787 research outputs found
Geodynamo alpha-effect derived from box simulations of rotating magnetoconvection
The equations for fully compressible rotating magnetoconvection are
numerically solved in a Cartesian box assuming conditions roughly suitable for
the geodynamo. The mean electromotive force describing the generation of mean
magnetic flux by convective turbulence in the rotating fluid is directly
calculated from the simulations, and the corresponding alpha-coefficients are
derived. Due to the very weak density stratification the alpha-effect changes
its sign in the middle of the box. It is positive at the top and negative at
the bottom of the convection zone. For strong magnetic fields we also find a
clear downward advection of the mean magnetic field. Both of the simulated
effects have been predicted by quasi-linear computations (Soward, 1979;
Kitchatinov and Ruediger, 1992). Finally, the possible connection of the
obtained profiles of the EMF with mean-field models of oscillating
alpha^2-dynamos is discussed.Comment: 17 pages, 9 figures, submitted to Phys. Earth Planet. Inte
Graphene-protected iron layer on Ni(111)
Here we report the photoemission studies of intercalation process of Fe
underneath graphene layer on Ni(111). The process of intercalation was
monitored via XPS of corresponding core levels and UPS of the graphene-derived
states in the valence band. \textit{fcc}-Fe films with thickness of 2-5
monolayers at the interface between graphene and Ni(111) form epitaxial
magnetic layer passivated from the reactive environment, like for example
oxygen gas.Comment: 8 pages, 3 figure
Multiscale model of defective interfering particle replication for influenza A virus infection in animal cell culture
Cell culture-derived defective interfering particles (DIPs) are considered for antiviral therapy due to their ability to inhibit influenza A virus (IAV) production. DIPs contain a large internal deletion in one of their eight viral RNAs (vRNAs) rendering them replication-incompetent. However, they can propagate alongside their homologous standard virus (STV) during infection in a competition for cellular and viral resources. So far, experimental and modeling studies for IAV have focused on either the intracellular or the cell population level when investigating the interaction of STVs and DIPs. To examine these levels simultaneously, we conducted a series of experiments using highly different multiplicities of infections for STVs and DIPs to characterize virus replication in Madin-Darby Canine Kidney suspension cells. At several time points post infection, we quantified virus titers, viable cell concentration, virus-induced apoptosis using imaging flow cytometry, and intracellular levels of vRNA and viral mRNA using real-time reverse transcription qPCR. Based on the obtained data, we developed a mathematical multiscale model of STV and DIP co-infection that describes dynamics closely for all scenarios with a single set of parameters. We show that applying high DIP concentrations can shut down STV propagation completely and prevent virus-induced apoptosis. Interestingly, the three observed viral mRNAs (full-length segment 1 and 5, defective interfering segment 1) accumulated to vastly different levels suggesting the interplay between an internal regulation mechanism and a growth advantage for shorter viral RNAs. Furthermore, model simulations predict that the concentration of DIPs should be at least 10000 times higher than that of STVs to prevent the spread of IAV. Ultimately, the model presented here supports a comprehensive understanding of the interactions between STVs and DIPs during co-infection providing an ideal platform for the prediction and optimization of vaccine manufacturing as well as DIP production for therapeutic use
The alpha-effect and current helicity for fast sheared rotators
We explore the alpha-effect and the small-scale current helicity, for the
case of weakly compressible magnetically driven turbulence that is subjected to
the differential rotation. No restriction is applied to the amplitude of
angular velocity, i.e., the derivations presented are valid for an arbitrary
Coriolis number, though the differential rotation itself is assumed to be weak.
The expressions obtained are used to explore the possible distributions of
alpha-effect and current helicity in convection zones (CZ) of the solar-type
stars. The implications of the obtained results to the mean-field dynamo models
are discussed.Comment: 20 pages, 6 figure
Magnetoresistance, Micromagnetism, and Domain Wall Scattering in Epitaxial hcp Co Films
Large negative magnetoresistance (MR) observed in transport measurements of
hcp Co films with stripe domains were recently reported and interpreted in
terms of a novel domain wall (DW) scattering mechanism. Here detailed MR
measurements, magnetic force microscopy, and micromagnetic calculations are
combined to elucidate the origin of MR in this material. The large negative
room temperature MR reported previously is shown to be due to ferromagnetic
resistivity anisotropy. Measurements of the resistivity for currents parallel
(CIW) and perpendicular to DWs (CPW) have been conducted as a function of
temperature. Low temperature results show that any intrinsic effect of DWs
scattering on MR of this material is very small compared to the anisotropic MR.Comment: 5 pages, 5 Figures, submitted to PR
Der Marinemaler Eduard Edler (1887-1969): eine biographische Annäherung
Eduard Edler's life and work have not been closely examined to date. Since documents and reports by his contemporaries can scarcely be found, only a biographical rapprochement can be undertaken. Paintings from Edler's studio keep turning up in the art trade unaccompanied by any information on their production. At present, the following is known about him: Edler first made a name for himself during the 1930s as a ship portraitist and poster-painter in the service of German shipping companies. It was in those years - preceding the Second World War - that he scored his greatest successes. During the 1940s, when the one-hundredth anniversary of Hapag, Germany's largest shipping company was approaching in 1947, Edler received a major order. He was asked to do portraits of all the ships that had sailed under the flag of Hapag since 1847 and never been illustrated or photographed. Pictures of sister-ships or shipyard drawings were made available to him as bases to work from. He even painted ships which had been under construction in 1944 and 1945 and never been delivered to the Hamburg shipping company due to the outcome of the war, depicting them sailing the high seas under the Hapag flag. This order, however, explains why the largest single collection of his paintings is today owned by the Hapag-Lloyd AG. The exact number of ship portraits Edler painted is unknown, since a catalogue of his works does not exist. The planned transfer of his estate to the Museum für Hamburgische Geschichte, as fixed in his will, never came about. The documentary value of the paintings has to be examined from case to case, for Edler also had the gift of portraying ships about whose appearance he knew little, or next to nothing. After World War II he seems to have become less productive. The paintings located so far are primarily rendered in tempera rather than in oils. As far as his artistic abilities are concerned, it must be said that they are inferior to those of contemporaries who also worked as ship portraitists, such as Robert Schmidt-Hamburg or Walter Zeeden
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