The morphology, evolution and seismic visibility of partial melt at the core-mantle boundary: Implications for ULVZs

SUMMARY Seismic observations indicate that the lowermost mantle above the core–mantle boundary (CMB) is strongly heterogeneous. Body waves reveal a variety of ultra-low velocity zones (ULVZs), which extend not more than 100 km above the CMB and have shear velocity reductions of up to 30 per cent. While the nature and origin of these ULVZs remain uncertain, some have suggested they are evidence of partial melting at the base of mantle plumes. Here we use coupled geodynamic/thermodynamic modelling to explore the hypothesis that present-day deep mantle melting creates ULVZs and introduces compositional heterogeneity in the mantle. Our models explore the generation and migration of melt in a deforming and compacting host rock at the base of a plume in the lowermost mantle. We test whether the balance of gravitational and viscous forces can generate partially molten zones that are consistent with the seismic observations. We find that for a wide range of plausible melt densities, permeabilities and viscosities, lower mantle melt is too dense to be stirred into convective flow and instead sinks down to form a completely molten layer, which is inconsistent with observations of ULVZs. Only if melt is less dense or at most ca. 1 per cent more dense than the solid, or if melt pockets are trapped within the solid, can melt remain suspended in the partial melt zone. In these cases, seismic velocities would be reduced in a cone at the base of the plume. Generally, we find partial melt alone does not explain the observed ULVZ morphologies and solid-state compositional variation is required to explain the anomalies. Our findings provide a framework for testing whether seismically observed ULVZ shapes are consistent with a partial melt origin, which is an important step towards constraining the nature of the heterogeneities in the lowermost mantle and their influence on the thermal, compositional and dynamic evolution of the Earth.ER

101 geodynamic modelling: how to design, interpret, and communicate numerical studies of the solid Earth

Geodynamic modelling provides a powerful tool to investigate processes in the Earth's crust, mantle, and core that are not directly observable. However, numerical models are inherently subject to the assumptions and simplifications on which they are based. In order to use and review numerical modelling studies appropriately, one needs to be aware of the limitations of geodynamic modelling as well as its advantages. Here, we present a comprehensive yet concise overview of the geodynamic modelling process applied to the solid Earth from the choice of governing equations to numerical methods, model setup, model interpretation, and the eventual communication of the model results. We highlight best practices and discuss their implementations including code verification, model validation, internal consistency checks, and software and data management. Thus, with this perspective, we encourage high-quality modelling studies, fair external interpretation, and sensible use of published work. We provide ample examples, from lithosphere and mantle dynamics specifically, and point out synergies with related fields such as seismology, tectonophysics, geology, mineral physics, planetary science, and geodesy. We clarify and consolidate terminology across geodynamics and numerical modelling to set a standard for clear communication of modelling studies. All in all, this paper presents the basics of geodynamic modelling for first-time and experienced modellers, collaborators, and reviewers from diverse backgrounds to (re)gain a solid understanding of geodynamic modelling as a whole

Artifical compound eyes - Different concepts and their application to ultra flat image acquisition sensors

Two different approaches for ultra flat image acquisition sensors on the basis of artificial compound eyes are examined. In apposition optics the image reconstruction is based on moiré- or static sampling while the superposition eye approach produces an overall image. Both types of sensors are compared with respect to theoretical limitations of resolution, sensitivity and system thickness. Explicit design rules are given. A paraxial 3×3 matrix formalism is used to describe the arrangement of three microlens arrays with different pitches to find first order parameters of artificial superposition eyes. The model is validated by analysis of the system with raytracing software. Measurements of focal length of anamorphic reflow lenses, which are key components of the superposition approach, under oblique incidence are performed. For the second approach, the artificial apposition eye, a first demonstrator system is presented. The monolithic device consists of a UV-replicated reflow microlens array on a thin silica-substrate with a pinhole array in a metal layer on the backside. The pitch of the pinholes differs from the lens array pitch to enable an individual viewing angle for each channel. Imaged test patterns are presented and measurements of the angular sensitivity function are compared to calculations using commercial raytracing software

Advanced packaging materials for optical applications: Bridging the gap between nm-size structures and large-area panel processing

During the last two decades, nano-materials have been intensively investigated due to their wide range of properties, resulting in a variety of applications. In order to serve as advanced packaging material, from an industrial point of view emphasis has also to be on cost reduction either for the materials, the processes, or for both. Materials are searched for which enable processing and integration from a nm up to a cm scale. A particular class of low-cost nanoscale materials fulfilling this requirement are inorganic-organic hybrid polymers (ORMOCER®)1 which are synthesized by catalytically controlled hydrolysis/polycondensation reactions, resulting in storage-stable resins. Due to the variety of chemical and physical parameters, the material and processing properties which directly influence the resulting structure and thus the physical properties, can be varied over wide ranges. Upon synthesis, functional organic groups are introduced into the material which allows one to photochemically pattern the resins. The materials are capable to be patterned on a nm up to a cm scale, employing a variety of different micro- and nanopatterning methods such as, UV lithography, UV replication/lithography, laser-direct writing, or two-photon polymerization, in order to generate micro- and nano-optical components. While for most of the techniques the patterning has to be repeated several times in order to achieve multi-functional layers, the latter method allows one to directly write arbitrary 3D structures into the hybrid polymer material. The combination of chemically designed low-cost materials with tunable material parameters such as low optical absorption, tunable refractive index, good processibility, and high chemical, thermal and mechanical stability, is very attractive for (integrated) optical applications. Examples for application of the materials for microoptics as well as for optical back-planes generated by large-area processing will be given

Mit den Augen einer Fliege

Seit Jahrmillionen ist das Facettenauge der Insekten ein Erfolgsmodell. Ihr Volumen ist sehr viel kleiner als das eines klassischen Ein-Linsen-Systems, das wir Menschen besitzen, und durch ihre große Tiefenschärfe kommt es ohne Autofokus aus. Nun haben deutsche Forscher ein künstliches Facettenauge entwickelt, das etwa 0,2 mm dick ist und eine Auflösung von 60 x 60 Pixel hat. Damit passt es beispielsweise auf Kreditkarten, Folien oder Displays

Driving microoptical imaging systems towards miniature camera applications

Up to now, multi channel imaging systems have been increasingly studied and approached from various directions in the academic domain due to their promising large field of view at small system thickness. However, specific drawbacks of each of the solutions prevented the diffusion into corresponding markets so far. Most severe problems are a low image resolution and a low sensitivity compared to a conventional single aperture lens besides the lack of a cost-efficient method of fabrication and assembly. We propose a microoptical approach to ultra-compact optics for real-time vision systems that are inspired by the compound eyes of insects. The demonstrated modules achieve a VGA resolution with 700x550 pixels within an optical package of 6.8mm x 5.2mm and a total track length of 1.4mm. The partial images that are separately recorded within different optical channels are stitched together to form a final image of the whole field of view by means of image processing. These software tools allow to correct the distortion of the individual partial images so that the final image is also free of distortion. The so-called electronic cluster eyes are realized by state-of-the-art microoptical fabrication techniques and offer a resolution and sensitivity potential that makes them suitable for consumer, machine vision and medical imaging applications