31,006 research outputs found
Correction to “Micromagnetic models of pseudo-single domain grains of magnetite near the Verwey Transition”
No full textDomain structures of small pseudo-single domain (PSD) magnetite near the Verwey transition (Tυ) at ≈120 K were modeled using an unconstrained three-dimensional micromagnetic algorithm. The single-domain (SD) threshold (d0) for the monoclinic phase below Tυ was calculated to be ≈0.14 μm at 110 K. However, it is postulated that as a result of the very high energy barriers in the monoclinic phase, grains near d0 in size and in vortex states are unlikely to denucleate domain walls to become SD. Low-temperature cycling of saturation isothermal remanence (SIRM), thermoremanence (TRM), and partial TRM (pTRM) through Tυ was simulated. Domain structures were found to align along the monoclinic “easy” magnetocrystalline anisotropy axis, i.e., the c axis, on simulated cooling through Tυ. This process was found to “destroy” SIRM structures giving rise to demagnetization; however, for TRM and pTRM structures only “closure” domains were removed increasing magnetostatic leakage giving rise to a reversible anomaly in rough agreement with experimental studies. SIRM displayed a smaller anomaly at Tυ, in agreement with experimental studies
Correction to:Regular participation in leisure time activities and high cardiovascular fitness improve motor sequence learning in older adults (Psychological Research, (2021), 85, 4, (1488-1502), 10.1007/s00426-020-01351-y)
Get PDFThe article “Regular participation in leisure time activities and high cardiovascular fitness improve motor sequence learning in older adults”, written by K. Zwingmann, L. Hübner, W. B. Verwey, J. S. Barnhoorn, B. Godde and C. Voelcker- Rehage, was originally published Online First without Open Access. After publication in volume 85, issue 4, pages 1488–1502 the author decided to opt for Open Choice and to make the article an Open Access publication. Therefore, the copyright of the article has been changed to</p
Low-temperature cooling behavior of single-domain magnetite: Forcing of the crystallographic axes and interactions
Get PDFLow-temperature cycling (LTC) of magnetic remanences carried by rocks has become a standard technique in paleomagnetism, rock magnetism, and environmental magnetism as a means of identifying mineralogy and grain size. LTC usually involves measuring low-temperature thermomagnetic curves on cooling through crystallographic transitions, such as magnetite's Verwey transition. Historically, it has been assumed that remanence carried by single-domain (SD) magnetite grains is not affected by cooling through the cubic/monoclinic Verwey transition, whereas larger multidomain (MD) magnetite grains partially demagnetize. However, it has been recently pointed out that the shape anisotropy even for an infinitely long cylinder is approximately 3 times smaller than the monoclinic magnetocrystalline anisotropy along the hardest axis, i.e., SD remanences are not impervious to LTC. Using a micromagnetic algorithm we simulate LTC curves for assemblages of effectively elongated SD magnetite grains and consider the contribution of magnetostatic interactions. Initially, we assume that relationship between the cubic and monoclinic symmetry is chosen randomly; however, there are key experimental features, which this model does not explain. A new “controlled switching” model is developed; the orientation of the low-temperature monoclinic axes are not chosen randomly, but instead are controlled by the direction of the magnetic moment on cooling through the Verwey transition. This new model correctly predicts experimentally observed low-temperature trends that the “random” model does not. We therefore propose a new model for the mechanism controlling the behavior of SD grains at the Verwey transition and show that the low-temperature behavior of SD and MD grains can yield ambiguously similar behavior
Light scattering from the critical modes of the Verwey transition in magnetite
No full textWe present inelastic light scattering data on a single crystal of magnetite (Fe3O4) across the Verwey transition. We identify anomalies of the lattice vibrations that originate from strong coupling to electronic excitations. We reveal spectroscopic signatures of diffusive modes in the electronic contribution to the Raman response function. We thereby provide information on the critical dynamics and the hierarchy of the structural and electronic modes in the mechanism of the Verwey transition.LUME
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Observations of viscous magnetization in multidomain magnetite
Get PDFThe viscous behavior of multidomain magnetite has been directly observed in both natural and synthetic samples using Bitter pattern imaging. A computer-controlled fully automated microscope fitted with a heating stage, field coils, and digital camera was used to record viscous acquisition and decay sequences as a function of time, temperature, and field. Domain walls (DW) were observed to move continuously through a series of quasi-static states over many hours rather than instantaneously. Viscosity was observed only on grains oriented near to the {111} surface. Generally, DWs moved perpendicular to their surface in the direction of the applied field; however, because observed domains respond primarily to the movement of main domains underneath the surface, occasionally, DWs moved in the opposite direction to the applied field. Small variations in temperature were found to strongly influence the viscosity, supporting the idea that viscosity is thermally activated. Viscous and nonviscous domain structures were examined using magnetic force microscopy. These images revealed that the domains displaying viscous behavior tended to be narrow (~2 ?m in width). Larger domains on grains oriented near the {111} surface did not display viscosity, reflecting the greater energy required to move larger domain structures. This may explain why no viscosity was observed on the {110} surfaces, as the domains were wider, that is, ~6–10 ?m. A complex spiraling vortex-like magnetic domain structure was imaged. Etch pit analysis found a corresponding dislocation pit at the same location. It is suggested that this corresponds to the microstructure around a screw dislocation line
Ochrona wód powierzchniowych w lubuskiem w kontekście realizacji polityki UE
No full textIn this article author – based on literature, documents and statistical data - attempted to analyze the problem of protection surface waters in Lubuskie in the context of the implementation of European Union policy. A review of concepts relating to the EU Water Framework Directive and integrated water management was made. Investment activities in the field of water and wastewater were compared with environmental data in order to obtain a synthetic evaluation of the scale of the province. In summary applied conclusions.W opracowaniu podjęto – na podstawie literatury, dokumentów oraz danych statystycznych – próbę analizy problemu ochrony wód powierzchniowych w województwie lubuskim w kontekście realizacji polityki Unii Europejskiej. Dokonano przeglądu pojęć dotyczących Ramowej Dyrektywy Wodnej UE i zintegrowanego zarządzania wodami. Działania inwestycyjne w zakresie gospodarki wodno-ściekowej porównano z danymi środowiskowymi w celu uzyskania syntetycznej oceny w skali omawianego województwa. W podsumowaniu opracowania zawarto wnioski
Low-temperature magnetic properties of magnetite
No full textAlthough several studies have recommended removal of secondary components of magnetic remanence by zero-field cycling from room temperature to a temperature much lower than the low temperature transition for magnetite (about 120 K), the method has not become a standard routine technique. This is partly due to the poor understanding of the behavior of magnetite particles at the low-temperature transition zone. Previous experiments by other researchers have used magnetite powders. In such powders it is always possible to attribute any discrepancy between the results observed and theory to possible existence of magnetostatic interaction effects or existence of elongated particles in samples presumed to contain only equant particles. Such factors need to be eliminated in order to have a better understanding of the low temperature behavior of magnetite particles. Low-temperature magnetic properties of lithographically produced arrays of both interacting and noninteracting cubic magnetite particles as well as those from powder particles have been measured as part of this study. A gradual increase in the amount of saturation isothermal rémanent magnetization (SIRM) lost at the Verwey transition Tv with increasing particle size in the pseudo-single-domain size range has been observed. This behavior is consistent with the vortex state domain structure. The grain size dependence of the amount of SIRM lost at Tv is most probably what previous researchers reported as a magnetic memory particle-size-dependent trend. Magnetic memory measured during the cooling and warming process is shown to be a stress-related phenomenon. Such measurements could be useful in assessing the nature of stress in a magnetite sample
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