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Umeå, Sweden

Mann I.,UmeaUniversity | Meyer-Vernet N.,University Paris Diderot | Czechowski A.,Polish Academy of Sciences
Physics Reports | Year: 2014

Cosmic dust particles are small solid objects observed in the solar planetary system and in many astronomical objects like the surrounding of stars, the interstellar and even the intergalactic medium. In the solar system the dust is best observed and most often found within the region of the orbits of terrestrial planets where the dust interactions and dynamics are observed directly from spacecraft. Dust is observed in space near Earth and also enters the atmosphere of the Earth where it takes part in physical and chemical processes. Hence space offers a laboratory to study dust-plasma interactions and dust dynamics. A recent example is the observation of nanodust of sizes smaller than 10 nm. We outline the theoretical considerations on which our knowledge of dust electric charges in space plasmas are founded. We discuss the dynamics of the dust particles and show how the small charged particles are accelerated by the solar wind that carries a magnetic field. Finally, as examples for the space observation of cosmic dust interactions, we describe the first detection of fast nanodust in the solar wind near Earth orbit and the first bi-static observations of PMSE, the radar echoes that are observed in the Earth ionosphere in the presence of charged dust. © 2013 Elsevier B.V.


Panchuk A.,Ukrainian Academy of Sciences | Puu T.,UmeaUniversity
Mathematics and Computers in Simulation | Year: 2015

The aim of the present paper is to investigate an oligopoly market, modelled by using CES production function in combination with the isoelastic demand function. It is supposed that the competitors act not under constant, but eventually decaying returns, and thus, from time to time they need to renew their capital equipment, choosing its optimal amount according to the current market situation. It is shown that the asymptotic trajectories depend essentially on the value of the global capital durability, and are also sensitive to the initial choice of individual inactivity times. In particular, the firms may merge into different groups renewing their capitals simultaneously, which lead to distinct dynamical patterns. It is also studied how the capital wearing out rate influences the system behaviour. © 2013 IMACS.


Wadbro E.,UmeaUniversity | Engstrom C.,Statistics Sweden
Computer Methods in Applied Mechanics and Engineering | Year: 2015

Metallic nano-antennas are devices used to concentrate the energy in light into regions that are much smaller than the wavelength. These structures are currently used to develop new measurement and printing techniques, such as optical microscopy with sub-wavelength resolution, and high-resolution lithography. Here, we analyze and design a nano-antenna in a two-dimensional setting with the source being a planar TE-polarized wave. The design problem is to place silver and air in a pre-specified design region to maximize the electric energy in a small given target region. At optical frequencies silver exhibits extreme dielectric properties, having permittivity with a negative real part. We prove existence and uniqueness of solutions to the governing non-standard Helmholtz equation with absorbing boundary conditions. To solve the design optimization problem, we develop a two-stage procedure. The first stage uses a material distribution parameterization and aims at finding a conceptual design without imposing any a priori information about the number of shapes of components comprising the nano-antenna. The second design stage uses a domain variation approach and aims at finding a precise shape. Both of the above design problems are formulated as non-linear mathematical programming problems that are solved using the method of moving asymptotes. The final designs perform very well and the electric energy in the target region is several orders of magnitude larger than when there is only air in the design region. The performance of the optimized designs is verified with a high order interior penalty method. © 2015 Elsevier B.V.


Holme P.,UmeaUniversity | Holme P.,Sungkyunkwan University | Holme P.,University of Stockholm | Saramaki J.,Aalto University
Physics Reports | Year: 2012

A great variety of systems in nature, society and technology-from the web of sexual contacts to the Internet, from the nervous system to power grids-can be modeled as graphs of vertices coupled by edges. The network structure, describing how the graph is wired, helps us understand, predict and optimize the behavior of dynamical systems. In many cases, however, the edges are not continuously active. As an example, in networks of communication via e-mail, text messages, or phone calls, edges represent sequences of instantaneous or practically instantaneous contacts. In some cases, edges are active for non-negligible periods of time: e.g.,the proximity patterns of inpatients at hospitals can be represented by a graph where an edge between two individuals is on throughout the time they are at the same ward. Like network topology, the temporal structure of edge activations can affect dynamics of systems interacting through the network, from disease contagion on the network of patients to information diffusion over an e-mail network. In this review, we present the emergent field of temporal networks, and discuss methods for analyzing topological and temporal structure and models for elucidating their relation to the behavior of dynamical systems. In the light of traditional network theory, one can see this framework as moving the information of when things happen from the dynamical system on the network, to the network itself. Since fundamental properties, such as the transitivity of edges, do not necessarily hold in temporal networks, many of these methods need to be quite different from those for static networks. The study of temporal networks is very interdisciplinary in nature. Reflecting this, even the object of study has many names-temporal graphs, evolving graphs, time-varying graphs, time-aggregated graphs, time-stamped graphs, dynamic networks, dynamic graphs, dynamical graphs, and so on. This review covers different fields where temporal graphs are considered, but does not attempt to unify related terminology-rather, we want to make papers readable across disciplines. © 2012 Elsevier B.V.


Lindgren H.,UmeaUniversity | Eriksson S.,Northern Sweden University Hospital
Studies in Health Technology and Informatics | Year: 2010

The need for improving dementia care has driven the development of the clinical decision support system DMSS (Dementia Management and Support System). A sociotechnical approach to design and development has been applied, with an activity-centered methodology and user participation throughout the process. Prototypes have been developed based on the characteristics of clinical practice and domain knowledge, while clinical practice has been subjected to different efforts for development such as education and organizational change. This paper addresses the lessons learned and role and impact DMSS has had, and is expected to have on the clinical assessment of dementia in different clinics in Sweden, South Korea and Japan. Furthermore, it will be described in what way the development of DMSS and the development of dementia care in these three areas are interlinked. Results indicate that the most important contribution of DMSS at the point of care, is the educational support that DMSS provides, part from the tailored explanatory support related to a patient case. This effect was partly manifested in a change of routines in the encounter with patients. © 2010 The authors and IOS Press. All rights reserved.

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