Science.gov

Sample records for nucleation heterogeneous multicomponent

  1. Heterogeneous nucleation and shape transformation of multicomponent metallic nanostructures.

    PubMed

    Kwon, Soon Gu; Krylova, Galyna; Phillips, Patrick J; Klie, Robert F; Chattopadhyay, Soma; Shibata, Tomohiro; Bunel, Emilio E; Liu, Yuzi; Prakapenka, Vitali B; Lee, Byeongdu; Shevchenko, Elena V

    2015-02-01

    To be able to control the functions of engineered multicomponent nanomaterials, a detailed understanding of heterogeneous nucleation at the nanoscale is essential. Here, by using in situ synchrotron X-ray scattering, we show that in the heterogeneous nucleation and growth of Au on Pt or Pt-alloy seeds the heteroepitaxial growth of the Au shell exerts high stress (∼2 GPa) on the seed by forming a core/shell structure in the early stage of the reaction. The development of lattice strain and subsequent strain relaxation, which we show using atomic-resolution transmission electron microscopy to occur through the slip of {111} layers, induces morphological changes from a core/shell to a dumbbell structure, and governs the nucleation and growth kinetics. We also propose a thermodynamic model for the nucleation and growth of dumbbell metallic heteronanostructures.

  2. Heterogeneous nucleation in multi-component vapor on a partially wettable charged conducting particle. II. The generalized Laplace, Gibbs-Kelvin, and Young equations and application to nucleation

    NASA Astrophysics Data System (ADS)

    Noppel, M.; Vehkamäki, H.; Winkler, P. M.; Kulmala, M.; Wagner, P. E.

    2013-10-01

    Based on the results of a previous paper [M. Noppel, H. Vehkamäki, P. M. Winkler, M. Kulmala, and P. E. Wagner, J. Chem. Phys. 139, 134107 (2013)], we derive a thermodynamically consistent expression for reversible or minimal work needed to form a dielectric liquid nucleus of a new phase on a charged insoluble conducting sphere within a uniform macroscopic one- or multicomponent mother phase. The currently available model for ion-induced nucleation assumes complete spherical symmetry of the system, implying that the seed ion is immediately surrounded by the condensing liquid from all sides. We take a step further and treat more realistic geometries, where a cap-shaped liquid cluster forms on the surface of the seed particle. We derive the equilibrium conditions for such a cluster. The equalities of chemical potentials of each species between the nucleus and the vapor represent the conditions of chemical equilibrium. The generalized Young equation that relates contact angle with surface tensions, surface excess polarizations, and line tension, also containing the electrical contribution from triple line excess polarization, expresses the condition of thermodynamic equilibrium at three-phase contact line. The generalized Laplace equation gives the condition of mechanical equilibrium at vapor-liquid dividing surface: it relates generalized pressures in neighboring bulk phases at an interface with surface tension, excess surface polarization, and dielectric displacements in neighboring phases with two principal radii of surface curvature and curvatures of equipotential surfaces in neighboring phases at that point. We also re-express the generalized Laplace equation as a partial differential equation, which, along with electrostatic Laplace equations for bulk phases, determines the shape of a nucleus. We derive expressions that are suitable for calculations of the size and composition of a critical nucleus (generalized version of the classical Kelvin-Thomson equation).

  3. 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.

  4. Heterogeneous nucleation of ice from supercooled water

    NASA Astrophysics Data System (ADS)

    Seeley, Lane Howard

    The relaxation of a metastable phase via the formation of a critical domain of the corresponding stable phase is a phenomenon that has been studied extensively in condensed matter physics. This dissertation describes laboratory studies of this phenomenon in the context of ice nucleation from undercooled liquid water. Such a study presents unique experimental challenges because the formation of a critical embryo is a statistical event, and once it occurs the entire sample relaxes to the stable phase. In order to study this statistical process it is necessary to create a large ensemble of separate, yet identical, domains of the metastable phase. The design of an apparatus is described which creates such an ensemble, in time, by repeatedly freezing and thawing a single water drop. This apparatus allows for the collection of a large data set and therefore can identify subtle changes in nucleation statistics that are produced by external controls. This dissertation describes a series of experiments intended to probe several aspects of ice nucleation. Results are presented for homogeneous ice nucleation as well as heterogeneous ice nucleation by; silanized and unsilanized glass, aliphatic alcohol Langmuir films, ionizing radiation, electric fields and motion at the three phase contact line. These experiments are analyzed largely in the context of classical nucleation theory. The unique experimental technique described here allows for sensitive tests of the temperature dependent nucleation rates, R( T), in these systems. Analysis of the R( T) within the context of classical nucleation theory constrains thermodynamic parameters and provides insight into these nucleation processes.

  5. 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.

  6. Repeatability and randomness in heterogeneous freezing nucleation

    NASA Astrophysics Data System (ADS)

    Vali, G.

    2008-08-01

    This study is aimed at clarifying the relative importance of the specific character of the nuclei and of the duration of supercooling in heterogeneous freezing nucleation by immersed impurities. Laboratory experiments were carried out in which sets of water drops underwent multiple cycles of freezing and melting. The drops contained suspended particles of mixtures of materials; the resulting freezing temperatures ranged from -6°C to -24°C. Rank correlation coefficients between observed freezing temperatures of the drops in successive runs were >0.9 with very high statistical significance, and thus provide strong support for the modified singular model of heterogeneous immersion freezing nucleation. For given drops, changes in freezing temperatures between cycles were relatively small (<1°C) for the majority of the events. These frequent small fluctuations in freezing temperatures are interpreted as reflections of the random nature of embryo growth and are associated with a nucleation rate that is a function of a temperature difference from the characteristic temperatures of nuclei. About a sixth of the changes were larger, up to ±5°C, and exhibited some systematic patterns. These are thought to arise from alterations of the nuclei, some being permanent and some transitory. The results are used to suggest ways of describing ice initiation in cloud models that account for both the temperature and the time dependence of freezing nucleation.

  7. Repeatability and randomness in heterogeneous freezing nucleation

    NASA Astrophysics Data System (ADS)

    Vali, G.

    2008-02-01

    This study is aimed at clarifying the relative importance of the specific character of the nuclei and of the duration of supercooling in heterogeneous freezing nucleation by immersed impurities. Laboratory experiments were carried out in which sets of water drops underwent multiple cycles of freezing and melting. The drops contained suspended particles of mixtures of materials; the resulting freezing temperatures ranged from -6°C to -24°C. Rank correlation coefficients between observed freezing temperatures of the drops in successive runs were >0.9 with very high statistical significance, and thus provide strong support for the modified singular model of heterogeneous immersion freezing nucleation. For given drops, changes in freezing temperatures between cycles were relatively small (<1°C) for the majority of the events. These frequent small fluctuations in freezing temperatures are interpreted as reflections of the random nature of embryo growth and are associated with a nucleation rate that is a function of a temperature difference from the characteristic temperatures of nuclei. About a sixth of the changes were larger, up to ±5°C, and exhibited some systematic patterns. These are thought to arise from alterations of the nuclei, some being permanent and some transitory. The results are used to suggest ways of describing ice initiation in cloud models that account for both the temperature and the time dependence of freezing nucleation.

  8. Freezing Rate Due to Heterogeneous Nucleation.

    NASA Astrophysics Data System (ADS)

    Vali, Gabor

    1994-07-01

    The heterogeneous nucleation of ice from supercooled water is influenced by the nature of the foreign nuclei that serve as the sites for ice embryo formation, and by the stochastic nature of the process of embryo growth to critical size. The relative roles of these two factors have been the subject of some debate, especially as they influence the way nucleation of ice is modeled in clouds. `Freezing rate' is defined as the time-dependent rate at which a population of macroscopically identical samples (e.g., drops in a volume of air) freeze due to the nuclei contained in them. Freezing rate is the combined result of nucleus content and of time dependence. The time-dependent freezing rate model (TDFR) is consistent with available empirical evidence. For droplets cooled at rates of the order of 1°C per min, the nucleus content, or nucleus spectrum, predicts the freezing rate with reasonable accuracy. For samples exposed to a fixed temperature, the time dependence of the freezing rate becomes important, but the probability of freezing is not the same for each individual of the sample population. Stochastic models are not supported by the results. Application of the TDFR model and use of measured freezing nucleus data for precipitation provide a basis for the description of ice formation via immersion-freezing nucleation in cloud models. Limitations to full development of these models arise from inadequate knowledge about the freezing nucleus content of cloud water as a function of cloud evolution.

  9. Ice nucleation on carbon surface supports the classical theory for heterogeneous nucleation

    NASA Astrophysics Data System (ADS)

    Cabriolu, Raffaela; Li, Tianshu

    2015-05-01

    The prevalence of heterogeneous nucleation in nature was explained qualitatively by the classical theory for heterogeneous nucleation established over more than 60 years ago, but the quantitative validity and the key conclusions of the theory have remained unconfirmed. Employing the forward flux sampling method and the coarse-grained water model (mW), we explicitly computed the heterogeneous ice nucleation rates in the supercooled water on a graphitic surface at various temperatures. The independently calculated ice nucleation rates were found to fit well according to the classical theory for heterogeneous nucleation. The fitting procedure further yields the estimate of the potency factor, which measures the ratio of the heterogeneous nucleation barrier to the homogeneous nucleation barrier. Remarkably, the estimated potency factor agrees quantitatively with the volumetric ratio of the critical nuclei between the heterogeneous and homogeneous nucleation. Our numerical study thus provides a strong support to the quantitative power of the theory and allows understanding ice nucleation behaviors under the most relevant freezing conditions.

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

    NASA Astrophysics Data System (ADS)

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

    2011-01-01

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

  11. Homogeneous vs. heterogeneous nucleation in water-dicarboxylic acid systems

    NASA Astrophysics Data System (ADS)

    Hienola, A. I.; Vehkamäki, H.; Riipinen, I.; Kulmala, M.

    2009-03-01

    Binary heterogeneous nucleation of water-succinic/glutaric/malonic/adipic acid on nanometer-sized particles is investigated within the frame of classical heterogeneous nucleation theory. Homogeneous nucleation is also included for comparison. It is found that the nucleation probabilities depend on the contact angle and on the size of the seed particles. New thermodynamical properties, such as saturation vapor pressure, density and surface tension for all the dicarboxylic acid aqueous solutions are included in the calculations. While the new surface tension and density formulations do not bring any significant difference in the computed nucleation rate for homogeneous nucleation for succinic and glutaric acids, the use of the newly derived equations for the vapor pressure decrease the acid concentrations in gas phase by 3 orders of magnitude. According to our calculations, the binary heterogeneous nucleation of succinic acid-water and glutaric acid-water - although it requires a 3-4 orders of magnitude lower vapor concentrations than the homogeneous nucleation - cannot take place under atmospheric conditions. On the other hand binary homogeneous nucleation of adipic acid-water systems might be possible under conditions occuring in upper boundary layer. However, a more detailed characterization of the interaction between the surface and the molecules of the nucleating vapor should be considered in the future.

  12. 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.

  13. 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.

  14. Direct Observations of Nucleation in a Nondilute Multicomponent Alloy

    NASA Technical Reports Server (NTRS)

    Sudbrack, Chantal K.; Noebe, Ronald D.; Seidman, David N.

    2006-01-01

    The chemical pathways leading to gamma'(L1(sub 2)) nucleation from nondilute Ni-5.2 Al-14.2 Cr at. %, gama(fcc), at 873 K are followed with radial distribution functions and isoconcentration surface analyses of direct-space atom-probe tomographic images. Although Cr atoms initially are randomly distributed, a distribution of congruent Ni3Al short-range-order domains (SRO), [R] approx. equals 0.6 nm, results from Al diffusion during quenching. Domain site occupancy develops as their number density increases leading to Al-rich phase separation by gamma'-nucleation, [R]=0.75 nm, after SRO occurs.

  15. 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.

  16. Thermokinetics of heterogeneous droplet nucleation on conically textured substrates

    NASA Astrophysics Data System (ADS)

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

    2015-11-01

    Within the framework of the classical theory of heterogeneous nucleation, a thermokinetic model is developed for line-tension-associated droplet nucleation on conical textures considering growth or shrinkage of the formed cluster due to both interfacial and peripheral monomer exchange and by considering different geometric configurations. Along with the principle of free energy extremization, Katz kinetic approach has been employed to study the effect of substrate conicity and wettability on the thermokinetics of heterogeneous water droplet nucleation. Not only the peripheral tension is found to have a considerable effect on the free energy barrier but also the substrate hydrophobicity and hydrophilicity are observed to switch over their roles between conical crest and trough for different growth rates of the droplet. Besides, the rate of nucleation increases and further promotes nucleation for negative peripheral tension as it diminishes the free energy barrier appreciably. Moreover, nucleation inhibition can be achievable for positive peripheral tension due to the enhancement of the free energy barrier. Analyzing all possible geometric configurations, the hydrophilic narrower conical cavity is found to be the most preferred nucleation site. These findings suggest a physical insight into the context of surface engineering for the promotion or the suppression of nucleation on real or engineered substrates.

  17. Physical aspects of heterogeneities in multi-component lipid membranes.

    PubMed

    Komura, Shigeyuki; Andelman, David

    2014-06-01

    Ever since the raft model for biomembranes has been proposed, the traditional view of biomembranes based on the fluid-mosaic model has been altered. In the raft model, dynamical heterogeneities in multi-component lipid bilayers play an essential role. Focusing on the lateral phase separation of biomembranes and vesicles, we review some of the most relevant research conducted over the last decade. We mainly refer to those experimental works that are based on physical chemistry approach, and to theoretical explanations given in terms of soft matter physics. In the first part, we describe the phase behavior and the conformation of multi-component lipid bilayers. After formulating the hydrodynamics of fluid membranes in the presence of the surrounding solvent, we discuss the domain growth-law and decay rate of concentration fluctuations. Finally, we review several attempts to describe membrane rafts as two-dimensional microemulsion.

  18. Heterogeneous Nucleation of Protein Crystals on Fluorinated Layered Silicate

    PubMed Central

    Ino, Keita; Udagawa, Itsumi; Iwabata, Kazuki; Takakusagi, Yoichi; Kubota, Munehiro; Kurosaka, Keiichi; Arai, Kazuhito; Seki, Yasutaka; Nogawa, Masaya; Tsunoda, Tatsuo; Mizukami, Fujio; Taguchi, Hayao; Sakaguchi, Kengo

    2011-01-01

    Here, we describe an improved system for protein crystallization based on heterogeneous nucleation using fluorinated layered silicate. In addition, we also investigated the mechanism of nucleation on the silicate surface. Crystallization of lysozyme using silicates with different chemical compositions indicated that fluorosilicates promoted nucleation whereas the silicates without fluorine did not. The use of synthesized saponites for lysozyme crystallization confirmed that the substitution of hydroxyl groups contained in the lamellae structure for fluorine atoms is responsible for the nucleation-inducing property of the nucleant. Crystallization of twelve proteins with a wide range of pI values revealed that the nucleation promoting effect of the saponites tended to increase with increased substitution rate. Furthermore, the saponite with the highest fluorine content promoted nucleation in all the test proteins regardless of their overall net charge. Adsorption experiments of proteins on the saponites confirmed that the density of adsorbed molecules increased according to the substitution rate, thereby explaining the heterogeneous nucleation on the silicate surface. PMID:21818343

  19. From embryos to precipitates: a study of nucleation and growth in a multicomponent ferritic steel

    SciTech Connect

    Zhang, Zhongwu; Liu, C T; Wang, Xun-Li; Littrell, Ken; Miller, Michael K; An, Ke; Chin, Bryan

    2011-01-01

    The nucleation and growth of nanoscale precipitates in a new class of high-strength, multicomponent, ferritic steels has been studied with complementary state-of-the-art microstructural characterization techniques of atom probe tomography for individual embryos and precipitates and small-angle neutron scattering for their statistical averages. Both techniques revealed a bimodal size distribution, with subnanometer embryos, and nanoscale precipitates. The embryos, which have a radius of {approx}0.4 nm, are enriched in Cu and served as preferential sites for nucleation. The critical radius for nucleation was determined to be {approx}0.7 nm. Subsequent growth of the precipitates is dictated by volumetric diffusion, as predicted by the Lifshitz-Slyozov-Wagner theory.

  20. 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.

  1. Critical humidities of homogeneous and heterogeneous ice nucleation: Inferences from extended classical nucleation theory

    NASA Astrophysics Data System (ADS)

    Khvorostyanov, Vitaly I.; Curry, Judith A.

    2009-02-01

    A generalization of classical ice nucleation theory is used to derive analytical expressions for the critical (threshold) humidities of homogeneous and heterogeneous freezing. The critical radius and energy of an ice embryo and nucleation rates were derived previously by the authors as functions of temperature, pressure, water saturation ratio, and radii of freezing particles. Here we invert the analytical expressions for the nucleation rates and solve them relative to the critical water and ice saturation ratios (or critical relative humidities). The critical humidities are expressed as analytical functions of temperature, pressure, nucleation or cooling rates, radius of freezing particles and their physico-chemical properties, misfit strain, and activation energy. Calculations of critical ice relative humidities are made using these equations over an extended temperature range down to -75°C and are compared with previous empirical parameterizations and experimental data, and differences are interpreted in the context of variation of the other parameters. It is shown that the critical humidities for heterogeneous ice nucleation are lower than those for homogeneous nucleation; however, this difference is not constant but depends substantially on the temperature and properties of freezing aerosol. Some simple parameterizations for cloud and climate models are suggested.

  2. 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).

  3. 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.

  4. 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

  5. Heterogeneous Nucleation of Dicalcium Phosphate Dihydrate on Modified Silica Surfaces.

    PubMed

    Miller, Carrie; Komunjer, Ljepša; Hlady, Vladimir

    2010-01-01

    Heterogeneous nucleation of dicalcium phosphate dihydrate, CaHPO4•2H2O (DCPD) was studied on untreated planar fused silica and on three modified silica surfaces: octadecylsilyl (OTS) modified silica, human serum albumin treated OTS silica, and UV-oxidized 3-mercaptopropyltriethoxysilyl (MTS) modified silica. The supersaturation ratio of calcium and phosphate solution with respect to DCPD was kept below ~10. The nucleated crystals were observed 24 hours and one week after initial contact between supersaturated solutions and substrate surfaces using bright field and reflectance interference contrast microscopy. No DCPD crystals nucleated on albumin-treated OTS-silica. Majority of the DCDP crystals formed on the other modified silica surfaces appeared to be morphologically similar irrespective of the nature of nucleating substrate. Reflectance interference contrast microscopy provided a proof that the majority of the crystals on these substrates do not develop an extended contact with the substrate surface. The images showed that the most extended contact planes were between the DCPD crystals and MTS modified silica surface. The crystals nucleated on OTS-treated and untreated silica surfaces showed only few or none well-developed contact planes.

  6. 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.

  7. 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.

  8. Ice nucleation in solutions and freeze-avoiding insects-homogeneous or heterogeneous?

    PubMed

    Zachariassen, Karl Erik; Kristiansen, Erlend; Pedersen, Sindre Andre; Hammel, Harold T

    2004-06-01

    This article challenges the common view that solutions and cold-hardy freeze-avoiding insects always freeze by heterogeneous nucleation. Data are presented to show that the nucleation temperatures of a variety of solutions and freeze-avoiding insects are a function of the water volume as described by the data previously published by Bigg in 1953. The article also points out that the relationships between melting point depression and depression of nucleation temperature are different for samples undergoing homogeneous nucleation and those undergoing heterogeneous nucleation. Aqueous solutions and freeze-avoiding insects display a relationship like that of homogeneously nucleated samples. It is also argued that the identity of the "impurities" assumed to cause heterogeneous nucleation in aqueous solutions and insects is obscure and that the "impurities" have features which make their existence rather unlikely.

  9. The Theory of Ice Nucleation by Heterogeneous Freezing of Deliquescent Mixed CCN. Part I: Critical Radius, Energy, and Nucleation Rate.

    NASA Astrophysics Data System (ADS)

    Khvorostyanov, Vitaly I.; Curry, Judith A.

    2004-11-01

    This paper extends previous work on the theory of heterogenous ice nucleation. The goals of this analysis are to explain empirical observations of ice nucleation and to provide a suitable framework for modeling and parameterizing the ice nucleation process in cloud-scale and large-scale atmospheric models. Considered are the processes of heterogeneous freezing of deliquescent mixed cloud condensation nuclei that may serve as ice nuclei, and the properties of an ice germ critical radius, energy, and nucleation rate of ice crystals are examined as functions of temperature and supersaturation. Expressions for nucleation in a polydisperse aerosol for the deliquescence-freezing mode are developed. Equations are derived for the threshold and critical saturation ratios as functions of temperature and nucleation rate, and for the threshold and critical temperatures as functions of saturation ratio. Equivalence of the new formulation for the freezing point depression with traditional expressions is shown and the concepts of the effective temperature and supercooling are introduced. These new formulations are used in a companion paper for simulations of ice nucleation using a cloud parcel model.


  10. Heterogeneous nucleation of catalyst-free InAs nanowires on silicon

    NASA Astrophysics Data System (ADS)

    Gomes, U. P.; Ercolani, D.; Zannier, V.; Battiato, S.; Ubyivovk, E.; Mikhailovskii, V.; Murata, Y.; Heun, S.; Beltram, F.; Sorba, L.

    2017-02-01

    We report on the heterogeneous nucleation of catalyst-free InAs nanowires on Si(111) substrates by chemical beam epitaxy. We show that nanowire nucleation is enhanced by sputtering the silicon substrate with energetic particles. We argue that particle bombardment introduces lattice defects on the silicon surface that serve as preferential nucleation sites. The formation of these nucleation sites can be controlled by the sputtering parameters, allowing the control of nanowire density in a wide range. Nanowire nucleation is accompanied by unwanted parasitic islands, but careful choice of annealing and growth temperature allows us to strongly reduce the relative density of these islands and to realize samples with high nanowire yield.

  11. The role of heterogeneity in long-range interacting systems: From nucleation to earthquake fault systems

    NASA Astrophysics Data System (ADS)

    Silva, James Brian

    The role of heterogeneity in two long-range systems is explored with a focus on the interplay of this heterogeneity with the component system interactions. The first will be the heterogeneous Ising model with long-range interactions. Earthquake fault systems under long-range stress transfer with varying types of heterogeneity will be the second system of interest. First I will review the use of the intervention method to determine the time and place of nucleation and extend its use as an indicator for spinodal nucleation. The heterogeneous Ising model with fixed magnetic sites will then be reformulated as a dilute random field Ising model. This reformulation will allow for the application of spinodal nucleation theory to the heterogeneous Ising model by correcting the spinodal field and the critical exponent sigma describing the critical behavior of clusters in spinodal nucleation theory. The applicability of this correction is shown by simulations that determine the cluster scaling of the nucleating droplets near the spinodal. Having obtained a reasonable definition of the saddle point object describing the nucleation droplet, the density profile of the nucleating droplet is measured and deviations from homogeneous spinodal nucleation are found due to the excess amount of sparseness in the nucleating droplet due to the heterogeneity. Earthquake fault systems are then introduced and a connection is shown of two earthquake models. Heterogeneity is introduced in the form of asperities with the intent of modeling the effect of hard rocks on earthquake statistics. The asperities are observed to be a crucial element in explaining the behavior of aftershocks resulting in Omori's law. A second form of heterogeneity is introduced by coupling the Olami-Feder-Christensen model to an invasion percolation model for the purpose of modeling an earthquake fault system undergoing hydraulic fracturing. The ergodicty and event size statistics are explored in this extended model. The

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

    NASA Astrophysics Data System (ADS)

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

    2011-08-01

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

  13. Atomic-scale heterogeneity of a multicomponent bulk metallic glass with excellent glass forming ability.

    PubMed

    Fujita, T; Konno, K; Zhang, W; Kumar, V; Matsuura, M; Inoue, A; Sakurai, T; Chen, M W

    2009-08-14

    We report the atomic structure of a multicomponent Cu45Zr45Ag10 bulk metallic glass investigated by state-of-the-art experimental and computational techniques. In comparison with a binary Cu50Zr50 metallic glass, Zr-rich interpenetrating clusters centered by paired and stringed Ag atoms and Cu-rich icosahedra are widely observed in the ternary Cu45Zr45Ag10 alloy. The atomic-scale heterogeneity caused by chemical short- and medium-range order is found to play a key role in stabilizing the liquid phase and in improving the glass forming ability of the multicomponent alloy.

  14. Heterogeneous ice nucleation of mineral dust particles exposed to ozone

    NASA Astrophysics Data System (ADS)

    Kanji, Zamin A.; Welti, André; Chou, Cédric; Stetzer, Olaf; Lohmann, Ulrike

    2013-05-01

    Deposition and immersion mode ice nucleation studies of kaolinite (Ka) and Arizona Test Dust (ATD) particles exposed to ozone at 430 ppbv, 1.4 and 4.3 ppmv for approximately 2 hours in a stainless steel aerosol tank are presented. The polydisperse particles used have a mode mobility diameter of 800 nm for Ka and 400 nm for ATD. The portable ice nucleation chamber (PINC) and immersion chamber (IMCA-ZINC) were used to study deposition and immersion mode ice nucleation respectively. Both instruments sampled through a particle impactor with a diameter cut-off size of 1 μm. Preliminary results indicate that ice nucleation can be enhanced or inhibited depending on ozone concentration used for the ageing process with higher concentrations suppressing ice nucleation in both immersion and deposition modes. Additionally, Ka and ATD respond differently to the ageing process and to the different modes of ice nucleation. Ozone surface coverage and initial uptake coefficients are presented for the low exposure studies to explain the ice nucleation behavior observed. Ice Active Surface Site Densities (IASSD) are presented as a means of comparison and parameterization of the data to predict potential atmospheric ice nuclei (IN) concentrations.

  15. The microscopic features of heterogeneous ice nucleation may affect the macroscopic morphology of atmospheric ice crystals.

    PubMed

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

    2013-01-01

    It is surprisingly difficult to freeze water. Almost all ice that forms under "mild" conditions (temperatures > -40 degrees C) requires the presence of a nucleating agent--a solid particle that facilitates the freezing process--such as clay mineral dust, soot or bacteria. In a computer simulation, the presence of such ice nucleating agents does not necessarily alleviate the difficulties associated with forming ice on accessible timescales. Nevertheless, in this work we present results from molecular dynamics simulations in which we systematically compare homogeneous and heterogeneous ice nucleation, using the atmospherically important clay mineral kaolinite as our model ice nucleating agent. From our simulations, we do indeed find that kaolinite is an excellent ice nucleating agent but that contrary to conventional thought, non-basal faces of ice can nucleate at the basal face of kaolinite. We see that in the liquid phase, the kaolinite surface has a drastic effect on the density profile of water, with water forming a dense, tightly bound first contact layer. Monitoring the time evolution of the water density reveals that changes away from the interface may play an important role in the nucleation mechanism. The findings from this work suggest that heterogeneous ice nucleating agents may not only enhance the ice nucleation rate, but also alter the macroscopic structure of the ice crystals that form.

  16. Competitive heterogeneous nucleation onto a microscopic impurity in a Potts model

    NASA Astrophysics Data System (ADS)

    Asuquo, Cletus C.; McArthur, Danielle; Bowles, Richard K.

    2016-08-01

    Many metastable systems can nucleate to multiple competing stable or intermediate metastable states. In this work, a Potts model, subject to external fields, is used to study the competitive nucleation of two phases attempting to grow on a microscopic impurity. Monte Carlo simulations are used to calculate the free energy surfaces for the system under different conditions, where the relative stability of the phases is adjusted by changing the interaction parameters, and the nucleation rates obtained using multicomponent transition state theory (TST) are compared with the rates measured using the survival probability method. We find that the two methods predict similar nucleation rates when the free energy barrier used in the transition state theory is defined as the work required to form a critical embryo from the metastable phase. An analysis of the free energy surfaces also reveals that the competition between the nucleating phases leads to an effective drying of the impurity which slows down the nucleation rate compared to the single phase case.

  17. Heterogeneous nucleation of ice on anthropogenic organic particles collected in Mexico City

    SciTech Connect

    Knopf, D.A.; Wang, B.; Laskin, A.; Moffet, R.C.; Gilles, M.K.

    2010-06-20

    This study reports on heterogeneous ice nucleation activity of predominantly organic (or coated with organic material) anthropogenic particles sampled within and around the polluted environment of Mexico City. The onset of heterogeneous ice nucleation was observed as a function of particle temperature (Tp), relative humidity (RH), nucleation mode, and particle chemical composition which is influenced by photochemical atmospheric aging. Particle analyses included computer controlled scanning electron microscopy with energy dispersive analysis of X-rays (CCSEM/EDX) and scanning transmission X-ray microscopy with near edge X-ray absorption fine structure spectroscopy (STXM/NEXAFS). In contrast to most laboratory studies employing proxies of organic aerosol, we show that anthropogenic organic particles collected in Mexico City can potentially induce ice nucleation at experimental conditions relevant to cirrus formation. The results suggest a new precedent for the potential impact of organic particles on ice cloud formation and climate.

  18. Heterogeneous Nucleation of Ice on Anthropogenic Organic Particles Collected in Mexico City

    SciTech Connect

    Knopf, Daniel A.; Wang, BingBing; Laskin, Alexander; Moffet, Ryan C.; Gilles, Marry K.

    2010-06-05

    This study reports on heterogeneous ice nucleation activity of predominantly organic or coated with organic material anthropogenic particles sampled within and around the polluted environment of Mexico City. The onset of heterogeneous ice nucleation was observed as a function of particle temperature (Tp), relative humidity (RH), nucleation mode, and chemical composition of particles influenced by their photochemical atmospheric aging. Particle analyses was conducted using computer controlled scanning electron microscopy with energy dispersive analysis of X-rays (CCSEM/EDX) and scanning transmission X-ray microscopy with near edge X-ray absorption fine structure spectroscopy (STXM/NEXAFS). In contrast to the majority of laboratory studies employing proxies of organic aerosol, we show that anthropogenic organic particles collected in Mexico City have can potentially induce ice nucleation at experimental conditions relevant to cirrus formation. The reported results suggest a new paradigm for the potential impact of organic particles on ice cloud formation and climate.

  19. 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.

  20. 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.

  1. Role of dynamic heterogeneities in crystal nucleation kinetics in an oxide supercooled liquid

    NASA Astrophysics Data System (ADS)

    Gupta, Prabhat K.; Cassar, Daniel R.; Zanotto, Edgar D.

    2016-12-01

    The temperature at which the classical critical nucleus size is equal to the average size of the cooperatively rearranging regions (CRR) in a supercooled liquid has been referred to as a "cross-over" temperature. We show, for the first time, using published nucleation rate, viscosity, and thermo-physical data, that the cross-over temperature for the lithium disilicate melt is significantly larger than the temperature of the kinetic spinodal and is equal or close to the temperature corresponding to the maximum in the experimentally observed nucleation rates. We suggest that the abnormal decrease in nucleation rates below the cross-over temperature is most likely because, in this regime, the CRR size controls the critical nucleus size and the nucleation rate. This finding links, for the first time, measured nucleation kinetics to the dynamic heterogeneities in a supercooled liquid.

  2. Heterogeneous ice nucleation and water uptake by field-collected atmospheric particles below 273 K

    SciTech Connect

    Wang, Bingbing; Laskin, Alexander; Roedel, Tobias R.; Gilles, Marry K.; Moffet, Ryan C.; Tivanski, Alexei V.; Knopf, Daniel A.

    2012-09-25

    Atmospheric ice formation induced by particles with complex chemical and physical properties through heterogeneous nucleation is not well understood. Heterogeneous ice nucleation and water uptake by ambient particles collected from urban environments in Los Angeles and Mexico City are presented. Using a vapour controlled cooling system equipped with an optical microscopy, the range of onset conditions for ice nucleation and water uptake by the collected particles was determined as a function of temperature (200{273 K) and relative humidity with respect to ice (RHice) up to water saturation. Three distinctly different types of authentic atmospheric particles were investigated including soot particles associated with organics/inorganics, inorganic particles of marine origin coated with organic material, and Pb/Zn containing inorganic particles apportioned to anthropogenic emissions relevant to waste incineration. Single particle characterization was provided by micro-spectroscopic analyses using computer controlled scanning electron microscopy with energy dispersive analysis of X-rays (CCSEM/EDX) and scanning transmission X-ray microscopy with near edge X-ray absorption ne structure spectroscopy (STXM/NEXAFS). Above 230 K, signicant differences in water uptake and immersion freezing effciencies of the different particle types were observed. Below 230 K, the particles exhibited high deposition ice nucleation effciencies and formed ice at RHice values well below homogeneous ice nucleation limits. The data show that the chemical composition of these eld{collected particles plays an important role in determining water uptake and immersion freezing. Heterogeneous ice nucleation rate coeffcients, cumulative ice nuclei (IN) spectrum, and IN activated fraction for deposition ice nucleation are derived. The presented ice nucleation data demonstrate that anthropogenic and marine particles comprising of various chemical and physical properties exhibit distinctly different ice

  3. Orientation dependence of heterogeneous nucleation at the Cu-Pb solid-liquid interface

    NASA Astrophysics Data System (ADS)

    Palafox-Hernandez, J. Pablo; Laird, Brian B.

    2016-12-01

    In this work, we examine the effect of surface structure on the heterogeneous nucleation of Pb crystals from the melt at a Cu substrate using molecular-dynamics (MD) simulation. In a previous work [Palafox-Hernandez et al., Acta Mater. 59, 3137 (2011)] studying the Cu/Pb solid-liquid interface with MD simulation, we observed that the structure of the Cu(111) and Cu(100) interfaces was significantly different at 625 K, just above the Pb melting temperature (618 K for the model). The Cu(100) interface exhibited significant surface alloying in the crystal plane in contact with the melt. In contrast, no surface alloying was seen at the Cu(111) interface; however, a prefreezing layer of crystalline Pb, 2-3 atomic planes thick and slightly compressed relative to bulk Pb crystal, was observed to form at the interface. We observe that at the Cu(111) interface the prefreezing layer is no longer present at 750 K, but surface alloying in the Cu(100) interface persists. In a series of undercooling MD simulations, heterogeneous nucleation of fcc Pb is observed at the Cu(111) interface within the simulation time (5 ns) at 592 K—a 26 K undercooling. Nucleation and growth at Cu(111) proceeded layerwise with a nearly planar critical nucleus. Quantitative analysis yielded heterogeneous nucleation barriers that are more than two orders of magnitude smaller than the predicted homogeneous nucleation barriers from classical nucleation theory. Nucleation was considerably more difficult on the Cu(100) surface-alloyed substrate. An undercooling of approximately 170 K was necessary to observe nucleation at this interface within the simulation time. From qualitative observation, the critical nucleus showed a contact angle with the Cu(100) surface of over 90°, indicating poor wetting of the Cu(100) surface by the nucleating phase, which according to classical heterogeneous nucleation theory provides an explanation of the large undercooling necessary to nucleate on the Cu(100) surface

  4. Heterogeneous formation of polar stratospheric clouds - Part 2: Nucleation of ice on synoptic scales

    NASA Astrophysics Data System (ADS)

    Engel, I.; Luo, B. P.; Pitts, M. C.; Poole, L. R.; Hoyle, C. R.; Grooß, J.-U.; Dörnbrack, A.; Peter, T.

    2013-04-01

    This paper provides unprecedented evidence for the importance of heterogeneous nucleation, likely on solid particles of meteoritic origin, and of small-scale temperature fluctuations, for the formation of ice particles in the Arctic stratosphere. During January 2010, ice PSCs (Polar Stratospheric Clouds) were shown by CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations) to have occurred on a synoptic scale (~ 1000 km dimension). CALIPSO observations also showed widespread PSCs containing nitric acid trihydrate (NAT) particles in December 2009, prior to the occurrence of synoptic-scale regions of ice PSCs during mid-January 2010. We demonstrate by means of detailed microphysical modeling along air parcel trajectories that the formation of these PSCs is not readily reconciled with expectations from the conventional understanding of PSC nucleation mechanisms. The measurements are at odds with the previous laboratory-based understanding of PSC formation, which deemed direct heterogeneous nucleation of NAT and ice on preexisting solid particles unlikely. While a companion paper (Part 1) addresses the heterogeneous nucleation of NAT during December 2009, before the existence of ice PSCs, this paper shows that also the large-scale occurrence of stratospheric ice in January 2010 cannot be explained merely by homogeneous ice nucleation but requires the heterogeneous nucleation of ice, e.g. on meteoritic dust or preexisting NAT particles. The required efficiency of the ice nuclei is surprisingly high, namely comparable to that of known tropospheric ice nuclei such as mineral dust particles. To gain model agreement with the ice number densities inferred from observations, the presence of small-scale temperature fluctuations, with wavelengths unresolved by the numerical weather prediction models, is required. With the derived rate parameterization for heterogeneous ice nucleation we are able to explain and reproduce CALIPSO observations throughout the

  5. Heterogeneous formation of polar stratospheric clouds - Part 2: Nucleation of ice on synoptic scales

    NASA Astrophysics Data System (ADS)

    Engel, I.; Luo, B. P.; Pitts, M. C.; Poole, L. R.; Hoyle, C. R.; Grooß, J.-U.; Dörnbrack, A.; Peter, T.

    2013-11-01

    This paper provides compelling evidence for the importance of heterogeneous nucleation, likely on solid particles of meteoritic origin, and of small-scale temperature fluctuations, for the formation of ice particles in the Arctic stratosphere. During January 2010, ice PSCs (polar stratospheric clouds) were shown by CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations) to have occurred on a synoptic scale (~1000 km dimension). CALIPSO observations also showed widespread PSCs containing NAT (nitric acid trihydrate) particles in December 2009, prior to the occurrence of synoptic-scale regions of ice PSCs during mid-January 2010. We demonstrate by means of detailed microphysical modeling along air parcel trajectories that the formation of these PSCs is not readily reconciled with expectations from the conventional understanding of PSC nucleation mechanisms. The measurements are at odds with the previous laboratory-based understanding of PSC formation, which deemed direct heterogeneous nucleation of NAT and ice on preexisting solid particles unlikely. While a companion paper (Part 1) addresses the heterogeneous nucleation of NAT during December 2009, before the existence of ice PSCs, this paper shows that also the large-scale occurrence of stratospheric ice in January 2010 cannot be explained merely by homogeneous ice nucleation but requires the heterogeneous nucleation of ice, e.g. on meteoritic dust or preexisting NAT particles. The required efficiency of the ice nuclei is surprisingly high, namely comparable to that of known tropospheric ice nuclei such as mineral dust particles. To gain model agreement with the ice number densities inferred from observations, the presence of small-scale temperature fluctuations, with wavelengths unresolved by the numerical weather prediction models, is required. With the derived rate parameterization for heterogeneous ice nucleation we are able to explain and reproduce CALIPSO observations throughout the

  6. BINARY: an optical freezing array for assessing temperature and time dependence of heterogeneous ice nucleation

    NASA Astrophysics Data System (ADS)

    Budke, C.; Koop, T.

    2015-02-01

    A new optical freezing array for the study of heterogeneous ice nucleation in microliter-sized droplets is introduced, tested and applied to the study of immersion freezing in aqueous Snomax® suspensions. In the Bielefeld Ice Nucleation ARraY (BINARY) ice nucleation can be studied simultaneously in 36 droplets at temperatures down to -40 °C (233 K) and at cooling rates between 0.1 and 10 K min-1. The droplets are separated from each other in individual compartments, thus preventing a Wegener-Bergeron-Findeisen type water vapor transfer between droplets as well as avoiding the seeding of neighboring droplets by formation and surface growth of frost halos. Analysis of freezing and melting occurs via an automated real-time image analysis of the optical brightness of each individual droplet. As an application ice nucleation in water droplets containing Snomax® at concentrations from 1 ng mL-1 to 1 mg mL-1 was investigated. Using different cooling rates, a small time dependence of ice nucleation induced by two different classes of ice nucleators (INs) contained in Snomax® was detected and the corresponding heterogeneous ice nucleation rate coefficient was quantified. The observed time dependence is smaller than those of other types of INs reported in the literature, suggesting that the BINARY setup is suitable for quantifying time dependence for most other INs of atmospheric interest, making it a useful tool for future investigations.

  7. Interfacial energies for heterogeneous nucleation of calcium carbonate on mica and quartz.

    PubMed

    Li, Qingyun; Fernandez-Martinez, Alejandro; Lee, Byeongdu; Waychunas, Glenn A; Jun, Young-Shin

    2014-05-20

    Interfacial free energies often control heterogeneous nucleation of calcium carbonate (CaCO3) on mineral surfaces. Here we report an in situ experimental study of CaCO3 nucleation on mica (muscovite) and quartz, which allows us to obtain the interfacial energies governing heterogeneous nucleation. In situ grazing incidence small-angle X-ray scattering (GISAXS) was used to measure nucleation rates at different supersaturations. The rates were incorporated into classical nucleation theory to calculate the effective interfacial energies (α'). Ex situ Raman spectroscopy identified both calcite and vaterite as CaCO3 polymorphs; however, vaterite is the most probable heterogeneous nuclei mineral phase. The α' was 24 mJ/m(2) for the vaterite-mica system and 32 mJ/m(2) for the vaterite-quartz system. The smaller α' of the CaCO3-mica system led to smaller particles and often higher particle densities on mica. A contributing factor affecting α' in our system was the smaller structural mismatch between CaCO3 and mica compared to that between CaCO3 and quartz. The extent of hydrophilicity and the surface charge could not explain the observed CaCO3 nucleation trend on mica and quartz. The findings of this study provide new thermodynamic parameters for subsurface reactive transport modeling and contribute to our understanding of mechanisms where CaCO3 formation on surfaces is of concern.

  8. Phase nucleation and evolution mechanisms in heterogeneous solids

    NASA Astrophysics Data System (ADS)

    Udupa, Anirudh

    Phase nucleation and evolution is a problem of critical importance in many applications. As the length scales are reduced, it becomes increasingly important to consider interfacial and micro-structural effects that can be safely ignored at larger length scales owing to randomness. The theory of phase nucleation has been addressed usually by the classical nucleation theory, which was originally derived for single component fluid systems, after making an assumption of equilibrium. The criterion has not been rigorously derived for solids, which are far from equilibrium due to dissipation by multiple physical drivers. In this thesis, a thermodynamically sound nucleation criterion is derived for systems with multiple interacting physical phenomena and multiple dissipating mechanisms. This is done, using the tools of continuum mechanics, by determining the change in free energy upon the introduction of a new nucleus into the system. The developed theory is demonstrated to be a generalization of the classical nucleation theory (CNT). The developed theory is then applied to the problem of electromigration driven void nucleation, a serious reliability concern for the microelectronics industry. The void grows and eventually severs the line making the chip nonfunctional. There are two classes of theories at present in the electromigration literature to address the problem of void nucleation, the vacancy supersaturation theory and the entropic dissipation theory, both of which are empirical and based on intuition developed from experimental observations. When the developed theory was applied to the problem of electromigration, it was found to be consistent with the vacancy supersaturation theory, but provided the correct energetic quantity, the chemical potential, which has contribution from both the vacancy concentration as well as the hydrostatic stress. An experiment, consisting of electromigration tests on serpentine lines, was developed to validate the developed

  9. Chemical processing does not always impair heterogeneous ice nucleation of mineral dust particles

    NASA Astrophysics Data System (ADS)

    Sullivan, R. C.; Demott, P. J.; Prenni, A. J.; Minambres, L.; Kreidenweis, S. M.; Moehler, O.

    2010-12-01

    Mineral dust particles are the most abundant heterogeneous ice nuclei in the atmosphere. They also frequently become mixed with secondary material during atmospheric transport. The effect that such atmospheric processing has on the ice nucleation properties of dust particles remains under investigation. We have studied changes in the ice nucleation ability of various mineral dust sources after exposure to nitric acid in an aerosol flow tube, and after heterogeneous nucleation of α-pinene secondary organic aerosol (SOA) in the AIDA cloud expansion chamber. Both chemical treatments altered and homogenized the dust particles’ heterogeneous ice nucleation properties below water-saturation, but had no apparent impact on the immersion-freezing fraction well above water saturation. The fraction of particles capable of nucleating ice at fixed mixed-phase cloud temperatures between -35 and -15 °C was determined using a continuous flow diffusion chamber (CFDC) as the relative humidity with respect to water (RHw) was scanned from 75% to 110% RHw. Exposure to both nitric acid and SOA impaired essentially all ice nucleation in the deposition-regime below water saturation, while causing the onset of condensation-freezing to occur in a step-wise manner over a small range of RHw just below water saturation. We interpret this as the result of an increase in particle hygroscopicity following chemical treatment. This allows the mineral particles to absorb enough water to overcome solute freezing point depression effects and nucleate ice via condensation-freezing at a slightly smaller and narrower range of RHw than the less hygroscopic untreated dust can. Immersion-freezing above water saturation was not affected by either treatment. This is in stark contrast to earlier experiments where dust was exposed to sulfuric acid from a heated vapor source; ice nucleation was notably impaired in both the deposition and immersion-freezing regimes following sulfuric acid treatment.

  10. FOREWORD: Heterogenous nucleation and microstructure formation—a scale- and system-bridging approach Heterogenous nucleation and microstructure formation—a scale- and system-bridging approach

    NASA Astrophysics Data System (ADS)

    Emmerich, H.

    2009-11-01

    Scope and aim of this volume. Nucleation and initial microstructure formation play an important role in almost all aspects of materials science [1-5]. The relevance of the prediction and control of nucleation and the subsequent microstructure formation is fully accepted across many areas of modern surface and materials science and technology. One reason is that a large range of material properties, from mechanical ones such as ductility and hardness to electrical and magnetic ones such as electric conductivity and magnetic hardness, depend largely on the specific crystalline structure that forms in nucleation and the subsequent initial microstructure growth. A very demonstrative example for the latter is the so called bamboo structure of an integrated circuit, for which resistance against electromigration [6] , a parallel alignment of grain boundaries vertical to the direction of electricity, is most favorable. Despite the large relevance of predicting and controlling nucleation and the subsequent microstructure formation, and despite significant progress in the experimental analysis of the later stages of crystal growth in line with new theoretical computer simulation concepts [7], details about the initial stages of solidification are still far from being satisfactorily understood. This is in particular true when the nucleation event occurs as heterogenous nucleation. The Priority Program SPP 1296 'Heterogenous Nucleation and Microstructure Formation—a Scale- and System-Bridging Approach' [8] sponsored by the German Research Foundation, DFG, intends to contribute to this open issue via a six year research program that enables approximately twenty research groups in Germany to work interdisciplinarily together following this goal. Moreover, it enables the participants to embed themselves in the international community which focuses on this issue via internationally open joint workshops, conferences and summer schools. An outline of such activities can be found

  11. Heterogeneous ice nucleation and water uptake by field-collected atmospheric particles below 273 K

    NASA Astrophysics Data System (ADS)

    Wang, Bingbing; Laskin, Alexander; Roedel, Tobias; Gilles, Mary K.; Moffet, Ryan C.; Tivanski, Alexei V.; Knopf, Daniel A.

    2011-11-01

    Ice formation induced by atmospheric particles through heterogeneous nucleation is not well understood. Onset conditions for heterogeneous ice nucleation and water uptake by particles collected in Los Angeles and Mexico City were determined as a function of temperature (200-273 K) and relative humidity with respect to ice (RHice). Four dominant particle types were identified including soot associated with organics, soot with organic and inorganics, inorganic particles of marine origin coated with organic material, and Pb/Zn-containing particles apportioned to emissions relevant to waste incineration. Single particle characterization was provided by micro-spectroscopic analyses using computer controlled scanning electron microscopy with energy dispersive analysis of X-rays (CCSEM/EDX) and scanning transmission X-ray microscopy with near edge X-ray absorption fine structure spectroscopy (STXM/NEXAFS). Above 230 K, significant differences in onsets of water uptake and immersion freezing of different particle types were observed. Below 230 K, particles exhibited high deposition ice nucleation efficiencies and formed ice atRHicewell below homogeneous ice nucleation limits. The data suggest that water uptake and immersion freezing are more sensitive to changes in particle chemical composition compared to deposition ice nucleation. The data demonstrate that anthropogenic and marine influenced particles, exhibiting various chemical and physical properties, possess distinctly different ice nucleation efficiencies and can serve as efficient IN at atmospheric conditions typical for cirrus and mixed-phase clouds.

  12. Heterogeneous ice nucleation and water uptake by field-collected atmospheric particles below 273 K

    NASA Astrophysics Data System (ADS)

    Wang, Bingbing; Laskin, Alexander; Roedel, Tobias; Gilles, Mary K.; Moffet, Ryan C.; Tivanski, Alexei V.; Knopf, Daniel A.

    2012-09-01

    Ice formation induced by atmospheric particles through heterogeneous nucleation is not well understood. Onset conditions for heterogeneous ice nucleation and water uptake by particles collected in Los Angeles and Mexico City were determined as a function of temperature (200-273 K) and relative humidity with respect to ice (RHice). Four dominant particle types were identified including soot associated with organics, soot with organic and inorganics, inorganic particles of marine origin coated with organic material, and Pb/Zn-containing particles apportioned to emissions relevant to waste incineration. Single particle characterization was provided by micro-spectroscopic analyses using computer controlled scanning electron microscopy with energy dispersive analysis of X-rays (CCSEM/EDX) and scanning transmission X-ray microscopy with near edge X-ray absorption fine structure spectroscopy (STXM/NEXAFS). Above 230 K, significant differences in onsets of water uptake and immersion freezing of different particle types were observed. Below 230 K, particles exhibited high deposition ice nucleation efficiencies and formed ice atRHicewell below homogeneous ice nucleation limits. The data suggest that water uptake and immersion freezing are more sensitive to changes in particle chemical composition compared to deposition ice nucleation. The data demonstrate that anthropogenic and marine influenced particles, exhibiting various chemical and physical properties, possess distinctly different ice nucleation efficiencies and can serve as efficient IN at atmospheric conditions typical for cirrus and mixed-phase clouds.

  13. Heterogeneous ice nucleation of viscous secondary organic aerosol produced from ozonolysis of α-pinene

    NASA Astrophysics Data System (ADS)

    Ignatius, Karoliina; Kristensen, Thomas B.; Järvinen, Emma; Nichman, Leonid; Fuchs, Claudia; Gordon, Hamish; Herenz, Paul; Hoyle, Christopher R.; Duplissy, Jonathan; Garimella, Sarvesh; Dias, Antonio; Frege, Carla; Höppel, Niko; Tröstl, Jasmin; Wagner, Robert; Yan, Chao; Amorim, Antonio; Baltensperger, Urs; Curtius, Joachim; Donahue, Neil M.; Gallagher, Martin W.; Kirkby, Jasper; Kulmala, Markku; Möhler, Ottmar; Saathoff, Harald; Schnaiter, Martin; Tomé, Antonio; Virtanen, Annele; Worsnop, Douglas; Stratmann, Frank

    2016-05-01

    There are strong indications that particles containing secondary organic aerosol (SOA) exhibit amorphous solid or semi-solid phase states in the atmosphere. This may facilitate heterogeneous ice nucleation and thus influence cloud properties. However, experimental ice nucleation studies of biogenic SOA are scarce. Here, we investigated the ice nucleation ability of viscous SOA particles. The SOA particles were produced from the ozone initiated oxidation of α-pinene in an aerosol chamber at temperatures in the range from -38 to -10 °C at 5-15 % relative humidity with respect to water to ensure their formation in a highly viscous phase state, i.e. semi-solid or glassy. The ice nucleation ability of SOA particles with different sizes was investigated with a new continuous flow diffusion chamber. For the first time, we observed heterogeneous ice nucleation of viscous α-pinene SOA for ice saturation ratios between 1.3 and 1.4 significantly below the homogeneous freezing limit. The maximum frozen fractions found at temperatures between -39.0 and -37.2 °C ranged from 6 to 20 % and did not depend on the particle surface area. Global modelling of monoterpene SOA particles suggests that viscous biogenic SOA particles are indeed present in regions where cirrus cloud formation takes place. Hence, they could make up an important contribution to the global ice nucleating particle budget.

  14. A novel optical freezing array for the examination of cooling rate dependence in heterogeneous ice nucleation

    NASA Astrophysics Data System (ADS)

    Budke, Carsten; Dreischmeier, Katharina; Koop, Thomas

    2014-05-01

    Homogeneous ice nucleation is a stochastic process, implying that it is not only temperature but also time dependent. For heterogeneous ice nucleation it is still under debate whether there is a significant time dependence or not. In case of minor time dependence it is probably sufficient to use a singular or slightly modified singular approach, which mainly supposes temperature dependence and just small stochastic variations. We contribute to this discussion using a novel optical freezing array termed BINARY (Bielefeld Ice Nucleation ARraY). The setup consists of an array of microliter-sized droplets on a Peltier cooling stage. The droplets are separated from each other with a polydimethylsiloxane (PDMS) spacer to prevent a Bergeron-Findeisen process, in which the first freezing droplets grow at the expense of the remaining liquid ones due to their vapor pressure differences. An automatic detection of nucleation events is realized optically by the change in brightness during freezing. Different types of ice nucleating agents were tested with the presented setup, e. g. pollen and clay mineral dust. Exemplarily, cooling rate dependent measurements are shown for the heterogeneous ice nucleation induced by Snomax®. The authors gratefully acknowledge funding by the German Research Foundation (DFG) through the project BIOCLOUDS (KO 2944/1-1) and through the research unit INUIT (FOR 1525) under KO 2944/2-1. We particularly thank our INUIT partners for fruitful collaboration and sharing of ideas and IN samples.

  15. Heterogeneous Nucleation of Trichloroethylene Ozonation Products in the Formation of New Fine Particles

    PubMed Central

    Wang, Ning; Sun, Xiaomin; Chen, Jianmin; Li, Xiang

    2017-01-01

    Free radicals in atmosphere have played an important role in the atmospheric chemistry. The chloro-Criegee free radicals are produced easily in the decomposition of primary ozonide (POZ) of the trichloroethylene, and can react with O2, NO, NO2, SO2 and H2O subsequently. Then the inorganic salts, polar organic nitrogen and organic sulfur compounds, oxygen-containing heterocyclic intermediates and polyhydroxy compounds can be obtained. The heterogeneous nucleation of oxidation intermediates in the formation of fine particles is investigated using molecular dynamics simulation. The detailed nucleation processes are reported. According to molecular dynamics simulation, the nucleation with a diameter of 2 nm is formed in the Organic Compounds-(NH4)2SO4-H2O system. The spontaneous nucleation is an important process in the formation of fine particles in atmosphere. The model study gives a good example from volatile organic compounds to new fine particles. PMID:28198438

  16. Heterogeneous Nucleation of Trichloroethylene Ozonation Products in the Formation of New Fine Particles

    NASA Astrophysics Data System (ADS)

    Wang, Ning; Sun, Xiaomin; Chen, Jianmin; Li, Xiang

    2017-02-01

    Free radicals in atmosphere have played an important role in the atmospheric chemistry. The chloro-Criegee free radicals are produced easily in the decomposition of primary ozonide (POZ) of the trichloroethylene, and can react with O2, NO, NO2, SO2 and H2O subsequently. Then the inorganic salts, polar organic nitrogen and organic sulfur compounds, oxygen-containing heterocyclic intermediates and polyhydroxy compounds can be obtained. The heterogeneous nucleation of oxidation intermediates in the formation of fine particles is investigated using molecular dynamics simulation. The detailed nucleation processes are reported. According to molecular dynamics simulation, the nucleation with a diameter of 2 nm is formed in the Organic Compounds-(NH4)2SO4-H2O system. The spontaneous nucleation is an important process in the formation of fine particles in atmosphere. The model study gives a good example from volatile organic compounds to new fine particles.

  17. Inclusion of line tension effect in classical nucleation theory for heterogeneous nucleation: A rigorous thermodynamic formulation and some unique conclusions

    SciTech Connect

    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 (θ{sub c}), obtained from the generalized Young’s equation and the stability analysis, is θ{sub ∞} < θ{sub c} < θ′ for positive line tension and is θ{sub M} < θ{sub c} < θ{sub ∞} for negative line tension. θ{sub ∞} 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 θ{sub M} 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{sub ∞} and higher values of θ{sub c} for positive line tension. The combined effect due to the presence of the triple line and the interfacial areas (f{sup L} + f{sup 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 θ{sub c}(0 < θ{sub c} < θ{sub ∞}) 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.

  18. The Many Faces of Heterogeneous Ice Nucleation: Interplay Between Surface Morphology and Hydrophobicity.

    PubMed

    Fitzner, Martin; Sosso, Gabriele C; Cox, Stephen J; Michaelides, Angelos

    2015-10-28

    What makes a material a good ice nucleating agent? Despite the importance of heterogeneous ice nucleation to a variety of fields, from cloud science to microbiology, major gaps in our understanding of this ubiquitous process still prevent us from answering this question. In this work, we have examined the ability of generic crystalline substrates to promote ice nucleation as a function of the hydrophobicity and the morphology of the surface. Nucleation rates have been obtained by brute-force molecular dynamics simulations of coarse-grained water on top of different surfaces of a model fcc crystal, varying the water-surface interaction and the surface lattice parameter. It turns out that the lattice mismatch of the surface with respect to ice, customarily regarded as the most important requirement for a good ice nucleating agent, is at most desirable but not a requirement. On the other hand, the balance between the morphology of the surface and its hydrophobicity can significantly alter the ice nucleation rate and can also lead to the formation of up to three different faces of ice on the same substrate. We have pinpointed three circumstances where heterogeneous ice nucleation can be promoted by the crystalline surface: (i) the formation of a water overlayer that acts as an in-plane template; (ii) the emergence of a contact layer buckled in an ice-like manner; and (iii) nucleation on compact surfaces with very high interaction strength. We hope that this extensive systematic study will foster future experimental work aimed at testing the physiochemical understanding presented herein.

  19. Heterogeneous ice nucleation: Exploring the transition from stochastic to singular freezing behavior

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

    Heterogeneous ice nucleation directly influences cloud physical processes, precipitation formation, global radiation balances, and therefore Earth's climate (Cantrell and Heymsfield, 2005 and references therein). It is important to understand the heterogeneous freezing process at a fundamental level in order to describe this process in a physically-based way that will behave robustly in weather and climate models. There is longstanding debate as to whether heterogeneous ice nucleation is a stochastic process (e.g., Carte, 1956) or whether it exhibits singular behaviour (e.g., Langham and Mason, 1958). Fundamentally, the stochastic ice nucleation behavior implies ice nucleation being time dependent, while singular behavior is characterized by ice nucleation taking place on specific particle surface sites at a certain temperature and being time independent (Vali and Stansbury, 1966). We addressed this issue using both experimental and theoretical methods. Experiments focused on immersion freezing of Arizona Test Dust (ATD) were carried out using the Leipzig Aerosol Cloud Interaction Simulator (LACIS), a seven meter long laminar flow diffusion chamber. Both, temperature and time dependencies of ATD-particle induced immersion freezing were investigated. It was found, that ATD-particle induced immersion freezing took place over a wide temperature range and exhibited no detectable time dependence within the range investigated. The theoretical investigations were carried out using a Classical Nucleation Theory (CNT) based, i.e., purely stochastic, numerical model. This idealized model treats statistically similar particles as being covered with surface sites (patches of finite area) characterized by different nucleation barriers, but with each surface site following the stochastic nature of ice embryo formation. The model provides a phenomenological explanation for seemingly contradictory experimental results obtained in the past. Based on CNT alone, a population of

  20. Formation mechanisms of gold-zinc oxide hexagonal nanopyramids by heterogeneous nucleation using microwave synthesis.

    PubMed

    Herring, Natalie P; AbouZeid, Khaled; Mohamed, Mona B; Pinsk, John; El-Shall, M Samy

    2011-12-20

    This work reports the development of a fast and simple "one-pot" route for the synthesis of hybrid Au-ZnO hexagonal nanopyramids by sequential homogeneous-heterogeneous nucleation steps involving both Au and Zn ions using microwave irradiation (MWI). The rapid decomposition of zinc acetate by MWI in the presence of a mixture of oleic acid (OAc) and oleylamine (OAm) results in the formation of hexagonal ZnO nanopyramids. In the presence of Au ions, the initially formed Au nanocrystals act as heterogeneous nuclei for the nucleation and growth of the ZnO nanopyramids. The Au nanoparticles promote the heterogeneous nucleation of ZnO and the formation of the hexagonal base of the ZnO nanopyramids. Using preformed Au nanoparticles instead of Au ions results in a narrow size distribution of uniform Au-ZnO nanopyramids, each consisting of a gold nanoparticle embedded in the center of the hexagonal base of the ZnO nanopyramid. We study the factors that control the nucleation and growth of these complex structures, and provide new insights into the stepwise homogeneous-heterogeneous mechanism and the conventional heterogeneous nucleation on preformed Au nanoparticles. The formation of the hetero nanostructures Au-ZnO nanopyramids is strongly dependent on the molar ratios of OAc to OAm. The presence of OAc with a considerable dipole moment results in strong electrostatic interaction with the polar surfaces of the growing ZnO nanocrystals thus resulting in slowing the growth rate of the polar planes and allowing the formation of well-developed facets. In the absence of Au nanoparticles, a high concentration of zinc acetate and longer MWI times are required for the production of the nanopyramids. The gold nanoparticles could provide the metallic contact points within the hybrid nanopyramids which could facilitate the bottom-up assembly of Au-ZnO devices. Furthermore, the Au-ZnO nanopyramids could have improved performance in solar energy conversion and photocatalysis.

  1. Irradiation-induced heterogeneous nucleation in uranium dioxide

    NASA Astrophysics Data System (ADS)

    Martin, G.; Garcia, P.; Sabathier, C.; Van Brutzel, L.; Dorado, B.; Garrido, F.; Maillard, S.

    2010-07-01

    Using classical molecular dynamics simulations, we have studied the first stages of defect cluster formation resulting from 10 keV displacement cascades in uranium dioxide. Nanometre size cavities and dislocation loops are shown to appear as a result of the irradiation process. A specifically designed TEM experiment involving He implanted thin foils have also been carried out to support this modelling work. These results, in conjunction with several other observations taken from the literature of ion implanted or neutron irradiated uranium dioxide, suggest a radiation damage controlled heterogeneous mechanism for insoluble fission product segregation in UO 2.

  2. Recent Developments in Modeling Heteroepitaxy/Heterogeneous Nucleation by Dynamical Density Functional Theory

    NASA Astrophysics Data System (ADS)

    Podmaniczky, Frigyes; Tóth, Gyula I.; Tegze, György; Gránásy, László

    2015-11-01

    Crystallization of supersaturated liquids usually starts by epitaxial growth or by heterogeneous nucleation on foreign surfaces. Herein, we review recent advances made in modeling heteroepitaxy and heterogeneous nucleation on flat/modulated surfaces and nanoparticles within the framework of a simple dynamical density functional theory, known as the phase-field crystal model. It will be shown that the contact angle and the nucleation barrier are nonmonotonous functions of the lattice mismatch between the substrate and the crystalline phase. In continuous cooling studies for substrates with lattice mismatch, we recover qualitatively the Matthews-Blakeslee mechanism of stress release via the misfit dislocations. The simulations performed for particle-induced freezing will be confronted with recent analytical results, exploring thus the validity range of the latter. It will be demonstrated that time-dependent studies are essential, as investigations based on equilibrium properties often cannot identify the preferred nucleation pathways. Modeling of these phenomena is essential for designing materials on the basis of controlled nucleation and/or nano-patterning.

  3. Heterogeneous dislocation nucleation in single crystal copper-antimony solid-solution alloys

    NASA Astrophysics Data System (ADS)

    Rajgarhia, Rahul K.; Spearot, Douglas E.; Saxena, Ashok

    2009-07-01

    Molecular dynamics (MD) simulations are employed to study the partial dislocation nucleation process in single crystal copper with varying concentrations of antimony (0.0-2.0 at%Sb) under uniaxial tension. A well-established embedded-atom method potential is used to represent the Cu-Cu interactions and a recently developed Lennard-Jones potential is used for the Cu-Sb and Sb-Sb interactions. Antimony atoms are randomly distributed as substitutional defects in the Cu single crystal. MD simulations indicate that the tensile stress required for partial dislocation nucleation in the crystal decreases with increasing concentration of Sb. The strain field around Sb dopant atoms in the Cu lattice reduces the unstable stacking fault energy, which promotes heterogeneous nucleation of partial dislocations and reduces the tensile stresses required for plastic deformation. In addition, the role of Sb on the reduction in the stress required for dislocation nucleation is found to be orientation-dependent. Finally, both temperature and Sb distribution play a role in the statistical variation of the stress required for heterogeneous partial dislocation nucleation; this variation is maximum at moderate levels of Sb concentration (0.20-0.50 at%Sb).

  4. The Role of Lattice Misfit on Heterogeneous Nucleation of Pure Aluminum

    NASA Astrophysics Data System (ADS)

    Wang, L.; Yang, L.; Zhang, D.; Xia, M.; Wang, Y.; Li, J. G.

    2016-10-01

    α-Alumina (Al2O3) single crystals with different termination planes were used as heterogeneous nucleation substrates for liquid aluminum to varying lattice misfits at the interface between substrate and newly nucleated aluminum grain. Undercooling during the nucleation process was measured for interface configurations with varied lattice misfit, while the solidified Al/Al2O3 interfaces were directly observed by high-resolution transmission electron microscopy (HRTEM). Based on experimental results, the effect of lattice misfit on nucleation behavior was systematically investigated following previous misfit-interfacial energy models, with clarification being made by the undercooling measurement and HRTEM observations of the interfaces in the Al/Al2O3 system. When the misfit is smaller than 13 pct, both experimental results and theoretical analysis show that the currently existing models through modification and incorporating energy calculation can be used to fit the detected undercooling of investigated system. Beyond 13 pct, a new hypothesis was developed to accommodate lattice misfit with stacking faults such as microtwins according to the HRTEM analysis. The interfacial energy is then replaced by the stacking fault energy accumulated in the strained area. It is shown that the lattice misfit plays an important role in determining the heterogeneous nucleation of liquid aluminum. The nucleation undercooling is then able to be predicted by the theoretically calculated interfacial energy using the integrated models developed in the work. The prediction results were also verified by the HRTEM analysis on the nucleation interface of the Al/Al2O3 systems and detected undercooling on corresponding systems.

  5. BINARY: an optical freezing array for assessing temperature and time dependence of heterogeneous ice nucleation

    NASA Astrophysics Data System (ADS)

    Budke, C.; Koop, T.

    2014-09-01

    A new optical freezing array for the study of heterogeneous ice nucleation in microliter-sized droplets is introduced, tested and applied to the study of immersion freezing in aqueous Snomax® suspensions. In the Bielefeld Ice Nucleation ARraY (BINARY) ice nucleation can be studied simultaneously in 36 droplets at temperatures down to -40 °C (233 K) and at cooling rates between 0.1 K min-1 and 10 K min-1. The droplets are separated from each other in individual compartments, thus preventing a Wegener-Bergeron-Findeisen type water vapor transfer between droplets as well as avoiding the seeding of neighboring droplets by formation and surface growth of frost halos. Analysis of freezing and melting occurs via an automated real time image analysis of the optical brightness of each individual droplet. As an application ice nucleation in water droplets containing Snomax® at concentrations from 1 ng mL-1 to 1 mg mL-1 was investigated. Using different cooling rates a minute time dependence of ice nucleation induced by Class A and Class C ice nucleators contained in Snomax® was detected. For the Class A IN a very strong increase of the heterogeneous ice nucleation rate coefficient with decreasing temperature of λ ≡ -dln(jhet)/dT = 8.7 K-1 was observed emphasizing the capability of the BINARY device. This value is larger than those of other types of IN reported in the literature, suggesting that the BINARY setup is suitable for quantifying time dependence for most other IN of atmospheric interest, making it a useful tool for future investigations.

  6. Probabilistic aspects of polymorph selection by heterogeneous nucleation on microporous hydrophobic membrane surfaces

    NASA Astrophysics Data System (ADS)

    Curcio, Efrem; Di Profio, Gianluca; Drioli, Enrico

    2008-12-01

    In this work, probabilistic aspects related to the heterogeneous nucleation on microporous hydrophobic surfaces, i.e. polymeric membranes, have been theoretically investigated to understand the ability of this innovative crystallization technique to promote the formation of different polymorphs. The theoretical results, which clarify the effects of physicochemical properties of membranes (i.e. porosity, contact angle between supersaturated solution, and polymeric substrate) on the nucleation process of polymorphs, have been used to discuss the experimentally observed selective crystallization of forms I and II of paracetamol.

  7. Influence of low-gravity solidification on heterogeneous nucleation in stable iron-carbon alloys

    NASA Technical Reports Server (NTRS)

    Tian, Huameng; Stefanescu, Doru M.; Curreri, Peter A.

    1990-01-01

    The effect of gravity on the processes of nucleation and growth of Fe-C alloys during directional solidification was investigated in experiments in which inoculated and uninoculated samples of an alloy of the gray iron type were solidified on ground (1 g) and under the low-gravity (low-g) and high-gravity (high-g) conditions obtained by aircraft parabolic flights. It was found that a higher number of grains was obtained during solidification in high-g condition, due to higher convection in high-g. It was demonstrated that grain multiplication due to convection can contribute up to 23 percent of the total number of grains resulting from heterogeneous nucleation of uninoculated samples. For the case of inoculated samples, it was found that the contribution of the convection-induced nucleation can be as high as 30 percent, but can be zero at very low or very high grain numbers.

  8. Heterogeneous nucleation from a supercooled ionic liquid on a carbon surface

    NASA Astrophysics Data System (ADS)

    He, Xiaoxia; Shen, Yan; Hung, Francisco R.; Santiso, Erik E.

    2016-12-01

    Classical molecular dynamics simulations were used to study the nucleation of the crystal phase of the ionic liquid [dmim+][Cl-] from its supercooled liquid phase, both in the bulk and in contact with a graphitic surface of D = 3 nm. By combining the string method in collective variables [Maragliano et al., J. Chem. Phys. 125, 024106 (2006)], with Markovian milestoning with Voronoi tessellations [Maragliano et al., J. Chem. Theory Comput. 5, 2589-2594 (2009)] and order parameters for molecular crystals [Santiso and Trout, J. Chem. Phys. 134, 064109 (2011)], we computed minimum free energy paths, the approximate size of the critical nucleus, the free energy barrier, and the rates involved in these nucleation processes. For homogeneous nucleation, the subcooled liquid phase has to overcome a free energy barrier of ˜85 kcal/mol to form a critical nucleus of size ˜3.6 nm, which then grows into the monoclinic crystal phase. This free energy barrier becomes about 42% smaller (˜49 kcal/mol) when the subcooled liquid phase is in contact with a graphitic disk, and the critical nucleus formed is about 17% smaller (˜3.0 nm) than the one observed for homogeneous nucleation. The crystal formed in the heterogeneous nucleation scenario has a structure that is similar to that of the bulk crystal, with the exception of the layers of ions next to the graphene surface, which have larger local density and the cations lie with their imidazolium rings parallel to the graphitic surface. The critical nucleus forms near the graphene surface separated only by these layers of ions. The heterogeneous nucleation rate (˜4.8 × 1011 cm-3 s-1) is about one order of magnitude faster than the homogeneous rate (˜6.6 × 1010 cm-3 s-1). The computed free energy barriers and nucleation rates are in reasonable agreement with experimental and simulation values obtained for the homogeneous and heterogeneous nucleation of other systems (ice, urea, Lennard-Jones spheres, and oxide glasses).

  9. The Theory of Ice Nucleation by Heterogeneous Freezing of Deliquescent Mixed CCN. Part II: Parcel Model Simulation.

    NASA Astrophysics Data System (ADS)

    Khvorostyanov, Vitaly I.; Curry, Judith A.

    2005-02-01

    The new theory of ice nucleation by heterogeneous freezing of deliquescent mixed cloud condensation nuclei (CCN) presented in Part I is incorporated into a parcel model with explicit water and ice bin microphysics to simulate the process of ice nucleation under transient thermodynamic conditions. Simulations are conducted over the temperature range -4° to -60°C, with vertical velocities varying from 1 to 100 cm s-1, for varying initial relative humidities and aerosol characteristics. These simulations show that the same CCN that are responsible for the drop nucleation may initiate crystal nucleation and can be identified as ice nuclei (IN) when crystals form. The simulated nucleation rates and concentrations of nucleated crystals depend on temperature and supersaturation simultaneously, showing good agreement with observations but with noticeable differences when compared with classical temperature-only and supersaturation-only parameterizations. The kinetics of heterogeneous ice nucleation exhibits a negative feedback via water supersaturation, whereby ice nucleation depends on the water supersaturation that is diminished by ice crystal diffusional growth. This feedback is stronger than the corresponding feedback for drop nucleation, and may explain discrepancies between observed ice nuclei concentrations and ice crystal concentrations, the very small fraction of CCN that may serve as IN, and the much smaller crystal concentrations as compared to drop concentrations. The relative importance of heterogeneous versus homogeneous nucleation is examined for a variety of cloud conditions. Based on these calculations, a simple parameterization for ice crystal concentration is suggested for use in cloud models and large-scale models.

  10. Heterogeneous formation of polar stratospheric clouds - Part 1: Nucleation of nitric acid trihydrate (NAT)

    NASA Astrophysics Data System (ADS)

    Hoyle, C. R.; Engel, I.; Luo, B. P.; Pitts, M. C.; Poole, L. R.; Grooß, J.-U.; Peter, T.

    2013-03-01

    Satellite based observations during the Arctic winter of 2009/2010 provide firm evidence that, in contrast to the current understanding, the nucleation of nitric acid trihydrate (NAT) in the polar stratosphere does not only occur on preexisting ice particles. In order to explain the NAT clouds observed over the Arctic in mid December 2009, a heterogeneous nucleation mechanism is required, occurring via immersion freezing on the surface of solid particles, likely of meteoritic origin. For the first time, a detailed microphysical modelling of this NAT formation pathway has been carried out. Heterogeneous NAT formation was calculated along more than sixty thousand trajectories, ending at Cloud Aerosol Lidar with Orthogonal Polarisation (CALIOP) observation points. Comparing the optical properties of the modelled NAT with these observations enabled the thorough validation of a newly developed NAT nucleation parameterisation, which has been built into the Zurich Optical and Microphysical box Model (ZOMM). The parameterisation is based on active site theory, is simple to implement in models and provides substantial advantages over previous approaches which involved a constant rate of NAT nucleation in a given volume of air. It is shown that the new method is capable of reproducing observed PSCs very well, despite the varied conditions experienced by air parcels travelling along the different trajectories. In a companion paper, ZOMM is applied to a later period of the winter, when ice PSCs are also present, and it is shown that the observed PSCs are also represented extremely well under these conditions.

  11. Heterogeneous formation of polar stratospheric clouds - Part 1: Nucleation of nitric acid trihydrate (NAT)

    NASA Astrophysics Data System (ADS)

    Hoyle, C. R.; Engel, I.; Luo, B. P.; Pitts, M. C.; Poole, L. R.; Grooß, J.-U.; Peter, T.

    2013-09-01

    Satellite-based observations during the Arctic winter of 2009/2010 provide firm evidence that, in contrast to the current understanding, the nucleation of nitric acid trihydrate (NAT) in the polar stratosphere does not only occur on preexisting ice particles. In order to explain the NAT clouds observed over the Arctic in mid-December 2009, a heterogeneous nucleation mechanism is required, occurring via immersion freezing on the surface of solid particles, likely of meteoritic origin. For the first time, a detailed microphysical modelling of this NAT formation pathway has been carried out. Heterogeneous NAT formation was calculated along more than sixty thousand trajectories, ending at Cloud Aerosol Lidar with Orthogonal Polarization (CALIOP) observation points. Comparing the optical properties of the modelled NAT with these observations enabled a thorough validation of a newly developed NAT nucleation parameterisation, which has been built into the Zurich Optical and Microphysical box Model (ZOMM). The parameterisation is based on active site theory, is simple to implement in models and provides substantial advantages over previous approaches which involved a constant rate of NAT nucleation in a given volume of air. It is shown that the new method is capable of reproducing observed polar stratospheric clouds (PSCs) very well, despite the varied conditions experienced by air parcels travelling along the different trajectories. In a companion paper, ZOMM is applied to a later period of the winter, when ice PSCs are also present, and it is shown that the observed PSCs are also represented extremely well under these conditions.

  12. Heterogeneous Formation of Polar Stratospheric Clouds- Part 1: Nucleation of Nitric Acid Trihydrate (NAT)

    NASA Technical Reports Server (NTRS)

    Hoyle, C. R.; Engel, I.; Luo, B. P.; Pitts, M. C.; Poole, L. R.; Grooss, J.-U.; Peter, T.

    2013-01-01

    Satellite-based observations during the Arctic winter of 2009/2010 provide firm evidence that, in contrast to the current understanding, the nucleation of nitric acid trihydrate (NAT) in the polar stratosphere does not only occur on preexisting ice particles. In order to explain the NAT clouds observed over the Arctic in mid-December 2009, a heterogeneous nucleation mechanism is required, occurring via immersion freezing on the surface of solid particles, likely of meteoritic origin. For the first time, a detailed microphysical modelling of this NAT formation pathway has been carried out. Heterogeneous NAT formation was calculated along more than sixty thousand trajectories, ending at Cloud Aerosol Lidar with Orthogonal Polarization (CALIOP) observation points. Comparing the optical properties of the modelled NAT with these observations enabled a thorough validation of a newly developed NAT nucleation parameterisation, which has been built into the Zurich Optical and Microphysical box Model (ZOMM). The parameterisation is based on active site theory, is simple to implement in models and provides substantial advantages over previous approaches which involved a constant rate of NAT nucleation in a given volume of air. It is shown that the new method is capable of reproducing observed polar stratospheric clouds (PSCs) very well, despite the varied conditions experienced by air parcels travelling along the different trajectories. In a companion paper, ZOMM is applied to a later period of the winter, when ice PSCs are also present, and it is shown that the observed PSCs are also represented extremely well under these conditions.

  13. Heterogeneous ice nucleation of viscous secondary organic aerosol produced from ozonolysis of α-pinene

    NASA Astrophysics Data System (ADS)

    Ignatius, K.; Kristensen, T. B.; Järvinen, E.; Nichman, L.; Fuchs, C.; Gordon, H.; Herenz, P.; Hoyle, C. R.; Duplissy, J.; Garimella, S.; Dias, A.; Frege, C.; Höppel, N.; Tröstl, J.; Wagner, R.; Yan, C.; Amorim, A.; Baltensperger, U.; Curtius, J.; Donahue, N. M.; Gallagher, M. W.; Kirkby, J.; Kulmala, M.; Möhler, O.; Saathoff, H.; Schnaiter, M.; Tomé, A.; Virtanen, A.; Worsnop, D.; Stratmann, F.

    2015-12-01

    There are strong indications that particles containing secondary organic aerosol (SOA) exhibit amorphous solid or semi-solid phase states in the atmosphere. This may facilitate deposition ice nucleation and thus influence cirrus cloud properties. However, experimental ice nucleation studies of biogenic SOA are scarce. Here, we investigated the ice nucleation ability of viscous SOA particles. The SOA particles were produced from the ozone initiated oxidation of α-pinene in an aerosol chamber at temperatures in the range from -38 to -10 °C at 5-15 % relative humidity with respect to water to ensure their formation in a highly viscous phase state, i.e. semi-solid or glassy. The ice nucleation ability of SOA particles with different sizes was investigated with a new continuous flow diffusion chamber. For the first time, we observed heterogeneous ice nucleation of viscous α-pinene SOA in the deposition mode for ice saturation ratios between 1.3 and 1.4 significantly below the homogeneous freezing limit. The maximum frozen fractions found at temperatures between -36.5 and -38.3 °C ranged from 6 to 20 % and did not depend on the particle surface area. Global modelling of monoterpene SOA particles suggests that viscous biogenic SOA particles are indeed present in regions where cirrus cloud formation takes place. Hence, they could make up an important contribution to the global ice nuclei (IN) budget.

  14. Investigation of heterogeneous ice nucleation in pollen suspensions and washing water

    NASA Astrophysics Data System (ADS)

    Dreischmeier, Katharina; Budke, Carsten; Koop, Thomas

    2014-05-01

    Biological particles such as pollen often show ice nucleation activity at temperatures higher than -20 °C. Immersion freezing experiments of pollen washing water demonstrate comparable ice nucleation behaviour as water containing the whole pollen bodies (Pummer et al., 2012). It was suggested that polysaccharide molecules leached from the grains are responsible for the ice nucleation. Here, heterogeneous ice nucleation in birch pollen suspensions and their washing water was investigated by two different experimental methods. The optical freezing array BINARY (Bielefeld Ice Nucleation ARraY) allows the direct observation of freezing of microliter-sized droplets. The IN spectra obtained from such experiments with birch pollen suspensions over a large concentration range indicate several different ice nucleation active species, two of which are present also in the washing water. The latter was probed also in differential scanning calorimeter (DSC) experiments of emulsified sub-picoliter droplets. Due to the small droplet size in the emulsion samples and at small concentration of IN in the washing water, such DSC experiments can exhibit the ice nucleation behaviour of a single nucleus. The two heterogeneous freezing signals observed in the DSC thermograms can be assigned to two different kinds of ice nuclei, confirming the observation from the BINARY measurements, and also previous studies on Swedish birch pollen washing water (Augustin et al., 2012). The authors gratefully acknowledge funding by the German Research Foundation (DFG) through the project BIOCLOUDS (KO 2944/1-1) and through the research unit INUIT (FOR 1525) under KO 2944/2-1. We particularly thank our INUIT partners for fruitful collaboration and sharing of ideas and IN samples. S. Augustin, H. Wex, D. Niedermeier, B. Pummer, H. Grothe, S. Hartmann, L. Tomsche, T. Clauss, J. Voigtländer, K. Ignatius, and F. Stratmann, Immersion freezing of birch pollen washing water, Atmos. Chem. Phys., 13, 10989

  15. Developing a new parameterization framework for the heterogeneous ice nucleation of atmospheric aerosol particles

    NASA Astrophysics Data System (ADS)

    Ullrich, Romy; Hiranuma, Naruki; Hoose, Corinna; Möhler, Ottmar; Niemand, Monika; Steinke, Isabelle; Wagner, Robert

    2014-05-01

    Developing a new parameterization framework for the heterogeneous ice nucleation of atmospheric aerosol particles Ullrich, R., Hiranuma, N., Hoose, C., Möhler, O., Niemand, M., Steinke, I., Wagner, R. Aerosols of different nature induce microphysical processes of importance for the Earth's atmosphere. They affect not only directly the radiative budget, more importantly they essentially influence the formation and life cycles of clouds. Hence, aerosols and their ice nucleating ability are a fundamental input parameter for weather and climate models. During the previous years, the AIDA (Aerosol Interactions and Dynamics in the Atmosphere) cloud chamber was used to extensively measure, under nearly realistic conditions, the ice nucleating properties of different aerosols. Numerous experiments were performed with a broad variety of aerosol types and under different freezing conditions. A reanalysis of these experiments offers the opportunity to develop a uniform parameterization framework of ice formation for many atmospherically relevant aerosols in a broad temperature and humidity range. The analysis includes both deposition nucleation and immersion freezing. The aim of this study is to develop this comprehensive parameterization for heterogeneous ice formation mainly by using the ice nucleation active site (INAS) approach. Niemand et al. (2012) already developed a temperature dependent parameterization for the INAS- density for immersion freezing on desert dust particles. In addition to a reanalysis of the ice nucleation behaviour of desert dust (Niemand et al. (2012)), volcanic ash (Steinke et al. (2010)) and organic particles (Wagner et al. (2010,2011)) this contribution will also show new results for the immersion freezing and deposition nucleation of soot aerosols. The next step will be the implementation of the parameterizations into the COSMO- ART model in order to test and demonstrate the usability of the framework. Hoose, C. and Möhler, O. (2012) Atmos

  16. Heterogeneous ice nucleation and phase transition of viscous α-pinene secondary organic aerosol

    NASA Astrophysics Data System (ADS)

    Ignatius, Karoliina; Kristensen, Thomas B.; Järvinen, Emma; Nichman, Leonid; Fuchs, Claudia; Gordon, Hamish; Herenz, Paul; Hoyle, Christopher R.; Duplissy, Jonathan; Baltensperger, Urs; Curtius, Joachim; Donahue, Neil M.; Gallagher, Martin W.; Kirkby, Jasper; Kulmala, Markku; Möhler, Ottmar; Saathoff, Harald; Schnaiter, Martin; Virtanen, Annele; Stratmann, Frank

    2016-04-01

    There are strong indications that particles containing secondary organic aerosol (SOA) exhibit amorphous solid or semi-solid phase states in the atmosphere. This may facilitate deposition ice nucleation and thus influence cirrus cloud properties. Global model simulations of monoterpene SOA particles suggest that viscous biogenic SOA are indeed present in regions where cirrus cloud formation takes place. Hence, they could make up an important contribution to the global ice nucleating particle (INP) budget. However, experimental ice nucleation studies of biogenic SOA are scarce. Here, we investigated the ice nucleation ability of viscous SOA particles at the CLOUD (Cosmics Leaving OUtdoor Droplets) experiment at CERN (Ignatius et al., 2015, Järvinen et al., 2015). In the CLOUD chamber, the SOA particles were produced from the ozone initiated oxidation of α-pinene at temperatures in the range from -38 to -10° C at 5-15 % relative humidity with respect to water (RHw) to ensure their formation in a highly viscous phase state, i.e. semi-solid or glassy. We found that particles formed and grown in the chamber developed an asymmetric shape through coagulation. As the RHw was increased to between 35 % at -10° C and 80 % at -38° C, a transition to spherical shape was observed with a new in-situ optical method. This transition confirms previous modelling of the viscosity transition conditions. The ice nucleation ability of SOA particles was investigated with a new continuous flow diffusion chamber SPIN (Spectrometer for Ice Nuclei) for different SOA particle sizes. For the first time, we observed heterogeneous ice nucleation of viscous α-pinene SOA in the deposition mode for ice saturation ratios between 1.3 and 1.4, significantly below the homogeneous freezing limit. The maximum frozen fractions found at temperatures between -36.5 and -38.3° C ranged from 6 to 20 % and did not depend on the particle surface area. References Ignatius, K. et al., Heterogeneous ice

  17. A novel approach to the theory of homogeneous and heterogeneous nucleation.

    PubMed

    Ruckenstein, Eli; Berim, Gersh O; Narsimhan, Ganesan

    2015-01-01

    A new approach to the theory of nucleation, formulated relatively recently by Ruckenstein, Narsimhan, and Nowakowski (see Refs. [7-16]) and developed further by Ruckenstein and other colleagues, is presented. In contrast to the classical nucleation theory, which is based on calculating the free energy of formation of a cluster of the new phase as a function of its size on the basis of macroscopic thermodynamics, the proposed theory uses the kinetic theory of fluids to calculate the condensation (W(+)) and dissociation (W(-)) rates on and from the surface of the cluster, respectively. The dissociation rate of a monomer from a cluster is evaluated from the average time spent by a surface monomer in the potential well as obtained from the solution of the Fokker-Planck equation in the phase space of position and momentum for liquid-to-solid transition and the phase space of energy for vapor-to-liquid transition. The condensation rates are calculated using traditional expressions. The knowledge of those two rates allows one to calculate the size of the critical cluster from the equality W(+)=W(-) as well as the rate of nucleation. The developed microscopic approach allows one to avoid the controversial application of classical thermodynamics to the description of nuclei which contain a few molecules. The new theory was applied to a number of cases, such as the liquid-to-solid and vapor-to-liquid phase transitions, binary nucleation, heterogeneous nucleation, nucleation on soluble particles and protein folding. The theory predicts higher nucleation rates at high saturation ratios (small critical clusters) than the classical nucleation theory for both solid-to-liquid as well as vapor-to-liquid transitions. As expected, at low saturation ratios for which the size of the critical cluster is large, the results of the new theory are consistent with those of the classical one. The present approach was combined with the density functional theory to account for the density

  18. The Effect of Spatial Heterogeneities on Nucleation Kinetics in Amorphous Aluminum Alloys

    NASA Astrophysics Data System (ADS)

    Shen, Ye

    The mechanical property of the Al based metallic glass could be enhanced significantly by introducing the high number density of Al-fcc nanocrystals (1021 ˜1023 m-3) to the amorphous matrix through annealing treatments, which motivates the study of the nucleation kinetics for the microstructure control. With the presence of a high number density (1025 m-3) of aluminum-like medium range order (MRO), the Al-Y-Fe metallic glass is considered to be spatially heterogeneous. Combining the classical nucleation theory with the structural configuration, a MRO seeded nucleation model has been proposed and yields theoretical steady state nucleation rates consistent with the experimental results. In addition, this model satisfies all the thermodynamic and kinetic constraints to be reasonable. Compared with the Al-Y-Fe system, the primary crystallization onset temperature decreases significantly and the transient delay time (tau) is shorter in the Al-Y-Fe-Pb(In) systems because the insoluble Pb and In nanoparticles in the amorphous matrix served as extrinsic spatial heterogeneity to provide the nucleation sites for Al-fcc precipitation and the high-resolution transmission electron microscopy (HRTEM) images of the Pb-Al interface revealed a good wetting behavior between the Al and Pb nanoparticles. The study of the transient delay time (tau) could provide insight on the transport behavior during the nucleation and a more convenient approach to evaluate the delay time has been developed by measuring the Al-Y-Fe amorphous alloy glass transition temperature (Tg) shift with the increasing annealing time (tannealing) in FlashDSC. The break point in the Tg vs. log(tannealing) plot has been identified to correspond to the delay time by the TEM characterization. FlashDSC tests with different heating rates and different compositions (Al-Y-Fe-Pb and Zn-Mg-Ca-Yb amorphous alloys) further confirmed the break point and delay time relationship. The amorphous matrix composition and the

  19. Modeling expected solute concentration in randomly heterogeneous flow systems with multicomponent reactions.

    PubMed

    Malmström, Maria E; Destouni, Georgia; Martinet, Philippe

    2004-05-01

    Many environmental problems require assessment of extensive reaction systems within natural subsurface flow systems exhibiting large physical and biogeochemical heterogeneity. We present an approach to couple stochastic advective-reactive modeling of physical solute transport (LaSAR) with the geochemical model PHREEQC for modeling solute concentrations in systems with variable flow velocity and multicomponent reactions. PHREEQC allows for general and flexible quantification of a multitude of linear and nonlinear geochemical processes, while LaSAR efficiently handles field-scale solute spreading in stochastic heterogeneous flow fields. The combined LaSAR-PHREEQC approach requires very modest computational efforts, thereby allowing a large number of reactive transport problems to be readily assessed and facilitating handling of quantifiable uncertainty in environmental model applications. Computational efficiency and explicit handling of field-scale dispersion without introduction of excessive fluid mixing that may impair model results are general advantages of the LaSAR compared with alternative solute transport modeling approaches. The LaSAR-PHREEQC approach is restricted to steady or unidirectional flow fields, and our specific application examples are limited to homogeneous reaction systems without local or transverse dispersion-diffusion, although these are not general methodological limitations. As a comprehensive application example, we simulate the spreading of acid mine drainage in a groundwater focusing on Zn2+ and including relevant, major-component geochemistry. Model results show that Zn2+ may be substantially attenuated by both sorption and precipitation, with flow heterogeneity greatly affecting expected solute concentrations downstream of the mine waste deposit in both cases.

  20. Modeling multicomponent ionic transport in groundwater with IPhreeqc coupling: Electrostatic interactions and geochemical reactions in homogeneous and heterogeneous domains

    NASA Astrophysics Data System (ADS)

    Muniruzzaman, Muhammad; Rolle, Massimo

    2016-12-01

    The key role of small-scale processes like molecular diffusion and electrochemical migration has been increasingly recognized in multicomponent reactive transport in saturated porous media. In this study, we propose a two-dimensional multicomponent reactive transport model taking into account the electrostatic interactions during transport of charged ions in physically and chemically heterogeneous porous media. The modeling approach is based on the local charge balance and on the description of compound-specific and spatially variable diffusive/dispersive fluxes. The multicomponent ionic transport code is coupled with the geochemical code PHREEQC-3 by utilizing the IPhreeqc module, thus enabling to perform the geochemical calculations included in the PHREEQC's reaction package. The multicomponent reactive transport code is benchmarked with different 1-D and 2-D transport problems. Successively, conservative and reactive transport examples are presented to demonstrate the capability of the proposed model to simulate transport of charged species in heterogeneous porous media with spatially variable physical and chemical properties. The results reveal that the Coulombic cross-coupling between dispersive fluxes can significantly influence conservative as well as reactive transport of charged species both at the laboratory and at the field scale.

  1. Control of heterogeneous nucleation and growth kinetics of dopamine-melanin by altering substrate chemistry.

    PubMed

    Klosterman, Luke; Riley, John K; Bettinger, Christopher John

    2015-03-24

    Dopamine-melanin (DM or "polydopamine") can be deposited on virtually any substrate from solution through autoxidation of dopamine. The versatility of this process has allowed surface-mediated assembly of DM for a wide variety of functional coatings. Here we report the impact of well-defined surface chemistries on the nucleation and growth of such films. DM was deposited on silicon dioxide (SiO2) and SiO2 substrates modified with self-assembled monolayers (SAMs) bearing octadecyl (C18), phenethyl, and aminopropyl functional groups. Atomic force microscopy revealed three-dimensional islands whose areal density and surface coverage are lowest on bare SiO2 substrates and highest on the neutral aromatic and aliphatic substrates. Increasing the pH of the solution from 8.2 to 10 dissociates catechol moieties in DM and inhibits adsorption on negatively charged SiO2 substrates. The growth rate of DM films on SAM-modified SiO2 is maximized at pH 9.5 and almost completely abolished at pH 10 because of increased DM solubility. The initial rates of DM adsorption were measured using quartz crystal microbalance with dissipation measurements. The initial adsorption rate is proportional to the nucleation density, which increases as the hydrophobicity of the substrate increases. Taken together, these data provide insight into the rates of heterogeneous nucleation and growth of DM on substrates with well-defined chemistries.

  2. Shear zone nucleation and deformation transient: effect of heterogeneities and loading conditions in experimentally deformed calcite

    NASA Astrophysics Data System (ADS)

    Morales, L. F. G.; Rybacki, E.; Dresen, G. H.; Kilian, R.

    2015-12-01

    In the Earth's middle to lower crust, strain is frequently localized along ductile shear zones, which commonly nucleate at structural and material heterogeneities. To investigate shear zone nucleation and development due to heterogeneities, we performed constant strain-rate (CSR) and constant stress (CS) simple shear (torsion) deformation experiments on Carrara marble samples containing weak (limestone) inclusions. The experiments were conducted in a Paterson-type gas deformation apparatus at 900 °C temperature and 400 MPa confining pressure and maximum bulk shear strains of 3. Peak shear stress was about 20 MPa for all the samples, followed by smooth weakening and steady state behavior. The strain is predominantly localized in the host marble within the process zone in front of the inclusion, defined by a zone of intense grain size reduction due to dynamic recrystallization. In CS tests a narrow shear zone developed in front of the inclusion, whereas in CSR experiments the deformation is more heterogeneously distributed, up to g=3.. In the later, secondary foliations oblique to the process zone and alternating thin, high-strain layers are common. In samples deformed at the same shear strain (g=1), the average recrystallized grain size in the process zone is similar for CS and CSR conditions. Crystallographic preferred orientation (CPO) measurements shows that different grain sizes have slightly different CPO patterns. CPO strength varies for different grain sizes, with a CPO strength peak between 40-50 μm, decreasing progressively within smaller grain size, but with secondary peaks for different coarse-grained sizes. Our observations suggest that the initial formation and transient deformation of shear zones is strongly affected by loading conditions.

  3. Revealing heterogeneous nucleation of primary Si and eutectic Si by AlP in hypereutectic Al-Si alloys

    PubMed Central

    Li, Jiehua; Hage, Fredrik S.; Liu, Xiangfa; Ramasse, Quentin; Schumacher, Peter

    2016-01-01

    The heterogeneous nucleation of primary Si and eutectic Si can be attributed to the presence of AlP. Although P, in the form of AlP particles, is usually observed in the centre of primary Si, there is still a lack of detailed investigations on the distribution of P within primary Si and eutectic Si in hypereutectic Al-Si alloys at the atomic scale. Here, we report an atomic-scale experimental investigation on the distribution of P in hypereutectic Al-Si alloys. P, in the form of AlP particles, was observed in the centre of primary Si. However, no significant amount of P was detected within primary Si, eutectic Si and the Al matrix. Instead, P was observed at the interface between the Al matrix and eutectic Si, strongly indicating that P, in the form of AlP particles (or AlP ‘patch’ dependent on the P concentration), may have nucleated on the surface of the Al matrix and thereby enhanced the heterogeneous nucleation of eutectic Si. The present investigation reveals some novel insights into heterogeneous nucleation of primary Si and eutectic Si by AlP in hypereutectic Al-Si alloys and can be used to further develop heterogeneous nucleation mechanisms based on adsorption. PMID:27120994

  4. Revealing heterogeneous nucleation of primary Si and eutectic Si by AlP in hypereutectic Al-Si alloys

    NASA Astrophysics Data System (ADS)

    Li, Jiehua; Hage, Fredrik S.; Liu, Xiangfa; Ramasse, Quentin; Schumacher, Peter

    2016-04-01

    The heterogeneous nucleation of primary Si and eutectic Si can be attributed to the presence of AlP. Although P, in the form of AlP particles, is usually observed in the centre of primary Si, there is still a lack of detailed investigations on the distribution of P within primary Si and eutectic Si in hypereutectic Al-Si alloys at the atomic scale. Here, we report an atomic-scale experimental investigation on the distribution of P in hypereutectic Al-Si alloys. P, in the form of AlP particles, was observed in the centre of primary Si. However, no significant amount of P was detected within primary Si, eutectic Si and the Al matrix. Instead, P was observed at the interface between the Al matrix and eutectic Si, strongly indicating that P, in the form of AlP particles (or AlP ‘patch’ dependent on the P concentration), may have nucleated on the surface of the Al matrix and thereby enhanced the heterogeneous nucleation of eutectic Si. The present investigation reveals some novel insights into heterogeneous nucleation of primary Si and eutectic Si by AlP in hypereutectic Al-Si alloys and can be used to further develop heterogeneous nucleation mechanisms based on adsorption.

  5. ZnO nanoparticles favours heterogeneous nucleation in PET-ZnO nanocomposites

    NASA Astrophysics Data System (ADS)

    Agrawal, Harshita; Awasthi, Kamlendra; Saraswat, Yogendra K.; Saraswat, Vibhav K.

    2015-07-01

    The structural and chemical properties with non-isothermal crystallization kinetics of PET-ZnO nanocomposites have been reported in this article. ZnO nanoparticles have been synthesized via chemical route with average diameter 19 nm which made confirm by transmission electron microscopy and X-ray diffractometer (XRD) techniques. PET-ZnO nanocomposites have been prepared by solution casting method. The structural and chemical changes occurred in poly (ethylene terephthalate) after inclusion of ZnO nanoparticles have been studied with the help of XRD and Fourier transform infrared spectroscopy, respectively. It was observed from differential scanning calorimeter that ZnO nanoparticles work as nucleating agent for heterogeneous nucleation in PET matrix under non-isothermal crystallization process. The combined Avrami and Ozawa models have been proved adequate to explain non-isothermal crystallization kinetics of PET-ZnO nanocomposites, and also, ZnO nanoparticles have been caused to reduce crystallization activation energy in pristine PET as per the applied Kissinger model.

  6. Epitaxy versus oriented heterogeneous nucleation of organic crystals on ionic substrates

    NASA Astrophysics Data System (ADS)

    Sarma, K. R.; Shlichta, P. J.; Wilcox, W. R.; Lefever, R. A.

    1997-04-01

    It is plausible to assume that epitaxy is a special case of heterogeneous nucleation in which a restrictive crystallographic relationship exists between substrate and deposit orientations. This would mean that epitaxial substrates should always induce a perceptible reduction in the critical supercooling for nucleation of the deposit. To test this hypothesis, the critical supercoolings of six organic compounds were measured on glass and 11 single-crystal cleaved substrates including (0001) graphite, (001) mica, (111) BaF 2, SrF 2, and CaF 2, and (100) KCl, KBr, KI, NaCl, NaF, and LiF. Reductions in supercooling (with reference to glass substrates) were checked many times for repeatability and reproducibility and shown in almost all cases to have a standard deviation of 1 C or less. Acetanilide, benzoic acid, and p-bromochlorobenzene showed a wide range of supercooling reductions and were oriented on all crystalline substrates. Naphthalene and p-dibromobenzene showed only slight supercooling reductions but were oriented on all substrates, including glass. Benzil showed strong supercooling reductions only for mica and KI but was oriented not only in these cases but also with KI, BaF 2, CaF 2, and graphite. There was little correlation between degree of lattice match and either supercooling reduction or degree of preferred orientation. These results suggest that, for the systems and geometry studied, forces such as molecular dipole binding and growth anisotropy had a stronger effect than lattice match.

  7. A case of type I polar stratospheric cloud formation by heterogeneous nucleation

    NASA Technical Reports Server (NTRS)

    Pueschel, R. F.; Ferry, G. V.; Snetsinger, K. G.; Goodman, J.; Dye, J. E.; Baumgardner, D.; Gandrud, B. W.

    1992-01-01

    The NASA ER-2 aircraft flew on January 24, 1989, from Stavanger to Spitsbergen, Norway, at the 430-440 K potential temperature surface (19.2-19.8 km pressure altitude). Aerosols were sampled continuously by an optical particle counter (PMS-FSSP300) for concentration and size analyses, and during five 10-min intervals by four wire and one replicator impactor for concentration, size, composition, and phase analysis. During sampling, the air saturation of H2O with respect to ice changed from 20 to 100 percent, and of HNO3 with respect to nitric acid trihydrate (NAT) from subsaturation to supersaturation. Data from both instruments indicate a condensation of hydrochloric acid and, later, nitric acid on the background aerosol particles as the ambient temperature decreases along the flight track. This heterogeneous nucleation mechanism generates type I polar stratospheric cloud particles of 10-fold enhanced optical depth, which could play a role in stratospheric ozone depletion.

  8. Line-tension-induced scenario of heterogeneous nucleation on a spherical substrate and in a spherical cavity

    NASA Astrophysics Data System (ADS)

    Iwamatsu, Masao

    2015-07-01

    Line-tension-induced scenario of heterogeneous nucleation is studied for a lens-shaped nucleus with a finite contact angle nucleated on a spherical substrate and on the bottom of the wall of a spherical cavity. The effect of line tension on the free energy of a critical nucleus can be separated from the usual volume term. By comparing the free energy of a lens-shaped critical nucleus of a finite contact angle with that of a spherical nucleus, we find that a spherical nucleus may have a lower free energy than a lens-shaped nucleus when the line tension is positive and large, which is similar to the drying transition predicted by Widom [B. Widom, J. Phys. Chem. 99, 2803 (1995)]. Then, the homogeneous nucleation rather than the heterogeneous nucleation will be favorable. Similarly, the free energy of a lens-shaped nucleus becomes negative when the line tension is negative and large. Then, the barrier-less nucleation with no thermal activation called athermal nucleation will be realized.

  9. Laboratory Measurements on Heterogeneous Nucleation and Growth of Water Vapor on Meteor Smoke Particle Analogues under Conditions of the Mesopause

    NASA Astrophysics Data System (ADS)

    Duft, D.; Nachbar, M.; Wilms, H.; Rapp, M.; Leisner, T.

    2014-12-01

    Heterogeneous nucleation of water vapor on charged nanometer sized (radius< 2nm) meteor smoke particles (MSP) is believed to be the dominating nucleation process in the mesopause region leading to the formation of polar mesospheric clouds (PMC). However, application of classical nucleation theory to the cold conditions of the polar summer mesopause comprises large uncertainties giving rise to strongly variant model predictions of PMC formation. To reduce these uncertainties laboratory measurements of nucleation and growth rates are required. We use an electrodynamic trap to investigate the nucleation and growth of water vapor on singly charged sub-3nm MSP analogues in the laboratory under mesospheric conditions typical during PMC growth initiation. The particles are created in a microwave plasma particle source and stored in a quadrupole ion trap under mesospheric pressure and temperature, where they are subjected to the high supersaturation necessary for nucleation and growth on nanometer sized particles. The particle mass and mass change by water accretion is monitored with a time-of-flight mass spectrometer as a function of residence time under supersaturated conditions. In this contribution we present for the first time measurements of nucleation and growth rates of water vapor on MSP analogues with an initial radius between 1.5nm and 3 nm. Contact parameter, sticking coefficient as well as charge effects on vapor pressure of small particles at mesospheric conditions are presented. These parameters are essential for the microphysical understanding and further global model calculations of PMC formation.

  10. Structural match of heterogeneously nucleated Mn(OH)2(s) nanoparticles on quartz under various pH conditions

    DOE PAGES

    Jung, Haesung; Lee, Byeongdu; Jun, Young -Shin

    2016-09-14

    The early nucleation stage of Mn (hydr)oxide on mineral surfaces is crucial to understand its occurrence and the cycling of nutrients in environmental systems. However, there are only limited studies on the heterogeneous nucleation of Mn(OH)2(s) as the initial stage of Mn (hydr)oxide precipitation. Here, we investigated the effect of pH on the initial nucleation of Mn(OH)2(s) on quartz. Under various pH conditions of 9.8, 9.9, and 10.1, we analyzed the structural matches between quartz and heterogeneously nucleated Mn(OH)2(s). The structural matches were calculated by measuring lateral and vertical dimensions using grazing incidence small angle X-ray scattering (GISAXS) and atomicmore » force microscopy (AFM), respectively. We found that a poorer structural match occurred at a higher pH than at a lower pH. The faster nucleation at a higher pH condition accounted for the observed poorer structural match. By fitting the structural match using classical nucleation theory, we also calculated the interfacial energy between Mn(OH)2(s) and water (γnf = 71 ± 7 mJ/m2). The calculated m values and γnf provided the variance of interfacial energy between quartz and Mn(OH)2(s): γsn = 262–272 mJ/m2. As a result, this study provides new qualitative and quantitative information about heterogeneous nucleation on environmentally an abundant mineral surface, quartz, and it offers important underpinnings for understanding the fate and transport of trace ions in environmental systems.« less

  11. Heterogeneous Nucleation and Growth of Barium Sulfate at Organic-Water Interfaces: Interplay between Surface Hydrophobicity and Ba2+ Adsorption

    DOE PAGES

    Dai, Chong; Stack, Andrew G.; Koishi, Ayumi; ...

    2016-05-10

    Barium sulfate (BaSO4) is a common scale-forming mineral in natural and engineered systems, yet the rates and mechanisms of heterogeneous BaSO4 nucleation are not understood. To address these, we created idealized interfaces on which to study heterogeneous nucleation rates and mechanisms, which also are good models for organic–water interfaces: self-assembled thin films terminated with different functional groups (i.e., -COOH, -SH, or mixed -SH & COOH) coated on glass slides. BaSO4 precipitation on coatings from Barite-supersaturated solutions (saturation index, SI, = 1.1) was investigated using grazing-incidence small-angle X-ray scattering. After reaction for 1 h, a little amount of BaSO4 formed onmore » hydrophilic bare and -COOH coated glasses. Meanwhile, BaSO4 nucleation was significantly promoted on hydrophobic -SH and mixed -SH & COOH coatings. This is because substrate hydrophobicity likely affected the interfacial energy and hence thermodynamic favorability of heterogeneous nucleation. The heterogeneous BaSO4 nucleation and growth kinetics were found to be affected by the amount of Ba2+ adsorption onto the substrate and incipient BaSO4 nuclei. The importance of Ba2+ adsorption was further corroborated by the finding that precipitation rate increased under [Ba2+]/[SO42–] concentration ratios >1. These observations suggest that thermodynamic favorability for nucleation is governed by substrate–water interfacial energy, while given favorable thermodynamics, the rate is governed by ion attachment to substrates and incipient nuclei.« less

  12. Laboratory Experiments on Heterogeneous CO2 Ice Nucleation and Growth Rates on Meteor Smoke Particle Analogues in the Martian Mesosphere

    NASA Astrophysics Data System (ADS)

    Nachbar, M.; Duft, D.; Mangan, T.; Gomez Martin, J. C.; Plane, J. M. C.; Leisner, T.

    2014-12-01

    CO2 ice particles with radii of about 100 nm have been detected in the Martian mesosphere region at heights between 80 km and 100 km. Gravity waves propagating upward cause a cooling of this region leading to temporary supersaturated conditions during which heterogeneous nucleation of CO2 can take place. Large uncertainties in describing the nucleation processes at the extreme conditions of the Martian mesopause region state the need of laboratory measurements. Sub-3 nanometer radius meteor smoke particle (MSP) analogues are created in a microwave plasma and stored in an electrodynamic trap for examining CO2 ice nucleation as well as growth rates at low particle temperatures between 60 K and 75 K and CO2 concentrations up to 1017 m-3 which are reasonably close to conditions present in the Martian mesosphere. Ice nucleation and growth processes of the particles are examined by analyzing the mass distribution of the particles with a time of flight spectrometer as a function of the residence time under supersaturated conditions. In this paper, first measurements of CO2 ice nucleation and growth on iron oxide and silicate particles will be presented. These results are extrapolated to realistic Martian conditions reducing the large uncertainty in dealing with CO2 ice nucleation on MSPs.

  13. In situ determination of interfacial energies between heterogeneously nucleated CaCO3 and quartz substrates: thermodynamics of CO2 mineral trapping.

    PubMed

    Fernandez-Martinez, Alejandro; Hu, Yandi; Lee, Byeongdu; Jun, Young-Shin; Waychunas, Glenn A

    2013-01-02

    The precipitation of carbonate minerals--mineral trapping--is considered one of the safest sequestration mechanisms ensuring long-term geologic storage of CO(2). However, little is known about the thermodynamic factors controlling the extent of heterogeneous nucleation at mineral surfaces exposed to the fluids in porous reservoirs. The goal of this study is to determine the thermodynamic factors controlling heterogeneous nucleation of carbonate minerals on pristine quartz (100) surfaces, which are assumed representative of sandstone reservoirs. To probe CaCO(3) nucleation on quartz (100) in solution and with nanoscale resolution, an in situ grazing incidence small-angle X-ray scattering technique has been utilized. With this method, a value of α' = 36 ± 5 mJ/m(2) for the effective interfacial free energy governing heterogeneous nucleation of CaCO(3) has been obtained by measuring nucleation rates at different solution supersaturations. This value is lower than the interfacial energy governing calcite homogeneous nucleation (α ≈ 120 mJ/m(2)), suggesting that heterogeneous nucleation of calcium carbonate is favored on quartz (100) at ambient pressure and temperature conditions, with nucleation barriers between 2.5% and 15% lower than those expected for homogeneous nucleation. These observations yield important quantitative parameters readily usable in reactive transport models of nucleation at the reservoir scale.

  14. Parameterization of heterogeneous ice nucleation on mineral dust particles: An application in a regional scale model

    NASA Astrophysics Data System (ADS)

    Niemand, M.; Vogel, B.; Vogel, H.; Connolly, P.; Klein, H.; Bingemer, H.; Hoose, C.; Moehler, O.; Leisner, T.

    2010-12-01

    In climate and weather models, the quantitative description of aerosol and cloud processes relies on simplified assumptions. This contributes major uncertainties to the prediction of global and regional climate change. The parameterization of heterogeneous ice nucleation is a step towards improving our current knowledge of the importance of the cloud ice phase in weather and climate models and can aid in the theoretical understanding of such processes. This contribution presents a new parameterization derived from a large number of experiments carried out at the aerosol and cloud chamber facility AIDA [1] of Karlsruhe Institute of Technology. AIDA is especially suitable to study ice nucleation processes at tropospheric and stratospheric cloud conditions covering a wide range of temperature and pressure. During pumping expansion, cooling rates between -0.3 and -5.0 K/min, equating to vertical wind velocities of 0.5 to 8 m/s, and a relative humidity range of up to more than 200% with respect to ice can be reached. The parameterization is valid for the temperature range -35°C to -15°C. In order to derive and test the parameterization a parameter called the ice-active surface site density was calculated for a number of different experiments with mineral dust acting as ice nuclei in the immersion and/or deposition mode. An exponential function was fitted to this data of ice-active surface site density vs. temperature. The curve fit was then used within the bin microphysical model ACPIM [2] to simulate the ice formation rates from the experiments. The major dust outbreak over the Sahara in May 2008 which was followed by a dust transport over the Mediterranean and Western Europe was simulated using the regional scale online coupled model system COSMO-ART (Vogel et al., 2009). Based on the model results the exponential curve fit was used to calculate the ice nuclei number concentration at Kleiner Feldberg (Germany). The results will be compared to measurements from

  15. Heterogeneous ice nucleation on dust particles sourced from nine deserts worldwide - Part 1: Immersion freezing

    NASA Astrophysics Data System (ADS)

    Boose, Yvonne; Welti, André; Atkinson, James; Ramelli, Fabiola; Danielczok, Anja; Bingemer, Heinz G.; Plötze, Michael; Sierau, Berko; Kanji, Zamin A.; Lohmann, Ulrike

    2016-12-01

    Desert dust is one of the most abundant ice nucleating particle types in the atmosphere. Traditionally, clay minerals were assumed to determine the ice nucleation ability of desert dust and constituted the focus of ice nucleation studies over several decades. Recently some feldspar species were identified to be ice active at much higher temperatures than clay minerals, redirecting studies to investigate the contribution of feldspar to ice nucleation on desert dust. However, so far no study has shown the atmospheric relevance of this mineral phase.For this study four dust samples were collected after airborne transport in the troposphere from the Sahara to different locations (Crete, the Peloponnese, Canary Islands, and the Sinai Peninsula). Additionally, 11 dust samples were collected from the surface from nine of the biggest deserts worldwide. The samples were used to study the ice nucleation behavior specific to different desert dusts. Furthermore, we investigated how representative surface-collected dust is for the atmosphere by comparing to the ice nucleation activity of the airborne samples. We used the IMCA-ZINC setup to form droplets on single aerosol particles which were subsequently exposed to temperatures between 233 and 250 K. Dust particles were collected in parallel on filters for offline cold-stage ice nucleation experiments at 253-263 K. To help the interpretation of the ice nucleation experiments the mineralogical composition of the dusts was investigated. We find that a higher ice nucleation activity in a given sample at 253 K can be attributed to the K-feldspar content present in this sample, whereas at temperatures between 238 and 245 K it is attributed to the sum of feldspar and quartz content present. A high clay content, in contrast, is associated with lower ice nucleation activity. This confirms the importance of feldspar above 250 K and the role of quartz and feldspars determining the ice nucleation activities at lower temperatures as found

  16. A first test of the hypothesis of biogenic magnetite-based heterogeneous ice-crystal nucleation in cryopreservation.

    PubMed

    Kobayashi, Atsuko; Golash, Harry N; Kirschvink, Joseph L

    2016-06-01

    An outstanding biophysical puzzle is focused on the apparent ability of weak, extremely low-frequency oscillating magnetic fields to enhance cryopreservation of many biological tissues. A recent theory holds that these weak magnetic fields could be inhibiting ice-crystal nucleation on the nanocrystals of biological magnetite (Fe3O4, an inverse cubic spinel) that are present in many plant and animal tissues by causing them to oscillate. In this theory, magnetically-induced mechanical oscillations disrupt the ability of water molecules to nucleate on the surface of the magnetite nanocrystals. However, the ability of the magnetite crystal lattice to serve as a template for heterogeneous ice crystal nucleation is as yet unknown, particularly for particles in the 10-100 nm size range. Here we report that the addition of trace-amounts of finely-dispersed magnetite into ultrapure water samples reduces strongly the incidence of supercooling, as measured in experiments conducted using a controlled freezing apparatus with multiple thermocouples. SQUID magnetometry was used to quantify nanogram levels of magnetite in the water samples. We also report a relationship between the volume change of ice, and the degree of supercooling, that may indicate lower degassing during the crystallization of supercooled water. In addition to supporting the role of ice-crystal nucleation by biogenic magnetite in many tissues, magnetite nanocrystals could provide inexpensive, non-toxic, and non-pathogenic ice nucleating agents needed in a variety of industrial processes, as well as influencing the dynamics of ice crystal nucleation in many natural environments.

  17. Importance of aerosol composition, mixing state, and morphology for heterogeneous ice nucleation: A combined field and laboratory approach

    NASA Astrophysics Data System (ADS)

    Baustian, Kelly J.; Cziczo, Daniel J.; Wise, Matthew E.; Pratt, Kerri A.; Kulkarni, Gourihar; Hallar, A. Gannet; Tolbert, Margaret A.

    2012-03-01

    In this study chemical compositions of background aerosol and ice nuclei were examined through laboratory investigations using Raman spectroscopy and field measurements by single-particle mass spectrometry. Aerosol sampling took place at Storm Peak Laboratory in Steamboat Springs, Colorado (elevation of 3210 m). A cascade impactor was used to collect coarse-mode aerosol particles for laboratory analysis by Raman spectroscopy; the composition, mixing state, and heterogeneous ice nucleation activity of individual particles were examined. For in situ analysis of fine-mode aerosol, ice nucleation on ambient particles was observed using a compact ice nucleation chamber. Ice crystals were separated from unactivated aerosol using a pumped counterflow virtual impactor, and ice nuclei were analyzed using particle analysis by laser mass spectrometry. For both fine and coarse modes, the ice nucleating particle fractions were enriched in minerals and depleted in sulfates and nitrates, compared to the background aerosol sampled. The vast majority of particles in both the ambient and ice active aerosol fractions contained a detectable amount of organic material. Raman spectroscopy showed that organic material is sometimes present in the form of a coating on the surface of inorganic particles. We find that some organic-containing particles serve as efficient ice nuclei while others do not. For coarse-mode aerosol, organic particles were only observed to initiate ice formation when oxygen signatures were also present in their spectra.

  18. Heterogeneous formation of polar stratospheric clouds-nucleation of nitric acid trihydrate (NAT) in the arctic stratosphere

    NASA Astrophysics Data System (ADS)

    Hoyle, C. R.; Engel, I.; Luo, B. P.; Pitts, M. C.; Poole, L. R.; Grooß, J.-U.; Peter, T.

    2013-05-01

    Satellite based observations during the Arctic winter of 2009/2010 provide firm evidence that, in contrast to the current theory, the nucleation of nitric acid trihydrate (NAT) in the polar stratosphere does not only occur on preexisting ice particles. In order to explain the NAT clouds observed over the Arctic in mid December 2009, a heterogeneous nucleation mechanism is required, occurring on the surface of dust or meteoritic particles. For the first time, a detailed microphysical modelling of this NAT formation pathway has been carried out. Heterogeneous NAT formation was calculated along tens of thousands of trajectories, ending at Cloud Aerosol Lidar with Orthogonal Polarisation (CALIOP) observation points. Comparing the optical properties of the modelled NAT PSCs with these observations enables the thorough validation of a newly developed NAT nucleation parameterisation, which has been built into the Zurich Optical and Microphysical box Model (ZOMM). The parameterisation is based on active site theory and is simple to implement in models. It is shown that the new method is capable of reproducing observed PSCs very well, despite the varied conditions experienced by air parcels travelling along the different trajectories.

  19. Effect of surface free energies on the heterogeneous nucleation of water droplet: A molecular dynamics simulation approach

    SciTech Connect

    Xu, W.; Lan, Z.; Peng, B. L.; Wen, R. F.; Ma, X. H.

    2015-02-07

    Heterogeneous nucleation of water droplet on surfaces with different solid-liquid interaction intensities is investigated by molecular dynamics simulation. The interaction potentials between surface atoms and vapor molecules are adjusted to obtain various surface free energies, and the nucleation process and wetting state of nuclei on surfaces are investigated. The results indicate that near-constant contact angles are already established for nano-scale nuclei on various surfaces, with the contact angle decreasing with solid-liquid interaction intensities linearly. Meanwhile, noticeable fluctuation of vapor-liquid interfaces can be observed for the nuclei that deposited on surfaces, which is caused by the asymmetric forces from vapor molecules. The formation and growth rate of nuclei are increasing with the solid-liquid interaction intensities. For low energy surface, the attraction of surface atoms to water molecules is comparably weak, and the pre-existing clusters can depart from the surface and enter into the bulk vapor phase. The distribution of clusters within the bulk vapor phase becomes competitive as compared with that absorbed on surface. For moderate energy surfaces, heterogeneous nucleation predominates and the formation of clusters within bulk vapor phase is suppressed. The effect of high energy particles that embedded in low energy surface is also discussed under the same simulation system. The nucleation preferably initiates on the high energy particles, and the clusters that formed on the heterogeneous particles are trapped around their original positions instead of migrating around as that observed on smooth surfaces. This feature makes it possible for the heterogeneous particles to act as fixed nucleation sites, and simulation results also suggest that the number of nuclei increases monotonously with the number of high energy particles. The growth of nuclei on high energy particles can be divided into three sub-stages, beginning with the formation

  20. New cloud chamber experiments on the heterogeneous ice nucleation ability of oxalic acid in the deposition nucleation and immersion freezing modes

    NASA Astrophysics Data System (ADS)

    Moehler, O.; Wagner, R.; Saathoff, H.; Schnaiter, M.; Leisner, T.

    2010-12-01

    crystallised from less supersaturated solution droplets and exposed to slow growth conditions in a supersaturated environment in the AIDA camber over a time period of several hours, were found to be much poorer heterogeneous ice nuclei. We speculate that under these conditions a crystal surface structure with less-active sites for the initiation of ice nucleation was generated. Such particles were found to be almost ice-inactive in both the deposition and condensation mode. At times, the heterogeneous ice nucleation ability of oxalic acid dihydrate significantly changed when the particles had been processed in preceding cloud droplet activation steps. Experimental methods, results, and atmospheric implications will be presented and discussed at the conference. [1] Kerminen et al., Atmos. Env., 33, 2089-2100, 1999. [2] Kerminen et al., J. Aerosol Sci., 31, 349-362, 2000. [3] Kawamura et al., Atmos. Env., 30, 1709-1722, 1996. [4] Marcolli et al., J. Phys. Chem. A, 108, 2216-2224, 2004. [5] Zobrist et al., Atmos. Chem. Phys., 6, 3115-3129, 2006. [6] Wagner et al., Atmos. Chem. Phys., 10, 7617-7641, 2010.

  1. Understanding cirrus ice crystal number variability for different heterogeneous ice nucleation spectra

    DOE PAGES

    Sullivan, Sylvia C.; Morales Betancourt, Ricardo; Barahona, Donifan; ...

    2016-03-03

    Along with minimizing parameter uncertainty, understanding the cause of temporal and spatial variability of the nucleated ice crystal number, Ni, is key to improving the representation of cirrus clouds in climate models. To this end, sensitivities of Ni to input variables like aerosol number and diameter provide valuable information about nucleation regime and efficiency for a given model formulation. Here we use the adjoint model of the adjoint of a cirrus formation parameterization (Barahona and Nenes, 2009b) to understand Ni variability for various ice-nucleating particle (INP) spectra. Inputs are generated with the Community Atmosphere Model version 5, and simulations are donemore » with a theoretically derived spectrum, an empirical lab-based spectrum and two field-based empirical spectra that differ in the nucleation threshold for black carbon particles and in the active site density for dust. The magnitude and sign of Ni sensitivity to insoluble aerosol number can be directly linked to nucleation regime and efficiency of various INP. The lab-based spectrum calculates much higher INP efficiencies than field-based ones, which reveals a disparity in aerosol surface properties. Ni sensitivity to temperature tends to be low, due to the compensating effects of temperature on INP spectrum parameters; this low temperature sensitivity regime has been experimentally reported before but never deconstructed as done here.« less

  2. A water activity based model of heterogeneous ice nucleation kinetics for freezing of water and aqueous solution droplets

    DOE PAGES

    Knopf, Daniel A.; Alpert, Peter A.

    2013-04-24

    Immersion freezing of water and aqueous solutions by particles acting as ice nuclei (IN) is a common process of heterogeneous ice nucleation which occurs in many environments, especially in the atmosphere where it results in the glaciation of clouds. Here we experimentally show, using a variety of IN types suspended in various aqueous solutions, that immersion freezing temperatures and kinetics can be described solely by temperature, T, and solution water activity, aw, which is the ratio of the vapour pressure of the solution and the saturation water vapour pressure under the same conditions and, in equilibrium, equivalent to relative humiditymore » (RH). This allows the freezing point and corresponding heterogeneous ice nucleation rate coefficient, Jhet, to be uniquely expressed by T and aw, a result we term the aw based immersion freezing model (ABIFM). This method is independent of the nature of the solute and accounts for several varying parameters, including cooling rate and IN surface area, while providing a holistic description of immersion freezing and allowing prediction of freezing temperatures, Jhet, frozen fractions, ice particle production rates and numbers. Our findings are based on experimental freezing data collected for various IN surface areas, A, and cooling rates, r, of droplets variously containing marine biogenic material, two soil humic acids, four mineral dusts, and one organic monolayer acting as IN. For all investigated IN types we demonstrate that droplet freezing temperatures increase as A increases. Similarly, droplet freezing temperatures increase as the cooling rate decreases. The log10(Jhet) values for the various IN types derived exclusively by T and aw, provide a complete description of the heterogeneous ice nucleation kinetics. Thus, the ABIFM can be applied over the entire range of T, RH, total particulate surface area, and cloud activation timescales typical of atmospheric conditions. Finally, we demonstrate that ABIFM can be

  3. Experiment and theory for heterogeneous nucleation of protein crystals in a porous medium.

    PubMed

    Chayen, Naomi E; Saridakis, Emmanuel; Sear, Richard P

    2006-01-17

    The determination of high-resolution structures of proteins requires crystals of suitable quality. Because of the new impetus given to structural biology by structural genomics/proteomics, the problem of crystallizing proteins is becoming increasingly acute. There is therefore an urgent requirement for the development of new efficient methods to aid crystal growth. Nucleation is the crucial step that determines the entire crystallization process. Hence, the holy grail is to design a "universal nucleant," a substrate that induces the nucleation of crystals of any protein. We report a theory for nucleation on disordered porous media and its experimental testing and validation using a mesoporous bioactive gel-glass. This material induced the crystallization of the largest number of proteins ever crystallized using a single nucleant. The combination of the model and the experimental results opens up the scope for the rational design of nucleants, leading to alternative means of controlling crystallization.

  4. Producing Solar Cells By Surface Preparation For Accelerated Nucleation Of Microcrystalline Silicon On Heterogeneous Substrates.

    DOEpatents

    Yang, Liyou; Chen, Liangfan

    1998-03-24

    Attractive multi-junction solar cells and single junction solar cells with excellent conversion efficiency can be produced with a microcrystalline tunnel junction, microcrystalline recombination junction or one or more microcrystalline doped layers by special plasma deposition processes which includes plasma etching with only hydrogen or other specified etchants to enhance microcrystalline growth followed by microcrystalline. nucleation with a doped hydrogen-diluted feedstock.

  5. Heterogeneous Ice Nucleation by Soufriere Hills Volcanic Ash Immersed in Water Droplets.

    PubMed

    Mangan, T P; Atkinson, J D; Neuberg, J W; O'Sullivan, D; Wilson, T W; Whale, T F; Neve, L; Umo, N S; Malkin, T L; Murray, B J

    2017-01-01

    Fine particles of ash emitted during volcanic eruptions may sporadically influence cloud properties on a regional or global scale as well as influencing the dynamics of volcanic clouds and the subsequent dispersion of volcanic aerosol and gases. It has been shown that volcanic ash can trigger ice nucleation, but ash from relatively few volcanoes has been studied for its ice nucleating ability. In this study we quantify the efficiency with which ash from the Soufriere Hills volcano on Montserrat nucleates ice when immersed in supercooled water droplets. Using an ash sample from the 11th February 2010 eruption, we report ice nucleating efficiencies from 246 to 265 K. This wide range of temperatures was achieved using two separate droplet freezing instruments, one employing nanolitre droplets, the other using microlitre droplets. Soufriere Hills volcanic ash was significantly more efficient than all other ash samples that have been previously examined. At present the reasons for these differences are not understood, but may be related to mineralogy, amorphous content and surface chemistry.

  6. Heterogeneous nucleation and growth of water vapor on meteoric smoke particle analogues at mesospheric conditions

    NASA Astrophysics Data System (ADS)

    Nachbar, Mario; Duft, Denis; Leisner, Thomas

    2016-04-01

    Sub 2 nm meteoric smoke particles (MSP) produced from the ablation and recondensation of meteoric material are believed to be the major kind of nuclei causing the formation of water ice particles in the mesopause of Earth at heights of 80-90 km. These so called noctiLucent clouds (NLC) are frequently detected during polar summer, whereas the microphysical nucleation process and subsequent growth on such small particles are understood only poorly. Parameterizing these processes results in large uncertainties especially due to a lack of experimental data on desorption energies and critical saturation for the activation of nucleation under realistic mesospheric conditions, which states the need of laboratory measurements. We produce charged nanometer sized (2-3 nm) MSP analogues in a microwave plasma particle source and transfer them to a novel linear ion trap which allows us to trap the particles under typical mesospheric temperatures and H2O concentrations. The adsorption of H2O molecules on the particles surface followed by nucleation and growth can be examined by analyzing the mass distribution of the particles with a time-of-flight mass spectrometer as function of the residence time under supersaturated conditions. In this contribution we present such measurements for single positively as well as negatively charged particles which allow us to determine the desorption energy of water vapor on the investigated nanoparticles as well as the critical saturation needed to activate nucleation and subsequent growth.

  7. Heterogeneous Ice Nucleation by Soufriere Hills Volcanic Ash Immersed in Water Droplets

    PubMed Central

    Atkinson, J. D.; Neuberg, J. W.; O’Sullivan, D.; Wilson, T. W.; Whale, T. F.; Neve, L.; Umo, N. S.; Malkin, T. L.; Murray, B. J.

    2017-01-01

    Fine particles of ash emitted during volcanic eruptions may sporadically influence cloud properties on a regional or global scale as well as influencing the dynamics of volcanic clouds and the subsequent dispersion of volcanic aerosol and gases. It has been shown that volcanic ash can trigger ice nucleation, but ash from relatively few volcanoes has been studied for its ice nucleating ability. In this study we quantify the efficiency with which ash from the Soufriere Hills volcano on Montserrat nucleates ice when immersed in supercooled water droplets. Using an ash sample from the 11th February 2010 eruption, we report ice nucleating efficiencies from 246 to 265 K. This wide range of temperatures was achieved using two separate droplet freezing instruments, one employing nanolitre droplets, the other using microlitre droplets. Soufriere Hills volcanic ash was significantly more efficient than all other ash samples that have been previously examined. At present the reasons for these differences are not understood, but may be related to mineralogy, amorphous content and surface chemistry. PMID:28056077

  8. A multicomponent assembly approach for the design of deep desulfurization heterogeneous catalysts.

    PubMed

    Xu, Yanqi; Xuan, Weimin; Zhang, Mengmeng; Miras, Haralampos N; Song, Yu-Fei

    2016-12-06

    Deep desulfurization is a challenging task and global efforts are focused on the development of new approaches for the reduction of sulfur-containing compounds in fuel oils. In this work, we have proposed a new design strategy for the development of deep desulfurization heterogeneous catalysts. Based on the adopted design strategy, a novel composite material of polyoxometalate (POM)-based ionic liquid-grafted layered double hydroxides (LDHs) was synthesized by an exfoliation/grafting/assembly process. The structural properties of the as-prepared catalyst were characterized using FT-IR, XRD, TG, NMR, XPS, BET, SEM and HRTEM. The heterogeneous catalyst exhibited high activity in deep desulfurization of DBT (dibenzothiophene), 4,6-DMDBT (4,6-dimethyldibenzothiophene) and BT (benzothiophene) at 70 °C in 25, 30 and 40 minutes, respectively. The catalyst can be easily recovered and reused at least ten times without obvious decrease of its catalytic activity. Such excellent sulfur removal ability as well as the cost efficiency of the novel heterogeneous catalyst can be attributed to the rational design, where the spatial proximity of the substrate and the active sites, the immobilization of ionic liquid onto the LDHs via covalent bonding and the recyclability of the catalyst are carefully considered.

  9. Pre-ordering of interfacial water in the pathway of heterogeneous ice nucleation does not lead to a two-step crystallization mechanism

    NASA Astrophysics Data System (ADS)

    Lupi, Laura; Peters, Baron; Molinero, Valeria

    2016-12-01

    According to Classical Nucleation Theory (CNT), the transition from liquid to crystal occurs in a single activated step with a transition state controlled by the size of the crystal embryo. This picture has been challenged in the last two decades by several reports of two-step crystallization processes in which the liquid first produces pre-ordered or dense domains, within which the crystal nucleates in a second step. Pre-ordering preceding crystal nucleation has been recently reported in simulations of ice crystallization, raising the question of whether the mechanism of ice nucleation involves two steps. In this paper, we investigate the heterogeneous nucleation of ice on carbon surfaces. We use molecular simulations with efficient coarse-grained models combined with rare event sampling methods and free energy calculations to elucidate the role of pre-ordering of liquid water at the carbon surface in the reaction coordinate for heterogeneous nucleation. We find that ice nucleation proceeds through a classical mechanism, with a single barrier between liquid and crystal. The reaction coordinate that determines the crossing of the nucleation barrier is the size of the crystal nucleus, as predicted by CNT. Wetting of the critical ice nuclei within pre-ordered domains decreases the nucleation barrier, increasing the nucleation rates. The preferential pathway for crystallization involves the early creation of pre-ordered domains that are the birthplace of the ice crystallites but do not represent a minimum in the free energy pathway from liquid to ice. We conclude that a preferential pathway through an intermediate-order precursor does not necessarily result in a two-step mechanism.

  10. Can we define an asymptotic value for the ice active surface site density for heterogeneous ice nucleation?

    NASA Astrophysics Data System (ADS)

    Niedermeier, Dennis; Augustin-Bauditz, Stefanie; Hartmann, Susan; Wex, Heike; Ignatius, Karoliina; Stratmann, Frank

    2015-04-01

    The formation of ice in atmospheric clouds has a substantial influence on the radiative properties of clouds as well as on the formation of precipitation. Therefore much effort has been made to understand and quantify the major ice formation processes in clouds. Immersion freezing has been suggested to be a dominant primary ice formation process in low and mid-level clouds (mixed-phase cloud conditions). It also has been shown that mineral dust particles are the most abundant ice nucleating particles in the atmosphere and thus may play an important role for atmospheric ice nucleation (Murray et al., 2012). Additionally, biological particles like bacteria and pollen are suggested to be potentially involved in atmospheric ice formation, at least on a regional scale (Murray et al., 2012). In recent studies for biological particles (SNOMAX and birch pollen), it has been demonstrated that freezing is induced by ice nucleating macromolecules and that an asymptotic value for the mass density of these ice nucleating macromolecules can be determined (Hartmann et al., 2013; Augustin et al., 2013, Wex et al., 2014). The question arises whether such an asymptotic value can also be determined for the ice active surface site density ns, a parameter which is commonly used to describe the ice nucleation activity of e.g., mineral dust. Such an asymptotic value for ns could be an important input parameter for atmospheric modeling applications. In the presented study, we therefore investigated the immersion freezing behavior of droplets containing size-segregated, monodisperse feldspar particles utilizing the Leipzig Aerosol Cloud Interaction Simulator (LACIS). For all particle sizes considered in the experiments, we observed a leveling off of the frozen droplet fraction reaching a plateau within the heterogeneous freezing temperature regime (T > -38°C) which was proportional to the particle surface area. Based on these findings, we could determine an asymptotic value for the ice

  11. A water activity based model of heterogeneous ice nucleation kinetics for freezing of water and aqueous solution droplets.

    PubMed

    Knopf, Daniel A; Alpert, Peter A

    2013-01-01

    Immersion freezing of water and aqueous solutions by particles acting as ice nuclei (IN) is a common process of heterogeneous ice nucleation which occurs in many environments, especially in the atmosphere where it results in the glaciation of clouds. Here we experimentally show, using a variety of IN types suspended in various aqueous solutions, that immersion freezing temperatures and kinetics can be described solely by temperature, T, and solution water activity, a(w), which is the ratio of the vapour pressure of the solution and the saturation water vapour pressure under the same conditions and, in equilibrium, equivalent to relative humidity (RH). This allows the freezing point and corresponding heterogeneous ice nucleation rate coefficient, J(het), to be uniquely expressed by T and a(w), a result we term the a(w) based immersion freezing model (ABIFM). This method is independent of the nature of the solute and accounts for several varying parameters, including cooling rate and IN surface area, while providing a holistic description of immersion freezing and allowing prediction of freezing temperatures, J(het), frozen fractions, ice particle production rates and numbers. Our findings are based on experimental freezing data collected for various IN surface areas, A, and cooling rates, r, of droplets variously containing marine biogenic material, two soil humic acids, four mineral dusts, and one organic monolayer acting as IN. For all investigated IN types we demonstrate that droplet freezing temperatures increase as A increases. Similarly, droplet freezing temperatures increase as the cooling rate decreases. The log10(J(het)) values for the various IN types derived exclusively by Tand a(w), provide a complete description of the heterogeneous ice nucleation kinetics. Thus, the ABIFM can be applied over the entire range of T, RH, total particulate surface area, and cloud activation timescales typical of atmospheric conditions. Lastly, we demonstrate that ABIFM can

  12. A water activity based model of heterogeneous ice nucleation kinetics for freezing of water and aqueous solution droplets

    SciTech Connect

    Knopf, Daniel A.; Alpert, Peter A.

    2013-04-24

    Immersion freezing of water and aqueous solutions by particles acting as ice nuclei (IN) is a common process of heterogeneous ice nucleation which occurs in many environments, especially in the atmosphere where it results in the glaciation of clouds. Here we experimentally show, using a variety of IN types suspended in various aqueous solutions, that immersion freezing temperatures and kinetics can be described solely by temperature, T, and solution water activity, aw, which is the ratio of the vapour pressure of the solution and the saturation water vapour pressure under the same conditions and, in equilibrium, equivalent to relative humidity (RH). This allows the freezing point and corresponding heterogeneous ice nucleation rate coefficient, Jhet, to be uniquely expressed by T and aw, a result we term the aw based immersion freezing model (ABIFM). This method is independent of the nature of the solute and accounts for several varying parameters, including cooling rate and IN surface area, while providing a holistic description of immersion freezing and allowing prediction of freezing temperatures, Jhet, frozen fractions, ice particle production rates and numbers. Our findings are based on experimental freezing data collected for various IN surface areas, A, and cooling rates, r, of droplets variously containing marine biogenic material, two soil humic acids, four mineral dusts, and one organic monolayer acting as IN. For all investigated IN types we demonstrate that droplet freezing temperatures increase as A increases. Similarly, droplet freezing temperatures increase as the cooling rate decreases. The log10(Jhet) values for the various IN types derived exclusively by T and aw, provide a complete description of the heterogeneous ice nucleation kinetics. Thus, the ABIFM can be applied over the entire range of

  13. Heterogeneous nucleation and growth dynamics in the light-induced phase transition in vanadium dioxide

    DOE PAGES

    Brady, Nathaniel F.; Appavoo, Kannatassen; Seo, Minah; ...

    2016-03-02

    Here we report on ultrafast optical investigations of the light-induced insulator-to-metal phase transition in vanadium dioxide with controlled disorder generated by substrate mismatch. These results reveal common dynamics of this optically-induced phase transition that are independent of this disorder. Lastly, above the fluence threshold for completing the transition to the rutile crystalline phase, we find a common time scale, independent of sample morphology, of 40.5 ± 2 ps that is consistent with nucleation and growth dynamics of the R phase from the parent M1 ground state.

  14. Sizes and spatial relationships of crystals in granitic plutons: Exploring the crystallization gaps, heterogeneous nucleation, and mechanical clustering of crystals

    NASA Astrophysics Data System (ADS)

    Špillar, V.; Dolejš, D.

    2012-04-01

    observed parameters were reproduced by a three-dimensional numerical model with time-dependent nucleation and growth rates, and with variable degree of clustering induced by changing the ratio of homogeneous vs. heterogeneous nucleation rate, between

  15. Overview: Application of heterogeneous nucleation in grain-refining of metals

    NASA Astrophysics Data System (ADS)

    Greer, A. L.

    2016-12-01

    In all of metallurgical processing, probably the most prominent example of nucleation control is the "inoculation" of melts to suppress columnar solidification and to obtain fine equiaxed grain structures in the as-cast solid. In inoculation, a master alloy is added to the melt to increase its solute content and to add stable particles that can act as nucleants for solid grains. This is important for alloys of many metals, and in other cases such as ice nucleation in living systems, but inoculation of aluminum alloys using Al-5Ti-1B (wt.%) master alloy is the exemplar. The key elements are (i) that the chemical interactions between nucleant TiB2 particles and the melt ensure that the solid phase (α-Al) exists on the surface of the particles even above the liquidus temperature of the melt, (ii) that these perfect nucleants can initiate grains only when the barrier for free growth of α-Al is surmounted, and (iii) that (depending on whether the melt is spatially isothermal or not) the release of latent heat, or the limited extent of constitutional supercooling, can act to limit the number of grains that is initiated and therefore the degree of grain refinement that can be achieved. We review recent studies that contribute to better understanding, and improvement, of grain refinement in general. We also identify priorities for future research. These include the study of the effects of nanophase dispersions in melts. Preliminary studies show that such dispersions may be especially effective in achieving grain refinement, and raise many questions about the underlying mechanisms. The stimulation of icosahedral short-range ordering in the liquid has been shown to lead to grain refinement, and is a further priority for study, especially as the refinement can be achieved with only minor additions of solute.

  16. Structural match of heterogeneously nucleated Mn(OH)2(s) nanoparticles on quartz under various pH conditions

    SciTech Connect

    Jung, Haesung; Lee, Byeongdu; Jun, Young -Shin

    2016-09-14

    The early nucleation stage of Mn (hydr)oxide on mineral surfaces is crucial to understand its occurrence and the cycling of nutrients in environmental systems. However, there are only limited studies on the heterogeneous nucleation of Mn(OH)2(s) as the initial stage of Mn (hydr)oxide precipitation. Here, we investigated the effect of pH on the initial nucleation of Mn(OH)2(s) on quartz. Under various pH conditions of 9.8, 9.9, and 10.1, we analyzed the structural matches between quartz and heterogeneously nucleated Mn(OH)2(s). The structural matches were calculated by measuring lateral and vertical dimensions using grazing incidence small angle X-ray scattering (GISAXS) and atomic force microscopy (AFM), respectively. We found that a poorer structural match occurred at a higher pH than at a lower pH. The faster nucleation at a higher pH condition accounted for the observed poorer structural match. By fitting the structural match using classical nucleation theory, we also calculated the interfacial energy between Mn(OH)2(s) and water (γnf = 71 ± 7 mJ/m2). The calculated m values and γnf provided the variance of interfacial energy between quartz and Mn(OH)2(s): γsn = 262–272 mJ/m2. As a result, this study provides new qualitative and quantitative information about heterogeneous nucleation on environmentally an abundant mineral surface, quartz, and it offers important underpinnings for understanding the fate and transport of trace ions in environmental systems.

  17. Heterogeneous Nucleation and Growth of Barium Sulfate at Organic-Water Interfaces: Interplay between Surface Hydrophobicity and Ba2+ Adsorption

    SciTech Connect

    Dai, Chong; Stack, Andrew G.; Koishi, Ayumi; Fernandez-Martinez, Alejandro; Lee, Sang Soo; Hu, Yandi

    2016-05-10

    Barium sulfate (BaSO4) is a common scale-forming mineral in natural and engineered systems, yet the rates and mechanisms of heterogeneous BaSO4 nucleation are not understood. To address these, we created idealized interfaces on which to study heterogeneous nucleation rates and mechanisms, which also are good models for organic–water interfaces: self-assembled thin films terminated with different functional groups (i.e., -COOH, -SH, or mixed -SH & COOH) coated on glass slides. BaSO4 precipitation on coatings from Barite-supersaturated solutions (saturation index, SI, = 1.1) was investigated using grazing-incidence small-angle X-ray scattering. After reaction for 1 h, a little amount of BaSO4 formed on hydrophilic bare and -COOH coated glasses. Meanwhile, BaSO4 nucleation was significantly promoted on hydrophobic -SH and mixed -SH & COOH coatings. This is because substrate hydrophobicity likely affected the interfacial energy and hence thermodynamic favorability of heterogeneous nucleation. The heterogeneous BaSO4 nucleation and growth kinetics were found to be affected by the amount of Ba2+ adsorption onto the substrate and incipient BaSO4 nuclei. The importance of Ba2+ adsorption was further corroborated by the finding that precipitation rate increased under [Ba2+]/[SO42–] concentration ratios >1. These observations suggest that thermodynamic favorability for nucleation is governed by substrate–water interfacial energy, while given favorable thermodynamics, the rate is governed by ion attachment to substrates and incipient nuclei.

  18. Heterogeneous Nucleation and Growth of Barium Sulfate at Organic–Water Interfaces: Interplay between Surface Hydrophobicity and Ba 2+ Adsorption

    SciTech Connect

    Dai, Chong; Stack, Andrew G.; Koishi, Ayumi; Fernandez-Martinez, Alejandro; Lee, Sang Soo; Hu, Yandi

    2016-05-31

    Barium sulfate (BaSO4) is a common scale-forming mineral in natural and engineered systems, yet the rates and mechanisms of heterogeneous BaSO4 nucleation are not understood. To address these, we created idealized interfaces on which to study heterogeneous nucleation rates and mechanisms, which also are good models for organic–water interfaces: self-assembled thin films terminated with different functional groups (i.e., -COOH, -SH, or mixed -SH & COOH) coated on glass slides. BaSO4 precipitation on coatings from Barite-supersaturated solutions (saturation index, SI, = 1.1) was investigated using grazing-incidence small-angle X-ray scattering. After reaction for 1 h, a little amount of BaSO4 formed on hydrophilic bare and -COOH coated glasses. Meanwhile, BaSO4 nucleation was significantly promoted on hydrophobic -SH and mixed -SH & COOH coatings. This is because substrate hydrophobicity likely affected the interfacial energy and hence thermodynamic favorability of heterogeneous nucleation. The heterogeneous BaSO4 nucleation and growth kinetics were found to be affected by the amount of Ba2+ adsorption onto the substrate and incipient BaSO4 nuclei. The importance of Ba2+ adsorption was further corroborated by the finding that precipitation rate increased under [Ba2+]/[SO42–] concentration ratios >1. These observations suggest that thermodynamic favorability for nucleation is governed by substrate–water interfacial energy, while given favorable thermodynamics, the rate is governed by ion attachment to substrates and incipient nuclei.

  19. Atomization of High-Viscosity Fluids for Aromatherapy Using Micro-heaters for Heterogeneous Bubble Nucleation

    PubMed Central

    Law, Junhui; Kong, Ka Wai; Chan, Ho-Yin; Sun, Winston; Li, Wen Jung; Chau, Eric Boa Fung; Chan, George Kak Man

    2017-01-01

    The development of a novel lead-free microelectromechanical-system (MEMS)-based atomizer using the principle of thermal bubble actuation is presented. It is a low-cost, lead-free design that is environmentally friendly and harmless to humans. It has been tested to be applicable over a wide range of fluid viscosities, ranging from 1 cP (e.g., water) to 200 cP (e.g., oil-like fluid) at room temperature, a range that is difficult to achieve using ordinary atomizers. The results demonstrate that the average power consumption of the atomizer is approximately 1 W with an atomization rate of 0.1 to 0.3 mg of deionized (DI) water per cycle. The relationships between the micro-heater track width and the track gap, the size of the micro-cavities and the nucleation energy were studied to obtain an optimal atomizer design. The particle image velocimetry (PIV) results indicate that the diameter of the ejected droplets ranges from 30 to 90 μm with a speed of 20 to 340 mm/s. In addition, different modes of spraying are reported for the first time. It is envisioned that the successful development of this MEMS-based atomizing technology will revolutionize the existing market for atomizers and could also benefit different industries, particularly in applications involving viscous fluids. PMID:28074925

  20. Atomization of High-Viscosity Fluids for Aromatherapy Using Micro-heaters for Heterogeneous Bubble Nucleation.

    PubMed

    Law, Junhui; Kong, Ka Wai; Chan, Ho-Yin; Sun, Winston; Li, Wen Jung; Chau, Eric Boa Fung; Chan, George Kak Man

    2017-01-11

    The development of a novel lead-free microelectromechanical-system (MEMS)-based atomizer using the principle of thermal bubble actuation is presented. It is a low-cost, lead-free design that is environmentally friendly and harmless to humans. It has been tested to be applicable over a wide range of fluid viscosities, ranging from 1 cP (e.g., water) to 200 cP (e.g., oil-like fluid) at room temperature, a range that is difficult to achieve using ordinary atomizers. The results demonstrate that the average power consumption of the atomizer is approximately 1 W with an atomization rate of 0.1 to 0.3 mg of deionized (DI) water per cycle. The relationships between the micro-heater track width and the track gap, the size of the micro-cavities and the nucleation energy were studied to obtain an optimal atomizer design. The particle image velocimetry (PIV) results indicate that the diameter of the ejected droplets ranges from 30 to 90 μm with a speed of 20 to 340 mm/s. In addition, different modes of spraying are reported for the first time. It is envisioned that the successful development of this MEMS-based atomizing technology will revolutionize the existing market for atomizers and could also benefit different industries, particularly in applications involving viscous fluids.

  1. Atomization of High-Viscosity Fluids for Aromatherapy Using Micro-heaters for Heterogeneous Bubble Nucleation

    NASA Astrophysics Data System (ADS)

    Law, Junhui; Kong, Ka Wai; Chan, Ho-Yin; Sun, Winston; Li, Wen Jung; Chau, Eric Boa Fung; Chan, George Kak Man

    2017-01-01

    The development of a novel lead-free microelectromechanical-system (MEMS)-based atomizer using the principle of thermal bubble actuation is presented. It is a low-cost, lead-free design that is environmentally friendly and harmless to humans. It has been tested to be applicable over a wide range of fluid viscosities, ranging from 1 cP (e.g., water) to 200 cP (e.g., oil-like fluid) at room temperature, a range that is difficult to achieve using ordinary atomizers. The results demonstrate that the average power consumption of the atomizer is approximately 1 W with an atomization rate of 0.1 to 0.3 mg of deionized (DI) water per cycle. The relationships between the micro-heater track width and the track gap, the size of the micro-cavities and the nucleation energy were studied to obtain an optimal atomizer design. The particle image velocimetry (PIV) results indicate that the diameter of the ejected droplets ranges from 30 to 90 μm with a speed of 20 to 340 mm/s. In addition, different modes of spraying are reported for the first time. It is envisioned that the successful development of this MEMS-based atomizing technology will revolutionize the existing market for atomizers and could also benefit different industries, particularly in applications involving viscous fluids.

  2. A~comprehensive parameterization of heterogeneous ice nucleation of dust surrogate: laboratory study with hematite particles and its application to atmospheric models

    NASA Astrophysics Data System (ADS)

    Hiranuma, N.; Paukert, M.; Steinke, I.; Zhang, K.; Kulkarni, G.; Hoose, C.; Schnaiter, M.; Saathoff, H.; Möhler, O.

    2014-06-01

    A new heterogeneous ice nucleation parameterization that covers a~wide temperature range (-36 to -78 °C) is presented. Developing and testing such an ice nucleation parameterization, which is constrained through identical experimental conditions, is critical in order to accurately simulate the ice nucleation processes in cirrus clouds. The surface-scaled ice nucleation efficiencies of hematite particles, inferred by ns, were derived from AIDA (Aerosol Interaction and Dynamics in the Atmosphere) cloud chamber measurements under water subsaturated conditions that were realized by continuously changing temperature (T) and relative humidity with respect to ice (RHice) in the chamber. Our measurements showed several different pathways to nucleate ice depending on T and RHice conditions. For instance, almost T-independent freezing was observed at -60 °C < T < -50 °C, where RHice explicitly controlled ice nucleation efficiency, while both T and RHice played roles in other two T regimes: -78 °C < T < -60 °C and -50 °C < T < -36 °C. More specifically, observations at T colder than -60 °C revealed that higher RHice was necessary to maintain constant ns, whereas T may have played a significant role in ice nucleation at T warmer than -50 °C. We implemented new ns parameterizations into two cloud models to investigate its sensitivity and compare with the existing ice nucleation schemes towards simulating cirrus cloud properties. Our results show that the new AIDA-based parameterizations lead to an order of magnitude higher ice crystal concentrations and inhibition of homogeneous nucleation in colder temperature regions. Our cloud simulation results suggest that atmospheric dust particles that form ice nuclei at lower temperatures, below -36 °C, can potentially have stronger influence on cloud properties such as cloud longevity and initiation when compared to previous parameterizations.

  3. Global model comparison of heterogeneous ice nucleation parameterizations in mixed phase clouds

    NASA Astrophysics Data System (ADS)

    Yun, Yuxing; Penner, Joyce E.

    2012-04-01

    A new aerosol-dependent mixed phase cloud parameterization for deposition/condensation/immersion (DCI) ice nucleation and one for contact freezing are compared to the original formulations in a coupled general circulation model and aerosol transport model. The present-day cloud liquid and ice water fields and cloud radiative forcing are analyzed and compared to observations. The new DCI freezing parameterization changes the spatial distribution of the cloud water field. Significant changes are found in the cloud ice water fraction and in the middle cloud fractions. The new DCI freezing parameterization predicts less ice water path (IWP) than the original formulation, especially in the Southern Hemisphere. The smaller IWP leads to a less efficient Bergeron-Findeisen process resulting in a larger liquid water path, shortwave cloud forcing, and longwave cloud forcing. It is found that contact freezing parameterizations have a greater impact on the cloud water field and radiative forcing than the two DCI freezing parameterizations that we compared. The net solar flux at top of atmosphere and net longwave flux at the top of the atmosphere change by up to 8.73 and 3.52 W m-2, respectively, due to the use of different DCI and contact freezing parameterizations in mixed phase clouds. The total climate forcing from anthropogenic black carbon/organic matter in mixed phase clouds is estimated to be 0.16-0.93 W m-2using the aerosol-dependent parameterizations. A sensitivity test with contact ice nuclei concentration in the original parameterization fit to that recommended by Young (1974) gives results that are closer to the new contact freezing parameterization.

  4. Cobalt nanowires prepared by heterogeneous nucleation in propanediol and their catalytic properties

    NASA Astrophysics Data System (ADS)

    Liu, Qiying; Guo, Xiaohui; Chen, Junli; Li, Juan; Song, Wei; Shen, Wenjie

    2008-09-01

    Co nanowires with a diameter of 10 nm and a length up to 1000 nm were synthesized by the chemical reduction of cobalt acetate in propanediol using Ru as the heterogeneous agent and stearic acid as the surfactant. The morphology of the Co nanomaterials depended strongly on the concentrations of stearic acid and sodium hydroxide and the temperature, which governed the reduction rate of Co2+ in the liquid and the growth rate of Co nanocrystals. Very tiny Ru nanoparticles formed at the beginning of the synthesis significantly lowered the reduction temperature of Co2+ species, affording an easy separation and growth of Co nanocrystals. Solid cobalt stearate and cobalt alkoxide were readily formed at the initial stage of the synthesis, which determined the reduction rate of Co2+ through a dynamic equilibrium between the solid and the solution. In addition to forming cobalt stearate, the stearic acid, as a structure-directing agent, mainly induced the anisotropic growth of Co nanocrystals. The Co nanowires as heterogeneous catalysts showed quite promising activity and selectivity for the hydrogenation of citral and the hydrogenolysis of glycerol.

  5. 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.

  6. New insights into selective heterogeneous nucleation of metal nanoparticles on oxides by microwave-assisted reduction: rapid synthesis of high-activity supported catalysts.

    PubMed

    Anumol, Erumpukuthickal Ashok; Kundu, Paromita; Deshpande, Parag Arvind; Madras, Giridhar; Ravishankar, Narayanan

    2011-10-25

    Microwave-based methods are widely employed to synthesize metal nanoparticles on various substrates. However, the detailed mechanism of formation of such hybrids has not been addressed. In this paper, we describe the thermodynamic and kinetic aspects of reduction of metal salts by ethylene glycol under microwave heating conditions. On the basis of this analysis, we identify the temperatures above which the reduction of the metal salt is thermodynamically favorable and temperatures above which the rates of homogeneous nucleation of the metal and the heterogeneous nucleation of the metal on supports are favored. We delineate different conditions which favor the heterogeneous nucleation of the metal on the supports over homogeneous nucleation in the solvent medium based on the dielectric loss parameters of the solvent and the support and the metal/solvent and metal/support interfacial energies. Contrary to current understanding, we show that metal particles can be selectively formed on the substrate even under situations where the temperature of the substrate is lower than that of the surrounding medium. The catalytic activity of the Pt/CeO(2) and Pt/TiO(2) hybrids synthesized by this method for H(2) combustion reaction shows that complete conversion is achieved at temperatures as low as 100 °C with Pt-CeO(2) catalyst and at 50 °C with Pt-TiO(2) catalyst. Our method thus opens up possibilities for rational synthesis of high-activity supported catalysts using a fast microwave-based reduction method.

  7. IgG particle formation during filling pump operation: a case study of heterogeneous nucleation on stainless steel nanoparticles.

    PubMed

    Tyagi, Anil K; Randolph, Theodore W; Dong, Aichun; Maloney, Kevin M; Hitscherich, Carl; Carpenter, John F

    2009-01-01

    This study investigated factors associated with vial filling with a positive displacement piston pump leading to formation of protein particles in a formulation of an IgG. We hypothesized that nanoparticles shed from the pump's solution-contact surfaces nucleated protein aggregation and particle formation. Vials of IgG formulation filled at a clinical manufacturing site contained a few visible particles and about 100,000 particles (1.5-3 microm) per mL. In laboratory studies with the same model (National Instruments FUS-10) of pump, pumping of 20 mg/mL IgG formulation resulted in about 300,000 particles (1.5-3 microm) per mL. Pumping of protein-free formulation resulted in 13,000 particles (1.5-15 microm) per mL. More than 99% of the particles were 0.25-0.95 microm in size. Mixing of protein-free pumped solution with an equal volume of 40 mg/mL IgG resulted in 300,000 particles (1.5-15 microm) per mL. Also, mixing IgG formulation with 30,000/mL stainless steel nanoparticles resulted in formation of 30,000 protein microparticles (1.5-15 microm) per mL. Infrared spectroscopy showed that secondary structure of IgG in microparticles formed by pumping or mixing with steel nanoparticles was minimally perturbed. Our results document that nanoparticles of foreign materials shed by pumps can serve as heterogeneous nuclei for formation of protein microparticles.

  8. A comprehensive parameterization of heterogeneous ice nucleation of dust surrogate: laboratory study with hematite particles and its application to atmospheric models

    NASA Astrophysics Data System (ADS)

    Hiranuma, N.; Paukert, M.; Steinke, I.; Zhang, K.; Kulkarni, G.; Hoose, C.; Schnaiter, M.; Saathoff, H.; Möhler, O.

    2014-12-01

    A new heterogeneous ice nucleation parameterization that covers a wide temperature range (-36 to -78 °C) is presented. Developing and testing such an ice nucleation parameterization, which is constrained through identical experimental conditions, is important to accurately simulate the ice nucleation processes in cirrus clouds. The ice nucleation active surface-site density (ns) of hematite particles, used as a proxy for atmospheric dust particles, were derived from AIDA (Aerosol Interaction and Dynamics in the Atmosphere) cloud chamber measurements under water subsaturated conditions. These conditions were achieved by continuously changing the temperature (T) and relative humidity with respect to ice (RHice) in the chamber. Our measurements showed several different pathways to nucleate ice depending on T and RHice conditions. For instance, almost T-independent freezing was observed at -60 °C < T < -50 °C, where RHice explicitly controlled ice nucleation efficiency, while both T and RHice played roles in other two T regimes: -78 °C < T < -60 °C and -50 °C < T < -36 °C. More specifically, observations at T lower than -60 °C revealed that higher RHice was necessary to maintain a constant ns, whereas T may have played a significant role in ice nucleation at T higher than -50 °C. We implemented the new hematite-derived ns parameterization, which agrees well with previous AIDA measurements of desert dust, into two conceptual cloud models to investigate their sensitivity to the new parameterization in comparison to existing ice nucleation schemes for simulating cirrus cloud properties. Our results show that the new AIDA-based parameterization leads to an order of magnitude higher ice crystal concentrations and to an inhibition of homogeneous nucleation in lower-temperature regions. Our cloud simulation results suggest that atmospheric dust particles that form ice nuclei at lower temperatures, below -36 °C, can potentially have a stronger influence on cloud

  9. A Comprehensive Parameterization of Heterogeneous Ice Nucleation of Dust Surrogate: Laboratory Study with Hematite Particles and Its Application to Atmospheric Models

    SciTech Connect

    Hiranuma, Naruki; Paukert, Marco; Steinke, Isabelle; Zhang, Kai; Kulkarni, Gourihar R.; Hoose, Corinna; Schnaiter, Martin; Saathoff, Harald; Mohler, Ottmar

    2014-12-10

    A new heterogeneous ice nucleation parameterization that covers a wide temperature range (-36 °C to -78 °C) is presented. Developing and testing such an ice nucleation parameterization, which is constrained through identical experimental conditions, is critical in order to accurately simulate the ice nucleation processes in cirrus clouds. The surface-scaled ice nucleation efficiencies of hematite particles, inferred by ns, were derived from AIDA (Aerosol Interaction and Dynamics in the Atmosphere) cloud chamber measurements under water subsaturated conditions that were realized by continuously changing temperature (T) and relative humidity with respect to ice (RHice) in the chamber. Our measurements showed several different pathways to nucleate ice depending on T and RHice conditions. For instance, almost independent freezing was observed at -60 °C < T < -50 °C, where RHice explicitly controlled ice nucleation efficiency, while both T and RHice played roles in other two T regimes: -78 °C < T < -60 °C and -50 °C < T < -36 °C. More specifically, observations at T colder than -60 °C revealed that higher RHice was necessary to maintain constant ns, whereas T may have played a significant role in ice nucleation at T warmer than -50 °C. We implemented new ns parameterizations into two cloud models to investigate its sensitivity and compare with the existing ice nucleation schemes towards simulating cirrus cloud properties. Our results show that the new AIDA-based parameterizations lead to an order of magnitude higher ice crystal concentrations and inhibition of homogeneous nucleation in colder temperature regions. Our cloud simulation results suggest that atmospheric dust particles that form ice nuclei at lower temperatures, below -36 °C, can potentially have stronger influence on cloud properties such as cloud longevity and initiation when compared to previous parameterizations.

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

    SciTech Connect

    Zhang, Yang; Chen, Ying; Fan, Jiwen; Leung, Lai-Yung

    2015-09-01

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

  11. Application of an online-coupled regional climate model, WRF-CAM5, over East Asia for examination of ice nucleation schemes. Part II. Sensitivity to heterogeneous ice nucleation parameterizations and dust emissions

    SciTech Connect

    Zhang, Yang; Chen, Ying; Fan, Jiwen; Leung, Lai -Yung

    2015-09-14

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

  12. Application of an online-coupled regional climate model, WRF-CAM5, over East Asia for examination of ice nucleation schemes. Part II. Sensitivity to heterogeneous ice nucleation parameterizations and dust emissions

    DOE PAGES

    Zhang, Yang; Chen, Ying; Fan, Jiwen; ...

    2015-09-14

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

  13. (NH4)2SO4 heterogeneous nucleation and glycerol evaporation of (NH4)2SO4-glycerol system in its dynamic efflorescence process

    NASA Astrophysics Data System (ADS)

    Cai, Chen; Luan, Ye-mei; Shi, Xiao-min; Zhang, Yun-hong

    2017-02-01

    Using the FTIR-ATR technique, we investigated the heterogeneous nucleation process of aqueous (NH4)2SO4 binary droplets and (NH4)2SO4/glycerol ternary droplets. From the red shift of δ-NH4+ with a linearly declining relative humidity (RH), the ERHs of pure (NH4)2SO4 droplets and mixed (NH4)2SO4/glycerol droplets with different organic-inorganic ratio (OIR) of 1:4, 1:2 and 1:1 ranges from ∼51.9 to ∼34.9%, ∼49.8 to ∼33.0%, ∼48.0 to ∼30.6% and ∼43.7 to ∼25.2%, respectively. From the changing absorbance of δ-NH4+ band, we determined the heterogeneous nucleation rates of crystalline (NH4)2SO4 in the pure and mixed droplets. The interfacial tension between an (NH4)2SO4 critical nucleus and surrounding (NH4)2SO4 solution was determined using classical nucleation theory and experimental data to be 0.031 ± 0.002 J m-2. Evaporation of glycerol in (NH4)2SO4/glycerol ternary droplets are also studied to be restrained by participation of (NH4)2SO4. Determined vapour pressure of glycerol is on the same magnitude with results from previous studies.

  14. Study of Heterogeneous Nucleation of Eutectic Si in High-Purity Al-Si Alloys with Sr Addition

    NASA Astrophysics Data System (ADS)

    Zarif, Muhammad; McKay, Brian; Schumacher, Peter

    2011-06-01

    Al-5 wt pct Si master-alloys with controlled Sr and/or P addition/s were produced using super purity Al 99.99 wt pct and Si 99.999 wt pct materials in an arc melter. The master-alloy was melt-spun resulting in the production of thin ribbons. The Al matrix of the ribbons contained entrained Al-Si eutectic droplets that were subsequently investigated. Differential scanning calorimetry, thermodynamic calculations, and transmission electron microscopy techniques were employed to examine the effect of the Sr and P additions on eutectic undercoolings and nucleation phenomenon. Results indicate that, unlike P, Sr does not promote nucleation. Increasing Sr additions depressed the eutectic nucleation temperature. This may be a result of the formation of a Sr phase that could consume or detrimentally affect potent AlP nucleation sites.

  15. Nanoscale heterogeneity, premartensitic nucleation, and a new plutonium structure in metastable δ fcc Pu-Ga alloys

    NASA Astrophysics Data System (ADS)

    Conradson, Steven D.; Bock, Nicolas; Castro, Julio M.; Conradson, Dylan R.; Cox, Lawrence E.; Dmowski, Wojciech; Dooley, David E.; Egami, Takeshi; Espinosa-Faller, Francisco J.; Freibert, Franz J.; Garcia-Adeva, Angel J.; Hess, Nancy J.; Holmström, Erik K.; Howell, Rafael C.; Katz, Barbara; Lashley, Jason C.; Martinez, Raymond J.; Moore, David P.; Morales, Luis A.; Olivas, J. David; Pereyra, Ramiro A.; Ramos, Michael; Rudin, Sven P.; Villella, Phillip M.

    2014-06-01

    The scientifically fascinating question of the spatial extent and bonding of the 5f orbitals of Pu and its six different phases extends to its δ-retained alloys and the mechanism by which Ga and a number of other unrelated elements stabilize its low density face-centered-cubic (fcc) structure. This issue of phase stability is also important technologically because of its significance to Science-Based Stockpile Stewardship. Answering these questions requires information on the local order and structure around the Ga and its effects on the Pu. We have addressed this by characterizing the structures of a large number of Pu-Ga and two Pu-In and one Pu-Ce δ alloys, including a set of high purity δ Pu1-xGax materials with 1.7 ≤ x ≤ 6.4 at. % Ga that span the low [Ga] portion of the δ region of the phase diagram across the ˜3.3 at. % Ga metastability boundary, with extended x-ray absorption fine structure (EXAFS) spectroscopy that probes the element specific local structure, supplemented by x-ray pair distribution function analysis that gives the total local structure to longer distances, and x-ray diffraction that gives the long-range average structure of the periodic component of the materials. Detailed analyses indicate that the alloys at and below a nominal composition of ˜3.3 at. % Ga are heterogeneous and in addition to the δ phase also contain up to ˜20% of a novel, coexisting "σ" structure for Pu that forms in nanometer scale domains that are locally depleted in Ga. The invariance of the Ga EXAFS with composition indicates that this σ structure forms in Ga-depleted domains that result from the Ga atoms in the δ phase self-organizing into a quasi-intermetallic with a stoichiometry of Pu25-35Ga so that δ Pu-Ga is neither a random solid solution nor the more stable Pu3Ga + α. Above this 3.3 at. % Ga nominal composition, the δ Pu-Ga alloy is homogeneous, and no σ phase is present. These results that demonstrate that collective and cooperative

  16. Preferential earthquake-nucleating locations on faults determined by heterogeneous direct- and evolution-effect parameters of rate- and state-dependent friction

    NASA Astrophysics Data System (ADS)

    Viesca, R. C.; Ray, S.

    2015-12-01

    Rock friction experiments show that low-velocity fault friction may have a direct and subsequent evolutionary response to changes in slip velocity; the magnitude of which are respectively proportional to parameters a and b in constitutive relations of such rate- and state-dependent friction [e.g., Dieterich 1979; Ruina, 1983]. When a and b are uniform on a fault, translational invariance implies any location is a potential nucleation site, the choice determined by pre-instability conditions and external forcing. With heterogeneous parameters, symmetry is broken, which can create preferred nucleation sites. Recent work showed such heterogeneity does create favorable sites (Ray and Viesca, AGU '14). Here we study how distributions of (i) relative (0nucleation occurs at the local minimum and maximum of (ii) for nonlocal and local interactions, respectively

  17. CRYSTALLIZATION IN MULTICOMPONENT GLASSES

    SciTech Connect

    KRUGER AA; HRMA PR

    2009-10-08

    In glass processing situations involving glass crystallization, various crystalline forms nucleate, grow, and dissolve, typically in a nonuniform temperature field of molten glass subjected to convection. Nuclear waste glasses are remarkable examples of multicomponent vitrified mixtures involving partial crystallization. In the glass melter, crystals form and dissolve during batch-to-glass conversion, melter processing, and product cooling. Crystals often agglomerate and sink, and they may settle at the melter bottom. Within the body of cooling glass, multiple phases crystallize in a non-uniform time-dependent temperature field. Self-organizing periodic distribution (the Liesegnang effect) is common. Various crystallization phenomena that occur in glass making are reviewed.

  18. An Atomistic View of Amyloidogenic Self-assembly: Structure and Dynamics of Heterogeneous Conformational States in the Pre-nucleation Phase

    PubMed Central

    Matthes, Dirk; Gapsys, Vytautas; Brennecke, Julian T.; de Groot, Bert L.

    2016-01-01

    The formation of well-defined filamentous amyloid structures involves a polydisperse collection of oligomeric states for which relatively little is known in terms of structural organization. Here we use extensive, unbiased explicit solvent molecular dynamics (MD) simulations to investigate the structural and dynamical features of oligomeric aggregates formed by a number of highly amyloidogenic peptides at atomistic resolution on the μs time scale. A consensus approach has been adopted to analyse the simulations in multiple force fields, yielding an in-depth characterization of pre-fibrillar oligomers and their global and local structure properties. A collision cross section analysis revealed structurally heterogeneous aggregate ensembles for the individual oligomeric states that lack a single defined quaternary structure during the pre-nucleation phase. To gain insight into the conformational space sampled in early aggregates, we probed their substructure and found emerging β-sheet subunit layers and a multitude of ordered intermolecular β-structure motifs with growing aggregate size. Among those, anti-parallel out-of-register β-strands compatible with toxic β-barrel oligomers were particularly prevalent already in smaller aggregates and formed prior to ordered fibrillar structure elements. Notably, also distinct fibril-like conformations emerged in the oligomeric state and underscore the notion that pre-nucleated oligomers serve as a critical intermediate step on-pathway to fibrils. PMID:27616019

  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. A computer model for one-dimensional mass and energy transport in and around chemically reacting particles, including complex gas-phase chemistry, multicomponent molecular diffusion, surface evaporation, and heterogeneous reaction

    NASA Technical Reports Server (NTRS)

    Cho, S. Y.; Yetter, R. A.; Dryer, F. L.

    1992-01-01

    Various chemically reacting flow problems highlighting chemical and physical fundamentals rather than flow geometry are presently investigated by means of a comprehensive mathematical model that incorporates multicomponent molecular diffusion, complex chemistry, and heterogeneous processes, in the interest of obtaining sensitivity-related information. The sensitivity equations were decoupled from those of the model, and then integrated one time-step behind the integration of the model equations, and analytical Jacobian matrices were applied to improve the accuracy of sensitivity coefficients that are calculated together with model solutions.

  1. Can we define an asymptotic value for the ice active surface site density for heterogeneous ice nucleation?

    NASA Astrophysics Data System (ADS)

    Niedermeier, Dennis; Augustin-Bauditz, Stefanie; Hartmann, Susan; Wex, Heike; Ignatius, Karoliina; Stratmann, Frank

    2015-05-01

    The immersion freezing behavior of droplets containing size-segregated, monodisperse feldspar particles was investigated. For all particle sizes investigated, a leveling off of the frozen droplet fraction was observed reaching a plateau within the heterogeneous freezing temperature regime (T >- 38°C). The frozen fraction in the plateau region was proportional to the particle surface area. Based on these findings, an asymptotic value for ice active surface site density ns, which we named ns⋆, could be determined for the investigated feldspar sample. The comparison of these results with those of other studies not only elucidates the general feasibility of determining such an asymptotic value but also shows that the value of ns⋆ strongly depends on the method of the particle surface area determination. However, such an asymptotic value might be an important input parameter for atmospheric modeling applications. At least it shows that care should be taken when ns is extrapolated to lower or higher temperature.

  2. Two-component spin-coated Ag/CNT composite films based on a silver heterogeneous nucleation mechanism adhesion-enhanced by mechanical interlocking and chemical grafting.

    PubMed

    Zhang, Yang; Kang, Zhixin; Bessho, Takeshi

    2017-03-10

    In this paper, a new method for the synthesis of silver carbon nanotube (Ag/CNT) composite films as conductive connection units for flexible electronic devices is presented. This method is about a two-component solution process by spin coating with an after-treatment annealing process. In this method, multi-walled carbon nanotubes (MWCNTs) act as the core of silver heterogeneous nucleation, which can be observed and analyzed by a field-emission scanning electron microscope. With the effects of mechanical interlocking, chemical grafting, and annealing, the interfacial adhesive strength between films and PET sheets was enhanced to 12 N cm(-1). The tensile strength of the Ag/CNT composite films was observed to increase by 38% by adding 5 g l(-1) MWCNTs. In the four-probe method, the resistivity of Ag/CNT-5 declined by 78.2% compared with pristine Ag films. The anti-fatigue performance of the Ag/CNT composite films was monitored by cyclic bending deformation and the results revealed that the growth rate of electrical resistance during the deformation was obviously retarded. As for industrial application, this method provides an efficient low-cost way to prepare Ag/CNT composite films and can be further applied to other coating systems.

  3. Two-component spin-coated Ag/CNT composite films based on a silver heterogeneous nucleation mechanism adhesion-enhanced by mechanical interlocking and chemical grafting

    NASA Astrophysics Data System (ADS)

    Zhang, Yang; Kang, Zhixin; Bessho, Takeshi

    2017-03-01

    In this paper, a new method for the synthesis of silver carbon nanotube (Ag/CNT) composite films as conductive connection units for flexible electronic devices is presented. This method is about a two-component solution process by spin coating with an after-treatment annealing process. In this method, multi-walled carbon nanotubes (MWCNTs) act as the core of silver heterogeneous nucleation, which can be observed and analyzed by a field-emission scanning electron microscope. With the effects of mechanical interlocking, chemical grafting, and annealing, the interfacial adhesive strength between films and PET sheets was enhanced to 12 N cm‑1. The tensile strength of the Ag/CNT composite films was observed to increase by 38% by adding 5 g l‑1 MWCNTs. In the four-probe method, the resistivity of Ag/CNT-5 declined by 78.2% compared with pristine Ag films. The anti-fatigue performance of the Ag/CNT composite films was monitored by cyclic bending deformation and the results revealed that the growth rate of electrical resistance during the deformation was obviously retarded. As for industrial application, this method provides an efficient low-cost way to prepare Ag/CNT composite films and can be further applied to other coating systems.

  4. 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

  5. Multicomponent membranes

    DOEpatents

    Kulprathipanja, Santi; Kulkarni, Sudhir S.; Funk, Edward W.

    1988-01-01

    A multicomponent membrane which may be used for separating various components which are present in a fluid feed mixture comprises a mixture of a plasticizer such as a glycol and an organic polymer cast upon a porous organic polymer support. The membrane may be prepared by casting an emulsion or a solution of the plasticizer and polymer on the porous support, evaporating the solvent and recovering the membrane after curing.

  6. Simulation Study of Heterogeneous Nucleation at Grain Boundaries During the Austenite-Ferrite Phase Transformation: Comparing the Classical Model with the Multi-Phase Field Nudged Elastic Band Method

    NASA Astrophysics Data System (ADS)

    Song, Huajing; Shi, Rongpei; Wang, Yunzhi; Hoyt, Jeffrey J.

    2016-08-01

    In this work, molecular dynamics (MD) simulations have been used to study the heterogeneous nucleation occurring at grain boundaries (GBs) during the austenite (FCC) phase to ferrite (BCC) phase transformation in a pure Fe polycrystalline system. The critical nucleus properties (including size, shape, and activation energy) determined by classical nucleation theory are compared with those obtained by using a combination of the multi-phase field method (MPFM) and the nudged elastic band (NEB) method. For nucleation events that exhibit low-energy facets completely embedded within the parent FCC phase, there is a good agreement between the MD and the MPFM result with respect to the critical nucleus size, shape, and nucleation energy barrier. For systems where the emerging nucleus contains facets that cross the GB plane, the MPFM-NEB, when compared to MD, yields a better prediction than the classical approach for the nucleus morphology. New observations from the MPFM-NEB method indicate that the critical nucleus shape may change with volume and therefore depends on the nucleation driving force (undercooling).

  7. Direct observation of metal nanoparticles as heterogeneous nuclei for the condensation of supersaturated organic vapors: Nucleation of size-selected aluminum nanoparticles in acetonitrile and n-hexane vapors

    NASA Astrophysics Data System (ADS)

    Abdelsayed, Victor; Samy El-Shall, M.

    2014-08-01

    This work reports the direct observation and separation of size-selected aluminum nanoparticles acting as heterogeneous nuclei for the condensation of supersaturated vapors of both polar and nonpolar molecules. In the experiment, we study the condensation of supersaturated acetonitrile and n-hexane vapors on charged and neutral Al nanoparticles by activation of the metal nanoparticles to act as heterogeneous nuclei for the condensation of the organic vapor. Aluminum seed nanoparticles with diameters of 1 and 2 nm are capable of acting as heterogeneous nuclei for the condensation of supersaturated acetonitrile and hexane vapors. The comparison between the Kelvin and Fletcher diameters indicates that for the heterogeneous nucleation of both acetonitrile and hexane vapors, particles are activated at significantly smaller sizes than predicted by the Kelvin equation. The activation of the Al nanoparticles occurs at nearly 40% and 65% of the onset of homogeneous nucleation of acetonitrile and hexane supersaturated vapors, respectively. The lower activation of the charged Al nanoparticles in acetonitrile vapor is due to the charge-dipole interaction which results in rapid condensation of the highly polar acetonitrile molecules on the charged Al nanoparticles. The charge-dipole interaction decreases with increasing the size of the Al nanoparticles and therefore at low supersaturations, most of the heterogeneous nucleation events are occurring on neutral nanoparticles. No sign effect has been observed for the condensation of the organic vapors on the positively and negatively charged Al nanoparticles. The present approach of generating metal nanoparticles by pulsed laser vaporization within a supersaturated organic vapor allows for efficient separation between nucleation and growth of the metal nanoparticles and, consequently controls the average particle size, particle density, and particle size distribution within the liquid droplets of the condensing vapor. Strong

  8. Direct observation of metal nanoparticles as heterogeneous nuclei for the condensation of supersaturated organic vapors: Nucleation of size-selected aluminum nanoparticles in acetonitrile and n-hexane vapors

    SciTech Connect

    Abdelsayed, Victor; Samy El-Shall, M.

    2014-08-07

    This work reports the direct observation and separation of size-selected aluminum nanoparticles acting as heterogeneous nuclei for the condensation of supersaturated vapors of both polar and nonpolar molecules. In the experiment, we study the condensation of supersaturated acetonitrile and n-hexane vapors on charged and neutral Al nanoparticles by activation of the metal nanoparticles to act as heterogeneous nuclei for the condensation of the organic vapor. Aluminum seed nanoparticles with diameters of 1 and 2 nm are capable of acting as heterogeneous nuclei for the condensation of supersaturated acetonitrile and hexane vapors. The comparison between the Kelvin and Fletcher diameters indicates that for the heterogeneous nucleation of both acetonitrile and hexane vapors, particles are activated at significantly smaller sizes than predicted by the Kelvin equation. The activation of the Al nanoparticles occurs at nearly 40% and 65% of the onset of homogeneous nucleation of acetonitrile and hexane supersaturated vapors, respectively. The lower activation of the charged Al nanoparticles in acetonitrile vapor is due to the charge-dipole interaction which results in rapid condensation of the highly polar acetonitrile molecules on the charged Al nanoparticles. The charge-dipole interaction decreases with increasing the size of the Al nanoparticles and therefore at low supersaturations, most of the heterogeneous nucleation events are occurring on neutral nanoparticles. No sign effect has been observed for the condensation of the organic vapors on the positively and negatively charged Al nanoparticles. The present approach of generating metal nanoparticles by pulsed laser vaporization within a supersaturated organic vapor allows for efficient separation between nucleation and growth of the metal nanoparticles and, consequently controls the average particle size, particle density, and particle size distribution within the liquid droplets of the condensing vapor. Strong

  9. Direct observation of metal nanoparticles as heterogeneous nuclei for the condensation of supersaturated organic vapors: nucleation of size-selected aluminum nanoparticles in acetonitrile and n-hexane vapors.

    PubMed

    Abdelsayed, Victor; El-Shall, M Samy

    2014-08-07

    This work reports the direct observation and separation of size-selected aluminum nanoparticles acting as heterogeneous nuclei for the condensation of supersaturated vapors of both polar and nonpolar molecules. In the experiment, we study the condensation of supersaturated acetonitrile and n-hexane vapors on charged and neutral Al nanoparticles by activation of the metal nanoparticles to act as heterogeneous nuclei for the condensation of the organic vapor. Aluminum seed nanoparticles with diameters of 1 and 2 nm are capable of acting as heterogeneous nuclei for the condensation of supersaturated acetonitrile and hexane vapors. The comparison between the Kelvin and Fletcher diameters indicates that for the heterogeneous nucleation of both acetonitrile and hexane vapors, particles are activated at significantly smaller sizes than predicted by the Kelvin equation. The activation of the Al nanoparticles occurs at nearly 40% and 65% of the onset of homogeneous nucleation of acetonitrile and hexane supersaturated vapors, respectively. The lower activation of the charged Al nanoparticles in acetonitrile vapor is due to the charge-dipole interaction which results in rapid condensation of the highly polar acetonitrile molecules on the charged Al nanoparticles. The charge-dipole interaction decreases with increasing the size of the Al nanoparticles and therefore at low supersaturations, most of the heterogeneous nucleation events are occurring on neutral nanoparticles. No sign effect has been observed for the condensation of the organic vapors on the positively and negatively charged Al nanoparticles. The present approach of generating metal nanoparticles by pulsed laser vaporization within a supersaturated organic vapor allows for efficient separation between nucleation and growth of the metal nanoparticles and, consequently controls the average particle size, particle density, and particle size distribution within the liquid droplets of the condensing vapor. Strong

  10. CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES: Improvement in Dielectric Tunability of Ba0.6Sr0.4TiO4-Mg2TiO4 Composite Ceramics via Heterogeneous Nucleation Processing

    NASA Astrophysics Data System (ADS)

    Wang, Zhuo; Li, Yong-Xiang

    2009-11-01

    Dielectric tunable composite ceramics Ba0.6Sr0.4 TiO3-Mg2TiO4 (BST-MT) are prepared with a heterogeneous nucleation sol-gel approach. The Mg2TiO4 powders are synthesized by the conventional solid-state reaction method. The micro-sized MT powders with dispersant Ciba-4010 are introduced into Ba-Sr-Ti sol to obtain uniform and homogeneous mixture compounds with nano-sized BST particles synthesized via heterogeneous nucleation (HN) in the sol-gel process. Thus, the microstructural and dielectric properties can be tailored. The dielectric constants of BST-MT composite ceramics can be adjusted in a large range from 294 to 1790, and the dielectric tunability can be adjusted from 29.4% to 37.0% with different MT contents from 60 wt% to 20 wt%. Compared to the samples prepared by the conventional solid-state (SS) process, the BST-MT composite ceramics by the heterogeneous nucleation sol-gel process exhibit a more uniform microstructure, and improve dielectric properties.

  11. Theoretical study of production of unique glasses in space. [kinetic relationships describing nucleation and crystallization phenomena

    NASA Technical Reports Server (NTRS)

    Larsen, D. C.; Sievert, J. L.

    1975-01-01

    The potential of producing the glassy form of selected materials in the weightless, containerless nature of space processing is examined through the development of kinetic relationships describing nucleation and crystallization phenomena. Transformation kinetics are applied to a well-characterized system (SiO2), an excellent glass former (B2O3), and a poor glass former (Al2O3) by conventional earth processing methods. Viscosity and entropy of fusion are shown to be the primary materials parameters controlling the glass forming tendency. For multicomponent systems diffusion-controlled kinetics and heterogeneous nucleation effects are considered. An analytical empirical approach is used to analyze the mullite system. Results are consistent with experimentally observed data and indicate the promise of mullite as a future space processing candidate.

  12. The C-protein tetramer binds 230 to 240 nucleotides of pre-mRNA and nucleates the assembly of 40S heterogeneous nuclear ribonucleoprotein particles.

    PubMed Central

    Huang, M; Rech, J E; Northington, S J; Flicker, P F; Mayeda, A; Krainer, A R; LeStourgeon, W M

    1994-01-01

    A series of in vitro protein-RNA binding studies using purified native (C1)3C2 and (A2)3B1 tetramers, total soluble heterogeneous nuclear ribonucleoprotein (hnRNP), and pre-mRNA molecules differing in length and sequence have revealed that a single C-protein tetramer has an RNA site size of 230 to 240 nucleotides (nt). Two tetramers bind twice this RNA length, and three tetramers fold monoparticle lengths of RNA (700 nt) into a unique 19S triangular complex. In the absence of this unique structure, the basic A- and B-group proteins bind RNA to form several different artifactual structures which are not present in preparations of native hnRNP and which do not function in hnRNP assembly. Three (A2)3B1 tetramers bind the 19S complex to form a 35S assembly intermediate. Following UV irradiation to immobilize the C proteins on the packaged RNA, the 19S triangular complex is recovered as a remnant structure from both native and reconstituted hnRNP particles. C protein-RNA complexes composed of three, six, or nine tetramers (one, two, or three triangular complexes) nucleate the stoichiometric assembly of monomer, dimer, and trimer hnRNP particles. The binding of C-protein tetramers to RNAs longer than 230 nt is through a self-cooperative combinatorial mode. RNA packaged in the 19S complex and in 40S hnRNP particles is efficiently spliced in vitro. These findings demonstrate that formation of the triangular C protein-RNA complex is an obligate first event in the in vitro and probably the in vivo assembly the 40S hnRNP core particle, and they provide insight into the mechanism through which the core proteins package 700-nt increments of RNA. These findings also demonstrate that unless excluded by other factors, the C proteins are likely to be located along the length of nascent transcripts. Images PMID:8264621

  13. 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.

  14. 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).

  15. Ice Nucleation Properties of Oxidized Carbon Nanomaterials.

    PubMed

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

    2015-08-06

    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.

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

    DOE PAGES

    Malila, Jussi; McGraw, Robert; Laaksonen, Ari; ...

    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

  17. 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.

  18. 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.

  19. Protein crystal nucleation in pores

    PubMed Central

    Nanev, Christo N.; Saridakis, Emmanuel; Chayen, Naomi E.

    2017-01-01

    The most powerful method for protein structure determination is X-ray crystallography which relies on the availability of high quality crystals. Obtaining protein crystals is a major bottleneck, and inducing their nucleation is of crucial importance in this field. An effective method to form crystals is to introduce nucleation-inducing heterologous materials into the crystallization solution. Porous materials are exceptionally effective at inducing nucleation. It is shown here that a combined diffusion-adsorption effect can increase protein concentration inside pores, which enables crystal nucleation even under conditions where heterogeneous nucleation on flat surfaces is absent. Provided the pore is sufficiently narrow, protein molecules approach its walls and adsorb more frequently than they can escape. The decrease in the nucleation energy barrier is calculated, exhibiting its quantitative dependence on the confinement space and the energy of interaction with the pore walls. These results provide a detailed explanation of the effectiveness of porous materials for nucleation of protein crystals, and will be useful for optimal design of such materials. PMID:28091515

  20. Dynamic density functional theory for nucleation: Non-classical predictions of mesoscopic nucleation theory

    NASA Astrophysics Data System (ADS)

    Duran-Olivencia, Miguel A.; Yatsyshin, Peter; Lutsko, James F.; Kalliadasis, Serafim

    2016-11-01

    Classical density functional theory (DFT) for fluids and its dynamic extension (DDFT) provide an appealing mean-field framework for describing equilibrium and dynamics of complex soft matter systems. For a long time, homogeneous nucleation was considered to be outside the limits of applicability of DDFT. However, our recently developed mesoscopic nucleation theory (MeNT) based on fluctuating hydrodynamics, reconciles the inherent randomness of the nucleation process with the deterministic nature of DDFT. It turns out that in the weak-noise limit, the most likely path (MLP) for nucleation to occur is determined by the DDFT equations. We present computations of MLPs for homogeneous and heterogeneous nucleation in colloidal suspensions. For homogeneous nucleation, the MLP obtained is in excellent agreement with the reduced order-parameter description of MeNT, which predicts a multistage nucleation pathway. For heterogeneous nucleation, the presence of impurities in the fluid affects the MLP, but remarkably, the overall qualitative picture of homogeneous nucleation persists. Finally, we highlight the use of DDFT as a simulation tool, which is especially appealing as there are no known applications of MeNT to heterogeneous nucleation. We acknowledge financial support from the European Research Council via Advanced Grant No. 247031 and from EPSRC via Grants No. EP/L020564 and EP/L025159.

  1. Physical and spectroscopic properties of multi-component Na2O-PbO-Bi2O3-SiO2 glass ceramics with Cr2O3 as nucleating agent

    NASA Astrophysics Data System (ADS)

    Sambasiva Rao, M. V.; Rajyasree, Ch.; Narendrudu, T.; Suresh, S.; Suneel Kumar, A.; Veeraiah, N.; Krishna Rao, D.

    2015-09-01

    Transparent glass ceramics, synthesized from melt quenching followed by heat treatment, of the composition 10Na2O-30PbO-10Bi2O3-(50 - x)SiO2:xCr2O3 (mol%), where 0 ⩽ x ⩽ 0.5, were characterized with XRD, DTA, SEM and EDS. Physical and spectroscopic studies, viz., optical absorption, electron paramagnetic resonance (EPR), FTIR and Raman were investigated. The characterization of the host glass ceramic has revealed that the formation of a major phase of sodium silicate along with two minor phases such as lead silicate and bismuth oxide. By integrating Cr2O3 to the host glass additional crystal phases viz., NaCrO2, Na2Cr2O7 and Pb(CrO4) which are the complexes of Cr3+ and Cr6+ ions were also developed. As the concentration of nucleating agent is increased, a part of the Cr6+ ions is found to reduce in to Cr3+ ions. Spectroscopic studies have revealed that with an increase in the concentration of Cr2O3 from 0.1 to 0.5 mol%, there is a gradual increase in the intensity of vibrational modes of various asymmetric structural units of silicate, bismuthate and chromate in the glass ceramic network at the expense of symmetrical structural units. The analysis of the results of these studies has indicated that in the samples containing higher concentration of Cr2O3, chromium ions exists predominantly in Cr3+ state and occupy the octahedral positions in glass ceramic matrix and such glass ceramic samples are suitable for lasing action.

  2. Pb, Nd, and Sr isotopic evidence for a multicomponent source for rocks of Cook-Austral Islands and heterogeneities of mantle plumes

    USGS Publications Warehouse

    Nakamura, Y.; Tatsumoto, M.

    1988-01-01

    Sr, Nd, and Pb isotopic compositions were measured in alkaline volcanic rocks (alkali basalt, ankaramite, nephelinite, phonolite, and trachyte) from the South Cook Islands (Aitutaki, Mauke, Rarotonga, Atiu, and Mangaia) and the Austral Islands (Rimatara and Rurutu). The results show that the Cook-Austral rocks have an extremely wide range in isotopic compositions of Pb: 206Pb 204Pb from 18.25 to 21.76, 207pb 204pb from 15.48 to 15.83, and sol208pb 204Pb from 38.37 to 40.62, whereas isotopic compositions of Sr and Nd are less variable. Isotopically, Mangaia, Rimatara, and Rurutu form one group (Mangaia group), which shows extremely radiogenic Pb isotopic compositions but near-MORB (mid-oceanic ridge basalts) values for Sr and Nd isotopic ratios. In contrast, samples from Aitutaki, Rarotonga, Mauke, and Atiu (Aitutaki group) have high 207Pb 204Pb and 208Pb 204Pb and moderately high 87Sr 86Sr (Dupal anomaly). The Aitutaki group could have been derived from heterogeneous mantle plumes, which rose from the enriched deep mantle (the almost primitive lower mantle or recycled continental and oceanic slabs). On the other hand, the Mangaia component could have been derived from the depleted upper mantle which may have been metasomatized with a CO2-rich fluid, as indicated by the near-MORB values of Sr and Nd isotopes. Although Pb isotopic data of the two groups cannot be distinguished from each other statistically, the end components of the Pb-Pb system do not match with those of the Nd-Sr system. Thus, the data must be explained by a multi-, at least three, component mixing model: the mantle plumes (Dupal component and a recycled oceanic slab), metasomatized upper mantle, and lithosphere. The K-Ar ages and isotopic characteristics of the Cook-Austral rocks indicate that if one mantle plume rises from the deep mantle in this region, it has separated into at least two segments on the way to the surface. ?? 1988.

  3. Pb, Nd, and Sr isotopic evidence for a multicomponent source for rocks of Cook-Austral Islands and heterogeneities of mantle plumes

    SciTech Connect

    Nakamura, Yoichi; Tatsumoto, Mitsunobu )

    1988-12-01

    Sr, Nd, and Pb isotopic compositions were measured in alkane volcanic rocks from the South Cook Islands and the Austral Islands. The results show that the Cook-Austral rocks have an extremely wide range in isotopic compositions of Pb: {sup 206}Pb/{sup 204}Pb from 18.25 to 21.76, {sup 207}Pb/{sup 204}Pb from 15.48 to 15.83, and {sup 208}Pb/{sup 204}Pb from 38.37 to 40.62, whereas isotopic compositions of Sr and Nd are less variable. Isotopically, Mangaia, Rimatara, and Rurutu form one group, which shows extremely ratiogenic Pb isotopic compositions but near-MORB (mid-ocean ridge basalts) values for Sr and Nd isotopic ratios. In contrast, samples from Aitutaki, Rarotonga, Mauke, and Atiu (Aitutaki group) have high {sup 207}Pb/{sup 204}Pb and {sup 208}Pb/{sup 204}Pb and moderately high {sup 87}Sr/{sup 86}Sr (Dupal anomaly). The Aitutaki group could have been derived from heterogeneous mantle plumes, which rose from the enriched deep mantle (the almost primitive lower mantle or recycled continental and oceanic slabs). On the other hand, the Mangaia component could have been derived from the depleted upper mantle which may have been metasomatized with a Co{sub 2}-rich fluid, as indicated by the near-MORB values of Sr and Nd isotopes. Although Pb isotopic data of the two groups cannot be distinguished from each other statistically, the end components of the Pb-Pb system do not match with those of the Nd-Sr system. Thus, the data must be explained by a multi-, at least three, component mixing model: the mantle plumes, metasomatized upper mantle, and lithosphere. The K-Ar ages and isotopic characteristics of the Cook-Austral rocks indicate that if one mantle plume rises from the deep mantle in this region, it has separated into at least two segments on the way to the surface.

  4. Heterogeneous nucleation of CdS to enhance visible-light photocatalytic hydrogen evolution of SiC/CdS composite

    NASA Astrophysics Data System (ADS)

    Peng, Yuan; Guo, Zhongnan; Wang, Da; Pan, Nanyan; Yuan, Wenxia

    2015-07-01

    Synthesis of composite photocatalyst is one of the most important strategies to enhance the yield of hydrogen produced by water splitting. However, one photocatalyst usually tends to randomly aggregate on the other's surface, which weakens the electron transport of the heterogeneous interface. Herein, we developed a hydrothermal reaction to synthesize the SiC/CdS composite with a feasible Z-scheme and well-controlled dispersion of CdS on SiC surface. Heterogeneous structure on the catalyst interface is obtained, leading to more light-absorption and effective electron-hole separation between the well-contacted components, which contribute to the doubly enhanced photocatalytic performance of the composite. This work provides a simple and practical route to improve the catalytic activity by optimizing the intrinsic contact of Z-scheme composite semiconductors.

  5. Heterogeneous nucleation of CdS to enhance visible-light photocatalytic hydrogen evolution of SiC/CdS composite

    SciTech Connect

    Peng, Yuan; Guo, Zhongnan E-mail: wxyuanwz@163.com; Wang, Da; Pan, Nanyan; Yuan, Wenxia E-mail: wxyuanwz@163.com

    2015-07-06

    Synthesis of composite photocatalyst is one of the most important strategies to enhance the yield of hydrogen produced by water splitting. However, one photocatalyst usually tends to randomly aggregate on the other's surface, which weakens the electron transport of the heterogeneous interface. Herein, we developed a hydrothermal reaction to synthesize the SiC/CdS composite with a feasible Z-scheme and well-controlled dispersion of CdS on SiC surface. Heterogeneous structure on the catalyst interface is obtained, leading to more light-absorption and effective electron-hole separation between the well-contacted components, which contribute to the doubly enhanced photocatalytic performance of the composite. This work provides a simple and practical route to improve the catalytic activity by optimizing the intrinsic contact of Z-scheme composite semiconductors.

  6. Solute Behavior in the Initial Nucleation of V- and Nb-Containing Carbide

    NASA Astrophysics Data System (ADS)

    Liu, Q. D.; Liu, W. Q.; Zhao, S. J.

    2011-12-01

    The three-dimensional atom probe (3DAP) is used to characterize the solute behavior at the initial nucleation stage of carbide that precipitates in a quench-temper processed multicomponent V-Nb microalloyed steel. The equilibrium (V,Nb)C phase does not precipitate directly from the ferrous matrix with martensite structure, whereas it is preceded by the formation of isostructural diffuse atmosphere, Fe-depleted V-Nb cluster, and metastable phase (Fe,V,Nb)C successively. The transient phases are considered to largely reduce the required high energy, which is often accompanied by the appearance of the fresh incoherent carbide/matrix boundary. During the evolution of these phases, vanadium and niobium diffuse to the previously existing carbon-enriched cluster concurrently but with different mobilities from the aspect of the kinetic pathway, leading to heterogeneous distribution of solutes in the transient phases.

  7. Photoinduced Multicomponent Reactions.

    PubMed

    Garbarino, Silvia; Ravelli, Davide; Protti, Stefano; Basso, Andrea

    2016-12-12

    The combination of multicomponent approaches with light-driven processes opens up new scenarios in the area of synthetic organic chemistry, where the need for sustainable, atom- and energy-efficient reactions is increasingly urgent. Photoinduced multicomponent reactions are still in their infancy, but significant developments in this area are expected in the near future.

  8. Multicomponent Syntheses of Macrocycles

    NASA Astrophysics Data System (ADS)

    Masson, Géraldine; Neuville, Luc; Bughin, Carine; Fayol, Aude; Zhu, Jieping

    How to access efficiently the macrocyclic structure remained to be a challenging synthetic topic. Although many elegant approaches/reactions have been developed, construction of diverse collection of macrocycles is still elusive. This chapter summarized the recently emerged research area dealing with multicomponent synthesis of macrocycles, with particular emphasis on the approach named "multiple multicomponent reaction using two bifunctional building blocks".

  9. Ice cloud processing of ultra-viscous/glassy aerosol particles leads to enhanced ice nucleation ability

    NASA Astrophysics Data System (ADS)

    Wagner, R.; Möhler, O.; Saathoff, H.; Schnaiter, M.; Skrotzki, J.; Leisner, T.; Wilson, T. W.; Malkin, T. L.; Murray, B. J.

    2012-09-01

    The ice nucleation potential of airborne glassy aqueous aerosol particles has been investigated by controlled expansion cooling cycles in the AIDA aerosol and cloud chamber of the Karlsruhe Institute of Technology at temperatures between 247 and 216 K. Four different solutes were used as proxies for oxygenated organic matter found in the atmosphere: raffinose, 4-hydroxy-3-methoxy-DL-mandelic acid (HMMA), levoglucosan, and a multi-component mixture of raffinose with five dicarboxylic acids and ammonium sulphate. Similar to previous experiments with citric acid aerosols, all particles were found to nucleate ice heterogeneously before reaching the homogeneous freezing threshold provided that the freezing cycles were started well below the respective glass transition temperatures of the compounds; this is discussed in detail in a separate article. In this contribution, we identify a further mechanism by which glassy aerosols can promote ice nucleation below the homogeneous freezing limit. If the glassy aerosol particles are probed in freezing cycles started only a few degrees below their respective glass transition temperatures, they enter the liquid regime of the state diagram upon increasing relative humidity (moisture-induced glass-to-liquid transition) before being able to act as heterogeneous ice nuclei. Ice formation then only occurs by homogeneous freezing at elevated supersaturation levels. When ice forms the remaining solution freeze concentrates and re-vitrifies. If these ice cloud processed glassy aerosol particles are then probed in a second freezing cycle at the same temperature, they catalyse ice formation at a supersaturation threshold between 5 and 30% with respect to ice. By analogy with the enhanced ice nucleation ability of insoluble ice nuclei like mineral dusts after they nucleate ice once, we refer to this phenomenon as pre-activation. We propose a number of possible explanations for why glassy aerosol particles that have re-vitrified in contact

  10. Ice cloud processing of ultra-viscous/glassy aerosol particles leads to enhanced ice nucleation ability

    NASA Astrophysics Data System (ADS)

    Wagner, R.; Möhler, O.; Saathoff, H.; Schnaiter, M.; Skrotzki, J.; Leisner, T.; Wilson, T. W.; Malkin, T. L.; Murray, B. J.

    2012-04-01

    The ice nucleation potential of airborne glassy aqueous aerosol particles has been investigated by controlled expansion cooling cycles in the AIDA aerosol and cloud chamber of the Karlsruhe Institute of Technology at temperatures between 247 and 216 K. Four different solutes were used as proxies for oxygenated organic matter found in the atmosphere: raffinose, 4-hydroxy-3-methoxy-DL-mandelic acid (HMMA), levoglucosan, and a multi-component mixture of raffinose with five dicarboxylic acids and ammonium sulphate. Similar to previous experiments with citric acid aerosols, all particles were found to nucleate ice heterogeneously before reaching the homogeneous freezing threshold provided that the freezing cycles were started well below the respective glass transition temperatures of the compounds; this is discussed in detail in a separate article. In this contribution, we identify a further mechanism by which glassy aerosols can promote ice nucleation below the homogeneous freezing limit. If the glassy aerosol particles are probed in freezing cycles started only a few degrees below their respective glass transition temperatures, they enter the liquid regime of the state diagram upon increasing relative humidity (moisture-induced glass-to-liquid transition) before being able to act as heterogeneous ice nuclei. Ice formation then only occurs by homogeneous freezing at elevated supersaturation levels. When ice forms the remaining solution freeze concentrates and re-vitrifies. If these ice cloud processed glassy aerosol particles are then probed in a second freezing cycle at the same temperature, they catalyse ice formation at a supersaturation threshold between 5 and 30% with respect to ice. By analogy with the enhanced ice nucleation ability of insoluble ice nuclei like mineral dusts after they nucleate ice once, we refer to this phenomenon as pre-activation. We propose a number of possible explanations for why glassy aerosols that have re-vitrified in contact with the

  11. Hydrophobic hydration driven self-assembly of curcumin in water: Similarities to nucleation and growth under large metastability, and an analysis of water dynamics at heterogeneous surfaces

    NASA Astrophysics Data System (ADS)

    Hazra, Milan Kumar; Roy, Susmita; Bagchi, Biman

    2014-11-01

    As the beneficial effects of curcumin have often been reported to be limited to its small concentrations, we have undertaken a study to find the aggregation properties of curcumin in water by varying the number of monomers. Our molecular dynamics simulation results show that the equilibrated structure is always an aggregated state with remarkable structural rearrangements as we vary the number of curcumin monomers from 4 to 16 monomers. We find that the curcumin monomers form clusters in a very definite pattern where they tend to aggregate both in parallel and anti-parallel orientation of the phenyl rings, often seen in the formation of β-sheet in proteins. A considerable enhancement in the population of parallel alignments is observed with increasing the system size from 12 to 16 curcumin monomers. Due to the prevalence of such parallel alignment for large system size, a more closely packed cluster is formed with maximum number of hydrophobic contacts. We also follow the pathway of cluster growth, in particular the transition from the initial segregated to the final aggregated state. We find the existence of a metastable structural intermediate involving a number of intermediate-sized clusters dispersed in the solution. We have constructed a free energy landscape of aggregation where the metatsable state has been identified. The course of aggregation bears similarity to nucleation and growth in highly metastable state. The final aggregated form remains stable with the total exclusion of water from its sequestered hydrophobic core. We also investigate water structure near the cluster surface along with their orientation. We find that water molecules form a distorted tetrahedral geometry in the 1st solvation layer of the cluster, interacting rather strongly with the hydrophilic groups at the surface of the curcumin. The dynamics of such quasi-bound water molecules near the surface of curcumin cluster is considerably slower than the bulk signifying a restricted

  12. Spatially resolved multicomponent gels

    NASA Astrophysics Data System (ADS)

    Draper, Emily R.; Eden, Edward G. B.; McDonald, Tom O.; Adams, Dave J.

    2015-10-01

    Multicomponent supramolecular systems could be used to prepare exciting new functional materials, but it is often challenging to control the assembly across multiple length scales. Here we report a simple approach to forming patterned, spatially resolved multicomponent supramolecular hydrogels. A multicomponent gel is first formed from two low-molecular-weight gelators and consists of two types of fibre, each formed by only one gelator. One type of fibre in this ‘self-sorted network’ is then removed selectively by a light-triggered gel-to-sol transition. We show that the remaining network has the same mechanical properties as it would have done if it initially formed alone. The selective irradiation of sections of the gel through a mask leads to the formation of patterned multicomponent networks, in which either one or two networks can be present at a particular position with a high degree of spatial control.

  13. Experiments on Nucleation in Different Flow Regimes

    NASA Technical Reports Server (NTRS)

    Bayuzick, R. J.; Hofmeister, W. H.; Morton, C. M.; Robinson, M. B.

    1999-01-01

    The vast majority of metallic engineering materials are solidified from the liquid phase. Understanding the solidification process is essential to control microstructure, which in turn, determines the properties of materials. The genesis of solidification is nucleation, where the first stable solid forms from the liquid phase. Nucleation kinetics determine the degree of undercooling and phase selection. As such, it is important to understand nucleation phenomena in order to control solidification or glass formation in metals and alloys. Early experiments in nucleation kinetics were accomplished by droplet dispersion methods. Dilatometry was used by Turnbull and others, and more recently differential thermal analysis and differential scanning calorimetry have been used for kinetic studies. These techniques have enjoyed success; however, there are difficulties with these experiments. Since materials are dispersed in a medium, the character of the emulsion/metal interface affects the nucleation behavior. Statistics are derived from the large number of particles observed in a single experiment, but dispersions have a finite size distribution which adds to the uncertainty of the kinetic determinations. Even though temperature can be controlled quite well before the onset of nucleation, the release of the latent heat of fusion during nucleation of particles complicates the assumption of isothermality during these experiments. Containerless processing has enabled another approach to the study of nucleation kinetics. With levitation techniques it is possible to undercool one sample to nucleation repeatedly in a controlled manner, such that the statistics of the nucleation process can be derived from multiple experiments on a single sample. The authors have fully developed the analysis of nucleation experiments on single samples following the suggestions of Skripov. The advantage of these experiments is that the samples are directly observable. The nucleation temperature

  14. 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

  15. 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.

  16. Multicomponent Implant Releasing Dexamethasone

    NASA Astrophysics Data System (ADS)

    Nikkola, L.; Vapalahti, K.; Ashammakhi, N.

    2008-02-01

    Several inflammatory conditions are usually treated with corticosteroids. There are various problems like side effects with traditional applications of steroids, e.g. topical, or systemic routes. Local drug delivery systems have been studied and developed to gain more efficient administration with fewer side effects. Earlier, we reported on developing Dexamethasone (DX) releasing biodegradable fibers. However, their drug release properties were not satisfactory in terms of onset of drug release. Thus, we assessed the development of multicomponent (MC) implant to enhance earlier drug release from such biodegradable fibers. Poly (lactide-co-glycolide) (PLGA) and 2 wt-% and 8 wt-% DX were compounded and extruded with twin-screw extruder to form of fibers. Some of the fibers were sterilized to obtain a change in drug release properties. Four different fiber classes were studied: 2 wt-%, 8 wt-%, sterilized 2 wt-%, and sterilized 8 wt-%. 3×4 different DX-releasing fibers were then heat-pressed to form one multicomponent rod. Half of the rods where sterilized. Drug release was measured from initial fibers and multicomponent rods using a UV/VIS spectrometer. Shear strength and changes in viscosity were also measured. Drug release studies showed that drug release commenced earlier from multicomponent rods than from component fibers. Drug release from multicomponent rods lasted from day 30 to day 70. The release period of sterilized rods extended from day 23 to day 57. When compared to the original component fibers, the drug release from MC rods commenced earlier. The initial shear strength of MC rods was 135 MPa and decreased to 105 MPa during four weeks of immersion in phosphate buffer solution. Accordingly, heat pressing has a positive effect on drug release. After four weeks in hydrolysis, no disintegration was observed.

  17. Nucleation of shear bands in amorphous alloys

    PubMed Central

    Perepezko, John H.; Imhoff, Seth D.; Chen, Ming-Wei; Wang, Jun-Qiang; Gonzalez, Sergio

    2014-01-01

    The initiation and propagation of shear bands is an important mode of localized inhomogeneous deformation that occurs in a wide range of materials. In metallic glasses, shear band development is considered to center on a structural heterogeneity, a shear transformation zone that evolves into a rapidly propagating shear band under a shear stress above a threshold. Deformation by shear bands is a nucleation-controlled process, but the initiation process is unclear. Here we use nanoindentation to probe shear band nucleation during loading by measuring the first pop-in event in the load–depth curve which is demonstrated to be associated with shear band formation. We analyze a large number of independent measurements on four different bulk metallic glasses (BMGs) alloys and reveal the operation of a bimodal distribution of the first pop-in loads that are associated with different shear band nucleation sites that operate at different stress levels below the glass transition temperature, Tg. The nucleation kinetics, the nucleation barriers, and the density for each site type have been determined. The discovery of multiple shear band nucleation sites challenges the current view of nucleation at a single type of site and offers opportunities for controlling the ductility of BMG alloys. PMID:24594599

  18. Size Dependant Nucleation of Confined 2-Decanol

    NASA Astrophysics Data System (ADS)

    Amanuel, Samuel; Bauer, Hillary; Safiq, Alexandrea; Dulmaa, Jargalsaikhan; Khraisat, Amer

    2012-02-01

    We have studied freezing and melting of physically confined 2-decanol in nano porous silica using a Differential Scanning Calorimeter (DSC). Both melting and freezing temperatures are suppressed for physically confined 2-decanol. In the presence of bulk, freezing of the confined system is triggered by freezing of the bulk where nucleation is heterogeneous. There is, however, a cutoff size between 100 nm and 300 nm where phase transition is no longer initiated through heterogeneous nucleation. Below the cutoff size, nucleation is homogeneous where the confined system has to be supercooled further before any phase transition can occur. Melting of the confined system, on the other hand, is not influenced by the presence or absence of the bulk.

  19. Nucleation and droplet growth at high pressure

    NASA Astrophysics Data System (ADS)

    Luijten, Carlo Cornelis Maria

    Homogeneous nucleation, the first stage of droplet formation in the absence of foreign particles, usually takes place in the presence of one or more supercritical carrier gases. The present work aimed at a systematic investigation of the effects of carrier gas pressure on nucleation and droplet growth. Using the so-called nucleation pulse method, nucleation and droplet growth can be separated in time, which facilitates quantitative study of these processes using Constant Angle Mie Scattering and light extinction. The method was implemented in a modified shock tube, using gas dynamic principles to create the pulse. In this way, nucleation and growth rates were measured as a function of temperature, pressure, and composition. Composition measurement at high pressure was achieved along two different routes. Water vapour concentrations were determined using a commercial humidity sensor, after calibration with total pressure as an independent parameter. Gas chromatography was used to determine hydrocarbon concentrations, after pressure reduction of the mixture over a thermostatic capillary tube. Using the above analysis techniques, nucleation and droplet growth experiments were performed for several vapour-gas mixtures, at pressures between 1 and 40 bar. Mixtures with a varying degree of interaction were selected, to allow for a systematic investigation of carrier gas influence. Besides these binary mixtures, the first quantitative nucleation and growth rates for- multicomponent-natural gas were obtained. Theoretical models for both nucleation and droplet growth were adapted to take into account the presence of a carrier gas, under condition of small carrier gas solubility. The main effects involved are the increase of saturated vapour density and decrease of surface tension with pressure. On the basis of our experiments, these effects were demonstrated to play important and counteracting roles in high pressure nucleation. Using Density Functional Theory, both effects

  20. Overview: Experimental studies of crystal nucleation: Metals and colloids

    NASA Astrophysics Data System (ADS)

    Herlach, Dieter M.; Palberg, Thomas; Klassen, Ina; Klein, Stefan; Kobold, Raphael

    2016-12-01

    Crystallization is one of the most important phase transformations of first order. In the case of metals and alloys, the liquid phase is the parent phase of materials production. The conditions of the crystallization process control the as-solidified material in its chemical and physical properties. Nucleation initiates the crystallization of a liquid. It selects the crystallographic phase, stable or meta-stable. Its detailed knowledge is therefore mandatory for the design of materials. We present techniques of containerless processing for nucleation studies of metals and alloys. Experimental results demonstrate the power of these methods not only for crystal nucleation of stable solids but in particular also for investigations of crystal nucleation of metastable solids at extreme undercooling. This concerns the physical nature of heterogeneous versus homogeneous nucleation and nucleation of phases nucleated under non-equilibrium conditions. The results are analyzed within classical nucleation theory that defines the activation energy of homogeneous nucleation in terms of the interfacial energy and the difference of Gibbs free energies of solid and liquid. The interfacial energy acts as barrier for the nucleation process. Its experimental determination is difficult in the case of metals. In the second part of this work we therefore explore the potential of colloidal suspensions as model systems for the crystallization process. The nucleation process of colloids is observed in situ by optical observation and ultra-small angle X-ray diffraction using high intensity synchrotron radiation. It allows an unambiguous discrimination of homogeneous and heterogeneous nucleation as well as the determination of the interfacial free energy of the solid-liquid interface. Our results are used to construct Turnbull plots of colloids, which are discussed in relation to Turnbull plots of metals and support the hypothesis that colloids are useful model systems to investigate crystal

  1. Ice-Nucleating Bacteria

    NASA Astrophysics Data System (ADS)

    Obata, Hitoshi

    Since the discovery of ice-nucleating bacteria in 1974 by Maki et al., a large number of studies on the biological characteristics, ice-nucleating substance, ice nucleation gene and frost damage etc. of the bacteria have been carried out. Ice-nucleating bacteria can cause the freezing of water at relatively warm temperature (-2.3°C). Tween 20 was good substrates for ice-nucleating activity of Pseudomonas fluorescens KUIN-1. Major fatty acids of Isolate (Pseudomonas fluorescens) W-11 grown at 30°C were palmitic, cis-9-hexadecenoic and cis-11-octadecenoic which amounted to 90% of the total fatty acids. Sequence analysis shows that an ice nucleation gene from Pseudomonas fluorescens is related to the gene of Pseudomonas syringae.

  2. Experiments on Nucleation in Different Flow Regimes

    NASA Technical Reports Server (NTRS)

    Bayuzick, Robert J.

    1999-01-01

    The vast majority of metallic engineering materials are solidified from the liquid phase. Understanding the solidification process is essential to control microstructure, which in turn, determines the properties of materials. The genesis of solidification is nucleation, where the first stable solid forms from the liquid phase. Nucleation kinetics determine the degree of undercooling and phase selection. As such, it is important to understand nucleation phenomena in order to control solidification or glass formation in metals and alloys. Early experiments in nucleation kinetics were accomplished by droplet dispersion methods [1-6]. Dilitometry was used by Turnbull and others, and more recently differential thermal analysis and differential scanning calorimetry have been used for kinetic studies. These techniques have enjoyed success; however, there are difficulties with these experiments. Since materials are dispersed in a medium, the character of the emulsion/metal interface affects the nucleation behavior. Statistics are derived from the large number of particles observed in a single experiment, but dispersions have a finite size distribution which adds to the uncertainty of the kinetic determinations. Even though temperature can be controlled quite well before the onset of nucleation, the release of the latent heat of fusion during nucleation of particles complicates the assumption of isothermality during these experiments. Containerless processing has enabled another approach to the study of nucleation kinetics [7]. With levitation techniques it is possible to undercool one sample to nucleation repeatedly in a controlled manner, such that the statistics of the nucleation process can be derived from multiple experiments on a single sample. The authors have fully developed the analysis of nucleation experiments on single samples following the suggestions of Skripov [8]. The advantage of these experiments is that the samples are directly observable. The nucleation

  3. 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.

  4. Shape-anisotropic heterogeneous nucleation and magnetic Gibbs-Thomson effect in itinerant-electron metamagnetic transition of La(Fe0.88Si0.12)13 magnetocaloric compound

    NASA Astrophysics Data System (ADS)

    Fujita, A.; Kondo, T.; Kano, M.; Yako, H.

    2013-01-01

    Macroscopic anisotropy of spatial selectivity in magnetic nucleation and growth was clarified for itinerant-electron metamagnetic transition of La(Fe0.88Si0.12)13 by the time-dependent Ginzburg-Landau model combined with the Maxwell electromagnetic equation. Spontaneous generation of voltage supports symmetric growth in the longitudinal direction of the specimen as predicted by the simulation. The difference between nucleation-growth behaviors in thermally induced transition and those in field-induced transition is also elucidated. Electrical resistivity measurements also detect anisotropic growth of the induced phase. These results imply that the magnetic-dipole version of Gibbs-Thomson effect governs growth behavior.

  5. Diamond nucleation using polyethene

    SciTech Connect

    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.

  6. 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.

  7. Magnetization of multicomponent ferrofluids.

    PubMed

    Szalai, I; Dietrich, S

    2011-08-17

    The solution of the mean spherical approximation (MSA) integral equation for isotropic multicomponent dipolar hard sphere fluids without external fields is used to construct a density functional theory (DFT), which includes external fields, in order to obtain an analytical expression for the external field dependence of the magnetization of ferrofluidic mixtures. This DFT is based on a second-order Taylor series expansion of the free energy density functional of the anisotropic system around the corresponding isotropic MSA reference system. The ensuing results for the magnetic properties are in quantitative agreement with our canonical ensemble Monte Carlo simulation data presented here.

  8. Nucleation and Crystallization in nucleated Polymers

    NASA Astrophysics Data System (ADS)

    Schick, Christoph; Zhuravlev, Evgeny; Wurm, Andreas

    2012-02-01

    Crystallization is commonly considered as nucleation followed by a growth process. Here we apply the recently developed technique, differential fast scanning calorimetry (DFSC), for a unique, new look at the crystal growth of poly(epsilon-caprolactone) (PCL) and PCL carbon nanotube composites from 185 K, below the glass transition temperature, to 330 K, close to the equilibrium melting temperature. The DFSC allows temperature control of the sample and determination of its heat capacity during temperature treatments by employing cooling and heating rates from 50 to 50,000 K/s. First, the crystal nucleation and overall crystallization half times were determined simultaneously in the range of temperatures where crystallization of PCL occurs. After attempting to analyze the experiments with the classical nucleation and growth model a new methodology is described, which addresses the specific problems of crystallization of flexible linear macromolecules. The structures seem to range from having practically unmeasurable latent heats of ordering (nuclei) to being clearly-recognizable, ordered species with rather sharp disordering endotherms at temperatures from the glass transition to equilibrium melting (increasingly perfect and larger crystals). The mechanisms and kinetics of growth (if any) involve a detailed understanding of the interaction with the surrounding rigid amorphous fraction (RAF) in dependence of crystal size and perfection. E. Zhuravlev, J.W.P. Schmelzer, B. Wunderlich and C. Schick, Kinetics of nucleation and crystallization in poly(epsilon-caprolactone) (PCL), Polymer 52 (2011) 1983-1997.

  9. 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

  10. Nucleation in food colloids

    NASA Astrophysics Data System (ADS)

    Povey, Malcolm J. W.

    2016-12-01

    Nucleation in food colloids has been studied in detail using ultrasound spectroscopy. Our data show that classical nucleation theory (CNT) remains a sound basis from which to understand nucleation in food colloids and analogous model systems using n-alkanes. Various interpretations and modifications of CNT are discussed with regard to their relevance to food colloids. Much of the evidence presented is based on the ultrasound velocity spectrometry measurements which has many advantages for the study of nucleating systems compared to light scattering and NMR due to its sensitivity at low solid contents and its ability to measure true solid contents in the nucleation and early crystal growth stages. Ultrasound attenuation spectroscopy also responds to critical fluctuations in the induction region. We show, however, that a periodic pressure fluctuation such as a quasi-continuous (as opposed to a pulse comprising only a few pressure cycles) ultrasound field can alter the nucleation process, even at very low acoustic intensity. Thus care must be taken when using ultrasound techniques that the measurements do not alter the studied processes. Quasi-continuous ultrasound fields may enhance or suppress nucleation and the criteria to determine such effects are derived. The conclusions of this paper are relevant to colloidal systems in foods, pharmaceuticals, agro-chemicals, cosmetics, and personal products.

  11. 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.

  12. Nonequilibrium thermodynamics of nucleation.

    PubMed

    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. Nonequilibrium thermodynamics of nucleation

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  14. 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.

  15. 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

  16. Experiments on Nucleation in Different Flow Regimes

    NASA Technical Reports Server (NTRS)

    Bayuzick, R. J.; Hofmeister, W. H.; Morton, C. M.; Robinson, M. B.

    1998-01-01

    can be measured by noncontact optical pyrometry, the mass of the sample is known, and post-processing analysis can be conducted on the sample. The disadvantages are that temperature measurement must have exceptionally high precision, and it is not possible to isolate specific heterogeneous sites as in droplet dispersions. Levitation processing of refractory materials in ultra high vacuum provides an avenue to conduct these kinetic studies on single samples. Two experimental methods have been identified where ultra high vacuum experiments are possible; electrostatic levitation in ground-based experiments and electromagnetic processing in low earth orbit on TEMPUS. Such experiments, reported here, were conducted on zirconium. Liquid zirconium is an excellent solvent and has a high solubility for contaminants contained in the bulk material as well as those contaminants found in the vacuum environment. Oxides, nitrides, and carbides do not exist in the melt, and do not form on the surface of molten zirconium, for the materials and vacuum levels used in this study. Ground-based experiments with electrostatic levitation have shown that the statistical nucleation kinetic experiments are viable and yield results which are consistent with classical nucleation theory. The advantage of low earth orbit experiments is the ability to vary the flow conditions in the liquid prior to nucleation. The put-pose of nucleation experiments in TEMPUS was to examine.

  17. Injection of highly supersaturated oxygen solutions without nucleation.

    PubMed

    Creech, J; Divino, V; Patterson, W; Zalesky, P J; Brennen, C E

    2002-12-01

    It is possible to inject highly supersaturated aqueous solutions of gas through a small capillary into an aqueous environment without the formation of significant gas bubbles. Such a technique has considerable potential therapeutic value in the treatment, for example, of heart attacks and strokes. The present paper is the second in a series (see Brereton et al. [1]) investigating the basic phenomenon behind this surprising effect. Recent experiments clearly demonstrate that the nucleation, when it does occur, results from heterogeneous nucleation on the interior surface of the distal end of the capillary. This paper describes the effects of the treatment of this interior surface on the nucleation processes and the results of high speed video observations of the phenomena. A heterogeneous nucleation model is presented which is in accord with the experimental observations.

  18. Ice Nucleation Near the Surfactant-Water Interface

    NASA Astrophysics Data System (ADS)

    Carlin, Caleb; Cantrell, Will; Taylor, Caroline

    2008-03-01

    Ice nucleation is a fundamental component of the atmospheric mechanisms driving the formation of clouds. Atmospheric nucleation occurs with a variety of compounds and conditions, but understanding the behavior of water is key in all cases. We have used multiscale molecular simulations to study heterogeneous nucleation in clouds, probing the influence of long-chain alcohols on the freezing of water droplets. Ice nucleation occurs at a finite distance from the heterogeneous surface, due to the disruption of the hydrogen bond network in response to the surfactant-water interface. The penetration depth of the disturbance is found to be dependent upon the chain length and surface organization, as well as the acidity of the terminal alcohol group.

  19. 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.

  20. Direct observation of ice nucleation events on individual atmospheric particles

    SciTech Connect

    Wang, Bingbing; Knopf, Daniel A.; China, Swarup; Arey, Bruce W.; Harder, Tristan H.; Gilles, Mary K.; Laskin, Alexander

    2016-01-01

    Heterogeneous ice nucleation is a physical chemistry process of critical relevance to a range of topics in the fundamental and the applied sciences and technologies. Heterogeneous ice nucleation remains insufficiently understood. This is in part due to the lack of experimental methods capable of in situ visualization of ice formation over nucleating substrates with microscopically characterized morphology and composition. We present development, validation and first applications of a novel electron microscopy platform allowing observation of individual ice nucleation events at temperature and relative humidity (RH) relevant for ice formation in a broad range of environmental and applied technology processes. The approach utilizes a custom-built ice nucleation cell, interfaced with an Environmental Scanning Electron Microscope (IN-ESEM system). The IN-ESEM system allows dynamic observations of individual ice formation events over particles of atmospheric relevance and determination of the ice nucleation mechanisms. Additional IN-ESEM experiments allow examination of the location of ice formation on the surface of individual particles and micro-spectroscopy analysis of the ice nucleating particles (INPs). This includes elemental composition detected by the energy dispersed analysis of X-rays (EDX), speciation of the organic content in particles using scanning transmission X-ray microscopy with near edge X-ray absorption fine structure spectroscopy (STXM/NEXAFS), and Helium ion microscopy (HeIM). The capabilities of the IN-ESEM experimental platform are demonstrated first on laboratory standards and then by chemical imaging of INPs using a complex sample of ambient particles.

  1. Gas Hydrate Nucleation Processes

    NASA Astrophysics Data System (ADS)

    David, R. E.; Zatsepina, O.; Phelps, T. J.

    2003-12-01

    The onset of gas hydrate nucleation is greatly affected by the thermal history of the water that forms its lattice structure. Hydrate formation experiments were performed in a 72 liter pressure vessel by bubbling carbon dioxide through a 1 liter column at hydrate formation pressures (1.4 to 3.7 MPa) and temperatures (275.0 to 278.0 K) to quantify this effect. They show that when even a fraction ( e. g. 20 %) of the water in which hydrate has formed was recently frozen and thawed, the overpressurization for nucleation was reduced by an average of 50 % versus experiments performed in distilled water. In those experiments where a lower overpressure is present when hydrate nucleated, they tended to form on the surface of bubbles, whereas when a higher amount of overpressure was necessary for hydrate to nucleate, they appeared to form abruptly on bubble surfaces as well as from the bulk liquid phase. In approximation of classical nucleation, hydrate formation could be described as occurring by the spontaneous joining together of arising components of the hydrate lattice. In water that was frozen, and kept at a low temperature (< 275 K), molecular simulation models predict the predominance of water molecules organized as penatmeters, a possible subunit of the hydrate lattice. Our results suggest that in nature, initiation of hydrate formation may be strongly influenced by temperature dependant pre-structuring of water molecules prior to their contact with gas.

  2. Homogeneous nucleation kinetics

    NASA Technical Reports Server (NTRS)

    Rasmussen, D. H.; Appleby, M. R.; Leedom, G. L.; Babu, S. V.; Naumann, R. J.

    1983-01-01

    Homogeneous nucleation kinetics are rederived in a manner fundamentally similar to the approach of classical nucleation theory with the following modifications and improvements. First, the cluster is a parent phase cluster and does not require energization to the parent state. Second, the thermodynamic potential used to describe phase stability is a continuous function along the pathway of phase decomposition. Third, the kinetics of clustering corresponds directly to the diffusional flux of monomers through the cluster distribution and are formally similar to classical theory with the resulting kinetic equation modified by two terms in the preexponential factor. These terms correct for the influence of a supersaturation dependent clustering within the parent phase and for the influence of an asymmetrical cluster concentration as a function of cluster size at the critical cluster size. Fourth, the supersaturation dependence of the nucleation rate is of the same form as that given by classical nucleation theory. This supersaturation dependence must however be interpreted in terms of a size dependent surface tension. Finally, there are two scaling laws which describe supersaturation to either constant nucleation rate or to the thermodynamically determined physical spinodal.

  3. Dimers in nucleating vapors

    NASA Astrophysics Data System (ADS)

    Lushnikov, A. A.; Kulmala, M.

    1998-09-01

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

  4. 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

  5. Focus: Nucleation kinetics of shear bands in metallic glass

    NASA Astrophysics Data System (ADS)

    Wang, J. Q.; Perepezko, J. H.

    2016-12-01

    The development of shear bands is recognized as the primary mechanism in controlling the plastic deformability of metallic glasses. However, the kinetics of the nucleation of shear bands has received limited attention. The nucleation of shear bands in metallic glasses (MG) can be investigated using a nanoindentation method to monitor the development of the first pop-in event that is a signature of shear band nucleation. The analysis of a statistically significant number of first pop-in events demonstrates the stochastic behavior that is characteristic of nucleation and reveals a multimodal behavior associated with local spatial heterogeneities. The shear band nucleation rate of the two nucleation modes and the associated activation energy, activation volume, and site density were determined by loading rate experiments. The nucleation activation energy is very close to the value that is characteristic of the β relaxation in metallic glass. The identification of the rate controlling kinetics for shear band nucleation offers guidance for promoting plastic flow in metallic glass.

  6. Nucleation of electrically charged droplets

    NASA Technical Reports Server (NTRS)

    De, B. R.

    1979-01-01

    The nucleating droplets or clusters in many nucleation environments (various colloidal plasmas in laboratory and technological applications, astrophysical condensation environments, etc.) are likely to be at a finite electric potential. This may be due either to the presence of electrons and ions in the gas phase or to the thermal ionization or photoionization of the droplets. The paper demonstrates that this potential may introduce a nontrivial modification in the conventional nucleation theory. Some results for the typical case of nucleation of water droplets are presented. The general conclusion is that the electric potential makes nucleation harder to achieve, thereby demonstrating the importance of a finite droplet potential in the theory of nucleation.

  7. 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

  8. Heterogeneous Catalysis: On Bathroom Mirrors and Boiling Stones

    ERIC Educational Resources Information Center

    Philipse, Albert P.

    2011-01-01

    Though heterogeneous nucleation of liquid droplets on a smooth surface (such as a bathroom mirror) is a classical topic in nucleation theory, it is not well-known that this topic is actually a pedagogical example of heterogeneous catalysis: the one and only effect of the surface is to lower the activation Gibbs energy of droplet formation. In…

  9. Effect of cloud-scale vertical velocity on the contribution of homogeneous nucleation to cirrus formation and radiative forcing

    NASA Astrophysics Data System (ADS)

    Shi, X.; Liu, X.

    2016-06-01

    Ice nucleation is a critical process for the ice crystal formation in cirrus clouds. The relative contribution of homogeneous nucleation versus heterogeneous nucleation to cirrus formation differs between measurements and predictions from general circulation models. Here we perform large-ensemble simulations of the ice nucleation process using a cloud parcel model driven by observed vertical motions and find that homogeneous nucleation occurs rather infrequently, in agreement with recent measurement findings. When the effect of observed vertical velocity fluctuations on ice nucleation is considered in the Community Atmosphere Model version 5, the relative contribution of homogeneous nucleation to cirrus cloud occurrences decreases to only a few percent. However, homogeneous nucleation still has strong impacts on the cloud radiative forcing. Hence, the importance of homogeneous nucleation for cirrus cloud formation should not be dismissed on the global scale.

  10. Overview: Understanding nucleation phenomena from simulations of lattice gas models

    NASA Astrophysics Data System (ADS)

    Binder, Kurt; Virnau, Peter

    2016-12-01

    Monte Carlo simulations of homogeneous and heterogeneous nucleation in Ising/lattice gas models are reviewed with an emphasis on the general insight gained on the mechanisms by which metastable states decay. Attention is paid to the proper distinction of particles that belong to a cluster (droplet), that may trigger a nucleation event, from particles in its environment, a problem crucial near the critical point. Well below the critical point, the lattice structure causes an anisotropy of the interface tension, and hence nonspherical droplet shapes result, making the treatment nontrivial even within the conventional classical theory of homogeneous nucleation. For temperatures below the roughening transition temperature facetted crystals rather than spherical droplets result. The possibility to find nucleation barriers from a thermodynamic analysis avoiding a cluster identification on the particle level is discussed, as well as the question of curvature corrections to the interfacial tension. For the interpretation of heterogeneous nucleation at planar walls, knowledge of contact angles and line tensions is desirable, and methods to extract these quantities from simulations will be mentioned. Finally, also the problem of nucleation near the stability limit of metastable states and the significance of the spinodal curve will be discussed, in the light of simulations of Ising models with medium range interactions.

  11. Timing of pathogen adaptation to a multicomponent treatment.

    PubMed

    Bourget, Romain; Chaumont, Loïc; Sapoukhina, Natalia

    2013-01-01

    The sustainable use of multicomponent treatments such as combination therapies, combination vaccines/chemicals, and plants carrying multigenic resistance requires an understanding of how their population-wide deployment affects the speed of the pathogen adaptation. Here, we develop a stochastic model describing the emergence of a mutant pathogen and its dynamics in a heterogeneous host population split into various types by the management strategy. Based on a multi-type Markov birth and death process, the model can be used to provide a basic understanding of how the life-cycle parameters of the pathogen population, and the controllable parameters of a management strategy affect the speed at which a pathogen adapts to a multicomponent treatment. Our results reveal the importance of coupling stochastic mutation and migration processes, and illustrate how their stochasticity can alter our view of the principles of managing pathogen adaptive dynamics at the population level. In particular, we identify the growth and migration rates that allow pathogens to adapt to a multicomponent treatment even if it is deployed on only small proportions of the host. In contrast to the accepted view, our model suggests that treatment durability should not systematically be identified with mutation cost. We show also that associating a multicomponent treatment with defeated monocomponent treatments can be more durable than associating it with intermediate treatments including only some of the components. We conclude that the explicit modelling of stochastic processes underlying evolutionary dynamics could help to elucidate the principles of the sustainable use of multicomponent treatments in population-wide management strategies intended to impede the evolution of harmful populations.

  12. Mediating conducting polymer growth within hydrogels by controlling nucleation

    NASA Astrophysics Data System (ADS)

    Patton, A. J.; Green, R. A.; Poole-Warren, L. A.

    2015-01-01

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

  13. 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.

  14. 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

  15. 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.

  16. Influence of Grain Boundary Properties and Orientation on Void Nucleation

    SciTech Connect

    Fensin, Saryu Jindal

    2016-03-01

    For ductile metals, dynamic fracture during shock loading is thought to occur through void nucleation, growth, and then coalescence that leads to material failure. Particularly for high purity metals, it has been observed by numerous investigators that, under incipient spall conditions, voids appear to heterogeneously nucleate at some grain boundaries, but not others. Several factors can affect the void nucleation stress at a grain boundary, such as grain boundary structure, orientation with respect to the loading direction, energy and excess volume, in addition to its interactions with dislocations. In this work, we focus on the influence of loading direction with respect to the grain boundary plane and grain boundary properties such as energy and excess volume on the stress required for void nucleation of a grain boundary, in copper from moleculardynamics simulations. Flyer plate simulations were carried out for four boundary types with different energies and excess volumes. These boundaries were chosen as model systems to represent various boundaries observed in “real” materials. Simulations indicate that there is no direct correlation between the void nucleation stress at a boundary and either its energy and excess volume. This result suggests that average properties of grain boundaries alone are not sufficient indicators of the spall strength of a boundary and perhaps local boundary properties need to be taken into account in order to predict its susceptibility to void nucleation for broad ranges of materials. We also present both experimental and simulation results corresponding to the affect of orientation on void nucleation.

  17. Overview: Nucleation of clathrate hydrates

    NASA Astrophysics Data System (ADS)

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

    2016-12-01

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

  18. Heterogeneous atmospheric chemistry

    NASA Technical Reports Server (NTRS)

    Schryer, D. R.

    1982-01-01

    The present conference on heterogeneous atmospheric chemistry considers such topics concerning clusters, particles and microparticles as common problems in nucleation and growth, chemical kinetics, and catalysis, chemical reactions with aerosols, electron beam studies of natural and anthropogenic microparticles, and structural studies employing molecular beam techniques, as well as such gas-solid interaction topics as photoassisted reactions, catalyzed photolysis, and heterogeneous catalysis. Also discussed are sulfur dioxide absorption, oxidation, and oxidation inhibition in falling drops, sulfur dioxide/water equilibria, the evidence for heterogeneous catalysis in the atmosphere, the importance of heterogeneous processes to tropospheric chemistry, soot-catalyzed atmospheric reactions, and the concentrations and mechanisms of formation of sulfate in the atmospheric boundary layer.

  19. Surface Nanobubbles Nucleate Microdroplets

    NASA Astrophysics Data System (ADS)

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

    2014-04-01

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

  20. Multicomponent Protein Cage Architectures for Photocatalysis

    SciTech Connect

    Gupta, Arunava; Prevelige, Peter E

    2016-01-04

    The primary goal of the project was to develop protein-templated approaches for the synthesis and directed assembly of semiconductor nanomaterials that are efficient for visible light absorption and hydrogen production. In general, visible-light-driven photocatalysis reactions exhibit low quantum efficiency for solar energy conversion primarily because of materials-related issues and limitations, such as the control of the band gap, band structure, photochemical stability, and available reactive surface area of the photocatalyst. Synthesis of multicomponent hierarchical nano-architectures, consisting of semiconductor nanoparticles (NPs) with desired optical properties fabricated to maximize spatial proximity for optimum electron and energy transfer represents an attractive route for addressing the problem. Virus capsids are highly symmetrical, self-assembling protein cage nanoparticles that exist in a range of sizes and symmetries. Selective deposition of inorganic, by design, at specific locations on virus capsids affords precise control over the size, spacing, and assembly of nanomaterials, resulting in uniform and reproducible nano-architectures. We utilized the self-assembling capabilities of the 420 subunit, 60 nm icosahedral, P22 virus capsid to direct the nucleation, growth, and proximity of a range of component materials. Controlled fabrication on the exterior of the temperature stable shell was achieved by genetically encoding specific binding peptides into an externally exposed loop which is displayed on each of the 420 coat protein subunits. Localization of complimentary materials to the interior of the particle was achieved through the use “scaffolding-fusion proteins. The scaffolding domain drives coat protein polymerization resulting in a coat protein shell surrounding a core of approximately 300 scaffolding/fusion molecules. The fusion domain comprises a peptide which specifically binds the semiconductor material of interest.

  1. Efficiency in chemistry: from hydrogen autotransfer to multicomponent catalysis.

    PubMed

    Alonso, Francisco; Foubelo, Francisco; González-Gómez, José C; Martínez, Ricardo; Ramón, Diego J; Riente, Paola; Yus, Miguel

    2010-08-01

    A hydrogen autotransfer reaction has been applied to the α-alkylation of ketones, with primary alcohols as the electrophilic component, either under homogeneous (using a Ru complex as catalyst) or under heterogeneous (using Ni nanoparticles) conditions. This process is both very efficient (concerning atom economy) and ecologically friendly (water as the only by-product generated). On the other hand, three multicomponent reactions, namely, the Strecker reaction (without any catalyst), the aza-Sakurai process (catalyzed by ferrite), and the addition of in situ generated Zn enolates to chiral sulfinylimines (catalyzed by Cu), have proven to be very efficient in the generation of a diversity of polyfunctionalized molecules.

  2. Multi-Component Dark Matter

    SciTech Connect

    Zurek, Kathryn M.

    2008-11-01

    We explore multi-component dark matter models where the dark sector consists of multiple stable states with different mass scales, and dark forces coupling these states further enrich the dynamics. The multi-component nature of the dark matter naturally arises in supersymmetric models, where both R parity and an additional symmetry, such as a Z{sub 2}, is preserved. We focus on a particular model where the heavier component of dark matter carries lepton number and annihilates mostly to leptons. The heavier component, which is essentially a sterile neutrino, naturally explains the PAMELA, ATIC and synchrotron signals, without an excess in antiprotons which typically mars other models of weak scale dark matter. The lighter component, which may have a mass from a GeV to a TeV, may explain the DAMA signal, and may be visible in low threshold runs of CDMS and XENON, which search for light dark matter.

  3. Scale Reliability Evaluation with Heterogeneous Populations

    ERIC Educational Resources Information Center

    Raykov, Tenko; Marcoulides, George A.

    2015-01-01

    A latent variable modeling approach for scale reliability evaluation in heterogeneous populations is discussed. The method can be used for point and interval estimation of reliability of multicomponent measuring instruments in populations representing mixtures of an unknown number of latent classes or subpopulations. The procedure is helpful also…

  4. Multicomponent reactions in nucleoside chemistry

    PubMed Central

    Buchowicz, Włodzimierz

    2014-01-01

    Summary This review covers sixty original publications dealing with the application of multicomponent reactions (MCRs) in the synthesis of novel nucleoside analogs. The reported approaches were employed for modifications of the parent nucleoside core or for de novo construction of a nucleoside scaffold from non-nucleoside substrates. The cited references are grouped according to the usually recognized types of the MCRs. Biochemical properties of the novel nucleoside analogs are also presented (if provided by the authors). PMID:25161730

  5. Nucleation processes occurring during dynamic recrystallization in ice

    NASA Astrophysics Data System (ADS)

    Chauve, T.; Montagnat, M.; Barou, F.; Hidas, K.; Tommasi, A.; Mainprice, D.; Piazolo, S.; Wheeler, J.

    2015-12-01

    The understanding of ice deformation mechanisms is a key point for ice flow modeling and interpretation of climatic signal extracted from ice cores. During deformation inside an ice sheet, recrystallization processes will impact texture and viscosity of ice. Recrystallization processes in ice are very similar to the ones observed in metals and rocks. Along ice cores, Continous (rotation) Dynamic Recrystallization (CDRX) and Discontinuous (migration) Dynamic Recrystallization (DDRX) occur, le later being observed mainly in the deeper part, where temperature and deviatoric stress are higher. The role of nucleation and grain boundary migration associated with DRX on texture development are still badly constrained. In this study, we associated ice creep experiments and high resolution EBSD observations (Electronic Microscopy) to better understand nucleation processes occurring during DRX. Ice is an hexagonal material in which deformation mainly occurs by dislocation glide along the basal plane conferring a strong viscoplastic anisotropy to the single crystal. Hence, during polycrystalline ice deformation the incompatibilty between grains lead to highly heterogeneous strain-field. DRX mechanisms arrise from these strong heterogeneities and induce a new microstructure and texture that relaxe the incompatibilites. The high resolution EBSD observations shown in this study are performed on selected samples of laboratory made polycrystalline columnar ice deformed until 3% macro strain (T=-7°C and σ=0.5 MPa). The analyse show that various kind of nucleation occur under these conditions such as polygonization (tilt bands, kink bands), bulge nucleation by SIGBM (strain Induced Grain Boundary Migration), and nucleation of grains with no obvious relationship with surrounding grains. All these nucleation processes are discussed regarding the associated dislocation fields using the Weigthed Burgers Vector analysis. These analyses highlight the strong heterogeneity of these fields

  6. Laboratory studies of cirrus clouds: the ins and outs of ice nucleation

    NASA Astrophysics Data System (ADS)

    Tolbert, M. A.; Schill, G. P.; Baustian, K. J.

    2012-12-01

    Although cirrus clouds are ever-present in the upper troposphere, the precise mechanisms governing their formation are still uncertain. Recent field observations suggest that ice nucleation in the atmosphere is often more consistent with a heterogeneous nucleation mechanism than a homogeneous one. In the present work, we use optical microscopy coupled with Raman spectroscopy to examine ice nucleation on individual micron-sized particles. Because upper tropospheric particles as well as sub-visible cirrus residues are enhanced in both sulfates and organics, our focus is on complex particles containing these two species. Particles with well-defined structures were generated by nebulization of solutions containing ammonium sulfate and an organic. As the relative humidity was decreased, the aqueous particles underwent liquid-liquid phase separation forming an organic coating over ammonium sulfate. Lowering the relative humidity further resulted in ammonium sulfate efflorescence to a crystalline solid. Ice nucleation was then studied on the layered particles as a function of temperature and relative humidity. During particle formation and ice nucleation, Raman mapping was used to determine the particle structures. Depending on the organic composition and temperature, ice was sometimes observed to nucleate on the ammonium sulfate core within the particle and sometimes nucleated on the organic outer layer. The combination of Raman and optical microscopy allows visualization of the ice nucleation process for complex particles. These studies reveal that the mechanism of heterogeneous ice nucleation depends not just on particle size, but also on particle composition, phase and mixing state.

  7. Nucleation and growth kinetics of biochemicals measured at high supersaturations

    NASA Astrophysics Data System (ADS)

    Mahajan, Amarjit J.; Kirwan, Donald J.

    1994-12-01

    A grid mixer device (characteristic micromixing time < 3 ms) was successfully used to measure both nucleation and growth kinetics of lovastatin in 60 vol% methanol and asparagine monohydrate in 50 vol% 2-propanol at 23°C at high supersaturations but in the absence of mixing limitations. The supersaturation ratios investigated were in the range 1.25-8.8 for the lovastatin system and 1.17-4.1 for the asparagine system. When plotted according to primary nucleation theory, the induction time and nucleation rate measurements for both systems exhibited a homogeneous nucleation region at high supersaturations and a heterogeneous nucleation region at low supersaturations. The values of interfacial free energy extracted from these measurements for lovastatin (1.4-1.6 mJ/m 2) and asparagine (4.5-6.1 mJ/m 2) were an order-of-magnitude lower than those for inorganic salts reflecting the weaker intermolecular bonding in such biochemical solutes. The measured crystal growth rates for both solutes over the entire range of supersaturation could be represented with a power law dependence on chemical potential driving force. The kinetic orders of crystal growth were found to be 6.7 and 2.9 for lovastatin and asparagine, respectively. These unusually high kinetic orders could be represented by a polynuclear surface nucleation growth mechanism. The activation energy for the growth of lovastatin was measured as 280 kJ/mol.

  8. 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

  9. 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.

  10. 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.)

  11. Dynamic decoupling and local atomic order of a model multicomponent metallic glass-former.

    PubMed

    Kim, Jeongmin; Sung, Bong June

    2015-06-17

    The dynamics of multicomponent metallic alloys is spatially heterogeneous near glass transition. The diffusion coefficient of one component of the metallic alloys may also decouple from those of other components, i.e., the diffusion coefficient of each component depends differently on the viscosity of metallic alloys. In this work we investigate the dynamic heterogeneity and decoupling of a model system for multicomponent Pd43Cu27Ni10P20 melts by using a hard sphere model that considers the size disparity of alloys but does not take chemical effects into account. We also study how such dynamic behaviors would relate to the local atomic structure of metallic alloys. We find, from molecular dynamics simulations, that the smallest component P of multicomponent Pd43Cu27Ni10P20 melts becomes dynamically heterogeneous at a translational relaxation time scale and that the largest major component Pd forms a slow subsystem, which has been considered mainly responsible for the stabilization of amorphous state of alloys. The heterogeneous dynamics of P atoms accounts for the breakdown of Stokes-Einstein relation and also leads to the dynamic decoupling of P and Pd atoms. The dynamically heterogeneous P atoms decrease the lifetime of the local short-range atomic orders of both icosahedral and close-packed structures by orders of magnitude.

  12. 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

  13. Phase nucleation in curved space

    NASA Astrophysics Data System (ADS)

    Gómez, Leopoldo; García, Nicolás; Vitelli, Vincenzo; Lorenzana, José; Daniel, Vega

    Nucleation and growth is the dominant relaxation mechanism driving first-order phase transitions. In two-dimensional flat systems, nucleation has been applied to a wide range of problems in physics, chemistry and biology. Here we study nucleation and growth of two-dimensional phases lying on curved surfaces and show that curvature modifies both critical sizes of nuclei and paths towards the equilibrium phase. In curved space, nucleation and growth becomes inherently inhomogeneous and critical nuclei form faster on regions of positive Gaussian curvature. Substrates of varying shape display complex energy landscapes with several geometry-induced local minima, where initially propagating nuclei become stabilized and trapped by the underlying curvature (Gómez, L. R. et al. Phase nucleation in curved space. Nat. Commun. 6:6856 doi: 10.1038/ncomms7856 (2015).).

  14. 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.

  15. Simulation of Regional-scale Nucleation Events and Prediction of Aerosol Number Concentration in a Regional Air Quality Model

    NASA Astrophysics Data System (ADS)

    Jung, J.; Adams, P.; Pandis, S.

    2006-12-01

    Nanoparticles can perturb Earth's climate by growing to cloud condensation nuclei sizes and also may be harmful to human health. Accurate simulation of the nucleation, growth, and removal of multicomponent nanoparticles demands enormous computational resources. Most regional-scale three-dimensional chemical transport models do not include nanoparticles and do not conserve number concentrations. A major challenge associated with the simulation of nucleation events is the uncertainty regarding the controlling nucleation mechanism under typical atmospheric conditions. Previous work indicates that nucleation events in the Pittsburgh area are well predicted using ternary (H2O-H2SO4-NH3) nucleation theory, which was successful in predicting on which days nucleation events occurred during summer and winter, as well as the beginning and end of the events. To predict the composition and growth of nanoparticles, we have developed a computationally efficient new approach based on the Two-Moment Aerosol Sectional (TOMAS) microphysics module. This model simulates inorganic and organic components of the nanoparticles describing both the number and the mass distribution of the particulate matter from approximately 1 nm to 10 micrometers. The model explains why nanoparticles were observed to be acidic during nucleation events that appear to involve ammonia. The simulation suggests that nanoparticles produced by ternary nucleation can be acidic due to depletion of ammonia vapor during the growth of the particles out of the nucleation sizes. The low CPU time requirements of the model using TOMAS make it suitable for incorporation in three- dimensional chemical transport models. The nucleation/coagulation/growth model has been added to the PMCAMx regional air quality model and is used for the investigation of nucleation events in the Eastern U.S. We can estimate number budget in the Eastern U.S. and predict frequency/size of nucleation events.

  16. 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.

  17. A Multicomponent Animal Virus Isolated from Mosquitoes.

    PubMed

    Ladner, Jason T; Wiley, Michael R; Beitzel, Brett; Auguste, Albert J; Dupuis, Alan P; Lindquist, Michael E; Sibley, Samuel D; Kota, Krishna P; Fetterer, David; Eastwood, Gillian; Kimmel, David; Prieto, Karla; Guzman, Hilda; Aliota, Matthew T; Reyes, Daniel; Brueggemann, Ernst E; St John, Lena; Hyeroba, David; Lauck, Michael; Friedrich, Thomas C; O'Connor, David H; Gestole, Marie C; Cazares, Lisa H; Popov, Vsevolod L; Castro-Llanos, Fanny; Kochel, Tadeusz J; Kenny, Tara; White, Bailey; Ward, Michael D; Loaiza, Jose R; Goldberg, Tony L; Weaver, Scott C; Kramer, Laura D; Tesh, Robert B; Palacios, Gustavo

    2016-09-14

    RNA viruses exhibit a variety of genome organization strategies, including multicomponent genomes in which each segment is packaged separately. Although multicomponent genomes are common among viruses infecting plants and fungi, their prevalence among those infecting animals remains unclear. We characterize a multicomponent RNA virus isolated from mosquitoes, designated Guaico Culex virus (GCXV). GCXV belongs to a diverse clade of segmented viruses (Jingmenvirus) related to the prototypically unsegmented Flaviviridae. The GCXV genome comprises five segments, each of which appears to be separately packaged. The smallest segment is not required for replication, and its presence is variable in natural infections. We also describe a variant of Jingmen tick virus, another Jingmenvirus, sequenced from a Ugandan red colobus monkey, thus expanding the host range of this segmented and likely multicomponent virus group. Collectively, this study provides evidence for the existence of multicomponent animal viruses and their potential relevance for animal and human health.

  18. Focus Article: Theoretical aspects of vapor/gas nucleation at structured surfaces

    NASA Astrophysics Data System (ADS)

    Meloni, Simone; Giacomello, Alberto; Casciola, Carlo Massimo

    2016-12-01

    Heterogeneous nucleation is the preferential means of formation of a new phase. Gas and vapor nucleation in fluids under confinement or at textured surfaces is central for many phenomena of technological relevance, such as bubble release, cavitation, and biological growth. Understanding and developing quantitative models for nucleation is the key to control how bubbles are formed and to exploit them in technological applications. An example is the in silico design of textured surfaces or particles with tailored nucleation properties. However, despite the fact that gas/vapor nucleation has been investigated for more than one century, many aspects still remain unclear and a quantitative theory is still lacking; this is especially true for heterogeneous systems with nanoscale corrugations, for which experiments are difficult. The objective of this focus article is analyzing the main results of the last 10-20 years in the field, selecting few representative works out of this impressive body of the literature, and highlighting the open theoretical questions. We start by introducing classical theories of nucleation in homogeneous and in simple heterogeneous systems and then discuss their extension to complex heterogeneous cases. Then we describe results from recent theories and computer simulations aimed at overcoming the limitations of the simpler theories by considering explicitly the diffuse nature of the interfaces, atomistic, kinetic, and inertial effects.

  19. Ice Nucleation and Droplet Formation by Bare and Coated Soot Particles

    SciTech Connect

    Friedman, Beth J.; Kulkarni, Gourihar R.; Beranek, Josef; Zelenyuk, Alla; Thornton, Joel A.; Cziczo, Daniel J.

    2011-09-13

    We have studied ice formation at temperatures relevant to homogeneous and heterogeneous ice nucleation, as well as droplet activation and hygroscopicity, of soot particles of variable size and composition. Coatings of adipic, malic, and oleic acid were applied to span an atmospherically relevant range of solubility, and both uncoated and oleic acid coated soot particles were exposed to ozone to simulate atmospheric oxidation. The results are interpreted in terms of onset ice nucleation, with a comparison to a mineral dust particle that acts as an efficient ice nucleus, and particle hygroscopicity. At 253K and 243K, we found no evidence of heterogeneous ice nucleation occurring above the level of detection for our experimental conditions. Above water saturation, only droplet formation was observed. At 233K, we observe the occurrence of homogeneous ice nucleation for all particles studied. Coatings also did not significantly alter the ice nucleation behavior of soot particles, but aided in the uptake of water. Hygroscopicity studies confirmed that pure soot particles were hydrophobic, and coated soot particles activated as droplets at high water supersaturations. A small amount of heterogeneous ice nucleation either below the detection limit of our instrument or concurrent with droplet formation and/or homogeneous freezing cannot be precluded, but we are able to set limits for its frequency. We conclude that both uncoated and coated soot particles representative of those generated in our studies are unlikely to significantly contribute to the global budget of heterogeneous ice nuclei at temperatures between 233K and 253K.

  20. Photosensitivity phenomena in multicomponent glasses

    NASA Astrophysics Data System (ADS)

    Czachor, K.; Jedrzejewski, K.; Stępień, R.

    2005-09-01

    Low cost, high bandwidth, narrowband and multifunctionality are main targets for new optical devices development. Planar optics is probably the best solution for future telecom long distance and access transmission networks but also for metrology sensing devices. Many different materials can be used for this purpose like PECVD silica, multicomponent glasses or even polymers. Bragg grating inscription in such material is another advantage to achieve narrowband spectral characteristic of device, which is essential in modern systems. The main purpose of presented work was the development in technology and measurement techniques of channels formed on the surface of the glass. Planar couplers and structures that are more complicated can also be made in the same technology in the future. Special multicomponent glasses SiO2-GeO2-B2O3-Na2O-SnO2 with up to 6 %mol of Sn were synthetized and thin rectangular polished plates were prepared. The UV 244 nm 100 mW Coherent argon ion frequency doubled laser was used in our experiments. Surface relief structures similar to the compaction-densification/expansion model of photosensitivity were developed on the glass surface. The optical microscope and alpha-step profiler were used for preliminary tests of photoinduced structures on the glass surface. The ability of the writing possibility in function of Sn content and different laser power levels were analyzed.

  1. Heterodimer formation and crystal nucleation of gramicidin D.

    PubMed Central

    Burkhart, B M; Gassman, R M; Langs, D A; Pangborn, W A; Duax, W L

    1998-01-01

    The linear pentadecapeptide antibiotic gramicidin D is a heterogeneous mixture of six components. Precise refinements of three-dimensional structures of naturally occurring gramicidin D in crystals obtained from methanol, ethanol, and n-propanol demonstrate the unexpected presence of stable left-handed antiparallel double-helical heterodimers that vary with the crystallization solvent. The side chains of Trp residues in the three structures exhibit sequence-specific patterns of conformational preference. Tyr substitution for Trp at position 11 appears to favor beta ribbon formation and stabilization of the antiparallel double helix that acts as a template for gramicidin folding and nucleation of different crystal forms. The fact that a minor component in a heterogeneous mixture influences aggregation and crystal nucleation has potential applications to other systems in which anomalous behavior is exhibited by aggregation of apparently homogeneous materials, such as the enigmatic behavior of prion proteins. PMID:9788907

  2. 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.

  3. Bacterial nucleators: actin' on actin

    PubMed Central

    Bugalhão, Joana N.; Mota, Luís Jaime; Franco, Irina S.

    2015-01-01

    The actin cytoskeleton is a key target of numerous microbial pathogens, including protozoa, fungi, bacteria and viruses. In particular, bacterial pathogens produce and deliver virulence effector proteins that hijack actin dynamics to enable bacterial invasion of host cells, allow movement within the host cytosol, facilitate intercellular spread or block phagocytosis. Many of these effector proteins directly or indirectly target the major eukaryotic actin nucleator, the Arp2/3 complex, by either mimicking nucleation promoting factors or activating upstream small GTPases. In contrast, this review is focused on a recently identified class of effector proteins from Gram-negative bacteria that function as direct actin nucleators. These effector proteins mimic functional activities of formins, WH2-nucleators and Ena/VASP assembly promoting factors demonstrating that bacteria have coopted the complete set of eukaryotic actin assembly pathways. Structural and functional analyses of these nucleators have revealed several motifs and/or mechanistic activities that are shared with eukaryotic actin nucleators. However, functional effects of these proteins during infection extend beyond plain actin polymerization leading to interference with other host cell functions such as vesicle trafficking, cell cycle progression and cell death. Therefore, their use as model systems could not only help in the understanding of the mechanistic details of actin polymerization but also provide novel insights into the connection between actin dynamics and other cellular pathways. PMID:26416078

  4. Containerless Liquid to Solid Nucleation Pathways in Two Representative Grades of Commercially Available Zirconium

    NASA Technical Reports Server (NTRS)

    Rulison, A. J.; Rhim, W.-K.; Bayuzick, R.; Hofmeister, W.; Morton, C.

    1997-01-01

    Experimental measurements were conducted to determine the solid metal nucleation pathways of radiatively cooling, molten zirconium spheres of two different commercially available purity grades in a high-vacuum, high-temperature electrostatic levitator. The ensemble distribution of maximum undercooling temperatures was interpreted using Poisson statistics to determine the temperature dependence of the solid metal nucleation rate. For a sample of nominally 99.95% pure zirconium, the results are consistent with heterogeneous solid metal nucleation either on static catalyst particles at least approx. 30 nm diameter or on a surface coating. For a sample of nominally 99% pure zirconium, however, it appears that heterogeneous solid metal nucleation occurred either on a polydispersion of approx. 10 nm (mean diameter) static catalyst particles or on dynamic catalyst particles that precipitated from a solution that became supersaturated as the melt cooled.

  5. Molecular dynamics simulations of ice nucleation by electric fields.

    PubMed

    Yan, J Y; Patey, G N

    2012-07-05

    Molecular dynamics simulations are used to investigate heterogeneous ice nucleation in model systems where an electric field acts on water molecules within 10-20 Å of a surface. Two different water models (the six-site and TIP4P/Ice models) are considered, and in both cases, it is shown that a surface field can serve as a very effective ice nucleation catalyst in supercooled water. Ice with a ferroelectric cubic structure nucleates near the surface, and dipole disordered cubic ice grows outward from the surface layer. We examine the influences of temperature and two important field parameters, the field strength and distance from the surface over which it acts, on the ice nucleation process. For the six-site model, the highest temperature where we observe field-induced ice nucleation is 280 K, and for TIP4P/Ice 270 K (note that the estimated normal freezing points of the six-site and TIP4P/Ice models are ∼289 and ∼270 K, respectively). The minimum electric field strength required to nucleate ice depends a little on how far the field extends from the surface. If it extends 20 Å, then a field strength of 1.5 × 10(9) V/m is effective for both models. If the field extent is 10 Å, then stronger fields are required (2.5 × 10(9) V/m for TIP4P/Ice and 3.5 × 10(9) V/m for the six-site model). Our results demonstrate that fields of realistic strength, that act only over a narrow surface region, can effectively nucleate ice at temperatures not far below the freezing point. This further supports the possibility that local electric fields can be a significant factor influencing heterogeneous ice nucleation in physical situations. We would expect this to be especially relevant for ice nuclei with very rough surfaces where one would expect local fields of varying strength and direction.

  6. Particle Lithography Enables Fabrication of Multicomponent Nanostructures

    PubMed Central

    Lin, Wei-feng; Swartz, Logan A.; Li, Jie-Ren; Liu, Yang; Liu, Gang-yu

    2014-01-01

    Multicomponent nanostructures with individual geometries have attracted much attention because of their potential to carry out multiple functions synergistically. The current work reports a simple method using particle lithography to fabricate multicomponent nanostructures of metals, proteins, and organosiloxane molecules, each with its own geometry. Particle lithography is well-known for its capability to produce arrays of triangular-shaped nanostructures with novel optical properties. This paper extends the capability of particle lithography by combining a particle template in conjunction with surface chemistry to produce multicomponent nanostructures. The advantages and limitations of this approach will also be addressed. PMID:24707328

  7. Collaborative Research: failure of RockMasses from Nucleation and Growth of Microscopic Defects and Disorder

    SciTech Connect

    Klein, William

    2016-09-12

    Over the 21 years of funding we have pursued several projects related to earthquakes, damage and nucleation. We developed simple models of earthquake faults which we studied to understand Gutenburg-Richter scaling, foreshocks and aftershocks, the effect of spatial structure of the faults and its interaction with underlying self organization and phase transitions. In addition we studied the formation of amorphous solids via the glass transition. We have also studied nucleation with a particular concentration on transitions in systems with a spatial symmetry change. In addition we investigated the nucleation process in models that mimic rock masses. We obtained the structure of the droplet in both homogeneous and heterogeneous nucleation. We also investigated the effect of defects or asperities on the nucleation of failure in simple models of earthquake faults.

  8. Enthalpy Diffusion in Multicomponent Flows

    SciTech Connect

    Cook, A W

    2008-11-12

    The enthalpy diffusion flux in the multicomponent energy equation is a well known yet frequently neglected term. It accounts for energy changes, associated with compositional changes, resulting from species diffusion. Enthalpy diffusion is important in flows where significant mixing occurs between species of dissimilar molecular weight. The term plays a critical role in preventing local violations of the entropy condition. In simulations of nonpremixed combustion, omission of the enthalpy flux can lead to anomalous temperature gradients, which may cause mixing regions to exceed ignition conditions. The term can also play a role in generating acoustic noise in turbulent mixing layers. Euler solvers that rely on numerical diffusion to mix fluids cannot accurately predict the temperature in mixed regions. On the other hand, Navier-Stokes solvers that incorporate enthalpy diffusion can provide much more accurate results.

  9. Multi-component assembly casting

    DOEpatents

    James, Allister W.

    2015-10-13

    Multi-component vane segment and method for forming the same. Assembly includes: positioning a pre-formed airfoil component (12) and a preformed shroud heat resistant material (18) in a mold, wherein the airfoil component (12) and the shroud heat resistant material (18) each comprises an interlocking feature (24); preheating the mold; introducing molten structural material (46) into the mold; and solidifying the molten structural material such that it interlocks the pre-formed airfoil component (12) with respect to the preformed shroud heat resistant material (18) and is effective to provide structural support for the shroud heat resistant material (18). Surfaces between the airfoil component (12) and the structural material (46), between the airfoil component (12) and the shroud heat resistant material (18), and between the shroud heat resistant material (18) and the structural material (46) are free of metallurgical bonds.

  10. Uphill diffusion in multicomponent mixtures.

    PubMed

    Krishna, Rajamani

    2015-05-21

    Molecular diffusion is an omnipresent phenomena that is important in a wide variety of contexts in chemical, physical, and biological processes. In the majority of cases, the diffusion process can be adequately described by Fick's law that postulates a linear relationship between the flux of any species and its own concentration gradient. Most commonly, a component diffuses down the concentration gradient. The major objective of this review is to highlight a very wide variety of situations that cause the uphill transport of one constituent in the mixture. Uphill diffusion may occur in multicomponent mixtures in which the diffusion flux of any species is strongly coupled to that of its partner species. Such coupling effects often arise from strong thermodynamic non-idealities. For a quantitative description we need to use chemical potential gradients as driving forces. The transport of ionic species in aqueous solutions is coupled with its partner ions because of the electro-neutrality constraints; such constraints may accelerate or decelerate a specific ion. When uphill diffusion occurs, we observe transient overshoots during equilibration; the equilibration process follows serpentine trajectories in composition space. For mixtures of liquids, alloys, ceramics and glasses the serpentine trajectories could cause entry into meta-stable composition zones; such entry could result in phenomena such as spinodal decomposition, spontaneous emulsification, and the Ouzo effect. For distillation of multicomponent mixtures that form azeotropes, uphill diffusion may allow crossing of distillation boundaries that are normally forbidden. For mixture separations with microporous adsorbents, uphill diffusion can cause supra-equilibrium loadings to be achieved during transient uptake within crystals; this allows the possibility of over-riding adsorption equilibrium for achieving difficult separations.

  11. Determining whether metals nucleate homogeneously on graphite: A case study with copper

    SciTech Connect

    Appy, David; Lei, Huaping; Han, Yong; Wang, Cai-Zhuang; Tringides, Michael C; Shao, Dahai; Kwolek, Emma J; Evans, J W; Thiel, P A

    2014-11-01

    We observe that Cu clusters grow on surface terraces of graphite as a result of physical vapor deposition in ultrahigh vacuum. We show that the observation is incompatible with a variety of models incorporating homogeneous nucleation and calculations of atomic-scale energetics. An alternative explanation, ion-mediated heterogeneous nucleation, is proposed and validated, both with theory and experiment. This serves as a case study in identifying when and whether the simple, common observation of metal clusters on carbon-rich surfaces can be interpreted in terms of homogeneous nucleation. We describe a general approach for making system-specific and laboratory-specific predictions.

  12. Determining whether metals nucleate homogeneously on graphite: A case study with copper

    DOE PAGES

    Appy, David; Lei, Huaping; Han, Yong; ...

    2014-11-05

    In this study, we observe that Cu clusters grow on surface terraces of graphite as a result of physical vapor deposition in ultrahigh vacuum. We show that the observation is incompatible with a variety of models incorporating homogeneous nucleation and calculations of atomic-scale energetics. An alternative explanation, ion-mediated heterogeneous nucleation, is proposed and validated, both with theory and experiment. This serves as a case study in identifying when and whether the simple, common observation of metal clusters on carbon-rich surfaces can be interpreted in terms of homogeneous nucleation. We describe a general approach for making system-specific and laboratory-specific predictions.

  13. Investigation of nucleation processes during dynamic recrystallization of ice using cryo-EBSD

    NASA Astrophysics Data System (ADS)

    Chauve, T.; Montagnat, M.; Barou, F.; Hidas, K.; Tommasi, A.; Mainprice, D.

    2017-02-01

    Nucleation mechanisms occurring during dynamic recrystallization play a crucial role in the evolution of microstructures and textures during high temperature deformation. In polycrystalline ice, the strong viscoplastic anisotropy induces high strain heterogeneities between grains which control the recrystallization mechanisms. Here, we study the nucleation mechanisms occurring during creep tests performed on polycrystalline columnar ice at high temperature and stress (T=-5°C;σ=0.5 MPa) by post-mortem analyses of deformation microstructures using cryogenic electron backscatter diffraction. The columnar geometry of the samples enables discrimination of the nuclei from the initial grains. Various nucleation mechanisms are deduced from the analysis of the nuclei relations with the dislocation sub-structures within grains and at grain boundaries. Tilt sub-grain boundaries and kink bands are the main structures responsible for development of polygonization and mosaic sub-structures. Nucleation by bulging at serrated grain boundaries is also an efficient nucleation mechanism near the grain boundaries where strain incompatibilities are high. Observation of nuclei with orientations not related to the `parent' ones suggests the possibility of `spontaneous' nucleation driven by the relaxation of the dislocation-related internal stress field. The complexity of the nucleation mechanisms observed here emphasizes the impact of stress and strain heterogeneities on dynamic recrystallization mechanisms. This article is part of the themed issue 'Microdynamics of ice'.

  14. Investigation of nucleation processes during dynamic recrystallization of ice using cryo-EBSD.

    PubMed

    Chauve, T; Montagnat, M; Barou, F; Hidas, K; Tommasi, A; Mainprice, D

    2017-02-13

    Nucleation mechanisms occurring during dynamic recrystallization play a crucial role in the evolution of microstructures and textures during high temperature deformation. In polycrystalline ice, the strong viscoplastic anisotropy induces high strain heterogeneities between grains which control the recrystallization mechanisms. Here, we study the nucleation mechanisms occurring during creep tests performed on polycrystalline columnar ice at high temperature and stress (T=-5°C;σ=0.5 MPa) by post-mortem analyses of deformation microstructures using cryogenic electron backscatter diffraction. The columnar geometry of the samples enables discrimination of the nuclei from the initial grains. Various nucleation mechanisms are deduced from the analysis of the nuclei relations with the dislocation sub-structures within grains and at grain boundaries. Tilt sub-grain boundaries and kink bands are the main structures responsible for development of polygonization and mosaic sub-structures. Nucleation by bulging at serrated grain boundaries is also an efficient nucleation mechanism near the grain boundaries where strain incompatibilities are high. Observation of nuclei with orientations not related to the 'parent' ones suggests the possibility of 'spontaneous' nucleation driven by the relaxation of the dislocation-related internal stress field. The complexity of the nucleation mechanisms observed here emphasizes the impact of stress and strain heterogeneities on dynamic recrystallization mechanisms.This article is part of the themed issue 'Microdynamics of ice'.

  15. Preferential nucleation during polymorphic transformations

    DOE PAGES

    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 thereforemore » nucleation more probable - with increasing number of special OR’s. As a result, 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.« less

  16. Preferential nucleation during polymorphic transformations

    SciTech Connect

    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. As a result, 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.

  17. Multicomponent fuel vaporization at high pressures.

    SciTech Connect

    Torres, D. J.; O'Rourke, P. J.

    2002-01-01

    We extend our multicomponent fuel model to high pressures using a Peng-Robinson equation of state, and implement the model into KIVA-3V. Phase equilibrium is achieved by equating liquid and vapor fugacities. The latent heat of vaporization and fuel enthalpies are also corrected for at high pressures. Numerical simulations of multicomponent evaporation are performed for single droplets for a diesel fuel surrogate at different pressures.

  18. Laser ultrasonic multi-component imaging

    DOEpatents

    Williams, Thomas K [Federal Way, WA; Telschow, Kenneth [Des Moines, WA

    2011-01-25

    Techniques for ultrasonic determination of the interfacial relationship of multi-component systems are discussed. In implementations, a laser energy source may be used to excite a multi-component system including a first component and a second component at least in partial contact with the first component. Vibrations resulting from the excitation may be detected for correlation with a resonance pattern indicating if discontinuity exists at the interface of the first and second components.

  19. 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

    2013-10-09

    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.

  20. Ice Nucleation and Droplet Formation by Bare and Coated Black Carbon Particles

    SciTech Connect

    Friedman, Beth J.; Kulkarni, Gourihar R.; Beranek, Josef; Zelenyuk, Alla; Thornton, Joel A.; Cziczo, Daniel J.

    2011-10-13

    We have studied the ice formation at heterogeneous and homogeneous temperatures, as well as droplet activation and hygroscopicity of soot particles of variable size and composition. Coatings of adipic, malic, and oleic acid were applied to span a relevant range of solubility, and both uncoated and oleic acid coated soot particles were exposed to ozone to simulate atmospheric oxidation. The results are interpreted in terms of onset ice nucleation with a comparison to a well characterized mineral dust particle that acts as an efficient ice nucleus, as well as particle hygroscopicity. At 253K and 243K, we found no evidence of heterogeneous ice nucleation occurring above the level of detection for our experimental conditions. Above water saturation, droplet formation was observed. At 233K, we observe the occurrence of homogeneous ice nucleation for all particles studied. Coatings also did not significantly alter the ice nucleation behavior of soot particles, but aided in the uptake of water. Hygroscopicity studies confirmed that pure soot particles were hydrophobic, and coated soot particles activated as droplets at high water supersaturations. A small amount of heterogeneous ice nucleation either below the detection limit of our instrument or concurrent with droplet formation and/or homogeneous freezing cannot be precluded, but we are able to set limits for its frequency. We conclude from our studies that both uncoated and coated soot particles are unlikely to contribute to the global budget of heterogeneous ice nuclei at temperatures between 233K and 253K.

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

    NASA Astrophysics Data System (ADS)

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

    2017-01-01

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

  2. Crystal nucleation in lithium borate glass

    NASA Technical Reports Server (NTRS)

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

    1988-01-01

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

  3. Transport-induced shifts in condensate dew-point and composition in multicomponent systems with chemical reaction

    NASA Technical Reports Server (NTRS)

    Rosner, D. E.; Nagarajan, R.

    1985-01-01

    Partial heterogeneous condensation phenomena in multicomponent reacting systems are analyzed taking into consideration the chemical element transport phenomena. It is demonstrated that the dew-point surface temperature in chemically reactive systems is not a purely thermodynamic quantity, but is influenced by the multicomponent diffusion and Soret-mass diffusion phenomena. Several distinct dew-points are shown to exist in such systems and, as a result of transport constraints, the 'sharp' locus between two chemically distinct condensates is systematically moved to a difference mainstream composition.

  4. A computationally efficient description of heterogeneous freezing: A simplified version of the Soccer ball model

    NASA Astrophysics Data System (ADS)

    Niedermeier, Dennis; Ervens, Barbara; Clauss, Tina; Voigtländer, Jens; Wex, Heike; Hartmann, Susan; Stratmann, Frank

    2014-01-01

    In a recent study, the Soccer ball model (SBM) was introduced for modeling and/or parameterizing heterogeneous ice nucleation processes. The model applies classical nucleation theory. It allows for a consistent description of both apparently singular and stochastic ice nucleation behavior, by distributing contact angles over the nucleation sites of a particle population assuming a Gaussian probability density function. The original SBM utilizes the Monte Carlo technique, which hampers its usage in atmospheric models, as fairly time-consuming calculations must be performed to obtain statistically significant results. Thus, we have developed a simplified and computationally more efficient version of the SBM. We successfully used the new SBM to parameterize experimental nucleation data of, e.g., bacterial ice nucleation. Both SBMs give identical results; however, the new model is computationally less expensive as confirmed by cloud parcel simulations. Therefore, it is a suitable tool for describing heterogeneous ice nucleation processes in atmospheric models.

  5. Dynamics of multicomponent lipid membranes

    NASA Astrophysics Data System (ADS)

    Camley, Brian Andrew

    We present theoretical and computational descriptions of the dynamics of multicomponent lipid bilayer membranes. These systems are both model systems for "lipid rafts" in cell membranes and interesting physical examples of quasi-two-dimensional fluids. Our chief tool is a continuum simulation that uses a phase field to track the composition of the membrane, and solves the hydrodynamic equations exactly using the appropriate Green's function (Oseen tensor) for the membrane. We apply this simulation to describe the diffusion of domains in phase-separated membranes, the dynamics of domain flickering, and the process of phase separation in lipid membranes. We then derive an analytical theory to describe domain flickering that is consistent with our simulation results, and use this to analyze experimental measurements of membrane domains. Through this method, we measure the membrane viscosity solely from fluorescence microscopy measurements. We study phase separation in quasi-two-dimensional membranes in depth with both simulations and scaling theory, and classify the different scaling regimes and morphologies, which differ from pure two-dimensional fluids. Our results may explain previous inconsistent measurements of the dynamical scaling exponent for phase separation in membranes. We also extend our theory beyond the simplest model, including the possibility that the membrane will be viscoelastic, as well as considering the inertia of the membrane and the fluid surrounding the membrane.

  6. Diclofenac Sodium Loaded Multicomponent Implant

    NASA Astrophysics Data System (ADS)

    Nikkola, Lila; Viitanen, Petrus; Ashammakhi, Nureddin

    2008-02-01

    Earlier we have reported on developing DS releasing bioabsorbable rods for inhibition of osteolysis [l]. Due to their unsatisfactory drug release profiles we assessed the use of sintering technique of enhancement of drug release in the current study. Melt extruded PLGA 80/20 rods were compounded 8 wt-% DS. Some rods were self reinforced (SR) and some of them were sterilized to get three different components with different drug release profiles. Different rods were sintered together with heat and pressure. Three different specimen groups with different construction were studied. Thermal properties were analyzed using differential scanning calorimetry (DSC). Changes of IV were performed with capillary analysis and drug release measurements with UV-Vis spectrophotometer. Mechanical strength were measured two weeks, when disintegration occurred. Release rate consisted of 1) sharp jump start peak, 2) second smoother peak, and 3) third smooth peak. Released DS concentrations reached local therapeutic levels and maintained at that stage for 24-36 days. All DS was released during 50-70 days. The drug release from multicomponent implant was more stable and commenced earlier than from initial rods. Such properties were favored ones. Initial shear strength was 82 MPa and it decreased to 15 MPa. The mechanical bonding was sufficient although the components disintegrated relatively fast. By sintering different PLGA/DS components with different release rates it is possible to construct a truly controlled release implant for bone fixation with anti-inflammatory properties.

  7. Multicomponent Therapeutics of Berberine Alkaloids

    PubMed Central

    Luo, Jiaoyang; Yan, Dan; Yang, Meihua; Dong, Xiaoping; Xiao, Xiaohe

    2013-01-01

    Although berberine alkaloids (BAs) are reported to be with broad-spectrum antibacterial and antiviral activities, the interactions among BAs have not been elucidated. In the present study, methicillin-resistant Staphylococcus aureus (MRSA) was chosen as a model organism, and modified broth microdilution was applied for the determination of the fluorescence absorption values to calculate the anti-MRSA activity of BAs. We have initiated four steps to seek the optimal combination of BAs that are (1) determining the anti-MRSA activity of single BA, (2) investigating the two-component combination to clarify the interactions among BAs by checkerboard assay, (3) investigating the multicomponent combination to determine the optimal ratio by quadratic rotation-orthogonal combination design, and (4) in vivo and in vitro validation of the optimal combination. The results showed that the interactions among BAs are related to their concentrations. The synergetic combinations included “berberine and epiberberine,” “jatrorrhizine and palmatine” and “jatrorrhizine and coptisine”; the antagonistic combinations included “coptisine and epiberberine”. The optimal combination was berberine : coptisine : jatrorrhizine : palmatine : epiberberine = 0.702 : 0.863 : 1 : 0.491 : 0.526, and the potency of the optimal combination on cyclophosphamide-immunocompromised mouse model was better than the natural combinations of herbs containing BAs. PMID:23634170

  8. 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.

  9. 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

  10. New Findings on Ice Nucleation in Mid-latitude Cirrus

    NASA Astrophysics Data System (ADS)

    Mishra, S.; Mitchell, D. L.; Lawson, P.; Baker, B. A.

    2011-12-01

    Recent GCM simulations (CESM1) show a global aerosol indirect effect of -1.39 W m-2 with -2.02 W m-2 from shortwave and +0.63 W m-2 from longwave cloud forcing, the longwave being due to homogeneous nucleation of ice crystals. However, the extent of homogeneous nucleation in ice clouds is poorly understood. This study uses results from a recent field campaign, SPARTICUS (Small PARTicles In CirrUS), to evaluate the impact of homogeneous nucleation on the ice particle size distribution (PSD) shape, as well as ice particle concentration, shape, PSD effective size and fall speed. While earlier measurements were difficult to evaluate for ice nucleation effects due to the problem of ice particle shattering, recent in-situ measurements using the 2 dimensional-stereo (2D-S) probe have greatly reduced this problem resulting in provocative findings for both synoptic and anvil cirrus sampled during SPARTICUS. For mid-latitude synoptic and anvil cirrus around -40°C, these new measurements show that clear changes in the ice PSD and its properties occur regarding (1) PSD shape, (2) total number concentration-to-ice water content ratio (N/IWC), (3) PSD mean size, (4) PSD mean area ratio and (5) the mass-weighted fall velocity (Vm). These changes are consistent with a change in ice nucleation mechanism, with heterogeneous nucleation processes active at temperatures warmer than -40°C and homogeneous freezing nucleation at temperatures colder than -40°C. The change in Vm implies that cirrus colder than -40°C will have longer lifetimes and greater cloud coverage than warmer cirrus clouds, all other relevant factors remaining equal. The increase in N/IWC with colder temperatures (T < -40°C) appears consistent with homogeneous nucleation theory. Figure 1 shows normalized frequency distribution of PSD area ratios for temperatures above and below -40°C. Area ratios (ice particle projected area/area of circle defined by particle maximum dimension) are a measure of ice particle shape

  11. Multicomponent liquid ion exchange with chabazite zeolites

    SciTech Connect

    Robinson, S.M.; Arnold, W.D. Jr.; Byers, C.W.

    1993-10-01

    In spite of the increasing commercial use of zeolites for binary and multicomponent sorption, the understanding of the basic mass-transfer processes associated with multicomponent zeolite ion-exchange systems is quite limited. This study was undertaken to evaluate Na-Ca-Mg-Cs-Sr ion exchange from an aqueous solution using a chabazite zeolite. Mass-transfer coefficients and equilibrium equations were determined from experimental batch-reactor data for single and multicomponent systems. The Langmuir isotherm was used to represent the equilibrium relationship for binary systems, and a modified Dubinin-Polyani model was used for the multicomponent systems. The experimental data indicate that diffusion through the microporous zeolite crystals is the primary diffusional resistance. Macropore diffusion also significantly contributes to the mass-transfer resistance. Various mass-transfer models were compared to the experimental data to determine mass-transfer coefficients. Effective diffusivities were obtained which accurately predicted experimental data using a variety of models. Only the model which accounts for micropore and macropore diffusion occurring in series accurately predicted multicomponent data using single-component diffusivities. Liquid and surface diffusion both contribute to macropore diffusion. Surface and micropore diffusivities were determined to be concentration dependent.

  12. Conscientiousness increases efficiency of multicomponent behavior

    PubMed Central

    Stock, Ann-Kathrin; Beste, Christian

    2015-01-01

    Many everyday situations require the flexible interruption and changing of different actions to achieve a goal. Several strategies can be applied to do so, but those requiring high levels of cognitive control seem to confer an efficiency (speed) advantage in situations requiring multi-component behavior. However, it is elusive in how far personality traits affect performance in such situations. Given that top-down control is an important aspect of personality and furthermore correlates with conscientiousness, N = 163 participants completed the NEO-FFI and performed an experimental (stop-change) paradigm assessing multicomponent behavior. Applying mathematical constraints to the behavioral data, we estimated the processing strategy of each individual. The results show that multicomponent behavior is selectively affected by conscientiousness which explained approximately 19% of the measured inter-individual behavioral variance. Conscientiousness should hence be seen as a major personality dimension modulating multicomponent behavior. Highly conscientious people showed a more effective, step-by-step processing strategy of different actions necessary to achieve a goal. In situations with simultaneous requirements, this strategy equipped them with an efficiency (speed) advantage towards individuals with lower conscientiousness. In sum, the results show that strategies and the efficiency with which people cope with situations requiring multicomponent behavior are strongly influenced by their personality. PMID:26503352

  13. Conscientiousness increases efficiency of multicomponent behavior.

    PubMed

    Stock, Ann-Kathrin; Beste, Christian

    2015-10-27

    Many everyday situations require the flexible interruption and changing of different actions to achieve a goal. Several strategies can be applied to do so, but those requiring high levels of cognitive control seem to confer an efficiency (speed) advantage in situations requiring multi-component behavior. However, it is elusive in how far personality traits affect performance in such situations. Given that top-down control is an important aspect of personality and furthermore correlates with conscientiousness, N = 163 participants completed the NEO-FFI and performed an experimental (stop-change) paradigm assessing multicomponent behavior. Applying mathematical constraints to the behavioral data, we estimated the processing strategy of each individual. The results show that multicomponent behavior is selectively affected by conscientiousness which explained approximately 19% of the measured inter-individual behavioral variance. Conscientiousness should hence be seen as a major personality dimension modulating multicomponent behavior. Highly conscientious people showed a more effective, step-by-step processing strategy of different actions necessary to achieve a goal. In situations with simultaneous requirements, this strategy equipped them with an efficiency (speed) advantage towards individuals with lower conscientiousness. In sum, the results show that strategies and the efficiency with which people cope with situations requiring multicomponent behavior are strongly influenced by their personality.

  14. Nucleation of bubbles on a solidification front—experiment and analysis

    NASA Astrophysics Data System (ADS)

    Wei, P. S.; Huang, C. C.; Lee, K. W.

    2003-06-01

    The heterogeneous nucleation of bubbles on an advancing solidification front during the freezing of water containing a dissolved gas has been experimentally and analytically studied. The formation of bubbles resulting from supersaturation of liquids is commonly encountered in different fields such as heat transfer, manufacturing, and bioscience. In this work, the sizes of nucleating bubbles and the concentration profiles of dissolved oxygen and carbon dioxide gases in the water ahead of the solidification front have been measured. From successful comparisons between the measured and predicted critical radii of nucleating bubbles and distributions of dissolved gas content, the phenomena of heterogeneous nucleation in a binary weak solution during the freezing process are quantitatively confirmed. The results show that an increase in gas content at the solidification front in the liquid decreases the free-energy barrier and critical radii of bubbles that are formed on the solidification front. The sizes of the critical radii decrease and the number of nucleating bubbles increase in the early stage of solidification. As the solidification rates decrease at longer times, the content of the dissolved gas in the liquid on the advancing interface decreases and the critical radii of nucleating bubbles increase.

  15. The double nucleation model for sickle cell haemoglobin polymerization: full integration and comparison with experimental data.

    PubMed

    Medkour, Terkia; Ferrone, Frank; Galactéros, Frédéric; Hannaert, Patrick

    2008-06-01

    Sickle cell haemoglobin (HbS) polymerization reduces erythrocyte deformability, causing deleterous vaso-occlusions. The double-nucleation model states that polymers grow from HbS aggregates, the nuclei, (i) in solution (homogeneous nucleation), (ii) onto existing polymers (heterogeneous nucleation). When linearized at initial HbS concentration, this model predicts early polymerization and its characteristic delay-time (Ferrone et al. J Mol Biol 183(4):591-610, 611-631, 1985). Addressing its relevance for describing complete polymerization, we constructed the full, non-linearized model (Simulink), The MathWorks). Here, we compare the simulated outputs to experimental progress curves (n = 6-8 different [HbS], 3-6 mM range, from Ferrone's group). Within 10% from start, average root mean square (rms) deviation between simulated and experimental curves is 0.04 +/- 0.01 (25 degrees C, n = 8; mean +/- standard error). Conversely, for complete progress curves, averaged rms is 0.48 +/- 0.04. This figure is improved to 0.13 +/- 0.01 by adjusting heterogeneous pathway parameters (p < 0.01): the nucleus stability (sigma(2) micro( cc ): + 40%), and the fraction of polymer surface available for nucleation (phi), from 5e(-7), (3 mM) to 13 (6 mM). Similar results are obtained at 37 degrees C. We conclude that the physico-chemical description of heterogeneous nucleation warrants refinements in order to capture the whole HbS polymerization process.

  16. Interpretation of freezing nucleation experiments: singular and stochastic; sites and surfaces

    NASA Astrophysics Data System (ADS)

    Vali, G.

    2014-06-01

    Publications of recent years dealing with laboratory experiments of immersion freezing reveal uncertainties about the fundamentals of heterogeneous freezing nucleation. While it appears well accepted that there are two major factors that determine the process, namely fluctuations in the size and configuration of incipient embryos of the solid phase and the role of the substrate to aid embryo formation, views have been evolving about the relative importance of these two elements. The importance of specific surface sites is being established in a growing number of experiments and a number of approaches have been proposed to incorporate these results into model descriptions. Many of these models share a common conceptual basis yet diverge in the way random and deterministic factors are combined. The divergence can be traced to uncertainty about the permanence of nucleating sites, to the lack of detailed knowledge about what surface features constitute nucleating sites, and to the consequent need to rely on empirical or parametric formulas to define the population of sites of different effectiveness. Recent experiments and models, consistent with earlier work, demonstrate the existence and primary role of permanent nucleating sites and the continued need for empirically based formulations of heterogeneous freezing. In order to clarify some aspects of the processes controlling immersion freezing, the paper focuses on three identifiably separate but interrelated issues: (i) the combination of singular and stochastic factors, (ii) the role of specific surface sites, and (iii) the modeling of heterogeneous ice nucleation.

  17. Interpretation of freezing nucleation experiments: singular and stochastic; sites and surfaces

    NASA Astrophysics Data System (ADS)

    Vali, G.

    2014-01-01

    Publications of recent years dealing with laboratory experiments of immersion freezing reveal uncertainties about the fundamentals of heterogeneous freezing nucleation. While it appears well accepted that there are two major factors that determine the process, namely fluctuations in the size and configuration of incipient embryos of the solid phase and the role of the substrate to aid embryo formation, views have been evolving about the relative importance of these two elements. The importance of specific surface sites is being established in a growing number of experiments and a number of approaches have been proposed to incorporate these results into model descriptions. Many of these models share a common conceptual basis yet diverge in the way random and deterministic factors are combined. The divergence can be traced to uncertainty about the permanence of nucleating sites, to the lack of detailed knowledge about what surface features constitute nucleating sites, and to the consequent need to rely on empirical or parametric formulas to define the population of sites of different effectiveness. The goal of this paper is to demonstrate that recent experiments and models, consistent with earlier work, point to the existence and primary role of permanent nucleating sites and to the continued need for empirically based formulations of heterogeneous freezing. The paper focuses on three identifiably separate but interrelated issues: (i) the combination of singular and stochastic factors, (ii) the role of specific surface sites, and (iii) the modeling of heterogeneous ice nucleation.

  18. Ice nucleation activity of diesel soot particles at Cirrus relevant conditions: Effects of hydration, secondary organics coating, hydration, soot morphology, and coagulation

    SciTech Connect

    Kulkarni, Gourihar R.; China, Swarup; Liu, Shang; Nandasiri, Manjula I.; Sharma, Noopur; Wilson, Jacqueline M.; Aiken, A. C.; Chand, Duli; Laskin, Alexander; Mazzoleni, Claudio; Pekour, Mikhail S.; Shilling, John E.; Shutthanandan, V.; Zelenyuk, Alla; Zaveri, Rahul A.

    2016-04-16

    The role of atmospheric relevant soot particles that are processed in the atmosphere toward ice nucleation at cirrus cloud condition is poorly understood. In this study, the ice nucleating properties of diesel soot particles subjected to various physical and chemical aging treatments were investigated at temperatures ranging from -40 to -50 °C. We show that bare soot particles nucleate ice in deposition mode, but coating with secondary organics suppresses the heterogeneous ice nucleation potential of soot particles requiring homogeneous freezing threshold conditions. However, the ice nucleation efficiency of soot particles coated with an aqueous organic layer was similar to bare soot particles. Hydration of bare soot particles slightly enhanced the ice nucleation efficiency, and the IN abilities of compact soot particles (roundness = ~ 0.6) were similar to bare lacey soot particles (roundness = ~ 0.4). These results indicate that ice nucleation properties are sensitive to the various aging treatments.

  19. Refreeze experiments with water droplets containing different types of ice nuclei interpreted by classical nucleation theory

    NASA Astrophysics Data System (ADS)

    Kaufmann, Lukas; Marcolli, Claudia; Luo, Beiping; Peter, Thomas

    2017-03-01

    Homogeneous nucleation of ice in supercooled water droplets is a stochastic process. In its classical description, the growth of the ice phase requires the emergence of a critical embryo from random fluctuations of water molecules between the water bulk and ice-like clusters, which is associated with overcoming an energy barrier. For heterogeneous ice nucleation on ice-nucleating surfaces both stochastic and deterministic descriptions are in use. Deterministic (singular) descriptions are often favored because the temperature dependence of ice nucleation on a substrate usually dominates the stochastic time dependence, and the ease of representation facilitates the incorporation in climate models. Conversely, classical nucleation theory (CNT) describes heterogeneous ice nucleation as a stochastic process with a reduced energy barrier for the formation of a critical embryo in the presence of an ice-nucleating surface. The energy reduction is conveniently parameterized in terms of a contact angle α between the ice phase immersed in liquid water and the heterogeneous surface. This study investigates various ice-nucleating agents in immersion mode by subjecting them to repeated freezing cycles to elucidate and discriminate the time and temperature dependences of heterogeneous ice nucleation. Freezing rates determined from such refreeze experiments are presented for Hoggar Mountain dust, birch pollen washing water, Arizona test dust (ATD), and also nonadecanol coatings. For the analysis of the experimental data with CNT, we assumed the same active site to be always responsible for freezing. Three different CNT-based parameterizations were used to describe rate coefficients for heterogeneous ice nucleation as a function of temperature, all leading to very similar results: for Hoggar Mountain dust, ATD, and larger nonadecanol-coated water droplets, the experimentally determined increase in freezing rate with decreasing temperature is too shallow to be described properly by

  20. Functional Display of Ice Nucleation Protein InaZ on the Surface of Bacterial Ghosts.

    PubMed

    Kassmannhuber, Johannes; Rauscher, Mascha; Schöner, Lea; Witte, Angela; Lubitz, Werner

    2017-01-25

    In a concept study the ability to induce heterogeneous ice formation by Bacterial Ghosts (BGs) from Escherichia coli carrying ice nucleation protein InaZ from Pseudomonas syringae in their outer membrane was investigated by a droplet-freezing assay of ultra-pure water. As determined by the median freezing temperature and cumulative ice nucleation spectra it could be demonstrated that both the living recombinant E. coli and their corresponding BGs functionally display InaZ on their surface. Under the production conditions chosen both samples belong to type II ice-nucleation particles inducing ice formation at a temperature range of between -5.6 °C and -6.7 °C, respectively. One advantage for the application of such BGs over their living recombinant mother bacteria is that they are non-living native cell envelopes retaining the biophysical properties of ice nucleation and do no longer represent genetically modified organisms (GMOs).

  1. Identification and quantification of ice nucleation active microorganisms by digital droplet PCR (ddPCR)

    NASA Astrophysics Data System (ADS)

    Linden, Martin; Pöschl, Ulrich; Fröhlich-Nowoisky, Janine

    2015-04-01

    Several bioaerosol types, including bacteria, fungi, pollen and lichen, have been identified as sources of biological ice nucleators (IN) which induce ice formation already at temperatures as high as -10 °C or above. Accordingly, they potentially contribute widely to environmental ice nucleation in the atmosphere and are of great interest in the study of natural heterogenous ice nucleation processes. Ice nucleation active microorganisms have been found and studied among bacteria (Proteobacteria) and fungi (phyla Basidiomycota and Ascomycota). The mechanisms enabling the microorganisms to ice nucleation are subject to ongoing research. While it has been demonstrated that whole cells can act as ice nucleators in the case of bacteria due to the presence of specific membrane proteins, cell-free ice nucleation active particles seem to be responsible for this phenomenon in fungi and lichen. The identification and quantification of these ice nucleation active microorganisms and their IN in atmospheric samples is crucial to understand their contribution to the pool of atmospheric IN. This is not a trivial task since the respective microorganisms are often prevalent in lowest concentrations and a variety of states, be it viable cells, spores or cell debris from dead cells. Molecular biology provides tools to identify and quantify ice nucleation active microorganisms independent of their state by detecting genetic markers specific for the organism of interest. Those methods are not without their drawbacks in terms of sample material concentration required or reliable standardization. Digital Droplet Polymerase Chain Reaction (ddPCR) was chosen for our demands as a more elegant, quick and specific method in the investigation of ice nucleation active microorganisms in atmospheric samples. The advantages of ddPCR lie in the simultaneous detection and quantification of genetic markers and their original copy numbers in a sample. This is facilitated by the fractionation of the

  2. Multi-Component Reactions in Heterocyclic Chemistry

    NASA Astrophysics Data System (ADS)

    Müller, Thomas J. J.; Orru, Romano V. A.; Chebanov, Valentin A.; Sakhno, Yana I.; Saraev, Vyacheslav E.; Muravyova, Elena A.; Andrushchenko, Anastasia Yu.; Desenko, Sergey M.; Akhmetova, V. R.; Khabibullina, G. R.; Rakhimova, E. B.; Vagapov, R. A.; Khairullina, R. R.; Niatshina, Z. T.; Murzakova, N. N.; Maslivets, Andrey N.; Voskressensky, Leonid G.; Danagulyan, Gevorg G.; Murtchyan, Armen D.; Tumanyan, Araksya K.; Banfi, Luca; Basso, Andrea; de Moliner, Fabio; Guanti, Giuseppe; Petricci, Elena; Riva, Renata; Taddei, Maurizio; Naimi-Jamal, M. Reza; Mashkouri, Sara; Sharifi, Ali; Przhevalski, Nikolai M.; Rozhkova, Elena N.; Tokmakov, Gennadii P.; Magedov, Igor V.; Armisheva, M. N.; Rassudihina, N. A.; Vahrin, M. I.; Gein, V. L.; Shaabani, Ahmad; Rezayan, Ali Hossein; Sarvary, Afshin; Heidary, Marjan; Ng, Seik Weng; Beliaev, Nikolai A.; Mokrushin, Vladimir S.; Paramonov, Igor V.; Ilyin, Alexey; Garkushenko, Anna K.; Dushek, Maria A.; Sagitullina, Galina P.; Sagitullin, Reva S.; Kysil, Volodymyr; Khvat, Alexander; Tsirulnikov, Sergey; Tkachenko, Sergey; Ivachtchenko, Alexandre; Gein, Vladimir L.; Panova, Olga S.; Ilyn, Alexey P.; Kravchenko, Dmitri V.; Potapov, Victor V.; Ivachtchenko, Alexandre V.; Vichegjanina, V. N.; Levandovskaya, E. B.; Gein, V. L.; Vahrin, M. I.; Vladimirov, I. N.; Zorina, A. A.; Nosova, N. V.; Gein, V. L.; Fedorova, O. V.; Vahrin, M. I.

    Multi-component and domino reactions are efficient and effective methods in the sustainable and diversity-oriented synthesis of heterocycles. In particular, transition metal-catalyzed multi-component sequences have recently gained considerable interest. Based upon the Sonogashira entry to alkynones, alkenones, and intermediate allenes, we have opened new avenues to the one-pot synthesis of numerous classes of heterocyclic frameworks in an MCR fashion. This methodological approach has now found various applications in one-pot syntheses of functional chromophores, pharmaceutically active compounds, and marine alkaloids and derivatives.

  3. Deposition of thin films of multicomponent materials

    NASA Technical Reports Server (NTRS)

    Thakoor, Sarita (Inventor)

    1993-01-01

    Composite films of multicomponent materials, such as oxides and nitrides, e.g., lead zirconate titanate, are deposited by dc magnetron sputtering, employing a rotating substrate holder, which rotates relative to a plurality of targets, one target for each metal element of the multicomponent material. The sputtering is carried out in a reactive atmosphere. The substrates on which the layers are deposited are at ambient temperature. Following deposition of the composite film, the film is heated to a temperature sufficient to initiate a solid state reaction and form the final product, which is substantially single phase and substantially homogeneous.

  4. Single Particle Laser Mass Spectrometry Applied to Differential Ice Nucleation Experiments at the AIDA Chamber

    SciTech Connect

    Gallavardin, S. J.; Froyd, Karl D.; Lohmann, U.; Moehler, Ottmar; Murphy, Daniel M.; Cziczo, Dan

    2008-08-26

    Experiments conducted at the Aerosol Interactions and Dynamics in the Atmosphere (AIDA) chamber located in Karlsruhe, Germany permit investigation of particle properties that affect the nucleation of ice at temperature and water vapor conditions relevant to cloud microphysics and climate issues. Ice clouds were generated by heterogeneous nucleation of Arizona test dust (ATD), illite, and hematite and homogeneous nucleation of sulfuric acid. Ice crystals formed in the chamber were inertially separated from unactivated, or ‘interstitial’ aerosol particles with a pumped counterflow virtual impactor (PCVI), then evaporated. The ice residue (i.e., the aerosol which initiated ice nucleation plus any material which was scavenged from the gas- and/or particle-phase), was chemically characterized at the single particle level using a laser ionization mass spectrometer. In this manner the species that first nucleated ice could be identified out of a mixed aerosol population in the chamber. Bare mineral dust particles were more effective ice nuclei (IN) than similar particles with a coating. Metallic particles from contamination in the chamber initiated ice nucleation before other species but there were few enough that they did not compromise the experiments. Nitrate, sulfate, and organics were often detected on particles and ice residue, evidently from scavenging of trace gas-phase species in the chamber. Hematite was a more effective ice nucleus than illite. Ice residue was frequently larger than unactivated test aerosol due to the formation of aggregates due to scavenging, condensation of contaminant gases, and the predominance of larger aerosol in nucleation.

  5. Experimental Tests of Nucleation Theory

    NASA Astrophysics Data System (ADS)

    Dea, Jack Yuen

    1982-03-01

    In recent years there has been controversy surrounding experimental nucleation data that did not conform to classical nucleation theory. More recent data, however, suggest good agreement between theory and experiment. At the Desert Research Institute (DRI), it was decided to perform sensitive tests of nucleation in soluble aerosol particles using newly developed instruments and techniques. Very steady aerosol generation was accomplished with a newly developed atomizer; very high monodispersity in the sample aerosol was achieved using two electrical mobility analyzers in series; and, very fine control over the supersaturation was achieved using a newly developed CFD (Continuous Flow Diffusion) cloud chamber built for NASA for use in zero -gravity situations. The results of a series of experiments indicated that the supersaturation needs to be about 15% greater than predicted by theory. However, a mass correction, taking into account the shape of the salt particles produced data that are in excellent agreement with theory. Moreover, the relative hygroscopicity of several soluble substances and the slopes of the Kohler curves obtained agreed very well with theory. The results mean that the hygroscopicity of various substances can be rated using the Kohler curves. Calculations have been done to determine the hygroscopicity of a number of sulfate compounds. The results of these calculations indicate that under restricted conditions (aerosol diameters < 0.1 (mu)m and aerosol particles composed of either one soluble compound or one soluble compound plus an insoluble component), it is possible to distinguish apart most of the sulfate species using either the DFC cloud chamber or an instantaneous version of the CFD cloud chamber. These results point to a possible application of nucleation theory to aerosol species differentiation in the atmosphere.

  6. Kinetics of crystal nucleation and growth in Pd(40)Ni(40)P(20) glass

    NASA Technical Reports Server (NTRS)

    Drehman, A. J.; Greer, A. L.

    1984-01-01

    Samples of Pd(40)Ni(40)P(20) glass, produced by cooling the melt at 1 or 800 K/s, are heated in a differential scanning calorimeter to determine the crystallization kinetics. Optical microscopy shows that eutectic crystallization proceeds both by growth from the surface of the samples and by the growth of spherical regions around preexisting nuclei in the interior. A modified Kissinger (1957) analysis is used to obtain the activation energy for crystal growth (3.49 eV). The steady state homogeneous nucleation frequency at 590 K is about 10 million/cu m per sec. This is estimated to be the maximum nucleation frequency: it is too low to account for the observed population of quenched-in nuclei, which are therefore presumed to be heterogeneous. The major practical obstacle to glass formation in this system is heterogeneous nucleation.

  7. Nucleation precursors in protein crystallization

    PubMed Central

    Vekilov, Peter G.; Vorontsova, Maria A.

    2014-01-01

    Protein crystal nucleation is a central problem in biological crystallography and other areas of science, technology and medicine. Recent studies have demonstrated that protein crystal nuclei form within crucial precursors. Here, methods of detection and characterization of the precursors are reviewed: dynamic light scattering, atomic force microscopy and Brownian microscopy. Data for several proteins provided by these methods have demonstrated that the nucleation precursors are clusters consisting of protein-dense liquid, which are metastable with respect to the host protein solution. The clusters are several hundred nanometres in size, the cluster population occupies from 10−7 to 10−3 of the solution volume, and their properties in solutions supersaturated with respect to crystals are similar to those in homogeneous, i.e. undersaturated, solutions. The clusters exist owing to the conformation flexibility of the protein molecules, leading to exposure of hydrophobic surfaces and enhanced intermolecular binding. These results indicate that protein conformational flexibility might be the mechanism behind the metastable mesoscopic clusters and crystal nucleation. Investigations of the cluster properties are still in their infancy. Results on direct imaging of cluster behaviors and characterization of cluster mechanisms with a variety of proteins will soon lead to major breakthroughs in protein biophysics. PMID:24598910

  8. Upscaling multi-component reactive transport in presence of connected subsurface structures

    NASA Astrophysics Data System (ADS)

    Willmann, M.; Mañé, R.; Tyukhova, A.

    2015-12-01

    Heterogeneity in hydraulic conductivity leads to incomplete mixing. Upscaling using the dispersion tensor in the advection-dispersion equation overestimates local mixing. Modelling multi-component reactive transport leads to an overestimation of reaction rates and overall reactions. Multi-rate mass transfer was shown previously to better represent mixing. But it is still unclear under what conditions this linear model is able to represent the underlying non-linear process. We study explicit multi-component transport in heterogeneous aquifers for the example of calcite-dissolution. We compare different types of heterogeneity from intermediately well connected (multigaussian) fields to very well connected fields. The fundamental difference stems from their connectivity structure. We observe for the well connected field different dominating channels with an almost uniform advective velocity while the multigaussian fields show dominating channels with a varying advective velocity. Then, we compare our results with an effective reactive mass transfer model where the distribution of exchanges rates or the memory function are derived from information of the hydraulic conductivity field only. We see that reactive multi-rate models show a good agreement for the well connected fields where the connected channels are more or less homogeneous and the immobile inclusions are of more or less equal size. We find connectivity important for upscaling reactive transport in highly heterogeneous conductivity fields.

  9. 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.

  10. Ice nucleation properties of agricultural soil dusts

    NASA Astrophysics Data System (ADS)

    Steinke, Isabelle; Funk, Roger; Busse, Jacqueline; Iturri, Antonela; Kirchen, Silke; Leue, Martin; Möhler, Ottmar; Schwartz, Thomas; Sierau, Berko; Toprak, Emre; Ulrich, Andreas; Hoose, Corinna; Leisner, Thomas

    2015-04-01

    Soil dust particles emitted from agricultural areas contain large amounts of organic material such as fungi, bacteria and plant debris. Being carrier for potentially highly ice-active biological particles, agricultural soil dusts are candidates for being very ice-active as well. In this work, we present ice nucleation experiments conducted in the AIDA cloud chamber. We investigated the ice nucleation efficiency of four types of soil dust from different regions of the world. Results are presented for the immersion freezing and the deposition nucleation mode: all soil dusts show higher ice nucleation efficiencies than desert dusts, especially at temperatures above 254 K. For one soil dust sample, the effect of heat treatments was investigated. Heat treatments did not affect the ice nucleation efficiency which presumably excludes primary biological particles as the only source of the increased ice nucleation efficiency. Therefore, organo-mineral complexes or organic compounds may contribute substantially to the high ice nucleation activity of agricultural soil dusts.

  11. Multiphase, multicomponent phase behavior prediction

    NASA Astrophysics Data System (ADS)

    Dadmohammadi, Younas

    Accurate prediction of phase behavior of fluid mixtures in the chemical industry is essential for designing and operating a multitude of processes. Reliable generalized predictions of phase equilibrium properties, such as pressure, temperature, and phase compositions offer an attractive alternative to costly and time consuming experimental measurements. The main purpose of this work was to assess the efficacy of recently generalized activity coefficient models based on binary experimental data to (a) predict binary and ternary vapor-liquid equilibrium systems, and (b) characterize liquid-liquid equilibrium systems. These studies were completed using a diverse binary VLE database consisting of 916 binary and 86 ternary systems involving 140 compounds belonging to 31 chemical classes. Specifically the following tasks were undertaken: First, a comprehensive assessment of the two common approaches (gamma-phi (gamma-ϕ) and phi-phi (ϕ-ϕ)) used for determining the phase behavior of vapor-liquid equilibrium systems is presented. Both the representation and predictive capabilities of these two approaches were examined, as delineated form internal and external consistency tests of 916 binary systems. For the purpose, the universal quasi-chemical (UNIQUAC) model and the Peng-Robinson (PR) equation of state (EOS) were used in this assessment. Second, the efficacy of recently developed generalized UNIQUAC and the nonrandom two-liquid (NRTL) for predicting multicomponent VLE systems were investigated. Third, the abilities of recently modified NRTL model (mNRTL2 and mNRTL1) to characterize liquid-liquid equilibria (LLE) phase conditions and attributes, including phase stability, miscibility, and consolute point coordinates, were assessed. The results of this work indicate that the ϕ-ϕ approach represents the binary VLE systems considered within three times the error of the gamma-ϕ approach. A similar trend was observed for the for the generalized model predictions using

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

    NASA Astrophysics Data System (ADS)

    Agarwal, Pulkit

    consistently simulate the dynamics and charging of particles during afterglow. It was found that dusty plasma afterglow is dominated by different time scales for electron and ion dynamics. Particle size and charge distribution changes significantly during the afterglow. Finally, a simplified chemistry model was included in dusty plasma numerical model to simulate the dynamics of argon-silane dusty plasma. The chemistry model treats silane dissociation and reactions of silicon hydrides containing up to two silicon atoms. The nucleation rate is equated to rate of formation of anions containing two Si atoms, and a heterogeneous reaction model is used to model particle surface growth. Evolution of particle size and concentration is explained and the importance of variable surface growth rate and nucleation rate is discussed.

  13. Ice nucleation and droplet formation by bare and coated soot particles

    NASA Astrophysics Data System (ADS)

    Friedman, Beth; Kulkarni, Gourihar; BeráNek, Josef; Zelenyuk, Alla; Thornton, Joel A.; Cziczo, Daniel J.

    2011-09-01

    We have studied ice formation at temperatures relevant to homogeneous and heterogeneous ice nucleation, as well as droplet activation and hygroscopicity, of soot particles of variable size and composition. Coatings of adipic, malic, and oleic acid were applied in order to span an atmospherically relevant range of solubility, and both uncoated and oleic acid coated soot particles were exposed to ozone in order to simulate atmospheric oxidation. The results are interpreted in terms of onset ice nucleation, with a comparison to a mineral dust particle that acts as an efficient ice nucleus, and particle hygroscopicity. At 253 K and 243 K, we found no evidence of heterogeneous ice nucleation occurring above the level of detection for our experimental conditions. Above water saturation, only droplet formation was observed. At 233 K, we observe the occurrence of homogeneous ice nucleation for all particles studied. Coatings also did not significantly alter the ice nucleation behavior of soot particles but aided in the uptake of water. Hygroscopicity studies confirmed that pure soot particles were hydrophobic, and coated soot particles activated as droplets at high water supersaturations. A small amount of heterogeneous ice nucleation either below the detection limit of our instrument or concurrent with droplet formation and/or homogeneous freezing cannot be precluded, but we are able to set limits for its frequency. We conclude that both uncoated and coated soot particles comparable to those generated in our studies are unlikely to significantly contribute to the global budget of heterogeneous ice nuclei at temperatures between 233 K and 253 K.

  14. Multicomponent Synthesis of α-Branched Amides

    PubMed Central

    DeBenedetto, Mikkel V.; Green, Michael E.; Wan, Shuangyi; Park, Jung-Hyun; Floreancig, Paul E.

    2009-01-01

    α-Branched amides are prepared by multicomponent reactions in which nitriles undergo hydrozirconation to form metalloimines that react with acyl chlorides. The resulting acylimines react with a variety of π-nucleophiles in the presence of Lewis acids to form the desired amides. PMID:19152262

  15. Role of the electric double layer in the ice nucleation of water droplets under an electric field

    NASA Astrophysics Data System (ADS)

    Zhang, Xiang-Xiong; Li, Xin-Hao; Chen, Min

    2016-09-01

    Figuring out the mechanism of ice nucleation on charged aerosols or in thunderstorms is of fundamental importance in atmospheric science. However, findings on whether the electric field promotes or suppresses heterogeneous ice nucleation are conflicting. In this work, we design an apparatus and test the influence of the electric field on ice nucleation by freezing a series of deionized water droplets resting on solid surfaces with an electric field perpendicular to the substrates. Results show that ice nucleation is obviously promoted under the electric field and is independent of the field direction. Theoretic analyses show that the promotion is due to the reduction of Gibbs free energy which can be partially rationalized by the electric field sustained in the electric double layer at the solid-water interface, with strength about two orders higher than that of the external electric field. Moreover, water-droplet deformation under the electric field is not expected to be the cause of the ice-nucleation promotion.

  16. Fast Imaging of Freezing Drops: Investigating Contact Nucleation at the Triple Line

    NASA Astrophysics Data System (ADS)

    Gurganus, C.

    2011-12-01

    Heterogeneous nucleation of cloud droplets is important for understanding cloud microphysical processes, but the relevant roles of the primary nucleation pathways remains an open question. The contact and immersion modes are two of the primary pathways in the troposphere. An interpretation of difference between the contact and immersion modes is based on the energy barrier for nucleation at a three-phase and two-phase interface, respectively. Previous laboratory experiments have noted a preference for nucleation in the contact mode, with freezing temperatures 2-5K warmer than in the immersion mode. However, our recent study [1] shows no preference for nucleation in the contact mode. This surprising null result may indicate the importance of other, non-thermodynamic factors for contact nucleation. We employ high speed imaging of supercooled water drops, to determine nucleation site spatial statistics. Our geometry avoids the "point-like contact" associated with seed particles by providing a simple, symmetric contact line (triple line defined by the substrate-liquid-air interface) for a drop resting on a homogeneous silicon substrate. Furthermore, the imaging configuration localizes nucleation sites in the horizontal plane. Initial tests used low cooling rates to minimize temperature variation within the water drop. The freezing events display nearly perfect spatial uniformity in the immersed (liquid-substrate) region and, thereby, no preference for nucleation at the triple line [1]. Using a related technique, but relying on a rapid cooling rate, Suzuki et al. [2] note preferential nucleation at the triple line, contrasting with our observations and possibly indicating a thermodynamic preference for contact nucleation. Aside from differences in imaging techniques, our experiment was utilized a very slow cooling system, so as to ensure equal opportunity for freezing throughout the water volume. A simple calculation of the rate of thermal diffusion in a rapidly cooled

  17. Bacterial Ice Nucleation in Monodisperse D2O and H2O-in-Oil Emulsions.

    PubMed

    Weng, Lindong; Tessier, Shannon N; Smith, Kyle; Edd, Jon F; Stott, Shannon L; Toner, Mehmet

    2016-09-13

    Ice nucleation is of fundamental significance in many areas, including atmospheric science, food technology, and cryobiology. In this study, we investigated the ice-nucleation characteristics of picoliter-sized drops consisting of different D2O and H2O mixtures with and without the ice-nucleating bacteria Pseudomonas syringae. We also studied the effects of commonly used cryoprotectants such as ethylene glycol, propylene glycol, and trehalose on the nucleation characteristics of D2O and H2O mixtures. The results show that the median freezing temperature of the suspension containing 1 mg/mL of a lyophilized preparation of P. syringae is as high as -4.6 °C for 100% D2O, compared to -8.9 °C for 100% H2O. As the D2O concentration increases every 25% (v/v), the profile of the ice-nucleation kinetics of D2O + H2O mixtures containing 1 mg/mL Snomax shifts by about 1 °C, suggesting an ideal mixing behavior of D2O and H2O. Furthermore, all of the cryoprotectants investigated in this study are found to depress the freezing phenomenon. Both the homogeneous and heterogeneous freezing temperatures of these aqueous solutions depend on the water activity and are independent of the nature of the solute. These findings enrich our fundamental knowledge of D2O-related ice nucleation and suggest that the combination of D2O and ice-nucleating agents could be a potential self-ice-nucleating formulation. The implications of self-nucleation include a higher, precisely controlled ice seeding temperature for slow freezing that would significantly improve the viability of many ice-assisted cryopreservation protocols.

  18. Fundamentals of microcrack nucleation mechanics

    NASA Technical Reports Server (NTRS)

    Fu, L. S.; Sheu, Y. C.; Co, C. M.; Zhong, W. F.; Shen, H. D.

    1985-01-01

    A foundation for ultrasonic evaluation of microcrack nucleation mechanics is identified in order to establish a basis for correlations between plane strain fracture toughness and ultrasonic factors through the interaction of elastic waves with material microstructures. Since microcracking is the origin of (brittle) fracture, it is appropriate to consider the role of stress waves in the dynamics of microcracking. Therefore, the following topics are discussed: (1) microstress distributions with typical microstructural defects located in the stress field; (2) elastic wave scattering from various idealized defects; and (3) dynamic effective-properties of media with randomly distributed inhomogeneities.

  19. Laser control of zeolite nucleation.

    PubMed

    Navarro, Marta; Mayoral, Alvaro; Mateo, Ester; Lahoz, Ruth; de la Fuente, Germán F; Coronas, Joaquín

    2012-02-01

    Precursor solutions for the synthesis of zeolites are irradiated by means of a Nd-YAG laser. These solutions are subsequently submitted to a hydrothermal treatment and the results analyzed by X-ray diffraction and electron microscopy. Laser irradiation promotes the formation of silica nanoparticles that nucleate into zeolite (silicalite-1), following a hydrothermal treatment. The average crystal size (in the 0.6-3.6 μm range) of the zeolite exponentially decreases as a function of laser irradiation time. In addition, a longer irradiation time results in a narrower crystal size distribution.

  20. Crystal nucleation of colloidal hard dumbbells.

    PubMed

    Ni, Ran; Dijkstra, Marjolein

    2011-01-21

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

  1. Effect of CaCO3(S) nucleation modes on algae removal from alkaline water.

    PubMed

    Choi, Jin Yong; Kinney, Kerry A; Katz, Lynn E

    2016-02-29

    The role of calcite heterogeneous nucleation was studied in a particle coagulation treatment process for removing microalgae from water. Batch experiments were conducted with Scenedesmus sp. and Chlorella sp. in the presence and absence of carbonate and in the presence and absence of Mg to delineate the role of CaCO3(S) nucleation on microalgae removal. The results indicate that effective algae coagulation (e.g., up to 81 % algae removal efficiency) can be achieved via heterogeneous nucleation with CaCO3(S); however, supersaturation ratios between 120 and 200 are required to achieve at least 50% algae removal, depending on ion concentrations. Algae removal was attributed to adsorption of Ca(2+) onto the cell surface which provides nucleation sites for CaCO3(S) precipitation. Bridging of calcite particles between the algal cells led to rapid aggregation and formation of larger flocs. However, at higher supersaturation conditions, algae removal was diminished due to the dominance of homogeneous nucleation of CaCO3(S). Removal of algae in the presence of Ca(2+) and Mg(2+) required higher supersaturation values; however, the shift from heteronucleation to homonucleation with increasing supersaturation was still evident. The results suggest that water chemistry, pH, ionic strength, alkalinity and Ca(2+) concentration can be optimized for algae removal via coagulation-sedimentation.

  2. Experiments on Nucleation in Different Flow Regimes

    NASA Technical Reports Server (NTRS)

    Bayuzick, Robert J.; Hofmeister, W. H.; Morton, C. M.; Robinson, M. B.

    1998-01-01

    The vast majority of metallic engineering materials are solidified from the liquid phase. Understanding the solidification process is essential to control microstructure, which in turn, determines the properties of materials. The genesis of solidification is nucleation, where the first stable solid forms from the liquid phase. Nucleation kinetics determine the degree of undercooling and phase selection. As such, it is important to understand nucleation phenomena in order to control solidification or glass formation in metals and alloys.

  3. 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.

  4. Elastic model of a dislocation center for martensite nucleation

    SciTech Connect

    Vereshchagin, V.P.; Kashchenko, M.P.

    1995-01-01

    The possibility of spontaneous nucleation of a crystal of new phase when the original structure is metastable is usually connected with the catalyzing effect of defects playing the role of nucleation centers. In the case of the {gamma}{r_arrow}{alpha} martensite transformation in iron alloys, even individual dislocations can act as such defects, based on analysis of long-range elastic fields of isolated linear dislocations in a linearly elastic anisotropic continuum, the authors established the existence of a correlation between the geometric characteristics of the elastically deformed state in the vicinity of 60-degree and 30-degree dislocations and the structure and morphological characteristics of {alpha}-martensite observed in massive iron alloy samples. These results suggest that the dislocation affects the pathway of the martensite reaction and allows the authors to say that the specific characteristics of heterogeneous nucleation of new phase for the martensite mechanism of the {gamma}{r_arrow}{alpha} transformation involves singling out a single structural rearrangement variant which is suitable from the standpoint of adapation of the transforming lattice to the characteristic features of the elastically deformed state created by the dislocation. The possibilities for such adaption are limited by the crystallography of the transformation and the reactions of the surrounding austenite occurring when regular connections exist with the morphological characteristics of the martensite crystal, and are not necessarily compatible with the individual features of the elastic field of each dislocation. Considering this, the authors can introduce the concept of a dislocation center for nucleation of a martensite crystal about the region of the dislocation where conditions are realized which are favorable for the formation of a nucleus of martensite crystal of a certain shape and orientation, and they can develop an elastic model corresponding to this concept.

  5. Heterogeneous Catalysis.

    ERIC Educational Resources Information Center

    Miranda, R.

    1989-01-01

    Described is a heterogeneous catalysis course which has elements of materials processing embedded in the classical format of catalytic mechanisms and surface chemistry. A course outline and list of examples of recent review papers written by students are provided. (MVL)

  6. Heterogeneous catalysis.

    PubMed

    Schlögl, Robert

    2015-03-09

    A heterogeneous catalyst is a functional material that continually creates active sites with its reactants under reaction conditions. These sites change the rates of chemical reactions of the reactants localized on them without changing the thermodynamic equilibrium between the materials.

  7. Nucleation and evolution of dynamic damage at Cu/Pb interfaces using molecular dynamics

    NASA Astrophysics Data System (ADS)

    Fensin, S. J.; Valone, S. M.; Cerreta, E. K.; Gray, G. T.; Shao, S.

    2017-01-01

    For ductile metals, the process of dynamic fracture occurs through nucleation, growth and coalescence of voids. For high purity single-phase metals, it has been observed by numerous investigators that voids tend to heterogeneously nucleate at grain boundaries and all grain boundaries are not equally susceptible to void nucleation. However, for materials of engineering significance, especially those with second phase particles, it is less clear if the type of bi-metal interface between the two phases will affect void nucleation and growth. To approach this problem in a systematic manner two bi-metal interfaces between Cu and Pb have been investigated: {111} and {100}. Qualitative and quantitative analysis of the collected data from molecular dynamics shock and spall simulations suggests that Pb becomes disordered during shock compression and is the preferred location for void nucleation under tension. Despite the interfaces being aligned with the spall plane (by design), they are not the preferred location for void nucleation irrespective of interface type.

  8. Deposition and immersion-mode nucleation of ice by three distinct samples of volcanic ash

    NASA Astrophysics Data System (ADS)

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

    2015-07-01

    Ice nucleation of volcanic ash controls both ash aggregation and cloud glaciation, which affect atmospheric transport and global climate. Previously, it has been suggested that there is one characteristic ice nucleation efficiency for all volcanic ash, regardless of its composition, when accounting for surface area; however, this claim is derived from data from only two volcanic eruptions. In this work, we have studied 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), Soufrière Hills (andesitic ash, Montserrat), and Taupo (Oruanui eruption, 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. In the present study, we find that all three samples of volcanic ash are excellent depositional ice nuclei, nucleating ice from 225 to 235 K at ice saturation ratios of 1.05 ± 0.01, comparable to the mineral dust proxy kaolinite. Since depositional ice nucleation will be more important at colder temperatures, fine volcanic ash may represent a global source of cold-cloud ice nuclei. For immersion freezing relevant to mixed-phase clouds, however, only the Oruanui ash exhibited appreciable 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.

  9. a Design of Experiment Study of the Nucleation of Chemical Vapor Deposited Diamond Films.

    NASA Astrophysics Data System (ADS)

    Tang, Chi

    1995-01-01

    diamond parameters are identified and correlated with the nucleation. Optimum conditions are determined for nucleating diamond under HFCVD and MACVD. Achieved reliable control of the nucleation density, from 10^6 to 10^9, under HFCVD and MACVD. Optimized deposition condition for generating heterogeneous diamond nuclei was found under biasing substrate technology.

  10. Ice nucleation properties of mineral dust particles: Determination of onset RHi, IN active fraction, nucleation time-lag, and the effect of active sites on contact angles

    NASA Astrophysics Data System (ADS)

    Kulkarni, G.; Dobbie, S.

    2009-05-01

    A newly developed ice nucleation experimental set up was used to investigate the heterogeneous ice nucleation properties of three Saharan and one Spanish dust particle samples. It was observed that the spread in the onset relative humidities with respect to ice (RHi) for Saharan dust particles varied from 104% to 110%, whereas for the Spanish dust from 106% to 110%. The elemental composition analysis shows a prominent Ca feature in the Spanish dust sample which could potentially explain the differences in nucleation threshold. Although the spread in the onset RHi) for the Saharan dust samples were in agreement, the active fractions and nucleation time-lags calculated at various temperature and RHi) conditions were found to differ. This could be due to the subtle variation in the elemental composition of the dust samples, and surface irregularities like steps, cracks, cavities etc. A combination of classical nucleation theory and active site theory is used to understand the importance of these surface irregularities on the nucleability parameter contact angle that is widely used in the ice cloud modeling. These calculations show that the surface irregularities can reduce the contact angle by approximately 10°.

  11. Ice nucleation properties of mineral dust particles: determination of onset RHi, IN active fraction, nucleation time-lag, and the effect of active sites on contact angles

    NASA Astrophysics Data System (ADS)

    Kulkarni, G.; Dobbie, S.

    2010-01-01

    A newly developed ice nucleation experimental set up was used to investigate the heterogeneous ice nucleation properties of three Saharan and one Spanish dust particle samples. It was observed that the spread in the onset relative humidities with respect to ice (RHi) for Saharan dust particles varied from 104% to 110%, whereas for the Spanish dust from 106% to 110%. The elemental composition analysis shows a prominent Ca feature in the Spanish dust sample which could potentially explain the differences in nucleation threshold. Although the spread in the onset RHi for the three Saharan dust samples were in agreement, the active fractions and nucleation time-lags calculated at various temperature and RHi conditions were found to differ. This could be due to the subtle variation in the elemental composition of the dust samples, and surface irregularities like steps, cracks, cavities etc. A combination of classical nucleation theory and active site theory is used to understand the importance of these surface irregularities on the nucleability parameter, contact angle that is widely used in ice cloud modeling. These calculations show that the surface irregularities can reduce the contact angle by approximately 10 degrees.

  12. Ice nucleation properties of mineral dust particles: Determination of onset RHi, IN active fraction, nucleation time-lag, and the effect of active sites on contact angles

    SciTech Connect

    Kulkarni, Gourihar R.; Dobbie, Steven

    2010-01-08

    A newly developed ice nucleation experimental set up was used to investigate the heterogeneous ice nucleation properties of three Saharan and one Spanish dust particle samples. It is observed that the spread in the onset relative humidities with respect to ice (RHi) for Saharan dust particles varies from 104% to 110%, whereas for the Spanish dust from 106% to 110%. The elemental composition analysis shows a prominent Ca feature in the Spanish dust sample which could potentially explain the differences in nucleation threshold. Although spread in the onset RHi for Saharan dust samples were in agreement, their active fractions and nucleation time-lags calculated at various temperature and RHi conditions, for two Saharan dust samples, were not found to be in complete agreement. This could be because of the subtle variation in the elemental composition of the dust samples, and the surface irregularities like steps, cracks, cavities etc. A combination of classical nucleation theory and active site theory is used to understand the importance of these surface irregularities, expressed in terms of active sites, on the nucleability parameter (contact angle) that is widely used in the ice cloud modeling studies. These calculations show that the surface irregularities reduce the contact angle by approximately 10 degrees.

  13. Silver and gold-catalyzed multicomponent reactions

    PubMed Central

    Abbiati, Giorgio

    2014-01-01

    Summary Silver and gold salts and complexes mainly act as soft and carbophilic Lewis acids even if their use as σ-activators has been rarely reported. Recently, transformations involving Au(I)/Au(III)-redox catalytic systems have been reported in the literature. In this review we highlight all these aspects of silver and gold-mediated processes and their application in multicomponent reactions. PMID:24605168

  14. Diffusion Of Mass In Evaporating Multicomponent Drops

    NASA Technical Reports Server (NTRS)

    Bellan, Josette; Harstad, Kenneth G.

    1992-01-01

    Report summarizes study of diffusion of mass and related phenomena occurring in evaporation of dense and dilute clusters of drops of multicomponent liquids intended to represent fuels as oil, kerosene, and gasoline. Cluster represented by simplified mathematical model, including global conservation equations for entire cluster and conditions on boundary between cluster and ambient gas. Differential equations of model integrated numerically. One of series of reports by same authors discussing evaporation and combustion of sprayed liquid fuels.

  15. Particle Characterization and Ice Nucleation Efficiency of Field-Collected Aerosol Particles

    NASA Astrophysics Data System (ADS)

    Wang, B.; Gilles, M. K.; Laskin, A.; Moffet, R.; Nizkorodov, S.; Roedel, T.; Sterckx, L.; Tivanski, A.; Knopf, D. A.

    2011-12-01

    Atmospheric ice formation by heterogeneous nucleation is one of the least understood processes resulting in cirrus and mixed-phase clouds which affect the global radiation budget, the hydrological cycle, and water vapor distribution. In particular, how organic aerosol affect ice nucleation is not well understood. Here we report on heterogeneous ice nucleation from particles collected during the CalNex campaign at the Caltech campus site, Pasadena, on May 19, 2010 at 6am-12pm (A2) and 12pm-6pm (A3) and May 23 at 6am-12pm (B2) and 6pm-12am (B4). The ice nucleation onsets and water uptake were determined as a function of temperature (200-273 K) and relative humidity with respect to ice (RHice). The ice nucleation efficiency was related to the particle chemical composition. Single particle characterization was provided by using computer controlled scanning electron microscopy with energy dispersive analysis of X-rays (CCSEM/EDX) and scanning transmission X-ray microscopy with near edge X-ray absorption fine structure spectroscopy (STXM/NEXAFS). The STXM/NEXAFS analysis indicates that the morning sample (A2) constitutes organic particles and organic particles with soot and inorganic inclusions. The afternoon sample (A3) is dominated by organic particles with a potentially higher degree of oxidation associated with soot. The B2 sample shows a higher number fraction of magnesium-containing particle indicative of a marine source and ~93% of the particles contained sulfur besides oxygen and carbon as derived from CCSEM/EDX analysis. The B4 sample lacks the strong marine influence and shows higher organic content. Above 230 K, we observed water uptake followed by condensation freezing at mean RH of 93-100% and 89-95% for A2 and A3, respectively. This indicates that the aged A3 particles are efficient ice nuclei (IN) for condensation freezing. Below 230 K A2 and A3 induced deposition ice nucleation between 125-155% RHice (at mean values of 134-150% RHice). The B2 and B4

  16. Multicomponent gas sorption Joule-Thomson refrigeration

    NASA Technical Reports Server (NTRS)

    Jones, Jack A. (Inventor); Petrick, S. Walter (Inventor); Bard, Steven (Inventor)

    1991-01-01

    The present invention relates to a cryogenic Joule-Thomson refrigeration capable of pumping multicomponent gases with a single stage sorption compressor system. Alternative methods of pumping a multicomponent gas with a single stage compressor are disclosed. In a first embodiment, the sorbent geometry is such that a void is defined near the output of the sorption compressor. When the sorbent is cooled, the sorbent primarily adsorbs the higher boiling point gas such that the lower boiling point gas passes through the sorbent to occupy the void. When the sorbent is heated, the higher boiling point gas is desorbed at high temperature and pressure and thereafter propels the lower boiling point gas out of the sorption compressor. A mixing chamber is provided to remix the constituent gases prior to expansion of the gas through a Joule-Thomson valve. Other methods of pumping a multicomponent gas are disclosed. For example, where the sorbent is porous and the low boiling point gas does not adsorb very well, the pores of the sorbent will act as a void space for the lower boiling point gas. Alternatively, a mixed sorbent may be used where a first sorbent component physically adsorbs the high boiling point gas and where the second sorbent component chemically absorbs the low boiling point gas.

  17. Binary nucleation at low temperatures

    NASA Technical Reports Server (NTRS)

    Zahoransky, R. A.; Peters, F.

    1985-01-01

    The onset of homogeneous condensation of binary vapors in the supersaturated state is studied in ethanol/n-propanol and water/ethanol via their unsteady expansion in a shock tube at temperatures below 273 K. Ethanol/n-propanol forms a nearly ideal solution, whereas water/ethanol is an example of a strongly nonideal mixture. Vapor mixtures of various compositions are diluted in dry air at small mole fractions and expanded in the driver section from room temperature. The onset of homogeneous condensation is detected optically and the corresponding thermodynamic state is evaluated. The experimental results are compared with the binary nucleation theory, and the particular problems of theoretical evaluation at low temperatures are discussed.

  18. Ice nucleation on hydrophilic silicon

    NASA Astrophysics Data System (ADS)

    Ochshorn, Eli; Cantrell, Will

    2008-04-01

    We have used Fourier transform infrared spectroscopy to study thin water films on a hydrophilic silicon surface in the temperature range from 20to-20°C. Throughout that range, the spectra of the water adjacent to the silicon surface are consistent with that of bulk water near 25°C. Thicker films (>1μm) freeze at -11±1°C. We reconcile the apparent paradox of a thin film of water which is quite liquidlike at a temperature where freezing of thicker films occurs by hypothesizing that the nucleation event in the thicker film is triggered by a critical ice embryo which forms at some small distance from the silicon surface, as opposed to in direct contact with it.

  19. 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.

  20. Nucleation in periodically driven electrochemical systems

    NASA Astrophysics Data System (ADS)

    Smelyanskiy, V. N.; Dykman, M. I.; Rabitz, H.; Vugmeister, B. E.; Bernasek, S. L.; Bocarsly, A. B.

    1999-06-01

    We calculate both the exponent and the prefactor in the nucleation rate of a periodically driven system. Nucleation dynamics is described by the Fokker-Planck equation for the probability distribution of the nuclei over their size. This distribution is found using the concept of the most probable (optimal) nucleation path. The results apply in a broad range of driving force amplitudes, from weak to moderately strong forces where the nucleation rate is changed exponentially strongly, and also in the broad range of the driving frequencies, from low-frequency driving, where the system follows the force adiabatically, to high-frequency nonadiabatic driving. For strong driving forces, the time dependence of the nucleation rate changes from strongly nonsinusoidal to a weak with the increasing frequency of driving. The response of the nucleation rate to the driving force is described in terms of logarithmic susceptibility (LS), which can be obtained from the optimal nucleation path in the absence of the driving. LS is a smooth function of frequency, and therefore even a driving force with comparatively high frequency can change the modulation rate exponentially strongly. LS and the Faraday current are calculated for simple models of electrochemical systems, where the ac driving is produced by modulation of the electrode potential. We also suggest how to find LS from measurements of the average nucleation rate.

  1. Stratospheric Heterogeneous Chemistry and Microphysics: Model Development, Validation and Applications

    NASA Technical Reports Server (NTRS)

    Turco, Richard P.

    1996-01-01

    being systematically evaluated to identify the principal relationships between ozone loss and aerosol state. Under this project, we formulated a detailed quantitative model that predicts the multicomponent composition of sulfate aerosols under stratospheric conditions, including sulfuric, nitric, hydrochloric, hydrofluoric and hydrobromic acids. This work defined for the first time the behavior of liquid ternary-system type-1b PSCS. The model also allows the compositions and reactivities of sulfate aerosols to be calculated over the entire range of environmental conditions encountered in the stratosphere (and has been incorporated into a trajectory/microphysics model-see above). Important conclusions that derived from this work over the last few years include the following: the HNO3 content of liquid-state aerosols dominate PSCs below about 195 K; the freezing of nitric acid ice from sulfate aerosol solutions is likely to occur within a few degrees K of the water vapor frost point; the uptake and reactions of HCl in liquid aerosols is a critical component of PSC heterogeneous chemistry. In a related application of this work, the inefficiency of chlorine injection into the stratosphere during major volcanic eruptions was explained on the basis of nucleation of sulfuric acid aerosols in rising volcanic plumes leading to the formation of supercooled water droplets on these aerosols, which efficiently scavenges HCl via precipitation.

  2. Nucleation pressure threshold in acoustic droplet vaporization

    NASA Astrophysics Data System (ADS)

    Miles, Christopher; Doering, Charles; Kripfgans, Oliver

    2016-11-01

    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 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. This research was supported by the Rackham Merit Fellowship, the University of Michigan Physics department, the University of Michigan's MCubed program, and NSF awards PHY-1205219 and DMS-1515161.

  3. A Course in Transport Phenomena in Multicomponent, Multiphase, Reacting Systems.

    ERIC Educational Resources Information Center

    Carbonell, R. G.; Whitaker, S.

    1978-01-01

    This course concentrates on a rigorous development of the multicomponent transport equations, boundary conditions at phase interfaces, and volume-averaged transport equations for multiphase reacting systems. (BB)

  4. 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

  5. Nucleation and dynamic rupture on weakly stressed faults sustained by thermal pressurization

    NASA Astrophysics Data System (ADS)

    Schmitt, Stuart V.; Segall, Paul; Dunham, Eric M.

    2015-11-01

    Earthquake nucleation requires that the shear stress τ locally reaches a fault's static strength, fσeff, the product of the friction coefficient and effective normal stress. Once rupture initiates, shear heating-induced thermal pressurization can sustain rupture at much lower τ/σeff ratios, a stress condition believed to be the case during most earthquakes. This requires that earthquakes nucleate at heterogeneities. We model nucleation and dynamic rupture on faults in a 2-D elastic medium with rate/state friction and thermal pressurization, subjected to globally low τ but with local stress heterogeneities that permit nucleation. We examine end-member cases of either high-τ or low-σeff heterogeneities. We find that thermal pressurization can sustain slip at τ/σeff values as low as 0.13, compared to static friction of ˜0.7. Background τ (and, to lesser extent, heterogeneity width) controls whether ruptures arrest or are sustained, with extremely low values resulting in arrest. For a small range of background τ, sustained slip is pulse-like. Cessation of slip in a pulse tail can result from either diffusive restrengthening of σeff or a wave-mediated stopping phase that follows the rupture tip. Slightly larger background τ leads to sustained crack-like rupture. Thermal pressurization is stronger at high-τ heterogeneities, resulting in a lower background τ threshold for sustained rupture and potentially larger arresting ruptures. High-stress events also initiate with higher moment rate, although this may be difficult to observe in nature. For arresting ruptures, stress drops and the dependence of fracture energy on mean slip are both consistent with values inferred for small earthquakes.

  6. Re-evaluating the Frankfurt isothermal static diffusion chamber for ice nucleation

    NASA Astrophysics Data System (ADS)

    Schrod, Jann; Danielczok, Anja; Weber, Daniel; Ebert, Martin; Thomson, Erik S.; Bingemer, Heinz G.

    2016-03-01

    Recently significant advances have been made in the collection, detection and characterization of ice nucleating particles (INPs). Ice nuclei are particles that facilitate the heterogeneous formation of ice within the atmospheric aerosol by lowering the free energy barrier to spontaneous nucleation and growth of ice from atmospheric water and/or vapor. The Frankfurt isostatic diffusion chamber (FRankfurt Ice nucleation Deposition freezinG Experiment: FRIDGE) is an INP collection and offline detection system that has become widely deployed and shows additional potential for ambient measurements. Since its initial development FRIDGE has gone through several iterations and improvements. Here we describe improvements that have been made in the collection and analysis techniques. We detail the uncertainties inherent in the measurement method and suggest a systematic method of error analysis for FRIDGE measurements. Thus what is presented herein should serve as a foundation for the dissemination of all current and future measurements using FRIDGE instrumentation.

  7. 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

  8. Investigating ice nucleation in cirrus clouds with an aerosol-enabled Multiscale Modeling Framework

    SciTech Connect

    Zhang, Chengzhu; Wang, Minghuai; Morrison, H.; Somerville, Richard C.; Zhang, Kai; Liu, Xiaohong; Li, J-L F.

    2014-11-06

    In this study, an aerosol-dependent ice nucleation scheme [Liu and Penner, 2005] has been implemented in an aerosol-enabled multi-scale modeling framework (PNNL MMF) to study ice formation in upper troposphere cirrus clouds through both homogeneous and heterogeneous nucleation. The MMF model represents cloud scale processes by embedding a cloud-resolving model (CRM) within each vertical column of a GCM grid. By explicitly linking ice nucleation to aerosol number concentration, CRM-scale temperature, relative humidity and vertical velocity, the new MMF model simulates the persistent high ice supersaturation and low ice number concentration (10 to 100/L) at cirrus temperatures. The low ice number is attributed to the dominance of heterogeneous nucleation in ice formation. The new model simulates the observed shift of the ice supersaturation PDF towards higher values at low temperatures following homogeneous nucleation threshold. The MMF models predict a higher frequency of midlatitude supersaturation in the Southern hemisphere and winter hemisphere, which is consistent with previous satellite and in-situ observations. It is shown that compared to a conventional GCM, the MMF is a more powerful model to emulate parameters that evolve over short time scales such as supersaturation. Sensitivity tests suggest that the simulated global distribution of ice clouds is sensitive to the ice nucleation schemes and the distribution of sulfate and dust aerosols. Simulations are also performed to test empirical parameters related to auto-conversion of ice crystals to snow. Results show that with a value of 250 μm for the critical diameter, Dcs, that distinguishes ice crystals from snow, the model can produce good agreement to the satellite retrieved products in terms of cloud ice water path and ice water content, while the total ice water is not sensitive to the specification of Dcs value.

  9. Investigating ice nucleation in cirrus clouds with an aerosol-enabled Multiscale Modeling Framework

    DOE PAGES

    Zhang, Chengzhu; Wang, Minghuai; Morrison, H.; ...

    2014-11-06

    In this study, an aerosol-dependent ice nucleation scheme [Liu and Penner, 2005] has been implemented in an aerosol-enabled multi-scale modeling framework (PNNL MMF) to study ice formation in upper troposphere cirrus clouds through both homogeneous and heterogeneous nucleation. The MMF model represents cloud scale processes by embedding a cloud-resolving model (CRM) within each vertical column of a GCM grid. By explicitly linking ice nucleation to aerosol number concentration, CRM-scale temperature, relative humidity and vertical velocity, the new MMF model simulates the persistent high ice supersaturation and low ice number concentration (10 to 100/L) at cirrus temperatures. The low ice numbermore » is attributed to the dominance of heterogeneous nucleation in ice formation. The new model simulates the observed shift of the ice supersaturation PDF towards higher values at low temperatures following homogeneous nucleation threshold. The MMF models predict a higher frequency of midlatitude supersaturation in the Southern hemisphere and winter hemisphere, which is consistent with previous satellite and in-situ observations. It is shown that compared to a conventional GCM, the MMF is a more powerful model to emulate parameters that evolve over short time scales such as supersaturation. Sensitivity tests suggest that the simulated global distribution of ice clouds is sensitive to the ice nucleation schemes and the distribution of sulfate and dust aerosols. Simulations are also performed to test empirical parameters related to auto-conversion of ice crystals to snow. Results show that with a value of 250 μm for the critical diameter, Dcs, that distinguishes ice crystals from snow, the model can produce good agreement to the satellite retrieved products in terms of cloud ice water path and ice water content, while the total ice water is not sensitive to the specification of Dcs value.« less

  10. Laboratory studies of immersion and deposition mode ice nucleation of ozone aged mineral dust particles

    NASA Astrophysics Data System (ADS)

    Kanji, Z. A.; Welti, A.; Chou, C.; Stetzer, O.; Lohmann, U.

    2013-04-01

    Ice nucleation in the atmosphere is central to the understanding the microphysical properties of mixed-phase and cirrus clouds. Ambient conditions such as temperature (T) and relative humidity (RH), as well as aerosol properties such as chemical composition and mixing state play an important role in predicting ice formation in the troposphere. Previous field studies have reported the absence of sulphate and organic compounds on mineral dust ice crystal residuals sampled at mountain top stations or aircraft based measurements despite the long range transport mineral dust is subjected to. We present laboratory studies of ice nucleation for immersion and deposition mode on ozone aged mineral dust particles for 233 < T < 263 K that will represent ageing but not internal mixing with in(organic) compounds. Heterogeneous ice nucleation of untreated kaolinite (Ka) and Arizona Test Dust (ATD) particles is compared to corresponding aged particles that are subjected to ozone exposures of 0.4-4.3 ppmv in a stainless steel aerosol tank. The portable ice nucleation counter (PINC) and immersion chamber combined with the Zurich ice nucleation chamber (IMCA - ZINC) are used to conduct deposition and immersion mode measurements respectively. Ice active fractions as well as ice active surface site densities (ns) are reported and observed to increase as a function of temperature. We present first results that demonstrate enhancement of the ice nucleation ability of aged mineral dust particles in both the deposition and immersion mode due to ageing. Additionally, these are also the first results to show a suppression of heterogeneous ice nucleation without the condensation of a coating of (in)organic material. In immersion mode, low exposure Ka particles showed enhanced ice activity requiring a median freezing temperature of 1.5 K warmer than that of untreated Ka whereas high exposure ATD particles showed suppressed ice nucleation requiring a median freezing temperature of 3 K colder

  11. Change of supercooling capability in solutions containing different kinds of ice nucleators by flavonol glycosides from deep supercooling xylem parenchyma cells in trees.

    PubMed

    Kuwabara, Chikako; Kasuga, Jun; Wang, Donghui; Fukushi, Yukiharu; Arakawa, Keita; Koyama, Toshie; Inada, Takaaki; Fujikawa, Seizo

    2011-12-01

    Deep supercooling xylem parenchyma cells (XPCs) in Katsura tree contain flavonol glycosides with high supercooling-facilitating capability in solutions containing the ice nucleation bacterium (INB) Erwinia ananas, which is thought to have an important role in deep supercooling of XPCs. The present study, in order to further clarify the roles of these flavonol glycosides in deep supercooling of XPCs, the effects of these supercooling-facilitating (anti-ice nucleating) flavonol glycosides, kaempferol 3-O-β-D-glucopyranoside (K3Glc), kaempferol 7-O-β-D-glucopyranoside (K7Glc) and quercetin 3-O-β-D-glucopyranoside (Q3Glc), in buffered Milli-Q water (BMQW) containing different kinds of ice nucleators, including INB Xanthomonas campestris, silver iodide and phloroglucinol, were examined by a droplet freezing assay. The results showed that all of the flavonol glycosides promoted supercooling in all solutions containing different kinds of ice nucleators, although the magnitudes of supercooling capability of each flavonol glycoside changed in solutions containing different kinds of ice nucleators. On the other hand, these flavonol glycosides exhibited complicated nucleating reactions in BMQW, which did not contain identified ice nucleators but contained only unidentified airborne impurities. Q3Glc exhibited both supercooling-facilitating and ice nucleating capabilities depending on the concentrations in such water. Both K3Glc and K7Glc exhibited only ice nucleation capability in such water. It was also shown by an emulsion freezing assay in BMQW that K3Glc and Q3Glc had no effect on homogeneous ice nucleation temperature, whereas K7Glc increased ice nucleation temperature. The results indicated that each flavonol glycoside affected ice nucleation by very complicated and varied reactions. More studies are necessary to determine the exact roles of these flavonol glycosides in deep supercooling of XPCs in which unidentified heterogeneous ice nucleators may exist.

  12. LDRD final report: Physical simulation of nonisothermal multiphase multicomponent flow in porous media

    SciTech Connect

    Martinez, M.J.; Hopkins, P.L.; Shadid, J.N.

    1997-07-01

    This document reports on the accomplishments of a laboratory-directed research and development (LDRD) project whose objective was to initiate a research program for developing a fundamental understanding of multiphase multicomponent subsurface transport in heterogeneous porous media and to develop parallel processing computational tools for numerical simulation of such problems. The main achievement of this project was the successful development of a general-purpose, unstructured grid, multiphase thermal simulator for subsurface transport in heterogeneous porous media implemented for use on massively parallel (MP) computers via message-passing and domain decomposition techniques. The numerical platform provides an excellent base for new and continuing project development in areas of current interest to SNL and the DOE complex including, subsurface nuclear waste disposal and cleanup, groundwater availability and contamination studies, fuel-spill transport for accident analysis, and DNAPL transport and remediation.

  13. 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.

  14. Metadynamics simulations of ice nucleation and growth.

    PubMed

    Quigley, D; Rodger, P M

    2008-04-21

    The metadynamics method for accelerating rate events in molecular simulations is applied to the problem of ice freezing. We demonstrate homogeneous nucleation and growth of ice at 180 K in the isothermal-isobaric ensemble without the presence of external fields or surfaces. This result represents the first report of continuous and dynamic ice nucleation in a system of freely evolving density. Simulations are conducted using a variety of periodic simulation domains. In all cases the cubic polymorph ice I(c) is grown. The influence of boundary effects on estimates of the nucleation free energy barrier are discussed in relation to differences between this and earlier work.

  15. 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.

  16. Simulation of paraequilibrium growth in multicomponent systems

    NASA Astrophysics Data System (ADS)

    Ghosh, G.; Olson, G. B.

    2001-03-01

    A methodology to simulate paraequilibrium (PE) growth in multicomponent systems using the DIC-TRA (Diffusion-Controlled Transformation) software is presented. For any given multicomponent system containing substitutional and interstitial elements, the basic approach is to define a hypothetical element Z, whose thermodynamic and mobility parameters are expressed in terms of the weighted average (with respect to site fraction) of the thermodynamic parameters and mobilities of the substitutional alloying elements. This procedure facilitates the calculation of PE phase diagrams and the PE growth simulations directly in the Thermo-Calc and DICTRA software, respectively. The results of two distinct case studies in multicomponent alloys are presented. In the first example, we simulate the isothermal growth of PE cementite in an Fe-C-Co-Cr-Mo-Ni secondary hardening steel during tempering. This is of practical importance in modeling the carbide precipitation kinetics during secondary hardening. In the second example, we have presented the results of PE ferrite growth during continuous cooling from an intercritical temperature in an Fe-Al-C-Mn-Si low-alloy steel. This is of importance to the design of triple-phase steels containing an austenite that has optimum stability, to facilitate stress-induced transformation under dynamic loading. The results of both simulations are in good accord with experimental results. The model calculations do not consider any resistive or dissipative forces, such as the interfacial energy, strain energy, or solute drag, and, as a result, the interface velocities represent an upper limit under the available chemical driving force.

  17. Containerless Liquid to Solid Nucleation Pathways in Two Representative Grades of Commercially Available Zirconium

    NASA Technical Reports Server (NTRS)

    Rulison, Aaron

    1995-01-01

    Experimental measurements were conducted to determine the solid metal nucleation pathways of radiatively cooling, molten zirconium spheres of two different commercially available purity grades in a high-vacuum, high-temperature electrostatic levitator. The ensemble distribution of maximum undercooling temperatures was interpreted using Poisson statistics to determine the temperature dependence of the solid metal nucleation rate. For a sample of nominally 99.95% pure zirconium, the results are consistent with heterogeneous solid metal nucleation either on static catalyst particles at least 30 nm diameter or on a surface coating. For a sample of nominally 99% pure zirconium, however, it appears that heterogeneous solid metal nucleation occurred either on a polydispersion of 10 nm (mean diameter) static catalyst particles or on dynamic catalyst particles which precipitated from a solution which became supersaturated as the melt cooled. A quantitative analysis of the compositions of both samples suggests that the catalysts probably consisted of one or more of the following elements: niobium, molybdenum, hafnium, and oxygen.

  18. General Model for Multicomponent Ablation Thermochemistry

    NASA Technical Reports Server (NTRS)

    Milos, Frank S.; Marschall, Jochen; Rasky, Daniel J. (Technical Monitor)

    1994-01-01

    A previous paper (AIAA 94-2042) presented equations and numerical procedures for modeling the thermochemical ablation and pyrolysis of thermal protection materials which contain multiple surface species. This work describes modifications and enhancements to the Multicomponent Ablation Thermochemistry (MAT) theory and code for application to the general case which includes surface area constraints, rate limited surface reactions, and non-thermochemical mass loss (failure). Detailed results and comparisons with data are presented for the Shuttle Orbiter reinforced carbon-carbon oxidation protection system which contains a mixture of sodium silicate (Na2SiO3), silica (SiO2), silicon carbide (SiC), and carbon (C).

  19. MULTICOMPONENT REACTIONS IN ALKALOID-BASED DRUG DISCOVERY

    PubMed Central

    Magedov, I. V.; Kornienko, A.

    2016-01-01

    Multicomponent reactions are emerging as a powerful tool in alkaloid-based drug discovery. This Highlight describes several recent (all published in 2011) examples of the employment of multicomponent reactions for the synthesis of biologically active alkaloids and their medicinally relevant analogues. PMID:27917001

  20. Anti-ice nucleation activity in xylem extracts from trees that contain deep supercooling xylem parenchyma cells.

    PubMed

    Kasuga, Jun; Mizuno, Kaoru; Arakawa, Keita; Fujikawa, Seizo

    2007-12-01

    Boreal hardwood species, including Japanese white birch (Betula platyphylla Sukat. var. japonica Hara), Japanese chestnut (Castanea crenata Sieb. et Zucc.), katsura tree (Cercidiphyllum japonicum Sieb. et Zucc.), Siebold's beech (Fagus crenata Blume), mulberry (Morus bombycis Koidz.), and Japanese rowan (Sorbus commixta Hedl.), had xylem parenchyma cells (XPCs) that adapt to subfreezing temperatures by deep supercooling. Crude extracts from xylem in all these trees were found to have anti-ice nucleation activity that promoted supercooling capability of water as measured by a droplet freezing assay. The magnitude of increase in supercooling capability of water droplets in the presence of ice-nucleation bacteria, Erwinia ananas, was higher in the ranges from 0.1 to 1.7 degrees C on addition of crude xylem extracts than freezing temperature of water droplets on addition of glucose in the same concentration (100 mosmol/kg). Crude xylem extracts from C. japonicum provided the highest supercooling capability of water droplets. Our additional examination showed that crude xylem extracts from C. japonicum exhibited anti-ice nucleation activity toward water droplets containing a variety of heterogeneous ice nucleators, including ice-nucleation bacteria, not only E. ananas but also Pseudomonas syringae (NBRC3310) or Xanthomonas campestris, silver iodide or airborne impurities. However, crude xylem extracts from C. japonicum did not affect homogeneous ice nucleation temperature as analyzed by emulsified micro-water droplets. The possible role of such anti-ice nucleation activity in crude xylem extracts in deep supercooling of XPCs is discussed.

  1. The SPectrometer for Ice Nuclei (SPIN): An instrument to investigate ice nucleation

    DOE PAGES

    Garimella, Sarvesh; Kristensen, Thomas Bjerring; Ignatius, Karolina; ...

    2016-07-06

    The SPectrometer for Ice Nuclei (SPIN) is a commercially available ice nucleating particle (INP) counter manufactured by Droplet Measurement Technologies in Boulder, CO. The SPIN is a continuous flow diffusion chamber with parallel plate geometry based on the Zurich Ice Nucleation Chamber and the Portable Ice Nucleation Chamber. This study presents a standard description for using the SPIN instrument and also highlights methods to analyze measurements in more advanced ways. It characterizes and describes the behavior of the SPIN chamber, reports data from laboratory measurements, and quantifies uncertainties associated with the measurements. Experiments with ammonium sulfate are used to investigatemore » homogeneous freezing of deliquesced haze droplets and droplet breakthrough. Experiments with kaolinite, NX illite, and silver iodide are used to investigate heterogeneous ice nucleation. SPIN nucleation results are compared to those from the literature. A machine learning approach for analyzing depolarization data from the SPIN optical particle counter is also presented (as an advanced use). Altogether, we report that the SPIN is able to reproduce previous INP counter measurements.« less

  2. The SPectrometer for Ice Nuclei (SPIN): An instrument to investigate ice nucleation

    SciTech Connect

    Garimella, Sarvesh; Kristensen, Thomas Bjerring; Ignatius, Karolina; Welti, Andre; Voigtlander, Jens; Kulkarni, Gourihar R.; Sagan, Frank; Kok, Gregory Lee; Dorsey, James; Nichman, Leonid; Rothenberg, Daniel Alexander; Rosch, Michael; Kirchgäßner, Amelie Catharina Ruth; Ladkin, Russell; Wex, Heike; Wilson, Theodore W.; Ladino, Luis Antonio; Abbatt, Jon P. D.; Stetzer, Olaf; Lohmann, Ulrike; Stratmann, Frank; Cziczo, Daniel James

    2016-07-06

    The SPectrometer for Ice Nuclei (SPIN) is a commercially available ice nucleating particle (INP) counter manufactured by Droplet Measurement Technologies in Boulder, CO. The SPIN is a continuous flow diffusion chamber with parallel plate geometry based on the Zurich Ice Nucleation Chamber and the Portable Ice Nucleation Chamber. This study presents a standard description for using the SPIN instrument and also highlights methods to analyze measurements in more advanced ways. It characterizes and describes the behavior of the SPIN chamber, reports data from laboratory measurements, and quantifies uncertainties associated with the measurements. Experiments with ammonium sulfate are used to investigate homogeneous freezing of deliquesced haze droplets and droplet breakthrough. Experiments with kaolinite, NX illite, and silver iodide are used to investigate heterogeneous ice nucleation. SPIN nucleation results are compared to those from the literature. A machine learning approach for analyzing depolarization data from the SPIN optical particle counter is also presented (as an advanced use). Altogether, we report that the SPIN is able to reproduce previous INP counter measurements.

  3. Multiple pathways of crystal nucleation in an extremely supersaturated aqueous potassium dihydrogen phosphate (KDP) solution droplet

    PubMed Central

    Lee, Sooheyong; Wi, Haeng Sub; Jo, Wonhyuk; Cho, Yong Chan; Lee, Hyun Hwi; Jeong, Se-Young; Kim, Yong-Il; Lee, Geun Woo

    2016-01-01

    Solution studies have proposed that crystal nucleation can take more complex pathways than previously expected in classical nucleation theory, such as formation of prenucleation clusters or densified amorphous/liquid phases. These findings show that it is possible to separate fluctuations in the different order parameters governing crystal nucleation, that is, density and structure. However, a direct observation of the multipathways from aqueous solutions remains a great challenge because heterogeneous nucleation sites, such as container walls, can prevent these paths. Here, we demonstrate the existence of multiple pathways of nucleation in highly supersaturated aqueous KH2PO4 (KDP) solution using the combination of a containerless device (electrostatic levitation), and in situ micro-Raman and synchrotron X-ray scattering. Specifically, we find that, at an unprecedentedly deep level of supersaturation, a high-concentration KDP solution first transforms into a metastable crystal before reaching stability at room temperature. However, a low-concentration solution, with different local structures, directly transforms into the stable crystal phase. These apparent multiple pathways of crystallization depend on the degree of supersaturation. PMID:27791068

  4. The SPectrometer for Ice Nuclei (SPIN): an instrument to investigate ice nucleation

    NASA Astrophysics Data System (ADS)

    Garimella, Sarvesh; Bjerring Kristensen, Thomas; Ignatius, Karolina; Welti, Andre; Voigtländer, Jens; Kulkarni, Gourihar R.; Sagan, Frank; Kok, Gregory Lee; Dorsey, James; Nichman, Leonid; Rothenberg, Daniel Alexander; Rösch, Michael; Kirchgäßner, Amélie Catharina Ruth; Ladkin, Russell; Wex, Heike; Wilson, Theodore W.; Ladino, Luis Antonio; Abbatt, Jon P. D.; Stetzer, Olaf; Lohmann, Ulrike; Stratmann, Frank; Cziczo, Daniel James

    2016-07-01

    The SPectrometer for Ice Nuclei (SPIN) is a commercially available ice nucleating particle (INP) counter manufactured by Droplet Measurement Technologies in Boulder, CO. The SPIN is a continuous flow diffusion chamber with parallel plate geometry based on the Zurich Ice Nucleation Chamber and the Portable Ice Nucleation Chamber. This study presents a standard description for using the SPIN instrument and also highlights methods to analyze measurements in more advanced ways. It characterizes and describes the behavior of the SPIN chamber, reports data from laboratory measurements, and quantifies uncertainties associated with the measurements. Experiments with ammonium sulfate are used to investigate homogeneous freezing of deliquesced haze droplets and droplet breakthrough. Experiments with kaolinite, NX illite, and silver iodide are used to investigate heterogeneous ice nucleation. SPIN nucleation results are compared to those from the literature. A machine learning approach for analyzing depolarization data from the SPIN optical particle counter is also presented (as an advanced use). Overall, we report that the SPIN is able to reproduce previous INP counter measurements.

  5. Depression of the ice-nucleation temperature of rapidly cooled mouse embryos by glycerol and dimethyl sulfoxide.

    PubMed Central

    Rall, W F; Mazur, P; McGrath, J J

    1983-01-01

    The temperature at which ice formation occurs in supercooled cytoplasm is an important element in predicting the likelihood of intracellular freezing of cells cooled by various procedures to subzero temperatures. We have confirmed and extended prior indications that permeating cryoprotective additives decrease the ice nucleation temperature of cells, and have determined some possible mechanisms for the decrease. Our experiments were carried out on eight-cell mouse embryos equilibrated with various concentrations (0-2.0 M) of dimethyl sulfoxide or glycerol and then cooled rapidly. Two methods were used to assess the nucleation temperature. The first, indirect, method was to determine the in vitro survival of the rapidly cooled embryos as a function of temperature. The temperatures over which an abrupt drop in survival occurs are generally diagnostic of the temperature range for intracellular freezing. The second, direct, method was to observe the microscopic appearance during rapid cooling and note the temperature at which nucleation occurred. Both methods showed that the nucleation temperature decreased from - 10 to - 15 degrees C in saline alone to between - 38 degrees and - 44 degrees C in 1.0-2.0 M glycerol and dimethyl sulfoxide. The latter two temperatures are close to the homogeneous nucleation temperatures of the solutions in the embryo cytoplasm, and suggest that embryos equilibrated in these solutions do not contain heterogeneous nucleating agents and are not accessible to any extracellular nucleating agents, such as extracellular ice. The much higher freezing temperatures of cells in saline or in low concentrations of additive indicate that they are being nucleated by heterogeneous agents or, more likely, by extracellular ice. Images FIGURE 5 FIGURE 6 PMID:6824748

  6. Unraveling the "pressure effect" in nucleation.

    PubMed

    Wedekind, Jan; Hyvärinen, Antti-Pekka; Brus, David; Reguera, David

    2008-09-19

    The influence of the pressure of a chemically inert carrier gas on the nucleation rate is one of the biggest puzzles in the research of gas-liquid nucleation. Experiments can show a positive effect, a negative effect, or no effect at all. The same experiment may show both trends for the same substance depending on temperature, or for different substances at the same temperature. We show how this ambiguous effect naturally arises from the competition of two contributions: nonisothermal effects and pressure-volume work. Our model clarifies seemingly contradictory experimental results and quantifies the variation of the nucleation ability of a substance in the presence of an ambient gas. Our findings are corroborated by molecular dynamics simulations and might have important implications since nucleation in experiments, technical applications, and nature practically always occurs in the presence of an ambient gas.

  7. 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.

  8. Mean-field kinetic nucleation theory

    NASA Astrophysics Data System (ADS)

    Kalikmanov, V. I.

    2006-03-01

    A new semiphenomenological model of homogeneous vapor-liquid nucleation is proposed in which the cluster kinetics follows the "kinetic approach to nucleation" and the thermodynamic part is based on the revised Fisher droplet model with the mean-field argument for the cluster configuration integral. The theory is nonperturbative in a cluster size and as such is valid for all clusters down to monomers. It contains two surface tensions: macroscopic (planar) and microscopic. The latter is a temperature dependent quantity related to the vapor compressibility factor at saturation. For Lennard-Jones fluids the microscopic surface tension possesses a universal behavior with the parameters found from the mean-field density functional calculations. The theory is verified against nucleation experiments for argon, nitrogen, water, and mercury, demonstrating very good agreement with experimental data. Classical nucleation theory fails to predict experimental results when a critical cluster becomes small.

  9. Formation of Protein Condensed Phases: Nucleation Mechanisms.

    PubMed

    Vekilov, Peter G

    2012-04-04

    Proteins in solution form a number of condensed phases. Even omitting the amyloid structures formed after partial protein unfolding, these phases include crystals, polymers, and other solid aggregates, as well as dense liquids and gels. Some of these condensed phases underlie pathological conditions, others play a crucial role in the biological function of the respective protein or are an essential part of its laboratory or industrial processing. In this review, we summarize the fundamentals and recent findings on the kinetics of nucleation of dense liquid droplets and crystals. We define the transition from nucleation to spinodal decomposition for these two phase transitions. We review the two-step mechanism of protein crystal nucleation, in which mesoscopic metastable protein clusters serve as precursors to the ordered crystal nuclei. The concepts and mechanisms reviewed here provide powerful tools for control of the nucleation process by varying the solution thermodynamic parameters.

  10. Microstructural Control via Copious Nucleation Manipulated by In Situ Formed Nucleants: Large-Sized and Ductile Metallic Glass Composites.

    PubMed

    Song, Wenli; Wu, Yuan; Wang, Hui; Liu, Xiongjun; Chen, Houwen; Guo, Zhenxi; Lu, Zhaoping

    2016-10-01

    A novel strategy to control the precipitation behavior of the austenitic phase, and to obtain large-sized, transformation-induced, plasticity-reinforced bulk metallic glass matrix composites, with good tensile properties, is proposed. By inducing heterogeneous nucleation of the transformable reinforcement via potent nucleants formed in situ, the characteristics of the austenitic phase are well manipulated.

  11. Rational design of self-assembly pathways for complex multicomponent structures.

    PubMed

    Jacobs, William M; Reinhardt, Aleks; Frenkel, Daan

    2015-05-19

    The field of complex self-assembly is moving toward the design of multiparticle structures consisting of thousands of distinct building blocks. To exploit the potential benefits of structures with such "addressable complexity," we need to understand the factors that optimize the yield and the kinetics of self-assembly. Here we use a simple theoretical method to explain the key features responsible for the unexpected success of DNA-brick experiments, which are currently the only demonstration of reliable self-assembly with such a large number of components. Simulations confirm that our theory accurately predicts the narrow temperature window in which error-free assembly can occur. Even more strikingly, our theory predicts that correct assembly of the complete structure may require a time-dependent experimental protocol. Furthermore, we predict that low coordination numbers result in nonclassical nucleation behavior, which we find to be essential for achieving optimal nucleation kinetics under mild growth conditions. We also show that, rather surprisingly, the use of heterogeneous bond energies improves the nucleation kinetics and in fact appears to be necessary for assembling certain intricate 3D structures. This observation makes it possible to sculpt nucleation pathways by tuning the distribution of interaction strengths. These insights not only suggest how to improve the design of structures based on DNA bricks, but also point the way toward the creation of a much wider class of chemical or colloidal structures with addressable complexity.

  12. Beyond classical nucleation theory of bubble nucleation during explosive volcanic eruptions (Invited)

    NASA Astrophysics Data System (ADS)

    Gonnermann, H. M.; Gardner, J. E.

    2013-12-01

    Magma degassing, a consequence of the pressure-dependent solubilities of magmatic gases, determines how volcanoes erupt. As magma rises toward the surface, ambient pressure decreases and the melt becomes supersaturated in volatiles, first causing bubbles to nucleate and then grow by diffusion of volatiles from the melt. Consequently, bubble nucleation is a rate-limiting process for magma degassing. It is exceedingly sensitive to the surface energy of a nucleating bubble, which thus exerts a fundamental control on eruptive dynamics. The rate at which bubbles nucleate during explosive magma ascent determines the bubble number density (BND). The conventional view that BND is correlated with magma discharge rate, itself a proxy for explosive intensity, is however not universally true. This is perhaps a consequence of our incomplete understanding of the nucleation work, which depends on the surface tension of the interface between a bubble nucleus and surrounding bulk phase, and which is inaccessible to direct experimental determination. Its effective value can, however, be estimated from nucleation experiments. Because relatively small changes in surface tension result in exceedingly large changes in nucleation rate, current estimates of surface tension result in significant uncertainties in predicted nucleation rates across a wide range of conditions. We show, based on combined decompression-nucleation experiments and numerical modeling thereof, that the surface tension between critical bubble nuclei and the surrounding rhyolitic melt depends on the degree of supersaturation and is lower than the macroscopically measurable value. This is consistent with the view that, far from equilibrium, the interface between a nucleus and surrounding metastable bulk phase is diffuse instead of sharp. As a consequence, the increase in nucleation rate with supersaturation is smaller (larger) than would be predicted from classical nucleation theory for supersaturation pressures less

  13. Controlled Nucleation and Growth of Semiconducting Diamond

    DTIC Science & Technology

    1992-12-18

    analytical measurements of film growth have been coupled with novel precursor chemistry to study the effect of precursor chemical structure on the...efficiency of diamond film nucleation and growth. The goal is to optimize source gases and substrate surface preparation methods for both doped and...undoped diamond film nucleation and growth, enabling the use of diamond in field emission, semiconductor, and optoelectronic applications. "Surface

  14. 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.

  15. Nucleation and Growth of Atmospheric Particles

    SciTech Connect

    McMurry, P.; Kuang, C.; Barsanti, K.; Eisele, F.; Friedli, H.; Scheckman, J.; Titcombe, M.; Williams, B.; Zhao, J.; Smith, J.

    2010-03-15

    New particle formation (NPF) in the atmospheric is a two-step process: Nucleation leads to the birth of stable nuclei that subsequently grow to sizes that can be detected and affect the atmosphere’s radiative properties. Our group is studying both of these processes. Our nucleation research is largely supported by NSF and involves measurements of neutral molecular clusters formed by nucleation with a new custom-designed mass spectrometer (the Cluster-CIMS) and measurements of nanoparticle size distributions as small as 1 nm with a new aerosol spectrometer (the DEG SMPS). These measurements are providing new insights into aspects of cluster behavior that affect nucleation rates. The U.S. DOE supports our research on nanoparticle growth rates. This research couples physical and chemical measurements of aerosol properties and behavior. The TDCIMS, which enables real-time measurements of composition for freshly nucleated particles as small as 8 nm and was developed with support from DOE, is the most important tool in this work. Our most important discoveries about processes that affect growth rates are summarized in a recent PNAS article (doi:10.1073/pnas.0912127107). In short, this work has shown that alkylammonium-carboxylate salts, formed, for example, by reactions between amines and carboxylic acids, account for 20–50% of the mass of freshly nucleated particles in locations that include Atlanta, Mexico City, Boulder, and Hyytiälä, while sulfates account for only about 10%. These newly discovered compounds help to explain the high growth rates of freshly nucleated particles that have been observed around the globe and help to explain why nucleation is an important atmospheric process, not just a scientific curiosity. Our poster will provide an overview of this work.

  16. Tuning ice nucleation with counterions on polyelectrolyte brush surfaces

    PubMed Central

    He, Zhiyuan; Xie, Wen Jun; Liu, Zhenqi; Liu, Guangming; Wang, Zuowei; Gao, Yi Qin; Wang, Jianjun

    2016-01-01

    Heterogeneous ice nucleation (HIN) on ionic surfaces is ubiquitous in a wide range of atmospheric aerosols and at biological interfaces. Despite its great importance in cirrus cloud formation and cryopreservation of cells, organs, and tissues, it remains unclear whether the ion-specific effect on ice nucleation exists. Benefiting from the fact that ions at the polyelectrolyte brush (PB)/water interface can be reversibly exchanged, we report the effect of ions on HIN on the PB surface, and we discover that the distinct efficiency of ions in tuning HIN follows the Hofmeister series. Moreover, a large HIN temperature window of up to 7.8°C is demonstrated. By establishing a correlation between the fraction of ice-like water molecules and the kinetics of structural transformation from liquid- to ice-like water molecules at the PB/water interface with different counterions, we show that our molecular dynamics simulation analysis is consistent with the experimental observation of the ion-specific effect on HIN. PMID:27386581

  17. Tuning ice nucleation with counterions on polyelectrolyte brush surfaces.

    PubMed

    He, Zhiyuan; Xie, Wen Jun; Liu, Zhenqi; Liu, Guangming; Wang, Zuowei; Gao, Yi Qin; Wang, Jianjun

    2016-06-01

    Heterogeneous ice nucleation (HIN) on ionic surfaces is ubiquitous in a wide range of atmospheric aerosols and at biological interfaces. Despite its great importance in cirrus cloud formation and cryopreservation of cells, organs, and tissues, it remains unclear whether the ion-specific effect on ice nucleation exists. Benefiting from the fact that ions at the polyelectrolyte brush (PB)/water interface can be reversibly exchanged, we report the effect of ions on HIN on the PB surface, and we discover that the distinct efficiency of ions in tuning HIN follows the Hofmeister series. Moreover, a large HIN temperature window of up to 7.8°C is demonstrated. By establishing a correlation between the fraction of ice-like water molecules and the kinetics of structural transformation from liquid- to ice-like water molecules at the PB/water interface with different counterions, we show that our molecular dynamics simulation analysis is consistent with the experimental observation of the ion-specific effect on HIN.

  18. 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

  19. Lattice Boltzmann algorithm for continuum multicomponent flow

    NASA Astrophysics Data System (ADS)

    Halliday, I.; Hollis, A. P.; Care, C. M.

    2007-08-01

    We present a multicomponent lattice Boltzmann simulation for continuum fluid mechanics, paying particular attention to the component segregation part of the underlying algorithm. In the principal result of this paper, the dynamics of a component index, or phase field, is obtained for a segregation method after U. D’Ortona [Phys. Rev. E 51, 3718 (1995)], due to Latva-Kokko and Rothman [Phys. Rev. E 71 056702 (2005)]. The said dynamics accord with a simulation designed to address multicomponent flow in the continuum approximation and underwrite improved simulation performance in two main ways: (i) by reducing the interfacial microcurrent activity considerably and (ii) by facilitating simulational access to regimes of flow with a low capillary number and drop Reynolds number [I. Halliday, R. Law, C. M. Care, and A. Hollis, Phys. Rev. E 73, 056708 (2006)]. The component segregation method studied, used in conjunction with Lishchuk’s method [S. V. Lishchuk, C. M. Care, and I. Halliday, Phys. Rev. E 67, 036701 (2003)], produces an interface, which is distributed in terms of its component index; however, the hydrodynamic boundary conditions which emerge are shown to support the notion of a sharp, unstructured, continuum interface.

  20. Theory of margination in confined multicomponent suspensions

    NASA Astrophysics Data System (ADS)

    Henriquez Rivera, Rafael; Sinha, Kushal; Graham, Michael

    2015-11-01

    In blood flow, leukocytes and platelets tend to segregate near the vessel walls; this is known as margination. Margination of leukocytes and platelets is important in physiological processes, medical diagnostics and drug delivery. A mechanistic theory is developed to describe flow-induced segregation in confined multicomponent suspensions of deformable particles such as blood. The theory captures the essential features of margination by describing it in terms of two key competing processes in these systems at low Reynolds number: wall-induced migration and hydrodynamic pair collisions. The theory also includes the effect of physical properties of the deformable particles and molecular diffusion. Several regimes of segregation are identified, depending on the value of a ``margination parameter'' M. Moreover, there is a critical value of M below which a sharp ``drainage transition'' occurs: one component is completely depleted from the bulk flow to the vicinity of the walls. Direct hydrodynamic simulations also display this transition in suspensions where the components differ in size or flexibility. The developed mechanistic theory leads to substantial insight into the origins of margination and will help in guiding development of new technologies involving multicomponent suspensions. This work was supported by NSF grant CBET-1436082.

  1. Mechanics of Turbulence of Multicomponent Gases

    NASA Astrophysics Data System (ADS)

    Marov, Mikhail Ya.; Kolesnichenko, Aleksander V.

    2002-02-01

    Turbulence in multicomponent reacting gas mixtures is an important mechanism underlying numerous natural phenomena closely related to the study of our space environment. This book develops a new mathematical approach for modelling multicomponent gas turbulence that adequately describes the combined processes of dynamics and heat and mass transfer when chemical kinetics and turbulent mixing are equally important. The developed models include the evolutionary transfer equations for the single-point second correlation moments of turbulent fluctuations of thermohydrodynamical parameters. The phenomenological approach to the closure problem in hydrodynamic equations of mean motion at the level of the first order moments is based on the thermodynamics of irreversible processes and enables defining relationships in a more general form as compared to those conventionally deduced using the mixing path concept. Based on the developed approach, turbulent exchange factors for a planetary upper atmosphere are evaluated, and a turbulent model of a protoplanetary accretion gas-dust disk involving heat and mass transfer and coagulation is also considered. As compared to previously published books on the problem of turbulence, this book deals, for the first time, with the complicated models of reacting gas mixtures. It is intended for graduate and postgraduate students in the fields of fluid gas dynamics, astrophysics, space physics, planetary sciences, and aeronomy, and especially for those dealing with computer modelling of the processes in such natural media. The book may also be of interest to specialists in the relevant fields of ecology, engineering, and material processing.

  2. 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.

  3. Biological ice nucleation initiates hailstone formation

    NASA Astrophysics Data System (ADS)

    Michaud, Alexander B.; Dore, John E.; Leslie, Deborah; Lyons, W. Berry; Sands, David C.; Priscu, John C.

    2014-11-01

    Cloud condensation and ice nuclei in the troposphere are required precursors to cloud and precipitation formation, both of which influence the radiative balance of Earth. The initial stage of hailstone formation (i.e., the embryo) and the subsequent layered growth allow hail to be used as a model for the study of nucleation processes in precipitation. By virtue of the preserved particle and isotopic record captured by hailstones, they represent a unique form of precipitation that allows direct characterization of the particles present during atmospheric ice nucleation. Despite the ecological and economic consequences of hail storms, the dynamics of hailstone nucleation, and thus their formation, are not well understood. Our experiments show that hailstone embryos from three Rocky Mountain storms contained biological ice nuclei capable of freezing water at warm, subzero (°C) temperatures, indicating that biological particles can act as nucleation sites for hailstone formation. These results are corroborated by analysis of δD and δ18O from melted hailstone embryos, which show that the hailstones formed at similarly warm temperatures in situ. Low densities of ice nucleation active abiotic particles were also present in hailstone embryos, but their low concentration indicates they were not likely to have catalyzed ice formation at the warm temperatures determined from water stable isotope analysis. Our study provides new data on ice nucleation occurring at the bottom of clouds, an atmospheric region whose processes are critical to global climate models but which has challenged instrument-based measurements.

  4. 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

  5. Laboratory studies of immersion and deposition mode ice nucleation of ozone aged mineral dust particles

    NASA Astrophysics Data System (ADS)

    Kanji, Z. A.; Welti, A.; Chou, C.; Stetzer, O.; Lohmann, U.

    2013-09-01

    Ice nucleation in the atmosphere is central to the understanding the microphysical properties of mixed-phase and cirrus clouds. Ambient conditions such as temperature (T) and relative humidity (RH), as well as aerosol properties such as chemical composition and mixing state play an important role in predicting ice formation in the troposphere. Previous field studies have reported the absence of sulfate and organic compounds on mineral dust ice crystal residuals sampled at mountain top stations or aircraft based measurements despite the long-range transport mineral dust is subjected to. We present laboratory studies of ice nucleation for immersion and deposition mode on ozone aged mineral dust particles for 233 < T < 263 K. Heterogeneous ice nucleation of untreated kaolinite (Ka) and Arizona Test Dust (ATD) particles is compared to corresponding aged particles that are subjected to ozone concentrations of 0.4-4.3 ppmv in a stainless steel aerosol tank. The portable ice nucleation counter (PINC) and immersion chamber combined with the Zurich ice nucleation chamber (IMCA-ZINC) are used to conduct deposition and immersion mode measurements, respectively. Ice active fractions as well as ice active surface site densities (ns) are reported and observed to increase as a function of decreasing temperature. We present first results that demonstrate enhancement of the ice nucleation ability of aged mineral dust particles in both the deposition and immersion mode due to ageing. We also present the first results to show a suppression of heterogeneous ice nucleation activity without the condensation of a coating of (in)organic material. In immersion mode, low ozone exposed Ka particles showed enhanced ice activity requiring a median freezing temperature of 1.5 K warmer than that of untreated Ka, whereas high ozone exposed ATD particles showed suppressed ice nucleation requiring a median freezing temperature of 3 K colder than that of untreated ATD. In deposition mode, low

  6. Cytoplasmic Nucleation and Atypical Branching Nucleation Generate Endoplasmic Microtubules in Physcomitrella patens[OPEN

    PubMed Central

    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. PMID:25616870

  7. Effect of Pt Doping on Nucleation and Crystallization in Li2O.2SiO2 Glass: Experimental Measurements and Computer Modeling

    NASA Technical Reports Server (NTRS)

    Narayan, K. Lakshmi; Kelton, K. F.; Ray, C. S.

    1996-01-01

    Heterogeneous nucleation and its effects on the crystallization of lithium disilicate glass containing small amounts of Pt are investigated. Measurements of the nucleation frequencies and induction times with and without Pt are shown to be consistent with predictions based on the classical nucleation theory. A realistic computer model for the transformation is presented. Computed differential thermal analysis data (such as crystallization rates as a function of time and temperature) are shown to be in good agreement with experimental results. This modeling provides a new, more quantitative method for analyzing calorimetric data.

  8. Gauge transformation and symmetries of the commutative multicomponent BKP hierarchy

    NASA Astrophysics Data System (ADS)

    Li, Chuanzhong

    2016-01-01

    In this paper, we defined a new multi-component B type Kadomtsev-Petviashvili (BKP) hierarchy that takes values in a commutative subalgebra of {gl}(N,{{C}}). After this, we give the gauge transformation of this commutative multicomponent BKP (CMBKP) hierarchy. Meanwhile, we construct a new constrained CMBKP hierarchy that contains some new integrable systems, including coupled KdV equations under a certain reduction. After this, the quantum torus symmetry and quantum torus constraint on the tau function of the commutative multi-component BKP hierarchy will be constructed.

  9. A laboratory study of the nucleation kinetics of nitric acid hydrates under stratospheric conditions

    NASA Astrophysics Data System (ADS)

    James, Alexander D.; Murray, Benjamin J.; Plane, John M. C.

    2016-04-01

    Measurements of the kinetics of crystallisation of ternary H2O-H2SO4-HNO3 mixtures to produce nitric acid hydrate phases, as occurs in the lower stratosphere, have been a long-standing challenge for investigators in the laboratory. Understanding polar stratospheric chlorine chemistry and thereby ozone depletion is increasingly limited by descriptions of nucleation processes. Meteoric smoke particles have been considered in the past as heterogeneous nuclei, however recent studies suggest that these particles will largely dissolve, leaving mainly silica and alumina as solid inclusions. In this study the nucleation kinetics of nitric acid hydrate phases have been measured in microliter droplets at polar stratospheric cloud (PSC) temperatures, using a droplet freezing assay. A clear heterogeneous effect was observed when silica particles were added. A parameterisation based on the number of droplets activated per nuclei surface area (ns) has been developed and compared to global model data. Nucleation experiments on identical droplets have been performed in an X-Ray Diffractometer (XRD) to determine the nature of the phase which formed. β-Nitric Acid Trihydrate (NAT) was observed alongside a mixture of Nitric Acid Dihydrate (NAD) phases. It is not possible to determine whether NAT nucleates directly or is formed by a phase transition from NAD (likely requiring the presence of a mediating liquid phase). Regardless, these results demonstrate the possibility of forming NAT on laboratory timescales. In the polar stratosphere, sulfuric acid (present at several weight percent of the liquid under equilibrium conditions) could provide such a liquid phase. This study therefor provides insight into previous discrepancies between phases formed in the laboratory and those observed in the atmosphere. It also provides a basis for future studies into atmospheric nucleation of solid PSCs.

  10. Validity of commonly used formula of nucleation work for bubble nucleation

    NASA Astrophysics Data System (ADS)

    Mori, Atsushi

    2013-08-01

    Nishioka and Kusaka [Journal of Chemical Physics 96 (1992) 5370] showed that the commonly used formula, W=n(μα-μβ)+γA, for work of formation of critical nucleus is derived by integrating the isothermal Gibbs-Duhem relation for the incompressible nucleating phase, such as an incompressible liquid phase nucleation in a vapor phase. In their paper as well as in a subsequent paper [Li, Nishioka, Holcomb, Journal of Crystal Growth 171 (1997) 259] it was stated that the commonly used formula was valid for an incompressible nucleating phase and no longer held for such as a bubble nucleation. In this paper, we will amend this statement; that is, the commonly used formula is shown to hold for incompressible parent phase, such as a bubble nucleation in an incompressible parent phase.

  11. 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.

  12. Observations of Nucleation and Early Stage Growth of Amorphous Silica on Carboxyl-Terminated Model Biosubstrates

    NASA Astrophysics Data System (ADS)

    Wallace, A. F.; Dove, P. M.

    2005-12-01

    Over Earth history, organisms have developed the ability to control the nucleation and growth of a broad range of nanocrystalline and amorphous materials. The formation of amorphous biosilica is of particular interest because silicifiers sequester gigatons of silica annually, and suppress dissolved silica levels in the ocean to current low levels. The ecological success of marine diatoms, which are arguably the most important silicifiers, places them alongside marine calcifiers as major players in the sequestration of organic carbon. Thus, the biologically mediated formation of amorphous silica plays a key role in the global cycling of silicon and carbon. During controlled biomineralization, nucleation typically occurs in designated locations. There is a substantial body of evidence suggesting that macromolecules in the cellular environment determine these locations by acting as templates to provide energetically favorable sites for the onset of mineral and amorphous material nucleation. In diatoms, silica formation is likely initiated through heterogeneous nucleation on functional portions of macromolecules inside the Silica Deposition Vesicle (SDV). Previous studies of silica nucleation have implicated multiple chemical moieties associated with the constituent amino acids and sugars of polysaccharides, proteins, and glycoproteins as probable sites for in vivo surface nucleation and patterning. These investigations have usually employed complex macromolecules that exhibit multiple functionalities, and un-characterized solution compositions, thus rendering a quantitative analysis of kinetic and thermodynamic processes impossible. The objective of this research is to experimentally test kinetic and thermodynamic controls exercised by surface moieties on silica nucleation. Our experimental model system uses synthetic organic substrates designed to mimic key features of the interfacial regions between the surrounding cellular environment and the amorphous silica

  13. Multicomponent Reactions, Union of MCRs and Beyond.

    PubMed

    Zarganes-Tzitzikas, Tryfon; Chandgude, Ajay L; Dömling, Alexander

    2015-10-01

    Multicomponent reactions (MCRs), which are located between one- and two-component and polymerization reactions, provide a number of valuable conceptual and synthetic advantages over stepwise sequential approaches towards complex and valuable molecules. To address current limitations in the number of MCRs and the resulting scaffolds, the concept of union of MCRs was introduced two decades ago by Dömling and Ugi and is rapidly advancing, as is apparent by several recently published works. MCR technology is now widely recognized for its impact on drug discovery projects and is strongly endorsed by industry in addition to academia. Clearly, novel scaffolds accessible in few steps including MCRs will further enhance the field of applications. Additionally, broad expansion of MCR applications in fields such as imaging, materials science, medical devices, agriculture, or futuristic applications in stem cell therapy and theragnostics or solar energy and superconductivity are predicted.

  14. Oximetry of retinal capillaries by multicomponent analysis.

    PubMed

    Furukawa, Hiromitsu; Arimoto, Hidenobu; Shirai, Tomohiro; Ooto, Sotaro; Hangai, Masanori; Yoshimura, Nagahisa

    2012-08-01

    Retinal oximetry of capillaries was performed for early detection of retinal vascular abnormalities, which are caused predominantly by complications of systemic circulatory diseases. As the conventional method for determining absorbance is not applicable to capillaries, multicomponent analysis was used to estimate the absorbance spectra of the retinal blood vessels. In this analysis, the capillary spectrum was classified as intermediate between those of the retinal arteries and veins, enabling relative estimation of oxygen saturation in the capillaries. This method could be useful for early recognition of disturbances in the peripheral circulation. Furthermore, a spectroscopic ophthalmoscope system based on the proposed method was developed to examine the human retina. A clinical trial of this system demonstrated that oximetry of the retinal capillaries may be an improvement over the present diagnosis for patients of malignant hypertension.

  15. Molecular Basis of Actin Nucleation Factor Cooperativity

    PubMed Central

    Zeth, Kornelius; Pechlivanis, Markos; Samol, Annette; Pleiser, Sandra; Vonrhein, Clemens; Kerkhoff, Eugen

    2011-01-01

    The distinct actin nucleation factors of the Spir and formin subgroup families cooperate in actin nucleation. The Spir/formin cooperativity has been identified to direct two essential steps in mammalian oocyte maturation, the asymmetric spindle positioning and polar body extrusion during meiosis. Understanding the nature and regulation of the Spir/Fmn cooperation is an important requirement to comprehend mammalian reproduction. Recently we dissected the structural elements of the Spir and Fmn family proteins, which physically link the two actin nucleation factors. The trans-regulatory interaction is mediated by the Spir kinase non-catalytic C-lobe domain (KIND) and the C-terminal formin Spir interaction motif (FSI). The interaction inhibits formin nucleation activity and enhances the Spir activity. To get insights into the molecular mechanism of the Spir/Fmn interaction, we determined the crystal structure of the KIND domain alone and in complex with the C-terminal Fmn-2 FSI peptide. Together they confirm the proposed structural homology of the KIND domain to the protein kinase fold and reveal the basis of the Spir/formin interaction. The complex structure showed a large interface with conserved and positively charged residues of the Fmn FSI peptide mediating major contacts to an acidic groove on the surface of KIND. Protein interaction studies verified the electrostatic nature of the interaction. The data presented here provide the molecular basis of the Spir/formin interaction and give a first structural view into the mechanisms of actin nucleation factor cooperativity. PMID:21705804

  16. Atmospheric Ion-induced Aerosol Nucleation

    NASA Astrophysics Data System (ADS)

    Curtius, J.; Lovejoy, E. R.; Froyd, K. D.

    2006-08-01

    Ion-induced nucleation has been suggested to be a potentially important mechanism for atmospheric aerosol formation. Ions are formed in the background atmosphere by galactic cosmic rays. A possible connection between galactic cosmic rays and cloudiness has been However, the predictions of current atmospheric nucleation models are highly uncertain because the models are usually based on the liquid drop model that estimates cluster thermodynamics based on bulk properties (e.g., liquid drop density and surface tension). Sulfuric acid (H2SO4) and water are assumed to be the most important nucleating agents in the free troposphere. Measurements of the molecular thermodynamics for the growth and evaporation of cluster ions containing H2SO4 and H2O were performed using a temperature-controlled laminar flow reactor coupled to a linear quadrupole mass spectrometer as well as a temperature-controlled ion trap mass spectrometer. The measurements were complemented by quantum chemical calculations of the cluster ion structures. The analysis yielded a complete set of H2SO4 and H2O binding thermodynamics extending from molecular cluster ions to the bulk, based on experimental thermodynamics for the small clusters. The data were incorporated into a kinetic aerosol model to yield quantitative predictions of the rate of ion-induced nucleation for atmospheric conditions. The model predicts that the negative ion-H2SO4-H2O nucleation mechanism is an efficient source of new particles in the middle and upper troposphere.

  17. Simulations of Evaporating Multicomponent Fuel Drops

    NASA Technical Reports Server (NTRS)

    Bellan, Josette; Le Clercq, Patrick

    2005-01-01

    A paper presents additional information on the subject matter of Model of Mixing Layer With Multicomponent Evaporating Drops (NPO-30505), NASA Tech Briefs, Vol. 28, No. 3 (March 2004), page 55. To recapitulate: A mathematical model of a three-dimensional mixing layer laden with evaporating fuel drops composed of many chemical species has been derived. The model is used to perform direct numerical simulations in continuing studies directed toward understanding the behaviors of sprays of liquid petroleum fuels in furnaces, industrial combustors, and engines. The model includes governing equations formulated in an Eulerian and a Lagrangian reference frame for the gas and drops, respectively, and incorporates a concept of continuous thermodynamics, according to which the chemical composition of a fuel is described by use of a distribution function. In this investigation, the distribution function depends solely on the species molar weight. The present paper reiterates the description of the model and discusses further in-depth analysis of the previous results as well as results of additional numerical simulations assessing the effect of the mass loading. The paper reiterates the conclusions reported in the cited previous article, and states some new conclusions. Some new conclusions are: 1. The slower evaporation and the evaporation/ condensation process for multicomponent-fuel drops resulted in a reduced drop-size polydispersity compared to their single-component counterpart. 2. The inhomogeneity in the spatial distribution of the species in the layer increases with the initial mass loading. 3. As evaporation becomes faster, the assumed invariant form of the molecular- weight distribution during evaporation becomes inaccurate.

  18. Undercooling measurement and nucleation study of silicon droplets on various substrates

    NASA Astrophysics Data System (ADS)

    Tsoutsouva, M. G.; Duffar, T.; Chaussende, D.; Kamguem, M.

    2016-10-01

    The heterogeneous nucleation of solid silicon is studied when molten droplets solidify on various substrates. An experimental installation has been developed in order to record in real time the melting-solidification process, measure the undercooling temperature and look at the solidification of the droplets. Three different categories of substrate materials are studied: oxides (silica, zyarock and sapphire), nitrides (silica+oxidized Si3N4 coating, zyarock+oxidized Si3N4 coating, sintered Si3N4, PBN and HIP-BN) and carbon-containing (isostatic graphite, glassy carbon and SiC). Higher undercooling values are measured in the case of oxide substrates where the solidified droplet is found to be mainly composed of a single-crystal. In the case of nitride substrates, a dissolution/precipitation process takes place and β-phase Si3N4 precipitates are found to act as nucleation centers for the silicon solidification. The nucleating power of Si3N4 is attributed to the good epitaxial fit with silicon. Oxidation of Si3N4 powder at a higher temperature increases the undercooling of the droplet. When the silicon droplet is solidified on BN substrates, BN particles are detected on the surface of the droplet as well as a Si3N4 layer at the substrate/Si interface which promotes nucleation. Carbon-containing substrates are found to favor the nucleation of silicon due to the creation of a SiC layer at the substrate/silicon interface and precipitation of SiC particles in the droplets. However, no explanation of the important nucleating effect of SiC has been found.

  19. Role of Dynamic Nucleation at Moving Boundaries in Phase and Microstructure Selection

    NASA Technical Reports Server (NTRS)

    Karma, Alain; Trivedi, Rohit

    1999-01-01

    Solidification microstructures that form under steady-state growth conditions (cells, dendrites, regular eutectics, etc.) are reasonably well understood in comparison to other, more complex microstructures, which form under intrinsically non-steady-state growth conditions due to the competition between the nucleation and growth of several phases. Some important practical examples in this latter class include microstructures forming in peritectic systems in highly undercooled droplets, and in strip cast stainless steels. Prediction of phase and microstructure selection in these systems has been traditionally based on (1) heterogeneous nucleation on a static interface, and (2) comparing the relative growth rate of different phase/microstructures under steady-state growth conditions. The formation of new phases, however, occurs via nucleation on, or ahead of, a moving boundary. In addition, the actual selection process is controlled by a complex interaction between the nucleation process and the growth competition between the nuclei and the pre-existing phase under non-steady-state conditions. As a result, it is often difficult to predict which microstructure will form and which phases will be selected under prescribed processing conditions. This research addresses this critical role of nucleation at moving boundaries in the selection of phases and solidification microstructures through quantitative experiments and numerical modeling in peritectic systems. In order to create a well characterized system in which to study this problem, we focus on the directional solidification of hypo- and hyper-peritectic alloys in the two-phase region, imposing a large enough ratio of temperature gradient/growth rate (G/V(sub p)) to suppress the morphological instability of both the parent (alpha) and peritectic (Beta) phases, i.e. each phase alone would grow as a planar front. Our combined experimental and theoretical results show that, already in this simplified case, the growth

  20. Cellulose and Their Characteristic Ice Nucleation Activity- Freezing on a Chip

    NASA Astrophysics Data System (ADS)

    Häusler, Thomas; Felgitsch, Laura; Grothe, Hinrich

    2016-04-01

    The influence of clouds on the Earth's climate system is well known (IPCC, 2013). Cloud microphysics determines for example cloud lifetime and precipitation properties. Clouds are cooling the climate system by reflecting incoming solar radiation and warm its surface by trapping outgoing infrared radiation (Baker and Peter, 2008). In all these processes, aerosol particles play a crucial role by acting as cloud condensation nuclei (CCN) for liquid droplets and as an ice nucleation particle (INP) for the formation of ice particles. Freezing processes at higher temperatures than -38°C occur heterogeneously (Pruppacher and Klett 1997). Therefore aerosol particles act like a catalyst, which reduces the energy barrier for nucleation. The nucleation mechanisms, especially the theory of functional sites are not entirely understood. It remains unclear which class of compound nucleates ice. Here we present a unique technique to perform drop- freezing experiments in a more efficient way. A self-made freezing- chip will be presented. Measurements done to proof the efficiency of our setup as well as advantages compared with other setups will be discussed. Furthermore we present a proxy for biological INPs, microcrystalline cellulose. Cellulose is the main component of herbal cell walls (about 50 wt%). It is a polysaccharide consisting of a linear chain of several hundred to many thousands of β(1→4) linked D-glucose units. Cellulose can contribute to the diverse spectrum of ice nucleation particles. We present results of the nucleation activity measurements of MCCs as well as the influence of concentration, preparation or chemical modification.

  1. 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.

  2. Temperature dependence of nucleation in Yukawa fluids

    NASA Astrophysics Data System (ADS)

    Li, J.-S.; Wilemski, G.

    2002-03-01

    We have studied the temperature dependence of gas-liquid nucleation in Yukawa fluids with gradient theory (GT) and density functional theory (DFT). Each of these nonclassical theories exhibits a weaker (i.e. better) temperature dependence than classical nucleation theory. At a given temperature, the difference between GT and DFT for the reversible work to form a critical nucleus gets smaller with increasing superaturation. For the temperature dependence, the reversible work for GT is very close to that for DFT at high temperatures. The difference between the two theories increases with decreasing temperature and supersaturation. Thus, in contrast to the behavior of a Peng-Robinson fluid, we find that GT can improve the temperature dependence over that of classical nucleation theory, although not always to the same degree as DFT.

  3. 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.

  4. 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.

  5. Deposition nucleation viewed as homogeneous or immersion freezing in pores and cavities

    NASA Astrophysics Data System (ADS)

    Marcolli, C.

    2013-06-01

    Heterogeneous ice nucleation is an important mechanism for the glaciation of mixed phase clouds and may also be relevant for cloud formation and dehydration at the cirrus cloud level. It is thought to proceed through different mechanisms, namely contact, condensation, immersion and deposition nucleation. Supposedly, deposition nucleation is the only pathway which does not involve liquid water but occurs by direct water vapor deposition on a surface. This study challenges this classical view by putting forward the hypothesis that what is called deposition nucleation is in fact homogeneous or immersion nucleation occurring in pores and cavities that may form between aggregated primary particles and fill with water at relative humidity RHw < 100% because of the inverse Kelvin effect. Evidence for this hypothesis of pore condensation and freezing (PCF) originates from a number of only loosely connected scientific areas. The prime example for PCF is ice nucleation in clay minerals and mineral dusts, for which the data base is best. Studies on freezing in confinement carried out on mesoporous silica materials such as SBA-15, SBA-16, MCM-41, zeolites and KIT have shown that homogeneous ice nucleation occurs abruptly at T=230-235 K in pores with diameters (D) of 3.5-4 nm or larger but only gradually at T=210-230 K in pores with D=2.5-3.5 nm. Melting temperatures in pores are depressed by an amount that can be described by the Gibbs-Thomson equation. Water adsorption isotherms of MCM-41 show that pores with D=3.5-4 nm fill with water at RHw = 56-60% in accordance with an inverse Kelvin effect. Water in such pores should freeze homogeneously for T < 235 K even before relative humidity with respect to ice (RHi) reaches ice saturation. Ice crystal growth by water vapor deposition from the gas phase is therefore expected to set in as soon as RHw > 100%. Pores with D > 7.5 nm fill with water at RHi > 100% for T < 235 K and are likely to freeze homogeneously as soon as they are

  6. Ice Formation via Deposition Mode Nucleation Onto Dust Particulates: The University of Toronto Continuous Flow Diffusion Chamber

    NASA Astrophysics Data System (ADS)

    Kanji, Z. A.; Abbatt, J. P.; Cotton, R.; Demott, P.; Jones, H.; Möhler, O.; Stetzer, O.

    2008-12-01

    Laboratory studies are described whereby the heterogeneous ice nucleating ability of various dust samples were studied, for particles suspended in a newly built thermal gradient continuous flow diffusion chamber (TG-CFDC). Ice formation is observed using an optical particle counter (OPC) and the relative humidity (RH) and temperature conditions of the flow system are validated by observing homogenous freezing of H2SO4 aerosols. At the Fourth International Ice Nucleation Workshop (ICIS 07) in Karslruhe, Germany this system was used to investigate ice nucleation primarily in the vapor deposition mode, for Arizona Test Dust (ATD), Israeli Desert Dust (ID), Canary Island Dust (CID), Saharan Dust (SD), Graphite Spark Soot, Snomax® (dead bacteria) and live bacteria. The aerosol size was in the submicron range with an approximate cut off of 700 nm and a mode of 350 nm. Temperatures for nucleation were varied from 265 - 230 K. The dust aerosols were generally found to be more efficient than soot. At warmer temperatures (263 K) the bacteria were found to be active in the deposition mode which was not the case for dusts. Among the various dust types at 248 K, the CID was more efficient than ATD at nucleating ice when efficiency is based on lowest onset RH conditions for ice formation in our chamber. We also present preliminary results for the effect of total surface area versus size of aerosols on ice nucleation using ATD as a surrogate for naturally occurring mineral dust.

  7. Deposition and immersion mode nucleation of ice by three distinct samples of volcanic ash using Raman spectroscopy

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

    Ice nucleation on volcanic ash controls both ash aggregation and cloud glaciation, which affect atmospheric transport and global climate. Previously, it has been suggested that there is one characteristic ice nucleation efficiency for all volcanic ash, regardless of its composition, when accounting for surface area; however, this claim is derived from data from only two volcanic eruptions. In this work, we have studied 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), Soufrière Hills (andesitic ash, Montserrat), and Taupo (Oruanui euption, 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. In the present study, we find that all three samples of volcanic ash are excellent depositional ice nuclei, nucleating ice from 225-235 K at ice saturation ratios of 1.05 ± 0.01, comparable to the mineral dust proxy kaolinite. Since depositional ice nucleation will be more important at colder temperatures, fine volcanic ash may represent a global source of cold-cloud ice nuclei. For immersion freezing relevant to mixed-phase clouds, however, only the Oruanui ash exhibited 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.

  8. 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.

  9. MPH: A library for distributed multi-component environment

    SciTech Connect

    Ding, Chris H.Q.; He, Yun

    2001-06-01

    Many current large and complex HPC applications are based on semi-independent program components developed by different groups or for different purposes. On distributed memory parallel supercomputers, how to perform component-name registration and initialize communications between independent components are among the first critical steps in establishing a distributed multi-component environment. Here we describe MPH, a multi-component handshaking library that resolves these tasks in a convenient and consistent way. MPH uses MPI for high performance and supports many PVM functionality. It supports two major parallel integration mechanism: multi-component multi-executable (MCME) and multi-component single-executable (MCME). It is a simple, easy-to-use module for developing practical codes, or as basis for larger software tools/frameworks.

  10. Erbium triflate promoted multicomponent synthesis of highly substituted imidazoles.

    PubMed

    Rajaguru, Kandasamy; Suresh, Rajendran; Mariappan, Arumugam; Muthusubramanian, Shanmugam; Bhuvanesh, Nattamai

    2014-02-07

    The synthesis of highly substituted imidazole derivatives has been achieved from various α-azido chalcones, aryl aldehydes, and anilines. This multicomponent protocol employs erbium triflate as a catalyst resulting in excellent yield of the imidazoles.

  11. MICROWAVE-ACCELERATED MULTICOMPONENT REACTIONS UNDER SOLVENT-FREE CONDITIONS

    EPA Science Inventory

    The application of microwave-accelerated solventless synthetic protocols in multicomponent (MCC) reactions will be exemplified by several condensation and cyclization reactions including the rapid one-pot assembly of valuable heterocyclic compounds from in situ generated intermed...

  12. Multicomponent cascade reactions of unprotected carbohydrates and amino acids.

    PubMed

    Voigt, Benjamin; Linke, Michael; Mahrwald, Rainer

    2015-06-05

    Herein an operationally simple multicomponent reaction of unprotected carbohydrates with amino acids and isonitriles is presented. By the extension of this Ugi-type reaction to an unprotected disaccharide a novel glycopeptide structure was accessible.

  13. Ion-Induced Nucleation Under Atmospheric Conditions

    NASA Astrophysics Data System (ADS)

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

    2007-12-01

    Experimental studies of aerosol nucleation in air, containing trace amounts of ozone, sulphur dioxide, and water vapor at concentrations relevant for the Earths atmosphere are reported. The production of new aerosol particles is found to be proportional to the negative ion density. These results suggest that ions are important for nucleation processes in the atmosphere and cloud cover -- and may thus link cosmic rays to Earth's climate. The production of aerosols in the Earth's atmosphere is an unresolved and challenging problem. Atmospheric and experimental observations have shown that the nucleation of aerosol particles can occur under conditions that cannot be explained by classical nucleation theory. Several ideas have been put forward to solve the nucleation problem, e.g., Ion-induced Nucleation and Ternary Nucleation. However, experimental investigations exploring the role of ions in particle production are scarce, and often at conditions far removed from those relevant for the lower part of the atmosphere. In our laboratory we have performed1 an experimental investigation of nucleation that confirms the importance of ions under conditions that do prevail in the lower atmosphere. The measurements were performed in a 7 m3 reaction chamber, which was continuously flushed with dry purified air. Variable concentrations of water vapor (H2O), ozone (O3), and sulphur dioxide (SO2) could be added to the chamber, where the pressure was held a few Pa above atmospheric pressure, and the temperature fixed at 296 K. UV-lamps (253.7 nm) were used to initiate a photochemical reaction that transforms (H2O), ozone (O3), and sulphur dioxide (SO2) to sulphuric acid (H2SO4). Ions were produced in the chamber by galactic cosmic radiation. This natural production of ions could be enhanced with gamma sources, mounted outside of the chamber. A Gerdien tube was used to measure the ion current, and aerosols generated in the chamber were measured with a TSI Ultra Fine Condensation

  14. Interfacial supersaturation, secondary nucleation, and crystal growth

    NASA Astrophysics Data System (ADS)

    Tai, Clifford Y.; Wu, Jenn-Fang; Rousseau, Ronald W.

    1992-02-01

    A theory describing the source of nuclei in secondary nucleation is presented and used to rationalize experimental data from the literature, some of which had appeared to be conflicting. The theory rests on a model in which an adsorption layer consisting of clusters of growth units of varying size is formed on the surface of growing crystals. The existence of the layer is related to the two-resistance model of crystal growth; by varying system conditions, the relative importance of the two resistances is altered and thereby changes the interfacial supersaturation even though overall supersaturation remains constant. Interracial supersaturation and contact energy determine kinetics in a system dominated by contact nucleation.

  15. Spider silk has an ice nucleation activity.

    PubMed

    Murase, N; Ruike, M; Matsunaga, N; Hayakawa, M; Kaneko, Y; Ono, Y

    2001-03-01

    Several ice nucleating substances have been identified, which exist in vivo or can be extracted from biological materials. Spider silk, which has a strong ability for water condensation, has also been found to possess an ice nucleation activity. The freezing temperature of water droplets was higher in the presence than in the absence of spider silk. Moreover, by means of environmental scanning electron microscopy, it was observed that the activity is not due to foreign matter attached to the silk but to the silk fibroin itself.

  16. Ice nucleation and antinucleation in nature.

    PubMed

    Zachariassen, K E; Kristiansen, E

    2000-12-01

    Plants and ectothermic animals use a variety of substances and mechanisms to survive exposure to subfreezing temperatures. Proteinaceous ice nucleators trigger freezing at high subzero temperatures, either to provide cold protection from released heat of fusion or to establish a protective extracellular freezing in freeze-tolerant species. Freeze-avoiding species increase their supercooling potential by removing ice nucleators and accumulating polyols. Terrestrial invertebrates and polar marine fish stabilize their supercooled state by means of noncolligatively acting antifreeze proteins. Some organisms also depress their body fluid melting point to ambient temperature by evaporation and/or solute accumulation.

  17. Diamond Nucleation of Surfaces Using Carbon Clusters

    DTIC Science & Technology

    1993-05-01

    initially expected that C60 would be a better nucleation 19 precursor than C7. The molecule is considered more stable than C70 and recent HRTEM 33 as well as...promoter as C7 will be discussed below. Figure S.c shows the SEK results of a comparison of C7 . nucleation enhancement to that of a DLC amorphous coating...of comparable thickness grown on the same substrate. Figure 7.c is the Raman spectrum of the deposited DLC film. For this series of experiments C

  18. Multicomponent reactions: A simple and efficient route to heterocyclic phosphonates

    PubMed Central

    2016-01-01

    Summary Multicomponent reactions (MCRs) are one of the most important processes for the preparation of highly functionalized organic compounds in modern synthetic chemistry. As shown in this review, they play an important role in organophosphorus chemistry where phosphorus reagents are used as substrates for the synthesis of a wide range of phosphorylated heterocycles. In this article, an overview about multicomponent reactions used for the synthesis of heterocyclic compounds bearing a phosphonate group on the ring is given. PMID:27559377

  19. A Weibull characterization for tensile fracture of multicomponent brittle fibers

    NASA Technical Reports Server (NTRS)

    Barrows, R. G.

    1977-01-01

    A statistical characterization for multicomponent brittle fibers in presented. The method, which is an extension of usual Weibull distribution procedures, statistically considers the components making up a fiber (e.g., substrate, sheath, and surface) as separate entities and taken together as in a fiber. Tensile data for silicon carbide fiber and for an experimental carbon-boron alloy fiber are evaluated in terms of the proposed multicomponent Weibull characterization.

  20. Modulated decay in the multi-component Universe

    SciTech Connect

    Enomoto, Seishi; Kohri, Kazunori; Matsuda, Tomohiro E-mail: kohri@post.kek.jp

    2013-08-01

    The early Universe after inflation may have oscillations, kinations (nonoscillatory evolution of a field), topological defects, relativistic and non-relativistic particles at the same time. The Universe whose energy density is a sum of those components can be called the multi-component Universe. The components, which may have distinguishable density scalings, may decay modulated. In this paper we study generation of the curvature perturbations caused by the modulated decay in the multi-component Universe.

  1. Conformational Regulation and Crystalline Manipulation of PLLA through a Self-Assembly Nucleator.

    PubMed

    Li, Chunhai; Luo, Shanshan; Wang, Jianfeng; Wu, Hong; Guo, Shaoyun; Zhang, Xi

    2017-03-24

    Self-assembly nucleators have been increasingly used to manipulate the crystallization of PLLA due to their strong intermolecular interaction with PLLA, while the molecular mechanism of such interaction is still unrevealed. In present work, one special self-assembly nucleator (TMC-300) with relatively high solubility in PLLA matrix, is chosen to investigate how the interaction works at molecular level to promote the crystallization of PLLA mainly through time-resolved spectroscopy. The results indicate that due to the dipole-dipole NH···O═C interaction between dissolved TMC-300 and PLLA, PLLA chains are transformed into gt conformer before TMC-300 phase-separating from PLLA melt, resulting in low energy barrier to pass for the following formation of PLLA α-crystal (α-crystal is consisted of gt conformer). Once the dissolved TMC-300 starts to self-assemble into frameworks upon cooling, the transformed PLLA chains with high population of gt conformer form the primary nuclei on the surface of such self-assembling TMC-300 frameworks. For the first time, not only the heterogeneous nucleation but also the conformational regulation of PLLA chains are proved to be responsible for the high efficiency of the self-assembly nucleators (TMC-300) in promoting the crystallization of PLLA. Therefore, conformational regulation is proposed for crystalline manipulation of PLLA, and this work brings new insight on promoting the crystallization of PLLA even other polymers by regulating their molecular conformation.

  2. Polysaccharide chemistry regulates kinetics of calcite nucleation through competition of interfacial energies

    PubMed Central

    Hamm, Laura M.; Han, Nizhou; De Yoreo, James J.; Dove, Patricia M.

    2013-01-01

    Calcified skeletons are produced within complex assemblages of proteins and polysaccharides whose roles in mineralization are not well understood. Here we quantify the kinetics of calcite nucleation onto a suite of high-purity polysaccharide (PS) substrates under controlled conditions. The energy barriers to nucleation are PS-specific by a systematic relationship to PS charge density and substrate structure that is rooted in minimization of the competing substrate–crystal and substrate–liquid interfacial energies. Chitosan presents a low-energy barrier to nucleation because its near-neutral charge favors formation of a substrate–crystal interface, thus reducing substrate interactions with water. Progressively higher barriers are measured for negatively charged alginates and heparin that favor contact with the solution over the formation of new substrate–crystal interfaces. The findings support a directing role for PS in biomineral formation and demonstrate that substrate–crystal interactions are one end-member in a larger continuum of competing forces that regulate heterogeneous crystal nucleation. PMID:23690577

  3. Impact of heterogeneous ice nuclei on homogeneous freezing events in cirrus clouds

    SciTech Connect

    Spichtinger, Peter; Cziczo, Daniel J.

    2010-07-29

    The influence of initial heterogeneous nucleation on subsequent homogeneous nucleation events in cirrus clouds is investigated using a box model which includes the explicit impact of aerosols on the nucleation of ice crystals and sedimentation. Different effects are discussed, namely the impact of external mixtures of heterogeneous ice nuclei and the influence of size-dependent freezing thresholds. Several idealized experiments are carried out, which show that the treatment of external mixtures of ice nuclei can strongly change later homogeneous nucleation events (i.e., the ice crystal number densities) in different matters. The use of size-dependent freezing thresholds can also change the cloud prop erties when compared to more simple parameterizations. This size effect is most important for large IN concentrations. Based upon these findings, recommendations for future modeling and measurement efforts are presented.

  4. Translational invariance in nucleation theories: theoretical formulation.

    PubMed

    Drossinos, Y; Kevrekidis, P G; Georgopoulos, P G

    2001-03-01

    The consequences of spontaneously broken translational invariance on the nucleation-rate statistical prefactor in theories of first-order phase transitions are analyzed. A hybrid, semiphenomenological approach based on field-theoretic analyses of condensation and modern density-functional theories of nucleation is adopted to provide a unified prescription for the incorporation of translational-invariance corrections to nucleation-rate predictions. A connection between these theories is obtained starting from a quantum-mechanical Hamiltonian and using methods developed in the context of studies on Bose-Einstein condensation. An extremum principle is used to derive an integro-differential equation for the spatially nonuniform mean-field order-parameter profile; the appropriate order parameter becomes the square root of the fluid density. The importance of the attractive intermolecular potential is emphasized, whereas the repulsive two-body potential is approximated by considering hard-sphere collisions. The functional form of the degenerate translational eigenmodes in three dimensions is related to the mean-field order parameter, and their contribution to the nucleation-rate prefactor is evaluated. The solution of the Euler-Lagrange variational equation is discussed in terms of either a proposed variational trial function or the complete numerical solution of the associated boundary-value integro-differential problem. Alternatively, if the attractive potential is not explicitly known, an approach that allows its formal determination from its moments is presented.

  5. Forest canopy interactions with nucleation mode particles

    NASA Astrophysics Data System (ADS)

    Pryor, S. C.; Hornsby, K. E.; Novick, K. A.

    2014-11-01

    Ultrafine particle size distributions through a deciduous forest canopy indicate that nucleation mode particle concentrations decline with depth into the canopy, such that number concentrations at the bottom of the canopy are an average of 16% lower than those at the top. However, growth rates of nucleation mode particles (diameters 6-30 nm) are invariant with height within the canopy, which implies that the semi-volatile gases contributing to their growth are comparatively well-mixed through the canopy. Growth rates of nucleation mode particles during a meteorological drought year (2012) were substantially lower than during a meteorologically normal year with high soil water potential (2013). This may reflect suppression of actual biogenic volatile organic compound (BVOC) emissions by drought and thus a reduction in the production of condensable products during the drought-affected vegetation season. This hypothesis is supported by evidence that growth rates during the normal year exhibit a positive correlation with emissions of BVOC modeled on observed forest composition, leaf area index, temperature and photosynthetically active radiation (PAR), but particle growth rates during the drought-affected vegetation season are not correlated with modeled BVOC emissions. These data thus provide indirect evidence that drought stress in forests may reduce BVOC emissions and limit growth of nucleation mode particles to climate-relevant sizes.

  6. Quantum pattern formation dynamics of photoinduced nucleation

    NASA Astrophysics Data System (ADS)

    Ishida, Kunio; Nasu, Keiichiro

    2008-06-01

    We study the dynamics of quantum pattern formation processes in molecular crystals which is concomitant with photoinduced nucleation. Since the nucleation process in coherent regime is driven by the nonadiabatic transition in each molecule followed by the propagation of phonons, it is necessary to take into account the quantum nature of both electrons and phonons in order to pursue the dynamics of the system. Therefore, we employ a model of localized electrons coupled with a quantized phonon mode and solve the time-dependent Schrödinger equation numerically. We found that there is a minimal size of clusters of excited molecules which triggers the photoinduced nucleation process; i.e., nucleation does not take place unless sufficient photoexcitation energy is concentrated within a narrow area of the system. We show that this result means that the spatial distribution of photoexcited molecules plays an important role in the nonlinearity of the dynamics and also in the optical properties observed in experiments. We calculate the conversion ratio, the rate of cluster formation, and correlation functions to reveal the dynamical properties of the pattern formation process; the initial dynamics of the photoinduced structural change is discussed from the viewpoint of pattern formation.

  7. Multistep nucleation of nanocrystals in aqueous solution

    NASA Astrophysics Data System (ADS)

    Loh, N. Duane; Sen, Soumyo; Bosman, Michel; Tan, Shu Fen; Zhong, Jun; Nijhuis, Christian A.; Král, Petr; Matsudaira, Paul; Mirsaidov, Utkur

    2017-01-01

    The nucleation and growth of solids from solutions impacts many natural processes and is fundamental to applications in materials engineering and medicine. For a crystalline solid, the nucleus is a nanoscale cluster of ordered atoms that forms through mechanisms still poorly understood. In particular, it is unclear whether a nucleus forms spontaneously from solution via a single- or multiple-step process. Here, using in situ electron microscopy, we show how gold and silver nanocrystals nucleate from supersaturated aqueous solutions in three distinct steps: spinodal decomposition into solute-rich and solute-poor liquid phases, nucleation of amorphous nanoclusters within the metal-rich liquid phase, followed by crystallization of these amorphous clusters. Our ab initio calculations on gold nucleation suggest that these steps might be associated with strong gold-gold atom coupling and water-mediated metastable gold complexes. The understanding of intermediate steps in nuclei formation has important implications for the formation and growth of both crystalline and amorphous materials.

  8. Amyloid fibril networks nucleated under oscillatory shear

    NASA Astrophysics Data System (ADS)

    Batzli, Kiersten; Love, Brian

    2013-03-01

    The process of amyloid fibril formation is of interest due to the link between these self-aggregating proteins and the progression of neurodegenerative disease. More recently, research has been directed at the exploitation of self-assembly properties of amyloid proteins for use as templates for nanowires and fibrillar networks. Insulin is an ideal protein for these purposes due to the ease of aggregation, as well as the large aspect ratio and high chemical stability of the produced fibrils. Insulin in pH 2 solution quickly forms aggregates in the presence of 65 °C heat. We have investigated the effect of oscillatory shear on the nucleation and growth of amyloid fibrillar networks using rheology and TEM to characterize the mechanical properties and structure of the network respectively. We contrast networks nucleated under oscillatory shear with networks nucleated in static and agitated conditions, and discuss network properties in the context of use in templating nanostructures. We find that the structural characteristics of the formed networks, including the density of fibrils, are affected by shear during the nucleation phase of amyloid growth.

  9. 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.

  10. 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.

  11. Polymorphic crystals selected in the nucleation stage

    NASA Astrophysics Data System (ADS)

    Zhang, Hui-Jun; Peng, Shu-Ming; Zhou, Xiao-Song; Ju, Xin

    2014-08-01

    Molecular dynamics simulations are used to explore the atomic mechanism of formation of polymorphic crystals. Cooling the Lennard-Jones systems, we observe that the system almost always evolves into a polymorphic crystal with either fivefold-symmetric stacking faults or single-direction stacking faults. The detailed analysis reveals that such an evolution depends on the configuration of fcc/hcp concomitance in the nucleation stage. A defect-induced model is then introduced to illustrate these two evolution routes. Through calculating the formation energies of the defective critical nuclei, we find that the polymorphic crystals seem to be determined by their critical nuclei, in which the relatively lower formation energy ensures the preponderance of the fivefold-symmetric cluster. Before the nucleation, we observe that thermal fluctuations prefer hcp-like particles over fcc-like ones while in the nucleation and growth stage this preference reverses. Notably, an extended step rule of Ostwald is seemingly suitable to characterise the growth process because of the temporary hcp layers appearing among fcc layers in the growth stage. Although the crystalline cluster with single-direction stacking faults has higher growth rate and structural order than its competitor, the component (fcc and hcp) proportion of the final crystals is almost always constant regardless of the polymorphic type. Our finding renews the understanding of the polymorphism of crystals, and possibly draws more attention of people intending to control the polymorphic structures through nucleation.

  12. Size matters in the water uptake and hygroscopic growth of atmospherically relevant multicomponent aerosol particles.

    PubMed

    Laskina, Olga; Morris, Holly S; Grandquist, Joshua R; Qin, Zhen; Stone, Elizabeth A; Tivanski, Alexei V; Grassian, Vicki H

    2015-05-14

    Understanding the interactions of water with atmospheric aerosols is crucial for determining the size, physical state, reactivity, and climate impacts of this important component of the Earth's atmosphere. Here we show that water uptake and hygroscopic growth of multicomponent, atmospherically relevant particles can be size dependent when comparing 100 nm versus ca. 6 μm sized particles. It was determined that particles composed of ammonium sulfate with succinic acid and of a mixture of chlorides typical of the marine environment show size-dependent hygroscopic behavior. Microscopic analysis of the distribution of components within the aerosol particles show that the size dependence is due to differences in the mixing state, that is, whether particles are homogeneously mixed or phase separated, for different sized particles. This morphology-dependent hygroscopicity has consequences for heterogeneous atmospheric chemistry as well as aerosol interactions with electromagnetic radiation and clouds.

  13. Forest canopy interactions with nucleation mode particles

    NASA Astrophysics Data System (ADS)

    Pryor, S. C.; Hornsby, K. E.; Novick, K. A.

    2014-07-01

    Forests play a key role in removal of particles from the atmosphere but may also significantly contribute to formation and growth of ultrafine particles. Ultrafine particle size distributions through a deciduous forest canopy indicate substantial capture of nucleation mode particles by the foliage. Concentrations decline with depth into the canopy, such that nucleation mode number concentrations at the bottom of the canopy are an average of 16% lower than those at the top. However, growth rates of nucleation mode particles (diameters 6-30 nm) are invariant with height within the canopy, which implies that the semi-volatile gases contributing to their growth are comparatively well-mixed through the canopy. Growth rates of nucleation mode particles during a meteorological drought year (2012) were substantially lower than during a meteorologically normal year with high soil water potential (2013). This may reflect suppression of actual BVOC emissions by drought and thus reduced production of condensable products (and thus particle growth) during the drought-affected vegetation season. This hypothesis is supported by evidence that growth rates during the normal year exhibit a positive correlation with emissions of biogenic volatile organic compounds (BVOC) modeled based on observed forest composition, leaf area index, temperature and PAR, but particle growth rates during the drought-affected vegetation season are not correlated with modeled BVOC emissions. These data thus provide direct evidence for the importance of canopy capture in atmospheric particle budgets and indirect evidence that drought-stress in forests may reduce BVOC emissions and limit growth of nucleation mode particles to climate-relevant sizes.

  14. Crystallization and nucleation kinetics in volcanic systems

    NASA Astrophysics Data System (ADS)

    Agostini, C.; Fortunati, A.; Carroll, M. R.; Scaillet, B.; Landi, P.

    2011-12-01

    The main objective of this experimental study is to constrain and quantitatively model the complex solidification process that transforms a magma in a solid material. Of major interest are crystal nucleation and growth driven by isothermal decompression of hydrous magmas, and comparison with results from more abundant crystal growth/nucleation data obtained in isobaric cooling experiments. This research concerns two different volcanic systems, Pantelleria (peralkaline rhyolite) and Stromboli (basalt), to better understand how crystallization kinetics can affect different magma compositions. For Stromboli volcanic system TZM apparatus has been used to perform decompression runs at Bayerisches Geoinstitut in Bayreuth (DE). As for Pantelleria composition, cooling experiments has been done using IHPV devices at ISTO of Orléans (FR), on the basis of previous phase equilibrium work (Di Carlo et al., 2010). First obtained results for Stromboli case show high rates of nucleation and crystal growth during the initial stages of crystallization which were followed by crystal growth at approximately constant number densities as equilibrium was approached. Shapes of crystals growing in melts are controlled by the kinetics of crystallization and may provide information about the degree of undercooling experienced by batches of magma en route to the surface (Lofgren, 1980). The study of crystallization kinetics through phases growth rates (Couch et al., 2003), together with the calculation of nucleation density and nucleation rates (Hammer et al., 1999) represent a step toward the estimation of the time scales of magmatic processes in volcanic systems and the interpretation of shallow magmatic processes. The results for Stromboli suggest average crystal growth timescales on the order of weeks, but this is complicated by clear evidence that some crystals have experienced repeated periods of both dissolution and growth (Landi et al., 2004).

  15. Deciphering the energetic barriers to calcium carbonate nucleation as a continuum of competing interfacial forces between polysaccharide chemistry and ionic strength

    NASA Astrophysics Data System (ADS)

    Giuffre, A. J.; De Yoreo, J. J.; Dove, P. M.

    2013-12-01

    Calcified skeletons are produced within complex assemblages of proteins and polysaccharides whose roles in mineralization are not well understood. Researchers have long-postulated that living organisms utilize organic matrices to actively guide the formation and growth of crystalline structures. The timing and placement of these features are most easily controlled during the nucleation stage. Our recent kinetic study of heterogeneous calcite nucleation found the energy barrier to formation is regulated by a systematic relationship to the competing interfacial energies between the substrate, crystal, and liquid (Giuffre et al., 2013). Chitosan presents a low energy barrier to nucleation because its near-neutral charge favors formation of a substrate-crystal interface, thus reducing substrate interactions with water. Progressively higher barriers are measured for negatively charged alginates and heparin that favor contact with the solution over the formation of new substrate-crystal interfaces. These results showed calcite nucleation is regulated by substrate-crystal interactions but could not quantify the larger continuum of competing forces that must regulate calcite nucleation. To determine these relationships, we estimate the energy barriers to nucleation and crystal-liquid interfacial energies by measuring the kinetics of homogeneous calcite nucleation in NaCl solutions at ionic strengths that extend to seawater salinity (0.6 M). The data show that solutions of greater ionic strength produce faster nucleation rates, smaller crystal-liquid interfacial energies, and lower barriers to nucleation, which concurs with recent theoretical and experimental findings that background electrolytes promote ion desolvation during nucleation. By applying this relationship to heterogeneous nucleation on chitosan and heparin in future work, we will quantify the relative contributions of substrate-crystal-liquid interfacial energies. The findings reiterate a directing role for PS

  16. 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.

  17. Measuring Quality Factors From Multicomponent Reflection Seismic Data and its Significance for Lithology and Fluid Type Prediction

    NASA Astrophysics Data System (ADS)

    Ortiz-Osornio, M.; Calder¢n-Macias, C.; Ramos-Matinez, J.

    2003-12-01

    Relationships among shear and compressional wave velocities (VP and VS) and quality factors (QP and QS) for predicting lithology and fluid content, have been previously studied and proposed by some researchers. Thus, for example, VP/VS has been used as a lithology indicator for sandstone, shale and limestone. Likewise, QP/QS has been related to fluid content, mainly to discriminate oil, brine, and gas saturation. The velocities and quality factors for both P and S waves can be obtained from multicomponent reflection seismic data. Multicomponent data are most commonly recorded from compressional sources in the oil industry. Converted P to S waves or PS waves are generally measured in the radial component. In cases where there are heterogeneity and/or azimuthal anisotropy, the transverse component is also considered. Processing of the converted wave results in a PS image and an interpreted converted-wave velocity field (VPS). Likewise, it is possible to estimate a converted-wave quality factor (QPS) field. The converted-wave quality factor can also be used as a lithology and fluid content indicator since this parameter depends on VP/VS and QP/QS ratios. Crossplots involving QPS obtained from previously published laboratory measurements of P- and S-wave velocities and quality factors, reveal the significance of estimating QPS from multicomponent seismic data. An important advantage of using QPS as a lithology indicator is that it can be mapped directly from multicomponent surface seismic data. In this work we present a new methodology to obtain QPS. In the pure mode case, approaches for estimating Q are well known. However for converted-waves, some simplifying assumptions need to be made due to the propagation characteristics of the converted P- to S-wavepath.

  18. Coulombic effects and multicomponent ionic dispersion during transport of electrolytes in porous media

    NASA Astrophysics Data System (ADS)

    Muniruzzaman, Muhammad; Haberer, Christina; Grathwohl, Peter; Rolle, Massimo

    2014-05-01

    We study the influence of Coulombic effects on transport of charged species in saturated porous media in advection-dominated flow regimes. We focus on transverse hydrodynamic dispersion and we performed quasi two-dimensional flow-through experiments in homogeneous and spatially variable flow fields to investigate transport of dilute electrolyte solutions. The experiments were conducted at flow velocities (1.0, 1.5 and 6 m/day) where advection is the dominant mass transfer process. High-resolution measurements at the outlet were performed to determine the concentration of different cations and anions. In order to interpret the laboratory experiments we develop a two-dimensional numerical model. The adopted modeling approach is based on a multicomponent formulation, charge conservation, and the accurate description of local transverse dispersion. The latter entails a non-linear dependence of the transverse dispersion coefficient on the flow velocity as well as a compound-specific dependence on the molecular diffusion of the transported solutes. The model was benchmarked by comparing the results of the 2D steady-state multicomponent simulations with 1D transient results of PHREEQC in homogeneous scenarios, and it was successively used to quantitatively evaluate the experimental results in both homogeneous and heterogeneous porous media. Our experimental and modeling results show that Coulombic cross-coupling of dispersive fluxes of charged species in porous media significantly affects the lateral displacement of charged ions in both homogeneous and heterogeneous flow-through systems. Such effects are remarkable not only in diffusion-dominated but also in advection-dominated flow regimes.

  19. Mineral Selection for Multicomponent Equilibrium Geothermometry

    DOE PAGES

    Plamer, C. D.; Ohly, S. R.; Smith, R. W.; ...

    2015-04-01

    Multicomponent geothermometry requires knowledge of the mineral phases in the reservoir with which the geothermal fluids may be equilibrated. These minerals phases are most often alteration products rather than primary minerals. We have reviewed the literature on geothermal systems representing most major geologic environments typically associated with geothermal activity and identified potential alteration products in various environments. We have included this information in RTEst, a code we have developed to estimate reservoir conditions (temperature, CO2 fugacity) from the geochemistry of near-surface geothermal waters. The information has been included in RTEst through the addition of filters that decrease the potential numbermore » of minerals from all possibilities based on the basis species to those that are more relevant to the particular conditions in which the user is interested. The three groups of filters include host rock type (tholeiitic, calc-alkaline, silicic, siliciclastic, carbonate), water type (acidic, neutral), and the temperature range over which the alteration minerals were formed (low, medium, high). The user-chosen mineral assemblage is checked to make sure that it does not violate the Gibbs phase rule. The user can select one of three mineral saturation weighting schemes that decrease the chance the optimization from being skewed by reaction stoichiometry or analytical uncertainty.« less

  20. Mineral Selection for Multicomponent Equilibrium Geothermometry

    SciTech Connect

    Plamer, C. D.; Ohly, S. R.; Smith, R. W.; Neupane, G.; McLing, T.; Mattson, E.

    2015-04-01

    Multicomponent geothermometry requires knowledge of the mineral phases in the reservoir with which the geothermal fluids may be equilibrated. These minerals phases are most often alteration products rather than primary minerals. We have reviewed the literature on geothermal systems representing most major geologic environments typically associated with geothermal activity and identified potential alteration products in various environments. We have included this information in RTEst, a code we have developed to estimate reservoir conditions (temperature, CO2 fugacity) from the geochemistry of near-surface geothermal waters. The information has been included in RTEst through the addition of filters that decrease the potential number of minerals from all possibilities based on the basis species to those that are more relevant to the particular conditions in which the user is interested. The three groups of filters include host rock type (tholeiitic, calc-alkaline, silicic, siliciclastic, carbonate), water type (acidic, neutral), and the temperature range over which the alteration minerals were formed (low, medium, high). The user-chosen mineral assemblage is checked to make sure that it does not violate the Gibbs phase rule. The user can select one of three mineral saturation weighting schemes that decrease the chance the optimization from being skewed by reaction stoichiometry or analytical uncertainty.

  1. An evaporation model of multicomponent solution drops

    NASA Astrophysics Data System (ADS)

    Sartori, Silvana; Liñán, Amable; Lasheras, Juan C.

    2010-11-01

    Solutions of polymers are widely used in the pharmaceutical industry as tablets coatings. These allow controlling the rate at which the drug is delivered, taste or appearance. The coating is performed by spraying and drying the tablets at moderate temperatures. The wetting of the coating solution on the pill's surface depends on the droplet Webber and Re numbers, angle of impact and on the rheological properties of the droplet. We present a model for the evaporation of multicomponent solutions droplets in a hot air environment with temperatures substantially lower than the boiling temperature of the solvent. As the liquid vaporizes from the surface the fluid in the drop increases in concentration, until reaching its saturation point. After saturation, precipitation occurs uniformly within the drop. As the surface regresses, a compacting front formed by the precipitate at its maximum packing density advances into the drop, while the solute continues precipitating uniformly. This porous shell grows fast due to the double effect of surface regression and precipitation. The evaporation rate is determined by the rates at which heat is transported to the droplet surface and at which liquid vapor diffuses away from it. When the drop is fully compacted, the evaporation is drastically reduced.

  2. Impact of multicomponent ionic transport on pH fronts propagation in saturated porous media

    NASA Astrophysics Data System (ADS)

    Muniruzzaman, Muhammad; Rolle, Massimo

    2016-04-01

    the transported ions in the flow-through system. The results of purely forward simulations show a very good agreement with the high-resolution measurements performed at the outlet of the flow-through setup and illustrate the importance of charge effects on pH fronts propagation in porous media. [1] Giambalvo, E. R., C. I. Steefel, A. T. Fisher, N. D. Rosenberg, and C. G. Wheat (2002), Effect of fluid-sediment reaction on hydrothermal fluxes of major elements, eastern flank of the Juan de Fuca Ridge, Geochim. Cosmochim. Acta, 66, 1739-1757. [2] Appelo, C. A. J., and P. Wersin (2007), Multicomponent diffusion modeling in clay systems with application to the diffusion of tritium, iodide, and sodium in opalinus clay, Environ. Sci. Technol., 41, 5002-5007. [3] Rolle, M., M. Muniruzzaman, C. M. Haberer, and P. Grathwohl (2013), Coulombic effects in advection-dominated transport of electrolytes in porous media: Multicomponent ionic dispersion, Geochim. Cosmochim. Acta, 120, 195-205. [4] Muniruzzaman, M., C. M. Haberer, P. Grathwohl, and M. Rolle (2014), Multicomponent ionic dispersion during transport of electrolytes in heterogeneous porous media: Experiments and model-based interpretation, Geochim. Cosmochim. Acta, 141, 656-669. [5] Rolle, M., G. Chiogna, D. L. Hochstetler, and P. K. Kitanidis (2013), On the importance of diffusion and compound-specific mixing for groundwater transport: An investigation from pore to field scale, J. Contam. Hydrol., 153, 51-68.

  3. Nucleate pool boiling of hydrocarbon mixtures

    SciTech Connect

    Sardesai, R.G.; Palen, J.W.; Thome, J.

    1986-01-01

    The Schlunder method can be correctly used to predict boiling heat transfer coefficient of multicomponent hydrocarbon mixtures. The method was tested against experimental mixtures containing up to five components. The Stephan-Abdelsalam correlation can be used to calculate a ''pseudo-single component'' boiling heat transfer coefficient for a mixture using weighted properties. The effective temperature driving force term and the high mass flux correction term in the Schlunder formulation are empirically adjusted to improve the accuracy of prediction. Predictions of the Schlunder method are sensitive to the VLE calculations. The UNIFAC method is used in this study for reasons discussed in the paper.

  4. Nucleation theorems, the statistical mechanics of molecular clusters, and a revision of classical nucleation theory

    NASA Astrophysics Data System (ADS)

    Ford, I. J.

    1997-11-01

    The nucleation theorems relate the temperature and supersaturation dependence of the rate of nucleation of droplets from a metastable vapor phase to properties of the critical molecular cluster, the size that is approximately equally likely to grow or decay. They are derived here using a combination of statistical mechanics and cluster population dynamics, using an arbitrary model cluster definition. The theorems are employed to test the validity of the classical theory of homogeneous nucleation and its ``internally consistent'' form. It is found that the properties of the critical cluster for these models are incorrect, and it emerges that this occurs because the classical theory employs the free energy of a fixed droplet, rather than one free to take any position in space. Thus a term representing positional, or mixing, entropy is missing from the cluster free energy. A revised model is proposed, based on the capillarity approximation but with such a term included, and it is shown that it is fully consistent with the nucleation theorems. The model increases classical rates by factors of approximately 104-106. Other nucleation models should be tested for internal consistency using the same methods. Finally, the nucleation theorems are used to extract the excess internal energies of molecular clusters from experimental data for several substances.

  5. Observations of premonitory acoustic emission and slip nucleation during a stick slip experiment in smooth faulted Westerly granite

    USGS Publications Warehouse

    Thompson, B.D.; Young, R.P.; Lockner, D.A.

    2005-01-01

    To investigate laboratory earthquakes, stick-slip events were induced on a saw-cut Westerly granite sample by triaxial loading at 150 MPa confining pressure. Acoustic emissions (AE) were monitored using an innovative continuous waveform recorder. The first motion of each stick slip was recorded as a large-amplitude AE signal. These events source locate onto the saw-cut fault plane, implying that they represent the nucleation sites of the dynamic failure stick-slip events. The precise location of nucleation varied between events and was probably controlled by heterogeneity of stress or surface conditions on the fault. The initial nucleation diameter of each dynamic instability was inferred to be less than 3 mm. A small number of AE were recorded prior to each macro slip event. For the second and third slip events, premonitory AE source mechanisms mimic the large scale fault plane geometry. Copyright 2005 by the American Geophysical Union.

  6. Re-evaluating the Frankfurt isothermal static diffusion chamber for ice nucleation

    NASA Astrophysics Data System (ADS)

    Schrod, J.; Danielczok, A.; Weber, D.; Ebert, M.; Thomson, E. S.; Bingemer, H. G.

    2015-12-01

    Recently significant advances have been made in the collection, detection, and characterization of ice nucleating particles (INP). Ice nuclei are particles that facilitate the heterogeneous formation of ice within the atmospheric aerosol by lowering the free energy barrier to spontaneous nucleation and growth of ice from atmospheric water and/or vapor. The Frankfurt isostatic diffusion chamber (FRIDGE) is an INP collection and offline detection system that has become widely deployed and shows additional potential for ambient measurements. Since its initial development FRIDGE has gone through several iterations and improvements. Here we describe improvements that have been made in the collection and analysis techniques. We detail the uncertainties inherent in the measurement method, and suggest a systematic method of error analysis for FRIDGE measurements. Thus what is presented herein should serve as a foundation for the dissemination of all current and future measurements using FRIDGE instrumentation.

  7. Micromechanisms of Twin Nucleation in TiAl: Effects of Neutron Irradiation

    SciTech Connect

    Hishinuma, A.; Yoo, M.H.

    1999-01-28

    The so-called radiation-induced ductility (RID) reported in neutron-irradiated 47at%Al alloys is attributed to the formation of effective twin embryos in the presence of interstitial-type Frank loops in {gamma}-TiAl and the subsequent nucleation and growth of microtwins during post-irradiation tensile deformation. The stability of large faulted Frank loops is explained in terms of the repulsive interaction between Shockley and Frank partials. Interaction of only six ordinary slip dislocations with a Frank loop can facilitate a pole mechanism for twin formation to work. The relative ease of heterogeneous twin nucleation is the reason for the RID and the lack of changes in yield strength and work hardening.

  8. Nucleation Chemical Physics: From Vapor Phase Clusters to Crystals in Solution

    SciTech Connect

    Kathmann, Shawn M.

    2007-08-03

    Both vapor-phase clusters and condensed-phase crystals are important in a wide variety of fundamental and applied problems in chemical physics. Favorable fluctuations in a supersaturated phase generate clusters of the new phase – exactly how one defines these new clusters as distinct from the mother phase represents a continuing challenge in molecular theories of nucleation. These incipient clusters can form homogeneously within the mother phase or heterogeneously on seeds, dust, impurities, ions, or others stability-inducing atomic/molecular structures (e.g., steps, edges, vacancies, etc.). Upon reaching a critical size the clusters may grow to macroscopic dimensions if enough nucleating material is present in surrounding environment or until relaxation processes dominate bringing the phase transformation to completion. This work was supported by the Chemical and Material Sciences Division, Office of Basic Energy Sciences, Department of Energy. The Pacific Northwest National Laboratory is operated by Battelle for the US Department of Energy.

  9. Multicomponent Protein Cage Architectures for Photocatalysis

    SciTech Connect

    Douglas, Trevor

    2014-11-21

    The central focus of the work performed under this award has been to develop the bacteriophage P22 viral capsid as a vehicle for the encapsulation of catalyticaly active cargo materials and study their utility towards economic energy harvesting systems. We have demonstrated that the capsid of the bacteriophage P22 can be used to genetically program the assembly and encapsulation of a range of inorganic nanoparticles and protein cargoes. The P22 capsid uses a scaffold protein (SP) to direct the assembly of its coat protein (CP) into icosahedral capsids. By creating a genetic fusion of a desired cargo enzyme or a small peptide that can act as a nucleation site for subsequent NP growth, we have demonstrated the co-assembly of these SP-fusions and CP into stable “nano-reactors”. The cargo is sequestered inside the engineered capsid and can either be used directly as a nanocatalyst or for the nucleation and growth of inorganic or organic nanoparticles or polymers. The synthetic cargos (NP or polymers) were shown to have photocatalytic activity. The time dependent photophysics of a select few of these systems were studied to determine the underlying mechanisms and efficiency of light harversting. Enzyme cargos encapsulated within the P22 were thermally activated catalysts and their kinetic behavior was characterized. During the course of this work we have demonstrated that the method is a robust means to harness biology for materials applications and have initiated work into assembling the P22 nanoreactors into hierarchically ordered materials. The successful implementation of the work performed under this DOE grant provides us with a great deal of knowledge and a library of components to go forward towards the development of bioinspired catalytic materials for energy harvesting.

  10. Direct Numerical Simulation of Transitional Multicomponent-Species Gaseous and Multicomponent-Liquid Drop-Laden Mixing

    NASA Technical Reports Server (NTRS)

    Selle, Laurent C.; Bellan, Josette

    2006-01-01

    A model of multicomponent-liquid (MC-liquid) drop evaporation in a three-dimensional mixing layer is here exercised at larger Reynolds numbers than in a previous study, and transitional states are obtained. The gas phase is followed in an Eulerian frame and the multitude of drops is described in a Lagrangian frame. Complete coupling between phases is included with source terms in the gas conservation equations accounting for the drop/flow interaction in terms of drop drag, drop heating and species evaporation. The liquid composition, initially specified as a single-Gamma (SG) probability distribution function (PDF) depending on the molar mass is allowed to evolve into a linear combination of two SGPDFs, called the double-Gamma PDF (DGPDF). The compositions of liquid and vapor emanating from the drops are calculated through four moments of the DGPDFs, which are drop-specific and location-specific, respectively. The mixing layer is initially excited to promote the double pairing of its four initial spanwise vortices into an ultimate vortex in which small scales proliferate. Simulations are performed for four liquids of different compositions and the effect of the initial mass loading and initial free-stream gas temperature are explored. For reference, Simulations are also performed for gaseous multicomponent mixing layers for which the effect of Reynolds number is investigated. The results encompass examination of the global layer characteristics, flow visualizations and homogeneous-plane statistics at transition. Comparisons are performed with previous pre-transitional MC-liquid simulations and with transitional single-component (SC) liquid studies. It is found that MCC flows at transition, the classical energy cascade is of similar strength, but that the smallest scales contain orders of magnitude less energy than SC flows, which is confirmed by the larger viscous dissipation in the former case. Contrasting to pre-transitional MC flows, the vorticity and drop

  11. Surface Hydrophilicity and Functional Group-Driven Iron(III) Hydroxide Nucleation on Organic-Coated Substrates in Aqueous Environments

    NASA Astrophysics Data System (ADS)

    Ray, J.; Lee, B.; Baltrusaitis, J.; Jun, Y.

    2012-12-01

    Homogeneous and heterogeneous iron hydroxide nanoparticle nucleation can occur continuously in both natural and complex aqueous systems. Iron oxide nanoparticles can act as sinks and/or carriers for heavy metal contaminants; therefore, it is important to develop a better understanding of factors affecting their formation. Organic coatings are ubiquitous in aqueous environments where they can exist on mineral surfaces (e.g., biofilm), as nanoparticle surface coatings (e.g., natural organic matter), or be introduced as coagulants in water treatment systems. These surface coatings could influence the formation of iron oxide nanoparticles and thus, the mobility of aqueous contaminants. Therefore, to better understand the fate and transport of contaminants in complex aqueous environments, we need more accurate information about mechanisms governing heterogeneous and homogeneous nucleation and growth of iron(III) hydroxide nanoparticles in the presence of organic surface coatings. In this work, we used a unique measurement technique allowing for simultaneous small-angle X-ray scattering (SAXS) and grazing incidence (GISAXS) analysis to monitor nanoparticle nucleation in solution and at substrate surfaces. Clean quartz, and polyaspartate- and alginate-coated substrates were chosen as model substrates to represent mineral coatings, engineered organic coatings and natural organic coatings. Polyaspartate was determined to be the most negatively charged substrate and quartz to be the least negatively charged substrate; however, after 2 h of reaction, the total nanoparticle volume calculations—determined from GISAXS—indicate that precipitation of positively-charged iron(III) hydroxide nanoparticles is 10 times higher on the quartz substrate than on the polyaspartate substrate. This implies that electrostatics do not govern iron(III) hydroxide nucleation. Furthermore, homogeneous nucleation approximately 250 μm above the substrate surface was highest in the presence of the

  12. Nucleation and growth of combustion flame deposited diamond coatings on silicon nitride

    NASA Astrophysics Data System (ADS)

    Rozbicki, Robert T.

    An investigation has been performed on the kinetics of diamond nucleation on silicon nitride (Si3N4) based materials during oxy-acetylene combustion flame chemical vapor deposition. The deposits were characterized using scanning electron microscopy (SEM), x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM) techniques. Kinetic parameters of the nucleation process, such as nucleation rate (I), period of initial nuclei formation (tng), and maximum nucleation density (Nd) were experimentally determined. It was concluded that at low temperatures (Ts < 875°C), the observed nucleation density is due to epitaxial or pseudo-epitaxial growth on residual particles on the substrate surface. At higher temperatures (Ts > 875°C), heterogeneous nucleation of diamond on Si3N4 occurs with an apparent activation energy ( Eahet ) of ˜ 18 kcal/mol. From an Arrhenius plot of particle growth rate, the activation energy (Ea) for diamond growth was calculated to be ˜ 9 kcal/mol. These results suggest that the energy barrier associated with the heterogeneous nucleation process ( Eahet > Ea) may in fact be responsible for the observed low nucleation densities on Si3N4 substrates. Consequently, nucleation density on Si3N4 is limited by the concentration of available sites for nuclei formation. As surface diffusion to those sites was determined to be negligible, growth of stable nuclei occurs via direct impingement of gas phase species. Based on these conclusions, a multistage deposition technique was developed to deposit continuous diamond coatings on untreated Si3N4 substrates. This two stage technique consisted of (i) an in situ flame pretreatment of the substrate to enhance nucleation through the formation of SiC and (ii) subsequent growth on the flame pretreated surface under optimized parameters. Using a previously developed compression test for brittle coating/substrate systems, the adhesion of multistage deposited coatings was compared

  13. Monte Carlo tests of nucleation concepts in the lattice gas model

    NASA Astrophysics Data System (ADS)

    Schmitz, Fabian; Virnau, Peter; Binder, Kurt

    2013-05-01

    The conventional theory of homogeneous and heterogeneous nucleation in a supersaturated vapor is tested by Monte Carlo simulations of the lattice gas (Ising) model with nearest-neighbor attractive interactions on the simple cubic lattice. The theory considers the nucleation process as a slow (quasistatic) cluster (droplet) growth over a free energy barrier ΔF*, constructed in terms of a balance of surface and bulk term of a critical droplet of radius R*, implying that the rates of droplet growth and shrinking essentially balance each other for droplet radius R=R*. For heterogeneous nucleation at surfaces, the barrier is reduced by a factor depending on the contact angle. Using the definition of physical clusters based on the Fortuin-Kasteleyn mapping, the time dependence of the cluster size distribution is studied for quenching experiments in the kinetic Ising model and the cluster size ℓ* where the cluster growth rate changes sign is estimated. These studies of nucleation kinetics are compared to studies where the relation between cluster size and supersaturation is estimated from equilibrium simulations of phase coexistence between droplet and vapor in the canonical ensemble. The chemical potential is estimated from a lattice version of the Widom particle insertion method. For large droplets it is shown that the physical clusters have a volume consistent with the estimates from the lever rule. Geometrical clusters (defined such that each site belonging to the cluster is occupied and has at least one occupied neighbor site) yield valid results only for temperatures less than 60% of the critical temperature, where the cluster shape is nonspherical. We show how the chemical potential can be used to numerically estimate ΔF* also for nonspherical cluster shapes.

  14. Immersion Condensation on Oil-Infused Heterogeneous Surfaces for Enhanced Heat Transfer

    PubMed Central

    Xiao, Rong; Miljkovic, Nenad; Enright, Ryan; Wang, Evelyn N.

    2013-01-01

    Enhancing condensation heat transfer is important for broad applications from power generation to water harvesting systems. Significant efforts have focused on easy removal of the condensate, yet the other desired properties of low contact angles and high nucleation densities for high heat transfer performance have been typically neglected. In this work, we demonstrate immersion condensation on oil-infused micro and nanostructured surfaces with heterogeneous coatings, where water droplets nucleate immersed within the oil. The combination of surface energy heterogeneity, reduced oil-water interfacial energy, and surface structuring enabled drastically increased nucleation densities while maintaining easy condensate removal and low contact angles. Accordingly, on oil-infused heterogeneous nanostructured copper oxide surfaces, we demonstrated approximately 100% increase in heat transfer coefficient compared to state-of-the-art dropwise condensation surfaces in the presence of non-condensable gases. This work offers a distinct approach utilizing surface chemistry and structuring together with liquid-infusion for enhanced condensation heat transfer. PMID:23759735

  15. Influence of Phosphorus on the Nucleation of Eutectic Silicon in Al-Si Alloys

    NASA Astrophysics Data System (ADS)

    Ludwig, Thomas Hartmut; Schaffer, Paul Louis; Arnberg, Lars

    2013-12-01

    The role of phosphorus (P) in the heterogeneous nucleation of eutectic silicon (Si) and the evolution of eutectic grains in hypoeutectic aluminum-silicon alloys were investigated. Systematic additions of P in the range of 0.5 to 20 ppm to Al-7 wt pct Si alloys of different purities have shown that the morphology of the eutectic Si changes from a fine plate- to a coarse flake-like structure. The growth of eutectic grains was investigated by interrupting the eutectic reaction by quenching experiments. Moreover, the macroscopic growth mode of the eutectic grains was characterized by electron backscatter diffraction. An increase in P concentration from 2 to 3 ppm resulted in a transition of the macroscopic growth mode of the Al-Si eutectic in high purity alloys from growth with a planar front with a strong dependence of the thermal gradient, to nucleation in the vicinity of the primary Al dendrites and subsequent growth of distinct eutectic grains. It is suggested that AlP particles are the key impurities acting as potential nucleation sites for eutectic Si. This is further substantiated as with increasing P concentration nucleation and growth of the Al-Si occurred at higher temperatures close the equilibrium Al-Si eutectic solidification temperature at 850 K (577 °C). In addition, the recalescence undercooling Δ T R,eu was reduced from 4.5 K (0.5 ppm P) to 1.5 K (20 ppm P) in high purity alloys. This was accompanied by a drastic increase of the nucleation rate of the eutectic grains.

  16. Pre-activation of ice-nucleating particles by the pore condensation and freezing mechanism

    NASA Astrophysics Data System (ADS)

    Wagner, Robert; Kiselev, Alexei; Möhler, Ottmar; Saathoff, Harald; Steinke, Isabelle

    2016-02-01

    In spite of the resurgence in ice nucleation research a comparatively small number of studies deal with the phenomenon of pre-activation in heterogeneous ice nucleation. Fifty years ago, it was shown that various mineral dust and volcanic ash particles can be pre-activated to become nuclei for ice crystal formation even at temperatures as high as 270-271 K. Pre-activation was achieved under ice-subsaturated conditions without any preceding macroscopic ice growth by just temporarily cooling the particles to temperatures below 228 K. A two-step mechanism involving capillary condensation of supercooled water and subsequent homogeneous freezing was proposed to account for the particles' enhanced ice nucleation ability at high temperatures. This work reinvestigates the efficiency of the proposed pre-activation mechanism in temperature-cycling experiments performed in a large cloud chamber with suspended particles. We find the efficiency to be highest for the clay mineral illite as well as for highly porous materials like zeolite and diatomaceous earth, whereas most aerosols generated from desert dust surface samples did not reveal a measurable pre-activation ability. The pre-activation efficiency is linked to particle pores in a certain size range. As estimated by model calculations, only pores with diameters between about 5 and 8 nm contribute to pre-activation under ice-subsaturated conditions. This range is set by a combination of requirements from the negative Kelvin effect for condensation and a critical size of ice embryos for ice nucleation and melting. In contrast to the early study, pre-activation is only observed for temperatures below 260 K. Above that threshold, the particles' improved ice nucleation ability disappears due to the melting of ice in the pores.

  17. The mechanism of morphogenesis in a phase-separating concentrated multicomponent alloy

    NASA Astrophysics Data System (ADS)

    Mao, Zugang; Sudbrack, Chantal K.; Yoon, Kevin E.; Martin, Georges; Seidman, David N.

    2007-03-01

    What determines the morphology of a decomposing alloy? Besides the well-established effect of the nucleation barrier, we demonstrate that, in a concentrated multicomponent Ni(Al,Cr) alloy, the details of the diffusion mechanism strongly affect the kinetic pathway of precipitation. Our argument is based on the combined use of atomic-scale observations, using three-dimensional atom-probe tomography (3D APT), lattice kinetic Monte Carlo simulations and the theory of diffusion. By an optimized choice of thermodynamic and kinetic parameters, we first reproduce the 3D APT observations, in particular the early-stage transient occurrence of coagulated precipitates. We then modify the kinetic correlations among the atomic fluxes in the simulation, without altering the thermodynamic driving force for phase separation, by changing the vacancy-solute interactions, resulting in a suppression of coagulation. Such changes can only be quantitatively accounted for with non-zero values for the off-diagonal terms of the Onsager matrix, at variance with classical models.

  18. Multicomponent seismic noise attenuation with multivariate order statistic filters

    NASA Astrophysics Data System (ADS)

    Wang, Chao; Wang, Yun; Wang, Xiaokai; Xun, Chao

    2016-10-01

    The vector relationship between multicomponent seismic data is highly important for multicomponent processing and interpretation, but this vector relationship could be damaged when each component is processed individually. To overcome the drawback of standard component-by-component filtering, multivariate order statistic filters are introduced and extended to attenuate the noise of multicomponent seismic data by treating such dataset as a vector wavefield rather than a set of scalar fields. According to the characteristics of seismic signals, we implement this type of multivariate filtering along local events. First, the optimal local events are recognized according to the similarity between the vector signals which are windowed from neighbouring seismic traces with a sliding time window along each trial trajectory. An efficient strategy is used to reduce the computational cost of similarity measurement for vector signals. Next, one vector sample each from the neighbouring traces are extracted along the optimal local event as the input data for a multivariate filter. Different multivariate filters are optimal for different noise. The multichannel modified trimmed mean (MTM) filter, as one of the multivariate order statistic filters, is applied to synthetic and field multicomponent seismic data to test its performance for attenuating white Gaussian noise. The results indicate that the multichannel MTM filter can attenuate noise while preserving the relative amplitude information of multicomponent seismic data more effectively than a single-channel filter.

  19. Effectiveness of multicomponent interventions in primary healthcare settings to promote continuous smoking cessation in adults: a systematic review

    PubMed Central

    Martín Cantera, Carlos; Puigdomènech, Elisa; Ballvé, Jose Luis; Arias, Olga Lucía; Clemente, Lourdes; Casas, Ramon; Roig, Lydia; Pérez-Tortosa, Santiago; Díaz-Gete, Laura; Granollers, Sílvia

    2015-01-01

    Objective The objective of the present review is to evaluate multicomponent/complex primary care (PC) interventions for their effectiveness in continuous smoking abstinence by adult smokers. Design A systematic review of randomised and non-randomised controlled trials was undertaken. Eligibility criteria for included studies Selected studies met the following criteria: evaluated effects of a multicomponent/complex intervention (with 2 or more intervention components) in achieving at least 6-month abstinence in adult smokers who visited a PC, biochemical confirmation of abstinence, intention-to-treat analysis and results published in English/Spanish. Methods We followed PRISMA statement to report the review. We searched the following data sources: MEDLINE, Web of Science, Scopus (from inception to February 2014), 3 key journals and a tobacco research bulletin. The Scottish Intercollegiate Guidelines Network checklists were used to evaluate methodological quality. Data selection, evaluation and extraction were done independently, using a paired review approach. Owing to the heterogeneity of interventions in the studies included, a meta-analysis was not conducted. Results Of 1147 references identified, 9 studies were selected (10 204 participants, up to 48 months of follow-up, acceptable methodological quality). Methodologies used were mainly individual or group sessions, telephone conversations, brochures or quit-smoking kits, medications and economic incentives for doctors and no-cost medications for smokers. Complex interventions achieved long-term continuous abstinence ranging from 7% to 40%. Behavioural interventions were effective and had a dose–response effect. Both nicotine replacement and bupropion therapy were safe and effective, with no observed differences. Conclusions Multicomponent/complex interventions in PC are effective and safe, appearing to achieve greater long-term continuous smoking cessation than usual care and counselling alone. Selected

  20. Determining Oxidation Rates in Multi-component Organic Aerosols

    NASA Astrophysics Data System (ADS)

    Sage, A. M.; Weitkamp, E. A.; Huff Hartz, K. E.; Robinson, A. L.; Donahue, N. M.

    2006-12-01

    Aerosol composition influences the kinetics of condensed-phase organic species, making extrapolation of rate constants from single-component systems to atmospherically-relevant mixtures difficult. Using a mixed-phase relative rate constants approach, we have overcome this difficulty, obtaining heterogeneous oxidation rate constants for each species in several multi-component organic mixtures. We have also derived a compound- specific uptake coefficient that relates these rate constants to previous uptake measurements. In the ozonolysis of model meat-cooking mixtures, we observe significant decay of saturated and unsaturated acids and sterols. By relating the observed decomposition of condensed-phase species to that of gas-phase standards, we track the evolution of effective rate constants for oleic acid and palmitoleic acid oxidation as the aerosol is chemically processed. Each decreases by nearly a factor of ten over the course of an experiment. Rate constants also depend strongly on aerosol composition, changing by more than an order of magnitude with increasing mixture complexity. To compare these results with previous results, we have derived a compound-specific uptake coefficient (γi' for condensed-phase species i), which describes the kinetics of reactive uptake in mixtures and can be meaningfully related to the traditional uptake coefficient. We express uptake in terms of the concentrations of condensed-phase species, and to do so accurately, we use alkanoic acids to correct the decay of reactive alkenoic acids for secondary chemistry. This correction is incorporated into the definition of γi', and in terms of γi', the standard uptake coefficient can be written as: γ=∑χiγi', where χi is the mass fraction of species i and the summation is over all oxidized species. By using condensed-phase decay to calculate the uptake, we have apportioned reactive uptake among responsible species. This provides information not only about the potential of a particle

  1. Expanding Conventional Seismic Stratigrphy into the Multicomponent Seismic Domain

    SciTech Connect

    Innocent Aluka

    2008-08-31

    Multicomponent seismic data are composed of three independent vector-based seismic wave modes. These wave modes are, compressional mode (P), and shear modes SV and SH. The three modes are generated using three orthogonal source-displacement vectors and then recorded using three orthogonal vector sensors. The components travel through the earth at differing velocities and directions. The velocities of SH and SV as they travel through the subsurface differ by only a few percent, but the velocities of SV and SH (Vs) are appreciably lower than the P-wave velocity (Vp). The velocity ratio Vp/Vs varies by an order of magnitude in the earth from a value of 15 to 1.5 depending on the degree of sedimentary lithification. The data used in this study were acquired by nine-component (9C) vertical seismic profile (VSP), using three orthogonal vector sources. The 9C vertical seismic profile is capable of generating P-wave mode and the fundamental S-wave mode (SH-SH and SV-SV) directly at the source station and permits the basic components of elastic wavefield (P, SH-SH and SV-SV) to be separated from one another for the purposes of imaging. Analysis and interpretations of data from the study area show that incident full-elastic seismic wavefield is capable of reflecting four different wave modes, P, SH , SV and C which can be utilized to fully understand the architecture and heterogeneities of geologic sequences. The conventional seismic stratigraphy utilizes only reflected P-wave modes. The notation SH mode is the same as SH-SH; SV mode means SV-SV and C mode which is a converted shear wave is a special SV mode and is the same as P-SV. These four wave modes image unique geologic stratigraphy and facies and at the same time reflect independent stratal surfaces because of the unique orientation of their particle-displacement vectors. As a result of the distinct orientation of individual mode's particle-displacement vector, one mode may react to a critical subsurface sequence more

  2. Experimental and theoretical investigation of nucleation and growth of atmospheric aerosols

    NASA Astrophysics Data System (ADS)

    Zhao, Jun

    Aerosol particles have profound impacts on human health, atmospheric radiation, and cloud microphysics and these impacts are strongly dependent on particle sizes. However, formation and growth of atmospheric particles are currently not well understood. In this work, laboratory and theoretical studies have been performed to investigate the formation and growth of atmospheric particles. The first two parts of the dissertation are a laboratory investigation of new particle formation and growth, and a theoretical study of atmospheric molecular complexes and clusters. The nucleation rate was considerably enhanced in the presence of cis-pinonic acid and ammonia. The composition of the critical cluster was estimated from the dependence of the nucleation rate on the precursor concentration and the time evolution of the clusters was then simulated using molecular dynamic simulations. Results from quantum chemical calculations and quantum theory of atoms in molecules (QTAIM) reveal that formation of strong hydrogen bonding between an organic acid and sulfuric acid is likely responsible for a reduction of the nucleation barrier by modifying the hydrophobic properties of the organic acid and allowing further addition of hydrophilic species (e.g., H2SO4, H2O, and possibly NH 3) to the hydrophilic side of the clusters. This promotes growth of the nascent cluster to overcome the nucleation barrier and thus enhances the nucleation in the atmosphere. The last part of this dissertation is the laboratory investigation of heterogeneous interactions of atmospheric carbonyls with sulfuric acid. Direct measurement has been performed to investigate the heterogeneous uptake of atmospheric carbonyls on sulfuric acid. Important parameters have been obtained from the time-dependent or time-independent uptake profiles. The results indicated that the acid-catalyzed reactions of larger aldehydes (e.g. octanal and 2, 4-hexadienal) in sulfuric acid solution were attributed to aldol condensation in

  3. Ionic Strength-Controlled Mn (Hydr)oxide Nanoparticle Nucleation on Quartz: Effect of Aqueous Mn(OH)2.

    PubMed

    Jung, Haesung; Jun, Young-Shin

    2016-01-05

    The early formation of manganese (hydr)oxide nanoparticles at mineral-water interfaces is crucial in understanding how Mn oxides control the fate and transport of heavy metals and the cycling of nutrients. Using atomic force microscopy, we investigated the heterogeneous nucleation and growth of Mn (hydr)oxide under varied ionic strengths (IS; 1-100 mM NaNO3). Experimental conditions (i.e., 0.1 mM Mn(2+) (aq) concentration and pH 10.1) were chosen to be relevant to Mn remediation sites. We found that IS controls Mn(OH)2 (aq) formation, and that the controlled Mn(OH)2 (aq) formation can affect the system's saturation and subsequent Mn(OH)2 (s) and further Mn3O4 (s) nanoparticle formation. In 100 mM IS system, nucleated Mn (hydr)oxide particles had more coverage on the quartz substrate than those in 1 mM and 10 mM IS systems. This high IS also resulted in low supersaturation ratio and thus favor heterogeneous nucleation, having better structural matching between nucleating Mn (hydr)oxides and quartz. The unique information obtained in this work improves our understanding of Mn (hydr)oxide formation in natural as well as engineered aqueous environments, such as groundwater contaminated by natural leachate and acid mine drainage remediation.

  4. Nucleation and Growth of Integrin Adhesions

    PubMed Central

    Atilgan, Erdinç; Ovryn, Ben

    2009-01-01

    We present a model that provides a mechanistic understanding of the processes that govern the formation of the earliest integrin adhesions ex novo from an approximately planar plasma membrane. Using an analytic analysis of the free energy of a dynamically deformable membrane containing freely diffusing receptors molecules and long repeller molecules that inhibit integrins from binding with ligands on the extracellular matrix, we predict that a coalescence of polymerizing actin filaments can deform the membrane toward the extracellular matrix and facilitate integrin binding. Monte Carlo simulations of this system show that thermally induced membrane fluctuations can either zip-up and increase the radius of a nucleated adhesion or unzip and shrink an adhesion, but the fluctuations cannot bend the ventral membrane to nucleate an adhesion. To distinguish this integrin adhesion from more mature adhesions, we refer to this early adhesion as a nouveau adhesion. PMID:19413961

  5. Observable effects of anisotropic bubble nucleation

    SciTech Connect

    Blanco-Pillado, Jose J.; Salem, Michael P. E-mail: salem@cosmos.phy.tufts.edu

    2010-07-01

    Our universe may have formed via bubble nucleation in an eternally-inflating background. Furthermore, the background may have a compact dimension — the modulus of which tunnels out of a metastable minimum during bubble nucleation — which subsequently grows to become one of our three large spatial dimensions. Then the reduced symmetry of the background is equivalent to anisotropic initial conditions in our bubble universe. We compute the inflationary spectrum in such a scenario and, as a first step toward understanding the effects of anisotropy, project it onto spherical harmonics. The resulting spectrum exhibits anomalous multipole correlations, their relative amplitude set by the present curvature parameter, which appear to extend to arbitrarily large multipole moments. This raises the possibility of future detection, if slow-roll inflation does not last too long within our bubble. A full understanding of the observational signal must account for the effects of background anisotropy on photon free streaming, and is left to future work.

  6. 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.

  7. 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.

  8. 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.

  9. Cyclic Peptidomimetics and Pseudopeptides from Multicomponent Reactions

    NASA Astrophysics Data System (ADS)

    Wessjohann, Ludger A.; Rhoden, Cristiano R. B.; Rivera, Daniel G.; Vercillo, Otilie Eichler

    Multicomponent reactions (MCRs) that provide in the final product amides are suitable to produce peptides and peptide-like moieties. The Passerini and Staudinger reactions provide one amide bond, and the Ugi-four-component reaction generates two amides from three or even four (or more) components, respectively. The Ugi-reaction thus is most important to produce peptides and peptoids while the Passerini reaction is useful to generate depsipeptoid moieties. In order to produce cyclic peptides and pseudopeptides, the linear peptidic MCR products have to be cyclized, usually with the help of bifunctional or activatable building blocks. Orthogonal but cyclizable secondary functionalities that need no protection in isonitrile MCRs commonly include alkenes (for ring closing metathesis), azide/alkyne (for Huisgen click reactions) or dienes and enoates (Diels-Alder) etc. If MCR-reactive groups are to be used also for the cyclisation, monoprotected bifunctional building blocks are used and deprotected after the MCR, e.g. for Ugi reactions as Ugi-Deprotection-Cyclisation (UDC). Alternatively one of the former building blocks or functional groups generated by the MCR can be activated. Most commonly these are activated amides (from so-called convertible isonitriles) which can be used e.g. for Ugi-Activation-Cyclisation (UAC) protocols, or most recently for a simultaneous use of both strategies Ugi-Deprotection/Activation-Cyclisation (UDAC). These methods mostly lead to small, medicinally relevant peptide turn mimics. In an opposing strategy, the MCR is rather used as ring-closing reaction, thereby introducing a (di-)peptide moiety. Most recently these processes have been combined to use MCRs for both, linear precursor synthesis and cyclisation. These multiple MCR approaches allow the most efficient and versatile one pot synthesis of macrocyclic pseudopeptides known to date.

  10. Communication: Bubbles, crystals, and laser-induced nucleation

    NASA Astrophysics Data System (ADS)

    Knott, Brandon C.; LaRue, Jerry L.; Wodtke, Alec M.; Doherty, Michael F.; Peters, Baron

    2011-05-01

    Short intense laser pulses of visible and infrared light can dramatically accelerate crystal nucleation from transparent solutions; previous studies invoke mechanisms that are only applicable for nucleation of ordered phases or high dielectric phases. However, we show that similar laser pulses induce CO2 bubble nucleation in carbonated water. Additionally, in water that is cosupersaturated with argon and glycine, argon bubbles escaping from the water can induce crystal nucleation without a laser. Our findings suggest a possible link between laser-induced nucleation of bubbles and crystals.

  11. Quality-by-design: an integrated process analytical technology approach to determine the nucleation and growth mechanisms during a dynamic pharmaceutical coprecipitation process.

    PubMed

    Wu, Huiquan; Khan, Mansoor A

    2011-05-01

    The objective of this study was to demonstrate the feasibility of using an integrated process analytical technology (PAT) approach to determine nucleation and growth mechanisms of a dynamic naproxen (drug)-Eudragit L100 (polymer) coprecipitation process. The influence of several thermodynamically important formulation and process variables (drug/polymer ratio, alcohol, and water usages) on coprecipitation process characteristics was investigated via real-time in situ focused beam reflectance measurement (FBRM) monitoring and near real-time particle vision microscopy measurement. The final products were characterized by near-infrared (NIR) spectroscopy and NIR chemical imaging microscopy. The coprecipitation nucleation induction time (t(ind) ) was measured by both FBRM trend statistics and process trajectory method, respectively. Furthermore, nucleation kinetics was evaluated based on t(ind) measurement and corresponding supersaturation ratio (S) estimated. It was found that plots of ln(t(ind) ) versus (ln(2) S)(-1) consist of two linear segments and are consistent with classical primary nucleation mechanisms. Apparently, the coprecipitation process is governed by heterogeneous primary nucleation mechanism at low S (14 ≤ S ≤ 503) and by homogeneous primary nucleation mechanism at high S (1216 ≤ S ≤ 3649). Off-line characterizations collectively supported this statement. Therefore, it demonstrated that integration real-time PAT process monitoring with first-principles modeling and off-line product characterization could enhance understanding to coprecipitation process dynamics and nucleation/growth mechanisms, which is impossible via off-line techniques alone.

  12. The Nucleation of Cavitation in Aqueous Media

    DTIC Science & Technology

    1985-01-25

    37 9. TllIstration of interfacila motion during - the compression phase of a compression/ decompression process . .................. .. .- 10a...special subcommittee to investigate this phenomenon. In 1917, Lord Rayleigh 5 became involved. His solution - of the equations governing vapor cavity...at the interface between a flat solid and a pure liquid to account for nucleation at the interface between two pure liquids. Apfel’s crevice model was

  13. Nucleation theory using equations of state

    NASA Astrophysics Data System (ADS)

    Obeidat, Abdalla A.

    Various equations of state (EOS) have been used with the most general Gibbsian form (P-form) of classical nucleation theory ( CNT) to see if any improvement could be realized in predicted rates for vapor-to-liquid nucleation. The standard or S-form of CNT relies on the assumption of an incompressible liquid droplet. With the use of realistic EOSs, this assumption is no longer needed. The P-form results for water and heavy water were made using the highly accurate IAPWS-95 EOS and the CREOS. The P-form successfully predicted the temperature (T) supersaturation (S ) dependence of the nucleation rate, although the absolute value was in error by roughly a factor of 100. The results for methanol and ethanol using a less accurate CPHB EOS showed little improvement over the S-form results. Gradient theory (GT), a form of density functional theory (DFT), was applied to water and alcohols using the CPHB EOS. The water results showed an improved T dependence, but the S dependence was slightly poorer compared to the S-form of CNT. The methanol and ethanol results were improved by several orders of magnitude in the predicted rates. GT and P-form CNT were also found to be in good agreement with a single high T molecular dynamics rate for TIP4P water. The P-form of binary nucleation theory was studied for a fictitious water-ethanol system whose properties were generated from DFT and a mean-field EOS for a hard sphere Yukawa fluid. The P-form was not successful in removing the unphysical behavior predicted by binary CNT in its simplest form. The DFT results were greatly superior to all forms of classical theory.

  14. Volume versus surface nucleation in freezing aerosols

    NASA Astrophysics Data System (ADS)

    Sigurbjörnsson, Ómar F.; Signorell, Ruth

    2008-05-01

    The present study puts an end to the ongoing controversy regarding volume versus surface nucleation in freezing aerosols: Our study on nanosized aerosol particles demonstrates that current state of the art measurements of droplet ensembles cannot distinguish between the two mechanisms. The reasons are inherent experimental uncertainties as well as approximations used to analyze the kinetics. The combination of both can lead to uncertainties in the rate constants of two orders of magnitude, with important consequences for the modeling of atmospheric processes.

  15. Nucleation and Heat Transfer in Liquid Nitrogen

    NASA Astrophysics Data System (ADS)

    Roth, Eric Warner

    1993-01-01

    With the advent of the new high Tc superconductors as well as the increasing use of cryo-cooled conventional electronics, liquid nitrogen will be one of the preferred cryogens used to cool these materials. Consequently, a more thorough understanding of the heat transfer characteristics of liquid nitrogen is required. In these investigations the transient heating characteristics of liquid nitrogen to states of nucleate and film boiling under different liquid flow conditions are examined. Using a metal hot wire/plate technique, it is verified that there is a premature transition to film boiling in the transient case at power levels as much as 30 percent lower than under steady state nucleate boiling conditions. It is also shown that the premature transition can be reduced or eliminated depending on the flow velocity. The second part of this research analyses the nucleation (boiling) process from a dynamical systems point of view. By observing how the boiling system variables evolve and fluctuate over time, it is hoped that physical insight and predictive information can be gained. One goal is to discover some indicator or signature in the data that anticipates the transition from nucleate boiling to film boiling. Some of the important variables that make up the boiling system are the temperature of the heater and the heat flux through the heater surface into the liquid nitrogen. The result, gained by plotting the system's trajectory in the heat flux-temperature plane, is that on average the system follows a counterclockwise trajectory. A physical model is constructed that explains this behavior. Also, as the applied heater power approaches levels at which the transition to film is known to occur, the area per unit time swept out in the heat flux-temperature plane is seen to reach a maximum. This could be of practical interest as the threshold to film boiling can be anticipated and possibly prevented.

  16. Nucleation of nitrogen: experiment and theory

    SciTech Connect

    Wegener, P.P.

    1987-05-07

    Experimental results on the condensation of pure nitrogen in the supersaturated state are collected. New experiments on pure N2 and N2 in He are added. A comparison of experiment and the classical theory of nucleation using the liquid drop approach and recent work by Pal and Hoare computing energies of formation of microclusters of Lennard-Jones N2 is made. The new results give satisfactory agreement with experiment in their range of applicability.

  17. High-resolution ice nucleation spectra of sea-ice bacteria: implications for cloud formation and life in frozen environments

    NASA Astrophysics Data System (ADS)

    Junge, K.; Swanson, B. D.

    2008-05-01

    Even though studies of Arctic ice forming particles suggest that a bacterial or viral source derived from open leads could be important for ice formation in Arctic clouds (Bigg and Leck, 2001), the ice nucleation potential of most polar marine psychrophiles or viruses has not been examined under conditions more closely resembling those in the atmosphere. In this paper, we examined the ice nucleation activity (INA) of several representative Arctic and Antarctic sea-ice bacterial isolates and a polar Colwellia phage virus. High-resolution ice nucleation spectra were obtained for droplets containing bacterial cells or virus particles using a free-fall freezing tube technique. The fraction of frozen droplets at a particular droplet temperature was determined by measuring the depolarized light scattering intensity from solution droplets in free-fall. Our experiments revealed that all sea-ice isolates and the virus nucleated ice at temperatures very close to the homogeneous nucleation temperature for the nucleation medium - which for artificial seawater was -42.2±0.3°C. Our results suggest that immersion freezing of these marine psychro-active bacteria and viruses would not be important for heterogeneous ice nucleation processes in polar clouds or to the formation of sea ice. These results also suggested that avoidance of ice formation in close proximity to cell surfaces might be one of the cold-adaptation and survival strategies for sea-ice bacteria. The fact that INA occurs at such low temperature could constitute one factor that explains the persistence of metabolic activities at temperatures far below the freezing point of seawater.

  18. High-resolution ice nucleation spectra of sea-ice bacteria: implications for cloud formation and life in frozen environments

    NASA Astrophysics Data System (ADS)

    Junge, K.; Swanson, B. D.

    2007-11-01

    Even though studies of Arctic ice forming particles suggest that a bacterial or viral source derived from open leads could be important for cloud formation in the Arctic (Bigg and Leck, 2001), the ice nucleation potential of most polar marine psychrophiles or viruses has not been examined under conditions more closely resembling those in the atmosphere. In this paper, we examined the ice nucleation activity (INA) of several representative Arctic and Antarctic sea-ice bacterial isolates and a polar Colwellia phage virus. High-resolution ice nucleation spectra were obtained for droplets containing bacterial cells or virus particles using a free-fall freezing tube technique. The fraction of frozen droplets at a particular droplet temperature was determined by measuring the depolarized light scattering intensity from solution droplets in free-fall. Our experiments revealed that all sea-ice isolates and the virus nucleated ice at temperatures very close to the homogeneous nucleation temperature for the nucleation medium - which for artificial seawater was -42.2±0.3°C. Our results indicated that these marine psychro-active bacteria and viruses are not important for heterogeneous ice nucleation processes in sea ice or polar clouds. These results also suggested that avoidance of ice formation in close proximity to cell surfaces might be one of the cold-adaptation and survival strategies for sea-ice bacteria. The fact that INA occurs at such low temperature could constitute one factor that explains the persistence of metabolic activities at temperatures far below the freezing point of seawater.

  19. High-Resolution ice Nucleation Spectra of Sea-Ice Bacteria: Implications for Cloud Formation and Life in Frozen Environments

    NASA Astrophysics Data System (ADS)

    Junge, K.; Swanson, B.

    2007-12-01

    Even though studies of Arctic ice forming particles suggest that a bacterial or viral source derived from open leads could be important for cloud formation in the Arctic (Bigg and Leck, 2002), the ice nucleation potential of most polar marine psychrophiles or viruses has not been examined under conditions more closely resembling those in the atmosphere. In this paper, we examined the ice nucleation activity (INA) of several representative Arctic and Antarctic sea-ice bacterial isolates and a polar Colwellia phage virus. High-resolution ice nucleation spectra were obtained for droplets containing bacterial cells or virus particles using a free-fall freezing tube technique. The fraction of frozen droplets at a particular droplet temperature was determined by measuring the depolarized light scattering intensity from solution droplets in free-fall. Our experiments revealed that all sea-ice isolates and the virus nucleated ice at temperatures very close to the homogeneous nucleation temperature for the nucleation medium -- which for artificial seawater was - 42.2 degC (standdev. 0.3 degC). Our results indicated that these marine psychro-active bacteria and viruses are not important for heterogeneous ice nucleation processes in sea ice or polar clouds. These results also suggested that avoidance of ice formation in close proximity to cell surfaces might be one of the cold-adaptation and survival strategies for sea-ice bacteria. The fact that INA occurs at such low temperature could constitute one factor that explains the persistence of metabolic activities at temperatures far below the freezing point of seawater (Junge et al., 2006).

  20. 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.

  1. 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.

  2. 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.

  3. Black holes as bubble nucleation sites

    NASA Astrophysics Data System (ADS)

    Gregory, Ruth; Moss, Ian G.; Withers, Benjamin

    2014-03-01

    We consider the effect of inhomogeneities on the rate of false vacuum decay. Modelling the inhomogeneity by a black hole, we construct explicit Euclidean instantons which describe the nucleation of a bubble of true vacuum centred on the inhomogeneity. We find that inhomogeneity significantly enhances the nucleation rate over that of the Coleman-de Luccia instanton — the black hole acts as a nucleation site for the bubble. The effect is larger than previously believed due to the contributions to the action from conical singularities. For a sufficiently low initial mass, the original black hole is replaced by flat space during this process, as viewed by a single causal patch observer. Increasing the initial mass, we find a critical value above which a black hole remnant survives the process. This resulting black hole can have a higher mass than the original black hole, but always has a lower entropy. We compare the process to bubble-to-bubble transitions, where there is a semi-classical Lorentzian description in the WKB approximation.

  4. 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.

  5. 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