Browsing by Subject "diffusion"

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  • Winberg-Wang, Helen; Neretnieks, Ivars; Voutilainen, Mikko (2019)
    Uranine is a dye commonly used in tracer experiments; it is chosen for its high visibility even at low concentrations. Uranine solutions are slightly denser than water at the same temperature. However, in laboratory experiments uranine solutions have been known to occasionally show unpredictable flow behaviors. This paper investigates the possible effect of light-induced density change to explain some of these behaviors. Uranine has a wide light absorption spectrum for visible light, which can heat the dye solution and lower its density to below that of the surrounding water, which induces buoyancy-driven flow. Simulations are made in both one dimension and two dimensions to determine the extent of the effect. The results are then compared to different experiments with unanticipated flow patterns.
  • Sairanen, Viljami; Kuusela, Linda; Sipilä, Outi; Savolainen, Sauli; Vanhatalo, Sampsa (2017)
    Diffusion Tensor Imaging (DTI) is commonly challenged by subject motion during data acquisition, which often leads to corrupted image data. Currently used procedure in DTI analysis is to correct or completely reject such data before tensor estimations, however assessing the reliability and accuracy of the estimated tensor in such situations has evaded previous studies. This work aims to define the loss of data accuracy with increasing image rejections, and to define a robust method for assessing reliability of the result at voxel level. We carried out simulations of every possible sub-scheme (N=1,073,567,387) of Jones30 gradient scheme, followed by confirming the idea with MRI data from four newborn and three adult subjects. We assessed the relative error of the most commonly used tensor estimates for DTI and tractography studies, fractional anisotropy (FA) and the major orientation vector (V1), respectively. The error was estimated using two measures, the widely used electric potential (EP) criteria as well as the rotationally variant condition number (CN). Our results show that CN and EP are comparable in situations with very few rejections, but CN becomes clearly more sensitive to depicting errors when more gradient vectors and images were rejected. The error in FA and V1 was also found depend on the actual FA level in the given voxel; low actual FA levels were related to high relative errors in the FA and V1 estimates. Finally, the results were confirmed with clinical MRI data. This showed that the errors after rejections are, indeed, inhomogeneous across brain regions. The FA and V1 errors become progressively larger when moving from the thick white matter bundles towards more superficial subcortical structures. Our findings suggest that i) CN is a useful estimator of data reliability at voxel level, and ii) DTI preprocessing with data rejections leads to major challenges when assessing brain tissue with lower FA levels, such as all newborn brain, as well as the adult superficial, subcortical areas commonly traced in precise connectivity analyses between cortical regions.
  • Iversen, L.L.; Winkel, A.; Baastrup-Spohr, L.; Hinke, A.B.; Alahuhta, J.; Baattrup-Pedersen, A.; Birk, S.; Brodersen, P.; Chambers, P. A.; Ecke, F; Feldmann, T.; Gebler, D.; Heino, J.; Jespersen, T. S.; Moe, S. J.; Riis, T.; Sass, L.; Vestergaard, O.; Maberly, S. C.; Sand-Jensen, K.; Pedersen, O. (American Association for the Advancement of Science, 2019)
    Science Vol. 366, Issue 6467, pp. 878-881
    Unlike in land plants, photosynthesis in many aquatic plants relies on bicarbonate in addition to carbon dioxide (CO2) to compensate for the low diffusivity and potential depletion of CO2 in water. Concentrations of bicarbonate and CO2 vary greatly with catchment geology. In this study, we investigate whether there is a link between these concentrations and the frequency of freshwater plants possessing the bicarbonate use trait. We show, globally, that the frequency of plant species with this trait increases with bicarbonate concentration. Regionally, however, the frequency of bicarbonate use is reduced at sites where the CO2 concentration is substantially above the air equilibrium, consistent with this trait being an adaptation to carbon limitation. Future anthropogenic changes of bicarbonate and CO2 concentrations may alter the species compositions of freshwater plant communities.
  • Albert, Katrina; Renko, Juho-Matti; Mätlik, Kert; Airavaara, Mikko; Voutilainen, Merja H. (2019)
    Cerebral dopamine neurotrophic factor (CDNF) has shown therapeutic potential in rodent and non-human primate models of Parkinson's disease by protecting the dopamine neurons from degeneration and even restoring their phenotype and function. Previously, neurorestorative efficacy of CDNF in the 6-hydroxydopamine (6-OHDA) model of Parkinson's disease as well as diffusion of the protein in the striatum (STR) has been demonstrated and studied. Here, experiments were performed to characterize the diffusion and transport of supra-nigral CDNF in non-lesioned rats. We injected recombinant human CDNF to the substantia nigra (SN) of naive male Wistar rats and analyzed the brains 2, 6, and 24 h after injections. We performed immunohistochemical stainings using an antibody specific to human CDNF and radioactivity measurements after injecting iodinated CDNF. Unlike the previously reported striatonigral retrograde transport seen after striatal injection, active anterograde transport of CDNF to the STR could not be detected after nigral injection. There was, however, clear diffusion of CDNF to the brain areas surrounding the SN, and CDNF colocalized with tyrosine hydroxylase (TH)-positive neurons. Overall, our results provide insight on how CDNF injected to the SN may act in this region of the brain.
  • Li, Xiaodong; Sammaljarvi, Juuso; Meng, Shuo; Liu, Longcheng; Siitari-Kauppi, Marja; Martin, Andrew (2022)
    Three cationic tracers, Sr2+, Co2+ and Cs+ were tested with a modified electromigration device by applying 2V, 3V and 4V voltage gradients over an intact Grimsel granodiorite rock sample. An ideal plug-flow model and an advection-dispersion model were applied to analyze the breakthrough curves. Matrix characterization by C-14-PMMA autoradiography and scanning electron microscopy showed that in the centimeter scale of Grimsel granodiorite rock, the interconnected matrix porosity forms a well-connected network for diffusion. Micrometer-scale fissures are transecting biotite and chlorite minerals, indicating sorption of the studied cations. The ideal plug-flow model indicated that the effective diffusion coefficients (D-e values) for Sr2+, Co2+ and Cs+ tracer ions within the Grimsel granodiorite rock were 3.20 x 10(-13) m(2)/s, 1.23 x 10(-13) m(2)/s and 2.25 x 10(-12) m(2)/s, respectively. D-e values were also derived from the advection-dispersion model, from which 2.86 x 10(-13) m(2)/s, 1.35 x 10(-13) m(2)/s and 2.26 x 10(-12) m(2)/s were calculated. The diffusion speed for the tracers was in the sequence of Cs+ > Sr2+ > Co2+ that is in the same sequence as their diffusion in diluted water. The distribution coefficients (K-d values) calculated from the models covered the range of two magnitudes (from 10(-7) m(3)/kg to 10(-5) m(3)/kg). The result indicated that the sorption process of the studied elements did not reach equilibrium during the electromigration process, mainly due to the too much acceleration of the migration speed by the voltage gradients applied over the rock sample.
  • Turunen, Tiina (Helsingfors universitet, 2016)
    Posterior eye segment diseases, such as age-related macular degeneration, are leading causes of preventable visual impairment in the developed countries. Direct intravitreal injections are currently routinely used to deliver therapeutic agents most efficiently to posterior eye segment. Regular injections can however cause ocular complications and some drugs may also be toxic to ocular tissues at high local concentrations of free drug. Different nano-sized particulate systems have been extensively studied as possible drug delivery systems for intravitreal administration offering sustained, local drug action with controlled release. The vitreous gel can form a barrier for diffusion of particles due to its macromolecular structure and composition. Furthermore, ageing and different disease states cause changes in the vitreous structure possibly resulting in shift in the intravitreal movement of particulate systems. In the literature part of this Master's thesis ocular drug delivery is reviewed with main focus on drug targeting in the posterior eye segment. In the experimental work liposomes with different lipid compositions and surface charges were prepared as model particulate systems to evaluate the intravitreal diffusion of nanoparticles with confocal microscope. Furthermore, the influence of aging on the intravitreal diffusion was modeled by enzymatic degradation of the vitreous gel structure. It is discovered that vitreous gel hinders the movement of nanoparticles. Level of hindrance depends on particle's characteristics. 100-200 nm anionic particles move quite freely in the negatively charged vitreous gel. Similarly sized cationic particles are immobile in the vitreous due to electrostatic interactions between surface of the cationic particle and anionic glycosaminoglycans in the vitreous. 1 µm anionic and cationic particles are sterically trapped inside the vitreous meshwork created by the 3-dimensional biopolymer network of the vitreal macromolecules. Vitreous liquefaction increases the diffusion rate of nanoparticles but the clinical impact on ocular pharmacokinetics needs further research.
  • Seppälä, Anniina; Puhakka, Eini; Olin, Markus (2016)
    The swelling and cation exchange properties of montmorillonite are fundamental in a wide range of applications ranging from nanocomposites to catalytic cracking of hydrocarbons. The swelling results from several factors and, though widely studied, information on the effects of a single factor at a time is lacking. In this study, density functional theory (DFT) calculations were used to obtain atomic-level information on the swelling of montmorillonite. Molecular dynamics (MD) was used to investigate the swelling properties of montmorillonites with different layer charges and interlayer cationic compositions. Molecular dynamics calculations, with CLAYFF force field, consider three layer charges (-1.0, -0.66 and -0.5 e per unit cell) arising from octahedral substitutions and interlayer counterions of Na, K and Ca. The swelling curves obtained showed that smaller layer charge results in greater swelling but the type of the interlayer cation also has an effect. The DFT calculations were also seen to predict larger d values than MD. The formation of 1, 2 and 3 water molecular layers in the interlayer spaces was observed. Finally, the data from MD calculations were used to predict the self-diffusion coefficients of interlayer water and cations in different montmorillonites and in general the coefficient increased with increasing water content and with decreasing layer charge.
  • Serri, Carla; Frigione, Mariaenrica; Ruponen, Marika; Urtti, Arto; Borzacchiello, Assunta; Biondi, Marco; Itkonen, Jaakko; Mayol, Laura (2019)
    The purpose of this study was to produce poly(DL-lactic-co-glycolic acid) (PLGA) - based microparticles (MPs), externally decorated with hyaluronic acid (HA). The MPs are intended for intravitreal injections in the treatment of posterior eye segment and have been designed to prolong the release of growth factors into the vitreous body, therefore aiming to increase the time interval between two consecutive injections. The MPs, prepared by a modified double emulsion-solvent evaporation technique and loaded with bovine serum albumins (BSA) and ciliary neurotrophic factor (CNTF), were spherical, with a diameter around 70 mu m and a > 90% encapsulation efficiency. Energy Dispersive Spectroscopy (EDS) outcomes indicated that HA presence in the external aqueous phase of the emulsion did affect the surface properties of MPs. Moreover, poloxamers drastically slowed down MP degradation properties which are, in turn, closely related to their ability to prolong drug release. This is promising for the envisaged application of the produced MPs. Further work will be devoted to optimizing MP formulation with respect to the envisaged intravitreal route of administration.
  • Kajamaa, Anu; Kerosuo, Hannele; Engeström, Yrjö (ESADE Business School, 2011)
  • Perea-Buceta, Jesus; Rico del Cerro, Daniel; Kilpeläinen, Ilkka; Heikkinen, Sami (2021)
    3D iDOSY-HMBC pulse sequences allow the simplification of HMBC data of mixtures via separation in the diffusion domain. The presented methods utilize incorporated DOSY approach, iDOSY, where the existing delays of the basic pulse sequence are utilized for diffusion attenuation. In the simplest form of the proposed 3D iDOSY-HMBC sequences, no extra delays or RF-pulses were required, only two diffusion gradients were added within HMBC polarization transfer delay.
  • Huovila, Miriam (Helsingin yliopisto, 2021)
    This thesis provides a transnational perspective to Lebanese Kurds, particularly regarding their activism and networks related to Rojava, the Kurdish areas in northern Syria. After Armenians, Kurds form the second-largest non-Arab ethnic group in Lebanon. By estimate, around 100,000-150,000 Kurds reside in Lebanon, most of them holding Lebanese citizenship. Since 2011, the war in Syria has led around 20,000 Syrian Kurds to seek shelter in neighboring Lebanon. In January 2018, Turkey launched an attack against the Kurdish forces in Afrin in northern Syria, which resulted in demonstrations in Kurdish communities worldwide, including Lebanon. The objective of the study was to find out whether, and by which means, Kurds in Lebanon try to influence the Rojava issue and whether they are part of some transnational networks related to Rojava. The primary material of the study is based on five semi-structured interviews conducted with the presidents of four Lebanese Kurdish associations and one unaffiliated Syrian Kurd in Beirut in July 2019. The material was transcribed, and thematic content analysis was used as the method to examine the textual data. The theoretical framework of the research is based on the study of transnational activism, transnational networks, and processes of transnational contention. Furthermore, characteristics of transnational practices of ethnic diasporas, transnational impacts on domestic activism, and transnationalism among the Kurds are presented. The substance of the study is also contextualized by an overview of the history of the Kurds in Lebanon, the recent political developments in northern Syria, the Kurdish women’s movement in Rojava, and media coverage regarding the Kurds in Lebanon. The research found out that the limited political opportunities of the Kurds in Lebanon have weakened their chances to influence the Rojava issue. The community is divided along the borderlines of the Kurdish party political, which affects the attitudes of the Kurds towards Rojava. The transnational networks and processes between Lebanese Kurds and Rojava center on the sympathizers of the PKK leader Abdullah Öcalan. Furthermore, transnational women’s organization networks form the most significant transnational links between Lebanese Kurds and Rojava. Two of the Lebanese Kurdish associations have relations with the women’s umbrella organization Congress Star in northern Syria, and their local activism is largely influenced by the women’s movement in the area. Thus, it is argued that the relationship between the Lebanese Kurds and Rojava is reciprocal.
  • Li, Mingwei (Helsingfors universitet, 2016)
    Nanofibrillar cellulose (NFC) can form hydrogels with high water content (> 98 %). It has been studied for drug release, and it has been used as a cell culture matrix, due to its similar structure to extracellular matrix (ECM). In addition it has been found that they has no cytotoxicity. Iontophoresis is the application of an electric current over a defined area for the purpose of enhancing permeation across a membrane for ionized drug species. The aim in the experimental work in this Master's thesis is twofold. First, to find out the suitable drug loading concentrations into NFC hydrogels, which can provide a good release profile, a release study with two model drugs, propranolol and ketoprofen, loaded into three types of NFC hydrogels at three different concentrations, was carried out for this purpose. Second, to see if NFC hydrogels are applicable as a drug reservoir in iontophoretic transdermal drug delivery applications, an iontophoresis study was carried out using porcine ear skin model in vitro for human skin with propranolol loaded into NFC hydrogel of type A. In addition, Stella models were used as an aid to find suitable ways to predict the release and permeation behaviour of models drugs in the abovementioned context. The UPLC results from the release study show for both model drugs, the wt. % released had linear correlation with squareroot of time. At 6 hours, more than 70 wt. % propranolol was released from hydrogel reservoir. For ketoprofen, the release varied between 30 - 87 wt. %, where higher initial loading concentrations produced a decrease in the wt. % released from hydrogel. The iontophoresis study did not show a significant difference between the tested current densities (0.50 mA/cm2; 0.25 mA/cm2) produced on the wt. % of drug released. Simulation models could be run with the mathematical equations for diffusion controlled drug release. In conclusion, the NFC hydrogels show potential as drug reservoir for drug release. Additional experimental data using other types of drug reservoirs should be obtained for a better understanding of the suitability of NFC hydrogels as a drug reservoir in iontophoretic transdermal drug delivery.
  • Luehmann, Tobias; Raatz, Nicole; John, Roger; Lesik, Margarita; Rödiger, Jasper; Portail, Marc; Wildanger, Dominik; Kleissler, Felix; Nordlund, Kai; Zaitsev, Alexander; Roch, Jean-Francois; Tallaire, Alexandre; Meijer, Jan; Pezzagna, Sebastien (2018)
    We present a high throughput and systematic method for the screening of colour centres in diamond with the aim of searching for and reproducibly creating new optical centres down to the single defect level, potentially of interest for a wide range of diamond-based quantum applications. The screening method presented here should, moreover, help to identify some already indexed defects among hundreds in diamond (Zaitsev 2001 Optical Properties of Diamond (Berlin: Springer)) but also some promising defects of a still unknown nature, such as the recently discovered ST1 centre (Lee et al 2013 Nat. Nanotechnol. 8 487; John et al 2017 New J. Phys. 19 053008). We use ion implantation in a systematic manner to implant several chemical elements. Ion implantation has the advantage of addressing single atoms inside the bulk with defined depth and high lateral resolution, but the disadvantage of producing intrinsic defects. The implanted samples are annealed in vacuum at different temperatures (between 600 degrees C and 1600 degrees C with 200 degrees C steps) and fully characterised at each step in order to follow the evolution of the defects: formation, dissociation, diffusion, re-formation and charge state, at the ensemble level and, if possible, at the single centre level. We review the unavoidable ion implantation defects (such as the GR1 and 3H centres), discuss ion channeling and thermal annealing and estimate the diffusion of the vacancies, nitrogen and hydrogen. We use different characterisation methods best suited for our study (from widefield fluorescence down to subdiffraction optical imaging of single centres) and discuss reproducibility issues due to diamond and defect inhomogeneities. Nitrogen is also implanted for reference, taking advantage of the considerable knowledge on NV centres as a versatile sensor in order to retrieve or deduce the conditions and local environment in which the different implanted chemical elements are embedded. We show here the preliminary promising results of a long-term study and focus on the elements O, Mg, Ca, F and P from which fluorescent centres were found.
  • Wang, Xiaoqing (Helsingfors universitet, 2015)
    The thesis starts with a review of literatures related to the topic. In the beginning, several speculations of water holding capacity (WHC) in meat are reviewed, and the joint effects of salt and phosphate addition on WHC are discussed in detail. In addition, the hydrolysis and diffusion of phosphates in meat are also explained. At the end of the literature review, several methods of phosphate measurement are listed and compared. The aim of this research was to determine an effective pattern for phosphate addition in meat processing by studying the dynamics of the phosphate diffusion in relation to their hydrolysis. To address this aim, the meat stripes were subjected to one-dimensional diffusion in TPP and PP brines (with the same salt and P2O5 content), and the phosphate contents of TPP, PP and MP at three diffusion levels (0.625, 1.875 and 3.125 cm) were analysed after 0.5, 2, 6, 24, or 48 h. Thin-layer chromatography (TLC) was used to determine phosphate contents. In addition, the effects of TPP, PP and MP on WHC of the laboratory scale cooked sausages with 0.5 h standing time were compared as a reference for the impact of different phosphates on improving WHC in meat. It was found that areas on the surface of the meat always had the lowest MP content; in addition, in every diffusion level, the initial MP content always decreased first before an increase took place. These results suggested that MP underwent two-way diffusion under the effect of naturally occurring concentration gradient between the meat and the brine, and the TPP/PP hydrolysis generated MP as products. Moreover, PP displayed higher stability then TPP: PP could be observed in the diffusion level as far as at 3.125 cm, and the PP content at 1.875 cm was stable during 2 days’ PP brine diffusion; on the other hand, no TPP was found at distances of 3.125 cm, and only a small amount of TPP was found in 1.875 cm. In addition, the acidic pH accelerated the phosphate diffusion, while the effect of metal ions on diffusivity was unclear. Within the 1.875 cm diffusion distances, which is the common size of meat cube used in meat industry, TPP did not exert a better effect in enhancing or prolonging the stability of PP, and it is possible that the application of PP can fulfil the task of common production schedules. In the sausage WHC test, MP sausages had the worst appearance, which suggests poor protein extraction and hence poor gelling properties. The appearance of PP and TPP sausages were similarly fine, while PP sausages had the best WHC.
  • Mieronkoski, Janiina (Helsingfors universitet, 2017)
    Syftet för min avhandling var att undersöka spridningen och implementeringen av Trappan-modellen i Finland. I min deskriptiva forskning ville jag få svar på följande frågor: 1) I hur stor omfattning används Trappan-modellen bland de som gått Trappan-utbildningen i Finland? 2) Finns det regionala skillnader i användningsgraden av Trappan-modellen? ‒ Skiljer sig regionerna från varandra med tanke på förutsättningarna för användningen av modellen, och i så fall hur? 3) Vilka faktorer verkar främja och vilka hämma användningen av modellen? Materialet för undersökningen samlades in med en elektronisk webbenkät som innehöll både kvantitativa och kvalitativa frågor. Materialet består av 45 enkätsvar av professionella som gått Folkhälsans Trappan-utbildning under åren 2010 till 2016. Undersökningen var en totalundersökning vars svarsfrekvens var 43,3 %. Materialet analyserades genom s.k. blandad metodologi där både kvantitativa och kvalitativa metoder användes. Den kvantitativa analysen bestod av beskrivande univariat statistik, samt bi- och multivariat analys i korstabeller, eftersom materialet var för litet för statistiska sambands-/signifikanstest. I den kvalitativa analysen användes både allmän innehållsanalys med tematiska indelningar och teoristyrd innehållsanalys. Det våldsförebyggande arbetet i Finland utgör kontexten för forskningen. Trappan-modellens spridning och användning analyserades i termer som härrör sig från teorier om diffusion av innovationer och implementering. Bland respondenterna har Trappan-modellen använts i relativt hög grad efter utbildningen. Regionala skillnader både i användningen och i förutsättningarna för användningen av Trappan-modellen verkar förekomma. Faktorer som verkar påverka användningen och implementeringen kunde urskiljas och diskuteras i avhandlingen. Användning av blankett för screening av våld eller förekomsten av handlingsplaner på arbetsplatserna verkar ha ett positivt samband med användning av Trappan. Det våldsförebyggande arbetet behöver vara strukturerat och planerat i regionen och Trappan-arbetarna behöver ha stöd av både förmannen och sina kolleger på sin egen arbetsplats. Modellen verkar inte vara förankrad i de politiska besluten på högre nivå. Denna avhandlings slutsats är att Trappan-modellen inte implementeras effektivt som en ”ensam” insats, utan den behöver utgöra en del av strukturerat och koordinerat våldsförebyggande arbete.