Turner S.,Macquarie University |
Beier C.,University Erlangen Nrnberg |
Niu Y.,Durham University |
Cook C.,University of Waikato
Geochemistry, Geophysics, Geosystems | Year: 2011
There is widespread interest in the distance that mid-ocean ridge magmatism extends beyond the neovolcanic zone. Off-axis magmas also provide a means to map out variations across the melting zone. We present 238U- 230Th-226Ra data for 35 well-characterized samples that extend up to 50 km away from the ridge axis across the East Pacific Rise at 9°30′N, 10°30′N, and 11°20′N. The ( 230Th/238U) ratios range from 1.00 to 1.19, and the ( 226Ra/230Th) ratios range from 1 to 2.78. The samples have a bimodal (230Th/238U) distribution with approximately half overlying published axial data on the U-Th diagram and the remainder lying close to the equiline. The U series disequilibria in the majority of the samples can be explained by aging subsequent to eruption in a zone ∼8 km wide about the neovolcanic zone, consistent with visual evidence for sample age. Nevertheless, seven of the samples lie above calculated (230Th/ 238U) axial decay curves and/or have 226Ra excesses implying eruption tens of kilometers off axis. These are consistent with evidence from seamounts and seismic interpretations that magmatism can extend up to 20 km off axis. The implication is that magma is not as efficiently focused beneath the ridge axis as has generally been believed. There is a decrease in initial (230Th/238U) in both these and published samples inferred to have formed off axis, but there is no compelling evidence that this reflects source heterogeneity. Simple modeling suggests that this could be explained by a decrease in fertility and melt column length as the overlying lithosphere thickens with age and the solidus shallows. Copyright 2011 by the American Geophysical Union.
Jonas J.B.,University of Heidelberg |
Jonas S.B.,Dietrich Bonhoeffer Gymnasium Weinheim |
Jonas R.A.,Dietrich Bonhoeffer Gymnasium Weinheim |
Holbach L.,University Erlangen Nrnberg |
Panda-Jonas S.,University of Heidelberg
American Journal of Ophthalmology | Year: 2011
Purpose: To examine histomorphometrically the parapapillary region in highly myopic eyes. Design: Retrospective laboratory investigation. Methods: We examined a highly myopic glaucomatous group (36 human globes; axial length >26.5 mm) and a nonhighly myopic group (28 globes with secondary angle-closure glaucoma; 17 eyes with malignant choroidal melanoma). Using light microscopy, pupil-optic nerve sections were assessed. Results: The length of the scleral flange (sclera between optic nerve border and optic nerve dura mater) increased with axial length (P <.001; correlation coefficient r = 0.70) and decreased with its thickness (P <.001; r = 0.75). In all highly myopic eyes (n = 15) with a distance of >0.5 mm between optic nerve border and beginning of Bruch membrane, the parapapillary region consisted of an elongated parapapillary scleral flange associated with a scleral flange thinning and a retrobulbar cerebrospinal fluid space extended into the retroparapapillary region. The parapapillary retina was composed of retinal nerve fiber layer (or its remnants) only, without elements of any other retinal layer, without underlying Bruch membrane or choroid. These histologic features were not detected in any of the nonhighly myopic eyes. Conclusions: Since parapapillary scleral thickness influences the lamina cribrosa biomechanics, the findings may partially explain the increased glaucoma susceptibility in highly myopic eyes. The implications of an absence of Bruch membrane and choroid in the highly myopic parapapillary region, and the implications of the retrobulbar parapapillary extension of the cerebrospinal spinal fluid space for the pathophysiology of the optic nerve head, have to be elucidated. © 2011 Elsevier Inc.
Zeeden C.,University of Bayreuth |
Hambach U.,University of Bayreuth |
Steguweit L.,University Erlangen Nrnberg |
Anghelinu M.,Universitaea Trgoviste
Quaternary International | Year: 2011
Palaeomagnetic investigations were carried out at the archaeological site of Poiana Cireşului (Romania) to check whether the loess records a reliable palaeomagnetic signal, and to compare this signal to reference data. The sediments are composed of loess and loess-like sediments. Pedogenic alterations and a pronounced cultural layer occur in the section. The archaeology-bearing sedimentary geoarchive spans the time interval from ca. 20 to ca. 55 ka, and was dated mainly by 14C and luminescence techniques. The record of geomagnetic palaeosecular variation from this European loess site is discussed. The presented palaeomagnetic record bears analogies to data from Lac du Bouchet (France), and is a reliable high resolution record (mean sedimentation rates are ca. 20 cm/ky) of palaeosecular variation. The results imply that European loess geoarchives may record palaeosecular variation features, even if loess is (pedogenically) altered. The palaeosecular variation pattern of loess is here employed as a stratigraphic tool. © 2010 Elsevier Ltd and INQUA.
Moulton B.J.A.,University of Toronto |
Henderson G.S.,University of Toronto |
Sonneville C.,Ecole Normale Superieure de Cachan |
O'Shaughnessy C.,University of Toronto |
And 3 more authors.
Chemical Geology | Year: 2016
X-ray absorption near-edge structure (XANES) spectroscopy has been used to investigate the local structural environments around each of the elements within the haplobasaltic system. The XANES results reveal both, linear changes in Ca, O and Si whereas non-linear changes are also observed for Si as well as Al and Mg. Unexpectedly, both Si and Al spectra show complex edge structure that varies non-linearly across the join. The Si L2,3-edge results suggest that the Si environment in An100 is very similar to that in crystalline anorthite whereas the Di100 and diopside spectra show large offsets. The L3 and L2 peaks display a linear behavior whereas peak B of the Si L2,3 spectra displays a non-linear behavior displaying a maximum position at the Di40 and Di100 compositions and decreasing in between. We estimate the SiO bond length from shift in the peak B position which suggests a change in bond length between 1.58 and 1.66Å across the join. The Al K-edge spectra suggests that there is a constant decrease in the inter-tetrahedral angle as Al is added. The local Mg environment displays non-linear changes in intensity and for compositions with An content greater than Di40 it appears that Mg plays an important role whereas Mg is dominant in diopside-rich melts, though octahedral coordinated Mg cannot be ruled out. The oxygen environment appears similar to crystalline anorthite in the haplobasaltic system. Calcium is present in highly distorted sites that are dominantly Ca in anorthite-rich glasses whereas Ca is more important in diopside-rich glasses. These results provide additional independent constraints on the atomic structure of haplobasaltic silicate melts and highlight the need for further investigation into the relationships between network formers, modifiers and the oxygen to which they are bound. © 2015 Elsevier B.V.
Beier C.,University Erlangen Nrnberg |
Vanderkluysen L.,University of Hawaii at Manoa |
Vanderkluysen L.,Arizona State University |
Regelous M.,University Erlangen Nrnberg |
And 2 more authors.
Geochemistry, Geophysics, Geosystems | Year: 2011
Major and trace element and Sr, Nd, and Pb isotope data for lavas from 12 seamounts along the western (older) 1500 km section of the Louisville Seamount Chain in the southwest Pacific show remarkably uniform compositions over a ∼30-40 Myr period of volcanism. All 56 samples analyzed are alkalic to transitional in composition. Unlike Hawaiian volcanoes, Louisville volcanoes appear not to pass through a sequence of evolutionary stages characterized by older tholeiitic basalts overlain by incompatible element enriched alkalic and silica-undersaturated lavas. The youngest lavas from a given Louisville seamount tend to have the least enriched incompatible element compositions. This unusual chemical evolution may be the result of re-melting of heterogeneous hot spot mantle that was partially depleted during the earlier, age progressive stages. The oldest Louisville seamounts were constructed close to the extinct Osbourn Trough spreading center, located north of the chain, but age-progressive lavas from these older seamounts are not significantly different to lavas from younger seamounts. This may indicate that spreading at this fossil ridge ceased several tens of millions of years before the oldest Louisville seamounts were constructed. Large fracture zones apparently had no significant effects on the composition of Louisville magmatism. However, lavas from the central part of the Louisville Seamount Chain, where volcanoes are smaller and more widely spaced, tend to have more variable and more enriched compositions. We suggest this may reflect smaller degrees of melting resulting from greater lithosphere thickness, and hence a shorter melting column for this section of the Louisville Seamounts. © 2011 by the American Geophysical Union.
Hesselmann A.,University Erlangen Nrnberg
Journal of Chemical Physics | Year: 2011
Several random-phase approximation (RPA) correlation methods were compared in third order of perturbation theory. While all of the considered approaches are exact in second order of perturbation theory, it is found that their corresponding third-order correlation energy contributions strongly differ from the exact third-order correlation energy contribution due to missing interactions of the particle-particle-hole-hole type. Thus a simple correction method is derived which makes the different RPA methods also exact to third-order of perturbation theory. By studying the reaction energies of 16 chemical reactions for 21 small organic molecules and intermolecular interaction energies of 23 intermolecular complexes comprising weakly bound and hydrogen-bridged systems, it is found that the third-order correlation energy correction considerably improves the accuracy of RPA methods if compared to coupled-cluster singles doubles with perturbative triples as a reference. © 2011 American Institute of Physics.
Deutscher J.,University Erlangen Nrnberg
Automatica | Year: 2011
In this article, the solution of the output regulation problem is considered for linear infinite-dimensional systems where the outputs to be controlled cannot be measured. It is shown that this problem can be solved by a finite-dimensional dual observer that is directly implementable so that the separation principle can be applied for the stabilization as in finite dimensions. A parametric design of these dual observers is proposed for Riesz-spectral systems that allows to achieve a low controller order and a desired control performance for the closed-loop system. The presented results are illustrated by determining a finite-dimensional regulator for an EulerBernoulli beam with KelvinVoigt damping that achieves tracking for steplike reference inputs and that asymptotically rejects sinusoidal disturbances. © 2011 Elsevier Ltd. All rights reserved.
Kopper C.,University Erlangen Nrnberg
Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment | Year: 2011
Up to now, most of the simulation work for the KM3NeT neutrino telescope has been performed using software tools adapted from the ANTARES project, which have originally neither been set up for a km3-scale detector nor for long-term maintenance on a modern computer system. New Monte-Carlo tools, including a Geant4-based muon propagator, a photon propagation tool including a full light scattering simulation and a new optical module acceptance and readout simulator have been developed and implemented in a simulation chain using a modular software framework. An overview of the new software tools and simulation results for a possible detector configuration will be presented. © 2010 Elsevier B.V. All rights reserved.
Eberl T.,University Erlangen Nrnberg
Progress in Particle and Nuclear Physics | Year: 2011
The ANTARES detector is the most sensitive neutrino telescope observing the southern sky and the worlds first particle detector operating in the deep sea. It is installed in the Mediterranean Sea at a depth of 2475 m. As example for the first results, the determination of the atmospheric muon flux is discussed; a fair agreement with previous measurements is found. Furthermore, the results of a search for high-energy events in excess of the atmospheric neutrino flux are reported and significant limits are set on the diffuse cosmic neutrino flux in the multi-TeV to PeV energy range. Using data taken during the construction phase, a first analysis searching for point-like excesses in the neutrino sky distribution has been performed. The resulting sensitivity of ANTARES is reported and compared to measurements of other detectors. © 2011 Elsevier B.V. All rights reserved.
Keller G.,University Erlangen Nrnberg
Dynamical Systems | Year: 2012
We discuss how an eigenvalue perturbation formula for transfer operators of dynamical systems is related to exponential hitting time distributions and extreme value theory for processes generated by chaotic dynamical systems. We also list a number of piecewise expanding systems to which this general theory applies and discuss the prospects to apply this theory to some classes of piecewise hyperbolic systems. In memory of Jaroslav Stark. © 2012 Copyright Taylor and Francis Group, LLC.