Polarimetric Microwave Inverse Scattering as Applied to Nondestructive Testing

The conventional procedures of nondestructive evaluation by means of ultrasonic techniques are limited by surface roughness and grain-boundary scattering of testmaterials. Especially ceramics must be coupled carefully with high-frequency ultrasonic transducers. Concerning these restrictions and in view of the possibility of contactless measurements of low-loss dielectric materials with microwaves, the application of electromagnetic waves in NDE appears to be a favourable alternative to conventional ultrasonic techniques [1]

Numerical Modeling and Imaging with ULIAS: Ultrasonic Inspection Applying Simulation

ULIAS is the short term for ULtrasonic Inspection Applying Simulation. ULIAS is a module based software package comprising modules for numerical modeling, imaging, data compression, signal processing, and visualization in 1-D/2-D/3-D

Electronic ground states of Fe2+_2^+ and Co2+_2^+ as determined by x-ray absorption and x-ray magnetic circular dichroism spectroscopy

The $^6\Pi$ electronic ground state of the Co$_2^+$ diatomic molecular cation has been assigned experimentally by x-ray absorption and x-ray magnetic circular dichroism spectroscopy in a cryogenic ion trap. Three candidates, $^6\Phi$, $^8\Phi$, and $^8\Gamma$, for the electronic ground state of Fe$_2^+$ have been identified. These states carry sizable orbital angular momenta that disagree with theoretical predictions from multireference configuration interaction and density functional theory. Our results show that the ground states of neutral and cationic diatomic molecules of $3d$ transition elements cannot generally be assumed to be connected by a one-electron process

Reconstruction of Defect Geometries in Ultrasonic NDT

The international activities in developing new flaw characterization methods with special emphasis on acoustic imaging have been increased. To reduce the dependency upon amplitude information and due to the fact that flaw information is buried in the shape and fine structure of wave fronts, considerable attention has been given to the development of methods using time-of-flight information from different probe positions. For this reason, with mechanical scanners and specially build data acquisition and evaluation systems, a vareity of ways to produce images has been developed. These include echotomography, linear or two dimensional mono- or multi-frequency holography, tip echo interference methods, ALOK (amplitude-,time-of-flight-locus curves), Phased Array, SAFT or Rayleigh-Sommerfeld Holography. These methods use mathematical algorithms which seem to be independent or which have been derived heuristically. Based upon the concept of elastodynamic diffraction theory together with that of tomography a concept can be derived which reveals the inner connection of these algorithms. Differences in the reconstructions arise due to limitations like limited aperture, limited bandwidth, use of mode converted signals or due to complex surface shapes. An attempt is made to cover the theoretical background, to give an overview on existing data acquisition systems and to describe the strength, weaknesses, and difficulties in producing acoustic images

Direct Observation of High-Spin States in Manganese Dimer and Trimer Cations by X-ray Magnetic Circular Dichroism Spectroscopy in an Ion Trap

The electronic structure and magnetic moments of free Mn$_2^+$ and Mn$_3^+$ are characterized by $2p$ x-ray absorption and x-ray magnetic circular dichroism spectroscopy in a cryogenic ion trap that is coupled to a synchrotron radiation beamline. Our results show directly that localized magnetic moments of 5 $\mu_B$ are created by $3d^5 (^6\mathrm{S})$ states at each ionic core, which are coupled in parallel to form molecular high-spin states via indirect exchange that is mediated in both cases by a delocalized valence electron in a singly-occupied $4s$ derived orbital with an unpaired spin. This leads to total magnetic moments of 11 $\mu_B$ for Mn$_2^+$ and 16 $\mu_B$ for Mn$_3^+$, with no contribution of orbital angular momentum

Elastic Wave Propagation and Scattering in Austenitic Steel

Ultrasonic nondestructive testing of austenitic steel welds is very difficult, because fundamental wave propagation and scattering effects in such complicated anisotropic environments are only hardly understood [1, 2]. Therefore, a step-by-step evaluation of elastic wave propagation in transversely isotropic media has been initiated. Under the assumption of transverse isotropy the numerical EFIT code (Elastodynamic Finite Integration Technique) [3] - [7] was extended to anisotropic homogeneous media. It allows 3D computation of quasi pressure and quasi shear as well as surface waves in transverse isotropic media. Results for finite aperture transducer radiation and crack scattering in a single crystal austenitic weld are presented; measurements of amplitude dynamics, A-Scans and C-Scans confirm the EFIT simulations [8]

Analytical and Numerical Predictions of Short Pulsed Elastic Waves on a Half-Space

The numerical modeling of ultrasonic wave propagation in elastic solids is particularly attractive for NDT applications because of the relative ease with which the boundaries of realistic defect shapes and testing geometries can be handled. A two-dimensional explicit finite element code [1] has been developed for this purpose

Postural control and head stability during natural gaze behaviour in 6- to 12-year-old children

We investigated how the influence of natural exploratory gaze behaviour on postural control develops from childhood into adulthood. In a cross-sectional design, we compared four age groups: 6-, 9-, 12-year-olds and young adults. Two experimental trials were performed: quiet stance with a fixed gaze (fixed) and quiet stance with natural exploratory gaze behaviour (exploratory). The latter was elicited by having participants watch an animated short film on a large screen in front of them. 3D head rotations in space and centre of pressure (COP) excursions on the ground plane were measured. Across conditions, both head rotation and COP displacement decreased with increasing age. Head movement was greater in the exploratory condition in all age groups. In all children—but not in adults—COP displacement was markedly greater in the exploratory condition. Bivariate correlations across groups showed highly significant positive correlations between COP displacement in ML direction and head rotation in yaw, roll, and pitch in both conditions. The regularity of COP displacements did not show a clear developmental trend, which indicates that COP dynamics were qualitatively similar across age groups. Together, the results suggest that the contribution of head movement to eye-head saccades decreases with age and that head instability—in part resulting from such gaze-related head movements—is an important limiting factor in children's postural control. The lack of head stabilisation might particularly affect children in everyday activities in which both postural control and visual exploration are require

Experimental Evaluation of Ultrasonic Simulation Techniques in Anisotropic Material

The high performance of the available computer technology provides the possibility to simulate the real life for ultrasonic inspections in terms of primary ultrasonic data like rf-time signals. For isotropic material codes like Generalized Point Source Synthesis (GPSS) or Elastodynamic Finite Integration Technique (EFIT) and the theoretical predictions correlate well with experimental results. Recently, the codes mentioned above have been extended to operate also in anisotropic material. In a first step the codes GPSS and EFIT have been expanded to work in materials of parallel oriented columnar grain structure with transversely isotropic symmetry. In order to verify these codes a set of experiments was carried out on weld metal pads and on welds of defined grain structure. Radiation, propagation, reflexion on boundaries and interaction of the sound field with defects for the modes “through transmission” and “pulse echo” were simulated and compared with the experiment

Modelling survival and connectivity of Mnemiopsis leidyi in the south-western North Sea and Scheldt estuaries

Three different models were applied to study the reproduction, survival and dispersal of Mnemiopsis leidyi in the Scheldt estuaries and the southern North Sea: a high-resolution particle tracking model with passive particles, a low-resolution particle tracking model with a reproduction model coupled to a biogeochemical model, and a dynamic energy budget (DEB) model. The results of the models, each with its strengths and weaknesses, suggest the following conceptual situation: (i) the estuaries possess enough retention capability to keep an overwintering population, and enough exchange with coastal waters of the North Sea to seed offshore populations; (ii) M. leidyi can survive in the North Sea, and be transported over considerable distances, thus facilitating connectivity between coastal embayments; (iii) under current climatic conditions, M. leidyi may not be able to reproduce in large numbers in coastal and offshore waters of the North Sea, but this may change with global warming; however, this result is subject to substantial uncertainty. Further quantitative observational work is needed on the effects of temperature, salinity and food availability on reproduction and on mortality at different life stages to improve models such as used here