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Aalto University is a university primarily located in Greater Helsinki, Finland. It was created as a merger of three leading Finnish universities: the Helsinki University of Technology , the Helsinki School of Economics , and the University of Art and Design Helsinki . The close collaboration between the scientific, business and arts communities is intended to foster multi-disciplinary education and research. The Finnish government, in 2010, set out to create a university that has innovation built into its foundations, merging three institutions into one along the way, forming an entity that serves as Finland's model for an innovation university.It comprises six schools with over 19,000 students and 5,000 staff members, thus being Finland's third-largest university. The six schools of Aalto University are all renowned institutions in their respective fields. The main campus of Aalto University is located in Otaniemi, Espoo, where the engineering schools operate, with two schools currently headquartered in Helsinki: the School of Business in Töölö and the School of Arts, Design and Architecture in Arabianranta . In addition, the university operates several units outside Greater Helsinki in Mikkeli, Pori and Vaasa.Aalto university's operations showcase Finland’s bold new experiment in higher education. The Aalto Design Factory, AppCampus, ADD LAB and Aalto Ventures Program, among others, drive the university's mission for a radical shift towards multidisciplinary learning and have contributed substantially to the emergence of Helsinki as a hotbed for startups. Aaltoes, which stands for Aalto Entrepreneurship Society, is Europe’s largest student run entrepreneurship community and organises the Startup Sauna accelerator program for startups, raising more than US$36 million in funding since 2010.The university is named in honour of Alvar Aalto, a prominent Finnish architect, designer and alumnus of the former Helsinki University of Technology, who was also instrumental in designing a large part of the university's main campus in Otaniemi. Wikipedia.

Volovik G.E.,Aalto University | Volovik G.E.,L D Landau Institute For Theoretical Physics | Zubkov M.A.,ITEP
Annals of Physics | Year: 2014

First of all, we reconsider the tight-binding model of monolayer graphene, in which the variations of the hopping parameters are allowed. We demonstrate that the emergent 2. D Weitzenbock geometry as well as the emergent U (1) gauge field appear. The emergent gauge field is equal to the linear combination of the components of the zweibein. Therefore, we actually deal with the gauge fixed version of the emergent 2 + 1 D teleparallel gravity. In particular, we work out the case, when the variations of the hopping parameters are due to the elastic deformations, and relate the elastic deformations with the emergent zweibein. Next, we investigate the tight-binding model with the varying intralayer hopping parameters for the multilayer graphene with the A B C stacking. In this case the emergent 2. D Weitzenbock geometry and the emergent U (1) gauge field appear as well, and the emergent low energy effective field theory has the anisotropic scaling. © 2013 Elsevier Inc.

In this paper, a novel strain-based approach for the fatigue strength modelling of welded steel joints is introduced. The actual weld notch geometry and the variation in the microstructure characteristics of the material are considered, and thus, the approach enables the fatigue crack growth simulation from the crack initiation to the critical crack length before the final fracture. The predicted fatigue strength is in line with the experimental results. By considering the crack tip plasticity and stress triaxiality, the approach is able to describe the different crack growth periods of the fatigue life: the short crack, long crack, and tearing-related long crack growth periods. For a welded joint with a smooth notch shape, the short crack growth period is observed to be dominant and to have a significant influence on fatigue life. © 2013 Elsevier Ltd. All rights reserved.

Kuosmanen N.,Mtt Agrifood Research Finland | Kuosmanen T.,Aalto University
Ecological Economics | Year: 2013

Nutrients such as nitrogen and phosphorus have a dual role as inputs to crop production and as pollutants to water, air, and soil. The nutrient surplus measures are frequently used as indicators of environmental performance or eco-efficiency at micro level of individual farms and at macro levels of regions and countries. However, the static material balance accounting ignores an important dimension of the nutrient cycle: the time. Nutrients accumulate in soil, causing delayed effects and persistent harm to the environment. In this paper we propose a dynamic model of material balance, following the standard model of capital accumulation used in production economics. Using data of agricultural production in Finland in the years 1961-2009, we show that it is possible to estimate the stocks of nitrogen and phosphorus accumulated in the soil using information and data that are readily available. The dynamic model allows us to estimate not only the stocks of nutrients, but also the outflow of nutrients to water and air. Better understanding of flows and stocks of nutrients can provide insights to support managerial and policy decisions. © 2013 Elsevier B.V.

Onnela J.-P.,Harvard University | Onnela J.-P.,University of Oxford | Onnela J.-P.,Aalto University | Reed-Tsochas F.,University of Oxford
Proceedings of the National Academy of Sciences of the United States of America | Year: 2010

Social influence drives both offline and online human behavior. It pervades cultural markets, and manifests itself in the adoption of scientific and technical innovations as well as the spread of social practices. Prior empirical work on the diffusion of innovations in spatial regions or social networkshas largely focusedonthespreadof one particular technology among a subset of all potential adopters. Here we choose an online context that allows us to study social influence processes by tracking the popularity of a complete set of applications installed by the user population of a social networking site, thus capturing the behavior of all individuals who can influence each other in this context. By extending standard fluctuation scaling methods, we analyze the collective behavior induced by 100 million application installations, and show that two distinct regimes of behavior emerge in the system. Once applications cross a particular threshold of popularity, social influence processes induce highly correlated adoption behavior among the users, which propels some of the applications to extraordinary levels of popularity. Below this threshold, the collective effect of social influence appears to vanish almost entirely, in a manner that has not been observed in the offline world. Our results demonstrate that even when external signals are absent, social influence can spontaneously assume an on-off nature in a digital environment. It remains to be seenwhether a similar outcome could be observed in the offlineworld if equivalent experimental conditions could be replicated.

Gelman A.,Columbia University | Hwang J.,Harvard University | Vehtari A.,Aalto University
Statistics and Computing | Year: 2013

We review the Akaike, deviance, and Watanabe-Akaike information criteria from a Bayesian perspective, where the goal is to estimate expected out-of-sample-prediction error using a bias-corrected adjustment of within-sample error. We focus on the choices involved in setting up these measures, and we compare them in three simple examples, one theoretical and two applied. The contribution of this paper is to put all these information criteria into a Bayesian predictive context and to better understand, through small examples, how these methods can apply in practice. © 2013 Springer Science+Business Media New York.

Gacanin H.,Motive | Salmela M.,Aalto University | Adachi F.,Tohoku University
IEEE Transactions on Wireless Communications | Year: 2012

Broadcast nature of the wireless channel enables wireless communications to make use of network coding at the physical layer (PNC) to improve the network capacity. Recently, narrowband and later broadband analog network coding (ANC) were introduced as a simpler implementation of PNC. The ANC schemes require two time slots while in PNC three time slots are required for bi-directional communication between two nodes and hence ANC is more spectrum efficient. The coherent detection and self-information removal in ANC require accurate channel state information (CSI). {In this paper, we theoretically analyze the bit error rate (BER) performance with imperfect knowledge of CSI for broadband ANC using orthogonal frequency division multiplexing (OFDM), where the channel estimation error is modeled as a zero-mean complex Gaussian random variable. We investigate the BER performance for three cases: (i) the effect of imperfect self-information removal due to channel estimation (CE) error with fading tracking errors, (ii) the effect of imperfect self-information removal due to CE error without fading tracking errors}, and (iii) the ideal CE case. We discuss how, and by how much, our results obtained by theoretical analysis can be used for design of broadband ANC system with the imperfect knowledge of CSI. Our results show that imperfect channel estimation due to the noise effect has less impact on self-information removal than the imperfect channel estimation due to fading tracking errors. The tracking against fading is an important problem for accurate self-information removal as well as coherent detection and thus, the effect of channel time-selectivity is also theoretically studied. The achievable BER performance gains due to the polynomial time-domain channel interpolation are investigated using the derived close-form BER expressions and it was shown that the broadband ANC schemes with practical CE in a time- and frequency-selective channel should include a more sophisticated channel interpolation techniques since the impact of Doppler shift has prevalent effect on the achievable BER performance. © 2012 IEEE.

Laurson L.,ISI Foundation | Miguel M.-C.,University of Barcelona | Alava M.J.,Aalto University
Physical Review Letters | Year: 2010

Dislocation assemblies exhibit a jamming or yielding transition at a critical external shear stress value σ=σc. Here we study the heterogeneous and collective nature of dislocation dynamics within a crystal plasticity model close to σc, by considering the first-passage properties of the dislocation dynamics. As the transition is approached in the moving phase, the first-passage time distribution exhibits scaling, and a related peak dynamical susceptibility χ4* diverges as χ4*∼(σ- σc)-α, with α ≈ 1.1. We relate this scaling to an avalanche description of the dynamics. While the static structural correlations are found to be independent of the external stress, we identify a diverging dynamical correlation length ξy in the direction perpendicular to the dislocation glide motion. © 2010 The American Physical Society.

Monni S.,Benviroc Ltd | Syri S.,Aalto University
Energy Policy | Year: 2011

Local authorities need timely information on their greenhouse gas (GHG) emissions and their causes, comparison with other municipalities and tools for dissemination of information to the citizens. This paper presents a weekly GHG emission calculation system, CO2-report, which provides such data for citizens and local decision-makers in a timely manner, in contrast to the official emissions statistics, which are available on an annual basis 1-2 years afterwards. In this paper, we present the methodology and three main outputs of CO2-report: (1) weekly GHG emissions; (2) advance annual emissions; and (3) final annual emissions for 2009 with comparison of 64 municipalities in Finland. We explain the reasons for the large variability of annual emissions, from 5 to 13t CO2-eq/capita, discuss the accuracy of advance and final emission estimates at local level, and show the weekly variability of emissions for three example municipalities with different emission profiles. © 2011 Elsevier Ltd.

Frank D.,Aalto University
International Journal of Fatigue | Year: 2015

This study investigates the applicability of local stress- and energy-based approaches to the fatigue strength assessment of laser stake-welded T-joints. The T-joint has two crack-like notches with infinitesimal tip rounding on each side of the weld. The local approaches used are fictitious tip rounding of 1 and 0.05 mm and the approaches that assume zero rounding within this study, namely the stress intensity factor, the average strain energy density and the J-integral. It is shown that the slopes of the fatigue resistance curves vary between 4 and 8 under different loading conditions imposed on the joint. The slope value exhibits a linear relation with the dimensionless gradient of the maximum principal stress evaluated at the critical notch tip. The same linear relation between the slope and the gradient is valid for all approaches. Because of the slopes, which differ from the usual 3, the agreement of the T-joints with other steel joints is obtained at five million load cycles. The exception is the fictitious rounding concept of 0.05 mm, in which case the recommended design S-N curve with a slope of 3 appears overly conservative in a high-cycle regime. © 2014 Elsevier Ltd. All rights reserved.

Maloney T.C.,Aalto University
Holzforschung | Year: 2015

This study examines the swelling of TEMPO-oxidized nanofibrillated cellulose (NFCTEMPO, shortly NFC) on both the particle and interparticle levels. The sum of the intraparticle and interparticle swelling is referred to as the network swelling. A centrifugal method, based on a modification of the water retention value test, was used to measure the network swelling of NFC, a pigment, and some pulp fibers. It was found that the network swelling of NFC is highly dependent on its concentration within a fiber matrix. The particle swelling of NFC and pulp fibers was analyzed by differential scanning calorimetry (DSC) and solute exclusion. The counterion for the NFC varied among the Na+, H+, and Ca2+ forms. The counterion has a very large effect on the particle and network swelling of NFC, with Ca2+ giving the lowest swelling and Na+ the highest swelling. An industrially feasible method for changing the counterion of NFC from the nominal Na+ to the Ca2+ form, and thus improving dewatering properties, is given. © 2015 by De Gruyter.

Ward P.J.,VU University Amsterdam | Jongman B.,VU University Amsterdam | Kummu M.,Aalto University | Dettinger M.D.,University of California at San Diego | And 2 more authors.
Proceedings of the National Academy of Sciences of the United States of America | Year: 2014

El Niño Southern Oscillation (ENSO) is the most dominant interannual signal of climate variability and has a strong influence on climate over large parts of the world. In turn, it strongly influences many natural hazards (such as hurricanes and droughts) and their resulting socioeconomic impacts, including economic damage and loss of life. However, although ENSO is known to influence hydrology in many regions of the world, little is known about its influence on the socioeconomic impacts of floods (i.e., flood risk). To address this, we developed a modeling framework to assess ENSO's influence on flood risk at the global scale, expressed in terms of affected population and gross domestic product and economic damages. We show that ENSO exerts strong and widespread influences on both flood hazard and risk. Reliable anomalies of flood risk exist during El Niño or La Niña years, or both, in basins spanning almost half (44%) of Earth's land surface. Our results show that climate variability, especially from ENSO, should be incorporated into disaster-risk analyses and policies. Because ENSO has some predictive skill with lead times of several seasons, the findings suggest the possibility to develop probabilistic flood-risk projections, which could be used for improved disaster planning. The findings are also relevant in the context of climate change. If the frequency and/or magnitude of ENSO events were to change in the future, this finding could imply changes in flood-risk variations across almost half of the world's terrestrial regions.

Jarvinen A.,Salk Institute for Biological Studies | Bellugi U.,Aalto University
Frontiers in Human Neuroscience | Year: 2013

Growing evidence on autonomic nervous system (ANS) function in individuals with Williams syndrome (WS) has begun to highlight aberrancies that may have important implications for the social profile characterized by enhanced social motivation and approach. In parallel, neurobiological investigations have identified alterations in the structure, function, and connectivity of the amygdala, as well as prosocial neuropeptide dysregulation, as some of the key neurogenetic features of WS. A recent social approach/withdrawal hypothesis (Kemp and Guastella, 2011) suggests that autonomic cardiac control may play a key role in regulating the relationship between oxytocin and social behavior. This article discusses evidence from these critical, new strands of research into social behavior in WS, to consider the extent to which data on WS may provide novel insight into the determinants of social behavior. Future research directions are suggested. © 2013 Järvinen and Bellugi.

Parviainen P.,KTH Royal Institute of Technology | Koivisto M.,Aalto University
Journal of Machine Learning Research | Year: 2013

We consider the problem of finding a directed acyclic graph (DAG) that optimizes a decomposable Bayesian network score. While in a favorable case an optimal DAG can be found in polynomial time, in the worst case the fastest known algorithms rely on dynamic programming across the node subsets, taking time and space 2n, to within a factor polynomial in the number of nodes n. In practice, these algorithms are feasible to networks of at most around 30 nodes, mainly due to the large space requirement. Here, we generalize the dynamic programming approach to enhance its feasibility in three dimensions: first, the user may trade space against time; second, the proposed algorithms easily and efficiently parallelize onto thousands of processors; third, the algorithms can exploit any prior knowledge about the precedence relation on the nodes. Underlying all these results is the key observation that, given a partial order P on the nodes, an optimal DAG compatible with P can be found in time and space roughly proportional to the number of ideals of P, which can be significantly less than 2n. Considering sufficiently many carefully chosen partial orders guarantees that a globally optimal DAG will be found. Aside from the generic scheme, we present and analyze concrete tradeoff schemes based on parallel bucket orders. © 2013 Pekka Parviainen and Mikko Koivisto.

Zhou M.,Beijing University of Posts and Telecommunications | Cui Q.,Beijing University of Posts and Telecommunications | Jantti R.,Aalto University | Tao X.,Beijing University of Posts and Telecommunications
IEEE Communications Letters | Year: 2012

In this letter, we consider a two-way relay channel (TWRC) with two end nodes and k relay nodes, where end nodes have the full channel-state information (CSI) and relay nodes only have the channel-amplitude information (CAI). With the objective of minimizing transmit power consumption at required end-to-end rates, energy-efficient relay selection (RS) and power allocation (PA) scheme is studied for TWRC based on analog network coding (ANC). Firstly, we propose an energy-efficient single RS and PA (E-SRS-PA) scheme, where the best relay node is selected to minimize total transmit power. Then, we prove that E-SRS-PA scheme is the optimal energy-efficient RS and PA (OE-RS-PA) scheme in ANC-based TWRC, and thus the optimal number of relay nodes to be selected in energy efficiency sense is equal to one. In addition, the closed-form expressions of optimal power allocation of E-SRS-PA scheme are derived. Numerical simulations confirm the optimality of proposed E-SRS-PA and demonstrate the energy efficiency of ANC-based TWRC compared with the other relaying schemes. © 2012 IEEE.

Laasonen K.,Aalto University | Panizon E.,CNR Institute of Materials for Electronics and Magnetism | Bochicchio D.,CNR Institute of Materials for Electronics and Magnetism | Ferrando R.,CNR Institute of Materials for Electronics and Magnetism
Journal of Physical Chemistry C | Year: 2013

The structures of AgCu, AgNi, and AgCo nanoalloys with icosahedral geometry have been computationally studied by a combination of atomistic and density-functional theory (DFT) calculations, for sizes up to about 1400 atoms. These nanoalloys preferentially assume core-shell chemical ordering, with Ag in the shell. These core-shell nanoparticles can have either centered or off-center cores; they can have an atomic vacancy in their central site or present different arrangements of the Ag shell. Here we compare these different icosahedral motifs and determine the factors influencing their stability by means of a local strain analysis. The calculations find that off-center cores are favorable for sufficiently large core sizes and that the central vacancy is favorable in pure Ag clusters but not in binary clusters with cores of small size. A quite good agreement between atomistic and DFT calculations is found in most cases, with some discrepancy only for pentakis-dodecahedral structures. Our results support the accuracy of the atomistic model. Spin structure and charge transfer in the nanoparticles are also analyzed. © 2013 American Chemical Society.

Jain T.,Aalto University | Yame J.J.,University of Lorraine | Sauter D.,University of Lorraine
IEEE Transactions on Sustainable Energy | Year: 2013

This paper presents a real-time mechanism to tolerate faults occurring in a wind turbine (WT) system. This system is a FAST coded simulator designed by the U.S. National Renewable Energy Laboratory's (NREL's) National Wind Turbine Center. The demonstrated mechanism lies under the taxonomy of active fault-tolerant control (AFTC) systems, namely the projection-based approach. In the proposed approach, we do not use any a priori information about the model of the turbine in real-time. In fact, we use the online measurements generated by WT. Based on the given control objectives, and the observed measurements, an occurring fault is accommodated by reconfiguring the controller such that the turbine generates the rated power even under faulty conditions. Second, no use of an explicit fault-diagnosis module is seen in this approach. Therefore, the fault accommodation delay in the proposed AFTC structure is smaller than the delay as experienced in the traditional structure of AFTC systems. © 2013 IEEE.

Komsa H.-P.,University of Helsinki | Krasheninnikov A.V.,University of Helsinki | Krasheninnikov A.V.,Aalto University
Physical Review B - Condensed Matter and Materials Physics | Year: 2012

Using GW first-principles calculations for few-layer and bulk MoS 2, we study the effects of quantum confinement on the electronic structure of this layered material. By solving the Bethe-Salpeter equation, we also evaluate the exciton energy in these systems. Our results are in excellent agreement with the available experimental data. Exciton binding energy is found to dramatically increase from 0.1 eV in the bulk to 1.1 eV in the monolayer. The fundamental band gap increases as well, so that the optical transition energies remain nearly constant. We also demonstrate that environments with different dielectric constants have a profound effect on the electronic structure of the monolayer. Our results can be used for engineering the electronic properties of MoS2 and other transition-metal dichalcogenides and may explain the experimentally observed variations in the mobility of monolayer MoS2. © 2012 American Physical Society.

Tuominen V.,Aalto University
International Journal of Advanced Manufacturing Technology | Year: 2015

This article introduces the concept of a measurement-aided welding cell (MAWC). It then focuses on developing the MAWC for body and chassis components in the automotive industry. Industry 4.0 requires flexibility and reconfigurability from manufacturing systems, which has been addressed by cellular manufacturing systems (CMS). Traditional automotive welding technology is not flexible enough to be used as a CMS. So, the core of automotive production does not meet the needs of next-generation manufacturing and Industry 4.0. For the first time, this demand has been answered—by the MAWC. The MAWC is based on two handling robots, a welding robot and an optical measurement system, all integrated into one welding cell. The measurement system controls guides and gives feedback to the handling and welding robots. This way, accurate welding is based on actual part-to-part adjustment, rather than hard mechanical tooling. The lack of hard mechanical tooling allows flexibility. Measurement-assisted assembly and machining is not new. However, it has not previously been applied to complex welding processes, because traditional measurement technologies have not been satisfactory. A newly developed system using multi-camera measurement technology meets the flexibility requirements. The technology required for a MAWC is reviewed and found to be in common use in the automotive industry. Three development projects are presented in which the main functions of a MAWC are successfully demonstrated. Two of these projects were done with BMW. A MAWC allows the manufacturing process to immediately swap to a different product on the same line, increasing the production line utilisation rate and making it possible to produce several low-volume products in one manufacturing system. So, the MAWC will not only yield benefits from its scalable capacity and global decentralization, but it will also open new business opportunities for manufacturing low-volume luxury car parts or post-production spare parts. © 2015 The Author(s)

Bjorkman T.,Aalto University
Physical Review B - Condensed Matter and Materials Physics | Year: 2012

The recent nonlocal correlation functional of Vydrov and van Voorhis is investigated and two new versions of the functional are suggested as being appropriate for describing van der Waals interactions in solids. A refitting of the original functional is demonstrated to result in very accurate interlayer binding energies for weakly bonded layered solids. A VV10 functional based on the generalized gradient approximation by Armiento and Mattsson, while performing slightly worse for interlayer binding, is highly successful in describing the equilibrium geometries of both weakly bonded and close packed solids. © 2012 American Physical Society.

Hamalainen R.P.,Aalto University
Environmental Modelling and Software | Year: 2015

The paper aims to demonstrate the importance of behavioural issues in environmental modelling. These issues can relate both to the modeler and to the modelling process including the social interaction in the modelling team. The origins of behavioural effects can be in the cognitive and motivational biases or in the social systems created as well as in the visual and verbal communication strategies used. The possible occurrence of these phenomena in the context of environmental modelling is discussed and suggestions for research topics are provided. © 2015 Elsevier Ltd.

This paper presents an optimization method for laser-welded web-core steel sandwich panels supported by girder system. The method utilizes homogenized plate theory and offset beams. The static and eigenfrequency analyses are carried out using the Finite Element Method (FEM). In order to assess the influence of periodic stresses within the sandwich panel, an envelope surface approach is developed. The approach is aimed to capture the maximum stresses on elemental basis even though the actual positioning of the web plates is unknown. This makes the method attractive for concept design stage where nesting process is not yet done. The envelope surface approach is validated with 3D FEM and periodic solution based on localization. The agreement between methods is found to be excellent. The method is demonstrated through a case study on weight optimization of passenger ship deck. The optimization problem is solved using Particle Swarm Optimization method. The paper shows that the proposed approach can be efficiently used to assess the stresses of the sandwich panel and thus to design steel sandwich structures at concept design stage. © 2014 Elsevier Ltd.

Koskinen A.M.P.,Aalto University
Chemical Record | Year: 2014

In 1976 Mukaiyama published a paper that was to make a major impact on the development of the aldol reaction in the future. Mild enolate formation by treatment of a ketone with dibutylboron triflate in the presence of a tertiary amine generates a relatively stable boron enolate, which can subsequently react with an aldehyde to give the cross-aldol product in good yields. This reaction has become a reliable tool for the practicing synthetic chemist. Nearly 10000 polyketides are known, and of these about 600 contain the tripropionate unit with a stereotetrad, four contiguous stereocenters with alternating methyl and hydroxyl substituents in the main chain. The versatility of the boron enolate aldol reaction is showcased with selected applications in the synthesis of these structural motifs. Today nearly 10000 polyketides are known, and of them about 600 contain the tripropionate unit with a stereotetrad, four contiguous stereocenters with alternating methyl and hydroxyl substituents in the main chain. On the basis of their relative stereochemistry these can be classified into eight structural types. In 1976 Mukaiyama described mild enolate formation by treatment of a ketone with dibutylboron triflate in the presence of a tertiary amine, in a paper that was to make a major impact on the development of the aldol reaction. The versatility of the Mukaiyama boron-mediated aldol reaction is showcased with examples from total syntheses. Copyright © 2014 The Chemical Society of Japan and Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Shevchenko A.,Aalto University | Hoenders B.J.,Zernike Institute for Advanced Materials
New Journal of Physics | Year: 2010

Macroscopic force density imposed on a linear isotropic magnetic dielectric medium by an arbitrary electromagnetic field is derived by spatially averaging the microscopic Lorentz force density. The obtained expression differs from the commonly used expressions, but the energy-momentum tensor derived from it corresponds to a so-called Helmholtz tensor written for a medium that obeys the Clausius-Mossotti law. Thus, our microscopic derivation unambiguously proves the correctness of the Helmholtz tensor for such media. Also, the expression for the momentum density of the field obtained in our theory is different from the expressions obtained by Minkowski, Abraham, Einstein and Laub, and others. We apply the theory to particular examples of static electric, magnetic and stationary electromagnetic phenomena, and show its agreement with experimental observations. We emphasize that in contrast to a widespread belief the Abraham-Minkowski controversy cannot be resolved experimentally because of incompleteness of the theories introduced by Abraham and Minkowski. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.

Haukkala T.,Aalto University
Energy Research and Social Science | Year: 2015

This article deals with solar energy policy and solar energy potential in Finland. Finland is one of the few countries in the EU that has taken hardly any direct subsidies into use for solar energy. At the same time, the transition to renewables is crucial in mitigating climate change. Finland's irradiation is almost the same as that of Germany, a country that is one of the top markets for photovoltaics in the world, also due to its successful support policy. Why does Finland not do likewise and adopt a support policy for solar energy to enforce its mix of renewables? What, if any, policy mechanisms would be needed to promote solar energy? The article provides an overview of supportive solar energy policy instruments in the EU countries, and an analysis of Finland's official energy strategies. The empirical part also consists of semi-structured interviews with different actors in the solar energy sector in Finland: politicians, corporations, entrepreneurs, industry representatives, public administrators and NGOs. The key finding is that the support measures envisaged depend on the vested interests of the actors involved. It would seem that some kind of support mechanism is required but the type of mechanism is of lesser significance. © 2014 Elsevier Ltd. All rights reserved.

Discrimination between three different sources of variability in a vibration-based structural health monitoring system is investigated: environmental or operational effects, sensor faults, and structural damage. Separating the environmental or operational effects from the other two is based on the assumption that measurements under different environmental or operational conditions are included in the training data. Distinguishing between sensor fault and structural damage utilizes the fact that the sensor faults are local, while structural damage is global. By localizing the change to a sensor which is then removed from the network, the two different influences can be separated. The sensor network is modelled as a Gaussian process and the generalized likelihood ratio test (GLRT) is then used to detect and localize a change in the system. A numerical and an experimental study are performed to validate the proposed method. © 2011 Elsevier Ltd. All rights reserved.

Miettinen J.,Aalto University | Vassilev G.,Plovdiv University
Journal of Phase Equilibria and Diffusion | Year: 2014

Thermodynamic description of the Fe-Cu-P system is developed within the frame of a new Fe-X-P (X = Al, Cr, Cu, Mn, Mo, Nb, Ni, Si, Ti) database. The thermodynamic parameters of the binary sub-systems, Fe-Cu, Fe-P and Cu-P, are taken from earlier assessments. Those of the Fe-Cu-P system are optimized in this study using the experimental thermodynamic and phase equilibrium data from the literature. The solution phases of the system are described using the substitutional solution model and the phosphides are treated as stoichiometric or semi-stoichiometric phases of the type (A,B)pCq. © 2014 ASM International.

Jarvinen K.,Aalto University
Integration, the VLSI Journal | Year: 2011

In this paper, we introduce an FPGA-based processor for elliptic curve cryptography on Koblitz curves. The processor targets specifically to applications requiring very high speed. The processor is optimized for performing scalar multiplications, which are the basic operations of every elliptic curve cryptosystem, only on one specific Koblitz curve; the support for other curves is achieved by reconfiguring the FPGA. We combine efficient methods from various recent papers into a very efficient processor architecture. The processor includes carefully designed processing units dedicated for different parts of the scalar multiplication in order to increase performance. The computation is pipelined providing simultaneous processing of up to three scalar multiplications. We provide experimental results on an Altera Stratix II FPGA demonstrating that the processor computes a single scalar multiplication on average in 11.71μs and achieves a throughput of 235,550 scalar multiplications per second on NIST K-163. © 2010 Elsevier B.V. All rights reserved.

Paraoanu G.S.,Aalto University
Journal of Low Temperature Physics | Year: 2014

Quantum systems are notoriously difficult to simulate with classical means. Recently, the idea of using another quantum system - which is experimentally more controllable - as a simulator for the original problem has gained significant momentum. Amongst the experimental platforms studied as quantum simulators, superconducting qubits are one of the most promising, due to relative straightforward scalability, easy design, and integration with standard electronics. Here I review the recent state-of-the art in the field and the prospects for simulating systems ranging from relativistic quantum fields to quantum many-body systems. © 2014 Springer Science+Business Media New York.

Karilainen A.O.,Nokia Inc. | Tretyakov S.A.,Aalto University
IEEE Transactions on Antennas and Propagation | Year: 2012

We propose to use an antenna composed of two orthogonal helices as a low-scattering sensor. The vector effective length is derived for the antenna using the small dipole approximation for the helices. The antenna can transmit and receive circular polarization in all directions with the Huygens' pattern. We observe that the antenna geometry does not backscatter, regardless of the polarization, when the incidence direction is normal to the plane of the helices. Scattered fields, scattered axial ratio, and the scattering cross section are presented. We show that the zero-backscattering property holds also for the antenna when it is capable to receive all the available power with conjugate loading. The approximate analytical model is validated with full-wave simulations. © 2012 IEEE.

Karilainen A.O.,Nokia Inc. | Tretyakov S.A.,Aalto University
IEEE Transactions on Antennas and Propagation | Year: 2012

We study electrically small chiral objects with isotropic response and zero backscattering. A bi-isotropic sphere is used as a simple example and its zero-backscattering conditions are studied. A theoretical model of an object composed of three orthogonal chiral particles made of conducting wire is presented as an analog of the zero-backscattering bi-isotropic sphere. A potential application of the object as a receiving antenna or a sensor with the ability to receive power from an arbitrary direction without backscattering is discussed. © 2012 IEEE.

Dlala E.,Aalto University
IEEE Transactions on Magnetics | Year: 2011

This paper deals with key problems that have been commonly encountered in the implementation of the Preisach model into finite-element (FE) programs. Such problems include the inverse problem imposed by certain FE formulations, the abundance use of experimental data needed for identification, and the complex hysteretic nonlinearity inherited in electromagnetic problems. The aim is to alleviate these problems using new efficient algorithms to facilitate the inclusion of the Preisach model in FE equations. The inversion of the model is evaded by systematically creating an inverted Everett function identified from a few parameters usually provided by the makers of electrical steel. The Everett function and its derivatives are ensured to be smooth and continuous by using cubic spline interpolation, which is important for producing stable iterative solutions in the FE computations. Thorough investigations and FE simulations supported by experiments show that the proposed algorithms are capable of successfully accomplishing good accuracy, fast computation, and numerical convergence. © 2006 IEEE.

Niinimaki K.,Aalto University
Sustainable Development | Year: 2010

This paper aims to contribute to a better understanding of eco-fashion consumption and consumer purchase decisions while constructing one's self with external symbols, such as appearance, clothing and fashion items. This study approaches sustainable clothing from a grounding in design research and the meanings of material culture. The study uses sociology and social psychology; hence, the meaning of appearance and especially clothing and fashion is understood in a social context. This paper also takes an interdisciplinary approach to eco-clothes as cultural and design objects in a social and sustainable development context, objects that intertwine consumers' ethical attitudes and values and how they construct a concept of 'self' using external symbols. © 2010 John Wiley & Sons, Ltd and ERP Environment.

Silaev M.A.,RAS Institute for Physics of Microstructures | Volovik G.E.,Aalto University | Volovik G.E.,L D Landau Institute For Theoretical Physics
Physical Review B - Condensed Matter and Materials Physics | Year: 2012

We consider fermionic states bound on domain walls in a Weyl superfluid 3He-A and on interfaces between 3He-A and a fully gapped topological superfluid 3He-B. We demonstrate that in both cases the fermionic spectrum contains Fermi arcs that are continuous nodal lines of energy spectrum terminating at the projections of two Weyl points to the plane of surface states in momentum space. The number of Fermi arcs is determined by the index theorem that relates bulk values of the topological invariant to the number of zero-energy surface states. The index theorem is consistent with an exact spectrum of Bogolubov-de Gennes equation obtained numerically, meanwhile, the quasiclassical approximation fails to reproduce the correct number of zero modes. Thus we demonstrate that topology describes the properties of the exact spectrum beyond the quasiclassical approximation. © 2012 American Physical Society.

Hakulinen L.,Aalto University
Proceedings - 11th Koli Calling International Conference on Computing Education Research, Koli Calling'11 | Year: 2011

Games are generally considered to be motivating and engaging and people spend a lot of time playing recreational games. Serious games can be used in Computer Science (CS) education to offer a different type of method to learn and discuss relevant topics. This paper presents a pilot study of using serious games at a Data Structures and Algorithms course. The games that were used were either card games or they were played on a blackboard. The results of the pilot study seem promising and we will use the games also in next year's course. In addition, this paper raises discussion about using serious games in CS education. The main points of discussion are, how serious games can be used effciently and how to evaluate the efects of using games? © 2011 ACM.

Lassila T.,Ecole Polytechnique Federale de Lausanne | Lassila T.,Aalto University | Rozza G.,Ecole Polytechnique Federale de Lausanne
Computer Methods in Applied Mechanics and Engineering | Year: 2010

We present a coupling of the reduced basis methods and free-form deformations for shape optimization and design of systems modelled by elliptic PDEs. The free-form deformations give a parameterization of the shape that is independent of the mesh, the initial geometry, and the underlying PDE model. The resulting parametric PDEs are solved by reduced basis methods. An important role in our implementation is played by the recently proposed empirical interpolation method, which allows approximating the non-affinely parameterized deformations with affinely parameterized ones. These ingredients together give rise to an efficient online computational procedure for a repeated evaluation design environment like the one for shape optimization. The proposed approach is demonstrated on an airfoil inverse design problem. © 2010 Elsevier B.V.

Krasnok A.E.,National Research University of Information Technologies | Simovski C.R.,Aalto University | Belov P.A.,National Research University of Information Technologies | Kivshar Y.S.,Australian National University
Nanoscale | Year: 2014

We introduce the novel concept of superdirective nanoantennas based on the excitation of higher-order magnetic multipole moments in subwavelength dielectric nanoparticles. Our superdirective nanoantenna is a small Si nanosphere containing a notch, and is excited by a dipole located within the notch. In addition to extraordinary directivity, this nanoantenna demonstrates efficient radiation steering at the nanoscale, resulting from the subwavelength sensitivity of the beam radiation direction to variation of the source position inside the notch. We compare our dielectric nanoantenna with a plasmonic nanoantenna of similar geometry, and reveal that the nanoantenna's high directivity in the regime of transmission is not associated with strong localization of near fields in the regime of reception. Likewise, the absence of hot spots inside the nanoantenna leads to low dissipation in the radiation regime, so that our dielectric nanoantenna has significantly smaller losses and high radiation efficiency of up to 70%. © 2014 the Partner Organisations.

Ullah I.,KTH Royal Institute of Technology | Parviainen P.,Aalto University | Lagergren J.,KTH Royal Institute of Technology
Molecular Biology and Evolution | Year: 2015

Species tree reconstruction has been a subject of substantial research due to its central role across biology and medicine. A species tree is often reconstructed using a set of gene trees or by directly using sequence data. In either of these cases, one of the main confounding phenomena is the discordance between a species tree and a gene tree due to evolutionary events such as duplications and losses. Probabilistic methods can resolve the discordance by coestimating gene trees and the species tree but this approach poses a scalability problem for larger data sets. We present MixTreEM-DLRS: A twophase approach for reconstructing a species tree in the presence of gene duplications and losses. In the first phase, MixTreEM, a novel structural expectation maximization algorithm based on a mixture model is used to reconstruct a set of candidate species trees, given sequence data for monocopy gene families from the genomes under study. In the second phase, PrIME-DLRS, a method based on the DLRS model (A° kerborg O, Sennblad B, Arvestad L, Lagergren J. 2009. Simultaneous Bayesian gene tree reconstruction and reconciliation analysis. Proc Natl Acad Sci USA. 106(14):5714-5719), is used for selecting the best species tree. PrIME-DLRS can handle multicopy gene families since DLRS, apart from modeling sequence evolution, models gene duplication and loss using a gene evolution model (Arvestad L, Lagergren J, Sennblad B. 2009. The gene evolution model and computing its associated probabilities. J ACM. 56(2):1-44).We evaluate MixTreEM-DLRS using synthetic and biological data, and compare its performance with a recent genome-scale species tree reconstruction method PHYLDOG (Boussau B, Sz öllosi GJ, Duret L, Gouy M, Tannier E, Daubin V. 2013. Genomescale coestimation of species and gene trees. Genome Res. 23(2):323-330) as well as with a fast parsimony-based algorithm Duptree (Wehe A, Bansal MS, Burleigh JG, Eulenstein O. 2008. Duptree: a program for large-scale phylogenetic analyses using gene tree parsimony. Bioinformatics 24(13):1540-1541). Our method is competitive with PHYLDOG in terms of accuracy and runs significantly faster and our method outperforms Duptree in accuracy. The analysis constituted by MixTreEM without DLRS may also be used for selecting the target species tree, yielding a fast and yet accurate algorithm for larger data sets. MixTreEM is freely available at http://prime. scilifelab.se/mixtreem/. © 2015 The Author.

Sihvola A.,Aalto University
Photonics and Nanostructures - Fundamentals and Applications | Year: 2013

This paper consists of two parts. First, a review of classical mixing principles lists the multitude of the various ways to characterize the effective permittivity of heterogeneous materials. Different connections between the various mixing formulas are underlined and the homogenization principles are classified into families of mixing rules. The second part emphasizes and analyzes the richness of the manner how the mixing process is able to create new types of dielectric behaviors, in particular with respect to enhancement of dielectric polarization, shifts of the dispersion parameters, and emergence of new effects in electrical response. © 2013 Elsevier B.V. All rights reserved.

Ojanen T.,Aalto University | Ojanen T.,Harvard University
Physical Review Letters | Year: 2012

Recent experiments in semiconductor nanowires with a spin-orbit coupling and proximity-induced superconductivity exhibit signatures of Majorana bound states predicted to exist in the topological phase. In this Letter we predict that these nanowire systems exhibit unconventional magnetoelectric effects showing a sharp crossover behavior at the topological phase transition. We find that magnetic fields with a component parallel to the spin-orbit field can give rise to currents in equilibrium. Surprisingly, also fields perpendicular to the spin-orbit field may induce currents and can be employed in adiabatic charge pumping. The perpendicular field magnetoelectric effect may be regarded as a manifestation of the anomalous Hall effect in one dimension. We discuss how the predicted phenomena could be observed in experiments and employed in probing the topological phase transition. © 2012 American Physical Society.

We introduce a new method to modify films of nanofibrillated cellulose (NFC) to produce non-porous, water-resistant substrates for diagnostics. First, water resistant NFC films were prepared from mechanically disintegrated NFC hydrogel, and then their surfaces were carboxylated via TEMPO-mediated oxidation. Next, the topologically functionalized film was activated via EDS/NHS chemistry, and its reactivity verified with bovine serum albumin and antihuman IgG. The surface carboxylation, EDC/NHS activation and the protein attachment were confirmed using quartz crystal microbalance with dissipation, contact angle measurements, conductometric titrations, X-ray photoelectron spectroscopy and fluorescence microscopy. The surface morphology of the prepared films was investigated using confocal laser scanning microscopy and atomic force microscopy. Finally, we demonstrate that antihuman IgG can be immobilized on the activated NFC surface using commercial piezoelectric inkjet printing.

Goli K.K.,North Carolina State University | Rojas O.J.,North Carolina State University | Rojas O.J.,Aalto University | Genzer J.,North Carolina State University
Biomacromolecules | Year: 2012

We describe the formation of amphiphilic polymeric assemblies via a three-step functionalization process applied to polypropylene (PP) nonwovens and to reference hydrophobic self-assembled n-octadecyltrichlorosilane (ODTS) monolayer surfaces. In the first step, denatured proteins (lysozyme or fibrinogen) are adsorbed onto the hydrophobic PP or the ODTS surfaces, followed by cross-linking with glutaraldehyde in the presence of sodium borohydride (NaBH4). The hydroxyl and amine functional groups of the proteins permit the attachment of initiator molecules, from which poly (2-hydroxyethyl methacrylate) (PHEMA) polymer grafts are grown directly through "grafting from" atom transfer radical polymerization. The terminal hydroxyls of HEMA's pendent groups are modified with fluorinating moieties of different chain lengths, resulting in amphiphilic brushes. A palette of analytical tools, including ellipsometry, contact angle goniometry, Fourier transform infrared spectroscopy in the attenuated total reflection mode, and X-ray photoelectron spectroscopy is employed to determine the changes in physicochemical properties of the functionalized surfaces after each modification step. Antifouling properties of the resultant amphiphilic coatings on PP are analyzed by following the adsorption of fluorescein isothiocyanate-labeled bovine serum albumin as a model fouling protein. Our results suggest that amphiphilic coatings suppress significantly adsorption of proteins as compared with PP fibers or PP surfaces coated with PHEMA brushes. The type of fluorinated chain grafted to PHEMA allows modulation of the surface composition of the topmost layer of the amphiphilic coating and its antifouling capability. © 2012 American Chemical Society.

Lankoski P.,Aalto University
Games and Culture | Year: 2011

This article argues how players can control a player character influence interpretation and facilitate engagement within a game. Engagement with player characters can be goal-related or empathic, where goal-related engagement depends on affects elicited by goal-status evaluations whereas characters facilitate empathic engagement. The concepts of recognition, alignment, and allegiance are used to describe how engagement is structured in games. Recognition describes aspects of character interpretation. Alignment describes what kind of access players have to a character's actions, knowledge, and affects. Allegiance describes how characters elicit sympathy or antipathy through positive or negative evaluation of the character. © The Author(s) 2011.

Karhunen J.,Aalto University
Neural Network World | Year: 2011

In this paper, we consider and introduce methods for robust principal component analysis (PCA), including also cases where there are missing values in the data. PCA is a widely applied standard statistical method for data preprocessing, compression, and analysis. It is based on the second-order statistics of the data and is optimal for Gaussian data, but it is often applied to data sets having unknown or other types of probability distributions. PCA can be derived from minimization of the mean-square representation error or maximization of variances under orthonormality constraints. However, these quadratic criteria are sensitive to outliers in the data and long-tailed distributions, which may considerably degrade the results given by PCA. We introduce robust methods for estimation of both the PCA eigenvectors directly or the PCA subspace spanned by them. Experimental results show that our methods provide often better results than standard PCA when outliers are present in the data. Furthermore, we extend our methods to incomplete data with missing values. The problems arising in such cases have several features typical for nonlinear models. © ICS AS CR 2011.

Palyulin V.V.,University of Potsdam | Ala-Nissila T.,Aalto University | Metzler R.,University of Potsdam | Metzler R.,Tampere University of Technology
Soft Matter | Year: 2014

Probably no other field of statistical physics at the borderline of soft matter and biological physics has caused such a flurry of papers as polymer translocation since the 1994 landmark paper by Bezrukov, Vodyanoy, and Parsegian and the study of Kasianowicz in 1996. Experiments, simulations, and theoretical approaches are still contributing novel insights to date, while no universal consensus on the statistical understanding of polymer translocation has been reached. We here collect the published results, in particular, the famous-infamous debate on the scaling exponents governing the translocation process. We put these results into perspective and discuss where the field is going. In particular, we argue that the phenomenon of polymer translocation is non-universal and highly sensitive to the exact specifications of the models and experiments used towards its analysis. This journal is © the Partner Organisations 2014.

Priimagi A.,Aalto University | Priimagi A.,Polytechnic of Milan | Barrett C.J.,McGill University | Shishido A.,Tokyo Institute of Technology
Journal of Materials Chemistry C | Year: 2014

The design of functional and stimuli-responsive materials is among the key goals of modern materials science. The structure and properties of such materials can be controlled via various stimuli, among which light is often times the most attractive choice. Light is ubiquitous and a gentle energy source and its properties can be optimized for a specific target remotely, with high spatial and temporal resolution. Light-control over molecular alignment has in recent years attracted particular interest, for potential applications such as reconfigurable photonic elements and optical-to-mechanical energy conversion. Herein, we bring forward some recent examples and emerging trends in this exciting field of research, focusing on liquid crystals, liquid-crystalline polymers and photochromic organic crystals, which we believe serve to highlight the immense potential of light-responsive materials to a wide variety of current and future high-tech applications in photonics, energy harvesting and conversion. This journal is © the Partner Organisations 2014.

Sarkka S.,Aalto University | Sarmavuori J.,Nokia Inc.
Signal Processing | Year: 2013

This paper is concerned with Bayesian optimal filtering and smoothing of non-linear continuous-discrete state space models, where the state dynamics are modeled with non-linear Itô-type stochastic differential equations, and measurements are obtained at discrete time instants from a non-linear measurement model with Gaussian noise. We first show how the recently developed sigma-point approximations as well as the multi-dimensional Gauss-Hermite quadrature and cubature approximations can be applied to classical continuous-discrete Gaussian filtering. We then derive two types of new Gaussian approximation based smoothers for continuous-discrete models and apply the numerical methods to the smoothers. We also show how the latter smoother can be efficiently implemented by including one additional cross-covariance differential equation to the filter prediction step. The performance of the methods is tested in a simulated application. © 2012 Elsevier B.V.

Hinkka V.,Aalto University
International Journal of RF Technologies: Research and Applications | Year: 2012

Even though numerous articles and real life cases have highlighted the benefits of radio frequency identification (RFID) tracking for supply chain management for almost a decade, companies are rather slow to implement the technology. This paper concentrates on researching the reasons for the slow adoption of RFID tracking in the supply chain management using literature review and multiple case studies as the research methodology. The literature review of the articles classifies different challenges for RFID tracking implementation and elicits the academic explanations for the slow acceptance of the technology. The conclusion of the literature review is that most of the published articles have been concentrating on presenting technological obstacles to RFID tracking implementation, while the problems nowadays are increasingly organizational or inter-organizational. Also companies usually settle for using RFID tracking to improve their operational processes instead of exploiting the full potential in the technology and the increased visibility for improving managerial processes of the company, or upgrading the efficiency of the whole supply chain. In addition to the literature review, five RFID tracking case surveys are presented to provide experience and insights into managerial decisions concerning supply chain-wide RFID tracking solutions. Followed by the literature review and case studies, this paper presents a framework, which suggests three levels, where different potential challenges to supply chain-wide RFID tracking system implementations should be handled: the supply chain, inside a company or inside a certain function. © 2012 IOS Press and the authors. All rights reserved.

Sanders S.A.,Institute of Chemical Technology | Sammalkorpi M.,Aalto University | Panagiotopoulos A.Z.,Institute of Chemical Technology
Journal of Physical Chemistry B | Year: 2012

Molecular dynamics simulations have been used to study the micellization behavior of atomistic models for sodium alkyl sulfates in explicit water. A major finding of the present work is the observation of a strong dependence of free surfactant concentration on overall surfactant concentration, that has not been reported previously and that is key to comparing simulation results for the critical micelle concentration (CMC) to experimental data. The CMC and aggregate size distributions were obtained for alkyl tail lengths from six to nine at temperatures from 268 to 363 K, from 400 ns simulations covering a number of surfactant and water model combinations. The free surfactant concentration is much lower than the critical micelle concentration for strongly micellizing systems at the relatively high concentrations accessible by simulations. Thus, counterion association must be accounted for in determining the CMC from the raw simulation data. Simulation results are in qualitative agreement with experimental trends for aggregate size and CMC as functions of alkyl tail length and temperature. © 2012 American Chemical Society.

Heikkila T.T.,Aalto University | Volovik G.E.,Russian Academy of Sciences
JETP Letters | Year: 2011

We consider the dimensional crossover in the topological matter, which involves the transformation of different types of topologically protected zeroes in the fermionic spectrum. In the considered case, the multiple Dirac (Fermi) point in quasi 2-dimensional system evolves into the flat band on the surface of the 3-dimensional system when the number of atomic layers increases. This is accompanied by formation of the spiral nodal lines in the bulk. We also discuss the topological quantum phase transition at which the surface flat band shrinks and changes its chirality, while the nodal spiral changes its helicity. © 2011 Pleiades Publishing, Ltd.

Volovik G.E.,Aalto University | Volovik G.E.,Russian Academy of Sciences
JETP Letters | Year: 2011

We discuss the dispersionless spectrum with zero energy in the linear topological defects-vortices. The flat band emerges inside the vortex living in the bulk medium containing topologically stable Fermi points in momentum space. The boundaries of the flat band in the vortex are determined by projections of the Fermi points in bulk to the vortex axis. This bulk-vortex correspondence for flat band is similar to the bulk-surface correspondence discussed earlier in the media with topologically protected lines of zeroes. In the latter case the flat band emerges on the surface of the system, and its boundary is determined by projection of the bulk nodal line on the surface. © 2011 Pleiades Publishing, Ltd.

Sippola H.,Aalto University
Journal of Chemical and Engineering Data | Year: 2013

The scope of this article is to study the ability of different equations for K2 and different sets of Pitzer parameters to model the thermodynamic properties of the H2SO4-H2O system over a wide temperature range. Three Pitzer parameters are found essential in modeling aqueous sulfuric acid, namely, Cφ for H+/SO4 2- interaction and parameters β(0) and β(1) for H+/HSO4 - interaction. Several thermodynamic models with different K2-equations consisting of only four Pitzer parameters, the mentioned three parameters extended by β(0) for H+/SO4 2- interaction with simple temperature dependency (a + b/T), can describe stoichiometric activity and osmotic coefficients as well as vapor pressure of aqueous sulfuric acid up to a 6 molal solution in the temperature range (0 to 170) C with good to moderate extrapolation capabilities. Increasing the number of parameters above four do not improve the assessment. The predicted values with different K2-equations are assumed experimentally accurate. One of the four parameters models, Hepler A, can predict the apparent heat of solution in the temperature range (0 to 50) C with reasonable accuracy even though no enthalpy or heat capacity data were included in the assessment. © 2013 American Chemical Society.

Liu Q.,Aalto University | Liu Q.,Guangxi University of Technology
Journal of Engineering Mechanics | Year: 2012

This paper describes a numerical method for calculation of the sensitivity and Hessian matrix of the response evolutionary power spectral density (PSD) functions of structures subjected to uniformly modulated evolutionary random seismic excitation. The method is formulated based on the pseudoexcitation method and the Gauss precise time step integration method. The evolutionary nonstationary random response analysis is converted into step-by-step integration computations using the pseudoexcitation method. The formulas of the pseudoresponses and their first and second derivatives with respect to the structural design variables are derived based on the Gauss precise time step integration method. The evolutionary PSD functions, their sensitivity, and the Hessian matrix are calculated using the pseudoresponses and their first and second derivatives, respectively. Finally, the evolutionary PSD functions' sensitivity and Hessian matrix analysis of a three-story, two-bay planar frame subjected to uniformly modulated evolutionary random earthquake ground motion has been studied to elucidate the proposed method. © 2012 American Society of Civil Engineers.

This work reviews a number of existing computational studies concentrated on the question of how spoken language can be learned from continuous speech in the absence of linguistically or phonetically motivated background knowledge, a situation faced by human infants when they first attempt to learn their native language. Specifically, the focus is on how phonetic categories and word-like units can be acquired purely on the basis of the statistical structure of speech signals, possibly aided by some articulatory or visual constraints. The outcomes and shortcomings of the existing work are reflected onto findings from experimental and theoretical studies. Finally, some of the open questions and possible future research directions related to the computational models of language acquisition are discussed. © 2012 Elsevier B.V. All rights reserved.

Assad M.E.H.,Aalto University
International Journal of Energy Research | Year: 2010

This paper presents a theoretical analysis of a heat exchanger with a negligible fluid flow pressure drop to determine whether it is better to operate the heat exchanger with the minimum or maximum heat capacity rate of the hot fluid from entropy generation point of view. Entropy generation numbers are derived for both cases, and the results show that they are identical, when the heat exchanger is running at a heat capacity ratio of 0.5 with heat exchanger effectiveness equaling 1. An entropy generation number ratio is defined for the first time, which has a maximum value at ε = 1/(1+R) for any inlet temperature ratio. When R equals 0.1, 0.5 and 0.9, the entropy generation number ratio receives a maximum value at an effectiveness equaling 0.91, 0.67 and 0.526, respectively. When R=0.9, the entropy generation number ratio is the same for all inlet temperature ratios at ε=0.8. The results show that the entropy generation number ratio is far from 1 depending on the inlet temperature ratio of the cold and hot fluid. The results are valid for parallel-flow and counterflow heat exchangers. © 2010 John Wiley & Sons, Ltd.

Fleten S.-E.,Norwegian University of Science and Technology | Nasakkala E.,Norwegian University of Science and Technology | Nasakkala E.,Aalto University
Energy Economics | Year: 2010

We analyze investments in gas-fired power plants based on stochastic electricity and natural gas prices. A simple but realistic two-factor model is used for price processes, enabling analysis of the value of operating flexibility, the opportunity to abandon the capital equipment, as well as finding thresholds for energy prices for which it is optimal to enter into the investment. We develop a method to compute upper and lower bounds on plant values and investment threshold levels. Our case study uses representative power plant investment and operations data, and historical forward prices from well-functioning energy markets. We find that when the decision to build is considered, the abandonment option does not have significant value, whereas the operating flexibility and time-to-build option have significant effect on the building threshold. Furthermore, the joint value of the operating flexibility and the abandonment option is much smaller than the sum of their separate values, because both are options to shut down. The effects of emission costs on the value of installing CO2 capture technology are also analyzed. © 2009 Elsevier B.V.

Kauppinen T.,Aalto University
Computers and Geosciences | Year: 2016

The exploration of mining has often been limited by time-consuming methods of analysis. This paper introduces Data Envelopment Analysis (DEA) as a new tool for the exploration phase of mining. DEA is a non-parametric method for data fusion, and it is used alongside with the on-site Raman analysis. Ten meters of halved rock drillcore from the Kittil mine (Suurikuusikko deposit) were pulverised and homogenised, thus ensuring that each meter had a representative sample. These 10 samples, one for each meter, were subsequently measured with a grid measurement (32×32 measurement each) using the Raman setup. All the data points were analysed using the point-count method. After identifying the frequency at which potentially valuable minerals appear in the samples, this information was analysed using DEA. The study ends by presenting an efficiency score for each meter of drillcore. These efficiency scores enable geologists to judge more rapidly which parts of the drillcore must be logged more carefully. In addition, Principal Component Analysis (PCA) is discussed as an alternative for producing similar results to DEA. © 2016 Elsevier Ltd.

The temporal change of the direction of sliding relative to the ultrahigh molecular weight polyethylene (UHMWPE) component of prosthetic joints is known to be of crucial importance with respect to wear. One complete revolution of the resultant friction vector is commonly called a wear cycle. It was hypothesized that in order to accelerate the wear test, the cycle frequency may be substantially increased if the circumference of the slide track is reduced in proportion, and still the wear mechanisms remain realistic and no overheating takes place. This requires an additional slow motion mechanism with which the lubrication of the contact is maintained and wear particles are conveyed away from the contact. A three-station, dual motion high frequency circular translation pin-on-disk (HF-CTPOD) device with a relative cycle frequency of 25.3. Hz and an average sliding velocity of 27.4. mm/s was designed. The pins circularly translated at high frequency (1.0. mm per cycle, 24.8. Hz, clockwise), and the disks at low frequency (31.4. mm per cycle, 0.5. Hz, counter-clockwise). In a 22 million cycle (10 day) test, the wear rate of conventional gamma-sterilized UHMWPE pins against polished CoCr disks in diluted serum was 1.8. mg per 24. h, which was six times higher than that in the established 1. Hz CTPOD device. The wear mechanisms were similar. Burnishing of the pin was the predominant feature. No overheating took place. With the dual motion HF-CTPOD method, the wear testing of UHMWPE as a bearing material in total hip arthroplasty can be substantially accelerated without concerns of the validity of the wear simulation. © 2014 Elsevier Ltd.

Lund P.D.,Aalto University
International Journal of Hydrogen Energy | Year: 2010

Fuel cell based energy systems are a potential large-scale future energy option. The key challenge for fuel cells is to reach a market breakthrough which in turn requires a major cost reduction from the present level. Using a combined learning and diffusion model we have investigated effective integrated strategies that combine optimally R&D and market measures to decrease the expenditure and time needed to reach the breakeven point. The results indicate that major efforts in R&D for enhancing fuel cell innovations such as the European fuel cell and hydrogen joint technology effort would be economically well justified. Such efforts could save several billion dollars in the market deployment efforts otherwise required. Through a balanced and integrated technology push and market pull effort the time to breakthrough could similarly be reduced by 60-70%. © 2009 Professor T. Nejat Veziroglu.

Valagiannopoulos C.A.,Aalto University | Tsitsas N.L.,Aristotle University of Thessaloniki
Radio Science | Year: 2012

Eliminating the electromagnetic interaction of a device with its background is a topic which attracts considerable attention both from a theoretical as well as from an experimental point of view. In this work, we analyze an infinite two-dimensional planar microstrip antenna, excited by an incident plane wave, and propose its potential operation as a low-profile receiving antenna, by suitably adjusting the parameters of its cloaking superstrate. We impose a semi-analytic integral equation method to determine the scattering characteristics of the microstrip antenna. The method utilizes the explicit expressions of the Green's function of the strip-free microstrip and yields the surface strip's current as the solution of a suitable linear system. Subsequently, the antenna's far-field response is obtained. Numerical results are presented for the achieved low profile of the receiving antenna, by choosing suitably the cloaking superstrate parameters. It is demonstrated that for specific cloaking parameters the scattered field by the antenna is considerably reduced, while the received signal from the antenna is maintained at sensible levels. We point out that the material values achieving this reduction correspond to a superstrate filled with an -near-zero or a low-index metamaterial. Finally, the variations of the device reaction for various superstrates are depicted, concluding that for optimized superstrate's parameters, the reaction values are significantly reduced, while at distinct scattering angles even approach zero.

Hanninen R.,Aalto University
Physical Review B - Condensed Matter and Materials Physics | Year: 2015

In this Comment we would like to emphasize that in Phys. Rev. B 90, 104506 (2014)PRBMDO1098-012110.1103/PhysRevB.90.104506 the calculated energy spectrum takes into account only the small interaction (cross) term and, additionally, this term is only calculated at the instant when the two vortices reconnect. The majority of the kinetic energy is contained in the self-energy term which has a characteristic spectrum of 1/k. If this, and the additional average over time, is taken into account the suggested Kolmogorov-type k-5/3 spectrum is likely not visible in the kinetic energy spectrum which contains both terms. Therefore, we find the suggestion misleading that the Kolmogorov spectrum in superfluids arises from the reconnection of vortices. © 2015 American Physical Society.

Salo J.,Aalto University
Computers in Human Behavior | Year: 2011

Social virtual worlds (SVWs) have become important environments for social interaction. At the same time, the supply and demand of virtual goods and services is rapidly increasing. For SVWs to be economically sustainable, retaining existing users and turning them into consumers are paramount challenges. This requires an understanding of the underlying reasons why users continuously engage in SVWs and purchase virtual items. This study builds upon Technology Acceptance Model, motivational model and theory of network externalities to examine continuous usage and purchase intention and it empirically tests the model with data collected from 2481 Habbo users. The results reveal a strong relationship between continuous usage and purchasing. Further, the results demonstrate the importance of the presence of other users in predicting the purchase behavior in the SVW. Continuous SVW usage in turn is predicted directly by perceived enjoyment and usefulness while the effect of attitude is marginal. Finally, perceived network externalities exert a significant influence of perceived enjoyment and usefulness of the SVW but do not have a direct effect on the continuous usage. © 2011 Elsevier Ltd. All rights reserved.

Valagiannopoulos C.A.,Aalto University
Progress in Electromagnetics Research | Year: 2011

Achieving and controlling highly selective response in an electronic component could be particularly beneficial for numerous practical applications. In this work, we consider a simple configuration of a discontinuous parallel-plate waveguide with a narrow rectangular ridge filled with axially anisotropic material. The formulated boundary value problem is rigorously treated with help from mode matching technique. The variables with respect to which the device exhibits highly selective behavior and the parameters through which the regulation of sharp variations becomes possible, have been identified. Several graphs demonstrating these properties are analyzed and discussed.

Sarkka S.,Aalto University
IEEE Transactions on Audio, Speech and Language Processing | Year: 2011

This paper is concerned with accurate discretization of linear analog filters such that the frequency response of the discrete time filter accurately matches that of the continuous time filter. The approach is based on formal reconstruction of the continuous time signal using Shannon's interpolation theorem and numerical solving of the differential equation corresponding to the analog filter. When the formal continuous time system is sampled, the resulting filter reduces to discrete linear filter, which can be realized either as a state space model or as an infinite impulse response (IIR) filter. The proposed methodology is applied to design of filters for parametric equalizers. © 2011 IEEE.

Bjorkman T.,Aalto University
Computer Physics Communications | Year: 2011

The CIF2Cell program generates the geometrical setup for a number of electronic structure programs based on the crystallographic information in a Crystallographic Information Framework (CIF) file. The program will retrieve the space group number, Wyckoff positions and crystallographic parameters, make a sensible choice for Bravais lattice vectors (primitive or principal cell) and generate all atomic positions. Supercells can be generated and alloys are handled gracefully. The code currently has output interfaces to the electronic structure programs ABINIT, CASTEP, CPMD, Crystal, Elk, Exciting, EMTO, Fleur, RSPt, Siesta and VASP. © 2011 Elsevier B.V. All rights reserved.

Alanne K.,Aalto University
European Journal of Engineering Education | Year: 2015

To ensure proper competence development and short graduation times for engineering students, it is essential that the study motivation is encouraged by new learning methods. In game-based learning, the learner's engagement is increased and learning is made meaningful by applying game-like features such as competition and rewarding through virtual promotions or achievement badges. In this paper, the state of the art of game-based learning in building services engineering education at university level is reviewed and discussed. A systematic literature review indicates that educational games have been reported in the field of related disciplines, such as mechanical and civil engineering. The development of system-level educational games that realistically simulate work life in building services engineering is still in its infancy. Novel rewarding practices and more comprehensive approaches entailing the state-of-the-art information tools such as building information modelling, geographic information systems, building management systems and augmented reality are needed in the future. © 2015 SEFI

Frenay B.,Catholic University of Louvain | Frenay B.,Aalto University | Verleysen M.,Catholic University of Louvain
Neurocomputing | Year: 2011

Support vector regression (SVR) is a state-of-the-art method for regression which uses the εsensitive loss and produces sparse models. However, non-linear SVRs are difficult to tune because of the additional kernel parameter. In this paper, a new parameter-insensitive kernel inspired from extreme learning is used for non-linear SVR. Hence, the practitioner has only two meta-parameters to optimise. The proposed approach reduces significantly the computational complexity yet experiments show that it yields performances that are very close from the state-of-the-art. Unlike previous works which rely on Monte-Carlo approximation to estimate the kernel, this work also shows that the proposed kernel has an analytic form which is computationally easier to evaluate. © 2011 Elsevier B.V.

Oikarinen E.,Aalto University | Woltran S.,Vienna University of Technology
Artificial Intelligence | Year: 2011

Since argumentation is an inherently dynamic process, it is of great importance to understand the effect of incorporating new information into given argumentation frameworks. In this work, we address this issue by analyzing equivalence between argumentation frameworks under the assumption that the frameworks in question are incomplete, i.e. further information might be added later to both frameworks simultaneously. In other words, instead of the standard notion of equivalence (which holds between two frameworks, if they possess the same extensions), we require here that frameworks F and G are also equivalent when conjoined with any further framework H. Due to the nonmonotonicity of argumentation semantics, this concept is different to (but obviously implies) the standard notion of equivalence. We thus call our new notion strong equivalence and study how strong equivalence can be decided with respect to the most important semantics for abstract argumentation frameworks. We also consider variants of strong equivalence in which we define equivalence with respect to the sets of arguments credulously (or skeptically) accepted, and restrict strong equivalence to augmentations H where no new arguments are raised. © 2011 Elsevier B.V. All rights reserved.

Surround modulation of perceived contrast has been almost exclusively studied in short-range conditions, i.e., in situations where a tiny gap, at most, separates center from surround. Existing long-range studies suggest that suppression extends to 12-cycle distance, whereas facilitation of perceived contrast is suggested to arise from visual field regions enclosing the center. In V1 neurons, however, long-range surround modulation involves both suppression and facilitation. Thus, we investigated short- and long-range surround modulation by measuring the perceived contrast of a center in the presence of a surround either near (0.3 cycles, 0.1 degree) or far (19.8 cycles, 6.6 degrees) from the center. This study demonstrates that in addition to the well-known suppression, surround modulation involves remarkably long-range facilitation of perceived contrast. At low center contrasts, the long-range facilitation was stronger than the long-range suppression, whereas at high center contrast we found mainly long-range suppression. Because the current models of perceived contrast could not account for our data, we considered our results in the context of models developed for surround modulation in V1 neurons. However, neither mechanistic nor phenomenological models proved satisfactory. Moreover, with the current knowledge, it seems that straightforward pooling of V1 neurons' responses cannot account for surround modulation of perceived contrast.

Mura M.,Kings College London | Gulans A.,Aalto University | Thonhauser T.,Wake forest University | Kantorovich L.,Kings College London
Physical Chemistry Chemical Physics | Year: 2010

The self-assembly of flat organic molecules on metal surfaces is controlled, apart from the kinetic factors, by the interplay between the molecule-molecule and molecule-surface interactions. These are typically calculated using standard density functional theory within the generalized gradient approximation, which significantly underestimates nonlocal correlations, i.e. van der Waals (vdW) contributions, and thus affects interactions between molecules and the metal surface in the junction. In this paper we address this question systematically for the Au(111) surface and a number of popular flat organic molecules which form directional hydrogen bonds with each other. This is done using the recently developed first-principles vdW-DF method which takes into account the nonlocal nature of electron correlation [M. Dion et al., Phys. Rev. Lett. 2004, 92, 246401]. We report here a systematic study of such systems involving completely self-consistent vdW-DF calculations with full geometry relaxation. We find that the hydrogen bonding between the molecules is only insignificantly affected by the vdW contribution, both in the gas phase and on the gold surface. However, the adsorption energies of these molecules on the surface increase dramatically as compared with the ordinary density functional (within the generalized gradient approximation, GGA) calculations, in agreement with available experimental data and previous calculations performed within approximate or semiempirical models, and this is entirely due to the vdW contribution which provides the main binding mechanism. We also stress the importance of self-consistency in calculating the binding energy by the vdW-DF method since the results of non-self-consistent calculations in some cases may be off by up to 20%. Our calculations still support the usually made assumption of the molecule-surface interaction changing little laterally suggesting that single molecules and their small clusters should be quite mobile at room temperature on the surface. These findings support a gas-phase modeling for some flat metal surfaces, such as Au(111), and flat molecules, at least as a first approximation. © the Owner Societies.

Suomela J.,Aalto University
Proceedings of the Annual ACM Symposium on Principles of Distributed Computing | Year: 2010

An edge dominating set for a graph G is a set D of edges such that each edge of G is in D or adjacent to at least one edge in D. This work studies deterministic distributed approximation algorithms for finding minimum-size edge dominating sets. The focus is on anonymous port-numbered networks: there are no unique identifiers, but a node of degree d can refer to its neighbours by integers l,2,...,d. The present work shows that in the port-numbering model, edge dominating sets can be approximated as follows: in d-regular graphs, to within 4 - 6/(d + 1) for an odd d and to within 4 - 2/d. for an even d; and in graphs with maximum degree Δ, to within 4 - 2/(Δ - 1) for an odd Δ and to within 4 - 2/Δ for an even Δ. These approximation ratios are tight for all values of d and Δ: there are matching lower bounds. Copyright 2010 ACM.

Taherkhani A.,Aalto University
IEEE International Conference on Program Comprehension | Year: 2010

We present a method for automatic algorithm recognition, which consists of two phases. First, the target algorithms are converted into characteristic vectors, which are computed based on static analysis of program code including various statistics of language constructs and analysis of Roles of Variables. In the second phase, the algorithms are classified based on these vectors using the C4.5 decision tree classifier. We have developed a prototype and successfully applied the method to sorting algorithms. Evaluated with leave-one-out technique, the accuracy of the constructed decision tree classifier is 97.1%. © 2010 IEEE.

Peltoniemi M.,Aalto University
Journal of Forest Economics | Year: 2013

In recent years researchers have shown increasing interest in capabilities as the foundation of competitive advantage in the forest industry. However, we still do not know how these capabilities change in the firms and in their interactions. Therefore we ask: through what mechanisms do capabilities evolve in the forest industry context? The study was conducted by interviewing 30 forest industry experts and the data was analyzed qualitatively. We find that the main mechanisms of capability evolution include capability gaps, capability selection, capability development and capability outcomes. The study contributes through a rich description of capability evolution and by identifying theoretically meaningful mechanisms through which capability evolution takes place. Furthermore, several implications for practitioners are presented. © 2013 Department of Forest Economics, Swedish University of Agricultural Sciences, Umeå.

Winning against an opponent in a competitive video game can be expected to be more rewarding than losing, especially when the opponent is a fellow human player rather than a computer. We show that winning versus losing in a first-person video game activates the brain's reward circuit and the ventromedial prefrontal cortex (vmPFC) differently depending on the type of the opponent. Participants played a competitive tank shooter game against alleged human and computer opponents while their brain activity was measured with functional magnetic resonance imaging. Brain responses to wins and losses were contrasted by fitting an event-related model to the hemodynamic data. Stronger activation to winning was observed in ventral and dorsal striatum as well as in vmPFC. Activation in ventral striatum was associated with participants' self-ratings of pleasure. During winning, ventral striatum showed stronger functional coupling with right insula, and weaker coupling with dorsal striatum, sensorimotor pre- and postcentral gyri, and visual association cortices. The vmPFC and dorsal striatum responses were stronger to winning when the subject was playing against a human rather than a computer. These results highlight the importance of social context in the neural encoding of reward value.

Tatti N.,Aalto University
Data Mining and Knowledge Discovery | Year: 2015

One of the biggest setbacks in traditional frequent pattern mining is that overwhelmingly many of the discovered patterns are redundant. A prototypical example of such redundancy is a freerider pattern where the pattern contains a true pattern and some additional noise events. A technique for filtering freerider patterns that has proved to be efficient in ranking itemsets is to use a partition model where a pattern is divided into two subpatterns and the observed support is compared to the expected support under the assumption that these two subpatterns occur independently. In this paper we develop a partition model for episodes, patterns discovered from sequential data. An episode is essentially a set of events, with possible restrictions on the order of events. Unlike with itemset mining, computing the expected support of an episode requires surprisingly sophisticated methods. In order to construct the model, we partition the episode into two subepisodes. We then model how likely the events in each subepisode occur close to each other. If this probability is high—which is often the case if the subepisode has a high support—then we can expect that when one event from a subepisode occurs, then the remaining events occur also close by. This approach increases the expected support of the episode, and if this increase explains the observed support, then we can deem the episode uninteresting. We demonstrate in our experiments that using the partition model can effectively and efficiently reduce the redundancy in episodes. © 2015, The Author(s).

Jarvenpaa S.L.,University of Texas at Austin | Jarvenpaa S.L.,Aalto University | Majchrzak A.,University of Southern California
Information Systems Research | Year: 2010

Online participation engenders both the benefits of knowledge sharing and the risks of harm. Vigilant interaction in knowledge collaboration refers to an interactive emergent dialogue in which knowledge is shared while it is protected, requiring deep appraisals of each others' actions in order to determine how each action may influence the outcomes of the collaboration. Vigilant interactions are critical in online knowledge collaborations under ambivalent relationships where users collaborate to gain benefits but at the same time protect to avoid harm from perceived vulnerabilities. Vigilant interactions can take place on discussion boards, open source development, wiki sites, social media sites, and online knowledge management systems and thus is a rich research area for information systems researchers. Three elements of vigilant interactions are described: trust asymmetry, deception and novelty. Each of these elements challenges prevailing theory-based assumptions about how people collaborate online. The study of vigilant interaction, then, has the potential to provide insight on how these elements can be managed by participants in a manner that allows knowledge sharing to proceed without harm. © 2010 INFORMS.

Simovski C.R.,Aalto University
Journal of Optics | Year: 2011

In this overview paper the trends in the modern literature concerning the characterization of linear electromagnetic properties of nanostructured metamaterials are briefly discussed. Electromagnetic characterization of bulk and surface metamaterials is discussed. The problem of characterization of metamaterials with spatial dispersion effects is addressed. It is shown that for bulk metamaterials formed as orthorhombic dipole lattices experimental electromagnetic characterization (retrieval of material parameters) becomes possible. However, standard schemes of material parameter retrieval contain pitfalls even for this kind of material. To clarify these pitfalls the concept of characteristic material parameters is suggested which is clearer and more restrictive that the concept of effective material parameters. For a special but important class of metamaterials (called Bloch lattices by the author) bulk material parameters are obtained which probably fit the concept of electromagnetic characterization because they satisfy basic physical limitations. Further, the problem of the violation of Maxwell boundary conditions for a macroscopic field at the physical boundary of the metamaterial lattice is discussed. The role of transition layers (perhaps transition sheets) in the characterization of metamaterials is explained. Finally, a relevant numerical example is presented as an illustration of the theory. © 2011 IOP Publishing Ltd.

Lu H.,KTH Royal Institute of Technology | Alanne K.,Aalto University | Martinac I.,KTH Royal Institute of Technology
Energy Conversion and Management | Year: 2014

Renewable energy systems entail a significant potential to meet the energy requirements of building clusters and districts (BCDs) provided that local energy sources are exploited efficiently. Besides improving the energy efficiency by reducing energy consumption and improving the match between energy supply and demand, energy quality issues have become a key topic of interest. Energy quality management is a technique that aims at optimally utilizing the exergy content of various renewable energy sources. In addition to minimizing life-cycle CO2 emissions related to exergy losses of an energy system, issues such as system reliability should be addressed. The present work contributes to the research by proposing a novel multi-objective design optimization scheme that minimizes the global warming potential during the life-cycle and maximizes the exergy performance, while the maximum allowable level of the loss of power supply probability (LPSP) is predefined by the user as a constraint. The optimization makes use of Genetic Algorithm (GA). Finally, a case study is presented, where the above methodology has been applied to an office BCD located in Norway. The proposed optimization scheme is proven to be efficient in finding the optimal design and can be easily enlarged to encompass more relevant objective functions. © 2014 Elsevier Ltd. All rights reserved.

Romanoff J.,Aalto University | Reddy J.N.,Texas A&M University
Composite Structures | Year: 2014

The paper presents experimental validation of the modified couple stress Timoshenko beam theory for web-core sandwich panels. The face and web-plates are assumed to be isotropic and to behave according to the kinematics of the Euler-Bernoulli beam theory. First, a modified couple stress theory for Timoshenko beams is reviewed. Then shear, bending and couple stress responses of homogenized web-core sandwich beams are examined. The developed theory is validated with experiments from open literature for beams in 3- and 4-point bending. The beams have 4, 9 and 15 unit cells along their length. It is seen that the developed theory is in excellent agreement with experiments. It is also seen that the theory converges to physically correct solutions in the cases of infinite and zero shear stiffness; while the first corresponds the case of Euler-Bernoulli sandwich beam, the second corresponds the case where the sandwich effect is lost and the bending is carried out purely by the bending of the faces. The paper also gives explicit expression for the couple stress stiffness in terms of unit cell dimensions and materials. © 2013 Elsevier Ltd.

Silvanto J.,University of Westminster | Silvanto J.,Aalto University
Consciousness and Cognition | Year: 2015

The neuropsychological phenomenon of blindsight has been taken to suggest that the primary visual cortex (V1) plays a unique role in visual awareness, and that extrastriate activation needs to be fed back to V1 in order for the content of that activation to be consciously perceived. The aim of this review is to evaluate this theoretical framework and to revisit its key tenets. Firstly, is blindsight truly a dissociation of awareness and visual detection? Secondly, is there sufficient evidence to rule out the possibility that the loss of awareness resulting from a V1 lesion simply reflects reduced extrastriate responsiveness, rather than a unique role of V1 in conscious experience? Evaluation of these arguments and the empirical evidence leads to the conclusion that the loss of phenomenal awareness in blindsight may not be due to feedback activity in V1 being the hallmark awareness. On the basis of existing literature, an alternative explanation of blindsight is proposed. In this view, visual awareness is a "global" cognitive function as its hallmark is the availability of information to a large number of perceptual and cognitive systems; this requires inter-areal long-range synchronous oscillatory activity. For these oscillations to arise, a specific temporal profile of neuronal activity is required, which is established through recurrent feedback activity involving V1 and the extrastriate cortex. When V1 is lesioned, the loss of recurrent activity prevents inter-areal networks on the basis of oscillatory activity. However, as limited amount of input can reach extrastriate cortex and some extrastriate neuronal selectivity is preserved, computations involving comparison of neural firing rates within a cortical area remain possible. This enables "local" read-out from specific brain regions, allowing for the detection and discrimination of basic visual attributes. Thus blindsight is blind due to lack of "global" long-range synchrony, and it functions via "local" neural readout from extrastriate areas. © 2014 The Author.

Huang C.,Shanghai JiaoTong University | Ye F.,Shanghai JiaoTong University | Sun Z.,Aalto University | Chen X.,Shanghai JiaoTong University
Optics Express | Year: 2014

We study linear and nonlinear mode properties in a periodically patterned graphene sheet. We demonstrate that a subwavelength one-dimensional photonic lattice can be defined across the graphene monolayer, with its modulation depth and correspondingly the associated photonic band structures being controlled rapidly, by an external gate voltage. We find the existences of graphene lattice solitons at the deep-subwavelength scales in both dimensions, thanks to the combination of graphene intrinsic self-focusing nonlinearity and the graphene plasmonic confinement effects. © 2014 Optical Society of America.

Aurell E.,KTH Royal Institute of Technology | Aurell E.,Aalto University | Aurell E.,Albanova University Center | Ekeberg M.,KTH Royal Institute of Technology
Physical Review Letters | Year: 2012

We show that a method based on logistic regression, using all the data, solves the inverse Ising problem far better than mean-field calculations relying only on sample pairwise correlation functions, while still computationally feasible for hundreds of nodes. The largest improvement in reconstruction occurs for strong interactions. Using two examples, a diluted Sherrington-Kirkpatrick model and a two-dimensional lattice, we also show that interaction topologies can be recovered from few samples with good accuracy and that the use of l 1 regularization is beneficial in this process, pushing inference abilities further into low-temperature regimes. © 2012 American Physical Society.

Rahmstorf S.,Potsdam Institute for Climate Impact Research | Vermeer M.,Aalto University
Journal of Coastal Research | Year: 2011

A recent article published in the Journal of Coastal Research analysed a number of different sea-level records and reported that they found no acceleration of sea-level rise. We show that this is due to their focusing on records that are either too short or only regional in character, and on their specific focus on acceleration since the year 1930, which represents a unique minimum in the acceleration curve. We find that global sea-level rise is accelerating in a way strongly correlated with global temperature. This correlation also explains the acceleration minimum for time periods starting around 1930; it is due to the mid-twentieth-century plateau in global temperature. © 2011, the Coastal Education & Research Foundation (CERF).

Hekking F.W.J.,Joseph Fourier University | Pekola J.P.,Aalto University
Physical Review Letters | Year: 2013

We apply the quantum jump approach to address the statistics of work in a driven two-level system coupled to a heat bath. We demonstrate how this question can be analyzed by counting photons absorbed and emitted by the environment in repeated experiments. We find that the common nonequilibrium fluctuation relations are satisfied identically. The usual fluctuation-dissipation theorem for linear response applies for weak dissipation and/or weak drive. We point out qualitative differences between the classical and quantum regimes. © 2013 American Physical Society.

Seppala A.,Aalto University
International Journal of Heat and Mass Transfer | Year: 2012

The specific irreversibility of solidification and of cyclic solidification-melting process was considered on a general level. The variables affecting the irreversibility most are the Biot number, the dimensionless interfacial speed during recalescense and the extent of supercooling. The process path involving supercooling can become less irreversible than the path where phase transition completely happens in an equilibrium state if a thermal conductivity ratio between solid and liquid phases is sufficiently below unity. A finite maximum and a non-zero minimum value of irreversibility can be detected. These extreme values are independent of the geometrical shape of the substance. © 2011 Elsevier Ltd. All rights reserved.

Pitkonen M.,Aalto University
Journal of Electromagnetic Waves and Applications | Year: 2010

Using the bipolar coordinate system, the electrostatic scattering problem of a dielectric double half-cylinder is solved. In particular, an expression for the polarizability of the half-cylinder is obtained in terms of two dilogarithm functions. Also the nonuniqueness of the solution is proven in a certain range of negative values of the permittivity. © 2010 VSP.

This paper proposes a method for deploying a nanosatellite constellation to several orbital planes from a single launch vehicle. The method is based on commercially available deorbit devices that are used to lower the initial orbit, and that are discarded after the correct altitude has been reached. Nodal precession of the right ascension of the ascending node at different altitudes results in spreading the orbital planes of the satellites. Maneuvering all satellites to a similar final altitude freezes the relative separation of the orbital planes. Calculations and simulations of the method are presented, and the results indicate that with a launch of 6 satellites to an initial 800 km sun-synchronous orbit, orbital plane separation of approximately 30° between each satellite can be achieved within 5 years, with each satellite in its own final 600 km orbital plane. Such a constellation could provide continuous global coverage, while requiring only one launch vehicle. Due to the timescales required by the method, it is best suited for nanosatellite missions designed for long lifetimes. Possible applications of such constellations are also discussed. © 2015 IAA.

Tretyakov S.,Aalto University
Plasmonics | Year: 2014

This is a review and tutorial paper which discusses the fundamental limitations on the maximal power which can be received, absorbed, and scattered by an electrically small electrically polarizable particle and infinite periodical arrays of such particles. © 2014 Springer Science+Business Media New York.

The boundary extension of a zero-energy building to integrate a new energy vehicle will facilitate the realization of the target set by the EU 2050 roadmap. In this study, either a hydrogen vehicle (HV) or an electric vehicle (EV) is integrated into a renewable-supported building system with appropriate control strategies. The focused variables in this study are renewable energy capacities, vehicle system options, extents to utilize vehicle storages for domestic purposes, and the Excess REe-HW recharging strategies. The analysing aspects include the energy and environmental impact as well as the energy matching and the grid interactions. The results show that the annual net-zero energy/emission balance can be met by a 16, 12, and 12 kW rated wind turbine, or by a 195.8, 160.2, and 142.4 m2 PV, for the building with the HV, the EV and no vehicle (NV), respectively. The building with the HV will be more demanding in meeting the balance due to the less efficient HV system than that with the EV. Moreover, better matching for the zero-energy system can be achieved by relieving the condition to discharge the vehicle storages for domestic usages and by using the Excess REe-HW recharging strategy. However, their negative effect will be a slight increase in the annual net-energy consumption, due to an increased loss from both the HV/EV integrated system and the thermal storage. © 2016 Elsevier Ltd.

Dorval E.,Aalto University
Annals of Nuclear Energy | Year: 2016

The treatment of neutron leakage at assembly level is an essential step in the generation of few-group cross section data for reactor calculations. This work compares methods used for the characterization of assembly leakage in the framework of Monte Carlo cross section generation, using nearly-critical colorset configurations in order to obtain approximate reference values. The B1 fundamental mode approximation and the albedo-search method are compared in terms of eigenvalue, multi-group homogeneous scalar fluxes and maximum pin power differences for several cell types. The performance of a novel heterogeneous leakage method is also tested. Whereas B1 corrections provide the best agreement in homogeneous fluxes, the new method furnishes the best consistence in terms of pin powers, whilst providing rich spectral information and reducing computational overheads associated with colorset calculations. Future investigations are suggested in order to test the performance of these methods in the calculation of few-group, leakage-corrected assembly cross sections and discontinuity factors. © 2015 Elsevier Ltd. All rights reserved.

Pinheiro F.,University of Stockholm | Pinheiro F.,KTH Royal Institute of Technology | Bruun G.M.,University of Aarhus | Martikainen J.-P.,Aalto University | Larson J.,University of Stockholm
Physical Review Letters | Year: 2013

We demonstrate how the spin-1/2 XYZ quantum Heisenberg model can be realized with bosonic atoms loaded in the p band of an optical lattice in the Mott regime. The combination of Bose statistics and the symmetry of the p-orbital wave functions leads to a nonintegrable Heisenberg model with antiferromagnetic couplings. Moreover, the sign and relative strength of the couplings characterizing the model are shown to be experimentally tunable. We display the rich phase diagram in the one-dimensional case and discuss finite size effects relevant for trapped systems. Finally, experimental issues related to preparation, manipulation, detection, and imperfections are considered. © 2013 American Physical Society.

Aurell E.,KTH Royal Institute of Technology | Aurell E.,Albanova University Center | Aurell E.,Aalto University | Mejia-Monasterio C.,University of Helsinki | And 2 more authors.
Physical Review Letters | Year: 2011

Thermodynamics of small systems has become an important field of statistical physics. Such systems are driven out of equilibrium by a control, and the question is naturally posed how such a control can be optimized. We show that optimization problems in small system thermodynamics are solved by (deterministic) optimal transport, for which very efficient numerical methods have been developed, and of which there are applications in cosmology, fluid mechanics, logistics, and many other fields. We show, in particular, that minimizing expected heat released or work done during a nonequilibrium transition in finite time is solved by the Burgers equation and mass transport by the Burgers velocity field. Our contribution hence considerably extends the range of solvable optimization problems in small system thermodynamics. © 2011 American Physical Society.

Koivisto J.J.,Aalto University
Chemical Communications | Year: 2013

The high spectral resolution provided by the pure shift TOCSY experiment can be significantly improved by zero-quantum filtering which eliminates dispersive anti-phase contributions from the spectrum. © 2012 The Royal Society of Chemistry.

Santos T.G.,New University of Lisbon | Miranda R.M.,New University of Lisbon | Vilaca P.,Aalto University
Journal of Materials Processing Technology | Year: 2014

This paper presents a variant of Friction Stir Welding (FSW) aiming to minimize or eliminate the root defects that still constitute a major constrain to a wider dissemination of FSW into industrial applications. The concept is based on the use of an external electrical energy source, delivering a high intensity current, passing through a thin layer of material between the back plate and the lower tip of the tool probe. Heat generated by Joule effect improves material viscoplasticity in this region, minimizing the root defects. The concept was validated by analytical and experimental analysis. For the later, a new dedicated tool was designed, manufactured and tested. Numerical simulations were performed to study the electrical current flow pattern and its effect on the material below the probe tip. The potential use of this variant was shown by reducing the size of the weld root defect, even for significant levels of lack of penetration, without affecting overall metallurgical characteristics of the welded joints. © 2014 Elsevier B.V.

Provatas N.,McMaster University | Majaniemi S.,Aalto University
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2010

A phase field crystal (PFC) density functional for binary mixtures is coarse grained and a formalism for calculating the simultaneous concentration, temperature, and density dependence of the surface energy anisotropy of a solid-liquid interface is developed. The methodology systematically relates bulk free energy coefficients arising from coarse graining to thermodynamic data, while gradient energy coefficients are related to molecular properties. Our coarse-grained formalism is applied to the determination of surface energy anisotropy in two-dimensional Zn-Al films, a situation relevant for quantitative phase field simulations of dendritic solidification in zinc coatings. © 2010 The American Physical Society.

The quality of few-group cross section data generated for core diffusion solvers depends on the treatment of the neutron leakage at lattice level. In this work, we propose a study about the relative performance of three assembly leakage models in the Monte Carlo code Serpent. Additionally, the extension of a novel method for the generation of directional diffusion coefficients to different reactor types is studied. Using Monte Carlo full core results as reference values, leakage and diffusion coefficient models are contrasted in terms of system eigenvalue and power distributions in a simplified heavy-water-moderated reactor system. Heterogeneous leakage models yielded the best results. Standard diffusion coefficients showed the best performance, due to difficulties arising from the volume-averaging of directional diffusion coefficients in cluster geometry. The results of this work suggest that the generation of directional diffusion coefficients could be extended to graphite-moderated gas-cooled reactors. © 2015 Elsevier Ltd. All rights reserved.

Sorva J.,Aalto University
ACM Transactions on Computing Education | Year: 2013

This article brings together, summarizes, and comments on several threads of research that have contributed to our understanding of the challenges that novice programmers face when learning about the runtime dynamics of programs and the role of the computer in program execution. More specifically, the review covers the literature on programming misconceptions, the cognitive theory of mental models, constructivist theory of knowledge and learning, phenomenographic research on experiencing programming, and the theory of threshold concepts. These bodies of work are examined in relation to the concept of a "notional machine"- an abstract computer for executing programs of a particular kind. As a whole, the literature points to notional machines as a major challenge in introductory programming education. It is argued that instructors should acknowledge the notional machine as an explicit learning objective and address it in teaching. Teaching within some programming paradigms, such as object-oriented programming, may benefit from using multiple notional machines at different levels of abstraction. Pointers to some promising pedagogical techniques are provided. ©2013 ACM.

Ricci M.,Ecole Polytechnique Federale de Lausanne | Spijker P.,Aalto University | Voitchovsky K.,Ecole Polytechnique Federale de Lausanne | Voitchovsky K.,Durham University
Nature Communications | Year: 2014

When immersed into water, most solids develop a surface charge, which is neutralized by an accumulation of dissolved counterions at the interface. Although the density distribution of counterions perpendicular to the interface obeys well-established theories, little is known about counterions' lateral organization at the surface of the solid. Here we show, by using atomic force microscopy and computer simulations, that single hydrated metal ions can spontaneously form ordered structures at the surface of homogeneous solids in aqueous solutions. The structures are laterally stabilized only by water molecules with no need for specific interactions between the surface and the ions. The mechanism, studied here for several systems, is controlled by the hydration landscape of both the surface and the adsorbed ions. The existence of discrete ion domains could play an important role in interfacial phenomena such as charge transfer, crystal growth, nanoscale self-assembly and colloidal stability. © 2014 Macmillan Publishers Limited. All rights reserved.

Kuusi T.,Aalto University | Mingione G.,University of Parma
Archive for Rational Mechanics and Analysis | Year: 2014

The spatial gradient of solutions to nonlinear degenerate parabolic equations can be pointwise estimated by the caloric Riesz potential of the right hand side datum, exactly as in the case of the heat equation. Heat kernels type estimates persist in the nonlinear case. © 2013 Springer-Verlag Berlin Heidelberg.

Chebykin A.V.,Saint Petersburg State University of Information Technologies, Mechanics and Optics | Orlov A.A.,Saint Petersburg State University of Information Technologies, Mechanics and Optics | Simovski C.R.,Aalto University | Kivshar Yu.S.,Australian National University | Belov P.A.,Queen Mary, University of London
Physical Review B - Condensed Matter and Materials Physics | Year: 2012

We consider multilayered metal-dielectric metamaterials composed of alternating nanolayers of two types and calculate the components of their effective dielectric permittivity tensors as functions of both frequency and wave vector. We demonstrate that such structures can be described as strongly nonlocal uniaxial effective media, and we analyze how the nonlocal permittivity tensor components are related to other manifestations of strong spatial dispersion in such structures, and how the resonance of permittivity depends on the propagation direction. © 2012 American Physical Society.

Korhonen J.M.,Aalto University
Acta Astronautica | Year: 2013

The possibility that extraterrestrial intelligences (ETIs) could be hostile to humanity has been raised as a reason to avoid even trying to contact ETIs. However, there is a distinct shortage of analytical discussion about the risks of an attack, perhaps because of an implicit premise that we cannot analyze the decision making of an alien civilization. This paper argues that we can draw some inferences from the history of the Cold War and nuclear deterrence in order to show that at least some attack scenarios are likely to be exaggerated. In particular, it would seem to be unlikely that the humanity would be attacked simply because it might, sometime in the future, present a threat to the ETI. Even if communication proves to be difficult, rational decision-makers should avoid unprovoked attacks, because their success would be very difficult to assure. In general, it seems believable that interstellar conflicts between civilizations would remain rare. The findings advise caution for proposed interstellar missions, however, as starfaring capability itself might be seen as a threat. On the other hand, attempting to contact ETIs seems to be a relatively low-risk strategy: paranoid ETIs must also consider the possibility that the messages are a deception designed to lure out hostile civilizations and preemptively destroy them. © 2013 IAA.

Salmi O.,Eero Paloheimo Ecocity Ltd | Wierink M.,Aalto University
Journal of Cleaner Production | Year: 2011

This article analyses the impact of waste recovery on climate change mitigation on a regional scale. We focus on the EU End of Waste (EoW) policy, which aims at reducing negative impacts on the environment through the minimization of generated waste. At the same time, the EU climate objectives set challenging goals for the industry to lower greenhouse gas emissions. We argue that the goals of these two policies are conflicting: under certain circumstances, the EoW will lead into increased greenhouse gas emissions because of a number of negative feedback effects that function on multiple spatial and temporal scales. To assess the effects of waste recovery on greenhouse gas emissions, we carry out a consequential life-cycle inventory on a proposed industrial ecosystem around the Gulf of Bothnia between Finland and Sweden. The system recovers currently unutilized steelmaking dust and slag from four steel mills in Finland and Sweden and converts them into iron and zinc raw materials in a novel rotary hearth furnace. The recovered iron is led back into the blast furnace of one of the steel mills and zinc is treated in an existing zinc plant. In the European scale, the model system is significant in size, serving thus as a model for integrated EoW and carbon footprint assessments in other similar cases within the EU. The analysis reveals the relative greenhouse gas emissions from raw material extraction and production, heat and power generation, transport and the production process itself, in comparison to the present system with limited material recovery. To test the model viability, we conduct a sensitivity analysis with respect to increasing energy and production capacity. Our analysis shows that from the point of view of a single operator, material recovery may bring noteworthy reductions in greenhouse gas emissions. If the scale of the assessment is expanded beyond the confines of a single plant, however, we find limited potential for reducing greenhouse gas emissions through further recovery of steelmaking residues. In conclusion, we provide policy recommendations with which the EoW paradigm can provide better support for climate change mitigation on a regional scale. © 2011 Elsevier Ltd. All rights reserved.

Kruskopf A.,Aalto University
Metallurgical and Materials Transactions B: Process Metallurgy and Materials Processing Science | Year: 2015

A process model for basic oxygen furnace is in development. The full model will include a 2-D axisymmetric turbulent flow model for iron melt, a steel scrap melting model, and a chemical reaction model. A theoretical basis for scrap melting model is introduced in this paper and an in-house implementation of the model is tested in this article independently from the other parts of the full process model. The model calculates a melting curve for the scrap piece and the heat and carbon mass exchange between the melt and the scrap. A temperature and carbon concentration-dependent material data are used for heat capacity, thermal conductivity, and diffusion coefficient. The equations are discretized into a moving grid, which is uncommon in literature in the context of scrap melting. A good agreement is found between the modeling results and experiments from literature. Also a heat transfer correlation for dimensionless Nusselt number is determined using the numerical results. © 2015, The Minerals, Metals & Materials Society and ASM International.

He K.,Tsinghua University | Wang X.,Aalto University
Journal of Bioactive and Compatible Polymers | Year: 2011

A tubular polyurethane (PU) sandwich-like, adipose-derived stem cell (ADSC)/gelatin/alginate/ fibrin construct was fabricated using a double-nozzle, low-temperature (-20°C) deposition technique. The ADSCs survived the fabrication and cryopreservation stages by incorporating a cryoprotectant (glycerol or dimethyl sulfoxide (DMSO)) in the cell/hydrogel system. With 5% DMSO or 10% glycerol alone in the hydrogel, the cell viabilities were retained (73% and 62%, respectively). The three-dimensional construct was effectively preserved below -80°C for more than 1 week. After the freeze/thaw processes, cell viability and proliferation ability were regained. This strategy has the potential to be widely used in complex organ manufacturing techniques. © 2011 The Author(s).

Lund P.D.,Aalto University
Renewable Energy | Year: 2014

For the new energy technology markets to grow, demand, prices, and business conditions need to be in balance. It is not just declining prices and increasing volumes that are important, but the business in the new energy sector also needs to be healthy, which is not always the case at present. We have analyzed the ability of businesses in the new energy sector to invest in new production capacity, which influences the total volume growth. Using the self-financeable growth rate (SGR) as an indicator, a declining trend was found among PV and wind power manufacturers. The prospects of initiating new investments through returns from operations are poor or negligible at present, which is explained by tougher competition, shrinking public support, and new entrants, among others. Reducing the cost of sales would be the most effective way to improve the growth prospects, though increasing revenues, e.g., through higher product prices, comes close to achieving the same result. Market measures such as consolidation, rationalization, better asset use, improving efficiency, etc. are equally important. The analysis results imply a growth limit of ca. 15-25% per year with present market conditions, which may also be a more permanent level, supported by findings from technology diffusion and growth model studies. The results suggest that it is not self-evident that the new energy technologies will meet the future goals set for these in the climate and energy policy strategies, unless policymakers and decision makers properly address the issue of restoring and securing sound business conditions. © 2013 Elsevier Ltd.

Kopnin N.B.,Aalto University | Kopnin N.B.,Russian Academy of Sciences
JETP Letters | Year: 2011

The supercurrent for the surface superconductivity of a flat-band multilayered rhombohedral graphene is calculated. Despite the absence of dispersion of the excitation spectrum, the supercurrent is finite. The critical current is proportional to the zero-temperature superconducting gap, i. e., to the superconducting critical temperature and to the size of the flat band in the momentum space. © 2011 Pleiades Publishing, Ltd.

Kullaa J.,Aalto University | Kullaa J.,Helsinki Metropolia University of Applied Sciences
Mechanical Systems and Signal Processing | Year: 2013

In structural health monitoring (SHM) and control, the structure can be instrumented with an array of sensors forming a redundant sensor network, which can be utilized in sensor fault diagnosis. In this study, the objective is to detect, identify, and quantify a sensor fault using the structural response data measured with the sensor network. Seven different sensor fault types are investigated and modelled: bias, gain, drifting, precision degradation, complete failure, noise, and constant with noise. The sensor network is modelled as a Gaussian process and each sensor in the network is estimated in turn using the minimum mean square error (MMSE) estimation The sensor fault is identified and quantified using the multiple hypothesis test utilizing the generalized likelihood ratio (GLR). The proposed approach is experimentally verified with an array of accelerometers assembled on a wooden bridge. Different sensor faults are simulated by modifying a single sensor. The method is able to detect a sensor fault, identify and correct the faulty sensor, as well as identify and quantify the fault type. © 2013 Elsevier Ltd.

Olkkonen M.-K.,Aalto University
IET Radar, Sonar and Navigation | Year: 2016

This study presents a new asphalt radar, operating in the band from 13 to 17 GHz, intended for mobile road surveying of road pavement surface layers. A wide frequency band is required since new asphalt overlays are very thin in Finland being less than 50 mm in thickness. Therefore, sufficient spatial resolution of the radar system is required so that the subgrade would not affect the measurement result of the surface course. This study presents new results of the measurement campaign carried out on a newly-laid highway lane in Finland during summer 2014. The permittivity values on the trial section of the lane varied between 2.1 and 6.4. Two samples were drilled from the road in order to obtain reference permittivity values, measured in a laboratory using a 7 to 17 GHz scanner producing a 2D image of the permittivity. The permittivity values obtained using the scanner varied between 4.3 and 9.5 and they relate to the structural variation of the permittivity with a 5 mm × 5 mm resolution. The results indicate that permittivity values can be used for monitoring the change in asphalt density condition when it is performed as a follow-up survey. © The Institution of Engineering and Technology.

Sehaqui H.,KTH Royal Institute of Technology | Zhou Q.,Albanova University Center | Zhou Q.,KTH Royal Institute of Technology | Ikkala O.,Aalto University | Berglund L.A.,KTH Royal Institute of Technology
Biomacromolecules | Year: 2011

In order to better understand nanostructured fiber networks, effects from high specific surface area of nanofibers are important to explore. For cellulose networks, this has so far only been achieved in nonfibrous regenerated cellulose aerogels. Here, nanofibrillated cellulose (NFC) is used to prepare high surface area nanopaper structures, and the mechanical properties are measured in tensile tests. The water in NFC hydrogels is exchanged to liquid CO 2, supercritical CO 2, and tert-butanol, followed by evaporation, supercritical drying, and sublimation, respectively. The porosity range is 40-86%. The nanofiber network structure in nanopaper is characterized by FE-SEM and nitrogen adsorption, and specific surface area is determined. High-porosity TEMPO-oxidized NFC nanopaper (56% porosity) prepared by critical point drying has a specific surface area as high as 482 m 2 g -1. The mechanical properties of this nanopaper structure are better than for many thermoplastics, but at a significantly lower density of only 640 kg m -3. The modulus is 1.4 GPa, tensile strength 84 MPa, and strain-to-failure 17%. Compared with water-dried nanopaper, the material is softer with substantiallly different deformation behavior. © 2011 American Chemical Society.

Liimatainen V.,Aalto University
8th Annual IEEE International Conference on Nano/Micro Engineered and Molecular Systems, IEEE NEMS 2013 | Year: 2013

In this paper, we report capillary self-alignment of 200 μm × 200 μm square parts on matching patterns with undercut edges. The undercut edge structure is a purely topographical feature that provides ultimate pinning for liquids of any surface tension without chemical treatment. We show contact angles close to 180° for low surface tension liquids, and capillary self-alignment using thermally curable adhesive. Sub-micron alignment accuracy after adhesive curing is verified in a scanning electron microscope (SEM). © 2013 IEEE.

This paper unifies the analytical models used widely but thus far mostly separately for electrical and optical small amplitude perturbation measurements of nanostructured electrochemical dye solar cells (DSC): electrochemical impedance spectroscopy (EIS), intensity-modulated photocurrent spectroscopy (IMPS) and intensity-modulated photovoltage spectroscopy (IMVS). The models are linked by expressing the kinetic boundary condition used for solving the time-dependent continuity equation of electrons in IMPS and IMVS analysis in terms of the series and parallel impedance components found in the complete equivalent circuit impedance model of DSC. As a result, analytical expressions are derived for potentiostatic IMPS and galvanostatic IMVS transfer functions of complete DSCs that are applicable at any operating point along the solar cell current-voltage (IV) curve. In agreement with the theory, impedance spectrum calculated as a ratio of IMVS and IMPS transfer functions measured near the maximum power point matches exactly with the impedance spectrum measured directly with EIS. Consequently, both IMPS-IMVS and EIS yield equal estimates for the electron diffusion length. The role of the chemical capacitance of the nanostructured semiconductor photoelectrode in the interpretation of the so-called RC attenuation of the IMPS response is clarified, as well as the capacitive frequency dispersion in IMPS and IMVS. © the Owner Societies 2011.

Lehtiranta L.,Aalto University
International Journal of Project Management | Year: 2014

Shared risks and opportunities set specific premises for risk management (RM) in temporary multi-organizations (TMOs). However, most project RM research is presented from the perspective of a single-organizational project delivery team or covers limited risk perceptions and RM approaches. This paper aims to address how well the body of knowledge on multi-organizational RM corresponds to a state-of-art understanding on project RM and to identify which gaps need to be addressed in future research. The review involves: 1) the preferred view of risk as threat and/or opportunity, 2) the nature of addressed risks as anticipated or unanticipated risks or unrealistic assumptions, 3) the role of the multi-organization as the source of risks and/or resources for risk management (RM), and 4) the allocation of risk responsibilities. The review covers research papers published between 2000 and 2012 in four journals: International Journal of Project Management (IJPM), Project Management Journal (PMJ), Journal of Construction Engineering and Management (JCEM), and IEEE Transactions on Software Engineering ( TSE). 105 eligible research papers were identified. The results and conclusion outline the identified main gaps in multi-organizational RM research compared to the state-of-art RM research and TMO-specific characteristics. The results can be used to inform research agendas on more holistic and dynamic multi-organizational RM concepts. © 2013 Elsevier Ltd.

Ahmed R.,University of Bristol | Priimagi A.,Aalto University | Priimagi A.,Tokyo Institute of Technology | Faul C.F.J.,University of Bristol | Manners I.,University of Bristol
Advanced Materials | Year: 2012

Organometallic Gratings: The ionic self-assembly of metal-containing block-copolymer polyelectrolytes and azobenzene chromophores is exploited for the efficient production of stable photo-induced surface-relief gratings. We show that feature sizes can be tuned using simple redox chemistry, and that the chromophores can be removed during plasma treatment to yield ceramic-based optical materials. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Khabbazibasmenj A.,University of Alberta | Vorobyov S.A.,University of Alberta | Vorobyov S.A.,Aalto University
IEEE Transactions on Signal Processing | Year: 2013

The robust adaptive beamforming (RAB) problem for general-rank signal model with an additional positive semi-definite constraint is considered. Using the principle of the worst-case performance optimization, such RAB problem leads to a difference-of-convex functions (DC) optimization problem. The existing approaches for solving the resulted non-convex DC problem are based on approximations and find only suboptimal solutions. Here, we aim at finding the globally optimal solution for the non-convex DC problem and clarify the conditions under which the solution is guaranteed to be globally optimal. Particularly, we rewrite the problem as the minimization of a one-dimensional optimal value function (OVF). Then, the OVF is replaced with another equivalent one, for which the corresponding optimization problem is convex. The new one-dimensional OVF is minimized iteratively via polynomial time DC (POTDC) algorithm. We show that the POTDC converges to a point that satisfies Karush-Kuhn-Tucker (KKT) optimality conditions, and such point is the global optimum under certain conditions. Towards this conclusion, we prove that the proposed algorithm finds the globally optimal solution if the presumed norm of the mismatch matrix that corresponds to the desired signal covariance matrix is sufficiently small. The new RAB method shows superior performance compared to the other state-of-the-art general-rank RAB methods. © 2013 IEEE.

Tenno R.,Aalto University
Journal of Process Control | Year: 2014

The evolution of source noises in space-time is analysed in this paper. It characterises the global effect of uncertainties in electrodeposition process control, where the source noises have an effect on the concentration field of relevant species in the diffusion layer and the field is controlled by the Neumann boundary using relatively simple boundary controls. The control errors evolve in the diffusion layer and are dependent upon the source noises and applied controls as a random field process. The covariance structure of the field is found analytically and confirmed numerically. The local source noises are incited by the uncertainties from a realistic control system; they are devised by the process physics and a control system structure. This paper demonstrates that even in a relatively simple system, the local uncertainties have a strong tendency to expand in space-time. Some source noises have a dispersed effect on the overall system uncertainty (control error), others are more local and do not expand in the same way. The noise of the mass flux, which is injected through the Neumann boundary, dies out quickly in the diffusion layer. © 2013 Elsevier Ltd. All rights reserved.

Rinkinen J.,Aalto University
Energy, Sustainability and Society | Year: 2013

Background: Interest in the role of the user has provided promising insights when considering the transition towards more decentralised forms of energy provision. There is, however, a shortage of analysis on the reflexivity and learning of 'regular' users and their understandings, competences and meanings attached to energy use practices. This paper analyses discontinuities and disruptions in domestic heating during long blackouts and whether power failures could serve as an entry point to the transition dynamics of the practice. Methods: The study is based on six in-depth interviews on understandings, meanings, materials and competences attached to power cuts with households living in detached houses having different wood-based hybrid systems of energy provision. The interviews were conducted in a rural Finnish municipality, which faced power cuts lasting from 7 h to 6 days in January 2011. Results: The reactions of the interviewed households to power cuts indicate that blackouts activate unused skills and resources, propose uncommon meanings for electricity and heat and revive dormant elements of practice. Resilience of practice was achieved by flexibility in terms of convenience. However, power cuts were not found to cause explicit, persistent changes in heating practices. Conclusions: It is argued that disruptions sensitise consumers to the perception of sovereignty and that resilience building and the capability to adjust bring new perspectives to the discussions of the 'pros' and 'cons' of hybrid systems of heat provision. © 2013 Rinkinen.

Kettunen J.,University of Calgary | Salo A.,Aalto University | Bunn D.W.,London Business School
IEEE Transactions on Power Systems | Year: 2010

When an electricity retailer faces volume risk in meeting load and spot price risk in purchasing from the wholesale market, conventional risk management optimization methods can be quite inefficient. For the management of an electricity contract portfolio in this context, we develop a multistage stochastic optimization approach which accounts for the uncertainties of both electricity prices and loads, and which permits the specification of conditional-value-at-risk requirements to optimize hedging across intermediate stages in the planning horizons. Our experimental results, based on real data from Nordpool, suggest that the modeling of price and load correlations is particularly important. The sensitivity analysis is extended to characterize the behavior of retailers with different risk attitudes. Thus, we observe that a risk neutral retailer is more susceptible to price-related than load-related uncertainties in terms of the expected cost of satisfying the load, and that a risk averse retailer is especially sensitive to the drivers of the forward risk premium. © 2009 IEEE.

Sabharwal A.,Rice University | Schniter P.,Ohio State University | Guo D.,Northwestern University | Bliss D.W.,Arizona State University | And 2 more authors.
IEEE Journal on Selected Areas in Communications | Year: 2014

In-band full-duplex (IBFD) operation has emerged as an attractive solution for increasing the throughput of wireless communication systems and networks. With IBFD, a wireless terminal is allowed to transmit and receive simultaneously in the same frequency band. This tutorial paper reviews the main concepts of IBFD wireless. One of the biggest practical impediments to IBFD operation is the presence of self-interference, i.e., the interference that the modem's transmitter causes to its own receiver. This tutorial surveys a wide range of IBFD self-interference mitigation techniques. Also discussed are numerous other research challenges and opportunities in the design and analysis of IBFD wireless systems. © 1983-2012 IEEE.

Yuan C.,Queens College, City University of New York | Malone B.,Aalto University
Journal of Artificial Intelligence Research | Year: 2013

In this paper, learning a Bayesian network structure that optimizes a scoring function for a given dataset is viewed as a shortest path problem in an implicit state-space search graph. This perspective highlights the importance of two research issues: The development of search strategies for solving the shortest path problem, and the design of heuristic functions for guiding the search. This paper introduces several techniques for addressing the issues. One is an A* search algorithm that learns an optimal Bayesian network structure by only searching the most promising part of the solution space. The others are mainly two heuristic functions. The first heuristic function represents a simple relaxation of the acyclicity constraint of a Bayesian network. Although admissible and consistent, the heuristic may introduce too much relaxation and result in a loose bound. The second heuristic function reduces the amount of relaxation by avoiding directed cycles within some groups of variables. Empirical results show that these methods constitute a promising approach to learning optimal Bayesian network structures. © 2013 AI Access Foundation.

Soderman J.,Abo Akademi University | Ahtila P.,Aalto University
Applied Thermal Engineering | Year: 2010

Large industrial plants have often hundreds of heating and cooling heat exchangers. A common situation is that cooling demands of the processes are satisfied without any deeper analysis of the overall impact of the cooling systems on the plant's economy or the environment. If cooling water is available it is used as much as needed and then pumped back to the river, some degrees warmer. An optimisation model was developed for integration of cooling and heating systems to tackle the problem. An industrial cooling system is a complex energy system comprising different options of producing cooling, distribution pipelines for cold media and cooling storages. Integration of power generation and heating systems to the cooling systems was included in the model. An illustrative example is presented in the paper. 10 process streams with cooling demand and 10 streams with heating demand were chosen, situated at different locations at the plant site. The optimal matches between the streams were found together with the sizes of the heat exchangers and the demands of hot and cold utilities. The costs of pipelines and the pumping costs of the streams are included in the model. The model can be used in the design of greenfield and retrofit investments and in versatile what-if analyses of the plant design or operation. © 2009 Elsevier Ltd. All rights reserved.

Haavisto O.,Aalto University
Control Engineering Practice | Year: 2010

A novel mineral slurry assaying method combining visible and near-infrared reflectance spectroscopy and traditional X-ray fluorescence has recently been developed. The improved method is capable of high-frequency assaying of slurry grades in zinc and copper flotation, thus being able to reveal possible rapid oscillations in the grades. In this study, the new measurements are used to detect oscillations in a copper flotation circuit. In addition, a recursive extension of a data-based signal analysis method, singular spectrum analysis, is introduced and applied to process data measured from the flotation circuit. The aim of the study is to pinpoint and eliminate the cause of the oscillations on-line in order to improve the performance of the circuit. It is shown that the oscillations can effectively be detected by the proposed method and that the structural similarity between the oscillatory signal and the other process signals can be quantified in real time. © 2009 Elsevier Ltd. All rights reserved.

Ermolova N.,Aalto University
IEEE Transactions on Wireless Communications | Year: 2010

This letter addresses the problem of OFDM analytical error rate evaluation over fading channels under nonlinear amplification. We obtain approximate solutions to the problem over Nakagami-m and compound gamma-log-normal fading radio channels. In the latter case, two approximations are used for the composite gamma-log-normal distribution. One of them is approximation by the generalized K distribution, and the other technique reduces the problem to that over Nakagami-m fading. © 2010 IEEE.

Electrodeposition process control problem is formulated and solved as a boundary control problem based on unknown parameter model set for a diffusion process controlled by a nonlinear reaction on the boundary. First, the concentration changes in the diffusion layer is feed-forward planned due to the set reference concentration on the cathode boundary and then adapted to a real process according to the certainty equivalent principle based on the measured current densities that compensates for the model uncertainties. In industry, the concentration of species is unobserved except the mass flux on the boundary is measured and controlled as the cathodic current. The diffusivity and apparent transfer coefficient of the deposition reaction are considered as unknown parameters; they are evaluated online along with the concentration on the boundary. The Zakai filtering method is applied for parameters estimation. This article demonstrates through simulation a relatively good convergence of the Zakai estimates to the exact parameters and convergence of the boundary concentration to the set references for tracking. © 2011 Taylor & Francis.

Simula H.,Aalto University
Proceedings of the Annual Hawaii International Conference on System Sciences | Year: 2013

Crowdsourcing has been discussed both in academic and managerial articles in recent years. Despite some critical voices, the overall attitude towards crowdsourcing has been quite positive in extant literature. In this paper we want to address potential drawbacks and issue that create shadows on top of crowdsourcing. The overall purpose of this paper is to discuss the reasons why crowdsourcing initiatives may not always live up to the expectations placed upon them. Despite some seemingly successful case examples, not every crowdsourcing initiative has taken off. While some of the barriers are case or industry specific, there are also certain overall reasons hindering crowdsourcing from reaching de facto modus operandi, especially in the innovation creation context. This paper is intentionally written through a critical lens by design and hopefully provides a constructive balance for those with an overly positive approach towards crowdsourcing. © 2012 IEEE.

Kataja J.,Aalto University | Toivanen J.I.,University of Jyvaskyla
Engineering Analysis with Boundary Elements | Year: 2013

This work presents shape derivatives of the system matrix representing electric field integral equation discretized with Raviart-Thomas basis functions. The arising integrals are easy to compute with similar methods as the entries of the original system matrix. The results are compared to derivatives computed with automatic differentiation technique and finite differences, and are found to be in an excellent agreement. Furthermore, the derived formulas are employed to analyze shape sensitivity of the input impedance of a planar inverted F-antenna, and the results are compared to those obtained using a finite difference approximation. © 2013 Elsevier Ltd.

Gagie T.,Aalto University
Journal of Discrete Algorithms | Year: 2012

We describe a new variation of a mathematical card trick, whose analysis leads to new lower bounds for data compression and estimating the entropy of a Markov source. © 2011 Elsevier B.V. All rights reserved.

Darde J.,Aalto University
Inverse Problems | Year: 2012

We propose a new framework to solve inverse obstacle problems with a Dirichlet condition, consisting in the construction of a decreasing sequence of open domains that contain the searched obstacle. We provide a theoretical justification of this new methodology, infer from it a new algorithm based on the coupling of the quasi-reversibility technique and a level-set method, and illustrate the functionality of the algorithm with the help of numerical experiments in 2D. © 2012 IOP Publishing Ltd.

Volovik G.E.,Aalto University | Volovik G.E.,L D Landau Institute For Theoretical Physics | Zubkov M.A.,ITEP
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2013

We review the known results on the bosonic spectrum in various Nambu-Jona-Lasinio models both in condensed matter physics and in relativistic quantum field theory including He3-B, He3-A, the thin films of superfluid He3, and QCD (Hadronic phase and the color-flavor locking phase). Next, we calculate the bosonic spectrum in the relativistic model of top quark condensation suggested in. In all considered cases, the sum rule appears, which relates the masses (energy gaps) Mboson of the bosonic excitations in each channel with the mass (energy gap) of the condensed fermion Mf as ΣMboson2=4Mf2. Previously, this relation was established by Nambu for He3-B and for the s-wave superconductor. We generalize this relation to the wider class of models and call it the Nambu sum rule. We discuss the possibility to apply this sum rule to various models of top quark condensation. In some cases, this rule allows us to calculate the masses of extra Higgs bosons that are the Nambu partners of the 125 GeV Higgs. © 2013 American Physical Society.

Hiipakka M.,Aalto University
The Journal of the Acoustical Society of America | Year: 2012

Direct measurements of individual head-related transfer functions (HRTFs) with a probe microphone at the eardrum are unpleasant, risky, and unreliable and therefore have not been widely used. Instead, the HRTFs are commonly measured from the blocked ear canal entrance, which excludes the effects of the individual ear canals and eardrums. This paper presents a method that allows obtaining individually correct magnitude frequency responses of HRTFs at the eardrum from pressure-velocity (PU) measurements at the ear canal entrance with a miniature PU sensor. The HRTFs of 25 test subjects with nine directions of sound incidence were estimated using real anechoic measurements and an energy-based estimation method. To validate the approach, measurements were also conducted with probe microphones near the eardrums as well as at blocked ear canal entrances. Comparisons between the different methods show that the method presented is a valid and reliable technique for obtaining magnitude frequency responses of HRTFs. The HRTF filters designed using the PU measurements are also shown to yield more correct frequency responses at the eardrum than the filters designed using measurements from the blocked ear canal entrance.

Martikainen J.-P.,Aalto University
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2012

We study small systems of strongly interacting ultracold atoms under the influence of gauge potentials and spin-orbit couplings. We use second-order perturbation theory in tunneling, derive an effective theory for the strongly correlated insulating states with one atom per site, and solve it exactly. We find dramatic changes in the level structure and in the amount of degeneracies expected. We also demonstrate the dynamical behavior as the barriers between plaquettes are gradually removed and find potentially high overlap with the resonating valence bond (RVB) state of the larger system. © 2012 American Physical Society.

Kinnunen J.J.,Aalto University
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2012

The Hartree energy shift is calculated for a unitary Fermi gas. By including the momentum dependence of the scattering amplitude explicitly, the Hartree energy shift remains finite even at unitarity. Extending the theory also for spin-imbalanced systems allows calculation of polaron properties. The results are in good agreement with more involved theories and experiments. © 2012 American Physical Society.

Kotakoski J.,University of Helsinki | Krasheninnikov A.V.,University of Helsinki | Krasheninnikov A.V.,Aalto University | Kaiser U.,University of Ulm | And 2 more authors.
Physical Review Letters | Year: 2011

While crystalline two-dimensional materials have become an experimental reality during the past few years, an amorphous 2D material has not been reported before. Here, using electron irradiation we create an sp2-hybridized one-atom-thick flat carbon membrane with a random arrangement of polygons, including four-membered carbon rings. We show how the transformation occurs step by step by nucleation and growth of low-energy multivacancy structures constructed of rotated hexagons and other polygons. Our observations, along with first-principles calculations, provide new insights to the bonding behavior of carbon and dynamics of defects in graphene. The created domains possess a band gap, which may open new possibilities for engineering graphene-based electronic devices. © 2011 American Physical Society.

Maloney T.C.,Aalto University
Journal of Thermal Analysis and Calorimetry | Year: 2015

In this study, the pore size distribution of silica aerogels is measured with thermoporosimetry and compared with results from cellulosic materials. The isothermal step melting method is shown to be a useful method to eliminate thermal lag and measures relatively large pores which have a small melting temperature depression. It is shown that for porous silica, pore volumes can be accurately measured by isothermal step melting and that pore diameter can be calculated from the Gibbs-Thomson equation. The nonfreezing water is found to be a monolayer on the pore wall, indicating that hydrated surface area may be probed with this method. The isothermal step melting method is also shown to be very useful to measure pore size distribution of cellulosic materials. However, the Gibbs-Thomson constant for cellulosic materials is markedly different than for porous silica. The pore size distribution for Kraft pulp fibers and for two types of nanocellulose is reported. © 2015 The Author(s).

Zurita G.A.,CONICET | Bellocq M.I.,CONICET | Rybicki J.,Aalto University
Proceedings of the National Academy of Sciences of the United States of America | Year: 2013

The species-area relationship (SAR) gives a quantitative description of the increasing number of species in a community with increasing area of habitat. In conservation, SARs have been used to predict the number of extinctions when the area of habitat is reduced. Such predictions are most needed for landscapes rather than for individual habitat fragments, but SAR-based predictions of extinctions for landscapes with highly fragmented habitat are likely to be biased because SAR assumes contiguous habitat. In reality, habitat loss is typically accompanied by habitat fragmentation. To quantify the effect of fragmentation in addition to the effect of habitat loss on the number of species, we extend the power-law SAR to the species-fragmented area relationship. This model unites the single-species metapopulation theory with the multispecies SAR for communities. We demonstrate with a realistic simulation model and with empirical data for forest-inhabiting subtropical birds that the species-fragmented area relationship gives a far superior prediction than SAR of the number of species in fragmented landscapes. The results demonstrate that for communities of species that are not well adapted to live in fragmented landscapes, the conventional SAR underestimates the number of extinctions for landscapes in which little habitat remains and it is highly fragmented. © PNAS 2013.

Simovski C.,Aalto University | Luukkonen O.,Nokia Inc.
Optics Communications | Year: 2012

In this paper we suggest, numerically simulate and discuss a tapered plasmonic nanostructure which allows efficient transmission of the wave beam energy into a weakly subwavelength (λ/4 ⋯ λ/2) spatial region within a broad frequency range. The frequency stable location of this region becomes possible due to unusual plasmonic modes we have theoretically revealed and used. Our structure is promising for prospective transducers between conventional optical waveguides and subwavelength nanoguides or nanocircuits. © 2012 Elsevier B.V. All rights reserved.

Hauk O.,MRC Cognition and Brain science Unit | Stenroos M.,MRC Cognition and Brain science Unit | Stenroos M.,Aalto University
Human Brain Mapping | Year: 2014

Brain activation estimated from EEG and MEG data is the basis for a number of time-series analyses. In these applications, it is essential to minimize "leakage" or "cross-talk" of the estimates among brain areas. Here, we present a novel framework that allows the design of flexible cross-talk functions (DeFleCT), combining three types of constraints: (1) full separation of multiple discrete brain sources, (2) minimization of contributions from other (distributed) brain sources, and (3) minimization of the contribution from measurement noise. Our framework allows the design of novel estimators by combining knowledge about discrete sources with constraints on distributed source activity and knowledge about noise covariance. These estimators will be useful in situations where assumptions about sources of interest need to be combined with uncertain information about additional sources that may contaminate the signal (e.g. distributed sources), and for which existing methods may not yield optimal solutions. We also show how existing estimators, such as maximum-likelihood dipole estimation, L2 minimum-norm estimation, and linearly-constrained minimum variance as well as null-beamformers, can be derived as special cases from this general formalism. The performance of the resulting estimators is demonstrated for the estimation of discrete sources and regions-of-interest in simulations of combined EEG/MEG data. Our framework will be useful for EEG/MEG studies applying time-series analysis in source space as well as for the evaluation and comparison of linear estimators. © 2013 Wiley Periodicals, Inc.

Gonen M.,Aalto University
IEEE Transactions on Knowledge and Data Engineering | Year: 2013

For supervised learning problems, dimensionality reduction is generally applied as a preprocessing step. However, coupled training of dimensionality reduction and supervised learning steps may improve the prediction performance. In this paper, we propose a novel dimensionality reduction algorithm coupled with a supervised kernel-based learner, called supervised multiple kernel embedding, that integrates multiple kernel learning to dimensionality reduction and performs prediction on the projected subspace with a joint optimization framework. Combining multiple kernels allows us to combine different feature representations and/or similarity measures toward a unified subspace. We perform experiments on one digit recognition and two bioinformatics data sets. Our proposed method significantly outperforms multiple kernel Fisher discriminant analysis followed by a standard kernel-based learner, especially on low dimensions. © 1989-2012 IEEE.

Liu Q.,Aalto University
International Journal of Mechanical Sciences | Year: 2015

This paper describes an analytical method to calculate the sensitivity of the frequencies and modes with respect to fibre volume fractions and orientations, for the large-scale composite laminated structures with complex boundaries. Structural stiffness, mass matrices and their first derivatives with respect to fibre volume fractions and orientations are derived based on classical laminated plate theory and nonconforming rectangular element theory. The analytical sensitivity of the frequencies and modes with respect to fibre volume fractions and orientations is formulated based on vibration theory. Finally, the sensitivity analysis of the dynamic characteristics of T-shape and square composite laminated plates is demonstrated using the proposed analytical method. The accuracy and efficiency of the proposed method are also discussed. The proposed method can be employed to analyze the sensitivity of the frequencies and modes for the composite laminated structures. © 2014 Elsevier Ltd. All rights reserved.

Demsar U.,National University of Ireland, Maynooth | Virrantaus K.,Aalto University
International Journal of Geographical Information Science | Year: 2010

Modern positioning and identification technologies enable tracking of almost any type of moving object. A remarkable amount of new trajectory data is thus available for the analysis of various phenomena. In cartography, a typical way to visualise and explore such data is to use a space-time cube, where trajectories are shown as 3D polylines through space and time.With increasingly large movement datasets becoming available, this type of display quickly becomes cluttered and unclear. In this article, we introduce the concept of 3D space-time density of trajectories to solve the problem of cluttering in the space-time cube. The space-time density is a generalisation of standard 2D kernel density around 2D point data into 3D density around 3D polyline data (i.e. trajectories). We present the algorithm for space-time density, test it on simulated data, show some basic visualisations of the resulting density volume and observe particular types of spatiotemporal patterns in the density that are specific to trajectory data. We also present an application to real-time movement data, that is, vessel movement trajectories acquired using the Automatic Identification System (AIS) equipment on ships in the Gulf of Finland. Finally, we consider the wider ramifications to spatial analysis of using this novel type of spatio-temporal visualisation. © 2010 Taylor & Francis.

Forsberg D.,Aalto University
Computer Communications | Year: 2010

Handover key management in mobile wireless networks targets to minimize the effects of a possible key compromise in the access points. We describe and analyze how the new 3GPP Long Term Evolution (LTE) security architecture and handover keying management fulfills this target. We discuss possible LTE handover key management enhancements and implementation alternatives without losing interoperability over the air interface. We have chosen to compare it with our session keys context concept to see what the strengths in both are to get some perspective for deployments that benefit from distributed key management. © 2010 Elsevier B.V. All rights reserved.

Hekkala R.,Aalto University | Urquhart C.,Manchester Metropolitan University
European Journal of Information Systems | Year: 2013

The broad aim of this interpretive study was to investigate the lived experiences of inter-organisational information system (IOIS) project members who worked in a 3-year-long IOIS project. The study presents an original longitudinal study of project member experiences. In this paper, we have described and analysed one core category, project power, which was derived from a grounded theory (GT) study. This study extends existing theories about power in organisational contexts, in particular the everyday use of power in projects. The paper shows how GT can be used to gain significant insights into a case study, and also generate new concepts. This paper gives detailed insights into the power issues as they played out in a complex IOIS project. This IOIS project spanned four user organisations, two suppliers, one national organisation, a research organisation and a government Ministry. One key finding is that, given the complexity of the project management structures in an IOIS project such as this, project members often resorted to formal authority as a means of getting things done, in the absence of informal links between organisations. The project history also had major ramifications on the use of power in this project. © 2013 Operational Research Society Ltd. All rights reserved.

Pohja M.,Aalto University
Journal of Web Engineering | Year: 2010

Server Push is an essential part of modern web applications. The ability to send relevant information to users in reaction to new events enables highly interactive applications on the WWW. User interfaces of desktop applications have had a two-way communication with underlying software since their advent, but web applications are only reaching the same state now. In addition, currently, server push is usually emulated using pull technology, as HTTP protocol alone is not sufficient to realize a real push. This paper evaluates how an instant messaging protocol, namely XMPP, can complement HTTP- based web applications. We present a communication paradigm of a push system and an implementation of it. In addition, another communication paradigm is sketched for inter-widget messaging on the Web. Based on that paradigm a new research problem is defined and presented. © Rinton Press.

Ostergard P.R.J.,Aalto University
IEEE Transactions on Information Theory | Year: 2011

Let A(n,d) denote the maximum size of a binary code with length n and minimum distance d. It has been known for decades that A(16,7) = A(17,8) = 36 or 37, that is, that the size of optimal 3-error-correcting binary codes of length 16 is either 36 or 37. By a recursive classification via subcodes and a clique search in the final stage, it is shown that the size of optimal such codes is 36. © 2011 IEEE.

Kuusi T.,Aalto University | Mingione G.,University of Parma | Sire Y.,Aix - Marseille University
Communications in Mathematical Physics | Year: 2015

We develop an existence, regularity and potential theory for nonlinear integrodifferential equations involving measure data. The nonlocal elliptic operators considered are possibly degenerate and cover the case of the fractional p-Laplacean operator with measurable coefficients. We introduce a natural function class where we solve the Dirichlet problem, and prove basic and optimal nonlinear Wolff potential estimates for solutions. These are the exact analogs of the results valid in the case of local quasilinear degenerate equations established by Boccardo and Gallouët (J Funct Anal 87:149–169, 1989, Partial Differ Equ 17:641–655, 1992) and Kilpeläinen and Malý (Ann Scuola Norm Sup Pisa Cl Sci (IV) 19:591–613, 1992, Acta Math 172:137–161, 1994). As a consequence, we establish a number of results that can be considered as basic building blocks for a nonlocal, nonlinear potential theory: fine properties of solutions, Calderón–Zygmund estimates, continuity and boundedness criteria are established via Wolff potentials. A main tool is the introduction of a global excess functional that allows us to prove a nonlocal analog of the classical theory due to Campanato (Ann Mat Pura Appl (IV) 69:321–381, 1965). Our results cover the case of linear nonlocal equations with measurable coefficients, and the one of the fractional Laplacean, and are new already in such cases. © 2015, Springer-Verlag Berlin Heidelberg.

Hyvarinen A.,University of Helsinki | Ramkumar P.,Aalto University
Frontiers in Human Neuroscience | Year: 2013

Independent component analysis (ICA) is increasingly used to analyze patterns of spontanous activity in brain imaging. However, there are hardly any methods for answering the fundamental question: Are the obtained components statistically significant? Most methods considering the significance of components either consider group-differences or use arbitrary thresholds with weak statistical justification. In previous work, we proposed a statistically principled method for testing if the coefficients in the mixing matrix are similar in different subjects or sessions. In many applications of ICA, however, we would like to test the reliability of the independent components themselves and not the mixing coefficients. Here, we develop a test for such an inter-subject consistency by extending our previous theory. The test is applicable, for example, to the spatial activity patterns obtained by spatial ICA in resting-state fMRI. We further improve both this and the previously proposed testing method by introducing a new way of correcting for multiple testing, new variants of the clustering method, and a computational approximation which greatly reduces the memory and computation required. © 2013 Hyvärinen and Ramkumar.

Ala-Laurila P.,University of Helsinki | Ala-Laurila P.,Aalto University
Current Biology | Year: 2016

A new study shows that moth vision trades speed and resolution for contrast sensitivity at night. These remarkable neural adaptations take place in the higher-order neurons of the hawkmoth motion vision pathway and allow the insects to see during night flights. © 2016 Elsevier Ltd All rights reserved.

Spiro N.,Nordoff Robbins | Himberg T.,Aalto University
Philosophical Transactions of the Royal Society B: Biological Sciences | Year: 2016

Music therapy has been found to improve communicative behaviours and joint attention in children with autism, but it is unclear what in the music therapy sessions drives those changes. We developed an annotation protocol and tools to accumulate large datasets of music therapy, for analysis of interaction dynamics. Analysis of video recordings of improvisational music therapy sessions focused on simple, unambiguous individual and shared behaviours: movement and facing behaviours, rhythmic activity and musical structures and the relationships between them. To test the feasibility of the protocol, early and late sessions of five client–therapist pairs were annotated and analysed to track changes in behaviours. To assess the reliability and validity of the protocol, inter-rater reliability of the annotation tiers was calculated, and the therapists provided feedback about the relevance of the analyses and results. This small-scale study suggests that there are both similarities and differences in the profiles of client–therapist sessions. For example, all therapists faced the clients most of the time, while the clients did not face back so often. Conversely, only two pairs had an increase in regular pulse from early to late sessions. More broadly, similarity across pairs at a general level is complemented by variation in the details. This perhaps goes some way to reconciling client- and context-specificity on one hand and generalizability on the other. Behavioural characteristics seem to influence each other. For instance, shared rhythmic pulse alternated with mutual facing and the occurrence of shared pulse was found to relate to the musical structure. These observations point towards a framework for looking at change in music therapy that focuses on networks of variables or broader categories. The results suggest that even when starting with simple behaviours, we can trace aspects of interaction and change in music therapy, which are seen as relevant by therapists. © 2016 The Authors.

The 16-station RandomPOD wear test system, previously validated for prosthetic hip wear, was used in the simulation of knee wear mechanisms with a ball-on-flat test configuration. This consisted of a CoCr pin with a ground and polished spherical bearing surface (radius 28mm) against a conventional, gamma-sterilized UHMWPE disk in serum lubrication. The biaxial motion, consisting of x and y translations, and the load was non-cyclic. Relative to the disk, the center of contact wandered within a circle of 10mm diameter, and the average sliding velocity was 15.5mm/s (ranging from 0 to 31mm/s). The load varied non-cyclically between 0 and 142N (average 73N). In the 60-day test with 16 similar wear couples, moderate adhesive wear, the principal wear mechanism of a well-functioning prosthetic knee, dominated. This showed as a burnished, circular wear mark (diameter 13.2mm, area 137mm2). The wear factor was 2.04±0.03×10-6mm3/Nm (mean±95 percent confidence limit). For the first time a truly multidirectional, realistic and uniform, large capacity pin-on-disk simulation of knee wear mechanisms was implemented. © 2014 Elsevier Ltd.

Vanhanen R.,Aalto University
Nuclear Science and Engineering | Year: 2015

It is not uncommon that the covariances of multigroup nuclear data do not obey the sum rules of nuclear data. We present a matrix nearness problem of finding a nearest symmetric matrix with given null vectors and solve it when the distance is measured in the Frobenius norm. The problem appears to be new. We propose that the method should be used to find nearest consistent multigroup covariance matrices with respect to the sum rules of redundant nuclear data. If the multigroup covariances cannot be easily interpreted in a consistent manner, there is some ambiguity in choosing values for the covariances that are not explicitly mentioned. We present and compare a simple and a heuristic characterization method. Three practical examples are processed and analyzed: relative covariances of cross sections of 40 94Zr and absolute covariances of cross sections of 24 50Cr and 90 232Th. We demonstrate that satisfactory results can be achieved. We discuss the properties of the proposed method and the characterization methods and suggest possible improvements. The methods can be used as a part of a quality assurance program and might be valuable additions to nuclear data processing codes. Copyright © 2015 by the American Nuclear Society, Inc. Trademark registered in India.

Silvanto J.,Aalto University
Handbook of Clinical Neurology | Year: 2013

The challenge in visual neuroscience is to characterize the neuronal properties and functional significance of the numerous regions of the visual cortex, and to understand how they interact during the processing of visual information. The strength of transcranial magnetic stimulation (TMS) in this endeavor is its ability to assess the necessity of visual cortical areas in perceptual functions and to trace the corticocortical interactions that underlie them. Most of the early studies in this field were carried out using the so-called "virtual lesion" approach, in which the impact of TMS was thought to be akin to inducing a brain lesion in the stimulated area. This approach established causal links between specific visual areas and perceptual functions such as motion perception, object processing, and visual awareness. Recently, the view of TMS as a tool for inducing "virtual lesion" has been challenged by a number of experimental findings, giving rise to the conceptualization of TMS effects as a state-dependent interaction between the initial state of the stimulated area and the parameters of the TMS pulse. This state dependency is the basis of paradigms aiming selectively to target specific neuronal representations and thus reveal neuronal tuning properties, a major challenge in the understanding of the cortical visual system. © 2013 Elsevier B.V.

Shi J.,Princeton University | Ikalainen S.,Aalto University | Vaara J.,University of Oulu | Romalis M.V.,Princeton University
Journal of Physical Chemistry Letters | Year: 2013

Nuclear spin optical rotation (NSOR) is a recently developed technique for detection of nuclear magnetic resonance via rotation of light polarization, instead of the usual long-range magnetic fields. NSOR signals depend on hyperfine interactions with virtual optical excitations, giving new information about the nuclear chemical environment. We use a multipass optical cell to perform the first precision measurements of NSOR signals for a range of organic liquids and find clear distinction between proton signals for different compounds, in agreement with our earlier theoretical predictions. Detailed first-principles quantum mechanical NSOR calculations are found to be in agreement with the measurements. © 2013 American Chemical Society.

Bonaccorso F.,CNR Institute of Neuroscience | Bonaccorso F.,University of Cambridge | Sun Z.,Aalto University
Optical Materials Express | Year: 2014

Graphene and other two-dimensional (2d) crystals are promising materials for photonic and optoelectronic applications. A key requirement for these applications is the development of industrial-scale, reliable, inexpensive production processes, while providing a balance between ease of fabrication and final material quality with on-demand properties. Solution-processing offers a simple and cost-effective pathway to fabricate various 2d crystal based photonic devices, presenting huge integration flexibility compared to conventional methods. Here we present an overview of graphene and other 2d crystals based ultrafast photonics, from solution processing of the raw bulk materials, the fabrication of saturable absorbers, to their applications in ultrafast lasers. © 2013 Optical Society of America.

Ferragina P.,University of Pisa | Gagie T.,Aalto University | Manzini G.,University of Piemonte Orientale
Algorithmica | Year: 2012

In this paper we describe algorithms for computing the Burrows-Wheeler Transform (bwt) and for building (compressed) indexes in external memory. The innovative feature of our algorithms is that they are lightweight in the sense that, for an input of size n, they use only n bits of working space on disk while all previous approaches use Θ(nlog n) bits. This is achieved by building the bwt directly without passing through the construction of the Suffix Array/Tree data structure. Moreover, our algorithms access disk data only via sequential scans, thus they take full advantage of modern disk features that make sequential disk accesses much faster than random accesses. We also present a scan-based algorithm for inverting the bwt that uses Θ(n) bits of working space, and a lightweight internal-memory algorithm for computing the bwt which is the fastest in the literature when the available working space is o(n) bits. Finally, we prove lower bounds on the complexity of computing and inverting the bwt via sequential scans in terms of the classic product: internalmemory space × number of passes over the disk data, showing that our algorithms are within an O(log n) factor of the optimal. © Springer Science+Business Media, LLC 2011.

Ojanen T.,Aalto University
Physical Review B - Condensed Matter and Materials Physics | Year: 2016

Recently, it was discovered that the ground-state orbital angular momentum in two-dimensional chiral superfluids with pairing symmetry (px+ipy)ν depends on the winding number ν in a striking manner. The ground-state value for the ν=1 case is Lz=N/2 as expected by counting the Cooper pairs, while a dramatic cancellation takes place for ν>1. The origin of the cancellation is associated with the topological edge states that appear in a finite geometry and give rise to a spectral asymmetry. Here, we study the reduction of orbital angular momentum for different potential profiles and pairing strengths, showing that the result Lz=N/2 is robust for ν=1 under all studied circumstances. We study how angular momentum depends on the gap size Δ/EF and obtain the result Lz=ν2N(1-μEF) for ν=2,3. Thus, the gap dependence of Lz for ν<4 enters at most through the chemical potential while ν≥4 is qualitatively different. In addition, we generalize the spectral asymmetry arguments to total angular momentum in the ground state of triplet superfluids where due to a spin-orbit coupling Lz is not a good quantum number. We find that the ground-state total angular momentum also behaves very differently depending on total angular momentum of the Cooper pairs. © 2016 American Physical Society.

Butler T.,University of Texas at Austin | Juntunen M.,Aalto University
Journal of Computational Physics | Year: 2012

The ensemble Kalman filter is a widely applied data assimilation technique useful for improving the forecast of computational models. The main computational cost of the ensemble Kalman filter comes from the numerical integration of each ensemble member forward in time. When the computational model involves a partial differential equation, the degrees of freedom of the solution in the discretization of the spatial domain are oftentimes used for the representation of the state of the system, and the filter is applied to this state vector. We propose a method of approximating the state of a partial differential equation in a representation space developed separately from the numerical method. This representation space represents a reparameterization of the state vector and can be chosen to retain desirable physical features of the solutions. We apply the ensemble Kalman filter to this representation of the state, and numerically demonstrate that acceptable results are obtained with substantially smaller ensemble sizes. © 2012 Elsevier Inc.

Takaluoma T.T.,University of Oulu | Laasonen K.,Aalto University | Laitinen R.S.,University of Oulu
Inorganic Chemistry | Year: 2013

Molecular dynamics simulations of the solid-state topochemical polymerization of four-membered S2N2 rings to (SN) x have been presented by involving DFT methods and periodic functions. Isotropic pressure compression and a slightly elevated temperature have been applied to lower the activation barriers and to increase the rate of the reaction to be within the framework of MD simulations. The polymer formation is initiated by the cleavage of one bond in one S2N2 ring with a virtually instantaneous attack of the fragment thus formed on the neighboring ring. The energetically most-favored reaction then quickly propagates along a axis throughout the lattice. The structures of the polymer chains are in good agreement with that observed experimentally in the crystal structure determination, but there is less long-range order between the neighboring chains. Upon polymerization the packing of the molecules changes from the herringbone structure of the S2N2 lattice to a layered structure in the (SN)x lattice. While not the same, the simulated and experimental packing changes bear a qualitative similarity. The simulated polymerization was also observed to propagate along c axis in addition to a axis, but these side effects generally disappear toward the end of the simulations. In some cases, the polymers propagating simultaneously in both a and c axis directions persist at the end of the simulation resulting in a complicated network of sulfur-nitrogen chains. This finds experimental support in the observation of several polymorphs (SN)x with severe disorder in the lattice. © 2013 American Chemical Society.

Lack of physical activity (PA) is a known risk factor for many health conditions. The workplace is a setting often used to promote activity and health. We investigated the effectiveness of an intervention on PA and productivity-related outcomes in an occupational setting. We conducted a randomized controlled trial of 12 months duration with two 1:1 allocated parallel groups of insurance company employees. Eligibility criteria included permanent employment and absence of any condition that risked the participant's health during PA. Subjects in the intervention group monitored their daily PA with an accelerometer, set goals, had access to an online service to help them track their activity levels, and received counseling via telephone or web messages for 12 months. The control group received the results of a fitness test and an information leaflet on PA at the beginning of the study. The intervention's aim was to increase PA, improve work productivity, and decrease sickness absence. Primary outcomes were PA (measured as MET minutes per week), work productivity (quantity and quality of work; QQ index), and sickness absence (SA) days at 12 months. Participants were assigned to groups using block randomization with a computer-generated scheme. The study was not blinded. There were 544 randomized participants, of which 521 were included in the analysis (64% female, mean age 43 years). At 12 months, there was no significant difference in physical activity levels between the intervention group (n = 264) and the control group (n = 257). The adjusted mean difference was -206 MET min/week [95% Bayesian credible interval -540 to 128; negative values favor control group]. There was also no significant difference in the QQ index (-0.5 [-4.4 to 3.3]) or SA days (0.0 [-1.2 to 0.9]). Of secondary outcomes, body weight (0.5 kg [0.0 to 1.0]) and percentage of body fat (0.6% [0.2% to 1.1%]) were slightly higher in the intervention group. An exploratory subgroup analysis revealed no subgroups in which the intervention affected physical activity. No adverse events were reported. The intervention was not found effective, and this study does not provide support for the effectiveness of the workplace PA intervention used here. ClinicalTrials.gov identifier: NCT00994565.

Dahl M.F.,Aalto University
International Journal of Geometric Methods in Modern Physics | Year: 2012

An area metric is a $0 \choose 4$-tensor with certain symmetries on a 4-manifold that represents a non-dissipative linear electromagnetic medium. A recent result by Schuller, Witte and Wohlfarth gives a pointwise algebraic classification for such area metrics. This result is similar to the Jordan normal form theorem for $1 \choose 1$-tensors, and the result shows that pointwise area metrics divide into 23 metaclasses and each metaclass requires two coordinate representations. For the first 7 metaclasses, we show that only one coordinate representation is needed. For the remaining 16 metaclasses we find an additional third coordinate representation. © 2012 World Scientific Publishing Company.

Giazotto F.,Normal School of Pisa | Heikkila T.T.,University of Jyvaskyla | Heikkila T.T.,Aalto University | Bergeret F.S.,Donostia International Physics Center
Physical Review Letters | Year: 2015

The concept of thermophase refers to the appearance of a phase gradient inside a superconductor originating from the presence of an applied temperature bias across it. The resulting supercurrent flow may, in suitable conditions, fully counterbalance the temperature-bias-induced quasiparticle current therefore preventing the formation of any voltage drop, i.e., a thermovoltage, across the superconductor. Yet, the appearance of a thermophase is expected to occur in Josephson-coupled superconductors as well. Here, we theoretically investigate the thermoelectric response of a thermally biased Josephson junction based on a ferromagnetic insulator. In particular, we predict the occurrence of a very large thermophase that can reach π/2 across the contact for suitable temperatures and structure parameters; i.e., the quasiparticle thermal current can reach the critical current. Such a thermophase can be several orders of magnitude larger than that predicted to occur in conventional Josephson tunnel junctions. In order to assess experimentally the predicted very large thermophase, we propose a realistic setup realizable with state-of-the-art nanofabrication techniques and well-established materials, based on a superconducting quantum interference device. This effect could be of strong relevance in several low-temperature applications, for example, for revealing tiny temperature differences generated by coupling the electromagnetic radiation to one of the superconductors forming the junction. © 2015 American Physical Society.

Hamari J.,University of Tampere | Hamari J.,Aalto University | Koivisto J.,University of Tampere
Computers in Human Behavior | Year: 2014

This paper measures flow in the context of gamification and investigates the psychometric properties of the Dispositional Flow Scale-2 (DFS-2). We employ data gathered from users of an exercise gamification service (N = 200). The results show that the original DFS-2 factorial structure does result in a similar model fit as the original work. However, we also present a factorial respecification that satisfies more recent model fit thresholds. Beyond validating the original DFS-2 instrument in the context of gamification, the psychometric analysis and the respecifications suggest that the components of flow divide into highly correlated conditions of flow (which were also found to be more salient in the context of gamification: autotelic experience, balance of skill and challenge, control, clear goals, and feedback) and into possible outcomes (merging action-awareness, concentration, loss of sense of time, and loss of self-consciousness) from achieving flow. © 2014 Elsevier Ltd. All rights reserved.

Galvez F.E.,University of Seville | Barnes P.R.F.,Imperial College London | Halme J.,Aalto University | Miguez H.,University of Seville
Energy and Environmental Science | Year: 2014

In order to enhance optical absorption, light trapping by multiple scattering is commonly achieved in dye sensitized solar cells by adding particles of a different sort. Herein we propose a theoretical method to find the structural parameters (particle number density and size) that optimize the conversion efficiency of electrodes of different thicknesses containing spherical inclusions of diverse composition. Our work provides a theoretical framework in which the response of solar cells containing diffuse scattering particles can be rationalized. Optical simulations are performed by combining a Monte Carlo approach with Mie theory, in which the angular distribution of scattered light is accounted for. Several types of scattering centers, such as anatase, gold and silver particles, as well as cavities, are considered and their effect compared. Estimates of photovoltaic performance, insight into the physical mechanisms responsible for the observed enhancements, and guidelines to improve the cell design are provided. We discuss the results in terms of light transport in weakly disordered optical media and find that the observed variations between the optimum scattering configurations attained for different electrode thicknesses can be understood as the result of the randomization of the light propagation direction at different depths within the active layer. A primary conclusion of our study is that photovoltaic performance is optimised when the scattering properties of the film are adjusted so that the distance over which incident photons are randomized is comparable to the thickness of the film. This simple relationship could also be used as a design rule to attain the optimum optical design in other photovoltaic materials. This journal is © The Royal Society of Chemistry.

Wang J.-J.,National University of Singapore | Lu X.X.,National University of Singapore | Kummu M.,Aalto University
River Research and Applications | Year: 2011

Although sediment issues have critical implications for aquatic ecology, agriculture, water supply and river navigation, studies regarding the sediment production, deposition and transportation in the Lower Mekong River are relatively sparse. With the construction and operation of dams in the Upper Mekong River, this issue has attracted more attention in recent years. The estimation of sediment loads has been hindered by the serious lack of sediment measurements in the Lower Mekong River. This study aimed to investigate the possibility of estimating the sediment loads for the years without good quality SSC measurements in the Lower Mekong River. To make this estimate, this study classified the rating curves on the basis of the synchronous nature of the suspended sediment concentration (SSC) and the water discharge among the adjacent stations (e.g. Chiang Saen, Luang Prabang, Nong Khai, Mukdahan and Khong Chiam). Together with other methods, it was possible to estimate the yearly sediment loads for the period of 1962-2003 at the five mainstream Lower Mekong River stations. Consequently, the spatial and temporal variations in the sediment loads and water discharge in the Lower Mekong River were examined. In addition, the possible impacts of Chinese dams as well as the annual sediment load of the Mekong River into the sea were also investigated. © 2009 John Wiley & Sons, Ltd.

Wicki A.,University of Basel | Witzigmann D.,University of Basel | Balasubramanian V.,Aalto University | Huwyler J.,University of Basel
Journal of Controlled Release | Year: 2015

Cancer is a leading cause of death worldwide. Currently available therapies are inadequate and spur demand for improved technologies. Rapid growth in nanotechnology towards the development of nanomedicine products holds great promise to improve therapeutic strategies against cancer. Nanomedicine products represent an opportunity to achieve sophisticated targeting strategies and multi-functionality. They can improve the pharmacokinetic and pharmacodynamic profiles of conventional therapeutics and may thus optimize the efficacy of existing anti-cancer compounds. In this review, we discuss state-of-the-art nanoparticles and targeted systems that have been investigated in clinical studies. We emphasize the challenges faced in using nanomedicine products and translating them from a preclinical level to the clinical setting. Additionally, we cover aspects of nanocarrier engineering that may open up new opportunities for nanomedicine products in the clinic. © 2014 Elsevier B.V. All rights reserved.

Salminen N.H.,Aalto University
Journal of the Acoustical Society of America | Year: 2015

Interaural level difference (ILD) is used as a cue in horizontal sound source localization. In free field, the magnitude of ILD depends on frequency: it is more prominent at high than low frequencies. Here, a magnetoencephalography experiment was conducted to test whether the sensitivity of the human auditory cortex to ILD is also frequency-dependent. Robust cortical sensitivity to ILD was found that could not be explained by monaural level effects, but this sensitivity did not differ between low- and high-frequency stimuli. This is consistent with previous psychoacoustical investigations showing that performance in ILD discrimination is not dependent on frequency. © 2015 Acoustical Society of America.

Sarkka S.,Aalto University
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2011

In this paper we shall discuss an extension to Gaussian process (GP) regression models, where the measurements are modeled as linear functionals of the underlying GP and the estimation objective is a general linear operator of the process. We shall show how this framework can be used for modeling physical processes involved in measurement of the GP and for encoding physical prior information into regression models in form of stochastic partial differential equations (SPDE). We shall also illustrate the practical applicability of the theory in a simulated application. © 2011 Springer-Verlag.

Holappa L.,Aalto University
Steel Research International | Year: 2010

Great progresses in steel cleanliness have been attained during the last decades. In the measures of oxygen the lowest levels are approaching 5 ppm in Otot i.e. close to the thermodynamic limit of Al deoxidation. As the thermodynamics of the reaction system is firmly anchored to the steel chemistry and thus to the properties of steel and the final product, it is useful to examine the thermodynamic constraints for selected steels in the refining and casting processes. In most steels Al-O equilibrium determines the limit of deoxidation. Calculations by applying thermodynamic software showed that in selected ''common'' steels the equilibrium oxygen content varied from below 5 ppm up to 30 ppm or higher depending on the aluminium content, interaction effect of other alloying elements and temperature. For lower oxygen content there are several possibilities. The first one is to use stronger deoxidizing additions like Ca, Zr, Ce etc. However, they can be problematic as substitutes as they produce inclusions which influence steel properties. The second way is to intensify the deoxidizing power of certain elements e.g. Si by bringing the steel in intimate contact with a proper slag with low SiO2 activity in ladle treatment with violent stirring. In the calculation example it was possible to decrease oxygen content from 30 ppm to the level below 10 ppm in C/Mn/Si steel at very low Al level. The third potential but unused process is vacuum deoxidation especially for medium and high carbon steels. Equilibriumoxygen contents below 1ppm are thermodynamically easily attainable. But in practice the vacuum treatment should be designed to intensify the carbon-oxygen reaction on the top surface of the stirred steel liquid. Also the eventual reactions with refractory materials should be suppressed. © 2010 Wiley-VCH Verlag GmbH & Co.

Alonso M.A.,University of Rochester | Alonso M.A.,Aalto University
Journal of Optics | Year: 2011

It is well known that, for any monochromatic field, the spatial extent of the focus has a lower bound dependent on the field's directional spread. The influences that the orbital angular momentum and, for vector fields, the (spin or intrinsic) angular momentum due to polarization have on this lower bound are studied here for fields not constrained by the paraxial approximation. © 2011 IOP Publishing Ltd.

Petersen R.,University of Aalborg | Pedersen T.G.,University of Aalborg | Jauho A.-P.,Technical University of Denmark | Jauho A.-P.,Aalto University
ACS Nano | Year: 2011

Pristine graphene is a semimetal and thus does not have a band gap. By making a nanometer scale periodic array of holes in the graphene sheet a band gap may form; the size of the gap is controllable by adjusting the parameters of the lattice. The hole diameter, hole geometry, lattice geometry, and the separation of the holes are parameters that all play an important role in determining the size of the band gap, which, for technological applications, should be at least of the order of tenths of an eV. We investigate four different hole configurations: the rectangular, the triangular, the rotated triangular, and the honeycomb lattice. It is found that the lattice geometry plays a crucial role for size of the band gap: the triangular arrangement displays always a sizable gap, while for the other types only particular hole separations lead to a large gap. This observation is explained using Clar sextet theory, and we find that a sufficient condition for a large gap is that the number of sextets exceeds one-third of the total number of hexagons in the unit cell. Furthermore, we investigate nonisosceles triangular structures to probe the sensitivity of the gap in triangular lattices to small changes in geometry. © 2011 American Chemical Society.

Jokinen V.,Aalto University
Soft Matter | Year: 2016

Directional imbibition of oils (hexadecane, tetradecane, and dodecane) and water is demonstrated on a chemically patterned silicon micropillar array. Four different directional imbibition types are shown: unidirectional, two types of bidirectional and tridirectional imbibition. The surfaces consist of a silicon micropillar array with an overlaid surface chemistry pattern. This configuration leads to anisotropic wetting behaviour into various directions of the advancing meniscus. Due to the free energy landscape obtained, the advancing meniscus gets pinned in some directions (determined by the surface chemistry pattern) while it is free to move to the remaining directions. The conditions for directional imbibition and design criteria for the surfaces are derived and discussed. © The Royal Society of Chemistry 2016.

Aaltonen K.,Aalto University
International Journal of Project Management | Year: 2011

International projects face a variety of pressures from their uncertain and complex external stakeholder environments. In order to reduce uncertainty, a project management team builds up interpretations about their environment by conducting stakeholder analysis. This study aims to examine the interpretation processes, through which project management teams come to know their external stakeholder environment. The point of departure for the study is Daft and Weick's (1984) typology about organizational interpretation modes. The paper identifies and describes distinctive interpretation modes of external stakeholder environments in four international projects. The interpretation modes differ in their stakeholder analysis characteristics. The project managers' beliefs about the stakeholder environment and the project's intrusiveness towards its stakeholder environment are hypothesized to be associated with the identified differences in the interpretation modes. © 2010 Elsevier Ltd and IPMA.

Climente-Alarcon V.,Aalto University | Antonino-Daviu J.A.,Polytechnic University of Valencia | Riera-Guasp M.,Polytechnic University of Valencia | Vlcek M.,Czech Technical University
IEEE Transactions on Industrial Electronics | Year: 2014

During the last years, several time-frequency decomposition tools have been applied for the diagnosis of induction motors, for those cases in which the traditional procedures, such as motor current signature analysis, cannot yield the necessary response. Among them, the Cohen distributions have been widely selected to study transient and even stationary operation due to their high-resolution and detailed information provided at all frequencies. Their main drawback, the cross-terms, has been tackled either modifying the distribution, or carrying out a pretreatment of the signal before computing its time-frequency decomposition. In this paper, a filtering process is proposed that uses advanced notch filters in order to remove constant frequency components present in the current of an induction motor, prior to the computation of its distribution, to study rotor asymmetries and mixed eccentricities. In transient operation of machines directly connected to the grid, this procedure effectively eliminates most of the artifacts that have prevented the use of these tools, allowing a wideband analysis and the definition of a precise quantification parameter able to follow the evolution of their state. © 1982-2012 IEEE.

Tenhiala A.,IE Business School | Helkio P.,Aalto University
Journal of Operations Management | Year: 2015

Enterprise resource planning (ERP) systems have a controversial reputation. Critics say that even if ERP systems may be beneficial for organizations operating in stable conditions, they are surely detrimental to organizations that face dynamic market requirements. This is because ERP systems are said to impose such procedures and constraints on organizations that make business processes inflexible to change. In contrast, proponents argue that the information-processing capabilities of ERP systems are crucial for organizations that face dynamic market requirements and also that the criticized procedures and constraints actually support process reengineering. These two contradictory arguments are often found in practitioner literature, but both of them can also be supported by management theory. The central tenets of the Organic Theory of organization design imply that ERP systems should be detrimental when market requirements change frequently, whereas the principles of Rigid Flexibility Theory suggest that they should be advantageous. In this study, we use cross-sectional data from 151 manufacturing plants to determine which argument is more applicable in the context of manufacturing planning and control. The results strongly favor the use of ERP systems under dynamic market requirements. To facilitate the reconciliation of the two contradictory arguments, we discuss how the results may have been influenced by two contextual factors: the predominantly technical nature of the studied organizational system and the tight interdependence of the studied activities. © 2014 Elsevier B.V.

Kumar Pan R.,Chennai Mathematical Institute | Kumar Pan R.,Aalto University | Sinha S.,Chennai Mathematical Institute
New Journal of Physics | Year: 2010

Are there general principles governing the process by which certain products or ideas become popular relative to other (often qualitatively similar) competitors? To investigate this question in detail, we have focused on the popularity of movies as measured by their box-office income. We observe that the log-normal distribution describes well the tail (corresponding to the most successful movies) of the empirical distributions for the total income, the income on the opening week, as well as the weekly income per theater. This observation suggests that popularity may be the outcome of a linear multiplicative stochastic process. In addition, the distributions of the total income and the opening income show a bimodal form, with the majority of movies either performing very well or very poorly in theaters.We also observe that the gross income per theater for a movie at any point during its lifetime is, on average, inversely proportional to the period that has elapsed after its release. We argue that (i) the log-normal nature of the tail, (ii) the bimodal form of the overall gross income distribution and (iii) the decay of gross income per theater with time as a power law, constitute the fundamental set of stylized facts (i.e. empirical 'laws') that can be used to explain other observations about movie popularity.We show that, in conjunction with an assumption of a fixed lower cut-off for income per theater below which a movie is withdrawn from a cinema, these laws can be used to derive a Weibulldistribution for the survival probability of movies that agrees with empirical data. The connection to extreme-value distributions suggests that popularity can be viewed as a process where a product becomes popular by avoiding 'failure' (i.e. being pulled out from circulation) for many successive time periods. We suggest that these results may apply beyond the particular case of movies to popularity in general. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.

Valagiannopoulos C.A.,Aalto University
Electromagnetics | Year: 2011

A metallic edge with arbitrary length and inclination is embedded into a coplanar waveguide forming a simple two-port network. The corresponding boundary value problem is rigorously solved by segmenting this perfectly conducting strip into a large number of consecutive pins; the procedure yields robust expressions for the scattering parameters of the device. Interesting properties characterizing its operation are observed through the corresponding diagrams, such as the correlation between different configurations. Additional conclusions have also been drawn from the discussion of the related graphs. © 2011 Copyright Taylor and Francis Group, LLC.

Lilius J.,Aalto University
Housing Studies | Year: 2014

This paper addresses the phenomenon of families returning to inner cities. With evidence from the first qualitative study done on families residing in inner-city Helsinki, it demonstrates that urban living reduces the sharp divide between life before having children and family life. Urban parents stay in the city much for the same reasons they first moved there: because they are attracted to population density, good amenities and good public transport. Living in the city enables a lifestyle where different life stages blend into each other. The paper, however, reveals that there is a lack of understanding among city planners and politicians about family needs in the inner city. By adopting a framework of the reviewed literature, the paper draws on the argument that modernist ideals on proper family living still prevail. The paper suggests that planning must acknowledge that exclusionary life stages are eroding and creating a need to facilitate multiple forms of lifestyles. © 2014 © 2014 Taylor & Francis.

Muller R.R.,Friedrich - Alexander - University, Erlangen - Nuremberg | Muller R.R.,Norwegian University of Science and Technology | Cottatellucci L.,Eurecom | Vehkapera M.,Aalto University | Vehkapera M.,KTH Royal Institute of Technology
IEEE Journal on Selected Topics in Signal Processing | Year: 2014

A subspace projection to improve channel estimation in massive multi-antenna systems is proposed and analyzed. Together with power-controlled hand-off, it can mitigate the pilot contamination problem without the need for coordination among cells. The proposed method is blind in the sense that it does not require pilot data to find the appropriate subspace. It is based on the theory of large random matrices that predicts that the eigenvalue spectra of large sample covariance matrices can asymptotically decompose into disjoint bulks as the matrix size grows large. Random matrix and free probability theory are utilized to predict under which system parameters such a bulk decomposition takes place. Simulation results are provided to confirm that the proposed method outperforms conventional linear channel estimation if bulk separation occurs. © 2014 IEEE.

Zhu L.,University of Vaasa | Zhu L.,Aalto University
Renewable and Sustainable Energy Reviews | Year: 2015

In response to energy crisis, global warming and climate changes, microalgae have received a great deal of interest as a biofuel feedstock. However, the development of microalgal biofuels witnesses an obvious and serious dilemma. The reported literature shows that "fuel only" option is not economically viable due to the overwhelming investments in capital and operation. Hence, it is questionable whether it is too luxurious to produce microalgae only for biofuel application. In addition, there are some voiced concerns related to the impacts of microalgal biofuel production on the conventional applications, such as cosmetics, pharmaceuticals and nutritious feed. It is therefore questionable whether the microalgal biofuel production will affect the original functions. From a sustainability point of view, the author explores the current challenges in microalgal applications and proposes an innovative framework for microalgal biorefinery, which can realize the production of multiple products in the form of high values and biofuels such as biodiesel, bioethanol and biogas. With the aim at maximizing the value derived from different microalgal components, the innovative microalgal biorefinery concept includes four pathways: high-value products-biodiesel-bioethanol-biogas; high-value products-bioethanol-biogas; high-value products-biodiesel-biogas; and high-value products-biogas. Special attention has been paid to the production of high-value products through system integration and engineering, which is expected to promote the economics of microalgal biofuels. Net energy ratio assessment and cost-effectiveness assessment have been highlighted to testify the feasibility of microalgal biorefinery options, and some crucial actions have been suggested to help establish the process. © 2014 Elsevier Ltd. All rights reserved.

Kohtala C.,Aalto University | Kohtala C.,NODUS Sustainable Design Research Group
Journal of Cleaner Production | Year: 2015

This paper presents an integrated literature review on how the environmental sustainability of distributed production is studied in a variety of disciplinary sources. The notion of distributed production suggests an alternative to mass production that differs in scale, location and consumer-producer relationship. Understanding its environmental implications (and thereby dematerialization potential) is regarded pertinent and timely. Key themes in the review included how distributed production can promote product longevity and closed material loops, as well as localizing production. New and closer ties between producer and consumer seemed central discussions but were underdeveloped with regard to sustainability potential. Empirical work was seen especially in research on Additive Manufacturing Processes, while the bulk of the studies were conceptual explorations with little testing in the real world as yet. This affirms the emerging nature of the topic and points to a clear need for more (and more diverse) empirical research. The review summarizes the opportunities for greater environmental sustainability as well as potential threats that could serve to guide and improve these novel practices today. It sets the stage for 'distributed production' to be examined as its own phenomenon by proposing how it can be characterized and suggests that a research agenda could build upon the work initiated here. © 2014 Elsevier Ltd. All rights reserved.

The wireless sensor network (WSN) has emerged as a promising technology. In WSNs, sensor nodes are distributedly deployed to collect interesting information from the environment. Because of the mission of WSNs, most node-wide as well as network-wide activities are manifested in packet traffic. As a result, packet traffic becomes a good data source for modeling sensor node as well as sensor network behaviors. In this article, the methodology of modeling node and network behavior profiles using packet traffic is exemplified. In addition, node as well as network anomalies are shown to be detectable by monitoring the evolution of node/network behavior profiles. © 2011 IEEE.

Different representations of valued preferences have been studied and used over the years; however, one common factor has been the prominence of the concept of consistency. Inconsistency indices have been introduced to estimate the deviation of preferences from a fully consistent form. In this note we shall recall two types of preference relations (reciprocal relations and multiplicative preference relations) and show that two inconsistency indices introduced in these two different frameworks are functionally related. Besides this main result, some reflections on the consequences of being functionally related are presented. © 2016 Elsevier Inc. All rights reserved.

Motivation: Identifying interactions between drug compounds and target proteins has a great practical importance in the drug discovery process for known diseases. Existing databases contain very few experimentally validated drug-target interactions and formulating successful computational methods for predicting interactions remains challenging. Results: In this study, we consider four different drug-target interaction networks from humans involving enzymes, ion channels, G-protein-coupled receptors and nuclear receptors. We then propose a novel Bayesian formulation that combines dimensionality reduction, matrix factorization and binary classification for predicting drug-target interaction networks using only chemical similarity between drug compounds and genomic similarity between target proteins. The novelty of our approach comes from the joint Bayesian formulation of projecting drug compounds and target proteins into a unified subspace using the similarities and estimating the interaction network in that subspace. We propose using a variational approximation in order to obtain an efficient inference scheme and give its detailed derivations. Finally, we demonstrate the performance of our proposed method in three different scenarios: (i) exploratory data analysis using low-dimensional projections, (ii) predicting interactions for the out-of-sample drug compounds and (iii) predicting unknown interactions of the given network. © The Author 2012. Published by Oxford University Press. All rights reserved.

Nevalainen P.,University of Helsinki | Lauronen L.,University of Helsinki | Pihko E.,Aalto University
Frontiers in Human Neuroscience | Year: 2014

The mysteries of early development of cortical processing in humans have started to unravel with the help of new non-invasive brain research tools like multichannel magnetoencephalography (MEG). In this review, we evaluate, within a wider neuroscientific and clinical context, the value of MEG in studying normal and disturbed functional development of the human somatosensory system. The combination of excellent temporal resolution and good localization accuracy provided by MEG has, in the case of somatosensory studies, enabled the differentiation of activation patterns from the newborn's primary (SI) and secondary somatosensory (SII) areas. Furthermore, MEG has shown that the functioning of both SI and SII in newborns has particular immature features in comparison with adults. In extremely preterm infants, the neonatal MEG response from SII also seems to potentially predict developmental outcome: those lacking SII responses at term show worse motor performance at age 2 years than those with normal SII responses at term. In older children with unilateral early brain lesions, bilateral alterations in somatosensory cortical activation detected in MEG imply that the impact of a localized insult may have an unexpectedly wide effect on cortical somatosensory networks.The achievements over the last decade show that MEG provides a unique approach for studying the development of the somatosensory system and its disturbances in childhood. MEG well complements other neuroimaging methods in studies of cortical processes in the developing brain. © 2014 Nevalainen, Lauronen and Pihko.

Campisi M.,CNR Institute of Neuroscience | Pekola J.,Aalto University | Fazio R.,CNR Institute of Neuroscience
New Journal of Physics | Year: 2015

We study stochastic energetic exchanges in quantum heat engines. Due to microreversibility, these obey a fluctuation relation, called the heat engine fluctuation relation, which implies the Carnot bound: no machine can have an efficiency greater than Carnot's efficiency. The stochastic thermodynamics of a quantum heat engine (including the joint statistics of heat and work and the statistics of efficiency) are illustrated by means of an optimal two-qubit heat engine, where each qubit is coupled to a thermal bath and a two-qubit gate determines energy exchanges between the two qubits.We discuss possible solid-state implementations with Cooper-pair boxes and flux qubits, quantum gate operations, and fast calorimetric on-chip measurements of single stochastic events. ©2015 IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.

Hiipakka M.,Aalto University
ICASSP, IEEE International Conference on Acoustics, Speech and Signal Processing - Proceedings | Year: 2011

It is difficult to measure or estimate accurately the pressure or the volume velocity at the eardrums of human subjects. A method that enables us to determine both the pressure and the volume velocity evoked by an insert earphone in the ear canal is developed. The method can be used to accurately estimate pressure frequency response at the eardrum. A pair of headphones with in-ear microphones is modeled as a Norton equivalent electroacoustic volume velocity source. A custom-made new miniature particle velocity sensor is used in the modeling of the velocity source. Measurements made with the particle velocity sensor and those made with miniature microphones show that the presented estimation method is accurate up to 12 kHz. The method can be applied to binaural reproduction as well as to audiological measurements. © 2011 IEEE.

Mousavi S.M.,Aalto University
International Journal of Solids and Structures | Year: 2016

In the present paper, the dislocation-based antiplane fracture mechanics is employed for the analysis of Mode III crack within nonlocal and (strain) gradient elasticity of bi-Helmholtz type. These frameworks are appropriate candidates of generalized continua for regularization of classical singularities of defects such as dislocations. Within nonlocal elasticity of bi-Helmholtz type, nonlocal stress is regularized, while the strain field remain singular. Interestingly, gradient elasticity of bi-Helmholtz type (second strain gradient elasticity) eliminates all physical singularities of discrete dislocation including stress and strain fields and dislocation density while the so-called total stress tensor still contains singularity at the dislocation core. Based on the distribution of dislocations, a fracture theory with nonsingular stress field is formulated in these nonlocal and gradient theories. Strain and displacement fields within nonlocal fracture theory are identical to the classical ones. In contrast, gradient elasticity of bi-Helmholtz type leads to a full nonsingular fracture theory in which stress, strain and dislocation density are regularized. However, the singular total stress of a discrete dislocation results in singular total stress of the plane weakened by a crack. Within classical fracture mechanics, Barenblatt's cohesive fracture theory assumes that cohesive forces is distributed ahead of the crack tip to model crack tip plasticity and remove the stress singularity. Here, considering the dislocations as the carriers of plasticity, the crack tip plasticity is captured without any assumption. Once the crack is modeled by distributing the dislocations along its surface, due to the gradient theory, the distribution function gives rise to a non-zero plastic distortion ahead of the crack. Consequently, regularized solutions of crack are developed incorporating crack tip plasticity. © 2016 Elsevier Ltd. All rights reserved.

Raij T.T.,Aalto University | Raij T.T.,University of Helsinki | Riekki T.J.J.,University of Helsinki
NeuroImage: Clinical | Year: 2012

Neuronal underpinnings of auditory verbal hallucination remain poorly understood. One suggested mechanism is brain activation that is similar to verbal imagery but occurs without the proper activation of the neuronal systems that are required to tag the origins of verbal imagery in one's mind. Such neuronal systems involve the supplementary motor area. The supplementary motor area has been associated with awareness of intention to make a hand movement, but whether this region is related to the sense of ownership of one's verbal thought remains poorly known. We hypothesized that the supplementary motor area is related to the distinction between one's own mental processing (auditory verbal imagery) and similar processing that is attributed to non-self author (auditory verbal hallucination). To test this hypothesis, we asked patients to signal the onset and offset of their auditory verbal hallucinations during functional magnetic resonance imaging. During non-hallucination periods, we asked the same patients to imagine the hallucination they had previously experienced. In addition, healthy control subjects signaled the onset and offset of self-paced imagery of similar voices. Both hallucinations and the imagery of hallucinations were associated with similar activation strengths of the fronto-temporal language-related circuitries, but the supplementary motor area was activated more strongly during the imagery than during hallucination. These findings suggest that auditory verbal hallucination resembles verbal imagery in language processing, but without the involvement of the supplementary motor area, which may subserve the sense of ownership of one's own verbal imagery. © 2012 The Authors. Published by Elsevier Inc. All rights reserved.

Breuer H.-P.,Albert Ludwigs University of Freiburg | Laine E.-M.,Aalto University | Laine E.-M.,University of Turku | Piilo J.,University of Turku | And 2 more authors.
Reviews of Modern Physics | Year: 2016

The dynamical behavior of open quantum systems plays a key role in many applications of quantum mechanics, examples ranging from fundamental problems, such as the environment-induced decay of quantum coherence and relaxation in many-body systems, to applications in condensed matter theory, quantum transport, quantum chemistry, and quantum information. In close analogy to a classical Markovian stochastic process, the interaction of an open quantum system with a noisy environment is often modeled phenomenologically by means of a dynamical semigroup with a corresponding time-independent generator in Lindblad form, which describes a memoryless dynamics of the open system typically leading to an irreversible loss of characteristic quantum features. However, in many applications open systems exhibit pronounced memory effects and a revival of genuine quantum properties such as quantum coherence, correlations, and entanglement. Here recent theoretical results on the rich non-Markovian quantum dynamics of open systems are discussed, paying particular attention to the rigorous mathematical definition, to the physical interpretation and classification, as well as to the quantification of quantum memory effects. The general theory is illustrated by a series of physical examples. The analysis reveals that memory effects of the open system dynamics reflect characteristic features of the environment which opens a new perspective for applications, namely, to exploit a small open system as a quantum probe signifying nontrivial features of the environment it is interacting with. This Colloquium further explores the various physical sources of non-Markovian quantum dynamics, such as structured environmental spectral densities, nonlocal correlations between environmental degrees of freedom, and correlations in the initial system-environment state, in addition to developing schemes for their local detection. Recent experiments addressing the detection, quantification, and control of non-Markovian quantum dynamics are also briefly discussed. © 2016 American Physical Society.

Chen W.,Aalto University
Journal of Chemical Physics | Year: 2013

I analyze the fluid-fluid phase separation of nonadditive hard sphere fluid mixture absorbed in random porous media. An equation of state is derived by using the perturbation theory to this complex system with quenched disorders. The results of this theory are in good agreement with those obtained from semi-grand canonical ensemble Monte Carlo simulations. The contact value of the fluid-fluid radial distribution functions of the reference which is the key point of the perturbation process is derived as well, the comparison against Monte Carlo simulations shows that it has an excellent accuracy. © 2013 AIP Publishing LLC.

Valorinta M.,Aalto University
Journal of Information Technology | Year: 2011

This study applies the concept of organizational boundary to examine how outsourcing and the management of external and internal boundaries of the information technology (IT) function impact IT alignment. The article argues that by decreasing the governance costs for the less strategic IT transactions, IT outsourcing enables the IT function, and IT management particularly, to focus more on aligning the IT activities and plans with business strategies and priorities, and thereby improve IT alignment. This article also suggests that organizations may improve IT alignment by effectively transmitting knowledge and supporting collaboration between IT and business functions through boundary spanning activities and with boundary objects. The concept of organizational boundaries and boundary management has not been explicitly addressed by the existing research on IT alignment. This study also contributes to the IT outsourcing literature by linking outsourcing to improved IT alignment. © 2011 JIT Palgrave Macmillan All rights reserved.

Barth C.,CNRS Interdisciplinary Center on Nanoscience in Marseille | Foster A.S.,Tampere University of Technology | Foster A.S.,Aalto University | Henry C.R.,CNRS Interdisciplinary Center on Nanoscience in Marseille | And 2 more authors.
Advanced Materials | Year: 2011

The current status and future prospects of non-contact atomic force microscopy (nc-AFM) and Kelvin probe force microscopy (KPFM) for studying insulating surfaces and thin insulating films in high resolution are discussed. The rapid development of these techniques and their use in combination with other scanning probe microscopy methods over the last few years has made them increasingly relevant for studying, controlling, and functionalizing the surfaces of many key materials. After introducing the instruments and the basic terminology associated with them, state-of-the-art experimental and theoretical studies of insulating surfaces and thin films are discussed, with specific focus on defects, atomic and molecular adsorbates, doping, and metallic nanoclusters. The latest achievements in atomic site-specific force spectroscopy and the identification of defects by crystal doping, work function, and surface charge imaging are reviewed and recent progress being made in high-resolution imaging in air and liquids is detailed. Finally, some of the key challenges for the future development of the considered fields are identified. Non-contact atomic force microscopy (nc-AFM) and Kelvin probe force microscopy (KPFM) for studying insulating surfaces and thin insulating films in high resolution are reviewed. The methods are introduced, then experimental and theoretical studies of insulating surfaces and thin films, with specific focus on defects, atomic and molecular adsorbates, doping, and metallic nanoclusters are discussed. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Cwirzen A.,Aalto University
Advanced Materials Research | Year: 2010

The majority of concrete used nowadays is based on matrixes formed by hydrating Portland cement. Latest developments in nanosciences introduced a new generation of nano-sized materials possessing often remarkable mechanical and physical properties. These materials can be also used to improve or alter the characteristics of the binder matrixes based on Portland cement. The results showed that mechanical properties such as compressive and flexural strength can be increased by up to 50% by addition of for example 0.23wt% of carbon nanotubes. Carbon nanotubes and carbon nanofibres and/or nanosilica appeared to improve also the frost resistance. Other properties, such as autogenous shrinkage decreased significantly after addition of carbon nanofibres. Nanosilica enabled an immense densification of the hydrated binder matrix, which in turn improved for instance the durability and mechanical properties. © (2010) Trans Tech Publications.

Antila H.S.,Aalto University
Methods in molecular biology (Clifton, N.J.) | Year: 2013

This chapter provides an overview of the most common methods for including an explicit description of electronic polarization in molecular mechanics force fields: the induced point dipole, shell, and fluctuating charge models. The importance of including polarization effects in biomolecular simulations is discussed, and some of the most important achievements in the development of polarizable biomolecular force fields to date are highlighted.

Mohamed F.A.,Omar Al-Mukhtar University | Koivo H.N.,Aalto University
International Journal of Electrical Power and Energy Systems | Year: 2010

This paper presents a generalized formulation to determine the optimal operating strategy and cost optimization scheme for a MicroGrid. Prior to the optimization of the MicroGrid itself, models for the system components are determined using real data. The proposed cost function takes into consideration the costs of the emissions, NOx, SO2, and CO2, start-up costs, as well as the operation and maintenance costs. A daily income and outgo from sold or purchased power is also added. The MicroGrid considered in this paper consists of a wind turbine, a micro turbine, a diesel generator, a photovoltaic array, a fuel cell, and a battery storage. In this work, the Mesh Adaptive Direct Search (MADS) algorithm is used to minimize the cost function of the system while constraining it to meet the customer demand and safety of the system. In comparison with previously proposed techniques, a significant reduction is obtained. © 2009 Elsevier Ltd. All rights reserved.

Maaspuro M.,Aalto University
Microelectronics Reliability | Year: 2016

This review discusses piezoelectric fans and their feasibility in a cooling of electronics components and LEDs. The discussion will be restricted to fans based on an oscillating cantilever, the construction which is best known. Other possible piezoelectric fan constructions will be just shortly mentioned. Since the invention of a piezoelectric fan in late 1970s, at least hundreds of science papers have been published about them. A general level presentation of the subject and a summary of the research outcomes will be presented. The construction and operation principles of a piezoelectric fan will be presented. An introduction to piezoelectric materials will be given. The most important equations covering the oscillation of a cantilever beam and the equations for designing fan's geometry will be presented. The generated air flows of a single piezoelectric fan will be issued. This subject will be approached by executing some computational fluid dynamics (CFD) simulations. Use of an air nozzle can force the air vortices closer to laminar flow and improve the cooling effect. The rather weak air flow of a single fan motivates to use multiple fans. A large number of studies have been published about multiple fan constructions. A piezoelectric fan will be compared with a conventional radial fan. An introduction to the electrical parts of a piezoelectric fan will be given. An experimental work demonstrating the use of a piezo fan for electronics cooling will be executed. © 2016 Elsevier Ltd.

Salmi J.,Aalto University | Molisch A.F.,University of Southern California
IEEE Transactions on Antennas and Propagation | Year: 2011

Ultrawideband (UWB) radar is a promising method for reliable remote monitoring of vital signs. The use of multiple antennas at transmitter and receiver (MIMO) allows not only improved reliability, but also better accuracy in localization and tracking of humans and their various types of movement. This paper describes an experimental demonstration of localizing a test subject and tracking his breathing under ideal conditions. The UWB MIMO channel, which includes the test subject as well as other objects, is modeled as a superposition of multipath components (MPCs). From the measured data one can extract the parameters of the MPCs, including their directions and delays, which allows localization of the test subject as well as tracking the breathing motion. Since the breathing pattern of the test subject induces delay variations of the diaphragm-reflected MPC that are much smaller than the Fourier resolution limits, the high-resolution RIMAX algorithm (iterative maximum-likelihood estimation scheme) is employed together with a path detection scheme for determining and tracking the MPC parameters. Furthermore, it is illustrated that with a wideband array model, the requirements for antenna spacing are not as limited as for conventional narrowband array processing. Through controlled experiments with a vector network analyzer and a virtual antenna array observing both an artificial breathing object as well as a human subject, it is shown that one can accurately estimate the small scale movement from human respiratory activity. This is achieved both for line-of-sight between transmitter, receiver, and objects, as well as for non-line-of sight. © 2011 IEEE.

Glaus P.,University of Manchester | Honkela A.,Aalto University | Rattray M.,University of Sheffield
Bioinformatics | Year: 2012

Motivation: High-throughput sequencing enables expression analysis at the level of individual transcripts. The analysis of transcriptome expression levels and differential expression (DE) estimation requires a probabilistic approach to properly account for ambiguity caused by shared exons and finite read sampling as well as the intrinsic biological variance of transcript expression. Results: We present Bayesian inference of transcripts from sequencing data (BitSeq), a Bayesian approach for estimation of transcript expression level from RNA-seq experiments. Inferred relative expression is represented by Markov chain Monte Carlo samples from the posterior probability distribution of a generative model of the read data. We propose a novel method for DE analysis across replicates which propagates uncertainty from the sample-level model while modelling biological variance using an expression-level-dependent prior. We demonstrate the advantages of our method using simulated data as well as an RNA-seq dataset with technical and biological replication for both studied conditions. © The Author(s) 2012. Published by Oxford University Press.

Lehtonen M.,Aalto University
PQ2010: 7th International Conference - 2010 Electric Power Quality and Supply Reliability, Conference Proceedings | Year: 2010

Society is increasingly dependent on continuous power supply. This is also taken into account in regulation models, where, in Finland, the customer's interruption costs CIC now directly affect the profit allowed for distribution system operators. This has led to the situation, where the CIC directly affects the network planning, including decisions on line types and line routing. Hence, more information is needed for detail planning, about the fault rates of different line types and how these depend on line routing, i.e. line location and surroundings. This paper gives a summary about what is known of fault rates, both in the case of short interruptions (fast and delayed reclosing) and long interruptions (permanent faults). The paper is based partly on fault statistics collected by Finnish Energy Industries and some power companies, partly on analytical studies. The core of the paper is the comparison of bare conductor overhead lines, covered conductor overhead lines, underground cables and air cables, located in forests, along the roads or in open spaces. © 2010 IEEE.

Casey T.R.,Aalto University | Toyli J.,University of Turku
Technovation | Year: 2012

This article aims to analyze the strategic management of two-sided platforms from the view point of a mobile communications platform manager and elaborate on the dynamics that result in either platform success or failure. A framework is created to model the endogenous formation and diffusion process of a two-sided platform, describing the interplay of strategy levers that platform managers have at their disposal and factors affecting user willingness to create platform affiliation. The framework is applied to the diffusion of public wireless local area access services and configured with extensive data reflecting a large European city and platform deployment costs. The results show the effect of subsidization, revenue sharing, and alliance strategies and highlight the importance of understanding feedback structure and dynamic complexity around two-sided platforms. The results also point out how strategy opportunities vary for different types of platform managers, for example mobile operators extending their mobile infrastructure or large internet companies managing adjacent service platforms and striving for disruptive platform envelopment. © 2012 Elsevier Ltd.

Ojanen T.,Aalto University | Borkje K.,Copenhagen University
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2014

We present a scheme for cooling mechanical motion to the ground state in an optomechanical system. Unlike standard sideband cooling, this scheme applies to the so-called unresolved sideband regime, where the resonance frequency of the mechanical mode is much smaller than the cavity linewidth. Ground-state cooling becomes possible when assuming the presence of an additional, auxiliary mechanical mode and exploiting the effect of optomechanically induced transparency. We first consider a system where one optical cavity interacts with two mechanical modes and show that ground-state cooling of the unresolved mechanical mode is possible when the auxiliary mode is in the resolved sideband regime. We then present a modified setup involving two cavity modes, where both mechanical modes are allowed to be in the unresolved sideband regime. © 2014 American Physical Society.

Cho J.Y.,Aalto University | Cho J.Y.,Nokia Inc.
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2010

PRESENT is a hardware-oriented block cipher suitable for resource constrained environment. In this paper we analyze PRESENT by the multidimensional linear cryptanalysis method. We claim that our attack can recover the 80-bit secret key of PRESENT up to 25 rounds out of 31 rounds with around 262.4 data complexity. Furthermore, we showed that the 26-round version of PRESENT can be attacked faster than key exhaustive search with the 264 data complexity by an advanced key search technique. Our results are superior to all the previous attacks. We demonstrate our result by performing the linear attacks on reduced variants of PRESENT. Our results exemplify that the performance of the multidimensional linear attack is superior compared to the classical linear attack. © 2010 Springer-Verlag.

Jannes G.,Aalto University
JETP Letters | Year: 2011

We use the tunneling formalism to calculate the Hawking radiation of massive particles. For E ≥ m, we recover the traditional result, identical to the massless case. But E < m particles can also tunnel across the horizon in a Hawking process. We study the probability for detecting such E < m particles as a function of the distance from the horizon and the energy of the particle in the tunneling formalism. We derive a general formula and obtain simple approximations in the near-horizon limit and in the limit of large radii. © 2011 Pleiades Publishing, Ltd.

Sinha A.,Aalto University
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2011

Bilevel multi-objective optimization problems are known to be highly complex optimization tasks which require every feasible upper-level solution to satisfy optimality of a lower-level optimization problem. Multi-objective bilevel problems are commonly found in practice and high computation cost needed to solve such problems motivates to use multi-criterion decision making ideas to efficiently handle such problems. Multi-objective bilevel problems have been previously handled using an evolutionary multi-objective optimization (EMO) algorithm where the entire Pareto set is produced. In order to save the computational expense, a progressively interactive EMO for bilevel problems has been presented where preference information from the decision maker at the upper level of the bilevel problem is used to guide the algorithm towards the most preferred solution (a single solution point). The procedure has been evaluated on a set of five DS test problems suggested by Deb and Sinha. A comparison for the number of function evaluations has been done with a recently suggested Hybrid Bilevel Evolutionary Multi-objective Optimization algorithm which produces the entire upper level Pareto-front for a bilevel problem. © 2011 Springer-Verlag.

Nakajima T.,Waseda University | Lehdonvirta V.,Aalto University
Personal and Ubiquitous Computing | Year: 2013

In this article, we describe four case studies of ubiquitous persuasive technologies that support behavior change through personalized feedback reflecting a user's current behavior or attitude. The first case study is Persuasive Art, reflecting the current status of a user's physical exercise in artistic images. The second system, Virtual Aquarium, reflects a user's toothbrushing behavior in a Virtual Aquarium. The third system, Mona Lisa Bookshelf, reflects the situation of a shared bookshelf on a Mona Lisa painting. The last case study is EcoIsland, reflecting cooperative efforts toward reducing CO2 emissions as a set of virtual islands shared by a neighborhood. Drawing from the experience of designing and evaluating these systems, we present guidelines for the design of persuasive ambient mirrors: systems that use visual feedback to effect changes in users' everyday living patterns. In particular, we feature findings in choosing incentive systems, designing emotionally engaging feedback, timing feedback, and persuasive interaction design. Implications for current design efforts as well as for future research directions are discussed. © 2011 Springer-Verlag London Limited.

Rishika R.,Texas A&M University | Kumar A.,Aalto University | Janakiraman R.,Texas A&M University | Bezawada R.,State University of New York at Buffalo
Information Systems Research | Year: 2013

In this study we examine the effect of customers' participation in a firm's social media efforts on the intensity of the relationship between the firm and its customers as captured by customers' visit frequency. We further hypothesize and test for the moderating roles of social media activity and customer characteristics on the link between social media participation and the intensity of customer-firm relationship. Importantly, we also quantify the impact of social media participation on customer profitability. We assemble a novel data set that combines customers' social media participation data with individual customer level transaction data. To account for endogeneity that could arise because of customer self-selection, we utilize the propensity score matching technique in combination with difference in differences analysis. Our results suggest that customer participation in a firm's social media efforts leads to an increase in the frequency of customer visits. We find that this participation effect is greater when there are high levels of activity in the social media site and for customers who exhibit a strong patronage with the firm, buy premium products, and exhibit lower levels of buying focus and deal sensitivity. We find that the above set of results holds for customer profitability as well. We discuss theoretical implications of our results and offer prescriptions for managers on how to engage customers via social media. Our study emphasizes the need for managers to integrate knowledge from customers' transactional relationship with their social media participation to better serve customers and create sustainable business value. © 2013 INFORMS.

This communication is to correct the sensitivity analysis formula of frequencies for composite structures in the paper [1]. It is further pointed out that even though the sensitivity analysis formula of frequencies has been corrected, the first derivatives of frequencies with respect to design variables cannot be achieved by direct differentiating the equations of eigenvalues and eigenvectors because the first derivatives of vibration modes with respect to design variables are still unknown. The readers are referred to the analytical solution of the sensitivity analysis of frequencies and modes for composite structures in the literature [2], which is derived using linear space theory. © 2015 Elsevier Ltd.

Tretyakov S.A.,Aalto University
Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences | Year: 2015

In this review paper I discuss electrically thin composite layers, designed to perform desired operations on applied electromagnetic fields. Starting from a historical overview and based on a general classification of metasurfaces, I give an overview of possible functionalities of the most general linear metasurfaces. The review is concluded with a short research outlook discussion. © 2015 The Author(s) Published by the Royal Society. All rights reserved.

Possible growth paths for new electricity generation technologies are investigated on the basis of an empirical analysis of past penetration rates. Finding and understanding high market penetration scenarios is relevant to formulating climate change mitigation strategies. The analysis shows that under favorable growth conditions, photovoltaics and wind could produce 15% and 25%, respectively, of world electricity by 2050. Under the same assumptions nuclear power could increase to 41% of world electricity. But it is unlikely that all three technology paths could be realized up to these values simultaneously and therefore the penetration rates presented here should be considered as indicative only. The results show that under positive conditions, an embryonic technology could move as a preferred option into a mainstream energy source within half a century. The introduction of growth constraints reflecting, e.g., severe economic, technical, or political limitations could reduce the above numbers by a factor of up to 2-3. The results indicate a decline in the relative year-to-year growth of new technologies when they have higher market shares. A comparison of the results with other short-term and long-term technology scenarios shows satisfactory agreement. © 2009 Elsevier Ltd. All rights reserved.

Dahl M.F.,Aalto University
Annals of Physics | Year: 2013

We study Maxwell's equations on a 4-manifold where the electromagnetic medium is modeled by an antisymmetric 22-tensor with 21 real coefficients. In this setting the Fresnel surface is a fourth-order polynomial surface that describes the dynamical response of the medium in the geometric optics limit. For example, in an isotropic medium the Fresnel surface is a Lorentz null cone. The contribution of this paper is the pointwise description of all electromagnetic medium tensors κ with real coefficients that satisfy the following three conditions: (i)medium κ is invertible,(ii)medium κ is skewon-free, or non-dissipative,(iii)the Fresnel surface of κ is the union of two distinct Lorentz null cones. We show that there are only three classes of media with these properties and give explicit expressions in local coordinates for each class. © 2012 Elsevier Inc.

Ojanen T.,Aalto University
Physical Review B - Condensed Matter and Materials Physics | Year: 2013

In this Rapid Communication we show that Rashba-based topological superconductor nanowires, where the spin-orbit coupling may change its sign, support three topological phases protected by chiral symmetry. When a superconducting phase gradient is applied over the interface of the two nontrivial phases, the Andreev spectrum is qualitatively phase shifted by π compared to usual Majorana weak links. The topological π junction has the striking property of exhibiting a maximum supercurrent in the vicinity of vanishing phase difference. Qualitative features of the junction are robust against disorder and magnetic fields violating chiral symmetry. The studied system could be realized by local gating of the wire or by an appropriate stacking of permanent magnets in synthetic Rashba systems. © 2013 American Physical Society.

Riepula M.,Aalto University
IEEE Software | Year: 2011

Open innovation and the recent emphasis on client involvement imply the emergence of hybrid software licensing models combining the limited openness of source code with traditional value appropriation logic. A practical hybrid licensing model responds to the needs of both business-to-business software vendors in vertical domains and consultancies that must maintain separate quasi-products. The central idea is that the vendor of commoditized products also licenses source code to select clients, who become participants in and subscribers to an ongoing closed development community. The tools and techniques are readily available from open source development, but the motivations and relationship management work differently than in a pure open source context. © 2011 IEEE.

Safdarian A.,Sharif University of Technology | Fotuhi-Firuzabad M.,Sharif University of Technology | Lehtonen M.,Aalto University
IEEE Transactions on Power Systems | Year: 2013

This paper presents a stochastic framework for short-term operation of a distribution company (disco). The proposed framework optimizes disco's operational decisions in two hierarchical stages. The first stage, called day-ahead operation stage (DAOS), deals with the operational decisions on purchases from the day-ahead market and commitment of distributed generation (DG) units. The objective of this stage is to minimize the expected operating cost while the financial risk exposed by uncertain real-time prices and loads is restricted to a given level. The model associated with this stage is based on the mixed-integer programming (MIP) format. The second stage, named real-time operation stage (RTOS), deals with disco's activities in real-time. In RTOS, decisions are made on real-time market transactions, dispatch of online DGs, and invocation of load curtailments (LCs) such that the expected operating cost is minimized. This stage is formulated as a nonlinear programming (NLP) problem. To investigate the effectiveness of the developed framework, it is applied to a typical Finnish 20-kV urban distribution network. © 2013 IEEE.

In some earlier hip simulator studies of large-diameter metal-on-metal (MoM) hip prostheses high, unexplained variation in wear has been observed. In the present study it was found that high variation occurs when the tribological endurance limit of the MoM device in question is being approached. When the limit is exceeded, high wear takes place uniformly, and the variation is low. Below the limit, both the wear and its variation are low. The endurance limit was exceeded by increasing the peak load from 2 kN to 3 kN, to simulate obesity. The acetabular cup inclination angle was high, 70°. Potential clinical wear problems can be predicted by hip simulator studies provided that relevant adverse test conditions are included. © 2016 Elsevier Ltd. All rights reserved.

Zubkov M.A.,ITEP | Volovik G.E.,Aalto University | Volovik G.E.,Russian Academy of Sciences
Nuclear Physics B | Year: 2012

Topological invariants for the 4D gapped system are discussed with application to the quantum vacua of relativistic quantum fields. Expression N~3 for the 4D systems with mass gap defined in Volovik (2010) [13] is considered. It is demonstrated that N~3 remains the topological invariant when the interacting theory in deep ultraviolet is effectively massless. We also consider the 5D systems and demonstrate how 4D invariants emerge as a result of the dimensional reduction. In particular, the new 4D invariant N~5 is suggested. The index theorem is proved that defines the number of massless fermions n F in the intermediate vacuum, which exists at the transition line between the massive vacua with different values of N~5. Namely, 2n F is equal to the jump δN~5 across the transition. The jump δN~3 at the transition determines the number of only those massless fermions, which live near the hypersurface ω=0. The considered invariants are calculated for the lattice model with Wilson fermions. © 2012.

Jokinen V.,Aalto University | Kostiainen R.,University of Helsinki | Sikanen T.,University of Helsinki
Advanced Materials | Year: 2012

Multiphase liquid droplets consisting of three connected but immiscible liquid phases are demonstrated. The droplets have designer geometries stabilized by surface energy patterns; aqueous phases prefer contact with hydrophilic surface while organic phases prefer contact with hydrophobic areas. The multiphase droplets are applied for liquid-liquid-liquid extraction. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

This article reviews defects in natural fibres and how, ultimately, they affect the properties of composite materials reinforced with such fibres. Under ideal circumstances, certain natural fibre like flax and hemp can display excellent tensile mechanical properties. However, the potential of the fibre is generally not realised in natural fibre-reinforced composites. Partly, this poor performance can be explained by the presence of defects in the fibres known variously as dislocations, kinks or microcompressions. After briefly considering the chemistry and structure of plant fibres, the properties of selected natural fibres are reviewed. The origin of defects and the impact that processing has on their presence is then considered. The effect that defects have on the mechanical properties of bast fibre and their susceptibility to chemical degradation is also reviewed. Finally, the effect that dislocations have on the properties of composites reinforced with natural fibres is discussed and areas of potential further research needed are highlighted. © 2011 Springer Science+Business Media, LLC.

Kuusi T.,Aalto University | Mingione G.,University of Parma
Archive for Rational Mechanics and Analysis | Year: 2013

Pointwise gradient bounds via Riesz potentials, such as those available for the linear Poisson equation, actually hold for general quasilinear degenerate equations of p-Laplacean type. The regularity theory of such equations completely reduces to that of the classical Poisson equation up to the C1-level. © 2012 Springer-Verlag.

Tuboltsev V.,University of Helsinki | Savin A.,Aalto University | Pirojenko A.,University of Helsinki | Raisanen J.,University of Helsinki
ACS Nano | Year: 2013

While bulk gold is well known to be diamagnetic, there is a growing body of convincing experimental and theoretical work indicating that nanostructured gold can be imparted with unconventional magnetic properties. Bridging the current gap in experimental study of magnetism in bare gold nanomaterials, we report here on magnetism in gold nanocrystalline films produced by cluster deposition in the aggregate form that can be considered as a crossover state between a nanocluster and a continuous film. We demonstrate ferromagnetic-like hysteretic magnetization with temperature dependence indicative of spin-glass-like behavior and find this to be consistent with theoretical predictions, available in the literature, based on first-principles calculations. © 2013 American Chemical Society.

Ojanen T.,Aalto University
Physical Review B - Condensed Matter and Materials Physics | Year: 2013

The pursuit for Majorana fermions is one of the top priorities in condensed matter physics at the moment. In this work, we propose a new method of fabricating Majorana Josephson devices in systems with a weak or no spin-orbit coupling and without external magnetic fields. Our proposal is based on curved semiconductor wires in the proximity of superconducting elements and a small number of nanomagnets. With this method it is possible to fabricate devices that are not feasible by employing straight topological wire segments. The proposed method is naturally scalable and opens up a possibility for a systematic fabrication of arrays of Majorana states where a pair of Majorana states is obtained from a single magnet. © 2013 American Physical Society.

Maslovski S.,University of Coimbra | Tretyakov S.,Aalto University
New Journal of Physics | Year: 2012

It is theoretically known that a pair of phase-conjugating surfaces can function as a perfect lens, focusing propagating waves and enhancing evanescent waves. However, the known experimental approaches based on thin sheets of nonlinear materials cannot fully realize the required phase conjugation boundary condition. In this paper, we show that the ideal phase-conjugating surface is, in principle, physically realizable and investigate the necessary properties of nonlinear and nonreciprocal particles which can be used to build a perfect lens system. The physical principle of the lens operation is discussed in detail and directions of possible experimental realizations are outlined. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.

Rinne M.,Aalto University
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2012

Complex event processing is currently done primarily with proprietary definition languages. Future smart environments will require collaboration of multi-platform sensors operated by multiple parties. The goal of my research is to verify the applicability of standard-compliant SPARQL for complex event processing tasks. If successful, semantic web standards RDF, SPARQL and OWL with their established base of tools have many other benefits for event processing including support for interconnecting disjoint vocabularies, enriching event information with linked open data and reasoning over semantically annotated content. A software platform capable of continuous incremental evaluation of multiple parallel SPARQL queries is a key enabler of the approach. © 2012 Springer-Verlag Berlin Heidelberg.

Time, harriedness and various time-related strategies of slowing down the pace of life have been introduced as critical standpoints in the literature on sustainable consumption. However, the pace of life has received relatively little attention in official policy documents on sustainable consumption. Slow living and wealth-in-time appear as promising and catchy slogans that nevertheless leave few or no marks on environmental policy as it unfolds. Focusing on the policy processes of Local Agenda 21 in Helsinki and of the Finnish National Committee on Sustainable Consumption, an attempt is made to understand how expertise and lay understandings about the pace of life are constituted, and to account for how these themes are introduced, debated and marginalised in policy formulation. © 2012 Copyright Taylor and Francis Group, LLC.

Rahaman M.M.,Aalto University
International Journal of Water Resources Development | Year: 2012

This paper analyzes the use of transboundary water resources management principles in two key regional water-related agreements in Central Asia: the Agreement on Cooperation in Joint Management, Use and Protection of Interstate Sources of Water Resources (1992) and the Statute of the Interstate Commission for Water Coordination of Central Asia (2008). These agreements incorporate several internationally recognized transboundary water resources management principles, though there are also some weaknesses. The presence of such principles in these regional agreements offers plenty of hope for the promotion of sustainable water resources management in Central Asia. © 2012 Taylor & Francis.

Soto D.,Imperial College London | Silvanto J.,University of Westminster | Silvanto J.,Aalto University
Trends in Cognitive Sciences | Year: 2014

Classically, the operation of working memory (WM) has been strongly coupled with conscious states; it is thought that WM operates on conscious input and that we are conscious of the contents and operations of WM. Here, we re-evaluate the relationship between WM and conscious awareness in light of current data and question the views that awareness is mandatory for the operation of WM and that WM contents are necessarily linked to experiential states that are consciously accessible for perceptual report. We propose a novel framework for the relationship between WM and conscious awareness. © 2014 Elsevier Ltd.

Tikka P.,Aalto University | Kaipainen M.Y.,Sodertorn University College
Frontiers in Human Neuroscience | Year: 2014

Mainstream cognitive neuroscience has begun to accept the idea of embodied mind, which assumes that the human mind is fundamentally constituted by the dynamical interactions of the brain, body, and the environment. In today’s paradigm of naturalistic neurosciences, subjects are exposed to rich contexts, such as video sequences or entire films, under relatively controlled conditions, against which researchers can interpret changes in neural responses within a time window. However, from the point of view of radical embodied cognitive neuroscience, the increasing complexity alone will not suffice as the explanatory apparatus for dynamical embodiment and situatedness of the mind. We suggest that narrative enactive systems with dynamically adaptive content as stimuli, may serve better to account for the embodied mind engaged with the surrounding world. Among the ensuing challenges for neuroimaging studies is how to interpret brain data against broad temporal contexts of previous experiences that condition the unfolding experience of nowness. We propose means to tackle this issue, as well as ways to limit the exponentially growing combinatoria of narrative paths to a controllable number. © 2014 Tikka and Kaipainen.

Groth M.,Aalto University
Journal of Nuclear Materials | Year: 2015

Abstract We study tungsten prompt re-deposition processes at the divertor plates via kinetic modelling of the JET SOL for different divertor plasma parameters. Our simulations demonstrate that the electric field and not the Lorentz Force is the major contributor to the prompt re-deposition process. The fraction of tungsten ions escaping from the divertor plasma is defined by the number of tungsten atoms ionized outside the magnetic sheath and does not exceed 3% of the ions sputtered from the divertor surface. We derived the corresponding fit function for estimation of the re-deposition coefficient. © 2014 EURATOM.

Jung A.,Aalto University
IEEE Transactions on Signal Processing | Year: 2015

We propose a method for inferring the conditional independence graph (CIG) of a high-dimensional Gaussian vector time series (discrete-time process) from a finite-length observation. By contrast to existing approaches, we do not rely on a parametric process model (such as, e.g., an autoregressive model) for the observed random process. Instead, we only require certain smoothness properties (in the Fourier domain) of the process. The proposed inference scheme works even for sample sizes much smaller than the number of scalar process components if the true underlying CIG is sufficiently sparse. A theoretical performance analysis provides sufficient conditions on the sample size such that the new method is consistent asymptotically. Some numerical experiments validate our theoretical performance analysis and demonstrate superior performance of our scheme compared to an existing (parametric) approach in case of model mismatch. © 2015 IEEE.

Vattulainen I.,Tampere University of Technology | Vattulainen I.,Aalto University | Vattulainen I.,University of Southern Denmark | Rog T.,Tampere University of Technology
Cold Spring Harbor Perspectives in Biology | Year: 2011

In this article,we provide an overviewof lipid simulations, describing howa computer can be used as a laboratory for lipid research. We briefly discuss the methodology of lipid simulations followed by a number of topical applications that show the benefit of computer modeling for complementing experiments. In particular, we show examples of cases in which simulations have made predictions of novel phenomena that have later been confirmed by experimental studies. Overall, the applications discussed in this article focus on the most recent state of the art and aim to provide a perspective of where the field of lipid simulations stands at the moment. © 2011 Cold Spring Harbor Laboratory Press.

Rajahonka M.,Aalto University
International Journal of Logistics Research and Applications | Year: 2013

The objective of this paper is to increase understanding of the concept of service modularity and to present examples of applications of modularity approach in logistics services. This aim is pursued with an empirical case study, consisting of interviews of 25 logistics service providers (LSPs). Themes found in the literature are used in the interviews and in the analysis of the interviews. The findings show that the LSPs consider modularity as a useful approach, and examples of applications of modularity can be found in the logistics industry. In the future, modularity thinking has potential to become a valuable tool for responding to the challenges facing the logistics service industry, as customers' demands become increasingly diversified, and services, processes and organisational networks become more complex. © 2013 Copyright Taylor and Francis Group, LLC.

Valagiannopoulos A.,Aalto University
Radioengineering | Year: 2013

A layered structure of magnetodielectric slabs, backed with a perfectly conducting plane, is illuminated by a Gaussian beam. The permittivities and permeabilities of each layer are selected so that the incident field penetrates smoothly into the subsequent layers and sustains gradually greater losses when reaching the internal ones. The performance of the device as an absorber is estimated through a newly defined indicator and it has been found that the absorbing capacity of the structure could be very high. This qualitative factor is robust and efficient when identifying which of the considered parameters are critical or insignificant as far as the performance of the layered configuration is concerned.

Hayes A.,Aalto University
IEEE Technology and Society Magazine | Year: 2013

Project Glass is a research and development program by Google to develop an augmented reality head-mounted display (HMD). The intended purpose of Project Glass products is the hands-free display of information currently available to most smart phone users, allowing for interaction with the Internet via natural language voice commands. The reality emerging from interactions in early 2013 between the general public and these body worn technologies brought to market by Google are evidenced in recent online interactions that are almost certain to explode upon mass adoption. In many of these cases the premise for deployment of these technologies is to build upon and improve existing work practices, selected by seemingly well informed and trusted technical experts, substantially guided by organizational policy and secure data management plans pursuant. The interoperability between these location-aware body-worn technologies now opens new domains of socio-ethical consideration as to the effects that an always-n network will have on humanity as a whole.

Jaaskelainen I.P.,Aalto University | Ahveninen J.,Harvard University
Neural Plasticity | Year: 2014

The ability to concentrate on relevant sounds in the acoustic environment is crucial for everyday function and communication. Converging lines of evidence suggests that transient functional changes in auditory-cortex neurons, "short-term plasticity", might explain this fundamental function. Under conditions of strongly focused attention, enhanced processing of attended sounds can take place at very early latencies (50 ms from sound onset) in primary auditory cortex and possibly even at earlier latencies in subcortical structures. More robust selective-attention short-term plasticity is manifested as modulation of responses peaking at 100 ms from sound onset in functionally specialized nonprimary auditory-cortical areas by way of stimulus-specific reshaping of neuronal receptive fields that supports filtering of selectively attended sound features from task-irrelevant ones. Such effects have been shown to take effect in seconds following shifting of attentional focus. There are findings suggesting that the reshaping of neuronal receptive fields is even stronger at longer auditory-cortex response latencies (300 ms from sound onset). These longer-latency short-term plasticity effects seem to build up more gradually, within tens of seconds after shifting the focus of attention. Importantly, some of the auditory-cortical short-term plasticity effects observed during selective attention predict enhancements in behaviorally measured sound discrimination performance. © 2014 Iiro P. Jääskeläinen and Jyrki Ahveninen.

Nefedov I.S.,Aalto University | Melnikov L.A.,Saratov State Technical University
Applied Physics Letters | Year: 2014

We demonstrate the production of strong directive thermal emissions in the far-field zone of asymmetric hyperbolic metamaterials (AHMs), exceeding that predicted by Planck's limit. Asymmetry is inherent to the uniaxial medium, where the optical axis is tilted with respect to medium interfaces. The use of AHMs is shown to enhance the free-space coupling efficiency of thermally radiated waves, resulting in Super-Planckian far-field thermal emission in certain directions. This effect is impossible in usual hyperbolic materials because emission of high density of states (DOS) photons into vacuum with smaller DOS is preserved by the total internal reflection. Different plasmonic metamaterials are proposed for realizing AHM media; the thermal emission from a AHM, based on a grapheme multilayer structure, is presented, as an example. © 2014 AIP Publishing LLC.

Jousimo J.,University of Helsinki | Tack A.J.M.,University of Helsinki | Ovaskainen O.,University of Helsinki | Mononen T.,University of Helsinki | And 4 more authors.
Science | Year: 2014

Ecological theory predicts that disease incidence increases with increasing density of host networks, yet evolutionary theory suggests that host resistance increases accordingly. To test the combined effects of ecological and evolutionary forces on host-pathogen systems, we analyzed the spatiotemporal dynamics of a plant (Plantago lanceolata) - fungal pathogen (Podosphaera plantaginis) relationship for 12 years in over 4000 host populations. Disease prevalence at the metapopulation level was low, with high annual pathogen extinction rates balanced by frequent (re-)colonizations. Highly connected host populations experienced less pathogen colonization and higher pathogen extinction rates than expected; a laboratory assay confirmed that this phenomenon was caused by higher levels of disease resistance in highly connected host populations.

Volovik G.E.,Aalto University | Volovik G.E.,Ld Landau Institute For Theoretical Physics
Journal of Superconductivity and Novel Magnetism | Year: 2013

Topological media are systems whose properties are protected by topology, and thus are robust to deformations of the system. In topological insulators and superconductors, the bulk-surface and bulk-vortex correspondence gives rise to the gapless Weyl, Dirac, or Majorana fermions on the surface of the system and inside vortex cores. In gapless topological media, the bulk-surface and bulk-vortex correspondence produce topologically protected gapless fermions without dispersion - the flat band. Fermion zero modes forming the flat band are localized on the surface of topological media with protected nodal lines and in the vortex core in systems with topologically protected Fermi points (Weyl points). Flat band has an extremely singular density of states, and this property may give rise in particular to surface superconductivity, which in principle could exist even at room temperature. © 2013 Springer Science+Business Media New York.