Helsingin yliopiston tutkijoiden julkaisemia artikkeleja.

Helsingin yliopiston tutkijat voivat rinnakkaistallentaa tutkimusjulkaisujansa HELDAan liittämällä kokotekstin julkaisuun TUHAT-tutkimustietojärjestelmässä. (Toimintaohje tutkijalle)


Nyligen publicerat

  • Martin, S. T.; Artaxo, P.; Machado, L.; Manzi, A. O.; Souza, R. A. F.; Schumacher, C.; Wang, J.; Biscaro, T.; Brito, J.; Calheiros, A.; Jardine, K.; Medeiros, A.; Portela, B.; de Sa, S. S.; Adachi, K.; Aiken, A. C.; Albrecht, R.; Alexander, L.; Andreae, M. O.; Barbosa, H. M. J.; Buseck, P.; Chand, D.; Comstock, J. M.; Day, D. A.; Dubey, M.; Fan, J.; Fast, J.; Fisch, G.; Fortner, E.; Giangrande, S.; Gilles, M.; Goldststein, A. H.; Guenther, A.; Hubbe, J.; Jensen, M.; Jimenez, J. L.; Keutsch, F. N.; Kim, S.; Kuang, C.; Laskin, A.; McKinney, K.; Mei, F.; Miller, M.; Nascimento, R.; Pauliquevis, T.; Pekour, M.; Peres, J.; Petäjä, T.; Poehlker, C.; Poeschl, U.; Rizzo, L.; Schmid, B.; Shilling, J. E.; Silva Dias, M. A.; Smith, J. N.; Tomlinson, J. M.; Tota, J.; Wendisch, M. (2017)
    The susceptibility of air quality, weather, terrestrial ecosystems, and climate to human activities was investigated in a tropical environment.
  • Kassamakov, Ivan; Lecler, Sylvain; Nolvi, Anton; Leong-Hoi, Audrey; Montgomery, Paul; Haeggström, Edward (2017)
    We present quantitative three dimensional images of grooves on a writable Blu-ray Disc based on a single objective Mirau type interferometric microscope, enhanced with a microsphere which is considered as a photonic nanojet source. Along the optical axis the resolution of this microsphere assisted interferometry system is a few nanometers while the lateral resolution is around 112 nm. To understand the physical phenomena involved in this kind of imaging we have modelled the interaction between the photonic jet and the complex disc surface. Agreement between simulation and experimental results is demonstrated. We underline that although the ability of the microsphere to generate a photonic nanojet does not alone explain the resolution of the interferometer, the nanojet can be used to try to understand the imaging process. To partly explain the lateral super-resolution, the potential role of coherence is illustrated. The presented modality may have a large impact on many fields from bio-medicine to nanotechnology.
  • Yung, Yeni P.; Wickramasinghe, Raveendra; Vaikkinen, Anu; Kauppila, Tiina J.; Veryovkin, Igor V.; Hanley, Luke (2017)
    A hand-held diode laser is implemented for solid sampling in portable ambient mass spectrometry (MS). Specifically, a pseudocontinuous wave battery powered surgical laser diode is employed for portable laser diode thermal desorption (LDTD) at 940 nm and compared with nanosecond pulsed laser ablation at 2940 nm. Postionization is achieved in both cases using atmospheric pressure photoionization (APPI). The laser ablation atmospheric pressure photoionization (LAAPPI) and LDTD-APPI mass spectra of sage leaves (Salvia officinalis) using a field-deployable quadrupole ion trap MS display many similar ion peaks, as do the mass spectra of membrane grown biofilms of Pseudomonas aeruginosa: These results indicate that LDTD-APPI method should be useful for in-field sampling of plant and microbial communities, for example, by portable ambient MS. The feasibility of many portable MS applications is facilitated by the availability of relatively low cost, portable, battery-powered diode lasers. LDTD could also be coupled with plasma- or electrospray-based ionization for the analysis of a variety of solid-samples.
  • Adamczyk, Bartosz; Simon, Judy; Kitunen, Veikko; Adamczyk, Sylwia; Smolander, Aino (2017)
    Tannins, an abundant group of plant secondary compounds, raise interest in different fields of science, owing to their unique chemical characteristics. In chemical ecology, tannins play a crucial role in plant defense against pathogens, herbivores, and changing environmental conditions. In the food industry and in medicine, tannins are important because of their proven positive effect on human health and disease treatment, Such wide interests fueled studies on tannin chemistry, especially on their flagship ability to precipitate proteins. In this Review, we expand the basic knowledge on tannin chemistry to the newest insights from the field. We focus especially on tannin reactions with different non-protein organic N compounds, as well as the complex interactions of tannins with enzymes, resulting in either an increase or decrease in enzyme activity.
  • Hoshian, Sasha; Kankuri, Esko; Ras, Robin H. A.; Franssila, Sami; Jokinen, Ville (2017)
    A top-down scalable method to produce flexible water and blood repellent tubes is introduced. The method is based on replication of overhanging nanostructures from an aluminum tube template to polydimethylsiloxane (PDMS) via atomic layer deposition (ALD) assisted sacrificial etching. The nanostructured PDMS/titania tubes are superhydrophobic with water contact angles 163 +/- 1 degrees (advancing) and 157 +/- 1 degrees (receding) without any further coating. Droplets are able to slide through a 4 mm (inner diameter) tube with low sliding angles of less than 10 degrees for a 35 mu L droplet. The superhydrophobic tube shows up to 5,000 times increase in acceleration of a sliding droplet compared to a control tube depending on the inclination angle. Compared to a free falling droplet, the superhydrophobic tube reduced the acceleration by only 38.55%, as compared to a 99.99% reduction for a control tube. The superhydrophobic tubes are blood repellent. Blood droplets (35 mu L) roll through the tubes at 15 degrees sliding angles without leaving a bloodstain. The tube surface is resistant to adhesion of activated platelets unlike planar control titania and smooth PDMS surfaces.
  • Plado, Juri; Preeden, Ulla; Joeleht, Argo; Pesonen, Lauri J.; Mertanen, Satu (2016)
    The hill range of Vaivara Sinimaed in northeast Estonia consists of several narrow east-to northeast-trending glaciotectonic fold structures. The folds include tilted (dips 4-75 degrees) Middle Ordovician (early Darriwilian) layered carbonate strata that were studied by mineralogical, palaeomagnetic, and rock magnetic methods in order to specify the post-sedimentational history of the area and to obtain a better control over the palaeogeographic position of Baltica during the Ordovician. Mineralogical studies revealed that (titano) magnetite, hematite, and goethite are carriers of magnetization. Based on data from 5 sites that positively passed a DC tilt test, a south-easterly downward directed component A (D-ref = 154.6 degrees +/- 15.3 degrees, I-ref = 60.9 degrees +/- 9.7 degrees) was identified. The component is carried by (titano) magnetite, dates to the Middle Ordovician (Plat = 17.9 degrees, Plon = 47.3 degrees, K = 46.7, A95 = 11.3 degrees), and places Baltica at mid-southerly latitudes. Observations suggest that in sites that do not pass the tilt test, the glaciotectonic event has caused some rotation of blocks around their vertical axis.
  • Miettunen, Jaakko; Dervin, Fred (2014)
    This study investigates how different types of teachers are represented and constructed in television fiction. Previous research indicates that fiction is as powerful as non-fiction in shaping and changing peoples’ attitudes, beliefs and opinions. In Finland, the context of this study, there have been many teacher characters in literature, TV and movies and, despite their esteemed status in society, their representation has been mainly negative. Motivated by the current ‘treacherous’ changes in Finnish education (introduction of a new core curriculum, problems of discipline, increasing number of dropouts and marginalized youth), we examine how a recent and popular Finnish TV-series centered on a school, display these societal issues and, at the same time, portray different facets of teacherhood. The main concept used as a tool for analysing the TV-series is representation while content and discourse analyses serve as analytical frameworks. The results of this study show that two main subsets of teachers are present in the TV series: art teachers vs. teachers in general. Compared to the traditional representation of teachers the art teacher is constructed as more positive and as some sort of independent warrior teacher. Yet her representations tend to be not only one-sided but also caricatures, which puts into question the respect and appreciation of teachers in Finnish society.
  • Gorda, Tyler (2016)
    We numerically investigate global properties of rotating neutron stars (NSs) using the allowed band of QCD equations of state derived by Kurkela et al. This band is constrained by chiral effective theory at low densities and perturbative QCD at high densities, and is thus, in essence, a controlled constraint from first-principles physics. Previously, this band of equations of state was used to investigate non-rotating NSs only; in this work, we extend these results to any rotation frequency below the mass-shedding limit. We investigate mass-radius curves, allowed mass-frequency regions, radius-frequency curves for a typical 1.4M(circle dot) star, and the values of the moment of inertia of the double pulsar PSR J0737-3039A, a pulsar for which the. moment of inertia may be constrained observationally in a few years. We present limits on observational data coming from these constraints, and identify values of observationally relevant parameters that would further constrain the allowed region for the QCD equation of state. We also discuss how much this region would be constrained by a measurement of the moment of inertia. of the double pulsar PSR J0737-3039A.
  • Dervin, Fred; Machart, Regis; Byrd Clark, Julie (2016)
  • Liu, Haiqin; Dervin, Fred (2016)
    With the current rise of China as a political, cultural, and economic superpower, Chinese as a foreign and second language has gained popularity worldwide. Finland is also responding to this global wave, as is reflected by the increasing number of Chinese courses in formal and informal settings in the Nordic country. Yet not all actors involved in the promotion of Chinese seem to experience instruction in the language in the same way. This study investigates how Chinese teachers of the Chinese language, who represent the majority of the ‘workforce’ for instruction in this language in Finland, perceive Chinese language education and their role in it. We argue that there is a need for a paradigm shift in evaluating the teachers’ experiences. Specifically, we support a move away from perspectives that see culture as static and identity as singular. Using the “analysis of multivoiceness,” which was developed from dialogism (Aveling, Gillespie, & Cornish, 2014), the authors of this article identify a number of positions assumed/taken up by the teachers and others in their discourses. Finally, we propose a critical intercultural approach to Chinese teacher education or professional development based on transdisciplinarity, which relies on problem-solving that recognizes an important triad: educational contexts—teachers’ experiences—society (McGregor & Volckmann, 2011).
  • Tortosa, Montserrat; Skorsepa, Marek; Guitart, Fina; Urban-Woldron, Hildegard; Aksela, Maija Katariina; Tolvanen, Simo Antti; Stratilová-Urvalková, Eva; Smejkal, Petr (European Science Education Research Association ESERA, 2014)
    This study is part of a European project that aims to design new microcomputer-based laboratory (MBL) activities to be used in secondary and high school to enhance on students scientific competencies. The aim of this work is to design and to implement research-based teaching materials that take advantage of the use of MBL and promote scientific competencies in students. Researchers from six universities belonging to five EU countries have collaboratively designed a new research-based framework for MBL activities. Activities are context- based and inquiry guided. When students take experimental data, it is proposed a Predict-Observe-Explain (White & Gunstone, 1992) sequence. The main scientific competencies that the designed activities aim to enhance in students are the design of experiments, the interpretation of results and its communication. First versions of activities have been translated into national languages (German, Czech, Slovak, Finnish and Catalan) to be implemented. The study has been conducted with 865 students from five countries who have implemented the activities. Students answered a post-implementation questionnaire to elicit if they believed that they knew the objectives of the activities and if they really did. They were also asked if MBL helped them to interpret the results and if the activity could have been done without such equipment. Results obtained in this study suggest that the research-based learning materials designed to work with MBL are useful and of quality as most students in different countries understand the point of the activities, and most of them think that these activities help them to learn and that the activities could not be done without MBL. Nevertheless, differences in results have been obtained for some activities. The results of this research will be used to refine teaching materials.
  • Byman, Reijo; Lavonen, Jari; Juuti, Kalle; Meisalo, Veijo (2012)
    The first objective of the present study was to test the factorial validity of the inventory designed to measure students’ motivation to study physics in school. Based on self-determination theory (SDT), it was hypothesised that the four factors of External Regulation, Introjected Regulation, Identified Regulation and Intrinsic Motivation account for the covariances among the items of the inventory. It was also expected that gender moderates the factorial validity of the inventory. A sample of 3626 Finnish comprehensive school students was used. A multilevel confirmatory factor analysis (MLCFA) was used to investigate the fit of the hypothesised four-factor model. The second objective of the present study was to investigate different educational correlates of the four motivation factors. Girls had a statistically higher mean score than did boys for all four factors. Otherwise only minor gender differences were found. Implications for physics teaching are discussed.