Unusual spin-wave population in nickel after femtosecond laser pulse excitation

The spin-wave relaxation mechanisms after intense laser excitation in ferromagnetic nickel films are investigated with all-optical pump-probe experiments. Uniform precession (Kittel mode), Damon-Eshbach surface modes and perpendicular standing spin waves can be identified by their dispersion f(H). However, different to other ferromagnets f(H) deviates from the expected behavior. Namely, a mode discontinuity is observed, that can be attributed to a non-linear process. Above a critical field the power spectrum reveals a redistribution of the energy within the spin-wave spectrum populated.Comment: 7 pages, 6 figure

Photo-magnonics in two-dimensional antidot lattices

Wesentlicher Gegenstand der vorliegenden (kumulativen) Dissertation ist die ausschließlich optische Erzeugung und Detektion sowie gezielte Manipulation magnetischer Anregungen, sogenannter Spinwellen oder Magnonen. Insbesondere werden die Mechanismen und Prozesse diskutiert, die zur Beobachtung wohldefinierter Spinwellenmoden in dünnen magnetischen Filmen führen, nachdem ein intensiver, ultrakurzer Laserpuls absorbiert wurde. Eine langreichweitig geordnete, periodische Strukturierung der magnetischen Filme (in diesem Fall mit Löchern) ist sodann gleichbedeutend mit der Schaffung magnetischer Metamaterialien (d.h. magnonischer Kristalle). Abhängig von Wirtsmaterial (Nickel oder Kobalt-Eisen-Bor) und strukturellen Eigenschaften der Lochgitter (Periodizität, strukturelle Einheit) ist die Erzeugung oder Unterdrückung bestimmter magnetischer Moden möglich. So führt die vergleichsweise große intrinsische magnetische Dämpfung in Nickel zur Ausbildung lokalisierter Spinwellen, während wegen der geringen Dämpfung in Kobalt-Eisen-Bor ausgedehnte Blochwellen beobachtet werden. Deren Wellenlänge ist zudem einstellbar mittels der Periodizität des Metamaterials und wird anhand numerischer Berechnungen der (magnonischen) Bandstrukturen nachvollzogen. Zuletzt werden auf Basis dieser Ergebnisse mögliche Anwendungen magnonischer Kristalle diskutiert. Hierbei liegt ein Schwerpunkt auf anisotropen Lochgittern und deren Perspektive als Spinwellenfilter

Tracking seasonal changes in North Sea zooplankton trophic dynamics using stable isotopes

Trophodynamics of meso-zooplankton in the North Sea (NS) were assessed at a site in the southern NS, and at a shallow and a deep site in the central NS. Offshore and neritic species from different ecological niches, including Calanus spp., Temora spp. and Sagitta spp., were collected during seven cruises over 14 months from 2007 to 2008. Bulk stable isotope (SI) analysis, phospholipid-derived fatty acid (PLFA) compositions, and δ 13CPLFA data of meso-zooplankton and particulate organic matter (POM) were used to describe changes in zooplankton relative trophic positions (RTPs) and trophodynamics. The aim of the study was to test the hypothesis that the RTPs of zooplankton in the North Sea vary spatially and seasonally, in response to hydrographic variability, with the microbial food web playing an important role at times. Zooplankton RTPs tended to be higher during winter and lower during the phytoplankton bloom in spring. RTPs were highest for predators such as Sagitta sp. and Calanus helgolandicus and lowest for small copepods such as Pseudocalanus elongatus and zoea larvae (Brachyura). δ 15NPOM-based RTPs were only moderate surrogates for animals’ ecological niches, because of the plasticity in source materials from the herbivorous and the microbial loop food web. Common (16:0) and essential (eicosapentaenoic acid, EPA and docosahexaenoic acid, DHA) structural lipids showed relatively constant abundances. This could be explained by incorporation of PLFAs with δ 13C signatures which followed seasonal changes in bulk δ 13CPOM and PLFA δ 13CPOM signatures. This study highlighted the complementarity of three biogeochemical approaches for trophodynamic studies and substantiated conceptual views of size-based food web analysis, in which small individuals of large species may be functionally equivalent to large individuals of small species. Seasonal and spatial variability was also important in altering the relative importance of the herbivorous and microbial food webs

Profiling host ANP32A splicing landscapes to predict influenza A virus polymerase adaptation

Species' differences in cellular factors limit avian influenza A virus (IAV) zoonoses and human pandemics. The IAV polymerase, vPol, harbors evolutionary sites to overcome restriction and determines virulence. Here, we establish host ANP32A as a critical driver of selection, and identify host-specific ANP32A splicing landscapes that predict viral evolution. We find that avian species differentially express three ANP32A isoforms diverging in a vPol-promoting insert. ANP32As with shorter inserts interact poorly with vPol, are compromised in supporting avian-like IAV replication, and drive selection of mammalian-adaptive vPol sequences with distinct kinetics. By integrating selection data with multi-species ANP32A splice variant profiling, we develop a mathematical model to predict avian species potentially driving (swallow, magpie) or maintaining (goose, swan) mammalian-adaptive vPol signatures. Supporting these predictions, surveillance data confirm enrichment of several mammalian-adaptive vPol substitutions in magpie IAVs. Profiling host ANP32A splicing could enhance surveillance and eradication efforts against IAVs with pandemic potential