High frequency magnetic permeability of nanocomposite film

The high frequency magnetic permeability of nanocomposite film consisting of the single-domain spherical ferromagnetic particles in the dielectric matrix is studied. The permeability is assumed to be determined by rotation of the ferromagnetic inclusion magnetic moments around equilibrium direction in AC magnetic field. The composite is modeled by a cubic array of ferromagnetic particles. The magnetic permeability tensor is calculated by solving the Landau-Lifshits-Gilbert equation accounting for the dipole interaction of magnetic particles. The permeability tensor components are found as functions of the frequency, temperature, ferromagnetic inclusions density and magnetic anisotropy. The obtained results show that nanocomposite films could have rather high value of magnetic permeability in the microwave range

Low-mass pre--main-sequence stars in the Magellanic Clouds

[Abridged] The stellar Initial Mass Function (IMF) suggests that sub-solar stars form in very large numbers. Most attractive places for catching low-mass star formation in the act are young stellar clusters and associations, still (half-)embedded in star-forming regions. The low-mass stars in such regions are still in their pre--main-sequence (PMS) evolutionary phase. The peculiar nature of these objects and the contamination of their samples by the evolved populations of the Galactic disk impose demanding observational techniques for the detection of complete numbers of PMS stars in the Milky Way. The Magellanic Clouds, the companion galaxies to our own, demonstrate an exceptional star formation activity. The low extinction and stellar field contamination in star-forming regions of these galaxies imply a more efficient detection of low-mass PMS stars than in the Milky Way, but their distance from us make the application of special detection techniques unfeasible. Nonetheless, imaging with the Hubble Space Telescope yield the discovery of solar and sub-solar PMS stars in the Magellanic Clouds from photometry alone. Unprecedented numbers of such objects are identified as the low-mass stellar content of their star-forming regions, changing completely our picture of young stellar systems outside the Milky Way, and extending the extragalactic stellar IMF below the persisting threshold of a few solar masses. This review presents the recent developments in the investigation of PMS stars in the Magellanic Clouds, with special focus on the limitations by single-epoch photometry that can only be circumvented by the detailed study of the observable behavior of these stars in the color-magnitude diagram. The achieved characterization of the low-mass PMS stars in the Magellanic Clouds allowed thus a more comprehensive understanding of the star formation process in our neighboring galaxies.Comment: Review paper, 26 pages (in LaTeX style for Springer journals), 4 figures. Accepted for publication in Space Science Review

Native diversity buffers against severity of non-native tree invasions

Determining the drivers of non-native plant invasions is critical for managing native ecosystems and limiting the spread of invasive species1,2. Tree invasions in particular have been relatively overlooked, even though they have the potential to transform ecosystems and economies3,4. Here, leveraging global tree databases5–7, we explore how the phylogenetic and functional diversity of native tree communities, human pressure and the environment influence the establishment of non-native tree species and the subsequent invasion severity. We find that anthropogenic factors are key to predicting whether a location is invaded, but that invasion severity is underpinned by native diversity, with higher diversity predicting lower invasion severity. Temperature and precipitation emerge as strong predictors of invasion strategy, with non-native species invading successfully when they are similar to the native community in cold or dry extremes. Yet, despite the influence of these ecological forces in determining invasion strategy, we find evidence that these patterns can be obscured by human activity, with lower ecological signal in areas with higher proximity to shipping ports. Our global perspective of non-native tree invasion highlights that human drivers influence non-native tree presence, and that native phylogenetic and functional diversity have a critical role in the establishment and spread of subsequent invasions

Integrated global assessment of the natural forest carbon potential

Forests are a substantial terrestrial carbon sink, but anthropogenic changes in land use and climate have considerably reduced the scale of this system1. Remote-sensing estimates to quantify carbon losses from global forests2,3,4,5 are characterized by considerable uncertainty and we lack a comprehensive ground-sourced evaluation to benchmark these estimates. Here we combine several ground-sourced6 and satellite-derived approaches2,7,8 to evaluate the scale of the global forest carbon potential outside agricultural and urban lands. Despite regional variation, the predictions demonstrated remarkable consistency at a global scale, with only a 12% difference between the ground-sourced and satellite-derived estimates. At present, global forest carbon storage is markedly under the natural potential, with a total deficit of 226 Gt (model range = 151–363 Gt) in areas with low human footprint. Most (61%, 139 Gt C) of this potential is in areas with existing forests, in which ecosystem protection can allow forests to recover to maturity. The remaining 39% (87 Gt C) of potential lies in regions in which forests have been removed or fragmented. Although forests cannot be a substitute for emissions reductions, our results support the idea2,3,9 that the conservation, restoration and sustainable management of diverse forests offer valuable contributions to meeting global climate and biodiversity targets

The global distribution and drivers of wood density and their impact on forest carbon stocks.

The density of wood is a key indicator of the carbon investment strategies of trees, impacting productivity and carbon storage. Despite its importance, the global variation in wood density and its environmental controls remain poorly understood, preventing accurate predictions of global forest carbon stocks. Here we analyse information from 1.1 million forest inventory plots alongside wood density data from 10,703 tree species to create a spatially explicit understanding of the global wood density distribution and its drivers. Our findings reveal a pronounced latitudinal gradient, with wood in tropical forests being up to 30% denser than that in boreal forests. In both angiosperms and gymnosperms, hydrothermal conditions represented by annual mean temperature and soil moisture emerged as the primary factors influencing the variation in wood density globally. This indicates similar environmental filters and evolutionary adaptations among distinct plant groups, underscoring the essential role of abiotic factors in determining wood density in forest ecosystems. Additionally, our study highlights the prominent role of disturbance, such as human modification and fire risk, in influencing wood density at more local scales. Factoring in the spatial variation of wood density notably changes the estimates of forest carbon stocks, leading to differences of up to 21% within biomes. Therefore, our research contributes to a deeper understanding of terrestrial biomass distribution and how environmental changes and disturbances impact forest ecosystems

Co-limitation towards lower latitudes shapes global forest diversity gradients

The latitudinal diversity gradient (LDG) is one of the most recognized global patterns of species richness exhibited across a wide range of taxa. Numerous hypotheses have been proposed in the past two centuries to explain LDG, but rigorous tests of the drivers of LDGs have been limited by a lack of high-quality global species richness data. Here we produce a high-resolution (0.025° × 0.025°) map of local tree species richness using a global forest inventory database with individual tree information and local biophysical characteristics from ~1.3 million sample plots. We then quantify drivers of local tree species richness patterns across latitudes. Generally, annual mean temperature was a dominant predictor of tree species richness, which is most consistent with the metabolic theory of biodiversity (MTB). However, MTB underestimated LDG in the tropics, where high species richness was also moderated by topographic, soil and anthropogenic factors operating at local scales. Given that local landscape variables operate synergistically with bioclimatic factors in shaping the global LDG pattern, we suggest that MTB be extended to account for co-limitation by subordinate drivers

Magnetic And Magnetotransport Properties Of Nanostructured Magnetic Materials

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Effects Of Dipolar Interactions On Magnetic Properties Of Granular Solids

The magnetic behavior of superparamagnetic Co nanoparticles (2-4 nm in diameter) dispersed in an amorphous, insulating SiO2 matrix was studied. Conventional fittings of magnetization curves present mean magnetic moments which diminish with decrease in temperature. In order to treat this anomalous behavior, we have applied the interacting superparamagnetic model (ISP). Mean diameters obtained from transmission electron microscopy (TEM) were compared with values obtained applying ISP model. © 2005 Elsevier B.V. All rights reserved.2942127132Battle, X., Labarta, A., (2002) J. Phys. D, 35, pp. R15Skomski, R., (2003) J. Phys.: Condens. Matter, 15, pp. R841Néel, L., (1949) Ann. Geophys., 5, p. 99Bean, C., Livingston, J.D., (1959) J. Appl. Phys., 30, pp. 120SFerrari, E.F., Da Silva, F.C.S., Knobel, M., (1997) Phys. Rev. B, 56, p. 6086Bastos, C.S.M., Bahiana, M., Nunes, W.C., Novak, M.A., Knobel, M., Vargas, P., Altbir, D., (2003) Phys. Rev. B, 66, p. 214407Mørup, S., Tronc, E., (1994) Phys. Rev. Lett., 72, p. 3278Dormann, J.L., Fiorani, D., Tronc, E., (1997) Adv. Chem. Phys., 98, p. 283Allia, P., Coisson, M., Tiberto, P., Vinai, F., Knobel, M., Novak, M.A., Nunes, W.C., (2001) Phys. Rev. B, 64, p. 144420Binns, C., Maher, M.J., Pankhurst, Q.A., Kechcrakos, D., Trohidou, K.N., (2002) Phys. Rev. B, 66, p. 184413Tartaj, P., Gonzalez-Carreño, T., Bomati-Miguel, O., Serna, C.J., Bonville, P., (2004) Phys. Rev. B, 69, p. 94401Allia, P., Tiberto, P., Vinai, F., (1997) J. Appl. Phys., 81, p. 4599Morrish, A.H., (1966) The Physical Principles of Magnetism, , Wiley New YorkKittel, C., (1968) Introduction to Solid State Physics, , Wiley New YorkSocolovsky, L.M., Denardin, J.C., Brandl, A.L., Knobel, M., Zhang, X.X., (2003) J. Magn. Magn. Mater., 262, p. 102Knobel, M., Nunes, W.C., Brandl, A.L., Vargas, J.M., Socolovsky, L.M., Zanchet, D., (2004) Phys. B: Cond. Matt., 354, p. 80noteAllia, P., Coisson, M., Tiberto, P., Vinai, F., Knobel, M., Novak, M.A., Nunes, W.C., (2001) Phys. Rev. B, 64, p. 144420Brandl, A.L., Denardin, J.C., Socolovsky, L.M., Knobel, M., Allia, P., (2004) J. Magn. Magn. Mater., 272-276, p. 1526Kechrakos, D., Trohidou, K.N., (2000) Phys. Rev. B, 62, p. 394