Articles

Recent Submissions

  • Kätsyri, Jari; Kinnunen, Teemu; Kusumoto, Kenta; Oittinen, Pirkko; Ravaja, Niklas (PUBLIC LIBRARY OF SCIENCE, 2016)
  • Nowak, K.; Wimmer, K.; Hellgartner, S.; Muecher, D.; Bildstein, V.; Diriken, J.; Elseviers, J.; Gaffney, L. P.; Gernhaeuser, R.; Iwanicki, J.; Johansen, J. G.; Huyse, M.; Konki, J.; Kroell, T.; Kruecken, R.; Lutter, R.; Orlandi, R.; Pakarinen, J.; Raabe, R.; Reiter, P.; Roger, T.; Schrieder, G.; Seidlitz, M.; Sorlin, O.; Van Duppen, P.; Warr, N.; De Witte, H.; Zielinska, M. (American Physical Society, 2016)
    States in the N = 28 nucleus Ar-46 have been studied by a two-neutron transfer reaction at REX-ISOLDE (CERN). A beam of radioactive Ar-44 at an energy of 2.16 AMeV and a tritium-loaded titanium target were used to populate Ar-46 by the H-3(Ar-44, p) two-neutron transfer reaction. Protons emitted from the target were identified in the T-REX silicon detector array. The excitation energies of states in Ar-46 have been reconstructed from the measured angles and energies of recoil protons. Angular distributions for three final states were measured and based on the shape of the differential cross section an excited state at 3695 keV was identified as J(pi) = 0(+). The angular differential cross section for the population of different states are compared to calculations using a reaction model employing both sequential and direct transfer of two neutrons. Results are compared to shell-model calculations using state-of-the-art effective interactions.
  • Lica, R.; Mach, H.; Fraile, L. M.; Gargano, A.; Borge, M. J. G.; Marginean, N.; Sotty, C. O.; Vedia, V.; Andreyev, A. N.; Benzoni, G.; Bomans, P.; Borcea, R.; Coraggio, L.; Costache, C.; De Witte, H.; Flavigny, F.; Fynbo, H.; Gaffney, L. P.; Greenlees, P. T.; Harkness-Brennan, L. J.; Huyse, M.; Ibanez, P.; Judson, D. S.; Konki, J.; Korgul, A.; Kroell, T.; Kurcewicz, J.; Lalkovski, S.; Lazarus, I.; Lund, M. V.; Madurga, M.; Marginean, R.; Marroquin, I.; Mihai, C.; Mihai, R. E.; Morales, A. I.; Nacher, E.; Negret, A.; Page, R. D.; Pakarinen, J.; Pascu, S.; Paziy, V.; Perea, A.; Perez-Liva, M.; Picado, E.; Pucknell, V.; Rapisarda, E.; Rahkila, P.; Rotaru, F.; Swartz, J. A.; Tengblad, O.; Van Duppen, P.; Vidal, M.; Wadsworth, R.; Walters, W. B.; Warr, N.; IDS Collaboration (American Physical Society, 2016)
    The levels in Sn-129 populated from the beta(-) decay of In-129 isomers were investigated at the ISOLDE facility of CERN using the newly commissioned ISOLDE Decay Station (IDS). The lowest 1/2(+) state and the 3/2(+) ground state in 129Sn are expected to have configurations dominated by the neutron s(1/2) (l = 0) and d(3/2) (l = 2) single-particle states, respectively. Consequently, these states should be connected by a somewhat slow l-forbidden M1 transition. Using fast-timing spectroscopy we havemeasured the half-life of the 1/2(+) 315.3-keV state, T-1/2 = 19(10) ps, which corresponds to a moderately fast M1 transition. Shell-model calculations using the CD-Bonn effective interaction, with standard effective charges and g factors, predict a 4-ns half-life for this level. We can reconcile the shell-model calculations to the measured T-1/2 value by the renormalization of the M1 effective operator for neutron holes.
  • Calderon, A.; Colling, D.; Huffman, A.; Lassila-Perini, K.; McCauley, T.; Rao, A.; Rodriguez-Marrero, A.; Sexton-Kennedy, E. (Institute of Physics Publishing, 2015)
    The CMS experiment, in recognition of its commitment to data preservation and open access as well as to education and outreach, has made its first public release of high-level data under the CC0 waiver: up to half of the proton-proton collision data (by volume) at 7 TeV from 2010 in CMS Analysis Object Data format. CMS has prepared, in collaboration with CERN and the other LHC experiments, an open-data web portal based on Invenio. The portal provides access to CMS public data as well as to analysis tools and documentation for the public. The tools include an event display and histogram application that run in the browser. In addition a virtual machine containing a CMS software environment along with XRootD access to the data is available. Within the virtual machine the public can analyse CMS data; example code is provided. We describe the accompanying tools and documentation and discuss the first experiences of data use.
  • Liu, Jinxiu; Heiskanen, Janne; Aynekulu, Ermias; Maeda, Eduardo Eiji; Pellikka, Petri Kauko Emil (MDPI, Molecular Diversity Preservation International, 2016)
  • Novikov, Sergei; Khriachtchev, Leonid (NATURE PUBLISHING GROUP, 2016)
    Surface-enhanced Raman scattering (SERS) is an intriguing effect, efficiency of which depends on many factors and whose applicability to a given system is not obvious before the experiment. The motivation of the present work is to demonstrate the SERS effect on silicon nanocrystals (Si-nc) embedded in silica, the material of high technological importance. Using the Ag overlayer method, we have found the SERS effect for this material. The best result is obtained for Ag layers of a weight thickness of 12 nm, whose surface plasmons are in a resonance with the laser wavelength (488 nm). The enhancement obtained for the Raman signal from 3-4-nm Si-nc in a 40-nm SiOx film is above 100. The SERS effect is about twice stronger for ultra-small Si-nc (similar to 1 nm) and/or disordered silicon compared to Si-nc with sizes of 3-4 nm. The SERS measurements with an Ag overlayer allow detecting silicon crystallization for ultrathin SiOx films and/or for very low Si excess and suppress the Raman signal from the substrate and the photoluminescence of the film.
  • Arneth, Almut; Makkonen, Risto; Olin, Stefan; Paasonen, Pauli; Holst, Thomas; Kajos, Maija K.; Kulmala, Markku; Maximov, Trofim; Miller, Paul A.; Schurgers, Guy (COPERNICUS GESELLSCHAFT MBH, 2016)
    Disproportional warming in the northern high latitudes and large carbon stocks in boreal and (sub)arctic ecosystems have raised concerns as to whether substantial positive climate feedbacks from biogeochemical process responses should be expected. Such feedbacks occur when increasing temperatures lead, for example, to a net release of CO2 or CH4. However, temperature-enhanced emissions of biogenic volatile organic compounds (BVOCs) have been shown to contribute to the growth of secondary organic aerosol (SOA), which is known to have a negative radiative climate effect. Combining measurements in Eastern Siberia with model-based estimates of vegetation and permafrost dynamics, BVOC emissions, and aerosol growth, we assess here possible future changes in ecosystem CO2 balance and BVOC-SOA interactions and discuss these changes in terms of possible climate effects. Globally, the effects of changes in Siberian ecosystem CO2 balance and SOA formation are small, but when concentrating on Siberia and the Northern Hemisphere the negative forcing from changed aerosol direct and indirect effects become notable - even though the associated temperature response would not necessarily follow a similar spatial pattern. While our analysis does not include other important processes that are of relevance for the climate system, the CO2 and BVOC-SOA interplay serves as an example for the complexity of the interactions between emissions and vegetation dynamics that underlie individual terrestrial processes and highlights the importance of addressing ecosystem-climate feedbacks in consistent, process-based model frameworks.
  • Kontkanen, Jenni; Olenius, Tinja; Lehtipalo, Katrianne; Vehkamäki, Hanna; Kulmala, Markku; Lehtinen, Kari E. J. (COPERNICUS GESELLSCHAFT MBH, 2016)
    We simulated the time evolution of atmospheric cluster concentrations in a one-component system where not only do clusters grow by condensation of monomers, but cluster-cluster collisions also significantly contribute to the growth of the clusters. Our aim was to investigate the consistency of the growth rates of sub-3aEuro-nm clusters determined with different methods and the validity of the common approach to use them to estimate particle formation rates. We compared the growth rate corresponding to particle fluxes (FGR), the growth rate derived from the appearance times of clusters (AGR), and the growth rate calculated based on irreversible vapor condensation (CGR). We found that the relation between the different growth rates depends strongly on the external conditions and the properties of the model substance. The difference between the different growth rates was typically highest at the smallest, sub-2aEuro-nm sizes. FGR was generally lower than AGR and CGR; at the smallest sizes the difference was often very large, while at sizes larger than 2aEuro-nm the growth rates were closer to each other. AGR and CGR were in most cases close to each other at all sizes. The difference between the growth rates was generally lower in conditions where cluster concentrations were high, and evaporation and other losses were thus less significant. Furthermore, our results show that the conventional method used to determine particle formation rates from growth rates may give estimates far from the true values. Thus, care must be taken not only in how the growth rate is determined but also in how it is applied.
  • Karl, Matthias; Kukkonen, Jaakko; Keuken, Menno P.; Lutzenkirchen, Susanne; Pirjola, Liisa; Hussein, Tareq (COPERNICUS GESELLSCHAFT MBH, 2016)
    This study evaluates the influence of aerosol processes on the particle number (PN) concentrations in three major European cities on the temporal scale of 1aEuro-h, i.e., on the neighborhood and city scales. We have used selected measured data of particle size distributions from previous campaigns in the cities of Helsinki, Oslo and Rotterdam. The aerosol transformation processes were evaluated using the aerosol dynamics model MAFOR, combined with a simplified treatment of roadside and urban atmospheric dispersion. We have compared the model predictions of particle number size distributions with the measured data, and conducted sensitivity analyses regarding the influence of various model input variables. We also present a simplified parameterization for aerosol processes, which is based on the more complex aerosol process computations; this simple model can easily be implemented to both Gaussian and Eulerian urban dispersion models. Aerosol processes considered in this study were (i) the coagulation of particles, (ii) the condensation and evaporation of two organic vapors, and (iii) dry deposition. The chemical transformation of gas-phase compounds was not taken into account. By choosing concentrations and particle size distributions at roadside as starting point of the computations, nucleation of gas-phase vapors from the exhaust has been regarded as post tail-pipe emission, avoiding the need to include nucleation in the process analysis. Dry deposition and coagulation of particles were identified to be the most important aerosol dynamic processes that control the evolution and removal of particles. The error of the contribution from dry deposition to PN losses due to the uncertainty of measured deposition velocities ranges from -76 to +64aEuro-%. The removal of nanoparticles by coagulation enhanced considerably when considering the fractal nature of soot aggregates and the combined effect of van der Waals and viscous interactions. The effect of condensation and evaporation of organic vapors emitted by vehicles on particle numbers and on particle size distributions was examined. Under inefficient dispersion conditions, the model predicts that condensational growth contributes to the evolution of PN from roadside to the neighborhood scale. The simplified parameterization of aerosol processes predicts the change in particle number concentrations between roadside and urban background within 10aEuro-% of that predicted by the fully size-resolved MAFOR model.
  • Enroth, Joonas; Saarikoski, Sanna; Niemi, Jarkko; Kousa, Anu; Jezek, Irena; Mocnik, Grisa; Carbone, Samara; Kuuluvainen, Heino; Rönkkö, Topi; Hillamo, Risto; Pirjola, Liisa (COPERNICUS GESELLSCHAFT MBH, 2016)
    Traffic-related pollution is a major concern in urban areas due to its deleterious effects on human health. The characteristics of the traffic emissions on four highway environments in the Helsinki metropolitan area were measured with a mobile laboratory, equipped with state-of-the-art instrumentation. Concentration gradients were observed for all traffic-related pollutants, particle number (CN), particulate mass (PM1), black carbon (BC), organics, and nitrogen oxides (NO and NO2). Flow dynamics in different environments appeared to be an important factor for the dilution of the pollutants. For example, the half-decay distances for the traffic-related CN concentrations varied from 8 to 83aEuro-m at different sites. The PM1 emissions from traffic mostly consisted of organics and BC. At the most open site, the ratio of organics to BC increased with distance to the highway, indicating condensation of volatile and semi-volatile organics on BC particles. These condensed organics were shown to be hydrocarbons as the fraction of hydrocarbon fragments in organics increased. Regarding the CN size distributions, particle growth during the dilution was not observed; however the mass size distributions measured with a soot particle aerosol mass spectrometer (SP-AMS), showed a visible shift of the mode, detected at aEuro-100aEuro-nm at the roadside, to a larger size when the distance to the roadside increased. The fleet average emission factors appeared to be lower for the CN and higher for the NO2 than ten years ago. The reason is likely to be the increased fraction of light-duty (LD) diesel vehicles in the past ten years. The fraction of heavy-duty (HD) traffic, although constituting less than 10aEuro-% of the total traffic flow, was found to have a large impact on the emissions.
  • Eggeling, Ralf; Koivisto, Mikko Kalle Henrik (2016)
    We give a novel algorithm for finding a parsimonious context tree (PCT) that best fits a given data set. PCTs extend traditional context trees by allowing context-specific grouping of the states of a context variable, also enabling skipping the variable. However, they gain statistical efficiency at the cost of computational efficiency, as the search space of PCTs is of tremendous size. We propose pruning rules based on efficiently computable score upper bounds with the aim of reducing this search space significantly. While our concrete bounds exploit properties of the BIC score, the ideas apply also to other scoring functions. Empirical results show that our algorithm is typically an order-of-magnitude faster than a recently proposed memory-intensive algorithm, or alternatively, about equally fast but using dramatically less memory.
  • Rainio, Riitta (SUOMEN LAMMASYHDISTYS, 2015)
  • Rainio, Riitta Johanna (2006)
    Santrauka: Varpeliai, varpai ir varpeliu pavidalo papuosalai - gelezies amziaus atgarsiai Suomijoje
  • Rainio, Riitta; Lahelma, Antti; Äikäs, Tiina; Lassfolk, Kai; Okkonen, Jari (2014)