Contact-induced charge contributions to non-local spin transport measurements in Co/MgO/graphene devices

Recently, it has been shown that oxide barriers in graphene-based non-local spin-valve structures can be the bottleneck for spin transport. The barriers may cause spin dephasing during or right after electrical spin injection which limit spin transport parameters such as the spin lifetime of the whole device. An important task is to evaluate the quality of the oxide barriers of both spin injection and detection contacts in a fabricated device. To address this issue, we discuss the influence of spatially inhomogeneous oxide barriers and especially conducting pinholes within the barrier on the background signal in non-local measurements of graphene/MgO/Co spin-valve devices. By both simulations and reference measurements on devices with non-ferromagnetic electrodes, we demonstrate that the background signal can be caused by inhomogeneous current flow through the oxide barriers. As a main result, we demonstrate the existence of charge accumulation next to the actual spin accumulation signal in non-local voltage measurements, which can be explained by a redistribution of charge carriers by a perpendicular magnetic field similar to the classical Hall effect. Furthermore, we present systematic studies on the phase of the low frequency non-local ac voltage signal which is measured in non-local spin measurements when applying ac lock-in techniques. This phase has so far widely been neglected in the analysis of non-local spin transport. We demonstrate that this phase is another hallmark of the homogeneity of the MgO spin injection and detection barriers. We link backgate dependent changes of the phase to the interplay between the capacitance of the oxide barrier to the quantum capacitance of graphene.Comment: 19 pages, 7 figure

RCP8.5-projected changes in German Bight storm surge characteristics from regionalized ensemble simulations for the end of the twenty-first century

This study investigates climate-induced changes in height, frequency and duration of storm surges in the German Bight. The regionally coupled climate model system MPIOM-REMO with a focus on the North Sea has been utilized to dynamically downscale 30 members of the global climate model system MPI-ESM1.1-LR for the historical period 1950–2005 and a continuation until 2099 with the RCP8.5 scenario. Results of all members have been collected into the historical (1970–1999) and the rcp85 (2070–2099) data pools amounting to 900 years of the corresponding climate state. The global mean sea level rise was not considered. Nevertheless, the mean ensemble German Bight SSH trend amounts to about 13 ± 1 cm/century (PI control: 3 cm/century) due to adaptation of the ocean circulation to the changing climatic conditions. Storm surges were defined as SSH above mean high tidal water plus 1.5, 2.5, 3.5 m for “regular”, heavy, extreme storm surges, and then clustered to events. Our simulated storm surge events show a clear location-dependent increase in frequency (6–11), median duration (4–24), and average duration (9–20) in the German Bight. Only along the central German Bight coast (Cuxhaven), longer lasting events gain more relevance. Heavy storm surge events show also a strong increase in frequency (7–34) and average duration (10–22). Maximum sea levels during storm events increase strongest and most significant along the northern German Bight and Danish coasts with more than 30 cm/century for the 60-year return period at Hörnum and 10–15 cm/century for shorter return periods. Levels of return periods shorter than a few years significantly increase everywhere along the southern German Bight coasts (around 5 cm/century for the 2-year return period). Highest SSH maxima do not change, and consequently, extreme storm surge events show hardly any response to climate change. Furthermore, our results indicate a shift of seasonality from the last to the first quarter of a year. As the main driver for the encountered alteration of German Bight storm surge characteristics, we identified a change in wind conditions with a pronounced increase of frequency of strong westerly winds

Inter-annual and inter-specific differences in the drift of fish eggs and yolksac larvae in the North Sea: A biophysical modeling approach

We employed 3-D biophysical modeling and dispersion kernel analysis to explore inter-annual and inter-specific differences in the drift trajectories of eggs and yolksac larvae of plaice (Pleuronectes platessa), Atlantic cod (Gadus morhua), sprat (Sprattus sprattus) and horse mackerel (Trachurus trachurus) in the North Sea. In this region, these four species exhibit peak spawning during the boreal winter, late winter/early spring, late spring/early summer, and mid-summer respectively, but utilize the same spawning locations (our simulations included Dogger Bank, Southern Bight and the German Bight). Inter-annual differences in the temperature history, and an increase in the area of dispersion and final distribution at the end of the yolksac phase were more pronounced (and related to the North Atlantic Oscillation) for winter- and early spring-spawners compared to late spring/summer spawners. The progeny of the latter experienced the largest (up to 10-fold) inter-annual differences in drift distances, although absolute drift distances were modest (~2 to 30 km) when compared to those of the former (~ 20 to 130 km). Our results highlight the complex interplay that exists between the specific life history strategies of the different species and the impacts of the variability in (climate-driven) physical factors during the earliest life stages of marine fish. Resumen: Diferencias interanuales e interespecíficas en la deriva de huevos y larvas lecitotróficas en el mar Norte: Aproximación a través un modelo biofísico. – En este trabajo utilizamos un modelo 3-D físico-biológico y un análisis de dispersión del núcleo para investigar las diferencias interespecíficas e interanuales en las trayectorias de la deriva de huevos y larvas lecitotróficas de la solla (Pleuronectes platessa), el bacalao Atlántico (Gadus morhua), el espadín (Sprattus sprattus) y el jurel (Trachurus trachurus) en el Mar del Norte. En esta región, las especies estudiadas muestran distintos picos de distintos desoves en el tiempo: invierno boreal, invierno tardío/primavera temprana, primavera tardía/verano temprano y mitad del verano, respectivamente, aunque comparten las mismas zonas de desove. Las simulaciones efectuadas corresponden a tres de estas zonas: Dogger Bank, Southern Bight y German Bight. Los resultados mostraron diferencias interanuales en la temperatura experimentada por las larvas, en el área de dispersión y en el patrón de distribución al final del estadio lecitotrófico, que fueron más evidentes en el bacalao Atlántico, en comparacion con el espadín. Así mismo, estos factores estuvieron correlacionados con la Oscilación del Atlántico Norte. La progenie del espadín, además, mostró la mayor variación interanual en la distancia de dispersión, siendo hasta 10 veces mayor, aunque la distancia absoluta alcanzada fue relativamente modesta (~2-30 km) en comparación con la observada para el bacalao Atlántico (~20-130 km). Nuestros resultados subrayan la compleja interacción que existe, durante los estadios tempranos del desarrollo de peces marinos, entre las estrategias ecológica

Performance of compressed sensing for fluorine-19 magnetic resonance imaging at low signal-to-noise ratio conditions

PURPOSE: To examine the performance of compressed sensing (CS) in reconstructing low signal-to-noise ratio (SNR) (19)F MR signals that are close to the detection threshold and originate from small signal sources with no a priori known location. METHODS: Regularization strength was adjusted automatically based on noise level. As performance metrics, root-mean-square deviations, true positive rates (TPRs), and false discovery rates were computed. CS and conventional reconstructions were compared at equal measurement time and evaluated in relation to high-SNR reference data. (19)F MR data were generated from a purpose-built phantom and benchmarked against simulations, as well as from the experimental autoimmune encephalomyelitis mouse model. We quantified the signal intensity bias and introduced an intensity calibration for in vivo data using high-SNR ex vivo data. RESULTS: Low-SNR (19)F MR data could be reliably reconstructed. Detection sensitivity was consistently improved and data fidelity was preserved for undersampling and averaging factors of α = 2 or = 3. Higher α led to signal blurring in the mouse model. The improved TPRs at α = 3 were comparable to a 2.5-fold increase in measurement time. Whereas CS resulted in a downward bias of the (19)F MR signal, Fourier reconstructions resulted in an unexpected upward bias of similar magnitude. The calibration corrected signal-intensity deviations for all reconstructions. CONCLUSION: CS is advantageous whenever image features are close to the detection threshold. It is a powerful tool, even for low-SNR data with sparsely distributed (19)F signals, to improve spatial and temporal resolution in (19)F MR applications

Investigation on the trophic state of the North Sea for three years (1994?1996) simulated with the ecosystem model ERSEM ? the role of a sharp NAOI decline

International audienceApplying the ecosystem model ERSEM to the Northwest-European shelf (48°?63°N, 15°W?12°E) the years 1994-1996 were simulated, which exhibit an extremely strong transition in North Atlantic Oscillation index (NAOI): from a high-NAOI to a low-NAOI regime. In order to be far enough from the boundaries of the model area the results and budgets are focussed on the North Sea area. For this region the model was validated against climatological values of nitrate as representative nutrient. For all three years the North Sea was found to be net heterotrophic: organic material was imported, inorganic material was exported. The strength of this "remineralisation-machine" was large during NAOI-high years (1994 and 1995). It was weaker in 1996 with a low NAOI. This was caused by higher net primary production in the northern North Sea during summer 1996. In this year the stratification was weaker and began later allowing the deep nutrient-rich water in the northern North Sea to be mixed into the upper layers also during early summer

Trajectory Model for Identification of Oil Spill Around the Coast of Pari Island, Seribu Islands, North Jakarta

Oil spills at sea are common in the shipping lanes of the ship as well as the locations of offshore oil drilling. Unfortunately, in every occurrence of the oil spill, we only see the effects after the occurrence, without knowing the original source. Indonesian Numerical Coastal Environmental Assessment (IndoNACE) is research collaboration between Indonesian and Germany by applying satellite data, numerical modeling, and field observations to make an assessment on environmental consequences to oil spills at sea. One of the locations of these research activities is Pari Island, Seribu Islands, North Jakarta. Simulation of hydrodynamic models around Pulau Pari with Hamburg Shelf Ocean Model (HAMSOM) was performed using tides, surface winds, and density difference of seawater as input. Afterwards, by utilizing results of the hydrodynamic model, the spreading of oil spills as well as the origin of the oil spills were estimated using forward and backward trajectory models, respectively. In the case study of Pari Island, there is a presence of thin film of oil in 5 November 2015 that disappears after one day. We suggest that the origin of oil spills were found on the beach Pari Island is expected from the east - northeast of Thousand Islands and is likely from the subsea pipeline which runs from the north to the city of Jakarta or shipping lanes through the Indonesian archipelagic sea lanes (ALKI) I of Karimata Strait up to Java Sea and the Jakarta Bay

Probing renal blood volume with magnetic resonance imaging

Damage to the kidney substantially reduces life expectancy. Renal tissue hypoperfusion and hypoxia are key elements in the pathophysiology of acute kidney injury and its progression to chronic kidney disease. In vivo assessment of renal haemodynamics and tissue oxygenation remains a challenge. Blood oxygenation level dependent (BOLD) magnetic resonance imaging (MRI) is sensitive to changes in the effective transversal relaxation time (T(2)*) in vivo, is non-invasive and indicative of renal tissue oxygenation. However, the renal T(2)* to tissue pO(2) relationship is not governed exclusively by renal blood oxygenation, but is affected by physiological confounders with alterations in renal blood volume fraction (BVf) being of particular relevance. To decipher this interference probing renal BVf is essential for the pursuit of renal MR oximetry. Superparamagnetic iron oxide nanoparticle (USPIO) preparations can be used as MRI visible blood pool markers for detailing alterations in BVf. This review promotes the opportunities of MRI based assessment of renal BVf. Following an outline on the specifics of renal oxygenation and perfusion, changes in renal BVf upon interventions and their potential impact on renal T(2)* are discussed. We also describe the basic principles of renal BVf assessment using ferumoxytol enhanced MRI in the equilibrium concentration regime. We demonstrate that ferumoxytol does not alter control of renal haemodynamics and oxygenation. Preclinical applications of ferumoxytol enhanced renal MRI as well as considerations for its clinical implementation for examining renal BVf changes are provided alongside practical considerations. Finally, we explore the future directions of MRI based assessment of renal BVf

Genetic population structure of sympatric and allopatric populations of Baltic ciscoes (Coregonus albula complex, Teleostei, Coregonidae)

<p>Abstract</p> <p>Background</p> <p>Teleost fishes of the Coregonidae are good model systems for studying postglacial evolution, adaptive radiation and ecological speciation. Of particular interest is whether the repeated occurrence of sympatric species pairs results from <it>in-situ </it>divergence from a single lineage or from multiple invasions of one or more different lineages. Here, we analysed the genetic structure of Baltic ciscoes (<it>Coregonus albula </it>complex), examining 271 individuals from 8 lakes in northern Germany using 1244 polymorphic AFLP loci. Six lakes had only one population of <it>C. albula </it>while the remaining two lakes had <it>C. albula </it>as well as a sympatric species (<it>C. lucinensis </it>or <it>C. fontanae</it>).</p> <p>Results</p> <p>AFLP demonstrated a significant population structure (Bayesian <it>θ</it>^B= 0.22). Lower differentiation between allopatric (<it>θ</it>^B= 0.028) than sympatric (0.063-0.083) populations contradicts the hypothesis of a sympatric origin of taxa, and there was little evidence for stocking or ongoing hybridization. Genome scans found only three loci that appeared to be under selection in both sympatric population pairs, suggesting a low probability of similar mechanisms of ecological segregation. However, removal of all non-neutral loci decreased the genetic distance between sympatric pairs, suggesting recent adaptive divergence at a few loci. Sympatric pairs in the two lakes were genetically distinct from the six other <it>C. albula </it>populations, suggesting introgression from another lineage may have influenced these two lakes. This was supported by an analysis of isolation-by-distance, where the drift-gene flow equilibrium observed among allopatric populations was disrupted when the sympatric pairs were included.</p> <p>Conclusions</p> <p>While the population genetic data alone can not unambiguously uncover the mode of speciation, our data indicate that multiple lineages may be responsible for the complex patterns typically observed in <it>Coregonus</it>. Relative differences within and among lakes raises the possibility that multiple lineages may be present in northern Germany, thus understanding the postglacial evolution and speciation in the <it>C. albula </it>complex requires a large-scale phylogenetic analysis of several potential founder lineages.</p

Essential practical steps for MRI of the kidney in experimental research

Magnetic resonance imaging (MRI) is an emerging method to obtain valuable functional and structural information about the kidney noninvasively. Before performing specialized MR measurements for probing tissue structure and function, some essential practical steps are needed, which are common for most applications. Here we describe in a step-by-step manner how to (1) achieve the double-oblique slice orientation coronal-to-the-kidney, (2) adapt the scan protocol for avoiding aortic flow artifacts and covering both kidneys, (3) perform localized shimming on the kidney, and (4) check perfusion in the large renal blood vessels using time-of-flight (TOF) angiography. The procedures are tailored to preclinical MRI but conceptionally are also applicable to human MRI.This chapter is based upon work from the COST Action PARENCHIMA, a community-driven network funded by the European Cooperation in Science and Technology (COST) program of the European Union, which aims to improve the reproducibility and standardization of renal MRI biomarkers. This experimental protocol chapter explains the initial and essential MRI steps that precede specific functional and structural MR imaging techniques (T(1)- and T(2)*-mapping, DWI , ASL , etc.), which are described in separate chapters