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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 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Evidence for equilibrium gels of valence-limited particles

We explore the formation and structure of gels produced from solutions of the aromatic dipeptide derivative molecule fluorenylmethoxycarbonyl–diphenylalanine (Fmoc–FF) in dimethyl sulfoxide (DMSO). Mixing these solutions with water results in the self-assembly of Fmoc–FF molecules into space-filling fibrous networks, exhibiting mechanical properties characteristic of gels. Using confocal fluorescence microscopy, we observe the gel transition in situ and find that, upon the addition of water, the solution undergoes a rapid transition to a non-equilibrium state forming ~2 μm spheres, followed by the formation of fibers 5–10 nm in diameter, nucleating at a sphere surface and expanding into the solution as the remaining spheres dissolve, extending the network. The gel aging process is associated with the network becoming increasingly uniform through apparent redissolution/reaggregation of the Fmoc–FF molecules, corresponding to the observed increase in the elastic modulus to a plateau value. We demonstrate that this increase in uniformity and elastic modulus can be expedited by controlling the temperature of the system, as well as that these gels are thermally reversible, further indicating that the system is in equilibrium in its fibrous network state. X-ray scattering information suggests that the packing of the molecules within a fiber is based on π–π stacking of β-sheets, consistent with models proposed in the literature for similar systems, implying that each particle (molecule) possesses a limited number of interaction sites. Furthermore, these observations provide experimental evidence that these low molecular weight gelator molecules can be considered valence-limited “patchy” particles, which associate at low enough temperature to form equilibrium gels.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Excitations of one-valence-proton, one-valence-neutron nucleus {sup 210}Bi from cold-neutron capture

The low-spin structure of one-proton, one-neutron {sup 210}Bi nucleus was investigated in cold-neutron capture reaction on {sup 209}Bi. The γ-coincidence measurements were performed with use of EXILL array consisted of 16 HPGe detectors. The experimental results were compared to shell-model calculations involving valence particles excitations. The {sup 210}Bi nucleus offers the potential to test the effective proton-neutron interactions because most of the states should arise from the proton-neutron excitations. Additionally, it was discovered that a few states should come from the couplings of valence particles to the 3{sup −} octupole vibration in {sup 208}Pb which provides also the possibility of testing the calculations involving the core excitations.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

Eye patches: Protein assembly of index-gradient squid lenses

A parabolic relationship between lens radius and refractive index allows spherical lenses to avoid spherical aberration. We show that in squid, patchy colloidal physics resulted from an evolutionary radiation of globular S-crystallin proteins. Small-angle x-ray scattering experiments on lens tissue show colloidal gels of S-crystallins at all radial positions. Sparse lens materials form via low-valence linkages between disordered loops protruding from the protein surface. The loops are polydisperse and bind via a set of hydrogen bonds between disordered side chains. Peripheral lens regions with low particle valence form stable, volume-spanning gels at low density, whereas central regions with higher average valence gel at higher densities. The proteins demonstrate an evolved set of linkers for self-assembly of nanoparticles into volumetric materials.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2025

Elastic scattering in the 12 N + 197 Au system at 𝐸 lab = 70 MeV

Halo structure is an interesting exotic configuration developed in some light weakly bound nuclei, where a valence particle orbits a nuclear core. Signatures of halo structure can be observed in the angular distributions of the elastic scattering induced by these nuclei at energies around the Coulomb barrier. There are some well-studied reactions with neutron-rich halo nuclei, such as 6 He and 11 Li . However, the information is scarce on the proton-rich side. Recent works confirm the halo structure in the 8B nuclei but still lack more experimental studies for other proton-halo candidates, such as 12 N and 17 F. In this work, we report experimental data for the elastic scattering of 12 N on 197 Au target at 𝐸 lab = 70 MeV. The 12 N is a proton-rich nucleus with proton separation energy 𝑆 𝑝 = 600 keV, which is higher than the 8 B (𝑆 𝑝 = 137 keV) and almost the same as the 17 F (𝑆 𝑝 = 601 keV). Data were obtained at the Cyclotron Institute of Texas A&M University where the 12 N radioactive beam was produced by the momentum achromatic recoil spectrometer. The calculation of the optical model was used to fit the measured angular distribution for the elastic scattering and to obtain the reaction cross section 𝜎 𝑅 . We also performed continuum discretized coupled-channel calculations to compare with the experimental data. The angular distribution of the elastic cross sections exhibits a suppression of the Fresnel peak. From the fitting of the optical model, we obtain the total reaction cross section, 𝜎 𝑅 = 1269 ± 41 mb. The agreement between the CDCC calculation and the experimental elastic scattering data is limited and the breakdown does not exhaust the measured 𝜎 𝑅 . The resulting reduced reaction cross section 𝜎 Red for 12 N + 197 Au is large and comparable to the one obtained for the 8 B + 208 Pb system. This suggests a strong decoupling of the valence proton from the core because of the low binding energy and a dynamic polarization effect. Here, more research is required to estimate the contribution of core excitation.

Elastic scattering reactions↗
DOE OSTI2025

Five-body systems with Bethe-Salpeter equations

We extend the Bethe-Salpeter formalism to systems made of five valence particles. Restricting ourselves to two-body interactions, we derive the subtraction terms necessary to prevent overcounting. We solve the five-body Bethe-Salpeter equation numerically for a system of five scalar particles interacting by a scalar exchange boson. To make the calculations tractable, we implement properties of the permutation group S 5 and construct an approximation based on intermediate two- and three-body poles. We extract the five-body ground and excited states along with the spectra obtained from the two-, three-, and four-body equations. In the limit of a massless exchange particle, the two-, three, four- and five-body states coexist within a certain range of the coupling strength, whereas for heavier exchange particles the five-body system becomes Borromean. Our study serves as a building block for the calculation of pentaquark properties using functional methods.

Eichmann, Gernot [Univ. of Graz (Austria)] (ORCID:↗
DOE OSTI2014

Nuclear structure studies close to N = Z = 50

The level structures in {sup 98,99}Rh, and {sup 99}Pd nuclei have been investigated through in beam γ-ray spectroscopic techniques following the {sup 75}As({sup 28}Si, xpyn) fusion-evaporation reaction at E{sub lab} = 120 MeV. These investigations were carried out using Indian-National-Gamma-Array (INGA) consisting of Compton-suppressed clover detectors at the Inter-University Accelerator Centre, New Delhi. The level structures observed in {sup 99}Pd, and {sup 98,99}Rh have been established up to ∼ 11 MeV, 10 MeV and 16 MeV excitation energy and spin ∼ 23ħ, 23ħ, and 28ħ respectively. In the doubly-odd {sup 98}Rh nucleus, new band structures and isomeric states have been identified at lower spins and new states below the previously identified 2{sup +} ground state (T{sub 1/2} = 8.5 m) are identified. In the present work {sup 99}Rh structure have been observed similar to {sup 101}Rh which is based on p{sub 1/2} and g{sub 9/2} orbitals. Various positive and negative parity states in these nuclei are observed to be energetically more favored with respect to the neighboring ones, and are likely to be the maximally aligned states obtained by angular momentum coupling of the valence particles (holes). The level structures observed in {sup 99}Pd have been interpreted in the framework of a microscopic theory based on the deformed Hartree-Fock (HF) and angular momentum projection techniques. Band structures at low excitation energy are based on the low-Ω νg{sub 7/2} and νd{sub 5/2} orbitals, have been observed in {sup 99}Pd. Band structure at higher spins are reproduced with the ν(g{sub 7/2}){sup 2}⊗ν(g{sub 9/2}){sup −1}⊗ν(h{sub 11/2}){sup 2}⊗π(g{sub 9/2}){sup 6} configurations. Observation of new E1 transitions linking the opposite parity νh{sub 11/2} and νd{sub 5/2} bands provide fingerprints of possible octupole correlations in {sup 99}Pd. The extracted values of the B(E1)/B(E2) ratios for the lower levels in the νh{sub 11/2} band are ∼ 10{sup −7} [fm]{sup −2}.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Realistic shell-model calculations for p -shell nuclei including contributions of a chiral three-body force

In this study we present an evolution of our derivation of the shell-model effective Hamiltonian, namely introducing effects of three-body contributions. More precisely, we consider a three-body potential at next-to-next-to-leading order in chiral perturbation theory, and the induced three-body forces that arise from many-body correlations among valence nucleons. The first one is included, in the derivation of the effective Hamiltonian for one- and two-valence nucleon-systems, at first order in the many-body perturbation theory. Namely, we include only the three-body interaction between one or two valence nucleons and those belonging to the core. For nuclei with more than two valence particles, both induced—turned on by the two-body potential—and genuine three-body forces come into play. Since it is difficult to perform shell-model calculations with three-body forces, these contributions are estimated for the ground-state energy only. To establish the reliability of our approximations, we focus attention on nuclei belonging to the p shell, aiming to benchmark our calculations against those performed with the ab initio no-core shell model. The obtained results are satisfactory, and pave the way to the application of our approach to nuclear systems with heavier masses.

6 ≤ A ≤ 19↗
DOE OSTI2022

Description for N = 126 Isotones 210 Po and 212 Rn with Particle-Hole Excited Nucleon-Pair Approximation and Realistic Effective Interaction

In this paper, we study yrast states of two N=126 isotones 210 Po and 212 Rn using the nucleon-pair approximation with particle–hole excitations and using a low-momentum interaction V low–k renormalized from the free CD-Bonn NN potential. An overall good agreement with experimental level structures, B(E2)s, and B(E3)s, is achieved. We also calculate the probabilities of neutron particle–hole excitations in these yrast states, with a focus on negative-parity states, which reflect the roles played by the neutron negative-parity configurations of one-particle-one-hole excitations across the N=126 shell gap and the negative-parity configurations of valence proton particles involving the 0i 13/2 orbit. The N=126 shell gap is discussed in terms of energies of neutron one-particle-one-hole excitations.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

Experimental study of the rearrangements of valence protons and neutrons amongst single-particle orbits during double- β decay in Mo 100

The rearrangements of protons and neutrons amongst the valence single-particle orbitals during double-beta decay of Mo-100 have been determined by measuring cross sections in (d, p), (p, d), (He-3, a), and (He-3, d) reactions on Mo-98,Mo-100 and Ru-100,Ru-102 targets. The deduced nucleon occupancies reveal significant discrepancies when compared with theoretical calculations; the same calculations have previously been used to determine the nuclear matrix element associated with the decay probability of double-beta decay of the Mo-100 system.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2019

Effective interactions in the s d shell

We perform here a quantitative study of the microscopic effective shell-model interactions in the valence sd shell, obtained from modern nucleon-nucleon potentials, chiral N3LO, JISP16 and Daejeon16, using No-Core Shell-Model wave functions and the Okubo-Lee-Suzuki transformation. We investigate the monopole properties of those interactions in comparison with the phenomenological universal sd-shell interaction, USDB. Theoretical binding energies and low-energy spectra of O isotopes and of selected sd-shell nuclei, are presented. We conclude that there is a noticeable improvement in the quality of the effective interaction when it is derived from the Daejeon16 potential. We show that its proton-neutron centroids are consistent with those from USDB. We then propose monopole modifications of the Daejeon16 centroids in order to provide an adjusted interaction yielding significantly improved agreement with the experiment. A spin-tensor decomposition of two-body effective interactions is applied in order to extract more information on the structure of the centroids and to understand the reason for deficiencies arising from our current theoretical approximations. The concern of the possible role of the three-nucleon forces is addressed.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2020

Programmable Anisotropy and Percolation in Supramolecular Patchy Particle Gels

Patchy particle interactions are predicted to facilitate the controlled self-assembly and arrest of particles into phase-stable and morphologically tunable "equilibrium" gels, which avoids the arrested phase separation and subsequent aging that is typically observed in traditional particle gels with isotropic interactions. Despite these promising traits of patchy particle interactions, such tunable equilibrium gels have yet to be realized in the laboratory due to experimental limitations associated with synthesizing patchy particles in high yield. Here, we introduce a supramolecular metal-coordination platform consisting of metallic nanoparticles linked by telechelic polymer chains, which validates the predictions associated with patchy particle interactions and facilitates the design of equilibrium particle hydrogels through limited valency interactions. We demonstrate that the interaction valency and self-assembly of the particles can be effectively controlled by adjusting the relative concentration of polymeric linkers to nanoparticles, which enables the gelation of patchy particle hydrogels with programmable local anisotropy, morphology, and low mechanical percolation thresholds. Moreover, by crowding the local environment around the patchy particles with competing interactions, we introduce an independent method to control the self-assembly of the nanoparticles, thereby enabling the design of highly anisotropic particle hydrogels with substantially reduced percolation thresholds. We thus establish a canonical platform that facilitates multifaceted control of the self-assembly of the patchy nanoparticles en route to the design of patchy particle gels with tunable valencies, morphologies, and percolation thresholds. These advances lay important foundations for further fundamental studies of patchy particle systems and for designing tunable gel materials that address a wide range of engineering applications.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Nanoscale dynamics and aging of fibrous peptide-based gels

Solutions of the aromatic dipeptide derivative molecule fluorenylmethoxycarbonyl-diphenylalanine (Fmoc-FF) in dimethyl sulfoxide produce fibrous gels when mixed with water. We study the evolution of density fluctuations of this three-component system using X-ray photon correlation spectroscopy (XPCS) and compare these results to the macroscopic rheology of the gels and optical observations of the microstructure evolution. At the investigated scattering angles, the intensity autocorrelation functions do not follow behavior expected for simple diffusion of individual Fmoc-FF molecules localized within cages of nearest neighbors. Instead, the dynamics are associated with density fluctuations on length scales of ∼10–100 nm arising from disaggregation and reformation of fibers, leading to an increasingly uniform network. This process is correlated with the growth of the elastic modulus, which saturates at long times. Autocorrelation functions and relaxation times acquired from XPCS measurements are consistent with relaxation rates of structures at dynamic equilibrium. This study provides further support to the concept of exploring peptide-based gelators as valence-limited patchy particles capable of forming equilibrium gels.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Structure and phase behavior of polymer-linked colloidal gels

Low-density “equilibrium” gels that consist of a percolated, kinetically arrested network of colloidal particles and are resilient to aging can be fabricated by restricting the number of effective bonds that form between the colloids. Valence-restricted patchy particles have long served as one archetypal example of such materials, but equilibrium gels can also be realized through a synthetically simpler and scalable strategy that introduces a secondary linker, such as a small ditopic molecule, to mediate the bonds between the colloids. Here, we consider the case where the ditopic linker molecules are low-molecular-weight polymers and demonstrate using a model colloid–polymer mixture how macroscopic properties such as the phase behavior as well as the microstructure of the gel can be designed through the polymer molecular weight and concentration. The low-density window for equilibrium gel formation is favorably expanded using longer linkers while necessarily increasing the spacing between all colloids. Furthermore, we show that blends of linkers with different sizes enable wider variation in microstructure for a given target phase behavior. Our computational study suggests a robust and tunable strategy for the experimental realization of equilibrium colloidal gels.

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

Toward a Balanced Description of Ground and Excited States with Transcorrelated F12 Methods

By correlating only the 1-particle states occupied in the reference determinant, the conventional design for the single-reference R12/F12 explicitly correlated methods biases them toward the ground-state description, thereby making the treatment of response properties of the ground state, and energies and other properties of excited states less robust. While the use of multireference methods and/or extensions of the standard SP-projected geminals can achieve a more balanced description of ground and excited states, here we show that the same goals can be achieved by extending the action of F12 correlators to the occupied and valence unoccupied 1-particle states only. This design choice reflects the strong dependence of the optimal correlation length scale of the F12 ansatz on the orbital energies/structure, and helps to avoid the unphysical raising of the ground-state energy if the F12 geminals are used to correlate pairs of all 1-particle states. The improved F12 geminal design is incorporated into the unitary transcorrelation framework to produce a unitary 2-body Hamiltonian that incorporates the short-range dynamical correlation physics for ground and low-energy excited states in a balanced manner. This explicitly correlated effective Hamiltonian reduces the basis set requirement on the correlation-consistent basis cardinal number by 1 or more over the uncorrelated counterpart for the description of ground-state coupled-cluster singles and doubles (CCSD) energies, vertical excitation energies, and harmonic vibrational frequencies of equation-of-motion CCSD low-energy excited states.

Hamiltonians↗
DOE OSTI2016

Particle size effect and the mechanism of hematite reduction by the outer membrane cytochrome OmcA of Shewanella oneidensis MR-1

The cycling of iron at the Earth’s near surface is profoundly influenced by dissimilatory metal reducing microorganisms, and many studies have focused on unraveling electron transfer mechanisms between these bacteria and Fe(III)-(oxyhydr)oxides. However, these efforts have been complicated by the fact that these minerals often occur in the micro- to nanosize regime, and in relevant natural environments as well as in the laboratory are subject to aggregation. The nature of the physical interface between the cellular envelope, the outer-membrane cytochromes responsible for facilitating the interfacial electron transfer step, and these complex mineral particulates is thus difficult to probe. Previous studies using whole cells have reported reduction rates that do not correlate with particle size. In the present study we isolate the interaction between the decaheme outer-membrane cytochrome OmcA of Shewanella oneidensis and nanoparticulate hematite, examining the reduction rate as a function of particle size and reaction products through detailed characterization of the electron balance and the structure and valence of iron at particle surfaces. By comparison with abiotic reduction via the smaller molecule ascorbic acid, we show that the reduction rate is systematically controlled by the sterically accessible interfacial contact area between OmcA and hematite in particle aggregates; rates increase once pore throat sizes in aggregates become as large as OmcA. Simultaneous measure of OmcA oxidation against Fe(II) release shows a ratio of 1:10, consistent with a cascade OmcA oxidation mechanism heme by heme. X-ray absorption spectroscopies reveal incipient magnetite on the reacted surfaces of the hematite nanoparticles after reaction. The collective findings establish the importance of accessibility of physical contact between the terminal reductases and iron oxide surfaces, and through apparent consistency of observations help reconcile behavior reported at the larger more complex scale of whole cell studies.

58 GEOSCIENCES↗
DOE OSTI2024

Extended Interacting Boson Model with Configuration Mixing Description For 98 Mo

An extended version of the interacting boson model (IBM), encompassing two-particle–two-hole (2p-2h) excitations originating from below a valence shell and one-particle–one-hole (1p-1h) excitations extending to the upper next-nearest major shell, is developed to investigate cross-shell excitation effects in the transitional nucleus 98 Mo. This extended IBM framework is utilized to reproduce experimentally observed properties such as low-lying positive-parity level energies, 𝐵⁡(𝐸⁢2) values, and the electric quadrupole moment of the 2$^{+}_{1}$ state, 𝜌 2 ⁡(𝐸⁢0, 0$^{+}_{2}$ → 0$^{+}_{g}$), as well as the strength functions of the isoscalar giant monopole resonance (ISGMR) and the isoscalar giant quadrupole resonance (ISGQR) in 98 Mo. It is shown that the extended consistent-𝑄 IBM, incorporating configuration mixing of both 2p-2h excitations from below the valence shell and 1p-1h excitations to the upper next-nearest major shell, describes the low-lying structural properties and the ISGMR and ISGQR strength distributions of 98 Mo quite well, with the ISGMR and the ISGQR strength distributions comparable to the results of the self-consistent quasiparticle random-phase approximation with Skyrme interactions.

90 ≤ A ≤ 149↗
DOE OSTI2021

Effective shell-model interaction for nuclei “southeast” of 100 Sn

We construct an effective shell-model interaction for the valence space spanned by single-particle neutron and single-hole proton states in 100 Sn. Starting from chiral nucleon-nucleon and three-nucleon forces and single-reference coupled-cluster theory for 100 Sn we apply a second similarity transformation that decouples the valence space. The particle-particle components of the resulting effective interaction can be used in shell model calculations for neutron deficient tin isotopes. The hole-hole interaction can be used to calculate the N=50 isotones south of 100 Sn, and the full particle-hole interaction describes nuclei in the region southeast of 100 Sn. We compute low-lying excited states in selected nuclei southeast of 100 Sn, and find reasonable agreement with data. The presented techniques can also be applied to construct effective shell-model interactions for other regions of the nuclear chart.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2016

Communication: XUV transient absorption spectroscopy of iodomethane and iodobenzene photodissociation

Time-resolved extreme ultraviolet (XUV) transient absorption spectroscopy of iodomethane and iodobenzene photodissociation at the iodine pre-N{sub 4,5} edge is presented, using femtosecond UV pump pulses and XUV probe pulses from high harmonic generation. For both molecules the molecular core-to-valence absorption lines fade immediately, within the pump-probe time-resolution. Absorption lines converging to the atomic iodine product emerge promptly in CH{sub 3}I but are time-delayed in C{sub 6}H{sub 5}I. We attribute this delay to the initial π → σ{sup *} excitation in iodobenzene, which is distant from the iodine reporter atom. We measure a continuous shift in energy of the emerging atomic absorption lines in CH{sub 3}I, attributed to relaxation of the excited valence shell. An independent particle model is used to rationalize the observed experimental findings.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗