor model for the trust-region subproblem, our algorithm is an inexact, matrix-free proximal Newton-type method that permits indefinite Hessians. We prove global convergence of our method in Hilbert space and demonstrate its efficacy on three examples from data science and PDE-constrained optimization.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2019

Proximity Effects of Superconductivity and Antiferromagnetism in a Nanowire

In this paper, we theoretically study the proximity effects of s-wave superconductivity(SC) and antiferromagnetism(AFM) in a nanowire. For the half-filling case, it was found that the Andreev bound states form near the boundary between the AFM and the SC which are accompanied by the strongly localized p-wave pairing. These in-gap states remain when the system is slightly doped. For the electron or hole doped system, they merge into the upper or the lower antiferromagnetic bands gradually with the increase of doping, respectively.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Analysis of heavy-ion fusion reactions using new parameterized form of the universal function of nuclear proximity potential

In the present work, we modify the original version of this formalism (Prox. 77) using a new analytical form of the universal function which is formulated based on the double-folding model with three density-dependent versions of the M3Y-type interactions, namely DDM3Y1, CDM3Y3 and BDM3Y1, for 46 fusion systems with condition 48≤Z{sub 1}Z{sub 2}≤2460 for charge product of their participant nuclei. It is found that when the Prox. 77 potential is accompanied by each of the formulated universal functions, the agreement between the theoretical and experimental data of the fusion barrier heights increase for our selected systems. The obtained results of this study reveal that the saturation property of cold nuclear matter plays a key role in the calculations of the fusion cross sections. We conclude that the Prox. 77 model with universal function based on the BDM3Y1 interactions provides the best results for fusion barrier heights and cross sections. On the basis of the prox. 77(BDM3Y1) potential model, we present the parameterized formulas for fusion barrier heights V{sub B} and positions R{sub B}. These formulas can calculate the values of R{sub B} andV{sub B} with good accuracy in comparison with the experimental data. A comparison is also presented among the theoretical results of the present work and those obtained by the modified form of the original version of proximity approach through the universal function and surface energy coefficients available in the literature.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2012

Iron repletion relocalizes hephaestin to a proximal basolateral compartment in polarized MDCK and Caco2 cells

Highlights: Black-Right-Pointing-Pointer Hephaestin localizes in the perinuclear space in non-polarized cells. Black-Right-Pointing-Pointer Hephaestin localizes in the perinuclear space in iron deficient and polarized cells. Black-Right-Pointing-Pointer Hephaestin with apical iron moves near to basolateral membrane of polarized cells. Black-Right-Pointing-Pointer Peri-basolateral location of hephaestin is accessible to the extracellular space. Black-Right-Pointing-Pointer Hephaestin is involved in iron mobilization from the intestine to circulation. -- Abstract: While intestinal cellular iron entry in vertebrates employs multiple routes including heme and non-heme routes, iron egress from these cells is exclusively channeled through the only known transporter, ferroportin. Reduced intestinal iron export in sex-linked anemia mice implicates hephaestin, a ferroxidase, in this process. Polarized cells are exposed to two distinct environments. Enterocytes contact the gut lumen via the apical surface of the cell, and through the basolateral surface, to the body. Previous studies indicate both local and systemic control of iron uptake. We hypothesized that differences in iron availability at the apical and/or basolateral surface may modulate iron uptake via cellular localization of hephaestin. We therefore characterized the localization of hephaestin in two models of polarized epithelial cell lines, MDCK and Caco2, with varying iron availability at the apical and basolateral surfaces. Our results indicate that hephaestin is expressed in a supra-nuclear compartment in non-polarized cells regardless of the iron status of the cells and in iron deficient and polarized cells. In polarized cells, we found that both apical (as FeSO{sub 4}) and basolateral iron (as the ratio of apo-transferrin to holo-transferrin) affect mobilization of hephaestin from the supra-nuclear compartment. We find that the presence of apical iron is essential for relocalization of hephaestin to a cellular compartment in close proximity but not overlapping with the basolateral surface. Surface biotinylation studies indicate that hephaestin in the peri-basolateral location is accessible to the extra-cellular environment. These results support the hypothesis that hephaestin is involved in iron mobilization of iron from the intestine to circulation.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2013

Macrophage-stimulating protein attenuates gentamicin-induced inflammation and apoptosis in human renal proximal tubular epithelial cells

Highlights: •MSP/RON system is activated in rat kidney damaged by gentamicin. •MSP inhibits GM-induced cellular apoptosis and inflammation in HK-2 cells. •MSP attenuates GM-induced activation of MAPKs and NF-κB pathways in HK-2 cells. -- Abstract: The present study aimed to investigate whether macrophage-stimulating protein (MSP) treatment attenuates renal apoptosis and inflammation in gentamicin (GM)-induced tubule injury and its underlying molecular mechanisms. To examine changes in MSP and its receptor, recepteur d’origine nantais (RON) in GM-induced nephropathy, rats were injected with GM for 7 days. Human renal proximal tubular epithelial (HK-2) cells were incubated with GM for 24 h in the presence of different concentrations of MSP and cell viability was measured by MTT assay. Apoptosis was determined by flow cytometry of cells stained with fluorescein isothiocyanate-conjugated annexin V protein and propidium iodide. Expression of Bcl-2, Bax, caspase-3, cyclooxygenase (COX)-2, inducible nitric oxide synthase (iNOS), nuclear factor-kappa B (NF-κB), IκB-α, and mitogen-activated protein kinases (MAPKs) was analyzed by semiquantitative immunoblotting. MSP and RON expression was significantly greater in GM-treated rats, than in untreated controls. GM-treatment reduced HK-2 cell viability, an effect that was counteracted by MSP. Flow cytometry and DAPI staining revealed GM-induced apoptosis was prevented by MSP. GM reduced expression of anti-apoptotic protein Bcl-2 and induced expression of Bax and cleaved caspase 3; these effects and GM-induced expression of COX-2 and iNOS were also attenuated by MSP. GM caused MSP-reversible induction of phospho-ERK, phospho-JNK, and phospho-p38. GM induced NF-κB activation and degradation of IκB-α; the increase in nuclear NF-κB was blocked by inhibitors of ERK, JNK, p-38, or MSP pretreatment. These findings suggest that MSP attenuates GM-induced inflammation and apoptosis by inhibition of the MAPKs/NF-κB signaling pathways.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

Calreticulin discriminates the proximal region at the N-glycosylation site of Glc1Man9GlcNAc2 ligand

Calreticulin (CRT) is well known as a lectin-like chaperone that recognizes Glc1Man9GlcNAc2 (G1M9)-glycoproteins in the endoplasmic reticulum (ER). However, whether CRT can directly interact with the aglycone moiety (protein portion) of the glycoprotein remains controversial. To improve our understanding of CRT interactions, structure-defined G1M9-derivatives with different aglycones (–OH, –Gly–NH{sub 2}, and –Gly–Glu–{sup t}Bu) were used as CRT ligands, and their interactions with recombinant CRT were analyzed using thermal shift analysis. The results showed that CRT binds strongly to a G1M9-ligand in the order –Gly–Glu–{sup t}Bu > –Gly–NH{sub 2} > –OH, which is the same as that of the reglucosylation of Man9GlcNAc2 (M9)-derivatives by the folding sensor enzyme UGGT (UDP-glucose: glycoprotein glucosyltransferase). Our results indicate that, similar to UGGT, CRT discriminates the proximal region at the N-glycosylation site, suggesting a similar mechanism mediating the recognition of aglycone moieties in the ER glycoprotein quality control system. - Highlights: • Glc1Man9GlcNAc2 (G1M9) ligands with different aglycones were chemically prepared. • Calreticulin (CRT) discriminates the aglycone of Glc1Man9GlcNAc2 (G1M9) ligand. • CRT binds with G1M9 ligands in a similar manner to folding sensor enzyme.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2018

Pioglitazone induces hypoxia-inducible factor 1 activation in human renal proximal tubular epithelial cell line HK-2

We previously reported that fatty acid-bearing albumin but not fatty acid-depleted albumin induces hypoxia-inducible factor-1 (HIF-1) activation in human renal proximal tubular epithelial cell line HK-2. Then, an increase in mRNA expression of peroxisome proliferator-activated receptor gamma (PPARγ) was observed on treatment with fatty acid-bearing albumin but not fatty acid-depleted albumin. The aim of this study was to determine whether a PPARγ agonist, pioglitazone, induces HIF-1 activation or not. Treatment with pioglitazone induced HIF-1α mRNA as well as PPARγ mRNA expression in a concentration dependent manner. In addition, pioglitazone increased HIF-1 target genes such as the mRNAs of glucose transporter 1 (GLUT1) and breast cancer resistance protein (BCRP/ABCG2), in a concentration-dependent manner. Consistent with the increases in GLUT1 and ABCG2 mRNAs, protein expression of GLUT1 and BCRP was increased by pioglitazone. In addition, GLUT inhibitor phloretin-sensitive D-[{sup 3}H]glucose uptake activity and BCRP inhibitor Ko143-sensitive accumulation of Hoecsht33342, a BCRP substrate, were significantly enhanced by treatment with pioglitazone. These findings suggest that PPARγ activation by pioglitazone leads to HIF-1 protein expression induction followed by changes in HIF-1 target gene expression and protein product activity.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

Proximity enhanced quantum spin Hall state in graphene

Graphene is the first model system of two-dimensional topological insulator (TI), also known as quantum spin Hall (QSH) insulator. The QSH effect in graphene, however, has eluded direct experimental detection because of its extremely small energy gap due to the weak spin–orbit coupling. Here we predict by ab initio calculations a giant (three orders of magnitude) proximity induced enhancement of the TI energy gap in the graphene layer that is sandwiched between thin slabs of Sb 2 Te 3 (or MoTe 2 ). This gap (1.5 meV) is accessible by existing experimental techniques, and it can be further enhanced by tuning the interlayer distance via compression. We reveal by a tight-binding study that the QSH state in graphene is driven by the Kane–Mele interaction in competition with Kekulé deformation and symmetry breaking. As a result, the present work identifies a new family of graphene-based TIs with an observable and controllable bulk energy gap in the graphene layer, thus opening a new avenue for direct verification and exploration of the long-sought QSH effect in graphene.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Mutations in Human Tubulin Proximal to the Kinesin-Binding Site Alter Dynamic Instability at Microtubule Plus- and Minus-Ends

The assembly of microtubule-based cellular structures depends on regulated tubulin polymerization and directional transport. In this research, we have purified and characterized tubulin heterodimers that have human β-tubulin isotype III (TUBB3), as well as heterodimers with one of two β-tubulin mutations (D417H or R262H). Both point mutations are proximal to the kinesin-binding site and have been linked to an ocular motility disorder in humans. Compared to wild-type, microtubules with these mutations have decreased catastrophe frequencies and increased average lifetimes of plus- and minus-end-stabilizing caps. Importantly, the D417H mutation does not alter microtubule lattice structure or Mal3 binding to growing filaments. Instead, this mutation reduces the affinity of tubulin for TOG domains and colchicine, suggesting that the distribution of tubulin heterodimer conformations is changed. Together, our findings reveal how residues on the surface of microtubules, distal from the GTP-hydrolysis site and inter-subunit contacts, can alter polymerization dynamics at the plus- and minus-ends of microtubules.

59 BASIC BIOLOGICAL SCIENCES↗