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Now showing 1 - 10 of 7117
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    Transient radiation from a circular string of dipoles excited at superluminal velocity
    (Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik, 2014) Arkhipov, Rostislav M.; Arkhipov, Mikhail V.; Babushkin, Ihar; Tolmachev, Yurii A.
    This paper discusses the features of transient radiation from periodic one-dimensional resonant medium excited by ultrashort pulse. The case of circular geometry is considered for the harmonic distribution of the density of the particles along the circle. It is shown that a new frequency component arises in the spectrum of the scattered radiation in addition to the resonance frequency of medium. The new frequency appears both in the case of linear and nonlinear interaction, its value depends on the velocity of excitation pulse propagation and on the period of spatial modulation. In addition, the case when excitation moves at superluminal velocity and Cherenkov radiation arises is also studied.
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    Effects of (complementary) polyelectrolytes characteristics on composite calcium carbonate microparticles properties
    (Bucureşti : [Verlag nicht ermittelbar], 2017) Mic, Cristian Barbu; Mihai, Marcela; Varganici, Cristian Dragos; Schwarz, Simona; Scutaru, Dan; Simionescu, Bogdan C.
    This study follows the possibility to tune the thermal stability of some CaCO3/polymer composites by crystal growth from supersaturated solutions controlled by polymer structure or by using nonstoichiometric polyelectrolyte complexes (NPECs). As the ratio between the organic and inorganic parts in the composites controls the Ca2+/polymer network crosslinking density, the CaCO3/polymer weight ratio was kept constant at 50/1, varying the initial concentration of the polyanions solutions (0.05 or 0.06 wt.%), the NPECs molar ratio , n+/n- (0.2 or 0.4), or the inorganic precursors concentration (0.25 or 0.3 M). Poly(2-acrylamido-2-methylpropanesulfonic acid-co-acrylic acid) (PSA) and chondroitin-4-sulfate (CSA) were used as polyanions. Some NPEC dispersions, prepared with the same polyanions and poly(allylamine hydrochloride) (PAH), were also used for calcium carbonate crystallization. The characteristics of the prepared composites were investigated by scanning electron microscopy (SEM), flow particle image analysis (FPIA), particles charge density (CD), zeta-potential (ZP). The thermal stability of the composite particles was investigated as compared to bare CaCO3 microparticles prepared at the same initial inorganic concentrations.
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    A new bifunctional hybrid nanostructure as an active platform for photothermal therapy and MR imaging
    (London : Nature Publishing Group, 2016) Khafaji, Mona; Vossoughi, Manouchehr; Hormozi-Nezhad, M. Reza; Dinarvand, Rassoul; Börrnert, Felix; Irajizad, Azam
    As a bi-functional cancer treatment agent, a new hybrid nanostructure is presented which can be used for photothermal therapy by exposure to one order of magnitude lower laser powers compared to similar nanostructures in addition to substantial enhancment in magnetic resonance imaging (MRI) contrast. This gold-iron oxide hybrid nanostructure (GIHN) is synthesized by a cost-effective and high yield water-based approach. The GIHN is sheilded by PEG. Therefore, it shows high hemo and biocompatibility and more than six month stability. Alongside earlier nanostructures, the heat generation rate of GIHN is compareable with surfactnat-capped gold nanorods (GNRs). Two reasons are behind this enhancement: Firstly the distance between GNRs and SPIONs is adjusted in a way that the surface plasmon resonance of the new nanostructure is similar to bare GNRs and secondly the fraction of GNRs is raised in the hybrid nanostructure. GIHN is then applied as a photothermal agent using laser irradiation with power as low as 0.5−2 and only 32% of human breast adenocarcinoma cells could survive. The GIHN also acts as a dose-dependent transvers relaxation time (T2) MRI contrast agent. The results show that the GINH can be considered as a good candidate for multimodal photothermal therapy and MRI.
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    Direct nitrous oxide emissions from oilseed rape cropping – a meta-analysis
    (Milton Park : Taylor & Francis, 2014) Walter, Katja; Don, Axel; Fuß, Roland; Kern, Jürgen; Drewer, Julia; Flessa, Heinz
    Oilseed rape is one of the leading feedstocks for biofuel production in Europe. The climate change mitigation effect of rape methyl ester (RME) is particularly challenged by the greenhouse gas (GHG) emissions during crop production, mainly as nitrous oxide (N2O) from soils. Oilseed rape requires high nitrogen fertilization and crop residues are rich in nitrogen, both potentially causing enhanced N2O emissions. However, GHG emissions of oilseed rape production are often estimated using emission factors that account for crop-type specifics only with respect to crop residues. This meta-analysis therefore aimed to assess annual N2O emissions from winter oilseed rape, to compare them to those of cereals and to explore the underlying reasons for differences. For the identification of the most important factors, linear mixed effects models were fitted with 43 N2O emission data points deriving from 12 different field sites. N2O emissions increased exponentially with N-fertilization rates, but interyear and site-specific variability were high and climate variables or soil parameters did not improve the prediction model. Annual N2O emissions from winter oilseed rape were 22% higher than those from winter cereals fertilized at the same rate. At a common fertilization rate of 200 kg N ha−1 yr−1, the mean fraction of fertilizer N that was lost as N2O-N was 1.27% for oilseed rape compared to 1.04% for cereals. The risk of high yield-scaled N2O emissions increased after a critical N surplus of about 80 kg N ha−1 yr−1. The difference in N2O emissions between oilseed rape and cereal cultivation was especially high after harvest due to the high N contents in oilseed rape's crop residues. However, annual N2O emissions of winter oilseed rape were still lower than predicted by the Stehfest and Bouwman model. Hence, the assignment of oilseed rape to the crop-type classes of cereals or other crops should be reconsidered.
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    Efficient coupling of inhomogeneous current spreading and dynamic electro-optical models for broad-area edge-emitting semiconductor devices
    (Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik, 2017) Radziunas, Mindaugas; Zeghuzi, Anissa; Fuhrmann, Jürgen; Koprucki, Thomas; Wünsche, Hans-Jürgen; Wenzel, Hans; Bandelow, Uwe
    We extend a 2 (space) + 1 (time)-dimensional traveling wave model for broad-area edgeemitting semiconductor lasers by a model for inhomogeneous current spreading from the contact to the active zone of the laser. To speedup the performance of the device simulations, we suggest and discuss several approximations of the inhomogeneous current density in the active zone.
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    Simulation of the future sea level contribution of Greenland with a new glacial system model
    (Katlenburg-Lindau : Copernicus, 2018) Calov, Reinhard; Beyer, Sebastian; Greve, Ralf; Beckmann, Johanna; Willeit, Matteo; Kleiner, Thomas; Rückamp, Martin; Humbert, Angelika; Ganopolski, Andrey
    We introduce the coupled model of the Greenland glacial system IGLOO 1.0, including the polythermal ice sheet model SICOPOLIS (version 3.3) with hybrid dynamics, the model of basal hydrology HYDRO and a parameterization of submarine melt for marine-terminated outlet glaciers. The aim of this glacial system model is to gain a better understanding of the processes important for the future contribution of the Greenland ice sheet to sea level rise under future climate change scenarios. The ice sheet is initialized via a relaxation towards observed surface elevation, imposing the palaeo-surface temperature over the last glacial cycle. As a present-day reference, we use the 1961-1990 standard climatology derived from simulations of the regional atmosphere model MAR with ERA reanalysis boundary conditions. For the palaeo-part of the spin-up, we add the temperature anomaly derived from the GRIP ice core to the years 1961-1990 average surface temperature field. For our projections, we apply surface temperature and surface mass balance anomalies derived from RCP 4.5 and RCP 8.5 scenarios created by MAR with boundary conditions from simulations with three CMIP5 models. The hybrid ice sheet model is fully coupled with the model of basal hydrology. With this model and the MAR scenarios, we perform simulations to estimate the contribution of the Greenland ice sheet to future sea level rise until the end of the 21st and 23rd centuries. Further on, the impact of elevation-surface mass balance feedback, introduced via the MAR data, on future sea level rise is inspected. In our projections, we found the Greenland ice sheet to contribute between 1.9 and 13.0 cm to global sea level rise until the year 2100 and between 3.5 and 76.4 cm until the year 2300, including our simulated additional sea level rise due to elevation-surface mass balance feedback. Translated into additional sea level rise, the strength of this feedback in the year 2100 varies from 0.4 to 1.7 cm, and in the year 2300 it ranges from 1.7 to 21.8 cm. Additionally, taking the Helheim and Store glaciers as examples, we investigate the role of ocean warming and surface runoff change for the melting of outlet glaciers. It shows that ocean temperature and subglacial discharge are about equally important for the melting of the examined outlet glaciers.
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    Inferring causation from time series in Earth system sciences
    ([London] : Nature Publishing Group UK, 2019) Runge, Jakob; Bathiany, Sebastian; Bollt, Erik; Camps-Valls, Gustau; Coumou, Dim; Deyle, Ethan; Glymour, Clark; Kretschmer, Marlene; Mahecha, Miguel D.; Muñoz-Marí, Jordi; van Nes, Egbert H.; Peters, Jonas; Quax, Rick; Reichstein, Markus; Scheffer, Marten; Schölkopf, Bernhard; Spirtes, Peter; Sugihara, George; Sun, Jie; Zhang, Kun; Zscheischler, Jakob
    The heart of the scientific enterprise is a rational effort to understand the causes behind the phenomena we observe. In large-scale complex dynamical systems such as the Earth system, real experiments are rarely feasible. However, a rapidly increasing amount of observational and simulated data opens up the use of novel data-driven causal methods beyond the commonly adopted correlation techniques. Here, we give an overview of causal inference frameworks and identify promising generic application cases common in Earth system sciences and beyond. We discuss challenges and initiate the benchmark platform to close the gap between method users and developers. © 2019, The Author(s).
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    Entwicklung eines Plasma-Emissionsdetektors für die Bestimmung von Schwermetall-Spezies für Anwendungen in der Umweltanalytik, Lebensmittel-Qualitätssicherung und Umweltmedizin : Schlussbericht ; (Bewilligungszeitraum: 01.02.2009 - 31.07.2012)
    (Greifswald : Leibniz-Institut für Plasmaforschung und Technologie, 2012) Wolfgang Buscher, Wolfgang Buscher; Ehlbeck, Jörg; Piechotta, Christian
    [no abstract available]
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    Chirped photonic crystal for spatially filtered optical feedback to a broad-area laser
    (Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik, 2018) Brée, Carsten; Gailevicius, Darius; Purlys, Vytautas; Werner, Guillermo Garre; Staliunas, Kestutis; Rathsfeld, Andreas; Schmidt, Gunther; Radziunas, Mindaugas
    We derive and analyze an efficient model for reinjection of spatially filtered optical feedback from an external resonator to a broad area, edge emitting semiconductor laser diode. Spatial filtering is achieved by a chirped photonic crystal, with variable periodicity along the optical axis and negligible resonant backscattering. The optimal chirp is obtained from a genetic algorithm, which yields solutions that are robust against perturbations. Extensive numerical simulations of the composite system with our optoelectronic solver indicate that spatially filtered reinjection enhances lower-order transversal optical modes in the laser diode and, consequently, improves the spatial beam quality.
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    Large-scale globally propagating coronal waves
    (Katlenburg-Lindau : MPS, 2015) Warmuth, Alexander
    Large-scale, globally propagating wave-like disturbances have been observed in the solar chromosphere and by inference in the corona since the 1960s. However, detailed analysis of these phenomena has only been conducted since the late 1990s. This was prompted by the availability of high-cadence coronal imaging data from numerous spaced-based instruments, which routinely show spectacular globally propagating bright fronts. Coronal waves, as these perturbations are usually referred to, have now been observed in a wide range of spectral channels, yielding a wealth of information. Many findings have supported the “classical” interpretation of the disturbances: fast-mode MHD waves or shocks that are propagating in the solar corona. However, observations that seemed inconsistent with this picture have stimulated the development of alternative models in which “pseudo waves” are generated by magnetic reconfiguration in the framework of an expanding coronal mass ejection. This has resulted in a vigorous debate on the physical nature of these disturbances. This review focuses on demonstrating how the numerous observational findings of the last one and a half decades can be used to constrain our models of large-scale coronal waves, and how a coherent physical understanding of these disturbances is finally emerging.