Radiation-Assisted Formation of Metal Nanoparticles in Molten Salts
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99 GENERAL AND MISCELLANEOUS↗
SEARCH · Engineering Papers
Results for “energy and behavior”
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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Persistence length regulates emergent dynamics in active roller ensembles
Active colloidal fluids, biological and synthetic, often demonstrate complex self-organization and the emergence of collective behavior. Spontaneous formation of multiple vortices has been recently observed in a variety of active matter systems, however, the generation and tunability of the active vortices not controlled by geometrical confinement remain challenging. Here, we exploit the persistence length of individual particles in ensembles of active rollers to tune the formation of vortices and to orchestrate their characteristic sizes. We use two systems and employ two different approaches exploiting shape anisotropy or polarization memory of individual units for control of the persistence length. We characterize the dynamics of emergent multi-vortex states and reveal a direct link between the behavior of the persistence length and properties of the emergent vortices. We further demonstrate common features between the two systems including anti-ferromagnetic ordering of the neighboring vortices and active turbulent behavior with a characteristic energy cascade in the particles velocity field energy spectra. Finally, our findings provide insights into the onset of spatiotemporal coherence in active roller systems and suggest a control knob for manipulation of dynamic self-assembly in active colloidal ensembles.
42 ENGINEERING↗
The electrode–electrolyte interface of Cu via modulation excitation X-ray absorption spectroscopy
The development and application of modulation excitation X-ray absorption spectroscopy with sub-second resolution and better than 0.02% detection sensitivity unveils the kinetics of the anodic oxidation of Cu in bicarbonate electrolytes. Accessing the electrode–electrolyte interface under operating conditions and capturing time-resolved kinetics remain challenging in electrochemical studies. Copper's interfacial oxidation dynamics remain unclear despite extensive research. Modulation excitation X-ray absorption spectroscopy (ME-XAS) was used to probe Cu in 100 mM KHCO 3 with sub-second sensitivity, revealing that hydroxide forms 30 ± 10 ms before the appearance of Cu 2 O at positive potentials (0 to 0.5 V vs. RHE) near open-circuit conditions. From −0.4 to 0.8 V vs. RHE, hydroxide coverage reaches 49%, accompanied by a balanced presence of Cu( i ) and Cu( ii ) oxides. These insights into Cu interfacial redox behavior under intermittent renewable energy operation—relevant to CO 2 electrolyzer durability—enhance our fundamental understanding of electrochemical interfaces.
Garcia-Esparza, Angel T↗
First characterization of the emission behavior of Mrk 421 from radio to very high-energy gamma rays with simultaneous X-ray polarization measurements
Aims.We have performed the first broadband study of Mrk 421 from radio to TeV gamma rays with simultaneous measurements of the X-ray polarization from IXPE. Methods.The data were collected as part of an extensive multiwavelength campaign carried out between May and June 2022 using MAGIC,Fermi-LAT,NuSTAR,XMM-Newton,Swift, and several optical and radio telescopes to complement IXPE data. Results.During the IXPE exposures, the measured 0.2–1 TeV flux was close to the quiescent state and ranged from 25% to 50% of the Crab Nebula without intra-night variability. Throughout the campaign, the very high-energy (VHE) and X-ray emission are positively correlated at a 4σsignificance level. The IXPE measurements reveal an X-ray polarization degree that is a factor of 2–5 higher than in the optical/radio bands; that implies an energy-stratified jet in which the VHE photons are emitted co-spatially with the X-rays, in the vicinity of a shock front. The June 2022 observations exhibit a rotation of the X-ray polarization angle. Despite no simultaneous VHE coverage being available during a large fraction of the swing, theSwift-XRT monitoring reveals an X-ray flux increase with a clear spectral hardening. This suggests that flares in high synchrotron peaked blazars can be accompanied by a polarization angle rotation, as observed in some flat spectrum radio quasars. Finally, during the polarization angle rotation,NuSTARdata reveal two contiguous spectral hysteresis loops in opposite directions (clockwise and counterclockwise), implying important changes in the particle acceleration efficiency on approximately hour timescales.
Astronomy & Astrophysics↗
Evolution of Efimov states
The Efimov phenomenon manifests itself as an emergent discrete scaling symmetry in the quantum three-body problem. In the unitarity limit, it leads to an infinite tower of three-body bound states with energies forming a geometric sequence. Here in this work, we study the evolution of these so-called Efimov states using relativistic scattering theory. We identify them as poles of the three-particle S matrix and trace their trajectories in the complex energy plane as they evolve from virtual states through bound states to resonances. We dial the scattering parameters toward the unitarity limit and observe the emergence of the universal scaling of energies and couplings - a behavior known from the non-relativistic case. Interestingly, we find that Efimov resonances follow unusual, cyclic trajectories accumulating at the three-body threshold and then disappear at some values of the two-body scattering length. We propose a partial resolution to this ?missing states? problem.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Dynamical properties of a driven dissipative dimerized $S$ =1/2 chain
We consider the dynamical properties of a gapped quantum spin system coupled to the electric field of a laser, which drives the resonant excitation of specific phonon modes that modulate the magnetic interactions. Here, we deduce the quantum master equations governing the time-evolution of both the lattice and spin sectors, by developing a Lindblad formalism with bath operators providing an explicit description of their respective phonon-mediated damping terms. We investigate the nonequilibrium steady states (NESS) of the spin system established by a continuous driving, delineating parameter regimes in driving frequency, damping, and spin-phonon coupling for the establishment of physically meaningful NESS and their related nontrivial properties. Focusing on the regime of generic weak spin-phonon coupling, we characterize the NESS by their frequency and wave-vector content, explore their transient and relaxation behavior, and discuss the energy flow, the system temperature, and the critical role of the type of bath adopted. Our study lays a foundation for the quantitative modeling of experiments currently being designed to control coherent many-body spin states in quantum magnetic materials.
1-dimensional spin chains↗
Superconductivity, charge density waves, and bipolarons in the Holstein model
The electron-phonon ( e-ph ) interaction remains of great interest in condensed matter physics and plays a vital role in realizing superconductors, charge density waves (CDW), and polarons. We study the two-dimensional Holstein model for e-ph coupling using determinant quantum Monte Carlo across a wide range of its phase diagram as a function of temperature, electron density, dimensionless e-ph coupling strength, and the adiabatic ratio of the phonon frequency to the Fermi energy. We describe the behavior of the CDW correlations, the competition between superconducting and CDW orders and polaron formation, the optimal conditions for superconductivity, and the transition from the weak-coupling regime to the strong-coupling regime. Superconductivity is optimized at intermediate e-ph coupling strength and intermediate electron density, and the superconducting correlations increase monotonically with phonon frequency. The global maximum for superconductivity in the Holstein model occurs at large phonon frequency, the limit where an attractive Hubbard model effectively describes the physics.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Logarithmic criticality in transverse thermoelectric conductivity of the ferromagnetic topological semimetal CoMnSb
Here we report the results of our experimental studies on the magnetic, transport, and thermoelectric properties of the ferromagnetic metal CoMnSb. A sizable anomalous Hall conductivity $σ_{yx}$ and transverse thermoelectric conductivity $α_{yx}$ are found experimentally and comparable in size to the values estimated from first-principles calculation. Our experiment further reveals that CoMnSb exhibits -T log T critical behavior in $α_{yx}$ (T), deviating from Fermi liquid behavior $α_{yx}$ ~ T over a decade of temperature between 10 and 400 K, similar to ferromagnetic Weyl and nodal-line semimetals. Our theoretical calculation for CoMnSb also predicts the - T log T behavior when the Fermi energy locates near the Weyl nodes in momentum space.
36 MATERIALS SCIENCE↗
Quantitative relationship between structural orthorhombicity, shear modulus, and heat capacity anomaly of the nematic transition in iron-based superconductors
Electronic nematicity in iron pnictide materials has been extensively studied by various experimental techniques, yet its heat capacity anomaly at the phase transition has not been examined quantitatively. In this paper, we review the thermodynamic description of nematicity in Ba(Fe 1- x Cox) 2 As 2 using the Landau free energy, which defines the behavior of three thermodynamic quantities: the structural orthorhombicity that develops below the nematic transition, the softening shear modulus above the transition, and the discontinuous heat capacity at the transition. We derive a quantitative relationship between these three quantities, which is found to hold for a range of dopings. We report this result shows that the nematic transition is exceedingly well described by a mean-field model in the underdoped regime of the phase diagram.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Relaxation and darkening of excitonic complexes in electrostatically doped monolayer $\mathrm{WSe_2}$: Roles of exciton-electron and trion-electron interactions
Here we present photoluminescence measurements in monolayer $\mathrm{WSe_2}$, which point to the importance of the interaction between charged particles and excitonic complexes. The theoretical analysis highlights the key role played by exchange scattering, referring to cases wherein the particle composition of the complex changes after the interaction. For example, exchange scattering renders bright excitonic complexes dark in monolayer $\mathrm{WSe_2}$ on accounts of the unique valley-spin configuration in this material. In addition to the ultrafast energy relaxation of hot excitonic complexes following their interaction with electrons or holes, our analysis sheds light on several key features that are commonly seen in the photoluminescence of this monolayer semiconductor. In particular, we can understand why the photoluminescence intensity of the neutral bright exciton is strongest when the monolayer is hole doped rather than charge neutral or electron doped. Similarly, we can understand the reason for the dramatic increase of the photoluminescence intensity of negatively charged excitons (trions) as soon as electrons are added to the monolayer. To self-consistently explain the findings, we further study the photoluminescence spectra at different excitation energies and analyze the behavior of the elusive indirect exciton.
36 MATERIALS SCIENCE↗
Proximity-induced equilibrium supercurrent and perfect superconducting diode effect due to band asymmetry
Herein we theoretically investigate the consequences of proximity-induced conventional superconductivity in metals that break time-reversal and inversion symmetries through their energy dispersion. We discover behaviors impossible in an isolated superconductor such as an equilibrium supercurrent that apparently violates a no-go theorem and, at suitable topological defects, nonconservation of electric charge reminiscent of the chiral anomaly. The equilibrium supercurrent is expected to be trainable by a helical electromagnetic field in the normal state. Remarkably, if the band asymmetry exceeds the critical current of the parent superconductor in appropriate units, we predict a perfect superconducting diode effect with diode coefficient unity. We propose toroidal metals such as UNi 4 B and metals with directional scalar spin chiral order as potential platforms.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Bulk properties of the system formed in Au + Au collisions at s N N = 14.5 GeV at the BNL STAR detector
We report systematic measurements of bulk properties of the system created in Au+Au collisions at √ S NN = 14.5 GeV recorded by the STAR detector at the Relativistic Heavy Ion Collider (RHIC). The transverse momentum spectra of π ± , K ± and p(p¯) are studied at mid-rapidity (|y| < 0.1) for nine centrality intervals. The centrality, transverse momentum (p T ), and pseudorapidity (η) 3 dependence of inclusive charged particle elliptic flow (v 2 ), and rapidity-odd charged particles directed flow (v 1 ) results near mid-rapidity are also presented. These measurements are compared with the published results from Au+Au collisions at other energies, and from Pb+Pb collisions at √ S NN =2.76 TeV. The results at √ S NN = 14.5 GeV show similar behavior as established at other energies and fit well in the energy dependence trend. Furthermore, these results are important as the 14.5 GeV energy fills the gap in μ B, which is of the order of 100 MeV, between √ S NN =11.5 and 19.6 GeV. Comparisons of the data with UrQMD and AMPT models show poor agreement in general.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Global Λ-hyperon polarization in Au + Au collisions at $\sqrt{S_{NN}}$ = 3 GeV
Global hyperon polarization, $\overline{P}$ H , in Au + Au collisions over a large range of collision energy, $\sqrt{S_{NN}}$, was recently measured and successfully reproduced by hydrodynamic and transport models with intense fluid vorticity of the quark-gluon plasma. While na¨ıve extrapolation of data trends suggests a large $\overline{P}$ H as the collision energy is reduced, the behavior of $\overline{P}$ H at small $\sqrt{S_{NN}}$ < 7.7 GeV is unknown. Operating the STAR experiment in fixed-target mode, we measured the polarization of Λ hyperons along the direction of global angular momentum in Au + Au collisions at $\sqrt{S_{NN}}$ = 3 GeV. As a result, the observation of substantial polarization of 4.91 ± 0.81 (stat.) ± 0.15 (syst.) % in these collisions may require a reexamination of the viscosity of any fluid created in the collision, of the thermalization timescale of rotational modes, and of hadronic mechanisms to produce global polarization.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Measurement of fragment-correlated γ-ray emission from 252 Cf(sf)
This paper presents recent experimental results on the yield of prompt fission γ rays from the spontaneous fission of 252 Cf. We use an ionization chamber to tag fission events and measure the masses and kinetic energies of the fission fragments and trans-stilbene organic scintillators to measure the neutrons and γ rays emitted by the fission fragments. The combination of the ionization chamber and trans-stilbene scintillators allows us to determine the properties of neutrons and γ rays in coincidence with the fragments. The yield of γ rays is known to be influenced by the angular momenta (AM) of the fission fragments. We present experimental evidence indicating that the total γ-ray multiplicity, i.e., the sum of both fragments' emission, saturates at sufficiently high internal fragment excitation energies. We also observe distinct behaviors for the yield of γ rays from the light and heavy fragments, which for certain mass and total kinetic energy (TKE) regions are weakly or anticorrelated, indicating the presence of complex AM generation modes. We also observed a mass- and TKE-dependent anisotropy of the γ rays, which challenges and expands on the conventional notion that the fragments' AM are always aligned perpendicularly to the fission axis. Furthermore, the dependence of the anisotropy on mass and TKE indicates a dependence of these properties on the specific fission channels, thus providing an insight into the deformations and dynamics in fission and their connection with experimentally observable quantities.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Varied phenomenology of models displaying dynamical large-deviation singularities
Singularities of dynamical large-deviation functions are often interpreted as the signal of a dynamical phase transition and the coexistence of distinct dynamical phases, by analogy with the correspondence between singularities of free energies and equilibrium phase behavior. Here we study models of driven random walkers on a lattice. These models display large-deviation singularities in the limit of large lattice size, but the extent to which each model's phenomenology resembles a phase transition depends on the details of the driving. We also compare the behavior of ergodic and nonergodic models that present large-deviation singularities. Finally, we argue that dynamical large-deviation singularities indicate the divergence of a model timescale, but not necessarily one associated with cooperative behavior or the existence of distinct phases.
74 ATOMIC AND MOLECULAR PHYSICS↗
First Observation of Multiple Transverse Wobbling Bands of Different Kinds in 183 Au
Here, we report the first observation of two wobbling bands in 183 Au, both of which were interpreted as the transverse wobbling (TW) band but with different behavior of their wobbling energies as a function of spin. It increases (decreases) with spin for the positive (negative) parity configuration. The crucial evidence for the wobbling nature of the bands, dominance of the $\textit{E}$2 component in the Δ$\textit{I}$ = 1 transitions between the partner bands, is provided by the simultaneous measurements of directional correlation from the oriented states ratio and the linear polarization of the $\textit{γ}$ rays. Particle rotor model calculations with triaxial deformation reproduce the experimental data well. A value of spin, $I_m$, has been determined for the observed TW bands below which the wobbling energy increases and above which it decreases with spin. The nucleus 183 Au is, so far, the only nucleus in which both the increasing and the decreasing parts are observed and thus gives the experimental evidence of the complete transverse wobbling phenomenon.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Observable signatures of initial state momentum anisotropies in nuclear collisions
In this work, we show that the correlation between the elliptic momentum anisotropy v 2 and the average transverse momentum [ p T ] at fixed multiplicity in small system nuclear collisions carries information on the origin of the observed momentum anisotropy. A calculation using a hybrid IP-Glasma+ music +UrQMD model that includes contributions from final state response to the initial geometry as well as initial state momentum anisotropies of the color glass condensate predicts a characteristic sign change of the correlator ρ ^ ( v 2 2 , [ p T ] ) as a function of charged particle multiplicity in p + Au and d + Au collisions at s = 200 GeV , and p + Pb collisions at s = 5.02 TeV . This sign change is absent in calculations without initial state momentum anisotropies. The model further predicts a qualitative difference between the centrality dependence of ρ ^ ( v 2 2 , [ p T ] ) in Au + Au collisions at s = 200 GeV and Pb + Pb collisions at s = 5.02 TeV , with only the latter showing a sign change in peripheral events. Predictions for O + O collisions at different collision energy show a similar behavior. Experimental observation of these distinct qualitative features of ρ ^ ( v 2 2 , [ p T ] ) in small and large systems would constitute strong evidence for the presence and importance of initial state momentum anisotropies predicted by the color glass condensate effective theory.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Electronic structure and small-hole polarons in YTiO 3
As a prototypical Mott insulator with ferromagnetic ordering, YTiO 3 (YTO) is of great interest in the study of strong electron correlation effects and orbital ordering. Here we report the first molecular beam epitaxy (MBE) growth of YTO films, combined with theoretical and experimental characterizations of the electronic structure and charge transport properties. The obstacles of YTO MBE growth are discussed and potential routes to overcome them are proposed. DC transport and Seebeck measurements on thin films and bulk single crystals identify p-type Arrhenius transport behavior with an activation energy of ~0.17 eV in thin films, consistent with the energy barrier for small hole polaron migration from hybrid density functional theory calculations. Hard x-ray photoelectron spectroscopy measurements show the lower Hubbard band at 1.1 eV below the Fermi level, whereas a Mott-Hubbard band gap of ~1.5 eV is determined from photoluminescence measurements. These findings provide critical insight into the electronic band structure of YTO and related materials.
36 MATERIALS SCIENCE↗