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  • 1
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    Micromagnetic understanding of the skyrmion Hall angle current dependence in perpendicular magnetized ferromagnets (2019)
    American Physical Society
    Details
    Publication Date: 2019-03-28
    Description: The understanding of the dynamical properties of skyrmion is a fundamental aspect for the realization of a competitive skyrmion based technology beyond CMOS. Most of the theoretical approaches are based on the approximation of a rigid skyrmion. However, thermal fluctuations can drive a continuous change of the skyrmion size via the excitation of thermal modes. Here, by taking advantage of the Hilbert-Huang transform, we demonstrate that at least two thermal modes can be excited which are non-stationary in time. In addition, one limit of the rigid skyrmion approximation is that this hypothesis does not allow for correctly describing the recent experimental evidence of skyrmion Hall angle dependence on the amplitude of the driving force, which is proportional to the injected current. In this work, we show that, in an ideal sample, the combined effect of field-like and damping-like torques on a breathing skyrmion can indeed give rise to such a current dependent skyrmion Hall angle. While here we design and control the breathing mode of the skyrmion, our results can be linked to the experiments by considering that the thermal fluctuations and/or disorder can excite the breathing mode. We also propose an experiment to validate our findings.
    Description: Published
    Description: 224418
    Description: 1A. Geomagnetismo e Paleomagnetismo
    Description: 2IT. Laboratori analitici e sperimentali
    Description: JCR Journal
    Keywords: Physics - Mesoscopic Systems and Quantum Hall Effect ; Physics - Mesoscopic Systems and Quantum Hall Effect
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 2
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    Dynamical mechanism of antifreeze proteins to prevent ice growth (2014)
    American Physical Society
    In:  EPIC3Physical Review E, American Physical Society, 90, pp. 022711-1, ISSN: 1539-3755
    Details
    Publication Date: 2014-11-04
    Description: The fascinating ability of algae, insects, and fishes to survive at temperatures below normal freezing is realized by antifreeze proteins (AFPs). These are surface-active molecules and interact with the diffusive water-ice interface thus preventing complete solidification. We propose a dynamical mechanism on how these proteins inhibit the freezing of water. We apply a Ginzburg-Landau-type approach to describe the phase separation in the two-component system (ice, AFP). The free-energy density involves two fields: one for the ice phase with a low AFP concentration and one for liquid water with a high AFP concentration. The time evolution of the ice reveals microstructures resulting from phase separation in the presence of AFPs. We observed a faster clustering of pre-ice structure connected to a locking of grain size by the action of AFP, which is an essentially dynamical process. The adsorption of additional water molecules is inhibited and the further growth of ice grains stopped. The interfacial energy between ice and water is lowered allowing the AFPs to form smaller critical ice nuclei. Similar to a hysteresis in magnetic materials we observe a thermodynamic hysteresis leading to a nonlinear density dependence of the freezing point depression in agreement with the experiments.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 3
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    Stable coexistence in a Lotka-Volterra model with heterogeneous resources and intraguild predation (2013)
    American Physical Society
    In:  EPIC3Physical Review E, American Physical Society, 88(6), ISSN: 1539-3755
    Details
    Publication Date: 2018-02-16
    Description: In this study we model population dynamics in a three-species food web with heterogeneous resources and intraguild predation by using a nonspatial Lotka-Volterra system with a density-dependent interaction of resource items. The model consists of two predators with an intraguild predation (IGP) relation competing for a common resource. The resource is subdivided into subpopulations of different quality that are distinguished by grazing rates of the two predators, contact rates between subpopulations and mortality rates. The proposed system describes an exchange of traits between species from distinct subpopulations by using a species interaction term. In particular, we examine the percentage of stable coexistence solutions versus resource carrying capacity and contact rates between distinct resource pools. We also present a numerical comparison of the percentage of stable food webs found for different numbers of subpopulations. While at high enrichment no stable coexistence was found in the IGP system with a single resource, our model predicts a stable coexistence of two IGP-related predators and resources at high and intermediate enrichment already at a low contact rate between subpopulations.
    Repository Name: EPIC Alfred Wegener Institut
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  • 4
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    Pond fractals in a tidal flat (2015)
    American Physical Society
    Details
    Publication Date: 2022-05-25
    Description: © The Author(s), 2015. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Physical Review E Statistical, Nonlinear, and Soft Matter Physics 92 (2015): 052128, doi: 10.1103/PhysRevE.92.052128.
    Description: Studies over the past decade have reported power-law distributions for the areas of terrestrial lakes and Arctic melt ponds, as well as fractal relationships between their areas and coastlines. Here we report similar fractal structure of ponds in a tidal flat, thereby extending the spatial and temporal scales on which such phenomena have been observed in geophysical systems. Images taken during low tide of a tidal flat in Damariscotta, Maine, reveal a well-resolved power-law distribution of pond sizes over three orders of magnitude with a consistent fractal area-perimeter relationship. The data are consistent with the predictions of percolation theory for unscreened perimeters and scale-free cluster size distributions and are robust to alterations of the image processing procedure. The small spatial and temporal scales of these data suggest this easily observable system may serve as a useful model for investigating the evolution of pond geometries, while emphasizing the generality of fractal behavior in geophysical surfaces.
    Description: This material is based upon work supported by the National Science Foundation Graduate Research Fellowship Program under Grant No. 2388357, the Gordon and Betty Moore Foundation, and the National Science Foundation, Award No. OCE-1315201.
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 5
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    The Molecular Fingerprint of Fluorescent Natural Organic Matter Offers Insight into Biogeochemical Sources and Diagenetic State (2018)
    American Chemical Society (ACS)
    In:  EPIC3Analytical Chemistry, American Chemical Society (ACS), 90(24), pp. 14188-14197, ISSN: 0003-2700
    Details
    Publication Date: 2024-04-09
    Description: Investigating the biogeochemistry of dissolved organic matter (DOM) requires the synthesis of data from several complementary analytical techniques. The traditional approach to data synthesis is to search for correlations between measurements made on the same sample using different instruments. In contrast, data fusion simultaneously decomposes data from multiple instruments into the underlying shared and unshared components. Here, Advanced Coupled Matrix and Tensor Factorization (ACMTF) was used to identify the molecular fingerprint of DOM fluorescence fractions in Arctic fjords. ACMTF explained 99.84% of the variability with six fully shared components. Individual molecular formulas were linked to multiple fluorescence components and vice versa. Molecular fingerprints differed in diversity and oceanographic patterns, suggesting a link to the biogeochemical sources and diagenetic state of DOM. The fingerprints obtained through ACMTF were more specific compared to traditional correlation analysis and yielded greater compositional insight. Multivariate data fusion aligns extremely complex, heterogeneous DOM data sets and thus facilitates a more holistic understanding of DOM biogeochemistry.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 6
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    Glucose as a Potential Chemical Marker for Ice Nucleating Activity in Arctic Seawater and Melt Pond Samples (2019)
    American Chemical Society (ACS)
    In:  EPIC3Environmental Science and Technology, American Chemical Society (ACS), 53(15), pp. 8747-8756, ISSN: 0013-936X
    Details
    Publication Date: 2024-04-12
    Description: Recent studies pointed to a high ice nucleating activity (INA) in the Arctic sea surface microlayer (SML). However, related chemical information is still sparse. In the present study, INA and free glucose concentrations were quantified in Arctic SML and bulk water samples from the marginal ice zone, the ice-free ocean, melt ponds, and open waters within the ice pack. T50 (defining INA) ranged from −17.4 to −26.8 °C. Glucose concentrations varied from 0.6 to 51 μg/L with highest values in the SML from the marginal ice zone and melt ponds (median 16.3 and 13.5 μg/L) and lower values in the SML from the ice pack and the ice-free ocean (median 3.9 and 4.0 μg/L). Enrichment factors between the SML and the bulk ranged from 0.4 to 17. A positive correlation was observed between free glucose concentration and INA in Arctic water samples (T50(°C) = (−25.6 ± 0.6) + (0.15 ± 0.04)·Glucose(μg/L), RP = 0.66, n = 74). Clustering water samples based on phytoplankton pigment composition resulted in robust but different correlations within the four clusters (RP between 0.67 and 0.96), indicating a strong link to phytoplankton-related processes. Since glucose did not show significant INA itself, free glucose may serve as a potential tracer for INA in Arctic water samples.
    Repository Name: EPIC Alfred Wegener Institut
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