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At least 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Nonlinear Magnetization Waves and Solitons in a Paramagnet with a Dipole Interaction

Based on a microscopic approach, we have derived equations for the local magnetization dynamics of a spin system coupled by a dipole–dipole interaction in a uniform magnetic field in the continuum approximation. Using the generalized method of multiple scales, we have found the corrections to the Larmor precession frequency of the magnetic moments due to the interparticle interaction, which lead to a broadening of spectral lines and the formation of satellites far from the Larmor frequency. We have derived nonlinear equations for the magnetization amplitude in higher expansion orders, which admit wave and soliton solutions. We have analyzed the influence of the nonsecular part of the dipole–dipole interaction on the stability of solitons and determined the conditions for their existence.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Dipole ordering and ionic conductivity in NASICON-Type Na{sub 3}Cr{sub 2}(PO{sub 4}){sub 3} structures

The aspects of structure, dipole ordering, and ionic conductivity of the Na{sub 3}Cr{sub 2}(PO{sub 4}){sub 3} crystal with the four polymorphic phases (α, α', β, and γ) have been investigated. The features of the α-Na{sub 3}Cr{sub 2}(PO{sub 4}){sub 3} crystal structure and its dipole ordering and relaxation polarization in the low-temperature α and α' phases have been refined. The occurrence of Na{sub 3}Cr{sub 2}(PO{sub 4}){sub 3} dipole ordering in the α and α' phases and high ionic conductivity in the β and γ phases is attributed to the structural changes in the rhombohedral [Me{sub 2}(PO{sub 4}){sub 3}]{sup –3}{sub 3∞} crystal frame upon phase transformations α → α', α' → β, and β → γ. A model for explaining the dipole ordering and ionic conductivity phenomena in Na{sub 3}Cr{sub 2}(PO{sub 4}){sub 3} is proposed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Breaking of axial symmetry in excited heavy nuclei as identified in giant dipole resonance data

Here, a recent theoretical prediction of a breaking of axial symmetry in quasi all heavy nuclei is confronted to a new critical analysis of photon strength functions of nuclei in the valley of stability. For the photon strength in the isovector giant dipole resonance (IVGDR) regime a parameterization of GDR shapes by the sum of three Lorentzians (TLO) is extrapolated to energies below and above the IVGDR. The impact of non-GDR modes adding to the low energy slope of photon strength is discussed including recent data on photon scattering and other radiative processes. These are shown to be concentrated in energy regions where various model calculations predict intermediate collective strength; thus they are obviously separate from the IVGDR tail. The triple Lorentzian (TLO) ansatz for giant dipole resonances is normalized in accordance to the dipole sum rule. The nuclear droplet model with surface dissipation accounts well for positions and widths without local, nuclide specific, parameters. Very few and only global parameters are needed when a breaking of axial symmetry already in the valley of stability is admitted and hence a reliable prediction for electric dipole strength functions also outside of it is expected.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2023

Quadrupole Effects in the Photoionisation of Sodium 3s in the Vicinity of the Dipole Cooper Minimum

A procedure to obtain relativistic expressions for photoionisation angular distribution parameters using the helicity formulation is discussed for open-shell atoms. Electric dipole and quadrupole transition matrix elements were considered in the present work, to study the photoionisation dynamics of the 3s electron of the sodium atom in the vicinity of the dipole Cooper minimum. We studied dipole–quadrupole interference effects on the photoelectron angular distribution in the region of the dipole Cooper minimum. Interference with quadrupole transitions was found to alter the photoelectron angular distribution, even at rather low photon energies. The initial ground and final ionised state discrete wavefunctions of the atom were obtained in the present work using GRASP, and we employed RATIP with discrete wavefunctions, to construct continuum wavefunctions and to calculate transition amplitudes, total cross-sections and angular distribution asymmetry parameters.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2017

Giant Primeval Magnetic Dipoles

Macroscopic magnetic dipoles are considered cosmic dark matter. Permanent magnetism in relativistic field structures can involve some form of superconductivity, one example being current-carrying string loops (“springs”) with vanishing net tension. We derive the cross-section for free classical dipoles to collide, finding it depends weakly on orientation when mutual precession is rapid. The collision rate of “spring” loops with tension T∼10{sup −8}c{sup 4}/G in galactic halos approaches the measured rate of fast radio bursts (FRBs) if the loops compose most of the dark matter. A large superconducting dipole (LSD) with mass ∼10{sup 20} g and size ∼1 mm will form a ∼100 km magnetosphere moving through interstellar plasma. Although hydromagnetic drag is generally weak, it is strong enough to capture some LSDs into long-lived rings orbiting supermassive black holes (SMBHs) that form by the direct collapse of massive gas clouds. Repeated collisions near young SMBHs could dominate the global collision rate, thereby broadening the dipole mass spectrum. Colliding LSDs produce tiny, hot electromagnetic explosions. The accompanying paper shows that these explosions couple effectively to propagating low-frequency electromagnetic modes, with output peaking at 0.01–1 THz. We describe several constraints on, and predictions of, LSDs as cosmic dark matter. The shock formed by an infalling LSD triggers self-sustained thermonuclear burning in a C/O (ONeMg) white dwarf (WD) of mass ≳1 M {sub ⊙} (1.3 M {sub ⊙}). The spark is generally located off the center of the WD. The rate of LSD-induced explosions matches the observed rate of Type Ia supernovae.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

One-loop matching for quark dipole operators in a gradient-flow scheme

The quark chromoelectric dipole (qCEDM) operator is a CP-violating operator describing, at hadronic energies, beyond-the-standard-model contributions to the electric dipole moment of particles with nonzero spin. In this paper we define renormalized dipole operators in a regularization-independent scheme using the gradient flow, and we perform the matching at one loop in perturbation theory to renormalized operators of the same and lower dimension in the more familiar MS scheme. We also determine the matching coefficients for the quark chromo-magnetic dipole operator (qCMDM), which contributes for example to matrix elements relevant to CP-violating and CP-conserving kaon decays. The calculation provides a basis for future lattice QCD computations of hadronic matrix elements of the qCEDM and qCMDM operators.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2022

Gluon dipole factorisation for diffractive dijets

Within the colour dipole picture for deep inelastic scattering at small Bjorken x , we study the production of a pair of relatively hard jets via coherent diffraction. By “relatively hard” we mean that the transverse momenta of the two jets — the quark ($q$) and the antiquark ($\overline{q}$) generated by the decay of the virtual photon — are much larger than the target saturation momentum Q s (Y P ) evaluated at the rapidity gap Y P . We argue that the typical final-state configurations are such that the hard $q$$\overline{q}$ dijets are accompanied by a semi-hard gluon jet, with a transverse momentum of the order of Q s (Y P ). The presence of this third jet ensures that the scattering is strong and thus avoids the strong suppression of exclusive (hard) dijet production due to colour transparency. For such “2+1” jet configurations, we demonstrate that both the emission of the semi-hard gluon and its scattering with the hadronic target can be factorised in terms of an effective gluon-gluon dipole. This effective description, originally proposed in [1–7], builds a bridge between the colour dipole picture and the transverse-momentum dependent (TMD) version of the collinear factorisation: the cross-section for diffractive 2+1 jets can be written as the product between a hard factor describing the $q$$\overline{q}$ dijets and a semi-hard factor expressing the unintegrated gluon distribution of the Pomeron. The latter is controlled by gluon dipole scattering in the black disk limit and hence is strongly sensitive to gluon saturation. By integrating out the kinematics of the 3 jets, we obtain the $q$$\overline{q}$$g$ contribution to the diffractive structure function in collinearly-factorised form.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Feasibility of FDEM cross-dipole and TDEM loop sources for monitoring CO 2 at the Kemper CarbonSAFE site

Electromagnetics has been shown to be a viable tool to monitor CO 2 plumes embedded in saline reservoirs. However, the majority of studies focus on measuring the electric field, which requires cumbersome equipment in the field and it is difficult to install permanent measurement stations. Magnetic field receivers offer an opportunity to reduce the form factor of the survey and increase the mobility by utilizing upcoming technologies, such as drones. We explore the use of frequency-domain electric dipole sources, and timedomain loops with a focus on measuring the secondary magnetic field at the surface for a conceptual injection scenario based on the Kemper CarbonSAFE site. We find that electric dipole sources give a response above the sensitivity of current sensor technology and, therefore, be a viable tool for CO 2 monitoring. The time domain loop source does provide fields that are useful for determining the location of the CO 2 plume, however the field magnitude is below the sensitivity of the current generation of instruments. To explore the use of a potential borehole receiver we generate a map of the magnetic field at depth to explore potential borehole placement for monitoring efforts. Finally, we limit the spatial extent of the electric dipole survey to a single parcel of land to help understand how the fields change with survey geometry. We find that the shape of the secondary fields change slightly with the small transmitter, but are still measurable provided that the cultural noise at the site is low. Thus, we conclude that at the Kemper site a frequency-domain cross-dipole source with magnetometer receivers is suitable to monitor the expansion of the CO 2 plume in the saline reservoir, even with a limited transmitter footprint on the surface.

58 GEOSCIENCES↗
DOE OSTI2017

CdSe Nanoplatelet Films with Controlled Orientation of their Transition Dipole Moment

With liquid–liquid interfacial assembly, we control the deposition of CdSe nanoplatelets into face-down or edge-up configurations. Controlled assembly, combined with back focal plane imaging, enabled unambiguous determination of the transition dipole orientation. The transition dipole moment of the emissive band-edge exciton in CdSe nanoplatelets was found to be isotropically oriented within the plane of the nanoplatelet with no measurable out-of-plane component and no preference for the long- or short-axis of the nanoplatelet. Importantly, CdSe nanoplatelet films in the face-down configuration exhibited unity dipole orientation within the plane of the film, which could improve the external efficiency of nanoplatelet LEDs, lasers, photodetectors, and photovoltaic cells beyond that which is possible with isotropic emitters. We also show that the two self-assembled configurations have different Förster energy transfer rates, as an effect of different dipole orientation and internanoplatelet distance.

2D materials↗
DOE OSTI2024

Electronic rotons and Wigner crystallites in a two-dimensional dipole liquid

A key concept proposed by Landau to explain superfluid liquid helium is the elementary excitation of quantum particles called rotons1–8. The irregular arrangement of atoms in a liquid leads to the aperiodic dispersion of rotons, which played a pivotal role in understanding fractional quantum Hall liquids (magneto-rotons)9,10 and the supersolidity of Bose–Einstein condensates11–13. Even for a two-dimensional electron or dipole liquid, in the absence of a magnetic field, the repulsive interactions have been predicted to form a roton minimum14–19, which can be used to trace the transition to Wigner crystals20–24 and superconductivity25–27, although this has not yet been observed. Here, we report the observation of such electronic rotons in a two-dimensional dipole liquid of alkali-metal ions donating electrons to surface layers of black phosphorus. Our data reveal the striking aperiodic dispersion of rotons, which is characterized by a local minimum of energy at finite momentum. As the density of dipoles decreases so that interactions dominate over the kinetic energy, the roton gap reduces to 0, as in a crystal, signalling Wigner crystallization. Our model shows the importance of short-range order arising from repulsion between dipoles, which can be viewed as the formation of Wigner crystallites (bubbles or stripes) floating in the sea of a Fermi liquid. Our results reveal that the primary origin of electronic rotons (and the pseudogap) is strong correlations.

Park, Soobin↗
DOE OSTI2020

Planck intermediate results. LVI. Detection of the CMB dipole through modulation of the thermal Sunyaev-Zeldovich effect: Eppur si muove II

The largest temperature anisotropy in the cosmic microwave background (CMB) is the dipole, which has been measured with increasing accuracy for more than three decades, particularly with the Planck satellite. The simplest interpretation of the dipole is that it is due to our motion with respect to the rest frame of the CMB. Since current CMB experiments infer temperature anisotropies from angular intensity variations, the dipole modulates the temperature anisotropies with the same frequency dependence as the thermal Sunyaev-Zeldovich (tSZ) effect. Here, we present the first, and significant, detection of this signal in the tSZ maps and find that it is consistent with direct measurements of the CMB dipole, as expected. The signal contributes power in the tSZ maps, which is modulated in a quadrupolar pattern, and we estimate its contribution to the tSZ bispectrum, noting that it contributes negligible noise to the bispectrum at relevant scales.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Dipole bands in high spin states of {sub 57}{sup 135}La{sub 78}

High spin states of {sup 135}La have been investigated using the reaction {sup 128}Te({sup 11}B,4n){sup 135}La at a beam energy of 50.5 MeV. Two negative parity dipole bands (ΔI = 1) have been established. Crossover E2 transitions have been observed for the first time in one of the dipole bands. For the Tilted Axis Cranking (TAC) calculations, a three-quasiparticle (3qp) configuration π(h{sub 11/2}){sup 1}⊗ν(h{sub 11/2}){sup −2} and a five-quasiparticle (5qp) configuration π(h{sub 11/2}){sup 1}(g{sub 7/2}/d{sub 5/2}){sup 2}⊗ν(h{sub 11/2}){sup −2} have been taken for the two negative parity dipole bands. The comparison of experimental observables with TAC calculations supports the configuration assignments for both the dipole bands.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Tracking surface photovoltage dipole geometry in Bi 2 Se 3 with time-resolved photoemission

Topological insulators have been shown to exhibit strong and long-lived surface photovoltages when excited by an infrared pump. The ability to generate long-lived potentials on these surfaces provides opportunities to manipulate the spin-momentum locked topological surface states. Moreover, the photo-induced nature of this effect allows for localized excitation of arbitrary geometries. Knowing precisely how these potentials form and evolve is critical in understanding how to manage the effect in applications. The uniqueness of the photoemission experimental geometry, in which the photoelectron must traverse the induced surface field in vacuum, provides an interesting probe of the electric dipole shape generated by the surface photovoltage. In this study, we are able to match the observed decay of the geometric effect on the photoelectron to an essential electrodynamics model of the light-induced dipole thereby tracking the fluence-dependent evolution of the dipole geometry. Finally, by utilizing a standard time-resolved angle-resolved photoemission experiment, we are able to determine real-space information of the dipole while simultaneously recovering time-resolved band structure.

42 ENGINEERING↗
DOE OSTI2025

Transverse spin effects and light-quark dipole moments at lepton colliders

We propose to probe light-quark dipole interactions at lepton colliders using the azimuthal asymmetry of a collinear dihadron pair (ℎ 1 ⁡ℎ 2 ) produced in association with another hadron ℎ′. This asymmetry, arising from quantum interference in the quark spin space, is exclusively sensitive to dipole interactions at the leading power of the new physics scale and simultaneously probes both the real and imaginary components of the dipole couplings. By combining all possible channels of ℎ′, this method allows for disentangling the up and down quark dipole moments and has the potential to significantly strengthen current constraints by one to two orders of magnitude.

Wen, Xin-Kai [Peking University, Beijing (China); ↗
DOE OSTI2020

Using Fourier-Plane Imaging Microscopy for Determining Transition-Dipole-Moment Orientations in Organic Light-Emitting Devices

Here, we use Fourier-plane imaging microscopy (FIM) to determine the transition-dipole-moment orientation in doped organic emissive thin films. The use of FIM enables precise, sensitive, and rapid measurement of dipole orientation in the emission layer of an organic light-emitting device (OLED). An optical model of a stratified birefringent multilayer is introduced for interpreting results obtained by FIM. Using the model, we determine the average orientation of transition-dipole-moment vectors of three phosphorescent dopant emitters. The dipole alignment measured by FIM quantitatively explains the difference in OLED efficiencies using these archetype dopant molecules. FIM provides a nondestructive tool to measure and ultimately improve the outcoupling efficiency of OLEDs and other light-emitting devices.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2019

Valence-shell dependence of the pygmy dipole resonance: E 1 strength difference in 50,54 Cr

The low-lying electric dipole strength provides insights into the parameters of the nuclear equation of state via its connection with the pygmy dipole resonance and nuclear neutron skin thickness. The aim was to complement the systematic of the pygmy dipole resonance and first study its behavior across the N = 28 neutron shell closure. Here, photon-scattering cross sections of states of 50,54 Cr were measured up to an excitation energy of 9.7 MeV via the nuclear resonance fluorescence method using γ-ray beams from bremsstrahlung and Compton backscattering. Transitions strengths, spin and parity quantum number, and average branching ratios for 55 excited states, 44 of which were observed for the first time, were determined. The comparison between the total observed strengths of the isotopes 50,52,54 Cr shows a significant increase above the shell closure. The evolution of the pygmy dipole resonance is heavily influenced by the shell structure.

39 ≤ A ≤ 58↗
DOE OSTI2025

Data-driven analysis of dipole strength functions using artificial neural networks

Here, we present a data-driven analysis of dipole strength functions across the nuclear chart, employing an artificial neural network to model nuclear dipole responses. We train the network on a dataset of experimentally measured dipole strength functions for 216 different nuclei. To assess its predictive capability, we test the trained model on an additional set of 10 new nuclei, where experimental data exist. We demonstrate that the artificial neural network not only accurately reproduces known data but also identifies potential inconsistencies in experimental datasets, indicating which results may warrant further review or possible rejection. For nuclei where experimental data are sparse or unavailable, the network confirms theoretical calculations, reinforcing its utility as a predictive tool in nuclear physics. Finally, utilizing the predicted electric dipole polarizability, we extract the value of the symmetry energy at saturation density and find it consistent with results from the literature.

artificial neural networks↗
DOE OSTI2023

How do axisymmetric black holes grow monopole and dipole hair?

Here, we study the dynamical formation of scalar monopole and dipole hair in scalar Gauss-Bonnet theory and dynamical Chern-Simons theory. We prove that the spherically symmetric mode of the dipole hair is completely determined by the product of the mass of the spacetime and the value of the monopole hair. We then show that the dynamics of the ℓ = 1 mode of the dipole hair is intimately tied to the appearance of the event horizon during axisymmetric collapse, which results in the radiation of certain modes that could have been divergent in the future of the collapse. We confirm these analytical predictions by simulating the gravitational collapse of a rapidly rotating neutron star in the decoupling limit, both in scalar Gauss-Bonnet and dynamical Chern-Simons theory. Our results, combined with those provide a clear physical picture of the dynamics of scalar monopole and dipole radiation in axisymmetric and spherical gravitational collapse in these theories.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗