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Sample records for nucleation centers sintesis

  1. Method for calculating the sizes of nucleation centers upon homogeneous crystallization from a supercooled liquid

    NASA Astrophysics Data System (ADS)

    Aleksandrov, V. D.; Pokyntelytsia, O. A.

    2016-09-01

    An alternative approach to calculating critical sizes l k of nucleation centers and work A k of their formation upon crystallization from a supercooled melt by analyzing the variation in the Gibbs energy during the phase transformation is considered. Unlike the classical variant, it is proposed that the transformation entropy be associated not with melting temperature T L but with temperature T < T L at which the nucleation of crystals occurs. New equations for l k and A k are derived. Based on the results from calculating these quantities for a series of compounds, it is shown that this approach is unbiased and it is possible to eliminate known conflicts in analyzing these parameters in the classical interpretation.

  2. Selective deposition of polycrystalline diamond films using photolithography with addition of nanodiamonds as nucleation centers

    NASA Astrophysics Data System (ADS)

    Okhotnikov, V. V.; Linnik, S. A.; Gaidaichuk, A. V.; Shashev, D. V.; Nazarova, G. Yu; Yurchenko, V. I.

    2016-02-01

    A new method of selective deposition of polycrystalline diamond has been developed and studied. The diamond coatings with a complex, predetermined geometry and resolution up to 5 μm were obtained. A high density of polycrystallites in the coating area was reached (up to 32·107 pcs/cm2). The uniformity of the film reached 100%, and the degree of the surface contamination by parasitic crystals did not exceed 2%. The technology was based on the application of the standard photolithography with an addition of nanodiamond suspension into the photoresist that provided the creation of the centers of further nucleation in the areas which require further overgrowth. The films were deposited onto monocrystalline silicon substrates using the method of “hot filaments” in the CVD reactor. The properties of the coating and the impact of the nanodiamond suspension concentration in the photoresist were also studied. The potential use of the given method includes a high resolution, technological efficiency, and low labor costs compared to the standard methods (laser treatment, chemical etching in aggressive environments,).

  3. Characterizing protein crystal nucleation

    NASA Astrophysics Data System (ADS)

    Akella, Sathish V.

    We developed an experimental microfluidic based technique to measure the nucleation rates and successfully applied the technique to measure nucleation rates of lysozyme crystals. The technique involves counting the number of samples which do not have crystals as a function of time. Under the assumption that nucleation is a Poisson process, the fraction of samples with no crystals decays exponentially with the decay constant proportional to nucleation rate and volume of the sample. Since nucleation is a random and rare event, one needs to perform measurements on large number of samples to obtain good statistics. Microfluidics offers the solution of producing large number of samples at minimal material consumption. Hence, we developed a microfluidic method and measured nucleation rates of lysozyme crystals in supersaturated protein drops, each with volume of ˜ 1 nL. Classical Nucleation Theory (CNT) describes the kinetics of nucleation and predicts the functional form of nucleation rate in terms of the thermodynamic quantities involved, such as supersaturation, temperature, etc. We analyzed the measured nucleation rates in the context of CNT and obtained the activation energy and the kinetic pre-factor characterizing the nucleation process. One conclusion is that heterogeneous nucleation dominates crystallization. We report preliminary studies on selective enhancement of nucleation in one of the crystal polymorprhs of lysozyme (spherulite) using amorphous mesoporous bioactive gel-glass te{naomi06, naomi08}, CaO.P 2O5.SiO2 (known as bio-glass) with 2-10 nm pore-size diameter distribution. The pores act as heterogeneous nucleation centers and claimed to enhance the nucleation rates by molecular confinement. The measured kinetic profiles of crystal fraction of spherulites indicate that the crystallization of spherulites may be proceeding via secondary nucleation pathways.

  4. Heterogeneous nucleation or homogeneous nucleation?

    NASA Astrophysics Data System (ADS)

    Liu, X. Y.

    2000-06-01

    The generic heterogeneous effect of foreign particles on three dimensional nucleation was examined both theoretically and experimentally. It shows that the nucleation observed under normal conditions includes a sequence of progressive heterogeneous processes, characterized by different interfacial correlation function f(m,x)s. At low supersaturations, nucleation will be controlled by the process with a small interfacial correlation function f(m,x), which results from a strong interaction and good structural match between the foreign bodies and the crystallizing phase. At high supersaturations, nucleation on foreign particles having a weak interaction and poor structural match with the crystallizing phase (f(m,x)→1) will govern the kinetics. This frequently leads to the false identification of homogeneous nucleation. Genuine homogeneous nucleation, which is the up-limit of heterogeneous nucleation, may not be easily achievable under gravity. In order to check these results, the prediction is confronted with nucleation experiments of some organic and inorganic crystals. The results are in excellent agreement with the theory.

  5. Cavitation nucleation

    NASA Astrophysics Data System (ADS)

    Crum, Lawrence A.

    2001-05-01

    For his dissertation research at Harvard, Bob Apfel chose the subject of homogeneous nucleation, and conceived of some ingenious experiments to test existing theories. By selecting a small microdroplet of liquid, he could make the reasonable assumption that no inhomogeneities were present to serve as preferential sites for liquid rupture. However, Bob also studied dirty liquids, as well as very clean ones, and wrote some seminal papers on inhomogeneous nucleation, in which he developed the Golden rule: Know thy liquid! Currently, considerable attention has been devoted to the study of cavitation generation in vivo, particularly in blood, and, for this case, the nucleation conditions are much different than those for normal liquids. In this presentation, I will review some of Bob's pioneering studies and present some of our latest studies of cavitation inception, both in vitro and in vivo.

  6. Transient nucleation in glasses

    NASA Technical Reports Server (NTRS)

    Kelton, K. F.

    1991-01-01

    Nucleation rates in condensed systems are frequently not at their steady state values. Such time dependent (or transient) nucleation is most clearly observed in devitrification studies of metallic and silicate glasses. The origin of transient nucleation and its role in the formation and stability of desired phases and microstructures are discussed. Numerical models of nucleation in isothermal and nonisothermal situations, based on the coupled differential equations describing cluster evolution within the classical theory, are presented. The importance of transient nucleation in glass formation and crystallization is discussed.

  7. Diamond nucleation under bias conditions

    SciTech Connect

    Stoeckel, R.; Stammler, M.; Janischowsky, K.; Ley, L.; Albrecht, M.; Strunk, H.P.

    1998-01-01

    The so-called bias pretreatment allows the growth of heteroepitaxial diamond films by plasma chemical vapor deposition on silicon (100) surfaces. We present plan-view and cross-sectional transmission electron micrographs of the substrate surface at different phases of the bias pretreatment. These observations are augmented by measurements of the etch rates of Si, SiC, and different carbon modifications under plasma conditions and the size distribution of oriented diamond crystals grown after bias pretreatment. Based on these results a new model for diamond nucleation under bias conditions is proposed. First, a closed layer of nearly epitaxially oriented cubic SiC with a thickness of about 10 nm is formed. Subplantation of carbon into this SiC layer causes a supersaturation with carbon and results in the subcutaneous formation of epitaxially oriented nucleation centers in the SiC layer. Etching of the SiC during the bias pretreatment as well as during diamond growth brings these nucleation centers to the sample surface and causes the growth of diamonds epitaxially oriented on the Si/SiC substrate. {copyright} {ital 1998 American Institute of Physics.}

  8. Effect of La{sub 2}O{sub 3}, CoO, Cr{sub 2}O{sub 3} and MoO{sub 3} nucleating agents on crystallization behavior and magnetic properties of ferromagnetic glass-ceramic in the system Fe{sub 2}O{sub 3}{center_dot}CaO{center_dot}ZnO{center_dot}SiO{sub 2}

    SciTech Connect

    Abdel-Hameed, Salwa A.M.; Elwan, Rawhia L.

    2012-05-15

    Highlights: Black-Right-Pointing-Pointer Crystallization of magnetic glass ceramic with different nucleating agents. Black-Right-Pointing-Pointer The effect of La{sub 2}O{sub 3}, CoO, Cr{sub 2}O{sub 3} and MoO{sub 3} as nucleating agents was studied. Black-Right-Pointing-Pointer XRD for as prepared samples revealed crystallization of pure magnetite. Black-Right-Pointing-Pointer Heat treatment revealed minor calcium silicate, hematite and cristobalite. Black-Right-Pointing-Pointer TEM revealed crystallization of crystallite size in the range 50-100 nm. -- Abstract: Preparation and characterization of ferromagnetic glass ceramic in the system Fe{sub 2}O{sub 3}{center_dot}CaO{center_dot}ZnO{center_dot}SiO{sub 2} with different nucleating agents was studied. The effect of La{sub 2}O{sub 3}, CoO, Cr{sub 2}O{sub 3} and MoO{sub 3} as nucleating agents was investigated. Differential thermal analysis; X-ray diffraction and transmission electron microscope were used to investigate thermal behavior, sequence of crystallization and microstructure of the samples. XRD analysis for as prepared samples revealed the crystallization of single magnetite phase. Heat treatment at 900 Degree-Sign C/2 h revealed the appearance of minor amounts of calcium silicate, hematite and cristobalite beside magnetite. TEM revealed crystallization of crystallite size in the range 50-100 nm. Lattice parameters, cell volume and crystallite size were stimulated from XRD data. Magnetic properties of quenched samples were measured under 20 kG.

  9. Diamond nucleation using polyethene

    DOEpatents

    Morell, Gerardo; Makarov, Vladimir; Varshney, Deepak; Weiner, Brad

    2013-07-23

    The invention presents a simple, non-destructive and non-abrasive method of diamond nucleation using polyethene. It particularly describes the nucleation of diamond on an electrically viable substrate surface using polyethene via chemical vapor deposition (CVD) technique in a gaseous environment.

  10. Diamond Nucleation Using Polyethene

    NASA Technical Reports Server (NTRS)

    Morell, Gerardo (Inventor); Makarov, Vladimir (Inventor); Varshney, Deepak (Inventor); Weiner, Brad (Inventor)

    2013-01-01

    The invention presents a simple, non-destructive and non-abrasive method of diamond nucleation using polyethene. It particularly describes the nucleation of diamond on an electrically viable substrate surface using polyethene via chemical vapor deposition (CVD) technique in a gaseous environment.

  11. Vapor liquid solid-hydride vapor phase epitaxy (VLS-HVPE) growth of ultra-long defect-free GaAs nanowires: Ab initio simulations supporting center nucleation

    SciTech Connect

    André, Yamina Lekhal, Kaddour; Hoggan, Philip; Avit, Geoffrey; Réda Ramdani, M.; Monier, Guillaume; Colas, David; Ajib, Rabih; Castelluci, Dominique; Gil, Evelyne; Cadiz, Fabian; Rowe, Alistair; Paget, Daniel; Petit, Elodie; Leroux, Christine; Trassoudaine, Agnès

    2014-05-21

    High aspect ratio, rod-like and single crystal phase GaAs nanowires (NWs) were grown by gold catalyst-assisted hydride vapor phase epitaxy (HVPE). High resolution transmission electron microscopy and micro-Raman spectroscopy revealed polytypism-free zinc blende (ZB) NWs over lengths of several tens of micrometers for a mean diameter of 50 nm. Micro-photoluminescence studies of individual NWs showed linewidths smaller than those reported elsewhere which is consistent with the crystalline quality of the NWs. HVPE makes use of chloride growth precursors GaCl of which high decomposition frequency after adsorption onto the liquid droplet catalysts, favors a direct and rapid introduction of the Ga atoms from the vapor phase into the droplets. High influxes of Ga and As species then yield high axial growth rate of more than 100 μm/h. The diffusion of the Ga atoms in the liquid droplet towards the interface between the liquid and the solid nanowire was investigated by using density functional theory calculations. The diffusion coefficient of Ga atoms was estimated to be 3 × 10{sup −9} m{sup 2}/s. The fast diffusion of Ga in the droplet favors nucleation at the liquid-solid line interface at the center of the NW. This is further evidence, provided by an alternative epitaxial method with respect to metal-organic vapor phase epitaxy and molecular beam epitaxy, of the current assumption which states that this type of nucleation should always lead to the formation of the ZB cubic phase.

  12. Nonequilibrium thermodynamics of nucleation

    SciTech Connect

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

    2014-12-14

    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 metastable phase and a nucleating phase, we derive the fundamental dynamics for this phenomenon, based on continuous Fokker-Planck equations. We are readily able to treat non-isothermal nucleation even when the nucleating cores cannot be attributed intensive thermodynamic properties. In addition, we capture the dynamics of the time-dependent metastable phase being continuously expelled from the nucleating phase, and keep rigorous track of the volume corrections to the dynamics. Within our framework the definition of a thermodynamic nuclei temperature is manifest. For the special case of nucleation of a gas phase towards its vapor-liquid coexistence, we illustrate that our approach is capable of reproducing recent literature results obtained by more microscopic considerations for the suppression of the nucleation rate due to nonisothermal effects.

  13. Homogeneous nucleation of nitrogen

    NASA Astrophysics Data System (ADS)

    Iland, Kristina; Wedekind, Jan; Wölk, Judith; Strey, Reinhard

    2009-03-01

    We investigated the homogeneous nucleation of nitrogen in a cryogenic expansion chamber [A. Fladerer and R. Strey, J. Chem. Phys. 124, 164710 (2006)]. Gas mixtures of nitrogen and helium as carrier gas were adiabatically expanded and cooled down from an initial temperature of 83 K until nucleation occurred. This onset was detected by constant angle light scattering at nitrogen vapor pressures of 1.3-14.2 kPa and temperatures of 42-54 K. An analytical fit function well describes the experimental onset pressures with an error of ±15%. We estimate the size of the critical nucleus with the Gibbs-Thomson equation yielding critical sizes of about 50 molecules at the lowest and 70 molecules at the highest temperature. In addition, we estimate the nucleation rate and compare it with nucleation theories. The predictions of classical nucleation theory (CNT) are 9 to 19 orders of magnitude below the experimental results and show a stronger temperature dependence. The Reguera-Reiss theory [Phys. Rev. Lett. 93, 165701 (2004)] predicts the correct temperature dependence at low temperatures and decreases the absolute deviation to 7-13 orders of magnitude. We present an empirical correction function to CNT describing our experimental results. These correction parameters are remarkably close to the ones of argon [Iland et al., J. Chem. Phys. 127, 154506 (2007)] and even those of water [J. Wölk and R. Strey, J. Phys. Chem. B 105, 11683 (2001)].

  14. Microtubule nucleation and organization in dendrites.

    PubMed

    Delandre, Caroline; Amikura, Reiko; Moore, Adrian W

    2016-07-01

    Dendrite branching is an essential process for building complex nervous systems. It determines the number, distribution and integration of inputs into a neuron, and is regulated to create the diverse dendrite arbor branching patterns characteristic of different neuron types. The microtubule cytoskeleton is critical to provide structure and exert force during dendrite branching. It also supports the functional requirements of dendrites, reflected by differential microtubule architectural organization between neuron types, illustrated here for sensory neurons. Both anterograde and retrograde microtubule polymerization occur within growing dendrites, and recent studies indicate that branching is enhanced by anterograde microtubule polymerization events in nascent branches. The polarities of microtubule polymerization events are regulated by the position and orientation of microtubule nucleation events in the dendrite arbor. Golgi outposts are a primary microtubule nucleation center in dendrites and share common nucleation machinery with the centrosome. In addition, pre-existing dendrite microtubules may act as nucleation sites. We discuss how balancing the activities of distinct nucleation machineries within the growing dendrite can alter microtubule polymerization polarity and dendrite branching, and how regulating this balance can generate neuron type-specific morphologies. PMID:27097122

  15. Colloids and Nucleation

    NASA Technical Reports Server (NTRS)

    Ackerson, Bruce

    1997-01-01

    The objectives of the work funded under this grant were to develop a microphotographic technique and use it to monitor the nucleation and growth of crystals of hard colloidal spheres. Special attention is given to the possible need for microgravity studies in future experiments. A number of persons have been involved in this work. A masters student, Keith Davis, began the project and developed a sheet illumination apparatus and an image processing system for detection and analysis. His work on a segmentation program for image processing was sufficient for his master's research and has been published. A post doctoral student Bernie Olivier and a graduate student Yueming He, who originally suggested the sheet illumination, were funded by another source but along with Keith made photographic series of several samples (that had been made by Keith Davis). Data extraction has been done by Keith, Bernie, Yueming and two undergraduates employed on the grant. Results are published in Langmuir. These results describe the sheet lighting technique as one which illuminates not only the Bragg scattering crystal, but all the crystals. Thus, accurate crystal counts can be made for nucleation rate measurements. The strange crystal length scale reduction, observed in small angle light scattering (SALS) studies, following the initial nucleation and growth period, has been observed directly. The Bragg scattering (and dark) crystal size decreases in the crossover region. This could be an effect due to gravitational forces or due to over- compression of the crystal during growth. Direct observations indicate a complex morphology for the resulting hard sphere crystals. The crystal edges are fairly sharp but the crystals have a large degree of internal structure. This structure is a result of (unstable) growth and not aggregation. As yet unpublished work compares growth exponents data with data obtained by SALS. The nucleation rate density is determined over a broad volume fraction range

  16. The adsorption theory of heterogeneous nucleation and its application to ice nucleation

    NASA Astrophysics Data System (ADS)

    Laaksonen, A.; Malila, J.

    2015-12-01

    In the classical picture of heterogeneous nucleation, spherical liquid caps, characterized by a contact angle, appear on a surface at supersaturated conditions, and if these caps are larger than so called critical size, they grow spontaneously, whereas smaller caps will evaporate. In reality, vapor adsorption takes place already at subsaturated conditions, and depending on the substrate-vapor interactions, the adsorbed layer may consist of clusters centered on so called active sites. The extent of adsorption can be calculated using adsorption isotherms which give the average adsorption layer thickness as a function of vapor saturation ratio, provided that adsorption constants (characterizing the substrate-vapor interactions) are known. We recently proposed a new theory (Laaksonen, J. Phys. Chem. A., 2015) that combines adsorption and heterogeneous nucleation so that it can be used to calculate both the adsorption layer thickness at subsaturated conditions, as well as the onset supersaturation for nucleation. We showed that the new theory performs much better than the classical theory both with flat surfaces, and in the case of water vapor nucleating on SiO2, TiO2, and Ag2O nanoparticles (Laaksonen and Malila, ACPD, in press). Here, we review the new theory, and compare its predictive capability to that of the classical heterogeneous nucleation theory. We furthermore discuss the potential use of the new theory for calculation of condensation and deposition mode ice nucleation in the atmosphere.

  17. Nucleation of Ice

    NASA Astrophysics Data System (ADS)

    Molinero, Valeria

    2009-03-01

    The freezing of water into ice is a ubiquitous transformation in nature, yet the microscopic mechanism of homogeneous nucleation of ice has not yet been elucidated. One of the reasons is that nucleation happens in time scales that are too fast for an experimental characterization and two slow for a systematic study with atomistic simulations. In this work we use coarse-grained molecular dynamics simulations with the monatomic model of water mW[1] to shed light into the mechanism of homogeneous nucleation of ice and its relationship to the thermodynamics of supercooled water. Cooling of bulk water produces either crystalline ice or low- density amorphous ice (LDA) depending on the quenching rate. We find that ice crystallization occurs faster at temperatures close to the liquid-liquid transition, defined as the point of maximum inflection of the density with respect to the temperature. At the liquid-liquid transition, the time scale of nucleation becomes comparable to the time scale of relaxation within the liquid phase, determining --effectively- the end of the metastable liquid state. Our results imply that no ultraviscous liquid water can exist at temperatures just above the much disputed glass transition of water. We discuss how the scenario is changed when water is in confinement, and the relationship of the mechanism of ice nucleation to that of other liquids that present the same phase behavior, silicon [2] and germanium [3]. [4pt] [1] Molinero, V. & Moore, E. B. Water modeled as an intermediate element between carbon and silicon. Journal of Physical Chemistry B (2008). Online at http://pubs.acs.org/cgi- bin/abstract.cgi/jpcbfk/asap/abs/jp805227c.html [0pt] [2] Molinero, V., Sastry, S. & Angell, C. A. Tuning of tetrahedrality in a silicon potential yields a series of monatomic (metal-like) glass formers of very high fragility. Physical Review Letters 97, 075701 (2006).

  18. Bleb Nucleation through Membrane Peeling

    NASA Astrophysics Data System (ADS)

    Alert, Ricard; Casademunt, Jaume

    2016-02-01

    We study the nucleation of blebs, i.e., protrusions arising from a local detachment of the membrane from the cortex of a cell. Based on a simple model of elastic linkers with force-dependent kinetics, we show that bleb nucleation is governed by membrane peeling. By this mechanism, the growth or shrinkage of a detached membrane patch is completely determined by the linker kinetics, regardless of the energetic cost of the detachment. We predict the critical nucleation radius for membrane peeling and the corresponding effective energy barrier. These may be typically smaller than those predicted by classical nucleation theory, implying a much faster nucleation. We also perform simulations of a continuum stochastic model of membrane-cortex adhesion to obtain the statistics of bleb nucleation times as a function of the stress on the membrane. The determinant role of membrane peeling changes our understanding of bleb nucleation and opens new directions in the study of blebs.

  19. Nucleation in Synoptically Forced Cirrostratus

    NASA Technical Reports Server (NTRS)

    Lin, R.-F.; Starr, D. OC.; Reichardt, J.; DeMott, P. J.

    2004-01-01

    Formation and evolution of cirrostratus in response to weak, uniform and constant synoptic forcing is simulated using a one-dimensional numerical model with explicit microphysics, in which the particle size distribution in each grid box is fully resolved. A series of tests of the model response to nucleation modes (homogeneous-freezing-only/heterogeneous nucleation) and heterogeneous nucleation parameters are performed. In the case studied here, nucleation is first activated in the prescribed moist layer. A continuous cloud-top nucleation zone with a depth depending on the vertical humidity gradient and one of the nucleation parameters is developed afterward. For the heterogeneous nucleation cases, intermittent nucleation zones in the mid-upper portion of the cloud form where the relative humidity is on the rise, because existent ice crystals do not uptake excess water vapor efficiently, and ice nuclei (IN) are available. Vertical resolution as fine as 1 m is required for realistic simulation of the homogeneous-freezing-only scenario, while the model resolution requirement is more relaxed in the cases where heterogeneous nucleation dominates. Bulk microphysical and optical properties are evaluated and compared. Ice particle number flux divergence, which is due to the vertical gradient of the gravity-induced particle sedimentation, is constantly and rapidly changing the local ice number concentration, even in the nucleation zone. When the depth of the nucleation zone is shallow, particle number concentration decreases rapidly as ice particles grow and sediment away from the nucleation zone. When the depth of the nucleation zone is large, a region of high ice number concentration can be sustained. The depth of nucleation zone is an important parameter to be considered in parametric treatments of ice cloud generation.

  20. On the Ice Nucleation Spectrum

    NASA Technical Reports Server (NTRS)

    Barahona, D.

    2012-01-01

    This work presents a novel formulation of the ice nucleation spectrum, i.e. the function relating the ice crystal concentration to cloud formation conditions and aerosol properties. The new formulation is physically-based and explicitly accounts for the dependency of the ice crystal concentration on temperature, supersaturation, cooling rate, and particle size, surface area and composition. This is achieved by introducing the concepts of ice nucleation coefficient (the number of ice germs present in a particle) and nucleation probability dispersion function (the distribution of ice nucleation coefficients within the aerosol population). The new formulation is used to generate ice nucleation parameterizations for the homogeneous freezing of cloud droplets and the heterogeneous deposition ice nucleation on dust and soot ice nuclei. For homogeneous freezing, it was found that by increasing the dispersion in the droplet volume distribution the fraction of supercooled droplets in the population increases. For heterogeneous ice nucleation the new formulation consistently describes singular and stochastic behavior within a single framework. Using a fundamentally stochastic approach, both cooling rate independence and constancy of the ice nucleation fraction over time, features typically associated with singular behavior, were reproduced. Analysis of the temporal dependency of the ice nucleation spectrum suggested that experimental methods that measure the ice nucleation fraction over few seconds would tend to underestimate the ice nuclei concentration. It is shown that inferring the aerosol heterogeneous ice nucleation properties from measurements of the onset supersaturation and temperature may carry significant error as the variability in ice nucleation properties within the aerosol population is not accounted for. This work provides a simple and rigorous ice nucleation framework where theoretical predictions, laboratory measurements and field campaign data can be

  1. Transient nucleation in condensed systems

    NASA Technical Reports Server (NTRS)

    Kelton, K. F.; Greer, A. L.; Thompson, C. V.

    1983-01-01

    Using classical nucleation theory we consider transient nucleation occurring in a one-component, condensed system under isothermal conditions. We obtain an exact closed-form expression for the time dependent cluster populations. In addition, a more versatile approach is developed: a numerical simulation technique which models directly the reactions by which clusters are produced. This simulation demonstrates the evolution of cluster populations and nucleation rate in the transient regime. Results from the simulation are verified by comparison with exact analytical solutions for the steady state. Experimental methods for measuring transient nucleation are assessed, and it is demonstrated that the observed behavior depends on the method used. The effect of preexisting cluster distributions is studied. Previous analytical and numerical treatments of transient nucleation are compared to the solutions obtained from the simulation. The simple expressions of Kashchiev are shown to give good descriptions of the nucleation behavior.

  2. Microgravity nucleation and particle coagulation experiments support

    NASA Technical Reports Server (NTRS)

    Lilleleht, L. U.; Ferguson, F. T.; Stephens, J. R.

    1988-01-01

    Researchers at NASA Goddard Space Flight Center have embarked on a program to study the formation and growth of cosmic grains. This includes experiments on the homogeneous nucleation of refractory vapors of materials such as magnesium, lead, tin, and silicon oxides. As part of this program, the Chemical Engineering Department of the University of Virginia has undertaken to develop a math model for these experiments, to assist in the design and construction of the apparatus, and to analyze the data once the experiments have begun. Status Reports 1 and 2 addressed the design of the apparatus and the development of math models for temperature and concentration fields. The bulk of this report discusses the continued refinement of these models, and the assembly and testing of the nucleation chamber along with its ancillary equipment, which began in the spring of 1988.

  3. Nucleation of nuclear bodies.

    PubMed

    Dundr, Miroslav

    2013-01-01

    The nucleus is a complex organelle containing numerous highly dynamic, structurally stable domains and bodies, harboring functions that have only begun to be defined. However, the molecular mechanisms for their formation are still poorly understood. Recently it has been shown that a nuclear body can form de novo by self-organization. But little is known regarding what triggers the formation of a nuclear body and how subsequent assembly steps are orchestrated. Nuclear bodies are frequently associated with specific active gene loci that directly contribute to their formation. Both coding and noncoding RNAs can initiate the assembly of nuclear bodies with which they are physiologically associated. Thus, the formation of nuclear bodies occurs via recruitment and consequent accumulation of resident proteins in the nuclear bodies by nucleating RNA acting as a seeder. In this chapter I describe how to set up an experimental cell system to probe de novo biogenesis of a nuclear body by nucleating RNA and nuclear body components tethered on chromatin. PMID:23980018

  4. On Capillary Rise and Nucleation

    ERIC Educational Resources Information Center

    Prasad, R.

    2008-01-01

    A comparison of capillary rise and nucleation is presented. It is shown that both phenomena result from a balance between two competing energy factors: a volume energy and a surface energy. Such a comparison may help to introduce nucleation with a topic familiar to the students, capillary rise. (Contains 1 table and 3 figures.)

  5. Nucleation of Crystals in Solution

    NASA Astrophysics Data System (ADS)

    Vekilov, Peter G.

    2010-07-01

    Solution crystallization is an essential part of processes in the chemical and pharmaceutical industries and a major step in physiological and pathological phenomena. Crystallization starts with nucleation and control of nucleation is crucial for the control of the number, size, perfection, polymorphism and other characteristics of the crystalline materials. Recently, there have been significant advances in the understanding of the mechanism of nucleation of crystals in solution. The most significant of these is the two-step mechanism of nucleation, according to which the crystalline nucleus appears inside pre-existing metastable clusters of size several hundred nanometers, which consist of dense liquid and are suspended in the solution. While initially proposed for protein crystals, the applicability of this mechanism has been demonstrated for small molecule organic materials, colloids, and biominerals. This mechanism helps to explain several long-standing puzzles of crystal nucleation in solution: nucleation rates which are many orders of magnitude lower than theoretical predictions, nucleation kinetic dependencies with steady or receding parts at increasing supersaturation, the role of heterogeneous substrates for polymorph selection, the significance of the dense protein liquid, and others. More importantly, this mechanism provides powerful tools for control of the nucleation process by varying the solution thermodynamic parameters so that the volume occupied by the dense liquid shrinks or expands.

  6. Twin nucleation and migration in FeCr single crystals

    SciTech Connect

    Patriarca, L.; Abuzaid, Wael; Sehitoglu, Huseyin; Maier, Hans J.; Chumlyakov, Y.

    2013-01-15

    Tension and compression experiments were conducted on body-centered cubic Fe -47.8 at pct. Cr single crystals. The critical resolved shear stress (CRSS) magnitudes for slip nucleation, twin nucleation and twin migration were established. We show that the nucleation of slip occurs at a CRSS of about 88 MPa, while twinning nucleates at a CRSS of about 191 MPa with an associated load drop. Following twin nucleation, twin migration proceeds at a CRSS that is lower than the initiation stress ( Almost-Equal-To 114-153 MPa). The experimental results of the nucleation stresses indicate that the Schmid law holds to a first approximation for the slip and twin nucleation cases, but to a lesser extent for twin migration particularly when considerable slip strains preceded twinning. The CRSSs were determined experimentally using digital image correlation (DIC) in conjunction with electron back scattering diffraction (EBSD). The DIC measurements enabled pinpointing the precise stress on the stress-strain curves where twins or slip were activated. The crystal orientations were obtained using EBSD and used to determine the activated twin and slip systems through trace analysis. - Highlights: Black-Right-Pointing-Pointer Digital image correlation allows to capture slip/twin initiation for bcc FeCr. Black-Right-Pointing-Pointer Crystal orientations from EBSD allow slip/twin system indexing. Black-Right-Pointing-Pointer Nucleation of slip always precedes twinning. Black-Right-Pointing-Pointer Twin growth is sustained with a lower stress than required for nucleation. Black-Right-Pointing-Pointer Twin-slip interactions provide high hardening at the onset of plasticity.

  7. Surface nanobubbles nucleate microdroplets.

    PubMed

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

    2014-04-11

    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. PMID:24765973

  8. Preferential Nucleation during Polymorphic Transformations

    PubMed Central

    Sharma, H.; Sietsma, J.; Offerman, S. E.

    2016-01-01

    Polymorphism is the ability of a solid material to exist in more than one phase or crystal structure. Polymorphism may occur in metals, alloys, ceramics, minerals, polymers, and pharmaceutical substances. Unresolved are the conditions for preferential nucleation during polymorphic transformations in which structural relationships or special crystallographic orientation relationships (OR’s) form between the nucleus and surrounding matrix grains. We measured in-situ and simultaneously the nucleation rates of grains that have zero, one, two, three and four special OR’s with the surrounding parent grains. These experiments show a trend in which the activation energy for nucleation becomes smaller – and therefore nucleation more probable - with increasing number of special OR’s. These insights contribute to steering the processing of polymorphic materials with tailored properties, since preferential nucleation affects which crystal structure forms, the average grain size and texture of the material, and thereby - to a large extent - the final properties of the material. PMID:27484579

  9. Nucleation rate in monotectic alloys

    NASA Astrophysics Data System (ADS)

    Falk, F.

    Cooling a melt of a monotectic system into the miscibility gap results in nucleation of fluid droplets in a fluid matrix prior to solidification. For homogeneous nucleation the temperature dependence of the nucleation rate is calculated. As material parameters the chemical potential of the species involved, the diffusion constant of the fluid, and the surface tension between adjacent phases are important. Since their temperature dependence is not well known from experiments, different theoretical models are used and their influence is discussed. The surface tension turns out to be the most crucial parameter in determining the nucleation rate. For AlIn numerical results are presented. In this system the undercooling with respect to homogeneous nucleation increases from zero at the critical point to 100 K at a composition near the monotectic point.

  10. Preferential Nucleation during Polymorphic Transformations

    NASA Astrophysics Data System (ADS)

    Sharma, H.; Sietsma, J.; Offerman, S. E.

    2016-08-01

    Polymorphism is the ability of a solid material to exist in more than one phase or crystal structure. Polymorphism may occur in metals, alloys, ceramics, minerals, polymers, and pharmaceutical substances. Unresolved are the conditions for preferential nucleation during polymorphic transformations in which structural relationships or special crystallographic orientation relationships (OR’s) form between the nucleus and surrounding matrix grains. We measured in-situ and simultaneously the nucleation rates of grains that have zero, one, two, three and four special OR’s with the surrounding parent grains. These experiments show a trend in which the activation energy for nucleation becomes smaller – and therefore nucleation more probable - with increasing number of special OR’s. These insights contribute to steering the processing of polymorphic materials with tailored properties, since preferential nucleation affects which crystal structure forms, the average grain size and texture of the material, and thereby - to a large extent - the final properties of the material.

  11. Preferential Nucleation during Polymorphic Transformations.

    PubMed

    Sharma, H; Sietsma, J; Offerman, S E

    2016-08-03

    Polymorphism is the ability of a solid material to exist in more than one phase or crystal structure. Polymorphism may occur in metals, alloys, ceramics, minerals, polymers, and pharmaceutical substances. Unresolved are the conditions for preferential nucleation during polymorphic transformations in which structural relationships or special crystallographic orientation relationships (OR's) form between the nucleus and surrounding matrix grains. We measured in-situ and simultaneously the nucleation rates of grains that have zero, one, two, three and four special OR's with the surrounding parent grains. These experiments show a trend in which the activation energy for nucleation becomes smaller - and therefore nucleation more probable - with increasing number of special OR's. These insights contribute to steering the processing of polymorphic materials with tailored properties, since preferential nucleation affects which crystal structure forms, the average grain size and texture of the material, and thereby - to a large extent - the final properties of the material.

  12. Preferential Nucleation during Polymorphic Transformations.

    PubMed

    Sharma, H; Sietsma, J; Offerman, S E

    2016-01-01

    Polymorphism is the ability of a solid material to exist in more than one phase or crystal structure. Polymorphism may occur in metals, alloys, ceramics, minerals, polymers, and pharmaceutical substances. Unresolved are the conditions for preferential nucleation during polymorphic transformations in which structural relationships or special crystallographic orientation relationships (OR's) form between the nucleus and surrounding matrix grains. We measured in-situ and simultaneously the nucleation rates of grains that have zero, one, two, three and four special OR's with the surrounding parent grains. These experiments show a trend in which the activation energy for nucleation becomes smaller - and therefore nucleation more probable - with increasing number of special OR's. These insights contribute to steering the processing of polymorphic materials with tailored properties, since preferential nucleation affects which crystal structure forms, the average grain size and texture of the material, and thereby - to a large extent - the final properties of the material. PMID:27484579

  13. Ice Nucleation Activity in Lichens

    PubMed Central

    Kieft, Thomas L.

    1988-01-01

    A newly discovered form of biological ice nucleus associated with lichens is described. Ice nucleation spectra of a variety of lichens from the southwestern United States were measured by the drop-freezing method. Several epilithic lichen samples of the genera Rhizoplaca, Xanthoparmelia, and Xanthoria had nuclei active at temperatures as warm as −2.3°C and had densities of 2.3 × 106 to more than 1 × 108 nuclei g−1 at −5°C (2 to 4 orders of magnitude higher than any plants infected with ice nucleation-active bacteria). Most lichens tested had nucleation activity above −8°C. Lichen substrates (rocks, plants, and soil) showed negligible activity above −8°C. Ice nucleation-active bacteria were not isolated from the lichens, and activity was not destroyed by heat (70°C) or sonication, indicating that lichen-associated ice nuclei are nonbacterial in origin and differ chemically from previously described biological ice nuclei. An axenic culture of the lichen fungus Rhizoplaca chrysoleuca showed detectable ice nucleation activity at −1.9°C and an ice nucleation density of 4.5 × 106 nuclei g−1 at −5°C. It is hypothesized that these lichens, which are both frost tolerant and dependent on atmospheric moisture, derive benefit in the form of increased moisture deposition as a result of ice nucleation. PMID:16347678

  14. Ice nucleation activity in lichens.

    PubMed

    Kieft, T L

    1988-07-01

    A newly discovered form of biological ice nucleus associated with lichens is described. Ice nucleation spectra of a variety of lichens from the southwestern United States were measured by the drop-freezing method. Several epilithic lichen samples of the genera Rhizoplaca, Xanthoparmelia, and Xanthoria had nuclei active at temperatures as warm as -2.3 degrees C and had densities of 2.3 x 10 to more than 1 x 10 nuclei g at -5 degrees C (2 to 4 orders of magnitude higher than any plants infected with ice nucleation-active bacteria). Most lichens tested had nucleation activity above -8 degrees C. Lichen substrates (rocks, plants, and soil) showed negligible activity above -8 degrees C. Ice nucleation-active bacteria were not isolated from the lichens, and activity was not destroyed by heat (70 degrees C) or sonication, indicating that lichen-associated ice nuclei are nonbacterial in origin and differ chemically from previously described biological ice nuclei. An axenic culture of the lichen fungus Rhizoplaca chrysoleuca showed detectable ice nucleation activity at -1.9 degrees C and an ice nucleation density of 4.5 x 10 nuclei g at -5 degrees C. It is hypothesized that these lichens, which are both frost tolerant and dependent on atmospheric moisture, derive benefit in the form of increased moisture deposition as a result of ice nucleation.

  15. Climate Impacts of Ice Nucleation

    NASA Technical Reports Server (NTRS)

    Gettelman, Andrew; Liu, Xiaohong; Barahona, Donifan; Lohmann, Ulrike; Chen, Celia

    2012-01-01

    Several different ice nucleation parameterizations in two different General Circulation Models (GCMs) are used to understand the effects of ice nucleation on the mean climate state, and the Aerosol Indirect Effects (AIE) of cirrus clouds on climate. Simulations have a range of ice microphysical states that are consistent with the spread of observations, but many simulations have higher present-day ice crystal number concentrations than in-situ observations. These different states result from different parameterizations of ice cloud nucleation processes, and feature different balances of homogeneous and heterogeneous nucleation. Black carbon aerosols have a small (0.06 Wm(exp-2) and not statistically significant AIE when included as ice nuclei, for nucleation efficiencies within the range of laboratory measurements. Indirect effects of anthropogenic aerosols on cirrus clouds occur as a consequence of increasing anthropogenic sulfur emissions with different mechanisms important in different models. In one model this is due to increases in homogeneous nucleation fraction, and in the other due to increases in heterogeneous nucleation with coated dust. The magnitude of the effect is the same however. The resulting ice AIE does not seem strongly dependent on the balance between homogeneous and heterogeneous ice nucleation. Regional effects can reach several Wm2. Indirect effects are slightly larger for those states with less homogeneous nucleation and lower ice number concentration in the base state. The total ice AIE is estimated at 0.27 +/- 0.10 Wm(exp-2) (1 sigma uncertainty). This represents a 20% offset of the simulated total shortwave AIE for ice and liquid clouds of 1.6 Wm(sup-2).

  16. Climate Impacts of Ice Nucleation

    SciTech Connect

    Gettelman, A.; Liu, Xiaohong; Barahona, Donifan; Lohmann, U.; Chen, Chih-Chieh

    2012-10-19

    [1] Several different ice nucleation parameterizations in two different General Circulation Models (GCMs) are used to understand the effects of ice nucleation on the mean climate state, and the Aerosol Indirect Effects (AIE) of cirrus clouds on climate. Simulations have a range of ice microphysical states that are consistent with the spread of observations, but many simulations have higher present-day ice crystal number concentrations than in-situ observations. These different states result from different parameterizations of ice cloud nucleation processes, and feature different balances of homogeneous and heterogeneous nucleation. Black carbon aerosols have a small (-0.06 Wm-2) and not statistically significant AIE when included as ice nuclei, for nucleation efficiencies within the range of laboratory measurements. Indirect effects of anthropogenic aerosols on cirrus clouds occur as a consequence of increasing anthropogenic sulfur emissions with different mechanisms important in different models. In one model this is due to increases in homogeneous nucleation fraction, and in the other due to increases in heterogeneous nucleation with coated dust. The magnitude of the effect is the same however. The resulting ice AIE does not seem strongly dependent on the balance between homogeneous and heterogeneous ice nucleation. Regional effects can reach several Wm-2. Indirect effects are slightly larger for those states with less homogeneous nucleation and lower ice number concentration in the base state. The total ice AIE is estimated at 0.27 ± 0.10 Wm-2 (1σ uncertainty). Finally, this represents a 20% offset of the simulated total shortwave AIE for ice and liquid clouds of -1.6 Wm-2.

  17. Metadynamics studies of crystal nucleation

    PubMed Central

    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

  18. Dew nucleation and growth

    NASA Astrophysics Data System (ADS)

    Beysens, Daniel

    2006-11-01

    Dew is the condensation of water vapor into liquid droplets on a substrate. It is characterized by an initial heterogeneous nucleation on a substrate and a further growth of droplets. The presence of a substrate that geometrically constrains the growth is the origin of the peculiarities and richness of the phenomenon. A key point is the drop interaction through drop fusion or coalescence, which leads to scaling in the growth and gives universality to the process. As a matter of fact, growth dynamics are only dependent on substrate and drop dimensionality. Coalescence events lead to temporal and spatio-temporal fluctuations in the substrate coverage, drop configuration, etc., which give rise to a very peculiar dynamics. When the substrate is a liquid or a liquid crystal, the drop pattern can exhibit special spatial order, such as crystalline, hexatic phases and fractal contours. Condensation on a solid substrate near its melting point can make the drop jump. The applications of monitoring dew formation are manifold. Examples can be found in medicine (sterilization process), agriculture (green houses) and hydrology (production of drinkable water). To cite this article: D. Beysens, C. R. Physique 7 (2006).

  19. Bubble nucleation in stout beers

    NASA Astrophysics Data System (ADS)

    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.

  20. Nanoparticulas basadas en complejos de Fe(II) con transicion de espin: sintesis, caracterizacion y aplicaciones en electronica molecular

    NASA Astrophysics Data System (ADS)

    Monrabal Capilla, Maria

    Esta tesis doctoral esta organizada en 5 capitulos y esta destinada al estudio de sistemas de Fe (II) que presentan el fenomeno de la transicion de espin a escala nanometrica. El capitulo 1 contiene una introduccion general sobre materiales moleculares multifuncionales, destacando aquellos ejemplos mas importantes. Por otro lado, se explicara el fenomeno de la transicion de espin, tratando aspectos conceptuales, los antecedentes mas importantes y la situacion actual. En el capitulo 2 se describen los diferentes procesos existentes para la obtencion de diferentes tipos de nanoparticulas. Ademas, se presenta la sintesis y caracterizacion de nanoparticulas del polimero de coordinacion unidimensional [Fe(Htrz)2(trz)]BF4, obtenidas mediante el metodo de micelas inversas. Estas nanoparticulas, con una estrecha distribucion de tamanos centrada alrededor de los 11 nm, presentan una transicion de espin muy abrupta, con un ancho ciclo de histeresis termica de unos 40K. En el capitulo 3 se describe el proceso de modificacion del tamano de las nanoparticulas descritas en el capitulo anterior, llevado a cabo variando la proporcion de surfactante/H2O en el medio. Ademas, con el objetivo de modificar las propiedades magneticas de las nanoparticulas obtenidas en el capitulo 2, se lleva a cabo la sintesis de nanoparticulas de polimeros de la misma familia del [Fe(Htrz)2(trz)]BF4. En concreto se sintetizaron 3 nuevos tipos de nanoparticulas basadas en el polimero [Fe(Htrz)1-x(NH2trz)x](ClO4)2, siendo x = 0.05, 0.15 y 0.3, en cada caso. Estas nanoparticulas siguen presentando una estrecha distribucion de tamanos y una transicion de espin muy abrupta y con un ancho ciclo de histeresis. Ademas, se observa que este ciclo se desplaza a temperaturas mas proximas a la temperatura ambiente a medida que se aumenta el porcentaje de 4-amino-1, 2, 4- triazol en la muestra. Pero al mismo tiempo se produce una disminucion de la anchura de este ciclo. Por ultimo, en este capitulo se presenta la

  1. Thermodynamics of heterogeneous crystal nucleation in contact and immersion modes.

    PubMed

    Djikaev, Y S; Ruckenstein, E

    2008-11-20

    One of the most intriguing problems of heterogeneous crystal nucleation in droplets is its strong enhancement in the contact mode (when the foreign particle is presumably in some kind of contact with the droplet surface) compared to the immersion mode (particle immersed in the droplet). Heterogeneous centers can have different nucleation thresholds when they act in contact or immersion modes. The underlying physical reasons for this enhancement have remained largely unclear. In this paper we present a model for the thermodynamic enhancement of heterogeneous crystal nucleation in the contact mode compared to the immersion one. To determine if and how the surface of a liquid droplet can thermodynamically stimulate its heterogeneous crystallization, we examine crystal nucleation in the immersion and contact modes by deriving and comparing with each other the reversible works of formation of crystal nuclei in these cases. The line tension of a three-phase contact gives rise to additional terms in the formation free energy of a crystal cluster and affects its Wulff (equilibrium) shape. As an illustration, the proposed model is applied to the heterogeneous nucleation of hexagonal ice crystals on generic macroscopic foreign particles in water droplets at T = 253 K. Our results show that the droplet surface does thermodynamically favor the contact mode over the immersion one. Surprisingly, the numerical evaluations suggest that the line tension contribution (from the contact of three water phases (vapor-liquid-crystal)) to this enhancement may be of the same order of magnitude as or even larger than the surface tension contribution.

  2. Classical nucleation theory from a dynamical approach to nucleation.

    PubMed

    Lutsko, James F; Durán-Olivencia, Miguel A

    2013-06-28

    It is shown that diffusion-limited classical nucleation theory (CNT) can be recovered as a simple limit of the recently proposed dynamical theory of nucleation based on fluctuating hydrodynamics [J. F. Lutsko, J. Chem. Phys. 136, 034509 (2012)]. The same framework is also used to construct a more realistic theory in which clusters have finite interfacial width. When applied to the dilute solution/dense solution transition in globular proteins, it is found that the extension gives corrections to the nucleation rate even for the case of small supersaturations due to changes in the monomer distribution function and to the excess free energy. It is also found that the monomer attachment/detachment picture breaks down at high supersaturations corresponding to clusters smaller than about 100 molecules. The results also confirm the usual assumption that most important corrections to CNT can be achieved by means of improved estimates of the free energy barrier. The theory also illustrates two topics that have received considerable attention in the recent literature on nucleation: the importance sub-dominant corrections to the capillary model for the free energy and of the correct choice of the reaction coordinate.

  3. Ice Nucleation in Deep Convection

    NASA Technical Reports Server (NTRS)

    Jensen, Eric; Ackerman, Andrew; Stevens, David; Gore, Warren J. (Technical Monitor)

    2001-01-01

    The processes controlling production of ice crystals in deep, rapidly ascending convective columns are poorly understood due to the difficulties involved with either modeling or in situ sampling of these violent clouds. A large number of ice crystals are no doubt generated when droplets freeze at about -40 C. However, at higher levels, these crystals are likely depleted due to precipitation and detrainment. As the ice surface area decreases, the relative humidity can increase well above ice saturation, resulting in bursts of ice nucleation. We will present simulations of these processes using a large-eddy simulation model with detailed microphysics. Size bins are included for aerosols, liquid droplets, ice crystals, and mixed-phase (ice/liquid) hydrometers. Microphysical processes simulated include droplet activation, freezing, melting, homogeneous freezing of sulfate aerosols, and heterogeneous ice nucleation. We are focusing on the importance of ice nucleation events in the upper part of the cloud at temperatures below -40 C. We will show that the ultimate evolution of the cloud in this region (and the anvil produced by the convection) is sensitive to these ice nucleation events, and hence to the composition of upper tropospheric aerosols that get entrained into the convective column.

  4. Foam nucleation system for fluoropolymers

    SciTech Connect

    Buckmaster, M.D.; Randa, S.K.

    1988-08-16

    A foamable composition is described comprising a melt-processible fluoropolymer containing a nucleating amount of boron nitride and a synergistic amount of at least one inorganic salt that is thermally stable at the fluoropolymer extrusion temperature, and consists of a metal cation and a polyatomic anion.

  5. Ice Nucleation Properties of Oxidized Carbon Nanomaterials.

    PubMed

    Whale, Thomas F; Rosillo-Lopez, Martin; Murray, Benjamin J; Salzmann, Christoph G

    2015-08-01

    Heterogeneous ice nucleation is an important process in many fields, particularly atmospheric science, but is still poorly understood. All known inorganic ice nucleating particles are relatively large in size and tend to be hydrophilic. Hence it is not obvious that carbon nanomaterials should nucleate ice. However, in this paper we show that four different readily water-dispersible carbon nanomaterials are capable of nucleating ice. The tested materials were carboxylated graphene nanoflakes, graphene oxide, oxidized single walled carbon nanotubes and oxidized multiwalled carbon nanotubes. The carboxylated graphene nanoflakes have a diameter of ∼30 nm and are among the smallest entities observed so far to nucleate ice. Overall, carbon nanotubes were found to nucleate ice more efficiently than flat graphene species, and less oxidized materials nucleated ice more efficiently than more oxidized species. These well-defined carbon nanomaterials may pave the way to bridging the gap between experimental and computational studies of ice nucleation. PMID:26267196

  6. Molecular simulations of heterogeneous ice nucleation. II. Peeling back the layers

    NASA Astrophysics Data System (ADS)

    Cox, Stephen J.; Kathmann, Shawn M.; Slater, Ben; Michaelides, Angelos

    2015-05-01

    Coarse grained molecular dynamics simulations are presented in which the sensitivity of the ice nucleation rate to the hydrophilicity of a graphene nanoflake is investigated. We find that an optimal interaction strength for promoting ice nucleation exists, which coincides with that found previously for a face centered cubic (111) surface. We further investigate the role that the layering of interfacial water plays in heterogeneous ice nucleation and demonstrate that the extent of layering is not a good indicator of ice nucleating ability for all surfaces. Our results suggest that to be an efficient ice nucleating agent, a surface should not bind water too strongly if it is able to accommodate high coverages of water.

  7. Molecular Simulations of Heterogeneous Ice Nucleation. II. Peeling back the Layers

    SciTech Connect

    Cox, Stephen J.; Kathmann, Shawn M.; Slater, B.; Michaelides, Angelos

    2015-05-14

    Coarse grained molecular dynamics simulations are presented in which the sensitivity of the ice nucleation rate to the hydrophilicity of a graphene nanoflake is investigated. We find that an optimal interaction strength for promoting ice nucleation exists, which coincides with that found previously for a face centered cubic (111) surface. We further investigate the role that the layering of interfacial water plays in heterogeneous ice nucleation and demonstrate that the extent of layering is not a good indicator of ice nucleating ability for all surfaces. Our results suggest that to be an efficient ice nucleating agent, a surface should not bind water too strongly if it is able to accommodate high coverages of water.

  8. A simple ice nucleation spectrometer.

    PubMed

    Wharton, David A; Mutch, Jodi S; Wilson, Peter W; Marshall, Craig J; Lim, Miang

    2004-01-01

    The construction of a simple ice nucleation spectrometer is described. It uses 10 microliter droplets loaded into glass capillary tubes which are then inserted into an aluminium holder. Each holder takes six capillary tubes surrounding a central thermocouple. Four holders are placed into a cooling block, cooled by fluid from a programmable refrigerated circulator, and the thermocouples interfaced to a computer to record temperatures. Freezing of each sample is detected by an exotherm on the temperature recording, with 24 samples recorded per run. The spectrometer was tested using deionized water, an extract from a New Zealand alpine cockroach and an extract of lawn grass. The cockroach extract is estimated to contain about 10(3) more nucleators, active at -5 degrees C, than the grass extract. PMID:15618985

  9. Ice nucleation activity of polysaccharides

    NASA Astrophysics Data System (ADS)

    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

  10. Role of nucleation in nanodiamond film growth

    SciTech Connect

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

    2006-06-12

    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{sub 2} dimer growth (CH{sub 4} and H{sub 2} in 90% Ar) cannot nucleate diamond and works only on existing diamond surfaces. The methyl radical process (up to 20% CH{sub 4} in H{sub 2}) allows some nucleation probability on appropriate substrates. Prolonged bias enhanced nucleation initiates both diamond nucleation and growth. C{sub 2} dimer growth results in pure nanodiamond free of amorphous carbon, while prolonged bias enhanced nucleation forms an amorphous carbon/nanodiamond composite.

  11. Nucleation and interfacial adsorption in ternary systems.

    PubMed

    Philippe, T

    2015-03-01

    Nucleation is studied in incompressible ternary fluids by examining the topology of the overall landscape of the energy surface. Minimum free energy paths for nucleation (MFEPs) of a single nucleus in an infinite matrix are computed with the string method in the framework of the continuum theory of nucleation for the regular solution. Properties of the critical nucleus are compared with the predictions of the classical nucleation theory. MFEPs are found to exhibit complex nucleation pathways with non-monotonic variations of compositions in the interfacial region, specifically adsorption of a component. In the symmetric regular solution, the minority component is found to segregate at the interface during nucleation with a concomitant depletion of the nucleus core, resulting in unpredicted partition of the non-selective component. Despite increasing the gradient energy, such inhomogeneity in composition is shown to lower the nucleation barrier. PMID:25747088

  12. Measuring induction times and crystal nucleation rates.

    PubMed

    Brandel, Clément; ter Horst, Joop H

    2015-01-01

    A large variation is observed in induction times measured under equal conditions in 1 ml solutions. Ruling out experimental errors, this variation originates from the nucleation process. The induction time distribution is explained by the stochastic nature of nucleation if the number of nuclei formed is approaching 1 per vial. Accurate heterogeneous crystal nucleation rates were determined from the induction time distributions on a 1 ml scale for racemic diprophylline in two solvents. The difference in nucleation behaviour in the two solvents originates from the energy barrier for nucleation, which is much higher in the solvent in which induction times are much longer. In addition the pre-exponential factor for the crystal nucleation rate in both solvents is rather low compared to predictions using Classical Nucleation Theory. Unfortunately, concentration and surface characteristics of the effective heterogeneous particles are not known which clouds a further molecular interpretation.

  13. Sigmoid kinetics of protein crystal nucleation

    NASA Astrophysics Data System (ADS)

    Nanev, Christo N.; Tonchev, Vesselin D.

    2015-10-01

    A non-linear differential equation expressing the new phase nucleation rate in the different steps of the process (non-stationary and stationary nucleation and in the plateau region) is derived from basic principles of the nucleation theory. It is shown that one and the same sigmoid (logistic) function describes both nucleation scenarios: the one according to the classical theory, and the other according to the modern two-stage mechanism of protein crystal formation. Comparison to experimental data on both insulin crystal nucleation kinetics and on bovine β-lactoglobulin crystallization indicates a good agreement with the sigmoidal prediction. Experimental data for electrochemical nucleation and glass crystallization obey the same sigmoid time dependence, and suggest universality of this nucleation kinetics law.

  14. Dynamic study of nanodroplet nucleation and growth on self-supported nanothick liquid films.

    PubMed

    Barkay, Z

    2010-12-01

    The dynamics of water condensation on self-supported thin films was studied at the nanoscale using transmitted electrons in an environmental scanning electron microscope. The initial stages of nucleation and growth over nanothick water films have been investigated. Irregularities at the water-film boundaries constituted nucleation sites for asymmetric dropwise and filmwise condensation. Nanodroplet growth was associated with center of mass movement, and the dynamic growth power law dependence was explored for the nanoscale.

  15. Communication. Kinetics of scavenging of small, nucleating clusters. First nucleation theorem and sum rules

    DOE PAGES

    Malila, Jussi; McGraw, Robert; Laaksonen, Ari; Lehtinen, Kari E. J.

    2015-01-07

    Despite recent advances in monitoring nucleation from a vapor at close-to-molecular resolution, the identity of the critical cluster, forming the bottleneck for the nucleation process, remains elusive. During past twenty years, the first nucleation theorem has been often used to extract the size of the critical cluster from nucleation rate measurements. However, derivations of the first nucleation theorem invoke certain questionable assumptions that may fail, e.g., in the case of atmospheric new particle formation, including absence of subcritical cluster losses and heterogeneous nucleation on pre-existing nanoparticles. Here we extend the kinetic derivation of the first nucleation theorem to give amore » general framework to include such processes, yielding sum rules connecting the size dependent particle formation and loss rates to the corresponding loss-free nucleation rate and the apparent critical size from a naïve application of the first nucleation theorem that neglects them.« less

  16. Communication. Kinetics of scavenging of small, nucleating clusters. First nucleation theorem and sum rules

    SciTech Connect

    Malila, Jussi; McGraw, Robert; Laaksonen, Ari; Lehtinen, Kari E. J.

    2015-01-07

    Despite recent advances in monitoring nucleation from a vapor at close-to-molecular resolution, the identity of the critical cluster, forming the bottleneck for the nucleation process, remains elusive. During past twenty years, the first nucleation theorem has been often used to extract the size of the critical cluster from nucleation rate measurements. However, derivations of the first nucleation theorem invoke certain questionable assumptions that may fail, e.g., in the case of atmospheric new particle formation, including absence of subcritical cluster losses and heterogeneous nucleation on pre-existing nanoparticles. Here we extend the kinetic derivation of the first nucleation theorem to give a general framework to include such processes, yielding sum rules connecting the size dependent particle formation and loss rates to the corresponding loss-free nucleation rate and the apparent critical size from a naïve application of the first nucleation theorem that neglects them.

  17. Fracture Statistics: Universality vs. Nucleation

    NASA Astrophysics Data System (ADS)

    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.

  18. Stochastic analysis of nucleation rates.

    PubMed

    Johansson, Jonas

    2016-02-01

    We show that approximating the Becker-Döring equations with a Langevin equation results in multiplicative noise, which in turn leads to a family of possible Fokker-Planck equations according to the Ito-Stratonovich dilemma. Using a simple and general model for the attachment and detachment rates, we find that the Ito choice approximates the nucleation rate best and also coincides with the Fokker-Planck equation resulting from the common way to Taylor expand the original set of rate equations.

  19. Stochastic analysis of nucleation rates

    NASA Astrophysics Data System (ADS)

    Johansson, Jonas

    2016-02-01

    We show that approximating the Becker-Döring equations with a Langevin equation results in multiplicative noise, which in turn leads to a family of possible Fokker-Planck equations according to the Ito-Stratonovich dilemma. Using a simple and general model for the attachment and detachment rates, we find that the Ito choice approximates the nucleation rate best and also coincides with the Fokker-Planck equation resulting from the common way to Taylor expand the original set of rate equations.

  20. Factors Affecting Ice Nucleation in Plant Tissues

    PubMed Central

    Ashworth, Edward N.; Davis, Glen A.; Anderson, Jeffrey A.

    1985-01-01

    Factors affecting the ice nucleation temperature of plants and plant tissues were examined. The mass of a sample had a marked effect on ice nucleation temperature. Small tissue samples supercooled to −10°C and were not accurate predictors of the nucleation temperature of intact plants in either laboratory or field experiments. This effect was not unique to plant tissues and was observed in autoclaved and control soil samples. Ice nucleation temperatures of bean, corn, cotton, and soybean seedlings were influenced by the length of subzero exposure, presence of ice nucleation active bacteria, and leaf surface wetness. The number of factors influencing ice nucleation temperature suggested that predicting the freezing behavior of plants in the field will be complex. PMID:16664524

  1. Properties of the seismic nucleation phase

    USGS Publications Warehouse

    Beroza, G.C.; Ellsworth, W.L.

    1996-01-01

    Near-source observations show that earthquakes begin abruptly at the P-wave arrival, but that this beginning is weak, with a low moment rate relative to the rest of the main shock. We term this initial phase of low moment rate the seismic nucleation phase. We have observed the seismic nucleation phase for a set of 48 earthquakes ranging in magnitude from 1.1-8.1. The size and duration of the seismic nucleation phase scale with the total seismic moment of the earthquake, suggesting that the process responsible for the seismic nucleation phase carries information about the eventual size of the earthquake. The seismic nucleation phase is characteristically followed by quadratic growth in the moment rate, consistent with self-similar rupture at constant stress drop. In this paper we quantify the properties of the seismic nucleation phase and offer several possible explanations for it.

  2. Time-dependent nucleation in partitioning systems

    SciTech Connect

    Kelton, K.F.; Narayan, K.L.

    1998-12-31

    Nucleation in multi-component systems is poorly understood, particularly when the rates of long-range diffusion are comparable with the rates of attachment at the cluster interface. For illustration, measurements of the time-dependent nucleation rates in silicate and metallic glasses are discussed. A new model for nucleation in partitioning systems, which explains many of devitrification microstructural features in bulk metallic glasses, is presented.

  3. Truncated Dual-Cap Nucleation Site Development

    NASA Technical Reports Server (NTRS)

    Matson, Douglas M.; Sander, Paul J.

    2012-01-01

    During heterogeneous nucleation within a metastable mushy-zone, several geometries for nucleation site development must be considered. Traditional spherical dual cap and crevice models are compared to a truncated dual cap to determine the activation energy and critical cluster growth kinetics in ternary Fe-Cr-Ni steel alloys. Results of activation energy results indicate that nucleation is more probable at grain boundaries within the solid than at the solid-liquid interface.

  4. Binary Nucleation of Water and Sodium Chloride

    SciTech Connect

    Nemec, Thomas; Marsik, Frantisek; Palmer, Donald

    2005-01-01

    Nucleation processes in the binary water-sodium chloride system are investigated in the sense of the classical nucleation theory (CNT). The CNT is modified to be able to handle the electrolytic nature of the system and is employed to investigate the acceleration of the nucleation process due to the presence of sodium chloride in the steam. This phenomenon, frequently observed in the Wilson zone of steam turbines, is called early condensation. Therefore, the nucleation rates of the water-sodium chloride mixture are of key importance in the power cycle industry.

  5. Assaying microtubule nucleation by the γ-tubulin ring complex.

    PubMed

    Choi, Yuk-Kwan; Qi, Robert Z

    2014-01-01

    Microtubule organization by microtubule-organizing centers such as the centrosome requires γ-tubulin, which exists in the γ-tubulin ring complex (γTuRC) that nucleates microtubules. The γTuRC is a ring-shaped, macromolecular complex whose core components are γ-tubulin and the γ-tubulin complex proteins. Despite the recent identification of additional γTuRC components, the molecular composition and regulatory properties of the complex remain poorly understood. The ability to purify the γTuRC at a large scale for characterization may hold a key to understanding the mechanism by which the γTuRC nucleates microtubules. In this chapter, we describe methods to isolate the γTuRC from human cell cultures and to perform assays on the purified γTuRC. PMID:24630104

  6. Dislocation nucleation in bcc Ta single crystals studied by nanoindentation

    SciTech Connect

    Biener, M M; Biener, J; Hodge, A M; Hamza, A V

    2007-08-08

    The study of dislocation nucleation in closed-packed metals by nanoindentation has recently attracted much interest. Here, we address the peculiarities of the incipient plasticity in body centered cubic (bcc) metals using low index Ta single-crystals as a model system. The combination of nanoindentation with high-resolution atomic force microscopy provides us with experimental atomic-scale information on the process of dislocation nucleation and multiplication. Our results reveal a unique deformation behavior of bcc Ta at the onset of plasticity which is distinctly different from that of closed-packed metals. Most noticeable, we observe only one rather than a sequence of discontinuities in the load-displacement curves. This and other differences are discussed in context of the characteristic plastic deformation behavior of bcc metals.

  7. Nucleation of crystals that are mixed composites of all three polymorphs in the Gaussian core model.

    PubMed

    Mithen, J P; Callison, A J; Sear, R P

    2015-06-14

    We present results of computer simulations of homogeneous crystal nucleation in the Gaussian core model. In our simulations, we study the competition between the body-centered-cubic (bcc), face-centered-cubic (fcc), and hexagonal-close-packed crystal phases. We find that the crystal nuclei that form from the metastable fluid phase are typically "mixed"; they do not consist of a single crystal polymorph. Furthermore, when the fcc phase is stable or fcc and bcc phases are equally stable, this mixed nature is found to persist far beyond the size at the top of the nucleation barrier, that is, far into what would be considered the growth (rather than nucleation) regime. In this region, the polymorph that forms is therefore selected long after nucleation. This has implications. When nucleation is slow, it will be the rate-limiting step for crystallization. Then, the step that determines the time scale for crystallisation is different from the step that controls which polymorph forms. This means that they can be independently controlled. Also between nucleation and polymorph selection, there is a growing phase that is clearly crystalline not fluid, but this phase cannot be assigned to any one polymorph.

  8. Atomistic simulations of dislocation nucleation in single crystals and grain boundaries

    NASA Astrophysics Data System (ADS)

    Tschopp, Mark A., Jr.

    The objective of this research is to use atomistic simulations to investigate dislocation nucleation from grain boundaries in face-centered cubic aluminum and copper. This research primarily focuses on asymmetric tilt grain boundaries and has three main components. First, this research uses molecular statics simulations of the structure and energy of these faceted, dissociated grain boundary structures to show that Sigma3 asymmetric boundaries can be decomposed into the structural units of the Sigma3 symmetric tilt grain boundaries, i.e., the coherent and incoherent twin boundaries. Moreover, the energy for all Sigma3 asymmetric boundaries is predicted with only the energies of the Sigma3 symmetric boundaries and the inclination angle. Understanding the structure of these boundaries provides insight into dislocation nucleation from these boundaries. Further work into the structure and energy of other low order Sigma asymmetric boundaries and the spatial distribution of free volume within the grain boundaries also provides insight into dislocation nucleation mechanisms. Second, this research uses molecular dynamics deformation simulations with uniaxial tension applied perpendicular to these boundaries to show that the dislocation nucleation mechanisms in asymmetric boundaries are highly dependent on the faceted, dissociated structure. Grain boundary dislocation sources can act as perfect sources/sinks for dislocations or may violate this premise by increasing the dislocation content of the boundary during nucleation. Furthermore, simulations under uniaxial tension and uniaxial compression show that nucleation of the second partial dislocation in copper exhibits tension-compression asymmetry. Third, this research explores the development of models that incorporate the resolved stress components on the slip system of dislocation nucleation to predict the atomic stress required for dislocation nucleation from single crystals and grain boundaries. Single crystal

  9. Heterogeneous nucleation in hypermonotectic aluminum alloys

    NASA Astrophysics Data System (ADS)

    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.

  10. Tuning Ice Nucleation with Supercharged Polypeptides.

    PubMed

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

    2016-07-01

    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 SUP backbone is another parameter to control it. PMID:27119590

  11. Ice nucleation by water-soluble macromolecules

    NASA Astrophysics Data System (ADS)

    Pummer, B. G.; Budke, C.; Augustin-Bauditz, S.; Niedermeier, D.; Felgitsch, L.; Kampf, C. J.; Huber, R. G.; Liedl, K. R.; Loerting, T.; Moschen, T.; Schauperl, M.; Tollinger, M.; Morris, C. E.; Wex, H.; Grothe, H.; Pöschl, U.; Koop, T.; Fröhlich-Nowoisky, J.

    2014-09-01

    Cloud glaciation is critically important for the global radiation budget (albedo) and for initiation of precipitation. But the freezing of pure water droplets requires cooling to temperatures as low as 235 K. Freezing at higher temperatures requires the presence of an ice nucleator, which is a foreign body in the water that functions as a template for arranging water molecules in an ice-like manner. It is often assumed that these ice nucleators have to be insoluble particles. We put in perspective that also dissolved single macromolecules can induce ice nucleation: they are several nanometers in size, which is also the size range of the necessary critical cluster. As the critical cluster size is temperature-dependent, we see a correlation between the size of such ice nucleating macromolecules and the ice nucleation temperature. Such ice nucleating macromolecules have been already found in many different biological species and are as manifold in their chemistry. Therefore, we additionally compare them to each other, based on a composition of former, recent and yet unpublished studies. Combining these data with calculations from Classical Nucleation Theory, we want to foster a more molecular view of ice nucleation among scientists.

  12. Simple improvements to classical bubble nucleation models.

    PubMed

    Tanaka, Kyoko K; Tanaka, Hidekazu; Angélil, Raymond; Diemand, Jürg

    2015-08-01

    We revisit classical nucleation theory (CNT) for the homogeneous bubble nucleation rate and improve the classical formula using a correct prefactor in the nucleation rate. Most of the previous theoretical studies have used the constant prefactor determined by the bubble growth due to the evaporation process from the bubble surface. However, the growth of bubbles is also regulated by the thermal conduction, the viscosity, and the inertia of liquid motion. These effects can decrease the prefactor significantly, especially when the liquid pressure is much smaller than the equilibrium one. The deviation in the nucleation rate between the improved formula and the CNT can be as large as several orders of magnitude. Our improved, accurate prefactor and recent advances in molecular dynamics simulations and laboratory experiments for argon bubble nucleation enable us to precisely constrain the free energy barrier for bubble nucleation. Assuming the correction to the CNT free energy is of the functional form suggested by Tolman, the precise evaluations of the free energy barriers suggest the Tolman length is ≃0.3σ independently of the temperature for argon bubble nucleation, where σ is the unit length of the Lennard-Jones potential. With this Tolman correction and our prefactor one gets accurate bubble nucleation rate predictions in the parameter range probed by current experiments and molecular dynamics simulations.

  13. Simple improvements to classical bubble nucleation models

    NASA Astrophysics Data System (ADS)

    Tanaka, Kyoko K.; Tanaka, Hidekazu; Angélil, Raymond; Diemand, Jürg

    2015-08-01

    We revisit classical nucleation theory (CNT) for the homogeneous bubble nucleation rate and improve the classical formula using a correct prefactor in the nucleation rate. Most of the previous theoretical studies have used the constant prefactor determined by the bubble growth due to the evaporation process from the bubble surface. However, the growth of bubbles is also regulated by the thermal conduction, the viscosity, and the inertia of liquid motion. These effects can decrease the prefactor significantly, especially when the liquid pressure is much smaller than the equilibrium one. The deviation in the nucleation rate between the improved formula and the CNT can be as large as several orders of magnitude. Our improved, accurate prefactor and recent advances in molecular dynamics simulations and laboratory experiments for argon bubble nucleation enable us to precisely constrain the free energy barrier for bubble nucleation. Assuming the correction to the CNT free energy is of the functional form suggested by Tolman, the precise evaluations of the free energy barriers suggest the Tolman length is ≃0.3 σ independently of the temperature for argon bubble nucleation, where σ is the unit length of the Lennard-Jones potential. With this Tolman correction and our prefactor one gets accurate bubble nucleation rate predictions in the parameter range probed by current experiments and molecular dynamics simulations.

  14. Simple improvements to classical bubble nucleation models.

    PubMed

    Tanaka, Kyoko K; Tanaka, Hidekazu; Angélil, Raymond; Diemand, Jürg

    2015-08-01

    We revisit classical nucleation theory (CNT) for the homogeneous bubble nucleation rate and improve the classical formula using a correct prefactor in the nucleation rate. Most of the previous theoretical studies have used the constant prefactor determined by the bubble growth due to the evaporation process from the bubble surface. However, the growth of bubbles is also regulated by the thermal conduction, the viscosity, and the inertia of liquid motion. These effects can decrease the prefactor significantly, especially when the liquid pressure is much smaller than the equilibrium one. The deviation in the nucleation rate between the improved formula and the CNT can be as large as several orders of magnitude. Our improved, accurate prefactor and recent advances in molecular dynamics simulations and laboratory experiments for argon bubble nucleation enable us to precisely constrain the free energy barrier for bubble nucleation. Assuming the correction to the CNT free energy is of the functional form suggested by Tolman, the precise evaluations of the free energy barriers suggest the Tolman length is ≃0.3σ independently of the temperature for argon bubble nucleation, where σ is the unit length of the Lennard-Jones potential. With this Tolman correction and our prefactor one gets accurate bubble nucleation rate predictions in the parameter range probed by current experiments and molecular dynamics simulations. PMID:26382410

  15. Nucleation and Growth of Discotic Liquid Crystals

    NASA Astrophysics Data System (ADS)

    Cheng, Zhengdong; Wang, Xuezhen; Zhang, Lecheng; Shinde, Abhijeet; Liquid Crystals of Nanoplates in Microgravity Team

    2015-03-01

    We investigate the nucleation and growth of liquid crystals of plate-shaped charged zirconium phosphate (ZrP) monolayers with various sizes, temperature and salt concentrations. The smaller the platelets size, or the higher the temperature, or the higher the salt concentration (from 0 to 0.6M), the faster the Isotropic-Nematic (I-N) separation took place. We established the I-N transition phase diagram of charged platelets in the temperature verse volume fraction plane, and discovered that N phase can be melted by increasing temperature, and coexistent samples are more sensitive to polydispersity at higher temperature and higher concentrations. We also found that salt concentration in the ZrP suspensions contributed to the formation of an apparently twisted phase. This work is supported by NSF (DMR-1006870) and NASA (NASA-NNX13AQ60G). X.Z. Wang acknowledges support from the Mary Kay O'Connor Process Safety Center (MKOPSC) at Texas A&M University.

  16. Nucleation pressure threshold in acoustic droplet vaporization

    NASA Astrophysics Data System (ADS)

    Miles, Christopher J.; Doering, Charles R.; Kripfgans, Oliver D.

    2016-07-01

    We combine classical nucleation theory with superharmonic focusing to predict necessary pressures to induce nucleation in acoustic droplet vaporization. We show that linear acoustics is a valid approximation to leading order when particle displacements in the sound field are small relative to the radius of the droplet. This is done by perturbation analysis of an axisymmetric compressible inviscid flow about a droplet with small surface perturbations relative to the mean radius subjected to an incoming ultrasonic wave. The necessary nucleation pressure threshold inside the droplet is calculated to be -9.33 ± 0.30 MPa for typical experimental parameters by employing results from classical homogeneous nucleation theory. As a result, we are able to predict if a given incident pressure waveform will induce nucleation.

  17. Minimum free-energy pathway of nucleation.

    PubMed

    Philippe, T; Blavette, D

    2011-10-01

    Nucleation in a two-component incompressible system was studied by examining the topology of the free-energy landscape. The properties of a single nucleus during nucleation were derived from the minimum free-energy pathway (MFEP) within the Cahn-Hilliard continuum theory of nucleation. MFEPs were computed using the string method. In particular, we have provided a detailed description of the nucleation process for a regular solution (T/T(c) = 0.8656) for increasing supersaturation up to the spinodal line. Two original results were found in terms of the physics of nucleation. A universal two-step behaviour was found whatever the supersaturation: nuclei sharply enrich up to equilibrium and then grow. Embryos show diffuse interfaces along the MFEP. The width of interfaces quickly saturates to its value at the critical nuclei and stays constant afterwards. PMID:21992325

  18. The materials processing research base of the Materials Processing Center

    NASA Technical Reports Server (NTRS)

    Flemings, M. C.; Bowen, H. K.; Kenney, G. B.

    1980-01-01

    The goals and activities of the center are discussed. The center activities encompass all engineering materials including metals, ceramics, polymers, electronic materials, composites, superconductors, and thin films. Processes include crystallization, solidification, nucleation, and polymer synthesis.

  19. Nucleation in an Ultra Low Ionization Environment

    NASA Astrophysics Data System (ADS)

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

    2010-12-01

    Atmospheric ions can enhance the nucleation of aerosols, as has been established by experiments, observation, and theory. In the clean marine atmosphere ionization is mainly caused by cosmic rays which in turn are controlled by the activity of the Sun, thus providing a potential link between solar activity and climate. In order to understand the effect ions may have on the production of cloud condensation nuclei the overall contribution of ion induced nucleation to the global production of secondary aerosols must be determined. One issue with determining this contribution is that several mechanisms for nucleation exist and it can be difficult to determine the relative importance of the various mechanisms in a given nucleation event when both ion induced and electrically neutral nucleation mechanisms are at work at the same time. We have carried out nucleation experiments in the Boulby Underground Laboratory, located 1100 meters below ground, thus reducing the flux of ionizing cosmic radiation by six orders of magnitude. Similarly we have reduced the gamma background by shielding the experiment in lead and copper. Finally we have used air stored for several weeks and passed through an active charcoal filter in order to reduce the Radon concentration. In this way we have been able to make nucleation experiments with very low ionizing background, meaning that we can rule out ion induced nucleation as a contributing mechanism. Our experimental setup is a 50 L electropolished stainless steel reactor at near atmospheric conditions. The chamber contains clean air with the addition of water vapor, ozone, and SO2. Using UV lights at 254 nm ozone is photolyzed, leading to the production of sulfuric acid and thus aerosols. An 18 MBq Caesium-137 gamma ray source with various amounts of lead in front allows us to alter the ionization in our chamber. By making series of nucleation bursts with varying amounts of ionizing radiation we then gauge the relative importance of ion

  20. Nucleation and crystallization behaviors of nano-crystalline lithium–mica glass–ceramic prepared via sol–gel method

    SciTech Connect

    Tohidifar, M.R.; Alizadeh, P.; Riello, P.

    2012-06-15

    Graphical abstract: The effects of nucleation and crystallization treatments on nano-crystalline lithium–mica glass–ceramic, synthesized by sol–gel technique, were investigated. It was found that MgF{sub 2} crystals act as nuclei centers for the mica crystallization so that a large quantity of mica crystallites was obtained following nucleation process. The crystallization activation energy for both the un-nucleated and nucleated samples was measured as 400.2 and 229.6 kJ mol{sup −1}, respectively. The calculated Avrami exponents demonstrated that the growth mechanism of mica crystallites changes from the needle-like to three-dimensional growth with applying the appropriate nucleation treatment ▪. Highlights: ► Crystallization temperature shifts to 625 from 680 °C following nucleation process. ► Activation energy of crystallization for the nucleated specimen is 229.6 kJ mol{sup −1}. ► Crystallization activation energy for the un-nucleated specimen is 400.2 kJ mol{sup −1}. ► Needle-like growth is predominant growth mechanism for un-nucleated sample. ► Three-dimensional growth is predominant growth mechanism for nucleated sample. -- Abstract: The paper investigates the effects of nucleation and crystallization treatments on nano-crystalline lithium–mica glass–ceramics, taking the composition LiMg{sub 3}AlSi{sub 3(1+x)}O{sub 10+6x}F{sub 2} (x = 0.5) and 8 mass% MgF{sub 2} synthesized by sol–gel technique. Here, X-ray diffraction, thermal analysis and transmission electron microscopy were used to assess the structural evolutions of as-synthesized nano-crystalline lithium–mica glass–ceramics. It was found that MgF{sub 2} crystals perform as nuclei centers for the mica crystallization hence; a large quantity of mica crystallites obtained following the nucleation process at 400 °C for 12 h. For both the un-nucleated and nucleated samples, the crystallization activation energy was measured as 400.2 and 229.6 kJ mol{sup −1

  1. Molecular dynamics simulations of He bubble nucleation at grain boundaries.

    PubMed

    Zhang, Yongfeng; Millett, Paul C; Tonks, Michael; Zhang, Liangzhe; Biner, Bulent

    2012-08-01

    The nucleation behavior of He bubbles in single-crystal (sc) and nano-grain body-centered-cubic (bcc) Mo is simulated using molecular dynamics (MD) simulations, focusing on the effects of the grain boundary (GB) structure. In sc Mo, the nucleation behavior of He bubbles depends on irradiation conditions. He bubbles nucleate by either clustering of He atoms with pre-existing vacancies or self-interstitial-atom (SIA) punching without initial vacancies. In nano-grain Mo, strong precipitation of He at the GBs is observed, and the density, size and spatial distribution of He bubbles vary with the GB structure. The corresponding He bubble density is higher in nano-grain Mo than that in sc Mo and the average bubble size is smaller. In the GB plane, He bubbles distribute along the dislocation cores for GBs consisting of GB dislocations and randomly for those without distinguishable dislocation structures. The simulation results in nano-grain Mo are in agreement with previous experiments in metal nano-layers, and they are further explained by the effect of excess volume associated with the GBs.

  2. Heterogeneous nucleation of calcium oxalate on native oxide surfaces

    SciTech Connect

    Song, L.; Pattillo, M.J.; Graff, G.L.; Campbell, A.A.; Bunker, B.C.

    1994-04-01

    The aqueous deposition of calcium oxalate onto colloidal oxides has been studied as a model system for understanding heterogeneous nucleation processes of importance in biomimetic synthesis of ceramic thin films. Calcium oxalate nucleation has been monitored by measuring induction times for nucleation using Constant Composition techniques and by measuring nucleation densities on extended oxide surfaces using an atomic force microscope. Results show that the dependence of calcium oxalate nucleation on solution supersaturation fits the functional form predicted by classical nucleation theories. Anionic surfaces appear to promote nucleation better than cationic surfaces, lowering the effective energy barrier to heterogeneous nucleation.

  3. Experimental Studies in Ice Nucleation

    NASA Astrophysics Data System (ADS)

    Wright, Timothy Peter

    Ice nuclei play a critical role in the formation of precipitation in mixed phase clouds. Modification of IN concentrations can lead to changes in cloud lifetimes and precipitation size. Presented in this study are experimental investigations into ice nuclei in an ongoing effort to reduce the uncertainties that ice nuclei have on cloud processes and climate. This research presents a new version of the cold stage drop freezing assay to investigate the time-dependence of heterogeneous nucleation. The temperature range for the instrument spans from the melting point of water to the homogeneous freezing limit of ˜-38 deg C. Temperature stability for the instrument allowed for experimental operation for up to four days while interrogating the same sample. Up to a one hundred fold increase in the number of analyzed drops was accomplished through an in-house written automated drop freezing detection software package. Combined instrument design improvements allow for the analysis of IN concentrations down to ˜10-8 ice nuclei per picoliter of sample water. A new variant of the multiple-component stochastic model for heterogeneous ice nucleation was used to investigate the time dependence of heterogeneous freezing processes. This was accomplished by analyzing how the changes in the cooling rate can impact the observed nucleation rate. The model employed four material-dependent parameters to accurately capture the observed freezing of water drops containing Arizona Test Dust. The parameters were then used to accurately predict the freezing behavior of the drops in time dependent experiments. The time dependence freezing of a wide range of materials was then investigated. These materials included the minerals montmorillonite and kaolinite, the biological proxy ice nuclei contained within the product Icemax, and flame soot generated from the incomplete combustion of ethylene gas. The time dependence for ice nuclei collected from rainwater samples was also investigated. The

  4. Foreshocks during the nucleation of stick-slip instability

    USGS Publications Warehouse

    McLaskey, Gregory C.; Kilgore, Brian D.

    2013-01-01

    We report on laboratory experiments which investigate interactions between aseismic slip, stress changes, and seismicity on a critically stressed fault during the nucleation of stick-slip instability. We monitor quasi-static and dynamic changes in local shear stress and fault slip with arrays of gages deployed along a simulated strike-slip fault (2 m long and 0.4 m deep) in a saw cut sample of Sierra White granite. With 14 piezoelectric sensors, we simultaneously monitor seismic signals produced during the nucleation phase and subsequent dynamic rupture. We observe localized aseismic fault slip in an approximately meter-sized zone in the center of the fault, while the ends of the fault remain locked. Clusters of high-frequency foreshocks (Mw ~ −6.5 to −5.0) can occur in this slowly slipping zone 5–50 ms prior to the initiation of dynamic rupture; their occurrence appears to be dependent on the rate at which local shear stress is applied to the fault. The meter-sized nucleation zone is generally consistent with theoretical estimates, but source radii of the foreshocks (2 to 70 mm) are 1 to 2 orders of magnitude smaller than the theoretical minimum length scale over which earthquake nucleation can occur. We propose that frictional stability and the transition between seismic and aseismic slip are modulated by local stressing rate and that fault sections, which would typically slip aseismically, may radiate seismic waves if they are rapidly stressed. Fault behavior of this type may provide physical insight into the mechanics of foreshocks, tremor, repeating earthquake sequences, and a minimum earthquake source dimension.

  5. Heterogeneous nucleation of ice on carbon surfaces.

    PubMed

    Lupi, Laura; Hudait, Arpa; Molinero, Valeria

    2014-02-26

    Atmospheric aerosols can promote the heterogeneous nucleation of ice, impacting the radiative properties of clouds and Earth's climate. The experimental investigation of heterogeneous freezing of water droplets by carbonaceous particles reveals widespread ice freezing temperatures. It is not known which structural and chemical characteristics of soot account for the variability in ice nucleation efficiency. Here we use molecular dynamics simulations to investigate the nucleation of ice from liquid water in contact with graphitic surfaces. We find that atomically flat carbon surfaces promote heterogeneous nucleation of ice, while molecularly rough surfaces with the same hydrophobicity do not. Graphitic surfaces and other surfaces that promote ice nucleation induce layering in the interfacial water, suggesting that the order imposed by the surface on liquid water may play an important role in the heterogeneous nucleation mechanism. We investigate a large set of graphitic surfaces of various dimensions and radii of curvature and find that variations in nanostructures alone could account for the spread in the freezing temperatures of ice on soot in experiments. We conclude that a characterization of the nanostructure of soot is needed to predict its ice nucleation efficiency.

  6. Temperature Gradient Field Theory of Nucleation

    NASA Astrophysics Data System (ADS)

    Das, S.; Ain, W. Q.; Azhari, A.; Prasada Rao, A. K.

    2016-02-01

    According to the proposed theory, ceramic particles present in molten metal, lose heat at a slower rate than the metallic liquid during cooling. Such condition results in the formation of a spherical thermal gradient field (TGF) around each particle. Hence, the interstitials (low temperature) of such TGFs are the regions to reach the nucleation temperature first, owing to low energy barrier than the liquid-particle interface (higher temperature). Analytics also indicate that the nucleation rate is higher at the TGF interstitials, than at the liquid-particle interface. Such TGF network results in simultaneous nucleation throughout the system, resulting in grain refinement.

  7. Viscosity of interfacial water regulates ice nucleation

    SciTech Connect

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

    2014-03-10

    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{sub 0} and Γ, in the context of classical nucleation theory. From the extracted J{sub 0} and Γ, we reveal the dominant role played by interfacial water. The results provide an insight into freezing mechanism on solid surfaces.

  8. Damage nucleation in Si during ion irradiation

    SciTech Connect

    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.

  9. Dislocation creation and void nucleation in FCC ductile metals under tensile loading: a general microscopic picture.

    PubMed

    Pang, Wei-Wei; Zhang, Ping; Zhang, Guang-Cai; Xu, Ai-Guo; Zhao, Xian-Geng

    2014-11-10

    Numerous theoretical and experimental efforts have been paid to describe and understand the dislocation and void nucleation processes that are fundamental for dynamic fracture modeling of strained metals. To date an essential physical picture on the self-organized atomic collective motions during dislocation creation, as well as the essential mechanisms for the void nucleation obscured by the extreme diversity in structural configurations around the void nucleation core, is still severely lacking in literature. Here, we depict the origin of dislocation creation and void nucleation during uniaxial high strain rate tensile processes in face-centered-cubic (FCC) ductile metals. We find that the dislocations are created through three distinguished stages: (i) Flattened octahedral structures (FOSs) are randomly activated by thermal fluctuations; (ii) The double-layer defect clusters are formed by self-organized stacking of FOSs on the close-packed plane; (iii) The stacking faults are formed and the Shockley partial dislocations are created from the double-layer defect clusters. Whereas, the void nucleation is shown to follow a two-stage description. We demonstrate that our findings on the origin of dislocation creation and void nucleation are universal for a variety of FCC ductile metals with low stacking fault energies.

  10. Ice Nucleation from Ship Emissions

    NASA Astrophysics Data System (ADS)

    Thomson, E. S.; Weber, D.; Tuomi, J.; Pettersson, J.; Bingemer, H. G.

    2015-12-01

    Atmospheric ice particles play a significant role in many atmospheric processes and are central to the role of clouds in determining the global radiative balance. Atmospheric ice originates when Ice Nucleating Particles (INP) lower the free energy barrier to phase transformation. The Earth's polar regions are well isolated from the middle and lower latitudes and thus have limited access to INP, and therefore small changes in terms of regional sources or large scale transport of particulate may have significant impacts on polar ice cloud formation. Here we describe field measurements of INP collected in the Port of Gothenburg, Gothenburg, Sweden. The port is the largest Scandinavian seaport and thus has heavy and diverse ocean vessel traffic. Unique to this study was the ability to isolate the INP contribution directly from the ship traffic by utilizing a sampling method that nearly simultaneously captured transiting ship plumes and the background aerosol. A small but potentially significant increase in IN from marine vessels was observed over two consecutive years. The results have implications for Arctic and global climate in the context of growing global commerce and trans-polar transport.

  11. Zinc Nucleation and Growth in Microgravity

    NASA Technical Reports Server (NTRS)

    Michael, B. Patrick; Nuth, J. A., III; Lilleleht, L. U.; Vondrak, Richard R. (Technical Monitor)

    2000-01-01

    We report our experiences with zinc nucleation in a microgravity environment aboard NASA's Reduced Gravity Research Facility. Zinc vapor is produced by a heater in a vacuum chamber containing argon gas. Nucleation is induced by cooling and its onset is easily detected visually by the appearance of a cloud of solid, at least partially crystalline zinc particles. Size distribution of these particles is monitored in situ by photon correlation spectroscopy. Samples of particles are also extracted for later analysis by SEM. The initially rapid increase in particle size is followed by a slower period of growth. We apply Scaled Nucleation Theory to our data and find that the derived critical temperature of zinc, the critical cluster size at nucleation, and the surface tension values are all in reasonably good agreement with their accepted literature values.

  12. Ice nucleation by water-soluble macromolecules

    NASA Astrophysics Data System (ADS)

    Pummer, B. G.; Budke, C.; Augustin-Bauditz, S.; Niedermeier, D.; Felgitsch, L.; Kampf, C. J.; Huber, R. G.; Liedl, K. R.; Loerting, T.; Moschen, T.; Schauperl, M.; Tollinger, M.; Morris, C. E.; Wex, H.; Grothe, H.; Pöschl, U.; Koop, T.; Fröhlich-Nowoisky, J.

    2015-04-01

    Cloud glaciation is critically important for the global radiation budget (albedo) and for initiation of precipitation. But the freezing of pure water droplets requires cooling to temperatures as low as 235 K. Freezing at higher temperatures requires the presence of an ice nucleator, which serves as a template for arranging water molecules in an ice-like manner. It is often assumed that these ice nucleators have to be insoluble particles. We point out that also free macromolecules which are dissolved in water can efficiently induce ice nucleation: the size of such ice nucleating macromolecules (INMs) is in the range of nanometers, corresponding to the size of the critical ice embryo. As the latter is temperature-dependent, we see a correlation between the size of INMs and the ice nucleation temperature as predicted by classical nucleation theory. Different types of INMs have been found in a wide range of biological species and comprise a variety of chemical structures including proteins, saccharides, and lipids. Our investigation of the fungal species Acremonium implicatum, Isaria farinosa, and Mortierella alpina shows that their ice nucleation activity is caused by proteinaceous water-soluble INMs. We combine these new results and literature data on INMs from fungi, bacteria, and pollen with theoretical calculations to develop a chemical interpretation of ice nucleation and water-soluble INMs. This has atmospheric implications since many of these INMs can be released by fragmentation of the carrier cell and subsequently may be distributed independently. Up to now, this process has not been accounted for in atmospheric models.

  13. Direct simulations of homogeneous bubble nucleation: Agreement with classical nucleation theory and no local hot spots.

    PubMed

    Diemand, Jürg; Angélil, Raymond; Tanaka, Kyoko K; Tanaka, Hidekazu

    2014-11-01

    We present results from direct, large-scale molecular dynamics simulations of homogeneous bubble (liquid-to-vapor) nucleation. The simulations contain half a billion Lennard-Jones atoms and cover up to 56 million time steps. The unprecedented size of the simulated volumes allows us to resolve the nucleation and growth of many bubbles per run in simple direct micro-canonical simulations while the ambient pressure and temperature remain almost perfectly constant. We find bubble nucleation rates which are lower than in most of the previous, smaller simulations. It is widely believed that classical nucleation theory (CNT) generally underestimates bubble nucleation rates by very large factors. However, our measured rates are within two orders of magnitude of CNT predictions; only at very low temperatures does CNT underestimate the nucleation rate significantly. Introducing a small, positive Tolman length leads to very good agreement at all temperatures, as found in our recent vapor-to-liquid nucleation simulations. The critical bubbles sizes derived with the nucleation theorem agree well with the CNT predictions at all temperatures. Local hot spots reported in the literature are not seen: Regions where a bubble nucleation event will occur are not above the average temperature, and no correlation of temperature fluctuations with subsequent bubble formation is seen.

  14. Bacterial ice nucleation: significance and molecular basis.

    PubMed

    Gurian-Sherman, D; Lindow, S E

    1993-11-01

    Several bacterial species are able to catalyze ice formation at temperatures as warm as -2 degrees C. These microorganisms efficiently catalyze ice formation at temperatures much higher than most organic or inorganic substances. Because of their ubiquity on the surfaces of frost-sensitive plants, they are responsible for initiating ice formation, which results in frost injury. The high temperature of ice catalysis conferred by bacterial ice nuclei makes them useful in ice nucleation-limited processes such as artificial snow production, the freezing of some food products, and possibly in future whether modification schemes. The rarity of other ice nuclei active at high subfreezing temperature, and the ease and sensitivity with which ice nuclei can be quantified, have made the use of a promoterless bacterial ice nucleation gene valuable as a reporter of transcription. Target genes to which this promoter is fused can be used in cells in natural habitats. Warm-temperature ice nucleation sites have also been extensively studied at a molecular level. Nucleation sites active at high temperatures (above -5 degrees C) are probably composed of bacterial ice nucleation protein molecules that form functionally aligned aggregates. Models of ice nucleation proteins predict that they form a planar array of hydrogen binding groups that closely complement that of an ice crystal face. Moreover, interdigitation of these molecules may produce a large contiguous template for ice formation.

  15. Bacterial ice nucleation: significance and molecular basis.

    PubMed

    Gurian-Sherman, D; Lindow, S E

    1993-11-01

    Several bacterial species are able to catalyze ice formation at temperatures as warm as -2 degrees C. These microorganisms efficiently catalyze ice formation at temperatures much higher than most organic or inorganic substances. Because of their ubiquity on the surfaces of frost-sensitive plants, they are responsible for initiating ice formation, which results in frost injury. The high temperature of ice catalysis conferred by bacterial ice nuclei makes them useful in ice nucleation-limited processes such as artificial snow production, the freezing of some food products, and possibly in future whether modification schemes. The rarity of other ice nuclei active at high subfreezing temperature, and the ease and sensitivity with which ice nuclei can be quantified, have made the use of a promoterless bacterial ice nucleation gene valuable as a reporter of transcription. Target genes to which this promoter is fused can be used in cells in natural habitats. Warm-temperature ice nucleation sites have also been extensively studied at a molecular level. Nucleation sites active at high temperatures (above -5 degrees C) are probably composed of bacterial ice nucleation protein molecules that form functionally aligned aggregates. Models of ice nucleation proteins predict that they form a planar array of hydrogen binding groups that closely complement that of an ice crystal face. Moreover, interdigitation of these molecules may produce a large contiguous template for ice formation. PMID:8224607

  16. Binary homogeneous nucleation of octane isomers

    NASA Astrophysics Data System (ADS)

    Doster, George Jay

    The measurement of the binary homogeneous nucleation of i-octane and n-octane (2,2,4-trimethylpentane) has been performed with a Wilson cloud chamber. This system of octane isomers has been chosen because it exhibits the desirable properties of a nearly ideal system. The octanes are non-polar, do not hydrogen bond, and have a low heat of mixing. The results from this experiment are presented and compared to the binary classical nucleation theory, the diffuse interface theory, and the binary scaled nucleation theory. The data from this experiment includes 3 mixtures of the octane isomers in mole fraction ratios of 1:1, 1:3, and 3:1 along with results from the pure octanes. Nucleation rates from approximately 100 to 50,000 cm3s and nucleation temperatures of 215 K to 260 K are included. This wide range of data is an effort to create a collection of data to which modified or new nucleation theories may be compared.

  17. Fluorescence Studies of Lysozyme Nucleation

    NASA Technical Reports Server (NTRS)

    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

  18. Nucleation in an ultra low ionization environment

    NASA Astrophysics Data System (ADS)

    Olaf Pepke Pedersen, Jens; Bødker Enghoff, Martin; Paling, Sean; Svensmark, Henrik

    2010-05-01

    Atmospheric ions can enhance the nucleation of aerosols, as has been established by experiments, observation, and theory. In the clean marine atmosphere ionization is mainly caused by cosmic rays which in turn are controlled by the activity of the Sun, thus providing a potential link between solar activity and climate. In order to understand the effect ions may have on the formation of cloud condensation nuclei and thus the Earth's radiation budget the overall contribution of ion induced nucleation to the global production of secondary aerosols must be determined. One issue with determining this contribution is that several mechanisms for nucleation exist and it can be difficult to determine the relative importance of the various mechanisms in a given nucleation event when both ion induced and electrically neutral nucleation mechanisms are at work at the same time. We have carried out nucleation experiments in the Boulby Underground Laboratory, located 1100 meters below ground, thus reducing the flux of ionizing cosmic radiation by six orders of magnitude. Similarly we have reduced the gamma background by shielding the experiment in lead and copper. Finally we have used air stored for several weeks and passed through an active charcoal filter in order to reduce the Radon concentration. In this way we have been able to make nucleation experiments with very low ionizing background, meaning that we can rule out ion induced nucleation as a contributing mechanism. Our experimental setup is a 50 L electropolished stainless steel reactor at near atmospheric conditions. The chamber contains clean air with the addition of water vapour, ozone, and sulphur dioxide. Using UV lights at 254 nm ozone is photolyzed, leading to the production of sulphuric acid and thus aerosols. An 18 MBq Caesium-137 gamma ray source with various amounts of lead in front allows us to alter the ionization in our chamber. By making series of nucleation bursts with varying amounts of ionizing

  19. Initial stage of nucleation-mediated crystallization of a supercooled melt

    NASA Astrophysics Data System (ADS)

    Chernov, A. A.; Pil'nik, A. A.; Islamov, D. R.

    2016-09-01

    The kinetic model of nucleation-mediated crystallization of a supercooled melt is presented in this work. It correctly takes into account the change in supercooling of the initial phase in the process of formation and evolution of a new phase. The model makes it possible to find the characteristic time of the process, time course of the crystal phase volume, solidified material microstructure. The distinctive feature of the model is the use of the "forbidden" zones in the volume where the formation of new nucleation centers is suppressed.

  20. Cytoplasmic nucleation and atypical branching nucleation generate endoplasmic microtubules in Physcomitrella patens.

    PubMed

    Nakaoka, Yuki; Kimura, Akatsuki; Tani, Tomomi; Goshima, Gohta

    2015-01-01

    The mechanism underlying microtubule (MT) generation in plants has been primarily studied using the cortical MT array, in which fixed-angled branching nucleation and katanin-dependent MT severing predominate. However, little is known about MT generation in the endoplasm. Here, we explored the mechanism of endoplasmic MT generation in protonemal cells of Physcomitrella patens. We developed an assay that utilizes flow cell and oblique illumination fluorescence microscopy, which allowed visualization and quantification of individual MT dynamics. MT severing was infrequently observed, and disruption of katanin did not severely affect MT generation. Branching nucleation was observed, but it showed markedly variable branch angles and was occasionally accompanied by the transport of nucleated MTs. Cytoplasmic nucleation at seemingly random locations was most frequently observed and predominated when depolymerized MTs were regrown. The MT nucleator γ-tubulin was detected at the majority of the nucleation sites, at which a single MT was generated in random directions. When γ-tubulin was knocked down, MT generation was significantly delayed in the regrowth assay. However, nucleation occurred at a normal frequency in steady state, suggesting the presence of a γ-tubulin-independent backup mechanism. Thus, endoplasmic MTs in this cell type are generated in a less ordered manner, showing a broader spectrum of nucleation mechanisms in plants.

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

    SciTech Connect

    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. Molecular Ice Nucleation Activity of Birch Pollen

    NASA Astrophysics Data System (ADS)

    Felgitsch, Laura; Bichler, Magdalena; Häusler, Thomas; Weiss, Victor U.; Marchetti-Deschmann, Martina; Allmaier, Günter; Grothe, Hinrich

    2015-04-01

    Heterogeneous ice nucleation plays a major part in ecosystem and climate. Due to the triggering of ice cloud formation it influences the radiation balance of the earth, but also on the ground it can be found to be important in many processes of nature. So far the process of heterogeneous ice nucleation is not fully understood and many questions remain to be answered. Biological ice nucleation is hereby from great interest, because it shows the highest freezing temperatures. Several bacteria and fungi act as ice nuclei. A famous example is Pseudomonas syringae, a bacterium in commercial use (Snomax®), which increases the freezing from homogeneous freezing temperatures of approx. -40° C (for small volumes as in cloud droplets) to temperatures up to -2° C. In 2001 it was found that birch pollen can trigger ice nucleation (Diehl et al. 2001; Diehl et al. 2002). For a long time it was believed that this is due to macroscopic features of the pollen surface. Recent findings of Bernhard Pummer (2012) show a different picture. The ice nuclei are not attached on the pollen surface directly, but on surface material which can be easily washed off. This shows that not only the surface morphology, but also specific molecules or molecular structures are responsible for the ice nucleation activity of birch pollen. With various analytic methods we work on elucidating the structure of these molecules as well as the mechanism with which they trigger ice nucleation. To solve this we use various instrumental analytic techniques like Nuclear Magnetic Resonance spectroscopy (NMR), Matrix-Assisted Laser Desorption/Ionization Mass Spectrometry (MALDI-MS), and Gas-phase Electrophoretic Mobility Molecular Analysis (GEMMA). Also standard techniques like various chromatographic separation techniques and solvent extraction are in use. We state here that this feature might be due to the aggregation of small molecules, with agglomerates showing a specific surface structure. Our results

  3. Nucleation and Dynamics of Golgi-derived Microtubules

    PubMed Central

    Sanders, Anna A. W. M.; Kaverina, Irina

    2015-01-01

    Integrity of the Golgi apparatus requires the microtubule (MT) network. A subset of MTs originates at the Golgi itself, which in this case functions as a MT-organizing center (MTOC). Golgi-derived MTs serve important roles in post-Golgi trafficking, maintenance of Golgi integrity, cell polarity and motility, as well as cell type-specific functions, including neurite outgrowth/branching. Here, we discuss possible models describing the formation and dynamics of Golgi-derived MTs. How Golgi-derived MTs are formed is not fully understood. A widely discussed model implicates that the critical step of the process is recruitment of molecular factors, which drive MT nucleation (γ-tubulin ring complex, or γ-TuRC), to the Golgi membrane via specific scaffolding interactions. Based on recent findings, we propose to introduce an additional level of regulation, whereby MT-binding proteins and/or local tubulin dimer concentration at the Golgi helps to overcome kinetic barriers at the initial nucleation step. According to our model, emerging MTs are subsequently stabilized by Golgi-associated MT-stabilizing proteins. We discuss molecular factors potentially involved in all three steps of MT formation. To preserve proper cell functioning, a balance must be maintained between MT subsets at the centrosome and the Golgi. Recent work has shown that certain centrosomal factors are important in maintaining this balance, suggesting a close connection between regulation of centrosomal and Golgi-derived MTs. Finally, we will discuss potential functions of Golgi-derived MTs based on their nucleation site location within a Golgi stack. PMID:26617483

  4. Nucleation in small scale multicrystalline silicon ingots

    NASA Astrophysics Data System (ADS)

    Brynjulfsen, I.; Arnberg, L.; Autruffe, A.

    2012-12-01

    Small scale solidification experiments were performed in order to study nucleation mechanisms of solar cell silicon. Ingots were grown in a Bridgman furnace; with a high rate (5 cm/min), inducing dendrite-like grains; and at a slow rate (0.2 mm/min), simulating the common slow crystal growth process. Two types of silicon were used, polysilicon and compensated material. The results showed that for the early stages of silicon solidification, the compensated material behaves similar to the polysilicon. A high undercooling of 11±3 K was obtained for one of the fast cooled experiments. This suggests that Si3N4-coating is not the important factor for nucleation, but Si3N4-precipitates in the melt could contribute as inoculants. Grains with similar orientation were observed for both the solidification rates, which indicates that the most important issue for grain growth selection in PV silicon is control of the vertical growth, rather than nucleation substrates.

  5. A parameterization of cloud droplet nucleation

    SciTech Connect

    Ghan, S.J.; Chuang, C.C.; Penner, J.E.

    1994-01-01

    Droplet nucleation is a fundamental cloud process. The number of aerosols activated to form cloud droplets influences not only the number of aerosols scavenged by clouds but also the size of the cloud droplets. Cloud droplet size influences the cloud albedo and the conversion of cloud water to precipitation. Global aerosol models are presently being developed with the intention of coupling with global atmospheric circulation models to evaluate the influence of aerosols and aerosol-cloud interactions on climate. If these and other coupled models are to address issues of aerosol-interactions, the droplet nucleation process must be adequately represented. Ghan et al. have introduced a droplet nucleation parameterization for a single aerosol type that offers certain advantages over the popular Twomey parameterization. Here we describe the generalization of that parameterization to the case of multiple aerosol types, with estimation of aerosol mass as well as number activated.

  6. Homogeneous freezing nucleation of stratospheric solution droplets

    NASA Technical Reports Server (NTRS)

    Jensen, Eric J.; Toon, Owen B.; Hamill, Patrick

    1991-01-01

    The classical theory of homogeneous nucleation was used to calculate the freezing rate of sulfuric acid solution aerosols under stratospheric conditions. The freezing of stratospheric aerosols would be important for the nucleation of nitric acid trihydrate particles in the Arctic and Antarctic stratospheres. In addition, the rate of heterogeneous chemical reactions on stratospheric aerosols may be very sensitive to their state. The calculations indicate that homogeneous freezing nucleation of pure water ice in the stratospheric solution droplets would occur at temperatures below about 192 K. However, the physical properties of H2SO4 solution at such low temperatures are not well known, and it is possible that sulfuric acid aerosols will freeze out at temperatures ranging from about 180 to 195 K. It is also shown that the temperature at which the aerosols freeze is nearly independent of their size.

  7. The ice nucleation activity of extremophilic algae.

    PubMed

    Kviderova, Jana; Hajek, Josef; Worland, Roger M

    2013-01-01

    Differences in the level of cold acclimation and cryoprotection estimated as ice nucleation activity in snow algae (Chlamydomonas cf. nivalis and Chloromonas nivalis), lichen symbiotic algae (Trebouxia asymmetrica, Trebouxia erici and Trebouxia glomerata), and a mesophilic strain (Chlamydomonas reinhardti) were evaluated. Ice nucleation activity was measured using the freezing droplet method. Measurements were performed using suspensions of cells of A750 (absorbance at 750 nm) ~ 1, 0.1, 0.01 and 0.001 dilutions for each strain. The algae had lower ice nucleation activity, with the exception of Chloromonas nivalis contaminated by bacteria. The supercooling points of the snow algae were higher than those of lichen photobionts. The supercooling points of both, mesophilic and snow Chlamydomonas strains were similar. The lower freezing temperatures of the lichen algae may reflect either the more extreme and more variable environmental conditions of the original localities or the different cellular structure of the strains examined.

  8. Nucleation of bubbles in binary fluids

    NASA Astrophysics Data System (ADS)

    Talanquer, V.; Oxtoby, David W.

    1995-02-01

    We have applied density functional methods to predict the nucleation rates of bubbles in superheated, stretched, or supersaturated binary fluid mixtures. Our model uses Lennard-Jones mixtures, with mixing rules chosen to allow either ideal or nonideal solution behavior. Deviations from the predictions of classical nucleation theory are in general quite large, with the locus of observable bubble nucleation (the kinetic stability limit) following the spinodal (the thermodynamic stability limit) reasonably closely. Comparisons are made with a variety of experiments, and puzzling earlier results are explained, such as the increase in solubility of some gases with temperature at the kinetic stability limit. Further experiments are needed to explore the variety of behavior predicted by the present calculations.

  9. Nonlinear Acoustical Assessment of Precipitate Nucleation

    NASA Technical Reports Server (NTRS)

    Cantrell, John H.; Yost, William T.

    2004-01-01

    The purpose of the present work is to show that measurements of the acoustic nonlinearity parameter in heat treatable alloys as a function of heat treatment time can provide quantitative information about the kinetics of precipitate nucleation and growth in such alloys. Generally, information on the kinetics of phase transformations is obtained from time-sequenced electron microscopical examination and differential scanning microcalorimetry. The present nonlinear acoustical assessment of precipitation kinetics is based on the development of a multiparameter analytical model of the effects on the nonlinearity parameter of precipitate nucleation and growth in the alloy system. A nonlinear curve fit of the model equation to the experimental data is then used to extract the kinetic parameters related to the nucleation and growth of the targeted precipitate. The analytical model and curve fit is applied to the assessment of S' precipitation in aluminum alloy 2024 during artificial aging from the T4 to the T6 temper.

  10. New approach to the kinetics of heterogeneous unary nucleation on liquid aerosols of a binary solution.

    PubMed

    Djikaev, Yuri; Ruckenstein, Eli

    2006-12-28

    The formation of a droplet on a hygroscopic center may occur either in a barrierless way via Kohler activation or via nucleation by overcoming a free energy barrier. Unlike the former, the latter mechanism of this process has been studied very little and only in the framework of the classical nucleation theory based on the capillarity approximation whereby a nucleating droplet behaves like a bulk liquid. In this paper the authors apply another approach to the kinetics of heterogeneous nucleation on liquid binary aerosols, based on a first passage time analysis which avoids the concept of surface tension for tiny droplets involved in nucleation. Liquid aerosols of a binary solution containing a nonvolatile solute are considered. In addition to modeling aerosols formed through the deliquescence of solid soluble particles, the considered aerosols constitute a rough model of "processed" marine aerosols. The theoretical results are illustrated by numerical calculations for the condensation of water vapor on binary aqueous aerosols with nonvolatile nondissociating solute molecules using Lennard-Jones potentials for the molecular interactions.

  11. Cavitation Bubble Nucleation by Energetic Particles

    SciTech Connect

    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.

  12. Molecular dynamics simulations of He bubble nucleation at grain boundaries

    SciTech Connect

    Yongfeng Zhang; Paul C Millett; Michael Tonks; Liangzhe Zhang; Bulent Biner

    2012-08-01

    The nucleation behavior of He bubbles in nano-grained body-centered-cubic (BCC) Mo is simulated using molecular dynamics (MD) simulations with a bicrystal model, focusing on the effect of grain boundary (GB) structure. Three types of GBs, the (100) twist S29, the ?110? symmetrical tilt (tilt angle of 10.1?), and the (112) twin boundaries, are studied as representatives of random GB, low angle GB with misfit dislocations, and special sigma boundaries. With the same amount of He, more He clusters form in nano-grained Mo with smaller average size compared to that in bulk. The effects of the GB structure originate from the excess volume in GBs. Trapping by excess volume results in reduction in mobility of He atoms, which enhances the nucleation with higher density of bubbles, and impedes the growth of He bubbles by absorption of mobile He atoms. Furthermore, the distribution of excess volume in GBs determines the distribution of He clusters. The effect of GBs becomes less pronounced with increasing vacancy concentration in the matrix.

  13. Nucleation of 360 deg DWs in a wire using a local circular field

    NASA Astrophysics Data System (ADS)

    Kaya, Fikriye Idil; Sarella, Anandakumar; Aidala, Katherine E.

    2015-03-01

    Understanding domain wall (DW) motion in ferromagnetic nanostructures is important to realize proposed magnetic data storage and logic devices. Interest in 360o DWs has increased recently with the recognition that their minimal stray field creates only short range interactions, leading to a potentially higher packing density compared to 180o DWs. Our simulations demonstrate the feasibility of nucleating a 360o DW at a specific location along a wire by applying a local circular field that is centered in close proximity to the wire. We simulate the field strength as if from a current carrying wire, which can be experimentally realized by passing current through the tip of an AFM [ 1 , 2 ]. The successful nucleation of a 360o DW depends on the dimensions of the Py wire, on the strength of the circular field, and on the distance of the center of the field from the wire. Once a 360o DW is nucleated, its position shifts with time. We use a notch to stabilize the location of the 360o DW. We investigate the optimal size and spacing of the notches to allow the greatest packing density with control over the nucleation and annihilation of individual domain walls. Supported by NSF DMR-1207924.

  14. Optical nucleation of bubble clouds in a high pressure spherical resonator.

    PubMed

    Anderson, Phillip; Sampathkumar, A; Murray, Todd W; Gaitan, D Felipe; Glynn Holt, R

    2011-11-01

    An experimental setup for nucleating clouds of bubbles in a high-pressure spherical resonator is described. Using nanosecond laser pulses and multiple phase gratings, bubble clouds are optically nucleated in an acoustic field. Dynamics of the clouds are captured using a high-speed CCD camera. The images reveal cloud nucleation, growth, and collapse and the resulting emission of radially expanding shockwaves. These shockwaves are reflected at the interior surface of the resonator and then reconverge to the center of the resonator. As the shocks reconverge upon the center of the resonator, they renucleate and grow the bubble cloud. This process is repeated over many acoustic cycles and with each successive shock reconvergence, the bubble cloud becomes more organized and centralized so that subsequent collapses give rise to stronger, better defined shockwaves. After many acoustic cycles individual bubbles cannot be distinguished and the cloud is then referred to as a cluster. Sustainability of the process is ultimately limited by the detuning of the acoustic field inside the resonator. The nucleation parameter space is studied in terms of laser firing phase, laser energy, and acoustic power used. PMID:22088012

  15. Optical nucleation of bubble clouds in a high pressure spherical resonator.

    PubMed

    Anderson, Phillip; Sampathkumar, A; Murray, Todd W; Gaitan, D Felipe; Glynn Holt, R

    2011-11-01

    An experimental setup for nucleating clouds of bubbles in a high-pressure spherical resonator is described. Using nanosecond laser pulses and multiple phase gratings, bubble clouds are optically nucleated in an acoustic field. Dynamics of the clouds are captured using a high-speed CCD camera. The images reveal cloud nucleation, growth, and collapse and the resulting emission of radially expanding shockwaves. These shockwaves are reflected at the interior surface of the resonator and then reconverge to the center of the resonator. As the shocks reconverge upon the center of the resonator, they renucleate and grow the bubble cloud. This process is repeated over many acoustic cycles and with each successive shock reconvergence, the bubble cloud becomes more organized and centralized so that subsequent collapses give rise to stronger, better defined shockwaves. After many acoustic cycles individual bubbles cannot be distinguished and the cloud is then referred to as a cluster. Sustainability of the process is ultimately limited by the detuning of the acoustic field inside the resonator. The nucleation parameter space is studied in terms of laser firing phase, laser energy, and acoustic power used.

  16. Microgravity nucleation and particle coagulation experiments support

    NASA Technical Reports Server (NTRS)

    Lilleleht, L. U.; Ferguson, F. T.; Stephens, J. R.

    1992-01-01

    Modifications to the nucleation apparatus suggested by our first microgravity flight campaign are complete. These included a complete 'repackaging' of the equipment into three racks along with an improved vapor spout shutter mechanism and additional thermocouples for gas temperature measurements. The 'repackaged' apparatus was used in two KC-135 campaigns: one during the week of June 3, 1991 consisting of two flights with Mg and two with Zn, and another series consisting of three flights with Zn during the week of September 23, 1991. Our effort then was focused on the analysis of these data, including further development of the mathematical models to generate the values of temperature and supersaturation at the observed points of nucleation. The efforts to apply Hale's Scaled Nucleation Theory to our experimental data have met with only limited success, most likely due to still inadequate temperature field determination. Work on the development of a preliminary particle collector system designed to capture particles from the region of nucleation and condensation, as well as from other parts of the chamber, are discussed.

  17. Microgravity nucleation and particle coagulation experiments support

    NASA Technical Reports Server (NTRS)

    Lilleleht, L. U.; Lass, T. J.

    1987-01-01

    A hollow sphere model is developed to predict the range of supersaturation ratio values for refractory metal vapors in a proposed experimental nucleation apparatus. Since the experiments are to be carried out in a microgravity environment, the model neglects the effects of convection and assumes that the only transfer of vapors through an inert gas atmosphere is by conduction and molecular diffusion. A consistent set of physical properties data is assembled for the various candidate metals and inert ambient gases expected to be used in the nucleation experiments. Transient partial pressure profiles are computed for the diffusing refractory species for two possible temperature distributions. The supersaturation ratio values from both candidate temperature profiles are compared with previously obtained experimetnal data on a silver-hydrogen system. The model is used to simulate the diffusion of magnesium vapor through argon and other inert gas atmospheres over ranges of initial and boundary conditions. These results identify different combinations of design and operating parameters which are liekly to produce supersaturation ratio values high enough to induce homogeneous nucleation in the apparatus being designed for the microgravity nucleation experiments.

  18. Heterogeneous nucleation of aspartame from aqueous solutions

    NASA Astrophysics Data System (ADS)

    Kubota, Noriaki; Kinno, Hiroaki; Shimizu, Kenji

    1990-03-01

    Waiting times, the time from the instant of quenching needed for a first nucleus to appear, were measured at constant supercoolings for primary nucleation of aspartame (α-L-aspartyl-L-phenylalanine methylester) from aqueous solutions, which were sealed into glass ampoules (solution volume = 3.16 cm 3). Since the waiting time became shorter by filtering the solution prior to quenching, the nucleation was concluded to be heterogeneously induced. The measured waiting time consisted of two parts: time needed for the nucleus to grow to a detactable size (growth time) and stochastic time needed for nucleation (true waiting time). The distribution of the true waiting time, is well explained by a stochastic model, in which nucleation is regarded to occur heterogeneously and in a stochastic manner by two kinds of active sites. The active sites are estimated to be located on foreign particles in which such elements as Si, Al and Mg were contained. The amount of each element is very small in the order of magnitude of ppb (mass basis) of the whole solution. The growth time was correlated with the degree of supercooling.

  19. Soot Aerosol Particles as Cloud Condensation Nuclei: from Ice Nucleation Activity to Ice Crystal Morphology

    NASA Astrophysics Data System (ADS)

    Pirim, Claire; Ikhenazene, Raouf; Ortega, Isamel Kenneth; Carpentier, Yvain; Focsa, Cristian; Chazallon, Bertrand; Ouf, François-Xavier

    2016-04-01

    Emissions of solid-state particles (soot) from engine exhausts due to incomplete fuel combustion is considered to influence ice and liquid water cloud droplet activation [1]. The activity of these aerosols would originate from their ability to be important centers of ice-particle nucleation, as they would promote ice formation above water homogeneous freezing point. Soot particles are reported to be generally worse ice nuclei than mineral dust because they activate nucleation at higher ice-supersaturations for deposition nucleation and at lower temperatures for immersion freezing than ratios usually expected for homogeneous nucleation [2]. In fact, there are still numerous opened questions as to whether and how soot's physico-chemical properties (structure, morphology and chemical composition) can influence their nucleation ability. Therefore, systematic investigations of soot aerosol nucleation activity via one specific nucleation mode, here deposition nucleation, combined with thorough structural and compositional analyzes are needed in order to establish any association between the particles' activity and their physico-chemical properties. In addition, since the morphology of the ice crystals can influence their radiative properties [3], we investigated their morphology as they grow over both soot and pristine substrates at different temperatures and humidity ratios. In the present work, Combustion Aerosol STandart soot samples were produced from propane using various experimental conditions. Their nucleation activity was studied in deposition mode (from water vapor), and monitored using a temperature-controlled reactor in which the sample's relative humidity is precisely measured with a cryo-hygrometer. Formation of water/ice onto the particles is followed both optically and spectroscopically, using a microscope coupled to a Raman spectrometer. Vibrational signatures of hydroxyls (O-H) emerge when the particle becomes hydrated and are used to characterize ice

  20. Nucleation Pathways For Freezing Of Two Grades Of Zirconium

    NASA Technical Reports Server (NTRS)

    Rhim, Won-Kyu; Rulison, Aaron; Bayuzick, Robert; Hofmeister, William; Morton, Craig

    1996-01-01

    Report discusses classical nucleation theory of freezing and describes experimental study of nucleation mechanisms that predominate during freezing of spherical specimens of initially molten zirconium levitated electrostatically in vacuum.

  1. Phase transformation kinetics in finite inhomogeneously nucleated systems

    NASA Technical Reports Server (NTRS)

    Weinberg, Michael; Kapral, Raymond

    1989-01-01

    Phase transformation kinetics that occur by a nucleation and growth process are investigated. A simple discrete space and time model is used for the dynamics and analytical results are obtained for the volume fraction of the material transformed for both finite systems and a special example of an inhomogeneously nucleated system. The theory is developed for two cases, initial nucleation, and continuous nucleation. The results are compared with simulations of the model.

  2. Predictive nucleation of crystals in small volumes and its consequences.

    PubMed

    Grossier, Romain; Hammadi, Zoubida; Morin, Roger; Veesler, Stéphane

    2011-07-01

    We propose another way of getting to the bottom of nucleation by using finite volume systems. Here we show, using a sharp tip, that a single nucleation event is launched as soon as the tip touches the supersaturated confined metastable solution. We thus control spatial and temporal location and demonstrate that confinement allows us to carry out predictive nucleation experiments. This control is a major step forward in understanding the factors influencing the nucleation process and its underlying physics.

  3. Ice nucleation in nature: supercooling point (SCP) measurements and the role of heterogeneous nucleation.

    PubMed

    Wilson, P W; Heneghan, A F; Haymet, A D J

    2003-02-01

    In biological systems, nucleation of ice from a supercooled aqueous solution is a stochastic process and always heterogeneous. The average time any solution may remain supercooled is determined only by the degree of supercooling and heterogeneous nucleation sites it encounters. Here we summarize the many and varied definitions of the so-called "supercooling point," also called the "temperature of crystallization" and the "nucleation temperature," and exhibit the natural, inherent width associated with this quantity. We describe a new method for accurate determination of the supercooling point, which takes into account the inherent statistical fluctuations of the value. We show further that many measurements on a single unchanging sample are required to make a statistically valid measure of the supercooling point. This raises an interesting difference in circumstances where such repeat measurements are inconvenient, or impossible, for example for live organism experiments. We also discuss the effect of solutes on this temperature of nucleation. Existing data appear to show that various solute species decrease the nucleation temperature somewhat more than the equivalent melting point depression. For non-ionic solutes the species appears not to be a significant factor whereas for ions the species does affect the level of decrease of the nucleation temperature.

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

    NASA Astrophysics Data System (ADS)

    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

  5. Control of nucleation and growth in protein crystal growth

    NASA Technical Reports Server (NTRS)

    Rosenberger, Franz; Meehan, Edward J.

    1988-01-01

    The potential advantages of nucleation and growth control through temperature, rather than the addition of precipitants or removal of solvent, are discussed. A simple light scattering arrangement for the characterization of nucleation and growth conditions in solutions is described. The temperature dependence of the solubility of low ionic strength lysozyme solutions is applied in preliminary nucleation and growth experiments.

  6. Nucleation in a Sheared Liquid Binary Mixture.

    NASA Astrophysics Data System (ADS)

    Min, Kyung-Yang

    When a binary liquid mixture of lutidine plus water (LW) is quenched to a temperature T and is exposed to a continuous shear rate S, the result is a steady-state droplet distribution. This steady state can be probed by measuring the unscattered intensity I_{f}, or the scattered intensity I_{s}, as a function of delta T and S. In the experiments described here, S is fixed and delta T is varied in a step-wise fashion. The absence of hysteresis was probed in two separate experiments: First, I_{f} was measured as a function of S for a given delta T. Next, I_{f} was measured as a function of delta T for a given S. In either case, the hysteresis associated with the shear-free nucleation is absent. In addition, a flow-history dependent hysteresis was studied. In the 2-dimensional parameter space consisting of S and delta T, the onset of nucleation uniquely determines a cloud point line. A plot of the cloud point line exhibits two segments of different slopes with a cross-over near the temperature corresponding to the Becker-Doring limit. The classical picture of a free energy barrier was reformulated to explain this cross-over behavior. Next, photon correlation spectroscopy was used to study the dependence of the transient nucleation behavior on the initial states. A unique feature of this study is that this initial state can be conveniently adjusted by varying the shear rate S to which the mixture is initially exposed. The shear is then turned off, and the number density N(t), as well as the mean radius of the growing droplets, is monitored as a function of time. It was possible to measure the droplet density at a very early stage of phase separation where the nucleation rate J was close to zero. The measurement reveals that N(t) depends critically on the initial state of the metastable system. When the shear is large enough to rupture the droplets as small as the critical size, N(t) increases very slowly. Measurements of the nucleation rates vs. the square of the

  7. Out-of-equilibrium nucleation in the solidification of helium

    NASA Astrophysics Data System (ADS)

    Johnson, Timothy Andrew

    Investigations into the nucleation of the solid phase from the liquid in He4 below the lower hcp-bcc-He-II triple point at temperatures of 1.3 to 1.46 K have revealed instances where the phase which nucleates and grows to macroscopic size first is not the stable hcp phase, but a metastable bcc phase. Although the hcp has the lower bulk free energy, because the bcc solid has a lower surface free energy, the nucleation barrier predicted by classical nucleation theory is lower for the bcc solid at suitably high overpressures. This is consistent with the preferential nucleation of the bcc phase. However, the data show several important inconsistencies with the classical nucleation theory. Theoretical nucleation rates at the overpressures for which nucleation actually occurs in these experiments is extremely small. Because solid He 4 wets the surfaces in the cell only poorly (the contact angle is much larger than 90°) models in which nucleation occurs on a uniform flat substrate (heterogeneous nucleation) are not sufficient to bring theoretical nucleation rates in accord with the experimental observations. Even in more favorable geometries, a contact angle of less than 90° is necessary to get the orders of magnitude of correction necessary. At 1.4 K, the overpressures at nucleation are consistent with overpressures required for the bcc to have the larger relative nucleation probability. As the temperature decreases, the theoretical value of overpressure for preferential nucleation of the bcc increases faster than the overpressure at which nucleation is observed to occur. However metastable nucleation was observed at temperatures below the predicted cut-off. Finally, the absolute nucleation pressures are, within the experimental scatter, the same for nucleation of the bcc as for nucleation of the hcp. This suggests a nucleation process which does not depend strongly on the process of phase selection. Implications of this result are examined in light of predictions

  8. Time dependent nucleation in a bulk metallic glass forming alloy

    SciTech Connect

    Croat, T.K.; Kelton, K.F.

    1998-12-31

    The effect of composition on the time-dependent nucleation rates in Zr{sub 65}Al{sub 7.5}Ni{sub 10}Cu{sub 17.5} glasses is investigated to better understand nucleation processes in partitioning systems. As-quenched glasses were annealed to produce a homogeneous dispersion of nanocrystals within the amorphous matrix. The nucleation rates were estimated from the number of crystallites produced as function of annealing time, using scanning and transmission electron microscopy. Experimental results for single and multiple-step annealing treatments are presented. The nucleation results are discussed briefly within the time-dependent model of the classical theory of nucleation.

  9. Dynamics and nucleation of vorticity in superfluids

    NASA Astrophysics Data System (ADS)

    Freire, Jose Arruda De Oliveira

    1997-11-01

    This thesis contains numerical studies on vortex dynamics and on quantum nucleation of vorticity in superfluids at zero temperature. In both cases the superfluid was described by the Gross-Pitaevskii model. In the first part of the thesis, the vortex mass problem is analyzed by a numerical integration of the condensate equation of motion, the nonlinear Schrodinger equation. We were able to extract, from the observed vortex dynamics in a time-dependent superflow, the frequency dependence of the vortex effective mass. In the second part, the problem of quantum nucleation of vorticity in superflows past obstacles, in both one and two dimensions, is studied by the application of the bounce formalism of Coleman (12) to the coherent state action of the Gross-Pitaevskii model. We obtained bounce solutions and tunneling rates by directly solving the field equations for the condensate in imaginary time.

  10. Onset of runaway nucleation in aerosol reactors

    NASA Technical Reports Server (NTRS)

    Wu, Jin Jwang; Flagan, Richard C.

    1987-01-01

    The onset of homogeneous nucleation of new particles from the products of gas phase chemical reactions was explored using an aerosol reactor in which seed particles of silicon were grown by silane pyrolysis. The transition from seed growth by cluster deposition to catastrophic nucleation was extremely abrupt, with as little as a 17 percent change in the reactant concentration leading to an increase in the concentration of measurable particles of four orders of magnitude. From the structure of the particles grown near this transition, it is apparent that much of the growth occurs by the accumulation of clusters on the growing seed particles. The time scale for cluster diffusion indicates, however, that the clusters responsible for growth must be much smaller than the apparent fine structure of the product particles.

  11. Direct observations of atmospheric aerosol nucleation.

    PubMed

    Kulmala, Markku; Kontkanen, Jenni; Junninen, Heikki; Lehtipalo, Katrianne; Manninen, Hanna E; Nieminen, Tuomo; Petäjä, Tuukka; Sipilä, Mikko; Schobesberger, Siegfried; Rantala, Pekka; Franchin, Alessandro; Jokinen, Tuija; Järvinen, Emma; Äijälä, Mikko; Kangasluoma, Juha; Hakala, Jani; Aalto, Pasi P; Paasonen, Pauli; Mikkilä, Jyri; Vanhanen, Joonas; Aalto, Juho; Hakola, Hannele; Makkonen, Ulla; Ruuskanen, Taina; Mauldin, Roy L; Duplissy, Jonathan; Vehkamäki, Hanna; Bäck, Jaana; Kortelainen, Aki; Riipinen, Ilona; Kurtén, Theo; Johnston, Murray V; Smith, James N; Ehn, Mikael; Mentel, Thomas F; Lehtinen, Kari E J; Laaksonen, Ari; Kerminen, Veli-Matti; Worsnop, Douglas R

    2013-02-22

    Atmospheric nucleation is the dominant source of aerosol particles in the global atmosphere and an important player in aerosol climatic effects. The key steps of this process occur in the sub-2-nanometer (nm) size range, in which direct size-segregated observations have not been possible until very recently. Here, we present detailed observations of atmospheric nanoparticles and clusters down to 1-nm mobility diameter. We identified three separate size regimes below 2-nm diameter that build up a physically, chemically, and dynamically consistent framework on atmospheric nucleation--more specifically, aerosol formation via neutral pathways. Our findings emphasize the important role of organic compounds in atmospheric aerosol formation, subsequent aerosol growth, radiative forcing and associated feedbacks between biogenic emissions, clouds, and climate.

  12. EHD enhancement of nucleate boiling. [Electrohydrodynamic

    SciTech Connect

    Cooper, P. )

    1990-05-01

    This paper describes: (a) an experimental investigation into the effect of an electric field applied to pool boiling of Freon (R114) on a finned tube and (b) a theoretical model of electrically enhanced nucleate boiling applicable to simple surfaces only. Experimental results have shown electrohydrodynamic (EHD) enhancement of heat transfer to be manifest in two ways: (1) elimination of boiling hysteresis, (2) augmentation of nulceate boiling heat transfer coefficients by up to an order of magnitude. These effects were also observed in electrically enhanced boiling of Freon/oil mixtures. A new analytical model is described whereby EHD nucleate boiling data from previous studies (employing simple apparatus comprising heated wires with concentric cylinder electrodes) have been correlated for the first time using the concept of an electrical influence number. This dimensionless parameter is based upon the relationship between applied electric field intensity and changes in bubble departure diameter at a heat transfer surface.

  13. Nucleation of flocs in dilute colloidal suspensions

    SciTech Connect

    Agrawal, D.C.; Raj, R.; Cohen, C. )

    1989-11-01

    In contrast to earlier theories which assume that coagulation of particles in dilute colloidal suspensions occurs by random collisions, the authors present evidence that coagulation is limited by a nucleation and growth phenomenon, typical of a phase transformation. They show that suspensions of well-dispersed particles, which are almost indefinitely stable, flocculate rapidly when seeded with pregrown flocs. The nucleation argument is supported further by the observation that flocs which are grown at low {zeta} potential, where the particles strongly attract, do not peptize when the pH is changed to high {zeta} potential, where the attraction is weak. The experiments were carried out with aqueous dispersions of alumina particles. The timedependent change in cluster sizes was measured by in situ photon correlation spectroscopy. The observations raise the question of agglomeration as a phase transformation, involving a change in entropy, when the system moves from a dispersed to a flocculated state.

  14. Buckyball Nucleation of HiPco Tubes

    NASA Technical Reports Server (NTRS)

    Smalley, Richard E.

    2012-01-01

    The purpose of this innovation is to enhance nucleation of single-wall nanotubes (SWNTs) in the HiPco process, selectively producing 10,10 tubes, something which until now has not been thought possible. This is accomplished by injecting C60, or a derivative of C60, solubilized in supercritical CO2 together with a transition metal carboneal cocatalyst into the HiPco reactor. This is a variant on the supercritical disclosure. C60 has never been used to nucleate carbon nanotubes in the gas phase. C60 itself may not have adequate solubility in supercritical CO2. However, fluorinated C60, e.g., C60F36, is easy to make cheaply and should have much enhanced solubility.

  15. High performance computations using dynamical nucleation theory

    SciTech Connect

    Windus, Theresa L.; Kathmann, Shawn M.; Crosby, Lonnie D.

    2008-07-14

    Chemists continue to explore the use of very large computations to perform simulations that describe the molecular level physics of critical challenges in science. In this paper, the Dynamical Nucleation Theory Monte Carlo (DNTMC) model - a model for determining molecular scale nucleation rate constants - and its parallel capabilities are described. The potential for bottlenecks and the challenges to running on future petascale or larger resources are delineated. A "master-slave" solution is proposed to scale to the petascale and will be developed in the NWChem software. In addition, mathematical and data analysis challenges are also described. This work was supported by the U.S. Department of Energy's (DOE) Office of Basic Energy Sciences, Chemical Sciences program. The Pacific Northwest National Laboratory is operated by Battelle for DOE.

  16. Glassy aerosols heterogeneously nucleate cirrus ice particles

    NASA Astrophysics Data System (ADS)

    Wilson, Theodore W.; Murray, Benjamin J.; Dobbie, Steven; Cui, Zhiqiang; Al-Jumur, Sardar M. R. K.; Möhler, Ottmar; Schnaiter, Martin; Wagner, Robert; Benz, Stefan; Niemand, Monika; Saathoff, Harald; Ebert, Volker; Wagner, Steven; Kärcher, Bernd

    2010-05-01

    Ice clouds in the tropical tropopause layer (TTL, ~12-18 km, ~180-200 K) play a key role in dehydrating air entering the stratosphere. However, in-situ measurements show that air within these clouds is unexpectedly supersaturated(1); normally the growth of ice crystals rapidly quenches any supersaturation. A number of explanations for high in-cloud humidity have been put forward, but recent research suggests high humidity may be related to the low numbers of ice crystals found within these clouds(1). Low ice number densities can be produced through selective nucleation by a small subset of aerosol particles. This is inconsistent with homogeneous nucleation of ice in liquid aerosols. However, droplets rich in organic material, ubiquitous in the TTL, are known to become glassy (amorphous, non-crystalline solid) under TTL conditions(2,3). Here we show, using a large cloud simulation chamber, that glassy solution droplets nucleate ice heterogeneously at low supersaturations. Using a one-dimensional cirrus model we also show that nucleation by glassy aerosol in the TTL may explain low TTL ice number densities and high in-cloud humidity. Recent measurements of the composition of TTL cirrus residues are consistent with our findings(4). (1) Krämer, M. et al. Ice supersaturations and cirrus cloud crystal numbers. Atm. Chem. Phys. 9, 3505-3522 (2009). (2) Murray, B. J. Inhibition of ice crystallisation in highly viscous aqueous organic acid droplets. Atm. Chem. Phys. 8, 5423-5433 (2008). (3) Zobrist, B., Marcolli, C., Pedernera, D. A. & Koop, T. Do atmospheric aerosols form glasses? Atm. Chem. Phys. 8, 5221-5244 (2008). (4) Froyd, K. D., Murphy, D. M., Lawson, P., Baumgardner, D. & Herman, R. L. Aerosols that form subvisible cirrus at the tropical tropopause. Atmos. Chem. Phys. 10, 209-218 (2010).

  17. A nanoscale temperature-dependent heterogeneous nucleation theory

    SciTech Connect

    Cao, Y. Y.; Yang, G. W.

    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.

  18. Nonclassical nucleation and growth of inorganic nanoparticles

    NASA Astrophysics Data System (ADS)

    Lee, Jisoo; Yang, Jiwoong; Kwon, Soon Gu; Hyeon, Taeghwan

    2016-08-01

    The synthesis of nanoparticles with particular compositions and structures can lead to nanoparticles with notable physicochemical properties, thus promoting their use in various applications. In this area of nanoscience, the focus is shifting from size- and shape-uniform single-component nanoparticles to multicomponent nanoparticles with enhanced performance and/or multifunctionality. With the increasing complexity of synthetic reactions, an understanding of the formation mechanisms of the nanoparticles is needed to enable a systematic synthetic approach. This Review highlights mechanistic studies underlying the synthesis of nanoparticles, with an emphasis on nucleation and growth behaviours that are not expected from classical theories. We discuss the structural properties of nanoclusters that are of a size that bridges molecules and solids. We then describe the role of nanoclusters in the prenucleation process as well as in nonclassical nucleation models. The growth of nanoparticles via the assembly and merging of primary particles is also overviewed. Finally, we present the heterogeneous nucleation mechanisms behind the synthesis of multicomponent nanoparticles.

  19. Visualizing dislocation nucleation by indenting colloidal crystals.

    PubMed

    Schall, Peter; Cohen, Itai; Weitz, David A; Spaepen, Frans

    2006-03-16

    The formation of dislocations is central to our understanding of yield, work hardening, fracture, and fatigue of crystalline materials. While dislocations have been studied extensively in conventional materials, recent results have shown that colloidal crystals offer a potential model system for visualizing their structure and dynamics directly in real space. Although thermal fluctuations are thought to play a critical role in the nucleation of these defects, it is difficult to observe them directly. Nano-indentation, during which a small tip deforms a crystalline film, is a common tool for introducing dislocations into a small volume that is initially defect-free. Here, we show that an analogue of nano-indentation performed on a colloidal crystal provides direct images of defect formation in real time and on the single particle level, allowing us to probe the effects of thermal fluctuations. We implement a new method to determine the strain tensor of a distorted crystal lattice and we measure the critical dislocation loop size and the rate of dislocation nucleation directly. Using continuum models, we elucidate the relation between thermal fluctuations and the applied strain that governs defect nucleation. Moreover, we estimate that although bond energies between particles are about fifty times larger in atomic systems, the difference in attempt frequencies makes the effects of thermal fluctuations remarkably similar, so that our results are also relevant for atomic crystals.

  20. Nucleation and particle coagulation experiments in microgravity

    NASA Technical Reports Server (NTRS)

    Nuth, J.

    1987-01-01

    Measurements of the conditions under which carbon, aluminum oxide, and silicon carbide smokes condense and of the morphology and crystal structure of the resulting grains are essential if the nature of the materials ejected into the interstellar medium and the nature of the grains which eventually became part of the proto solar nebular are to be understood. Little information is currently available on the vapor-solid phase transitions of refractory metals and solids. What little experimental data do exist are, however, not in agreement with currently accepted models of the nucleation process for more volatile materials. The major obstacle to performing such experiments in earth-based laboratories is the susceptibility of these systems to convection. Evaporation of refractory materials into a low-pressure environment with a carefully controlled temperature gradient will produce refractory smokes when the critical supersaturation of the system is exceeded. Measurement of the point at which nucleation occurs, via light scattering or extinction, can not only yield nucleation data but also, information on the chemical composition and crystal structure of the condensate. Experimental requirements are presented.

  1. Microgravity nucleation and particle coagulation experiments support

    NASA Technical Reports Server (NTRS)

    Lilleleht, L. U.; Ferguson, F. T.; Stephens, J. R.

    1992-01-01

    This project is a part of a program at GSFC to study to formation and growth of cosmic dust grain analogs under terrestrial as well as microgravity conditions. Its primary scientific objective is to study the homogeneous nucleation of refractory metal vapors and a variety of their oxides among others, while the engineering, and perhaps a more immediate objective is to develop a system capable of producing mono-dispersed, homogeneous suspensions of well-characterized refractory particles for various particle interaction experiments aboard the Space Shuttle and Space Station Freedom. Both of these objectives are to be met by a judicious combination of laboratory experiments on the ground and aboard NASA's KC-135 experimental research aircraft. Major effort during the current reporting period was devoted to the evaluation of our very successful first series of microgravity test runs in Feb. 1990. Although the apparatus performed well, it was decided to 'repackage' the equipment for easier installation on the KC-135 and access to various components. It will now consist of three separate racks: one each for the nucleation chamber, the power subsystem, and the electronic packages. The racks were fabricated at the University of Virginia and the assembly of the repackaged units is proceeding well. Preliminary analysis of the video data from the first microgravity flight series was performed and the results appear to display some trends expected from Hale's Scaled Nucleation Theory of 1986. The data acquisition system is currently being refined.

  2. Enhancements of Nucleate Boiling Under Microgravity Conditions

    NASA Technical Reports Server (NTRS)

    Zhang, Nengli; Chao, David F.; Yang, W. J.

    2000-01-01

    This paper presents two means for enhancing nucleate boiling and critical heat flux under microgravity conditions: using micro-configured metal-graphite composites as the boiling surface and dilute aqueous solutions of long-chain alcohols as the working fluid. In the former, thermocapillary force induced by temperature difference between the graphite-fiber tips and the metal matrix plays an important role in bubble detachment. Thus boiling-heat transfer performance does not deteriorate in a reduced-gravity environment. In the latter cases, the surface tension-temperature gradient of the long-chain alcohol solutions turns positive as the temperature exceeds a certain value. Consequently, the Marangoni effect does not impede, but rather aids in bubble departure from the heating surface. This feature is most favorable in microgravity. As a result, the bubble size of departure is substantially reduced at higher frequencies. Based on the existing experimental data, and a two-tier theoretical model, correlation formulas are derived for nucleate boiling on the copper-graphite and aluminum-graphite composite surfaces, in both the isolated and coalesced bubble regimes. In addition, performance equations for nucleate boiling and critical heat flux in dilute aqueous solutions of long-chain alcohols are obtained.

  3. Images and properties of individual nucleated particles

    NASA Astrophysics Data System (ADS)

    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.

  4. Systematic coarse-graining in nucleation theory

    SciTech Connect

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

    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.

  5. Kinetic theory of diffusion-limited nucleation.

    PubMed

    Philippe, T; Bonvalet, M; Blavette, D

    2016-05-28

    We examine binary nucleation in the size and composition space {R,c} using the formalism of the multivariable theory [N. V. Alekseechkin, J. Chem. Phys. 124, 124512 (2006)]. We show that the variable c drops out of consideration for very large curvature of the new phase Gibbs energy with composition. Consequently nuclei around the critical size have the critical composition, which is derived from the condition of criticality for the canonical variables and is found not to depend on surface tension. In this case, nucleation kinetics can be investigated in the size space only. Using macroscopic kinetics, we determine the general expression for the condensation rate when growth is limited by bulk diffusion, which accounts for both diffusion and capillarity and exhibits a different dependence with the critical size, as compared with the interface-limited regime. This new expression of the condensation rate for bulk diffusion-limited nucleation is the counterpart of the classical interface-limited result. We then extend our analysis to multicomponent solutions.

  6. Systematic coarse-graining in nucleation theory

    NASA Astrophysics Data System (ADS)

    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.

  7. Ice nucleation of bioaerosols - a resumee

    NASA Astrophysics Data System (ADS)

    Pummer, Bernhard G.; Atanasova, Lea; Bauer, Heidi; Bernardi, Johannes; Chazallon, Bertrand; Druzhinina, Irina S.; Grothe, Hinrich

    2013-04-01

    The role of biological particles for ice nucleation (IN) is still debated. Here, we present a summary of investigation and comparison of different ice nuclei. Apart from the bacterial ice nucleation proteins in Snomax, we further investigated a broad spectrum of pollen and fungal spores in the search for ice nucleation activity. Apart from Snomax, only few samples showed vital IN activity, like Fusarium avenaceum spores and Betula pendula pollen. Chemical characterization accentuated the differences between bacterial and pollen ice nuclei. Exposure to natural stresses, like UV and NOx, led to a significant decrease in IN activity. Furthermore, the releasable fraction of the pollen material, which includes the ice nuclei, was extracted with water and dried up. These residues were investigated with Raman spectroscopy and compared with the spectra of whole pollen grains. Measurements clearly demonstrated that the aqueous fraction contained mainly saccharides, lipids and proteins, but no sporopollenin, which is the bulk material of the outer pollen wall. Fungal spores of ecologically, economically or otherwise relevant species were also investigated. Most species showed no significant IN activity at all. A few species showed a slight increase in freezing temperature, but still significantly below the activity of the most active pollen or mineral dusts. Only Fusarium avenaceum showed strong IN activity. Cultivation of Fusarium and Trichoderma (close relatives of Fusarium) at different temperatures showed changes in total protein expression, but no impact on the IN activity.

  8. Kinetic theory of diffusion-limited nucleation

    NASA Astrophysics Data System (ADS)

    Philippe, T.; Bonvalet, M.; Blavette, D.

    2016-05-01

    We examine binary nucleation in the size and composition space {R,c} using the formalism of the multivariable theory [N. V. Alekseechkin, J. Chem. Phys. 124, 124512 (2006)]. We show that the variable c drops out of consideration for very large curvature of the new phase Gibbs energy with composition. Consequently nuclei around the critical size have the critical composition, which is derived from the condition of criticality for the canonical variables and is found not to depend on surface tension. In this case, nucleation kinetics can be investigated in the size space only. Using macroscopic kinetics, we determine the general expression for the condensation rate when growth is limited by bulk diffusion, which accounts for both diffusion and capillarity and exhibits a different dependence with the critical size, as compared with the interface-limited regime. This new expression of the condensation rate for bulk diffusion-limited nucleation is the counterpart of the classical interface-limited result. We then extend our analysis to multicomponent solutions.

  9. Nucleation and structural growth of cluster crystals

    NASA Astrophysics Data System (ADS)

    Leitold, Christian; Dellago, Christoph

    2016-08-01

    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.

  10. Kinetic theory of diffusion-limited nucleation.

    PubMed

    Philippe, T; Bonvalet, M; Blavette, D

    2016-05-28

    We examine binary nucleation in the size and composition space {R,c} using the formalism of the multivariable theory [N. V. Alekseechkin, J. Chem. Phys. 124, 124512 (2006)]. We show that the variable c drops out of consideration for very large curvature of the new phase Gibbs energy with composition. Consequently nuclei around the critical size have the critical composition, which is derived from the condition of criticality for the canonical variables and is found not to depend on surface tension. In this case, nucleation kinetics can be investigated in the size space only. Using macroscopic kinetics, we determine the general expression for the condensation rate when growth is limited by bulk diffusion, which accounts for both diffusion and capillarity and exhibits a different dependence with the critical size, as compared with the interface-limited regime. This new expression of the condensation rate for bulk diffusion-limited nucleation is the counterpart of the classical interface-limited result. We then extend our analysis to multicomponent solutions. PMID:27250310

  11. The Nucleation and Growth of Protein Crystals

    NASA Technical Reports Server (NTRS)

    Pusey, Marc

    2004-01-01

    Obtaining crystals of suitable size and high quality continues to be a major bottleneck in macromolecular crystallography. Currently, structural genomics efforts are achieving on average about a 10% success rate in going from purified protein to a deposited crystal structure. Growth of crystals in microgravity was proposed as a means of overcoming size and quality problems, which subsequently led to a major NASA effort in microgravity crystal growth, with the agency also funding research into understanding the process. Studies of the macromolecule crystal nucleation and growth process were carried out in a number of labs in an effort to understand what affected the resultant crystal quality on Earth, and how microgravity improved the process. Based upon experimental evidence, as well as simple starting assumptions, we have proposed that crystal nucleation occurs by a series of discrete self assembly steps, which 'set' the underlying crystal symmetry. This talk will review the model developed, and its origins, in our laboratory for how crystals nucleate and grow, and will then present, along with preliminary data, how we propose to use this model to improve the success rate for obtaining crystals from a given protein.

  12. Crystallization of Nucleator Nanofibrils in Polypropylene Melt

    NASA Astrophysics Data System (ADS)

    Lipp, J.; Cohen, Y.; Khalfin, R. L.; Shuster, M.; Terry, A. E.

    2007-03-01

    Self-associating molecules act as nucleating agents in polypropylene (PP) in order to increase the crystallization rate and decrease the crystallite size, by forming a fine network of nanofibrils within the polymer melt. The thermodynamic and kinetic basis for formation of this structure is not clear. Current models usually invoke a spinodal decomposition mechanism, as temperature is lowered into an immiscibility gap. This presentation deals with 1,3:2,4-Di(3,4-dimethylbenzylidene)sorbitol [dMdBS] in PP. The kinetics of structure formation was evaluated using small angle x-ray scattering, including synchrotron measurements. The results indicate a crystallization process by means of a nucleation and growth mechanism, which is controlled by the rate of homogeneous nucleation. The thermodynamic temperature of this process, determined for two different dMdBS concentrations from the temperature dependence of the crystallization half-time, agrees with that obtained by group-contribution calculation of the solubility parameters. dMdBS nanofibril formation has a remarkable effect on PP crystallization in melt-spun fibers. Just 0.4% additive at a moderate spin-draw ratio yields a crystalline morphology comprised of parallel chain-folded lamellae, with the lamellar normal highly aligned along the fiber axis.

  13. Nucleation and structural growth of cluster crystals.

    PubMed

    Leitold, Christian; Dellago, Christoph

    2016-08-21

    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. PMID:27544116

  14. Role of Nucleation and Growth in Two-Phase Microstructure Formation

    SciTech Connect

    Shin, Jong Ho

    2007-01-01

    oscillatory microstructures that depend on the imposed velocity and the size of the sample. At low thermal gradient to velocity ratio, a steady-state composite microstructure is observed. Two mechanisms of composite microstructure formation were examined: (1) the formation of the peritectic phase in the intercellular region of the primary phase where the solute rejected by the primary phase is absorbed by the peritectic phase. The peritectic phase forms a small distance behind the growing primary phase front. (2) The second mechanism is the coupled growth of the two phases with a macroscopically planar interface, as in the case of eutectic growth. Detailed studies showed that this composite microstructure, although it appears as a eutectic microstructure, did not grow in the coupled manner at the advancing interface in the Sn-cd system. However, a new observation was made when experiments were carried out in thin ampoule of Ta. The peritectic phase nucleated at the wall-interface triple junction and grew along the wall, while the primary phase continued to grow at the center, giving rise to a steady-state couple growth at some specific velocity. The mechanism of coupled growth in this case was shown to be operative due to the presence of a finite contact angle at the wall, and this was demonstrated by including the contact angle effect at the wall in the rod eutectic growth model. The experimental results were summarized to map out the conditions of thermal gradient and velocity on the regimes of composite and oscillatory microstructure formation. The formation of complex time-dependent microstructures was then discussed in terms of the time-dependent dynamics of planar interface growth.

  15. Microtubule nucleation remote from centrosomes may explain how asters span large cells.

    PubMed

    Ishihara, Keisuke; Nguyen, Phuong A; Groen, Aaron C; Field, Christine M; Mitchison, Timothy J

    2014-12-16

    A major challenge in cell biology is to understand how nanometer-sized molecules can organize micrometer-sized cells in space and time. One solution in many animal cells is a radial array of microtubules called an aster, which is nucleated by a central organizing center and spans the entire cytoplasm. Frog (here Xenopus laevis) embryos are more than 1 mm in diameter and divide with a defined geometry every 30 min. Like smaller cells, they are organized by asters, which grow, interact, and move to precisely position the cleavage planes. It has been unclear whether asters grow to fill the enormous egg by the same mechanism used in smaller somatic cells, or whether special mechanisms are required. We addressed this question by imaging growing asters in a cell-free system derived from eggs, where asters grew to hundreds of microns in diameter. By tracking marks on the lattice, we found that microtubules could slide outward, but this was not essential for rapid aster growth. Polymer treadmilling did not occur. By measuring the number and positions of microtubule ends over time, we found that most microtubules were nucleated away from the centrosome and that interphase egg cytoplasm supported spontaneous nucleation after a time lag. We propose that aster growth is initiated by centrosomes but that asters grow by propagating a wave of microtubule nucleation stimulated by the presence of preexisting microtubules. PMID:25468969

  16. Inorganic Nanoparticle Nucleation on Polymer Matrices

    NASA Astrophysics Data System (ADS)

    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

  17. The ice nucleation activity of biological aerosols

    NASA Astrophysics Data System (ADS)

    Grothe, H.; Pummer, B.; Bauer, H.; Bernardi, J.

    2012-04-01

    Primary Biological Aerosol Particles (PBAPs), including bacteria, spores and pollen may be important for several atmospheric processes. Particularly, the ice nucleation caused by PBAPs is a topic of growing interest, since their impact on ice cloud formation and thus on radiative forcing, an important parameter in global climate is not yet fully understood. In laboratory model studies we investigated the ice nucleation activity of selected PBAPs. We studied the immersion mode freezing using water-oil emulsion, which we observed by optical microscopy. We particularly focused on pollen. We show that pollen of different species strongly differ in their ice nucleation behavior. The average freezing temperatures in laboratory experiments range from 240 K to 255 K. As the most efficient nuclei (silver birch, Scots pine and common juniper pollen) have a distribution area up to the Northern timberline, their ice nucleation activity might be a cryoprotective mechanism. For comparison the ice nucleation activity of Snomax, fungal spores, and mushrooms will be discussed as well. In the past, pollen have been rejected as important atmospheric IN, as they are not as abundant in the atmosphere as bacteria or mineral dust and are too heavy to reach higher altitudes. However, in our experiments (Pummer et al. 2011) it turned out that water, which had been in contact with pollen and then been separated from the bodies, nucleates as good as the pollen grains themselves. So the ice nuclei have to be easily-suspendable macromolecules (100-300 kDa) located on the pollen. Once extracted, they can be distributed further through the atmosphere than the heavy pollen grains and so augment the impact of pollen on ice cloud formation even in the upper troposphere. It is widely known, that material from the pollen, like allergens and sugars, can indeed leave the pollen body and be distributed independently. The most probable mechanism is the pollen grain bursting by rain, which releases

  18. Molecular simulations of heterogeneous ice nucleation. I. Controlling ice nucleation through surface hydrophilicity

    SciTech Connect

    Cox, Stephen J.; Kathmann, Shawn M.; Slater, B.; Michaelides, Angelos

    2015-05-14

    Ice formation is one of the most common and important processes on earth and almost always occurs at the surface of a material. A basic understanding of how the physicochemical properties of a material’s surface affect its ability to form ice has remained elusive. Here, we use molecular dynamics simulations to directly probe heterogeneous ice nucleation at a hexagonal surface of a nanoparticle of varying hydrophilicity. Surprisingly, we find that structurally identical surfaces can both inhibit and promote ice formation and analogous to a chemical catalyst, it is found that an optimal interaction between the surface and the water exists for promoting ice nucleation.We use our microscopic understanding of the mechanism to design a modified surface in silico with enhanced ice nucleating ability. C 2015 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.

  19. Molecular simulations of heterogeneous ice nucleation. I. Controlling ice nucleation through surface hydrophilicity.

    PubMed

    Cox, Stephen J; Kathmann, Shawn M; Slater, Ben; Michaelides, Angelos

    2015-05-14

    Ice formation is one of the most common and important processes on earth and almost always occurs at the surface of a material. A basic understanding of how the physicochemical properties of a material's surface affect its ability to form ice has remained elusive. Here, we use molecular dynamics simulations to directly probe heterogeneous ice nucleation at a hexagonal surface of a nanoparticle of varying hydrophilicity. Surprisingly, we find that structurally identical surfaces can both inhibit and promote ice formation and analogous to a chemical catalyst, it is found that an optimal interaction between the surface and the water exists for promoting ice nucleation. We use our microscopic understanding of the mechanism to design a modified surface in silico with enhanced ice nucleating ability. PMID:25978902

  20. Rate of Homogenous Nucleation of Ice in Supercooled Water.

    PubMed

    Atkinson, James D; Murray, Benjamin J; O'Sullivan, Daniel

    2016-08-25

    The homogeneous freezing of water is of fundamental importance to a number of fields, including that of cloud formation. However, there is considerable scatter in homogeneous nucleation rate coefficients reported in the literature. Using a cold stage droplet system designed to minimize uncertainties in temperature measurements, we examined the freezing of over 1500 pure water droplets with diameters between 4 and 24 μm. Under the assumption that nucleation occurs within the bulk of the droplet, nucleation rate coefficients fall within the spread of literature data and are in good agreement with a subset of more recent measurements. To quantify the relative importance of surface and volume nucleation in our experiments, where droplets are supported by a hydrophobic surface and surrounded by oil, comparison of droplets with different surface area to volume ratios was performed. From our experiments it is shown that in droplets larger than 6 μm diameter (between 234.6 and 236.5 K), nucleation in the interior is more important than nucleation at the surface. At smaller sizes we cannot rule out a significant contribution of surface nucleation, and in order to further constrain surface nucleation, experiments with smaller droplets are necessary. Nevertheless, in our experiments, it is dominantly volume nucleation controlling the observed nucleation rate. PMID:27410458

  1. Effects of shear flow on phase nucleation and crystallization

    NASA Astrophysics Data System (ADS)

    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.

  2. A review of phosphate mineral nucleation in biology and geobiology.

    PubMed

    Omelon, Sidney; Ariganello, Marianne; Bonucci, Ermanno; Grynpas, Marc; Nanci, Antonio

    2013-10-01

    Relationships between geological phosphorite deposition and biological apatite nucleation have often been overlooked. However, similarities in biological apatite and phosphorite mineralogy suggest that their chemical formation mechanisms may be similar. This review serves to draw parallels between two newly described phosphorite mineralization processes, and proposes a similar novel mechanism for biologically controlled apatite mineral nucleation. This mechanism integrates polyphosphate biochemistry with crystal nucleation theory. Recently, the roles of polyphosphates in the nucleation of marine phosphorites were discovered. Marine bacteria and diatoms have been shown to store and concentrate inorganic phosphate (Pi) as amorphous, polyphosphate granules. Subsequent release of these P reserves into the local marine environment as Pi results in biologically induced phosphorite nucleation. Pi storage and release through an intracellular polyphosphate intermediate may also occur in mineralizing oral bacteria. Polyphosphates may be associated with biologically controlled apatite nucleation within vertebrates and invertebrates. Historically, biological apatite nucleation has been attributed to either a biochemical increase in local Pi concentration or matrix-mediated apatite nucleation control. This review proposes a mechanism that integrates both theories. Intracellular and extracellular amorphous granules, rich in both calcium and phosphorus, have been observed in apatite-biomineralizing vertebrates, protists, and atremate brachiopods. These granules may represent stores of calcium-polyphosphate. Not unlike phosphorite nucleation by bacteria and diatoms, polyphosphate depolymerization to Pi would be controlled by phosphatase activity. Enzymatic polyphosphate depolymerization would increase apatite saturation to the level required for mineral nucleation, while matrix proteins would simultaneously control the progression of new biological apatite formation.

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

    NASA Astrophysics Data System (ADS)

    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.; Kurten, T.; Ortega, I. K.; Dal Maso, M.; Brus, D.; Hyvärinen, A.; Lihavainen, H.; Leppä, J.; Lehtinen, K. E. J.; Mirme, A.; Mirme, S.; Hõrrak, U.; Berndt, T.; Stratmann, F.; Birmili, W.; Wiedensohler, A.; Metzger, A.; Dommen, J.; Baltensperger, U.; Kiendler-Scharr, 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.

    2010-07-01

    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, in addition to which other vapours, especially organic ones, are needed to explain the nucleation and the subsequent growth processes. 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 lower troposphere. The most concrete outcome of the EUCAARI nucleation studies are the new semi-empirical nucleation rate parameterizations based on field observations, along with

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

    NASA Astrophysics Data System (ADS)

    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.; Kurten, T.; Ortega, I. K.; Dal Maso, M.; Brus, D.; Hyvärinen, A.; Lihavainen, H.; Leppä, J.; Lehtinen, K. E. J.; Mirme, A.; Mirme, S.; Hõrrak, U.; Berndt, T.; Stratmann, F.; Birmili, W.; Wiedensohler, A.; Metzger, A.; Dommen, J.; Baltensperger, U.; Kiendler-Scharr, 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.

    2010-11-01

    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 outcome of

  5. Identification & Characterization of Fungal Ice Nucleation Proteins

    NASA Astrophysics Data System (ADS)

    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.

  6. Ice nucleation temperature of individual leaves in relation to population sizes of ice nucleation active bacteria and frost injury.

    PubMed

    Hirano, S S; Baker, L S; Upper, C D

    1985-02-01

    Ice nucleation temperatures of individual leaves were determined by a tube nucleation test. With this assay, a direct quantitative relationship was obtained between the temperatures at which ice nucleation occurred on individual oat (Avena sativa L.) leaves and the population sizes of ice nucleation active (INA) bacteria present on those leaves. In the absence of INA bacteria, nucleation of supercooled growth-chamber grown oat leaves did not occur until temperatures were below approximately -5 degrees C. Both nucleation temperature and population size of INA bacteria were determined on the same individual, field-grown oat leaves. Leaves with higher ice nucleation temperatures harbored larger populations of INA bacteria than did leaves with lower nucleation temperatures. Log(10) mean populations of INA bacteria per leaf were 5.14 and 3.51 for leaves with nucleation temperatures of -2.5 degrees C and -3.0 degrees C, respectively. Nucleation frequencies (the ratio of ice nuclei to viable cells) of INA bacteria on leaves were lognormally distributed. Strains from two very different collections of Pseudomonas syringae and one of Erwinia herbicola were cultured on nutrient glycerol agar and tested for nucleation frequency at -5 degrees C. Nucleation frequencies of these bacterial strains were also lognormally distributed within each of the three sets. The tube nucleation test was used to determine the frequency with which individual leaves in an oat canopy harbored large populations of INA bacteria throughout the growing season. This test also predicted relative frost hazard to tomato (Lycopersicon esculentum Mill) plants. PMID:16664039

  7. Ice Nucleation Temperature of Individual Leaves in Relation to Population Sizes of Ice Nucleation Active Bacteria and Frost Injury

    PubMed Central

    Hirano, Susan S.; Baker, L. Stuart; Upper, Christen D.

    1985-01-01

    Ice nucleation temperatures of individual leaves were determined by a tube nucleation test. With this assay, a direct quantitative relationship was obtained between the temperatures at which ice nucleation occurred on individual oat (Avena sativa L.) leaves and the population sizes of ice nucleation active (INA) bacteria present on those leaves. In the absence of INA bacteria, nucleation of supercooled growth-chamber grown oat leaves did not occur until temperatures were below approximately −5°C. Both nucleation temperature and population size of INA bacteria were determined on the same individual, field-grown oat leaves. Leaves with higher ice nucleation temperatures harbored larger populations of INA bacteria than did leaves with lower nucleation temperatures. Log10 mean populations of INA bacteria per leaf were 5.14 and 3.51 for leaves with nucleation temperatures of −2.5°C and −3.0°C, respectively. Nucleation frequencies (the ratio of ice nuclei to viable cells) of INA bacteria on leaves were lognormally distributed. Strains from two very different collections of Pseudomonas syringae and one of Erwinia herbicola were cultured on nutrient glycerol agar and tested for nucleation frequency at −5°C. Nucleation frequencies of these bacterial strains were also lognormally distributed within each of the three sets. The tube nucleation test was used to determine the frequency with which individual leaves in an oat canopy harbored large populations of INA bacteria throughout the growing season. This test also predicted relative frost hazard to tomato (Lycopersicon esculentum Mill) plants. PMID:16664039

  8. Kinetics of Ice Nucleation Confined in Nanoporous Alumina.

    PubMed

    Suzuki, Yasuhito; Steinhart, Martin; Butt, Hans-Jürgen; Floudas, George

    2015-09-01

    The nucleation mechanism of water (heterogeneous/homogeneous) can be regulated by confinement within nanoporous alumina. The kinetics of ice nucleation is studied in confinement by employing dielectric permittivity as a probe. Both heterogeneous and homogeneous nucleation, obtained at low and high undercooling, respectively, are stochastic in nature. The temperature interval of metastability extends over ∼4 and 0.4 °C for heterogeneous and homogeneous nucleation, respectively. Nucleation within a pore is spread to all pores in the template. We have examined a possible coupling of all pores through a heat wave and a sound wave, with the latter being a more realistic scenario. In addition, dielectric spectroscopy indicates that prior to crystallization undercooled water molecules relax with an activation energy of ∼50 kJ/mol, and this process acts as precursor to ice nucleation. PMID:26241561

  9. Effect of solute on the nucleation and propagation of ice.

    PubMed

    Charoenrein, S; Goddard, M; Reid, D S

    1991-01-01

    Using the emulsion technique, we have studied nucleation of ice in aqueous solutions containing silver iodide or Pseudomonas syringae. Using a Differential Scanning Calorimeter (DSC), we determined characteristic temperatures of nucleation, and also rates of nucleation at selected temperatures. The freezing point depression induced by added solute is linearly related to the lowering of both homogeneous and heterogeneous nucleation temperature. Nucleation kinetics depend on a fifth power function of the temperature. Solute is found to affect the parameters of this relationship in different ways, dependent upon the nature of the catalytic site for ice nucleation. We have also studied the effect of composition on the linear propagation velocity (LPV) of ice in undercooled solutions contained in a U-tube. We have determined velocities in a range of concentrations of sugar solution at the same undercooling, and also as a function of undercooling. The role of added polymer has also been investigated. It is affected by the sugar concentration. PMID:1746327

  10. Solute Nucleation and Growth in Supercritical Fluid Mixtures

    NASA Technical Reports Server (NTRS)

    Smedley, Gregory T.; Wilemski, Gerald; Rawlins, W. Terry; Joshi, Prakash; Oakes, David B.; Durgin, William W.

    1996-01-01

    This research effort is directed toward two primary scientific objectives: (1) to determine the gravitational effect on the measurement of nucleation and growth rates near a critical point and (2) to investigate the nucleation process in supercritical fluids to aid in the evaluation and development of existing theoretical models and practical applications. A nucleation pulse method will be employed for this investigation using a rapid expansion to a supersaturated state that is maintained for approximately 1 ms followed by a rapid recompression to a less supersaturated state that effectively terminates nucleation while permitting growth to continue. Nucleation, which occurs during the initial supersaturated state, is decoupled from growth by producing rapid pressure changes. Thermodynamic analysis, condensation modeling, apparatus design, and optical diagnostic design necessary for the initiation of a theoretical and experimental investigation of naphthalene nucleation from supercritical CO2 have been completed.

  11. Effect of radiation-induced segregation on void nucleation

    SciTech Connect

    Si-Ahmed, A.; Wolfer, W.G.

    1982-01-01

    The effect of segregation on void nucleation is investigated utilizing previous results for the capture efficiency of coated void. First, it is shown that any segregation, whether or not it leads to actual precipitation, leads to a modification of the bias factors for any sink. Small increases of either the lattice parameters or the elastic moduli result in reduced interstitial bias factors. Second, segregations to void embryos not only changes their capture efficiencies but also the surface energy. The effect of these changes on the void nucleation rate is studied in quantitative terms. When the segregation to voids results in an increase of the local lattice parameters by 0.4% or an increase of the shear modulus by 3%, the ultimate void nucleation rate is reached. Further increases no longer enhance void nucleation. Void nucleation without segregation effects would only be possible if the dislocation bias exceeds 50%. With segregation, void nucleation is not strongly dependent on the dislocation bias.

  12. [Distribution of nitrogen and hydrogen in diamond and its significance to nucleation and growth of diamond].

    PubMed

    Yang, Zhi-Jun; Peng, Ming-Sheng; Meng, Yu-Fei; Yuan, Zhi-Zhong; Su, Yu-Wei; Li, Hong-Zhong

    2007-06-01

    From the center to the rim of natural diamond there are differences in nitrogen and C-H bond contents, suggesting that diamond was formed under varying substance conditions. Both the nitrogen and C-H bond contents tend to decrease from the center to the rim as a whole, indicaing that nitrogen and hydrogen are expended little by little during the formation of diamond. But in the middle area of the sample both the nitrogen and C-H bond contents have a tendency to increase. This implies that nitrogen and hydrogen are added into the environment of diamond formation, meanwhile nitrogen is added earlier. So the procedure of diamond formation may be divided into three stages, namely nucleation and growth in the early stage, growth in the middle stage and in the late stage. In the early and late stages nitrogen and hydrogen are consumed in the environment of diamond formation. In the middle stage nitrogen and hydrogen must be replenished for the growth of diamond, and nitrogen should be replenished earlier than hydrogen. Hydrogen is useful to the nucleation and growth of diamond. During the formation of diamond the compounds of nitrogen and hydrogen do not exist. So we must avoid the formation of compounds of nitrogen and hydrogen for the nucleation and growth of diamond if we plan to introduce hydrogen to the synthesis of diamond at high temperature and high pressure (HPHT). Implanted hydrogen in graphite for the HPHT synthesis of diamond is a good choice.

  13. Identification of a novel ice-nucleating bacterium of Antarctic origin and its ice nucleation properties.

    PubMed

    Obata, H; Muryoi, N; Kawahara, H; Yamade, K; Nishikawa, J

    1999-03-01

    A novel ice-nucleating bacterium (INB) was isolated from Ross Island, Antarctica. INBs could be isolated more frequently than was generally thought. INB strain IN-74 was found in the white colony group. Strain IN-74 was identified from its taxonomic characteristics as a novel INB, Pseudomonas antarctica IN-74. When strain IN-74 was cultured aerobically in a medium consisting of the ice-nucleating broth (pH 7.0) for 6 days at 4 degrees C, the ice-nucleating activity of strain IN-74 cells was obtained. Strain IN-74 cells produced ice nuclei only at extremely low growth temperatures. The nuclei appeared to be less thermolabile than those of INB Pseudomonas fluorescens KUIN-1. The freezing difference spectra in D2O and H2O at ice-nucleating temperature for strain IN-74 cells and conventional INBs (Pseudomonas fluorescens KUIN-1, Pseudomonas viridiflava KUIN-2, and Pseudomonas syringae C-9) exhibited different curves. PMID:10191036

  14. Comment on "Simple improvements to classical bubble nucleation models".

    PubMed

    Schmelzer, Jürn W P; Baidakov, Vladimir G

    2016-08-01

    A critical analysis of several statements concerning experimental studies, molecular dynamics simulations, and the theoretical interpretation of bubble nucleation processes is performed. In particular, it is shown that the Tolman equation does not supply us, in general, with a satisfactory theoretically founded description of the curvature dependence of the surface tension and the dependence of the steady-state nucleation rate of bubbles and droplets on supersaturation in the framework of classical nucleation theory. PMID:27627427

  15. Binary nucleation of n-octane and i-octane

    NASA Astrophysics Data System (ADS)

    Doster, G. Jay; Schmitt, John L.; Bertrand, Gary L.

    2000-11-01

    The authors used a Wilson expansion cloud chamber to measure binary homogeneous nucleation rates for pure n-octane, pure i-octane, and 3:1, 1:1, 1:3 (mole ratio) mixtures in a temperature range from 215 to 260 K. The nucleation rates range from approximately 100 to 50 000 drops/cm3 s. Current binary nucleation theory is unable to predict the data for this nearly ideal system.

  16. The influence of finite impurity size on heterogeneous nucleation

    NASA Technical Reports Server (NTRS)

    Weinberg, Michael C.

    1992-01-01

    The effects of the finite size of impurities upon the heterogeneous nucleation rate is examined. Simple arguments based upon probability theory are used to find the relative nucleation rate, p(j), on particles containing j nuclei. The expression for p(j) is used in turn to compute the overall nucleation rate and average number of nuclei on an impurity as a function of time.

  17. Comment on "Simple improvements to classical bubble nucleation models"

    NASA Astrophysics Data System (ADS)

    Schmelzer, Jürn W. P.; Baidakov, Vladimir G.

    2016-08-01

    A critical analysis of several statements concerning experimental studies, molecular dynamics simulations, and the theoretical interpretation of bubble nucleation processes is performed. In particular, it is shown that the Tolman equation does not supply us, in general, with a satisfactory theoretically founded description of the curvature dependence of the surface tension and the dependence of the steady-state nucleation rate of bubbles and droplets on supersaturation in the framework of classical nucleation theory.

  18. Ice Nucleation properties of Air-Plane Soot Surrogates Using Vibrational Micro-spectroscopy: a preliminary study

    NASA Astrophysics Data System (ADS)

    Pirim, Claire; Ikhenazene, Raouf; Ortega, Ismael; Carpentier, Yvain; Focsa, Cristian; Chazallon, Bertrand

    2015-04-01

    Aircraft emissions have been studied extensively since the late 1960s and the interest was mainly driven by their direct and indirect effects on climate and the generation of contrails [1-4]. Emissions of solid-state particles (soots) from engine exhausts due to incomplete fuel combustion are considered to influence ice and liquid water cloud droplet activation [4]. The activity of these aerosols would originate from their ability to be important centers of ice-particle nucleation by promoting ice formation above water homogeneous freezing point. While some experiments focused on ice nucleation on soot particles did not yet reach definitive conclusions, soot are reported to be generally worse ice nuclei than mineral dust, nucleating at higher ice-supersaturations for deposition nucleation and at lower temperatures for immersion freezing. However, there are still numerous opened questions on the ice nucleation properties of soot particles [5], most likely due to the lack of information on the abundance, on the physico-chemical properties (structure and chemical compositions) of these aerosols, competition between different ice nucleation modes and dynamical factors that affect ice nucleation. Furthermore, the soot emitted from aircraft may be associated with soluble components like sulphate that can act as heterogeneous ice nuclei and initiate freezing at supersaturation of only 120-130% [6]. Therefore, more detailed studies of aerosol nucleation activity combined with throughout structural and compositional analyzes are needed in order to establish any association between the particles' hygroscopicity and their physico-chemical properties. In the present preliminary work, nucleation activity of air-plane soot particle surrogates is monitored using a temperature-controlled reactor in which the sample's relative humidity is precisely measured with a cryo-hygrometer. Formation of water/ice onto the particles is followed both optically and spectroscopically, using a

  19. Physiological and ecological significance of biological ice nucleators.

    PubMed Central

    Lundheim, Rolv

    2002-01-01

    When a pure water sample is cooled it can remain in the liquid state at temperatures well below its melting point (0 degrees C). The initiation of the transition from the liquid state to ice is called nucleation. Substances that facilitate this transition so that it takes place at a relatively high sub-zero temperature are called ice nucleators. Many living organisms produce ice nucleators. In some cases, plausible reasons for their production have been suggested. In bacteria, they could induce frost damage to their hosts, giving the bacteria access to nutrients. In freeze-tolerant animals, it has been suggested that ice nucleators help to control the ice formation so that it is tolerable to the animal. Such ice nucleators can be called adaptive ice nucleators. There are, however, also examples of ice nucleators in living organisms where the adaptive value is difficult to understand. These ice nucleators might be structures with functions other than facilitating ice formation. These structures might be called incidental ice nucleators. PMID:12171657

  20. Thermal interaction effect on nucleation site distribution in subcooled boiling

    SciTech Connect

    Ling Zou; Barclay Joned

    2012-05-01

    An experimental work on subcooled boiling of refrigerant, R134a, to examine nucleation site distributions on both copper and stainless steel heating surfaces was performed. In order to obtain high fidelity active nucleation site density and distribution data, a high-speed digital camera was utilized to record bubble emission images from a view normal to heating surfaces. Statistical analyses on nucleation site data were done and their statistical distributions were obtained. Those experimentally observed nucleation site distributions were compared to the random spatial Poisson distribution. The comparisons showed that, rather than purely random, active nucleation site distributions on boiling surfaces are relatively more uniform. Experimental results also showed that on the copper heating surface, nucleation site distributions are slightly more uniform than on the stainless steel surface. This was concluded as the results of thermal interactions between nucleation sites with different solid thermal conductivities. A two dimensional thermal interaction model was then developed to quantitatively examine the thermal interactions between nucleation sites. The results give a reasonable explanation to the experimental observation on nucleation site distributions.

  1. Final technical report. [Heterogeneous nucleation and growth in metal alloys

    SciTech Connect

    G.J. Shiflet

    1997-09-14

    We have refined a heat treatment to obtain coherent, heterogeneous nucleation of precipitates on dislocations in a high purity binary alloy. This allowed, for the first time, a quantitative comparison to be made for coherent heterogeneous nucleation. This part of the research resulted from our concern about the role of dislocations in sub-boundaries in aluminum alloys and directed us to first examine isolated dislocations in the binary Al-Li systems. We were able to design the experiment so the heterogeneous nucleation of AL{sub 3}Li occurred. Previously, only homogeneous nucleation of Al{sub 3}Li had been examined.

  2. Homogeneous nucleation rate measurements and the properties of critical clusters

    SciTech Connect

    Wyslouzil, Barbara E.; Strey, Reinhard; Wölk, Judith; Wilemski, Gerald; Kim, Yoojeong

    2009-10-06

    By combining a range of experimental techniques, quantitative nucleation rate measurements can now be made over {approx} 20 orders of magnitude. These rates can be used to directly test the predictions of nucleation theories or scaling laws. They can also provide direct information regarding the properties of the critical clusters - the first fragments of the new phase that are in unstable equilibrium with the supersaturated mother phase. This paper reviews recent progress in the field of vapor phase nucleation with a special focus on integrating the results from supersonic nozzle and nucleation pulse chamber studies.

  3. Earthquake nucleation in weak subducted carbonates

    NASA Astrophysics Data System (ADS)

    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.

  4. Thermodynamics of ice nucleation in liquid water.

    PubMed

    Wang, Xin; Wang, Shui; Xu, Qinzhi; Mi, Jianguo

    2015-01-29

    We present a density functional theory approach to investigate the thermodynamics of ice nucleation in supercooled water. Within the theoretical framework, the free-energy functional is constructed by the direct correlation function of oxygen-oxygen of the equilibrium water, and the function is derived from the reference interaction site model in consideration of the interactions of hydrogen-hydrogen, hydrogen-oxygen, and oxygen-oxygen. The equilibrium properties, including vapor-liquid and liquid-solid phase equilibria, local structure of hexagonal ice crystal, and interfacial structure and tension of water-ice are calculated in advance to examine the basis for the theory. The predicted phase equilibria and the water-ice surface tension are in good agreement with the experimental data. In particular, the critical nucleus radius and free-energy barrier during ice nucleation are predicted. The critical radius is similar to the simulation value, suggesting that the current theoretical approach is suitable in describing the thermodynamic properties of ice crystallization.

  5. Homogeneous nucleation in vapor-liquid phase transition of Lennard-Jones fluids: a density functional theory approach.

    PubMed

    Ghosh, Satinath; Ghosh, Swapan K

    2011-01-14

    Density functional theory (DFT) with square gradient approximation for the free energy functional and a model density profile are used to obtain an analytical expression for the size-dependent free energy of formation of a liquid drop from the vapor through the process of homogeneous nucleation, without invoking the approximations used in classical nucleation theory (CNT). The density of the liquid drop in this work is not the same as the bulk liquid density but it corresponds to minimum free energy of formation of the liquid drop. The theory is applied to study the nucleation phenomena from supersaturated vapor of Lennard-Jones fluid. The barrier height predicted by this theory is significantly lower than the same in CNT which is rather high. The density at the center of the small liquid drop as obtained through optimization is less than the bulk density which is in agreement with other earlier works. Also proposed is a sharp interface limit of the proposed DFT of nucleation, which is as simple as CNT but with a modified barrier height and this modified classical nucleation theory, as we call it, is shown to lead to improved results.

  6. A detailed study of ice nucleation by feldspar minerals

    NASA Astrophysics Data System (ADS)

    Whale, T. F.; Murray, B. J.; Wilson, T. W.; Carpenter, M. A.; Harrison, A.; Holden, M. A.; Vergara Temprado, J.; Morris, J.; O'Sullivan, D.

    2015-12-01

    Immersion mode heterogeneous ice nucleation plays a crucial role in controlling the composition of mixed phase clouds, which contain both supercooled liquid water and ice particles. The amount of ice in mixed phase clouds can affect cloud particle size, lifetime and extent and so affects radiative properties and precipitation. Feldspar minerals are probably the most important minerals for ice nucleation in mixed phase clouds because they nucleate ice more efficiently than other components of atmospheric mineral dust (Atkinson et al. 2013). The feldspar class of minerals is complex, containing numerous chemical compositions, several crystal polymorphs and wide variations in microscopic structure. Here we present the results of a study into ice nucleation by a wide range of different feldspars. We found that, in general, alkali feldspars nucleate ice more efficiently than plagioclase feldspars. However, we also found that particular alkali feldspars nucleate ice relatively inefficiently, suggesting that chemical composition is not the only important factor that dictates the ice nucleation efficiency of feldspar minerals. Ice nucleation by feldspar is described well by the singular model and is probably site specific in nature. The alkali feldspars that do not nucleate ice efficiently possess relatively homogenous structure on the micrometre scale suggesting that the important sites for nucleation are related to surface topography. Ice nucleation active site densities for the majority of tested alkali feldspars are similar to those found by Atkinson et al (2013), meaning that the validity of global aerosol modelling conducted in that study is not affected. Additionally, we have found that ice nucleation by feldspars is strongly influenced, both positively and negatively, by the solute content of droplets. Most other nucleants we have tested are unaffected by solutes. This provides insight into the mechanism of ice nucleation by feldspars and could be of importance

  7. Inhibition of bacterial ice nucleation by polyglycerol polymers.

    PubMed

    Wowk, Brian; Fahy, Gregory M

    2002-02-01

    The simple linear polymer polyglycerol (PGL) was found to apparently bind and inhibit the ice nucleating activity of proteins from the ice nucleating bacterium Pseudomonas syringae. PGL of molecular mass 750 Da was added to a solution consisting of 1 ppm freeze-dried P. syringae 31A in water. Differential ice nucleator spectra were determined by measuring the distribution of freezing temperatures in a population of 98 drops of 1 microL volume. The mean freezing temperature was lowered from -6.8 degrees C (control) to -8.0,-9.4,-12.5, and -13.4 degrees C for 0.001, 0.01, 0.1, and 1% w/w PGL concentrations, respectively (SE < 0.2 degrees C). PGL was found to be an ineffective inhibitor of seven defined organic ice nucleating agents, whereas the general ice nucleation inhibitor polyvinyl alcohol (PVA) was found to be effective against five of the seven. The activity of PGL therefore seems to be specific against bacterial ice nucleating protein. PGL alone was an ineffective inhibitor of ice nucleation in small volumes of environmental or laboratory water samples, suggesting that the numerical majority of ice nucleating contaminants in nature may be of nonbacterial origin. However, PGL was more effective than PVA at suppressing initial ice nucleation events in large volumes, suggesting a ubiquitous sparse background of bacterial ice nucleating proteins with high nucleation efficiency. The combination of PGL and PVA was particularly effective for reducing ice formation in solutions used for cryopreservation by vitrification.

  8. Pulse-Expansion Wave Tube Experiments on Nucleation

    NASA Astrophysics Data System (ADS)

    van Dongen, Marinus E. H.

    1998-03-01

    A wave driven expansion cloud chamber is described to determine nucleation rates: the pulse-expansion wave tube. The tube is based on the nucleation pulse principle of Allard and Kassner and is a modification of the wave tube designed by F. Peters. The tube operates in the nucleation pressure range of 0.5-50 bar. The effect of nitrogen on water nucleation at high pressures is discussed. There are two opposing effects: the equilibrium vapour pressure of water is enhanced by the presence of nitrogen and the surface tension of water decreases due to nitrogen adsorption at the water surface. Similar and even stronger effects are shown for the clearly non-ideal mixture n-nonane/methane. With helium as a carrier gas, pressure effects on nucleation are much smaller, both for water and n-nonane nucleation. An example is shown of multi-component nucleation in a very complicated gas mixture: natural gas. Natural gas contains numerous heavy hydrocarbons and shows retrograde phase behaviour. Experimental lines of constant nucleation rates are shown in the p-T phase diagram of natural gas and are compared with BCNT calculations for the binary model system n-octane/methane.

  9. New Understandings for Three-Dimensional Nucleation (I)

    NASA Astrophysics Data System (ADS)

    Liu, X. Y.

    The generic heterogeneous effect of foreign particles on 3D nucleation was examined both theoretically and experimentally. It shows that the nucleation observed under normal conditions includes a sequence of progressive heterogeneous processes, characterized by different interfacial correlation function f(m, x)s. At low supersaturations, nucleation will be controlled by the process with a small interfacial correlation function f(m, x), which results from a strong interaction and good structural match between the foreign bodies and the crystallizing phase. At high supersaturations, nucleation on foreign particles having a weak interaction and poor structural match with the crystallizing phase (f(m, x)-->1) will govern the kinetics. This frequently leads to the false identification of homogeneous nucleation. Genuine homogeneous nucleation, which is the up-limit of heterogeneous nucleation, may not be easily achievable under gravity. In order to check these results, the prediction is confronted with nucleation experiments of some crystals. The results are in excellent agreement with the theory. Apart from this, the implications for epitaxial growth have also been discussed. In order to grow crystals epitaxially, the supersaturation should be kept at a low level, despite a good structural match between the crystal and substrate.

  10. Aggregate Geometry in Amyloid Fibril Nucleation

    NASA Astrophysics Data System (ADS)

    Irbäck, Anders; Jónsson, Sigurður Æ.; Linnemann, Niels; Linse, Björn; Wallin, Stefan

    2013-02-01

    We present and study a minimal structure-based model for the self-assembly of peptides into ordered β-sheet-rich fibrils. The peptides are represented by unit-length sticks on a cubic lattice and interact by hydrogen bonding and hydrophobicity forces. Using Monte Carlo simulations with >105 peptides, we show that fibril formation occurs with sigmoidal kinetics in the model. To determine the mechanism of fibril nucleation, we compute the joint distribution in length and width of the aggregates at equilibrium, using an efficient cluster move and flat-histogram techniques. This analysis, based on simulations with 256 peptides in which aggregates form and dissolve reversibly, shows that the main free-energy barriers that a nascent fibril has to overcome are associated with changes in width.

  11. Microgravity nucleation and particle coagulation experiments support

    NASA Technical Reports Server (NTRS)

    Lilleleht, L. U.; Ferguson, F. T.

    1987-01-01

    A preliminary model for diffusion between concentric hemispheres was adapted to the cylindrical geometry of a microgravity nucleation apparatus, and extended to include the effects of radiation and conduction through the containment walls. Computer programs were developed to calculate first the temperature distribution and then the evolving concentration field using a finite difference formulation of the transient diffusion and radiation processes. The following estimations are made: (1) it takes approximately 35 minutes to establish a steady temperature field; (2) magnesium vapors released into the argon environment at the steady temperature distribution will reach a maximum supersaturation ratio of approximately 10,000 in the 20-second period at a distance of 15 cm from the source of vapors; and (3) approximately 750W electrical power will be required to maintain steady operating temperatures within the chamber.

  12. Bubble nucleation of spatial vector fields

    NASA Astrophysics Data System (ADS)

    Masoumi, Ali; Xiao, Xiao; Yang, I.-Sheng

    2013-02-01

    We study domain walls and bubble nucleation in a nonrelativistic vector field theory with different longitudinal and transverse speeds of sound. We describe analytical and numerical methods to calculate the orientation-dependent domain-wall tension σ(θ). We then use this tension to calculate the critical bubble shape and show that the tunneling exponent is modified by a factor of sound speed ratio. This implies a big modification in the tunneling rate. The longitudinally oriented domain wall tends to be the heaviest and sometime suffers an instability. It can spontaneously break into zigzag segments. In this case, the critical bubble develops kinks, and its energy, and therefore the tunneling rate, scales with the sound speeds very differently than what would be expected for a smooth bubble.

  13. Fluorescence Studies of Protein Crystal Nucleation

    NASA Technical Reports Server (NTRS)

    Pusey, Marc L.; Sumida, John

    2000-01-01

    One of the most powerful and versatile methods for studying molecules in solution is fluorescence. Crystallization typically takes place in a concentrated solution environment, whereas fluorescence typically has an upper concentration limit of approximately 1 x 10(exp -5)M, thus intrinsic fluorescence cannot be employed, but a fluorescent probe must be added to a sub population of the molecules. However the fluorescent species cannot interfere with the self-assembly process. This can be achieved with macromolecules, where fluorescent probes can be covalently attached to a sub population of molecules that are subsequently used to track the system as a whole. We are using fluorescence resonance energy transfer (FRET) to study the initial solution phase self-assembly process of tetragonal lysozyme crystal nucleation, using covalent fluorescent derivatives which crystallize in the characteristic P432121 space group. FRET studies are being carried out between cascade blue (CB-lys, donor, Ex 376 nm, Em 420 nm) and lucifer yellow (LY-lys, acceptor, Ex 425 nm, Em 520 nm) asp101 derivatives. The estimated R0 for this probe pair, the distance where 50% of the donor energy is transferred to the acceptor, is approximately 1.2 nm, compared to 2.2 nm between the side chain carboxyls of adjacent asp101's in the crystalline 43 helix. The short CB-lys lifetime (approximately 5 ns), coupled with the large average distances between the molecules ((sup 3) 50 nm) in solution, ensure that any energy transfer observed is not due to random diffusive interactions. Addition of LY-lys to CB-lys results in the appearance of a second, shorter lifetime (approximately 0.2 ns). Results from these and other ongoing studies will be discussed in conjunction with a model for how tetragonal lysozyme crystals nucleate and grow, and the relevance of that model to microgravity protein crystal growth

  14. The dependence of homogeneous nucleation rate on supersaturation.

    PubMed

    Girshick, Steven L

    2014-07-14

    The claim that classical nucleation theory (CNT) correctly predicts the dependence on supersaturation of the steady-state rate of homogeneous nucleation is reexamined in light of recent experimental studies of nucleation of a range of substances, including water, argon, nitrogen, and several 1-alcohols. Based on these studies (which include, for water, a compilation of nine different studies), it is concluded that the dependence of nucleation rate on supersaturation is not correctly predicted by CNT. It is shown that CNT's incorrect prediction of the supersaturation dependence of nucleation rate is due to its incorrect prediction of the Gibbs free energy change associated with formation of small clusters from the monomer vapor, evaluated at the substance's equilibrium vapor pressure, even though that free energy change is itself a function only of temperature. PMID:25028019

  15. Pseudo-one-dimensional nucleation in dilute polymer solutions

    NASA Astrophysics Data System (ADS)

    Zhang, Lingyun; Schmit, Jeremy D.

    2016-06-01

    Pathogenic protein fibrils have been shown in vitro to have nucleation-dependent kinetics despite the fact that one-dimensional structures do not have the size-dependent surface energy responsible for the lag time in classical theory. We present a theory showing that the conformational entropy of the peptide chains creates a free-energy barrier that is analogous to the translational entropy barrier in higher dimensions. We find that the dynamics of polymer rearrangement make it very unlikely for nucleation to succeed along the lowest free-energy trajectory, meaning that most of the nucleation flux avoids the free-energy saddle point. We use these results to construct a three-dimensional model for amyloid nucleation that accounts for conformational entropy, backbone H bonds, and side-chain interactions to compute nucleation rates as a function of concentration.

  16. Homogeneous nucleation rate measurements in supersaturated water vapor.

    PubMed

    Brus, David; Zdímal, Vladimír; Smolík, Jirí

    2008-11-01

    The rate of homogeneous nucleation in supersaturated vapors of water was studied experimentally using a thermal diffusion cloud chamber. Helium was used as a carrier gas. Our study covers a range of nucleation rates from 3x10(-1) to 3x10(2) cm(-3) s(-1) at four isotherms: 290, 300, 310, and 320 K. The molecular content of critical clusters was estimated from the slopes of experimental data. The measured isothermal dependencies of nucleation rate of water on saturation ratio were compared with the prediction of the classical theory of homogeneous nucleation, the empirical prediction of Wolk et al. [J. Chem. Phys. 117, 10 (2002)], the scaled model of Hale [Phys. Rev. A 33, 4156 (1986)], and the former nucleation onset data. PMID:19045352

  17. Energy dependence of island nucleation density during ion beam deposition

    NASA Astrophysics Data System (ADS)

    Pomeroy, Joshua M.; Brock, Joel D.

    2002-03-01

    Thin copper films were grown on single crystal copper substrates using highly collimated copper ion beams with precisely controlled incidence energies. The energetic collisions between the copper ions and the surface can form adatom-vacancy pairs or sputter eject atoms into the vaccuum. Island nucleation densities are affected by these atomistic mechanisms, which increase surface adatom densities and surface defect densities. This paper reports STM measurements of the island nucleation density for films grown both thermally and at energies between 10-150 eV. The measured island nucleation density systematically deviates with increasing energy from the density predicted by mean field nucleation theory (J.A. Venables, et.al., Rep. Prog. Phys. 47 (1984) p. 399-459). This deviation can be understood using a phenomenological extension of mean field nucleation theory that includes the effects of adatom-vacancy pair production and sputter ejection on the effective flux.

  18. Pseudo-one-dimensional nucleation in dilute polymer solutions.

    PubMed

    Zhang, Lingyun; Schmit, Jeremy D

    2016-06-01

    Pathogenic protein fibrils have been shown in vitro to have nucleation-dependent kinetics despite the fact that one-dimensional structures do not have the size-dependent surface energy responsible for the lag time in classical theory. We present a theory showing that the conformational entropy of the peptide chains creates a free-energy barrier that is analogous to the translational entropy barrier in higher dimensions. We find that the dynamics of polymer rearrangement make it very unlikely for nucleation to succeed along the lowest free-energy trajectory, meaning that most of the nucleation flux avoids the free-energy saddle point. We use these results to construct a three-dimensional model for amyloid nucleation that accounts for conformational entropy, backbone H bonds, and side-chain interactions to compute nucleation rates as a function of concentration. PMID:27415194

  19. Determination of critical nucleation number for a single nucleation amyloid-β aggregation model

    PubMed Central

    Ghosh, Preetam; Vaidya, Ashwin; Kumar, Amit; Rangachari, Vijayaraghavan

    2016-01-01

    Aggregates of amyloid-β (Aβ) peptide are known to be the key pathological agents in Alzheimer disease (AD). Aβ aggregates to form large, insoluble fibrils that deposit as senile plaques in AD brains. The process of aggregation is nucleation–dependent in which the formation of a nucleus is the rate–limiting step, and controls the physiochemical fate of the aggregates formed. Therefore, understanding the properties of nucleus and pre-nucleation events will be significant in reducing the existing knowledge–gap in AD pathogenesis. In this report, we have determined the plausible range of critical nucleation number (n*), the number of monomers associated within the nucleus for a homogenous aggregation model with single unique nucleation event, by two independent methods: A reduced-order stability analysis and ordinary differential equation based numerical analysis, supported by experimental biophysics. The results establish that the most likely range of n* is between 7 and 14 and within, this range, n* = 12 closely supports the experimental data. These numbers are in agreement with those previously reported, and importantly, the report establishes a new modeling framework using two independent approaches towards a convergent solution in modeling complex aggregation reactions. Our model also suggests that the formation of large protofibrils is dependent on the nature of n*, further supporting the idea that pre-nucleation events are significant in controlling the fate of larger aggregates formed. This report has re-opened an old problem with a new perspective and holds promise towards revealing the molecular events in amyloid pathologies in the future. PMID:26774039

  20. Nucleation Rate Analysis of Methane Hydrate from Molecular Dynamics Simulations

    SciTech Connect

    Yuhara, Daisuke; Barnes, Brian C.; Suh, Donguk; Knott, Brandon C.; Beckham, Gregg T.; Yasuoka, Kenji; Wu, David T.; Amadeu K. Sum

    2015-01-06

    Clathrate hydrates are solid crystalline structures most commonly formed from solutions that have nucleated to form a mixed solid composed of water and gas. Understanding the mechanism of clathrate hydrate nucleation is essential to grasp the fundamental chemistry of these complex structures and their applications. Molecular dynamics (MD) simulation is an ideal method to study nucleation at the molecular level because the size of the critical nucleus and formation rate occur on the nano scale. Moreover, various analysis methods for nucleation have been developed through MD to analyze nucleation. In particular, the mean first-passage time (MFPT) and survival probability (SP) methods have proven to be effective in procuring the nucleation rate and critical nucleus size for monatomic systems. This study assesses the MFPT and SP methods, previously used for monatomic systems, when applied to analyzing clathrate hydrate nucleation. Because clathrate hydrate nucleation is relatively difficult to observe in MD simulations (due to its high free energy barrier), these methods have yet to be applied to clathrate hydrate systems. In this study, we have analyzed the nucleation rate and critical nucleus size of methane hydrate using MFPT and SP methods from data generated by MD simulations at 255 K and 50 MPa. MFPT was modified for clathrate hydrate from the original version by adding the maximum likelihood estimate and growth effect term. The nucleation rates were calculated by MFPT and SP methods and are within 5%; the critical nucleus size estimated by the MFPT method was 50% higher, than values obtained through other more rigorous but computationally expensive estimates. These methods can also be extended to the analysis of other clathrate hydrates.

  1. Probing Individual Ice Nucleation Events with Environmental Scanning Electron Microscopy

    NASA Astrophysics Data System (ADS)

    Wang, Bingbing; China, Swarup; Knopf, Daniel; Gilles, Mary; Laskin, Alexander

    2016-04-01

    Heterogeneous ice nucleation is one of the processes of critical relevance to a range of topics in the fundamental and the applied science and technologies. Heterogeneous ice nucleation initiated by particles proceeds where microscopic properties of particle surfaces essentially control nucleation mechanisms. Ice nucleation in the atmosphere on particles governs the formation of ice and mixed phase clouds, which in turn influence the Earth's radiative budget and climate. Heterogeneous ice nucleation is still insufficiently understood and poses significant challenges in predictive understanding of climate change. We present a novel microscopy platform allowing observation of individual ice nucleation events at temperature range of 193-273 K and relative humidity relevant for ice formation in the atmospheric clouds. The approach utilizes a home built novel ice nucleation cell interfaced with Environmental Scanning Electron Microscope (IN-ESEM system). The IN-ESEM system is applied for direct observation of individual ice formation events, determining ice nucleation mechanisms, freezing temperatures, and relative humidity onsets. Reported microanalysis of the ice nucleating particles (INP) include elemental composition detected by the energy dispersed analysis of X-rays (EDX), and advanced speciation of the organic content in particles using scanning transmission x-ray microscopy with near edge X-ray absorption fine structure spectroscopy (STXM/NEXAFS). The performance of the IN-ESEM system is validated through a set of experiments with kaolinite particles with known ice nucleation propensity. We demonstrate an application of the IN-ESEM system to identify and characterize individual INP within a complex mixture of ambient particles.

  2. Temperature dependence of heterogeneous nucleation: Extension of the Fletcher model

    NASA Astrophysics Data System (ADS)

    McGraw, Robert; Winkler, Paul; Wagner, Paul

    2015-04-01

    Recently there have been several cases reported where the critical saturation ratio for onset of heterogeneous nucleation increases with nucleation temperature (positive slope dependence). This behavior contrasts with the behavior observed in homogeneous nucleation, where a decreasing critical saturation ratio with increasing nucleation temperature (negative slope dependence) seems universal. For this reason the positive slope dependence is referred to as anomalous. Negative slope dependence is found in heterogeneous nucleation as well, but because so few temperature-dependent measurements have been reported, it is not presently clear which slope condition (positive or negative) will become more frequent. Especially interesting is the case of water vapor condensation on silver nanoparticles [Kupc et al., AS&T 47: i-iv, 2013] where the critical saturation ratio for heterogeneous nucleation onset passes through a maximum, at about 278K, with higher (lower) temperatures showing the usual (anomalous) temperature dependence. In the present study we develop an extension of Fletcher's classical, capillarity-based, model of heterogeneous nucleation that explicitly resolves the roles of surface energy and surface entropy in determining temperature dependence. Application of the second nucleation theorem, which relates temperature dependence of nucleation rate to cluster energy, yields both necessary and sufficient conditions for anomalous temperature behavior in the extended Fletcher model. In particular it is found that an increasing contact angle with temperature is a necessary, but not sufficient, condition for anomalous temperature dependence to occur. Methods for inferring microscopic contact angle and its temperature dependence from heterogeneous nucleation probability measurements are discussed in light of the new theory.

  3. Probing methane hydrate nucleation through the forward flux sampling method.

    PubMed

    Bi, Yuanfei; Li, Tianshu

    2014-11-26

    Understanding the nucleation of hydrate is the key to developing effective strategies for controlling methane hydrate formation. Here we present a computational study of methane hydrate nucleation, by combining the forward flux sampling (FFS) method and the coarse-grained water model mW. To facilitate the application of FFS in studying the formation of methane hydrate, we developed an effective order parameter λ on the basis of the topological analysis of the tetrahedral network. The order parameter capitalizes the signature of hydrate structure, i.e., polyhedral cages, and is capable of efficiently distinguishing hydrate from ice and liquid water while allowing the formation of different hydrate phases, i.e., sI, sII, and amorphous. Integration of the order parameter λ with FFS allows explicitly computing hydrate nucleation rates and obtaining an ensemble of nucleation trajectories under conditions where spontaneous hydrate nucleation becomes too slow to occur in direct simulation. The convergence of the obtained hydrate nucleation rate was found to depend crucially on the convergence of the spatial distribution for the spontaneously formed hydrate seeds obtained from the initial sampling of FFS. The validity of the approach is also verified by the agreement between the calculated nucleation rate and that inferred from the direct simulation. Analyzing the obtained large ensemble of hydrate nucleation trajectories, we show hydrate formation at 220 K and 500 bar is initiated by the nucleation events occurring in the vicinity of water-methane interface, and facilitated by a gradual transition from amorphous to crystalline structure. The latter provides the direct support to the proposed two-step nucleation mechanism of methane hydrate. PMID:24849698

  4. Nucleation Rate Analysis of Methane Hydrate from Molecular Dynamics Simulations

    DOE PAGES

    Yuhara, Daisuke; Barnes, Brian C.; Suh, Donguk; Knott, Brandon C.; Beckham, Gregg T.; Yasuoka, Kenji; Wu, David T.; Amadeu K. Sum

    2015-01-06

    Clathrate hydrates are solid crystalline structures most commonly formed from solutions that have nucleated to form a mixed solid composed of water and gas. Understanding the mechanism of clathrate hydrate nucleation is essential to grasp the fundamental chemistry of these complex structures and their applications. Molecular dynamics (MD) simulation is an ideal method to study nucleation at the molecular level because the size of the critical nucleus and formation rate occur on the nano scale. Moreover, various analysis methods for nucleation have been developed through MD to analyze nucleation. In particular, the mean first-passage time (MFPT) and survival probability (SP)more » methods have proven to be effective in procuring the nucleation rate and critical nucleus size for monatomic systems. This study assesses the MFPT and SP methods, previously used for monatomic systems, when applied to analyzing clathrate hydrate nucleation. Because clathrate hydrate nucleation is relatively difficult to observe in MD simulations (due to its high free energy barrier), these methods have yet to be applied to clathrate hydrate systems. In this study, we have analyzed the nucleation rate and critical nucleus size of methane hydrate using MFPT and SP methods from data generated by MD simulations at 255 K and 50 MPa. MFPT was modified for clathrate hydrate from the original version by adding the maximum likelihood estimate and growth effect term. The nucleation rates were calculated by MFPT and SP methods and are within 5%; the critical nucleus size estimated by the MFPT method was 50% higher, than values obtained through other more rigorous but computationally expensive estimates. These methods can also be extended to the analysis of other clathrate hydrates.« less

  5. Do protein crystals nucleate within dense liquid clusters?

    SciTech Connect

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

    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

  6. AEROSOL NUCLEATION AND GROWTH DURING LAMINAR TUBE FLOW: MAXIMUM SATURATIONS AND NUCLEATION RATES. (R827354C008)

    EPA Science Inventory

    An approximate method of estimating the maximum saturation, the nucleation rate, and the total number nucleated per second during the laminar flow of a hot vapour–gas mixture along a tube with cold walls is described. The basis of the approach is that the temperature an...

  7. Homogeneous ice nucleation from aqueous inorganic/organic particles representative of biomass burning: water activity, freezing temperatures, nucleation rates.

    PubMed

    Knopf, Daniel A; Rigg, Yannick J

    2011-02-10

    Homogeneous ice nucleation plays an important role in the formation of cirrus clouds with subsequent effects on the global radiative budget. Here we report on homogeneous ice nucleation temperatures and corresponding nucleation rate coefficients of aqueous droplets serving as surrogates of biomass burning aerosol. Micrometer-sized (NH(4))(2)SO(4)/levoglucosan droplets with mass ratios of 10:1, 1:1, 1:5, and 1:10 and aqueous multicomponent organic droplets with and without (NH(4))(2)SO(4) under typical tropospheric temperatures and relative humidities are investigated experimentally using a droplet conditioning and ice nucleation apparatus coupled to an optical microscope with image analysis. Homogeneous freezing was determined as a function of temperature and water activity, a(w), which was set at droplet preparation conditions. The ice nucleation data indicate that minor addition of (NH(4))(2)SO(4) to the aqueous organic droplets renders the temperature dependency of water activity negligible in contrast to the case of aqueous organic solution droplets. The mean homogeneous ice nucleation rate coefficient derived from 8 different aqueous droplet compositions with average diameters of ∼60 μm for temperatures as low as 195 K and a(w) of 0.82-1 is 2.18 × 10(6) cm(-3) s(-1). The experimentally derived freezing temperatures and homogeneous ice nucleation rate coefficients are in agreement with predictions of the water activity-based homogeneous ice nucleation theory when taking predictive uncertainties into account. However, the presented ice nucleation data indicate that the water activity-based homogeneous ice nucleation theory overpredicts the freezing temperatures by up to 3 K and corresponding ice nucleation rate coefficients by up to ∼2 orders of magnitude. A shift of 0.01 in a(w), which is well within the uncertainty of typical field and laboratory relative humidity measurements, brings experimental and predicted freezing temperatures and homogeneous ice

  8. The nucleation process and the roles of structure and density fluctuations in supercooled liquid Fe

    SciTech Connect

    Li, Rong; Wu, Yongquan Xiao, Junjiang

    2014-01-21

    We observed homogeneous nucleation process of supercooled liquid Fe by molecular dynamics simulations. Using bond-orientational order parameters together with Voronoi polyhedron method, we characterized local structure, calculated the volume of Voronoi polyhedra of atoms and identified the structure and density fluctuations. We monitored the formation of nucleus and analyzed its inner structure. The birth and growth of the pre-nucleus and nucleus are accompanied with aggregating and disaggregating processes in the time scale of femtosecond. Only the initial solid-like clusters (ISLC), ranging from 1 to 7 atoms, pop up directly from liquid. The relation between the logarithm of number of clusters and the cluster size was found to be linear for ISLCs and was observed to be parabolic for all solid-like clusters (SLC) due to aggregating and disaggregating effects. The nucleus and pre-nuclei mainly consist of body centered cubic (BCC) and hexagonal close packed atoms, while the BCC atoms tend to be located at the surface. Medium-range structure fluctuations induce the birth of ISLCs, benefit the aggregation of embryos and remarkably promote the nucleation. But density fluctuations contribute little to nucleation. The lifetime of most icosahedral-like atoms (ICO) is shorter than 0.7 ps. No obvious relationship was found between structure/density fluctuations and the appearance of ICO atoms.

  9. The nucleation process and the roles of structure and density fluctuations in supercooled liquid Fe.

    PubMed

    Li, Rong; Wu, Yongquan; Xiao, Junjiang

    2014-01-21

    We observed homogeneous nucleation process of supercooled liquid Fe by molecular dynamics simulations. Using bond-orientational order parameters together with Voronoi polyhedron method, we characterized local structure, calculated the volume of Voronoi polyhedra of atoms and identified the structure and density fluctuations. We monitored the formation of nucleus and analyzed its inner structure. The birth and growth of the pre-nucleus and nucleus are accompanied with aggregating and disaggregating processes in the time scale of femtosecond. Only the initial solid-like clusters (ISLC), ranging from 1 to 7 atoms, pop up directly from liquid. The relation between the logarithm of number of clusters and the cluster size was found to be linear for ISLCs and was observed to be parabolic for all solid-like clusters (SLC) due to aggregating and disaggregating effects. The nucleus and pre-nuclei mainly consist of body centered cubic (BCC) and hexagonal close packed atoms, while the BCC atoms tend to be located at the surface. Medium-range structure fluctuations induce the birth of ISLCs, benefit the aggregation of embryos and remarkably promote the nucleation. But density fluctuations contribute little to nucleation. The lifetime of most icosahedral-like atoms (ICO) is shorter than 0.7 ps. No obvious relationship was found between structure/density fluctuations and the appearance of ICO atoms.

  10. The nucleation process and the roles of structure and density fluctuations in supercooled liquid Fe

    NASA Astrophysics Data System (ADS)

    Li, Rong; Wu, Yongquan; Xiao, Junjiang

    2014-01-01

    We observed homogeneous nucleation process of supercooled liquid Fe by molecular dynamics simulations. Using bond-orientational order parameters together with Voronoi polyhedron method, we characterized local structure, calculated the volume of Voronoi polyhedra of atoms and identified the structure and density fluctuations. We monitored the formation of nucleus and analyzed its inner structure. The birth and growth of the pre-nucleus and nucleus are accompanied with aggregating and disaggregating processes in the time scale of femtosecond. Only the initial solid-like clusters (ISLC), ranging from 1 to 7 atoms, pop up directly from liquid. The relation between the logarithm of number of clusters and the cluster size was found to be linear for ISLCs and was observed to be parabolic for all solid-like clusters (SLC) due to aggregating and disaggregating effects. The nucleus and pre-nuclei mainly consist of body centered cubic (BCC) and hexagonal close packed atoms, while the BCC atoms tend to be located at the surface. Medium-range structure fluctuations induce the birth of ISLCs, benefit the aggregation of embryos and remarkably promote the nucleation. But density fluctuations contribute little to nucleation. The lifetime of most icosahedral-like atoms (ICO) is shorter than 0.7 ps. No obvious relationship was found between structure/density fluctuations and the appearance of ICO atoms.

  11. Novel Electric Nucleation Technique for Growing Large Single Crystal in Space

    NASA Technical Reports Server (NTRS)

    Abdeldayem, Hossin; Frazier, Donald O.

    1999-01-01

    We present, herein, an electrical model for growing crystals without a seed which might not be free of defects and thereby still hinder the growth of a perfect crystal in space. The system is designed to confine nucleation to a single site automatically in an under saturated solution to avoid multiple nucleation. The technique is based on the effect of electrostriction, which is the tendency of a material to become more compressed in the presence of an electric field. The system is designed to create an electrical potential well between two hyperboloid electrodes with applied voltage at low frequency. The induced potential well between the electrodes oscillates at low frequency and attracts the solute and condenses it into the region of maximum field intensity. The alternating voltage prevents molecules with intrinsic charge from being attracted to the electrodes. The continuous presence of the electric field during the duration of the experiment, provides a continuous migration of the molecules toward the trapping site. This will eliminate the creation of a depletion region around the nucleation center and will enhance the crystal growth rate. Aside from the above mentioned advantages, the system is compact, safe to operate, and inexpensive to build.

  12. Three separate classes of bacterial ice nucleation structures.

    PubMed Central

    Turner, M A; Arellano, F; Kozloff, L M

    1990-01-01

    Studies of the properties of the ice nucleation structure exposed on the surfaces of various bacteria such as Pseudomonas syringae, Erwinia herbicola, or various strains of Ice+ recombinant Escherichia coli have shown that there are clearly three major related but chemically distinct types of structures on these cells. First, the ability of Ice+ cells to nucleate super-cooled D2O has been examined, and it has been found that this ability (relative to the ability of the same cells to nucleate super-cooled H2O) exhibited three characteristic nucleating patterns. The rarest structure, called class A, is found on only a small fraction of cells in a culture, nucleates H2O at temperatures above -4.4 degrees C, and is an effective nucleator of super-cooled D2O. A second class of structure, called class B, is found on a larger portion of the cells, nucleates H2O between -4.8 and -5.7 degrees C, and is a relatively poor nucleator of super-cooled D2O. The class C structure is found on almost all cells and nucleates at -7.6 degrees C or colder. These three classes of structures were also differentiated by their sensitivities to low concentrations of water-miscible organic solvents such as dioxane or dimethyl sulfoxide. Depending on the specific bacterial strain, the addition of these solvents to bacterial suspensions lowered the nucleation activity of the class A structure by 1,000-fold or more. The nucleation activities of class B structures in the same culture were highly resistant to these compounds and were lowered only by 20 to 40%. The class C structures were more sensitive than Class B structures were, and the nucleation activities decreased 70 to 90%. Finally, the pH sensitivity of these three classes of structures was examined. The class A structure was destroyed in buffers at pH 4.5 lower but was stable in buffers at higher pHs. The class B structure was less sensitive to acidic buffers but was destroyed at pH 5.5 or lower and was stable at higher pHs. However, the

  13. Reconciling disparate views of template-directed nucleation through measurement of calcite nucleation kinetics and binding energies

    PubMed Central

    Hamm, Laura M.; Giuffre, Anthony J.; Han, Nizhou; Tao, Jinhui; Wang, Debin; De Yoreo, James J.; Dove, Patricia M.

    2014-01-01

    The physical basis for how macromolecules regulate the onset of mineral formation in calcifying tissues is not well established. A popular conceptual model assumes the organic matrix provides a stereochemical match during cooperative organization of solute ions. In contrast, another uses simple binding assays to identify good promoters of nucleation. Here, we reconcile these two views and provide a mechanistic explanation for template-directed nucleation by correlating heterogeneous nucleation barriers with crystal–substrate-binding free energies. We first measure the kinetics of calcite nucleation onto model substrates that present different functional group chemistries (carboxyl, thiol, phosphate, and hydroxyl) and conformations (C11 and C16 chain lengths). We find rates are substrate-specific and obey predictions of classical nucleation theory at supersaturations that extend above the solubility of amorphous calcium carbonate. Analysis of the kinetic data shows the thermodynamic barrier to nucleation is reduced by minimizing the interfacial free energy of the system, γ. We then use dynamic force spectroscopy to independently measure calcite–substrate-binding free energies, ΔGb. Moreover, we show that within the classical theory of nucleation, γ and ΔGb should be linearly related. The results bear out this prediction and demonstrate that low-energy barriers to nucleation correlate with strong crystal–substrate binding. This relationship is general to all functional group chemistries and conformations. These findings provide a physical model that reconciles the long-standing concept of templated nucleation through stereochemical matching with the conventional wisdom that good binders are good nucleators. The alternative perspectives become internally consistent when viewed through the lens of crystal–substrate binding. PMID:24434555

  14. Relative importance of perch and facilitative effects on nucleation in tropical woodland in Malawi

    NASA Astrophysics Data System (ADS)

    Fujita, Tomohiro

    2016-01-01

    Individual trees in open vegetation such as woodlands can act as "nuclei" for the colonization of forest tree species, which consequently lead to the formation of forest patches. This phenomenon is known as nucleation. The mechanism of nucleation is generally attributed to two factors: trees provide perches for frugivores that increase seed deposition (perch effect), and tree crowns ameliorate environmental conditions, which improves seedling establishment (facilitative effect). Few studies have attempted to distinguish the relative importance of these two factors. In this study, I separated these two effects in a woodland in northern Malawi. I chose Ficus natalensis as a potential nuclei tree because large individuals of this species are commonly located at the center of forest patches within open woodland at the study site. I monitored several environmental variables, seedling survival, seedling composition, and seed rain at three microsites: under F. natalensis, under Brachystegia floribunda (a dominant woodland species), and in open sites. Both tree species provided similar favorable conditions for the establishment of forest species compared to open sites. Thus, the survival of forest tree seedlings under F. natalensis and B. floribunda was similar, and substantially higher than seedling survival in open sites. However, communities of naturally occurring seedlings differed significantly between F. natalensis and B. floribunda. These results indicate that the facilitative effect alone cannot explain the nucleation pattern. I attribute this result to the perch effect of F. natalensis because the forest seedling species recorded under F. natalensis reportedly have small, brightly colored diaspores, which are indicative of dispersal by birds. Seed deposition of forest species under F. natalensis was significantly higher than that under B. floribunda or in open sites. My findings reinforce the idea that trees will lead to nucleation when they enhance seed

  15. Patterned Growth of Organic Semiconductors: Selective Nucleation of Perylene on Self-Assembled Monolayers.

    PubMed

    Pick, André; Witte, Gregor

    2016-08-16

    Organic semiconductors (OSC) have received a large amount of attention because they afford the fabrication of flexible electronic devices. However, the limited resistance to radiation and etching of such materials does not permit their patterning by photolithography, which has been a driving force for the development of integrated circuits and therefore requires alternative structuring techniques. One approach is based on precoating the substrate with self-assembled monolayers (SAMs) to control the nucleation of subsequently deposited OSC layers, but the underlying mechanism is barely understood. Here, we used alkanethiols with different chemical terminations to prepare SAMs on gold substrates serving as model systems to identify the mechanism of selective nucleation for the case of the OSC perylene. Using atomic force microscopy and fluorescence microscopy, we demonstrate that the chemical functionalization of the SAMs determines the adhesion forces for the OSC that are smallest for CF3-terminated and largest for OH-terminated SAMs, hence yielding distinctly different sticking probabilities upon perylene deposition at room temperature. Microcontact printing and immersion were employed to prepare SAM patterns that enable the selective growth of polycrystalline perylene films. A quite different situation is found upon printing long-chain thiols with low vapor pressure, which leads to the transfer of multilayers and favors the growth of perylene single crystallites. In a more abstract scenario, patterns of silicone oil droplets were printed on a gold substrate, which was previously covered with a repelling fluorinated SAM. Such droplets provide nucleation centers for liquid-mediated growth, often yielding platelet-shaped perylene single crystallites without unwanted perylene nucleation on the remaining surface. PMID:27441921

  16. Bubble nucleation in polymer–CO2 mixtures.

    PubMed

    Xu, Xiaofei; Cristancho, Diego E; Costeux, Stéphane; Wang, Zhen-Gang

    2013-10-28

    We combine density-functional theory with the string method to calculate the minimum free energy path of bubble nucleation in two polymer–CO2 mixture systems, poly(methyl methacrylate) (PMMA)–CO2 and polystyrene (PS)–CO2. Nucleation is initiated by saturating the polymer liquid with high pressure CO2 and subsequently reducing the pressure to ambient condition. Below a critical temperature (Tc), we find that there is a discontinuous drop in the nucleation barrier as a function of increased initial CO2 pressure (P0), as a result of an underlying metastable transition from a CO2-rich-vapor phase to a CO2-rich-liquid phase. The nucleation barrier is generally higher for PS–CO2 than for PMMA–CO2 under the same temperature and pressure conditions, and both higher temperature and higher initial pressure are required to lower the nucleation barrier for PS–CO2 to experimentally relevant ranges. Classical nucleation theory completely fails to capture the structural features of the bubble nucleus and severely underestimates the nucleation barrier. PMID:26029777

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

    PubMed

    Wilson, Theodore W; Ladino, Luis A; Alpert, Peter A; Breckels, Mark N; Brooks, Ian M; Browse, Jo; Burrows, Susannah M; Carslaw, Kenneth S; Huffman, J Alex; Judd, Christopher; Kilthau, Wendy P; Mason, Ryan H; McFiggans, Gordon; Miller, Lisa A; Nájera, Juan J; Polishchuk, Elena; Rae, Stuart; Schiller, Corinne L; Si, Meng; Temprado, Jesús Vergara; Whale, Thomas F; Wong, Jenny P S; Wurl, Oliver; Yakobi-Hancock, Jacqueline D; Abbatt, Jonathan P D; Aller, Josephine Y; Bertram, Allan K; Knopf, Daniel A; Murray, Benjamin J

    2015-09-10

    The amount of ice present in clouds can affect cloud lifetime, precipitation and radiative properties. The formation of ice in clouds is facilitated by the presence of airborne ice-nucleating particles. 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 ice. Sea-spray aerosol contains large amounts of organic material that is ejected into the atmosphere during bubble bursting at the organically enriched sea-air interface or sea surface microlayer. Here we show that organic material in the sea surface microlayer nucleates ice under conditions relevant for mixed-phase cloud and high-altitude ice cloud formation. The ice-nucleating material is probably biogenic and less than approximately 0.2 micrometres in size. We find that exudates separated from cells of the marine diatom Thalassiosira pseudonana nucleate ice, and propose that organic material associated with phytoplankton cell exudates is a likely candidate for the observed ice-nucleating ability of the microlayer samples. Global model simulations of marine organic aerosol, in combination with our measurements, suggest that marine organic material may be an important source of ice-nucleating particles in remote marine environments such as the Southern Ocean, North Pacific Ocean and North Atlantic Ocean. PMID:26354482

  18. SUCCESS Evidence for Cirrus Cloud Ice Nucleation Mechanisms

    NASA Technical Reports Server (NTRS)

    Jensen, Eric; Gore, Warren J. Y. (Technical Monitor)

    1997-01-01

    During the SUCCESS mission, several measurements were made which should improve our understanding of ice nucleation processes in cirrus clouds. Temperature and water vapor concentration were made with a variety of instruments on the NASA DC-8. These observations should provide accurate upper tropospheric humidities. In particular, we will evaluate what humidities are required for ice nucleation. Preliminary results suggest that substantial supersaturations frequently exist in the upper troposphere. The leading-edge region of wave-clouds (where ice nucleation occurs) was sampled extensively at temperatures near -40 and -60C. These observations should give precise information about conditions required for ice nucleation. In addition, we will relate the observed aerosol composition and size distributions to the ice formation observed to evaluate the role of soot or mineral particles on ice nucleation. As an alternative technique for determining what particles act as ice nuclei, numerous samples of aerosols inside ice crystals were taken. In some cases, large numbers of aerosols were detected in each crystal, indicating that efficient scavenging occurred. Analysis of aerosols in ice crystals when only one particle per crystal was detected should help with the ice nucleation issue. Direct measurements of the ice nucleating activity of ambient aerosols drawn into airborne cloud chambers were also made. Finally, measurements of aerosols and ice crystals in contrails should indicate whether aircraft exhaust soot particles are effective ice nuclei.

  19. Controlled ice nucleation in cryopreservation--a review.

    PubMed

    Morris, G John; Acton, Elizabeth

    2013-04-01

    We review here for the first time, the literature on control of ice nucleation in cryopreservation. Water and aqueous solutions have a tendency to undercool before ice nucleation occurs. Control of ice nucleation has been recognised as a critical step in the cryopreservation of embryos and oocytes but is largely ignored for other cell types. We review the processes of ice nucleation and crystal growth in the solution around cells and tissues during cryopreservation with an emphasis on non IVF applications. The extent of undercooling that is encountered during the cooling of various cryocontainers is defined and the methods that have been employed to control the nucleation of ice are examined. The effects of controlled ice nucleation on the structure of the sample and the outcome of cryopreservation of a range of cell types and tissues are presented and the physical events which define the cellular response are discussed. Nucleation of ice is the most significant uncontrolled variable in conventional cryopreservation leading to sample to sample variation in cell recovery, viability and function and should be controlled to allow standardisation of cryopreservation protocols for cells for biobanking, cell based assays or clinical application. This intervention allows a way of increasing viability of cells and reducing variability between samples and should be included as standard operating procedures are developed.

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

    PubMed

    Wilson, Theodore W; Ladino, Luis A; Alpert, Peter A; Breckels, Mark N; Brooks, Ian M; Browse, Jo; Burrows, Susannah M; Carslaw, Kenneth S; Huffman, J Alex; Judd, Christopher; Kilthau, Wendy P; Mason, Ryan H; McFiggans, Gordon; Miller, Lisa A; Nájera, Juan J; Polishchuk, Elena; Rae, Stuart; Schiller, Corinne L; Si, Meng; Temprado, Jesús Vergara; Whale, Thomas F; Wong, Jenny P S; Wurl, Oliver; Yakobi-Hancock, Jacqueline D; Abbatt, Jonathan P D; Aller, Josephine Y; Bertram, Allan K; Knopf, Daniel A; Murray, Benjamin J

    2015-09-10

    The amount of ice present in clouds can affect cloud lifetime, precipitation and radiative properties. The formation of ice in clouds is facilitated by the presence of airborne ice-nucleating particles. 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 ice. Sea-spray aerosol contains large amounts of organic material that is ejected into the atmosphere during bubble bursting at the organically enriched sea-air interface or sea surface microlayer. Here we show that organic material in the sea surface microlayer nucleates ice under conditions relevant for mixed-phase cloud and high-altitude ice cloud formation. The ice-nucleating material is probably biogenic and less than approximately 0.2 micrometres in size. We find that exudates separated from cells of the marine diatom Thalassiosira pseudonana nucleate ice, and propose that organic material associated with phytoplankton cell exudates is a likely candidate for the observed ice-nucleating ability of the microlayer samples. Global model simulations of marine organic aerosol, in combination with our measurements, suggest that marine organic material may be an important source of ice-nucleating particles in remote marine environments such as the Southern Ocean, North Pacific Ocean and North Atlantic Ocean.

  1. Nucleation at the Contact Line Observed on Nanotextured Surfaces

    NASA Astrophysics Data System (ADS)

    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.

  2. The nucleation kinetics of ammonium metavanadate precipitated by ammonium chloride

    NASA Astrophysics Data System (ADS)

    Du, Guangchao; Sun, Zhaohui; Xian, Yong; Jing, Han; Chen, Haijun; Yin, Danfeng

    2016-05-01

    The nucleation kinetics of ammonium metavanadate (NH4VO3) was investigated under conditions of the simulated process for precipitation of NH4VO3 from the vanadium-containing solution. Induction periods for the nucleation of NH4VO3 were experimentally determined as a function of supersaturation at temperatures from 30 to 45 °C. Using the classical nucleation theory, the interfacial tension between NH4VO3 and supersaturated solution, the nucleation rate and critical radius of nucleus for the homogeneous nucleation of NH4VO3 were estimated. With temperature increasing, the calculated interfacial tension gradually decreased from 29.78 mJ/m2 at 30 °C to 23.66 mJ/m2 at 45 °C. The nucleation rate was found to proportionally increase but the critical radius of nucleus exponentially decreased, with increase in supersaturation ratio at a constant temperature. The activation energy for NH4VO3 nucleation was obtained from the relationship between temperature and induction period, ranging from 79.17 kJ/mol at S=25 to 115.50 kJ/mol at S=15. FT-IR and Raman spectrum indicated that the crystals obtained in the precipitation process were NH4VO3.

  3. Do protein crystals nucleate within dense liquid clusters?

    PubMed Central

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

    2015-01-01

    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. PMID:26144225

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

    NASA Astrophysics Data System (ADS)

    Wilson, Theodore W.; Ladino, Luis A.; Alpert, Peter A.; Breckels, Mark N.; Brooks, Ian M.; Browse, Jo; Burrows, Susannah M.; Carslaw, Kenneth S.; Huffman, J. Alex; Judd, Christopher; Kilthau, Wendy P.; Mason, Ryan H.; McFiggans, Gordon; Miller, Lisa A.; Nájera, Juan J.; Polishchuk, Elena; Rae, Stuart; Schiller, Corinne L.; Si, Meng; Temprado, Jesús Vergara; Whale, Thomas F.; Wong, Jenny P. S.; Wurl, Oliver; Yakobi-Hancock, Jacqueline D.; Abbatt, Jonathan P. D.; Aller, Josephine Y.; Bertram, Allan K.; Knopf, Daniel A.; Murray, Benjamin J.

    2015-09-01

    The amount of ice present in clouds can affect cloud lifetime, precipitation and radiative properties. The formation of ice in clouds is facilitated by the presence of airborne ice-nucleating particles. 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 ice. Sea-spray aerosol contains large amounts of organic material that is ejected into the atmosphere during bubble bursting at the organically enriched sea-air interface or sea surface microlayer. Here we show that organic material in the sea surface microlayer nucleates ice under conditions relevant for mixed-phase cloud and high-altitude ice cloud formation. The ice-nucleating material is probably biogenic and less than approximately 0.2 micrometres in size. We find that exudates separated from cells of the marine diatom Thalassiosira pseudonana nucleate ice, and propose that organic material associated with phytoplankton cell exudates is a likely candidate for the observed ice-nucleating ability of the microlayer samples. Global model simulations of marine organic aerosol, in combination with our measurements, suggest that marine organic material may be an important source of ice-nucleating particles in remote marine environments such as the Southern Ocean, North Pacific Ocean and North Atlantic Ocean.

  5. Intragranular ferrite nucleation in medium-carbon vanadium steels

    SciTech Connect

    Ishikawa, Fusao; Takahashi, Toshihiko ); Ochi, Tatsurou . Muroran R D Lab.)

    1994-05-01

    In this study, the mechanism of intragranular ferrite nucleation is investigated. It is found that intragranular ferrite idiomorphs'' nucleate at vanadium nitrides which precipitate at manganese sulfide particles during cooling in the austenite region. It is observed that intragranular ferrite has the Baker-Nutting orientation relationship with vanadium nitride which precipitated at manganese sulfide. According to classical nucleation theory, the proeutectoid ferrite nucleation rate depends on the following factors: (1) the driving free energy for ferrite nucleation, (2) the diffusivity of carbon atoms in austenite, and (3) the increase in the interfacial energy associated with ferrite nucleation. In the Baker-Nutting orientation relationship, the lattice mismatch across the habit planes is likely to be very small. Depleted zones of solute atoms such as vanadium are assumed to be formed in the austenite matrix around precipitates. The effect of the depleted zones on factors (1) and (2) is estimated thermodynamically and it is proved that those effects are negligibly small. Thus, the authors conclude that the most important factor in nucleation kinetics of intragranular ferrite is the formation of precipitates which can develop coherent, low energy interfaces with ferrite.

  6. Do protein crystals nucleate within dense liquid clusters?

    PubMed

    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.

  7. Actin filament nucleation and elongation factors--structure-function relationships.

    PubMed

    Dominguez, Roberto

    2009-01-01

    The spontaneous and unregulated polymerization of actin filaments is inhibited in cells by actin monomer-binding proteins such as profilin and Tbeta4. Eukaryotic cells and certain pathogens use filament nucleators to stabilize actin polymerization nuclei, whose formation is rate-limiting. Known filament nucleators include the Arp2/3 complex and its large family of nucleation promoting factors (NPFs), formins, Spire, Cobl, VopL/VopF, TARP and Lmod. These molecules control the time and location for polymerization, and additionally influence the structures of the actin networks that they generate. Filament nucleators are generally unrelated, but with the exception of formins they all use the WASP-Homology 2 domain (WH2 or W), a small and versatile actin-binding motif, for interaction with actin. A common architecture, found in Spire, Cobl and VopL/VopF, consists of tandem W domains that bind three to four actin subunits to form a nucleus. Structural considerations suggest that NPFs-Arp2/3 complex can also be viewed as a specialized form of tandem W-based nucleator. Formins are unique in that they use the formin-homology 2 (FH2) domain for interaction with actin and promote not only nucleation, but also processive barbed end elongation. In contrast, the elongation function among W-based nucleators has been "outsourced" to a dedicated family of proteins, Eva/VASP, which are related to WASP-family NPFs.

  8. Heterogeneous nucleation on surfaces of the ellipsoid of rotation

    NASA Astrophysics Data System (ADS)

    Li, Xiang-Ming; Liu, Qing-Hui

    2016-08-01

    This paper focusses on the heterogeneous nucleation on the surface with the non-constant curvature. The formation of a spherical nucleus on the ellipsoid of rotation is considered. Following the classical nucleation theory, the work of formation of a critical nucleus on the ellipsoid of rotation has been given, and the effects of geometry sizes and the material properties of the ellipsoid of rotation on the work of formation of a critical nucleus have been obtained. When the geometry size of the substrate is about value of the critical nucleus radius, there may exist twice nucleation on the ellipsoid of rotation for the case of the smaller value of λ and ϕ < π / 2. As the work of formation of a nucleus has only one extremum (the maximum), the nucleation on the oblate rotational ellipsoid is more easy than on the spherical surface, while nucleation on the prolate ellipsoid of rotation is more difficult than on the spherical surface. Furthermore, if the particles of the ellipsoid are added into the parent phase as nucleation agents or catalysts, for some geometry sizes, they would not have the effects on the heterogeneous nucleation.

  9. Bubble nucleation in polymer–CO2 mixtures.

    PubMed

    Xu, Xiaofei; Cristancho, Diego E; Costeux, Stéphane; Wang, Zhen-Gang

    2013-10-28

    We combine density-functional theory with the string method to calculate the minimum free energy path of bubble nucleation in two polymer–CO2 mixture systems, poly(methyl methacrylate) (PMMA)–CO2 and polystyrene (PS)–CO2. Nucleation is initiated by saturating the polymer liquid with high pressure CO2 and subsequently reducing the pressure to ambient condition. Below a critical temperature (Tc), we find that there is a discontinuous drop in the nucleation barrier as a function of increased initial CO2 pressure (P0), as a result of an underlying metastable transition from a CO2-rich-vapor phase to a CO2-rich-liquid phase. The nucleation barrier is generally higher for PS–CO2 than for PMMA–CO2 under the same temperature and pressure conditions, and both higher temperature and higher initial pressure are required to lower the nucleation barrier for PS–CO2 to experimentally relevant ranges. Classical nucleation theory completely fails to capture the structural features of the bubble nucleus and severely underestimates the nucleation barrier.

  10. Nucleation and Growth According to Lysozyme

    NASA Technical Reports Server (NTRS)

    Pusey, Marc L.; 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 that may be very germane to other monomeric proteins. The first species formed is postulated to be a dimer. Through repeating associations involving the same intermolecular interactions this becomes the 4(sub 3) helix, that in turn serves as the basic unit for nucleation and crystal growth. High salt attenuates surface charges while promoting hydrophobic interactions. Symmetry facilitates 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(sub 3)2(sub 1)2(sub 1) unit cell are filled. From the above, 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 solution 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. Lysozyme is atypical in the breadth of its crystallization conditions; many proteins only crystallize under narrowly defined conditions, pointing to the criticality of the empirical balancing process. Lack of a singularly defined association pathway

  11. Cross-Linking Studies of Lysozyme Nucleation

    NASA Technical Reports Server (NTRS)

    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

  12. Nonclassical nucleation and growth of cohesive tensile cracks

    NASA Astrophysics Data System (ADS)

    Rundle, John B.; Klein, W.

    1989-07-01

    We analyze the nucleation and growth of cohesive tensile cracks using a field-theoretic formulation in which the free energy is written as a functional of the crack separation (offset field). Our results indicate that for certain materials, crack nucleation and growth proceed through the formation and extension of a diffuse ``halo'' surrounding the classical portion of the crack. This is similar to nonclassical nucleation in magnetic systems. Theoretical considerations and numerical calculations strongly suggest that the diffuse halo can be identified with the fracture ``process zone'' seen in laboratory studies of advancing cracks.

  13. Nanoindentation. Simulation of defect nucleation in a crystal.

    PubMed

    Gouldstone, A; Van Vliet, K J; Suresh, S

    2001-06-01

    Nanoindentation is the penetration of a surface to nanometre depths using an indenting device. It can be simulated using the Bragg bubble-raft model, in which a close-packed array of soap bubbles corresponds to the equilibrium positions of atoms in a crystalline solid. Here we show that homogeneous defect nucleation occurs within a crystal when its surface roughness is comparable to the radius of the indenter tip, and that the depth of the nucleation site below the surface is proportional to the half-width of the contact. Our results may explain the unusually high local stress required for defect nucleation in nano-indented face-centred cubic crystals.

  14. The Vaguries of Pyroxene Nucleation and the Resulting Chondrule Textures

    NASA Technical Reports Server (NTRS)

    Lofgren, G. E.; Le, L.

    2004-01-01

    Pyroxene is a major phase in chondrules, but often follows olivine in the crystallization sequence and depending on the melting temperature and time may not nucleate readily upon cooling. Dynamic crystallization experiments based on total or near total melting were used to study PO (porphyritic olivine) and PP (Porphyritic pyroxene) compositions as defined by. The experiments showed that pyroxene nucleated only at subliquidus temperatures in the PP melts and rarely in the PO melts. Porphyritic chondrules with phenocrysts of both olivine and pyroxene (POP chondrules) were not easily produced in the experiments. POP chondrules are common and it is important for deciphering their formation that we understand pyroxene nucleation properties of chondrule melts.

  15. Nucleation and chiral symmetry breaking under controlled hydrodynamic flows

    NASA Technical Reports Server (NTRS)

    Wu, Xiao-Lun; Martin, Brian; Tharrington, Arnold

    1994-01-01

    The effects of hydrodynamic convection on nucleation and broken chiral symmetry have been investigated for a simple inorganic molecule, sodium chlorate (NaClO3). Our experiment suggests that the symmetry breaking is a result of hydrodynamic amplification of rare nucleation events. The effect is more pronounced when the primary nucleation occurs on the solute-vapor interface, where mixing in the surface sublayer becomes important. The transition from the achiral to the chiral states appears to be smooth as the hydrodynamic parameters, such as flow rate, are varied.

  16. Temperature dependence of nucleation rate in a binary solid solution

    NASA Astrophysics Data System (ADS)

    Wang, H. Y.; Philippe, T.; Duguay, S.; Blavette, D.

    2012-12-01

    The influence of regression (partial dissolution) effects on the temperature dependence of nucleation rate in a binary solid solution has been studied theoretically. The results of the analysis are compared with the predictions of the simplest Volmer-Weber theory. Regression effects are shown to have a strong influence on the shape of the curve of nucleation rate versus temperature. The temperature TM at which the maximum rate of nucleation occurs is found to be lowered, particularly for low interfacial energy (coherent precipitation) and high-mobility species (e.g. interstitial atoms).

  17. Direct imaging of quantum wires nucleated at diatomic steps

    SciTech Connect

    Molina, S. I.; Varela, M.; Sales, D. L.; Ben, T.; Pizarro, J.; Galindo, P. L.; Fuster, D.; Gonzalez, Y.; Gonzalez, L.; Pennycook, S. J.

    2007-10-01

    Atomic steps at growth surfaces are important heterogeneous sources for nucleation of epitaxial nano-objects. In the presence of misfit strain, we show that the nucleation process takes place preferentially at the upper terrace of the step as a result of the local stress relaxation. Evidence for strain-induced nucleation comes from the direct observation by postgrowth, atomic resolution, Z-contrast imaging of an InAs-rich region in a nanowire located on the upper terrace surface of an interfacial diatomic step.

  18. Estimation of the nucleation rate by differential scanning calorimetry

    NASA Technical Reports Server (NTRS)

    Kelton, Kenneth F.

    1992-01-01

    A realistic computer model is presented for calculating the time-dependent volume fraction transformed during the devitrification of glasses, assuming the classical theory of nucleation and continuous growth. Time- and cluster-dependent nucleation rates are calculated by modeling directly the evolving cluster distribution. Statistical overlap in the volume fraction transformed is taken into account using the standard Johnson-Mehl-Avrami formalism. Devitrification behavior under isothermal and nonisothermal conditions is described. The model is used to demonstrate that the recent suggestion by Ray and Day (1990) that nonisothermal DSC studies can be used to determine the temperature for the peak nucleation rate, is qualitatively correct for lithium disilicate, the glass investigated.

  19. Actin nucleation and elongation factors: mechanisms and interplay.

    PubMed

    Chesarone, Melissa A; Goode, Bruce L

    2009-02-01

    Cells require actin nucleators to catalyze the de novo assembly of filaments and actin elongation factors to control the rate and extent of polymerization. Nucleation and elongation factors identified to date include Arp2/3 complex, formins, Ena/VASP, and newcomers Spire, Cobl, and Lmod. Here, we discuss recent advances in understanding their activities and mechanisms and new evidence for their cooperation and interaction in vivo. Earlier models had suggested that different nucleators function independently to assemble distinct actin arrays. However, more recent observations indicate that the construction of most cellular actin networks depends on the activities of multiple actin assembly-promoting factors working in concert.

  20. Polymorphism, crystal nucleation and growth in the phase-field crystal model in 2D and 3D.

    PubMed

    Tóth, Gyula I; Tegze, György; Pusztai, Tamás; Tóth, Gergely; Gránásy, László

    2010-09-15

    We apply a simple dynamical density functional theory, the phase-field crystal (PFC) model of overdamped conservative dynamics, to address polymorphism, crystal nucleation, and crystal growth in the diffusion-controlled limit. We refine the phase diagram for 3D, and determine the line free energy in 2D and the height of the nucleation barrier in 2D and 3D for homogeneous and heterogeneous nucleation by solving the respective Euler-Lagrange (EL) equations. We demonstrate that, in the PFC model, the body-centered cubic (bcc), the face-centered cubic (fcc), and the hexagonal close-packed structures (hcp) compete, while the simple cubic structure is unstable, and that phase preference can be tuned by changing the model parameters: close to the critical point the bcc structure is stable, while far from the critical point the fcc prevails, with an hcp stability domain in between. We note that with increasing distance from the critical point the equilibrium shapes vary from the sphere to specific faceted shapes: rhombic dodecahedron (bcc), truncated octahedron (fcc), and hexagonal prism (hcp). Solving the equation of motion of the PFC model supplied with conserved noise, solidification starts with the nucleation of an amorphous precursor phase, into which the stable crystalline phase nucleates. The growth rate is found to be time dependent and anisotropic; this anisotropy depends on the driving force. We show that due to the diffusion-controlled growth mechanism, which is especially relevant for crystal aggregation in colloidal systems, dendritic growth structures evolve in large-scale isothermal single-component PFC simulations. An oscillatory effective pair potential resembling those for model glass formers has been evaluated from structural data of the amorphous phase obtained by instantaneous quenching. Finally, we present results for eutectic solidification in a binary PFC model. PMID:21386517

  1. Nucleation and growth of cadherin adhesions

    SciTech Connect

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

    2007-11-15

    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.

  2. Nucleation and growth of geological faults

    NASA Astrophysics Data System (ADS)

    Stoyan, D.; Gloaguen, R.

    2011-08-01

    We present a new model of fault nucleation and growth based on the Weibull theory, already widely used in fracture research engineering. We propose that, according to a birth-and-growth process, germs (nuclei) are born at random instants at random spatial locations and then grow with time. This leads to a satisfactory formulation of fault length distribution, different from classical statistical laws. Especially, this formulation reconciles previous analyses of fault datasets displaying power-law and/or exponential behaviors. The Weibull parameters can be statistically estimated in a simple way. We show that the model can be successfully fitted to natural data in Kenya and Ethiopia. In contrast to existing descriptive models developed for geological fault systems, such as fractal approaches, the Weibull theory allows to characterize the strength of the material, i.e. its resistance to deformation. Since this model is very general, we expect that it can be applied in many situations, and for simulations of geological fracture processes. The model is independent of deformation intensity and type and therefore allows a better constraint of the seismic risk in threatened regions.

  3. Modelling ice nucleation due to dust

    NASA Astrophysics Data System (ADS)

    Nickovic, Slobodan; Petkovic, Slavko; Pejanovic, Goran; Madonna, Fabio

    2015-04-01

    Formation of cold clouds is enhanced if ice nuclei (IN) are available. Cold clouds contribute at global scale with 60% in average in precipitation and their presence significantly affects the atmospheric radiation properties. It is expected that better description of the IN process should substantially improve cloud parameterization in climate and numerical weather prediction models. Observations show that mineral dust particles are the dominant residuals found in cloud ice. In this study we employ the regional dust DREAM model based on high horizontal and vertical grid resolution to parameterize IN caused by mineral dust. DREAM has been already deployed in a study related to IN process (Klein et al, 2010), also in model experiments using several IN parameterization schemes in support of the IN field experiment CALIMA over Canaries. The model has been also extended by adding the major dust mineral fractions as tracers in order to facilitate staying a role of dust mineralogy in ice nucleation. This study will present parameterization of IN using the simulated dust concentration, water moisture and temperature. Preliminary results of simulated IN will be shown, as well as IN validation against lidar aerosol profiles and ice cloud water profiles observed by cloud radar in the Potenza EARLINET site. This study is an initial step in improving a cloud physics parameterization using IN as an input variable in an integrated dust-atmospheric modelling system.

  4. The adsorption of fungal ice-nucleating proteins on mineral dusts: a terrestrial reservoir of atmospheric ice-nucleating particles

    NASA Astrophysics Data System (ADS)

    O'Sullivan, Daniel; Murray, Benjamin J.; Ross, James; Webb, Michael E.

    2016-04-01

    The occurrence of ice-nucleating particles (INPs) in our atmosphere has a profound impact on the properties and lifetime of supercooled clouds. However, the identities, sources and abundances of airborne particles capable of efficiently nucleating ice at relatively low supercoolings (T > -15 °C) remain enigmatic. Recently, several studies have suggested that unidentified biogenic residues in soil dusts are likely to be an important source of these efficient atmospheric INPs. While it has been shown that cell-free proteins produced by common soil-borne fungi are exceptional INPs, whether these fungi are a source of ice-nucleating biogenic residues in soils has yet to be shown. In particular, it is unclear whether upon adsorption to soil mineral particles, the activity of fungal ice-nucleating proteins is retained or is reduced, as observed for other soil enzymes. Here we show that proteins from a common soil fungus (Fusarium avenaceum) do in fact preferentially bind to and impart their ice-nucleating properties to the common clay mineral kaolinite. The ice-nucleating activity of the proteinaceous INPs is found to be unaffected by adsorption to the clay, and once bound the proteins do not readily desorb, retaining much of their activity even after multiple washings with pure water. The atmospheric implications of the finding that nanoscale fungal INPs can effectively determine the nucleating abilities of lofted soil dusts are discussed.

  5. Nonclassical Nucleation and Growth of Cohesive Tensile Cracks

    NASA Astrophysics Data System (ADS)

    Gran, Joseph; Rundle, John; Klein, William

    2011-03-01

    We analyze the nucleation and growth of cohesive tensile cracks using a Hamiltonian which is written as a functional of the crack separation (offset field). We simulate the nucleation events on a square lattice using a Metropolis Monte Carlo algorithm. Several modes of crack propagation are seen in the simulations. Our results indicate that for certain materials, crack nucleation and growth proceed through the formation and extension of a diffuse ``halo'' surrounding the classical portion of the crack. This is similar to nonclassical nucleation near the spinodal in magnetic systems. Theoretical considerations and numerical calculations strongly suggest that the diffuse halo can be identified with the fracture ``process zone'' seen in laboratory studies of advancing cracks. We are investigating scaling exponents associated with this apparent phase transition.

  6. The Molecular Mechanism of Iron(III) Oxide Nucleation.

    PubMed

    Scheck, Johanna; Wu, Baohu; Drechsler, Markus; Rosenberg, Rose; Van Driessche, Alexander E S; Stawski, Tomasz M; Gebauer, Denis

    2016-08-18

    A molecular understanding of the formation of solid phases from solution would be beneficial for various scientific fields. However, nucleation pathways are still not fully understood, whereby the case of iron (oxyhydr)oxides poses a prime example. We show that in the prenucleation regime, thermodynamically stable solute species up to a few nanometers in size are observed, which meet the definition of prenucleation clusters. Nucleation then is not governed by a critical size, but rather by the dynamics of the clusters that are forming at the distinct nucleation stages, based on the chemistry of the linkages within the clusters. This resolves a longstanding debate in the field of iron oxide nucleation, and the results may generally apply to oxides forming via hydrolysis and condensation. The (molecular) understanding of the chemical basis of phase separation is paramount for, e.g., tailoring size, shape and structure of novel nanocrystalline materials.

  7. Chamber Design For Slow Nucleation Protein Crystal Growth

    NASA Technical Reports Server (NTRS)

    Pusey, Marc Lee

    1995-01-01

    Multiple-chamber dialysis apparatus grows protein crystals on Earth or in microgravity with minimum of intervention by technician. Use of multiple chambers provides gradation of nucleation and growth rates.

  8. Measuring surface dislocation nucleation in defect-scarce nanostructures.

    PubMed

    Chen, Lisa Y; He, Mo-rigen; Shin, Jungho; Richter, Gunther; Gianola, Daniel S

    2015-07-01

    Linear defects in crystalline materials, known as dislocations, are central to the understanding of plastic deformation and mechanical strength, as well as control of performance in a variety of electronic and photonic materials. Despite nearly a century of research on dislocation structure and interactions, measurements of the energetics and kinetics of dislocation nucleation have not been possible, as synthesizing and testing pristine crystals absent of defects has been prohibitively challenging. Here, we report experiments that directly measure the surface dislocation nucleation strengths in high-quality 〈110〉 Pd nanowhiskers subjected to uniaxial tension. We find that, whereas nucleation strengths are weakly size- and strain-rate-dependent, a strong temperature dependence is uncovered, corroborating predictions that nucleation is assisted by thermal fluctuations. We measure atomic-scale activation volumes, which explain both the ultrahigh athermal strength as well as the temperature-dependent scatter, evident in our experiments and well captured by a thermal activation model. PMID:25985457

  9. Atomic scale simulation of carbon nanotube nucleation from hydrocarbon precursors.

    PubMed

    Khalilov, Umedjon; Bogaerts, Annemie; Neyts, Erik C

    2015-12-22

    Atomic scale simulations of the nucleation and growth of carbon nanotubes is essential for understanding their growth mechanism. In spite of over twenty years of simulation efforts in this area, limited progress has so far been made on addressing the role of the hydrocarbon growth precursor. Here we report on atomic scale simulations of cap nucleation of single-walled carbon nanotubes from hydrocarbon precursors. The presented mechanism emphasizes the important role of hydrogen in the nucleation process, and is discussed in relation to previously presented mechanisms. In particular, the role of hydrogen in the appearance of unstable carbon structures during in situ experimental observations as well as the initial stage of multi-walled carbon nanotube growth is discussed. The results are in good agreement with available experimental and quantum-mechanical results, and provide a basic understanding of the incubation and nucleation stages of hydrocarbon-based CNT growth at the atomic level.

  10. Kinetics of nucleation with decreasing rate of growth

    NASA Astrophysics Data System (ADS)

    Kurasov, Victor

    2015-10-01

    Extension of analytical description of the stage of nucleation to the case of the slow growth rates of the embryos growth has been constructed. The metastable phase consumption by the already formed embryos affects the nucleation rate which leads to the non-linear evolution. The power exponentials which are smaller than that for the diffusion growth are chosen as the model laws of the embryos growth. All main characteristics of the nucleation period including the form of the embryos sizes spectrum are found. Analytical description of nucleation in the closed systems as well as in the open systems with the metastable phase influx is presented. It is shown that the relative errors of this description are small.

  11. The Molecular Mechanism of Iron(III) Oxide Nucleation.

    PubMed

    Scheck, Johanna; Wu, Baohu; Drechsler, Markus; Rosenberg, Rose; Van Driessche, Alexander E S; Stawski, Tomasz M; Gebauer, Denis

    2016-08-18

    A molecular understanding of the formation of solid phases from solution would be beneficial for various scientific fields. However, nucleation pathways are still not fully understood, whereby the case of iron (oxyhydr)oxides poses a prime example. We show that in the prenucleation regime, thermodynamically stable solute species up to a few nanometers in size are observed, which meet the definition of prenucleation clusters. Nucleation then is not governed by a critical size, but rather by the dynamics of the clusters that are forming at the distinct nucleation stages, based on the chemistry of the linkages within the clusters. This resolves a longstanding debate in the field of iron oxide nucleation, and the results may generally apply to oxides forming via hydrolysis and condensation. The (molecular) understanding of the chemical basis of phase separation is paramount for, e.g., tailoring size, shape and structure of novel nanocrystalline materials. PMID:27466739

  12. Atomic scale simulation of carbon nanotube nucleation from hydrocarbon precursors

    PubMed Central

    Khalilov, Umedjon; Bogaerts, Annemie; Neyts, Erik C.

    2015-01-01

    Atomic scale simulations of the nucleation and growth of carbon nanotubes is essential for understanding their growth mechanism. In spite of over twenty years of simulation efforts in this area, limited progress has so far been made on addressing the role of the hydrocarbon growth precursor. Here we report on atomic scale simulations of cap nucleation of single-walled carbon nanotubes from hydrocarbon precursors. The presented mechanism emphasizes the important role of hydrogen in the nucleation process, and is discussed in relation to previously presented mechanisms. In particular, the role of hydrogen in the appearance of unstable carbon structures during in situ experimental observations as well as the initial stage of multi-walled carbon nanotube growth is discussed. The results are in good agreement with available experimental and quantum-mechanical results, and provide a basic understanding of the incubation and nucleation stages of hydrocarbon-based CNT growth at the atomic level. PMID:26691537

  13. Modelling the effect of acoustic waves on nucleation

    NASA Astrophysics Data System (ADS)

    Haqshenas, S. R.; Ford, I. J.; Saffari, N.

    2016-07-01

    A phase transformation in a metastable phase can be affected when it is subjected to a high intensity ultrasound wave. In this study we determined the effect of oscillation in pressure and temperature on a phase transformation using the Gibbs droplet model in a generic format. The developed model is valid for both equilibrium and non-equilibrium clusters formed through a stationary or non-stationary process. We validated the underlying model by comparing the predicted kinetics of water droplet formation from the gas phase against experimental data in the absence of ultrasound. Our results demonstrated better agreement with experimental data in comparison with classical nucleation theory. Then, we determined the thermodynamics and kinetics of nucleation and the early stage of growth of clusters in an isothermal sonocrystallisation process. This new contribution shows that the effect of pressure on the kinetics of nucleation is cluster size-dependent in contrast to classical nucleation theory.

  14. Nucleation and growth of Nb nanoclusters during plasma gas condensation

    SciTech Connect

    Bray, K. R.; Jiao, C. Q.; DeCerbo, J. N.

    2013-06-21

    Niobium nanoclusters were produced using a plasma gas condensation process. The influence of gas flow rate, aggregation length, and source current on the nanocluster nucleation and growth were analyzed. Nanoclusters with an average diameter from 4 nm to 10 nm were produced. Cluster size and concentration were tuned by controlling the process inputs. The effects of each parameter on the nucleation zone, growth length, and residence time was examined. The parameters do not affect the cluster formation and growth independently; their influence on cluster formation can be either cumulative or competing. Examining the nucleation and growth over a wide combination of parameters provided insight into their interactions and the impact on the growth process. These results provide the opportunity for a broader understanding into the nucleation and growth of nanoclusters and some insights into how process parameters interact during deposition. This knowledge will enhance the ability to create nanoclusters with desired size dispersions.

  15. A dynamical theory of nucleation for colloids and macromolecules.

    PubMed

    Lutsko, James F

    2012-01-21

    A general theory of nucleation for colloids and macromolecules in solution is formulated within the context of fluctuating hydrodynamics. A formalism for the determination of nucleation pathways is developed and stochastic differential equations for the evolution of order parameters are given. The conditions under which the elements of classical nucleation theory are recovered are determined. The theory provides a justification and extension of more heuristic equilibrium approaches based solely on the free energy. It is illustrated by application to the low-concentration/high-concentration transition in globular proteins, where a novel two-step mechanism is identified, where the first step involves the formation of long-wavelength density fluctuations, and the second step is the actual nucleation event occurring within the fluctuation.

  16. Laboratory Studies of Ice Nucleation on Volcanic Ash

    NASA Astrophysics Data System (ADS)

    Tolbert, M. A.; Schill, G. P.; Genareau, K. D.

    2014-12-01

    Ice nucleation on volcanic ash controls both ash aggregation and cloud glaciation, which affect human respiratory health, atmospheric transport, and global climate. We have performed laboratory studies of the depositional and immersion freezing efficiency of three distinct samples of volcanic ash using Raman Microscopy coupled to an environmental cell. Ash from the Fuego (Basaltic Ash, Guatemala), Soufriere Hills (Andesetic Ash, Montserrat), and Taupo (Rhyolitic Ash, New Zealand) volcanoes were chosen to represent different geographical locations and silica content. All ash samples were quantitatively analyzed for both percent crystallinity and mineralogy using X-ray diffraction. We find that all three samples of volcanic ash are excellent depositional ice nuclei, nucleating ice at ice saturation ratios of 1.05 ± 0.1. For immersion freezing, however, only the Taupo ash exhibited efficient heterogeneous ice nucleation activity. Similar to recent studies on mineral dust, we suggest that the mineralogy of volcanic ash may dictate its ice nucleation activity in the immersion mode.

  17. THEORETICAL STUDIES OF NUCLEATION KINETICS AND NANODROPLET MICROSTRUCTURE

    SciTech Connect

    Wilemski, Gerald

    2009-01-31

    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.

  18. Modelling the effect of acoustic waves on nucleation.

    PubMed

    Haqshenas, S R; Ford, I J; Saffari, N

    2016-07-14

    A phase transformation in a metastable phase can be affected when it is subjected to a high intensity ultrasound wave. In this study we determined the effect of oscillation in pressure and temperature on a phase transformation using the Gibbs droplet model in a generic format. The developed model is valid for both equilibrium and non-equilibrium clusters formed through a stationary or non-stationary process. We validated the underlying model by comparing the predicted kinetics of water droplet formation from the gas phase against experimental data in the absence of ultrasound. Our results demonstrated better agreement with experimental data in comparison with classical nucleation theory. Then, we determined the thermodynamics and kinetics of nucleation and the early stage of growth of clusters in an isothermal sonocrystallisation process. This new contribution shows that the effect of pressure on the kinetics of nucleation is cluster size-dependent in contrast to classical nucleation theory. PMID:27421413

  19. Investigations on the nucleation kinetics of bis glycine sodium nitrate

    NASA Astrophysics Data System (ADS)

    Selvaraju, K.; Kirubavathi, K.; Vijayan, N.; Kumararaman, S.

    2008-05-01

    The nucleation parameters such as, energy per unit volume, radius of critical nucleus, critical free energy barrier, number of molecules in the critical nucleus and nucleation rate have been evaluated for bis glycine sodium nitrate single crystals. The interfacial energy of the solution at various temperatures has been estimated from existing solubility data. The metastable zone width and induction period measurements have been carried out experimentally.

  20. Nonextensive treatment of nucleation and growth in a thin layer

    NASA Astrophysics Data System (ADS)

    Cetinel, Hakan; Kayacan, Ozhan

    2007-01-01

    In this study, a generalized method based upon nonextensive statistics is presented for nucleation and growth processes in a thin layer between two interfaces. It is shown that the presented mathematical model, which uses an index called the entropic index that measures the nonextensivity of the physical system, successfully deals with the nucleation and growth processes, and works better than Johnson-Mehl-Avrami-Kolmogorov model. The presented model also contains Austin-Rickett model as a special case.

  1. Hydrocarbon nucleation and aerosol formation in Neptune's atmosphere.

    PubMed

    Moses, J I; Allen, M; Yung, Y L

    1992-10-01

    Photodissociation of methane at high altitude levels in Neptune's atmosphere leads to the production of complex hydrocarbon species such as acetylene (C2H2), ethane (C2H6), methylacetylene (CH3C2H), propane (C3H8), diacetylene (C4H2), and butane (C4H8). These gases diffuse to the lower stratosphere where temperatures are low enough to initiate condensation. Particle formation may not occur readily, however, as the vapor species become supersaturated. We present a theoretical analysis of particle formation mechanisms at conditions relevant to Neptune's troposphere and stratosphere and show that hydrocarbon nucleation is very inefficient under Neptunian conditions: saturation ratios much greater than unity are required for aerosol formation by either homogeneous, heterogeneous, or ion-induced nucleation. Homogeneous nucleation will not be important for any of the hydrocarbon species considered; however, both heterogeneous and ion-induced nucleation should be possible on Neptune for most of the above species. The relative effectiveness of heterogeneous and ion-induced nucleation depends on the physical and thermodynamic properties of the particular species, the abundance of the condensable species, the temperature at which the vapor becomes supersaturated, and the number and type of condensation nuclei or ions available. Typical saturation ratios required for observable particle formation rates on Neptune range from approximately 3 for heterogeneous nucleation of methane in the upper troposphere to greater than 1000 for heterogeneous nucleation of methylacetylene, diacetylene, and butane in the lower stratosphere. Thus, methane clouds may form slightly above, and stratospheric hazes far below, their saturation levels. When used in conjunction with the results of detailed models of atmospheric photochemistry, our nucleation models place realistic constraints on the altitude levels at which we expect hydrocarbon hazes or clouds to form on Neptune. PMID:11538166

  2. Nucleation and transients at the onset of vortex turbulence

    NASA Technical Reports Server (NTRS)

    Huber, Greg; Alstrom, Preben; Bohr, Tomas

    1992-01-01

    We present analytical and numerical results that explain the transient turbulent dynamics observed in the complex Ginzburg-Landau equation. Just below the transition to turbulence, we observe that metastable turbulent states break down by the nucleation and growth of single-vortex droplets, leading to a 'frozen' state with a low (but finite) density of stationary vortices. We derive the relation between nucleation time and radius, and determine their dependence on the distance to the turbulence transition line.

  3. Hydrocarbon nucleation and aerosol formation in Neptune's atmosphere.

    PubMed

    Moses, J I; Allen, M; Yung, Y L

    1992-10-01

    Photodissociation of methane at high altitude levels in Neptune's atmosphere leads to the production of complex hydrocarbon species such as acetylene (C2H2), ethane (C2H6), methylacetylene (CH3C2H), propane (C3H8), diacetylene (C4H2), and butane (C4H8). These gases diffuse to the lower stratosphere where temperatures are low enough to initiate condensation. Particle formation may not occur readily, however, as the vapor species become supersaturated. We present a theoretical analysis of particle formation mechanisms at conditions relevant to Neptune's troposphere and stratosphere and show that hydrocarbon nucleation is very inefficient under Neptunian conditions: saturation ratios much greater than unity are required for aerosol formation by either homogeneous, heterogeneous, or ion-induced nucleation. Homogeneous nucleation will not be important for any of the hydrocarbon species considered; however, both heterogeneous and ion-induced nucleation should be possible on Neptune for most of the above species. The relative effectiveness of heterogeneous and ion-induced nucleation depends on the physical and thermodynamic properties of the particular species, the abundance of the condensable species, the temperature at which the vapor becomes supersaturated, and the number and type of condensation nuclei or ions available. Typical saturation ratios required for observable particle formation rates on Neptune range from approximately 3 for heterogeneous nucleation of methane in the upper troposphere to greater than 1000 for heterogeneous nucleation of methylacetylene, diacetylene, and butane in the lower stratosphere. Thus, methane clouds may form slightly above, and stratospheric hazes far below, their saturation levels. When used in conjunction with the results of detailed models of atmospheric photochemistry, our nucleation models place realistic constraints on the altitude levels at which we expect hydrocarbon hazes or clouds to form on Neptune.

  4. Nucleation of mesospheric cloud particles: Sensitivities and limits

    NASA Astrophysics Data System (ADS)

    Wilms, Henrike; Rapp, Markus; Kirsch, Annekatrin

    2016-03-01

    Nucleation of mesospheric ice particles is thought to occur via heterogeneous nucleation on meteor smoke particles. However, several factors determining the nucleation rate are poorly known. To study the effect of uncertainties in the nucleation rate on cloud properties, we use the Community Aerosol and Radiation Model for Atmospheres and systematically vary the nucleation rate over ±10 orders of magnitude. In one set of simulations, the background state of the atmosphere is described by climatological conditions. In a second set, gravity wave-perturbed profiles from the Kühlungsborn Mechanistic general Circulation Model (KMCM) are used with typical temperature (vertical wind) perturbations at the mesopause on the order of 9 K (0.45 m/s). The resulting noctilucent cloud (NLC) characteristics are compared to lidar and satellite measurements. Realistic NLCs compared to the lidar measurements can only be modeled if the nucleation rate is reduced by up to 3 orders of magnitude compared to standard assumptions. For the same cases, the simulated NLCs compare best to the satellite measurements if the nucleation rate is reduced by 2 orders of magnitude or more. Dynamical processes at the mesopause strongly influence the NLC development. In a gravity wave-perturbed atmosphere, the ice particles have only limited time for nucleation and growth. The growth time is limited by the vertical wind, because the vertical wind determines the residence time of the ice particles in the supersaturated region. Since the vertical wind amplitudes reach 1.5 m/s in KMCM (compared to a mean upwelling of ˜4 cm/s in the climatology), the ice particles remain significantly smaller in a gravity wave-perturbed atmosphere than in climatological background conditions.

  5. Nucleation of strange matter in dense stellar cores

    SciTech Connect

    Horvath, J.E. Sao Paulo, Sao Paulo ); Benvenuto, O.G. La Plata ); Vucetich, H. La Plata )

    1992-05-15

    We investigate the nucleation of strange quark matter inside hot, dense nuclear matter. Applying Zel'dovich's kinetic theory of nucleation we find a lower limit of the temperature {ital T} for strange-matter bubbles to appear, which happens to be satisfied inside the Kelvin-Helmholtz cooling era of a compact star life but not much after it. Our bounds thus suggest that a prompt conversion could be achieved, giving support to earlier expectations for nonstandard type-II supernova scenarios.

  6. Homogeneous nucleation of non-metals and metals

    NASA Astrophysics Data System (ADS)

    Rudek, Markus Martin

    1998-11-01

    Homogeneous nucleation rates as functions of both supersaturation and temperature were measured in an upward thermal diffusion cloud chamber for four n- alkanes, i.e., n-heptane, n-octane, n-nonane, and n- decane, for two n-alcohols, i.e., n-pentanol and n- hexanol, and for m-xylene. Nucleation rates from about 10-4 to 5×100 drops cm-3 s- 1 were obtained in the temperature range, 241 K to 340 K. Their dependences on supersaturation and temperature were compared to predictions of several nucleation theories: Classical Theory, the Internally Consistent Classical Theory, two versions of the Kalikmanov-van Dongen Theory, and the Delale-Meier Theory. Each theory predicted the dependence of the nucleation rate on supersaturation reasonably well, but large temperature dependent correlation factors were needed for quantitative agreement between measured and predicted nucleation rates. However, all substances had a very similar temperature dependence to their multiplicative correction factor. The homogeneous nucleation of supersaturated cesium vapor was investigated in a thermal diffusion cloud chamber operating in both the upward and the downward mode. In the upward operating mode, critical supersaturations were measured in the temperature range, 421K to 554K. In the downward operating mode, it was possible to circumvent experimental difficulties due to phoretic effects which arise at low pressures in measurements in the upward mode. This enabled measurements of critical supersaturations over the temperature range, 289K to 452K. The use of the downward mode enabled the extension of the temperature range of the measurements by 70K towards lower temperatures. This makes cesium the substance whose homogeneous nucleation has been measured, in a thermal diffusion cloud chamber, over the largest range of temperatures, 289K to 554K. These measured critical supersaturations were compared to the predictions of the Internally Consistent version of Classical nucleation Theory and to

  7. Ice nucleation activity of bacteria isolated from cloud water

    NASA Astrophysics Data System (ADS)

    Joly, Muriel; Attard, Eléonore; Sancelme, Martine; Deguillaume, Laurent; Guilbaud, Caroline; Morris, Cindy E.; Amato, Pierre; Delort, Anne-Marie

    2013-05-01

    Some Gamma-Proteobacteria can catalyze ice formation thereby potentially contributing to the induction of precipitation in supercooled clouds and subsequently to bacterial deposition. Forty-four bacterial strains from cloud water were screened for their capacity to induce freezing. Seven strains (16%) were active at -8 °C or warmer and were identified as Pseudomonas syringae, Xanthomonas spp. and Pseudoxanthomonas sp. Phylogenetic analysis revealed that the P. syringae strains in clouds at the Puy de Dôme belonged to clades that are among the most infrequently detected in the environment, while widespread clades were absent suggesting some extent of selection or unusual biogeography of the bacteria at the sampling site. Three strains induced freezing at -3 °C while the others nucleated ice at -4 °C to -6 °C. The freezing profiles revealed that the peaks of activity were centered around -3.5 °C, -5 °C and/or -8.5 °C depending on the strain. The frequency of ice-nuclei (IN) per cell at -6 °C was generally below 0.5% and reached up to 4.2% in one strain. We estimated that clouds influenced by vegetated areas would carry between less than 1 and ˜500 bacterial IN mL-1 of water active between -3 °C and -10 °C depending on the season. These data will contribute to modeling the impact of bacterial IN on precipitation at regional scales.

  8. γ-Tubulin Is Essential for Acentrosomal Microtubule Nucleation and Coordination of Late Mitotic Events in Arabidopsis[W

    PubMed Central

    Binarová, Pavla; Cenklová, Věra; Procházková, Jiřina; Doskočilová, Anna; Volc, Jindřich; Vrlík, Martin; Bögre, László

    2006-01-01

    γ-Tubulin is required for microtubule (MT) nucleation at MT organizing centers such as centrosomes or spindle pole bodies, but little is known about its noncentrosomal functions. We conditionally downregulated γ-tubulin by inducible expression of RNA interference (RNAi) constructs in Arabidopsis thaliana. Almost complete RNAi depletion of γ-tubulin led to the absence of MTs and was lethal at the cotyledon stage. After induction of RNAi expression, γ-tubulin was gradually depleted from both cytoplasmic and microsomal fractions. In RNAi plants with partial loss of γ-tubulin, MT recovery after drug-induced depolymerization was impaired. Similarly, immunodepletion of γ-tubulin from Arabidopsis extracts severely compromised in vitro polymerization of MTs. Reduction of γ-tubulin protein levels led to randomization and bundling of cortical MTs. This finding indicates that MT-bound γ-tubulin is part of a cortical template guiding the microtubular network and is essential for MT nucleation. Furthermore, we found that cells with decreased levels of γ-tubulin could progress through mitosis, but cytokinesis was strongly affected. Stepwise diminution of γ-tubulin allowed us to reveal roles for MT nucleation in plant development, such as organization of cell files, anisotropic and polar tip growth, and stomatal patterning. Some of these functions of γ-tubulin might be independent of MT nucleation. PMID:16603653

  9. Ice nucleation by particles immersed in supercooled cloud droplets.

    PubMed

    Murray, B J; O'Sullivan, D; Atkinson, J D; Webb, M E

    2012-10-01

    The formation of ice particles in the Earth's atmosphere strongly affects the properties of clouds and their impact on climate. Despite the importance of ice formation in determining the properties of clouds, the Intergovernmental Panel on Climate Change (IPCC, 2007) was unable to assess the impact of atmospheric ice formation in their most recent report because our basic knowledge is insufficient. Part of the problem is the paucity of quantitative information on the ability of various atmospheric aerosol species to initiate ice formation. Here we review and assess the existing quantitative knowledge of ice nucleation by particles immersed within supercooled water droplets. We introduce aerosol species which have been identified in the past as potentially important ice nuclei and address their ice-nucleating ability when immersed in a supercooled droplet. We focus on mineral dusts, biological species (pollen, bacteria, fungal spores and plankton), carbonaceous combustion products and volcanic ash. In order to make a quantitative comparison we first introduce several ways of describing ice nucleation and then summarise the existing information according to the time-independent (singular) approximation. Using this approximation in combination with typical atmospheric loadings, we estimate the importance of ice nucleation by different aerosol types. According to these estimates we find that ice nucleation below about -15 °C is dominated by soot and mineral dusts. Above this temperature the only materials known to nucleate ice are biological, with quantitative data for other materials absent from the literature. We conclude with a summary of the challenges our community faces.

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

    SciTech Connect

    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.

  11. Entropic effect on the rate of dislocation nucleation.

    PubMed

    Ryu, Seunghwa; Kang, Keonwook; Cai, Wei

    2011-03-29

    Dislocation nucleation is essential to our understanding of plastic deformation, ductility, and mechanical strength of crystalline materials. Molecular dynamics simulation has played an important role in uncovering the fundamental mechanisms of dislocation nucleation, but its limited timescale remains a significant challenge for studying nucleation at experimentally relevant conditions. Here we show that dislocation nucleation rates can be accurately predicted over a wide range of conditions by determining the activation free energy from umbrella sampling. Our data reveal very large activation entropies, which contribute a multiplicative factor of many orders of magnitude to the nucleation rate. The activation entropy at constant strain is caused by thermal expansion, with negligible contribution from the vibrational entropy. The activation entropy at constant stress is significantly larger than that at constant strain, as a result of thermal softening. The large activation entropies are caused by anharmonic effects, showing the limitations of the harmonic approximation widely used for rate estimation in solids. Similar behaviors are expected to occur in other nucleation processes in solids. PMID:21402933

  12. Relationship between Ice Nucleation Frequency of Bacteria and Frost Injury.

    PubMed

    Lindow, S E; Hirano, S S; Barchet, W R; Arny, D C; Upper, C D

    1982-10-01

    Not every cell of a given bacterial isolate that has ice-nucleating properties can serve as an ice nucleus at any given time and temperature. The ratio between the number of ice nuclei and number of bacterial cells in a culture (i.e. nucleation frequency) was found to vary with incubation temperature, growth medium composition, culture age, and genotype. Optimal conditions for ice nucleus production in vitro included incubation of the bacterial cells at 20 to 24 degrees C on nutrient agar containing glycerol. The relationship between nucleation frequency and frost injury was examined by subjecting corn seedlings to -4 degrees C immediately after they were sprayed with bacterial suspensions with different nucleation frequencies and by following both ice nucleus concentration and bacterial population size on leaves of corn seedlings as a function of time after bacterial application. The amount of frost injury to growth chamber-grown corn seedlings at -4 degrees C was a function of the number of ice nuclei active at that temperature on the leaves. The number of ice nuclei, in turn, is the product of the nucleation frequency and population size of ice-nucleation-active bacteria present on the leaves. PMID:16662619

  13. Nucleation and growth of zinc from chloride concentrated solutions

    SciTech Connect

    Trejo, G.; Ortega B, R.; Meas V, Y.; Ozil, P.; Chainet, E.; Nguyen, B.

    1998-12-01

    The electrodeposition of metals is a complex phenomenon influenced by a number of factors that modify the rates of nucleation and growth and determine the properties of the deposits. In this work the authors study the influence of the zinc chloride (ZnCl{sub 2}) concentration on the zinc nucleation process on glassy carbon, in a KCl electrolyte under conditions close to those employed in commercial acid deposition baths for zinc. The electrochemical study was performed using cyclic voltammetry and potentiostatic current-time transients. The charge-transfer coefficient and the formal potential for ZnCl{sub 2} reduction were evaluated from cyclic voltammetry experiments. The nucleation process was analyzed by comparing the transients obtained with the known dimensionless (i/i{sub m}){sup 2} vs. t/t{sub m} response for instantaneous or progressive nucleation. The results show that the nucleation process and the number density of sites are dependent on ZnCl{sub 2} concentration. Scanning electron microscopy analysis of the deposits shows that the deposits are homogeneous and compact although a change in the morphology is observed as a function of ZnCl{sub 2} concentration. Evaluation of the corrosion resistance reveals the influence of the nucleation process on the subsequent corrosion resistance of the zinc deposits.

  14. Effects of ensembles on methane hydrate nucleation kinetics.

    PubMed

    Zhang, Zhengcai; Liu, Chan-Juan; Walsh, Matthew R; Guo, Guang-Jun

    2016-06-21

    By performing molecular dynamics simulations to form a hydrate with a methane nano-bubble in liquid water at 250 K and 50 MPa, we report how different ensembles, such as the NPT, NVT, and NVE ensembles, affect the nucleation kinetics of the methane hydrate. The nucleation trajectories are monitored using the face-saturated incomplete cage analysis (FSICA) and the mutually coordinated guest (MCG) order parameter (OP). The nucleation rate and the critical nucleus are obtained using the mean first-passage time (MFPT) method based on the FS cages and the MCG-1 OPs, respectively. The fitting results of MFPT show that hydrate nucleation and growth are coupled together, consistent with the cage adsorption hypothesis which emphasizes that the cage adsorption of methane is a mechanism for both hydrate nucleation and growth. For the three different ensembles, the hydrate nucleation rate is quantitatively ordered as follows: NPT > NVT > NVE, while the sequence of hydrate crystallinity is exactly reversed. However, the largest size of the critical nucleus appears in the NVT ensemble, rather than in the NVE ensemble. These results are helpful for choosing a suitable ensemble when to study hydrate formation via computer simulations, and emphasize the importance of the order degree of the critical nucleus.

  15. Observer dependence of bubble nucleation and Schwinger pair production

    SciTech Connect

    Garriga, Jaume; Kanno, Sugumi; Vilenkin, Alexander; Sasaki, Misao; Soda, Jiro E-mail: sugumi@cosmos.phy.tufts.edu E-mail: jiro@tap.scphys.kyoto-u.ac.jp

    2012-12-01

    Pair production in a constant electric field is closely analogous to bubble nucleation in a false vacuum. The classical trajectories of the pairs are Lorentz invariant, but it appears that this invariance should be broken by the nucleation process. Here, we use a model detector, consisting of other particles interacting with the pairs, to investigate how pair production is seen by different Lorentzian observers. We focus on the idealized situation where a constant external electric field is present for an infinitely long time, and we consider the in-vacuum state for a charged scalar field that describes the nucleating pairs. The in-vacuum is defined in terms of modes which are positive frequency in the remote past. Even though the construction uses a particular reference frame and a gauge where the vector potential is time dependent, we show explicitly that the resulting quantum state is Lorentz invariant. We then introduce a ''detector'' particle which interacts with the nucleated pairs, and show that all Lorentzian observers will see the particles and antiparticles nucleating preferentially at rest in the detector's rest frame. Similar conclusions are expected to apply to bubble nucleation in a sufficiently long lived vacuum. We also comment on certain unphysical aspects of the Lorentz invariant in-vacuum, associated with the fact that it contains an infinite density of particles. This can be easily remedied by considering Lorentz breaking initial conditions.

  16. The Nucleation and growth of Calcium Phosphate by Amelogenin

    SciTech Connect

    Tarasevich, Barbara J.; Howard, Christopher J.; Larson, Jenna L.; Snead, Malcolm L.; Simmer, Jim; Paine, Michael L.; Shaw, Wendy J.

    2007-06-15

    The nucleation processes involved in calcium phosphate formation in tooth enamel are not well understood but are believed to involve proteins in the extracellular matrix. The ability of one enamel protein, amelogenin, to promote the nucleation and growth of calcium phosphate was studied in an in vitro system involving metastable supersaturated solutions. It was found that recombinant amelogenin (rM179 and rp(H)M180) promoted the nucleation of calcium phosphate compared to solutions without protein. The amount of calcium phosphate increased with increasing supersaturation of the solutions and increasing protein concentrations up to 6.5 µg/ml. At higher protein concentrations, the amount of calcium phosphate decreased. The kinetics of nucleation were studied in situ and in real time using a quartz crystal microbalance (QCM) and showed that the protein reduced the induction time for nucleation compared to solutions without protein. This work shows a nucleation role for amelogenin in vitro which may be promoted by the association of amelogenin into nanosphere templates, exposing charged functionality at the surface. This research was performed at Pacific Northwest National Laboratory, operated by Battelle for the US-DOE. A portion of the research was performed in the EMSL, a national scientific user facility sponsored by the DOE-OBER at PNNL.

  17. Nucleation from seawater emissions during mesocosm experiments

    NASA Astrophysics Data System (ADS)

    Rose, Clémence; Culot, Anais; Pey, Jorge; Schwier, Allison; Mas, Sébastien; Charriere, Bruno; Sempéré, Richard; Marchand, Nicolas; D'Anna, Barbara; Sellegri, Karine

    2015-04-01

    Nucleation and new particle formation in the marine atmosphere is usually associated to the presence of macroalgea emerged at low tides in coastal areas, while these processes were very rarely detected away from coastlines. In the present study, we evidence the formation of new particles from the 1 nm size above the seawater surface in the absence of any macroalgea population. Within the SAM project (Sources of marine Aerosol in the Mediterranean),seawater mesocosms experiments were deployed in May 2013 at the STARESO in western Corsica, with the goal of investigating the relationship between marine aerosol emissions and the seawater biogeochemical properties. Three mesocosms imprisoned 3,3 m3 of seawater each and their emerged part was flushed with aerosol-filtered natural air. One of these mesocosms was left unchanged as control and the two others were enriched by addition of nitrates and phosphates respecting Redfield ratio (N:P = 16) in order to create different levels of phytoplanctonic activities. We followed both water and air characteristics of three mesocosms during a period of three weeks by using online water and atmospheric probes as well as seawater daily samples for chemical and biological analysis. Secondary new particle formation was followed on-line in the emerged parts of the mesocosms, using a SMPS for the size distribution above 6 nm and a Particle Size Magnifyer (PSM) for the number of cluster particles between 1 and 6 nm. We will present how the cluster formation rates and early growth rates relate to the gaz-phase emissions from the seawater and to its biogeochemical properties. Aknowledgemnts: The authors want to acknowledge the financial support of the ANR "Source of marine Aerosol in the Mediterranean" (SAM), and the support of MISTRAL CHARMEX and MERMEX programs.

  18. Multiple-to-dominant path collapse of linked-flux model for diffusion-limited nucleation

    NASA Astrophysics Data System (ADS)

    Lau, Y. H.; Wu, D. T.

    2013-01-01

    While capable of estimating diffusion-limited nucleation rates, Kelton's linked-flux model has no simple solution. To increase the model's usability, we simplify the model by retaining only the dominant nucleation path to obtain a series solution. The solution agrees well with the Kelton's model's predictions of the nucleation rate, and thus provides a simple estimate of diffusion-limited nucleation rates.

  19. Immersion freezing of ice nucleation active protein complexes

    NASA Astrophysics Data System (ADS)

    Hartmann, S.; Augustin, S.; Clauss, T.; Wex, H.; Šantl-Temkiv, T.; Voigtländer, J.; Niedermeier, D.; Stratmann, F.

    2013-06-01

    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 nucleation are attached

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

    PubMed

    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.

  1. Nucleation of a new phase on a surface that is changing irreversibly with time.

    PubMed

    Sear, Richard P

    2014-02-01

    Nucleation of a new phase almost always starts at a surface. This surface is almost always assumed not to change with time. However, surfaces can roughen, partially dissolve, and change chemically with time. Each of these irreversible changes will change the nucleation rate at the surface, resulting in a time-dependent nucleation rate. Here we use a simple model to show that partial surface dissolution can qualitatively change the nucleation process in a way that is testable in experiment. The changing surface means that the nucleation rate is increasing with time. There is an initial period during which no nucleation occurs, followed by relatively rapid nucleation. PMID:25353480

  2. Improving ice nucleation activity of zein film through layer-by-layer deposition of extracellular ice nucleators.

    PubMed

    Shi, Ke; Yu, Hailong; Lee, Tung-Ching; Huang, Qingrong

    2013-11-13

    Zein protein has been of scientific interest in the development of biodegradable functional food packaging. This study aimed at developing a novel zein-based biopolymer film with ice nucleation activity through layer-by-layer deposition of biogenic ice nucleators, that is, extracellular ice nucleators (ECINs) isolated from Erwinia herbicola , onto zein film surface. The adsorption behaviors and mechanisms were investigated using quartz crystal microbalance with dissipation monitoring (QCM-D). On unmodified zein surface, the highest ECINs adsorption occurred at pH 5.0; on UV/ozone treated zein surface followed by deposition of poly(diallyldimethylammonium chloride) (PDADMAC) layer, the optimum condition for ECINs adsorption occurred at pH 7.0 and I 0.05 M, where the amount of ECINs adsorbed was also higher than that on unmodified zein surface. QCM-D analyses further revealed a two-step adsorption process on unmodified zein surfaces, compared to a one-step adsorption process on PDADMAC-modified zein surface. Also, significantly, in order to quantify the ice nucleation activity of ECINs-coated zein films, an empirical method was developed to correlate the number of ice nucleators with the ice nucleation temperature measured by differential scanning calorimetry. Calculated using this empirical method, the highest ice nucleation activity of ECINs on ECINs-modified zein film reached 64.1 units/mm(2), which was able to elevate the ice nucleation temperature of distilled water from -15.5 °C to -7.3 °C.

  3. The adsorption of fungal ice-nucleating proteins on mineral dusts: a terrestrial reservoir of atmospheric ice-nucleating particles

    NASA Astrophysics Data System (ADS)

    O'Sullivan, Daniel; Murray, Benjamin J.; Ross, James F.; Webb, Michael E.

    2016-06-01

    The occurrence of ice-nucleating particles (INPs) in our atmosphere has a profound impact on the properties and lifetime of supercooled clouds. To date, the identities, sources and abundances of particles capable of nucleating ice at relatively low supercoolings (T > -15 °C) remain enigmatic. While biomolecules such as proteins and carbohydrates have been implicated as important high-temperature INPs, the lack of knowledge on the environmental fates of these species makes it difficult to assess their potential atmospheric impacts. Here we show that such nanoscale ice-nucleating proteins from a common soil-borne fungus (Fusarium avenaceum) preferentially bind to and confer their ice-nucleating properties to kaolinite. The ice-nucleating activity of the proteinaceous INPs is unaffected by adsorption to the clay, and once bound the proteins do not readily desorb, retaining much of the activity even after multiple washings with pure water. The atmospheric implications of the finding that biological residues can confer their ice-nucleating ability to dust particles are discussed.

  4. Fluorescence Studies of Protein Crystal Nucleation

    NASA Technical Reports Server (NTRS)

    Pusey, Marc L.

    1999-01-01

    Fluorescence can be used to study protein crystal nucleation through methods such as anisotropy, quenching, and resonance energy transfer (FRET), to follow pH and ionic strength changes, and follow events occurring at the growth interface. We have postulated, based upon a range of experimental evidence that the growth unit of tetragonal hen egg white lysozyme is an octamer. Several fluorescent derivatives of chicken egg white lysozyme have been prepared. The fluorescent probes lucifer yellow (LY), cascade blue, and 5-((2-aminoethyl)aminonapthalene-1-sulfonic acid (EDANS), have been covalently attached to ASP 101. All crystallize in the characteristic tetragonal form, indicating that the bound probes are likely laying within the active site cleft. Crystals of the LY and EDANS derivatives have been found to diffract to at least 1.7 A. A second group of derivatives is to the N-terminal amine group, and these do not crystallize as this site is part of the contact region between the adjacent 43 helix chains. However derivatives at these sites would not interfere with formation of the 43 helices in solution. Preliminary FRET studies have been carried out using N-terminal bound pyrene acetic acid (Ex 340 nm, Em 376 nm) lysozyme as a donor and LY (Ex -425 nm, Em 525 nm) labeled lysozyme as an acceptor. FRET data have been obtained at pH 4.6, 0.1 M NaAc buffer, at 5 and 7% NaCl, 4 C. The corresponding Csat values are 0.471 and 0.362 mg/ml (approximately 3.3 and approximately 2.5 x 10(exp -5) M respectively). The data at both salt concentrations show a consistent trend of decreasing fluorescence intensity of the donor species (PAA) with increasing total protein concentration. This decrease is more pronounced at 7% NaCl, consistent with the expected increased intermolecular interactions at higher salt concentrations reflected in the lower solubility. The calculated average distance between any two protein molecules at 5 x 10(exp -6) M is approximately 70nm, well beyond the

  5. Thermodynamic Derivation of the Activation Energy for Ice Nucleation

    NASA Technical Reports Server (NTRS)

    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

  6. Thermodynamic derivation of the activation energy for ice nucleation

    NASA Astrophysics Data System (ADS)

    Barahona, D.

    2015-12-01

    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

  7. The effect of nucleation and crystal growth on isotope fractionation

    NASA Astrophysics Data System (ADS)

    Wang, Z.; Gaetani, G. A.; Liu, C.; Hu, P.; Cohen, A. L.

    2011-12-01

    A set of "free-drift" experiments is conducted to precipitate aragonites from seawater at controlled temperature (25-55oC) and CO2 degassing rate in the lab. These experiments help to calibrate a coupled degassing-nucleation-crystal growth model, which not only can reproduce measured pH and alkalinity over the course of the experiments, but also predict crystal size within a factor of two of the measured values, the activation energy of the precipitation reaction constant to be 24.3±1.3 kJ/mol, the surface energy of aragonite crystals that is consistent with estimation by atomistic simulation and crystal morphology. Forward simulation of our precipitation experiments using calibrated parameters reveal the supersaturation of seawater arrives at a critical value (~13-50 in our experiment) before nucleation initiates and when the concentration of the total dissolved inorganic carbon (DIC) reduces to that of Ca. This result cannot be explained by classical nucleation theory (CNT), but is consistent with recently proposed "two-step" nucleation model, implying solution chemistry determines when the nucleation starts but the surface properties of crystal (surface energy and crystal morphology) determine the size of the crystal. It also requires not only carbonate ions but all other DIC species within a sphere of a-few-micron radius actively participate into the nucleation process. This model is then used as a framework to understand oxygen and Mg isotope fractionation between carbonates and fluid. Our results suggest nucleation and crystal growth will affect isotope fractionation at different levels depending on experimental conditions. A quantitative analysis using our model can help reconcile the isotope fractionation factors determined by various experimental approaches.

  8. A Study of Nucleate Boiling with Forced Convection in Microgravity

    NASA Technical Reports Server (NTRS)

    Merte, Herman, Jr.

    1999-01-01

    The ultimate objective of basic studies of flow boiling in microgravity is to improve the understanding of the processes involved, as manifested by the ability to predict its behavior. This is not yet the case for boiling heat transfer even in earth gravity, despite the considerable research activity over the past 30 years. The elements that constitute the nucleate boiling process - nucleation, growth, motion, and collapse of the vapor bubbles (if the bulk liquid is subcooled) - are common to both pool and flow boiling. It is well known that the imposition of bulk liquid motion affects the vapor bubble behavior relative to pool boiling, but does not appear to significantly influence the heat transfer. Indeed, it has been recommended in the past that empirical correlations or experimental data of pool boiling be used for design purposes with forced convection nucleate boiling. It is anticipated that such will most certainly not be possible for boiling in microgravity, based on observations made with pool boiling in microgravity. In earth gravity buoyancy will act to remove the vapor bubbles from the vicinity of the heater surface regardless of how much the imposed bulk velocity is reduced, depending, of course, on the geometry of the system. Vapor bubbles have been observed to dramatically increase in size in pool boiling in microgravity, and the heat flux at which dryout took place was reduced considerably below what is generally termed the critical heat flux (CHF) in earth gravity, depending on the bulk liquid subcooling. However, at heat flux levels below dryout, the nucleate pool boiling process was enhanced considerably over that in earth gravity, in spite of the large vapor bubbles formed in microgravity and perhaps as a consequence. These large vapor bubbles tended to remain in the vicinity of the heater surface, and the enhanced heat transfer appeared to be associated with the presence of what variously has been referred to as a liquid microlayer between the

  9. Recent developments in the kinetic theory of nucleation.

    PubMed

    Ruckenstein, E; Djikaev, Y S

    2005-12-30

    A review of recent progress in the kinetics of nucleation is presented. In the conventional approach to the kinetic theory of nucleation, it is necessary to know the free energy of formation of a new-phase particle as a function of its independent variables at least for near-critical particles. Thus the conventional kinetic theory of nucleation is based on the thermodynamics of the process. The thermodynamics of nucleation can be examined by using various approaches, such as the capillarity approximation, density functional theory, and molecular simulation, each of which has its own advantages and drawbacks. Relatively recently a new approach to the kinetics of nucleation was proposed [Ruckenstein E, Nowakowski B. J Colloid Interface Sci 1990;137:583; Nowakowski B, Ruckenstein E. J Chem Phys 1991;94:8487], which is based on molecular interactions and does not employ the traditional thermodynamics, thus avoiding such a controversial notion as the surface tension of tiny clusters involved in nucleation. In the new kinetic theory the rate of emission of molecules by a new-phase particle is determined with the help of a mean first passage time analysis. This time is calculated by solving the single-molecule master equation for the probability distribution function of a surface layer molecule moving in a potential field created by the rest of the cluster. The new theory was developed for both liquid-to-solid and vapor-to-liquid phase transitions. In the former case the single-molecule master equation is the Fokker-Planck equation in the phase space which can be reduced to the Smoluchowski equation owing to the hierarchy of characteristic time scales. In the latter case, the starting master equation is a Fokker-Planck equation for the probability distribution function of a surface layer molecule with respect to both its energy and phase coordinates. Unlike the case of liquid-to-solid nucleation, this Fokker-Planck equation cannot be reduced to the Smoluchowski equation

  10. Heterogeneous nucleation of ice on model carbon surfaces

    NASA Astrophysics Data System (ADS)

    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

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

    NASA Astrophysics Data System (ADS)

    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

  12. Effect of gravity wave temperature variations on homogeneous ice nucleation

    NASA Astrophysics Data System (ADS)

    Dinh, Tra; Podglajen, Aurélien; Hertzog, Albert; Legras, Bernard; Plougonven, Riwal

    2015-04-01

    Observations of cirrus clouds in the tropical tropopause layer (TTL) have shown various ice number concentrations (INC) (e.g., Jensen et al. 2013), which has lead to a puzzle regarding their formation. In particular, the frequently observed low numbers of ice crystals seemed hard to reconcile with homogeneous nucleation knowing the ubuquity of gravity waves with vertical velocity of the order of 0.1 m/s. Using artificial time series, Spichtinger and Krämer (2013) have illustrated that the variation of vertical velocity during a nucleation event could terminate it and limit the INC. However, their study was limited to constructed temperature time series. Here, we carry out numerical simulations of homogeneous ice nucleation forced by temperature time series data collected by isopycnic balloon flights near the tropical tropopause. The balloons collected data at high frequency (30 s), so gravity wave signals are well resolved in the temperature time series. With the observed temperature time series, the numerical simulations with homogeneous freezing show a full range of ice number concentrations (INC) as previously observed in the tropical upper troposphere. The simulations confirm that the dynamical time scale of temperature variations (as seen from observations) can be shorter than the nucleation time scale. They show the existence of two regimes for homogeneous ice nucleation : one limited by the depletion of water vapor by the nucleated ice crystals (those we name vapor events) and one limited by the reincrease of temperature after its initial decrease (temperature events). Low INC may thus be obtained for temperature events when the gravity wave perturbations produce a non-persistent cooling rate (even with large magnitude) such that the absolute change in temperature remains small during nucleation. This result for temperature events is explained analytically by a dependence of the INC on the absolute drop in temperature (and not on the cooling rate). This

  13. The Ice Nucleation Ability of Selected Atmospherically Abundant Fungal Spores

    NASA Astrophysics Data System (ADS)

    Iannone, R.; Chernoff, D. I.; Bertram, A. K.

    2010-12-01

    Ice clouds are widely recognized for their roles in the earth’s radiation budget and climate systems. However, their formation mechanisms are poorly understood thus constituting an uncertainty in the evaluation of the global radiation budget. An important mechanism of ice cloud formation is heterogeneous nucleation on aerosol particles. The surface properties of these particles, called ice nuclei (IN), directly affect the temperature at which ice nucleation occurs. There is a growing emphasis on the study of bioaerosols (e.g., bacteria, fungi, pollen) as IN since they are ubiquitous in the atmosphere. The focus of the current study is to determine the ice nucleation properties of spores obtained from a variety of fungi. Aerosolized spores were impacted onto a hydrophobic glass substrate and immersed in ultrapure water. A technique involving an optical light microscope coupled to a flow cell was used to precisely control temperature and humidity within the cell. A digital camera captured high-resolution video of the particles undergoing ice nucleation, allowing for the analyses of freezing events and particle sizes. The first experimental results using spores obtained from the fungal genera Cladosporium and Penicillium reveal an average temperature increase of ~1-5 K in the ice nucleation temperature compared to homogeneous nucleation (i.e., freezing of pure liquid water). Furthermore, there appears to be a relationship between the amount of spores present per droplet and the freezing temperature of water. These results are presented and discussed, and the potential contribution of these data to further the understanding of heterogeneous nucleation in the atmosphere is provided. Box plot summarizing freezing data for homogeneous nucleation experiments (leftmost box) and binned data from heterogeneous nucleation experiments involving spores of Cladosporium. Freezing data are distributed into 200 µm2 bins that represent the total area of all observable inclusions

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

    NASA Astrophysics Data System (ADS)

    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

  15. Self Nucleation and Crystallization of Poly(vinyl alcohol)

    NASA Astrophysics Data System (ADS)

    Thomas, David; Cebe, Peggy

    Polyvinyl alcohol (PVA) is a hydrophilic, biodegradable, semi-crystalline polymer with uses ranging from textiles to medicine. Film samples of PVA were investigated to assess crystallization and melting behavior during self-nucleation experiments, and thermal degradation, using differential scanning calorimetry (DSC) and thermogravimetric (TG) analysis, respectively. TG results show that degradation occurred at temperatures close to the observed peak melting temperature of 223 C. Using conventional DSC, PVA was heated at a rate of 10 C/min to various self-nucleation temperatures, Ts, within its melting range, briefly annealed, cooled and reheated. Three distinct crystallization regimes were observed upon cooling, depending upon self nucleation temperature. At low values of Ts, below 227 C, PVA only partially melts; residual crystal anneals while new, less perfect crystals form during cooling. Between 228 C and 234 C, PVA was found to crystallize exclusively by self-nucleation. For Ts above 235 C the PVA melts completely. Fast scanning chip-based calorimetry was used to heat and cool at 2000 K/s, to prevent degradation. Results of self nucleation experiments using fast scanning and conventional DSC will be compared. NSF DMR-1206010.

  16. The Kelvin equation and self-consistent nucleation theory

    SciTech Connect

    Wilemski, G. |

    1995-07-15

    Issues of self-consistency are reviewed for several unary equilibrium size distributions based on the capillarity approximation. Some apparent difficulties of interpretation are resolved. In terms of the kinetic approach to nucleation theory, the influence of self-consistency on the nucleation rate is shown to arise entirely from differences in the dimer evaporation rates for nearly all versions of classical theory. The nucleation rate behavior of the Kelvin model is explored. In this model, the Kelvin equation is used to prescribe all cluster evaporation rates. Nucleation rates predicted by the Kelvin model are quantitatively similar to those of the self-consistent classical (SCC) theory, but not to other simple versions of the classical theory. This behavior arises entirely from the relatively close coincidence of the SCC and Kelvin dimer evaporation rates. This means that, for the distribution-based versions of classical theory, the SCC model is the closest analogue of the Kelvin model. Because the Kelvin equation is fundamentally inadequate for very small clusters, the close relationship between the Kelvin and SCC formulations indicates that both are equally lacking in fundamental justification. The Kelvin model may, however, have some pragmatic utility, and a simple analytical rate expression is also derived for it to simplify the calculation of nucleation rates for this model. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.

  17. Ice Nucleation by High Molecular Weight Organic Compounds

    NASA Astrophysics Data System (ADS)

    Cantrell, W.

    2003-12-01

    Deep convection in the tropics is frequently associated with biomass burning. Recent work has suggested that the size of ice crystals in the anvils of tropical cumulonimbus clouds may be affected by biomass burning, though the mechanism for such an effect is uncertain (Sherwood, 2002). We will present results of an investigation of the role that high molecular weight organic compounds, known to be produced in biomass burning (Elias et al., 1999), may play in tropical cirrus anvils through heterogeneous nucleation of ice. In particular, we examine the mechanisms underlying heterogeneous nucleation of ice by films of long chain alcohols by studying the interaction of the alcohols and water/ice using temperature controlled, Attenuated Total Reflection - Fourier Transform Infrared spectroscopy. The mechanisms are interpreted in the context of recent criticisms of some aspects of classical nucleation theory (Seeley and Seidler, 2001; Oxtoby, 1998). References V. Elias, B. Simoneit, A. Pereira, J. Cabral, and J. Cardoso, Detection of high molecular weight organic tracers in vegetation smoke samples by high-temperature gas chromatography-mass spectrometry. Environ. Sci. Tecnol., 33, 2369-2376, 1999. D. Oxtoby, Nucleation of first-order phase transitions. Acc. Chem. Res., 31, 91-97, 1998. L. Seeley and G. Seidler, Preactivation in the nucleation of ice by Langmuir films of aliphatic alcohols. J. Chem. Phys., 114, 10464-10470, 2001. S. Sherwood, Aerosols and ice particle size in tropical cumulonimbus. J. Climate, 15, 1051-1063, 2002.

  18. Heterogeneous ice nucleation on simulated secondary organic aerosol.

    PubMed

    Schill, Gregory P; De Haan, David O; Tolbert, Margaret A

    2014-01-01

    In this study, we have explored the phase behavior and the ice nucleation properties of secondary organic aerosol made from aqueous processing (aqSOA). AqSOA was made from the dark reactions of methylglyoxal with methylamine in simulated evaporated cloud droplets. The resulting particles were probed from 215 to 250 K using Raman spectroscopy coupled to an environmental cell. We find these particles are in a semisolid or glassy state based upon their behavior when exposed to mechanical pressure as well as their flow behavior. Further, we find that these aqSOA particles are poor depositional ice nuclei, in contrast to previous studies on simple mixtures of glassy organics. Additionally, we have studied the effect of ammonium sulfate on the phase, morphology, and ice nucleation behavior of the aqSOA. We find that the plasticizing effect of ammonium sulfate lowers the viscosity of the aqSOA, allowing the ammonium sulfate to effloresce within the aqSOA matrix. Upon humidification, the aqSOA matrix liquefies before it can depositionally nucleate ice, and the effloresced ammonium sulfate can act as an immersion mode ice nucleus. This change in the mode of nucleation is accompanied by an increase in the overall ice nucleation efficiency of the aqSOA particles.

  19. Nucleation and solidification in static arrays of monodisperse drops.

    PubMed

    Edd, Jon F; Humphry, Katherine J; Irimia, Daniel; Weitz, David A; Toner, Mehmet

    2009-07-01

    The precise measurement of nucleation and non-equilibrium solidification are vital to fields as diverse as atmospheric science, food processing, cryopreservation and metallurgy. The emulsion technique, where the phase under study is partitioned into many droplets suspended within an immiscible continuous phase, is a powerful method for uncovering rates of nucleation and dynamics of phase changes as it isolates nucleation events to single droplets. However, averaging the behavior of many drops in a bulk emulsion leads to the loss of any drop-specific information, and drop polydispersity clouds the analysis. Here we adapt a microfluidic technique for trapping monodisperse drops in planar arrays to characterize solidification of highly supercooled aqueous solutions of glycerol. This system measured rates of nucleation between 10(-5) and 10(-2) pL(-1) s(-1), yielded an ice-water interfacial energy of 33.4 mJ m(-2) between -38 and -35 degrees C, and enabled the specific dynamics of solidification to be observed for over a hundred drops in parallel without any loss of specificity. In addition to the physical insights gained, the ability to observe the time and temperature of nucleation and subsequent growth of the solid phase in static arrays of uniform drops provides a powerful tool to discover thermodynamic protocols that generate desirable crystal structures.

  20. Comparison of parameterizations for homogeneous and heterogeneous ice nucleation

    NASA Astrophysics Data System (ADS)

    Koop, T.; Zobrist, B.

    2009-04-01

    The formation of ice particles from liquid aqueous aerosols is of central importance for the physics and chemistry of high altitude clouds. In this paper, we present new laboratory data on ice nucleation and compare them with two different parameterizations for homogeneous as well as heterogeneous ice nucleation. In particular, we discuss and evaluate the effect of solutes and ice nuclei. One parameterization is the λ-approach which correlates the depression of the freezing temperature of aqueous droplets in comparison to pure water droplets, Tf, with the corresponding depression, Tm, of the equilibrium ice melting point: Tf = λ × Tm. Here, λ is independent of concentration and a constant that is specific for a particular solute or solute/ice nucleus combination. The other approach is water-activity-based ice nucleation theory which describes the effects of solutes on the freezing temperature Tf via their effect on water activity: aw(Tf) = awi(Tf) + aw. Here, awi is the water activity of ice and aw is a constant that depends on the ice nucleus but is independent of the type of solute. We present new data on both homogeneous and heterogeneous ice nucleation with varying types of solutes and ice nuclei. We evaluate and discuss the advantages and limitations of the two approaches for the prediction of ice nucleation in laboratory experiments and atmospheric cloud models.

  1. The Global Distribution of Atmospheric Ice Nucleating Particles

    NASA Astrophysics Data System (ADS)

    Vergara Temprado, J.; Wilson, T. W.; Burrows, S. M.; Murray, B. J.; Carslaw, K. S.

    2015-12-01

    Ice nucleating particles (INP) affect the amount of ice in clouds, changing many of their properties. However, the relevance of different aerosol species towards causing atmospheric ice nucleation in different contexts is not well-understood. In this presentation, I will show the simulated spatial and seasonal distributions of ice nucleating particles from K-feldspar (the ice-active component of desert dust), marine organics (from sea spray) and black carbon (from combustion). The global distribution of these materials is simulated using two global aerosol model (GLOMAP-mode and EMAC). The contribution of each aerosol species to the INP distribution is calculated using parameterizations of their ice nucleating ability developed from laboratory studies of the materials involved, founding good agreement with INP observations. We found that K-feldspar dominates the atmospheric distribution of ice nucleating particles; however, marine organic INPs and black carbon are important regionally in some seasons. This study advances our understanding of which aerosol species have to be included in order to adequately describe the global and regional distribution of INPs in models.

  2. Bacterial ice nucleation: a factor in frost injury to plants.

    PubMed

    Lindow, S E; Arny, D C; Upper, C D

    1982-10-01

    Heterogeneous ice nuclei are necessary, and the common epiphytic ice nucleation active (INA) bacteria Pseudomonas syringae van Hall and Erwinia herbicola (Löhnis) Dye are sufficient to incite frost injury to sensitive plants at -5 degrees C. The ice nucleation activity of the bacteria occurs at the same temperatures at which frost injury to sensitive plants occurs in nature. Bacterial ice nucleation on leaves can be detected at about -2 degrees C, whereas the leaves themselves, i.e. without INA bacteria, contain nuclei active only at much lower temperatures. The temperature at which injury to plants occurs is predictable on the basis of the ice nucleation activity of leaf discs, which in turn depends on the number and ice nucleation activity of their resident bacteria. Bacterial isolates which are able to incite injury to corn at -5 degrees C are always active as ice nuclei at -5 degrees C. INA bacteria incited frost injury to all of the species of sensitive plants tested. PMID:16662618

  3. Homogeneous nucleation rate measurements in supersaturated water vapor II.

    PubMed

    Brus, David; Zdímal, Vladimír; Uchtmann, Hermann

    2009-08-21

    The homogeneous nucleation of water was studied experimentally in this work using a thermal diffusion cloud chamber; droplets were counted by the photomultiplier method and helium was used as a carrier gas. The nucleation rates range from 3x10(-2) to 3x10(1) cm(-3) s(-1) and six isotherms from 295 to 320 K with step of 5 K are measured. The experimental setup and obtained data are mutually compared to our previous publication [Brus et al., J. Chem. Phys. 129, 174501 (2008)], where the droplets were counted using digital photography and image processing. The molecular content of the critical clusters was estimated from the slopes of experimental data. The measured isothermal dependencies of the nucleation rate of water on the saturation ratio were compared with previously published data of others, several theoretical predictions, and the former nucleation onset data. The aim of the present investigation was to show for the first time that nucleation results can be quantitatively reproduced with two different experimental setups operated in different ways. PMID:19708751

  4. The Contribution of Constitutional Supercooling to Nucleation and Grain Formation

    NASA Astrophysics Data System (ADS)

    StJohn, D. H.; Prasad, A.; Easton, M. A.; Qian, M.

    2015-11-01

    The concept of constitutional supercooling (CS) including the term itself was first described and discussed qualitatively by Rutter and Chalmers in order to understand the formation of cellular structures during the solidification of tin, and then quantified by Tiller et al. On that basis, Winegard and Chalmers further considered `supercooling and dendritic freezing of alloys' where they described how CS promotes the heterogeneous nucleation of new crystals and the formation of an equiaxed zone. Since then the importance of CS in promoting the formation of equiaxed microstructures in both grain refined and unrefined alloys has been clearly revealed and quantified. This paper describes our current understanding of the role of CS in promoting nucleation and grain formation. It also highlights that CS, on the one hand, develops a nucleation-free zone surrounding each nucleated and growing grain and, on the other hand, protects this grain from readily remelting when temperature fluctuations occur due to convection. Further, due to the importance of the diffusion field that generates CS, recent analytical models are evaluated and compared with a numerical model. A comprehensive description of the mechanisms affecting nucleation and grain formation and the prediction of grain size is presented with reference to the influence of the casting conditions applied during the practical casting of an alloy.

  5. Nucleation at surfaces: the importance of interfacial energy.

    PubMed

    Wu, W; Gerard, D E; Nancollas, G H

    1999-11-01

    The nucleation and growth of stone-forming minerals on the surfaces of other crystalline phases, cellular material, and immobilized macromolecules must be important in the formation of stones in the urinary tract. The nucleation and growth of calcium oxalate monohydrate (COM) crystals were studied using the constant composition kinetics technique, in solution supersaturated with respect to COM (sigmaCOM = 1.44). The solid phases during the reaction were examined by x-ray diffraction, scanning electron microscopy, and diffuse reflectance Fourier transform infrared spectroscopy. Human serum albumin was found to nucleate COM crystals when immobilized on hydroxyapatite (HAP) surfaces. The induction period for nucleation of COM on HAP surfaces preadsorbed with albumin significantly decreased to about 65 min from about 230 min for pure HAP particles. The initial growth rate of COM on pure HAP particles, Rm approximately/= 0.56 X 10(-7) mol/min per m2, was slower than that for HAP surfaces preadsorbed with albumin, 2.14 x 10(-7) mol/min per m2. The surface properties were characterized using contact angle measurements by sessile drop and thin layer wicking. The thermodynamic results suggested that surfaces with high Lewis base parameter values (gamma-) and low interfacial tension with water (gammaSL) are more effective in the nucleation and growth of crystal phases.

  6. Fluorescence Studies of Protein Crystal Nucleation

    NASA Technical Reports Server (NTRS)

    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.

  7. Sub-surface alloying largely influences graphene nucleation and growth over transition metal substrates.

    PubMed

    Zhang, Liying; Zhao, Xingju; Xue, Xinlian; Shi, Jinlei; Li, Chong; Ren, Xiaoyan; Niu, Chunyao; Jia, Yu; Guo, Zhengxiao; Li, Shunfang

    2015-11-11

    Sub-surface alloying (SSA) can be an effective approach to tuning surface functionalities. Focusing on Rh(111) as a typical substrate for graphene nucleation, we show strong modulation by SSA atoms of both the energetics and kinetics of graphene nucleation simulated by first-principles calculations. Counter-intuitively, when the sub-surface atoms are replaced by more active solute metal elements to the left of Rh in the periodic table, such as the early transition metals (TMs), Ru and Tc, the binding between a C atom and the substrate is weakened and two C atoms favor dimerization. Alternatively, when the alloying elements are the late TMs to the right of Rh, such as the relatively inert Pd and Ag, the repulsion between the two C atoms is enhanced. Such distinct results can be well addressed by the delicately modulated activities of the surface host atoms in the framework of the d-band theory. More specifically, we establish a very simple selection rule for optimizing the metal substrate for high quality graphene growth: the introduction of an early (late) solute TM in the SSA lowers (raises) the d-band center and the activity of the top-most host metal atoms, weakening (strengthening) the C-substrate binding, meanwhile both energetically and kinetically facilitating (hindering) the graphene nucleation, and simultaneously promoting (suppressing) the orientation disordering the graphene domains. Importantly, our preliminary theoretical results also show that such a simple rule is also proposed to be operative for graphene growth on the widely invoked Cu(111) catalytic substrate. PMID:26257125

  8. Heterogenous nucleation in a cave with an apex and iso-curvature lateral surface

    NASA Astrophysics Data System (ADS)

    Li, Xiang-Ming; Liu, Qing-Hui

    2015-09-01

    A cave surface for heterogeneous nucleation is always assumed as a concave spherical or conical substrate. Nucleation in such assumed geometries has been well understood. However, a cave or a groove always has some cusps and certain lateral surface curvature. These geometries of a cave will have important effects on heterogenous nucleation. Here the nucleation in a cave with iso-curvature lateral surface and one apex was investigated in the scope of classical nucleation theory. Nucleation in a cave was described by comparing with nucleation on spherical and conical substrates. Results show that when the contact angle is the acute angle, nucleation in a cave with the convex or concave lateral surface is easier than nucleation on the corresponding spherical surfaces. Furthermore, nucleation in a cave with the concave surface is the easiest and nucleation on the convex surface of a cave is the most difficult, while nucleation in a conical cavity is always in between. However, whether a nucleus is more easily formed in a cave is dependent on the sizes of the cave geometry for the contact angle being the obtuse angle. As the apex angle is close to zero, nucleation in a conical cavity is easier than in a cave with the concave surface but more difficult than in a cave with the convex surface for the contact angle being the obtuse angle. The effect degree of the surface curvature of a cave on nucleation is dependent on the apex angle and the contact angle.

  9. Bubble nucleation and growth in open-cycle OTEC subsystems

    NASA Astrophysics Data System (ADS)

    Bugby, D. C.; Wassel, A. T.; Mills, A. F.

    1983-05-01

    Bubble nucleation and growth in the evaporator, condenser, upcomers, and feedwater distribution systems of open-cycle ocean thermal energy conversion (OTEC) power plants are examined. The phenomenon that will probably have the most impact on system design is cavitation in the warm water feed near the entrance of the evaporator. The critical bubble size for cavitation is about 105 microns. Sources of bubbles in the warm water feed are those entering from the ocean, those nucleating on suspended particles, and those nucleating on the upcomer wall. Analyses of bubble growth induced by changes in hydrostatic pressure, mass transfer, and coalescence are presented. Using available information for bubble size distribution in seawater at California locations, it is shown that cavitation will probably have a significant impact on evaporator performance unless a debubbler is provided upstream of the evaporator entrance.

  10. Clustering of amines and hydrazines in atmospheric nucleation

    NASA Astrophysics Data System (ADS)

    Li, Siyang; Qu, Kun; Zhao, Hailiang; Ding, Lei; Du, Lin

    2016-06-01

    It has been proved that the presence of amines in the atmosphere can enhance aerosol formation. Hydrazine (HD) and its substituted derivatives, monomethylhydrazine (MMH) and unsymmetrical dimethylhydrazine (UDMH), which are organic derivatives of amine and ammonia, are common trace atmospheric species that may contribute to the growth of nucleation clusters. The structures of the hydrazine and amine clusters containing one or two common nucleation molecules (ammonia, water, methanol and sulfuric acid) have been optimized using density functional theory (DFT) methods. The clusters growth mechanism has been explored from the thermochemistry by calculating the Gibbs free energies of adding an ammonia, water, methanol or sulfuric acid molecule step by step at room temperature, respectively. The results show that hydrazine and its derivatives could enhance heteromolecular homogeneous nucleation in the earth's atmosphere.

  11. γ-Tubulin complexes in microtubule nucleation and beyond.

    PubMed

    Oakley, Berl R; Paolillo, Vitoria; Zheng, Yixian

    2015-09-01

    Tremendous progress has been made in understanding the functions of γ-tubulin and, in particular, its role in microtubule nucleation since the publication of its discovery in 1989. The structure of γ-tubulin has been determined, and the components of γ-tubulin complexes have been identified. Significant progress in understanding the structure of the γ-tubulin ring complex and its components has led to a persuasive model for how these complexes nucleate microtubule assembly. At the same time, data have accumulated that γ-tubulin has important but less well understood functions that are not simply a consequence of its function in microtubule nucleation. These include roles in the regulation of plus-end microtubule dynamics, gene regulation, and mitotic and cell cycle regulation. Finally, evidence is emerging that γ-tubulin mutations or alterations of γ-tubulin expression play an important role in certain types of cancer and in other diseases.

  12. Nucleation and electrolytic deposition of lead on model carbon electrodes

    NASA Astrophysics Data System (ADS)

    Cericola, D.; Spahr, M.

    2016-08-01

    There is a general consensus in the lead acid battery industry for the use of carbon additives as a functional component in the negative paste to boost the battery performance with regards to charge acceptance and cycle life especially for upcoming automotive and energy storage applications. Several mechanisms are discussed in the scientific literature and the affinity of the carbon surfaces to lead species seems to play a key role. With a set of experiments on model carbon electrodes we gave evidence to the fact that some carbon materials promote spontaneous nucleation of lead crystals. We propose a mechanism such that the carbon, as soon as in a lead containing environment, immobilizes some lead on its surface. Such immobilized lead acts as nucleation seed for the deposition of lead when a current is passed through the material. It is therefore possible to differentiate and select the carbon materials based on their ability to form nucleation seeds.

  13. Transient nucleation induction time from the birth-death equations

    NASA Technical Reports Server (NTRS)

    Shneidman, Vitaly A.; Weinberg, Michael C.

    1992-01-01

    For the set of finite-difference equations of Becker-Doering an exact formula for the induction time, which is expressed in terms of rapidly convergent sums, is presented. The form of the result is particularly amenable for analytical study, and the latter is carried out to obtain approximations of the exact expression in a rigorous manner and to assess its sensitivity to the choice of the nucleation model. The induction time is found to be governed by two main nucleation parameters, the normalized barrier height, and the number of molecules in the critical cluster. The ratio of these two parameters provides an assessment of the importance of discreteness effects. The exact expression is studied in both the continuous and the asymptotic limits. The accuracy of the Zeldovich equation, which is produced in the continuous limit, is discussed for several nucleation models.

  14. Main features of nucleation in model solutions of oral cavity

    NASA Astrophysics Data System (ADS)

    Golovanova, O. A.; Chikanova, E. S.; Punin, Yu. O.

    2015-05-01

    The regularities of nucleation in model solutions of oral cavity have been investigated, and the induction order and constants have been determined for two systems: saliva and dental plaque fluid (DPF). It is shown that an increase in the initial supersaturation leads to a transition from the heterogeneous nucleation of crystallites to a homogeneous one. Some additives are found to enhance nucleation: HCO{3/-} > C6H12O6 > F-, while others hinder this process: protein (casein) > Mg2+. It is established that crystallization in DPF occurs more rapidly and the DPF composition is favorable for the growth of small (52.6-26.1 μm) crystallites. On the contrary, the conditions implemented in the model saliva solution facilitate the formation of larger (198.4-41.8 μm) crystals.

  15. Actin nucleation at the centrosome controls lymphocyte polarity

    PubMed Central

    Obino, Dorian; Farina, Francesca; Malbec, Odile; Sáez, Pablo J.; Maurin, Mathieu; Gaillard, Jérémie; Dingli, Florent; Loew, Damarys; Gautreau, Alexis; Yuseff, Maria-Isabel; Blanchoin, Laurent; Théry, Manuel; Lennon-Duménil, Ana-Maria

    2016-01-01

    Cell polarity is required for the functional specialization of many cell types including lymphocytes. A hallmark of cell polarity is the reorientation of the centrosome that allows repositioning of organelles and vesicles in an asymmetric fashion. The mechanisms underlying centrosome polarization are not fully understood. Here we found that in resting lymphocytes, centrosome-associated Arp2/3 locally nucleates F-actin, which is needed for centrosome tethering to the nucleus via the LINC complex. Upon lymphocyte activation, Arp2/3 is partially depleted from the centrosome as a result of its recruitment to the immune synapse. This leads to a reduction in F-actin nucleation at the centrosome and thereby allows its detachment from the nucleus and polarization to the synapse. Therefore, F-actin nucleation at the centrosome—regulated by the availability of the Arp2/3 complex—determines its capacity to polarize in response to external stimuli. PMID:26987298

  16. γ-Tubulin complexes in microtubule nucleation and beyond

    PubMed Central

    Oakley, Berl R.; Paolillo, Vitoria; Zheng, Yixian

    2015-01-01

    Tremendous progress has been made in understanding the functions of γ-tubulin and, in particular, its role in microtubule nucleation since the publication of its discovery in 1989. The structure of γ-tubulin has been determined, and the components of γ-tubulin complexes have been identified. Significant progress in understanding the structure of the γ-tubulin ring complex and its components has led to a persuasive model for how these complexes nucleate microtubule assembly. At the same time, data have accumulated that γ-tubulin has important but less well understood functions that are not simply a consequence of its function in microtubule nucleation. These include roles in the regulation of plus-end microtubule dynamics, gene regulation, and mitotic and cell cycle regulation. Finally, evidence is emerging that γ-tubulin mutations or alterations of γ-tubulin expression play an important role in certain types of cancer and in other diseases. PMID:26316498

  17. Nanoindentation. Simulation of defect nucleation in a crystal.

    PubMed

    Gouldstone, A; Van Vliet, K J; Suresh, S

    2001-06-01

    Nanoindentation is the penetration of a surface to nanometre depths using an indenting device. It can be simulated using the Bragg bubble-raft model, in which a close-packed array of soap bubbles corresponds to the equilibrium positions of atoms in a crystalline solid. Here we show that homogeneous defect nucleation occurs within a crystal when its surface roughness is comparable to the radius of the indenter tip, and that the depth of the nucleation site below the surface is proportional to the half-width of the contact. Our results may explain the unusually high local stress required for defect nucleation in nano-indented face-centred cubic crystals. PMID:11395759

  18. Multicomponent nucleation and droplet growth in natural gas

    NASA Astrophysics Data System (ADS)

    Luijten, C. C. M.; van Hooy, R. G. P.; Janssen, J. W. F.; van Dongen, M. E. H.

    1998-09-01

    The first quantitative experimental results are presented on homogeneous nucleation and droplet growth in a multicomponent gas-vapor mixture. Using the pulse-expansion wave tube technique, we investigated the condensation behavior of natural gas consisting of over 30 components. Data were obtained in the pressure range between 6 and 24 bar and at temperatures ranging from 221 to 237 K. The observed droplet growth rates are quantitatively explained using a multicomponent model for diffusion controlled growth. The nucleation rate data are for the moment mainly presented as a challenge to theoreticians, although some qualitative arguments are presented that could be helpful in the interpretation. The data appear to agree at least qualitatively with theoretical values (according to the revised binary classical nucleation theory) for a mixture of n-octane and methane, a model mixture which also shows the same macroscopic phase behavior as natural gas.

  19. Atomic insight into copper nanostructures nucleation on bending graphene.

    PubMed

    He, Yezeng; Li, Hui; Li, Yunfang; Zhang, Kun; Jiang, Yanyan; Bian, Xiufang

    2013-06-21

    Some findings in heterogeneous nucleation that the structural features of a growing crystal are usually inherited from the heterogeneous nucleus, although attracting more and more attention, are not yet well understood. Here we report numerical simulations of copper nucleation on bending graphene (BG) to explore the microscopic details of how the curved surface influences the freezing structure of the liquid metal. The simulation result clearly shows that copper atoms become layered at the solid-liquid interface in a "C"-shaped pattern resembling the BG. This kind of shape control decays with increasing distance from the wall and the outmost layers transform into twin crystal composed of two fcc wedges. It is found that the final structures have striking correlations with the curvature radius, central angle and arc length of the BG. Our study would provide an opportunity for comprehensive and satisfactory understanding of the heterogeneous nucleation on curved surfaces.

  20. Pathways to self-organization: Crystallization via nucleation and growth.

    PubMed

    Jungblut, S; Dellago, C

    2016-08-01

    Crystallization, a prototypical self-organization process during which a disordered state spontaneously transforms into a crystal characterized by a regular arrangement of its building blocks, usually proceeds by nucleation and growth. In the initial stages of the transformation, a localized nucleus of the new phase forms in the old one due to a random fluctuation. Most of these nuclei disappear after a short time, but rarely a crystalline embryo may reach a critical size after which further growth becomes thermodynamically favorable and the entire system is converted into the new phase. In this article, we will discuss several theoretical concepts and computational methods to study crystallization. More specifically, we will address the rare event problem arising in the simulation of nucleation processes and explain how to calculate nucleation rates accurately. Particular attention is directed towards discussing statistical tools to analyze crystallization trajectories and identify the transition mechanism. PMID:27498980

  1. Neutrons for probing the ice nucleation on atmospheric soot particles

    NASA Astrophysics Data System (ADS)

    Demirdjian, B.; Tishkova, V.; Ferry, D.

    2012-11-01

    Soot resulting from combustion of kerosene in aircraft engines can act as condensation nuclei for water/ice in the atmosphere and promote the formation of contrails that turn into artificial cirrus clouds and affect the climate. The mechanisms of nucleation of water/ice particles are not well identified. Studies "in situ" are difficult to realize, so we try to determine by neutron diffraction the nucleation of water/ice adsorbed on soot collected at the outlet of an aircraft engine combustor within the conditions of the upper troposphere. The results are compared with those obtained on model laboratory soot. The comparison highlights the role of chemical impurities and structural defects of original aircraft engine soot on the nucleation of water/ice in atmospheric conditions.

  2. The Leipzig Ice Nucleation chamber Comparison (LINC): An overview of ice nucleation measurements observed with four on-line ice nucleation devices

    NASA Astrophysics Data System (ADS)

    Kohn, Monika; Wex, Heike; Grawe, Sarah; Hartmann, Susan; Hellner, Lisa; Herenz, Paul; Welti, André; Stratmann, Frank; Lohmann, Ulrike; Kanji, Zamin A.

    2016-04-01

    Mixed-phase clouds (MPCs) are found to be the most relevant cloud type leading to precipitation in mid-latitudes. The formation of ice crystals in MPCs is not completely understood. To estimate the effect of aerosol particles on the radiative properties of clouds and to describe ice nucleation in models, the specific properties of aerosol particles acting as ice nucleating particles (INPs) still need to be identified. A number of devices are able to measure INPs in the lab and in the field. However, methods can be very different and need to be tested under controlled conditions with respect to aerosol generation and properties in order to standardize measurement and data analysis approaches for subsequent ambient measurements. Here, we present an overview of the LINC campaign hosted at TROPOS in September 2015. We compare four ice nucleation devices: PINC (Portable Ice Nucleation Chamber, Chou et al., 2011) and SPIN (SPectrometer for Ice Nuclei) are operated in deposition nucleation and condensation freezing mode. LACIS (Leipzig Aerosol Cloud Interaction Simulator, Hartmann et al., 2011) and PIMCA (Portable Immersion Mode Cooling chamber) measure in the immersion freezing mode. PIMCA is used as a vertical extension to PINC and allows activation and droplet growth prior to exposure to the investigated ice nucleation temperature. Size-resolved measurements of multiple aerosol types were performed including pure mineral dust (K-feldspar, kaolinite) and biological particles (Birch pollen washing waters) as well as some of them after treatment with sulfuric or nitric acid prior to experiments. LACIS and PIMCA-PINC operated in the immersion freezing mode showed very good agreement in the measured frozen fraction (FF). For the comparison between PINC and SPIN, which were scanning relative humidity from below to above water vapor saturation, an agreement was found for the obtained INP concentration. However, some differences were observed, which may result from ice

  3. Transgranular Crack Nucleation in Carrara Marble of Brittle Failure

    NASA Astrophysics Data System (ADS)

    Cheng, Yi; Wong, Louis Ngai Yuen; Maruvanchery, Varun

    2016-08-01

    Understanding the microcrack nucleation is of a fundamental importance in the study of rock fracturing process. Due to variations in texture and mineralogy, different rocks may show different distinctive microcrack nucleation mechanisms. In order to understand the microcrack nucleation mechanisms in Carrara marble comprehensively, localized damage zones are artificially produced by loading specimens containing an array of en-echelon flaws in this study. Then, representative samples were cut from those loaded specimens and prepared for optical observation. Four types of microcrack nucleation mechanisms leading to the formation of transgranular cracks have been identified in Carrara marble. Type I and II mechanisms are favored by the distinctive polygonal shape of the crystal grains in Carrara marble. Local tensile stress concentration in these two mechanisms is attributed to grain sliding and divergent normal contact force, respectively. Type III mechanism is associated with the gliding along twin lamellae. The resultant tensile stress concentration could nucleate microcracks within the grain containing these lamellae or in the grain boundary. No microcracks in the adjoining grains were observed in this study. Our statistical analysis suggests that type III mechanism favors the nucleation of new cracks which are nearly perpendicular to the gently inclined twin lamellae and thus have a small angle with the maximum loading direction (about 15°). Type IV mechanism operates in grains failed mainly due to compressive stress rather than tensile stress concentration. Sets of parallel microcracks of this mechanism seem to be related to the crystallographic planes of calcite. The microcracking results also suggest that most of the grain boundaries in damaged zone have been cracked at the loading about 80 % of the specimen strength, while transgranular cracks begin to occur at that time and flourish after about 90 % loading of the strength.

  4. Particle Nucleation and Growth During the NIFTy Experiment

    NASA Astrophysics Data System (ADS)

    Barthelmie, R. J.; Pryor, S. C.; Spaulding, A. M.; Rossner, A.; Crimmins, B.; Hopke, P. K.; Mauldin, L.; Jobson, T.; Petaja, T.

    2008-12-01

    The measurements presented herein are being collected in order to assess the frequency and characteristics of nucleation events and high ultra-fine particle concentrations in this rural (but regionally polluted) setting, including the chemical composition of the ultra-fine particles, the principal mechanisms of nucleation, limitations on nucleation and growth and the ultimate fate of the resulting ultra-fine particles. We present a year of data from continuous measurements of particle size distributions (6 to 400 nm) at three- levels above and within a deciduous forest in southern Indiana (in the Ohio River Valley). These data are collected using two SMPS and one FMPS, and are supplemented with data concerning the spatial extent and the composition of ultra-fine particles using samples collected during May 2008 as part of the Nucleation In ForesTs (NIFTY) campaign. The long-term measurements indicate evidence of class A nucleation events on approximately 1 day in 5, and lesser magnitude or less well defined events on another 15% of days. These data indicate nucleation is most frequently observed in spring, but occurs in all seasons and subsequent growth is more rapid during leaf-on. During the NIFTY field experiment we enhanced the ongoing data collection at the forest site to include sulfuric acid, ammonia and VOC concentrations, and particle composition using two MOUDI-nano-MOUDI combinations. Preliminary analyses of these data indicate that the sub-32 nm diameter particles are almost completely ammonium-sulfate or ammonium-bisulfate and associated water but there is evidence that continued growth is aided by the addition of condensable organics. We further instrumented two additional sites - one directly south of the forest in a relatively rural setting, and one to the north in the city of Indianapolis. Results from these sites indicate strong evidence that the events are regional but the sites differ in terms of the magnitude of the events and the relative

  5. Homogeneous ice nucleation at moderate supercooling from molecular simulation.

    PubMed

    Sanz, E; Vega, C; Espinosa, J R; Caballero-Bernal, R; Abascal, J L F; Valeriani, C

    2013-10-01

    Among all of the freezing transitions, that of water into ice is probably the most relevant to biology, physics, geology, or atmospheric science. In this work, we investigate homogeneous ice nucleation by means of computer simulations. We evaluate the size of the critical cluster and the nucleation rate for temperatures ranging between 15 and 35 K below melting. We use the TIP4P/2005 and the TIP4P/ice water models. Both give similar results when compared at the same temperature difference with the model's melting temperature. The size of the critical cluster varies from ∼8000 molecules (radius = 4 nm) at 15 K below melting to ∼600 molecules (radius = 1.7 nm) at 35 K below melting. We use Classical Nucleation Theory (CNT) to estimate the ice-water interfacial free energy and the nucleation free-energy barrier. We obtain an interfacial free energy of 29(3) mN/m from an extrapolation of our results to the melting temperature. This value is in good agreement both with experimental measurements and with previous estimates from computer simulations of TIP4P-like models. Moreover, we obtain estimates of the nucleation rate from simulations of the critical cluster at the barrier top. The values we get for both models agree within statistical error with experimental measurements. At temperatures higher than 20 K below melting, we get nucleation rates slower than the appearance of a critical cluster in all water of the hydrosphere during the age of the universe. Therefore, our simulations predict that water freezing above this temperature must necessarily be heterogeneous.

  6. Heterogeneous Nucleation and Growth of Nanoparticles at Environmental Interfaces.

    PubMed

    Jun, Young-Shin; Kim, Doyoon; Neil, Chelsea W

    2016-09-20

    Mineral nucleation is a phase transformation of aqueous components to solids with an accompanying creation of new surfaces. In this evolutional, yet elusive, process, nuclei often form at environmental interfaces, which provide remarkably reactive sites for heterogeneous nucleation and growth. Naturally occurring nucleation processes significantly contribute to the biogeochemical cycles of important components in the Earth's crust, such as iron and manganese oxide minerals and calcium carbonate. However, in recent decades, these cycles have been significantly altered by anthropogenic activities, which affect the aqueous chemistry and equilibrium of both surface and subsurface systems. These alterations can trigger the dissolution of existing minerals and formation of new nanoparticles (i.e., nucleation and growth) and consequently change the porosity and permeability of geomedia in subsurface environments. Newly formed nanoparticles can also actively interact with components in natural and engineered aquatic systems, including those posing a significant hazard such as arsenic. These interactions can bilaterally influence the fate and transport of both newly formed nanoparticles and aqueous components. Due to their importance in natural and engineered processes, heterogeneous nucleation at environmental interfaces has started to receive more attention. However, a lack of time-resolved in situ analyses makes the evaluation of heterogeneous nucleation challenging because the physicochemical properties of both the nuclei and surfaces significantly and dynamically change with time and aqueous chemistry. This Account reviews our in situ kinetic studies of the heterogeneous nucleation and growth behaviors of iron(III) (hydr)oxide, calcium carbonate, and manganese (hydr)oxide minerals in aqueous systems. In particular, we utilized simultaneous small-angle and grazing incidence small-angle X-ray scattering (SAXS/GISAXS) to investigate in situ and in real-time the effects of

  7. Interpretation of DTA experiments used for crystal nucleation rate determinations

    NASA Technical Reports Server (NTRS)

    Weinberg, Michael C.

    1991-01-01

    An analysis is presented of two schemes which have been proposed for the determination of the temperature dependence of homogeneous crystal nucleation rates in glasses via DTA measurements. The first method is based upon the postulate that the inverse of the temperature at which the DTA crystallization rate is maximum, will increase monotonically as the number density of nucleated particles increases. The secone method is based on the observation that the intensity at T(p) (peak height) increases as T(p) grows. The validity of both of these methods is assessed for inorganic glasses for two specific crystal growth models.

  8. Immersion freezing of ice nucleating active protein complexes

    NASA Astrophysics Data System (ADS)

    Hartmann, S.; Augustin, S.; Clauss, T.; Voigtländer, J.; Niedermeier, D.; Wex, H.; Stratmann, F.

    2012-08-01

    Biological particles, e.g. bacteria and their Ice Nucleating Active (INA) protein complexes, might play an important role for the ice formation in atmospheric mixed-phase clouds. Therefore, the immersion freezing behavior of INA protein complexes generated from a SnomaxTM solution/suspension was investigated as function of temperature in a range of -5 °C to -38 °C at the Leipzig Aerosol Cloud Interaction Simulator (LACIS). The immersion freezing of droplets containing small numbers of INA protein complexes occurs in a temperature range of -7 °C and -10 °C. The experiments performed in the lower temperature range, where all droplets freeze which contain at least one INA protein complex, are used to determine the average number of INA protein complexes present, assuming that the INA protein complexes are Poisson distributed over the droplet ensemble. Knowing the average number of INA protein complexes, the heterogeneous ice nucleation rate and rate coefficient of a single INA protein complex is determined by using the newly-developed CHESS model (stoCHastic model of idEntical poiSSon distributed ice nuclei). Therefore, we assume the ice nucleation process to be of stochastic nature, and a parameterization of the INA protein complex's nucleation rate. Analyzing the results of immersion freezing experiments from literature (SnomaxTM and Pseudomonas syringae bacteria), to results gained in this study, demonstrates that first, a similar temperature dependence of the heterogeneous ice nucleation rate for a single INA protein complex was found in all experiments, second, the shift of the ice fraction curves to higher temperatures can be explained consistently by a higher average number of INA protein complexes being present in the droplet ensemble, and finally the heterogeneous ice nucleation rate of one single INA protein complex might be also applicable for intact Pseudomonas syringae bacteria cells. The results obtained in this study allow a new perspective on the

  9. Investigations of organic and microbiological atmospheric ice nucleating particles (Invited)

    NASA Astrophysics Data System (ADS)

    DeMott, P. J.; Hill, T. C.; Tobo, Y.; Prenni, A. J.; McMeeking, G. R.; Levin, E. J.; McCluskey, C.; Huffman, J. A.; Mason, R.; Bertram, A. K.; Kreidenweis, S. M.

    2013-12-01

    Measurements in a number of laboratory and field campaigns have offered the opportunity to compare and contrast ice nucleation by soil-and plant-based inorganic, organic, and microbiological particles versus ice nucleating particles (INP) actually sampled in the atmosphere. This presentation reviews these recent studies. Plants support sometimes prodigious populations of INA bacteria as well as fungi and other potential biological ice nucleating particles, such as fragments of plant tissues themselves. The means of release of plant-sourced INP to the atmosphere is not fully documented, but our recent studies have found clear cases of release of ice nuclei from disturbances such as rain, both in forests and over grasslands, and harvesting. Composition of such ice nuclei in air has been inferred at these times based on simultaneous measurements of ice nuclei and biological aerosols. At quiescent times, measurements of the labile fraction of ice nucleating particles in air over agricultural regions suggest that organic and possibly microbiological organisms dominate ice nuclei populations, but INA bacteria are only selective and modest contributors at the warmest activation temperatures. Our results therefore suggest the presence of a spectrum of biological and organic ice nucleating particles over land regions. The ice nucleating activity of mineral soils is well documented and the presence of these particles in air is certain on the basis of many measurement campaigns which identified mineral particles to represent up to half or more of ice nuclei sampled in parts of the free troposphere. Our recent measurements have also documented a clear organic ice nucleating particle source within arable, sagebrush, grassland and forest soils, a source that may dominate over the mineral ice nuclei in such soils. Investigations of their compositions will be described. These ice nuclei are strongly resistant to heat, and may represent a separate population and source compared to

  10. Rayleigh Scattering Density Measurements, Cluster Theory, and Nucleation Calculations at Mach 10

    NASA Technical Reports Server (NTRS)

    Balla, R. Jeffrey; Everhart, Joel L.

    2012-01-01

    In an exploratory investigation, quantitative unclustered laser Rayleigh scattering measurements of density were performed in the air in the NASA Langley Research Center's 31 in. Mach 10 wind tunnel. A review of 20 previous years of data in supersonic and Mach 6 hypersonic flows is presented where clustered signals typically overwhelmed molecular signals. A review of nucleation theory and accompanying nucleation calculations are also provided to interpret the current observed lack of clustering. Data were acquired at a fixed stagnation temperature near 990Kat five stagnation pressures spanning 2.41 to 10.0 MPa (350 to 1454 psi) using a pulsed argon fluoride excimer laser and double-intensified charge-coupled device camera. Data averaged over 371 images and 210 pixels along a 36.7mmline measured freestream densities that agree with computed isentropic-expansion densities to less than 2% and less than 6% at the highest and lowest densities, respectively. Cluster-free Mach 10 results are compared with previous clustered Mach 6 and condensation-free Mach 14 results. Evidence is presented indicating vibrationally excited oxygen and nitrogen molecules are absorbed as the clusters form, release their excess energy, and inhibit or possibly reverse the clustering process. Implications for delaying clustering and condensation onset in hypersonic and hypervelocity facilities are discussed.

  11. Cell-cycle dependent phosphorylation of yeast pericentrin regulates γ-TuSC-mediated microtubule nucleation.

    PubMed

    Lin, Tien-Chen; Neuner, Annett; Schlosser, Yvonne T; Scharf, Annette N D; Weber, Lisa; Schiebel, Elmar

    2014-01-01

    Budding yeast Spc110, a member of γ-tubulin complex receptor family (γ-TuCR), recruits γ-tubulin complexes to microtubule (MT) organizing centers (MTOCs). Biochemical studies suggest that Spc110 facilitates higher-order γ-tubulin complex assembly (Kollman et al., 2010). Nevertheless the molecular basis for this activity and the regulation are unclear. Here we show that Spc110 phosphorylated by Mps1 and Cdk1 activates γ-TuSC oligomerization and MT nucleation in a cell cycle dependent manner. Interaction between the N-terminus of the γ-TuSC subunit Spc98 and Spc110 is important for this activity. Besides the conserved CM1 motif in γ-TuCRs (Sawin et al., 2004), a second motif that we named Spc110/Pcp1 motif (SPM) is also important for MT nucleation. The activating Mps1 and Cdk1 sites lie between SPM and CM1 motifs. Most organisms have both SPM-CM1 (Spc110/Pcp1/PCNT) and CM1-only (Spc72/Mto1/Cnn/CDK5RAP2/myomegalin) types of γ-TuCRs. The two types of γ-TuCRs contain distinct but conserved C-terminal MTOC targeting domains.DOI: http://dx.doi.org/10.7554/eLife.02208.001. PMID:24842996

  12. Binary nucleation rates for ethanol/water mixtures in supersonic Laval nozzles: Analyses by the first and second nucleation theorems

    NASA Astrophysics Data System (ADS)

    Tanimura, Shinobu; Pathak, Harshad; Wyslouzil, Barbara E.

    2013-11-01

    We performed pressure trace measurements and small angle x-ray scattering measurements to determine the vapor-liquid nucleation rates of EtOH/H2O mixtures including pure EtOH and pure H2O in two supersonic Laval nozzles with different expansion rates. The nucleation rates varied from 0.9 × 1017 to 16 × 1017 cm-3 s-1 over the temperature range of 210 K to 230 K, EtOH activity range of 0 to 11.6, and H2O activity range of 0 to 124. The first and second nucleation theorems were applied to the nucleation rates to estimate the sizes, compositions, and excess energies of the critical clusters. The critical clusters contained from 4 to 15 molecules for pure H2O and EtOH/H2O clusters, and from 16 to 23 molecules for pure EtOH clusters. Comparing the excess energies of the pure H2O critical clusters with the results of a quantum-chemistry calculation suggested that the pre-factor of the theoretical nucleation rate is almost constant regardless of the monomer concentration. One possible explanation for this result is that cooling of the critical clusters limits the nucleation rate under the highly supersaturated conditions. The results of the analyses also yielded the relation between the surface energy and the composition of the critical clusters, where the latter are predicted to consist only of surface molecules. Applying this relationship to the EtOH/H2O bulk liquid mixtures, we estimated the EtOH mole fraction in the surface layer and found it is higher than that derived from the surface tension based on the Gibbs adsorption equation when the EtOH mole fraction in the liquid is higher than about 0.2 mol/mol. This discrepancy was attributed to the existence of the EtOH depletion layer just below the surface layer of the liquid.

  13. The composition of nucleation and Aitken modes particles during coastal nucleation events: evidence for marine secondary organic contribution

    NASA Astrophysics Data System (ADS)

    Vaattovaara, P.; Huttunen, P. E.; Yoon, Y. J.; Joutsensaari, J.; Lehtinen, K. E. J.; O'Dowd, C. D.; Laaksonen, A.

    2006-04-01

    Newly-formed nanometer-sized particles have been observed at coastal and marine environments worldwide. Interestingly, organic species have so far not been detected in those newly-formed nucleation mode particles. In this study, we applied the UFO-TDMA (ultrafine organic tandem differential mobility analyzer) method to study the possible existence of an organic fraction in recently formed coastal nucleation mode particles (d<20 nm) at the Mace Head research station. Furthermore, effects of those nucleation events to potential CCN (cloud condensation nuclei) were studied. The coastal events were typical for the Mace Head region and they occurred at low tide conditions during efficient solar radiation and high biological activity (HBA, i.e. a high mass concentration of chlorophyll a of the ocean) in spring 2002. Additionally, a PHA-UCPC (pulse height analyzer ultrafine condensation particle counter) technique was used to study the composition of newly-formed particles formed in low tide conditions during a lower biological activity (LBA, i.e. a lower mass concentration of chlorophyll a of the ocean) in October 2002. The overall results of the UFO-TDMA and the PHA-UCPC measurements indicate that those coastally/marinely formed nucleation mode particles include a remarkable fraction of secondary organic products, beside iodine oxides, which are likely to be responsible for the nucleation. During clean marine air mass conditions, the origin of those secondary organic oxidation compounds can be related to marine/coastal biota and thus a major fraction of the organics may originate from biosynthetic production of alkenes such as isoprene and their oxidation by iodine, hydroxyl radical, and ozone. During modified marine conditions, also anthropogenic secondary organic compounds may contribute to the nucleation mode organic mass, in addition to biogenic secondary organic compounds. Thus, the UFO-TDMA results suggest that the secondary organic compounds may, in addition to

  14. Impact of controlled ice nucleation on process performance and quality attributes of a lyophilized monoclonal antibody.

    PubMed

    Awotwe-Otoo, David; Agarabi, Cyrus; Read, Erik K; Lute, Scott; Brorson, Kurt A; Khan, Mansoor A; Shah, Rakhi B

    2013-06-25

    An efficient and potentially scalable technology was evaluated to control the ice nucleation step of the freezing process for a model monoclonal antibody formulation and the effect on process performance and quality attributes of the final lyophilized product was compared with the conventional shelf ramping method of freezing. Controlled ice nucleation resulted in uniform nucleation at temperatures between -2.3 and -3.2 °C while uncontrolled nucleation resulted in random nucleation at temperatures between -10 and -16.4 °C. The sublimation rate (dm/dt) during primary drying was higher in the controlled nucleation cycle (0.13 g/h/vial) than in the uncontrolled nucleation cycle (0.11 g/h/vial). This was due to the formation of larger ice crystals, leading to lower product resistance (Rp) and 19% reduction in the primary drying for the controlled nucleation cycle. Controlled ice nucleation resulted in lyophilized cakes with more acceptable appearance, no visible collapse or shrinkage and decreased reconstitution times compared with uncontrolled nucleation. There were no observed differences in the particle size, concentration (A280 nm) and presence of aggregates (A410 nm) between the two nucleation cycles when the lyophilized cakes were reconstituted. These were confirmed by SEC and protein A-HPLC analyses which showed similar peak shapes and retention times between the two cycles. However, uncontrolled nucleation resulted in cakes with larger specific surface area (0.90 m(2)/g) than controlled nucleation (0.46 m(2)/g). SEM images of the lyophilized cakes from uncontrolled nucleation revealed a sponge-like morphology with smaller pores while cakes from controlled nucleation cycle revealed plate-like structures with more open and larger pores. While controlled nucleation resulted in a final product with a higher residual moisture content (2.1±0.08%) than uncontrolled nucleation (1.62±0.11%), this was resolved by increasing the secondary drying temperature.

  15. Computer centers

    NASA Astrophysics Data System (ADS)

    The National Science Foundation has renewed grants to four of its five supercomputer centers. Average annual funding will rise from $10 million to $14 million so facilities can be upgraded and training and education expanded. As cooperative projects, the centers also receive money from states, universities, computer vendors and industry. The centers support research in fluid dynamics, atmospheric modeling, engineering geophysics and many other scientific disciplines.

  16. An adsorption model of the heterogeneous nucleation of solidification

    SciTech Connect

    Kim, W.T.; Cantor, B. . Oxford Centre for Advanced Materials and Composites)

    1994-09-01

    An adsorption model has been developed to describe the heterogeneous nucleation of solidification in an A-B eutectic or monotectic alloy system. The interface between A-rich [alpha] solid and B-rich liquid is treated as a mixture of A solid, B solid, A liquid and B liquid atoms, randomly distributed as a monolayer between the two phases. The interfacial energy is calculated by summing pairwise bonding energies, and is then minimized to determine the equilibrium interface solid fraction and composition. With decreasing temperature, the interface monolayer changes sharply from liquid to solid, with a composition close to pure B. This sharp onset of interface adsorption of solid B atoms corresponds to [alpha] acting as a catalyst for the heterogeneous nucleation of B-rich [beta] solid. Adsorption close to the eutectic temperature and therefore efficient nucleation catalysis is promoted by a large difference between the melting points of A and B, and a small difference between the solid and liquid immiscibilities of A and B. Predicted undercoolings for the onset of adsorption and nucleation catalysis can be obtained directly from simple phase diagram data, and give good agreement with previous measurements in the Ag-Pb and Al-Sn alloy systems.

  17. Ultrasonic emissions during ice nucleation and propagation in plant xylem.

    PubMed

    Charrier, Guillaume; Pramsohler, Manuel; Charra-Vaskou, Katline; Saudreau, Marc; Améglio, Thierry; Neuner, Gilbert; Mayr, Stefan

    2015-08-01

    Ultrasonic acoustic emission analysis enables nondestructive monitoring of damage in dehydrating or freezing plant xylem. We studied acoustic emissions (AE) in freezing stems during ice nucleation and propagation, by combining acoustic and infrared thermography techniques and controlling the ice nucleation point. Ultrasonic activity in freezing samples of Picea abies showed two distinct phases: the first on ice nucleation and propagation (up to 50 AE s(-1) ; reversely proportional to the distance to ice nucleation point), and the second (up to 2.5 AE s(-1) ) after dissipation of the exothermal heat. Identical patterns were observed in other conifer and angiosperm species. The complex AE patterns are explained by the low water potential of ice at the ice-liquid interface, which induced numerous and strong signals. Ice propagation velocities were estimated via AE (during the first phase) and infrared thermography. Acoustic activity ceased before the second phase probably because the exothermal heating and the volume expansion of ice caused decreasing tensions. Results indicate cavitation events at the ice front leading to AE. Ultrasonic emission analysis enabled new insights into the complex process of xylem freezing and might be used to monitor ice propagation in natura.

  18. Observations of nucleation of new particles in a volcanic plume.

    PubMed

    Boulon, Julien; Sellegri, Karine; Hervo, Maxime; Laj, Paolo

    2011-07-26

    Volcanic eruptions caused major weather and climatic changes on timescales ranging from hours to centuries in the past. Volcanic particles are injected in the atmosphere both as primary particles rapidly deposited due to their large sizes on time scales of minutes to a few weeks in the troposphere, and secondary particles mainly derived from the oxidation of sulfur dioxide. These particles are responsible for the atmospheric cooling observed at both regional and global scales following large volcanic eruptions. However, large condensational sinks due to preexisting particles within the plume, and unknown nucleation mechanisms under these circumstances make the assumption of new secondary particle formation still uncertain because the phenomenon has never been observed in a volcanic plume. In this work, we report the first observation of nucleation and new secondary particle formation events in a volcanic plume. These measurements were performed at the puy de Dôme atmospheric research station in central France during the Eyjafjallajokull volcano eruption in Spring 2010. We show that the nucleation is indeed linked to exceptionally high concentrations of sulfuric acid and present an unusual high particle formation rate. In addition we demonstrate that the binary H(2)SO(4) - H(2)O nucleation scheme, as it is usually considered in modeling studies, underestimates by 7 to 8 orders of magnitude the observed particle formation rate and, therefore, should not be applied in tropospheric conditions. These results may help to revisit all past simulations of the impact of volcanic eruptions on climate. PMID:21746910

  19. Study on Nucleation of Water on Solid Surface

    NASA Astrophysics Data System (ADS)

    Okawa, Seiji; Saito, Akio; Matsui, Tatsuyuki

    Heterogeneous nucleation of water was investigated using Molecular Dynamics method. Solid with fcc(111) surface was placed at the bottom of a cell consisting of 864 water molecules. ST2 model with NPT ensemble was used. The pressure and temperature were set at 0.1MPa and 275K, respectively. The interaction between water and the solid was based on the equations proposed by Spohr. Exception was made on the lattice constant which was slightly modified to fit with that for ice structure. The shape of the solid surface was considered. It was found that the only one layer of water molecules was adsorbed in a case of a flat surface, whereas ice nucleation occurred by removing some of the atoms from the surface. Spohr's interaction was also modified so that the dipole moment of water became anti-ferroelectric. It was found that the modification increased the ice growth, further. The effect of lattice constant of solid on nucleation was also investigated. It was found that the variation on lattice constant with a few percent from that of ice was acceptable for nucleation, especially on shrinking side. On expanding side, however, it gave some gaps for water molecules to fit in other than that for ice structure, and it prevented the growth of ice.

  20. Recent progress in understanding particle nucleation and growth

    PubMed Central

    Eisele, F. L.; McMurry, P. H.

    1997-01-01

    In the past half decade, several new tools have become available for investigating particle nucleation and growth. A number of joint field and laboratory studies exploiting some of these new measurement capabilities will be described and new insights shared. the ability to measure OH, SO2, H2SO4 and aerosol number and size distributions has made possible a comparison between H2SO4 production and loss onto particles in continental air masses. In regions remote from urban emissions, agreement is typically quite good. In contrast, joint field measurements of nucleation precursors such as gas phase H2SO4 and ultrafine particles suggest that classical bimolecular nucleation theory may not properly describe the tropospheric nucleation process. An alternative mechanism, possibly involving ammonia as a stabilizing agent for H2SO4/H2O molecular clusters is discussed. Finally, ultrafine particle measurements are shown to offer new opportunities for studying particle growth rates. Preliminary results suggest that in a remote continental air mass, gas phase H2SO4 uptake is far too slow to explain observed growth rates.

  1. Surface or internal nucleation and crystallization of glass-ceramics

    NASA Astrophysics Data System (ADS)

    Höland, W.; Rheinberger, V. M.; Ritzberger, C.; Apel, E.

    2013-07-01

    Fluoroapatite (Ca5(PO4)3F) was precipitated in glass-ceramics via internal crystallization of base glasses. The crystals grew with a needle-like morphology in the direction of the crystallographic c-axis. Two different reaction mechanisms were analyzed: precipitation via a disordered primary apatite crystals and a solid state parallel reaction to rhenanite (NaCaPO4) precipitation. In contrast to the internal nucleation used in the formation of fluoroapatite, surface crystallization was induced to precipitate a phosphate-free oxyapatite of NaY9(SiO4)6O2-type. Internal nucleation and crystallization have been shown to be a very useful tool for developing high-strength lithium disilicate (Li2Si2O5) glass-ceramics. A very controlled process was conducted to transform the lithium metasilicate glass-ceramic precursor material into the final product of the lithium disilicate glass-ceramic without the major phase of the precursor material. The combination of all these methods allowed the driving forces of the internal nucleation and crystallization mechanisms to be explained. An amorphous phosphate primary phase was discovered in the process. Nucleation started at the interface between the amorphous phosphate phase and the glass matrix. The final products of all these glass-ceramics are biomaterials for dental restoration showing special optical properties, e.g. translucence and color close to dental teeth.

  2. Ion-induced nucleation of pure biogenic particles.

    PubMed

    Kirkby, Jasper; Duplissy, Jonathan; 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

    2016-05-25

    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 α-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 by quantum chemical calculations of the cluster binding energies of representative HOMs. Ion-induced nucleation of pure organic particles constitutes a potentially widespread source of aerosol particles in terrestrial environments with low sulfuric acid pollution.

  3. Observations of nucleation of new particles in a volcanic plume

    PubMed Central

    Boulon, Julien; Sellegri, Karine; Hervo, Maxime; Laj, Paolo

    2011-01-01

    Volcanic eruptions caused major weather and climatic changes on timescales ranging from hours to centuries in the past. Volcanic particles are injected in the atmosphere both as primary particles rapidly deposited due to their large sizes on time scales of minutes to a few weeks in the troposphere, and secondary particles mainly derived from the oxidation of sulfur dioxide. These particles are responsible for the atmospheric cooling observed at both regional and global scales following large volcanic eruptions. However, large condensational sinks due to preexisting particles within the plume, and unknown nucleation mechanisms under these circumstances make the assumption of new secondary particle formation still uncertain because the phenomenon has never been observed in a volcanic plume. In this work, we report the first observation of nucleation and new secondary particle formation events in a volcanic plume. These measurements were performed at the puy de Dôme atmospheric research station in central France during the Eyjafjallajokull volcano eruption in Spring 2010. We show that the nucleation is indeed linked to exceptionally high concentrations of sulfuric acid and present an unusual high particle formation rate. In addition we demonstrate that the binary H2SO4 - H2O nucleation scheme, as it is usually considered in modeling studies, underestimates by 7 to 8 orders of magnitude the observed particle formation rate and, therefore, should not be applied in tropospheric conditions. These results may help to revisit all past simulations of the impact of volcanic eruptions on climate. PMID:21746910

  4. Reducing the nucleation barrier in magnetocaloric Heusler alloys by nanoindentation

    NASA Astrophysics Data System (ADS)

    Niemann, R.; Hahn, S.; Diestel, A.; Backen, A.; Schultz, L.; Nielsch, K.; Wagner, M. F.-X.; Fähler, S.

    2016-06-01

    Magnetocaloric materials are promising as solid state refrigerants for more efficient and environmentally friendly cooling devices. The highest effects have been observed in materials that exhibit a first-order phase transition. These transformations proceed by nucleation and growth which lead to a hysteresis. Such irreversible processes are undesired since they heat up the material and reduce the efficiency of any cooling application. In this article, we demonstrate an approach to decrease the hysteresis by locally changing the nucleation barrier. We created artificial nucleation sites and analyzed the nucleation and growth processes in their proximity. We use Ni-Mn-Ga, a shape memory alloy that exhibits a martensitic transformation. Epitaxial films serve as a model system, but their high surface-to-volume ratio also allows for a fast heat transfer which is beneficial for a magnetocaloric regenerator geometry. Nanoindentation is used to create a well-defined defect. We quantify the austenite phase fraction in its proximity as a function of temperature which allows us to determine the influence of the defect on the transformation.

  5. Ion-induced nucleation of pure biogenic particles

    NASA Astrophysics Data System (ADS)

    Kirkby, Jasper; Duplissy, Jonathan; 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

    2016-05-01

    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 α-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 by quantum chemical calculations of the cluster binding energies of representative HOMs. Ion-induced nucleation of pure organic particles constitutes a potentially widespread source of aerosol particles in terrestrial environments with low sulfuric acid pollution.

  6. Nucleation kinetics of urea succinic acid -ferroelectric single crystal

    NASA Astrophysics Data System (ADS)

    Dhivya, R.; Vizhi, R. Ezhil; Babu, D. Rajan

    2015-06-01

    Single crystals of Urea Succinic Acid (USA) were grown by slow cooling technique. The crystalline system was confirmed by powder X-ray diffraction. The metastable zonewidth were carried out for various temperatures i.e., 35°, 40°, 45° and 50°C. The induction period is experimentally determined and various nucleation parameters have been estimated.

  7. Atmospheric nucleation and growth in the CLOUD experiment at CERN

    NASA Astrophysics Data System (ADS)

    Kirkby, Jasper; Cloud Collaboration

    2013-05-01

    Nucleation and growth of new particles in the atmosphere is thought to account for up to half of all cloud condensation nuclei. However the vapours and formation rates that underly this process are poorly understood, due both to the ultra low concentrations of participating vapours in the presence of high backgrounds and to the many sources of uncontrolled variability in the atmosphere. In consequence, laboratory measurements made under clean and precisely controlled conditions play an important role in identifying the vapours responsible and quantifying their associated nucleation and growth rates. The CLOUD experiment at CERN is studying the nucleation and growth of aerosol particles, and their interaction with clouds, in a 3 m stainless steel aerosol/cloud chamber. The experiment is optimised to study the influence of ions, for which the CERN Proton Synchrotron (PS) provides an adjustable source of 'cosmic rays'. Extraordinary care has been paid in the design and construction of CLOUD and its associated systems-gas, thermal, UV and electric field-to suppress contaminants at the technological limit. The unprecedented low contamination achieved in the CLOUD chamber has revealed that atmospheric nucleation and growth is sensitive to certain atmospheric vapours at mixing ratios of only a few parts-per-trillion by volume (pptv). Here we provide an overview of the design of CLOUD and its experimental programme over four years of operation at CERN.

  8. Nucleation and growth of nanoscaled one-dimensional materials

    NASA Astrophysics Data System (ADS)

    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.

  9. Thermodynamic and kinetic consistency of calculated binary nucleation rates

    SciTech Connect

    Wilemski, G.; Wyslouzil, B.E.

    1996-04-02

    To establish the accuracy and applicability of analytical expressions for the steady state rate of binary nucleation, we numerically solved the birth-death equations for the vapor-to-liquid transition. These calculations were performed using rate coefficients that are consistent with the principle of detailed balance and a new self-consistent form of the equilibrium distribution function for binary cluster concentrations. We found that the customary saddle point and growth path approximations are almost always valid and can fail only if the nucleating solution phase is significantly nonideal. For example, problems can arise when the vapor composition puts the system on the verge of partial liquid phase miscibility. When this occurs for comparable monomer impingement rates, nucleation still occurs through the saddle point, but the usual quadratic expansion for the cluster free energy is inadequate. When the two impingement rates differ significantly, however, the major particle flux may bypass the saddle point and cross a low ridge on the free energy surface. The dependence of the saddle point location on the gas phase composition is also important in initiating or terminating ridge crossing nucleation.

  10. The impact of carboxylic acids on ice nucleation

    NASA Astrophysics Data System (ADS)

    Weiss, F.; Baloh, P.; Grothe, H.

    2012-04-01

    Ice nucleation is a process which is not fully understood yet. Especially the influence of carboxylic acids has to be investigated. As shown by Pratt et al.[1] carboxylic acids are present in the troposphere and their influence on cloud formation is still unknown. Recent studies showed that pure soot aerosol is unable to nucleate ice and citric acid suppresses the nucleation to a certain extent in laboratory models.[2], [3] Therefore it is consequent to further investigate organic acids with different molecular masses and functional groups. Starting with oxalic acid as the smallest carboxylic acid, several other carboxylic acids with different molecular masses and functional groups have been investigated. Every sample has been observed by ESEM, XRD and optical Microscopy. The same preparation procedure has been applied to all samples to gain comparable results and reveal trends on nucleation abilities. [1] Pratt et al. "In situ detection of biological particles in cloud ice-crystals" Nature Geoscience, 2, 398-401, 2009 [2] O.Möhler et al., Meteorol.Z.14, 477, 2005 [3] B.J. Murray "Inhibition of ice crystallization in highly viscous aqueous organic acid droplets." Atmos.Chem.Phys., 8, 5423-5433, 2008

  11. Scaling properties of induction times in heterogeneous nucleation

    NASA Technical Reports Server (NTRS)

    Shneidman, Vitaly A.; Weinberg, Michael C.

    1991-01-01

    The heterogeneous-to-homogeneous induction time ratio is obtained as a function of the contact angle in the asymptotic limit of a high nucleation barrier. Model-dependent corrections to t(ind) are investigated, particularly in cases of the Turnbull-Fisher model used in numerical simulations by Greer et al. (1990).

  12. Turn nucleation perturbs amyloid β self-assembly and cytotoxicity.

    PubMed

    Doran, Todd M; Anderson, Elizabeth A; Latchney, Sarah E; Opanashuk, Lisa A; Nilsson, Bradley L

    2012-08-10

    The accumulation of senile plaques composed of amyloid β (Aβ) fibrils is a hallmark of Alzheimer's disease, although prefibrillar oligomeric species are believed to be the primary neurotoxic congeners in the pathogenesis of Alzheimer's disease. Uncertainty regarding the mechanistic relationship between Aβ oligomer and fibril formation and the cytotoxicity of these aggregate species persists. β-Turn formation has been proposed to be a potential rate-limiting step during Aβ fibrillogenesis. The effect of turn nucleation on Aβ self-assembly was probed by systematically replacing amino acid pairs in the putative turn region of Aβ (residues 24-27) with d-ProGly ((D)PG), an effective turn-nucleating motif. The kinetic, thermodynamic, and cytotoxic effects of these mutations were characterized. It was found that turn formation dramatically accelerated Aβ fibril self-assembly dependent on the site of turn nucleation. The cytotoxicity of the three (D)PG-containing Aβ variants was significantly lower than that of wild-type Aβ40, presumably due to decreased oligomer populations as a function of a more rapid progression to mature fibrils; oligomer populations were not eliminated, however, suggesting that turn formation is also a feature of oligomer structures. These results indicate that turn nucleation is a critical step in Aβ40 fibril formation.

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

    NASA Astrophysics Data System (ADS)

    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.

  14. Total sulphate vs. sulphuric acid monomer in nucleation studies

    NASA Astrophysics Data System (ADS)

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

    2014-10-01

    Sulphuric acid is known to be a key component for atmospheric nucleation. Precise determination of sulphuric acid concentration is crucial factor for prediction of nucleation rates and subsequent growth. In our study, we have noticed a substantial discrepancy between sulphuric acid monomer and total sulphate concentrations measured from the same source of sulphuric acid vapour. The discrepancy of about one to two orders of magnitude was found with similar formation rates. To investigate this discrepancy and its effect on nucleation, a method of thermally controlled saturator filled with pure sulphuric acid (97% wt.) for production of sulphuric acid vapour is introduced and tested. Sulphuric acid-water nucleation experiment was done using a laminar flow tube. Two independent methods of mass spectrometry and online ion chromatography were used for detecting sulphuric acid concentrations. The results are compared to our previous results, where a method of furnace was used to produce sulphuric acid vapour (Brus et al., 2010, 2011). Measured sulphuric acid concentrations are compared to theoretical prediction calculated using vapour pressure and a mixing law. The calculated prediction of sulphuric acid concentrations agrees very well with the measured values when total sulphate is considered. Sulphuric acid monomer concentration was found to be about two orders of magnitude lower than the prediction, but with similar temperature dependency as the prediction and the results obtained with ion chromatograph method. Formation rates agree well when compared to our previous results with both sulphuric acid detection and sulphuric acid production methods separately.

  15. Ion-induced nucleation of pure biogenic particles.

    PubMed

    Kirkby, Jasper; Duplissy, Jonathan; 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

    2016-05-26

    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 α-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 by quantum chemical calculations of the cluster binding energies of representative HOMs. Ion-induced nucleation of pure organic particles constitutes a potentially widespread source of aerosol particles in terrestrial environments with low sulfuric acid pollution. PMID:27225125

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

    NASA Astrophysics Data System (ADS)

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

    2002-07-01

    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.

  17. New Instrument INKA for Ice Nucleation and Growth Experiments

    NASA Astrophysics Data System (ADS)

    Schmitt, Thea; Levin, Ezra; Höhler, Kristina; Nadolny, Jens; Möhler, Ottmar; DeMott, Paul

    2015-04-01

    Microphysical processes in clouds, such as the formation and growth of ice crystals, significantly influence the weather and the climate. Particularly the transition from the supercooled water to the solid ice phase is of great relevance since ice formation initiates the formation of precipitation and thereby strongly affects the cloud structure and life time. However, the formulation and parameterization of these processes and further laboratory studies are needed to obtain quantitative information on the ice activity of various atmospheric aerosol species. Therefore, we have constructed and built a new continuous flow diffusion chamber (CFDC) called INKA (Ice Nucleation Instrument of the KArlsruhe Institut of Technology) to be used both in the AIDA laboratory for detailed studies of ice nucleation and growth processes and in field applications for measuring the temperature-dependent abundance of ice nucleating particles (INPs). The CFDC design was originally developed and theoretically described by Rogers et al. (1988). The main part of the new INKA instrument, the chamber, consists of two vertically-oriented, concentric tubes with a total length of 150 cm. Together with particle-free, dry sheath air, the sampled aerosol particles flow through the annular space between these two cylinders. The wall temperatures of the cylinders can be adjusted and the walls of the annular gap are coated with thin ice layers. The bottom part (about 50 cm) of the outer cylinder of INKA is separately cooled, which allows operation in two different modes: In the ice nucleation mode, the CFDC is operated with a nucleation and growth section, covering the upper 100 cm of its length, which exposes the aerosol particles to a defined temperature and supersaturation. The bottom part is the so called droplet evaporation section which allows the ice particles to grow to a detectable size on the expense of present droplets. In the ice growth mode, the full length of the cylinders is operated

  18. Transient nucleate pool boiling in microgravity: Some initial results

    NASA Technical Reports Server (NTRS)

    Merte, Herman, Jr.; Lee, H. S.; Ervin, J. S.

    1994-01-01

    Variable gravity provides an opportunity to test the understanding of phenomena which are considered to depend on buoyancy, such as nucleate pool boiling. The active fundamental research in nucleate boiling has sought to determine the mechanisms or physical processes responsible for its high effectiveness, manifested by the high heat flux levels possible with relatively low temperature differences. Earlier research on nucleate pool boiling at high gravity levels under steady conditions demonstrated quantitatively that the heat transfer is degraded as the buoyancy normal to the heater surfaced increases. Correspondingly, it was later shown, qualitatively for short periods of time only, that nucleate boiling heat transfer is enhanced as the buoyancy normal to the heater surface is reduced. It can be deduced that nucleate pool boiling can be sustained as a quasi-steady process provided that some means is available to remove the vapor generated from the immediate vicinity of the heater surface. One of the objectives of the research, the initial results of which are presented here, is to quantify the heat transfer associated with boiling in microgravity. Some quantitative results of nucleate pool boiling in high quality microgravity (a/g approximately 10(exp -5)) of 5s duration, obtained in an evacuated drop tower, are presented here. These experiments were conducted as precursors of longer term space experiments. A transient heating technique is used, in which the heater surface is a transparent gold film sputtered on a qua rtz substrate, simultaneously providing the mean surface temperature from resistance thermometry and viewing of the boiling process both from beneath and across the surface. The measurement of the transient mean heater surface temperature permits the computation, by numerical means, of the transient mean heat transfer coefficient. The preliminary data obtained demonstrates that a quasi-steady boiling process can occur in microgravity if the bulk

  19. Numerical Modeling of Plasmas in which Nanoparticles Nucleate and Grow

    NASA Astrophysics Data System (ADS)

    Agarwal, Pulkit

    Dusty plasmas refer to a broad category of plasmas. Plasmas such as argon-silane plasmas in which particles nucleate and grow are widely used in semiconductor processing and nanoparticle manufacturing. In such dusty plasmas, the plasma and the dust particles are strongly coupled to each other. This means that the presence of dust particles significantly affects the plasma properties and vice versa. Therefore such plasmas are highly complex and they involve several interesting phenomena like nucleation, growth, coagulation, charging and transport. Dusty plasma afterglow is equally complex and important. Especially, residual charge on dust particles carries special significance in several industrial and laboratory situations and it has not been well understood. A 1D numerical model was developed of a low-pressure capacitively-coupled plasma in which nanoparticles nucleate and grow. Polydispersity of particle size distributions can be important in such plasmas. Sectional method, which is well known in aerosol literature, was used to model the evolving particle size and charge distribution. The numerical model is transient and one-dimensional and self consistently accounts for nucleation, growth, coagulation, charging and transport of dust particles and their effect on plasma properties. Nucleation and surface growth rates were treated as input parameters. Results were presented in terms of particle size and charge distribution with an emphasis on importance of polydispersity in particle growth and dynamics. Results of numerical model were compared with experimental measurements of light scattering and light emission from plasma. Reasonable qualitative agreement was found with some discrepancies. Pulsed dusty plasma can be important for controlling particle production and/or unwanted particle deposition. In this case, it is important to understand the behavior of the particle cloud during the afterglow following plasma turn-off. Numerical model was modified to self

  20. A Comparative Study of Nucleation Parameterizations: 2. Three-Dimensional Model Application and Evaluation

    EPA Science Inventory

    Following the examination and evaluation of 12 nucleation parameterizations presented in part 1, 11 of them representing binary, ternary, kinetic, and cluster‐activated nucleation theories are evaluated in the U.S. Environmental Protection Agency Community Multiscale Air Quality ...

  1. Observing classical nucleation theory at work by monitoring phase transitions with molecular precision

    PubMed Central

    Sleutel, Mike; Lutsko, Jim; Van Driessche, Alexander E.S.; Durán-Olivencia, Miguel A.; Maes, Dominique

    2014-01-01

    It is widely accepted that many phase transitions do not follow nucleation pathways as envisaged by the classical nucleation theory. Many substances can traverse intermediate states before arriving at the stable phase. The apparent ubiquity of multi-step nucleation has made the inverse question relevant: does multistep nucleation always dominate single-step pathways? Here we provide an explicit example of the classical nucleation mechanism for a system known to exhibit the characteristics of multi-step nucleation. Molecular resolution atomic force microscopy imaging of the two-dimensional nucleation of the protein glucose isomerase demonstrates that the interior of subcritical clusters is in the same state as the crystalline bulk phase. Our data show that despite having all the characteristics typically associated with rich phase behaviour, glucose isomerase 2D crystals are formed classically. These observations illustrate the resurfacing importance of the classical nucleation theory by re-validating some of the key assumptions that have been recently questioned. PMID:25465441

  2. Ice Nucleation Properties of Amospherically Aged Biomass Burning Aerosol

    NASA Astrophysics Data System (ADS)

    Polen, M.; Lawlis, E.; Sullivan, R. C.

    2015-12-01

    Biomass burning can sometimes emit surprisingly active ice nucleating particles, though these emissions are not at all consistent between biomass fuel sources and burns. Soot from biomass combustion has been attributed to some but not all of the ice nucleating potential of biomass burning aerosol (BBA), while fossil fuel combustion soot emits very weak ice nucleants. The causes of the sometimes significant but variable ice nucleating ability of BBA are still largely unknown. BBA experiences significant atmospheric aging as the plume evolves and mixes with background air, yet almost no reports exploring the effects of atmospheric aging on the freezing properties of BBA have been made. We have performed some of the first experiments to determine the effects of simulated atmospheric aging on these ice nucleation properties, using a chamber reactor. The fresh and aged BBA was collected for subsequent droplet freezing array analysis using an impinger sampler to collect aerosol in water, and by deposition onto substrates in a MOUDI sampler. Droplets containing the chamber particles were then suspended in oil on a cold plate for freezing temperature spectrum measurement. Aging of Sawgrass flaming-phase combustion BBA by exposure to hydroxyl radicals (from H2O2 photolysis) enhanced the ice nucleation ability, observed by a shift to warmer droplet freezing temperatures by ~2-3°C. The changes in the aerosol's chemical composition during aging were observed using a laser ablation single-particle mass spectrometer and a soot-particle aerosol mass spectrometer. We will report our observations of the effects of other types of simulated aging (including photochemistry under high and low NOx conditions, dark ozonolysis, and nitric acid exposure) on Sawgrass and BBA from other grass and palm fuels.

  3. Homogenous Surface Nucleation of Solid Polar Stratospheric Cloud Particles

    NASA Technical Reports Server (NTRS)

    Tabazadeh, A.; Hamill, P.; Salcedo, D.; Gore, Warren J. (Technical Monitor)

    2002-01-01

    A general surface nucleation rate theory is presented for the homogeneous freezing of crystalline germs on the surfaces of aqueous particles. While nucleation rates in a standard classical homogeneous freezing rate theory scale with volume, the rates in a surface-based theory scale with surface area. The theory is used to convert volume-based information on laboratory freezing rates (in units of cu cm, seconds) of nitric acid trihydrate (NAT) and nitric acid dihydrate (NAD) aerosols into surface-based values (in units of sq cm, seconds). We show that a surface-based model is capable of reproducing measured nucleation rates of NAT and NAD aerosols from concentrated aqueous HNO3 solutions in the temperature range of 165 to 205 K. Laboratory measured nucleation rates are used to derive free energies for NAT and NAD germ formation in the stratosphere. NAD germ free energies range from about 23 to 26 kcal mole, allowing for fast and efficient homogeneous NAD particle production in the stratosphere. However, NAT germ formation energies are large (greater than 26 kcal mole) enough to prevent efficient NAT particle production in the stratosphere. We show that the atmospheric NAD particle production rates based on the surface rate theory are roughly 2 orders of magnitude larger than those obtained from a standard volume-based rate theory. Atmospheric volume and surface production of NAD particles will nearly cease in the stratosphere when denitrification in the air exceeds 40 and 78%, respectively. We show that a surface-based (volume-based) homogeneous freezing rate theory gives particle production rates, which are (not) consistent with both laboratory and atmospheric data on the nucleation of solid polar stratospheric cloud particles.

  4. A compact setup to study homogeneous nucleation and condensation

    NASA Astrophysics Data System (ADS)

    Karlsson, Mattias; Alxneit, Ivo; Rütten, Frederik; Wuillemin, Daniel; Tschudi, Hans Rudolf

    2007-03-01

    An experiment is presented to study homogeneous nucleation and the subsequent droplet growth at high temperatures and high pressures in a compact setup that does not use moving parts. Nucleation and condensation are induced in an adiabatic, stationary expansion of the vapor and an inert carrier gas through a Laval nozzle. The adiabatic expansion is driven against atmospheric pressure by pressurized inert gas its mass flow carefully controlled. This allows us to avoid large pumps or vacuum storage tanks. Because we eventually want to study the homogeneous nucleation and condensation of zinc, the use of carefully chosen materials is required that can withstand pressures of up to 106 Pa resulting from mass flow rates of up to 600 lN min-1 and temperatures up to 1200 K in the presence of highly corrosive zinc vapor. To observe the formation of droplets a laser beam propagates along the axis of the nozzle and the light scattered by the droplets is detected perpendicularly to the nozzle axis. An ICCD camera allows to record the scattered light through fused silica windows in the diverging part of the nozzle spatially resolved and to detect nucleation and condensation coherently in a single exposure. For the data analysis, a model is needed to describe the isentropic core part of the flow along the nozzle axis. The model must incorporate the laws of fluid dynamics, the nucleation and condensation process, and has to predict the size distribution of the particles created (PSD) at every position along the nozzle axis. Assuming Rayleigh scattering, the intensity of the scattered light can then be calculated from the second moment of the PSD.

  5. A compact setup to study homogeneous nucleation and condensation.

    PubMed

    Karlsson, Mattias; Alxneit, Ivo; Rütten, Frederik; Wuillemin, Daniel; Tschudi, Hans Rudolf

    2007-03-01

    An experiment is presented to study homogeneous nucleation and the subsequent droplet growth at high temperatures and high pressures in a compact setup that does not use moving parts. Nucleation and condensation are induced in an adiabatic, stationary expansion of the vapor and an inert carrier gas through a Laval nozzle. The adiabatic expansion is driven against atmospheric pressure by pressurized inert gas its mass flow carefully controlled. This allows us to avoid large pumps or vacuum storage tanks. Because we eventually want to study the homogeneous nucleation and condensation of zinc, the use of carefully chosen materials is required that can withstand pressures of up to 10(6) Pa resulting from mass flow rates of up to 600 l(N) min(-1) and temperatures up to 1200 K in the presence of highly corrosive zinc vapor. To observe the formation of droplets a laser beam propagates along the axis of the nozzle and the light scattered by the droplets is detected perpendicularly to the nozzle axis. An ICCD camera allows to record the scattered light through fused silica windows in the diverging part of the nozzle spatially resolved and to detect nucleation and condensation coherently in a single exposure. For the data analysis, a model is needed to describe the isentropic core part of the flow along the nozzle axis. The model must incorporate the laws of fluid dynamics, the nucleation and condensation process, and has to predict the size distribution of the particles created (PSD) at every position along the nozzle axis. Assuming Rayleigh scattering, the intensity of the scattered light can then be calculated from the second moment of the PSD.

  6. Palaeomagnetic field intensity variations suggest Mesoproterozoic inner-core nucleation.

    PubMed

    Biggin, A J; Piispa, E J; Pesonen, L J; Holme, R; Paterson, G A; Veikkolainen, T; Tauxe, L

    2015-10-01

    The Earth's inner core grows by the freezing of liquid iron at its surface. The point in history at which this process initiated marks a step-change in the thermal evolution of the planet. Recent computational and experimental studies have presented radically differing estimates of the thermal conductivity of the Earth's core, resulting in estimates of the timing of inner-core nucleation ranging from less than half a billion to nearly two billion years ago. Recent inner-core nucleation (high thermal conductivity) requires high outer-core temperatures in the early Earth that complicate models of thermal evolution. The nucleation of the core leads to a different convective regime and potentially different magnetic field structures that produce an observable signal in the palaeomagnetic record and allow the date of inner-core nucleation to be estimated directly. Previous studies searching for this signature have been hampered by the paucity of palaeomagnetic intensity measurements, by the lack of an effective means of assessing their reliability, and by shorter-timescale geomagnetic variations. Here we examine results from an expanded Precambrian database of palaeomagnetic intensity measurements selected using a new set of reliability criteria. Our analysis provides intensity-based support for the dominant dipolarity of the time-averaged Precambrian field, a crucial requirement for palaeomagnetic reconstructions of continents. We also present firm evidence for the existence of very long-term variations in geomagnetic strength. The most prominent and robust transition in the record is an increase in both average field strength and variability that is observed to occur between a billion and 1.5 billion years ago. This observation is most readily explained by the nucleation of the inner core occurring during this interval; the timing would tend to favour a modest value of core thermal conductivity and supports a simple thermal evolution model for the Earth. PMID:26450058

  7. Environmental Scanning Electron Microscopy of Ice Crystal Nucleation and Growth

    NASA Astrophysics Data System (ADS)

    Amaral, M.; Miller, A. L.; Magee, N. B.

    2012-12-01

    Ice crystal nucleation and growth are dual processes that can be studied uniquely through Environmental Scanning Electron Microscopy (ESEM). By utilizing differential pumping systems and a Peltier element to vary the vapor pressure and to achieve temperatures below the freezing point, respectively, it is possible to obtain supersaturated conditions relative to ice in the sample chamber of an Environmental Scanning Electron Microscope. Ice crystals were nucleated on a variety of atmospherically relevant substrates and grown in a pure water vapor environment in the chamber of a FEI-Quanta 200 ESEM. To initiate ice crystal nucleation, the Peltier element was set at a temperature between -10°C and -25°C, while the chamber water vapor pressure was adjusted to just below the frost point. Ice crystal nucleation and growth was then controlled by careful adjustments of chamber pressure and temperature, where high-magnification images of hexagonal ice crystals were acquired at nanoscale resolution. These images display prominent mesoscopic surface topography including linear strands, crevasses, islands, and steps. The surface features are seen to be ubiquitously present at all observed temperatures, at many supersaturated and subsaturated conditions, and on all crystal facets. Additionally, a pre-growth "shadow" resembling a dark spot sometimes appeared on areas of the sample stage immediately preceding ice crystal nucleation and growth. The observations represent the most highly magnified images of ice surfaces yet reported and significantly expand the range of ambient conditions where the features are conspicuous. New knowledge of the presence and characteristics of these features could transform the fundamental understanding of ice crystal growth kinetics and its physical parameterization in the context of atmospheric and cryospheric science. To the extent these observations are applicable to atmospheric ice, the results suggest that the radiative representation of ice

  8. Experimental and Theoretical Studies of Nucleation in Supercooled Liquid Silicon. Final Program Report

    SciTech Connect

    Im, J.

    2004-04-29

    The original objectives of the present program consisted of two specific nucleation-related research activities; (1) to provide a set of experimental data that will enable the quantitative examination of classical nucleation theory, and (2) to describe the phenomenon of nucleation by developing general expressions of nucleation that include both the thermal and athermal components and that correctly consider and incorporate the transient effects that arise from the nonstationary cluster distribution profile.

  9. Skills Center.

    ERIC Educational Resources Information Center

    Canter, Patricia; And Others

    The services of the Living Skills Center for the Visually Handicapped, a habilitative service for blind young adults, are described. It is explained that the Center houses its participants in their own apartments in a large complex and has served over 70 young people in 4 years. The evaluation section describes such assessment instruments as an…

  10. Purification and properties of an ice-nucleating protein from an ice-nucleating bacterium, Pantoea ananatis KUIN-3.

    PubMed

    Muryoi, Naomi; Matsukawa, Kenji; Yamade, Kazuhiro; Kawahara, Hidehisa; Obata, Hitoshi

    2003-01-01

    An ice-nucleating protein (INP) from the extracellular ice-nucleating matter (EIM) of Pantoea ananatis (Erwinia uredovora) KUIN-3 was purified and characterized. The EIM produced by the strain KUIN-3 was purified by ultrafiltration, sucrose density-gradient ultracentrifugation and gel filtration. The INP was purified using of column chromatography on hydroxyapatite and Superdex 200 in the nondenaturing detergent of 0.1% (w/v) Triton X-100. The purified INP was composed of one subunit of 117 kDa according to SDS-PAGE. It has become apparent that the INP was the ice-nucleating lipoglycoprotein based on the reaction of carbohydrate stain and lipid stain with the INP. It was inhibited by p-mercuribenzoate and N-bromosuccinimide. The activity of the INP gradually decreased from 65 degrees C. The pH stability was held between pH 7.0 and pH 11.0. The INP had a lower ice-nucleating temperature below pH 6.0. It has become apparent that the INP consisted of the class C structure in the EIM based on its freezing difference spectrum in D2O versus H2O. PMID:16233385

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

    NASA Astrophysics Data System (ADS)

    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

  12. Ultrasound assisted nucleation and growth characteristics of glycine polymorphs--a combined experimental and analytical approach.

    PubMed

    Renuka Devi, K; Raja, A; Srinivasan, K

    2015-05-01

    For the first time, the effect of ultrasound in the diagnostic frequency range of 1-10 MHz on the nucleation and growth characteristics of glycine has been explored. The investigation employing the ultrasonic interferometer was carried out at a constant insonation time over a wide range of relative supersaturation from σ=-0.09 to 0.76 in the solution. Ultrasound promotes only α nucleation and completely inhibits both the β and γ nucleation in the system. The propagation of ultrasound assisted mass transport facilitates nucleation even at very low supersaturation levels in the solution. The presence of ultrasound exhibits a profound effect on nucleation and growth characteristics in terms of decrease in induction period, increase in nucleation rate and decrease in crystal size than its absence in the solution. With an increase in the frequency of ultrasound, a further decrease in induction period, increase in nucleation rate and decrease in the size of the crystal is noticed even at the same relative supersaturation levels. The increase in the nucleation rate explains the combined dominating effects of both the ultrasound frequency and the supersaturation in the solution. Analytically, the nucleation parameters of the nucleated polymorph have been deduced at different ultrasonic frequencies based on the classical nucleation theory and correlations with the experimental results have been obtained. Structural affirmation of the nucleated polymorph has been ascertained by powder X-ray diffraction. PMID:25465875

  13. Studies in SiO(2)-based glass systems devitrifying by nucleation and growth

    NASA Astrophysics Data System (ADS)

    Krishnamurthy, Lakshmi Narayan

    Experimental and computational studies have been made on SiOsb2-based glasses crystallizing by homogenous nucleation (nucleation occurring randomly in space and time), heterogenous nucleation (nucleation occurring at specific sites through the glass), or non-polymorphic nucleation (nucleation occurring in systems where the composition of the crystallizing phase is different from that of the glass phase). A comprehensive computer model based on the classical theory of nucleation has been developed to simulate the process of crystallization occurring in differential thermal analysis experiments. The model, which takes into account the mode of the crystallization as well as the finite-size of the glass particles used in the measurements, is used to study homogenous and heterogenous crystallization of Lisb2O.2SiOsb2 glasses. The first measurements in any system of the composition dependence of the time-dependent nucleation rate are presented. An analysis of the steady-state nucleation rates in Nasb2O.2CaO.3SiOsb2 glasses made with different SiOsb2 concentrations show that the data are consistent with predictions from the classical theory of nucleation, assuming a composition-dependent interfacial energy. Further measurements of the transient nucleation rates resulting from multi-step annealing treatments support this claim, though small systematic differences suggest possible deviations from the kinetic model for nucleation.

  14. Protein crystal nucleation kinetics using relative light-scattering techniques: Center director's discretionary fund

    NASA Technical Reports Server (NTRS)

    Pusey, Marc Lee

    1989-01-01

    Light-scattering intensity measurements are a sensitive method for following changes in the hydrodynamic radius of particles in solution. The approach used in this report utilizes the light-scattering intensity ratios of a polydisperse to a monodisperse system. By numerically modeling the process, and fitting the model curves to the data, estimates have been obtained for the dimerization equilibrium constant, the dimer + dimer yields tetramer equilibrium constant, and the association rate constant for the dimerization process.

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

    NASA Astrophysics Data System (ADS)

    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

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

    NASA Astrophysics Data System (ADS)

    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

  17. Senior Centers

    MedlinePlus Videos and Cool Tools

    ... something many older adults would like to do as long as they can. Senior centers, adult day care, transportation, ... adults who live independently can go to find a variety of social and recreational activities. [Karen Albers] ...

  18. Review of nucleation and incipient boiling under pool and forced convection conditions

    NASA Technical Reports Server (NTRS)

    Merte, Herman, Jr.

    1987-01-01

    An overview of liquid-vapor nucleation is given. The result of thermodynamic equilibrium across curved liquid-vapor interfaces is presented. The extension of this to include the interaction with idealizations of surface cavities is made to demonstrate how superheat requirements for nucleation will be affected by surface roughness, flow velocity and buoyancy. Experimental measurements of high liquid superheats and nucleation delay times are presented as examples of homogeneous nucleation. Examples of nucleation and boiling on smooth glass substrates and on metal surfaces with various surface roughnesses are presented.

  19. Nucleation of holin domains and holes optimizes lysis timing of E. coli by phage λ

    NASA Astrophysics Data System (ADS)

    Ryan, Gillian; Rutenberg, Andrew

    2007-03-01

    Holin proteins regulate the precise scheduling of Escherichia coli lysis during infection by bacteriophage λ. Inserted into the host bacterium's inner membrane during infection, holins aggregate to form rafts and then holes within those rafts. We present a two-stage nucleation model of holin action, with the nucleation of condensed holin domains followed by the nucleation of holes within these domains. Late nucleation of holin rafts leads to a weak dependence of lysis timing on host cell size, though both nucleation events contribute equally to timing errors. Our simulations recover the accurate scheduling observed experimentally, and also suggest that phage-λ lysis of E.coli is optimized.

  20. Experimental studies of the vapor phase nucleation of refractory compounds. VI. The condensation of sodium.

    PubMed

    Martínez, Daniel M; Ferguson, Frank T; Heist, Richard H; Nuth, Joseph A

    2005-08-01

    In this paper we discuss the condensation of sodium vapor and the formation of a sodium aerosol as it occurs in a gas evaporation condensation chamber. A one-dimensional model describing the vapor transport to the vapor/aerosol interface was employed to determine the onset supersaturation, in which we assume the observed location of the interface is coincident with a nucleation rate maximum. We then present and discuss the resulting nucleation onset supersaturation data within the context of nucleation theory based on the liquid droplet model. Nucleation results appear to be consistent with a cesium vapor-to-liquid nucleation study performed in a thermal diffusion cloud chamber. PMID:16108655

  1. Homogeneous nucleation rates from the piston-expansion tube using a digital camera

    NASA Astrophysics Data System (ADS)

    Peters, Franz; Graßmann, Arne

    2000-08-01

    Homogeneous nucleation rates of n-pentanol in nitrogen are obtained from a piston-expansion tube (pex-tube) involving the nucleation pulse method which generates a limited number of nuclei that grow into droplets. The detection of the droplets is achieved by a new counting method developed on the basis of a CCD camera in combination with a laser light sheet. Nucleation rates between 104 and 109cm-3 s-1 are covered for the nucleation temperature 260 K. The rates are plotted as isotherms versus supersaturation. An influence of the initial expansion temperature on the nucleation rate is identified. Literature data from other expansion experiments agree with our finding.

  2. Coastal Center

    NASA Astrophysics Data System (ADS)

    The U.S. Geological Survey dedicated its new Center for Coastal Geology June 12 at the University of South Florida in St. Petersburg. Robert Halley leads the staff of nine USGS scientists studying coastal erosion and pollution and underwater mineral resources in cooperation with the university's Marine Science Department. Current research is on erosion along Lake Michigan and the Gulf Coast of Louisiana. The number of USGS scientists at the center should increase to 30 over five years.

  3. Impluse response experiments of secondary nucleation of potassium alum

    NASA Astrophysics Data System (ADS)

    Kubota, Noriaki; Sato, Tsutomu; Shimizu, Kenji

    1990-01-01

    The dynamic response of the number of secondary nuclei to an impulse caused by the mechanical impact on a seed crystal was measured in a continuously operated well-stirred vessel of 125 cm 3 working volume. The dynamic response curves show that two kinds of nuclei were produced by the impact; nuclei that were born just at the instant of impact and nuclei that were born after a delay. The former (named born nuclei) seem to be fragments of the seed crystal but the latter (delayed nuclei) are believed to be crystalline particles which precursors turned into after a delay. The response curves are well explained by a delayed-nucleation model assuming the existence of the two kinds of nuclei. The reason why secondary nucleation increases with increasing supersaturation is also discussed using this model.

  4. Crystal nucleation and glass formation in metallic alloy melts

    NASA Technical Reports Server (NTRS)

    Spaepen, F.

    1984-01-01

    Homogeneous nucleation, containerless solidification, and bulk formation of metallic glasses are discussed. Homogeneous nucleation is not a limiting factor for metallic glass formation at slow cooling rates if the reduced glass transition temperature is high enough. Such glasses can be made in bulk if heterogeneous nucleants are removed. Containerless processing eleminates potential sources of nucleants, but as drop tube experiments on the Pd-Si alloys show, the free surface may still be a very effective heterogeneous nucleant. Combination of etching and heating in vacuum or fluxing can be effective for cleaning fairly large ingots of nucleants. Reduced gravity processing has a potentially useful role in the fluxing technique, for example to keep large metallic ingots surrounded by a low density, low fluidity flux if this proved difficult under ground conditions. For systems where heterogeneous nucleants in the bulk of the ingot need gravity to segregate to the flux-metal interface, reduced gravity processing may not be appropriate for bulk glass formation.

  5. Nucleation and spreading of a heterochromatic domain in fission yeast

    PubMed Central

    Obersriebnig, Michaela J.; Pallesen, Emil M. H.; Sneppen, Kim; Trusina, Ala; Thon, Geneviève

    2016-01-01

    Outstanding questions in the chromatin field bear on how large heterochromatin domains are formed in space and time. Positive feedback, where histone-modifying enzymes are attracted to chromosomal regions displaying the modification they catalyse, is believed to drive the formation of these domains; however, few quantitative studies are available to assess this hypothesis. Here we quantified the de novo establishment of a naturally occurring ∼20-kb heterochromatin domain in fission yeast through single-cell analyses, measuring the kinetics of heterochromatin nucleation in a region targeted by RNAi and its subsequent expansion. We found that nucleation of heterochromatin is stochastic and can take from one to ten cell generations. Further silencing of the full region takes another one to ten generations. Quantitative modelling of the observed kinetics emphasizes the importance of local feedback, where a nucleosome-bound enzyme modifies adjacent nucleosomes, combined with a feedback where recruited enzymes can act at a distance. PMID:27167753

  6. Bypass transition and spot nucleation in boundary layers

    NASA Astrophysics Data System (ADS)

    Kreilos, Tobias; Khapko, Taras; Schlatter, Philipp; Duguet, Yohann; Henningson, Dan S.; Eckhardt, Bruno

    2016-08-01

    The spatiotemporal aspects of the transition to turbulence are considered in the case of a boundary-layer flow developing above a flat plate exposed to free-stream turbulence. Combining results on the receptivity to free-stream turbulence with the nonlinear concept of a transition threshold, a physically motivated model suggests a spatial distribution of spot nucleation events. To describe the evolution of turbulent spots a probabilistic cellular automaton is introduced, with all parameters directly obtained from numerical simulations of the boundary layer. The nucleation rates are then combined with the cellular automaton model, yielding excellent quantitative agreement with the statistical characteristics for different free-stream turbulence levels. We thus show how the recent theoretical progress on transitional wall-bounded flows can be extended to the much wider class of spatially developing boundary-layer flows.

  7. Predictions of nucleation theory applied to Ehrenfest thermodynamic transitions

    NASA Technical Reports Server (NTRS)

    Barker, R. E., Jr.; Campbell, K. W.

    1984-01-01

    A modified nucleation theory is used to determine a critical nucleus size and a critical activation-energy barrier for second-order Ehrenfest thermodynamic transitions as functions of the degree of undercooling, the interfacial energy, the heat-capacity difference, the specific volume of the transformed phase, and the equilibrium transition temperature. The customary approximations of nucleation theory are avoided by expanding the Gibbs free energy in a Maclaurin series and applying analytical thermodynamic expressions to evaluate the expansion coefficients. Nonlinear correction terms for first-order-transition calculations are derived, and numerical results are presented graphically for water and polystyrene as examples of first-order and quasi-second-order transitions, respectively.

  8. Application of scaled nucleation theory to metallic vapor condensation

    NASA Astrophysics Data System (ADS)

    Martínez, Daniel M.; Ferguson, Frank T.; Heist, Richard H.; Nuth, Joseph A.

    2001-07-01

    In this paper we report that scaled nucleation theory (SNT) can describe moderately well the observed nucleation behavior of a significant number of refractory materials if a more appropriate value of a quantity commonly referred to as the excess surface entropy is used. With the availability of more reliable critical point and liquid property data, we are better able to calculate this quantity and we find that for refractory materials it can be as small as one half to one third the quantity traditionally used in its approximation. As a result of using more accurate values, we find considerably better agreement between SNT and experiment than what was originally determined. We also explain why using surface tension slope information to determine the excess surface entropy can lead to substantial errors in the SNT supersaturation prediction.

  9. Identification of ice nucleation active sites on feldspar dust particles.

    PubMed

    Zolles, Tobias; Burkart, Julia; Häusler, Thomas; Pummer, Bernhard; Hitzenberger, Regina; Grothe, Hinrich

    2015-03-19

    Mineral dusts originating from Earth's crust are known to be important atmospheric ice nuclei. In agreement with earlier studies, feldspar was found as the most active of the tested natural mineral dusts. Here we investigated in closer detail the reasons for its activity and the difference in the activity of the different feldspars. Conclusions are drawn from scanning electron microscopy, X-ray powder diffraction, infrared spectroscopy, and oil-immersion freezing experiments. K-feldspar showed by far the highest ice nucleation activity. Finally, we give a potential explanation of this effect, finding alkali-metal ions having different hydration shells and thus an influence on the ice nucleation activity of feldspar surfaces. PMID:25584435

  10. Toxicity of smoke to epiphytic ice nucleation-active bacteria.

    PubMed

    Zagory, D; Lindow, S E; Parmeter, J R

    1983-07-01

    Wheat straw smoke aerosols and liquid smoke condensates reduced significantly both the viability and the ice-nucleating activity of Pseudomonas syringae pv. syringae and Erwinia herbicola in vitro and on leaf surfaces in vivo. Highly significant reductions in numbers of bacterial ice nuclei on the surface of both corn and almond were observed after exposure to smoke aerosols. At -5 degrees C, frost injury to corn seedlings colonized by ice nucleation-active bacteria was reduced after exposure to smoke aerosols. Effects on -9 degrees C ice nuclei, although significant, were less than on ice nuclei active at -5 degrees C. These results suggest that smoke from wildfires or smudge pots may reduce plant frost susceptibility and sources of ice nuclei important in other natural processes under some conditions. PMID:16346333

  11. Nucleation and spreading of a heterochromatic domain in fission yeast.

    PubMed

    Obersriebnig, Michaela J; Pallesen, Emil M H; Sneppen, Kim; Trusina, Ala; Thon, Geneviève

    2016-01-01

    Outstanding questions in the chromatin field bear on how large heterochromatin domains are formed in space and time. Positive feedback, where histone-modifying enzymes are attracted to chromosomal regions displaying the modification they catalyse, is believed to drive the formation of these domains; however, few quantitative studies are available to assess this hypothesis. Here we quantified the de novo establishment of a naturally occurring ∼20-kb heterochromatin domain in fission yeast through single-cell analyses, measuring the kinetics of heterochromatin nucleation in a region targeted by RNAi and its subsequent expansion. We found that nucleation of heterochromatin is stochastic and can take from one to ten cell generations. Further silencing of the full region takes another one to ten generations. Quantitative modelling of the observed kinetics emphasizes the importance of local feedback, where a nucleosome-bound enzyme modifies adjacent nucleosomes, combined with a feedback where recruited enzymes can act at a distance. PMID:27167753

  12. Nucleation of the diamond phase in aluminium-solid solutions

    NASA Technical Reports Server (NTRS)

    Hornbogen, E.; Mukhopadhyay, A. K.; Starke, E. A., Jr.

    1993-01-01

    Precipitation was studied from fcc solid solutions with silicon, germanium, copper and magnesium. Of all these elements only silicon and germanium form diamond cubic (DC) precipitates in fcc Al. Nucleation of the DC structure is enhanced if both types of atom are dissolved in the fcc lattice. This is interpreted as due to atomic size effects in the prenucleation stage. There are two modes of interference of fourth elements with nucleation of the DC phase in Al + Si, Ge. The formation of the DC phase is hardly affected if the atoms (for example, copper) are rejected from the (Si, Ge)-rich clusters. If additional types of atom are attracted by silicon and/or germanium, DC nuclei are replaced by intermetallic compounds (for example Mg2Si).

  13. Quantum Nucleation of Phase Slips in 1-d Superfluids

    NASA Astrophysics Data System (ADS)

    Arovas, Daniel

    1998-03-01

    The rate for quantum nucleation of phase slips past an impurity in a one-dimensional superfluid is computed. Real time evolution of the nonlinear Schrödinger equation shows that there is a critical velocity vc below which solutions are time-independent [1,2]; this is the regime of quantum phase slip nucleation. We start with the Gross-Pitaevskii model in the presence of an impurity potential, and derive the Euclidean action for a space-time vortex-antivortex pair, which describes a phase slip event. The action is computed as a function of the superfluid velocity v and the impurity potential width and depth.l [1] V. Hakim, Phys. Rev. E 55, 2835 (1997).l [1] J. A. Freire, D. P. Arovas, and H. Levine, Phys. Rev. Lett (in press, 1997).l

  14. Identification of Ice Nucleation Active Sites on Feldspar Dust Particles

    PubMed Central

    2015-01-01

    Mineral dusts originating from Earth’s crust are known to be important atmospheric ice nuclei. In agreement with earlier studies, feldspar was found as the most active of the tested natural mineral dusts. Here we investigated in closer detail the reasons for its activity and the difference in the activity of the different feldspars. Conclusions are drawn from scanning electron microscopy, X-ray powder diffraction, infrared spectroscopy, and oil-immersion freezing experiments. K-feldspar showed by far the highest ice nucleation activity. Finally, we give a potential explanation of this effect, finding alkali-metal ions having different hydration shells and thus an influence on the ice nucleation activity of feldspar surfaces. PMID:25584435

  15. Crystallization in supercooled liquid Cu: Homogeneous nucleation and growth

    SciTech Connect

    E, J. C.; Wang, L.; Luo, S. N.; Cai, Y.; Wu, H. A.

    2015-02-14

    Homogeneous nucleation and growth during crystallization of supercooled liquid Cu are investigated with molecular dynamics simulations, and the microstructure is characterized with one- and two-dimensional x-ray diffraction. The resulting solids are single-crystal or nanocrystalline, containing various defects such as stacking faults, twins, fivefold twins, and grain boundaries; the microstructure is subject to thermal fluctuations and extent of supercooling. Fivefold twins form via sequential twinning from the solid-liquid interfaces. Critical nucleus size and nucleation rate at 31% supercooling are obtained from statistical runs with the mean first-passage time and survival probability methods, and are about 14 atoms and 10{sup 32} m{sup −3}s{sup −1}, respectively. The bulk growth dynamics are analyzed with the Johnson-Mehl-Avrami law and manifest three stages; the Avrami exponent varies in the range of 1–19, which also depends on thermal fluctuations and supercooling.

  16. Nucleation and Convection Effects in Protein Crystal Growth

    NASA Technical Reports Server (NTRS)

    Vekilow, Peter G.

    1998-01-01

    Our work under this grant has significantly contributed to the goals of the NASA supported protein crystallization program. We have achieved the main objectives of the proposed work, as outlined in the original proposal: (1) We have provided important insight into protein nucleation and crystal growth mechanisms to facilitate a rational approach to protein crystallization; (2) We have delineated the factors that currently limit the x-ray diffraction resolution of protein crystals, and their correlation to crystallization conditions; (3) We have developed novel technologies to study and monitor protein crystal nucleation and growth processes, in order to increase the reproducibility and yield of protein crystallization. We have published 17 papers in peer-reviewed scientific journals and books and made more than 15 invited and 9 contributed presentations of our results at international and national scientific meetings.

  17. Binary nucleation rates for ethanol/water mixtures in supersonic Laval nozzles: analyses by the first and second nucleation theorems.

    PubMed

    Tanimura, Shinobu; Pathak, Harshad; Wyslouzil, Barbara E

    2013-11-01

    We performed pressure trace measurements and small angle x-ray scattering measurements to determine the vapor-liquid nucleation rates of EtOH/H2O mixtures including pure EtOH and pure H2O in two supersonic Laval nozzles with different expansion rates. The nucleation rates varied from 0.9 × 10(17) to 16 × 10(17) cm(-3) s(-1) over the temperature range of 210 K to 230 K, EtOH activity range of 0 to 11.6, and H2O activity range of 0 to 124. The first and second nucleation theorems were applied to the nucleation rates to estimate the sizes, compositions, and excess energies of the critical clusters. The critical clusters contained from 4 to 15 molecules for pure H2O and EtOH/H2O clusters, and from 16 to 23 molecules for pure EtOH clusters. Comparing the excess energies of the pure H2O critical clusters with the results of a quantum-chemistry calculation suggested that the pre-factor of the theoretical nucleation rate is almost constant regardless of the monomer concentration. One possible explanation for this result is that cooling of the critical clusters limits the nucleation rate under the highly supersaturated conditions. The results of the analyses also yielded the relation between the surface energy and the composition of the critical clusters, where the latter are predicted to consist only of surface molecules. Applying this relationship to the EtOH/H2O bulk liquid mixtures, we estimated the EtOH mole fraction in the surface layer and found it is higher than that derived from the surface tension based on the Gibbs adsorption equation when the EtOH mole fraction in the liquid is higher than about 0.2 mol/mol. This discrepancy was attributed to the existence of the EtOH depletion layer just below the surface layer of the liquid. PMID:24206302

  18. Binary nucleation rates for ethanol/water mixtures in supersonic Laval nozzles: Analyses by the first and second nucleation theorems

    SciTech Connect

    Tanimura, Shinobu; Pathak, Harshad; Wyslouzil, Barbara E.

    2013-11-07

    We performed pressure trace measurements and small angle x-ray scattering measurements to determine the vapor-liquid nucleation rates of EtOH/H{sub 2}O mixtures including pure EtOH and pure H{sub 2}O in two supersonic Laval nozzles with different expansion rates. The nucleation rates varied from 0.9 × 10{sup 17} to 16 × 10{sup 17} cm{sup −3} s{sup −1} over the temperature range of 210 K to 230 K, EtOH activity range of 0 to 11.6, and H{sub 2}O activity range of 0 to 124. The first and second nucleation theorems were applied to the nucleation rates to estimate the sizes, compositions, and excess energies of the critical clusters. The critical clusters contained from 4 to 15 molecules for pure H{sub 2}O and EtOH/H{sub 2}O clusters, and from 16 to 23 molecules for pure EtOH clusters. Comparing the excess energies of the pure H{sub 2}O critical clusters with the results of a quantum-chemistry calculation suggested that the pre-factor of the theoretical nucleation rate is almost constant regardless of the monomer concentration. One possible explanation for this result is that cooling of the critical clusters limits the nucleation rate under the highly supersaturated conditions. The results of the analyses also yielded the relation between the surface energy and the composition of the critical clusters, where the latter are predicted to consist only of surface molecules. Applying this relationship to the EtOH/H{sub 2}O bulk liquid mixtures, we estimated the EtOH mole fraction in the surface layer and found it is higher than that derived from the surface tension based on the Gibbs adsorption equation when the EtOH mole fraction in the liquid is higher than about 0.2 mol/mol. This discrepancy was attributed to the existence of the EtOH depletion layer just below the surface layer of the liquid.

  19. Did template-directed nucleation precede molecular replication?

    NASA Technical Reports Server (NTRS)

    Orgel, Leslie E.

    1986-01-01

    It is proposed that mononucleotides incorporated into the surfaces of microcrystals of inorganic phosphates such as hydroxyapatite can act as templates to assemble complementary mononucleotides from solution, and that the phosphate groups of the assembled nucleotides can facilitate nucleation of a second hydroxyapatite crystal. This would provide a mechanism of replication that is subject to natural selection. The possible role of a replicating system of this kind in the origins of life on the earth is discussed.

  20. Method and apparatus for nucleating the crystallization of undercooled materials

    DOEpatents

    Benson, David K.; Barret, Peter F.

    1989-01-01

    A method of storing and controlling a release of latent heat of transition of a phase-change material is disclosed. The method comprises trapping a crystallite of the material between two solid objects and retaining it there under high pressure by applying a force to press the two solid objects tightly together. A crystallite of the material is exposed to a quantity of the material that is in a supercooled condition to nucleate the crystallization of the supercooled material.

  1. Alteration of Heterogeneous Ice Nucleation Properties Induced by Particle Aging

    NASA Astrophysics Data System (ADS)

    Sullivan, R. C.; Polen, M.; Beydoun, H.; Lawlis, E.; Ahern, A.; Jahn, L.; Hill, T. C. J.

    2015-12-01

    Aerosol particles that can serve as ice nuclei frequently experience rapid and extensive chemical aging during atmospheric transport. This is known to significantly alter some ice nucleation modes of the few types of ice nucleation particle systems where aging effects have been simulated, such as for mineral dust. Yet much of our understanding of atmospheric particle freezing properties is derived from measurements of fresh or unaged particles. We know almost nothing regarding how atmospheric aging might alter the freezing properties of biomass burning aerosol or biological particle nucleants. We have investigated the effects of simulated aging using a chamber reactor on the heterogeneous ice nucleation properties of biomass burning aerosol (BBA) and ice-active bacteria particles. Some types of aging were found to enhance the freezing ability of BBA, exhibited as a shift in a portion of the droplet freezing curve to warmer temperatures by a few °C. Ice-active bacteria were found to consistently loose their most ice-active nucleants after repeated aging cycles. The bacterial systems always retained significantly efficient ice active sites that still allowed them to induce freezing at mild/warm temperatures, despite this decrease in freezing ability. A comprehensive series of online single-particle mass spectrometry and offline spectromicroscopic analysis of individual particles was used to determine how the aging altered the aerosol's composition, and gain mechanistic insights into how this in turn altered the freezing properties. Our new ice nucleation framework that uses a continuous distribution of ice active site ability (contact angle) was used to interpret the droplet freezing spectra and understand how aging alters the internal and external variability, and rigidity, of the ice active sites.

  2. Non-extensive treatment of surface nucleation on glass particles

    NASA Astrophysics Data System (ADS)

    Nascimento, Marcio Luis Ferreira

    2012-12-01

    Experimental data of phase transformation kinetics was used to fit a new model based on a non-extensive formalism derived from Tsallis thermostatistics and another based on the Johnson-Mehl-Avrami-Yerofeyev-Kolmogorov (JMAYK) theory. For this we considered the same experimental parameters such as crystal geometric factor g, the density of nucleation sites, NS and crystal growth rates U on glass powders. The kinetics of nucleation and growth of diopside crystals (MgOṡCaOṡ2SiO2) on the glass surface at 825 °C (Tg˜727 °C) were studied. Treatments for sinter-crystallization were performed in compacts of diopside glass particles by varying the treatment time. The crystallized fraction of the samples subjected to such treatments, which develop from the particles’ surface toward their volume, was characterized by means of optical microscopy and X-ray diffraction. The two models were then fitted to the measured crystallized fraction data and compared to each other. It was found that surface nucleation occurs very rapidly from a random number of active sites. The JMAYK theory describes the case of fast heterogeneous nucleation from a constant number of sites on the glass surface. The Tsallis approach is better than the JMAYK model considering that the q factor equals 1.268±0.062 and does not require taking into account the change in crystallization mode from three dimensional to one dimensional as JMAYK predicts, and this is advantageous. Furthermore, Tsallis thermostatistics contains the Austin-Rickett model as a special and limiting case study for this system. A generalized Avrami plot is also presented.

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

    NASA Astrophysics Data System (ADS)

    Yu, F.; Luo, G.; Liu, X.; Easter, R. C.; Ma, X.; Ghan, S. J.

    2012-12-01

    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.

  4. A marine biogenic source of atmospherically relevant ice nucleating particles

    NASA Astrophysics Data System (ADS)

    Wilson, Theodore W.; Ladino, Luis A.; Alpert, Peter A.; Chance, Rosie; Whale, Thomas F.; Vergara Temprado, Jesús; Burrows, Susannah M.; Breckels, Mark N.; Kilthau, Wendy P.; Browse, Jo; Bertram, Allan K.; Miller, Lisa A.; Carpenter, Lucy J.; Hamilton, Jacqui F.; Carslaw, Kenneth S.; Brooks, Ian M.; Abbatt, Jonathan P. D.; Aller, Josephine Y.; Knopf, Daniel A.; Murray, Benjamin J.

    2016-04-01

    There are limited observations describing marine sources of ice nucleating particles (INPs), despite sea spray aerosol being one of the dominant sources of atmospheric particles globally. Evidence indicates that some marine aerosol particles act as INPs, but the source of these particles is unclear. The sea surface microlayer is enriched in surface active organic material representative of that found in sub-micron sea-spray aerosol. We show that the sea surface microlayer is enriched in INPs that nucleate ice under conditions pertinent to both high-altitude ice clouds and low to mid-altitude mixed-phase clouds. The INPs pass through 0.2 μm pore filters, are heat sensitive and spectroscopic analysis indicates the presence of material consistent with phytoplankton exudates. Mass spectrometric analysis of solid phase extracted dissolved organic material from microlayer and sub-surface water samples showed that the relative abundance of certain ions correlated with microlayer ice nucleation activity. However, these ions were not themselves directly responsible for ice nucleation. We propose that material associated with phytoplankton exudates is a candidate for the observed activity of the microlayer samples. We show that laboratory produced exudate from a ubiquitous marine diatom contains INPs despite its separation from diatom cells. Finally we use a parameterisation of our field data to estimate the atmospheric INP contribution from primary marine organic emissions using a global model and test the model against existing INP measurements in the remote oceans. We find that biogenic marine INPs can be dominant in remote marine environments, such as the Southern Ocean.

  5. Electrochemical Nucleation of Stable N2 Nanobubbles at Pt Nanoelectrodes.

    PubMed

    Chen, Qianjin; Wiedenroth, Hilke S; German, Sean R; White, Henry S

    2015-09-23

    Exploring the nucleation of gas bubbles at interfaces is of fundamental interest. Herein, we report the nucleation of individual N2 nanobubbles at Pt nanodisk electrodes (6–90 nm) via the irreversible electrooxidation of hydrazine (N2H4 → N2 + 4H(+) + 4e(–)). The nucleation and growth of a stable N2 nanobubble at the Pt electrode is indicated by a sudden drop in voltammetric current, a consequence of restricted mass transport of N2H4 to the electrode surface following the liquid-to-gas phase transition. The critical surface concentration of dissolved N2 required for nanobubble nucleation, CN2,critical(s), obtained from the faradaic current at the moment just prior to bubble formation, is measured to be ∼0.11 M and is independent of the electrode radius and the bulk N2H4 concentration. Our results suggest that the size of stable gas bubble nuclei depends only on the local concentration of N2 near the electrode surface, consistent with previously reported studies of the electrogeneration of H2 nanobubbles. CN2,critical(s) is ∼160 times larger than the N2 saturation concentration at room temperature and atmospheric pressure. The residual current for N2H4 oxidation after formation of a stable N2 nanobubble at the electrode surface is proportional to the N2H4 concentration as well as the nanoelectrode radius, indicating that the dynamic equilibrium required for the existence of a stable N2 nanobubble is determined by N2H4 electrooxidation at the three phase contact line.

  6. Magnetostatic Effects in the Nucleation of Rare Earth Ferromagnetic Phases

    NASA Astrophysics Data System (ADS)

    Durfee, C. S.; Flynn, C. P.

    2001-07-01

    It has been reported that superheating, supercooling, and explosive kinetics coupled to other degrees of freedom occur at the ferromagnetic transitions of Er and Dy, and that metastable phases occur during the transition kinetics of Er. We explain these observations in terms of magnetostatic energy, which requires highly eccentric nuclei in the homogeneous nucleation of magnetic transitions in heavy rare earths. The magnetostatics favor transitions through ferrimagnetic intermediaries. The unusual kinetics derive from effective spin lattice relaxation.

  7. Magnetostatic Effects in the Nucleation of Rare Earth Ferromagnetic Phases

    SciTech Connect

    Durfee, C. S.; Flynn, C. P.

    2001-07-30

    It has been reported that superheating, supercooling, and explosive kinetics coupled to other degrees of freedom occur at the ferromagnetic transitions of Er and Dy, and that metastable phases occur during the transition kinetics of Er. We explain these observations in terms of magnetostatic energy, which requires highly eccentric nuclei in the homogeneous nucleation of magnetic transitions in heavy rare earths. The magnetostatics favor transitions through ferrimagnetic intermediaries. The unusual kinetics derive from effective spin lattice relaxation.

  8. Production of organic micro-crystals by using templated crystallization as nucleation trigger

    NASA Astrophysics Data System (ADS)

    Yamamoto, Hirokuni; Takiyama, Hiroshi

    2013-06-01

    Fine monomodal crystalline particles are required in many fields such as pharmaceuticals and fine chemicals. In this study, the effect of template at the air/solution interface on the nucleation phenomenon was investigated. And the relationship between the nucleation time and the time at which the template interfaces were introduced into the supersaturated solution became clear, and the nucleation phenomenon of templated crystallization was also investigated. If the time of nucleation can be controlled by using template effects, monomodal crystalline particles can also be produced. The glycine- water-L-leucine (template compound) system was used. The air bubble insertion experiments and nucleation and growth experiments at re-created air/solution interface were carried out. As a result, the nucleation time after the template interface was introduced into the supersaturated solution was important for controlling size distribution. The formation of new template interface into the supersaturated solution acted as the nucleation trigger which induced controlled nucleation. By using this nucleation trigger, monomodal crystalline particles were obtained at the air/solution interface. By collecting crystalline particles immediately after nucleation was induced by nucleation trigger, submicron-order particles were obtained.

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

    PubMed

    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. PMID:23091030

  10. Thermodynamics and Kinetics of Prenucleation Clusters, Classical and Non-Classical Nucleation

    PubMed Central

    Zahn, Dirk

    2015-01-01

    Recent observations of prenucleation species and multi-stage crystal nucleation processes challenge the long-established view on the thermodynamics of crystal formation. Here, we review and generalize extensions to classical nucleation theory. Going beyond the conventional implementation as has been used for more than a century now, nucleation inhibitors, precursor clusters and non-classical nucleation processes are rationalized as well by analogous concepts based on competing interface and bulk energy terms. This is illustrated by recent examples of species formed prior to/instead of crystal nucleation and multi-step nucleation processes. Much of the discussed insights were obtained from molecular simulation using advanced sampling techniques, briefly summarized herein for both nucleation-controlled and diffusion-controlled aggregate formation. PMID:25914369

  11. Nucleation and growth of cracks in vitreous-bonded aluminum oxide at elevated temperatures

    SciTech Connect

    Jakus, K.; Wiederhorn, S.M.; Hockey, B.J.

    1986-10-01

    The nucleation and growth of cracks was studied at elevated temperatures on a grade of vitreous-bonded aluminium oxide that contained approx. =8 vol% glass at the grain boundaries. Cracks were observed to nucleate within the vitreous phase, close to the tensile surface of the flexural test specimens used in these experiments. Crack nucleation occurred at a strain of approx. =0.08% to 0.12% which corresponded to a crack nucleation time of approx. =35% of the time to failure by creep rupture. Once nucleated, cracks propagated along grain boundaries, as long as the stress for crack propagation was maintained. The crack velocity for cracks that were nucleated by the creep process was found to be linearly proportional to the apparent stress intensity factor, whereas for cracks that were nucleated by indentation, the crack velocity was proportional to the fourth power of the apparent stress intensity factor.

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

    PubMed

    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.

  13. Homogeneous nucleation rates of n-pentanol in nitrogen measured in a piston-expansion tube

    NASA Astrophysics Data System (ADS)

    Graßmann, A.; Peters, F.

    2000-10-01

    Homogeneous nucleation rates of n-pentanol in nitrogen are presented. They are obtained from a piston-expansion tube (pex-tube) involving the nucleation pulse method which generates a limited number of nuclei that grow into droplets. The detection of the droplets is achieved by a new counting method developed on the basis of a CCD camera in combination with a laser light sheet. Nucleation rates between 104 and 109cm-3 s-1 are covered for three nucleation temperatures 250, 260, and 270 K. The rates are plotted as isotherms vs supersaturation. Influence of the initial expansion temperature and the nucleation pressure on the nucleation rate is identified. Comparison with results available in literature and classical nucleation theory (CNT) is provided.

  14. A quantitative parameter-free prediction of simulated crystal nucleation times

    SciTech Connect

    Aga, Rachel S; Morris, James R; Hoyt, Jeffrey John; Mendelev, Mikhail I.

    2006-01-01

    We present direct comparisons between simulated crystal-nucleation times and theoretical predictions using a model of aluminum, and demonstrate that a quantitative prediction can be made. All relevant thermodynamic properties of the system are known, making the agreement of our simulation data with nucleation theories free of any adjustable parameters. The role of transient nucleation is included in the classical nucleation theory approach, and shown to be necessary to understand the observed nucleation times. The calculations provide an explanation on why nucleation is difficult to observe in simulations at moderate undercoolings. Even when the simulations are significantly larger than the critical nucleus, and when simulation times are sufficiently long, at moderate undercoolings the small concentration of critical nuclei makes the probability of the nucleation low in molecular dynamics simulations.

  15. Simulation studies of nucleation of ferroelectric polarization reversal.

    SciTech Connect

    Brennecka, Geoffrey L.; Winchester, Benjamin Michael

    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.

  16. Activation energy paths for graphene nucleation and growth on Cu.

    PubMed

    Kim, HoKwon; Mattevi, Cecilia; Calvo, M Reyes; Oberg, Jenny C; Artiglia, Luca; Agnoli, Stefano; Hirjibehedin, Cyrus F; Chhowalla, Manish; Saiz, Eduardo

    2012-04-24

    The synthesis of wafer-scale single crystal graphene remains a challenge toward the utilization of its intrinsic properties in electronics. Until now, the large-area chemical vapor deposition of graphene has yielded a polycrystalline material, where grain boundaries are detrimental to its electrical properties. Here, we study the physicochemical mechanisms underlying the nucleation and growth kinetics of graphene on copper, providing new insights necessary for the engineering synthesis of wafer-scale single crystals. Graphene arises from the crystallization of a supersaturated fraction of carbon-adatom species, and its nucleation density is the result of competition between the mobility of the carbon-adatom species and their desorption rate. As the energetics of these phenomena varies with temperature, the nucleation activation energies can span over a wide range (1-3 eV) leading to a rational prediction of the individual nuclei size and density distribution. The growth-limiting step was found to be the attachment of carbon-adatom species to the graphene edges, which was independent of the Cu crystalline orientation.

  17. Actin nucleators in the nucleus: an emerging theme.

    PubMed

    Weston, Louise; Coutts, Amanda S; La Thangue, Nicholas B

    2012-08-01

    Actin is an integral component of the cytoskeleton, forming a plethora of macromolecular structures that mediate various cellular functions. The formation of such structures relies on the ability of actin monomers to associate into polymers, and this process is regulated by actin nucleation factors. These factors use monomeric actin pools at specific cellular locations, thereby permitting rapid actin filament formation when required. It has now been established that actin is also present in the nucleus, where it is implicated in chromatin remodelling and the regulation of eukaryotic gene transcription. Notably, the presence of typical actin filaments in the nucleus has not been demonstrated directly. However, studies in recent years have provided evidence for the nuclear localisation of actin nucleation factors that promote cytoplasmic actin polymerisation. Their localisation to the nucleus suggests that these proteins mediate collaboration between the cytoskeleton and the nucleus, which might be dependent on their ability to promote actin polymerisation. The nature of this cooperation remains enigmatic and it will be important to elucidate the physiological relevance of the link between cytoskeletal actin networks and nuclear events. This Commentary explores the current evidence for the nuclear roles of actin nucleation factors. Furthermore, the implication of actin-associated proteins in relaying exogenous signals to the nucleus, particularly in response to cellular stress, will be considered.

  18. Analytic modeling of soot nucleation under fuel rich conditions

    NASA Technical Reports Server (NTRS)

    Yang, C. H.

    1983-01-01

    The objective of the present research is to construct a soot nucleation model according to a proposed chemical kinetic scheme to delineate quantitatively the nucleation mechanism in the soot formation process. Instead of following the traditional views which generally associate sooting with the homogeneous nucleation process in phase transformation or polymerization, we choose a chemical kinetic approach. In our proposed scheme the number of carbon atoms in the intermediate species between the fuel molecule and soot nuclei is continuously increased by radical additions. The number of hydrogen atoms in the intermediate species on the other hand is steadily decreased by radical dehydrogenation. When the number of carbon atoms in each of the intermediate molecules has exceeded a certain limit and the number of hydrogen atoms has fallen below a certain level, they may coagulate with one and another to form a larger molecule which is regarded as the initial soot nuclei in the present theory. Further coagulation and surface growth of the nuclei will lead to observable soot particles.

  19. Exploring Carbon Nanomaterial Diversity for Nucleation of Protein Crystals

    NASA Astrophysics Data System (ADS)

    Govada, Lata; Leese, Hannah S.; Saridakis, Emmanuel; Kassen, Sean; Chain, Benny; Khurshid, Sahir; Menzel, Robert; Hu, Sheng; Shaffer, Milo S. P.; Chayen, Naomi E.

    2016-02-01

    Controlling crystal nucleation is a crucial step in obtaining high quality protein crystals for structure determination by X-ray crystallography. Carbon nanomaterials (CNMs) including carbon nanotubes, graphene oxide, and carbon black provide a range of surface topographies, porosities and length scales; functionalisation with two different approaches, gas phase radical grafting and liquid phase reductive grafting, provide routes to a range of oligomer functionalised products. These grafted materials, combined with a range of controls, were used in a large-scale assessment of the effectiveness for protein crystal nucleation of 20 different carbon nanomaterials on five proteins. This study has allowed a direct comparison of the key characteristics of carbon-based nucleants: appropriate surface chemistry, porosity and/or roughness are required. The most effective solid system tested in this study, carbon black nanoparticles functionalised with poly(ethylene glycol) methyl ether of mean molecular weight 5000, provides a novel highly effective nucleant, that was able to induce crystal nucleation of four out of the five proteins tested at metastable conditions.

  20. Exploring Carbon Nanomaterial Diversity for Nucleation of Protein Crystals.

    PubMed

    Govada, Lata; Leese, Hannah S; Saridakis, Emmanuel; Kassen, Sean; Chain, Benny; Khurshid, Sahir; Menzel, Robert; Hu, Sheng; Shaffer, Milo S P; Chayen, Naomi E

    2016-02-04

    Controlling crystal nucleation is a crucial step in obtaining high quality protein crystals for structure determination by X-ray crystallography. Carbon nanomaterials (CNMs) including carbon nanotubes, graphene oxide, and carbon black provide a range of surface topographies, porosities and length scales; functionalisation with two different approaches, gas phase radical grafting and liquid phase reductive grafting, provide routes to a range of oligomer functionalised products. These grafted materials, combined with a range of controls, were used in a large-scale assessment of the effectiveness for protein crystal nucleation of 20 different carbon nanomaterials on five proteins. This study has allowed a direct comparison of the key characteristics of carbon-based nucleants: appropriate surface chemistry, porosity and/or roughness are required. The most effective solid system tested in this study, carbon black nanoparticles functionalised with poly(ethylene glycol) methyl ether of mean molecular weight 5000, provides a novel highly effective nucleant, that was able to induce crystal nucleation of four out of the five proteins tested at metastable conditions.

  1. Neonatal nucleated red blood cells in G6PD deficiency.

    PubMed

    Yeruchimovich, Mark; Shapira, Boris; Mimouni, Francis B; Dollberg, Shaul

    2002-05-01

    The objective of this study is to study the absolute number of nucleated red blood cells (RBC) at birth, an index of active fetal erythropoiesis, in infants with G6PD deficiency and in controls. We tested the hypothesis that hematocrit and hemoglobin would be lower, and absolute nucleated RBC counts higher, in the G6PD deficient and that these changes would be more prominent in infants exposed passively to fava bean through maternal diet. Thirty-two term infants with G6PD deficiency were compared with 30 term controls. Complete blood counts with manual differential counts were obtained within 12 hours of life. Absolute nucleated RBC and corrected leukocyte counts were computed from the Coulter results and the differential count. G6PD deficient patients did not differ from controls in terms of gestational age, birth weight, or Apgar scores or in any of the hematologic parameters studied, whether or not the mother reported fava beans consumption in the days prior to delivery. Although intrauterine hemolysis is possible in G6PD deficient fetuses exposed passively to fava beans, our study supports that such events must be very rare.

  2. Ice nucleation efficiency of soot from biomass combustion

    NASA Astrophysics Data System (ADS)

    Umo, N. S.; Murray, B. J.; O'Sullivan, D.; Baeza-Romero, M. T.; Plane, J. C.

    2013-05-01

    Do Soot aerosols in the atmosphere indirectly influence the radiative budget of the Earth by modifying cloud properties, either by acting as cloud condensation nuclei (CCN) or as ice nuclei (IN). The ice nucleation activity of soot remains poorly quantified and there is a need to parameterise its impact for use in cloud-aerosol models. Here, we investigate the ice nucleation activity of eugenol soot in the immersion mode at conditions relevant to mixed-phase clouds. Eugenol is used as a proxy for a biomass combustion source. The efficiency of soot as an IN was quantified using droplet freezing techniques with droplet volumes ranging from nanolitre (˜100 μm diameter) to microliter (˜1 mm diameter). We show that soot nucleates ice in our experiments at temperatures up to -14°C, although the efficiency with which it does so is less than for mineral dust on a per surface area basis. An estimation of the IN number concentration that could result from our eugenol soot showed that, on a global average basis, IN from soot is secondary in importance to mineral dust below about -20°C. However, it may be important as IN in some locations which are deficient in dust, but rich in soot particles. We conclude that its overall impact can be significant considering its relative regional and global abundance.

  3. Accelerated Nucleation of Hydroxyapatite Using an Engineered Hydrophobin Fusion Protein.

    PubMed

    Melcher, Melanie; Facey, Sandra J; Henkes, Thorsten M; Subkowski, Thomas; Hauer, Bernhard

    2016-05-01

    Calcium phosphate mineralization is of particular interest in dental repair. A biomimetic approach using proteins or peptides is a highly promising way to reconstruct eroded teeth. In this study, the screening of several proteins is described for their binding and nucleating activities toward hydroxyapatite. Out of 27 tested candidates, only two hydrophobin fusion proteins showed binding abilities to hydroxyapatite in a mouthwash formulation and an increased nucleation in artificial saliva. Using a semirational approach, one of the two candidates (DEWA_5), a fusion protein consisting of a truncated section of the Bacillus subtilis synthase YaaD, the Aspergillus nidulans hydrophobin DEWA, and the rationally designed peptide P11-4 described in the literature, could be further engineered toward a faster mineral formation. The variants DEWA_5a (40aaYaaD-SDSDSD-DEWA) and DEWA_5b (40aaYaaD-RDRDRD-DEWA) were able to enhance the nucleation activity without losing the ability to form hydroxyapatite. In the case of variant DEWA_5b, an additional increase in the binding toward hydroxyapatite could be achieved. Especially with the variant DEWA_5a, the protein engineering of the rationally designed peptide sequence resulted in a resemblance of an amino acid motif that is found in nature. The engineered peptide resembles the amino acid motif in dentin phosphoprotein, one of the major proteins involved in dentinogenesis. PMID:27010648

  4. Neonatal nucleated red blood cells in G6PD deficiency.

    PubMed

    Yeruchimovich, Mark; Shapira, Boris; Mimouni, Francis B; Dollberg, Shaul

    2002-05-01

    The objective of this study is to study the absolute number of nucleated red blood cells (RBC) at birth, an index of active fetal erythropoiesis, in infants with G6PD deficiency and in controls. We tested the hypothesis that hematocrit and hemoglobin would be lower, and absolute nucleated RBC counts higher, in the G6PD deficient and that these changes would be more prominent in infants exposed passively to fava bean through maternal diet. Thirty-two term infants with G6PD deficiency were compared with 30 term controls. Complete blood counts with manual differential counts were obtained within 12 hours of life. Absolute nucleated RBC and corrected leukocyte counts were computed from the Coulter results and the differential count. G6PD deficient patients did not differ from controls in terms of gestational age, birth weight, or Apgar scores or in any of the hematologic parameters studied, whether or not the mother reported fava beans consumption in the days prior to delivery. Although intrauterine hemolysis is possible in G6PD deficient fetuses exposed passively to fava beans, our study supports that such events must be very rare. PMID:12012283

  5. Influence of solvent on crystal nucleation of risperidone.

    PubMed

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

    2015-01-01

    Over 2100 induction time experiments were carried out for the medium-sized, antipsychotic drug molecule, risperidone in seven different organic solvents. To reach the same induction time the required driving force increases in the order: cumene, toluene, acetone, ethyl acetate, methanol, propanol, and butanol, which reasonably well correlates to the interfacial energies as determined within classical nucleation theory. FTIR spectroscopy has been used to investigate any shifts in the spectra and to estimate the interaction of solute and solvent at the corresponding site. The solution condition has also been investigated by Density Functional Theory (DFT) calculations over (1 : 1) solvent-solute binding interactions at 8 different sites on the risperidone molecule. The DFT computational results agree with the spectroscopic data suggesting that these methods do capture the binding strength of solvent molecules to the risperidone molecule. The difficulty of nucleation correlates reasonably to the DFT computations and the spectroscopic measurements. The results of the different measurements suggest that the stronger the solvent binds to the risperidone molecule in solution, the slower the nucleation becomes. PMID:25886651

  6. Nucleated assembly of Chlamydomonas and Volvox cell walls.

    PubMed

    Adair, W S; Steinmetz, S A; Mattson, D M; Goodenough, U W; Heuser, J E

    1987-11-01

    The Chlamydomonas reinhardtii cell wall is made up of hydroxyproline-rich glycoproteins, arranged in five distinct layers. The W6 (crystalline) layer contains three major glycoproteins (GP1, GP2, GP3), selectively extractable with chaotropic agents, that self-assemble into crystals in vitro. A system to study W6 assembly in a quantitative fashion was developed that employs perchlorate-extracted Chlamydomonas cells as nucleating agents. Wall reconstitution by biotinylated W6 monomers was monitored by FITC-streptavidin fluorescence and quick-freeze/deep-etch electron microscopy. Optimal reconstitution was obtained at monomer concentrations (0.2-0.3 mg/ml) well below those required for nonnucleated assembly. Assembly occurred from multiple nucleation sites, and faithfully reflected the structure of the intact W6 layer. Specificity of nucleated assembly was demonstrated using two cell-wall mutants (cw-2 and cw-15); neither served as a substrate for assembly of wild-type monomers. In addition, W6 sublayers were assembled from purified components: GP2 and GP3 coassembled to form the inner (W6A) sublayer; this then served as a substrate for self-assembly of GP1 into the outer (W6B) sublayer. Finally, evolutionary relationships between C. reinhardtii and two additional members of the Volvocales (Chlamydomonas eugametos and Volvox carteri) were explored by performing interspecific reconstitutions. Hybrid walls were obtained between C. reinhardtii and Volvox but not with C. eugametos, confirming taxonomic assignments based on structural criteria. PMID:3680387

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

    NASA Astrophysics Data System (ADS)

    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.

  8. Nucleation and control of clathrate hydrates: insights from simulation.

    PubMed

    Moon, C; Hawtin, R W; Rodger, P Mark

    2007-01-01

    Clathrate hydrates are important in both industrial and geological settings. They give rise to many technological and environmental applications, including energy production, gas transport, global warming and CO2 capture and sequestration. In all of these applications there is a need to exert a high degree of control on the crystallisation process, either to promote or inhibit it according to the application. This crystallisation process involves the formation of a tetrahedral hydrogen bonding network (as occurs with ice), but is complicated by mass transport limitations due to the poor mixing of the common guest molecules, such as methane, and the water that forms the host lattice. The net effect is that the mechanisms for hydrate formation and growth are still poorly understood, with the consequence that development of additives to control nucleation and growth is still largely governed by trial-and-error approaches. In this paper we show how classical molecular dynamics simulations can be used to provide a direct simulation of the nucleation process for methane hydrate and consequently to allow direct simulation of the effect of additives on the nucleation and growth process. Data are presented for oligomers of PVP and compared with existing data for PDMAEMA. The results show that the two additives work by very different mechanisms, with PVP increasing the surface energy of the interfacial region and PDMAEMA adsorbing to the surface of hydrate nanocrystals. The surface energy effect is a mechanism that has not previously been considered for hydrate inhibitors.

  9. Condensation of water vapor in rarefaction waves. I - Homogeneous nucleation

    NASA Technical Reports Server (NTRS)

    Sislian, J. P.; Glass, I. I.

    1976-01-01

    A detailed theoretical investigation has been made of the condensation of water vapor/carrier gas mixtures in the nonstationary rarefaction wave generated in a shock tube. It is assumed that condensation takes place by homogeneous nucleation. The equations of motion together with the nucleation rate and the droplet growth equations were solved numerically by the method of characteristics and Lax's method of implicit artificial viscosity. It is found that, for the case considered, the condensation wave formed by the collapse of the metastable nonequilibrium state is followed by a shock wave generated by the intersection of characteristics of the same family. The expansion is practically isentropic up to the onset of condensation. The condensation front accelerates in the x,t plane. The results of the computations for a chosen case of water vapor/nitrogen mixture are presented by plotting variations of pressure, nucleation rate, number density of critical clusters, and condensate mass-fraction along three particle paths. Some consideration is given to homogeneous condensation experiments conducted in a shock tube. Although a direct comparison of the present theoretical work and these experiments is not possible, several worthwhile interpretative features have resulted nevertheless.

  10. Nucleation, growth and evolution of calcium phosphate films on calcite.

    PubMed

    Naidu, Sonia; Scherer, George W

    2014-12-01

    Marble, a stone composed of the mineral calcite, is subject to chemically induced weathering in nature due to its relatively high dissolution rate in acid rain. To protect monuments and sculpture from corrosion, we are investigating the application of thin layers of hydroxyapatite (HAP) onto marble. The motivation for using HAP is its low dissolution rate and crystal and lattice compatibility with calcite. A mild, wet chemical synthesis route, in which diammonium hydrogen phosphate salt was reacted with marble, alone and with cationic and anionic precursors under different reaction conditions, was used to produce inorganic HAP layers on marble. Nucleation and growth on the calcite substrate was studied, as well as metastable phase evolution, using scanning electron microscopy, grazing incidence X-ray diffraction, and atomic force microscopy. Film nucleation was enhanced by surface roughness. The rate of nucleation and the growth rate of the film increased with cationic (calcium) and anionic (carbonate) precursor additions. Calcium additions also influenced phase formation, introducing a metastable phase (octacalcium phosphate) and a different phase evolution sequence.

  11. Effective binary theory of multi-component nucleation

    SciTech Connect

    Kalikmanov, V. I.

    2015-03-28

    Classical theory of multi-component nucleation [O. Hirschfelder, J. Chem. Phys. 61, 2690 (1974)] belongs to the class of the so-called intractable problems: it requires computational time which is an exponential function of the number of components N. For a number of systems of practical interest with N > 10, the brute-force use of the classical theory becomes virtually impossible and one has to resort to an effective medium approach. We present an effective binary model which captures important physics of multi-component nucleation. The distinction between two effective species is based on the observation that while all N components contribute to the cluster thermodynamic properties, there is only a part of them which trigger the nucleation process. The proposed 2D-theory takes into account adsorption by means of the Gibbs dividing surface formalism and uses statistical mechanical considerations for the treatment of small clusters. Theoretical predictions for binary-, ternary-, and 14-component mixtures are compared with available experimental data and other models.

  12. Dynamics of vortex nucleation in sup 3 He- A flow

    SciTech Connect

    Kopnin, N.B.; Soininen, P.I.; Salomaa, M.M. )

    1992-03-01

    Quantum phase slippage in superfluid {sup 3}He flow is simulated numerically in rectangular slab geometries. Assuming that the flow is confined to a channel having horizontal surfaces close to each other, the spatial problem reduces to the two transverse dimensions; we report time-dependent computer simulations of superfluid {sup 3}He flow in 2+1 dimensions using the time-dependent Ginzburg-Landau equations. The quantum-dynamic processes of phase slippage in {sup 3}He are demonstrated to be associated with superfluid vortex nucleation; we thus confirm Anderson's assumption for phase slippage through vortex motion in superfluids. We also find several other phase-slip scenarios involving vortices, phase-slip lines, and combinations thereof for the coupled multicomponent order-parameter amplitudes. We consider both diffuse and specular boundary conditions at the side walls and demonstrate that our results are essentially independent of the boundaries. We compute the critical current for vortex nucleation as a function of the channel width, and compare it with existing theories of vortex nucleation; we also discuss our calculations in connection with experiments on phase slippage in {sup 3}He flow. One of our most important results is that the superfluid order parameter for the vortices generated in the computer simulations does not vanish anywhere; i.e., the vortices possess superfluid core structures; hence the processes of phase slip for superfluid {sup 3}He are nonlocal in space-time.

  13. Nucleation processes of nanobubbles at a solid/water interface.

    PubMed

    Fang, Chung-Kai; Ko, Hsien-Chen; Yang, Chih-Wen; Lu, Yi-Hsien; Hwang, Ing-Shouh

    2016-01-01

    Experimental investigations of hydrophobic/water interfaces often return controversial results, possibly due to the unknown role of gas accumulation at the interfaces. Here, during advanced atomic force microscopy of the initial evolution of gas-containing structures at a highly ordered pyrolytic graphite/water interface, a fluid phase first appeared as a circular wetting layer ~0.3 nm in thickness and was later transformed into a cap-shaped nanostructure (an interfacial nanobubble). Two-dimensional ordered domains were nucleated and grew over time outside or at the perimeter of the fluid regions, eventually confining growth of the fluid regions to the vertical direction. We determined that interfacial nanobubbles and fluid layers have very similar mechanical properties, suggesting low interfacial tension with water and a liquid-like nature, explaining their high stability and their roles in boundary slip and bubble nucleation. These ordered domains may be the interfacial hydrophilic gas hydrates and/or the long-sought chemical surface heterogeneities responsible for contact line pinning and contact angle hysteresis. The gradual nucleation and growth of hydrophilic ordered domains renders the original homogeneous hydrophobic/water interface more heterogeneous over time, which would have great consequence for interfacial properties that affect diverse phenomena, including interactions in water, chemical reactions, and the self-assembly and function of biological molecules. PMID:27090291

  14. Ice Nucleation Activity in the Widespread Soil Fungus Mortierella alpina

    NASA Astrophysics Data System (ADS)

    Fröhlich-Nowoisky, J.; Hill, T. C. J.; Pummer, B. G.; Franc, G. D.; Pöschl, U.

    2014-08-01

    Biological residues in soil dust are a potentially strong source of atmospheric ice nuclei (IN). So far, however, the abundance, diversity, sources, seasonality, and role of biological - in particular, fungal - IN in soil dust have not been characterized. By analysis of the culturable fungi in topsoils, from a range of different land use and ecosystem types in south-east Wyoming, we found ice nucleation active (INA) fungi to be both widespread and abundant, particularly in soils with recent inputs of decomposable organic matter. Across all investigated soils, 8% of fungal isolates were INA. All INA isolates initiated freezing at -5 to -6 °C, and belonged to a single zygomycotic species, Mortierella alpina (Mortierellales, Mortierellomycotina). By contrast, the handful of fungal species so far reported as INA all belong within the Ascomycota or Basidiomycota phyla. M. alpina is known to be saprobic, widespread in soil and present in air and rain. Sequencing of the ITS region and the gene for γ-linolenic-elongase revealed four distinct clades, affiliated to different soil types. The IN produced by M. alpina seem to be proteinaceous, <300 kDa in size, and can be easily washed off the mycelium. Ice nucleating fungal mycelium will ramify topsoils and probably also release cell-free IN into it. If these IN survive decomposition or are adsorbed onto mineral surfaces, their contribution might accumulate over time, perhaps to be transported with soil dust and influencing its ice nucleating properties.

  15. Molecular simulation of crystal nucleation in n-octane melts

    NASA Astrophysics Data System (ADS)

    Yi, Peng; Rutledge, Gregory C.

    2009-10-01

    Homogeneous nucleation of the crystal phase in n-octane melts was studied by molecular simulation with a realistic, united-atom model for n-octane. The structure of the crystal phase and the melting point of n-octane were determined through molecular dynamics simulation and found to agree with experimental results. Molecular dynamics simulations were performed to observe the nucleation events at constant pressure and constant temperature corresponding to about 20% supercooling. Umbrella sampling Monte Carlo simulations were used to calculate the nucleation free energy for three temperatures, ranging from 8% to 20% supercooling, and to reveal details of the critical nucleus for the first time. The cylindrical nucleus model was found to provide a better quantitative description of the critical nucleus than the spherical nucleus model. The interfacial free energies of the cylinder model were calculated from the simulation data. As the temperature increased, the interfacial free energy of the side surface remained relatively unchanged, at 7-8 mJ/m2, whereas the interfacial free energy of the end surface decreased significantly from 5.4 mJ/m2 to about 3 mJ/m2. These results, and the methods employed, provide valuable and quantitative information regarding the rate-limiting step during the solidification of chain molecules, with ramifications for both short alkanes and polymers.

  16. Nucleation, growth and evolution of calcium phosphate films on calcite.

    PubMed

    Naidu, Sonia; Scherer, George W

    2014-12-01

    Marble, a stone composed of the mineral calcite, is subject to chemically induced weathering in nature due to its relatively high dissolution rate in acid rain. To protect monuments and sculpture from corrosion, we are investigating the application of thin layers of hydroxyapatite (HAP) onto marble. The motivation for using HAP is its low dissolution rate and crystal and lattice compatibility with calcite. A mild, wet chemical synthesis route, in which diammonium hydrogen phosphate salt was reacted with marble, alone and with cationic and anionic precursors under different reaction conditions, was used to produce inorganic HAP layers on marble. Nucleation and growth on the calcite substrate was studied, as well as metastable phase evolution, using scanning electron microscopy, grazing incidence X-ray diffraction, and atomic force microscopy. Film nucleation was enhanced by surface roughness. The rate of nucleation and the growth rate of the film increased with cationic (calcium) and anionic (carbonate) precursor additions. Calcium additions also influenced phase formation, introducing a metastable phase (octacalcium phosphate) and a different phase evolution sequence. PMID:25233226

  17. Nucleation processes of nanobubbles at a solid/water interface

    NASA Astrophysics Data System (ADS)

    Fang, Chung-Kai; Ko, Hsien-Chen; Yang, Chih-Wen; Lu, Yi-Hsien; Hwang, Ing-Shouh

    2016-04-01

    Experimental investigations of hydrophobic/water interfaces often return controversial results, possibly due to the unknown role of gas accumulation at the interfaces. Here, during advanced atomic force microscopy of the initial evolution of gas-containing structures at a highly ordered pyrolytic graphite/water interface, a fluid phase first appeared as a circular wetting layer ~0.3 nm in thickness and was later transformed into a cap-shaped nanostructure (an interfacial nanobubble). Two-dimensional ordered domains were nucleated and grew over time outside or at the perimeter of the fluid regions, eventually confining growth of the fluid regions to the vertical direction. We determined that interfacial nanobubbles and fluid layers have very similar mechanical properties, suggesting low interfacial tension with water and a liquid-like nature, explaining their high stability and their roles in boundary slip and bubble nucleation. These ordered domains may be the interfacial hydrophilic gas hydrates and/or the long-sought chemical surface heterogeneities responsible for contact line pinning and contact angle hysteresis. The gradual nucleation and growth of hydrophilic ordered domains renders the original homogeneous hydrophobic/water interface more heterogeneous over time, which would have great consequence for interfacial properties that affect diverse phenomena, including interactions in water, chemical reactions, and the self-assembly and function of biological molecules.

  18. Exploring Carbon Nanomaterial Diversity for Nucleation of Protein Crystals

    PubMed Central

    Govada, Lata; Leese, Hannah S.; Saridakis, Emmanuel; Kassen, Sean; Chain, Benny; Khurshid, Sahir; Menzel, Robert; Hu, Sheng; Shaffer, Milo S. P.; Chayen, Naomi E.

    2016-01-01

    Controlling crystal nucleation is a crucial step in obtaining high quality protein crystals for structure determination by X-ray crystallography. Carbon nanomaterials (CNMs) including carbon nanotubes, graphene oxide, and carbon black provide a range of surface topographies, porosities and length scales; functionalisation with two different approaches, gas phase radical grafting and liquid phase reductive grafting, provide routes to a range of oligomer functionalised products. These grafted materials, combined with a range of controls, were used in a large-scale assessment of the effectiveness for protein crystal nucleation of 20 different carbon nanomaterials on five proteins. This study has allowed a direct comparison of the key characteristics of carbon-based nucleants: appropriate surface chemistry, porosity and/or roughness are required. The most effective solid system tested in this study, carbon black nanoparticles functionalised with poly(ethylene glycol) methyl ether of mean molecular weight 5000, provides a novel highly effective nucleant, that was able to induce crystal nucleation of four out of the five proteins tested at metastable conditions. PMID:26843366

  19. Nucleation processes of nanobubbles at a solid/water interface

    PubMed Central

    Fang, Chung-Kai; Ko, Hsien-Chen; Yang, Chih-Wen; Lu, Yi-Hsien; Hwang, Ing-Shouh

    2016-01-01

    Experimental investigations of hydrophobic/water interfaces often return controversial results, possibly due to the unknown role of gas accumulation at the interfaces. Here, during advanced atomic force microscopy of the initial evolution of gas-containing structures at a highly ordered pyrolytic graphite/water interface, a fluid phase first appeared as a circular wetting layer ~0.3 nm in thickness and was later transformed into a cap-shaped nanostructure (an interfacial nanobubble). Two-dimensional ordered domains were nucleated and grew over time outside or at the perimeter of the fluid regions, eventually confining growth of the fluid regions to the vertical direction. We determined that interfacial nanobubbles and fluid layers have very similar mechanical properties, suggesting low interfacial tension with water and a liquid-like nature, explaining their high stability and their roles in boundary slip and bubble nucleation. These ordered domains may be the interfacial hydrophilic gas hydrates and/or the long-sought chemical surface heterogeneities responsible for contact line pinning and contact angle hysteresis. The gradual nucleation and growth of hydrophilic ordered domains renders the original homogeneous hydrophobic/water interface more heterogeneous over time, which would have great consequence for interfacial properties that affect diverse phenomena, including interactions in water, chemical reactions, and the self-assembly and function of biological molecules. PMID:27090291

  20. Intermediate Nucleation State of GaN Growth

    NASA Astrophysics Data System (ADS)

    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.

  1. Surface dislocation nucleation controlled deformation of Au nanowires

    SciTech Connect

    Roos, B.; Kapelle, B.; Volkert, C. A.; Richter, G.

    2014-11-17

    We investigate deformation in high quality Au nanowires under both tension and bending using in-situ transmission electron microscopy. Defect evolution is investigated during: (1) tensile deformation of 〈110〉 oriented, initially defect-free, single crystal nanowires with cross-sectional widths between 30 and 300 nm, (2) bending deformation of the same wires, and (3) tensile deformation of wires containing coherent twin boundaries along their lengths. We observe the formation of twins and stacking faults in the single crystal wires under tension, and storage of full dislocations after bending of single crystal wires and after tension of twinned wires. The stress state dependence of the deformation morphology and the formation of stacking faults and twins are not features of bulk Au, where deformation is controlled by dislocation interactions. Instead, we attribute the deformation morphologies to the surface nucleation of either leading or trailing partial dislocations, depending on the Schmid factors, which move through and exit the wires producing stacking faults or full dislocation slip. The presence of obstacles such as neutral planes or twin boundaries hinder the egress of the freshly nucleated dislocations and allow trailing and leading partial dislocations to combine and to be stored as full dislocations in the wires. We infer that the twins and stacking faults often observed in nanoscale Au specimens are not a direct size effect but the result of a size and obstacle dependent transition from dislocation interaction controlled to dislocation nucleation controlled deformation.

  2. First Principles Simulations of Ice Nucleation at Metal Surfaces

    NASA Astrophysics Data System (ADS)

    Michaelides, Angelos

    2005-03-01

    Ice nucleation at solid surfaces is of relevance to countless scientific and technological processes. In particular the nucleation of ice nano-crystals on metal surfaces is often a key first step in cloud formation and corrosion [1]. Yet unfortunately this remains one of the most poorly understood natural phenomena; severely lacking in atomic level understanding. Here, we discuss detailed density functional theory studies aimed at putting our understanding of ice nucleation at metals on a much firmer footing. Specifically the properties of H2O hexamers - the smallest `building blocks' of ice - adsorbed on a number of close-packed transition metal surfaces have been examined. We find that the competing influences of substrate reactivity and hexamer-substrate epitaxial mismatch conspire to yield a rich variety of (novel) hexameric ice structures, some of which have been observed by recent scanning tunnelling microscopy experiments [2]. [1] H.R. Pruppacher and J.D. Klett, Microphysics of Clouds and Precipitation, (Kluwer, Dordrecht, 2003). [2] K. Morgenstern, et al., (To be published).

  3. Nucleation and crystal growth in laser patterned lines in glasses

    NASA Astrophysics Data System (ADS)

    Komatsu, Takayuki; Honma, Tsuyoshi

    2016-07-01

    Laser-induced crystallization is a new method for the design and control of the crystallization of glasses and opens a new door in the study of nucleation and crystal growth in glasses. Nonlinear optical Sm-doped -BaB2O4 (-BBO) crystal lines were patterned by continuous wave Yb:YVO4 fiber laser (wavelength 1080 nm) in 8Sm2O3-42BaO-50B2O3 glass as an example, and nucleation and crystal growth behaviors in the laser-patterned bending and crossing lines were examined. It was confirmed that the growth of c-axis oriented -BBO crystals follows along the laser scanning direction even if laser scanning direction changes. The model of self-organized homo-epitaxial crystal growth was demonstrated for the orientation of -BBO crystals at the crossing point of two lines, in which the first crystal line at the crossing point acts as nucleation site for the second crystal line. This study proposes a new crystal growth technology.

  4. Toward a self-consistent formulation for predicting bubble nucleation in silicate melts

    NASA Astrophysics Data System (ADS)

    Gonnermann, Helge M.; Gardner, James E.

    2014-05-01

    Magma degassing is a consequence of the pressure-dependent solubility of magmatic gases and significantly affects how volcanoes erupt. During magma ascent the ambient pressure decreases and the melt becomes supersaturated in volatiles. Consequently, bubbles nucleate and then grow by diffusion of volatiles from the melt into existing bubbles. Bubble nucleation is therefore a rate-limiting process for magma degassing, which is exceedingly sensitive to the surface energy (i.e., surface tension) of a nucleating bubble. Thus, the surface energy of a nucleating bubble exerts a fundamental control on the dynamics of volcanic eruptions, by affecting the rate at which bubbles nucleate. The rate at which bubbles nucleate during explosive eruptions, in turn, determines the bubble number density, which is thought to be correlated with magma discharge rate, itself a proxy for explosive intensity. We find, however, that this may not be universally true. To facilitate a deeper assessment of this problem requires an improved understanding of the surface energy during bubble nucleation, which is inaccessible to direct experimental determination. Its effective value can, however, be estimated from nucleation experiments. Because relatively small changes in surface energy result in exceedingly large changes in nucleation rate, accurate estimation requires careful modeling of the nucleation experiments. We show, based on combined decompression-nucleation experiments of rhyolitic melt with dissolved H2O and CO2, and numerical modeling thereof, that the surface energy between critical bubble nuclei and the surrounding rhyolitic melt depends on the degree of supersaturation. Its value is lower than the macroscopically measureable value, which is consistent with the view that far from equilibrium the interface between a nucleus and the surrounding melt is diffuse, instead of sharp. As a consequence, the dependence of nucleation rate on the degree of supersaturation can significantly

  5. Analysis of feedbacks between nucleation rate, survival probability and cloud condensation nuclei formation

    NASA Astrophysics Data System (ADS)

    Westervelt, D. M.; Pierce, J. R.; Adams, P. J.

    2014-06-01

    Aerosol nucleation is an important source of particle number in the atmosphere. However, in order to become cloud condensation nuclei (CCN), freshly nucleated particles must undergo significant condensational growth while avoiding coagulational scavenging. In an effort to quantify the contribution of nucleation to CCN, this work uses the GEOS-Chem-TOMAS global aerosol model to calculate changes in CCN concentrations against a broad range of nucleation rates and mechanisms. We then quantify the factors that control CCN formation from nucleation, including daily nucleation rates, growth rates, coagulation sinks, condensation sinks, survival probabilities, and CCN formation rates, in order to examine feedbacks that may limit growth of nucleated particles to CCN. Nucleation rate parameterizations tested in GEOS-Chem-TOMAS include ternary nucleation (with multiple tuning factors), activation nucleation (with two pre-factors), binary nucleation, and ion-mediated nucleation. We find that nucleation makes a significant contribution to boundary layer CCN(0.2%), but this contribution is only modestly sensitive to the choice of nucleation scheme, ranging from 49 to 78% increase in concentrations over a control simulation with no nucleation. Moreover, a two order-of-magnitude increase in the globally averaged nucleation rate (via changes to tuning factors) results in small changes (less than 10%) to global CCN(0.2%) concentrations. To explain this, we present a simple theory showing that survival probability has an exponentially decreasing dependence on the square of the condensation sink. This functional form stems from a negative correlation between condensation sink and growth rate and a positive correlation between condensation sink and coagulational scavenging. Conceptually, with a fixed condensable vapor budget (sulfuric acid and organics), any increase in CCN concentrations due to higher nucleation rates necessarily entails an increased aerosol surface area in the

  6. Nature and evolution of the fusion boundary in ferritic-austenitic dissimilar weld metals. Part 1 -- Nucleation and growth

    SciTech Connect

    Nelson, T.W.; Lippold, J.C.; Mills, M.J.

    1999-10-01

    A fundamental investigation of fusion boundary microstructure evolution in dissimilar-metal welds (DMWs) between ferritic base metals and a face-centered-cubic (FCC) filler metal was conducted. The objective of the work presented here was to characterize the nature and character of the elevated-temperature fusion boundary to determine the nucleation and growth characteristics of DMWs. Type 409 ferritic stainless steel and 1080 pearlitic steel were utilized as base metal substrates, and Monel (70Ni-30Cu) was used as the filler metal. The Type 409 base metal provided a fully ferritic or body-centered-cubic (BCC) substrate at elevated temperatures and exhibited no on-cooling phase transformations to mask or disguise the original character of the fusion boundary. The 1080 pearlitic steel was selected because it is austenitic at the solidus temperature, providing an austenite substrate at the fusion boundary. The weld microstructure generated with each of the base metals in combination with Monel was fully austenitic. In the Type 409/Monel system, there was no evidence of epitaxial nucleation and growth as normally observed in homogeneous weld metal combinations. The fusion boundary in this system exhibited random grain boundary misorientations between the heat-affected zone (HAZ) and weld metal grains. In the 1080/Monel system, evidence of normal epitaxial growth was observed at the fusion boundary, where solidification and HAZ grain boundaries converged. The fusion boundary morphologies are a result of the crystal structure present along the fusion boundary during the initial stages of solidification. Based on the results of this investigation, a model for heterogeneous nucleation along the fusion boundary is proposed when the base and weld metals exhibit ferritic (BCC) and FCC crystal structures, respectively.

  7. Ice nucleation by soil dust compared to desert dust aerosols

    NASA Astrophysics Data System (ADS)

    Moehler, O.; Steinke, I.; Ullrich, R.; Höhler, K.; Schiebel, T.; Hoose, C.; Funk, R.

    2015-12-01

    A minor fraction of atmospheric aerosol particles, so-called ice-nucleating particles (INPs), initiates the formation of the ice phase in tropospheric clouds and thereby markedly influences the Earth's weather and climate systems. Whether an aerosol particle acts as an INP depends on its size, morphology and chemical compositions. The INP fraction of certain aerosol types also strongly depends on the temperature and the relative humidity. Because both desert dust and soil dust aerosols typically comprise a variety of different particles, it is difficult to assess and predict their contribution to the atmospheric INP abundance. This requires both accurate modelling of the sources and atmospheric distribution of atmospheric dust components and detailed investigations of their ice nucleation activities. The latter can be achieved in laboratory experiments and parameterized for use in weather and climate models as a function of temperature and particle surface area, a parameter called ice-nucleation active site (INAS) density. Concerning ice nucleation activity studies, the soil dust is of particular interest because it contains a significant fraction of organics and biological components, both with the potential for contributing to the atmospheric INP abundance at relatively high temperatures compared to mineral components. First laboratory ice nucleation experiments with a few soil dust samples indicated their INP fraction to be comparable or slightly enhanced to that of desert dust. We have used the AIDA (Aerosol Interaction and Dynamics in the Atmosphere) cloud simulation chamber to study the immersion freezing ability of four different arable soil dusts, sampled in Germany, China and Argentina. For temperatures higher than about -20°C, we found the INP fraction of aerosols generated from these samples by a dry dispersion technique to be significantly higher compared to various desert dust aerosols also investigated in AIDA experiments. In this contribution, we

  8. Characteristics of Microcracks in the Nucleation Stage of Natural Earthquake

    NASA Astrophysics Data System (ADS)

    Fujinawa, Y.; Noda, Y.; Takahashi, K.; Kobayashi, M.; Takamatsu, K.; Natsumeda, J.

    2013-12-01

    At the last AGU Fall meeting we reported that that an electric field measurement using special antenna could detect micro-cracks appearing in the nucleation stage. Here we report several results of analysis on the phenomena. 1) Detection Distance: Some events of B-type variation have clear first and second phases (Fig.1). The S-P time is 25ms corresponding to 181m of the epicentral distance. Almost events have no apparent P phases due to the small strength. The detection distance of P phase is about 200m. But a B-1 type suggests detection distance of some 11km, much larger than the AE emission observation. Moreover, the converted seismic wave to electric mode at the conductivity contrast can be detected at several tens km (Fujinawa et al., 2011). The characteristic electric field variation induced by crack through electro-kinetic mechanism can be discussed on the systematic formulations ( Pride, 1994). There are four kinds of wave, slow P and fast P (ordinary p wave), S-wave (ordinary S wave) and electromagnetic wave. Events containing P phase have occasionally small forerunners at about the origin time (EM in Figure 1). The arrival time difference agrees with the electric wave propagation velocity suggesting that that it is the EM pahse.. 2) Correspondence to main shock: The seismological approaches (e.g., Kato et al., 2012) showed that there were two slow seismic slip events as well as microearthquake activities around the forshocks and mainshock. Those activities were whole limited in the epicentral zone, about 300 km northeast from our observation site. Our observational evidence including temporal evolution of the microcrack activity suggest that the micro-cracks of B-type at the edge of the rupture area are related to the nucleation process of the main shock , the asperity. We propose that the nucleation process is not limited at around the asperity. 3). Intermittent Criticality There appeared undulation of microcrack activity after the most active period

  9. Total sulfate vs. sulfuric acid monomer concenterations in nucleation studies

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

    Sulfuric acid is known to be a key component for atmospheric nucleation. Precise determination of sulfuric-acid concentration is a crucial factor for prediction of nucleation rates and subsequent growth. In our study, we have noticed a substantial discrepancy between sulfuric-acid monomer concentrations and total-sulfate concentrations measured from the same source of sulfuric-acid vapor. The discrepancy of about 1-2 orders of magnitude was found with similar particle-formation rates. To investigate this discrepancy, and its effect on nucleation, a method of thermally controlled saturator filled with pure sulfuric acid (97% wt.) for production of sulfuric-acid vapor is applied and rigorously tested. The saturator provided an independent vapor-production method, compared to our previous method of the furnace (Brus et al., 2010, 2011), to find out if the discrepancy is caused by the production method itself. The saturator was used in a H2SO4-H2O nucleation experiment, using a laminar flow tube to check reproducibility of the nucleation results with the saturator method, compared to the furnace. Two independent methods of mass spectrometry and online ion chromatography were used for detecting sulfuric-acid or sulfate concentrations. Measured sulfuric-acid or total-sulfate concentrations are compared to theoretical predictions calculated using vapor pressure and a mixing law. The calculated prediction of sulfuric-acid concentrations agrees very well with the measured values when total sulfate is considered. Sulfuric-acid monomer concentration was found to be about 2 orders of magnitude lower than theoretical predictions, but with a temperature dependency similar to the predictions and the results obtained with the ion-chromatograph method. Formation rates are reproducible when compared to our previous results with both sulfuric-acid or total-sulfate detection and sulfuric-acid production methods separately, removing any doubts that the vapor-production method would

  10. Ice nucleating particles in the Saharan Air Layer

    NASA Astrophysics Data System (ADS)

    Boose, Yvonne; Sierau, Berko; García, M. Isabel; Rodríguez, Sergio; Alastuey, Andrés; Linke, Claudia; Schnaiter, Martin; Kupiszewski, Piotr; Kanji, Zamin A.; Lohmann, Ulrike

    2016-07-01

    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 in INPs compared to the ambient

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

    NASA Astrophysics Data System (ADS)

    Pinti, V.; Marcolli, C.; Zobrist, B.; Hoyle, C. R.; Peter, T.

    2012-07-01

    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 Knucleation 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 demonstrate that immersion freezing temperatures of clay minerals strongly depend on the amount of clay mineral present per droplet and on

  12. Earthquake nucleation mechanisms and periodic loading: Models, Experiments, and Observations

    NASA Astrophysics Data System (ADS)

    Dahmen, K.; Brinkman, B.; Tsekenis, G.; Ben-Zion, Y.; Uhl, J.

    2010-12-01

    The project has two main goals: (a) Improve the understanding of how earthquakes are nucleated ¬ with specific focus on seismic response to periodic stresses (such as tidal or seasonal variations) (b) Use the results of (a) to infer on the possible existence of precursory activity before large earthquakes. A number of mechanisms have been proposed for the nucleation of earthquakes, including frictional nucleation (Dieterich 1987) and fracture (Lockner 1999, Beeler 2003). We study the relation between the observed rates of triggered seismicity, the period and amplitude of cyclic loadings and whether the observed seismic activity in response to periodic stresses can be used to identify the correct nucleation mechanism (or combination of mechanisms). A generalized version of the Ben-Zion and Rice model for disordered fault zones and results from related recent studies on dislocation dynamics and magnetization avalanches in slowly magnetized materials are used in the analysis (Ben-Zion et al. 2010; Dahmen et al. 2009). The analysis makes predictions for the statistics of macroscopic failure events of sheared materials in the presence of added cyclic loading, as a function of the period, amplitude, and noise in the system. The employed tools include analytical methods from statistical physics, the theory of phase transitions, and numerical simulations. The results will be compared to laboratory experiments and observations. References: Beeler, N.M., D.A. Lockner (2003). Why earthquakes correlate weakly with the solid Earth tides: effects of periodic stress on the rate and probability of earthquake occurrence. J. Geophys. Res.-Solid Earth 108, 2391-2407. Ben-Zion, Y. (2008). Collective Behavior of Earthquakes and Faults: Continuum-Discrete Transitions, Evolutionary Changes and Corresponding Dynamic Regimes, Rev. Geophysics, 46, RG4006, doi:10.1029/2008RG000260. Ben-Zion, Y., Dahmen, K. A. and J. T. Uhl (2010). A unifying phase diagram for the dynamics of sheared solids

  13. Laboratory Investigations into Micromechanical Mechanisms Controlling Earthquake Nucleation

    NASA Astrophysics Data System (ADS)

    Selvadurai, P. A.; Glaser, S. D.; Kiwan, R. H.

    2013-12-01

    Improving our understanding of factors controlling spontaneous shear rupture nucleation on a frictional fault would help better define the important physical processes contributing to earthquake rupture and faulting. Our current laboratory investigations quantify the local stress states on a laboratory fault, which control the transition of sliding from stable (quasi-static) to unstable (dynamic), commonly referred to as earthquake nucleation. A fault is experimentally modeled using two Poly(methyl methacrylate) samples in a direct shear configuration. During nucleation, we observed sudden, elastodynamic stress changes using an array of 16 acoustic emission (AE) sensors. Measurements of absolute displacement from these sensors allowed us to characterize general source mechanics using moment tensor inversion. This technique is widely used in seismology and we observe double-couple (DC) focal mechanisms; a source commonly used to characterize in situ earthquakes. During nucleation, we sometimes observe swarms of smaller, ';foreshock' earthquakes (Mw ~ -7), localized in time and space, prior to the incipient mainshock (Mw ~ -3.25). In general, the local perturbations in the stress field induced by the stress drop (Δσ) from a single foreshock was insufficient to cause the subsequent foreshock at the spatial distances recorded experimentally. This implied that the underlying process driving the foreshock sequence (and eventual mainshock) was aseismic slip over the nucleation zone recorded using non-contact sensors. Spatio-temporal distributions of the foreshocks and the near-fault aseismic motions were shown to be directly related to: i) the rate at which the average bulk stress accumulates across the fault (dτf /dt) and ii) the heterogeneity of normal stress caused by the irregular distribution of asperities, respectively. (A) Locations of the foreshocks (FS1-FS9) determined using p-wave travel times from multiple AE sensors. The locations were superimposed on

  14. Screening of nucleation conditions using levitated drops for protein crystallization.

    PubMed

    Santesson, Sabina; Cedergren-Zeppezauer, Eila S; Johansson, Thomas; Laurell, Thomas; Nilsson, Johan; Nilsson, Staffan

    2003-04-01

    The growth of suitable protein crystals is an essential step in the structure determination of a protein by X-ray crystallography. At present, crystals are mostly grown using trial-and-error procedures, and protocols that rapidly screen for the crystal nucleation step are rare. Presented here is an approach to minimize the consumption of precious protein material while searching for the nucleation conditions. Acoustically levitated drops of known protein concentration (0.25-1.5-microL volumes) are injected with crystallizing agents using piezoelectric flow-through dispensers (ejecting 50-100-pL droplets at 1-9000 droplets/s). A restricted number of crystallizing agents representing three classes are used: poly(ethylene glycol), salts, and the viscous alcohol 2-methyl 2,4-pentanediol. From a digitized picture of the levitated drop volume, calculations are performed giving the concentrations of all components in the drop at any time during a "precipitation experiment". Supersaturation is the prerequisite for crystal nucleation, and protein precipitation indicates high supersaturation. A light source illuminates the levitated drop, and protein precipitation is monitored using right-angle light scattering. On the basis of these intensity measurements and the volume determination, precipitation diagrams for each crystallizing agent are constructed that give the protein/crystallizing agent concentration boundaries between the minimum and the maximum detectable protein precipitation. Guided by the concentration values obtained from such plots, when approaching the supersaturation region, separate crystallization drops are mixed and allowed to equilibrate under paraffin oil. At conditions in which microcrystals can be observed, the nucleation tendency of the macromolecule is confirmed. Optimization of crystallization conditions can then follow. Proteins tested include alcohol dehydrogenase and D-serine dehydratase. Alcohol dehydrogenase, known to crystallize easily, was

  15. Freezing activities of flavonoids in solutions containing different ice nucleators.

    PubMed

    Kuwabara, Chikako; Wang, Donghui; Kasuga, Jun; Fukushi, Yukiharu; Arakawa, Keita; Koyama, Toshie; Inada, Takaaki; Fujikawa, Seizo

    2012-06-01

    In this study, we examined the effects on freezing of 26 kinds of flavonoid compounds, which were randomly selected as compounds with structures similar to those of flavonoid compounds existing in deep supercooling xylem parenchyma cells (XPCs) in trees, in solutions containing different kinds of ice nucleators, including the ice nucleation bacterium (INB) Erwinia ananas, INB Xanthomonas campestris, silver iodide, phloroglucinol and unidentified airborne impurities in buffered Milli-Q water (BMQW). Cumulative freezing spectra were obtained in each solution by cooling 2 μL droplets at 0.2 °C/min by a droplet freezing assay. Freezing temperature of 50% droplets (FT(50)) was obtained from each spectra in a separate analysis with more than 20 droplets and mean FT(50) were obtained from more than five separate analyses using more than 100 droplets in total in each flavonoid. Supercooling-promoting activities (SCA) or ice nucleation-enhancing activities (INA) of these flavonoids were determined by the difference in FT(50) between control solutions without flavonoids and experimental solutions with flavonoids. In mean values, most of the compounds examined exhibited SCA in solutions containing the INB E. ananas, INB X. campestris, silver iodide, and phloroglucinol although the magnitudes of their activities were different depending on the ice nucleator. In solutions containing the INB E. ananas, 10 compounds exhibited SCAs with significant differences (p<0.05) in the range of 1.4-4.2 °C. In solutions containing silver iodide, 23 compounds exhibited SCAs with significant differences in the range of 2.0-7.1 °C. In solutions containing phloroglucinol, six compounds exhibited SCAs with significant differences in the range of 2.4-3.5 °C. In solutions containing the INB X. campestris, only three compounds exhibited SCAs with significant differences in the range of 0.9-2.3 °C. In solutions containing unidentified airborne impurities (BMQW alone), on the other hand, many

  16. Freezing activities of flavonoids in solutions containing different ice nucleators.

    PubMed

    Kuwabara, Chikako; Wang, Donghui; Kasuga, Jun; Fukushi, Yukiharu; Arakawa, Keita; Koyama, Toshie; Inada, Takaaki; Fujikawa, Seizo

    2012-06-01

    In this study, we examined the effects on freezing of 26 kinds of flavonoid compounds, which were randomly selected as compounds with structures similar to those of flavonoid compounds existing in deep supercooling xylem parenchyma cells (XPCs) in trees, in solutions containing different kinds of ice nucleators, including the ice nucleation bacterium (INB) Erwinia ananas, INB Xanthomonas campestris, silver iodide, phloroglucinol and unidentified airborne impurities in buffered Milli-Q water (BMQW). Cumulative freezing spectra were obtained in each solution by cooling 2 μL droplets at 0.2 °C/min by a droplet freezing assay. Freezing temperature of 50% droplets (FT(50)) was obtained from each spectra in a separate analysis with more than 20 droplets and mean FT(50) were obtained from more than five separate analyses using more than 100 droplets in total in each flavonoid. Supercooling-promoting activities (SCA) or ice nucleation-enhancing activities (INA) of these flavonoids were determined by the difference in FT(50) between control solutions without flavonoids and experimental solutions with flavonoids. In mean values, most of the compounds examined exhibited SCA in solutions containing the INB E. ananas, INB X. campestris, silver iodide, and phloroglucinol although the magnitudes of their activities were different depending on the ice nucleator. In solutions containing the INB E. ananas, 10 compounds exhibited SCAs with significant differences (p<0.05) in the range of 1.4-4.2 °C. In solutions containing silver iodide, 23 compounds exhibited SCAs with significant differences in the range of 2.0-7.1 °C. In solutions containing phloroglucinol, six compounds exhibited SCAs with significant differences in the range of 2.4-3.5 °C. In solutions containing the INB X. campestris, only three compounds exhibited SCAs with significant differences in the range of 0.9-2.3 °C. In solutions containing unidentified airborne impurities (BMQW alone), on the other hand, many

  17. Vapor-liquid nucleation in two dimensions: on the intriguing sign switch of the errors of the classical nucleation theory.

    PubMed

    Loeffler, Troy D; Henderson, David E; Chen, Bin

    2012-11-21

    A nucleation study of a two-dimensional (2D) Lennard-Jones (LJ) system is done using the aggregation-volume-bias Monte Carlo with umbrella sampling method. The results obtained from this simulation study was compared to those predicted by the classical nucleation theory (CNT). It was found that the nucleation free energy obtained for this 2D LJ system was underestimated by CNT; however, this result is significantly different from that found for the 3D LJ system where CNT overestimates the free energy. These results are generally in agreement with previous studies on these systems. While both errors can be traced to the incorrect description of the smallest clusters by the theory, structural analysis reveals striking differences between 2D and 3D clusters, leading to a possible source for this observed sign switch. In particular, the radius of gyration data indicates that for the 3D LJ system, clusters formed at the beginning are fractal and the cluster growth is accompanied by an increase of the dimensionality, whereas clusters in 2D show little sign of this dimensionality transition.

  18. Electrical Properties of Poly-Lactic Acid with Nucleating Agent Added

    NASA Astrophysics Data System (ADS)

    Shinyama, Katsuyoshi; Oi, Toru; Fujita, Shigetaka

    We examined electrical properties of polylactic acid (PLA) with nucleating agent added. At that time, nucleating agent was added to PLA was then heat-treated at 100°C for 30 seconds. The crystallinity of the nucleating agent was added to PLA increased to more than 40%, and its crystallization speed also increased significantly. The temperature dependence of the conductivity (σ) was investigated, the σ of PLA to which nucleating agent had been added showed the tendency to become lower than the σ of PLA to which nucleating agent had not been added in σ at temperatures higher than 60°C. Furthermore, the temperature dependence of the dielectric breakdown strength (EB) was investigated, EB of nucleating agent was added to PLA was around 5.0 MV/cm at a temperature of 25°C. Of particular note was the fact that EB of nucleating agent was added to PLA measured at 100°C was around 4.7 MV/cm, around 3 times greater than the EB value for PLA to which nucleating agent had not been added. The temperature dependence of the relative dielectric constant (εr‧) and the relative dielectric loss factor (εr″) was investigated, the peak dielectric absorption value of εr″ for the PLA to which nucleating agent had been added showed a tendency that lower than that of the PLA to which nucleating agent had not been added.

  19. The onset of laboratory earthquakes explained by nucleating rupture on a rate-and-state fault

    NASA Astrophysics Data System (ADS)

    Kaneko, Yoshihiro; Nielsen, Stefan B.; Carpenter, Brett M.

    2016-08-01

    Precursory aseismic slip lasting days to months prior to the initiation of earthquakes has been inferred from seismological observations. Similar precursory slip phenomena have also been observed in laboratory studies of shear rupture nucleation on frictional interfaces. However, the mechanisms that govern rupture nucleation, even in idealized laboratory settings, have been widely debated. Here we show that a numerical model incorporating rate-and-state friction laws and elastic continuum can reproduce the behaviors of rupture nucleation seen in laboratory experiments. In particular, we find that both in laboratory experiments and simulations with a wide range of normal stresses, the nucleation consists of two distinct phases: initial slow propagation phase and faster acceleration phase, both of which are likely aseismic processes, followed by dynamic rupture propagation that radiates seismic waves. The distance at which the rupture transitions from the initial slow phase to the acceleration phase can be roughly predicted by a theoretical estimate of critical nucleation length. Our results further show that the critical nucleation length depends on the background loading rate. In addition, our analysis suggests that critical nucleation length and breakdown power derived from the Griffith crack energy balance control the scaling of nucleating ruptures. Moreover, the background loading rate and loading configuration significantly affect the rupture propagation speed. Furthermore, if the same nucleation mechanism applies to natural faults, the migration speed of foreshocks triggered by the propagation of slow rupture within the nucleation zone would depend on the effective normal stress and hence fluid pressure in the fault zone.

  20. Hotspots organize clathrin-mediated endocytosis by efficient recruitment and retention of nucleating resources

    PubMed Central

    Nunez, Daniel; Antonescu, Costin; Mettlen, Marcel; Liu, Allen; Schmid, Sandra L.; Loerke, Dinah; Danuser, Gaudenz

    2011-01-01

    The formation of clathrin-coated pits (CCPs) at the plasma membrane has been reported to sometimes occur repeatedly at predefined sites. However, defining such CCP `hotspots' structurally and mechanistically has been difficult due to the dynamic and heterogeneous nature of CCPs. Here we explore the molecular requirements for hotspots using a global assay of CCP dynamics. Our data confirmed that a subset of CCPs is nucleated at spatially distinct sites. The degree of clustering of nucleation events at these sites is dependent on the integrity of cortical actin, and the availability of certain resources, including the adaptor protein AP-2 and the phospholipid PI(4,5)P2. We observe that modulation in the expression of FCHo1 and 2, which have been reported to initiate CCPs, affect only the number of nucleations. Modulation in the expression levels of other accessory proteins, such as SNX9, affects the spatial clustering of CCPs but not the number of nucleations. Based on these findings we distinguish two classes of accessory proteins in clathrin-mediated endocytosis (CME): nucleation factors and nucleation organizers. Finally, we observe that clustering of transferrin receptors spatially randomizes pit nucleation and thus reduces the role of hotspots. Based on these data, we propose that hotspots are specialized cortical actin patches that organize CCP nucleations from within the cell by more efficient recruitment and/or retention of resources required for CCP nucleation partially due to the action of nucleation organizers. PMID:21883765

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

    NASA Astrophysics Data System (ADS)

    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

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

    PubMed

    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.

  3. Binary nucleation kinetics. I. Self-consistent size distribution

    SciTech Connect

    Wilemski, G.; Wyslouzil, B.E. ||

    1995-07-15

    Using the principle of detailed balance, we derive a new self-consistency requirement, termed the kinetic product rule, relating the evaporation coefficients and equilibrium cluster distribution for a binary system. We use this result to demonstrate and resolve an inconsistency for an idealized Kelvin model of nucleation in a simple binary mixture. We next examine several common forms for the equilibrium distribution of binary clusters based on the capillarity approximation and ideal vapor behavior. We point out fundamental deficiencies for each expression. We also show that each distribution yields evaporation coefficients that formally satisfy the new kinetic product rule but are physically unsatisfactory because they depend on the monomer vapor concentrations. We then propose a new form of the binary distribution function that is free of the deficiencies of the previous functions except for its reliance on the capillarity approximation. This new self-consistent classical (SCC) size distribution for binary clusters has the following properties: It satisfies the law of mass action; it reduces to an SCC unary distribution for clusters of a single component; and it produces physically acceptable evaporation rate coefficients that also satisfy the new kinetic product rule. Since it is possible to construct other examples of similarly well-behaved distributions, our result is not unique in this respect, but it does give reasonable predictions. As an illustration, we calculate binary nucleation rates and vapor activities for the ethanol--hexanol system at 260 K using the new SCC distribution and compare them to experimental results. The theoretical rates are uniformly higher than the experimental values over the entire vapor composition range. Although the predicted activities are lower, we find good agreement between the measured and theoretical slope of the critical vapor activity curve at a constant nucleation rate of 10{sup 7} cm{sup {minus}3} s{sup {minus}2}.

  4. Quark matter nucleation in neutron stars and astrophysical implications

    NASA Astrophysics Data System (ADS)

    Bombaci, Ignazio; Logoteta, Domenico; Vidaña, Isaac; Providência, Constança

    2016-03-01

    A phase of strong interacting matter with deconfined quarks is expected in the core of massive neutron stars. We investigate the quark deconfinement phase transition in cold (T=0 and hot β -stable hadronic matter. Assuming a first order phase transition, we calculate and compare the nucleation rate and the nucleation time due to quantum and thermal nucleation mechanisms. We show that above a threshold value of the central pressure a pure hadronic star (HS) (i.e. a compact star with no fraction of deconfined quark matter) is metastable to the conversion to a quark star (QS) (i.e. a hybrid star or a strange star). This process liberates an enormous amount of energy, of the order of 1053erg, which causes a powerful neutrino burst, likely accompanied by intense gravitational waves emission, and possibly by a second delayed (with respect to the supernova explosion forming the HS) explosion which could be the energy source of a powerful gamma-ray burst (GRB). This stellar conversion process populates the QS branch of compact stars, thus one has in the Universe two coexisting families of compact stars: pure hadronic stars and quark stars. We introduce the concept of critical mass M_{cr} for cold HSs and proto-hadronic stars (PHSs), and the concept of limiting conversion temperature for PHSs. We show that PHSs with a mass M < M_{cr} could survive the early stages of their evolution without decaying to QSs. Finally, we discuss the possible evolutionary paths of proto-hadronic stars.

  5. Macrosegregation and nucleation in undercooled Pb-Sn alloys

    NASA Technical Reports Server (NTRS)

    Degroh, Henry C., III

    1989-01-01

    A technique resulting in large undercoolings in bulk samples (23g) of lead-tin alloys was developed. Samples of Pb-12.5 wt percent Sn, Pb-61 wt percent Sn, and Pb-77 wt percent Sn were processed with undercoolings ranging from 4 to 34 K and with cooling rates varying between 0.04 and 4 K/sec. The nucleation behavior of the Pb-Sn system was found to be nonreciprocal. The solid Sn phase effectively nucleated the Pb phase of the eutectic; however, large undercoolings developed in Sn-rich eutectic liquid in the presence of the solid Pb phase. This phenomenon is believed to be mainly the result of differences in interfacial energies between solid Sn-eutectic liquid, and solid Pb-eutectic liquid rather than lattice misfit between Pb and Sn. Large amounts of segregation developed in the highly undercooled eutectic ingots. This macrosegregation was found to increase as undercooling increases. Macrosegregation in these undercooled eutectic alloys was found to be primarily due to a sink/float mechanism and the nucleation behavior of the alloy. Lead-rich dendrites are the primary phase in the undercooled eutectic system. These dendrites grow rapidly into the undercooled bath and soon break apart due to recalescence and Sn enrichment of the liquid. These fragmented Pb dendrites are then free to settle to the bottom portion of the ingot causing the macrosegregation observed in this study. A eutectic Pb-Sn alloy undercooled 20 K and cooled at 4 K/sec had a composition of about Pb-72 wt percent Sn at the top and 55 percent Sn at the bottom.

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

    NASA Astrophysics Data System (ADS)

    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

  7. Macrosegregation and nucleation in undercooled Pb-Sn alloys

    NASA Technical Reports Server (NTRS)

    Degroh, Henry C., III

    1989-01-01

    A novel technique resulting in large undercoolings in bulk samples (23 g) of lead-tin alloys was developed. Samples of Pb-12.5 wt percent Sn, Pb-61.9 wt.% Sn, and Pb-77 wt.% Sn were processed with undercoolings ranging from 4 to 34 K and with cooling rates varying between 0.04 and 4 K/s. The nucleation behavior of the Pb-Sn system was found to be nonreciprocal. The solid Sn phase effectively nucleated the Pb phase of the eutectic; however, large undercoolings developed in Sn-rich eutectic liquid in the presence of the solid Pb phase. This phenomenon is believed to be mainly the result of differences in interfacial energies between solid Sn-eutectic liquid, and solid Pb-eutectic liquid rather than lattice misfit between Pb and Sn. Large amounts of segregation developed in the highly undercooled eutectic ingots. This macrosegregation was found to increase as undercooling increases. Macrosegregation in these undercooled eutectic alloys was found to be primarily due to a sink/float mechanism and the nucleation behavior of the alloy. Lead-rich dendrites are the primary phase in the undercooled eutectic system. These dendrites grow rapidly into the undercooled bath and soon break apart due to recalescence and Sn enrichment of the liquid. These fragmented Pb dendrites are then free to settle to the bottom portion of the ingot causing the macrosegregation observed in this study. A eutectic Pb-Sn alloy undercooled 20 K and cooled at 4 K/s had a composition of about Pb-72 wt.% Sn at the top and 55% Sn at the bottom.

  8. Nucleation of metastable aragonite CaCO3 in seawater

    DOE PAGES

    Sun, Wenhao; Jayaraman, Saivenkataraman; Chen, Wei; Persson, Kristin A.; Ceder, Gerbrand

    2015-03-04

    Predicting the conditions in which a compound adopts a metastable structure when it crystallizes out of solution is an unsolved and fundamental problem in materials synthesis, and one which, if understood and harnessed, could enable the rational design of synthesis pathways toward or away from metastable structures. Crystallization of metastable phases is particularly accessible via low-temperature solution-based routes, such as chimie douce and hydrothermal synthesis, but although the chemistry of the solution plays a crucial role in governing which polymorph forms, how it does so is poorly understood. Here, we demonstrate an ab initio technique to quantify thermodynamic parameters ofmore » surfaces and bulks in equilibrium with an aqueous environment, enabling the calculation of nucleation barriers of competing polymorphs as a function of solution chemistry, thereby predicting the solution conditions governing polymorph selection. We apply this approach to resolve the long-standing “calcite–aragonite problem”––the observation that calcium carbonate precipitates as the metastable aragonite polymorph in marine environments, rather than the stable phase calcite––which is of tremendous relevance to biomineralization, carbon sequestration, paleogeochemistry, and the vulnerability of marine life to ocean acidification. We identify a direct relationship between the calcite surface energy and solution Mg–Ca ion concentrations, showing that the calcite nucleation barrier surpasses that of metastable aragonite in solutions with Mg:Ca ratios consistent with modern seawater, allowing aragonite to dominate the kinetics of nucleation. Our ability to quantify how solution parameters distinguish between polymorphs marks an important step toward the ab initio prediction of materials synthesis pathways in solution.« less

  9. Investigation of Nucleate Boiling Mechanisms Under Microgravity Conditions

    NASA Technical Reports Server (NTRS)

    Dhir, V. K.; Qiu, D. M.; Ramanujapu, N.; Hasan, M. M.

    1999-01-01

    The present work is aimed at the experimental studies and numerical modeling of the bubble growth mechanisms of a single bubble attached to a heating surface and of a bubble sliding along an inclined heated plate. Single artificial cavity of 10 microns in diameter was made on the polished Silicon wafer which was electrically heated at the back side in order to control the surface nucleation superheat. Experiments with a sliding bubble were conducted at different inclination angles of the downward facing heated surface for the purpose of studying the effect of magnitude of components of gravity acting parallel to and normal to the heat transfer surface. Information on the bubble shape and size, the bubble induced liquid velocities as well as the surface temperature were obtained using the high speed imaging and hydrogen bubble techniques. Analytical/numerical models were developed to describe the heat transfer through the micro-macro layer underneath and around a bubble formed at a nucleation site. In the micro layer model the capillary and disjoining pressures were included. Evolution of the bubble-liquid interface along with induced liquid motion was modeled. As a follow-up to the studies at normal gravity, experiments are being conducted in the KC-135 aircraft to understand the bubble growth/detachment under low gravity conditions. Experiments have been defined to be performed under long duration of microgravity conditions in the space shuttle. The experiment in the space shuttle will provide bubble growth and detachment data at microgravity and will lead to validation of the nucleate boiling heat transfer model developed from the preceding studies conducted at normal and low gravity (KC-135) conditions.

  10. Nucleation of metastable aragonite CaCO3 in seawater

    PubMed Central

    Sun, Wenhao; Jayaraman, Saivenkataraman; Chen, Wei; Persson, Kristin A.; Ceder, Gerbrand

    2015-01-01

    Predicting the conditions in which a compound adopts a metastable structure when it crystallizes out of solution is an unsolved and fundamental problem in materials synthesis, and one which, if understood and harnessed, could enable the rational design of synthesis pathways toward or away from metastable structures. Crystallization of metastable phases is particularly accessible via low-temperature solution-based routes, such as chimie douce and hydrothermal synthesis, but although the chemistry of the solution plays a crucial role in governing which polymorph forms, how it does so is poorly understood. Here, we demonstrate an ab initio technique to quantify thermodynamic parameters of surfaces and bulks in equilibrium with an aqueous environment, enabling the calculation of nucleation barriers of competing polymorphs as a function of solution chemistry, thereby predicting the solution conditions governing polymorph selection. We apply this approach to resolve the long-standing “calcite–aragonite problem”––the observation that calcium carbonate precipitates as the metastable aragonite polymorph in marine environments, rather than the stable phase calcite––which is of tremendous relevance to biomineralization, carbon sequestration, paleogeochemistry, and the vulnerability of marine life to ocean acidification. We identify a direct relationship between the calcite surface energy and solution Mg–Ca ion concentrations, showing that the calcite nucleation barrier surpasses that of metastable aragonite in solutions with Mg:Ca ratios consistent with modern seawater, allowing aragonite to dominate the kinetics of nucleation. Our ability to quantify how solution parameters distinguish between polymorphs marks an important step toward the ab initio prediction of materials synthesis pathways in solution. PMID:25739963

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

    SciTech Connect

    Yu, Fangqun; Luo, Gan; Liu, Xiaohong; Easter, Richard C.; Ma, Xiaoyan; Ghan, Steven J.

    2012-12-03

    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 for the first time a physically based treatment of IMN into the Community Atmosphere Model version 5. Our simulations show that, compared to globally averaged results based on 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 by 3.67 W/m2 (more negative) and longwave cloud forcing by 1.78 W/m2 (more positive), resulting in a -1.9 W/m2 net change in cloud radiative forcing associated with IMN. The significant impacts of ionization on global aerosol formation, CCN abundance, and cloud radiative forcing may provide an important physical mechanism linking the global energy balance to various processes affecting atmospheric ionization, which should be properly represented in climate models.

  12. Ice nucleation activity in the widespread soil fungus Mortierella alpina

    NASA Astrophysics Data System (ADS)

    Fröhlich-Nowoisky, Janine; Hill, Thomas C. J.; Pummer, Bernhard G.; Yordanova, Petya; Franc, Gary D.; Pöschl, Ulrich

    2015-04-01

    Biological residues in soil dust are a potentially strong source of atmospheric ice nucleators (IN). However, the sources and characteristics of biological - in particular, fungal - IN in soil dust have not been characterized. By analysis of the culturable fungi in topsoils, from a range of different land use and ecosystem types in south-east Wyoming, we found ice nucleation active (INA, i.e., inducing ice formation in the probed range of temperature and concentration) fungi to be both widespread and abundant, particularly in soils with recent inputs of decomposable organic matter. For example, in harvested and ploughed sugar beet and potato fields, and in the organic horizon beneath Lodgepole pine forest, their relative abundances and concentrations among the cultivable fungi were 25% (8 x 103 CFU g-1), 17% (4.8 x 103 CFU g-1) and 17% (4 x 103 CFU g-1), respectively. Across all investigated soils, 8% (2.9 x 103 CFU g-1) of fungal isolates were INA. All INA isolates initiated freezing at -5° C to -6° C and all belonged to a single zygomycotic species, Mortierella alpina (Mortierellales, Mortierellomycotina). By contrast, the handful of fungal species so far reported as INA all belong within the Ascomycota or Basidiomycota phyla. Mortierella alpina is known to be saprobic (utilizing non-living organic matter), widespread in soil and present in air and rain. Sequencing of the ITS region and the gene for γ-linolenic elongase revealed four distinct clades, affiliated to different soil types. The IN produced by M. alpina seem to be extracellular proteins of 100-300 kDa in size which are not anchored in the fungal cell wall. Ice nucleating fungal mycelium will ramify topsoils and probably also release cell-free IN into it. If these IN survive decomposition or are adsorbed onto mineral surfaces, these small cell-free IN might contribute to the as yet uncharacterized pool of atmospheric IN released by soils as dusts.

  13. Effects of atmospheric conditions on ice nucleation activity of Pseudomonas

    NASA Astrophysics Data System (ADS)

    Attard, E.; Yang, H.; Delort, A.-M.; Amato, P.; Pöschl, U.; Glaux, C.; Koop, T.; Morris, C. E.

    2012-11-01

    Although ice nuclei from bacterial origin are known to be efficient at the highest temperatures known for ice catalysts, quantitative data are still needed to assess their role in cloud processes. Here we studied the effects of three typical cloud conditions (i) acidic pH (ii) NO2 and O3 exposure and (iii) UV-A exposure on the ice nucleation activity (INA) of four Pseudomonas strains. Three of the Pseudomonas syringae strains were isolated from cloud water and the phyllosphere and Pseudomonas fluorescens strain CGina-01 was isolated from Antarctic glacier ice melt. Among the three conditions tested, acidic pH caused the most significant effects on INA likely due to denaturation of the ice nucleation protein complex. Exposure to NO2 and O3 gases had no significant or only weak effects on the INA of two P. syringae strains whereas the INA of P. fluorescens CGina-01 was significantly affected. The INA of the third P. syringae strain showed variable responses to NO2 and O3 exposure. These differences in the INA of different Pseudomonas suggest that the response to atmospheric conditions could be strain-specific. After UV-A exposure, a substantial loss of viability of all four strains was observed whereas their INA decreased only slightly. This corroborates the notion that under certain conditions dead bacterial cells can maintain their INA. Overall, the negative effects of the three environmental factors on INA were more significant at the warmer temperatures. Our results suggest that in clouds where temperatures are near 0 °C, the importance of bacterial ice nucleation in precipitation processes could be reduced by some environmental factors.

  14. Effects of atmospheric conditions on ice nucleation activity of Pseudomonas

    NASA Astrophysics Data System (ADS)

    Attard, E.; Yang, H.; Delort, A.-M.; Amato, P.; Pöschl, U.; Glaux, C.; Koop, T.; Morris, C. E.

    2012-04-01

    Although ice nuclei from bacterial origin are known to be efficient at the highest temperatures known for ice catalysts, quantitative data are still needed to assess their role in cloud processes. Here we studied the effects of three typical cloud conditions (i) acidic pH (ii) NO2 and O3 exposure and (iii) UV-A exposure on the ice nucleation activity (INA) of four Pseudomonas strains. Three of the Pseudomonas syringae strains were isolated from cloud water and the phyllosphere and Pseudomonas fluorescens strain CGina-01 was isolated from Antarctic glacier ice melt. Among the three conditions tested, acidic pH caused the most significant effects on INA likely due to denaturation of the ice nucleation protein complex. Exposure to NO2 and O3 gases had no significant or only weak effects on the INA of two P. syringae strains whereas the INA of P. fluorescens CGina-01 was significantly affected. The INA of the third P. syringae strain showed variable responses to NO2 and O3 exposure. These differences in the INA of different Pseudomonas suggest that the response to atmospheric conditions could be strain-specific. After UV-A exposure, a substantial loss of viability of all four strains was observed whereas their INA decreased only slightly. This corroborates the notion that under certain conditions dead bacterial cells can maintain their INA. Overall, the negative effects of the three environmental factors on INA were more significant at the warmer temperatures. Our results suggest that in clouds where temperatures are near 0 °C, the importance of bacterial ice nucleation in precipitation processes could be reduced by some environmental factors.

  15. Effect of surface properties on nucleate pool boiling

    SciTech Connect

    Haze, Ikuya; Tomemori, Hideki; Motoya, Daiju; Osakabe, Masahiro

    1999-07-01

    A series of experiments on nucleate pool boiling was performed by use of an oxygen-free copper rod and platinum wires of different surface properties under both normal gravity condition and microgravity condition. As a result of the experiments, under normal gravity condition, the bubbling on thick cracked silicone-coated surfaces and that on scale surfaces were more vigorous than that on mirror-finished (copper) surfaces, that on bare (Pt) surfaces, that on thin silicone-coated surfaces and that on thick silicone-coated surfaces. The boiling curves on the mirror-finished surface, the bare surface, the thin silicone-coated surface and the thick cracked silicone-coated surface were equal to those predicted by the Rohsenow's correlation. The superheats on the thick silicone-coated surface and the scale surface were larger than those predicted by the Rohsenow's correlation. The boiling curves on the non-cracked silicone-coated surface and the scale surface corrected by those heat resistance were equal to those predicted by the Rohsenow's correlation. The superheat on the thick silicone-coated surface corrected by its heat resistance was smaller than that predicted by the Rohsenow's correlation. The thick cracked silicone-coated surface enhanced the nucleate boiling heat transfer. On the other hand, under microgravity condition, the bubbles stayed around heated surfaces except scale surfaces. The boiling curve on the bare surface under microgravity condition was equal to that under normal gravity condition. The effect of surface properties on the nucleate boiling heat transfer under microgravity condition was equal to that under normal gravity condition.

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

    NASA Astrophysics Data System (ADS)

    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), 10.1063/1.1724333], 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.

  17. Characterization of Ice Nucleating Particles at the Western US Coast

    NASA Astrophysics Data System (ADS)

    Rocci, K.; McCluskey, C. S.; Hill, T. C. J.; DeMott, P. J.; Kreidenweis, S. M.

    2015-12-01

    In temperate climates, ice nucleating particles (INPs) are vital for precipitation initiation. Because INPs may affect precipitation efficiency, and thereby the supply of water resources, it is paramount to have a clear understanding of both natural and anthropogenic sources of INPs. This is especially important to understand in California where drought continues to be a major problem. The CalWater 2015 field campaign, which took place in California from January 15 - March 9, 2015, included comprehensive characterizations of aerosols and their ice nucleating ability via ground-, air-, and ship-based measurements. As part of this campaign, we characterized and analyzed the intra-air mass differences of INPs at a coastal site (Bodega Bay) using immersion freezing measurements of particles collected on filters. Aerosol filters collected throughout the campaign were characterized by their loading and dominant type using meteorology, aerosol size distributions, aerosol composition, and trace gas concentration data. Samples contained a variety of aerosol influences, including biomass burning, nitrogen pollution, sulfur pollution, and sea spray. This study had a particular focus on the INP activity spectra of sea spray aerosol (SSA). We used the online aerosol data to infer variations in SSA types and heat-treated specific samples to look for the presence of heat-labile biological INPs. Furthermore, we ran the NOAA HYSPLIT model to obtain back trajectories for samples dominated by SSA. We found that air masses dominated by distinct terrestrial source types are not well distinguished by their INP number concentrations. However, we did see significantly higher (up to 5000-fold) INP number concentrations in SSA samples taken at the coast compared with number concentrations in samples obtained over open ocean. This difference could be attributable to differences in overall aerosol abundance, which will be evaluated in future studies. Overall, our findings suggest that an

  18. Cirrus crystal nucleation by homogeneous freezing of solution droplets

    NASA Technical Reports Server (NTRS)

    Heymsfield, Andrew J.; Sabin, Robert M.

    1989-01-01

    A numerical model consisting of a system of differential equations is used to study cirrus crystal nucleation in a rising parcel containing a distribution of cloud condensation nuclei. The evolution of the particle population and the thermodynamic variables in the parcel are examined. The results suggest that, if homogeneous freezing is not considered, liquid water should be detected below -40 C. If homogeneous freezing is considered, the rapid growth of ice crystals and vapor depletion prevent water saturation from being reached. It is shown that the likelihood of a droplet being frozen is increased by lower temperatures, larger droplet diameter, or lower solution density.

  19. Sources of organic ice nucleating particles in soils

    NASA Astrophysics Data System (ADS)

    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

  20. Geodesic evolution and nucleation of a de Sitter brane

    SciTech Connect

    Davidson, Aharon; Karasik, David; Lederer, Yoav

    2005-09-15

    Within the framework of geodesic brane gravity, the deviation from general relativity is parametrized by the conserved bulk energy. The corresponding geodesic evolution/nucleation of a de Sitter brane is shown to be exclusively driven by a double-well Higgs potential, rather than by a plain cosmological constant. The (hairy) horizon serves then as the locus of unbroken Z{sub 2} symmetry. The quartic structure of the scalar potential, singled out on finiteness grounds of the total (including the dark component) energy density, chooses the Hartle-Hawking no-boundary proposal.

  1. A New Theory of Nucleate Pool Boiling in Arbitrary Gravity

    NASA Technical Reports Server (NTRS)

    Buyevich, Y. A.; Webbon, Bruce W.

    1995-01-01

    Heat transfer rates specific to nucleate pool boiling under various conditions are determined by the dynamics of vapour bubbles that are originated and grow at nucleation sites of a superheated surface. A new dynamic theory of these bubbles has been recently developed on the basis of the thermodynamics of irreversible processes. In contrast to other existing models based on empirically postulated equations for bubble growth and motion, this theory does not contain unwarrantable assumptions, and both the equations are rigorously derived within the framework of a unified approach. The conclusions of the theory are drastically different from those of the conventional models. The bubbles are shown to detach themselves under combined action of buoyancy and a surface tension force that is proven to add to buoyancy in bubble detachment, but not the other way round as is commonly presumed. The theory ensures a sound understanding of a number of so far unexplained phenomena, such as effect caused by gravity level and surface tension on the bubble growth rate and dependence of the bubble characteristics at detachment on the liquid thermophysical parameters and relevant temperature differences. The theoretical predictions are shown to be in a satisfactory qualitative and quantitative agreement with observations. When being applied to heat transfer at nucleate pool boiling, this bubble dynamic theory offers an opportunity to considerably improve the main formulae that are generally used to correlate experimental findings and to design boiling heat removal in various industrial applications. Moreover, the theory makes possible to pose and study a great deal of new problems of essential impact in practice. Two such problems are considered in detail. One problem concerns the development of a principally novel physical model for the first crisis of boiling. This model allows for evaluating critical boiling heat fluxes under various conditions, and in particular at different

  2. Heterogeneous Nucleation of Naphthalene Vapor on Water Surface

    PubMed

    Smolík; Schwarz

    1997-01-15

    The evaporation of a water drop into a ternary gaseous mixture of air, steam, and naphthalene vapor was investigated. The experimental results were compared with a theoretical prediction based on a numerical solution of coupled boundary layer equations for heat and mass transfer from a drop moving in ternary gas. In the experiments the naphthalene vapor condensed on the water drop as a supercooled liquid even at temperatures far below the melting point of naphthalene. The condensation on drop surface is discussed in terms of classical theory of heterogeneous nucleation on smooth surfaces. PMID:9028892

  3. An assessment of warm fog: Nucleation, control, and recommended research

    NASA Technical Reports Server (NTRS)

    Corrin, M. L.; Connell, J. R.; Gero, A. J.

    1974-01-01

    A state-of-the-art survey is given of warm fog research which has been performed up to, and including, 1974. Topics covered are nucleation, growth, coalescence, fog structures and visibility, effects of surface films, drop size spectrum, optical properties, instrumentation, liquid water content, condensation nuclei. Included is a summary of all reported fog modification experiments. Additional data is provided on air flow, turbulence, a summary of recommendations on instruments to be developed for determining turbulence, air flow, etc., as well as recommendations of various fog research tasks which should be performed for a better understanding of fog microphysics.

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

    NASA Astrophysics Data System (ADS)

    Nekuda Malik, Jennifer A.; Treat, Neil D.; Abdelsamie, Maged; Yu, Liyang; Li, Ruipeng; Smilgies, Detlef-M.; Amassian, Aram; Hawker, Craig J.; Chabinyc, Michael L.; Stingelin, Natalie

    2014-11-01

    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.

  5. Peculiarities of plastic deformation nucleation in copper under nanoindentation

    SciTech Connect

    Kryzhevich, Dmitrij S. Korchuganov, Aleksandr V.; Zolnikov, Konstantin P.; Psakhie, Sergey G.

    2015-10-27

    The computer simulation results on the atomic structure of the copper crystallite and its behavior in nanoindentation demonstrate the key role of local structural transformations in nucleation of plasticity. The generation of local structural transformations can be considered as an elementary event during the formation of higher scale defects, including partial dislocations and stacking faults. The cause for local structural transformations, both direct fcc-hcp and reverse hcp-fcc, is an abrupt local increase in atomic volume. A characteristic feature is that the values of local volume jumps in direct and reverse structural transformations are comparable with that in melting and lie in the range 5–7%.

  6. Charging state of atmospheric nanoparticles during the nucleation burst events

    NASA Astrophysics Data System (ADS)

    Vana, M.; Tamm, E.; Hõrrak, U.; Mirme, A.; Tammet, H.; Laakso, L.; Aalto, P. P.; Kulmala, M.

    2006-12-01

    In this work, the charging state of atmospheric nanoparticles was estimated through simultaneous measurements of aerosol size distribution and air ions mobility distribution with the aim to elucidate the formation mechanisms of atmospheric aerosols. The measurements were performed as a part of the QUEST 2 campaign at a boreal forest station in Finland. The overlapping part of the measurement ranges of the particle size spectrometers and air ion mobility spectrometers in the mass diameter interval of 2.6-40 nm was used to assess the percentage of charged particles (charging probability). This parameter was obtained as the slope of the linear regression line on the scatterplot of the measured concentrations of total (neutral + charged) and charged particles for the same diameter interval. Charging probabilities as a function of particle diameter were calculated for different days and were compared with the steady state charging probabilities of the particles in the bipolar ion atmosphere. For the smallest particles detectable by the particle size spectrometers (2.6-5 nm), the high percentages of negatively charged particles were found during the nanometer particle concentration bursts. These values considerably exceeded the values for the steady charging state and it was concluded that negative cluster ions preferably act as condensation nuclei. This effect was found to be the highest in the case of comparatively weak nucleation bursts of nanoparticles, when the rate of the homogeneous nucleation and the concentration of freshly nucleated particles were low. The nucleation burst days were classified according to the concentration of the generated smallest detectable new particles (weak and strong bursts). Approximately the same classification was obtained based on the charge asymmetry on particles with respect to the charge sign (polarity). The probabilities of negative and positive charge on the particles with the diameter of 5-20 nm were found to be nearly equal

  7. Theory of homogeneous nucleation - A chemical kinetic view

    NASA Technical Reports Server (NTRS)

    Yang, C. H.; Qiu, H.

    1986-01-01

    A simple function with two undetermined parameters has been used in place of the Thomson-Gibbs relation to relate the activation energy of the vaporization reaction to cluster size. The parameters are iterated to assume optimum values in numerical computation so experimental data may be correlated. Calculations show this approach closely predicts and correlates available data for water, benzene, and ethanol. The nucleation formulism is redeveloped with an emphasis on the chemical kinetic view. Surface tension of the liquid and free energy of droplet formation are not used in its derivation.

  8. Nucleation of Quantized Vortices from Rotating Superfluid Drops

    NASA Technical Reports Server (NTRS)

    Donnelly, Russell J.

    2001-01-01

    The long-term goal of this project is to study the nucleation of quantized vortices in helium II by investigating the behavior of rotating droplets of helium II in a reduced gravity environment. The objective of this ground-based research grant was to develop new experimental techniques to aid in accomplishing that goal. The development of an electrostatic levitator for superfluid helium, described below, and the successful suspension of charged superfluid drops in modest electric fields was the primary focus of this work. Other key technologies of general low temperature use were developed and are also discussed.

  9. Controllable Magnetization Processes Induced by Nucleation Sites in Permalloy Rings

    NASA Astrophysics Data System (ADS)

    Ying-Jiun Chen,; Chia-Jung Hsu,; Chun-Neng Liao,; Hao-Ting Huang,; Chiun-Peng Lee,; Yi-Hsun Chiu,; Tzu-Yun Tung,; Mei-Feng Lai,

    2010-02-01

    Different arrangements of notches as nucleation sites are demonstrated experimentally and numerically to effectively control the magnetization processes of permalloy rings. In the ring with notches at the same side with respect to field direction, two same-helicity vortex domain walls in the onion state lead to two-step switching going through flux-closure state; in the ring with diagonal notches two opposite-helicity vortex domain walls lead to one-step switching skipping flux-closure state. The switching processes are repeatable in contrast to rings without notches where helicites of two vortex domain walls are random so the switching processes can not be controlled.

  10. The effect of ultrasonic waves on the nucleation of pure water and degassed water.

    PubMed

    Yu, Deyang; Liu, Baolin; Wang, Bochun

    2012-05-01

    In order to clarify the mechanism of nucleation of ice induced by ultrasound, ultrasonic waves have been applied to supercooled pure water and degassed water, respectively. For each experiment, water sample is cooled at a constant cooling rate of 0.15 °C/min and the ultrasonic waves are applied from the water temperature of 0 °C until the water in a sample vessel nucleates. This nucleation temperature is measured. The use of ultrasound increased the nucleation temperature of both degassed water and pure water. However, the undercooling temperature for pure water to nucleate is less than that of degassed water. It is concluded that cavitation and fluctuations of density, energy and temperature induced by ultrasound are factors that affect the nucleation of water. Cavitation is a major factor for sonocrystallisation of ice. PMID:21925917

  11. Sensitivity of partially purified ice nucleation activity of Fusarium acuminatum SRSF 616.

    PubMed

    Humphreys, T L; Castrillo, L A; Lee, M R

    2001-05-01

    Factors that affect bacterial ice nucleation, including growth medium, growth phase, nutrient deprivation, and cold-temperature exposure, were investigated in the ice nucleation active (INA) fungus Fusarium acuminatum SRSF 616. Ice nucleation activity remained relatively constant throughout the growth cycle, and the cell-free culture supernatant consistently displayed higher ice nucleation activity than the hyphal pellet. Although nutrient starvation and low-temperature exposure enhance bacterial ice nucleation activity, reducing the concentration of C, N, or P in synthetischer nährstoffarmer broth (SNB) did not increase fungal ice nucleation activity, nor did exposure to 4 degrees C or 15 degrees C. From the SNB supernatant, selected INA chromatography fractions were obtained that demonstrated increased sensitivity to proteinase K and heat compared with culture supernatant. We propose that partial purification of the fungal ice nuclei resulted in removal of low-molecular-weight stabilizing factors. PMID:11400053

  12. Condensation of a supersaturated vapor. XII. The homogeneous nucleation of the n-alkanes

    NASA Astrophysics Data System (ADS)

    Rudek, Markus M.; Fisk, Jeffery A.; Chakarov, Vasil M.; Katz, Joseph L.

    1996-09-01

    Homogeneous nucleation rates as functions of both supersaturation and temperature were measured in an upward thermal diffusion cloud chamber for four n-alkanes: n-heptane, n-octane, n-nonane, and n-decane. Nucleation rates from about 10-4 to 5×100 drops cm-3 s-1 were obtained in the temperature range, 241 to 330 K. Their dependences on supersaturation and temperature were compared to predictions of several nucleation theories: the internally consistent Classical theory, two versions of the Kalikmanov-van Dongen theory, and the Delale-Meier theory. Each theory predicted the dependence of the nucleation rate on supersaturation reasonably well. However, large temperature dependent correction factors were needed for quantitative agreement between measured and predicted nucleation rates. A plot of the ratio of measured to predicted nucleation rates vs reduced temperature shows that all n-alkanes investigated can be represented to within a factor of ten by a single, best fit line.

  13. A fractal study for nucleate pool boiling heat transfer of nanofluids

    NASA Astrophysics Data System (ADS)

    Xiao, Boqi; Jiang, Guoping; Chen, Lingxia

    2010-01-01

    In this paper, a fractal model for nucleate pool boiling heat transfer of nanofluids is developed based on the fractal distribution of nanoparticles and nucleation sites on boiling surfaces. The model shows the dependences of the heat flux on nanoparticle size and the nanoparticle volume fraction of the suspension, the fractal dimension of the nanoparticle and nucleation site, temperature of nanofluids and properties of fluids. The fractal model predictions show that the natural convection stage continues relatively longer in the case of nanofluids. The addition of nanoparticles causes a decrease of the pool nucleate boiling heat transfer. The nucleate pool boiling heat transfer coefficient is decreased by increasing particle concentration. An excellent agreement between the proposed model predictions and experimental data is found. The validity of the fractal model for nucleate pool boiling heat transfer is thus verified.

  14. A simple apparatus for controlling nucleation and size in protein crystal growth

    NASA Technical Reports Server (NTRS)

    Gernert, Kim M.; Smith, Robert; Carter, Daniel C.

    1988-01-01

    A simple device is described for controlling vapor equilibrium in macromolecular crystallization as applied to the protein crystal growth technique commonly referred to as the 'hanging drop' method. Crystal growth experiments with hen egg white lysozyme have demonstrated control of the nucleation rate. Nucleation rate and final crystal size have been found to be highly dependent upon the rate at which critical supersaturation is approached. Slower approaches show a marked decrease in the nucleation rate and an increase in crystal size.

  15. Sublimating icy planetesimals as the source of nucleation seeds for grain condensation in classical novae

    NASA Technical Reports Server (NTRS)

    Matese, John J.; Whitmire, D. P.; Reynolds, R. T.

    1989-01-01

    The problem of grain nucleation during novae outbursts is a major obstacle to our understanding of dust formation in these systems. How nucleation seeds can form in the hostile post-outburst environment remains an unresolved matter. It is suggested that the material for seeding the condensation of ejecta outflow is stored in a primordial disk of icy planetesimals surrounding the system. Evidence is presented that the requisite number of nucleation seeds can be released by sublimation of the planetesimals during outbursts.

  16. Characterization and Quantification of Intrinsic Ice Nucleators in Winter Rye (Secale cereale) Leaves.

    PubMed

    Brush, R. A.; Griffith, M.; Mlynarz, A.

    1994-02-01

    Extracellular ice formation in frost-tolerant organisms is often initiated at specific sites by ice nucleators. In this study, we examined ice nucleation activity (INA) in the frost-tolerant plant winter rye (Secale cereale). Plants were grown at 20[deg]C, at 5[deg]C with a long day, and at 5[deg]C with a short day (5[deg]C-SD). The threshold temperature for INA was -5 to -12[deg]C in winter rye leaves from all three growth treatments. Epiphytic ice nucleation-active bacteria could not account for INA observed in the leaves. Therefore, the INA must have been produced endogenously. Intrinsic rye ice nucleators were quantified and characterized using single mesophyll cell suspensions obtained by pectolytic degradation of the leaves. The most active ice nucleators in mesophyll cell suspensions exhibited a threshold ice nucleation temperature of -7[deg]C and occurred infrequently at the rate of one nucleator per 105 cells. Rye cells were treated with chemicals and enzymes to characterize the ice nucleators, which proved to be complexes of proteins, carbohydrates, and phospholipids, in which both disulfide bonds and free sulfhydryl groups were important for activity. Carbohydrates and phospholipids were important components of ice nucleators derived from 20[deg]C leaves, whereas the protein component was more important in 5[deg]C-SD leaves. This difference in composition or structure of the ice nucleators, combined with a tendency for more frequent INA, suggests that more ice nucleators are produced in 5[deg]C-SD leaves. These additional ice nucleators may be a component of the mechanism for freezing tolerance observed in winter rye. PMID:12232122

  17. Note: Homogeneous TIP4P/2005 ice nucleation at low supercooling.

    PubMed

    Reinhardt, Aleks; Doye, Jonathan P K

    2013-09-01

    We present a partial free energy profile for the homogeneous nucleation of ice using an all-atom model of water at low supercooling, at which ice growth dynamics are reasonably accessible to simulation. We demonstrate that the free energy profile is well described by classical nucleation theory, and that the nucleation barrier is entropic in origin. We also estimate to first order the temperature dependence of the interfacial free energy.

  18. Surface induced nucleation of a Lennard-Jones system on an implicit surface at sub-freezing temperatures: a comparison with the classical nucleation theory.

    PubMed

    Loeffler, Troy D; Chen, Bin

    2013-12-21

    The aggregation-volume-bias Monte Carlo method was employed to study surface-induced nucleation of Lennard-Jonesium on an implicit surface below the melting point. It was found that surfaces catalyze not only the formation of the droplets (where the nucleation free energy barriers were shown to decrease with increasing surface interaction strength), but also the transition of these droplets into crystal structures due to the surface-induced layering effects. However, this only occurs under suitable interaction strength. When surface attraction is too strong, crystallization is actually inhibited due to the spread of the particles across the surface and corresponding formation of two-dimensional clusters. The simulation results were also used to examine the bulk-droplet based classical nucleation theory for surface-induced nucleation, particularly the additional contact angle term used to describe both the nucleation free energy barrier heights and the critical cluster sizes compared to its homogeneous nucleation formalism. Similar to what has been found previously for homogeneous nucleation, the theory does poorly toward the high-supersaturation region when the critical clusters are small and fractal, but the theoretical predictions on both barrier heights and critical cluster sizes improve rapidly with the decrease of the supersaturation.

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

    NASA Technical Reports Server (NTRS)

    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.

  20. Inclusion of line tension effect in classical nucleation theory for heterogeneous nucleation: A rigorous thermodynamic formulation and some unique conclusions.

    PubMed

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

    2015-03-14

    A rigorous thermodynamic formulation of the geometric model for heterogeneous nucleation including line tension effect is missing till date due to the associated mathematical hurdles. In this work, we develop a novel thermodynamic formulation based on Classical Nucleation Theory (CNT), which is supposed to illustrate a systematic and a more plausible analysis for the heterogeneous nucleation on a planar surface including the line tension effect. The appreciable range of the critical microscopic contact angle (θc), obtained from the generalized Young's equation and the stability analysis, is θ∞ < θc < θ' for positive line tension and is θM < θc < θ∞ for negative line tension. θ∞ is the macroscopic contact angle, θ' is the contact angle for which the Helmholtz free energy has the minimum value for the positive line tension, and θM is the local minima of the nondimensional line tension effect for the negative line tension. The shape factor f, which is basically the dimensionless critical free energy barrier, becomes higher for lower values of θ∞ and higher values of θc for positive line tension. The combined effect due to the presence of the triple line and the interfacial areas (f(L) + f(S)) in shape factor is always within (0, 3.2), resulting f in the range of (0, 1.7) for positive line tension. A formerly presumed appreciable range for θc(0 < θc < θ∞) is found not to be true when the effect of negative line tension is considered for CNT. Estimation based on the property values of some real fluids confirms the relevance of the present analysis.