Uncertainties in the relative positions of the Australia, Antarctica, Lord Howe, and Pacific Plates since the Late Cretaceous

We determined parameters that describe finite rotations and their uncertainty regions for relative plate motion at the spreading centers between the Pacific and Antarctica plates, between Australia and Antarctica, and between the Lord Howe Rise and Australia. We combined these to yield a range of possible finite rotations describing the relative positions of the Pacific, Australia, Antarctica, and Lord Howe plates since the Late Cretaceous. If the Pacific-Australia plate boundary has had its present trend since anomaly 18 time, reconstructions show 330±110 km of motion of the Pacific plate relative to the Lord Howe Rise since anomaly 5 time (9.8 m.y.), 420±110 km since anomaly 6 time (19.5 m.y.), 770±330 km since anomaly 13 time (35.6 m.y.), and 820±260 km since anomaly 18 time (43.0 m.y.). We examined two cases for times prior to anomaly 18, assuming a Late Cretaceous age of Australia-Antarctica separation. If a plate boundary existed between the Lord Howe Rise and Pacific plates since the Late Cretaceous, with no plate boundary in Antarctica, reconstructions with the Lord Howe Rise fixed predict 610 ± 200 km of westward motion of the Pacific plate between the times of anomalies 31 and 22, followed by 260±100 km of northward motion between the times of anomalies 22 and 18. If the Lord Howe Rise was fixed to the Pacific plate until the Eocene, but a plate boundary existed between East and West Antarctica, reconstructions show very little motion across this boundary between the times of anomalies 31 and 22, followed by convergence between the times of anomalies 22 and 18. This second case also brings 70–80 m.y. paleomagnetic poles from the Pacific and East Antarctica plates into better agreement than the first case, but large uncertainties in the reconstructions do not allow the first case to be conclusively eliminated

Uncertainties and implications of the Late Cretaceous and Tertiary position of North America relative to the Farallon, Kula, and Pacific Plates

We present updated global plate reconstructions and calculated uncertainties of the Pacific, Kula, and Farallon/Vancouver plates relative to North America for selected times since 68 Ma. Improved magnetic data from the Indian Ocean decrease the uncertainties in. the global plate circuit approach; these uncertainties are now considerably smaller than those inherent in equivalent reconstructions based on the assumption of fixed hotspots. Major differences between these results and those of others are due to our use of more detailed Africa-North America reconstructions, separate Vancouver and Farallon plate reconstructions, and the assumption of a rigid Antarctica plate during Cenozoic time. The uncertainties in the relative positions of the Pacific and North America plates since the time of anomaly 7 (26 Ma) range up to ±100 km in position, or from 1 to 3 m.y. in time. If the Mendocino triple junction initiated at about 28.5 Ma, its position would have been at 31.3°N ± 130 km relative to fixed North America. Unacceptable overlap of oceanic crust of the Pacific plate with continental crust of western North America in the anomaly 10 (30 Ma) reconstruction is a minimum of 340±200 km along an azimuth of N60°E and may be accounted for by Basin and Range extension. Pacific-North America displacement in the past 20 Ma is found to be considerably less than that calculated by fixed hotspot reconstructions. Farallon (Vancouver)-North America convergence velocity decreased greatly between the times of anomalies 24 and 21 (56 to 50 Ma), prior to the 43 Ma age of the Hawaiian-Emperor bend and the often quoted 40 Ma “end” of the Laramide orogeny. A change in direction of Farallon-North America convergence occurred sometime between 50 and 42 Ma and also may not correlate with the time of the Hawaiian-Emperor bend. The lack of data from subducted parts of the Farallon and Kula plates permits many possibilities regarding the position of the Kula-Farallon ridge, the age of subducted crust, or the position of oceanic plateaus during the Laramide orogeny, leaving open the question of the relationship between plate tectonic scenarios and tectonic style during Laramide time. Displacements of points on the various oceanic plates along the west coast of an arbitrarily fixed North America during the interval between anomalies 30/31 and 18 (68 to 42 Ma) are found to be: Pacific plate, 1700±200 km northward; Farallon plate, 3200±400 km northeastward; Vancouver plate, 3000±400 km northeastward; Kula plate, if attached to the Pacific plate after A24 time, 2500±400 km northward

A method for bounding uncertainties in combined plate reconstructions

We present a method for calculating uncertainties in plate reconstructions that does not describe the uncertainty in terms of uncertainties in pole positions and rotation angles. If a fit of magnetic anomalies of the same age and fracture zones that were active as transform faults at that time can be found, such a reconstruction can be perturbed and degraded by small rotations about each of three orthogonal axes (partial uncertainty poles). If the uncertainty in the reconstruction is a consequence of independent, small, but acceptable, rotations about these axes, then the uncertainties in reconstructed points will be elliptical in shape. The dimensions and orientation of such ellipses will depend upon the magnitudes of the perturbing rotations and upon the relative geometry of the partial uncertainty poles and the points in question. In a sequence of rotations, each rotation will contribute an elliptical region of uncertainty for each reconstructed point, and these ellipses can be combined as independent statistical quantities to obtain a confidence ellipse for the sequence of rotations. As a test, we calculated uncertainties for three points on the Pacific plate with respect to North America at the time of anomaly 6 (20 Ma). The computed uncertainties are similar in shape to those that we previously obtained for a sequence of marginally acceptable rotations, but the major axes of the ellipses presented here are about 25% shorter

Reply to Jurdy & Stefanick comment

We disagree with virtually all of what Jurdy & Stefanick have written. Part of our disagreement stems from personal opinions about what is ‘simple’, ‘arbitrary’, ‘artificial’, ‘undesirable’, etc., but other disagreements are more profound and reveal a very different understanding of finite rotations. Jurdy & Stefanick raise two basic objections. One concerns statistical questions that were not meant to be part of Chang et al. (1990). The other addresses the main issue of our paper, the parametrization of uncertainties of rotations. They suggest that both our approach is flawed and that theirs, outlined in Jurdy & Stefanick (1987), is better. Except possibly for their opinion of what constitutes a covariance matrix, we try not to indulge the reader with long discussions of questions of personal preference, but instead to confine our response to these basic questions

Magnetic-crystallographic phase diagram of superconducting parent compound Fe1+x_{1+x}Te

hrough neutron diffraction experiments, including spin-polarized measurements, we find a collinear incommensurate spin-density wave with propagation vector $\mathbf k =$ ($0.4481(4) \, \,0 \, \, \frac1 2$) at base temperature in the superconducting parent compound Fe$_{1+x}$Te. This critical concentration of interstitial iron corresponds to $x \approx 12$ and leads crystallographic phase separation at base temperature. The spin-density wave is short-range ordered with a correlation length of 22(3) \AA, and as the ordering temperature is approached its propagation vector decreases linearly in the H-direction and becomes long-range ordered. Upon further populating the interstitial iron site, the spin-density wave gives way to an incommensurate helical ordering with propagation vector $\mathbf k =$ ($0.3855(2) \, \,0 \, \, \frac1 2$) at base temperature. For a sample with $x \approx 9(1)$, we also find an incommensurate spin-density wave that competes with the bicollinear commensurate ordering close to the N\'eel point. The shifting of spectral weight between competing magnetic orderings observed in several samples is supporting evidence for the phase separation being electronic in nature, and hence leads to crystallographic phase separation around the critical interstitial iron concentration of 12%. With results from both powder and single crystal samples, we construct a magnetic-crystallographic phase diagram of Fe$_{1+x}$Te for $ 5% < x <17%

SIEC-ISBE: Quo vadis? Strategy suggestions for the SIEC-ISBE

In order to escape the danger of stagnation, the SIEC-ISBE needs fresh perspectives. A strategy to increase membership numbers will be introduced in this paper, based on a study instigated from the Austrian chapter. After a short introduction of the status quo of the SIEC-ISBE, the paper will focus on the USP (Unique Selling Proposition) and the benefits of SIEC-ISBE membership. Some selected recommendations (for instance lowering the threshold for attending conferences or increased targeting of students) form the completion of this thesis

Yaw control for 20MW offshore multi rotor system

A Simulink model of a 20MW multi rotor system (MRS) is built containing all the necessary detail to demonstrate yaw control for a novel yawing technique. The aerodynamics of each rotor are based on blade element momentum theory summed across a single actuator with the rotor and power conversion system modelled as a lumped mass model. A yaw controller is designed which operates by manipulating the thrusts of the rotors. The feasibility of this yaw mechanism is demonstrated by implementing it at wind speeds of 8m/s, 11m/s and 15m/s. At each wind speed the system remained stable with the yaw error kept within a maximum of 5 degrees over a two hour period

Dynamic origin of the morphotropic phase boundary - Soft modes and phase instability in 0.68Pb(Mg1/3Nb2/3O3)-0.32PbTiO3

We report neutron inelastic scattering on single crystal 0.68Pb(Mg1/3Nb2/3O3)-0.32PbTiO3 (PMN-0.32PT), a relaxor ferroelectric material that lies within the compositional range of the morphotropic phase boundary (MPB). Data were obtained between 100 K and 600 K under zero and non-zero electric field applied along the cubic [001] direction. The lowest energy, zone-center, transverse optic phonon is strongly damped and softens slowly at high temperature; however the square of the soft mode energy begins to increase linearly with temperature as in a conventional ferroelectric, which we term the soft mode "recovery," upon cooling into the tetragonal phase at TC. Our data show that the soft mode in PMN-0.32PT behaves almost identically to that in pure PMN, exhibiting the same temperature dependence and recovery temperature even though PMN exhibits no well-defined structural transition (no TC). The temperature dependence of the soft mode in PMN-0.32PT is also similar to that in PMN-0.60PT; however in PMN-0.60PT the recovery temperature equals TC. These results suggest that the temperature dependence and the energy scale of the soft mode dynamics in PMN-xPT are independent of concentration on the Ti-poor side of the MPB, but scale with TC for Ti-rich compositions. Thus the MPB may be defined in lattice dynamical terms as the concentration where TC first matches the recovery temperature of the soft mode. High-resolution x-ray studies show that the cubic-to-ferroelectric phase boundary shifts to higher temperatures by an abnormal amount within the MPB region in the presence of an electric field. This suggests that an unusual instability exists within the apparently cubic phase at the MPB.Comment: 13 pages, 6 figure

Competence-oriented instruction in vocational education in Austria: An empirical comparison between two instructional approaches

A distinct feature of the Austrian education system is its differentiation of programs in vocational education. Among these programs, the dual education system has a long tradition: Students undergo an apprenticeship in a company while also attending a vocational school in part-time. More than other forms of education, this combination of on-the-job training at the work place and instruction in vocational school requires constant adaptation to economic requirements. Against this background, a new instructional approach, so called areas of learning with a focus on competence were introduced in the vocational school Eisenstadt in the year 2010. The introduction of this approach offered an opportunity for comparing it with a “traditional” subject-oriented approach. Results of the comparison will be presented and discussed in this article