Signal-to-noise ratio enhancement based on wavelet filtering in ultrasonic testing

In ultrasonic non-destructive testing of materials with a coarse-grained structure the scattering from the grains causes backscattering noise, which masks flaw echoes in the measured signal. Several filtering methods have been proposed for improving the signal-to-noise ratio. In this paper we present a comparative study of methods based on the wavelet transform. Experiments with stationary, discrete and wavelet packet de-noising are evaluated by means of signal-to-noise ratio enhancement. Measured and simulated ultrasonic signals are used to verify the proposed de-noising methods. For comparison, we use signal-to-noise ratio enhancement related to fault echo amplitudes and filtering efficiency specific for ultrasonic signals. The best results in our setup were achieved with the wavelet packet de-noising method.     

Solitonic mechanism of structural transformations in a nondegenerate chain of particles with anharmonic and competing interactions

A new type of dynamics of an infinite atomic chain of particles with anharmonic and competing interactions is investigated in the general case when its homogeneous equilibrium states have different energies. Cooperative transformations realized by topological and nontopological solitons are revealed. The soliton velocity spectrum is calculated in the framework of an approximate continuous second-order theory. Solitons with vanishing velocity are shown to be in good asymptotical correspondence with the exact static solutions of the Reichert-Schilling model.     

Multilayer Heisenberg models: linear spin wave analysis

The effect of the interlayer and intralayer anisotropies on the energy gap and sublattice magnetization is investigated using the linear spin wave theory for multilayer Heisenberg models with odd number of coupled layers. In the isotropic case, such systems exhibit a long-range order and no energy gap, while, in the anisotropic case, they are still ordered and the energy gap opens for certain anisotropies.     

Compton scattering by the proton through θcms = 75° and 90° in the Δ-resonance region

Differential cross sections for Compton scattering by the proton have been measured in the energy interval between 200 and 500 MeV at scattering angles of θ_cms = 75° and θ_cms = 90° using the CATS, the CATS/TRAJAN, and the COPP setups with the Glasgow Tagger at MAMI (Mainz). The data are compared with predictions from dispersion theory using photo-meson amplitudes from the recent VPI solution SM95. The experiment and the theoretical procedure are described in detail. It is found that the experiment and predictions are in agreement as far as the energy dependence of the differential cross sections in the Δ-range is concerned. However, there is evidence that a scaling down of the resonance part of the photo-meson amplitude by (2.8 ± 0.9)% is required in comparison with the VPI analysis. The deduced value of the amplitude at the resonance energy of 320 MeV is: .     

Exact renormalization group study of fermionic theories

The exact renormalization group approach (ERG) is developed for the case of pure fermionic theories by deriving a Grassmann version of the ERG equation and applying it to the study of fixed point solutions and critical exponents of the two-dimensional chiral Gross-Neveu model. An approximation based on the derivative expansion and a further truncation in the number of fields is used. Two solutions are obtained analytically in the limit N → ∞, with N being the number of fermionic species. For finite N some fixed point solutions, with their anomalous dimensions and critical exponents, are computed numerically. The issue of separation of physical results from the numerous spurious ones is discussed. We argue that one of the solutions we find can be identified with that of Dashen and Frishman, whereas the others seem to be new ones.     

Critical currents and the critical state in superconductors with magnetic ions

The critical state model is used to derive equations that relate the additional magnetic moment (ΔM) produced by the flux pinning to the critical current density (J_c) measured in transport measurements. The equations derived for conventional superconductors can be used for superconductors that contain magnetic ions, if ΔM is replaced by ΔM/(1 + χ′(H)) where χ′(H) is the differential susceptibility. In the critical state, the field gradient has contributions from both the macroscopic supercurrents and the Amperian currents from the magnetic ions. Magnetic measurements are sensitive to both contributions. Transport measurements only characterise the macroscopic supercurrents. For superconductors which contain rare-earth elements, the J_c values calculated using hysteretic magnetisation measurements without including the term χ′(H), can be in error by factors of 7.     

Lamb wave detection of limpet mines on ship hulls

This paper describes the use of ultrasonic guided waves for identifying the mass loading due to underwater limpet mines on ship hulls. The Dynamic Wavelet Fingerprint Technique (DFWT) is used to render the guided wave mode information in two-dimensional binary images because the waveform features of interest are too subtle to identify in time domain. The use of wavelets allows both time and scale features from the original signals to be retained, and image processing can be used to automatically extract features that correspond to the arrival times of the guided wave modes. For further understanding of how the guided wave modes propagate through the real structures, a parallel processing, 3D elastic wave simulation is developed using the finite integration technique (EFIT). This full field, technique models situations that are too complex for analytical solutions, such as built up 3D structures. The simulations have produced informative visualizations of the guided wave modes in the structures as well as mimicking directly the output from sensors placed in the simulation space for direct comparison to experiments. Results from both drydock and in-water experiments with dummy mines are also shown.     

Random bond Potts model: The test of the replica symmetry breaking

The averaged spin-spin correlation function squared is calculated for the ferro-magnetic random bond Potts model in two dimensions. The technique being used is the renormalization group plus conformal field theory. The results are of the E-expansion type fixed point calculation, E being the deviation of the central charge (or the number of components) of the Potts model from the Ising model value. Calculations are done both for the replica symmetric and the replica symmetry broken fixed points. The results obtained allow for numerical simulation tests to decide between the two different criticalities of the random bond Potts model.     

Equilibrium of a gravitating plasma in a dipolar magnetic field

The equilibria of plasma in a dipolar magnetic field under the gravitational influence of a massive body (a star or black hole) and a self gravitating plasma are considered. Analytical solutions are found that can be useful for understanding the physics of plasma flows in accretion disks and star formation.     

Multifrequency characterization of viscoelastic polymers and vapor sensing based on SAW oscillators

Simplified relations for the changes in SAW velocity and attenuation due to thin polymer coatings and vapor sorption are presented by making analytic approximations to the complex theoretical model developed earlier by Martin et al. [Anal. Chem. 66 (14) (1994) 2201–2219]. The approximate velocity relation is accurate within 4% for the film thicknesses up to 20% of the acoustic wavelength in the polymer film, and is useful for analyzing the mass loading, swelling and viscoelastic effects in SAW vapor sensors. The approximate attenuation relation is accurate within 20% for very thin films, (less than 2% of the acoustic wavelength in the film). Based on these relations, a new procedure for determination of polymer viscoelastic properties is described that exploits the frequency dependence of the velocity and attenuation perturbations, and employs multifrequency measurement on the same SAW platform. Expressions for individual contributions from the mass loading, film swelling and viscoelastic effects in SAW vapor sensors are derived, and their implications for the sensor design and operation are discussed. Also, a new SAW comb filter design is proposed that offers possibility for multimode SAW oscillator operation over a decade of frequency variation, and illustrates feasibility for experimental realization of wide bandwidth multifrequency SAW platforms.     

The NN → NNη reaction close to threshold

The pp → ppη and np → npη reactions at energies near the η production threshold are studied in a non-relativistic one boson exchange model, where the (1535 MeV) S11 resonance is excited through the exchange of π, η, ? and ω mesons and subsequently decays into an ηN pair. Energy integrated cross sections and energy spectra of the out going η's are reported. Providing NN and ηN final state interactions are taken into account coherently, the model reproduces both the scale and energy dependence of the cross section for the pp → ppη reactions up to 100 MeV. Final state interaction corrections due to the nucleon-nucleon and meson-nucleon forces influence strongly the scale and shape of the cross sections. The shape of the energy spectra of the outgoing η's provides a clear signature of the ηN force.     

Investigation of transmit and receive performance at the fundamental and third harmonic resonance frequency of a medical ultrasound transducer

In this study, the phenomenon of higher harmonic thickness resonance of a piezoelectric transducer was used to investigate potentially additional sensitivity at the third harmonic frequency for conventional medical transducers. The motivation for this research is that some applications in medical ultrasound (e.g. third harmonic transmit phasing and contrast imaging) need probes which are sensitive around both the fundamental and third harmonic frequencies, and that these higher harmonic thickness modes, although often considered as undesired, might be used beneficially. The novelty aspect in this study is the presented transmit and receive potential at both the fundamental and third harmonic of a conventional cardiac probe with modified electrical tuning. Elements of an experimental PZT-based phased-array probe (f_c = 3 MHz, 64 elements, element width = 0.3 mm, elevation aperture = 13 mm) were electrically retuned with series inductors around the third harmonic resonance frequency at 10 MHz. Hydrophone measurements with 10-MHz-tuned elements showed that, as compared to a conventionally tuned element, the transmit transfer function at the third harmonic increased more than 23 dB, while the sensitivity at the fundamental frequency was only 6 dB lower. Pulse-echo measurements showed that the two-way transfer function of a 10-MHz-tuned element resulted in 20 dB increased sensitivity around the third harmonic as compared to an untuned element. Simulated transfer functions, from both a 1D KLM and 2D finite element model of an element of the experimental array transducer, confirmed the measured sensitivity peaks at the fundamental and third harmonic. In conclusion, this study demonstrated the effect of changing the electrical tuning on a conventional array transducer which increased the sensitivity around the third harmonic resonance frequency, while maintaining good sensitivity at the fundamental frequency.     

Summing the derivative expansion of the effective action

The derivative expansion of the effective action is a perturbative development in derivatives of the fields. The expansion breaks down when some of the derivatives are too large. We show how to sum exactly the first and second derivatives and treat perturbatively derivatives higher than second.     

Heavy flavour contributions to the deep inelastic scattering sum rules

We calculate the effect of the less singular terms at small x on the evolution of the coefficient function in φ³ theory in six dimensions, which result from a complete solution of the ladder equation. Scale-invariant next-to-leading order contributions are also studied. We show that the small-x approximation does not deliver the dominant contributions.     

Fixed-t partial wave analysis of πN scattering

The last full Karlsruhe PW analysis of πN scattering was finished ca. 20 years ago. After that a huge pile of new accurate πN scattering data has emerged, with which the old analysis is not completely compatible. We are making a highly modernized version of the old analysis to all (recent and old) data, aiming to pay particular attention to the discrepancies between different data sets and to the handling of the experimental errors as well as to the electromagnetic corrections and the effects of isospin breaking.     

Barium ferrite films with in-plane orientation grown on silicon by pulsed laser deposition

For the first time, barium ferrite films with in-plane orientation were prepared at 700°C by pulsed laser deposition technique (PLD) on Si(1 1 1) without any post-annealing. An amorphous Ba–Fe–O film is used as underlayer to facilitate the crystallization and improve the orientation of films. Sharp (1 1 0) and (2 2 0) peaks appeared in the XRD pattern. The surface morphologies observed by SEM are similar to the typical computer generated grain arrangements obtained by Suzuki et al. in their micromagnetics study. Furthermore, a particular kind of structure of film cross-section was identified in PLD for barium ferrite films. The grain size is about 3 μm, and the coercivity is around 1500 Oe.     

Low energy excitations in CeNiSn

We have studied the magnetic excitation spectrum of CeNiSn at low energies both on a polycrystalline sample using time-of-flight technique and on a single crystal with a triple axis spectrometer. The energy gap in the excitation spectrum is clearly observed in the polycrystalline sample reconciling the earlier discrepancies between the two kinds of measurements. The experimental results are consistent with the occurrence of a quasielastic signal within the gap without any significant wave vector dependence and characterized by an energy scale Γ≈0.2 meV.     

Nonlinear responses and optical limiting behavior of Basic Violet 16 dye under CW laser illumination

Nonlinear optical properties of Basic Violet 16 dye solution in water are studied employing different optical techniques. Experiments are performed using the second harmonic of a continuous Nd-Yag laser beam at 532 nm wavelength and 100 mW power. The effect of nonlinearity of Basic Violet 16 dye in broadening the laser beam is observed. The optical limiting behavior is investigated by measuring the transmission of the samples. The third-order nonlinearity, χ³ of Basic Violet 16 dye, is measured using Z-scan data. The nonlinear absorption coefficient is calculated using the open aperture Z-scan data, while its nonlinear refractive index is measured using the closed aperture Z-scan data. All experiments are done for different concentrations and thicknesses of Basic Violet 16 dye solution. The effect of intensity of input laser beam on the nonlinear susceptibility is studied experimentally. Results indicate that Basic Violet 16 dye is a potential candidate for low-power optical limiting applications.     

Chiral symmetry amplitudes in the S-wave isoscalar and isovector channels and the σ, f0(980), a0(980) scalar mesons

We use a non-perturbative approach which combines coupled channel Lippmann-Schwinger equations with meson-meson potentials provided by the lowest order chiral Lagrangian. By means of one parameter, a cut off in the momentum of the loop integrals, which results of the order of 1 GeV, we obtain singularities in the S-wave amplitudes corresponding to the σ, f₀ and a₀ resonances. The ππ → ππ, phase shifts and inelasticities in the T = 0 scalar channel are well reproduced as well as the π⁰η and mass distributions in the T = 1 channel. Furthermore, the total and partial strong decay widths of the f₀ and a₀ resonances are properly reproduced. The results seem to indicate that chiral symmetry constraints at low energy and unitarity in coupled channels is the basic information contained in the meson-meson interaction below GeV.