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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 451 records · Page 25
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Quenched crystal-field disorder and magnetic liquid ground states in Tb 2 Sn 2 - x Ti x O 7 [Crystal field disorder in the quantum spin ice ground state of Tb2Sn2-xTixO7]

Solid-solutions of the "soft" quantum spin ice pyrochlore magnets Tb 2 B 2 O 7 with B=Ti and Sn display a novel magnetic ground state in the presence of strong B-site disorder, characterized by a low susceptibility and strong spin fluctuations to temperatures below 0.1 K. These materials have been studied using ac-susceptibility and muSR techniques to very low temperatures, and time-of-flight inelastic neutron scattering techniques to 1.5 K. Remarkably, neutron spectroscopy of the Tb 3+ crystal field levels appropriate to at high B-site mixing (0.5 < x < 1.5 in Tb 2 Sn 2-x Ti x O 7 ) reveal that the doublet ground and first excited states present as continua in energy, while transitions to singlet excited states at higher energies simply interpolate between those of the end members of the solid solution. The resulting ground state suggests an extreme version of a random-anisotropy magnet, with many local moments and anisotropies, depending on the precise local configuration of the six B sites neighboring each magnetic Tb 3+ ion.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Effects of chemical pressure on the magnetic ground states of the osmate double perovskites SrCaCoOs 6 and Ca 2 CoOsO 6

The magnetic ground state in the double perovskite system Sr 2-x Ca x CoOsO 6 changes from an antiferromagnet (x=0), to a spin glass (x=1), to a ferrimagnet (x=2) as the Ca content increases. Moreover, this crossover is driven by chemical pressure effects that control the relative strength of magnetic exchange interactions. The synthesis, crystal structure, and magnetism of SrCaCoOsO 6 and Ca 2 CoOsO 6 are investigated and compared with Sr 2 CoOsO 6 . Both compounds adopt a monoclinic crystal structure with rock-salt ordering of Co 2+ and Os 6+ and a - a - b + octahedral tilting, but the average Co–O–Os bond angle evolves from 158.0(3) in SrCaCoOsO 6 to 150.54(9)° in Ca 2 CoOsO 6 as the smaller Ca 2 + ion replaces Sr 2+ . And while this change may seem minor, it has a profound effect on the magnetism, changing the magnetic ground state from antiferromagnetic in Sr 2 CoOsO 6 (TN1=108K, T N2 =70K), to a spin glass in SrCaCoOsO 6 (T f1 =32K, T f2 =13K), to ferrimagnetic in Ca 2 CoOsO 6 (T C =145K). Finally, in the first two compounds the observation of two transitions is consistent with weak coupling between the Co and Os sublattices.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Local chiral potentials with Δ -intermediate states and the structure of light nuclei

In this paper, we present fully local versions of the minimally nonlocal nucleon-nucleon potentials constructed in a previous paper [Piarulli et al., Phys. Rev. C 91, 024003 (2015)], and use them in hypersperical harmonics and quantum Monte Carlo calculations of ground and excited states of $^3$H, $^3$He, $^4$He, $^6$He, and $^6$Li nuclei. The long-range part of these local potentials includes one- and two-pion exchange contributions without and with $\Delta$-isobars in the intermediate states up to order $Q^3$ ($Q$ denotes generically the low momentum scale) in the chiral expansion, while the short-range part consists of contact interactions up to order $Q^4$. The low-energy constants multiplying these contact interactions are fitted to the 2013 Granada database in two different ranges of laboratory energies, either 0–125 MeV or 0–200 MeV, and to the deuteron binding energy and $nn$ singlet scattering length. Fits to these data are performed for three models characterized by long- and short-range cutoffs, $R_{\rm L}$ and $R_{\rm S}$, respectively, ranging from $(R_{\rm L},R_{\rm S})=(1.2,0.8)$ fm down to $(0.8,0.6)$ fm. Finally, the long-range (short-range) cutoff regularizes the one- and two-pion exchange (contact) part of the potential.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2017

Structure of Ne 20 states in resonance O 16 + α elastic scattering

Background: The nuclear structure of the cluster bands in 20 Ne presents a challenge for different theoretical approaches. It is especially difficult to explain the broad 0 + , 2 + states at 9 MeV excitation energy. Simultaneously, it is important to obtain more reliable experimental data for these levels in order to quantitatively assess the theoretical framework. Purpose: To obtain new data on 20 Ne α- cluster structure. Method: Thick target inverse kinematics technique was used to study the 16 O+α resonance elastic scattering and the data were analyzed using an R matrix approach. The 20 Ne spectrum, the cluster and nucleon spectroscopic factors were calculated using cluster-nucleon configuration interaction model (CNCIM). Results: We determined the parameters of the broad resonances in 20 Ne: 0 + level at 8.77 ± 0.150 MeV with a width of 750 $^{+500}_{-220}$ keV; 2 + level at 8.75 ± 0.100 MeV with the width of 695 ± 120 keV; the width of 9.48 MeV level of 65 ± 20 keV and showed that 9.19 MeV, 2 + level (if exists) should have width ≤ 10 keV. The detailed comparison of the theoretical CNCIM predictions with the experimental data on cluster states was made. Conclusions: Our experimental results by the TTIK method generally confirm the adopted data on α-cluster levels in 20 Ne. The CNCIM gives a good description of the 20 Ne positive parity states up to an excitation energy of ~7 MeV, predicting reasonably well the excitation energy of the states and their cluster and single particle properties. At higher excitations, the qualitative disagreement with the experimentally observed structure is evident, especially for broad resonances.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

α decay of the T = 1 , 2 + state in B 10 and isospin symmetry breaking in the A = 10 triplet

Here, the rate of the T =1, 2+ to T =1, 0 + transition in 10 B ( T =1, T z =0) is compared to the analog transitions in 10 Be ( T =1, T z =–1) and 10 C ( T =1, T z =+1) to provide constraints on ab initio calculations using realistic nuclear forces. The relevant state in 10 B, at E x =5.164 MeV, is particle unbound. Therefore, a determination of the B ( E 2) electromagnetic transition rate requires a precise and accurate determination of the width of the state, as well as the α-particle and γ-ray branching ratios. Previous measurements of the α-particle branching ratio are just barely in agreement. We report on a new study of the α-particle branch by studying the 10 B(p,p') 10 B* reaction in inverse kinematics with the HELIOS spectrometer. The α-particle branching ratio that we observe, 0.144±0.027, is in good agreement with the evaluated value and improves the associated uncertainty. The resulting experimental B ( E 2) value is 7.0±2.2 e 2 fm 4 and is more consistent with a flat trend across the A=10 triplet than previously reported. This is inconsistent with Green's function Monte Carlo predictions using realistic three-nucleon Hamiltonians, which overpredict the B ( E 2) value in 10 C and 10 B.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2013

Measurement of exclusive Υ ( 1 S ) and Υ ( 2 S ) decays into vector-pseudoscalar final states

Using samples of 102 million $Υ(1S)$ and 158 million $Υ(2S)$ events collected with the Belle detector, we study exclusive hadronic decays of these two bottomonium resonances to $K^0_sK^+ \pi^-$ and charge-conjugate (c.c.) states, $π^+π^-π^0π^0$, and $π^+π^-π^0$, and to the two-body Vector-Pseudoscalar $(K^*(892)^0\bar{K}^0+c.c.$, $K^*(892)^-K^++c.c.$, $ωπ^0$, and $ρπ$) final states. For the first time, signals are observed in the modes $Υ(1S)$ → $K^0_sK^+\pi^- + c.c.$, $π^+π^-π^0π^0$, and $Υ(2S)$→$π^+π^-π^0π^0$, and evidence is found for the modes $Υ(1S)$→$π^+π^-π^0$, $K^*(892)^0\bar{K}^0+c.c.$, and $Υ(2S)$ → $K^0_sK^+\pi^- + c.c.$ Branching fractions are measured for all the processes, while 90% confidence level upper limits on the branching fractions are also set for the modes with a statistical significance of less than $3σ$. The ratios of the branching fractions of $Υ(2S)$ and $Υ(1S)$ decays into the same final state are used to test a perturbative QCD prediction for OZI-suppressed bottomonium decays.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

Simultaneous measurement of forward-backward asymmetry and top polarization in dilepton final states from $t\bar t$ production at the Tevatron

We present a simultaneous measurement of the forward-backward asymmetry and the top-quark polarization in tt¯ production in dilepton final states using 9.7 fb –1 of proton-antiproton collisions at √s=1.96 TeV with the D0 detector. To reconstruct the distributions of kinematic observables we employ a matrix element technique that calculates the likelihood of the possible tt¯ kinematic configurations. After accounting for the presence of background events and for calibration effects, we obtain a forward-backward asymmetry of A tt¯ =(15.0±6.4(stat)±4.9(syst))% and a top-quark polarization times spin analyzing power in the beam basis of κP=(7.2±10.5(stat)±4.2(syst))%, with a correlation of –56% between the measurements. If we constrain the forward-backward asymmetry to its expected standard model value, we obtain a measurement of the top polarization of κP=(11.3±9.1(stat)±1.9(syst))%. If we constrain the top polarization to its expected standard model value, we measure a forward-backward asymmetry of A tt¯ =(17.5±5.6(stat)±3.1(syst))%. A combination with the D0 A tt¯ measurement in the lepton+jets final state yields an asymmetry of Att¯=(11.8±2.5(stat)±1.3(syst))%. Within their respective uncertainties, all these results are consistent with the standard model expectations.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

Search for pair production of Higgs bosons in the b b ¯ b b ¯ final state using proton-proton collisions at s = 13 TeV with the ATLAS detector with the ATLAS detector

A search for Higgs-boson pair production in the b b ¯ b b ¯ final state using proton-proton collisions at s = 13 TeV final state is carried out with 3.2 fb -1 of proton-proton collision data collected at √s=13 TeV with the ATLAS detector. The data are consistent with the estimated background and are used to set upper limits on the production cross section of Higgs-boson pairs times branching ratio to b b ¯ b b ¯ final state using proton-proton collisions at s = 13 TeV for both nonresonant and resonant production. In the case of resonant production of Kaluza-Klein gravitons within the Randall-Sundrum model, upper limits in the 24 to 91 fb range are obtained for masses between 600 and 3000 GeV, at the 95% confidence level. The production cross section times branching ratio for nonresonant Higgs-boson pairs is also constrained to be less than 1.22 pb, at the 95% confidence level.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

Measurement of top quark polarization in t t ¯ lepton + jets final states

We present a measurement of top quark polarization in t ¯ t pair production in p ¯ p collisions at √ s = 1.96 TeV using data corresponding to 9.7 fb -1 of integrated luminosity recorded with the D0 detector at the Fermilab Tevatron Collider. We consider final states containing a lepton and at least three jets. The polarization is measured through the distribution of lepton angles along three axes: the beam axis, the helicity axis, and the transverse axis normal to the t ¯ t production plane. This is the first measurement of top quark polarization at the Tevatron using lepton + jet final states and the first measurement of the transverse polarization in t ¯ t production. The observed distributions are consistent with standard model predictions of nearly no polarization.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

Search for D 0 decays to invisible final states at Belle

Here, we report the result from the first search for D 0 decays to invisible final states. The analysis is performed on a data sample of 924 fb - 1 collected at and near the Υ ( 4 S ) and Υ ( 5 S ) resonances with the Belle detector at the KEKB asymmetric-energy e + e - collider. The absolute branching fraction is confirmed using an inclusive D 0 sample, obtained by fully reconstructing the rest of the particle system including the other charmed particle. No significant signal yield is observed and an upper limit of 9.4 × 10 - 5 is set on the branching fraction of D 0 to invisible final states at 90% confidence level.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2013

Study of e + e - → π + π - J / ψ and Observation of a Charged Charmoniumlike State at Belle

The cross section for $e^+e^-→π^+π^-J/ψ$ between 3.8 GeV and 5.5 GeV is measured with a 967 fb -1 data sample collected by the Belle detector at or near the $\Upsilon(nS)$ ($n=1, 2, ..., 5$) resonances. The $\Upsilon$(4260) state is observed, and its resonance parameters are determined. In addition, an excess of $π^+π^-J/ψ$ production around 4 GeV is observed. This feature can be described by a Breit-Wigner parameterization with properties that are consistent with the $\Upsilon$(4008) state that was previously reported by Belle. In a study of $\Upsilon$(4260)→$π^+π^-J/ψ$ decays, a structure is observed in the $M(\pi^{\pm}J/ψ)$ mass spectrum with 5.2$σ$ significance, with mass M=(3894.5±6.6±4.5)MeV/$c^2$ and width $Γ$=(63±24±26) MeV/$c^2$, where the errors are statistical and systematic, respectively. This structure can be interpreted as a new charged charmonium-like state.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

Direct lifetime measurements of the excited states in Ni 72

The lifetimes of the first excited 2 + and 4 + states in 72 Ni were measured at the National Superconducting Cyclotron Laboratory with the recoil-distance Doppler-shift method, a model-independent probe to obtain the reduced transition probability. Excited states in 72 Ni were populated by the one-proton knockout reaction of an intermediate energy 73 Cu beam. γ-ray-recoil coincidences were detected with the γ-ray tracking array GRETINA and the S800 spectrograph. Our results provide evidence of enhanced transition probability B(E2;2 + → 0 + ) as compared to 68 Ni, but do not confirm the trend of large B(E2) values reported in the neighboring isotope 70 Ni obtained from Coulomb excitation measurement. The results are compared to shell model calculations. Here, the lifetime obtained for the excited 4 + 1 state is consistent with models showing decay of a seniority ν = 4, 4 + state, which is consistent with the disappearance of the 8+ isomer in 72 Ni.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2023

Experimental Limit on Nonlinear State-Dependent Terms in Quantum Theory

Linear time evolution is one of the fundamental postulates of quantum theory. Past theoretical attempts to introduce nonlinearity into quantum evolution have violated causality. However, a recent theory has introduced nonlinear state-dependent terms in quantum field theory, preserving causality [D. E. Kaplan and S. Rajendran, Phys. Rev. D 105, 055002 (2022)]. We report the results of an experiment that searches for such terms. Our approach, inspired by the Everett many-worlds interpretation of quantum theory, correlates a binary macroscopic classical voltage with the outcome of a projective measurement of a quantum bit, prepared in a coherent superposition state. Measurement results are recorded in a bit string, which is used to control a voltage switch. Presence of a nonzero voltage reading in cases of no applied voltage is the experimental signature of a nonlinear state-dependent shift of the electromagnetic field operator. We implement blinded measurement and data analysis with three control bit strings. Control of systematic effects is realized by producing one of the control bit strings with a classical random-bit generator. The other two bit strings are generated by measurements performed on a superconducting qubit in an IBM Quantum processor and on a N 15 nuclear spin in a nitrogen-vacancy center in diamond. Our measurements find no evidence for electromagnetic quantum state-dependent nonlinearity. We set a bound on the parameter that quantifies this nonlinearity | ε γ | < 4.7 × 10 - 11 , at 90% confidence level.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2017

Low-energy surface states in the normal state of α - PdBi 2 superconductor

Topological superconductors as characterized by Majorana surface states have been actively searched for their significance in fundamental science and technological implication. The large spin-orbit coupling in Bi-Pd binaries has stimulated extensive investigations on the topological surface states in these superconducting compounds. Here we report a study of normal-state electronic structure in a centrosymmetric α-PdBi 2 within density functional theory calculations. By investigating the electronic structure from the bulk to slab geometries in this system, we predict for the first time that α-PdBi 2 can host orbital-dependent and asymmetric Rashba surface states near the Fermi energy. This study suggests that α-PdBi 2 will be a good candidate to explore the relationship between superconductivity and topology in condensed matter physics.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Defect-induced states, defect-induced phase transition, and excitonic states in bent tungsten disulfide (WS 2 ) nanoribbons: Density functional vs. many body theory

Two-dimensional (2D) transition metal dichalcogenide (TMD) materials have versatile electronic and optical properties. TMD nanoribbons exhibit interesting properties due to reduced dimensionality, quantum confinement, and edge states, which make them suitable for various electronic and optoelectronic applications. In a previous work conducted by our group, we demonstrated that the edge bands evolved with bending can tune the optical properties for various widths of TMD nanoribbons. Defects are commonly present in 2D TMD materials, and can dramatically change the material properties. Here, in this following work, we investigate the interaction between the edge and the defect states in tungsten disulfide (WS 2 ) nanoribbons with lines of W- or S-atom vacancies defects under different bending conditions, using density functional theory (DFT). To gain understanding about the limits of density functional approximations, we compare results on band gaps and energies of defect states with quasiparticle GW. We reveal interesting semiconductor-metal phase transitions, suggesting potential applications in nanoelectronics or molecular electronics. We also calculate the optical absorption of the bent and defective nanoribbons with the many-body GW-BSE (Bethe-Salpeter equation) approach, revealing a tunable optical spectrum and diverse exciton states in the defective WS 2 nanoribbons.

36 MATERIALS SCIENCE↗
DOE OSTI2018

State and Parameter Estimation for Natural Gas Pipeline Networks Using Transient State Data

Here, we formulate two estimation problems for pipeline systems in which measurements of the compressible gas flowing through a network of pipes are affected by time-varying injections, withdrawals, and compression. We consider a state estimation problem that is then extended to a joint state and parameter estimation problem that can be used for data assimilation. In both formulations, the flow dynamics are described on each pipe by space- and time-dependent densities and mass flux which evolve according to a system of coupled partial differential equations, in which momentum dissipation is modeled using the Darcy-Wiesbach friction approximation. These dynamics are first spatially discretized to obtain a system of nonlinear ordinary differential equations on which state and parameter estimation formulations are given as nonlinear least squares problems. A rapid, scalable computational method for performing a nonlinear least squares estimation is developed. Extensive simulations and computational experiments on multiple pipeline test networks demonstrate the effectiveness of the formulations in obtaining state and parameter estimates in the presence of measurement and process noise.

03 NATURAL GAS↗
DOE OSTI2016

Response of vegetation phenology to urbanization in the conterminous United States

The influence of urbanization on vegetation phenology is gaining considerable attention due to its implications for human health, cycling of carbon and other nutrients in Earth system. In this study, we examined the relationship between change in vegetation phenology and urban size, an indicator of urbanization, for the conterminous United States. We studied more than 4500 urban clusters of varying size to determine the impact of urbanization on plant phenology, with the aids of remotely sensed observations since 2003–2012. We found that phenology cycle (changes in vegetation greenness) in urban areas starts earlier (start of season, SOS) and ends later (end of season, EOS), resulting in a longer growing season length (GSL), when compared to the respective surrounding urban areas. The average difference of GSL between urban and rural areas over all vegetation types, considered in this study, is about 9 days.Also, the extended GSL in urban area is consistent among different climate zones in the United States, whereas their magnitudes are varying across regions. We found that a tenfold increase in urban size could result in an earlier SOS of about 1.3 days and a later EOS of around 2.4 days. As a result, the GSL could be extended by approximately 3.6 days with a range of 1.6–6.5 days for 25th ~ 75th quantiles, with a median value of about 2.1 days. For different vegetation types, the phenology response to urbanization, as defined by GSL, ranges from 1 to 4 days. In conclusion, the quantitative relationship between phenology and urbanization is of great use for developing improved models of vegetation phenology dynamics under future urbanization, and for developing change indicators to assess the impacts of urbanization on vegetation phenology.

54 ENVIRONMENTAL SCIENCES↗