Assessing the role of slab rheology in coupled plate-mantle convection models

International audienceAssessing the role of slab rheology in coupled plate-mantle convection models. Earth and Planetary Science Letters 430, 191-201. Abstract Reconstructing the 3D structure of the Earth's mantle has been a challenge for geodynamicists for about 40 years. Although numerical models and computational capabilities have substantially progressed, parameterizations used for modeling convection forced by plate motions are far from being Earth-like. Among the set of parameters, rheology is fundamental because it defines in a non-linear way the dynamics of slabs and plumes, and the organization of lithosphere deformation. In this study, we evaluate the role of the temperature dependence of viscosity (variations up to 6 orders of magnitude) and the importance of pseudo-plasticity on reconstructing slab evolution in 3D spherical models of convection driven by plate history models. Pseudo-plasticity, which produces plate-like behavior in convection models, allows a consistent coupling between imposed plate motions and global convection, which is not possible with temperature-dependent viscosity alone. Using test case models, we show that increasing temperature dependence of viscosity enhances vertical and lateral coherence of slabs, but leads to unrealistic slab morphologies for large viscosity contrasts. Introducing pseudo-plasticity partially solves this issue, producing thin laterally and vertically more continuous slabs, and flat subduction where trench retreat is fast. We evaluate the differences between convection reconstructions employing different viscosity laws to be very large, and similar to the differences between two models with the same rheology but using two different plate histories or initial conditions

Neuropsychological indicators of heteromodal cortex (dys)function relevant to conditioned blocking measures of attention in schizophrenia

Background. Learning a predictive relationship between two events can block learning about an added event (conditioned blocking, CB). Patients with nonparanoid schizophrenia can show reduced CB and learn about the similar consequences of the added event. What parts of the brain are involved in the functions required in learning the CB task and actually showing 'blocking' - a part of normal selective attention processes? As a first approximation, we ask if neuropsychological test performance sensitive to specific cortical regions is associated with these two functions. Methods. This study reports on the relationship of associative learning and CB measures of attention obtained with a visuospatial maze-like task to signs of heteromodal cortex function provided by performance on a battery of 10 neuropsychological tasks. These tasks were sensitive to frontal, parietal and temporal lobe function of the left and right hemisphere. Acquisition criteria for the task were achieved by 62 patients with schizophrenia and 62 matched controls but not by 39 other people with schizophrenia. Results. First right-hemisphere, visuo-spatial abilities were generally associated with faster task-learning (e.g. visual reproduction, immediate and delayed, picture-completion), and patients that could not learn the task were poorer on tests emphasising set-switching and problem-solving abilities associated with left frontal lobe function (e.g. trail-making, block-design). Second CB expression depended on Stroop- and Mooney-faces-task performance that are reported to require cingulate and parietal lobe function. Conclusions. As would be predicted right hemisphere function was implicated in performing a visuospatial learning task. The additional CB requirement incurred additional anterior cingulate and right parietal involvement. Functionally this probably reflected effortful attentional processes, and illustrates the problems of patients with schizophrenia in switching between automatic and controlled processing strategies. The results are astonishingly consistent with imaging studies implicating brain regions such as the cingulate and intra-parietal sulcus in attention (Mesulam, 1999)

Phase control of La2CuO4 in thin-film synthesis

The lanthanum copper oxide, La2CuO4, which is an end member of the prototype high-Tc superconductors (La,Sr)2CuO4 and (La,Ba)2CuO4, crystallizes in the "K2NiF4" structure in high-temperature bulk synthesis. The crystal chemistry, however, predicts that La2CuO4 is at the borderline of the K2NiF4 stability and that it can crystallize in the Nd2CuO4 structure at low synthesis temperatures. In this article we demonstrate that low-temperature thin-film synthesis actually crystallizes La2CuO4 in the Nd2CuO4 structure. We also show that the phase control of "K2NiF4"-type La2CuO4 versus "Nd2CuO4"-type La2CuO4 can be achieved by varying the synthesis temperature and using different substrates.Comment: 4 pages, 5 figures, submitted to PRB, revte

Extraction of the pion distribution amplitude from polarized muon pair production

We consider the production of muon pairs from the scattering of pions on longitudinally polarized protons. We calculate the cross section and the single spin asymmetry for this process, taking into account pion bound state effects. We work in the kinematic region where the photon has a large longitudinal momentum fraction, which allows us to treat the bound state problem perturbatively. Our predictions are directly proportional to the pion distribution amplitude. A measurement of the polarized Drell-Yan cross section thus allows the determination of the shape of the pion distribution amplitude.Comment: 13 pages, using revtex, two figures added separately as one uuencoded Z-compressed fil

Next-to-next-to-leading order prediction for the photon-to-pion transition form factor

We evaluate the next-to-next-to-leading order corrections to the hard-scattering amplitude of the photon-to-pion transition form factor. Our approach is based on the predictive power of the conformal operator product expansion, which is valid for a vanishing $\beta$-function in the so-called conformal scheme. The Wilson--coefficients appearing in the non-forward kinematics are then entirely determined from those of the polarized deep-inelastic scattering known to next-to-next-to-leading accuracy. We propose different schemes to include explicitly also the conformal symmetry breaking term proportional to the $\beta$-function, and discuss numerical predictions calculated in different kinematical regions. It is demonstrated that the photon-to-pion transition form factor can provide a fundamental testing ground for our QCD understanding of exclusive reactions.Comment: 62 pages LaTeX, 2 figures, 9 tables; typos corrected, some references added, to appear in Phys. Rev.

The liquid-vapor interface of an ionic fluid

We investigate the liquid-vapor interface of the restricted primitive model (RPM) for an ionic fluid using a density-functional approximation based on correlation functions of the homogeneous fluid as obtained from the mean-spherical approximation (MSA). In the limit of a homogeneous fluid our approach yields the well-known MSA (energy) equation of state. The ionic interfacial density profiles, which for the RPM are identical for both species, have a shape similar to those of simple atomic fluids in that the decay towards the bulk values is more rapid on the vapor side than on the liquid side. This is the opposite asymmetry of the decay to that found in earlier calculations for the RPM based on a square-gradient theory. The width of the interface is, for a wide range of temperatures, approximately four times the second moment correlation length of the liquid phase. We discuss the magnitude and temperature dependence of the surface tension, and argue that for temperatures near the triple point the ratio of the dimensionless surface tension and critical temperature is much smaller for the RPM than for simple atomic fluids.Comment: 6 postscript figures, submitted to Phys. Rev.

Microtubule length dependence of motor traffic in cells

In living cells, motor proteins, such as kinesin and dynein can move processively along microtubule (MT), and also detach from or attach to MT stochastically. Experiments have found that, the traffic of motor might be jammed, and various theoretical models have been designed to understand this traffic jam phenomenon. But previous studies mainly focus on motor attachment/detachment rate dependent properties. Recent experiment of Leduc {\it et al.} found that the traffic jam formation of motor protein kinesin depends also on the length of MT [Proc. Natl. Acad. Sci. U.S.A. {\bf 109}, 6100-6105 (2012)]. In this study, the MT length dependent properties of motor traffic will be analyzed. We found that MT length has one {\it critical value} $N_c$, traffic jam occurs only when MT length $N>N_c$. The jammed length of MT increases with total MT length, while the non-jammed MT length might not change monotonically with the total MT length. The critical value $N_c$ increases with motor detachment rate from MT, but decreases with motor attachment rate to MT

Questioning Glutamate Excitotoxicity in Acute Brain Damage: The Importance of Spreading Depolarization

Background: Within 2 min of severe ischemia, spreading depolarization (SD) propagates like a wave through compromised gray matter of the higher brain. More SDs arise over hours in adjacent tissue, expanding the neuronal damage. This period represents a therapeutic window to inhibit SD and so reduce impending tissue injury. Yet most neuroscientists assume that the course of early brain injury can be explained by glutamate excitotoxicity, the concept that immediate glutamate release promotes early and downstream brain injury. There are many problems with glutamate release being the unseen culprit, the most practical being that the concept has yielded zero therapeutics over the past 30 years. But the basic science is also flawed, arising from dubious foundational observations beginning in the 1950s Methods: Literature pertaining to excitotoxicity and to SD over the past 60 years is critiqued. Results: Excitotoxicity theory centers on the immediate and excessive release of glutamate with resulting neuronal hyperexcitation. This instigates poststroke cascades with subsequent secondary neuronal injury. By contrast, SD theory argues that although SD evokes some brief glutamate release, acute neuronal damage and the subsequent cascade of injury to neurons are elicited by the metabolic stress of SD, not by excessive glutamate release. The challenge we present here is to find new clinical targets based on more informed basic science. This is motivated by the continuing failure by neuroscientists and by industry to develop drugs that can reduce brain injury following ischemic stroke, traumatic brain injury, or sudden cardiac arrest. One important step is to recognize that SD plays a central role in promoting early neuronal damage. We argue that uncovering the molecular biology of SD initiation and propagation is essential because ischemic neurons are usually not acutely injured unless SD propagates through them. The role of glutamate excitotoxicity theory and how it has shaped SD research is then addressed, followed by a critique of its fading relevance to the study of brain injury. Conclusions: Spreading depolarizations better account for the acute neuronal injury arising from brain ischemia than does the early and excessive release of glutamate.Grants to RDA from the Canadian Heart & Stroke Foundation, National Science Engineering and Research Council and the New Frontiers in Research Fund, to E.F from the National Research, Development and Innovation Office of Hungary, grant no. K134377; and the EU’s Horizon 2020 research and innovation program under grant agreement No. 739593, and to JPD from the DFG (German research Council) (DFG DR323/5-1,DFG DR 323/10-1) BMBF Bundesministerium fuer Bildung und Forschung (Era-Net Neuron EBio2, with funds from BMBF 01EW2004)