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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 703 records · Page 39
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Mixing A -type and G -type B -site antiferromagnetism in A M n 1 - x F e x O 3 ( A = La , Nd )

Using a classical Heisenberg model with anisotropic nearest-neighbor superexchange and uniaxial anisotropy, I investigate the magnetic order of the transition metals on the B sites in AMn 1-x Fe x O 3 (A=La, Nd; x=[0,1]) with Monte Carlo methods. Magnetic parameters are extracted from preexisting experimental data when available and otherwise estimated with calculations. Superexchange energies are compared to density functional theory and anisotropy energies to ligand field theory, and the potential for doping-induced strain affecting these parameters is considered. I find coexistence regions of different types of magnetic order (A-type and G-type antiferromagnetism), regions with distinct magnetic transitions for the two order parameters, noncollinear ground states for intermediate values of x that decrease the amplitude of the ordered moment in a way consistent with experiment for low dopings, and a reproduction of the experimentally determined, nonmonotonic interpolation of the ordering temperatures. The detailed shape of the phase boundaries in (x,T) space is found to be diagnostic of the magnetic interactions. Finally, these results also suggest a ferrimagnetic ground state for the A 2 MnFeO 6 double perovskite with T N ≈270K for A=La and Nd.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2011

Two-phonon {gamma}-vibrational states in rotating triaxial odd-A nuclei

The distribution of the two-phonon {gamma}-vibrational collectivity in the rotating triaxial odd-A nucleus {sup 103}Nb, which is one of the three nuclides for which experimental data were reported recently, is calculated in the framework of the particle vibration coupling model based on the cranked shell model plus random phase approximation. This framework was previously utilized for analyses of the zero- and one-phonon bands in another mass region and is applied to the two-phonon band for the first time. In the present calculation, three sequences of two-phonon bands share collectivity almost equally at finite rotation whereas the K={Omega}+4 state is the purest at zero rotation.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2010

Multi-quasiparticle structures up to spin {approx}44({h_bar}/2{pi}) in the odd-odd nucleus {sup 168}Ta

High-spin states in the odd-odd nucleus {sup 168}Ta have been populated in the {sup 120}Sn({sup 51}V,3n) reaction. Two multi-quasiparticle structures have been extended significantly from spin {approx}20({h_bar}/2{pi}) to above 40({h_bar}/2{pi}). As a result, the first rotational alignment has been fully delineated and a second band crossing has been observed for the first time in this nucleus. Configurations for these strongly coupled rotational bands are proposed based on signature splitting, B(M1)/B(E2) ratio information, and observed rotation-alignment behavior. Properties of the observed bands in {sup 168}Ta are compared to related structures in the neighboring odd-Z, odd-N, and odd-odd nuclei and are discussed within the framework of the cranked shell model.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2026

High-Rate, Selective Electrosynthesis of Cyclohexanone Oxime via In Situ Generation and Release of Hydroxylamine on Bismuth

Oxime compounds are key industrial intermediates for nylon precursors and commodity chemicals. However, conventional routes rely on multistep reactions and hydroxylamine (NH 2 OH) salts, raising significant safety and sustainability concerns. Although electrosynthesis offers an alternative, oxime formation on d-block transition metals suffers from poor selectivity, as nitrogen oxyanion intermediates bind strongly to the surface and are readily over-reduced to ammonia. Here, we report morphology-controlled p-block bismuth rhombic dodecahedra (Bi RDs) that promote in situ NH 2 OH generation and its desorption into the electrolyte, enabling an electrochemical-chemical decoupled route for cyclohexanone oxime (CHO) synthesis. Bi RDs deliver nearly 100% Faradaic efficiency (FE) at −0.5 V vs. RHE and a yield of 1.4 mmol h –1 cm –2 at −0.9 V vs. RHE in an H-cell, while maintaining a CHO selectivity of nearly 100% at 100 mA cm –2 in a flow cell. Under identical conditions, d-block electrodes (Cu, Pd, Ag) show FE below 30%. Density functional theory calculations reveal that Bi 6p orbital-derived surface states weaken intermediate binding and facilitate NH 2 OH desorption, suppressing over-reduction. Kinetic analysis, post-addition trapping experiments, and in situ ATR-FTIR and Raman spectroscopy suggest the following reaction mechanism: NH 2 OH is selectively generated at the electrode surface, released as a freely diffusing intermediate, and undergoes homogeneous condensation with cyclohexanone in the bulk electrolyte, bypassing the surface-confined Langmuir–Hinshelwood pathway. These findings demonstrate that regulating intermediate desorption through p-block orbital chemistry provides a general strategy for achieving high selectivity in electro-organic nitrogen synthesis.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Keto-enol tautomerization and intermolecular proton transfer in photoionized cyclopentanone dimer in the gas phase

Time-of-flight mass spectra of cyclopentanone and its clusters cooled in a supersonic jet expansion have been measured following 4-, 3-, and 2-photon ionizations by the 2nd, 3rd, and 4th harmonic wavelengths, respectively, of a Q-switched Nd:YAG laser. The mass spectra reveal signatures of energetically favored keto to enol tautomerization of the molecular ion leading to intermolecular proton transfer, and this observation is found sharply dependent on the ionization wavelengths used. Electronic structure calculation predicts that in spite of the energetic preference, keto-enol conversion barrier of isolated molecular ion is high. However, the barrier is significantly reduced in a CH⋯O hydrogen-bonded dimer of the molecule. The transition states associated with tautomeric conversion of both cyclopentanone monomer and dimer cations have been identified by means of intrinsic reaction co-ordinate calculation. In a supersonic jet expansion, although a weakly bound dimer is readily generated, the corresponding cation and also the protonated counterpart are observed only for ionization by 532 nm. For other two ionization wavelengths, these species do not register in the mass spectra, where the competing reaction channels via α-cleavage of the ring become dominant. In contrast to the report of a recent study, we notice that the intact molecular ion largely survives fragmentations when ionized from the 2-photon resonant 3p Rydberg state as intermediate using nanosecond laser pulses, and the corresponding resonant 3-photon ionization spectrum has been recorded probing the intact molecular ion.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2011

Structure of the yrast band in the odd-odd deformed nucleus {sup 156}Pm

The six-level sequence deduced for the odd-odd nucleus {sup 156}Pm in the high-spin studies following spontaneous fission of {sup 252}Cf is shown to constitute the K{sup {pi}=}4{sup +} yrast band having the two-quasiparticle configuration {l_brace}p:5/2[532]+ n:3/2[521]{r_brace}. Spin parities I{sup {pi}=}4{sup +} through 9{sup +} are assigned to the earlier suggested six levels. The location and the decay {gamma}'s of the 10{sup +} level of this band are indicated. It is also pointed out that there are no {gamma} rays common to these postfission high-spin spectra and those seen in the {sup 156}Nd {beta}-decay studies.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2016

Hadronic resonance production measured by the ALICE experiment at LHC

Hadronic resonances are among the most interesting probes of the hot and dense matter created in Pb-Pb collisions. Due to their short lifetime, they are sensitive to the anticipated chiral symmetry restoration as well as to suppression and regeneration due to hadronic interactions in the final state. At intermediate and high transverse momenta the hadron resonances, which cover the range of masses between the light pions and heavier protons, contribute to the systematic study of the baryon anomaly and parton energy loss in the dense medium. Measurements in pp collisions are used as a reference for collision of heavier systems and contribute to precision tests of pQCD and of the currently available parameterizations of fragmentation functions. Studies in p-Pb collisions are important for the interpretation of heavy ion results as they allow the decoupling of the initial nuclear effects from hot matter final state effects.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2020

Structural basis of the activation of a metabotropic GABA receptor

Metabotropic γ-aminobutyric acid receptors (GABA B ) are involved in the modulation of synaptic responses in the central nervous system and have been implicated in neuropsychological conditions that range from addiction to psychosis. GABA B belongs to class C of the G-protein-coupled receptors, and its functional entity comprises an obligate heterodimer that is composed of the GB1 and GB2 subunits. Each subunit possesses an extracellular Venus flytrap domain, which is connected to a canonical seven-transmembrane domain. In this paper we present four cryo-electron microscopy structures of the human full-length GB1–GB2 heterodimer: one structure of its inactive apo state, two intermediate agonist-bound forms and an active form in which the heterodimer is bound to an agonist and a positive allosteric modulator. The structures reveal substantial differences, which shed light on the complex motions that underlie the unique activation mechanism of GABA B . Our results show that agonist binding leads to the closure of the Venus flytrap domain of GB1, triggering a series of transitions, first rearranging and bringing the two transmembrane domains into close contact along transmembrane helix 6 and ultimately inducing conformational rearrangements in the GB2 transmembrane domain via a lever-like mechanism to initiate downstream signalling. This active state is stabilized by a positive allosteric modulator binding at the transmembrane dimerization interface.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2011

State-resolved investigation of the photodesorption dynamics of NO from (NO){sub 2} on Ag nanoparticles of various sizes in comparison with Ag(111)

The translational and internal state energy distributions of NO desorbed by laser light (2.3, 3.5, and 4.7 eV) from adsorbed (NO){sub 2} on Ag nanoparticles (NPs) (mean diameters, D= 4, 8, and 11 nm) have been investigated by the (1 + 1) resonance enhanced multiphoton ionization technique. For comparison, the same experiments have also been carried out on Ag(111). Detected NO molecules are hyperthermally fast and both rotationally and vibrationally hot, with temperatures well above the sample temperature. The translational and rotational excitations are positively correlated, while the vibrational excitation is decoupled from the other two degrees of freedom. Most of the energy content of the desorbing NO is contained in its translation. The translational and internal energy distributions of NO molecules photodesorbed by 2.3, 3.5, and in part also 4.7 eV light are approximately constant as a function of Ag NPs sizes, and they are the same on Ag(111). This suggests that for these excitations a common mechanism is operative on the bulk single crystal and on NPs, independent of the size regime. Notably, despite the strongly enhanced cross section seen on NP at 3.5 eV excitation energy in p-polarization, i.e., in resonance with the plasmon excitation, the mechanism is also unchanged. At 4.7 eV and for small particles, however, an additional desorption channel is observed which results in desorbates with higher energies in all degrees of freedom. The results are well compatible with our earlier measurements of size-dependent translational energy distributions. We suggest that the broadly constant mechanism over most of the investigated range runs via a transient negative ion state, while at high excitation energy and for small particles the transient state is suggested to be a positive ion.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Transition strengths and the role of the f{sub 7/2} orbital in {sup 71}As

High-spin states in {sup 71}As were studied using the {sup 54}Fe({sup 23}Na,{alpha}2p) reaction at 80 MeV. Prompt {gamma}-{gamma} coincidences were measured using the Florida State University Compton-suppressed Ge array consisting of three clover detectors and seven single-crystal detectors. The existing high-spin level scheme has been verified, and 21 new transitions have been added based on an investigation of weak {gamma}-ray coincidence relations and relative {gamma}-ray intensities. Lifetimes of 16 excited states were measured using the Doppler-shift attenuation method applied to the experimental line shapes of decays in all of the known rotational bands. The B(E2) strengths inferred from the lifetimes indicate that moderate to high collective behavior persists to the highest observed spins in the lowest positive- and negative-parity bands, in qualitative agreement with projected shell-model calculations. The band suggested to be based on the {pi}f{sub 7/2} orbital shows a similar degree of collectivity within the same spin range, with B(E2) values in good agreement with those predicted by the projected shell model assuming a constant prolate deformation of {epsilon}{sub 2}=+0.27. The experimental Q{sub t} values in this band are somewhat smaller than predicted by cranked Woods-Saxon calculations.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2010

High-spin states and level structure in {sup 84}Rb

High-spin states in {sup 84}Rb have been studied by using the {sup 70}Zn({sup 18}O,p3n){sup 84}Rb reaction at beam energy of 75 MeV. The gamma-gamma coincidence, excitation function, and ratios for directional correlation of oriented states were determined. A new level scheme was established in which the positive- and negative-parity bands have been extended up to 17{sup +} and 17{sup -} with an excitation energy of about 7 MeV. The signature splitting and signature inversion of the positive-parity yrast band were observed. To understand the microscopic origin of the signature inversion in the yrast positive-parity bands of doubly odd Rb nuclei, as an example, we performed calculations using the projected shell model to describe the energy spectra in {sup 84}Rb. It can be seen that the main features are reproduced in the calculations. This analysis shows that the signature splitting, especially its inversion, can be reproduced by varying only the gamma deformation with increasing spin. To research the deformation of {sup 84}Rb carefully, we calculate the total Routhian surfaces of positive-parity yrast states by the cranking shell model formalism. In addition, the results of theoretical calculations about the negative-parity yrast band in {sup 84}Rb with configuration pi(p{sub 3/2},f{sub 5/2}) x nug{sub 9/2} are compared with experimental data, and a band diagram calculated for this band is also shown to extract physics from the numerical results.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2014

Collapse of ferromagnetism in itinerant-electron system: A magnetic, transport properties, and high pressure study of (Hf,Ta)Fe{sub 2} compounds

The magnetism and transport properties were studied for Laves (Hf,Ta)Fe{sub 2} itinerant-electron compounds, which exhibit a temperature-induced first-order transition from the ferromagnetic (FM) to the antiferromagnetic (AFM) state upon heating. At finite temperatures, the field-induced metamagnetic phase transition between the AFM and FM has considerable effects on the transport properties of these model metamagnetic compounds. A large negative magnetoresistance of about 14% is observed in accordance with the metamagnetic transition. The magnetic phase diagram is determined for the Laves Hf{sub 1−x}Ta{sub x}Fe{sub 2} series and its Ta concentration dependence discussed. An unusual behavior is revealed in the paramagnetic state of intermediate compositions, it gives rise to the rapid increase and saturation of the local spin fluctuations of the 3d electrons. This new result is analysed in the frame of the theory of Moriya. For a chosen composition Hf{sub 0.825}Ta{sub 0.175}Fe{sub 2}, exhibiting such remarkable features, a detailed investigation is carried out under hydrostatic pressure up to 1 GPa in order to investigate the volume effect on the magnetic properties. With increasing pressure, the magnetic transition temperature T{sub FM-AFM} from ferromagnetic to antiferromagnetic order decreases strongly non-linearly and disappears at a critical pressure of 0.75 GPa. In the pressure-induced AFM state, the field-induced first-order AFM-FM transition appears and the complex temperature dependence of the AFM-FM transition field is explained by the contribution from both the magnetic and elastic energies caused by the significant temperature variation of the amplitude of the local Fe magnetic moment. The application of an external pressure leads also to the progressive decrease of the Néel temperature T{sub N}. In addition, a large pressure effect on the spontaneous magnetization M{sub S} for pressures below 0.45 GPa, dln(M{sub s})/dP = −6.3 × 10{sup −2 }GPa{sup −1} was discovered. The presented results are consistent with Moriya's theoretical predictions and can significantly help to better understand the underlying physics of itinerant electron magnetic systems nowadays widely investigated for both fundamental and applications purposes.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2026

Anode-less Solid-State Li–S Batteries Enabled by Fe-Stabilized Polysulfides

Anode-less solid-state lithium-sulfur batteries (SSLSBs) with lithium sulfide (Li 2 S) as the cathode promise a high energy density and ease of manufacturing. However, Li 2 S is plagued by poor conductivity, sluggish activation kinetics, and a poor cycle life. Here, in this study, we report an FeCl 3 -activated Li 2 S (FLS) cathode with solid-state polysulfide intermediates generated through a redox reaction between FeCl 3 and Li 2 S. This strategy is shown to boost the electrical conductivity of Li 2 S by 7 orders of magnitude and lower the activation barrier. During cycling, Fe plays a significant role in stabilizing the highly active polysulfide species, contributing to the exceptional electrochemical performance. The FLS cathode achieves 80% capacity retention over 500 cycles with >99% Li 2 S utilization. Furthermore, a Li-metal-free (anode-less) full cell retained over 80% of its initial capacity after 240 cycles. This work underscores the promise of leveraging Fe-stabilized polysulfides in enabling high-energy, long-lasting, solid-state Li-S batteries.

25 ENERGY STORAGE↗
DOE OSTI2010

New Band Structures in Aapprox110 Neutron-Rich Nuclei

The high spin states of neutron-rich nuclei in Aapprox110 region have been carefully investigated by measuring prompt gamma-gamma-gamma coincident measurements populated in the spontaneous fission of {sup 252}Cf with the Gammasphere detector array. Many new collective bands have been discovered. In this proceeding paper, we introduce some interesting new band structures recently observed by our cooperative groups, that is, the one-phonon- and two-phonon gamma-vibrational bands in odd-A {sup 103}Nb, {sup 105}Mo and {sup 107}Tc, the chiral doublet bands in even-even {sup 106}Mo, {sup 110}Ru and {sup 112}Ru, and the pseudospin partner bands with in {sup 108}Tc. The characteristics of these band structures have been discussed.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗