6,571 research outputs found
Empirical Methods for Modeling Landscape Change, Ecosystem Services, and Biodiversity
Resource /Energy Economics and Policy,
A Framework for Studying Emotions across Species
Since the 19th century, there has been disagreement over the fundamental question of whether “emotions” are cause or consequence of their associated behaviors. This question of causation is most directly addressable in genetically tractable model organisms, including invertebrates such as Drosophila. Yet there is ongoing debate about whether such species even have “emotions,” as emotions are typically defined with reference to human behavior and neuroanatomy. Here, we argue that emotional behaviors are a class of behaviors that express internal emotion states. These emotion states exhibit certain general functional and adaptive properties that apply across any specific human emotions like fear or anger, as well as across phylogeny. These general properties, which can be thought of as “emotion primitives,” can be modeled and studied in evolutionarily distant model organisms, allowing functional dissection of their mechanistic bases and tests of their causal relationships to behavior. More generally, our approach not only aims at better integration of such studies in model organisms with studies of emotion in humans, but also suggests a revision of how emotion should be operationalized within psychology and psychiatry
Curie temperature of multiphase nanostructures
The Curie temperature and the local spontaneous magnetization of ferromagnetic nanocomposites are investigated. The macroscopic character of the critical fluctuations responsible for the onset of ferromagnetic order means that there is only one Curie temperature, independent of the number of magnetic phases present. The Curie temperature increases with the grain size and is, in general, larger than predicted from the volume averages of the exchange constants. However, the Curie-temperature enhancement is accompanied by a relative reduction of the spontaneous magnetization. Due to the quadratic dependence of the permanent-magnet energy product on the spontaneous magnetization, this amounts to a deterioration of the magnets performance. The length scale on which an effective intergranular exchange coupling is realized (coupling length) depends on the Curie-temperature difference between the phases and on the spacial distribution of the local interatomic exchange. As a rule, it is of the order of a few interatomic distances; for much bigger grain sizes the structures mimic an interaction-free ensemble of different ferromagnetic materials. This must be compared to the magnetic-anisotropy coupling length, which is of the order of 10 nm. The difference is explained by the nonrelativistic character of the Curie-temperature problem
Structure and Magnetism of Mn5Ge3 Nanoparticles
In this work, we investigated the magnetic and structural properties of isolated Mn5Ge3 nanoparticles prepared by the cluster-beam deposition technique. Particles with sizes between 7.2 and 12.6 nm were produced by varying the argon pressure and power in the cluster gun. X-ray diffraction (XRD)and selected area diffraction (SAD) measurements show that the nanoparticles crystallize in the hexagonal Mn5Si3-type crystal structure, which is also the structure of bulk Mn5Ge3. The temperature dependence of the magnetization shows that the as-made particles are ferromagnetic at room temperature and have slightly different Curie temperatures. Hysteresis-loop measurements show that the saturation magnetization of the nanoparticles increases significantly with particle size, varying from 31 kA/m to 172 kA/m when the particle size increases from 7.2 to 12.6 nm. The magnetocrystalline anisotropy constant K at 50 K, determined by fitting the high-field magnetization data to the law of approach to saturation, also increases with particle size, from 0.4 × 105 J/m3 to 2.9 × 105 J/m3 for the respective sizes. This trend is mirrored by the coercivity at 50 K, which increases from 0.04 T to 0.13 T. A possible explanation for the magnetization trend is a radial Ge concentration gradient
Quasicoherent nucleation mode in two-phase nanomagnets
Magnetization processes in advanced magnetic nanostructures are investigated. For the case of spherical soft or semihard grains surrounded by a very hard matrix a bulging nucleation mode is discovered. The bulging mode exhibits the radial angular symmetry of the coherent mode, but it is incoherent due to its radial variation. The radial dependence of the bulging mode is obtained by solving a spherical Bessel equation which is subject to appropriate boundary conditions. In contrast to the coherent mode, the bulging mode yields a nucleationfield coercivity which depends on the exchange stiffness and on the size of the grain. There is a critical grain radius 7.869√A/μ0Ms2 above which the bulging mode is replaced by a modified curling mode. The nucleation modes realized in nanostructures affect the demagnetizing-field corrections necessary to account for the external shape of magnetic samples. Since strong but short-range exchange and weak but long-range magnetostatic interactions compete on nanostructural length scales, the sample-shape dependence of the hysteresis loops cannot be mapped onto a purely magnetostatic demagnetizing factor
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