Multipole Data Research Articles

Full-Wave Computation of Monostatic RCS Using Ray-Tracing and Adaptive Macro-Basis Functions

This article presents a technique for the computation of the monostatic radar cross section of complex objects based on a combination of macro-basis functions (MBFs) and the multilevel fast multipole algorithm. An initial pool of excitation-independent MBFs is first obtained, generating the corresponding reduced coupling matrix as well as the multipole data. For each excitation, ray-tracing processing is performed, extracting a number of critical points that are used to obtain a mask that allows to dynamically select the basis functions to be considered in the analysis. This strategy allows a noticeable reduction in the size of the problems with minimal CPU-time preprocessing overhead.

Joint inversion of logging-while-drilling multipole acoustic data to determine P- and S-wave velocities in unconsolidated slow formations

We have developed a joint inversion method for logging-while-drilling (LWD) multipole acoustic data processing to simultaneously determine the formation of P- and S-wave velocities. The presence of the LWD tool strongly influences the dispersion characteristics of quadrupole and monopole leaky-P-waves, especially in unconsolidated slow formations. We have verified that an equivalent-tool theory can be adequately used to model the LWD multipole wave dispersion characteristics and can therefore be used to do forward modeling for the inversion. A major advantage of jointly inverting the multipole data sets, as compared with separately inverting each individual data set, is the reduction of uncertainties in the estimated formation of P- and S-wave velocities. We have applied the method to field data processing. The results found that the method not only corrected the dispersion effect in the quadrupole and leaky-P-wave data but also simultaneously obtained the formation of P- and S-wave velocities.

Testing distance duality with CMB anisotropies

We constrain deviations of the form T ∝ (1+z)1+ϵ from the standard redshift-temperature relation, corresponding to modifying distance duality as DL = (1+z)2(1+ϵ) DA. We consider a consistent model, in which both the background and perturbation equations are changed. For this purpose, we introduce a species of dark radiation particles to which photon energy density is transferred, and assume ϵ ≥ 0. The Planck 2015 release high multipole temperature plus low multipole data give the limit ϵ < 4.5 × 10−3 at 95% C.L. The main obstacle to improving this CMB-only result is strong degeneracy between ϵ and the physical matter densities ωb and ωc. A constraint on deuterium abundance improves the limit to ϵ < 1.8 × 10−3. Adding the Planck high-multipole CMB polarisation and BAO data leads to a small improvement; with this maximal dataset we obtain ϵ < 1.3 × 10−3. This dataset constrains the present dark radiation energy density to at most 12% of the total photon plus dark radiation density. Finally, we discuss the degeneracy between dark radiation and the effective number of relativistic species Neff, and consider the impact of dark radiation perturbations and allowing ϵ < 0 on the results.

MEASURING THE LARGEST ANGULAR SCALE CMB B-MODE POLARIZATION WITH GALACTIC FOREGROUNDS ON A CUT SKY

We consider the effectiveness of foreground cleaning in the recovery of Cosmic Microwave Background (CMB) polarization sourced by gravitational waves for tensor-to-scalar ratios in the range $0<r<0.1$. Using the planned survey area, frequency bands, and sensitivity of the Cosmology Large Angular Scale Surveyor (CLASS), we simulate maps of Stokes $Q$ and $U$ parameters at 40, 90, 150, and 220 GHz, including realistic models of the CMB, diffuse Galactic thermal dust and synchrotron foregrounds, and Gaussian white noise. We use linear combinations (LCs) of the simulated multifrequency data to obtain maximum likelihood estimates of $r$, the relative scalar amplitude $s$, and LC coefficients. We find that for 10,000 simulations of a CLASS-like experiment using only measurements of the reionization peak ($\ell\leq23$), there is a 95% C.L. upper limit of $r<0.017$ in the case of no primordial gravitational waves. For simulations with $r=0.01$, we recover at 68% C.L. $r=0.012^{+0.011}_{-0.006}$. The reionization peak corresponds to a fraction of the multipole moments probed by CLASS, and simulations including $30\leq\ell\leq100$ further improve our upper limits to $r<0.008$ at 95% C.L. ($r=0.01^{+0.004}_{-0.004}$ for primordial gravitational waves with $r=0.01$). In addition to decreasing the current upper bound on $r$ by an order of magnitude, these foreground-cleaned low multipole data will achieve a cosmic variance limited measurement of the E-mode polarization's reionization peak.

Rapid 1D/3D inversion of shallow resistivity multipole data: Examples in archaeological prospection

Fifteen years ago, the introduction of mobile multipole arrays led to substantial improvements in shallow electric prospection because it allowed information related to the vertical distribution of ground resistivity, in complement to the horizontal pattern of the detected features, to be extracted. However, to make full use of this wealth of information, further progress is needed to extend the qualitative interpretation of data to a more quantitative evaluation of the explored terrain. To that intent, we developed a two-step process: In the first step, a 1D electric model is fitted to the data over the full explored area, and in the second step, using the moment method, localized 3D interpretation is applied to limited areas, for which the characteristics of a given feature require closer scrutiny. After a first test with synthetic data generated using the surface integral 3D modeling method, this process was applied to three different archaeological sites and one test site, for both handheld pole-pole array systems and a multipole continuous electric profiling mechanically pulled system. At the test site, the characteristics of a known wall were accurately recovered. At the Duntzenheim site, the thickness and width of the archaeological remains determined by 3D interpretation corresponded to the features observed through excavation. At the other two sites, 3D interpretation made it possible to establish that the conductive features extend across the full extent of the superficial resistive second layers.

PARAMETRIC TENSION BETWEEN EVEN AND ODD MULTIPOLE DATA OF THEWMAPPOWER SPECTRUM: UNACCOUNTED CONTAMINATION OR MISSING PARAMETERS?

There exist power contrast in even and odd multipoles of WMAP power spectrum at low and intermediate multipole range. This anomaly is explicitly associated with the angular power spectrum, which are heavily used for cosmological model fitting. Having noted this, we have investigated whether even(odd) multipole data set is consistent with the WMAP concordance model. Our investigation shows WMAP concordance model does not make a good fit for even(odd) multipole data set, and there exist tension between two data subsets. Noting tension is highest in primordial power spectrum parameters, we have additionally considered a running spectral index, but find tension increases to even a higher level. We believe these parametric tensions may be indications of unaccounted contamination or imperfection of the model.

Comparison between wavelet and fast multipole data sparse approximations for Poisson and kinematics boundary – domain integral equations

The boundary element method applied on non-homogenous partial differential equations requires calculation of a fully populated matrix of domain integrals. This paper compares two techniques: the fast multipole method and the fast wavelet transform, which are used to reduce the complexity of such domain matrices. The employed fast multipole method utilizes the expansion of integral kernels into series of spherical harmonics. The wavelet transform for vectors of arbitrary length, based on Haar wavelets and variable thresholding limit, is used. Both methods are tested and compared by solving the scalar Poisson equation and the velocity–vorticity vector kinematics equation. The results show comparable accuracy for both methods for a given data storage size. Wavelets are somewhat better for high and low compression ratios, and the fast multipole methods gives better results for moderate compressions. Considering implementation of the methods, the wavelet transform can easily be adapted for any problem, while the fast multipole method requires different expansion for each integral kernel.

Angular momentum partitioning and the subshell multipole moments in impulsively excited argon ions

˛ s 1 Dd4p 2 F5/2 s463.7 nmd, s 1 Pd3d 2 D5/2˛ s 1 Dd4p 2 D5/2 s448.2 nmd, and s 1 Dd4s 2 D3/2˛ s 1 Dd4p 2 P3/2 s423.7 nmd. We develop the angular momentum algebra necessary to extract from these data, starting from the overall atomic J multipoles, the partitioning of orbital angular momentum into the 1 D core electric quadrupole and hexadecapole moments, and the outer 4p electric quadrupole moment. The magnetic dipole of the outer electron is also determined. This procedure requires the assumption of good LS coupling for these states, which is justified. We recouple these individual core- and outer-electron moments to calculate the initial electric quadrupoles, hexadecapoles, and hexacontatetrapoles of the initial excited-state manifold. The detailed time structure of the electron-atom collision is considered, as well as the time evolution of the excited ionic state. The Rubin-Bederson hypothesis is thus shown to hold for the initial ionic L and S terms. The consequences of the breakdown of LS coupling are considered. From the circular polarization data, estimates of the relative importance of direct and exchange excitation cross section are made. We discuss experimental issues related to background contributions, Hanle depolarization of the fluorescence signal, and cascade contributions. Nonlinearity of the equations relating the Stokes parameters to the subshell multipole moments complicates the data analysis. Details of the Monte Carlo terrain-search algorithm used to extract multipole data is discussed, and the implications of correlation between the various subshell multipole moments is analyzed. The physical significance of the higher-order multipole moments is discussed, and graphical representations of the effects of these multipoles on the excited ionic charge clouds is presented.

Electromagnetic couplings of nucleon resonances

An effective Lagrangian calculation of pion photoproduction including all nucleon resonances up to s = 1.7 GeV is presented. We compare our results with recent calculations and show the influence of different width parametrizations and off-shell cutoffs on the photoproduction multipoles. We determine the electromagnetic couplings of the resonances from a new fit to the multipole data.

Effective Lagrangian approach to the theory of eta photoproduction in the N*(1535) region.

We investigate theoretical uncertainties and model dependence in the extraction of the nucleon-{Delta}(1232) electromagnetic transition amplitudes from the multipole data base. Our starting point is an effective Lagrangian incorporating chiral symmetry, which includes, at the tree level, the pseudovector nucleon Born terms, leading {ital t}-channel vector-meson exchanges, and {ital s}- and {ital u}-channel {Delta} exchanges. We express the nucleon-{Delta} transition magnetic dipole ({ital M}1) and electric quadrupole ({ital E}2) amplitudes in terms of two independent gauge couplings at the {gamma}{ital N}{Delta} vertex, and fit these to various multipole data sets. We find a large sensitivity to the method used in unitarizing the amplitude, and extract the {ital E}2/{ital M}1 ratio (EMR) to be {ital negative}, with a magnitude of around 1.5%. The resonant amplitudes in this work are of interest to the test of topical hadron models inspired by QCD: the sign of the EMR, extracted by us, is in accord with that predicted by most realistic models, and its magnitude lies between the predictions of the quark shell model and the Skyrmion model. Finally, our work provides a phenomenologically satisfying unitary amplitude for pion photoproduction off nucleons, which can be used as a realistic starting point for theoretical studiesmore » of this process in complex nuclei.« less

Effective-Lagrangian approach to the theory of pion photoproduction in the Delta (1232) region.

We investigate theoretical uncertainties and model dependence in the extraction of the nucleon-$\ensuremath{\Delta}(1232)$ electromagnetic transition amplitudes from the multipole data base. Our starting point is an effective Lagrangian incorporating chiral symmetry, which includes, at the tree level, the pseudovector nucleon Born terms, leading $t$-channel vector-meson exchanges, and $s$- and $u$-channel $\ensuremath{\Delta}$ exchanges. We express the nucleon-$\ensuremath{\Delta}$ transition magnetic dipole ($M1$) and electric quadrupole ($E2$) amplitudes in terms of two independent gauge couplings at the $\ensuremath{\gamma}N\ensuremath{\Delta}$ vertex, and fit these to various multipole data sets. We find a large sensitivity to the method used in unitarizing the amplitude, and extract the $\frac{E2}{M1}$ ratio (EMR) to be negative, with a magnitude of around 1.5%. The resonant amplitudes in this work are of interest to the test of topical hadron models inspired by QCD: the sign of the EMR, extracted by us, is in accord with that predicted by most realistic models, and its magnitude lies between the predictions of the quark shell model and the Skyrmion model. Finally, our work provides a phenomenologically satisfying unitary amplitude for pion photoproduction off nucleons, which can be used as a realistic starting point for theoretical studies of this process in complex nuclei.

A dynamical model of pion photoproduction on the nucleon

Pion photoproduction on the nucleon is investigated using a model hamiltonian defined in the channel-space H = πN⊕γN⊕B with B = δ and N. The basic electromagnetic matrix elements are deduced from the low-order Feynman amplitudes calculated from a lagrangian describing interactions among γ-, π-, ρ-, ω-, N- and Δ-fields. The πN interaction is described by B↔πN vertices, and a two-body separable potential. A scattering formalism is introduced to assure that the constructed pion photoproduction amplitude is unitary and gauge invariant. The πN parameters are determined by fitting the phase-shift data up to 500 MeV incident pion energy. The remaining three free parameters of the model, cutoff Λ for the form factor which regularizes the Born (nonresonant) terms, g m and G E for the γN↔Δ vertex, are determined by fitting the M 1+( 3 2 ) and E 1+( 3 2 ) multipole data. The resulting E2/M1 ratio of the γN↔Δ excitation is −3.1%. The model can to a large extent describe the existing cross-section and polarization data for γp → π +n, γp→π 0p and γn → π −p up to 400 MeV incident photon energy. The importance of unitary in extracting the basic parameters from the data is demonstrated explicitly. It is also shown, that within the present unitary model, the πN off-shell effects can account for up to 50% of the cross section. For the interpretation of experimental data, this indicates a significant difference between the present hamiltonian approach and those that use only the Watson theorem to impose unitarity. The model is consistent with the existing unitary πNN models, and hence can be directly applied to study pion photoproduction on the deuteron and heavier nuclei.

Model-independent determination of K-matrix poles and residues in the Delta (1232) region from the multipole data for pion photoproduction.

Using only the analytic structure of the $K$ matrix and the assumption that the Compton-scattering amplitude is small compared to strong and electrostrong amplitudes, we extract the pole position and the residues for the resonant multipoles, in a model-independent and background-free fashion, directly from the experimentally obtained multipole data base in the $\ensuremath{\Delta}(1232)$ region, posing a challenge for QCD-inspired hadron models.

High Gradient Superconducting Quadrupoles

Prototype superconducting quadrupoles with a 5 cm aperture and gradient of 16 kG/cm have been built and tested as candidate magnets for the final focus at SLC. The magnets are made from NbTi Tevatron style cable with 10 inner and 14 outer turns per quadrant. Quench performance and multipole data are presented. Design and data for a low current, high gradient quadrupole, similar in cross section but wound with a cable consisting of five insulated conductors are also discussed.

Room temperature harmonic analysis of superconducting energy saver quadrupoles

The multipole structure of Fermilab Energy Saver quadrupoles is obtained from low current, room temperature measurements using a rotational Morgan coil and lock-in amplifier. Multipole data are presented for the first forty Tevatron quadrupoles.

ALPHA-GAMMA ANGULAR CORRELATIONS IN THE REACTION C12(C12,α)Ne20

Angular correlations between gamma rays and alpha particles detected at 0 deg were measured in the reaction C/sup 12/(C/sup 12/ alpha )Ne using 17-, and 18-Mev triply charged carbon ions. The detectors employed were p-n silicon junction counters. Previous spin assignment for the 4.97-Mev and 4.25-Mev levels and multipole mixing data for the 3.34-Mev level were confirmed and negative parity for the 3.34-Mev level was established. (L.N.N.)