TY - JOUR A1 - Cai, Gaochao A1 - Tötzke, Christian A1 - Kaestner, Anders A1 - Ahmed, Mutez Ali T1 - Quantification of root water uptake and redistribution using neutron imaging: a review and future directions JF - The plant journal N2 - Quantifying root water uptake is essential to understanding plant water use and responses to different environmental conditions. However, non-destructive measurement of water transport and related hydraulics in the soil-root system remains a challenge. Neutron imaging, with its high sensitivity to hydrogen, has become an unparalleled tool to visualize and quantify root water uptake in vivo. In combination with isotopes (e.g., deuterated water) and a diffusion-convection model, root water uptake and hydraulic redistribution in root and soil can be quantified. Here, we review recent advances in utilizing neutron imaging to visualize and quantify root water uptake, hydraulic redistribution in roots and soil, and root hydraulic properties of different plant species. Under uniform soil moisture distributions, neutron radiographic studies have shown that water uptake was not uniform along the root and depended on both root type and age. For both tap (e.g., lupine [Lupinus albus L.]) and fibrous (e.g., maize [Zea mays L.]) root systems, water was mainly taken up through lateral roots. In mature maize, the location of water uptake shifted from seminal roots and their laterals to crown/nodal roots and their laterals. Under non-uniform soil moisture distributions, part of the water taken up during the daytime maintained the growth of crown/nodal roots in the upper, drier soil layers. Ultra-fast neutron tomography provides new insights into 3D water movement in soil and roots. We discuss the limitations of using neutron imaging and propose future directions to utilize neutron imaging to advance our understanding of root water uptake and soil-root interactions. KW - attenuation coefficient KW - convection KW - diffusion KW - radiography KW - root hydraulics KW - root water uptake KW - tomography Y1 - 2022 U6 - https://doi.org/10.1111/tpj.15839 SN - 0960-7412 SN - 1365-313X VL - 111 IS - 2 SP - 348 EP - 359 PB - Wiley-Blackwell CY - Oxford [u.a.] ER - TY - GEN A1 - Jousset, Philippe A1 - Reinsch, Thomas A1 - Ryberg, Trond A1 - Blanck, Hanna A1 - Clarke, Andy A1 - Aghayev, Rufat A1 - Hersir, Gylfi P. A1 - Henninges, Jan A1 - Weber, Michael A1 - Krawczyk, Charlotte M. T1 - Dynamic strain determination using fibre-optic cables allows imaging of seismological and structural features T2 - Postprints der Universität Potsdam Mathematisch-Naturwissenschaftliche Reihe N2 - Natural hazard prediction and efficient crust exploration require dense seismic observations both in time and space. Seismological techniques provide ground-motion data, whose accuracy depends on sensor characteristics and spatial distribution. Here we demonstrate that dynamic strain determination is possible with conventional fibre-optic cables deployed for telecommunication. Extending recently distributed acoustic sensing (DAS) studies, we present high resolution spatially un-aliased broadband strain data. We recorded seismic signals from natural and man-made sources with 4-m spacing along a 15-km-long fibre-optic cable layout on Reykjanes Peninsula, SW-Iceland. We identify with unprecedented resolution structural features such as normal faults and volcanic dykes in the Reykjanes Oblique Rift, allowing us to infer new dynamic fault processes. Conventional seismometer recordings, acquired simultaneously, validate the spectral amplitude DAS response between 0.1 and 100 Hz bandwidth. We suggest that the networks of fibre-optic telecommunication lines worldwide could be used as seismometers opening a new window for Earth hazard assessment and exploration. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 691 KW - North-America KW - fault zone KW - tomography KW - frequency Y1 - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-426770 IS - 691 ER - TY - JOUR A1 - Kochovski, Zdravko A1 - Chen, Guosong A1 - Yuan, Jiayin A1 - Lu, Yan T1 - Cryo-Electron microscopy for the study of self-assembled poly(ionic liquid) nanoparticles and protein supramolecular structures JF - Colloid and polymer science : official journal of the Kolloid-Gesellschaft N2 - Cryo-electron microscopy (cryo-EM) is a powerful structure determination technique that is well-suited to the study of protein and polymer self-assembly in solution. In contrast to conventional transmission electron microscopy (TEM) sample preparation, which often times involves drying and staining, the frozen-hydrated sample preparation allows the specimens to be kept and imaged in a state closest to their native one. Here, we give a short overview of the basic principles of Cryo-EM and review our results on applying it to the study of different protein and polymer self-assembled nanostructures. More specifically, we show how we have applied cryo-electron tomography (cryo-ET) to visualize the internal morphology of self-assembled poly(ionic liquid) nanoparticles and cryo-EM single particle analysis (SPA) to determine the three-dimensional (3D) structures of artificial protein microtubules. KW - self-assembly KW - poly(ionic liquid) nanoparticles KW - protein self-assembly KW - cryo-electron microscopy KW - single particle analysis KW - cryo-electron KW - tomography Y1 - 2020 U6 - https://doi.org/10.1007/s00396-020-04657-w SN - 0303-402X SN - 1435-1536 VL - 298 IS - 7 SP - 707 EP - 717 PB - Springer CY - New York ER - TY - THES A1 - Maercklin, Nils T1 - Seismic structure of the Arava Fault, Dead Sea Transform N2 - Ein transversales Störungssystem im Nahen Osten, die Dead Sea Transform (DST), trennt die Arabische Platte von der Sinai-Mikroplatte und erstreckt sich von Süden nach Norden vom Extensionsgebiet im Roten Meer über das Tote Meer bis zur Taurus-Zagros Kollisionszone. Die sinistrale DST bildete sich im Miozän vor etwa 17 Ma und steht mit dem Aufbrechen des Afro-Arabischen Kontinents in Verbindung. Das Untersuchungsgebiet liegt im Arava Tal zwischen Totem und Rotem Meer, mittig über der Arava Störung (Arava Fault, AF), die hier den Hauptast der DST bildet. Eine Reihe seismischer Experimente, aufgebaut aus künstlichen Quellen, linearen Profilen über die Störung und entsprechend entworfenen Empfänger-Arrays, zeigt die Untergrundstruktur in der Umgebung der AF und der Verwerfungszone selbst bis in eine Tiefe von 3-4 km. Ein tomographisch bestimmtes Modell der seismischen Geschwindigkeiten von P-Wellen zeigt einen starken Kontrast nahe der AF mit niedrigeren Geschwindigkeiten auf der westlichen Seite als im Osten. Scherwellen lokaler Erdbeben liefern ein mittleres P-zu-S Geschwindigkeitsverhältnis und es gibt Anzeichen für Änderungen über die Störung hinweg. Hoch aufgelöste tomographische Geschwindigkeitsmodelle bestätigen der Verlauf der AF und stimmen gut mit der Oberflächengeologie überein. Modelle des elektrischen Widerstands aus magnetotellurischen Messungen im selben Gebiet zeigen eine leitfähige Schicht westlich der AF, schlecht leitendes Material östlich davon und einen starken Kontrast nahe der AF, die den Fluss von Fluiden von einer Seite zur anderen zu verhindern scheint. Die Korrelation seismischer Geschwindigkeiten und elektrischer Widerstände erlaubt eine Charakterisierung verschiedener Lithologien im Untergrund aus deren physikalischen Eigenschaften. Die westliche Seite lässt sich durch eine geschichtete Struktur beschreiben, wogegen die östliche Seite eher einheitlich erscheint. Die senkrechte Grenze zwischen den westlichen Einheiten und der östlichen scheint gegenüber der Oberflächenausprägung der AF nach Osten verschoben zu sein. Eine Modellierung von seismischen Reflexionen an einer Störung deutet an, dass die Grenze zwischen niedrigen und hohen Geschwindigkeiten eher scharf ist, sich aber durch eine raue Oberfläche auf der Längenskala einiger hundert Meter auszeichnen kann, was die Streuung seismischer Wellen begünstigte. Das verwendete Abbildungsverfahren (Migrationsverfahren) für seismische Streukörper basiert auf Array Beamforming und der Kohärenzanalyse P-zu-P gestreuter seismischer Phasen. Eine sorgfältige Bestimmung der Auflösung sichert zuverlässige Abbildungsergebnisse. Die niedrigen Geschwindigkeiten im Westen entsprechen der jungen sedimentären Füllung im Arava Tal, und die hohen Geschwindigkeiten stehen mit den dortigen präkambrischen Magmatiten in Verbindung. Eine 7 km lange Zone seismischer Streuung (Reflektor) ist gegenüber der an der Oberfläche sichtbaren AF um 1 km nach Osten verschoben und lässt sich im Tiefenbereich von 1 km bis 4 km abbilden. Dieser Reflektor markiert die Grenze zwischen zwei lithologischen Blöcken, die vermutlich wegen des horizontalen Versatzes entlang der DST nebeneinander zu liegen kamen. Diese Interpretation als lithologische Grenze wird durch die gemeinsame Auswertung der seismischen und magnetotellurischen Modelle gestützt. Die Grenze ist möglicherweise ein Ast der AF, der versetzt gegenüber des heutigen, aktiven Asts verläuft. Der Gesamtversatz der DST könnte räumlich und zeitlich auf diese beiden Äste und möglicherweise auch auf andere Störungen in dem Gebiet verteilt sein. N2 - The Dead Sea Transform (DST) is a prominent shear zone in the Middle East. It separates the Arabian plate from the Sinai microplate and stretches from the Red Sea rift in the south via the Dead Sea to the Taurus-Zagros collision zone in the north. Formed in the Miocene about 17 Ma ago and related to the breakup of the Afro-Arabian continent, the DST accommodates the left-lateral movement between the two plates. The study area is located in the Arava Valley between the Dead Sea and the Red Sea, centered across the Arava Fault (AF), which constitutes the major branch of the transform in this region. A set of seismic experiments comprising controlled sources, linear profiles across the fault, and specifically designed receiver arrays reveals the subsurface structure in the vicinity of the AF and of the fault zone itself down to about 3-4 km depth. A tomographically determined seismic P velocity model shows a pronounced velocity contrast near the fault with lower velocities on the western side than east of it. Additionally, S waves from local earthquakes provide an average P-to-S velocity ratio in the study area, and there are indications for a variations across the fault. High-resolution tomographic velocity sections and seismic reflection profiles confirm the surface trace of the AF, and observed features correlate well with fault-related geological observations. Coincident electrical resistivity sections from magnetotelluric measurements across the AF show a conductive layer west of the fault, resistive regions east of it, and a marked contrast near the trace of the AF, which seems to act as an impermeable barrier for fluid flow. The correlation of seismic velocities and electrical resistivities lead to a characterisation of subsurface lithologies from their physical properties. Whereas the western side of the fault is characterised by a layered structure, the eastern side is rather uniform. The vertical boundary between the western and the eastern units seems to be offset to the east of the AF surface trace. A modelling of fault-zone reflected waves indicates that the boundary between low and high velocities is possibly rather sharp but exhibits a rough surface on the length scale a few hundreds of metres. This gives rise to scattering of seismic waves at this boundary. The imaging (migration) method used is based on array beamforming and coherency analysis of P-to-P scattered seismic phases. Careful assessment of the resolution ensures reliable imaging results. The western low velocities correspond to the young sedimentary fill in the Arava Valley, and the high velocities in the east reflect mainly Precambrian igneous rocks. A 7 km long subvertical scattering zone reflector is offset about 1 km east of the AF surface trace and can be imaged from 1 km to about 4 km depth. The reflector marks the boundary between two lithological blocks juxtaposed most probably by displacement along the DST. This interpretation as a lithological boundary is supported by the combined seismic and magnetotelluric analysis. The boundary may be a strand of the AF, which is offset from the current, recently active surface trace. The total slip of the DST may be distributed spatially and in time over these two strands and possibly other faults in the area. KW - Arava-Störung KW - Totes Meer Störungssystem KW - Seitenverschiebung KW - Seismik KW - seismische Geschwindigkeit KW - Tomographie KW - Migration KW - Magnetotellurik KW - Arava Fault KW - Dead Sea Transform KW - strike-slip fault KW - seismics KW - seismic velocity KW - tomography KW - seismic imaging KW - migration KW - magnetotellurics Y1 - 2004 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-0001469 ER - TY - GEN A1 - Müller, Bernd Randolf A1 - Kupsch, Andreas A1 - Laquai, Rene A1 - Nellesen, Jens A1 - Tillmann, Wolfgang A1 - Kasperovich, Galina A1 - Bruno, Giovanni T1 - Microstructure Characterisation of Advanced Materials via 2D and 3D X-Ray Refraction Techniques T2 - Materials Science Forum N2 - 3D imaging techniques have an enormous potential to understand the microstructure, its evolution, and its link to mechanical, thermal, and transport properties. In this conference paper we report the use of a powerful, yet not so wide-spread, set of X-ray techniques based on refraction effects. X-ray refraction allows determining internal specific surface (surface per unit volume) in a non-destructive fashion, position and orientation sensitive, and with a nanometric detectability. We demonstrate showcases of ceramics and composite materials, where microstructural parameters could be achieved in a way unrivalled even by high-resolution techniques such as electron microscopy or computed tomography. We present in situ analysis of the damage evolution in an Al/Al2O3 metal matrix composite during tensile load and the identification of void formation (different kinds of defects, particularly unsintered powder hidden in pores, and small inhomogeneity’s like cracks) in Ti64 parts produced by selective laser melting using synchrotron X-ray refraction radiography and tomography. KW - X-ray refraction KW - radiography KW - tomography KW - synchrotron X-ray refraction radiography KW - CT KW - microscopy KW - creep KW - porosity KW - damage evolution KW - additive manufacturing KW - metal matrix composite Y1 - 2018 SN - 978-3-0357-1208-7 U6 - https://doi.org/10.4028/www.scientific.net/MSF.941.2401 SN - 0255-5476 VL - 941 SP - 2401 EP - 2406 PB - Trans Tech Publications Ltd CY - Zurich ER - TY - JOUR A1 - Stankiewicz, Jacek A1 - Weber, Michael H. A1 - Mohsen, Ayman A1 - Hofstetter, Rami T1 - Dead Sea Basin imaged by ambient seismic noise tomography JF - Pure and applied geophysics N2 - In the framework of the Dead Sea Integrated Research project (DESIRE), 59 seismological stations were deployed in the region of the Dead Sea Basin. Twenty of these stations recorded data of sufficiently high quality between May and September 2007 to be used for ambient seismic noise analysis. Empirical Green's functions are extracted from cross-correlations of long term recordings. These functions are dominated by Rayleigh waves, whose group velocities can be measured in the frequency range from 0.1 to 0.5 Hz. Analysis of positive and negative correlation lags of the Green's functions makes it possible to identify the direction of the source of the incoming energy. Signals with frequencies higher than 0.2 Hz originate from the Mediterranean Sea, while low frequencies arrive from the direction of the Red Sea. Travel times of the extracted Rayleigh waves were measured between station pairs for different frequencies, and tomographically inverted to provide independent velocity models. Four such 2D models were computed for a set of frequencies, all corresponding to different sampling depths, and thus together giving an indication of the velocity variations in 3D extending to a depth of 10 km. The results show low velocities in the Dead Sea Basin, consistent with previous studies suggesting up to 8 km of recent sedimentary infill in the Basin. The complex structure of the western margin of the Basin is also observed, with sedimentary infill present to depths not exceeding 5 km west of the southern part of the Dead Sea. The high velocities associated with the Lisan salt diapir are also observed down to a depth of similar to 5 km. The reliability of the results is confirmed by checkerboard recovery tests. KW - Dead Sea Basin KW - ambient noise KW - tomography Y1 - 2012 U6 - https://doi.org/10.1007/s00024-011-0350-y SN - 0033-4553 VL - 169 IS - 4 SP - 615 EP - 623 PB - Springer CY - Basel ER - TY - THES A1 - Weber, Michael H. T1 - Robotic telescopes & Doppler imaging : measuring differential rotation on long-period active stars N2 - Auf der Sonne sind viele Phänomene zu sehen die mit der solaren magnetischen Aktivität zusammenhängen. Das dafür zuständige Magnetfeld wird durch einen Dynamo erzeugt, der sich vermutlich am Boden der Konvektionszone in der sogenannten Tachocline befindet. Angetrieben wird der Dynamo teils von der differenziellen Rotation, teils von den magnetischen Turbulenzen in der Konvektionszone. Die differentielle Rotation kann an der Sonnenoberfläche durch beobachten der Sonnenfleckbewegungen gemessen werden.Um einen größeren Parameterraum zum Testen von Dynamotheorien zu erhalten, kann man diese Messungen auch auf andere Sterne ausdehnen. Das primäre Problem dabei ist, dass die Oberflächen von Sternen nicht direkt beobachtet werden können. Indirekt kann man dies jedoch mit Hilfe der Doppler-imaging Methode erreichen, die die Doppler-Verbreitung der Spektrallinien von schnell rotierenden Sternen benützt. Um jedoch ein Bild der Sternoberfläche zu erhalten, bedarf es vieler hochaufgelöster spektroskopischer Beobachtungen, die gleichmäßig über eine Sternrotation verteilt sein müssen. Für Sterne mit langen Rotationsperioden sind diese Beobachtungen nur schwierig durchzuführen. Das neue robotische Observatorium STELLA adressiert dieses Problem und bietet eine auf Dopplerimaging abgestimmte Ablaufplanung der Beobachtungen an. Dies wird solche Beobachtungen nicht nur leichter durchführbar machen, sondern auch effektiver gestalten.Als Vorschau welche Ergebnisse mit STELLA erwartet werden können dient eine Studie an sieben Sternen die allesamt eine lange (zwischen sieben und 25 Tagen) Rotationsperiode haben. Alle Sterne zeigen differentielle Rotation, allerdings sind die Messfehler aufgrund der nicht zufriedenstellenden Datenqualität von gleicher Größenordnung wie die Ergebnisse, ein Problem das bei STELLA nicht auftreten wird. Um die Konsistenz der Ergebnisse zu prüfen wurde wenn möglich sowohl eine Kreuzkorrelationsanalyse als auch die sheared-image Methode angewandt. Vier von diesen sieben Sternen weisen eine differentielle Rotation in umgekehrter Richtung auf als auf der Sonne zu sehen ist. Die restlichen drei Sterne weisen schwache, aber in der Richtung sonnenähnliche differentielle Rotation auf.Abschließend werden diese neuen Messungen mit bereits publizierten Werten kombiniert, und die so erhaltenen Daten auf Korrelationen zwischen differentieller Rotation, Rotationsperiode, Evolutionsstaus, Spektraltyp und Vorhandensein eines Doppelsterns überprüft. Alle Sterne zusammen zeigen eine signifikante Korrelation zwischen dem Betrag der differenziellen Rotation und der Rotationsperiode. Unterscheidet man zwischen den Richtungen der differentiellen Rotation, so bleibt nur eine Korrelation der Sterne mit antisolarem Verhalten. Darüberhinaus zeigt sich auch, dass Doppelsterne schwächer differentiell rotieren. N2 - The sun shows a wide variety of magnetic-activity related phenomena. The magnetic field responsible for this is generated by a dynamo process which is believed to operate in the tachocline, which is located at the bottom of the convection zone. This dynamo is driven in part by differential rotation and in part by magnetic turbulences in the convection zone. The surface differential rotation, one key ingredient of dynamo theory, can be measured by tracing sunspot positions.To extend the parameter space for dynamo theories, one can extend these measurements to other stars than the sun. The primary obstacle in this endeavor is the lack of resolved surface images on other stars. This can be overcome by the Doppler imaging technique, which uses the rotation-induced Doppler-broadening of spectral lines to compute the surface distribution of a physical parameter like temperature. To obtain the surface image of a star, high-resolution spectroscopic observations, evenly distributed over one stellar rotation period are needed. This turns out to be quite complicated for long period stars. The upcoming robotic observatory STELLA addresses this problem with a dedicated scheduling routine, which is tailored for Doppler imaging targets. This will make observations for Doppler imaging not only easier, but also more efficient.As a preview of what can be done with STELLA, we present results of a Doppler imaging study of seven stars, all of which show evidence for differential rotation, but unfortunately the errors are of the same order of magnitude as the measurements due to unsatisfactory data quality, something that will not happen on STELLA. Both, cross-correlation analysis and the sheared image technique where used to double check the results if possible. For four of these stars, weak anti-solar differential rotation was found in a sense that the pole rotates faster than the equator, for the other three stars weak differential rotation in the same direction as on the sun was found.Finally, these new measurements along with other published measurements of differential rotation using Doppler imaging, were analyzed for correlations with stellar evolution, binarity, and rotation period. The total sample of stars show a significant correlation with rotation period, but if separated into antisolar and solar type behavior, only the subsample showing anti-solar differential rotation shows this correlation. Additionally, there is evidence for binary stars showing less differential rotation as single stars, as is suggested by theory. All other parameter combinations fail to deliver any results due to the still small sample of stars available. T2 - Robotic telescopes & Doppler imaging : measuring differential rotation on long-period active stars KW - Teleskop KW - Robotik KW - Differentielle Rotation KW - Tomographie KW - Sternoberfläche KW - Sternaktivität KW - telescope KW - robotic KW - differential rotation KW - tomography KW - stellar surface KW - stellar activity Y1 - 2004 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-0001834 ER -