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At least 397 records · Page 22
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on Ac3Tb by Materials Project

Ac3Tb is Magnesium-derived structured and crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. Ac is bonded to eight equivalent Ac and four equivalent Tb atoms to form AcAc8Tb4 cuboctahedra that share corners with four equivalent TbAc12 cuboctahedra, corners with fourteen equivalent AcAc8Tb4 cuboctahedra, edges with six equivalent TbAc12 cuboctahedra, edges with twelve equivalent AcAc8Tb4 cuboctahedra, faces with four equivalent TbAc12 cuboctahedra, and faces with sixteen equivalent AcAc8Tb4 cuboctahedra. There are a spread of Ac–Ac bond distances ranging from 3.84–3.97 Å. There are two shorter (3.88 Å) and two longer (3.91 Å) Ac–Tb bond lengths. Tb is bonded to twelve equivalent Ac atoms to form TbAc12 cuboctahedra that share corners with six equivalent TbAc12 cuboctahedra, corners with twelve equivalent AcAc8Tb4 cuboctahedra, edges with eighteen equivalent AcAc8Tb4 cuboctahedra, faces with eight equivalent TbAc12 cuboctahedra, and faces with twelve equivalent AcAc8Tb4 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ac3Ho by Materials Project

Ac3Ho is beta Cu3Ti-like structured and crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. Ac is bonded to eight equivalent Ac and four equivalent Ho atoms to form AcAc8Ho4 cuboctahedra that share corners with four equivalent HoAc12 cuboctahedra, corners with fourteen equivalent AcAc8Ho4 cuboctahedra, edges with six equivalent HoAc12 cuboctahedra, edges with twelve equivalent AcAc8Ho4 cuboctahedra, faces with four equivalent HoAc12 cuboctahedra, and faces with sixteen equivalent AcAc8Ho4 cuboctahedra. There are a spread of Ac–Ac bond distances ranging from 3.84–3.99 Å. There are two shorter (3.87 Å) and two longer (3.91 Å) Ac–Ho bond lengths. Ho is bonded to twelve equivalent Ac atoms to form HoAc12 cuboctahedra that share corners with six equivalent HoAc12 cuboctahedra, corners with twelve equivalent AcAc8Ho4 cuboctahedra, edges with eighteen equivalent AcAc8Ho4 cuboctahedra, faces with eight equivalent HoAc12 cuboctahedra, and faces with twelve equivalent AcAc8Ho4 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on KAc3 by Materials Project

KAc3 is Uranium Silicide structured and crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. K is bonded to twelve equivalent Ac atoms to form KAc12 cuboctahedra that share corners with twelve equivalent KAc12 cuboctahedra, edges with twenty-four equivalent AcK4Ac8 cuboctahedra, faces with six equivalent KAc12 cuboctahedra, and faces with twelve equivalent AcK4Ac8 cuboctahedra. All K–Ac bond lengths are 4.06 Å. Ac is bonded to four equivalent K and eight equivalent Ac atoms to form AcK4Ac8 cuboctahedra that share corners with twelve equivalent AcK4Ac8 cuboctahedra, edges with eight equivalent KAc12 cuboctahedra, edges with sixteen equivalent AcK4Ac8 cuboctahedra, faces with four equivalent KAc12 cuboctahedra, and faces with fourteen equivalent AcK4Ac8 cuboctahedra. All Ac–Ac bond lengths are 4.06 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on LiAc3 by Materials Project

LiAc3 is Uranium Silicide structured and crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. Li is bonded to twelve equivalent Ac atoms to form LiAc12 cuboctahedra that share corners with twelve equivalent LiAc12 cuboctahedra, edges with twenty-four equivalent AcLi4Ac8 cuboctahedra, faces with six equivalent LiAc12 cuboctahedra, and faces with twelve equivalent AcLi4Ac8 cuboctahedra. All Li–Ac bond lengths are 3.85 Å. Ac is bonded to four equivalent Li and eight equivalent Ac atoms to form AcLi4Ac8 cuboctahedra that share corners with twelve equivalent AcLi4Ac8 cuboctahedra, edges with eight equivalent LiAc12 cuboctahedra, edges with sixteen equivalent AcLi4Ac8 cuboctahedra, faces with four equivalent LiAc12 cuboctahedra, and faces with fourteen equivalent AcLi4Ac8 cuboctahedra. All Ac–Ac bond lengths are 3.85 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ac3Cd by Materials Project

Ac3Cd is beta Cu3Ti-like structured and crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. Ac is bonded in a 12-coordinate geometry to eight equivalent Ac and four equivalent Cd atoms. There are a spread of Ac–Ac bond distances ranging from 3.70–4.03 Å. There are two shorter (3.69 Å) and two longer (3.86 Å) Ac–Cd bond lengths. Cd is bonded to twelve equivalent Ac atoms to form a mixture of corner and face-sharing CdAc12 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Tailored mesoporous structures of lignin-derived nano-carbons for multiple applications

This work uses a one-step KOH activation for lignin precursors to produce ultra-high mesoporous activated carbons (ACs) with an unprecedented combination of the surface area of 3207 m 2 g -1 and mesopore ratio of 76%. The ACs are applied for supercapacitors (SCs) and methylene blue (MB) adsorption. The capacitance of the SCs in the three-electrode system reaches 812.3 F g -1 and demonstrates a remarkable maximum MB adsorption capacity of 1250 mg g -1 . By modifying the process conditions, the mesopore ratio of ACs could be controlled from 10% to 80%. Compared with one-step activation, a two-step method produced microporous carbons with a lower surface area of 1227 m 2 g -1 and a high micropore ratio of 73%. The capacitance of SCs with two-step ACs reached 228.1 F g -1 and the maximum adsorption capacity of 476.19 mg g -1 for MB adsorption. The two-step method limited the surface area but had a higher oxygen surface functionality, benefiting its electrochemical performance. A techno-economic analysis reveals that the one-step KOH activation-based process develops ACs with a minimum selling price of $7648/ton. In conclusion, this work demonstrates tuning the processing-structure-property-performance relationship of lignin-based ACs to make an economically viable domestic carbon source.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

The coordination properties and ionic radius of actinium: A 120-year-old enigma

Actinium is an elusive element with untamed properties and represents a peculiar case in the periodic table, as its isotopes are all radioactive, the longest-lived one having only a 22-year half-life, and the availability of actinium isotopes remains very low (microgram level, at best), hindering research on its compounds. Despite being a natural element discovered more than 120 years ago, and despite an increasing interest in using one of its isotopes ( 225 Ac) for highly efficient cancer therapies, the chemistry of actinium is still largely unknown relative to other elements. Since Ac is the first element of the actinide series, it is accepted that its ion, Ac 3+ , is the most voluminous trivalent cation of the periodic table. However, the structural data available on Ac 3+ compounds are scarce and have mainly been collected in the 1940-1960's, when actinide chemistry was still in its infancy, and have not been put in perspective with the advances in the chemistry of other elements, making it difficult to accurately evaluate its actual size and coordination chemistry. Here, we review progress made on the chemistry of lanthanides and actinides and reevaluate the structural data published on Ac 3+ since the era of the Manhattan Project. The data are combined across different spectroscopic and characterization methods and presented in the context of periodic trends. When considering crystallographic data, solution chemistry results, and the nuclear properties of actinium isotopes, it appears that some structural parameters ascribed to the Ac 3+ ion may have been overestimated. This review can guide researchers interested in actinide sciences and those who are pursuing the development of actinium-based radiotherapies, from isotope production to clinical trials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Separation of radium and actinium in acetic acid/acetate solutions using TK101 resin

Here, the uptake and elution behavior of Ra and Ac was studied on TK101 resin using acetic acid and acetate buffer (acetic acid/lithium acetate) solutions. There is high extraction of Ra (>10 3 ) over a wide range of acetic acid concentrations (0.02 to 4 M) with slightly lower extraction (>10 2 ) in the acetate buffer solutions (pH 3.9 to 5.6). The Ac extraction is considerably lower with a maximum D w of ∼100, and negligible extraction at high acetic acid concentrations (> 1 M) and in the acetate buffer solutions. The difference in D w can be leveraged for highly efficient separations of Ac from Ra, with no detectable Ra in the Ac fractions and high Ac yields (∼100%). These separations may be useful for radiopharmaceutical applications as the Ac purity is extremely high and the elution conditions can be optimized to be biologically safe and appropriate for chelation to molecules relevant to targeted alpha therapy.

and nuclear chemistry↗
DOE OSTI2023

Cyber threat assessment of machine learning driven autonomous control systems of nuclear power plants

We report advanced cyber-attacks against critical infrastructure and the energy sector are becoming more common. With the invention of autonomous control systems (ACS) within advanced nuclear reactor designs, system designers, reactor operators, and regulators must consider cybersecurity during the design and operational phases. This article provides a cyber threat assessment of machine learning (ML)-based digital twinning (DT) technologies in the context of advanced reactor ACS. A cyber–physical testbed was created to emulate nuclear reactor digital instrumentation and controls (I&C) and act as a basis for the ACS. The ACS was designed as two plant-level DTs predicting reactor malfunctions and determining control actions and two component-level DTs responsible for classifying component states and forecasting component inputs and outputs (I/O). Two duplicate ACS designs– one using a traditional ML framework and one using an automated ML (AutoML) framework– were created and tested against cyber-attacks on training data, real-time process data, and ML model architectures to determine their respective qualitative cyber-risk in terms of likelihood and impact. Both frameworks showed similar cyber-resilience against training, real-time, and ML architecture attacks, proving that neither is inherently more secure. Recommended safeguard and security measures are posed to system designers, reactor operators, and regulators to maintain the cybersecurity of ML-based DT technologies such as ACS, prompting a holistic view of shared responsibility for maintaining cyber-secure ML-based systems.

99 GENERAL AND MISCELLANEOUS↗
DOE OSTI2024

Actinium chelation and crystallization in a macromolecular scaffold

Abstract Targeted alpha therapy (TAT) pairs the specificity of antigen targeting with the lethality of alpha particles to eradicate cancerous cells. Actinium-225 [ 225 Ac; t 1/2 = 9.920(3) days] is an alpha-emitting radioisotope driving the next generation of TAT radiopharmaceuticals. Despite promising clinical results, a fundamental understanding of Ac coordination chemistry lags behind the rest of the Periodic Table due to its limited availability, lack of stable isotopes, and inadequate systems poised to probe the chemical behavior of this radionuclide. In this work, we demonstrate a platform that combines an 8-coordinate synthetic ligand and a mammalian protein to characterize the solution and solid-state behavior of the longest-lived Ac isotope, 227 Ac [t 1/2 = 21.772(3) years]. We expect these results to direct renewed efforts for 225 Ac-TAT development, aid in understanding Ac coordination behavior relative to other +3 lanthanides and actinides, and more broadly inform this element’s position on the Periodic Table.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Toward more accurate adiabatic connection approach for multireference wavefunctions

A multiconfigurational adiabatic connection (AC) formalism is an attractive approach to compute the dynamic correlation within the complete active space self-consistent field and density matrix renormalization group (DMRG) models. Practical realizations of AC have been based on two approximations: (i) fixing one- and two-electron reduced density matrices (1- and 2-RDMs) at the zero-coupling constant limit and (ii) extended random phase approximation (ERPA). This work investigates the effect of removing the “fixed-RDM” approximation in AC. The analysis is carried out for two electronic Hamiltonian partitionings: the group product function- and the Dyall Hamiltonians. Exact reference AC integrands are generated from the DMRG full configuration interaction solver. Two AC models are investigated, employing either exact 1- and 2-RDMs or their second-order expansions in the coupling constant in the ERPA equations. Calculations for model molecules indicate that lifting the fixed-RDM approximation is a viable way toward improving the accuracy of existing AC approximations.

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

Thioester synthesis by a designed nickel enzyme models prebiotic energy conversion

The formation of carbon–carbon bonds from prebiotic precursors such as carbon dioxide represents the foundation of all primordial life processes. In extant organisms, this reaction is carried out by the carbon monoxide dehydrogenase (CODH)/acetyl coenzyme A synthase (ACS) enzyme, which performs the cornerstone reaction in the ancient Wood–Ljungdahl metabolic pathway to synthesize the key biological metabolite, acetyl-CoA. Despite its significance, a fundamental understanding of this transformation is lacking, hampering efforts to harness analogous chemistry. To address these knowledge gaps, we have designed an artificial metalloenzyme within the azurin protein scaffold as a structural, functional, and mechanistic model of ACS. We demonstrate the intermediacy of the Ni I species and requirement for ordered substrate binding in the bioorganometallic carbon–carbon bond-forming reaction from the one-carbon ACS substrates. The electronic and geometric structures of the nickel-acetyl intermediate have been characterized using time-resolved optical, electron paramagnetic resonance, and X-ray absorption spectroscopy in conjunction with quantum chemical calculations. Moreover, we demonstrate that the nickel-acetyl species is chemically competent for selective acyl transfer upon thiol addition to biosynthesize an activated thioester. Drawing an analogy to the native enzyme, a mechanism for thioester generation by this ACS model has been proposed. The fundamental insight into the enzymatic process provided by this rudimentary ACS model has implications for the evolution of primitive ACS-like proteins. Ultimately, these findings offer strategies for development of highly active catalysts for sustainable generation of liquid fuels from one-carbon substrates, with potential for broad applications across diverse fields ranging from energy storage to environmental remediation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Secondary electron emission measurements from imidazolium-based ionic liquids

The electron-induced secondary electron emission (SEE) yields of imidazolium-based ionic liquids are presented for primary electron beam energies between 30 and 1000 eV. These results are important for understanding plasma synthesis of nanoparticles in plasma discharges with an ionic liquid electrode. Due to their low vapor pressure and high conductivity, ionic liquids can produce metal nanoparticles in low-pressure plasmas through reduction of dissolved metal salts. In this work, the low vapor pressure of ionic liquids is exploited to directly measure SEE yields by bombarding the liquid with electrons and measuring the resulting currents. The ionic liquids studied are [BMIM][Ac], [EMIM][Ac], and [BMIM][BF 4 ]. The SEE yields vary significantly over the energy range, with maximum yields of around 2 at 200 eV for [BMIM][Ac] and [EMIM][Ac], and 1.8 at 250 eV for [BMIM][BF 4 ]. Molecular orbital calculations indicate that the acetate anion is the likely electron donor for [BMIM][Ac] and [EMIM][Ac], while in [BMIM][BF 4 ], the electrons likely originate from the [BMIM] + cation. The differences in SEE yields are attributed to varying ionization potentials and molecular structures of the ionic liquids. These findings are essential for accurate modeling of plasma discharges and understanding SEE mechanisms in ionic liquids.

ionic liquids↗
DOE OSTI2020

Dynamic pair-breaking current, critical superfluid velocity, and nonlinear electromagnetic response of nonequilibrium superconductors

Here, we report numerical calculations of a dynamic pair-breaking current density $J_d$ and a critical superfluid velocity $v_d$ in a nonequilibrium superconductor carrying a uniform, large-amplitude AC current density $J(t) = J_a$sinΩ$\textit{t}$ with Ω well below the gap frequency Ω $\ll Δ_0/ℏ$. The dependencies $J_d$(Ω, $\textit{T}$) and $v_d$(Ω, $\textit{T}$) near the critical temperature $T_c$ were calculated from either the full time-dependent nonequilibrium equations for a dirty $\textit{s}$-wave superconductor or the time-dependent Ginzburg-Landau (TDGL) equations for a gapped superconductor, taking into account the GL relaxation time of the order parameter $τ_{\text{GL}}$ and the inelastic electron-phonon relaxation time of quasiparticles $τ_E$. We show that both approaches give similar frequency dependencies of $J_d$(Ω) and $v_d$(Ω) which gradually increase from their static pair-breaking GL values $J_c$ and $v_c$ at Ω$τ_E \ll$1 to $\sqrt{2}J_c$ and $\sqrt{2}v_c$ at Ω$τ_E \gg$ 1. Here $J_d, v_d$ and a dynamic superheating field at which the Meissner state becomes unstable were calculated in two different regimes of a fixed AC current and a fixed AC superfluid velocity induced by the applied AC magnetic field $H = H_a$ sinΩ$\textit{t}$ in a thin superconducting filament or a type-II superconductor with a large GL parameter. We also calculated a nonlinear electromagnetic response of a nonequilibrium superconducting state, particularly a dynamic kinetic inductance and a dissipative quasiparticle conductivity, taking into account the oscillatory dynamics of superconducting condensate and the kinetics of quasiparticles driven by a strong AC current. It is shown that an AC current density produces multiple harmonics of the electric field, the amplitudes of the higher-order harmonics diminishing as $τ_E$ increases.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

BEEAM (Building Electrical Efficiency Analysis Model) [SWR-20-107]

Modern high-performance buildings exhibit an increasing number of building loads that use direct current (DC) electricity internally, rather than alternating current (AC), due to the advent of low-cost computing and advanced power electronics. Powering DC devices from the AC grid requires AC/DC power conversion, which introduces energy losses and reduces efficiency. As DC loads proliferate, the cumulative wasted energy associated with hundreds of millions of AC/DC converters has become one of the broadest energy savings opportunities in buildings. DC power distribution systems have been proposed as an elegant and transformative solution to the problem of DC devices. In a DC distribution system, the building's wires carry DC electricity, rather than AC; and a few centralized, highly efficient AC/DC converters replace the many smaller, less efficient converters that serve individual DC loads. Unfortunately, the trade-offs associated with DC distribution systems are not well understood. Reported energy savings associated with DC power distribution differ widely and have not been well validated. The Building Electrical Efficiency Analysis Model (BEEAM) is a Modelica library that simulates the efficiency of building electrical distribution systems using harmonic power flow. BEEAM can model a wide variety of building distribution topologies, including three-phase AC, single-phase AC, unipolar DC, bipolar DC, and hybrid networks under both balanced and unbalanced load conditions. BEEAM accurately models power electronic converter losses, provides granular estimates of losses throughout the distribution system, and properly models efficiency at part load conditions. Users can package BEEAM within a functional mockup unit (FMU), enabling co-simulation with other modeling platform, such as EnergyPlus. In summary, BEEAM provides a tool suite for fair and accurate comparison of the efficiency of building electrical distribution systems, including AC, DC, and hybrid systems.

Frank, Stephen↗
DOE OSTI2020

Materials Data on AcMg3 by Materials Project

Mg3Ac is alpha bismuth trifluoride structured and crystallizes in the cubic Fm-3m space group. The structure is three-dimensional. there are two inequivalent Mg sites. In the first Mg site, Mg is bonded in a 8-coordinate geometry to eight equivalent Mg and six equivalent Ac atoms. All Mg–Mg bond lengths are 3.34 Å. All Mg–Ac bond lengths are 3.86 Å. In the second Mg site, Mg is bonded in a body-centered cubic geometry to four equivalent Mg and four equivalent Ac atoms. All Mg–Ac bond lengths are 3.34 Å. Ac is bonded in a distorted body-centered cubic geometry to fourteen Mg atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ac2AgIr by Materials Project

Ac2IrAg is Heusler structured and crystallizes in the cubic Fm-3m space group. The structure is three-dimensional. Ac is bonded in a body-centered cubic geometry to four equivalent Ir and four equivalent Ag atoms. All Ac–Ir bond lengths are 3.31 Å. All Ac–Ag bond lengths are 3.31 Å. Ir is bonded in a body-centered cubic geometry to eight equivalent Ac atoms. Ag is bonded in a body-centered cubic geometry to eight equivalent Ac atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ac2HgGe by Materials Project

Ac2HgGe is Heusler structured and crystallizes in the cubic Fm-3m space group. The structure is three-dimensional. Ac is bonded in a body-centered cubic geometry to four equivalent Hg and four equivalent Ge atoms. All Ac–Hg bond lengths are 3.44 Å. All Ac–Ge bond lengths are 3.44 Å. Hg is bonded in a body-centered cubic geometry to eight equivalent Ac atoms. Ge is bonded in a body-centered cubic geometry to eight equivalent Ac atoms.

36 MATERIALS SCIENCE↗