3,864 research outputs found
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
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
Well Balanced Finite Volume Methods for Nearly Hydrostatic Flows
In numerical approximations of nearly hydrostatic flows, a proper representation of the dominant hydrostatic balance is of crucial importance: unbalanced truncation errors can induce unacceptable spurious motions, e.g., in dynamical cores of models for numerical weather prediction (NWP) in particular near steep topography. In this paper we develop a new strategy for the construction of discretizations that are “well-balanced” with respect to dominant hydrostatics. The classical idea of formulating the momentum balance in terms of deviations of pressure from a balanced background distribution is realized here through local, time dependent hydrostatic reconstructions. Balanced discretizations of the pressure gradient and of the gravitation source term are achieved through a “discrete Archimedes' buoyancy principle”. This strategy is applied to extend an explicit standard finite volume Godunov-type scheme for compressible flows with minimal modifications. The resulting method has the following features: (i) It inherits its conservation properties from the underlying base scheme. (ii) It is exactly balanced, even on curvilinear grids, for a large class of near-hydrostatic flows. (iii) It solves the full compressible flow equations without reference to a background state that is defined for an entire vertical column of air. (iv) It is robust with respect to details of the implementation, such as the choice of slope limiting functions, or the particularities of boundary condition discretizations
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
Coordination-driven magnetic-to-nonmagnetic transition in manganese doped silicon clusters
The interaction of a single manganese impurity with silicon is analyzed in a
combined experimental and theoretical study of the electronic, magnetic, and
structural properties of manganese-doped silicon clusters. The structural
transition from exohedral to endohedral doping coincides with a quenching of
high-spin states. For all geometric structures investigated, we find a similar
dependence of the magnetic moment on the manganese coordination number and
nearest neighbor distance. This observation can be generalized to manganese
point defects in bulk silicon, whose magnetic moments fall within the observed
magnetic-to-nonmagnetic transition, and which therefore react very sensitively
to changes in the local geometry. The results indicate that high spin states in
manganese-doped silicon could be stabilized by an appropriate lattice
expansion
Phase Modulated Thermal Conductance of Josephson Weak Links
We present a theory for quasiparticle heat transport through superconducting
weak links. The thermal conductance depends on the phase difference () of
the superconducting leads. Branch conversion processes, low-energy Andreev
bound states near the contact and the suppression of the local density of
states near the gap edge are related to phase-sensitive transport processes.
Theoretical results for the influence of junction transparency, temperature and
disorder, on the phase modulation of the conductance are reported. For
high-transmission weak links, , the formation of an Andreev bound state
at leads to suppression of the
density of states for the continuum excitations that transport heat, and thus,
to a reduction in the conductance for . For low-transmission
() barriers resonant scattering at energies
leads to an increase in the thermal conductance
as drops below (for phase differences near ).Comment: 4 pages, 3 figures Expanded discussion of boundary conditions for
Ricatti amplitude
Геомеханика разрушения и регламент тампонажного упрочнения пород вокруг наклонных стволов вязкопластическими растворами
Наведено підсумки шахтних досліджень руйнування порід навколо стволів вугільних шахт та обґрунтовано параметри їх зміцнення вязкопластичними розчинами.Research results are mine destruction of rocks around the shafts of coal mines and reasonable options to strengthen viscoplastic solutions
A Finite Element Test Bed for Diffraction Tomography
Finite element analysis methods have been successfully applied to the study of ultrasonic wave propagation in elastic solids [1–4]. As a natural part of such numerical solutions. displacements are predicted for every node of the spatial discretization describing the solids geometry and at every instant of time in the temporal discretization used to define the pulse propagation through the material. All of the data constitute a solution to the forward problem and can be used to visualize wavefront propagation and interactions with defects, thus predicting displacement signals at any point in or on the solid
Polar-Graded Multiferroic SrMnO3 Thin Films
Engineering defects and strains in oxides provides a promising route for the quest of thin film materials with coexisting ferroic orders, multiferroics, with efficient magnetoelectric coupling at room temperature. Precise control of the strain gradient would enable custom tailoring of the multiferroic properties but presently remains challenging. Here we explore the existence of a polar-graded state in epitaxially strained antiferromagnetic SrMnO3 thin films, whose polar nature was predicted theoretically and recently demonstrated experimentally. By means of aberration-corrected scanning transmission electron microscopy we map the polar rotation of the ferroelectric polarization with atomic resolution, both far from and near the domain walls, and find flexoelectricity resulting from vertical strain gradients. The origin of this particular strain state is a gradual distribution of oxygen vacancies across the film thickness, according to electron energy loss spectroscopy. Herein we present a chemistry-mediated route to induce polar rotations in oxygen-deficient multiferroic films, resulting in flexoelectric polar rotations and with potentially enhanced piezoelectricity
- …