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Sample records for amorphous ice transition

  1. The glass transition in high-density amorphous ice

    PubMed Central

    Loerting, Thomas; Fuentes-Landete, Violeta; Handle, Philip H.; Seidl, Markus; Amann-Winkel, Katrin; Gainaru, Catalin; Böhmer, Roland

    2015-01-01

    There has been a long controversy regarding the glass transition in low-density amorphous ice (LDA). The central question is whether or not it transforms to an ultraviscous liquid state above 136 K at ambient pressure prior to crystallization. Currently, the most widespread interpretation of the experimental findings is in terms of a transformation to a superstrong liquid above 136 K. In the last decade some work has also been devoted to the study of the glass transition in high-density amorphous ice (HDA) which is in the focus of the present review. At ambient pressure HDA is metastable against both ice I and LDA, whereas at > 0.2 GPa HDA is no longer metastable against LDA, but merely against high-pressure forms of crystalline ice. The first experimental observation interpreted as the glass transition of HDA was made using in situ methods by Mishima, who reported a glass transition temperature Tg of 160 K at 0.40 GPa. Soon thereafter Andersson and Inaba reported a much lower glass transition temperature of 122 K at 1.0 GPa. Based on the pressure dependence of HDA's Tg measured in Innsbruck, we suggest that they were in fact probing the distinct glass transition of very high-density amorphous ice (VHDA). Very recently the glass transition in HDA was also observed at ambient pressure at 116 K. That is, LDA and HDA show two distinct glass transitions, clearly separated by about 20 K at ambient pressure. In summary, this suggests that three glass transition lines can be defined in the p–T plane for LDA, HDA, and VHDA. PMID:25641986

  2. Molecular Reorientation Dynamics Govern the Glass Transitions of the Amorphous Ices.

    PubMed

    Shephard, J J; Salzmann, C G

    2016-06-16

    The glass transitions of low-density amorphous ice (LDA) and high-density amorphous ice (HDA) are the topic of controversial discussions. Understanding their exact nature may be the key to explaining the anomalies of liquid water but has also got implications in the general context of polyamorphism, the occurrence of multiple amorphous forms of the same material. We first show that the glass transition of hydrogen-disordered ice VI is associated with the kinetic unfreezing of molecular reorientation dynamics by measuring the calorimetric responses of the corresponding H2O, H2(18)O, and D2O materials in combination with X-ray diffraction. Well-relaxed LDA and HDA show identical isotopic-response patterns in calorimetry as ice VI, and we conclude that the glass transitions of the amorphous ices are also governed by molecular reorientation processes. This "reorientation scenario" seems to resolve the previously conflicting viewpoints and is consistent with the fragile-to-strong transition from water to the amorphous ices. PMID:27243277

  3. SURVIVAL OF AMORPHOUS WATER ICE ON CENTAURS

    SciTech Connect

    Guilbert-Lepoutre, Aurelie

    2012-10-01

    Centaurs are believed to be Kuiper Belt objects in transition between Jupiter and Neptune before possibly becoming Jupiter family comets. Some indirect observational evidence is consistent with the presence of amorphous water ice in Centaurs. Some of them also display a cometary activity, probably triggered by the crystallization of the amorphous water ice, as suggested by Jewitt and this work. Indeed, we investigate the survival of amorphous water ice against crystallization, using a fully three-dimensional thermal evolution model. Simulations are performed for varying heliocentric distances and obliquities. They suggest that crystallization can be triggered as far as 16 AU, though amorphous ice can survive beyond 10 AU. The phase transition is an efficient source of outgassing up to 10-12 AU, which is broadly consistent with the observations of the active Centaurs. The most extreme case is 167P/CINEOS, which barely crystallizes in our simulations. However, amorphous ice can be preserved inside Centaurs in many heliocentric distance-obliquity combinations, below a {approx}5-10 m crystallized crust. We also find that outgassing due to crystallization cannot be sustained for a time longer than 10{sup 4}-10{sup 4} years, leading to the hypothesis that active Centaurs might have recently suffered from orbital changes. This could be supported by both observations (although limited) and dynamical studies.

  4. New transformations between crystalline and amorphous ice

    NASA Technical Reports Server (NTRS)

    Hemley, R. J.; Chen, L. C.; Mao, H. K.

    1989-01-01

    High-pressure optical and spectroscopic techniques were used to obtain directly the ice I(h) - hda-ice transformation in a diamond-anvil cell, and the stability of the amorphous form is examined as functions of pressure and temperature. It is demonstrated that hda-ice transforms abruptly at 4 GPa and 77 K to a crystalline phase close in structure to orientationally disordered ice-VII and to a more highly ordered, ice-VIII-like structure at higher temperatures. This is the first time that an amorphous solid is observed to convert to a crystalline solid at low temperatures by compression alone. Phase transitions of this type may be relevant on icy planetary satellites, and there may also be implications for the high-pressure behavior of silica.

  5. Ice formation in amorphous cellulose

    NASA Astrophysics Data System (ADS)

    Czihak, C.; Müller, M.; Schober, H.; Vogl, G.

    2000-03-01

    We investigate the formation of ice in wet amorphous cellulose in the temperature range of 190 K⩽T⩽280 K. Due to voids and pores in the cellulose film, water molecules are able to form crystalline aggregates. Beyond that, water is able to penetrate between cellulose chains where it can adsorb to hydroxyl side groups. From diffraction data we suggest an aggregation of low-density amorphous (lda) ice at cellulose surfaces. The formation of lda ice shows a clear temperature dependence which will be discussed together with recent inelastic neutron scattering results.

  6. High-Density Amorphous Ice, the Frost on Interstellar Grains

    NASA Technical Reports Server (NTRS)

    Jenniskens, P.; Blake, D. F.; Wilson, M. A.; Pohorille, A.

    1995-01-01

    Most water ice in the universe is in a form which does not occur naturally on Earth and of which only minimal amounts have been made in the laboratory. We have encountered this 'high-density amorphous ice' in electron diffraction experiments of low-temperature (T less than 30 K) vapor-deposited water and have subsequently modeled its structure using molecular dynamics simulations. The characteristic feature of high-density amorphous ice is the presence of 'interstitial' oxygen pair distances between 3 and 4 A. However, we find that the structure is best described as a collapsed lattice of the more familiar low-density amorphous form. These distortions are frozen in at temperatures below 38 K because, we propose, it requires the breaking of one hydrogen bond, on average, per molecule to relieve the strain and to restructure the lattice to that of low-density amorphous ice. Several features of astrophysical ice analogs studied in laboratory experiments are readily explained by the structural transition from high-density amorphous ice into low-density amorphous ice. Changes in the shape of the 3.07 gm water band, trapping efficiency of CO, CO loss, changes in the CO band structure, and the recombination of radicals induced by low-temperature UV photolysis all covary with structural changes that occur in the ice during this amorphous to amorphous transition. While the 3.07 micrometers ice band in various astronomical environments can be modeled with spectra of simple mixtures of amorphous and crystalline forms, the contribution of the high-density amorphous form nearly always dominates.

  7. Peculiarities of Vibration Characteristics of Amorphous Ices

    NASA Astrophysics Data System (ADS)

    Gets, Kirill V.; Subbotin, Oleg S.; Belosludov, Vladimir R.

    2012-03-01

    Dynamic properties of low (LDA), high (HDA) and very high (VHDA) density amorphous ices were investigated within the approach based on Lattice Dynamics simulations. In this approach, we assume that the short-range molecular order mainly determines the dynamic and thermodynamic properties of amorphous ices. Simulation cell of 512 water molecules with periodical boundary conditions and disordering allows us to study dynamical properties and dispersion curves in the Brillouin zone of pseudo-crystal. Existence of collective phenomena in amorphous ices which is usual for crystals but anomalous for disordered phase was confirmed in our simulations. Molecule amplitudes of delocalized (collective) as well as localized vibrations have been considered.

  8. Structure and dynamics of amorphous water ice

    NASA Technical Reports Server (NTRS)

    Laufer, D.; Kochavi, E.; Bar-Nun, A.; Owen, T. (Principal Investigator)

    1987-01-01

    Further insight into the structure and dynamics of amorphous water ice, at low temperatures, was obtained by trapping in it Ar, Ne, H2, and D2. Ballistic water-vapor deposition results in the growth of smooth, approximately 1 x 0.2 micrometer2, ice needles. The amorphous ice seems to exist in at least two separate forms, at T < 85 K and at 85 < T < 136.8 K, and transform irreversibly from one form to the other through a series of temperature-dependent metastable states. The channels formed by the water hexagons in the ice are wide enough to allow the free penetration of H2 and D2 into the ice matrix even in the relatively compact cubic ice, resulting in H2-(D2-) to-ice ratios (by number) as high as 0.63. The larger Ar atoms can penetrate only into the wider channels of amorphous ice, and Ne is an intermediate case. Dynamic percolation behavior explains the emergence of Ar and Ne (but not H2 and D2) for the ice, upon warming, in small and big gas jets. The big jets, each containing approximately 5 x 10(10) atoms, break and propel the ice needles. Dynamic percolation also explains the collapse of the ice matrix under bombardment by Ar , at a pressure exceeding 2.6 dyn cm-2, and the burial of huge amounts of gas inside the collapsed matrix, up to an Ar-to-ice of 3.3 (by number). The experimental results could be relevant to comets, icy satellites, and icy grain mantles in dense interstellar clouds.

  9. Crystallization of amorphous water ice in the solar system

    NASA Technical Reports Server (NTRS)

    Jenniskens, P.; Blake, D. F.

    1996-01-01

    Electron diffraction studies of vapor-deposited water ice have characterized the dynamical structural changes during crystallization that affect volatile retention in cometary materials. Crystallization is found to occur by nucleation of small domains, while leaving a significant part of the amorphous material in a slightly more relaxed amorphous state that coexists metastably with cubic crystalline ice. The onset of the amorphous relaxation is prior to crystallization and coincides with the glass transition. Above the glass transition temperature, the crystallization kinetics are consistent with the amorphous solid becoming a "strong" viscous liquid. The amorphous component can effectively retain volatiles during crystallization if the volatile concentration is approximately 10% or less. For higher initial impurity concentrations, a significant amount of impurities is released during crystallization, probably because the impurities are trapped on the surfaces of micropores. A model for crystallization over long timescales is described that can be applied to a wide range of impure water ices under typical astrophysical conditions if the fragility factor D, which describes the viscosity behavior, can be estimated.

  10. Cryoflotation: densities of amorphous and crystalline ices.

    PubMed

    Loerting, Thomas; Bauer, Marion; Kohl, Ingrid; Watschinger, Katrin; Winkel, Katrin; Mayer, Erwin

    2011-12-01

    We present an experimental method aimed at measuring mass densities of solids at ambient pressure. The principle of the method is flotation in a mixture of liquid nitrogen and liquid argon, where the mixing ratio is varied until the solid hovers in the liquid mixture. The temperature of such mixtures is in the range of 77-87 K, and therefore, the main advantage of the method is the possibility of determining densities of solid samples, which are instable above 90 K. The accessible density range (~0.81-1.40 g cm(-3)) is perfectly suitable for the study of crystalline ice polymorphs and amorphous ices. As a benchmark, we here determine densities of crystalline polymorphs (ices I(h), I(c), II, IV, V, VI, IX, and XII) by flotation and compare them with crystallographic densities. The reproducibility of the method is about ±0.005 g cm(-3), and in general, the agreement with crystallographic densities is very good. Furthermore, we show measurements on a range of amorphous ice samples and correlate the density with the d spacing of the first broad halo peak in diffraction experiments. Finally, we discuss the influence of microstructure, in particular voids, on the density for the case of hyperquenched glassy water and cubic ice samples prepared by deposition of micrometer-sized liquid droplets. PMID:21879742

  11. Matrix sublimation method for the formation of high-density amorphous ice

    NASA Astrophysics Data System (ADS)

    Kouchi, A.; Hama, T.; Kimura, Y.; Hidaka, H.; Escribano, R.; Watanabe, N.

    2016-08-01

    A novel method for the formation of amorphous ice involving matrix sublimation has been developed. A CO-rich CO:H2O mixed ice was deposited at 8-10 K under ultra-high vacuum condition, which was then allowed to warm. After the sublimation of matrix CO at 35 K, amorphous ice remained. The amorphous ice formed exhibits a highly porous microscale texture; however, it also rather exhibits a density similar to that of high-density amorphous ice formed under high pressure. Furthermore, unlike conventional vapor-deposited amorphous ice, the amorphous ice is stable up to 140 K, where it transforms directly to cubic ice Ic.

  12. The Metastable Persistence of Vapor-Deposited Amorphous Ice at Anomalously High Temperatures

    NASA Technical Reports Server (NTRS)

    Blake, David F.; Jenniskens, Peter; DeVincenzi, Donald L. (Technical Monitor)

    1995-01-01

    in each pattern are determined by subtracting a percentage of crystalline component relative to amorphous and pure crystalline endmembers. Vapor-deposited water ice undergoes two amorphous to amorphous structural transformations in the temperature range 15-130 K with important astrophysical implications. The onset of cubic crystallization occurs at 142-160 K (at 1K per minute heating rates) during which the 220 and 311 diffraction maxima appear and 0.1 micrometer crystallites can be seen in bright field images. This transition is time dependent.

  13. Clathrate hydrate formation in amorphous cometary ice analogs in vacuo

    NASA Technical Reports Server (NTRS)

    Blake, David; Allamandola, Louis; Sandford, Scott; Hudgins, Doug; Freund, Friedemann

    1991-01-01

    Experiments conducted in clathrate hydrates with a modified electron microscope have demonstrated the possibility of such compounds' formation during the warming of vapor-deposited amorphous ices in vacuo, through rearrangements in the solid state. Subsolidus crystallization of compositionally complex amorphous ices may therefore be a general and ubiquitous process. Phase separations and microporous textures thus formed may be able to account for such anomalous cometary phenomena as the release of gas at large radial distances from the sun and the retention of volatiles to elevated temperatures.

  14. Mimas: Preliminary Evidence For Amorphous Water Ice from VIMS

    NASA Technical Reports Server (NTRS)

    Cruikshank, Dale P.; Marzo, G. A.; Pinilla-Alonso, N.; Roush, T. L.; Mastrapa, R. M.; DalleOre, C. M.; Buratti, B. J.; Stephan, K.

    2010-01-01

    We have conducted a statistical clustering analysis (1,2) on a mosaic of VIMS data cubes obtained on February 13, 2010, for Saturn s satellite Mimas. Seven VIMS cubes were geometrically projected and re-sampled to a common spatial resolution. The clustering technique consists of a partitioning algorithm coupled to a criterion that prevents sub-optimal solutions and tests for the influence of random noise in the measurements. The clustering technique is agnostic about the meaning of the clusters, and scientific interpretation requires their a posteriori evaluation. The preliminary results yielded five clusters, demonstrating that spectral variability across Mimas surface is statistically significant. The ratios of the means calculated for each of the clusters show structure within the 1.6- micron water ice band, as well as the shape and the central wavelength of the strong ice band at 2 micron, that map spatially in patterns apparently related to the topography of Mimas, in particular certain regions in and around Herschel crater. The mean spectra of the five clusters, show similarities with laboratory spectra of amorphous and crystalline H2O ice (3) that are suggestive of the presence of an amorphous ice component in certain regions of Mimas, notably on the central peak of Herschel, on the crater floor, and in faults surrounding the crater. This may represent a mixture of both ice phases, or perhaps a layer of amorphous ice on a base of crystalline ice. Another possible occurrence of amorphous ice appears southwest of Herschel, close to the south pole.

  15. CO Diffusion into Amorphous H2O Ices

    NASA Astrophysics Data System (ADS)

    Lauck, Trish; Karssemeijer, Leendertjan; Shulenberger, Katherine; Rajappan, Mahesh; Öberg, Karin I.; Cuppen, Herma M.

    2015-03-01

    The mobility of atoms, molecules, and radicals in icy grain mantles regulates ice restructuring, desorption, and chemistry in astrophysical environments. Interstellar ices are dominated by H2O, and diffusion on external and internal (pore) surfaces of H2O-rich ices is therefore a key process to constrain. This study aims to quantify the diffusion kinetics and barrier of the abundant ice constituent CO into H2O-dominated ices at low temperatures (15-23 K), by measuring the mixing rate of initially layered H2O(:CO2)/CO ices. The mixed fraction of CO as a function of time is determined by monitoring the shape of the infrared CO stretching band. Mixing is observed at all investigated temperatures on minute timescales and can be ascribed to CO diffusion in H2O ice pores. The diffusion coefficient and final mixed fraction depend on ice temperature, porosity, thickness, and composition. The experiments are analyzed by applying Fick’s diffusion equation under the assumption that mixing is due to CO diffusion into an immobile H2O ice. The extracted energy barrier for CO diffusion into amorphous H2O ice is ˜160 K. This is effectively a surface diffusion barrier. The derived barrier is low compared to current surface diffusion barriers in use in astrochemical models. Its adoption may significantly change the expected timescales for different ice processes in interstellar environments.

  16. Crystallization of CO2 ice and the absence of amorphous CO2 ice in space

    PubMed Central

    Escribano, Rafael M.; Muñoz Caro, Guillermo M.; Cruz-Diaz, Gustavo A.; Rodríguez-Lazcano, Yamilet; Maté, Belén

    2013-01-01

    Carbon dioxide (CO2) is one of the most relevant and abundant species in astrophysical and atmospheric media. In particular, CO2 ice is present in several solar system bodies, as well as in interstellar and circumstellar ice mantles. The amount of CO2 in ice mantles and the presence of pure CO2 ice are significant indicators of the temperature history of dust in protostars. It is therefore important to know if CO2 is mixed with other molecules in the ice matrix or segregated and whether it is present in an amorphous or crystalline form. We apply a multidisciplinary approach involving IR spectroscopy in the laboratory, theoretical modeling of solid structures, and comparison with astronomical observations. We generate an unprecedented highly amorphous CO2 ice and study its crystallization both by thermal annealing and by slow accumulation of monolayers from the gas phase under an ultrahigh vacuum. Structural changes are followed by IR spectroscopy. We also devise theoretical models to reproduce different CO2 ice structures. We detect a preferential in-plane orientation of some vibrational modes of crystalline CO2. We identify the IR features of amorphous CO2 ice, and, in particular, we provide a theoretical explanation for a band at 2,328 cm−1 that dominates the spectrum of the amorphous phase and disappears when the crystallization is complete. Our results allow us to rule out the presence of pure and amorphous CO2 ice in space based on the observations available so far, supporting our current view of the evolution of CO2 ice. PMID:23858474

  17. A new structural relaxation pathway of low-density amorphous ice.

    PubMed

    Shephard, Jacob J; Klotz, Stefan; Vickers, Martin; Salzmann, Christoph G

    2016-05-28

    Low-density amorphous (LDA) ice is involved in critical cosmological processes and has gained prominence as one of the at least two distinct amorphous forms of ice. Despite these accolades, we still have an incomplete understanding of the structural diversity that is encompassed within the LDA state and the dynamic processes that take place upon heating LDA. Heating the high-pressure ice VIII phase at ambient pressure is a remarkable example of temperature-induced amorphisation yielding LDA. We investigate this process in detail using X-ray diffraction and Raman spectroscopy and show that the LDA obtained from ice VIII is structurally different from the more "traditional" states of LDA which are approached upon thermal annealing. This new structural relaxation pathway involves an increase of structural order on the intermediate range length scale. In contrast with other LDA materials the local structure is more ordered initially and becomes slightly more disordered upon annealing. We also show that the cascade of phase transitions upon heating ice VIII at ambient pressure includes the formation of ice IX which may be connected with the structural peculiarities of LDA from ice VIII. Overall, this study shows that LDA is a structurally more diverse material than previously appreciated. PMID:27250311

  18. Trapping of gas mixtures by amorphous water ice

    NASA Technical Reports Server (NTRS)

    Bar-Nun, A.; Kleinfeld, I.; Kochavi, E.; Owen, T. (Principal Investigator)

    1988-01-01

    Our studies on gas trapping in amorphous water ice at 24-100 K were extended, by using mixtures of CH4, CO, N2, and Ar, rather than single gases. In 1:1 gas:(water vapor) mixtures, the competition among these gases on the available sites in the ice showed that the trapping capacity for the various gases is determined not only by the structure and dynamics of the ice, but is also influenced by the gas itself. Whereas at 24-35 K all four gases are trapped in the ice indiscriminantly, at 50-75 K there is a clear enhancement, in the order of CH4 > CO > N2 > or approximately Ar. This order is influenced by the gas-water interaction energy, the size of the trapped gas atom or molecule, the type of clathrate-hydrate formed (I or II) and, possibly, other factors. It seems that the gas can be trapped in the amorphous ice in several different locations, each being affected in a different way by the deposition temperature and gas composition. Once a gas atom or molecule is trapped in a specific location, it is predestined to emerge in one of eight different temperature ranges, which are associated with changes in the ice. The experimentally observed enhancements, together with the findings on the gas composition of comet Halley, might enable an estimation of the gas composition in the region of comet formation.

  19. Vapor deposition of water on graphitic surfaces: Formation of amorphous ice, bilayer ice, ice I, and liquid water

    SciTech Connect

    Lupi, Laura; Kastelowitz, Noah; Molinero, Valeria

    2014-11-14

    Carbonaceous surfaces are a major source of atmospheric particles and could play an important role in the formation of ice. Here we investigate through molecular simulations the stability, metastability, and molecular pathways of deposition of amorphous ice, bilayer ice, and ice I from water vapor on graphitic and atomless Lennard-Jones surfaces as a function of temperature. We find that bilayer ice is the most stable ice polymorph for small cluster sizes, nevertheless it can grow metastable well above its region of thermodynamic stability. In agreement with experiments, the simulations predict that on increasing temperature the outcome of water deposition is amorphous ice, bilayer ice, ice I, and liquid water. The deposition nucleation of bilayer ice and ice I is preceded by the formation of small liquid clusters, which have two wetting states: bilayer pancake-like (wetting) at small cluster size and droplet-like (non-wetting) at larger cluster size. The wetting state of liquid clusters determines which ice polymorph is nucleated: bilayer ice nucleates from wetting bilayer liquid clusters and ice I from non-wetting liquid clusters. The maximum temperature for nucleation of bilayer ice on flat surfaces, T{sub B}{sup max} is given by the maximum temperature for which liquid water clusters reach the equilibrium melting line of bilayer ice as wetting bilayer clusters. Increasing water-surface attraction stabilizes the pancake-like wetting state of liquid clusters leading to larger T{sub B}{sup max} for the flat non-hydrogen bonding surfaces of this study. The findings of this study should be of relevance for the understanding of ice formation by deposition mode on carbonaceous atmospheric particles, including soot.

  20. Crystalline-amorphous transition in silicate perovskites

    SciTech Connect

    Hemmati, M.; Chizmeshya, A.; Wolf, G.H.; Poole, P.H.; Shao, J.; Angell, C.A.

    1995-06-01

    CaSiO{sub 3} and MgSiO{sub 3} perovskites are known to undergo solid-state crystal to amorphous transitions near ambient pressure when decompressed from their high-pressure stability fields. In order to elucidate the mechanistic aspects of this transition we have performed detailed molecular-dynamics simulations and lattice-dynamical calculations on model silicate perovskite systems using empirical rigid-ion pair potentials. In the simulations at low temperatures, the model perovskite systems transform under tension to a low-density glass composed of corner shared chains of tetrahedral silicon. The amorphization is initiated by a thermally activated step involving a soft polar optic mode in the perovskite phase at the Brillouin zone center. Progression of the system along this reaction coordinate triggers, in succession, multiple barrierless modes of instability ultimately producing a catastrophic decohesion of the lattice. An important intermediary along the reaction path is a crystalline phase where silicon is in a five-coordinate site and the alkaline-earth metal atom is in eightfold coordination. At the onset pressure, this transitory phase is itself dynamically unstable to a number of additional vibrational modes, the most relevant being those which result in transformation to a variety of tetrahedral chain silicate motifs. These results support the conjecture that stress-induced amorphization arises from the near simultaneous accessibility of multiple modes of instability in the highly metastable parent crystalline phase.

  1. Phase transitions in biogenic amorphous calcium carbonate

    NASA Astrophysics Data System (ADS)

    Gong, Yutao

    Geological calcium carbonate exists in both crystalline phases and amorphous phases. Compared with crystalline calcium carbonate, such as calcite, aragonite and vaterite, the amorphous calcium carbonate (ACC) is unstable. Unlike geological calcium carbonate crystals, crystalline sea urchin spicules (99.9 wt % calcium carbonate and 0.1 wt % proteins) do not present facets. To explain this property, crystal formation via amorphous precursors was proposed in theory. And previous research reported experimental evidence of ACC on the surface of forming sea urchin spicules. By using X-ray absorption near-edge structure (XANES) spectroscopy and photoelectron emission microscopy (PEEM), we studied cross-sections of fresh sea urchin spicules at different stages (36h, 48h and 72h after fertilization) and observed the transition sequence of three mineral phases: hydrated ACC → dehydrated ACC → biogenic calcite. In addition, we unexpectedly found hydrated ACC nanoparticles that are surrounded by biogenic calcite. This observation indicates the dehydration from hydrated ACC to dehydrated ACC is inhibited, resulting in stabilization of hydrated ACC nanoparticles. We thought that the dehydration was inhibited by protein matrix components occluded within the biomineral, and we designed an in vitro assay to test the hypothesis. By utilizing XANES-PEEM, we found that SM50, the most abundant occluded matrix protein in sea urchin spicules, has the function to stabilize hydrated ACC in vitro.

  2. Clathrate hydrate formation in amorphous cometary ice analogs in vacuo.

    PubMed

    Blake, D; Allamandola, L; Sandford, S; Hudgins, D; Freund, F

    1991-10-25

    The presence of clathrate hydrates in cometary ice has been suggested to account for anomalous gas release at large radial distances from the sun as well as the retention of volatiles in comets to elevated temperatures. However, how clathrate hydrates can form in low-pressure environments, such as in cold interstellar molecular clouds, in the outer reaches of the early solar nebula, or in cometary ices, has been poorly understood. Experiments performed with the use of a modified electron microscope demonstrate that during the warming of vapor-deposited amorphous ices in vacuo, clathrate hydrates can form by rearrangements in the solid state. Phase separations and microporous textures that are the result of these rearrangements may account for a variety of anomalous cometary phenomena. PMID:11538372

  3. Amorphous and Crystalline H2O-Ice

    NASA Astrophysics Data System (ADS)

    Mastrapa, Rachel M. E.; Grundy, William M.; Gudipati, Murthy S.

    On the surfaces of Solar System objects, H2O-ice can form in several different phases, including amorphous and crystalline. The stability of these phases as a function of thermal and radiation history is an active area of laboratory research. Meanwhile, remote detection of H2O-ice depends on the interpretation of infrared absorptions that are also dependent on phase and temperature. Surface processes, such as surface chemistry, micrometeorite gardening, and cryovolcanic resurfacing, on the surfaces of objects are linked to H2O-ice phase. We review the current state of laboratory measurements in the context of observations of Solar System objects and list the areas where new measurements are needed.

  4. The sticking of atomic hydrogen on amorphous water ice

    SciTech Connect

    Veeraghattam, Vijay K.; Manrodt, Katie; Lewis, Steven P.; Stancil, P. C. E-mail: lewis@physast.uga.edu

    2014-07-20

    Using classical molecular dynamics, we have simulated the sticking and scattering process of a hydrogen atom on an amorphous ice film to predict the sticking probability of hydrogen on ice surfaces. A wide range of initial kinetic energies of the incident hydrogen atom (10 K-600 K) and two different ice temperatures (10 K and 70 K) were used to investigate this fundamental process in interstellar chemistry. We report here the sticking probability of atomic hydrogen as a function of incident kinetic energy, gas temperature, and substrate temperature, which can be used in astrophysical models. The current results are compared to previous theoretical and experimental studies that have reported a wide range in the sticking coefficient.

  5. Atypical water lattices and their possible relevance to the amorphous ices: A density functional study

    NASA Astrophysics Data System (ADS)

    Anick, David J.

    2013-04-01

    Of the fifteen known crystalline forms of ice, eleven consist of a single topologically connected hydrogen bond network with four H-bonds at every O. The other four, Ices VI-VIII and XV, consist of two topologically connected networks, each with four H-bonds at every O. The networks interpenetrate but do not share H-bonds. This article presents two new periodic water lattice families whose topological connectivity is "atypical": they consist of many two-dimensional layers that share no H-bonds. Layers are held together only by dispersion forces. Within each layer there are still four H-bonds at each O. Called "Hexagonal Bilayer Water" (HBW) and "Pleated Sheet Water" (PSW), they have computed densities of about 1.1 g/mL and 1.3 g/mL respectively, and nearest neighbor O-coordination is 4.5 to 5.5 and 6 to 8 respectively. Using density functional theory (BLYP-D/TZVP), various proton ordered forms of HBW and PSW are optimized and categorized. There are simple pathways connecting Ice-Ih to HBW and HBW to PSW. Their computed properties suggest similarities to the high density and very high density amorphous ices (HDA and VHDA) respectively. It is unknown whether HDA, VHDA, and Low Density Amorphous Ice (LDA) are fully disordered glasses down to the molecular level, or whether there is some short-range local order. Based on estimated radial distribution functions (RDFs), one proton ordered form of HBW matches HDA best. The idea is explored that HDA could contain islands with this underlying structure, and likewise, that VHDA could contain regions of PSW. A "microlattice model version 1" (MLM1) is presented as a device to compare key experimental data on the amorphous ices with these atypical structures and with a microlattice form of Ice-XI for LDA. Resemblances are found with the amorphs' RDFs, densities, Raman spectra, and transition behaviors. There is not enough information in the static models to assign either a microlattice structure or a partial microlattice

  6. Visual Observations of the Amorphous-Amorphous Transition in H2O Under Pressure.

    PubMed

    Mishima, O; Takemura, K; Aoki, K

    1991-10-18

    The vapor-deposited low-density amorphous phase of H(2)O was directly compressed at 77 kelvin with a diamond-anvil cell, and the boundary between the low-density amorphous phase and the high-density amorphous phase was observed while the sample was warmed under compression. The transition from the low-density amorphous phase to the high-density amorphous phase was distinct and reversible in an apparently narrow pressure range at approximately 130 to approximately 150 kelvin, which provided experimental evidence for polymorphism in amorphous H(2)O. PMID:17742228

  7. The Infrared Spectra and Absorption Intensities of Amorphous Ices

    NASA Astrophysics Data System (ADS)

    Gerakines, Perry A.; Hudson, Reggie L.; Loeffler, Mark

    2016-06-01

    Our research group is carrying out new IR measurements of icy solids relevant to the outer solar system and to the interstellar medium, with an emphasis on amorphous and crystalline ices below ~ 120 K. Our goal is to update and add to the relatively meager literature on this subject and to provide electronic versions of state-of-the-art data, since the abundances of such molecules cannot be deduced without accurate reference spectra and IR band strengths. In the past year, we have focused on three of the simplest and most abundant components of interstellar and solar-system ices: methane (CH4), carbon dioxide (CO2), and methanol (CH3OH). Infrared spectra from ∼ 4500 to 500 cm-1 have been measured for each of these molecules in μm-thick films at temperatures from 10 to 120 K. All known amorphous and crystalline phases have been reproduced and, for some, presented for the first time. We also report measurements of the index of refraction at 670 nm and the mass densities for each ice phase. Comparisons are made to earlier work where possible. Electronic versions of our new results are available at http://science.gsfc.nasa.gov/691/cosmicice/ constants.html.

  8. The structure and dynamics of amorphous and crystalline phases of ice

    SciTech Connect

    Klug, D. D.; Tse, J. S.; Tulk, C. A.; Svensson, E. C.; Swainson, I.; Loong, C.-K.

    2000-07-14

    The structures of the high and low-density amorphous phases of ice are studied using several techniques. The diffraction patterns of high and low density amorphous ice are analyzed using reverse Monte Carlo methods and compared with molecular dynamics simulations of these phases. The spectra of crystalline and amorphous phases of ice obtained by Raman and incoherent inelastic neutron scattering are analyzed to yield structural features for comparison with the results of molecular dynamics and Reverse Monte Carlo analysis. The structural details obtained indicate that there are significant differences between the structure of liquid water and the amorphous phases of ice.

  9. In situ observation of amorphous-amorphous apparently first-order phase transition in zeolites

    NASA Astrophysics Data System (ADS)

    Ovsyuk, Nikolay; Goryainov, Sergei

    2006-09-01

    In this letter, the authors present the observation of the phase transition between low-density amorphous (LDA) and high-density amorphous (HDA) zeolites using a high pressure Raman spectroscopy. It is found that this transition is apparently of the first order and occurs with a silicon coordination rise. It is shown that the Raman spectra of the LDA-HDA phase transitions in zeolites and in silicon are almost identical, suggesting a generality of amorphous-amorphous transformations both in simple substances and in complex polyatomic materials with tetrahedral configurations.

  10. Amorphous and Crystalline H20 Ice at Rhea's Inktomi Crater

    NASA Technical Reports Server (NTRS)

    Lewis, Emma M.; Dalle Ore, Cristina M.; Cruikshank, Dale P.; White, Oliver L.

    2014-01-01

    We present the analysis of Cassini spectral data from spectral mapping of Saturnian icy moons Dione and Rhea, to investigate possible effects of impact crater formation on the relative abundances of crystalline and amorphous water ice in the moons' ice crusts. Both moons display morphologically young ray craters as well as older craters. Possible changes in ice properties due to crater formation are conjectured to be more visible in younger craters, and as such Rhea's well imaged ray crater Inktomi is analysed, as are older craters for comparison. We used data from Cassini's Visual and Infrared Mapping Spectrometer (VIMS). For each pixel in the VIMS maps, spectral data were extracted in the near-infrared range (1.75 micrometers less than lambda less than 2.45 micrometers). Analysis was begun by fitting a single Gaussian to the peak in absorption at 2.0 micrometers, which was then subtracted from the data, leaving residuals with a minimum on either side of the original 2.0-micrometers band. The spectra of the individual spatial pixels were then clustered by the differences between these minima, which are sensitive to changes in both ice grain size and crystallinity. This yielded preliminary maps which approximated the physical characteristics of the landscape and were used to identify candidates for further analysis. Spectra were then clustered by the properties of the 1.5-micrometers band, to divide the map into regions based on inferred grain size. For each region, the predicted differences in minima from the Gaussian residuals, over a range of crystallinities, were calculated based on the found grain sizes. This model was used to find the crystallinity of each pixel via grain size and characteristics of the residual function. Preliminary results show a greater degree of crystallization of young crater interiors, particularly in Rhea's ray crater Inktomi, where ice showed crystalline ice abundances between 33 percent and 61 percent. These patterns in ice

  11. Amorphous and polycrystalline water ices in space environments

    NASA Astrophysics Data System (ADS)

    Andrade, Diana; Pilling, Sergio; Da Silveira, Enio; Barros, Ana

    2016-07-01

    Ices are an important reservoir of more complex molecular species in several space environments, containing information about the composition and formation of these regions. Water ice is the dominant constituent of interstellar ices in most lines of sight and is about 70 % of the composition in comets, being a key molecule in astrochemical models. It is believed that one of the reactive species possibly evaporated from the water ices is the hydronium ion, H_{3}O^{+}, which plays an important role in the oxygen chemistry network. This ion has been detected in the lunar surface of Enceladus and Titan, and toward the Sagittarius B2 molecular Clouds, where H_{2}O and OH were also identified. In this work, the ion desorption due to radiolysis in ices constituted by water at three different temperatures (40, 70 and 125 K) is studied, to investigate the different allotropic water ices. A discussion on the rate of H_{3}O^{+} and water delivered to gas phase, as well as the half-life of water ice grains, inside dense molecular clouds considering a constants cosmic ray flux is given. The ions desorbed from water ice have been mass/charge analyzed by a time-of-flight spectrometer. Among the results, it is seen that in the positive ion spectrum of high density amorphous water ice at 40 K the highest desorption yields (ejected ions/impact) correspond to H^{+}, H_{3}O^{+} and clusters formed by (H_{2}O)_{n}R^{+}, where R^{+} is H_{3}O^{+} and 1 ≤ n ≤ 25. At T = 125 K, the ice is in its low density polycrystalline form and new clusters are present, such as (H_{2}O)_{n}R^{+}, where R^{+} is H_{2}^{+} and H_{3}^{+} (for low n), beyond H_{3}O^{+}. Therefore, it is seen that (H_{2}O)_{n}H_{3}O^{+} series (with n between 1 and 25) is dominant in all cases. The H_{3}O^{+} desorption yield at 40 K is about 5times10^{-3} ions/impact. This value is 4-5 times higher than the one obtained at T > 125 K. This behavior is also seen to all series member and consequently to the sum (Yn).

  12. State transformations and ice nucleation in amorphous (semi-)solid organic aerosol

    NASA Astrophysics Data System (ADS)

    Baustian, K. J.; Wise, M. E.; Jensen, E. J.; Schill, G. P.; Freedman, M. A.; Tolbert, M. A.

    2013-06-01

    Amorphous (semi-)solid organic aerosol particles have the potential to serve as surfaces for heterogeneous ice nucleation in cirrus clouds. Raman spectroscopy and optical microscopy have been used in conjunction with a cold stage to examine water uptake and ice nucleation on individual amorphous (semi-)solid particles at atmospherically relevant temperatures (200-273 K). Three organic compounds considered proxies for atmospheric secondary organic aerosol (SOA) were used in this investigation: sucrose, citric acid and glucose. Internally mixed particles consisting of each organic and ammonium sulfate were also investigated. Results from water uptake experiments followed the shape of a humidity-induced glass transition (Tg(RH)) curve and were used to construct state diagrams for each organic and corresponding mixture. Experimentally derived Tg(RH) curves are in good agreement with theoretical predictions of Tg(RH) following the approach of Koop et al. (2011). A unique humidity-induced glass transition point on each state diagram, Tg'(RH), was used to quantify and compare results from this study to previous works. Values of Tg'(RH) determined for sucrose, glucose and citric acid glasses were 236, 230 and 220 K, respectively. Values of Tg'(RH) for internally mixed organic/sulfate particles were always significantly lower; 210, 207 and 215 K for sucrose/sulfate, glucose/sulfate and citric acid/sulfate, respectively. All investigated SOA proxies were observed to act as heterogeneous ice nuclei at tropospheric temperatures. Heterogeneous ice nucleation on pure organic particles occurred at Sice = 1.1-1.4 for temperatures below 235 K. Particles consisting of 1:1 organic-sulfate mixtures took up water over a greater range of conditions but were in some cases also observed to heterogeneously nucleate ice at temperatures below 202 K (Sice= 1.25-1.38). Polynomial curves were fitted to experimental water uptake data and then incorporated into the Community Aerosol Radiation

  13. Experimental Evidence for a Crossover between Two Distinct Mechanisms of Amorphization in Ice Ih under Pressure

    SciTech Connect

    Straessle, Thierry; Klotz, Stefan; Hamel, Gerard; Koza, Michael M.; Schober, Helmut

    2007-10-26

    We report neutron scattering data which reveal the central role of phonon softening leading to a negative melting line, solid-state amorphization, and negative thermal expansion of ice. We find that pressure-induced amorphization is due to mechanical melting at low temperatures, while at higher temperatures amorphization is governed by thermal melting (violations of Born's and Lindemann's criteria, respectively). This confirms earlier conjectures of a crossover between two distinct amorphization mechanisms and provides a natural explanation for the strong annealing observed in high-density amorphous ice.

  14. Polyamorphous transition in amorphous fullerites C{sub 70}

    SciTech Connect

    Borisova, P. A.; Agafonov, S. S.; Glazkov, V. P.; D'yakonova, N. P.; Somenkov, V. A.

    2011-12-15

    Samples of amorphous fullerites C{sub 70} have been obtained by mechanical activation (grinding in a ball mill). The structure of the samples has been investigated by neutron and X-ray diffraction. The high-temperature (up to 1200 Degree-Sign C) annealing of amorphous fullerites revealed a polyamorphous transition from molecular to atomic glass, which is accompanied by the disappearance of fullerene halos at small scattering angles. Possible structural versions of the high-temperature amorphous phase are discussed.

  15. Two species/nonideal solution model for amorphous/amorphous phase transitions

    SciTech Connect

    Moynihan, C.T.

    1997-12-31

    A simple macroscopic thermodynamic model for first order transitions between two amorphous phases in a one component liquid is reviewed, augmented and evaluated. The model presumes the existence in the liquid of two species, whose concentrations are temperature and pressure dependent and which form a solution with large, positive deviations from ideality. Application of the model to recent data indicates that water can undergo an amorphous/amorphous phase transition below a critical temperature T{sub c} of 217K and above a critical pressure P{sub c} of 380 atm.

  16. Hydrogen Sticking on Amorphous Water-Ice: A Numerical Study

    NASA Astrophysics Data System (ADS)

    Dupuy, John; Lewis, Steven; Stancil, Phillip C.

    2016-01-01

    Gas-grain and gas-phase reactions dominate the formation of molecules in the interstellar medium (ISM). Gas-grain reactions require a substrate on which the reaction is able to occur. The formation of molecular hydrogen (H2) in the ISM is a prime example of a gas-grain reaction. In these reactions, an atom of hydrogen will strike a surface, adsorb to the surface, interact with the molecular structure of substrate (in this case water), form molecular hydrogen, and then be ejected from the surface. We perform classical molecular dynamics (MD) simulations of hydrogen atoms sticking to an amorphous water-ice surface. This study examines the first step in the process; the sticking of the atom to the substrate. This talk emphasizes the importance of accurately defining a sticking event in calculating sticking probabilities which are used to obtain a reasonable model for H2 formation in the ISM. With these sticking probabilities calculated, sticking coefficients are obtained for various ice substrate temperatures and incident H-atom kinetic energies.

  17. Experimental studies of gas trapping in amorphous ice and thermal modelling of comets: Implications for Rosetta

    NASA Technical Reports Server (NTRS)

    Bar-Nun, Akiva

    1989-01-01

    The trapping of mixtures of CO, CH4, N2 and Ar in amorphous water ice was studied experimentally. It is shown that the ice particles could not have been formed at a higher temperature and, subsequently, cool down. Experiments where ice was deposited at elevated temperatures, then cooled down and gas was flowed into the ice, showed that the amount of trapped gas depends only on the highest temperature at which the ice was formed, or resided, prior to cooling and gas flow into it. Consequently, the cometary ice had to be formed at approx. 48 K and the ice is therefore amorphous. The thermal profile of a comet in Halley's orbit was calculated, including the build-up of an insulating dust layer. It was found that an insulating dust layer a few cm thick is enough to choke most of the water emission from the surface. A similar thermal model was calculated for comet P/Temple-1, a candidate for both CRAF and Rosetta (CNSR) missions. The temperature at a depth of 10 m is approx. 160 K for all models considered and, hence, the ice at this depth is crystalline. A crystalline ice layer 40 to 240 m thick was found to overly the gas-laden amorphous ice. Consequently, it should be difficult for the probes of the two comet missions to sample pristine amorphous ice, unless they are aimed at the bottom of an active crater.

  18. Extremely low thermal conductivity of amorphous ice - Relevance to comet evolution

    NASA Technical Reports Server (NTRS)

    Kouchi, A.; Greenberg, J. M.; Yamamoto, T.; Mukai, T.

    1992-01-01

    The thermal conductivity of very slowly deposited amorphous ice derived from experimental results is shown to be a factor of 0.0001 to 0.00001 less than hitherto estimated. Using the exceedingly low value of the thermal conductivity of comets deduced from the amorphous ice properties leads to the expectation that internal heating of comets is negligible below the outer several tens of centimeters.

  19. New Optical Constants of Amorphous and Crystalline H2O-ice, 3-20_m

    NASA Technical Reports Server (NTRS)

    Mastrapa, Rachel Michelle Elizab

    2008-01-01

    We will present new optical constants forth amorphous and crystalline H2O-ice in the spectral range 3-20 _m. Our new measurements provide high temperature resolution for crystalline H2O-ice, 10 K intervals from 20-150 K, including temperatures relevant to Solar System ices. We have found that the shape of the 3 _m feature in amorphous H2O-ice is strongly dependant on deposition temperature and the high and low density phases of amorphous H2O-ice are not easily distinguishable. We will present methods of measuring the change in band shape with phase and temperature. We acknowledge financial support from the NASA Origins of the Solar System Program and the NASA Planetary Geology and Geophysics Program.

  20. Ice Ih anomalies: Thermal contraction, anomalous volume isotope effect, and pressure-induced amorphization.

    PubMed

    Salim, Michael A; Willow, Soohaeng Yoo; Hirata, So

    2016-05-28

    Ice Ih displays several anomalous thermodynamic properties such as thermal contraction at low temperatures, an anomalous volume isotope effect (VIE) rendering the volume of D2O ice greater than that of H2O ice, and a pressure-induced transition to the high-density amorphous (HDA) phase. Furthermore, the anomalous VIE increases with temperature, despite its quantum-mechanical origin. Here, embedded-fragment ab initio second-order many-body perturbation (MP2) theory in the quasiharmonic approximation (QHA) is applied to the Gibbs energy of an infinite, proton-disordered crystal of ice Ih at wide ranges of temperatures and pressures. The quantum effect of nuclei moving in anharmonic potentials is taken into account from first principles without any empirical or nonsystematic approximation to either the electronic or vibrational Hamiltonian. MP2 predicts quantitatively correctly the thermal contraction at low temperatures, which is confirmed to originate from the volume-contracting hydrogen-bond bending modes (acoustic phonons). It qualitatively reproduces (but underestimates) the thermal expansion at higher temperatures, caused by the volume-expanding hydrogen-bond stretching (and to a lesser extent librational) modes. The anomalous VIE is found to be the result of subtle cancellations among closely competing isotope effects on volume from all modes. Consequently, even ab initio MP2 with the aug-cc-pVDZ and aug-cc-pVTZ basis sets has difficulty reproducing this anomaly, yielding qualitatively varied predictions of the sign of the VIE depending on such computational details as the choice of the embedding field. However, the temperature growth of the anomalous VIE is reproduced robustly and is ascribed to the librational modes. These solid-state MP2 calculations, as well as MP2 Born-Oppenheimer molecular dynamics, find a volume collapse and a loss of symmetry and long-range order in ice Ih upon pressure loading of 2.35 GPa or higher. Concomitantly, rapid softening of

  1. Ice Ih anomalies: Thermal contraction, anomalous volume isotope effect, and pressure-induced amorphization

    NASA Astrophysics Data System (ADS)

    Salim, Michael A.; Willow, Soohaeng Yoo; Hirata, So

    2016-05-01

    Ice Ih displays several anomalous thermodynamic properties such as thermal contraction at low temperatures, an anomalous volume isotope effect (VIE) rendering the volume of D2O ice greater than that of H2O ice, and a pressure-induced transition to the high-density amorphous (HDA) phase. Furthermore, the anomalous VIE increases with temperature, despite its quantum-mechanical origin. Here, embedded-fragment ab initio second-order many-body perturbation (MP2) theory in the quasiharmonic approximation (QHA) is applied to the Gibbs energy of an infinite, proton-disordered crystal of ice Ih at wide ranges of temperatures and pressures. The quantum effect of nuclei moving in anharmonic potentials is taken into account from first principles without any empirical or nonsystematic approximation to either the electronic or vibrational Hamiltonian. MP2 predicts quantitatively correctly the thermal contraction at low temperatures, which is confirmed to originate from the volume-contracting hydrogen-bond bending modes (acoustic phonons). It qualitatively reproduces (but underestimates) the thermal expansion at higher temperatures, caused by the volume-expanding hydrogen-bond stretching (and to a lesser extent librational) modes. The anomalous VIE is found to be the result of subtle cancellations among closely competing isotope effects on volume from all modes. Consequently, even ab initio MP2 with the aug-cc-pVDZ and aug-cc-pVTZ basis sets has difficulty reproducing this anomaly, yielding qualitatively varied predictions of the sign of the VIE depending on such computational details as the choice of the embedding field. However, the temperature growth of the anomalous VIE is reproduced robustly and is ascribed to the librational modes. These solid-state MP2 calculations, as well as MP2 Born-Oppenheimer molecular dynamics, find a volume collapse and a loss of symmetry and long-range order in ice Ih upon pressure loading of 2.35 GPa or higher. Concomitantly, rapid softening of

  2. New Optical Constants for Amorphous and Crystalline H2O-ice

    NASA Technical Reports Server (NTRS)

    Mastrapa, Rachel; Bernstein, Max; Sandford, Scott

    2006-01-01

    We have used the infrared spectra of laboratory ices to calculate the real and imaginary indices of refraction for amorphous and crystalline H2O-ice. We create H2O-ice samples in vacuum (approx. 10(exp ^-8)Torr). We measure the thickness of the sample by reflecting a He-Ne laser off of the sample and counting interference fringes as it grows and then collect transmission spectra of the samples in the wavelength range 1.25-22 micrometers. Using the ice thickness and transmission spectrum we calculate the imaginary part of the index of refraction. A Kramers-Kronig calculation is then used to calculate the real part of the index of refraction (Berland et al. 1994; Hudgins et al. 1993). These optical constants can be used to create model spectra for comparison to spectra from Solar System objects. We will summarize the differences between the amorphous and crystalline H2O-ice spectra. These include weakening of features and shifting of features to shorter wavelength in amorphous H,O-ice spectra. We will also discuss methods of using band area ratios to quickly estimate the fraction of amorphous to crystalline H2O-ice. We acknowledge financial support from the NASA Origins of the Solar System Program, the NASA Planetary Geology and Geophysics Program, and the NASA Postdoctoral Program.

  3. AN INFRARED SPECTROSCOPIC STUDY OF AMORPHOUS AND CRYSTALLINE ICES OF VINYLACETYLENE AND IMPLICATIONS FOR SATURN'S SATELLITE TITAN

    SciTech Connect

    Kim, Y. S.; Kaiser, R. I.

    2009-04-15

    Laboratory infrared spectra of amorphous and crystalline vinylacetylene ices were recorded in the range of 7000-400 cm{sup -1}. The spectra showed several amorphous features in the ice deposited at 10 K, which were then utilized to monitor a phase transition between 93 {+-} 1 K to form the crystalline structure. Successive heating allows monitoring of the sublimation profile of the vinylacetylene sample in the range of 101-120 K. Considering Titan's surface temperature of 94 K, vinylacetylene ice is likely to be crystalline. Analogous studies on related planetary-bound molecules such as triaceylene and cyanoacetylene may be further warranted to gain better perspectives into the composition of the condensed phases in the Titan's atmosphere (aerosol particles) and of Titan's surface. Based on our studies, we recommend utilizing the {nu}{sub 1} and {nu}{sub 16}//{nu}{sub 11}/{nu}{sub 17} fundamentals at about 3300 and 650 cm{sup -1} to determine if solid vinylacetylene is crystalline or amorphous on Titan.

  4. A Molecular Dynamics Study of the Helium Absorption by Amorphous and Crystalline Ice

    NASA Astrophysics Data System (ADS)

    Bilic, Ante; Jónsson, Hannes; Kay, Bruce D.

    2001-03-01

    Molecular Dynamics simulations employing classical trajectory techniques are used to study the absorption of He atoms by thin amorphous and crystalline ice films at low temperatures. On the basal plane of hexagonal crystalline ice the He absorption probability increases strongly with increasing translational energy and decreases dramatically as the incident angle is moved away from the surface normal. Analysis of the trajectories indicates that absorption occurs through hexagonal ring structures existing at the ice surface and that the active absorption zone is highly-localized near the center of these rings. Furthermore, the area of this active absorption zone increases dramatically with increasing translational energy. These findings are indicative of a large activation barrier and a strong steric effect for the insertion of the He atoms into the bulk. Helium uptake by amorphous ice is studied on a glassy solid formed by rapid quenching of a thermally equilibrated, high-temperature liquid. The He absorption probability increases with incident translation energy and decreases with incident angle but in a much less dramatic manner than on crystalline ice. The differences between crystalline and amorphous ice arise from a broader distribution of absoprtion sites on the amorphous sample. The details of the simulations and comparison with recent experiments will be presented. *Pacific Northwest National Laboratory is a multiprogram national laboratory operated for the U.S. Department of Energy by Battelle Memorial Institute under contract DE-AC06-76RLO 1830.

  5. Phase diagram of amorphous solid water: low-density, high-density, and very-high-density amorphous ices.

    PubMed

    Giovambattista, Nicolas; Stanley, H Eugene; Sciortino, Francesco

    2005-09-01

    We calculate the phase diagram of amorphous solid water by performing molecular dynamics simulations using the extended simple point charge (SPC/E) model. Our simulations follow different paths in the phase diagram: isothermal compression/decompression, isochoric cooling/heating, and isobaric cooling/heating. We are able to identify low-density amorphous (LDA), high-density amorphous (HDA), and very-high density amorphous (VHDA) ices. The density rho of these glasses at different pressure P and temperature T agree well with experimental values. We also study the radial distribution functions of glassy water. In agreement with experiments, we find that LDA, HDA, and VHDA are characterized by a tetrahedral hydrogen-bonded network and that, as compared to LDA, HDA has an extra interstitial molecule between the first and second shell. VHDA appears to have two such extra molecules. We obtain VHDA, as in experiment, by isobaric heating of HDA. We also find that "other forms" of glassy water can be obtained upon isobaric heating of LDA, as well as amorphous ices formed during the transformation of LDA to HDA. We argue that these other forms of amorphous ices, as well as VHDA, are not altogether new glasses but rather are the result of aging induced by heating. Samples of HDA and VHDA with different densities are recovered at normal P, showing that there is a continuum of glasses. Furthermore, the two ranges of densities of recovered HDA and recovered VHDA overlap at ambient P. Our simulations reproduce the experimental findings of HDA --> LDA and VHDA --> LDA transformations. We do not observe a VHDA --> HDA transformation, and our final phase diagram of glassy water together with equilibrium liquid data suggests that for the SPC/E model the VHDA --> HDA transformation cannot be observed with the present heating rates accessible in simulations. Finally, we discuss the consequences of our findings for the understanding of the transformation between the different amorphous

  6. Low thermal inertias of icy planetary surfaces. Evidence for amorphous ice?

    NASA Astrophysics Data System (ADS)

    Ferrari, C.; Lucas, A.

    2016-04-01

    Context. Thermal inertias of atmosphereless icy planetary bodies happen to be very low. Aims: We relate the thermal inertia to the regolith properties such as porosity, grain size, ice form and heat transfer processes to understand why it is low. We interpret the dichotomy in thermal inertia of the surface of Mimas in terms of changes in regolith properties. We predict how the thermal inertia of these bodies may vary with heliocentric distance depending on these properties. Methods: We combine available models of conductivity by contact or radiation to understand what heat transfer process is predominant. Results: The magnitude of the thermal inertia of a porous icy regolith is mainly governed by the crystalline or amorphous ice forms, and the quality of contacts between grains. Beyond the orbit of Jupiter, thermal inertias as low as a few tens J/m2/ K/s1/2 are difficult to reproduce with plausible porosity and grains sizes made of crystalline ice unless contacts are loose. This is, on the contrary, straightforward for regoliths of sub-cm-sized grains made of amorphous water ice. This study points out the importance of including the temperature dependence of thermophysical properties of water ice forms and the radiative conduction in thermal models of these bodies. The relatively high thermal inertia of the leading face of Mimas can be explained by a regolith of crystalline ice grains in tight contacts, which are eventually sintered by the bombardment of high energy electrons. The low thermal inertia of its trailing face is easily reproduced by a regolith of moderate porosity with sub-mm-sized grains of amorphous ice. The characteristic decrease of thermal inertia with heliocentric distance of icy atmosphereless surfaces and the very low thermal inertia of relevant trans-Neptunian objects are easily explained if amorphous ice is present at cm depths below a thin layer of crystalline ice.

  7. First Infrared Band Strengths for Amorphous CO2, an Overlooked Component of Interstellar Ices

    NASA Astrophysics Data System (ADS)

    Gerakines, Perry A.; Hudson, Reggie L.

    2015-08-01

    Solid carbon dioxide (CO2) has long been recognized as a component of both interstellar and solar system ices, but a recent literature search has revealed significant qualitative and quantitative discrepancies in the laboratory spectra on which the abundances of extraterrestrial CO2 are based. Here we report new infrared (IR) spectra of amorphous CO2-ice along with band intensities (band strengths) of four mid-IR absorptions, the first such results in the literature. A possible thickness dependence for amorphous-CO2 IR band shapes and positions also is investigated, and the three discordant reports of amorphous CO2 spectra in the literature are addressed. Applications of our results are discussed with an emphasis on laboratory investigations and results from astronomical observations. A careful comparison with earlier work shows that the IR spectra calculated from several databases for CO2 ices, all ices being made near 10 K, are not for amorphous CO2, but rather for crystalline CO2 or crystalline-amorphous mixtures.

  8. Interaction of acetonitrile with the surfaces of amorphous and crystalline ice

    SciTech Connect

    Schaff, J.E.; Roberts, J.T.

    1999-10-12

    The adsorption of acetonitrile (CH{sub 3}CN) on ultrathin films of ice under ultrahigh vacuum was investigated with temperature-programmed desorption ass spectrometry (TPD) and Fourier transform infrared reflection absorption spectroscopy (FTIRAS). Two types of film were studied, amorphous and crystalline. On the amorphous films, two sates of adsorbed acetonitrile were observed by TPD and FTIRAS. One of the states is attributed to acetonitrile that is hydrogen bonded to agree OH group at the ice surface; the other state is assigned to acetonitrile that is purely physiorbed. Evidence for the hydrogen-bonded state is two-fold. First, there is a large kinetic isotope effect for desorption from H{sub 2}O-and D{sub 2}O-ice: the desorption temperatures from ice-h{sub 2} and ice-d{sub 2} are {approximately}161 and {approximately}176 K, respectively. Second, the C{triple{underscore}bond}N stretching frequency (2,265 cm{sup {minus}1}) is 16 cm{sup {minus}1} is greater than that of physisorbed acetonitrile, and it is roughly equal to that of acetonitrile which is hydrogen bonded to an OH group at the air-liquid water interface. On the crystalline films, there is no evidence for a hydrogen-bonded state in the TPD spectra. The FTIRAS spectra do show that some hydrogen-bonded acetonitrile is present but at a maximum coverage that is roughly one-sixth of that on the amorphous surface. The difference between the amorphous and crystalline surfaces cannot be attributed to a difference n surface areas. Rather, this work provides additional evidence that the surface chemical properties of amorphous ice are different from those of crystalline ice.

  9. First-order transition in confined water between high-density liquid and low-density amorphous phases.

    PubMed

    Koga, K; Tanaka, H; Zeng, X C

    2000-11-30

    Supercooled water and amorphous ice have a rich metastable phase behaviour. In addition to transitions between high- and low-density amorphous solids, and between high- and low-density liquids, a fragile-to-strong liquid transition has recently been proposed, and supported by evidence from the behaviour of deeply supercooled bilayer water confined in hydrophilic slit pores. Here we report evidence from molecular dynamics simulations for another type of first-order phase transition--a liquid-to-bilayer amorphous transition--above the freezing temperature of bulk water at atmospheric pressure. This transition occurs only when water is confined in a hydrophobic slit pore with a width of less than one nanometre. On cooling, the confined water, which has an imperfect random hydrogen-bonded network, transforms into a bilayer amorphous phase with a perfect network (owing to the formation of various hydrogen-bonded polygons) but no long-range order. The transition shares some characteristics with those observed in tetrahedrally coordinated substances such as liquid silicon, liquid carbon and liquid phosphorus. PMID:11117739

  10. Neutron Scattering Analysis of Water's Glass Transition and Micropore Collapse in Amorphous Solid Water

    NASA Astrophysics Data System (ADS)

    Hill, Catherine R.; Mitterdorfer, Christian; Youngs, Tristan G. A.; Bowron, Daniel T.; Fraser, Helen J.; Loerting, Thomas

    2016-05-01

    The question of the nature of water's glass transition has continued to be disputed over many years. Here we use slow heating scans (0.4 K min-1 ) of compact amorphous solid water deposited at 77 K and an analysis of the accompanying changes in the small-angle neutron scattering signal, to study mesoscale changes in the ice network topology. From the data we infer the onset of rotational diffusion at 115 K, a sudden switchover from nondiffusive motion and enthalpy relaxation of the network at <121 K to diffusive motion across sample grains and sudden pore collapse at >121 K , in excellent agreement with the glass transition onset deduced from heat capacity and dielectric measurements. This indicates that water's glass transition is linked with long-range transport of water molecules on the time scale of minutes and, thus, clarifies its nature. Furthermore, the slow heating rates combined with the high crystallization resistance of the amorphous sample allow us to identify the glass transition end point at 136 K, which is well separated from the crystallization onset at 144 K—in contrast to all earlier experiments in the field.

  11. Neutron Scattering Analysis of Water's Glass Transition and Micropore Collapse in Amorphous Solid Water.

    PubMed

    Hill, Catherine R; Mitterdorfer, Christian; Youngs, Tristan G A; Bowron, Daniel T; Fraser, Helen J; Loerting, Thomas

    2016-05-27

    The question of the nature of water's glass transition has continued to be disputed over many years. Here we use slow heating scans (0.4  K min^{-1}) of compact amorphous solid water deposited at 77 K and an analysis of the accompanying changes in the small-angle neutron scattering signal, to study mesoscale changes in the ice network topology. From the data we infer the onset of rotational diffusion at 115 K, a sudden switchover from nondiffusive motion and enthalpy relaxation of the network at <121  K to diffusive motion across sample grains and sudden pore collapse at >121  K, in excellent agreement with the glass transition onset deduced from heat capacity and dielectric measurements. This indicates that water's glass transition is linked with long-range transport of water molecules on the time scale of minutes and, thus, clarifies its nature. Furthermore, the slow heating rates combined with the high crystallization resistance of the amorphous sample allow us to identify the glass transition end point at 136 K, which is well separated from the crystallization onset at 144 K-in contrast to all earlier experiments in the field. PMID:27284664

  12. A unified description of crystalline-to-amorphous transitions

    SciTech Connect

    Lam, N.Q.; Okamoto, P.R.; Devanathan, R. |; Meshii, M.

    1993-07-01

    Amorphous metallic alloys can now be synthesized by a variety of solid-state processes demonstrating the need for a more general approach to crystalline-to-amorphous (c-a) transitions. By focusing on static atomic displacements as a measure of chemical and topological disorder, we show that a unified description of c-a transformations can be based on a generalization of the phenomenological melting criterion proposed by Lindemann. The generalized version assumes that melting of a defective crystal occurs whenever the sum of thermal and static mean-square displacements exceeds a critical value identical to that for melting of the defect-free crystal. This implies that chemical or topological disorder measured by static displacements is thermodynamically equivalent to heating, and therefore that the melting temperature of the defective crystal will decrease with increasing amount of disorder. This in turn implies the existence of a critical state of disorder where the melting temperature becomes equal to a glass-transition temperature below which the metastable crystal melts to a glass. The generalized Lindemann melting criterion leads naturally to an interpretation of c-a transformations as defect-induced, low-temperature melting of critically disordered crystals. Confirmation of this criterion is provided by molecular-dynamics simulations of heat-induced melting and of defect-induced amorphization of intermetallic compounds caused either by the production of Frenkel pairs or anti-site defects. The thermodynamic equivalence between static atomic disorder and heating is reflected in the identical softening effects which they have on elastic properties and also in the diffraction analysis of diffuse scattering from disordered crystals, where the effect of static displacements appears as an artificially-enlarged thermal Debye-Waller factor. Predictions of this new, unified approach to melting and amorphization are compared with available experimental information.

  13. Plastic Instability in Amorphous Selenium near its Glass Transition Temperature

    SciTech Connect

    Su, Caijun; Lamanna Jr, James; Gao, Yanfei; Oliver, Warren C.; Pharr, George M

    2010-01-01

    Deformation behavior of amorphous selenium near its glass transition temperature (31 C) has been investigated by uniaxial compression and nanoindentation creep tests. Cylindrical specimens compressed at high temperatures and low strain rates deform into drum-like shape, while tests at low temperatures and high strain rates lead to fragmentation. These results agree nicely with the stress exponent and kinetic activation parameters extracted from the nanoindentation creep tests by using a similarity analysis. The dependence of deformation modes on temperature and strain rate is understood as a consequence of material instability and strain localization in the rate-dependent solids.

  14. Formation of gas hydrate during crystallization of ethane-saturated amorphous ice

    NASA Astrophysics Data System (ADS)

    Faizullin, M. Z.; Vinogradov, A. V.; Skokov, V. N.; Koverda, V. P.

    2014-10-01

    Layers of ethane-saturated amorphous ice were prepared by depositing molecular beams of water and gas on a substrate cooled with liquid nitrogen. The heating of the layers was accompanied by vitrification (softening) followed by spontaneous crystallization. Crystallization of condensates under the conditions of deep metastability proceeded with gas hydrate formation. The vitrification and crystallization temperatures of the condensates were determined from the changes in their dielectric properties on heating. The thermal effects of transformations were recorded by differential thermal analysis. The crystallization of the amorphous water layers was studied by electron diffraction. Formation of a metastable packing with elements of a cubic diamond-like structure was noted.

  15. Investigation of the atypical glass transition and recrystallization behavior of amorphous prazosin salts.

    PubMed

    Kumar, Lokesh; Popat, Dharmesh; Bansal, Arvind K

    2011-01-01

    This manuscript studied the effect of counterion on the glass transition and recrystallization behavior of amorphous salts of prazosin. Three amorphous salts of prazosin, namely, prazosin hydrochloride, prazosin mesylate and prazosin tosylate were prepared by spray drying, and characterized by optical-polarized microscopy, differential scanning calorimetry and powder X-ray diffraction. Modulated differential scanning calorimetry was used to determine the glass transition and recrystallization temperature of amorphous salts. Glass transition of amorphous salts followed the order: prazosin mesylate > prazosin tosylate ~ prazosin hydrochloride. Amorphous prazosin mesylate and prazosin tosylate showed glass transition, followed by recrystallization. In contrast, amorphous prazosin hydrochloride showed glass transition and recrystallization simultaneously. Density Functional Theory, however, suggested the expected order of glass transition as prazosin hydrochloride > prazosin mesylate > prazosin tosylate. The counterintuitive observation of amorphous prazosin hydrochloride having lower glass transition was explained in terms of its lower activation energy (206.1 kJ/mol) for molecular mobility at Tg, compared to that for amorphous prazosin mesylate (448.5 kJ/mol) and prazosin tosylate (490.7 kJ/mol), and was further correlated to a difference in hydrogen bonding strength of the amorphous and the corresponding recrystallized salts. This study has implications in selection of an optimal amorphous salt form for pharmaceutical development. PMID:24310595

  16. Study of ice cluster impacts on amorphous silica using the ReaxFF reactive force field molecular dynamics simulation method

    NASA Astrophysics Data System (ADS)

    Rahnamoun, A.; van Duin, A. C. T.

    2016-03-01

    We study the dynamics of the collisions between amorphous silica structures and amorphous and crystal ice clusters with impact velocities of 1 km/s, 4 km/s, and 7 km/s using the ReaxFF reactive molecular dynamics simulation method. The initial ice clusters consist of 150 water molecules for the amorphous ice cluster and 128 water molecules for the crystal ice cluster. The ice clusters are collided on the surface of amorphous fully oxidized and suboxide silica. These simulations show that at 1 km/s impact velocities, all the ice clusters accumulate on the surface and at 4 km/s and 7 km/s impact velocities, some of the ice cluster molecules bounce back from the surface. At 4 km/s and 7 km/s impact velocities, few of the water molecules dissociations are observed. The effect of the second ice cluster impacts on the surfaces which are fully covered with ice, on the mass loss/accumulation is studied. These studies show that at 1 km/s impacts, the entire ice cluster accumulates on the surface at both first and second ice impacts. At higher impact velocities, some ice molecules which after the first ice impacts have been attached to the surface will separate from the surface after the second ice impacts at 7 km/s impact velocity. For the 4 km/s ice cluster impact, ice accumulation is observed for the crystal ice cluster impacts and ice separation is observed for the amorphous ice impacts. Observing the temperatures of the ice clusters during the collisions indicates that the possibility of electron excitement at impact velocities less than 10 km/s is minimal and ReaxFF reactive molecular dynamics simulation can predict the chemistry of these hypervelocity impacts. However, at impact velocities close to 10 km/s the average temperature of the impacting ice clusters increase to about 2000 K, with individual molecules occasionally reaching temperatures of over 8000 K and thus it will be prudent to consider the concept of electron excitation at these higher impact velocities

  17. Modeling Amorphization of Crystalline Water Ice on Europa, Ganymede, and Callisto

    NASA Astrophysics Data System (ADS)

    Mastrapa, R. M.; Brown, R. H.

    2002-12-01

    We have used the collision cascade program MARLOWE to simulate radiation damage of crystalline water ice on the surfaces of Callisto, Europa, and Ganymede. The conversion of crystalline water ice to its amorphous phase by UV and ion radiation has been well studied [1], [2]. This amorphization process is countered by temperature dependent crystallization. We have previously modeled amorphization of water in the Kuiper Belt where the crystallization process is negligible [3], [4]. We then modeled the amorphization process on the icy Galilean satellites, however, the model failed at timescales over 10000 seconds [5]. We have changed the model to run at long timescales for this meeting. We have also implemented a transformation method to randomize the initial energies of ions. We plan to run simulations with Hydrogen, Oxygen and Sulfur ions to determine the extent of damage and how it compares with the rate of crystallization. [1] Kouchi, A. and T. Kuroda, Nature, 1990. 344: 134. [2] Strazzulla, G., et al., JGR, 1991. 96(E2): 17547. [3] Mastrapa, R.M.E. and R.H. Brown, LPSC #32 #1381, 2001. [4] Mastrapa, R.M.E. and R.H. Brown, DPS #33 #08.07, 2001. [5] Mastrapa, R.M.E. and R.H. Brown, LPSC #33 #1111, 2002.

  18. Modeling Amorphization of Crystalline Water Ice on Europa, Ganymede, and Callisto

    NASA Astrophysics Data System (ADS)

    Mastrapa, R. M. E.; Brown, R. H.

    2002-09-01

    We have used the collision cascade program MARLOWE to simulate radiation damage of crystalline water ice on the surfaces of Callisto, Europa, and Ganymede. The conversion of crystalline water ice to its amorphous phase by uv and ion radiation has been well studied [1], [2]. This amorphization process is countered by temperature dependent crystallization. We have previously modeled amorphization of water in the Kuiper Belt where the crystallization process is negligible [3], [4]. We then modelled the amorphization process on the icy Galilean satellites, however, the model failed at timescales over 10000 seconds [5]. We have changed the model to run at long timescales for this meeting. We plan to run simulations with Hydrogen, Oxygen and Sulfur ions to determine the extent of damage and how it compares with the rate of crystallization. [1] Kouchi, A. and T. Kuroda, Nature, 1990. 344: 134. [2] Strazzulla, G., et al., JGR, 1991. 96(E2): 17547. [3] Mastrapa, R.M.E. and R.H. Brown, LPSC #32 #1381, 2001. [4] Mastrapa, R.M.E. and R.H. Brown, DPS #33 #08.07, 2001. [5] Mastrapa, R.M.E. and R.H. Brown, LPSC #33 #1111, 2002.

  19. Sticking of Molecules on Nonporous Amorphous Water Ice

    NASA Astrophysics Data System (ADS)

    He, Jiao; Acharyya, Kinsuk; Vidali, Gianfranco

    2016-05-01

    Accurate modeling of physical and chemical processes in the interstellar medium (ISM) requires detailed knowledge of how atoms and molecules adsorb on dust grains. However, the sticking coefficient, a number between 0 and 1 that measures the first step in the interaction of a particle with a surface, is usually assumed in simulations of ISM environments to be either 0.5 or 1. Here we report on the determination of the sticking coefficient of H2, D2, N2, O2, CO, CH4, and CO2 on nonporous amorphous solid water. The sticking coefficient was measured over a wide range of surface temperatures using a highly collimated molecular beam. We showed that the standard way of measuring the sticking coefficient—the King–Wells method—leads to the underestimation of trapping events in which there is incomplete energy accommodation of the molecule on the surface. Surface scattering experiments with the use of a pulsed molecular beam are used instead to measure the sticking coefficient. Based on the values of the measured sticking coefficient, we suggest a useful general formula of the sticking coefficient as a function of grain temperature and molecule-surface binding energy. We use this formula in a simulation of ISM gas–grain chemistry to find the effect of sticking on the abundance of key molecules both on grains and in the gas phase.

  20. Crystallization of amorphous ice as the cause of Comet P/Halley's outburst at 14 AU

    NASA Technical Reports Server (NTRS)

    Prialnik, D.; Bar-Nun, A.

    1992-01-01

    An explanation is provided for the postperihelion eruption of Comet P/Halley, detected in February 1991 and believed to have started three months earlier, namely, the crystallization of amorphous ice taking place in the interior of the porous nucleus, at depths of a few tens of meters, accompanied by the release of trapped gases. Numerical calculations show that for a bulk density of 0.5 g/cu cm and a pore size of 1 micron crystallization occurs on the outbound leg of Comet P/Halley's orbit, at heliocentric distances between 5 AU and 17 AU. The trapped gas is released and flows to the surface through the porous medium. It may also open wider channels, as the internal pressures obtained surpass the tensile strength of cometary ice. The outflowing gas carries with it grains of ice and dust, and thus can explain the large amounts of dust observed in the coma at 14.3 AU and beyond.

  1. Statistical physics of the yielding transition in amorphous solids.

    PubMed

    Karmakar, Smarajit; Lerner, Edan; Procaccia, Itamar

    2010-11-01

    The art of making structural, polymeric, and metallic glasses is rapidly developing with many applications. A limitation is that under increasing external strain all amorphous solids (like their crystalline counterparts) have a finite yield stress which cannot be exceeded without effecting a plastic response which typically leads to mechanical failure. Understanding this is crucial for assessing the risk of failure of glassy materials under mechanical loads. Here we show that the statistics of the energy barriers ΔE that need to be surmounted changes from a probability distribution function that goes smoothly to zero as ΔE=0 to a pdf which is finite at ΔE=0 . This fundamental change implies a dramatic transition in the mechanical stability properties with respect to external strain. We derive exact results for the scaling exponents that characterize the magnitudes of average energy and stress drops in plastic events as a function of system size. PMID:21230534

  2. Possible existence of two amorphous phases of d-mannitol related by a first-order transition

    NASA Astrophysics Data System (ADS)

    Zhu, Men; Wang, Jun-Qiang; Perepezko, John H.; Yu, Lian

    2015-06-01

    We report that the common polyalcohol d-mannitol may have two amorphous phases related by a first-order transition. Slightly above its glass transition temperature Tg (284 K), the supercooled liquid (SCL) of d-mannitol transforms to a low-energy, apparently amorphous phase with stronger hydrogen bonds. The enthalpy of this so-called Phase X is approximately halfway between those of the known amorphous and crystalline phases, a position low for glass aging and high for crystal polymorphs. Similar to the SCL, Phase X is transparent with broad X-ray diffraction and Raman scattering; upon temperature cycling, it exhibits a glass-transition-like change of heat capacity. On fast heating, Phase X transforms back to the SCL near Tg + 50 K, enabling a determination of their equilibrium temperature. The presence of d-sorbitol as a plasticizer enables observation of a first-order transition from the SCL to Phase X entirely in the liquid state (liquid-liquid transition). The transition from d-mannitol's SCL to Phase X has intriguing similarities with the formation of the glacial phase of triphenyl phosphite (TPP) and the conversion from high-density to low-density amorphous ice, both studied intensely in the context of polyamorphism. All three processes occur near Tg with substantial enthalpy decrease toward the crystalline phases; the processes in water and d-mannitol both strengthen the hydrogen bonds. In contrast to TPP, d-mannitol's Phase X forms more rapidly and can transform back to the SCL. These features make d-mannitol a valuable new model for understanding polyamorphism.

  3. Possible existence of two amorphous phases of D-mannitol related by a first-order transition

    SciTech Connect

    Zhu, Men; Yu, Lian; Wang, Jun-Qiang; Perepezko, John H.

    2015-06-28

    We report that the common polyalcohol D-mannitol may have two amorphous phases related by a first-order transition. Slightly above its glass transition temperature T{sub g} (284 K), the supercooled liquid (SCL) of D-mannitol transforms to a low-energy, apparently amorphous phase with stronger hydrogen bonds. The enthalpy of this so-called Phase X is approximately halfway between those of the known amorphous and crystalline phases, a position low for glass aging and high for crystal polymorphs. Similar to the SCL, Phase X is transparent with broad X-ray diffraction and Raman scattering; upon temperature cycling, it exhibits a glass-transition-like change of heat capacity. On fast heating, Phase X transforms back to the SCL near T{sub g} + 50 K, enabling a determination of their equilibrium temperature. The presence of D-sorbitol as a plasticizer enables observation of a first-order transition from the SCL to Phase X entirely in the liquid state (liquid-liquid transition). The transition from D-mannitol’s SCL to Phase X has intriguing similarities with the formation of the glacial phase of triphenyl phosphite (TPP) and the conversion from high-density to low-density amorphous ice, both studied intensely in the context of polyamorphism. All three processes occur near T{sub g} with substantial enthalpy decrease toward the crystalline phases; the processes in water and D-mannitol both strengthen the hydrogen bonds. In contrast to TPP, D-mannitol’s Phase X forms more rapidly and can transform back to the SCL. These features make D-mannitol a valuable new model for understanding polyamorphism.

  4. Low-pressure clathrate-hydrate formation in amorphous astrophysical ice analogs

    NASA Technical Reports Server (NTRS)

    Blake, D. F.; Allamandola, L. J.; Sandford, S.; Hudgins, D.; Freund, F.

    1991-01-01

    In modeling cometary ice, the properties of clathrate hydrates were used to explain anomalous gas release at large radial distances from the Sun, and the retention of particular gas inventories at elevated temperatures. Clathrates may also have been important early in solar system history. However, there has never been a reasonable mechanism proposed for clathrate formation under the low pressures typical of these environments. For the first time, it was shown that clathrate hydrates can be formed by warming and annealing amorphous mixed molecular ices at low pressures. The complex microstructures which occur as a result of clathrate formation from the solid state may provide an explanation for a variety of unexplained phenomena. The vacuum and imaging systems of an Hitachi H-500H Analytical Electron Microscope was modified to study mixed molecular ices at temperatures between 12 and 373 K. The resulting ices are characterized by low-electron dose Transmission Electron Microscopy (TEM) and Selected Area Electron Diffraction (SAED). The implications of these results for the mechanical and gas release properties of comets are discussed. Laboratory IR data from similar ices are presented which suggest the possibility of remotely observing and identifying clathrates in astrophysical objects.

  5. A Molecular Beam Study of the Helium Absorption by Amorphous and Crystalline Ice

    NASA Astrophysics Data System (ADS)

    Ayotte, Patrick; Daschbach, John L.; Kimmel, Greg A.; Dohnálek, Zdenek; Smith, R. Scott; Kay, Bruce D.

    2001-03-01

    Molecular beam and thermal desorption techniques are employed to study the absorption of He atoms by thin amorphous and crystalline ice films at low temperatures. The He absorption probability increases strongly with increasing translational energy and decreases dramatically as the incident angle is moved away from the surface normal. These findings are indicative of a large activation barrier and a strong steric effect for the insertion of the He atoms into the bulk. Comparison between crystalline and amorphous ice suggests that absorption into the bulk occurs through hexagonal ring structures existing at the ice surface. We also observe significant diffusion of the absorbed He atoms deeper into the bulk at temperatures as low as 20 K. This diffusion occurs at a rate several orders of magnitude greater than expected classically from the known barrier of 12 kJ/mole and is consistent with a low-temperature transport mechanism involving thermally assisted tunneling. The details of the experimental findings and their implications will be presented. Pacific Northwest National Laboratory is a multiprogram national laboratory operated for the U.S. Department of Energy by Battelle Memorial Institute under contract DE-AC06-76RLO 1830.

  6. Thermal Properties of Amorphous Selenium over the Glass- Transition Range

    NASA Astrophysics Data System (ADS)

    Ismail, Mukhtar Veliev

    1997-02-01

    In has been shown that the heat capacity (Cp), coefficients of heat conductivity, (l) and thermal expansion, (a), for the amorphous selenium are dependent on the temperature of the transition from glass-forming state into a high elasticity condition. On this transition these quantities are increased by ACp=3,47 kal/deg\\cdotmol, D l=0,32\\cdot 10-3 cal/sec\\cdot deg., da=0,79\\cdot 10-5 deg-1. These increments are due to the contribution by the increased concentration of holes. Contribution of holes in the glass-forming region was calculated using the formulae by Hirai and Eyring for 1 mol of "heads", which is equal to Cp=3,06 kal/deg\\cdotmol. The "hole" theory for liquids is used as a strating point in the calculation of the l and a. The obtained resuls are: l =0,28\\cdot 10-3 kal/cm\\cdotsec\\cdotdeg. a=0,73\\cdot 10-5 deg-1. These quantities for Cp, l and a are in satisfactory agreement with experimental data.

  7. Radionuclides in Arctic sea ice: Tracers of sources, fates and ice transit time scales

    NASA Astrophysics Data System (ADS)

    Masqué, P.; Cochran, J. K.; Hirschberg, D. J.; Dethleff, D.; Hebbeln, D.; Winkler, A.; Pfirman, S.

    2007-08-01

    Arctic sea ice can incorporate sediment and associated chemical species during its formation in shallow shelf environments and can also intercept atmospherically transported material during transit. Release of this material in ice ablation areas (e.g. the Fram Strait) enhances fluxes of both sediments and associated species in such areas. We have used a suite of natural ( 7Be, 210Pb) and anthropogenic ( 137Cs, 239Pu, 240Pu) radionuclides in sea ice, sea-ice sediments (SIS), sediment trap material and bottom sediments from the Fram Strait to estimate transit times of sea ice from source to ablation areas, calculate radionuclide fluxes to the Fram Strait and investigate the role of sea-ice entrained sediments in sedimentation processes. Sea ice intercepts and transports the atmospherically supplied radionuclides 7Be and 210Pb, which are carried in the ice and are scavenged by any entrained SIS. All of the 7Be and most of the excess 210Pb measured in SIS collected in the Fram Strait are added to the ice during transit through the Arctic Ocean, and we use these radionuclides as chronometers to calculate ice transit times for individual ice floes. Transit times estimated from the 210Pb inventories in two ice cores are 1-3 years. Values estimated from the 7Be/ 210Pb excess activity ratio of SIS are about 3-5 years. Finally, equilibrium values of the activity ratio of 210Pb to its granddaughter 210Po in the ice cores indicate transit times of at least 2 years. These transit times are consistent with back-trajectory analyses of the ice floes. The latter, as well as the clay-mineral assemblage of the SIS (low smectite and high illite content), suggest that the sampled sea-ice floes originated from the eastern Siberian Arctic shelf seas such as the eastern Laptev Sea and the East Siberian Sea. This result is in agreement with the relatively low activities of 239,240Pu and 137Cs and the 240Pu/ 239Pu atom ratios (˜0.18, equivalent to that in global fallout) in SIS, indicating

  8. Pressure-induced reversible amorphization and an amorphous–amorphous transition in Ge2Sb2Te5 phase-change memory material

    PubMed Central

    Sun, Zhimei; Zhou, Jian; Pan, Yuanchun; Song, Zhitang; Mao, Ho-Kwang; Ahuja, Rajeev

    2011-01-01

    Ge2Sb2Te5 (GST) is a technologically very important phase-change material that is used in digital versatile disks-random access memory and is currently studied for the use in phase-change random access memory devices. This type of data storage is achieved by the fast reversible phase transition between amorphous and crystalline GST upon heat pulse. Here we report pressure-induced reversible crystalline-amorphous and polymorphic amorphous transitions in NaCl structured GST by ab initio molecular dynamics calculations. We have showed that the onset amorphization of GST starts at approximately 18 GPa and the system become completely random at approximately 22 GPa. This amorphous state has a cubic framework (c-amorphous) of sixfold coordinations. With further increasing pressure, the c-amorphous transforms to a high-density amorphous structure with trigonal framework (t-amorphous) and an average coordination number of eight. The pressure-induced amorphization is investigated to be due to large displacements of Te atoms for which weak Te–Te bonds exist or vacancies are nearby. Upon decompressing to ambient conditions, the original cubic crystalline structure is restored for c-amorphous, whereas t-amorphous transforms to another amorphous phase that is similar to the melt-quenched amorphous GST. PMID:21670255

  9. 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

  10. 2D ice from first principles: structures and phase transitions

    NASA Astrophysics Data System (ADS)

    Chen, Ji; Schusteritsch, Georg; Pickard, Chris J.; Salzmann, Christoph G.; Michaelides, Angelos

    Despite relevance to disparate areas such as cloud microphysics and tribology, major gaps in the understanding of the structures and phase transitions of low-dimensional water ice remain. Here we report a first principles study of confined 2D ice as a function of pressure. We find that at ambient pressure hexagonal and pentagonal monolayer structures are the two lowest enthalpy phases identified. Upon mild compression the pentagonal structure becomes the most stable and persists up to ca. 2 GPa at which point square and rhombic phases are stable. The square phase agrees with recent experimental observations of square ice confined within graphene sheets. We also find a double layer AA stacked square ice phase, which clarifies the difference between experimental observations and earlier force field simulations. This work provides a fresh perspective on 2D confined ice, highlighting the sensitivity of the structures observed to both the confining pressure and width.

  11. Far infrared spectra of amorphous and crystalline water ice and changes in these phases as the result of proton irradiation

    NASA Technical Reports Server (NTRS)

    Hudson, Reggie L.; Moore, Marla H.

    1992-01-01

    Far infrared spectra from 20 microns (500 cm(sup -1)) to 100 microns (100 cm(sup -1)) of water ice were measured. Amorphous ice deposited at 13 K has one absorption band at 45 microns (220 cm(sup -1)). Amorphous ice evolves into a crystalline form with absorptions at 44 microns (229 cm(sup -1)) and 62 microns (162 cm(sup -1)) as the temperature is increased to 155 K. Spectra documenting this phase change are presented as well as spectra of crystalline ice at temperatures between 13 K and 155 K. Far infrared spectra of amorphous and crystalline water ice before and after proton irradiation are also presented. Changes in these two forms are discussed in relation to ices in comets, grains, and planetary satellites in various radiation environments. Observations of non-terrestrial clathrate hydrates are still lacking despite the fact that clathrates first were suggested to exist in cometary and interstellar ices over forty years ago. Spectroscopy, the most direct method of astronomical detection, has been hampered by the similarity of clathrate hydrate spectra to those of unenclathrated guest molecules and solid H2O. A methanol (CH3OH) clathrate hydrate, using a recently published procedure, was prepared and its far-IR spectrum investigated. The spectrum is quite differenct from that of either unenclathrated CH3OH or solid H2O and so should be of value in astronomical searches for this clathrate.

  12. Dynamical aspects of intermolecular proton transfer in liquid water and low-density amorphous ices.

    PubMed

    Tahat, Amani; Martí, Jordi

    2014-05-01

    The microscopic dynamics of an excess proton in water and in low-density amorphous ices has been studied by means of a series of molecular dynamics simulations. Interaction of water with the proton species was modelled using a multistate empirical valence bond Hamiltonian model. The analysis of the effects of low temperatures on proton diffusion and transfer rates has been considered for a temperature range between 100 and 298 K at the constant density of 1 g cm(-3). We observed a marked slowdown of proton transfer rates at low temperatures, but some episodes are still seen at 100 K. In a similar fashion, mobility of the lone proton gets significantly reduced when temperature decreases below 273 K. The proton transfer in low-density amorphous ice is an activated process with energy barriers between 1-10 kJ/mol depending of the temperature range considered and eventually showing Arrhenius-like behavior. Spectroscopic data indicated the survival of both Zundel and Eigen structures along the whole temperature range, revealed by significant spectral frequency shifts. PMID:25353762

  13. The Infrared Spectra and Absorption Intensities of Amorphous Ices: Methane and Carbon Dioxide

    NASA Astrophysics Data System (ADS)

    Gerakines, Perry A.; Hudson, Reggie L.; Loeffler, Mark J.

    2015-11-01

    Our research group is carrying out new IR measurements of icy solids relevant to the outer solar system and the interstellar medium, with an emphasis on amorphous and crystalline ices below ~70 K. Our goal is to add to the relatively meager literature on this subject and to provide electronic versions of state-of-the-art data, since the abundances of such molecules cannot be deduced without accurate reference spectra and IR band strengths. In the past year, we have focused on two of the simplest and most abundant components of icy bodies in the solar system - methane (CH4) and carbon dioxide (CO2). Infrared spectra from ˜ 4500 to 500 cm-1 have been measured for each of these molecules in μm-thick films at temperatures from 10 to 70 K. All known amorphous and crystalline phases have been reproduced and, for some, presented for the first time. We also report measurements of the index of refraction at 670 nm and the mass densities for each ice phase. Comparisons are made to earlier work where possible. Electronic versions of our new results are available at http://science.gsfc.nasa.gov/691/cosmicice/ constants.html.

  14. Water formation through O2 + D pathway on cold silicate and amorphous water ice surfaces of interstellar interest

    NASA Astrophysics Data System (ADS)

    Chaabouni, H.; Minissale, M.; Manicò, G.; Congiu, E.; Noble, J. A.; Baouche, S.; Accolla, M.; Lemaire, J. L.; Pirronello, V.; Dulieu, F.

    2012-12-01

    The formation of the first monolayer of water molecules on bare dust grains is of primary importance to understand the growth of the icy mantles that cover dust in the interstellar medium. In this work, we explore experimentally the formation of water molecules from O2 + D reaction on bare silicate surfaces that simulates the grains present in the diffuse interstellar clouds at visual extinctions (AV < 3 mag). For comparison, we also study the formation of water molecules on surfaces covered with amorphous water ice representing the dense clouds (AV ⩾ 3 mag). Our studies focus on the formation of water molecules in the sub-monolayer and monolayer regimes using reflection absorption infrared spectroscopy and temperature-programmed desorption techniques. We provide the fractions of the products, such as D2O and D2O2 molecules formed on three astrophysically relevant surfaces held at 10 K (amorphous olivine-type silicate, porous amorphous water ice, and nonporous amorphous water ice). Our results showed that the formation of D2O molecules occurs with an efficiency of about 55%-60% on nonporous amorphous water ice and about 18% on bare silicate grains surfaces. We explain the low efficiency of D2O water formation on the silicate surfaces by the desorption upon formation of certain products once the reaction occurs between O2 and D atoms on the surface. A kinetic model taking into account the chemical desorption of newly formed water supports our conclusions.

  15. Photodissociation of methyl iodide adsorbed on low-temperature amorphous ice surfaces

    SciTech Connect

    DeSimone, Alice J.; Olanrewaju, Babajide O.; Grieves, Gregory A.; Orlando, Thomas M.

    2013-02-28

    Photodissociation dynamics of methyl iodide (CH{sub 3}I) adsorbed on both amorphous solid water (ASW) and porous amorphous solid water (PASW) has been investigated. The ejected ground-state I({sup 2}P{sub 3/2}) and excited-state I({sup 2}P{sub 1/2}) photofragments produced by 260- and 290-nm photons were detected using laser resonance-enhanced multiphoton ionization. In contrast to gas-phase photodissociation, (i) the I({sup 2}P{sub 3/2}) photofragment is favored compared to I({sup 2}P{sub 1/2}) at both wavelengths, (ii) I({sup 2}P{sub 3/2}) and I({sup 2}P{sub 1/2}) have velocity distributions that depend upon ice morphology, and (iii) I{sub 2} is produced on ASW. The total iodine [I({sup 2}P{sub 3/2})+I({sup 2}P{sub 1/2})+I{sub 2}] yield varies with substrate morphology, with greater yield from ASW than PASW using both 260- and 290-nm photons. Temperature-programmed desorption studies demonstrate that ice porosity enhances the trapping of adsorbed CH{sub 3}I, while pore-free ice likely allows monomer adsorption and the formation of two-dimensional CH{sub 3}I clusters. Reactions or collisions involving these clusters, I atomic fragments, or I-containing molecular fragments at the vacuum-surface interface can result in I{sub 2} formation.

  16. Probing of 2 dimensional confinement-induced structural transitions in amorphous oxide thin film

    PubMed Central

    Lee, Sung Keun; Ahn, Chi Won

    2014-01-01

    Whereas the atomic structure of surface of crystals is known to be distinct from that of bulk, experimental evidence for thickness-induced structural transitions in amorphous oxides is lacking. We report the NMR result for amorphous alumina with varying thickness from bulk up to 5 nm, revealing the nature of structural transitions near amorphous oxide surfaces/interfaces. The coordination environments in the confined amorphous alumina thin film are distinct from those of bulk, highlighted by a decrease in the fractions of high-energy clusters (and thus the degree of disorder) with thickness. The result implies that a wide range of variations in amorphous structures may be identified by controlling its dimensionality. PMID:24569515

  17. Two Dimensional Ice from First Principles: Structures and Phase Transitions.

    PubMed

    Chen, Ji; Schusteritsch, Georg; Pickard, Chris J; Salzmann, Christoph G; Michaelides, Angelos

    2016-01-15

    Despite relevance to disparate areas such as cloud microphysics and tribology, major gaps in the understanding of the structures and phase transitions of low-dimensional water ice remain. Here, we report a first principles study of confined 2D ice as a function of pressure. We find that at ambient pressure hexagonal and pentagonal monolayer structures are the two lowest enthalpy phases identified. Upon mild compression, the pentagonal structure becomes the most stable and persists up to ∼2  GPa, at which point the square and rhombic phases are stable. The square phase agrees with recent experimental observations of square ice confined within graphene sheets. This work provides a fresh perspective on 2D confined ice, highlighting the sensitivity of the structures observed to both the confining pressure and the width. PMID:26824547

  18. Two Dimensional Ice from First Principles: Structures and Phase Transitions

    NASA Astrophysics Data System (ADS)

    Chen, Ji; Schusteritsch, Georg; Pickard, Chris J.; Salzmann, Christoph G.; Michaelides, Angelos

    2016-01-01

    Despite relevance to disparate areas such as cloud microphysics and tribology, major gaps in the understanding of the structures and phase transitions of low-dimensional water ice remain. Here, we report a first principles study of confined 2D ice as a function of pressure. We find that at ambient pressure hexagonal and pentagonal monolayer structures are the two lowest enthalpy phases identified. Upon mild compression, the pentagonal structure becomes the most stable and persists up to ˜2 GPa , at which point the square and rhombic phases are stable. The square phase agrees with recent experimental observations of square ice confined within graphene sheets. This work provides a fresh perspective on 2D confined ice, highlighting the sensitivity of the structures observed to both the confining pressure and the width.

  19. Effect of Water Ice Transition on Murchison Meteorite

    NASA Astrophysics Data System (ADS)

    Páchová, H.; Kletetschka, G.

    2014-12-01

    Uncertainty of magnetic field existence during formation of our solar system may be resolved by studying the details of carbonaceous meteorite. We chose Murchison meteorite to represent this group of carbonaceous meteorites. Murchison contains magnetic minerals like magnetite and pyrhottite. Their presence suggests that there were oxidizing conditions during the formation of these two minerals. This material may have been exposed to water-ice proximity that caused neo-formation of these two minerals. Such chemical change in magnetic mineralogy may resulted from multiple exposure of the meteorite material to transition between the liquid and solid water (ice). We expose Murchison fragments to multiple cycles of water/ice transition. Our data shows changes in both magnetic susceptibility and remanence. We interpret these findings in terms of the past nebular magnetic fields.

  20. Chaos on Europa: Transition from solid ice to slush

    NASA Astrophysics Data System (ADS)

    Collins, G. C.

    2011-12-01

    About a quarter of Jupiter's moon Europa is covered by patches of "chaotic" terrain where some parts of the preexisting surface have been disrupted into "plates" that are tilted and translated, and other parts have been replaced by an irregular hummocky matrix of jumbled ice blocks. Catastrophic ice-fluid interactions on the Earth offer attractive analogies to advance our understanding of the formation of chaotic terrain on Europa. The morphology of chaos terrain indicates a sharp change in mechanical properties between the undisrupted plates and the highly disrupted matrix. Where plates are locally higher than the matrix, the boundary is a steep cliff, but where the matrix is locally higher, the boundary is rounded like a viscous flow. This indicates that the plates are behaving as solid ice, while the adjacent matrix is behaving as a fluid. The horizontal translation and tilting of the solid ice plates indicates that the material beneath them must also be acting as a fluid. The transition from solid ice to slushy matrix is not always accompanied by horizontal motion; for example background ridges can be continuously traced over large areas of chaos matrix in Thrace Macula. In some areas, the boundary between plates and matrix appears to be controlled by the existence of prominent ridges, but the matrix may either go around the ridge, or be contained entirely within the outline of the ridge. Perhaps fractures associated with preexisting ridges affect the subsurface flow of liquid within the ice shell, and control the transition between solid ice and slush. In color and spectroscopic data, chaos matrix is accompanied by an unknown dark substance, which could include hydrated salts or sulfuric acid (Carlson et al. 2009). Dark material can also be found separate from the matrix, in topographically low areas immediately surrounding chaos terrain. After chaos formation, the matrix may still exhibit mechanical properties different from the surrounding ice, as evidenced

  1. Infrared optical constants of H2O ice, amorphous nitric acid solutions, and nitric acid hydrates

    NASA Technical Reports Server (NTRS)

    Toon, Owen B.; Koehler, Birgit G.; Middlebrook, Ann M.; Tolbert, Margaret A.; Jordon, Joseph

    1994-01-01

    We determined the infrared optical constants of nitric acid trihydrate, nitric acid dihydrate, nitric acid monohydrate, and solid amorphous nitric acid solutions which crystallize to form these hydrates. We have also found the infrared optical constants of H2O ice. We measured the transmission of infrared light throught thin films of varying thickness over the frequency range from about 7000 to 500/cm at temperatures below 200 K. We developed a theory for the transmission of light through a substrate that has thin films on both sides. We used an iterative Kramers-Kronig technique to determine the optical constants which gave the best match between measured transmission spectra and those calculated for a variety of films of different thickness. These optical constants should be useful for calculations of the infrared spectrum of polar stratospheric clouds.

  2. Infrared Spectra and Optical Constants of Astronomical Ices: I. Amorphous and Crystalline Acetylene

    NASA Technical Reports Server (NTRS)

    Hudson, R. L.; Ferrante, R. F.; Moore, M. H.

    2013-01-01

    Here we report recent measurements on acetylene (C2H2) ices at temperatures applicable to the outer Solar System and the interstellar medium. New near- and mid-infrared data, including optical constants (n, k), absorption coefficients (alpha), and absolute band strengths (A), are presented for both amorphous and crystalline phases of C2H2 that exist below 70 K. Comparisons are made to earlier work. Electronic versions of the data are made available, as is a computer routine to use our reported n and k values to simulate the observed IR spectra. Suggestions are given for the use of the data and a comparison to a spectrum of Makemake is made.

  3. Thon rings from amorphous ice and implications of beam-induced Brownian motion in single particle electron cryo-microscopy.

    PubMed

    McMullan, G; Vinothkumar, K R; Henderson, R

    2015-11-01

    We have recorded dose-fractionated electron cryo-microscope images of thin films of pure flash-frozen amorphous ice and pre-irradiated amorphous carbon on a Falcon II direct electron detector using 300 keV electrons. We observe Thon rings [1] in both the power spectrum of the summed frames and the sum of power spectra from the individual frames. The Thon rings from amorphous carbon images are always more visible in the power spectrum of the summed frames whereas those of amorphous ice are more visible in the sum of power spectra from the individual frames. This difference indicates that while pre-irradiated carbon behaves like a solid during the exposure, amorphous ice behaves like a fluid with the individual water molecules undergoing beam-induced motion. Using the measured variation in the power spectra amplitude with number of electrons per image we deduce that water molecules are randomly displaced by a mean squared distance of ∼1.1 Å(2) for every incident 300 keV e(-)/Å(2). The induced motion leads to an optimal exposure with 300 keV electrons of 4.0 e(-)/Å(2) per image with which to observe Thon rings centred around the strong 3.7 Å scattering peak from amorphous ice. The beam-induced movement of the water molecules generates pseudo-Brownian motion of embedded macromolecules. The resulting blurring of single particle images contributes an additional term, on top of that from radiation damage, to the minimum achievable B-factor for macromolecular structure determination. PMID:26103047

  4. Thon rings from amorphous ice and implications of beam-induced Brownian motion in single particle electron cryo-microscopy

    PubMed Central

    G. McMullan; Vinothkumar, K.R.; Henderson, R.

    2015-01-01

    We have recorded dose-fractionated electron cryo-microscope images of thin films of pure flash-frozen amorphous ice and pre-irradiated amorphous carbon on a Falcon II direct electron detector using 300 keV electrons. We observe Thon rings [1] in both the power spectrum of the summed frames and the sum of power spectra from the individual frames. The Thon rings from amorphous carbon images are always more visible in the power spectrum of the summed frames whereas those of amorphous ice are more visible in the sum of power spectra from the individual frames. This difference indicates that while pre-irradiated carbon behaves like a solid during the exposure, amorphous ice behaves like a fluid with the individual water molecules undergoing beam-induced motion. Using the measured variation in the power spectra amplitude with number of electrons per image we deduce that water molecules are randomly displaced by a mean squared distance of ∼1.1 Å2 for every incident 300 keV e−/Å2. The induced motion leads to an optimal exposure with 300 keV electrons of 4.0 e−/Å2 per image with which to observe Thon rings centred around the strong 3.7 Å scattering peak from amorphous ice. The beam-induced movement of the water molecules generates pseudo-Brownian motion of embedded macromolecules. The resulting blurring of single particle images contributes an additional term, on top of that from radiation damage, to the minimum achievable B-factor for macromolecular structure determination. PMID:26103047

  5. New Optical Constants for Amorphous and Crystalline H2O-ice and H2O-mixtures.

    NASA Technical Reports Server (NTRS)

    Mastrapa, Rachel; Bernstein, Max; Sandford, Scott

    2006-01-01

    We will present the products of new laboratory measurements of ices relevant to Trans-Neptunian Objects. We have calculated the real and imaginary indices of refraction for amorphous and crystalline H2O-ice and also H2O-rich ices containing other molecular species. We create ice samples by condensing gases onto a cold substrate. We measure the thickness of the sample by reflecting a He-Ne laser off of the sample and counting interference fringes as it grows. We then collect transmission spectra of the samples in the wavelength range from 0.7-22 micrometers. Using the thickness and the transmission spectra of the ice we calculate the imaginary part of the index of refraction. We then use a Kramers-Kronig calculation to calculate the real part of the index of refraction (Berland et al. 1994; Hudgins et al. 1993). These optical constants can then be used to create model spectra for comparison to spectra from Solar System objects, including TNOs. We will summarize the difference between the amorphous and crystalline H2O-ice spectra. These changes include weakening of features and shifting of features to shorter wavelength. One important result is that the 2 pm feature is stronger in amorphous H2O ice than it is in crystalline H2O-ice. We will also discuss the changes seen when H2O is mixed with other components, including CO2, CH4, HCN, and NH3 (Bernstein et al. 2005; Bernstein et al. 2006).

  6. Three-dimensional nanomechanical mapping of amorphous and crystalline phase transitions in phase-change materials.

    PubMed

    Grishin, Ilja; Huey, Bryan D; Kolosov, Oleg V

    2013-11-13

    The nanostructure of micrometer-sized domains (bits) in phase-change materials (PCM) that undergo switching between amorphous and crystalline phases plays a key role in the performance of optical PCM-based memories. Here, we explore the dynamics of such phase transitions by mapping PCM nanostructures in three dimensions with nanoscale resolution by combining precision Ar ion beam cross-sectional polishing and nanomechanical ultrasonic force microscopy (UFM) mapping. Surface and bulk phase changes of laser written submicrometer to micrometer sized amorphous-to-crystalline (SET) and crystalline-to-amorphous (RESET) bits in chalcogenide Ge2Sb2Te5 PCM are observed with 10-20 nm lateral and 4 nm depth resolution. UFM mapping shows that the Young's moduli of crystalline SET bits exceed the moduli of amorphous areas by 11 ± 2%, with crystalline content extending from a few nanometers to 50 nm in depth depending on the energy of the switching pulses. The RESET bits written with 50 ps pulses reveal shallower depth penetration and show 30-50 nm lateral and few nanometer vertical wavelike topography that is anticorrelated with the elastic modulus distribution. Reverse switching of amorphous RESET bits results in the full recovery of subsurface nanomechanical properties accompanied with only partial topography recovery, resulting in surface corrugations attributed to quenching. This precision sectioning and nanomechanical mapping approach could be applicable to a wide range of amorphous, nanocrystalline, and glass-forming materials for 3D nanomechanical mapping of amorphous-crystalline transitions. PMID:24111915

  7. OPTICAL CONSTANTS OF AMORPHOUS AND CRYSTALLINE H{sub 2}O-ICE: 2.5-22 {mu}m (4000-455 cm{sup -1}) OPTICAL CONSTANTS OF H{sub 2}O-ICE

    SciTech Connect

    Mastrapa, R. M.; Dalle Ore, C. M.; Sandford, S. A.; Cruikshank, D. P.; Roush, T. L.

    2009-08-20

    Using new laboratory spectra, we have calculated the real and imaginary parts of the index of refraction of amorphous and crystalline H{sub 2}O-ice from 20-150 K in the wavelength range 2.5-22 {mu}m (4000-455 cm{sup -1}) and joined these results with previous measurement from 1.25 to 2.5 {mu}m. These optical constants improve on previous measurements by having better temperature and spectral resolution and can be used to create model spectra for comparison to spectra of solar system objects and interstellar materials. In this wavelength range, the infrared band shapes and positions of amorphous H{sub 2}O-ice are strongly dependent on deposition temperature. Amorphous and crystalline H{sub 2}O-ice have distinctive spectral bands at all wavelengths in this region with bands weakening and shifting to shorter wavelength in amorphous H{sub 2}O-ice compared to crystalline H{sub 2}O-ice. Some notable exceptions are the band near 6 {mu}m, which is stronger in amorphous H{sub 2}O-ice, and the bands near 4.5 {mu}m and 12.5 {mu}m, which shift to longer wavelength in amorphous H{sub 2}O-ice.

  8. Tin tetrabromide at high pressures: Reversible crystalline-to-amorphous and electronic transitions

    NASA Astrophysics Data System (ADS)

    Williamson, W., III; Lee, S. A.

    1991-11-01

    Several phase transitions have been observed in SnBr4 up to 23 GPa. Measurements of the Raman spectra show that additional modes are observed in the lattice region at about 4 GPa, suggesting that the symmetry of the unit cell is changing. All lattice modes disappear and the internal vibrational modes lose their splitting in the 13-15-GPa region, indicating that a crystal-to-amorphous transition occurs in this pressure range. Upon release of pressure, the amorphous phase is stable to about 1 GPa. A crystalline phase is observed below 1 GPa. Optical absorption experiments indicate that the optical band gap displays a continuous (and reversible) closure with increasing pressure. A photoluminescence signal is observed to red shift with increasing pressure and is quenched in the amorphous state.

  9. Roughening transition in nanoporous hydrogenated amorphous germanium: Roughness correlation to film stress

    NASA Astrophysics Data System (ADS)

    Carroll, M. S.; Verley, J. C.; Sheng, J. J.; Banks, J.

    2007-03-01

    Hydrogenated amorphous germanium (a-Ge:H) is a material of interest for optoelectronic applications such as solar cells and radiation detectors because of the material's potential to extend the wavelength sensitivity of hydrogenated amorphous silicon (a-Si:H). An increase in porosity is observed in amorphous germanium compared to a-Si :H, and this increase in porosity has been correlated with a degradation of the electrical performance. Improved understanding of the mechanisms of porous formation in a-Ge :H films is therefore desirable in order to better control it. In this paper we describe a correlation between film stress and surface roughness, which evolves with increasing thickness of a-Ge :H. A roughening transition from planar two-dimensional growth to three-dimensional growth at a critical thickness less than 800Å results in a network of needlelike nanotrench cavities which stretch from the transition thickness to the surface in films up to 4000Å thick. Surface roughness measurements by atomic force microscope and transmission electron microscopy indicate that the transition is abrupt and that the roughness increases linearly after the transition thickness. The roughening transition thickness is, furthermore, found to correlate with the maxima of the integrated compressive stress. The compressive stress is reduced after this transition thickness due to the incorporation of nanovoids into the film that introduce tensile stress as the islands coalesce together. The roughening transition behavior is similar to that found in a general class of Volmer-Weber mode thin film deposition (e.g., Cu, Ag, and nonhydrogenated amorphous silicon), which offers additional insight into the underlying mechanisms of the stress and roughening in these a-Ge :H films. The suppression of the roughening transition by changing the kinetics of the deposition rates (e.g., slowing the deposition rate with a weak sputtering bias) is also observed and discussed.

  10. Universal amorphous-amorphous transition in GexSe100−x glasses under pressure

    PubMed Central

    Yildirim, Can; Micoulaut, Matthieu; Boolchand, Punit; Kantor, Innokenty; Mathon, Olivier; Gaspard, Jean-Pierre; Irifune, Tetsuo; Raty, Jean-Yves

    2016-01-01

    Pressure induced structural modifications in vitreous GexSe100−x (where 10 ≤ x ≤ 25) are investigated using X-ray absorption spectroscopy (XAS) along with supplementary X-ray diffraction (XRD) experiments and ab initio molecular dynamics (AIMD) simulations. Universal changes in distances and angle distributions are observed when scaled to reduced densities. All compositions are observed to remain amorphous under pressure values up to 42 GPa. The Ge-Se interatomic distances extracted from XAS data show a two-step response to the applied pressure; a gradual decrease followed by an increase at around 15–20 GPa, depending on the composition. This increase is attributed to the metallization event that can be traced with the red shift in Ge K edge energy which is also identified by the principal peak position of the structure factor. The densification mechanisms are studied in details by means of AIMD simulations and compared to the experimental results. The evolution of bond angle distributions, interatomic distances and coordination numbers are examined and lead to similar pressure-induced structural changes for any composition. PMID:27273197

  11. Universal amorphous-amorphous transition in GexSe100‑x glasses under pressure

    NASA Astrophysics Data System (ADS)

    Yildirim, Can; Micoulaut, Matthieu; Boolchand, Punit; Kantor, Innokenty; Mathon, Olivier; Gaspard, Jean-Pierre; Irifune, Tetsuo; Raty, Jean-Yves

    2016-06-01

    Pressure induced structural modifications in vitreous GexSe100‑x (where 10 ≤ x ≤ 25) are investigated using X-ray absorption spectroscopy (XAS) along with supplementary X-ray diffraction (XRD) experiments and ab initio molecular dynamics (AIMD) simulations. Universal changes in distances and angle distributions are observed when scaled to reduced densities. All compositions are observed to remain amorphous under pressure values up to 42 GPa. The Ge-Se interatomic distances extracted from XAS data show a two-step response to the applied pressure; a gradual decrease followed by an increase at around 15–20 GPa, depending on the composition. This increase is attributed to the metallization event that can be traced with the red shift in Ge K edge energy which is also identified by the principal peak position of the structure factor. The densification mechanisms are studied in details by means of AIMD simulations and compared to the experimental results. The evolution of bond angle distributions, interatomic distances and coordination numbers are examined and lead to similar pressure-induced structural changes for any composition.

  12. Slow positron study of positronium formation and diffusion in crystalline and amorphous ice

    SciTech Connect

    Lynn, K.G.; Eldrup, M.; Vehanen, A.; Schultz, P.J.

    1984-10-01

    The aim of the present work has been to study the interaction of low energy positrons and of Ps with a molecular solid. As a first example we have chosen ice which has been extensively investigated both by conventional positron annihilation methods as well as by many other techniques. Unlike in metals, positrons injected into most molecular solids may have a certain probability to form Ps in the bulk of the material. The process by which Ps is formed in condensed molecular materials has been a matter of strong debate. According to the Ore model of Ps formation, which is recognized as being valid for low density gases, the positron during its slowing down picks off an electron from a molecule with which it simultaneously forms Ps. For energies below E/sub L/ = I-6.8 eV, where I is the lowest ionisation energy and 6.8 eV is the Ps binding energy in vacuum, this process is not energetically possible. Above an energy E/sub u/ approx. I the model predicts a reduction of the yield of stable Ps, because of rapid slowing down of the positron by ionisation or by splitting up again of a Ps atom which may have been formed. The energy range E/sub L/ less than or equal to E approximately less than E/sub u/ is the so-called Ore gap in gases. In the present work both crystalline and amorphous ice have been studied using positrons of energies in the range 0 to 4.5 keV. The experimental methods used were determination of the yields of 3..gamma..-annihilations as well as Doppler broadening measurements in the temperature range 45 to 150 K. The main results obtained were a determination of the Ps diffusion constant, and a demonstration that in the present experiments one contribution to the total Ps yield comes from positrons with typical Ore gap energies, and another contribution, due to spur processes, from positrons with initial energies of several hundred eV. 57 references, 9 figures.

  13. Theoretical studies of electronic band-tail states, Anderson transition and surfaces of amorphous semiconductors

    NASA Astrophysics Data System (ADS)

    Dong, Jianjun

    In this dissertation, we study the Anderson transition within the electronic band tail states, and amorphous surfaces. The disorder induced band tail states is one of the unique character of amorphous semiconductors. Because of the proximity to the Fermi level, the nature of these band tail states is of obvious interest to theory of doping and transport. The study of amorphous solid surface is also an interesting area for theory. It is possible to have some major rearrangements near surfaces of amorphous solids (the amorphous analog of surface reconstruction), and the local bonding environment could be dramatically different from that of bulk. The study of the surfaces can also help people toward understanding the growth mechanism. First, electronic band tail states of amorphous silicon and amorphous diamond were studied based on the large (4096 atom) and realistic structural models. To solve the large tight-binding Hamiltonian matrices, we used two order N methods: the maximum entropy method for computing the total densities of states, and the modified Lanczos techniques for computing the individual energy eigenstates in the band gap regions. The DC conductivity was estimated with the Kubo formula. Next, the structural and electronic properties of the surfaces of tetrahedral amorphous carbon (ta-C) were also studied with a first-principles, local basis LDA technique. We reported two structural models made under different conditions, and examined the transition of the local bonding environment from the bulk to the surface. In the study of band tail states, we observe that Anderson (local-to-extended) transition within the band states proceeds by "cluster proliferation". We interpret the nature of band tail states in terms of a "resonant cluster model" through which one can qualitatively understand the evolution of the states from midgap toward the mobility edges. In the study of ta-C surfaces, we observe that nearly 50% surface atoms are threefold coordinated and

  14. Nanomechanical morphology of amorphous, transition, and crystalline domains in phase change memory thin films

    NASA Astrophysics Data System (ADS)

    Bosse, J. L.; Grishin, I.; Huey, B. D.; Kolosov, O. V.

    2014-09-01

    In the search for phase change materials (PCM) that may rival traditional random access memory, a complete understanding of the amorphous to crystalline phase transition is required. For the well-known Ge2Sb2Te5 (GST) and GeTe (GT) chalcogenides, which display nucleation and growth dominated crystallization kinetics, respectively, this work explores the nanomechanical morphology of amorphous and crystalline phases in 50 nm thin films. Subjecting these PCM specimens to a lateral thermal gradient spanning the crystallization temperature allows for a detailed morphological investigation. Surface and depth-dependent analyses of the resulting amorphous, transition and crystalline regions are achieved with shallow angle cross-sections, uniquely implemented with beam exit Ar ion polishing. To resolve the distinct phases, ultrasonic force microscopy (UFM) with simultaneous topography is implemented revealing a relative stiffness contrast between the amorphous and crystalline phases of 14% for the free film surface and 20% for the cross-sectioned surface. Nucleation is observed to occur preferentially at the PCM-substrate and free film interface for both GST and GT, while fine subsurface structures are found to be sputtering direction dependent. Combining surface and cross-section nanomechanical mapping in this manner allows 3D analysis of microstructure and defects with nanoscale lateral and depth resolution, applicable to a wide range of materials characterization studies where the detection of subtle variations in elastic modulus or stiffness are required.

  15. Helium Diffusion Through H2O and D2O Amorphous Ice: A Lattice Inverse Istope Effect

    SciTech Connect

    Daschbach, John L.; Schenter, Gregory K.; Ayotte, Patrick; Smith, R. Scott; Kay, Bruce D.

    2004-05-14

    The diffusion of helium through both H2O and D2O amorphous solid water (ASW) has been measured between 55K and 110K. We find the diffusion rate is dependent on the isotopic composition of the ASW lattice. This lattice isotope effect is the "inverse" of a normal isotope effect, in that diffusion is faster in the heavier (D2O) isotope. Transition state theory calculations show that the isotope effect is due to a tight transition state results in a large zero point vibrational energy differences at the transition state predominantly due to hindered rotations of water in the lattice.

  16. Disorder-Assisted Melting and the Glass Transition in Amorphous Solids

    NASA Astrophysics Data System (ADS)

    Zaccone, Alessio; Terentjev, Eugene M.

    2013-04-01

    The mechanical response of solids depends on temperature, because the way atoms and molecules respond collectively to deformation is affected at various levels by thermal motion. This is a fundamental problem of solid state science and plays a crucial role in materials science. In glasses, the vanishing of shear rigidity upon increasing temperature is the reverse process of the glass transition. It remains poorly understood due to the disorder leading to nontrivial (nonaffine) components in the atomic displacements. Our theory explains the basic mechanism of the melting transition of amorphous (disordered) solids in terms of the lattice energy lost to this nonaffine motion, compared to which thermal vibrations turn out to play only a negligible role. The theory is in good agreement with classic data on melting of amorphous polymers (for which no alternative theory can be found in the literature) and offers new opportunities in materials science.

  17. Physico-ecobiogeochemistry of East Antarctic pack ice during the winter-spring transition

    NASA Astrophysics Data System (ADS)

    Meiners, Klaus M.; Norman, Louiza; Granskog, Mats A.; Krell, Andreas; Heil, Petra; Thomas, David N.

    2011-05-01

    Our study provides information on the relationships between physical, chemical, and biological properties of East Antarctic sea ice sampled as part of the Sea Ice Physics and Ecosystem eXperiment (SIPEX) during the winter-spring transition in 2007. The sampled sea ice showed a high contribution of granular ice, indicating the turbulent conditions during sea ice formation off East Antarctica. The sea ice was cold, with brine volumes often below or very close to the theoretical percolation threshold of sea ice. Dissolved inorganic nutrient concentrations showed both positive and negative deviations from theoretical dilution lines, indicating both nutrient uptake as well as nutrient remineralisation in sea ice brines. Cold temperatures, high brine salinities, and low brine volumes limited high ice algal biomass to the warmer and more porous sea ice layers at the ice-water interface. We hypothesise that East Antarctic sea ice shows generally low ice algal biomass accumulation due to a combination of relatively low snow-loading, relatively cold ice temperatures, and short persistence of sea ice into the warm forcing regime, all of which prevent the development of significant internal and surface communities.

  18. Interaction of atomic and molecular deuterium with a nonporous amorphous water ice surface between 8 and 30 K.

    PubMed

    Amiaud, L; Dulieu, F; Fillion, J-H; Momeni, A; Lemaire, J L

    2007-10-14

    Molecular and atomic interactions of hydrogen on dust grains covered with ice at low temperatures are key mechanisms for star formation and chemistry in dark interstellar clouds. We have experimentally studied the interaction of atomic and molecular deuterium on nonporous amorphous water ice surfaces between 8 and 30 K, in conditions compatible with an extrapolation to an astrophysical context. The adsorption energy of D(2) presents a wide distribution, as already observed on porous water ice surfaces. At low coverage, the sticking coefficient of D(2) increases linearly with the number of deuterium molecules already adsorbed on the surface. Recombination of atomic D occurs via a prompt reaction that releases molecules into the gas phase. Part of the newly formed molecules are in vibrationally excited states (v=1-7). The atomic recombination efficiency increases with the presence of D(2) molecules already adsorbed on the water ice, probably because these increase the sticking coefficient of the atoms, as in the case of incident D(2). We have measured the atomic recombination efficiency in the presence of already absorbed D(2), as it is expected to occur in the interstellar medium. The recombination efficiency decreases rapidly with increasing temperature and is zero at 13 K. This allows us to estimate an upper limit to the value of the atom adsorption energy E(a) approximately 29 meV, in agreement with previous calculations. PMID:17935425

  19. Tuning electronic properties of graphene heterostructures by amorphous-to-crystalline phase transitions

    NASA Astrophysics Data System (ADS)

    Kulju, S.; Akola, J.; Prendergast, D.; Jones, R. O.

    2016-05-01

    The remarkable ability of phase change materials (PCM) to switch between amorphous and crystalline states on a nanosecond time scale could provide new opportunities for graphene engineering. We have used density functional calculations to investigate the structures and electronic properties of heterostructures of thin amorphous and crystalline films of the PCM GeTe (16 Å thick) and Ge2Sb2Te5 (20 Å) between graphene layers. The interaction between graphene and PCM is very weak, charge transfer is negligible, and the structures of the chalcogenide films differ little from those of bulk phases. A crystalline GeTe (111) layer induces a band gap opening of 80 meV at the Dirac point. This effect is absent for the amorphous film, but the Fermi energy shifts down along the Dirac cone by -60 meV. Ge2Sb2Te5 shows similar features, although inherent disorder in the crystalline rocksalt structure reduces the contrast in band structure from that in the amorphous structure. These features originate in charge polarization within the crystalline films, which show electromechanical response (piezoelectricity) upon compression, and show that the electronic properties of graphene structures can be tuned by inducing ultrafast structural transitions within the chalcogenide layers. Graphene can also be used to manipulate the structural state of the PCM layer and its electronic and optical properties.

  20. Mechanisms for pressure-induced crystal-crystal transition, amorphization, and devitrification of Snl4

    DOE PAGESBeta

    Liu, Hanyu; Tse, John S.; Hu, Michael Y.; Bi, Wenli; Zhao, Jiyong; Alp, E. Ercan; Pasternak, Moshe; Taylor, R. Dean; Lashley, Jason C.

    2015-10-27

    The pressure-induced amorphization and subsequent recrystallization of SnI4 have been investigated using first principles molecular dynamics calculations together with high-pressure 119Sn nuclear resonant inelastic x-ray scattering measurements. Above ~8 GPa, we observe a transformation from an ambient crystalline phase to an intermediate crystal structure and a subsequent recrystallization into a cubic phase at ~64 GPa. The crystalline-to-amorphous transition was identified on the basis of elastic compatibility criteria. The measured tin vibrational density of states shows large amplitude librations of SnI4 under ambient conditions. Although high pressure structures of SnI4 were thought to be determined by random packing of equal-sized spheres,more » we detected electron charge transfer in each phase. As a result, this charge transfer results in a crystal structure packing determined by larger than expected iodine atoms. (C) 2015 AIP Publishing LLC.« less

  1. Thermal history of comets during residence in the Oort cloud - Effect of radiogenic heating in combination with the very low thermal conductivity of amorphous ice

    NASA Technical Reports Server (NTRS)

    Haruyama, Jun'ichi; Yamamoto, Tetsuo; Mizutani, Hitoshi; Greenberg, J. M.

    1993-01-01

    The thermal history of long-period comets initially composed of amorphous ice is studied. It is shown that such comets with a small nucleus thermal conductivity (kappa) experience a runaway increase in the internal temperature during residence in the Oort cloud. The temperature increase is a result of rapid release of the latent heat at crystallization triggered by gradual heating due to decay of radioactive nuclides. The time of the runaway temperature increase is about ten to a hundred million years after the formation of the nucleus depending on the fraction of refractory grains which contain radioactive nuclides. Most of the amorphous ice in the nuclides except just beneath the surface transforms into crystalline ice due to the runaway temperature increase. This implies that the ice in short-period comets is crystalline from the initial time when the long-period comet becomes a short-period one. In comets with large kappa the temperature does not rise much compared to the small kappa case and the initial amorphous ice is preserved. A criterion for the crystallization of the nucleus ice is derived.

  2. Thermal analysis of frozen solutions: multiple glass transitions in amorphous systems.

    PubMed

    Sacha, Gregory A; Nail, Steven L

    2009-09-01

    Frozen aqueous solutions of sucrose exhibit two "glass transition-like" thermal events below the melting endotherm of ice when examined by DSC, but the physical basis of these events has been a source of some disagreement. In this study, a series of sugars, including sucrose, lactose, trehalose, maltose, fructose, galactose, fucose, mannose, and glucose were studied by modulated DSC and freeze-dry microscopy in order to better understand whether sucrose is unique in any way with respect to this behavior, as well as to explore the physical basis, and the pharmaceutical significance of these multiple transitions. Double transitions were found to be a common feature of all sugars examined. The results are consistent with both thermal events being glass transitions in that (1) both events have second-order characteristics that appear in the reversing signals, (2) annealing experiments reveal that enthalpy recovery is associated with each transition, and (3) Lissajous plots indicate that no detectable latent heat of melting is associated with either transition. The data in this study are consistent with the idea that the lower temperature transition arises from a metastable glassy mixture containing more water than that in the maximally freeze-concentrated solute. Freeze-dry microscopy observations show that for all of the sugars examined, it is the higher temperature transition that is associated with structural collapse during freeze-drying. There is no apparent pharmaceutical significance associated with the lower-temperature transition. PMID:19384925

  3. Deviations of the glass transition temperature in amorphous conjugated polymer thin films

    NASA Astrophysics Data System (ADS)

    Liu, Dan; Osuna Orozco, Rodrigo; Wang, Tao

    2013-08-01

    The deviations of the glass transition temperature (Tg) in thin films of an amorphous conjugated polymer poly(9,9-dioctylfluorene-co-N-(4-butylphenyl)diphenylamine) (TFB) are reported. Monotonic and nonmonotonic Tg deviations are observed in TFB thin films supported on Si-SiOx and poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS), respectively. A three-layer model is developed to fit both monotonic and nonmonotonic Tg deviations in these films. A 5-nm PEDOT:PSS capping layer was not found to be effective to remove the free-surface effect in Si-SiOx supported TFB films.

  4. Frustration of photocrystallization in amorphous selenium films and film-polymer structures near the glass transition

    NASA Astrophysics Data System (ADS)

    Lindberg, G. P.; Tallman, R. E.; Abbaszadeh, S.; Karim, K. S.; Rowlands, J. A.; Reznik, A.; Weinstein, B. A.

    2013-12-01

    We investigate the stability against photo-induced crystallization (PiC) and photo-induced darkening (PiD) in a series of amorphous selenium (a-Se) films grown with and without polyimide buffer layers[1] for temperatures below and above the glass transition (Tg ˜ 313 K). The a-Se films are bulk-like (˜16.5 μm thick), and contain a low concentration of As (< 0.2%). We find that due to strain relief, a thin layer (˜1 μm) of polyimide greatly stabilizes the samples against PiC and reduces the effect of PiD.

  5. 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.

  6. Molecular relaxation behavior and isothermal crystallization above glass transition temperature of amorphous hesperetin.

    PubMed

    Shete, Ganesh; Khomane, Kailas S; Bansal, Arvind Kumar

    2014-01-01

    The purpose of this paper was to investigate the relaxation behavior of amorphous hesperetin (HRN), using dielectric spectroscopy, and assessment of its crystallization kinetics above glass transition temperature (Tg ). Amorphous HRN exhibited both local (β-) and global (α-) relaxations. β-Relaxation was observed below Tg , whereas α-relaxation prominently emerged above Tg . β-Relaxation was found to be of Johari-Goldstein type and was correlated with α-process by coupling model. Secondly, isothermal crystallization experiments were performed at 363 K (Tg + 16.5 K), 373 K (Tg + 26.5 K), and 383 K (Tg + 36.5 K). The kinetics of crystallization, obtained from the normalized dielectric strength, was modeled using the Avrami model. Havriliak-Negami (HN) shape parameters, αHN and αHN .βHN , were analyzed during the course of crystallization to understand the dynamics of amorphous phase during the emergence of crystallites. HN shape parameters indicated that long range (α-like) were motions affected to a greater extent than short range (β-like) motions during isothermal crystallization studies at all temperature conditions. The variable behavior of α-like motions at different isothermal crystallization temperatures was attributed to evolving crystallites with time and increase in electrical conductivity with temperature. PMID:24186540

  7. Structure of Water Ice in the Solar System

    NASA Technical Reports Server (NTRS)

    Blake, David; Jenniskens, Peter; Chang, Sherwood (Technical Monitor)

    1996-01-01

    Nearly all of the properties of solar system ices (chemical reaction rates, volatile retention and release, vaporization behavior, thermal conductivity, infrared spectral characteristics and the like) are a direct consequence of ice structure. However, the characterization of astrophysical ices and their laboratory analogs has typically utilized indirect measurements which yield phenomenological interpretations. When water ice is vapor-deposited at 14 K and warmed until it volatilizes in moderate vacuum, the ice undergoes a series of amorphous to amorphous and amorphous to crystalline structural transitions which we have characterized by diffraction methods. These structural transitions correlate with and underlie many phenomena observed in laboratory infrared and gas release experiments. The elucidation of the dynamic structural changes which occur in vapor-deposited water ice as a function of time, temperature and radiation history allows for the more complete interpretation of remote observations of astrophysical ices and their laboratory analogs.

  8. The photoexcitation of crystalline ice and amorphous solid water: A molecular dynamics study of outcomes at 11 K and 125 K

    SciTech Connect

    Crouse, J.; Loock, H.-P. Cann, N. M.

    2015-07-21

    Photoexcitation of crystalline ice Ih and amorphous solid water at 7-9 eV is examined using molecular dynamics simulations and a fully flexible water model. The probabilities of photofragment desorption, trapping, and recombination are examined for crystalline ice at 11 K and at 125 K and for amorphous solid water at 11 K. For 11 K crystalline ice, a fully rigid water model is also employed for comparison. The kinetic energy of desorbed H atoms and the distance travelled by trapped fragments are correlated to the location and the local environment of the photoexcited water molecule. In all cases, H atom desorption is found to be the most likely outcome in the top bilayer while trapping of all photofragments is most probable deeper in the solid where the likelihood for recombination of the fragments into H{sub 2}O molecules also rises. Trajectory analysis indicates that the local hydrogen bonding network in amorphous solid water is more easily distorted by a photodissociation event compared to crystalline ice. Also, simulations indicate that desorption of OH radicals and H{sub 2}O molecules are more probable in amorphous solid water. The kinetic energy distributions for desorbed H atoms show a peak at high energy in crystalline ice, arising from photoexcited water molecules in the top monolayer. This peak is less pronounced in amorphous solid water. H atoms that are trapped may be displaced by up to ∼10 water cages, but migrate on average 3 water cages. Trapped OH fragments tend to stay near the original solvent cage.

  9. Amorphous/microcrystalline transition of thick silicon film deposited by PECVD

    NASA Astrophysics Data System (ADS)

    Elarbi, N.; Jemaï, R.; Outzourhit, A.; Khirouni, K.

    2016-06-01

    Thick silicon films were deposited by plasma-enhanced chemical vapor deposition at different plasma power densities. Annealing treatment was performed on these deposited films. As-deposited and annealed films were characterized by X-ray diffraction, Raman scattering spectroscopy and reflectance spectroscopy. Before annealing, only the film deposited at the plasma power density of 500 mW/cm2 exhibits a diffraction peak corresponding to the (111) plane orientation. Raman spectrum of this film confirms the presence of crystalline phase. After annealing, a transition from amorphous phase to crystalline one occurs for all samples. This transition is accompanied by an increase of the crystalline fraction volume deduced from Raman spectra analysis and by a reduction of optical gap energy.

  10. Mechanical Yield in Amorphous Solids: A First-Order Phase Transition

    NASA Astrophysics Data System (ADS)

    Jaiswal, Prabhat K.; Procaccia, Itamar; Rainone, Corrado; Singh, Murari

    2016-02-01

    Amorphous solids yield at a critical value of the strain (in strain-controlled experiments); for larger strains, the average stress can no longer increase—the system displays an elastoplastic steady state. A long-standing riddle in the materials community is what the difference is between the microscopic states of the material before and after yield. Explanations in the literature are material specific, but the universality of the phenomenon begs a universal answer. We argue here that there is no fundamental difference in the states of matter before and after yield, but the yield is a bona fide first-order phase transition between a highly restricted set of possible configurations residing in a small region of phase space to a vastly rich set of configurations which include many marginally stable ones. To show this, we employ an order parameter of universal applicability, independent of the microscopic interactions, that is successful in quantifying the transition in an unambiguous manner.

  11. Stoichiometry determined exchange interactions in amorphous ternary transition metal oxides: Theory and experiment

    SciTech Connect

    Hu, Shu-jun; Yan, Shi-shen Zhang, Yun-peng; Zhao, Ming-wen; Kang, Shi-shou; Mei, Liang-mo

    2014-07-28

    Amorphous transition metal oxides exhibit exotic transport and magnetic properties, while the absence of periodic structure has long been a major obstacle for the understanding of their electronic structure and exchange interaction. In this paper, we have formulated a theoretical approach, which combines the melt-quench approach and the spin dynamic Monte-Carlo simulations, and based on it, we explored amorphous Co{sub 0.5}Zn{sub 0.5}O{sub 1−y} ternary transition metal oxides. Our theoretical results reveal that the microstructure, the magnetic properties, and the exchange interactions of Co{sub 0.5}Zn{sub 0.5}O{sub 1−y} are strongly determined by the oxygen stoichiometry. In the oxygen-deficient sample (y > 0), we have observed the long-range ferromagnetic spin ordering which is associated with the non-stoichiometric cobalt-rich region rather than metallic clusters. On the other hand, the microstructure of stoichiometric sample takes the form of continuous random networks, and no long-range ferromagnetism has been observed in it. Magnetization characterization of experimental synthesized Co{sub 0.61}Zn{sub 0.39}O{sub 1−y} films verifies the relation between the spin ordering and the oxygen stoichiometry. Furthermore, the temperature dependence of electrical transport shows a typical feature of semiconductors, in agreement with our theoretical results.

  12. Bosonic Magnetic Field Driven Superconductor-Insulator Transitions in Amorphous Nano-honeycomb Films

    NASA Astrophysics Data System (ADS)

    Stewart, M. D., Jr.; Yin, Aijun; Xu, J. M.; Valles, James M., Jr.

    2008-03-01

    We have observed multiple magnetic field driven superconductor-insulator transitions (SIT) in amorphous Bi films perforated with a nano-honeycomb (NHC) array of holes. The magneto-resistance across the SITs is periodic, with a period H=HM=h/2eS, where S is the area of a unit cell of holes. These transitions are, therefore, boson dominated. In constant field the temperature dependence of the resistance can be parameterized by R(T)=R0(H)(T0(H)/T) on both sides of the transition so that the evolution between the superconducting and insulating states is controlled by the vanishing of T0->0. We compare these data to the thickness driven transition in NHC films and the field driven transitions in unpatterned Bi films, other materials, and Josephson junction arrays. Our results suggest a structural source for similar behavior found in some materials and that despite the clear bosonic nature of the SITs, quasiparticle degrees of freedom likely also play an important part in the evolution of the SIT.

  13. Interaction of D2 with H2O amorphous ice studied by temperature-programmed desorption experiments.

    PubMed

    Amiaud, L; Fillion, J H; Baouche, S; Dulieu, F; Momeni, A; Lemaire, J L

    2006-03-01

    The gas-surface interaction of molecular hydrogen D2 with a thin film of porous amorphous solid water (ASW) grown at 10 K by slow vapor deposition has been studied by temperature-programmed-desorption (TPD) experiments. Molecular hydrogen diffuses rapidly into the porous network of the ice. The D2 desorption occurring between 10 and 30 K is considered here as a good probe of the effective surface of ASW interacting with the gas. The desorption kinetics have been systematically measured at various coverages. A careful analysis based on the Arrhenius plot method has provided the D2 binding energies as a function of the coverage. Asymmetric and broad distributions of binding energies were found, with a maximum population peaking at low energy. We propose a model for the desorption kinetics that assumes a complete thermal equilibrium of the molecules with the ice film. The sample is characterized by a distribution of adsorption sites that are filled according to a Fermi-Dirac statistic law. The TPD curves can be simulated and fitted to provide the parameters describing the distribution of the molecules as a function of their binding energy. This approach contributes to a correct description of the interaction of molecular hydrogen with the surface of possibly porous grain mantles in the interstellar medium. PMID:16526867

  14. Computational study of structural change through the glass transition in an amorphous and liquid Zr-Ni alloy

    SciTech Connect

    Aihara, Tomoyasu Jr.; Aoki, Kiyoshi; Masumoto, Tsuyoshi )

    1993-04-15

    Amorphous alloys are experimentally or industrially produced by rapid quenching (RQ) from the melt. If a liquid alloy is rapidly cooled at a rate on the order of 10[sup 6]Ks[sup [minus]1], it enters the supercooled liquid regime and its viscosity increases. Finally, the system reaches a state of frozen random structure, which is called the amorphous state. In the attempt to control the properties of amorphous alloys, it is important to understand their structural changes through the glass transition. By a laboratory experiment, however, it is usually difficult to obtain information about the glass transition and supercooled state of an amorphous alloy because of competitive crystallization. Molecular dynamics (MD) simulation, a numerical experiment to solve the N-body problem of Newtonian mechanics, has been performed to investigate the structure of solid and liquid. As the MD simulation can be carried out on the order of picoseconds, one can detect the glass transition without crystallization during RQ. Thus, the authors performed the MD simulation for the production of an amorphous Zr-Ni alloy by RQ and detected static structure and thermodynamic changes through the glass transition. Both properties are related with interatomic potentials.

  15. IceCube simulation production and the transition to IceProd2

    NASA Astrophysics Data System (ADS)

    Schultz, David

    2016-04-01

    IceCube's simulation production relies largely on dynamic, heterogeneous resources spread around the world. Datasets consist of many thousands of job workflow subsets running in parallel as directed acyclic graphs (DAGs) and using varying resources. IceProd is a set of Python daemons which process job workflow and maintain configuration and status information on jobs before, during, and after processing. IceProd manages a complex workflow of DAGs to distribute jobs across all computing grids and optimize resource usage. IceProd2 is a new version of IceProd with substantial increases in security, reliability, scalability, and ease of use. It is undergoing testing and will be deployed this fall.

  16. Influence of compression on water sorption, glass transition, and enthalpy relaxation behavior of freeze-dried amorphous sugar matrices.

    PubMed

    Imamura, Koreyoshi; Kagotani, Ryo; Nomura, Mayo; Tanaka, Kazuhiro; Kinugawa, Kohshi; Nakanishi, Kazuhiro

    2011-04-15

    An amorphous matrix comprised of sugar molecules are frequently used in the pharmaceutical industry. The compression of the amorphous sugar matrix improves the handling. Herein, the influence of compression on the water sorption of an amorphous sugar matrix was investigated. Amorphous sugar samples were prepared by freeze-drying, using several types of sugars, and compressed at 0-443 MPa. The compressed amorphous sugar samples as well as uncompressed samples were rehumidified at given RHs, and the equilibrium water content and glass transition temperature (T(g)) were then measured. Compression resulted in a decrease in the equilibrium water content of the matrix, the magnitude of which was more significant for smaller sized sugars. Diffusivity of water vapor in the sample was also decreased to one-hundredth by the compression. The T(g) value for a given RH remained unchanged, irrespective of the compression. Accordingly, the decrease in T(g) with increasing water content increased as the result of compression. The structural relaxation of the amorphous sugar matrices were also examined and found to be accelerated to the level of a non-porous amorphous sugar matrix as the result of the compression. The findings indicate that pores contained in freeze-dried sugar samples interfere with the propagation of structural relaxation. PMID:21291973

  17. Possible Existence of Two Amorphous Phases of D-Mannitol Related by a First-Order Transition

    NASA Astrophysics Data System (ADS)

    Zhu, Men; Wang, Jun-Qiang; Perepezko, John; Yu, Lian

    We report that the common polyalcohol D-mannitol may have two amorphous phases related by a first-order transition. Slightly above Tg (284 K), the supercooled liquid (SCL) of D-mannitol transforms to a low-energy, apparently amorphous phase (Phase X). The enthalpy of Phase X is roughly halfway between those of the known amorphous and crystalline phases. The amorphous nature of Phase X is suggested by its absence of birefringence, transparency, broad X-ray diffraction, and broad Raman and NIR spectra. Phase X has greater molecular spacing, higher molecular order, fewer intra- and more inter-molecular hydrogen bonds than the normal liquid. On fast heating, Phase X transforms back to SCL near 330 K. Upon temperature cycling, it shows a glass-transition-like change of heat capacity. The presence of D-sorbitol enables a first-order liquid-liquid transition (LLT) from SCL to Phase X. This is the first report of polyamorphism at 1 atm for a pharmaceutical relevant substance. As amorphous solids are explored for many applications, polyamorphism could offer a tool to engineer the properties of materials. (Ref: M. Zhu et al., J. Chem. Phys. 2015, 142, 244504)

  18. Deviations of the glass transition temperature in amorphous conjugated polymer thin films.

    PubMed

    Liu, Dan; Osuna Orozco, Rodrigo; Wang, Tao

    2013-08-01

    The deviations of the glass transition temperature (T(g)) in thin films of an amorphous conjugated polymer poly(9,9-dioctylfluorene-co-N-(4-butylphenyl)diphenylamine) (TFB) are reported. Monotonic and nonmonotonic T(g) deviations are observed in TFB thin films supported on Si-SiOx and poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS), respectively. A three-layer model is developed to fit both monotonic and nonmonotonic T(g) deviations in these films. A 5-nm PEDOT:PSS capping layer was not found to be effective to remove the free-surface effect in Si-SiOx supported TFB films. PMID:24032856

  19. Coercivity of domain wall motion in thin films of amorphous rare earth-transition metal alloys

    NASA Technical Reports Server (NTRS)

    Mansuripur, M.; Giles, R. C.; Patterson, G.

    1991-01-01

    Computer simulations of a two dimensional lattice of magnetic dipoles are performed on the Connection Machine. The lattice is a discrete model for thin films of amorphous rare-earth transition metal alloys, which have application as the storage media in erasable optical data storage systems. In these simulations, the dipoles follow the dynamic Landau-Lifshitz-Gilbert equation under the influence of an effective field arising from local anisotropy, near-neighbor exchange, classical dipole-dipole interactions, and an externally applied field. Various sources of coercivity, such as defects and/or inhomogeneities in the lattice, are introduced and the subsequent motion of domain walls in response to external fields is investigated.

  20. Bacterial communities in Arctic first-year drift ice during the winter/spring transition.

    PubMed

    Eronen-Rasimus, Eeva; Piiparinen, Jonna; Karkman, Antti; Lyra, Christina; Gerland, Sebastian; Kaartokallio, Hermanni

    2016-08-01

    Horizontal and vertical variability of first-year drift-ice bacterial communities was investigated along a North-South transect in the Fram Strait during the winter/spring transition. Two different developmental stages were captured along the transect based on the prevailing environmental conditions and the differences in bacterial community composition. The differences in the bacterial communities were likely driven by the changes in sea-ice algal biomass (2.6-5.6 fold differences in chl-a concentrations). Copiotrophic genera common in late spring/summer sea ice, such as Polaribacter, Octadecabacter and Glaciecola, dominated the bacterial communities, supporting the conclusion that the increase in the sea-ice algal biomass was possibly reflected in the sea-ice bacterial communities. Of the dominating bacterial genera, Polaribacter seemed to benefit the most from the increase in algal biomass, since they covered approximately 39% of the total community at the southernmost stations with higher (>6 μg l(-1) ) chl-a concentrations and only 9% at the northernmost station with lower chl-a concentrations (<6 μg l(-1) ). The sea-ice bacterial communities also varied between the ice horizons at all three stations and thus we recommend that for future studies multiple ice horizons be sampled to cover the variability in sea-ice bacterial communities in spring. PMID:27264318

  1. Scaling description of the yielding transition in soft amorphous solids at zero temperature.

    PubMed

    Lin, Jie; Lerner, Edan; Rosso, Alberto; Wyart, Matthieu

    2014-10-01

    Yield stress materials flow if a sufficiently large shear stress is applied. Although such materials are ubiquitous and relevant for industry, there is no accepted microscopic description of how they yield, even in the simplest situations in which temperature is negligible and in which flow inhomogeneities such as shear bands or fractures are absent. Here we propose a scaling description of the yielding transition in amorphous solids made of soft particles at zero temperature. Our description makes a connection between the Herschel-Bulkley exponent characterizing the singularity of the flow curve near the yield stress Σc, the extension and duration of the avalanches of plasticity observed at threshold, and the density P(x) of soft spots, or shear transformation zones, as a function of the stress increment x beyond which they yield. We argue that the critical exponents of the yielding transition may be expressed in terms of three independent exponents, θ, df, and z, characterizing, respectively, the density of soft spots, the fractal dimension of the avalanches, and their duration. Our description shares some similarity with the depinning transition that occurs when an elastic manifold is driven through a random potential, but also presents some striking differences. We test our arguments in an elasto-plastic model, an automaton model similar to those used in depinning, but with a different interaction kernel, and find satisfying agreement with our predictions in both two and three dimensions. PMID:25246567

  2. Scaling description of the yielding transition in soft amorphous solids at zero temperature

    PubMed Central

    Lin, Jie; Lerner, Edan; Rosso, Alberto; Wyart, Matthieu

    2014-01-01

    Yield stress materials flow if a sufficiently large shear stress is applied. Although such materials are ubiquitous and relevant for industry, there is no accepted microscopic description of how they yield, even in the simplest situations in which temperature is negligible and in which flow inhomogeneities such as shear bands or fractures are absent. Here we propose a scaling description of the yielding transition in amorphous solids made of soft particles at zero temperature. Our description makes a connection between the Herschel–Bulkley exponent characterizing the singularity of the flow curve near the yield stress Σc, the extension and duration of the avalanches of plasticity observed at threshold, and the density P(x) of soft spots, or shear transformation zones, as a function of the stress increment x beyond which they yield. We argue that the critical exponents of the yielding transition may be expressed in terms of three independent exponents, θ, df, and z, characterizing, respectively, the density of soft spots, the fractal dimension of the avalanches, and their duration. Our description shares some similarity with the depinning transition that occurs when an elastic manifold is driven through a random potential, but also presents some striking differences. We test our arguments in an elasto-plastic model, an automaton model similar to those used in depinning, but with a different interaction kernel, and find satisfying agreement with our predictions in both two and three dimensions. PMID:25246567

  3. OPTICAL CONSTANTS OF NH{sub 3} AND NH{sub 3}:N{sub 2} AMORPHOUS ICES IN THE NEAR-INFRARED AND MID-INFRARED REGIONS

    SciTech Connect

    Zanchet, Alexandre; Rodríguez-Lazcano, Yamilet; Gálvez, Óscar; Herrero, Víctor J.; Escribano, Rafael; Maté, Belén

    2013-11-01

    Ammonia ice has been detected on different astrophysical media ranging from interstellar medium (ISM) particles to the surface of various icy bodies of our solar system, where nitrogen is also present. We have carried out a detailed study of amorphous NH{sub 3} ice and NH{sub 3}:N{sub 2} ice mixtures, based on infrared (IR) spectra in the mid-IR (MIR) and near-IR (NIR) regions, supported by theoretical quantum chemical calculations. Spectra of varying ice thicknesses were obtained and optical constants were calculated for amorphous NH{sub 3} at 15 K and 30 K and for a NH{sub 3}:N{sub 2} mixture at 15 K over a 500-7000 cm{sup –1} spectral range. These spectra have improved accuracy over previous data, where available. Moreover, we also obtained absolute values for the band strengths of the more prominent IR features in both spectral regions. Our results indicate that the estimated NH{sub 3} concentration in ISM ices should be scaled upward by ∼30%.

  4. Dynamics enhanced by HCl doping triggers full Pauling entropy release at the ice XII–XIV transition

    PubMed Central

    Köster, K. W.; Fuentes-Landete, V.; Raidt, A.; Seidl, M.; Gainaru, C.; Loerting, T.; Böhmer, R.

    2015-01-01

    The pressure–temperature phase diagram of ice displays a perplexing variety of structurally distinct phases. In the century-long history of scientific research on ice, the proton-ordered ice phases numbered XIII through XV were discovered only recently. Despite considerable effort, none of the transitions leading from the low-temperature ordered ices VIII, IX, XI, XIII, XIV and XV to their high-temperature disordered counterparts were experimentally found to display the full Pauling entropy. Here we report calorimetric measurements on suitably high-pressure-treated, hydrogen chloride-doped ice XIV that demonstrate just this at the transition to ice XII. Dielectric spectroscopy on undoped and on variously doped ice XII crystals reveals that addition of hydrogen chloride, the agent triggering complete proton order in ice XIV, enhances the precursor dynamics strongest. These discoveries provide new insights into the puzzling observation that different dopants trigger the formation of different proton-ordered ice phases. PMID:26076946

  5. Magnetic phase transitions and monopole excitations in spin ice under uniaxial pressure: A Monte Carlo simulation

    SciTech Connect

    Xie, Y. L. Yan, Z. B.; Liu, J.-M.; Lin, L.

    2015-05-07

    In this work, we explore the spin ice model under uniaxial pressure using the Monte Carlo simulation method. For the known spin ices, the interaction correction (δ) introduced by the uniaxial pressure varies in quite a wide range from positive to negative. When δ is positive, the ground state characterized by the ferromagnetic spin chains is quite unstable, and in real materials it serves as intermediate state connecting the ice state and the long range ordered dipolar spin ice ground state. In the case of negative δ, the system relaxes from highly degenerate ice state to ordered ferromagnetic state via a first order phase transition. Furthermore, the domain walls in such ferromagnetic state are the hotbed of the excitations of magnetic monopoles, thus indicating that the uniaxial pressure can greatly increase the monopole density.

  6. Surface transition on ice induced by the formation of a grain boundary.

    PubMed

    Pedersen, Christian; Mihranyan, Albert; Strømme, Maria

    2011-01-01

    Interfaces between individual ice crystals, usually referred to as grain boundaries, play an important part in many processes in nature. Grain boundary properties are, for example, governing the sintering processes in snow and ice which transform a snowpack into a glacier. In the case of snow sintering, it has been assumed that there are no variations in surface roughness and surface melting, when considering the ice-air interface of an individual crystal. In contrast to that assumption, the present work suggests that there is an increased probability of molecular surface disorder in the vicinity of a grain boundary. The conclusion is based on the first detailed visualization of the formation of an ice grain boundary. The visualization is enabled by studying ice crystals growing into contact, at temperatures between -20°C and -15°C and pressures of 1-2 Torr, using Environmental Scanning Electron Microscopy. It is observed that the formation of a grain boundary induces a surface transition on the facets in contact. The transition does not propagate across facet edges. The surface transition is interpreted as the spreading of crystal dislocations away from the grain boundary. The observation constitutes a qualitatively new finding, and can potentially increase the understanding of specific processes in nature where ice grain boundaries are involved. PMID:21915317

  7. Radical-Molecule Reaction C3H + H2O on Amorphous Water Ice: A Promising Route for Interstellar Propynal

    NASA Astrophysics Data System (ADS)

    Xie, Hong-bin; Shao, Chang-bin; Ding, Yi-hong

    2007-11-01

    Intriguing propynal (HCCCHO) has been attracting chemist's attention since 1955. However, to date, no satisfying conclusion concerning its formation mechanism in the interstellar medium (ISM) has been reached, although a variety of gas-reaction models, including ion-molecule, radical-molecule, and molecule-molecule, have been postulated. In this paper, we consider for the first time the gas-grain interaction model that involves heterogeneous reaction at the surface of dust grain or in the icy mantles to account for the propynal's formation. Based on the detailed density functional theory (DFT) and Gaussian-3 potential energy surface studies, we found that although the gaseous process C3H+H2O-->propynal+H must surmount a considerable entrance barrier (around 10 kcal mol-1), amorphous water ice can significantly catalyze the propynal's formation to be barrierless. So, this model should be a more reasonable one for propynal's formation in the low-temperature interstellar space. This result may also represent one rare case of the water-catalyzed reaction associated with a molecular radical in space. Future experimental studies are greatly desired to probe such interesting processes.

  8. Dielectric properties of water ice, the ice Ih/XI phase transition, and an assessment of density functional theory.

    PubMed

    Schönherr, Mandes; Slater, Ben; Hutter, Jürg; VandeVondele, Joost

    2014-01-16

    The dielectric properties of the hydrogen disordered hexagonal phase (Ih) of water ice have been computed using density functional theory (DFT) based Monte Carlo simulations in the isobaric-isothermal ensemble. Temperature dependent data yield a fit for the Curie-Weiss law of the system and hence a prediction of the temperature of the phase transition from the Ih phase to the hydrogen ordered ice XI phase. Direct simulations around the phase transition temperature confirm and refine the predicted phase transition temperatures and provide data for further properties, such as the linear thermal expansion coefficient. Results have been obtained with both hybrid and semilocal density functionals, which yields insight in the performance of the electronic structure method. In particular, the hybrid functional yields significantly more realistic dielectric constants than the semilocal variant, namely ε ≈ 116 as opposed to ε ≈ 151 at 273 K (εexperiment = 95). This can be attributed to the tendency of semilocal functionals to be biased to configurations with a large dipole moment, and their overestimation of the dipole moments of these configurations. This is also reflected in the estimates of the Ih/XI transition temperature, which is 70-80 and 90-100 K for the hybrid and semilocal functional respectively. DFT based sampling of the millions of configurations necessary for this work has been enabled by a Tree Monte Carlo algorithm, designed for massively parallel computers. PMID:24392971

  9. Low-temperature thermal conductances of amorphous dielectric microbridges in the diffusive to ballistic transition

    NASA Astrophysics Data System (ADS)

    Withington, S.; Goldie, D. J.; Velichko, A. V.

    2011-05-01

    Through a lossy acoustic-wave model we explore the effect of inelastic scattering on the low-temperature thermal conductances of amorphous dielectric microbridges in the diffusive to ballistic transition. The model gives not only the thermal flux as a function of geometry and temperature, but also the temperature distribution of the internal degrees of freedom that constitute the loss, which in turn can be used for calculating noise. The approach leads to powerful conceptual insights and provides a numerical framework for analyzing experimental data. SixNy tends to behave ballistically at low frequencies and diffusively at high frequencies, and when integrated over all frequency, the diffusive to ballistic transition becomes apparent at lengths of around a few hundred microns. It is possible to include flux-dependent acoustic loss, which leads to counterintuitive thermal behavior. A sample can behave diffusively when measured using a small temperature difference, but ballistically when measured using a large temperature difference. There is compelling circumstantial evidence that the effects of acoustic saturation have been seen, but not explicitly recognized, on many occasions.

  10. Trapping of CH4, CO, and CO2 in Amorphous Water Ice

    NASA Astrophysics Data System (ADS)

    Mastrapa, R. M. E.; Brown, R. H.; Anicich, V. G.; Cohen, B. A.; Dai, W.; Lunine, J. I.

    1999-09-01

    In this study, CO, CH4, and CO2 were trapped in H2O at temperatures as low as 20 K and pressures between 10-5 and 10-8 Torr. IR spectra were taken of each sample before sublimation to confirm the presence of volatiles. The samples were then heated at rates from 0.25 K/min to 1 K/min and the escape ranges were measured with a mass spectrometer. The volatiles escaped from the ice mixtures in temperature ranges similar to those found in previous work (1, 2, 3), namely 48-52 K, 145-160 K, 170-185 K. H2O is released from 150 K to 185 K. However, the temperature range of escape is strongly dependent on deposition temperature and heating rate. If the deposition temperature is below the point where the solid volatile rapidly sublimates in the ambient environment of our experiment, then the first range of volatile escape is centered around it's sublimation point, and there is little of the volatile remaining from 170-185 K. The location of the third escape range shifts to lower temperatures with slower sublimation rate. It was determined that 0.5 K/min is the ideal sample heating rate to determine these escape ranges. In our data, the infrared spectrum of CO trapped in water ice shows a splitting of the 2145 cm-1 solid CO line into two bands at 2343 cm-1 and 2135 cm-1. These shifts are similar to those seen by Sandford, et al. (4). (1) Bar-Nun, A., G. Herman, D. Laufer, and M. L. Rappaport, (1985), Icarus, 63, 317-332. (2) Bar-Nun, A., J. Dror, E. Kochavi, and D. Laufer, (1987), Physical Review B, 35, no. 5, 2427-2435. (3) Hudson, R. L., and B. Donn, (1991), Icarus, 94, 326-332. (4) Sandford, S. A., L. J. Allamandola, A. G. G. M. Tielens, and G. J. Valero, (1988), Astrophysical Journal, 329, 498-510.

  11. A study of the glass transition in the amorphous interlamellar phase of highly crystallized poly(ethylene terephthalate)

    NASA Astrophysics Data System (ADS)

    Sellarès, J.; Diego, J. A.; Belana, J.

    2010-09-01

    The glass transition of poly(ethylene terephthalate) (PET) crystallized for 4 h at temperatures between 413 and 453 K was studied. Secondary crystallization processes were monitored by differential scanning calorimetry and the glass transition of the remaining interlamellar amorphous phase was studied by thermally stimulated depolarization currents measurements. Non-isothermal window polarization is employed to resolve the relaxation in modes with a well-defined relaxation time that is subsequently adjusted to several standard models. An analysis of experimental results reveals that cooperativity can be disregarded in the modelization of data. The evolution of modes during secondary crystallization, once primary crystallization has been completed, gives more weight to lower energy modes. As a consequence, secondary crystallization tends to lower the glass transition temperature of the amorphous interlamellar phase, although remaining noticeably higher than in amorphous samples. The evolution of calorimetric scans of the glass transition is simulated from the obtained results and shows the same behaviour. Regarding the glass transition temperature of the material, it can be concluded that primary and secondary crystallization act in opposite directions even though the effect of secondary crystallization is much smaller. The interpretation of these results in terms of current views about secondary crystallization is discussed.

  12. Charging and Discharging of Amorphous Solid Water Ice: Effects of Porosity

    NASA Astrophysics Data System (ADS)

    Bu, Caixia; Baragiola, Raul A.

    2015-11-01

    Introduction: Amorphous solid water (ASW) is abundant on Saturn’s icy satellites and rings [1,2], where it is subject to bombardment of energetic ions, electrons, and photons; together with secondary electron and ion emission, this may leave the surfaces charged. Surface potential can affect the flux of incoming charged particles, altering surface evolution. We examined the role of porosity [3] on electrostatic charging and discharging of ASW films at 30-140 K.Experiment: Experiments were performed in ultra-high vacuum [4]. ASW films were deposited at 30 K onto a liquid-He-cooled quartz crystal microbalance (QCM). Film porosity was calculated from the areal mass via the QCM and thickness via a UV-visible interferometry. ASW films were charged at 30 K using 500 eV He+. Surface potentials (Vs) of the films were measured with a Kelvin probe, and infrared spectra were collected using a Fourier transform infrared spectrometer.Results: We measured Vs of the ASW film at 30 K as a function of ion fluence (F). The Vs(F) deviates from a straight line at low fluence, attributed to emitted secondary electrons due to the negative polarization voltage [5,6], and increases linearly when the Vs is positive. We also measured Vs as a function of annealing temperature. We prepared ASW films with various porosities by annealing the films to different temperatures (Ta) prior to irradiation or varying the vapor-beam incidence angle (θ). Upon heating, we observed sharp decreases of the Vs at temperatures that strongly depend on Ta and θ. Decreases of the infrared absorbance of the dangling OH bands of the charged film share similar trends as that of the Vs. We propose a model that includes porosity for electrostatic charging/discharging of ASW films at temperatures below 100 K. Results are applicable to the study of plasma-surface interactions of icy satellites and rings.References: [1] Jurac et al., J. Geophys. Res. 100, 14821 (1995); [2] A. L. Graps et al., Space Sci. Rev. 137, 435

  13. Theoretical Investigation of OCN(-) Charge Transfer Complexes in Condensed Phase Media: Spectroscopic Properties in Amorphous Ice

    NASA Technical Reports Server (NTRS)

    Park, Jin-Young; Woon, David E.

    2004-01-01

    Density functional theory (DFT) calculations of cyanate (OCN(-)) charge-transfer complexes were performed to model the "XCN" feature observed in interstellar icy grain mantles. OCN(-) charge-transfer complexes were formed from precursor combinations of HNCO or HOCN with either NH3 or H2O. Three different solvation strategies for realistically modeling the ice matrix environment were explored, including (1) continuum solvation, (2) pure DFT cluster calculations, and (3) an ONIOM DFT/PM3 cluster calculation. The model complexes were evaluated by their ability to reproduce seven spectroscopic measurements associated with XCN: the band origin of the OCN(-) asymmetric stretching mode, shifts in that frequency due to isotopic substitutions of C, N, O, and H, plus two weak features. The continuum solvent field method produced results consistent with some of the experimental data but failed to account for other behavior due to its limited capacity to describe molecular interactions with solvent. DFT cluster calculations successfully reproduced the available spectroscopic measurements very well. In particular, the deuterium shift showed excellent agreement in complexes where OCN(-) was fully solvated. Detailed studies of representative complexes including from two to twelve water molecules allowed the exploration of various possible solvation structures and provided insights into solvation trends. Moreover, complexes arising from cyanic or isocyanic acid in pure water suggested an alternative mechanism for the formation of OCN(-) charge-transfer complexes without the need for a strong base such as NH3 to be present. An extended ONIOM (B3LYP/PM3) cluster calculation was also performed to assess the impact of a more realistic environment on HNCO dissociation in pure water.

  14. Transition from one-dimensional water to ferroelectric ice within a supramolecular architecture.

    PubMed

    Zhao, Hai-Xia; Kong, Xiang-Jian; Li, Hui; Jin, Yi-Chang; Long, La-Sheng; Zeng, Xiao Cheng; Huang, Rong-Bin; Zheng, Lan-Sun

    2011-03-01

    Ferroelectric materials are characterized by spontaneous electric polarization that can be reversed by inverting an external electric field. Owing to their unique properties, ferroelectric materials have found broad applications in microelectronics, computers, and transducers. Water molecules are dipolar and thus ferroelectric alignment of water molecules is conceivable when water freezes into special forms of ice. Although the ferroelectric ice XI has been proposed to exist on Uranus, Neptune, or Pluto, evidence of a fully proton-ordered ferroelectric ice is still elusive. To date, existence of ferroelectric ice with partial ferroelectric alignment has been demonstrated only in thin films of ice grown on platinum surfaces or within microdomains of alkali-hydroxide doped ice I. Here we report a unique structure of quasi-one-dimensional (H(2)O)(12n) wire confined to a 3D supramolecular architecture of H(4)CDTA, trans-1,2-diaminocyclohexane-N,N,N',N'-tetraacetic acid; 4,4'-bpy, 4,4'-bipyridine). In stark contrast to the bulk, this 1D water wire not only exhibits enormous dielectric anomalies at approximately 175 and 277 K, respectively, but also undergoes a spontaneous transition between "1D liquid" and "1D ferroelectric ice" at approximately 277 K. Hitherto unrevealed properties of the 1D water wire will be valuable to the understanding of anomalous properties of water and synthesis of novel ferroelectric materials. PMID:21321232

  15. Radiation-induced crystalline-to-amorphous transition in intermetallic compounds of the Cu-Ti alloy system

    SciTech Connect

    Lam, N.Q.; Okamoto, P.R.; Devanathan, R. ); Sabochick, M.J. . Computer Applications Div.)

    1992-02-01

    Recent progress in molecular-dynamics studies of radiation-induced crystalline-to-amorphous transition in the ordered intermetallic compounds of the Cu-Ti system is discussed. The effect of irradiation was simulated by the generation of Frenkel pairs,which resulted in both the formation of stable point defects and chemical disorder upon defect recombination. The thermodynamic, structural and mechanical responses of the compounds during irradiation were determined by monitoring changes in the system potential energy, volume expansion, pair correlation function, diffraction patterns, and elastic constants. It was found that the intermetallics Cu{sub 4}Ti{sub 3}, CuTi, and CuTi{sub 2} could be rendered amorphous by the creation of Frenkel pairs, but Cu{sub 4}Ti could not, consistent with experimental observations during electron irradiation. However, the simulations showed that Cu{sub 4}Ti did become amorphous when clusters of Frenkel pairs were introduced, indicating that this compound may be susceptible to amorphization by heavy-ion bombardment. A generalization of the Lindemann criterion was used to develop a thermodynamic description of solid-state amorphization as a disorder- induced melting process.

  16. Evidence from Ice-Rafted Debris and Sediment Provenance for a Dynamic East Antarctic Ice Sheet During the Mid-Miocene Climate Transition

    NASA Astrophysics Data System (ADS)

    Williams, T.; Pierce, E. L.; van de Flierdt, T.; Hemming, S. R.; Cook, C. P.; Passchier, S.; Sangiorgi, F.; Bijl, P.

    2015-12-01

    The Antarctic ice sheets underwent a major expansion during the Mid-Miocene Climate Transition, around 14 Ma, lowering eustatic sea level by perhaps 50m, based on evidence from benthic oxygen isotope records and sea level indicators. However, direct evidence of changes in the ice sheet is limited to sites in or close to the Transantarctic Mountains. Here we present evidence for ice sheet change from two widely separated sites offshore of East Antarctica, IODP Site U1356, Wilkes Land, and ODP Site 1165, Prydz Bay. Between 14.1 and 13.8 Ma at these sites, episodic pulses of ice-rafted debris (IRD), including dropstones, were deposited in concentrations exceeding those in the rest of the Miocene. These repeated pulses of IRD-bearing icebergs indicate large and repeated advances and retreats of the ice sheet during the course of the transition to a larger and relatively more stable ice sheet. We conducted provenance analyses on the mid-Miocene IRD and sediments. At Site U1356, 40Ar/39Ar ages of ice-rafted hornblende grains show that a major ice drainage was situated along the inland part of the Mertz Shear Zone and its southward extension along the west side of the Wilkes Subglacial Basin, while Nd isotope data from the terrigenous fine fraction show that the ice margin periodically expanded from high ground well into the Wilkes Subglacial Basin during periods of ice growth. At Site 1165, 40Ar/39Ar on dropstones indicate provenance from both the Lambert Glacier region and the part of Wilkes Land that contains the Aurora Subglacial Basin. The two sites provide a direct record of repeated collapse and re-growth of ice in at least two of East Antarctica's main drainage basins during the mid-Miocene climate transition. We will set our ice-rafted debris and provenance evidence for cryosphere change in the context of mid-Miocene climate records.

  17. Direct evidence for Antarctic Ice-Sheet variability across the Eocene-Oligocene boundary climate transition

    NASA Astrophysics Data System (ADS)

    Galeotti, S.; DeConto, R.; Florindo, F.; Lanci, L.; Naish, T.; Pagani, M.; Pollard, D.; Talarico, F.

    2011-12-01

    About ~34 million years ago, at the Eocene-Oligocene (E-O) boundary, Earth's climate underwent a substantial change from relatively ice-free "greenhouse" conditions to a glacial state marked by the establishment of a permanent ice sheet on Antarctica. Geochemical data and modeling suggests that decline of atmospheric pCO2 to a threshold level around 2.5X pre-industrial levels concomitant with an optimal orbital configuration for cold southern hemisphere summers provided the precursory conditions for extensive glaciation of Antarctica. Previous geological drill core records from the Antarctic margin indicate that the ice sheet reached continental extent and was calving at the coastline by the Earliest Oligocene. Notwithstanding these, our understanding of Antarctic cryospheric evolution across the E-O climate transition, relies almost entirely on marine geochemical proxies and reconstruction of sea-level changes from continental margin sequences. Hitherto it has not been possible to reconcile the pattern of inferred ice-sheet growth from these "far-field" proxy records with direct physical evidence of ice-volume changes from the Antarctic continental margin. Here we correlate cyclical changes recorded in sediment cores from western Ross Sea, which are related to oscillations in the volume of a growing East Antarctic Ice Sheet, with well-dated lower latitude records of orbital forcing and climate change across the E-O transition. We show that the EAIS was relatively small and unstable during the first ~200 thousands of years (kyr) of the E-O transition and that fully glaciated conditions did not occur until ~32.8 Ma, more than a million years after the glacial maximum of the climatic transition as recorded by geochemical proxies.

  18. Effect of patch borders on coercivity in amorphous rare earth-transition metal thin films

    NASA Technical Reports Server (NTRS)

    Patterson, G.; Fu, H.; Giles, R. C.; Mansuripur, M.

    1991-01-01

    The coercivity at the micron scale is a very important property of magneto-optical media. It is a key factor that determines the magnetic domain wall movement and domain reversal. How the coercivity is influenced by a special type of patch borders is discussed. Patch formation is a general phenomenon in growth processes of amorphous rare earth transition metal thin films. Different patches may stem from different seeds and the patch borders are formed when they merge. Though little is known about the exact properties of the borders, we may expect that the exchange interaction at the patch border is weaker than that within a patch, since there is usually a spatial gap between two patches. Computer simulations were performed on a 2-D hexagonal lattice consisting of 37 complete patches with random shape and size. From the series of simulations we may conclude that the domain in the patch with borders of 30 percent exchange strength can expand most easily to the whole lattice, because the exchange strength can expand most easily to the whole lattice, because the exchange strength of the border is not too high to prevent the domain from growing within the patch and it is not too low to prevent the domain from expanding beyond the patch.

  19. Structural transition and amorphization in compressed α - Sb 2 O 3

    DOE PAGESBeta

    Zhao, Zhao; Zeng, Qiaoshi; Zhang, Haijun; Wang, Shibing; Hirai, Shigeto; Zeng, Zhidan; Mao, Wendy L.

    2015-05-27

    Sb₂O₃-based materials are of broad interest in materials science and industry. High-pressure study using diamond anvil cells shows promise in obtaining new crystal and electronic structures different from their pristine states. Here, we conducted in situ angle dispersive synchrotron x-ray-diffraction and Raman spectroscopy experiments on α-Sb₂O₃ up to 50 GPa with neon as the pressure transmitting medium. A first-order structural transition was observed in between 15 and 20 GPa, where the cubic phase I gradually transformed into a layered tetragonal phase II through structural distortion and symmetry breaking. To explain the dramatic changes in sample color and transparency, we performedmore » first-principles calculations to track the evolution of its density of states and electronic structure under pressure. At higher pressure, a sluggish amorphization was observed. Our results highlight the structural connections among the sesquioxides, where the lone electron pair plays an important role in determining the local structures.« less

  20. Amorphous to crystalline phase transition in pulsed laser deposited silicon carbide

    NASA Astrophysics Data System (ADS)

    Tabbal, M.; Said, A.; Hannoun, E.; Christidis, T.

    2007-06-01

    SiC thin films were grown on Si (1 0 0) substrates by excimer laser ablation of a SiC target in vacuum. The effect of deposition temperature (up to 950 °C), post-deposition annealing and laser energy on the nanostructure, bonding and crystalline properties of the films was studied, in order to elucidate their transition from an amorphous to a crystalline phase. Infra-red spectroscopy shows that growth at temperatures greater than 600 °C produces layers with increasingly uniform environment of the Si-C bonds, while the appearance of large crystallites is detected, by X-ray diffraction, at 800 °C. Electron paramagnetic resonance confirms the presence of clustered paramagnetic centers within the sp 2 carbon domains. Increasing deposition temperature leads to a decrease of the spin density and to a temperature-dependent component of the EPR linewidth induced by spin hopping. For films grown below 650 °C, post-deposition annealing at 1100 °C reduces the spin density as a result of a more uniform Si-C nanostructure, though large scale crystallization is not observed. For greater deposition temperatures, annealing leads to little changes in the bonding properties, but suppresses the temperature dependent component of the EPR linewidth. These findings are explained by a relaxation of the stress in the layers, through the annealing of the bond angle disorder that inhibits spin hopping processes.

  1. Structural transition in sputter-deposited amorphous germanium films by aging at ambient temperature

    NASA Astrophysics Data System (ADS)

    Okugawa, M.; Nakamura, R.; Ishimaru, M.; Watanabe, K.; Yasuda, H.; Numakura, H.

    2016-06-01

    The structure of amorphous Ge (a-Ge) films prepared by sputter-deposition and the effects of aging at ambient temperature and pressure were studied by pair-distribution-function (PDF) analysis from electron scattering and molecular dynamics simulations. The PDFs of the as-deposited and aged samples for 3-13 months showed that the major peaks for Ge-Ge bonds decrease in intensity and broaden with aging for up to 7 months. In the PDFs of a-Ge of molecular dynamics simulation obtained by quenching liquid at different rates, the major peak intensities of a slowly cooled model are higher than those of a rapidly cooled model. Analyses on short- and medium-range configurations show that the slowly cooled model includes a certain amount of medium-range ordered (MRO) clusters, while the rapidly cooled model includes liquid-like configurations rather than MRO clusters. The similarity between experimental and computational PDFs implies that as-deposited films are similar in structure to the slowly cooled model, whereas the fully aged films are similar to the rapidly cooled model. It is assumed that as they undergo room-temperature aging, the MRO clusters disintegrate and transform into liquid-like regions in the same matrix. This transition in local configurations is discussed in terms of instability and the non-equilibrium of nanoclusters produced by a vapor-deposition process.

  2. Tunneling Spectroscopy of Amorphous Magnetic Rare Earth-Si Alloys near the Metal-Insulator Transition

    NASA Astrophysics Data System (ADS)

    Xiong, P.; Zink, B. L.; Tran, M. Q.; Gebala, A. E.; Wilcox, E. M.; Hellman, F.; Dynes, R. C.

    1997-03-01

    Amorphous dilute magnetic semiconductors exhibit striking differences in the electrical and magneto-transport behavior from their crystalline or nonmagnetic analogs.(F. Hellman et al., Phys. Rev. Lett. 77, 4652 (1996).) Magnetic impurities cause a large suppression of conductivity below 50 K in a-Si_xGd_1-x and a-Si_xTb_1-x relative to the nonmagnetic a-Si_xY_1-x (x ~ 0.85-0.9). Application of a magnetic field increases the conductivity by orders of magnitude. We have fabricated good quality tunnel junctions on a-Si:Gd and the nonmagnetic a-Si:Y to probe the electronic density of states in these two systems. We present the results of the tunneling spectroscopy and its magnetic field dependence for a series of the two alloys at different compositions. We will discuss the correlation between the tunneling spectra and the transport properties and its implications on the possible origin of the magnetic field tuned insulator-metal transition in a-Si:Gd. Research Supported by ONR Grant No. N000149151320 and NSF Grant No. DMR-9208599.

  3. Transport behavior across the field-driven superconductor-insulator transition in amorphous indium oxide films

    NASA Astrophysics Data System (ADS)

    Kim, Min-Soo

    Superconductor-insulator transition (SIT) in two-dimensional (2D) thin films is a beautiful realization of a zero temperature quantum phase transition (QPT) and has been explored both theoretically and experimentally over the last two decades. In addition to the several intrinsic ways (such as thickness) of tuning the transition, external magnetic field has been used to tune from one ground state to another in various condensed matter systems. Amorphous indium oxide thin films, with their unique capability of tuning the disorder level in the system easily, have been proven to be an excellent model system to study the transport mechanisms near and across the SIT in 2D. In this thesis, magnetic field-driven SIT in 2D films of amorphous InO x is studied. The goal of this work is to understand the microscopic transport mechanisms responsible for driving the SIT when the magnetic field direction is continually varied from being perpendicular to the sample plane to parallel. Applying a perpendicular magnetic field resulting in a clear field-driven SIT and a magneto-resistance peak on the insulating side in InO x films have been previously understood in a bosonic picture put forward by M. P. A. Fisher and coworkers. However, this boson-vortex duality picture is expected to give rise to markedly different transport characteristics when the magnetic field is applied parallel to the sample plane. Features found in the parallel-field transport data however can also be explained by the bosonic picture, thereby questioning the applicability of the hitherto successful models to the physics of SIT. An isotropic magnetic field value, where the sample has the exact same resistance irrespective of the angle between the sample plane and magnetic field direction, is found. This isotropic point lies at field values above the critical field (Bc) of the SIT (in both perpendicular and parallel configurations) and above the magnetoresistance peak. The isotropic point is very weakly

  4. The radiation-induced crystalline-to-amorphous transition in zircon

    SciTech Connect

    Weber, W.J. ); Ewing, R.C.; Wang, L. )

    1994-03-01

    A comprehensive understanding of radiation effects in zircon, ZrSiO[sub 4], over a broad range of time scales (0.5 h to 570 million years) has been obtained by a study of natural zircon, Pu-doped zircon, and ion-beam irradiated zircon. Radiation damage in zircon results in the simultaneous accumulation of both point defects and amorphous regions. The amorphization process is consistent with models based on the multiple overlap of particle tracks, suggesting that amorphization occurs as a result of a critical defect concentration. The amorphization dose increases with temperature in two stages (below 300 K and above 473 K) and is nearly independent of the damage source ([alpha]-decay events or heavy-ion beams) at 300 K. Recrystallization of completely amorphous zircon occurs above 1300 K and is a two-step process that involves the initial formation of pseudo-cubic ZrO[sub 2].

  5. Transition from one-dimensional water to ferroelectric ice within a supramolecular architecture

    PubMed Central

    Zhao, Hai-Xia; Kong, Xiang-Jian; Li, Hui; Jin, Yi-Chang; Long, La-Sheng; Zeng, Xiao Cheng; Huang, Rong-Bin; Zheng, Lan-Sun

    2011-01-01

    Ferroelectric materials are characterized by spontaneous electric polarization that can be reversed by inverting an external electric field. Owing to their unique properties, ferroelectric materials have found broad applications in microelectronics, computers, and transducers. Water molecules are dipolar and thus ferroelectric alignment of water molecules is conceivable when water freezes into special forms of ice. Although the ferroelectric ice XI has been proposed to exist on Uranus, Neptune, or Pluto, evidence of a fully proton-ordered ferroelectric ice is still elusive. To date, existence of ferroelectric ice with partial ferroelectric alignment has been demonstrated only in thin films of ice grown on platinum surfaces or within microdomains of alkali-hydroxide doped ice I. Here we report a unique structure of quasi-one-dimensional (H2O)12n wire confined to a 3D supramolecular architecture of H4CDTA, trans-1,2-diaminocyclohexane-N,N,N′,N′-tetraacetic acid; 4,4′-bpy, 4,4′-bipyridine). In stark contrast to the bulk, this 1D water wire not only exhibits enormous dielectric anomalies at approximately 175 and 277 K, respectively, but also undergoes a spontaneous transition between “1D liquid” and “1D ferroelectric ice” at approximately 277 K. Hitherto unrevealed properties of the 1D water wire will be valuable to the understanding of anomalous properties of water and synthesis of novel ferroelectric materials. PMID:21321232

  6. Scratching the surface of ice: Interfacial phase transitions and their kinetic implications

    NASA Astrophysics Data System (ADS)

    Limmer, David

    The surface structure of ice maintains a high degree of disorder down to surprisingly low temperatures. This is due to a number of underlying interfacial phase transitions that are associated with incremental changes in broken symmetry relative to the bulk crystal. In this talk I summarize recent work attempting to establish the nature and locations of these different phase transitions as well as how they depend on external conditions and nonequilibrium driving. The implications of this surface disorder is discussed in the context of simple kinetic processes that occur at these interfaces. Recent experimental work on the roughening transition is highlighted.

  7. Mapping the Bølling-Allerød transition in the Greenland Ice Sheet using radio-echo sounding data

    NASA Astrophysics Data System (ADS)

    Karlsson, Nanna B.; Dahl-Jensen, Dorthe; Prasad Gogineni, S.; Paden, John D.

    2013-04-01

    Ice cores have provided high resolution data of the chronology of the Greenland Ice Sheet enabling reconstructions of temperature, accumulation and surface elevation back in time. However, ice core data are inherently point-measurements and are thus spatially limited. The introduction of radio-echo sounding (RES) in glaciology provides a method for linking independent ice core chronologies between drill sites by using the internal reflectors observed in the RES data. Here we apply the ice core chronology from the NorthGRIP drill site in combination with RES data (acquired by the Center for Remote Sensing of Ice Sheets) to map the extent and depth of Holocene ice in North Greenland. We make use of the fact that the transition from the last glacial to the warm Bølling-Allerød interstadial (at 14.7kyr b2k) is clearly visible in the majority of the RES data from central Greenland. The depths and extent of the transition are influenced by past surface accumulation, basal properties as well as temporal and spatial changes in ice flow dynamics. This provides not only a basis for directly mapping the existing pre-Holocene ice in the Greenland Ice Sheet but also a valuable tool for obtaining information on past mass balance and ice flow. Results show that the transition is located in the upper 30%-50% of the ice column in the central part of the ice sheet indicating that a substantial amount of ice pre-dating the Holocene is present in the central part of North Greenland. At the margins the transition is located significantly deeper which is most likely due to high velocity areas dragging the layers down. However, this effect varies between different areas and may be related to the geometry and ice flow dynamics of the particular region and/or the timing of the initialization of the ice stream. Modelling studies of the Greenland Ice Sheet may incorporate this dataset to answer questions related to large scale dynamics of the ice sheet such as the extent of the ice during

  8. Atomic-Level Simulations of Epitaxial Recrystallization and Amorphous-to-Crystalline Transition in 4H-SiC

    SciTech Connect

    Gao, Fei; Zhang, Yanwen; Posselt, Matthias; Weber, William J.

    2006-09-01

    The amorphous-to-crystalline (a-c) transition in 4H-SiC has been studied using molecular dynamics (MD) methods, with simulation times of up to a few hundred ns and at temperatures ranging from 1000 to 2000 K. Two nano-sized amorphous layers, one with the normal of a-c interfaces along the [ -12-10] direction and the other along the [ -1010] direction, were created within a crystalline cell to study expitaxial recrystallization and the formation of secondary phases. The recovery of bond defects at the interfaces is an important process driving the epitaxial recrystallization of the amorphous layers. The amorphous layer with the a-c interface normal along the [-12-10] direction can be completely recrystallized at the temperatures of 1500 and 2000 K, but the recrystallized region is defected with dislocations and stacking faults. On the other hand, the recrystallization process for the a-c interface normal along [-1010] direction is hindered by the nucleation of polycrystalline phases, and these secondary ordered phases are stable for longer simulation times. A general method to calculate activation energy spectra is employed to analyze the MD annealing simulations, and the recrystallization mechanism in SiC consists of multiple stages with activation energies ranging from 0.8 to 1.7 eV.

  9. Influence of phase transitions of ice on near-surface cathodoluminescence

    NASA Astrophysics Data System (ADS)

    Kurt, K.; Ramachandran, V.; Maghrabi, M.; Townsend, P. D.; Yang, B.

    2002-05-01

    Luminescence signals respond to phase transitions both of the host material and of impurities on the nanoparticle-size scale. During cathodoluminescence spectral measurements of many insulators, strong intensity changes (up to 100 times) have been recorded at ~170 K, which are here ascribed to the phase transitions of water that has diffused into the near-surface regions, or is trapped within the bulk material in nanoparticle quantities. The intensity step correlates with the ice transition between the cubic and hexagonal phases. In many materials there are also weaker features near 230 K which match the low-pressure ice-to-vapour transition. Some signals are apparent in radioluminescence data when the water is within the bulk material. The impurity phase changes can modify the emission spectra of the host. Examples are given for several insulators (Nd:YAG, zircon, MgO:Cr, PbWO4, strontium barium niobate) and a superconductor. The data have implications for quantitative luminescence analyses and underline the significant and influential presence of water contaminants. In many surface layers, such as surface optical waveguides or those of superconductors, the ice may significantly influence the behaviour of the host material.

  10. Liquid-solid and solid-solid phase transition of monolayer water: High-density rhombic monolayer ice

    NASA Astrophysics Data System (ADS)

    Kaneko, Toshihiro; Bai, Jaeil; Yasuoka, Kenji; Mitsutake, Ayori; Zeng, Xiao Cheng

    2014-05-01

    Liquid-solid and solid-solid phase transitions of a monolayer water confined between two parallel hydrophobic surfaces are studied by molecular dynamics simulations. The solid phase considered is the high-density rhombic monolayer ice. Based on the computed free energy surface, it is found that at a certain width of the slit nanopore, the monolayer water exhibits not only a high freezing point but also a low energy barrier to crystallization. Moreover, through analyzing the oxygen-hydrogen-oxygen angle distribution and oxygen-hydrogen radial distribution, the high-density monolayer ice is classified as either a flat ice or a puckered ice. The transition between a flat ice and a puckered ice reflects a trade-off between the water-wall interactions and the electrostatic interactions among water molecules.

  11. Liquid-solid and solid-solid phase transition of monolayer water: high-density rhombic monolayer ice.

    PubMed

    Kaneko, Toshihiro; Bai, Jaeil; Yasuoka, Kenji; Mitsutake, Ayori; Zeng, Xiao Cheng

    2014-05-14

    Liquid-solid and solid-solid phase transitions of a monolayer water confined between two parallel hydrophobic surfaces are studied by molecular dynamics simulations. The solid phase considered is the high-density rhombic monolayer ice. Based on the computed free energy surface, it is found that at a certain width of the slit nanopore, the monolayer water exhibits not only a high freezing point but also a low energy barrier to crystallization. Moreover, through analyzing the oxygen-hydrogen-oxygen angle distribution and oxygen-hydrogen radial distribution, the high-density monolayer ice is classified as either a flat ice or a puckered ice. The transition between a flat ice and a puckered ice reflects a trade-off between the water-wall interactions and the electrostatic interactions among water molecules. PMID:24832288

  12. Phase transitions and charge ordering in a square spin ice model with conserved monopole density

    NASA Astrophysics Data System (ADS)

    Xie, Yunlong; Zhou, Xiaohui; Liu, Jun-Ming

    2015-03-01

    Artificial spin ices represent a class of highly interested frustrated magnetic systems under intensive investigations for fascinating ground states and thermodynamics/dynamics of spin excitations in recent years. As one of these issues, magnetic charge ordering and the corresponding phase transitions in the two-dimensional system are emerging topics in condensed matter physics. In this work, we investigate all the monopole-ordered phases of the square spin ice model using the conserved monopole density algorithm. In low monopole density (ρ ~ 0), the Coulomb potential determines the monopoles' dynamics. We test the Coulomb's law in a two-dimension lattice and justify the monopole dimerization which is quite different from the three-dimensional pyrochlore spin ice. These monopole dimers are charge neutral, and the interactions between them have also been investigated using our algorithm. In the cases of high monopole density (ρ ~ 1), the system is similar to the dipolar kagome spin ice model, and our simulation results show that there exists an intermediate phase between the paramagnetic phase and the ordered magnetic phase. Such intermediate phase can be distinguished by the order of magnetic charges. In a cooling process, the system undergoes a two-stage magnetic phase transition before freezing to the long range magnetic ordered phase via a staggered charge ordering. Furthermore, a liquefaction process of monopole dimers can be justified upon the increasing effective internal pressure in the isothermal condition.

  13. Direct Observation of Amorphous to Crystalline Phase Transitions in Nano-Particle Arrays of Phase Change Materials

    SciTech Connect

    Raoux,S.; Rettner, C.; Jordan-Sweet, J.; Kellock, A.; Topuria, T.; Rice, P.; Miller, D.

    2007-01-01

    We have used time-resolved x-ray diffraction to study the amorphous-crystalline phase transition in 20-80?nm particles of the phase change materials Ge2Sb2Te5, nitrogen-doped Ge2Sb2Te5, Ge15Sb85, Sb2Te, and Sb2Te doped with Ag and In. We find that all samples undergo the phase transition with crystallization temperatures close to those of similarly prepared blanket films of the same materials with the exception of Sb2Te that shows the transition at a temperature that is about 40? C higher than that of blanket films. Some of the nanoparticles show a difference in crystallographic texture compared to thick films. Large area arrays of these nanoparticles were fabricated using electron-beam lithography, keeping the sample temperatures well below the crystallization temperatures so as to produce particles that were entirely in the amorphous phase. The observation that particles with diameters as small as 20?nm can still undergo this phase transition indicates that phase change solid-state memory technology should scale to these dimensions.

  14. Mechanisms for pressure-induced crystal-crystal transition, amorphization, and devitrification of Snl4

    SciTech Connect

    Liu, Hanyu; Tse, John S.; Hu, Michael Y.; Bi, Wenli; Zhao, Jiyong; Alp, E. Ercan; Pasternak, Moshe; Taylor, R. Dean; Lashley, Jason C.

    2015-10-27

    The pressure-induced amorphization and subsequent recrystallization of SnI4 have been investigated using first principles molecular dynamics calculations together with high-pressure 119Sn nuclear resonant inelastic x-ray scattering measurements. Above ~8 GPa, we observe a transformation from an ambient crystalline phase to an intermediate crystal structure and a subsequent recrystallization into a cubic phase at ~64 GPa. The crystalline-to-amorphous transition was identified on the basis of elastic compatibility criteria. The measured tin vibrational density of states shows large amplitude librations of SnI4 under ambient conditions. Although high pressure structures of SnI4 were thought to be determined by random packing of equal-sized spheres, we detected electron charge transfer in each phase. As a result, this charge transfer results in a crystal structure packing determined by larger than expected iodine atoms. (C) 2015 AIP Publishing LLC.

  15. Mechanisms for pressure-induced crystal-crystal transition, amorphization, and devitrification of SnI{sub 4}

    SciTech Connect

    Liu, H.; Tse, J. S.; Hu, M. Y.; Bi, W.; Zhao, J.; Alp, E. E.; Pasternak, M.; Taylor, R. D.; Lashley, J. C.

    2015-10-28

    The pressure-induced amorphization and subsequent recrystallization of SnI{sub 4} have been investigated using first principles molecular dynamics calculations together with high-pressure {sup 119}Sn nuclear resonant inelastic x-ray scattering measurements. Above ∼8 GPa, we observe a transformation from an ambient crystalline phase to an intermediate crystal structure and a subsequent recrystallization into a cubic phase at ∼64 GPa. The crystalline-to-amorphous transition was identified on the basis of elastic compatibility criteria. The measured tin vibrational density of states shows large amplitude librations of SnI{sub 4} under ambient conditions. Although high pressure structures of SnI{sub 4} were thought to be determined by random packing of equal-sized spheres, we detected electron charge transfer in each phase. This charge transfer results in a crystal structure packing determined by larger than expected iodine atoms.

  16. Magnetic-charge ordering and phase transitions in monopole-conserved square spin ice

    PubMed Central

    Xie, Y.-L.; Du, Z.-Z.; Yan, Z.-B.; Liu, J.-M.

    2015-01-01

    Magnetic-charge ordering and corresponding magnetic/monopole phase transitions in spin ices are the emergent topics of condensed matter physics. In this work, we investigate a series of magnetic-charge (monopole) phase transitions in artificial square spin ice model using the conserved monopole density algorithm. It is revealed that the dynamics of low monopole density lattices is controlled by the effective Coulomb interaction and the Dirac string tension, leading to the monopole dimerization which is quite different from the dynamics of three-dimensional pyrochlore spin ice. The condensation of the monopole dimers into monopole crystals with staggered magnetic-charge order can be predicted clearly. For the high monopole density cases, the lattice undergoes two consecutive phase transitions from high-temperature paramagnetic/charge-disordered phase into staggered charge-ordered phase before eventually toward the long-range magnetically-ordered phase as the ground state which is of staggered charge order too. A phase diagram over the whole temperature-monopole density space, which exhibits a series of emergent spin and monopole ordered states, is presented. PMID:26511870

  17. Magnetic-charge ordering and phase transitions in monopole-conserved square spin ice

    NASA Astrophysics Data System (ADS)

    Xie, Y.-L.; Du, Z.-Z.; Yan, Z.-B.; Liu, J.-M.

    2015-10-01

    Magnetic-charge ordering and corresponding magnetic/monopole phase transitions in spin ices are the emergent topics of condensed matter physics. In this work, we investigate a series of magnetic-charge (monopole) phase transitions in artificial square spin ice model using the conserved monopole density algorithm. It is revealed that the dynamics of low monopole density lattices is controlled by the effective Coulomb interaction and the Dirac string tension, leading to the monopole dimerization which is quite different from the dynamics of three-dimensional pyrochlore spin ice. The condensation of the monopole dimers into monopole crystals with staggered magnetic-charge order can be predicted clearly. For the high monopole density cases, the lattice undergoes two consecutive phase transitions from high-temperature paramagnetic/charge-disordered phase into staggered charge-ordered phase before eventually toward the long-range magnetically-ordered phase as the ground state which is of staggered charge order too. A phase diagram over the whole temperature-monopole density space, which exhibits a series of emergent spin and monopole ordered states, is presented.

  18. Magnetic-charge ordering and phase transitions in monopole-conserved square spin ice.

    PubMed

    Xie, Y-L; Du, Z-Z; Yan, Z-B; Liu, J-M

    2015-01-01

    Magnetic-charge ordering and corresponding magnetic/monopole phase transitions in spin ices are the emergent topics of condensed matter physics. In this work, we investigate a series of magnetic-charge (monopole) phase transitions in artificial square spin ice model using the conserved monopole density algorithm. It is revealed that the dynamics of low monopole density lattices is controlled by the effective Coulomb interaction and the Dirac string tension, leading to the monopole dimerization which is quite different from the dynamics of three-dimensional pyrochlore spin ice. The condensation of the monopole dimers into monopole crystals with staggered magnetic-charge order can be predicted clearly. For the high monopole density cases, the lattice undergoes two consecutive phase transitions from high-temperature paramagnetic/charge-disordered phase into staggered charge-ordered phase before eventually toward the long-range magnetically-ordered phase as the ground state which is of staggered charge order too. A phase diagram over the whole temperature-monopole density space, which exhibits a series of emergent spin and monopole ordered states, is presented. PMID:26511870

  19. Arrhenian and Non-Arrhenian Temperature Dependent Relaxation Time Development in the Solid-Liquid Transition Area of Amorphous Bodies

    NASA Astrophysics Data System (ADS)

    Hlaváček, Bořivoj; Drašar, Čestmír; Kalendová, Andréa; Menc, Pavel; Veselý, David

    The temperature-dependent changes of molecular and sub-molecular motions are studied in amorphous substances. The solid and liquid phases of amorphous bodies are characterized at the micro-level by two types of oscillators, linear and non-linear. It is accepted that an amorphous liquid is formed by domains that group the linear oscillators into the form of icebergs. The serial connection of the viscoelastic elements are arranged inside of these icebergs. The size of the linear connection within the domains is characterized by the number "n", which increases during the cooling process. The linear viscoelastic behavior of the individual serial connections is connected to the individual relaxation processes α, β, and γ. Only the "alpha" process exhibits growth of "n" to infinity on cooling. Therefore, the corresponding relaxation time, τα, for the infinite chain of "n" elements (Voigt or Maxwell elements) can also reach infinity as the material transforms to a glassy state. In contrast to the "alpha" process, the β and γ processes are limited in growth for serial connections in a chain structure. Therefore, the relaxation times for the β and γ processes, τβ and τγ, will only follow the temperature dependence of the sample viscosity on cooling, which is, of course, Arrhenian. We discuss the role of non-linear oscillators in the solid-liquid transition in relation to Brownian motion.

  20. Reorganization of ice sheet flow patterns in Arctic Canada and the mid-Pleistocene transition

    NASA Astrophysics Data System (ADS)

    Refsnider, Kurt A.; Miller, Gifford H.

    2010-07-01

    Evidence for the evolution of Laurentide Ice Sheet (LIS) basal thermal regime patterns during successive glaciations is poorly preserved in the geologic record. Here we explore a new approach to constrain the distribution of cold-based ice across central Baffin Island in the eastern Canadian Arctic over many glacial-interglacial cycles by combining till geochemistry and cosmogenic radionuclide (CRN) data. Parts of the landscaped with geomorphic evidence for limited glacial erosion are covered by till characterized by high chemical index of alteration (CIA) values and CRN concentrations requiring complicated burial-exposure histories. Till from regions scoured by glacial erosion have CIA values indistinguishable from local bedrock and CRN concentrations that can be explained by simple exposure following deglaciation. CRN modeling results based on these constraints suggest that the weathered tills were deposited by 1.9 to 1.2 Ma, and by that time the fiorded Baffin Island coastline must have developed close to its modern configuration as piracy of ice flow by the most efficient fiord systems resulted in a major shift in the basal thermal regime across the northeastern LIS. The resultant concentration of ice flow in fewer outlet systems may help explain the cause of the mid-Pleistocene transition from 41- to 100-kyr glacial cycles.

  1. Glass transition of aqueous solutions involving annealing-induced ice recrystallization resolves liquid-liquid transition puzzle of water

    PubMed Central

    Zhao, Li-Shan; Cao, Ze-Xian; Wang, Qiang

    2015-01-01

    Liquid-liquid transition of water is an important concept in condensed-matter physics. Recently, it was claimed to have been confirmed in aqueous solutions based on annealing-induced upshift of glass-liquid transition temperature, . Here we report a universal water-content, , dependence of for aqueous solutions. Solutions with vitrify/devitrify at a constant temperature, , referring to freeze-concentrated phase with left behind ice crystallization. Those solutions with totally vitrify at under conventional cooling/heating process though, of the samples annealed at temperatures   to effectively evoke ice recrystallization is stabilized at . Experiments on aqueous glycerol and 1,2,4-butanetriol solutions in literature were repeated, and the same samples subject to other annealing treatments equally reproduce the result. The upshift of by annealing is attributable to freeze-concentrated phase of solutions instead of ‘liquid II phase of water’. Our work also provides a reliable method to determine hydration formula and to scrutinize solute-solvent interaction in solution. PMID:26503911

  2. Structural mechanisms of the Ih–II and II → Ic transitions between the crystalline phases of aqueous ice

    SciTech Connect

    Zheligovskaya, E. A.

    2015-09-15

    Structural mechanisms are proposed for experimentally observed phase transitions between crystalline modifications of aqueous ice, Ih and II, as well as II and Ic. It is known that the Ih–II transition occurs with the conservation of large structural units (hexagonal channels) common for these ices. It is shown that the Ih → II transition may occur with the conservation of 5/6 of all hydrogen bonds in crystal, including all hydrogen bonds in the retained channels (3/4 of the total number of bonds in crystal) and 1/3 of the bonds between these channels (1/12 of the total number). The transformation of other hydrogen bonds between the retained channels leads to the occurrence of proton order in ice II. A structural mechanism is proposed to explain the transformation of single crystals of ice Ih either into single crystals of ice II or into crystalline twins of ice II with c axes rotated by 180° with respect to each other, which is often observed at the Ih → II transition. It is established that up to 7/12 of all hydrogen bonds are retained at the irreversible cooperative II → Ic transition.

  3. Sea ice melt onset associated with lead opening during the spring/summer transition near the North Pole

    NASA Astrophysics Data System (ADS)

    Vivier, Frédéric; Hutchings, Jennifer K.; Kawaguchi, Yusuke; Kikuchi, Takashi; Morison, James H.; Lourenço, Antonio; Noguchi, Tomohide

    2016-04-01

    In the central Arctic Ocean, autonomous observations of the ocean mixed layer and ice documented the transition from cold spring to early summer in 2011. Ice-motion measurements using GPS drifters captured three events of lead opening and ice ridge formation in May and June. Satellite sea ice concentration observations suggest that locally observed lead openings were part of a larger-scale pattern. We clarify how these ice deformation events are linked with the onset of basal sea ice melt, which preceded surface melt by 20 days. Observed basal melt and ocean warming are consistent with the available input of solar radiation into leads, once the advent of mild atmospheric conditions prevents lead refreezing. We use a one-dimensional numerical simulation incorporating a Local Turbulence Closure scheme to investigate the mechanisms controlling basal melt and upper ocean warming. According to the simulation, a combination of rapid ice motion and increased solar energy input at leads promotes basal ice melt, through enhanced mixing in the upper mixed layer, while slow ice motion during a large lead opening in mid-June produced a thin, low-density surface layer. This enhanced stratification near the surface facilitates storage of solar radiation within the thin layer, instead of exchange with deeper layers, leading to further basal ice melt preceding the upper surface melt.

  4. Deep water temperature, carbonate ion, and ice volume changes across the Eocene-Oligocene climate transition

    NASA Astrophysics Data System (ADS)

    Pusz, A. E.; Thunell, R. C.; Miller, K. G.

    2011-06-01

    Paired benthic foraminiferal stable isotope and Mg/Ca data are used to estimate bottom water temperature (BWT) and ice volume changes associated with the Eocene-Oligocene Transition (EOT), the largest global climate event of the past 50 Myr. We utilized ODP Sites 1090 and 1265 in the South Atlantic to assess seawater δ18O (δw), Antarctic ice volume, and sea level changes across the EOT (˜33.8-33.54 Ma). We also use benthic δ13C data to reconstruct the sources of the deep water masses in this region during the EOT. Our data, together with previously published records, indicate that a pulse of Northern Component Water influenced the South Atlantic immediately prior to and following the EOT. Benthic δ18O records show a 0.5‰ increase at ˜33.8 Ma (EOT-1) that represents a ˜2°C cooling and a small (˜10 m) eustatic fall that is followed by a 1.0‰ increase associated with Oi-1. The expected cooling of deep waters at Oi-1 (˜33.54 Ma) is not apparent in our Mg/Ca records. We suggest the cooling is masked by coeval changes in the carbonate saturation state (Δ[CO32-]) which affect the Mg/Ca data. To account for this, the BWT, ice volume, and δw estimates are corrected for a change in the Δ[CO32-] of deep waters on the basis of recently published work. Corrected BWT at Sites 1090 and 1265 show a ˜1.5°C cooling coincident with Oi-1 and an average δw increase of ˜0.75‰. The increase in ice volume during Oi-1 resulted in a ˜70 m drop in global sea level and the development of an Antarctic ice sheet that was near modern size or slightly larger.

  5. On the role of thermohaline advection and sea ice in glacial transitions

    NASA Astrophysics Data System (ADS)

    Kravtsov, S.; Dewar, W. K.

    2003-06-01

    A two-dimensional, one-basin thermohaline oceanic circulation (THC) model coupled to an atmospheric energy balance model (EBM) with land ice albedo effect and a thermodynamic sea ice model is used to study global climate on centennial, and longer, timescales. The model is interpreted to represent the effect of the global ocean, rather than the Atlantic, as is commonly done. It is forced by symmetric insolation and includes a diagnostic parameterization of the hydrologic cycle. Here the strength of the ocean's haline forcing is controlled by a parameter, which reflects the effect of river runoff. This parameter is varied in a set of experiments, which also differ by the magnitude of solar insolation. In wide ranges of the hydrologic cycle, multiple climatic equilibria exist, consisting of circulations with different degrees of asymmetry. More symmetric states have a higher global atmospheric temperature, characteristic of modern climate, whereas less symmetric states are colder and resemble glacial conditions. The maximum global atmospheric temperature difference between such states is consistent with proxy-data-derived temperature drop of about 4°C during the glacial, in contrast to EBM-only sensitivity of about 0.4°C. The mechanics of climate transitions in the model are due to amplification of the orbitally induced global heat budget changes by a major reorganization of the oceanic heat transport. In our model this reorganization is caused by the nonlinear dynamics of the ocean's THC, whose stability regime shifts subject to variable external forcing. Sea ice enhances model climate sensitivity by anchoring deep-ocean temperature to be near freezing [, 2000] and by affecting atmospheric temperature and land ice extent near the poles because of sea ice insulating properties.

  6. The peculiar behavior of the glass transition temperature of amorphous drug-polymer films coated on inert sugar spheres.

    PubMed

    Dereymaker, Aswin; Van Den Mooter, Guy

    2015-05-01

    Fluid bed coating has been proposed in the past as an alternative technology for manufacturing of drug-polymer amorphous solid dispersions, or so-called glass solutions. It has the advantage of being a one-step process, and thus omitting separate drying steps, addition of excipients, or manipulation of the dosage form. In search of an adequate sample preparation method for modulated differential scanning calorimetry analysis of beads coated with glass solutions, glass transition broadening and decrease of the glass transition temperature (Tg ) were observed with increasing particle size of crushed coated beads and crushed isolated films of indomethacin (INDO) and polyvinylpyrrolidone (PVP). Substituting INDO with naproxen gave comparable results. When ketoconazole was probed or the solvent in INDO-PVP films was switched to dichloromethane (DCM) or a methanol-DCM mixture, two distinct Tg regions were observed. Small particle sizes had a glass transition in the high Tg region, and large particle sizes had a glass transition in the low Tg region. This particle size-dependent glass transition was ascribed to different residual solvent amounts in the bulk and at the surface of the particles. A correlation was observed between the deviation of the Tg from that calculated from the Gordon-Taylor equation and the amount of residual solvent at the Tg of particles with different sizes. PMID:25702912

  7. The Structural Properties of Vapor Deposited Water Ice and Astrophysical Implications

    NASA Technical Reports Server (NTRS)

    Jenniskens, P.; Blake, D. F.; Chang, Sherwood (Technical Monitor)

    1996-01-01

    Films of vapor deposited water ice at low temperature (T<30 K) show a number of interesting structural changes during a gradual warmup. We would like to talk about the structure of the low temperature high density amorphous form of water ice, the process of crystallization, and some recent work on the morphological changes of water ice films at high temperature. The studies of the high density amorphous form are from in-situ electron microscopy as well as numerical simulations of molecular dynamics and have lead to new insights into the physical distinction between this high density amorphous form and the low density amorphous form. For the process of crystallization, we propose a model that describes the crystallization of water ice from the amorphous phase to cubic ice in terms of the nucleation of small domains in the ice. This model agrees well with the behavior of water ice in our electron microscopy studies and finds that pure water above the glass transition is a strong liquid. In more recent work, we have concentrated on temperatures above the crystallization temperature and we find interesting morphological changes related to the decrease in viscosity of the amorphous component in the cubic crystalline regime. Given enough time, we would like to put these results in an astrophysical context and discuss some observed features of the frost on interstellar grains and the bulk ice in comets.

  8. Solubility of crystalline organic compounds in high and low molecular weight amorphous matrices above and below the glass transition by zero enthalpy extrapolation.

    PubMed

    Amharar, Youness; Curtin, Vincent; Gallagher, Kieran H; Healy, Anne Marie

    2014-09-10

    Pharmaceutical applications which require knowledge of the solubility of a crystalline compound in an amorphous matrix are abundant in the literature. Several methods that allow the determination of such data have been reported, but so far have only been applicable to amorphous polymers above the glass transition of the resulting composites. The current work presents, for the first time, a reliable method for the determination of the solubility of crystalline pharmaceutical compounds in high and low molecular weight amorphous matrices at the glass transition and at room temperature (i.e. below the glass transition temperature), respectively. The solubilities of mannitol and indomethacin in polyvinyl pyrrolidone (PVP) K15 and PVP K25, respectively were measured at different temperatures. Mixtures of undissolved crystalline solute and saturated amorphous phase were obtained by annealing at a given temperature. The solubility at this temperature was then obtained by measuring the melting enthalpy of the crystalline phase, plotting it as a function of composition and extrapolating to zero enthalpy. This new method yielded results in accordance with the predictions reported in the literature. The method was also adapted for the measurement of the solubility of crystalline low molecular weight excipients in amorphous active pharmaceutical ingredients (APIs). The solubility of mannitol, glutaric acid and adipic acid in both indomethacin and sulfadimidine was experimentally determined and successfully compared with the difference between their respective calculated Hildebrand solubility parameters. As expected from the calculations, the dicarboxylic acids exhibited a high solubility in both amorphous indomethacin and sulfadimidine, whereas mannitol was almost insoluble in the same amorphous phases at room temperature. This work constitutes the first report of the methodology for determining an experimentally measured solubility for a low molecular weight crystalline solute

  9. The respective role of atmospheric carbon dioxide and orbital parameters on ice sheet evolution at the Eocene-Oligocene transition

    NASA Astrophysics Data System (ADS)

    Ladant, Jean-Baptiste; Donnadieu, Yannick; Lefebvre, Vincent; Dumas, Christophe

    2014-08-01

    The continental scale initiation of the Antarctic ice sheet at the Eocene-Oligocene boundary (Eocene-Oligocene transition (EOT), 34 Ma) is associated with a global reorganization of the climate. If data studies have assessed the precise timing and magnitudes of the ice steps, modeling studies have been unable to reproduce a transient ice evolution during the Eocene-Oligocene transition in agreement with the data. Here we simulate this transition using general circulation models coupled to an ice sheet model. Our simulations reveal a threshold for continental scale glaciation of 900 ppm, 100 to 150 ppm higher than previous studies. This result supports the existence of ephemeral ice sheets during the middle Eocene, as similar CO2 levels (900-1000 ppm) have been reached episodically during this period. Transient runs show that the ice growth is accurately timed with EOT-1 and Oi-1, the two δ18O excursions occurring during the transition. We show that CO2 and orbital variations are crucial in initiating these steps, with EOT-1 corresponding to the occurrence of low summer insolation, whereas Oi-1 is controlled by a major CO2 drop. The two δ18O steps record both ice growth and temperature, representing some 10-30 m eustatic sea level fall and 2-4°C cooling at EOT-1 and 70 ± 20 m and 0-2°C for Oi-1. The simulated magnitude of the ice steps (10 m for EOT-1 and 63 m for Oi-1) and the overall cooling at various locations show a good agreement with the data, which supports our results concerning this critical transition.

  10. Iceberg calving during transition from grounded to floating ice: Columbia Glacier, Alaska

    USGS Publications Warehouse

    Walter, Fabian; O'Neel, Shad; McNamara, Daniel; Pfeffer, W.T.; Bassis, Jeremy N.; Fricker, Helen Amanda

    2010-01-01

    The terminus of Columbia Glacier, Alaska, unexpectedly became ungrounded in 2007 during its prolonged retreat. Visual observations showed that calving changed from a steady release of low-volume bergs, to episodic flow-perpendicular rifting, propagation, and release of very large icebergs - a style reminiscent of calving from ice shelves. Here, we compare passive seismic and photographic observations through this transition to examine changes in calving. Mechanical changes accompany the visible changes in calving style post flotation: generation of seismic energy during calving is substantially reduced. We propose this is partly due to changes in source processes.

  11. An observation of amorphous-crystalline phase transitions at severe plastic deformation of the Ti{sub 50}Ni{sub 25}Cu{sub 25} alloy

    SciTech Connect

    Nosova, G. I.; Shalimova, A. V.; Sundeev, R. V.; Glezer, A. M. Pankova, M. N.; Shelyakov, A. V.

    2009-11-15

    The features of structural and phase transitions during severe plastic deformation (in Bridgman anvils) of the amorphous Ti{sub 50}Ni{sub 25}Cu{sub 25} alloy have been studied by X-ray diffraction and transmission electron microscopy. Application of successively increasing deformation has revealed three cycles of successive phase transitions from amorphous to crystalline state and vice versa. The results obtained are explained in terms of the superposition of the different channels of elastic energy dissipation, which are activated during severe plastic deformation.

  12. Electronic Origin For The Phase Transition From Amorphous LixSi To Crystalline Li15Si4

    SciTech Connect

    Gu, Meng; Wang, Zhiguo; Connell, Justin G.; Perea, Daniel E.; Lauhon, Lincoln J.; Gao, Fei; Wang, Chong M.

    2013-06-24

    Silicon has been widely explored as an anode material for lithium ion battery. Upon lithiation, silicon transforms to amorphous LixSi (a-LixSi) via electrochemical driven solid state amorphization. With increasing lithium concentration, a-LixSi transforms to crystalline Li15Si4 (c-Li15Si4). The mechanism of this crystallization process is not known. In this paper, we report the fundamental characteristics of the phase transition of a-LixSi to c-Li15Si4 using in-situ scanning transmission electron microscopy (STEM), electron energy loss spectroscopy (EELS), and density function theory (DFT) calculation. We find that when the lithium concentration in a-LixSi reaches a critical value of x = 3.75, the a-Li3.75Si spontaneously and congruently transforms to c-Li15Si4 by a process that is solely controlled by the lithium concentration in the a-LixSi, involving neither large scale atomic migration nor phase separation. DFT calculations indicate that c-Li15Si4 formation is favored over other possible crystalline phases due to the similarity in electronic structure with a-Li3.75Si.

  13. Understanding the amorphous-to-microcrystalline silicon transition in SiF4/H2/Ar gas mixtures

    NASA Astrophysics Data System (ADS)

    Dornstetter, Jean-Christophe; Bruneau, Bastien; Bulkin, Pavel; Johnson, Erik V.; Roca i Cabarrocas, Pere

    2014-06-01

    We report on the growth of microcrystalline silicon films from the dissociation of SiF4/H2/Ar gas mixtures. For this growth chemistry, the formation of HF molecules provides a clear signature of the amorphous to microcrystalline growth transition. Depositing films from silicon tetrafluoride requires the removal of F produced by SiF4 dissociation, and this removal is promoted by the addition of H2 which strongly reacts with F to form HF molecules. At low H2 flow rates, the films grow amorphous as all the available hydrogen is consumed to form HF. Above a critical flow rate, corresponding to the full removal of F, microcrystalline films are produced as there is an excess of atomic hydrogen in the plasma. A simple yet accurate phenomenological model is proposed to explain the SiF4/H2 plasma chemistry in accordance with experimental data. This model provides some rules of thumb to achieve high deposition rates for microcrystalline silicon, namely, that increased RF power must be balanced by an increased H2 flow rate.

  14. Amorphous-to-crystalline phase transition of (InTe)x(GeTe) thin films

    NASA Astrophysics Data System (ADS)

    Song, Ki-Ho; Beak, Seung-Cheol; Lee, Hyun-Yong

    2010-07-01

    The crystallization speed (v) of the amorphous (InTe)x(GeTe) (x=0.1, 0.3, and 0.5) films and their thermal, optical, and electrical behaviors were investigated by using a nanopulse scanner (wavelength=658 nm, laser beam diameter <2 μm), x-ray diffraction, a four-point probe, and a UV-vis-IR spectrophotometer. These results were compared to the results for a Ge2Sb2Te5 (GST) film, which was comprehensively utilized for phase-change random access memory (PRAM). Both the v—value and the thermal stability of the (InTe)0.1(GeTe) and (InTe)0.3(GeTe) films were enhanced in comparison to the GST film. Contrarily, the v—value of the (InTe)0.5(GeTe) film was so drastically deteriorated that it could not be quantitatively evaluated. This deterioration occurred because the amorphous (InTe)0.5(GeTe) film had relatively high reflectance, resulting in the absorption being too low to cause the crystallization. Conclusively, proper compositional (InTe)x(GeTe) films (e.g., x<0.3) could be good candidates for PRAM application with both high crystallization speed and thermal stability.

  15. Geographical Patterns of Sea-Ice Retreat in the Transition to a Seasonally Ice-Free Arctic

    NASA Astrophysics Data System (ADS)

    DeRepentigny, P.; Tremblay, B.; Newton, R.; Pfirman, S. L.

    2015-12-01

    The September sea-ice extent minimum is influenced by summertime processes, primarily thermodynamic, as well as dynamic processes during the previous winter. In this paper, we focus on the effect of the large-scale winter mean sea-ice circulation on the following September minimum sea-ice extent and, in particular, how coastal divergence in the western and eastern Arctic dictates the geographical pattern of retreat. We compare the Community Climate System Model 4 (CCSM4) and the Community Earth System Model 1 Large Ensemble (CESM-LE) with sea-ice motion vectors from NOAA/NSIDC for the past three decades. We find that the large-scale mean winter atmospheric circulation in CCSM4 is characterized by a positive Arctic Oscillation (AO) index with a broad Transpolar Drift Stream, sea-ice divergence in the western Arctic and a large negative bias in its Arctic mean sea-level pressure (around -7 mb). On the other hand, CESM-LE has a mean winter sea-ice circulation more similar to observations in its late 20th century climate and no bias in its mean sea-level pressure, although there are some spatial differences.We use a Lagrangian ice trajectory model to quantify the amount of ice divergence along the Alaskan and Eurasian coastlines by backtracking the September sea-ice extent minimum ice edge to its position throughout the previous year. We find that the sea-ice retreat in CCSM4 occurs mostly on the Pacific side of the Arctic Ocean with more coastal divergence in the Chukchi and Beaufort seas - in line with the more positive AO. On the other hand, the sea-ice retreat is found to be more symmetric around the North Pole in CESM-LE. Given that a positive trend in the AO index is a robust feature of Global Climate Models participating in CMIP5, our results suggest that sea ice will continue to retreat preferentially from the Pacific sector, as has been observed in the last decade.

  16. Inception and variability of the Antarctic ice sheet across the Eocene-Oligocene transition

    NASA Astrophysics Data System (ADS)

    Stocchi, Paolo; Galeotti, Simone; Ladant, Jan-Baptiste; DeConto, Robert; Vermeersen, Bert; Rugenstein, Maria

    2014-05-01

    Climate cooling throughout middle to late Eocene (~48 - 34 Million years ago, Ma) triggered the transition from hot-house to ice-house conditions. Based on deep-sea marine δ18O values, a continental-scale Antarctic Ice Sheet (AIS) rapidly developed across the Eocene-Oligocene transition (EOT) in two ~200 kyr-spaced phases between 34.0 - 33.5 Ma. Regardless of the geographical configuration of southern ocean gateways, geochemical data and ice-sheet modelling show that AIS glaciation initiated as atmospheric CO2 fell below ~2.5 times pre-industrial values. AIS likely reached or even exceeded present-day dimensions. Quantifying the magnitude and timing of AIS volume variations by means of δ18O records is hampered by the fact that the latter reflect a coupled signal of temperature and ice-sheet volume. Besides, bathymetric variations based on marine geologic sections are affected by large uncertainties and, most importantly, reflect the local response of relative sea level (rsl) to ice volume fluctuations rather than the global eustatic signal. AIS proximal and Northern Hemisphere (NH) marine settings show an opposite trend of rsl change across the EOT. In fact, consistently with central values based on δ18O records, an 60 ± 20m rsl drop is estimated from NH low-latitude shallow marine sequences. Conversely, sedimentary facies from shallow shelfal areas in the proximity of the AIS witness an 50 - 150m rsl rise across the EOT. Accounting for ice-load-induced crustal and geoidal deformations and for the mutual gravitational attraction between the growing AIS and the ocean water is a necessary requirement to reconcile near- and far-field rsl sites, regardless of tectonics and of any other possible local contamination. In this work we investigate the AIS inception and variability across the EOT by combining the observed rsl changes with predictions based on numerical modeling of Glacial Isostatic Adjustment (GIA). We solve the gravitationally self-consistent Sea Level

  17. Nucleation of Ice

    NASA Astrophysics Data System (ADS)

    Molinero, Valeria

    2009-03-01

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

  18. Crystalline to amorphous phase transition of tin oxide nanocrystals induced by SHI at low temperature

    SciTech Connect

    Kumar, Vijay; Pratap, Deepti; Jain, Anshul; Agarwal, D. C.; Sulania, I.; Tripathi, A.; Chaudhary, R. J.; Chauhan, R. S.

    2012-06-05

    Tin oxide (SnO{sub 2}) thin films were deposited using pulsed laser deposition (PLD) technique on Si substrates. The as-deposited films were irradiated using 100 MeV Ag ions at different fluences ranging from 3x10{sup 13} to 3x10{sup 14} ions/cm{sup 2} at an incidence angle of 75 deg. with respect to surface normal at liquid nitrogen (LN2) temperature. The as-deposited and irradiated films have been characterized using X-ray diffraction (XRD) and atomic force microscopy (AFM) techniques to study the modifications in structural and surface morphological properties. Nanocrystalline film become completely amorphous and nanograins of tin oxide disappeared from the surface as indicated by XRD spectra and AFM micrographs respectively.

  19. Simulating the last glacial-interglacial transition with a coupled atmosphere-ocean-ice sheet model

    NASA Astrophysics Data System (ADS)

    Mikolajewicz, Uwe; Ziemen, Florian

    2015-04-01

    One of the major challenges in climate modeling is the simulation of glacial-interglacial transitions. A few models of intermediate complexity have been successful in simulating the last termination. Complex atmosphere-ocean general circulation models have been shown to be able to yield realistic climate changes with prescribed ice sheets. Here we presents results from a first attempt to simulate a substantial part of the last glacial cycle with an AOGCM coupled interactively with a state-of-the-art ice sheet model. The ECHAM5/MPIOM AOGCM has been interactively coupled to the dynamical ice sheet model PISM. The latter is run for most of the northern hemisphere with a horizontal resolution of 20 km. An earlier version of this model ( Ziemen et al. 2014) has been applied to a steady state simulation of the last glacial maximum (LGM). The model was integrated from the late Glacial into the Holocene using insolation and greenhouse gas concentrations as transient forcing. Land sea mask and ocean topography are fixed at LGM conditions, river routing and surface elevation for the atmospheric model component are calculated interactively depending on the simulated ice sheets. To make these long simulations feasible, the atmosphere is accelerated by a factor of 10 relative to the other model components using a periodically-synchronous coupling technique. A mini-ensemble with different initial conditions has been run. In all simulation the northern hemispheric deglaciation starts between 18 and 17 kyr BP, consistent with the onset of global warming. The model produces Heinrich event like variability as part of its internal variability. These rapid ice discharge events have a strong impact on the North Atlantic meridional overturning circulation (NAMOC). During the peak deglaciation the NAMOC is collapsed (with a few short interruptions) for several thousand years, which is longer than the estimates from reconstructions. This seems to be an artifact due to keeping ocean

  20. Interaction of marine ice-sheet instabilities in two drainage basins: simple scaling of geometry and transition time

    NASA Astrophysics Data System (ADS)

    Feldmann, J.; Levermann, A.

    2015-04-01

    The initiation of a marine ice-sheet instability (MISI) is generally discussed from the ocean side of the ice sheet. It has been shown that the reduction in ice-shelf buttressing and softening of the coastal ice can destabilize a marine ice sheet if the bedrock is sloping upward towards the ocean. Using a conceptional flow-line geometry, we investigate the possibility of whether a MISI can be triggered from the direction of the ice divide as opposed to coastal forcing and explore the interaction between connected basins. We find that the initiation of a MISI in one basin can induce a destabilization in the other. The underlying mechanism of basin interaction is based on dynamic thinning and a consecutive motion of the ice divide which induces a thinning in the adjacent basin and a successive initiation of the instability. Our simplified and symmetric topographic setup allows scaling both the geometry and the transition time between both instabilities. We find that the ice profile follows a universal shape that is scaled with the horizontal extent of the ice sheet and that the same exponent of 1/2 applies for the scaling relation between central surface elevation and horizontal extent as in the pure shallow ice approximation (Vialov profile). Altering the central bed elevation, we find that the extent of grounding-line retreat in one basin determines the degree of interaction with the other. Different scenarios of basin interaction are discussed based on our modeling results as well as on a conceptual flux-balance analysis. We conclude that for the three-dimensional case, the possibility of drainage basin interaction on timescales on the order of 1 kyr or larger cannot be excluded and hence needs further investigation.

  1. Nanocrystals in compression: unexpected structural phase transition and amorphization due to surface impurities

    NASA Astrophysics Data System (ADS)

    Liu, Gang; Kong, Lingping; Yan, Jinyuan; Liu, Zhenxian; Zhang, Hengzhong; Lei, Pei; Xu, Tao; Mao, Ho-Kwang; Chen, Bin

    2016-06-01

    We report an unprecedented surface doping-driven anomaly in the compression behaviors of nanocrystals demonstrating that the change of surface chemistry can lead to an interior bulk structure change in nanoparticles. In the synchrotron-based X-ray diffraction experiments, titania nanocrystals with low concentration yttrium dopants at the surface are found to be less compressible than undoped titania nanocrystals. More surprisingly, an unexpected TiO2(ii) phase (α-PbO2 type) is induced and obvious anisotropy is observed in the compression of yttrium-doped TiO2, in sharp contrast to the compression behavior of undoped TiO2. In addition, the undoped brookite nanocrystals remain with the same structure up to 30 GPa, whereas the yttrium-doped brookite amorphizes above 20 GPa. The abnormal structural evolution observed in yttrium-doped TiO2 does not agree with the reported phase stability of nano titania polymorphs, thus suggesting that the physical properties of the interior of nanocrystals can be controlled by the surface, providing an unconventional and new degree of freedom in search for nanocrystals with novel tunable properties that can trigger applications in multiple areas of industry and provoke more related basic science research.We report an unprecedented surface doping-driven anomaly in the compression behaviors of nanocrystals demonstrating that the change of surface chemistry can lead to an interior bulk structure change in nanoparticles. In the synchrotron-based X-ray diffraction experiments, titania nanocrystals with low concentration yttrium dopants at the surface are found to be less compressible than undoped titania nanocrystals. More surprisingly, an unexpected TiO2(ii) phase (α-PbO2 type) is induced and obvious anisotropy is observed in the compression of yttrium-doped TiO2, in sharp contrast to the compression behavior of undoped TiO2. In addition, the undoped brookite nanocrystals remain with the same structure up to 30 GPa, whereas the yttrium

  2. Elliptical halos, Bottlinger's rings, and the ice-plate snow-star transition.

    PubMed

    Tränkle, E; Riikonen, M

    1996-08-20

    Elliptical halos and Bottlinger's rings are simulated by the use of a Monte Carlo algorithm that includes multiple scattering. High multiple reflections are required to obtain a sufficient brightness of the elliptical halos. By introducing three populations of nearly horizontal, gyrating, and swinging crystals, we obtain good agreement for four photographs of displays with ringlike and disklike structures. Through model experiments on the aerodynamical behavior of crystals, we find a new interpretation of the three populations. In this view elliptical halos and Bottlinger's rings occur in the transition region of ice plates with broad branches and stellar crystals at temperatures near -15 °C and large supersaturations. This interpretation is supported by a review of 23 reports of elliptical halo phenomena by members of the Finnish Halo Observers Network. PMID:21102913

  3. Nanocrystals in compression: unexpected structural phase transition and amorphization due to surface impurities.

    PubMed

    Liu, Gang; Kong, Lingping; Yan, Jinyuan; Liu, Zhenxian; Zhang, Hengzhong; Lei, Pei; Xu, Tao; Mao, Ho-Kwang; Chen, Bin

    2016-06-01

    We report an unprecedented surface doping-driven anomaly in the compression behaviors of nanocrystals demonstrating that the change of surface chemistry can lead to an interior bulk structure change in nanoparticles. In the synchrotron-based X-ray diffraction experiments, titania nanocrystals with low concentration yttrium dopants at the surface are found to be less compressible than undoped titania nanocrystals. More surprisingly, an unexpected TiO2(ii) phase (α-PbO2 type) is induced and obvious anisotropy is observed in the compression of yttrium-doped TiO2, in sharp contrast to the compression behavior of undoped TiO2. In addition, the undoped brookite nanocrystals remain with the same structure up to 30 GPa, whereas the yttrium-doped brookite amorphizes above 20 GPa. The abnormal structural evolution observed in yttrium-doped TiO2 does not agree with the reported phase stability of nano titania polymorphs, thus suggesting that the physical properties of the interior of nanocrystals can be controlled by the surface, providing an unconventional and new degree of freedom in search for nanocrystals with novel tunable properties that can trigger applications in multiple areas of industry and provoke more related basic science research. PMID:27280175

  4. Amorphous to crystalline phase transition: Onset of pattern formation during ion erosion of Si(001)

    NASA Astrophysics Data System (ADS)

    Engler, Martin; Michely, Thomas

    2016-02-01

    The morphological evolution of Si(001) is investigated for normal incidence 2 keV Kr+ion irradiation under ultra-high vacuum conditions as a function of temperature and ion fluence through scanning tunneling microscopy and low energy electron diffraction. Under the conditions chosen, the selvage of Si(001) amorphizes below the critical temperature Tc of 670 K, while above it remains crystalline. Below Tc the sample remains flat, irrespective of the ion fluence. Above Tc, the crystalline sample displays for fixed ion fluence and as a function of sample temperature a pronounced roughness maximum at 700 K. Around this temperature, with increasing ion fluence a strong increase of roughness as well as coarsening are observed. Pyramidal pits and mounds develop, with facets formed by Si steps and narrow reconstructed terraces. Most exciting, with increasing ion fluence the pattern reorients from pits and mounds with edges along the <110 > directions to ridges and valleys rotated ≈45 ∘ to the <110 > directions.

  5. Superconductor-Metal-Insulator Transitions in two dimensional amorphous NbxSi1-x

    NASA Astrophysics Data System (ADS)

    Humbert, Vincent; Couëdo, François; Crauste, Olivier; Bergé, Laurent; Drillien, Anne-Aelle; Akiko Marrache-Kikuchi, Claire; Dumoulin, Louis

    2014-12-01

    We report on the study of the two-dimensional Disorder-induced Superconductor- Insulator Transition (D-SIT) in NbxSi1-x thin films. In this proceeding, we present new results on the emergence of an insulating state from a 2d metallic state.

  6. Observed microphysical changes in Arctic mixed-phase clouds when transitioning from sea-ice to open ocean

    NASA Astrophysics Data System (ADS)

    Young, Gillian; Jones, Hazel M.; Crosier, Jonathan; Bower, Keith N.; Darbyshire, Eoghan; Taylor, Jonathan W.; Liu, Dantong; Allan, James D.; Williams, Paul I.; Gallagher, Martin W.; Choularton, Thomas W.

    2016-04-01

    The Arctic sea-ice is intricately coupled to the atmosphere[1]. The decreasing sea-ice extent with the changing climate raises questions about how Arctic cloud structure will respond. Any effort to answer these questions is hindered by the scarcity of atmospheric observations in this region. Comprehensive cloud and aerosol measurements could allow for an improved understanding of the relationship between surface conditions and cloud structure; knowledge which could be key in validating weather model forecasts. Previous studies[2] have shown via remote sensing that cloudiness increases over the marginal ice zone (MIZ) and ocean with comparison to the sea-ice; however, to our knowledge, detailed in-situ data of this transition have not been previously presented. In 2013, the Aerosol-Cloud Coupling and Climate Interactions in the Arctic (ACCACIA) campaign was carried out in the vicinity of Svalbard, Norway to collect in-situ observations of the Arctic atmosphere and investigate this issue. Fitted with a suite of remote sensing, cloud and aerosol instrumentation, the FAAM BAe-146 aircraft was used during the spring segment of the campaign (Mar-Apr 2013). One case study (23rd Mar 2013) produced excellent coverage of the atmospheric changes when transitioning from sea-ice, through the MIZ, to the open ocean. Clear microphysical changes were observed, with the cloud liquid-water content increasing by almost four times over the transition. Cloud base, depth and droplet number also increased, whilst ice number concentrations decreased slightly. The surface warmed by ~13 K from sea-ice to ocean, with minor differences in aerosol particle number (of sizes corresponding to Cloud Condensation Nuclei or Ice Nucleating Particles) observed, suggesting that the primary driver of these microphysical changes was the increased heat fluxes and induced turbulence from the warm ocean surface as expected. References: [1] Kapsch, M.L., Graversen, R.G. and Tjernström, M. Springtime

  7. Dynamic and thermodynamic characteristics associated with the glass transition of amorphous trehalose-water mixtures

    PubMed Central

    Weng, Lindong; Elliott, Gloria D.

    2014-01-01

    The glass transition temperature Tg of biopreservative formulations is important for predicting the longterm storage of biological specimens. As a complementary tool to thermal analysis techniques, which are the mainstay for determining Tg, molecular dynamics simulations have been successfully applied to predict the Tg of several protectants and their mixtures with water. These molecular analyses, however, rarely focused on the glass transition behavior of aqueous trehalose solutions, a subject that has attracted wide scientific attention via experimental approaches. Important behavior, such as hydrogen-bonding dynamics and self-aggregation has yet to be explored in detail, particularly below, or in the vicinity of, Tg. Using molecular dynamics simulations of several dynamic and thermodynamic properties, this study reproduced the supplemented phase diagram of trehalose-water mixtures (i.e., Tg as a function of the solution composition) based on experimental data. The structure and dynamics of the hydrogen-bonding network in the trehalose-water systems were also analyzed. The hydrogen-bonding lifetime was determined to be an order of magnitude higher in the glassy state than in the liquid state, while the constitution of the hydrogen-bonding network exhibited no noticeable change through the glass transition. It was also found that trehalose molecules preferred to form small, scattered clusters above Tg, but self-aggregation was substantially increased below Tg. The average cluster size in the glassy state was observed to be dependent on the trehalose concentration. Our findings provided insights into the glass transition characteristics of aqueous trehalose solutions as they relate to biopreservation. PMID:24803351

  8. Dynamic and thermodynamic characteristics associated with the glass transition of amorphous trehalose-water mixtures.

    PubMed

    Weng, Lindong; Elliott, Gloria D

    2014-06-21

    The glass transition temperature Tg of biopreservative formulations is important for predicting the long-term storage of biological specimens. As a complementary tool to thermal analysis techniques, which are the mainstay for determining Tg, molecular dynamics simulations have been successfully applied to predict the Tg of several protectants and their mixtures with water. These molecular analyses, however, rarely focused on the glass transition behavior of aqueous trehalose solutions, a subject that has attracted wide scientific attention via experimental approaches. Important behavior, such as hydrogen-bonding dynamics and self-aggregation has yet to be explored in detail, particularly below, or in the vicinity of, Tg. Using molecular dynamics simulations of several dynamic and thermodynamic properties, this study reproduced the supplemented phase diagram of trehalose-water mixtures (i.e., Tg as a function of the solution composition) based on experimental data. The structure and dynamics of the hydrogen-bonding network in the trehalose-water systems were also analyzed. The hydrogen-bonding lifetime was determined to be an order of magnitude higher in the glassy state than in the liquid state, while the constitution of the hydrogen-bonding network exhibited no noticeable change through the glass transition. It was also found that trehalose molecules preferred to form small, scattered clusters above Tg, but self-aggregation was substantially increased below Tg. The average cluster size in the glassy state was observed to be dependent on the trehalose concentration. Our findings provided insights into the glass transition characteristics of aqueous trehalose solutions as they relate to biopreservation. PMID:24803351

  9. Automatic Detection of the Holocene Transition in Radio-Echo Sounding Data from the Greenland Ice Sheet

    NASA Astrophysics Data System (ADS)

    Karlsson, N. B.; Dahl-Jensen, D.; Gogineni, S. P.; Paden, J.; Hvidberg, C. S.

    2012-04-01

    Radio-echo sounding has provided important insights into the subsurface properties of the Greenland Ice-Sheet. Recent years have seen increasing interest in englacial radio reflectors (or internal layers) because their stratigraphy reflects both mass balance rates and flow dynamics. Thus patterns of internal layers contain information about the past behaviour of an ice mass. Unfortunately retrieving this information often relies on a large amount of user interaction and can be very time consuming. As the amount of radio-echo sounding data increases, the development of quantitative techniques for digitising internal layers in radar data is a logical step forward. In this study we present an automated method for estimating the elevation of the Holocene transition in radio-echo sounding data from Greenland. The data was collected by the Center for Remote Sensing of Ice Sheets (CReSIS), University of Kansas. The automated method is based on the observation that the CReSIS radio-echo data often display a characteristic appearance: the upper half of the radio-echo data contains numerous internal layering and appears much darker than the lower, older part, where only a few visible layers can be seen. Compared to the depth-age relationship from the NorthGRIP ice core this change in the radar-echo data coincides with the transition to the Holocene period. The method obtains a good match with manually traced data and also returns an estimate of the confidence in its output. The depth of the Holocene transition will provide insight into the large-scale variation of mass balance and basal melt rate over the Greenland Ice Sheet and will assist in efforts to model the past evolution of the ice sheet.

  10. Nanocrystal dispersed amorphous alloys

    NASA Technical Reports Server (NTRS)

    Perepezko, John H. (Inventor); Allen, Donald R. (Inventor); Foley, James C. (Inventor)

    2001-01-01

    Compositions and methods for obtaining nanocrystal dispersed amorphous alloys are described. A composition includes an amorphous matrix forming element (e.g., Al or Fe); at least one transition metal element; and at least one crystallizing agent that is insoluble in the resulting amorphous matrix. During devitrification, the crystallizing agent causes the formation of a high density nanocrystal dispersion. The compositions and methods provide advantages in that materials with superior properties are provided.

  11. Molecular transport and phase transition of polycrystalline ice doped with HCl and SO2 near its melting point

    NASA Astrophysics Data System (ADS)

    Lu, H.; McCartney, S.; Sadtchenko, V.

    2007-12-01

    HCl and SO2 are major trace gases in atmosphere, which greatly affects chemical properties of atmospheric ice particles. A particular interest to atmospheric science is the effects of impurities on molecular transport and phase transition at grain boundaries in polycrystalline ice. Effects of doped HCl and SO2 on transport and phase transition at grain boundary of 2-4 micrometer polycrystalline ice were studied using a novel technique - Fast Thermal Desorption Spectroscopy (FTDS) [1] in the temperature range from -2 to -20 deg. C. In these experiments, H2O/D2O/H2O sandwich-like polycrystalline ice films doped with HCl and SO2 were vapor- deposited on the surface of a thin filament positioned in a vacuum chamber and maintained initially at cryogenic temperatures. After the deposition, the temperature of the filament was rapidly raised to a value near ice melting point, thus, initiating rapids H/D exchange reaction at the interface of H2O and D2O layers. Diffusion controlled rate of isotopic exchange in the desorbing film was monitored with a sensitive mass-spectrometer making it possible to gain quantitative information of the extent of diffusion of chemical species along the grain boundaries in polycrystalline ice samples. Comparisons of the experimental results in pure and doped polycrystalline ice show that water self diffusivity at the grain boundaries is significantly enhanced (by at least an order of magnitude) in the presence of HCl or SO2. The strong, non- Arrhenius, dependence of the water self-diffusivity on temperature indicates that this is due to grain boundary premelting [2], which may occur at temperatures as low as 10 deg. below ice melting point. We will discuss implication of this and other results of our FTDS experiments to various environmental phenomena. References: 1. Haiping Lu, Stephanie A. McCartney, M. Chonde, D. Smyla, and Vlad Sadtchenko, Fast thermal desorption spectroscopy study of morphology and vaporization kinetics of polycrystalline

  12. Mechanism of Pressure-Induced Phase Transitions, Amorphization, and Absorption-Edge Shift in Photovoltaic Methylammonium Lead Iodide.

    PubMed

    Szafrański, Marek; Katrusiak, Andrzej

    2016-09-01

    Our single-crystal X-ray diffraction study of methylammonium lead triiodide, MAPbI3, provides the first comprehensive structural information on the tetragonal phase II in the pressure range to 0.35 GPa, on the cubic phase IV stable between 0.35 and 2.5 GPa, and on the isostructural cubic phase V observed above 2.5 GPa, which undergoes a gradual amorphization. The optical absorption study confirms that up to 0.35 GPa, the absorption edge of MAPbI3 is red-shifted, allowing an extension of spectral absorption. The transitions to phases IV and V are associated with the abrupt blue shifts of the absorption edge. The strong increase of the energy gap in phase V result in a spectacular color change of the crystal from black to red around 3.5 GPa. The optical changes have been correlated with the pressure-induced strain of the MAPbI3 inorganic framework and its frustration, triggered by methylammonium cations trapped at random orientations in the squeezed voids. PMID:27538989

  13. High-throughput exploration of thermoelectric and mechanical properties of amorphous NbO2 with transition metal additions

    NASA Astrophysics Data System (ADS)

    Music, Denis; Geyer, Richard W.; Hans, Marcus

    2016-07-01

    To increase the thermoelectric efficiency and reduce the thermal fatigue upon cyclic heat loading, alloying of amorphous NbO2 with all 3d and 5d transition metals has systematically been investigated using density functional theory. It was found that Ta fulfills the key design criteria, namely, enhancement of the Seebeck coefficient and positive Cauchy pressure (ductility gauge). These quantum mechanical predictions were validated by assessing the thermoelectric and elastic properties on combinatorial thin films, which is a high-throughput approach. The maximum power factor is 2813 μW m-1 K-2 for the Ta/Nb ratio of 0.25, which is a hundredfold increment compared to pure NbO2 and exceeds many oxide thermoelectrics. Based on the elasticity measurements, the consistency between theory and experiment for the Cauchy pressure was attained within 2%. On the basis of the electronic structure analysis, these configurations can be perceived as metallic, which is consistent with low electrical resistivity and ductile behavior. Furthermore, a pronounced quantum confinement effect occurs, which is identified as the physical origin for the Seebeck coefficient enhancement.

  14. Emplacement and fluctuations of the Antarctic Ice Sheet across the Eocene-Oligocene transition

    NASA Astrophysics Data System (ADS)

    Stocchi, P.; Galeotti, S.; Rugenstein, M.; Deconto, R. M.; Ladant, J. B.; Vermeersen, B. L. A.; Brinkhuis, H.

    2014-12-01

    A ~1.5‰ positive increase in deep-sea oxygen isotopic values marks the establishment of a continental-scale Antarctic Ice Sheet (AIS) at the Oi-1 event (~33.6 Ma) across the Eocene-Oligocene transition (EOT). Quantifying the magnitude and timing of EOT AIS volume variations by means of δ18O records is hampered by the fact that the latter reflect a coupled signal of temperature and ice-sheet volume. Furthermore, bathymetric variations based on marine geologic sections are affected by large uncertainties and, most importantly, reflect the local response of relative sea level (rsl) to ice volume fluctuations rather than the global eustatic signal. AIS proximal and Northern Hemisphere (NH) shallow marine settings show, in fact, an opposite trend of rsl change across the EOT. In particular, low-latitude NH sequences record a 70 ± 20m rsl fall, suggesting that AIS volume could have expanded to either near modern dimensions or as much as 25% larger than present day. Conversely, sedimentary facies from shelf areas in the proximity of the AIS margins show that local rsl rose up to ~150 m during the EOT glaciation. In this work we reconcile near- and far-field rsl sites by solving the gravitationally self-consistent Sea Level Equation that accounts for Glacial Isostatic Adjustment (GIA). Our GIA simulations show that the deviations from eustasy significantly increase towards Antarctica. Accordingly, the cyclo-chronological record of sedimentary cycles retrieved from Cape Roberts Project Drillcore CRP-3 indicates a deepening across the EOT. CRP-3 record also shows that full glacial conditions only occurred at the Oi-1a event (32.0 Ma). The strong gradients of rsl change around AIS result in heterogeneous bathymetric variations that might affect the circumpolar ocean flow. In fact, our novel GIA-forced ocean current model predicts along-meridian shifts of current frontal patterns of the order of several degrees. Also, differences in current velocity are locally more than

  15. Ice polyamorphism in the minimal Mercedes-Benz model of water

    NASA Astrophysics Data System (ADS)

    Cartwright, Julyan H. E.; Piro, Oreste; Sánchez, Pedro A.; Sintes, Tomás

    2012-12-01

    We investigate ice polyamorphism in the context of the two-dimensional Mercedes-Benz model of water. We find a first-order phase transition between a crystalline phase and a high-density amorphous phase. Furthermore, we find a reversible transformation between two amorphous structures of high and low density; however, we find this to be a continuous and not an abrupt transition, as the low-density amorphous phase does not show structural stability. We discuss the origin of this behavior and its implications with regard to the minimal generic modeling of polyamorphism.

  16. Ice polyamorphism in the minimal Mercedes-Benz model of water.

    PubMed

    Cartwright, Julyan H E; Piro, Oreste; Sánchez, Pedro A; Sintes, Tomás

    2012-12-28

    We investigate ice polyamorphism in the context of the two-dimensional Mercedes-Benz model of water. We find a first-order phase transition between a crystalline phase and a high-density amorphous phase. Furthermore, we find a reversible transformation between two amorphous structures of high and low density; however, we find this to be a continuous and not an abrupt transition, as the low-density amorphous phase does not show structural stability. We discuss the origin of this behavior and its implications with regard to the minimal generic modeling of polyamorphism. PMID:23277941

  17. Antarctic ice growth before and after the Eocene-Oligocene transition: New estimates from clumped isotope paleothermometry

    NASA Astrophysics Data System (ADS)

    Petersen, S. V.; Schrag, D. P.

    2015-10-01

    Across the Eocene-Oligocene transition, the oxygen isotopic composition (δ18O) of benthic and planktonic foraminifera increased by over 1‰. This shift is thought to represent a combination of global cooling and the growth of a large ice sheet on the Antarctic continent. To determine the contribution of each of these factors to the total change in δ18O, we measured the clumped isotopic composition of planktonic foraminifera tests from Ocean Drilling Program Site 689 in the Southern Ocean. Near-surface temperatures were ~12°C in the intervals 0-1.5 Myr before and 1-2 Myr after the major (Oi-1) transition, in agreement with estimates made using other proxies at nearby sites. Temperatures cooled by 0.4 ± 1.1°C between these intervals, indicating that the long-term change in δ18O seen in planktonic foraminifera at this site is predominantly due to changes in ice volume. A larger instantaneous cooling may have occurred during Oi-1 but is not captured in this study due to sampling resolution. The corresponding change in the isotopic composition of seawater (δ18Osw) is 0.75 ± 0.23‰, which is within the range of previous estimates, and represents global ice growth equivalent to roughly ~110-120% of the volume of the modern Antarctic ice sheet or ~80-90 m of eustatic sea level change.

  18. Protist diversity in a permanently ice-covered Antarctic lake during the polar night transition.

    PubMed

    Bielewicz, Scott; Bell, Elanor; Kong, Weidong; Friedberg, Iddo; Priscu, John C; Morgan-Kiss, Rachael M

    2011-09-01

    The McMurdo Dry Valleys of Antarctica harbor numerous permanently ice-covered lakes, which provide a year-round oasis for microbial life. Microbial eukaryotes in these lakes occupy a variety of trophic levels within the simple aquatic food web ranging from primary producers to tertiary predators. Here, we report the first molecular study to describe the vertical distribution of the eukaryotic community residing in the photic zone of the east lobe (ELB) and west lobe (WLB) of the chemically stratified Lake Bonney. The 18S ribosomal RNA (rRNA) libraries revealed vertically stratified populations dominated by photosynthetic protists, with a cryptophyte dominating shallow populations (ELB-6 m; WLB-10 m), a haptophyte occupying mid-depths (both lobes 13 m) and chlorophytes residing in the deepest layers (ELB-18 and 20 m; WLB-15 and 20 m) of the photic zone. A previously undetected stramenopile occurred throughout the water column of both lobes. Temporal variation in the eukaryotic populations was examined during the transition from Antarctic summer (24-h sunlight) to polar night (complete dark). Protist diversity was similar between the two lobes of Lake Bonney due to exchange between the photic zones of the two basins via a narrow bedrock sill. However, vertical and temporal variation in protist distribution occurred, indicating the influence of the unique water chemistry on the biology of the two dry valley watersheds. PMID:21390078

  19. Is simulated amorphous'' silica really amorphous

    SciTech Connect

    Binggeli, N. , PHB Ecublens, 1015 Lausanne ); Chelikowsky, J.R. )

    1994-07-10

    We have carried out extensive molecular dynamics simulations for the pressure induced amorphization of quartz by means of a classical force-field model. In agreement with earlier simulations, we find that a phase transition occurs within the experimental pressure range of the amorphization. However, in contrast to the interpretation of previous simulations, we demonstrate that the new phase is [ital not] amorphous, since the correlation functions for the equilibrated structure can be shown to be consistent with those of a crystalline phase. In addition, two transformations to ordered structures are found to occur sequentially during the simulations. The first transformation is likely to be related to the recently discovered transition of quartz to an intermediate crystalline phase before its amorphization. The second transformation, instead, yields a compact, octahedrally coordinated Si sublattice. The latter may be an artifact of the pair-potential simulation. [copyright] 1994 American Institute of Physics

  20. Phonon renormalization and Raman spectral evolution through amorphous to crystalline transitions in Sb{sub 2}Te{sub 3} thin films

    SciTech Connect

    Secor, Jeff; Zhao, Lukas; Krusin-Elbaum, Lia; Harris, Matt A.; Deng, Haiming; Raoux, Simone

    2014-06-02

    A symmetry specific phonon mode renormalization is observed across an amorphous to crystalline phase transformation in thin films of the topological material Sb{sub 2}Te{sub 3} using Raman spectroscopy. We present evidence for local crystalline symmetry in the amorphous state, eventhough, the q = 0 Raman selection rule is broken due to strong structural disorder. At crystallization, the in-plane polarized (E{sub g}{sup 2}) mode abruptly sharpens while the out-of-plane polarized (A{sub 1g}) modes are only weakly effected. This effect unique to the E{sub g} symmetry is exceptional considering that polarized spectra and comparison of the single phonon density of states between the amorphous and crystalline phases suggest that short range order of the amorphous phase is, on the average, similar to that of the crystalline material while electrical transport measurements reveal a sharp insulator-to-metal transition. Our findings point to the important role of anisotropic disorder affecting potential applications of topological and phase-change based electronics.

  1. Ultrafast crystalline-to-amorphous phase transition in Ge{sub 2}Sb{sub 2}Te{sub 5} chalcogenide alloy thin film using single-shot imaging spectroscopy

    SciTech Connect

    Takeda, Jun Oba, Wataru; Minami, Yasuo; Katayama, Ikufumi; Saiki, Toshiharu

    2014-06-30

    We have observed an irreversible ultrafast crystalline-to-amorphous phase transition in Ge{sub 2}Sb{sub 2}Te{sub 5} chalcogenide alloy thin film using broadband single-shot imaging spectroscopy. The absorbance change that accompanied the ultrafast amorphization was measured via single-shot detection even for laser fluences above the critical value, where a permanent amorphized mark was formed. The observed rise time to reach the amorphization was found to be ∼130–200 fs, which was in good agreement with the half period of the A{sub 1} phonon frequency in the octahedral GeTe{sub 6} structure. This result strongly suggests that the ultrafast amorphization can be attributed to the rearrangement of Ge atoms from an octahedral structure to a tetrahedral structure. Finally, based on the dependence of the absorbance change on the laser fluence, the stability of the photoinduced amorphous phase is discussed.

  2. Ice Age Reboot: Thermohaline Circulation Crisis during the Mid-Pleistocene Transition

    NASA Astrophysics Data System (ADS)

    Pena, L.; Goldstein, S. L.

    2014-12-01

    The mid-Pleistocene transition (MPT) marked a fundamental change in glacial-interglacial periodicity, when it increased from ~41- to 100-kyr cycles and developed higher amplitude climate variability. Because it took place without significant changes in the Milankovitch forcing, this fundamental change must reflect either non-linear responses of the climate system to these external forcings, or internal changes in the ocean-atmosphere-cryosphere system that led to longer periodicities and more intense glacial periods. We document using Nd isotopes a major disruption of the ocean thermohaline circulation (THC) system during the MPT between MIS 25-21 at ~950-860 ka, which effectively marks the first 100-kyr cycle, including an exceptional weakening through critical interglacial MIS 23 at ~900 ka. The data are from ODP Sites 1088 (41°8.163'S, 13°33.77'E, 2082m) and 1090 (42°54.82'S, 8°53.98E', 3702m) in the SE Atlantic Subantarctic Zone, near the upper and lower boundaries of NADW and Circumpolar Deep Water (CDW). Given evidence for nearly stable NADW and North Pacific Water (NPW) ɛNd-values over the last 2 Ma, we interpret the ɛNd variations to reflect changes in the NADW:NPW mixing fractions. During the studied pre-MPT 41-kyr world (MIS 31-25, 1,100-950 ka), at both sites the differences in glacial and interglacial ɛNd-values are small, indicating strong glacial as well as interglacial export of NADW. A major weakening of NADW export occurred during MIS 24-22, including MIS 23, which is unique as the only known interglacial in which the THC did not strengthen, and thus can be considered as a 'trans-glacial' period. The recovery into the post-MPT 100-kyr world is characterized by continued weak glacial THC. We conclude that the MPT ocean circulation crisis 'rebooted' the pacing and intensity of ice ages and facilitated the coeval drawdown of atmospheric CO2 and high latitude ice sheet growth, generating the conditions that stabilized 100-kyr cycles.

  3. Effect of Si additions on thermal stability and the phase transition sequence of sputtered amorphous alumina thin films

    SciTech Connect

    Bolvardi, H.; Baben, M. to; Nahif, F.; Music, D. Schnabel, V.; Shaha, K. P.; Mráz, S.; Schneider, J. M.; Bednarcik, J.; Michalikova, J.

    2015-01-14

    Si-alloyed amorphous alumina coatings having a silicon concentration of 0 to 2.7 at. % were deposited by combinatorial reactive pulsed DC magnetron sputtering of Al and Al-Si (90-10 at. %) split segments in Ar/O{sub 2} atmosphere. The effect of Si alloying on thermal stability of the as-deposited amorphous alumina thin films and the phase formation sequence was evaluated by using differential scanning calorimetry and X-ray diffraction. The thermal stability window of the amorphous phase containing 2.7 at. % of Si was increased by more than 100 °C compared to that of the unalloyed phase. A similar retarding effect of Si alloying was also observed for the α-Al{sub 2}O{sub 3} formation temperature, which increased by more than 120 °C. While for the latter retardation, the evidence for the presence of SiO{sub 2} at the grain boundaries was presented previously, this obviously cannot explain the stability enhancement reported here for the amorphous phase. Based on density functional theory molecular dynamics simulations and synchrotron X-ray diffraction experiments for amorphous Al{sub 2}O{sub 3} with and without Si incorporation, we suggest that the experimentally identified enhanced thermal stability of amorphous alumina with addition of Si is due to the formation of shorter and stronger Si–O bonds as compared to Al–O bonds.

  4. An amorphous-to-crystalline phase transition within thin silicon films grown by ultra-high-vacuum evaporation and its impact on the optical response

    NASA Astrophysics Data System (ADS)

    Orapunt, Farida; Tay, Li-Lin; Lockwood, David J.; Baribeau, Jean-Marc; Noël, Mario; Zwinkels, Joanne C.; O'Leary, Stephen K.

    2016-02-01

    A number of thin silicon films are deposited on crystalline silicon, native oxidized crystalline silicon, and optical quality fused quartz substrates through the use of ultra-high-vacuum evaporation at growth temperatures ranging from 98 to 572 °C. An analysis of their grazing incidence X-ray diffraction and Raman spectra indicates that a phase transition, from amorphous-to-crystalline, occurs as the growth temperature is increased. Through a peak decomposition process, applied to the Raman spectroscopy results, the crystalline volume fractions associated with these samples are plotted as a function of the growth temperature for the different substrates considered. It is noted that the samples grown on the crystalline silicon substrates have the lowest crystallanity onset temperature, whereas those grown on the optical quality fused quartz substrates have the highest crystallanity onset temperature; the samples grown on the native oxidized crystalline silicon substrates have a crystallanity onset temperature between these two limits. These resultant dependencies on the growth temperature provide a quantitative means of characterizing the amorphous-to-crystalline phase transition within these thin silicon films. It is noted that the thin silicon film grown on an optical quality fused quartz substrate at 572 °C, possessing an 83% crystalline volume fraction, exhibits an optical absorption spectrum which is quite distinct from that associated with the other thin silicon films. We suggest that this is due to the onset of sufficient long-range order in the film for wave-vector conservation to apply, at least partially. Finally, we use a semi-classical optical absorption analysis to study how this phase transition, from amorphous-to-crystalline, impacts the spectral dependence of the optical absorption coefficient.

  5. Amorphous layer coating induced brittle to ductile transition in single crystalline SiC nanowires: an atomistic simulation

    SciTech Connect

    Wang, Zhiguo; Zu, Xiaotao T.; Li, Zhijie; Gao, Fei

    2008-08-07

    Molecular dynamics simulations with Tersoff potentials were used to study the response of SiC nanowires with and without amorphous coating to a tensile strain along the axial direction. The uncoated nanowires show brittle properties and fail through bond breaking. Although the amorphous coating leads to the decrease of Young’s modulus of nanowires, yet it also leads the appearance of plastic deformation under axial strain. These results provide an effective way to modify the brittle properties of some other semiconductor nanowires.

  6. Data on energy-band-gap characteristics of composite nanoparticles obtained by modification of the amorphous potassium polytitanate in aqueous solutions of transition metal salts.

    PubMed

    Zimnyakov, D A; Sevrugin, A V; Yuvchenko, S A; Fedorov, F S; Tretyachenko, E V; Vikulova, M A; Kovaleva, D S; Krugova, E Y; Gorokhovsky, A V

    2016-06-01

    Here we present the data on the energy-band-gap characteristics of composite nanoparticles produced by modification of the amorphous potassium polytitanate in aqueous solutions of different transition metal salts. Band gap characteristics are investigated using diffuse reflection spectra of the obtained powders. Calculated logarithmic derivative quantity of the Kubelka-Munk function reveals a presence of local maxima in the regions 0.5-1.5 eV and 1.6-3.0 eV which correspond to band gap values of the investigated materials. The values might be related to the constituents of the composite nanoparticles and intermediate products of their chemical interaction. PMID:27158654

  7. THz time-domain spectroscopy of mixed CO2-CH3OH interstellar ice analogs.

    PubMed

    McGuire, Brett A; Ioppolo, Sergio; Allodi, Marco A; Blake, Geoffrey A

    2016-07-27

    The icy mantles of interstellar dust grains are the birthplaces of the primordial prebiotic molecular inventory that may eventually seed nascent solar systems and the planets and planetesimals that form therein. Here, we present a study of two of the most abundant species in these ices after water: carbon dioxide (CO2) and methanol (CH3OH), using TeraHertz (THz) time-domain spectroscopy and mid-infrared spectroscopy. We study pure and mixed-ices of these species, and demonstrate the power of the THz region of the spectrum to elucidate the long-range structure (i.e. crystalline versus amorphous) of the ice, the degree of segregation of these species within the ice, and the thermal history of the species within the ice. Finally, we comment on the utility of the THz transitions arising from these ices for use in astronomical observations of interstellar ices. PMID:27306081

  8. Quantum simulation of thermally-driven phase transition and oxygen K-edge x-ray absorption of high-pressure ice

    PubMed Central

    Kang, Dongdong; Dai, Jiayu; Sun, Huayang; Hou, Yong; Yuan, Jianmin

    2013-01-01

    The structure and phase transition of high-pressure ice are of long-standing interest and challenge, and there is still a huge gap between theoretical and experimental understanding. The quantum nature of protons such as delocalization, quantum tunneling and zero-point motion is crucial to the comprehension of the properties of high-pressure ice. Here we investigated the temperature-induced phase transition and oxygen K-edge x-ray absorption spectra of ice VII, VIII and X using ab initio path-integral molecular dynamics simulations. The tremendous difference between experiments and the previous theoretical predictions is closed for the phase diagram of ice below 300 K at pressures up to 110 GPa. Proton tunneling assists the proton-ordered ice VIII to transform into proton-disordered ice VII where only thermal activated proton-transfer cannot occur. The oxygen K edge with its shift is sensitive to the order-disorder transition, and therefore can be applied to diagnose the dynamics of ice structures. PMID:24253589

  9. Antarctic Ice Sheet variability across the Eocene-Oligocene boundary climate transition

    NASA Astrophysics Data System (ADS)

    Galeotti, Simone; DeConto, Robert; Naish, Timothy; Stocchi, Paolo; Florindo, Fabio; Pagani, Mark; Barrett, Peter; Bohaty, Steven M.; Lanci, Luca; Pollard, David; Sandroni, Sonia; Talarico, Franco M.; Zachos, James C.

    2016-04-01

    About 34 million years ago, Earth’s climate cooled and an ice sheet formed on Antarctica as atmospheric carbon dioxide (CO2) fell below ~750 parts per million (ppm). Sedimentary cycles from a drillcore in the western Ross Sea provide direct evidence of orbitally controlled glacial cycles between 34 million and 31 million years ago. Initially, under atmospheric CO2 levels of ≥600 ppm, a smaller Antarctic Ice Sheet (AIS), restricted to the terrestrial continent, was highly responsive to local insolation forcing. A more stable, continental-scale ice sheet calving at the coastline did not form until ~32.8 million years ago, coincident with the earliest time that atmospheric CO2 levels fell below ~600 ppm. Our results provide insight into the potential of the AIS for threshold behavior and have implications for its sensitivity to atmospheric CO2 concentrations above present-day levels.

  10. Antarctic Ice Sheet variability across the Eocene-Oligocene boundary climate transition.

    PubMed

    Galeotti, Simone; DeConto, Robert; Naish, Timothy; Stocchi, Paolo; Florindo, Fabio; Pagani, Mark; Barrett, Peter; Bohaty, Steven M; Lanci, Luca; Pollard, David; Sandroni, Sonia; Talarico, Franco M; Zachos, James C

    2016-04-01

    About 34 million years ago, Earth's climate cooled and an ice sheet formed on Antarctica as atmospheric carbon dioxide (CO2) fell below ~750 parts per million (ppm). Sedimentary cycles from a drill core in the western Ross Sea provide direct evidence of orbitally controlled glacial cycles between 34 million and 31 million years ago. Initially, under atmospheric CO2 levels of ≥600 ppm, a smaller Antarctic Ice Sheet (AIS), restricted to the terrestrial continent, was highly responsive to local insolation forcing. A more stable, continental-scale ice sheet calving at the coastline did not form until ~32.8 million years ago, coincident with the earliest time that atmospheric CO2 levels fell below ~600 ppm. Our results provide insight into the potential of the AIS for threshold behavior and have implications for its sensitivity to atmospheric CO2 concentrations above present-day levels. PMID:27034370

  11. Superconductor-Insulator Transition in Amorphous NbxSi1-x Thin Films. Comparison between Thickness, Density of State and Microscopic Disorder.

    NASA Astrophysics Data System (ADS)

    Crauste, O.; Couedo, F.; Bergé, L.; Marrache, C.; Dumoulin, L.

    2012-12-01

    We report on the study of the Disordered-induced Superconductor-Insulator Transition (D-SIT) in NbxSi1-x thin films. These films, synthesized by electron-beam co-deposition, are continuous, amorphous, homogeneously disordered and structurally stable for a wide range of compositions, thicknesses and annealing temperature and thus particularly well suited for the study of D-SIT. We present an analysis of the D-SIT induced by three different parameters: the thickness, the Nb composition that changes the electronic density of states and the annealing temperature that changes the microscopic disorder. The annealing changes quantum interference patterns that decreases the local conductance. Our results show that the effect of the thickness on the destruction of superconductivity is very distinct from those of the composition or the annealing. We point out this material is particularly interesting to disentangle the effect of the parameters driving this quantum phase transition.

  12. Exploring controls on ice stream destabilisation during the LGM/Holocene transition in West Greenland

    NASA Astrophysics Data System (ADS)

    Roberts, D. H.; Lane, T. P.; Rea, B. R.; Ó Cofaigh, C.; Jamieson, S.; Vieli, A.

    2015-12-01

    Deglacial chronologies from West Greenland enable investigation of the role of climate and topography in controlling ice stream dynamics. The Uummannaq ice stream system (UIS) in particular has a comprehensive deglacial chronology which, when coupled with geometry, provides a framework for exploring controls on ice stream dynamics under changing climatic conditions. Here, we use a 2D numerical model to simulate grounding line-retreat behaviour and surface thinning in order explore the principal drivers of linear and non-linear ice stream behaviour during the end of the last glacial cycle. Deglaciation of the UIS began on the outer shelf at ~14.8 ka with ice retreat eastward to Ubekendt Ejland by ~12.4 ka. This initial retreat coincided with increasing air temperature, increasing solar radiation and sea-level rise. Awide, mid-shelf, trough also facilitated rapid retreat. The UIS then withdrew eastward ~ 100 km by ~11.4 ka - 10.8 ka as the northern and southern feeder zones unzipped. This coincided with increasing insolation and peak sea-level, but bathymetric over-deepening and fjord widening were also influential. Staircases of lateral moraines throughout the region point to step-wise thinning as ice retreated between 14.8 - 11.0 ka. By 8.7 ka the southern arm of the UIS had reached Store Gletscher and thereafter it retreated beyond the present day grounding line. This coincided with increased air/ocean temperatures and peak summer insolation. In contrast, the northern arm of the UIS stabilised until ~6.5 ka and became unresponsive to both atmospheric and ocean forcing due to topographic pinning. New research has adopted a 2D model approach to establish and quantify the relative importance of various mechanisms in governing UIS dynamics. These model results indicate that the non-linear retreat of the UIS is strongly influenced by vertical and lateral constrictions in the marine trough system which regulates grounding line stability. In turn, grounding line

  13. Sedimentary provenance insights to East Antarctic ice sheet oscillations and growth during the mid-Miocene Climate Transition

    NASA Astrophysics Data System (ADS)

    Pierce, E. L.; van de Flierdt, T.; Williams, T.; Hemming, S. R.; Cook, C.; Passchier, S.

    2012-12-01

    A major step in the evolution of the East Antarctic ice sheet (EAIS) occurred ~ 14 Ma during the Mid-Miocene Climate Transition (MMCT), a period with a global climatic shift that had a profound effect on many components of the Earth system, including terrestrial biota, ocean circulation, both ocean and terrestrial temperatures, sea-level, and ice volume. Of particular interest during this transition is the variability in the extent of the EAIS at its marine-grounded margins. Despite inferences on the total amount of ice growth on Antarctica as a whole, little is known of the temporal and spatial evolution of the East Antarctic ice expansion at this time. Here we apply isotopic provenance studies in order to determine the source of glacially derived sediments deposited ca. 14.7 to 12.6 Ma off the coast of East Antarctica at IODP Site U1356. A total of 672 hornblendes grains from 40 samples were analyzed for their 40Ar/39Ar ages, showing a dominant and unvarying age population of 1400 -1550 Ma for all of the samples. Neodymium (Nd) isotope measurements on the terrigenous <63 μm sediment fraction in contrast show a large range of 8 epsilon units (-8.4 to -16.4). We interpret our results to indicate a greatly retreated EAIS in the Wilkes subglacial basin prior to and during the MMCT. Observed Ar ages are best explained by an ice sheet that sat along the extension of the Mertz Shear Zone, at the western edge of the Wilkes Basin. Three distinct excursions to more radiogenic Nd isotope values require significant input from a more radiogenic source, such as the Ferrar Group, which consists of the Ferrar Doloerite, Kirkpatrick Basalt and Dufek Gabbro, and has epsilon Nd values of approximately -5. The Ferrar Group outcrops extensively along the spine of the Transantarctic Mountains, and geophysical surveys (Ferraccioli et al., 2009, Tectonophysics) indicate that Ferrar dolerite intrudes Beacon Sandstone in areas within the Wilkes subglacial basin. Given the decoupling in

  14. Impact of suborbital climate changes in the North Atlantic on ice sheet dynamics at the Mid-Pleistocene Transition

    NASA Astrophysics Data System (ADS)

    HernáNdez-Almeida, I.; Sierro, F. J.; Cacho, I.; Flores, J. A.

    2012-09-01

    Early and Mid-Pleistocene climate, ocean hydrography and ice sheet dynamics have been reconstructed using a high-resolution data set (planktonic and benthicδ18O time series, faunal-based sea surface temperature (SST) reconstructions and ice-rafted debris (IRD)) record from a high-deposition-rate sedimentary succession recovered at the Gardar Drift formation in the subpolar North Atlantic (Integrated Ocean Drilling Program Leg 306, Site U1314). Our sedimentary record spans from late in Marine Isotope Stage (MIS) 31 to MIS 19 (1069-779 ka). Different trends of the benthic and planktonic oxygen isotopes, SST and IRD records before and after MIS 25 (˜940 ka) evidence the large increase in Northern Hemisphere ice-volume, linked to the cyclicity change from the 41-kyr to the 100-kyr that occurred during the Mid-Pleistocene Transition (MPT). Beside longer glacial-interglacial (G-IG) variability, millennial-scale fluctuations were a pervasive feature across our study. Negative excursions in the benthicδ18O time series observed at the times of IRD events may be related to glacio-eustatic changes due to ice sheets retreats and/or to changes in deep hydrography. Time series analysis on surface water proxies (IRD, SST and planktonicδ18O) of the interval between MIS 31 to MIS 26 shows that the timing of these millennial-scale climate changes are related to half-precessional (10 kyr) components of the insolation forcing, which are interpreted as cross-equatorial heat transport toward high latitudes during both equinox insolation maxima at the equator.

  15. From amorphous to microcrystalline: Phase transition in rapid synthesis of hydrogenated silicon thin film in low frequency inductively coupled plasmas

    SciTech Connect

    Xiao, S. Q.; Xu, S.; Wei, D. Y.; Huang, S. Y.; Zhou, H. P.; Xu, Y.

    2010-12-01

    Hydrogenated silicon (Si:H) thin films were fabricated on glass substrates by low frequency inductively coupled plasma-assisted chemical vapor deposition using a silane precursor with low hydrogen dilution at room temperature. The crystallinity and microstructure properties of the Si:H thin films deposited at different inductive radio-frequency (rf) power density were systematically studied by Raman spectroscopy, x-ray diffraction, and scanning electron microscopy. We found that at a low rf power density of 16.7 to 20.8 mW/cm{sup 3}, the structure of silicon thin films evolves from a completely amorphous phase to an intermediate phase containing both amorphous and microcrystalline silicon. As the power density is increased to a moderate value of 25 mW/cm{sup 3}, a highly crystallized (111)-preferred hydrogenated microcrystalline silicon ({mu}c-Si:H) film featuring a vertically aligned cone-shaped structure, is emerging. Both the crystallinity and deposition rate exhibit a monotonic increase with the increase in the rf power density, reaching a maximum value of 85% and 1.07 nm/s, respectively, at a power density of 41.7 mW/cm{sup 3}. Scanning electron microscopy reveals that continuous and dense {mu}c-Si:H films with grain size of tens to hundreds nanometers can be achieved deterministically without the formation of amorphous incubation layer, and this is of great importance for synthesis of multilayer structures in p-i-n solar cells. The formation mechanism of the {mu}c-Si:H films and the elimination of the amorphous incubation layer are explained in terms of the high electron density and the plasma-surface interactions.

  16. Subsurface Thermal Erosion Of Ice-Wedge Polygon Terrains: Implications For Arctic Geosystem In Transition

    NASA Astrophysics Data System (ADS)

    Fortier, D.; Godin, E.; Lévesque, E.; Veillette, A.

    2014-12-01

    Subsurface thermal erosion is triggered by convective heat transfers between flowing water and permafrost. For inland ice-wedge polygon terrains, heat advection due to infiltration of run-off in the massive ice wedges and the ice-rich upper portion of permafrost creates sink holes and networks of interconnected tunnels in the permafrost. Mass movements such as collapse of tunnel's roof, retrogressive thaw-slumping along exposed permafrost and active layer detachment slides lead to the development of extensive gully networks in the landscape. These gullies drastically change the hydrology of ice-wedge polygon terrains and the fluxes of heat, water, sediment and carbon within the permafrost geosystem. Exportation of sediments by fluvial processes within gullies are positive mechanical feed-back effects that keep gully channels active over decades. Along gully margins, drainage of disturbed polygons and ponds, slope drainage, soil consolidation, plant colonization of disturbed gully slopes and wet to mesic plant succession of drained polygons change the thermal properties of the active layer and create negative feedback effects that stabilize active erosion processes and promote permafrost recovery in gully slopes and adjacent disturbed polygons. On Bylot Island (Nunavut), over 40 gullies were mapped and monitored to characterize gully geomorphology, thermal and mechanical processes of gully erosion, rates of gully erosion over time within different sedimentary deposits, total volume of eroded permafrost at the landscape scale and gully hydrology. We conducted field and laboratory experiments to quantify heat convection processes and speed of ice wedge ablation in order to derive empirical equations to develop a numerical, fully-coupled, heat and mass (water) transfer model of ice-wedge thermal erosion. We used data collected over 10 years of geomorphological gully monitoring, regional climate scenarios, our physics-based numerical thermal erosion model and our field

  17. An experimental study of the ice column habit transitions. [crystal growth in atmosphere

    NASA Technical Reports Server (NTRS)

    Cho, N.; Hallett, J.

    1982-01-01

    The influence of supersaturation on column growth of ice crystals forming from atmospheric water vapor was investigated. A high density of crystals was generated on a glass fiber cooled by liquid N2 in a thermal diffusion chamber. Attention was focused on a neighbor-free hollow prism during a stepwise decrease in supersaturation while the crystal temperature was maintained constant. Another experiment involved epitaxial growth of ice crystals on CuS, where nonthickening crystals could only be grown below -7 C. A critical supersaturation was found to be necessary for growth of the basal plane. Beyound the critical value, surface kinetics do not control the growth rate, which is then dominated by the penetration of water molecules through the diffusion field surrounding the crystal.

  18. Permafrost landscapes in transition - towards modeling interactions, thresholds and feedbacks related to ice-rich ground

    NASA Astrophysics Data System (ADS)

    Westermann, Sebastian; Langer, Moritz; Lee, Hanna; Berntsen, Terje; Boike, Julia; Krinner, Gerhard; Aalstad, Kristoffer; Schanke Aas, Kjetil; Peter, Maria; Heikenfeld, Max; Etzelmüller, Bernd

    2016-04-01

    Thawing of permafrost is governed by a complex interplay of different processes, of which only conductive heat transfer is taken into account in most model studies. However, heat conduction alone can not account for the dynamical evolution of many permafrost landscapes, e.g. in areas rich in ground ice shaped by thermokarst ponds and lakes. Novel process parameterizations are required to include such phenomena in future projections of permafrost thaw and hereby triggered climatic feedbacks. Recently, we have demonstrated a physically-based parameterization for thaw process in ice-rich ground in the permafrost model CryoGrid 3, which can reproduce the formation of thermokarst ponds and subsidence of the ground following thawing of ice-rich subsurface layers. Long-term simulations for different subsurface stratigraphies in the Lena River Delta, Siberia, demonstrate that the hydrological regime can both accelerate and delay permafrost thawing. If meltwater from thawed ice-rich layers can drain, the ground subsides while at the same time the formation of a talik is delayed. If the meltwater pools at the surface, a pond is formed which enhances heat transfer in the ground and leads to the formation of a talik. The PERMANOR project funded by the Norwegian Research Council until 2019 will extend this work by integrating such small-scale processes in larger-scale Earth System Models (ESMs). For this purpose, the project will explore and develop statistical approaches, in particular tiling, to represent permafrost landscape dynamics on subgrid scale. Ultimately, PERMANOR will conceptualize process understanding from in-situ studies to develop new model algorithms and pursue their implementation in a coupled ESM framework.

  19. A direct evidence of vibrationally delocalized response at ice surface

    SciTech Connect

    Ishiyama, Tatsuya; Morita, Akihiro

    2014-11-14

    Surface-specific vibrational spectroscopic responses at isotope diluted ice and amorphous ice are investigated by molecular dynamics (MD) simulations combined with quantum mechanics/molecular mechanics calculations. The intense response specific to the ordinary crystal ice surface is predicted to be significantly suppressed in the isotopically diluted and amorphous ices, demonstrating the vibrational delocalization at the ordinary ice surface. The collective vibration at the ice surface is also analyzed with varying temperature by the MD simulation.

  20. On the origin of Gaussian network theory in the thermo/chemo-responsive shape memory effect of amorphous polymers undergoing photo-elastic transition

    NASA Astrophysics Data System (ADS)

    Lu, Haibao; Huang, Wei Min; Leng, Jinsong

    2016-06-01

    Amorphous polymers are normally isotropic in their physical properties, however, upon stress their structural randomness is disturbed and they become anisotropic. There is a close connection between the optical anisotropy and the elastic (or mechanical) anisotropy, since both are related to the type of symmetry exhibited by the molecular structure. On the origin of Gaussian network theory, a phenomenological constitutive framework was proposed to study the photo-elastic transition and working mechanism of the thermo-/chemo-responsive shape-memory effect (SME) in amorphous shape memory polymers (SMPs). Optically refractive index was initially employed to couple the stress, strain and the anisotropy of the random link in macromolecule chain. Based on the Arrhenius law, a constitutive framework was then applied for the temperature dependence of optical (or elastic or mechanical) anisotropy according to the fictive temperature parameter. Finally, the phenomenological photo-elastic model was proposed to quantitatively identify the influential factors behind the thermo-/chemo-responsive SME in SMPs, of which the shape recovery behavior is predicted and verified by the available experimental data reported in the literature.

  1. Data on energy-band-gap characteristics of composite nanoparticles obtained by modification of the amorphous potassium polytitanate in aqueous solutions of transition metal salts

    PubMed Central

    Zimnyakov, D.A.; Sevrugin, A.V.; Yuvchenko, S.A.; Fedorov, F.S.; Tretyachenko, E.V.; Vikulova, M.A.; Kovaleva, D.S.; Krugova, E.Y.; Gorokhovsky, A.V.

    2016-01-01

    Here we present the data on the energy-band-gap characteristics of composite nanoparticles produced by modification of the amorphous potassium polytitanate in aqueous solutions of different transition metal salts. Band gap characteristics are investigated using diffuse reflection spectra of the obtained powders. Calculated logarithmic derivative quantity of the Kubelka–Munk function reveals a presence of local maxima in the regions 0.5–1.5 eV and 1.6–3.0 eV which correspond to band gap values of the investigated materials. The values might be related to the constituents of the composite nanoparticles and intermediate products of their chemical interaction. PMID:27158654

  2. Magnetic monopole condensation transition out of quantum spin ice: application to Pr2 Ir2 O7 and Yb2 Ti2 O7

    NASA Astrophysics Data System (ADS)

    Chen, Gang

    We study the proximate magnetic orders and the related quantum phase transition out of quantum spin ice (QSI). We apply the electromagnetic duality of the compact quantum electrodynamics to analyze the condensation of the magnetic monopoles for QSI. The monopole condensation transition represents a unconventional quantum criticality with unusual scaling laws. The magnetic monopole condensation leads to the magnetic states that belong to the ``2-in 2-out'' spin ice manifold and generically have an enlarged magnetic unit cell. We demonstrate that the antiferromagnetic state with the ordering wavevector Q = 2p(001) is proximate to QSI while the ferromagnetic state with the ordering wavevector Q = (000) is not proximate to QSI. This implies that if there exists a direct transition from QSI to the ferromagnetic state, the transition must be strongly first order. We apply the theory to the puzzling experiments on two pyrochlore systems Pr2Ir2O7 and Yb2Ti2O7. chggst@gmail.com.

  3. Formation mechanisms of oxygen atoms in the O({sup 1}D{sub 2}) state from the 157 nm photoirradiation of amorphous water ice at 90 K

    SciTech Connect

    Hama, Tetsuya; Yabushita, Akihiro; Yokoyama, Masaaki; Kawasaki, Masahiro; Watanabe, Naoki

    2009-09-21

    Vacuum ultraviolet photolysis of water ice in the first absorption band was studied at 157 nm. Translational and internal energy distributions of the desorbed species, O({sup 1}D) and OH(v=0,1), were directly measured with resonance-enhanced multiphoton ionization method. Two different mechanisms are discussed for desorption of electronically excited O({sup 1}D) atoms from the ice surface. One is unimolecular dissociation of H{sub 2}O to H{sub 2}+O({sup 1}D) as a primary photoprocess. The other is the surface recombination reaction of hot OH radicals that are produced from photodissociation of hydrogen peroxide as a secondary photoprocess. H{sub 2}O{sub 2} is one of the major photoproducts in the vacuum ultraviolet photolysis of water ice.

  4. Water’s second glass transition

    PubMed Central

    Amann-Winkel, Katrin; Gainaru, Catalin; Handle, Philip H.; Seidl, Markus; Nelson, Helge; Böhmer, Roland

    2013-01-01

    The glassy states of water are of common interest as the majority of H2O in space is in the glassy state and especially because a proper description of this phenomenon is considered to be the key to our understanding why liquid water shows exceptional properties, different from all other liquids. The occurrence of water’s calorimetric glass transition of low-density amorphous ice at 136 K has been discussed controversially for many years because its calorimetric signature is very feeble. Here, we report that high-density amorphous ice at ambient pressure shows a distinct calorimetric glass transitions at 116 K and present evidence that this second glass transition involves liquid-like translational mobility of water molecules. This “double Tg scenario” is related to the coexistence of two liquid phases. The calorimetric signature of the second glass transition is much less feeble, with a heat capacity increase at Tg,2 about five times as large as at Tg,1. By using broadband-dielectric spectroscopy we resolve loss peaks yielding relaxation times near 100 s at 126 K for low-density amorphous ice and at 110 K for high-density amorphous ice as signatures of these two distinct glass transitions. Temperature-dependent dielectric data and heating-rate–dependent calorimetric data allow us to construct the relaxation map for the two distinct phases of water and to extract fragility indices m = 14 for the low-density and m = 20–25 for the high-density liquid. Thus, low-density liquid is classified as the strongest of all liquids known (“superstrong”), and also high-density liquid is classified as a strong liquid. PMID:24101518

  5. Transition from amorphous boron carbide to hexagonal boron carbon nitride thin films induced by nitrogen ion assistance

    NASA Astrophysics Data System (ADS)

    Gago, R.; Jiménez, I.; Agulló-Rueda, F.; Albella, J. M.; Czigány, Zs.; Hultman, L.

    2002-11-01

    Boron carbon nitride films (BCN) were grown by B4C evaporation under concurrent N2 ion beam assistance. The films were characterized by x-ray absorption near-edge spectroscopy, infrared and Raman spectroscopies, and high-resolution transmission electron microscopy. The bonding structure and film composition correlate with the momentum transfer per incoming atom during deposition. As the momentum transfer is increased, the film structure evolves from an amorphous boron carbide network towards a hexagonal ternary compound (h-BCN) with standing basal planes. The growth of h-BCN takes place for momentum transfer in the window between 80 and 250 (eV×amu)1/2. The characteristic vibrational features of the h-BCN compounds have also been studied. Finally, the solubility limit of carbon in the hexagonal BN structure, under the working conditions of this article, is found to be ˜15 at. %.

  6. Assessment of East Antarctic ice flow directions, ice grounding events, and glacial thermal regime across the middle Miocene climate transition from the ANDRILL-SMS and CRP drill holes

    NASA Astrophysics Data System (ADS)

    Passchier, S.; Hauptvogel, D.; Hansen, M.; Falk, C.; Martin, L.

    2010-12-01

    Here we present a synthesis of early and middle Miocene ice sheet development based on facies analyses and multiple compositional studies on the AND-2A and CRP drillcores from the Ross Sea, ca. 10 km off the coast of East Antarctica. The middle Miocene is characterized by one of the three largest shifts in deep-sea oxygen isotope records. During this time the East Antarctic ice sheet became dry-based at high elevation in the Transantarctic Mountains and advanced across the Ross Sea continental shelf to create widespread glacial unconformities. However, detailed proxy records also indicate that ice development was complex and may have occurred in a stepwise fashion, instead of one major episode. Our analyses of “grounded ice” diamictites from both the CRP and AND-2A cores show a significant change in composition across the middle Miocene transition. More detailed analyses of the stratigraphic distribution of facies, heavy mineral provenance, particle size, and major and trace element geochemistry in AND-2A show that relatively large polythermal ice-sheets similar in size to the modern were already present between 17.6 and 17.1 Ma. These results are in agreement with proxy records suggesting that Antarctic ice volumes were larger than today’s volume during the Mi-1b glaciation. Between 17.1 and 15.6-14.9 Ma, a predominance of iceberg debris sourced from the Ferrar Group in the Transantarctic Mountains suggests vigorous glacial erosion and fjord incision by East Antarctic outlet glaciers. The facies characteristics and comparison with compositional data from Neogene tills in the Transantarctic Mountains further suggest that the East Antarctic ice sheet may have been smaller than today during the Miocene climatic optimum (~17-15 Ma) with ice possibly reaching sea level only near the central Transantarctic Mountains. Advance of the grounding line and the development of glacial flow patterns compatible with a larger ice sheet than the modern commenced between 15

  7. Critical speeding-up in the magnetoelectric response of spin-ice near its monopole liquid-gas transition.

    PubMed

    Grams, Christoph P; Valldor, Martin; Garst, Markus; Hemberger, Joachim

    2014-01-01

    Competing interactions in the so-called spin-ice compounds stabilize a frustrated ground state with finite zero-point entropy and, interestingly, emergent magnetic monopole excitations. The properties of these monopoles are at the focus of recent research with particular emphasis on their quantum dynamics. It is predicted that each monopole also possesses an electric dipole moment, which allows to investigate their dynamics via the dielectric function ε(ν). Here we report on broadband spectroscopic measurements of ε(ν) in Dy2Ti2O7 down to temperatures of 200 mK with a specific focus on the critical end point present for a magnetic field along the crystallographic [111] direction. Clear critical signatures are revealed in the dielectric response when, similarly as in the liquid-gas transition, the density of monopoles changes in a critical manner. The dielectric relaxation time τ exhibits a critical speeding-up with a significant enhancement of 1/τ as the temperature is lowered towards the critical temperature. Besides demonstrating the magnetoelectric character of the emergent monopole excitations, our results corroborate the unique critical dynamics near the monopole condensation transition. PMID:25188290

  8. Colloquium: Water's controversial glass transitions

    NASA Astrophysics Data System (ADS)

    Amann-Winkel, Katrin; Böhmer, Roland; Fujara, Franz; Gainaru, Catalin; Geil, Burkhard; Loerting, Thomas

    2016-01-01

    Water is the most common and, judged from its numerous anomalous properties, the weirdest of all known liquids and the complexity of its pressure-temperature map is unsurpassed. A major obstacle on the way to a full understanding of water's structure and dynamics is the hard-to-explore territory within this map, colloquially named the no man's land. Many experiments suggest that just before stepping across its low-temperature border, amorphous ices undergo glass-to-liquid transitions while other interpretations emphasize the importance of underlying disordered (nano)crystalline states. Prospects for reconciling the conflicting views regarding the nature of water's glass transitions are discussed.

  9. Photometric Measurements of H2O Ice Crystallinity on Trans-Neptunian Objects

    NASA Astrophysics Data System (ADS)

    Terai, Tsuyoshi; Itoh, Yoichi; Oasa, Yumiko; Furusho, Reiko; Watanabe, Junichi

    2016-08-01

    We present a measurement of H2O ice crystallinity on the surface of trans-neptunian objects with near-infrared narrow-band imaging. The newly developed photometric technique allows us to efficiently determine the strength of a 1.65 μm absorption feature in crystalline H2O ice. Our data for three large objects—Haumea, Quaoar, and Orcus—which are known to contain crystalline H2O ice on the surfaces, show a reasonable result with high fractions of the crystalline phase. It can also be pointed out that if the grain size of H2O ice is larger than ∼20 μm, the crystallinities of these objects are obviously below 1.0, which suggests the presence of the amorphous phase. In particular, Orcus exhibits a high abundance of amorphous H2O ice compared to Haumea and Quaoar, possibly indicating a correlation between the bulk density of the bodies and the degree of surface crystallization. We also found the presence of crystalline H2O ice on Typhon and 2008 AP129, both of which are smaller than the minimum size limit for inducing cryovolcanism as well as a transition from amorphous to crystalline phase through thermal evolution due to the decay of long-lived isotopes. Based on data collected at Subaru Telescope, which is operated by the National Astronomical Observatory of Japan (NAOJ).

  10. Photometric Measurements of H2O Ice Crystallinity on Trans-Neptunian Objects

    NASA Astrophysics Data System (ADS)

    Terai, Tsuyoshi; Itoh, Yoichi; Oasa, Yumiko; Furusho, Reiko; Watanabe, Junichi

    2016-08-01

    We present a measurement of H2O ice crystallinity on the surface of trans-neptunian objects with near-infrared narrow-band imaging. The newly developed photometric technique allows us to efficiently determine the strength of a 1.65 μm absorption feature in crystalline H2O ice. Our data for three large objects—Haumea, Quaoar, and Orcus—which are known to contain crystalline H2O ice on the surfaces, show a reasonable result with high fractions of the crystalline phase. It can also be pointed out that if the grain size of H2O ice is larger than ˜20 μm, the crystallinities of these objects are obviously below 1.0, which suggests the presence of the amorphous phase. In particular, Orcus exhibits a high abundance of amorphous H2O ice compared to Haumea and Quaoar, possibly indicating a correlation between the bulk density of the bodies and the degree of surface crystallization. We also found the presence of crystalline H2O ice on Typhon and 2008 AP129, both of which are smaller than the minimum size limit for inducing cryovolcanism as well as a transition from amorphous to crystalline phase through thermal evolution due to the decay of long-lived isotopes. Based on data collected at Subaru Telescope, which is operated by the National Astronomical Observatory of Japan (NAOJ).

  11. Semiconductor to metallic transition in bulk accumulated amorphous indium-gallium-zinc-oxide dual gate thin-film transistor

    SciTech Connect

    Chun, Minkyu; Chowdhury, Md Delwar Hossain; Jang, Jin

    2015-05-15

    We investigated the effects of top gate voltage (V{sub TG}) and temperature (in the range of 25 to 70 {sup o}C) on dual-gate (DG) back-channel-etched (BCE) amorphous-indium-gallium-zinc-oxide (a-IGZO) thin film transistors (TFTs) characteristics. The increment of V{sub TG} from -20V to +20V, decreases the threshold voltage (V{sub TH}) from 19.6V to 3.8V and increases the electron density to 8.8 x 10{sup 18}cm{sup −3}. Temperature dependent field-effect mobility in saturation regime, extracted from bottom gate sweep, show a critical dependency on V{sub TG}. At V{sub TG} of 20V, the mobility decreases from 19.1 to 15.4 cm{sup 2}/V ⋅ s with increasing temperature, showing a metallic conduction. On the other hand, at V{sub TG} of - 20V, the mobility increases from 6.4 to 7.5cm{sup 2}/V ⋅ s with increasing temperature. Since the top gate bias controls the position of Fermi level, the temperature dependent mobility shows metallic conduction when the Fermi level is above the conduction band edge, by applying high positive bias to the top gate.

  12. Timing of the Northern Prince Gustav Ice Stream retreat and the deglaciation of northern James Ross Island, Antarctic Peninsula during the last glacial-interglacial transition

    NASA Astrophysics Data System (ADS)

    Nývlt, Daniel; Braucher, Régis; Engel, Zbyněk; Mlčoch, Bedřich

    2014-09-01

    The Northern Prince Gustav Ice Stream located in Prince Gustav Channel, drained the northeastern portion of the Antarctic Peninsula Ice Sheet during the last glacial maximum. Here we present a chronology of its retreat based on in situ produced cosmogenic 10Be from erratic boulders at Cape Lachman, northern James Ross Island. Schmidt hammer testing was adopted to assess the weathering state of erratic boulders in order to better interpret excess cosmogenic 10Be from cumulative periods of pre-exposure or earlier release from the glacier. The weighted mean exposure age of five boulders based on Schmidt hammer data is 12.9 ± 1.2 ka representing the beginning of the deglaciation of lower-lying areas (< 60 m a.s.l.) of the northern James Ross Island, when Northern Prince Gustav Ice Stream split from the remaining James Ross Island ice cover. This age represents the minimum age of the transition from grounded ice stream to floating ice shelf in the middle continental shelf areas of the northern Prince Gustav Channel. The remaining ice cover located at higher elevations of northern James Ross Island retreated during the early Holocene due to gradual decay of terrestrial ice and increase of equilibrium line altitude. Schmidt hammer R-values are inversely correlated with 10Be exposure ages and could be used as a proxy for exposure history of individual granite boulders in this region and favour the hypothesis of earlier release of boulders with excessive 10Be concentrations from glacier directly at this site. These data provide evidences for an earlier deglaciation of northern James Ross Island when compared with other recently presented cosmogenic nuclide based deglaciation chronologies, but this timing coincides with rapid increase of atmospheric temperature in this marginal part of Antarctica.

  13. A review of the slow relaxation processes in the glass-rubber transition region of amorphous polymers

    NASA Astrophysics Data System (ADS)

    Zhang, Rui; He, Xianru; Huang, Guangsu

    2015-09-01

    This article is a review that introduces several articles about slow relaxation processes, also known as slower segmental dynamics. According to the literature, the coupling effect and free volume holes are two important elements for slower micro-dynamics. In addition, the slower processes of many-body systems (blend and diluted systems) are summarised. A good numerical method for detecting multiple modes in the glass-rubber transition region is introduced.

  14. Magneto-optical measurement of anisotropy energy constant(s) for amorphous rare earth, transition metal alloys

    SciTech Connect

    Uber, R.E.; Mansuripur, M.

    1988-11-01

    Optical investigation of magneto-optical films is complementary to conventional torque and VSM magnetometry. In the authors' laboratory, they are now measuring anisotropy energy constants of RE-TM thin films at temperatures from ambient to 150/sup 0/C. An in-plane magnetic field (up to 16.5 KOe) is applied to a saturated sample with perpendicular magnetization. The movement away from the perpendicular direction is monitored using the polar Kerr effect. At the HeNe wavelength, the Kerr effect is principally due to the top 500 angstroms of the transition metal subnetwork in the films.

  15. Liquid water in the domain of cubic crystalline ice Ic

    NASA Technical Reports Server (NTRS)

    Jenniskens, P.; Banham, S. F.; Blake, D. F.; McCoustra, M. R.

    1997-01-01

    Vapor-deposited amorphous water ice when warmed above the glass transition temperature (120-140 K), is a viscous liquid which exhibits a viscosity vs temperature relationship different from that of liquid water at room temperature. New studies of thin water ice films now demonstrate that viscous liquid water persists in the temperature range 140-210 K. where it coexists with cubic crystalline ice. The liquid character of amorphous water above the glass transition is demonstrated by (1) changes in the morphology of water ice films on a nonwetting surface observed in transmission electron microscopy (TEM) at around 175 K during slow warming, (2) changes in the binding energy of water molecules measured in temperature programmed desorption (TPD) studies, and (3) changes in the shape of the 3.07 micrometers absorption band observed in grazing angle reflection-absorption infrared spectroscopy (RAIRS) during annealing at high temperature. whereby the decreased roughness of the water surface is thought to cause changes in the selection rules for the excitation of O-H stretch vibrations. Because it is present over such a wide range of temperatures, we propose that this form of liquid water is a common material in nature. where it is expected to exist in the subsurface layers of comets and on the surfaces of some planets and satellites.

  16. Infrared spectra of crystalline phase ices condensed on silicate smokes at T less than 20 K

    NASA Technical Reports Server (NTRS)

    Moore, Marla H.; Ferrante, Robert F.; Hudson, Reggie L.; Nuth, Joseph A., III; Donn, Bertram

    1994-01-01

    Infrared spectra of H2O, CH3OH, and NH3 condensed at T less than 20 K on amorphous silicate smokes reveal that predominantly crystalline phase ice forms directly on deposit. Spectra of these molecules condensed on aluminum substrates at T less than 20 K indicate that amorphous phase ice forms. On aluminum, crystalline phase H2O and CH3OH are formed by annealing amorphous deposits to 155 K and 130 K, respectively (or by direct deposit at these temperatures); crystalline NH3 is formed by direct deposit at 88 K. Silicate smokes are deposited onto aluminum substrates by evaporation of SiO solid or by combustion of SiH4 with O2 in flowing H2 followed by vapor phase nucleation and growth. Silicate smokes which are oxygen-deficient may contain active surface sites which facilitate the amorphous-to-crystalline phase transition during condensation. Detailed experiments to understand the mechanism are currently in progress. The assumption that amorphous phase ice forms routinely on grains at T less than 80 K is often used in models describing the volatile content of comets or in interpretations of interstellar cloud temperatures. This assumption needs to be reexamined in view of these results.

  17. Disorder-induced amorphization

    SciTech Connect

    Lam, N.Q.; Okamoto, P.R.; Li, Mo

    1997-03-01

    Many crystalline materials undergo a crystalline-to-amorphous (c-a) phase transition when subjected to energetic particle irradiation at low temperatures. By focusing on the mean-square static atomic displacement as a generic measure of chemical and topological disorder, we are led quite naturally to a generalized version of the Lindemann melting criterion as a conceptual framework for a unified thermodynamic approach to solid-state amorphizing transformations. In its simplest form, the generalized Lindemann criterion assumes that the sum of the static and dynamic mean-square atomic displacements is constant along the polymorphous melting curve so that c-a transformations can be understood simply as melting of a critically-disordered crystal at temperatures below the glass transition temperature where the supercooled liquid can persist indefinitely in a configurationally-frozen state. Evidence in support of the generalized Lindemann melting criterion for amorphization is provided by a large variety of experimental observations and by molecular dynamics simulations of heat-induced melting and of defect-induced amorphization of intermetallic compounds.

  18. Amorphous effect on the advancing of wide-range absorption and structural-phase transition in γ-In2Se3 polycrystalline layers

    NASA Astrophysics Data System (ADS)

    Ho, Ching-Hwa

    2014-04-01

    The exploitation of potential functions in material is crucial in materials research. In this study, we demonstrate a III-VI chalcogenide, polycrystalline γ-In2Se3, which simultaneously possesses the capabilities of thickness-dependent optical gaps and wide-energy-range absorption existed in the polycrystalline layers of γ-In2Se3. Transmission electron microscopy and Raman measurement show a lot of γ-phase nanocrystals contained in the disordered and polycrystalline state of the chalcogenide with medium-range order (MRO). The MRO effects on the γ-In2Se3 layers show thickness-dependent absorption-edge shift and thickness-dependent resistivities. The amorphous effect of MRO also renders a structural-phase transition of γ --> α occurred inside the γ-In2Se3 layer with a heat treatment of about 700°C. Photo-voltage-current (Photo V-I) measurements of different-thickness γ-In2Se3 layers propose a wide-energy-range photoelectric conversion unit ranging from visible to ultraviolet (UV) may be achieved by stacking γ-In2Se3 layers in a staircase form containing dissimilar optical gaps.

  19. Amorphous effect on the advancing of wide-range absorption and structural-phase transition in γ-In2Se3 polycrystalline layers.

    PubMed

    Ho, Ching-Hwa

    2014-01-01

    The exploitation of potential functions in material is crucial in materials research. In this study, we demonstrate a III-VI chalcogenide, polycrystalline γ-In2Se3, which simultaneously possesses the capabilities of thickness-dependent optical gaps and wide-energy-range absorption existed in the polycrystalline layers of γ-In2Se3. Transmission electron microscopy and Raman measurement show a lot of γ-phase nanocrystals contained in the disordered and polycrystalline state of the chalcogenide with medium-range order (MRO). The MRO effects on the γ-In2Se3 layers show thickness-dependent absorption-edge shift and thickness-dependent resistivities. The amorphous effect of MRO also renders a structural-phase transition of γ → α occurred inside the γ-In2Se3 layer with a heat treatment of about 700 °C. Photo-voltage-current (Photo V-I) measurements of different-thickness γ-In2Se3 layers propose a wide-energy-range photoelectric conversion unit ranging from visible to ultraviolet (UV) may be achieved by stacking γ-In2Se3 layers in a staircase form containing dissimilar optical gaps. PMID:24755902

  20. Amorphous effect on the advancing of wide-range absorption and structural-phase transition in γ-In2Se3 polycrystalline layers

    PubMed Central

    Ho, Ching-Hwa

    2014-01-01

    The exploitation of potential functions in material is crucial in materials research. In this study, we demonstrate a III-VI chalcogenide, polycrystalline γ-In2Se3, which simultaneously possesses the capabilities of thickness-dependent optical gaps and wide-energy-range absorption existed in the polycrystalline layers of γ-In2Se3. Transmission electron microscopy and Raman measurement show a lot of γ-phase nanocrystals contained in the disordered and polycrystalline state of the chalcogenide with medium-range order (MRO). The MRO effects on the γ-In2Se3 layers show thickness-dependent absorption-edge shift and thickness-dependent resistivities. The amorphous effect of MRO also renders a structural-phase transition of γ → α occurred inside the γ-In2Se3 layer with a heat treatment of about 700°C. Photo-voltage-current (Photo V-I) measurements of different-thickness γ-In2Se3 layers propose a wide-energy-range photoelectric conversion unit ranging from visible to ultraviolet (UV) may be achieved by stacking γ-In2Se3 layers in a staircase form containing dissimilar optical gaps. PMID:24755902

  1. Computer Modeling of the Thermal Conductivity of Cometary Ice

    NASA Technical Reports Server (NTRS)

    Bunch, Theodore E.; Wilson, Michael A.; Pohorille, Andrew

    1998-01-01

    The main objective of this research was to estimate the thermal conductivity of cometry ices from computer simulations of model amorphous ices. This was divided into four specific tasks: (1) Generating samples of amorphous water ices at different microporosities; (2) Comparing the resulting molecular structures of the ices with experimental results, for those densities where data was available; (3) Calculating the thermal conductivities of liquid water and bulk amorphous ices and comparing these results with experimentally determined thermal conductivities; and (4) Investigating how the thermal conductivity of amorphous ice depends upon the microscopic porosity of the samples. The thermal conductivity was found to be only weakly dependent on the microstructure of the amorphous ice. In general, the amorphous ices were found to have thermal conductivities of the same order of magnitude as liquid water. This is in contradiction to recent experimental estimates of the thermal conductivity of amorphous ice, and it is suggested that the extremely low value obtained experimentally is due to larger-scale defects in the ice, such as cracks, but it is not an intrinsic property of the bulk amorphous ice.

  2. AB-stacked square-like bilayer ice in graphene nanocapillaries.

    PubMed

    Zhu, YinBo; Wang, FengChao; Bai, Jaeil; Zeng, Xiao Cheng; Wu, HengAn

    2016-08-10

    Water, when constrained between two graphene sheets and under ultrahigh pressure, can manifest dramatic differences from its bulk counterparts such as the van der Waals pressure induced water-to-ice transformation, known as the metastability limit of two-dimensional (2D) liquid. Here, we present result of a new crystalline structure of bilayer ice with the AB-stacking order, observed from molecular dynamics simulations of constrained water. This AB-stacked bilayer ice (BL-ABI) is transformed from the puckered monolayer square-like ice (pMSI) under higher lateral pressure in the graphene nanocapillary at ambient temperature. BL-ABI is a proton-ordered ice with square-like pattern. The transition from pMSI to BL-ABI is through crystal-to-amorphous-to-crystal pathway with notable hysteresis-loop in the potential energy during the compression/decompression process, reflecting the compression/tensile limit of the 2D monolayer/bilayer ice. In a superheating process, the BL-ABI transforms into the AB-stacked bilayer amorphous ice with the square-like pattern. PMID:27468430

  3. Influence of isotopic disorder on solid state amorphization and polyamorphism in solid H2O -D2O solutions

    NASA Astrophysics Data System (ADS)

    Gromnitskaya, E. L.; Danilov, I. V.; Lyapin, A. G.; Brazhkin, V. V.

    2015-10-01

    We present a low-temperature and high-pressure ultrasonic study of elastic properties of isotopic H2O-D2O solid solutions, comparing their properties with those of the isotopically pure H2O and D2O ices. Measurements were carried out for solid state amorphization (SSA) from 1h to high-density amorphous (HDA) ice upon compression up to 1.8 GPa at 77 K and for the temperature-induced (77 -190 K ) u-HDA (unrelaxed HDA) → e-HDA (expanded HDA) → low-density amorphous (LDA )→1 c cascade of ice transformations near room pressure. There are many similarities in the elasticity behaviour of H2O ,D2O , and H2O-D2O solid solutions, including the softening of the shear elastic modulus as a precursor of SSA and the HDA →LDA transition. We have found significant isotopic effects during H/D substitution, including elastic softening of H2O -D2O solid solutions with respect to the isotopically pure ices in the case of the bulk moduli of ices 1c and 1h and for both bulk and shear elastic moduli of HDA ice at high pressures (>1 GPa ) . This softening is related to the configurational isotopic disorder in the solid solutions. At low pressures, the isotope concentration dependence of the elastic moduli of u-HDA ice changes remarkably and becomes monotonic with pronounced change of the bulk modulus (≈20 %) .

  4. Tropical and High-latitude Surface Ocean Circulation Across The Mid-Pleistocene Transition: Teleconnections And Impacts For Ice-sheet Growth And Environmental Change Onshore

    NASA Astrophysics Data System (ADS)

    McClymont, E. L.; Rosell-Mele, A.; Lloyd, J. M.

    2006-12-01

    The Mid-Pleistocene Transition (MPT) is a major event in the Quaternary record, marking the shift to a dominant glacial/interglacial period of 100-kyr and the development of larger northern hemisphere ice-sheets at ca. 0.9 Ma. The significance of the MPT lies in the change of the global climate system response to external insolation forcing, which cannot account for the strength of the 100-kyr cycles. Existing hypotheses link the MPT to falling atmospheric CO2 concentrations, cooler deep-water temperatures, changes in sea-ice distribution and to the basal conditions of the northern hemisphere ice-sheets. We present alkenone-derived records of sea-surface temperature from the tropical Pacific and the south-east Atlantic spanning 1.5-0.5 Ma, coupled with evidence of arctic/polar water mass distributions in the high northern latitudes of the Atlantic and Pacific Oceans. Interaction between the tropics and high-latitudes across the MPT is suggested by the results presented here. At all sites we find evidence for cooling beginning from 1.15 Ma, supporting the hypotheses invoking cooling of both the atmosphere and deep-waters as a driver of the MPT. Sea-ice expansion from 1.15 Ma is suggested by the equatorward migration of arctic/polar water masses in both the Atlantic and Pacific, which reached their maximum extent at 1.0 Ma. The negative impact of more expansive sea-ice cover to the transport of moisture to the ice-sheet source regions may have been critical to the later development of larger northern hemisphere ice-sheets from 0.9 Ma. Significantly, we find that the MPT was not simply a high-latitude phenomenon, but was accompanied by (and perhaps driven by) significant changes to circulation in the tropical Pacific. Between 1.15 0.9 Ma a secular decrease in mean sea-surface temperatures of c.1.5*C in the eastern tropical Pacific marks an intensification of Walker Circulation and a shift towards a `La Niña'-like circulation state. The associated Trade Wind

  5. Radiation damage and associated phase change effect on photodesorption rates from ices—Lyα studies of the surface behavior of CO{sub 2}(ice)

    SciTech Connect

    Yuan, Chunqing; Yates, John T. Jr.

    2014-01-01

    Photodesorption from a crystalline film of CO{sub 2}(ice) at 75 K has been studied using Lyα (10.2 eV) radiation. We combine quantitative mass spectrometric studies of gases evolved and transmission IR studies of species trapped in the ice. Direct CO desorption is observed from the primary CO{sub 2} photodissociation process, which occurs promptly for CO{sub 2} molecules located on the outermost surface of the ice (Process I). As the fluence of Lyα radiation increases to ∼5.5 × 10{sup 17} photons cm{sup –2}, extensive damage to the crystalline ice occurs and photo-produced CO molecules from deeper regions (Process II) are found to desorb at a rapidly increasing rate, which becomes two orders of magnitude greater than Process I. It is postulated that deep radiation damage to produce an extensive amorphous phase of CO{sub 2} occurs in the 50 nm ice film and that CO (and CO{sub 2}) diffusive transport is strongly enhanced in the amorphous phase. Photodesorption in Process II is a combination of electronic and thermally activated processes. Radiation damage in crystalline CO{sub 2} ice has been monitored by its effects on the vibrational line shapes of CO{sub 2}(ice). Here the crystalline-to-amorphous phase transition has been correlated with the occurrence of efficient molecular transport over long distances through the amorphous phase of CO{sub 2}(ice). Future studies of the composition of the interstellar region, generated by photodesorption from ice layers on grains, will have to consider the significant effects of radiation damage on photodesorption rates.

  6. Evidence of Complex Ice-Volcano Interactions in the Transition Zone Between Elysium Rise and Utopia Basin

    NASA Astrophysics Data System (ADS)

    Pedersen, G. B. M.; Head, J. W.

    2012-03-01

    We report on morphologic evidence of a complex succession of ice-volcano interactions in the Galaxias region, Mars, and reconsider the emplacement properties of volcanoclastic outflow deposit under martian conditions.

  7. Turbulence modeling in aircraft icing

    NASA Technical Reports Server (NTRS)

    Potapczuk, Mark G.

    1993-01-01

    The Icing and Cryogenic Technology Branch develops computational tools which predict ice growth on aircraft surfaces and uses existing CFD technology to evaluate the aerodynamic changes associated with such accretions. Surface roughness, transition location, and laminar, transition, or turbulent convective heat transfer all influence the ice growth process on aircraft surfaces. Turbulence modeling is a critical element within the computational tools used for both ice shape prediction and for performance degradation evaluation.

  8. An ice lithography instrument

    NASA Astrophysics Data System (ADS)

    Han, Anpan; Chervinsky, John; Branton, Daniel; Golovchenko, J. A.

    2011-06-01

    We describe the design of an instrument that can fully implement a new nanopatterning method called ice lithography, where ice is used as the resist. Water vapor is introduced into a scanning electron microscope (SEM) vacuum chamber above a sample cooled down to 110 K. The vapor condenses, covering the sample with an amorphous layer of ice. To form a lift-off mask, ice is removed by the SEM electron beam (e-beam) guided by an e-beam lithography system. Without breaking vacuum, the sample with the ice mask is then transferred into a metal deposition chamber where metals are deposited by sputtering. The cold sample is then unloaded from the vacuum system and immersed in isopropanol at room temperature. As the ice melts, metal deposited on the ice disperses while the metals deposited on the sample where the ice had been removed by the e-beam remains. The instrument combines a high beam-current thermal field emission SEM fitted with an e-beam lithography system, cryogenic systems, and a high vacuum metal deposition system in a design that optimizes ice lithography for high throughput nanodevice fabrication. The nanoscale capability of the instrument is demonstrated with the fabrication of nanoscale metal lines.

  9. An ice lithography instrument

    SciTech Connect

    Han, Anpan; Chervinsky, John; Branton, Daniel; Golovchenko, J. A.

    2011-06-15

    We describe the design of an instrument that can fully implement a new nanopatterning method called ice lithography, where ice is used as the resist. Water vapor is introduced into a scanning electron microscope (SEM) vacuum chamber above a sample cooled down to 110 K. The vapor condenses, covering the sample with an amorphous layer of ice. To form a lift-off mask, ice is removed by the SEM electron beam (e-beam) guided by an e-beam lithography system. Without breaking vacuum, the sample with the ice mask is then transferred into a metal deposition chamber where metals are deposited by sputtering. The cold sample is then unloaded from the vacuum system and immersed in isopropanol at room temperature. As the ice melts, metal deposited on the ice disperses while the metals deposited on the sample where the ice had been removed by the e-beam remains. The instrument combines a high beam-current thermal field emission SEM fitted with an e-beam lithography system, cryogenic systems, and a high vacuum metal deposition system in a design that optimizes ice lithography for high throughput nanodevice fabrication. The nanoscale capability of the instrument is demonstrated with the fabrication of nanoscale metal lines.

  10. An ice lithography instrument.

    PubMed

    Han, Anpan; Chervinsky, John; Branton, Daniel; Golovchenko, J A

    2011-06-01

    We describe the design of an instrument that can fully implement a new nanopatterning method called ice lithography, where ice is used as the resist. Water vapor is introduced into a scanning electron microscope (SEM) vacuum chamber above a sample cooled down to 110 K. The vapor condenses, covering the sample with an amorphous layer of ice. To form a lift-off mask, ice is removed by the SEM electron beam (e-beam) guided by an e-beam lithography system. Without breaking vacuum, the sample with the ice mask is then transferred into a metal deposition chamber where metals are deposited by sputtering. The cold sample is then unloaded from the vacuum system and immersed in isopropanol at room temperature. As the ice melts, metal deposited on the ice disperses while the metals deposited on the sample where the ice had been removed by the e-beam remains. The instrument combines a high beam-current thermal field emission SEM fitted with an e-beam lithography system, cryogenic systems, and a high vacuum metal deposition system in a design that optimizes ice lithography for high throughput nanodevice fabrication. The nanoscale capability of the instrument is demonstrated with the fabrication of nanoscale metal lines. PMID:21721733

  11. An ice lithography instrument

    PubMed Central

    Han, Anpan; Chervinsky, John; Branton, Daniel; Golovchenko, J. A.

    2011-01-01

    We describe the design of an instrument that can fully implement a new nanopatterning method called ice lithography, where ice is used as the resist. Water vapor is introduced into a scanning electron microscope (SEM) vacuum chamber above a sample cooled down to 110 K. The vapor condenses, covering the sample with an amorphous layer of ice. To form a lift-off mask, ice is removed by the SEM electron beam (e-beam) guided by an e-beam lithography system. Without breaking vacuum, the sample with the ice mask is then transferred into a metal deposition chamber where metals are deposited by sputtering. The cold sample is then unloaded from the vacuum system and immersed in isopropanol at room temperature. As the ice melts, metal deposited on the ice disperses while the metals deposited on the sample where the ice had been removed by the e-beam remains. The instrument combines a high beam-current thermal field emission SEM fitted with an e-beam lithography system, cryogenic systems, and a high vacuum metal deposition system in a design that optimizes ice lithography for high throughput nanodevice fabrication. The nanoscale capability of the instrument is demonstrated with the fabrication of nanoscale metal lines. PMID:21721733

  12. Amorphic complexity

    NASA Astrophysics Data System (ADS)

    Fuhrmann, G.; Gröger, M.; Jäger, T.

    2016-02-01

    We introduce amorphic complexity as a new topological invariant that measures the complexity of dynamical systems in the regime of zero entropy. Its main purpose is to detect the very onset of disorder in the asymptotic behaviour. For instance, it gives positive value to Denjoy examples on the circle and Sturmian subshifts, while being zero for all isometries and Morse-Smale systems. After discussing basic properties and examples, we show that amorphic complexity and the underlying asymptotic separation numbers can be used to distinguish almost automorphic minimal systems from equicontinuous ones. For symbolic systems, amorphic complexity equals the box dimension of the associated Besicovitch space. In this context, we concentrate on regular Toeplitz flows and give a detailed description of the relation to the scaling behaviour of the densities of the p-skeletons. Finally, we take a look at strange non-chaotic attractors appearing in so-called pinched skew product systems. Continuous-time systems, more general group actions and the application to cut and project quasicrystals will be treated in subsequent work.

  13. Development and comparison of layer-counted chronologies from the WAIS Divide and EDML ice cores, Antarctica, over the last glacial transition (10-15 ka BP)

    NASA Astrophysics Data System (ADS)

    Winstrup, Mai; Vinther, Bo M.; Sigl, Michael; McConnell, Joe; Svensson, Anders M.; Wegner, Anna

    2014-05-01

    Some ice cores can be very precisely dated far back in time by counting the annual layering in various impurity records, and the most robust chronologies rely on the parallel analysis of annual features expressed in multiple data sets. Layer-counted Antarctic ice-core chronologies are now emerging: Multi-parameter layer counting has been carried out for the Holocene and late glacial section of the EDML ice core, Dronning Maud Land (Vinther et al., in prep.), and a layer-counted timescale for the WAIS Divide core, West Antarctica, reaching back to 30 kyr BP, was recently completed (WDC06A-7; WAIS Divide Members, 2013). Beyond 24 kyr b2k, the main part of this timescale relies solely on electrical measurements on the core. We here use a novel statistical framework for automated annual layer counting (Winstrup et al., 2012) to extend and improve the two chronologies from EDML and WAIS Divide. Using this method, we have 1) revised the multi-parameter layer counts for the EDML ice core back to 15 kyr BP, and 2) employed high-resolution chemistry measurements from WAIS Divide to obtain a layer-counted multi-parameter timescale for WAIS Divide over the same period (10-15 ka b2k). The EDML and WAIS Divide ice cores have been tightly synchronized using volcanic marker horizons, thus allowing a detailed comparison of annual layer counts between tie points using the various approaches. The corresponding timescales are compared also to the EDML timescale from the flow-model based AICC2012 chronology (Veres, 2012). For the Holocene section of the period (10-11.7 ka BP), all timescales show very good agreement. The peculiar accumulation anomaly observed in the WAIS Divide layer thicknesses in the beginning of the Holocene is confirmed by the multi-parameter layer counts from both WAIS Divide and EDML. The transition into the Holocene has generally proven a difficult period to date by annual layer counting, since the appearance of an annual layer in the various records can change

  14. Relation between the High Density Phase and the Very-High Density Phase of Amorphous Solid Water

    NASA Astrophysics Data System (ADS)

    Giovambattista, Nicolas; Stanley, H. Eugene; Sciortino, Francesco

    2005-03-01

    It has been suggested that high-density amorphous (HDA) ice is a structurally arrested form of high-density liquid (HDL) water, while low-density amorphous ice is a structurally arrested form of low-density liquid (LDL) water. Recent experiments and simulations have been interpreted to support the possibility of a second distinct high-density structural state, named very high-density amorphous (VHDA) ice, questioning the LDL-HDL hypothesis. We test this interpretation using extensive computer simulations and find that VHDA is a more stable form of HDA and that, in fact, VHDA should be considered as the amorphous ice of the quenched HDL.

  15. Transitions.

    ERIC Educational Resources Information Center

    Nathanson, Jeanne H., Ed.

    1993-01-01

    This theme issue on transitions for individuals with disabilities contains nine papers discussing transition programs and issues. "Transition Issues for the 1990s," by Michael J. Ward and William D. Halloran, discusses self-determination, school responsibility for transition, continued educational engagement of at-risk students, and service…

  16. Glass-to-cryogenic-liquid transitions in aqueous solutions suggested by crack healing.

    PubMed

    Kim, Chae Un; Tate, Mark W; Gruner, Sol M

    2015-09-22

    Observation of theorized glass-to-liquid transitions between low-density amorphous (LDA) and high-density amorphous (HDA) water states had been stymied by rapid crystallization below the homogeneous water nucleation temperature (∼235 K at 0.1 MPa). We report optical and X-ray observations suggestive of glass-to-liquid transitions in these states. Crack healing, indicative of liquid, occurs when LDA ice transforms to cubic ice at 160 K, and when HDA ice transforms to the LDA state at temperatures as low as 120 K. X-ray diffraction study of the HDA to LDA transition clearly shows the characteristics of a first-order transition. Study of the glass-to-liquid transitions in nanoconfined aqueous solutions shows them to be independent of the solute concentrations, suggesting that they represent an intrinsic property of water. These findings support theories that LDA and HDA ice are thermodynamically distinct and that they are continuously connected to two different liquid states of water. PMID:26351671

  17. Glass-to-cryogenic-liquid transitions in aqueous solutions suggested by crack healing

    PubMed Central

    Kim, Chae Un; Tate, Mark W.; Gruner, Sol M.

    2015-01-01

    Observation of theorized glass-to-liquid transitions between low-density amorphous (LDA) and high-density amorphous (HDA) water states had been stymied by rapid crystallization below the homogeneous water nucleation temperature (∼235 K at 0.1 MPa). We report optical and X-ray observations suggestive of glass-to-liquid transitions in these states. Crack healing, indicative of liquid, occurs when LDA ice transforms to cubic ice at 160 K, and when HDA ice transforms to the LDA state at temperatures as low as 120 K. X-ray diffraction study of the HDA to LDA transition clearly shows the characteristics of a first-order transition. Study of the glass-to-liquid transitions in nanoconfined aqueous solutions shows them to be independent of the solute concentrations, suggesting that they represent an intrinsic property of water. These findings support theories that LDA and HDA ice are thermodynamically distinct and that they are continuously connected to two different liquid states of water. PMID:26351671

  18. Transition from a nanocrystalline phase to an amorphous phase in In-Si-O thin films: The correlation between the microstructure and the optical properties

    SciTech Connect

    Park, Jun-Woo; So, Hyeon Seob; Lee, Hosun; Lee, Hye-Min; Kim, Hyo-Joong; Kim, Han-Ki

    2015-04-21

    We investigated the structural and optical properties of In-Si-O thin films as the phase abruptly changes from nanocrystalline (nc) to amorphous (a) with increasing Si content. In-Si-O thin films were deposited on Si substrate using a co-sputtering deposition method. The RF power of the In{sub 2}O{sub 3} target was fixed at 100 W, while the power applied to the SiO{sub 2} target was varied between 0 W and 60 W. At the Si = 2.8 at. %, i.e., at the onset of amorphous phase, the optical properties, including the dielectric functions, optical gap energies, and phonon modes, changed abruptly which were triggered by changes in the crystallinity and surface morphology. X-ray diffraction (XRD) spectra showed crystalline (c-) In{sub 2}O{sub 3}-like peaks below Si = 2.2%. Additionally, a broad peak associated with an amorphous (a-) In{sub 2}O{sub 3} phase appeared above 2.8%. However, the Raman spectra of In-Si-O showed very weak peaks associated with c-In{sub 2}O{sub 3} below 2.2%, and then showed a strong Raman peak associated with a-In-Si-O above 2.8%. X-ray photoelectron spectroscopy measurements showed that oxygen vacancy-related peak intensities increased abruptly above Si = 2.8%. The contrasting results of XRD and Raman measurements can be explained as follows: first, the large enhancement in Drude tails in the a-In-Si-O phase was caused by Si-induced amorphization and a large increase in the density of oxygen vacancies in the In-Si-O thin films. Second, the apparently drastic increase of the Raman peak intensity near 364 cm{sup −1} (for amorphous phase, i.e., above Si = 2.8%) is attributed to a disorder-activated infrared mode caused by both the amorphization and the increase in the oxygen vacancy density in In-Si-O thin films.

  19. Grain sizes, surface areas, and porosities of vapor-deposited H2O ices used to simulate planetary icy surfaces.

    PubMed

    Boxe, C S; Bodsgard, B R; Smythe, W; Leu, M T

    2007-05-15

    Mean grain sizes and specific surface areas (SSAs) of ice substrates formed by vapor deposition at low temperatures are of importance in simulating external surfaces of icy satellites in the solar system. Environmental scanning electron microscopy (ESEM) was used to obtain granule sizes and to observe the phase of ice granules prepared on borosilicate, silicon, and metallic plates. Ices prepared at a temperature lower than 140 K appear to be amorphous, and their granule sizes are typically submicrometer. At slightly warmer temperatures, near 180-200 K, ice films are composed of either hexagonal or cubic granules with sizes up to a few micrometers. When briefly annealed to even warmer temperatures, ice granule sizes approach approximately 10 microm. SSAs of ice substrates were determined from BET (Brunauer, Emmett, and Teller) analysis of gas adsorption isotherms in the temperature range from 83.5 to 261 K. SSAs decrease drastically from 102 m2/g at 83.5 K to 0.87 m2/g at 150 K and further decrease slowly to 0.22 m2/g at 261 K, suggesting that the transition from amorphous to crystalline forms occurs at approximately 150 K. The overall decrease in SSAs is primarily due to metamorphism and sintering. These results are comparable to recent field and laboratory measurements. Possible implications for theoretical models of icy satellites of outer planets using remote sensing techniques are also discussed. PMID:17306289

  20. A regime shift in the subpolar gyre strength due to a sudden transition in the North Atlantic climate during the Little Ice Age

    NASA Astrophysics Data System (ADS)

    Moreno-Chamarro, Eduardo; Zanchettin, Davide; Lohmann, Katja; Jungclaus, Johann

    2015-04-01

    Recent paleoceanographic reconstructions of the subpolar North Atlantic variability during the last millennium describe oceanic conditions associated with a weaker subpolar gyre during the Little Ice Age (~1400-1700) after a relatively strong phase during the Medieval Climate Anomaly (~950-1250). However, mechanism(s) behind such a relatively rapid shift remains unclear. Here, we investigate the dynamics of the subpolar gyre and its role on driving the exchanges of heat and freshwater between the northern North Atlantic and the Arctic Ocean over the last millennium in an ensemble of three transient and an unperturbed-climate simulation performed with the Max Planck Institute-Earth system model for paleo-applications. In particular, we focus on the dynamics underlying a decadal-scale transition in the subpolar gyre from an initial strong to a later weak state, which is found in one of the last-millennium transient simulations and shows characteristic features similar to the reconstructed event. Our results indicate that the simulated shift is triggered by a rapid increase in the sea-ice transport from the Arctic toward the subpolar North Atlantic, which causes a broad freshening of the Labrador Sea surface and, thereby, a shut-down in deep oceanic mixing. As a result, the subpolar gyre weakens. This in turn activates a series of long-lasting feedbacks relating oceanic and atmospheric circulation, sea-ice extent, and oceanic deep convection in the Labrador Sea that keep the North Atlantic in an anomalous state for about 250 years. A reorganization of the North Atlantic/Arctic ocean-atmosphere coupled system, sustained by internal feedbacks acting on multicentennial time scales, can therefore result in a new subpolar gyre state. The simulated shift coincides in time with a two-decade-long cluster of relatively small volcanic eruptions which leads to prominent thickening of the Arctic ice cap previous to the shift. Sensitivity experiments will be performed to further

  1. The length and time scales of water's glass transitions

    NASA Astrophysics Data System (ADS)

    Limmer, David T.

    2014-06-01

    Using a general model for the equilibrium dynamics of supercooled liquids, I compute from molecular properties the emergent length and time scales that govern the nonequilibrium relaxation behavior of amorphous ice prepared by rapid cooling. Upon cooling, the liquid water falls out of equilibrium whereby the temperature dependence of its relaxation time is predicted to change from super-Arrhenius to Arrhenius. A consequence of this crossover is that the location of the apparent glass transition temperature depends logarithmically on cooling rate. Accompanying vitrification is the emergence of a dynamical length-scale, the size of which depends on the cooling rate and varies between angstroms and tens of nanometers. While this protocol dependence clarifies a number of previous experimental observations for amorphous ice, the arguments are general and can be extended to other glass forming liquids.

  2. Wavelength dependent photodesorption of astrophysical ice analogs

    NASA Astrophysics Data System (ADS)

    Fillion, Jean-Hugues

    During the cold and dense phase of star- and planet-formation, ices frozen out on microscopic interstellar dust particles are the dominant reservoir of molecules other than H2. When exposed to UV radiation from protostars, background stars or through secondary H2 emission induced by cosmic rays, the mantle molecules non-thermally desorb into the gas phase. Because of negligible thermal evaporation in these cold regions, this process is crucial to explain the abundance of gas phase species below their accretion temperatures. In the past, most of laboratory experiments have been focused on the solid phase irradiated by broad-band discharge sources, delivering radiation peaking at Ly-α (10.2 eV). We present a novel approach which focuses on the detection of species into the gas phase with high sensitivity. Amorphous ice films of various composition (pure, binary) and various structure (mixed, layered) have been systematically investigated using tunable monochromatic synchrotron radiation source between 7-14 eV (SOLEIL facility, France). The Photon Induced Desorption spectra (PSD) from simples ices (CO, N2, O2) and isotopologues reveal a very interesting indirect desorption mechanism induced by electronic transition and occurring within the upper layers of the ice film. This indirect mechanism is clearly observed for mixed N2:CO ices, in which excited CO molecule transfers its energy to neighboring molecules. The role of CO as a promoter of the photodesorption of other species has been also observed in the case of the pure CO2 photodesorption, where CO is produced in situ by CO2 photolysis. The importance of this mechanism in the context of the interstellar medium is discussed.

  3. Transitions.

    ERIC Educational Resources Information Center

    Field, David; And Others

    1992-01-01

    Includes four articles: "Career Aspirations" (Field); "Making the Transition to a New Curriculum" (Baker, Householder); "How about a 'Work to School' Transition?" (Glasberg); and "Technological Improvisation: Bringing CNC to Woodworking" (Charles, McDuffie). (SK)

  4. First-principles calculations of the electronic structure and magnetic properties of 3d transition-metal impurities in bcc and amorphous iron

    NASA Astrophysics Data System (ADS)

    Kontsevoi, O. Yu.; Gubanov, V. A.

    1995-06-01

    We present the results of the first-principles calculations of electronic structure, magnetic moments, and effective-exchange-interaction parameters for 3d impurities in ferromagnetic bcc and amorphous iron as obtained by the self-consistent tight-binding linear-muffin-tin-orbital recursion method. Impurities in bcc Fe have been modeled both in the single-site approximation and taking into account up to four shells of the nearest-to-the-impurity neighbors. The results for crystalline iron agree well with the previous more precise Korringa-Kohn-Rostoker Green's function calculations [Phys. Rev. B 40, 8203 (1989)], and confirm the sufficient accuracy of the method developed. The perturbations of electronic states for Fe atoms in different coordinational shells around impurity are considered. Peculiarities of impurity electronic states in amorphous Fe and their influence on magnetic behavior of the system are discussed. The role of impurities in possible stabilization of ferromagnetic ordering in amorphous Fe is investigated in terms of effective-exchange-interaction parameters calculated for the nearest-to-impurity host atoms.

  5. Transition.

    ERIC Educational Resources Information Center

    Thompson, Sandy, Ed.; And Others

    1990-01-01

    This "feature issue" focuses on transition from school to adult life for persons with disabilities. Included are "success stories," brief program descriptions, and a list of resources. Individual articles include the following titles and authors: "Transition: An Energizing Concept" (Paul Bates); "Transition Issues for the 1990s" (William Halloran…

  6. Naled ice growth

    NASA Astrophysics Data System (ADS)

    Schohl, G. A.; Ettema, R.

    1986-02-01

    Based on theoretical formulation and dimensional analysis, supported by the results of laboratory experiments, a theory and a detailed description of naled ice growth are presented. The theory, concepts, and data should be of interest to engineers concerned with the effects of naleds (also referred to as aufeis or icings) on engineering works. The growth of a two dimensional, or laterally confined (flume), naled is shown to depend primarily on seven, independent, dimensionless parameters. The early, two dimensional, phase of growth, a naled consists of a mixture of ice and water, or ice-water slush, forming on a frigid base. The influence of two of the three remaining parameters is not felt until after a transition time has passed. The continuing, cyclic process by which slush layers form and eventually freeze results in the ice laminations that are a feature of naled ice.

  7. Ion-beam amorphization of semiconductors: A physical model based on the amorphous pocket population

    SciTech Connect

    Mok, K.R.C.; Jaraiz, M.; Martin-Bragado, I.; Rubio, J.E.; Castrillo, P.; Pinacho, R.; Barbolla, J.; Srinivasan, M.P.

    2005-08-15

    We introduce a model for damage accumulation up to amorphization, based on the ion-implant damage structures commonly known as amorphous pockets. The model is able to reproduce the silicon amorphous-crystalline transition temperature for C, Si, and Ge ion implants. Its use as an analysis tool reveals an unexpected bimodal distribution of the defect population around a characteristic size, which is larger for heavier ions. The defect population is split in both size and composition, with small, pure interstitial and vacancy clusters below the characteristic size, and amorphous pockets with a balanced mixture of interstitials and vacancies beyond that size.

  8. Dynamics of colloidal particles in ice

    NASA Astrophysics Data System (ADS)

    Spannuth, Melissa; Mochrie, S. G. J.; Peppin, S. S. L.; Wettlaufer, J. S.

    2011-03-01

    Solidification of the solvent phase of a colloidal suspension occurs in many natural and technological settings and is becoming a popular technique for creating microporous structures and composite materials. During freezing, regions of high particle density can form as particles are rejected from the growing solid and guided into a variety of macroscopic morphologies. The particles in the high density regions form an amorphous colloidal solid that deforms in response to internal and external stresses. Using X-ray Photon Correlation Spectroscopy, we studied this deformation for silica particles in polycrystalline ice. We found that the particles in the high density regions underwent ballistic motion coupled with a non-exponential decay of the intensity autocorrelation function (ACF) that transitions from a stretched to a compressed exponential with increasing scattering vector q. While ballistic motion and a compressed exponential decay of the ACF is common, the coupling with a stretched exponential decay is very rare and a transition with increasing q has not previously been reported. We explain this behavior in terms of ice grain boundary migration.

  9. Amorphous metal composites

    DOEpatents

    Byrne, Martin A.; Lupinski, John H.

    1984-01-01

    An improved amorphous metal composite and process of making the composite. The amorphous metal composite comprises amorphous metal (e.g. iron) and a low molecular weight thermosetting polymer binder. The process comprises placing an amorphous metal in particulate form and a thermosetting polymer binder powder into a container, mixing these materials, and applying heat and pressure to convert the mixture into an amorphous metal composite.

  10. Structure, thermodynamics, and crystallization of amorphous hafnia

    NASA Astrophysics Data System (ADS)

    Luo, Xuhui; Demkov, Alexander A.

    2015-09-01

    We investigate theoretically amorphous hafnia using the first principles melt and quench method. We identify two types of amorphous structures of hafnia. Type I and type II are related to tetragonal and monoclinic hafnia, respectively. We find type II structure to show stronger disorder than type I. Using the phonon density of states, we calculate the specific heat capacity for type II amorphous hafnia. Using the nudged elastic band method, we show that the averaged transition barrier between the type II amorphous hafnia and monoclinic phase is approximately 0.09 eV/HfO2. The crystallization temperature is estimated to be 421 K. The calculations suggest an explanation for the low thermal stability of amorphous hafnia.

  11. Structure, thermodynamics, and crystallization of amorphous hafnia

    SciTech Connect

    Luo, Xuhui; Demkov, Alexander A.

    2015-09-28

    We investigate theoretically amorphous hafnia using the first principles melt and quench method. We identify two types of amorphous structures of hafnia. Type I and type II are related to tetragonal and monoclinic hafnia, respectively. We find type II structure to show stronger disorder than type I. Using the phonon density of states, we calculate the specific heat capacity for type II amorphous hafnia. Using the nudged elastic band method, we show that the averaged transition barrier between the type II amorphous hafnia and monoclinic phase is approximately 0.09 eV/HfO{sub 2}. The crystallization temperature is estimated to be 421 K. The calculations suggest an explanation for the low thermal stability of amorphous hafnia.

  12. Nanomoulding with amorphous metals.

    PubMed

    Kumar, Golden; Tang, Hong X; Schroers, Jan

    2009-02-12

    Nanoimprinting promises low-cost fabrication of micro- and nano-devices by embossing features from a hard mould onto thermoplastic materials, typically polymers with low glass transition temperature. The success and proliferation of such methods critically rely on the manufacturing of robust and durable master moulds. Silicon-based moulds are brittle and have limited longevity. Metal moulds are stronger than semiconductors, but patterning of metals on the nanometre scale is limited by their finite grain size. Amorphous metals (metallic glasses) exhibit superior mechanical properties and are intrinsically free from grain size limitations. Here we demonstrate direct nanopatterning of metallic glasses by hot embossing, generating feature sizes as small as 13 nm. After subsequently crystallizing the as-formed metallic glass mould, we show that another amorphous sample of the same alloy can be formed on the crystallized mould. In addition, metallic glass replicas can also be used as moulds for polymers or other metallic glasses with lower softening temperatures. Using this 'spawning' process, we can massively replicate patterned surfaces through direct moulding without using conventional lithography. We anticipate that our findings will catalyse the development of micro- and nanoscale metallic glass applications that capitalize on the outstanding mechanical properties, microstructural homogeneity and isotropy, and ease of thermoplastic forming exhibited by these materials. PMID:19212407

  13. Far-infrared spectral studies of phase changes in water ice induced by proton irradiation

    NASA Technical Reports Server (NTRS)

    Moore, Marla H.; Hudson, Reggie L.

    1992-01-01

    Changes in the FIR spectrum of crystalline and amorphous water ice as a function of temperature are reported. The dramatic differences between the spectra of these ices in the FIR are used to examine the effect of proton irradiation on the stability of the crystalline and amorphous ice phases from 13 to 77 K. In particular, the spectra near 13 K show interconversion between the amorphous and crystalline ice phases beginning at doses near 2 eV/molecule and continuing cyclically with increased dose. The results are used to estimate the stability of irradiated ices in astronomical environments.

  14. Amorphous Computing

    NASA Astrophysics Data System (ADS)

    Sussman, Gerald

    2002-03-01

    agents constructed by engineered cells, but we have few ideas for programming them effectively: How can one engineer prespecified, coherent behavior from the cooperation of immense numbers of unreliable parts that are interconnected in unknown, irregular, and time-varying ways? This is the challenge of Amorphous Computing.

  15. The Role of Ice Streams in Deglaciation

    NASA Astrophysics Data System (ADS)

    Robel, A.; Schoof, C.; Tziperman, E.

    2014-12-01

    Ice streams are regions of fast flow within ice sheets that can exhibit variability on time scales ranging from years to millennia. Observations and model reconstructions indicate that ice streams likely played a major role in the most recent deglaciation of the Laurentide Ice Sheet. The variability of these ice streams may have dictated the spatiotemporal progression of deglaciation, as some ice sheet domes may have been more sensitive to dynamic changes in ice stream activity. We analyze the behavior of both idealized and realistic ice sheet configurations to determine the role of ice streams in setting ice sheet steady states and the spatiotemporal sequence of deglacial transitions. We also examine the way in which climate feedbacks could have amplified the response of ice streams to Milankovitch forcing, thereby initiating ice sheet collapse. We use the Parallel Ice Sheet Model (PISM), by itself and coupled to an energy balance atmospheric model. The presence of ice streams dramatically alters steady-state ice sheet configurations, allowing for the existence of thin, widely extended margins. There is a marked transition from binge-purge-like ice stream variability (that is believed to have occurred as part of Heinrich events during the last glacial period) to steady ice stream flow as climate (temperature, precipitation) is varied over a range corresponding to glacial variability. This qualitative transition in ice sheet dynamics amplifies small changes in external forcing (e.g. Milankovitch cycles) sufficiently to activate strong climate feedbacks. We discuss how the reorganization of ice sheet configuration, through changes in ice sheet extent and elevation, may favor certain climate feedbacks (e.g. ice-albedo and lapse rate feedbacks). We also relate these analyses to observations of Laurentide deglaciation and discuss implications for the future of the Greenland and Antarctic Ice Sheets.

  16. A study on the properties of C-doped Ge8Sb2Te11 thin films during an amorphous-to-crystalline phase transition

    NASA Astrophysics Data System (ADS)

    Park, Cheol-Jin; Kong, Heon; Lee, Hyun-Yong; Yeo, Jong-Bin

    2016-04-01

    In this work, we evaluated the structural, electrical and optical properties of carbon-doped Ge8Sb2Te11 thin films. In a previous work, GeSbTe alloys were doped with different materials in an attempt to improve the thermal stability. Ge8Sb2Te11 and carbon-doped Ge8Sb2Te11 films of 250 nm in thickness were deposited on p-type Si (100) and glass substrates by using a RF magnetron reactive co-sputtering system at room temperature. The fabricated films were annealed in a furnance in the 0 ~ 400°C temperature range. The structural properties were analyzed by using X-ray diffraction (XRD), and the result showed that the carbon-doped Ge8Sb2Te11 had a face-centeredcubic (fcc) crystalline structure and an increased crystallization temperature ( T c ). An increase in the T c leads to thermal stability in the amorphous state. The optical properties were analyzed by using an UV-Vis-IR spectrophotometer, and the result showed an increase in the optical-energy band gap ( E op ) in the crystalline materials and an increase in the E op difference (Δ E op ), which is a good effect for reducing the noise in the memory device. The electrical properties were analyzed by using a 4-point probe, which showed an increase in the sheet resistance ( R s ) in the amorphous state and the crystalline state, which means a reduced programming current in the memory device.

  17. Interplay of the Glass Transition and the Liquid-Liquid Phase Transition in Water

    PubMed Central

    Giovambattista, Nicolas; Loerting, Thomas; Lukanov, Boris R.; Starr, Francis W.

    2012-01-01

    Water has multiple glassy states, often called amorphous ices. Low-density (LDA) and high-density (HDA) amorphous ice are separated by a dramatic, first-order like phase transition. It has been argued that the LDA-HDA transformation connects to a first-order liquid-liquid phase transition (LLPT) above the glass transition temperature Tg. Direct experimental evidence of the LLPT is challenging to obtain, since the LLPT occurs at conditions where water rapidly crystallizes. In this work, we explore the implications of a LLPT on the pressure dependence of Tg(P) for LDA and HDA by performing computer simulations of two water models – one with a LLPT, and one without. In the absence of a LLPT, Tg(P) for all glasses nearly coincide. When there is a LLPT, different glasses exhibit dramatically different Tg(P) which are directly linked with the LLPT. Available experimental data for Tg(P) are only consistent with the scenario including a LLPT. PMID:22550566

  18. Layered kagome spin ice

    NASA Astrophysics Data System (ADS)

    Hamp, James; Dutton, Sian; Mourigal, Martin; Mukherjee, Paromita; Paddison, Joseph; Ong, Harapan; Castelnovo, Claudio

    Spin ice materials provide a rare instance of emergent gauge symmetry and fractionalisation in three dimensions: the effective degrees of freedom of the system are emergent magnetic monopoles, and the extensively many `ice rule' ground states are those devoid of monopole excitations. Two-dimensional (kagome) analogues of spin ice have also been shown to display a similarly rich behaviour. In kagome ice however the ground-state `ice rule' condition implies the presence everywhere of magnetic charges. As temperature is lowered, an Ising transition occurs to a charge-ordered state, which can be mapped to a dimer covering of the dual honeycomb lattice. A second transition, of Kosterlitz-Thouless or three-state Potts type, occurs to a spin-ordered state at yet lower temperatures, due to small residual energy differences between charge-ordered states. Inspired by recent experimental capabilities in growing spin ice samples with selective (layered) substitution of non-magnetic ions, in this work we investigate the fate of the two ordering transitions when individual kagome layers are brought together to form a three-dimensional pyrochlore structure coupled by long range dipolar interactions. We also consider the response to substitutional disorder and applied magnetic fields.

  19. Nuclear Zero Point Effects as a Function of Density in Ice-like Structures and Liquid Water from vdW-DF Ab Initio Calculations

    NASA Astrophysics Data System (ADS)

    Pamuk, Betül; Allen, Philip B.; Soler, Jose M.; Fernández-Serra, Marivi

    2014-03-01

    The contributions of nuclear zero point vibrations to the structures of liquid water and ice are not negligible. Recently, we have explained the source of an anomalous isotope shift in hexagonal ice, representing itself as an increase in the lattice volume when H is replaced by D, by calculating free energy within the quasiharmonic approximation, with ab initio density functional theory. In this work, we extend our studies to analyze the zero point effect in other ice-like structures under different densities: clathrate hydrates, LDL and HDL-like amorphous ices with different densities, and a highly dense ice phase, ice VIII. We show that there is a transition from anomalous isotope effect to normal isotope effect as the density increases. We also analyze nuclear zero point effects in liquid water using different vdW-DFs and make connections to this anomalous-normal isotope effect transition in ice. This work is supported by DOE Early Career Award No. DE-SC0003871.

  20. Amorphous Solid Water (ASW): Macroscale Environmentally-Neutral Application for Remediation of Hazardous Pollutants using Condensed-Phase Cryogenic Fluids

    NASA Astrophysics Data System (ADS)

    de Strulle, Ronald; Rheinhart, Maximilian

    2012-03-01

    We report macroscale environmentally-neutral use of cryogenic fluids to induce phase transitions from crystalline water-ices to amorphous solid water (ASW). New IP and uses in remediation of oil-spills and hazardous immiscibles from aquatic environments. We display high-resolution images of the transitions from hexagonal to cubic crystalline water-ice, then to hydrophobic ASW. Accretion and encapsulation of viscous pollutants within crystalline water-ice, and sequestration of condensed volatiles (PAH, methane) and low viscosity fluids within the interstitial cavities of ASW are shown and differentiated for: crude oils, diesel (heating) and blended oils, petroleum byproducts, vegetable and mineral oils, lipids, and light immiscible fluids. The effects of PdV work and thermal energy transfers during phase changes are shown, along with the sequestration efficiencies for hexagonal and cubic ice lattices vs. non-crystalline ASW, for a range of pollutant substances. The viability of ASW as a medium for study of quantum criticality phases is also proposed. The process is environmentally-neutral in that only substantially condensed-phase air liquefaction products, e.g. nitrogen in >90% liquid phase are employed as an active agent. The applications are also presented in terms of the scale-up of experiments performed at the nanoscale.

  1. Fire beneath the ice

    SciTech Connect

    Monastersky, R.

    1993-02-13

    A volcano discovered six years ago by researchers Blankenship and Bell under Antarctica poses questions about a potential climatic catastrophe. The researchers claim that the volcano is still active, erupting occasionally and growing. A circular depression on the surface of the ice sheet has ice flowing into it and is used to provide a portrait of the heat source. The volcano is on a critical transition zone within West Antarctica with fast flowing ice streams directly downhill. Work by Blankenship shows that a soft layer of water-logged sediments called till provide the lubricating layer on the underside of the ice streams. Volcanos may provide the source of this till. The ice streams buffer the thick interior ice from the ocean and no one know what will happen if the ice streams continue to shorten. These researchers believe their results indicate that the stability of West Antarctica ultimately depends less on the current climate than on the location of heat and sediments under the ice and the legacy of past climatic changes.

  2. The Structure and Properties of Amorphous Indium Oxide

    PubMed Central

    2015-01-01

    A series of In2O3 thin films, ranging from X-ray diffraction amorphous to highly crystalline, were grown on amorphous silica substrates using pulsed laser deposition by varying the film growth temperature. The amorphous-to-crystalline transition and the structure of amorphous In2O3 were investigated by grazing angle X-ray diffraction (GIXRD), Hall transport measurement, high resolution transmission electron microscopy (HRTEM), electron diffraction, extended X-ray absorption fine structure (EXAFS), and ab initio molecular dynamics (MD) liquid-quench simulation. On the basis of excellent agreement between the EXAFS and MD results, a model of the amorphous oxide structure as a network of InOx polyhedra was constructed. Mechanisms for the transport properties observed in the crystalline, amorphous-to-crystalline, and amorphous deposition regions are presented, highlighting a unique structure–property relationship. PMID:25678743

  3. Embrittlement and conditions of the optimization of magnetic properties in the amorphous alloy Co69Fe3.7Cr3.8Si12.5B11 in the absence of a viscous-brittle transition

    NASA Astrophysics Data System (ADS)

    Kekalo, I. B.; Mogil'nikov, P. S.

    2016-07-01

    The influence of the holding time upon annealing on the temperature of the viscous-brittle transition (temperature of embrittlement) T f in a cobalt-based amorphous alloy of the composition Co69Fe3.7Cr3.8Si12.5B11 with a very low saturation magnetostriction λs (<10-7) has been studied. It has been established that the dependence of the embrittlement temperature T f on the of time of holding t a can be described by an Arrhenius equation and that the embrittlement at the annealing temperatures above and below 300°C is described by different kinetic parameters. In the alloy under study, irrespective of the holding time, embrittlement occurs in a very narrow range of annealing temperatures, which does not exceed 5 K. Based on the experimental data on the evolution of the hysteresis magnetic properties upon the isochronous annealings and upon the isothermal holding, the regime of heat treatment that ensures a very high (about 50000) magnitude of the permeability µ5 ( H = 5 mOe, f = 1 kHz) without the transition of the alloy into a brittle state has been determined.

  4. Porosity effects on crystallization kinetics of Amorphous Solid Water: Implications for cold icy objects in the Outer Solar System

    NASA Astrophysics Data System (ADS)

    Mitchell, Emily H.; Raut, Ujjwal; Baragiola, Raul A.

    2015-11-01

    Crystalline ice has been identified on the cold surfaces of most icy satellites and TNOs [1]. This is surprising since accretion of water vapor at temperatures (T < 100 K) should result in the amorphous phase [2]. There are several possible explanations for the unexpected presence of crystalline ice on cold bodies, including cryovolcanism [3] and pulsed heating by micrometeoritic impacts [4].A salient feature of ice films condensed at low T is microporosity, known to increase with deposition angle [5]. Here we investigate the dependence of the crystallization rate on the ice porosity, which could contribute to the observed variation in crystallization time τc reported in the literature [2]. Such dependence is noted in other porous materials such as zeolites and titania [6, 7].Amorphous ice films were deposited on a CsI substrate from a collimated water vapor source at 10 K at incidences varying from 0 to 70°, as well as from an omnidirectional water vapor source. The films were heated to temperatures between 130 and 140 K following deposition. The isothermal transition from amorphous to fully crystalline phase was characterized by analyzing the time-dependent evolution of the OH-stretch absorption band using transmission infrared spectroscopy. Our initial results show that τc decreases with increasing porosity; for instance, a film deposited at 45° was observed to crystallize ~6 times faster than a film deposited at 0°. The preliminary estimate of the porosity of the 45° film is ~50% higher than that of the film deposited at normal incidence. Our findings can explain the reported variation in temperature-dependent τc [2] and contribute to the understanding of crystalline ice on cold bodies in the Outer Solar System.1. Mastrapa, R.M.E. et al. In: Gudipati, M.S. & Castillo-Rogez, J., Eds, The Science of Solar System Ices, Springer, New York, 2013.2. Baragiola, R.A. In: Devlin & Buch, Eds, Water in Confining Geometries, Springer-Verlag, 2003.3. Jewitt, D

  5. Water Freezing and Ice Melting.

    PubMed

    Małolepsza, Edyta; Keyes, Tom

    2015-12-01

    The generalized replica exchange method (gREM) is designed to sample states with coexisting phases and thereby to describe strong first order phase transitions. The isobaric MD version of the gREM is presented and applied to the freezing of liquid water and the melting of hexagonal and cubic ice. It is confirmed that coexisting states are well-sampled. The statistical temperature as a function of enthalpy, TS(H), is obtained. Hysteresis between freezing and melting is observed and discussed. The entropic analysis of phase transitions is applied and equilibrium transition temperatures, latent heats, and surface tensions are obtained for hexagonal ice ↔ liquid and cubic ice ↔ liquid with excellent agreement with published values. A new method is given to assign water molecules among various symmetry types. Pathways for water freezing, ultimately leading to hexagonal ice, are found to contain intermediate layered structures built from hexagonal and cubic ice. PMID:26642983

  6. Amorphous Phases on the Surface of Mars

    NASA Technical Reports Server (NTRS)

    Rampe, E. B.; Morris, R. V.; Ruff, S. W.; Horgan, B.; Dehouck, E.; Achilles, C. N.; Ming, D. W.; Bish, D. L.; Chipera, S. J.

    2014-01-01

    Both primary (volcanic/impact glasses) and secondary (opal/silica, allophane, hisingerite, npOx, S-bearing) amorphous phases appear to be major components of martian surface materials based on orbital and in-situ measurements. A key observation is that whereas regional/global scale amorphous components include altered glass and npOx, local scale amorphous phases include hydrated silica/opal. This suggests widespread alteration at low water-to-rock ratios, perhaps due to snow/ice melt with variable pH, and localized alteration at high water-to-rock ratios. Orbital and in-situ measurements of the regional/global amorphous component on Mars suggests that it is made up of at least three phases: npOx, amorphous silicate (likely altered glass), and an amorphous S-bearing phase. Fundamental questions regarding the composition and the formation of the regional/global amorphous component(s) still remain: Do the phases form locally or have they been homogenized through aeolian activity and derived from the global dust? Is the parent glass volcanic, impact, or both? Are the phases separate or intimately mixed (e.g., as in palagonite)? When did the amorphous phases form? To address the question of source (local and/or global), we need to look for variations in the different phases within the amorphous component through continued modeling of the chemical composition of the amorphous phases in samples from Gale using CheMin and APXS data. If we find variations (e.g., a lack of or enrichment in amorphous silicate in some samples), this may imply a local source for some phases. Furthermore, the chemical composition of the weathering products may give insight into the formation mechanisms of the parent glass (e.g., impact glasses contain higher Al and lower Si [30], so we might expect allophane as a weathering product of impact glass). To address the question of whether these phases are separate or intimately mixed, we need to do laboratory studies of naturally altered samples made

  7. Pressure-induced amorphous-to-amorphous reversible transformation in Pr{sub 75}Al{sub 25}

    SciTech Connect

    Lin, C. L.; Ahmad, A. S.; Lou, H. B.; Wang, X. D.; Cao, Q. P.; Jiang, J. Z.; Li, Y. C.; Liu, J.; Hu, T. D.; Zhang, D. X.

    2013-12-07

    A pressure-induced amorphous-to-amorphous reversible transformation was revealed in Pr{sub 75}Al{sub 25} metallic glass (MG) using in situ high-pressure synchrotron x-ray diffraction technique. The transition began at about 21 GPa with a ∼ 5% volume collapse and ended at about 35 GPa. This transition is reversible with hysteresis. Based on the high-pressure behaviors of Ce-based metallic glasses and Pr metal here, we suggest that the pressure-induced polyamorphic transition in Pr{sub 75}Al{sub 25} MG stems from 4f-electron delocalization of Pr metal which leads to abrupt change in bond shortening. These results obtained here provide new insights into the underlying mechanism of the amorphous-to-amorphous phase transition in metallic glasses and will trigger more theoretical and experimental investigations for such transition.

  8. Coupling of CO2 and ice sheet stability over major climate transitions of the last 20 million years.

    PubMed

    Tripati, Aradhna K; Roberts, Christopher D; Eagle, Robert A

    2009-12-01

    The carbon dioxide (CO2) content of the atmosphere has varied cyclically between approximately 180 and approximately 280 parts per million by volume over the past 800,000 years, closely coupled with temperature and sea level. For earlier periods in Earth's history, the partial pressure of CO2 (pCO2) is much less certain, and the relation between pCO2 and climate remains poorly constrained. We use boron/calcium ratios in foraminifera to estimate pCO2 during major climate transitions of the past 20 million years. During the Middle Miocene, when temperatures were approximately 3 degrees to 6 degrees C warmer and sea level was 25 to 40 meters higher than at present, pCO2 appears to have been similar to modern levels. Decreases in pCO(2) were apparently synchronous with major episodes of glacial expansion during the Middle Miocene (approximately 14 to 10 million years ago) and Late Pliocene (approximately 3.3 to 2.4 million years ago). PMID:19815724

  9. Impact craters: An ice study on Rhea

    NASA Astrophysics Data System (ADS)

    Dalle Ore, Cristina M.; Cruikshank, Dale P.; Mastrapa, Rachel M. E.; Lewis, Emma; White, Oliver L.

    2015-11-01

    The goal of this project is to study the properties of H2O ice in the environment of the Saturn satellites and in particular to measure the relative amounts of crystalline and amorphous H2O ice in and around two craters on Rhea. The craters are remnants of cataclysmic events that, by raising the local temperature, melted the ice, which subsequently crystallized. Based on laboratory experiments it is expected that, when exposed to ion bombardment at the temperatures typical of the Saturn satellites, the crystalline structure of the ice will be broken, resulting in the disordered, amorphous phase. We therefore expect the ice in and around the craters to be partially crystalline and partially amorphous. We have designed a technique that estimates the relative amounts of crystalline and amorphous H2O ice based on measurements of the distortion of the 2-μm spectral absorption band. The technique is best suited for planetary surfaces that are predominantly icy, but works also for surfaces slightly contaminated with other ices and non-ice components. We apply the tool to two areas around the Inktomi and the Obatala craters. The first is a young impact crater on the leading hemisphere of Rhea, the second is an older one on the trailing hemisphere. For each crater we obtain maps of the fraction of crystalline ice, which were overlain onto Imaging Science Subsystem (ISS) images of the satellite searching for correlations between crystallinity and geography. For both craters the largest fractions of crystalline ice are in the center, as would be intuitively expected since the 'ground zero' areas should be most affected by the effects of the impact. The overall distribution of the crystalline ice fraction maps the shape of the crater and, in the case of Inktomi, of the rays. The Inktomi crater ranges between a maximum fraction of 67% crystalline ice to a minimum of 39%. The Obatala crater varies between a maximum of 51% and a minimum of 33%. Based on simplifying assumptions

  10. Evolution of first-year and second-year snow properties on sea ice in the Weddell Sea during spring-summer transition

    NASA Astrophysics Data System (ADS)

    Nicolaus, Marcel; Haas, Christian; Willmes, Sascha

    2009-09-01

    Observations of snow properties, superimposed ice, and atmospheric heat fluxes have been performed on first-year and second-year sea ice in the western Weddell Sea, Antarctica. Snow in this region is particular as it does usually survive summer ablation. Measurements were performed during Ice Station Polarstern (ISPOL), a 5-week drift station of the German icebreaker RV Polarstern. Net heat flux to the snowpack was 8 W m-2, causing only 0.1 to 0.2 m of thinning of both snow cover types, thinner first-year and thicker second-year snow. Snow thinning was dominated by compaction and evaporation, whereas melt was of minor importance and occurred only internally at or close to the surface. Characteristic differences between snow on first-year and second-year ice were found in snow thickness, temperature, and stratigraphy. Snow on second-year ice was thicker, colder, denser, and more layered than on first-year ice. Metamorphism and ablation, and thus mass balance, were similar between both regimes, because they depend more on surface heat fluxes and less on underground properties. Ice freeboard was mostly negative, but flooding occurred mainly on first-year ice. Snow and ice interface temperature did not reach the melting point during the observation period. Nevertheless, formation of discontinuous superimposed ice was observed. Color tracer experiments suggest considerable meltwater percolation within the snow, despite below-melting temperatures of lower layers. Strong meridional gradients of snow and sea-ice properties were found in this region. They suggest similar gradients in atmospheric and oceanographic conditions and implicate their importance for melt processes and the location of the summer ice edge.

  11. Electric breakdown effect in the current-voltage characteristics of amorphous indium oxide thin films near the superconductor-insulator transition

    NASA Astrophysics Data System (ADS)

    Cohen, O.; Ovadia, M.; Shahar, D.

    2011-09-01

    Current-voltage characteristics in the insulator bordering superconductivity in disordered thin films exhibit current jumps of several orders of magnitude due to the development of a thermally bistable electronic state at very low temperatures. In this high-resolution study we find that the jumps can be composed of many (up to 100) smaller jumps that appear to be random. This indicates that inhomogeneity develops near the transition to the insulator and that the current breakdown proceed via percolative paths spanning from one electrode to the other.

  12. Sea Ice

    NASA Technical Reports Server (NTRS)

    Parkinson, Claire L.; Cavalieri, Donald J.

    2005-01-01

    Sea ice covers vast areas of the polar oceans, with ice extent in the Northern Hemisphere ranging from approximately 7 x 10(exp 6) sq km in September to approximately 15 x 10(exp 6) sq km in March and ice extent in the Southern Hemisphere ranging from approximately 3 x 10(exp 6) sq km in February to approximately 18 x 10(exp 6) sq km in September. These ice covers have major impacts on the atmosphere, oceans, and ecosystems of the polar regions, and so as changes occur in them there are potential widespread consequences. Satellite data reveal considerable interannual variability in both polar sea ice covers, and many studies suggest possible connections between the ice and various oscillations within the climate system, such as the Arctic Oscillation, North Atlantic Oscillation, and Antarctic Oscillation, or Southern Annular Mode. Nonetheless, statistically significant long-term trends are also apparent, including overall trends of decreased ice coverage in the Arctic and increased ice coverage in the Antarctic from late 1978 through the end of 2003, with the Antarctic ice increases following marked decreases in the Antarctic ice during the 1970s. For a detailed picture of the seasonally varying ice cover at the start of the 21st century, this chapter includes ice concentration maps for each month of 2001 for both the Arctic and the Antarctic, as well as an overview of what the satellite record has revealed about the two polar ice covers from the 1970s through 2003.

  13. Ancient ice

    NASA Astrophysics Data System (ADS)

    2009-11-01

    Simon Belt, Guillaume Massé and colleagues rammed their way through sheets of ice, spotting some polar bears on the way, in their attempt to reconstruct Arctic sea-ice records covering thousands of years.

  14. Over Ice

    NASA Video Gallery

    All about NASA's IceBridge P-3B plane and its IceBridge retrofit. Upgraded with 21st century "special modifications", the aircraft is less a cold war relic and more like the Space Agency's Millenni...

  15. Deterministic multi-zone ice accretion modeling

    NASA Technical Reports Server (NTRS)

    Yamaguchi, K.; Hansman, R. J., Jr.; Kazmierczak, M.

    1991-01-01

    The study focuses on a deterministic model of the surface roughness transition behavior of glaze ice and analyzes the initial smooth/rough transition location, bead formation, and the propagation of the transition location. Based on a hypothesis that the smooth/rough transition location coincides with the laminar/turbulent boundary-layer transition location, a multizone model is implemented in the LEWICE code. In order to verify the effectiveness of the model, ice accretion predictions for simple cylinders calculated by the multizone LEWICE are compared to experimental ice shapes. The glaze ice shapes are found to be sensitive to the laminar surface roughness and bead thickness parameters controlling the transition location, while the ice shapes are found to be insensitive to the turbulent surface roughness.

  16. Deterministic multi-zone ice accretion modeling

    NASA Technical Reports Server (NTRS)

    Yamaguchi, K.; Hansman, R. John, Jr.; Kazmierczak, Michael

    1991-01-01

    The focus here is on a deterministic model of the surface roughness transition behavior of glaze ice. The initial smooth/rough transition location, bead formation, and the propagation of the transition location are analyzed. Based on the hypothesis that the smooth/rough transition location coincides with the laminar/turbulent boundary layer transition location, a multizone model is implemented in the LEWICE code. In order to verify the effectiveness of the model, ice accretion predictions for simple cylinders calculated by the multizone LEWICE are compared to experimental ice shapes. The glaze ice shapes are found to be sensitive to the laminar surface roughness and bead thickness parameters controlling the transition location, while the ice shapes are found to be insensitive to the turbulent surface roughness.

  17. Upper ocean stratification and sea ice growth rates during the summer-fall transition, as revealed by Elephant seal foraging in the Adélie Depression, East Antarctica

    NASA Astrophysics Data System (ADS)

    Williams, G. D.; Hindell, M.; Houssais, M.-N.; Tamura, T.; Field, I. C.

    2010-11-01

    Southern elephant seals (Mirounga leonina), fitted with Conductivity-Temperature-Depth sensors at Macquarie Island in January 2005 and 2010, collected unique oceanographic observations of the Adélie and George V Land continental shelf (140-148° E) during the summer-fall transition (late February through April). This is a key region of dense shelf water formation from enhanced sea ice growth/brine-rejection in the local coastal polynyas. In 2005 two seals occupied the continental shelf break near the grounded icebergs at the northern end of the Mertz Glacier Tongue for nearly two weeks at the onset of sea ice growth. One of the seals migrated north thereafter and the other headed west, possibly utilising the Antarctic Slope Front current near the continental shelf break. In 2010, after that years calving of the Mertz Glacier Tongue, two seals migrated to the same region but penetrated much further southwest across the Adélie Depression and occupied the Commonwealth Bay polynya from March through April. Here we present unique observations of the regional oceanography during the summer-fall transition, in particular (a) the zonal distribution of modified Circumpolar Deep Water exchange across the shelf break, (b) the upper ocean stratification across the Adélie Depression, including alongside iceberg C-28 that calved from the Mertz Glacier and (c) the convective overturning of the deep remnant seasonal mixed layer in Commonwealth Bay from sea ice growth (7.5-12.5 cm s-1). Heat and freshwater budgets to 200-300 m are used to estimate the ocean heat content, heat flux and sea ice growth rates. We speculate that the continuous foraging by the seals within Commonwealth Bay during the summer-fall transition was due to favorable feeding conditions resulting from the convective overturning of the deep seasonal mixed layer and chlorophyll maximum that is a reported feature of this location.

  18. Diversity and Expression of RubisCO Genes in a Perennially Ice-Covered Antarctic Lake during the Polar Night Transition

    PubMed Central

    Kong, Weidong; Ream, David C.; Priscu, John C.

    2012-01-01

    The autotrophic communities in the lakes of the McMurdo Dry Valleys, Antarctica, have generated interest since the early 1960s owing to low light transmission through the permanent ice covers, a strongly bimodal seasonal light cycle, constant cold water temperatures, and geographical isolation. Previous work has shown that autotrophic carbon fixation in these lakes provides an important source of organic matter to this polar desert. Lake Bonney has two lobes separated by a shallow sill and is one of several chemically stratified lakes in the dry valleys that support year-round biological activity. As part of an International Polar Year initiative, we monitored the diversity and abundance of major isoforms of RubisCO in Lake Bonney by using a combined sequencing and quantitative PCR approach during the transition from summer to polar winter. Form ID RubisCO genes related to a stramenopile, a haptophyte, and a cryptophyte were identified, while primers specific for form IA/B RubisCO detected a diverse autotrophic community of chlorophytes, cyanobacteria, and chemoautotrophic proteobacteria. Form ID RubisCO dominated phytoplankton communities in both lobes of the lake and closely matched depth profiles for photosynthesis and chlorophyll. Our results indicate a coupling between light availability, photosynthesis, and rbcL mRNA levels in deep phytoplankton populations. Regulatory control of rbcL in phytoplankton living in nutrient-deprived shallow depths does not appear to be solely light dependent. The distinct water chemistries of the east and west lobes have resulted in depth- and lobe-dependent variability in RubisCO diversity, which plays a role in transcriptional activity of the key gene responsible for carbon fixation. PMID:22492447

  19. Pressure-induced transformations in amorphous silicon: A computational study

    SciTech Connect

    Garcez, K. M. S.; Antonelli, A.

    2014-02-14

    We study the transformations between amorphous phases of Si through molecular simulations using the environment dependent interatomic potential (EDIP) for Si. Our results show that upon pressure, the material undergoes a transformation from the low density amorphous (LDA) Si to the high density amorphous (HDA) Si. This transformation can be reversed by decompressing the material. This process, however, exhibits clear hysteresis, suggesting that the transformation LDA ↔ HDA is first-order like. The HDA phase is predominantly five-fold coordinated, whereas the LDA phase is the normal tetrahedrally bonded amorphous Si. The HDA phase at 400 K and 20 GPa was submitted to an isobaric annealing up to 800 K, resulting in a denser amorphous phase, which is structurally distinct from the HDA phase. Our results also show that the atomic volume and structure of this new amorphous phase are identical to those of the glass obtained by an isobaric quenching of the liquid in equilibrium at 2000 K and 20 GPa down to 400 K. The similarities between our results and those for amorphous ices suggest that this new phase is the very high density amorphous Si.

  20. Pressure-induced crystallization of amorphous red phosphorus

    NASA Astrophysics Data System (ADS)

    Rissi, Erin N.; Soignard, Emmanuel; McKiernan, Keri A.; Benmore, Chris. J.; Yarger, Jeffery L.

    2012-03-01

    Structural transitions in amorphous red phosphorus were studied at ambient temperature and pressures up to 12 GPa. Amorphous (red) phosphorus was observed to transform into crystalline black phosphorus at 7.5 ± 0.5 GPa using diamond anvil cell Raman spectroscopy, x-ray diffraction and a direct equation of state (EoS) measurement. The transition was found to be irreversible and the material recovered upon pressure cycling to 10 to 12 GPa was crystalline orthorhombic black phosphorus. A third order Birch-Murnaghan EoS was fit to the data and a bulk modulus (B0) of 11.2 GPa was measured for amorphous red phosphorus.

  1. The Nature of the Medieval Warm Period - Little Ice Ace Transition in an Annually Resolved Speleothem Record from Voli Voli Cave, Fiji

    NASA Astrophysics Data System (ADS)

    Mattey, D.; Stephens, M.; Garcia-Anton, E.; Hoffmann, D.; Dredge, J. A.; Fisher, R. E.; Lowry, D.

    2011-12-01

    The modern tropical Fiji climate is characterised by seasonal rainfall controlled by the position of the South Pacific Convergance Zone, which is closest to the islands during the wet summer season and weakens when migrating north during the drier winter season. Annual rainfall is strongly modulated on decadal timescales by ENSO with higher rainfall associated with La Nina events with dry spells sometimes leading to drought conditions during El Nino events. A laminated speleothem from Voli Voli cave Fiji spans a 1500 year interval across the transition from the Medieval Warm Period into the Little Ice Age. Fabrics change from calcite with thin clay layers at the base to white laminated calcite and the older record is characterised by elevated δ13C values then a rapid decrease in δ13C, dated at 1200-1300 AD, coinciding with the onset of clean calcite deposition. δ18O values define a simpler trend that monotonically decreases by ≈1% across the transition but high resolution micromilling at 100 micron resolution reveals smooth oscillations in δ18O and a key question is whether these cycles are annual or multi-annual features. To understand relationships between local cave processes and seasonal weather patterns, a program of cave monitoring has been underway since 2009. Voli Voli cave is a descending passage that terminates near a fissured cliff facing the SE trade winds; these are more persistent during the winter and weaken during the summer and cave monitoring shows that high cave air CO2 levels decline near the cave termination as a result of weak incoming ventilation by atmosphere driven by wind strength or chimney ventilation. The high resolution δ13C record shows regular peaks that are correlated with cycles in P and Sr and are interpreted as annual markers driven by rainfall and seasonal ventilation. The smooth δ18O cycles are quasi-decadal features possessing a similar frequency to ENSO with an amplitude of 2-3% equivalent to an amount-effect related

  2. Effect of ion irradiation on the stability of amorphous Ge 2Sb 2Te 5 thin films

    NASA Astrophysics Data System (ADS)

    De Bastiani, R.; Piro, A. M.; Crupi, I.; Grimaldi, M. G.; Rimini, E.

    2008-05-01

    The archival life of phase-change memories (PCM) is determined by the thermal stability of amorphous phase in a crystalline matrix. In this paper, we report the effect of ion beam irradiation on the crystallization kinetics of amorphous Ge2Sb2Te5 alloy (GST). The transition rate of amorphous GST films was measured by in situ time resolved reflectivity (TRR). The amorphous to crystal transformation time decreases considerably in irradiated amorphous GST samples when ion fluence increases. The stability of amorphous Ge2Sb2Te5 thin films subjected to ion irradiation is discussed in terms of the free energy variation of the amorphous state because of damage accumulation.

  3. Reversibility and criticality in amorphous solids

    PubMed Central

    Regev, Ido; Weber, John; Reichhardt, Charles; Dahmen, Karin A.; Lookman, Turab

    2015-01-01

    The physical processes governing the onset of yield, where a material changes its shape permanently under external deformation, are not yet understood for amorphous solids that are intrinsically disordered. Here, using molecular dynamics simulations and mean-field theory, we show that at a critical strain amplitude the sizes of clusters of atoms undergoing cooperative rearrangements of displacements (avalanches) diverges. We compare this non-equilibrium critical behaviour to the prevailing concept of a ‘front depinning' transition that has been used to describe steady-state avalanche behaviour in different materials. We explain why a depinning-like process can result in a transition from periodic to chaotic behaviour and why chaotic motion is not possible in pinned systems. These findings suggest that, at least for highly jammed amorphous systems, the irreversibility transition may be a side effect of depinning that occurs in systems where the disorder is not quenched. PMID:26564783

  4. Reversibility and criticality in amorphous solids.

    PubMed

    Regev, Ido; Weber, John; Reichhardt, Charles; Dahmen, Karin A; Lookman, Turab

    2015-01-01

    The physical processes governing the onset of yield, where a material changes its shape permanently under external deformation, are not yet understood for amorphous solids that are intrinsically disordered. Here, using molecular dynamics simulations and mean-field theory, we show that at a critical strain amplitude the sizes of clusters of atoms undergoing cooperative rearrangements of displacements (avalanches) diverges. We compare this non-equilibrium critical behaviour to the prevailing concept of a 'front depinning' transition that has been used to describe steady-state avalanche behaviour in different materials. We explain why a depinning-like process can result in a transition from periodic to chaotic behaviour and why chaotic motion is not possible in pinned systems. These findings suggest that, at least for highly jammed amorphous systems, the irreversibility transition may be a side effect of depinning that occurs in systems where the disorder is not quenched. PMID:26564783

  5. Reversibility and criticality in amorphous solids

    SciTech Connect

    Regev, Ido; Weber, John; Reichhardt, Charles; Dahmen, Karin A.; Lookman, Turab

    2015-11-13

    The physical processes governing the onset of yield, where a material changes its shape permanently under external deformation, are not yet understood for amorphous solids that are intrinsically disordered. Here, using molecular dynamics simulations and mean-field theory, we show that at a critical strain amplitude the sizes of clusters of atoms undergoing cooperative rearrangements of displacements (avalanches) diverges. We compare this non-equilibrium critical behaviour to the prevailing concept of a ‘front depinning’ transition that has been used to describe steady-state avalanche behaviour in different materials. We explain why a depinning-like process can result in a transition from periodic to chaotic behaviour and why chaotic motion is not possible in pinned systems. As a result, these findings suggest that, at least for highly jammed amorphous systems, the irreversibility transition may be a side effect of depinning that occurs in systems where the disorder is not quenched.

  6. Reversibility and criticality in amorphous solids

    DOE PAGESBeta

    Regev, Ido; Weber, John; Reichhardt, Charles; Dahmen, Karin A.; Lookman, Turab

    2015-11-13

    The physical processes governing the onset of yield, where a material changes its shape permanently under external deformation, are not yet understood for amorphous solids that are intrinsically disordered. Here, using molecular dynamics simulations and mean-field theory, we show that at a critical strain amplitude the sizes of clusters of atoms undergoing cooperative rearrangements of displacements (avalanches) diverges. We compare this non-equilibrium critical behaviour to the prevailing concept of a ‘front depinning’ transition that has been used to describe steady-state avalanche behaviour in different materials. We explain why a depinning-like process can result in a transition from periodic to chaoticmore » behaviour and why chaotic motion is not possible in pinned systems. As a result, these findings suggest that, at least for highly jammed amorphous systems, the irreversibility transition may be a side effect of depinning that occurs in systems where the disorder is not quenched.« less

  7. Swift heavy ion irradiation of water ice from MeV to GeV energies. Approaching true cosmic ray compaction

    NASA Astrophysics Data System (ADS)

    Dartois, E.; Ding, J. J.; de Barros, A. L. F.; Boduch, P.; Brunetto, R.; Chabot, M.; Domaracka, A.; Godard, M.; Lv, X. Y.; Mejía Guamán, C. F.; Pino, T.; Rothard, H.; da Silveira, E. F.; Thomas, J. C.

    2013-09-01

    Context. Cosmic ray ion irradiation affects the chemical composition of and triggers physical changes in interstellar ice mantles in space. One of the primary structural changes induced is the loss of porosity, and the mantles evolve toward a more compact amorphous state. Previously, ice compaction was monitored at low to moderate ion energies. The existence of a compaction threshold in stopping power has been suggested. Aims: In this article we experimentally study the effect of heavy ion irradiation at energies closer to true cosmic rays. This minimises extrapolation and allows a regime where electronic interaction always dominates to be explored, providing the ice compaction cross section over a wide range of electronic stopping power. Methods: High-energy ion irradiations provided by the GANIL accelerator, from the MeV up to the GeV range, are combined with in-situ infrared spectroscopy monitoring of ice mantles. We follow the IR spectral evolution of the ice as a function of increasing fluence (induced compaction of the initial microporous amorphous ice into a more compact amorphous phase). We use the number of OH dangling bonds of the water molecule, i.e. pending OH bonds not engaged in a hydrogen bond in the initially porous ice structure as a probe of the phase transition. These high-energy experiments are combined with lower energy experiments using light ions (H, He) from other facilities in Catania, Italy, and Washington, USA. Results: We evaluated the cross section for the disappearance of OH dangling bonds as a function of electronic stopping power. A cross-section law in a large energy range that includes data from different ice deposition setups is established. The relevant phase structuring time scale for the ice network is compared to interstellar chemical time scales using an astrophysical model. Conclusions: The presence of a threshold in compaction at low stopping power suggested in some previous works seems not to be confirmed for the high

  8. Excess electrons in ice: a density functional theory study.

    PubMed

    Bhattacharya, Somesh Kr; Inam, Fakharul; Scandolo, Sandro

    2014-02-21

    We present a density functional theory study of the localization of excess electrons in the bulk and on the surface of crystalline and amorphous water ice. We analyze the initial stages of electron solvation in crystalline and amorphous ice. In the case of crystalline ice we find that excess electrons favor surface states over bulk states, even when the latter are localized at defect sites. In contrast, in amorphous ice excess electrons find it equally favorable to localize in bulk and in surface states which we attribute to the preexisting precursor states in the disordered structure. In all cases excess electrons are found to occupy the vacuum regions of the molecular network. The electron localization in the bulk of amorphous ice is assisted by its distorted hydrogen bonding network as opposed to the crystalline phase. Although qualitative, our results provide a simple interpretation of the large differences observed in the dynamics and localization of excess electrons in crystalline and amorphous ice films on metals. PMID:24401958

  9. Hydrogen in amorphous silicon

    SciTech Connect

    Peercy, P. S.

    1980-01-01

    The structural aspects of amorphous silicon and the role of hydrogen in this structure are reviewed with emphasis on ion implantation studies. In amorphous silicon produced by Si ion implantation of crystalline silicon, the material reconstructs into a metastable amorphous structure which has optical and electrical properties qualitatively similar to the corresponding properties in high-purity evaporated amorphous silicon. Hydrogen studies further indicate that these structures will accomodate less than or equal to 5 at.% hydrogen and this hydrogen is bonded predominantly in a monohydride (SiH/sub 1/) site. Larger hydrogen concentrations than this can be achieved under certain conditions, but the excess hydrogen may be attributed to defects and voids in the material. Similarly, glow discharge or sputter deposited amorphous silicon has more desirable electrical and optical properties when the material is prepared with low hydrogen concentration and monohydride bonding. Results of structural studies and hydrogen incorporation in amorphous silicon were discussed relative to the different models proposed for amorphous silicon.

  10. Upper ocean stratification and sea ice growth rates during the summer-fall transition, as revealed by Elephant seal foraging in the Adélie Depression, East Antarctica

    NASA Astrophysics Data System (ADS)

    Williams, G. D.; Hindell, M.; Houssais, M.-N.; Tamura, T.; Field, I. C.

    2011-03-01

    Southern elephant seals (Mirounga leonina), fitted with Conductivity-Temperature-Depth sensors at Macquarie Island in January 2005 and 2010, collected unique oceanographic observations of the Adélie and George V Land continental shelf (140-148° E) during the summer-fall transition (late February through April). This is a key region of dense shelf water formation from enhanced sea ice growth/brine rejection in the local coastal polynyas. In 2005, two seals occupied the continental shelf break near the grounded icebergs at the northern end of the Mertz Glacier Tongue for several weeks from the end of February. One of the seals migrated west to the Dibble Ice Tongue, apparently utilising the Antarctic Slope Front current near the continental shelf break. In 2010, immediately after that year's calving of the Mertz Glacier Tongue, two seals migrated to the same region but penetrated much further southwest across the Adélie Depression and sampled the Commonwealth Bay polynya from March through April. Here we present observations of the regional oceanography during the summer-fall transition, in particular (i) the zonal distribution of modified Circumpolar Deep Water exchange across the shelf break, (ii) the upper ocean stratification across the Adélie Depression, including alongside iceberg C-28 that calved from the Mertz Glacier and (iii) the convective overturning of the deep remnant seasonal mixed layer in Commonwealth Bay from sea ice growth. Heat and freshwater budgets to 200-300 m are used to estimate the ocean heat content (400→50 MJ m-2), flux (50-200 W m-2 loss) and sea ice growth rates (maximum of 7.5-12.5 cm day-1). Mean seal-derived sea ice growth rates were within the range of satellite-derived estimates from 1992-2007 using ERA-Interim data. We speculate that the continuous foraging by the seals within Commonwealth Bay during the summer/fall transition was due to favorable feeding conditions resulting from the convective overturning of the deep

  11. Crystallization of CO2 ice at astronomical conditions

    NASA Astrophysics Data System (ADS)

    Escribano, R. M.; Munoz-Caro, G.; Cruz-Diaz, G.; Mate, B.; Rodriguez-Lazcano, Y.

    2013-12-01

    Carbon dioxide is, after water and comparable to carbon monoxide, one of the most abundant frozen molecular species observed in the lines of sight towards many astrophysical media. We present here an experimental and theoretical investigation on carbon dioxide ices, generated in the lab in a range of temperature, density, amorphicity, and growing conditions (1), and simulated via high level theoretical calculations. Amorphous CO2 ice was generated at CAB by deposition onto a CsI substrate at 8 K under ultrahigh vacuum conditions in the 10-11 mbar range. The pressure increase used for the deposition of CO2 was very low, 10-9 mbar, to enable the formation of highly amorphous CO2 ice, at very low deposition rate. The transmittance infrared spectra, collected at several stages of sample growth, from 20 to 360 monolayers, are shown in the Figure. In a different set of experiments performed at IEM, the morphology of the amorphous CO2 ice has been studied using reflexion-absorption infrared (RAIR) spectroscopy. Calculated spectra of amorphous CO2 ice are obtained using the SIESTA code (2). In a first step, crystalline structures are processed by molecular dynamics to generate amorphous samples, which are subsequently relaxed until an equilibrium configuration is reached. The vibrational spectra of the amorphous solids are then calculated. The spectra of amorphous ice can change significantly depending on the density of the sample. An IR band, red-shifted with respect to ν3, has been identified as a witness of pure and amorphous CO2 ice. It vanishes when the sample becomes crystalline, either by temperature increase or by accumulation of increasing number of layers. The absence of this band in the observed spectra of solid CO2 is an indication that there is no pure and amorphous CO2 ice in inter- and circumstellar mantles References 1. Escribano, R., Muñoz Caro, G., Cruz-Díaz, G.A. Rodríguez-Lazcano, Y. and Maté, B., PNAS, accepted for publication, July 2013.. 2

  12. Investigation of the amorphous to crystalline phase transition of chemical solution deposited Pb(Zr30Ti70)O3 thin films by soft x-ray absorption and soft x-ray emission spectroscopy

    SciTech Connect

    Schneller, T.; Schneller, T.; Kohlstedt, H.; Petraru, A.; Waser, R.; Guo, J.; Denlinger, J.; Learmonth, T.; Glans, Per-Andres; Smith, K. E.

    2008-08-01

    Chemical solution deposited (CSD) complex oxide thin films attract considerable interest in various emerging fields as for example, fuel cells, ferroelectric random access memories or coated conductors. In the present paper the results of soft-x-ray spectroscopy between 100 eV and 500 eV on the amorphous to crystalline phase transition of ferroelectric PbZr{sub 0.3}Ti{sub 0.7}O{sub 3} (PZT) thin films are presented. Five CSD samples derived from the same wafer coated with a PZT film pyrolyzed at 350 C were heat treated at different temperatures between 400 C and 700 C. At first the sample were morphologically and electrically characterized. Subsequently the soft-x-ray absorption and emission experiments were performed at the undulator beamline 8.0 of the Advanced Light Source of the Lawrence Berkeley National Laboratory. Soft-x-ray absorption spectra were acquired for the Ti L{sub 2,3-}, O K-, and C K-edge thresholds by using simultaneously the total electron yield (TEY) and total fluorescence yield (TFY) detection methods. For two samples, annealed at 400 C and 700 C, respectively, the resonant inelastic soft-x-ray spectroscopy (RIXS) was applied for various excitation energies near the Ti L-, O K-edges. We observed clear evidence of a rutile phase at untypically low temperatures. This rutile phase transforms into the perovskite phase upon increasing annealing temperature. These results are discussed in the framework of current microscopic models of the PZT (111) texture selection.

  13. Sea Ice

    NASA Technical Reports Server (NTRS)

    Perovich, D.; Gerland, S.; Hendricks, S.; Meier, Walter N.; Nicolaus, M.; Richter-Menge, J.; Tschudi, M.

    2013-01-01

    During 2013, Arctic sea ice extent remained well below normal, but the September 2013 minimum extent was substantially higher than the record-breaking minimum in 2012. Nonetheless, the minimum was still much lower than normal and the long-term trend Arctic September extent is -13.7 per decade relative to the 1981-2010 average. The less extreme conditions this year compared to 2012 were due to cooler temperatures and wind patterns that favored retention of ice through the summer. Sea ice thickness and volume remained near record-low levels, though indications are of slightly thicker ice compared to the record low of 2012.

  14. Sea ice terminology

    SciTech Connect

    Not Available

    1980-09-01

    A group of definitions of terms related to sea ice is presented, as well as a graphic representation of late winter ice zonation of the Beaufort Sea Coast. Terms included in the definition list are belt, bergy bit, bight, brash ice, calving, close pack ice, compacting, compact pack ice, concentration, consolidated pack ice, crack, diffuse ice edge, fast ice, fast-ice boundary, fast-ice edge, first-year ice, flaw, flaw lead, floe, flooded ice, fractured, fractured zone, fracturing, glacier, grey ice, grey-white ice, growler, hummock, iceberg, iceberg tongue, ice blink, ice boundary, ice cake, ice edge, ice foot, ice free, ice island, ice shelf, large fracture, lead, medium fracture, multiyear ice, nilas, old ice, open pack ice, open water, pack ice, polar ice, polynya, puddle, rafted ice, rafting, ram, ridge, rotten ice, second-year ice, shearing, shore lead, shore polynya, small fracture, strip, tabular berg, thaw holes, very close pack ice, very open pack ice, water sky, young coastal ice, and young ice.

  15. Structure of the Ice-Clathrate Interface

    NASA Astrophysics Data System (ADS)

    Nguyen, Andrew; Koc, Matthew; Shepherd, Tricia; Molinero, Valeria

    2015-03-01

    In the laboratory, clathrates are customarily synthesized from ice and gas guest. It is not clear how and whether ice assists in the nucleation of clathrate hydrates. The structure of the ice-clathrate interface can help assess the role of ice in clathrate nucleation. However, only few studies have addressed the structure of the ice-clathrate interface. Here, we use molecular dynamic simulations to study the structure of the ice-clathrate interface. There is no lattice matching between any plane of ice and clathrate hydrates, therefore an interfacial transition layer has to form to connect the two crystals. We investigate the structure of the ice-clathrate interface produced by alignment and equilibration of the crystals, competitive growth of the two crystals from a common solution, and nucleation of hydrate in the presence of a growing ice front. We find that the interfacial transition layer between ice and clathrate has a width of two to three water layers and it is disordered in all cases. Water in the interfacial transition layer has tetrahedral order lower than either ice or clathrate and higher than liquid water under the same thermodynamic conditions. The work is supported by NSF Grant Number CHE-1012651.

  16. The influence of ice accretion physics on the forecasting of aircraft icing conditions

    NASA Technical Reports Server (NTRS)

    Hansman, R. John, Jr.

    1990-01-01

    The physics which control aircraft ice accretion are reviewed in the context of identifying and forecasting hazardous icing conditions. The severity of aircraft icing is found to be extremely sensitive to temperature, liquid water content and droplet size distribution particularly near the transition between rime and mixed icing. The difficulty in measurement and the variability of these factors with altitude, position and time coupled with variable aircraft sensitivity make forecasting and identifying icing conditions difficult. Automated Pilot Reports (PIREPS) are suggested as one mechanism for improving the data base necessary to forecast icing conditions.

  17. The influence of ice accretion physics on the forecasting of aircraft icing conditions

    NASA Technical Reports Server (NTRS)

    Hansman, R. John, Jr.

    1989-01-01

    The physics which control aircraft ice accretion are reviewed in the context of identifying and forecasting hazardous icing conditions. The severity of aircraft icing is found to be extremely sensitive to temperature, liquid water content and droplet size distribution particularly near the transition between rime and mixed icing. The difficulty in measurement and the variability of these factors with altitude, position and time coupled with variable aircraft sensitivity make forecasting and identifying icing conditions difficult. Automated Pilot Reports (PIREPS) are suggested as one mechanism for improving the data base necessary to forecast icing conditions.

  18. Hugoniot of water ice

    SciTech Connect

    Gaffney, E.S.

    1984-01-19

    Hugoniot data for water ice are available for pressures ranging from about 150 MPa to about 50 GPa from initial states near 260 K. Limited data on porous ice (snow) at the same initial temperatures are available from 3.5 to 38 GPa and initial densities of 600 and 350 Mg/m/sup 3/. Above about 5 GPa, the data are fairly well-fit by a linear relation between shock and particle velocity: D(km/s) = 1.79 + 1.42u. However, a quadratic form fits the data better: D(km/s) = 1.32 + 1.68u - 0.035u/sup 2/. At lower stresses the velocity is a very complicated function of particle velocity due to elastic propagation, yielding and several possible phase changes. The Hugoniot elastic limit (HEL) of ice at these temperatures is about 180 +- 20 MPa with the elastic waves travelling at about 3900 m/s. The mean stress at the HEL is 115 +- 14 MPa. Comparison with strength measurements at lower strain rate indicates that failure at the HEL probably involves fracture and is almost independent of both temperature and strain rate. Ice V has been reported at about 600 MPa, and ice VI at 1.9 GPa and possibly at 3.7 GPa. Transition to ice III probably commences at the HEL at 200 MPa. Relations between volume, enthalpy and internal energy indicate that states below about 1 GPa maintain their shear strength even after undergoing complete transition to a high pressure phase. Time-resolved stress measurements indicate that equilibrium is achieved in about three microseconds for a 695 MPa shock. Melting is definitely complete below 10 GPa.

  19. Amorphous diamond films

    DOEpatents

    Falabella, S.

    1998-06-09

    Amorphous diamond films having a significant reduction in intrinsic stress are prepared by biasing a substrate to be coated and depositing carbon ions thereon under controlled temperature conditions. 1 fig.

  20. Slow dissolution behaviour of amorphous capecitabine.

    PubMed

    Meulenaar, Jelte; Beijnen, Jos H; Schellens, Jan H M; Nuijen, Bastiaan

    2013-01-30

    In this article, we report the anomalous dissolution behaviour of amorphous capecitabine. In contrast to what is expected from thermodynamic theory, amorphous capecitabine dissolves significantly slower compared to its crystalline counterpart. Our experiments show that this is due to the "gelling" properties of amorphous capecitabine in an aqueous environment. The "gel", which is immediately formed upon contact with water, entraps the capecitabine and significantly slows down its dissolution. This "gelling" property is hypothesized to be related to the low glass transition temperature (Tg 19°C) of amorphous capecitabine, resulting in an instant collapse ("gelling") in an aqueous environment. From IR and DSC analysis it is shown that this collapsed capecitabine is remarkably stable and does not recrystallize upon an increased water content or temperature. This highly reproducible dissolution behaviour can be applied in the development of a sustained release dosage form as substantially less sustained release excipient is required in order to attain the desired release profile. As capecitabine is a high-dosed drug, this is highly favourable in view of the size and thus clinical feasibility of the final dosage form. Currently, we are developing and clinically testing a sustained release formulation making use of amorphous capecitabine and its remarkable dissolution behaviour. PMID:23219704

  1. Crystallization of amorphous Zr-Be alloys

    NASA Astrophysics Data System (ADS)

    Golovkova, E. A.; Surkov, A. V.; Syrykh, G. F.

    2015-02-01

    The thermal stability and structure of binary amorphous Zr100 - x Be x alloys have been studied using differential scanning calorimetry and neutron diffraction over a wide concentration range (30 ≤ x ≤ 65). The amorphous alloys have been prepared by rapid quenching from melt. The studied amorphous system involves the composition range around the eutectic composition with boundary phases α-Zr and ZrBe2. It has been found that the crystallization of alloys with low beryllium contents ("hypoeutectic" alloys with x ≤ 40) proceeds in two stages. Neutron diffraction has demonstrated that, at the first stage, α-Zr crystallizes and the remaining amorphous phase is enriched to the eutectic composition; at the second stage, the alloy crystallizes in the α-Zr and ZrBe2 phases. At higher beryllium contents ("hypereutectic" alloys), one phase transition of the amorphous phase to a mixture of the α-Zr and ZrBe2 phases has been observed. The concentration dependences of the crystallization temperature and activation energy have been revealed.

  2. Amorphous metal alloy

    DOEpatents

    Wang, R.; Merz, M.D.

    1980-04-09

    Amorphous metal alloys of the iron-chromium and nickel-chromium type have excellent corrosion resistance and high temperature stability and are suitable for use as a protective coating on less corrosion resistant substrates. The alloys are stabilized in the amorphous state by one or more elements of titanium, zirconium, hafnium, niobium, tantalum, molybdenum, and tungsten. The alloy is preferably prepared by sputter deposition.

  3. Amorphous molybdenum silicon superconducting thin films

    SciTech Connect

    Bosworth, D. Sahonta, S.-L.; Barber, Z. H.; Hadfield, R. H.

    2015-08-15

    Amorphous superconductors have become attractive candidate materials for superconducting nanowire single-photon detectors due to their ease of growth, homogeneity and competitive superconducting properties. To date the majority of devices have been fabricated using W{sub x}Si{sub 1−x}, though other amorphous superconductors such as molybdenum silicide (Mo{sub x}Si{sub 1−x}) offer increased transition temperature. This study focuses on the properties of MoSi thin films grown by magnetron sputtering. We examine how the composition and growth conditions affect film properties. For 100 nm film thickness, we report that the superconducting transition temperature (Tc) reaches a maximum of 7.6 K at a composition of Mo{sub 83}Si{sub 17}. The transition temperature and amorphous character can be improved by cooling of the substrate during growth which inhibits formation of a crystalline phase. X-ray diffraction and transmission electron microscopy studies confirm the absence of long range order. We observe that for a range of 6 common substrates (silicon, thermally oxidized silicon, R- and C-plane sapphire, x-plane lithium niobate and quartz), there is no variation in superconducting transition temperature, making MoSi an excellent candidate material for SNSPDs.

  4. Flow of ices in the Ammonia-Water System

    NASA Technical Reports Server (NTRS)

    Durham, W. B.; Kirby, S. H.; Stern, L. A.

    1993-01-01

    We have fabricated in the laboratory and subsequently deformed crystalline hydrates and partial melts of the water-rich end of the NH3-H2O system, with the aim of improving our understanding of physical processes occurring in icy moons of the outer solar system. Deformation experiments were carried out at constant strain rate. The range of experimental variables are given. Phase relationships in the NH3-H2O system indicate that water ice and ammonia dihydrate, NH3-2H2O, are the stable phases under our experiment conditions. X-ray diffraction of our samples usually revealed these as the dominant phases, but we have also observed an amorphous phase (in unpressurized samples only) and occasionally significant ammonia monohydrate, NH3-H2O. The onset of partial melting at the peritectic temperature at about 176 K appeared as a sharp transition in strength observed in samples of x(sub NH3) = 0.05 and 0.01, the effect of melt was less pronounced. For any given water ice + dihydrate alloy in the subsolidus region, we observed one rheological law over the entire temperature range from 175 K to about 140 K. Below 140 K, a shear instability similar to that occurring in pure water ice under the same conditions limited our ability to measure ductile flow. The rheological laws for the several alloys vary systematically from that of pure ice to that of dihydrate. Pure dihydrate is about 4 orders of magnitude less viscous than water ice just below the peritectic temperature, but because of a very pronounced temperature dependence in dihydrate (100 kJ/mol versus 43 kJ/mol for water ice) the viscosity of dihydrate equals or exceeds that of water ice at T less than 140 K. The large variation in viscosity of dihydrate with relatively small changes in temperature may be helpful in explaining the rich variety of tectonic and volcanic features seen on the surfaces of icy moons in the outer solar system.

  5. Ice detector

    NASA Technical Reports Server (NTRS)

    Weinstein, Leonard M. (Inventor)

    1988-01-01

    An ice detector is provided for the determination of the thickness of ice on the outer surface on an object (e.g., aircraft) independently of temperature or the composition of the ice. First capacitive gauge, second capacitive gauge, and temperature gauge are embedded in embedding material located within a hollowed out portion of the outer surface. This embedding material is flush with the outer surface to prevent undesirable drag. The first capacitive gauge, second capacitive gauge, and the temperature gauge are respectively connected to first capacitive measuring circuit, second capacitive measuring circuit, and temperature measuring circuit. The geometry of the first and second capacitive gauges is such that the ratio of the voltage outputs of the first and second capacitance measuring circuits is proportional to the thickness of ice, regardless of ice temperature or composition. This ratio is determined by offset and dividing circuit.

  6. Catalytic crystallization of ices by small silicate smokes at temperatures less than 20K

    NASA Technical Reports Server (NTRS)

    Moore, M.; Ferrante, R.; Hudson, R.; Tanabe, T.; Nuth, J.

    1993-01-01

    Samples of methanol and water ices condensed from the vapor onto aluminum substrates at low temperatures (below approximately 80 K) form amorphous ices; annealing at temperatures in excess of 140-155 K is usually required to convert such amorphous samples to crystalline ices. However, we have found that when either methanol or water vapor is deposited on to aluminum substrates that have been coated with a thin (0.1-0.5 mm) layer of amorphous silicate smoke, the ices condense in crystalline form. We believe that crystalline ice forms as the result of energy liberated at the ice/silicate interface perhaps due to weak bonding of the ice at defect sites on the grains and the very high surface to volume ratio and defect density of these smokes. Annealing of amorphous water ice mixed with more volatile components such as methane, carbon monoxide, etc., has been suggested as an efficient way to produce clatherates in the outer solar nebula and thus explain the volatile content of comets and icy satellites of the outer planets. This hypothesis may need to be re-examined if amorphous ice does not form on cold silicate grains.

  7. Infrared Spectra and Optical Constants of Elusive Amorphous Methane

    NASA Technical Reports Server (NTRS)

    Gerakines, Perry A.; Hudson, Reggie L.

    2015-01-01

    New and accurate laboratory results are reported for amorphous methane (CH4) ice near 10 K for the study of the interstellar medium (ISM) and the outer Solar System. Near- and mid-infrared (IR) data, including spectra, band strengths, absorption coefficients, and optical constants, are presented for the first time for this seldom-studied amorphous solid. The apparent IR band strength near 1300 cm(exp -1) (7.69 micrometer) for amorphous CH4 is found to be about 33% higher than the value long used by IR astronomers to convert spectral observations of interstellar CH4 into CH4 abundances. Although CH4 is most likely to be found in an amorphous phase in the ISM, a comparison of results from various laboratory groups shows that the earlier CH4 band strength at 1300 cm(exp -1) (7.69 micrometer) was derived from IR spectra of ices that were either partially or entirely crystalline CH4 Applications of the new amorphous-CH4 results are discussed, and all optical constants are made available in electronic form.

  8. Moringa coagulant as a stabilizer for amorphous solids: Part I.

    PubMed

    Bhende, Santosh; Jadhav, Namdeo

    2012-06-01

    Stabilization of amorphous state is a focal area for formulators to reap benefits related with solubility and consequently bioavailability of poorly soluble drugs. In the present work, an attempt has been made to explore the potential of moringa coagulant as an amorphous state stabilizer by investigating its role in stabilization of spray-dried (amorphous) ibuprofen, meloxicam and felodipine. Thermal studies like glass forming ability, glass transition temperature, hot stage microscopy and DSC were carried out for understanding thermodynamic stabilization of drugs. PXRD and dissolution studies were performed to support contribution of moringa coagulant. Studies showed that hydrogen bonding and electrostatic interactions between drug and moringa coagulant are responsible for amorphous state stabilization as explored by ATR-FTIR and molecular docking. Especially, H-bonding was found to be predominant mechanism for drug stabilization. Therein, arginine (basic amino acid in coagulant) exhibited various interactions and played important role in stabilization of aforesaid amorphous drugs. PMID:22359158

  9. THE PHASES OF WATER ICE IN THE SOLAR NEBULA

    SciTech Connect

    Ciesla, Fred J.

    2014-03-20

    Understanding the phases of water ice that were present in the solar nebula has implications for understanding cometary and planetary compositions as well as the internal evolution of these bodies. Here we show that amorphous ice formed more readily than previously recognized, with formation at temperatures <70 K being possible under protoplanetary disk conditions. We further argue that photodesorption and freeze-out of water molecules near the surface layers of the solar nebula would have provided the conditions needed for amorphous ice to form. This processing would be a natural consequence of ice dynamics and would allow for the trapping of noble gases and other volatiles in water ice in the outer solar nebula.

  10. Ice Thickness in the Northwest Passage

    NASA Astrophysics Data System (ADS)

    Haas, C.; Howell, S.

    2015-12-01

    Recently the feasibility of commercial shipping in the ice-prone Northwest Passage has attracted a lot of attention. However, very little ice thickness information actually exists. We present results of the first-ever airborne electromagnetic ice thickness surveys over the NWP carried out in April and May 2011 and 2015 over first-year and multiyear ice. Results show modal thicknesses between 1.8 and 2.0 m in all regions. Mean thicknesses over 3 m and thick, deformed ice were observed over some multiyear ice regimes shown to originate from the Arctic Ocean. Thick ice features more than 100 m wide and thicker than 4 m occurred frequently. There are few other data to compare with to evaluate if the ice of the Northwest Passage has transitioned as other parts of the Arctic have. Although likely thinner than some 20 or more years ago, ice conditions must still be considered severe, and the Canadian Arctic Archipelao may well be considered the last ice refuge of the Arctic. These results have important implications for the prediction of ice break-up and summer ice conditions, and the assessment of sea ice hazards during the summer shipping season.

  11. Only Amorphous Ethanethiol Exists in the Interstellar Medium

    NASA Astrophysics Data System (ADS)

    Sivaraman, Bhalamurugan; Mason, Nigel; Chakrabarti, Sandip Kumar; Das, Ankan; Gorai, Prasanta; Rajan, Rabin; Pradeep, T.; Sundararajan, Pavithraa; Cheng, Bing-Ming

    2016-07-01

    In the ISM, it is now recognised that many molecular species are synthesised on the surface of dust grains which remain within the icy mantles on these grains until desorbed or sputtered (e.g., during star or planetary formation processes). Spitzer has revealed the presence of molecular ices in the dense clouds of the ISM but it is the advent of ALMA and then JWST that is expected to reveal the chemical complexity of such ices. Since the detection of methanol (CH_3OH) in Sgr A and Sgr B2 and hydrogen sulphide (H_2S) in Sgr B2, and other sources, it was long expected that a molecule containing thiol group could the synthesized in the complex chemical regions of the ISM. In 1979, first detection of methanethiol in Sgr B2 was reported. However, the first report on the detection of the higher order thiol, ethanethiol, has only been made recently in Orion KL, 30 years after the first observations of methanethiol, although the necessary precursors were detected earlier, ethylene in IRC +10216, ethanol in Sgr B2 and hydrogen sulfide. In the laboratory for experimental astrochemistry facility in PRL, thiol ices on cold dust grains are simulated and are probed by the FTIR for the first time. Ethanethiol ices were formed on zinc selenide substrate cooled to 10 K in an ultrahigh vacuum chamber. An infrared spectrum recorded after forming the ethanethiol ice at 10K revealed the ice formed to be amorphous in nature. Ices thus formed are then gradually warmed to higher temperatures with subsequent recording of infrared spectra. From the spectrum recorded at 180K, ethanethiol molecules from the ice phase were found to sublime. Until sublimation, which is typical indication for molecules turning from amorphous to crystalline phase, significant change in the infrared spectra, was not observed. Therefore we conclude that ethanethiol exists only in amorphous phase in the icy mantles of the cold dust grains. It is also the first known largest molecule to be present only in the

  12. East Antarctic Ice Sheet fluctuations during the Middle Miocene Climatic Transition inferred from faunal and biogeochemical data on planktonic foraminifera (ODP Hole 747A, Kerguelen Plateau)

    USGS Publications Warehouse

    Verducci, M.; Foresi, L.M.; Scott, G.H.; Tiepolo; Sprovieri, M.; Lirer, F.

    2007-01-01

    This research focuses on a detailed study of faunal and biogeochemical changes that occurred at ODP Hole 747A in the Kerguelen Plateau region of the Southern Ocean during the middle Miocene (14.8-11.8 Ma). Abundance fluctuations of several planktonic foraminiferal taxa, stable oxygen isotope and Mg/Ca ratios have been integrated as a multi-proxy approach to reach a better understanding of the growth modality and fluctuations of the East Antarctic Ice Sheet (EAIS) during this period. A 7°C decrease in Sea Surface Temperature (SST), an abrupt turnover in the planktonic foraminiferal assemblage, a 1.5‰ shift towards heavier δ18O values (Mi3 event) and a related shift towards heavier seawater δ118O values between 13.9 and 13.7 Ma, are interpreted to reflect rapid surface water cooling and EAIS expansion. Hole 747A data suggest a major change in the variability of the climate system fostered by EAIS expansion between 13.9 and 13.7 Ma. Ice sheet fluctuations were greater during the interval 14.8-13.9 Ma compared with those from 13.7 to 11.8 Ma, whereas the latter interval was characterized by a more stable EAIS. In our opinion, the middle Miocene ice sheet expansion in Antarctica represents a first step towards the development of the modern permanent ice sheet

  13. North-south contrast in climate change across northwestern North America during the mid-Holocene transition and the possible relation to western Arctic Ocean sea ice

    NASA Astrophysics Data System (ADS)

    McKay, N.; Kaufman, D. S.

    2013-12-01

    Here we summarize the proxy climate time series from northwestern North America (Alaska and Yukon) included in a new systematic compilation of previously published Arctic Holocene proxy climate records. We identified 27 sites north of 58°N latitude where published proxy records are resolved at sub-millennial scale (at least one value every 400 years) and extend back to at least 6 ka. Each record has a demonstrated relationship with temperature, precipitation or the strength of the Aleutian Low (AL) pressure system. The primary feature of the 20 sites with temperature-sensitive records is a gradual cooling between 6 and 2 ka. These sites are mainly located in southern Alaska and Yukon near the Gulf of Alaska. The three northernmost sites show the opposite trend: warming between 6 and 2 ka. The 13 sites with moisture-sensitive records show a similar north-south disparity in mid-Holocene trends; moisture at the northernmost sites increased between 4 and 2 ka, whereas southerly sites trended towards drier conditions during the interval. AL-sensitive records indicate a decrease in AL strength over the interval, reaching a minimum around 2 ka. Direct orbital forcing would cause gradual cooling throughout the region as summer insolation decreased, and cannot explain the evidence for increasingly warm and wet conditions in the north. Climate model simulations also do not replicate this result: the Transient Climate Evolution of the last 21 ka (TraCE-21) experiment, run with Community Climate System Model (CCSM3), which includes a coupled sea-ice model, does not simulate warming trends anywhere in the western Arctic. One hypothesis to explain this discrepancy is variability in Holocene sea-ice cover in the Chukchi and Beaufort Seas north of the region. Multiple records from marine cores in the Chukchi Sea indicate decreasing sea-ice cover during this interval; high concentrations during the early Holocene may have been associated with Laurentide meltwater, or enhanced sea-ice

  14. Simulating the amorphization of [alpha]-quartz under pressure

    SciTech Connect

    Binggeli, N. , PHB-Ecublens, 1015 Lausanne ); Chelikowsky, J.R. ); Wentzcovitch, R.M. )

    1994-04-01

    Extensive molecular-dynamics simulations have been performed within a classical force-field model for the pressure-induced amorphization of quartz. In agreement with earlier molecular-dynamics studies, we find that a phase transition occurs within the experimental pressure range of the amorphization transformation. However, at variance with previous interpretations, we find that the resulting phase is not amorphous. The correlation functions of the equilibrated structure can be shown to be consistent with those of a crystalline phase. Two transformations to ordered structures occur sequentially during the simulations. The first transformation is likely to be related to the recently discovered transition of quartz to an intermediate crystalline phase before its amorphization. The second transformation, instead, yields a compact octahedrally coordinated Si sublattice. The latter structure may be an artifact of the classical force field.

  15. Water freezing and ice melting

    DOE PAGESBeta

    Malolepsza, Edyta; Keyes, Tom

    2015-10-12

    The generalized replica exchange method (gREM) is designed to sample states with coexisting phases and thereby to describe strong first order phase transitions. The isobaric MD version of the gREM is presented and applied to freezing of liquid water, and melting of hexagonal and cubic ice. It is confirmed that coexisting states are well sampled. The statistical temperature as a function of enthalpy, TS(H), is obtained. Hysteresis between freezing and melting is observed and discussed. The entropic analysis of phase transitions is applied and equilibrium transition temperatures, latent heats, and surface tensions are obtained for hexagonal ice↔liquid and cubic ice↔liquid,more » with excellent agreement with published values. A new method is given to assign water molecules among various symmetry types. As a result, pathways for water freezing, ultimately leading to hexagonal ice, are found to contain intermediate layered structures built from hexagonal and cubic ice.« less

  16. Water freezing and ice melting

    SciTech Connect

    Malolepsza, Edyta; Keyes, Tom

    2015-10-12

    The generalized replica exchange method (gREM) is designed to sample states with coexisting phases and thereby to describe strong first order phase transitions. The isobaric MD version of the gREM is presented and applied to freezing of liquid water, and melting of hexagonal and cubic ice. It is confirmed that coexisting states are well sampled. The statistical temperature as a function of enthalpy, TS(H), is obtained. Hysteresis between freezing and melting is observed and discussed. The entropic analysis of phase transitions is applied and equilibrium transition temperatures, latent heats, and surface tensions are obtained for hexagonal ice↔liquid and cubic ice↔liquid, with excellent agreement with published values. A new method is given to assign water molecules among various symmetry types. As a result, pathways for water freezing, ultimately leading to hexagonal ice, are found to contain intermediate layered structures built from hexagonal and cubic ice.

  17. Synthesis of new amorphous metallic spin glasses

    DOEpatents

    Haushalter, Robert C.

    1988-01-01

    Amorphous metallic precipitates having the formula (M.sub.1).sub.a (M.sub.2).sub.b wherein M.sub.1 is at least one transition metal, M.sub.2 is at least one main group metal and the integers "a" and "b" provide stoichiometric balance; the precipitates having a degree of local order characteristic of chemical compounds from the precipitation process and useful electrical and mechanical properties.

  18. Synthesis of new amorphous metallic spin glasses

    DOEpatents

    Haushalter, Robert C.

    1986-01-01

    Amorphous metallic precipitates having the formula (M.sub.1).sub.a (M.sub.2).sub.b wherein M.sub.1 is at least one transition metal, M.sub.2 is at least one main group metal and the integers "a" and "b" provide stoichiometric balance; the precipitates having a degree of local order characteristic of chemical compounds from the precipitation process and useful electrical and mechanical properties.

  19. Synthesis of new amorphous metallic spin glasses

    DOEpatents

    Haushalter, R.C.

    1985-02-11

    Disclosed are: amorphous metallic precipitates having the formula (M/sub 1/)/sub a/(M/sub 2/)/sub b/ wherein M/sub 1/ is at least one transition metal, M/sub 2/ is at least one main group metal and the integers ''a'' and ''b'' provide stoichiometric balance; the precipitates having a degree of local order characteristic of chemical compounds from the precipitation process and useful electrical and mechanical properties.

  20. Secondary ion emission induced by fission fragment impact in CO-NH(3) and CO-NH(3)-H(2)O ices: modification in the CO-NH(3) ice structure.

    PubMed

    Martinez, R; Farenzena, L S; Iza, P; Ponciano, C R; Homem, M G P; de Brito, A Naves; Wien, K; da Silveira, E F

    2007-10-01

    CO-NH(3) and CO-NH(3)-H(2)O ices at 25-130 K were bombarded by (252)Cf fission fragments ( approximately 65 MeV at the target surface) and the emitted secondary ions were analyzed by time-of-flight mass spectrometry (TOF-SIMS). It is observed that the mass spectra obtained from both ices have similar patterns. The production of hybrid ions (formed from CO and NH(3) molecules) emitted from CO-NH(3) ice has already been reported by R. Martinez et al., Int. J. Mass. Spectrom. 262 (2006) 195; here, the secondary ion emission and the modifications of the CO--NH(3) ice structure during the temperature increase of the ice are addressed. These studies are expected to throw light on the sputtering from planetary and interstellar ices and the possible formation of new organic molecules in CO-NH(3)-H(2)O ice by megaelectronvolt ion bombardment. The presence of water in the CO-NH(3) ice mixture generates molecular ion series such as (NH(3))(p-q)(H(2)O)(q)CO(+) and replaces the cluster series (NH(3))(n)NH(4) (+) emission by the hybrid series (NH(3))(I-i)(H(2)O)(i=1, 2...I)H(+). The distribution of NH(3) and H(2)O molecules within the cluster groups indicates that ammonia and water mix homogeneously in the icy condensate at T = 25 K. The desorption yield distribution of the cluster series (NH(3))(n)NH(4) (+) is described by the sum of two exponential functions: one, slow-decreasing, attributed to the fragmentation of the solid target into clusters; and another, fast-decreasing, due to a local sublimation followed by recombination of ammonia molecules. The analysis of the time-temperature dependence of these two yield components gives information on the formation process of molecular ions, the transient composition of the ice target and structural changes of the ice. Data suggest that the amorphous and porous structure of the NH(3) ice, formed by the condensation of the CO--NH(3) gas at T = 25 K, survives CO sublimation until the occurrence of a phase transition around 80 K

  1. Square ice in graphene nanocapillaries

    NASA Astrophysics Data System (ADS)

    Algara-Siller, G.; Lehtinen, O.; Wang, F. C.; Nair, R. R.; Kaiser, U.; Wu, H. A.; Geim, A. K.; Grigorieva, I. V.

    2015-03-01

    Bulk water exists in many forms, including liquid, vapour and numerous crystalline and amorphous phases of ice, with hexagonal ice being responsible for the fascinating variety of snowflakes. Much less noticeable but equally ubiquitous is water adsorbed at interfaces and confined in microscopic pores. Such low-dimensional water determines aspects of various phenomena in materials science, geology, biology, tribology and nanotechnology. Theory suggests many possible phases for adsorbed and confined water, but it has proved challenging to assess its crystal structure experimentally. Here we report high-resolution electron microscopy imaging of water locked between two graphene sheets, an archetypal example of hydrophobic confinement. The observations show that the nanoconfined water at room temperature forms `square ice'--a phase having symmetry qualitatively different from the conventional tetrahedral geometry of hydrogen bonding between water molecules. Square ice has a high packing density with a lattice constant of 2.83 Å and can assemble in bilayer and trilayer crystallites. Molecular dynamics simulations indicate that square ice should be present inside hydrophobic nanochannels independently of their exact atomic nature.

  2. Square ice in graphene nanocapillaries.

    PubMed

    Algara-Siller, G; Lehtinen, O; Wang, F C; Nair, R R; Kaiser, U; Wu, H A; Geim, A K; Grigorieva, I V

    2015-03-26

    Bulk water exists in many forms, including liquid, vapour and numerous crystalline and amorphous phases of ice, with hexagonal ice being responsible for the fascinating variety of snowflakes. Much less noticeable but equally ubiquitous is water adsorbed at interfaces and confined in microscopic pores. Such low-dimensional water determines aspects of various phenomena in materials science, geology, biology, tribology and nanotechnology. Theory suggests many possible phases for adsorbed and confined water, but it has proved challenging to assess its crystal structure experimentally. Here we report high-resolution electron microscopy imaging of water locked between two graphene sheets, an archetypal example of hydrophobic confinement. The observations show that the nanoconfined water at room temperature forms 'square ice'--a phase having symmetry qualitatively different from the conventional tetrahedral geometry of hydrogen bonding between water molecules. Square ice has a high packing density with a lattice constant of 2.83 Å and can assemble in bilayer and trilayer crystallites. Molecular dynamics simulations indicate that square ice should be present inside hydrophobic nanochannels independently of their exact atomic nature. PMID:25810206

  3. DETECTIONS OF TRANS-NEPTUNIAN ICE IN PROTOPLANETARY DISKS

    SciTech Connect

    McClure, M. K.; Calvet, N.; Bergin, E.; Cleeves, L. I.; Espaillat, C.; D'Alessio, P.; Watson, D. M.; Manoj, P.; Sargent, B. E-mail: ncalvet@umich.edu E-mail: cleeves@umich.edu E-mail: p.dalessio@crya.unam.mx E-mail: manoj.puravankara@tifr.res.in

    2015-02-01

    We present Herschel Space Observatory PACS spectra of T Tauri stars, in which we detect amorphous and crystalline water ice features. Using irradiated accretion disk models, we determine the disk structure and ice abundance in each of the systems. Combining a model-independent comparison of the ice feature strength and disk size with a detailed analysis of the model ice location, we estimate that the ice emitting region is at disk radii >30 AU, consistent with a proto-Kuiper belt. Vertically, the ice emits most below the photodesorption zone, consistent with Herschel observations of cold water vapor. The presence of crystallized water ice at a disk location (1) colder than its crystallization temperature and (2) where it should have been re-amorphized in ∼1 Myr suggests that localized generation is occurring; the most likely cause appears to be micrometeorite impact or planetesimal collisions. Based on simple tests with UV models and different ice distributions, we suggest that the SED shape from 20 to 50 μm may probe the location of the water ice snowline in the disk upper layers. This project represents one of the first extra-solar probes of the spatial structure of the cometary ice reservoir thought to deliver water to terrestrial planets.

  4. Formation of amorphous materials

    DOEpatents

    Johnson, William L.; Schwarz, Ricardo B.

    1986-01-01

    Metastable amorphous or fine crystalline materials are formed by solid state reactions by diffusion of a metallic component into a solid compound or by diffusion of a gas into an intermetallic compound. The invention can be practiced on layers of metals deposited on an amorphous substrate or by intermixing powders with nucleating seed granules. All that is required is that the diffusion of the first component into the second component be much faster than the self-diffusion of the first component. The method is practiced at a temperature below the temperature at which the amorphous phase transforms into one or more crystalline phases and near or below the temperature at which the ratio of the rate of diffusion of the first component to the rate of self-diffusion is at least 10.sup.4. This anomalous diffusion criteria is found in many binary, tertiary and higher ordered systems of alloys and appears to be found in all alloy systems that form amorphous materials by rapid quenching. The method of the invention can totally convert much larger dimensional materials to amorphous materials in practical periods of several hours or less.

  5. The determination of ice composition with instruments on cometary landers.

    PubMed

    Boynton, W V; D'Uston, L C; Young, D T; Lunine, J I; Waite, J H; Bailey, S H; Berthelier, J J; Bertaux, J L; Borrel, V; Burke, M F; Cohen, B A; McComas, D H; Nordholt, J E; Evans, L G; Trombka, J I

    1997-05-01

    The determination of the composition of materials that make up comets is essential in trying to understand the origin of these primitive objects. The ices especially could be made in several different astrophysical settings including the solar nebula, protosatellite nebulae of the giant planets, and giant molecular clouds that predate the formation of the solar system. Each of these environments makes different ices with different composition. In order to understand the origin of comets, one needs to determine the composition of each of the ice phases. For example, it is of interest to know that comets contain carbon monoxide, CO, but it is much more important to know how much of it is a pure solid phase, is trapped in clathrate hydrates, or is adsorbed on amorphous water ice. In addition, knowledge of the isotopic composition of the constituents will help determine the process that formed the compounds. Finally, it is important to understand the bulk elemental composition of the nucleus. When these data are compared with solar abundances, they put strong constraints on the macro-scale processes that formed the comet. A differential scanning calorimeter (DSC) and an evolved gas analyzer (EGA) will make the necessary association between molecular constituents and their host phases. This combination of instruments takes a small (tens of mg) sample of the comet and slowly heats it in a sealed oven. As the temperature is raised, the DSC precisely measures the heat required, and delivers the gases to the EGA. Changes in the heat required to raise the temperature at a controlled rate are used to identify phase transitions, e.g., crystallization of amorphous ice or melting of hexagonal ice, and the EGA correlates the gases released with the phase transition. The EGA consists of two mass spectrometers run in tandem. The first mass spectrometer is a magnetic-sector ion-momentum analyzer (MAG), and the second is an electrostatic time-of-flight analyzer (TOF). The TOF acts as

  6. The 'depletion layer' of amorphous p-n junctions

    NASA Technical Reports Server (NTRS)

    Von Roos, O.

    1981-01-01

    It is shown that within reasonable approximations for the density of state distribution within the mobility gap of a:Si, a one-to-one correspondence exists between the electric field distribution in the transition region of an amorphous p-n junction and that in the depletion layer of a crystalline p-n junction. Thus it is inferred that the depletion layer approximation which leads to a parabolic potential distribution within the depletion layer of crystalline junctions also constitutes a fair approximation in the case of amorphous junctions. This fact greatly simplifies an analysis of solid-state electronic devices based on amorphous material (i.e., solar cells).

  7. Growth Induced Magnetic Anisotropy in Crystalline and Amorphous Thin Films

    SciTech Connect

    Hellman, Frances

    1998-10-03

    OAK B204 Growth Induced Magnetic Anisotropy in Crystalline and Amorphous Thin Films. The work in the past 6 months has involved three areas of magnetic thin films: (1) amorphous rare earth-transition metal alloys, (2) epitaxial Co-Pt and hTi-Pt alloy thin films, and (3) collaborative work on heat capacity measurements of magnetic thin films, including nanoparticles and CMR materials.

  8. Thermal and nonthermal physiochemical processes in nanoscale films of amorphous solid water.

    PubMed

    Smith, R Scott; Petrik, Nikolay G; Kimmel, Greg A; Kay, Bruce D

    2012-01-17

    Amorphous solid water (ASW) is a disordered version of ice created by vapor deposition onto a cold substrate (typically less than 130 K). It has a higher free energy than the crystalline phase of ice, and when heated above its glass transition temperature, it transforms into a metastable supercooled liquid. This unusual form of water exists on earth only in laboratories, after preparation with highly specialized equipment. It is thus fair to ask why there is any interest in studying such an esoteric material. Much of the scientific interest results from the ability to use ASW as a model system for exploring the physical and reactive properties of liquid water and aqueous solutions. ASW is also thought to be the predominant form of water in the extremely cold temperatures of many interstellar and planetary environments. In addition, ASW is a convenient model system for studying the stability of amorphous and glassy materials as well as the properties of highly porous materials. A fundamental understanding of such properties is invaluable in a diverse range of applications, including cryobiology, food science, pharmaceuticals, astrophysics, and nuclear waste storage, among others. Over the past 15 years, we have used molecular beams and surface science techniques to probe the thermal and nonthermal properties of nanoscale films of ASW. In this Account, we present a survey of our research on the properties of ASW using this approach. We use molecular beams to precisely control the deposition conditions (flux, incident energy, and incident angle) and create compositionally tailored, nanoscale films of ASW at low temperatures. To study the transport properties (viscosity and diffusivity), we heat the amorphous films above their glass transition temperature, T(g), at which they transform into deeply supercooled liquids prior to crystallization. The advantage of this approach is that at temperatures near T(g), the viscosity is approximately 15 orders of magnitude larger

  9. Structural Amorphous Steels

    NASA Astrophysics Data System (ADS)

    Lu, Z. P.; Liu, C. T.; Thompson, J. R.; Porter, W. D.

    2004-06-01

    Recent advancement in bulk metallic glasses, whose properties are usually superior to their crystalline counterparts, has stimulated great interest in fabricating bulk amorphous steels. While a great deal of effort has been devoted to this field, the fabrication of structural amorphous steels with large cross sections has remained an alchemist’s dream because of the limited glass-forming ability (GFA) of these materials. Here we report the discovery of structural amorphous steels that can be cast into glasses with large cross-section sizes using conventional drop-casting methods. These new steels showed interesting physical, magnetic, and mechanical properties, along with high thermal stability. The underlying mechanisms for the superior GFA of these materials are discussed.

  10. Environment at the Grounding Zone of the Whillans Ice Stream-Ross Ice Shelf, West Antarctica

    NASA Astrophysics Data System (ADS)

    Hodson, T. O.; Powell, R. D.; Mikucki, J.; Scherer, R. P.; Tulaczyk, S. M.; Coenen, J. J.; Puttkammer, R.; Branecky, C.

    2015-12-01

    Grounding zones where grounded ice sheets transition to floating ice shelves, are the primary gateways through which the Antarctic Ice Sheet loses mass to the ocean. In these environments, ice, ocean, meltwater and sediment meet and interact, influencing both the ice sheet and ocean circulation beneath the ice shelf. Here, we report on conditions near the grounding zone of the Whillans Ice Stream, which feeds into the Ross Ice Shelf. Cameras and instruments lowered through an access borehole to the ocean cavity beneath the ice shelf found a 10m-thick water column comprising an upper layer of colder ice shelf water formed from mixing between meltwater with the lower layer of warmer higher salinity shelf water. This style of stratification is typical of large ice shelves, but it was uncertain whether it existed so near the grounding zone, where stronger tidal currents and/or strong subglacial stream discharges could mix the water column. Salinity and temperature of the water suggest it formed from sea ice production in the Western Ross Sea, with minimal modification beneath the ice shelf. This source region is distinct from waters previously observed at the nearby J-9 borehole, illustrating the importance of the sub-ice shelf bathymetry in steering circulation between the ocean and the grounding zone. Preliminary data suggest an active exchange of heat and nutrients between the grounding zone and the open ocean, despite being separated by 600km. Thus life found near the grounding line is probably not an isolated oasis, but may instead be part of a much broader ecosystem that spans the ice shelf. Although sea ice formation presently maintains water in the sub-ice shelf cavity near the surface freezing point, buffering many larger ice shelves from gradual ocean warming, these findings suggest that even grounding zones of extensive ice shelves may respond quickly to abrupt changes in ocean circulation, such as that observed in the Amundsen Sea.

  11. Compressibility and phase transition studies for amorphous materials under high pressure: Approach combined of synchrotron high energy x-ray diffraction and micro tomography techniques using diamond anvil cell

    NASA Astrophysics Data System (ADS)

    Liu, H.; Wang, L.; Xiao, X.; Lee, P.; Hemley, R.; Mao, H.

    2007-12-01

    The structural evolution of amorphous materials under high pressure conditions is a virgin field that has not been extensively explored. Investigations by reaching large Q range using synchrotron high energy x-ray diffraction and diamond anvil cell (DAC) techniques were performed. The study of polyamorphism will undoubtedly broaden our horizons and perspectives of the states of matter in general, and may have a significant impact on the existing theories about the structure, formation, and evolution of amorphous materials. The procedure of the pressure- induced amorphous state to crystalline state is another interesting subject. Combine the high energy x-ray diffraction with the time resolved area detector, we not only could accurately measure the structural factors evolution of amorphous materials under pressure, but also could record the time dependence of the crystallization procedure. These will provide new insight on the nature of crystallization, provide new invitation for the electronic theoretical studies for the phase stability and competition in time and spatial domains, and improve our understanding of the kinetic process of the common pressure induced crystallization. Another technical development effort is the micro tomography study using DAC at radial geometrical setting. Although the two-dimensional imaging, i. e. x-ray radiography, is used in routine way for high pressure DAC experiments, the ¡®volume imaging', i. e. x-ray tomography, will offer us more information regarding direct volume measurement, relative density measurement, and shear deformation under high pressure. The application in high pressure conditions by using DAC will greatly push our understanding of deformation mechanism down to lower mantle conditions. Another major application for DAC tomography will be the relative density measurement for the amorphous materials, metallic glasses, and liquid or melt in DAC under pressure, which will provide better information for the density

  12. Polyamorphism in tetrahedral substances: Similarities between silicon and ice.

    PubMed

    Garcez, K M S; Antonelli, A

    2015-07-21

    Tetrahedral substances, such as silicon, water, germanium, and silica, share various unusual phase behaviors. Among them, the so-called polyamorphism, i.e., the existence of more than one amorphous form, has been intensively investigated in the last three decades. In this work, we study the metastable relations between amorphous states of silicon in a wide range of pressures, using Monte Carlo simulations. Our results indicate that the two amorphous forms of silicon at high pressures, the high density amorphous (HDA) and the very high density amorphous (VHDA), can be decompressed from high pressure (∼20 GPa) down to the tensile regime, where both convert into the same low density amorphous. Such behavior is also observed in ice. While at high pressure (∼20 GPa), HDA is less stable than VHDA, at the pressure of 10 GPa both forms exhibit similar stability. On the other hand, at much lower pressure (∼5 GPa), HDA and VHDA are no longer the most stable forms, and, upon isobaric annealing, an even less dense form of amorphous silicon emerges, the expanded high density amorphous, again in close similarity to what occurs in ice. PMID:26203030

  13. The influence of subtemperate sliding on the formation of temperate ice in ice stream margins

    NASA Astrophysics Data System (ADS)

    Haseloff, M.; Schoof, C.; Gagliardini, O.

    2015-12-01

    The Siple Coast ice streams are regions of ice that move significantly faster than surrounding ice. Their fast velocities are facilitated by a water-saturated bed, while the bed of the adjacent regions is frozen. The transition between these two regimes takes place in the ice stream margin, where the fast flow transitions to the slow flow of the surrounding regions, resulting in locally high shear stresses and heat dissipation rates. Previous research has shown that this can lead to the formation of temperate ice in the ice stream margin and to outward migration of this margin. Typically, the transition between the frozen and temperate bed is modelled as a no slip to free slip transition. However, this assumption introduces singular stresses at the transition point and neglects the possibility that high stresses or residual water films on the subtemperate side of the bed can lead to subtemperate sliding, as has been observed in other glaciological settings. In this study, we investigate how subtemperate sliding affects the formation of temperate ice in ice stream margins and the migration of these margins. By analysing the boundary layer structure in the margin, we derive asymptotic solutions for the migration speed and quantify its dependence on properties that are available in continental-scale ice sheet models.

  14. Creating Arctic Sea Ice Protected Areas?

    NASA Astrophysics Data System (ADS)

    Pfirman, S.; Hoff, K.; Temblay, B.; Fowler, C.

    2008-12-01

    As Arctic sea ice retreats and the Northwest Passage and Northern Sea Route open, the Arctic will experience more extensive human activity than it has ever encountered before. New development will put pressure on a system already struggling to adapt to a changing environment. In this analysis, locations are identified within the Arctic that could be protected from resource extraction, transportation and other development in order to create refuges and protect remnants of sea ice habitat, as the Arctic transitions to ice-free summer conditions. Arctic sea ice forms largely along the Siberian and Alaskan coasts and is advected across the North Pole towards Fram Strait, the Canadian Archipelago and the Barents Sea. In addition to the future loss of ice itself, contaminants entrained in sea ice in one part of the ocean can affect other regions as the ice drifts. Using observations and models of sea ice origins, trajectories and ages, we track sea ice from its origins towards marginal ice zones, mapping pathways and termination locations. Critical sea ice source areas and collection regions are identified with the goal of aiding in the protection of the remaining Arctic sea ice habitat for as long as possible.

  15. Observation of viscosity transition in α-pinene secondary organic aerosol

    NASA Astrophysics Data System (ADS)

    Järvinen, E.; Ignatius, K.; Nichman, L.; Kristensen, T. B.; Fuchs, C.; Höppel, N.; Corbin, J. C.; Craven, J.; Duplissy, J.; Ehrhart, S.; El Haddad, I.; Frege, C.; Gates, S. J.; Gordon, H.; Hoyle, C. R.; Jokinen, T.; Kallinger, P.; Kirkby, J.; Kiselev, A.; Naumann, K.-H.; Petäjä, T.; Pinterich, T.; Prevot, A. S. H.; Saathoff, H.; Schiebel, T.; Sengupta, K.; Simon, M.; Tröstl, J.; Virtanen, A.; Vochezer, P.; Vogt, S.; Wagner, A. C.; Wagner, R.; Williamson, C.; Winkler, P. M.; Yan, C.; Baltensperger, U.; Donahue, N. M.; Flagan, R. C.; Gallagher, M.; Hansel, A.; Kulmala, M.; Stratmann, F.; Worsnop, D. R.; Möhler, O.; Leisner, T.; Schnaiter, M.

    2015-10-01

    Under certain conditions, secondary organic aerosol (SOA) particles can exist in the atmosphere in an amorphous solid or semi-solid state. To determine their relevance to processes such as ice nucleation or chemistry occurring within particles requires knowledge of the temperature and relative humidity (RH) range for SOA to exist in these states. In the CLOUD experiment at CERN, we deployed a new in-situ optical method to detect the viscosity of α-pinene SOA particles and measured their transition from the amorphous viscous to liquid state. The method is based on the depolarising properties of laboratory-produced non-spherical SOA particles and their transformation to non-depolarising spherical liquid particles during deliquescence. We found that particles formed and grown in the chamber developed an asymmetric shape through coagulation. A transition to spherical shape was observed as the RH was increased to between 35 % at -10 °C and 80 % at -38 °C, confirming previous calculations of the viscosity transition conditions. Consequently, α-pinene SOA particles exist in a viscous state over a wide range of ambient conditions, including the cirrus region of the free troposphere. This has implications for the physical, chemical and ice-nucleation properties of SOA and SOA-coated particles in the atmosphere.

  16. Observation of viscosity transition in α-pinene secondary organic aerosol

    NASA Astrophysics Data System (ADS)

    Järvinen, Emma; Ignatius, Karoliina; Nichman, Leonid; Kristensen, Thomas B.; Fuchs, Claudia; Hoyle, Christopher R.; Höppel, Niko; Corbin, Joel C.; Craven, Jill; Duplissy, Jonathan; Ehrhart, Sebastian; El Haddad, Imad; Frege, Carla; Gordon, Hamish; Jokinen, Tuija; Kallinger, Peter; Kirkby, Jasper; Kiselev, Alexei; Naumann, Karl-Heinz; Petäjä, Tuukka; Pinterich, Tamara; Prevot, Andre S. H.; Saathoff, Harald; Schiebel, Thea; Sengupta, Kamalika; Simon, Mario; Slowik, Jay G.; Tröstl, Jasmin; Virtanen, Annele; Vochezer, Paul; Vogt, Steffen; Wagner, Andrea C.; Wagner, Robert; Williamson, Christina; Winkler, Paul M.; Yan, Chao; Baltensperger, Urs; Donahue, Neil M.; Flagan, Rick C.; Gallagher, Martin; Hansel, Armin; Kulmala, Markku; Stratmann, Frank; Worsnop, Douglas R.; Möhler, Ottmar; Leisner, Thomas; Schnaiter, Martin

    2016-04-01

    Under certain conditions, secondary organic aerosol (SOA) particles can exist in the atmosphere in an amorphous solid or semi-solid state. To determine their relevance to processes such as ice nucleation or chemistry occurring within particles requires knowledge of the temperature and relative humidity (RH) range for SOA to exist in these states. In the Cosmics Leaving Outdoor Droplets (CLOUD) experiment at The European Organisation for Nuclear Research (CERN), we deployed a new in situ optical method to detect the viscous state of α-pinene SOA particles and measured their transition from the amorphous highly viscous state to states of lower viscosity. The method is based on the depolarising properties of laboratory-produced non-spherical SOA particles and their transformation to non-depolarising spherical particles at relative humidities near the deliquescence point. We found that particles formed and grown in the chamber developed an asymmetric shape through coagulation. A transition to a spherical shape was observed as the RH was increased to between 35 % at -10 °C and 80 % at -38 °C, confirming previous calculations of the viscosity-transition conditions. Consequently, α-pinene SOA particles exist in a viscous state over a wide range of ambient conditions, including the cirrus region of the free troposphere. This has implications for the physical, chemical, and ice-nucleation properties of SOA and SOA-coated particles in the atmosphere.

  17. Molecular dynamics simulation of amorphous indomethacin.

    PubMed

    Xiang, Tian-Xiang; Anderson, Bradley D

    2013-01-01

    Molecular dynamics (MD) simulations have been conducted using an assembly consisting of 105 indomethacin (IMC) molecules and 12 water molecules to investigate the underlying dynamic (e.g., rotational and translational diffusivities and conformation relaxation rates) and structural properties (e.g., conformation, hydrogen-bonding distributions, and interactions of water with IMC) of amorphous IMC. These properties may be important in predicting physical stability of this metastable material. The IMC model was constructed using X-ray diffraction data with the force-field parameters mostly assigned by analogy with similar groups in Amber-ff03 and atomic charges calculated with the B3LYP/ccpVTZ30, IEFPCM, and RESP models. The assemblies were initially equilibrated in their molten state and cooled through the glass transition temperature to form amorphous solids. Constant temperature dynamic runs were then carried out above and below the T(g) (i.e., at 600 K (10 ns), 400 K (350 ns), and 298 K (240 ns)). The density (1.312 ± 0.003 g/cm(3)) of the simulated amorphous solid at 298 K was close to the experimental value (1.32 g/cm(3)) while the estimated T(g) (384 K) was ~64 degrees higher than the experimental value (320 K) due to the faster cooling rate. Due to the hindered rotation of its amide bond, IMC can exist in different diastereomeric states. Different IMC conformations were sufficiently sampled in the IMC melt or vapor, but transitions occurred rarely in the glass. The hydrogen-bonding patterns in amorphous IMC are more complex in the amorphous state than in the crystalline polymorphs. Carboxylic dimers that are dominant in α- and γ-crystals were found to occur at a much lower probability in the simulated IMC glasses while hydrogen-bonded IMC chains were more easily identified patterns in the simulated amorphous solids. To determine molecular diffusivity, a novel analytical method is proposed to deal with the non-Einsteinian behavior, in which the temporal

  18. Ancient ice streams and their megalineated beds

    NASA Astrophysics Data System (ADS)

    Eyles, Nick; Ross, Martin

    2016-06-01

    Ice streams are corridors of fast-flowing (~ 800 m yr- 1) ice inset within otherwise sluggish-moving ice sheets. According to reported estimates, as much as 90% of the total discharge of the Antarctic Ice Sheet, for example, occurs through such corridors. Recognition of ice stream records in paleo-ice sheet research has profoundly changed the discipline of glacial geology. The key has been identification of the distinctive corrugated or 'megalineated' geomorphology of their beds, consisting of elongate ridges that are parallel to ice flow direction and often transitional to drumlins. Access to new satellite imagery has enabled mapping of megascale glacial lineations (MSGLs) over large swaths of terrain and the recognition of regional-scale ice stream flow paths and origins. At the peak of the last ice age, just after 20,000 years ago, there were more than 100 ice streams within the Laurentide Ice Sheet. Only now are we beginning to fully appreciate the fundamental role that such streams (which have been called the 'arteries' of ice sheets) have had on glaciated landscapes, by moving enormous volumes of sediment and releasing armadas of floating ice to the Arctic and Atlantic oceans. There is also a growing awareness of the erosional role of ice streams in overdeepening of lakes, fiords and other troughs along coastlines. Much remains to be learnt and new discoveries surely await. The picture of past ice sheets, like the Laurentide and Fennoscandian Ice Sheets, that is emerging today is very different from that of 20 years ago.

  19. Study of thermal conductivity of ice clusters after impact deposition on the silica surfaces using the ReaxFF reactive force field.

    PubMed

    Rahnamoun, A; van Duin, A C T

    2016-01-21

    During aircraft or spacecraft missions, ice accumulates on different parts of their surface elements. An important parameter affecting the ability to remove this ice from the surface is the heat transfer characteristics of the accumulated ice. The ice heat transfer is related to the process of ice formation and its density and internal structure. In this study we investigate the effects of the ice and silica structure and the ice cluster attachment mechanism to the silica surface on the thermal conductivity (TC) of the attached ice cluster using the ReaxFF reactive force field. The purpose of this study is to investigate the thermal transport in amorphous and crystalline ice after high-velocity deposition on the silica surfaces. A dual thermostat method has been applied for the calculation of TC values. The validity of this method has been verified by comparing the calculated values of TC for crystal and amorphous ice with available experimental values. Our calculations show that the TC values of both crystal and amorphous ice drop after deposition on the silica surfaces. This decrease in the TC is more significant for the ice deposition on suboxide silica surfaces. Furthermore, crystal ice shows higher TC values than amorphous ice after accumulation. However, when crystal ice impacts on the silica surface at 1 km s(-1) impact speed, the crystalline shape of the ice cluster is lost to a considerable level and the TC values obtained for the ice clusters in such cases are closer to amorphous ice TC values. We observed a decrease in the TC values when ionic species are added inside the ice clusters. PMID:26670950

  20. Amorphous semiconductor solar cell

    DOEpatents

    Dalal, Vikram L.

    1981-01-01

    A solar cell comprising a back electrical contact, amorphous silicon semiconductor base and junction layers and a top electrical contact includes in its manufacture the step of heat treating the physical junction between the base layer and junction layer to diffuse the dopant species at the physical junction into the base layer.

  1. Amorphous silicon photovoltaic devices

    SciTech Connect

    Carlson, David E.; Lin, Guang H.; Ganguly, Gautam

    2004-08-31

    This invention is a photovoltaic device comprising an intrinsic or i-layer of amorphous silicon and where the photovoltaic device is more efficient at converting light energy to electric energy at high operating temperatures than at low operating temperatures. The photovoltaic devices of this invention are suitable for use in high temperature operating environments.

  2. New Fluid Prevents Railway Ice

    NASA Technical Reports Server (NTRS)

    2001-01-01

    Through a licensing agreement between NASA's Ames Research Center and Midwest Industrial Supply, Inc. (MIS), two MIS products have been enhanced with NASA's anti-icing fluid technology. MIS offers the new fluid in two commercial products, the Zero Gravity(TM) Third Rail Anti-Icer/Deicer and the Ice Free Switch(R). Using NASA's fluid technology, these products form a protective-coating barrier that prevents the buildup of ice and snow. Applying the fluid to the railway components prior to ice or snowstorm works as an anti-icing fluid, remaining in place to melt precipitation as it hits the surface. It also functions as a deicing fluid. If applied to an already frozen switch or rail, it will quickly melt the ice, free the frozen parts, and then remain in place to prevent refreezing. Additional benefits include the ability to cling to vertical rail surfaces and resist the effects of rain and wind. With the Ice Free Switch, it takes only five minutes to treat the switch by spraying, brushing, or pouring on the product. Ice Free Switch requires as little as one gallon per switch whereas other deicing fluids require five to ten gallons of liquid to effectively melt ice. Zero Gravity serves the same anti-icing/deicing purposes but applies fluid to the third rail through a system that is easily installed onto mass transit cars. A tank of fluid and a dispensing system are placed underneath the train car and the fluid is applied as the train runs its route.

  3. Hunting liquid micro-pockets in snow and ice: Phase transition in salt solutions at the bulk and interface with X-ray photoelectron spectroscopy.

    NASA Astrophysics Data System (ADS)

    Bartels-Rausch, Thorsten; Orlando, Fabrizio; Kong, Xiangrui; Waldner, Astrid; Artiglia, Luca; Ammann, Markus; Huthwelker, Thomas

    2016-04-01

    Sea salt, and in particular chloride, is an important reactant in the atmosphere. Chloride in air-borne sea salt aerosol is - once chemically converted to a molecular halogen (Cl2, BrCl) and released to the atmosphere - well known as important atmospheric reactant, driving large-scale changes to the atmospheric composition and in particular to ozone levels in remote areas, but also in coastal mega cities. Similar chemistry has been proposed for sea salt deposits in polar snow covers. A crucial factor determining the overall reactivity is the local physical environment of the chloride ion. For example, the reactivity of liquid aerosols decreases significantly upon crystallization. Surprisingly, the phases of NaCl-containing systems are still under debate, partially due to the limited availability of in situ measurements directly probing the local environment at the surface of frozen NaCl-water binary systems. Using core electron spectroscopy of the oxygen atoms in water, we previously showed that these systems follow the phase rules at the air-ice interface. This finding contrasts some earlier observations, where the presence of liquid below the eutectic point of bulk solutions was postulated. In the present study, we present new electron yield near-edge X-ray absorption fine structure spectroscopy (NEXAFS) data obtained at near-ambient pressures up to 20 mbar of NaCl frozen solutions. The method is sensitive to small changes in the local environment of the chlorine atom. The measurements were performed at the PHOENIX beamline at SLS. The study indicates frapant differences in the phases of NaCl - water mixtures at temperatures blow the freezing point for the surface of the ice vs. the bulk. This has significant impact on modelling chemical reactions in snow or ice and it's environmental consequences.

  4. Operation IceBridge: Sea Ice Interlude

    NASA Video Gallery

    Sea ice comes in an array of shapes and sizes and has its own ephemeral beauty. Operation IceBridge studies sea ice at both poles, and also runs across interesting formations en route to other targ...

  5. Relating C-band Microwave and Optical Satellite Observations as A Function of Snow Thickness on First-Year Sea Ice during the Winter to Summer Transition

    NASA Astrophysics Data System (ADS)

    Zheng, J.; Yackel, J.

    2015-12-01

    The Arctic sea ice and its snow cover have a direct impact on both the Arctic and global climate system through their ability to moderate heat exchange across the ocean-sea ice-atmosphere (OSA) interface. Snow cover plays a key role in the OSA interface radiation and energy exchange, as it controls the growth and decay of first-year sea ice (FYI). However, meteoric accumulation and redistribution of snow on FYI is highly stochastic over space and time, which makes it poorly understood. Previous studies have estimated local-scale snow thickness distributions using in-situ technique and modelling but it is spatially limited and challenging due to logistic difficulties. Moreover, snow albedo is also critical for determining the surface energy balance of the OSA during the critical summer ablation season. Even then, due to persistent and widespread cloud cover in the Arctic at various spatio-temporal scales, it is difficult and unreliable to remotely measure albedo of snow cover on FYI in the optical spectrum. Previous studies demonstrate that only large-scale sea ice albedo was successfully estimated using optical-satellite sensors. However, space-borne microwave sensors, with their capability of all-weather and 24-hour imaging, can provide enhanced information about snow cover on FYI. Daily spaceborne C-band scatterometer data (ASCAT) and MODIS data are used to investigate the the seasonal co-evolution of the microwave backscatter coefficient and optical albedo as a function of snow thickness on smooth FYI. The research focuses on snow-covered FYI near Cambridge Bay, Nunavut (Fig.1) during the winter to advanced-melt period (April-June, 2014). The ACSAT time series (Fig.2) show distinct increase in scattering at melt onset indicating the first occurrence of melt water in the snow cover. The corresponding albedo exhibits no decrease at this stage. We show how the standard deviation of ASCAT backscatter on FYI during winter can be used as a proxy for surface roughness

  6. Phase transitions and convection in icy satellites

    NASA Technical Reports Server (NTRS)

    Bercovici, D.; Schubert, G.; Reynolds, R. T.

    1986-01-01

    The effects of solid-solid phase changes on subsolidus convection in the large icy moons of the outer solar system are considered. Phase transitions affect convection via processes that distort the phase change boundary and/or influence buoyancy through thermal expansion. Linear stability analyses are carried out for ice layers with a phase change at the midplane. Two exothermic phase transitions (ice I - ice II, ice VI - ice VIII) and two endothermic transitions (ice I - ice III, ice II - ice V) are considered. For the exothermic cases, the phase change can either impede or enhance whole-layer convection. For the endothermic cases, the phse change always inhibits whole-layer convective overturn and tends to enforce two-layer convection. These results play some constraints on possible models of icy satellite evolution and structure.

  7. Breakup of Pack Ice, Antarctic Ice Shelf

    NASA Technical Reports Server (NTRS)

    1991-01-01

    Breakup of Pack Ice along the periphery of the Antarctic Ice Shelf (53.5S, 3.0E) produced this mosaic of ice floes off the Antarctic Ice Shelf. Strong offshore winds, probably associated with strong katabatic downdrafts from the interior of the continent, are seen peeling off the edges of the ice shelf into long filamets of sea ice, icebergs, bergy bits and growlers to flow northward into the South Atlantic Ocean. 53.5S, 3.0E

  8. Molecular mobility of the paracetamol amorphous form.

    PubMed

    di Martino, P; Palmieri, G F; Martelli, S

    2000-08-01

    The purpose of this paper is to study the molecular mobility of paracetamol molecules in their amorphous state below the glass transition temperature (Tg) in order to evaluate the thermodynamic driving force which allows the amorphous form to recrystallize under different polymorphic modifications. Samples were aged at temperatures of -15, 0, 6, and 12 degrees C for periods of time from 1 h to a maximum of 360 h. The extent of physical aging was measured by a DSC study of enthalpy recovery in the glass transition region. The onset temperature of glass transition was also determined (Tg). Enthalpy recovery (deltaH) and change in heat capacity (deltaCp) were used to calculate the mean molecular relaxation time constant (tau) using the empirical Kohlausch-Williams-Watts (KWW) equation. Enthalpy recovery and onset glass transition temperature increased gradually with aging and aging temperatures. Structural equilibrium was reached experimentally only at an aging temperature of 12 degrees C (Tg-10 degrees C), according to the deltaH(infinity) results. The experimental model used is appropriate only at lower aging temperatures, while at higher ones the complexity of the system increases and molecular polymorphic arrangement could be involved. When structural equilibrium is experimentally reached, molecules can be arranged in their lowest energy state, and the polymorphic form I formation is the one preferred. PMID:10959571

  9. Ice VII from aqueous salt solutions: From a glass to a crystal with broken H-bonds.

    PubMed

    Klotz, S; Komatsu, K; Pietrucci, F; Kagi, H; Ludl, A-A; Machida, S; Hattori, T; Sano-Furukawa, A; Bove, L E

    2016-01-01

    It has been known for decades that certain aqueous salt solutions of LiCl and LiBr readily form glasses when cooled to below ≈160 K. This fact has recently been exploited to produce a « salty » high-pressure ice form: When the glass is compressed at low temperatures to pressures higher than 4 GPa and subsequently warmed, it crystallizes into ice VII with the ionic species trapped inside the ice lattice. Here we report the extreme limit of salt incorporation into ice VII, using high pressure neutron diffraction and molecular dynamics simulations. We show that high-pressure crystallisation of aqueous solutions of LiCl∙RH2O and LiBr∙RH2O with R = 5.6 leads to solids with strongly expanded volume, a destruction of the hydrogen-bond network with an isotropic distribution of water-dipole moments, as well as a crystal-to-amorphous transition on decompression. This highly unusual behaviour constitutes an interesting pathway from a glass to a crystal where translational periodicity is restored but the rotational degrees of freedom remaining completely random. PMID:27562476

  10. Ice VII from aqueous salt solutions: From a glass to a crystal with broken H-bonds

    PubMed Central

    Klotz, S.; Komatsu, K.; Pietrucci, F.; Kagi, H.; Ludl, A.-A.; Machida, S.; Hattori, T.; Sano-Furukawa, A.; Bove, L. E.

    2016-01-01

    It has been known for decades that certain aqueous salt solutions of LiCl and LiBr readily form glasses when cooled to below ≈160 K. This fact has recently been exploited to produce a « salty » high-pressure ice form: When the glass is compressed at low temperatures to pressures higher than 4 GPa and subsequently warmed, it crystallizes into ice VII with the ionic species trapped inside the ice lattice. Here we report the extreme limit of salt incorporation into ice VII, using high pressure neutron diffraction and molecular dynamics simulations. We show that high-pressure crystallisation of aqueous solutions of LiCl∙RH2O and LiBr∙RH2O with R = 5.6 leads to solids with strongly expanded volume, a destruction of the hydrogen-bond network with an isotropic distribution of water-dipole moments, as well as a crystal-to-amorphous transition on decompression. This highly unusual behaviour constitutes an interesting pathway from a glass to a crystal where translational periodicity is restored but the rotational degrees of freedom remaining completely random. PMID:27562476

  11. Controls on Arctic sea ice from first-year and multi-year survival rates

    SciTech Connect

    Hunke, Jes

    2009-01-01

    The recent decrease in Arctic sea ice cover has transpired with a significant loss of multi year ice. The transition to an Arctic that is populated by thinner first year sea ice has important implications for future trends in area and volume. Here we develop a reduced model for Arctic sea ice with which we investigate how the survivability of first year and multi year ice control the mean state, variability, and trends in ice area and volume.

  12. On the state of water ice on saturn's moon Titan and implications to icy bodies in the outer solar system.

    PubMed

    Zheng, Weijun; Jewitt, David; Kaiser, Ralf I

    2009-10-22

    The crystalline state of water ice in the Solar System depends on the temperature history of the ice and the influence of energetic particles to which it has been exposed. We measured the infrared absorption spectra of amorphous and crystalline water ice in the 10-50 K and 10-140 K temperature ranges, respectively, and conducted a systematic experimental study to investigate the amorphization of crystalline water ice via ionizing radiation irradiation at doses of up to 160 +/- 30 eV per molecule. We found that crystalline water ice can be converted only partially to amorphous ice by electron irradiation. The experiments showed that a fraction of the 1.65 microm band, which is characteristic for crystalline water ice, survived the irradiation, to a degree that strongly depends on the temperature. Quantitative kinetic fits of the temporal evolution of the 1.65 mum band clearly demonstrate that there is a balance between thermal recrystallization and irradiation-induced amorphization, with thermal recrystallizaton dominant at higher temperatures. Our experiments show the amorphization at 40 K was incomplete, in contradiction to Mastrapa and Brown's conclusion (Icarus 2006, 183, 207.). At 50 K, the recrystallization due to thermal effects is strong, and most of the crystalline ice survived. Temperatures of most icy objects in the Solar System, including Jovian satellites, Saturnian satellites (including Titan), and Kuiper Belt Objects, are equal to or above 50 K; this explains why water ice detected on those objects is mostly crystalline. PMID:19827849

  13. Low-temperature relaxations in amorphous polyolefins

    NASA Technical Reports Server (NTRS)

    Hiltner, A.; Baer, E.; Martin, J. R.; Gillham, J. K.

    1974-01-01

    The dynamic mechanical relaxation behavior of two series of amorphous polyolefins, was investigated from 4.2 K to the glass transition. Most of the polymers show a damping maximum or plateau in the 40 to 50 K region. Various mechanisms which have been suggested for cryogenic relaxations in amorphous polymers are considered as they might relate to the polyolefins. Two secondary relaxation processes above 80 K are distinguished. A relaxation at about 160 K (beta) in the second and third member of each series is associated with restricted blackbone motion. This process requires a certain degree of chain flexibility since it is not observed in the first member of each series. A lower temperature process (gamma) is observed in each member of the second series and is attributed to motion of the ethyl side group.

  14. Chromic Mechanism in Amorphous WO3 Films

    SciTech Connect

    Zhang, J. G.; Benson, D. K.; Tracy, C. E.; Deb, S. K.; Czanderna, A. W.

    1997-06-01

    We propose a new model for the chromic mechanism in amorphous tungsten oxide films (WO3-y .cntdot. nH2O). This model not only explains a variety of seemingly conflicting experimental results reported in the literature that cannot be explained by existing models, it also has practical implications with respect to improving the coloring efficiency and durability of electrochromic devices. According to this model, a typical as-deposited tungsten oxide film has tungsten mainly in W6+ and W4+ states and can be represented as W6+(1-y) W4+(y)O(3-y) .cntdot. nH2O. The proposed chromic mechanism is based on the small polaron transition between the charge-induced W5+ state and the orignial W4+ state insteasd of the W5+ and W6+ states as suggested in previous models. The correlation between the electrochromic and photochromic behavior in amorphous tungsten oxide films is also discussed.

  15. Controls on Arctic sea ice from first-year and multi-year ice survival rates

    NASA Astrophysics Data System (ADS)

    Armour, K.; Bitz, C. M.; Hunke, E. C.; Thompson, L.

    2009-12-01

    The recent decrease in Arctic sea ice cover has transpired with a significant loss of multi-year (MY) ice. The transition to an Arctic that is populated by thinner first-year (FY) sea ice has important implications for future trends in area and volume. We develop a reduced model for Arctic sea ice with which we investigate how the survivability of FY and MY ice control various aspects of the sea-ice system. We demonstrate that Arctic sea-ice area and volume behave approximately as first-order autoregressive processes, which allows for a simple interpretation of September sea-ice in which its mean state, variability, and sensitivity to climate forcing can be described naturally in terms of the average survival rates of FY and MY ice. This model, used in concert with a sea-ice simulation that traces FY and MY ice areas to estimate the survival rates, reveals that small trends in the ice survival rates explain the decline in total Arctic ice area, and the relatively larger loss of MY ice area, over the period 1979-2006. Additionally, our model allows for a calculation of the persistence time scales of September area and volume anomalies. A relatively short memory time scale for ice area (~ 1 year) implies that Arctic ice area is nearly in equilibrium with long-term climate forcing at all times, and therefore observed trends in area are a clear indication of a changing climate. A longer memory time scale for ice volume (~ 5 years) suggests that volume can be out of equilibrium with climate forcing for long periods of time, and therefore trends in ice volume are difficult to distinguish from its natural variability. With our reduced model, we demonstrate the connection between memory time scale and sensitivity to climate forcing, and discuss the implications that a changing memory time scale has on the trajectory of ice area and volume in a warming climate. Our findings indicate that it is unlikely that a “tipping point” in September ice area and volume will be

  16. Amorphous silicon radiation detectors

    DOEpatents

    Street, R.A.; Perez-Mendez, V.; Kaplan, S.N.

    1992-11-17

    Hydrogenated amorphous silicon radiation detector devices having enhanced signal are disclosed. Specifically provided are transversely oriented electrode layers and layered detector configurations of amorphous silicon, the structure of which allow high electric fields upon application of a bias thereby beneficially resulting in a reduction in noise from contact injection and an increase in signal including avalanche multiplication and gain of the signal produced by incoming high energy radiation. These enhanced radiation sensitive devices can be used as measuring and detection means for visible light, low energy photons and high energy ionizing particles such as electrons, x-rays, alpha particles, beta particles and gamma radiation. Particular utility of the device is disclosed for precision powder crystallography and biological identification. 13 figs.

  17. Amorphous silicon radiation detectors

    DOEpatents

    Street, Robert A.; Perez-Mendez, Victor; Kaplan, Selig N.

    1992-01-01

    Hydrogenated amorphous silicon radiation detector devices having enhanced signal are disclosed. Specifically provided are transversely oriented electrode layers and layered detector configurations of amorphous silicon, the structure of which allow high electric fields upon application of a bias thereby beneficially resulting in a reduction in noise from contact injection and an increase in signal including avalanche multiplication and gain of the signal produced by incoming high energy radiation. These enhanced radiation sensitive devices can be used as measuring and detection means for visible light, low energy photons and high energy ionizing particles such as electrons, x-rays, alpha particles, beta particles and gamma radiation. Particular utility of the device is disclosed for precision powder crystallography and biological identification.

  18. ICE AND DUST IN THE PRESTELLAR DARK CLOUD LYNDS 183: PREPLANETARY MATTER AT THE LOWEST TEMPERATURES

    SciTech Connect

    Whittet, D. C. B.; Poteet, C. A.; Bajaj, V. M.; Horne, D.; Chiar, J. E.; Pagani, L.; Shenoy, S. S.; Adamson, A. J.

    2013-09-10

    Dust grains are nucleation centers and catalysts for the growth of icy mantles in quiescent interstellar clouds, the products of which may accumulate into preplanetary matter when new stars and solar systems form within the clouds. In this paper, we present the first spectroscopic detections of silicate dust and the molecular ices H{sub 2}O, CO, and CO{sub 2} in the vicinity of the prestellar core L183 (L134N). An infrared photometric survey of the cloud was used to identify reddened background stars, and we present spectra covering solid-state absorption features in the wavelength range 2-20 {mu}m for nine of them. The mean composition of the ices in the best-studied line of sight (toward J15542044-0254073) is H{sub 2}O:CO:CO{sub 2} Almost-Equal-To 100:40:24. The ices are amorphous in structure, indicating that they have been maintained at low temperature ({approx}< 15 K) since formation. The ice column density N(H{sub 2}O) correlates with reddening by dust, exhibiting a threshold effect that corresponds to the transition from unmantled grains in the outer layers of the cloud to ice-mantled grains within, analogous to that observed in other dark clouds. A comparison of results for L183 and the Taurus and IC 5146 dark clouds suggests common behavior, with mantles first appearing in each case at a dust column corresponding to a peak optical depth {tau}{sub 9.7} = 0.15 {+-} 0.03 in the silicate feature. Our results support a previous conclusion that the color excess E{sub J-K} does not obey a simple linear correlation with the total dust column in lines of sight that intercept dense clouds. The most likely explanation is a systematic change in the optical properties of the dust as the density increases.

  19. Search for the First-Order Liquid-to-Liquid Phase Transition in Low-Temperature Confined Water by Neutron Scattering

    SciTech Connect

    Chen, Sow-Hsin; Wang, Zhe; Kolesnikov, Alexander I; Zhang, Yang; Liu, Kao-Hsiang

    2013-01-01

    It has been conjectured that a 1st order liquid-to-liquid (L-L) phase transition (LLPT) between high density liquid (HDL) and low density liquid (LDL) in supercooled water may exist, as a thermodynamic extension to the liquid phase of the 1st order transition established between the two bulk solid phases of amorphous ice, the high density amorphous ice (HDA) and the low density amorphous ice (LDA). In this paper, we first recall our previous attempts to establish the existence of the 1st order L-L phase transition through the use of two neutron scattering techniques: a constant Q elastic diffraction study of isobaric temperature scan of the D2O density, namely, the equation of state (EOS) measurements. A pronounced density hysteresis phenomenon in the temperature scan of the density above P = 1500 bar is observed which gives a plausible evidence of crossing the 1st order L-L phase transition line above this pressure; an incoherent quasi-elastic scattering measurements of temperature-dependence of the alpha-relaxation time of H2O at a series of pressures, namely, the study of the Fragile-to-Strong dynamic crossover (FSC) phenomenon as a function of pressure which we interpreted as the results of crossing the Widom line in the one-phase region. In this new experiment, we used incoherent inelastic neutron scattering (INS) to measure the density of states (DOS) of H atoms in H2O molecules in confined water as function of temperature and pressure, through which we may be able to follow the emergence of the LDL and HDL phases at supercooled temperature and high pressures. We here report for the first time the differences of librational and translational DOSs between the hypothetical HDL and LDL phases, which are similar to the corresponding differences between the well-established HDA and LDA ices. This is plausible evidence that the HDL and LDL phases are the thermodynamic extensions of the corresponding amorphous solid water HDA and LDA ices.

  20. Search for the first-order liquid-to-liquid phase transition in low-temperature confined water by neutron scattering

    NASA Astrophysics Data System (ADS)

    Chen, Sow-Hsin; Wang, Zhe; Kolesnikov, Alexander I.; Zhang, Yang; Liu, Kao-Hsiang

    2013-02-01

    It has been conjectured that a 1st order liquid-to-liquid (L-L) phase transition (LLPT) between high density liquid (HDL) and low density liquid (LDL) in supercooled water may exist, as a thermodynamic extension to the liquid phase of the 1st order transition established between the two bulk solid phases of amorphous ice, the high density amorphous ice (HDA) and the low density amorphous ice (LDA). In this paper, we first recall our previous attempts to establish the existence of the 1st order L-L phase transition through the use of two neutron scattering techniques: a constant Q elastic diffraction study of isobaric temperature scan of the D2O density, namely, the equation of state (EOS) measurements. A pronounced density hysteresis phenomenon in the temperature scan of the density above P = 1500 bar is observed which gives a plausible evidence of crossing the 1st order L-L phase transition line above this pressure; an incoherent quasi-elastic scattering measurements of temperature-dependence of the α-relaxation time of H2O at a series of pressures, namely, the study of the Fragile-to-Strong dynamic crossover (FSC) phenomenon as a function of pressure which we interpreted as the results of crossing the Widom line in the one-phase region. In this new experiment, we used incoherent inelastic neutron scattering (INS) to measure the density of states (DOS) of H atoms in H2O molecules in confined water as function of temperature and pressure, through which we may be able to follow the emergence of the LDL and HDL phases at supercooled temperature and high pressures. We here report for the first time the differences of librational and translational DOSs between the hypothetical HDL and LDL phases, which are similar to the corresponding differences between the well-established HDA and LDA ices. This is plausible evidence that the HDL and LDL phases are the thermodynamic extensions of the corresponding amorphous solid water HDA and LDA ices.

  1. Free energy contributions and structural characterization of stacking disordered ices.

    PubMed

    Hudait, Arpa; Qiu, Siwei; Lupi, Laura; Molinero, Valeria

    2016-04-14

    Crystallization of ice from deeply supercooled water and amorphous ices - a process of fundamental importance in the atmosphere, interstellar space, and cryobiology - results in stacking disordered ices with a wide range of metastabilities with respect to hexagonal ice. The structural origin of this high variability, however, has not yet been elucidated. Here we use molecular dynamics simulations with the mW water model to characterize the structure of ice freshly grown from supercooled water at temperatures from 210 to 270 K, the thermodynamics of stacking faults, line defects, and interfaces, and to elucidate the interplay between kinetics and thermodynamics in determining the structure of ice. In agreement with experiments, the ice grown in the simulations is stacking disordered with a random distribution of cubic and hexagonal layers, and a cubicity that decreases with growth temperature. The former implies that the cubicity of ice is determined by processes at the ice/liquid interface, without memory of the structure of buried ice layers. The latter indicates that the probability of building a cubic layer at the interface decreases upon approaching the melting point of ice, which we attribute to a more efficient structural equilibration of ice at the liquid interface as the driving force for growth wanes. The free energy cost for creating a pair of cubic layers in ice is 8.0 J mol(-1) in experiments, and 9.7 ± 1.9 J mol(-1) for the mW water model. This not only validates the simulations, but also indicates that dispersion in cubicity is not sufficient to explain the large energetic variability of stacking disordered ices. We compute the free energy cost of stacking disorder, line defects, and interfaces in ice and conclude that a characterization of the density of these defects is required to predict the degree of metastability and vapor pressure of atmospheric ices. PMID:26983558

  2. Effect of counterions on the properties of amorphous atorvastatin salts.

    PubMed

    Sonje, Vishal M; Kumar, Lokesh; Puri, Vibha; Kohli, Gunjan; Kaushal, Aditya M; Bansal, Arvind K

    2011-11-20

    Amorphous systems have gained importance as a tool for addressing delivery challenges of poorly water soluble drugs. A careful assessment of thermodynamic and kinetic behavior of amorphous form is necessary for successful use of amorphous form in drug delivery. The present study was undertaken to evaluate effect of monovalent sodium (Na(+); ATV Na), and bivalent calcium (Ca(2+); ATV Ca) and magnesium (Mg(2+); ATV Mg) counterions on properties of amorphous salts of atorvastatin (ATV) model drug. Amorphous form was generated from crystalline salts of ATV by spray drying, and characterized for glass transition temperature (T(g)), fragility and devitrification tendency. In addition, chemical stability of the amorphous salt forms was evaluated. Fragility was studied by calculating activation enthalpy for structural relaxation at T(g), from heating rate dependency of T(g). Density functional theory and relative pK(a)'s of counterions were evaluated to substantiate trend in glass transition temperature. T(g) of salts followed order: ATV Ca>ATV Mg>ATV Na. All salts were fragile to moderately fragile, with D value ranging between 9 and 16. Ease of devitrification followed the order: ATV Na∼ATV Mg≫ATV Ca, using isothermal crystallization and reduced crystallization temperature method. Chemical stability at 80°C showed higher degradation of amorphous ATV Ca (∼5%), while ATV Na and ATV Mg showed degradation of 1-2%. Overall, ATV Ca was better in terms of glass forming ability, higher T(g) and physical stability. The study has importance in selection of a suitable amorphous form, during early drug development phase. PMID:21907794

  3. Ice friction: Role of non-uniform frictional heating and ice premelting

    NASA Astrophysics Data System (ADS)

    Persson, B. N. J.

    2015-12-01

    The low friction of ice is usually attributed to the formation of a thin water film due to melting of ice by frictional heating. Melting of ice is a first order phase transition where physical quantities like mass density, the elastic modulus or the shear strength changes abruptly at the transition temperature. Thus, one may expect the friction coefficient to change abruptly at some characteristic sliding speed, when the melt water film is produced. We show that taking into account that, due to non-uniform frictional heating, melting does not occur simultaneously in all the ice contact regions, the transition is not abrupt but still more rapid (as a function of sliding speed) than observed experimentally. The slower than expected drop in the friction with increasing sliding speed may be a consequence of the following paradoxical phenomena: before the melt-water film is formed, the friction of ice is high and a large frictional heating occur which may result in the melting of the ice. If a thin (nanometer) water film would form, the friction becomes low which results in small frictional heating and the freezing of the water film. This suggests a region in sliding speed where a thin (nanometer) surface layer of the ice may be in a mixed state with small ice-like and water-like domains, which fluctuate rapidly in space and time. Alternatively, and more likely, heat-softening of the ice may occur resulting in a thin, statistically homogeneous (in the lateral direction) layer of disordered ice, with a shear strength which decreases continuously as the ice surface temperature approaches the bulk melting temperature. This layer could be related to surface premelting of ice. Using a phenomenological expression for the frictional shear stress, I show that the calculated ice friction is in good agreement with experimental observations.

  4. Large-Scale Surveys of Snow Depth on Arctic Sea Ice from Operation IceBridge

    NASA Technical Reports Server (NTRS)

    Kurtz, Nathan T.; Farrell, Sinead L.

    2011-01-01

    We show the first results of a large ]scale survey of snow depth on Arctic sea ice from NASA fs Operation IceBridge snow radar system for the 2009 season and compare the data to climatological snow depth values established over the 1954.1991 time period. For multiyear ice, the mean radar derived snow depth is 33.1 cm and the corresponding mean climatological snow depth is 33.4 cm. The small mean difference suggests consistency between contemporary estimates of snow depth with the historical climatology for the multiyear ice region of the Arctic. A 16.5 cm mean difference (climatology minus radar) is observed for first year ice areas suggesting that the increasingly seasonal sea ice cover of the Arctic Ocean has led to an overall loss of snow as the region has transitioned away from a dominantly multiyear ice cover.

  5. Thermomechanical behavior of amorphous tactic methacrylate polymers

    NASA Technical Reports Server (NTRS)

    Kiran, E.; Gillham, J. K.; Gipstein, E.

    1974-01-01

    Dynamic mechanical spectra of amorphous stereoregular poly(methyl methacrylate)s and poly(t-butyl methacrylate)s with assigned microtacticities are presented and discussed. An intermolecular argument is invoked to account for the higher glass transition temperature of syndiotactic vis a vis isotactic PMMA, in spite of the higher density of the latter at 30 C. An argument is presented to show that the ratio of glassy-region relaxation temperature to glass transition temperature is not only a measure of the degree of coupling of the beta and glass transition processes, but also of the degree to which intermolecular factors influence these processes. The greater extent of the low-temperature irreversibilities observed in the thermomechanical spectra of poly(t-butyl methacrylate)s is attributed to the brittle character induced by the bulky side groups which presumably weaken cohesive forces.

  6. Interstellar ice analogs: band strengths of H2O, CO2, CH3OH, and NH3 in the far-infrared region

    NASA Astrophysics Data System (ADS)

    Giuliano, B. M.; Escribano, R. M.; Martín-Doménech, R.; Dartois, E.; Muñoz Caro, G. M.

    2014-05-01

    Context. Whereas observational astronomy now routinely extends to the far-infrared region of the spectrum, systematic laboratory studies are sparse. In particular, experiments on laboratory analogs performed through the years have provided information mainly about the band positions and shapes, while information about the band strengths are scarce and derivable principally from the optical constants. Aims: We measure the band strengths in the far-infrared region of interstellar ice analogs of astrophysically relevant species, such as H2O, CO2, CH3OH, and NH3, deposited at low temperature (8-10 K), followed by warm-up, to induce amorphous-crystalline phase transitions when relevant. Methods: The spectra of pure H2O, NH3, and CH3OH ices have been measured in the near-, mid- and far-infrared spectroscopic regions using the Interstellar Astrochemistry Chamber (ISAC) ultra-high-vacuum setup. In addition, far-infrared spectra of NH3 and CO2 were measured using a different set-up equipped with a bolometer detector. Band strengths in the far-infrared region were estimated using the corresponding near- and mid-infrared values as a reference. We also performed theoretical calculations of the amorphous and crystalline structures of these molecules using solid state computational programs at density functional theory (DFT) level. Vibrational assignment and mode intensities for these ices were predicted. Results: Infrared band strengths in the 25-500 μm range have been determined for the considered ice samples by direct comparison in the near- and mid-infrared regions. Our values were compared to those we calculated from the literature complex index of refraction. We found differences of a factor of two between the two sets of values. Conclusions: The calculated far-infrared band strengths provide a benchmark for interpreting the observational data from future space telescope missions, allowing the estimation of the ice column densities.

  7. The structural changes of water ice I during warmup

    NASA Technical Reports Server (NTRS)

    Jenniskens, Peter; Blake, David F.

    1994-01-01

    The polymorph transitions of vapor deposited water ice I during warmup from 15 K to 210 K was mapped by means of selected area electron diffraction. The polymorph transitions account for many phenomena observed in laboratory analog studies of cometary outgassing and radial diffusion in UV photolyzed interstellar ices.

  8. Small-angle neutron scattering study of micropore collapse in amorphous solid water.

    PubMed

    Mitterdorfer, Christian; Bauer, Marion; Youngs, Tristan G A; Bowron, Daniel T; Hill, Catherine R; Fraser, Helen J; Finney, John L; Loerting, Thomas

    2014-08-14

    Vapor-deposited amorphous solid water (ASW) is the most abundant solid molecular material in space, where it plays a direct role in both the formation of more complex chemical species and the aggregation of icy materials in the earliest stages of planet formation. Nevertheless, some of its low temperature physics such as the collapse of the micropore network upon heating are still far from being understood. Here we characterize the nature of the micropores and their collapse using neutron scattering of gram-quantities of D2O-ASW of internal surface areas up to 230 ± 10 m(2) g(-1) prepared at 77 K. The model-free interpretation of the small-angle scattering data suggests micropores, which remain stable up to 120-140 K and then experience a sudden collapse. The exact onset temperature to pore collapse depends on the type of flow conditions employed in the preparation of ASW and, thus, the specific surface area of the initial deposit, whereas the onset of crystallization to cubic ice is unaffected by the flow conditions. Analysis of the small-angle neutron scattering signal using the Guinier-Porod model suggests that a sudden transition from three-dimensional cylindrical pores with 15 Å radius of gyration to two-dimensional lamellae is the mechanism underlying the pore collapse. The rather high temperature of about 120-140 K of micropore collapse and the 3D-to-2D type of the transition unraveled in this study have implications for our understanding of the processing and evolution of ices in various astrophysical environments. PMID:24963740

  9. Neutron diffraction study of the interaction of iron with amorphous fullerite

    NASA Astrophysics Data System (ADS)

    Borisova, P. A.; Agafonov, S. S.; Blanter, M. S.; Somenkov, V. A.

    2014-01-01

    The amorphous fullerite C60 has been prepared by mechanical activation (grinding in a ball mill), and its interaction with iron during sintering of powders with 0-95 at % Fe has been studied. After sintering in the range 800-1200°C under a pressure of 70 MPa, the samples have nonequilibrium structures different from the structures of both annealed and quenched steels. In this case, the carbon phase, i.e., amorphous fullerite, undergoes a polyamorphous transition to amorphous graphite. It has also been shown that the interaction of amorphous fullerite with iron is weaker compared to crystalline fullerite or crystalline graphite.

  10. Growth induced magnetic anisotropy in crystalline and amorphous thin films

    SciTech Connect

    Hellman, F.

    1998-07-20

    The work in the past 6 months has involved three areas of magnetic thin films: (1) amorphous rare earth-transition metal alloys, (2) epitaxial Co-Pt and Ni-Pt alloy thin films, and (3) collaborative work on heat capacity measurements of magnetic thin films, including nanoparticles and CMR materials. A brief summary of work done in each area is given.

  11. Laboratory Spectroscopy of Ices of Astrophysical Interest

    NASA Technical Reports Server (NTRS)

    Hudson, Reggie; Moore, M. H.

    2011-01-01

    Ongoing and future NASA and ESA astronomy missions need detailed information on the spectra of a variety of molecular ices to help establish the identity and abundances of molecules observed in astronomical data. Examples of condensed-phase molecules already detected on cold surfaces include H2O, CO, CO2, N2, NH3, CH4, SO2, O2, and O3. In addition, strong evidence exists for the solid-phase nitriles HCN, HC3N, and C2N2 in Titan's atmosphere. The wavelength region over which these identifications have been made is roughly 0.5 to 100 micron. Searches for additional features of complex carbon-containing species are in progress. Existing and future observations often impose special requirements on the information that comes from the laboratory. For example, the measurement of spectra, determination of integrated band strengths, and extraction of complex refractive indices of ices (and icy mixtures) in both amorphous and crystalline phases at relevant temperatures are all important tasks. In addition, the determination of the index of refraction of amorphous and crystalline ices in the visible region is essential for the extraction of infrared optical constants. Similarly, the measurement of spectra of ions and molecules embedded in relevant ices is important. This laboratory review will examine some of the existing experimental work and capabilities in these areas along with what more may be needed to meet current and future NASA and ESA planetary needs.

  12. Superconducting state parameters of amorphous metals

    NASA Astrophysics Data System (ADS)

    Vora, Aditya M.

    2007-07-01

    The theoretical computation of the superconducting state parameters (SSP) viz; electron-phonon coupling strength λ, Coulomb pseudopotential μ∗, transition temperature TC, isotope effect exponent α and effective interaction strength N0V of some monovalent (Li, Na, K, Rb and Cs), divalent (Mg, Zn, Be, Cd and Hg) and polyvalent (In, Tl, Ga, Al, La, Sn, Pb, Ti, Zr, Th, Bi, Nb and W) amorphous metals have been carried out by well known Ashcroft’s empty core (EMC) model pseudopotential. We have employed here five different types of local field correction functions proposed by Hartree (H), Taylor (T), Ichimaru-Utsumi (IU), Farid et al. (F) and Sarkar et al. (S) to study the exchange and correlation effects on the present investigations. The SSP for Be, Cd, Ga, Al, La, Ti, Zr, Th, Nb and W amorphous metals are reported first time in the present study. A very strong influence of all the exchange and correlation functions is found in the present study. Our results are in fair agreement with other available theoretical as well as experimental data. A strong dependency of the SSP of amorphous metals on the valency Z is found.

  13. Ethane Ices in the Outer Solar System: Spectroscopy and Chemistry

    NASA Technical Reports Server (NTRS)

    Hudson, R. L.; Moore, M. H.; Raines, L. L.

    2009-01-01

    We report recent experiments on ethane ices made at temperatures applicable to the outer Solar System. New near- and mid-infrared data for crystalline and amorphous ethane, including new spectra for a seldom-studied solid phase that exists at 35-55 K, are presented along with radiation-chemical experiments showing the formation of more-complex hydrocarbons,

  14. Solar radiation interactions with seasonal sea ice

    NASA Astrophysics Data System (ADS)

    Ehn, Jens Kristian

    Presently, the Arctic Ocean is undergoing an escalating reduction in sea ice and a transition towards a seasonal sea ice environment. This warrants detailed investigations into improving our understanding of the seasonal evolution of sea ice and snow covers, and their representation in climate models. The interaction of solar radiation with sea ice is an important process influencing the energy balance and biological activity in polar seas, and consequently plays a key role in the earth's climate system. This thesis focuses on characterization of the optical properties---and the underlying physical properties that determine them---of seasonal sea ice during the fall freeze-up and the spring melt periods. Both periods display high spatial heterogeneity and rapid temporal changes in sea ice properties, and are therefore poorly understood. Field data were collected in Amundsen Gulf/Franklin Bay (FB), southern-eastern Beaufort Sea, in Oct.-Nov. 2003 and Apr. 2004 and in Button Bay (BB), western Hudson Bay, in Mar.-May 2005 to address (1) the temporal and spatial evolution of surface albedo and transmittance, (2) how radiative transfer in sea ice is controlled by its physical nature, and (3) the characteristics of the bottom ice algae community and its effect on the optical properties. The fall study showed the importance of surface features such as dry or slushy bare ice, frost flowers and snow cover in determining the surface albedo. Ice thickness was also important, however, mostly because surface features were associated with thickness. For example, nilas (<10 cm thick) was typically not covered by a snow layer as snow grains were dissolved or merged with the salty and warm brine skim layer on the surface, while surface conditions on thicker ice types were cold and dry enough to support a snow cover. In general, the surface albedo increased exponentially with an ice thickness increase, however, variability within ice thickness types were very large. It is apparent

  15. Stabilization of amorphous structure in silicon thin film by adding germanium

    SciTech Connect

    Makino, Nobuaki; Shigeta, Yukichi

    2015-06-21

    The stabilization of the amorphous structure in amorphous silicon film by adding Ge atoms was studied using Raman spectroscopy. Amorphous Si{sub 1−x}Ge{sub x} (x = 0.0, 0.03, 0.14, and 0.27) films were deposited on glass substrates from electron beam evaporation sources and annealed in N{sub 2} atmosphere. The change in the amorphous states and the phase transition from amorphous to crystalline were characterized using the TO, LO, and LA phonons in the Raman spectra. The temperature of the transition from the amorphous phase to the crystalline phase was higher for the a-Si{sub 1−x}Ge{sub x} (x = 0.03, 0.14) films, and the crystallization was hindered. The reason why the addition of a suitable quantity of Ge atoms into the three-dimensional amorphous silicon network stabilizes its amorphous structure is discussed based on the changes in the Raman signals of the TO, LO, and LA phonons during annealing. The characteristic bond length of the Ge atoms allows them to stabilize the random network of the amorphous Si composed of quasi-tetrahedral Si units, and obstruct its rearrangement.

  16. Reversible Avalanches and Criticality in Amorphous Solids

    NASA Astrophysics Data System (ADS)

    Reichhardt, Charles

    2015-03-01

    Despite its importance for basic science and industry, the physical process that causes a solid to change its shape permanently under external deformation is still not well understood. In this paper we use molecular dynamics simulations of amorphous solids under oscillatory shear to study this phenomenon, and show that at a critical strain amplitude, the size of the cooperative atomic motion that allows for a permanent deformation diverges. We compare this non-equilibrium critical behavior to that of a ``front depinning'' transition. This viewpoint, based on fluctuations and statistics, is complementary to the dynamical ``transition to chaos'' which was previously identified at the same strain amplitude. Below this irreversibile-depinning transition, we observe large avalanches which are completely repetitive with each shear strain cycle. This suggests that while avalanches on their own do not cause irreversible deformation, it is likely that the irreversibility transition and the ``depinning-like'' transition are two aspects of the same phenomena. One implication is that the transition could be detected before the onset of irreversible flow by an analysis of the power spectra of avalanches. Work done in collaboration with Ido Regev, Karin Dahmen, John Weber, and Turab Lookman.

  17. Heavy ion irradiation of crystalline water ice. Cosmic ray amorphisation cross-section and sputtering yield

    NASA Astrophysics Data System (ADS)

    Dartois, E.; Augé, B.; Boduch, P.; Brunetto, R.; Chabot, M.; Domaracka, A.; Ding, J. J.; Kamalou, O.; Lv, X. Y.; Rothard, H.; da Silveira, E. F.; Thomas, J. C.

    2015-04-01

    Context. Under cosmic irradiation, the interstellar water ice mantles evolve towards a compact amorphous state. Crystalline ice amorphisation was previously monitored mainly in the keV to hundreds of keV ion energies. Aims: We experimentally investigate heavy ion irradiation amorphisation of crystalline ice, at high energies closer to true cosmic rays, and explore the water-ice sputtering yield. Methods: We irradiated thin crystalline ice films with MeV to GeV swift ion beams, produced at the GANIL accelerator. The ice infrared spectral evolution as a function of fluence is monitored with in-situ infrared spectroscopy (induced amorphisation of the initial crystalline state into a compact amorphous phase). Results: The crystalline ice amorphisation cross-section is measured in the high electronic stopping-power range for different temperatures. At large fluence, the ice sputtering is measured on the infrared spectra, and the fitted sputtering-yield dependence, combined with previous measurements, is quadratic over three decades of electronic stopping power. Conclusions: The final state of cosmic ray irradiation for porous amorphous and crystalline ice, as monitored by infrared spectroscopy, is the same, but with a large difference in cross-section, hence in time scale in an astrophysical context. The cosmic ray water-ice sputtering rates compete with the UV photodesorption yields reported in the literature. The prevalence of direct cosmic ray sputtering over cosmic-ray induced photons photodesorption may be particularly true for ices strongly bonded to the ice mantles surfaces, such as hydrogen-bonded ice structures or more generally the so-called polar ices. Experiments performed at the Grand Accélérateur National d'Ions Lourds (GANIL) Caen, France. Part of this work has been financed by the French INSU-CNRS programme "Physique et Chimie du Milieu Interstellaire" (PCMI) and the ANR IGLIAS.

  18. Topographically mediated ice stream subglacial drainage networks

    NASA Astrophysics Data System (ADS)

    Hiester, J.; Sergienko, O. V.; Hulbe, C. L.

    2016-02-01

    Satellite laser altimetry reveals short timescale changes in Antarctic ice sheet surface elevation that are suggested to be driven by subglacial water transport and storage. Here details of the interaction between the dynamics of ice stream flow, subglacial water system, and bed elevation relief are examined in the context of idealized, heterogeneous bed geometries. Using a two-way coupled model of ice and subglacial water flow, we show that basal topography controls the temporal and spatial variability of the sub-ice stream hydraulic system. The orientation and characteristic dimensions of the topographic undulations determine the morphology (connected subglacial ponds or channel-like subglacial water features) and timescales of the sub-ice stream drainage system. The short-term (several years to decades) variability of the simulated coupled ice stream/subglacial water system suggests that the short-term surface variations detected in remote sensing observations may be indicative of a rapidly evolving subglacial water system. Our simulations also show that interaction between ice flow and the highly dynamic subglacial water system has a strong effect on effective stress in the ice. Large effective stress magnitudes arise over areas where the basal traction is characterized by strong spatial gradients, that is, transitions from high to low basal traction or vise versa. These transitions migrate on multiyear timescales and thus cause large effective stress variability on the same temporal scales.

  19. Effect of different "states" of sorbed water on amorphous celecoxib.

    PubMed

    Shete, Ganesh; Kuncham, Swathi; Puri, Vibha; Gangwal, Rahul P; Sangamwar, Abhay T; Bansal, Arvind Kumar

    2014-07-01

    Glass transition temperature (Tg) of an amorphous drug is a vital physical phenomenon that influences its visco-elastic properties, physical, and chemical stability. Water acts as a plasticizer for amorphous drugs thus increasing their recrystallization kinetics. This reduces the solubility advantage of an amorphous drug. Hence, there is an interest in understanding the relationship between water content and Tg of amorphous drug. We have studied the effect of "state" of sorbed water on Tg of amorphous celecoxib (ACLB). ACLB was allowed to sorb water at relative humidity of 33%, 53%, 75%, and 93%. ALCB showed biphasic sorption of water designated as "bound" and "solvent-like" state of water associated with ACLB. Molecular modeling studies provided deeper insights into the interaction of water with ACLB. A distinct co-relationship between the state of water and its plasticization capacity was observed. Bound state of water had a very profound effect on the fall in experimentally observed Tg (T(g-exp)) value. Solvent-like state of water had little impact on T(g-exp) value. Tg of ACLB-water mixture was predicted by Gordon-Taylor equation (T(g-pre)). The deviations in T(g-exp) and Tg-pre were correlated to volume non-additivity and non-ideal mixing. This study has implications on the development of formulations based on amorphous forms. PMID:24801826

  20. The role of the martensite transformation for the mechanical amorphization of NiTi

    SciTech Connect

    Ewert, J.C.; Boehm, I.; Haider, F.; Peter, R.

    1997-05-01

    Mechanical amorphization by cold rolling and uniaxial deformation of the intermetallic compound NiTi was studied by TEM and DSC. In cold rolled samples it could be clearly shown that amorphization occurs and that the amorphous regions recrystallize at T {approx} 350 C. In uniaxially deformed material a microstructure similar to that of cold rolled samples and a DSC-peak at the same temperature was found. In the TEM, extended amorphous regions could only be identified after a moderate heat treatment at 250 C. After deformation at temperatures above room temperature, a considerably lower degree of amorphization was found, and the fraction of amorphous volume was found to depend on the martensite transition temperature of the material.

  1. Basal Crevasses at the Ice-Ocean Interface of Whillans Ice Stream, West Antarctica

    NASA Astrophysics Data System (ADS)

    Jacobel, R. W.; Christianson, K. A.; Wood, A. C.; Dalla Santa, K. L.; Gobel, R. M.

    2013-12-01

    The transition from limited- or no-slip conditions at the base of grounded ice to free-slip conditions beneath floating ice occurs across the few-kilometers-wide grounding zone of ice sheets. This transition is either an elastic flexural transition from bedrock to hydrostatically supported elevations (often tidally influenced), or a transition from thicker to thinner ice over a flat bed, or some combination of these processes. In either case, ice must flow across a changing stress field, often resulting in brittle deformation, which is manifested as basal crevassing at the ice sheet base and tidal strand cracking on the ice sheet surface. Thus the position and morphology of basal crevasses reveal important information about the stress state across this transition where ice and ocean interact. We acquired gridded ground-based radar surveys at two locations of the Whillans Ice Stream grounding zone, one over a subglacial peninsula where the transition to floatation is abrupt and the second over a subglacial embayment where several dynamic subglacial lakes drain to the ocean, likely resulting in episodic high sediment and water flux across the grounding line. Our surveys indicate a complex pattern of basal crevasses; some are related to basal topography, but others are more likely associated with ice flexure across the basal channel carrying water and sediment to the ocean. Due to the high reflectivity of seawater and the relatively shallow ice thickness, we image many off-nadir crevasses where the radar energy is first reflected from the ice-water interface and then from the crevasse, producing an echo signature with a reversed phase due to the second reflection. In several cases these crevasse echoes appear to mimic the geometry of a sub-ice 'wedge' dipping into the sediment, while in reality the radar never penetrates below the basal interface. Elsewhere we image pairs of crevasses from either side of a channel incised into the bed that produce curious signatures

  2. Cenozoic ice volume and temperature simulations with a 1-D ice-sheet model

    NASA Astrophysics Data System (ADS)

    de Boer, B.; van de Wal, R. S. W.; Bintanja, R.; Lourens, L. J.; Tuenter, E.

    2009-04-01

    Ice volume and temperature for the past 35 Million years is investigated with a 1-D ice-sheet model, simulating ice-sheets on both hemispheres. The simulations include two continental Northern Hemisphere (NH) ice-sheets representative for glaciation on the two major continents, i.e. Eurasia (EAZ) and North America (NAM). Antarctic glaciation is simulated with two separate ice-sheets, respectively for West and East Antarctica. The surface air temperature is reconstructed with an inventive inverse procedure, forced with benthic δ18O data. The procedure linearly relates the temperature to the difference between the modelled and observed marine δ18O 100 years later. The derived temperature, representative for the NH, is used to run the ice-sheet model over 100 years, to obtain a mutually consistent record of marine δ18O, sea level and temperature for the last 35 Ma of the Cenozoic. For Northern Hemispheric glaciations results are good compared to similar simulations performed with a much more comprehensive 3-D ice-sheet model. On average, differences are only 1.9 ˚ C for temperature and 6.1 m for sea level. Results with ice-sheets on both hemispheres are very similar. Most notably, the reconstructed ice volume as function of temperature shows a transition from climate dominated by Antarctic ice volume variation towards NH ice-sheets controlled climate. The transition period falls within the range of interglacials (about -2 to +8 ˚ C with respect to present day) and is thus characterized by lower ice volume changes per ˚ C. The relationship between temperature, sea level and δ18O input is tested with an equilibrium experiment, which results in a linear and symmetric relationship for both temperature and total sea level, providing limited evidence for hysteresis, though transient behaviour is still important. Furthermore results show a rather good comparison with other simulations of Antarctic ice volume and observed sea level and deep-sea temperature.

  3. Characterization, quantification and stability of differently prepared amorphous forms of some oral hypoglycaemic agents.

    PubMed

    Chadha, Renu; Bhandari, Swati; Arora, Poonam; Chhikara, Rekha

    2013-01-01

    The study deals with the investigation of possible differences induced in the physicochemical properties within the amorphous forms prepared by different methods. Enthalpy of solution measured by solution calorimetry was utilized to highlight the differences prevailing within the amorphous forms and to determine the percentage of amorphous content. Emphasis is laid on the quantification and physical stability of these forms. Amorphization was induced in poorly water-soluble oral hypoglycaemic agents (repaglinide, gliclazide and glipizide), by quench cooling, vaporization under reduced pressure and lyophilization. The amorphous nature was evident from a halo pattern in powder X-ray diffraction. A glass transition event is evident in differential scanning calorimetry thermograms of the amorphous forms of the three drugs. As expected, the amorphous forms show improvement in solubility and dissolution profiles. On subjecting these amorphous forms to different relative humidities at 25°C for three months and subsequent analysis showed that amorphous form of repaglinide prepared by quench cooling is most stable and has the potential to be formulated without any additive while amorphous form of gliclazide tends to devitrify pointing towards its unstable nature. PMID:23061933

  4. Structural Characterization of Crystalline Ice Nanoclusters

    NASA Technical Reports Server (NTRS)

    Blake, David

    2000-01-01

    Water ice nanoclusters are useful analogs for studying a variety of processes that occur within icy grains in the extraterrestrial environment. The surface of ice nanoclusters prepared in the laboratory is similar to the surface of interstellar ice grains. In cold molecular clouds, the silicate cores of interstellar grains are typically approx. 100 nm in diameter and have a coating of impure amorphous water ice. Depositional, thermal and radiolytic processes leave the surface and subsurface molecules in a disordered state. In this state, structural defects become mobile and reactions of trapped gases and small molecules can occur. The large surface area of nanocluster deposits relative to their bulk allows for routine observation of such surface-mediated processes. Furthermore, the disordered surface and subsurface layers in nanocluster deposits mimic the structure of amorphous ice rinds found on interstellar dust grains. Transmission Electron Microscopy (TEM has been used tn characterize the crystallinity, growth mechanism, and size distribution of nanoclusters formed from a mixture of water vapor with an inert carrier gas that has been rapidly cooled to 77K. E M imaging reveals a Gaussian size distribution around a modal diameter that increases from approx. 15 to 30 nm as the percentage of water vapor within the mixture increases from 0.5 to 2.007, respectively . TEM bright and dark field imaging also reveals the crystalline nature of the clusters. h4any of the clusters show a mosaic structure in which crystalline domains originate at the center Other images show mirror planes that are separated by approx. 10 nm. Electron diffraction patterns of these clusters show that the clusters are composed of cubic ice with only a small hexagonal component. Further, the crystalline domain size is approximately the same as the modal diameter suggesting that the clusters are single crystals.

  5. The ice plumes of Europa

    NASA Astrophysics Data System (ADS)

    Sparks, William

    2014-10-01

    It is of extreme interest to NASA and the scientific community that evidence has been found for plumes of water ice venting from the polar regions of Europa (Roth et al 2014) - spectroscopic detection of off-limb line emission from the dissociation products of water. We were awarded Cycle 21 time to seek direct images of the Europa exosphere, including Enceladus-like plumes if present, basing our study on FUV images of Europa as it transits the smooth face of Jupiter. We also obtained a necessary FUV image of Europa out of transit. These observations provide additional evidence for the presence of ice plumes on Europa. Here, we propose to augment our previous imaging work and to seek an initial, efficient characterization of off-limb emission as Europa orbits Jupiter. Such images provide sensitive flux and column density limits, with exceptional spatial resolution. In transit, our strategy can place firm limits on, or measurements of, absorbing columns, their distribution with altitude above the surface of Europa, and constrain their wavelength dependence and hence composition. Out of transit, geometrical and surface brightness considerations can help us distinguish between continuum FUV emission from forward- or back-scattering, from line emission, or, though we might prefer otherwise, from more subtle instrumental artifacts than hitherto understood. If the ice fountains of Europa arise from the deep ocean, we have gained access to probably the most astrobiologically interesting location in the Solar System.

  6. Structure and Properties of Amorphous Transparent Conducting Oxides

    NASA Astrophysics Data System (ADS)

    Medvedeva, Julia

    Driven by technological appeal, the research area of amorphous oxide semiconductors has grown tremendously since the first demonstration of the unique properties of amorphous indium oxide more than a decade ago. Today, amorphous oxides, such as a-ITO, a-IZO, a-IGZO, or a-ZITO, exhibit the optical, electrical, thermal, and mechanical properties that are comparable or even superior to those possessed by their crystalline counterparts, pushing the latter out of the market. Large-area uniformity, low-cost low-temperature deposition, high carrier mobility, optical transparency, and mechanical flexibility make these materials appealing for next-generation thin-film electronics. Yet, the structural variations associated with crystalline-to-amorphous transition as well as their role in carrier generation and transport properties of these oxides are far from being understood. Although amorphous oxides lack grain boundaries, factors like (i) size and distribution of nanocrystalline inclusions; (ii) spatial distribution and clustering of incorporated cations in multicomponent oxides; (iii) formation of trap defects; and (iv) piezoelectric effects associated with internal strains, will contribute to electron scattering. In this work, ab-initio molecular dynamics (MD) and accurate density-functional approaches are employed to understand how the properties of amorphous ternary and quaternary oxides depend on quench rates, cation compositions, and oxygen stoichiometries. The MD results, combined with thorough experimental characterization, reveal that interplay between the local and long-range structural preferences of the constituent oxides gives rise to a complex composition-dependent structural behavior in the amorphous oxides. The proposed network models of metal-oxygen polyhedra help explain the observed intriguing electrical and optical properties in In-based oxides and suggest ways to broaden the phase space of amorphous oxide semiconductors with tunable properties. The

  7. Physicochemical investigations and stability studies of amorphous gliclazide.

    PubMed

    Jondhale, Shital; Bhise, Satish; Pore, Yogesh

    2012-06-01

    Gliclazide (GLI), a poorly water-soluble antidiabetic, was transformed into a glassy state by melt quench technique in order to improve its physicochemical properties. Chemical stability of GLI during formation of glass was assessed by monitoring thin-layer chromatography, and an existence of amorphous form was confirmed by differential scanning calorimetry and X-ray powder diffractometry. The glass transition occurred at 67.5°C. The amorphous material thus generated was examined for its in vitro dissolution performance in phosphate buffer (pH 6.8). Surprisingly, amorphous GLI did not perform well and was unable to improve the dissolution characteristics compared to pure drug over entire period of dissolution studies. These unexpected results might be due to the formation of a cohesive supercooled liquid state and structural relaxation of amorphous form toward the supercooled liquid region which indicated functional inability of amorphous GLI from stability point of view. Hence, stabilization of amorphous GLI was attempted by elevation of T(g) via formation of solid dispersion systems involving comprehensive antiplasticizing as well as surface adsorption mechanisms. The binary and ternary amorphous dispersions prepared with polyvinylpyrrolidone K30 (as antiplasticizer for elevation of T (g)) and Aerosil 200® and/or Sylysia® 350 (as adsorbent) in the ratio of 1:1:1 (w/w) using kneading and spray-drying techniques demonstrated significant enhancement in rate and extent of dissolution of drug initially. During accelerated stability studies, ternary systems showed no significant reduction in drug dissolution performance over a period of 3 months indicating excellent stabilization of amorphous GLI. PMID:22382730

  8. Structural transition and amorphization in compressed α - Sb 2 O 3

    SciTech Connect

    Zhao, Zhao; Zeng, Qiaoshi; Zhang, Haijun; Wang, Shibing; Hirai, Shigeto; Zeng, Zhidan; Mao, Wendy L.

    2015-05-27

    Sb₂O₃-based materials are of broad interest in materials science and industry. High-pressure study using diamond anvil cells shows promise in obtaining new crystal and electronic structures different from their pristine states. Here, we conducted in situ angle dispersive synchrotron x-ray-diffraction and Raman spectroscopy experiments on α-Sb₂O₃ up to 50 GPa with neon as the pressure transmitting medium. A first-order structural transition was observed in between 15 and 20 GPa, where the cubic phase I gradually transformed into a layered tetragonal phase II through structural distortion and symmetry breaking. To explain the dramatic changes in sample color and transparency, we performed first-principles calculations to track the evolution of its density of states and electronic structure under pressure. At higher pressure, a sluggish amorphization was observed. Our results highlight the structural connections among the sesquioxides, where the lone electron pair plays an important role in determining the local structures.

  9. Analysis and Application of the Amorphous Properties in Freeze-Dried Foods

    NASA Astrophysics Data System (ADS)

    Kawai, Kiyoshi

    The dynamic properties of amorphous materials drastically change by the phase transition between glassy state and rubber state. Furthermore, the dynamic properties of amorphous materials in glassy state are affected by the thermal history such as processing and/or storage conditions. In this paper, effect of the glass transition of freeze-dried food systems on the storage stability was summarized. Moreover, analytical approaches of the amorphous properties for glassy products with enthalpy relaxation measurements by using differential scanning calorimetry were presented and its application to food industry was proposed.

  10. N2 and CO Desorption Energies from Water Ice

    NASA Astrophysics Data System (ADS)

    Fayolle, Edith C.; Balfe, Jodi; Loomis, Ryan; Bergner, Jennifer; Graninger, Dawn; Rajappan, Mahesh; Öberg, Karin I.

    2016-01-01

    The relative desorption energies of CO and N2 are key to interpretations of observed interstellar CO and N2 abundance patterns, including the well-documented CO and N2H+ anti-correlations in disks, protostars, and molecular cloud cores. Based on laboratory experiments on pure CO and N2 ice desorption, the difference between CO and N2 desorption energies is small; the N2-to-CO desorption energy ratio is 0.93 ± 0.03. Interstellar ices are not pure, however, and in this study we explore the effect of water ice on the desorption energy ratio of the two molecules. We present temperature programmed desorption experiments of different coverages of 13CO and 15N2 on porous and compact amorphous water ices and, for reference, of pure ices. In all experiments, 15N2 desorption begins a few degrees before the onset of 13CO desorption. The 15N2 and 13CO energy barriers are 770 and 866 K for the pure ices, 1034-1143 K and 1155-1298 K for different submonolayer coverages on compact water ice, and 1435 and 1575 K for ˜1 ML of ice on top of porous water ice. For all equivalent experiments, the N2-to-CO desorption energy ratio is consistently 0.9. Whenever CO and N2 ice reside in similar ice environments (e.g., experience a similar degree of interaction with water ice) their desorption temperatures should thus be within a few degrees of one another. A smaller N2-to-CO desorption energy ratio may be present in interstellar and circumstellar environments if the average CO ice molecules interacts more with water ice compared to the average N2 molecules.

  11. N2 and CO Desorption Energies from Water Ice

    NASA Astrophysics Data System (ADS)

    Fayolle, Edith C.; Balfe, Jodi; Loomis, Ryan; Bergner, Jennifer; Graninger, Dawn; Rajappan, Mahesh; Öberg, Karin I.

    2016-01-01

    The relative desorption energies of CO and N2 are key to interpretations of observed interstellar CO and N2 abundance patterns, including the well-documented CO and N2H+ anti-correlations in disks, protostars, and molecular cloud cores. Based on laboratory experiments on pure CO and N2 ice desorption, the difference between CO and N2 desorption energies is small; the N2-to-CO desorption energy ratio is 0.93 ± 0.03. Interstellar ices are not pure, however, and in this study we explore the effect of water ice on the desorption energy ratio of the two molecules. We present temperature programmed desorption experiments of different coverages of 13CO and 15N2 on porous and compact amorphous water ices and, for reference, of pure ices. In all experiments, 15N2 desorption begins a few degrees before the onset of 13CO desorption. The 15N2 and 13CO energy barriers are 770 and 866 K for the pure ices, 1034–1143 K and 1155–1298 K for different submonolayer coverages on compact water ice, and 1435 and 1575 K for ∼1 ML of ice on top of porous water ice. For all equivalent experiments, the N2-to-CO desorption energy ratio is consistently 0.9. Whenever CO and N2 ice reside in similar ice environments (e.g., experience a similar degree of interaction with water ice) their desorption temperatures should thus be within a few degrees of one another. A smaller N2-to-CO desorption energy ratio may be present in interstellar and circumstellar environments if the average CO ice molecules interacts more with water ice compared to the average N2 molecules.

  12. Amorphous silicon ionizing particle detectors

    DOEpatents

    Street, R.A.; Mendez, V.P.; Kaplan, S.N.

    1988-11-15

    Amorphous silicon ionizing particle detectors having a hydrogenated amorphous silicon (a--Si:H) thin film deposited via plasma assisted chemical vapor deposition techniques are utilized to detect the presence, position and counting of high energy ionizing particles, such as electrons, x-rays, alpha particles, beta particles and gamma radiation. 15 figs.

  13. Amorphous silicon ionizing particle detectors

    DOEpatents

    Street, Robert A.; Mendez, Victor P.; Kaplan, Selig N.

    1988-01-01

    Amorphous silicon ionizing particle detectors having a hydrogenated amorphous silicon (a--Si:H) thin film deposited via plasma assisted chemical vapor deposition techniques are utilized to detect the presence, position and counting of high energy ionizing particles, such as electrons, x-rays, alpha particles, beta particles and gamma radiation.

  14. Ice Observatory

    NASA Astrophysics Data System (ADS)

    blugerman, n.

    2015-10-01

    My project is to make ice observatories to perceive astral movements as well as light phenomena in the shape of cosmic rays and heat, for example.I find the idea of creating an observation point in space, that in time will change shape and eventually disappear, in consonance with the way we humans have been approaching the exploration of the universe since we started doing it. The transformation in the elements we use to understand big and small transformations, within the universe elements.

  15. Investigation of the Rigid Amorphous Fraction in Nylon-6

    SciTech Connect

    Chen,H.; Cebe, P.

    2007-01-01

    A three-phase model, comprising crystalline, mobile amorphous, and rigid amorphous fractions (X{sub c}, X{sub MA}, X{sub rA}, respectively) has been applied in the study of semicrystalline Nylon-6. The samples studied were Nylon-6 alpha phase prepared by subsequent annealing of a parent sample slowly cooled from the melt. The treated samples were annealed at 110 C, then briefly heated to 136 C, then re-annealed at 110 C. Temperature-modulated differential scanning calorimetry (TMDSC) measurements allow the devitrification of the rigid amorphous fraction to be examined. We observe a lower endotherm, termed the 'annealing' peak in the non-reversing heat flow after annealing at 110 C. By brief heating above this lower endotherm and immediately quenching in LN{sub 2}-cooled glass beads, the glass transition temperature and X{sub RA} decrease substantially, X{sub MA} increases, and the annealing peak disappears. The annealing peak corresponds to the point at which partial de-vitrification of the rigid amorphous fraction (RAF) occurs. Re-annealing at 110 C causes the glass transition and X{sub RA} to increase, and X{sub MA} to decrease. None of these treatments affected the measured degree of crystallinity, but it cannot be excluded that crystal reorganization or recrystallization may also occur at the annealing peak, contributing to the de-vitrification of the rigid amorphous fraction. Using a combined approach of thermal analysis with wide and small angle X-ray scattering, we analyze the location of the rigid amorphous and mobile amorphous fractions within the context of the Heterogeneous and Homogeneous Stack Models. Results show the homogeneous stack model is the correct one for Nylon-6. The cooperativity length ({var_epsilon}{sub A}) increases with a decrease of rigid amorphous fraction, or, increase of the mobile amorphous fraction. Devitrification of some of the RAF leads to the broadening of the glass transition region and shift of T{sub g}.

  16. Mapping Layer Sequence and Folds of Pre-Holocene Ice at the Pakitsoq "Horizontal Ice Coring"-Site, West Greenland.

    NASA Astrophysics Data System (ADS)

    Reeh, N.; Severinghaus, J.; Ahlstrom, A.; Brook, E.; Petrenko, V.

    2005-12-01

    Since 1985, the δ18O content of the surface ice has been studied at several ice-margin locations in Greenland. A provisional chronology for the ice margin records was established by correlating characteristic δ18O-features in the ice margin records with similar features in dated Greenland deep ice core records. This demonstrated that, at many ice-margin locations, a several hundred metre wide band of ice pre-dating the present warm interglacial occurs adjacent to the ice edge. A main concern with utilizing this aincient ice for studies of the past has been the fear of likely disturbances of the layer sequence by folds and faults. Recent trace element analyses of ice samples from the ice-sheet margin at Pakitsoq, 50 km northeast of Ilulissat/Jakobshavn, West Greenland have unambiguously demonstrated the occurrence of ice from the transition from the Last Glacial Maximum to the Holocene including ice from the Bølling-Allerød and Younger Dryas intervals. Thus large amounts of well-dated old ice with intact content of trace constituents are available at the Pakitsoq ice-margin. However, analysis of the trace constituents as well as visual inspection also demonstrated the occurrence of a large-scale fold in ice representing the Allerød/Younger Dryas/Pre-Boreal climate oscillation. Moreover, observations of ice ablation and dynamics clearly showed that the Pakitsoq ice-margin sector is presently far from a balanced state, stressing the need for developing a model for the evolution of the ice margin in order to support future ice-mining activities. Here, we report on the development of such a model based on mapping of the large-scale structures on the ice margin by using GPS, ground-penetrating radar (GPR), and trace element geo-chemical analysis (mainly δ18O-analysis of ice samples). Samples for δ18O-analysis were collected each year in the period 2001 - 2005 in several profiles across the large scale fold in order to document the time evolution. Altogether more

  17. Partially ordered state of ice XV.

    PubMed

    Komatsu, K; Noritake, F; Machida, S; Sano-Furukawa, A; Hattori, T; Yamane, R; Kagi, H

    2016-01-01

    Most ice polymorphs have order-disorder "pairs" in terms of hydrogen positions, which contributes to the rich variety of ice polymorphs; in fact, three recently discovered polymorphs- ices XIII, XIV, and XV-are ordered counter forms to already identified disordered phases. Despite the considerable effort to understand order-disorder transition in ice crystals, there is an inconsistency among the various experiments and calculations for ice XV, the ordered counter form of ice VI, i.e., neutron diffraction observations suggest antiferroelectrically ordered structures, which disagree with dielectric measurement and theoretical studies, implying ferroelectrically ordered structures. Here we investigate in-situ neutron diffraction measurements and density functional theory calculations to revisit the structure and stability of ice XV. We find that none of the completely ordered configurations are particular favored; instead, partially ordered states are established as a mixture of ordered domains in disordered ice VI. This scenario in which several kinds of ordered configuration coexist dispels the contradictions in previous studies. It means that the order-disorder pairs in ice polymorphs are not one-to-one correspondent pairs but rather have one-to-n correspondence, where there are n possible configurations at finite temperature. PMID:27375120

  18. Partially ordered state of ice XV

    PubMed Central

    Komatsu, K.; Noritake, F.; Machida, S.; Sano-Furukawa, A.; Hattori, T.; Yamane, R.; Kagi, H.

    2016-01-01

    Most ice polymorphs have order–disorder “pairs” in terms of hydrogen positions, which contributes to the rich variety of ice polymorphs; in fact, three recently discovered polymorphs— ices XIII, XIV, and XV—are ordered counter forms to already identified disordered phases. Despite the considerable effort to understand order–disorder transition in ice crystals, there is an inconsistency among the various experiments and calculations for ice XV, the ordered counter form of ice VI, i.e., neutron diffraction observations suggest antiferroelectrically ordered structures, which disagree with dielectric measurement and theoretical studies, implying ferroelectrically ordered structures. Here we investigate in-situ neutron diffraction measurements and density functional theory calculations to revisit the structure and stability of ice XV. We find that none of the completely ordered configurations are particular favored; instead, partially ordered states are established as a mixture of ordered domains in disordered ice VI. This scenario in which several kinds of ordered configuration coexist dispels the contradictions in previous studies. It means that the order–disorder pairs in ice polymorphs are not one-to-one correspondent pairs but rather have one-to-n correspondence, where there are n possible configurations at finite temperature. PMID:27375120

  19. Compensated amorphous silicon solar cell

    DOEpatents

    Devaud, Genevieve

    1983-01-01

    An amorphous silicon solar cell including an electrically conductive substrate, a layer of glow discharge deposited hydrogenated amorphous silicon over said substrate and having regions of differing conductivity with at least one region of intrinsic hydrogenated amorphous silicon. The layer of hydrogenated amorphous silicon has opposed first and second major surfaces where the first major surface contacts the electrically conductive substrate and an electrode for electrically contacting the second major surface. The intrinsic hydrogenated amorphous silicon region is deposited in a glow discharge with an atmosphere which includes not less than about 0.02 atom percent mono-atomic boron. An improved N.I.P. solar cell is disclosed using a BF.sub.3 doped intrinsic layer.

  20. Bulk amorphous materials

    SciTech Connect

    Schwarz, R.B.; Archuleta, J.I.; Sickafus, K.E.

    1998-12-01

    This is the final report for a three-year, Laboratory Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). The objective of this work was to develop the competency for the synthesis of novel bulk amorphous alloys. The authors researched their synthesis methods and alloy properties, including thermal stability, mechanical, and transport properties. The project also addressed the development of vanadium-spinel alloys for structural applications in hostile environments, the measurement of elastic constants and thermal expansion in single-crystal TiAl from 300 to 750 K, the measurement of elastic constants in gallium nitride, and a study of the shock-induced martensitic transformations in NiTi alloys.

  1. Amorphous and Cellular Computing

    NASA Astrophysics Data System (ADS)

    Abelson, Harold; Sussman, Gerald J.; Knight, Thomas F., Jr

    2001-08-01

    The objective of this research is to create the architectural, algorithmic, and technological foundations for exploiting programmable materials. These are materials that incorporate vast numbers of programmable elements that react to each other and to their environment. Such materials can be fabricated economically, provided that the computing elements are amassed in bulk without arranging for precision interconnect and testing. In order to exploit programmable materials we must identify engineering principles for organizing and instructing myriad programmable entities to cooperate to robustly achieve pre-established goals, even though the individual entities are unreliable and interconnected in unknown, irregular, and time-varying ways. Progress in microfabrication and in bioengineering will make it possible to assemble such amorphous systems at almost no cost, provided that (1) the units need not all work correctly; (2) the units are identically programmed; and (3) there is no need to manufacture precise geometrical arrangements of the units or precise interconnections among them.

  2. Heat transfer on accreting ice surfaces

    NASA Technical Reports Server (NTRS)

    Yamaguchi, Keiko; Hansman, R. John, Jr.

    1990-01-01

    Based on previous observations of glaze ice accretion, a 'Multi-Zone' model with distinct zones of different surface roughness is demonstrated. The use of surface roughness in the LEWICE ice accretion prediction code is examined. It was found that roughness is used in two ways: to determine the laminar to turbulent transition location and to calculate the turbulent heat transfer coefficient. A two zone version of the Multi-Zone model is implemented in the LEWICE code, and compared with experimental heat transfer coefficient and ice accretin results. The analysis of the boundary layer transition, surface roughness, and viscous flow field effects significantly increased the accuracy in predicting heat transfer coefficients. The Multi-Zone model was found to greatly improve the ice accretion prediction for the cases compared.

  3. Heat transfer on accreting ice surfaces

    NASA Technical Reports Server (NTRS)

    Yamaguchi, Keiko; Hansman, R. John, Jr.

    1993-01-01

    Based on previous observations of glaze ice accretion on aircraft surfaces, a multizone model with distinct zones of different surface roughness is demonstrated. The use of surface roughness in the LEWICE ice accretion prediction code is examined. It was found that roughness is used in two ways: (1) to determine the laminar to turbulent boundary-layer transition location; and (2) to calculate the convective turbulent heat-transfer coefficient. A two-zone version of the multizone model is implemented in the LEWICE code, and compared with experimental convective heat-transfer coefficient and ice accretion results. The analysis of the boundary-layer transition, surface roughness, and viscous flowfield effects significantly increased the accuracy in predicting heat-transfer coefficients. The multizone model was found to significantly improve the ice accretion prediction for the cases compared.

  4. Crystalline and amorphous H2O on Charon

    NASA Astrophysics Data System (ADS)

    Dalle Ore, Cristina M.; Cruikshank, Dale P.; Grundy, Will M.; Ennico, Kimberly; Olkin, Catherine B.; Stern, S. Alan; Young, Leslie A.; Weaver, Harold A.

    2015-11-01

    Charon, the largest satellite of Pluto, is a gray-colored icy world covered mostly in H2O ice, with spectral evidence for NH3, as previously reported (Cook et al. 2007, Astrophys. J. 663, 1406-1419 Merlin, et al. 2010, Icarus, 210, 930; Cook, et al. 2014, AAS/Division for Planetary Sciences Meeting Abstracts, 46, #401.04). Images from the New Horizons spacecraft reveal a surface with terrains of widely different ages and a moderate degree of localized coloration. The presence of H2O ice in its crystalline form (Brown & Calvin 2000 Science 287, 107-109; Buie & Grundy 2000 Icarus 148, 324-339; Merlin et al, 2010) along with NH3 is consistent with a fresh surface.The phase of H2O ice is a key tracer of variations in temperature and physical conditions on the surface of outer Solar System objects. At Charon’s surface temperature H2O is expected to be amorphous, but ground-based observations (e.g., Merlin et al. 2010) show a clearly crystalline signature. From laboratory experiments it is known that amorphous H2O ice becomes crystalline at temperatures of ~130 K. Other mechanisms that can change the phase of the ice from amorphous to crystalline include micro-meteoritic bombardment (Porter et al. 2010, Icarus, 208, 492) or resurfacing processes such as cryovolcanism.New Horizons observed Charon with the LEISA imaging spectrometer, part of the Ralph instrument (Reuter, D.C., Stern, S.A., Scherrer, J., et al. 2008, Space Science Reviews, 140, 129). Making use of high spatial resolution (better than 10 km/px) and spectral resolving power of 240 in the wavelength range 1.25-2.5 µm, and 560 in the range 2.1-2.25 µm, we report on an analysis of the phase of H2O ice on parts of Charon’s surface with a view to investigate the recent history and evolution of this small but intriguing object.This work was supported by NASA’s New Horizons project.

  5. Colloidal assembly by ice templating.

    PubMed

    Kumaraswamy, Guruswamy; Biswas, Bipul; Choudhury, Chandan Kumar

    2016-04-12

    We investigate ice templating of aqueous dispersions of polymer coated colloids and crosslinkers, at particle concentrations far below that required to form percolated monoliths. Freezing the aqueous dispersions forces the particles into close proximity to form clusters, that are held together as the polymer chains coating the particles are crosslinked. We observe that, with an increase in the particle concentration from about 10(6) to 10(8) particles per ml, there is a transition from isolated single particles to increasingly larger clusters. In this concentration range, most of the colloidal clusters formed are linear or sheet like particle aggregates. Remarkably, the cluster size distribution for clusters smaller than about 30 particles, as well as the size distribution of linear clusters, is only weakly dependent on the dispersion concentration in the range that we investigate. We demonstrate that the main features of cluster formation are captured by kinetic simulations that do not consider hydrodynamics or instabilities at the growing ice front due to particle concentration gradients. Thus, clustering of colloidal particles by ice templating dilute dispersions appears to be governed only by particle exclusion by the growing ice crystals that leads to their accumulation at ice crystal boundaries. PMID:26780838

  6. Tributaries of West Antarctic Ice Streams Revealed by RADARSAT Interferometry.

    PubMed

    Joughin; Gray; Bindschadler; Price; Morse; Hulbe; Mattar; Werner

    1999-10-01

    Interferometric RADARSAT data are used to map ice motion in the source areas of four West Antarctic ice streams. The data reveal that tributaries, coincident with subglacial valleys, provide a spatially extensive transition between slow inland flow and rapid ice stream flow and that adjacent ice streams draw from shared source regions. Two tributaries flow into the stagnant ice stream C, creating an extensive region that is thickening at an average rate of 0.49 meters per year. This is one of the largest rates of thickening ever reported in Antarctica. PMID:10514370

  7. Electronic excitation induced amorphization in titanate pyrochlores: an ab initio molecular dynamics study

    DOE PAGESBeta

    Xiao, Haiyan Y.; Weber, William J.; Zhang, Yanwen; Zu, X. T.; Li, Sean

    2015-02-09

    In this study, the response of titanate pyrochlores (A2Ti2O7, A = Y, Gd and Sm) to electronic excitation is investigated utilizing an ab initio molecular dynamics method. All the titanate pyrochlores are found to undergo a crystalline-to-amorphous structural transition under a low concentration of electronic excitations. The transition temperature at which structural amorphization starts to occur depends on the concentration of electronic excitations. During the structural transition, O2-like molecules are formed, and this anion disorder further drives cation disorder that leads to an amorphous state. This study provides new insights into the mechanisms of amorphization in titanate pyrochlores under laser,more » electron and ion irradiations.« less

  8. Ice crystallization in ultrafine water-salt aerosols: nucleation, ice-solution equilibrium, and internal structure.

    PubMed

    Hudait, Arpa; Molinero, Valeria

    2014-06-01

    Atmospheric aerosols have a strong influence on Earth's climate. Elucidating the physical state and internal structure of atmospheric aqueous aerosols is essential to predict their gas and water uptake, and the locus and rate of atmospherically important heterogeneous reactions. Ultrafine aerosols with sizes between 3 and 15 nm have been detected in large numbers in the troposphere and tropopause. Nanoscopic aerosols arising from bubble bursting of natural and artificial seawater have been identified in laboratory and field experiments. The internal structure and phase state of these aerosols, however, cannot yet be determined in experiments. Here we use molecular simulations to investigate the phase behavior and internal structure of liquid, vitrified, and crystallized water-salt ultrafine aerosols with radii from 2.5 to 9.5 nm and with up to 10% moles of ions. We find that both ice crystallization and vitrification of the nanodroplets lead to demixing of pure water from the solutions. Vitrification of aqueous nanodroplets yields nanodomains of pure low-density amorphous ice in coexistence with vitrified solute rich aqueous glass. The melting temperature of ice in the aerosols decreases monotonically with an increase of solute fraction and decrease of radius. The simulations reveal that nucleation of ice occurs homogeneously at the subsurface of the water-salt nanoparticles. Subsequent ice growth yields phase-segregated, internally mixed, aerosols with two phases in equilibrium: a concentrated water-salt amorphous mixture and a spherical cap-like ice nanophase. The surface of the crystallized aerosols is heterogeneous, with ice and solution exposed to the vapor. Free energy calculations indicate that as the concentration of salt in the particles, the advance of the crystallization, or the size of the particles increase, the stability of the spherical cap structure increases with respect to the alternative structure in which a core of ice is fully surrounded by

  9. Scrambled Ice

    NASA Technical Reports Server (NTRS)

    1998-01-01

    This complex area on the side of Europa which faces away from Jupiter shows several types of features which are formed by disruptions of Europa's icy crust. North is to the top of the image, taken by NASA's Galileo spacecraft, and the Sun illuminates the surface from the left. The prominent wide, dark bands are up to 20 kilometers (12 miles) wide and over 50 kilometers (30 miles) long. They are believed to have formed when Europa's icy crust fractured, separated and filled in with darker, 'dirtier' ice or slush from below. A relatively rare type of feature on Europa is the 15-kilometer-diameter (9.3-mile) impact crater in the lower left corner. The small number of impact craters on Europa's surface is an indication of its relatively young age. A region of chaotic terrain south of this impact crater contains crustal plates which have broken apart and rafted into new positions. Some of these 'ice rafts' are nearly 1 kilometer (about half a mile) across. Other regions of chaotic terrain are visible and indicate heating and disruption of Europa's icy crust from below. The youngest features in this scene are the long, narrow cracks in the ice which cut across all other features. One of these cracks is about 30 kilometers (18 miles) to the right of the impact crater and extends for hundreds of miles from the top to the bottom of the image.

    The image, centered near 23 degrees south latitude and 179 degrees longitude, covers an area about 240 by 215 kilometers (150 by 130 miles) across. The finest details that can be discerned in this picture are about 460 meters (500 yards) across. The image was taken as Galileo flew by Europa on March 29, 1998. The image was taken by the onboard solid state imaging system camera from an altitude of 23,000 kilometers (14,000 miles).

    The Jet Propulsion Laboratory, Pasadena, CA manages the Galileo mission for NASA's Office of Space Science, Washington, DC. JPL is an operating division of California Institute of Technology (Caltech

  10. Perspective on photovoltaic amorphous silicon

    SciTech Connect

    Luft, W.; Stafford, B.; von Roedern, B.

    1992-05-01

    Amorphous silicon is a thin film option that has the potential for a cost-effective product for large-scale utility photovoltaics application. The initial efficiencies for single-junction and multijunction amorphous silicon cells and modules have increased significantly over the past 10 years. The emphasis of research and development has changed to stabilized efficiency, especially that of multijunction modules. NREL has measured 6.3%--7.2% stabilized amorphous silicon module efficiencies for US products, and 8.1% stable efficiencies have been reported by Fuji Electric. This represents a significant increase over the stabilized efficiencies of modules manufactured only a few years ago. An increasing portion of the amorphous silicon US government funding is now for manufacturing technology development to reduce cost. The funding for amorphous silicon for photovoltaics by Japan over the last 5 years has been about 50% greater than that in the United State, and by Germany in the last 2--3 years more than twice that of the US Amorphous silicon is the only thin-film technology that is selling large-area commercial modules. The cost for amorphous silicon modules is now in the $4.50 range; it is a strong function of plant production capacity and is expected to be reduced to $1.00--1.50/W{sub p} for plants with 10 MW/year capacities. 10 refs.

  11. Perspective on photovoltaic amorphous silicon

    SciTech Connect

    Luft, W.; Stafford, B.; von Roedern, B. )

    1992-12-01

    Amorphous silicon is a thin film option that has the potential for a cost-effective product for large-scale utility photovoltaics application. The initial efficiencies for single-junction and multijunction amorphous silicon cells and modules have increased significantly over the past 10 years. The emphasis of research and development has changed to stabilized efficiency, especially that of multijunction modules. NREL has measured 6.3%--7.2% stabilized amorphous silicon module efficiencies for U.S. products, and 8.1% stable efficiencies have been reported by Fuji Electric. This represents a significant increase over the stabilized efficiencies of modules manufactured only a few years ago. An increasing portion of the amorphous silicon U.S. government funding is now for manufacturing technology development to reduce cost. The funding for amorphous silicon for photovoltaics by Japan over the last 5 years has been about 50% greater than that in the United States, and by Germany in the last 2--3 years more than twice that of the U.S. Amorphous silicon is the only thin-film technology that is selling large-area commercial modules. The cost for amorphous silicon modules is now in the $4.50 range; it is a strong function of plant production capacity and is expected to be reduced to $1.00--1.50/W[sub [ital p

  12. Changes on the ice plain of Ice Stream B and Ross Ice Shelf

    NASA Technical Reports Server (NTRS)

    Shabtaie, Sion

    1993-01-01

    During the 1970's and 1980's, nearly 200 stations from which accurate, three dimensional position fixes have been obtained from TRANSIT satellites were occupied throughout the Ross Ice Shelf. We have transformed the elevations obtained by satellite altimetry to the same geodetic datum, and then applied a second transformation to reduce the geodetic heights to elevations above mean sea level using the GEM-10C geoidal height. On the IGY Ross Ice Shelf traverse between Oct. 1957 and Feb. 1958, an accurate method of barometric altimetry was used on a loop around the ice shelf that was directly tied to the sea at both ends of the travel route, thus providing absolute elevations. Comparisons of the two sets of data at 32 station pairs on floating ice show a mean difference of 0 +/- 1 m. The elevation data were also compared with theoretical values of elevations for a hydrostatically floating ice shelf. The mean difference between theoretical and measured values of elevations is -2 +/- 1 m.

  13. Containerless processing of amorphous ceramics

    NASA Technical Reports Server (NTRS)

    Weber, J. K. Richard; Krishnan, Shankar; Schiffman, Robert A.; Nordine, Paul C.

    1990-01-01

    The absence of gravity allows containerless processing of materials which could not otherwise be processed. High melting point, hard materials such as borides, nitrides, and refractory metals are usually brittle in their crystalline form. The absence of dislocations in amorphous materials frequently endows them with flexibility and toughness. Systematic studies of the properties of many amorphous materials have not been carried out. The requirements for their production is that they can be processed in a controlled way without container interaction. Containerless processing in microgravity could permit the control necessary to produce amorphous forms of hard materials.

  14. A shear localization mechanism for lubricity of amorphous carbon materials

    PubMed Central

    Ma, Tian-Bao; Wang, Lin-Feng; Hu, Yuan-Zhong; Li, Xin; Wang, Hui

    2014-01-01

    Amorphous carbon is one of the most lubricious materials known, but the mechanism is not well understood. It is counterintuitive that such a strong covalent solid could exhibit exceptional lubricity. A prevailing view is that lubricity of amorphous carbon results from chemical passivation of dangling bonds on surfaces. Here we show instead that lubricity arises from shear induced strain localization, which, instead of homogeneous deformation, dominates the shearing process. Shear localization is characterized by covalent bond reorientation, phase transformation and structural ordering preferentially in a localized region, namely tribolayer, resulting in shear weakening. We further demonstrate an anomalous pressure induced transition from stick-slip friction to continuous sliding with ultralow friction, due to gradual clustering and layering of graphitic sheets in the tribolayer. The proposed shear localization mechanism sheds light on the mechanism of superlubricity, and would enrich our understanding of lubrication mechanism of a wide variety of amorphous materials. PMID:24412998

  15. Amorphous copper tungsten oxide with tunable band gaps

    SciTech Connect

    Chen Le; Shet, Sudhakar; Tang Houwen; Wang Heli; Yan Yanfa; Turner, John; Al-Jassim, Mowafak; Ahn, Kwang-soon

    2010-08-15

    We report on the synthesis of amorphous copper tungsten oxide thin films with tunable band gaps. The thin films are synthesized by the magnetron cosputtering method. We find that due to the amorphous nature, the Cu-to-W ratio in the films can be varied without the limit of the solubility (or phase separation) under appropriate conditions. As a result, the band gap and conductivity type of the films can be tuned by controlling the film composition. Unfortunately, the amorphous copper tungsten oxides are not stable in aqueous solution and are not suitable for the application of photoelectrochemical splitting of water. Nonetheless, it provides an alternative approach to search for transition metal oxides with tunable band gaps.

  16. A shear localization mechanism for lubricity of amorphous carbon materials.

    PubMed

    Ma, Tian-Bao; Wang, Lin-Feng; Hu, Yuan-Zhong; Li, Xin; Wang, Hui

    2014-01-01

    Amorphous carbon is one of the most lubricious materials known, but the mechanism is not well understood. It is counterintuitive that such a strong covalent solid could exhibit exceptional lubricity. A prevailing view is that lubricity of amorphous carbon results from chemical passivation of dangling bonds on surfaces. Here we show instead that lubricity arises from shear induced strain localization, which, instead of homogeneous deformation, dominates the shearing process. Shear localization is characterized by covalent bond reorientation, phase transformation and structural ordering preferentially in a localized region, namely tribolayer, resulting in shear weakening. We further demonstrate an anomalous pressure induced transition from stick-slip friction to continuous sliding with ultralow friction, due to gradual clustering and layering of graphitic sheets in the tribolayer. The proposed shear localization mechanism sheds light on the mechanism of superlubricity, and would enrich our understanding of lubrication mechanism of a wide variety of amorphous materials. PMID:24412998

  17. A shear localization mechanism for lubricity of amorphous carbon materials

    NASA Astrophysics Data System (ADS)

    Ma, Tian-Bao; Wang, Lin-Feng; Hu, Yuan-Zhong; Li, Xin; Wang, Hui

    2014-01-01

    Amorphous carbon is one of the most lubricious materials known, but the mechanism is not well understood. It is counterintuitive that such a strong covalent solid could exhibit exceptional lubricity. A prevailing view is that lubricity of amorphous carbon results from chemical passivation of dangling bonds on surfaces. Here we show instead that lubricity arises from shear induced strain localization, which, instead of homogeneous deformation, dominates the shearing process. Shear localization is characterized by covalent bond reorientation, phase transformation and structural ordering preferentially in a localized region, namely tribolayer, resulting in shear weakening. We further demonstrate an anomalous pressure induced transition from stick-slip friction to continuous sliding with ultralow friction, due to gradual clustering and layering of graphitic sheets in the tribolayer. The proposed shear localization mechanism sheds light on the mechanism of superlubricity, and would enrich our understanding of lubrication mechanism of a wide variety of amorphous materials.

  18. The rheology of collapsing zeolites amorphized by temperature and pressure.

    PubMed

    Greaves, G N; Meneau, F; Sapelkin, A; Colyer, L M; ap Gwynn, I; Wade, S; Sankar, G

    2003-09-01

    Low-density zeolites collapse to the rigid amorphous state at temperatures that are well below the melting points of crystals of the same composition but of conventional density. Here we show, by using a range of experimental techniques, how the phenomenon of amorphization is time dependent, and how the dynamics of order-disorder transitions in zeolites under temperature and pressure are equivalent. As a result, thermobaric regions of instability can be charted, which are indicative of polyamorphism. Moreover, the boundaries of these zones depend on the rate at which temperature or pressure is ramped. By directly comparing the rheology of collapse with structural relaxation in equivalent melts, we conclude that zeolites amorphize like very strong liquids and, if compression occurs slowly, this is likely to lead to the synthesis of perfect glasses. PMID:12942072

  19. Connecting Local Yield Stresses with Plastic Activity in Amorphous Solids

    NASA Astrophysics Data System (ADS)

    Patinet, Sylvain; Vandembroucq, Damien; Falk, Michael L.

    2016-07-01

    In model amorphous solids produced via differing quench protocols, a strong correlation is established between local yield stress measured by direct local probing of shear stress thresholds and the plastic rearrangements observed during remote loading in shear. This purely local measure shows a higher predictive power for identifying sites of plastic activity when compared with more conventional structural properties. Most importantly, the sites of low local yield stress, thus defined, are shown to be persistent, remaining predictive of deformation events even after fifty or more such plastic rearrangements. This direct and nonperturbative approach gives access to relevant transition pathways that control the stability of amorphous solids. Our results reinforce the relevance of modeling plasticity in amorphous solids based on a gradually evolving population of discrete and local zones preexisting in the structure.

  20. Superconducting Metallic Glass Transition-Edge-Sensors

    NASA Technical Reports Server (NTRS)

    Hays, Charles C. (Inventor)

    2013-01-01

    A superconducting metallic glass transition-edge sensor (MGTES) and a method for fabricating the MGTES are provided. A single-layer superconducting amorphous metal alloy is deposited on a substrate. The single-layer superconducting amorphous metal alloy is an absorber for the MGTES and is electrically connected to a circuit configured for readout and biasing to sense electromagnetic radiation.

  1. Experimental studies of ice grain ejection by massive gas flow from ice and implications to Comets, Triton and Mars

    NASA Astrophysics Data System (ADS)

    Laufer, Diana; Bar-Nun, Akiva; Pat-El, Igal; Jacovi, Ronen

    2013-01-01

    This is an experimental study of ice grain ejection when trapped gases are released from water ice. When ice is formed by adherence of water molecules at low temperatures, it forms an amorphous structure with many pores, where gas molecules can reside. When further ice layers are formed, the gases are trapped in the ice. Upon its warming-up, the ice structure changes, releasing fractions of the trapped gas. If they do not encounter obstacles, they are released quiescently by dynamic percolation. In a non-dense ice a huge flux of ice grains emanates from the ice, propelled by gas jets and covering its entire surface. When the overlying ice is denser, due to back-migration of water vapor during its sublimation, gas trying to escape from below cannot penetrate the dense ice and breaks it, producing non-circular craters and a chaotic terrain, as observed experimentally and in close encounters with Comets Wild 2, Tempel 1 and Hartley 2. These experimental findings explain several observations of Solar System bodies: ice grain ejection from Comets Temple 1 and Hartley 2. Also explained are the dark jets observed on Triton, where their ejection speed suggests a deep source. On Mars, dark streaks are observed in the southern pole in spring, most likely by plumes carrying dark dust, carried by winds and falling on the surface. As found by us experimentally, only frozen CO2 covered by water ice or mixed with it will work to form jets, whereas pure frozen CO2 will sublimate quiescently.

  2. Physiological and ecological significance of biological ice nucleators.

    PubMed Central

    Lundheim, Rolv

    2002-01-01

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

  3. Apatite Formation from Amorphous Calcium Phosphate and Mixed Amorphous Calcium Phosphate/Amorphous Calcium Carbonate.

    PubMed

    Ibsen, Casper J S; Chernyshov, Dmitry; Birkedal, Henrik

    2016-08-22

    Crystallization from amorphous phases is an emerging pathway for making advanced materials. Biology has made use of amorphous precursor phases for eons and used them to produce structures with remarkable properties. Herein, we show how the design of the amorphous phase greatly influences the nanocrystals formed therefrom. We investigate the transformation of mixed amorphous calcium phosphate/amorphous calcium carbonate phases into bone-like nanocrystalline apatite using in situ synchrotron X-ray diffraction and IR spectroscopy. The speciation of phosphate was controlled by pH to favor HPO4 (2-) . In a carbonate free system, the reaction produces anisotropic apatite crystallites with large aspect ratios. The first formed crystallites are highly calcium deficient and hydrogen phosphate rich, consistent with thin octacalcium phosphate (OCP)-like needles. During growth, the crystallites become increasingly stoichiometric, which indicates that the crystallites grow through addition of near-stoichiometric apatite to the OCP-like initial crystals through a process that involves either crystallite fusion/aggregation or Ostwald ripening. The mixed amorphous phases were found to be more stable against phase transformations, hence, the crystallization was inhibited. The resulting crystallites were smaller and less anisotropic. This is rationalized by the idea that a local phosphate-depletion zone formed around the growing crystal until it was surrounded by amorphous calcium carbonate, which stopped the crystallization. PMID:27460160

  4. Ice sheet margins and ice shelves

    NASA Technical Reports Server (NTRS)

    Thomas, R. H.

    1984-01-01

    The effect of climate warming on the size of ice sheet margins in polar regions is considered. Particular attention is given to the possibility of a rapid response to warming on the order of tens to hundreds of years. It is found that the early response of the polar regions to climate warming would be an increase in the area of summer melt on the ice sheets and ice shelves. For sufficiently large warming (5-10C) the delayed effects would include the breakup of the ice shelves by an increase in ice drainage rates, particularly from the ice sheets. On the basis of published data for periodic changes in the thickness and melting rates of the marine ice sheets and fjord glaciers in Greenland and Antarctica, it is shown that the rate of retreat (or advance) of an ice sheet is primarily determined by: bedrock topography; the basal conditions of the grounded ice sheet; and the ice shelf condition downstream of the grounding line. A program of satellite and ground measurements to monitor the state of ice sheet equilibrium is recommended.

  5. High pressure ices

    PubMed Central

    Hermann, Andreas; Ashcroft, N. W.; Hoffmann, Roald

    2012-01-01

    H2O will be more resistant to metallization than previously thought. From computational evolutionary structure searches, we find a sequence of new stable and meta-stable structures for the ground state of ice in the 1–5 TPa (10 to 50 Mbar) regime, in the static approximation. The previously proposed Pbcm structure is superseded by a Pmc21 phase at p = 930 GPa, followed by a predicted transition to a P21 crystal structure at p = 1.3 TPa. This phase, featuring higher coordination at O and H, is stable over a wide pressure range, reaching 4.8 TPa. We analyze carefully the geometrical changes in the calculated structures, especially the buckling at the H in O-H-O motifs. All structures are insulating—chemistry burns a deep and (with pressure increase) lasting hole in the density of states near the highest occupied electronic levels of what might be component metallic lattices. Metallization of ice in our calculations occurs only near 4.8 TPa, where the metallic C2/m phase becomes most stable. In this regime, zero-point energies much larger than typical enthalpy differences suggest possible melting of the H sublattice, or even the entire crystal. PMID:22207625

  6. Unveiling the complex electronic structure of amorphous metal oxides

    PubMed Central

    Århammar, C.; Pietzsch, Annette; Bock, Nicolas; Holmström, Erik; Araujo, C. Moyses; Gråsjö, Johan; Zhao, Shuxi; Green, Sara; Peery, T.; Hennies, Franz; Amerioun, Shahrad; Föhlisch, Alexander; Schlappa, Justine; Schmitt, Thorsten; Strocov, Vladimir N.; Niklasson, Gunnar A.; Wallace, Duane C.; Rubensson, Jan-Erik; Johansson, Börje; Ahuja, Rajeev

    2011-01-01

    Amorphous materials represent a large and important emerging area of material’s science. Amorphous oxides are key technological oxides in applications such as a gate dielectric in Complementary metal-oxide semiconductor devices and in Silicon-Oxide-Nitride-Oxide-Silicon and TANOS (TaN-Al2O3-Si3N4-SiO2-Silicon) flash memories. These technologies are required for the high packing density of today’s integrated circuits. Therefore the investigation of defect states in these structures is crucial. In this work we present X-ray synchrotron measurements, with an energy resolution which is about 5–10 times higher than is attainable with standard spectrometers, of amorphous alumina. We demonstrate that our experimental results are in agreement with calculated spectra of amorphous alumina which we have generated by stochastic quenching. This first principles method, which we have recently developed, is found to be superior to molecular dynamics in simulating the rapid gas to solid transition that takes place as this material is deposited for thin film applications. We detect and analyze in detail states in the band gap that originate from oxygen pairs. Similar states were previously found in amorphous alumina by other spectroscopic methods and were assigned to oxygen vacancies claimed to act mutually as electron and hole traps. The oxygen pairs which we probe in this work act as hole traps only and will influence the information retention in electronic devices. In amorphous silica oxygen pairs have already been found, thus they may be a feature which is characteristic also of other amorphous metal oxides.

  7. Molecular mobility in amorphous state: Implications on physical stability

    NASA Astrophysics Data System (ADS)

    Bhardwaj, Sunny Piyush

    Amorphous pharmaceuticals are desirable in drug development due to their advantageous biopharmaceutical properties of higher apparent aqueous solubility and dissolution rate. The main obstacle in their widespread use, however, is their higher physicochemical instability than their crystalline counterparts. The goal of the present research project was to investigate correlations between the molecular mobility and physical stability in model amorphous compounds. The objective was to identify the specific mobility which is responsible for the physical instability in each case. This will potentially enable the development of effective strategies for the stabilization of amorphous pharmaceuticals. Moreover, these correlations can be used to develop predictive models for the stability at the pharmaceutically relevant storage conditions. Subtraction of dc conductivity enabled the comprehensive characterization of molecular mobility in amorphous trehalose. This was followed by investigation of correlation between crystallization behavior and different relaxations. Global mobility was found to be strongly coupled to both crystallization onset time and rate. Different preparation methods imparted different mobility states to amorphous trehalose which was postulated to be the reason for the significant physical stability differences. Predictive models were developed and a good agreement was found between the predicted and the experimental crystallization onset times at temperatures around and below the glass transition temperature (Tg). Effect of annealing was investigated on water sorption, enthalpic recovery and dielectric relaxation times in amorphous trehalose. Global mobility was found to be linearly correlated to the water sorption potential which enabled the development of predictive models. Global mobility was also found to be strongly correlated to physical instability in amorphous itraconazole. Effect of polymer (PVP and HPMCAS) on itraconazole mobility and

  8. Atomic-scale simulations of atomic and molecular mobility in models of interstellar ice

    NASA Astrophysics Data System (ADS)

    Andersson, Stefan

    The mobility of atoms and molecular radicals at ice-covered dust particles controls the surprisingly rich chemistry of circumstellar and interstellar environments, where a large number of different organic molecules have been observed. Both thermal and non-thermal processes, for instance caused by UV radiation, have been inferred to play important roles in this chemistry. A growing number of experimental studies support previously suggested mechanisms and add to the understanding of possible astrochemical processes. Simulations, of both experiments and astrophysical environments, aid in interpreting experiments and suggesting important mechanisms. Still, the exact mechanisms behind the mobility of species in interstellar ice are far from fully understood. We have performed calculations at the molecular level on the mobility of H atoms and OH radicals at water ice surfaces of varying morphology. Calculations of binding energies and diffusion barriers of H atoms at crystalline and amorphous ice surfaces show that the experimentally observed slower diffusion at amorphous ice is due to considerably stronger binding energies and higher diffusion barriers than at crystalline ice. These results are in excellent agreement with recent experiments. It was also found that quantum tunneling is important for H atom mobility below 10 K. The binding energies and diffusion barriers of OH radicals at crystalline ice have been studied using the ONIOM(QM:AMOEBA) approach. Results indicate that OH diffusion over crystalline ice, contrary to the case of H atoms, might be slower at crystalline ice than at amorphous ice, due to a higher surface density of stronger binding sites at crystalline ice. We have also performed molecular dynamics simulations of the photoexcitation of vapor-deposited water at a range of surface temperatures. These results support that the experimentally observed desorption of H atoms following UV excitation is best explained by release of H atoms from

  9. Icing: Accretion, Detection, Protection

    NASA Technical Reports Server (NTRS)

    Reinmann, John J.

    1994-01-01

    The global aircraft industry and its regulatory agencies are currently involved in three major icing efforts: ground icing; advanced technologies for in-flight icing; and tailplane icing. These three major icing topics correspondingly support the three major segments of any aircraft flight profile: takeoff; cruise and hold; and approach and land. This lecture addressess these three topics in the same sequence as they appear in flight, starting with ground deicing, followed by advanced technologies for in-flight ice protection, and ending with tailplane icing.

  10. Fabrication of amorphous diamond films

    DOEpatents

    Falabella, S.

    1995-12-12

    Amorphous diamond films having a significant reduction in intrinsic stress are prepared by biasing a substrate to be coated and depositing carbon ions thereon under controlled temperature conditions. 1 fig.

  11. Raman Spectroscopy of Amorphous Carbon

    SciTech Connect

    Tallant, D.R.; Friedmann, T.A.; Missert, N.A.; Siegal, M.P.; Sullivan, J.P.

    1998-01-01

    Amorphous carbon is an elemental form of carbon with low hydrogen content, which may be deposited in thin films by the impact of high energy carbon atoms or ions. It is structurally distinct from the more well-known elemental forms of carbon, diamond and graphite. It is distinct in physical and chemical properties from the material known as diamond-like carbon, a form which is also amorphous but which has a higher hydrogen content, typically near 40 atomic percent. Amorphous carbon also has distinctive Raman spectra, whose patterns depend, through resonance enhancement effects, not only on deposition conditions but also on the wavelength selected for Raman excitation. This paper provides an overview of the Raman spectroscopy of amorphous carbon and describes how Raman spectral patterns correlate to film deposition conditions, physical properties and molecular level structure.

  12. Amorphization of hard crystalline materials by electrosprayed nanodroplet impact

    SciTech Connect

    Gamero-Castaño, Manuel Torrents, Anna; Borrajo-Pelaez, Rafael; Zheng, Jian-Guo

    2014-11-07

    A beam of electrosprayed nanodroplets impacting on single-crystal silicon amorphizes a thin surface layer of a thickness comparable to the diameter of the drops. The phase transition occurs at projectile velocities exceeding a threshold, and is caused by the quenching of material melted by the impacts. This article demonstrates that the amorphization of silicon is a general phenomenon, as nanodroplets impacting at sufficient velocity also amorphize other covalently bonded crystals. In particular, we bombard single-crystal wafers of Si, Ge, GaAs, GaP, InAs, and SiC in a range of projectile velocities, and characterize the samples via electron backscatter diffraction and transmission electron microscopy to determine the aggregation state under the surface. InAs requires the lowest projectile velocity to develop an amorphous layer, followed by Ge, Si, GaAs, and GaP. SiC is the only semiconductor that remains fully crystalline, likely due to the relatively low velocities of the beamlets used in this study. The resiliency of each crystal to amorphization correlates well with the specific energy needed to melt it except for Ge, which requires projectile velocities higher than expected.

  13. Amorphous metal alloy and composite

    DOEpatents

    Wang, Rong; Merz, Martin D.

    1985-01-01

    Amorphous metal alloys of the iron-chromium and nickel-chromium type have excellent corrosion resistance and high temperature stability and are suitable for use as a protective coating on less corrosion resistant substrates. The alloys are stabilized in the amorphous state by one or more elements of titanium, zirconium, hafnium, niobium, tantalum, molybdenum, and tungsten. The alloy is preferably prepared by sputter deposition.

  14. Signatures of Quantum-Tunneling Diffusion of Hydrogen Atoms on Water Ice at 10 K

    NASA Astrophysics Data System (ADS)

    Kuwahata, K.; Hama, T.; Kouchi, A.; Watanabe, N.

    2015-09-01

    Reported here is the first observation of the tunneling surface diffusion of a hydrogen (H) atom on water ice. Photostimulated desorption and resonance-enhanced multiphoton ionization methods were used to determine the diffusion rates at 10 K on amorphous solid water and polycrystalline ice. H-atom diffusion on polycrystalline ice was 2 orders of magnitude faster than that of deuterium atoms, indicating the occurrence of tunneling diffusion. Whether diffusion is by tunneling or thermal hopping also depends on the diffusion length of the atoms and the morphology of the surface. Our findings contribute to a better understanding of elementary physicochemical processes of hydrogen on cosmic ice dust.

  15. Signatures of Quantum-Tunneling Diffusion of Hydrogen Atoms on Water Ice at 10 K.

    PubMed

    Kuwahata, K; Hama, T; Kouchi, A; Watanabe, N

    2015-09-25

    Reported here is the first observation of the tunneling surface diffusion of a hydrogen (H) atom on water ice. Photostimulated desorption and resonance-enhanced multiphoton ionization methods were used to determine the diffusion rates at 10 K on amorphous solid water and polycrystalline ice. H-atom diffusion on polycrystalline ice was 2 orders of magnitude faster than that of deuterium atoms, indicating the occurrence of tunneling diffusion. Whether diffusion is by tunneling or thermal hopping also depends on the diffusion length of the atoms and the morphology of the surface. Our findings contribute to a better understanding of elementary physicochemical processes of hydrogen on cosmic ice dust. PMID:26451552

  16. Marine ice sheet profiles and stability under Coulomb basal conditions

    NASA Astrophysics Data System (ADS)

    Tsai, Victor; Stewart, Andrew; Thompson, Andrew

    2015-04-01

    The behavior of marine-terminating ice sheets, like the West Antarctic Ice Sheet, is of interest due to the possibility of rapid grounding line retreat and consequent catastrophic loss of ice. Critical to modeling this behavior is a choice of basal rheology, where the most popular approach is to relate the ice sheet velocity to a power-law function of basal stress. Recent experiments, however, suggest that near-grounding line tills exhibit Coulomb friction behavior. Here we address how Coulomb conditions modify ice sheet profiles and stability criteria. The basal rheology necessarily transitions to Coulomb friction near the grounding line due to low effective stresses, leading to changes in ice sheet properties within a narrow boundary layer. Ice sheet profiles 'taper off' towards a flatter upper surface, compared to the power-law case, and basal stresses vanish at the grounding line, consistent with observations. In the Coulomb case, the grounding line ice flux also depends more strongly on flotation ice thickness, which implies that ice sheets are more sensitive to climate perturbations. Furthermore, with Coulomb friction, the ice sheet grounds stably in shallower water than with a power-law rheology. This implies that smaller perturbations are required to push the grounding line into regions of negative bed slope, where it would become unstable. These results have important implications for ice sheet stability in a warming climate.

  17. Ice phases under ambient and high pressure: Insights from density functional theory

    NASA Astrophysics Data System (ADS)

    Fang, Yuan; Xiao, Bing; Tao, Jianmin; Sun, Jianwei; Perdew, John P.

    2013-06-01

    Water is common and plays a crucial role in biological, chemical, and physical processes, but its crystalline or ice state has a complicated structure. In this work, we study the lattice mismatch challenge for ice nucleation on silver iodide, the sublimation energy for different ice phases, and the structural phase-transition pressures of ice, with various density functionals. Our calculations show that the recently developed meta-generalized gradient approximation made simple (MGGA_MS) yields a lattice mismatch (3%) of hexagonal ice (ice Ih) with β-AgI in good agreement with experiment (2%), significantly better than the Perdew-Burke-Ernzerhof (PBE) GGA mismatch (6%). MGGA_MS is a computationally efficient semilocal functional that incorporates intermediate-range van der Waals (vdW) interaction, which, overall, performs well for ice and may be expected to improve upon PBE for liquid water. While MGGA_MS predicts the most realistic volumes and volume changes in the phase transitions of ice Ih to trigonal ice (ice II) and tetragonal ice (ice VIII), a more accurate description of some other properties of the higher-pressure phases (ice II and ice VIII) is provided by some functionals that include long-range vdW corrections (e.g., revised Tao-Perdew-Staroverov-Scuseria+vdW for sublimation energy and optB88-vdW for transition pressure).

  18. Arctic ice islands

    SciTech Connect

    Sackinger, W.M.; Jeffries, M.O.; Lu, M.C.; Li, F.C.

    1988-01-01

    The development of offshore oil and gas resources in the Arctic waters of Alaska requires offshore structures which successfully resist the lateral forces due to moving, drifting ice. Ice islands are floating, a tabular icebergs, up to 60 meters thick, of solid ice throughout their thickness. The ice islands are thus regarded as the strongest ice features in the Arctic; fixed offshore structures which can directly withstand the impact of ice islands are possible but in some locations may be so expensive as to make oilfield development uneconomic. The resolution of the ice island problem requires two research steps: (1) calculation of the probability of interaction between an ice island and an offshore structure in a given region; and (2) if the probability if sufficiently large, then the study of possible interactions between ice island and structure, to discover mitigative measures to deal with the moving ice island. The ice island research conducted during the 1983-1988 interval, which is summarized in this report, was concerned with the first step. Monte Carlo simulations of ice island generation and movement suggest that ice island lifetimes range from 0 to 70 years, and that 85% of the lifetimes are less then 35 years. The simulation shows a mean value of 18 ice islands present at any time in the Arctic Ocean, with a 90% probability of less than 30 ice islands. At this time, approximately 34 ice islands are known, from observations, to exist in the Arctic Ocean, not including the 10-meter thick class of ice islands. Return interval plots from the simulation show that coastal zones of the Beaufort and Chukchi Seas, already leased for oil development, have ice island recurrences of 10 to 100 years. This implies that the ice island hazard must be considered thoroughly, and appropriate safety measures adopted, when offshore oil production plans are formulated for the Alaskan Arctic offshore. 132 refs., 161 figs., 17 tabs.

  19. The Interactions of Stratospherically Abundant Compounds with Ultrathin Ice Films

    NASA Astrophysics Data System (ADS)

    Graham, James Douglas

    To gain understanding of heterogeneous chemistry that occurs in the stratosphere, ultrahigh vacuum-based analysis techniques have been used to study the interactions of HCl, OClO, and Cl_2 with amorphous and crystalline ice films between 10-100 monolayers thick. The study of ultrathin films allows for the distinction between phenomena occurring on the surface and those occurring within the film bulk. Hydrogen chloride interacts with ice to produce two states, one associated with ionized HCl in the bulk and the second with HCl adsorption on the surface. The bulk state, which is the only one present at low HCl exposures, has been assigned to HCl cdot6H_2O. The adsorbed state has been tentatively assigned to molecularly adsorbed HCl. Adsorption of tert-butyl alcohol on amorphous HCl cdot6H_2O results in tert-butyl chloride formation, indicating that chloride ions in the near surface region can react with adsorbates. It was also determined that the sticking coefficient of HCl on crystalline ice is ~40% of that on amorphous ice. Coadsorption of propene and chlorine on ice results in 1,2-dichloropropane formation. The observation that chlorine adsorbed on ice is reactive suggests that there may be heterogeneous pathways for chlorine consumption in the stratosphere. The interaction of OClO with ice was studied in order to predict whether ice particles perturb OClO photochemistry. The desorption rate parameters and sticking coefficient of OClO on ice were used to estimate the equilibrium OClO coverage on ice at stratospherically relevant temperatures and pressures. The value was estimated to be ~10^{ -4} monolayer. Although this value is too low to lead to a significant amount of ozone depletion via heterogeneous chemistry, the value does match well with the equilibrium coverage measured at stratospherically mimetic conditions. The good agreement between the calculated and measured OClO coverages show that ultrahigh vacuum -based techniques can be used to study atmospheric

  20. Amorphous carbon for photovoltaics

    NASA Astrophysics Data System (ADS)

    Risplendi, Francesca; Grossman, Jeffrey C.

    2015-03-01

    All-carbon solar cells have attracted attention as candidates for innovative photovoltaic devices. Carbon-based materials such as graphene, carbon nanotubes (CNT) and amorphous carbon (aC) have the potential to present physical properties comparable to those of silicon-based materials with advantages such as low cost and higher thermal stability.In particular a-C structures are promising systems in which both sp2 and sp3 hybridization coordination are present in different proportions depending on the specific density, providing the possibility of tuning their optoelectronic properties and achieving comparable sunlight absorption to aSi. In this work we employ density functional theory to design suitable device architectures, such as bulk heterojunctions (BHJ) or pn junctions, consisting of a-C as the active layer material.Regarding BHJ, we study interfaces between aC and C nanostructures (such as CNT and fullerene) to relate their optoelectronic properties to the stoichiometry of aC. We demonstrate that the energy alignment between the a-C mobility edges and the occupied and unoccupied states of the CNT or C60 can be widely tuned by varying the aC density to obtain a type II interface.To employ aC in pn junctions we analyze the p- and n-type doping of a-C focusingon an evaluation of the Fermi level and work function dependence on doping.Our results highlight promising features of aC as the active layer material of thin-film solar cells.

  1. West Antarctic Ice Sheet formed earlier than thought

    NASA Astrophysics Data System (ADS)

    Balcerak, Ernie

    2013-10-01

    About 34 million years ago, Earth transitioned from a warm "greenhouse" climate to a cold "icehouse" climate, marking the transition between the Eocene and Oligocene epochs. This transition has been associated with the formation of a large ice sheet on Antarctica.

  2. Anisotropic mechanical amorphization drives wear in diamond

    NASA Astrophysics Data System (ADS)

    Pastewka, Lars; Moser, Stefan; Gumbsch, Peter; Moseler, Michael

    2011-01-01

    Diamond is the hardest material on Earth. Nevertheless, polishing diamond is possible with a process that has remained unaltered for centuries and is still used for jewellery and coatings: the diamond is pressed against a rotating disc with embedded diamond grit. When polishing polycrystalline diamond, surface topographies become non-uniform because wear rates depend on crystal orientations. This anisotropy is not fully understood and impedes diamond’s widespread use in applications that require planar polycrystalline films, ranging from cutting tools to confinement fusion. Here, we use molecular dynamics to show that polished diamond undergoes an sp3-sp2 order-disorder transition resulting in an amorphous adlayer with a growth rate that strongly depends on surface orientation and sliding direction, in excellent correlation with experimental wear rates. This anisotropy originates in mechanically steered dissociation of individual crystal bonds. Similarly to other planarization processes, the diamond surface is chemically activated by mechanical means. Final removal of the amorphous interlayer proceeds either mechanically or through etching by ambient oxygen.

  3. Amorphous metallic foam: Synthesis and mechanical properties

    NASA Astrophysics Data System (ADS)

    Veazey, Chris

    2007-12-01

    Bulk metallic glass alloys were processed into foam by several synthesis routes. These methods utilize the thermodynamic stability and thermoplastic formability of the supercooled liquid state to produce low-density homogeneous foams. The cellular structure is shown to evolve by growth of randomly distributed spherical bubbles towards polyhedral-like cells separated by microscopic intracellular membranes exhibiting random orientations and aspect ratios. The ability of amorphous metals to develop such random cellular morphologies is attributed primarily to the high ductility exhibited by their softened state, which enables large superplastic membrane elongations during foaming. Upon loading, moderate porosity foams are known to deform plastically by recurring non-linear yielding transitions followed by non-catastrophic collapse events. The ability of these foams to yield non-catastrophically is a result of the plastic deformability of amorphous metals in sub-millimeter dimensions. Nonlinear yielding is found to be accommodated by clusters involving 4--6 cells, which yield by intracellular membrane buckling and ultimately collapse plastically to produce a localized plastic collapse band. By comparison, high-porosity foams deform plastically by multiple recurring non-catastrophic collapse events without undergoing macroscopic failure. The numerous minor collapse events are associated with localized ligament collapse, and the few major collapse events are associated with the cooperative collapse of several adjacent ligaments and the formation of a collapse band. On average, the serrated flow responses between major events appear to be self-similar and resemble the recurring nonlinear yielding responses exhibited by moderate porosity foams.

  4. Amorphous phase formation in mechanically alloyed iron-based systems

    NASA Astrophysics Data System (ADS)

    Sharma, Satyajeet

    Bulk metallic glasses have interesting combination of physical, chemical, mechanical, and magnetic properties which make them attractive for a variety of applications. Consequently there has been a lot of interest in understanding the structure and properties of these materials. More varied applications can be sought if one understands the reasons for glass formation and the methods to control them. The glass-forming ability (GFA) of alloys can be substantially increased by a proper selection of alloying elements and the chemical composition of the alloy. High GFA will enable in obtaining large section thickness of amorphous alloys. Ability to produce glassy alloys in larger section thicknesses enables exploitation of these advanced materials for a variety of different applications. The technique of mechanical alloying (MA) is a powerful non-equilibrium processing technique and is known to produce glassy (or amorphous) alloys in several alloy systems. Metallic amorphous alloys have been produced by MA starting from either blended elemental metal powders or pre-alloyed powders. Subsequently, these amorphous alloy powders could be consolidated to full density in the temperature range between the glass transition and crystallization temperatures, where the amorphous phase has a very low viscosity. This Dissertation focuses on identifying the various Fe-based multicomponent alloy systems that can be amorphized using the MA technique, studying the GFA of alloys with emphasis on improving it, and also on analyzing the effect of extended milling time on the constitution of the amorphous alloy powder produced at earlier times. The Dissertation contains seven chapters, where the lead chapter deals with the background, history and introduction to bulk metallic glasses. The following four chapters are the published/to be published work, where the criterion for predicting glass formation, effect of Niobium addition on glass-forming ability (GFA), lattice contraction on

  5. Modeling of surface roughness effects on glaze ice accretion

    NASA Technical Reports Server (NTRS)

    Hansman, R. John, Jr.; Yamaguchi, Keiko; Berkowitz, Brian M.; Potapczuk, Mark

    1990-01-01

    A series of experimental investigations focused on studying the cause and effect of roughness on accreting glaze ice surfaces were conducted. Detailed microvideo observations were made of glaze ice accretions on 1 to 4 inch diameter cylinders in three icing wind tunnels (the Data Products of New England six inch test facility, the NASA Lewis Icing Research Tunnel, and the B. F. Goodrich Ice Protection Research Facility). Infrared thermal video recordings were made of accreting ice surfaces in the Goodrich facility. Distinct zones of surface water behavior were observed; a smooth wet zone in the stagnation region with a uniform water film; a rough zone where surface tension effects caused coalescence of surface water into stationary beads; a horn zone where roughness elements grow into horn shapes; a runback zone where surface water ran back as rivulets; and a dry zone where rime feathers formed. The location of the transition from the smooth to the rough zone was found to migrate with time towards the stagnation point. The behavior of the transition appeared to be controlled by boundary layer transition and bead formation mechanisms at the interface between the smooth and rough zones. Regions of wet ice growth and enhanced heat transfer were clearly visible in the infrared video recordings of glaze ice surfaces. A simple multi-zone modification to the current glaze ice accretion model was proposed to include spatial variability in surface roughness.

  6. Stochastic ice stream dynamics

    NASA Astrophysics Data System (ADS)

    Mantelli, Elisa; Bertagni, Matteo Bernard; Ridolfi, Luca

    2016-08-01

    Ice streams are narrow corridors of fast-flowing ice that constitute the arterial drainage network of ice sheets. Therefore, changes in ice stream flow are key to understanding paleoclimate, sea level changes, and rapid disintegration of ice sheets during deglaciation. The dynamics of ice flow are tightly coupled to the climate system through atmospheric temperature and snow recharge, which are known exhibit stochastic variability. Here we focus on the interplay between stochastic climate forcing and ice stream temporal dynamics. Our work demonstrates that realistic climate fluctuations are able to (i) induce the coexistence of dynamic behaviors that would be incompatible in a purely deterministic system and (ii) drive ice stream flow away from the regime expected in a steady climate. We conclude that environmental noise appears to be crucial to interpreting the past behavior of ice sheets, as well as to predicting their future evolution.

  7. Sea ice ecosystems.

    PubMed

    Arrigo, Kevin R

    2014-01-01

    Polar sea ice is one of the largest ecosystems on Earth. The liquid brine fraction of the ice matrix is home to a diverse array of organisms, ranging from tiny archaea to larger fish and invertebrates. These organisms can tolerate high brine salinity and low temperature but do best when conditions are milder. Thriving ice algal communities, generally dominated by diatoms, live at the ice/water interface and in recently flooded surface and interior layers, especially during spring, when temperatures begin to rise. Although protists dominate the sea ice biomass, heterotrophic bacteria are also abundant. The sea ice ecosystem provides food for a host of animals, with crustaceans being the most conspicuous. Uneaten organic matter from the ice sinks through the water column and feeds benthic ecosystems. As sea ice extent declines, ice algae likely contribute a shrinking fraction of the total amount of organic matter produced in polar waters. PMID:24015900

  8. Stochastic ice stream dynamics.

    PubMed

    Mantelli, Elisa; Bertagni, Matteo Bernard; Ridolfi, Luca

    2016-08-01

    Ice streams are narrow corridors of fast-flowing ice that constitute the arterial drainage network of ice sheets. Therefore, changes in ice stream flow are key to understanding paleoclimate, sea level changes, and rapid disintegration of ice sheets during deglaciation. The dynamics of ice flow are tightly coupled to the climate system through atmospheric temperature and snow recharge, which are known exhibit stochastic variability. Here we focus on the interplay between stochastic climate forcing and ice stream temporal dynamics. Our work demonstrates that realistic climate fluctuations are able to (i) induce the coexistence of dynamic behaviors that would be incompatible in a purely deterministic system and (ii) drive ice stream flow away from the regime expected in a steady climate. We conclude that environmental noise appears to be crucial to interpreting the past behavior of ice sheets, as well as to predicting their future evolution. PMID:27457960

  9. Top Sounder Ice Penetration

    NASA Astrophysics Data System (ADS)

    Porter, D. L.; Goemmer, S. A.; Sweeney, J. H.

    2014-12-01

    Ice draft measurements are made as part of normal operations for all US Navy submarines operating in the Arctic Ocean. The submarine ice draft data are unique in providing high resolution measurements over long transects of the ice covered ocean. The data has been used to document a multidecadal drop in ice thickness, and for validating and improving numerical sea-ice models. A submarine upward-looking sonar draft measurement is made by a sonar transducer mounted in the sail or deck of the submarine. An acoustic beam is transmitted upward through the water column, reflecting off the bottom of the sea ice and returning to the transducer. Ice thickness is estimated as the difference between the ship's depth (measured by pressure) and the acoustic range to the bottom of the ice estimated from the travel time of the sonar pulse. Digital recording systems can provide the return off the water-ice interface as well as returns that have penetrated the ice. Typically, only the first return from the ice hull is analyzed. Information regarding ice flow interstitial layers provides ice age information and may possibly be derived with the entire return signal. The approach being investigated is similar to that used in measuring bottom sediment layers and will involve measuring the echo level from the first interface, solving the reflection loss from that transmission, and employing reflection loss versus impedance mismatch to ascertain ice structure information.

  10. Sonochemical preparation of nanosized amorphous Fe-Ni alloys

    NASA Astrophysics Data System (ADS)

    Shafi, K. V. P. M.; Gedanken, A.; Goldfarb, R. B.; Felner, I.

    1997-05-01

    Nanosized amorphous alloy powders of Fe20Ni80, Fe40Ni60, and Fe60Ni40 were prepared by sonochemical decomposition of solutions of volatile organic precursors, Fe(CO)5 and Ni(CO)4 in decalin, under an argon pressure of 100 to 150 kPa at 273 K. Magnetic susceptibility of Fe40Ni60 and Fe60Ni40 indicates blocking temperatures of 35 K and a magnetic particle size of about 6 nm. Thermogravimetric measurements of Fe20Ni80 give Curie temperatures of 322 °C for amorphous and 550 °C for crystallized forms. Differential scanning calorimetry exhibits an endothermic transition at 335 °C from a combination of the magnetic phase transition and alloy crystallization. The Mössbauer spectrum of crystallized Fe20Ni80 shows a sextet pattern with a hyperfine field of 25.04 T.

  11. Growing timescales and lengthscales characterizing vibrations of amorphous solids.

    PubMed

    Berthier, Ludovic; Charbonneau, Patrick; Jin, Yuliang; Parisi, Giorgio; Seoane, Beatriz; Zamponi, Francesco

    2016-07-26

    Low-temperature properties of crystalline solids can be understood using harmonic perturbations around a perfect lattice, as in Debye's theory. Low-temperature properties of amorphous solids, however, strongly depart from such descriptions, displaying enhanced transport, activated slow dynamics across energy barriers, excess vibrational modes with respect to Debye's theory (i.e., a boson peak), and complex irreversible responses to small mechanical deformations. These experimental observations indirectly suggest that the dynamics of amorphous solids becomes anomalous at low temperatures. Here, we present direct numerical evidence that vibrations change nature at a well-defined location deep inside the glass phase of a simple glass former. We provide a real-space description of this transition and of the rapidly growing time- and lengthscales that accompany it. Our results provide the seed for a universal understanding of low-temperature glass anomalies within the theoretical framework of the recently discovered Gardner phase transition. PMID:27402768

  12. Preparation of an amorphous sodium furosemide salt improves solubility and dissolution rate and leads to a faster Tmax after oral dosing to rats.

    PubMed

    Nielsen, Line Hagner; Gordon, Sarah; Holm, René; Selen, Arzu; Rades, Thomas; Müllertz, Anette

    2013-11-01

    Amorphous forms of furosemide sodium salt and furosemide free acid were prepared by spray drying. For the preparation of the amorphous free acid, methanol was utilised as the solvent, whereas the amorphous sodium salt was formed from a sodium hydroxide-containing aqueous solvent in equimolar amounts of NaOH and furosemide. Information about the structural differences between the two amorphous forms was obtained by Fourier Transform Infrared Spectroscopy (FTIR), and glass transition temperature (Tg) was determined using Differential Scanning Calorimetry (DSC). The stability and devitrification tendency of the two amorphous forms were investigated by X-ray Powder Diffraction (XRPD). The apparent solubility of the two amorphous forms and the crystalline free acid form of furosemide in various gastric and intestinal stimulated media was determined. Moreover, the dissolution characteristics of the two amorphous forms and of crystalline free acid were investigated. FTIR confirmed molecular differences between the amorphous free acid and salt. The amorphous salt showed a Tg of 101.2 °C, whereas the Tg for the amorphous free acid was found to be 61.8 °C. The amorphous free acid was physically stable for 4 days at 22 °C and 33% relative humidity (RH), while the amorphous salt exhibited physical stability for 291 days at the same storage conditions. When storing the amorphous forms at 40 °C and 75% RH both forms converted to crystalline forms after 2 days. The apparent solubility of the amorphous salt form was higher than that of both amorphous and crystalline free acid in all media studied. All three forms of furosemide exhibited a greater solubility in the presence of biorelevant media as compared to buffer, however, an overall trend for a further increase in solubility in relation to an increase in media surfactant concentration was not seen. The amorphous salt demonstrated an 8- and 20-fold higher intrinsic dissolution rate (IDR) when compared to amorphous and

  13. Effects of Ice Accretion on Aircraft Aerodynamics

    NASA Technical Reports Server (NTRS)

    Bragg, Michael B.

    1998-01-01

    The primary objective of this research was to support the development of a new ice accretion model by improving our physical understanding of the ice accretion process through experimental measurements. The focus was on the effect of the initial ice roughness (smooth/rough boundary) on the accretion process. This includes understanding the boundary-layer development over the roughness and especially its effect on the heat transfer which is fundamental to the ice accretion process. The research focused on acquiring the experimental data needed to formulate a new ice accretion physical model. Research was conducted to analyze boundary-layer data taken on a NACA 0012 airfoil with roughness to simulate the smooth/rough boundary. The effect of isolated roughness on boundary-layer transition was studied experimentally to determine if the classical critical roughness Reynolds number criteria could be applied to transition in the airfoil leading-edge area. The effect of simulated smooth/rough boundary roughness on convective heat transfer was studied to complete the study. During the course of this research the effect of free-stream wind tunnel turbulence on the boundary layer was measured. Since this quantity was not well known, research to accurately measure the wind tunnel turbulence in an icing cloud was undertaken. Preliminary results were attained and the final data were acquired, reduced and presented under a subsequent grant.

  14. Measurement of ice thickness (icing) in aeronautics

    NASA Technical Reports Server (NTRS)

    Hansman, R. John; Kirby, Mark S. JR.

    1988-01-01

    Pulsed ultrasonic techniques have been used to measure the formation of ice in flight in an icing wind tunnel with a precision of + or - 0.5 mm. Two icing regimes, humid and dry, are identified. Both natural and artificial conditions are considered. On the basis of ice formation rates obtained by the ultrasound technique and the observed surface conditions, it is found that the heat transfer coefficients are larger in the wind tunnel tests than in actual flight, presumably due to the higher level of turbulence in the wind tunnel tests. Profiles obtained during flight under natural conditions are compared with mechanical-type measurements and with the results of stereographic analysis.

  15. Phytoplankton spring bloom beneath heavily snow-covered arctic sea ice during the N-ICE2015 cruise

    NASA Astrophysics Data System (ADS)

    Assmy, Philipp; Fernández-Méndez, Mar; Olsen, Lasse M.; Kauko, Hanna; Duarte, Pedro; Mundy, Christopher J.; Hop, Haakon; Fransson, Agneta; Chierici, Melissa; Gerland, Sebastian; Granskog, Mats A.; Hudson, Stephen R.; Roesel, Anja; Meyer, Amelie; Hughes, Nick; Steen, Harald

    2016-04-01

    The arctic icescape is rapidly transforming from a thick multi-year ice cover to a thinner and largely seasonal first-year ice cover with significant consequences for Arctic primary production. Recent studies have reported extensive phytoplankton blooms beneath ponded sea ice during summer, indicating that satellite-based arctic net primary production estimates may be significantly underestimated. We studied phytoplankton seasonal dynamics under changing sea-ice and snow conditions in the drifting pack-ice north of Svalbard from 11 January to 24 June 2015 during the Norwegian Young Sea ICE cruise (N-ICE2015). N-ICE2015 provided a unique time-series of under-ice bloom dynamics during the winter-spring transition in the high Arctic pack-ice ecosystem. Phytoplankton productivity stayed low throughout winter and early spring. By late May a large under-ice bloom (>300 mg Chl a m-2) dominated by Phaeocystis pouchetii developed over the Yermak plateau underneath 1.1 - 1.3 m thick sea ice and 0.3 - 0.5 m thick snow cover. The circulation characteristics over the plateau indicate that the bloom developed in situ and was not advected. The high lead activity, characteristic for the area, apparently provided enough open or thin ice covered area for sufficient light to penetrate into the underlying water column and initiate and sustain the bloom, despite the thick snow cover. Our observation of a spring under-ice phytoplankton bloom extends the spatial and temporal scale of under-ice blooms and indicates that these phenomena might become increasingly important in the future Arctic under changing sea-ice but also snow dynamics.

  16. Formation of amorphous metal alloys by chemical vapor deposition

    DOEpatents

    Mullendore, A.W.

    1988-03-18

    Amorphous alloys are deposited by a process of thermal dissociation of mixtures of organometallic compounds and metalloid hydrides,e.g., transition metal carbonyl, such as nickel carbonyl and diborane. Various sizes and shapes of deposits can be achieved, including near-net-shape free standing articles, multilayer deposits, and the like. Manipulation or absence of a magnetic field affects the nature and the structure of the deposit. 1 fig.

  17. Formation of amorphous metal alloys by chemical vapor deposition

    DOEpatents

    Mullendore, Arthur W.

    1990-01-01

    Amorphous alloys are deposited by a process of thermal dissociation of mixtures or organometallic compounds and metalloid hydrides, e.g., transition metal carbonyl such as nickel carbonyl, and diborane. Various sizes and shapes of deposits can be achieved, including near-net-shape free standing articles, multilayer deposits, and the like. Manipulation or absence of a magnetic field affects the nature and the structure of the deposit.

  18. Hysteresis and Temporal Scales of Ice Stream Variability

    NASA Astrophysics Data System (ADS)

    Robel, A.; DeGiuli, E.; Schoof, C.; Tziperman, E.

    2012-12-01

    Understanding the mechanisms governing temporal variability of ice stream flow remains one of the major barriers to developing accurate models of ice sheet dynamics and ice-climate interactions. Previous efforts considered the effects of heating at the bed and consequent basal melting on ice stream dynamics, as well as the effect of a dynamic drainage system on ice flow. We consider the effects of both basal heating and dynamic drainage on ice stream flow for the first time, and model ice dynamics, melt water production and drainage evolution. We determine which processes contribute to ice stream variability and the physical controls on the temporal scales of ice stream stagnation and activation. Our tools of choice are both simple and intermediate complexity models of subglacial processes and simple ice dynamics. Analytic and numerical results from the simple model indicate that there are two major modes of ice stream behavior: steady-streaming and binge-purge-like variability. The steady-streaming mode arises either from drainage- or friction-mediated subglacial meltwater production. The binge-purge mode arises from a sufficiently cold environment sustaining successive cycles of thinning-induced basal cooling and stagnation. We characterize both the parameter regimes that produce each of the modes as well as the period of ice stream variability. Modern Siple Coast ice streams are found to reside in the binge-purge parameter regime near a transition to the steady-streaming mode. Changing the prescribed atmospheric temperature can lead to a transition between these modes through a subcritical Hopf bifurcation. The properties of this type of bifurcation and our numerical experiments indicate that this may lead to significant hysteresis in ice stream variability as the surface temperature is varied. Upon atmospheric warming, modern Siple Coast ice streams would transition from binge-purge behavior to steady-streaming at a very different temperature than the reverse

  19. Metastable Nitric Acid Trihydrate in Ice Clouds

    PubMed Central

    Weiss, Fabian; Kubel, Frank; Gálvez, Óscar; Hoelzel, Markus; Parker, Stewart F.; Baloh, Philipp; Iannarelli, Riccardo; Rossi, Michel J.

    2016-01-01

    Abstract The composition of high‐altitude ice clouds is still a matter of intense discussion. The constituents in question are ice and nitric acid hydrates, but the exact phase composition of clouds and its formation mechanisms are still unknown. In this work, conclusive evidence for a long‐predicted phase, alpha‐nitric acid trihydrate (alpha‐NAT), is presented. This phase was characterized by a combination of X‐ray and neutron diffraction experiments, allowing a convincing structure solution. Furthermore, vibrational spectra (infrared and inelastic neutron scattering) were recorded and compared with theoretical calculations. A strong interaction between water ice and alpha‐NAT was found, which explains the experimental spectra and the phase‐transition kinetics. On the basis of these results, we propose a new three‐step mechanism for NAT formation in high‐altitude ice clouds. PMID:26879259

  20. Metastable Nitric Acid Trihydrate in Ice Clouds.

    PubMed

    Weiss, Fabian; Kubel, Frank; Gálvez, Óscar; Hoelzel, Markus; Parker, Stewart F; Baloh, Philipp; Iannarelli, Riccardo; Rossi, Michel J; Grothe, Hinrich

    2016-03-01

    The composition of high-altitude ice clouds is still a matter of intense discussion. The constituents in question are ice and nitric acid hydrates, but the exact phase composition of clouds and its formation mechanisms are still unknown. In this work, conclusive evidence for a long-predicted phase, alpha-nitric acid trihydrate (alpha-NAT), is presented. This phase was characterized by a combination of X-ray and neutron diffraction experiments, allowing a convincing structure solution. Furthermore, vibrational spectra (infrared and inelastic neutron scattering) were recorded and compared with theoretical calculations. A strong interaction between water ice and alpha-NAT was found, which explains the experimental spectra and the phase-transition kinetics. On the basis of these results, we propose a new three-step mechanism for NAT formation in high-altitude ice clouds. PMID:26879259

  1. National Ice Center Visiting Scientist Program

    NASA Technical Reports Server (NTRS)

    Austin, Meg

    2001-01-01

    The objectives of the work done by Dr. Kim Partington were to manage NASA's polar research program, including its strategic direction, research funding and interagency and international collaborations. The objectives of the UCAR Visiting Scientist Program at the National Ice Center (NIC) are to: (1) Manage a visiting scientist program for the NIC Science Center in support of the mission of the NIC; (2) Provide a pool of researchers who will share expertise with the NIC and the science community; (3) Facilitate communications between the research and operational communities for the purpose of identifying work ready for validation and transition to an operational environment; and (4) Act as a focus for interagency cooperation. The NIC mission is to provide worldwide operational sea ice analyses and forecasts for the armed forces of the US and allied nations, the Departments of Commerce and Transportation, and other US Government and international agencies, and the civil sector. The NIC produces these analyses and forecasts of Arctic, Antarctic, Great Lakes, and Chesapeake Bay ice conditions to support customers with global, regional, and tactical scale interests. The NIC regularly deploys Naval Ice Center NAVICECEN Ice Reconnaissance personnel to the Arctic and Antarctica in order to perform aerial ice observation and analysis in support of NIC customers. NIC ice data are a key part of the US contribution to international global climate and ocean observing systems.

  2. Stochastic approach to plasticity and yield in amorphous solids.

    PubMed

    Hentschel, H G E; Jaiswal, Prabhat K; Procaccia, Itamar; Sastry, Srikanth

    2015-12-01

    We focus on the probability distribution function (PDF) P(Δγ;γ) where Δγ are the measured strain intervals between plastic events in a athermal strained amorphous solids, and γ measures the accumulated strain. The tail of this distribution as Δγ→0 (in the thermodynamic limit) scales like Δγ(η). The exponent η is related via scaling relations to the tail of the PDF of the eigenvalues of the plastic modes of the Hessian matrix P(λ) which scales like λ(θ), η=(θ-1)/2. The numerical values of η or θ can be determined easily in the unstrained material and in the yielded state of plastic flow. Special care is called for in the determination of these exponents between these states as γ increases. Determining the γ dependence of the PDF P(Δγ;γ) can shed important light on plasticity and yield. We conclude that the PDF's of both Δγ and λ are not continuous functions of γ. In slowly quenched amorphous solids they undergo two discontinuous transitions, first at γ=0(+) and then at the yield point γ=γ(Y) to plastic flow. In quickly quenched amorphous solids the second transition is smeared out due to the nonexisting stress peak before yield. The nature of these transitions and scaling relations with the system size dependence of 〈Δγ〉 are discussed. PMID:26764687

  3. The use of MTDSC to assess the amorphous phase content of a micronized drug substance.

    PubMed

    Guinot, S; Leveiller, F

    1999-12-01

    Mechanical treatments such as grinding, milling or micronization applied to crystalline drug substances may induce changes such as the occurrence of crystal defects and/or amorphous regions. These changes are likely to affect the chemical and physical properties of the material as well as the corresponding drug product performances. Various analytical techniques such as standard differential scanning calorimetry, isothermal and solution microcalorimetry as well as dynamic vapour sorption can be used to characterise and possibly quantify the amorphous phase content of these materials. These techniques have been applied for the development of analytical methods based on temperature- or solvent-induced (including water) recrystallization of the amorphous phase in semi-crystalline drug substances and excipients and have sometimes allowed for detecting low amounts of amorphous phase. We have developed an alternative MTDSC method for the quantitation of the amorphous content in samples of a micronized drug substance co-crystal (form A), an antibiotic drug substance which does not recrystallize even when exposed to temperature or solvent vapours. This is performed through measurement of the heat capacity jump associated with the amorphous phase glass transition. The MTDSC parameters and experimental conditions were optimised for this system. The amorphous content calibration curve was established using pure crystalline and amorphous drug substance samples and their known mixtures. Limits of detection and quantification of 0.9 and 3.0% (w/w) respectively were obtained for specimen mass less than 5 mg. PMID:10572200

  4. Nanostructures having crystalline and amorphous phases

    SciTech Connect

    Mao, Samuel S; Chen, Xiaobo

    2015-04-28

    The present invention includes a nanostructure, a method of making thereof, and a method of photocatalysis. In one embodiment, the nanostructure includes a crystalline phase and an amorphous phase in contact with the crystalline phase. Each of the crystalline and amorphous phases has at least one dimension on a nanometer scale. In another embodiment, the nanostructure includes a nanoparticle comprising a crystalline phase and an amorphous phase. The amorphous phase is in a selected amount. In another embodiment, the nanostructure includes crystalline titanium dioxide and amorphous titanium dioxide in contact with the crystalline titanium dioxide. Each of the crystalline and amorphous titanium dioxide has at least one dimension on a nanometer scale.

  5. Amorphous Alloy Membranes for High Temperature Hydrogen Separation

    SciTech Connect

    Coulter, K

    2013-09-30

    At the beginning of this project, thin film amorphous alloy membranes were considered a nascent but promising new technology for industrial-scale hydrogen gas separations from coal- derived syngas. This project used a combination of theoretical modeling, advanced physical vapor deposition fabricating, and laboratory and gasifier testing to develop amorphous alloy membranes that had the potential to meet Department of Energy (DOE) targets in the testing strategies outlined in the NETL Membrane Test Protocol. The project is complete with Southwest Research Institute® (SwRI®), Georgia Institute of Technology (GT), and Western Research Institute (WRI) having all operated independently and concurrently. GT studied the hydrogen transport properties of several amorphous alloys and found that ZrCu and ZrCuTi were the most promising candidates. GT also evaluated the hydrogen transport properties of V, Nb and Ta membranes coated with different transition-metal carbides (TMCs) (TM = Ti, Hf, Zr) catalytic layers by employing first-principles calculations together with statistical mechanics methods and determined that TiC was the most promising material to provide catalytic hydrogen dissociation. SwRI developed magnetron coating techniques to deposit a range of amorphous alloys onto both porous discs and tubular substrates. Unfortunately none of the amorphous alloys could be deposited without pinhole defects that undermined the selectivity of the membranes. WRI tested the thermal properties of the ZrCu and ZrNi alloys and found that under reducing environments the upper temperature limit of operation without recrystallization is ~250 °C. There were four publications generated from this project with two additional manuscripts in progress and six presentations were made at national and international technical conferences. The combination of the pinhole defects and the lack of high temperature stability make the theoretically identified most promising candidate amorphous alloys

  6. Amorphous-diamond electron emitter

    DOEpatents

    Falabella, Steven

    2001-01-01

    An electron emitter comprising a textured silicon wafer overcoated with a thin (200 .ANG.) layer of nitrogen-doped, amorphous-diamond (a:D-N), which lowers the field below 20 volts/micrometer have been demonstrated using this emitter compared to uncoated or diamond coated emitters wherein the emission is at fields of nearly 60 volts/micrometer. The silicon/nitrogen-doped, amorphous-diamond (Si/a:D-N) emitter may be produced by overcoating a textured silicon wafer with amorphous-diamond (a:D) in a nitrogen atmosphere using a filtered cathodic-arc system. The enhanced performance of the Si/a:D-N emitter lowers the voltages required to the point where field-emission displays are practical. Thus, this emitter can be used, for example, in flat-panel emission displays (FEDs), and cold-cathode vacuum electronics.

  7. Generalized melting criterion for amorphization

    SciTech Connect

    Devanathan, R. |; Lam, N.Q.; Okamoto, P.R.; Meshii, M.

    1992-12-01

    We present a thermodynamic model of solid-state amorphization based on a generalization of the well-known Lindemann criterion. The original Lindemann criterion proposes that melting occurs when the root-mean-square amplitude of thermal displacement exceeds a critical value. This criterion can be generalized to include solid-state amorphization by taking into account the static displacements. In an effort to verify the generalized melting criterion, we have performed molecular dynamics simulations of radiation-induced amorphization in NiZr, NiZr{sub 2}, NiTi and FeTi using embedded-atom potentials. The average shear elastic constant G was calculated as a function of the total mean-square atomic displacement following random atom-exchanges and introduction of Frenkel pairs. Results provide strong support for the generalized melting criterion.

  8. Doped Artificial Spin Ice

    NASA Astrophysics Data System (ADS)

    Olson Reichhardt, Cynthia; Libal, Andras; Reichhardt, Charles

    We examine square and kagome artificial spin ice for colloids confined in arrays of double-well traps. Unlike magnetic artificial spin ices, colloidal and vortex artificial spin ice realizations allow creation of doping sites through double occupation of individual traps. We find that doping square and kagome ice geometries produces opposite effects. For square ice, doping creates local excitations in the ground state configuration that produce a local melting effect as the temperature is raised. In contrast, the kagome ice ground state can absorb the doping charge without generating non-ground-state excitations, while at elevated temperatures the hopping of individual colloids is suppressed near the doping sites. These results indicate that in the square ice, doping adds degeneracy to the ordered ground state and creates local weak spots, while in the kagome ice, which has a highly degenerate ground state, doping locally decreases the degeneracy and creates local hard regions.

  9. Greenland Ice Flow

    NASA Video Gallery

    Greenland looks like a big pile of snow seen from space using a regular camera. But satellite radar interferometry helps us detect the motion of ice beneath the snow. Ice starts flowing from the fl...

  10. Investigating the Pressure-Induced Amorphization of Zeolitic Imidazolate Framework ZIF-8: Mechanical Instability Due to Shear Mode Softening.

    PubMed

    Ortiz, Aurélie U; Boutin, Anne; Fuchs, Alain H; Coudert, François-Xavier

    2013-06-01

    We provide the first molecular dynamics study of the mechanical instability that is the cause of pressure-induced amorphization of zeolitic imidazolate framework ZIF-8. By measuring the elastic constants of ZIF-8 up to the amorphization pressure, we show that the crystal-to-amorphous transition is triggered by the mechanical instability of ZIF-8 under compression, due to shear mode softening of the material. No similar softening was observed under temperature increase, explaining the absence of temperature-induced amorphization in ZIF-8. We also demonstrate the large impact of the presence of adsorbate in the pores on the mechanical stability and compressibility of the framework, increasing its shear stability. This first molecular dynamics study of ZIF mechanical properties under variations of pressure, temperature, and pore filling opens the way to a more comprehensive understanding of their mechanical stability, structural transitions, and amorphization. PMID:26283122

  11. Ice rule correlations in stuffed spin ice

    NASA Astrophysics Data System (ADS)

    Aldus, R. J.; Fennell, T.; Deen, P. P.; Ressouche, E.; Lau, G. C.; Cava, R. J.; Bramwell, S. T.

    2013-01-01

    Stuffed spin ice is a chemical variation of a spin ice material like Ho2Ti2O7 in which extra magnetic ions are inserted into the crystal structure. Previous studies have shown that the degree of stuffing has very little effect on the residual entropy in the system, which takes a value very close to the spin ice entropy. We argue, however, that the observation of this entropy does not imply long range coherence of the ice rules, that determine the local spin configurations. We have characterized deviations from the ice rules by means of a polarized neutron diffraction study of a single crystal of Ho2+δTi2-δO7-δ/2 with δ = 0.3. Our results demonstrate that the ice rules in stuffed spin ice are strictly valid only over a relatively short range, and that at longer range stuffed spin ice exhibits some characteristics of a ‘cluster glass’, with a tendency to more conventional ferromagnetic correlations.

  12. Ice electrode electrolytic cell

    DOEpatents

    Glenn, D.F.; Suciu, D.F.; Harris, T.L.; Ingram, J.C.

    1993-04-06

    This invention relates to a method and apparatus for removing heavy metals from waste water, soils, or process streams by electrolytic cell means. The method includes cooling a cell cathode to form an ice layer over the cathode and then applying an electric current to deposit a layer of the heavy metal over the ice. The metal is then easily removed after melting the ice. In a second embodiment, the same ice-covered electrode can be employed to form powdered metals.

  13. Ice electrode electrolytic cell

    DOEpatents

    Glenn, David F.; Suciu, Dan F.; Harris, Taryl L.; Ingram, Jani C.

    1993-01-01

    This invention relates to a method and apparatus for removing heavy metals from waste water, soils, or process streams by electrolytic cell means. The method includes cooling a cell cathode to form an ice layer over the cathode and then applying an electric current to deposit a layer of the heavy metal over the ice. The metal is then easily removed after melting the ice. In a second embodiment, the same ice-covered electrode can be employed to form powdered metals.

  14. Ice electrode electrolytic cell

    SciTech Connect

    Glenn, D.F.; Suciu, D.F.; Harris, T.L.; Ingram, J.C.

    1992-12-31

    This invention relates to a method and apparatus for removing heavy metals from waste water, soils, or process streams by electrolytic cell means. The method includes cooling a cell cathode to form an ice layer over the cathode and then applying an electric current to deposit a layer of the heavy metal over the ice. The metal is then easily removed after melting the ice. In a second embodiment, the same ice-covered electrode can be employed to form powdered metals.

  15. Triggers for the Collapse of Ice Shelves in Antarctica: Investigating Compressive Arch Failure with Numerical Models

    NASA Astrophysics Data System (ADS)

    Huth, A.; Smith, B. E.

    2015-12-01

    Antarctic ice shelves restrain, or buttress, grounded ice from flowing freely into the ocean by redistributing the force of the ice flow to pinning points (ice rises) at the ice front and shear margins at adjacent bay walls. This buttressing process typically defines a 'compressive arch' in the strain rate-field of the ice shelf, where the smallest principal component transitions from compressive inland of the arch to extensive seaward of the arch. If the compressive arch is breached due to iceberg calving at the ice front or thinning at the shear margins, the ice shelf will retreat irreversibly to a new stable configuration or collapse entirely. This retreat can compromise ice shelf buttressing, resulting in sea-level rise and ocean freshening as grounded ice flows unrestricted into the ocean. Here, we investigate the dynamics of compressive arch failure using Larsen C ice shelf as a test case for a larger study that will include several other ice shelves and projections for sea-level rise. We use satellite observations to develop a steady state model of Larsen C in Elmer/ICE, a finite element ice sheet/ice flow software package. We run calving and thinning simulations to determine the conditions needed to trigger ice shelf retreat via compressive arch failure and discuss the likelihood of these scenarios occurring in relation to extrapolations of current melt profiles and calving trends.

  16. Ice Formation on Wings

    NASA Technical Reports Server (NTRS)

    Ritz, L

    1939-01-01

    This report makes use of the results obtained in the Gottingen ice tunnel in which the atmospheric conditions are simulated and the process of ice formation photographed. The effect of ice formation is threefold: 1) added weight to the airplane; 2) a change in the lift and drag forces; 3) a change in the stability characteristics.

  17. The Antarctic Ice.

    ERIC Educational Resources Information Center

    Radok, Uwe

    1985-01-01

    The International Antarctic Glaciological Project has collected information on the East Antarctic ice sheet since 1969. Analysis of ice cores revealed climatic history, and radar soundings helped map bedrock of the continent. Computer models of the ice sheet and its changes over time will aid in predicting the future. (DH)

  18. Experiments in Ice Physics.

    ERIC Educational Resources Information Center

    Mart