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Sample records for stronger neutral nucleation

  1. Insight into acid-base nucleation experiments by comparison of the chemical composition of positive, negative, and neutral clusters.

    Science.gov (United States)

    Bianchi, Federico; Praplan, Arnaud P; Sarnela, Nina; Dommen, Josef; Kürten, Andreas; Ortega, Ismael K; Schobesberger, Siegfried; Junninen, Heikki; Simon, Mario; Tröstl, Jasmin; Jokinen, Tuija; Sipilä, Mikko; Adamov, Alexey; Amorim, Antonio; Almeida, Joao; Breitenlechner, Martin; Duplissy, Jonathan; Ehrhart, Sebastian; Flagan, Richard C; Franchin, Alessandro; Hakala, Jani; Hansel, Armin; Heinritzi, Martin; Kangasluoma, Juha; Keskinen, Helmi; Kim, Jaeseok; Kirkby, Jasper; Laaksonen, Ari; Lawler, Michael J; Lehtipalo, Katrianne; Leiminger, Markus; Makhmutov, Vladimir; Mathot, Serge; Onnela, Antti; Petäjä, Tuukka; Riccobono, Francesco; Rissanen, Matti P; Rondo, Linda; Tomé, António; Virtanen, Annele; Viisanen, Yrjö; Williamson, Christina; Wimmer, Daniela; Winkler, Paul M; Ye, Penglin; Curtius, Joachim; Kulmala, Markku; Worsnop, Douglas R; Donahue, Neil M; Baltensperger, Urs

    2014-12-02

    We investigated the nucleation of sulfuric acid together with two bases (ammonia and dimethylamine), at the CLOUD chamber at CERN. The chemical composition of positive, negative, and neutral clusters was studied using three Atmospheric Pressure interface-Time Of Flight (APi-TOF) mass spectrometers: two were operated in positive and negative mode to detect the chamber ions, while the third was equipped with a nitrate ion chemical ionization source allowing detection of neutral clusters. Taking into account the possible fragmentation that can happen during the charging of the ions or within the first stage of the mass spectrometer, the cluster formation proceeded via essentially one-to-one acid-base addition for all of the clusters, independent of the type of the base. For the positive clusters, the charge is carried by one excess protonated base, while for the negative clusters it is carried by a deprotonated acid; the same is true for the neutral clusters after these have been ionized. During the experiments involving sulfuric acid and dimethylamine, it was possible to study the appearance time for all the clusters (positive, negative, and neutral). It appeared that, after the formation of the clusters containing three molecules of sulfuric acid, the clusters grow at a similar speed, independent of their charge. The growth rate is then probably limited by the arrival rate of sulfuric acid or cluster-cluster collision.

  2. Amines are likely to enhance neutral and ion-induced sulfuric acid-water nucleation in the atmosphere more effectively than ammonia

    Directory of Open Access Journals (Sweden)

    T. Kurtén

    2008-07-01

    Full Text Available We have studied the structure and formation thermodynamics of dimer clusters containing H2SO4 or HSO4 together with ammonia and seven different amines possibly present in the atmosphere, using the high-level ab initio methods RI-MP2 and RI-CC2. As expected from e.g. proton affinity data, the binding of all studied amine-H2SO4 complexes is significantly stronger than that of NH3•H2SO4, while most amine-HSO4 complexes are only somewhat more strongly bound than NH3•HSO4. Further calculations on larger cluster structures containing dimethylamine or ammonia together with two H2SO4 molecules or one H2SO4 molecule and one HSO4 ion demonstrate that amines, unlike ammonia, significantly assist the growth of not only neutral but also ionic clusters along the H2SO4 co-ordinate. A sensitivity analysis indicates that the difference in complexation free energies for amine- and ammonia-containing clusters is large enough to overcome the mass-balance effect caused by the fact that the concentration of amines in the atmosphere is probably 2 or 3 orders of magnitude lower than that of ammonia. This implies that amines might be more important than ammonia in enhancing neutral and especially ion-induced sulfuric acid-water nucleation in the atmosphere.

  3. New Parameterizations for Neutral and Ion-Induced Sulfuric Acid-Water Particle Formation in Nucleation and Kinetic Regimes

    Science.gov (United States)

    Määttänen, Anni; Merikanto, Joonas; Henschel, Henning; Duplissy, Jonathan; Makkonen, Risto; Ortega, Ismael K.; Vehkamäki, Hanna

    2018-01-01

    We have developed new parameterizations of electrically neutral homogeneous and ion-induced sulfuric acid-water particle formation for large ranges of environmental conditions, based on an improved model that has been validated against a particle formation rate data set produced by Cosmics Leaving OUtdoor Droplets (CLOUD) experiments at European Organization for Nuclear Research (CERN). The model uses a thermodynamically consistent version of the Classical Nucleation Theory normalized using quantum chemical data. Unlike the earlier parameterizations for H2SO4-H2O nucleation, the model is applicable to extreme dry conditions where the one-component sulfuric acid limit is approached. Parameterizations are presented for the critical cluster sulfuric acid mole fraction, the critical cluster radius, the total number of molecules in the critical cluster, and the particle formation rate. If the critical cluster contains only one sulfuric acid molecule, a simple formula for kinetic particle formation can be used: this threshold has also been parameterized. The parameterization for electrically neutral particle formation is valid for the following ranges: temperatures 165-400 K, sulfuric acid concentrations 104-1013 cm-3, and relative humidities 0.001-100%. The ion-induced particle formation parameterization is valid for temperatures 195-400 K, sulfuric acid concentrations 104-1016 cm-3, and relative humidities 10-5-100%. The new parameterizations are thus applicable for the full range of conditions in the Earth's atmosphere relevant for binary sulfuric acid-water particle formation, including both tropospheric and stratospheric conditions. They are also suitable for describing particle formation in the atmosphere of Venus.

  4. Stronger synergies

    CERN Document Server

    Antonella Del Rosso

    2012-01-01

    CERN was founded 58 years ago under the auspices of UNESCO. Since then, both organisations have grown to become world leaders in their respective fields. The links between the two have always existed but today they are even stronger, with new projects under way to develop a more efficient way of exchanging information and devise a common strategy on topics of mutual interest.   CERN and UNESCO are a perfect example of natural partners: their common field is science and education is one of the pillars on which both are built. Historically, they share a common heritage. Both UNESCO and CERN were born of the desire to use scientific cooperation to rebuild peace and security in the aftermath of the Second World War. "Recently, building on our common roots and in close collaboration with UNESCO, we have been developing more structured links to ensure the continuity of the actions taken over the years," says Maurizio Bona, who is in charge of CERN relations with international orga...

  5. Atmospheric nucleation: highlights of the EUCAARI project and future directions

    Directory of Open Access Journals (Sweden)

    V.-M. Kerminen

    2010-11-01

    Full Text Available Within the project EUCAARI (European Integrated project on Aerosol Cloud Climate and Air Quality interactions, atmospheric nucleation was studied by (i developing and testing new air ion and cluster spectrometers, (ii conducting homogeneous nucleation experiments for sulphate and organic systems in the laboratory, (iii investigating atmospheric nucleation mechanism under field conditions, and (iv applying new theoretical and modelling tools for data interpretation and development of parameterisations. The current paper provides a synthesis of the obtained results and identifies the remaining major knowledge gaps related to atmospheric nucleation. The most important technical achievement of the project was the development of new instruments for measuring sub-3 nm particle populations, along with the extensive application of these instruments in both the laboratory and the field. All the results obtained during EUCAARI indicate that sulphuric acid plays a central role in atmospheric nucleation. However, also vapours other than sulphuric acid are needed to explain the nucleation and the subsequent growth processes, at least in continental boundary layers. Candidate vapours in this respect are some organic compounds, ammonia, and especially amines. Both our field and laboratory data demonstrate that the nucleation rate scales to the first or second power of the nucleating vapour concentration(s. This agrees with the few earlier field observations, but is in stark contrast with classical thermodynamic nucleation theories. The average formation rates of 2-nm particles were found to vary by almost two orders of magnitude between the different EUCAARI sites, whereas the formation rates of charged 2-nm particles varied very little between the sites. Overall, our observations are indicative of frequent, yet moderate, ion-induced nucleation usually outweighed by much stronger neutral nucleation events in the continental lower troposphere. The most concrete

  6. Synthetic Hemozoin (β-Hematin) Crystals Nucleate at the Surface of Neutral Lipid Droplets that Control Their Sizes

    Science.gov (United States)

    Ambele, Melvin A.; Sewell, B. Trevor; Cummings, Franscious R.; Smith, Peter J.; Egan, Timothy J.

    2013-01-01

    Emulsions of monopalmitoylglycerol (MPG) and of a neutral lipid blend (NLB), consisting of MPG, monostearoylglycerol, dipalmitoylglycerol, dioleoylglycerol and dilineoylglycerol (4:2:1:1:1), the composition associated with hemozoin from the malaria parasite Plasmodium falciparum, have been used to mediate the formation of β-hematin microcrystals. Transmission electron microscopy (TEM), electron diffraction and electron spectroscopic imaging/electron energy loss spectroscopy (ESI/EELS) have been used to characterize both the lipid emulsion and β-hematin crystals. The latter have been compared with β-hematin formed at a pentanol/aqueous interface and with hemozoin both within P. falciparum parasites and extracted from the parasites. When lipid and ferriprotoporphyrin IX solutions in 1:9 v/v acetone/methanol were thoroughly pre-mixed either using an extruder or ultrasound, β-hematin crystals were found formed in intimate association with the lipid droplets. These crystals resembled hemozoin crystals, with prominent {100} faces. Lattice fringes in TEM indicated that these faces made contact with the lipid surface. The average length of these crystals was 0.62 times the average diameter of NLB droplets and their size distributions were statistically equivalent after 10 min incubation, suggesting that the lipid droplets also controlled the sizes of the crystals. This most closely resembles hemozoin formation in the helminth worm Schistosoma mansoni, while in P. falciparum, crystal formation appears to be associated with the much more gently curved digestive vacuole membrane which apparently leads to formation of much larger hemozoin crystals, similar to those formed at the flat pentanol-water interface. PMID:24244110

  7. Dynamics of homogeneous nucleation

    DEFF Research Database (Denmark)

    Toxværd, Søren

    2015-01-01

    The classical nucleation theory for homogeneous nucleation is formulated as a theory for a density fluctuation in a supersaturated gas at a given temperature. But molecular dynamics simulations reveal that it is small cold clusters which initiates the nucleation. The temperature in the nucleating...

  8. Prospects for stronger calandria tubes

    International Nuclear Information System (INIS)

    Ells, C.E.; Coleman, C.E.; Hosbons, R.R.; Ibrahim, E.F.; Doubt, G.L.

    1990-12-01

    The CANDU calandria tubes, made of seam welded and annealed Zircaloy-2, have given exemplary service in-reactor. Although not designed as a system pressure containment, calandria tubes may remain intact even in the face of pressure tube rupture. One such incident at Pickering Unit 2 demonstrated the economic advantage of such an outcome, and a case can be made for increasing the probability that other calandria tubes would perform in a similar fashion. Various methods of obtaining stronger calandria tubes are available, and reviewed here. When the tubes are internally pressurized, the weld is the weak section of the tube. Increasing the oxygen concentration in the starting sheet, and thickening the weld, are promising routes to a stronger tube

  9. Principles of nucleation theory

    International Nuclear Information System (INIS)

    Clement, C.F.; Wood, M.H.

    1980-01-01

    The nucleation of small stable species is described in the problem of void growth by discrete rate equations. When gas is being produced the problem reduces to one of calculating the incubation dose for the gas bubble to void transition. A general expression for the steady state nucleation rate is derived for the case when voids are formed by vacancy fluctuations which enable an effective nucleation barrier to be crossed. (author)

  10. The role of ammonia in sulfuric acid ion induced nucleation

    Directory of Open Access Journals (Sweden)

    I. K. Ortega

    2008-06-01

    Full Text Available We have developed a new multi-step strategy for quantum chemical calculations on atmospherically relevant cluster structures that makes calculation for large clusters affordable with a good accuracy-to-computational effort ratio. We have applied this strategy to evaluate the relevance of ternary ion induced nucleation; we have also performed calculations for neutral ternary nucleation for comparison. The results for neutral ternary nucleation agree with previous results, and confirm the important role of ammonia in enhancing the growth of sulfuric acid clusters. On the other hand, we have found that ammonia does not enhance the growth of ionic sulfuric acid clusters. The results also confirm that ion-induced nucleation is a barrierless process at high altitudes, but at ground level there exists a barrier due to the presence of a local minimum on the free energy surface.

  11. Dimers in nucleating vapors

    Science.gov (United States)

    Lushnikov, A. A.; Kulmala, M.

    1998-09-01

    The dimer stage of nucleation may affect considerably the rate of the nucleation process at high supersaturation of the nucleating vapor. Assuming that the dimer formation limits the nucleation rate, the kinetics of the particle formation-growth process is studied starting with the definition of dimers as bound states of two associating molecules. The partition function of dimer states is calculated by summing the Boltzmann factor over all classical bound states, and the equilibrium population of dimers is found for two types of intermolecular forces: the Lennard-Jones (LJ) and rectangular well+hard core (RW) potentials. The principle of detailed balance is used for calculating the evaporation rate of dimers. The kinetics of the particle formation-growth process is then investigated under the assumption that the trimers are stable with respect to evaporation and that the condensation rate is a power function of the particle mass. If the power exponent λ=n/(n+1) (n is a non-negative integer), the kinetics of the process is described by a finite set of moments of particle mass distribution. When the characteristic time of the particle formation by nucleation is much shorter than that of the condensational growth, n+2 universal functions of a nondimensional time define the kinetic process. These functions are calculated for λ=2/3 (gas-to-particle conversion in the free molecular regime) and λ=1/2 (formation of islands on surfaces).

  12. Critical radius for nucleation

    Energy Technology Data Exchange (ETDEWEB)

    Alexiades, V.; Solomon, A.D.

    1986-04-01

    The free energy of formation and the critical radius for homogeneous nucleation of a spherical nucleus in supercooled liquid, at given temperature and ambient pressure, are determined, taking fully into account surface area, curvature, and pressure effects. The specific heats and densities of the two phases are allowed to be different and all thermophysical properties are temperature dependent. In the simple case in which classical nucleation theory is valid, the results predict a critical radius of about 40% larger than the classical value, and an activation energy barrier of almost three times larger than the classical value. 8 refs.

  13. Return to nucleate boiling

    International Nuclear Information System (INIS)

    Shumway, R.W.

    1985-01-01

    This paper presents a collection of TMIN (temperature of return to nucleate boiling) correlations, evaluates them under several conditions, and compares them with a wide range of data. Purpose is to obtain the best one for use in a water reactor safety computer simulator known as TRAC-B. Return to nucleate boiling can occur in a reactor accident at either high or low pressure and flow rates. Most of the correlations yield unrealistic results under some conditions. A new correlation is proposed which overcomes many of the deficiencies

  14. Nonequilibrium thermodynamics of nucleation

    NARCIS (Netherlands)

    Schweizer, M.; Sagis, L.M.C.

    2014-01-01

    We present a novel approach to nucleation processes based on the GENERIC framework (general equation for the nonequilibrium reversible-irreversible coupling). Solely based on the GENERIC structure of time-evolution equations and thermodynamic consistency arguments of exchange processes between a

  15. Acid-base chemical reaction model for nucleation rates in the polluted atmospheric boundary layer.

    Science.gov (United States)

    Chen, Modi; Titcombe, Mari; Jiang, Jingkun; Jen, Coty; Kuang, Chongai; Fischer, Marc L; Eisele, Fred L; Siepmann, J Ilja; Hanson, David R; Zhao, Jun; McMurry, Peter H

    2012-11-13

    Climate models show that particles formed by nucleation can affect cloud cover and, therefore, the earth's radiation budget. Measurements worldwide show that nucleation rates in the atmospheric boundary layer are positively correlated with concentrations of sulfuric acid vapor. However, current nucleation theories do not correctly predict either the observed nucleation rates or their functional dependence on sulfuric acid concentrations. This paper develops an alternative approach for modeling nucleation rates, based on a sequence of acid-base reactions. The model uses empirical estimates of sulfuric acid evaporation rates obtained from new measurements of neutral molecular clusters. The model predicts that nucleation rates equal the sulfuric acid vapor collision rate times a prefactor that is less than unity and that depends on the concentrations of basic gaseous compounds and preexisting particles. Predicted nucleation rates and their dependence on sulfuric acid vapor concentrations are in reasonable agreement with measurements from Mexico City and Atlanta.

  16. Surface Nanobubbles Nucleate Microdroplets

    OpenAIRE

    Zhang , Xuehua; Lhuissier , Henri; Sun , Chao; Lohse , Detlef

    2014-01-01

    International audience; When a hydrophobic solid is in contact with water, surface nanobubbles often form at the interface. They have a lifetime many orders of magnitude longer than expected. Here, we show that they even withstand a temperature increase to temperatures close to the boiling point of bulk water; i.e., they do not nucleate larger bubbles (" superstability "). On the contrary, when the vapor-liquid contact line passes a nanobubble, a liquid film remains around it, which, after pi...

  17. Overview: Nucleation of clathrate hydrates

    Science.gov (United States)

    Warrier, Pramod; Khan, M. Naveed; Srivastava, Vishal; Maupin, C. Mark; Koh, Carolyn A.

    2016-12-01

    Molecular level knowledge of nucleation and growth of clathrate hydrates is of importance for advancing fundamental understanding on the nature of water and hydrophobic hydrate formers, and their interactions that result in the formation of ice-like solids at temperatures higher than the ice-point. The stochastic nature and the inability to probe the small length and time scales associated with the nucleation process make it very difficult to experimentally determine the molecular level changes that lead to the nucleation event. Conversely, for this reason, there have been increasing efforts to obtain this information using molecular simulations. Accurate knowledge of how and when hydrate structures nucleate will be tremendously beneficial for the development of sustainable hydrate management strategies in oil and gas flowlines, as well as for their application in energy storage and recovery, gas separation, carbon sequestration, seawater desalination, and refrigeration. This article reviews various aspects of hydrate nucleation. First, properties of supercooled water and ice nucleation are reviewed briefly due to their apparent similarity to hydrates. Hydrate nucleation is then reviewed starting from macroscopic observations as obtained from experiments in laboratories and operations in industries, followed by various hydrate nucleation hypotheses and hydrate nucleation driving force calculations based on the classical nucleation theory. Finally, molecular simulations on hydrate nucleation are discussed in detail followed by potential future research directions.

  18. Surface Nanobubbles Nucleate Microdroplets

    Science.gov (United States)

    Zhang, Xuehua; Lhuissier, Henri; Sun, Chao; Lohse, Detlef

    2014-04-01

    When a hydrophobic solid is in contact with water, surface nanobubbles often form at the interface. They have a lifetime many orders of magnitude longer than expected. Here, we show that they even withstand a temperature increase to temperatures close to the boiling point of bulk water; i.e., they do not nucleate larger bubbles ("superstability"). On the contrary, when the vapor-liquid contact line passes a nanobubble, a liquid film remains around it, which, after pinch-off, results in a microdroplet in which the nanobubbles continue to exist. Finally, the microdroplet evaporates and the nanobubble consequently bursts. Our results support that pinning plays a crucial role for nanobubble stability.

  19. Chemical reaction due to stronger Ramachandran interaction

    Indian Academy of Sciences (India)

    The origin of a chemical reaction between two reactant atoms is associated with the activation energy, on the assumption that, high-energy collisions between these atoms, are the ones that overcome the activation energy. Here, we show that a stronger attractive van der Waals (vdW) and electron-ion Coulomb interactions ...

  20. Connection of sulfuric acid to atmospheric nucleation in boreal forest.

    Science.gov (United States)

    Nieminen, T; Manninen, H E; Sihto, S L; Yli-Juuti, T; Mauldin, R L; Petäjä, T; Riipinen, I; Kerminen, V M; Kulmala, M

    2009-07-01

    Gas to particle conversion in the boundary layer occurs worldwide. Sulfuric acid is considered to be one of the key components in these new particle formation events. In this study we explore the connection between measured sulfuric acid and observed formation rate of both charged 2 nm as well as neutral clusters in a boreal forest environment A very short time delay of the order of ten minutes between these two parameters was detected. On average the event days were clearly associated with higher sulfuric acid concentrations and lower condensation sink (CS) values than the nonevent days. Although there was not a clear sharp boundary between the nucleation and no-nucleation days in sulfuric acid-CS plane, at our measurement site a typical threshold concentration of 3.10(5) molecules cm(-3) of sulfuric acid was needed to initiate the new particle formation. Two proposed nucleation mechanisms were tested. Our results are somewhat more in favor of activation type nucleation than of kinetic type nucleation, even though our data set is too limited to omit either of these two mechanisms. In line with earlier studies, the atmospheric nucleation seems to start from sizes very close to 2 nm.

  1. Nucleate boiling heat transfer

    Energy Technology Data Exchange (ETDEWEB)

    Saiz Jabardo, J.M. [Universidade da Coruna (Spain). Escola Politecnica Superior], e-mail: mjabardo@cdf.udc.es

    2009-07-01

    Nucleate boiling heat transfer has been intensely studied during the last 70 years. However boiling remains a science to be understood and equated. In other words, using the definition given by Boulding, it is an 'insecure science'. It would be pretentious of the part of the author to explore all the nuances that the title of the paper suggests in a single conference paper. Instead the paper will focus on one interesting aspect such as the effect of the surface microstructure on nucleate boiling heat transfer. A summary of a chronological literature survey is done followed by an analysis of the results of an experimental investigation of boiling on tubes of different materials and surface roughness. The effect of the surface roughness is performed through data from the boiling of refrigerants R-134a and R-123, medium and low pressure refrigerants, respectively. In order to investigate the extent to which the surface roughness affects boiling heat transfer, very rough surfaces (4.6 {mu}m and 10.5 {mu}m ) have been tested. Though most of the data confirm previous literature trends, the very rough surfaces present a peculiar behaviour with respect to that of the smoother surfaces (Ra<3.0 {mu}m). (author)

  2. Aerosol nucleation in an ultra-low ion density environment

    DEFF Research Database (Denmark)

    Pedersen, Jens Olaf Pepke; Enghoff, Martin Andreas Bødker; Paling, Sean M.

    2012-01-01

    sulfuric acid–water clusters over a range of sulfuric acid concentrations although neutral nucleation mechanisms remain evident at low ionization levels. The effect of ions is found both to enhance the nucleation rate of stable clusters and the initial growth rate. The effects of possible contaminations...... are also discussed and are believed to be small, but cannot be excluded. If our results can be extrapolated to conditions that resemble the clean air atmosphere over the Earth's oceans they suggest that ions may dominate the production of small (4nm) aerosols here....

  3. Theory and Simulation of Nucleation

    NARCIS (Netherlands)

    Kuipers, J.|info:eu-repo/dai/nl/304832049

    2009-01-01

    Nucleation is the process where a stable nucleus spontaneously emerges in a metastable environment. Examples of nucleation abound, for instance the formation of droplets in undercooled gasses and of crystals in undercooled liquids. The process is thermally activated and is key to understanding

  4. A dynamical theory of nucleation

    Science.gov (United States)

    Lutsko, James F.

    2013-05-01

    A dynamical theory of nucleation based on fluctuating hydrodynamics is described. It is developed in detail for the case of diffusion-limited nucleation appropriate to colloids and macro-molecules in solution. By incorporating fluctuations, realistic fluid-transport and realistic free energy models the theory is able to give a unified treatment of both the pre-critical development of fluctuations leading to a critical cluster as well as of post-critical growth. Standard results from classical nucleation theory are shown to follow in the weak noise limit while the generality of the theory allows for many extensions including the description of very high supersaturations (small clusters), multiple order parameters and strong-noise effects to name a few. The theory is applied to homogeneous and heterogeneous nucleation of a model globular protein in a confined volume and it is found that nucleation depends critically on the existence of long-wavelength, small-amplitude density fluctuations.

  5. The barrier to ice nucleation in monatomic water

    Science.gov (United States)

    Prestipino, Santi

    2018-03-01

    Crystallization from a supercooled liquid initially proceeds via the formation of a small solid embryo (nucleus), which requires surmounting an activation barrier. This phenomenon is most easily studied by numerical simulation, using specialized biased-sampling techniques to overcome the limitations imposed by the rarity of nucleation events. Here, I focus on the barrier to homogeneous ice nucleation in supercooled water, as represented by the monatomic-water model, which in the bulk exhibits a complex interplay between different ice structures. I consider various protocols to identify solidlike particles on a computer, which perform well enough for the Lennard-Jones model, and compare their respective impact on the shape and height of the nucleation barrier. It turns out that the effect is stronger on the nucleus size than on the barrier height. As a by-product of the analysis, I determine the structure of the nucleation cluster, finding that the relative amount of ice phases in the cluster heavily depends on the method used for classifying solidlike particles. Moreover, the phase which is most favored during the earlier stages of crystallization may happen, depending on the nucleation coordinate adopted, to be different from the stable polymorph. Therefore, the quality of a reaction coordinate cannot be assessed simply on the basis of the barrier height obtained. I explain how this outcome is possible and why it just points out the shortcoming of collective variables appropriate to simple fluids in providing a robust method of particle classification for monatomic water.

  6. Ion-induced nucleation of pure biogenic particles

    CERN Document Server

    Kirkby, Jasper; Sengupta, Kamalika; Frege, Carla; Gordon, Hamish; Williamson, Christina; Heinritzi, Martin; Simon, Mario; Yan, Chao; Almeida, João; Tröstl, Jasmin; Nieminen, Tuomo; Ortega, Ismael K; Wagner, Robert; Adamov, Alexey; Amorim, Antonio; Bernhammer, Anne-Kathrin; Bianchi, Federico; Breitenlechner, Martin; Brilke, Sophia; Chen, Xuemeng; Craven, Jill; Dias, antonio; Ehrhart, Sebastian; Flagan, Richard C; Franchin, Alessandro; Fuchs, Claudia; Guida, Roberto; Hakala, Jani; Hoyle, Christopher R; Jokinen, Tuija; Junninen, Heikki; Kangasluoma, Juha; Kim, Jaeseok; Krapf, Manuel; Kürten, andreas; Laaksonen, Ari; Lehtipalo, Katrianne; Makhmutov, Vladimir; Mathot, Serge; Molteni, Ugo; Onnela, antti; Peräkylä, Otso; Piel, Felix; Petäjä, Tuukka; Praplan, Arnaud P; Pringle, Kirsty; Rap, Alexandru; Richards, Nigel A D; Riipinen, Ilona; Rissanen, Matti P; Rondo, Linda; Sarnela, Nina; Schobesberger, Siegfried; Scott, Catherine E; Seinfeld, John H; Sipilä, Mikko; Steiner, Gerhard; Stozhkov, Yuri; Stratmann, Frank; Tomé, Antonio; Virtanen, Annele; Vogel, Alexander L; Wagner, Andrea C; Wagner, Paul E; Weingartner, Ernest; Wimmer, Daniela; Winkler, Paul M; Ye, Penglin; Zhang, Xuan; Hansel, Armin; Dommen, Josef; Donahue, Neil M; Worsnop, Douglas R; Baltensperger, Urs; Kulmala, Markku; Carslaw, Kenneth S; Curtius, Joachim

    2016-01-01

    Atmospheric aerosols and their effect on clouds are thought to be important for anthropogenic radiative forcing of the climate, yet remain poorly understood. Globally, around half of cloud condensation nuclei originate from nucleation of atmospheric vapours. It is thought that sulfuric acid is essential to initiate most particle formation in the atmosphere and that ions have a relatively minor role. Some laboratory studies, however, have reported organic particle formation without the intentional addition of sulfuric acid, although contamination could not be excluded. Here we present evidence for the formation of aerosol particles from highly oxidized biogenic vapours in the absence of sulfuric acid in a large chamber under atmospheric conditions. The highly oxygenated molecules (HOMs) are produced by ozonolysis of $\\alpha$-pinene. We find that ions from Galactic cosmic rays increase the nucleation rate by one to two orders of magnitude compared with neutral nucleation. Our experimental findings are supported...

  7. Comparison of the SAWNUC model with CLOUD measurements of sulphuric acid-water nucleation

    CERN Document Server

    Ehrhart, Sebastian; Almeida, Joao; Amorim, Antonio; Barmet, Peter; Bianchi, Federico; Dommen, Josef; Dunne, Eimear M; Duplissy, Jonathan; Franchin, Alessandro; Kangasluoma, Juha; Kirkby, Jasper; Kürten, Andreas; Kupc, Agnieszka; Lehtipalo, Katrianne; Nieminen, Tuomo; Riccobono, Francesco; Rondo, Linda; Schobesberger, Siegfried; Steiner, Gerhard; Tomé, António; Wimmer, Daniela; Baltensperger, Urs; Wagner, Paul E; Curtius, Joachim

    2016-01-01

    Binary nucleation of sulphuric acid-water particles is expected to be an important process in the free troposphere at low temperatures. SAWNUC (Sulphuric Acid Water Nucleation) is a model of binary nucleation that is based on laboratory measurements of the binding energies of sulphuric acid and water in charged and neutral clusters. Predictions of SAWNUC are compared for the first time comprehensively with experimental binary nucleation data from the CLOUD chamber at European Organization for Nuclear Research. The experimental measurements span a temperature range of 208–292 K, sulphuric acid concentrations from 1·106 to 1·109 cm−3, and distinguish between ion-induced and neutral nucleation. Good agreement, within a factor of 5, is found between the experimental and modeled formation rates for ion-induced nucleation at 278 K and below and for neutral nucleation at 208 and 223 K. Differences at warm temperatures are attributed to ammonia contamination which was indicated by the presence of ammonia-sulphu...

  8. Review: The nucleation of disorder

    International Nuclear Information System (INIS)

    Cahn, R.W.; Johnson, W.L.

    1986-01-01

    Four types of phase transformation that involve the conversion of crystalline phases into more disordered forms are reviewed: melting, disordering of superlattices, amorphization by diffusion between crystalline phases, and irradation amorphization. In the review emphasis is placed on evidence for the heterogeneous nucleation of the product phases; in this connection, the role of surfaces, antiphase domain boundaries, dislocations, vacancies, and grain boundaries is specifically discussed. All of these features have been either observed, or hypothesized, to play a role as heterogeneous nucleation sites in one or more of the four transformations. An attempt is made to draw parallels between nucleation mechanisms in the various processes

  9. Metadynamics studies of crystal nucleation

    Science.gov (United States)

    Giberti, Federico; Salvalaglio, Matteo; Parrinello, Michele

    2015-01-01

    Crystallization processes are characterized by activated events and long timescales. These characteristics prevent standard molecular dynamics techniques from being efficiently used for the direct investigation of processes such as nucleation. This short review provides an overview on the use of metadynamics, a state-of-the-art enhanced sampling technique, for the simulation of phase transitions involving the production of a crystalline solid. In particular the principles of metadynamics are outlined, several order parameters are described that have been or could be used in conjunction with metadynamics to sample nucleation events and then an overview is given of recent metadynamics results in the field of crystal nucleation. PMID:25866662

  10. Metadynamics studies of crystal nucleation

    Directory of Open Access Journals (Sweden)

    Federico Giberti

    2015-03-01

    Full Text Available Crystallization processes are characterized by activated events and long timescales. These characteristics prevent standard molecular dynamics techniques from being efficiently used for the direct investigation of processes such as nucleation. This short review provides an overview on the use of metadynamics, a state-of-the-art enhanced sampling technique, for the simulation of phase transitions involving the production of a crystalline solid. In particular the principles of metadynamics are outlined, several order parameters are described that have been or could be used in conjunction with metadynamics to sample nucleation events and then an overview is given of recent metadynamics results in the field of crystal nucleation.

  11. LHC Season 2: A stronger machine

    CERN Multimedia

    Dominguez, Daniel

    2015-01-01

    1) New magnets / De nouveaux aimants 2) Stronger connections / Des jonctions électriques renforcées 3) Safer magnets / Des aimants plus sûrs 4) Higher energy beams / Des faisceaux d’énergie plus élevée 5) Narrower beams / Des faisceaux plus serrés 6) Smaller but closer proton packets / Des groupes de protons plus petits mais plus rapprochés 7) Higher voltage / Une tension plus haute 8) Superior cryogenics / Un système cryogénique amélioré 9) Radiation-resistant electronics / Une électronique qui résiste aux radiations 10) More secure vacuum / Un vide plus sûr

  12. Bubble nucleation in stout beers

    Science.gov (United States)

    Lee, W. T.; McKechnie, J. S.; Devereux, M. G.

    2011-05-01

    Bubble nucleation in weakly supersaturated solutions of carbon dioxide—such as champagne, sparkling wines, and carbonated beers—is well understood. Bubbles grow and detach from nucleation sites: gas pockets trapped within hollow cellulose fibers. This mechanism appears not to be active in stout beers that are supersaturated solutions of nitrogen and carbon dioxide. In their canned forms these beers require additional technology (widgets) to release the bubbles which will form the head of the beer. We extend the mathematical model of bubble nucleation in carbonated liquids to the case of two gases and show that this nucleation mechanism is active in stout beers, though substantially slower than in carbonated beers and confirm this by observation. A rough calculation suggests that despite the slowness of the process, applying a coating of hollow porous fibers to the inside of a can or bottle could be a potential replacement for widgets.

  13. Gas hydrate nucleation

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    1997-12-31

    The overall aim of the project was to gain more knowledge about the kinetics of gas hydrate formation especially the early growth phase. Knowledge of kinetics of gas hydrate formation is important and measurements of gas hydrate particle size and concentration can contribute to improve this knowledge. An experimental setup for carrying out experimental studies of the nucleation and growth of gas hydrates has been constructed and tested. Multi wavelength extinction (MWE) was the experimental technique selected for obtaining particle diameter and concentration. The principle behind MWE is described as well as turbidity spectrum analysis that in an initial stage of the project was considered as an alternative experimental technique. Details of the experimental setup and its operation are outlined. The measuring cell consists of a 1 litre horizontal tube sustaining pressures up to 200 bar. Laser light for particle size determination can be applied through sapphire windows. A description of the various auxiliary equipment and of another gas hydrate cell used in the study are given. A computer program for simulation and analysis of gas hydrate experiments is based on the gas hydrate kinetics model proposed by Skovborg and Rasmussen (1993). Initial measurements showed that knowledge of the refractive index of gas hydrates was important in order to use MWE. An experimental determination of the refractive index of methane and natural gas hydrate is described. The test experiments performed with MWE on collectives of gas hydrate particles and experiments with ethane, methane and natural gas hydrate are discussed. Gas hydrate particles initially seem to grow mainly in size and at latter stages in number. (EG) EFP-94; 41 refs.

  14. Role of nucleation in nanodiamond film growth

    International Nuclear Information System (INIS)

    Lifshitz, Y.; Lee, C.H.; Wu, Y.; Zhang, W.J.; Bello, I.; Lee, S.T.

    2006-01-01

    Nanodiamond films were deposited using different microwave plasma chemical vapor deposition schemes following several nucleation pretreatment methods. The nucleation efficiency and the films structure were investigated using scanning and transmission electron microscopy and Raman spectroscopy. C 2 dimer growth (CH 4 and H 2 in 90% Ar) cannot nucleate diamond and works only on existing diamond surfaces. The methyl radical process (up to 20% CH 4 in H 2 ) allows some nucleation probability on appropriate substrates. Prolonged bias enhanced nucleation initiates both diamond nucleation and growth. C 2 dimer growth results in pure nanodiamond free of amorphous carbon, while prolonged bias enhanced nucleation forms an amorphous carbon/nanodiamond composite

  15. Gas Marbles: Much Stronger than Liquid Marbles

    Science.gov (United States)

    Timounay, Yousra; Pitois, Olivier; Rouyer, Florence

    2017-06-01

    Enwrapping liquid droplets with hydrophobic particles allows the manufacture of so-called "liquid marbles" [Aussillous and Quéré Nature (London) 411, 924 (2001); , 10.1038/35082026Mahadevan Nature (London)411, 895 (2001), 10.1038/35082164]. The recent intensive research devoted to liquid marbles is justified by their very unusual physical and chemical properties and by their potential for various applications, from microreactors to water storage, including water pollution sensors [Bormashenko Curr. Opin. Colloid Interface Sci. 16, 266 (2011), 10.1016/j.cocis.2010.12.002]. Here we demonstrate that this concept can be successfully applied for encapsulating and protecting small gas pockets within an air environment. Similarly to their liquid counterparts, those new soft-matter objects, that we call "gas marbles," can sustain external forces. We show that gas marbles are surprisingly tenfold stronger than liquid marbles and, more importantly, they can sustain both positive and negative pressure differences. This magnified strength is shown to originate from the strong cohesive nature of the shell. Those interesting properties could be exploited for imprisoning valuable or polluted gases or for designing new aerated materials.

  16. Organic Aerosol Nucleation and Growth at the CERN CLOUD chamber

    Science.gov (United States)

    Tröstl, Jasmin; Lethipalo, Katrianne; Bianchi, Federico; Sipilä, Mikko; Nieminen, Tuomo; Wagner, Robert; Frege, Carla; Simon, Mario; Weingartner, Ernest; Gysel, Martin; Dommen, Josef; Baltensperger, Urs

    2014-05-01

    It is well known that atmospheric aerosols influence the climate by changing Earth's radiation balance (IPCC 2007 and 2013). Recent models have shown (Merikanto et al. 2009) that aerosol nucleation is one of the biggest sources of low level cloud condensation nuclei. Still, aerosol nucleation and growth are not fully understood. The driving force of nucleation and growth is sulfuric acid. However ambient nucleation and growth rates cannot be explained by solely sulfuric acid as precursor. Recent studies have shown that only traces of precursors like ammonia and dimethylamine enhance the nucleation rates dramatically (Kirkby et al. 2011, Almeida et al., 2013). Thus the role of different aerosol precursor needs to be studied not only in ambient but also in very well controlled chamber experiments. The CLOUD (Cosmics Leaving OUtdoor Droplets) experiment enables conducting experiments very close to atmospheric conditions and with a very low contaminant background. The latest CLOUD experiments focus on the role of organics in aerosol nucleation and growth. For this purpose, numerous experiments with alpha-pinene have been conducted at the CERN CLOUD chamber. Several state-of-the-art instruments were used to cover the whole complexity of the experiment. Chamber conditions were set to 40% relative humidity and 5° C. Atmospheric concentrations of SO2, O3, HONO, H2O and alpha-pinene were injected to the chamber. Different oxidation conditions were used, yielding different levels of oxidized organics: (1) OH radicals, (2) Ozone with the OH scavenger H2 (pure ozonolysis) and (3) both. SO2 was injected to allow for sulfuric acid production. Optical UV fibers were used to enable photochemical reactions. A high field cage (30 kV) can be turned on to remove all charged particles in the chamber to enable completely neutral conditions. Comparing neutral conditions to the beam conditions using CERN's proton synchrotron, the fraction of ion-induced nucleation can be studied. Using

  17. A note on the nucleation with multiple steps: Parallel and series nucleation

    OpenAIRE

    Iwamatsu, Masao

    2012-01-01

    Parallel and series nucleation are the basic elements of the complex nucleation process when two saddle points exist on the free-energy landscape. It is pointed out that the nucleation rates follow formulas similar to those of parallel and series connection of resistors or conductors in an electric circuit. Necessary formulas to calculate individual nucleation rates at the saddle points and the total nucleation rate are summarized and the extension to the more complex nucleation process is su...

  18. States agree on stronger physical protection regime

    International Nuclear Information System (INIS)

    2005-01-01

    Full text: Delegates from 89 countries agreed on 8 July to fundamental changes that will substantially strengthen the Convention on the Physical Protection of Nuclear Material (CPPNM). IAEA Director General Mohamed ElBaradei welcomed the agreement in saying 'This new and stronger treaty is an important step towards greater nuclear security by combating, preventing, and ultimately punishing those who would engage in nuclear theft, sabotage or even terrorism. It demonstrates that there is indeed a global commitment to remedy weaknesses in our nuclear security regime.' The amended CPPNM makes it legally binding for States Parties to protect nuclear facilities and material in peaceful domestic use, storage as well as transport. It will also provide for expanded cooperation between and among States regarding rapid measures to locate and recover stolen or smuggled nuclear material, mitigate any radiological consequences of sabotage, and prevent and combat related offences. The original CPPNM applied only to nuclear material in international transport. Conference President Dr. Alec Baer said 'All 89 delegations demonstrated real unity of purpose. They put aside some very genuine national concerns in favour of the global interest and the result is a much improved convention that is better suited to addressing the nuclear security challenges we currently face.' The new rules will come into effect once they have been ratified by two-thirds of the 112 States Parties of the Convention, expected to take several years. 'But concrete actions are already taking place around the world. For more than 3 years, the IAEA has been implementing a systematic Nuclear Security plan, including physical protection activities designed to prevent, detect and respond to malicious acts,' said Anita Nillson, Director of the IAEA's Office of Nuclear Security. The Agency's Nuclear Security Fund, set up after the events of 9/11, has delivered $19.5 million in practical assistance to 121 countries

  19. Earth's inner core nucleation paradox

    Science.gov (United States)

    Huguet, Ludovic; Van Orman, James A.; Hauck, Steven A.; Willard, Matthew A.

    2018-04-01

    The conventional view of Earth's inner core is that it began to crystallize at Earth's center when the temperature dropped below the melting point of the iron alloy and has grown steadily since that time as the core continued to cool. However, this model neglects the energy barrier to the formation of the first stable crystal nucleus, which is commonly represented in terms of the critical supercooling required to overcome the barrier. Using constraints from experiments, simulations, and theory, we show that spontaneous crystallization in a homogeneous liquid iron alloy at Earth's core pressures requires a critical supercooling of order 1000 K, which is too large to be a plausible mechanism for the origin of Earth's inner core. We consider mechanisms that can lower the nucleation barrier substantially. Each has caveats, yet the inner core exists: this is the nucleation paradox. Heterogeneous nucleation on a solid metallic substrate tends to have a low energy barrier and offers the most straightforward solution to the paradox, but solid metal would probably have to be delivered from the mantle and such events are unlikely to have been common. A delay in nucleation, whether due to a substantial nucleation energy barrier, or late introduction of a low energy substrate, would lead to an initial phase of rapid inner core growth from a supercooled state. Such rapid growth may lead to distinctive crystallization texturing that might be observable seismically. It would also generate a spike in chemical and thermal buoyancy that could affect the geomagnetic field significantly. Solid metal introduced to Earth's center before it reached saturation could also provide a nucleation substrate, if large enough to escape complete dissolution. Inner core growth, in this case, could begin earlier and start more slowly than standard thermal models predict.

  20. Nucleation and cavitation in parahydrogen

    International Nuclear Information System (INIS)

    Pi, Martí; Barranco, Manuel; Navarro, Jesús; Ancilotto, Francesco

    2012-01-01

    Highlights: ► We have constructed a density functional (DF) for parahydrogen between 14 and 32 K. ► The experimental equation of state and the surface tension are well reproduced. ► We have investigated nucleation and cavitations processes in the metastable phase. ► We have obtained the electron bubble explosion within the capillary model. - Abstract: We have used a density functional approach to investigate thermal homogeneous nucleation and cavitation in parahydrogen. The effect of electrons as seeds of heterogeneous cavitation in liquid parahydrogen is also discussed within the capillary model.

  1. Nucleation in Sheared Granular Matter

    Science.gov (United States)

    Rietz, Frank; Radin, Charles; Swinney, Harry L.; Schröter, Matthias

    2018-02-01

    We present an experiment on crystallization of packings of macroscopic granular spheres. This system is often considered to be a model for thermally driven atomic or colloidal systems. Cyclically shearing a packing of frictional spheres, we observe a first order phase transition from a disordered to an ordered state. The ordered state consists of crystallites of mixed fcc and hcp symmetry that coexist with the amorphous bulk. The transition, initiated by homogeneous nucleation, overcomes a barrier at 64.5% volume fraction. Nucleation consists predominantly of the dissolving of small nuclei and the growth of nuclei that have reached a critical size of about ten spheres.

  2. Nucleation in Sheared Granular Matter.

    Science.gov (United States)

    Rietz, Frank; Radin, Charles; Swinney, Harry L; Schröter, Matthias

    2018-02-02

    We present an experiment on crystallization of packings of macroscopic granular spheres. This system is often considered to be a model for thermally driven atomic or colloidal systems. Cyclically shearing a packing of frictional spheres, we observe a first order phase transition from a disordered to an ordered state. The ordered state consists of crystallites of mixed fcc and hcp symmetry that coexist with the amorphous bulk. The transition, initiated by homogeneous nucleation, overcomes a barrier at 64.5% volume fraction. Nucleation consists predominantly of the dissolving of small nuclei and the growth of nuclei that have reached a critical size of about ten spheres.

  3. Kinetic nucleation and ions in boreal forest particle formation events

    Directory of Open Access Journals (Sweden)

    L. Laakso

    2004-01-01

    Full Text Available In order to gain a more comprehensive picture on different mechanisms behind atmospheric particle formation, measurement results from QUEST 2-campaign are analyzed with an aid of an aerosol dynamic model. A special emphasis is laid on air ion and charged aerosol dynamics. Model simulations indicate that kinetic nucleation of ammonia and sulphuric acid together with condensation of sulphuric acid and low-volatile organic vapours onto clusters and particles explain basic features of particle formation events as well as ion characteristics. However, an observed excess of negative ions in the diameter range 1.5-3nm and overcharge of 3-5nm particles demonstrate that ions are also involved in particle formation. These observations can be explained by preferential condensation of sulphuric acid onto negatively charged clusters and particles and/or contribution of ion-induced nucleation on particle formation. According to model simulations, which assume that the nucleation rate is equal to the sulfuric acid collision rate, the relative contribution of ion-based particle formation seems to be smaller than kinetic nucleation of neutral clusters. Conducted model simulations also corroborate the recently-presented hypothesis according to which a large number of so-called thermodynamically stable clusters (TSCs having a diameter between 1-3nm exist in the atmosphere. TSCs were found to grow to observable sizes only under favorable conditions, e.g. when the pre-existing particle concentration was low.

  4. Beam heating of the neutralizer gas of neutral beam injectors

    International Nuclear Information System (INIS)

    Ott, W.

    1989-02-01

    It was shown by Pamela that the target thickness of the neutralizer gas in neutral beam injectors is smaller than to be expected from gas flow calculations. He explained his findings by direct and indirect beam heating of the gas and a consequent flow acceleration. The role of the neutralizer plasma electrons in the gas heating scenario is reconsidered here. To this end the particle and energy balances of the electrons are solved with allowance for ionization and dissociation of the gas by the electrons. It is shown that the direct contribution of the electrons to heating is not dominant. Their indirect contribution via ion acceleration in the space charge sheath in front of the walls is usually stronger. Methods to increase the neutralizer target thickness are investigated. They are essentially (1) structuring the neutralizer surface in order to reduce the reflection of medium energy particles and to increase the gas accommodation, (2) cooling down the neutralizer to LN 2 -temperature. The scaling of the target thickness with various parameters is investigated and compared with 'cold' flow. Initially it was assumed that the neutralizer plasma electrons are hot and able to excite Balmer alpha radiation in collisions with H 2 molecules. The investigation shows that the electrons must be cold instead (T e + 2 and H + 3 ions leading to excited hydrogen atoms. (orig.)

  5. Crystal nucleation in lithium borate glass

    Science.gov (United States)

    Smith, Gary L.; Neilson, George F.; Weinberg, Michael C.

    1988-01-01

    Crystal nucleation measurements were made on three lithium borate compositions in the vicinity of Li2O-2Br2O3. All nucleation measurements were performed at 500 C. Certain aspects of the nucleation behavior indicated (tentatively) that it proceeded by a homogeneous mechanism. The steady state nucleation rate was observed to have the largest value when the Li2O concentration was slightly in excess of the diborate composition. The change in nucleation rate with composition is controlled by the variation of viscosity as well as the change in free energy with composition. The variation of nucleation rate is explained qualitatively in these terms.

  6. Investigations on nucleation thermodynamical parameters of ...

    Indian Academy of Sciences (India)

    Unknown

    ation thermodynamical parameters like interfacial energy between the solid Nd123 and its flux BaO–CuO, metastable zone-width, Gibbs free energy, critical energy barrier for nucleation and critical nucleation radius have been calculated from the knowledge of solubility data and by applying the classical nucleation theory.

  7. From Clusters to Atmospheric Aerosol Particles: Nucleation in the CLOUD Experiment at CERN

    Science.gov (United States)

    Baltensperger, Urs

    2015-03-01

    Globally, a significant source of cloud condensation nuclei for cloud formation is thought to originate from new particle formation (aerosol nucleation). Despite extensive research, many questions remain about the dominant nucleation mechanisms. Specifically, a quantitative understanding of the dependence of the nucleation rate on the concentration of the nucleating substances such as gaseous sulfuric acid, ammonia, water vapor and others has not been reached. This is of relevance for climate as the atmospheric concentrations of sulfuric acid, ammonia and other nucleating agents are strongly influenced by anthropogenic emissions. By providing extremely well controlled and essentially contaminant free conditions in the CLOUD chamber, we were able to show that indeed sulfuric acid is an important component for such new particle formation, however, for the typical temperatures encountered in the planetary boundary layer the concentrations of sulfuric acid are not high enough to explain the atmospheric observations. Moreover, the effect of ammonia, amines and oxidized organic molecules on the nucleation rate of sulfuric acid has been investigated in CLOUD so far. Recent developments in instrument technology such as the Atmospheric Pressure interface-Time Of Flight (APi-TOF) mass spectrometer have allowed us to investigate the chemical composition of charged as well as neutral clusters during such nucleation experiments. The CLOUD (Cosmics Leaving OUtdoor Droplets) collaboration consists of 20 institutions from Europe and the United States and is funded by national funding institutions as well as the EU training network CLOUD-TRAIN (http://www.cloud-train.eu/).

  8. Ice nucleation activity of polysaccharides

    Science.gov (United States)

    Bichler, Magdalena; Felgitsch, Laura; Haeusler, Thomas; Seidl-Seiboth, Verena; Grothe, Hinrich

    2015-04-01

    Heterogeneous ice nucleation is an important process in the atmosphere. It shows direct impact on our climate by triggering ice cloud formation and therefore it has much influence on the radiation balance of our planet (Lohmann et al. 2002; Mishchenko et al. 1996). The process itself is not completely understood so far and many questions remain open. Different substances have been found to exhibit ice nucleation activity (INA). Due to their vast differences in chemistry and morphology it is difficult to predict what substance will make good ice nuclei and which will not. Hence simple model substances must be found and be tested regarding INA. Our work aims at gaining to a deeper understanding of heterogeneous ice nucleation. We intend to find some reference standards with defined chemistry, which may explain the mechanisms of heterogeneous ice nucleation. A particular focus lies on biological carbohydrates in regards to their INA. Biological carbohydrates are widely distributed in all kingdoms of life. Mostly they are specific for certain organisms and have well defined purposes, e.g. structural polysaccharides like chitin (in fungi and insects) and pectin (in plants), which has also water-binding properties. Since they are widely distributed throughout our biosphere and mostly safe to use for nutrition purposes, they are well studied and easily accessible, rendering them ideal candidates as proxies. In our experiments we examined various carbohydrates, like the already mentioned chitin and pectin, as well as their chemical modifications. Lohmann U.; A Glaciation Indirect Aerosol Effect Caused by Soot Aerosols; J. Geoph. Res.; Vol. 24 No.4; pp 11-1 - 11-4; 2002 Mishchenko M.I., Rossow W.B., Macke A., Lacis A. A.; Sensitivity of Cirrus Cloud Albedo, Bidirectional Reflectance and Optical Thickness Retrieval Accuracy to Ice Particle Shape, J. Geoph. Res.; Vol. 101, No D12; pp. 16,973 - 16,985; 1996

  9. Thermodynamic and Dynamic Aspects of Ice Nucleation

    Science.gov (United States)

    Barahona, Donifan

    2018-01-01

    It is known that ice nucleating particles (INP) immersed within supercooled droplets promote the formation of ice. Common theoretical models used to represent this process assume that the immersed particle lowers the work of ice nucleation without significantly affecting the dynamics of water in the vicinity of the particle. This is contrary to evidence showing that immersed surfaces significantly affect the viscosity and diffusivity of vicinal water. To study how this may affect ice formation this work introduces a model linking the ice nucleation rate to the modification of the dynamics and thermodynamics of vicinal water by immersed particles. It is shown that INP that significantly reduce the work of ice nucleation also pose strong limitations to the growth of the nascent ice germs. This leads to the onset of a new ice nucleation regime, called spinodal ice nucleation, where the dynamics of ice germ growth instead of the ice germ size determines the nucleation rate. Nucleation in this regime is characterized by an enhanced sensitivity to particle area and cooling rate. Comparison of the predicted ice nucleation rate against experimental measurements for a diverse set of species relevant to cloud formation suggests that spinodal ice nucleation may be common in nature.

  10. A note on the nucleation with multiple steps: parallel and series nucleation.

    Science.gov (United States)

    Iwamatsu, Masao

    2012-01-28

    Parallel and series nucleation are the basic elements of the complex nucleation process when two saddle points exist on the free-energy landscape. It is pointed out that the nucleation rates follow formulas similar to those of parallel and series connection of resistors or conductors in an electric circuit. Necessary formulas to calculate individual nucleation rates at the saddle points and the total nucleation rate are summarized, and the extension to the more complex nucleation process is suggested. © 2012 American Institute of Physics

  11. Stronger Schrödinger-like uncertainty relations

    International Nuclear Information System (INIS)

    Song, Qiu-Cheng; Qiao, Cong-Feng

    2016-01-01

    Highlights: • A stronger Schrödinger-like uncertainty relation in the sum of variances of two observables is obtained. • An improved Schrödinger-like uncertainty relation in the product of variances of two observables is obtained. • A stronger uncertainty relation in the sum of variances of three observables is proposed. - Abstract: Uncertainty relation is one of the fundamental building blocks of quantum theory. Nevertheless, the traditional uncertainty relations do not fully capture the concept of incompatible observables. Here we present a stronger Schrödinger-like uncertainty relation, which is stronger than the relation recently derived by Maccone and Pati (2014) [11]. Furthermore, we give an additive uncertainty relation which holds for three incompatible observables, which is stronger than the relation newly obtained by Kechrimparis and Weigert (2014) [12] and the simple extension of the Schrödinger uncertainty relation.

  12. Fracture Statistics: Universality vs. Nucleation

    Science.gov (United States)

    Shekhawat, Ashivni

    2012-02-01

    We reexamine several common assumptions about fracture strength, utilizing large-scale simulations of a fuse network model and applying both renormalization-group and nucleation theory methods. Statistical distributions of fracture strengths are believed to be universal and material independent. The universal Weibull and Gumbel distributions emerge as a consequence of the ``weakest-link hypothesis'' and have been studied in the classical theory of extreme value statistics. These distributions are also the fixed points of a renormalization group (RG) flow. However, the engineering community often ignores the Gumbel distribution and uses the Weibull form almost exclusively to fit experimental data. Further, such fits are often extrapolated beyond the available data to estimate the probability of rare events in a variety of applications ranging from structural reliability to insurance pricing. Our recent studies of the random fuse network model raises doubts about most of these practices. We find that the emergent distribution of fracture strengths is the Gumbel distribution. However, the extremely slow convergence to the universal Gumbel form renders it unusable at least in this case. On the other hand, we show that a non-universal distribution derived by using a Griffiths type nucleation theory (due to Duxbury et al.) converges rapidly even for moderate system sizes. We find that while extrapolating the RG based universal Gumbel distribution is perilous and gives wildly incorrect predictions, the nucleation based non-universal results can be extrapolated with confidence. It is entertaining that fracture provides wonderful examples of the statistical mechanics tools developed to study both continuous as well as abrupt phase transitions.

  13. Nucleation and dissociation of nano-particles in gas phase; Nucleation et evaporation de nanoparticules en phase gazeuse

    Energy Technology Data Exchange (ETDEWEB)

    Feiden, P

    2007-09-15

    This work deals with the study of nano-particles formation in gas phase and their dissociation pathways after an optical excitation. The clusters formation decomposes in two steps: a seed is formed (nucleation phase) and sticks atoms during its propagation in a sodium atomic vapor (growth phase). Those two steps have been observed separately for homogeneous Na{sub n} and heterogeneous Na{sub n}X particles (X = (NaOH){sub 2} or (Na{sub 2}O){sub 2}). The growth mechanism is well interpreted by a Monte Carlo simulation taking into account an accretion mechanism with hard-sphere cross section. The homogeneous nucleation mechanism has been highlighted by a direct comparison with the Classical Nucleation Theory predictions. The clusters fragmentation of ionic Na{sup +}(NaOH){sub p} et Na{sup +}(NaF){sub p} particles is studied in the second part. The way clusters fragment with size when they are excited optically is compared with theoretical previsions: this highlights the existence of an energetic barrier for special size of clusters. Finally, the fragmentation of doubly charged Na{sup +} Na{sup +} (NaOH){sub p} clusters shows a competition between the fission into two single charged fragments and the unimolecular evaporation of a neutral fragment. (author)

  14. Crystal nucleation of colloidal hard dumbbells.

    Science.gov (United States)

    Ni, Ran; Dijkstra, Marjolein

    2011-01-21

    Using computer simulations, we investigate the homogeneous crystal nucleation in suspensions of colloidal hard dumbbells. The free energy barriers are determined by Monte Carlo simulations using the umbrella sampling technique. We calculate the nucleation rates for the plastic crystal and the aperiodic crystal phase using the kinetic prefactor as determined from event driven molecular dynamics simulations. We find good agreement with the nucleation rates determined from spontaneous nucleation events observed in event driven molecular dynamics simulations within error bars of one order of magnitude. We study the effect of aspect ratio of the dumbbells on the nucleation of plastic and aperiodic crystal phases, and we also determine the structure of the critical nuclei. Moreover, we find that the nucleation of the aligned close-packed crystal structure is strongly suppressed by a high free energy barrier at low supersaturations and slow dynamics at high supersaturations.

  15. Study on nucleation kinetics of lysozyme crystallization

    Science.gov (United States)

    Lin, Chen; Zhang, Yang; Liu, Jing J.; Wang, Xue Z.

    2017-07-01

    The nucleation kinetics of hen egg-white lysozyme crystallization was investigated using a hot stage cooling crystallizer and a microscope to monitor the solution crystallization process in real time. Images of crystals were continuously recorded under varied precipitant and protein concentrations. The nucleation rate was found to be higher at higher precipitant concentration, and increase monotonically with protein concentration if the precipitant concentration was held constant. Attempt was made to interpret the experimental data using classical nucleation theory. It was found that the model predictions are lower than the experimental values at low supersaturations but agree well with experimental data at high supersaturations. The trends in the experimental data suggest that two nucleation mechanisms might co-exist: heterogeneous nucleation seems to be the dominant at low supersaturation while at higher supersaturation homogeneous nucleation seems to play the major role.

  16. Effects of clustered nucleation on recrystallization

    DEFF Research Database (Denmark)

    Storm, Søren; Juul Jensen, Dorte

    2009-01-01

    Computer simulations are used to study effects of an experimentally determined 3D distribution of nucleation sites on the recrystallization kinetics and on the evolution of the recrystallized microstructure as compared to simulations with random nucleation. It is found that although...... the experimentally observed clustering is not very strong, it changes the kinetics and the recrystallized microstructural morphology plus leads to a recrystallized grain size distribution, which is significantly broadened compared to that of random nucleation simulations. (C) 2009 Published by Elsevier Ltd...

  17. Structuring effects in binary nucleation : Molecular dynamics simulatons and coarse-grained nucleation theory

    NARCIS (Netherlands)

    Braun, S.; Kraska, T.; Kalikmanov, V.I.

    2013-01-01

    Binary clusters formed by vapor-liquid nucleation are frequently nonhomogeneous objects in which components are not well mixed. The structure of a cluster plays an important role in nucleation and cluster growth. We demonstrate structuring effects by studying high-pressure nucleation and cluster

  18. New trends in the nucleation research

    Science.gov (United States)

    Anisimov, M. P.; Hopke, P. K.

    2017-09-01

    During the last half of century the most of efforts have been directed towards small molecule system modeling using intermolecular potentials. Summarizing the nucleation theory, it can be concluded that the nowadays theory is far from complete. The vapor-gas nucleation theory can produce values that deviate from the experimental results by several orders of magnitude currently. Experiments on the vapor-gas nucleation rate measurements using different devices show significant inconsistencies in the measured rates as well. Theoretical results generally are quite reasonable for sufficiently low vapor nucleation rates where the capillary approximation is applicable. In the present research the advantages and current problems of the vapor-gas nucleation experiments are discussed briefly and a view of the future studies is presented. Using the brake points of the first derivative for the nucleation rate surface as markers of the critical embryos phase change is fresh idea to show the gas-pressure effect for the nucleating vapor-gas systems. To test the accuracy of experimental techniques, it is important to have a standard system that can be measured over a range of nucleation conditions. Several results illustrate that high-pressure techniques are needed to study multi-channel nucleation. In practical applications, parametric theories can be used for the systems of interest. However, experimental measurements are still the best source of information on nucleation rates. Experiments are labor intensive and costly, and thus, it is useful to extend the value of limited experimental measurements to a broader range of nucleation conditions. Only limited experimental data one needs for use in normalizing the slopes of the linearized nucleation rate surfaces. The nucleation rate surface is described in terms of steady-state nucleation rates. It is supposed that several new measuring systems, such as High Pressure Flow Diffusion Chamber for pressure limit up to 150 bar will be

  19. Systematic coarse-graining in nucleation theory

    NARCIS (Netherlands)

    Schweizer, M.; Sagis, L.M.C.

    2015-01-01

    In this work, we show that the standard method to obtain nucleation rate-predictions with the aid of atomistic Monte Carlo simulations leads to nucleation rate predictions that deviate 3 - 5 orders of magnitude from the recent brute-force molecular dynamics simulations [Diemand et al., J. Chem.

  20. Heterogeneous nucleation in hypermonotectic aluminum alloys

    Science.gov (United States)

    Köhler, M.; Ratke, L.; Kaban, I.; Hoyer, W.

    2012-01-01

    Simple casting experiments were set up to solve the question, if heterogeneous nucleation of the liquid-liquid decomposition in monotectic systems is possible. Al-Pb alloys with different inoculants were solidified, and the resulting microstructure was analysed by SEM and X-ray microtomography. Pronounced changes in the distribution of the lead precipitations indicate that it is possible to trigger the nucleation.

  1. Tuning Ice Nucleation with Supercharged Polypeptides

    NARCIS (Netherlands)

    Yang, Huige; Ma, Chao; Li, Kaiyong; Liu, Kai; Loznik, Mark; Teeuwen, Rosalie; van Hest, Jan C. M.; Zhou, Xin; Herrmann, Andreas; Wang, Jianjun

    2016-01-01

    Supercharged unfolded polypeptides (SUPs) are exploited for controlling ice nucleation via tuning the nature of charge and charge density of SUPs. The results show that positively charged SUPs facilitate ice nucleation, while negatively charged ones suppress it. Moreover, the charge density of the

  2. Crystal nucleation of colloidal hard dumbbells

    NARCIS (Netherlands)

    Ni, R.; Dijkstra, M.

    2011-01-01

    Using computer simulations, we investigate the homogeneous crystal nucleation in suspensions of colloidal hard dumbbells. The free energy barriers are determined by Monte Carlo simulations using the umbrella sampling technique. We calculate the nucleation rates for the plastic crystal and the

  3. Investigations on nucleation thermodynamical parameters of ...

    Indian Academy of Sciences (India)

    Investigations on nucleation thermodynamical parameters are very essential for the successful growth of good quality single crystals from high temperature solution. A theoretical estimation of the nucleation thermodynamical parameters like interfacial energy between the solid Nd123 and its flux BaO–CuO, metastable ...

  4. Fatigue crack nucleation in metallic materials

    Energy Technology Data Exchange (ETDEWEB)

    Peralta, P. [Arizona State Univ., Tempe, AZ (United States). Dept. of Mechanical and Aerospace Engineering; Laird, C. [Univ. of Pennsylvania, Philadelphia, PA (United States). Dept. of Materials Science and Engineering; Ramamurty, U. [Nanyang Technological Univ. (Singapore). School of Mechanical and Production Engineering; Suresh, S. [Massachusetts Inst. of Tech., Cambridge, MA (United States). Dept. of Materials Science and Engineering; Campbell, G.H.; King, W.E. [Lawrence Livermore National Lab., CA (United States); Mitchell, T.E. [Los Alamos National Lab., NM (United States). Center for Materials Science

    1999-04-01

    The process of fatigue crack nucleation in metallic materials is reviewed placing emphasis in results derived for pure FCC metals with wavy slip behavior. The relationship between Persistent Slip Bands (PSB`s) and crack initiation will be examined for both single crystals and polycrystals, including the conditions for inter- and transgranular crack nucleation and their connection to type of loading, crystallography and slip geometry. The latter has been found to be an important parameter in the nucleation of intergranular cracks in polycrystals subjected to high strain fatigue, whereby primary slip bands with long slip lengths impinging on a grain boundary produce intergranular crack nucleation under the right conditions. Recent results related to intergranular crack nucleation in copper bicrystals and crack nucleation in Cu/Sapphire interfaces indicate that this mechanism controls crack nucleation in those simpler systems as well. Furthermore, it is found that under multiple slip conditions the crack nucleation location is controlled by the presence of local single slip conditions and long slip lengths for a particular Burgers vector that does not have to be in the primary slip system.

  5. Damage instability and Earthquake nucleation

    Science.gov (United States)

    Ionescu, I. R.; Gomez, Q.; Campillo, M.; Jia, X.

    2017-12-01

    Earthquake nucleation (initiation) is usually associated to the loss of the stability of the geological structure under a slip-weakening friction acting on the fault. The key parameters involved in the stability of the fault are the stress drop, the critical slip distance but also the elastic stiffness of the surrounding materials (rocks). We want to explore here how the nucleation phenomena are correlated to the material softening during damage accumulation by dynamic and/or quasi-static processes. Since damage models are describing micro-cracks growth, which is generally an unstable phenomenon, it is natural to expect some loss of stability on the associated micro-mechanics based models. If the model accurately captures the material behavior, then this can be due to the unstable nature of the brittle material itself. We obtained stability criteria at the microscopic scale, which are related to a large class of damage models. We show that for a given continuous strain history the quasi-static or dynamic problems are instable or ill-posed (multiplicity of material responses) and whatever the selection rule is adopted, shocks (time discontinuities) will occur. We show that the quasi-static equilibria chosen by the "perfect delay convention" is always stable. These stability criteria are used to analyze how NIC (Non Interacting Crack) effective elasticity associated to "self similar growth" model work in some special configurations (one family of micro-cracks in mode I, II and III and in plane strain or plain stress). In each case we determine a critical crack density parameter and critical micro-crack radius (length) which distinguish between stable and unstable behaviors. This critical crack density depends only on the chosen configuration and on the Poisson ratio.

  6. Taking directions: the role of microtubule-bound nucleation in the self-organization of the plant cortical array

    International Nuclear Information System (INIS)

    Deinum, Eva E; Tindemans, Simon H; Mulder, Bela M

    2011-01-01

    The highly aligned cortical microtubule array of interphase plant cells is a key regulator of anisotropic cell expansion. Recent computational and analytical work has shown that the non-equilibrium self-organization of this structure can be understood on the basis of experimentally observed collisional interactions between dynamic microtubules attached to the plasma membrane. Most of these approaches assumed that new microtubules are homogeneously and isotropically nucleated on the cortical surface. Experimental evidence, however, shows that nucleation mostly occurs from other microtubules and under specific relative angles. Here, we investigate the impact of directed microtubule-bound nucleations on the alignment process using computer simulations. The results show that microtubule-bound nucleations can increase the degree of alignment achieved, decrease the timescale of the ordering process and widen the regime of dynamic parameters for which the system can self-organize. We establish that the major determinant of this effect is the degree of co-alignment of the nucleations with the parent microtubule. The specific role of sideways branching nucleations appears to allow stronger alignment while maintaining a measure of overall spatial homogeneity. Finally, we investigate the suggestion that observed persistent rotation of microtubule domains can be explained through a handedness bias in microtubule-bound nucleations, showing that this is possible only for an extreme bias and over a limited range of parameters

  7. Using rheometry to determine nucleation density in a colored system containing a nucleating agent

    Energy Technology Data Exchange (ETDEWEB)

    Ma, Zhe; Steenbakkers, Rudi J.A.; Peters, Gerrit W.M. [Eindhoven University of Technology, Materials Technology, Department of Mechanical Engineering, Eindhoven (Netherlands); Giboz, Julien [Universite de Savoie, LMOPS, CNRS UMR5041, Le Bourget-du-Lac (France)

    2011-12-15

    A new suspension-based rheological method was applied to experimentally study the crystallization of a nucleating agent (NA) filled isotactic polypropylene. This method allows for determination of point nucleation densities where other methods fail. For example, optical microscopy can fail because nucleation densities become too high to be counted (materials with effective NA) or crystallites are not easily visible (colored materials), while differential scanning calorimetry does not allow the effect of flow to be studied. Both quiescent and mild-shear-induced crystallization were investigated. The results show that the addition of a nucleating agent increases the nucleation density by six decades for quiescent crystallization. The effect of shear on crystallization in the presence of a nucleating agent was assessed, and it is demonstrated that, at least for this system, the effect of shear is much smaller than the effect of the nucleating agent. (orig.)

  8. Nucleation and growth kinetics of palladium nanoparticles on thin ...

    African Journals Online (AJOL)

    1073 K and deposition time of 1000 s. The nucleation kinetics is interpreted according to the theory of random nucleation. The general scheme is consisting of three stages namely, nucleation, growth and coalescence. The saturation density of ...

  9. What is Neutrality?

    NARCIS (Netherlands)

    Pierik, R.; van der Burg, W.

    2014-01-01

    This paper reinvestigates the question of liberal neutrality. We contend that current liberal discussions have been dominated - if not hijacked - by one particular interpretation of what neutrality could imply, namely, exclusive neutrality, that aims to exclude religious and cultural expressions

  10. Surface-charge-induced orientation of interfacial water suppresses heterogeneous ice nucleation on α-alumina (0001)

    Science.gov (United States)

    Abdelmonem, Ahmed; Backus, Ellen H. G.; Hoffmann, Nadine; Sánchez, M. Alejandra; Cyran, Jenée D.; Kiselev, Alexei; Bonn, Mischa

    2017-06-01

    Surface charge is one of the surface properties of atmospheric aerosols, which has been linked to heterogeneous ice nucleation and hence cloud formation, microphysics, and optical properties. Despite the importance of surface charge for ice nucleation, many questions remain on the molecular-level mechanisms at work. Here, we combine droplet-freezing assay studies with vibrational sum frequency generation (SFG) spectroscopy to correlate interfacial water structure to surface nucleation strength. We study immersion freezing of aqueous solutions of various pHs on the atmospherically relevant aluminum oxide α-Al2O3 (0001) surface using an isolated droplet on the surface. The high-pH solutions freeze at temperatures higher than that of the low-pH solution, while the neutral pH has the highest freezing temperature. On the molecular level, the SFG spectrum of the interfacial water changes substantially upon freezing. At all pHs, crystallization leads to a reduction of intensity of the 3400 cm-1 water resonance, while the 3200 cm-1 intensity drops for low pH but increases for neutral and high pHs. We find that charge-induced surface templating suppresses nucleation, irrespective of the sign of the surface charge. Heterogeneous nucleation is most efficient for the nominally neutral surface.

  11. Nonclassical nucleation pathways in protein crystallization

    Science.gov (United States)

    Zhang, Fajun

    2017-11-01

    Classical nucleation theory (CNT), which was established about 90 years ago, has been very successful in many research fields, and continues to be the most commonly used theory in describing the nucleation process. For a fluid-to-solid phase transition, CNT states that the solute molecules in a supersaturated solution reversibly form small clusters. Once the cluster size reaches a critical value, it becomes thermodynamically stable and favored for further growth. One of the most important assumptions of CNT is that the nucleation process is described by one reaction coordinate and all order parameters proceed simultaneously. Recent studies in experiments, computer simulations and theory have revealed nonclassical features in the early stage of nucleation. In particular, the decoupling of order parameters involved during a fluid-to-solid transition leads to the so-called two-step nucleation mechanism, in which a metastable intermediate phase (MIP) exists between the initial supersaturated solution and the final crystals. Depending on the exact free energy landscapes, the MIPs can be a high density liquid phase, mesoscopic clusters, or a pre-ordered state. In this review, we focus on the studies of nonclassical pathways in protein crystallization and discuss the applications of the various scenarios of two-step nucleation theory. In particular, we focus on protein solutions in the presence of multivalent salts, which serve as a model protein system to study the nucleation pathways. We wish to point out the unique features of proteins as model systems for further studies.

  12. Damage nucleation in Si during ion irradiation

    International Nuclear Information System (INIS)

    Holland, O.W.; Fathy, D.; Narayan, J.

    1984-01-01

    Damage nucleation in single crystals of silicon during ion irradiation is investigated. Experimental results and mechanisms for damage nucleation during both room and liquid nitrogen temperature irradiation with different mass ions are discussed. It is shown that the accumulation of damage during room temperature irradiation depends on the rate of implantation. These dose rate effects are found to decrease in magnitude as the mass of the ions is increased. The significance of dose rate effects and their mass dependence on nucleation mechanisms is discussed

  13. Viscosity of interfacial water regulates ice nucleation

    International Nuclear Information System (INIS)

    Li, Kaiyong; Chen, Jing; Zhang, Qiaolan; Zhang, Yifan; Xu, Shun; Zhou, Xin; Cui, Dapeng; Wang, Jianjun; Song, Yanlin

    2014-01-01

    Ice formation on solid surfaces is an important phenomenon in many fields, such as cloud formation and atmospheric icing, and a key factor for applications in preventing freezing. Here, we report temperature-dependent nucleation rates of ice for hydrophilic and hydrophobic surfaces. The results show that hydrophilic surface presents a lower ice nucleation rate. We develop a strategy to extract the thermodynamic parameters, J 0 and Γ, in the context of classical nucleation theory. From the extracted J 0 and Γ, we reveal the dominant role played by interfacial water. The results provide an insight into freezing mechanism on solid surfaces

  14. The Relative Influences of Neutralizing Behavior and Subcultural Values on Academic Dishonesty

    Science.gov (United States)

    Curasi, Carolyn F.

    2013-01-01

    The author examined the influence of neutralizing techniques and subcultural values on academic dishonesty using a sample of 327 ethnically diverse business majors. Findings suggest that both neutralizing behavior and subcultural norms are correlated with academic dishonesty; however, neutralization techniques have a stronger association. Findings…

  15. Women's political participation leads to stronger local economies ...

    International Development Research Centre (IDRC) Digital Library (Canada)

    Edgard Rodriguez - IDRC. Women attend a self-help group meeting near Hyderabad, India. Keenara Khanderia. Under changes to India's constitution, Indian women are gaining a stronger political voice. Legal reforms are encouraging women to contribute to economic growth and investments in community growth.

  16. A Stronger Reason for the Right to Sign Languages

    Science.gov (United States)

    Trovato, Sara

    2013-01-01

    Is the right to sign language only the right to a minority language? Holding a capability (not a disability) approach, and building on the psycholinguistic literature on sign language acquisition, I make the point that this right is of a stronger nature, since only sign languages can guarantee that each deaf child will properly develop the…

  17. Nucleation versus instability race in strained films

    Science.gov (United States)

    Liu, Kailang; Berbezier, Isabelle; David, Thomas; Favre, Luc; Ronda, Antoine; Abbarchi, Marco; Voorhees, Peter; Aqua, Jean-Noël

    2017-10-01

    Under the generic term "Stranski-Krastanov" are grouped two different growth mechanisms of SiGe quantum dots. They result from the self-organized Asaro-Tiller-Grinfel'd (ATG) instability at low strain, while at high strain, from a stochastic nucleation. While these regimes are well known, we elucidate here the origin of the transition between these two pathways thanks to a joint theoretical and experimental work. Nucleation is described within the master equation framework. By comparing the time scales for ATG instability development and three-dimensional (3D) nucleation onset, we demonstrate that the transition between these two regimes is simply explained by the crossover between their divergent evolutions. Nucleation exhibits a strong exponential deviation at low strain while ATG behaves only algebraically. The associated time scale varies with exp(1 /x4) for nucleation, while it only behaves as 1 /x8 for the ATG instability. Consequently, at high (low) strain, nucleation (instability) occurs faster and inhibits the alternate evolution. It is then this different kinetic evolution which explains the transition from one regime to the other. Such a kinetic view of the transition between these two 3D growth regimes was not provided before. The crossover between nucleation and ATG instability is found to occur both experimentally and theoretically at a Ge composition around 50% in the experimental conditions used here. Varying the experimental conditions and/or the system parameters does not allow us to suppress the transition. This means that the SiGe quantum dots always grow via ATG instability at low strain and nucleation at high strain. This result is important for the self-organization of quantum dots.

  18. Homogeneous nucleation with magic numbers: aluminum.

    Science.gov (United States)

    Girshick, Steven L; Agarwal, Pulkit; Truhlar, Donald G

    2009-10-07

    Homogeneous nucleation of clusters that exhibit magic numbers is studied numerically, using as an example aluminum at 2000 K, based on recent calculations of free energies [Li et al., J. Phys. Chem. C 111, 16227 (2007)] and condensation rate constants [Li and Truhlar, J. Phys. Chem. C 112, 11109 (2008)] that provide a database for Al(i) up to i=60. The nucleation behavior for saturation ratios greater than about 4.5 is found to be dominated by a peak in the free energy change associated with the reaction iAl-->Al(i) at i=55, making it the critical size over a wide range of saturation ratios. Calculated steady-state nucleation rates are many orders of magnitude lower than predicted by classical nucleation theory (CNT). The onset of nucleation is predicted to occur at a saturation ratio of about 13.3, compared to about 5.1 in CNT, while for saturation ratios greater than about 25 the abundance of magic-numbered clusters becomes high enough to invalidate the assumption that cluster growth occurs solely by monomer addition. Transient nucleation is also predicted to be substantially different than predicted by CNT, with a much longer time required to reach steady state: about 10(-4) s at a saturation ratio of 20, compared to about 10(-7) s from CNT. Magic numbers are seen to play an important role in transient nucleation, as the nucleation currents for clusters of adjacent sizes become equal to each other in temporally successive groups, where the largest cluster in each group is the magic-numbered one.

  19. New mechanism for bubble nucleation: Classical transitions

    International Nuclear Information System (INIS)

    Easther, Richard; Giblin, John T. Jr; Hui Lam; Lim, Eugene A.

    2009-01-01

    Given a scalar field with metastable minima, bubbles nucleate quantum mechanically. When bubbles collide, energy stored in the bubble walls is converted into kinetic energy of the field. This kinetic energy can facilitate the classical nucleation of new bubbles in minima that lie below those of the 'parent' bubbles. This process is efficient and classical, and changes the dynamics and statistics of bubble formation in models with multiple vacua, relative to that derived from quantum tunneling.

  20. Fluorescence Studies of Lysozyme Nucleation

    Science.gov (United States)

    Pusey, Marc L.; Smith, Lori

    1998-01-01

    Fluorescence is one of the most powerful tools available for the study of macromolecules. For example, fluorescence can be used to study self association through methods such as anisotropy (the rotational rate of the molecule in solution), quenching (the accessibility of a bound probe to the bulk solution), and resonance energy transfer (measurement of the distance between two species). Fluorescence can also be used to study the local environment of the probe molecules, and the changes in that environment which accompany crystal nucleation and growth. However fluorescent techniques have been very much underutilized in macromolecular growth studies. One major advantage is that the fluorescent species generally must be at low concentration, typically ca 10-5 to 10-6 M. Thus one can study a very wide range of solution conditions, ranging from very high to very low protein concentration, he latter of which are not readily accessible to scattering techniques. We have prepared a number of fluorescent derivatives of chicken egg white lysozyme (CEWL). Fluorescent probes have been attached to two different sites, ASP 101 and the N-terrninal amine, with a sought for use in different lines of study. Preliminary resonance energy transfer studies have been -carried out using pyrene acetic acid (Ex 340 mn, Em 376 nm) lysozyme as a donor and cascade blue (Ex 377 run, Em 423 nm) labeled lysozyme as an acceptor. The emission of both the pyrene and cascade blue probes was followed as a function of the salt protein concentrations. The data show an increase in cascade blue and a concomitant decrease in the pyrene fluorescence as either the salt or protein concentrations are increased, suggesting that the two species are approaching each other close enough for resonance energy transfer to occur. This data can be analyzed to measure the distance between the probe molecules and, knowing their locations on the protein molecule their distances from and orientations with respect to each

  1. Vapour–to–liquid nucleation: Nucleation theorems for nonisothermal–nonideal case

    Energy Technology Data Exchange (ETDEWEB)

    Malila, J.; McGraw, R.; Napari, I.; Laaksonen, A.

    2010-08-29

    Homogeneous vapour-to-liquid nucleation, a basic process of aerosol formation, is often considered as a type example of nucleation phenomena, while most treatment of the subject introduce several simplifying assumptions (ideal gas phase, incompressible nucleus, isothermal kinetics, size-independent surface free energy...). During last decades, nucleation theorems have provided new insights into properties of critical nuclei facilitating direct comparison between laboratory experiments and molecular simulations. These theorems are, despite of their generality, often applied in forms where the aforementioned assumptions are made. Here we present forms of nucleation theorems that explicitly take into account these effects and allow direct estimation of their importance. Only assumptions are Arrhenius-type kinetics of nucleation process and exclusion carrier gas molecules from the critical nucleus.

  2. Modelling the stochastic behaviour of primary nucleation.

    Science.gov (United States)

    Maggioni, Giovanni Maria; Mazzotti, Marco

    2015-01-01

    We study the stochastic nature of primary nucleation and how it manifests itself in a crystallisation process at different scales and under different operating conditions. Such characteristics of nucleation are evident in many experiments where detection times of crystals are not identical, despite identical experimental conditions, but instead are distributed around an average value. While abundant experimental evidence has been reported in the literature, a clear theoretical understanding and an appropriate modelling of this feature is still missing. In this contribution, we present two models describing a batch cooling crystallisation, where the interplay between stochastic nucleation and deterministic crystal growth is described differently in each. The nucleation and growth rates of the two models are estimated by a comprehensive set of measurements of paracetamol crystallisation from aqueous solution in a 1 mL vessel [Kadam et al., Chemical Engineering Science, 2012, 72, 10-19]. Both models are applied to the cooling crystallisation process above under different operating conditions, i.e. different volumes, initial concentrations, cooling rates. The advantages and disadvantages of the two approaches are illustrated and discussed, with particular reference to their use across scales of nucleation rate measured in very small crystallisers.

  3. Can Hail and Rain Nucleate Cloud Droplets?

    Science.gov (United States)

    Weiss, S.; Prabhakaran, P.; Krekhov, A.; Pumir, A.; Bodenschatz, E.

    2017-12-01

    We present results from a laboratory scale moist convection experiment composed of a mixture of pressurized sulphur hexafluoride (SF6 - liquid and vapor phase) and helium (He - gas phase) to mimic the wet (saturated water vapor) and dry components (nitrogen, oxygen etc.) of the earth's atmosphere. We operate the experiments close to critical conditions to allow for homogeneous nucleation of sulphur hexafluoride droplets. The liquid SF6 pool is heated from below and the warm SF6 vapor from the liquid-vapor interface rise and condense underneath the cold top plate. We observe the nucleation of microdroplets in the wake of cold drops falling through the SF6-He atmosphere. Using classical nucleation theory, we show that the nucleation is caused by isobaric cooling of SF6 vapor in the wake of the cold drop. Furthermore, we argue that in an atmospheric cloud, falling hail and large cold raindrops may induce heterogeneous nucleation of microdroplets in their wake. We also observe that under appropriate conditions these microdroplets form a stable horizontal layer, thus separating regions of super and sub-critical saturation.

  4. Neutral Buoyancy Laboratory (NBL)

    Data.gov (United States)

    Federal Laboratory Consortium — The Neutral Buoyancy Laboratory (NBL) is an astronaut training facility and neutral buoyancy pool operated by NASA and located at the Sonny Carter Training Facility,...

  5. Stronger declines in youth alcohol consumption thanks to stronger integrated alcohol policies? A qualitative comparison of ten Dutch municipalities.

    Science.gov (United States)

    de Goeij, Moniek C M; Harting, Janneke; Kunst, Anton E

    2017-03-02

    Little detailed evidence is available on how integrated policies could impact population health and under what conditions such policies could be realized. The aim of this study was to assess how youth alcohol consumption trends in the province of Noord-Brabant, The Netherlands, were related to the development and implementation of integrated policies. In a retrospective multiple case study, alcohol policies of six municipalities with stronger declines in youth alcohol consumption between 2007 and 2011 (cases) were compared to four municipalities with weaker declines (controls). Information on the policy process in the same period was obtained through semi-structured in-depth interviews with policy advisors. Information on implemented interventions was extracted from policy documents and checked by the interviewees. Interviews were analyzed for thematic content. Only municipalities with stronger declines in alcohol consumption involved sectors other than public health and had started to implement interventions that use regulatory or enforcement strategies. Their involvement was facilitated by framing youth alcohol consumption as a safety rather than a health problem, whereby local media played a substantial role. Implementation of integrated policies was further facilitated by dedicated leadership and sufficient resources. Reductions in youth alcohol consumption in Noord-Brabant were stronger when municipalities started to develop integrated policies. Results suggest that integrated policies framing a health problem as a broader societal problem could positively influence population health.

  6. The right of the stronger: The play Sisyphus and critias

    Directory of Open Access Journals (Sweden)

    Jordović Ivan

    2004-01-01

    Full Text Available The Focus of this study is the standpoint of the play Sisyphus and critias the leader of the thirty towards the right of the stronger. this is a question of constant interest in scientific circles, since its answer can serve as the indicator of the influence this famous theory has had. this interest has been encouraged by the fact that critias’ authorship of the play is questionable. however, the question of the author is not of primary importance for this article, because there are some arguments, among some well known ones, which were not considered and which Show that in this satire, regardless of the author and the purpose of this fragment, the right of the stronger is actually non-existant. the first argument to support this theory is that nomosphysis antithesis is nowhere explicitly mentioned although it is the crucial element of the right of the stronger. in addition there is no claim in the play that the exploitation of the strong by the week or by law accrued. the second argument is that despite the incapability of laws to prevent the secret injustice, they and their importance for the human society are depicted in a positive light. it should also be noted that, unlike callicles and glaucon, laws are created to stop the bad and not the good. the third argument is that the invention of religion is accepted as a positive achievement, which finally enables the overcoming of primeval times and lawlessness. the reflection of this argument is a positive characterization of the individual who invented the fear of gods. the fourth argument, which has not been taken into consideration so far is the way the supporters and opponents of lawlessness are described and marked as κακοί and έσξλοί in the satire only physically strong are considered as strong as opposed to callicles, where they are also spiritually superior. intelectually superior in Sisyphus is the inventor of the fear of gods who is also in favor of law and order. the fact

  7. Stronger misdirection in curved than in straight motion

    Directory of Open Access Journals (Sweden)

    Jorge eOtero-Millan

    2011-11-01

    Full Text Available Illusions developed by magicians are a rich and largely untapped source of insight into perception and cognition. Here we show that curved motion, as employed by the magician in a classic sleight of hand trick, generates stronger misdirection than rectilinear motion, and that this difference can be explained by the differential engagement of the smooth pursuit and the saccadic oculomotor systems. This research moreover exemplifies how the magician’s intuitive understanding of the spectator’s mindset can surpass that of the cognitive scientist in specific instances, and that observation-based behavioral insights developed by magicians are worthy of quantitative investigation in the neuroscience laboratory.

  8. A variational approach to nucleation simulation.

    Science.gov (United States)

    Piaggi, Pablo M; Valsson, Omar; Parrinello, Michele

    2016-12-22

    We study by computer simulation the nucleation of a supersaturated Lennard-Jones vapor into the liquid phase. The large free energy barriers to transition make the time scale of this process impossible to study by ordinary molecular dynamics simulations. Therefore we use a recently developed enhanced sampling method [Valsson and Parrinello, Phys. Rev. Lett.113, 090601 (2014)] based on the variational determination of a bias potential. We differ from previous applications of this method in that the bias is constructed on the basis of the physical model provided by the classical theory of nucleation. We examine the technical problems associated with this approach. Our results are very satisfactory and will pave the way for calculating the nucleation rates in many systems.

  9. ON THE PRECISION OF THE NUCLEATOR

    Directory of Open Access Journals (Sweden)

    Javier González-Villa

    2017-06-01

    Full Text Available The nucleator is a design unbiased method of local stereology for estimating the volume of a bounded object. The only information required lies in the intersection of the object with an isotropic random ray emanating from a fixed point (called the pivotal point associated with the object. For instance, the volume of a neuron can be estimated from a random ray emanating from its nucleolus. The nucleator is extensively used in biosciences because it is efficient and easy to apply. The estimator variance can be reduced by increasing the number of rays. In an earlier paper a systematic sampling design was proposed, and theoretical variance predictors were derived, for the corresponding volume estimator. Being the only variance predictors hitherto available for the nucleator, our basic goal was to check their statistical performance by means of Monte Carlo resampling on computer reconstructions of real objects. As a plus, the empirical distribution of the volume estimator revealed statistical properties of practical relevance.

  10. Cavitation Bubble Nucleation by Energetic Particles

    Energy Technology Data Exchange (ETDEWEB)

    West, C.D.

    1998-12-01

    In the early sixties, experimental measurements using a bubble chamber confirmed quantitatively the thermal spike theory of bubble nucleation by energetic particles: the energy of the slow, heavy alpha decay recoils used in those experiments matched the calculated bubble nucleation energy to within a few percent. It was a triumph, but was soon to be followed by a puzzle. Within a couple of years, experiments on similar liquids, but well below their normal boiling points, placed under tensile stress showed that the calculated bubble nucleation energy was an order of magnitude less than the recoil energy. Why should the theory work so well in the one case and so badly in the other? How did the liquid, or the recoil particle, "know" the difference between the two experiments? Another mathematical model of the same physical process, introduced in 1967, showed qualitatively why different analyses would be needed for liquids with high and low vapor pressures under positive or negative pressures. But, the quantitative agreement between the calculated nucleation energy and the recoil energy was still poor--the former being smaller by a factor of two to three. In this report, the 1967 analysis is extended and refined: the qualitative understanding of the difference between positive and negative pressure nucleation, "boiling" and "cavitation" respectively, is retained, and agreement between the negative pressure calculated to be needed for nucleation and the energy calculated to be available is much improved. A plot of the calculated negative pressure needed to induce bubble formation against the measured value now has a slope of 1.0, although there is still considerable scatter in the individual points.

  11. A unified kinetic approach to binary nucleation

    Energy Technology Data Exchange (ETDEWEB)

    Kevrekidis, P.G. [Department of Physics, Rutgers University, 136 Frelinghuysen Road]|[E.O.H.S.I., Rutgers University]|[UMDNJ, 170 Frelinghuysen Road, Piscataway, New Jersey 08854-8019 (United States); Lazaridis, M. [Norwegian Institute for Air Research (NILU), Instittutvein 18, P. O. Box 100, N-2007 Kjeller (Norway); Drossinos, Y. [European Commission, Joint Research Centre, I-21020 Ispra (Vatican City State, Holy See) (Italy); Georgopoulos, P.G. [E.O.H.S.I., Rutgers University]|[UMDNJ, 170 Frelinghuysen Road, Piscataway, New Jersey 08854 (United States)

    1999-11-01

    Two different methods to calculate the steady-state nucleation rate in heteromolecular systems proposed by Stauffer (1976) and Langer (1969) are analyzed. Their mathematical equivalence is explicitly demonstrated, thereby obtaining a generic expression for the rate of binary nucleation. Its numerical evaluation does not entail rotation of the coordinate system at the saddle point, but it only requires data in the natural coordinate system of number fluctuations, namely molecular impingement rates, the droplet free energy and its second order derivatives at the saddle point, and the total density of condensible vapors. {copyright} {ital 1999 American Institute of Physics.}

  12. Dumbbells and onions in ternary nucleation.

    Science.gov (United States)

    Nellas, Ricky B; Chen, Bin; Siepmann, J Ilja

    2007-06-14

    Molecular simulations for a ternary nucleation system (water/n-nonane/1-butanol) demonstrate a more complex nucleation mechanism than previously thought, where critical nuclei with different compositions are present even for a given vapour-phase composition; the spatial distribution in these critical nuclei is heterogeneous and dumbbell and onion motifs are found; in the former, water and nonane nano-droplets are connected through a butanol handle, while in the latter a water core is surrounded by a nonane corona with an interfacial butanol shell.

  13. Crystal nucleation in simple and complex fluids.

    Science.gov (United States)

    Oxtoby, David W

    2003-03-15

    The application of density-functional methods from statistical mechanics to the nucleation of crystals from the melt is described. Simple fluids such as metals, with sizes comparable with the range of their attractive forces, are compared with complex fluids such as colloidal suspensions and proteins dissolved in solution. A different mechanism for crystal nucleation is proposed in the latter case, in which density (concentration) changes before periodic crystalline order appears. This leads to a theoretical foundation for empirical observations on the 'crystallization window' in protein crystallization. Comparisons are made with the results of computer simulation via molecular dynamics.

  14. Study of neutral particles

    International Nuclear Information System (INIS)

    Bartel, W.; Bulos, F.; Eisner, A.

    1975-01-01

    The range of physics problems for which a detector emphasizing neutrals is most suitable is discussed. The primary goals are the all neutrals cross section, sigma/sub o/ (e + e - → neutrals), the characterization of the neutral energy in multi-hadronic events, the search for monoenergetic photons, and good sensitivity in the difficult region of low energy photons. Those features of multi-hadronic events which are most relevant to a neutral detector were calculated using a jet model with parameters extrapolated from SPEAR energies. These distributions are presented and discussed

  15. Temperature Dependence in Homogeneous and Heterogeneous Nucleation

    Energy Technology Data Exchange (ETDEWEB)

    McGraw R. L.; Winkler, P. M.; Wagner, P. E.

    2017-08-01

    Heterogeneous nucleation on stable (sub-2 nm) nuclei aids the formation of atmospheric cloud condensation nuclei (CCN) by circumventing or reducing vapor pressure barriers that would otherwise limit condensation and new particle growth. Aerosol and cloud formation depend largely on the interaction between a condensing liquid and the nucleating site. A new paper published this year reports the first direct experimental determination of contact angles as well as contact line curvature and other geometric properties of a spherical cap nucleus at nanometer scale using measurements from the Vienna Size Analyzing Nucleus Counter (SANC) (Winkler et al., 2016). For water nucleating heterogeneously on silver oxide nanoparticles we find contact angles around 15 degrees compared to around 90 degrees for the macroscopically measured equilibrium angle for water on bulk silver. The small microscopic contact angles can be attributed via the generalized Young equation to a negative line tension that becomes increasingly dominant with increasing curvature of the contact line. These results enable a consistent theoretical description of heterogeneous nucleation and provide firm insight to the wetting of nanosized objects.

  16. The ice nucleation activity of extremophilic algae

    Czech Academy of Sciences Publication Activity Database

    Kvíderová, Jana; Hájek, J.; Worland, M. R.

    2013-01-01

    Roč. 34, č. 2 (2013), s. 137-148 ISSN 0143-2044 R&D Projects: GA AV ČR KJB601630808; GA AV ČR KJB600050708 Institutional support: RVO:67985939 Keywords : Ice nucleation * snow algae * lichen photobionts Subject RIV: EF - Botanics Impact factor: 0.640, year: 2013

  17. Transformation kinetics for surface and bulk nucleation

    Energy Technology Data Exchange (ETDEWEB)

    Villa, Elena, E-mail: elena.villa@unimi.it [University of Milan, Department of Mathematics, via Saldini 50, 20133 Milano (Italy); Rios, Paulo R., E-mail: prrios@metal.eeimvr.uff.br [Universidade Federal Fluminense, Escola de Engenharia Industrial Metalurgica de Volta Redonda, Av. dos Trabalhadores 420, 27255-125 Volta Redonda, RJ (Brazil)] [RWTH Aachen University, Institut fuer Metallkunde und Metallphysik, D-52056 Aachen (Germany)

    2010-04-15

    A rigorous mathematical approach based on the causal cone and stochastic geometry concepts is used to derive new exact expressions for transformation kinetics theory. General expressions for the mean volume density and the volume fraction are derived for both surface and bulk nucleation in a general Borel subset of R{sup 3}. In practice, probably any specimen shape of engineering interest is going to be a Borel set. An expression is also derived for the important case of polyhedral shape, in which surface nucleation may take place on the faces, edges and vertices of the polyhedron as well as within the bulk. Moreover, explicit expressions are given for surface and bulk nucleation for three specific shapes of engineering relevance: two parallel planes, an infinitely long cylinder and a sphere. Superposition is explained in detail and it permits the treatment of situations in which surface and bulk nucleation take place simultaneously. The new exact expressions presented here result in a significant increase in the number of exactly solvable cases available to formal kinetics.

  18. Binary nucleation of water and sodium chloride

    Czech Academy of Sciences Publication Activity Database

    Němec, Tomáš; Maršík, František; Palmer, A.

    2006-01-01

    Roč. 124, č. 4 (2006), 0445091-0445096 ISSN 0021-9606 R&D Projects: GA ČR(CZ) GA101/05/2536 Institutional research plan: CEZ:AV0Z20760514 Keywords : binary nucleation * sodium chloride * water Subject RIV: BJ - Thermodynamics Impact factor: 3.166, year: 2006

  19. Nanoscale-Agglomerate-Mediated Heterogeneous Nucleation.

    Science.gov (United States)

    Cha, Hyeongyun; Wu, Alex; Kim, Moon-Kyung; Saigusa, Kosuke; Liu, Aihua; Miljkovic, Nenad

    2017-12-13

    Water vapor condensation on hydrophobic surfaces has received much attention due to its ability to rapidly shed water droplets and enhance heat transfer, anti-icing, water harvesting, energy harvesting, and self-cleaning performance. However, the mechanism of heterogeneous nucleation on hydrophobic surfaces remains poorly understood and is attributed to defects in the hydrophobic coating exposing the high surface energy substrate. Here, we observe the formation of high surface energy nanoscale agglomerates on hydrophobic coatings after condensation/evaporation cycles in ambient conditions. To investigate the deposition dynamics, we studied the nanoscale agglomerates as a function of condensation/evaporation cycles via optical and field emission scanning electron microscopy (FESEM), microgoniometric contact angle measurements, nucleation statistics, and energy dispersive X-ray spectroscopy (EDS). The FESEM and EDS results indicated that the nanoscale agglomerates stem from absorption of sulfuric acid based aerosol particles inside the droplet and adsorption of volatile organic compounds such as methanethiol (CH 3 SH), dimethyl disulfide (CH 3 SSCH), and dimethyl trisulfide (CH 3 SSSCH 3 ) on the liquid-vapor interface during water vapor condensation, which act as preferential sites for heterogeneous nucleation after evaporation. The insights gained from this study elucidate fundamental aspects governing the behavior of both short- and long-term heterogeneous nucleation on hydrophobic surfaces, suggest previously unexplored microfabrication and air purification techniques, and present insights into the challenges facing the development of durable dropwise condensing surfaces.

  20. Effect of Air Injection on Nucleation Rates

    DEFF Research Database (Denmark)

    Capellades Mendez, Gerard; Kiil, Søren; Dam-Johansen, Kim

    2017-01-01

    was reduced from 69 to 13 min, and the mean induction time decreased from 128 to 36 min. The effect on aqueous solutions of l-arginine was less apparent, with a detection delay reduction from 15 to 3 min, and no significant changes on the rate of primary nucleation. These results demonstrate the potential...

  1. Homogeneous crystal nucleation in Ni droplets

    Czech Academy of Sciences Publication Activity Database

    Kožíšek, Zdeněk; Demo, Pavel

    2017-01-01

    Roč. 475, Oct (2017), s. 247-250 ISSN 0022-0248 R&D Projects: GA MŠk LD15004 Institutional support: RVO:68378271 Keywords : nucleation * crystallization * phase transition * nickel Subject RIV: BM - Solid Matter Physics ; Magnetism OBOR OECD: Condensed matter physics (including formerly solid state physics, supercond.) Impact factor: 1.751, year: 2016

  2. NUCLEATION STUDIES OF GOLD ON CARBON ELECTRODES

    Directory of Open Access Journals (Sweden)

    S. SOBRI

    2008-04-01

    Full Text Available Interest has grown in developing non-toxic electrolytes for gold electrodeposition to replace the conventional cyanide-based bath for long term sustainability of gold electroplating. A solution containing thiosulphate and sulphite has been developed specially for microelectronics applications. However, at the end of the electrodeposition process, the spent electrolyte can contain a significant amount of gold in solution. This study has been initiated to investigate the feasibility of gold recovery from a spent thiosulphate-sulphite electrolyte. We have used flat-plate glassy carbon and graphite electrodes to study the mechanism of nucleation and crystal growth of gold deposition from the spent electrolyte. It was found that at the early stages of reduction process, the deposition of gold on glassy carbon exhibits an instantaneous nucleation of non-overlapping particles. At longer times, the particles begin to overlap and the deposition follows a classic progressive nucleation phenomenon. On the other hand, deposition of gold on graphite does not follow the classical nucleation phenomena.

  3. Surface nucleation in complex rheological systems

    Science.gov (United States)

    Herfurth, J.; Ulrich, J.

    2017-07-01

    Forced nucleation induced by suitable foreign seeds is an important tool to control the production of defined crystalline products. The quality of a surface provided by seed materials represents an important variable in the production of crystallizing layers that means for the nucleation process. Parameters like shape and surface structure, size and size distribution of the seed particles as well as the ability to hold up the moisture (the solvent), can have an influence on the nucleation process of different viscous supersaturated solutions. Here the properties of different starch powders as seeds obtained from corn, potato, rice, tapioca and wheat were tested. It could be found, that the best nucleation behavior of a sugar solution could be reached with the use of corn starch as seed material. Here the surface of the crystallized sugar layer is smooth, crystallization time is short (<3 h) and the shape of the product is easily reproducible. Beneficial properties of seed materials are therefore an edged, uneven surface, small particle sizes as well as low moisture content at ambient conditions within the seed materials.

  4. Crystal nucleation kinetics in confined systems

    Czech Academy of Sciences Publication Activity Database

    Kožíšek, Zdeněk

    2013-01-01

    Roč. 15, č. 12 (2013), 2269-2274 ISSN 1466-8033 R&D Projects: GA ČR GAP108/12/0891 Institutional support: RVO:68378271 Keywords : nucleation * phase transtion Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.858, year: 2013

  5. Predictions of homogeneous nucleation rates for n-alkanes accounting for the diffuse phase interface and capillary waves.

    Science.gov (United States)

    Planková, Barbora; Vinš, Václav; Hrubý, Jan

    2017-10-28

    Homogeneous droplet nucleation has been studied for almost a century but has not yet been fully understood. In this work, we used the density gradient theory (DGT) and considered the influence of capillary waves (CWs) on the predicted size-dependent surface tensions and nucleation rates for selected n-alkanes. The DGT model was completed by an equation of state (EoS) based on the perturbed-chain statistical associating fluid theory and compared to the classical nucleation theory and the Peng-Robinson EoS. It was found that the critical clusters are practically free of CWs because they are so small that even the smallest wavelengths of CWs do not fit into their finite dimensions. The CWs contribute to the entropy of the system and thus decrease the surface tension. A correction for the effect of CWs on the surface tension is presented. The effect of the different EoSs is relatively small because by a fortuitous coincidence their predictions are similar in the relevant range of critical cluster sizes. The difference of the DGT predictions to the classical nucleation theory computations is important but not decisive. Of the effects investigated, the most pronounced is the suppression of CWs which causes a sizable decrease of the predicted nucleation rates. The major difference between experimental nucleation rate data and theoretical predictions remains in the temperature dependence. For normal alkanes, this discrepancy is much stronger than observed, e.g., for water. Theoretical corrections developed here have a minor influence on the temperature dependency. We provide empirical equations correcting the predicted nucleation rates to values comparable with experiments.

  6. Copper Oxidation through Nucleation Sites of Chemical Vapor Deposited Graphene

    DEFF Research Database (Denmark)

    Luo, Birong; Whelan, Patrick Rebsdorf; Shivayogimath, Abhay

    2016-01-01

    We investigate the nucleation defect-triggered oxidation of Cu covered by CVD graphene during postannealing in air. The results reveal that different growth conditions may induce imperfect nucleation of graphene, and cause creation of defects near the nucleation point such as pin holes and amorph...

  7. Nucleation, Melting Behaviour and Mechanical Properties of Poly(L ...

    African Journals Online (AJOL)

    Anew category of nucleating agent for poly(L-lactic acid) (PLLA) was developed. An organic nucleating agent; N,N'-bis(benzoyl) suberic acid dihydrazide (NA) was synthesized from benzoyl hydrazine and suberoyl chloride which was deprived from suberic acid via acylation. The nucleation, melting behaviour and ...

  8. Detection of bubble nucleation event in superheated drop detector ...

    Indian Academy of Sciences (India)

    2016-12-08

    Dec 8, 2016 ... the low cost. The bubble nucleation event is detected by measuring the acoustic shock wave released dur- ing the nucleation process. The present work demonstrates the detection of bubble nucleation events by .... This noise level does not affect the characteristics or performance of the sensor–amplifier.

  9. Mechanism of cube grain nucleation during recrystallization of ...

    Indian Academy of Sciences (India)

    The subject of cube texture nucleation i.e. cube grain nucleation, from the deformed state of aluminium and copper is of scientific curiosity with concurrent technological implications. There are essentially two models currently in dispute over the mechanism of cube grain nucleation i.e. the differential stored energy model ...

  10. Nucleation of colloidal crystals on configurable seed structures

    NARCIS (Netherlands)

    Hermes, M; Vermolen, E.C.M.; Leunissen, M.E.; Vossen, D.L.J.; van Oostrum, P.D.J.; Dijkstra, M.; van Blaaderen, A.

    2011-01-01

    Nucleation is an important stage in the growth of crystals. During this stage, the structure and orientation of a crystal are determined. However, short time- and length-scales make nucleation poorly understood. Micrometer-sized colloidal particles form an ideal model system to study nucleation due

  11. Vapor nucleation paths in lyophobic nanopores.

    Science.gov (United States)

    Tinti, Antonio; Giacomello, Alberto; Casciola, Carlo Massimo

    2018-04-19

    In recent years, technologies revolving around the use of lyophobic nanopores gained considerable attention in both fundamental and applied research. Owing to the enormous internal surface area, heterogeneous lyophobic systems (HLS), constituted by a nanoporous lyophobic material and a non-wetting liquid, are promising candidates for the efficient storage or dissipation of mechanical energy. These diverse applications both rely on the forced intrusion and extrusion of the non-wetting liquid inside the pores; the behavior of HLS for storage or dissipation depends on the hysteresis between these two processes, which, in turn, are determined by the microscopic details of the system. It is easy to understand that molecular simulations provide an unmatched tool for understanding phenomena at these scales. In this contribution we use advanced atomistic simulation techniques in order to study the nucleation of vapor bubbles inside lyophobic mesopores. The use of the string method in collective variables allows us to overcome the computational challenges associated with the activated nature of the phenomenon, rendering a detailed picture of nucleation in confinement. In particular, this rare event method efficiently searches for the most probable nucleation path(s) in otherwise intractable, high-dimensional free-energy landscapes. Results reveal the existence of several independent nucleation paths associated with different free-energy barriers. In particular, there is a family of asymmetric transition paths, in which a bubble forms at one of the walls; the other family involves the formation of axisymmetric bubbles with an annulus shape. The computed free-energy profiles reveal that the asymmetric path is significantly more probable than the symmetric one, while the exact position where the asymmetric bubble forms is less relevant for the free energetics of the process. A comparison of the atomistic results with continuum models is also presented, showing how, for simple

  12. Conservatives Anticipate and Experience Stronger Emotional Reactions to Negative Outcomes.

    Science.gov (United States)

    Joel, Samantha; Burton, Caitlin M; Plaks, Jason E

    2014-02-01

    The present work examined whether conservatives and liberals differ in their anticipation of their own emotional reactions to negative events. In two studies, participants imagined experiencing positive or negative outcomes in domains that do not directly concern politics. In Study 1, 190 American participants recruited online (64 male, Mage  = 32 years) anticipated their emotional responses to romantic relationship outcomes. In Study 2, 97 Canadian undergraduate students (26 male, Mage  = 21 years) reported on their anticipated and experienced emotional responses to academic outcomes. In both studies, more conservative participants predicted they would feel stronger negative emotions following negative outcomes than did more liberal participants. Furthermore, a longitudinal follow-up of Study 2 participants revealed that more conservative participants actually felt worse than more liberal participants after receiving a lower-than-desired exam grade. These effects remained even when controlling for the Big Five traits, prevention focus, and attachment style (Study 1), and optimism (Study 2). We discuss how the relationship between political orientation and anticipated affect likely contributes to differences between conservatives and liberals in styles of decision and policy choices. © 2013 Wiley Periodicals, Inc.

  13. Stronger inducible defences enhance persistence of intraguild prey.

    Science.gov (United States)

    Kratina, Pavel; Hammill, Edd; Anholt, Bradley R

    2010-09-01

    1. Intraguild predation is widespread in nature despite its potentially destabilizing effect on food web dynamics. 2. Anti-predator inducible defences affect both birth and death rates of populations and have the potential to substantially modify food web dynamics and possibly increase persistence of intraguild prey. 3. In a chemostat experiment, we investigated the long-term effects of inducible defences on the dynamics of aquatic microbial food webs consisting of an intraguild predator, intraguild prey, and a basal resource. We controlled environmental conditions and selected strains of intraguild prey that varied in the strength of expressed inducible defences. 4. We found that intraguild prey with a stronger tendency to induce an anti-predator morphology persist for significantly longer periods of time. In addition, model selection analysis implied that flexibility in defensive phenotype (inducibility itself) is most likely the factor responsible for the enhanced persistence. 5. As patterns at the community level often emerge as a result of the life-history traits of individuals, we propose that inducible defences increase the persistence of populations and may contribute to the widespread occurrence of theoretically unstable intraguild predation systems in nature.

  14. Investigation of nucleation events vertical extent: a long term study at two different altitude sites

    Directory of Open Access Journals (Sweden)

    J. Boulon

    2011-06-01

    Full Text Available In this work we present an analysis of the occurrence of nucleation events during more than three years of measurements at two different rural altitude sites, the puy de Dôme research station (1465 m a.s.l. and the Opme station (660 m a.s.l., central France. The collected database is a unique combination of scanning mobility particle sizer (10–400 nm, air ion spectrometers (from 0.8 to 42 nm for NTP-conditions, and, neutral clusters and air ion spectrometers (from 0.8 to 42 nm for NTP-conditions measurements at these two different altitudes nearly located research stations, from February 2007 to June 2010. The seasonality of the frequency of nucleation events was studied at the puy de Dôme station and maximum of events frequency was found during early spring and early autumn. During the measurement period, neither the particle formation rates (J2= 1.382 ± 0.195 s−1 nor the growth rates (GR1.3−20 nm = 6.20 ± 0.12 nm h−1 differ from one site to the other on average. Hovewer, we found that, on 437 sampling days in common to the two sites, the nucleation frequency was higher at the puy de Dôme station (35.9 %, 157 days than at the low elevation station of Opme (20.8 %, 91 days. LIDAR measurements and the evolution of the potential equivalent temperature revealed that the nucleation could be triggered either (i within the whole low tropospheric column at the same time from the planetary boundary layer to the top of the interface layer (29.2 %, 47 events, (ii above the planetary boundary layer upper limit (43.5 %, 70 events, and (iii at low altitude and then transported, conserving dynamic and properties, at high altitude (24.8 %, 40 events. This is the first time that the vertical extent of nucleation can be studied over a long observational period, allowing for a rigorous

  15. Dislocation nucleation facilitated by atomic segregation

    Science.gov (United States)

    Zou, Lianfeng; Yang, Chaoming; Lei, Yinkai; Zakharov, Dmitri; Wiezorek, Jörg M. K.; Su, Dong; Yin, Qiyue; Li, Jonathan; Liu, Zhenyu; Stach, Eric A.; Yang, Judith C.; Qi, Liang; Wang, Guofeng; Zhou, Guangwen

    2018-01-01

    Surface segregation--the enrichment of one element at the surface, relative to the bulk--is ubiquitous to multi-component materials. Using the example of a Cu-Au solid solution, we demonstrate that compositional variations induced by surface segregation are accompanied by misfit strain and the formation of dislocations in the subsurface region via a surface diffusion and trapping process. The resulting chemically ordered surface regions acts as an effective barrier that inhibits subsequent dislocation annihilation at free surfaces. Using dynamic, atomic-scale resolution electron microscopy observations and theory modelling, we show that the dislocations are highly active, and we delineate the specific atomic-scale mechanisms associated with their nucleation, glide, climb, and annihilation at elevated temperatures. These observations provide mechanistic detail of how dislocations nucleate and migrate at heterointerfaces in dissimilar-material systems.

  16. Acoustic vibration effects in classical nucleation theory

    Science.gov (United States)

    Baird, James K.; Su, C.-H.

    2018-04-01

    Acoustic vibration is often used to improve the yield of crystals and nanoparticles growing from solutions and melts. As there is still a debate on how acoustic vibration actually works, we have examined the possibility that acoustic pressure can affect the rate of nucleation. Our method is based on an expansion of the free energy of the nucleus in powers of the acoustic pressure. With the assumption that the period of the sound wave is short as compared to the time scale for nucleation, we replace the powers of the acoustic pressure by their time averages, retaining the average of the square of the acoustic pressure as the leading term. By assuming a nucleus having spherical shape, we use the Young-Laplace equation to relate the pressure inside the nucleus to the ambient pressure. Without making further approximations not already standard in classical nucleation theory, we find that the proximate effect of acoustic pressure is to reduce both the size of the critical nucleus as well as the work required to form it from monomers. As the work serves as the activation energy, the ultimate effect of acoustic pressure is to increase the rate of nucleation. If we assume that the atomic structure of the nucleus is the same as that of an ordinary solid, however, we find the compressibility is too small for acoustic vibration effects to be noticeable. If on the other hand, we assume that the structure is similar to that of a loosely bound colloidal particle, then the effects of acoustic vibration become potentially observable.

  17. The emergence of modern nucleation theory

    International Nuclear Information System (INIS)

    Cahn, J.W.

    1987-01-01

    A series of important papers by David Turnbull and his collaborators in the late 1940's and early 1950's laid the experimental and theoretical foundation of modern nucleation theory. The elegance, versatility, and generality of the phenomenological approach, coupled with brilliant and insightful experimental confirmation, sparked widespread application which continues today. Much of David Turnbull's subsequent work in other subjects grew directly or indirectly from this work

  18. Nucleation of (4)R brane universes

    International Nuclear Information System (INIS)

    Cordero, Ruben; Rojas, EfraIn

    2004-01-01

    The creation of brane universes induced by a totally antisymmetric tensor living in a fixed background spacetime is presented, where a term involving the intrinsic curvature of the brane is considered. A canonical quantum mechanical approach employing the Wheeler-DeWitt equation is used. The probability nucleation for the brane is calculated by means of the corresponding instanton and the WKB approximation. Some cosmological implications from the model are presented

  19. Nucleation of {sup (4)}R brane universes

    Energy Technology Data Exchange (ETDEWEB)

    Cordero, Ruben [Departamento de FIsica, Escuela Superior de FIsica y Matematicas del IPN, Unidad Adolfo Lopez Mateos, Edificio 9, 07738 Mexico, DF (Mexico); Rojas, EfraIn [Facultad de FIsica e Inteligencia Artificial, Universidad Veracruzana, Sebastian Camacho 5, Xalapa, Veracruz, 91000 (Mexico)

    2004-09-07

    The creation of brane universes induced by a totally antisymmetric tensor living in a fixed background spacetime is presented, where a term involving the intrinsic curvature of the brane is considered. A canonical quantum mechanical approach employing the Wheeler-DeWitt equation is used. The probability nucleation for the brane is calculated by means of the corresponding instanton and the WKB approximation. Some cosmological implications from the model are presented.

  20. A nanoscale temperature-dependent heterogeneous nucleation theory

    Energy Technology Data Exchange (ETDEWEB)

    Cao, Y. Y. [Nanosurface Science and Engineering Research Institute, College of Mechatronics and Control Engineering, Shenzhen University, Shenzhen, 518060 Guangdong (China); Yang, G. W., E-mail: stsygw@mail.sysu.edu.cn [State Key Laboratory of Optoelectronic Materials and Technologies, Nanotechnology Research Center, School of Materials Science and Engineering, School of Physics and Engineering, Sun Yat-Sen University, Guangzhou, 510275 Guangdong (China)

    2015-06-14

    Classical nucleation theory relies on the hypothetical equilibrium of the whole nucleation system, and neglects the thermal fluctuations of the surface; this is because the high entropic gains of the (thermodynamically extensive) surface would lead to multiple stable states. In fact, at the nanometer scale, the entropic gains of the surface are high enough to destroy the stability of the thermal equilibrium during nucleation, comparing with the whole system. We developed a temperature-dependent nucleation theory to elucidate the heterogeneous nucleation process, by considering the thermal fluctuations based on classical nucleation theory. It was found that the temperature not only affected the phase transformation, but also influenced the surface energy of the nuclei. With changes in the Gibbs free energy barrier, nucleation behaviors, such as the nucleation rate and the critical radius of the nuclei, showed temperature-dependent characteristics that were different from those predicted by classical nucleation theory. The temperature-dependent surface energy density of a nucleus was deduced based on our theoretical model. The agreement between the theoretical and experimental results suggested that the developed nucleation theory has the potential to contribute to the understanding and design of heterogeneous nucleation at the nanoscale.

  1. Systematic coarse-graining in nucleation theory

    Energy Technology Data Exchange (ETDEWEB)

    Schweizer, M., E-mail: marco.schweizer@math.ethz.ch [Department of Materials, Polymer Physics, ETH Zurich, Vladimir-Prelog-Weg 5, 8093 Zurich (Switzerland); Sagis, L. M. C., E-mail: leonard.sagis@wur.nl [Department of Materials, Polymer Physics, ETH Zurich, Vladimir-Prelog-Weg 5, 8093 Zurich (Switzerland); Food Physics Group, Wageningen University, Bornse Weilanden 9, 6708 WG Wageningen (Netherlands)

    2015-08-21

    In this work, we show that the standard method to obtain nucleation rate-predictions with the aid of atomistic Monte Carlo simulations leads to nucleation rate predictions that deviate 3 − 5 orders of magnitude from the recent brute-force molecular dynamics simulations [Diemand et al., J. Chem. Phys. 139, 074309 (2013)] conducted in the experimental accessible supersaturation regime for Lennard-Jones argon. We argue that this is due to the truncated state space the literature mostly relies on, where the number of atoms in a nucleus is considered the only relevant order parameter. We here formulate the nonequilibrium statistical mechanics of nucleation in an extended state space, where the internal energy and momentum of the nuclei are additionally incorporated. We show that the extended model explains the lack in agreement between the molecular dynamics simulations by Diemand et al. and the truncated state space. We demonstrate additional benefits of using the extended state space; in particular, the definition of a nucleus temperature arises very naturally and can be shown without further approximation to obey the fluctuation law of McGraw and LaViolette. In addition, we illustrate that our theory conveniently allows to extend existing theories to richer sets of order parameters.

  2. Systematic coarse-graining in nucleation theory

    Science.gov (United States)

    Schweizer, M.; Sagis, L. M. C.

    2015-08-01

    In this work, we show that the standard method to obtain nucleation rate-predictions with the aid of atomistic Monte Carlo simulations leads to nucleation rate predictions that deviate 3 - 5 orders of magnitude from the recent brute-force molecular dynamics simulations [Diemand et al., J. Chem. Phys. 139, 074309 (2013)] conducted in the experimental accessible supersaturation regime for Lennard-Jones argon. We argue that this is due to the truncated state space the literature mostly relies on, where the number of atoms in a nucleus is considered the only relevant order parameter. We here formulate the nonequilibrium statistical mechanics of nucleation in an extended state space, where the internal energy and momentum of the nuclei are additionally incorporated. We show that the extended model explains the lack in agreement between the molecular dynamics simulations by Diemand et al. and the truncated state space. We demonstrate additional benefits of using the extended state space; in particular, the definition of a nucleus temperature arises very naturally and can be shown without further approximation to obey the fluctuation law of McGraw and LaViolette. In addition, we illustrate that our theory conveniently allows to extend existing theories to richer sets of order parameters.

  3. Nucleation and structural growth of cluster crystals

    International Nuclear Information System (INIS)

    Leitold, Christian; Dellago, Christoph

    2016-01-01

    We study the nucleation of crystalline cluster phases in the generalized exponential model with exponent n = 4. Due to the finite value of this pair potential for zero separation, at high densities the system forms cluster crystals with multiply occupied lattice sites. Here, we investigate the microscopic mechanisms that lead to the formation of cluster crystals from a supercooled liquid in the low-temperature region of the phase diagram. Using molecular dynamics and umbrella sampling, we calculate the free energy as a function of the size of the largest crystalline nucleus in the system, and compare our results with predictions from classical nucleation theory. Employing bond-order parameters based on a Voronoi tessellation to distinguish different crystal structures, we analyze the average composition of crystalline nuclei. We find that even for conditions where a multiply occupied fcc crystal is the thermodynamically stable phase, the nucleation into bcc cluster crystals is strongly preferred. Furthermore, we study the particle mobility in the supercooled liquid and in the cluster crystal. In the cluster crystal, the motion of individual particles is captured by a simple reaction-diffusion model introduced previously to model the kinetics of hydrogen bonds.

  4. Images and properties of individual nucleated particles

    Science.gov (United States)

    Németh, Zoltán; Pósfai, Mihály; Nyirő-Kósa, Ilona; Aalto, Pasi; Kulmala, Markku; Salma, Imre

    2015-12-01

    Atmospheric aerosol particles were collected in Budapest, Hungary in April-June onto lacey Formvar substrates by using an electrostatic precipitator during the beginning phase of the particle growth process in ten nucleation and growth events. Median contribution of the nucleated particles - expressed as the concentration of particles with a diameter between 6 and 25 nm to the total particle number concentration - was 55%, and the median electrical mobility diameter of the particles was approximately 20 nm. The sample was investigated using high-resolution transmission electron microscopy (TEM) and electron energy-loss spectroscopy. Major types of individual particles such as soot, sulphate/organic and tar ball particles were identified in the sample. In addition, particles with an optical diameter range of 10-30 nm were also observed. They clearly differed from the other particle types, showed homogeneous contrast in the bright-field TEM images, and evaporated within tens of seconds when exposed to the electron beam. They were interpreted as representatives of freshly nucleated particles.

  5. Molecular-dynamics simulations of urea nucleation from aqueous solution

    Science.gov (United States)

    Salvalaglio, Matteo; Perego, Claudio; Giberti, Federico; Mazzotti, Marco; Parrinello, Michele

    2015-01-01

    Despite its ubiquitous character and relevance in many branches of science and engineering, nucleation from solution remains elusive. In this framework, molecular simulations represent a powerful tool to provide insight into nucleation at the molecular scale. In this work, we combine theory and molecular simulations to describe urea nucleation from aqueous solution. Taking advantage of well-tempered metadynamics, we compute the free-energy change associated to the phase transition. We find that such a free-energy profile is characterized by significant finite-size effects that can, however, be accounted for. The description of the nucleation process emerging from our analysis differs from classical nucleation theory. Nucleation of crystal-like clusters is in fact preceded by large concentration fluctuations, indicating a predominant two-step process, whereby embryonic crystal nuclei emerge from dense, disordered urea clusters. Furthermore, in the early stages of nucleation, two different polymorphs are seen to compete. PMID:25492932

  6. Leipzig Ice Nucleation chamber Comparison (LINC): intercomparison of four online ice nucleation counters

    Science.gov (United States)

    Burkert-Kohn, Monika; Wex, Heike; Welti, André; Hartmann, Susan; Grawe, Sarah; Hellner, Lisa; Herenz, Paul; Atkinson, James D.; Stratmann, Frank; Kanji, Zamin A.

    2017-09-01

    Ice crystal formation in atmospheric clouds has a strong effect on precipitation, cloud lifetime, cloud radiative properties, and thus the global energy budget. Primary ice formation above 235 K is initiated by nucleation on seed aerosol particles called ice-nucleating particles (INPs). Instruments that measure the ice-nucleating potential of aerosol particles in the atmosphere need to be able to accurately quantify ambient INP concentrations. In the last decade several instruments have been developed to investigate the ice-nucleating properties of aerosol particles and to measure ambient INP concentrations. Therefore, there is a need for intercomparisons to ensure instrument differences are not interpreted as scientific findings.In this study, we intercompare the results from parallel measurements using four online ice nucleation chambers. Seven different aerosol types are tested including untreated and acid-treated mineral dusts (microcline, which is a K-feldspar, and kaolinite), as well as birch pollen washing waters. Experiments exploring heterogeneous ice nucleation above and below water saturation are performed to cover the whole range of atmospherically relevant thermodynamic conditions that can be investigated with the intercompared chambers. The Leipzig Aerosol Cloud Interaction Simulator (LACIS) and the Portable Immersion Mode Cooling chAmber coupled to the Portable Ice Nucleation Chamber (PIMCA-PINC) performed measurements in the immersion freezing mode. Additionally, two continuous-flow diffusion chambers (CFDCs) PINC and the Spectrometer for Ice Nuclei (SPIN) are used to perform measurements below and just above water saturation, nominally presenting deposition nucleation and condensation freezing.The results of LACIS and PIMCA-PINC agree well over the whole range of measured frozen fractions (FFs) and temperature. In general PINC and SPIN compare well and the observed differences are explained by the ice crystal growth and different residence times in

  7. Neutral surfaces in neutral four-spaces

    Directory of Open Access Journals (Sweden)

    Gary Jensen

    1990-11-01

    Full Text Available Properties of the Gauss map of neutral surfaces are studied. Special attention is given to surfaces of parallel, or zero, mean curvature. Bilagrangian structures are defined and used in ways analogous to the use of complex structures in the Riemannian case. The nonsimplicity of the structure group SO(2,2 is used to factor the Gauss map and to construct analogs of the twistor space, called in this context reflector space.

  8. Inorganic Nanoparticle Nucleation on Polymer Matrices

    Science.gov (United States)

    Kosteleski, Adrian John

    The introduction of inorganic nanoparticles into organic materials enhances both the mechanical and chemical properties of the material. Metallic nanoparticles, like silver and gold, have been introduced into polymers for use as antimicrobial coatings or dielectric materials, respectively. The challenge in creating these materials currently is the difficulty to homogeneously disperse the particles throughout the polymer matrix. The uneven dispersion of nanoparticles can lead to less than optimal quality and undesired properties. By creating a polymer nanocomposite material with well-controlled size inorganic materials that are evenly dispersed throughout the polymer matrix; we can improve the materials performance and properties. The objective for this research is to use polymer networks for the in situ mineralization of silver and other metallic materials to create intricate inorganic structures. The work performed here studied the ability to nucleate silver nanoparticles using poly (acrylic acid) (PAA) as the templating agent. Ionic silver was chemically reduced by sodium borohydride (NaBH4) in the presence of PAA. The effect of varying reactant concentrations of silver, NaBH 4, and PAA on particle size was studied. Reaction conditions in terms of varying temperature and pH levels of the reaction solution were monitored to observe the effect of silver nanoparticle size, shape, and concentration. By monitoring the UV spectra over time the reaction mechanism of the silver reduction process was determined to be an autocatalytic process: a period of slow, continuous nucleation followed by rapid, autocatalytic growth. The reaction kinetics for this autocatalytic process is also reported. PAA was crosslinked both chemically and physically to 3 biopolymers; ELP, an elastin like peptide, cotton fabrics, and calcium alginate hydrogels. Various compositions of PAA were physically crosslinked with calcium alginate gels to design an antimicrobial hydrogel for use in wound

  9. Is Polar Amplification Deeper and Stronger than Dynamicists Assume?

    Science.gov (United States)

    Scheff, J.; Maroon, E.

    2017-12-01

    In the CMIP multi-model mean under strong future warming, Arctic amplification is confined to the lower troposphere, so that the meridional gradient of warming reverses around 500 mb and the upper troposphere is characterized by strong "tropical amplification" in which warming weakens with increasing latitude. This model-derived pattern of warming maxima in the upper-level tropics and lower-level Arctic has become a canonical assumption driving theories of the large-scale circulation response to climate change. Yet, several lines of evidence and reasoning suggest that Arctic amplification may in fact extend through the entire depth of the troposphere, and/or may be stronger than commonly modeled. These include satellite Microwave Sounding Unit (MSU) temperature trends as a function of latitude and vertical level, the recent discovery that the extratropical negative cloud phase feedback in models is largely spurious, and the very strong polar amplification observed in past warm and lukewarm climates. Such a warming pattern, with deep, dominant Arctic amplification, would have very different implications for the circulation than a canonical CMIP-like warming: instead of slightly shifting poleward and strengthening, eddies, jets and cells might shift equatorward and considerably weaken. Indeed, surface winds have been mysteriously weakening ("stilling") at almost all stations over the last half-century or so, there has been no poleward shift in northern hemisphere circulation metrics, and past warm climates' subtropics were apparently quite wet (and their global ocean circulations were weak.) To explore these possibilities more deeply, we examine the y-z structure of warming and circulation changes across a much broader range of models, scenarios and time periods than the CMIP future mean, and use an MSU simulator to compare them to the satellite warming record. Specifically, we examine whether the use of historical (rather than future) forcing, AMIP (rather than CMIP

  10. Increasing Arctic sea ice export driven by stronger winds

    Science.gov (United States)

    Sorteberg, A.; Smedsrud, L. H.; Sirevaag, A.; Kloster, K.

    2010-12-01

    Arctic sea ice area has decreased steadily over the last three decades. A thinner and more seasonal Arctic ice cover, related to increased long wave radiation, has become evident. Changes in circulation, including drift patterns of the Arctic pack ice, have been less obvious. Arctic sea ice export estimates have been hampered by low resolution spatial and temporal satellite imagery, especially during summer, making accurate detection difficult. Here we present a new ice area export dataset calculated from sea ice motion and concentration profiles along 79N. Ice drift vectors are calculated from ice feature displacement using Envisat ASAR WideSwath images every 3 days from 2004 while ice concentration is based on DMSP F13 SSMI and AQUA AMSR-E brightness temperature data. The two data sets are combined to give the ice-area flux in consecutive 3-day periods, uninterrupted year-round coverage along 79N. It is shown that sea ice export variability is closely linked to the geostrophic wind in the Fram Strait (correlation of 0.84). Using geostrophic winds from reanalysis back to the 1950s as a proxy for ice export indicates that the Arctic sea ice has annually lost an increasing area since the 1950's driven by stronger winds. Ice concentration has decreased slightly, but does not contribute significantly. The ice export has overall increased by ~25% over the period. Using cyclone tracking the changes in winds seems directly related to a higher low pressure activity in the Nordic Seas. Our results demonstrate that the changes in atmospheric circulation over the Arctic and sub-Arctic have contributed to a trend in the Fram Strait ice export. The Fram Strait between Greenland and Svalbard with average sea ice concentration for summer (red, June through August) and winter (black, January through March). Solid lines are 50%, dashed lines are 15%. Above mean southward ice drift across 79N from August 2004 to July 2010 in 1 degree bins based on SAR imagery, and mean ice

  11. Ice nucleation on mineral dust particles: Onset conditions, nucleation rates and contact angles

    Science.gov (United States)

    Eastwood, Michael L.; Cremel, Sebastien; Gehrke, Clemens; Girard, Eric; Bertram, Allan K.

    2008-11-01

    An optical microscope coupled to a flow cell was used to investigate the onset conditions for ice nucleation on five atmospherically relevant minerals at temperatures ranging from 233 to 246 K. Here we define the onset conditions as the humidity and temperature at which the first ice nucleation event was observed. Kaolinite and muscovite were found to be efficient ice nuclei in the deposition mode, requiring relative humidities with respect to ice (RHi) below 112% in order to initiate ice crystal formation. Quartz and calcite, by contrast, were poor ice nuclei, requiring relative humidities close to water saturation before ice crystals would form. Montmorillonite particles were efficient ice nuclei at temperatures below 241 K but were poor ice nuclei at higher temperatures. In several cases, there was a lack of quantitative agreement between our data and previously published work. This can be explained by several factors including the mineral source, the particle sizes, the surface area available for nucleation, and observation time. Heterogeneous nucleation rates (Jhet) were calculated from the measurements of the onset conditions (temperature and RHi) required from ice nucleation. The Jhet values were then used to calculate contact angles (θ) between the mineral substrates and an ice embryo using classical nucleation theory. The contact angles measured for kaolinite and muscovite ranged from 6° to 12°, whereas for quartz and calcite, the contact angles ranged from 25° to 27°. The reported Jhet and θ values may allow for a more direct comparison between laboratory studies and can be used when modeling ice cloud formation in the atmosphere.

  12. Effects of shear flow on phase nucleation and crystallization

    Science.gov (United States)

    Mura, Federica; Zaccone, Alessio

    2016-04-01

    Classical nucleation theory offers a good framework for understanding the common features of new phase formation processes in metastable homogeneous media at rest. However, nucleation processes in liquids are ubiquitously affected by hydrodynamic flow, and there is no satisfactory understanding of whether shear promotes or slows down the nucleation process. We developed a classical nucleation theory for sheared systems starting from the molecular level of the Becker-Doering master kinetic equation and we analytically derived a closed-form expression for the nucleation rate. The theory accounts for the effect of flow-mediated transport of molecules to the nucleus of the new phase, as well as for the mechanical deformation imparted to the nucleus by the flow field. The competition between flow-induced molecular transport, which accelerates nucleation, and flow-induced nucleus straining, which lowers the nucleation rate by increasing the nucleation energy barrier, gives rise to a marked nonmonotonic dependence of the nucleation rate on the shear rate. The theory predicts an optimal shear rate at which the nucleation rate is one order of magnitude larger than in the absence of flow.

  13. Achieving Airport Carbon Neutrality

    Science.gov (United States)

    2016-03-01

    This report is a guide for airports that wish to reduce or eliminate greenhouse gas (GHG) emissions from existing buildings and operations. Reaching carbon neutrality typically requires the use of multiple mechanisms to first minimize energy consumpt...

  14. Lamellipodia nucleation by filopodia depends on integrin occupancy and downstream Rac1 signaling

    International Nuclear Information System (INIS)

    Guillou, Herve; Depraz-Depland, Adeline; Planus, Emmanuelle; Vianay, Benoit; Chaussy, Jacques; Grichine, Alexei; Albiges-Rizo, Corinne; Block, Marc R.

    2008-01-01

    Time-lapse video-microscopy unambiguously shows that fibroblast filopodia are the scaffold of lamellipodia nucleation that allows anisotropic cell spreading. This process was dissected into elementary stages by monitoring cell adhesion on micropatterned extracellular matrix arrays of various pitches. Adhesion structures are stabilized by contact with the adhesive plots and subsequently converted into lamellipodia-like extensions starting at the filopodia tips. This mechanism progressively leads to full cell spreading. Stable expression of the dominant-negative Rac1 N17 impairs this change in membrane extension mode and stops cell spreading on matrix arrays. Similar expression of the dominant-negative Cdc42 N17 impairs cell spreading on homogenous and structured substrate, suggesting that filopodia extension is a prerequisite for cell spreading in this model. The differential polarity of the nucleation of lamellipodial structures by filopodia on homogenous and structured surfaces starting from the cell body and of filopodia tip, respectively, suggested that this process is triggered by areas that are in contact with extracellular matrix proteins for longer times. Consistent with this view, wild-type cells cannot spread on microarrays made of function blocking or neutral anti-β 1 integrin antibodies. However, stable expression of a constitutively active Rac1 mutant rescues the cell ability to spread on these integrin microarrays. Thereby, lamellipodia nucleation by filopodia requires integrin occupancy by matrix substrate and downstream Rac1 signaling

  15. One Year After Fukushima, Nuclear Safety Is Stronger

    International Nuclear Information System (INIS)

    2012-01-01

    Full text: Nuclear power is safer than it was a year ago as the nuclear industry, regulators and governments act on the lessons of Fukushima, but that safety must never be taken for granted, said Yukiya Amano, Director General of the International Atomic Energy Agency (IAEA). Speaking ahead of the first anniversary of the Fukushima Daiichi nuclear accident on 11 March, Amano said a culture of constant vigilance and improvement was vital to ensure that the benefits of nuclear power could be harnessed as safely as humanly possible. 'Nuclear safety is stronger than it was a year ago', he said. 'Fukushima Daiichi was a very serious accident, but we know what went wrong and we have a clear course of action to tackle those causes - not only in Japan, but anywhere in the world. 'Now we have to keep up the momentum. Complacency can kill'. On 11 March 2011 a huge earthquake and tsunami left more than 20 000 people dead or missing in eastern Japan. Amidst widespread destruction, the tsunami slammed into the Fukushima Daiichi Nuclear Power Station, disabling cooling systems and leading to fuel meltdowns in three of the six Units. The accident was a jolt to the nuclear industry, regulators and governments. It was triggered by a massive force of nature, but it was existing weaknesses of design regarding defence against natural hazards, regulatory oversight, accident management and emergency response that allowed it to unfold as it did. For example: The nuclear regulator was not sufficiently independent, allowing weak oversight of the operator, TEPCO, and regulatory requirements fell short of international best practice; Not enough attention was paid to guarding against possible extreme events at the Fukushima Daiichi site, leaving critical safety functions such as cooling systems vulnerable to the tsunami; Training to respond to serious accidents was inadequate, as were mitigation measures to prevent hydrogen explosions and protect the venting system; and Accident command lines

  16. Differences in ice nucleation behavior of arable and desert soil dust in deposition nucleation regime

    Science.gov (United States)

    Ullrich, Romy; Vogel, Franziska; Möhler, Ottmar; Höhler, Kristina; Schiebel, Thea

    2017-04-01

    Soil dust from arid and semi-arid regions is one of the most abundant aerosol types in the atmosphere with emission rates of about 1600 Tg per year (Andreae et al. (2009)). Therewith, soil dust plays an important role for the atmospheric radiative transfer and also for the formation of clouds. Soil dust refers to dust sampled from agricultural used areas, to dust from bare soil as well as to dust from desert regions. By mass-spectrometric measurements of the chemical composition of ice residuals, mineral dust as component of soil dust was found to be the major heterogeneous ice nucleating particle (INP) type (e.g. Cziczo et al. (2013)), in particular in the upper troposphere. Also in laboratory studies the ice nucleation efficiency of the different soil dusts was investigated. It was shown that desert dusts (Ullrich et al. (2017)) as well as soil dusts from arable regions (O'Sullivan et al. (2014), Tobo et al. (2014)) are efficient INP. However, there is still a lack of data for ice nucleation on soil dusts for temperatures below about 220 K. With the AIDA (Aerosol Interactions and Dynamics in the Atmosphere) cloud chamber, we are able to characterize the ice nucleation efficiency for different aerosol types to temperatures down to 180 K and high ice supersaturations. In order to extend the already existing AIDA data base for deposition nucleation on desert dusts and agricultural soil dusts, new experiments were done in the upper tropospheric temperature regime. This contribution will show the results of the new experiments with desert dust in comparison to existing data for higher temperatures. The first data analysis confirms the temperature dependent trend of the ice nucleation activity as discussed and parameterized in a recent paper by Ullrich et al. (2017). Furthermore, the update and extension of the recently published parameterization of deposition nucleation for desert dust to lower temperatures will be discussed. The experiments with agricultural soil

  17. Identification & Characterization of Fungal Ice Nucleation Proteins

    Science.gov (United States)

    Scheel, Jan Frederik; Kunert, Anna Theresa; Kampf, Christopher Johannes; Mauri, Sergio; Weidner, Tobias; Pöschl, Ulrich; Fröhlich-Nowoisky, Janine

    2016-04-01

    Freezing of water at relatively warm subfreezing temperatures is dependent on ice nucleation catalysis facilitated by ice nuclei (IN). These IN can be of various origins and although extensive research was done and progress was achieved, the nature and mechanisms leading to an effective IN are to date still poorly understood. Some of the most important processes of our geosphere like the water cycle are highly dependent on effective ice nucleation at temperatures between -2°C - -8°C, a temperature range which is almost exclusively covered by biological IN (BioIN). BioIN are usually macromolecular structures of biological polymers. Sugars as well as proteins have been reported to serve as IN and the best characterized BioIN are ice nucleation proteins (IN-P) from gram negative bacteria. Fungal strains from Fusarium spp. were described to be effective IN at subfreezing temperatures up to -2°C already 25 years ago and more and more fungal species are described to serve as efficient IN. Fungal IN are also thought to be proteins or at least contain a proteinaceous compound, but to date the fungal IN-P primary structure as well as their coding genetic elements of all IN active fungi are unknown. The aim of this study is a.) to identify the proteins and their coding genetic elements from IN active fungi (F. acuminatum, F. avenaceum, M. alpina) and b.) to characterize the mechanisms by which fungal IN serve as effective IN. We designed an interdisciplinary approach using biological, analytical and physical methods to identify fungal IN-P and describe their biological, chemical, and physical properties.

  18. Binary Homogeneous Nucleation in Selected Aqueous

    Czech Academy of Sciences Publication Activity Database

    Maršík, František; Němec, Tomáš; Hrubý, Jan; Demo, Pavel; Kožíšek, Zdeněk; Petr, V.; Kolovratník, M.

    2008-01-01

    Roč. 37, č. 12 (2008), s. 1671-1708 ISSN 0095-9782 R&D Projects: GA ČR(CZ) GA101/05/2524; GA AV ČR KJB400760701; GA MŠk(CZ) 1M06031; GA AV ČR IBS2076003 Institutional research plan: CEZ:AV0Z20760514; CEZ:AV0Z10100520 Keywords : nucleation * steam * theory Subject RIV: BJ - Thermodynamics Impact factor: 1.241, year: 2008 http://www.springerlink.com/content/104381/

  19. Investigating the role of solvent-solute interaction in crystal nucleation of salicylic acid from organic solvents.

    Science.gov (United States)

    Khamar, Dikshitkumar; Zeglinski, Jacek; Mealey, Donal; Rasmuson, Åke C

    2014-08-20

    In previous work, it has been shown that the crystal nucleation of salicylic acid (SA) in different solvents becomes increasingly more difficult in the order: chloroform, ethyl acetate acetonitrile, acetone, methanol, and acetic acid. In the present work, vibration spectroscopy, calorimetric measurements, and density functional theory (DFT) calculations are used to reveal the underlying molecular mechanisms. Raman and infrared spectra suggest that SA exists predominately as dimers in chloroform, but in the other five solvents there is no clear evidence of dimerization. In all solvents, the shift in the SA carbonyl peak reflecting the strength in the solvent-solute interaction is quite well correlated to the nucleation ranking. This shift is corroborated by DFT calculated energies of binding one solvent molecule to the carboxyl group of SA. An even better correlation of the influence of the solvent on the nucleation is provided by DFT calculated energy of binding the complete first solvation shell to the SA molecule. These solvation shell binding energies are corroborated by the enthalpy of solvent-solute interaction as estimated from experimentally determined enthalpy of solution and calculated enthalpy of cavity formation using the scaled particle theory. The different methods reveal a consistent picture and suggest that the stronger the solvent binds to the SA molecule in solution, the slower the nucleation becomes.

  20. Heterogeneous ice nucleation: bridging stochastic and singular freezing behavior

    Science.gov (United States)

    Niedermeier, D.; Shaw, R. A.; Hartmann, S.; Wex, H.; Clauss, T.; Voigtländer, J.; Stratmann, F.

    2011-01-01

    Heterogeneous ice nucleation, a primary pathway for ice formation in the atmosphere, has been described alternately as being stochastic, in direct analogy with homogeneous nucleation, or singular, with ice nuclei initiating freezing at deterministic temperatures. We present an idealized model that bridges these stochastic and singular descriptions of heterogeneous ice nucleation. This "soccer ball" model treats statistically similar particles as being covered with surface sites (patches of finite area) characterized by different nucleation barriers, but with each surface site following the stochastic nature of ice embryo formation. The model provides a phenomenological explanation for seemingly contradictory experimental results obtained in our research groups. We suggest that ice nucleation is fundamentally a stochastic process but that for realistic atmospheric particle populations this process can be masked by the heterogeneity of surface properties. Full evaluation of the model will require experiments with well characterized ice nucleating particles and the ability to vary both temperature and waiting time for freezing.

  1. Nucleation and growth of voids by radiation. Pt. 2

    International Nuclear Information System (INIS)

    Mayer, R.M.; Brown, L.M.

    1980-01-01

    The original model of Brown, Kelly and Mayer [1] for the nucleation of interstitial loops has been extended to take into account the following: (i) mobility of the vacancies, (ii) generation and migration of gas atoms during irradiation, (iii) nucleation and growth of voids, and (iv) vacancy emission from voids and clusters at high temperatures. Using chemicalrate equations, additional expressions are formulated for the nucleation and growth of vacancy loops and voids. (orig.)

  2. Aerosol nucleation induced by a high energy particle beam

    DEFF Research Database (Denmark)

    Enghoff, Martin Andreas Bødker; Pedersen, Jens Olaf Pepke; Uggerhøj, Ulrik I.

    2011-01-01

    -effect on aerosol nucleation using a particle beam under conditions that resemble the Earth's atmosphere. By comparison with ionization using a gamma source we further show that the nature of the ionizing particles is not important for the ion-induced component of the nucleation. This implies that inexpensive...... ionization sources - as opposed to expensive accelerator beams - can be used for investigations of ion-induced nucleation....

  3. Fatigue crack nucleation of type 316LN stainless steel

    International Nuclear Information System (INIS)

    Kim, Dae Whan; Kim, Woo Gon; Hong, Jun Hwa; Ryu, Woo Seog

    2000-01-01

    Low Cycle Fatigue (LCF) life decreases drastically with increasing temperature but increases with the addition of nitrogen at room and high temperatures. The effect of nitrogen on LCF life may be related to crack nucleation at high temperatures in austenitic stainless steel because the fraction of crack nucleation in LCF life is about 40%. The influence of nitrogen on the crack nucleation of LCF in type 316LN stainless steel is investigated by observations of crack population and crack depth after testing at 40% of fatigue life. Nitrogen increases the number of cycles to nucleate microcracks of 100 μm but decreases the crack population

  4. Controlling the quantum dot nucleation site

    International Nuclear Information System (INIS)

    Motta, Nunzio; Sgarlata, Anna; Rosei, Federico; Szkutnik, P.D.; Nufris, S.; Scarselli, M.; Balzarotti, A.

    2003-01-01

    Quantum dots (QDs) are actually easily produced by self-assembling during heteroepitaxial growth of semiconductors. In order to exploit the unique electronic properties of semiconductor QDs in novel quantum effect devices, the lateral dimensions of these structures have to be reduced to the order of tens of nanometers, which is the range of the De Broglie wavelength of electrons inside these materials. Moreover, millions of QDs must be arranged in dense ordered arrays to achieve the necessary active volume for optoelectronic applications. Nowadays it is possible to control size and shape of the nanocrystals, but it is still difficult to decide their nucleation site. Many approaches have been undertaken to overcome this problem, like using regular dislocation networks, lithographically and Atomic Force Microscopy (AFM) patterned substrates, naturally patterned surfaces. We present results obtained by some of these methods, visualized by Scanning Tunnelling Microscopy (STM) or AFM microscopy. STM measurements at high temperature during the epitaxial growth are of great help in these studies. Images and movies of the growth of Ge on Si help to identify the real nucleation sites of the islands and to follow their evolution. The influence of the 'step bunching' on the self-organization of Ge islands on Si(111) surfaces will be analysed, as an example of growth on self-nanostructured surfaces

  5. Earthquake nucleation in weak subducted carbonates

    Science.gov (United States)

    Kurzawski, Robert M.; Stipp, Michael; Niemeijer, André R.; Spiers, Christopher J.; Behrmann, Jan H.

    2016-09-01

    Ocean-floor carbonate- and clay-rich sediments form major inputs to subduction zones, especially at low-latitude convergent plate margins. Therefore, knowledge of their frictional behaviour is fundamental for understanding plate-boundary earthquakes. Here we report results of mechanical tests performed on simulated fault gouges prepared from ocean-floor carbonates and clays, cored during IODP drilling offshore Costa Rica. Clay-rich gouges show internal friction coefficients (that is, the slope of linearized shear stress versus normal stress data) of μint = 0.44 - 0.56, irrespective of temperature and pore-fluid pressure (Pf). By contrast, μint for the carbonate gouge strongly depends on temperature and pore-fluid pressure, with μint decreasing dramatically from 0.84 at room temperature and Pf = 20 MPa to 0.27 at T = 140 °C and Pf = 120 MPa. This effect provides a fundamental mechanism of shear localization and earthquake generation in subduction zones, and makes carbonates likely nucleation sites for plate-boundary earthquakes. Our results imply that rupture nucleation is prompted by a combination of temperature-controlled frictional instability and temperature- and pore-pressure-dependent weakening of calcareous fault gouges.

  6. A nucleation theory of cell surface capping

    International Nuclear Information System (INIS)

    Coutsias, E.A.; Wester, M.J.; Perelson, A.S.

    1997-01-01

    We propose a new theory of cell surface capping based on the principles of nucleation. When antibody interacts with cell surface molecules, the molecules initially form small aggregates called patches that later coalesce into a large aggregate called a cap. While a cap can form by patches being pulled together by action of the cell''s cytoskeleton, in the case of some molecules, disruption of the cytoskeleton does not prevent cap formation. Diffusion of large aggregates on a cell surface is slow, and thus we propose that a cap can form solely through the diffusion of small aggregates containing just one or a few cell surface molecules. Here we consider the extreme case in which single molecules are mobile, but aggregates of all larger sizes are immobile. We show that a set of patches in equilibrium with a open-quotes seaclose quotes of free cell surface molecules can undergo a nucleation-type phase transition in which the largest patch will bind free cell surface molecules, deplete the concentration of such molecules in the open-quotes seaclose quotes and thus cause the other patches to shrink in size. We therefore show that a cap can form without patches having to move, collide with each other, and aggregate

  7. Epitaxial nucleation and growth of molecular films

    Science.gov (United States)

    Hooks, Daniel Edwin

    2000-10-01

    The last decade has witnessed an increased emphasis on the design and use of molecular-based materials, commonly in thin film form, as components in electronic devices, sensors, displays, and logic elements. The growing interest in films based on molecular components, rather than their more traditional inorganic counterparts, stems largely from the premise that collective optical and electronic properties can be systematically manipulated through molecular design. Many of these properties depend strongly upon film structure and orientation with respect to the substrate upon which they are deposited. This relationship mandates careful attention to the interface between the primary molecular overlayer and the substrate. Further advances in molecular films and multilayer composites based on molecular films require improved understanding of the role of epitaxy in molecular organization as well as the nucleation events that precede film formation. Determination of critical nucleus dimensions and elucidation of the factors that govern critical size are particularly important for fabricating nanoscale molecular features and controlling domain defects in contiguous molecular films. This thesis describes an examination of the role of epitaxy in the growth of molecular films, including a hierarchical classification and grammar of molecular epitaxy, an atomic force microscopy (AFM) investigation of the intercalation of molecular components into multilayer organic-inorganic composites, and an AFM investigation of the nucleation of molecular films.

  8. Evaluation of onset of nucleate boiling models

    Energy Technology Data Exchange (ETDEWEB)

    Huang, LiDong [Heat Transfer Research, Inc., College Station, TX (United States)], e-mail: lh@htri.net

    2009-07-01

    This article discusses available models and correlations for predicting the required heat flux or wall superheat for the Onset of Nucleate Boiling (ONB) on plain surfaces. It reviews ONB data in the open literature and discusses the continuing efforts of Heat Transfer Research, Inc. in this area. Our ONB database contains ten individual sources for ten test fluids and a wide range of operating conditions for different geometries, e.g., tube side and shell side flow boiling and falling film evaporation. The article also evaluates literature models and correlations based on the data: no single model in the open literature predicts all data well. The prediction uncertainty is especially higher in vacuum conditions. Surface roughness is another critical criterion in determining which model should be used. However, most models do not directly account for surface roughness, and most investigators do not provide surface roughness information in their published findings. Additional experimental research is needed to improve confidence in predicting the required wall superheats for nucleation boiling for engineering design purposes. (author)

  9. Using measurements of the aerosol charging state in determination of the particle growth rate and the proportion of ion-induced nucleation

    Directory of Open Access Journals (Sweden)

    J. Leppä

    2013-01-01

    Full Text Available The fraction of charged nucleation mode particles as a function of particle diameter depends on the particle growth rate and the proportion of particles formed via ion-induced nucleation. In this study we have tested the applicability of recent data analysis methods to determine the growth rate and the proportion of ion-induced nucleation from the measured charged fractions. For this purpose we have conducted a series of aerosol dynamic simulations covering a wide range of atmospheric conditions. The growth rate and initial fraction of charged particles were estimated from simulated data using these methods and compared with the values obtained directly from the simulations. We found that the data analysis methods used in this study should not be used when the nuclei growth rate is less than ~3 nm h−1, or when charged particles grow much more rapidly than neutral ones. Furthermore, we found that the difference in removal rates of neutral and charged particles should be taken into account when estimating the proportion of ion-induced nucleation. Neglecting the higher removal rate of charged particles compared with that of neutral ones could result in an underestimation of the proportion of ion-induced nucleation by up to a factor of 2. This underestimation is further increased if charged particles grow more rapidly than neutral ones. We also provided a simple way of assessing whether these methods are suitable for analyzing data measured under specific conditions. The assessment procedure was illustrated using a few examples of actual measurement sites with a more detailed examination of the typical conditions observed at the SMEAR II station in Hyytiälä, Finland.

  10. CO2-Neutral Fuels

    NARCIS (Netherlands)

    Goede, A.; van de Sanden, M. C. M.

    2016-01-01

    Mimicking the biogeochemical cycle of System Earth, synthetic hydrocarbon fuels are produced from recycled CO2 and H2O powered by renewable energy. Recapturing CO2 after use closes the carbon cycle, rendering the fuel cycle CO2 neutral. Non-equilibrium molecular CO2 vibrations are key to high energy

  11. Issues in neutral currents

    International Nuclear Information System (INIS)

    Sehgal, L.M.

    1980-01-01

    The experimental results on low energy confirming the structure of the effective Lagrangian of the weak neutral current processes as predicted by the Salam-Weinberg model are reviewed. Some possible modifications of the effective Lagrangian and the feasibility of their experimental verification are also considered. (P.L.)

  12. Dynamics of neutral and charged aerosol particles

    Energy Technology Data Exchange (ETDEWEB)

    Leppae, J.

    2012-07-01

    Atmospheric aerosol particles have various climate effects and adverse health effects, which both depend on the size and number concentration of the particles. Freshly-formed particles are not large enough to impact neither health nor climate and they are most susceptible to removal by collisions with larger pre-existing particles. Consequently, the knowledge of both the formation and the growth rate of particles are crucially important when assessing the health and climate effects of atmospheric new particle formation. The purpose of this thesis is to increase our knowledge of the dynamics of neutral and charged aerosol particles with a specific interest towards the particle growth rate and processes affecting the aerosol charging state. A new model, Ion-UHMA, which simulates the dynamics of neutral and charged particles, was developed for this purpose. Simple analytical formulae that can be used to estimate the growth rate due to various processes were derived and used to study the effects of charged particles on the growth rate. It was found that the growth rate of a freshly-formed particle population due to condensation and coagulation could be significantly increased when a considerable fraction of the particles are charged. Finally, recent data-analysis methods that have been applied to the aerosol charging states obtained from the measurements were modified for a charge asymmetric framework. The methods were then tested on data obtained from aerosol dynamics simulations. The methods were found to be able to provide reasonable estimates on the growth rate and proportion of particles formed via ion-induced nucleation, provided that the growth rate is high enough and that the charged particles do not grow much more rapidly than the neutral ones. A simple procedure for estimating whether the methods are suitable for analysing data obtained in specific conditions was provided. In this thesis, the dynamics of neutral and charged aerosol particles were studied in

  13. Some ice nucleation characteristics of Asian and Saharan desert dust

    Directory of Open Access Journals (Sweden)

    P. R. Field

    2006-01-01

    Full Text Available The large (7 m×4 m cylinder, 84 m3 AIDA (Aerosol Interactions and Dynamics in the Atmosphere cloud chamber facility at Forschungszentrum, Karlsruhe, Germany was used to test the ice nucleating ability of two desert dust samples from the Sahara and Asia. Aerosol samples were lognormally distributed with a mode diameter of 0.4(±0.1 μm and geometric standard deviation of ~1.7(±0.2. At temperatures warmer than −40°C droplets were formed before ice crystals formed and there was generally no deposition nucleation observed. At temperatures colder than −40°C both dust samples exhibited dual nucleation events that were observed during the same expansion experiment. The primary nucleation event occurred at ice saturation ratios of 1.1 to 1.3 and is likely to be a deposition nucleation mode. The secondary nucleation event occurred at ice saturation ratios between 1.35 and 1.5. We cannot categorically determine whether this ice nucleation event is via a further deposition mode or a condensation mode, but the presence of some soluble material in the dust samples leads us to favour the latter process. The activated fractions of desert dust ranged from ~5–10% at −20°C to 20–40% at temperatures colder than −40°C. There was no obvious difference between the nucleation behaviour of the two dust samples.

  14. Nucleation of domains under the influence of temperature in ...

    Indian Academy of Sciences (India)

    Abstract. It is found that the nucleation of domains can take place in Ba5Ti2O7Cl4 under the influence of temperature unlike in many other ferroelectrics. The nucleated domain can also be removed from the structure under the randomizing effect of tem- perature. These observations have been explained on the basis of a ...

  15. Mechanism of cube grain nucleation during recrystallization of ...

    Indian Academy of Sciences (India)

    Unknown

    Abstract. Cube texture is a sharp recrystallization texture component in fcc metals like aluminium, copper, etc. It is described by an ideal orientation i.e. (100) 〈100〉. The subject of cube texture nucleation i.e. cube grain nucleation, from the deformed state of aluminium and copper is of scientific curiosity with concurrent.

  16. Nucleation and growth of polycrystalline SiC

    DEFF Research Database (Denmark)

    Kaiser, M.; Schimmel, S.; Jokubavicius, V.

    2014-01-01

    The nucleation and bulk growth of polycrystalline SiC in a 2 inch PVT setup using isostatic and pyrolytic graphite as substrates was studied. Textured nucleation occurs under near-thermal equilibrium conditions at the initial growth stage with hexagonal platelet shaped crystallites of 4H, 6H and ...

  17. Local structure of liquid carbon controls diamond nucleation

    NARCIS (Netherlands)

    Ghiringhelli, L.M.; Valeriani, C.; Meijer, E.J.; Frenkel, D.

    2009-01-01

    Diamonds melt at temperatures above 4000 K. There are no measurements of the steady-state rate of the reverse process: diamond nucleation from the melt, because experiments are difficult at these extreme temperatures and pressures. Using numerical simulations, we estimate the diamond nucleation rate

  18. Trapping crystal nucleation of cholesterol monohydrate

    DEFF Research Database (Denmark)

    Solomonov, I.; Weygand, M.J.; Kjær, K.

    2005-01-01

    Crystalline nucleation of cholesterol at the air-water interface has been studied via grazing incidence x-ray diffraction using synchrotron radiation. The various stages of cholesterol molecular assembly from monolayer to three bilayers incorporating interleaving hydrogen-bonded water layers...... in a monoclinic cholesterol . H2O phase, has been monitored and their structures characterized to near atomic resolution. Crystallographic evidence is presented that this multilayer phase is similar to that of a reported metastable cholesterol phase of undetermined structure obtained from bile before...... transformation to the triclinic phase of cholesterol . H2O, the thermodynamically stable macroscopic form. According to grazing incidence x-ray diffraction measurements and crystallographic data, a transformation from the monoclinic film structure to a multilayer of the stable monohydrate phase involves...

  19. Nucleation of microcrystalline silicon: on the effect of the substrate surface nature and nano-imprint topography

    International Nuclear Information System (INIS)

    Palmans, J; Faraz, T; Verheijen, M A; Kessels, W M M; Creatore, M

    2016-01-01

    The nucleation of microcrystalline silicon thin-films has been investigated for various substrate natures and topographies. An earlier nucleation onset on aluminium-doped zinc oxide compared to glass substrates has been revealed, associated with a microstructure enhancement and reduced surface energy. Both aspects resulted in a larger crystallite density, following classical nucleation theory. Additionally, the nucleation onset was (plasma deposition) condition-dependent. Therefore, surface chemistry and its interplay with the plasma have been proposed as key factors affecting nucleation and growth. As such, preliminary proof of the substrate nature’s role in microcrystalline silicon growth has been provided. Subsequently, the impact of nano-imprint lithography prepared surfaces on the initial microcrystalline silicon growth has been explored. Strong topographies, with a 5-fold surface area enhancement, led to a reduction in crystalline volume fraction of ∼20%. However, no correlation between topography and microstructure has been found. Instead, the suppressed crystallization has been partially ascribed to a reduced growth flux, limited surface diffusion and increased incubation layer thickness, originating from the surface area enhancement when transiting from flat to nanostructured surfaces. Furthermore, fundamental plasma parameters have been reviewed in relation with surface topography. Strong topographies are not expected to affect the ion-to-growth flux ratio. However, the reduced ion flux (due to increasing surface area) further limited the already weak ion energy transfer to surface processes. Additionally, the atomic hydrogen flux, i.e. the driving force for microcrystalline growth, has been found to decrease by a factor of 10 when transiting from flat to nanostructured topography. This resulted in an almost 6-fold reduction of the hydrogen-to-growth flux ratio, a much stronger effect than the ion-to-growth flux ratio. Since previous studies regarding

  20. Observations on the nucleation of ice VII in compressed water

    Science.gov (United States)

    Stafford, Samuel J. P.; Chapman, David J.; Bland, Simon N.; Eakins, Daniel E.

    2017-01-01

    Water can freeze upon multiple shock compression, but the window material determines the pressure of the phase transition. Several plate impact experiments were conducted with liquid targets on a single-stage gas gun, diagnosed simultaneously using photonic doppler velocimetry (PDV) and high speed imaging through the water. The experiments investigated why silica windows instigate freezing above 2.5 GPa whilst sapphire windows do not until 7 GPa. We find that the nucleation of ice occurs on the surfaces of windows and can be affected by the surface coating suggesting the surface energy of fused silica, likely due to hydroxyl groups, encourages nucleation of ice VII crystallites. Aluminium coatings prevent nucleation and sapphire surfaces do not nucleate until approximately 6.5 GPa. This is believed to be the threshold pressure for the homogeneous nucleation of water.

  1. Do protein crystals nucleate within dense liquid clusters?

    Energy Technology Data Exchange (ETDEWEB)

    Maes, Dominique, E-mail: dommaes@vub.ac.be [Vrije Universiteit Brussel, 1050 Brussels (Belgium); Vorontsova, Maria A. [University of Houston, Houston, TX 77204 (United States); Potenza, Marco A. C.; Sanvito, Tiziano [Universita di Milano, 20133 Milano (Italy); Sleutel, Mike [Vrije Universiteit Brussel, 1050 Brussels (Belgium); Giglio, Marzio [Universita di Milano, 20133 Milano (Italy); Vekilov, Peter G. [Vrije Universiteit Brussel, 1050 Brussels (Belgium); University of Houston, Houston, TX 77204 (United States); University of Houston, Houston, TX 77204 (United States)

    2015-06-27

    The evolution of protein-rich clusters and nucleating crystals were characterized by dynamic light scattering (DLS), confocal depolarized dynamic light scattering (cDDLS) and depolarized oblique illumination dark-field microscopy. Newly nucleated crystals within protein-rich clusters were detected directly. These observations indicate that the protein-rich clusters are locations for crystal nucleation. Protein-dense liquid clusters are regions of high protein concentration that have been observed in solutions of several proteins. The typical cluster size varies from several tens to several hundreds of nanometres and their volume fraction remains below 10{sup −3} of the solution. According to the two-step mechanism of nucleation, the protein-rich clusters serve as locations for and precursors to the nucleation of protein crystals. While the two-step mechanism explained several unusual features of protein crystal nucleation kinetics, a direct observation of its validity for protein crystals has been lacking. Here, two independent observations of crystal nucleation with the proteins lysozyme and glucose isomerase are discussed. Firstly, the evolutions of the protein-rich clusters and nucleating crystals were characterized simultaneously by dynamic light scattering (DLS) and confocal depolarized dynamic light scattering (cDDLS), respectively. It is demonstrated that protein crystals appear following a significant delay after cluster formation. The cDDLS correlation functions follow a Gaussian decay, indicative of nondiffusive motion. A possible explanation is that the crystals are contained inside large clusters and are driven by the elasticity of the cluster surface. Secondly, depolarized oblique illumination dark-field microscopy reveals the evolution from liquid clusters without crystals to newly nucleated crystals contained in the clusters to grown crystals freely diffusing in the solution. Collectively, the observations indicate that the protein-rich clusters in

  2. Do protein crystals nucleate within dense liquid clusters?

    International Nuclear Information System (INIS)

    Maes, Dominique; Vorontsova, Maria A.; Potenza, Marco A. C.; Sanvito, Tiziano; Sleutel, Mike; Giglio, Marzio; Vekilov, Peter G.

    2015-01-01

    The evolution of protein-rich clusters and nucleating crystals were characterized by dynamic light scattering (DLS), confocal depolarized dynamic light scattering (cDDLS) and depolarized oblique illumination dark-field microscopy. Newly nucleated crystals within protein-rich clusters were detected directly. These observations indicate that the protein-rich clusters are locations for crystal nucleation. Protein-dense liquid clusters are regions of high protein concentration that have been observed in solutions of several proteins. The typical cluster size varies from several tens to several hundreds of nanometres and their volume fraction remains below 10 −3 of the solution. According to the two-step mechanism of nucleation, the protein-rich clusters serve as locations for and precursors to the nucleation of protein crystals. While the two-step mechanism explained several unusual features of protein crystal nucleation kinetics, a direct observation of its validity for protein crystals has been lacking. Here, two independent observations of crystal nucleation with the proteins lysozyme and glucose isomerase are discussed. Firstly, the evolutions of the protein-rich clusters and nucleating crystals were characterized simultaneously by dynamic light scattering (DLS) and confocal depolarized dynamic light scattering (cDDLS), respectively. It is demonstrated that protein crystals appear following a significant delay after cluster formation. The cDDLS correlation functions follow a Gaussian decay, indicative of nondiffusive motion. A possible explanation is that the crystals are contained inside large clusters and are driven by the elasticity of the cluster surface. Secondly, depolarized oblique illumination dark-field microscopy reveals the evolution from liquid clusters without crystals to newly nucleated crystals contained in the clusters to grown crystals freely diffusing in the solution. Collectively, the observations indicate that the protein-rich clusters in

  3. Neutral atom traps.

    Energy Technology Data Exchange (ETDEWEB)

    Pack, Michael Vern

    2008-12-01

    This report describes progress in designing a neutral atom trap capable of trapping sub millikelvin atom in a magnetic trap and shuttling the atoms across the atom chip from a collection area to an optical cavity. The numerical simulation and atom chip design are discussed. Also, discussed are preliminary calculations of quantum noise sources in Kerr nonlinear optics measurements based on electromagnetically induced transparency. These types of measurements may be important for quantum nondemolition measurements at the few photon limit.

  4. Ion-Ion Neutralization.

    Science.gov (United States)

    1982-05-31

    of Birmingam, P 0 Box 363, 2310/A2 Birmingham B15 2TT, England. 2303/GlAC II. Controlling Office Name and Address 12. Report Date Air Force Geophysics...source. Thus unwanted molecular excitation and dissociation can be avoided and greater control can be exercised in the creation of suitable plasma...The Fall fractigRal ionization density in these afterglow plagas (%-10 -𔃺) ensures that electron- neutral collisions are the most effective. This

  5. Exercise Equipment: Neutral Buoyancy

    Science.gov (United States)

    Shackelford, Linda; Valle, Paul

    2016-01-01

    Load Bearing Equipment for Neutral Buoyancy (LBE-NB) is an exercise frame that holds two exercising subjects in position as they apply counter forces to each other for lower extremity and spine loading resistance exercises. Resistance exercise prevents bone loss on ISS, but the ISS equipment is too massive for use in exploration craft. Integrating the human into the load directing, load generating, and motion control functions of the exercise equipment generates safe exercise loads with less equipment mass and volume.

  6. Gargamelle: neutral current event

    CERN Multimedia

    1973-01-01

    This event shows real tracks of particles from the 1200 litre Gargamelle bubble chamber that ran on the PS from 1970 to 1976 and on the SPS from 1976 to 1979. In this image a neutrino passes close to a nucleon and reemerges as a neutrino. Such events are called neutral curent, as they are mediated by the Z0 boson which has no electric charge.

  7. Antihypertensive neutral lipid

    Science.gov (United States)

    Snyder, F.L.; Blank, M.L.

    1984-10-26

    The invention relates to the discovery of a class of neutral acetylated either-linked glycerolipids having the capacity to lower blood presure in warm-blooded animals. This physiological effect is structure sensitive requiring a long chain alkyl group at the sn-1 position and a short carbon chain acyl group (acetyl or propionyl) at the sn-2 position, and a hydroxyl group at the sn-3 position.

  8. Stronger learning recruits additional cell-signaling cascades: c-Jun-N-terminal kinase 1 (JNK1) is necessary for expression of stronger contextual fear conditioning.

    Science.gov (United States)

    Leach, Prescott T; Kenney, Justin W; Gould, Thomas J

    2015-02-01

    Increased training often results in stronger memories but the neural changes responsible for these stronger memories are poorly understood. It is proposed here that higher levels of training that result in stronger memories recruit additional cell signaling cascades. This study specifically examined if c-Jun N-terminal kinase 1 (JNK1) is involved in the formation of stronger fear conditioning memories. Wildtype (WT), JNK1 heterozygous (Het), and JNK1 knockout (KO) mice were fear conditioned with 1 trial, 2 trials, or 4 trials. All mice learned both contextual (hippocampus-dependent) and cued (hippocampus-independent) fear conditioning but for contextual fear conditioning only, the JNK1 KO mice did not show higher levels of learning with increased trials. That is, WT mice showed a significant linear increase in contextual fear conditioning as training trials increased from 1 to 2 to 4 trials whereas KO mice showed the same level of contextual fear conditioning as WT mice for 1 trial training but did not have increased levels of contextual fear conditioning with additional trials. These data suggest that JNK1 may not be critical for learning but when higher levels of hippocampus-dependent learning occur, JNK1 signaling is recruited and is necessary for stronger hippocampus-dependent memory formation. Copyright © 2014 Elsevier Inc. All rights reserved.

  9. Nucleation at the Contact Line Observed on Nanotextured Surfaces

    Science.gov (United States)

    Kostinski, A. B.; Gurganus, C.; Charnawskas, J. C.; Shaw, R. A.

    2015-12-01

    Surface nucleation, and contact nucleation in particular, are important for many physical processes, including pharmaceutical drug synthesis, metallurgy, and heterogeneous ice nucleation. It has been conjectured that roughness plays a role in surface nucleation, the tendency for freezing to begin preferentially at the liquid-gas interface. Using high speed imaging, we sought evidence for freezing at the contact line on catalyst substrates with imposed characteristic length scales (texture). It is found that nano-scale texture causes a shift in the nucleation of ice in super-cooled water to the three-phase contact line, while micro-scale texture does not. The reduction in the Gibbs barrier for nucleation at the droplet triple line suggests that a line tension, inversely proportional to the surface feature length scale, may be the relevant physical mechanism. A survey of line tension values in literature supports this hypothesis. This work suggests that the physical morphology of a particle, and not just its chemical composition, is important for characterizing a nucleation catalyst.

  10. Heterogeneous nucleation of protein crystals on fluorinated layered silicate.

    Directory of Open Access Journals (Sweden)

    Keita Ino

    Full Text Available Here, we describe an improved system for protein crystallization based on heterogeneous nucleation using fluorinated layered silicate. In addition, we also investigated the mechanism of nucleation on the silicate surface. Crystallization of lysozyme using silicates with different chemical compositions indicated that fluorosilicates promoted nucleation whereas the silicates without fluorine did not. The use of synthesized saponites for lysozyme crystallization confirmed that the substitution of hydroxyl groups contained in the lamellae structure for fluorine atoms is responsible for the nucleation-inducing property of the nucleant. Crystallization of twelve proteins with a wide range of pI values revealed that the nucleation promoting effect of the saponites tended to increase with increased substitution rate. Furthermore, the saponite with the highest fluorine content promoted nucleation in all the test proteins regardless of their overall net charge. Adsorption experiments of proteins on the saponites confirmed that the density of adsorbed molecules increased according to the substitution rate, thereby explaining the heterogeneous nucleation on the silicate surface.

  11. Do protein crystals nucleate within dense liquid clusters?

    Science.gov (United States)

    Maes, Dominique; Vorontsova, Maria A; Potenza, Marco A C; Sanvito, Tiziano; Sleutel, Mike; Giglio, Marzio; Vekilov, Peter G

    2015-07-01

    Protein-dense liquid clusters are regions of high protein concentration that have been observed in solutions of several proteins. The typical cluster size varies from several tens to several hundreds of nanometres and their volume fraction remains below 10(-3) of the solution. According to the two-step mechanism of nucleation, the protein-rich clusters serve as locations for and precursors to the nucleation of protein crystals. While the two-step mechanism explained several unusual features of protein crystal nucleation kinetics, a direct observation of its validity for protein crystals has been lacking. Here, two independent observations of crystal nucleation with the proteins lysozyme and glucose isomerase are discussed. Firstly, the evolutions of the protein-rich clusters and nucleating crystals were characterized simultaneously by dynamic light scattering (DLS) and confocal depolarized dynamic light scattering (cDDLS), respectively. It is demonstrated that protein crystals appear following a significant delay after cluster formation. The cDDLS correlation functions follow a Gaussian decay, indicative of nondiffusive motion. A possible explanation is that the crystals are contained inside large clusters and are driven by the elasticity of the cluster surface. Secondly, depolarized oblique illumination dark-field microscopy reveals the evolution from liquid clusters without crystals to newly nucleated crystals contained in the clusters to grown crystals freely diffusing in the solution. Collectively, the observations indicate that the protein-rich clusters in lysozyme and glucose isomerase solutions are locations for crystal nucleation.

  12. Cross-Linking Studies of Lysozyme Nucleation

    Science.gov (United States)

    Forsythe, Elizabeth; Pusey, Marc

    2000-01-01

    Tetragonal chicken egg white crystals consist of 4(sub 3) helices running in alternating directions, the helix rows having a two fold symmetry with each other. The unit cell consists of one complete tetrameric turn from each of two adjacent helices (an octamer). PBC analysis indicates that the helix intermolecular bonds are the strongest in the crystal, therefore likely formed first. AFM analysis of the (110) surface shows only complete helices, no half steps or bisected helices being found, while AFM line scans to measure the growth step increments show that they are multiples of the 4(sub 3) helix tetramer dimensions. This supports our thesis that the growth units are in fact multiples of the four molecule 4(sub 3) helix unit, the "average" growth unit size for the (110) face being an octamer (two turns about the helix) and the (101) growth unit averaging about the size of a hexamer. In an effort to better understand the species involved in the crystal nucleation and growth process, we have initiated an experimental program to study the species formed in solution compared to what is found in the crystal through covalent cross-linking studies. These experiments use the heterobifunctional cross-linking agent aminoethyl-4-azidonitroanaline (AEANA). An aliphatic amine at one end is covalently attached to the protein by a carbodiimide-mediated reaction, and a photo reactive group at the other can be used to initiate crosslinking. Modifications to the parent structure can be used to alter the distance between the two reactive groups and thus the cross-linking agents "reach". In practice, the cross-linking agent is first coupled to the asp101 side chain through the amine group. Asp101 lies within the active site cleft, and previous work with fluorescent probes had shown that derivatives at this site still crystallize in the tetragonal space group. This was also found to be the case with the AEANA derivative, which gave red tetragonal crystals. The protein now has a

  13. Neutral particle beam intensity controller

    Science.gov (United States)

    Dagenhart, W.K.

    1984-05-29

    The neutral beam intensity controller is based on selected magnetic defocusing of the ion beam prior to neutralization. The defocused portion of the beam is dumped onto a beam dump disposed perpendicular to the beam axis. Selective defocusing is accomplished by means of a magnetic field generator disposed about the neutralizer so that the field is transverse to the beam axis. The magnetic field intensity is varied to provide the selected partial beam defocusing of the ions prior to neutralization. The desired focused neutral beam portion passes along the beam path through a defining aperture in the beam dump, thereby controlling the desired fraction of neutral particles transmitted to a utilization device without altering the kinetic energy level of the desired neutral particle fraction. By proper selection of the magnetic field intensity, virtually zero through 100% intensity control of the neutral beam is achieved.

  14. Measurement of neutral sulfuric acid-dimethylamine clusters using CI-APi-TOF-MS

    Science.gov (United States)

    Simon, Mario; Kürten, Andreas; Jokinen, Tuija; Sarnela, Nina; Sipilä, Mikko; Rondo, Linda; Ehrhart, Sebastian; Junninen, Heikki; Hutterli, Manuel; Kirkby, Jasper; Worsnop, Douglas R.; Curtius, Joachim; Cloud Collaboration

    2013-05-01

    Recent studies suggest that dimethylamine could be a key ternary species in the formation and early growth of atmospheric aerosol particles. We report on nucleation studies for the ternary system of sulfuric acid, water and dimethylamine which have been performed at the CERN CLOUD chamber. These studies were conducted at atmospherically relevant concentrations of sulfuric acid and dimethylamine at 278 K and 38% RH. Two newly developed Chemical Ionization-Atmospheric Pressure interface-Time of Flight-Mass Spectrometers (CIAPi-TOF-MS) were used to measure the time-resolved concentration of neutral clusters containing sulfuric acid and dimethylamine. Results from other instrumental techniques are included in the analysis as well to obtain a deeper insight into the occurring mechanisms. It is the first time that the neutral nucleation pathway has been studied in such detail from the early generation of sulfuric acid monomers up to particle sizes reaching several nanometers.

  15. HIV-1 binding and neutralizing antibodies of injecting drug users

    Directory of Open Access Journals (Sweden)

    Ouverney E.P.

    2005-01-01

    Full Text Available Previous studies have demonstrated a stronger seroreactivity against some synthetic peptides responsible for inducing neutralizing antibodies in injecting drug users (IDU compared to that of individuals sexually infected with HIV-1 (S, but the effectiveness in terms of the neutralizing ability of these antibodies has not been evaluated. Our objective was to study the humoral immune response of IDU by determining the specificity of their antibodies and the presence of neutralizing antibodies. The neutralization capacity against the HIV-1 isolate MN (genotype B, the primary HIV-1 isolate 95BRRJ021 (genotype F, and the seroreactivity with peptides known to induce neutralizing antibodies, from the V2 and V3 loops of different HIV-1 subtypes, were analyzed. Seroreactivity indicates that IDU plasma are more likely to recognize a broader range of peptides than S plasma, with significantly higher titers, especially of V3 peptides. Similar neutralization frequencies of the MN isolate were observed in plasma of the IDU (16/47 and S (20/60 groups in the 1:10 dilution. The neutralization of the 95BRRJ021 isolate was more frequently observed for plasma from the S group (15/23 than from the IDU group (15/47, P = 0.0108. No correlation between neutralization and seroreactivity with the peptides tested was observed. These results suggest that an important factor responsible for the extensive and broad humoral immune response observed in IDU is their infection route. There was very little difference in neutralizing antibody response between the IDU and S groups despite their differences in seroreactivity and health status.

  16. Nucleation of recrystallization at selected sites in deformed fcc metals

    DEFF Research Database (Denmark)

    Xu, Chaoling

    have higher average hardness values and higher nucleation probabilities. In general, indentations with higher hardness values have higher nucleation potentials. The orientations of the nuclei from different indentations in a given grain are observed not to be randomly distributed, but clustered...... indentations is also investigated non-destructively by the DAXM technique. By first characterizing the deformation microstructure within a selected gauge volume near a hardness indentation, then annealing the sample and measuring the same volume again, nucleation is directly correlated to the deformation...

  17. Non-self-averaging nucleation rate due to quenched disorder

    International Nuclear Information System (INIS)

    Sear, Richard P

    2012-01-01

    We study the nucleation of a new thermodynamic phase in the presence of quenched disorder. The quenched disorder is a generic model of both impurities and disordered porous media; both are known to have large effects on nucleation. We find that the nucleation rate is non-self-averaging. This is in a simple Ising model with clusters of quenched spins. We also show that non-self-averaging behaviour is straightforward to detect in experiments, and may be rather common. (fast track communication)

  18. Saturation and nucleation in hot nuclear systems

    International Nuclear Information System (INIS)

    Deangelis, A.R.

    1990-07-01

    We investigate nuclear fragmentation in a supersaturated system using classical nucleation theory. This allows us to go outside the normally applied constraint of chemical equilibrium. The system is governed by a virial equation of state, which we use to find an expression for the density as a function of pressure and temperature. The evolution of the system is discussed in terms of the phase diagram. Corrections are included to account for the droplet surface and all charges contained in the system. Using this model we investigate and discuss the effects of temperature and saturation, and compare the results to those of other models of fragmentation. We also discuss the limiting temperatures of the system for the cases with and without chemical equilibrium. We find that large nuclei will be formed in saturated systems, even above the limiting temperature as previously defined. We also find that saturation and temperature dominate surface and Coulomb effects. The effects are quite large, thus even a qualitative inspection of the yields may give an indication of the conditions during fragmentation

  19. Nucleation and growth of cadherin adhesions

    International Nuclear Information System (INIS)

    Lambert, Mireille; Thoumine, Olivier; Brevier, Julien; Choquet, Daniel; Riveline, Daniel; Mege, Rene-Marc

    2007-01-01

    Cell-cell contact formation relies on the recruitment of cadherin molecules and their anchoring to actin. However, the precise chronology of events from initial cadherin trans-interactions to adhesion strengthening is unclear, in part due to the lack of access to the distribution of cadherins within adhesion zones. Using N-cadherin expressing cells interacting with N-cadherin coated surfaces, we characterized the formation of cadherin adhesions at the ventral cell surface. TIRF and RIC microscopies revealed streak-like accumulations of cadherin along actin fibers. FRAP analysis indicated that engaged cadherins display a slow turnover at equilibrium, compatible with a continuous addition and removal of cadherin molecules within the adhesive contact. Association of cadherin cytoplasmic tail to actin as well as actin cables and myosin II activity are required for the formation and maintenance of cadherin adhesions. Using time lapse microscopy we deciphered how cadherin adhesions form and grow. As lamellipodia protrude, cadherin foci stochastically formed a few microns away from the cell margin. Neo-formed foci coalesced aligned and coalesced with preformed foci either by rearward sliding or gap filling to form cadherin adhesions. Foci experienced collapse at the rear of cadherin adhesions. Based on these results, we present a model for the nucleation, directional growth and shrinkage of cadherin adhesions

  20. Ultracold neutral plasmas

    Science.gov (United States)

    Lyon, M.; Rolston, S. L.

    2017-01-01

    By photoionizing samples of laser-cooled atoms with laser light tuned just above the ionization limit, plasmas can be created with electron and ion temperatures below 10 K. These ultracold neutral plasmas have extended the temperature bounds of plasma physics by two orders of magnitude. Table-top experiments, using many of the tools from atomic physics, allow for the study of plasma phenomena in this new regime with independent control over the density and temperature of the plasma through the excitation process. Characteristic of these systems is an inhomogeneous density profile, inherited from the density distribution of the laser-cooled neutral atom sample. Most work has dealt with unconfined plasmas in vacuum, which expand outward at velocities of order 100 m/s, governed by electron pressure, and with lifetimes of order 100 μs, limited by stray electric fields. Using detection of charged particles and optical detection techniques, a wide variety of properties and phenomena have been observed, including expansion dynamics, collective excitations in both the electrons and ions, and collisional properties. Through three-body recombination collisions, the plasmas rapidly form Rydberg atoms, and clouds of cold Rydberg atoms have been observed to spontaneously avalanche ionize to form plasmas. Of particular interest is the possibility of the formation of strongly coupled plasmas, where Coulomb forces dominate thermal motion and correlations become important. The strongest impediment to strong coupling is disorder-induced heating, a process in which Coulomb energy from an initially disordered sample is converted into thermal energy. This restricts electrons to a weakly coupled regime and leaves the ions barely within the strongly coupled regime. This review will give an overview of the field of ultracold neutral plasmas, from its inception in 1999 to current work, including efforts to increase strong coupling and effects on plasma properties due to strong coupling.

  1. Quantifying the Effect of Stress on Sn Whisker Nucleation Kinetics

    Science.gov (United States)

    Chason, Eric; Vasquez, Justin; Pei, Fei; Jain, Nupur; Hitt, Andrew

    2018-01-01

    Although Sn whiskers have been studied extensively, there is still a need to understand the driving forces behind whisker nucleation and growth. Many studies point to the role of stress, but confirming this requires a quantitative comparison between controlled stress and the resulting whisker evolution. Recent experimental studies applied stress to a Sn layer via thermal cycling and simultaneously monitored the evolution of the temperature, stress and number of nuclei. In this work, we analyze these nucleation kinetics in terms of classical nucleation theory to relate the observed behavior to underlying mechanisms including a stress dependent activation energy and a temperature and stress-dependent whisker growth rate. Non-linear least squares fitting of the data taken at different temperatures and strain rates to the model shows that the results can be understood in terms of stress decreasing the barrier for whisker nucleation.

  2. Nucleation from a cluster of inclusions, leading to void coalescense

    DEFF Research Database (Denmark)

    Tvergaard, Viggo

    2017-01-01

    A cell model analysis is used to study the nucleation and subsequent growth of voids from a non-uniform distribution of inclusions in a ductile material. Nucleation is modeled as either stress controlled or strain controlled. The special clusters considered consist of a number of uniformly spaced...... inclusions located along a plane perpendicular to the maximum principal tensile stress. A plane strain approximation is used, where the inclusions are parallel cylinders perpendicular to the plane. Clusters with different numbers of inclusions are compared with the nucleation and growth from a single...... inclusion, such that the total initial volume of the inclusions is the same for the clusters and the single inclusion. After nucleation, local void coalescence inside the clusters is accounted for, since this makes it possible to compare the rate of growth of the single larger void that results from...

  3. Mediating conducting polymer growth within hydrogels by controlling nucleation

    Directory of Open Access Journals (Sweden)

    A. J. Patton

    2015-01-01

    Full Text Available This study examines the efficacy of primary and secondary nucleation for electrochemical polymerisation of conductive polymers within poly(vinyl alcohol methacrylate hydrogels. The two methods of nucleation investigated were a primary heterogeneous mechanism via introduction of conductive bulk metallic glass (Mg64Zn30Ca5Na1 particles and a secondary mechanism via introduction of “pre-polymerised” conducting polymer within the hydrogel (PEDOT:PSS. Evidence of nucleation was not seen in the bulk metallic glass loaded gels, however, the PEDOT:PSS loaded gels produced charge storage capacities over 15 mC/cm2 when sufficient polymer was loaded. These studies support the hypothesis that secondary nucleation is an efficient approach to producing stand-alone conducting hydrogels.

  4. Dynamic damage nucleation and evolution in multiphase materials

    Science.gov (United States)

    Fensin, S. J.; Escobedo, J. P.; Gray, G. T.; Patterson, B. M.; Trujillo, C. P.; Cerreta, E. K.

    2014-05-01

    For ductile metals, dynamic fracture occurs through void nucleation, growth, and coalescence. Previous experimental works in high purity metals have shown that microstructural features such as grain boundaries, inclusions, vacancies, and heterogeneities can act as initial void nucleation sites. However, for materials of engineering significance, those with, second phase particles it is less clear what the role of a soft second phase will be on damage nucleation and evolution. To approach this problem in a systematic manner, two materials have been investigated: high purity copper and copper with 1% lead. These materials have been shock loaded at ˜1.5 GPa and soft recovered. In-situ free surface velocity information and post mortem metallography reveals the presence of a high number of small voids in CuPb in comparison to a lower number of large voids in Cu. This suggests that damage evolution is nucleation dominated in the CuPb and growth dominated in the pure Cu.

  5. Availability analysis for heterogeneous nucleation in a uniform electric field

    CERN Document Server

    Saidi, M H

    2003-01-01

    Industrial demands for more compact heat exchangers are a motivation to find new technology features. Electrohydrodynamics (EHD) is introduced as a promising phenomenon for heat transfer enhancement mechanisms. Similar to any new technology, EHD has not been understood completely yet and require more fundamental studies. In boiling phase change phenomena, nucleation is the dominant mechanism in heat transfer. Because of higher performance in heat transfer, nucleate boiling is considered as the main regime in thermal components. Hence, bubble dynamic investigation is a means to evaluate heat transfer. This study investigate bubble formation, including homogeneous and heterogeneous nucleation, from a thermodynamic point of view. Change in availability due to bubble embryo nucleation is discussed. Stability criteria for these systems are theoretically studied and results are discussed considering experimental data. In addition, a conceptual discussion on entropy generation in a thermodynamic system under electri...

  6. Analysis of nucleation modelling in ductile cast iron

    DEFF Research Database (Denmark)

    Moumeni, Elham; Tutum, Cem Celal; Tiedje, Niels Skat

    2012-01-01

    Heterogeneous nucleation of nodular graphite at inclusions in ductile iron during eutectic solidification has been investigated. The experimental part of this work deals with casting of ductile iron samples with two different inoculants in four different thicknesses. Chemical analysis, metallogra...

  7. Evolution of a magnetic bubble after quantum nucleation

    Science.gov (United States)

    Defranzo, A.; Gunther, L.

    1989-06-01

    Chudnovsky and Gunther recently presented a theory of quantum nucleation in a ferromagnet [Phys. Rev. B 37, 9455 (1989)]. As a sequel, this paper is concerned with the evolution of the magnetic bubble after its materialization.

  8. Theoretical Studies Of Nucleation Kinetics And Nanodroplet Microstructure

    International Nuclear Information System (INIS)

    Wilemski, Gerald

    2009-01-01

    The goals of this project were to (1) explore ways of bridging the gap between fundamental molecular nucleation theories and phenomenological approaches based on thermodynamic reasoning, (2) test and improve binary nucleation theory, and (3) provide the theoretical underpinning for a powerful new experimental technique, small angle neutron scattering (SANS) from nanodroplet aerosols, that can probe the compositional structure of nanodroplets. This report summarizes the accomplishments of this project in realizing these goals. Publications supported by this project fall into three general categories: (1) theoretical work on nucleation theory (2) experiments and modeling of nucleation and condensation in supersonic nozzles, and (3) experimental and theoretical work on nanodroplet structure and neutron scattering. These publications are listed and briefly summarized in this report.

  9. Development of an experimental apparatus for nucleate boiling analysis

    International Nuclear Information System (INIS)

    Castro, A.J.A. de.

    1984-01-01

    An experimental apparatus is developed for the study of the parameters that affect nucleate boiling. The experimental set up is tested for nucleate boiling in an annular test section with subcooled water flow. The following parameters are analysed: pressure, fluid velocity and the fluid temperature at the test section entrance. The performance of the experimental apparatus is analysed by the results and by the problems raised by the operation of the setup. (Author) [pt

  10. Effect of nucleating agents on crystallization kinetics of PET

    Directory of Open Access Journals (Sweden)

    2007-04-01

    Full Text Available Effects of three nucleating agents concluding talc, sodium benzoate (SB and an ionomer (Ion., Na+ on crystallization of poly(ethylene terephthalate (PET were studied by differential scanning calorimetry (DSC and polarized optical microscope (POM, the parameters of crystallization kinetics were obtained through Avrami and Ozawa equations. The fold surface free energy σe of pure PET and PET/nucleating agent blends were calculated by Hoffman-Lauritzen theory. The results indicate that the three kinds of nucleating agents increase the crystallization rate constant through promoting their nucleating effect for PET crystallization, among which SB is the best one with the same content. The crystallization mode of PET might shift from three-dimensional growth to two-dimensional growth by the addition of the nucleating agents. The values of σe of PET/nucleating agent blends are much less than that of pure PET, and PET/SB (99:1 blend has the least value of σe (18.2 mJ/m2. The conclusion based on Hoffman theory is similar to the analysis by Avrami and Ozawa equations.

  11. Computer simulations of homogeneous nucleation of benzene from the melt.

    Science.gov (United States)

    Shah, Manas; Santiso, Erik E; Trout, Bernhardt L

    2011-09-08

    Nucleation is the key step in crystallization by which the molecules (or atoms or ions) aggregate together, find the right relative orientations, and start to grow to form the final crystal structure. Since nucleation is an activated step involving a large gap in time scales between molecular motions and the nucleation event itself, nucleation must be studied using rare events methods. We employ a technique developed previously in our group known as aimless shooting [Peters, B.; Trout, B. L. J. Chem. Phys., 2006, 125, 054108], which is based on transition path sampling, to generate reactive trajectories between the disordered and ordered phases of benzene. Using the likelihood maximization algorithm, we analyze the aimless shooting trajectories to identify the key order parameters or collective variables to describe the reaction coordinate for the nucleation of benzene from the melt. We find that the local bond orientation and local relative orientation order parameters are the most important collective variables in describing the reaction coordinate for homogeneous nucleation from the melt, as compared to cluster size and space-averaged order parameters. This study also demonstrates the utility of recently developed order parameters for molecular crystals [Santiso, E. E.; Trout, B. L. J. Chem. Phys., 2011, 134, 064109].

  12. A marine biogenic source of atmospheric ice-nucleating particles

    Energy Technology Data Exchange (ETDEWEB)

    Wilson, T. W.; Ladino, L. A.; Alpert, Peter A.; Breckels, M. N.; Brooks, I. M.; Browse, J.; Burrows, Susannah M.; Carslaw, K. S.; Huffman, J. A.; Judd, C.; Kilthau, W. P.; Mason, R. H.; McFiggans, Gordon; Miller, L. A.; Najera, J.; Polishchuk, E. A.; Rae, S.; Schiller, C. L.; Si, M.; Vergara Temprado, J.; Whale, Thomas; Wong, J P S; Wurl, O.; Yakobi-Hancock, J. D.; Abbatt, JPD; Aller, Josephine Y.; Bertram, Allan K.; Knopf, Daniel A.; Murray, Benjamin J.

    2015-09-09

    The formation of ice in clouds is facilitated by the presence of airborne ice nucleating particles1,2. Sea spray is one of the major global sources of atmospheric particles, but it is unclear to what extent these particles are capable of nucleating ice3–11. Here we show that material in the sea surface microlayer, which is enriched in surface active organic material representative of that found in sub-micron sea- spray aerosol12–21, nucleates ice under conditions that occur in mixed-phase clouds and high-altitude ice clouds. The ice active material is likely biogenic and is less than ~0.2 ?m in size. We also show that organic material (exudate) released by a common marine diatom nucleates ice when separated from cells and propose that organic material associated with phytoplankton cell exudates are a candidate for the observed ice nucleating ability of the microlayer samples. By combining our measurements with global model simulations of marine organic aerosol, we show that ice nucleating particles of marine origin are dominant in remote marine environments, such as the Southern Ocean, the North Pacific and the North Atlantic.

  13. Immersion freezing of ice nucleation active protein complexes

    Directory of Open Access Journals (Sweden)

    S. Hartmann

    2013-06-01

    Full Text Available Utilising the Leipzig Aerosol Cloud Interaction Simulator (LACIS, the immersion freezing behaviour of droplet ensembles containing monodisperse particles, generated from a Snomax™ solution/suspension, was investigated. Thereto ice fractions were measured in the temperature range between −5 °C to −38 °C. Snomax™ is an industrial product applied for artificial snow production and contains Pseudomonas syringae} bacteria which have long been used as model organism for atmospheric relevant ice nucleation active (INA bacteria. The ice nucleation activity of such bacteria is controlled by INA protein complexes in their outer membrane. In our experiments, ice fractions increased steeply in the temperature range from about −6 °C to about −10 °C and then levelled off at ice fractions smaller than one. The plateau implies that not all examined droplets contained an INA protein complex. Assuming the INA protein complexes to be Poisson distributed over the investigated droplet populations, we developed the CHESS model (stoCHastic modEl of similar and poiSSon distributed ice nuclei which allows for the calculation of ice fractions as function of temperature and time for a given nucleation rate. Matching calculated and measured ice fractions, we determined and parameterised the nucleation rate of INA protein complexes exhibiting class III ice nucleation behaviour. Utilising the CHESS model, together with the determined nucleation rate, we compared predictions from the model to experimental data from the literature and found good agreement. We found that (a the heterogeneous ice nucleation rate expression quantifying the ice nucleation behaviour of the INA protein complex is capable of describing the ice nucleation behaviour observed in various experiments for both, Snomax™ and P. syringae bacteria, (b the ice nucleation rate, and its temperature dependence, seem to be very similar regardless of whether the INA protein complexes inducing ice

  14. Controlled ice nucleation in the field of freeze-drying: fundamentals and technology review.

    Science.gov (United States)

    Geidobler, R; Winter, G

    2013-10-01

    In the scientific community as well as in commercial freeze-drying, controlled ice nucleation has received a lot of attention because increasing the ice nucleation temperature can significantly reduce primary drying duration. Furthermore, controlled ice nucleation enables to reduce the randomness of the ice nucleation temperature, which can be a serious scale-up issue during process development. In this review, fundamentals of ice nucleation in the field of freeze-drying are presented. Furthermore, the impact of controlled ice nucleation on product qualities is discussed, and methods to achieve controlled ice nucleation are presented. Copyright © 2013 Elsevier B.V. All rights reserved.

  15. Cooperativity Enables Non-neutralizing Antibodies to Neutralize Ebolavirus

    Directory of Open Access Journals (Sweden)

    Katie A. Howell

    2017-04-01

    Full Text Available Drug combinations are synergistic when their combined efficacy exceeds the sum of the individual actions, but they rarely include ineffective drugs that become effective only in combination. We identified several “enabling pairs” of neutralizing and non-neutralizing anti-ebolavirus monoclonal antibodies, whose combination exhibited new functional profiles, including transforming a non-neutralizing antibody to a neutralizer. Sub-neutralizing concentrations of antibodies 2G4 or m8C4 enabled non-neutralizing antibody FVM09 (IC50 >1 μM to exhibit potent neutralization (IC50 1–10 nM. While FVM09 or m8C4 alone failed to protect Ebola-virus-infected mice, a combination of the two antibodies provided 100% protection. Furthermore, non-neutralizers FVM09 and FVM02 exponentially enhanced the potency of two neutralizing antibodies against both Ebola and Sudan viruses. We identified a hotspot for the binding of these enabling antibody pairs near the interface of the glycan cap and GP2. Enabling cooperativity may be an underappreciated phenomenon for viruses, with implications for the design and development of immunotherapeutics and vaccines.

  16. Increased fire frequency promotes stronger spatial genetic structure and natural selection at regional and local scales in Pinus halepensis Mill.

    Science.gov (United States)

    Budde, Katharina B; González-Martínez, Santiago C; Navascués, Miguel; Burgarella, Concetta; Mosca, Elena; Lorenzo, Zaida; Zabal-Aguirre, Mario; Vendramin, Giovanni G; Verdú, Miguel; Pausas, Juli G; Heuertz, Myriam

    2017-04-01

    The recurrence of wildfires is predicted to increase due to global climate change, resulting in severe impacts on biodiversity and ecosystem functioning. Recurrent fires can drive plant adaptation and reduce genetic diversity; however, the underlying population genetic processes have not been studied in detail. In this study, the neutral and adaptive evolutionary effects of contrasting fire regimes were examined in the keystone tree species Pinus halepensis Mill. (Aleppo pine), a fire-adapted conifer. The genetic diversity, demographic history and spatial genetic structure were assessed at local (within-population) and regional scales for populations exposed to different crown fire frequencies. Eight natural P. halepensis stands were sampled in the east of the Iberian Peninsula, five of them in a region exposed to frequent crown fires (HiFi) and three of them in an adjacent region with a low frequency of crown fires (LoFi). Samples were genotyped at nine neutral simple sequence repeats (SSRs) and at 251 single nucleotide polymorphisms (SNPs) from coding regions, some of them potentially important for fire adaptation. Fire regime had no effects on genetic diversity or demographic history. Three high-differentiation outlier SNPs were identified between HiFi and LoFi stands, suggesting fire-related selection at the regional scale. At the local scale, fine-scale spatial genetic structure (SGS) was overall weak as expected for a wind-pollinated and wind-dispersed tree species. HiFi stands displayed a stronger SGS than LoFi stands at SNPs, which probably reflected the simultaneous post-fire recruitment of co-dispersed related seeds. SNPs with exceptionally strong SGS, a proxy for microenvironmental selection, were only reliably identified under the HiFi regime. An increasing fire frequency as predicted due to global change can promote increased SGS with stronger family structures and alter natural selection in P. halepensis and in plants with similar life history traits

  17. Neutral polypropylene laser welding

    Science.gov (United States)

    Mandolfino, Chiara; Lertora, Enrico; Gambaro, Carla

    2016-10-01

    The joining of polymeric materials is a technology used in many industrial applications, from transport to telecommunications and the medical sector. A new technology for the joining of polymers is the laser welding process. In particular, fibre laser welding is a flexible technology which allows high process speed and the realization of good quality joints. Despite its application becoming more widespread in the production of assemblies of high precision, the application of laser technology for the welding of polymers has not been the subject of many studies up to now. This study focused on the welding of neutral polypropylene. The window process parameter was identified, without the use of additives to increase radiation absorption, and a mechanical characterization was conducted in order to evaluate the quality of the joints realized.

  18. Mod en neutral seksualitet!

    DEFF Research Database (Denmark)

    Leer, Jonatan

    2013-01-01

    Towards a Neutral Sexuality! or Roland Barthes as a Queer Thinker? This article argues that the work of Roland Barthes has interesting perspectives in common with the queer theory. This argument will be put forward by using his concept of ‘the neutral’ that Barthes defines as “that which outplays...... the paradigm”. This notion was presented at a series of lectures at Collège de France in 1977. Through a reading of Barthes’s autobiography, Roland Barthes par Roland Barthes (1975), the article demonstrates how Barthes in this text tries to outplay the paradigms that rules over the hegemonic understanding...... theory” in the late 1970’s that beside Barthes includes Jean Baudrillard....

  19. Neutral Kaon Spectrometer 2

    Science.gov (United States)

    Kaneta, M.; Beckford, B.; Fujii, T.; Fujii, Y.; Futatsukawa, K.; Han, Y. C.; Hashimoto, O.; Hirose, K.; Ishikawa, T.; Kanda, H.; Kimura, C.; Maeda, K.; Nakamura, S. N.; Suzuki, K.; Tsukada, K.; Yamamoto, F.; Yamazaki, H.

    2018-04-01

    A large-acceptance spectrometer, Neutral Kaon Spectrometer 2 (NKS2), was newly constructed to explore various photoproduction reactions in the gigaelectronvolt region at the Laboratory of Nuclear Science (LNS, currently ELPH), Tohoku University. The spectrometer consisted of a dipole magnet, drift chambers, and plastic scintillation counters. NKS2 was designed to separate pions and protons in a momentum range of less than 1 GeV/ c, and was placed in a tagged photon beamline. A cryogenic H2/D2 target fitted to the spectrometer were designed. The design and performance of the detectors are described. The results of the NKS2 experiment on analyzing strangeness photoproduction data using a 0.8-1.1 GeV tagged photon beam are also presented.

  20. Spectroscopy of neutral radium

    Energy Technology Data Exchange (ETDEWEB)

    Mol, Aran; De, Subhadeep; Jungmann, Klaus; Wilschut, Hans; Willmann, Lorenz [KVI, University of Groningen, Groningen (Netherlands)

    2008-07-01

    The heavy alkaline earth atoms radium is uniquely sensitive towards parity and time reversal symmetry violations due to a large enhancement of an intrinsic permanent electric dipole moment of the nucleous or the electron. Furthermore, radium is sensitive to atomic parity violation and the nuclear anapole moment. To prepare such experiments spectroscopy of relevant atomic states need to be done. At a later stage we will build a neutral atom trap for radium. We have built an atomic beam of the short lived isotope {sup 225}Ra with a flux of several 10{sup 4} atoms/sec. We are preparing the laser spectroscopy using this beam setup. In the preparation for efficient laser cooling and trapping we have successfully trapped barium, which is similar in it's requirements for laser cooling. The techniques which we have developed with barium can be used to trap rare radium isotopes. We report on the progress of the experiments.

  1. Response of Cloud Condensation Nuclei (> 50 nm) to changes in ion-nucleation

    Science.gov (United States)

    Pedersen, J. O.; Enghoff, M. B.; Svensmark, H.

    2012-12-01

    increase in small aerosols persists all the way to the largest size bin. Similar experiments where the aerosol burst was produced with either the ionization source or an aerosol generator (neutralized aerosols) were made and compared with each other and model runs. The runs using neutral aerosol bursts agree with the model predictions, where the initial burst is dampened such that there is little or no change in the largest sizes. Thus there seems to be a fundamental difference between the bursts produced by ionization and those produced by the aerosol generator. Growth of aerosols, nucleated by ionization.

  2. Can an amine be a stronger acid than a carboxylic acid? The surprisingly high acidity of amine-borane complexes.

    Science.gov (United States)

    Martín-Sómer, Ana; Lamsabhi, Al Mokhtar; Yáñez, Manuel; Dávalos, Juan Z; González, Javier; Ramos, Rocío; Guillemin, Jean-Claude

    2012-12-03

    The gas-phase acidity of a series of amine-borane complexes has been investigated through the use of electrospray mass spectrometry (ESI-MS), with the application of the extended Cooks kinetic method, and high-level G4 ab initio calculations. The most significant finding is that typical nitrogen bases, such as aniline, react with BH(3) to give amine-borane complexes, which, in the gas phase, have acidities as high as those of either phosphoric, oxalic, or salicylic acid; their acidity is higher than many carboxylic acids, such as formic, acetic, and propanoic acid. Indeed the complexation of different amines with BH(3) leads to a substantial increase (from 167 to 195 kJ mol(-1)) in the intrinsic acidity of the system; in terms of ionization constants, this increase implies an increase as large as fifteen orders of magnitude. Interestingly, this increase in acidity is almost twice as large as that observed for the corresponding phosphine-borane analogues. The agreement between the experimental and the G4-based calculated values is excellent. The analysis of the electron-density rearrangements of the amine and the borane moieties indicates that the dative bond is significantly stronger in the N-deprotonated anion than in the corresponding neutral amine-borane complex, because the deprotonated amine is a much better electron donor than the neutral amine. On the top of that, the newly created lone pair on the nitrogen atom in the deprotonated species, conjugates with the BN bonding pair. The dispersion of the extra electron density into the BH(3) group also contributes to the increased stability of the deprotonated species. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  3. Thermodynamic Derivation of the Activation Energy for Ice Nucleation

    Science.gov (United States)

    Barahona, D.

    2015-01-01

    Cirrus clouds play a key role in the radiative and hydrological balance of the upper troposphere. Their correct representation in atmospheric models requires an understanding of the microscopic processes leading to ice nucleation. A key parameter in the theoretical description of ice nucleation is the activation energy, which controls the flux of water molecules from the bulk of the liquid to the solid during the early stages of ice formation. In most studies it is estimated by direct association with the bulk properties of water, typically viscosity and self-diffusivity. As the environment in the ice-liquid interface may differ from that of the bulk, this approach may introduce bias in calculated nucleation rates. In this work a theoretical model is proposed to describe the transfer of water molecules across the ice-liquid interface. Within this framework the activation energy naturally emerges from the combination of the energy required to break hydrogen bonds in the liquid, i.e., the bulk diffusion process, and the work dissipated from the molecular rearrangement of water molecules within the ice-liquid interface. The new expression is introduced into a generalized form of classical nucleation theory. Even though no nucleation rate measurements are used to fit any of the parameters of the theory the predicted nucleation rate is in good agreement with experimental results, even at temperature as low as 190 K, where it tends to be underestimated by most models. It is shown that the activation energy has a strong dependency on temperature and a weak dependency on water activity. Such dependencies are masked by thermodynamic effects at temperatures typical of homogeneous freezing of cloud droplets; however, they may affect the formation of ice in haze aerosol particles. The new model provides an independent estimation of the activation energy and the homogeneous ice nucleation rate, and it may help to improve the interpretation of experimental results and the

  4. LADEE Neutral Mass Spectrometer Data

    Data.gov (United States)

    National Aeronautics and Space Administration — This bundle contains the data collected by the Neutral Mass Spectrometer (NMS) instrument aboard the Lunar Atmosphere and Dust Environment Explorer (LADEE)...

  5. Surface structure, crystallographic and ice-nucleating properties of cellulose

    Science.gov (United States)

    Hiranuma, Naruki; Möhler, Ottmar; Kiselev, Alexei; Saathoff, Harald; Weidler, Peter; Shutthanandan, Shuttha; Kulkarni, Gourihar; Jantsch, Evelyn; Koop, Thomas

    2015-04-01

    Increasing evidence of the high diversity and efficient freezing ability of biological ice-nucleating particles is driving a reevaluation of their impact upon climate. Despite their potential importance, little is known about their atmospheric abundance and ice nucleation efficiency, especially non-proteinaceous ones, in comparison to non-biological materials (e.g., mineral dust). Recently, microcrystalline cellulose (MCC; non-proteinaceous plant structural polymer) has been identified as a potential biological ice-nucleating particle. However, it is still uncertain if the ice-nucleating activity is specific to the MCC structure or generally relevant to all cellulose materials, such that the results of MCC can be representatively scaled up to the total cellulose content in the atmosphere to address its role in clouds and the climate system. Here we use the helium ion microscopy (HIM) imaging and the X-ray diffraction (XRD) technique to characterize the nanoscale surface structure and crystalline properties of the two different types of cellulose (MCC and fibrous cellulose extracted from natural wood pulp) as model proxies for atmospheric cellulose particles and to assess their potential accessibility for water molecules. To complement these structural characterizations, we also present the results of immersion freezing experiments using the cold stage-based droplet freezing BINARY (Bielefeld Ice Nucleation ARaY) technique. The HIM results suggest that both cellulose types have a complex porous morphology with capillary spaces between the nanoscale fibrils over the microfiber surface. These surface structures may make cellulose accessible to water. The XRD results suggest that the structural properties of both cellulose materials are in agreement (i.e., P21 space group; a=7.96 Å, b=8.35 Å, c=10.28 Å) and comparable to the crystallographic properties of general monoclinic cellulose (i.e., Cellulose Iβ). The results obtained from the BINARY measurements suggest

  6. Heterogeneous nucleation of ice on model carbon surfaces

    Science.gov (United States)

    Molinero, V.; Lupi, L.; Hudait, A.

    2014-12-01

    Carbonaceous particles account for 10% of the particulate matter in the atmosphere. The experimental investigation of heterogeneous freezing of water droplets by carbonaceous particles reveals widespread ice freezing temperatures. The origin of the soot and its oxidation and aging modulate its ice nucleation ability, however, it is not known which structural and chemical characteristics of soot account for the variability in ice nucleation efficiency. We find that atomically flat carbon surfaces promote heterogeneous nucleation of ice, while molecularly rough surfaces with the same hydrophobicity do not. We investigate a large set of graphitic surfaces of various dimensions and radii of curvature consistent with those of soot in experiments, and find that variations in nanostructures alone could account for the spread in the freezing temperatures of ice on soot in experiments. A characterization of the nanostructure of soot is needed to predict its ice nucleation efficiency. Atmospheric oxidation and aging of soot modulates its ice nucleation ability. It has been suggested that an increase in the ice nucleation ability of aged soot results from an increase in the hydrophilicity of the surfaces upon oxidation. Oxidation, however, also impacts the nanostructure of soot, making it difficult to assess the separate effects of soot nanostructure and hydrophilicity in experiments. We investigate the effect of changes in hydrophilicity of model graphitic surfaces on the freezing temperature of ice. Our results indicate that the hydrophilicity of the surface is not in general a good predictor of ice nucleation ability. We find a correlation between the ability of a surface to promote nucleation of ice and the layering of liquid water at the surface. The results of this work suggest that ordering of liquid water in contact with the surface plays an important role in the heterogeneous ice nucleation mechanism. References: L. Lupi, A. Hudait and V. Molinero, J. Am. Chem. Soc

  7. CO2-neutral fuels

    Science.gov (United States)

    Goede, A. P. H.

    2015-08-01

    The need for storage of renewable energy (RE) generated by photovoltaic, concentrated solar and wind arises from the fact that supply and demand are ill-matched both geographically and temporarily. This already causes problems of overcapacity and grid congestion in countries where the fraction of RE exceeds the 20% level. A system approach is needed, which focusses not only on the energy source, but includes conversion, storage, transport, distribution, use and, last but not least, the recycling of waste. Furthermore, there is a need for more flexibility in the energy system, rather than relying on electrification, integration with other energy systems, for example the gas network, would yield a system less vulnerable to failure and better adapted to requirements. For example, long-term large-scale storage of electrical energy is limited by capacity, yet needed to cover weekly to seasonal demand. This limitation can be overcome by coupling the electricity net to the gas system, considering the fact that the Dutch gas network alone has a storage capacity of 552 TWh, sufficient to cover the entire EU energy demand for over a month. This lecture explores energy storage in chemicals bonds. The focus is on chemicals other than hydrogen, taking advantage of the higher volumetric energy density of hydrocarbons, in this case methane, which has an approximate 3.5 times higher volumetric energy density. More importantly, it allows the ready use of existing gas infrastructure for energy storage, transport and distribution. Intermittent wind electricity generated is converted into synthetic methane, the Power to Gas (P2G) scheme, by splitting feedstock CO2 and H2O into synthesis gas, a mixture of CO and H2. Syngas plays a central role in the synthesis of a range of hydrocarbon products, including methane, diesel and dimethyl ether. The splitting is accomplished by innovative means; plasmolysis and high-temperature solid oxygen electrolysis. A CO2-neutral fuel cycle is

  8. CO2-neutral fuels

    Directory of Open Access Journals (Sweden)

    Goede A. P. H.

    2015-01-01

    Full Text Available The need for storage of renewable energy (RE generated by photovoltaic, concentrated solar and wind arises from the fact that supply and demand are ill-matched both geographically and temporarily. This already causes problems of overcapacity and grid congestion in countries where the fraction of RE exceeds the 20% level. A system approach is needed, which focusses not only on the energy source, but includes conversion, storage, transport, distribution, use and, last but not least, the recycling of waste. Furthermore, there is a need for more flexibility in the energy system, rather than relying on electrification, integration with other energy systems, for example the gas network, would yield a system less vulnerable to failure and better adapted to requirements. For example, long-term large-scale storage of electrical energy is limited by capacity, yet needed to cover weekly to seasonal demand. This limitation can be overcome by coupling the electricity net to the gas system, considering the fact that the Dutch gas network alone has a storage capacity of 552 TWh, sufficient to cover the entire EU energy demand for over a month. This lecture explores energy storage in chemicals bonds. The focus is on chemicals other than hydrogen, taking advantage of the higher volumetric energy density of hydrocarbons, in this case methane, which has an approximate 3.5 times higher volumetric energy density. More importantly, it allows the ready use of existing gas infrastructure for energy storage, transport and distribution. Intermittent wind electricity generated is converted into synthetic methane, the Power to Gas (P2G scheme, by splitting feedstock CO2 and H2O into synthesis gas, a mixture of CO and H2. Syngas plays a central role in the synthesis of a range of hydrocarbon products, including methane, diesel and dimethyl ether. The splitting is accomplished by innovative means; plasmolysis and high-temperature solid oxygen electrolysis. A CO2-neutral fuel

  9. Using Ice Nucleating Particles to Enable Desublimation on Chilled Substrates

    Science.gov (United States)

    O'Brien, Julia; Failor, Kevin; Bisbano, Caitlin; Mulroe, Megan; Nath, Saurabh; Vinatzer, Boris; Boreyko, Jonathan

    2017-11-01

    On a subfreezing surface, nucleating embryos usually form as supercooled condensate that later freeze into ice, as opposed to desublimation. Ice nucleating particles (INPs) have been widely used to freeze existing water; however, nobody has studied how they might affect the initial mode of nucleation. Here, we show that INPs deposited on a substrate can switch the mode of embryo nucleation to desublimation, rather than supercooled condensation. Deposition was achieved by evaporating a water droplet containing INPs on a hydrophobic silicon wafer. A Peltier stage was used to cool the wafer down inside of a controlled humidity chamber, such that the desired set point temperature correlated with the dew point and onset of nucleation. Beneath a critical surface temperature, microscopy indicated that desublimation occurred on the circular patch of deposited INPs, compared to supercooled condensation outside the circle. The hydrophobic surface was then patterned with hydrophilic stripe arrays, which facilitated the deposition of stripes of INPs via the same evaporation method. The resulting array of desublimating ice stripes created dry zones free of condensation or frost in the intermediate areas, as the hygroscopic ice stripes served as overlapping humidity sinks.

  10. Nucleation of Salt Crystals in Clay Minerals: Molecular Dynamics Simulation.

    Science.gov (United States)

    Dashtian, Hassan; Wang, Haimeng; Sahimi, Muhammad

    2017-07-20

    Nucleation of salt crystals in confined media occurs in many processes of high importance, such as injection of CO 2 in geological formations for its sequestration. In particular, salt precipitation in clays, a main component of sedimentary rock, is an important phenomenon. The crystals precipitate on the pores' surface, modify the pore space morphology, and reduce its flow and transport properties. Despite numerous efforts to understand the mechanisms of nucleation of salt crystals in confined media, the effect of the clay's chemistry on the growth, distribution, and properties of the crystals is not well understood. We report the results of extensive molecular dynamics simulation of nucleation and growth of NaCl crystals in a clay pore using molecular models of two types of clay minerals, Na-montmorillonite and kaolinite. Clear evidence is presented for the nucleation of the salt crystals that indicates that the molecular structure of clay minerals affects their spatial distribution, although the nucleation mechanism is the same in both types of clays.

  11. Nucleated red blood cells in infants of mothers with asthma.

    Science.gov (United States)

    Littner, Yoav; Mandel, Dror; Sheffer-Mimouni, Galit; Mimouni, Francis B; Deutsch, Varda; Dollberg, Shaul

    2003-02-01

    The purpose of this study was to evaluate whether the absolute nucleated red blood cell and lymphocyte count is elevated in term, appropriate-for-gestational-age infants born to women with asthma. We compared absolute nucleated red blood cell counts taken during the first 12 hours of life in two groups of term, vaginally delivered, appropriate-for-gestational-age infants; one group was born to mothers with active asthma during pregnancy (n = 28 infants), and the other group was born to control mothers (n = 29 infants). Asthma severity was classified according to the National Asthma Education and Prevention Program. We excluded infants of women with diabetes mellitus, hypertension, alcohol, and tobacco or drug abuse and infants with fetal heart rate abnormalities, hemolysis, blood loss, or chromosomal anomalies. There were no differences between groups in birth weight, gestational age, maternal age, gravidity, parity, maternal analgesia during labor, 1- and 5-minute Apgar scores, and infant sex. The hematocrit level, red blood cell count, absolute nucleated red blood cell count, and corrected leukocyte and lymphocyte counts were significantly higher in the asthma group than in the control group. The platelet count was not significantly different between groups. The absolute nucleated red blood cell count correlated significantly with the asthma severity score (r (2) = 28%, P cell count with the presence of asthma and its severity (P mothers with asthma have increased circulating absolute nucleated red blood cell and lymphocyte counts compared with control infants.

  12. Nucleated red blood cells in infants of smoking mothers.

    Science.gov (United States)

    Yeruchimovich, M; Dollberg, S; Green, D W; Mimouni, F B

    1999-03-01

    To evaluate whether the absolute nucleated red blood cell (RBC) count is elevated in term, appropriate for gestational age (AGA) infants born to smoking women. We compared absolute nucleated RBC counts taken during the first 12 hours of life in two groups of term, vaginally delivered, AGA infants, one group born to mothers who smoked during pregnancy (n = 30) and the other born to mothers who did not smoke (n = 30). We excluded infants of women with diabetes, hypertension, or alcohol or drug abuse, and infants with heart rate abnormalities, hemolysis, blood loss, or chromosomal anomalies. There were no differences between the groups in birth weight, gestational age, maternal age, gravidity, parity, maternal analgesia during labor, 1- and 5-minute Apgar scores, corrected white blood cell counts, lymphocyte counts, or hematocrits. The median absolute nucleated RBC count in infants of smoking mothers was 0.5 x 10(9)/L (range 0 to 5.0) versus 0.0005 x 10(9)/L (range 0 to 0.6) in nonsmoking controls (P mothers have increased circulating absolute nucleated RBC counts compared with controls. The absolute nucleated RBC count in newborns correlates with the number of cigarettes smoked during pregnancy.

  13. Supersolubility and induction of aluminosilicate nucleation from clear solution

    Science.gov (United States)

    Zhang, Yifei; Li, Yinghui; Zhang, Yi

    2003-06-01

    The supersolubility of silica in supersaturated aluminate solution and the sodium aluminosilicate precipitation nucleation mechanism from the clear solution were investigated by experiment. The obtained semi-empirical expression of the induction ( tind) of sodium aluminosilicate precipitation from clear solution is significant for zeolite A membranes synthesis, desilication and more important for valuating the stability of the supersaturated SiO 2 in the aluminate solution during the hydrolysis operation in the most used alkaline alumina manufacture. The semi-empirical expressions of the silica supersolubility in clear supersaturated sodium aluminate solution for both homogeneous and heterogeneous nucleation were originally conducted. The homogeneous nucleation predominated with the supersaturation ( S) above 6.0, conversely, heterogeneous nucleation with S below 4.0. The inferred activation energy ( Ea) of the homogeneous nucleated reaction was 14.9 kJ/mol, and that of the heterogeneous 50.5 kJ/mol. The interfacial tension ( γs) between the precipitate of sodium aluminosilicate and the surrounding aqueous solution was obtained at 15.1 mJ/m 2, negligibly decreased with increasing temperature. It was much larger than the value of 12.4 mJ/m 2 in pure water (J. Phys. Chem. B 105 (2001) 5383), but very much smaller than the estimated value of 38.64-50 mJ/m 2 in the solution for traditional zeolite synthesis.

  14. Pressure control in interfacial systems: Atomistic simulations of vapor nucleation

    Science.gov (United States)

    Marchio, S.; Meloni, S.; Giacomello, A.; Valeriani, C.; Casciola, C. M.

    2018-02-01

    A large number of phenomena of scientific and technological interest involve multiple phases and occur at constant pressure of one of the two phases, e.g., the liquid phase in vapor nucleation. It is therefore of great interest to be able to reproduce such conditions in atomistic simulations. Here we study how popular barostats, originally devised for homogeneous systems, behave when applied straightforwardly to heterogeneous systems. We focus on vapor nucleation from a super-heated Lennard-Jones liquid, studied via hybrid restrained Monte Carlo simulations. The results show a departure from the trends predicted for the case of constant liquid pressure, i.e., from the conditions of classical nucleation theory. Artifacts deriving from standard (global) barostats are shown to depend on the size of the simulation box. In particular, for Lennard-Jones liquid systems of 7000 and 13 500 atoms, at conditions typically found in the literature, we have estimated an error of 10-15 kBT on the free-energy barrier, corresponding to an error of 104-106 s-1σ-3 on the nucleation rate. A mechanical (local) barostat is proposed which heals the artifacts for the considered case of vapor nucleation.

  15. Urediospores of Puccinia spp. and other rusts are warm-temperature ice nucleators and harbor ice nucleation active bacteria

    Science.gov (United States)

    Morris, C. E.; Sands, D. C.; Glaux, C.; Samsatly, J.; Asaad, S.; Moukahel, A. R.; Gonçalves, F. L. T.; Bigg, E. K.

    2012-10-01

    In light of various features of the biology of the rust fungi and of the epidemiology of the plant diseases they cause that illustrate the important role of rainfall in their life history, we have characterized the ice nucleation activity (INA) of the aerially disseminated spores (urediospores) of this group of fungi. Urediospores of this obligate plant parasite were collected from natural infections from 7 species of weeds in France, from coffee in Brazil and from field and greenhouse-grown wheat in France, the USA, Turkey and Syria. Immersion freezing was used to determine freezing onset temperatures and the abundance of ice nuclei in suspensions of washed spores. Microbiological analyses of spores and subsequent tests of the ice nucleation activity of the bacteria associated with spores were deployed to quantify the contribution of bacteria to the ice nucleation activity of the spores. All samples of spores were ice nucleation active having freezing onset temperatures as warm as -4 °C. Spores in most of the samples carried cells of ice nucleation-active strains of the bacterium Pseudomonas syringae (at rates of less than 1 bacterial cell per 100 urediospores), but bacterial INA accounted for only a small fraction of the INA observed in spore suspensions. Changes in the INA of spore suspensions after treatment with lysozyme suggest that the INA of urediospores involves a polysaccharide. Based on data from the literature, we have estimated the concentrations of urediospores in air at cloud height and in rainfall. These quantities are very similar to those reported for other biological ice nucleators in these same substrates. We suggest that air sampling techniques have ignored the spatial and temporal variability of atmospheric concentrations that occur under conditions propitious for precipitation that could increase their local abundance intermittently. Nevertheless, we propose that the relative low abundance of warm-temperature biological ice nucleators in the

  16. Electromagnetic radiation optimum neutralizer

    International Nuclear Information System (INIS)

    Smirnov, Igor

    2002-01-01

    This particular article relates to subtle electrical effects, and provides some evidence of a fundamental nature on how subtle low frequency electromagnetic fields might be utilized to protect human body against harmful effects of high frequencies electromagnetic radiation. I have focused my efforts on definite polar polymer compound named EMRON which is patented in the USA. This polar polymer compound can be excited by external high frequencies electromagnetic fields to generate subtle low frequency oscillations that are beneficial for cellular life structures. This concept is based on the possibility of existence of resonance phenomenon between polar polymers and biopolymers such as proteins, nucleic acids, lipids, etc. Low frequency patterns generated by defined polar polymer compound can interact with biostructures and transmit the signals that support and improve cellular functions in the body. The mechanism of this process was confirmed by number of studies. The animal (including human) brain is affected by electromagnetic waves to the extent that production of Alpha or Theta waves can be directly induced into brain by carrying an ELF (extremely low frequency, 5-12 Hz) signal on a microwave carrier frequency. EMRON does not reduce the power of electromagnetic fields. It 'shields' the cellular structures of the body against the harmful effects of EMR. The radiation is still entering the body but the neutralizing effect of EMRON renders the radiation harmless

  17. Attentional bias in restrictive eating disorders. Stronger attentional avoidance of high-fat food compared to healthy controls?

    Science.gov (United States)

    Veenstra, Esther M; de Jong, Peter J

    2012-02-01

    A striking feature of the restricting subtype of anorexia nervosa (AN) is that these patients are extremely successful in restricting their food intake. Possibly, they are highly efficient in avoiding attentional engagement of food cues, thereby preventing more elaborate processing of food cues and thus subsequent craving. This study examined whether patients diagnosed with restrictive eating disorders ('restricting AN-like patients'; N=88) indeed show stronger attentional avoidance of visual food stimuli than healthy controls (N=76). Attentional engagement and disengagement were assessed by means of a pictorial exogenous cueing task, and (food and neutral) pictures were presented for 300, 500, or 1000 ms. In the 500 ms condition, both restricting AN-like patients and healthy controls demonstrated attentional avoidance of high-fat food as indexed by a negative cue-validity effect and impaired attentional engagement with high-fat food, whereas no evidence was found for facilitated disengagement from high-fat food. Within the group of restricting AN-like patients, patients with relatively severe eating pathology showed relatively strong attentional engagement with low-fat food. There was no evidence for attentional bias in the 300 and 1000 ms condition. The pattern of findings indicate that attentional avoidance of high-fat food is a common phenomenon that may become counterproductive in restricting AN-like patients, as it could facilitate their restricted food intake. Copyright © 2011 Elsevier Ltd. All rights reserved.

  18. Fluorescence Studies of Protein Crystal Nucleation

    Science.gov (United States)

    Pusey, Marc; Sumida, John

    2000-01-01

    -association process is a function of the protein concentration relative to the saturation concentration, and observing it in dilute solution (conc. less than or equal to 10(exp -5)M) requires that the experiments be performed under low solubility conditions, i.e., low temperatures and high salt concentrations. Data from preliminary steady state FRET studies with N-terminal bound pyrene acetic acid (PAA-lys, donor, Ex 340 nm, Em 376 nm) and asp101 LY-lys as an acceptor showed a consistent trend of decreasing donor fluorescence intensity with increasing total protein concentration. The FRET data have been obtained at pH 4.6, 0.1M NaAc buffer, at 5 and 7% NaCl, 4 C. The corresponding C(sub sat) values are 0.471 and 0.362 mg/ml (approx. 3.3 and approx. 2.5 x 10(exp -5)M respectively). The donor fluorescence decrease is more pronounced at7% NaCl, consistent with the expected increased intermolecular interactions at higher salt concentrations as reflected in the lower solubility. Results from these and other ongoing studies will be discussed in conjunction with an emerging model for how tetragonal lysozyme crystals nucleate and the relevance of that model to other proteins.

  19. Modulating Nucleation by Kosmotropes and Chaotropes: Testing the Waters

    Directory of Open Access Journals (Sweden)

    Ashit Rao

    2017-10-01

    Full Text Available Water is a fundamental solvent sustaining life, key to the conformations and equilibria associated with solute species. Emerging studies on nucleation and crystallization phenomena reveal that the dynamics of hydration associated with mineral precursors are critical in determining material formation and growth. With certain small molecules affecting the hydration and conformational stability of co-solutes, this study systematically explores the effects of these chaotropes and kosmotropes as well as certain sugar enantiomers on the early stages of calcium carbonate formation. These small molecules appear to modulate mineral nucleation in a class-dependent manner. The observed effects are finite in comparison to the established, strong interactions between charged polymers and intermediate mineral forms. Thus, perturbations to hydration dynamics of ion clusters by co-solute species can affect nucleation phenomena in a discernable manner.

  20. Nucleation of Recrystallization studied by EBSP and 3DXRD

    DEFF Research Database (Denmark)

    West, Stine

    2009-01-01

    When a deformed crystalline material is annealed, recrystallization will typically take place. In this process new perfect crystals nucleate and grow, consuming the deformation structure. Traditionally, nucleation theories state that the crystal orientations of these new grains were already present...... in order to ease determination of the nucleation sites and the analysis of orientation relationships between nuclei and parent grains. A series of experiments was carried out using Electron Backscattered diffraction Patterns (EBSP). These were considered to provide a valuable background to support...... in the bulk of a sample after annealing. An orientation imaging map was reconstructed from the bulk of the sample before and after annealing. Such reconstructions have only been done before with completely recrystallized samples, so this was a unique opportunity to compare orientations observed locally...

  1. A two-parameter extension of classical nucleation theory

    Science.gov (United States)

    Lutsko, James F.; Durán-Olivencia, Miguel A.

    2015-06-01

    A two-variable stochastic model for diffusion-limited nucleation is developed using a formalism derived from fluctuating hydrodynamics. The model is a direct generalization of the standard classical nucleation theory (CNT). The nucleation rate and pathway are calculated in the weak-noise approximation and are shown to be in good agreement with direct numerical simulations for the weak-solution/strong-solution transition in globular proteins. We find that CNT underestimates the time needed for the formation of a critical cluster by two orders of magnitude and that this discrepancy is due to the more complex dynamics of the two variable model and not, as often is assumed, a result of errors in the estimation of the free energy barrier.

  2. A two-parameter extension of classical nucleation theory

    International Nuclear Information System (INIS)

    Lutsko, James F; Durán-Olivencia, Miguel A

    2015-01-01

    A two-variable stochastic model for diffusion-limited nucleation is developed using a formalism derived from fluctuating hydrodynamics. The model is a direct generalization of the standard classical nucleation theory (CNT). The nucleation rate and pathway are calculated in the weak-noise approximation and are shown to be in good agreement with direct numerical simulations for the weak-solution/strong-solution transition in globular proteins. We find that CNT underestimates the time needed for the formation of a critical cluster by two orders of magnitude and that this discrepancy is due to the more complex dynamics of the two variable model and not, as often is assumed, a result of errors in the estimation of the free energy barrier. (paper)

  3. Homogeneous bulk, surface, and edge nucleation in crystalline nanodroplets

    Science.gov (United States)

    Carvalho, Jessica L.; Dalnoki-Veress, Kari

    2011-03-01

    We present a study on the homogeneous nucleation of dewetted poly(ethylene oxide) droplets on a substrate that is itself crystallisable. While the chemical properties of the substrate prepared in either the amorphous or crystalline state are identical, the surface landscape varies widely. We observe a large difference in the substrate's nucleating ability depending on how it is prepared. Furthermore, the scaling dependence of the nucleation rate on the size of the droplets depends on the substrate surface properties. The birth of the crystalline state can be directed to originate predominantly within the bulk, at the substrate surface or at the droplet's edge depending on how we tune the substrate. J.L. Carvalho and K. Dalnoki-Veress, Phys. Rev. Lett in press, 2010.

  4. Visualization of nucleate pool boiling of freon 113

    International Nuclear Information System (INIS)

    Afify, M.A.; Fruman, D.H.

    1987-01-01

    The purpose of this investigation is to give a fine description of the behaviour of vapour bubbles in nucleate pool boiling at sites of known sizes using high speed photography. The shapes and growth history of isolated bubbles were determined for a variety of experimental conditions. Coalescence effects between two adjacent or consecutive bubbles were also visualized and the occurrence of vapour patches and continuous vapour columns was demonstrated. Quantitative analysis of the films allows to determine the history and nucleation characteristics of bubbles as a function of various parameters such as heat flux, liquid subcooling and size and nature of nucleation sites. These results are in good agreement with those found in the literature

  5. Bubble nucleation and growth in slow cosmological phase transitions

    Science.gov (United States)

    Mégevand, Ariel; Ramírez, Santiago

    2018-03-01

    We study the dynamics of cosmological phase transitions in the case of small velocities of bubble walls, vw development of the phase transition. We consider different kinds of approximations and refinements for relevant aspects of the dynamics, such as the dependence of the wall velocity on hydrodynamics, the distribution of the latent heat, and the variation of the nucleation rate. Although in this case the common simplifications of a constant wall velocity and an exponential nucleation rate break down due to reheating, we show that a delta-function rate and a velocity which depends linearly on the temperature give a good description of the dynamics and allow to solve the evolution analytically. We also consider a Gaussian nucleation rate, which gives a more precise result for the bubble size distribution. We discuss the implications for the computation of cosmic remnants.

  6. Designing magnetic droplet soliton nucleation employing spin polarizer

    Science.gov (United States)

    Mohseni, Morteza; Mohseni, Majid

    2018-04-01

    We show by means of micromagnetic simulations that spin polarizer in nano-contact (NC) spin torque oscillators as the representative of the fixed layer in an orthogonal pseudo-spin valve can be employed to design and to control magnetic droplet soliton nucleation and dynamics. We found that using a tilted spin polarizer layer decreases the droplet nucleation time which is more suitable for high speed applications. However, a tilted spin polarizer increases the nucleation current and decreases the frequency stability of the droplet. Additionally, by driving the magnetization inhomogenously at the NC region, it is found that a tilted spin polarizer reduces the precession angle of the droplet and through an interplay with the Oersted field of the DC current, it breaks the spatial symmetry of the droplet profile. Our findings explore fundamental insight into nano-scale magnetic droplet soliton dynamics with potential tunability parameters for future microwave electronics.

  7. International Workshop on Comparing Ice Nucleation Measuring Systems 2014

    Energy Technology Data Exchange (ETDEWEB)

    Cziczo, Daniel [Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)

    2016-04-30

    The relationship of ambient aerosol particles to the formation of ice-containing clouds is one of the largest uncertainties in understanding the Earth’s climate. The uncertainty is due to several poorly understood processes and measurements including, but not limited to: (1) the microphysics of how particles nucleate ice, (2) the number of ice forming particles as a function of atmospheric properties such as temperature and relative humidity, (3) the atmospheric distribution of ice forming particles and (4) the role of anthropogenic activities in producing or changing the behavior of ice forming particles. The ways in which ice forming particles can impact climate is also multi-faceted. More ice forming particles can lead to clouds with more ice crystals and different optical properties than clouds with less ice forming particles. More effective ice forming particles can lead to ice at higher temperature and/or lower saturation, resulting in clouds at lower altitude or latitude which also changes the Earth’s radiative balance. Ice nucleation also initiates most of the Earth’s precipitation, even in the mid- and low-latitudes, since cloud-top temperatures are often below freezing. The limited measurements and lack of understanding directly translates to restrictions in our ability to model atmospheric ice formation and project changes into the future. The importance of ice nucleation research is further exemplified by Figure 1 which shows the publications per decade and citations per year on the topic of ice nucleation [DeMott et al., 2011]. After a lull at the end of the last century, there has been a dramatic increase in both publications and citations related to ice nucleation; this directly corresponds to the importance of ice nucleation on the Earth’s climate and the uncertainty in this area noted by the Solomon [2007].

  8. Application of an Online-Coupled Regional Climate Model, WRF-CAM5, over East Asia for Examination of Ice Nucleation Schemes: Part II. Sensitivity to Heterogeneous Ice Nucleation Parameterizations and Dust Emissions

    Directory of Open Access Journals (Sweden)

    Yang Zhang

    2015-09-01

    Full Text Available Aerosol particles can affect cloud microphysical properties by serving as ice nuclei (IN. Large uncertainties exist in the ice nucleation parameterizations (INPs used in current climate models. In this Part II paper, to examine the sensitivity of the model predictions to different heterogeneous INPs, WRF-CAM5 simulation using the INP of Niemand et al. (N12 [1] is conducted over East Asia for two full years, 2006 and 2011, and compared with simulation using the INP of Meyers et al. (M92 [2], which is the original INP used in CAM5. M92 calculates the nucleated ice particle concentration as a function of ice supersaturation, while N12 represents the nucleated ice particle concentration as a function of temperature and the number concentrations and surface areas of dust particles. Compared to M92, the WRF-CAM5 simulation with N12 produces significantly higher nucleated ice crystal number concentrations (ICNCs in the northern domain where dust sources are located, leading to significantly higher cloud ice number and mass concentrations and ice water path, but the opposite is true in the southern domain where temperatures and moistures play a more important role in ice formation. Overall, the simulation with N12 gives lower downward shortwave radiation but higher downward longwave radiation, cloud liquid water path, cloud droplet number concentrations, and cloud optical depth. The increase in cloud optical depth and the decrease in downward solar flux result in a stronger shortwave and longwave cloud forcing, and decreases temperature at 2-m and precipitation. Changes in temperature and radiation lower surface concentrations of OH, O3, SO42−, and PM2.5, but increase surface concentrations of CO, NO2, and SO2 over most of the domain. By acting as cloud condensation nuclei (CCN and IN, dust particles have different impacts on cloud water and ice number concentrations, radiation, and temperature at 2-m and precipitation depending on whether the

  9. Regulation of microtubule nucleation mediated by gamma-tubulin complexes

    Czech Academy of Sciences Publication Activity Database

    Sulimenko, Vadym; Hájková, Zuzana; Klebanovych, Anastasiya; Dráber, Pavel

    2017-01-01

    Roč. 254, č. 3 (2017), s. 1187-1199 ISSN 0033-183X R&D Projects: GA MŠk(CZ) LD13015 Institutional support: RVO:68378050 Keywords : mitotic spindle formation * ring complex * fission yeast * organizing centers * protein complex * golgi-complex * cell -cycle * pole body * augmin * centrosome * Centrosomes * Microtubule nucleation * Microtubule-organizing centers * Non-centrosomal nucleation sites * Spindle pole bodies * gamma-Tubulin complexes Subject RIV: EB - Genetics ; Molecular Biology OBOR OECD: Cell biology Impact factor: 2.870, year: 2016

  10. Gas diffusion and temperature dependence of bubble nucleation during irradiation

    DEFF Research Database (Denmark)

    Foreman, A. J. E.; Singh, Bachu Narain

    1986-01-01

    The continuous production of gases at relatively high rates under fusion irradiation conditions may enhance the nucleation of cavities. This can cause dimensional changes and could induce embrittlement arising from gas accumulation on grain boundaries. Computer calculations have been made...... of the diatomic nucleation of helium bubbles, assuming helium to diffuse substitutionally, with radiation-enhanced diffusion at lower temperatures. The calculated temperature dependence of the bubble density shows excellent agreement with that observed in 600 MeV proton irradiations, including a reduction...

  11. Gas diffusion and temperature dependence of bubble nucleation during irradiation

    DEFF Research Database (Denmark)

    Foreman, A. J. E.; Singh, Bachu Narain

    1986-01-01

    of the diatomic nucleation of helium bubbles, assuming helium to diffuse substitutionally, with radiation-enhanced diffusion at lower temperatures. The calculated temperature dependence of the bubble density shows excellent agreement with that observed in 600 MeV proton irradiations, including a reduction...... in activation energy below Tm/2. The coalescence of diatomic nuclei due to Brownian motion markedly improves the agreement and also provides a well-defined terminal density. Bubble nucleation by this mechanism is sufficiently fast to inhibit any appreciable initial loss of gas to grain boundaries during...

  12. Noise-induced wave nucleations in an excitable chemical reaction

    Science.gov (United States)

    Beato, V.; Sendiña-Nadal, I.; Gerdes, I.; Engel, H.

    2005-03-01

    We study both experimentally and numerically the temporal coherence of noise-induced wave nucleations in excitable media subjected to external fluctuations with finite correlation time. The experiments are performed with the light-sensitive variant of the Belousov-Zhabotinsky (BZ) reaction forced by an exponentially correlated dichotomous fluctuating illumination. We find that there exists an optimal correlation time for which nucleations coherence reaches a maximum. The same behavior is obtained in numerical simulations with a stochastic Oregonator model, modified to describe the light-sensitive BZ reaction.

  13. Neutral molecular cluster formation of sulfuric acid–dimethylamine observed in real time under atmospheric conditions

    CERN Document Server

    Kürten, Andreas; Simon, Mario; Sipilä, Mikko; Sarnela, Nina; Junninen, Heikki; Adamov, Alexey; Almeida, João; Amorim, Antonio; Bianchi, Federico; Breitenlechner, Martin; Dommen, Josef; Donahue, Neil M; Duplissy, Jonathan; Ehrhart, Sebastian; Flagan, Richard C; Franchin, Alessandro; Hakala, Jani; Hansel, Armin; Heinritzi, Martin; Hutterli, Manuel; Kangasluoma, Juha; Kirkby, Jasper; Laaksonen, Ari; Lehtipalo, Katrianne; Leiminger, Markus; Makhmutov, Vladimir; Mathot, Serge; Onnela, Antti; Petäjä, Tuukka; Praplan, Arnaud P; Riccobono, Francesco; Rissanen, Matti P; Rondo, Linda; Schobesberger, Siegfried; Seinfeld, John H; Steiner, Gerhard; Tomé, António; Tröstl, Jasmin; Winkler, Paul M; Williamson, Christina; Wimmer, Daniela; Ye, Penglin; Baltensperger, Urs; Carslaw, Kenneth S; Kulmala, Markku; Worsnop, Douglas R; Curtius, Joachim

    2014-01-01

    For atmospheric sulfuric acid (SA) concentrations the presence of dimethylamine (DMA) at mixing ratios of several parts per trillion by volume can explain observed boundary layer new particle formation rates. However, the concentration and molecular composition of the neutral (uncharged) clusters have not been reported so far due to the lack of suitable instrumentation. Here we report on experiments from the Cosmics Leaving Outdoor Droplets chamber at the European Organization for Nuclear Research revealing the formation of neutral particles containing up to 14 SA and 16 DMA molecules, corresponding to a mobility diameter of about 2 nm, under atmospherically relevant conditions. These measurements bridge the gap between the molecular and particle perspectives of nucleation, revealing the fundamental processes involved in particle formation and growth. The neutral clusters are found to form at or close to the kinetic limit where particle formation is limited only by the collision rate of SA molecules. Even tho...

  14. Current disruptions in the near-earth neutral sheet region

    International Nuclear Information System (INIS)

    Liu, A.T.Y.; Anderson, B.J.; Takahashi, K.; Zanetti, L.J.; McEntire, R.W.; Potemra, T.A.; Lopez, R.E.; Klumpar, D.M.; Greene, E.M.; Strangeway, R.

    1992-01-01

    Observations from the Charge Composition Explorer in 1985 and 1986 revealed fifteen current disruption events in which the magnetic field fluctuations were large and their onsets coincided well with ground onsets of substorm expansion or intensification. Over the disruption interval, the local magnetic field can change by as much as a factor of ∼7. In general, the stronger the current buildup and the closer the neutral sheet, the larger the resultant field change. There is also a tendency for a larger subsequent enhancement in the AE index with a stronger current buildup prior to current disruption. For events with good pitch angle coverage and extended observation in the neutral sheet region the authors find that the particle pressure increases toward the disruption onset and decreases afterward. Just prior to disruption, either the total particle pressure is isotropic, or the perpendicular component (P perpendicular ) dominates the parallel component (P parallel ), the plasma beta is seen to be as high as ∼70, and the observed plasma pressure gradient at the neutral sheet is large along the tail axis. The deduced local current density associated with pressure gradient is ∼27-80 n/Am 2 and is ∼85-105 mA/m when integrated over the sheet thickness. They infer from these results that just prior to the onset of current disruption, (1) an extremely thin current sheet requiring P parallel > P perpendicular for stress balance does not develop at these distances, (2) the thermal ion orbits are in the chaotic or Speiser regime while the thermal electrons are in the adiabatic regime and, in one case, exhibit peaked fluxes perpendicular to the magnetic field, thus implying no electron orbit chaotization to possibly initiate ion tearing instability, and (3) the neutral sheet is in the unstable regime specified by the cross-field current instability

  15. Influence of temperature on the molecular composition of ions and charged clusters during pure biogenic nucleation

    Science.gov (United States)

    Frege, Carla; Ortega, Ismael K.; Rissanen, Matti P.; Praplan, Arnaud P.; Steiner, Gerhard; Heinritzi, Martin; Ahonen, Lauri; Amorim, António; Bernhammer, Anne-Kathrin; Bianchi, Federico; Brilke, Sophia; Breitenlechner, Martin; Dada, Lubna; Dias, António; Duplissy, Jonathan; Ehrhart, Sebastian; El-Haddad, Imad; Fischer, Lukas; Fuchs, Claudia; Garmash, Olga; Gonin, Marc; Hansel, Armin; Hoyle, Christopher R.; Jokinen, Tuija; Junninen, Heikki; Kirkby, Jasper; Kürten, Andreas; Lehtipalo, Katrianne; Leiminger, Markus; Mauldin, Roy Lee; Molteni, Ugo; Nichman, Leonid; Petäjä, Tuukka; Sarnela, Nina; Schobesberger, Siegfried; Simon, Mario; Sipilä, Mikko; Stolzenburg, Dominik; Tomé, António; Vogel, Alexander L.; Wagner, Andrea C.; Wagner, Robert; Xiao, Mao; Yan, Chao; Ye, Penglin; Curtius, Joachim; Donahue, Neil M.; Flagan, Richard C.; Kulmala, Markku; Worsnop, Douglas R.; Winkler, Paul M.; Dommen, Josef; Baltensperger, Urs

    2018-01-01

    It was recently shown by the CERN CLOUD experiment that biogenic highly oxygenated molecules (HOMs) form particles under atmospheric conditions in the absence of sulfuric acid, where ions enhance the nucleation rate by 1-2 orders of magnitude. The biogenic HOMs were produced from ozonolysis of α-pinene at 5 °C. Here we extend this study to compare the molecular composition of positive and negative HOM clusters measured with atmospheric pressure interface time-of-flight mass spectrometers (APi-TOFs), at three different temperatures (25, 5 and -25 °C). Most negative HOM clusters include a nitrate (NO3-) ion, and the spectra are similar to those seen in the nighttime boreal forest. On the other hand, most positive HOM clusters include an ammonium (NH4+) ion, and the spectra are characterized by mass bands that differ in their molecular weight by ˜ 20 C atoms, corresponding to HOM dimers. At lower temperatures the average oxygen to carbon (O : C) ratio of the HOM clusters decreases for both polarities, reflecting an overall reduction of HOM formation with decreasing temperature. This indicates a decrease in the rate of autoxidation with temperature due to a rather high activation energy as has previously been determined by quantum chemical calculations. Furthermore, at the lowest temperature (-25 °C), the presence of C30 clusters shows that HOM monomers start to contribute to the nucleation of positive clusters. These experimental findings are supported by quantum chemical calculations of the binding energies of representative neutral and charged clusters.

  16. Nucleation and growth of a multicomponent metallic glass

    Indian Academy of Sciences (India)

    Unknown

    of modified Kissinger and Matusita equations for the non-isothermal crystallization. The results show enhanced bulk nucleation in general. At high heating rates added to it is surface induced abnormal grain growth resulting in fractal dimensionality. Keywords. Activation energy; isothermal annealing; abnormal grain growth; ...

  17. New particle formation by ion-induced nucleation during dissipation ...

    Indian Academy of Sciences (India)

    ticle formation. Cluster ions can grow to form new particles and rate of such new particle forma- tion will be proportional to ion concentration or the ionization rate in the atmosphere (Dickinson. 1975). Later, many studies have identified ion- induced nucleation (IIN) as one of the most important source of atmospheric particles ...

  18. How Ambient Pressure Influences Water Droplet Nucleation at Tropospheric Conditions

    Czech Academy of Sciences Publication Activity Database

    Hyvärinen, A.-P.; Brus, David; Wedekind, J.; Lihavainen, H.

    2010-01-01

    Roč. 37, - (2010), L21802 ISSN 0094-8276 Institutional research plan: CEZ:AV0Z40720504 Keywords : nucleations theories * ambient pressure * condensation of droplets Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 3.505, year: 2010

  19. The role of ions in particle nucleation under atmospheric conditions

    DEFF Research Database (Denmark)

    Enghoff, Martin B.; Pedersen, J. O. P.; Bondo, T.

    2008-01-01

    Aerosol nucleation has been studied experimentally in purified, atmospheric air, containing trace amounts of water vapor, ozone, and sulfur dioxide. The results are compared with model calculations. It is found that an increase in ionization by a factor of 10 increases the production rate of stable...

  20. The role of ions in particle nucleation under atmospheric conditions

    DEFF Research Database (Denmark)

    Enghoff, Martin B.; Pedersen, J. O. P.; Bondo, T.

    2008-01-01

    Aerosol nucleation has been studied experimentally in purified, atmospheric air, containing trace amounts of water vapor, ozone, and sulfur dioxide. The results are compared with model calculations. It is found that an increase in ionization by a factor of 10 increases the production rate of stab...

  1. Nucleation and growth kinetics of palladium nanoparticles on thin ...

    African Journals Online (AJOL)

    1073 K and deposition .... The entry parameters are: the velocity of nucleation, velocity of growth, the average means life time, the ... Ts = 573 K and 673 K, we can see that the density of clusters is increasing rapidly after 10 to 70 s (see table 1) ...

  2. Void nucleation at elevated temperatures under cascade-damage irradiation

    International Nuclear Information System (INIS)

    Semenov, A.A.; Woo, C.H.

    2002-01-01

    The effects on void nucleation of fluctuations respectively due to the randomness of point-defect migratory jumps, the random generation of free point defects in discrete packages, and the fluctuating rate of vacancy emission from voids are considered. It was found that effects of the cascade-induced fluctuations are significant only at sufficiently high total sink strength. At lower sink strengths and elevated temperatures, the fluctuation in the rate of vacancy emission is the dominant factor. Application of the present theory to the void nucleation in annealed pure copper neutron-irradiated at elevated temperatures with doses of 10 -4 -10 -2 NRT dpa showed reasonable agreement between theory and experiment. This application also predicts correctly the temporal development of large-scale spatial heterogeneous microstructure during the void nucleation stage. Comparison between calculated and experimental void nucleation rates in neutron-irradiated molybdenum at temperatures where vacancy emission from voids is negligible showed reasonable agreement as well. It was clearly demonstrated that the athermal shrinkage of relatively large voids experimentally observable in molybdenum at such temperatures may be easily explained in the framework of the present theory

  3. Breakdown of classical nucleation theory near isostructural phase transitions

    NARCIS (Netherlands)

    Cacciuto, A.; Auer, S.; Frenkel, D.

    2004-01-01

    We report simulations of crystal nucleation in binary mixtures of hard spherical colloids with a size ratio of 1:10. The stable crystal phase of this system can be either dense or expanded. We find that, in the vicinity of the solid-solid critical point where the crystallites are highly

  4. Modelling the role of compositional fluctuations in nucleation kinetics

    Czech Academy of Sciences Publication Activity Database

    Ženíšek, J.; Kozeschnik, E.; Svoboda, Jiří; Fischer, F. D.

    2015-01-01

    Roč. 91, JUN (2015), s. 365-376 ISSN 1359-6454 R&D Projects: GA ČR(CZ) GA14-24252S Institutional support: RVO:68081723 Keywords : Kinetics * Nucleation and growth * Precipitates * Interface energy * Fluctuations of chemical composition Subject RIV: BJ - Thermodynamics Impact factor: 5.058, year: 2015

  5. Annealing Twinning and the Nucleation of Recrystallization at Grain Boundaries

    DEFF Research Database (Denmark)

    Jones, A R.

    1981-01-01

    boundaries during recovery might stimulate nucleation of recrystallization in low stacking fault energy materials. The experimental observations also lead to the implication that the density of recrystallization nuclei formed in such materials may be directly related to the strength of the deformation...

  6. Nucleation at hardness indentations in cold rolled Al

    DEFF Research Database (Denmark)

    Xu, C.L.; Zhang, Yubin; Wu, G.L.

    2015-01-01

    Nucleation of recrystallization near hardness indentations has been investigated in slightly cold rolled high purity aluminium. Samples were cold rolled to 12% and 20% reductions in thickness and indentations were done with two different loads (500 g and 2000 g). The samples were annealed at 300 ...

  7. Containerless Undercooled Melts: Ordering, Nucleation, and Dendrite Growth

    Science.gov (United States)

    Herlach, Dieter M.; Binder, Sven; Galenko, Peter; Gegner, Jan; Holland-Moritz, Dirk; Klein, Stefan; Kolbe, Matthias; Volkmann, Thomas

    2015-11-01

    Electromagnetic and electrostatic levitation are applied to containerless undercool and solidify metallic melts. A large undercooling range becomes accessible with the extra benefit that the freely suspended drop is accessible directly for in situ observation. The short-range order in undercooled melts is investigated by combining levitation with elastic neutron scattering and X-ray scattering using synchrotron radiation. Muon Spin Rotation ( µSR) experiments show magnetic ordering in deeply undercooled Co80Pd20 alloys. The onset of magnetic ordering stimulates nucleation. Results on nucleation undercooling of zirconium are presented showing the limit of maximum undercoolability set by the onset of homogeneous nucleation. Metastable phase diagrams are determined by applying energy-dispersive X-ray diffraction of Ni-V alloys with varying concentration. Nucleation is followed by crystal growth. Rapid dendrite growth velocity is measured on levitation-processed samples as a function of undercooling ∆ T by using high-speed video camera technique. Solute trapping in dilute solid solutions and disorder trapping in intermetallic compounds are experimentally verified. Measurements of glass-forming Cu-Zr alloy show a maximum in the V(∆ T) relation that is indicative for diffusion-controlled growth. The influence of convection on dendrite growth of Al50Ni50 is shown by comparative measurements of dendrite growth velocity on Earth and in reduced gravity. Eventually, faceting of a rough interface by convection is presented as observed on Ni2B alloys.

  8. New Ion-Nucleation Mechanism Relevant for the Earth's Atmosphere

    DEFF Research Database (Denmark)

    Marsh, N.D.; Svensmark, Henrik; Pedersen, Jens Olaf Pepke

    Experimental studies of ultra-fine aerosol nucleation in clean atmospheric air, containing trace amounts of ozone, sulphur dioxide, and water vapour suggest that the production rate of critical clusters is sensitive to ionisation. To assess this sensitivity numerical simulations of the initial...

  9. Total Sulfate vs. Sulfuric Acid Monomer Concenterations in Nucleation Studies.

    Czech Academy of Sciences Publication Activity Database

    Neitola, K.; Brus, David; Makkonen, U.; Sipilä, M.; Mauldin III, R.L.; Sarnela, N.; Jokinen, T.; Lihavainen, H.; Kulmala, M.

    2015-01-01

    Roč. 15, č. 6 (2015), s. 3429-3443 ISSN 1680-7316 Grant - others:AFCE(FI) 1118615 Institutional support: RVO:67985858 Keywords : ion-induced nucleation * particle formation * experimental setup Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 5.114, year: 2015

  10. Nanocellular polymer foams nucleated by core-shell nanoparticles

    NARCIS (Netherlands)

    Liu, Shanqiu; Zoetebier, Bram; Hulsman, Lars; Zhang, Yuanyuan; Duvigneau, Joost; Vancso, Gyula J.

    2016-01-01

    The synthesis of low surface energy polymer grafted silica nanoparticles is reported for the utilization as highly efficient cell nucleation agents to obtain nanocellular, CO2 blown polystyrene (PS) and poly(methyl methacrylate) (PMMA) films in a batch process. For nanoparticle surface

  11. The role of specific nucleation in polypropylene photodegradation

    Czech Academy of Sciences Publication Activity Database

    Výchopňová, J.; Čermák, R.; Obadal, M.; Raab, Miroslav; Verney, V.; Commereuc, S.

    2007-01-01

    Roč. 92, č. 10 (2007), s. 1763-1768 ISSN 0141-3910 Institutional research plan: CEZ:AV0Z40500505 Keywords : polymorphism * photooxidation * crystallization * nucleating agent Subject RIV: CD - Macromolecular Chemistry Impact factor: 2.073, year: 2007

  12. Local Structure of Liquid Carbon Controls Diamond Nucleation

    NARCIS (Netherlands)

    Ghiringhelli, L.M.; Valeriani, C.; Meijer, E.J.; Frenkel, D.

    2007-01-01

    Diamonds melt at temperatures above 4000 K. There are no measurements of the steady-state rate of the reverse process, i.e., diamond nucleation from the melt, because experiments are difficult at these extreme temperatures and pressures. Using numerical simulations, we estimate the diamond

  13. New particle formation by ion-induced nucleation during dissipation ...

    Indian Academy of Sciences (India)

    jess/120/05/0843-0850. Keywords. New particle formation; ion-induced nucleation; lightning intensity and rain. Abstract. A case of new particle formation observed during dissipation stage of a thunderstorm at a tropical station, Pune, India on 3 ...

  14. Nucleation and growth of nanoscaled one-dimensional materials

    Science.gov (United States)

    Cui, Hongtao

    Nanoscaled one-dimensional materials have attracted great interest due to their novel physical and chemical properties. The purpose of this dissertation is to study the nucleation and growth mechanisms of carbon nanotubes and silicon nitride nanowires with their field emission applications in mind. As a result of this research, a novel methodology has been developed to deposit aligned bamboo-like carbon nanotubes on substrates using a methane and ammonia mixture in microwave plasma enhanced chemical deposition. Study of growth kinetics suggests that the carbon diffusion through bulk catalyst particles controls growth in the initial deposition process. Microstructures of carbon nanotubes are affected by the growth temperature and carbon concentration in the gas phase. High-resolution transmission electron microscope confirms the existence of the bamboo-like structure. Electron diffraction reveals that the iron-based catalyst nucleates and sustains the growth of carbon nanotubes. A nucleation and growth model has been constructed based upon experimental data and observations. In the study of silicon nitride nanoneedles, a vapor-liquid-solid model is employed to explain the nucleation and growth processes. Ammonia plasma etching is proposed to reduce the size of the catalyst and subsequently produce the novel needle-like nanostructure. High-resolution transmission electron microscope shows the structure is well crystallized and composed of alpha-silicon nitride. Other observations in the structure are also explained.

  15. Polymer-based nucleation for chemical vapour deposition of diamond

    Czech Academy of Sciences Publication Activity Database

    Domonkos, Mária; Ižák, Tibor; Kromka, Alexander; Varga, Marián

    2016-01-01

    Roč. 133, č. 29 (2016), 1-7, č. článku 43688. ISSN 0021-8995 R&D Projects: GA ČR GC15-22102J Institutional support: RVO:68378271 Keywords : copolymers * composites * diamond * nucleation Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.860, year: 2016

  16. The Role of Sulfuric Acid in Atmospheric Nucleation

    Czech Academy of Sciences Publication Activity Database

    Sipilä, M.; Berndt, T.; Petäjä, T.; Brus, David; Vanhanen, J.; Stratmann, F.; Patokoski, J.; Mauldin, III, R.L.; Hyvärinen, A.-P.; Lihavainen, H.; Kulmala, M.

    2010-01-01

    Roč. 327, č. 5970 (2010), s. 1243-1246 ISSN 0036-8075 Grant - others:EUCAARI(XE) 036833-2 Institutional research plan: CEZ:AV0Z40720504 Keywords : nucleation * sulfuric acid * climate Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 31.364, year: 2010

  17. Forgetting emotional and neutral words: an ERP study.

    Science.gov (United States)

    Brandt, Karen R; Nielsen, Maria Kragh; Holmes, Amanda

    2013-03-21

    Previous research has demonstrated that emotional material is more likely to be remembered than neutral material (Hamann, 2001). The present study employed the item-method of directed forgetting in order to examine whether emotionally negative words are not only easier to remember, but also harder to forget. Event-related potentials (ERPs) were additionally measured in order to investigate the processes of selective rehearsal and active inhibition in directed forgetting. The results demonstrated directed forgetting effects for both neutral and negative words, with a stronger effect for negative items. Late positive potentials (LPPs) for 'to-be-remembered' (TBR) relative to 'to-be-forgotten' (TBF) cues were enhanced when the cues followed negative in comparison to neutral words, indicating the greater selective rehearsal of TBR negative items. Frontal positivities to TBF relative to TBR cues were not modulated by word valence, indicating that inhibitory processes were unaffected by emotion. Taken together, the present research demonstrates for the first time that, not only are emotionally negative words prone to the same directed forgetting effects as neutral words, but that these effects are in fact enhanced for negative words and due to increased selective rehearsal of TBR negative items. The discrepancies between the present findings and those of previous studies are discussed. Copyright © 2013 Elsevier B.V. All rights reserved.

  18. Predatory blue crabs induce stronger nonconsumptive effects in eastern oysters Crassostrea virginica than scavenging blue crabs

    Directory of Open Access Journals (Sweden)

    Avery E. Scherer

    2017-02-01

    Full Text Available By influencing critical prey traits such as foraging or habitat selection, predators can affect entire ecosystems, but the nature of cues that trigger prey reactions to predators are not well understood. Predators may scavenge to supplement their energetic needs and scavenging frequency may vary among individuals within a species due to preferences and prey availability. Yet prey reactions to consumers that are primarily scavengers versus those that are active foragers have not been investigated, even though variation in prey reactions to scavengers or predators might influence cascading nonconsumptive effects in food webs. Oysters Crassostrea virginica react to crab predators by growing stronger shells. We exposed oysters to exudates from crabs fed live oysters or fed aged oyster tissue to simulate scavenging, and to controls without crab cues. Oysters grew stronger shells when exposed to either crab exudate, but their shells were significantly stronger when crabs were fed live oysters. The stronger response to predators than scavengers could be due to inherent differences in diet cues representative of reduced risk in the presence of scavengers or to degradation of conspecific alarm cues in aged treatments, which may mask risk from potential predators subsisting by scavenging.

  19. Stronger Accent Following a Stroke: The Case of a Trilingual with Aphasia

    Science.gov (United States)

    Levy, Erika S.; Goral, Mira; De Diesbach, Catharine Castelluccio; Law, Franzo, II

    2011-01-01

    This study documents patterns of change in speech production in a multilingual with aphasia following a cerebrovascular accident (CVA). EC, a right-handed Hebrew-English-French trilingual man, had a left fronto-temporo-parietal CVA, after which he reported that his (native) Hebrew accent became stronger in his (second language) English. Recordings…

  20. Peptide-MHC class I stability is a stronger predictor of CTL immunogenicity than peptide affinity

    DEFF Research Database (Denmark)

    Harndahl, Mikkel Nors; Rasmussen, Michael; Nielsen, Morten

    2012-01-01

    Peptide-MHC class I stability is a stronger predictor of CTL immunogenicity than peptide affinity Mikkel Harndahla, Michael Rasmussena, Morten Nielsenb, Soren Buusa,∗ a Laboratory of Experimental Immunology, Faculty of Health Sciences, University of Copenhagen, Denmark b Center for Biological Seq...... al., 2007. J. Immunol. 178, 7890–7901. doi:10.1016/j.molimm.2012.02.025...

  1. First-order dominance: stronger characterization and a bivariate checking algorithm

    DEFF Research Database (Denmark)

    Range, Troels Martin; Østerdal, Lars Peter Raahave

    2018-01-01

    distributions. Utilizing that this problem can be formulated as a transportation problem with a special structure, we provide a stronger characterization of multivariate first-order dominance and develop a linear time complexity checking algorithm for the bivariate case. We illustrate the use of the checking...

  2. Fasting insulin is a stronger cardiovascular risk factor in women than in men

    NARCIS (Netherlands)

    Oterdoom, Leendert H.; de Vries, Aiko P. J.; Gansevoort, Ron T.; de Jong, Paul E.; Gans, Reinold O. B.; Bakker, Stephan J. L.

    Diabetes is a stronger risk factor for cardiovascular disease (CVD) in women than in men. It is not known whether there is also a sex difference in the association between hyperinsulinaemia, reflecting insulin resistance, and CVD. Fasting insulin was assessed with a specific assay in 6916 fasting,

  3. A stronger patch test elicitation reaction to the allergen hydroxycitronellal plus the irritant sodium lauryl sulfate

    DEFF Research Database (Denmark)

    Heydorn, S; Andersen, Klaus Ejner; Johansen, Jeanne Duus

    2003-01-01

    Household and cleaning products often contain both allergens and irritants. The aim of this double-blinded, randomized, paired study was to determine whether patch testing with an allergen (hydroxycitronellal) combined with an irritant [sodium lauryl sulfate (SLS)] cause a stronger patch test...

  4. A Human Capital Framework for a Stronger Teacher Workforce. Advancing Teaching--Improving Learning. White Paper

    Science.gov (United States)

    Myung, Jeannie; Martinez, Krissia; Nordstrum, Lee

    2013-01-01

    Building a stronger teacher workforce requires the thoughtful orchestration of multiple processes working together in a human capital system. This white paper presents a framework that can be used to take stock of current efforts to enhance the teacher workforce in school districts or educational organizations, as well as their underlying theories…

  5. Harmful drinking after job loss: a stronger association during the post-2008 economic crisis?

    NARCIS (Netherlands)

    de Goeij, Moniek C. M.; Bruggink, Jan-Willem; Otten, Ferdy; Kunst, Anton E.

    2017-01-01

    This study investigated, among the Dutch working population, whether job loss during the post-2008 economic crisis is associated with harmful drinking and whether this association is stronger than before the crisis. Repeated cross-sectional data from the Dutch Health Interview Survey 2004-2013 were

  6. The Effect of Volcanic Ash Composition on Ice Nucleation Affinity

    Science.gov (United States)

    Genareau, K. D.; Cloer, S.; Primm, K.; Woods, T.; Tolbert, M. A.

    2017-12-01

    Understanding the role that volcanic ash plays in ice nucleation is important for knowledge of lightning generation in both volcanic plumes and in clouds developing downwind from active volcanoes. Volcanic ash has long been suggested to influence heterogeneous ice nucleation following explosive eruptions, but determining precisely how composition and mineralogy affects ice nucleation affinity (INA) is poorly constrained. For the study presented here, volcanic ash samples with different compositions and mineral/glass contents were tested in both the deposition and immersion modes, following the methods presented in Schill et al. (2015). Bulk composition was determined with X-ray fluorescence (XRF), grain size distribution was determined with laser diffraction particle size analysis (LDPSA), and mineralogy was determined with X-ray diffraction (XRD) and scanning electron microscopy (SEM). Results of the deposition-mode experiments reveal that there is no relationship between ice saturation ratios (Sice) and either mineralogy or bulk ash composition, as all samples have similar Sice ratios. In the immersion-mode experiments, frozen fractions were determined from -20 °C to -50 °C using three different amounts of ash (0.5, 1.0, and 2.0 wt% of slurry). Results from the immersion freezing reveal that the rhyolitic samples (73 wt% SiO2) nucleate ice at higher temperatures compared to the basaltic samples (49 wt% SiO2). There is no observed correlation between frozen fractions and mineral content of ash samples, but the two most efficient ice nuclei are rhyolites that contain the greatest proportion of amorphous glass (> 90 %), and are enriched in K2O relative to transition metals (MnO and TiO2), the latter of which show a negative correlation with frozen fraction. Higher ash abundance in water droplets increases the frozen fraction at all temperatures, indicating that ash amount plays the biggest role in ice nucleation. If volcanic ash can reach sufficient abundance (

  7. Ordered Nucleation Sites for the Growth of Zinc Oxide Nanofibers

    Energy Technology Data Exchange (ETDEWEB)

    Wang, J.; Ginley, D.S.; Shaheen, S.

    2006-01-01

    Organic photovoltaics (OPVs) offer a promising route to low cost photovoltaic (PV) technology that can be inexpensively manufactured on a large scale for use in power generation and commercial products. Solar power conversion efficiencies of laboratory scale OPV devices have recently reached ~5%; however, projected efficiencies of at least 10% will be required for commercialization. An analogous approach that has arisen recently that can potentially increase efficiencies employs metal oxide semiconductors as the electron acceptor, creating a hybrid organic-inorganic device. This approach offers the advantage that the conduction band of the oxide can be tuned in a systematic way through doping, thus potentially achieving higher photovoltages in the device. Additionally, nanostructures of these materials can be easily grown from precursor solutions, providing a technique to precisely control the nanoscale geometry. This work focuses on using ZnO, which is known to have high electron mobility (>100 cm2/Vs), as the electron acceptor. Nanofibers of ZnO can be grown from precursors such as zinc acetate or zinc nitrate to form arrays of nanofibers into which a conjugated polymer can be intercalated to form a composite PV device. The morphology of the nanofiber array is critical to the performance of the device, but current methods of nanofiber growth from a flat, polycrystalline nucleation layer allow for little morphological control. To overcome this limitation, we have created ordered arrays of ZnO nucleation sites with controllable size and spacing. Toluene solutions of diblock copolymer micelles with ZnCl2 incorporated into the micellar cores were spin-coated onto glass substrates and etched with an O2 plasma to yield hexagonally ordered arrays of ZnO nanoparticles that functioned as nucleation sites. Changing the concentration of ZnCl2 and the molecular weight and ratio of the diblock copolymer resulted in systematic variation in the size and spacing of the

  8. Neutrality Versus Materiality: A Thermodynamic Theory of Neutral Surfaces

    Directory of Open Access Journals (Sweden)

    Rémi Tailleux

    2016-09-01

    Full Text Available In this paper, a theory for constructing quasi-neutral density variables γ directly in thermodynamic space is formulated, which is based on minimising the absolute value of a purely thermodynamic quantity J n . Physically, J n has a dual dynamic/thermodynamic interpretation as the quantity controlling the energy cost of adiabatic and isohaline parcel exchanges on material surfaces, as well as the dependence of in-situ density on spiciness, in a description of water masses based on γ, spiciness and pressure. Mathematically, minimising | J n | in thermodynamic space is showed to be equivalent to maximising neutrality in physical space. The physics of epineutral dispersion is also reviewed and discussed. It is argued, in particular, that epineutral dispersion is best understood as the aggregate effect of many individual non-neutral stirring events (being understood here as adiabatic and isohaline events with non-zero buoyancy, so that it is only the net displacement aggregated over many events that is approximately neutral. This new view resolves an apparent paradox between the focus in neutral density theory on zero-buoyancy motions and the overwhelming evidence that lateral dispersion in the ocean is primarily caused by non-zero buoyancy processes such as tides, residual currents and sheared internal waves. The efficiency by which a physical process contributes to lateral dispersion can be characterised by its energy signature, with those processes releasing available potential energy (negative energy cost being more efficient than purely neutral processes with zero energy cost. The latter mechanism occurs in the wedge of instability, and its source of energy is the coupling between baroclinicity, thermobaricity, and density compensated temperature/salinity anomalies. Such a mechanism, which can only exist in a salty ocean, is speculated to be important for dissipating spiciness anomalies and neutral helicity. The paper also discusses potential

  9. Investigation of primary nucleation phenomena of acetylsalicylic acid crystals induced by ultrasonic irradiation—ultrasonic energy needed to activate primary nucleation

    Science.gov (United States)

    Miyasaka, Etsuko; Ebihara, Satomi; Hirasawa, Izumi

    2006-09-01

    The purpose of our study is to clarify ultrasonic primary nucleation phenomena for controlling final product size by adjusting the number of primary nuclei. In our previous study, the effect of ultrasonic irradiation on the number of nuclei was investigated under the same supersaturated condition, as a result two novel phenomena were observed. First, there is a region where ultrasonic irradiation inhibits primary nucleation. Second, a specific amount of energy is needed to activate primary nucleation. From this result, it was expected that the ultrasonic energy needed to activate primary nucleation has a certain relationship to the energy necessary to form a stable nucleus. Therefore, we investigated the following: whether ultrasonic irradiation inhibits and activates primary nucleation at various degrees of supersaturation, whether final crystal size relates to the number of nuclei, and whether the ultrasonic energy needed to activate primary nucleation relates to the energy necessary to form a stable nucleus. First, we found that ultrasonic irradiation inhibits and activates primary nucleation at various supersaturated degrees. Second, we found that final crystal size increases or decreases depending on the number of nuclei. Therefore, it was indicated that ultrasonic energy could yield the desired crystal size by inducing suitable nucleation. Third, we found that the ultrasonic energy needed to activate primary nucleation decreases with a decrease in the energy necessary to form a stable nucleus. From this, we can propose criteria for determining the effect of ultrasonic irradiation on primary nucleation by showing diagrams correlating Δ Gcrit with Ecrit.

  10. Can absolute and proportional anthropometric characteristics distinguish stronger and weaker powerlifters?

    Science.gov (United States)

    Keogh, Justin W L; Hume, Patria A; Pearson, Simon N; Mellow, Peter J

    2009-11-01

    This study sought to compare the anthropometric profiles of 17 weaker and 17 stronger Australasian and Pacific powerlifters who had competed in a regional-, national-, or international-level powerlifting competition in New Zealand. Stronger lifters were defined as those having a Wilks score greater than 410, whereas those in the weaker group had a Wilks score less than 370. Each powerlifter was assessed for 37 anthropometric dimensions by International Society for the Advancement of Kinanthropometry (ISAK) level II and III accredited anthropometrists. Because all powerlifters were highly mesomorphic and possessed large girths and bone breadths, both in absolute terms and when expressed as Phantom-Z scores compared through the Phantom, relatively few significant anthropometric differences were observed. However, stronger lifters had significantly greater muscle mass and larger muscular girths in absolute terms as well as greater Brugsch Index (chest girth/height) and "Phantom"-normalized muscle mass, upper arm, chest, and forearm girths. In terms of the segment lengths and bone breadths, the only significant difference was that stronger lifters had a significantly shorter lower leg than weaker lifters. Because the majority of the significant differences were for muscle mass and muscular girths, it would appear likely that these differences contributed to the stronger lifters' superior performance. Powerlifters may therefore need to devote some of their training to the development of greater levels of muscular hypertrophy if they wish to continue to improve their performance. To better understand the anthropometric determinants of muscular strength, future research should recruit larger samples (particularly of elite lifters) and follow these subjects prospectively.

  11. Interaction potentials and their effect on crystal nucleation and symmetry

    International Nuclear Information System (INIS)

    Hsu, C.S.; Rahman, A.

    1979-01-01

    Molecular dynamics technique has been used to study the effect of the interaction potential on crystal nucleation and the symmetry of the nucleated phase. Four systems, namely rubidium, Lennard-Jones, rubidium-truncated, and Lennard-Jones-truncated, have been studied each at reduced density 0.95. Two types of calculations were performed. Firstly, starting from a liquid state, each system was quenched rapidly to a reduced temperature of approx.0.1. The nucleation process for these systems was monitored by studying the time dependence of temperature and the pair correlation function, and the resulting crystalline structure analyzed using among other properties the Voronoi polyhedra. Only in the case of rubidium was a b.c.c. structure nucleated. In the other three cases we obtained a f.c.c. ordering. Secondly, we have studied the effect of changing the interaction potential in a system which has already achieved an ordered state under the action of some other potential. After establishing a b.c.c. structure in a rubidium system, the change in the symmetry of the system was studied when the pair potential was modified to one of the other three forms. The results from both types of calculations are consistent: the rubidium potential leads to a b.c.c. structure while the other three potentials give an f.c.c. structure. Metastable disordered structures were not obtained in any of the calculations. However, the time elapse between the moment when the system is quick-quenched and the moment when nucleation occurs appears to depend upon the potential of interaction

  12. Droplet Nucleation: Physically-Based Parameterizations and Comparative Evaluation

    Directory of Open Access Journals (Sweden)

    Steve Ghan

    2011-10-01

    Full Text Available One of the greatest sources of uncertainty in simulations of climate and climate change is the influence of aerosols on the optical properties of clouds. The root of this influence is the droplet nucleation process, which involves the spontaneous growth of aerosol into cloud droplets at cloud edges, during the early stages of cloud formation, and in some cases within the interior of mature clouds. Numerical models of droplet nucleation represent much of the complexity of the process, but at a computational cost that limits their application to simulations of hours or days. Physically-based parameterizations of droplet nucleation are designed to quickly estimate the number nucleated as a function of the primary controlling parameters: the aerosol number size distribution, hygroscopicity and cooling rate. Here we compare and contrast the key assumptions used in developing each of the most popular parameterizations and compare their performances under a variety of conditions. We find that the more complex parameterizations perform well under a wider variety of nucleation conditions, but all parameterizations perform well under the most common conditions. We then discuss the various applications of the parameterizations to cloud-resolving, regional and global models to study aerosol effects on clouds at a wide range of spatial and temporal scales. We compare estimates of anthropogenic aerosol indirect effects using two different parameterizations applied to the same global climate model, and find that the estimates of indirect effects differ by only 10%. We conclude with a summary of the outstanding challenges remaining for further development and application.

  13. Distinct actin oligomers modulate differently the activity of actin nucleators.

    Science.gov (United States)

    Qu, Zheng; Silvan, Unai; Jockusch, Brigitte M; Aebi, Ueli; Schoenenberger, Cora-Ann; Mannherz, Hans Georg

    2015-10-01

    Polymerization of actin monomers into filaments requires the initial formation of nuclei composed of a few actin subunits; however, their instability has hindered their detailed study. Therefore we used chemically crosslinked actin oligomers to analyse their effect on actin polymerization. Actin dimer (upper dimer, UD), trimer and tetramer intermolecularly crosslinked by phenylene-bismaleimide along the genetic helix (between Lys199 and Cys374) were isolated by gel filtration and found to increasingly stimulate actin polymerization as shown by the pyrene assay and total internal reflection fluorescence microscopy. In contrast, the so-called lower actin dimer (LD) characterized by a Cys374-Cys374 crosslink stimulated actin polymerization only at low but inhibited it at high concentrations. UD and trimer stimulated the repolymerization of actin from complexes with thymosin β4 (Tβ4) or profilin, whereas the LD stimulated repolymerization only from the profilin : actin but not the actin : Tβ4 complex. In vivo, actin polymerization is stimulated by nucleation factors. Therefore the interaction and effects of purified LD, UD and trimer on the actin-nucleating activity of gelsolin, mouse diaphanous related (mDia) formin and the actin-related protein 2/3 (Arp2/3) complex were analysed. Native gel electrophoresis demonstrated binding of LD, UD and trimer to gelsolin and its fragment G1-3, to the FH2 domains of the formins mDia1 and mDia3, and to Arp2/3 complex. UD and trimer increased the nucleating activity of gelsolin and G1-3, but not of the mDia-FH2 domain nor of the Arp2/3 complex. In contrast, LD at equimolar concentration to Arp2/3 complex stimulated its nucleating activity, but inhibited that of mDia-FH2 domains, gelsolin and G1-3, demonstrating differential regulation of their nucleating activity by dimers containing differently oriented actin subunits. © 2015 FEBS.

  14. Weak neutral-current interactions

    International Nuclear Information System (INIS)

    Barnett, R.M.

    1978-08-01

    The roles of each type of experiment in establishing uniquely the values of the the neutral-current couplings of u and d quarks are analyzed together with their implications for gauge models of the weak and electromagnetic interactions. An analysis of the neutral-current couplings of electrons and of the data based on the assumption that only one Z 0 boson exists is given. Also a model-independent analysis of parity violation experiments is discussed. 85 references

  15. Weak neutral-current interactions

    Energy Technology Data Exchange (ETDEWEB)

    Barnett, R.M.

    1978-08-01

    The roles of each type of experiment in establishing uniquely the values of the the neutral-current couplings of u and d quarks are analyzed together with their implications for gauge models of the weak and electromagnetic interactions. An analysis of the neutral-current couplings of electrons and of the data based on the assumption that only one Z/sup 0/ boson exists is given. Also a model-independent analysis of parity violation experiments is discussed. 85 references. (JFP)

  16. Vendor neutral archive in PACS.

    Science.gov (United States)

    Agarwal, Tapesh Kumar; Sanjeev

    2012-10-01

    An archive is a location containing a collection of records, documents, or other materials of historical importance. An integral part of Picture Archiving and Communication System (PACS) is archiving. When a hospital needs to migrate a PACS vendor, the complete earlier data need to be migrated in the format of the newly procured PACS. It is both time and money consuming. To address this issue, the new concept of vendor neutral archive (VNA) has emerged. A VNA simply decouples the PACS and workstations at the archival layer. This is achieved by developing an application engine that receives, integrates, and transmits the data using the different syntax of a Digital Imaging and Communication in Medicine (DICOM) format. Transferring the data belonging to the old PACS to a new one is performed by a process called migration of data. In VNA, a number of different data migration techniques are available to facilitate transfer from the old PACS to the new one, the choice depending on the speed of migration and the importance of data. The techniques include simple DICOM migration, prefetch-based DICOM migration, medium migration, and the expensive non-DICOM migration. "Vendor neutral" may not be a suitable term, and "architecture neutral," "PACS neutral," "content neutral," or "third-party neutral" are probably better and preferred terms. Notwithstanding this, the VNA acronym has come to stay in both the medical IT user terminology and in vendor nomenclature, and radiologists need to be aware of its impact in PACS across the globe.

  17. Vendor neutral archive in PACS

    Directory of Open Access Journals (Sweden)

    Tapesh Kumar Agarwal

    2012-01-01

    Full Text Available An archive is a location containing a collection of records, documents, or other materials of historical importance. An integral part of Picture Archiving and Communication System (PACS is archiving. When a hospital needs to migrate a PACS vendor, the complete earlier data need to be migrated in the format of the newly procured PACS. It is both time and money consuming. To address this issue, the new concept of vendor neutral archive (VNA has emerged. A VNA simply decouples the PACS and workstations at the archival layer. This is achieved by developing an application engine that receives, integrates, and transmits the data using the different syntax of a Digital Imaging and Communication in Medicine (DICOM format. Transferring the data belonging to the old PACS to a new one is performed by a process called migration of data. In VNA, a number of different data migration techniques are available to facilitate transfer from the old PACS to the new one, the choice depending on the speed of migration and the importance of data. The techniques include simple DICOM migration, prefetch-based DICOM migration, medium migration, and the expensive non-DICOM migration. "Vendor neutral" may not be a suitable term, and "architecture neutral," "PACS neutral," "content neutral," or "third-party neutral" are probably better and preferred terms. Notwithstanding this, the VNA acronym has come to stay in both the medical IT user terminology and in vendor nomenclature, and radiologists need to be aware of its impact in PACS across the globe.

  18. Nucleation of polypropylene with gold nanoparticles. Part 1: Introduction of sandwich method for evaluation of very weak nucleation activity

    Czech Academy of Sciences Publication Activity Database

    Pavlova, Ewa; Šlouf, Miroslav; Šandová, Hana; Baldrian, Josef; Sikora, Antonín; Lednický, František; Masirek, R.; Piorkowska, E.

    2010-01-01

    Roč. 49, č. 2 (2010), s. 392-404 ISSN 0022-2348 R&D Projects: GA AV ČR KAN200520704 Institutional research plan: CEZ:AV0Z40500505 Keywords : gold nanoparticles * isotactic polypropylene nucleation * transcrystallization Subject RIV: EB - Genetics ; Molecular Biology Impact factor: 0.602, year: 2010

  19. Urediospores of rust fungi are ice nucleation active at > -10 °C and harbor ice nucleation active bacteria

    Science.gov (United States)

    Morris, C. E.; Sands, D. C.; Glaux, C.; Samsatly, J.; Asaad, S.; Moukahel, A. R.; Gonçalves, F. L. T.; Bigg, E. K.

    2013-04-01

    Various features of the biology of the rust fungi and of the epidemiology of the plant diseases they cause illustrate the important role of rainfall in their life history. Based on this insight we have characterized the ice nucleation activity (INA) of the aerially disseminated spores (urediospores) of this group of fungi. Urediospores of this obligate plant parasite were collected from natural infections of 7 species of weeds in France, from coffee in Brazil and from field and greenhouse-grown wheat in France, the USA, Turkey and Syria. Immersion freezing was used to determine freezing onset temperatures and the abundance of ice nuclei in suspensions of washed spores. Microbiological analyses of spores from France, the USA and Brazil, and subsequent tests of the ice nucleation activity of the bacteria associated with spores were deployed to quantify the contribution of bacteria to the ice nucleation activity of the spores. All samples of spores were ice nucleation active, having freezing onset temperatures as high as -4 °C. Spores in most of the samples carried cells of ice nucleation-active strains of the bacterium Pseudomonas syringae (at rates of less than 1 bacterial cell per 100 urediospores), but bacterial INA accounted for only a small fraction of the INA observed in spore suspensions. Changes in the INA of spore suspensions after treatment with lysozyme suggest that the INA of urediospores involves a polysaccharide. Based on data from the literature, we have estimated the concentrations of urediospores in air at cloud height and in rainfall. These quantities are very similar to those reported for other biological ice nucleators in these same substrates. However, at cloud level convective activity leads to widely varying concentrations of particles of surface origin, so that mean concentrations can underestimate their possible effects on clouds. We propose that spatial and temporal concentrations of biological ice nucleators active at temperatures > -10

  20. Nucleation and droplet growth from supersaturated vapor at temperatures below the triple point temperature

    DEFF Research Database (Denmark)

    Toxværd, Søren

    2016-01-01

    nucleation without the use of a thermostat. The simulations of homogeneous nucleation in a Lennard-Jones system from supersaturated vapor at temperatures below Ttr.p. reveals that the nucleation to a liquid-like critical nucleus is initiated by a small cold cluster [S. Toxvaerd, J. Chem. Phys. \\textbf{143...

  1. Thermodynamic formulation of the barrier for heterogeneous pinned nucleation: Implication to the crossover scenarios associated with barrierless and homogeneous nucleation.

    Science.gov (United States)

    Singha, Sanat K; Das, Prasanta K; Maiti, Biswajit

    2017-06-21

    The effect of contact line pinning on nucleation is reported using continuum thermodynamics. Based on the principle of the free-energy maximization, closed-form expressions in the dimensionless form for the free-energy of the three-phase metastable system and the thermodynamic barrier are formulated with respect to the system geometry and the substrate wettability. The condition of maximality limits the dynamic contact angle within the cluster-phase-phobic regime. The dimensionless nucleation barrier or the potency factor can be divided into two components related to the system geometry and the pinning effect. Depending on the relative value of the equilibrium and the critical dynamic contact angle, the contact line pinning can either have favorable or adverse effects. Associated pinning-depinning transition can also lead to the crossovers related to barrierless and homogeneous nucleation. Contact line tension is found to have a considerable effect during these transitional scenarios. Complete wetting transition associated with barrierless nucleation can take place due to the presence of tensile (negative) line tension. On the other hand, complete drying transition related to homogeneous nucleation can occur when line tension is compressive (positive) in nature. The pinning has a favorable effect only when the substrate wettability is within the cluster-phase-philic regime. There can be favorable, adverse, or no pinning effects when the substrate wettability is within the cluster-phase-phobic regime. Although the contact line is pinned, the minimum value of the potency factor is obtained when equilibrium and dynamic contact angles are equal.

  2. Ice Nucleation Activity of Various Agricultural Soil Dust Aerosol Particles

    Science.gov (United States)

    Schiebel, Thea; Höhler, Kristina; Funk, Roger; Hill, Thomas C. J.; Levin, Ezra J. T.; Nadolny, Jens; Steinke, Isabelle; Suski, Kaitlyn J.; Ullrich, Romy; Wagner, Robert; Weber, Ines; DeMott, Paul J.; Möhler, Ottmar

    2016-04-01

    Recent investigations at the cloud simulation chamber AIDA (Aerosol Interactions and Dynamics in the Atmosphere) suggest that agricultural soil dust has an ice nucleation ability that is enhanced up to a factor of 10 compared to desert dust, especially at temperatures above -26 °C (Steinke et al., in preparation for submission). This enhancement might be caused by the contribution of very ice-active biological particles. In addition, soil dust aerosol particles often contain a considerably higher amount of organic matter compared to desert dust particles. To test agricultural soil dust as a source of ice nucleating particles, especially for ice formation in warm clouds, we conducted a series of laboratory measurements with different soil dust samples to extend the existing AIDA dataset. The AIDA has a volume of 84 m3 and operates under atmospherically relevant conditions over wide ranges of temperature, pressure and humidity. By controlled adiabatic expansions, the ascent of an air parcel in the troposphere can be simulated. As a supplement to the AIDA facility, we use the INKA (Ice Nucleation Instrument of the KArlsruhe Institute of Technology) continuous flow diffusion chamber based on the design by Rogers (1988) to expose the sampled aerosol particles to a continuously increasing saturation ratio by keeping the aerosol temperature constant. For our experiments, soil dust was dry dispersed into the AIDA vessel. First, fast saturation ratio scans at different temperatures were performed with INKA, sampling soil dust aerosol particles directly from the AIDA vessel. Then, we conducted the AIDA expansion experiment starting at a preset temperature. The combination of these two different methods provides a robust data set on the temperature-dependent ice activity of various agriculture soil dust aerosol particles with a special focus on relatively high temperatures. In addition, to extend the data set, we investigated the role of biological and organic matter in more

  3. Investigating the Sensitivity of Nucleation Parameterization on Ice Growth

    Science.gov (United States)

    Gaudet, L.; Sulia, K. J.

    2017-12-01

    The accurate prediction of precipitation from lake-effect snow events associated with the Great Lakes region depends on the parameterization of thermodynamic and microphysical processes, including the formation and subsequent growth of frozen hydrometeors. More specifically, the formation of ice hydrometeors has been represented through varying forms of ice nucleation parameterizations considering the different nucleation modes (e.g., deposition, condensation-freezing, homogeneous). These parameterizations have been developed from in-situ measurements and laboratory observations. A suite of nucleation parameterizations consisting of those published in Meyers et al. (1992) and DeMott et al. (2010) as well as varying ice nuclei data sources are coupled with the Adaptive Habit Model (AHM, Harrington et al. 2013), a microphysics module where ice crystal aspect ratio and density are predicted and evolve in time. Simulations are run with the AHM which is implemented in the Weather Research and Forecasting (WRF) model to investigate the effect of ice nucleation parameterization on the non-spherical growth and evolution of ice crystals and the subsequent effects on liquid-ice cloud-phase partitioning. Specific lake-effect storms that were observed during the Ontario Winter Lake-Effect Systems (OWLeS) field campaign (Kristovich et al. 2017) are examined to elucidate this potential microphysical effect. Analysis of these modeled events is aided by dual-polarization radar data from the WSR-88D in Montague, New York (KTYX). This enables a comparison of the modeled and observed polarmetric and microphysical profiles of the lake-effect clouds, which involves investigating signatures of reflectivity, specific differential phase, correlation coefficient, and differential reflectivity. Microphysical features of lake-effect bands, such as ice, snow, and liquid mixing ratios, ice crystal aspect ratio, and ice density are analyzed to understand signatures in the aforementioned modeled

  4. Crosstalk in concurrent repeated games impedes direct reciprocity and requires stronger levels of forgiveness.

    Science.gov (United States)

    Reiter, Johannes G; Hilbe, Christian; Rand, David G; Chatterjee, Krishnendu; Nowak, Martin A

    2018-02-07

    Direct reciprocity is a mechanism for cooperation among humans. Many of our daily interactions are repeated. We interact repeatedly with our family, friends, colleagues, members of the local and even global community. In the theory of repeated games, it is a tacit assumption that the various games that a person plays simultaneously have no effect on each other. Here we introduce a general framework that allows us to analyze "crosstalk" between a player's concurrent games. In the presence of crosstalk, the action a person experiences in one game can alter the person's decision in another. We find that crosstalk impedes the maintenance of cooperation and requires stronger levels of forgiveness. The magnitude of the effect depends on the population structure. In more densely connected social groups, crosstalk has a stronger effect. A harsh retaliator, such as Tit-for-Tat, is unable to counteract crosstalk. The crosstalk framework provides a unified interpretation of direct and upstream reciprocity in the context of repeated games.

  5. A stronger patch test elicitation reaction to the allergen hydroxycitronellal plus the irritant sodium lauryl sulfate

    DEFF Research Database (Denmark)

    Heydorn, S; Andersen, K E; Johansen, J D

    2003-01-01

    elicitation reaction than patch testing with the allergen (hydroxycitronellal) alone, in patients previously patch tested positive to hydroxycitronellal. A stronger patch test elicitation reaction was defined as at least 1 day of patch test reading showing more positive patch tests......Household and cleaning products often contain both allergens and irritants. The aim of this double-blinded, randomized, paired study was to determine whether patch testing with an allergen (hydroxycitronellal) combined with an irritant [sodium lauryl sulfate (SLS)] cause a stronger patch test...... (+, ++ or +++) on the forearm patch tested with 6 concentrations of SLS plus hydroxycitronellal than on the forearm tested with 6 concentrations of hydroxycitronellal alone and no day of patch test readings showing more positive tests on the hydroxycitronellal forearm. 15/20 (75%) had at least 1 day of patch test reading...

  6. Daytime warming has stronger negative effects on soil nematodes than night-time warming

    OpenAIRE

    Yan, Xiumin; Wang, Kehong; Song, Lihong; Wang, Xuefeng; Wu, Donghui

    2017-01-01

    Warming of the climate system is unequivocal, that is, stronger warming during night-time than during daytime. Here we focus on how soil nematodes respond to the current asymmetric warming. A field infrared heating experiment was performed in the western of the Songnen Plain, Northeast China. Three warming modes, i.e. daytime warming, night-time warming and diurnal warming, were taken to perform the asymmetric warming condition. Our results showed that the daytime and diurnal warming treatmen...

  7. World Bank: Management Controls Stronger, But Challenges in Fighting Corruption Remain

    Science.gov (United States)

    2000-04-01

    outline for possible World Development Report on institutions, including corruption . Completed • Prepare Europe and Central Asia Region...Management Controls Stronger, but Challenges in Fighting Corruption Remain If , 20000417 062 G A O Accountability * Integrity * Reliability GAO... corruption —broadly defined as the abuse of public office for private gain— ’The "World Bank" and "Bank" refer to the World Bank Group of institutions

  8. A stronger version of matrix convexity as applied to functions of Hermitian matrices

    Directory of Open Access Journals (Sweden)

    Kagan Abram

    1999-01-01

    Full Text Available A stronger version of matrix convexity, called hyperconvexity is introduced. It is shown that the function is hyperconvex on the set of Hermitian matrices and is hyperconvex on the set of positive definite Hermitian matrices. The new concept makes it possible to consider weighted averages of matrices of different orders. Proofs use properties of the Fisher information matrix, a fundamental concept of mathematical statistics.

  9. Electromagnetic trapping of neutral atoms

    International Nuclear Information System (INIS)

    Metcalf, H.J.

    1986-01-01

    Cooling and trapping of neutral atoms is a new branch of applied physics that has potential for application in many areas. The authors present an introduction to laser cooling and magnetic trapping. Some basic ideas and fundamental limitations are discussed, and the first successful experiments are reviewed. Trapping a neutral object depends on the interaction between an inhomogeneous electromagnetic field and a multiple moment that results in the exchange of kinetic for potential energy. In neutral atom traps, the potential energy must be stored as internal atomic energy, resulting in two immediate and extremely important consequences. First, the atomic energy levels will necessarily shift as the atoms move in the trap, and, second, practical traps for ground state neutral atoms atr necessarily very shallow compared to thermal energy. This small depth also dictates stringent vacuum requirements because a trapped atom cannot survive a single collision with a thermal energy background gas molecule. Neutral trapping, therefore, depends on substantial cooling of a thermal atomic sample and is inextricably connected with the cooling process

  10. Duplex Heterogeneous Nucleation Behavior of Precipitates in C-Mn Steel Containing Sn

    Science.gov (United States)

    Sun, Guilin; Tao, Sufen

    2018-04-01

    The two successive heterogeneous nucleation behaviors of FeSn2-MnS-Al2O3 complex precipitates in ultrahigh Sn-bearing steel were investigated. First, Al2O3 was the nucleation site of the MnS at the end of solidification. Then, FeSn2 nucleated heterogeneously on the MnS particles that nucleated on the Al2O3 particles. The formation sequence of the precipitated phase caused the duplex heterogeneous nucleation to occur consecutively at most twice.

  11. Novel synthesis of gibbsite by laser-stimulated nucleation in supersaturated sodium aluminate solutions

    Science.gov (United States)

    Blanks, K. A.

    2000-12-01

    Laser-induced localized density fluctuations are shown to stimulate primary nucleation of nano-sized aluminum trihydroxide seed crystals in flowing supersaturated industrial sodium aluminate solutions (Bayer liquor). The post-nucleation mass deposition rate is greatly increased over rates attainable through more traditional seeding methods. Near-ideal single-crystal gibbsite is formed under diffusion-limited growth conditions. Laser-stimulated nucleation represents an in situ method for the active local modulation of the supersaturation state, so that the stimulated nucleation occurs under macroscopic solution conditions that are unfavorable for spontaneous nucleation.

  12. Calculating free energy profiles using entropy as a reaction coordinate: Application to water nucleation

    Science.gov (United States)

    Desgranges, Caroline; Delhommelle, Jerome

    2018-03-01

    We identify the nucleation pathway for a liquid droplet of a water-like system. In order to calculate the free energy barrier associated with the droplet formation, we use the recently developed μVT- S simulation method to unravel the nucleation process. We analyze the interdependence between droplet size, entropy and free energy of nucleation. Three key features emerge: the droplet size increases as entropy decreases during the process, the nucleation free energy increases as supersaturation decreases, and the nucleation free energy increases as T decreases. This method can be readily applied to calculate free energy barriers of activated events with entropy as the reaction coordinate.

  13. Quantum nucleation of phase slips in Bose-Einstein condensates

    International Nuclear Information System (INIS)

    Buechler, H.P.; Blatter, G.; Geschkenbein, V.B.; Rossijskaya Akademiya Nauk, Moscow

    2001-01-01

    We present a theoretical study of quantum fluctuations in a Bose-Einstein condensate confined within a thin cylindrical trap and perturbed by a moving impurity. We derive an effective action which maps the problem to that of a massive particle with damping in a periodic potential. Quantum fluctuations lead to a finite nucleation rate of phase slips and we make use of known results in our determination of the transport characteristic. Real Bose-Einstein condensate are finite systems and exhibit interesting effects depending on topology: in superfluid rings we obtain a critical velocity below which the nucleation rate is quenched. In a cigar shaped condensate the low-energy action is equivalent to that of a capacitively shunted Josephson junction. The state with a well defined phase difference across the impurity then is unstable towards a decoupled state with a fixed number of particles on either side of the impurity. (orig.)

  14. Suppression of graphene nucleation on Cu(111) thin films

    Science.gov (United States)

    Gannett, Will; Miller, David L.; Keller, Mark W.

    2014-03-01

    Chemical vapor deposition (CVD) of graphene on Cu substrates depends on a large number of factors and currently suffers from a lack of reproducibility, both within and between research groups. We used Cu(111) thin films with centimeter-sized grains to avoid variations in surface roughness, crystalline orientation, and impurity content that may affect growth on polycrystalline Cu foils. We found that exposing these films (or commercial foils) to a variety of surface treatments prior to CVD can dramatically reduce the nucleation density of graphene islands. This allowed us to select the resulting average domain size of the graphene film. In addition, this suppression of nucleation may enable seeding of graphene growth at particular locations.

  15. Time-dependent distributions in self-quenching nucleation

    Science.gov (United States)

    Shneidman, Vitaly A.

    2011-09-01

    Diffusion- and interface-limited Becker-Döring (BD) -type nucleation is considered in a closed system, where supersaturation is depleted by growing nuclei. Special focus is on nonadiabatic effects, which become increasingly pronounced for barriers lower than 20-25kBT, and which lead to nucleation rates deviating from their quasi-steady-state (QSS) values. Several essential modifications of the QSS distribution are observed. For example, the front is continuous rather than sharp and has a double-exponential shape, which is in agreement with the earlier matched asymptotic solution obtained in neglect of depletion. The total number of nuclei is larger than predicted by the QSS approximation. The obtained distributions are compared with numerical solutions of the BD equations and can serve as initial conditions for further transition to the Ostwald Ripening stage.

  16. Synaptic Bistability Due to Nucleation and Evaporation of Receptor Clusters

    KAUST Repository

    Burlakov, V. M.

    2012-01-10

    We introduce a bistability mechanism for long-term synaptic plasticity based on switching between two metastable states that contain significantly different numbers of synaptic receptors. One state is characterized by a two-dimensional gas of mobile interacting receptors and is stabilized against clustering by a high nucleation barrier. The other state contains a receptor gas in equilibrium with a large cluster of immobile receptors, which is stabilized by the turnover rate of receptors into and out of the synapse. Transitions between the two states can be initiated by either an increase (potentiation) or a decrease (depotentiation) of the net receptor flux into the synapse. This changes the saturation level of the receptor gas and triggers nucleation or evaporation of receptor clusters. © 2012 American Physical Society.

  17. Suppressing Ice Nucleation of Supercooled Condensate with Biphilic Topography

    Science.gov (United States)

    Hou, Youmin; Yu, Miao; Shang, Yuhe; Zhou, Peng; Song, Ruyuan; Xu, Xiaonan; Chen, Xuemei; Wang, Zuankai; Yao, Shuhuai

    2018-02-01

    Preventing or minimizing ice formation in supercooled water is of prominent importance in many infrastructures, transportation, and cooling systems. The overall phase change heat transfer on icephobic surfaces, in general, is intentionally sacrificed to suppress the nucleation of water and ice. However, in a condensation frosting process, inhibiting freezing without compromising the water condensation has been an unsolved challenge. Here we show that this conflict between anti-icing and efficient condensation cooling can be resolved by utilizing biphilic topography with patterned high-contrast wettability. By creating a varying interfacial thermal barrier underneath the supercooled condensate, the biphilic structures tune the nucleation rates of water and ice in the sequential condensation-to-freezing process. Our experimental and theoretical investigation of condensate freezing dynamics further unravels the correlation between the onset of droplet freezing and its characteristic radius, offering a new insight for controlling the multiphase transitions among vapor, water, and ice in supercooled conditions.

  18. Interactions between bubble formation and heating surface in nucleate boiling

    International Nuclear Information System (INIS)

    Luke, Andrea

    2009-01-01

    The heat transfer and bubble formation is investigated in pool boiling of propane. Size distributions of active nucleation sites on single horizontal copper and steel tubes with different diameter and surface finishes have been calculated from heat transfer measurements over wide ranges of heat flux and selected pressure. The model assumptions of Luke and Gorenflo for the heat transfer near growing and departing bubbles, which were applied in the calculations, have been slightly modified and the calculated results have been compared to experimental investigations by high speed video techniques. The calculated number of active sites shows a good coincidence for the tube with smaller diameter, while the results for the tube with larger diameter describe the same relative increase of the active sites. The comparison of the cumulative size distribution of the active and potential nucleation sites demonstrates the same slope of the curve and that the critical radius of a stable bubble nuclei is smaller than the average cavity size. (author)

  19. Neutral B meson flavor tagging

    CERN Document Server

    Wilson, R J

    2001-01-01

    We present an investigation of the use of net charge and kaon identification to tag the flavor of neutral B mesons. The net charge of the neutral B meson decay products is zero if all charged particles are used and slightly non-zero if only undiscriminated hadronic final states are used. The net charge of the kaons alone correctly tags the identity of the neutral meson in at least a third of all decays. We have parametrized the particle identification capability of several techniques, such as dE/dx in time projection chambers, LEP/SLC ring-imaging chambers and an enhanced BaBar DIRC. Using these parametrisations we compare the relative tagging power of each technique to that of an ideal detector. (8 refs).

  20. Molecular nucleation mechanisms and control strategies for crystal polymorph selection

    Science.gov (United States)

    van Driessche, Alexander E. S.; van Gerven, Nani; Bomans, Paul H. H.; Joosten, Rick R. M.; Friedrich, Heiner; Gil-Carton, David; Sommerdijk, Nico A. J. M.; Sleutel, Mike

    2018-04-01

    The formation of condensed (compacted) protein phases is associated with a wide range of human disorders, such as eye cataracts, amyotrophic lateral sclerosis, sickle cell anaemia and Alzheimer’s disease. However, condensed protein phases have their uses: as crystals, they are harnessed by structural biologists to elucidate protein structures, or are used as delivery vehicles for pharmaceutical applications. The physiochemical properties of crystals can vary substantially between different forms or structures (‘polymorphs’) of the same macromolecule, and dictate their usability in a scientific or industrial context. To gain control over an emerging polymorph, one needs a molecular-level understanding of the pathways that lead to the various macroscopic states and of the mechanisms that govern pathway selection. However, it is still not clear how the embryonic seeds of a macromolecular phase are formed, or how these nuclei affect polymorph selection. Here we use time-resolved cryo-transmission electron microscopy to image the nucleation of crystals of the protein glucose isomerase, and to uncover at molecular resolution the nucleation pathways that lead to two crystalline states and one gelled state. We show that polymorph selection takes place at the earliest stages of structure formation and is based on specific building blocks for each space group. Moreover, we demonstrate control over the system by selectively forming desired polymorphs through site-directed mutagenesis, specifically tuning intermolecular bonding or gel seeding. Our results differ from the present picture of protein nucleation, in that we do not identify a metastable dense liquid as the precursor to the crystalline state. Rather, we observe nucleation events that are driven by oriented attachments between subcritical clusters that already exhibit a degree of crystallinity. These insights suggest ways of controlling macromolecular phase transitions, aiding the development of protein

  1. Nucleation of relativistic first-order phase transitions

    International Nuclear Information System (INIS)

    Csernai, L.P.; Kapusta, J.I.

    1992-01-01

    The authors apply the general formalism of Langer to compute the nucleation rate for systems of relativistic particles with zero or small baryon number density and which undergo first-order phase transitions. In particular, the pre-exponential factor is computed and it is proportional to the viscosity. The initial growth rate of a critical size bubble or droplet is limited by the ability of dissipative processes to transport latent heat away from the surface. 30 refs., 4 figs

  2. Interface tracking computations of bubble dynamics in nucleate flow boiling

    International Nuclear Information System (INIS)

    Giustini, G.

    2015-01-01

    The boiling process is of utter importance for the design and operation of water-cooled nuclear reactors. Despite continuous effort over the past decades, a fully mechanistic model of boiling in the presence of a solid surface has not yet been achieved. Uncertainties exist at fundamental level, since the microscopic phenomena governing nucleate boiling are still not understood, and as regards 'component scale' modelling, which relies heavily on empirical representations of wall boiling. Accurate models of these phenomena at sub-milli-metric scale are capable of elucidating the various processes and to produce quantitative data needed for up-scaling. Within this context, Direct Numerical Simulation (DNS) represents a powerful tool for CFD analysis of boiling flows. In this contribution, DNS coupled with an Interface Tracking method (Y. Sato, B. Niceno, Journal of Computational Physics, Volume 249, 15 September 2013, Pages 127-161) are used to analyse the hydrodynamics and heat transfer associated with heat diffusion controlled bubble growth at a solid substrate during nucleate flow boiling. The growth of successive bubbles from a single nucleation site is simulated with a computational model that includes heat conduction in the solid substrate and evaporation from the liquid film (micro-layer) present beneath the bubble. Bubble evolution is investigated and the additional (with respect to single phase convection) heat transfer mechanisms due to the ebullition cycle are quantified. The simulations show that latent heat exchange due to evaporation in the micro-layer and sensible heat exchange during the waiting time after bubble departure are the main heat transfer mechanisms. It is found that the presence of an imposed flow normal to the bubble rising path determines a complex velocity and temperature distribution near the nucleation site. This conditions can result in bubble sliding, and influence bubble shape, departure diameter and departure frequency

  3. Surface nucleation and growth in the system of interacting particles

    Czech Academy of Sciences Publication Activity Database

    Chvoj, Zdeněk; Chromcová, Zdeňka

    2012-01-01

    Roč. 24, č. 13 (2012), 1-8 ISSN 0953-8984 R&D Projects: GA ČR GPP204/10/P331; GA MŠk ME09048; GA AV ČR IAA100100903 Institutional research plan: CEZ:AV0Z10100521 Keywords : epitaxy * nucleation * island density * graphene * long-range interaction Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 2.355, year: 2012

  4. Fracture of Rolled Homogeneous Steel Armor (Nucleation Threshold Stress).

    Science.gov (United States)

    1980-01-01

    November 1976. (AD #BO16015L) 9R. F. Benck and J. L. Robitaille, "Teneile Strees -Strain Curves--IIl, Rolled Homogeneous Armor at a Strain Rate of 0.42 s...unloading at void interfaces must either be treated independently or be reduced to negligible effects. The approach used was to try to render the...nucleation can be interpreted in several ways . For example, a stable nucleus could quite naturally be envisioned as a cracked inclusion. Here

  5. Atmospheric Nucleation: Highlights of the EUCAARI Project and Future Directions

    Czech Academy of Sciences Publication Activity Database

    Kerminen, V.-M.; Petäjä, T.; Manninen, H.E.; Paasonen, P.; Nieminen, T.; Sipilä, M.; Junninen, H.; Ehn, M.; Gagné, S.; Laakso, L.; Riipinen, I.; Vehkamäki, H.; Kutren, T.; Ortega, I.K.; Dal Maso, M.; Brus, David; Hyvärinen, A-P.; Lihavainen, H.; Leppä, J.; Lehtinen, K.E.J.; Mirme, A.; Mirme, S.; Hörrak, U.; Berndt, T.; Stratmann, F.; Birmili, W.; Wiedensohler, A.; Metzger, A.; Dommen, J.; Baltensperger, U.; Kiendler-Scarr, A.; Mentel, T.F.; Wildt, J.; Winkler, P.M.; Wagner, P.E.; Petzold, A.; Minikin, A.; Plass-Dülmer, C.; Pöschl, U.; Laaksonen, A.; Kulmala, M.

    2010-01-01

    Roč. 10, č. 22 (2010), s. 10829-10848 ISSN 1680-7316 EU Projects: European Commission(XE) 36833 - EUCAARI; European Commission(XE) 26140 - EUSAAR Grant - others:AFCE(FI) 211483; AFCE(FI) 211484; AFCE(FI) 1118615 Institutional research plan: CEZ:AV0Z40720504 Keywords : atmospheric nucleation * boundary layers * particle size Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 5.309, year: 2010

  6. Neutral currents in semileptonic reactions

    International Nuclear Information System (INIS)

    Paschos, E.A.

    1975-05-01

    The evidence for weak neutral currents is analyzed in semileptonic reactions with special emphasis on their Lorentz and internal symmetry structure. It is found that present observations are consistent with the expectations of gauge theories, but other possibilities can not be ruled out. Of particular interest in this respect is the presence of a large isoscalar component. The excitation of the Δ-resonance by neutral currents is analyzed, and pion-nucleon mass distributions are presented. Charge asymmetries sensitive to isoscalar-isovector interferences are discussed. (U.S.)

  7. Nucleation speed limit on remote fluid induced earthquakes

    Science.gov (United States)

    Parsons, Thomas E.; Akinci, Aybige; Malignini, Luca

    2017-01-01

    Earthquakes triggered by other remote seismic events are explained as a response to long-traveling seismic waves that temporarily stress the crust. However, delays of hours or days after seismic waves pass through are reported by several studies, which are difficult to reconcile with the transient stresses imparted by seismic waves. We show that these delays are proportional to magnitude and that nucleation times are best fit to a fluid diffusion process if the governing rupture process involves unlocking a magnitude-dependent critical nucleation zone. It is well established that distant earthquakes can strongly affect the pressure and distribution of crustal pore fluids. Earth’s crust contains hydraulically isolated, pressurized compartments in which fluids are contained within low-permeability walls. We know that strong shaking induced by seismic waves from large earthquakes can change the permeability of rocks. Thus, the boundary of a pressurized compartment may see its permeability rise. Previously confined, overpressurized pore fluids may then diffuse away, infiltrate faults, decrease their strength, and induce earthquakes. Magnitude-dependent delays and critical nucleation zone conclusions can also be applied to human-induced earthquakes.

  8. Nucleation speed limit on remote fluid-induced earthquakes

    Science.gov (United States)

    Parsons, Tom; Malagnini, Luca; Akinci, Aybige

    2017-01-01

    Earthquakes triggered by other remote seismic events are explained as a response to long-traveling seismic waves that temporarily stress the crust. However, delays of hours or days after seismic waves pass through are reported by several studies, which are difficult to reconcile with the transient stresses imparted by seismic waves. We show that these delays are proportional to magnitude and that nucleation times are best fit to a fluid diffusion process if the governing rupture process involves unlocking a magnitude-dependent critical nucleation zone. It is well established that distant earthquakes can strongly affect the pressure and distribution of crustal pore fluids. Earth’s crust contains hydraulically isolated, pressurized compartments in which fluids are contained within low-permeability walls. We know that strong shaking induced by seismic waves from large earthquakes can change the permeability of rocks. Thus, the boundary of a pressurized compartment may see its permeability rise. Previously confined, overpressurized pore fluids may then diffuse away, infiltrate faults, decrease their strength, and induce earthquakes. Magnitude-dependent delays and critical nucleation zone conclusions can also be applied to human-induced earthquakes. PMID:28845448

  9. Investigation of PLC band nucleation in AA5754

    Energy Technology Data Exchange (ETDEWEB)

    Feng, X., E-mail: Xiaoqun.Feng@tu-dortmund.de [Technische Universitaet Dortmund, Fakultaet Maschinenbau, Lehrstuhl fuer Werkstofftechnologie, D-44221 Dortmund (Germany); Fischer, G., E-mail: Gottfried.Fischer@rif-ev.de [RIF e.V., Joseph-von-Fraunhofer-Str. 20, D-44227 Dortmund (Germany); Zielke, R., E-mail: Reiner.Zielke@tu-dortmund.de [Technische Universitaet Dortmund, Fakultaet Maschinenbau, Lehrstuhl fuer Werkstofftechnologie, D-44221 Dortmund (Germany); Svendsen, B., E-mail: Bob.Svendsen@udo.edu [Technische Universitaet Dortmund, Fakultaet Maschinenbau, Lehrstuhl fuer Mechanik, D-44221 Dortmund (Germany); Tillmann, W., E-mail: Wolfgang.Tillmann@udo.edu [Technische Universitaet Dortmund, Fakultaet Maschinenbau, Lehrstuhl fuer Werkstofftechnologie, D-44221 Dortmund (Germany)

    2012-03-30

    Highlights: Black-Right-Pointing-Pointer Simultaneous propagation of bands in transverse and longitudinal directions. Black-Right-Pointing-Pointer PLC band nucleation at the back front of Lueders bands. Black-Right-Pointing-Pointer Characteristic time of critical strain decreases with strain rate. Black-Right-Pointing-Pointer Simultaneous existence of two type-B bands at specimen shoulder. - Abstract: The purpose of the present work is the experimental investigation of the nucleation of PLC deformation bands in the aluminium alloy AA5754. The PLC bands are investigated using both mechanical methods and infrared (IR) thermography. The latter employs a high-speed IR camera which captures local changes of radiated power resulting from mechanical dissipation and heating due to the nucleation of PLC bands. The resulting IR images are used to determine spatio-temporal power field variations via image subtraction. Furthermore, band trajectories obtained from the IR images are used to study possible correlations between the spatio-temporal evolution of stress and radiated power in the specimens and PLC band development.

  10. Ion implantation induced martensite nucleation in SUS301 steel

    International Nuclear Information System (INIS)

    Kinoshita, Hiroshi; Takahashi, Heishichiro; Gustiono, Dwi; Sakaguchi, Norihito; Shibayama, Tamaki; Watanabe, Seiichi

    2007-01-01

    Phase transformation behaviors of the austenitic 301 stainless steel was studied under Fe + , Ti + and Ar + ions implantation at room temperature with 100, 200 and 300 keV up to fluence of 1x10 21 ions/m 2 and the microstructures were observed by means of transmission electron microscopy (TEM). The plane and cross-sectional observations of the implanted specimen showed that the induced-phases due to implantation from the γ matrix phase were identified as α' martensite phases with the orientation relationship of (11-bar0) α parallel (111-bar) γ and [111] α parallel [011] γ close to the Kurdjumov-Sachs (K-S). The ion implantation induced phases nucleated near the surface region and the depth position of the nucleation changed depending on the ion accelerating energy and ion species. It was also found that the induced marten sites phases nucleate under the influence of the stress distribution, which is introduced due to the concentration of implanted ions, especially due to the stress gradient caused by the corresponding concentration gradient. (author)

  11. Non-equilibrium Quasi-Chemical Nucleation Model

    Science.gov (United States)

    Gorbachev, Yuriy E.

    2018-04-01

    Quasi-chemical model, which is widely used for nucleation description, is revised on the basis of recent results in studying of non-equilibrium effects in reacting gas mixtures (Kolesnichenko and Gorbachev in Appl Math Model 34:3778-3790, 2010; Shock Waves 23:635-648, 2013; Shock Waves 27:333-374, 2017). Non-equilibrium effects in chemical reactions are caused by the chemical reactions themselves and therefore these contributions should be taken into account in the corresponding expressions for reaction rates. Corrections to quasi-equilibrium reaction rates are of two types: (a) spatially homogeneous (caused by physical-chemical processes) and (b) spatially inhomogeneous (caused by gas expansion/compression processes and proportional to the velocity divergency). Both of these processes play an important role during the nucleation and are included into the proposed model. The method developed for solving the generalized Boltzmann equation for chemically reactive gases is applied for solving the set of equations of the revised quasi-chemical model. It is shown that non-equilibrium processes lead to essential deviation of the quasi-stationary distribution and therefore the nucleation rate from its traditional form.

  12. Homogeneous ice nucleation evaluated for several water models

    Science.gov (United States)

    Espinosa, J. R.; Sanz, E.; Valeriani, C.; Vega, C.

    2014-11-01

    In this work, we evaluate by means of computer simulations the rate for ice homogeneous nucleation for several water models such as TIP4P, TIP4P/2005,TIP4P/ICE, and mW (following the same procedure as in Sanz et al. [J. Am. Chem. Soc. 135, 15008 (2013)]) in a broad temperature range. We estimate the ice-liquid interfacial free-energy, and conclude that for all water models γ decreases as the temperature decreases. Extrapolating our results to the melting temperature, we obtain a value of the interfacial free-energy between 25 and 32 mN/m in reasonable agreement with the reported experimental values. Moreover, we observe that the values of γ depend on the chosen water model and this is a key factor when numerically evaluating nucleation rates, given that the kinetic prefactor is quite similar for all water models with the exception of the mW (due to the absence of hydrogens). Somewhat surprisingly the estimates of the nucleation rates found in this work for TIP4P/2005 are slightly higher than those of the mW model, even though the former has explicit hydrogens. Our results suggest that it may be possible to observe in computer simulations spontaneous crystallization of TIP4P/2005 at about 60 K below the melting point.

  13. Homogeneous nucleation in liquid nitrogen at negative pressures

    Energy Technology Data Exchange (ETDEWEB)

    Baidakov, V. G., E-mail: baidakov@itp.uran.ru; Vinogradov, V. E.; Pavlov, P. A. [Russian Academy of Sciences, Institute of Thermal Physics, Ural Branch (Russian Federation)

    2016-10-15

    The kinetics of spontaneous cavitation in liquid nitrogen at positive and negative pressures has been studied in a tension wave formed by a compression pulse reflected from the liquid–vapor interface on a thin platinum wire heated by a current pulse. The limiting tensile stresses (Δp = p{sub s}–p, where p{sub s} is the saturation pressure), the corresponding bubble nucleation frequencies J (10{sup 20}–10{sup 22} s{sup –1} m{sup –3}), and temperature induced nucleation frequency growth rate G{sub T} = dlnJ/dT have been experimentally determined. At T = 90 K, the limiting tensile stress was Δp = 8.3 MPa, which was 4.9 MPa lower than the value corresponding to the boundary of thermodynamic stability of the liquid phase (spinodal). The measurement results were compared to classical (homogeneous) nucleation theory (CNT) with and without neglect of the dependence of the surface tension of critical bubbles on their dimensions. In the latter case, the properties of new phase nuclei were described in terms of the Van der Waals theory of capillarity. The experimental data agree well with the CNT theory when it takes into account the “size effect.”.

  14. Simulation studies of nucleation of ferroelectric polarization reversal.

    Energy Technology Data Exchange (ETDEWEB)

    Brennecka, Geoffrey L. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Winchester, Benjamin Michael [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)

    2014-08-01

    Electric field-induced reversal of spontaneous polarization is the defining characteristic of a ferroelectric material, but the process(es) and mechanism(s) associated with the initial nucleation of reverse-polarity domains are poorly understood. This report describes studies carried out using phase field modeling of LiTaO3, a relatively simple prototype ferroelectric material, in order to explore the effects of either mechanical deformation or optically-induced free charges on nucleation and resulting domain configuration during field-induced polarization reversal. Conditions were selected to approximate as closely as feasible those of accompanying experimental work in order to provide not only support for the experimental work but also ensure that additional experimental validation of the simulations could be carried out in the future. Phase field simulations strongly support surface mechanical damage/deformation as effective for dramatically reducing the overall coercive field (Ec) via local field enhancements. Further, optically-nucleated polarization reversal appears to occur via stabilization of latent nuclei via the charge screening effects of free charges.

  15. Intermediate Nucleation State of GaN Growth

    Science.gov (United States)

    Zheng, L. X.; Xie, M. H.; Tong, S. Y.

    2001-03-01

    Homoexpitaxial nucleation of GaN during molecular-beam epitaxy is followed by scanning tunneling microcopy (STM). We observe a metastable nucleation state, which manifests as “ghost” islands in STM images. These “ghost” islands can be irreversibly driven into normal islands by continuous STM imaging. It is further established that the “ghost” island formation is related to the presence of excess Ga atoms on the surface: Normal islands are only seen under the N-rich or stoichiometric flux condition, whereas “ghost” islands are observed under Ga-rich conditions. For intermediate excess-Ga coverages, both normal and “ghost” islands are present, however, they show distinctly different sizes, suggesting different nucleation states for the two. A growth model is proposed to account for the formation of metastable, “ghost” islands. Kinetic Monte Carlo simulation is carried out and main features of the surface are reproduced. We acknowledge financial support from HK RGC under grant Nos. 7396/00P, 7142/99P, and 7121/00P.

  16. Effect of system compliance on crack nucleation in soft materials

    Science.gov (United States)

    Rattan, Shruti; Crosby, Alfred

    Puncture mechanics in soft materials is critical for the development of new surgical instruments, robot assisted-surgery as well as new materials used in personal protective equipment. However, analytical techniques to study this important deformation process are limited. We have previously described a simple experimental method to study the resistive forces and failure of a soft gel being indented with a small tip needle. We showed that puncture stresses can reach two orders of magnitude greater than the material modulus and that the force response is insensitive to the geometry of the indenter at large indentation depths. Currently, we are examining the influence of system compliance on crack nucleation (e.g. puncture) in soft gels. It is well known that system compliance influences the peak force in adhesion and traditional fracture experiments; however, its influence on crack nucleation is unresolved. We find that as the system becomes more compliant, lower peak forces required to puncture a gel of certain stiffness with the same indenter were measured. We are developing scaling relationships to relate the peak puncture force and system compliance. Our findings introduce new questions with regard to the possibility of intrinsic materials properties related to the critical stress and energy for crack nucleation in soft materials.

  17. Autocatalytic microtubule nucleation determines the size and mass of Xenopus laevis egg extract spindles.

    Science.gov (United States)

    Decker, Franziska; Oriola, David; Dalton, Benjamin; Brugués, Jan

    2018-01-11

    Regulation of size and growth is a fundamental problem in biology. A prominent example is the formation of the mitotic spindle, where protein concentration gradients around chromosomes are thought to regulate spindle growth by controlling microtubule nucleation. Previous evidence suggests that microtubules nucleate throughout the spindle structure. However, the mechanisms underlying microtubule nucleation and its spatial regulation are still unclear. Here, we developed an assay based on laser ablation to directly probe microtubule nucleation events in Xenopus laevis egg extracts. Combining this method with theory and quantitative microscopy, we show that the size of a spindle is controlled by autocatalytic growth of microtubules, driven by microtubule-stimulated microtubule nucleation. The autocatalytic activity of this nucleation system is spatially regulated by the limiting amounts of active microtubule nucleators, which decrease with distance from the chromosomes. This mechanism provides an upper limit to spindle size even when resources are not limiting. © 2018, Decker et al.

  18. Nucleation and swelling in electron irradiated austenitic stainless steels in temperature range 400∼720 degree C

    International Nuclear Information System (INIS)

    Qian Jiapu; Lu Liping; Chen Jiming; Sun Jiguang; Zhao Zhuoyong

    1994-10-01

    A study of the influence of temperature on swelling behavior in electron irradiated austenitic stainless steels has been performed with a high voltage electron microscope (HVEM) in the temperature range 400 to 720 degree C. The specimen materials were solution annealed (SA) 316 stainless steel (SS), cold worked (CW) 316 SS and Ti-modified austenitic stainless steel (Ti-mod. SS). The electron energy in HVEM was 1 MeV. The results of mean void density, mean void diameter, void swelling, swelling rate and incubation dose vs. dose and temperature are presented. It is suggested that the irradiation temperature influenced the microstructure, overall sink strength and relative strength of neutral sinks to that of biased sinks in the specimens and so made the void nucleation, void growth and swelling behavior differently in 316 SA, 316 CW and Ti-mod. SS. The influence of He pre-implantation on void nucleation in electron irradiated austenitic stainless steels has also been studied. The experiments indicated that the helium was active void nucleus but had no direct impact on void growth

  19. Ice nucleating particles in the Saharan Air Layer

    Directory of Open Access Journals (Sweden)

    Y. Boose

    2016-07-01

    Full Text Available This study aims at quantifying the ice nucleation properties of desert dust in the Saharan Air Layer (SAL, the warm, dry and dust-laden layer that expands from North Africa to the Americas. By measuring close to the dust's emission source, before aging processes during the transatlantic advection potentially modify the dust properties, the study fills a gap between in situ measurements of dust ice nucleating particles (INPs far away from the Sahara and laboratory studies of ground-collected soil. Two months of online INP concentration measurements are presented, which were part of the two CALIMA campaigns at the Izaña observatory in Tenerife, Spain (2373 m a.s.l., in the summers of 2013 and 2014. INP concentrations were measured in the deposition and condensation mode at temperatures between 233 and 253 K with the Portable Ice Nucleation Chamber (PINC. Additional aerosol information such as bulk chemical composition, concentration of fluorescent biological particles as well as the particle size distribution was used to investigate observed variations in the INP concentration. The concentration of INPs was found to range between 0.2 std L−1 in the deposition mode and up to 2500 std L−1 in the condensation mode at 240 K. It correlates well with the abundance of aluminum, iron, magnesium and manganese (R: 0.43–0.67 and less with that of calcium, sodium or carbonate. These observations are consistent with earlier results from laboratory studies which showed a higher ice nucleation efficiency of certain feldspar and clay minerals compared to other types of mineral dust. We find that an increase of ammonium sulfate, linked to anthropogenic emissions in upwind distant anthropogenic sources, mixed with the desert dust has a small positive effect on the condensation mode INP per dust mass ratio but no effect on the deposition mode INP. Furthermore, the relative abundance of biological particles was found to be significantly higher

  20. ITER Neutral Beam Injection System

    International Nuclear Information System (INIS)

    Ohara, Yoshihiro; Tanaka, Shigeru; Akiba, Masato

    1991-03-01

    A Japanese design proposal of the ITER Neutral Beam Injection System (NBS) which is consistent with the ITER common design requirements is described. The injection system is required to deliver a neutral deuterium beam of 75MW at 1.3MeV to the reactor plasma and utilized not only for plasma heating but also for current drive and current profile control. The injection system is composed of 9 modules, each of which is designed so as to inject a 1.3MeV, 10MW neutral beam. The most important point in the design is that the injection system is based on the utilization of a cesium-seeded volume negative ion source which can produce an intense negative ion beam with high current density at a low source operating pressure. The design value of the source is based on the experimental values achieved at JAERI. The utilization of the cesium-seeded volume source is essential to the design of an efficient and compact neutral beam injection system which satisfies the ITER common design requirements. The critical components to realize this design are the 1.3MeV, 17A electrostatic accelerator and the high voltage DC acceleration power supply, whose performances must be demonstrated prior to the construction of ITER NBI system. (author)

  1. Net Neutrality in the Netherlands

    NARCIS (Netherlands)

    van Eijk, N.

    2014-01-01

    The Netherlands is among the first countries that have put specific net neutrality standards in place. The decision to implement specific regulation was influenced by at least three factors. The first was the prevailing social and academic debate, partly due to developments in the United States. The

  2. PLT neutral beam injection systems

    International Nuclear Information System (INIS)

    Menon, M.M.; Barber, G.C.; Blue, C.W.

    1979-01-01

    A brief description of the Princeton Large Torus (PLT) neutral beam injection system is given and its performance characteristics are outlined. A detailed operational procedure is included, as are some tips on troubleshooting. Proper operation of the source is shown to be a crucial factor in system performance

  3. Money neutrality: Rethinking the myth

    Directory of Open Access Journals (Sweden)

    Issaoui Fakhri

    2015-01-01

    Full Text Available Considered as an axiomatic basis of classical, neoclassical, and monetarist theories, the long-run money neutrality assumption does not always seem to be verified. Indeed, in our view, the money, in the sense of M2, can constitute a long-run channel of growth transmission. Thus, this paper examines the long-term relationship among money supply (M2, income (GDP, and prices (CPI. The subprime crisis in 2007 has shown that the demand for money does not only meet motives of transaction, precaution, and speculation but also of fictional or quasi-fictional future demands due to the fact that they are created without real counterparts. The capacity of production systems in developed countries to respond to increases in money supply by creating more wealth, involves the assumption of money neutrality in the long-run. However, in developing countries, the excess of money supply may lead to inflation trends. The present study has confirmed the long-term non-neutrality of money supply in the USA, and its neutrality in Gabon and Morocco.

  4. Laser cooling of neutral atoms

    International Nuclear Information System (INIS)

    1993-01-01

    A qualitative description of laser cooling of neutral atoms is given. Two of the most important mechanisms utilized in laser cooling, the so-called Doppler Cooling and Sisyphus Cooling, are reviewed. The minimum temperature reached by the atoms is derived using simple arguments. (Author) 7 refs

  5. RE: Pedagogy--After Neutrality

    Science.gov (United States)

    I'Anson, John

    2010-01-01

    Within the UK and in many parts of the world, official accounts of what it is to make sense of religion are framed within a rhetorics of neutrality in which such study is premised upon the possibility of dispassionate engagement and analysis. This paper, which is largely theoretical in scope, explores both the affordances and the costs of such an…

  6. Sexual harassment and emotional and behavioural symptoms in adolescence: stronger associations among boys than girls.

    Science.gov (United States)

    Kaltiala-Heino, Riittakerttu; Fröjd, Sari; Marttunen, Mauri

    2016-08-01

    To study the associations between subjection to sexual harassment and emotional (depression) and behavioural (delinquency) symptoms among 14-to-18-year-old adolescents, and gender differences within these associations. 90,953 boys and 91,746 girls aged 14-18 participated in the School Health Promotion Study (SHPS), a school-based survey designed to examine the health, health behaviours, and school experiences of teenagers. Experiences of sexual harassment were elicited with five questions addressing five separate forms of harassment. Depression was measured by the 13-item Beck Depression Inventory and delinquency with a modified version of the International Self-Report Delinquency Study (ISRD) instrument. Data were analysed using cross-tabulations with Chi-square statistics and logistic regression. All sexual harassment experiences studied were associated with both depression (adjusted odds ratios varied from 2.2 to 2.7 in girls and from 2.0 to 5.1 in boys) and delinquency (adjusted odds ratios 3.1-5.0 in girls and 1.7-6.9 in boys). Sexual name-calling had a stronger association with depression and with delinquency in girls (adjusted odds ratios, respectively, 2.4 and 4.2), than in boys (adjusted odds ratios, respectively, 2.0 and 1.7), but otherwise stronger associations with emotional and behavioural symptoms were seen in boys. Subjection to sexual harassment is associated with both emotional and behavioural symptoms in both girls and boys. The associations are mostly stronger for boys. Boys subjected to sexual harassment may feel particularly threatened regarding their masculinity, and there may be less support available for boys traumatised due to sexual harassment.

  7. Building Stronger State Energy Partnerships with the U.S. Department of Energy

    Energy Technology Data Exchange (ETDEWEB)

    David Terry

    2008-09-30

    This final technical report details the results of total work efforts and progress made from July 2000 - July 2008 under the National Association of State Energy Officials (NASEO) cooperative agreement DE-FC26-00NT40802, Building Stronger State Energy Partnerships with the U.S. Department of Energy. Major topical project areas in this final report include work efforts in the following areas: Rebuild America/Energy Smart Schools, Higher Education Initiative, Winter/Summer Fuels Outlook Conferences, Energy Emergency, Clean Energy Integration, Energy Star, and Office of Electricity Delivery and Energy Reliability. All required deliverables have been provided to the National Energy Technology Laboratory and DOE program officials.

  8. The University of Florida Department of Surgery: building a stronger tomorrow on yesterday's foundation.

    Science.gov (United States)

    Behrns, Kevin E; Copeland, Edward M; Howard, Richard J

    2012-01-01

    Established in 1957, the University of Florida Department of Surgery has a solid foundation on which current faculty are driven to build a stronger tomorrow. The department is focused on promoting patient-centered care, expanding its research portfolio to improve techniques and outcomes, and training the surgical leaders of tomorrow. It fosters an environment where faculty, residents, students, and staff challenge long-held traditions with the goal of improving the health of our patients, the quality of our care, and the vitality of our work environment.

  9. Production of plastified wood with stronger static bending strength means of polymerization induced by gamma radiation

    International Nuclear Information System (INIS)

    Silva Filho, Elias

    1999-01-01

    The use of gamma radiation to obtain wood-polymer composites is one of the applications of radiation that presents the most commercial interest. The process, denominated radiopolymerization, comprises the impregnation of monomers into the completely dried wood followed by exposure to gamma radiation to induce polymerization of the impregnated monomers. I this context, the present work aimed the application of this process to seven kinds of wood existing in the brazilian forests. The considered monomer is styrene and the gamma source is Cobalt-60. The obtained wood-polystyrene composites were found to have stronger static bending strength. (author)

  10. Building Stronger State Energy Partnerships with the U.S. Department of Energy

    Energy Technology Data Exchange (ETDEWEB)

    Marks, Kate

    2011-09-30

    This final technical report details the results of total work efforts and progress made from October 2007 – September 2011 under the National Association of State Energy Officials (NASEO) cooperative agreement DE-FC26-07NT43264, Building Stronger State Energy Partnerships with the U.S. Department of Energy. Major topical project areas in this final report include work efforts in the following areas: Energy Assurance and Critical Infrastructure, State and Regional Technical Assistance, Regional Initiative, Regional Coordination and Technical Assistance, and International Activities in China. All required deliverables have been provided to the National Energy Technology Laboratory and DOE program officials.

  11. Ice nucleation activity of agricultural soil dust aerosols from Mongolia, Argentina, and Germany

    Science.gov (United States)

    Steinke, I.; Funk, R.; Busse, J.; Iturri, A.; Kirchen, S.; Leue, M.; Möhler, O.; Schwartz, T.; Schnaiter, M.; Sierau, B.; Toprak, E.; Ullrich, R.; Ulrich, A.; Hoose, C.; Leisner, T.

    2016-11-01

    Soil dust particles emitted from agricultural areas contain considerable mass fractions of organic material. Also, soil dust particles may act as carriers for potentially ice-active biological particles. In this work, we present ice nucleation experiments conducted in the Aerosol Interaction and Dynamics in the Atmosphere (AIDA) cloud chamber. We investigated the ice nucleation efficiency of four types of soil dust from different regions of the world. The results are expressed as ice nucleation active surface site (INAS) densities and presented for the immersion freezing and the deposition nucleation mode. For immersion freezing occurring at 254 K, samples from Argentina, China, and Germany show ice nucleation efficiencies which are by a factor of 10 higher than desert dusts. On average, the difference in ice nucleation efficiencies between agricultural and desert dusts becomes significantly smaller at temperatures below 247 K. In the deposition mode the soil dusts showed higher ice nucleation activity than Arizona Test Dust over a temperature range between 232 and 248 K and humidities RHice up to 125%. INAS densities varied between 109 and 1011 m-2 for these thermodynamic conditions. For one soil dust sample (Argentinian Soil), the effect of treatments with heat was investigated. Heat treatments (383 K) did not affect the ice nucleation efficiency observed at 249 K. This finding presumably excludes proteinaceous ice-nucleating entities as the only source of the increased ice nucleation efficiency.

  12. Do External or Internal Technology Spillovers Have a Stronger Influence on Innovation Efficiency in China?

    Directory of Open Access Journals (Sweden)

    Xionghe Qin

    2017-09-01

    Full Text Available In this study, we bridge an important gap in the literature by comparing the extent to which external technology spillovers, as indicated by foreign direct investment (FDI, and internal technology spillovers, as indicated by university-institute-industry cooperation (UIC, influence innovation efficiency in China. We divide the innovation process into two sequential stages, namely the knowledge creation and technology commercialization stages, and employ a network data envelopment analysis approach to measure innovation efficiency at each stage. The spatial analysis of the distribution of knowledge creation efficiency and technology commercialization efficiency reveals the heterogeneity of innovation efficiency at the provincial level. Then, a panel data regression is used to analyze the effect of FDI and UIC on innovation efficiency at each stage, using data from 2009 to 2015 for 30 provinces in China. By comparing FDI with UIC, we find that FDI has a higher coefficient and stronger significance level at the knowledge creation stage, while only industry-institute linkages exhibit a stronger association with innovation efficiency at the technology commercialization stage.

  13. The El Niño Southern Oscillation is Getting Bigger and Stronger

    Science.gov (United States)

    McNaught, C.; O'Brien, J.; Strazzo, S. E.

    2012-12-01

    The El Niño Southern Oscillation (ENSO) is an important natural climate variation that affects large portions of the world. We measure ENSO both in terms of its frequency and its magnitude. The different phases of ENSO - El Niño and La Niña - have different properties, and impact the global weather pattern differently. We examine the hypothesis that ENSO's frequency distribution is changing. We demonstrate that, indeed, El Niño's are getting stronger as measured by the maximum anomaly in sea surface temperature (SST). An analysis of the ENSO principal component is conducted using a fast Fourier transform to estimate the spectrum of the SST of the time series. We conclude that the intensity of El Niño events during the period 1970-2010 is statistically significantly higher when compared to the 1930—1970, with a broad spectral peak centered around 4 years. When we compare the SST spectrum for the period 1930-1970 with the spectrum for 1971- 2010, we find the latter period to be much stronger in power. Additionally recently classified ENSO types, including El Niño Modoki and Warm Pool ENSO, are briefly studied.; The first empirical orthogonal function of sea-surface temperatures (1930-2010) accounting for 75% of the variance. The values are indicative of departures from the mean, in °C. Positive (negative) values indicate anomalously higher (lower) sea-surface temperatures ; Normalized first principal component

  14. Stronger interference from distractors in the right hemifield during visual search.

    Science.gov (United States)

    Carlei, Christophe; Kerzel, Dirk

    2018-03-01

    The orientation-bias hypothesis states that there is a bias to attend to the right visual hemifield (RVF) when there is spatial competition between stimuli in the left and right hemifield [Pollmann, S. (1996). A pop-out induced extinction-like phenomenon in neurologically intact subjects. Neuropsychologia, 34(5), 413-425. doi: 10.1016/0028-3932(95)00125-5 ]. In support of this hypothesis, stronger interference was reported for RVF distractors with contralateral targets. In contrast, previous studies using rapid serial visual presentation (RSVP) found stronger interference from distractors in the left visual hemifield (LVF). We used the additional singleton paradigm to test whether this discrepancy was due to the different distractor features that were employed (colour vs. orientation). Interference from the colour distractor with contralateral targets was larger in the RVF than in the LVF. However, the asymmetrical interference disappeared when observers had to search for an inconspicuous colour target instead of the inconspicuous shape target. We suggest that the LVF orienting-bias is limited to situations where search is driven by bottom-up saliency (singleton search) instead of top-down search goals (feature search). In contrast, analysis of the literature suggests the opposite for the LVF bias in RSVP tasks. Thus, the attentional asymmetry may depend on whether the task involves temporal or spatial competition, and whether search is based on bottom-up or top-down signals.

  15. When surging seas meet stronger rain: Nuclear techniques in flood management

    International Nuclear Information System (INIS)

    Quevenco, Rodolfo

    2015-01-01

    Unusually high rainfall in many parts of the world is a result of climate change, scientists say. Since warmer air can hold more water, the rationale goes, increased temperatures will increase the chances of stronger rainfall events. And when surging seas combine with stronger rain, the outcome is almost certain: floods. Floods are the most frequently occurring natural disasters, and south-east Asia is particularly vulnerable. Climate change and variability are expected to bring about increased typhoon activities, rising sea levels and off-season monsoon rains in southeast Asia and other regions. These can cause devastating floods in countries like Cambodia, Laos, Pakistan, the Philippines, Thailand and Viet Nam. For the residents of these countries who have survived the ravages of major floods, the road to recovery can be long and arduous. As the flood water recedes, they have to contend with new forms of flood: floods of concern and worries as to how to rebuild their houses, their lives and their cities. Governments, too, face huge challenges in rebuilding roads, public buildings, infrastructure and natural resources destroyed or polluted by the flood.

  16. Nucleation mechanisms of refined alpha microstructure in beta titanium alloys

    Science.gov (United States)

    Zheng, Yufeng

    Due to a great combination of physical and mechanical properties, beta titanium alloys have become promising candidates in the field of chemical industry, aerospace and biomedical materials. The microstructure of beta titanium alloys is the governing factor that determines their properties and performances, especially the size scale, distribution and volume fraction of precipitate phase in parent phase matrix. Therefore in order to enhance the performance of beta titanium alloys, it is critical to obtain a thorough understanding of microstructural evolution in beta titanium alloys upon various thermal and/or mechanical processes. The present work is focusing on the study of nucleation mechanisms of refined alpha microstructure and super-refined alpha microstructure in beta titanium alloys in order to study the influence of instabilities within parent phase matrix on precipitates nucleation, including compositional instabilities and/or structural instabilities. The current study is primarily conducted in Ti-5Al-5Mo-5V-3Cr (wt%, Ti-5553), a commercial material for aerospace application. Refined and super-refined precipitates microstructure in Ti-5553 are obtained under specific accurate temperature controlled heat treatments. The characteristics of either microstructure are investigated in details using various characterization techniques, such as SEM, TEM, STEM, HRSTEM and 3D atom probe to describe the features of microstructure in the aspect of morphology, distribution, structure and composition. Nucleation mechanisms of refined and super-refined precipitates are proposed in order to fully explain the features of different precipitates microstructure in Ti-5553. The necessary thermodynamic conditions and detailed process of phase transformations are introduced. In order to verify the reliability of proposed nucleation mechanisms, thermodynamic calculation and phase field modeling simulation are accomplished using the database of simple binary Ti-Mo system

  17. Theories of nucleation and growth of bubbles and voids

    International Nuclear Information System (INIS)

    Speight, M.V.

    1977-01-01

    The application of classical nucleation theory to the formation of voids from a supersaturated concentration of vacancies is reviewed. The effect of a dissolved concentration of barley soluble gas on the nucleation rate of voids is emphasized. Exposure to a damaging flux of irradiation is the most effective way of introducing a vacancy supersaturation, but interstitials are produced at an equal rate. The concentration of interstitials inhibits the nucleation of voids which can occur only in the presence of dislocations since they preferentially absorb interstitials. It is well known that a definite value of internal gas pressure is necessary to stabilize a bubble so that it shows no tendencies to either shrink or grow. The arguments are reviewed which conclude that this pressure is determined by the specific surface free energy of the solid rather than the surface tension. While the former property refers to the energy necessary to create new surface, the latter is a measure of the work done in elastically stretching a a given surface. The presence of an equilibrium gas bubble leaves the stresses in the surrounding solid unperturbed only when surface energy and surface tension are numerically equal. A bubble with internal pressure greater than the restraint offered by surface energy tends to grow to relieve the excess pressure. The mechanism of growth can involve the migration of vacancies from remote sources to the bubble surface or the plastic straining of the solid surrounding the bubble. The kinetics of both mechanisms are developed and compared. The theory of growth of grain-boundary voids by vacancy condensation under an applied stress is also considered. (author)

  18. Nucleation of microwave plasma CVD diamond on molybdenum (Mo) substrate

    International Nuclear Information System (INIS)

    Inderjeet, K.; Ramesh, S.

    2000-01-01

    Molybdenum is a metal, which is gaining increasing significance in industrial applications. The main use of Mo is as all alloying element added in small amounts to steel, irons and non- ferrous alloys in order to enhance the strength, toughness and wear resistance. Mo is also vastly being employed in the automotive and aircraft industries, mainly due to its low coefficient of friction. Diamond, on be other hand, is a unique material for innumerable applications because of its usual combination of physical and chemical properties. Several potential applications can be anticipated for diamond in many sectors including electronics, optics, as protective corrosion resistant coatings, cutting tools, etc. With the enhancement in science and technology, diamond microcrystals and thin films are now being produced from the vapour phase by a variety of chemical vapour deposition (CVD) techniques; such as microwave plasma CVD. With such technology being made available, it is envisage that diamond-coated molybdenum would further enhance the performance and to open up new avenue for Mo in various industries. Therefore, it is the aim of the present work to study the nucleation and growth of diamond particles on Mo surface by employing microwave plasma CVD (MAPCVD). In the present work, diamond deposition was carried out in several stages by varying the deposition distance. The nucleation and growth rate were studied using scanning electron microscopy (SEM). In addition, the existence of diamond was verified by X-ray diffraction (XRD) analysis. It has been found that the nucleation and growth rate of diamond particles were influenced by the deposition height between the substrate and plasma. Under the optimum condition, well defined diamond crystallites distributed homogeneously throughout the surface, could be obtained. Some of the important parameters controlling the deposition and growth of diamond particles on Mo surface are discussed. (author)

  19. Molecular dynamics simulations of bubble nucleation in dark matter detectors.

    Science.gov (United States)

    Denzel, Philipp; Diemand, Jürg; Angélil, Raymond

    2016-01-01

    Bubble chambers and droplet detectors used in dosimetry and dark matter particle search experiments use a superheated metastable liquid in which nuclear recoils trigger bubble nucleation. This process is described by the classical heat spike model of F. Seitz [Phys. Fluids (1958-1988) 1, 2 (1958)PFLDAS0031-917110.1063/1.1724333], which uses classical nucleation theory to estimate the amount and the localization of the deposited energy required for bubble formation. Here we report on direct molecular dynamics simulations of heat-spike-induced bubble formation. They allow us to test the nanoscale process described in the classical heat spike model. 40 simulations were performed, each containing about 20 million atoms, which interact by a truncated force-shifted Lennard-Jones potential. We find that the energy per length unit needed for bubble nucleation agrees quite well with theoretical predictions, but the allowed spike length and the required total energy are about twice as large as predicted. This could be explained by the rapid energy diffusion measured in the simulation: contrary to the assumption in the classical model, we observe significantly faster heat diffusion than the bubble formation time scale. Finally we examine α-particle tracks, which are much longer than those of neutrons and potential dark matter particles. Empirically, α events were recently found to result in louder acoustic signals than neutron events. This distinction is crucial for the background rejection in dark matter searches. We show that a large number of individual bubbles can form along an α track, which explains the observed larger acoustic amplitudes.

  20. Formation of colloidal semiconductor nanocrystals. The aspect of nucleation

    Energy Technology Data Exchange (ETDEWEB)

    Kudera, S.

    2007-08-17

    The present work describes different techniques to control some major parameters of colloidal nanocrystals. The individual techniques rely on the manipulation of the nucleation event. The sensitive control of the nanocrystals' size and shape is discussed. Furthermore the formation of hybrid nanocrystals composed of different materials is presented. The synthesis technique for the production of the different samples involves organic solvents and surfactants and reactions at elevated temperatures. The presence of magic size clusters offers a possibility to control the size of the nanocrystals even at very small dimensions. The clusters produced comprise ca. 100 atoms. In the case of CdSe, nanocrystals of this size emit a blue fluorescence and therefore extend the routinely accessible spectrum for this material over the whole visible range. Samples fluorescing in the spectral range from green to red are produced with standard recipes. In this work a reaction scheme for magic size clusters is presented and a theoretical model to explain the particular behaviour of their growth dynamics is discussed. The samples are investigated by optical spectroscopy, transmission electron microscopy, X-ray diffraction and elemental analysis. A method to form branched nanocrystals is discussed. The branching point is analysed by high resolution transmission electron microscopy and proves for the occurrence of a multiple twinned structure are strengthened by simulation of the observed patterns. Two different techniques to generate nanocrystals of this type are presented. The first relies on a seeded growth approach in which the nucleation of the second material is allowed only on de ned sites of the seeds. The second technique uses the tips of pre-formed nano-dumbbells as sacrificial domains. The material on the tips is replaced by gold. Hybrid materials are formed by a seeded-growth mechanism. Pre-formed nanocrystals provide the nucleation sites for the second material. (orig.)

  1. Physical and chemical characterization of bioaerosols - Implications for nucleation processes

    Science.gov (United States)

    Ariya, P. A.; Sun, J.; Eltouny, N. A.; Hudson, E. D.; Hayes, C. T.; Kos, G.

    The importance of organic compounds in the oxidative capacity of the atmosphere, and as cloud condensation and ice-forming nuclei, has been recognized for several decades. Organic compounds comprise a significant fraction of the suspended matter mass, leading to local (e.g. toxicity, health hazards) and global (e.g. climate change) impacts. The state of knowledge of the physical chemistry of organic aerosols has increased during the last few decades. However, due to their complex chemistry and the multifaceted processes in which they are involved, the importance of organic aerosols, particularly bioaerosols, in driving physical and chemical atmospheric processes is still very uncertain and poorly understood. Factors such as solubility, surface tension, chemical impurities, volatility, morphology, contact angle, deliquescence, wettability, and the oxidation process are pivotal in the understanding of the activation processes of cloud droplets, and their chemical structures, solubilities and even the molecular configuration of the microbial outer membrane, all impact ice and cloud nucleation processes in the atmosphere. The aim of this review paper is to assess the current state of knowledge regarding chemical and physical characterization of bioaerosols with a focus on those properties important in nucleation processes. We herein discuss the potential importance (or lack thereof) of physical and chemical properties of bioaerosols and illustrate how the knowledge of these properties can be employed to study nucleation processes using a modeling exercise. We also outline a list of major uncertainties due to a lack of understanding of the processes involved or lack of available data. We will also discuss key issues of atmospheric significance deserving future physical chemistry research in the fields of bioaerosol characterization and microphysics, as well as bioaerosol modeling. These fundamental questions are to be addressed prior to any definite conclusions on the

  2. Heterogeneous ice nucleation on atmospheric aerosols: a review of results from laboratory experiments

    Directory of Open Access Journals (Sweden)

    C. Hoose

    2012-10-01

    Full Text Available A small subset of the atmospheric aerosol population has the ability to induce ice formation at conditions under which ice would not form without them (heterogeneous ice nucleation. While no closed theoretical description of this process and the requirements for good ice nuclei is available, numerous studies have attempted to quantify the ice nucleation ability of different particles empirically in laboratory experiments. In this article, an overview of these results is provided. Ice nucleation "onset" conditions for various mineral dust, soot, biological, organic and ammonium sulfate particles are summarized. Typical temperature-supersaturation regions can be identified for the "onset" of ice nucleation of these different particle types, but the various particle sizes and activated fractions reported in different studies have to be taken into account when comparing results obtained with different methodologies. When intercomparing only data obtained under the same conditions, it is found that dust mineralogy is not a consistent predictor of higher or lower ice nucleation ability. However, the broad majority of studies agrees on a reduction of deposition nucleation by various coatings on mineral dust. The ice nucleation active surface site (INAS density is discussed as a simple and empirical normalized measure for ice nucleation activity. For most immersion and condensation freezing measurements on mineral dust, estimates of the temperature-dependent INAS density agree within about two orders of magnitude. For deposition nucleation on dust, the spread is significantly larger, but a general trend of increasing INAS densities with increasing supersaturation is found. For soot, the presently available results are divergent. Estimated average INAS densities are high for ice-nucleation active bacteria at high subzero temperatures. At the same time, it is shown that INAS densities of some other biological aerosols, like certain pollen grains, fungal

  3. Neutral atom traps of radioactives

    International Nuclear Information System (INIS)

    Behr, J.A.

    2003-01-01

    Neutral atoms trapped with modern laser cooling techniques offer the promise of improving several broad classes of experiments with radioactive isotopes. In nuclear β decay, neutrino spectroscopy from beta-recoil coincidences, along with highly polarized samples, enable experiments to search for non-Standard Model interactions, test whether parity symmetry is maximally violated, and search for new sources of time reversal violation. Ongoing efforts at TRIUMF, Los Alamos and Berkeley will be highlighted. The traps also offer bright sources for Doppler-free spectroscopy, particularly in high-Z atoms where precision measurements could measure the strength of weak neutral nucleon-nucleon and electron-nucleon interactions. Physics with francium atoms has been vigorously pursued at Stony Brook. Several facilities plan work with radioactive atom traps; concrete plans and efforts at KVI Groningen and Legnaro will be among those summarized. Contributions to the multidisciplinary field of trace analysis will be left up to other presenters

  4. Neutral atom traps of radioactives

    CERN Document Server

    Behr, J A

    2003-01-01

    Neutral atoms trapped with modern laser cooling techniques offer the promise of improving several broad classes of experiments with radioactive isotopes. In nuclear beta decay, neutrino spectroscopy from beta-recoil coincidences, along with highly polarized samples, enable experiments to search for non-Standard Model interactions, test whether parity symmetry is maximally violated, and search for new sources of time reversal violation. Ongoing efforts at TRIUMF, Los Alamos and Berkeley will be highlighted. The traps also offer bright sources for Doppler-free spectroscopy, particularly in high-Z atoms where precision measurements could measure the strength of weak neutral nucleon-nucleon and electron-nucleon interactions. Physics with francium atoms has been vigorously pursued at Stony Brook. Several facilities plan work with radioactive atom traps; concrete plans and efforts at KVI Groningen and Legnaro will be among those summarized. Contributions to the multidisciplinary field of trace analysis will be left...

  5. Radiative lifetimes of neutral samarium

    International Nuclear Information System (INIS)

    Den Hartog, E A; Lawler, J E

    2013-01-01

    Radiative lifetimes of 120 odd-parity levels of neutral samarium, ranging in energy from 17 190 to 33 507 cm −1 , are measured using the technique of time-resolved laser-induced fluorescence on a slow atomic beam. This work is part of an ongoing study of radiative properties of rare earth neutral atoms, and is motivated by research needs in astrophysics and lighting technology. This set of Sm i lifetimes substantially increases the available published lifetime data, with 49 of the 120 level lifetimes measured for the first time. These data, most of which are accurate to ±5%, will be combined with branching fractions determined from Fourier transform spectroscopy to produce a large set of measured Sm i transition probabilities. (paper)

  6. Radiative lifetimes of neutral gadolinium

    International Nuclear Information System (INIS)

    Den Hartog, E A; Bilty, K A; Lawler, J E

    2011-01-01

    The current work is part of an ongoing study of radiative properties of rare earth neutral atoms motivated by research needs in several disparate fields including astrophysics, laser chemistry and lighting technology. Time-resolved laser-induced fluorescence on a slow atomic beam has been used to measure radiative lifetimes, accurate to ±5%, for 136 levels of neutral gadolinium. Of the 136 levels, 6 are odd parity ranging in energy from 32 929 to 36 654 cm -1 , and the remaining 130 are even parity ranging from 17 750 to 34 175 cm -1 . This set of Gd i lifetimes represents a significant extension to the available published data, with 93 of the 136 level lifetimes measured for the first time. These lifetimes will provide the absolute normalization for a large set of measured Gd i transition probabilities.

  7. Radiative lifetimes of neutral neodymium

    International Nuclear Information System (INIS)

    Den Hartog, E A; Fittante, A J; Lawler, J E

    2011-01-01

    This work is part of an on-going study of radiative properties of rare earth neutral atoms. This work is motivated by research needs in several disparate fields including astrophysics and lighting technology. Radiative lifetimes of 100 levels of neutral neodymium are measured using the technique of time-resolved laser-induced fluorescence on a slow atomic beam. Of the 100 levels, 3 are even parity ranging in energy from 25 746 to 26 835 cm -1 , and the remaining 97 are odd parity ranging from 17 787 to 27 786 cm -1 . This set of Nd i lifetimes represents a significant extension to the available published data, with 51 of the 100 level lifetimes measured for the first time. These data, which are accurate to ±5%, provide the absolute normalization for a large set of measured Nd i transition probabilities.

  8. Microcrystalline silicon prepared at magnetic field modified nucleation

    Czech Academy of Sciences Publication Activity Database

    Kočka, Jan; Mates, Tomáš; Ledinský, Martin; Stuchlíková, The-Ha; Stuchlík, Jiří; Fejfar, Antonín

    2006-01-01

    Roč. 352, - (2006), s. 901-905 ISSN 0022-3093 R&D Projects: GA MŽP(CZ) SM/300/1/03; GA MŽP(CZ) SN/3/172/05; GA AV ČR(CZ) IAA1010316; GA AV ČR(CZ) IAA1010413; GA MŠk(CZ) LC510 Institutional research plan: CEZ:AV0Z10100521 Keywords : amorphous semiconductors * nucleation * electrical and electronic properties * chemical vapor deposition * atomic force and scanning tunneling microscopy * microcrystallinity * optical properties Subject RIV: BM - Solid Matter Physics ; Magnet ism Impact factor: 1.362, year: 2006

  9. Understanding the ice nucleation characteristics of feldspars suspended in solution

    Science.gov (United States)

    Kumar, Anand; Marcolli, Claudia; Kaufmann, Lukas; Krieger, Ulrich; Peter, Thomas

    2017-04-01

    Freezing of liquid droplets and subsequent ice crystal growth affects optical properties of clouds and precipitation. Field measurements show that ice formation in cumulus and stratiform clouds begins at temperatures much warmer than those associated with homogeneous ice nucleation in pure water, which is ascribed to heterogeneous ice nucleation occurring on the foreign surfaces of ice nuclei (IN). Various insoluble particles such as mineral dust, soot, metallic particles, volcanic ash, or primary biological particles have been suggested as IN. Among these the suitability of mineral dusts is best established. The ice nucleation ability of mineral dust particles may be modified when secondary organic or inorganic substances are accumulating on the dust during atmospheric transport. If the coating is completely wetting the mineral dust particles, heterogeneous ice nucleation occurs in immersion mode also below 100 % RH. A previous study by Zobrist et al. (2008) Arizona test dust, silver iodide, nonadecanol and silicon dioxide suspensions in various solutes showed reduced ice nucleation efficiency (in immersion mode) of the particles. Though it is still quite unclear how surface modifications and coatings influence the ice nucleation activity of the components present in natural dust particles at a microphysical scale. To improve our understanding how solute and mineral dust particle surface interaction, we run freezing experiments using a differential scanning calorimeter (DSC) with microcline, sanidine, plagioclase, kaolinite and quartz particles suspended in pure water and solutions containing ammonia, ammonium bisulfate, ammonium sulfate, ammonium chloride, ammonium nitrate, potassium chloride, potassium sulfate, sodium sulfate and sulfuric acid. Methodology Suspensions of mineral dust samples (2 - 5 wt%) are prepared in water with varying solute concentrations (0 - 15 wt%). 20 vol% of this suspension plus 80 vol% of a mixture of 95 wt% mineral oil (Aldrich

  10. Sources of organic ice nucleating particles in soils

    Science.gov (United States)

    Hill, Tom C. J.; DeMott, Paul J.; Tobo, Yutaka; Fröhlich-Nowoisky, Janine; Moffett, Bruce F.; Franc, Gary D.; Kreidenweis, Sonia M.

    2016-06-01

    Soil organic matter (SOM) may be a significant source of atmospheric ice nucleating particles (INPs), especially of those active > -15 °C. However, due to both a lack of investigations and the complexity of the SOM itself, the identities of these INPs remain unknown. To more comprehensively characterize organic INPs we tested locally representative soils in Wyoming and Colorado for total organic INPs, INPs in the heat-labile fraction, ice nucleating (IN) bacteria, IN fungi, IN fulvic and humic acids, IN plant tissue, and ice nucleation by monolayers of aliphatic alcohols. All soils contained ≈ 106 to ≈ 5 × 107 INPs g-1 dry soil active at -10 °C. Removal of SOM with H2O2 removed ≥ 99 % of INPs active > -18 °C (the limit of testing), while heating of soil suspensions to 105 °C showed that labile INPs increasingly predominated > -12 °C and comprised ≥ 90 % of INPs active > -9 °C. Papain protease, which inactivates IN proteins produced by the fungus Mortierella alpina, common in the region's soils, lowered INPs active at ≥ -11 °C by ≥ 75 % in two arable soils and in sagebrush shrubland soil. By contrast, lysozyme, which digests bacterial cell walls, only reduced INPs active at ≥ -7.5 or ≥ -6 °C, depending on the soil. The known IN bacteria were not detected in any soil, using PCR for the ina gene that codes for the active protein. We directly isolated and photographed two INPs from soil, using repeated cycles of freeze testing and subdivision of droplets of dilute soil suspensions; they were complex and apparently organic entities. Ice nucleation activity was not affected by digestion of Proteinase K-susceptible proteins or the removal of entities composed of fulvic and humic acids, sterols, or aliphatic alcohol monolayers. Organic INPs active colder than -10 to -12 °C were resistant to all investigations other than heat, oxidation with H2O2, and, for some, digestion with papain. They may originate from decomposing plant material, microbial

  11. The Ice Nucleation Activity of Surface Modified Soot

    Science.gov (United States)

    Häusler, Thomas; Witek, Lorenz; Felgitsch, Laura; Hitzenberger, Regina; Grothe, Hinrich

    2017-04-01

    The ice nucleation efficiency of many important atmospheric particles remains poorly understood. Since soot is ubiquitous in the Earth's troposphere, they might have the potential to significantly impact the Earth's climate (Finlayson-Pitts and Pitts, 2000; Seinfeld and Pandis, 1998). Here we present the ice nucleation activity (INA) in immersion freezing mode of different types of soot. Therefor a CAST (combustion aerosol standard) generator was used to produce different kinds of soot samples. The CAST generator combusts a propane-air-mixture and deposits thereby produced soot on a polyvinyl fluoride filter. By varying the propane to air ratio, the amount of organic portion of the soot can be varied from black carbon (BC) with no organic content to brown carbon (BrC) with high organic content. To investigate the impact of functional sites of ice nuclei (IN), the soot samples were exposed to NO2 gas for a certain amount of time (30 to 360 minutes) to chemically modify the surface. Immersion freezing experiments were carried out in a unique reaction gadget. In this device a water-in-oil suspension (with the soot suspended in the aqueous phase) was cooled till the freezing point and was observed through a microscope (Pummer et al., 2012; Zolles et al., 2015) It was found that neither modified nor unmodified BC shows INA. On the contrary, unmodified BrC shows an INA at -32˚ C, which can be increased up to -20˚ C. The INA of BrC depends on the duration of NO2- exposure. To clarify the characteristics of the surface modifications, surface sensitive analysis like infrared spectroscopy and X-ray photoelectron spectroscopy were carried out. Finlayson-Pitts, B. J. and Pitts, J. N. J.: Chemistry of the Upper and Lower Atmosphere, Elsevier, New York, 2000. Pummer, B. G., Bauer, H., Bernardi, J., Bleicher, S., and Grothe, H.: Suspendable macromolecules are responsible for ice nucleation activity of birch and conifer pollen, Atmos Chem Phys, 12, 2541-2550, 2012. Seinfeld, J

  12. New Ion-Nucleation Mechanism Relevant for the Earth's Atmosphere

    DEFF Research Database (Denmark)

    Enghoff, Martin Andreas Bødker; Svensmark, Henrik; Pedersen, Jens Olaf Pepke

    An experiment has been set up in order to investigate the role of ionization in Earth's climate. We have chosen to start our investigation at the smallest scales, namely by studying the effect of cosmic ray produced ions on atmospheric aerosol nucleation and growth processes. This experiment...... is conducted at the Danish National Space Center, Center for Sun-Climate Research. It comprises a 7 m3 reaction chamber where atmospheric conditions can be simulated. The number of ions can be increased by exposure to radioactive sources and decreased by applying an electric field; this will enable experiments...

  13. Cohesive zone modelling of nucleation, growth and coalesce of cavities

    DEFF Research Database (Denmark)

    Biel, Anders; Stigh, U.

    2017-01-01

    The stress-deformation relation i.e. cohesive law representing the fracture process in an almost incompressible adhesive tape is measured using the double cantilever beam specimen. As in many ductile materials, the fracture process of the tape involves nucleation, growth and coalesce of cavities....... This process is studied carefully by exploiting the transparency of the used materials and the inherent stability of the specimen configuration. Utilising the path independence of the J-integral, the cohesive law is measured. The law is compared to the results of butt-joint tests. The law contains two stress...

  14. Nucleation and growth of the Naica giant gypsum crystals.

    Science.gov (United States)

    Otálora, Fermín; García-Ruiz, JuanMa

    2014-04-07

    The Cave of Giant Crystals in the Naica mine (Mexico) is one of the most amazing displays of mineral beauty ever created in nature. In addition to the colossal crystals of gypsum, which in some cases exceed eleven meters in length and one meter in thickness, the scenery fashioned by the crystalline beams that thrust through the darkness of the cave from floor to ceiling with a luster like moonlight is a unique example of harmony based on crystal symmetry. We review the crystallogenesis of this remarkable and challenging phenomenon of mineralization near equilibrium that can be used to teach the basics of nucleation and crystal growth.

  15. Indirect radiative forcing by ion-mediated nucleation of aerosol

    Directory of Open Access Journals (Sweden)

    F. Yu

    2012-12-01

    Full Text Available A clear understanding of particle formation mechanisms is critical for assessing aerosol indirect radiative forcing and associated climate feedback processes. Recent studies reveal the importance of ion-mediated nucleation (IMN in generating new particles and cloud condensation nuclei (CCN in the atmosphere. Here we implement the IMN scheme into the Community Atmosphere Model version 5 (CAM5. Our simulations show that, compared to globally averaged results based on H2SO4-H2O binary homogeneous nucleation (BHN, the presence of ionization (i.e., IMN halves H2SO4 column burden, but increases the column integrated nucleation rate by around one order of magnitude, total particle number burden by a factor of ~3, CCN burden by ~10% (at 0.2% supersaturation to 65% (at 1.0% supersaturation, and cloud droplet number burden by ~18%. Compared to BHN, IMN increases cloud liquid water path by 7.5%, decreases precipitation by 1.1%, and increases total cloud cover by 1.9%. This leads to an increase of total shortwave cloud radiative forcing (SWCF by 3.67 W m−2 (more negative and longwave cloud forcing by 1.78 W m−2 (more positive, with large spatial variations. The effect of ionization on SWCF derived from this study (3.67 W m−2 is a factor of ~3 higher that of a previous study (1.15 W m−2 based on a different ion nucleation scheme and climate model. Based on the present CAM5 simulation, the 5-yr mean impacts of solar cycle induced changes in ionization rates on CCN and cloud forcing are small (~−0.02 W m−2 but have larger inter-annual (from −0.18 to 0.17 W m−2 and spatial variations.

  16. Controlling the Solidification of Organic Photovoltaic Blends with Nucleating Agents

    KAUST Repository

    Nekuda Malik, Jennifer A.

    2014-11-20

    Blending fullerenes with a donor polymer for the fabrication of organic solar cells often leads to at least partial vitrification of one, if not both, components. For prototypical poly(3-hexylthiophene):fullerene blend, we show that the addition of a commercial nucleating agent, di(3,4-dimethyl benzylidene)sorbitol, to such binary blends accelerates the crystallization of the donor, resulting in an increase in its degree of crystallinity in as-cast structures. This allows manipulation of the extent of intermixing/ phase separation of the donor and acceptor directly from solution, offering a tool to improve device characteristics such as power conversion efficiency.

  17. Experimental investigation of the role of ions in aerosol nucleation

    DEFF Research Database (Denmark)

    Enghoff, Martin Andreas Bødker

    rays and Earth's climate and there is thus a need to corroborate the results in a different experiment. The present results are obtained in the same laboratory, but using a new setup The experiments were conducted in a 50 L cylindrical reaction chamber made of electropolished stainless steel. Aerosols...... were grown using photochemically produced sulphuric acid and ionization levels were controlled with a Cs-137 gamma-source. An increase in nucleation was observed when the chamber was exposed to the radioactive source. The results were analyzed using a model based on the General Dynamic Equation...

  18. Neutral Pion Photoproduction on Neutron

    Science.gov (United States)

    Bulychev, S. A.; Kudryavtsev, A. E.; Kulikov, V. V.; Martem'yanov, M. A.; Tarasov, V. E.; Briscoe, W. J.; Strakovsky, I. I.

    2017-12-01

    The reaction γ n → π0 n is investigated both theoretically and experimentally as an important step toward determining the electromagnetic coupling constants of the N* and Δ* resonances [1]. We analyze the data on the collisions of γ quanta with energies between 200 and 800 MeV with a deuterium target collected by the A2 experiment in Mainz, Germany. These complement the data for neutral-pion photoproduction on protons obtained by the same experiment [2].

  19. Money neutrality: Rethinking the myth

    OpenAIRE

    Issaoui Fakhri; Boufateh Talel; Guesmi Mourad

    2015-01-01

    Considered as an axiomatic basis of classical, neoclassical, and monetarist theories, the long-run money neutrality assumption does not always seem to be verified. Indeed, in our view, the money, in the sense of M2, can constitute a long-run channel of growth transmission. Thus, this paper examines the long-term relationship among money supply (M2), income (GDP), and prices (CPI). The subprime crisis in 2007 has shown that the demand for money does not only...

  20. Vendor neutral archive in PACS

    International Nuclear Information System (INIS)

    Agarwal, Tapesh Kumar; Sanjeev

    2012-01-01

    An archive is a location containing a collection of records, documents, or other materials of historical importance. An integral part of Picture Archiving and Communication System (PACS) is archiving. When a hospital needs to migrate a PACS vendor, the complete earlier data need to be migrated in the format of the newly procured PACS. It is both time and money consuming. To address this issue, the new concept of vendor neutral archive (VNA) has emerged. A VNA simply decouples the PACS and workstations at the archival layer. This is achieved by developing an application engine that receives, integrates, and transmits the data using the different syntax of a Digital Imaging and Communication in Medicine (DICOM) format. Transferring the data belonging to the old PACS to a new one is performed by a process called migration of data. In VNA, a number of different data migration techniques are available to facilitate transfer from the old PACS to the new one, the choice depending on the speed of migration and the importance of data. The techniques include simple DICOM migration, prefetch-based DICOM migration, medium migration, and the expensive non-DICOM migration. “Vendor neutral” may not be a suitable term, and “architecture neutral,” “PACS neutral,” “content neutral,” or “third-party neutral” are probably better and preferred terms. Notwithstanding this, the VNA acronym has come to stay in both the medical IT user terminology and in vendor nomenclature, and radiologists need to be aware of its impact in PACS across the globe

  1. Neutral beams for magnetic fusion

    International Nuclear Information System (INIS)

    Hooper, B.

    1977-01-01

    Significant advances in forming energetic beams of neutral hydrogen and deuterium atoms have led to a breakthrough in magnetic fusion: neutral beams are now heating plasmas to thermonuclear temperatures, here at LLL and at other laboratories. For example, in our 2XIIB experiment we have injected a 500-A-equivalent current of neutral deuterium atoms at an average energy of 18 keV, producing a dense plasma (10 14 particles/cm 3 ) at thermonuclear energy (14 keV or 160 million kelvins). Currently, LLL and LBL are developing beam energies in the 80- to 120-keV range for our upcoming MFTF experiment, for the TFTR tokamak experiment at Princeton, and for the Doublet III tokamak experiment at General Atomic. These results increase our long-range prospects of producing high-intensity beams of energies in the hundreds or even thousands of kilo-electron-volts, providing us with optimistic extrapolations for realizing power-producing fusion reactors

  2. Heterogeneous ice nucleation: exploring the transition from stochastic to singular freezing behavior

    Science.gov (United States)

    Niedermeier, D.; Shaw, R. A.; Hartmann, S.; Wex, H.; Clauss, T.; Voigtländer, J.; Stratmann, F.

    2011-08-01

    Heterogeneous ice nucleation, a primary pathway for ice formation in the atmosphere, has been described alternately as being stochastic, in direct analogy with homogeneous nucleation, or singular, with ice nuclei initiating freezing at deterministic temperatures. We present an idealized, conceptual model to explore the transition between stochastic and singular ice nucleation. This "soccer ball" model treats particles as being covered with surface sites (patches of finite area) characterized by different nucleation barriers, but with each surface site following the stochastic nature of ice embryo formation. The model provides a phenomenological explanation for seemingly contradictory experimental results obtained in our research groups. Even with ice nucleation treated fundamentally as a stochastic process this process can be masked by the heterogeneity of surface properties, as might be typical for realistic atmospheric particle populations. Full evaluation of the model findings will require experiments with well characterized ice nucleating particles and the ability to vary both temperature and waiting time for freezing.

  3. Peptide-MHC class I stability is a stronger predictor of CTL immunogenicity than peptide affinity

    DEFF Research Database (Denmark)

    Harndahl, Mikkel Nors; Rasmussen, Michael; Nielsen, Morten

    2012-01-01

    of antigen processing and presentation in defining cytotoxic T lymphocyte (CTL) immunogenicity Assarsson et al., 2007. Using an affinity-balanced approach, we demonstrated that immunogenic peptides tend to be more stably bound to MHC-I molecules compared with non-immunogenic peptides. We also developed......Peptide-MHC class I stability is a stronger predictor of CTL immunogenicity than peptide affinity Mikkel Harndahla, Michael Rasmussena, Morten Nielsenb, Soren Buusa,∗ a Laboratory of Experimental Immunology, Faculty of Health Sciences, University of Copenhagen, Denmark b Center for Biological...... Sequence Analysis, Department of Systems Biology, Technical University of Denmark, Denmark Efficient presentation of peptide-MHC class I (pMHC-I) complexes to immune T cells should benefit from a stable peptide- MHC-I interaction. However, it has been difficult to distinguish stability from other...

  4. Understanding and Controlling Cu-Catalyzed Graphene Nucleation: The Role of Impurities, Roughness, and Oxygen Scavenging

    OpenAIRE

    Braeuninger-Weimer, Philipp; Brennan, B; Pollard, AJ; Hofmann, Stephan

    2016-01-01

    The mechanism by which Cu catalyst pretreatments control graphene nucleation density in scalable chemical vapor deposition (CVD) is systematically explored. The intrinsic and extrinsic carbon contamination in the Cu foil is identified by time-of-flight secondary ion mass spectrometry as a major factor influencing graphene nucleation and growth. By selectively oxidizing the backside of the Cu foil prior to graphene growth, a drastic reduction of the graphene nucleation density by 6 orders of m...

  5. Percolation and nucleation approaches to nuclear fragmentation: criticality in very small systems

    Energy Technology Data Exchange (ETDEWEB)

    Santiago, A.J. [Universidade do Estado, Rio de Janeiro, RJ (Brazil). Inst. de Fisica; Chung, K.C.

    1994-12-01

    Different criteria for criticality in very small systems are discussed in the context of percolation and nucleation approaches to nuclear fragmentation. It is shown that the probability threshold in percolation and interaction radius threshold in nucleation are very strongly dependent upon the adopted criterion. By using Monte Carlo method, similarities and dissimilarities between nucleation and percolation pictures are also pointed out. (author). 17 refs, 5 figs, 2 tabs.

  6. Percolation and nucleation approaches to nuclear fragmentation: criticality in very small systems

    International Nuclear Information System (INIS)

    Santiago, A.J.; Chung, K.C.

    1994-12-01

    Different criteria for criticality in very small systems are discussed in the context of percolation and nucleation approaches to nuclear fragmentation. It is shown that the probability threshold in percolation and interaction radius threshold in nucleation are very strongly dependent upon the adopted criterion. By using Monte Carlo method, similarities and dissimilarities between nucleation and percolation pictures are also pointed out. (author). 17 refs, 5 figs, 2 tabs

  7. Weakly-bound Dimers that Underlie the Crystal Nucleation Precursors in Lysozyme Solutions

    OpenAIRE

    Safari, Mohammad; Lubchenko, Vassiliy; Conrad, Jacinta; Vekilov, Peter; Mccabe, Jacob; Angel, Laurence; Hawke, David; Byington, Michael

    2018-01-01

    Protein crystallization is central to understanding of molecular structure in biology, a vital part of processes in the pharmaceutical industry, and a crucial component of numerous disease pathologies. Crystallization starts with nucleation and how nucleation proceeds determines the crystallization rate and essential properties of the resulting crystal population. Recent results with several proteins indicate that crystals nucleate within preformed mesoscopic protein-rich clusters. The origin...

  8. Bone mineral content has stronger association with lean mass than fat mass among Indian urban adolescents

    Directory of Open Access Journals (Sweden)

    Raman K Marwaha

    2015-01-01

    Full Text Available Introduction: There are conflicting reports on the relationship of lean mass (LM and fat mass (FM with bone mineral content (BMC. Given the high prevalence of Vitamin D deficiency in India, we planned the study to evaluate the relationship between LM and FM with BMC in Indian children and adolescents. The objective of the study was to evaluate the relationship of BMC with LM and FM. Materials and Methods: Total and regional BMC, LM, and FM using dual energy X-ray absorptiometry and pubertal staging were assessed in 1403 children and adolescents (boys [B]: 826; girls [G]: 577. BMC index, BMC/LM and BMC/FM ratio, were calculated. Results: The age ranged from 5 to 18 years, with a mean age of 13.2 ± 2.7 years. BMC adjusted for height (BMC index and BMC/height ratio was comparable in both genders. There was no difference in total BMC between genders in the prepubertal group but were higher in more advanced stages of pubertal maturation. The correlation of total as well as regional BMC was stronger for LM (B: Total BMC - 0.880, trunk - 0.715, leg - 0.894, arm - 0.891; G: Total BMC - 0.827, leg - 0.846, arm - 0.815 (all value indicate r2 , P < 0.0001 for all when compared with FM (B: Total BMC - 0.776, trunk - 0.676, leg - 0.772, arm - 0.728; G: Total BMC - 0.781, leg - 0.741, arm - 0.689; all P < 0.0001 except at trunk BMC (LM - 0.682 vs. FM - 0.721; all P < 0.0001, even after controlling for age, height, pubertal stage, and biochemical parameters. Conclusions: BMC had a stronger positive correlation with LM than FM.

  9. The Effects of Thermal History on Nucleation of Tetragonal Lysozyme Crystals, or Hot Protein and Cold Nucleation

    Science.gov (United States)

    Burke, Michael; Judge, Russell; Pusey, Marc

    2000-01-01

    Chicken egg white lysozyme has a well characterized thermally driven phase transition. Between pH 4.2 and 5.2, the transition temperature, as defined by the point where the tetragonal and orthorhombic solubilities are equal, is a function of the pH, salt (precipitant) type and concentration, and most likely of the buffer concentration as well. This phase transition can be carried out with protein solution alone, prior to addition of precipitant solution. Warming a lysozyme solution above the phase transition point, then cooling it back below this point, has been shown to affect the subsequent nucleation rate, as determined by the numbers and size of crystals formed, but not the growth rate for the tetragonal crystal form . We have now measured the kinetics of this process and investigated its reversibility. The transition effects are progressive with temperature, having a half time of about 1 hour at 37C at pH 4.8. After holding a lysozyme solution at 37C (prior to addition of precipitant) for 16 hours, then cooling it back to 4C no return to the pre-warmed nucleation kinetics are observed after at least 4 weeks. Orthorhombic lysozyme crystals apparently do not undergo the flow-induced growth cessation of tetragonal lysozyme crystals. Putting the protein in the orthorhombic form does not affect the averaged face growth kinetics, only nucleation, for tetragonal crystals. This differential behaviour may be exploited to elucidate how and where flow affects the lysozyme crystal growth process. The presentation will focus on the results of these and ongoing studies in this area.

  10. Nucleated red blood cells and early EEG: predicting Sarnat stage and two year outcome.

    LENUS (Irish Health Repository)

    Walsh, B H

    2012-01-31

    AIMS: Hypoxic Ischaemic Encephalopathy (HIE) causes characteristic changes of the electroencephalogram (EEG), and a raised Nucleated Red Blood Cell (NRBC) count compared to controls. We wished to examine whether combining these markers could improve their ability to predict HIE severity in the first 24h. METHODS: Term infants with HIE were recruited. NRBC count and continuous multi-channel EEG were recorded within the first 24h. Neurological assessment was carried out at 24 months. A control population with NRBC counts in the first 24h was recruited. RESULTS: 44 infants with HIE and 43 control infants were recruited. Of the HIE population 39 completed a 2 year follow-up. The median NRBC count differed significantly between the controls and those with HIE (3\\/100 WBC [range of 0-11] vs 12.3\\/100 WBC [0-240]) (p<0.001). Within the HIE population the median NRBC count was significantly greater in infants with moderate\\/severe HIE than mild (16\\/100 WBC [range of 0-240] vs 8\\/100 WBC [1-23]) (p=0.016), and among infants with abnormal outcome compared to normal (21.3\\/100 WBC [1-239.8] vs 8.3\\/100 WBC [0-50])(p=0.03). The predictive ability of EEG changed with time post-delivery, therefore results are given at both 12 and 24h of age. At both time points the combined marker had a stronger correlation than EEG alone; with HIE severity (12h: r=0.661 vs r=0.622), (24h: r=0.645 vs r=0.598), and with outcome at 2 years (12h: r=0.756 vs r=0.652), (24h: r=0.802 vs r=0.746). CONCLUSION: Combining early EEG and NRBC count to predict HIE severity and neurological outcome, improved the predictive ability of either in isolation.

  11. On the Role of Ammonia in Arctic Aerosol Nucleation and Cloud Formation

    Science.gov (United States)

    Browse, J.; Dall'Osto, M.; Geels, C.; Skov, H.; Massling, A.; Boertmann, D.; Beddows, D.; Gordon, H.; Pringle, K.

    2017-12-01

    This study investigates the importance of ammonia in Arctic aerosol nucleation and the formation of cloud condensation nuclei (CCN) at high-latitudes. The importance of atmospheric nucleation processes to summertime Arctic aerosol concentration has been frequently noted at ground-stations, during campaigns and within models (which typically predict that the majority of aerosol in the Arctic summertime boundary layer derives from nucleation). However, as nucleation mechanisms in global models have increased in complexity (improving model skill globally) our skill in the Arctic has generally decreased. This decrease in model skill is likely due to a lack of organic compounds (monterpenes etc.) in the modelled high Arctic which have been identified as a key component in atmospheric nucleation in the mid-latitudes and thus incorporated into many global nucleation parametrisations. Recently it has been suggested that ammonia (also identified as a potentially important component in atmospheric nucleation) may control nucleation processes in the Arctic. However, the source (or sources) of Arctic ammonia remain unclear. Here, we use modelling, long-term aerosol in-situ observations, high resolution sea-ice satellite observations and new emission inventories to investigate the link between ammonia sources (including bird colonies, sea-ice melt and open ocean in the marginal ice zones) and nucleation events in the mid-to-high Arctic, and thus quantify the importance of individual ammonia sources to Arctic-wide CCN and cloud droplet populations.

  12. Plasma/Neutral-Beam Etching Apparatus

    Science.gov (United States)

    Langer, William; Cohen, Samuel; Cuthbertson, John; Manos, Dennis; Motley, Robert

    1989-01-01

    Energies of neutral particles controllable. Apparatus developed to produce intense beams of reactant atoms for simulating low-Earth-orbit oxygen erosion, for studying beam-gas collisions, and for etching semiconductor substrates. Neutral beam formed by neutralization and reflection of accelerated plasma on metal plate. Plasma ejected from coaxial plasma gun toward neutralizing plate, where turned into beam of atoms or molecules and aimed at substrate to be etched.

  13. Homogeneous nucleation: a problem in nonequilibrium quantum statistical mechanics

    Energy Technology Data Exchange (ETDEWEB)

    1978-08-01

    The master equation for cluster growth and evaporation is derived for many-body quantum mechanics and from a modified version of quantum damping theory used in laser physics. For application to nucleation theory, the quantum damping theory is generalized to include system and reservoir states that are not separate entities. Formulas for rate constants are obtained. Solutions of the master equation yield equations of state and system-averaged quantities recognized as thermodynamic variables. Formulas for Helmholtz free energies of clusters in a Debye approximation are derived. Coexistence-line equations for pressure, volume, and number of clusters are obtained from equations-of-state analysis. Coexistence-line and surface-tension data are used to obtain values of parameters for the Debye approximation. These data are employed in calculating both the nucleation current in diffusion cloud chamber experiments and the onset of condensation in expansion nozzle experiments. Theoretical and experimental results are similar for both cloud chamber and nozzle experiments, which measure water. Comparison with other theories reveals that classical theory only accidently agrees with experiment and that the Helmholtz free-energy formula used in the Lothe--Pound theory is incomplete. 27 figures, 3 tables, 149 references.

  14. Hysteresis, nucleation and growth phenomena in spin-crossover solids

    Science.gov (United States)

    Ridier, Karl; Molnár, Gábor; Salmon, Lionel; Nicolazzi, William; Bousseksou, Azzedine

    2017-12-01

    The observation and the study of first-order phase transitions in cooperative spin-crossover (SCO) solids exhibiting hysteresis behaviours are of particular interest and currently constitute a burgeoning area in the field of bistable molecular materials. The understanding and the control of the transition mechanisms (nucleation and growth processes) and their dynamics within the hysteresis region appear to be a general and appealing problem from a fundamental point of view and for technological applications as well. This review reports on the recent progresses and most important findings made on the spatiotemporal dynamics of the spin transition in SCO solids, particularly through the universal nucleation and growth process. Both thermally induced and light-induced spin transitions are discussed. We open up this review to the central question of the evolution of the transition mechanisms and dynamics in SCO nano-objects, which constitute promising systems to reach ultra-fast switching, and the experimental issues inherent to such studies at the micro- and nanometric scale.

  15. Convergent evolution of germ granule nucleators: A hypothesis.

    Science.gov (United States)

    Kulkarni, Arpita; Extavour, Cassandra G

    2017-10-01

    Germ cells have been considered "the ultimate stem cell" because they alone, during normal development of sexually reproducing organisms, are able to give rise to all organismal cell types. Morphological descriptions of a specialized cytoplasm termed 'germ plasm' and associated electron dense ribonucleoprotein (RNP) structures called 'germ granules' within germ cells date back as early as the 1800s. Both germ plasm and germ granules are implicated in germ line specification across metazoans. However, at a molecular level, little is currently understood about the molecular mechanisms that assemble these entities in germ cells. The discovery that in some animals, the gene products of a small number of lineage-specific genes initiate the assembly (also termed nucleation) of germ granules and/or germ plasm is the first step towards facilitating a better understanding of these complex biological processes. Here, we draw on research spanning over 100years that supports the hypothesis that these nucleator genes may have evolved convergently, allowing them to perform analogous roles across animal lineages. Copyright © 2017 The Authors. Published by Elsevier B.V. All rights reserved.

  16. The nucleation of microtubules in Aspergillus nidulans germlings

    Directory of Open Access Journals (Sweden)

    Andrade-Monteiro Cristina de

    1999-01-01

    Full Text Available Microtubules are filaments composed of dimers of alpha- and beta-tubulins, which have a variety of functions in living cells. In fungi, the spindle pole bodies usually have been considered to be microtubule-organizing centers. We used the antimicrotubule drug Benomyl in block/release experiments to depolymerize and repolymerize microtubules in Aspergillus nidulans germlings to learn more about the microtubule nucleation process in this filamentous fungus. Twenty seconds after release from Benomyl short microtubules were formed from several bright (immunofluorescent dots distributed along the germlings, suggesting that microtubule nucleation is randomly distributed in A. nidulans germlings. Since nuclear movement is dependent on microtubules in A. nidulans we analyzed whether mutants defective in nuclear distribution along the growing hyphae (nud mutants have some obvious microtubule defect. Cytoplasmic, astral and spindle microtubules were present and appeared to be normal in all nud mutants. However, significant changes in the percentage of short versus long mitotic spindles were observed in nud mutants. This suggests that some of the nuclei of nud mutants do not reach the late stage of cell division at normal temperatures.

  17. Ice nucleation active particles are efficiently removed by precipitating clouds.

    Science.gov (United States)

    Stopelli, Emiliano; Conen, Franz; Morris, Cindy E; Herrmann, Erik; Bukowiecki, Nicolas; Alewell, Christine

    2015-11-10

    Ice nucleation in cold clouds is a decisive step in the formation of rain and snow. Observations and modelling suggest that variations in the concentrations of ice nucleating particles (INPs) affect timing, location and amount of precipitation. A quantitative description of the abundance and variability of INPs is crucial to assess and predict their influence on precipitation. Here we used the hydrological indicator δ(18)O to derive the fraction of water vapour lost from precipitating clouds and correlated it with the abundance of INPs in freshly fallen snow. Results show that the number of INPs active at temperatures ≥ -10 °C (INPs-10) halves for every 10% of vapour lost through precipitation. Particles of similar size (>0.5 μm) halve in number for only every 20% of vapour lost, suggesting effective microphysical processing of INPs during precipitation. We show that INPs active at moderate supercooling are rapidly depleted by precipitating clouds, limiting their impact on subsequent rainfall development in time and space.

  18. Isolation of fetal DNA from nucleated erythrocytes in maternal blood

    Energy Technology Data Exchange (ETDEWEB)

    Bianchi, D.W.; Knoll, J.H.M. (Children' s Hospital, Boston, MA (USA) Harvard Medical School, Boston, MA (USA)); Flint, A.F. (Howard Hughes Medical Institute, Boston, MA (USA)); Pizzimenti, M.F. (Brigham and Women' s Hospital, Boston, MA (USA)); Latt, S.A. (Children' s Hospital, Boston, MA (USA) Harvard Medical School, Boston, MA (USA))

    1990-05-01

    Fetal nucleated cells within maternal blood represent a potential source of fetal genes obtainable by venipuncture. The authors used monoclonal antibody against the transferrin receptor (TIR) to identify nucleated erythrocytes in the peripheral blood of pregnant women. Candidate fetal cells from 19 pregnancies were isolated by flow sorting at 12 1/2-17 weeks gestation. The DNA in these cells was amplified for a 222-base-pair (bp) sequence present on the short arm of the Y chromosome as proof that the cells were derived from the fetus. The amplified DNA was compared with standardized DNA concentrations. In the case of the female fetus, DNA prepared from samples at 32 weeks of gestation and cord blood at delivery also showed the presence of the Y chromosomal sequence, suggesting Y sequence mosaicism or translocation. In 10/12 cases where the 222-bp band was absent, the fetuses were female. Thus, they were successful in detecting the Y chromosomal sequence in 75% of the male-bearing pregnancies, demonstrating that it is possible to isolate fetal gene sequences from cells in maternal blood. Further refinement in methodology should increase sensitivity and facilitate noninvasive screening for fetal gene mutations.

  19. Laser-induced nucleation of carbon dioxide bubbles

    Science.gov (United States)

    Ward, Martin R.; Jamieson, William J.; Leckey, Claire A.; Alexander, Andrew J.

    2015-04-01

    A detailed experimental study of laser-induced nucleation (LIN) of carbon dioxide (CO2) gas bubbles is presented. Water and aqueous sucrose solutions supersaturated with CO2 were exposed to single nanosecond pulses (5 ns, 532 nm, 2.4-14.5 MW cm-2) and femtosecond pulses (110 fs, 800 nm, 0.028-11 GW cm-2) of laser light. No bubbles were observed with the femtosecond pulses, even at high peak power densities (11 GW cm-2). For the nanosecond pulses, the number of bubbles produced per pulse showed a quadratic dependence on laser power, with a distinct power threshold below which no bubbles were observed. The number of bubbles observed increases linearly with sucrose concentration. It was found that filtering of solutions reduces the number of bubbles significantly. Although the femtosecond pulses have higher peak power densities than the nanosecond pulses, they have lower energy densities per pulse. A simple model for LIN of CO2 is presented, based on heating of nanoparticles to produce vapor bubbles that must expand to reach a critical bubble radius to continue growth. The results suggest that non-photochemical laser-induced nucleation of crystals could also be caused by heating of nanoparticles.

  20. Atomistic simulation of helium bubble nucleation in palladium

    Energy Technology Data Exchange (ETDEWEB)

    Wang Liang [Department of Applied Physics, Hunan University, Changsha 410082 (China); Hu, Wangyu [Department of Applied Physics, Hunan University, Changsha 410082 (China)], E-mail: wangyuhu2001cn@yahoo.com.cn; Xiao Shifang [Department of Applied Physics, Hunan University, Changsha 410082 (China)], E-mail: sfxiao@yahoo.com.cn; Yang Jianyu [Department of Maths and Physics, Hunan Institute of Engineering, Xiangtan 411104 (China); Deng Huiqiu [Department of Applied Physics, Hunan University, Changsha 410082 (China)

    2009-09-15

    A palladium crystal has been constructed with 11808 atoms. 55 helium atoms occupied the octahedral position of palladium crystal are introduced and retained in a spherical region. Molecular dynamic simulations are performed in a constant temperature and constant volume ensemble (NVT) with temperature controlled by Nose-Hoover thermostat. The interactions between palladium atoms are described with modified analytic embedded atom method (MAEAM), the interactions between palladium atom and helium atom are in the form of Morse potential, and the interactions between helium atoms are in the form of L-J potential function. With the analysis of the radial distribution function (RDF) and microstructure, it reveals that some of helium atoms form a series of clusters with different size, and the nucleation core is random at low temperature, and which is the embryo of helium bubble. Increasing temperature can accelerate the process of bubble nucleation, and the clusters will aggregate and coalesce into a bigger one in which there are no palladium atoms, and it is considered as a helium bubble.

  1. Ion-beam Plasma Neutralization Interaction Images

    Energy Technology Data Exchange (ETDEWEB)

    Igor D. Kaganovich; Edward Startsev; S. Klasky; Ronald C. Davidson

    2002-04-09

    Neutralization of the ion beam charge and current is an important scientific issue for many practical applications. The process of ion beam charge and current neutralization is complex because the excitation of nonlinear plasma waves may occur. Computer simulation images of plasma neutralization of the ion beam pulse are presented.

  2. Neutral beamline with improved ion energy recovery

    Science.gov (United States)

    Kim, Jinchoon

    1984-01-01

    A neutral beamline employing direct energy recovery of unneutralized residual ions is provided which enhances the energy recovery of the full energy ion component of the beam exiting the neutralizer cell, and thus improves the overall neutral beamline efficiency. The unneutralized full energy ions exiting the neutralizer are deflected from the beam path and the electrons in the cell are blocked by a magnetic field applied transverse to the beam direction in the neutral izer exit region. The ions which are generated at essentially ground potential and accelerated through the neutralizer cell by a negative acceleration voltage are collected at ground potential. A neutralizer cell exit end region is provided which allows the magnetic and electric fields acting on the exiting ions to be loosely coupled. As a result, the fractional energy ions exiting the cell are reflected onto and collected at an interior wall of the neutralizer formed by the modified end geometry, and thus do not detract from the energy recovery efficiency of full energy ions exiting the cell. Electrons within the neutralizer are prevented from exiting the neutralizer end opening by the action of crossed fields drift (ExB) and are terminated to a collector collar around the downstream opening of the neutralizer. The correct combination of the extended neutralizer end structure and the magnet region is designed so as to maximize the exit of full energy ions and to contain the fractional energy ions.

  3. Ice nucleation efficiency of clay minerals in the immersion mode

    Directory of Open Access Journals (Sweden)

    V. Pinti

    2012-07-01

    Full Text Available Emulsion and bulk freezing experiments were performed to investigate immersion ice nucleation on clay minerals in pure water, using various kaolinites, montmorillonites, illites as well as natural dust from the Hoggar Mountains in the Saharan region. Differential scanning calorimeter measurements were performed on three different kaolinites (KGa-1b, KGa-2 and K-SA, two illites (Illite NX and Illite SE and four natural and acid-treated montmorillonites (SWy-2, STx-1b, KSF and K-10. The emulsion experiments provide information on the average freezing behaviour characterized by the average nucleation sites. These experiments revealed one to sometimes two distinct heterogeneous freezing peaks, which suggest the presence of a low number of qualitatively distinct average nucleation site classes. We refer to the peak at the lowest temperature as "standard peak" and to the one occurring in only some clay mineral types at higher temperatures as "special peak". Conversely, freezing in bulk samples is not initiated by the average nucleation sites, but by a very low number of "best sites". The kaolinites and montmorillonites showed quite narrow standard peaks with onset temperatures 238 K<Tonstd<242 K and best sites with averaged median freezing temperature Tmedbest=257 K, but only some featuring a special peak (i.e. KSF, K-10, K-SA and SWy-2 with freezing onsets in the range 240–248 K. The illites showed broad standard peaks with freezing onsets at 244 K Tonstd<246 K and best sites with averaged median freezing temperature Tmedbest=262 K. The large difference between freezing temperatures of standard and best sites shows that characterizing ice nucleation efficiencies of dust particles on the basis of freezing onset temperatures from bulk experiments, as has been done in some atmospheric studies, is not appropriate. Our investigations

  4. Satellite drag effects due to uplifted oxygen neutrals during super magnetic storms

    Science.gov (United States)

    Lakhina, Gurbax S.; Tsurutani, Bruce T.

    2017-12-01

    During intense magnetic storms, prompt penetration electric fields (PPEFs) through E × B forces near the magnetic equator uplift the dayside ionosphere. This effect has been called the dayside super-fountain effect. Ion-neutral drag forces between the upward moving O+ (oxygen ions) and oxygen neutrals will elevate the oxygen atoms to higher altitudes. This paper gives a linear calculation indicating how serious the effect may be during an 1859-type (Carrington) superstorm. It is concluded that the oxygen neutral densities produced at low-Earth-orbiting (LEO) satellite altitudes may be sufficiently high to present severe satellite drag. It is estimated that with a prompt penetrating electric field of ˜ 20 mV m-1 turned on for 20 min, the O atoms and O+ ions are uplifted to 850 km where they produce about 40-times-greater satellite drag per unit mass than normal. Stronger electric fields will presumably lead to greater uplifted mass.

  5. Neutral molecular cluster formation of sulfuric acid–dimethylamine observed in real time under atmospheric conditions

    Science.gov (United States)

    Kürten, Andreas; Jokinen, Tuija; Simon, Mario; Sipilä, Mikko; Sarnela, Nina; Junninen, Heikki; Adamov, Alexey; Almeida, João; Amorim, Antonio; Bianchi, Federico; Breitenlechner, Martin; Dommen, Josef; Donahue, Neil M.; Duplissy, Jonathan; Ehrhart, Sebastian; Flagan, Richard C.; Franchin, Alessandro; Hakala, Jani; Hansel, Armin; Heinritzi, Martin; Hutterli, Manuel; Kangasluoma, Juha; Kirkby, Jasper; Laaksonen, Ari; Lehtipalo, Katrianne; Leiminger, Markus; Makhmutov, Vladimir; Mathot, Serge; Onnela, Antti; Petäjä, Tuukka; Praplan, Arnaud P.; Riccobono, Francesco; Rissanen, Matti P.; Rondo, Linda; Schobesberger, Siegfried; Seinfeld, John H.; Steiner, Gerhard; Tomé, António; Tröstl, Jasmin; Winkler, Paul M.; Williamson, Christina; Wimmer, Daniela; Ye, Penglin; Baltensperger, Urs; Carslaw, Kenneth S.; Kulmala, Markku; Worsnop, Douglas R.; Curtius, Joachim

    2014-01-01

    For atmospheric sulfuric acid (SA) concentrations the presence of dimethylamine (DMA) at mixing ratios of several parts per trillion by volume can explain observed boundary layer new particle formation rates. However, the concentration and molecular composition of the neutral (uncharged) clusters have not been reported so far due to the lack of suitable instrumentation. Here we report on experiments from the Cosmics Leaving Outdoor Droplets chamber at the European Organization for Nuclear Research revealing the formation of neutral particles containing up to 14 SA and 16 DMA molecules, corresponding to a mobility diameter of about 2 nm, under atmospherically relevant conditions. These measurements bridge the gap between the molecular and particle perspectives of nucleation, revealing the fundamental processes involved in particle formation and growth. The neutral clusters are found to form at or close to the kinetic limit where particle formation is limited only by the collision rate of SA molecules. Even though the neutral particles are stable against evaporation from the SA dimer onward, the formation rates of particles at 1.7-nm size, which contain about 10 SA molecules, are up to 4 orders of magnitude smaller compared with those of the dimer due to coagulation and wall loss of particles before they reach 1.7 nm in diameter. This demonstrates that neither the atmospheric particle formation rate nor its dependence on SA can simply be interpreted in terms of cluster evaporation or the molecular composition of a critical nucleus. PMID:25288761

  6. Space station neutral external environment

    Science.gov (United States)

    Ehlers, H.; Leger, L.

    1988-01-01

    Molecular contamination levels arising from the external induced neutral environment of the Space Station (Phase 1 configuration) were calculated using the MOLFLUX model. Predicted molecular column densities and deposition rates generally meet the Space Station contamination requirements. In the doubtful cases of deposition due to materials outgassing, proper material selection, generally excluding organic products exposed to the external environment, must be considered to meet contamination requirements. It is important that the Space Station configuration, once defined, is not significantly modified to avoid introducing new unacceptable contamination sources.

  7. Thermostability analysis of line-tension-associated nucleation at a gas-liquid interface

    Science.gov (United States)

    Singha, Sanat Kumar; Das, Prasanta Kumar; Maiti, Biswajit

    2017-01-01

    The influence of line tension on the thermostability of a droplet nucleated from an oversaturated vapor at the interface of the vapor and another immiscible liquid is investigated. Along with the condition of mechanical equilibrium, the notion of extremization of the reversible work of formation is considered to obtain the critical parameters related to heterogeneous nucleation. From the energetic formulation, the critical reversible work of formation is found to be greater than that of homogeneous nucleation for high value of the positive line tension. On the other hand, for high value of the negative line tension, the critical reversible work of formation becomes negative. Therefore, these thermodynamic instabilities under certain substrate wettability situations necessitate a free-energetics-based stability of the nucleated droplet, because the system energy is not minimized under these conditions. This thermostability is analogous to the transition-based stability proposed by Widom [B. Widom, J. Phys. Chem. 99, 2803 (1995)], 10.1021/j100009a041 in the case of partial wetting phenomena along with the positive line tension. The thermostability analysis limits the domain of the solution space of the present critical-value problem as the thermodynamic transformation in connection with homogeneous and workless nucleation is considered. Within the stability range of the geometry-based wetting parameters, three limiting modes of nucleation, i.e., total-dewetting-related homogeneous nucleation, and total-wetting-associated and total-submergence-associated workless nucleation scenarios, are identified. Either of the two related limiting wetting scenarios of workless nucleation, namely, total wetting and total submergence, is found to be favorable depending on the geometry-based wetting conditions. The line-tension-associated nucleation on a liquid surface can be differentiated from that on a rigid substrate, as in the former, the stability based on mechanical

  8. Regular Exercisers Have Stronger Pelvic Floor Muscles than Non-Regular Exercisers at Midpregnancy.

    Science.gov (United States)

    Bø, Kari; Ellstrøm Engh, Marie; Hilde, Gunvor

    2017-12-26

    Today, all healthy pregnant women are encouraged to be physically active throughout pregnancy, with recommendations to participate in at least 30 min of aerobic activity on most days of the week, in addition to perform strength training of the major muscle groups 2-3 days per week, and also pelvic floor muscle training. There is, however, an ongoing debate whether general physical activity enhances or declines pelvic floor muscle function. To compare vaginal resting pressure, pelvic floor muscle strength and endurance in regular exercisers (exercise ≥ 30 minutes ≥ 3 times per week) and non-exercisers at mid-pregnancy. Furthermore, to assess whether regular general exercise or pelvic floor muscle strength was associated with urinary incontinence. This was a cross-sectional study at mean gestational week 20.9 (± 1.4) including 218 nulliparous pregnant women, mean age 28.6 years (range 19-40) and pre-pregnancy body mass index 23.9 kg/m 2 (SD 4.0). Vaginal resting pressure, pelvic floor muscle strength and pelvic floor muscle endurance were measured by a high precision pressure transducer connected to a vaginal balloon. International Consultation on Incontinence Questionnaire Urinary Incontinence Short Form was used to assess urinary incontinence. Differences between groups were analyzed using Independent Sample T-test. Linear regression analysis was conducted to adjust for pre-pregnancy body mass index, age, smoking during pregnancy and regular pelvic floor muscle training during pregnancy. P-value was set to ≤ 0.05. Regular exercisers had statistically significant stronger ( mean 6.4 cm H 2 O (95% CI: 1.7, 11.2)) and more enduring ( mean 39.9 cm H 2 Osec (95% CI: 42.2, 75.7)) pelvic floor muscles. Only pelvic floor muscle strength remained statistically significant, when adjusting for possible confounders. Pelvic floor muscle strength and not regular general exercise was associated with urinary continence (adjusted B: -6.4 (95% CI: -11.5, -1.4)). Regular

  9. Hippocampal-Prefrontal Reactivation during Learning Is Stronger in Awake Compared with Sleep States.

    Science.gov (United States)

    Tang, Wenbo; Shin, Justin D; Frank, Loren M; Jadhav, Shantanu P

    2017-12-06

    Hippocampal sharp-wave ripple (SWR) events occur during both behavior (awake SWRs) and slow-wave sleep (sleep SWRs). Awake and sleep SWRs both contribute to spatial learning and memory, thought to be mediated by the coordinated reactivation of behavioral experiences in hippocampal-cortical circuits seen during SWRs. Current hypotheses suggest that reactivation contributes to memory consolidation processes, but whether awake and sleep reactivation are suited to play similar or different roles remains unclear. Here we addressed that issue by examining the structure of hippocampal (area CA1) and prefrontal (PFC) activity recorded across behavior and sleep stages in male rats learning a spatial alternation task. We found a striking state difference: prefrontal modulation during awake and sleep SWRs was surprisingly distinct, with differing patterns of excitation and inhibition. CA1-PFC synchronization was stronger during awake SWRs, and spatial reactivation, measured using both pairwise and ensemble measures, was more structured for awake SWRs compared with post-task sleep SWRs. Stronger awake reactivation was observed despite the absence of coordination between network oscillations, namely hippocampal SWRs and cortical delta and spindle oscillations, which is prevalent during sleep. Finally, awake CA1-PFC reactivation was enhanced most prominently during initial learning in a novel environment, suggesting a key role in early learning. Our results demonstrate significant differences in awake and sleep reactivation in the hippocampal-prefrontal network. These findings suggest that awake SWRs support accurate memory storage and memory-guided behavior, whereas sleep SWR reactivation is better suited to support integration of memories across experiences during consolidation. SIGNIFICANCE STATEMENT Hippocampal sharp-wave ripples (SWRs) occur both in the awake state during behavior and in the sleep state after behavior. Awake and sleep SWRs are associated with memory

  10. SWAN: NGC 253’s Nucleated Star Bursting Environment

    Science.gov (United States)

    Gorski, Mark; Ott, Juergen; Meier, David; Momjian, Emmanuel; Walter, Fabian; Rand, Richard

    2015-08-01

    We present the first results from SWAN: Survey of Water and Ammonia in Nearby galaxies. Nearby galaxies are conveniently located to probe molecular gas properties on scales of 10 to 200 pc, which are appropriate for Giant Molecular Clouds (GMCs). The resolution of the VLA in D and C configurations maps to a few 10’s of parsecs in these galaxies. To advance studies of galaxy evolution it is paramount to understand how processes in the molecular ISM and star formation are linked on these scales. We have observed the metastable transitions of ammonia and the 22GHz water maser line in four nearby galaxies: NGC 253, IC 342, NGC 2146, and NGC 6946. These galaxies were chosen to span an order of magnitude in star formation rate, and a range of galactic ecosystems. We use the ammonia transitions to derive kinetic temperatures, which exposes the heating and cooling balance of the ISM. We then aim to relate these conditions to energetic feedback from star formation indicated by water masers. Currently our analysis is focused on NGC 253. NGC 253 is a barred spiral galaxy with a nucleated starburst of ≈3M⊙ per year. We have observed ammonia transitions (1,1) to (5,5) and the 22GHz water maser line with a resolution of ≈63pc. We have identified nine regions across the nucleated starburst for study. The ammonia (3,3) line appears to be masing in the centermost 200pc. In combination with Large Velocity Gradient models (LVG) we find that the properties of the molecular gas is warm, ranging from 100K to 160K, with molecular hydrogen densities from 2.2e3 cm-3 to 4.8e3 cm-3. We have identified two regions of water maser emission. The first region is a north south extension, about the center of the galaxy, with a major axis of ≈7”(150pc) and a minor axis of ≈3”(90pc), and the second is a nearby region ≈6”(100pc) to the southeast of the galaxy center. By means of these measurements, we gain an understanding of the molecular ISM associated with the nucleated

  11. Discrete symmetries with neutral mesons

    Science.gov (United States)

    Bernabéu, José

    2018-01-01

    Symmetries, and Symmetry Breakings, in the Laws of Physics play a crucial role in Fundamental Science. Parity and Charge Conjugation Violations prompted the consideration of Chiral Fields in the construction of the Standard Model, whereas CP-Violation needed at least three families of Quarks leading to Flavour Physics. In this Lecture I discuss the Conceptual Basis and the present experimental results for a Direct Evidence of Separate Reversal-in-Time T, CP and CPT Genuine Asymmetries in Decaying Particles like Neutral Meson Transitions, using Quantum Entanglement and the Decay as a Filtering Measurement. The eight transitions associated to the Flavour-CP eigenstate decay products of entangled neutral mesons have demonstrated with impressive significance a separate evidence of TRV and CPV in Bd-physics, whereas a CPTV asymmetry shows a 2σ effect interpreted as an upper limit. Novel CPTV observables are discussed for K physics at KLOE-2, including the difference between the semileptonic asymmetries from KL and KS, the ratios of double decay rate Intensities to Flavour-CP eigenstate decay products and the ω-effect. Their observation would lead to a change of paradigm beyond Quantum Field Theory, however there is nothing in Quantum Mechanics forbidding CPTV.

  12. Stronger associations of obesity with prehypertension and hypertension in young women than in young men.

    Science.gov (United States)

    Wakabayashi, Ichiro

    2012-07-01

    Obesity is an important risk factor for prehypertension and hypertension, and there are sex-specific differences in prevalences of obesity and hypertension. The aim of this study was to determine whether sex influences the relationships of obesity with prehypertension and hypertension. The participants were 28,325 Japanese men and women aged 20-39 years. Obesity was evaluated by BMI (≥ 25 kg/m) and waist-to-height ratio (WHtR ≥ 0.5). Associations of obesity with prehypertension and hypertension were compared in men and women by using odds ratio (OR) and area under the curve (AUC). ORs for prehypertension and hypertension in participants with vs. participants without high BMI or WHtR were significantly higher than a reference level of 1.00 both in men and women and were significantly higher in women than in men. ORs for prehypertension and hypertension of participants with vs. participants without high BMI were 3.10 (2.84-3.38) (men) vs. 5.54 (4.80-6.40) (women) (P men) vs. 34.58 (26.55-45.04) (women) (P men. The results suggest that the associations of obesity with prehypertension and hypertension are stronger in women than in men.

  13. Stronger activation of SREBP-1a by nucleus-localized HBx

    International Nuclear Information System (INIS)

    Wu, Qi; Qiao, Ling; Yang, Jian; Zhou, Yan; Liu, Qiang

    2015-01-01

    We previously showed that hepatitis B virus (HBV) X protein activates the sterol regulatory element-binding protein-1a (SREBP-1a). Here we examined the role of nuclear localization of HBx in this process. In comparison to the wild-type and cytoplasmic HBx, nuclear HBx had stronger effects on SREBP-1a and fatty acid synthase transcription activation, intracellular lipid accumulation and cell proliferation. Furthermore, nuclear HBx could activate HBV enhancer I/X promoter and was more effective on up-regulating HBV mRNA level in the context of HBV replication than the wild-type HBx, while the cytoplasmic HBx had no effect. Our results demonstrate the functional significance of the nucleus-localized HBx in regulating host lipogenic pathway and HBV replication. - Highlights: • Nuclear HBx is more effective on activating SREBP-1a and FASN transcription. • Nuclear HBx is more effective on enhancing intracellular lipid accumulation. • Nuclear HBx is more effective on enhancing cell proliferation. • Nuclear HBx up-regulates HBV enhancer I/X promoter activity. • Nuclear HBx increases HBV mRNA level in the context of HBV replication

  14. Stronger activation of SREBP-1a by nucleus-localized HBx

    Energy Technology Data Exchange (ETDEWEB)

    Wu, Qi [VIDO-InterVac, Veterinary Microbiology, University of Saskatchewan, Saskatoon (Canada); Qiao, Ling [VIDO-InterVac, University of Saskatchewan, Saskatoon, Saskatchewan (Canada); Yang, Jian [Drug Discovery Group, University of Saskatchewan, Saskatoon, Saskatchewan (Canada); Zhou, Yan [VIDO-InterVac, Veterinary Microbiology, Vaccinology and Immunotherapeutics, University of Saskatchewan, Saskatoon, Saskatchewan (Canada); Liu, Qiang, E-mail: qiang.liu@usask.ca [VIDO-InterVac, Veterinary Microbiology, Vaccinology and Immunotherapeutics, University of Saskatchewan, Saskatoon, Saskatchewan (Canada)

    2015-05-08

    We previously showed that hepatitis B virus (HBV) X protein activates the sterol regulatory element-binding protein-1a (SREBP-1a). Here we examined the role of nuclear localization of HBx in this process. In comparison to the wild-type and cytoplasmic HBx, nuclear HBx had stronger effects on SREBP-1a and fatty acid synthase transcription activation, intracellular lipid accumulation and cell proliferation. Furthermore, nuclear HBx could activate HBV enhancer I/X promoter and was more effective on up-regulating HBV mRNA level in the context of HBV replication than the wild-type HBx, while the cytoplasmic HBx had no effect. Our results demonstrate the functional significance of the nucleus-localized HBx in regulating host lipogenic pathway and HBV replication. - Highlights: • Nuclear HBx is more effective on activating SREBP-1a and FASN transcription. • Nuclear HBx is more effective on enhancing intracellular lipid accumulation. • Nuclear HBx is more effective on enhancing cell proliferation. • Nuclear HBx up-regulates HBV enhancer I/X promoter activity. • Nuclear HBx increases HBV mRNA level in the context of HBV replication.

  15. Length effects in pseudo-word spelling: stronger in dyslexic than in non-dyslexic students.

    Science.gov (United States)

    Juul, Holger; Petersen, Dorthe Klint

    2017-10-01

    It is often discussed whether dyslexics show a deviant pattern of reading and spelling development when compared to typically developing students, or whether they follow the same pattern as other students, only at markedly slower rate. The present cross-sectional study investigated phonological encoding skills in dyslexic Danish students. We compared dyslexic and non-dyslexic students from grades 3, 5, 7, and 9 and examined whether effects of item length were stronger in the dyslexic groups. Mixed between-within subjects analyses of variance revealed significant interactions between dyslexia status and item length as the dyslexics at all grade levels were more affected by item length than their non-dyslexic peers. A marked developmental delay was apparent as the dyslexic group from grade 9 performed on approximately the same level as the non-dyslexic group from grade 3. Although the overall difference between these two groups was not significant, a significant interaction between dyslexia status and item length remained because the grade 9 dyslexics were more affected by item length than the younger non-dyslexic students. This difference in error profiles suggests a difference in the developmental patterns of dyslexic vs. non-dyslexic students.

  16. Brain Potentials Highlight Stronger Implicit Food Memory for Taste than Health and Context Associations.

    Science.gov (United States)

    Hoogeveen, Heleen R; Jolij, Jacob; Ter Horst, Gert J; Lorist, Monicque M

    2016-01-01

    Increasingly consumption of healthy foods is advised to improve population health. Reasons people give for choosing one food over another suggest that non-sensory features like health aspects are appreciated as of lower importance than taste. However, many food choices are made in the absence of the actual perception of a food's sensory properties, and therefore highly rely on previous experiences of similar consumptions stored in memory. In this study we assessed the differential strength of food associations implicitly stored in memory, using an associative priming paradigm. Participants (N = 30) were exposed to a forced-choice picture-categorization task, in which the food or non-food target images were primed with either non-sensory or sensory related words. We observed a smaller N400 amplitude at the parietal electrodes when categorizing food as compared to non-food images. While this effect was enhanced by the presentation of a food-related word prime during food trials, the primes had no effect in the non-food trials. More specifically, we found that sensory associations are stronger implicitly represented in memory as compared to non-sensory associations. Thus, this study highlights the neuronal mechanisms underlying previous observations that sensory associations are important features of food memory, and therefore a primary motive in food choice.

  17. Phytoplankton Communities Exhibit a Stronger Response to Environmental Changes than Bacterioplankton in Three Subtropical Reservoirs.

    Science.gov (United States)

    Liu, Lemian; Yang, Jun; Lv, Hong; Yu, Xiaoqing; Wilkinson, David M; Yang, Jun

    2015-09-15

    The simultaneous analysis of multiple components of ecosystems is crucial for comprehensive studies of environmental changes in aquatic ecosystems, but such studies are rare. In this study, we analyzed simultaneously the bacterioplankton and phytoplankton communities in three Chinese subtropical reservoirs and compared the response of these two components to seasonal environmental changes. Time-lag analysis indicated that the temporal community dynamics of both bacterioplankton and phytoplankton showed significant directional changes, and variance partitioning suggested that the major reason was the gradual improvement of reservoir water quality from middle eutrophic to oligo-mesotrophic levels during the course of our study. In addition, we found a higher level of temporal stability or stochasticity in the bacterioplankton community than in the phytoplankton community. Potential explanations are that traits associated with bacteria, such as high abundance, widespread dispersal, potential for rapid growth rates, and rapid evolutionary adaptation, may underlie the different stability or stochasticity of bacterioplankton and phytoplankton communities to the environmental changes. In addition, the indirect response of bacterioplankton to nitrogen and phosphorus may result in the fact that environmental deterministic selection was stronger for the phytoplankton than for the bacterioplankton communities.

  18. Age differences in autobiographical memory across the adult lifespan: older adults report stronger phenomenology.

    Science.gov (United States)

    Luchetti, Martina; Sutin, Angelina R

    2018-01-01

    As an individual's life story evolves across adulthood, the subjective experience (phenomenology) of autobiographical memory likely changes. In addition to age at retrieval, both the recency of the memory and the age when a memory is formed may be particularly important to its phenomenology. The present work examines the effect of three temporal factors on phenomenology ratings: (a) age of the participant, (b) age at the event reported in the memory, and (c) memory age (recency). A large sample of Americans (N = 1120), stratified by chronological age, recalled and rated two meaningful memories, a Turning Point and an Early Childhood Memory. Ratings of phenomenology (e.g., vividness of turning points) were higher among older adults compared to younger adults. Memories of events from the reminiscence bump were more positive in valence than events from other time periods but did not differ on other phenomenological dimensions; recent memories had stronger phenomenology than remote memories. In contrast to phenomenology, narrative content was generally unrelated to participant age, age at the event, or memory age. Overall, the findings indicate age-related differences in how meaningful memories are re-experienced.

  19. Speed versus endurance tradeoff in plants: Leaves with higher photosynthetic rates show stronger seasonal declines.

    Science.gov (United States)

    Zhang, Yong-Jiang; Sack, Lawren; Cao, Kun-Fang; Wei, Xue-Mei; Li, Nan

    2017-02-10

    We tested for a tradeoff across species between plant maximum photosynthetic rate and the ability to maintain photosynthesis under adverse conditions in the unfavorable season. Such a trade-off would be consistent with the observed trade-off between maximum speed and endurance in athletes and some animals that has been explained by cost-benefit theory. This trend would have importance for the general understanding of leaf design, and would simplify models of annual leaf carbon relations. We tested for such a trade-off using a database analysis across vascular plants and using an experimental approach for 29 cycad species, representing an ancient plant lineage with diversified evergreen leaves. In both tests, a higher photosynthetic rate per mass or per area in the favorable season was associated with a stronger absolute or percent decline in the unfavorable season. We resolved a possible mechanism based on biomechanics and nitrogen allocation; cycads with high leaf toughness (leaf mass per area) and higher investment in leaf construction than in physiological function (C/N ratio) tended to have lower warm season photosynthesis but less depression in the cool season. We propose that this trade-off, consistent with cost-benefit theory, represents a significant physio-phenological constraint on the diversity and seasonal dynamics of photosynthetic rate.

  20. A stronger necessary condition for the multistationarity of chemical reaction networks.

    Science.gov (United States)

    Soliman, Sylvain

    2013-11-01

    Biochemical reaction networks grow bigger and bigger, fed by the high-throughput data provided by biologists and bred in open repositories of models allowing merging and evolution. Nevertheless, since the available data is still very far from permitting the identification of the increasing number of kinetic parameters of such models, the necessity of structural analyses for describing the dynamics of chemical networks appears stronger every day. Using the structural information, notably from the stoichiometric matrix, of a biochemical reaction system, we state a more strict version of the famous Thomas' necessary condition for multistationarity. In particular, the obvious cases where Thomas' condition was trivially satisfied, mutual inhibition due to a multimolecular reaction and mutual activation due to a reversible reaction, can now easily be ruled out. This more strict condition shall not be seen as some version of Thomas' circuit functionality for the continuous case but rather as related and complementary to the whole domain of the structural analysis of (bio)chemical reaction systems, as pioneered by the chemical reaction network theory.

  1. Plant Identity Exerts Stronger Effect than Fertilization on Soil Arbuscular Mycorrhizal Fungi in a Sown Pasture.

    Science.gov (United States)

    Zheng, Yong; Chen, Liang; Luo, Cai-Yun; Zhang, Zhen-Hua; Wang, Shi-Ping; Guo, Liang-Dong

    2016-10-01

    Arbuscular mycorrhizal (AM) fungi play key roles in plant nutrition and plant productivity. AM fungal responses to either plant identity or fertilization have been investigated. However, the interactive effects of different plant species and fertilizer types on these symbiotic fungi remain poorly understood. We evaluated the effects of the factorial combinations of plant identity (grasses Avena sativa and Elymus nutans and legume Vicia sativa) and fertilization (urea and sheep manure) on AM fungi following 2-year monocultures in a sown pasture field study. AM fungal extraradical hyphal density was significantly higher in E. nutans than that in A. sativa and V. sativa in the unfertilized control and was significantly increased by urea and manure in A. sativa and by manure only in E. nutans, but not by either fertilizers in V. sativa. AM fungal spore density was not significantly affected by plant identity or fertilization. Forty-eight operational taxonomic units (OTUs) of AM fungi were obtained through 454 pyrosequencing of 18S rDNA. The OTU richness and Shannon diversity index of AM fungi were significantly higher in E. nutans than those in V. sativa and/or A. sativa, but not significantly affected by any fertilizer in all of the three plant species. AM fungal community composition was significantly structured directly by plant identity only and indirectly by both urea addition and plant identity through soil total nitrogen content. Our findings highlight that plant identity has stronger influence than fertilization on belowground AM fungal community in this converted pastureland from an alpine meadow.

  2. Harmful drinking after job loss: a stronger association during the post-2008 economic crisis?

    Science.gov (United States)

    de Goeij, Moniek C M; Bruggink, Jan-Willem; Otten, Ferdy; Kunst, Anton E

    2017-06-01

    This study investigated, among the Dutch working population, whether job loss during the post-2008 economic crisis is associated with harmful drinking and whether this association is stronger than before the crisis. Repeated cross-sectional data from the Dutch Health Interview Survey 2004-2013 were used to define episodic drinking (≥6 glasses on 1 day ≥1/week) and chronic drinking (≥14 glasses/week for women and ≥21 for men). These data were linked to longitudinal data from tax registries, to measure the experience and duration of job loss during a 5-year working history. Before the crisis, job loss experience and duration were not associated with harmful drinking. During the crisis, job loss for more than 6 months was associated with episodic drinking [OR 1.40 (95% CI 1.01; 1.94)], while current job loss was associated with chronic drinking [OR 1.43 (95% CI 1.03; 1.98)]. These associations were most clear in men and different between the pre-crisis and crisis period (p interaction = 0.023 and 0.035, respectively). The results suggest that economic crises strengthen the potential impact of job loss on harmful drinking, predominately among men.

  3. Why Selection Might Be Stronger When Populations Are Small: Intron Size and Density Predict within and between-Species Usage of Exonic Splice Associated cis-Motifs

    Science.gov (United States)

    Wu, XianMing; Hurst, Laurence D.

    2015-01-01

    The nearly neutral theory predicts that small effective population size provides the conditions for weakened selection. This is postulated to explain why our genome is more “bloated” than that of, for example, yeast, ours having large introns and large intergene spacer. If a bloated genome is also an error prone genome might it, however, be the case that selection for error-mitigating properties is stronger in our genome? We examine this notion using splicing as an exemplar, not least because large introns can predispose to noisy splicing. We thus ask whether, owing to genomic decay, selection for splice error-control mechanisms is stronger, not weaker, in species with large introns and small populations. In humans much information defining splice sites is in cis-exonic motifs, most notably exonic splice enhancers (ESEs). These act as splice-error control elements. Here then we ask whether within and between-species intron size is a predictor of the commonality of exonic cis-splicing motifs. We show that, as predicted, the proportion of synonymous sites that are ESE-associated and under selection in humans is weakly positively correlated with the size of the flanking intron. In a phylogenetically controlled framework, we observe, also as expected, that mean intron size is both predicted by Ne.μ and is a good predictor of cis-motif usage across species, this usage coevolving with splice site definition. Unexpectedly, however, across taxa intron density is a better predictor of cis-motif usage than intron size. We propose that selection for splice-related motifs is driven by a need to avoid decoy splice sites that will be more common in genes with many and large introns. That intron number and density predict ESE usage within human genes is consistent with this, as is the finding of intragenic heterogeneity in ESE density. As intronic content and splice site usage across species is also well predicted by Ne.μ, the result also suggests an unusual circumstance in

  4. Nucleation rate of the quark-gluon plasma droplet at finite quark ...

    Indian Academy of Sciences (India)

    evolution of the system [4]. Another important issue is that while calculating the nucle- ation rate of the QGP droplet, it is necessary to consider the finite size of hadrons [5]. These corrections are properly taken care of in the workout of this paper. Now, in the framework of the homogeneous nucleation theory, the nucleation ...

  5. Forward flux sampling calculation of homogeneous nucleation rates from aqueous NaCl solutions

    Science.gov (United States)

    Jiang, Hao; Haji-Akbari, Amir; Debenedetti, Pablo G.; Panagiotopoulos, Athanassios Z.

    2018-01-01

    We used molecular dynamics simulations and the path sampling technique known as forward flux sampling to study homogeneous nucleation of NaCl crystals from supersaturated aqueous solutions at 298 K and 1 bar. Nucleation rates were obtained for a range of salt concentrations for the Joung-Cheatham NaCl force field combined with the Extended Simple Point Charge (SPC/E) water model. The calculated nucleation rates are significantly lower than the available experimental measurements. The estimates for the nucleation rates in this work do not rely on classical nucleation theory, but the pathways observed in the simulations suggest that the nucleation process is better described by classical nucleation theory than an alternative interpretation based on Ostwald's step rule, in contrast to some prior simulations of related models. In addition to the size of NaCl nucleus, we find that the crystallinity of a nascent cluster plays an important role in the nucleation process. Nuclei with high crystallinity were found to have higher growth probability and longer lifetimes, possibly because they are less exposed to hydration water.

  6. Relative Role of Gas Generation and Displacement Rates in Cavity Nucleation and Growth

    DEFF Research Database (Denmark)

    Singh, Bachu Narain; Foreman, A. J E.

    1984-01-01

    Problems of helium diffusion and clustering during irradiation are analysed. Using the “homogeneous” nucleation theory , the effect of damage rate on cavity density is calculated for different gas generation to damage rate ratios. The influence of gas mobility on cavity nucleation has been...

  7. Heat-flux enhancement by vapour-bubble nucleation in Rayleigh-Bénard turbulence

    NARCIS (Netherlands)

    Narezo Guzman, Daniela; Xie, Yanbo; Chen, S.; Fernandez Rivas, David; Sun, Chao; Lohse, Detlef; Ahlers, Günter

    2016-01-01

    We report on the enhancement of turbulent convective heat transport due to vapour-bubble nucleation at the bottom plate of a cylindrical Rayleigh–Bénard sample (aspect ratio 1.00, diameter 8.8 cm) filled with liquid. Microcavities acted as nucleation sites, allowing for well-controlled bubble

  8. Effect of oxygen on the bias-enhanced nucleation of diamond on silicon

    DEFF Research Database (Denmark)

    Schreck, M.; Christensen, Carsten; Stritzker, B.

    1999-01-01

    The influence of traces of oxygen in the process gas on the bias-enhanced nucleation (BEN) of diamond on silicon has been studied in the present work. CO2 in concentrations ranging from 0 to 3000 ppm was added during the nucleation procedure at U-bias = -200 V in microwave plasma chemical vapour...

  9. Parametrization of the homogeneous ice nucleation rate for the numerical simulation of multiphase flow

    Czech Academy of Sciences Publication Activity Database

    Němec, Tomáš; Eisenschmidt, K.; Rauschenberger, P.; Weigand, B.

    2012-01-01

    Roč. 12, č. 1 (2012), s. 533-534 ISSN 1617-7061 R&D Projects: GA ČR GAP101/10/1819 Institutional research plan: CEZ:AV0Z20760514 Keywords : ice nucleation * ice-water surface energy * classical nucleation theory Subject RIV: BJ - Thermodynamics http://onlinelibrary.wiley.com/doi/10.1002/pamm.201210255/abstract

  10. Enhancement of the droplet nucleation in a dense supersaturated Lennard-Jones vapor

    Energy Technology Data Exchange (ETDEWEB)

    Zhukhovitskii, D. I., E-mail: dmr@ihed.ras.ru [Joint Institute of High Temperatures, Russian Academy of Sciences, Izhorskaya 13, Bd. 2, 125412 Moscow (Russian Federation)

    2016-05-14

    The vapor–liquid nucleation in a dense Lennard-Jones system is studied analytically and numerically. A solution of the nucleation kinetic equations, which includes the elementary processes of condensation/evaporation involving the lightest clusters, is obtained, and the nucleation rate is calculated. Based on the equation of state for the cluster vapor, the pre-exponential factor is obtained. The latter diverges as a spinodal is reached, which results in the nucleation enhancement. The work of critical cluster formation is calculated using the previously developed two-parameter model (TPM) of small clusters. A simple expression for the nucleation rate is deduced and it is shown that the work of cluster formation is reduced for a dense vapor. This results in the nucleation enhancement as well. To verify the TPM, a simulation is performed that mimics a steady-state nucleation experiments in the thermal diffusion cloud chamber. The nucleating vapor with and without a carrier gas is simulated using two different thermostats for the monomers and clusters. The TPM proves to match the simulation results of this work and of other studies.

  11. Control of Reaction Surface in Low Temperature CVD to Enhance Nucleation and Conformal Coverage

    Science.gov (United States)

    Kumar, Navneet

    2009-01-01

    The Holy Grail in CVD community is to find precursors that can afford the following: good nucleation on a desired substrate and conformal deposition in high AR features. Good nucleation is not only necessary for getting ultra-thin films at low thicknesses; it also offers films that are smooth at higher thickness values. On the other hand,…

  12. Effect of Controlled Ice Nucleation on Stability of Lactate Dehydrogenase During Freeze-Drying.

    Science.gov (United States)

    Fang, Rui; Tanaka, Kazunari; Mudhivarthi, Vamsi; Bogner, Robin H; Pikal, Michael J

    2018-03-01

    Several controlled ice nucleation techniques have been developed to increase the efficiency of the freeze-drying process as well as to improve the quality of pharmaceutical products. Owing to the reduction in ice surface area, these techniques have the potential to reduce the degradation of proteins labile during freezing. The objective of this study was to evaluate the effect of ice nucleation temperature on the in-process stability of lactate dehydrogenase (LDH). LDH in potassium phosphate buffer was nucleated at -4°C, -8°C, and -12°C using ControLyo™ or allowed to nucleate spontaneously. Both the enzymatic activity and tetramer recovery after freeze-thawing linearly correlated with product ice nucleation temperature (n = 24). Controlled nucleation also significantly improved batch homogeneity as reflected by reduced inter-vial variation in activity and tetramer recovery. With the correlation established in the laboratory, the degradation of protein in manufacturing arising from ice nucleation temperature differences can be quantitatively predicted. The results show that controlled nucleation reduced the degradation of LDH during the freezing process, but this does not necessarily translate to vastly superior stability during the entire freeze-drying process. The capability of improving batch homogeneity provides potential advantages in scaling-up from lab to manufacturing scale. Copyright © 2018 American Pharmacists Association®. Published by Elsevier Inc. All rights reserved.

  13. Dislocation nucleation and vacancy formation during high-speed deformation of fcc metals

    DEFF Research Database (Denmark)

    Schiøtz, J.; Leffers, T.; Singh, B.N.

    2001-01-01

    . The dislocations are nucleated as single Shockley partials. The large stresses required before dislocations are nucleated result in a very high dislocation density, and therefore in many inelastic interactions between the dislocations. These interactions create vacancies and a very large vacancy concentration...

  14. Nucleation rate of the quark-gluon plasma droplet at finite quark ...

    Indian Academy of Sciences (India)

    The nucleation rate of quark-gluon plasma (QGP) droplet is computed at finite quark chemical potential. In the course of computing the nucleation rate, the finite size effects of the QGP droplet are taken into account. We consider the phenomenological flow parameter of quarks and gluons, which is dependent on quark ...

  15. Nucleation and evaporation of domains due to electric field at room ...

    Indian Academy of Sciences (India)

    A study of nucleation and evaporation of 90° and 180° domains by external direct current (dc) electric field at room temperature in barium titanate single crystals has been carried out using reflecting microscope. It was observed that both the 90° and 180° domains were nucleated at some sites, while evaporated at some ...

  16. Investigating Freezing Point Depression and Cirrus Cloud Nucleation Mechanisms Using a Differential Scanning Calorimeter

    Science.gov (United States)

    Bodzewski, Kentaro Y.; Caylor, Ryan L.; Comstock, Ashley M.; Hadley, Austin T.; Imholt, Felisha M.; Kirwan, Kory D.; Oyama, Kira S.; Wise, Matthew E.

    2016-01-01

    A differential scanning calorimeter was used to study homogeneous nucleation of ice from micron-sized aqueous ammonium sulfate aerosol particles. It is important to understand the conditions at which these particles nucleate ice because of their connection to cirrus cloud formation. Additionally, the concept of freezing point depression, a topic…

  17. Improved success of sparse matrix protein crystallization screening with heterogeneous nucleating agents.

    Directory of Open Access Journals (Sweden)

    Anil S Thakur

    2007-10-01

    Full Text Available Crystallization is a major bottleneck in the process of macromolecular structure determination by X-ray crystallography. Successful crystallization requires the formation of nuclei and their subsequent growth to crystals of suitable size. Crystal growth generally occurs spontaneously in a supersaturated solution as a result of homogenous nucleation. However, in a typical sparse matrix screening experiment, precipitant and protein concentration are not sampled extensively, and supersaturation conditions suitable for nucleation are often missed.We tested the effect of nine potential heterogenous nucleating agents on crystallization of ten test proteins in a sparse matrix screen. Several nucleating agents induced crystal formation under conditions where no crystallization occurred in the absence of the nucleating agent. Four nucleating agents: dried seaweed; horse hair; cellulose and hydroxyapatite, had a considerable overall positive effect on crystallization success. This effect was further enhanced when these nucleating agents were used in combination with each other.Our results suggest that the addition of heterogeneous nucleating agents increases the chances of crystal formation when using sparse matrix screens.

  18. Nucleation of iron nitrides during gaseous nitriding of iron; the effect of a preoxidation treatment

    DEFF Research Database (Denmark)

    Friehling, Peter B.; Poulsen, Finn Willy; Somers, Marcel A.J.

    2001-01-01

    grains. On prolonged nitriding, immediate nucleation at the surface of iron grains becomes possible. Calculated incubation times for the nucleation of gamma'-Fe4N1-x during nitriding are generally longer than those observed experimentally in the present work. The incubation time is reduced dramatically...

  19. An inverse modeling procedure to determine particle growth and nucleation rates from measured aerosol size distributions

    Directory of Open Access Journals (Sweden)

    B. Verheggen

    2006-01-01

    Full Text Available Classical nucleation theory is unable to explain the ubiquity of nucleation events observed in the atmosphere. This shows a need for an empirical determination of the nucleation rate. Here we present a novel inverse modeling procedure to determine particle nucleation and growth rates based on consecutive measurements of the aerosol size distribution. The particle growth rate is determined by regression analysis of the measured change in the aerosol size distribution over time, taking into account the effects of processes such as coagulation, deposition and/or dilution. This allows the growth rate to be determined with a higher time-resolution than can be deduced from inspecting contour plots ('banana-plots''. Knowing the growth rate as a function of time enables the evaluation of the time of nucleation of measured particles of a certain size. The nucleation rate is then obtained by integrating the particle losses from time of measurement to time of nucleation. The regression analysis can also be used to determine or verify the optimum value of other parameters of interest, such as the wall loss or coagulation rate constants. As an example, the method is applied to smog chamber measurements. This program offers a powerful interpretive tool to study empirical aerosol population dynamics in general, and nucleation and growth in particular.

  20. Genetic Algorithms and Nucleation in VIH-AIDS transition.

    Science.gov (United States)

    Barranon, Armando

    2003-03-01

    VIH to AIDS transition has been modeled via a genetic algorithm that uses boom-boom principle and where population evolution is simulated with a cellular automaton based on SIR model. VIH to AIDS transition is signed by nucleation of infected cells and low probability of infection are obtained for different mutation rates in agreement with clinical results. A power law is obtained with a critical exponent close to the critical exponent of cubic, spherical percolation, colossal magnetic resonance, Ising Model and liquid-gas phase transition in heavy ion collisions. Computations were carried out at UAM-A Supercomputing Lab and author acknowledges financial support from Division of CBI at UAM-A.

  1. Growth Kinetics of the Homogeneously Nucleated Water Droplets: Simulation Results

    International Nuclear Information System (INIS)

    Mokshin, Anatolii V; Galimzyanov, Bulat N

    2012-01-01

    The growth of homogeneously nucleated droplets in water vapor at the fixed temperatures T = 273, 283, 293, 303, 313, 323, 333, 343, 353, 363 and 373 K (the pressure p = 1 atm.) is investigated on the basis of the coarse-grained molecular dynamics simulation data with the mW-model. The treatment of simulation results is performed by means of the statistical method within the mean-first-passage-time approach, where the reaction coordinate is associated with the largest droplet size. It is found that the water droplet growth is characterized by the next features: (i) the rescaled growth law is unified at all the considered temperatures and (ii) the droplet growth evolves with acceleration and follows the power law.

  2. Carbides nucleation and growth processes in austenitic stainless steel

    International Nuclear Information System (INIS)

    Calvo, F.A.; Otero, E.; Ballester, A.; Leiro, J.

    1986-01-01

    The nucleation and growth process at some carbides with high chromium content inside an austenitic matrix corresponding to a 304 type inoxidable steel are studied. The precipitate growth seems to be controlled, at least at temperatures above 973 K, by the diffusion of carbon atoms from the matrix phase to the beginning of the second phase which is normally placed in the grain boundaries. A relationship between the percentage of precipitated carbide, as a function of the carbon excess in the saturated austenitic solid solution, and the time employed for each work temperature is established. From these data, some aspects relating to the morphologie, the carbide localization and the influence of these factors in the steel sensibilization to the grain corrosion, are interpreted. (author)

  3. Evolution of particle composition in CLOUD nucleation experiments

    CERN Document Server

    Keskinen, H; Joutsensaari, J; Tsagkogeorgas, G; Duplissy, J; Schobesberger, S; Gysel, M; Riccobono, F; Bianchi, F; Yli-Juuti, T; Lehtipalo, K; Rondo, L; Breitenlechner, M; Kupc, A; Almeida, J; Amorim, A; Dunne, E M; Downard, A J; Ehrhart, S; Franchin, A; Kajos, M K; Kirkby, J; Kurten, A; Nieminen, T; Makhmutov, V; Mathot, S; Miettinen, P; Onnela, A; Petaja, T; Praplan, A; Santos, F D; Schallhart, S; Sipila, M; Stozhkov, Y; Tome, A; Vaattovaara, P; Wimmer, D; Prevot, A; Dommen, J; Donahue, N M; Flagan, R C; Weingartner, E; Viisanen, Y; Riipinen, I; Hansel, A; Curtius, J; Kulmala, M; Worsnop, D R; Baltensperger, U; Wex, H; Stratmann, F; Laaksonen, A; Slowik, J G

    2013-01-01

    Sulphuric acid, ammonia, amines, and oxidised organics play a crucial role in nanoparticle formation in the atmosphere. In this study, we investigate the composition of nucleated nanoparticles formed from these compounds in the CLOUD (Cosmics Leaving Outdoor Droplets) chamber experiments at CERN (Centre europ ́ een pour la recherche nucl ́ eaire). The investigation was carried out via analysis of the particle hygroscopicity, ethanol affinity, oxidation state, and ion composition. Hygroscopicity was studied by a hygroscopic tandem differential mobility analyser and a cloud condensation nuclei counter, ethanol affinity by an organic differential mobility analyser and particle oxidation level by a high-resolution time-of-flight aerosol mass spectrometer. The ion composition was studied by an atmospheric pressure interface time-of-flight mass spectrometer. The volume fraction of the organics in the particles during theirgrowth from sizes of a few nanometers to tens of nanometers was derived from measured hygros...

  4. Export of ice nucleating particles from a watershed

    Science.gov (United States)

    Larsen, Jarl Are; Conen, Franz; Alewell, Christine

    2017-08-01

    Ice nucleating particles (INP) active at a few degrees below 0°C are produced by a range of organisms and released into the environment. They may affect cloud properties and precipitation when becoming airborne. So far, our knowledge about sources of biological INP is based on grab samples of vegetation, soil or water studied in the laboratory. By combining measurements of INP concentrations in river water with river water discharge rates over the course of 16 months, we obtained a lower limit for the production rate of INP in a watershed covering most of Switzerland (4 × 105 INP-8 m-2 d-1). Coincidentally, we found that INP-8 are likely to retain their potential for catalysing ice formation in the natural environment for at least several months before they are mobilized by an intensive rainfall, washed into the river and exported from the watershed.

  5. The acceleration of solid particles subjected to cavitation nucleation

    DEFF Research Database (Denmark)

    Borkent, B.M.; Arora, M.; Ohl, C.-D.

    2008-01-01

    The cavity -particle dynamics at cavitation inception on the surface of spherical particles suspended in water and exposed to a strong tensile stress wave is experimentally studied with high-speed photography. Particles, which serve as nucleation sites for cavitation bubbles, are set into a fast...... translatory motion during the explosive growth of the cavity. They reach velocities of ~40 ms-1 and even higher. When the volume growth of the cavity slows down, the particle detaches from the cavity through a process of neck-breaking, and the particle is shot away. The experimental observations are simulated...... with (i) a spherical cavity model and (ii) with an axisymmetric boundary element method (BEM). The input for both models is a pressure pulse, which is obtained from the observed radial cavity dynamics during an individual experiment. The model then allows us to calculate the resulting particle trajectory...

  6. Surface wettability and subcooling on nucleate pool boiling heat transfer

    Science.gov (United States)

    Suroto, Bambang Joko; Kohno, Masamichi; Takata, Yasuyuki

    2018-02-01

    The effect of varying surface wettabilities and subcooling on nucleate pool boiling heat transfer at intermediate heat flux has been examined and investigated. The experiments were performed using pure water as the working fluid and subcooling ranging from 0, 5 and 10 K, respectively. The three types of heat transfer block were used that are bare surface/hydrophilic (polished copper), superhydrophilic/TiO2-coated on copper and hydrophobic/PTFE surface. The experimental results will be examined by the existing model. The results show that the heat transfer performance of surfaces with PTFE coating is better at low heat flux. While for an intermediate heat flux, superhydrophilic surface (TiO2) is superior compared to hydrophilic and hydrophobic surfaces. It is observed that the heat transfer performance is decreasing when the sub cooling degree is increased.

  7. Sources of organic ice nucleating particles in soils

    Directory of Open Access Journals (Sweden)

    T. C. J. Hill

    2016-06-01

    Full Text Available Soil organic matter (SOM may be a significant source of atmospheric ice nucleating particles (INPs, especially of those active  >  −15 °C. However, due to both a lack of investigations and the complexity of the SOM itself, the identities of these INPs remain unknown. To more comprehensively characterize organic INPs we tested locally representative soils in Wyoming and Colorado for total organic INPs, INPs in the heat-labile fraction, ice nucleating (IN bacteria, IN fungi, IN fulvic and humic acids, IN plant tissue, and ice nucleation by monolayers of aliphatic alcohols. All soils contained  ≈  106 to  ≈  5 × 107 INPs g−1 dry soil active at −10 °C. Removal of SOM with H2O2 removed  ≥  99 % of INPs active  >  −18 °C (the limit of testing, while heating of soil suspensions to 105 °C showed that labile INPs increasingly predominated  >  −12 °C and comprised  ≥  90 % of INPs active  >  −9 °C. Papain protease, which inactivates IN proteins produced by the fungus Mortierella alpina, common in the region's soils, lowered INPs active at  ≥  −11 °C by  ≥  75 % in two arable soils and in sagebrush shrubland soil. By contrast, lysozyme, which digests bacterial cell walls, only reduced INPs active at  ≥  −7.5 or  ≥  −6 °C, depending on the soil. The known IN bacteria were not detected in any soil, using PCR for the ina gene that codes for the active protein. We directly isolated and photographed two INPs from soil, using repeated cycles of freeze testing and subdivision of droplets of dilute soil suspensions; they were complex and apparently organic entities. Ice nucleation activity was not affected by digestion of Proteinase K-susceptible proteins or the removal of entities composed of fulvic and humic acids, sterols, or aliphatic alcohol monolayers. Organic INPs active colder than −10 to −12 °C were

  8. Nucleation and diffusion-controlled growth of electroactive centers

    Energy Technology Data Exchange (ETDEWEB)

    Palomar-Pardave, M. [Universidad Autonoma Metropolitana-Azcapotzalco, Departamento de Materiales, C.P. 02200 Mexico, D.F. (Mexico)]. E-mail: mepp@correo.azc.uam.mx; Scharifker, B.R. [Universidad Simon Bolivar, Departamento de Quimica, Apartado 89000, Caracas 1080A (Venezuela); Arce, E.M. [Instituto Politecnico Nacional-ESIQIE, Departamento de Ingenieria Metalurgica, Apartado 75-876, C.P. 07300 Mexico, D.F. (Mexico); Romero-Romo, M. [Universidad Autonoma Metropolitana-Azcapotzalco, Departamento de Materiales, C.P. 02200 Mexico, D.F. (Mexico)

    2005-08-30

    A theory is presented describing, for the first time, the temporal evolution of the fractional surface area, S(t), of 3D non-interacting nuclei growing at a rate limited by diffusion of electrodepositing ions onto substrates of a different nature. Likewise, an equation has been derived describing the potentiostatic current-time transients arising from the formation and growth of such nuclei with redox reactions occurring simultaneously on their surfaces. An equation is also proposed to describe the current due to redox reactions taking place on the surface of interacting growing nuclei. The latter is used to describe the experimental current transients recorded during nucleation and growth of cobalt at applied potentials where the proton reduction reaction occurs simultaneously with the electrocrystallization process.

  9. Earthquake Nucleation on Faults With Heterogeneous Frictional Properties, Normal Stress

    Science.gov (United States)

    Ray, Sohom; Viesca, Robert C.

    2017-10-01

    We examine the development of an instability of fault slip rate. We consider a slip rate and state dependence of fault frictional strength, in which frictional properties and normal stress are functions of position. We pose the problem for a slip rate distribution that diverges quasi-statically within finite time in a self-similar fashion. Scenarios of property variations are considered and the corresponding self-similar solutions found. We focus on variations of coefficients, a and b, respectively, controlling the magnitude of a direct effect on strength due to instantaneous changes in slip rate and of strength evolution due to changes in a state variable. These results readily extend to variations in fault-normal stress, σ, or the characteristic slip distance for state evolution, Dc. We find that heterogeneous properties lead to a finite number of self-similar solutions, located about critical points of the distributions: maxima, minima, and between them. We examine the stability of these solutions and find that only a subset is asymptotically stable, occurring at just one of the critical point types. Such stability implies that during instability development, slip rate and state evolution can be attracted to develop in the manner of the self-similar solution, which is also confirmed by solutions to initial value problems for slip rate and state. A quasi-static slip rate divergence is ultimately limited by inertia, leading to the nucleation of an outward expanding dynamic rupture: asymptotic stability of self-similar solutions then implies preferential sites for earthquake nucleation, which are determined by distribution of frictional properties.

  10. Native bare zone assemblage nucleates myosin filament assembly.

    Science.gov (United States)

    Niederman, R; Peters, L K

    1982-11-15

    Native myosin filaments from rabbit psoas muscle are always 1.5 micrometer long. The regulated assembly of these filaments is generally considered to occur by an initial antiparallel and subsequent parallel aggregation of identical myosin subunits. In this schema myosin filament length is controlled by either a self-assembly or a Vernier process. We present evidence which refines these ideas. Namely, that the intact myosin bare zone assemblage nucleates myosin filament assembly. This suggestion is based on the following experimental evidence. (1) A native bare zone assemblage about 0.3 micrometer long can be formed by dialysis of native myosin filaments to either a pH 8 or a 0.2 M-KCl solution. (2) Upon dialysis back to 0.1 M-KCl, bare zone assemblages and distal myosin molecules recombine to form 1.5 micrometer long bipolar filaments. (3) The bare zone assemblage can be separated from the distal myosin molecules by column chromatography in 0.2 M-KCl. Upon dialysis of the fractionated subsets back to 0.1 M-KCl, the bare zone assemblage retains its length of about 0.3 micrometer. However, the distal molecules reassemble to form filaments about 5 micrometers long. (4) Filaments are formed from mixes of the isolated subsets. The lengths of these filaments vary with the amount of distal myosin present. (5) When native filaments, isolated bare zone assemblages or distal myosin molecules are moved sequentially to 0.6 M-KCl and then to 0.1 M-KCl, the final filament lengths are all about 5 micrometers. The capacity of the bare zone assemblage to nucleate filament assembly may be due to the bare zone myosin molecules, the associated M band components or both.

  11. Assessment of Nucleation Site Density Models for CFD Simulations of Subcooled Flow Boiling

    International Nuclear Information System (INIS)

    Hoang, N. H.; Chu, I. C.; Euh, D. J.; Song, C. H.

    2015-01-01

    The framework of a CFD simulation of subcooled flow boiling basically includes a block of wall boiling models communicating with governing equations of a two-phase flow via parameters like temperature, rate of phasic change, etc. In the block of wall boiling models, a heat flux partitioning model, which describes how the heat is taken away from a heated surface, is combined with models quantifying boiling parameters, i.e. nucleation site density, and bubble departure diameter and frequency. It is realized that the nucleation site density is an important parameter for predicting the subcooled flow boiling. The number of nucleation sites per unit area decides the influence region of each heat transfer mechanism. The variation of the nucleation site density will mutually change the dynamics of vapor bubbles formed at these sites. In addition, the nucleation site density is needed as one initial and boundary condition to solve the interfacial area transport equation. A lot of effort has been devoted to mathematically formulate the nucleation site density. As a consequence, numerous correlations of the nucleation site density are available in the literature. These correlations are commonly quite different in their mathematical form as well as application range. Some correlations of the nucleation site density have been applied successfully to CFD simulations of several specific subcooled boiling flows, but in combination with different correlations of the bubble departure diameter and frequency. In addition, the values of the nucleation site density, and bubble departure diameter and frequency obtained from simulations for a same problem are relatively different, depending on which models are used, even when global characteristics, e.g., void fraction and mean bubble diameter, agree well with experimental values. It is realized that having a good CFD simulations of the subcooled flow boiling requires a detailed validations of all the models used. Owing to the importance

  12. New species of ice nucleating fungi in soil and air

    Science.gov (United States)

    Fröhlich-Nowoisky, Janine; Hill, Thomas C. J.; Pummer, Bernhard G.; Franc, Gray D.; Pöschl, Ulrich

    2014-05-01

    Primary biological aerosol particles (PBAP) are ubiquitous in the atmosphere (1,2). Several types of PBAP have been identified as ice nuclei (IN) that can initiate the formation of ice at relatively high temperatures (3, 4). The best-known biological IN are common plant-associated bacteria. The IN activity of these bacteria is due to a surface protein on the outer cell membrane that catalyses ice formation, for which the corresponding gene has been identified and detected by DNA analysis (3). Fungal spores or hyphae can also act as IN, but the biological structures responsible for their IN activity have not yet been elucidated. Furthermore, the abundance, diversity, sources, seasonality, properties, and effects of fungal IN in the atmosphere have neither been characterized nor quantified. Recent studies have shown that airborne fungi are highly diverse (1), and that atmospheric transport leads to efficient exchange of species among different ecosystems (5, 6). The results presented in Fröhlich-Nowoisky et al. 2012 (7) clearly demonstrate the presence of geographic boundaries in the global distribution of microbial taxa in air, and indicate that regional differences may be important for the effects of microorganisms on climate and public health. DNA analyses of aerosol samples collected during rain events showed higher diversity and frequency of occurrence for fungi belonging to the Sordariomycetes, than samples that were collected under dry conditions (8). Sordariomycetes is the class that comprises known ice nucleation active species (Fusarium spp.). By determination of freezing ability of fungal colonies isolated from air samples two species of ice nucleation active fungi that were not previously known as biological ice nucleators were found. By DNA-analysis they were identified as Isaria farinosa and Acremonium implicatum. Both fungi belong to the phylum Ascomycota, produce fluorescent spores in the range of 1-4 µm in diameter, and induced freezing at -4 and

  13. Insights Regarding Ice Nucleating Particle Measurement Capabilities from Laboratory and Field Measurements During the Fifth International Ice Nucleation Workshop

    Science.gov (United States)

    DeMott, P. J.; Mohler, O.; Cziczo, D. J.; Hiranuma, N.; Brooks, S. D.; Petters, M.

    2017-12-01

    Improvement in the ability to quantify the role of aerosols in primary ice formation in clouds is vital to improving prediction of natural and anthropogenic impacts on cold cloud properties and reducing uncertainties in climate predictions. A host of common and new methods for quantifying the atmospheric abundance of ice nucleating particles (INPs) have recently been developed. To realize the utility of such data for numerical model parameterization development and validation, it is important to understand similarities, differences, and biases in different methods. To achieve this goal, it is common to challenge instruments with a range of aerosol types in laboratory studies. Only a few comparisons have occurred in atmospheric situations. This presentation highlights comparisons made in laboratory and field phases of the Fifth International Ice Nucleation workshop (FIN) during 2015. The FIN-2 laboratory workshop was conducted at the AIDA facility of the Karlsruhe Institute of Technology, involving nine real-time INP instruments and several sampling methods for wet suspensions and filter collection and resuspension for INP measurements. The FIN-3 atmospheric activity was conducted at the Desert Research Institute's Storm Peak Laboratory (SPL), with a reduced set of participants. Lessons and insights were gained during analyses of data from both workshops regarding the capabilities and comparability of present ice nucleation measurement systems. The FIN-2 and FIN-3 results show typical one order of magnitude agreement within basic measurement types and overall for characterizing the concentrations (over several orders of magnitude dynamic range from -5 to -35 C) of a variety of INP types and ambient INPs active in the immersion-freezing mode. Discrepancies are least for lab sampling of natural soil particle INPs and greatest for materials with steep d[INP]/dT functions, such as K-feldspar or bacterial INPs processed warmer than -8 C. Varied reasons and implications

  14. Collaborative Research: failure of RockMasses from Nucleation and Growth of Microscopic Defects and Disorder

    Energy Technology Data Exchange (ETDEWEB)

    Klein, William [Boston Univ., MA (United States)

    2016-09-12

    Over the 21 years of funding we have pursued several projects related to earthquakes, damage and nucleation. We developed simple models of earthquake faults which we studied to understand Gutenburg-Richter scaling, foreshocks and aftershocks, the effect of spatial structure of the faults and its interaction with underlying self organization and phase transitions. In addition we studied the formation of amorphous solids via the glass transition. We have also studied nucleation with a particular concentration on transitions in systems with a spatial symmetry change. In addition we investigated the nucleation process in models that mimic rock masses. We obtained the structure of the droplet in both homogeneous and heterogeneous nucleation. We also investigated the effect of defects or asperities on the nucleation of failure in simple models of earthquake faults.

  15. Statistical simulation of small fatigue crack nucleation and coalescence in a lamellar TiAl alloy

    Science.gov (United States)

    Chan, Kwais; Wittkowsky, Bettina; Pfuff, Michael

    1999-05-01

    This article examines the possibility of fatigue failure as the result of fatigue crack nucleation and coalescence at stress ranges below the fatigue limit and the large crack threshold where fatigue cracks are expected not to grow. By representing the material as a two-dimensional array of beam elements, the nucleation of nonpropagating small cracks at various material locations is modeled via a statistical approach that considers fatigue crack nucleation by accumulation of damage at randomly distributed weak regions. Once nucleated, the fatigue cracks do not propagate but extend only by linking with fatigue cracks subsequently formed in the contiguous elements. Result of the computer simulation suggests that fatigue failure by crack nucleation and coalescence is feasible, but the cycles-to-coalescence is much longer than the cycles-to-initiation for the first crack. Implications of the results in fatigue life assessment based on the Kitagawa diagram are discussed for TiAl alloys.

  16. Cumulative distribution functions associated with bubble-nucleation processes in cavitation

    KAUST Repository

    Watanabe, Hiroshi

    2010-11-15

    Bubble-nucleation processes of a Lennard-Jones liquid are studied by molecular dynamics simulations. Waiting time, which is the lifetime of a superheated liquid, is determined for several system sizes, and the apparent finite-size effect of the nucleation rate is observed. From the cumulative distribution function of the nucleation events, the bubble-nucleation process is found to be not a simple Poisson process but a Poisson process with an additional relaxation time. The parameters of the exponential distribution associated with the process are determined by taking the relaxation time into account, and the apparent finite-size effect is removed. These results imply that the use of the arithmetic mean of the waiting time until a bubble grows to the critical size leads to an incorrect estimation of the nucleation rate. © 2010 The American Physical Society.

  17. Nucleation and Atmospheric Aerosols 17th International Conference, Galway, Ireland, 2007

    CERN Document Server

    O'Dowd, Colin D

    2007-01-01

    Atmospheric particles are ubiquitous in the atmosphere: they form the seeds for cloud droplets and they form haze layers, blocking out incoming radiation and contributing to a partial cooling of our climate. They also contribute to poor air quality and health impacts. A large fraction of aerosols are formed from nucleation processes – that is a phase transition from vapour to liquid or solid particles. Examples are the formation of stable clusters about 1 nm in size from molecular collisions and these in turn can grow into larger (100 nm or more) haze particles via condensation to the formation of ice crystals in mixed phase or cold clouds. This book brings together the leading experts from the nucleation and atmospheric aerosols research communities to present the current state-of-the-art knowledge in these related fields. Topics covered are: Nucleation Experiment & Theory, Binary, Homogeneous and Heterogeneous Nucleation, Ion & Cluster Properties During Nucleation, Aerosol Characterisation & P...

  18. Ice nucleation at the nanoscale probes no man's land of water.

    Science.gov (United States)

    Li, Tianshu; Donadio, Davide; Galli, Giulia

    2013-01-01

    At a given thermodynamic condition, nucleation events occur at a frequency that scales with the volume of the system. Therefore at the nanoscale, one may expect to obtain supercooled liquids below the bulk homogeneous nucleation temperature. Here we report direct computational evidence that in supercooled water nano-droplets ice nucleation rates are strongly size dependent and at the nanoscale they are several orders of magnitude smaller than in bulk water. Using a thermodynamic model based on classical nucleation theory, we show that the Laplace pressure is partially responsible for the suppression of ice crystallization. Our simulations show that the nucleation rates found for droplets are similar to those of liquid water subject to a pressure of the order of the Laplace pressure within droplets. Our findings aid the interpretation of molecular beam experiments and support the hypothesis of surface crystallization of ice in microscopic water droplets in clouds.

  19. Effect of daunorubicin drug with and without cimetidine on the nucleated cells of bone marrow of balb/c mouse

    Directory of Open Access Journals (Sweden)

    ali asghar Kiani

    2004-01-01

    Full Text Available Introduction: Hematopoiesis is an on going process mammalian marrow system. A few cells from the nucleated cells of bone marrow are hematopoietic cells which include primary stem cells, precursor cells and progenitor cells. Primary stem cells and progenitor cells are able to produce colonies in culture medium (CFU-C and irradiated mouse spleen (CFU-S. A hematopoietic cell is alive and active when it can produce colonies and proliferate otherwise it is practically a dead cell. These cells are subject to damage from chemical or physical agents such as chemothrapeutic drugs or ionizing radiation . Materials and Methods: In the present research 150 balb/c mice were bought from Razi institute, as well as daunorubicin, which is an important drug for treatment of acute myeloid leukemia, was used as a destructive agent for bone marrow and cimetidine was used as a protective agent for bone marrow against daunorubicin. In this research one of the methods of in vivo stem cell assay. Which is called spleen colony assay, is used. The basis of this method is injection of bone marrow hematopietic cells into irradiated mouse (Supralethal irradiation . 8 to 10 days after injecting bone marrow cells stem cells produce colonies in spleen of irradiated mouse each colony represents one primary hematopoietic cell. Findings: By the method of spleen colony assay it was shown that daunorubicin at doses of 5 to 20 mg/kg will decrease the number of colonies formed in spleen . On the other hand it was shown that cimetidine in concentration of 15 mg/kg will decrease the toxic effects of these drugs and will cause an increase in spleen colonies and relative survival of mouse bone marrow cells. Cimetidine will possibly cause its relieving effects by neutralizing histamine free radicals through decreasing the activity of cytochrome P450 and increasing glutathione and increasing glutathione activity. Conclusion: Cimetidine is able to reduce the cytolytic and cytotoxic effect of

  20. Anti-ice nucleating activity of polyphenol compounds against silver iodide.

    Science.gov (United States)

    Koyama, Toshie; Inada, Takaaki; Kuwabara, Chikako; Arakawa, Keita; Fujikawa, Seizo

    2014-10-01

    Freeze-avoiding organisms survive sub-zero temperatures without freezing in several ways, such as removal of ice nucleating agents (INAs), production of polyols, and dehydration. Another way is production of anti-ice nucleating agents (anti-INAs), such as has been reported for several antifreeze proteins (AFPs) and polyphenols, that inhibit ice nucleation by inactivating INAs. In this study, the anti-ice nucleating activity of five polyphenol compounds, including flavonoid and tannin compounds of both biological and synthetic origin, against silver iodide (AgI) was examined by measuring the ice nucleation temperature in emulsified polyphenol solutions containing AgI particles. The emulsified solutions eliminated the influence of contamination by unidentified INAs, thus enabling examination of the anti-ice nucleating activity of the polyphenols against AgI alone. Results showed that all five polyphenol compounds used here have anti-ice nucleating activities that are unique compared with other known anti-INAs, such as fish AFPs (type I and III) and synthetic polymers (poly(vinyl alcohol), poly(vinylpyrrolidone) and poly(ethylene glycol)). All five polyphenols completely inactivated the ice nucleating activity of AgI even at relatively low temperatures, and the first ice nucleation event was observed at temperatures between -14.1 and -19.4°C, compared with between -8.6 and -11.8°C for the fish AFPs and three synthetic polymers. These anti-ice nucleating activities of the polyphenols at such low temperatures are promising properties for practical applications where freezing should be prevented. Copyright © 2014 Elsevier Inc. All rights reserved.

  1. Microbial ice nucleators scavenged from the atmosphere during simulated rain events

    Science.gov (United States)

    Hanlon, Regina; Powers, Craig; Failor, Kevin; Monteil, Caroline L.; Vinatzer, Boris A.; Schmale, David G.

    2017-08-01

    Rain and snow collected at ground level have been found to contain biological ice nucleators. These ice nucleators have been proposed to have originated in clouds, where they may have participated in the formation of precipitation via ice phase nucleation. We conducted a series of field experiments to test the hypothesis that at least some of the microbial ice nucleators (prokaryotes and eukaryotes) present in rain may not originate in clouds but instead be scavenged from the lower atmosphere by rainfall. Thirty-three simulated rain events were conducted over four months off the side of the Smart Road Bridge in Blacksburg, VA, USA. In each event, sterile water was dispensed over the side of the bridge and recovered in sterile containers in an open fallow agricultural field below (a distance of ∼55 m). Microbes scavenged from the simulated rain events were cultured and their ice nucleation activity was examined. Putative microbial ice nucleators were cultured from 94% (31/33) of the simulated rain events, and represented 1.5% (121/8331) of the total colonies assayed. Putative ice nucleators were subjected to additional droplet freezing assays, and those confirmed through these repeated assays represented 0.4% (34/8331) of the total. Mean CFUs scavenged by simulated rain ranged from 2 to 267 CFUs/mL. Scavenged ice nucleators belong to a number of taxa including the bacterial genera Pseudomonas, Pantoea, and Xanthomonas, and the fungal genera Fusarium, Humicola, and Mortierella. An ice-nucleating strain of the fungal genus Penicillium was also recovered from a volumetric air sampler at the study site. This work expands our knowledge of the scavenging properties of rainfall, and suggests that at least some ice nucleators in natural precipitation events may have been scrubbed from the atmosphere during rainfall, and thus are not likely to be involved in precipitation.

  2. Implicit and Explicit Gender Beliefs in Spatial Ability: Stronger Stereotyping in Boys than Girls

    Directory of Open Access Journals (Sweden)

    Karin Vander Heyden

    2016-07-01

    Full Text Available Sex differences in spatial ability are a seriously debated topic, given the importance of spatial ability for success in the fields of science, technology, engineering and mathematics (STEM and girls’ underrepresentation in these domains. In the current study we investigated the presence of stereotypic gender beliefs on spatial ability (i.e., ‘spatial ability is for boys’ in 10- and 12-year-old children. We used both an explicit measure (i.e., a self-report questionnaire and an implicit measure (i.e., a child IAT. Results of the explicit measure showed that both sexes associated spatial ability with boys, with boys holding more male stereotyped attitudes than girls. On the implicit measure, boys associated spatial ability with boys, while girls were gender-neutral. In addition, we examined the effects of gender beliefs on spatial performance, by experimentally activating gender beliefs within a pretest – instruction – posttest design. We compared three types of instruction: boys are better, girls are better, and no sex differences. No effects of these gender belief instructions were found on children’s spatial test performance (i.e., mental rotation and paper folding. The finding that children of this age already have stereotypic beliefs about the spatial capacities of their own sex is important, as these beliefs may influence children’s choices for spatial leisure activities and educational tracks in the STEM domain.

  3. Implicit and Explicit Gender Beliefs in Spatial Ability: Stronger Stereotyping in Boys than Girls

    Science.gov (United States)

    Vander Heyden, Karin M.; van Atteveldt, Nienke M.; Huizinga, Mariette; Jolles, Jelle

    2016-01-01

    Sex differences in spatial ability are a seriously debated topic, given the importance of spatial ability for success in the fields of science, technology, engineering, and mathematics (STEM) and girls' underrepresentation in these domains. In the current study we investigated the presence of stereotypic gender beliefs on spatial ability (i.e., “spatial ability is for boys”) in 10- and 12-year-old children. We used both an explicit measure (i.e., a self-report questionnaire) and an implicit measure (i.e., a child IAT). Results of the explicit measure showed that both sexes associated spatial ability with boys, with boys holding more male stereotyped attitudes than girls. On the implicit measure, boys associated spatial ability with boys, while girls were gender-neutral. In addition, we examined the effects of gender beliefs on spatial performance, by experimentally activating gender beliefs within a pretest—instruction—posttest design. We compared three types of instruction: boys are better, girls are better, and no sex differences. No effects of these gender belief instructions were found on children's spatial test performance (i.e., mental rotation and paper folding). The finding that children of this age already have stereotypic beliefs about the spatial capacities of their own sex is important, as these beliefs may influence children's choices for spatial leisure activities and educational tracks in the STEM domain. PMID:27507956

  4. Implicit and Explicit Gender Beliefs in Spatial Ability: Stronger Stereotyping in Boys than Girls.

    Science.gov (United States)

    Vander Heyden, Karin M; van Atteveldt, Nienke M; Huizinga, Mariette; Jolles, Jelle

    2016-01-01

    Sex differences in spatial ability are a seriously debated topic, given the importance of spatial ability for success in the fields of science, technology, engineering, and mathematics (STEM) and girls' underrepresentation in these domains. In the current study we investigated the presence of stereotypic gender beliefs on spatial ability (i.e., "spatial ability is for boys") in 10- and 12-year-old children. We used both an explicit measure (i.e., a self-report questionnaire) and an implicit measure (i.e., a child IAT). Results of the explicit measure showed that both sexes associated spatial ability with boys, with boys holding more male stereotyped attitudes than girls. On the implicit measure, boys associated spatial ability with boys, while girls were gender-neutral. In addition, we examined the effects of gender beliefs on spatial performance, by experimentally activating gender beliefs within a pretest-instruction-posttest design. We compared three types of instruction: boys are better, girls are better, and no sex differences. No effects of these gender belief instructions were found on children's spatial test performance (i.e., mental rotation and paper folding). The finding that children of this age already have stereotypic beliefs about the spatial capacities of their own sex is important, as these beliefs may influence children's choices for spatial leisure activities and educational tracks in the STEM domain.

  5. Oxytocin's impact on social face processing is stronger in homosexual than heterosexual men.

    Science.gov (United States)

    Thienel, Matthias; Heinrichs, Markus; Fischer, Stefan; Ott, Volker; Born, Jan; Hallschmid, Manfred

    2014-01-01

    Oxytocin is an evolutionarily highly preserved neuropeptide that contributes to the regulation of social interactions including the processing of facial stimuli. We hypothesized that its improving effect on social approach behavior depends on perceived sexual features and, consequently, on sexual orientation. In 19 homosexual and 18 heterosexual healthy young men, we investigated the acute effect of intranasal oxytocin (24IU) and placebo, respectively, on the processing of social stimuli as assessed by ratings of trustworthiness, attractiveness and approachability for male and female faces. Faces were each presented with a neutral, a happy, and an angry expression, respectively. In heterosexual subjects, the effect of oxytocin administration was restricted to a decrease in ratings of trustworthiness for angry female faces (poxytocin administration robustly increased ratings of attractiveness and approachability for male faces regardless of the facial expression (all p ≤ 0.05), as well as ratings of approachability for happy female faces (poxytocin's enhancing impact on social approach tendencies, suggesting that differences in sexual orientation imply differential oxytocinergic signaling. Copyright © 2013 The Authors. Published by Elsevier Ltd.. All rights reserved.

  6. Perceived stress and biological risk: is the link stronger in Russians than in Taiwanese and Americans?

    Science.gov (United States)

    Glei, Dana A; Goldman, Noreen; Shkolnikov, Vladimir M; Jdanov, Dmitri; Shkolnikova, Maria; Vaupel, James W; Weinstein, Maxine

    2013-07-01

    Allostatic load theory implies a relationship between exposure to psychological stress and multi-system physiological dysregulation. We used data from population-based samples of men and women in Russia (Moscow; n = 1800; age, mean 68.6 years), Taiwan (n = 1036; 65.6 years) and the United States (US; n = 1054; 58.0 years) -- which are likely to vary widely with respect to levels of stress exposure and biological markers -- to determine the magnitude of the association between perceived stress and physiological dysregulation. The measure of overall dysregulation was based on 15 markers including standard cardiovascular/metabolic risk factors as well as markers of inflammation and neuroendocrine activity. Subjective psychological stress was measured by the perceived stress scale. Only the Moscow sample demonstrated a positive association with overall dysregulation in both sexes. In the US, we found an association among women but not men. Among the Taiwanese, who report the lowest perceived stress, there was no association in women but an unexpected inverse relationship in men. The effects also varied across system-level subscores: the association with perceived stress was most consistent for standard cardiovascular/metabolic factors. Perceived stress was associated with inflammation and neuroendocrine activity in some samples. Although the evidence that perceived stress is the primary source of physiological dysregulation is generally modest, it was stronger in Russia where the level of perceived stress was particularly high. For Russia only, we had information about heart function based on a 24 h ambulatory electrocardiogram; perceived stress was consistently associated with heart rate dysregulation in Russian men and women.

  7. Stronger tests of mechanisms underlying geographic gradients of biodiversity: insights from the dimensionality of biodiversity.

    Directory of Open Access Journals (Sweden)

    Richard D Stevens

    Full Text Available Inference involving diversity gradients typically is gathered by mechanistic tests involving single dimensions of biodiversity such as species richness. Nonetheless, because traits such as geographic range size, trophic status or phenotypic characteristics are tied to a particular species, mechanistic effects driving broad diversity patterns should manifest across numerous dimensions of biodiversity. We develop an approach of stronger inference based on numerous dimensions of biodiversity and apply it to evaluate one such putative mechanism: the mid-domain effect (MDE. Species composition of 10,000-km(2 grid cells was determined by overlaying geographic range maps of 133 noctilionoid bat taxa. We determined empirical diversity gradients in the Neotropics by calculating species richness and three indices each of phylogenetic, functional and phenetic diversity for each grid cell. We also created 1,000 simulated gradients of each examined metric of biodiversity based on a MDE model to estimate patterns expected if species distributions were randomly placed within the Neotropics. For each simulation run, we regressed the observed gradient onto the MDE-expected gradient. If a MDE drives empirical gradients, then coefficients of determination from such an analysis should be high, the intercept no different from zero and the slope no different than unity. Species richness gradients predicted by the MDE fit empirical patterns. The MDE produced strong spatially structured gradients of taxonomic, phylogenetic, functional and phenetic diversity. Nonetheless, expected values generated from the MDE for most dimensions of biodiversity exhibited poor fit to most empirical patterns. The MDE cannot account for most empirical patterns of biodiversity. Fuller understanding of latitudinal gradients will come from simultaneous examination of relative effects of random, environmental and historical mechanisms to better understand distribution and abundance of the

  8. BUILDING STRONGER STATE ENERGY PARTNERSHIPS WITH THE U.S. DEPARTMENT OF ENERGY

    Energy Technology Data Exchange (ETDEWEB)

    Kate Burke

    2003-09-01

    This technical progress report includes an update of the progress during the third year of cooperative agreement DE-FC26-00NT40802, Building Stronger State Energy Partnerships with the U.S. Department of Energy. The report also describes the barriers in conduct of the effort, and our assessment of future progress and activities. The approach of the project included three tasks during year three. First, NASEO and its Buildings Committee were to focus on raising awareness and coordination of Rebuild activities. Through education, one-on-one communications, and presentations at NASEO meetings and other events, staff and the committee will assist Rebuild officials in stimulating interest in the program and building greater support among State Energy Office Directors. The most recent subtasks added to the project, though not directly related to Rebuild America, fall under this initial task, and support: (a) state plans to implement integrated energy and environmental initiatives, including distributed generation technologies, and (b) initiation of a state collaborative on advanced turbines and hybrid systems. The advanced turbine piece was completed during this year. During the year, a new workplan was accepted by Rebuild America's Dan Sze to supplement the work in this task. This workplan is outlined below. Second, NASEO would work to improve the efficiency of America's schools by assisting states and DOE in promoting projects that result in more energy efficient and clean energy schools and a better learning environment. This task was fully completed during this year. The third task involves energy security issues which NASEO addressed by way of a Summer Fuels Outlook Conference held Tuesday, April 8, 2003. The purpose of this educational event was to inform state, federal, local, and other energy officials about the most recent transportation fuels data and trends. The public benefits part of this task was not funded for Year 3, thus no activity occurred.

  9. Association Between Self-Esteem and Depressive Symptoms Is Stronger Among Black than White Older Adults.

    Science.gov (United States)

    Assari, Shervin

    2017-08-01

    Although poor self-esteem is a core component of depression, we still do not know if racial and ethnic groups differ in the magnitude of this link. This study compared Black and White older adults on the association between self-esteem and depressive symptoms. With a cross-sectional design, this study enrolled 1493 older individuals (age 66 or more) from the 2001 Religion, Aging, and Health Survey, a nationally representative study in the United States. Participants were either Blacks (n = 734) or Whites (n = 759). Depressive symptoms and self-esteem were measured using brief measures of the Center for Epidemiological Studies-Depression scale (CES-D) and the Rosenberg Self-Esteem Scale, respectively. Demographics, socioeconomics, and self-rated health (SRH) were covariates and self-identified race was the moderator. Linear regression models were used for data analysis. Low self-esteem was associated with more depressive symptoms (B = 0.17, 95 % CI 0.15-0.28), above and beyond all covariates. We found a significant and positive interaction between race (Black) and poor self-esteem on depressive symptoms (B = 0.34, 95 % CI 0.17-0.36), suggesting a stronger association between self-esteem and depressive symptoms among Blacks compared to Whites. Although low self-esteem is associated with higher depressive symptoms in both Whites and Blacks (p self-esteem and high depressive symptoms are more closely associated among Blacks than Whites. It is not clear whether depression leaves a larger scar on self-esteem for Blacks, or Blacks are more vulnerable to the effect of low self-esteem on depression.

  10. Gargamelle and the neutral currents

    International Nuclear Information System (INIS)

    Rousset, A.

    1996-06-01

    In order to simplify the description of forces, the physicists want to reduce the number of four interactions to a smaller one. They want to unify them. Einstein tried to unify the electromagnetic interaction and the gravitation interaction but it was probably the most difficult to unify. during the sixties, the American physicists Sheldon Glashow and Steven Weinberg and the Pakistani Abdus Salam ( each rewarded by the Nobel price of 1979) propose to unify the weak and electromagnetic interactions interactions under the form of an only interaction, the electro-weak interaction. To check the validity of this theory exist the demonstration by the weak neutral currents. In 1973, European physicians which analyzed photos taken in the bubble chamber called Gargamelle brought the experimental proof. This book tells the story of this discovery. (N.C.)

  11. Laser sputter neutral mass spectrometry

    Energy Technology Data Exchange (ETDEWEB)

    King, B.V.; Clarke, M.; Hu, H.; Betz [Newcastle Univ., NSW (Australia). Dept. of Physics

    1993-12-31

    Laser sputter neutral mass spectrometry (LSNMS) is an emerging technique for highly sensitive surface analysis. In this technique a target is bombarded with a pulsed beam of keV ions. The sputtered particles are intercepted by a high intensity pulsed laser beam above the surface and ionised with almost 100% efficiency. The photions may then be mass analysed using a quadrupole or, more commonly, using time of flight (TOF) techniques. In this method photoions are extracted from the ionisation region, accelerated to a known energy E{sub o} and strike a channelplate detector a distance `d` away. The flight time `t` of the photoions is then related to their mass by `d` {radical}m / {radical} 2E{sub o} so measurement of `t` allows mass spectra to be obtained. It is found that LSNMS is an emerging technique of great sensitivity and flexibility, useful for both applied analysis and to investigate basic sputtering processes. 4 refs., 3 figs.

  12. TFTR neutral beam power system

    International Nuclear Information System (INIS)

    Deitz, A.; Murray, H.; Winje, R.

    1977-01-01

    The TFTR NB System will be composed of four beam lines, each containing three ion sources presently being developed for TFTR by the Lawrence Berkeley Laboratories (LBL). The Neutral Beam Power System (NBPS) will provide the necessary power required to operate these Ion Sources in both an experimental or operational mode as well as test mode. This paper describes the technical as well as the administrative/management aspects involved in the development and building of this system. The NBPS will combine the aspects of HV pulse (120 kV) and long pulse width (0.5 sec) together to produce a high power system that is unique in the Electrical Engineering field

  13. Autologous HIV-1 neutralizing antibodies: emergence of neutralization-resistant escape virus and subsequent development of escape virus neutralizing antibodies

    DEFF Research Database (Denmark)

    Arendrup, M; Nielsen, C; Hansen, J E

    1992-01-01

    The capacity of consecutive human sera to neutralize sequentially obtained autologous virus isolates was studied. HIV-1 was isolated three times over a 48-164-week period from three individuals immediately after seroconversion and from two individuals in later stages of infection. Development...... escape virus may be part of the explanation of the apparent failure of the immune system to control HIV infection....... of neutralizing antibodies to the primary virus isolates was detected 13-45 weeks after seroconversion. Emergence of escape virus with reduced sensitivity to neutralization by autologous sera was demonstrated. The patients subsequently developed neutralizing antibodies against the escape virus but after a delay...

  14. Neutral meson measurement using different neutral pion reconstruction techniques in ALICE in pp collisions at $\\sqrt s = 7$ TeV

    CERN Document Server

    Jonas, Florian

    2017-01-01

    In this analysis, which is carried out as part of a summer student project, the $\\omega$ and $\\eta$ mesons are measured in pp collisions at $\\sqrt s = 7$ TeV using ALICE's two calorimeters PHOS and EMCal, the so called Photon Conversion Method (PCM) and two hybrid methods that combine one photon that was reconstructed with PCM and the other photon measured with the different calorimeters for neutral pion reconstruction. The analysis was carried out on LHC data from 2010 resulting in visible peaks for all mentioned methods. Investigations of the invariant mass distributions using Monte Carlo Event Generator PYTHIA6 show a main contribution to the background by false identifications of neutral pions, that are reduced by stronger cuts on the photon pairs invariant-mass. Furthermore, the chain of afterburners that was put in place to further process the extracted peaks and compare the different reconstruction methods is demonstrated.

  15. The nature of the water nucleation sites on TiO2(110) surfacesrelvealed by ambient pressure x-ray photoelectron spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Ketteler, Guido; Yamamoto, Susumu; Bluhm, Hendrik; Andersson,Klas; Starr, David E.; Ogletree, D. Frank; Ogasawara, Hirohito; Nilsson,Anders; Salmeron, Miquel

    2007-05-01

    X-ray photoelectron spectroscopy at ambient conditions of pressure (up to 1.5 Torr) and temperature (265Knucleation sites for subsequent water adsorption. The adsorption enthalpy of water binding to these sites is {approx}70 kJ/mol, much stronger than that in the bulk liquid (45 kJ/mol). A model is proposed that relates the structure of the oxide surface to its hydrophilic character.

  16. Modeling Secondary Neutral Helium in the Heliosphere

    International Nuclear Information System (INIS)

    Müller, Hans-Reinhard; Möbius, Eberhard; Wood, Brian E.

    2016-01-01

    An accurate, analytic heliospheric neutral test-particle code for helium atoms from the interstellar medium (ISM) is coupled to global heliospheric models dominated by hydrogen and protons from the solar wind and the ISM. This coupling enables the forward-calculation of secondary helium neutrals from first principles. Secondaries are produced predominantly in the outer heliosheath, upwind of the heliopause, by charge exchange of helium ions with neutral atoms. The forward model integrates the secondary production terms along neutral trajectories and calculates the combined neutral helium phase space density in the innermost heliosphere where it can be related to in-situ observations. The phase space density of the secondary component is lower than that of primary neutral helium, but its presence can change the analysis of primaries and the ISM, and can yield valuable insight into the characteristics of the plasma in the outer heliosheath. (paper)

  17. BEAMS3D Neutral Beam Injection Model

    Energy Technology Data Exchange (ETDEWEB)

    Lazerson, Samuel

    2014-04-14

    With the advent of applied 3D fi elds in Tokamaks and modern high performance stellarators, a need has arisen to address non-axisymmetric effects on neutral beam heating and fueling. We report on the development of a fully 3D neutral beam injection (NBI) model, BEAMS3D, which addresses this need by coupling 3D equilibria to a guiding center code capable of modeling neutral and charged particle trajectories across the separatrix and into the plasma core. Ionization, neutralization, charge-exchange, viscous velocity reduction, and pitch angle scattering are modeled with the ADAS atomic physics database [1]. Benchmark calculations are presented to validate the collisionless particle orbits, neutral beam injection model, frictional drag, and pitch angle scattering effects. A calculation of neutral beam heating in the NCSX device is performed, highlighting the capability of the code to handle 3D magnetic fields.

  18. Ice nucleation from aqueous NaCl droplets with and without marine diatoms

    Directory of Open Access Journals (Sweden)

    P. A. Alpert

    2011-06-01

    Full Text Available Ice formation in the atmosphere by homogeneous and heterogeneous nucleation is one of the least understood processes in cloud microphysics and climate. Here we describe our investigation of the marine environment as a potential source of atmospheric IN by experimentally observing homogeneous ice nucleation from aqueous NaCl droplets and comparing against heterogeneous ice nucleation from aqueous NaCl droplets containing intact and fragmented diatoms. Homogeneous and heterogeneous ice nucleation are studied as a function of temperature and water activity, aw. Additional analyses are presented on the dependence of diatom surface area and aqueous volume on heterogeneous freezing temperatures, ice nucleation rates, ωhet, ice nucleation rate coefficients, Jhet, and differential and cumulative ice nuclei spectra, k(T and K(T, respectively. Homogeneous freezing temperatures and corresponding nucleation rate coefficients are in agreement with the water activity based homogeneous ice nucleation theory within experimental and predictive uncertainties. Our results confirm, as predicted by classical nucleation theory, that a stochastic interpretation can be used to describe the homogeneous ice nucleation process. Heterogeneous ice nucleation initiated by intact and fragmented diatoms can be adequately represented by a modified water activity based ice nucleation theory. A horizontal shift in water activity, Δaw, het = 0.2303, of the ice melting curve can describe median heterogeneous freezing temperatures. Individual freezing temperatures showed no dependence on available diatom surface area and aqueous volume. Determined at median diatom freezing temperatures for aw from 0.8 to 0.99, ωhet~0.11+0.06−0.05 s−1, Jhet~1.0+1.16−0.61×104 cm−2

  19. On implicit abstract neutral nonlinear differential equations

    Energy Technology Data Exchange (ETDEWEB)

    Hernández, Eduardo, E-mail: lalohm@ffclrp.usp.br [Universidade de São Paulo, Departamento de Computação e Matemática, Faculdade de Filosofia Ciências e Letras de Ribeirão Preto (Brazil); O’Regan, Donal, E-mail: donal.oregan@nuigalway.ie [National University of Ireland, School of Mathematics, Statistics and Applied Mathematics (Ireland)

    2016-04-15

    In this paper we continue our developments in Hernández and O’Regan (J Funct Anal 261:3457–3481, 2011) on the existence of solutions for abstract neutral differential equations. In particular we extend the results in Hernández and O’Regan (J Funct Anal 261:3457–3481, 2011) for the case of implicit nonlinear neutral equations and we focus on applications to partial “nonlinear” neutral differential equations. Some applications involving partial neutral differential equations are presented.

  20. A New Method to Monitor the Primary Neutral Integrity in Multi-Grounded Neutral Systems

    Directory of Open Access Journals (Sweden)

    Xiangmin Xie

    2017-03-01

    Full Text Available In the three-phase four-wire system, there are usually multiple grounding points in the primary neutral line due to safety and economic considerations. The rising “neutral to earth voltage (NEV” caused by a broken primary neutral can threaten the safety of nearby facilities and humans; therefore, the integrity of the primary neutral conductor is of vital importance for the multi-grounded neutral (MGN system. In this paper, a new passive method is proposed to monitor the integrity of the primary neutral line in the MGN system. The method is based on the measured voltage and current data at the service transformer, and there is no need to install any signal generators. Therefore, it causes no disturbance to the utility and customer. In the paper, the equivalent analysis circuit is established and a new parameter is proposed to reflect the neutral condition. The value of the parameter is estimated based on the measured data, and then, the equivalent impedance of the primary neutral groundings can be obtained. On the other hand, the impedance value for the primary neutral under normal operating conditions can be estimated based on the derived analytical formulas. By comparing the monitored primary neutral impedance with its normal value, the broken neutral condition in the primary system can be detected. Different primary neutral broken cases are analyzed in the paper based on the Monte Carlo simulation. The results indicate that the integrity condition in the primary neutral can be accurately monitored by the proposed method.

  1. Liberal Neutrality : Constructivist, not foundationalist

    Directory of Open Access Journals (Sweden)

    Lendell Horne

    2009-06-01

    Full Text Available In defending the principle of neutrality, liberals have often appealed to a more general moral principle that forbids coercing persons in the name of reasons those persons themselves cannot reasonably be expected to share. Yet liberals have struggled to articulate a non-arbitrary, non-dogmatic distinction between the reasons that persons can reasonably be expected to share and those they cannot. The reason for this, I argue, is that what it means to “share a reason” is itself obscure. In this paper I articulate two different conceptions of what it is to share a reason; I call these conceptions “foundationalist” and “constructivist.” On the foundationalist view, two people “share” a reason just in the sense that the same reason applies to each of them independently. On this view, I argue, debates about the reasons we share collapse into debates about the reasons we have, moving us no closer to an adequate defense of neutrality. On the constructivist view, by contrast, “sharing reasons” is understood as a kind of activity, and the reasons we must share are just those reasons that make this activity possible. I argue that the constructivist conception of sharing reasons yields a better defense of the principle of neutrality. À travers leur défense du principe de neutralité, les libéraux ont souvent interpellé un principe moral plus général qui interdit de contraindre des personnes pour des raisons dont on ne peut raisonnablement attendre que ces personnes elles-mêmes les partagent. Les libéraux éprouvent cependant de la difficulté à articuler une distinction non-arbitraire et non-dogmatique entre les raisons dont on peut raisonnablement attendre que les personnes les partagent et celles dont on ne le peut pas. Je soutiens dans cet article que cette difficulté provient du fait que «partager une raison » est une notion obscure. Pour illustrer cela, je me pencherai sur deux conceptions distinctes de ce que veut dire

  2. Understanding homogeneous nucleation in solidification of aluminum by molecular dynamics simulations

    Science.gov (United States)

    Mahata, Avik; Asle Zaeem, Mohsen; Baskes, Michael I.

    2018-02-01

    Homogeneous nucleation from aluminum (Al) melt was investigated by million-atom molecular dynamics simulations utilizing the second nearest neighbor modified embedded atom method potentials. The natural spontaneous homogenous nucleation from the Al melt was produced without any influence of pressure, free surface effects and impurities. Initially isothermal crystal nucleation from undercooled melt was studied at different constant temperatures, and later superheated Al melt was quenched with different cooling rates. The crystal structure of nuclei, critical nucleus size, critical temperature for homogenous nucleation, induction time, and nucleation rate were determined. The quenching simulations clearly revealed three temperature regimes: sub-critical nucleation, super-critical nucleation, and solid-state grain growth regimes. The main crystalline phase was identified as face-centered cubic, but a hexagonal close-packed (hcp) and an amorphous solid phase were also detected. The hcp phase was created due to the formation of stacking faults during solidification of Al melt. By slowing down the cooling rate, the volume fraction of hcp and amorphous phases decreased. After the box was completely solid, grain growth was simulated and the grain growth exponent was determined for different annealing temperatures.

  3. Single Particle Laser Mass Spectrometry Applied to Differential Ice Nucleation Experiments at the AIDA Chamber

    International Nuclear Information System (INIS)

    Gallavardin, S. J.; Froyd, Karl D.; Lohmann, U.; Moehler, Ottmar; Murphy, Daniel M.; Cziczo, Dan

    2008-01-01

    Experiments conducted at the Aerosol Interactions and Dynamics in the Atmosphere (AIDA) chamber located in Karlsruhe, Germany permit investigation of particle properties that affect the nucleation of ice at temperature and water vapor conditions relevant to cloud microphysics and climate issues. Ice clouds were generated by heterogeneous nucleation of Arizona test dust (ATD), illite, and hematite and homogeneous nucleation of sulfuric acid. Ice crystals formed in the chamber were inertially separated from unactivated, or 'interstitial' aerosol particles with a pumped counterflow virtual impactor (PCVI), then evaporated. The ice residue (i.e., the aerosol which initiated ice nucleation plus any material which was scavenged from the gas- and/or particle-phase), was chemically characterized at the single particle level using a laser ionization mass spectrometer. In this manner the species that first nucleated ice could be identified out of a mixed aerosol population in the chamber. Bare mineral dust particles were more effective ice nuclei (IN) than similar particles with a coating. Metallic particles from contamination in the chamber initiated ice nucleation before other species but there were few enough that they did not compromise the experiments. Nitrate, sulfate, and organics were often detected on particles and ice residue, evidently from scavenging of trace gas-phase species in the chamber. Hematite was a more effective ice nucleus than illite. Ice residue was frequently larger than unactivated test aerosol due to the formation of aggregates due to scavenging, condensation of contaminant gases, and the predominance of larger aerosol in nucleation

  4. Depositional ice nucleation on solid ammonium sulfate and glutaric acid particles

    Directory of Open Access Journals (Sweden)

    K. J. Baustian

    2010-03-01

    Full Text Available Heterogeneous ice nucleation on solid ammonium sulfate and glutaric acid particles was studied using optical microscopy and Raman spectroscopy. Optical microscopy was used to detect selective nucleation events as water vapor was slowly introduced into an environmental sample cell. Particles that nucleated ice were dried via sublimation and examined in detail using Raman spectroscopy. Depositional ice nucleation is highly selective and occurred preferentially on just a few ammonium sulfate and glutaric acid particles in each sample. For freezing temperatures between 214 K and 235 K an average ice saturation ratio of S = 1.10±0.07 for solid ammonium sulfate was observed. Over the same temperature range, S values observed for ice nucleation on glutaric acid particles increased from 1.2 at 235 K to 1.6 at 218 K. Experiments with externally mixed particles further show that ammonium sulfate is a more potent ice nucleus than glutaric acid. Our results suggest that heterogeneous nucleation on ammonium sulfate may be an important pathway for atmospheric ice nucleation and cirrus cloud formation when solid ammonium sulfate aerosol particles are available for ice formation. This pathway for ice formation may be particularly significant near the tropical tropopause region where sulfates are abundant and other species known to be good ice nuclei are depleted.

  5. Investigation of nucleation processes during dynamic recrystallization of ice using cryo-EBSD.

    Science.gov (United States)

    Chauve, T; Montagnat, M; Barou, F; Hidas, K; Tommasi, A; Mainprice, D

    2017-02-13

    Nucleation mechanisms occurring during dynamic recrystallization play a crucial role in the evolution of microstructures and textures during high temperature deformation. In polycrystalline ice, the strong viscoplastic anisotropy induces high strain heterogeneities between grains which control the recrystallization mechanisms. Here, we study the nucleation mechanisms occurring during creep tests performed on polycrystalline columnar ice at high temperature and stress (T=-5°C;σ=0.5 MPa) by post-mortem analyses of deformation microstructures using cryogenic electron backscatter diffraction. The columnar geometry of the samples enables discrimination of the nuclei from the initial grains. Various nucleation mechanisms are deduced from the analysis of the nuclei relations with the dislocation sub-structures within grains and at grain boundaries. Tilt sub-grain boundaries and kink bands are the main structures responsible for development of polygonization and mosaic sub-structures. Nucleation by bulging at serrated grain boundaries is also an efficient nucleation mechanism near the grain boundaries where strain incompatibilities are high. Observation of nuclei with orientations not related to the 'parent' ones suggests the possibility of 'spontaneous' nucleation driven by the relaxation of the dislocation-related internal stress field. The complexity of the nucleation mechanisms observed here emphasizes the impact of stress and strain heterogeneities on dynamic recrystallization mechanisms.This article is part of the themed issue 'Microdynamics of ice'. © 2016 The Author(s).

  6. Crystal Nucleation in Liquids: Open Questions and Future Challenges in Molecular Dynamics Simulations

    Science.gov (United States)

    2016-01-01

    The nucleation of crystals in liquids is one of nature’s most ubiquitous phenomena, playing an important role in areas such as climate change and the production of drugs. As the early stages of nucleation involve exceedingly small time and length scales, atomistic computer simulations can provide unique insights into the microscopic aspects of crystallization. In this review, we take stock of the numerous molecular dynamics simulations that, in the past few decades, have unraveled crucial aspects of crystal nucleation in liquids. We put into context the theoretical framework of classical nucleation theory and the state-of-the-art computational methods by reviewing simulations of such processes as ice nucleation and the crystallization of molecules in solutions. We shall see that molecular dynamics simulations have provided key insights into diverse nucleation scenarios, ranging from colloidal particles to natural gas hydrates, and that, as a result, the general applicability of classical nucleation theory has been repeatedly called into question. We have attempted to identify the most pressing open questions in the field. We believe that, by improving (i) existing interatomic potentials and (ii) currently available enhanced sampling methods, the community can move toward accurate investigations of realistic systems of practical interest, thus bringing simulations a step closer to experiments. PMID:27228560

  7. Microstructurally-sensitive fatigue crack nucleation in Ni-based single and oligo crystals

    Science.gov (United States)

    Chen, Bo; Jiang, Jun; Dunne, Fionn P. E.

    2017-09-01

    An integrated experimental, characterisation and computational crystal plasticity study of cyclic plastic beam loading has been carried out for nickel single crystal (CMSX4) and oligocrystal (MAR002) alloys in order to assess quantitatively the mechanistic drivers for fatigue crack nucleation. The experimentally validated modelling provides knowledge of key microstructural quantities (accumulated slip, stress and GND density) at experimentally observed fatigue crack nucleation sites and it is shown that while each of these quantities is potentially important in crack nucleation, none of them in its own right is sufficient to be predictive. However, the local (elastic) stored energy density, measured over a length scale determined by the density of SSDs and GNDs, has been shown to predict crack nucleation sites in the single and oligocrystals tests. In addition, once primary nucleated cracks develop and are represented in the crystal model using XFEM, the stored energy correctly identifies where secondary fatigue cracks are observed to nucleate in experiments. This (Griffith-Stroh type) quantity also correctly differentiates and explains intergranular and transgranular fatigue crack nucleation.

  8. BINARY: an optical freezing array for assessing temperature and time dependence of heterogeneous ice nucleation

    Directory of Open Access Journals (Sweden)

    C. Budke

    2015-02-01

    Full Text Available A new optical freezing array for the study of heterogeneous ice nucleation in microliter-sized droplets is introduced, tested and applied to the study of immersion freezing in aqueous Snomax® suspensions. In the Bielefeld Ice Nucleation ARraY (BINARY ice nucleation can be studied simultaneously in 36 droplets at temperatures down to −40 °C (233 K and at cooling rates between 0.1 and 10 K min−1. The droplets are separated from each other in individual compartments, thus preventing a Wegener–Bergeron–Findeisen type water vapor transfer between droplets as well as avoiding the seeding of neighboring droplets by formation and surface growth of frost halos. Analysis of freezing and melting occurs via an automated real-time image analysis of the optical brightness of each individual droplet. As an application ice nucleation in water droplets containing Snomax® at concentrations from 1 ng mL−1 to 1 mg mL−1 was investigated. Using different cooling rates, a small time dependence of ice nucleation induced by two different classes of ice nucleators (INs contained in Snomax® was detected and the corresponding heterogeneous ice nucleation rate coefficient was quantified. The observed time dependence is smaller than those of other types of INs reported in the literature, suggesting that the BINARY setup is suitable for quantifying time dependence for most other INs of atmospheric interest, making it a useful tool for future investigations.

  9. In-situ observation of nucleated polymer crystallization in polyoxymethylene sandwich composites

    Directory of Open Access Journals (Sweden)

    Miroslav eSlouf

    2015-03-01

    Full Text Available We introduce a dynamic sandwich method, which can be used for in-situ observation and quantification of polymer crystallization nucleated by micro/nanoparticles. The method was applied on polyoxymethylene (POM composites with three nucleating agents: talc micropowder (POM/mTalc, chalk nanopowder (POM/nChalk and titanate nanotubes (POM/TiNT. The nucleating agents were deposited between polymer films, the resulting sandwich samples were consolidated by thermal treatment, and their microtomed cross-sections were observed during isothermal crystallization by polarized light microscopy. As the intensity of polarized light was shown to be proportional to the relative crystallinity, the PLM results could be fitted to Avrami equation and the nucleating activity of all investigated particles could be quantified by means of Avrami parameters (n, k. The crystallization half-times increased reproducibly in the following order: POM/nChalk < POM/mTalc < POM/TiNT ~ POM. For strong nucleating agents (mTalc, nChalk, the crystallization kinetics corresponded to spontaneous crystallization starting from central nucleating layer, which was verified by computer simulations. The results were also confirmed by DSC. We concluded that the sandwich method is an efficient microscopic technique for detailed evaluation of nucleating activity of arbitrary micro/nanoparticles in polymer systems.

  10. A Proposed Model for Protein Crystal Nucleation and Growth

    Science.gov (United States)

    Pusey, Marc; Curreri, Peter A. (Technical Monitor)

    2002-01-01

    How does one take a molecule, strongly asymmetric in both shape and charge distribution, and assemble it into a crystal? We propose a model for the nucleation and crystal growth process for tetragonal lysozyme, based upon fluorescence, light, neutron, and X-ray scattering data, size exclusion chromatography experiments, dialysis kinetics, AFM, and modeling of growth rate data, from this and other laboratories. The first species formed is postulated to be a 'head to side' dimer. Through repeating associations involving the same intermolecular interactions this grows to a 4(sub 3) helix structure, that in turn serves as the basic unit for nucleation and subsequent crystal growth. High salt attenuates surface charges while promoting hydrophobic interactions. Symmetry facilitates subsequent helix-helix self-association. Assembly stability is enhanced when a four helix structure is obtained, with each bound to two neighbors. Only two unique interactions are required. The first are those for helix formation, where the dominant interaction is the intermolecular bridging anion. The second is the anti-parallel side-by-side helix-helix interaction, guided by alternating pairs of symmetry related salt bridges along each side. At this stage all eight unique positions of the P4(sub3)2(sub 1),2(sub 1) unit cell are filled. The process is one of a) attenuating the most strongly interacting groups, such that b) the molecules begin to self-associate in defined patterns, so that c) symmetry is obtained, which d) propagates as a growing crystal. Simple and conceptually obvious in hindsight, this tells much about what we are empirically doing when we crystallize macromolecules. By adjusting the growth parameters we are empirically balancing the intermolecular interactions, preferentially attenuating the dominant strong (for lysozyme the charged groups) while strengthening the lesser strong (hydrophobic) interactions. In the general case for proteins the lack of a singularly defined

  11. Bell inequalities stronger than the Clauser-Horne-Shimony-Holt inequality for three-level isotropic states

    International Nuclear Information System (INIS)

    Ito, Tsuyoshi; Imai, Hiroshi; Avis, David

    2006-01-01

    We show that some two-party Bell inequalities with two-valued observables are stronger than the CHSH inequality for 3x3 isotropic states in the sense that they are violated by some isotropic states in the 3x3 system that do not violate the CHSH inequality. These Bell inequalities are obtained by applying triangular elimination to the list of known facet inequalities of the cut polytope on nine points. This gives a partial solution to an open problem posed by Collins and Gisin. The results of numerical optimization suggest that they are candidates for being stronger than the I 3322 Bell inequality for 3x3 isotropic states. On the other hand, we found no Bell inequalities stronger than the CHSH inequality for 2x2 isotropic states. In addition, we illustrate an inclusion relation among some Bell inequalities derived by triangular elimination

  12. Autologous HIV-1 neutralizing antibodies: emergence of neutralization-resistant escape virus and subsequent development of escape virus neutralizing antibodies

    DEFF Research Database (Denmark)

    Arendrup, M; Nielsen, C; Hansen, J E

    1992-01-01

    The capacity of consecutive human sera to neutralize sequentially obtained autologous virus isolates was studied. HIV-1 was isolated three times over a 48-164-week period from three individuals immediately after seroconversion and from two individuals in later stages of infection. Development of ...... escape virus may be part of the explanation of the apparent failure of the immune system to control HIV infection.......The capacity of consecutive human sera to neutralize sequentially obtained autologous virus isolates was studied. HIV-1 was isolated three times over a 48-164-week period from three individuals immediately after seroconversion and from two individuals in later stages of infection. Development...... of neutralizing antibodies to the primary virus isolates was detected 13-45 weeks after seroconversion. Emergence of escape virus with reduced sensitivity to neutralization by autologous sera was demonstrated. The patients subsequently developed neutralizing antibodies against the escape virus but after a delay...

  13. Molecular sizes of lichen ice nucleation sites determined by gamma radiation inactivation analysis

    International Nuclear Information System (INIS)

    Kieft, T.L.; Ruscetti, T.

    1992-01-01

    It has previously been shown that some species of lichen fungi contain proteinaceous ice nuclei which are active at temperatures as warm as −2 °C. This experiment was undertaken to determine the molecular sizes of ice nuclei in the lichen fungus Rhizoplaca chrysoleuca and to compare them to bacterial ice nuclei from Pseudomonas syringae. Gamma radiation inactivation analysis was used to determine molecular weights. Radiation inactivation analysis is based on target theory, which states that the likelihood of a molecule being inactivated by gamma rays increases as its size increases. Three different sources of ice nuclei from the lichen R. chrysoleuca were tested: field-collected lichens, extract of lichen fungus, and a pure culture of the fungus R. chrysoleuca. P. syringae strain Cit7 was used as a source of bacterial ice nuclei. Samples were lyophilized, irradiated with gamma doses ranging from 0 to 10.4 Mrads, and then tested for ice nucleation activity using a droplet-freezing assay. Data for all four types of samples were in rough agreement; sizes of nucleation sites increased logarithmically with increasing temperatures of ice nucleation activity. Molecular weights of nucleation sites active between −3 and −4 °C from the bacteria and from the field-collected lichens were approximately 1.0 × 10 6 Da. Nuclei from the lichen fungus and in the lichen extract appeared to be slightly smaller but followed the same log-normal pattern with temperature of ice nucleation activity. The data for both the bacterial and lichen ice nuclei are in agreement with ice nucleation theory which states that the size of ice nucleation sites increases logarithmically as the temperature of nucleation increases linearly. This suggests that although some differences exist between bacterial and lichen ice nucleation sites, their molecular sizes are quite similar

  14. Structure of a Longitudinal Actin Dimer Assembled by Tandem W Domains: Implications for Actin Filament Nucleation

    Energy Technology Data Exchange (ETDEWEB)

    Rebowski, Grzegorz; Namgoong, Suk; Boczkowska, Malgorzata; Leavis, Paul C.; Navaza, Jorge; Dominguez, Roberto (IBS); (BBRI); (UPENN-MED)

    2013-11-20

    Actin filament nucleators initiate polymerization in cells in a regulated manner. A common architecture among these molecules consists of tandem WASP homology 2 domains (W domains) that recruit three to four actin subunits to form a polymerization nucleus. We describe a low-resolution crystal structure of an actin dimer assembled by tandem W domains, where the first W domain is cross-linked to Cys374 of the actin subunit bound to it, whereas the last W domain is followed by the C-terminal pointed end-capping helix of thymosin {beta}4. While the arrangement of actin subunits in the dimer resembles that of a long-pitch helix of the actin filament, important differences are observed. These differences result from steric hindrance of the W domain with intersubunit contacts in the actin filament. We also determined the structure of the first W domain of Vibrio parahaemolyticus VopL cross-linked to actin Cys374 and show it to be nearly identical with non-cross-linked W-Actin structures. This result validates the use of cross-linking as a tool for the study of actin nucleation complexes, whose natural tendency to polymerize interferes with most structural methods. Combined with a biochemical analysis of nucleation, the structures may explain why nucleators based on tandem W domains with short inter-W linkers have relatively weak activity, cannot stay bound to filaments after nucleation, and are unlikely to influence filament elongation. The findings may also explain why nucleation-promoting factors of the Arp2/3 complex, which are related to tandem-W-domain nucleators, are ejected from branch junctions after nucleation. We finally show that the simple addition of the C-terminal pointed end-capping helix of thymosin {beta}4 to tandem W domains can change their activity from actin filament nucleation to monomer sequestration.

  15. Significant advantages of sulfur-doped graphene in neutral media as electrocatalyst for oxygen reduction comparing with Pt/C

    Science.gov (United States)

    Shi, Xinxin; Zhang, Jiaona; Huang, Tinglin

    2018-02-01

    Sulfur-doped graphene (SDG) has been found to be an efficient electrocatalyst for oxygen reduction reaction. However, previous studies on the catalytic activity of SDG have been mainly confined to O2-saturated alkaline media which is a typical alkaline fuel cell environment. Air-cathode microbial fuel cells (ACMFCs), as a novel energy conversion and wastewater treatment technology, use the oxygen from air as cathodic reactant in neutral media with low concentration of O2. Thus, it is meaningful to explore the catalytic performance of SDG in such ACMFC environment. The result showed that in ACMFC environment, the peak current density of SDG in CV test was surprisingly 4.5 times higher than that of Pt/C, indicating a much stronger catalytic activity of SDG. Moreover, SDG exhibited a stronger tolerance against the crossover of glucose (a typical anodic fuel in ACMFC) and better stability than Pt/C in neutral media.

  16. Field Observation of the Green Ocean Amazon. Neutral Cluster Air Ion Spectrometer (NAIS) Final Campaign Summary

    Energy Technology Data Exchange (ETDEWEB)

    Petaja, T. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Backman, J. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Manninen, H. E. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Wimmer, D. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States)

    2016-03-01

    The neutral cluster and air ion spectrometer (NAIS) was deployed to the T3 site for Intensive Operations Periods 1 and 2 (IOP1 and IOP2). The NAIS is an instrument that measures aerosol particle and ion number size distributions in the mobility diameter range of 0.8 to 42 nm, corresponding to electrical mobility range between 3.2 and 0.0013 cm2 V-1 s-1. New particle formation (NPF) events were detected using the NAIS at the T3 field site during IOP1 and IOP2. Secondary NPF is a globally important source of aerosol number. To fully explain atmospheric NPF and subsequent growth, we need to directly measure the initial steps of the formation processes in different environments, including rain forest. Particle formation characteristics, such as formation and growth rates, were used as indicators of the relevant processes and participating compounds in the initial formation. In a case of parallel ion and neutral cluster measurements, we estimated the relative contribution of ion-induced and neutral nucleation to the total particle formation.

  17. TORE SUPRA neutral injection system

    International Nuclear Information System (INIS)

    Bayetti, P.; Becherer, R.; Bottiglioni, F.; Jacquot, C.; Jequier, F.; Fumelli, M.; Lotte, P.; Pamela, J.; Sledziewski, Z.

    1989-01-01

    The Neutral Beam Injection on TS consists of three boxes, each housing two injectors. Each of them is designed to accelerate 40 A at 100 kV in D 2 ar 40A at 80 kV in H 2 , in shots of 30 s. The power on the plasma is expected to be 7.5 MW (full energy) and 9 MW (total) for the D-beams; 2.5 MW and 3.8 MW for H-beams. This for a species mix of 0.85 19 m -2 and a transmission efficiency of 0.7. Four injectors are in co and two through another one, and they are tilted of 20 deg from the radial direction. Injectors are designed for the energy recovery of the full energy ions. A prototype line, operated in 1987-88, has given the imput for the demensioning of the present system.First injectors are expected to be operational by the end of 1988. The present contribution describes the injection boxes, injection line, magnetic shielding, electrical circuity and power supplies, control and data acquisition systems, and the Fast Interlock Safety System (FISS). 7 refs.; 6 figs

  18. Breakdown studies for neutral injectors

    International Nuclear Information System (INIS)

    Bottiglioni, F.; Bussac, J.P.

    1981-01-01

    Reliable operation of high energy neutral injectors is challenged by the voltage hold-off capability of the extraction systems. The high voltage behavior of a gap depends not only on a large number of macroscopic parameters, e.g. the electrodes material, geometry, separation, and residual gas pressure, but also upon dimly defined and badly controlled microscopic electric properties such as electrodes surface conditions, which are in turn affected by the conditioning procedures and by the operational history of the gap. In fact, it is merely due to the microscopic surface conditions of electrodes, especially cathodes, that for most favorable regimes, macroscopic breakdown fields are two orders of magnitude lower than what can be expected from the field emission theory (E greater than or equal to 3 10 9 V/m). At FAR, experimental data on the voltage hold-off problems are obtained in a large injector (Megawatt Beam Line - MWBL) and in L.E.O., a smaller but more flexible facility where single beam studies will be made, up to 160 keV. Some results are described

  19. Nucleation and Growth of GaN on GaAs (001) Substrates

    Energy Technology Data Exchange (ETDEWEB)

    Drummond, Timothy J.; Hafich, Michael J.; Heller, Edwin J.; Lee, Stephen R.; Liliental-Weber, Zuzanna; Ruvimov, Sergei; Sullivan, John P.

    1999-05-03

    The nucleation of GaN thin films on GaAs is investigated for growth at 620 "C. An rf plasma cell is used to generate chemically active nitrogen from N2. An arsenic flux is used in the first eight monolayer of nitride growth to enhance nucleation of the cubic phase. Subsequent growth does not require an As flux to preserve the cubic phase. The nucleation of smooth interfaces and GaN films with low stacking fault densities is dependent upon relative concentrations of active nitrogen species in the plasma and on the nitrogen to gallium flux ratio.

  20. Nucleation of voids. Final report, October 1, 1971--January 31, 1977

    International Nuclear Information System (INIS)

    Katz, J.L.

    1977-10-01

    The successful prediction of the conditions under which nucleation occurs in metals, as a result of the high concentrations of vacancies and interstitial atoms (and gas atoms) present in reactor environments, has been accomplished by (1) generalizing homogeneous nucleation theory to account for nucleation of matter (i.e., vacancies) in the presence of its antimatter (i.e., interstitials), (2) further generalizing the theory to account for the effects of both trapped and soluble gas, and (3) modifying the theory to describe interstitial loop formation and including the effects of external stress

  1. Nucleation site in CVD graphene growth investigated by radiation-mode optical microscopy

    Science.gov (United States)

    Taira, Takanobu; Obata, Seiji; Saiki, Koichiro

    2017-05-01

    We investigate the graphene nucleation site in real space using radiation-mode optical microscopy (Rad-OM), which we have developed for the real-time observation of the graphene growth in chemical vapor deposition (CVD) conditions. We found the bright spot in the Rad-OM image worked as a nucleation site through continuous observation of a Cu substrate from pretreatment to graphene growth. The bright spot, considered as a C impurity, was effectively removed by Ar bombardment, which significantly reduced the nucleation density. The present result directly elucidates the role of C impurities and provides a means to grow single-crystalline and large-area graphene via CVD.

  2. Passive measurement of flux nucleation in the current-induced resistive state of type I superconductors

    International Nuclear Information System (INIS)

    Selig, K.P.; Chimenti, D.E.; Huebener, R.P.

    1978-01-01

    Flux-tube nucleation rates have been measured in the current-induced resistive state of type I superconducting In films between 1.5 and 2.0 K by a completely passive technique. Indication of periodic nucleation is observed only in narrow regions of sample voltage drop, whose position is a sensitive function of temperature. Frequency bandwidth measurements of the nucleation rate yield a spectral purity of one part in 10 4 within the narrow regions where an experimental signal can be detected. (orig.) [de

  3. Nucleation of carbon nanotubes and their bundles at the surface of catalyst melt

    Science.gov (United States)

    Alekseev, N. I.; Charykov, N. A.

    2008-12-01

    The kinetics of nanotube nucleation from a carbon-supersaturated nanodrop of a catalytic metal was considered. The problem of nucleation of the solid phase from a supersaturated melt was considered with allowance for the particular boundary conditions and the specificity of carbon structure. The solutions are obtained for the cases of extended and surface substrate nanopores, in which the carbon-supersaturated nanodrops are located. The threshold nucleation temperatures were determined for the single-and multiwall nanotubes and their bundles. The dependences of the nanotube size and the required supersaturation level on the temperature and nanodrop size are determined.

  4. Direct measurement of free-energy barrier to nucleation of crystallites in amorphous silicon thin films

    Science.gov (United States)

    Shi, Frank G.

    1994-01-01

    A method is introduced to measure the free-energy barrier W(sup *), the activation energy, and activation entropy to nucleation of crystallites in amorphous solids, independent of the energy barrier to growth. The method allows one to determine the temperature dependence of W(sup *), and the effect of the preparation conditions of the initial amorphous phase, the dopants, and the crystallization methds on W(sup *). The method is applied to determine the free-energy barrier to nucleation of crystallites in amorphous silicon (a-Si) thin films. For thermally induced nucleation in a-Si thin films with annealing temperatures in the range of from 824 to 983 K, the free-energy barrier W(sup *) to nucleation of silicon crystals is about 2.0 - 2.1 eV regardless of the preparation conditions of the films. The observation supports the idea that a-Si transforms into an intermediate amorphous state through the structural relaxation prior to the onset of nucleation of crystallites in a-Si. The observation also indicates that the activation entropy may be an insignificant part of the free-energy barrier for the nucleation of crystallites in a-Si. Compared with the free-energy barrier to nucleation of crystallites in undoped a-Si films, a significant reduction is observed in the free-energy barrier to nucleation in Cu-doped a-Si films. For a-Si under irradiation of Xe(2+) at 10(exp 5) eV, the free-energy barrier to ion-induced nucleation of crystallites is shown to be about half of the value associated with thermal-induced nucleation of crystallites in a-Si under the otherwise same conditions, which is much more significant than previously expected. The present method has a general kinetic basis; it thus should be equally applicable to nucleation of crystallites in any amorphous elemental semiconductors and semiconductor alloys, metallic and polymeric glasses, and to nucleation of crystallites in melts and solutions.

  5. Investigation of a GaN Nucleation Layer on a Patterned Sapphire Substrate

    International Nuclear Information System (INIS)

    Wu Meng; Zeng Yi-Ping; Wang Jun-Xi; Hu Qiang

    2011-01-01

    A low-temperature GaN (LT-GaN) nucleation layer is grown on a patterned sapphire substrate (PSS) using metal-organic chemical vapor deposition (MOCVD). The surface morphology of the LT-GaN is investigated and the selective nucleation phenomenon in the growth process of the LT-GaN nucleation layer is discovered. Meanwhile, effects of thickness of the LT-GaN and the annealing process on the phenomenon are also discussed. A pattern model is also proposed to analyze the possible mechanisms in atomic scale. (cross-disciplinary physics and related areas of science and technology)

  6. Investigation of a GaN nucleation layer on a patterned sapphire substrate

    International Nuclear Information System (INIS)

    Wu Meng; Zeng Yiping; Wang Junxi; Hu Qiang

    2011-01-01

    A low-temperature GaN (LT-GaN) nucleation layer is grown on a patterned sapphire substrate (PSS) using metal-organic chemical vapor deposition (MOCVD). The surface morphology of the LT-GaN is investigated and the selective nucleation phenomenon in the growth process of the LT-GaN nucleation layer is discovered. Meanwhile, effects of thickness of the LT-GaN and the annealing process on the phenomenon are also discussed. A pattern model is also proposed to analyze the possible mechanisms in atomic scale. (authors)

  7. Nucleation and growth kinetics of zirconium hydroxide by precipitation with ammonium hydroxide

    International Nuclear Information System (INIS)

    Carleson, T.E.; Chipman, N.A.

    1987-01-01

    The results of a study of the nucleation and growth kinetics of the precipitation of zirconium hydroxide from the reaction of hexafluorozirconate solution with ammonium hydroxide are reported. The McCabe linear growth rate model was used to correlate the results. The growth rate decreased with residence time and supersaturation for studies with 7 residence times (3.5 - 90 minutes and two supersaturation ratios (0.03 - 0.04, and 0.4). The nucleation rate increased with residence time and supersaturation. A negative kinetic order of nucleation was observed that may be due to the inhibition of particle growth by adsorption of reacting species on the crystal surfaces

  8. Weak preservation of local neutral substitution rates across mammalian genomes

    Directory of Open Access Journals (Sweden)

    Karro John E

    2009-05-01

    Full Text Available Abstract Background The rate at which neutral (non-functional bases undergo substitution is highly dependent on their location within a genome. However, it is not clear how fast these location-dependent rates change, or to what extent the substitution rate patterns are conserved between lineages. To address this question, which is critical not only for understanding the substitution process but also for evaluating phylogenetic footprinting algorithms, we examine ancestral repeats: a predominantly neutral dataset with a significantly higher genomic density than other datasets commonly used to study substitution rate variation. Using this repeat data, we measure the extent to which orthologous ancestral repeat sequences exhibit similar substitution patterns in separate mammalian lineages, allowing us to ascertain how well local substitution rates have been preserved across species. Results We calculated substitution rates for each ancestral repeat in each of three independent mammalian lineages (primate – from human/macaque alignments, rodent – from mouse/rat alignments, and laurasiatheria – from dog/cow alignments. We then measured the correlation of local substitution rates among these lineages. Overall we found the correlations between lineages to be statistically significant, but too weak to have much predictive power (r2 5%. These correlations were found to be primarily driven by regional effects at the scale of several hundred kb or larger. A few repeat classes (e.g. 7SK, Charlie8, and MER121 also exhibited stronger conservation of rate patterns, likely due to the effect of repeat-specific purifying selection. These classes should be excluded when estimating local neutral substitution rates. Conclusion Although local neutral substitution rates have some correlations among mammalian species, these correlations have little predictive power on the scale of individual repeats. This indicates that local substitution rates have changed

  9. "This one is stronger". Spotlights on the lifelong learning professional-in-action

    Directory of Open Access Journals (Sweden)

    Josje van der Linden

    2016-06-01

    Full Text Available ABSTRACT“This one is stronger.” Spotlights on the lifelong learning professional-in-action Around the world, lifelong learning is being promoted as a strategy for coping with the changing realities of life and work. The fourth Sustainable Development Goal, agreed in September 2015, reflects this: “ensure equitable and inclusive quality education and promote lifelong learning opportunities for all”. Despite its importance, doubts remain about the implementation of this goal in practice (Van der Kamp, 2000; Regmi, 2015. This article looks at the practice of lifelong learning from the point of view of the professionals involved, their actions and the way these actions are challenged, supported and further developed. Following Schön’s “reflection-in-action” (1983, the term “professional-in-action” is used to stress the role of the professional in making the difference on the ground. The leading question is: how can lifelong learning professionals be supported in their contribution to surrounding society and its citizens? The professionals-in-action featured in this article include professionals based in the Netherlands as well as in other, less privileged contexts. Meaningful experiences are used to build a story about challenges, the right to exist, commitment, recognition and room to manoeuvre. The experiences reveal the importance of interacting with the learner and the professional space that is necessary to achieve this. Professionalization in professional learning communities and practice-oriented research must accompany this professional space. SAMENVATTING“Deze is sterker”. Spotlights op de leven lang leren professional-in-actieOm te kunnen omgaan met de veranderende realiteit in leven en werk, wordt wereldwijd een leven lang leren aangemoedigd. Het vierde duurzame ontwikkelingsdoel, vastgesteld in september 2015, weerspiegelt dit: “het verzekeren van kwalitatief goed onderwijs en het bevorderen van de mogelijkheden

  10. Electrostatics Control Actin Filament Nucleation and Elongation Kinetics*

    Science.gov (United States)

    Crevenna, Alvaro H.; Naredi-Rainer, Nikolaus; Schönichen, André; Dzubiella, Joachim; Barber, Diane L.; Lamb, Don C.; Wedlich-Söldner, Roland

    2013-01-01

    The actin cytoskeleton is a central mediator of cellular morphogenesis, and rapid actin reorganization drives essential processes such as cell migration and cell division. Whereas several actin-binding proteins are known to be regulated by changes in intracellular pH, detailed information regarding the effect of pH on the actin dynamics itself is still lacking. Here, we combine bulk assays, total internal reflection fluorescence microscopy, fluorescence fluctuation spectroscopy techniques, and theory to comprehensively characterize the effect of pH on actin polymerization. We show that both nucleation and elongation are strongly enhanced at acidic pH, with a maximum close to the pI of actin. Monomer association rates are similarly affected by pH at both ends, although dissociation rates are differentially affected. This indicates that electrostatics control the diffusional encounter but not the dissociation rate, which is critical for the establishment of actin filament asymmetry. A generic model of protein-protein interaction, including electrostatics, explains the observed pH sensitivity as a consequence of charge repulsion. The observed pH effect on actin in vitro agrees with measurements of Listeria propulsion in pH-controlled cells. pH regulation should therefore be considered as a modulator of actin dynamics in a cellular environment. PMID:23486468

  11. Electrostatics control actin filament nucleation and elongation kinetics.

    Science.gov (United States)

    Crevenna, Alvaro H; Naredi-Rainer, Nikolaus; Schönichen, André; Dzubiella, Joachim; Barber, Diane L; Lamb, Don C; Wedlich-Söldner, Roland

    2013-04-26

    The actin cytoskeleton is a central mediator of cellular morphogenesis, and rapid actin reorganization drives essential processes such as cell migration and cell division. Whereas several actin-binding proteins are known to be regulated by changes in intracellular pH, detailed information regarding the effect of pH on the actin dynamics itself is still lacking. Here, we combine bulk assays, total internal reflection fluorescence microscopy, fluorescence fluctuation spectroscopy techniques, and theory to comprehensively characterize the effect of pH on actin polymerization. We show that both nucleation and elongation are strongly enhanced at acidic pH, with a maximum close to the pI of actin. Monomer association rates are similarly affected by pH at both ends, although dissociation rates are differentially affected. This indicates that electrostatics control the diffusional encounter but not the dissociation rate, which is critical for the establishment of actin filament asymmetry. A generic model of protein-protein interaction, including electrostatics, explains the observed pH sensitivity as a consequence of charge repulsion. The observed pH effect on actin in vitro agrees with measurements of Listeria propulsion in pH-controlled cells. pH regulation should therefore be considered as a modulator of actin dynamics in a cellular environment.

  12. A correlation to the heat transfer coefficient in nucleate boiling

    International Nuclear Information System (INIS)

    Ribatski, Gherhardt; Jabardo, Jose M. Saiz

    1999-01-01

    Nucleate boiling heat transfer is a complex phenomenon, making the development of a correlation for the heat transfer coefficient rather cumbersome due to the number of physical parameters involved in it. Some authors have followed a pragmatic approach to the problem by correlating the heat transfer coefficient in terms of reduced primitive properties. Two of the most knowledgeable authors who have followed this approach are Gorenflo and Cooper. Comparisons have been performed among results from the correlations proposed by these researchers and experimental results obtained elsewhere for refrigerants R-11, R-113 and R-114. These comparisons have shown that Cooper's correlation is best fitted for halocarbon refrigerants. The correlation proposed by Gorenflo ads the difficulty of including a numerical factor specific for each fluid. Leiner modified Gorenflo's correlation to determine the numerical factor as a function of known physical parameters of the fluid. In present study, the form of this function has been investigated for halocarbon refrigerants. The obtained correlation is written in terms of the following parameters: reduced pressure, eccentric and compressibility factors at the critical state, and a dimensionless specific heat of the vapor phase. The correlation compares well with experimental results. (author)

  13. Latent heat transport and microlayer evaporation in nucleate boiling

    International Nuclear Information System (INIS)

    Jawurek, H.H.

    1977-08-01

    Part 1 of this work provides a broad overview and, where possible, a quantitative assessment of the complex physical processes which together constitute the mechanism of nucleate boiling heat transfer. It is shown that under a wide range of conditions the primary surface-to-liquid heat flows within an area of bubble influence are so redistributed as to manifest themselves predominantly as latent heat transport, that is, as vaporisation into attached bubbles. Part 2 deals in greater detail with one of the component processes of latent heat transport, namely microlayer evaporation. A literature review reveals the need for synchronised records of microlayer geometry versus time and of normal bubble growth and departure. An apparatus developed to provide such records is described. High-speed cine interference photography from beneath and through a transparent heating surface provided details of microlayer geometry and an image reflection system synchronised these records with the bubble profile views. Results are given for methanol and ethanol boiling at sub-atmospheric pressures and at various heat fluxes and bulk subcoolings. In all cases it is found that microlayers were of sub-micron thickness, that microlayer thinning was restricted to the inner layer edge (with the thickness elsewhere remaining constant or increasing with time) and that the contribution of this visible evaporation to the total vapour flow into bubbles was negligible. The observation of thickening towards the outer microlayer edge, however, demonstrates that a liquid replenishment flow occurred simultaneously with the evaporation process

  14. A new correlation for nucleate pool boiling of aqueous mixtures

    International Nuclear Information System (INIS)

    Thome, J.R.; Shakir, S.

    1987-01-01

    A new mixture boiling correlation was developed for nucleate pool boiling of aqueous mixtures on plain, smooth tubes. The semi-empirical correlation models the rise in the local bubble point temperature in a mixture caused by the preferential evaporation of the more volatile component during bubble growth. This rise varies from zero at low heat fluxes (where only single-phase natural convection is present) up to nearly the entire boiling range at the peak heat flux (where latent heat transport is dominant). The boiling range, which is the temperature difference between the dew point and bubble point of a mixture, is used to characterize phase equilibrium effects. An exponential term models the rise in the local bubble point temperature as a function of heat flux. The correlation was compared against binary mixture boiling data for ethanol-water, methanol-water, n-propanol-water, and acetone-water. The majority of the data was predicted to within 20%. Further experimental research is currently underway to obtain multicomponent boiling data for aqueous mixtures with up to five components and for wider boiling ranges

  15. Microlayer Topology And Bubble Growth In Nucleate Boiling

    Science.gov (United States)

    Jawurek, H. H.; Macgregor, H. G.; Bodenheimer, J. S.

    1987-09-01

    During nucleate boiling thin liquid films (nicrolayers) form beneath the base of bubbles and evaporate into the bubble interiors. A technique is presented which permits the simultaneous determination of microlayer topology and the contribution of microlayer evaporation to bubble growth. Isolated-bubble boiling takes place on an electrically heated, transparent tin-oxide coating deposited on a glass plate, the latter forming the floor of a vessel. With coherent Claser) illumination from beneath, the microlayers reflect fringe patterns similar to Newton's rings. Owing to the rapid evaporation of the layers (the process is completed within milliseconds) the fringes are in rapid motion and are recorded by eine photography at some 4 000 frames per second and exposure times of 50 μs. The resulting interferograms provide details of microlayer shape and thickness versus time, and thus evaporation rate. Simultaneously, and on the same film, bubble profiles (and thus volumes) are obtained under white light illumination. The two bubble images are manipulated by mirrors and lenses so as to appear side by side on the same frame of film, the fringes magnified and the profiles reduced. Sample results for methanol boiling at a pressure of 58.5 kPa and with the liquid bulk at saturation temperature, are presented. Under such conditions microlayer evaporation accounts for 37 per cent of the total bubble volume at detachment.

  16. Nucleation of reaction-diffusion waves on curved surfaces

    International Nuclear Information System (INIS)

    Kneer, Frederike; Schöll, Eckehard; Dahlem, Markus A

    2014-01-01

    We study reaction-diffusion waves on curved two-dimensional surfaces, and determine the influence of curvature upon the nucleation and propagation of spatially localized waves in an excitable medium modelled by the generic FitzHugh–Nagumo model. We show that the stability of propagating wave segments depends crucially on the curvature of the surface. As they propagate, they may shrink to the uniform steady state, or expand, depending on whether they are smaller or larger, respectively, than a critical nucleus. This critical nucleus for wave propagation is modified by the curvature acting like an effective space-dependent local spatial coupling, similar to diffuson, thus extending the regime of propagating excitation waves beyond the excitation threshold of flat surfaces. In particular, a negative gradient of Gaussian curvature Γ, as on the outside of a torus surface (positive Γ), when the wave segment symmetrically extends into the inside (negative Γ), allows for stable propagation of localized wave segments remaining unchanged in size and shape, or oscillating periodically in size. (paper)

  17. Photoproduction of neutral pions off protons

    NARCIS (Netherlands)

    Crede, V.; Sparks, N.; Wilson, A.; Anisovich, A. V.; Bacelar, J. C. S.; Bantes, R.; Bartholomy, O.; Bayadilov, D.; Beck, R.; Beloglazov, Y. A.; Castelijns, R.; Dutz, H.; Elsner, D.; Ewald, R.; Frommberger, F.; Funke, Chr; Gregor, R.; Gridnev, A.; Gutz, E.; Hillert, W.; Hoffmeister, P.; Jaegle, I.; Junkersfeld, J.; Kalinowsky, H.; Kammer, S.; Klein, Frank; Klein, Friedrich; Klempt, E.; Kotulla, M.; Krusche, B.; Löhner, H.; Lopatin, I. V.; Lugert, S.; Menze, D.; Mertens, T.; Messchendorp, J. G.; Metag, V.; Nanova, M.; Nikonov, V. A.; Novinski, D.; Novotny, R.; Ostrick, M.; Pant, L. M.; van Pee, H.; Pfeiffer, M.; Roy, A.; Sarantsev, A. V.; Schadmand, S.; Schmidt, C.; Schmieden, H.; Schoch, B.; Shende, S.; Sokhoyan, V.; Suele, A.; Sumachev, V. V.; Szczepanek, T.; Thoma, U.; Trnka, D.; Varma, R.; Walther, D.; Wendel, Ch

    2011-01-01

    Photoproduction of neutral pions has been studied with the CBELSA/TAPS detector in the reaction gamma p -> p pi(0) for photon energies between 0.85 and 2.50 GeV. The pi(0) mesons are observed in their dominant neutral decay mode: pi(0) -> gamma gamma. For the first time, the differential cross

  18. 32 CFR 644.323 - Neutral language.

    Science.gov (United States)

    2010-07-01

    ... 32 National Defense 4 2010-07-01 2010-07-01 true Neutral language. 644.323 Section 644.323 National Defense Department of Defense (Continued) DEPARTMENT OF THE ARMY (CONTINUED) REAL PROPERTY REAL ESTATE HANDBOOK Disposal § 644.323 Neutral language. Wherever the words “man”, “men”, or their related...

  19. Targets for high power neutral beams

    International Nuclear Information System (INIS)

    Kim, J.

    1980-01-01

    Stopping high-power, long-pulse beams is fast becoming an engineering challenge, particularly in neutral beam injectors for heating magnetically confined plasmas. A brief review of neutral beam target technology is presented along with heat transfer calculations for some selected target designs

  20. Auditors' Professional Skepticism: Neutrality versus Presumptive Doubt

    NARCIS (Netherlands)

    Groot, T.L.C.M.; Quadackers, L.M.; Wright, A.

    2014-01-01

    Although skepticism is widely viewed as essential to audit quality, there is a debate about what form is optimal. The two prevailing perspectives that have surfaced are "neutrality" and "presumptive doubt." With neutrality, auditors neither believe nor disbelieve client management. With presumptive