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Sökning: WFRF:(Müller Jürgen)

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21.
  • Müller, Birgit, et al. (författare)
  • Standardised and transparent model descriptions for agent-based models : Current status and prospects
  • 2014
  • Ingår i: Environmental Modelling & Software. - : Elsevier BV. - 1364-8152 .- 1873-6726. ; 55, s. 156-163
  • Tidskriftsartikel (refereegranskat)abstract
    • Agent-based models are helpful to investigate complex dynamics in coupled human natural systems. However, model assessment, model comparison and replication are hampered to a large extent by a lack of transparency and comprehensibility in model descriptions. In this article we address the question of whether an ideal standard for describing models exists. We first suggest a classification for structuring types of model descriptions. Secondly, we differentiate purposes for which model descriptions are important. Thirdly, we review the types of model descriptions and evaluate each on their utility for the purposes. Our evaluation finds that the choice of the appropriate model description type is purpose-dependent and that no single description type alone can fulfil all requirements simultaneously. However, we suggest a minimum standard of model description for good modelling practice, namely the provision of source code and an accessible natural language description, and argue for the development of a common standard.
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22.
  • Müller, Christoph A., et al. (författare)
  • Dynamic 2D and 3D mapping of hyperpolarized pyruvate to lactate conversion in vivo with efficient multi-echo balanced steady-state free precession at 3 T
  • 2020
  • Ingår i: NMR in Biomedicine. - : Wiley. - 0952-3480 .- 1099-1492. ; 33:6
  • Tidskriftsartikel (refereegranskat)abstract
    • The aim of this study was to acquire the transient MRI signal of hyperpolarized tracers and their metabolites efficiently, for which specialized imaging sequences are required. In this work, a multi-echo balanced steady-state free precession (me-bSSFP) sequence with Iterative Decomposition with Echo Asymmetry and Least squares estimation (IDEAL) reconstruction was implemented on a clinical 3 T positron-emission tomography/MRI system for fast 2D and 3D metabolic imaging. Simulations were conducted to obtain signal-efficient sequence protocols for the metabolic imaging of hyperpolarized biomolecules. The sequence was applied in vitro and in vivo for probing the enzymatic exchange of hyperpolarized [1–13C]pyruvate and [1–13C]lactate. Chemical shift resolution was achieved using a least-square, iterative chemical species separation algorithm in the reconstruction. In vitro, metabolic conversion rate measurements from me-bSSFP were compared with NMR spectroscopy and free induction decay-chemical shift imaging (FID-CSI). In vivo, a rat MAT-B-III tumor model was imaged with me-bSSFP and FID-CSI. 2D metabolite maps of [1–13C]pyruvate and [1–13C]lactate acquired with me-bSSFP showed the same spatial distributions as FID-CSI. The pyruvate-lactate conversion kinetics measured with me-bSSFP and NMR corresponded well. Dynamic 2D metabolite mapping with me-bSSFP enabled the acquisition of up to 420 time frames (scan time: 180-350 ms/frame) before the hyperpolarized [1–13C]pyruvate was relaxed below noise level. 3D metabolite mapping with a large field of view (180 × 180 × 48 mm3) and high spatial resolution (5.6 × 5.6 × 2 mm3) was conducted with me-bSSFP in a scan time of 8.2 seconds. It was concluded that Me-bSSFP improves the spatial and temporal resolution for metabolic imaging of hyperpolarized [1–13C]pyruvate and [1–13C]lactate compared with either of the FID-CSI or EPSI methods reported at 3 T, providing new possibilities for clinical and preclinical applications.
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23.
  • Müller, Carsten, et al. (författare)
  • Quantum Monte Carlo Calculation of Correlation Effects on Bond Orders
  • 2007
  • Ingår i: Theoretical Chemistry accounts. - : Springer Science and Business Media LLC. - 1432-881X .- 1432-2234. ; 117:1, s. 41-48
  • Tidskriftsartikel (refereegranskat)abstract
    • We present a computational approach, using quantum Monte Carlo, that provides some insight into the effect of electron correlation on chemical bonding between individual pairs of atoms. Our approach rests upon a recently suggested relation between the bond order and charge fluctuations with respect to atomic domains. Within the present implementation we have taken a compromise between conceptual rigour and computational simplicity. In a first step atomic domains were obtained from Hartree-Fock (HF) densities, using Bader’s definition of atoms in molecules. These domains were used in a second step in quantum Monte Carlo calculations to determine bond orders for pairs of atoms. Correlation effects have been studied by comparison of HF bond orders with those obtained from pure diffusion quantum Monte Carlo calculations. We illustrate this concept for C–O and C–S bonds in different molecular environments. Our results suggest an approximate linear relation between bond order and bond length for these kinds of bonds.
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24.
  • Müller-Hansen, Finn, et al. (författare)
  • A matrix clustering method to explore patterns of land-cover transitions in satellite-derived maps of the Brazilian Amazon
  • 2017
  • Ingår i: Nonlinear processes in geophysics. - : Copernicus GmbH. - 1023-5809 .- 1607-7946. ; 24:1, s. 113-123
  • Tidskriftsartikel (refereegranskat)abstract
    • Changes in land-use systems in tropical regions, including deforestation, are a key challenge for global sustainability because of their huge impacts on green-house gas emissions, local climate and biodiversity. However, the dynamics of land-use and land-cover change in regions of frontier expansion such as the Brazilian Amazon are not yet well understood because of the complex interplay of ecological and socioeconomic drivers. In this paper, we combine Markov chain analysis and complex network methods to identify regimes of land-cover dynamics from land-cover maps (TerraClass) derived from high-resolution (30 m) satellite imagery. We estimate regional transition probabilities between different land-cover types and use clustering analysis and community detection algorithms on similarity networks to explore patterns of dominant land- cover transitions. We find that land- cover transition probabilities in the Brazilian Amazon are heterogeneous in space, and adjacent subregions tend to be assigned to the same clusters. When focusing on transitions from single land- cover types, we uncover patterns that reflect major regional differences in land-cover dynamics. Our method is able to summarize regional patterns and thus complements studies performed at the local scale.
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25.
  • Müller-Hansen, Finn, et al. (författare)
  • Can Intensification of Cattle Ranching Reduce Deforestation in the Amazon? Insights From an Agent-based Social-Ecological Model
  • 2019
  • Ingår i: Ecological Economics. - : Elsevier BV. - 0921-8009 .- 1873-6106. ; 159, s. 198-211
  • Tidskriftsartikel (refereegranskat)abstract
    • Deforestation in the Amazon with its vast consequences for the ecosystem and climate is largely related to subsequent land use for cattle ranching. In addition to conservation policies, proposals to reduce deforestation include measures to intensify cattle ranching. However, the effects of land-use intensification on deforestation are debated in the literature. This paper introduces the abacra model, a stylized agent-based model to study the interplay of deforestation and the intensification of cattle ranching in the Brazilian Amazon. The model combines social learning and ecological processes with market dynamics. In the model, agents adopt either an extensive or semi-intensive strategy of cattle ranching based on the success of their neighbors. They earn their income by selling cattle on a stylized market. We present a comprehensive analysis of the model with statistical methods and find that it produces highly non-linear transient outcomes in dependence on key parameters like the rate of social interaction and elasticity of the cattle price. We show that under many environmental and economic conditions, intensification does not reduce deforestation rates and sometimes even has a detrimental effect on deforestation. Anti-deforestation policies incentivizing fast intensification can only lower deforestation rates under conditions in which the local cattle market saturates.
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26.
  • Ott, Jürgen, et al. (författare)
  • Cm and mm Survey of Molecular Absorption Lines in Centaurus A
  • 2012
  • Ingår i: American Astronomical Society, AAS Meeting. ; 219, s. 349.26-
  • Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
    • We present Australia Telescope Array data of molecular absorption lines toward the bright central core of Centaurus A. The line of sight crosses the prominent dust lane and continues through the disk and eventually through gas that may be very close to the central supermassive black hole. The goal of our the survey is to determine the physical conditions of the gas via analyses of molecular line tracers including molecular abundances and excitation that is sensitive to changes in temperature, density, ionization, and shocks. This study allows us to derive the physical conditions of every absorption line complex and finally let us assign the most likely environments. We present ATCA data in the 20-50GHz range at medium resolution of a few km/s and possibly ALMA data at 3mm and 1mm wavelengths. The project continues with sub-km/s higher spectral resolution for the most important lines in 2012.
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27.
  • Piiper, Albrecht, et al. (författare)
  • Cyclic AMP induces transactivation of the receptors for epidermal growth factor and nerve growth factor, thereby modulating activation of MAP kinase, Akt, and neurite outgrowth in PC12 cells.
  • 2002
  • Ingår i: J Biol Chem. - 0021-9258. ; 277:46, s. 43623-30
  • Tidskriftsartikel (refereegranskat)abstract
    • In PC12 cells, a well studied model for neuronal differentiation, an elevation in the intracellular cAMP level increases cell survival, stimulates neurite outgrowth, and causes activation of extracellular signal-regulated protein kinase 1 and 2 (ERK1/2). Here we show that an increase in the intracellular cAMP concentration induces tyrosine phosphorylation of two receptor tyrosine kinases, i.e. the epidermal growth factor (EGF) receptor and the high affinity receptor for nerve growth factor (NGF), also termed Trk(A). cAMP-induced tyrosine phosphorylation of the EGF receptor is rapid and correlates with ERK1/2 activation. It occurs also in Panc-1, but not in human mesangial cells. cAMP-induced tyrosine phosphorylation of the NGF receptor is slower and correlates with Akt activation. Inhibition of EGF receptor tyrosine phosphorylation, but not of the NGF receptor, reduces cAMP-induced neurite outgrowth. Expression of dominant-negative Akt does not abolish cAMP-induced survival in serum-free media, but increases cAMP-induced ERK1/2 activation and neurite outgrowth. Together, our results demonstrate that cAMP induces dual signaling in PC12 cells: transactivation of the EGF receptor triggering the ERK1/2 pathway and neurite outgrowth; and transactivation of the NGF receptor promoting Akt activation and thereby modulating ERK1/2 activation and neurite outgrowth.
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28.
  • Poutanen, Markku, et al. (författare)
  • DynaQlim – Upper Mantle Dynamics and Quaternary Climate in Cratonic Areas
  • 2010
  • Ingår i: New Frontiers in Integrated Solid Earth Sciences. - Dordrecht : Springer. - 9789048127368 - 9789048127375 ; , s. 349-372
  • Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
    • The isostatic adjustment of the solid Earth to the glacial loading (GIA, Glacial Isostatic Adjustment) with its temporal signature offers a great opportunity to retrieve information of Earth’s upper mantle to the changing mass of glaciers and ice sheets, which in turn is driven by variations in Quaternary climate. DynaQlim (Upper Mantle Dynamics and Quaternary Climate in Cratonic Areas) has its focus to study the relations between upper mantle dynamics, its composition and physical properties, temperature, rheology, and Quaternary climate. Its regional focus lies on the cratonic areas of northern Canada and Scandinavia.Geodetic methods like repeated precise levelling, tide gauges, high-resolution observations of recent movements, gravity change and monitoring of postglacial faults have given information on the GIA process for more than 100 years. They are accompanied by more recent techniques like GPS observations and the GRACE and GOCE satellite missions which provide additional global and regional constraints on the gravity field. Combining geodetic observations with seismological investigations, studies of the postglacial faults and continuum mechanical modelling of GIA, DynaQlim offers new insights into properties of the lithosphere. Another step toward a better understanding of GIA has been the joint inversion of different types of observational data – preferentially connected with geological relative sea-level evidence of the Earth’s rebound during the last 10,000 years.Due to the changes in the lithospheric stress state large faults ruptured violently at the end of the last glaciation in large earthquakes, up to the magnitudes MW = 7–8. Whether the rebound stress is still able to trigger a significant fraction of intraplate seismic events in these regions is not completely understood due to the complexity and spatial heterogeneity of the regional stress field. Understanding of this mechanism is of societal importance.Glacial ice sheet dynamics are constrained by the coupled process of the deformation of the viscoelastic solid Earth, the ocean and climate variability. Exactly how the climate and oceans reorganize to sustain growth of ice sheets that ground to continents and shallow continental shelves is poorly understood. Incorporation of nonlinear feedback in modelling both ocean heat transport systems and atmospheric CO2 is a major challenge. Climate-related loading cycles and episodes are expected to be important, hence also more short-term features of palaeoclimate should be explicitly treated.Within this Chapter View ChapterIntroductionObservational BasisCurrent Models and Problems to be SolvedClimateChallenges with DynaQlimReferencesReferencesOther actionsExport citationsAbout this BookReprints and Permissions
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29.
  • Sandin, Peter, et al. (författare)
  • Diastereoselective self-assembly of clofarabine lipids
  • 2014
  • Ingår i: New Journal of Chemistry. - 1144-0546 .- 1369-9261. ; 38:11, s. 5247-5253
  • Tidskriftsartikel (refereegranskat)abstract
    • Clofarabine is a nucleosidic chemotherapeutic approved for the treatment of acute lymphoblastic leukemia, currently undergoing clinical trials for the treatment of solid tumors. Like for many others, lipidic derivatization of this drug improves pharmacokinetics and relieves the heavy side effects. Since the self-assembly pattern can modulate the bioactivity profile, a precise knowledge of the aggregation behavior of these nucleolipids and of the microstructure of the aggregates is central to design formulations that efficiently provide sufficient bioavailability. In this contribution we investigate the self-assembly behavior of two Clofarabine dioxy-ether derivatives, the diastereomers (1-2S and 1-2R). These clofarabine lipid derivatives showed an unexpected diastereoselective self-assembly effect, which we have monitored by observing the time evolution of self-assemblies and their microstructural response to thermal treatment. Dynamic Light Scattering and Circular Dichroism provide an ensemble of results which correlate with the occurrence of a hierarchical association of wormlike aggregates, imaged using Electron Microcopy. A strikingly different behavior for the two diastereomers was observed. This behavior can be crucial for the different bioavailability observed in vivo.
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30.
  • Schlüter, Maja, et al. (författare)
  • A framework for mapping and comparing behavioural theories in models of social-ecological systems
  • 2017
  • Ingår i: Ecological Economics. - : Elsevier BV. - 0921-8009 .- 1873-6106. ; 131, s. 21-35
  • Tidskriftsartikel (refereegranskat)abstract
    • Formal models are commonly used in natural resource management (NRM) to study human-environment interactions and inform policy making. In the majority of applications, human behaviour is represented by the rational actor model despite growing empirical evidence of its shortcomings in NRM contexts. While the importance of accounting for the complexity of human behaviour is increasingly recognized, its integration into formal models remains a major challenge. The challenges are multiple: i) there exist many theories scattered across the social sciences, ii) most theories cover only a certain aspect of decision-making, iii) they vary in their degree of formalization, iv) causal mechanisms are often not specified. We provide a framework- MoHuB (Modelling Human Behavior) - to facilitate a broader inclusion of theories on human decision-making in formal NRM models. It serves as a tool and common language to describe, compare and communicate alternative theories. In doing so, we not only enhance understanding of commonalities and differences between theories, but take a first step towards tackling the challenges mentioned above. This approach may enable modellers to find and formalize relevant theories, and be more explicit and inclusive about theories of human decision making in the analysis of social ecological systems.
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