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At least 1,063 records · Page 59
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

High pressure suppression of plasticity due to an overabundance of shear embryo formation

Abstract High pressure shear band formation is a critical phenomenon in energetic materials due to its influence on both mechanical strength and mechanochemical activation. While shear banding is known to occur in a variety of these materials, the governing dynamics of the mechanisms are not well defined for molecular crystals. We conduct molecular dynamics simulations of shock wave induced shear band formation in the energetic material 1,3,5-trinitroperhydro-1,3,5-triazine (RDX) to assess shear band nucleation processes. We find, that at high pressures, the initial formation sites for shear bands, “embryos”, form in excess and rapidly lower deviatoric stresses prior to shear band formation and growth. This results in the suppression of plastic deformation. A local cluster analysis is used to quantify and contrast this mechanism with a more typical shear banding seen at lower pressures. These results demonstrate a mechanism that is reversible in nature and that supersedes shear band formation at increased pressures. We anticipate that these results will have a broad impact on the modeling and development of high-strain rate application materials such as those for high explosives and hypersonic systems.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Si nanowire growth on sapphire: Classical incubation, reverse reaction, and steady state supersaturation

Si nanowire growth on sapphire substrates by the vapor-liquid-solid (VLS) method using Au catalyst particles has been studied. Sapphire was chosen as the substrate to ensure that the vapor phase is the only source of Si. Three hitherto unreported observations are described. First, an incubation period of 120–480 s, which is shown to be the incubation period as defined in classical nucleation theory, is reported. This incubation period permits the determination of a desolvation energy of Si from Au-Si alloys of 15 kT. Two, transmission electron microscopy studies of incubation, point to Si loss by reverse reaction as an important part of the mechanism of Si nanowire growth by VLS. Three, calculations using these physico-chemical parameters determined from incubation and measured steady state growth rates of Si nanowires show that wire growth happens from a supersaturated catalyst droplet.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2015

A seven-degree-of-freedom, time-dependent quantum dynamics study on the energy efficiency in surmounting the central energy barrier of the OH + CH{sub 3} → O + CH{sub 4} reaction

A time-dependent, quantum reaction dynamics calculation with seven degrees of freedom was carried out to study the energy efficiency in surmounting the approximate center energy barrier of OH + CH{sub 3}. The calculation shows the OH vibration excitations greatly enhance the reactivity, whereas the vibrational excitations of CH{sub 3} and the rotational excitations hinder the reactivity. On the basis of equal amount of total energy, although this reaction has a slight early barrier, it is the OH vibrational energy that is the dominate force in promoting the reactivity, not the translational energy. The studies on both the forward O + CH{sub 4} and reverse OH + CH{sub 3} reactions demonstrate, for these central barrier reactions, a small change of the barrier location can significantly change the energy efficacy roles on the reactivity. The calculated rate constants agree with the experimental data.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Synthesis, optical and electrochemical properties of Zn-porphyrin for dye sensitized solar cell applications

Zn-Porphyrin dye has been synthesized by the reaction between aldehydes and pyrrole. The dye structure was confirmed by {sup 1}H NMR, {sup 13}C NMR spectrum. The functional group of the dye molecule was confirmed by FTIR spectrum. The UV-Vis-NIR absorption spectrum of Zn-Porphyrin in DMF solution was recorded in spectrophotometer. The UV-Vis NIR spectrum of dye exhibits a strong Soret band and Q-band. Cyclic Voltammograms were obtained with three electrode systems: Pt as counter electrode, saturated calomel used as a reference electrode and glassy carbon as working electrode at a scan rate of 100 mV/s. The curves recorded the oxidation of 0.5 mM compound Zn-Porphyrin in a dichloromethane solution containing 0.1M TBAP as supporting electrolyte, reveal two successive quasi reversible redox couples with the first anodic and cathodic peak potentials of -0.2 V and -1 V. The second anodic and cathodic peak potentials are 0.82 V and 0.01 V respectively.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Modelling electron transfer in photosystem I: limits and perspectives

Uncovering the parameters underlying the electron transfer (ET) in photosynthetic reaction centres is of importance for understanding the molecular mechanisms underpinning their functionality. The reductive nature of most cofactors involved in photosynthetic ET makes the direct estimation of their properties difficult. Photosystem I (PSI) operates in a highly reducing regime, making the assessment of cofactor properties even more difficult. Kinetic modelling coupled to a non-adiabatic description of ET is a useful approach in overcoming this hindrance. Here we review the theory and modelling approaches that have been used in assessing parameters associated with ET reactions in PSI, with particular attention to ET reactions involving the phylloquinones and the iron–sulphur clusters. In most modelling studies, the goal is to estimate the driving force of ET, which is usually associated with the cofactor midpoint potentials. The driving force is sensitive to many factors, which define the ET rate, i.e. the reorganisation energy, the coupling with nuclear modes and the electronic matrix elements, which are explored and discussed here. The importance of an inclusive modelling of both forward and reverse ET processes is discussed and highlighted. It is shown that although estimates are indeed sensitive to the exact parameter sets employed in the modelling, a general consensus is still attained, pointing to a scenario where $ΔG^0_{A_{tA→Fx}}/ΔG^0_{A_{tB→Fx}}$ is weakly endergonic/exergonic, respectively. It is emphasised that to further refine those estimates, it will require a joint effort between computational modelling and more wide-ranging experimental studies.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2023

Trimer Quinoxalines as Organic Cathode Materials for Lithium-Ion Batteries

Due to synthetic ease, high redox potentials, low solubility in polar electrolytes, and good electric conductivity of their semiconducting crystals, discotic quinoxaline trimers (3Q) have been considered as possible candidates for 4 V organic cathodes in lithium-ion batteries. To assess their feasibility as such materials, several 3Q derivatives have been synthesized and tested in half-cells. In voltage limited cycling tests at 1.2–3.9 V vs Li/Li + , the specific discharge capacities of 40–180 mAh g -1 were obtained at a rate of 1 C, and multiple lithiation of 3Q and its derivatives was observed during discharge. However, the obtained discharge capacity was only a fraction of the theoretical capacity expected for reversible six-electron reduction; there was also rapid capacity fade. Our spectroscopic studies indicate the reversible three-electron lithiation at 2 V vs Li/Li + , but suggest instability of more highly discharged states. Finally, our conclusion is that while the 3Q derivatives combine several traits that are desirable in an organic cathode material (including negligible solubility, capacity for multiple charging, and near-100% coulombic efficiency), these materials are still impractical to use.

25 ENERGY STORAGE↗
DOE OSTI2026

Superstructure Optimization for Brine Valorization from Brackish Water Desalination

This poster presents preliminary results from a superstructure optimization framework developed to identify cost-optimal brine valorization configurations for brackish water desalination plants across diverse U.S. regional feed chemistries. The study uses brackish groundwater compositions from Arizona, California, Florida, New Mexico, and Texas. Using Pyomo Generalized Disjunctive Programming (GDP) within the WaterTAP modeling environment, the optimization framework simultaneously evaluates thousands of candidate treatment configurations, spanning nanofiltration, reverse osmosis, and chemical precipitation, to minimize the levelized cost of water (LCOW) while meeting water recovery targets and product recovery constraints. Results across eight representative feed clusters demonstrate water recovery rates of 57–87% and net LCOW values ranging from -$0.032/m³ (net revenue-positive) to $0.80/m. Notably, no single process configuration was optimal across all feed types, underscoring the necessity of feed-specific optimization. Products targeted include calcium carbonate (CaCO₃) at $0.01/kg and sodium chloride (NaCl) at $0.10/kg, both at 95% purity, with product revenues offsetting treatment costs in several scenarios. The work advances NAWI's process systems engineering capabilities for multi-configuration screening.

58 GEOSCIENCES↗
DOE OSTI2022

Cryptic Methane-Cycling by Methanogens During Multi-Year Incubation of Estuarine Sediment

As marine sediments are buried, microbial communities transition from sulfate-reduction to methane-production after sulfate is depleted. When this biogenic methane diffuses into the overlying sulfate-rich sediments, it forms a sulfate-methane transition zone (SMTZ) because sulfate reducers deplete hydrogen concentrations and make hydrogenotrophic methanogenesis exergonic in the reverse direction, a process called the anaerobic oxidation of methane (AOM). Microbial participation in these processes is often inferred from geochemistry, genes, and gene expression changes with sediment depth, using sedimentation rates to convert depth to time. Less is known about how natural sediments transition through these geochemical states transition in real-time. We examined 16S rRNA gene amplicon libraries and metatranscriptomes in microcosms of anoxic sediment from the White Oak River estuary, NC, with three destructively sampled replicates with methane added (586-day incubations) and three re-sampled un-amended replicates (895-day incubations). Sulfate dropped to a low value (∼0.3 mM) on similar days for both experiments (312 and 320 days, respectively), followed by a peak in hydrogen, intermittent increases in methane-cycling archaea starting on days 375 and 362 (mostly Methanolinea spp. and Methanosaeta spp., and Methanococcoides sp. ANME-3), and a methane peak 1 month later. However, methane δ 13 C values only show net methanogenesis 6 months after methane-cycling archaea increase and 4 months after the methane peak, when sulfate is consistently below 0.1 mM and hydrogen increases to a stable 0.61 ± 0.13 nM (days 553–586, n = 9). Sulfate-reducing bacteria (mostly Desulfatiglans spp. and Desulfosarcina sp. SEEP-SRB1) increase in relative abundance only during this period of net methane production, suggesting syntrophy with methanogens in the absence of sulfate. The transition from sulfate reduction to methane production in marine sediments occurs through a prolonged period of methane-cycling by methanogens at low sulfate concentrations, and steady growth of sulfate reducers along with methanogens after sulfate is depleted.

59 BASIC BIOLOGICAL SCIENCES↗
NASA NTRS1980

The stability properties of cylindrical force-free fields - Effect of an external potential field

A large-scale potential field with an embedded smaller-scale force-free structure gradient x B equals alpha B is studied in cylindrical geometry. Cases in which alpha goes continuously from a constant value alpha 0 on the axis to zero at large r are considered. Such a choice of alpha (r) produces fields which are realistic (few field reversals) but not completely stable. The MHD-unstable wavenumber regime is found. Since the considered equilibrium field exhibits a certain amount of magnetic shear, resistive instabilities can arise. The growth rates of the tearing mode in the limited MHD-stable region of k space are calculated, showing time-scales much shorter than the resistive decay time.

Chiuderi, C.↗
NASA NTRS1984

Global variation of the para hydrogen fraction in Jupiter's atmosphere and implications for dynamics on the outer planets

A detailed analysis of the Voyager infrared spectrometer measurements on Jupiter's atmosphere is presented, and possible implications of para hydrogen disequilibrium for the energetics and dynamics of that atmosphere are examined. The method of data analysis is described, and results for the large scale latitude variation of the para hydrogen fraction are presented. The Jovian results show pronounced latitude variation, and are compared with other parameters including wind fields, thermal structure, and various indicators of atmospheric clouds. The problem of equilibration rate is reexamined, and it is concluded that on Jupiter the equilibration time is longer than the radiative time constant at the level of emission to space, but that this inequality reverses at greater depths. A model for the interaction of fluid motions with the ortho-para conversion process is presented, and a consistent mixing length theory for the reacting ortho-para mixture is developed. Several implications of the Jovian data for atmospheric energetics and stability on the outer planets are presented.

Conrath, B. J.↗
NASA NTRS1986

Utilization of membranes for H2O recycle system

Conceptual studies of closed ecological life support systems (CELSS) carried out at NAL in Japan for a water recycle system using membranes are reviewed. The system will treat water from shower room, urine, impure condensation from gas recycle system, and so on. The H2O recycle system is composed of prefilter, ultrafiltration membrane, reverse osmosis membrane, and distillator. Some results are shown for a bullet train of toilet-flushing water recycle equipment with an ultraviltration membrane module. The constant value of the permeation rate with a 4.7 square meters of module is about 70 1/h after 500th of operation. Thermovaporization with porous polytetrafluorocarbon membrane is also proposed to replce the distillator.

Ohya, H.↗
NASA NTRS1989

On the driving force of PAH production

The kinetic factors affecting the production of polycyclic aromatic hydrocarbons (PAH) in high-temperature pyrolysis and combustion environments are analyzed. A lumped kinetic model representing polymerization-type growth by one irreversible step and two reversible steps is considered. It is shown that at high temperatures, PAH growth is controlled by the superequilibrium of hydrogen atoms; at low temperatures and low H2 concentrations, the PAH growth rate is proportional to the rate of the H-abstraction of a hydrogen atom from aromatic molecules; while at low temperatures and high H2 concentrations, it is controlled by the thermodynamics of the H-abstraction and the kinetics of acetylene addition to aromatic radicals. The presence of oxygen mainly affects the small-molecule reactions during the induction period.

Frenklach, Michael↗
NASA NTRS1991

The magnification of stars crossing a caustic. I - Lenses with smooth potentials

The possibility is explored of observing highly magnified images of individual stars within the long arcs that have been observed in rich clusters of galaxies. These images appear when a star crosses a caustic of the cluster's potential. When the cluster mass is distributed smoothly, the maximum magnification reached is typically of the order of 10 to the 7th. The star's image appears suddenly and reaches the maximum magnification in a few hours; then the magnification decreases slowly as the inverse of the square root of the time. This can also occur in the reverse order in time. For typical arcs, stars with bolometric luminosities of around 300 solar luminosities reach a maximum visual apparent magnitude of about 25. If brighter events are detected, the rate of detection is of the order of one every five years, for every arc intersecting a caustic. If the source galaxy is forming stars with a Saltpeter IMF, the probability that a 30-solar-mass star is magnified to a magnitude of 28 at any time is of the order of 20 percent.

Miralda-Escude, Jordi↗
NASA NTRS1991

Hydrostatic factors affect the gravity responses of algae and roots

The hypothesis of Wayne et al. (1990) that plant cells perceive gravity by sensing a pressure differential between the top and the bottom of the cell was tested by subjecting rice roots and cells of Caracean algae to external solutions of various densities. It was found that increasing the density of the external medium had a profound effect on the polar ratio (PR, the ratio between velocities of the downwardly and upwardly streaming cytoplasm) of the Caracean algae cells. When these cells were placed in solutions of denser compound, the PR decreased to less than 1, as the density of the external medium became higher than that of the cell; thus, the normal gravity-induced polarity was reversed, indicating that the osmotic pressure of the medium affects the cell's ability to respond to gravity. In rice roots, an increase of the density of the solution inhibited the rate of gravitropism. These results agree with predictions of a hydrostatic model for graviperception.

Staves, Mark P.↗
NASA NTRS2012

Performance Evaluation of Staged Bosch Process for CO2 Reduction to Produce Life Support Consumables

Utilizing carbon dioxide to produce water and hence oxygen is critical for sustained manned missions in space, and to support both NASA's cabin Atmosphere Revitalization System (ARS) and In-Situ Resource Utilization (ISRU) concepts. For long term missions beyond low Earth orbit, where resupply is significantly more difficult and costly, open loop ARS, like Sabatier, consume inputs such as hydrogen. The Bosch process, on the other hand, has the potential to achieve complete loop closure and is hence a preferred choice. However, current single stage Bosch reactor designs suffer from a large recycle penalty due to slow reaction rates and the inherent limitation in approaching thermodynamic equilibrium. Developmental efforts are seeking to improve upon the efficiency (hence reducing the recycle penalty) of current single stage Bosch reactors which employ traditional steel wool catalysts. Precision Combustion, Inc. (PCI), with support from NASA, has investigated the potential for utilizing catalysts supported over short-contact time Microlith substrates for the Bosch reaction to achieve faster reaction rates, higher conversions, and a reduced recycle flows. Proof-of-concept testing was accomplished for a staged Bosch process by splitting the chemistry in two separate reactors, first being the reverse water-gas-shift (RWGS) and the second being the carbon formation reactor (CFR) via hydrogenation and/or Boudouard. This paper presents the results from this feasibility study at various operating conditions. Additionally, results from two 70 hour durability tests for the RWGS reactor are discussed.

Vilekar, Saurabh A.↗
DOE OSTI2013

Bicyclic imidazolium ionic liquids as potential electrolytes for rechargeable lithium ion batteries

A bicyclic imidazolium ionic liquids, 1-ethyl-2,3-trimethyleneimidazolium bis(tri fluoromethane sulfonyl)imide ([ETMIm][TFSI]), and reference imidazolium compounds, 1-ethyl-3-methylimidazolium bis(trifluoromethane sulfonyl)imide ([EMIm][TFSI]) and 1, 2-dimethyl-3-butylimidazolium bis(trifluoromethane sulfonyl)imide ([DMBIm][TFSI]), were synthesized and investigated as solvents for lithium ion batteries. Although the alkylation at the C-2 position of the imidazolium ring does not affect the thermal stability of the ionic liquids, with or without the presence of 0.5 molar lithium bis(trifluoromethane sulfonyl)imide (LiTFSI), the stereochemical structure of the molecules has shown profound influences on the electrochemical properties of the corresponding ionic liquids. [ETMIm][TFSI] shows better reduction stability than do [EMIm][TFSI] and [DMBIm][TFSI], as confirmed by both linear sweep voltammery (LSV) and theoretical calculation. The Li||Li cell impedance of 0.5M LiTFSI/[ETMIm][TFSI] is stabilized, whereas that of 0.5M LiTFSI/[DMBIm][TFSI] is still fluctuating after 20 hours, indicating a relatively stable solid electrolyte interphase (SEI) is formed in the former. Furthermore, the Li||graphite half-cell based on 0.5M LiTFSI/[BTMIm][TFSI] exhibits reversible capacity of 250mAh g-1 and 70mAh g-1 at 25 C, which increases to 330 mAh g-1 and 250 mAh g-1 at 50 C, under the current rate of C/20 and C/10, respectively. For comparison, the Li||graphite half-cell based on 0.5M LiTFSI/[DMBIm][TFSI] exhibits poor capacity retention under the same current rate at both temperatures.

1-ethyl-2↗
DOE OSTI2019

Near-infrared [Fe ii] and H{sub 2} Emission-line Study of Galactic Supernova Remnants in the First Quadrant

We report the detection of near-infrared (NIR) [Fe ii] (1.644 μm) and H{sub 2} 1–0 S(1) (2.122 μm) line features associated with Galactic supernova remnants (SNRs) in the first quadrant using two narrowband imaging surveys, UWIFE and UWISH2. Among the total of 79 SNRs fully covered by both surveys, we found 19 [Fe ii]-emitting and 19 H{sub 2}-emitting SNRs, giving a detection rate of 24% for each. Eleven SNRs show both emission features. The detection rate of [Fe ii] and H{sub 2} peaks at the Galactic longitude (l) of 40°–50° and 30°–40°, respectively, and gradually decreases toward smaller/larger l. Five out of the eleven SNRs emitting both emission lines clearly show an “[Fe ii]–H{sub 2} reversal,” where H{sub 2} emission features are found outside the SNR boundary in [Fe ii] emission. Our NIR spectroscopy shows that the H{sub 2} emission originates from collisionally excited H{sub 2} gas. The brightest SNR in both [Fe ii] and H{sub 2} emissions is W49B, contributing more than 70% and 50% of the total [Fe ii] 1.644 μm (2.0 × 10{sup 4} L{sub ⊙}) and H{sub 2} 2.122 μm (1.2 × 10{sup 3} L{sub ⊙}) luminosities of the detected SNRs. The total [Fe ii] 1.644 μm luminosity of our Galaxy is a few times smaller than that expected from the SN rate using the correlation found in nearby starburst galaxies. We discuss possible explanations for this.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

Dynamical Janus Interface Design for Reversible and Fast-Charging Zinc–Iodine Battery under Extreme Operating Conditions

Aqueous zinc (Zn) iodine (I 2 ) batteries have emerged as viable alternatives to conventional metal-ion batteries. However, undesirable Zn deposition and irreversible iodine conversion during cycling have impeded their progress. Here, to overcome these concerns, we report a dynamical interface design by cation chemistry that improves the reversibility of Zn deposition and four-electron iodine conversion. Due to this design, we demonstrate an excellent Zn-plating/-stripping behavior in Zn||Cu asymmetric cells over 1000 cycles with an average Coulombic efficiency (CE) of 99.95%. Moreover, the Zn||I 2 full cells achieve a high-rate capability (217.1 mA h g –1 at 40 A g –1 ; C rate of 189.5C) at room temperature and enable stable cycling with a CE of more than 99% at -50 °C at a current density of 0.05 A g –1 . In situ spectroscopic investigations and simulations reveal that introducing tetraethylammonium cations as ion sieves can dynamically modulate the electrode–electrolyte interface environment, forming the unique water-deficient and chloride ion (Cl – )-rich interface. Such Janus interface accounts for the suppression of side reactions, the prevention of ICl decomposition, and the enrichment of reactants, enhancing the reversibility of Zn-stripping/-plating and four-electron iodine chemistry. This fundamental understanding of the intrinsic interplay between the electrode–electrolyte interface and cations offers a rational standpoint for tuning the reversibility of iodine conversion.

25 ENERGY STORAGE↗