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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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118 records · Page 7
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

S -factor and scattering-parameter extractions from ${}^{3}\mathrm{He}+{}^{4}\mathrm{He}{ \rightarrow }^{7}\mathrm{Be}+\gamma $

Previous studies of the reaction ${}^{3}\mathrm{He}+{}^{4}\mathrm{He}\to {}^{7}\mathrm{Be}+\gamma $ have mainly focused on providing the best central value and error bar for the S factor at solar energies. Experimental measurements of this capture reaction at higher energies, the ${}^{3}\mathrm{He}$–${}^{4}\mathrm{He}$ scattering phase shifts, as well as properties of ${}^{7}\mathrm{Be}$ and its excited state, have been used to constrain the theoretical models employed for this purpose. Here we show that much more information than was previously appreciated can be extracted from angle-integrated capture data alone. We use the next-to-leading-order (NLO) amplitude in an effective field theory (EFT) for ${}^{3}\mathrm{He}+{}^{4}\mathrm{He}\to {}^{7}\mathrm{Be}+\gamma $ to perform the extrapolation. At this order the EFT describes the capture process using an s-wave scattering length and effective range, the asymptotic properties of ${}^{7}\mathrm{Be}$ and its excited state, and short-distance contributions to the E1 capture amplitude. We extract the multi-dimensional posterior of all these parameters via a Bayesian analysis that uses capture data below 2 MeV. We find that properties of the ${}^{7}\mathrm{Be}$ ground and excited states are well constrained. The total S factor $S(0)\,={0.577}_{-0.016}^{+0.015}$ keV b, while the branching ratio for excited- to ground-state capture at zero energy, ${Br}(0)={0.406}_{-0.011}^{+0.013}$, both at 68% degree of belief. This S(0) is broadly consistent with other recent evaluations, and agrees with the previously recommended value $S(0)=0.56\pm 0.03\,\,\mathrm{keV}$ b, but has a smaller error bar. We also find significant constraints on ${}^{3}\mathrm{He}$–${}^{4}\mathrm{He}$ scattering parameters, and we obtain constraints on the angular distribution of capture gamma rays, which is important for interpreting experiments. The path forward for this reaction seems to lie with better measurements of the scattering phase shifts and S(E)'s angular dependence away from zero energy, together with better understanding of the asymptotic normalization coefficients of the ${}^{7}$Be bound states' wave functions. Lastly, data on these could further reduce the uncertainty on S(0).

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2022

Superior CO 2 /N 2 separation performance of highly branched Poly(1,3 dioxolane) plasticized by polyethylene glycol

With its high content of CO 2 -philic ether oxygen groups, poly(1,3-dioxolane) (PDXLA) has emerged as an attractive platform to achieve excellent CO 2 /N 2 separation properties for post-combustion carbon capture. Herein we demonstrate that the separation properties of PDXLA can be further enhanced by plasticizing with miscible polyethylene glycol (PEG)-based additives using an integrated experimentation and modeling approach. The effects of the chain end groups and loading level of the additives on the physical properties of the blends are thoroughly investigated, including glass transition temperature (T g ), fractional free volume, and gas transport properties, and the effects can be satisfactorily described using models available for homogeneous blends. Notably, a T g -integrated free volume model is adapted to successfully interpret the unified effect of the blend composition and temperature on gas diffusivity and permeability. A sample containing 45 mass% PEG dimethyl ether (PEGDME with a molecular mass of 240 g/mol) displays stable mixed-gas CO 2 permeability of 1540 Barrer and CO 2 /N 2 selectivity of 40 when challenged with a model flue gas at 60 °C, outperforming Robeson's 2008 upper bound. Elucidating how small plasticizers impact gas transport in homogeneous blends may unravel a facile way to design high-performance membranes for gas separations.

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

Jets from main sequence and white dwarf companions during common envelope evolution

ABSTRACT It has long been speculated that jet feedback from accretion on to the companion during a common envelope (CE) event could affect the orbital evolution and envelope unbinding process. We present global 3D hydrodynamical simulations of CE evolution (CEE) that include a jet subgrid model and compare them with an otherwise identical model without a jet. Our binary consists of a 2-M⊙ red giant branch primary and a 1- or 0.5-M⊙ main sequence (MS) or white dwarf (WD) secondary companion modelled as a point particle. We run the simulations for 10 orbits (40 d). Our jet model adds mass at a constant rate $\dot{M}_\mathrm{j}$ of the order of the Eddington rate, with maximum velocity vj of the order of the escape speed, to two spherical sectors with the jet axis perpendicular to the orbital plane. We explore the influence of the jet on orbital evolution, envelope morphology and envelope unbinding, and assess the dependence of the results on the jet mass-loss rate, launch speed, companion mass, opening angle, and accretion rate. In line with our theoretical estimates, jets are choked around the time of first periastron passage and remain choked thereafter. Subsequent to choking, but not before, jets efficiently transfer energy to bound envelope material. This leads to increases in unbound mass of up to $\sim 10{{\ \rm per\ cent}}$, as compared to the simulations without jets. We also estimate the cumulative effects of jets over a full CE phase, finding that jets launched by MS and WD companions are unlikely to dominate envelope unbinding.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

How negative feedback and the ambient environment limit the influence of recombination in common envelope evolution

ABSTRACT We perform 3D hydrodynamical simulations to study recombination and ionization during the common envelope (CE) phase of binary evolution, and develop techniques to track the ionic transitions in time and space. We simulate the interaction of a $2\, \mathrm{M_\odot }$ red giant branch primary and a $1\, \mathrm{M_\odot }$ companion modelled as a particle. We compare a run employing a tabulated equation of state (EOS) that accounts for ionization and recombination, with a run employing an ideal gas EOS. During the first half of the simulations, ∼15 per cent more mass is unbound in the tabulated EOS run due to the release of recombination energy, but by simulation end the difference has become negligible. We explain this as being a consequence of (i) the tabulated EOS run experiences a shallower inspiral and hence smaller orbital energy release at late times because recombination energy release expands the envelope and reduces drag, and (ii) collision and mixing between expanding envelope gas, ejecta and circumstellar ambient gas assists in unbinding the envelope, but does so less efficiently in the tabulated EOS run where some of the energy transferred to bound envelope gas is used for ionization. The rate of mass unbinding is approximately constant in the last half of the simulations and the orbital separation steadily decreases at late times. A simple linear extrapolation predicts a CE phase duration of ${\sim}2\, {\rm yr}$, after which the envelope would be unbound.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

The cosmological moduli problem and naturalness

Nowadays, the cosmological moduli problem (CMP) comes in three parts: 1. potential violation of Big-Bang nucleosynthesis (BBN) constraints from late decaying moduli fields, 2. the moduli-induced gravitino problem wherein gravitinos are overproduced and their decays violate BBN or dark matter overproduction bounds and 3. the moduli-induced lightest SUSY particle (LSP) overproduction problem. Also, the CMP may be regarded as either a problem or else a solution to scenarios with dark matter over- or under-production. We examine the cosmological moduli problem and its connection to electroweak naturalness. We calculate the various two-body decay widths of a light modulus field into MSSM particles and gravitinos within general supersymmetric models. We include both phase space and mixing effects. We examine cases without and with helicity suppression of modulus decays to gravitinos (cases 1 & 2) and/or gauginos (cases A & B). For case B1, we evaluate regions of gravitino mass m 3/2 vs. modulus mass mΦ parameter space constrained by BBN, by overproduction of gravitinos and by overproduction of neutralino dark matter, along with connections to naturalness. For this case, essentially all of parameter space is excluded unless mΦ ≳ 2.5 × 10 3 TeV with mΦ< 2m 3/2 For a potentially most propitious case B2 with Φ decay to Higgs and matter turned off, then modulus branching fractions to SUSY and to gravitinos become highly suppressed at large m Φ . But since the modulus number density increases faster than the branching fractions decrease, there is still gross overproduction of neutralino dark matter. We also show that in this scenario the thermally produced gravitino problem is fixed by huge entropy dilution, but non-thermal gravitino production from moduli decay remains a huge problem unless it is kinematically suppressed with m Φ < 2m 3/2 . In a pedagogical appendix, we present detailed calculations of modulus field two-body decay widths.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2021

Characterization of a broadly specific cadaverine N-hydroxylase involved in desferrioxamine B biosynthesis in Streptomyces sviceus

N-hydroxylating flavin-dependent monooxygenases (FMOs) are involved in the biosynthesis of hydroxamate siderophores, playing a key role in microbial virulence. Herein, we report the first structural and kinetic characterization of a novel alkyl diamine N-hydroxylase DesB from Streptomyces sviceus (SsDesB). This enzyme catalyzes the first committed step in the biosynthesis of desferrioxamine B, a clinical drug used to treat iron overload disorders. X-ray crystal structures of the SsDesB holoenzyme with FAD and the ternary complex with bound NADP + were solved at 2.86 Å and 2.37 Å resolution, respectively, providing a structural view of the active site environment. SsDesB crystallized as a tetramer and the structure of the individual protomers closely resembles the structures of homologous N-hydroxylating FMOs from Erwinia amylovora (DfoA), Pseudomonas aeruginosa (PvdA), and Aspergillus fumigatus (SidA). Using NADPH oxidation, oxygen consumption, and product formation assays, kinetic parameters were determined for various substrates with SsDesB. SsDesB exhibited typical saturation kinetics with substrate inhibition at high concentrations of NAD(P)H as well as cadaverine. The apparent k cat values for NADPH in steady-state NADPH oxidation and oxygen consumption assays were 0.28 ± 0.01 s -1 and 0.24 ± 0.01 s -1 , respectively. However, in product formation assays used to measure the rate of N-hydroxylation, the apparent k cat for NADPH (0.034 ± 0.008 s -1 ) was almost 10-fold lower under saturating FAD and cadaverine concentrations, reflecting an uncoupled reaction, and the apparent NADPH K M was 33 ± 24 μM. Under saturating FAD and NADPH concentrations, the apparent k cat and K M for cadaverine in Csaky assays were 0.048 ± 0.004 s -1 and 19 ± 9 μM, respectively. SsDesB also N-hydroxylated putrescine, spermidine, and L-lysine substrates but not alkyl (di)amines that were branched or had fewer than four methylene units in an alkyl chain. These data demonstrate that SsDesB has wider substrate scope compared to other well-studied ornithine and lysine N-hydroxylases, making it an amenable biocatalyst for the production of desferrioxamine B, derivatives, and other N-substituted products.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2024

Potent Inhibition of E. coli DXP Synthase by a gem -Diaryl Bisubstrate Analog

New antimicrobial strategies are needed to address pathogen resistance to currently used antibiotics. Bacterial central metabolism is a promising target space for the development of agents that selectively target bacterial pathogens. 1-Deoxy- D -xylulose 5-phosphate synthase (DXPS) converts pyruvate and d-glyceraldehyde 3-phosphate ( D -GAP) to DXP, which is required for synthesis of essential vitamins and isoprenoids in bacterial pathogens. Thus, DXPS is a promising antimicrobial target. Toward this goal, our lab has demonstrated selective inhibition of Escherichia coli DXPS by alkyl acetylphosphonate (alkylAP)-based bisubstrate analogs that exploit the requirement for ternary complex formation in the DXPS mechanism. Here, we present the first DXPS structure with a bisubstrate analog bound in the active site. Insights gained from this cocrystal structure guided structure–activity relationship studies of the bisubstrate scaffold. A low nanomolar inhibitor (compound 8) bearing a gem-dibenzyl glycine moiety conjugated to the acetylphosphonate pyruvate mimic via a triazole-based linker emerged from this study. Compound 8 was found to exhibit slow, tight-binding inhibition, with contacts to E. coli DXPS residues R99 and R478 demonstrated to be important for this behavior. This work has discovered the most potent DXPS inhibitor to date and highlights a new role of R99 that can be exploited in future inhibitor designs toward the development of a novel class of antimicrobial agents.

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

Constraints on the normal branch of DGP gravity from SPT galaxy clusters with DES and HST weak-lensing mass calibration and from P l a n c k PR4 CMB anisotropies

We present constraints on the normal branch of the Dvali-Gabadadze-Porrati (nDGP) braneworld gravity model from the abundance of massive galaxy clusters. On scales below the nDGP crossover scale r c , the nDGP model features an effective gravitylike fifth force that alters the growth of structure, leading to an enhancement of the halo mass function (HMF) on cluster scales. The enhanced cluster abundance allows for constraints on the nDGP model using cluster samples. We employ the South Pole Telescope (SPT) cluster sample, selected through the thermal Sunyaev-Zel’dovich effect with the SPT and with mass calibration using weak-lensing data from the Dark Energy Survey (DES) and the Hubble Space Telescope (HST). The cluster sample contains 1,005 clusters with redshifts 0.25 < z < 1.78 , which are confirmed with the multicomponent matched filter algorithm using optical and near-infrared data. Weak-lensing data from DES and HST enable a robust mass measurement of the cluster sample. We use DES Year 3 data for 688 clusters with redshifts z < 0.95 , and HST data for 39 clusters with redshifts 0.6 < z < 1.7 . We account for the enhancement in the HMF through a semi-analytic correction factor to the standard cosmology HMF derived from the spherical collapse model in the nDGP model. We then further calibrate this model using N -body simulations. In addition, for the first time, we analyze the primary CMB temperature and polarization anisotropy measurements from Planck PR4 within the nDGP model. We obtain a competitive constraint from the joint analysis of the SPT cluster abundance with the Planck PR4 data, and report an upper bound of 1 / H 0 r c < 1.41 at 95% when assuming a cosmology with massive neutrinos.

Vogt, S. M.L. [Munich U. Observ.; LMU Munich (main↗
DOE OSTI2023

Study of e + e - → η Φ via initial state radiation at Belle

Using 980 fb -1 of data collected on and around the (n = 1, 2, 3, 4, 5) resonances with the Belle detector at the KEKB collider, we measure the cross section of e + ⁢e - → η⁢Φ from threshold to 3.95 GeV via initial state radiation. There are clear Φ⁡(1680) and J/ψ signals but no significant Φ⁡(2170) signal in the ηΦ final state. The branching fraction $\mathscr{B}$⁡[J/ψ →η⁢Φ] is measured to be (7.2 ±0.8 ±0.5) ×10 -4 . The resonant parameters of Φ⁡(1680) are determined to be m Φ(1680) = (1696±8±10) MeV/c 2 (statistical and systematic errors, respectively), Γ Φ⁡(1680) =(175±13±16) MeV and, depending on the possible presence of predominantly constructive or destructive interference between Φ⁡(1680) and continuum production, Γ$^{e^+e^-}_{Φ⁡(1680)}$·$\mathscr{B}$⁡[Φ⁡(1680)→ηΦ] and $\mathscr{B}$⁡[Φ(1680)→η⁢Φ] are determined to be (75 ±10 ±11) eV and (25±12±2)% or (207±16±20) eV and (23 ±10 ±2)%, respectively. The upper limit for Γ$^{e^+e^-}_{Φ⁡(2170)}$·$\mathscr{B}$⁡[Φ⁡(2170) → ηΦ] is determined to be either 0.17 or 18.6 eV at the 90% confidence level.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗