| 1. |
- Kemppinen, Julia, et al.
(author)
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Microclimate, an important part of ecology and biogeography
- 2024
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In: GLOBAL ECOLOGY AND BIOGEOGRAPHY. - 1466-822X .- 1466-8238. ; 33:6
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Journal article (peer-reviewed)abstract
- Brief introduction: What are microclimates and why are they important?Microclimate science has developed into a global discipline. Microclimate science is increasingly used to understand and mitigate climate and biodiversity shifts. Here, we provide an overview of the current status of microclimate ecology and biogeography in terrestrial ecosystems, and where this field is heading next.Microclimate investigations in ecology and biogeographyWe highlight the latest research on interactions between microclimates and organisms, including how microclimates influence individuals, and through them populations, communities and entire ecosystems and their processes. We also briefly discuss recent research on how organisms shape microclimates from the tropics to the poles.Microclimate applications in ecosystem managementMicroclimates are also important in ecosystem management under climate change. We showcase new research in microclimate management with examples from biodiversity conservation, forestry and urban ecology. We discuss the importance of microrefugia in conservation and how to promote microclimate heterogeneity.Methods for microclimate scienceWe showcase the recent advances in data acquisition, such as novel field sensors and remote sensing methods. We discuss microclimate modelling, mapping and data processing, including accessibility of modelling tools, advantages of mechanistic and statistical modelling and solutions for computational challenges that have pushed the state-of-the-art of the field.What's next?We identify major knowledge gaps that need to be filled for further advancing microclimate investigations, applications and methods. These gaps include spatiotemporal scaling of microclimate data, mismatches between macroclimate and microclimate in predicting responses of organisms to climate change, and the need for more evidence on the outcomes of microclimate management.
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| 2. |
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| 3. |
- Akansel, Serkan, et al.
(author)
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Enhanced Gilbert damping in Re-doped FeCo films : Combined experimental and theoretical study
- 2019
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In: Physical Review B. - 2469-9950 .- 2469-9969. ; 99:17
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Journal article (peer-reviewed)abstract
- The effects of rhenium doping in the range 0-10 at.% on the static and dynamic magnetic properties of Fe65Co35 thin films have been studied experimentally as well as with first-principles electronic structure calculations focusing on the change of the saturation magnetization (M-s) and the Gilbert damping parameter (alpha). Both experimental and theoretical results show that M-s decreases with increasing Re-doping level, while at the same time alpha increases. The experimental low temperature saturation magnetic induction exhibits a 29% decrease, from 2.31 to 1.64 T, in the investigated doping concentration range, which is more than predicted by the theoretical calculations. The room temperature value of the damping parameter obtained from ferromagnetic resonance measurements, correcting for extrinsic contributions to the damping, is for the undoped sample 2.1 x 10(-3), which is close to the theoretically calculated Gilbert damping parameter. With 10 at.% Re doping, the damping parameter increases to 7.8 x 10(-3), which is in good agreement with the theoretical value of 7.3 x 10(-3). The increase in damping parameter with Re doping is explained by the increase in the density of states at the Fermi level, mostly contributed by the spin-up channel of Re. Moreover, both experimental and theoretical values for the damping parameter weakly decrease with decreasing temperature.
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| 4. |
- Chen, Xingqi, et al.
(author)
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Structural phase transition in monolayer gold(I) telluride : From a room-temperature topological insulator to an auxetic semiconductor
- 2021
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In: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 103:7
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Journal article (peer-reviewed)abstract
- Structural phase transitions between semiconductors and topological insulators have rich applications in nanoelectronics but are rarely found in two-dimensional (2D) materials. In this work, by combining ab initio computations and evolutionary structure search, we investigate two stable 2D forms of gold(I) telluride (Au2Te) with square symmetry, noted as s(I)- and s(II)-Au2Te. s(II)-Au2Te is the global minimum structure and is a room-temperature topological insulator. s(I)-Au2Te is a direct-gap semiconductor with high carrier mobilities and unusual in-plane negative Poisson's ratio. Both s(I) and s(II) phases have ultralow Young's modulus, implying high flexibility. By applying a small tensile strain, s(II)-Au2Te can be transformed into s(I)-Au2Te. Hence, a structural phase transition from a room-temperature topological insulator to an auxetic semiconductor is found in the 2D forms of Au2Te, which enables potential applications in phase-change electronic devices. Moreover, we elucidate the mechanism of the phase transition with the help of phonon spectra and group theory analysis.
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| 5. |
- Esteban, Luis García, et al.
(author)
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Juvenile and mature wood of Abies pinsapoBoissie : sorption and thermodynamic properties
- 2015
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In: Wood Science and Technology. - : Springer Science and Business Media LLC. - 0043-7719 .- 1432-5225. ; 49:4, s. 725-738
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Journal article (peer-reviewed)abstract
- For industrial processes, it is important to study the hygroscopicity and thermodynamic properties of juvenile and mature wood. Samples of Abies pinsapo Boiss. collected in the natural areas of the species in Spain were used to study these properties in both types of wood. The equilibrium moisture contents were obtained, and the 15, 35 and 50 °C isotherms were plotted following the Guggenheim–Anderson–Boer–Dent model. The thermodynamic parameters were calculated using the integration method of the Clausius–Clapeyron equation. Chemical analyses, infrared spectra and X-ray diffractograms were applied to assess chemical modifications and possible changes in the cell wall structure. The chemical composition of the mature wood shows a decrease in the lignin and hemicelluloses content and an increase in the extracts and α-cellulose. The sorption isotherms for the three temperatures studied are higher in the mature wood than in the juvenile wood. Causes of this include the higher content of α-cellulose, the higher crystallinity index and the shorter crystallite length in the mature wood. No difference was found between the juvenile and mature wood in relation to the point of inflexion where the multilayer starts to predominate over the monolayer (approximately 30 %). In terms of the thermodynamic properties, the heat involved is greater in desorption than in adsorption, and more heat is involved in the mature wood than in the juvenile wood.
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| 6. |
- Esteban-Puyuelo, Raquel, et al.
(author)
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Complexity of mixed allotropes of MoS2 unraveled by first-principles theory
- 2020
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In: Physical Review B. - : AMER PHYSICAL SOC. - 2469-9950 .- 2469-9969. ; 102:16
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Journal article (peer-reviewed)abstract
- Two-dimensional MoS2 forms stable and several metastable allotropes of semimetallic, metallic, and semiconducting characters, depending on the experimental growth conditions. In this paper we consider intergrowth of the two most frequently reported metastable phases of MoS2 (1T and 1T') within the stable 1H phase to establish the effect of geometric and electronic reconstructions of the interface region between 1H and T/1T' phases using first-principles density functional calculations. We show that a complex structural reconstruction at the interfaces is responsible for the opening of an energy gap driving the electronic and geometric structures to resemble that of the 1T' phase. It is also found that the size of the patches inside the 1H matrix crucially controls the geometry and electronic structure close to the Fermi level. These results establish that remarkable properties of chemically exfoliated MoS2 with patches of metastable structures are to be understood as arising fundamentally from intergrowths necessarily strained due to lattice mismatch across the interface between the H and the distorted T phase, rather than in terms of any pure metastable phase.
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| 7. |
- Esteban-Puyuelo, Raquel
(author)
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Dynamics of excited electronic states in functional materials
- 2021
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Doctoral thesis (other academic/artistic)abstract
- Non-equilibrium processes involving excited electron states are very common in nature. This work summarizes some of the theoretical developments available to study them in finite and ex-tended systems. The focus lays in the class of Mixed Quantum-Classical methods that describe electrons as quantum-mechanical particles but approximate ionic motion to behave classically. In particular, Non-Adiabatic Molecular Dynamics and Real Time Density Functional Theory are described and applied to answer questions regarding non-equilibrium dynamics in diverse functional materials. First, the effect of phase boundaries and defects in monolayer MoS2 sam-ples is studied. This material has been suggested as a good candidate to substitute silicon in many applications, such as flexible electronics and solar cells. It is known that defects and dif-ferent polymorphs are present in experimental samples, and therefore it is extremely important to understand how realistic samples perform. We present how the electron-hole recombination times are accelerated in presence of defects, as well as how the structural changes in sam-ples that mix several phases of MoS2 affect their electronic structure. After that, rectangular graphene nanoflakes are explored. As an application to finite systems, we show in rectangu-lar graphene nanoflakes how different magnetic configurations have distinct optical absorption spectra and how this can be used for opto-electronic applications. Furthermore, the high har-monic generation for different magnetic couplings is studied, showing how some harmonics can be suppressed or enhanced depending on the underlying electronic structure. Finally, dif-fuse scattering in SnSe is investigated in an experimental collaboration in order to understand how phonon-phonon interactions affect the scattering dynamics, which may lead to profound insight into its thermoelectric properties.
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| 8. |
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| 9. |
- Esteban-Puyuelo, Raquel, et al.
(author)
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Role of defects in ultrafast charge recombination in monolayer MoS2
- 2021
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In: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 103:23
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Journal article (peer-reviewed)abstract
- In this work, we have systematically studied the role of point defects in the recombination time of monolayer MoS2 using time-dependent ab initio non-adiabatic molecular dynamics simulations. Various types of point defects, such as S vacancy, S interstitial, Mo vacancy and Mo interstitial have been considered. We show that defects strongly accelerate the electron-hole recombination, especially interstitial S atoms do that by 3 orders of magnitude higher compared to pristine MoS2. Mo defects (both vacancy and interstitial) introduce a multitude of de-excitation pathways via various defect levels in the energy gap. The results of this study provide some fundamental understanding of photoinduced de-excitation dynamics in presence of defects in highly technologically relevant 2D MoS2.
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| 10. |
- Esteban-Puyuelo, Raquel, et al.
(author)
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Tailoring the opto-electronic response of graphene nanoflakes by size and shape optimization
- 2020
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In: Physical Chemistry, Chemical Physics - PCCP. - : ROYAL SOC CHEMISTRY. - 1463-9076 .- 1463-9084. ; 22:15, s. 8212-8218
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Journal article (peer-reviewed)abstract
- The long spin-diffusion length, spin-lifetime and excellent optical absorption coefficient of graphene provide an excellent platform for building opto-electronic devices and spin-based logic in a nanometer regime. In this study, by using density functional theory and its time-dependent version, we provide a detailed analysis of how the size and shape of graphene nanoflakes can be used to alter their magnetic structures and optical properties. As the edges of zigzag graphene nanoribbons are known to align anti-ferromagnetically and armchair nanoribbons are typically non-magnetic, a combination of both in a nanoflake geometry can be used to optimize the ground-state magnetic structure and tailor the exchange coupling decisive for ferro- or anti-ferromagnetic edge magnetism, thereby offering the possibility to optimize the external fields needed to switch magnetic ordering. Most importantly, we show that the magnetic state alters the optical response of the flake leading to the possibility of opto-spintronic applications.
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