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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 1,549 records · Page 86
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Biodegradable Tragacanth Gum Based Silver Nanocomposite Hydrogels and Their Antibacterial Evaluation

In this article, biodegradable tragacanth gum (TG) biopolymer based silver nanocomposite hydrogels (SNCHs) were prepared with acrylamide as monomer using a simple redox polymerization method. TG acts as stabilizer to produce uniform and large silver nanoparticles (Ag-NPs) in presence of Terminalia chebula (TC) leaf extract in the hydrogel network. Forier transform infrared spectroscopy demonstrated the structural units of functional groups of polymeric backbone of the hydrogels. The formation of Ag-NPs in TG based hydrogels was confirmed by UV–Vis spectra. The morphology of homogeneously dispersed Ag-NPs throughout hydrogel networks was confirmed by scanning electron microscopy. TEM analysis indicates that Ag-NPs with average diameters of around 5 nm formed within the hydrogel networks. The evaluation of antibacterial activity of Ag-NPs performed against gram-negative Escherichia coli and gram-positive Bacillus subtilis bacteria and obtained results proved that these newly developed hydrogels have great potential for use in wound healing as well as water purification applications.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Structural and Optical Properties of Wurtzite AlGaAs Nanowires Grown by MBE on Si(111) Substrate

Abstract—: We present the results of photoluminescence measurements of Al{sub x}Ga{sub 1 – x}As nanowires, together with the transmission electron microscopy structural analysis. Al{sub x}Ga{sub 1 – x}As nanowires were grown by molecular beam epitaxy under the nominal aluminum contents х = 0.3–0.7. The obtained results demonstrate the presence of wurtzite structure in Al{sub x}Ga{sub 1 – x}As nanowires.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Post-irradiation examination to assess performance and safety of nuclear fuel

This work presents some results from testing campaigns performed at JRC-ITU on irradiated fuels and analogues aimed at characterizing fuel alterations during and after irradiation. The characterization of local structural and property changes is the first step towards the description of the overall behaviour of the fuel, including safety- and performance-relevant properties. High burnup light water reactor (LWR) UO{sub 2} fuel (= 60 GWd/tHM) was used for morphology and mechanical property studies. Radial profiles of porosity obtained from scanning electron microscopy image analysis were compared with corresponding sub-surface data obtained using acoustic microscopy. An increase of porosity was observed at the rim of the pellet in correspondence with the high burnup structure (HBS), and also at intermediate radius locations in correspondence with the occurrence of the so-called dark zone. This zone is characterized by several features similar to the HBS: in addition to increased local porosity, grain subdivision features were observed. The examination of grain free surface morphology along the pellet radius revealed the onset of surface alteration which resulted in almost complete loss of the original grain shape in conjunction with the formation of the dark zone. Additionally, possible ageing effects due to accumulation of microstructural decay damage during storage were investigated and compared to the results obtained under accelerated ageing conditions using alpha-doped analogues. Similar hardening trends were observed by comparing the hardness evolution as a function of accumulated damaged in unirradiated analogues and spent fuel. No significant hardness increase was observed on the same high burnup/high dose spent fuel after >10 years of additional storage in hot cell, confirming that hardening saturates at a damage level near 0.1 dpa. These experimental campaigns contribute establishing a basis of data for further analysis, in combination with suitable modelling tools. The final goal is to achieve the full scientific understanding of mechanisms and processes affecting fuel properties and behaviour, as a necessary step to establish the basis for developing advanced fuel systems with optimized performance and safety. (authors)

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2019

The Effect of Weld Metal Composition on Microstructural and Mechanical Properties of Dissimilar Welds Between Monel 400 and Inconel 600

The current work was carried out to characterize welding of Inconel 600 superalloy and Monel 400. In the present study, gas tungsten arc welding (GTAW) with four types of filler metals (ENiCu, ENiCu-7, ENiCr-3 and ENiCrFe-3) was utilized. The filler metals were categorized into two groups based on the presence of Cr and Nb in their chemical composition. This paper describes the selection and application of welding consumables in manufacturing dissimilar metal combinations. It was found that (Nb/Cr) ratio and Fe content can affect on the size and amount of carbides. During solidification of ENiCr-3 and ENiCrFe-3 filler metals, Nb leaves dendritic cores and is rejected to inter-dendritic regions because of its high tendency for segregation. However, No brittle Laves phase was detected in the welds. The interface between weld metal and base metal and gradual changes in alloying elements were also investigated by scanning electron microscopy. EDX analysis was also applied for different samples. Microhardness measurements and tensile test were performed on the joints. The average hardness value in the weld metal obtained from ENiCrFe-3 is higher than the other welds. ENiCu-7 weld exhibited the highest tensile strength of 540 MPa and percent elongation of 53% in contrast to ENiCrFe-3 weld with the lowest tensile strength (518 MPa) and percent elongation (39%).

36 MATERIALS SCIENCE↗
DOE OSTI2021

Ultrasonic additive manufacturing of zirconium: Pilot results

Ultrasonic additive manufacturing (UAM) was successfully applied to the Zirconium material system to create a three-dimensional component prototype. The UAM process resulted in grain size refinement and significant localized deformation. Electron backscatter diffraction analysis revealed activated slip systems only applicable at high deformation temperatures, while texture analysis showed a decrease in measurable texture of the UAM build in comparison to the initial Zr-foil. Average tensile strengths in the X (sonotrode travel), Y (vibration), and Z (build) directions averaged 435 MPa, 458 MPa, and 359 MPa, respectively, demonstrating the viability of UAM for Zr-based materials. Furthermore, the delamination of some Z specimens along foil boundaries during loading suggests an interplay between interfacial Ti impurities introduced during welding and the spatial dependence of weld quality for this material system.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Spin-State and Reorganization Energy Considerations for Metal-Centered Photoredox Catalysis

Transition-metal complexes featuring metal-centered excited states have recently emerged as mechanistically distinct platforms for selective photochemistry, including photoredox catalysis. Among these, Co(III) complexes have demonstrated productive photoinduced electron transfer via the 3 T 1 metal-centered state. In contrast, photoreactivity from the 5 T 2 metal-centered state in Fe(II) polypyridyl complexes remains limited. Building on our prior report concerning reactivity associated with the 5 T 2 state in [Fe(tren(py) 3 )] 2+ (tren(py) 3 = tris(2-pyridylmethyliminoethyl)-amine), we introduced stronger-field ligands in an effort to increase excited-state energies of Fe(II) polypyridyl complexes and enhance reactivity. Despite achieving nanosecond-scale excited-state lifetimes and favorable thermodynamic driving forces, no photoreactivity was observed. Reinvestigation of the observations previously reported for [Fe(tren(py) 3 )] 2+ revealed interactions between the metal complex and the substrate in their respective ground states that mimicked dynamic quenching of the chromophore, prompting a reassessment of mechanistic considerations inherent in leveraging reductive chemistry from the 5 T 2 excited state of Fe(II). Our analysis indicates that electron transfer from the 5 T 2 excited state of a low-spin d6 metal is subject to significant barriers both in terms of reorganization energies and spin conservation that undermines its ability to act as an electron donor for photoredox catalysis. In contrast, ligand fields that are sufficient to stabilize the 3 T 1 excited state have available to them numerous spin-allowed and, in certain cases, near-barrierless pathways to engage in excited-state electron transfer (both oxidative and reductive depending on the identity of the metal). These results highlight the critical role of spin-state changes and their associated reorganization energy requirements in metal-centered photoredox catalysis.

charge transfer↗
DOE OSTI2016

Polyethylene glycol (PEG) assisted size-controlled SnO{sub 2} nanoparticles by sol-gel process

Tetragonal phase tin oxide (SnO{sub 2}) nanoparticles have been synthesized by sol–gel method using SnCl{sub 4}.5H{sub 2}O and polyethylene glycol (PEG) of different concentration. The phase, size and purity of the final products are characterized by X-ray diffraction (XRD). The morphology is confirmed by scanning electron microscopy (SEM) analysis. There exists relationship between the concentration of PEG and particle size of SnO{sub 2} nanoparticles. Increase in concentration of PEG caused the reduction of particle size of tin oxide nanoparticles. The results suggest that the concentration of PEG plays a significant role in determining the size of SnO{sub 2} nanoparticles synthesized via this method. The optical property of the product has been explored by Ultraviolet (UV-visible) and Fourier Transform Infrared (FTIR) spectroscopic techniques.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Experimental Study on Heat Transfer and Pressure Drop of In-House Synthesized Graphene Oxide Nanofluids

In this work, first, graphene oxide nanosheets were synthesized in-house according to the modified Hummers method, and these nanosheets were used to prepare graphene oxide nanofluids at two concentrations. Then the thermo-physical properties of nanofluids characterized using X-ray diffraction analysis, a scanning electron microscope, and UV-Vis spectrophotometry. The particle size distribution was investigated using dynamic light scattering. Then, a fundamental study was conducted on the thermal-hydraulic characteristics of graphene oxide nanofluids flowing through a straight copper tube. An experimental setup was developed to find the heat transfer characteristics and pressure drop of nanofluids in the test section consisting of a copper tube with constant heat flux. The flow regimes and associated pressure drop and heat transfer characteristics at varying flow rate were investigated at three different heat flux conditions of 7.4, 9.1, and 12.6 kW/m 2 . Due to the increase in viscosity, flowrate and Reynolds number decreased from 0.01 wt.% to 0.1 wt.% of graphene oxide nanofluids at constant pump frequency. Experimental data obtained for water was validated with the findings from the literature, and the correlations were formulated for the Nusselt number and Reynolds number by considering the multiple regression analysis. The convective heat transfer coefficient for graphene oxide at 0.01 wt.% was higher when compared to graphene oxide at 0.1 wt.% and water. Finally, the variation of Nusselt number with the heat flux and velocity was insignificant.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Effect of TiN Addition on 3Y-TZP Ceramics with Emphasis on Making EDM-Able Bodies

In this study, to produce electrically conductive ceramics, rapid hot press (RHP) sintering of 3 mol.% yttria-stabilized tetragonal zirconia polycrystal (3Y-TZP) and 3Y-TZP/TiN composites with TiN amounts of 25, 35, and 45 vol.% was performed at 1300, 1350, and 1400 °C. Interestingly, the toughness and hardness were improved in the presence of TiN up to 35 vol.% and maximum fracture toughness and hardness of 5.40 ± 0.05 MPa m{sup 1/2} and 14.50 ± 0.06 GPa, respectively, were obtained. However, the bending strength was decreased which could be attributed to the rather weak interfaces of nitride and oxide phases. Regarding the zirconia matrix, the effect of grain size on fracture toughness of the samples has been studied using x-ray diffraction and field emission scanning electron microscope (FESEM) analysis. It was also found that electrical resistivity decreased to the value of 6.88 × 10{sup −6} Ω m at 45 vol.% of TiN. It seems the TiN grains form a network to impose conductivity on the ZrO{sub 2} body; however, below 35 vol.% TiN, due to lack of percolation effect, this conductivity could not be maintained according to FESEM studies. Finally, electrically conductive samples were successfully machined by electrical discharge machining (EDM).

36 MATERIALS SCIENCE↗
DOE OSTI2021

Modeling and analyzing parasitic parameters in high frequency converters

This research focuses on electromagnetic interference (EMI) / electromagnetic compatibility (EMC) design and analysis in power electronics systems. To limit the EMI under the standards, different methods and strategies are investigated. Parasitic parameters of high frequency (HF) transformer are analyzed using a novel analytical method, finite element method (FEM), and experimental measurements for different structures and windings arrangements. Also, the magnetic field, electric field, electric displacement, and electric potential distribution are simulated and analyzed. Moreover, a high voltage system is considered and analyzed to improve the EMC. The EMI propagation paths are analyzed. The EMI noise level of the system is obtained and compared to the IEC61800-3 standard. To improve the EMC, the parasitic parameters of the transformer, as the main path of EMI circulation, are analyzed and optimized to block the propagation. Furthermore, the geometry structure of the HF transformer is optimized to lower the parasitics in the system. Three pareto-optimal techniques are investigated for the optimization. The models and results are verified by 3D-FEM and experimental results for several given scenarios. Furthermore, the EMC modeling and conducted EMI analysis are developed for a system including an AC-DC-DC power supply (rectifier and dual active bridge (DAB) converter). Moreover, the common mode (CM) EMI noise propagation through the system is discussed and the noise sources and effect of components on the noise are analyzed. Additionally, the CM impedance of different parts of the system and the noise levels are discussed. Finally, EMI attenuation techniques were applied to the system.

24 POWER TRANSMISSION AND DISTRIBUTION↗
DOE OSTI2019

2D axial-azimuthal particle-in-cell benchmark for low-temperature partially magnetized plasmas

The increasing need to demonstrate the correctness of computer simulations has highlighted the importance of benchmarks. We define in this paper a representative simulation case to study low-temperature partially-magnetized plasmas. Seven independently developed particle-in-cell codes have simulated this benchmark case, with the same specified conditions. The characteristics of the codes used, such as implementation details or computing times and resources, are given. First, we compare at steady-state the time-averaged axial profiles of three main discharge parameters (axial electric field, ion density and electron temperature). We show that the results obtained exhibit a very good agreement within 5% between all the codes. As E x B discharges are known to cause instabilities propagating in the direction of electron drift, an analysis of these instabilities is then performed and a similar behaviour is retrieved between all the codes. A particular attention has been paid to the numerical convergence by varying the number of macroparticles per cell and we show that the chosen benchmark case displays a good convergence. Detailed outputs are given in the supplementary data, to be used by other similar codes in the perspective of code verification.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2025

Driving Electron Transfer in Photosystem I Using Far-Red Light: Overall Perspectives

Photosystem I (PSI) is a photosynthetic protein–pigment complex that, upon photoexcitation, transfers electrons to ferredoxin, facilitating the production of NADPH. Isolated PSI reaction centers (RCs) have also been used in hybrid systems to reduce protons and produce ‘biohydrogen’. This review article examines how various cyanobacteria with similar photosynthetic machinery utilize different wavelengths of light to execute photosynthetic electron transport through PSI. Key factors, such as, the structure of the electron transfer cofactors, the protein environment surrounding the primary donor pigments and hydrogen-bonding interactions with the surrounding protein matrix are analyzed to understand their roles in maintaining efficient electron transfer when it is driven using photons of different energies. We compare PSI complexes with known atomic structures from four species of cyanobacteria, Thermosynechococcus elongatus, Acaryochloris marina, Halomicronema hongdechloris, and Fischerella thermalis. T. elongatus is typical of most oxygenic photosynthetic organisms in that it requires visible light and uses only chlorophyll a (Chl a ) in PSI. In contrast, H. hongdechloris and F. thermalis are photoacclimating species capable of producing Chl f and Chl d that use red light when little visible light is available. A. marina , on the other hand, is adapted to red light conditions and consistently utilizes Chl d as its primary photosynthetic pigment, maintaining a stable pigment composition. Here, we explore the structural and functional differences between the PSI RCs of these organisms and the impact of these differences on electron transport. The structural differences in the cofactors influence both the absorption wavelengths of the cofactors and the energy levels of the intermediate states of electron transfer. An analysis of the surrounding protein shows how it has been adapted and underscores the interplay between the pigment structure, protein environment, and hydrogen bonding networks in tuning the efficiency and adaptability of photosynthetic mechanisms across different species of cyanobacteria.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Spectroscopic investigation of the electronic and excited state properties of para-substituted tetraphenyl porphyrins and their electrochemically generated ions

Porphyrins play pivotal roles in many crucial biological processes including photosynthesis. However, there is still a knowledge gap in understanding electronic and excited state implications associated with functionalization of the porphyrin ring system. These effects can have electrochemical and spectroscopic signatures that reveal the complex nature of these somewhat minor substitutions, beyond simple inductive or electronic effect correlations. To obtain a deeper insight into the influences of porphyrin functionalization, four free-base, meso-substituted porphyrins: tetraphenyl porphyrin (TPP), tetra(4-hydroxyphenyl) porphyrin (THPP), tetra(4-carboxyphenyl) porphyrin (TCPP), and tetra(4-nitrophenyl) porphyrin (TNPP), were synthesized, characterized, and investigated. The influence of various substituents, (-hydroxy,-carboxy, and -nitro) in the para position of the meso-substituted phenyl moieties were evaluated by spectroelectrochemical techniques (absorption and fluorescence), femtosecond transient absorption spectroscopy, cyclic and differential pulse voltammetry, ultraviolet photoelectron spectroscopy (UPS), and time-dependent density functional theory (TD-DFT). Spectral features were evaluated for the neutral porphyrins and differences observed among the various porphyrins were further explained using rendered frontier molecular orbitals pertaining to the relevant transitions. Electrochemically generated anionic and cationic porphyrin species indicate similar absorbance spectroscopic signatures attributed to a red-shift in the Soret band. Emissive behavior reveals the emergence of one new fluorescence decay pathway for the ionic porphyrin, distinct from the neutral macrocycle. Femtosecond transient absorption spectroscopy analysis provided further analysis of the implications on the excited-state as a function of the para substituent of the free-base meso-substituted tetraphenyl porphyrins. Herein, we provide an in-depth and comprehensive analysis of the electronic and excited state effects associated with systematically varying the induced dipole at the methine bridge of the free-base porphyrin macrocycle and the spectroscopic signatures related to the neutral, anionic, and cationic species of these porphyrins.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2022

Designing linear lattices for round beam in electron storage rings using the solution by linear matrices analysis

For some synchrotron light source beamline applications, a round beam is preferable to a flat one. A conventional method of obtaining round beam in an electron storage ring is to shift its tune close to a linear difference resonance. The linearly coupled beam dynamics is analyzed with perturbation theories, which have certain limitations. In this paper, we adopt the Solution by LInear Matrices (SLIM) analysis to calculate exact beam sizes to design round beam lattices. The SLIM analysis can deal with a generally linearly coupled accelerator lattice. The effects of various coupling sources on beam emittances and sizes can be studied within a self-consistent frame. Both the on- and off-resonance schemes to obtain round beams are explained with examples. The SLIM formalism for two widely used magnet models: combined-function bending magnets, and planar wigglers and undulators, is also derived.

43 PARTICLE ACCELERATORS↗
DOE OSTI2018

Enhanced photon collection of high surface area carbonate-doped mesoporous TiO2 nanospheres in dye sensitized solar cells

Highlights: • Carbonate-doped mesoporous TiO{sub 2} showed enhanced DSSC efficiency (5.4%). • Carbonate-doped TiO{sub 2} indicated higher surface area and incident photon conversion efficiency. • Carbonate-doped TiO{sub 2} showed lower resistance and longer life time. - Abstract: Carbonate-doped mesoporous TiO{sub 2} nanospheres with anatase phase were successfully synthesized by the simple solvothermal method. The synthesized nanospheres were monodispersed and composed of particles having the size of 10–15 nm. Scanning transmission electron microscopy (STEM) analysis showed nanosphere with large number particles. STEM-mapping clearly showed that Ti, O, and C were homogeneously distributed. Incorporation of carbonate in TiO{sub 2} was confirmed by XPS analysis. The peak at 284.3 eV was assigned to CO and indicated the formation TiOC structure due to carbonate doping in TiO{sub 2} lattice. Dye-sensitized solar cells (DSSCs) containing the nanospheres were fabricated by spray coating technique using N719 dye. Carbonate-doped mesoporous TiO{sub 2} showed enhanced DSSC efficiency (5.4%) compared to undoped (3.4%) and commercially available TiO{sub 2} (P25) (2.4%). It indicated (1) higher surface area and incident photon conversion efficiency, (2) lower resistance and longer life time compared with undoped TiO{sub 2}.

14 SOLAR ENERGY↗
DOE OSTI2018

Physical characterization of uranium oxide pellets and powder applied in the Nuclear Forensics International Technical Working Group Collaborative Materials Exercise 4

Physical characterization is one of the most broad and important categories of techniques to apply in a nuclear forensic examination. Physical characterization techniques vary from simple weighing and dimensional measurements to complex sample preparation and scanning electron microscopy-electron backscatter diffraction analysis. This paper reports on the physical characterization conducted by several international laboratories participating in the fourth Collaborative Materials Exercise, organized by the Nuclear Forensics International Technical Working Group. Methods include a range of physical measurements, microscopy-based observations, and profilometry. In conclusion, the value of these results for addressing key investigative questions concerning two uranium dioxide pellets and a uranium dioxide powder is discussed.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2016

Deltamethrin induced RIPK3-mediated caspase-independent non-apoptotic cell death in rat primary hepatocytes

Deltamethrin (DLM), a synthetic pyrethroid insecticide, is used all over the world for indoor and field pest management. In the present study, we investigated the elicited pathogenesis of DLM-induced hepatotoxicity in rat primary hepatocytes. DLM-induced cell death was accompanied with increased ROS generation, decreased mitochondrial membrane potential and G2/M arrest. Pre-treatment with N-acetyl cysteine/butylated hydroxyanisole/IM54 could partly rescue hepatocytes suggesting that ROS might play a role in DLM-induced toxicity. Interestingly, DLM treatment resulted in a caspase-independent but non-apoptotic cell death. Pre-treatment with pan-caspase inhibitor (ZVAD-FMK) could not rescue hepatocytes. Unaltered caspase-3 activity and absence of cleaved caspase-3 also corroborated our findings. Further, LDH release and Transmission electron microscopy (TEM) analysis demonstrated that DLM incites membrane disintegrity and necrotic damage. Immunochemical staining revealed an increased expression of inflammatory markers (TNFα, NFκB, iNOS, COX-2) following DLM treatment. Moreover, the enhanced RIPK3 expression in DLM treated groups and prominent rescue from cell death by GSK-872 indicated that DLM exposure could induce programmed necrosis in hepatocytes. The present study demonstrates that DLM could induce hepatotoxicity via non-apoptotic mode of cell death. - Highlights: • Deltamethrin (DLM) induces caspase-independent death in rat primary hepatocytes. • RIPK3 played a central role in DLM-mediated programmed necrosis in liver cells. • Reactive oxygen species played a role in DLM mediated hepatotoxity.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

First-principles study of atomic and electronic structures of 60° perfect and 30°/90° partial glide dislocations in CdTe

The atomic and electronic structures of 60° glide perfect and 30°/90° glide partial dislocations in CdTe are studied using combined semi-empirical and density functional theory calculations. The calculations predict that the dislocation cores tend to undergo significant reconstructions along the dislocation lines from the singly-periodic (SP) structures, yielding either doubly-periodic (DP) ordering by forming a dimer or quadruply-periodic (QP) ordering by alternating a dimer and a missing dimer. Charge modulation along the dislocation line, accompanied by the QP reconstruction for the Cd-/Te-core 60° perfect and 30° partials or the DP reconstruction for the Cd-core 90° partial, results in semiconducting character, as opposed to the metallic character of the SP dislocation cores. Dislocation-induced defect states for the 60° Cd-/Te-core are located relatively close to the band edges, whereas the defect states lie in the middle of the band gap for the 30° Cd-/Te-core partial dislocations. In addition to the intracore charge modulation within each QP core, the possibility of intercore charge transfer between two different dislocation cores when they are paired together in the same system is discussed. As a result, the analysis of the electronic structures reveals the potential role of the dislocations on charge transport in CdTe, particularly in terms of charge trapping and recombination.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗