Browsing by Subject "SURFACE"

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  • Brugnara, Y.; Auchmann, R.; Broennimann, S.; Allan, R. J.; Auer, I.; Barriendos, M.; Bergstrom, H.; Bhend, J.; Brazdil, R.; Compo, G. P.; Cornes, R. C.; Dominguez-Castro, F.; van Engelen, A. F. V.; Filipiak, J.; Holopainen, J.; Jourdain, S.; Kunz, M.; Luterbacher, J.; Maugeri, M.; Mercalli, L.; Moberg, A.; Mock, C. J.; Pichard, G.; Reznckova, L.; van der Schrier, G.; Slonosky, V.; Ustrnul, Z.; Valente, M. A.; Wypych, A.; Yin, X. (2015)
    The eruption of Mount Tambora (Indonesia) in April 1815 is the largest documented volcanic eruption in history. It is associated with a large global cooling during the following year, felt particularly in parts of Europe and North America, where the year 1816 became known as the "year without a summer". This paper describes an effort made to collect surface meteorological observations from the early instrumental period, with a focus on the years of and immediately following the eruption (1815-1817). Although the collection aimed in particular at pressure observations, correspondent temperature observations were also recovered. Some of the series had already been described in the literature, but a large part of the data, recently digitised from original weather diaries and contemporary magazines and newspapers, is presented here for the first time. The collection puts together more than 50 sub-daily series from land observatories in Europe and North America and from ships in the tropics. The pressure observations have been corrected for temperature and gravity and reduced to mean sea level. Moreover, an additional statistical correction was applied to take into account common error sources in mercury barometers. To assess the reliability of the corrected data set, the variance in the pressure observations is compared with modern climatologies, and single observations are used for synoptic analyses of three case studies in Europe. All raw observations will be made available to the scientific community in the International Surface Pressure Databank.
  • Eibl, Manuel; Virtanen, Sinikka; Pischel, Felix; Bok, Frank; Lönnrot, Satu; Shaw, Samuel; Huittinen, Nina (2019)
    This study investigates the retention of trivalent actinides (Cm3+) and their lanthanide analogues (Eu3+) on monoclinic zirconia (ZrO2), a solid phase known to form on the zircaloy cladding material surrounding spent nuclear fuel (SNF) rods. Two zirconia solids with varying carbon content were utilized. The influence of carbon impurities on the ZrO2 surface charge was investigated via zeta-potential measurements. Batch data was collected for various Eu3+ concentrations, while the Cm3+ surface speciation was studied on the molecular level with laser spectroscopy (TRLFS). The spectroscopic sorption data was modelled using the Diffuse Double Layer (DDL) model. The ZrO2 surface charge measurements yielded a pH(IEP) of 6 which was influenced by the presence of inorganic and organic carbon species. The pH-dependent uptake of Eu3+ showed a maximum sorption above pH 5.5, with no impact of the carbon concentration. The speciation of the trivalent metal, however, was different in the presence of intrinsic organic carbon in the sample, resulting in the formation of an organic Cm3+-complex on the surface. This ternary complex was absent on the ZrO2 material with low carbon content. Here, the surface speciation was dominated by Cm3+ and Cm3+-hydrolysis complexes which could be well described by our DDL model.
  • Paton, Mark; Harri, Ari-Matti; Vierkens, Oliver; Savijärvi, Hannu (2019)
    As spacecraft missions return ever more data from Mars, additional tools will be required to explore and analyse these datasets efficiently. To streamline research into the atmosphere of Mars, a user-orientated modelling capability is developed that enables automatic initialisation and running of a column model. As a demonstration we utilise the modelling framework to provide additional verification for the University of Helsinki and Finnish Meteorological Institute Mars column model temperature profiles above the height of typical lander meteorological measurements, i.e. above 2 m. We utilise the framework at landing site locations that are well characterised to understand the model's applicability and to identify future opportunities for modifications to the framework. We do this by using the framework to compare the column model to temperature soundings made by the Mars Reconnaissance Orbiter. We find that the column model, without any modification, is able to reproduce the observed lapse rates and average temperatures closely in most cases except for a 20-60 K increase over the northern hemisphere mid-winter. We can reproduce this discrepancy by incorporating an adiabatic heating term into the column model. Fitting of the modified column model to the observations results in estimated maximum downward vertical wind velocities of similar to 10 cm s(-1) at altitudes of 15-20 km over the winter solstice at the VL-1 and VL-2 sites. The approach developed here may possibly provide a way to independently estimate or observe the vertical motion in the Martian atmosphere. However, even though the magnitude of the vertical wind speed appears reasonable, it is not clear at this point how much the atmospheric heating is due to other mechanisms such as advection. We have introduced new application software that can quickly find and display the requested data and can be immediately analysed using the included tools. We have demonstrated the potential of this type of software application with a glimpse into the upper atmosphere of Mars.
  • Daub, Christopher D.; Hänninen, Vesa; Halonen, Lauri (2019)
    We present the results of ab initio molecular dynamics simulations of the solution-air interface of aqueous lithium bromide (LiBr). We find that, in agreement with the experimental data and previous simulation results with empirical polarizable force field models, Br- anions prefer to accumulate just below the first molecular water layer near the interface, whereas Li+ cations remain deeply buried several molecular layers from the interface, even at very high concentration. The separation of ions has a profound effect on the average orientation of water molecules in the vicinity of the interface. We also find that the hydration number of Li+ cations in the center of the slab Na-c,Na-Li+-H2O approximate to 4.7 +/- 0.3, regardless of the salt concentration. This estimate is consistent with the recent experimental neutron scattering data, confirming that results from nonpolarizable empirical models, which consistently predict tetrahedral coordination of Li+ to four solvent molecules, are incorrect. Consequently, disruption of the hydrogen bond network caused by Li+ may be overestimated in nonpolarizable empirical models. Overall, our results suggest that empirical models, in particular nonpolarizable models, may not capture all of the properties of the solution-air interface necessary to fully understand the interfacial chemistry.
  • Enders, Lukas; Casadio, David S.; Aikonen, Santeri; Lenarda, Anna; Wirtanen, Tom; Hu, Tao; Hietala, Sami; Ribeiro, Lucilia S.; Pereira, Manuel Fernando R.; Helaja, Juho (2021)
    A simple "reagent-free" thermal air treatment turns active carbon into a mildly oxidized material with increased quinoidic content that catalytically dehydrogenates saturated N-heterocycles to the corresponding aromatic compounds. Thermal decarboxylation improves the activity of the catalyst further, making it overall more efficient compared to other widely used carbocatalysts such as oxidized carbon nanotubes, graphene oxide and untreated active carbons. The substrate scope covers 1,2,3,4-tetrahydroquinolines (THQ), 1,2,3,4-tetrahydro-beta-carbolines and related N-heterocyclic structures. The developed protocol also successfully dehydrogenates 3-(cyclohexenyl)indoles to 3-aryl indoles, opening a concise transition metal-free approach to (hetero)biaryls as exemplified with the synthesis of the core structure of progesterone receptor antagonist. Hammett plots, deuterium KIE measurements and computations at DFT level suggest that bimolecular hydride transfer mechanism is more likely to operate between THQs and the o-quinoidic sites of the catalyst, than the addition-elimination hemiaminal route. Comparison of structural parameters and catalytic performance of various oxidized carbon materials, prepared by different oxidative and optional post treatments, revealed that quinoidic content and surface area correlate with the obtained yields, while carboxylic acid content has a clear inhibiting effect for the studied oxidative dehydrogenations (ODHs). The carbocatalyst itself can be prepared from inexpensive and environmentally benign starting materials and its catalytic activity can be enhanced by a simple thermal oxidation in air that produces no reagent waste. Furthermore, oxygen is used as terminal oxidant, and the carbocatalyst is recyclable at least six times without a notable loss of activity.
  • Räisänen, Jouni (2017)
    An energy balance decomposition of temperature changes is conducted for idealized transient CO2-only simulations in the fifth phase of the Coupled Model Intercomparison Project. The multimodel global mean warming is dominated by enhanced clear-sky greenhouse effect due to increased CO2 and water vapour, but other components of the energy balance substantially modify the geographical and seasonal patterns of the change. Changes in the net surface energy flux are important over the oceans, being especially crucial for the muted warming over the northern North Atlantic and for the seasonal cycle of warming over the Arctic Ocean. Changes in atmospheric energy flux convergence tend to smooth the gradients of temperature change and reduce its land-sea contrast, but they also amplify the seasonal cycle of warming in northern North America and Eurasia. The three most important terms for intermodel differences in warming are the changes in the clear-sky greenhouse effect, clouds, and the net surface energy flux, making the largest contribution to the standard deviation of annual mean temperature change in 34, 29 and 20 % of the world, respectively. Changes in atmospheric energy flux convergence mostly damp intermodel variations of temperature change especially over the oceans. However, the opposite is true for example in Greenland and Antarctica, where the warming appears to be substantially controlled by heat transport from the surrounding sea areas.
  • Jonassen, Marius; Välisuo, Ilona; Vihma, Timo; Uotila, Petteri; Makshtas, Alexander; Launiainen, Jouko (2019)
    Surface layer and upper-air in situ observations from two research vessel cruises and an ice station in the Weddell Sea from 1992 and 1996 are used to validate four current atmospheric reanalysis products: ERA-Interim, CFSR, JRA-55, and MERRA-2. Three of the observation data sets were not available for assimilation, providing a rare opportunity to validate the reanalyses in the otherwise datasparse region of the Antarctic against independent data. All four reanalyses produce 2 m temperatures warmer than the observations, and the biases vary from +2.0 K in CFSR to +2.8 K in MERRA-2. All four reanalyses are generally too warm also higher up in the atmospheric boundary layer (ABL), with biases up to +1.4 K (ERA-Interim). Cloud fractions are relatively poorly reproduced by the reanalyses, MERRA-2 and JRA-55 having the strongest positive and negative biases of about +30 % and -17 %, respectively. Skill scores of the error statistics reveal that ERA-Interim compares generally the most favorably against both the surface layer and the upper-air observations. CFSR compares the second best and JRA-55 and MERRA-2 have the least favorable scores. The ABL warm bias is consistent with previous evaluation studies in high latitudes, where more recent observations have been applied. As the amount of observations has varied depending on the decade, season, and region, the consistency of the warm bias suggests a need to improve the modeling systems, including data assimilation as well as ABL and surface parameterizations.
  • Seppa, Jeremias; Reischl, Bernhard; Sairanen, Hannu; Korpelainen, Virpi; Husu, Hannu; Heinonen, Martti; Raiteri, Paolo; Rohl, Andrew L.; Nordlund, Kai; Lassila, Antti (2017)
    Due to their operation principle atomic force microscopes (AFMs) are sensitive to all factors affecting the detected force between the probe and the sample. Relative humidity is an important and often neglected-both in experiments and simulations-factor in the interaction force between AFM probe and sample in air. This paper describes the humidity control system designed and built for the interferometrically traceable metrology AFM (IT-MAFM) at VTT MIKES. The humidity control is based on circulating the air of the AFM enclosure via dryer and humidifier paths with adjustable flow and mixing ratio of dry and humid air. The design humidity range of the system is 20-60 % rh. Force-distance adhesion studies at humidity levels between 25 % rh and 53 % rh are presented and compared to an atomistic molecular dynamics (MD) simulation. The uncertainty level of the thermal noise method implementation used for force constant calibration of the AFM cantilevers is 10 %, being the dominant component of the interaction force measurement uncertainty. Comparing the simulation and the experiment, the primary uncertainties are related to the nominally 7 nm radius and shape of measurement probe apex, possible wear and contamination, and the atomistic simulation technique details. The interaction forces are of the same order of magnitude in simulation and measurement (5 nN). An elongation of a few nanometres of the water meniscus between probe tip and sample, before its rupture, is seen in simulation upon retraction of the tip in higher humidity. This behaviour is also supported by the presented experimental measurement data but the data is insufficient to conclusively verify the quantitative meniscus elongation.
  • Bakharev, F. L.; Taskinen, J. (2017)
    We study the spectral linear elasticity problem in an unbounded periodic waveguide, which consists of a sequence of identical bounded cells connected by thin ligaments of diameter of order h > 0. The essential spectrum of the problem is known to have band-gap structure. We derive asymptotic formulas for the position of the spectral bands and gaps, as h -> 0.
  • Pihajoki, Pauli; Mannerkoski, Matias; Johansson, Peter H. (2019)
    Interpolation of data represented in curvilinear coordinates and possibly having some non-trivial, typically Riemannian or semi-Riemannian geometry is a ubiquitous task in all of physics. In this work, we present a covariant generalization of the barycentric coordinates and the barycentric interpolation method for Riemannian and semi-Riemannian spaces of arbitrary dimension. We show that our new method preserves the linear accuracy property of barycentric interpolation in a coordinate-invariant sense. In addition, we show how the method can be used to interpolate constrained quantities so that the given constraint is automatically respected. We showcase the method with two astrophysics related examples situated in the curved Kerr space-time. The first problem is interpolating a locally constant vector field, in which case curvature effects are expected to be maximally important. The second example is a general relativistic magnetohydrodynamics simulation of a turbulent accretion flow around a black hole, wherein high intrinsic variability is expected to be at least as important as curvature effects.
  • Bimbo, Luis M.; Sarparanta, Mirkka; Santos, Helder A.; Airaksinen, Anu J.; Makila, Ermei; Laaksonen, Timo; Peltonen, Leena; Lehto, Vesa-Pekka; Hirvonen, Jouni; Salonen, Jarno (AMERICAN CHEMICAL SOCIETY., 2010)
  • Bimbo, Luis M.; Sarparanta, Mirkka; Santos, Helder A.; Airaksinen, Anu J.; Makila, Ermei; Laaksonen, Timo; Peltonen, Leena; Lehto, Vesa-Pekka; Hirvonen, Jouni; Salonen, Jarno (AMERICAN CHEMICAL SOCIETY., 2010)
  • Bowles, N. E.; Snodgrass, C.; Gibbings, A.; Sanchez, J. P.; Arnold, J. A.; Eccleston, P.; Andert, T.; Probst, A.; Naletto, G.; Vandaele, A. C.; de Leon, J.; Nathues, A.; Thomas, I. R.; Thomas, N.; Jorda, L.; Da Deppo, V.; Haack, H.; Green, S. F.; Carry, B.; Hanna, K. L. Donaldson; Jorgensen, J. Leif; Kereszturi, A.; DeMeo, F. E.; Patel, M. R.; Davies, J. K.; Clarke, F.; Kinch, K.; Guilbert-Lepoutre, A.; Agarwal, J.; Rivkin, A. S.; Pravec, P.; Fornasier, S.; Granvik, M.; Jones, R. H.; Murdoch, N.; Joy, K. H.; Pascale, E.; Tecza, M.; Barnes, J. M.; Licandro, J.; Greenhagen, B. T.; Calcutt, S. B.; Marriner, C. M.; Warren, T.; Tosh, I. (2018)
    CASTAway is a mission concept to explore our Solar System's main asteroid belt. Asteroids and comets provide a window into the formation and evolution of our Solar System and the composition of these objects can be inferred from space-based remote sensing using spectroscopic techniques. Variations in composition across the asteroid populations provide a tracer for the dynamical evolution of the Solar System. The mission combines a long-range (point source) telescopic survey of over 10,000 objects, targeted close encounters with 10-20 asteroids and serendipitous searches to constrain the distribution of smaller (e.g. 10 m) size objects into a single concept. With a carefully targeted trajectory that loops through the asteroid belt, CASTAway would provide a comprehensive survey of the main belt at multiple scales. The scientific payload comprises a 50 cm diameter telescope that includes an integrated low-resolution (R = 30-100) spectrometer and visible context imager, a thermal (e.g. 6-16 mu m) imager for use during the flybys, and modified star tracker cameras to detect small (similar to 10 m) asteroids. The CASTAway spacecraft and payload have high levels of technology readiness and are designed to fit within the programmatic and cost caps for a European Space Agency medium class mission, while delivering a significant increase in knowledge of our Solar System. (C) 2017 COSPAR. Published by Elsevier Ltd. All rights reserved.
  • Filppu, Pauliina; Ramanathan, Jayendrakishore Tanjore; Granberg, Kirsi J.; Gucciardo, Erika; Haapasalo, Hannu; Lehti, Kaisa; Nykter, Matti; Le Joncour, Vadim; Laakkonen, Pirjo (2021)
    Glioma stem cells (GSCs) drive propagation and therapeutic resistance of glioblastomas, the most aggressive diffuse brain tumors. However, the molecular mechanisms that maintain the stemness and promote therapy resistance remain poorly understood. Here we report CD109/STAT3 axis as crucial for the maintenance of stemness and tumorigenicity of GSCs and as a mediator of chemoresistance. Mechanistically, CD109 physically interacts with glycoprotein 130 to promote activation of the IL-6/STAT3 pathway in GSCs. Genetic depletion of CD109 abolished the stemness and self-renewal of GSCs and impaired tumorigenicity. Loss of stemness was accompanied with a phenotypic shift of GSCs to more differentiated astrocytic-like cells. Importantly, genetic or pharmacologic targeting of CD109/STAT3 axis sensitized the GSCs to chemotherapy, suggesting that targeting CD109/STAT3 axis has potential to overcome therapy resistance in glioblastoma.
  • Orosz, Zsuzsanna Z.; Bardos, Helga; Shemirani, Amir H.; Debreceni, Ildiko Beke; Lassila, Riitta; Riikonen, Antti S.; Hovinga, Johanna A. Kremer; Seiler, Theo G.; van Dorland, Hendrika A.; Schroeder, Verena; Boda, Zoltan; Nemes, Laszlo; Frueh Eppstein, Beatrice; Nagy, Bence; Facsko, Andrea; Kappelmayer, Janos; Muszbek, Laszlo (2019)
    Cellular factor XIII (cFXIII, FXIII-A(2)), a transglutaminase, has been demonstrated in a few cell types. Its main function is to cross-link proteins by isopeptide bonds. Here, we investigated the presence of cFXIII in cells of human cornea. Tissue sections of the cornea were immunostained for FXIII-A in combination with staining for CD34 antigen or isopeptide cross-links. Isolated corneal keratocytes were also evaluated by immunofluorescent microscopy and flow cytometry. FXIII-A in the corneal stroma was quantified by Western blotting. FXIII-A mRNA was detected by RT-qPCR. The cornea of FXIII-A-deficient patients was evaluated by cornea topography. FXIII-A was detected in 68 +/- 13% of CD34+ keratocytes. Their distribution in the corneal stroma was unequal; they were most abundant in the subepithelial tertile. cFXIII was of cytoplasmic localization. In the stroma, 3.64 ng cFXIII/mg protein was measured. The synthesis of cFXIII by keratocytes was confirmed by RT-qPCR. Isopeptide cross-links were detected above, but not within the corneal stroma. Slight abnormality of the cornea was detected in six out of nine FXIII-A-deficient patients. The presence of cFXIII in human keratocytes was established for the first time. cFXIII might be involved in maintaining the stability of the cornea and in the corneal wound healing process.
  • Odeh, Issam; Arar, Sharif; Al-Hunaiti, Afnan; Sa'aydeh, Hiyam; Hammad, Ghada; Duplissy, Jonathan; Vuollekoski, Henri; Korpela, Antti; Petäjä, Tuukka; Kulmala, Markku; Hussein, Tareq (2017)
    The quality and chemical composition of urban dew collections with dust precipitates without pre-cleaning of the collecting surface WSF (white standard foil) were investigated for 16 out of 20 collected samples with collected volumes ranging from 22 to 230 ml. The collection period was from March to July 2015 at an urban area, Jubaiha, which is located in the northern part of the capital city Amman, Jordan. The obtained results indicated the predominance of Ca2+ and SO42- ions (ratio 2.2: 1) that originated from Saharan soil dust; where the collected samples were alkaline (mean pH = 7.35) with high mineralization (429.22 mg/L) exceeding the previously reported dew values in Amman-Jordan. A relocation of NaCl and to a less extent Mg2+ from sea to land by Saharan wind is indicated by the percent sea-salt fraction calculations (over 100 and 52, respectively). The collected samples exhibited high total organic carbon (TOC) values ranging from 11.86 to 74.60 mg/L, presence of particulate settled material with turbidity ranging from 20.10 to 520.00 NTU, and presence of undesired elements like boron (mean = 1.48 mg/L) that made it different in properties from other dew water collections at clean surfaces, and exceeding the standard limits for drinking water for these parameters set by Jordanian Drinking Water standards (JS286/2015)/WHO standard. The quality of this water is more close to that for raw or agricultural water but if it is meant to be used as potable source of water, at least sand and activated charcoal filters are needed to purify it.
  • Sporre, Moa K.; O'Connor, Ewan J.; Håkansson, Nina; Thoss, Anke; Swietlicki, Erik; Petäjä, Tuukka (2016)
    Cloud retrievals from the Moderate Resolution Imaging Spectroradiometer (MODIS) instruments aboard the satellites Terra and Aqua and the Visible Infrared Imaging Radiometer Suite (VIIRS) instrument aboard the Suomi-NPP satellite are evaluated using a combination of ground-based instruments providing vertical profiles of clouds. The ground-based measurements are obtained from the Atmospheric Radiation Measurement (ARM) programme mobile facility, which was deployed in Hyytiala, Finland, between February and September 2014 for the Biogenic Aerosols - Effects on Clouds and Climate (BAECC) campaign. The satellite cloud parameters cloud top height (CTH) and liquid water path (LWP) are compared with ground-based CTH obtained from a cloud mask created using lidar and radar data and LWP acquired from a multi-channel microwave radiometer. Clouds from all altitudes in the atmosphere are investigated. The clouds are diagnosed as single or multiple layer using the ground-based cloud mask. For single-layer clouds, satellites overestimated CTH by 326 (14 %) on average. When including multilayer clouds, satellites underestimated CTH by on average 169 m (5.8 %). MODIS collection 6 overestimated LWP by on average 13 g m(-2) (11 %). Interestingly, LWP for MODIS collection 5.1 is slightly overestimated by Aqua (4.56 %) but is underestimated by Terra (14.3 %). This underestimation may be attributed to a known issue with a drift in the reflectance bands of the MODIS instrument on Terra. This evaluation indicates that the satellite cloud parameters selected show reasonable agreement with their ground-based counterparts over Finland, with minimal influence from the large solar zenith angle experienced by the satellites in this high-latitude location.
  • Wang, Qingkai; Lu, Peng; Zu, Yongheng; Li, Zhijun; Lepparanta, Matti; Zhang, Guiyong (2019)
    Arctic sea ice concentration (SIC) has been studied extensively using passive microwave (PM) remote sensing. This technology could be used to improve navigation along vessel cruise paths; however, investigations on this topic have been limited. In this study, shipborne photographic observation (P-OBS) of sea ice was conducted using oblique-oriented cameras during the Chinese National Arctic Research Expedition in the summer of 2016. SIC and the areal fractions of open water, melt ponds, and sea ice (A(w), A(p), and A(i), respectively) were determined along the cruise path. The distribution of SIC along the cruise path was U-shaped, and open water accounted for a large proportion of the path. The SIC derived from the commonly used PM algorithms was compared with the moving average (MA) P-OBS SIC, including Bootstrap and NASA Team (NT) algorithms based on Special Sensor Microwave Imager/Sounder (SSMIS) data; and ARTIST sea ice, Bootstrap, Sea Ice Climate Change Initiative, and NASA Team 2 (NT2) algorithms based on Advanced Microwave Scanning Radiometer 2 (AMSR2) data. P-OBS performed better than PM remote sensing at detecting low SIC (<10%). Our results indicate that PM SIC overestimates MA P-OBS SIC at low SIC, but underestimates it when SIC exceeds a turnover point (TP). The presence of melt ponds affected the accuracy of the PM SIC; the PM SIC shifted from an overestimate to an underestimate with increasing A(p), compared with MA P-OBS SIC below the TP, while the underestimation increased above the TP. The PM algorithms were then ranked; SSMIS-NT and AMSR2-NT2 are the best and worst choices for Arctic navigation, respectively.
  • Tanaka, Atsushi; Khakalo, Alexey; Hauru, Lauri; Korpela, Antti; Orelma, Hannes (2018)
    In this study, we investigate the “chemical welding” of paper with the ionic liquid (IL) 1-ethyl-3-methylimidazolium acetate ([EMIM]OAc) using a two-step process. First, the IL is transported into the structure of the paper as a water solution. Then, partial dissolution is achieved by activation with heat (80–95 °C), where the water evaporates and the surfaces of the fibres partially dissolve. The activated paper is washed with water to remove IL, and dried to fuse fibre surfaces into each other. The “chemically welded” paper structure has both elevated dry and wet strength. The treatment conditions can be adjusted to produce both paper-like materials and films. The most severe treatment conditions produce films that are fully transparent and their oxygen and grease barrier properties are excellent. As an all-cellulose material, the “chemically welded” paper is fully biodegradable and is a potential alternative to fossil fuel-based plastics.
  • Veske, Mihkel; Kyritsakis, Andreas; Djurabekova, Flyura; Sjobak, Kyrre Ness; Aabloo, Alvo; Zadin, Vahur (2020)
    We propose a method to directly couple molecular dynamics, the finite element method, and particle-in-cell techniques to simulate metal surface response to high electric fields. We use this method to simulate the evolution of a field-emitting tip under thermal runaway by fully including the three-dimensional space-charge effects. We also present a comparison of the runaway process between two tip geometries of different widths. The results show with high statistical significance that in the case of sufficiently narrow field emitters, the thermal runaway occurs in cycles where intensive neutral evaporation alternates with cooling periods. The comparison with previous works shows that the evaporation rate in the regime of intensive evaporation is sufficient to ignite a plasma arc above the simulated field emitters.