High-resolution simulations of planetesimal formation in turbulent protoplanetary discs

We present high-resolution computer simulations of dust dynamics and planetesimal formation in turbulence generated by the magnetorotational instability. We show that the turbulent viscosity associated with magnetorotational turbulence in a non-stratified shearing box increases when going from 256^3 to 512^3 grid points in the presence of a weak imposed magnetic field, yielding a turbulent viscosity of $\alpha\approx0.003$ at high resolution. Particles representing approximately meter-sized boulders concentrate in large-scale high-pressure regions in the simulation box. The appearance of zonal flows and particle concentration in pressure bumps is relatively similar at moderate (256^3) and high (512^3) resolution. In the moderate-resolution simulation we activate particle self-gravity at a time when there is little particle concentration, in contrast with previous simulations where particle self-gravity was activated during a concentration event. We observe that bound clumps form over the next ten orbits, with initial birth masses of a few times the dwarf planet Ceres. At high resolution we activate self-gravity during a particle concentration event, leading to a burst of planetesimal formation, with clump masses ranging from a significant fraction of to several times the mass of Ceres. We present a new domain decomposition algorithm for particle-mesh schemes. Particles are spread evenly among the processors and the local gas velocity field and assigned drag forces are exchanged between a domain-decomposed mesh and discrete blocks of particles. We obtain good load balancing on up to 4096 cores even in simulations where particles sediment to the mid-plane and concentrate in pressure bumps.Comment: Accepted for publication in Astronomy & Astrophysics, with some changes in response to referee repor

Paradigms in environmental management research : outline of an ecosophical-hermeneutic alternative

Doctoral thesis (Ph.D.) – Bodø Graduate School of Business, 2011The first aim of the dissertation is to develop a conceptual tool (two paradigms) for the purpose of analyzing Environmental Impact Assessments (EIA). This positions the dissertation in a field which includes environmental management, the philosophy of science, environmental philosophy and ethics. Thus making the research at hand, to a great extent, an interdisciplinary piece of research. Using two research paradigms, Johansen discusses six Norwegian EIA cases with regard to ontology (nature and human), perception of science, scientific ideals, ethics and esthetics. The intention of the analysis is to illuminate the paradigmatic presuppositions governing Norwegian EIA-кesearch. Part V of the dissertation discusses the transition from atomistic to holistic EIA-research. Through applying hermeneutical reflexive methodology, the thesis reveals findings of significance: the manuals on EIA and EIA reports are characterized by an ever increasing incoherence (from EIA report on Veslefrikk of 1987 to Goliat, 2009). Concretely this means that contemporary Norwegian EIA-research can be characterized as much “talk”, or promises about sound ethical and humanistic concerns, and less “walk”, or little actual research and implementation of the norms and values promised; hence then the lack of correspondence (incoherence) between values (ontology) and method/practice. The kernel message of this dissertation is to make it clear that the reason why humanistic and environmental concerns are absent and left out in the shade can be explained by the epistemological and methodological choices of EIA-researchers. These choices in turn result in consequences for ontology. The dissertation discusses it being necessary to use the epistemological position of hermeneutics in order to gain a deeper (intuitive and emphatic) understanding (‘Verstehen’) of social and environmental impacts. This method utilizes a subject-subject relationship between the researcher and the study object in order to understand the inner unique experience of subjects and social phenomena. The thesis suggests several ways forward (ontologically, epistemologically and methodologically) with regard to how current atomistic EIA-research can be developed into holistic EIA-research

Fast and rewritable colloidal assembly via field synchronized particle swapping

We report a technique to realize reconfigurable colloidal crystals by using the controlled motion of particle defects above an externally modulated magnetic substrate. The transport of particles is induced by applying a uniform rotating magnetic field to a ferrite garnet film characterized by a periodic lattice of magnetic bubbles. For filling factor larger than one colloid per bubble domain, the particle current arises from propagating defects where particles synchronously exchange their position when passing from one occupied domain to the next. The amplitude of an applied alternating magnetic field can be used to displace the excess particles via a swapping mechanism, or to mobilize the entire colloidal system at a predefined speed

Monism in Aristotle’s Metaphysics I.3–5

Scholars have often seen Parmenides as entirely opposed to earlier materialistic philosophy. In this paper I argue that what is more striking in Aristotle’s Metaphysics Book I is the degree of continuity that he sees between Parmenides and the material monists. I explore this coupling of Parmenides with the material monists to understand better what he takes to be distinctive and problematic with Parmenides’ monism

Leveraging Computer Vision for Applications in Biomedicine and Geoscience

Skin cancer is one of the most common types of cancer and is usually classified as either non-melanoma and melanoma skin cancer. Melanoma skin cancer accounts for about half of all skin cancer-related deaths. The 5-year survival rate is 99% when the cancer is detected early but drops to 25% once it becomes metastatic. In other words, the key to preventing death is early detection. Foraminifera are microscopic single-celled organisms that exist in marine environments and are classified as living a benthic or planktic lifestyle. In total, roughly 50,000 species are known to have existed, of which about 9,000 are still living today. Foraminifera are important proxies for reconstructing past ocean and climate conditions and as bio-indicators of anthropogenic pollution. Since the 1800s, the identification and counting of foraminifera have been performed manually. The process is resource-intensive. In this dissertation, we leverage recent advances in computer vision, driven by breakthroughs in deep learning methodologies and scale-space theory, to make progress towards both early detection of melanoma skin cancer and automation of the identification and counting of microscopic foraminifera. First, we investigate the use of hyperspectral images in skin cancer detection by performing a critical review of relevant, peer-reviewed research. Second, we present a novel scale-space methodology for detecting changes in hyperspectral images. Third, we develop a deep learning model for classifying microscopic foraminifera. Finally, we present a deep learning model for instance segmentation of microscopic foraminifera. The works presented in this dissertation are valuable contributions in the fields of biomedicine and geoscience, more specifically, towards the challenges of early detection of melanoma skin cancer and automation of the identification, counting, and picking of microscopic foraminifera