Browsing by Subject "SURFACES"

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  • Hänninen, Vesa; Murdachaew, Garold; Nathanson, Gilbert M.; Gerber, R. Benny; Halonen, Lauri (2018)
    Ab initio molecular dynamics simulations of formic acid (FA) dimer colliding with liquid water at 300 K have been performed using density functional theory. The two energetically lowest FA dimer isomers were collided with a water slab at thermal and high kinetic energies up to 68k(B)T. Our simulations agree with recent experimental observations of nearly a complete uptake of gas-phase FA dimer: the calculated average kinetic energy of the dimers immediately after collision is 5 +/- 4% of the incoming kinetic energy, which compares well with the experimental value of 10%. Simulations support the experimental observation of no delayed desorption of FA dimers following initial adsorption. Our analysis shows that the FA dimer forms hydrogen bonds with surface water molecules, where the hydrogen bond order depends on the dimer structure, such that the most stable isomer possesses fewer FA-water hydrogen bonds than the higher energy isomer. Nevertheless, even the most stable isomer can attach to the surface through one hydrogen bond despite its reduced hydrophilicity. Our simulations further show that the probability of FA dimer dissociation is increased by high collision energies, the dimer undergoes isomerization from the higher energy to the lowest energy isomer, and concerted double-proton transfer occurs between the FA monomers. Interestingly, proton transfer appears to be driven by the release of energy arising from such isomerization, which stimulates those internal vibrational degrees of freedom that overcome the barrier of a proton transfer.
  • Harjumaki, Riina; Zhang, Xue; Nugroho, Robertus Wahyu N.; Farooq, Muhammad; Lou, Yan-Ru; Yliperttula, Marjo; Valle-Delgado, Juan Jose; Osterberg, Monika (2020)
    Transmembrane protein integrins play a key role in cell adhesion. Cell-biomaterial interactions are affected by integrin expression and conformation, which are actively controlled by cells. Although integrin structure and function have been studied in detail, quantitative analyses of integrin-mediated cell-biomaterial interactions are still scarce. Here, we have used atomic force spectroscopy to study how integrin distribution and activation (via intracellular mechanisms in living cells or by divalent cations) affect the interaction of human pluripotent stem cells (WA07) and human hepatocarcinoma cells (HepG2) with promising biomaterials.human recombinant laminin-521 (LN-521) and cellulose nanofibrils (CNF). Cell adhesion to LN-521-coated probes was remarkably influenced by cell viability, divalent cations, and integrin density in WA07 colonies, indicating that specific bonds between LN-521 and activated integrins play a significant role in the interactions between LN-521 and HepG2 and WA07 cells. In contrast, the interactions between CNF and cells were nonspecific and not influenced by cell viability or the presence of divalent cations. These results shed light on the underlying mechanisms of cell adhesion, with direct impact on cell culture and tissue engineering applications.
  • Friman, Mari; Kakko, Leila; Constantin, Camelia; Simojoki, Heli; Andersson, Maria A.; Nagy, Szabolcs; Salonen, Heidi; Andersson, Magnus (2019)
    Bacillus anthracis infecting cattle is usually identified based on the typical symptom: sudden death. Bacillus anthracis causing atypical symptoms may remain undiagnosed and represent a potential occupational health hazard for, that is veterinarians and producers, butchers and tanners. In the year 2004, one case of sudden death in a dairy farm in southern Finland was diagnosed as bovine anthrax. Four years later 2008, an atypical case of anthrax was diagnosed in the same holding. The bull was taken to the Production Animal Hospital of the Faculty of Veterinary Medicine, University of Helsinki because of fever, loss of appetite and a symmetrically swollen scrotal sac. Penicillin treatment cured the fever but not the swollen scrotum. Before the intended therapeutic castration, a punctuate consisting of 10 ml fluid collected into a syringe from the scrotal sac was cultivated on blood agar at 37 degrees C. After 24 hr, an almost pure culture of a completely non-hemolytic Bacillus cereus-like bacteria was obtained. The strain was identified as B. anthracis using Ba-specific primers by the Finnish Food Safety Authority (RUOKAVIRASTO). After the diagnosis, the bull was euthanized and destroyed, the personnel were treated with prophylactic antibiotics and the clinic was disinfected. In this particular case, treatment with water, Virkon S and lime seemed to be effective to eliminate endospores and vegetative cells since no relapses of anthrax have occurred in 10 years. This case is the last reported anthrax case in Finland.
  • Casteras, Jean-Baptiste; Holopainen, Ilkka; Ripoll, Jaime B. (2019)
    We study the asymptotic Dirichlet problem for A-harmonic equations and for the minimal graph equation on a Cartan-Hadamard manifold M whose sectional curvatures are bounded from below and above by certain functions depending on the distance r = d(., o) to a fixed point o is an element of M. We are, in particular, interested in finding optimal (or close to optimal) curvature upper bounds. In the special case of the Laplace-Beltrami equation we are able to solve the asymptotic Dirichlet problem in dimensions n >= 3 if radial sectional curvatures satisfy -(logr(x))(2 (epsilon) over bar)/r(x)(2 ) outside a compact set for some epsilon > (epsilon) over bar > 0. The upper bound is close to optimal since the nonsolvability is known if K >= -1/(2r(x)(2)log r(x)). Our results (in the non-rotationally symmetric case) improve on the previously known case of the quadratically decaying upper bound.
  • Casteras, Jean-Baptiste; Holopainen, Ilkka; Ripoll, Jaime B. (2020)
    We prove the existence of solutions to the asymptotic Plateau problem for hypersurfaces of prescribed mean curvature in Cartan-Hadamard manifolds N. More precisely, given a suitable subset L of the asymptotic boundary of N and a suitable function H on N, we are able to construct a set of locally finite perimeter whose boundary has generalized mean curvature H provided that N satisfies the so-called strict convexity condition and that its sectional curvatures are bounded from above by a negative constant. We also obtain a multiplicity result in low dimensions.
  • Liu, Jingbin; Liang, Xinlian; Hyyppä, Juha; Yu, Xiaowei; Lehtomäki, Matti; Pyörälä, Jiri; Zhu, Lingli; Wang, Yunsheng; Chen, Ruizhi (2017)
    Terrestrial laser scanning has been widely used to analyze the 3D structure of a forest in detail and to generate data at the level of a reference plot for forest inventories without destructive measurements. Multi-scan terrestrial laser scanning is more commonly applied to collect plot-level data so that all of the stems can be detected and analyzed. However, it is necessary to match the point clouds of multiple scans to yield a point cloud with automated processing. Mismatches between datasets will lead to errors during the processing of multi-scan data. Classic registration methods based on flat surfaces cannot be directly applied in forest environments; therefore, artificial reference objects have conventionally been used to assist with scan matching. The use of artificial references requires additional labor and expertise, as well as greatly increasing the cost. In this study, we present an automated processing method for plot-level stem mapping that matches multiple scans without artificial references. In contrast to previous studies, the registration method developed in this study exploits the natural geometric characteristics among a set of tree stems in a plot and combines the point clouds of multiple scans into a unified coordinate system. Integrating multiple scans improves the overall performance of stem mapping in terms of the correctness of tree detection, as well as the bias and the root-mean-square errors of forest attributes such as diameter at breast height and tree height. In addition, the automated processing method makes stem mapping more reliable and consistent among plots, reduces the costs associated with plot-based stem mapping, and enhances the efficiency. (C) 2016 The Authors. Published by Elsevier B.V.
  • Lang, Adam R.; Engelberg, Dirk L.; Walther, Clemens; Weiss, Martin; Bosco, Hauke; Jenkins, Alex; Livens, Francis R.; Law, Gareth T. W. (2019)
    Stainless steels can become contaminated with radionuclides at nuclear sites. Their disposal as radioactive waste would be costly. If the nature of steel contamination could be understood, effective decontamination strategies could be designed and implemented during nuclear site decommissioning in an effort to release the steels from regulatory control. Here, batch uptake experiments have been used to understand Sr and Cs (fission product radionuclides) uptake onto AISI Type 304 stainless steel under conditions representative of spent nuclear fuel storage (alkaline ponds) and PUREX nuclear fuel reprocessing (HNO3). Solution (ICP-MS) and surface measurements (GD-OES depth profiling, TOF-SIMS, and XPS) and kinetic modeling of Sr and Cs removal from solution were used to characterize their uptake onto the steel and define the chemical composition and structure of the passive layer formed on the steel surfaces. Under passivating conditions (when the steel was exposed to solutions representative of alkaline ponds and 3 and 6 M HNO3), Sr and Cs were maintained at the steel surface by sorption/selective incorporation into the Cr-rich passive film. In 12 M HNO3, corrosion and severe intergranular attack led to Sr diffusion into the passive layer and steel bulk. In HNO3, Sr and Cs accumulation was also commensurate with corrosion product (Fe and Cr) readsorption, and in the 12 M HNO3 system, XPS documented the presence of Sr and Cs chromates.
  • Rodriguez, C.; Taminiau, B.; Bouchafa, L.; Romijn, S.; Rajamaki, M. M.; Van Broeck, J.; Delmee, M.; Clercx, C.; Daube, G. (2019)
    Zoonotic transmission of Clostridium difficile has been largely hypothesised to occur after direct or indirect contact with contaminated animal faeces. Recent studies have reported the presence of the bacterium in the natural environment, including in soils and rivers. If C. difficile spores are scattered in the environment, they can easily enter the respiratory tract of dogs, and therefore, dog nasal discharge could be a direct route of transmission not previously investigated. This study reports for the first time the presence of C. difficile in the respiratory tracts of dogs. The bacterium was isolated from 6 (17.1%) out of 35 nasal samples, with a total of 4 positive dogs (19%). C. difficile was recovered from both proximal and distal nasal cavities. All isolates were toxigenic and belonged to PCR- ribotype 014, which is one of the most predominant types in animals and in community- acquired C. difficile infections in recent years. The findings of this study demonstrate that the nasal cavity of dogs is contaminated with toxigenic C. difficile, and therefore, its secretions could be considered as a new route by which bacteria are spread and transmitted.
  • Dominguez-Gutierrez, F. J.; Byggmastar, J.; Nordlund, K.; Djurabekova, F.; von Toussaint, U. (2021)
    In this work, we study the damage in crystalline molybdenum material samples due to neutron bombardment in a primary knock-on atom (PKA) range of 0.5-10 keV at room temperature. We perform classical molecular dynamics (MD) simulations using a previously derived machine learning (ML) interatomic potential based on the Gaussian approximation potential (GAP) framework. We utilize a recently developed software workflow for fingerprinting and visualizing defects in damaged crystal structures to analyze the Mo samples with respect to the formation of point defects during and after a collision cascade. As a benchmark, we report results for the total number of Frenkel pairs (a self-interstitial atom and a single vacancy) formed and atom displacements as a function of the PKA energy. A comparison to results obtained using an embedded atom method (EAM) potential is presented to discuss the advantages and limits of the MD simulations utilizing ML-based potentials. The formation of Frenkel pairs follows a sublinear scaling law as xi ( b ) where b is a fitting parameter and xi = E (PKA)/E (0) with E (0) as a scaling factor. We found that the b = 0.54 for the GAP MD results and b = 0.667 for the EAM simulations. Although the average number of total defects is similar for both methods, the MD results show different atomic geometries for complex point defects, where the formation of crowdions by the GAP potential is closer to the DFT-based expectation. Finally, ion beam mixing results for GAP MD simulations are in a good agreement with experimental mixing efficiency data. This indicates that the modeling of atom relocation in cascades by machine learned potentials is suited to interpret the corresponding experimental findings.
  • Buchs, Gilles; Krasheninnikov, Arkady V.; Ruffieux, Pascal; Groening, Pierangelo; Foster, Adam S.; Nieminen, Risto M.; Groening, Oliver (2007)
  • Hassan, Ghada Ali Mohamed Saber; Forsman, Nina; Wan, Xing; Keurulainen, Leena; Bimbo, Luis M.; Johansson, Leena-Sisko; Sipari, Nina; Yli-Kauhaluoma, Jari Tapani; Zimmermann, Ralf; Stehl, Susanne; Werner, Carsten; Saris, Per E. J.; Österberg, Monika; Moreira, Vânia M. (2019)
    The design of antimicrobial surfaces as integral parts of advanced biomaterials is nowadays a high research priority, as the accumulation of microorganisms on surfaces inflicts substantial costs on the health and industry sectors. At present, there is a growing interest in designing functional materials from polymers abundant in nature, such as cellulose, that combine sustainability with outstanding mechanical properties and economic production. There is also the need to find suitable replacements for antimicrobial silver-based agents due to environmental toxicity and spread of resistance to metal antimicrobials. Herein we report the unprecedented decoration of cellulose nanofibril (CNF) films with dehydroabietylamine 1 (CNF-CMC-1), to give an innovative contact-active surface active against Gram-positive and Gram-negative bacteria including the methicillin-resistant S. aureus MRSA14TK301, with low potential to spread resistance and good biocompatibility, all achieved with low surface coverage. CNF-CMC-1 was particularly effective against S. aureus ATCC12528, causing virtually complete reduction of the total cells from 10(5) colony forming units (CFU)/mL bacterial suspensions, after 24 h of contact. This gentle chemical modification of the surface of CNF fully retained the beneficial properties of the original film, including moisture buffering and strength, relevant in many potential applications. Our originally designed surface represents a new class of ecofriendly biomaterials that optimizes the performance of CNF by adding antimicrobial properties without the need for environmentally toxic silver.
  • Wang, Xiaobin; Muinonen, Karri (Astronomical Society of the Pacific, 2018)
    Astronomical Society of the Pacific Conference Series
    The ground-based photometric observations of asteroids still is the main source to understand their basic physical properties, even though some space mission and space-based instruments have been applied in physical studies of asteroids. Owing to developments on scattering theories and 3D shape models of asteroid, we can carry out determination for basic physical parameters of asteroids from the photometric data. Here, we present photometric observations for some selected asteroids and light inversion results for these asteroids. In detail, they are: (1) To determine photometric phase functions of asteroids (107)Camilla and (106) Dione considering an ellipsoid shape and a cellinoid shape respectively; and (2) To inverse convex shape of main-belt slow rotating asteroids (168) Sibylla and (346)Hermentaria and a near Earth asteroid (3200) Phaethon. Based on derived photometric phase functions, the geometric albedo, and even rough taxonomic classification of asteroids are inferred. With the virtual photometry Monta Carlo method, the uncertainties of spin parameters of selected asteroids were compared.
  • Lopez-Cazalilla, A.; Djurabekova, F.; Ilinov, A.; Fridlund, C.; Nordlund, K. (2020)
    Patterns on sand generated by blowing winds are one of the most commonly seen phenomena driven by such a self-organization process, as has been observed at the nanoscale after ion irradiation. The origins of this effect have been under debate for decades. Now, a new methodology allows to simulate directly the ripple formation by high-fluence ion-irradiation. Since this approach does not pre-assume a mechanism to trigger self-organization, it can provide answers to the origin of the ripple formation mechanism. The surface atom displacement and a pile-up effect are the driving force of ripple formation, analogously to the macroscopic one. IMPACT STATEMENT The presented model allows to follow the ripple formation and propagation in different steps, at the atomic level, for the first time under low irradiation energies.
  • Pulkkinen, Petri M. S.; Hassinen, Jukka; Ras, Robin H. A.; Tenhu, Heikki (2014)
  • Summa, M.; Henttonen, H.; Maunula, L. (2018)
    Human noroviruses (HuNoVs) are one of the leading global causes of diarrhoeal diseases and are transmitted mainly from person to person but also through contaminated food, water and fomites. The possible zoonotic nature of NoVs has occasionally been discussed, although the viruses are generally considered to be host-species-specific. We investigated whether wild birds and rodents could serve as carriers of HuNoVs, thereby transmitting the virus to humans directly or indirectly by contaminating foods. All samples, 115 avian and 100 rat faeces collected in springs 2009-2013 from dump sites, and 85 faeces from yellow-necked mice trapped in late autumn 2008 and 2009 after the rodents entered human settlements due to the first night frosts, were screened for HuNoV using real-time reverse transcription PCR. HuNoVs were detected in 31 (27%) faecal samples of wild birds, in two (2%) faecal samples of rats and in no samples of mice. Most (25) of the positive bird samples and both rat samples contained genogroup II, and six positive bird samples contained genogroup I HuNoV. The avian species shedding faeces containing HuNoVs were identified as gulls and crows using DNA barcoding. Our results show that wildlife, birds and rats in particular, is capable of spreading HuNoVs in the environment.
  • Iwaniec, Tadeusz; Onninen, Jani (2017)
    Let X; Y subset of R-2 be topologically equivalent bounded Lipschitz domains. We prove that weak and strong limits of homeomorphisms h: X (onto)-> Y in the Sobolev space W-1,W-p (X, R-2), p >= 2; are the same. As an application, we establish the existence of 2D-traction free minimal deformations for fairly general energy integrals.
  • Casteras, Jean-Baptiste; Holopainen, Ilkka; Ripoll, Jaime B. (2017)
    We study the Dirichlet problem at infinity on a Cartan-Hadamard manifold M of dimension n 2 for a large class of operators containing, in particular, the p-Laplacian and the minimal graph operator. We extend several existence results obtained for the p-Laplacian to our class of operators. As an application of our main result, we prove the solvability of the asymptotic Dirichlet problem for the minimal graph equation for any continuous boundary data on a (possibly non rotationally symmetric) manifold whose sectional curvatures are allowed to decay to 0 quadratically.
  • Holman, Sean; Uhlmann, Gunther (2018)
    We study the microlocal properties of the geodesic X-ray transform X on a manifold with boundary allowing the presence of conjugate points. Assuming that there are no self-intersecting geodesics and all conjugate pairs are nonsingular we show that the normal operator N = X-t o X can be decomposed as the sum of a pseudodifferential operator of order -1 and a sum of Fourier integral operators. We also apply this decomposition to prove inversion of X is only mildly ill-posed when all conjugate points are of order 1, and a certain graph condition is satisfied, in dimension three or higher.
  • Tang, Jincheng; Gu, Yong; Zhang, Hongbo; Wu, Liang; Xu, Yun; Mao, Jiannan; Xin, Tianwen; Ye, Tingjun; Deng, Lianfu; Cui, Wenguo; Santos, Hélder A.; Chen, Liang (2019)
    Biomimetic scaffolds have been extensively studied for guiding osteogenesis through structural cues. Inspired by the natural bone growth process, we have employed a hierarchical outer-inner dual reinforcing strategy, which relies on the interfacial ionic bond interaction between amine/calcium and carboxyl group, to build a nanofiber/particle dual strengthened hierarchical silk fibroin scaffold. The scaffold can provide applicable form of osteogenic structural cue and mimic the natural bone forming process. Owing to the active interaction between compositions located in the outer pore space and the inner pore wall, the scaffold has over 4 times improvement on mechanical property, followed by significant alteration on cell-scaffold interaction pattern, demonstrated by over 2 times’ elevation on the spreading area and enhanced osteogenic activity potentially involving activities of integrin, Vinculin and Yes-associated protein (YAP). In vivo performance of the scaffold identified the inherent osteogenic effect of structural cue, which promotes rapid and uniform regeneration. Overall, the hierarchical scaffold is promising in promoting uniform bone regeneration through its specific structural cue endowed by its micro-nano construction.
  • Wilkman, Olli; Gritsevich, Maria; Zubko, Nataliya; Peltoniemi, Jouni I.; Muinonen, Karri (2016)
    We have performed laboratory measurements of the bidirectional reflectance factor (BRF) of a sample of dark volcanic sand. The measurements were carried out with three different treatments of the sample to produce different porosity and roughness characteristics. We model the measured BRF with a semi-numerical scattering model for particulate media, meant especially for dark planetary regoliths. We compare the BRF in two different spectral bands, 500-600 nm and 800-900 nm. The particulate medium (PM). scattering model is found to fit the measured data well, with a phase function representing the differences between the spectral bands. The interpretation of the physical parameters of the PM model is qualitatively sound, but remains somewhat uncertain due in part to the difficulty of characterizing the measured sample. (C) 2016 Elsevier Ltd. All rights reserved.