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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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Angular power spectrum of the diffuse gamma-ray emission as measured by the Fermi Large Area Telescope and constraints on its dark matter interpretation
The isotropic gamma-ray background arises from the contribution of unresolved sources, including members of confirmed source classes and proposed gamma-ray emitters such as the radiation induced by dark matter annihilation and decay. Clues about the properties of the contributing sources are imprinted in the anisotropy characteristics of the gamma-ray background. We use 81 months of Pass 7 Reprocessed data from the Fermi Large Area Telescope to perform a measurement of the anisotropy angular power spectrum of the gamma-ray background. Here, we analyze energies between 0.5 and 500 GeV, extending the range considered in the previous measurement based on 22 months of data. We also compute, for the first time, the cross-correlation angular power spectrum between different energy bins. The derived angular spectra are compatible with being Poissonian, i.e. constant in multipole. Furthermore, the energy dependence of the anisotropy suggests that the signal is due to two populations of sources, contributing, respectively, below and above ~ 2 GeV . Finally, using data from state-of-the-art numerical simulations to model the dark matter distribution, we constrain the contribution from dark matter annihilation and decay in Galactic and extra-Galactic structures to the measured anisotropy. These constraints are competitive with those that can be derived from the average intensity of the isotropic gamma-ray background.
Possible interpretation of the newly observed Ω ( 2012 ) state
Inspired by the newly observed $Ω (2012)$ state at Belle II, we investigate the two-body strong decays of $Ω$ baryons up to $N = 2$ shell within the chiral quark model. Our results indicate that (i) the newly observed $Ω (2012)$ state could be assigned to the spin-parity $J^P = 3 / 2^-$ state |$70,^{2}10, 1, 1, \frac{3^-}{2}$$\rangle$ and the experimental data can be reasonably described. However, the spin-parity $J^P = 1 / 2^-$ state |$70,^{2}10, 1, 1, \frac{1^-}{2}$$\rangle$ and spin-parity $J^P = 3 / 2^+$ state |$56, ^{4}10, 2, 0, \frac{3^+}{2}$$\rangle$ cannot be completely excluded. (ii) The $D$-wave states in the $N = 2$ shell are most likely to be narrow states with a width of dozens of MeV and have a good potential to be observed in the $\Xi$$K$ and/or $\Xi(1530)K$ channels in future experiments. The $Ω(2250)$ resonance listed in PDG may be a good candidate for the $J^P$ = $5/2^+$ $1D$ wave state |$56$,$^{4}10$, $2, 2$, $5/2^+$ $\rangle$ .
Point-particle drag, lift, and torque closure models using machine learning: Hierarchical approach and interpretability
Developing deterministic neighborhood-informed point-particle closure models using machine learning has garnered interest recently from the dispersed multiphase flow community. The robustness of neural models for this complex multibody problem is hindered by the availability of particle-resolved data. Here, the present work addresses this unavoidable limitation of data paucity by implementing two strategies: (1) by using a rotation and reflection equivariant neural network and (2) by pursuing a physics-based hierarchical machine learning approach. The resulting machine-learned models are observed to achieve a maximum accuracy of 85% and 96% in the prediction of neighbor-induced force and torque fluctuations, respectively, for a wide range of Reynolds number and volume fraction conditions considered. Furthermore, we pursue force and torque network architectures that provide universal prediction spanning a wide range of Reynolds number (0.25 ≤ Re ≤250) and particle volume fraction (0 ≤ φ ≤0.4). The hierarchical nature of the approach enables improved prediction of quantities such as streamwise torque, by going beyond binary interactions to include trinary interactions.
Protophobic Fifth-Force Interpretation of the Observed Anomaly in Be 8 Nuclear Transitions
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Dark Matter Interpretation of the Neutron Decay Anomaly
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Severely Constraining Dark-Matter Interpretations of the 21-cm Anomaly
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Interpretation of the LHCb P c ( 4312 ) + Signal
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binary junipr: An Interpretable Probabilistic Model for Discrimination
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Constraining the Self-Interacting Neutrino Interpretation of the Hubble Tension
Large, nonstandard neutrino self-interactions have been shown to resolve the ~4σ tension in Hubble constant measurements and a milder tension in the amplitude of matter fluctuations. Herein we demonstrate that interactions of the necessary size imply the existence of a force carrier with a large neutrino coupling (>10 -4 ) and mass in the keV–100 MeV range. This mediator is subject to stringent cosmological and laboratory bounds, and we find that nearly all realizations of such a particle are excluded by existing data unless it carries spin 0 and couples almost exclusively to $τ$-flavored neutrinos. Furthermore, we find that the light neutrinos must be Majorana particles, and that a UV-complete model requires a nonminimal mechanism to simultaneously generate neutrino masses and appreciable self-interactions.
Interpretation of Neutral Charm Mesons near Threshold as Unparticles
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MicroBooNE and the ν e Interpretation of the MiniBooNE Low-Energy Excess
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Interpreting machine learning of topological quantum phase transitions
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A challenging interpretation of a hexagonally layered protein structure
The authors describe the structure determination of a hexagonally layered protein structure that suffered from a complicated combination of translational non-crystallographic symmetry and hemihedral twinning. This case serves as a reminder that broken crystallographic symmetry resulting from doubling of a unit-cell axis often requires a new choice of origin. The carboxysome is a giant protein complex that acts as a metabolic organelle in cyanobacteria and some chemoautotrophs. Its outer structure is formed by the assembly of thousands of copies of hexameric shell protein subunits into a molecular layer. The structure determination of a CcmK1 shell protein mutant (L11K) from the β-carboxysome of the cyanobacterium Synechocystis PCC6803 led to challenges in structure determination. Twinning, noncrystallographic symmetry and packing of hexameric units in a special arrangement led to initial difficulties in space-group assignment. The correct space group was clarified after initial model refinement revealed additional symmetry. This study provides an instructive example in which broken symmetry requires a new choice of unit-cell origin in order to identify the highest symmetry space group. An additional observation related to the packing arrangement of molecules in this crystal suggests that these hexameric shell proteins might have lower internal symmetry than previously believed.
Interpretation of solution scattering data from lipid nanodiscs
The structural information contained in solution scattering data from empty lipid nanodiscs is examined in the context of a multi-component geometric model. X-ray scattering data were collected on nanodiscs of different compositions at scattering vector magnitudes up to 2.0 Å −1 . Through the calculation of the partial form factor for each of the nanodisc components before the isotropic average, structural parameters in the model were correlated to the features observed in the X-ray scattering data and to the corresponding distance distribution function. It is shown that, in general, the features at ∼0.3–0.6 Å −1 in the scattering data correlate to the bilayer structure. The data also support the argument that the elliptical shape of nanodiscs found in model fitting is physical, rather than an artefact due to the nanodisc size distribution. The lipid chain packing peak at ∼1.5 Å −1 is visible in the data and reflects the lipid bilayer phase transition. The shape change in the distance distribution function across the phase transition suggests that the nanodiscs are more circular in the fluid phase. The implication of these findings for model fitting of empty and protein-loaded nanodiscs is discussed.