12. Artikkelit / Articles
Permanent URI for this communityhttps://aaltodoc.aalto.fi/handle/123456789/79
Arkisto - Ei ole enää käytössä. Tässä kokoelmassa on rinnakkaistallennettuja artikkeleita vuoteen 2022 asti. Uudet rinnakkaistallennetut artikkelit löytyvät Aalto-yliopiston tutkimustietojärjestelmästä.
Archive - No longer in use. This collection contains green open access articles up until the year 2022. New green open access articles can be found in Aalto University’s research information system.
Archive - No longer in use. This collection contains green open access articles up until the year 2022. New green open access articles can be found in Aalto University’s research information system.
Browse
Browsing 12. Artikkelit / Articles by Title
Now showing 1 - 20 of 1239
- Results Per Page
- Sort Options
- 1/f noise and avalanche scaling in plastic deformation
School of Science | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2006) Laurson, L.; Alava, Mikko J.We study the intermittency and noise of dislocation systems undergoing shear deformation. Simulations of a simple two-dimensional discrete dislocation dynamics model indicate that the deformation rate exhibits a power spectrum scaling of the type 1/fα. The noise exponent is far away from a Lorentzian, with α≈1.5. This result is directly related to the way the durations of avalanches of plastic deformation activity scale with their size. - 151Eu Mössbauer spectroscopy and x-ray-diffraction studies on the Pb2Ba2EuCu3O8+[delta] system
School of Chemical Technology | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(1994) Lindén, J.; Lippmaa, M.; Miettinen, J.; Tittonen, I.; Katila, T.; Karppinen, Maarit; Niinistö, L.Simultaneous replacement of Sr by Ba and Y by Eu in the Pb-2213 system was found to yield single-phase Pb2Ba2EuCu3O8+δ samples, suitable for Eu151 Mössbauer measurements. The samples were synthesized by a solid-state reaction of metal oxides and carbonates under an inert atmosphere. An oxygen-rich sample corresponding to δ=1.79 was obtained by annealing the as-synthesized material (δ=0.16) in oxygen. The oxygen annealing increased the size of the lattice constants and led to an orthorhombic-to-tetragonal phase transition of the structure. The samples were also oriented in an 11.7-T magnetic field. The x-ray-diffraction spectra showed that the c axes tended to orient perpendicular to the applied field. The measured Mössbauer spectra exhibited an electric quadrupole interaction typical of the Eu site in high-Tc cuprates. The average orientation angles obtained from fittings of the Mössbauer spectra were in accordance with the results from the x-ray-diffraction measurements. - A12-station anatomic hip joint simulator
School of Engineering | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2005) Saikko, Vesa - Aalto University Undergraduate Centre : The Accessible Renovation of Alvar Aalto's Heritage
Services | D1 Artikkeli ammattilehdessä(2016) Raike, Antti; Ahlava, Antti; Skyttä, Pauliina; Tuomi, TeemuThe main building of the former Helsinki University of Technology (TKK) designed by Alvar Aalto is part of the cultural heritage in Finland. The building underwent a major renovation in 2011–2015 and has now become an awarded Undergraduate Centre for the modern interdisciplinary education of Aalto University. This paper presents how the architectural masterpiece from the 1960’s was renovated and updated into a modern and accessible university building. Particular attention was paid for entering the building by wheelchairs, prams and pushchairs. The successful renovation was awarded in 2015 by the ‘Esteetön Suomi -palkinto’ (Accessible Finland Award), given every two years as a mark of recognition to activities or locations implementing the principles of accessibility and universal design for all on a broad scale and in a nationally significant way. - Ab initio study of Cu diffusion in alpha-cristobalite
School of Science | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2012) Zelený, M.; Hegedüs, J.; Foster, Adam S.; Drabold, D.A.; Elliott, S.R.; Nieminen, Risto M.We have studied the geometries, formation energies, migration barriers and diffusion of a copper interstitial with different charge states with and without an external electric field in the α-cristobalite crystalline form of SiO2 using ab initio computer simulation. The most stable state almost throughout the band gap is charge q = + 1. The height of the migration barrier depends slightly on the charge state and varies between 0.11 and 0.18 eV. However, the charge has a strong influence on the shape of the barrier, as metastable states exist in the middle of the diffusion path for Cu with q = + 1. The heights and shapes of barriers also depend on the density of SiO2, because volume expansion has a similar effect to increase the positive charge on Cu. Furthermore, diffusion coefficients have been deduced from our calculations according to transition-state theory and these calculations confirm the experimental result that oxidation of Cu is a necessary condition for diffusion. Our molecular dynamics simulations show a similar ion diffusion, and dependence on charge state. These simulations also confirm the fact that diffusion of ions can be directly simulated using ab initio molecular dynamics. - Ab initio study of fully relaxed divacancies in GaAs
School of Science | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(1996) Pöykkö, S.; Puska, Martti J.; Nieminen, Risto M.We report calculations of the electronic and atomic structures of neutral and charged divacancies in GaAs using the first-principles Car-Parrinello method. It is found that the divacancy relaxes inwards in all charge states (2-,1-,0,1+) studied. The defect-induced electron levels lie in the lower half of the fundamental band gap. The doubly negative divacancy is the most stable one for nearly all values of the electron chemical potential within the band gap. The deep-level electron density is localized at the Ga-vacancy end of the divacancy and the ionic relaxation is stronger there than at the As-vacancy end. We have also calculated the thermodynamic concentrations for several different native defects in GaAs, and the implications for self-diffusion are discussed. - Ab initio study of gamma-Al2O3 surfaces
School of Science | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2004) Pinto, Henry P.; Nieminen, Risto M.; Elliott, Simon D.Starting from the theoretical prediction of the γ−Al2O3 structure using density-functional theory in the generalized gradient approximation, we have studied the (1 1 1), (0 0 1), (1 1 0), and (1 5 0) surfaces. The surface energies and their corresponding structures are computed and compared with predictions for (0 0 0 1) α−Al2O3 and available experimental results for γ-alumina surfaces. (1 1 1) and (0 0 1) surfaces are predicted to be equally stable, but to show quite different structure and reactivity. Whereas a low coverage of highly reactive trigonal Al occurs on (1 1 1), (0 0 1) exhibits a more dense plane of both five-coordinate and tetrahedral Al. Microfaceting of a (1 1 0) surface into (1 1 1)-like planes is also observed. The implications for the structure of ultrathin dielectric films and for the surfaces of disordered transition aluminas are discussed. - Ab initio study of oxygen point defects in GaAs, GaN, and AlN
School of Science | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(1996) Mattila, T.; Nieminen, Risto M.We have studied oxygen point defects with the plane-wave pseudopotential method in GaAs, GaN, and AlN. The calculations demonstrate a qualitatively different behavior of oxygen impurities in these materials. OAs in GaAs acts as a deep center with an off-center displacement and negative-U behavior, in agreement with the experimental data. ON in GaN is found to be a shallow donor with a low formation energy, and is suggested to act as a partial source for the unintentional n-type conductivity commonly observed in GaN. O in AlN is also found to easily substitute for N, which is consistent with the experimentally observed large oxygen concentrations in AlN. However, ON in AlN is shown to be a deep center due to the wide band gap, in contrast with ON in GaN. Our calculations thus predict that isolated oxygen acts as a DX-type center in AlxGa1−xN alloys. Results for other oxygen point defect configurations and for the dominant native defects are also presented. © 1996 The American Physical Society. - Ab initio study of point defects in CdF2
School of Science | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(1997) Mattila, T.; Pöykkö, S.; Nieminen, Risto M.The plane-wave pseudopotential method is used to study point defects in CdF2. We present comprehensive results for the native defects as well as for dominant impurities. In addition to Fi, VCd and OF were found to be easily formed compensating acceptors. For In and Ga impurities the experimentally observed large Stokes shift could not be established, and the results rule out symmetric atomic relaxation as the mechanism leading to the bistable behavior. The limitations of the present approach utilizing density-functional theory and the local-density approximation in the case of ionic materials are addressed. - Ab initio transport fingerprints for resonant scattering in graphene
School of Science | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2012) Saloriutta, Karri; Uppstu, Andreas; Harju, Ari; Puska, Martti J.We have recently shown that by using a scaling approach for randomly distributed topological defects in graphene, reliable estimates for transmission properties of macroscopic samples can be calculated based even on single-defect calculations [A. Uppstu et al., Phys. Rev. B 85, 041401 (2012)]. We now extend this approach of energy-dependent scattering cross sections to the case of adsorbates on graphene by studying hydrogen and carbon adatoms as well as epoxide and hydroxyl groups. We show that a qualitative understanding of resonant scattering can be gained through density functional theory results for a single-defect system, providing a transmission “fingerprint” characterizing each adsorbate type. This information can be used to reliably predict the elastic mean free path for moderate defect densities directly using ab initio methods. We present tight-binding parameters for carbon and epoxide adsorbates, obtained to match the density-functional theory based scattering cross sections. - Abnormal Auditory Cortical Activation in Dyslexia 100 msec after Speech Onset
School of Science | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2002) Helenius, Päivi; Salmelin, Riitta; Richardson, Ulla; Leinonen, Seija; Lyytinen, HeikkiReading difficulties are associated with problems in processing and manipulating speech sounds. Dyslexic individuals seem to have, for instance, difficulties in perceiving the length and identity of consonants. Using magnetoencephalography (MEG), we characterized the spatio-temporal pattern of auditory cortical activation in dyslexia evoked by three types of natural bisyllabic pseudowords (/ata/, /atta/, and /a a/), complex nonspeech sound pairs (corresponding to /atta/ and /a a/) and simple 1-kHz tones. The most robust difference between dyslexic and non-reading-impaired adults was seen in the left supratemporal auditory cortex 100 msec after the onset of the vowel /a/. This N100m response was abnormally strong in dyslexic individuals. For the complex nonspeech sounds and tone, the N100m response amplitudes were similar in dyslexic and nonimpaired individuals. The responses evoked by syllable /ta/ of the pseudoword /atta/ also showed modest latency differences between the two subject groups. The responses evoked by the corresponding nonspeech sounds did not differ between the two subject groups. Further, when the initial formant transition, that is, the consonant, was removed from the syllable /ta/, the N100m latency was normal in dyslexic individuals. Thus, it appears that dyslexia is reflected as abnormal activation of the auditory cortex already 100 msec after speech onset, manifested as abnormal response strengths for natural speech and as delays for speech sounds containing rapid frequency transition. These differences between the dyslexic and nonimpaired individuals also imply that the N100m response codes stimulus-specific features likely to be critical for speech perception. Which features of speech (or nonspeech stimuli) are critical in eliciting the abnormally strong N100m response in dyslexic individuals should be resolved in future studies. - Accelerated light-induced degradation for detecting copper contamination in p-type silicon
School of Electrical Engineering | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2015) Inglese, Alessandro; Lindroos, Jeanette; Savin, HeleCopper is a harmful metal impurity that significantly impacts the performance of silicon-based devices if present in active regions. In this contribution, we propose a fast method consisting of simultaneous illumination and annealing for the detection of copper contamination in p-type silicon. Our results show that, within minutes, such method is capable of producing a significant reduction of the minority carrier lifetime. A spatial distribution map of copper contamination can then be obtained through the lifetime values measured before and after degradation. In order to separate the effect of the light-activated copper defects from the other metastable complexes in low resistivity Cz-silicon, we carried out a dark anneal at 200 C, which is known to fully recover the boron-oxygen defect. Similar to the boron-oxygen behavior, we show that the dark anneal also recovers the copper defects. However, the recovery is only partial and it can be used to identify the possible presence of copper contamination. - Accessing nanomechanical resonators via a fast microwave circuit
School of Science | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2009) Sillanpää, Mika A.; Sarkar, Jayanta; Sulkko, Jaakko; Muhonen, Juha; Hakonen, Pertti J.We demonstrate how to fully electrically detect the vibrations of conductive nanomechanical resonators up to the microwave regime. We use the electrically actuated vibrations to modulate an LC tank circuit, which blocks the stray capacitance and detect the created sideband voltage by a microwave analyzer. We prove the technique up to mechanical frequencies of 200 MHz. Finally, we estimate how one could approach the quantum limit of mechanical systems. - Acoustic Emission from Paper Fracture
School of Science | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2002) Salminen, L. I.; Tolvanen, A. I.; Alava, Mikko J.We report tensile failure experiments on paper sheets. The acoustic emission energy and the waiting times between acoustic events follow power-law distributions. This remains true while the strain rate is varied by more than 2 orders of magnitude. The energy statistics has the exponent β∼1.25±0.10 and the waiting times the exponent τ∼1.0±0.1, in particular, for the energy roughly independent of the strain rate. These results do not compare well with fracture models, for (brittle) disordered media, which as such exhibit criticality. One reason may be residual stresses, neglected in most theories. - Activation of Auditory Cortex by Anticipating and Hearing Emotional Sounds: An MEG Study
School of Science | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2013) Yokosawa, Koichi; Pamilo, Siina; Hirvenkari, Lotta; Hari, Riitta; Pihko, ElinaTo study how auditory cortical processing is affected by anticipating and hearing of long emotional sounds, we recorded auditory evoked magnetic fields with a whole-scalp MEG device from 15 healthy adults who were listening to emotional or neutral sounds. Pleasant, unpleasant, or neutral sounds, each lasting for 6 s, were played in a random order, preceded by 100-ms cue tones (0.5, 1, or 2 kHz) 2 s before the onset of the sound. The cue tones, indicating the valence of the upcoming emotional sounds, evoked typical transient N100m responses in the auditory cortex. During the rest of the anticipation period (until the beginning of the emotional sound), auditory cortices of both hemispheres generated slow shifts of the same polarity as N100m. During anticipation, the relative strengths of the auditory-cortex signals depended on the upcoming sound: towards the end of the anticipation period the activity became stronger when the subject was anticipating emotional rather than neutral sounds. During the actual emotional and neutral sounds, sustained fields were predominant in the left hemisphere for all sounds. The measured DC MEG signals during both anticipation and hearing of emotional sounds implied that following the cue that indicates the valence of the upcoming sound, the auditory-cortex activity is modulated by the upcoming sound category during the anticipation period. - Adapting to the changing needs of managing innovative projects
Factories | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2016) Rekonen, Satu; Björklund, Tua A.Purpose – The purpose of this paper is to explore the changes in managerial activities and challengesat different phases of innovative projects. Design/methodology/approach – Six NPD project managers were interviewed in three differentproject phases in a qualitative, longitudinal design. The resulting 18 semi-structured face-to-faceinterviews were content analyzed and categorized according to thematic similarity. Findings – Altogether 19 categories describing managerial concerns in managing innovative projectswere recognized. Task-oriented, rather than people-oriented, approaches were dominant throughoutthe projects, although the reported concerns clearly varied at each phase. The early development phaseemerged as a transition point, where managers had to transform their roles, reported activitiesdecreased, and reported challenges increased. Research limitations/implications – Although based on a small number of participants in a singlesetting, the results highlight the need for longitudinal studies and differentiating between the variousphases of the innovation process, as there was great variance in the concerns of each phase.Furthermore, domain expertise seemed to have a large impact on how the managers reformulated theirrole in transitioning from the front-end to the development phases. Practical implications – The present study emphasizes the need to support managers intransitioning between different innovation phases and to recognize the need to adjust managerial roles.Further, it seemed crucial to establish the practices supporting successful teamwork in the front-endphase before the first phase transition. Originality/value – The study is a rare example of a longitudinal research design examining theimplications and transition between different phases of the innovation process within the sameprojects for project managers. - Adaptive Full-Order Observer With High-Frequency Signal Injection for Synchronous Reluctance Motor Drives
School of Electrical Engineering | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2014) Tuovinen, Toni; Hinkkanen, MarkoA back electromotive force-based position observer for motion-sensorless synchronous reluctance motor (SyRM) drives is augmented with high-frequency signal-injection method for improved low-speed operation. Previously proposed observer structure is further improved to account for the cross saturation in the motor. The combined observer is experimentally evaluated using a 6.7-kW SyRM drive in low-speed operation and under various load conditions. The resulting position error at low speeds and standstill is small. - Adaptive Full-Order Observer With High-Frequency Signal Injection for Synchronous Reluctance Motor Drives
School of Electrical Engineering | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2014) Tuovinen, Toni; Hinkkanen, MarkoA back electromotive force-based position observer for motion-sensorless synchronous reluctance motor (SyRM) drives is augmented with high-frequency signal-injection method for improved low-speed operation. Previously proposed observer structure is further improved to account for the cross saturation in the motor. The combined observer is experimentally evaluated using a 6.7-kW SyRM drive in low-speed operation and under various load conditions. The resulting position error at low speeds and standstill is small. - Adsorption and migration of carbon adatoms on carbon nanotubes: Density-functional ab initio and tight-binding studies
School of Science | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2004) Krasheninnikov, A. V.; Nordlund, K.; Lehtinen, P. O.; Foster, Adam S.; Ayuela, A.; Nieminen, Risto M.We employ density-functional plane-wave ab initio and tight-binding methods to study the adsorption and migration of carbon adatoms on single-walled carbon nanotubes. We show that the adatom adsorption and migration energies strongly depend on the nanotube diameter and chirality, which makes the model of the carbon adatom on a flat graphene sheet inappropriate. Calculated migration energies for the adatoms agree well with the activation energies obtained from experiments on annealing of irradiation damage in single-walled nanotubes and attributed to single carbon interstitials. - Adsorption of acetic and trifluoroacetic acid on the TiO2(110) surface
School of Science | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2004) Foster, Adam S.; Nieminen, Risto M.We use the first-principles static and dynamic simulations to study the adsorption of acetic (CH3COOH) and trifluoroacetic (CF3COOH)acid on the TiO2(110)surface. The most favorable adsorption for both molecules is a dissociative process, which results in the two oxygens of the carboxylate ion bonding to in-plane titanium atoms in the surface. The remaining proton then bonds to a bridging oxygen site, forming a hydroxyl group. We further show that, by comparing the calculated dipoles of the molecules on the surface, it is possible to understand the difference in contrast over the acetate and trifluoroacetate molecules in the atomically resolved noncontact atomic force microscopy images.