| 1. |
- Silverå Ejneby, Malin, 1987-, et al.
(författare)
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Atom-by-atom tuning of the electrostatic potassium-channel modulator dehydroabietic acid
- 2018
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Ingår i: The Journal of General Physiology. - New York, United States : Rockefeller Institute for Medical Research. - 0022-1295 .- 1540-7748. ; 150:5, s. 731-750
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Tidskriftsartikel (refereegranskat)abstract
- Dehydroabietic acid (DHAA) is a naturally occurring component of pine resin that was recently shown to open voltage-gated potassium (KV) channels. The hydrophobic part of DHAA anchors the compound near the channel’s positively charged voltage sensor in a pocket between the channel and the lipid membrane. The negatively charged carboxyl group exerts an electrostatic effect on the channel’s voltage sensor, leading to the channel opening. In this study, we show that the channel-opening effect increases as the length of the carboxyl-group stalk is extended until a critical length of three atoms is reached. Longer stalks render the compounds noneffective. This critical distance is consistent with a simple electrostatic model in which the charge location depends on the stalk length. By combining an effective anchor with the optimal stalk length, we create a compound that opens the human KV7.2/7.3 (M type) potassium channel at a concentration of 1 µM. These results suggest that a stalk between the anchor and the effector group is a powerful way of increasing the potency of a channel-opening drug.
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| 2. |
- Ekeroth, Sebastian, 1988-, et al.
(författare)
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Catalytic nanotruss structures realized by magnetic self-assembly in pulsed plasma
- 2018
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 18:5, s. 3132-3137
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Tidskriftsartikel (refereegranskat)abstract
- Tunable nanostructures that feature a high surface area are firmly attached to a conducting substrate and can be fabricated efficiently over significant areas, which are of interest for a wide variety of applications in, for instance, energy storage and catalysis. We present a novel approach to fabricate Fe nanoparticles using a pulsed-plasma process and their subsequent guidance and self-organization into well-defined nanostructures on a substrate of choice by the use of an external magnetic field. A systematic analysis and study of the growth procedure demonstrate that nondesired nanoparticle agglomeration in the plasma phase is hindered by electrostatic repulsion, that a polydisperse nanoparticle distribution is a consequence of the magnetic collection, and that the formation of highly networked nanotruss structures is a direct result of the polydisperse nanoparticle distribution. The nanoparticles in the nanotruss are strongly connected, and their outer surfaces are covered with a 2 nm layer of iron oxide. A 10 μm thick nanotruss structure was grown on a lightweight, flexible and conducting carbon-paper substrate, which enabled the efficient production of H2 gas from water splitting at a low overpotential of 210 mV and at a current density of 10 mA/cm2.
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| 3. |
- Ekeroth, Sebastian, 1988-, et al.
(författare)
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Impact of nanoparticle magnetization on the 3D formation of dual-phase Ni/NiO nanoparticle-based nanotrusses
- 2019
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Ingår i: Journal of nanoparticle research. - : Springer-Verlag New York. - 1388-0764 .- 1572-896X. ; 21:11
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Tidskriftsartikel (refereegranskat)abstract
- Magnetic nanoparticles with average size 30 nm were utilized to build three-dimensional framework structures—nanotrusses. In dual-phase Ni/NiO nanoparticles, there is a strong correlation between the amount of magnetic Ni and the final size and shape of the nanotruss. As it decreases, the length of the individual nanowires within the trusses also decreases, caused by a higher degree of branching of the wires. The position and orientation of the non-magnetic material within the truss structure was also investigated for the different phase compositions. For lower concentrations of NiO phase, the electrically conducting Ni-wire framework is maintained through the preferential bonding between the Ni crystals. For larger concentrations of NiO phase, the Ni-wire framework is interrupted by the NiO. The ability to use nanoparticles that are only partly oxidized in the growth of nanotruss structures is of great importance. It opens the possibility for using not only magnetic metals such as pure Ni, Fe, and Co, but also to use dual-phase nanoparticles that can strongly increase the efficiency of e.g. catalytic electrodes and fuel cells.
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| 4. |
- Gilljam, David, 1978-
(författare)
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Structure and Stability of Ecological Networks : The role of dynamic dimensionality and species variability in resource use
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The main focus of this thesis is on the response of ecological communities to environmental variability and species loss. My approach is theoretical; I use mathematical models of networks where species population dynamics are described by ordinary differential equations. A common theme of the papers in my thesis is variation – variable link structure (Paper I) and within-species variation in resource use (Paper III and IV). To explore how such variation affect the stability of ecological communities in variable environments, I use numerical methods evaluating for example community persistence (the proportion of species surviving over time; Paper I, II and IV). I also develop a new method for quantifying the dynamical dimensionality of an ecological community and investigate its effect on community persistence in stochastic environments (Paper II). Moreover, if we are to gain trustworthy model output, it is of course of major importance to create study systems that reflect the structures of natural systems. To this end, I also study highly resolved, individual based empirical food web data sets (Paper III, IV).In Paper I, the effects of adaptive rewiring induced by resource loss on the persistence of ecological networks is investigated. Loss of one species in an ecosystem can trigger extinctions of other dependent species. For instance, specialist predators will go extinct following the loss of their only prey unless they can change their diet. It has therefore been suggested that an ability of consumers to rewire to novel prey should mitigate the consequences of species loss by reducing the risk of cascading extinction. Using a new modelling approach on natural and computer-generated food webs I find that, on the contrary, rewiring often aggravates the effects of species loss. This is because rewiring can lead to overexploitation of resources, which eventually causes extinction cascades. Such a scenario is particularly likely if prey species cannot escape predation when rare and if predators are efficient in exploiting novel prey. Indeed, rewiring is a two-edged sword; it might be advantageous for individual predators in the short term, yet harmful for long-term system persistence.The persistence of an ecological community in a variable world depends on the strength of environmental variation pushing the community away from equilibrium compared to the strength of the deterministic feedbacks, caused by interactions among and within species, pulling the community towards the equilibrium. However, it is not clear which characteristics of a community that promote its persistence in a variable world. In Paper II, using a modelling approach on natural and computer-generated food webs, I show that community persistence is strongly and positively related to its dynamic dimensionality (DD), as measured by the inverse participation ratio (IPR) of the real part of the eigenvalues of the community matrix. A high DD means that the real parts of the eigenvalues are of similar magnitude and the system will therefore approach equilibrium from all directions at a similar rate. On the other hand, when DD is low, one of the eigenvalues has a large magnitude of the real part compared to the others and the deterministic forces pulling the system towards equilibrium is therefore weak in many directions compared to the stochastic forces pushing the system away from the equilibrium. As a consequence the risk of crossing extinction thresholds and boundaries separating basins of attractions increases, and hence persistence decreases, as DD decreases. Given the forecasted increase in climate variability caused by global warming, Paper II suggests that the dynamic dimensionality of ecological systems is likely to become an increasingly important property for their persistence.In Paper III, I investigate patterns in the size structure of one marine and six running freshwater food webs: that is, how the trophic structure of such ecological networks is governed by the body size of its interacting entities. The data for these food webs are interactions between individuals, including the taxonomic identity and body mass of the prey and the predator. Using these detailed data, I describe how patterns in diet variation and predator variation scales with the body mass of predators or prey, using both a species- and a size-class-based approach. I also compare patterns of size structure derived from analysis of individual-based data with those patterns that result when data are aggregated into species (or size class-based) averages. This comparison shows that analysis based on species averaging can obscure interesting patterns in the size structure of ecological communities. For example, I find that the strength of the relationship between prey body mass and predator body mass is consistently underestimated when species averages are used instead of the individual level data. In some cases, no relationship is found when species averages are used, but when individual-level data are used instead, clear and significant patterns are revealed. These results have potentially important implications for parameterisation of models of ecological communities and hence for predictions concerning their dynamics and response to different kinds of disturbances.Paper IV continues the analysis of the highly resolved individual-based empirical data set used in Paper III and investigates patterns and effects of within- and between species resource specialisation in ecological communities. Within-species size variation can be considerable. For instance, in fishes and reptiles, where growth is continuous, individuals pass through a wide spectrum of sizes, possibly more than four orders of magnitude, during the independent part of their life cycle. Given that the size of an organism is correlated with many of its fundamental ecological properties, it should come as no surprise that an individual’s size affects the type of prey it can consume and what predators will attack it (Paper III). In Paper IV, I quantify within- and between species differences in predator species’ prey preferences in natural food webs and subsequently explore its consequences for dynamical dimensionality (Paper II) and community stability in stage structured food web models. Among the natural food webs there are webs where species overlap widely in their resource use while the resource use of size-classes within species differs. There are also webs where differences in resource use among species is relatively large and the niches of sizeclasses within species are more similar. Model systems with the former structure are found to have low dynamical dimensionality and to be less stable compared to systems with the latter structure. Thus, although differential resource use among individuals within a species is likely to decrease the intensity of intraspecific competition and favor individuals specializing on less exploited resources it can destabilize the community in which the individuals are embedded.
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| 5. |
- Lü, Bo, et al.
(författare)
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Coalescence-controlled and coalescence-free growth regimes during deposition of pulsed metal vapor fluxes on insulating surfaces
- 2015
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Ingår i: Journal of Applied Physics. - : American Institute of Physics (AIP). - 0021-8979 .- 1089-7550. ; 117:13
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Tidskriftsartikel (refereegranskat)abstract
- The morphology and physical properties of thin films deposited by vapor condensation on solid surfaces are predominantly set by the processes of island nucleation, growth, and coalescence. When deposition is performed using pulsed vapor fluxes, three distinct nucleation regimes are known to exist depending on the temporal profile of the flux. These regimes can be accessed by tuning deposition conditions; however, their effect on film microstructure becomes marginal when coalescence sets in and erases morphological features obtained during nucleation. By preventing coalescence from being completed, these nucleation regimes can be used to control microstructure evolution and thus access a larger palette of film morphological features. Recently, we derived the quantitative criterion to stop coalescence during continuous metal vapor flux deposition on insulating surfaceswhich typically yields 3-dimensional growthby describing analytically the competition between island growth by atomic incorporation and the coalescence rate of islands [Lu et al., Appl. Phys. Lett. 105, 163107 (2014)]. Here, we develop the analytical framework for entering a coalescence-free growth regime for metal vapor deposition on insulating substrates using pulsed vapor fluxes, showing that there exist three distinct criteria for suppressing coalescence that correspond to the three nucleation regimes of pulsed vapor flux deposition. The theoretical framework developed herein is substantiated by kinetic Monte Carlo growth simulations. Our findings highlight the possibility of using atomistic nucleation theory for pulsed vapor deposition to control morphology of thin films beyond the point of island density saturation. (C) 2015 AIP Publishing LLC.
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| 6. |
- Lü, Bo, 1986-
(författare)
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Nano- and mesoscale morphology evolution of metal films on weakly-interacting surfaces
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Thin films are structures consisting of one or several nanoscale atomic layers of material that are used to either functionalize a surface or constitute components in more complex devices. Many properties of a film are closely related to its microstructure, which allows films to be tailored to meet specific technological requirements. Atom-by-atom film growth from the vapor phase involves a multitude of atomic processes that may not be easily studied experimentally in real-time because they occur in small length- (≤ Å) and timescales (≤ ns). Therefore, different types of computer simulation methods have been developed in order to test theoretical models of thin film growth and unravel what experiments cannot show. In order to compare simulated and experimental results, the simulations must be able to model events on experimental time-scales, i.e. on the order of microseconds to seconds. This is achievable with the kinetic Monte Carlo (kMC) method.In this work, the initial growth stages of metal deposition on weakly-interacting substrates is studied using both kMC simulations as well as experiments whereby growth was monitored using in situ probes. Such film/substrate material combinations are widely encountered in technological applications including low-emissivity window coatings to parts of microelectronics components. In the first part of this work, a kMC algorithm was developed to model the growth processes of island nucleation, growth and coalescence when these are functions of deposition parameters such as the vapor deposition rate and substrate temperature. The dynamic interplay between these growth processes was studied in terms of the scaling behavior of the film thickness at the elongation transition, for both continuous and pulsed deposition fluxes, and revealed in both cases two distinct growth regimes in which coalescence is either active or frozen out during deposition. These growth regimes were subsequently confirmed in growth experiments of Ag on SiO2, again for both pulsed and continuous deposition, by measuring the percolation thickness as well as the continuous film formation thickness. However, quantitative agreement with regards to scaling exponents in the two growth regimes was not found between simulations and experiments, and this prompted the development of a method to determine the elongation transition thickness experimentally. Using this method, the elongation transition of Ag on SiO2 was measured, with scaling exponents found in much better agreement with the simulation results. Further, these measurement data also allowed the calculation of surface properties such as the terrace diffusion barrier of Ag on SiO2 and the average island coalescence rate.In the second part of this thesis, pioneering work is done to develop a fully atomistic, on-lattice model which describes the growth of Ag on weakly-interacting substrates. Simulations performed using this model revealed several key atomic-scale processes occurring at the film/substrate interface and on islands which govern island shape evolution, thereby contributing to a better understanding of how 3D island growth occurs at the atomic scale for a wide class of materials. The latter provides insights into the directed growth of metal nanostructures with controlled shapes on weakly-interacting substrates, including twodimensional crystals for use in catalytic and nano-electronic applications.
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| 7. |
- Pilch, Iris, et al.
(författare)
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Nanoparticle growth by collection of ions : orbital motion limited theory and collision-enhanced collection
- 2016
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Ingår i: Journal of Physics D. - : Institute of Physics Publishing (IOPP). - 0022-3727 .- 1361-6463. ; 49:39
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Tidskriftsartikel (refereegranskat)abstract
- The growth of nanoparticles in plasma is modeled for situations where the growth is mainly due to the collection of ions of the growth material. The model is based on the classical orbit motion limited (OML) theory with the addition of a collision-enhanced collection (CEC) of ions. The limits for this type of model are assessed with respect to three processes that are not included: evaporation of the growth material, electron field emission, and thermionic emission of electrons. It is found that both evaporation and thermionic emission can be disregarded below a temperature that depends on the nanoparticle material and on the plasma parameters; for copper in our high-density plasma this limit is about 1200 K. Electron field emission can be disregarded above a critical nanoparticle radius, in our case around 1.4 nm. The model is benchmarked, with good agreement, to the growth of copper nanoparticles from a radius of 5 nm-20 nm in a pulsed power hollow cathode discharge. Ion collection by collisions contributes with approximately 10% of the total current to particle growth, in spite of the fact that the collision mean free path is four orders of magnitude longer than the nanoparticle radius.
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| 8. |
- Skagius, Peter, et al.
(författare)
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Professional reinventions : Swedish psychologists, 1990-2010
- 2016
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Ingår i: History of Psychology. - : American Psychological Association (APA). - 1093-4510 .- 1939-0610. ; 19:4, s. 274-297
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Tidskriftsartikel (refereegranskat)abstract
- Since the early 20th century, the Swedish psychology profession has undergone several changes in its essential tasks, epistemological foundations, and social roles. These changes occurred through an ongoing “tuning” with Swedish society, in which the profession strove to appear relevant to society’s concerns and problems as well as enroll others to share the profession’s goals and aims. Studying the history of the profession can thus shed light on the changing definitions and contours of the psychology profession itself as well as on the organization of the society in which it acts. This article examines the history of the Swedish psychology profession from 1990 to 2010, through an analysis of the discussions and debates taking place in the Swedish Psychological Association’s journal. The analytical framework used draws on work done within actor–network theory and science studies. We argue that the profession’s institutional connections, defining tasks, epistemological underpinnings, and social position have changed in major ways during these 2 decades. Overall, as a result of an increasingly felt insecurity, the profession has turned outward and tried to find new ways to legitimize itself to politicians, the media, patients, and customers through means such as a more economized vocabulary and novel forms of empirical research. These changes have led to a more socialized profession, now more closely tuned to other actors in Swedish society, leading to conflicts within the profession over whether this is an opportunity to better control their own destiny or if it will lead to a loss of autonomy.
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| 9. |
- Tal, Alexey, 1990-
(författare)
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Electronic and structural properties of nanoclusters
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Nanoclusters have gained a huge interest due to their unique properties. They represent an intermediate state between an atom and a solid, which manifests itself in their atomic configurations and electronic structure. The applications of nanoclusters require detailed understanding of their properties and strongly depend on the ability to control their synthesis process. Significant effort has been invested in modelling of nanoclusters properties. However, the complexity of these systems is such that many aspects of their growth process and properties are yet to be understood.My thesis focuses on describing structural and electronic properties of nanoclusters. In particular, the model for nanoparticles growth in plasma condition is developed and applied, allowing to describe the influence of the plasma conditions on the evaporation, growth and morphological transformation processes. The mechanism driving the morphology transition from icosahedral to decahedral phase is suggested based on force-fields models. Spectroscopic methods allow for precise characterization of nanoclusters and constitute an important tool for analysis of their electronic structure of valence band as well as core-states. The special attention in the thesis is paid to the core-states of nanoclusters and influences that affect them. In particular, the effects of local coordination, interatomic distances and confinement effects are investigated in metal nanoclusters by density functional theory methods. These effects and their contribution to spectroscopic features of nanoclusters in X-ray photoemission are modelled. The relation between the reactivity of nanoclusters and their spectroscopic features calculated in different approximations are revealed and explained. Ceria is a very important system for many applications due to the ability of cerium atoms to change their oxidation state depending on the environment. The shift of the oxidation state and its effects on the core-states is examined with X-ray absorption measurements and modelling allowing to build a rigid foundation for interpretation of the measured spectra and characterization of electronic structure of ceria nanoparticles.
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| 10. |
- Tal, Alexey, et al.
(författare)
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Morphology transition mechanism from icosahedral to decahedral phase during growth of Cu nanoclusters
- 2015
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 92:2, s. 020102-
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Tidskriftsartikel (refereegranskat)abstract
- The morphology transition from the thermodynamically favorable to the unfavorable phase during growth of freestanding copper nanoclusters is studied by molecular dynamics simulations. We give a detailed description of the kinetics and thermodynamics of the process. A universal mechanism of a solid-solid transition, from icosahedral to decahedral morphology in the nanoclusters, is proposed. We show that a formation of distorted NC during the growth process with islands of incoming atoms localized in certain parts of the grown particle may shift the energy balance between Ih and Dh phases in favor of the latter leading to the morphology transition deep within the thermodynamic stability field of the former. The role of diffusion in the morphology transition is revealed. In particular, it is shown that fast diffusion should suppress the morphology transition and favor homogeneous growth of the nanoclusters.
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| 11. |
- Wang, Li-San, et al.
(författare)
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Rarity of the Alzheimer Disease-Protective APP A673T Variant in the United States.
- 2015
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Ingår i: JAMA neurology. - : American Medical Association (AMA). - 2168-6157 .- 2168-6149. ; 72:2
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Tidskriftsartikel (refereegranskat)abstract
- Recently, a rare variant in the amyloid precursor protein gene (APP) was described in a population from Iceland. This variant, in which alanine is replaced by threonine at position 673 (A673T), appears to protect against late-onset Alzheimer disease (AD). We evaluated the frequency of this variant in AD cases and cognitively normal controls to determine whether this variant will significantly contribute to risk assessment in individuals in the United States.
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