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At least 1,711 records · Page 95

Helium diffusivity in oxide nuclear fuel: Critical data analysis and new correlations

Helium is relevant in determining nuclear fuel behaviour. It affects the performance of nuclear fuel both in reactor and in storage conditions. Helium becomes important in reactor conditions when high burnups are targeted or MOX fuel is used, whereas for storage conditions it can represent a threat to the fuel rods integrity. The accurate knowledge of helium behaviour combined with predictive model capabilities is fundamental for the safe management of nuclear fuel, with helium diffusivity being a critical property. For this reason, a considerable number of separate effect experiments in the last fifty years investigated helium diffusivity in nuclear fuel. The aim of this work is to critically review and assess the experimental results concerning the helium diffusivity. Experimental results are critically analysed in terms of the helium introduction technique used (either infusion, implantation or doping) and of sample characteristics (single crystal, poly-crystal or powder). Accordingly, we derived two different correlations for the diffusivity. Clearly, each of the new correlations corresponds to a limited range of application conditions, depending on the experimental data used to derive it. We provide recommendations regarding the proper application conditions for each correlation (e.g., in reactor or storage conditions).

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗

Possible multiparticle ridge-like correlations in very high multiplicity proton–proton collisions

The CMS Collaboration at the LHC has reported a remarkable and unexpected phenomenon in very high-multiplicity high energy proton–proton collisions: a positive correlation between two particles produced at similar azimuthal angles, spanning a large range in rapidity. We suggest that this “ridge”-like correlation may be a reflection of the rare events generated by the collision of aligned flux tubes connecting the valence quarks in the wave functions of the colliding protons. The “spray” of particles resulting from the approximate line source produced in such inelastic collisions then gives rise to events with a strong correlation between particles produced over a large range of both positive and negative rapidity. We suggest an additional variable that is sensitive to such a line source which is related to a commonly used measure, ellipticity.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

Exploring the NΛ–NΣ coupled system with high precision correlation techniques at the LHC

The interaction of Λ and Σ hyperons (Y) with nucleons (N) is strongly influenced by the coupled-channel dynamics. Due to the small mass difference of the NΛ and NΣ systems, the sizable coupling strength of the NΣ↔NΛ processes constitutes a crucial element in the determination of the NΛ interaction. In this letter we present the most precise measurements on the interaction of pΛ pairs, from zero relative momentum up to the opening of the NΣ channel. The correlation function in the relative momentum space for pΛ ⊕$\bar{p}$$\bar{Λ}$ pairs measured in high-multiplicity triggered pp collisions at $\sqrt{s}$=13 TeV at the LHC is reported. The opening of the inelastic NΣ channels is visible in the extracted correlation function as a cusp-like structure occurring at relative momentum k*=289 MeV/c. This represents the first direct experimental observation of the NΣ↔NΛ coupled channel in the pΛ system. The correlation function is compared with recent chiral effective field theory calculations, based on different strengths of the NΣ↔NΛ transition potential. A weaker coupling, as possibly supported by the present measurement, would require a more repulsive three-body NNΛ interaction for a proper description of the Λ in-medium properties, which has implications on the nuclear equation of state and for the presence of hyperons inside neutron stars.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

Collision-energy dependence of deuteron cumulants and proton-deuteron correlations in Au+Au collisions at RHIC

We report the first measurements of cumulants, up to 4th order, of deuteron number distributions and proton-deuteron correlations in Au+Au collisions recorded by the STAR experiment in phase-I of Beam Energy Scan (BES) program at the Relativistic Heavy Ion Collider. Deuteron cumulants, their ratios, and proton-deuteron mixed cumulants are presented for different collision centralities covering a range of center-of-mass energy per nucleon pair $\sqrt{s_{NN}} = 7.7$ to 200 GeV. It is found that the cumulant ratios at lower collision energies favor a canonical ensemble over a grand canonical ensemble in thermal models. An anti-correlation between proton and deuteron multiplicity is observed across all collision energies and centralities, consistent with the expectation from global baryon number conservation. The UrQMD model coupled with a phase-space coalescence mechanism qualitatively reproduces the collision-energy dependence of cumulant ratios and proton-deuteron correlations.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

Search for the Chiral Magnetic Effect with charge-dependent azimuthal correlations in Xe–Xe collisions at s NN = 5.44 TeV

Charge-dependent two- and three-particle correlations measured in Xe–Xe collisions at $\sqrt{s_{NN}}$ = TeV are presented. Results are obtained for charged particles in the pseudorapidity range |η| and transverse momentum interval 02. ≤ p T < GeV/c for different collision centralities. The three-particle correlator γ αβ ≡ $\langle$cos(φ α + φ β - 2Ψ a )$\rangle$, calculated for different combinations of charge sign α and β, is expected to be sensitive to the presence of the Chiral Magnetic Effect (CME). Its magnitude is similar to the one observed in Pb–Pb collisions in contrast to a smaller CME signal in Xe–Xe collisions than in Pb–Pb collisions predicted by Monte Carlo (MC) calculations including a magnetic field induced by the spectator protons. These observations point to a large non-CME contribution to the correlator. Furthermore, the charge dependence of γ αβ can be described by a blast wave model calculation that incorporates background effects and by the Anomalous Viscous Fluid Dynamics model with values of the CME signal consistent with zero. The Xe–Xe and Pb–Pb results are combined with the expected CME signal dependence on the system size from the MC calculations including a magnetic field to obtain the fraction of CME contribution in γ αβ , $f$ CME . The CME fraction is compatible with zero for the 30% most central events in both systems and then becomes positive. This yields an upper limit of 2% (3%) and 25% (32%) at 95% (99.7%) confidence level for the CME signal contribution to γ αβ in the 0–70% Xe–Xe and Pb–Pb collisions, respectively.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

Investigating the composition of the $K$$^{*}_{0}$(700) state with π ± $K$$^{0}_{S}$ correlations at the LHC

The first measurements of femtoscopic correlations with the particle pair combinations π ± $K$$^{0}_{S}$ in pp collisions at $\sqrt{s}$ = 13 TeV at the Large Hadron Collider (LHC) are reported by the ALICE experiment. Using the femtoscopic approach, it is shown that it is possible to study the elusive $K$$^{*}_{0}$(700) particle that has been considered a tetraquark candidate for over forty years. Source and final-state interaction parameters are extracted by fitting a model assuming a Gaussian source to the experimentally measured two-particle correlation functions. The final-state interaction in the π ± $K$$^{0}_{S}$ system is modeled through a resonant scattering amplitude, defined in terms of a mass and a coupling parameter, The extracted mass and Breit–Wigner width, derived from the coupling parameter, of the final-state interaction are found to be consistent with previous measurements of the $K$$^{*}_{0}$ (700). The small value and increase of the correlation strength with increasing source size support the hypothesis that the $K$$^{*}_{0}$(700) is a four-quark state, i.e. a tetraquark state of the form (q 1 , $\bar{q}$ 2 , q 3 , $\bar{q}$ 3 ) in which q 1 , q 2 and q 3 indicate the flavor of the valence quarks of the π and $K$$^{0}_{S}$. This latter trend is also confirmed via a simple geometric model that assumes a tetraquark structure of the $K$$^{*}_{0}$(700) resonance.

13 TeV pp collisions↗

Ab initio calculations of the carbon and oxygen isotopes: Energies, correlations, and superfluid pairing

We perform ab initio nuclear lattice calculations of the neutron-rich carbon and oxygen isotopes using high-fidelity chiral interactions. We find good agreement with the observed binding energies and compute correlations associated with each two-nucleon interaction channel. For the isospin T = 1 channels, we show that the dependence on T z provides a measure of the correlations among the extra neutrons in the neutron-rich nuclei. For the spin-singlet S-wave channel, we observe that any paired neutron interacts with the nuclear core as well as its neutron pair partner, while any unpaired neutron interacts primarily with only the nuclear core. For the other partial waves, the correlations among the extra neutrons grow more slowly and smoothly with the number of neutrons. These general patterns are observed in both the carbon and oxygen isotopes and may be universal features that appear in many neutron-rich nuclei.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

Measurement of the p–$Σ^+$ correlation function in pp collisions at $\sqrt{s}$ = 13 TeV

In this letter, the first measurement of the femtoscopic correlation of protons and $Σ^+$ hyperons is presented and used to study the p–$Σ^+$ interaction. The measurement is performed with the ALICE detector in high-multiplicity triggered pp collisions at $\sqrt{s}$ = 13 TeV. The $Σ^+$ hyperons are reconstructed using a missing-mass approach in the decay channel to p + π 0 with π 0 → $γγ$, while both $Σ^+$ and protons are identified using a machine learning approach. These techniques result in a high reconstruction efficiency and purity, which allows the measurement of the p–$Σ^+$ correlation function for the first time. Thanks to the high significance achieved in the p–$Σ^+$ correlation signal, it is possible to discriminate between the predictions of different models of the N–$Σ$ interaction and to accomplish a first determination of the p–$Σ^+$ scattering parameters.

Femtoscopy↗

Suppressing 1 H Spin Diffusion in Fast MAS Proton Detected Heteronuclear Correlation Solid-State NMR Experiments

Fast magic angle spinning (MAS) and indirect detection by high gyromagnetic ratio (γ) nuclei such as proton or fluorine are increasingly utilized to obtain 2D heteronuclear correlation (HETCOR) solid-state NMR spectra of spin-1/2 nuclei by using cross polarization (CP) for coherence transfer. However, one major drawback of CP HETCOR pulse sequences is that 1 H spin diffusion during the back X→ 1 H CP transfer step results in relayed correlations. This problem is particularly pronounced for the indirect detection of very low-γ nuclei such as 89 Y, 103 Rh, 109 Ag and 183 W where long contact times on the order of 10 to 30 ms are necessary for optimal CP transfer. In this work, we propose two methods that eliminate relayed correlations and allow more reliable distance information to be obtained from 2D HETCOR NMR spectra. The first method uses Lee-Goldburg (LG) CP during the X→ 1 H back-transfer step to suppress 1 H spin diffusion. We determine LG conditions compatible with fast MAS frequencies (ν rot ) of 40- 95 kHz and show that 1 H spin diffusion can be efficiently suppressed at low effective radiofrequency (RF) fields (ν 1,eff << 0.5ν rot ) and also at high effective RF fields (ν 1,eff >> 2ν rot ). We describe modified Hartmann-Hahn LG-CP match conditions compatible with fast MAS and suitable for indirect detection of moderate-γ nuclei such as 13 C, and low-γ nuclei such as 89 Y. The second method uses D-RINEPT (dipolar refocused insensitive nuclei enhanced by polarization transfer) during the X→ 1 H back-transfer step of the HETCOR pulse sequence. The effectiveness of these methods for acquiring HETCOR spectra with reduced relayed signal intensities is demonstrated with 1 H{ 13 C} HETCOR NMR experiments on L-histidine•HCl•H 2 O and 1 H{ 89 Y} HETCOR NMR experiments on an organometallic yttrium complex.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

Dimethadione embryotoxicity in the rat is neither correlated with maternal systemic drug concentrations nor embryonic tissue levels

Pregnant rats treated with dimethadione (DMO), the N-demethylated metabolite of the anticonvulsant trimethadione, produce offspring having a 74% incidence of congenital heart defects (CHD); however, the incidence of CHD has high inter-litter variability (40–100%) that presents a challenge when studying the initiating events prior to the presentation of an abnormal phenotype. We hypothesized that the variability in CHD incidence was the result of differences in maternal systemic concentrations or embryonic tissue concentrations of DMO. To test this hypothesis, dams were administered 300 mg/kg DMO every 12 h from the evening of gestational day (GD) 8 until the morning of GD 11 (six total doses). Maternal serum levels of DMO were assessed on GD 11, 12, 13, 14, 15, 18 and 21. Embryonic tissue concentrations of DMO were assessed on GD 11, 12, 13 and 14. In a separate cohort of GD 12 embryos, DMO concentrations and parameters of growth and development were assessed to determine if tissue levels of DMO were correlated with these endpoints. Embryos were exposed directly to different concentrations of DMO with whole embryo culture (WEC) and their growth and development assessed. Key findings were that neither maternal systemic concentrations nor tissue concentrations of DMO identified embryos that were sensitive or resistant to DMO in vivo. Direct exposure of embryos to DMO via WEC also failed to show correlations between embryonic concentrations of DMO with developmental outcomes in vitro. We conclude that neither maternal serum nor embryonic tissue concentrations of DMO predict embryonic outcome. - Highlights: • Dimethadione (DMO) induces septation defects (VSD) in rat offspring. • Despite high rate of VSD defects inter-litter variability is 40–100%. • Maternal and embryonic concentrations of DMO were assessed. • Neither serum nor tissue levels of DMO were correlated with embryotoxicity.

60 APPLIED LIFE SCIENCES↗

Evaluation and optimization of flow boiling frictional pressure drop correlations using the data from traditional and next-generation refrigerants in a micro-fin tube

This study presents an experimental evaluation and optimization of flow boiling frictional pressure drop correlations for conventional and next-generation refrigerants in a horizontal micro-fin tube, with particular emphasis on the newly emerging refrigerant blends R-454C and R-455A, for which pressure-drop data in enhanced tubes remain limited. Experiments were conducted with R-410A, R-454C, R-455A, R-134a, R-1234yf, and R-1234ze(E) in a copper micro-fin tube with an inner diameter of 8.468 mm, over mass fluxes ranging from 100 to 300 kg/(m²·s) depending on the refrigerant, and evaporation temperatures of 7, 12, and 14 °C. Frictional pressure gradients were determined from measured total pressure drops after subtracting acceleration pressure drop, and the resulting database was used to assess four existing models: Kuo and Wang (1996), Cavallini et al. (1997), Goto et al. (2001), and Diani et al. (2014). The measured frictional pressure gradient increased with vapor quality and mass flux for all refrigerants and increased further at lower evaporation temperatures, with the overall trend strongly related to liquid viscosity. Among the four correlations, the Goto et al. (2001) model provided the best overall agreement with the measured data before optimization. To further improve prediction accuracy, the Kuo and Wang (1996) and Goto et al. (2001) models were optimized using the complete experimental database. After optimization, both models reduced the overall mean absolute deviation to below 15%, while the optimized Goto et al. (2001) model maintained the best and most consistent overall performance. The results provide new pressure-drop data for next-generation refrigerants and demonstrate that parameter optimization can significantly enhance the applicability of existing micro-fin-tube correlations.

Hu, Yifeng [ORNL] (ORCID:0000000242875185)↗

A field–particle correlation analysis of a perpendicular magnetized collisionless shock

Using the field–particle correlation technique, we examine the particle energization in a three-dimensional (one spatial dimension and two velocity dimensions; 1D-2V) continuum Vlasov–Maxwell simulation of a perpendicular magnetized collisionless shock. The combination of the field–particle correlation technique with the high-fidelity representation of the particle distribution function provided by a direct discretization of the Vlasov equation allows us to ascertain the details of the exchange of energy between the electromagnetic fields and the particles in phase space. We identify the velocity-space signatures of shock-drift acceleration of the ions and adiabatic heating of the electrons arising from the perpendicular collisionless shock by constructing a simplified model with the minimum ingredients necessary to produce the observed energization signatures in the self-consistent Vlasov–Maxwell simulation. We are thus able to completely characterize the energy transfer in the perpendicular collisionless shock considered here and provide predictions for the application of the field–particle correlation technique to spacecraft measurements of collisionless shocks.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

Correlated Displacement of Dynamic Elastic Dipoles Produces Nonclassical Electrostriction in Zr-Doped Ceria

By combining experimental data with density functional theory-based ab initio molecular dynamics modeling, this work provides evidence that nonclassical electrostriction in isovalent Zr-doped ceria is due to the correlated anharmonic motion of dynamic elastic dipoles associated with multiple [ZrO 8 ]-local bonding units with a high Zr concentration (Zr 0.1 Ce 0.9 O 2 ). Introduction of 0.5 mol % trivalent or divalent codopants (Sc, Yb, La, or Ca) reduces the longitudinal electrostriction strain coefficient by more than a factor of 10, produces a 3-fold decrease in the relative dielectric permittivity, and increases the elastic modulus. Since these changes depend neither on the radius nor on the valency of the codopant, we conclude that the responsible species are charge-compensating oxygen vacancies (VO). For trivalent dopants (Do 0.005 Zr 0.1 Ce 0.895 O 1.9975 ), oxygen vacancies are present at a concentration ratio 1:40 with respect to Zr, giving, for random distribution, a characteristic interaction distance of ≤2.3 unit cells (1.2 nm). Oxygen vacancies participate in [ZrO 7 -V O ] local bonding units, disrupting the correlated dynamic displacements of the connected [ZrO 8 ]-local bonding units. Finally, such correlated motion of dynamic elastic dipoles may also explain the exponential increase in the longitudinal electrostriction strain coefficient with an increase in Zr concentration to <0.2 mole fraction and must be taken into account for further development of nonclassical electrostrictors based on Zr-doped ceria.

36 MATERIALS SCIENCE↗

Correlations of the Elemental Compositions of Primary Coal Tar and Char

We report that simulations of large-scale coal combustors rely on accurate submodels to describe the chemical and physical changes in coal during reaction. Typically, researchers use simplified empirical submodels tuned to experimental data to reduce the computational complexity. When data are not readily available, researchers use simplifying assumptions, which can create inaccuracies and biases in a large simulation. One such simplifying assumption in coal research is how to describe the elemental composition of primary pyrolysis products. This paper explores several different empirical model forms to predict the dry, ash-free fractions of C, H, O, N, and S in both the char and the tar, using variables such as parent coal composition, reaction conditions (temperatures and particle residence times), and key coal structural parameters derived from NMR measurements. These model forms were correlated to existing data using a wide range of experimental data using a cross-validation procedure. Since coal structural values can be expensive to measure, several correlations from the literature were used to estimate these values based on information from the proximate and ultimate analyses of the parent coal, including a new correlation for the coal aromaticity. These model forms were tested against a set of measured elemental compositions of tar and char to find the best fit to use in the cross-validation process. Lastly, the best empirical models are presented that predict elemental composition of the coal char and tar after devolatilization.

01 COAL, LIGNITE, AND PEAT↗

Correlative Cryogenic Spectromicroscopy to Investigate Selenium Bioreduction Products

Accurate mapping of the composition and structure of minerals and associated biological materials is critical in geomicrobiology and environmental research. Here we developed an apparatus allowing correlation of cryogenic transmission electron microscopy (TEM) and synchrotron hard X-ray microprobe (SHXM) datasets to precisely determine the distribution, valence state and structure of selenium in biofilms sampled from a contaminated aquifer near Rifle, CO, USA. Results were replicated in the laboratory via anaerobic selenate-reducing enrichment cultures. 16S rRNA analyses of field-derived biofilm indicated the dominance of Beta proteobacteria from the Comamonadaceae family, and uncultivated members of the Simplicispira genus. The major product in field and culture-derived biofilms is &sim;25-300nm red amorphous Se 0 aggregates of colloidal nanoparticles. Correlative analyses of the cultures provided direct evidence for microbial dissimilatory reduction of Se(VI) to Se(IV) to Se 0 . Extended X-ray absorption fine structure spectroscopy showed red amorphous Se 0 with a first shell Se-Se interatomic distance of 2.339 ± 0.003Å. Complementary scanning transmission X-ay microscopy revealed that these aggregates are strongly associated with a protein-rich biofilm matrix. These findings have important implications for predicting the stability and mobility of Se bioremediation products and understanding of Se biogeochemical cycling. The approach, involving correlation of cryo-SHXM and cryo-TEM datasets from the same specimen area, is broadly applicable to biological and environmental samples Published by American Chemical Society.

58 GEOSCIENCES↗

Strategies to Obtain Reliable Energy Landscapes from Embedded Multireference Correlated Wavefunction Methods for Surface Reactions

Embedded correlated wavefunction (ECW) theory is a powerful tool for studying ground- and excited-state reaction mechanisms and associated energetics in heterogeneous catalysis. Several factors are important to obtaining reliable ECW energies, critically the construction of consistent active spaces (ASs) along reaction pathways when using a multireference correlated wavefunction (CW) method that relies on a subset of orbital spaces in the configuration interaction expansion to account for static electron correlation, e.g., complete AS self-consistent field theory, in addition to the adequate partitioning of the system into a cluster and environment, as well as the choice of a suitable basis set and number of states included in excited-state simulations. Here, in this work, we conducted a series of systematic studies to develop best-practice guidelines for ground- and excited-state ECW theory simulations, utilizing the decomposition of NH 3 on Pd(111) as an example. We determine that ECW theory results are relatively insensitive to cluster size, the aug-cc-pVDZ basis set provides an adequate compromise between computational complexity and accuracy, and that a fixed-clean-surface approximation holds well for the derivation of the embedding potential. Additionally, we demonstrate that a merging approach, which involves generating ASs from the molecular fragments at each configuration, is preferable to a creeping approach, which utilizes ASs from adjacent structures as an initial guess, for the generation of consistent potential energy curves involving open-d-shell metal surfaces, and, finally, we show that it is essential to include bands of excited states in their entirety when simulating excited-state reaction pathways.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

Role of Electron Correlation beyond the Active Space in Achieving Quantitative Predictions of Spin-Phonon Relaxation

Single-molecule magnets (SMMs) are promising candidates for molecular-scale data storage and processing due to their strong magnetic anisotropy and long spin relaxation times. However, as temperature rises, interactions between electronic states and lattice vibrations accelerate spin relaxation, significantly limiting their practical applications. Recently, ab initio simulations have made it possible to advance our understanding of phonon-induced magnetic relaxation, but significant deviations from experiments have often been observed. The description of molecules’ electronic structure has been mostly based on complete active space self-consistent field (CASSCF) calculations, and the impact of electron correlation beyond the active space remains largely unexplored. In this study, we provide the first systematic investigation of spin-phonon relaxation in SMMs with post-CASSCF multiconfigurational methods, specifically CAS followed by second-order perturbation theory and multiconfiguration pair-density functional theory. Taking Co(II)- and Dy(III)-based SMMs as case studies, we analyze how electron correlation influences spin-phonon relaxation rates across a range of temperatures, comparing theoretical predictions with experimental observations. Our findings demonstrate that post-CASSCF treatments make it possible to achieve quantitative predictions for Co(II)-based SMMs. For Dy(III)-based systems, however, accurate predictions require consideration of additional effects, underscoring the urgent necessity of further advancing the study of the effects of electronic correlation in these complex systems.

Energy↗

Transfer Learning Meets Embedded Correlated Wavefunction Theory for Chemically Accurate Molecular Simulations: Application to Calcium Carbonate Ion Pairing

Achieving chemical accuracy for molecular simulations remains a central challenge in computational chemistry. Here, we present an embedded correlated wavefunction transfer learning (ECW-TL) framework for accurately simulating molecular dynamics in the condensed phase. ECW-TL incorporates high-level electron exchange and correlation effects in ECW theory while preserving the training and computational efficiency of machine-learned interatomic potentials. We demonstrate the framework on Ca 2+ –CO 3 2– ion pairing in aqueous solution, a key process underlying CO 2 mineralization in seawater. As proof of principle, we first show that fine-tuning a DFT-revPBE-D3(BJ) baseline model with embedded-DFT-SCAN data reproduces the DFT-SCAN free-energy surface within 1 kcal/mol across all solvation states. Extending the framework to embedded MP2 and localized natural-orbital CCSD(T) further refines the free-energy profile, revealing the crucial role of exact electron exchange and correlation in determining ion-pair stability and structure. The computed ion-pair association free energy is in quantitative agreement with experimental measurements, further validating the accuracy of the ECW-TL framework. ECW-TL thus provides a general, data-efficient route for transferring CW accuracy to efficient simulations of complex aqueous and interfacial chemical processes.

cluster chemistry↗