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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 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

Measurement of the asymmetry in angular distributions of leptons produced in dilepton t t ¯ final states in p p ¯ collisions at s = 1.96 TeV

We present measurements of asymmetries in angular distributions of leptons produced in ttbar events in proton-antiproton collisions at the Fermilab Tevatron Collider. We consider final states where the W bosons from top quark and antiquark decays both decay into l nu (l=e, mu) resulting in oppositely charged dilepton final states with accompanying jets. Using 9.7 fb -1 of integrated luminosity collected with the D0 detector, we find the asymmetries in lepton pseudorapidity compatible with predictions based on the standard model.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2022

Experimental constraints on the properties of $P_c$ states

Using new experimental data on photoproduction and $\Lambda _b^0$ decays, we derive constraints on the properties of the LHCb $P_c$ states. We conclude that $P_c(4312)$, $P_c(4380)$ and $P_c(4440)$ can be described as $\Sigma _c\bar{D}$, $\Sigma _c^*\bar{D}$ and $\Sigma _c\bar{D}^*$ molecules, but that $P_c(4457)$ does not fit into the same picture. Based on the apparent absence of additional partner states, and the striking disparity between $\Lambda _c^+\bar{D}^0$ and $\Lambda _c^+\bar{D}^{*0}$ decays, we conclude that $P_c(4440)$ has $3/2^-$ quantum numbers. Using heavy-quark symmetry we predict large experimental signals for $P_c$ states in $\eta _c p K^-$, $\Lambda _c^+\bar{D}^{*0}K^-$, and $\Sigma _c^{(*)}\bar{D}K^-$. We also argue that current experimental data on photoproduction is almost at the level of sensitivity required to observe $P_c$ states.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

Understanding oxygen adsorption on 9.375 at. % Ga-stabilized δ-Pu (111) surface: A DFT study

Plutonium (Pu) metal reacts rapidly in the presence of oxygen (O), resulting in an oxide layer that will eventually have an olive green rust appearance over time. Recent experimental work suggested that the incorporation of gallium (Ga) as an alloying impurity to stabilize the highly symmetric high temperature δ-phase lattice may also provide resistance against corrosion/oxidation of plutonium. In this paper, we modeled a 9.375 at. % Ga stabilized δ-Pu (111) surface and investigated adsorption of atomic O using all-electron density functional theory. Key findings revealed that the O bonded strongly to a Pu-rich threefold hollow fcc site with a chemisorption energy of –5.06 eV. Migration of the O atom to a Pu-rich environment was also highly sensitive to the surface chemistry of the Pu–Ga surface; when the initial on-surface O adsorption site included a bond to a nearest neighboring Ga atom, the O atom relaxed to a Ga deficient environment, thus affirming the O preference for Pu. Only one calculated final on-surface O adsorption site included a Ga-O bond, but this chemisorption energy was energetically unfavorable. Chemisorption energies for interstitial adsorption sites that included a Pu or Pu-Ga environment suggested that over-coordination of the O atom was energetically unfavorable as well. Electronic structure properties of the on-surface sites, illustrated by the partial density of states, implied that the Ga 4 p states indirectly but strongly influenced the Pu 6 d states strongly to hybridize with the O 2 p states, while also weakly influenced the Pu 5 f states to hybridize with the O 2 p states, even though Ga was not participating in bonding with O.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Experimental study of the Si 30 ( He 3 , d ) P 31 reaction and thermonuclear reaction rate of Si 30 ( p , γ ) P 31

Background: Abundance anomalies in some globular clusters, such as the enhancement of potassium and the depletion of magnesium, can be explained in terms of an earlier generation of stars polluting the presently observed ones. It was shown that the potential range of temperatures and densities of the polluting sites depends on the strength of a few critical reaction rates. The 30 Si(p,γ) 31 P reaction has been identified as one of these important reactions. Purpose: The key ingredient for evaluating the thermonuclear 30 Si(p,γ) 31 P reaction rate is the strength of the resonances which, at low energy, are proportional to their proton width. Therefore, the goal of this work is to determine the proton widths of unbound 31 P states. Method: States in 31 P were studied at the Maier-Leibnitz-Laboratorium using the one-proton 30 Si( 3 He,d) 31 P transfer reaction. Deuterons were detected with the high resolution one quadrupole three dipoles (Q3D) magnetic spectrometer. Angular distribution and spectroscopic factors were extracted for 27 states, and proton widths and resonance strengths were calculated for the unbound states. Results: Several 31 P unbound states have been observed for the first time in a one-proton transfer reaction. Above 20 MK, the 30 Si(p,γ) 31 P reaction rate is now entirely estimated from the observed properties of 31 P states. The reaction rate uncertainty from all resonances other than the E$^{c.m.}_{r}$ = 149 keV resonance has been reduced down to less than a factor of 2 above that temperature. The unknown spin and parity of the E$^{c.m.}_{r}$ = 149 keV resonance dominates the uncertainty in the rate in the relevant temperature range. Conclusion: Here, the remaining source of uncertainty on the 30 Si(p,γ) 31 P reaction rate comes from the unknown spin and parity of the E$^{c.m.}_{r}$ = 149 keV resonance which can change the reaction rate by a factor of 10 in the temperature range of interest.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2022

High Yield of B-Side Electron Transfer at 77 K in the Photosynthetic Reaction Center Protein from Rhodobacter sphaeroides

In this work, the primary electron transfer (ET) processes at 295 K and 77 K are compared for the Rhodobacter sphaeroides reaction center (RC) pigment-protein complex from thirteen mutants including a wild-type control. The engineered RCs bear mutations in the L and M polypeptides that largely inhibit ET from the excited state P* of the primary electron donor (P, a bacteriochlorophyll dimer) to the normally photoactive A-side cofactors and enhance ET to the C 2 -symmetry related, and normally photoinactive, B-side cofactors. P* decay is multi-exponential at both temperatures and modeled as arising from subpopulations that differ in contributions of two-step ET (e.g., P* → P + B B – → P + H B – ), one-step superexchange ET (e.g., P* → P + H B – ) and P* → ground state. [H B and B B are monomeric bacteriopheophytin and bacteriochlorophyll, respectively.] The relative abundances of the subpopulations and the inherent rate constants of the P* decay routes vary with temperature. Regardless, ET to produce P + H B – is generally faster at 77 K than at 295 K by about a factor of two. A key finding is that the yield of P + H B – , which ranges from ~5% to ~90% among the mutant RCs, is essentially the same at 77 K as at 295 K in each case. Overall, the results show that ET from P* to the B-side cofactors in these mutants does not require thermal activation and involves combinations of ET mechanisms analogous to those operative on the A side in the native RC.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1996

Investigation of Oxygen-Induced Quenching of Phosphorescence in Photoexcited Aromatic Molecules by Positron Annihilation Spectroscopy

Platinum OctaEthyl Porphyrin (Pt.OEP) is an efficient phosphor under ultraviolet excitation. The phosphorescent triplet state P(T(Sup 1)) is readily quenched by the oxygen O2 molecules. This phenomenon is being utilized as the basis for global air pressure measurements in aerodynamic facilities at various laboratories. The exact mechanism by which O2 molecules quench the P(T(Sup 1) approaches P(S(Sub O)) transitions is still unknown. The diamagnetic singlet states P(S(Sub n)), which feed P(T(Sub 1)) states via intersystem crossings, would presumably not be affected by O2. It must be only the magnetic P(T(Sub 1)) states, which can interact with the paramagnetic O2 molecules, that are affected. However, our positron lifetime and Doppler broadening studies suggest the formation of O2P(S(Sub n)), complexes which can also eventually reduce the population of the P(T(Sub 1)) states (i.e., quench phosphorescence). This reduction is possible because higher triplet states in (Pt.OEP) are admixed with the P(S(Sub 1)), states via spin orbit interactions. The experimental procedures and the results of various measurements are presented in this paper.

Singh, Jag J.↗
DOE OSTI2014

The electronic structure of the antimony chalcogenide series: Prospects for optoelectronic applications

In this study, density functional theory is used to evaluate the electronic structure of the antimony chalcogenide series. Analysis of the electronic density of states and charge density shows that asymmetric density, or ‘lone pairs’, forms on the Sb{sup III} cations in the distorted oxide, sulphide and selenide materials. The asymmetric density progressively weakens down the series, due to the increase in energy of valence p states from O to Te, and is absent for Sb{sub 2}Te{sub 3}. The fundamental and optical band gaps were calculated and Sb{sub 2}O{sub 3}, Sb{sub 2}S{sub 3} and Sb{sub 2}Se{sub 3} have indirect band gaps, while Sb{sub 2}Te{sub 3} was calculated to have a direct band gap at Γ. The band gaps are also seen to reduce from Sb{sub 2}O{sub 3} to Sb{sub 2}Te{sub 3}. The optical band gap for Sb{sub 2}O{sub 3} makes it a candidate as a transparent conducting oxide, while Sb{sub 2}S{sub 3} and Sb{sub 2}Se{sub 3} have suitable band gaps for thin film solar cell absorbers. - Graphical abstract: A schematic illustrating the interaction between the Sb{sup III} cations and the chalcogenide anions and the change in their respective energy levels down the series. - Highlights: • The electronic structure of the antimony chalcogenide series is modelled using DFT. • Asymmetric density is present on distorted systems and absent on the symmetric telluride system. • Asymmetric density is formed from the mixing of Sb 5s and anion p states, where the anti-bonding combination is stabilised by the Sb 5p states. • The asymmetric density weakens down the series due to the increase in energy of chalcogenide p states. • The increase in energy of the anion p states reduces the fundamental and optical band gaps.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Hyperfine structure of the S- and P-wave states of muonic deuterium

Corrections of order α{sup 5} and α{sup 6} to the hyperfine structure of the S- and P-wave states of muonic deuteriumwere calculated on the basis of the quasipotential approach in quantum electrodynamics. Relativistic corrections, vacuum-polarization and deuteron-structure effects, and recoil corrections were taken into account in this calculation. The resulting hyperfine-splitting values can be used in a comparison with experimental data obtained by the CREMA Collaboration.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2018

Search for pair production of heavy vector-like quarks decaying into high- p T W bosons and top quarks in the lepton-plus-jets final state in p p collisions at s = 13 TeV with the ATLAS detector

CERN-LHC, ATLAS. Limits on pair production of a heavy vector-like B quark together with its antiparticle, where the B quark decays to a W boson and a top quark. The search is based on 36.1 +\- 0.8 fb^{-1} of pp collisions at sqrt{s} = 13 TeV recorded in 2015 and 2016 with the ATLAS detector at the CERN Large Hadron Collider. Data are analysed in the lepton plus jets final state, including at least four small jets out of which at least one is required to be b-tagged jet and a large-radius jet. Mass limits on B production are set as a function of the decay branching ratios.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2012

Measurements of WW and WZ Production in W+jets Final States in pp̄ Collisions

We study WW and WZ production with lνqq (l=e,μ) final states using data collected by the D0 detector at the Fermilab Tevatron Collider corresponding to 4.3 fb⁻¹ of integrated luminosity from pp̄ collisions at √s=1.96 TeV. Assuming the ratio between the production cross sections σ(WW) and σ(WZ) as predicted by the standard model, we measure the total WV (V=W,Z) cross section to be σ(WV)=19.6 +3.2 -3.0 pb and reject the background-only hypothesis at a level of 7.9 standard deviations. We also use b-jet discrimination to separate the WZ component from the dominant WW component. Simultaneously fitting WW and WZ contributions, we measure σ(WW)=15.9 +3.7 -3.2 pb and σ(WZ)=3.3 +4.1 -3.3 pb, which is consistent with the standard model predictions.

Abazov, V. M.↗
DOE OSTI2016

2D {sup 31}P solid state NMR spectroscopy, electronic structure and thermochemistry of PbP{sub 7}

Phase pure polycrystalline PbP{sub 7} was prepared from the elements via a lead flux. Crystalline pieces with edge-lengths up to 1 mm were obtained. The assignment of the previously published {sup 31}P solid state NMR spectrum to the seven distinct crystallographic sites was accomplished by radio-frequency driven dipolar recoupling (RFDR) experiments. As commonly found in other solid polyphosphides there is no obvious correlation between the {sup 31}P chemical shift and structural parameters. PbP{sub 7} decomposes incongruently under release of phosphorus forming liquid lead as remainder. The thermal decomposition starts at T>550 K with a vapor pressure almost similar to that of red phosphorus. Electronic structure calculations reveal PbP{sub 7} as a semiconductor according to the Zintl description and clearly shows the stereo-active Pb-6s{sup 2} lone pairs in the electron localization function ELF. - Graphical abstract: Coordination of the lead atoms in PbP{sub 7}.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1999

Static Properties and Stark Effect of the Ground State of the HD Molecular Ion

We have calculated static properties of the ground state of the HD(+) ion and its lowest-lying P-state without making use of the Born-Oppenheimer approximation, as was done in the case of H2(+) and D2(+) [Phys. Rev. A 58, 2787 (1998)]. The ion is treated as a three-body system whose ground state is spherically symmetric. The wavefunction is of generalized Hylleraas type, but it is necessary to include high powers of the internuclear distance to localize the nuclear motion. We obtain good values of the energies of the ground S-state and lowest P-state and compare them with earlier calculations. Expectation values are obtained for various operators, the Fermi contact parameters, and the permanent quadrupole moment. The cusp conditions are also calculated. The polarizability was then calculated using second-order perturbation theory with intermediate P pseudostates. Since the nuclei in HD(+) are not of equal mass there is dipole coupling between the lowest two rotational states, which are almost degenerate. This situation is carefully analyzed, and the Stark shift is calculated variationally as a function of the applied electric field.

Bhatia, A. K.↗
DOE OSTI2017

Confirmation of the isomeric state in P 26

Here, we report the independent experimental confirmation of an isomeric state in the proton drip-line nucleus 26 P. The γ-ray energy and half-life determined are 164.4 ± 0.3(sys) ± 0.2(stat) keV and 104 ± 14 ns, respectively, which are in agreement with the previously reported values. These values are used to set a semiempirical limit on the proton separation energy of 26 P, with the conclusion that it can be bound or unbound.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2016

The structure of liquid water up to 360 MPa from x-ray diffraction measurements using a high Q-range and from molecular simulation

X-ray diffraction measurements of liquid water are reported at pressures up to 360 MPa corresponding to a density of 0.0373 molecules per Å{sup 3}. The measurements were conducted at a spatial resolution corresponding to Q{sub max} = 16 Å{sup −1}. The method of data analysis and measurement in this study follows the earlier benchmark results reported for water under ambient conditions having a density of 0.0333 molecules per Å{sup 3} and Q{sub max} = 20 Å{sup −1} [J. Chem. Phys. 138, 074506 (2013)] and at 70 °C having a density of 0.0327 molecules per Å{sup 3} and Q{sub max} = 20 Å{sup −1} [J. Chem. Phys. 141, 214507 (2014)]. The structure of water is very different at these three different T and P state points and thus they provide the basis for evaluating the fidelity of molecular simulation. Measurements show that at 360 MPa, the 4 waters residing in the region between 2.3 and 3 Å are nearly unchanged: the peak position, shape, and coordination number are nearly identical to their values under ambient conditions. However, in the region above 3 Å, large structural changes occur with the collapse of the well-defined 2nd shell and shifting of higher shells to shorter distances. The measured structure is compared to simulated structure using intermolecular potentials described by both first-principles methods (revPBE-D3) and classical potentials (TIP4P/2005, MB-pol, and mW). The DFT-based, revPBE-D3, method and the many-body empirical potential model, MB-pol, provide the best overall representation of the ambient, high-temperature, and high-pressure data. The revPBE-D3, MB-pol, and the TIP4P/2005 models capture the densification mechanism, whereby the non-bonded 5th nearest neighbor molecule, which partially encroaches the 1st shell at ambient pressure, is pushed further into the local tetrahedral arrangement at higher pressures by the more distant molecules filling the void space in the network between the 1st and 2nd shells.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Rationally-Designed Configuration of Directly-Coated Ni3S2/Ni Electrode by RGO Providing Superior Sodium Storage

Designing nanocomposite materials is an effective approach for enhancing the performance of sodium-ion batteries (SIBs), and understanding the synergy among components is critically important for new, better materials design. Herein, a directly reduced graphene oxide (RGO) decorated anode electrode was designed and tested for SIBs, in which uniform RGO coating onto the Ni3S2/Ni electrode was realized using facile hydrothermal reactions. The results indicate that the RGO/Ni3S2/Ni electrode delivers a high reversible specific capacity of 448.6 mAh g-1, high capacity retention of 96.5% after 100 cycles, and excellent rate capability of 263.1 mAh g-1 at 800 mA g-1. Compared with the Ni3S2/Ni electrode, the improved performance of the RGO/Ni3S2/Ni electrode benefits from RGO-promoted displacement reaction of Ni3S2 with sodium. DFT calculations reveal that the RGO layer can significantly improve the electron mobility of the RGO/Ni3S2 + Na structure, and the hybrid interaction between the C-p state of RGO and the Ni-p, Ni-d, and S-p states of Ni3S2 is the major reason for why RGO can improve the electrical transport properties.

Song, Xiaosheng↗
DOE OSTI2017

Search for pair production of heavy vector-like quarks decaying to high- p m a t h r m T W bosons and b quarks in the lepton-plus-jets final state in p p collisions at s =13 TeV with the ATLAS detector

CERN-LHC, ATLAS. Limits on pair production of a heavy vector-like T quark together with its antiparticle, where the T quark decays to a W boson and a b quark. The search is based on 36.1 +\- 1.2 fb^{-1} of pp collisions at sqrt{s} = 13 TeV recorded in 2015 and 2016 with the ATLAS detector at the CERN Large Hadron Collider. Data are analysed in the lepton plus jets final state, including at least one b-tagged jet and a large-radius jet identified as originating from the hadronic decay of a high-momentum W boson. The search is also sensitive to a heavy vector-like B quark, in particular in the decay to Wt and the results are thus reinterpreted to provide limits on the B mass. Mass limits on both T and B production are also set as a function of the decay branching ratios.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2012

On the electronic structure and thermoelectric properties of BiTeBr and BiTeI single crystals and of BiTeI with the addition of BiI{sub 3} and CuI

The electronic structures were calculated for BiTeBr and BiTeI using the density-functional theory approach and accounting for the strong spin-orbital interaction. Qualitatively, the band structures for two compounds are similar, showing strong mixing of the p states of all elements in vicinity of the Fermi level, with the band gaps of 0.595 and 0.478 eV for BiTeBr and BiTeI, respectively. The optimized crystal structures show a tendency for the Bi-X (X=Br, I) bond elongation compared to the Bi-Te one. Both compounds are intrinsic n-type semiconductors but display a metallic-like conductivity coupled to rather large thermopower, which is rationalized within the frames of the acoustic phonons scattering model. Because of larger thermopower BiTeBr exhibits a twice higher thermoelectric figure-of-merit near room temperature, ZT=0.17, compared to BiTeI. The addition of 1 mass% of BiI{sub 3} or CuI to BiTeI decreases the mobility of electrons by two orders of magnitude, leading to significantly lower electrical conductivity, but at the same time effectively reduces the thermal conductivity. The prospects of further enhancing the thermoelectric efficiency are briefly discussed. - Graphical abstract: View of the crystal structure of BiTeBr is shown in the figure The optimized crystal structures show a tendency for the Bi-X (X=Br, I) bond elongation compared to the Bi-Te one. The electronic structures were calculated for BiTeBr and BiTeI using the density-functional theory approach and accounting for the strong spin-orbital interaction. Qualitatively, the band structures for two compounds are similar, showing strong mixing of the p states of all elements in vicinity of the Fermi level, with the band gaps of 0.595 and 0.478 eV for BiTeBr and BiTeI, respectively. Both compounds are intrinsic n-type semiconductors but display a metallic-like conductivity coupled to rather large thermopower, which is rationalized within the frames of the acoustic phonons scattering model. The addition of 1 mass% of BiI{sub 3} or CuI to BiTeI effectively reduces the thermal conductivity. The prospects of further enhancing the thermoelectric efficiency are briefly discussed. Highlights: Black-Right-Pointing-Pointer BiTeBr and BiTeI feature mixing of p states of Bi, Te, and halogen near Fermi level. Black-Right-Pointing-Pointer BiTeBr has thermoelectric figure-of-merit ZT=0.17, two times that of BiTeI. Black-Right-Pointing-Pointer 1% CuI or BiI{sub 3} decrease dramatically electron mobility in BiTeI. Black-Right-Pointing-Pointer 1% CuI decreases thermal conductivity of BiTeI by a factor of 4, reaching 0.5 W m{sup -1} K.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗