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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Elucidating the geometric and electronic structure of a fully sulfided analog of an Anderson polyoxomolybdate cluster

The catalytic activity of transition metal sulfide (TMS) clusters in small molecule activation, redox transformations, and charge transfer has inspired the design of novel TMS-based materials for energy-related catalysis and chemical applications. Polyoxometalates (POMs), known for their structural diversity, can in principle be transformed into TMS clusters; however, fully sulfided analogs are rarely isolated, likely due to the strong tendency of uncapped TMS clusters to agglomerate. Here, we report the geometric and electronic structure of a capping ligand-free fully sulfided analog of heptamolybdate Anderson POM [Mo VI 7 O 24 ] 6− , synthesized through the sulfidation of a nanoconfined POM secured within a porous Zr-metal organic framework (NU-1000). A combined computational and experimental analysis indicates that the sulfided counterpart of the Anderson POM is geometrically and electronically more sophisticated than the parent POM. Comparison of experimental pair distribution function (PDF) data with computational simulations confirms that, unlike the oxygen-only [Mo VI 7 O 24 ] 6− cluster, the [Mo IV 7 (μ 3 -S) 6 (μ 2 -SH) 6 (S 2 ) 6 ] 2− polythiometalate (PTM) exhibits diverse sulfur anions (S 2− , HS − , S 2 2− ). DFT calculations indicate that H 2 S acts as a reducing agent, and together with terminal disulfide (S 2 2− ) ligands in the PTM structure, facilitates the complete reduction of all seven Mo VI centers in the parent POM to Mo IV . These findings are supported by X-ray photoelectron spectroscopy (XPS), which confirms exclusive Mo IV , and elemental analysis, which shows quantitative sulfur incorporation. Difference envelope density (DED) mapping further reveals that the PTM clusters are spatially confined within the MOF pores, preventing agglomeration and preserving molecular integrity.

Rabbani, S. M. Gulam [The Ohio State University, C↗
NASA NTRS1985

Virgo cluster as a high energy cosmic rays source

The extragalactic charged particles are reflecting from the Galaxy by its magnetic field. Assuming magnetic field in the Galaxy as quasilongitudinal, the mean transparency of Galaxy has been evaluated for extragalactic protons defined as a fraction of particles at a given energy from a given direction passing by the galactic plane. The anisotropy caused by the Galactic magnetic field reflection of protons can explain observed arrival directions of extensive air showers at large angle to the galactic plane. Our analysis shows that the increase with energy observed in sin b sup 11 is self-consistent with changing in the cosmic ray energy spectrum at high energy (E 10 to the 19th power eV) in the case when extragalactic cosmic ray source with spectral index -2.2 is at the position of the Virgo Cluster.

Karakula, S.↗
NASA NTRS1999

Low-Energy Sputtering Studies of Boron Nitride with Xenon Ions

Sputtering of boron nitride with xenon ions was investigated using secondary ion (SIMS) and secondary neutral (SNMS) mass spectrometry. The ions generated from the ion gun were incident on the target at an angle of 50' with respect to the surface'normal. The energy of ions ranged from 100 eV to 3 keV. A flood electron gun was used to neutralize the positive charge build-up on the target surface. The intensities of sputtered neutral and charged particles, including single atoms, molecules, and clusters, were measured as a function of ion energy. Positive SIMS spectra were dominated by the two boron isotopes whereas BN- and B- were the two major constituents of the negative SIMS spectra. Nitrogen could be detected only in the SNMS spectra. The intensity-energy curves of the sputtered particles were similar in shape. The knees in P-SIMS and SNMS intensity-energy curves appear at around I keV which is significantly higher that 100 to 200 eV energy range at which knees appear in the sputtering of medium and heavy elements by ions of argon and xenon. This difference in the position of the sputter yield knee between boron nitride and heavier targets is due to the reduced ion energy differences. The isotopic composition of secondary ions of boron were measured by bombarding boron nitride with xenon ions at energies ranging from 100 eV to 1.5 keV using a quadrupole mass spectrometer. An ion gun was used to generate the ion beam. A flood electron gun was used to neutralize the positive charge buildup on the target surface. The secondary ion flux was found to be enriched in heavy isotopes at lower incident ion energies. The heavy isotope enrichment was observed to decrease with increasing primary ion energy. Beyond 350 eV, light isotopes were sputtered preferentially with the enrichment increasing to an asymptotic value of 1.27 at 1.5 keV. The trend is similar to that of the isotopic enrichment observed earlier when copper was sputtered with xenon ions in the same energy range.

Ray, P. K.↗
NASA NTRS2020

Predicting Cell Death and Mutation Frequency for a Wide Spectrum of LET by Assuming DNA Break Clustering Inside Repair Domains

Cosmic radiation, which is composed of high charged and energy (HZE) particles, is responsible for cell death and mutation, which may be involved in cancer induction. Mutations are consequences of mis-repaired DNA breaks – especially double-strand breaks (DSBs) – that induce inter- and intra-chromosomal rearrangements (translocations, deletions, inversion). In this study, a computer simulation model is used to investigate the clustering of DSBs in repair domains, previously evidenced by our group in human breast cells [1]. This model is calibrated with experimental data measuring persistent 53BP1 radiation-induced foci (RIF) and is used to explain the high relative biological effectiveness (RBE) of HZE for both cell death and DNA mutation frequencies. We first validate our DSB cluster model using a new track structure model deployed on a simple geometrical configuration for repair domains in the nucleus; then we extend the scope from cell death to mutation induction. This work suggests that mechanism based on DSB repair process can explain several biological effects induced by HZE particles on different type of living cells

Plante, Ianik↗
NASA NTRSDate not supplied

Predicting cell death and mutation frequency for a wide spectrum of LET and across cell lines from DNA break clustering inside repair domains

Cosmic radiation, which is composed of high charged and energy (HZE) particles, is responsible for cell death and mutation, which may be involved in cancer induction. Mutations are consequences of mis-repaired DNA breaks – especially double-strand breaks (DSBs) – that induce inter- and intra-chromosomal rearrangements (translocations, deletions, inversion). In this study, a computer simulation model is used to investigate the clustering of DSBs in repair domains, previously evidenced by our group in human breast cells. This model is calibrated with experimental data measuring persistent 53BP1 radiation-induced foci (RIF) and is used to explain the high relative biological effectiveness (RBE) of HZE for both cell death and DNA mutation frequencies. We first validate our DSB cluster model using a new track structure model deployed on a simple geometrical configuration for repair domains in the nucleus; then we extend the scope from cell death to mutation induction. This work suggests that mechanism based on DSB repair process can explain several biological effects induced by HZE particles on different type of living cells.

Ianik Plante↗
DOE OSTI2025

Optimization of Ag Electrocatalyst Performance for CO2 to CO Conversion: Pairing Atomic Simulations with Experiments

Density-functional theory- based calculations that complement our series of experimental efforts on optimizing Ag electrocatalyst performance for CO2 to CO conversion were presented. Three key findings are drawn out from the combined UHV surface science, STM and electrochemical measurements: (1) Using a series of Ag nanoparticles with 2-6 nm average diameters, CO2 reduction reaction (CO2RR) activity increases, with particle between 2 nm and ∼4 nm demonstrating the highest combination of activity and selectivity; (2) Electronic metal−support interactions (EMSIs) between Ag and C dramatically improve CO2RR performance as evidenced by a scaling relationship between particle size and the relative Ag−C EMSIs strength, which improves the CO2-to-CO Faradaic efficiency of sub-2 nm Ag particles from 2 to ∼100% and increases the CO turnover frequency ∼15-fold compared with similarly sized bare Ag particles; (3) The performance Ag electrocatalysts is improved when supported on S-doped C materials. Computational modeling of 1−10 nm Ag particles predicts a nearly identical size-dependent trend with maximum CO2RR activity predicted for 3.7nm particles. The calculations support the promotional effect of C materials, showing a large charge transfer of 1.02 e from Ag clusters to defective C and a 0.41 eV less endergonic step of forming COOH intermediate on Ag/defective-C compared to the Ag/C system. Calculations indicate a more favorable energetic pathway of CO2-to-CO at the C-S-Ag interface, consistent with experiments.

CO2 utilization↗
DOE OSTI2024

Light-Induced Charge Separation in Photosystem I from Different Biological Species Characterized by Multifrequency Electron Paramagnetic Resonance Spectroscopy

Photosystem I (PSI) serves as a model system for studying fundamental processes such as electron transfer (ET) and energy conversion, which are not only central to photosynthesis but also have broader implications for bioenergy production and biomimetic device design. In this study, we employed electron paramagnetic resonance (EPR) spectroscopy to investigate key light-induced charge separation steps in PSI isolated from several green algal and cyanobacterial species. Following photoexcitation, rapid sequential ET occurs through either of two quasi-symmetric branches of donor/acceptor cofactors embedded within the protein core, termed the A and B branches. Using high-frequency (130 GHz) time-resolved EPR (TR-EPR) and deuteration techniques to enhance spectral resolution, we observed that at low temperatures prokaryotic PSI exhibits reversible ET in the A branch and irreversible ET in the B branch, while PSI from eukaryotic counterparts displays either reversible ET in both branches or exclusively in the B branch. Furthermore, we observed a notable correlation between low-temperature charge separation to the terminal [4Fe-4S] clusters of PSI, termed F A and F B , as reflected in the measured F A /F B ratio. These findings enhance our understanding of the mechanistic diversity of PSI’s ET across different species and underscore the importance of experimental design in resolving these differences. Though further research is necessary to elucidate the underlying mechanisms and the evolutionary significance of these variations in PSI charge separation, this study sets the stage for future investigations into the complex interplay between protein structure, ET pathways, and the environmental adaptations of photosynthetic organisms.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Recent advancements in atomic many-body methods for high-precision studies of isotope shifts

The development of atomic many-body methods, capable of incorporating electron correlation effects accurately, is required for isotope shift (IS) studies. In combination with precise measurements, such calculations help to extract nuclear charge radii differences, and to probe for signatures of physics beyond the Standard Model of particle physics. Here, we review here a few recently-developed methods in the relativistic many-body perturbation theory (RMBPT) and relativistic coupled-cluster (RCC) theory frameworks for calculations of IS factors in the highly charged ions (HCIs), and neutral or singly-charged ions, respectively. The results are presented for a wide range of atomic systems in order to demonstrate the interplay between quantum electrodynamics (QED) and electron correlation effects. In view of this, we start our discussions with the RMBPT calculations for a few HCIs by rigorously treating QED effects; then we outline methods to calculate IS factors in the one-valence atomic systems using two formulations of the RCC approach. Then we present calculations for two valence atomic systems, by employing the Fock-space RCC methods. For completeness, we briefly discuss theoretical input required for the upcoming experiments, their possibilities to probe nuclear properties and implications to fundamental physics studies.

QED effects↗
DOE OSTI2025

Morphology Effects on Free Energies of Proton-Coupled Electron Transfer in Polyoxotungstates

Polyoxotungstates have previously been established to facilitate the hydrogenation of small molecule substrates via hydrogen atom transfer from reactive hydroxyl groups formed at the assembly surface. Understanding structure−function relationships that dictate the thermochemistry and kinetics of protoncoupled electron transfer is key to controlling this chemistry. In this work, we combine comprehensive electrochemical experiments and density functional theory calculations to address how different polyoxotungstate morphologies, specifically W 6 O 19 −2 , W 10 O 32 −4 , SiW 12 O 40 −4 , and P 2 W 18 O 62 −6 , affect the bond dissociation free energies of surface hydroxides (BDFE(O−H)) formed upon reduction of the assembly in acidic media. Our results reveal increasing hydroxide bond strengths with increasing cluster size, and that anisotropic cluster geometries result in substantial thermodynamic differentiation of H-binding sites. We demonstrate an excellent agreement between theory and experiments on the reported BDFE(O−H) values and, importantly, we elucidate how cluster size and shape affect electronic properties (local charges and frontier molecular orbitals), giving rise to sites with increased preference for hydrogen binding, demonstrated in higher BDFE(O−H). Overall, this work aids the understanding and design of polyoxometalates exhibiting surface sites with tailored interaction strengths.

anions↗
DOE OSTI2025

Conductive Organometallic Polymers from Soluble Superatom Ions

Superatomic crystals comprising ligand-capped, metal chalcogenide clusters and fullerenes are modular materials that exhibit enhanced electronic, magnetic, and thermal conductivity properties. We find that neutral, M 4 S 4 (M = Fe, Co) clusters stabilized with N -heterocyclic carbenes (NHCs) can transfer charge to C 60 fullerene to form binary superatomic crystals. Notably, these compounds are soluble in various organic solvents, allowing their properties to be investigated in solution, unlike traditional fullerene-based superatomic crystals. The ion pairs can be further assembled into organometallic polymers using Janus-bis(NHCs) to cross-link the oxidized M 4 S 4 units. We show that the superatomic polymers are more conductive than both the precursor superatomic crystals and the polymers containing only neutral M 4 S 4 clusters. Similar conductivity values can be obtained when neutral M 4 S 4 –NHC polymers are doped with solutions of C 60 fullerene. These findings demonstrate that next generation superatomic materials can be prepared via the combination of charge transfer and polymerization with appropriate cross-linking agents.

carbon nanomaterials↗
NASA NTRS1982

Electronic levels and charge distribution near the interface of nickel

The energy levels in clusters of nickel atoms were investigated by means of a series of cluster calculations using both the multiple scattering and computational techniques (designated SSO) which avoids the muffin-tin approximation. The point group symmetry of the cluster has significant effect on the energy of levels nominally not occupied. This influences the electron transfer process during chemisorption. The SSO technique permits the approaching atom or molecule plus a small number of nickel atoms to be treated as a cluster. Specifically, molecular levels become more negative in the O atom, as well as in a CO molecule, as the metal atoms are approached. Thus, electron transfer from the nickel and bond formation is facilitated. This result is of importance in understanding chemisorption and catalytic processes.

Waber, J. T.↗
DOE OSTI2025

Density Functional Theory Study of Iron–Oxygen Divacancies in Magnetite (Fe 3 O 4 ) and Hematite (Fe 2 O 3 )

Density functional theory (DFT) calculations are employed to investigate the formation energies, charge redistribution, and binding energies of iron–oxygen divacancies in magnetite (Fe 3 O 4 ) and hematite (Fe 2 O 3 ). For magnetite, we focus on the low-temperature phase to explore variations with local environments. Building on previous DFT calculations of the variations in formation energies for oxygen vacancies with local charge and spin order in magnetite, we extend this analysis to include octahedral iron vacancies before analyzing the iron–oxygen divacancies. We also assessed the relative stability of iron–oxygen divacancies by comparing their formation energies with those of individual vacancies. Our findings reveal a significant energetic driving force for the formation of divacancy clusters, particularly in magnetite, where divacancies in the +1 charge state exhibit formation energies comparable to those of neutral iron vacancies under oxidizing conditions. In hematite, the results indicate a strong tendency for oxygen vacancies to bind to iron vacancies. These results highlight the significance of iron–oxygen vacancy complexes in the transport properties of iron oxides, with particular relevance to diffusion mechanisms under irradiation conditions.

36 MATERIALS SCIENCE↗
NASA NTRS1986

An apparent gravitational lens with an image separation of 2.6 arc min

Observations are reported which confirm Paczynski's 1986 speculation that the previously known (Arp and Hazard, 1980) pair of 19th magnitude quasars 1146+111B,C are actually two images of a single object produced by a gravitational lens. The image split is 157 arcsec, more than 20 times greater than any previously reported, thus indicating an exceptionally massive lensing object. The data supporting the lens hypothesis are remarkably similar, high signal-to-noise, moderate resolution spectra of the two components. Both spectra show strong Mg II 2798-angstrom emission at z = 1.012 plus or minus 0.001 with indistinguishable redshifts (delta v = 126 plus or minus 309 km/s), widths (FWHM = 64 plus or minus 4 angstroms) and detailed profile shapes. Both spectra also show broad troughs at 6180 angstroms and several weaker continuum features. Neither object exhibits the O II 3727-A forbidden line which is frequently strong in Mg II emission objects. If the foreground galaxy clustering apparent in a deep R band charge-coupled device image proves insufficient to explain the large image splitting, other possibilities such as massive dark objects (e.g. a black hole of about 10 to the 15th solar masses) or a cosmic string may be indicated.

Turner, E. L.↗
NASA NTRS1988

Active spacecraft potential control: An ion emitter experiment

The cluster spacecraft are instrumented with ion emitters for charge neutralization. The emitters produce indium ions at 6 keV. The ion current is adjusted in a feedback loop with instruments measuring the spacecraft potential. The system is based on the evaporation of indium in the apex field of a needle. The design of the active spacecraft potential control instruments, and the ion emitters is presented.

Riedler, W.↗
NASA NTRS2008

NASA Tech Briefs, August 2008

Customizable Digital Receivers for Radar Two-Camera Acquisition and Tracking of a Flying Target Visual Data Analysis for Satellites A Data Type for Efficient Representation of Other Data Types Hand-Held Ultrasonic Instrument for Reading Matrix Symbols Broadband Microstrip-to-Coplanar Strip Double-Y Balun A Topographical Lidar System for Terrain-Relative Navigation Programmable Low-Voltage Circuit Breaker and Tester Electronic Switch Arrays for Managing Microbattery Arrays Topics covered include: Lower-Dark-Current, Higher-Blue-Response CMOS Imagers; Fabricating Large-Area Sheets of Single-Layer Graphene by CVD; Support for Diagnosis of Custom Computer Hardware; Providing Goal-Based Autonomy for Commanding a Spacecraft; Dynamic Method for Identifying Collected Sample Mass; Optimal Planning and Problem-Solving; Attitude-Control Algorithm for Minimizing Maneuver Execution Errors; Grants Document-Generation System; Heat-Storage Modules Containing LiNO3 3H2O and Graphite Foam; Precipitation-Strengthened, High-Temperature, High-Force Shape Memory Alloys; Improved Relief Valve Would Be Less Susceptible to Failure; Safety Modification of Cam-and-Groove Hose Coupling; Using Composite Materials in a Cryogenic Pump; Using Electronic Noses to Detect Tumors During Neurosurgery; Producing Newborn Synchronous Mammalian Cells; Smaller, Lower-Power Fast-Neutron Scintillation Detectors; Rotationally Vibrating Electric-Field Mill; Estimating Hardness from the USDC Tool-Bit Temperature Rise; Particle-Charge Spectrometer; Automated Production of Movies on a Cluster of Computers; FIDO-Class Development Rover; and Tone-Based Command of Deep Space Probes Using Ground Antennas.

Source record↗
NASA NTRS2017

Predicting Cell Death and Mutation Frequency for a Wide Spectrum of LET by Assuming DNA Break Clustering Inside Repair Domains

The high relative biological effectiveness (RBE) of high charged and energy (HZE) particles for cell death, DNA mutations and cancer remain based on experimental data. In this work, we propose that the existence of DNA repair domains is sufficient to predict both cell death and mutation frequencies for any LET by only taking into account experimental data from low-LET, offering one mechanism for RBE across LET. We hypothesize that whenever multiple DNA double-strand breaks (DSBs) are generated within the same DNA repair domain, DSBs are actively regrouped for more efficient repair [1]. This hypothesis has been supported by the low-LET sublinear dose response observed at doses greater than ~1Gy for 53BP1 radiation-induced foci (RIF) reflecting increasing DSB/RIF with dose [2]. Previously, we modeled radiation-induced cell death of human breast cells by first inferring the size of these domains from the dose dependence of low-LET RIF, and by associating a lethality factor to the number of pairs of DSBs in each RIF [1]. In this work, we first integrate the new NASA computer models RITCARD (Relativistic Ion Tracks, Chromosome Aberrations, Repair, and Damage) [3] and BDSTracks (Biological Damage by Stochastic Tracks) for a more accurate microdosimetry and a better model of the nuclear organization to predict the location of DSBs. A large array of particles and energy are simulated, covering more than three orders of magnitude for LET (~1-1000 keV/µm). Next, we extend our previous model to predict mutation frequencies by assuming that clustered DSBs increase mutation probability, which is formalized by the mutation frequency being linearly dependent on both the number of DSBs and the number of pairs of DSBs inside individual RIF. Linear coefficients are estimated so that simulations predict accurately mutation frequencies observed in Chinese hamster cells exposed to low-LET. Keeping these coefficients unchanged, we then predict mutation frequencies induced by HZE by simulating DSBs and obtain RBEs for mutations and cell death following the expected experimental bell shape for LET dependence. We also observe an orientation effect that needs to be confirmed, showing different RBE depending on the angle of the HZE beam hitting the main axis of the cell.

Plante, Ianik↗
NASA NTRS1999

A Novel Acousto-Electric Levitator for Studies of Drop and Particle Clusters and Arrays

A novel and compact instrumentation for studying the behavior of drop sprays and of clusters of drops now permits fundamental research into the behavior of reacting and non-reacting fluid and solid species. The new capability is made possible by simultaneous acousto-electric levitation and charging of "seed" droplets (10-30 microns in diameter) which come together in 2-D clusters (with up to 300 droplets). These clusters are interesting in their own right because of their crystalline and quasi-crystalline forms, which depend on the acoustic and electric field parameters. By varying the electric and acoustic field intensities, one can cause a cluster of droplets to condense into larger drops (e.g. 50-300 microns) which, because of their charge, form uniformly spaced 2-D arrays of monodispersed drops (e.g. 30-40 array drops in preliminary experiments). One or more layers of these 2-D arrays can form in the acoustic standing wave. Such a configuration permits a wide range of fundamental studies of drop evaporation, combustion, and nucleation. The drops can be single or multicomponent. Therefore, fundamental materials studies can also be performed. Using this same Cluster and Array Generation (CAG) instrumentation, it has been also possible in preliminary experiments to demonstrate the clustering and arraying of solid particles, both coated with an electrically conducting layer and uncoated, and both charged and uncharged.

Tian, Yuren↗
NASA NTRS1989

Characterization of multiple-bit errors from single-ion tracks in integrated circuits

The spread of charge induced by an ion track in an integrated circuit and its subsequent collection at sensitive nodal junctions can cause multiple-bit errors. The authors have experimentally and analytically investigated this phenomenon using a 256-kb dynamic random-access memory (DRAM). The effects of different charge-transport mechanisms are illustrated, and two classes of ion-track multiple-bit error clusters are identified. It is demonstrated that ion tracks that hit a junction can affect the lateral spread of charge, depending on the nature of the pull-up load on the junction being hit. Ion tracks that do not hit a junction allow the nearly uninhibited lateral spread of charge.

Zoutendyk, J. A.↗