Microscopic Theory for Coupled Atomistic Magnetization and Lattice Dynamics

A coupled atomistic spin and lattice dynamics approach is developed which merges the dynamics of these two degrees of freedom into a single set of coupled equations of motion. The underlying microscopic model comprises local exchange interactions between the electron spin and magnetic moment and the local couplings between the electronic charge and lattice displacements. An effective action for the spin and lattice variables is constructed in which the interactions among the spin and lattice components are determined by the underlying electronic structure. In this way, expressions are obtained for the electronically mediated couplings between the spin and lattice degrees of freedom, besides the well known inter-atomic force constants and spin-spin interactions. These former susceptibilities provide an atomistic ab initio description for the coupled spin and lattice dynamics. It is important to notice that this theory is strictly bilinear in the spin and lattice variables and provides a minimal model for the coupled dynamics of these subsystems and that the two subsystems are treated on the same footing. Questions concerning time-reversal and inversion symmetry are rigorously addressed and it is shown how these aspects are absorbed in the tensor structure of the interaction fields. By means of these results regarding the spin-lattice coupling, simple explanations of ionic dimerization in double anti-ferromagnetic materials, as well as, charge density waves induced by a non-uniform spin structure are given. In the final parts, a set of coupled equations of motion for the combined spin and lattice dynamics are constructed, which subsequently can be reduced to a form which is analogous to the Landau-Lifshitz-Gilbert equations for spin dynamics and damped driven mechanical oscillator for the ...Comment: 22 pages, including 7 pages of Appendix and references, 6 figure

Droplet digital PCR as a tool for investigating dynamics of cryptic symbionts

Interactions among symbiotic organisms and their hosts are major drivers of ecological and evolutionary processes. Monitoring the infection patterns among natural populations and identifying factors affecting these interactions are critical for understanding symbiont–host relationships. However, many of these interactions remain understudied since the knowledge about the symbiont species is lacking, which hinders the development of appropriate tools. In this study, we developed a digital droplet PCR (ddPCR) assay based on apicomplexan COX1 gene to detect an undescribed agamococcidian symbiont. We show that the method gives precise and reproducible results and enables detecting cryptic symbionts in low target concentration. We further exemplify the assay's use to survey seasonally sampled natural host (Pygospio elegans) populations for symbiont infection dynamics. We found that symbiont prevalence differs spatially but does not show seasonal changes. Infection load differed between populations and was low in spring and significantly increased towards fall in all populations. We also found that the symbiont prevalence is affected by host length and population density. Larger hosts were more likely to be infected, and high host densities were found to have a lower probability of infection. The observed variations could be due to characteristics of both symbiont and host biology, especially the seasonal variation in encounter rates. Our findings show that the developed ddPCR assay is a robust tool for detecting undescribed symbionts that are otherwise difficult to quantify, enabling further insight into the impact cryptic symbionts have on their hosts.peerReviewe

Sediment Characterization from the Saale 2013 Flooding Event

Die Sedimentablagerungen des Saale-Hochwassers im Frühjahr 2013 werden charakterisiert auf der Basis von Probenahmen aus den überfluteten Uferbereichen im Stadtgebiet von Halle. Diese Ablagerungen werden zum einen klassifiziert nach Art des Sediments (Sedimenteigenschaften: Mächtigkeit, Grobkorn-Anteil, Anteil an organischer Substanz, Trockenfestigkeit) und zum anderen nach Art ihres Ablagerungsraumes  (Lokationseigenschaften: Abstand vom Saale-Flussbett, Bedeckung durch Vegetation, Relief, Untergrundbeschaffenheit). Diese Sediment- und Lokationskriterien werden hinsichtlich der Häufigkeit ihres Auftretens und eines möglichen  Zusammenhangs zwischen Sediment- und Lokationseigenschaften untersucht. Es wird gezeigt, dass sich die Zusammensetzung der Sedimente im Laufe ihres Transports von Süd nach Nord durch das Stadtgebiet von Halle verändert.  Es kommt bis in das Gebiet von Throta/Lettin zu einer  Verringerung der mittleren Korngröße und zugleich zu einer Veränderung der Kornverteilung der abgelagerten Hochwasser-Sedimente. Die Dominanz feinkörniger Sedimentanteile wird zunehmend deutlich, je weiter nördlich die Ablagerung  stattgefunden hat. Außerdem begünstigen weiche  Untergrundbedingungen (wie Wiesen, Kieswege oder  unbefestigte Straßen) die Ablagerung von relativ mächtigeren Sedimenten > 1mm. Im Gegensatz dazu dominieren auf festem Untergrund (wie befestigten Straßen und Wegen) Sedimentablagerungen von < 1 mm Mächtigkeit. Aus der durchschnittlichen Mächtigkeit der beprobten, feinkörnigen Hochwasserablagerungen mit Korndurchmessern < 2 mm lässt sich ein transportiertes Sedimentvolumen von 5 bis 15 l/m2 ableiten. Im gesamten Überflutungsgebiet von ca. 32,8 km2 in Halle ergibt sich ein geschätztes Sedimentvolumen von 3x105 m3 an feinkörnigen Ablagerungen durch das Frühjahrs-Hochwasser 2013.Sediment deposition, after the Saale river flooding event of 2013, is characterized here based on samples taken along the river banks in the flooded region. Based on classifications having to do with both sediment (thickness of sediment; percentage of coarse material; organic material presence; dry strength of the sediment) as well as location (distance to the Saale river; vegetation cover; relief; firmness of the basal layer beneath the flood sediments) it is shown that the transport of fine-grained sediment along the Saale had its direction changed by the flooding in the region between Halle-Trotha and Lettin. There was a sorting of the grain sizes that, on the one hand, lowered the medium grain sizes and, on the other hand, altered the grain size distribution at the same time. The preponderance of fine-grained sediment is more noticeable the further north one progresses along the Saale river. In addition, soft basal  materials such as meadows, gravel paths or dirt roads are associated with relatively thick sediment that is almost always more than 1 mm. In contrast on firm grounds, such as paved roads and sidewalks, the dominance is one of thicknesses smaller than 1 mm. The average thickness of the fine-grained material indicates a transported sediment volume of between about 5 to 15 l/m2. In the total flooded region in Halle of around 32.8 km2 one can estimate some 3x105 m3 of fine-grained material was deposited

Europium cyclooctatetraene nanowire carpets: A low-dimensional, organometallic, and ferromagnetic insulator

We investigate the magnetic and electronic properties of europium cyclooctatetraene (EuCot) nanowires by means of low-temperature X-ray magnetic circular dichroism (XMCD) and scanning tunneling microscopy (STM) and spectroscopy (STS). The EuCot nanowires are prepared in situ on a graphene surface. STS measurements identify EuCot as an insulator with a minority band gap of 2.3 eV. By means of Eu M5,4 edge XMCD, orbital and spin magnetic moments of (−0.1 ± 0.3)μB and (+7.0 ± 0.6)μB, respectively, were determined. Field-dependent measurements of the XMCD signal at the Eu M5 edge show hysteresis for grazing X-ray incidence at 5 K, thus confirming EuCot as a ferromagnetic material. Our density functional theory calculations reproduce the experimentally observed minority band gap. Modeling the experimental results theoretically, we find that the effective interatomic exchange interaction between Eu atoms is on the order of millielectronvolts, that magnetocrystalline anisotropy energy is roughly half as big, and that dipolar energy is approximately ten times lower