Science.gov

Sample records for ice dynamics joint

  1. Arctic odyssey - Five years of data buoys in AIDJEX. [Arctic Ice Dynamics Joint Experiment

    NASA Technical Reports Server (NTRS)

    Martin, P.; Gillespie, C. R.

    1976-01-01

    The Arctic Ice Dynamics Joint Experiment of 1975-1976 used data bouys in conjunction with tracking satellites to study the interaction of Arctic Sea ice with the environment, and, more specifically, to define the motion of ice on the perimeter of the area of interest and to measure surface barometeric pressure over the same area. Charts are presented, indicating the position of the buoy array along with a table detailing buoy characteristics. The position fix accuracy of RAMS (Random Access Measurement System) buoys is discussed together with position errors due to the along-track motion of the observing satellites. Polar satellite data collection and tracking efficiency is assessed together with satellite system flexibility concepts.

  2. 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.

  3. Stochastic ice stream dynamics

    PubMed Central

    Bertagni, Matteo Bernard; Ridolfi, Luca

    2016-01-01

    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

  4. Spin ice dynamics

    NASA Astrophysics Data System (ADS)

    Snyder, Joseph William

    2003-07-01

    Geometrically frustrated magnets (GFMs) are materials in which it is impossible to satisfy all exchange interactions due the geometry of the lattice. The frustration of interactions is the origin of many unique and interesting material properties. GFMs are typified by large ground state degeneracy and will undergo spin fluctuations down to temperatures well below theta W, where un-frustrated materials display long-range order. This results in the development of correlated magnetic states that are analogous to various structural phases of matter such as spin glasses and spin liquids. Very recently, another magnetic-structural analog has been discovered where the magnetic properties show distinct similarities with the structural properties of a common substance that has itself long perplexed scientists, water ice. The aptly named spin ice compounds have been shown to exhibit the same "ground state entropy" as water ice and to be well characterized by consideration in terms of the "ice model". In this thesis, we explore the low temperature dynamics of the spins in the spin ice compound Dy2Ti2O7 through measurements of the magnetization and ac susceptibility. We show that the ground state represents a unique form of glassiness in a dense magnetic system. Our results show the onset of irreversibility and the development of a metastable state where the dynamics are significantly slowed but no long-range order is achieved below Tirr ˜ 650 mK. The system is also shown to display unique properties at higher temperatures with a partial freezing of the ac susceptibility at T ˜ 16 K. This freezing is shown to be thermally activated in nature above Tcross ˜ 12 K below which it is driven by quantum tunneling until it assumes faster than activated behavior at T ice ˜ 4 K. The freezing is shown to occur over a very narrow range of relaxation time constants, similar to that seen in the dielectric constants of ice. Measurements of Dy2-xYxTi2O 7, where the J = 15/2 Dy3+ ions were

  5. Analysis of sea ice dynamics

    NASA Technical Reports Server (NTRS)

    Zwally, J.

    1988-01-01

    The ongoing work has established the basis for using multiyear sea ice concentrations from SMMR passive microwave for studies of largescale advection and convergence/divergence of the Arctic sea ice pack. Comparisons were made with numerical model simulations and buoy data showing qualitative agreement on daily to interannual time scales. Analysis of the 7-year SMMR data set shows significant interannual variations in the total area of multiyear ice. The scientific objective is to investigate the dynamics, mass balance, and interannual variability of the Arctic sea ice pack. The research emphasizes the direct application of sea ice parameters derived from passive microwave data (SMMR and SSMI) and collaborative studies using a sea ice dynamics model. The possible causes of observed interannual variations in the multiyear ice area are being examined. The relative effects of variations in the large scale advection and convergence/divergence within the ice pack on a regional and seasonal basis are investigated. The effects of anomolous atmospheric forcings are being examined, including the long-lived effects of synoptic events and monthly variations in the mean geostrophic winds. Estimates to be made will include the amount of new ice production within the ice pack during winter and the amount of ice exported from the pack.

  6. Dynamic Crush Characterization of Ice

    NASA Technical Reports Server (NTRS)

    Fasanella, Edwin L.; Boitnott, Richard L.; Kellas, Sotiris

    2006-01-01

    During the space shuttle return-to-flight preparations following the Columbia accident, finite element models were needed that could predict the threshold of critical damage to the orbiter's wing leading edge from ice debris impacts. Hence, an experimental program was initiated to provide crushing data from impacted ice for use in dynamic finite element material models. A high-speed drop tower was configured to capture force time histories of ice cylinders for impacts up to approximately 100 ft/s. At low velocity, the force-time history depended heavily on the internal crystalline structure of the ice. However, for velocities of 100 ft/s and above, the ice fractured on impact, behaved more like a fluid, and the subsequent force-time history curves were much less dependent on the internal crystalline structure.

  7. Investigation of Ice Dynamics in the Marginal Ice Zone.

    DTIC Science & Technology

    2014-09-26

    Report (see also Lepp~ranta and Hibler, 1984 b). The manuscript was sent to Journal of Geophysical Research late 1984 and was revised according to...and ice rheology can substantially modify the character of marginal ice zone dynamics. For constant forcing the steady state solution of ice drift in...these modeling studies. *o. 5. References Hibler, W.D., III, 1979: A dynamic thermodynamic sea ice model. - Journal of Physical Oceanography, 9, 815-845

  8. Does ice immersion influence ankle joint position sense?

    PubMed

    Hopper, D; Whittington, D; Davies, J; Chartier, J D

    1997-01-01

    The purpose of this study was to determine whether a fifteen minute ice immersion treatment influenced the normal ankle joint position sense at 40% and 80% range of inversion and to establish the length of treatment effect through monitoring the rewarming process. Forty nine healthy volunteers between the ages of 17 and 28 were tested. Subjects were screened to exclude those with a history of ankle injuries. The subject's skin temperature over antero-lateral aspect of the ankle was measured using a thermocouple device during the fifteen minutes ice intervention and thirty minutes post-intervention. Testing of ankle joint position sense using the pedal goniometer was performed before and after a clinical application of ice immersion. The testing required the subject to actively reposition their ankle at 40% and 80% of their total range of inversion. The majority of subjects experienced numbness of the foot and ankle by the fifth or sixth minute during ice immersion. One minute after immersion skin temperatures averaged 15 degrees C + 1.7 degrees C. Skin temperature was seen to rise relatively rapidly for the first ten minutes and then slowed considerably. Subjects had not returned to the pre-test skin temperatures by thirty minutes. A significant difference in ankle joint position sense (p < 0.0499) following fifteen minutes of ice immersion was found. However, the magnitude of this difference (0.5 degree) would not be deemed significant in clinical practice. The research found no significant difference in joint position sense between 40% and 80% of the range of inversion both before and after cryotherapy. These findings suggest that the clinical application of cryotherapy is not deleterious to joint position sense and assuming normal joint integrity patients may resume exercise without increased risk of injury.

  9. Frazil ice dynamics in polynyas and leads

    NASA Astrophysics Data System (ADS)

    Wells, Andrew; Rees Jones, David

    2016-04-01

    The initial stage of sea ice formation in a turbulent ocean typically involves the growth of a suspension of frazil ice crystals in supercooled waters. In competition with turbulent mixing, these crystals rise buoyantly and eventually settle at the ocean surface. The resulting rapid growth of granular ice has been observed to make up a significant fraction of ice cover in certain locations. Our recent theoretical work suggests that the growth of individual frazil ice crystals may be significantly faster than had commonly been supposed. We here explore the consequences for the dynamics of a suspension of many frazil ice crystals in a well mixed layer. Frazil suspensions are affected by many processes, including the fluid dynamics of suspensions, nucleation, the collision and sintering of crystals, as well as crystal growth. These processes combine to control the evolving distribution of crystal sizes. We apply a model of the crystal size distribution in a well mixed layer to investigate the comparative importance of these mechanisms, quantify the controls on ice growth, and compare to available laboratory data. We complement our theoretical model with two-dimensional direct numerical simulations of turbulent convection with a suspension of resolved crystals, in order to elucidate the fluid dynamical coupling between ocean convection with crystal rise, and its impact on ice precipitation rates.

  10. Initial results from the joint NASA-Lewis/U.S. Army icing flight research tests

    NASA Technical Reports Server (NTRS)

    Belte, Daumants; Ranaudo, Richard J.

    1989-01-01

    The U.S. Army/NASA joint testing of the various aspects of in-flight and ground-based icing simulation facilities and instrumentation is reviewed. The NASA DN-6 icing research aircraft, the U.S. Army JU-21A aircraft, the portable spray rig, helicopter icing spray system, and icing research tunnel are examined. Natural and artificial icing tests, turbulence measurements, and calibration and icing research tunnel tests are described and test results are reported.

  11. AVHRR imagery reveals Antarctic ice dynamics

    NASA Technical Reports Server (NTRS)

    Bindschadler, Robert A.; Vornberger, Patricia L.

    1990-01-01

    A portion of AVHRR data taken on December 5, 1987 at 06:15 GMT over a part of Antarctica is used here to show that many of the most significant dynamic features of ice sheets can be identified by a careful examination of AVHRR imagery. The relatively low resolution of this instrument makes it ideal for obtaining a broad view of the ice sheets, while its wide swath allows coverage of areas beyond the reach of high-resolution imagers either currently in orbit or planned. An interpretation is given of the present data, which cover the area of ice streams that drain the interior of the West Antarctic ice sheet into the Ross Ice Shelf.

  12. AVHRR imagery reveals Antarctic ice dynamics

    SciTech Connect

    Bindschadler, R.A.; Vornberger, P.L. STX Corp., Lanham, MD )

    1990-06-01

    A portion of AVHRR data taken on December 5, 1987 at 06:15 GMT over a part of Antarctica is used here to show that many of the most significant dynamic features of ice sheets can be identified by a careful examination of AVHRR imagery. The relatively low resolution of this instrument makes it ideal for obtaining a broad view of the ice sheets, while its wide swath allows coverage of areas beyond the reach of high-resolution imagers either currently in orbit or planned. An interpretation is given of the present data, which cover the area of ice streams that drain the interior of the West Antarctic ice sheet into the Ross Ice Shelf. 21 refs.

  13. Arctic Ice Dynamics Joint Experiment 1975-1976. Physical Oceanography Data Report, Salinity, Temperature and Depth Data, Camp Blue Fox. Volume II.

    DTIC Science & Technology

    1980-02-01

    LISTING PARAMETERS I DEPTH Depth in meters TEMP Temperature in degrees C PTEMP Potential temperature in degree C SALIN Salinity in parts per thousand SIG ...T Sigma-t density where: I density (p) - 1.0 + (( Sig T) *1000.0) SPVOL Specific volume anomaly (x 10-5 cm3/gm) DYNHT Dynamic height (dynamic meters...to LM b. a w ewe%- ww re mOOc 4" o 0.NWmotvviiOf wt 00 f4Crfl ft -wm o.e. &*1 NO P..w N N o%9 a in - - -da inN 4p m a - U . .......0...V N m

  14. The role of ice stream dynamics in deglaciation

    NASA Astrophysics Data System (ADS)

    Robel, Alexander A.; Tziperman, Eli

    2016-08-01

    Since the mid-Pleistocene transition, deglaciation has occurred only after ice sheets have grown large while experiencing several precession and obliquity cycles, indicating that large ice sheets are more sensitive to Milankovitch forcing than small ice sheets are. Observations and model simulations suggest that the development of ice streams in the Laurentide Ice Sheet played an as yet unknown role in deglaciations. In this study, we propose a mechanism by which ice streams may enhance deglaciation and render large ice sheets more sensitive to Milankovitch forcing. We use an idealized configuration of the Parallel Ice Sheet Model that permits the formation of ice streams. When the ice sheet is large and ice streams are sufficiently developed, an upward shift in equilibrium line altitude, commensurate with Milankovitch forcing, results in rapid deglaciation, while the same shift applied to an ice sheet without fully formed ice streams results in continued ice sheet growth or slower deglaciation. Rapid deglaciation in ice sheets with significant streaming behavior is caused by ice stream acceleration and the attendant enhancement of calving and surface melting at low elevations. Ice stream acceleration is ultimately the result of steepening of the ice surface and increased driving stresses in ice stream onset zones, which come about due to the dependence of surface mass balance on elevation. These ice sheet simulations match the broad features of geomorphological observations and add ice stream dynamics that are missing from previous model studies of deglaciation.

  15. Dynamic Analyses Including Joints Of Truss Structures

    NASA Technical Reports Server (NTRS)

    Belvin, W. Keith

    1991-01-01

    Method for mathematically modeling joints to assess influences of joints on dynamic response of truss structures developed in study. Only structures with low-frequency oscillations considered; only Coulomb friction and viscous damping included in analysis. Focus of effort to obtain finite-element mathematical models of joints exhibiting load-vs.-deflection behavior similar to measured load-vs.-deflection behavior of real joints. Experiments performed to determine stiffness and damping nonlinearities typical of joint hardware. Algorithm for computing coefficients of analytical joint models based on test data developed to enable study of linear and nonlinear effects of joints on global structural response. Besides intended application to large space structures, applications in nonaerospace community include ground-based antennas and earthquake-resistant steel-framed buildings.

  16. A surface ice module for wind turbine dynamic response simulation using FAST

    SciTech Connect

    Yu, Bingbin; Karr, Dale G.; Song, Huimin; Sirnivas, Senu

    2016-06-03

    It is a fact that developing offshore wind energy has become more and more serious worldwide in recent years. Many of the promising offshore wind farm locations are in cold regions that may have ice cover during wintertime. The challenge of possible ice loads on offshore wind turbines raises the demand of modeling capacity of dynamic wind turbine response under the joint action of ice, wind, wave, and current. The simulation software FAST is an open source computer-aided engineering (CAE) package maintained by the National Renewable Energy Laboratory. In this paper, a new module of FAST for assessing the dynamic response of offshore wind turbines subjected to ice forcing is presented. In the ice module, several models are presented which involve both prescribed forcing and coupled response. For conditions in which the ice forcing is essentially decoupled from the structural response, ice forces are established from existing models for brittle and ductile ice failure. For conditions in which the ice failure and the structural response are coupled, such as lock-in conditions, a rate-dependent ice model is described, which is developed in conjunction with a new modularization framework for FAST. In this paper, analytical ice mechanics models are presented that incorporate ice floe forcing, deformation, and failure. For lower speeds, forces slowly build until the ice strength is reached and ice fails resulting in a quasi-static condition. For intermediate speeds, the ice failure can be coupled with the structural response and resulting in coinciding periods of the ice failure and the structural response. A third regime occurs at high speeds of encounter in which brittle fracturing of the ice feature occurs in a random pattern, which results in a random vibration excitation of the structure. An example wind turbine response is simulated under ice loading of each of the presented models. This module adds to FAST the capabilities for analyzing the response of wind

  17. Dynamics and morphology of Beaufort Sea ice determined from satellites, aircraft, and drifting stations

    NASA Technical Reports Server (NTRS)

    Campbell, W. J.; Gloersen, P.; Nordberg, W.; Wilheit, T. T.

    1973-01-01

    A series of measurements from drifting stations, aircraft, the ERTS-1, Nimbus 4, and Nimbus 5 satellites have jointly provided a new description of the dynamics and morphology of the ice cover of the Beaufort Sea. The combined analysis of these data show that the eastern Beaufort Sea ice cover is made up of large multiyear floes while the western part is made of small, predominantly first-year floes. The analysis suggests that this distribution might be quasi-steady and that the dynamics and thermodynamics of the region are more complex than hitherto known. The measurements consist of: (1) high resolution ERTS-1 imagery which is used to describe floe size and shape distribution, short term floe dynamics, and lead and polynya dynamics; (2) tracking by Nimbus 4 of IRLS drifting buoys to provide ice drift information which enhances the interpretation of the ERTS-1 imagery; (3) Nimbus 5 microwave (1.55 cm wavelength) imagery which provides synoptic, sequential maps on the distribution of multiyear and first-year ice types; (4) airborne microwave surveys and surface based observations made during 1971 and 1972 in conjunction with the AIDJEX (Arctic Ice Dynamics Joint Experiment) program.

  18. Handbook on dynamics of jointed structures.

    SciTech Connect

    Ames, Nicoli M.; Lauffer, James P.; Jew, Michael D.; Segalman, Daniel Joseph; Gregory, Danny Lynn; Starr, Michael James; Resor, Brian Ray

    2009-07-01

    The problem of understanding and modeling the complicated physics underlying the action and response of the interfaces in typical structures under dynamic loading conditions has occupied researchers for many decades. This handbook presents an integrated approach to the goal of dynamic modeling of typical jointed structures, beginning with a mathematical assessment of experimental or simulation data, development of constitutive models to account for load histories to deformation, establishment of kinematic models coupling to the continuum models, and application of finite element analysis leading to dynamic structural simulation. In addition, formulations are discussed to mitigate the very short simulation time steps that appear to be required in numerical simulation for problems such as this. This handbook satisfies the commitment to DOE that Sandia will develop the technical content and write a Joints Handbook. The content will include: (1) Methods for characterizing the nonlinear stiffness and energy dissipation for typical joints used in mechanical systems and components. (2) The methodology will include practical guidance on experiments, and reduced order models that can be used to characterize joint behavior. (3) Examples for typical bolted and screw joints will be provided.

  19. Equivalent dynamic model of DEMES rotary joint

    NASA Astrophysics Data System (ADS)

    Zhao, Jianwen; Wang, Shu; Xing, Zhiguang; McCoul, David; Niu, Junyang; Huang, Bo; Liu, Liwu; Leng, Jinsong

    2016-07-01

    The dielectric elastomer minimum energy structure (DEMES) can realize large angular deformations by a small voltage-induced strain of the dielectric elastomer (DE), so it is a suitable candidate to make a rotary joint for a soft robot. Dynamic analysis is necessary for some applications, but the dynamic response of DEMESs is difficult to model because of the complicated morphology and viscoelasticity of the DE film. In this paper, a method composed of theoretical analysis and experimental measurement is presented to model the dynamic response of a DEMES rotary joint under an alternating voltage. Based on measurements of equivalent driving force and damping of the DEMES, the model can be derived. Some experiments were carried out to validate the equivalent dynamic model. The maximum angle error between model and experiment is greater than ten degrees, but it is acceptable to predict angular velocity of the DEMES, therefore, it can be applied in feedforward-feedback compound control.

  20. The dynamics of climate-induced deglacial ice stream acceleration

    NASA Astrophysics Data System (ADS)

    Robel, A.; Tziperman, E.

    2015-12-01

    Geological observations indicate that ice streams were a significant contributor to ice flow in the Laurentide Ice Sheet during the Last Glacial Maximum. Conceptual and simple model studies have also argued that the gradual development of ice streams increases the sensitivity of large ice sheets to weak climate forcing. In this study, we use an idealized configuration of the Parallel Ice Sheet Model to explore the role of ice streams in rapid deglaciation. In a growing ice sheet, ice streams develop gradually as the bed warms and the margin expands outward onto the continental shelf. Then, a weak change in equilibrium line altitude commensurate with Milankovitch forcing results in a rapid deglacial response, as ice stream acceleration leads to enhanced calving and surface melting at low elevations. We explain the dynamical mechanism that drives this ice stream acceleration and its broader applicability as a feedback for enhancing ice sheet decay in response to climate forcing. We show how our idealized ice sheet simulations match geomorphological observations of deglacial ice stream variability and previous model-data analyses. We conclude with observations on the potential for interaction between ice streams and other feedback mechanisms within the earth system.

  1. Changing structures and dynamics of western Antarctic Peninsula Ice Shelves

    NASA Astrophysics Data System (ADS)

    Glasser, N. F.; Holt, T. O.; Quincey, D. J.; Fricker, H.; Siegfried, M. R.

    2013-12-01

    Over the last three decades, Antarctic Peninsula Ice Shelves have shown a pattern of sustained retreat, often ending in catastrophic and rapid breakup. This study provides a detailed analysis of the structures and dynamics of three western Antarctic Peninsula ice shelves: Bach, Stange and George VI Ice Shelves. Spatial extent and glaciological surface features were mapped for each ice shelf from 1973 to 2010 using optical and radar satellite images to assess their structural evolution, historical dynamics and stability. InSAR and feature-tracking methods were used to assess the recent dynamic configurations of the ice shelves from 1989 to 2010. Repeat ICESat measurements were used to evaluate their vertical changes from 2003 to 2008. On Bach Ice Shelf, the formation of two large fractures near the ice front is linked to widespread thinning (~2 ma-1) and sustained retreat (~360 km2). It looks likely that iceberg calving along these fractures will alter the frontal geometry sufficiently to promote enhanced, irreversible retreat within the next decade. On George VI Ice Shelf, acceleration is observed at both ice fronts; linked to a release of back-stresses through continued ice loss (1995 km2 in total). The most significant changes are recorded at its southern ice front, with ice flow accelerating up to 360% between ca. 1989 and ca. 2010, coupled with widespread rifting and a mean thinning rate of 2.1 ma-1. On Stange Ice Shelf, shear-induced fracturing was observed between two flow units, also linked to widespread thinning (~4.2 ma-1). A semi-quantitative assessment reveals that the southern margin of George VI Ice Shelf is most susceptible to rapid retreat, whilst its northern ice front, Bach Ice Shelf and the northern front of Stange Ice Shelf are more vulnerable than those situated on the east Antarctic Peninsula.

  2. A surface ice module for wind turbine dynamic response simulation using FAST

    DOE PAGES

    Yu, Bingbin; Karr, Dale G.; Song, Huimin; ...

    2016-06-03

    It is a fact that developing offshore wind energy has become more and more serious worldwide in recent years. Many of the promising offshore wind farm locations are in cold regions that may have ice cover during wintertime. The challenge of possible ice loads on offshore wind turbines raises the demand of modeling capacity of dynamic wind turbine response under the joint action of ice, wind, wave, and current. The simulation software FAST is an open source computer-aided engineering (CAE) package maintained by the National Renewable Energy Laboratory. In this paper, a new module of FAST for assessing the dynamicmore » response of offshore wind turbines subjected to ice forcing is presented. In the ice module, several models are presented which involve both prescribed forcing and coupled response. For conditions in which the ice forcing is essentially decoupled from the structural response, ice forces are established from existing models for brittle and ductile ice failure. For conditions in which the ice failure and the structural response are coupled, such as lock-in conditions, a rate-dependent ice model is described, which is developed in conjunction with a new modularization framework for FAST. In this paper, analytical ice mechanics models are presented that incorporate ice floe forcing, deformation, and failure. For lower speeds, forces slowly build until the ice strength is reached and ice fails resulting in a quasi-static condition. For intermediate speeds, the ice failure can be coupled with the structural response and resulting in coinciding periods of the ice failure and the structural response. A third regime occurs at high speeds of encounter in which brittle fracturing of the ice feature occurs in a random pattern, which results in a random vibration excitation of the structure. An example wind turbine response is simulated under ice loading of each of the presented models. This module adds to FAST the capabilities for analyzing the response of wind

  3. Impact of ice-shelf sediment content on the dynamics of plumes under melting ice shelves

    NASA Astrophysics Data System (ADS)

    Wells, A.

    2015-12-01

    When a floating ice shelf melts into an underlying warm salty ocean, the resulting fresh meltwater can rise in a buoyant Ice-Shelf-Water plume under the ice. In certain settings, ice flowing across the grounding line carries a basal layer of debris rich ice, entrained via basal freezing around till in the upstream ice sheet. Melting of this debris-laden ice from floating ice shelves provides a flux of dense sediment to the ocean, in addition to the release of fresh buoyant meltwater. This presentation considers the impact of the resulting suspended sediment on the dynamics of ice shelf water plumes, and identifies two key flow regimes depending on the sediment concentration frozen into the basal ice layer. For large sediment concentration, melting of the debris-laden ice shelf generates dense convectively unstable waters that drive convective overturning into the underlying ocean. For lower sediment concentration, the sediment initially remains suspended in a buoyant meltwater plume rising along the underside of the ice shelf, before slowly depositing into the underlying ocean. A theoretical plume model is used to evaluate the significance of the negatively buoyant sediment on circulation strength and the feedbacks on melting rate, along with the expected depositional patterns under the ice shelf.

  4. Potassium chloride-bearing ice VII and ice planet dynamics

    NASA Astrophysics Data System (ADS)

    Frank, Mark R.; Scott, Henry P.; Aarestad, Elizabeth; Prakapenka, Vitali B.

    2016-02-01

    Accurate modeling of planetary interiors requires that the pressure-volume-temperature (PVT) properties of phases present within the body be well understood. The high-pressure polymorphs of H2O have been studied extensively due to the abundance of ice phases in icy moons and, likely, vast number of extra-solar planetary bodies, with only select studies evaluating impurity-laden ices. In this study, ice formed from a 1.6 mol percent KCl-bearing aqueous solution was studied up to 32.89 ± 0.19 GPa and 625 K, and the incorporation of K+ and Cl- ionic impurities into the ice VII structure was documented. The compression data at 295 K were fit with a third order Birch-Murnaghan equation of state and yielded a bulk modulus (KT0), its pressure derivative (KT0 ‧), and zero pressure volume (V0) of 24.7 ± 0.9 GPa, 4.44 ± 0.09, and 39.2 ± 0.2 Å3, respectively. The impurity-laden ice was found to be 6-8% denser than ice VII formed from pure H2O. Thermal expansion coefficients were also determined for several isothermal compression curves at elevated temperatures, and a PVT equation of state was obtained. The melting curve of ice VII with incorporated K+ and Cl- was estimated by fitting experimental data up to 10.2 ± 0.4 GPa, where melting occurred at 625 K, to the Simon-Glatzel equation. The melting curve of this impurity-laden ice is systematically depressed relative to that of pure H2O by approximately 45 K and 80 K at 4 and 11 GPa, respectively. A portion of the K+ and Cl- contained within the ice VII structure was observed to exsolve with increasing temperature. This suggests that an internal differentiating process could concentrate a K-rich phase deep within H2O-rich planets, and we speculate that this could supply an additional source of heat through the radioactive decay of 40K. Our data illustrate ice VII can incorporate significant concentrations of K+ and Cl- and increasing the possibility of deep-sourced and solute-rich plumes in moderate to large sized H2O

  5. Coupled ice-ocean dynamics in the marginal ice zones Upwelling/downwelling and eddy generation

    NASA Technical Reports Server (NTRS)

    Hakkinen, S.

    1986-01-01

    This study is aimed at modeling mesoscale processes such as upwelling/downwelling and ice edge eddies in the marginal ice zones. A two-dimensional coupled ice-ocean model is used for the study. The ice model is coupled to the reduced gravity ocean model through interfacial stresses. The parameters of the ocean model were chosen so that the dynamics would be nonlinear. The model was tested by studying the dynamics of upwelling. Wings parallel to the ice edge with the ice on the right produce upwelling because the air-ice momentum flux is much greater than air-ocean momentum flux; thus the Ekman transport is greater than the ice than in the open water. The stability of the upwelling and downwelling jets is discussed. The downwelling jet is found to be far more unstable than the upwelling jet because the upwelling jet is stabilized by the divergence. The constant wind field exerted on a varying ice cover will generate vorticity leading to enhanced upwelling/downwelling regions, i.e., wind-forced vortices. Steepening and strengthening of vortices are provided by the nonlinear terms. When forcing is time-varying, the advection terms will also redistribute the vorticity. The wind reversals will separate the vortices from the ice edge, so that the upwelling enhancements are pushed to the open ocean and the downwelling enhancements are pushed underneath the ice.

  6. Analysis of dynamic recrystallization of ice from EBSD orientation mapping

    NASA Astrophysics Data System (ADS)

    Montagnat, Maurine; Chauve, Thomas; Barou, Fabrice; Tommasi, Andrea; Beausir, Benoît; Fressengeas, Claude

    2015-12-01

    We present high resolution observations of microstructure and texture evolution during dynamic recrystallization (DRX) of ice polycrystals deformed in the laboratory at high temperature (≈0.98Tm). Ice possesses a significant viscoplastic anisotropy that induces strong strain heterogeneities, which result in an early occurrence of DRX mechanisms. It is therefore a model material to explore these mechanisms. High resolution c-axis measurements at sample scale by optical techniques and full crystallographic orientation measurements by cryo- Electron Back Scattering Diffraction (EBSD) provide a solid database for analyzing the relative impact of the macroscopic imposed stress versus the local and internal stress field on DRX mechanisms. Analysis of misorientation gradients in the EBSD data highlights a heterogeneous dislocation distribution, which is quantified by the Nye tensor estimation. Joint analyses of the dislocation density maps and microstructural observations highlight spatial correlation between high dislocation density sites and the onset of nucleation taking place by grain-boundary bulging, subgrain rotation or by the formation of kink-bands.

  7. Joint Chance-Constrained Dynamic Programming

    NASA Technical Reports Server (NTRS)

    Ono, Masahiro; Kuwata, Yoshiaki; Balaram, J. Bob

    2012-01-01

    This paper presents a novel dynamic programming algorithm with a joint chance constraint, which explicitly bounds the risk of failure in order to maintain the state within a specified feasible region. A joint chance constraint cannot be handled by existing constrained dynamic programming approaches since their application is limited to constraints in the same form as the cost function, that is, an expectation over a sum of one-stage costs. We overcome this challenge by reformulating the joint chance constraint into a constraint on an expectation over a sum of indicator functions, which can be incorporated into the cost function by dualizing the optimization problem. As a result, the primal variables can be optimized by a standard dynamic programming, while the dual variable is optimized by a root-finding algorithm that converges exponentially. Error bounds on the primal and dual objective values are rigorously derived. We demonstrate the algorithm on a path planning problem, as well as an optimal control problem for Mars entry, descent and landing. The simulations are conducted using a real terrain data of Mars, with four million discrete states at each time step.

  8. Dynamics of ice ages on Mars.

    PubMed

    Schorghofer, Norbert

    2007-09-13

    Unlike Earth, where astronomical climate forcing is comparatively small, Mars experiences dramatic changes in incident sunlight that are capable of redistributing ice on a global scale. The geographic extent of the subsurface ice found poleward of approximately +/-60 degrees latitude on both hemispheres of Mars coincides with the areas where ice is stable. However, the tilt of Mars' rotation axis (obliquity) changed considerably in the past several million years. Earlier work has shown that regions of ice stability, which are defined by temperature and atmospheric humidity, differed in the recent past from today's, and subsurface ice is expected to retreat quickly when unstable. Here I explain how the subsurface ice sheets could have evolved to the state in which we see them today. Simulations of the retreat and growth of ground ice as a result of sublimation loss and recharge reveal forty major ice ages over the past five million years. Today, this gives rise to pore ice at mid-latitudes and a three-layered depth distribution in the high latitudes of, from top to bottom, a dry layer, pore ice, and a massive ice sheet. Combined, these layers provide enough ice to be compatible with existing neutron and gamma-ray measurements.

  9. Smoothed particle hydrodynamics non-Newtonian model for ice-sheet and ice-shelf dynamics

    SciTech Connect

    Pan, W.; Tartakovsky, A. M.; Monaghan, J. J.

    2013-06-01

    Mathematical modeling of ice sheets is complicated by the non-linearity of the governing equations and boundary conditions. Standard grid-based methods require complex front tracking techniques and have limited capability to handle large material deformations and abrupt changes in bottom topography. As a consequence, numerical methods are usually restricted to shallow ice sheet and ice shelf approximations. We propose a new smoothed particle hydrodynamics (SPH) non-Newtonian model for coupled ice sheet and ice shelf dynamics. SPH, a fully Lagrangian particle method, is highly scalable and its Lagrangian nature and meshless discretization are well suited to the simulation of free surface flows, large material deformation, and material fragmentation. In this paper, SPH is used to study 3D ice sheet/ice shelf behavior, and the dynamics of the grounding line. The steady state position of the grounding line obtained from SPH simulations is in good agreement with laboratory observations for a wide range of simulated bedrock slopes, and density ratios, similar to those of ice and sea water. The numerical accuracy of the SPH algorithm is verif;ed by simulating Poiseuille flow, plane shear flow with free surface and the propagation of a blob of ice along a horizontal surface. In the laboratory experiment, the ice was represented with a viscous Newtonian fluid. In the present work, however, the ice is modeled as both viscous Newtonian fluid and non-Newtonian fluid, such that the effect of non-Newtonian rheology on the dynamics of grounding line was examined. The non-Newtonian constitutive relation is prescribed to be Glen’s law for the creep of polycrystalline ice. A V-shaped bedrock ramp is further introduced to model the real geometry of bedrock slope.

  10. A Smoothed Particle Hydrodynamics Model for Ice Sheet and Ice Shelf Dynamics

    SciTech Connect

    Pan, Wenxiao; Tartakovsky, Alexandre M.; Monaghan, Joseph J.

    2012-02-08

    Mathematical modeling of ice sheets is complicated by the non-linearity of the governing equations and boundary conditions. Standard grid-based methods require complex front tracking techniques and have limited capability to handle large material deformations and abrupt changes in bottom topography. As a consequence, numerical methods are usually restricted to shallow ice sheet and ice shelf approximations. We propose a new smoothed particle hydrodynamics (SPH) model for coupled ice sheet and ice shelf dynamics. SPH is a fully Lagrangian particle method. It is highly scalable and its Lagrangian nature and meshless discretization are well suited to the simulation of free surface flows, large material deformation, and material fragmentation. In this paper SPH is used to study ice sheet/ice shelf behavior, and the dynamics of the grounding line. The steady state position of the grounding line obtained from the SPH simulations is in good agreement with laboratory observations for a wide range of simulated bedrock slopes, and density ratios similar to those of ice and sea water. The numerical accuracy of the SPH algorithm is further verified by simulating the plane shear flow of two immiscible fluids and the propagation of a highly viscous blob of fluid along a horizontal surface. In the experiment, the ice was represented with a viscous newtonian fluid. For consistency, in the described SPH model the ice is also modeled as a viscous newtonian fluid. Typically, ice sheets are modeled as a non-Newtonian fluid, accounting for the changes in the mechanical properties of ice. Implementation of a non-Newtonian rheology in the SPH model is the subject of our ongoing research.

  11. Role of ground ice dynamics and ecological feedbacks in recent ice wedge degradation and stabilization

    USGS Publications Warehouse

    Mark Torre Jorgenson,; Mikhail Kanevskiy,; Yuri Shur,; Natalia Moskalenko,; Dana Brown,; Wickland, Kimberly P.; Striegl, Robert G.; Koch, Joshua C.

    2015-01-01

    Ground ice is abundant in the upper permafrost throughout the Arctic and fundamentally affects terrain responses to climate warming. Ice wedges, which form near the surface and are the dominant type of massive ice in the Arctic, are particularly vulnerable to warming. Yet processes controlling ice wedge degradation and stabilization are poorly understood. Here we quantified ice wedge volume and degradation rates, compared ground ice characteristics and thermal regimes across a sequence of five degradation and stabilization stages and evaluated biophysical feedbacks controlling permafrost stability near Prudhoe Bay, Alaska. Mean ice wedge volume in the top 3 m of permafrost was 21%. Imagery from 1949 to 2012 showed thermokarst extent (area of water-filled troughs) was relatively small from 1949 (0.9%) to 1988 (1.5%), abruptly increased by 2004 (6.3%) and increased slightly by 2012 (7.5%). Mean annual surface temperatures varied by 4.9°C among degradation and stabilization stages and by 9.9°C from polygon center to deep lake bottom. Mean thicknesses of the active layer, ice-poor transient layer, ice-rich intermediate layer, thermokarst cave ice, and wedge ice varied substantially among stages. In early stages, thaw settlement caused water to impound in thermokarst troughs, creating positive feedbacks that increased net radiation, soil heat flux, and soil temperatures. Plant growth and organic matter accumulation in the degraded troughs provided negative feedbacks that allowed ground ice to aggrade and heave the surface, thus reducing surface water depth and soil temperatures in later stages. The ground ice dynamics and ecological feedbacks greatly complicate efforts to assess permafrost responses to climate change.

  12. A Lagrangian analysis of sea ice dynamics in the Arctic

    NASA Astrophysics Data System (ADS)

    Szanyi, S.; Lukovich, J. V.; Haller, G.; Barber, D. G.

    2014-12-01

    Recent studies have highlighted acceleration in sea ice drift and deformation in the Arctic over the last several decades, underlining the need for improved understanding of sea ice dynamics and dispersion. In this study we present Lagrangian diagnostics to quantify changes in the dynamical characteristics of the Arctic sea ice cover from 1979 to 2012 during the transition from a predominantly multi-year to a first-year ice regime. Examined in particular is the evolution in finite-time Lyapunov exponents (FTLEs), which monitor the rate at which neighboring particle trajectories diverge, and stretching rates throughout the Arctic. In this analysis we compute FTLEs for the Arctic ice drift field using National Snow and Ice Data Centre (NSIDC) Polar Pathfinder Daily 25 km EASE-Grid weekly sea ice motion vectors for the annual cycle beginning both from the sea ice minimum in September, and maximum in March. Sensitivity analyses show that maximal FTLEs, or ridges, are robust even with the introduction of significant noise. Probability density functions and mean values of FTLEs show a trend towards higher FTLE values characteristic of increased mixing in the Arctic in the last decade, in keeping with a transition to a weaker, thinner ice cover.

  13. Smoluchowski coagulation models of sea ice thickness distribution dynamics

    NASA Astrophysics Data System (ADS)

    Godlovitch, D.; Illner, R.; Monahan, A.

    2011-12-01

    Sea ice thickness distributions display a ubiquitous exponential decrease with thickness. This tail characterizes the range of ice thickness produced by mechanical redistribution of ice through the process of ridging, rafting, and shearing. We investigate how well the thickness distribution can be simulated by representing mechanical redistribution as a generalized stacking process. Such processes are naturally described by a well-studied class of models known as Smoluchowski Coagulation Models (SCMs), which describe the dynamics of a population of fixed-mass "particles" which combine in pairs to form a "particle" with the combined mass of the constituent pair at a rate which depends on the mass of the interacting particles. Like observed sea ice thickness distributions, the mass distribution of the populations generated by SCMs has an exponential or quasi-exponential form. We use SCMs to model sea ice, identifying mass-increasing particle combinations with thickness-increasing ice redistribution processes. Our model couples an SCM component with a thermodynamic component and generates qualitatively accurate thickness distributions with a variety of rate kernels. Our results suggest that the exponential tail of the sea ice thickness distribution arises from the nature of the ridging process, rather than specific physical properties of sea ice or the spatial arrangement of floes, and that the relative strengths of the dynamic and thermodynamic processes are key in accurately simulating the rate at which the sea ice thickness tail drops off with thickness.

  14. Investigation of Dynamic Flight Maneuvers With an Iced Tailplane

    NASA Technical Reports Server (NTRS)

    VanZante, Judith Foss; Ratvasky, Thomas P.

    1999-01-01

    A detailed analysis of two of the dynamic maneuvers, the pushover and elevator doublet, from the NASA/FAA Tailplane Icing Program are discussed. For this series of flight tests, artificial ice shapes were attached to the leading edge of the horizontal stabilizer of the NASA Lewis Research Center icing aircraft, a DHC-6 Twin Otter. The purpose of these tests was to learn more about ice-contaminated tailplane stall (ICTS), the known cause of 16 accidents resulting in 139 fatalities. The pushover has been employed by the FAA, JAA and Transport Canada for tailplane icing certification. This research analyzes the pushover and reports on the maneuver performance degradation due to ice shape severity and flap deflection. A repeatability analysis suggests tolerances for meeting the required targets of the maneuver. A second maneuver, the elevator doublet, is also studied.

  15. Impact of bedrock description on modeling ice sheet dynamics

    NASA Astrophysics Data System (ADS)

    Durand, G.; Gagliardini, O.; Favier, L.; Zwinger, T.; le Meur, E.

    2011-10-01

    Recent glaciological surveys have revealed a significant increase of ice discharge from polar ice caps into the ocean. In parallel, ice flow models have been greatly improved to better reproduce current changes and forecast the future behavior of ice sheets. For these models, surface topography and bedrock elevation are crucial input parameters that largely control the dynamics and the ensuing overall mass balance of the ice sheet. For obvious reasons of inaccessibility, only sparse and uneven bedrock elevation data is available. This raw data is processed to produce Digital Elevation Models (DEMs) on a regular 5 km grid. These DEMs are used to constrain the basal boundary conditions of all ice sheet models. Here, by using a full-Stokes finite element code, we examine the sensitivity of an ice flow model to the accuracy of the bedrock description. In the context of short-term ice sheet forecast, we show that in coastal regions, the bedrock elevation should be known at a resolution of the order of one kilometer. Conversely, a crude description of the bedrock in the interior of the continent does not affect modeling of the ice outflow into the ocean. These findings clearly indicate that coastal regions should be prioritized during future geophysical surveys. They also indicate that a paradigm shift is required to change the current design of DEMs describing the bedrock below the ice sheets: they must give users the opportunity to incorporate high-resolution bedrock elevation data in regions of interest.

  16. Smoluchowski Coagulation Models Of Sea Ice Thickness Distribution Dynamics

    NASA Astrophysics Data System (ADS)

    Godlovitch, D.; Illner, R.; Monahan, A. H.

    2011-12-01

    Sea ice thickness distributions display a ubiquitous exponential decrease with thickness. This tail characterises the range of ice thickness produced by mechanical redistribution of ice through the process of ridging, rafting, and shearing. It is possible to simulate thickness distribution dynamics by representing mechanical redistribution as a generalized stacking process. Stacking processes may be described by a class of models known as Smoluchowski Coagulation models, which originated in Statistical Mechanics and describe the dynamics of a population of fixed-mass "particles" which combine in pairs to form a "particle" with the combined mass of the constituent pair at a rate which depends on the mass of the interacting particles. We use SCMs to model sea ice, identifying mass-increasing particle combinations with thickness-increasing ice redistribution processes. Our model couples an SCM component with a thermodynamic component and generates qualitatively accurate thickness distributions. The model behaviour suggests that the exponential tail of the sea ice thickness distribution arises from the nature of the ridging process, rather than specific physical properties of sea ice or the spatial arrangement of floes, and that the relative strengths of the dynamic and thermodynamic processes are key in accurately simulating the rate at which the sea ice thickness tail drops off with thickness.

  17. Fracture-induced softening for large-scale ice dynamics

    NASA Astrophysics Data System (ADS)

    Albrecht, T.; Levermann, A.

    2014-04-01

    Floating ice shelves can exert a retentive and hence stabilizing force onto the inland ice sheet of Antarctica. However, this effect has been observed to diminish by the dynamic effects of fracture processes within the protective ice shelves, leading to accelerated ice flow and hence to a sea-level contribution. In order to account for the macroscopic effect of fracture processes on large-scale viscous ice dynamics (i.e., ice-shelf scale) we apply a continuum representation of fractures and related fracture growth into the prognostic Parallel Ice Sheet Model (PISM) and compare the results to observations. To this end we introduce a higher order accuracy advection scheme for the transport of the two-dimensional fracture density across the regular computational grid. Dynamic coupling of fractures and ice flow is attained by a reduction of effective ice viscosity proportional to the inferred fracture density. This formulation implies the possibility of non-linear threshold behavior due to self-amplified fracturing in shear regions triggered by small variations in the fracture-initiation threshold. As a result of prognostic flow simulations, sharp across-flow velocity gradients appear in fracture-weakened regions. These modeled gradients compare well in magnitude and location with those in observed flow patterns. This model framework is in principle expandable to grounded ice streams and provides simple means of investigating climate-induced effects on fracturing (e.g., hydro fracturing) and hence on the ice flow. It further constitutes a physically sound basis for an enhanced fracture-based calving parameterization.

  18. Basal Dynamics and Internal Structure of Ice Sheets

    NASA Astrophysics Data System (ADS)

    Wolovick, Michael J.

    The internal structure of ice sheets reflects the history of flow and deformation experienced by the ice mass. Flow and deformation are controlled by processes occurring within the ice mass and at its boundaries, including surface accumulation or ablation, ice rheology, basal topography, basal sliding, and basal melting or freezing. The internal structure and basal environment of ice sheets is studied with ice-penetrating radar. Recently, radar observations in Greenland and Antarctica have imaged large englacial structures rising from near the bed that deform the overlying stratigraphy into anticlines, synclines, and overturned folds. The mechanisms that may produce these structures include basal freeze-on, travelling slippery patches at the ice base, and rheological contrasts within the ice column. In this thesis, I explore the setting and mechanisms that produce large basal stratigraphic structures inside ice sheets. First, I use radar data to map subglacial hydrologic networks that deliver meltwater uphill towards freeze-on structures in East Antarctica. Next, I use a thermomechanical flowline model to demonstrate that trains of alternating slippery and sticky patches can form underneath ice sheets and travel downstream over time. The disturbances to the ice flow field produced by these travelling patches produce stratigraphic folds resembling the observations. I then examine the overturned folds produced by a single travelling sticky patch using a kinematic flowline model. This model is used to interpret stratigraphic measurements in terms of the dynamic properties of basal slip. Finally, I use a simple local one-dimensional model to estimate the thickness of basal freeze-on that can be produced based on the supply of available meltwater, the thermal boundary conditions, ice sheet geometry, and the ice flow regime.

  19. Dynamic characterization of bolted joints using FRF decoupling and optimization

    NASA Astrophysics Data System (ADS)

    Tol, Şerife; O¨zgu¨ven, H. Nevzat

    2015-03-01

    Mechanical connections play a significant role in predicting dynamic characteristics of assembled structures. Therefore, equivalent dynamic models for joints are needed. Due to the complexity of joints, it is difficult to describe joint dynamics with analytical models. Reliable models are generally obtained using experimental measurements. In this paper an experimental identification method based on FRF decoupling and optimization algorithm is proposed for modeling joints. In the method the FRFs of two substructures connected with a joint are measured, while the FRFs of the substructures are obtained numerically or experimentally. Then the joint properties are calculated in terms of translational, rotational and cross-coupling stiffness and damping values by using FRF decoupling. In order to eliminate the numerical errors associated with matrix inversion an optimization algorithm is used to update the joint values obtained from FRF decoupling. The validity of the proposed method is demonstrated with experimental studies with bolted joints.

  20. Injury Criteria for Dynamic Hyperextension of the Female Elbow Joint

    DTIC Science & Technology

    2006-11-01

    1 INJURY CRITERIA FOR DYNAMIC HYPEREXTENSION OF THE FEMALE ELBOW JOINT Stefan M. Duma*, Gail A. Hansen, Eric A. Kennedy, Joel D. Stitzel...Laboratory Fort Rucker, AL 36362 ABSTRACT This paper describes an analysis to develop dynamic hyperextension injury criteria for the female elbow ...joint. Dynamic hyperextension tests were performed on 24 female cadaver elbow joints. The energy source was a drop tower utilizing a three-point

  1. connecting the dots between Greenland ice sheet surface melting and ice flow dynamics (Invited)

    NASA Astrophysics Data System (ADS)

    Box, J. E.; Colgan, W. T.; Fettweis, X.; Phillips, T. P.; Stober, M.

    2013-12-01

    This presentation is of a 'unified theory' in glaciology that first identifies surface albedo as a key factor explaining total ice sheet mass balance and then surveys a mechanistic self-reinforcing interaction between melt water and ice flow dynamics. The theory is applied in a near-real time total Greenland mass balance retrieval based on surface albedo, a powerful integrator of the competing effects of accumulation and ablation. New snowfall reduces sunlight absorption and increases meltwater retention. Melting amplifies absorbed sunlight through thermal metamorphism and bare ice expansion in space and time. By ';following the melt'; we reveal mechanisms linking existing science into a unified theory. Increasing meltwater softens the ice sheet in three ways: 1.) sensible heating given the water temperature exceeds that of the ice sheet interior; 2.) Some infiltrating water refreezes, transferring latent heat to the ice; 3.) Friction from water turbulence heats the ice. It has been shown that for a point on the ice sheet, basal lubrication increases ice flow speed to a time when an efficient sub-glacial drainage network develops that reduces this effect. Yet, with an increasing melt duration the point where the ice sheet glides on a wet bed increases inland to a larger area. This effect draws down the ice surface elevation, contributing to the ';elevation feedback'. In a perpetual warming scenario, the elevation feedback ultimately leads to ice sheet loss reversible only through much slower ice sheet growth in an ice age environment. As the inland ice sheet accelerates, the horizontal extension pulls cracks and crevasses open, trapping more sunlight, amplifying the effect of melt accelerated ice. As the bare ice area increases, the direct sun-exposed crevassed and infiltration area increases further allowing the ice warming process to occur more broadly. Considering hydrofracture [a.k.a. hydrofracking]; surface meltwater fills cracks, attacking the ice integrity

  2. Dynamical mechanism of antifreeze proteins to prevent ice growth

    NASA Astrophysics Data System (ADS)

    Kutschan, B.; Morawetz, K.; Thoms, S.

    2014-08-01

    The fascinating ability of algae, insects, and fishes to survive at temperatures below normal freezing is realized by antifreeze proteins (AFPs). These are surface-active molecules and interact with the diffusive water-ice interface thus preventing complete solidification. We propose a dynamical mechanism on how these proteins inhibit the freezing of water. We apply a Ginzburg-Landau-type approach to describe the phase separation in the two-component system (ice, AFP). The free-energy density involves two fields: one for the ice phase with a low AFP concentration and one for liquid water with a high AFP concentration. The time evolution of the ice reveals microstructures resulting from phase separation in the presence of AFPs. We observed a faster clustering of pre-ice structure connected to a locking of grain size by the action of AFP, which is an essentially dynamical process. The adsorption of additional water molecules is inhibited and the further growth of ice grains stopped. The interfacial energy between ice and water is lowered allowing the AFPs to form smaller critical ice nuclei. Similar to a hysteresis in magnetic materials we observe a thermodynamic hysteresis leading to a nonlinear density dependence of the freezing point depression in agreement with the experiments.

  3. Dynamical mechanism of antifreeze proteins to prevent ice growth.

    PubMed

    Kutschan, B; Morawetz, K; Thoms, S

    2014-08-01

    The fascinating ability of algae, insects, and fishes to survive at temperatures below normal freezing is realized by antifreeze proteins (AFPs). These are surface-active molecules and interact with the diffusive water-ice interface thus preventing complete solidification. We propose a dynamical mechanism on how these proteins inhibit the freezing of water. We apply a Ginzburg-Landau-type approach to describe the phase separation in the two-component system (ice, AFP). The free-energy density involves two fields: one for the ice phase with a low AFP concentration and one for liquid water with a high AFP concentration. The time evolution of the ice reveals microstructures resulting from phase separation in the presence of AFPs. We observed a faster clustering of pre-ice structure connected to a locking of grain size by the action of AFP, which is an essentially dynamical process. The adsorption of additional water molecules is inhibited and the further growth of ice grains stopped. The interfacial energy between ice and water is lowered allowing the AFPs to form smaller critical ice nuclei. Similar to a hysteresis in magnetic materials we observe a thermodynamic hysteresis leading to a nonlinear density dependence of the freezing point depression in agreement with the experiments.

  4. Nucleation processes occurring during dynamic recrystallization in ice

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

  5. Ice formation on kaolinite: Insights from molecular dynamics simulations

    NASA Astrophysics Data System (ADS)

    Sosso, Gabriele C.; Tribello, Gareth A.; Zen, Andrea; Pedevilla, Philipp; Michaelides, Angelos

    2016-12-01

    The formation of ice affects many aspects of our everyday life as well as important technologies such as cryotherapy and cryopreservation. Foreign substances almost always aid water freezing through heterogeneous ice nucleation, but the molecular details of this process remain largely unknown. In fact, insight into the microscopic mechanism of ice formation on different substrates is difficult to obtain even if state-of-the-art experimental techniques are used. At the same time, atomistic simulations of heterogeneous ice nucleation frequently face extraordinary challenges due to the complexity of the water-substrate interaction and the long time scales that characterize nucleation events. Here, we have investigated several aspects of molecular dynamics simulations of heterogeneous ice nucleation considering as a prototypical ice nucleating material the clay mineral kaolinite, which is of relevance in atmospheric science. We show via seeded molecular dynamics simulations that ice nucleation on the hydroxylated (001) face of kaolinite proceeds exclusively via the formation of the hexagonal ice polytype. The critical nucleus size is two times smaller than that obtained for homogeneous nucleation at the same supercooling. Previous findings suggested that the flexibility of the kaolinite surface can alter the time scale for ice nucleation within molecular dynamics simulations. However, we here demonstrate that equally flexible (or non flexible) kaolinite surfaces can lead to very different outcomes in terms of ice formation, according to whether or not the surface relaxation of the clay is taken into account. We show that very small structural changes upon relaxation dramatically alter the ability of kaolinite to provide a template for the formation of a hexagonal overlayer of water molecules at the water-kaolinite interface, and that this relaxation therefore determines the nucleation ability of this mineral.

  6. Arctic ice shelves and ice islands: Origin, growth and disintegration, physical characteristics, structural-stratigraphic variability, and dynamics

    SciTech Connect

    Jeffries, M.O. )

    1992-08-01

    Ice shelves are thick, floating ice masses most often associated with Antarctica where they are seaward extensions of the grounded Antarctic ice sheet and sources of many icebergs. However, there are also ice shelves in the Arctic, primarily located along the north coast of Ellesmere Island in the Canadian High Arctic. The only ice shelves in North America and the most extensive in the north polar region, the Ellesmere ice shelves originate from glaciers and from sea ice and are the source of ice islands, the tabular icebergs of the Arctic Ocean. The present state of knowledge and understanding of these ice features is summarized in this paper. It includes historical background to the discovery and early study of ice shelves and ice islands, including the use of ice islands as floating laboratories for polar geophysical research. Growth mechanisms and age, the former extent and the twentieth century disintegration of the Ellesmere ice shelves, and the processes and mechanisms of ice island calving are summarized. Surface features, thickness, thermal regime, and the size, shape, and numbers of ice islands are discussed. The structural-stratigraphic variability of ice islands and ice shelves and the complex nature of their growth and development are described. Large-scale and small-scale dynamics of ice islands are described, and the results of modeling their drift and recurrence intervals are presented. The conclusion identifies some unanswered questions and future research opportunities and needs. 97 refs., 18 figs.

  7. Dynamic Ice-Water Interactions Form Europa's Chaos Terrains

    NASA Astrophysics Data System (ADS)

    Blankenship, D. D.; Schmidt, B. E.; Patterson, G. W.; Schenk, P.

    2011-12-01

    Unique to the surface of Europa, chaos terrain is diagnostic of the properties and dynamics of its icy shell. We present a new model that suggests large melt lenses form within the shell and that water-ice interactions above and within these lenses drive the production of chaos. This model is consistent with key observations of chaos, predicts observables for future missions, and indicates that the surface is likely still active today[1]. We apply lessons from ice-water interaction in the terrestrial cryosphere to hypothesize a dynamic lense-collapse model to for Europa's chaos terrain. Chaos terrain morphology, like that of Conamara chaos and Thera Macula, suggests a four-phase formation [1]: 1) Surface deflection occurs as ice melts over ascending thermal plumes, as regularly occurs on Earth as subglacial volcanoes activate. The same process can occur at Europa if thermal plumes cause pressure melt as they cross ice-impurity eutectics. 2) Resulting hydraulic gradients and driving forces produce a sealed, pressurized melt lense, akin to the hydraulic sealing of subglacial caldera lakes. On Europa, the water cannot escape the lense due to the horizontally continuous ice shell. 3) Extension of the brittle ice lid above the lense opens cracks, allowing for the ice to be hydrofractured by pressurized water. Fracture, brine injection and percolation within the ice and possible iceberg toppling produces ice-melange-like granular matrix material. 4) Refreezing of the melt lense and brine-filled pores and cracks within the matrix results in raised chaos. Brine soaking and injection concentrates the ice in brines and adds water volume to the shell. As this englacial water freezes, the now water-filled ice will expand, not unlike the process of forming pingos and other "expansion ice" phenomena on Earth. The refreezing can raise the surface and create the oft-observed matrix "domes" In this presentation, we describe how catastrophic ice-water interactions on Earth have

  8. Self-consistent ice-sheet properties: ice dynamics, temperature, accumulation, delta-age and chronologies for ice cores and radar isochrones

    NASA Astrophysics Data System (ADS)

    Lundin, J.; Waddington, E. D.; Conway, H.

    2011-12-01

    Ice sheet behavior has not previously been modeled to force self-consistency, to determine histories of accumulation, temperature, and ice dynamics that incorporate the ice-age/gas-age offset (delta-age) and sparse depth-age measurements from ice cores. An iterative scheme is used to combine several modular components into one self-consistent model. The goal is to determine a suite of histories constrained by the depth-age data from ice cores and ice radar that are part of a physically self-consistent ice sheet. The model is tested using a synthetic data set resembling WAIS divide. Using synthetic data provides proof of concept that histories of accumulation, temperature and ice dynamics can be recovered by the self-consistent model, and that the depth-age from ice cores and ice radar can be matched. Results from synthetic data show we can recover the ice-sheet properties used to generate the data and we can improve the depth-age chronologies by interpolating with an ice-flow model where data are sparse. When this self-consistent model can be applied to field data, results will (1) improve chronologies for ice cores and radar layers, (2) determine histories of accumulation for GCM modelling, and (3) improve estimates of past ice sheet configurations, incorporating data from ice cores and ice radar.

  9. Nonlinear dynamic characteristic analysis of jointed beam with clearance

    NASA Astrophysics Data System (ADS)

    Zhang, Jing; Guo, Hong-Wei; Liu, Rong-Qiang; Wu, Juan; Kou, Zi-Ming; Deng, Zong-Quan

    2016-12-01

    The impact and elasticity of discontinuous beams with clearance frequently affect the dynamic response of structures used in space missions. This study investigates the dynamic response of jointed beams which are the periodic units of deployable structures. The vibration process of jointed beams includes free-play and impact stages. A method for the dynamic analysis of jointed beams with clearance is proposed based on mode superposition and instantaneous static deformation. Transfer matrix, which expresses the relationship of the responses before and after the impact of jointed beams, is derived to calculate the response of the jointed beams after a critical position. The dynamic responses of jointed beams are then simulated. The effects of various parameters on the displacement and velocity of beams are investigated.

  10. Sensitivity study of a dynamic thermodynamic sea ice model

    SciTech Connect

    Holland, D.M.; Mysak, L.A.; Manak, D.K. )

    1993-02-15

    A numerical simulation of the seasonal sea ice cover in the Arctic Ocean and the Greenland, Iceland, and Norwegian seas is presented. The sea ice model is extracted from Oberhuber's (1990) coupled sea ice-mixed layer-isopycnal general circulation model and is written in spherical coordinates. The advantage of such a model over previous sea ice models is that it can be easily coupled to either global atmospheric or ocean general circulation models written in spherical coordinates. In this model, the thermodynamics are a modification of that of Parkinson and Washington, while the dynamics use the full Hibler viscous-plastic rheology. Monthly thermodynamic and dynamic forcing fields for the atmosphere and ocean are specified. The simulations of the seasonal cycle of ice thickness, compactness, and velocity, for a control set of parameters, compare favorably with the known seasonal characteristics of these fields. A sensitivity study of the control simulation of the seasonal sea ice cover is presented. The sensitivity runs are carried out under three different themes, namely, numerical conditions, parameter values, and physical processes. This last theme refers to experiments in which physical processes are either newly added or completely removed from the model. Approximately 80 sensitivity runs have been performed in which a change from the control run environment has been implemented. Comparisons have been made between the control run and a particular sensitivity run based on time series of the seasonal cycle of the domain-averaged ice thickness, compactness, areal coverage, and kinetic energy. In addition, spatially varying fields of ice thickness, compactness, velocity, and surface temperature for each season are presented for selected experiments. A brief description and discussion of the more interesting experiments are presented. The simulation of the seasonal cycle of Arctic sea ice cover is shown to be robust. 31 refs., 20 figs., 5 tabs.

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

    PubMed

    Yan, J Y; Patey, G N

    2012-07-05

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

  12. Uncertainties and dynamic problems of bolted joints and other fasteners

    NASA Astrophysics Data System (ADS)

    Ibrahim, R. A.; Pettit, C. L.

    2005-01-01

    This review article provides an overview of the problems pertaining to structural dynamics with bolted joints. These problems are complex in nature because every joint involves different sources of uncertainty and non-smooth non-linear characteristics. For example, the contact forces are not ideally plane due to manufacturing tolerances of contact surfaces. Furthermore, the initial forces will be redistributed non-uniformly in the presence of lateral loads. This is in addition to the prying loading, which is non-linear tension in the bolt and non-linear compression in the joint. Under environmental dynamic loading, the joint preload experiences some relaxation that results in time variation of the structure's dynamic properties. Most of the reported studies focused on the energy dissipation of bolted joints, linear and non-linear identification of the dynamic properties of the joints, parameter uncertainties and relaxation, and active control of the joint preload. Design issues of fully and partially restrained joints, sensitivity analysis to variations of joint parameters, and fatigue prediction for metallic and composite joints will be discussed.

  13. Joint inversion of multi-component seismic and ground-penetrating radar GPR) data for ice-physical properties, and application to the Larsen C ice shelf

    NASA Astrophysics Data System (ADS)

    Kulessa, B.; King, E. C.; Barrett, B. E.; Jansen, D.; Luckman, A. J.; Sammonds, P.

    2010-12-01

    Present and next-generation ice-sheet and ice-shelf models require constraints on spatial variations in ice physical properties such as temperature, density, preferred crystal alignment or the porosity of basal marine-ice layers. In-situ or airborne geophysical measurements are a powerful means of generating multi-proxy information for modelling purposes, and new airborne and land-based geophysical acquisition platforms promise to generate vast quantities of high-quality data covering rapidly large areas of the Antarctic and Greenland ice sheets. It is therefore timely to develop new, or adapt from other areas of the geosciences, geophysical processing and joint inversion techniques that exploit these data sets to their full capacity to maximise their value to ice-sheet models. Here we report on the application of state-of-the-science geophysical joint inversion and interpretation techniques to multi-azimuth, multi-component seismic and ground-penetrating radar (GPR) data collected at two control sites on the southeastern Larsen C ice shelf. The southern site was located on an ice flow unit that derives from discharge through the Mobile Oil Inlet, and is characterised by basal melting. The northern site was located on a thin flow unit that originated downflow of the Joerg Peninsula, and is characterised by a thick (up to ~ half the total ice thickness) basal layer of marine ice. We identify the scope of joint, as compared with more conventional separate, inversion of seismic and GPR attributes for multi-proxy properties of these two contrasting sites, and discuss the implications for ice-shelf flow as well as an optimised acquisition and processing strategy.

  14. Dynamics of the Ross Ice Shelf

    NASA Technical Reports Server (NTRS)

    Casassa, Gino; Turner, John

    1991-01-01

    The changing flow of the Ross Ice Shelf is described based on AVHRR data from 18 cloud-free images which evince flow stripes and form the data for a glaciological map. The discharge region of the valley glaciers in the Transantarctic Mountains is found to have curvilinear stripes, and the brightness contrast is enhanced to examine the feature. The map of the region also shows rifts, ridge crests, surface folds, and large-scale lineaments.

  15. Antarctic Ice-Shelf Front Dynamics from ICESat

    NASA Technical Reports Server (NTRS)

    Robbins, John W.; Zwally, H. Jay; Saba, Jack L.; Yi, Donghui

    2012-01-01

    Time variable elevation profiles from ICESat Laser Altimetry over the period 2003-2009 provide a means to quantitatively detect and track topographic features on polar ice surfaces. The results of this study provide a measure of the horizontal motion of ice-shelf fronts. We examine the time histories of elevation profiles crossing the ice fronts of the Ross, Ronne, Filchner, Riiser-Larson and Fimbul shelves. This provides a basis for estimating dynamics in two dimensions, i.e. in elevation and horizontally in the along-track direction. Ice front velocities, corrected for ground-track intersection angle, range from nearly static to 1.1 km/yr. In many examples, a decrease in elevation up to 1 m/yr near the shelf frontis also detectable. Examples of tabular calving along shelf fronts are seen in some elevation profiles and are confirmed by corresponding MODIS imagery.

  16. Skill improvement of dynamical seasonal Arctic sea ice forecasts

    NASA Astrophysics Data System (ADS)

    Krikken, Folmer; Schmeits, Maurice; Vlot, Willem; Guemas, Virginie; Hazeleger, Wilco

    2016-05-01

    We explore the error and improve the skill of the outcome from dynamical seasonal Arctic sea ice reforecasts using different bias correction and ensemble calibration methods. These reforecasts consist of a five-member ensemble from 1979 to 2012 using the general circulation model EC-Earth. The raw model reforecasts show large biases in Arctic sea ice area, mainly due to a differently simulated seasonal cycle and long term trend compared to observations. This translates very quickly (1-3 months) into large biases. We find that (heteroscedastic) extended logistic regressions are viable ensemble calibration methods, as the forecast skill is improved compared to standard bias correction methods. Analysis of regional skill of Arctic sea ice shows that the Northeast Passage and the Kara and Barents Sea are most predictable. These results show the importance of reducing model error and the potential for ensemble calibration in improving skill of seasonal forecasts of Arctic sea ice.

  17. Dynamics of coupled ice-ocean system in the marginal ice zone: Study of the mesoscale processes and of constitutive equations for sea ice

    NASA Technical Reports Server (NTRS)

    Hakkinen, S.

    1984-01-01

    This study is aimed at the modelling of mesoscale processed such as up/downwelling and ice edge eddies in the marginal ice zones. A 2-dimensional coupled ice-ocean model is used for the study. The ice model is coupled to the reduced gravity ocean model (f-plane) through interfacial stresses. The constitutive equations of the sea ice are formulated on the basis of the Reiner-Rivlin theory. The internal ice stresses are important only at high ice concentrations (90-100%), otherwise the ice motion is essentially free drift, where the air-ice stress is balanced by the ice-water stress. The model was tested by studying the upwelling dynamics. Winds parallel to the ice edge with the ice on the right produce upwilling because the air-ice momentum flux is much greater that air-ocean momentum flux, and thus the Ekman transport is bigger under the ice than in the open water. The upwelling simulation was extended to include temporally varying forcing, which was chosen to vary sinusoidally with a 4 day period. This forcing resembles successive cyclone passings. In the model with a thin oceanic upper layer, ice bands were formed.

  18. Changes in Ice Flow Dynamics of Totten Glacier, East Antarctica and Impacts on Ice Mass Balance

    NASA Astrophysics Data System (ADS)

    Li, X.; Rignot, E. J.; Mouginot, J.; Scheuchl, B.; An, L.

    2014-12-01

    Totten Glacier, East Antarctica is one of the largest glaciers in Antarctica, draining an area of 5.3*105 km2 and containing ice at an equivalent 9 m sea level rise. Lidar/radar altimetry data from 2003-2009 suggests that the glacier is thinning. Thinning is concentrated in areas of fast flow and therefore indicative of changes in ice dynamics. Here, we employ time series of ice velocity from ERS-1/2, RADARSAT-1, LANDSAT-7, ALOS PALSAR, TanDEM/TerraSAR-X and COSMO-Skymed to measure the glacier velocity from 1996 till present. We find significant temporal changes in ice velocity, especially in 1996-2007, followed by a period of slow decrease in 2010-2013. Comparing the results with RACMO2 surface mass balance in the interior suggests that the glacier mass balance was already negative in 1996 and became more negative into the 2000s. The resulting mass loss and stretching of the ice is compatible with the 1.5 m/yr thinning detected by the radar altimeters near the grounding zone. The grounding zone of the glacier includes a vast 15 km long ice plain where the glacier is only grounded a few 10m above hydrostatic equilibrium. We detect a retreat of the region of partial floatation with time, but not solid migration of the grounding line of the glacier. Inverted bathymetry results from gravity data collected offshore suggest the presence of a paleo subglacial channel conducive to the transfer of surface ocean heat, likely diluted circumpolar deep water, whose transfer to the ice shelf cavity may have affected the glacier stability. We suggest that further transfer of ocean heat to the ice shelf could trigger a rapid glacier retreat in this region.

  19. Ionization dynamics of water dimer on ice surface

    NASA Astrophysics Data System (ADS)

    Tachikawa, Hiroto

    2016-05-01

    The solid surface provides an effective two-dimensional reaction field because the surface increases the encounter probability of bi-molecular collision reactions. Also, the solid surface stabilizes a reaction intermediate because the excess energy generated by the reaction dissipates into the bath modes of surface. The ice surface in the universe is one of the two dimensional reaction fields. However, it is still unknown how the ice surface affects to the reaction mechanism. In the present study, to elucidate the specific property of the ice surface reaction, ionization dynamics of water dimer adsorbed on the ice surface was theoretically investigated by means of direct ab-initio molecular dynamics (AIMD) method combined with ONIOM (our own n-layered integrated molecular orbital and molecular mechanics) technique, and the result was compared with that of gas phase reaction. It was found that a proton is transferred from H2O+ to H2O within the dimer and the intermediate complex H3O+(OH) is formed in both cases. However, the dynamic features were different from each other. The reaction rate of the proton transfer on the ice surface was three times faster than that in the gas phase. The intermediate complex H3O+(OH) was easily dissociated to H3O+ and OH radical on the ice surface, and the lifetime of the complex was significantly shorter than that of gas phase (100 fs vs. infinite). The reason why the ice surface accelerates the reaction was discussed in the present study.

  20. Inter-annual sea-ice dynamics and micro-algal biomass in winter pack ice of Marguerite Bay, Antarctica

    NASA Astrophysics Data System (ADS)

    Fritsen, Christian H.; Memmott, Jeramie; Stewart, Frank J.

    2008-09-01

    The geographic remoteness, the lack of remote sensing capabilities, and the lack of appropriate environmental sensors make the detection of seasonal trends or inter-annual variations in sea-ice microbial biomass or production processes within the pack ice of the Antarctic extremely rare. The evaluation of their inter-annual variability in the context of ice dynamics and trends in regional climate has not been possible. During the late winters of 2001 (July-August) and 2002 (August-September) we assessed sea-ice dynamics, sea-ice characteristics, and biomass of sea-ice microbiota along the Western Antarctic Peninsula. These two winters were marked by large contrasts in the dates of initial ice formation (late June in 2001 and April in 2002), which resulted in differences in the physical pack-ice characteristics. Chlorophyll a (chl a) content in ice cores differed between the study years, with 2002 having 10-fold higher chl a content. The difference in ice-core chl a content is best explained by the timing of ice formation that leads to less phytoplankton scavenging from the water column and a lack of transfer of solar energy into the pack-ice ecosystem. Such a tractable atmosphere ocean-ice-biota coupling may help in evaluating underlying processes responsible for long-term trends in recruitment cycles of upper trophic levels as well as future projections on the response of the Antarctic marine ecosystems to variability in local climate.

  1. Wrist rhythm during wrist joint motion evaluated by dynamic radiography.

    PubMed

    Kawashima, Hiroki; Tada, Kaoru; Suganuma, Seigo; Tsuchiya, Hiroyuki; Sanada, Shigeru

    2014-01-01

    We hypothesized that wrist joint motion involves a "wrist rhythm" similar to the scapulohumeral rhythm. Therefore, we used a flat-panel detector to evaluate the ratio of radiolunate and capitolunate joint motions during wrist joint motion by dynamic radiography. The subjects were 20 healthy men. Dynamic imaging of the wrist joint was performed during active exercise for a total of ten seconds. In this study, we defined the radiocarpal (RL angle) and midcarpal joint angle (CL angle) as the wrist joint angle in the obtained images and measured the variation of these angles. The average curve was plotted and regression lines calculated from the average curve. The ratio was calculated from the slopes of the regression lines of the RL CL angles. These findings indicated that the ratio of the RL and CL angle motions was approximately 1:4 during palmar flexion and approximately 2:1 during dorsiflexion.

  2. Laser altimetry reveals complex pattern of Greenland Ice Sheet dynamics.

    PubMed

    Csatho, Beata M; Schenk, Anton F; van der Veen, Cornelis J; Babonis, Gregory; Duncan, Kyle; Rezvanbehbahani, Soroush; van den Broeke, Michiel R; Simonsen, Sebastian B; Nagarajan, Sudhagar; van Angelen, Jan H

    2014-12-30

    We present a new record of ice thickness change, reconstructed at nearly 100,000 sites on the Greenland Ice Sheet (GrIS) from laser altimetry measurements spanning the period 1993-2012, partitioned into changes due to surface mass balance (SMB) and ice dynamics. We estimate a mean annual GrIS mass loss of 243 ± 18 Gt ⋅ y(-1), equivalent to 0.68 mm ⋅ y(-1) sea level rise (SLR) for 2003-2009. Dynamic thinning contributed 48%, with the largest rates occurring in 2004-2006, followed by a gradual decrease balanced by accelerating SMB loss. The spatial pattern of dynamic mass loss changed over this time as dynamic thinning rapidly decreased in southeast Greenland but slowly increased in the southwest, north, and northeast regions. Most outlet glaciers have been thinning during the last two decades, interrupted by episodes of decreasing thinning or even thickening. Dynamics of the major outlet glaciers dominated the mass loss from larger drainage basins, and simultaneous changes over distances up to 500 km are detected, indicating climate control. However, the intricate spatiotemporal pattern of dynamic thickness change suggests that, regardless of the forcing responsible for initial glacier acceleration and thinning, the response of individual glaciers is modulated by local conditions. Recent projections of dynamic contributions from the entire GrIS to SLR have been based on the extrapolation of four major outlet glaciers. Considering the observed complexity, we question how well these four glaciers represent all of Greenland's outlet glaciers.

  3. Feedbacks between ice and ocean dynamics at the West Antarctic Filchner-Ronne Ice Shelf in future global warming scenarios

    NASA Astrophysics Data System (ADS)

    Goeller, Sebastian; Timmermann, Ralph

    2016-04-01

    The ice flow at the margins of the West Antarctic Ice Sheet is moderated by large ice shelves. Their buttressing effect substantially controls the mass balance of the WAIS and thus its contribution to sea level rise. The stability of these ice shelves results from the balance of mass gain by accumulation and ice flow from the adjacent ice sheet and mass loss by calving and basal melting due to the ocean heat flux. Recent results of ocean circulation models indicate that warm circumpolar water of the Southern Ocean may override the submarine slope front of the Antarctic Continent and boost basal ice shelf melting. In particular, ocean simulations for several of the IPCC's future climate scenarios demonstrate the redirection of a warm coastal current into the Filchner Trough and underneath the Filchner-Ronne Ice Shelf within the next decades. In this study, we couple the finite elements ocean circulation model FESOM and the three-dimensional thermomechanical ice flow model RIMBAY to investigate the complex interactions between ocean and ice dynamics at the Filchner-Ronne Ice Shelf. We focus on the impact of a changing ice shelf cavity on ocean dynamics as well as the feedback of the resulting sub-shelf melting rates on the ice shelf geometry and implications for the dynamics of the adjacent marine-based Westantarctic Ice Sheet. Our simulations reveal the high sensitivity of grounding line migration to ice-ocean interactions within the Filchner-Ronne Ice Shelf and emphasize the importance of coupled model studies for realistic assessments of the Antarctic mass balance in future global warming scenarios.

  4. Framework for Control of Dynamic Ice Breakup by River Regulation

    DTIC Science & Technology

    1989-06-01

    and if ration. Other important characteristics of these wave formation occurs upstream or in a tribu - waves are significant stage increase, short dura...stage must occur to produce the high forces cut River danis for a controlled ice lireakup experi- needed for a dynamic breakup, and very high 1e1it

  5. Dynamics of ice drop explosions in supercooled clouds

    NASA Astrophysics Data System (ADS)

    Lohse, Detlef; Wildeman, Sander; Sterl, Sebastian; Sun, Chao

    2016-11-01

    The rate at which ice particles are produced in the cold top of natural clouds is crucial in predicting whether a cloud will finally develop precipitation. It has been speculated that ice particles could multiply through freezing and subsequent bursting of supercooled cloud droplets. Here we present high-speed footage of cracking and explosive bursting of spherical water droplets that freeze radially inwards under carefully controlled conditions. We model the processes of freezing, the stress build up in the ice shell, and the fast dynamics following the crack formation. This allows us to predict the time it takes for a freezing droplet to explode and the energy released in this event as a function of the size of the droplet and the temperature of the surroundings. Both predictions are in good agreement with our experiments. The models also predict a minimum droplet radius of approximately 50 μm below which ice explosions are unlikely to occur. This finding has direct consequences in the modeling of cloud microphysics, as the droplet sizes in clouds generally fall in this critical range. Furthermore, we identify several mechanisms, besides the final explosion, by which a freezing drop can shed ice particles. This is important for the formation of ice nucleation avalanches.

  6. Airborne radar evidence for tributary flow switching in Institute Ice Stream, West Antarctica: Implications for ice sheet configuration and dynamics

    NASA Astrophysics Data System (ADS)

    Winter, Kate; Woodward, John; Ross, Neil; Dunning, Stuart A.; Bingham, Robert G.; Corr, Hugh F. J.; Siegert, Martin J.

    2015-09-01

    Despite the importance of ice streaming to the evaluation of West Antarctic Ice Sheet (WAIS) stability we know little about mid- to long-term dynamic changes within the Institute Ice Stream (IIS) catchment. Here we use airborne radio echo sounding to investigate the subglacial topography, internal stratigraphy, and Holocene flow regime of the upper IIS catchment near the Ellsworth Mountains. Internal layer buckling within three discrete, topographically confined tributaries, through Ellsworth, Independence, and Horseshoe Valley Troughs, provides evidence for former enhanced ice sheet flow. We suggest that enhanced ice flow through Independence and Ellsworth Troughs, during the mid-Holocene to late Holocene, was the source of ice streaming over the region now occupied by the slow-flowing Bungenstock Ice Rise. Although buckled layers also exist within the slow-flowing ice of Horseshoe Valley Trough, a thicker sequence of surface-conformable layers in the upper ice column suggests slowdown more than ~4000 years ago, so we do not attribute enhanced flow switch-off here, to the late Holocene ice-flow reorganization. Intensely buckled englacial layers within Horseshoe Valley and Independence Troughs cannot be accounted for under present-day flow speeds. The dynamic nature of ice flow in IIS and its tributaries suggests that recent ice stream switching and mass changes in the Siple Coast and Amundsen Sea sectors are not unique to these sectors, that they may have been regular during the Holocene and may characterize the decline of the WAIS.

  7. Tunable nonequilibrium dynamics of field quenches in spin ice

    PubMed Central

    Mostame, Sarah; Castelnovo, Claudio; Moessner, Roderich; Sondhi, Shivaji L.

    2014-01-01

    We present nonequilibrium physics in spin ice as a unique setting that combines kinematic constraints, emergent topological defects, and magnetic long-range Coulomb interactions. In spin ice, magnetic frustration leads to highly degenerate yet locally constrained ground states. Together, they form a highly unusual magnetic state—a “Coulomb phase”—whose excitations are point-like defects—magnetic monopoles—in the absence of which effectively no dynamics is possible. Hence, when they are sparse at low temperature, dynamics becomes very sluggish. When quenching the system from a monopole-rich to a monopole-poor state, a wealth of dynamical phenomena occur, the exposition of which is the subject of this article. Most notably, we find reaction diffusion behavior, slow dynamics owing to kinematic constraints, as well as a regime corresponding to the deposition of interacting dimers on a honeycomb lattice. We also identify potential avenues for detecting the magnetic monopoles in a regime of slow-moving monopoles. The interest in this model system is further enhanced by its large degree of tunability and the ease of probing it in experiment: With varying magnetic fields at different temperatures, geometric properties—including even the effective dimensionality of the system—can be varied. By monitoring magnetization, spin correlations or zero-field NMR, the dynamical properties of the system can be extracted in considerable detail. This establishes spin ice as a laboratory of choice for the study of tunable, slow dynamics. PMID:24379372

  8. Tunable nonequilibrium dynamics of field quenches in spin ice.

    PubMed

    Mostame, Sarah; Castelnovo, Claudio; Moessner, Roderich; Sondhi, Shivaji L

    2014-01-14

    We present nonequilibrium physics in spin ice as a unique setting that combines kinematic constraints, emergent topological defects, and magnetic long-range Coulomb interactions. In spin ice, magnetic frustration leads to highly degenerate yet locally constrained ground states. Together, they form a highly unusual magnetic state--a "Coulomb phase"--whose excitations are point-like defects--magnetic monopoles--in the absence of which effectively no dynamics is possible. Hence, when they are sparse at low temperature, dynamics becomes very sluggish. When quenching the system from a monopole-rich to a monopole-poor state, a wealth of dynamical phenomena occur, the exposition of which is the subject of this article. Most notably, we find reaction diffusion behavior, slow dynamics owing to kinematic constraints, as well as a regime corresponding to the deposition of interacting dimers on a honeycomb lattice. We also identify potential avenues for detecting the magnetic monopoles in a regime of slow-moving monopoles. The interest in this model system is further enhanced by its large degree of tunability and the ease of probing it in experiment: With varying magnetic fields at different temperatures, geometric properties--including even the effective dimensionality of the system--can be varied. By monitoring magnetization, spin correlations or zero-field NMR, the dynamical properties of the system can be extracted in considerable detail. This establishes spin ice as a laboratory of choice for the study of tunable, slow dynamics.

  9. Mertz Ice Shelf Dynamics in the Last Twenty Years

    NASA Astrophysics Data System (ADS)

    Wang, X.; Cheng, X.; Shum, C.

    2013-12-01

    . These parameters extracted from remote sensing and altimetry data will provide additional information for studies of the evolution of iceberg, especially in iceberg tracking system. Mertz Ice Shelf Dynamics in the last 20 years

  10. Kinematic Model of River Ice Motion During Dynamic Breakup

    DTIC Science & Technology

    1993-09-01

    Texas: Gulf Publish- nal of Computational Physics, 101: 130-139. ing Co. Shen, H.T. and Y.C. Chen (1992) Lagrangian discrete Calkins , DJ. (1978...OTIC9 ~jjELECTE0 lV 919 3 AD-A273 141 * Kinematic Model of River Ice Motion During Dynamic Breakup Michael G . Ferrick, Patricia B. Weyrick and David...Bottom) Looking across the river during brash ice motion at about 1 m /s. (Photos by M . Ferrick.) For conversion of SI metric units to U.S./British

  11. Dynamic dependence to domain wall propagation through artificial spin ice

    NASA Astrophysics Data System (ADS)

    Burn, D. M.; Chadha, M.; Branford, W. R.

    2017-03-01

    Domain wall propagation dynamics has been studied in nanostructured artificial kagome spin-ice structures. A stripline circuit has been used to provide localized pulsed magnetic fields within the artificial spin-ice (ASI) structure. This provides control of the system through electrically assisted domain wall nucleation events. Synchronization of the pulsed fields with additional global magnetic fields and the use of a focused magneto-optical Kerr effect magnetometer allows our experiments to probe the domain wall transit through an extended ASI structure. We find that the propagation distance depends on the driving field revealing field-driven properties of domain walls below their intrinsic nucleation field.

  12. Structural dynamic analysis of a ball joint

    NASA Astrophysics Data System (ADS)

    Hwang, Seok-Cheol; Lee, Kwon-Hee

    2012-11-01

    Ball joint is a rotating and swiveling element that is typically installed at the interface between two parts. In an automobile, the ball joint is the component that connects the control arms to the steering knuckle. The ball joint can also be installed in linkage systems for motion control applications. This paper describes the simulation strategy for a ball joint analysis, considering manufacturing process. Its manufacturing process can be divided into plugging and spinning. Then, the interested responses is selected as the stress distribution generated between its ball and bearing. In this paper, a commercial code of NX DAFUL using an implicit integration method is introduced to calculate the response. In addition, the gap analysis is performed to investigate the fitness, focusing on the response of the displacement of a ball stud. Also, the optimum design is suggested through case studies.

  13. Non-equilibrium dynamics and structure of interfacial ice

    NASA Astrophysics Data System (ADS)

    Andreussi, Oliviero; Donadio, Davide; Parrinello, Michele; Zewail, Ahmed H.

    2006-07-01

    Stimulated by recent experiments [C.-Y. Ruan et al. Science 304, (2004) 81], we have performed molecular dynamics and ab initio structural studies of the laser-induced heating and restructuring processes of nanometer-scale ice on a substrate of chlorine terminated Si(1 1 1). Starting from proton disordered cubic ice configurations the thin film behavior has been characterized at several temperatures up to the melting point. The surface induces order with crystallization in the Ic lattice, but with void amorphous regions. The structure changes on the ultrashort time scale and restructures by heat dissipation depending on the relaxation time and final temperature. Our results show the general behavior observed experimentally, thus providing the nature of forces in the atomic-scale description of interfacial ice.

  14. An elastic-viscous-plastic model for sea ice dynamics

    SciTech Connect

    Hunke, E.C.; Dukowicz, J.K.

    1996-10-01

    The standard model for sea ice dynamics treats the ice pack as a viscous-plastic material that flows plastically under typical stress conditions but behaves as a linear viscous fluid where strain rates are small and the ice becomes nearly rigid. Because of large viscosities in these regions, implicit numerical methods are necessary for timesteps larger than a few seconds. Current solution methods for these equations use iterative relaxation methods, which are time consuming, scale poorly with mesh resolution, and are not well adapted to parallel computation. To remedy this, we have developed and tested two separate methods. First, by demonstrating that the viscous-plastic rheology can be represented by a symmetric, negative definite matrix operator, we have implemented the faster and better behaved preconditioned conjugate gradient method. Second, realizing that only the response of the ice on time scales associated with wind forcing need be accurately resolved, we have modified the model to reduce to the viscous-plastic model at these time scales; at shorter time scales the adjustment process takes place by a numerically efficient elastic wave mechanism. This modification leads to a fully explicit numerical scheme which further improves the computational efficiency and is an advantage for implementations on parallel machines. Furthermore, we observe that the standard viscous-plastic model has poor dynamic response to forcing on a daily time scale, given the standard time step (1 day) used by the ice modeling community. In contrast, the explicit discretization of the elastic wave mechanism allows the elastic-viscous-plastic model to capture the ice response to variations in the imposed stress more accurately. Thus, the elastic-viscous-plastic model provides more accurate results for shorter time scales associated with physical forcing, reproduces viscous-plastic model behavior on longer time scales, and is computationally more efficient. 49 refs., 13 figs., 6 tabs.

  15. Dynamics analysis of space robot manipulator with joint clearance

    NASA Astrophysics Data System (ADS)

    Zhao, Yang; Bai, Zheng Feng

    2011-04-01

    A computational methodology for analysis of space robot manipulator systems, considering the effects of the clearances in the joint, is presented. The contact dynamics model in joint clearance is established using the nonlinear equivalent spring-damp model and the friction effect is considered using the Coulomb friction model. The space robot system dynamic equation of manipulator with clearance is established. Then the dynamics simulation is presented and the dynamics characteristics of robot manipulator with clearance are analyzed. This work provides a practical method to analyze the dynamics characteristics of space robot manipulator with joint clearance and improves the engineering application. The computational methodology can predict the effects of clearance on space robot manipulator preferably, which is the basis of space robot manipulator design, precision analysis and ground test.

  16. Insights into the Dynamic Response of Tunnels in Jointed Rocks

    SciTech Connect

    Heuze, F E

    2004-11-01

    Tunnels in jointed rocks can be subjected to severe dynamic loads because of rock bursts, coal bumps, and large earthquakes. A series of 3-dimensional simulations was performed, based on discrete element analysis to gain insights into the parameters that influence the response of such tunnels. The simulations looked at the effect of joint set orientation, the effect of joint spacing, the effect of pulse shape for a given displacement, and the influence of using rigid versus deformable blocks in the analyses. The results of this modeling were also compared to field evidence of dynamic tunnel failures. This comparison reinforced the notion that 3-dimensional discrete element analysis can capture very well the kinematics of structures in jointed rock under dynamic loading.

  17. Investigation of Controls on Ice Dynamics in Northeast Greenland from Ice-Thickness Change Record Using Ice Sheet System Model (ISSM)

    NASA Astrophysics Data System (ADS)

    Csatho, B. M.; Larour, E. Y.; Schenk, A. F.; Schlegel, N.; Duncan, K.

    2015-12-01

    We present a new, complete ice thickness change reconstruction of the NE sector of the Greenland Ice Sheet for 1978-2014, partitioned into changes due to surface processes and ice dynamics. Elevation changes are computed from all available stereoscopic DEMs, and laser altimetry data (ICESat, ATM, LVIS). Surface Mass Balance and firn-compaction estimates are from RACMO2.3. Originating nearly at the divide of the Greenland Ice Sheet (GrIS), the dynamically active North East Ice Stream (NEGIS) is capable of rapidly transmitting ice-marginal forcing far inland. Thus, NEGIS provides a possible mechanism for a rapid drawdown of ice from the ice sheet interior as marginal warming, thinning and retreat continues. Our altimetry record shows accelerating dynamic thinning of Zachariæ Isstrom, initially limited to the deepest part of the fjord near the calving front (1978-2000) and then extending at least 75 km inland. At the same time, changes over the Nioghalvfjerdsfjorden (N79) Glacier are negligible. We also detect localized large dynamic changes at higher elevations on the ice sheet. These thickness changes, often occurring at the onset of fast flow, could indicate rapid variations of basal lubrication due to rerouting of subglacial drainage. We investigate the possible causes of the observed spatiotemporal pattern of ice sheet elevation changes using the Ice Sheet System Model (ISSM). This work build on our previous studies examining the sensitivity of ice flow within the Northeast Greenland Ice Stream (NEGIS) to key fields, including ice viscosity, basal drag. We assimilate the new altimetry record into ISSM to improve the reconstruction of basal friction and ice viscosity. Finally, airborne geophysical (gravity, magnetic) and ice-penetrating radar data is examined to identify the potential geologic controls on the ice thickness change pattern. Our study provides the first comprehensive reconstruction of ice thickness changes for the entire NEGIS drainage basin during

  18. Hydrocarbon production concepts for dynamic annual sea ice regions

    SciTech Connect

    Wang, A.T.; Poplin, J.P.; Heure, C.E.

    1995-02-01

    Petroleum production from Russian seas such as the northern Timan-Pechora Basin (Pechora Sea) and the northeastern Sakhalin island Shelf (Sea of Okhotsk) is likely to occur in the near future. Several different types of offshore structures may be needed in the Russian arctic offshore to support development activities. These structures may include: a number of production structures for offshore fields, subsea pipelines, a regional tanker terminal, and ice-breaking tankers. Dynamic first-year sea ice will be a major design consideration for offshore structures considered for use in these areas. Exxon previously performed engineering studies for petroleum development in Norton Sound off the west coast of Alaska. Norton Sound is also an area of dynamic first-year sea ice, so many of the lessons learned and much of the technology developed for that region are considered to be applicable to the Pechora Sea and the Sakhalin Shelf. Several of the concepts for production structures, pipelines, terminals, and tankers are presented along with a discussion of the related ice technology. Field and laboratory studies undertaken to collect environmental data are described along with a probabilistic load calculation procedure for structure design. More recent work by Exxon to enhance technology since the Norton Sound studies is also presented along with a discussion of recommended future work activities.

  19. EBSD observations of dynamic recrystallization mechanisms in ice.

    NASA Astrophysics Data System (ADS)

    Montagnat, Maurine; Chauve, Thomas; Barou, Fabrice; Beausir, Benoît; Fressengeas, Claude; Tommasi, Andrea

    2014-05-01

    Dynamic recrystallization (DRX) strongly affects the evolution of microstructure (grain size and shape) and texture (crystal preferred orientation) in materials during deformation at high temperature. Since texturing leads to anisotropic physical properties, predicting the effect of DRX in metals is essential for industrial applications, in rocks for interpreting geophysical data and modeling geodynamic flows, or in ice for predicting ice sheet flow and climate evolution. Owing to its high viscoplastic anisotropy, ice has long been considered as a "model material". This happens to be particularly true in the case of the understanding of the fundamental of DRX mechanisms as they occur under a relatively easily controlled environment. Creep compression experiments were performed on polycrystalline ice samples in the laboratory in order to observe the evolution of the fabrics and microstructures during DRX. During the tests, performed at temperatures of -5°C and -7°C, under 0.8 MPa compressive stress, dynamic recrystallization was initiated after 1% macroscopic strain and could be followed up to 18% strain on separated samples. Fabrics and microstructures were analysed post-mortem using an Automatic Ice Texture Analyser (AITA, Russell-Head and Wilson 2001) and EBSD measurements with the Crystal Probe of Géosciences Montpellier. Both techniques enable high resolution observations, both in space and orientation (5 to 50 microns, EBSD: 0.7° - AITA: 3°), which is new for DRX observations in ice. While AITA provides only the c-axis orientations, EBSD provides full orientations (c- and a-axes). In particular, we could access to an estimate of a relative dislocation density (from the Nye tensor obtained with EBSD) and its evolution with strain. Fabric evolution with strain is very similar to what was measured by Jacka and Maccagnan (1984) with a strong strengthening toward a few maxima for c- and a-axes. The c-axes maxima are oriented about 30° from the compression

  20. Modeling the tidal ice drift and ice-induced changes in tidal dynamics on the Siberian continental shelf

    NASA Astrophysics Data System (ADS)

    Kagan, B. A.; Romanenkov, D. A.; Sofina, E. V.

    2007-12-01

    The tidal ice drift is treated as an element of the three-dimensional tidal dynamics in a sea covered by ice. This dynamics is described by the QUODDY-4 finite-element model, and the tidal ice drift is described by a continuous viscous-elastic approximation. We present the results of modeling not only the tidal ice drift ( M 2 wave) (its velocity, direction, and tidal variations in the concentration and pressure of ice compression) but also ice-induced changes in tidal dynamics and the residual tidal ice drift. The modeling results indicate that the maximum velocity of tidal ice drift, which is determined by a combination of various factors responsible for ice evolution and primarily by the horizontal gradient of the level and local tidal velocity, can be higher or lower than the velocity of the surface tidal current in the ice-free sea. This depends on the sign of deviations of tidal sea level elevations in the sea covered by ice from their values in the ice-free sea. In addition, it has been found that ice cover has a stronger effect on the energetics of tides than on their dynamics: the area-mean relative deviations constitute 1.5% for the density of the total tidal energy, 61.5% for the dissipation, 0.1% for the amplitudes of tidal sea level elevations, and 0.9% for the amplitudes of maximum barotropic tidal velocity. In this sense, the conclusion that the role of sea ice is insignificant in the formation of tides can be justified only partially. The main results of this paper are as follows: (1) the development of a module for tidal ice drift, (2) the inclusion of this module into the three-dimensional finite-element hydrothermodynamic model QUODDY-4 to extend its capabilities, and (3) the reproduction (on the basis of the modified model) of qualitative features of the practically important tidal ice drift and ice-induced changes in the tidal dynamics of marginal seas on the Siberian continental shelf.

  1. Laser altimetry reveals complex pattern of Greenland Ice Sheet dynamics

    PubMed Central

    Csatho, Beata M.; Schenk, Anton F.; van der Veen, Cornelis J.; Babonis, Gregory; Duncan, Kyle; Rezvanbehbahani, Soroush; van den Broeke, Michiel R.; Simonsen, Sebastian B.; Nagarajan, Sudhagar; van Angelen, Jan H.

    2014-01-01

    We present a new record of ice thickness change, reconstructed at nearly 100,000 sites on the Greenland Ice Sheet (GrIS) from laser altimetry measurements spanning the period 1993–2012, partitioned into changes due to surface mass balance (SMB) and ice dynamics. We estimate a mean annual GrIS mass loss of 243 ± 18 Gt⋅y−1, equivalent to 0.68 mm⋅y−1 sea level rise (SLR) for 2003–2009. Dynamic thinning contributed 48%, with the largest rates occurring in 2004–2006, followed by a gradual decrease balanced by accelerating SMB loss. The spatial pattern of dynamic mass loss changed over this time as dynamic thinning rapidly decreased in southeast Greenland but slowly increased in the southwest, north, and northeast regions. Most outlet glaciers have been thinning during the last two decades, interrupted by episodes of decreasing thinning or even thickening. Dynamics of the major outlet glaciers dominated the mass loss from larger drainage basins, and simultaneous changes over distances up to 500 km are detected, indicating climate control. However, the intricate spatiotemporal pattern of dynamic thickness change suggests that, regardless of the forcing responsible for initial glacier acceleration and thinning, the response of individual glaciers is modulated by local conditions. Recent projections of dynamic contributions from the entire GrIS to SLR have been based on the extrapolation of four major outlet glaciers. Considering the observed complexity, we question how well these four glaciers represent all of Greenland’s outlet glaciers. PMID:25512537

  2. Ice crystal growth in a dynamic thermal diffusion chamber

    NASA Technical Reports Server (NTRS)

    Keller, V. W.

    1980-01-01

    Ice crystals were grown in a supersaturated environment produced by a dynamic thermal diffusion chamber, which employed two horizontal plates separated by a distance of 2.5 cm. Air was circulated between and along the 1.2 m length of the plates past ice crystals which nucleated and grew from a fiber suspended vertically between the two plates. A zoom stereo microscope with a magnification which ranged from 3X to 80X and both 35 mm still photographs and 16 mm time lapse cine films taken through the microscope were used to study the variation of the shape and linear growth rate of ice crystals as a function of the ambient temperature, the ambient supersaturation, and the forced ventilation velocity. The ambient growth conditions were varied over the range of temperature 0 to -40 C, over the range of supersaturation 4% to 50% with respect to ice, and over the range of forced ventilation velocities 0 cm/s to 20 cm/s.

  3. The role of sea ice dynamics in global climate change

    NASA Technical Reports Server (NTRS)

    Hibler, William D., III

    1992-01-01

    The topics covered include the following: general characteristics of sea ice drift; sea ice rheology; ice thickness distribution; sea ice thermodynamic models; equilibrium thermodynamic models; effect of internal brine pockets and snow cover; model simulations of Arctic Sea ice; and sensitivity of sea ice models to climate change.

  4. Dynamic Inland Propagation of Thinning Due to Ice Loss at the Margins of the Greenland Ice Sheet

    NASA Technical Reports Server (NTRS)

    Wang, Wei Li; Li, Jun J.; Zwally, H. Jay

    2012-01-01

    Mass-balance analysis of the Greenland ice sheet based on surface elevation changes observed by the European Remote-sensing Satellite (ERS) (1992-2002) and Ice, Cloud and land Elevation Satellite (ICESat) (2003-07) indicates that the strongly increased mass loss at lower elevations (<2000 m) of the ice sheet, as observed during 2003-07, appears to induce interior ice thinning at higher elevations. In this paper, we perform a perturbation experiment with a three-dimensional anisotropic ice-flow model (AIF model) to investigate this upstream propagation. Observed thinning rates in the regions below 2000m elevation are used as perturbation inputs. The model runs with perturbation for 10 years show that the extensive mass loss at the ice-sheet margins does in fact cause interior thinning on short timescales (i.e. decadal). The modeled pattern of thinning over the ice sheet agrees with the observations, which implies that the strong mass loss since the early 2000s at low elevations has had a dynamic impact on the entire ice sheet. The modeling results also suggest that even if the large mass loss at the margins stopped, the interior ice sheet would continue thinning for 300 years and would take thousands of years for full dynamic recovery.

  5. Results of the US contribution to the joint US/USSR Bering Sea experiment. [atmospheric circulation and sea ice cover

    NASA Technical Reports Server (NTRS)

    Campbell, W. J.; Chang, T. C.; Fowler, M. G.; Gloersen, P.; Kuhn, P. M.; Ramseier, R. O.; Ross, D. B.; Stambach, G.; Webster, W. J., Jr.; Wilheit, T. T.

    1974-01-01

    The atmospheric circulation which occurred during the Bering Sea Experiment, 15 February to 10 March 1973, in and around the experiment area is analyzed and related to the macroscale morphology and dynamics of the sea ice cover. The ice cover was very complex in structure, being made up of five ice types, and underwent strong dynamic activity. Synoptic analyses show that an optimum variety of weather situations occurred during the experiment: an initial strong anticyclonic period (6 days), followed by a period of strong cyclonic activity (6 days), followed by weak anticyclonic activity (3 days), and finally a period of weak cyclonic activity (4 days). The data of the mesoscale test areas observed on the four sea ice option flights, and ship weather, and drift data give a detailed description of mesoscale ice dynamics which correlates well with the macroscale view: anticyclonic activity advects the ice southward with strong ice divergence and a regular lead and polynya pattern; cyclonic activity advects the ice northward with ice convergence, or slight divergence, and a random lead and polynya pattern.

  6. Dynamics and control of space robot considering joint friction

    NASA Astrophysics Data System (ADS)

    Liu, Xiao-Feng; Li, Hai-Quan; Chen, Yi-Jun; Cai, Guo-Ping

    2015-06-01

    It is well known that friction is an inevitable phenomenon existing in almost all mechanical systems including robotic systems. It can affect dynamic characteristics of mechanical systems and even harm accuracy of manual control. In this paper, we have conducted comprehensive study in detail on dynamics and control of a space robot with joint friction. Dynamic equation of the system is established based on Jourdain's velocity variation principle and the single direction recursive construction method. The Coulomb friction model, the Stribeck friction model and the LuGre friction model are adopted to describe the joint friction. Meanwhile, the calculation method for joint friction is discussed in detail, and the relationship between ideal constraint force and Lagrange multipliers is derived. Moreover, an active controller is designed by the nonlinear decoupling method for the trajectory tracking for the system. The validity of the proposed dynamic model is verified by comparison of numerical simulation results and results obtained from the software ADAMS. And then we carry out a series of simulations in order to observe the influence of joint friction on operating a space robot with different friction models. We also study the interaction between the low-speed motion and joint friction in the process of trajectory tracking.

  7. Tectonics and ice sheet dynamics of West Antarctic margins

    NASA Astrophysics Data System (ADS)

    Gohl, Karsten

    2010-05-01

    An understanding of the glacial history of the Amundsen Sea Embayment (ASE) and Pine Island Bay (PIB) is essential for proposing models on the future development of the West Antarctic Ice Sheet. This requires an understanding of the tectonic history and knowledge of tectonic features such as lineaments, ridges, sills and basins, because basement morphology and inherited erosional features control the flow direction of ice-sheets and the influx of Circum-Polar Deep Water (CDW). This is an attempt to reconstruct the tectonic history with the aim to search for basement features and crustal boundaries which may be correlated to the flow and dynamics of the ice-sheet. The Amundsen Sea Embayment of West Antarctica is in a prominent location for a series of tectonic and magmatic events from Paleozoic to Cenozoic times. Seismic, magnetic and gravity data from the embayment and PIB reveal the crustal thickness and significant tectonic features. NE-SW trending magnetic and gravity anomalies and the thin crust indicate a former rift zone which was active during or in the run-up to the breakup process between Chatham Rise and West Antarctica before or at 90 Ma. NW-SE trending gravity and magnetic anomalies, following a prolongation of Peacock Sound, indicate the extensional southern boundary to the Bellingshausen Plate which was active between 79 and 61 Ma. It is likely that the prominent Pine Island Trough follows a structural boundary between the crustal blocks of Ellsworth Land and Marie Byrd Land. Data are shown from the ASE and PIB which can be interpreted in context with the reconstruction of the ice advance and retreat history in this area. Differences in the behaviour of the ice-sheet are shown to exist for the western and eastern parts of PIB due to basement structures affecting the inflow of CDW.

  8. LETTER TO THE EDITOR: Dynamical crossover in 'hot' spin ice

    NASA Astrophysics Data System (ADS)

    Ehlers, G.; Cornelius, A. L.; Orendác, M.; Kajnaková, M.; Fennell, T.; Bramwell, S. T.; Gardner, J. S.

    2003-01-01

    The magnetic dynamics of the spin ice material Ho2Ti2O7 in its paramagnetic ('hot') phase have been investigated by a combination of neutron spin echo and ac-susceptibility techniques. Relaxation at high temperatures (T > 15 K) is proved to occur by a thermally activated single-ion process that is distinct from the process that dominates at lower temperatures (1 K < T < 15 K). It is argued that the low-temperature process must involve quantum mechanical spin tunnelling, as quasi-classical channels of relaxation are exhausted in this temperature range. Our results resolve a mystery in the physics of spin ice: why has a 15 K ac-susceptibility peak been observed in Dy2Ti2O7 but not in Ho2Ti2O7 or Ho2Sn2O7?

  9. Dynamic response of an artificial square spin ice

    DOE PAGES

    Jungfleisch, M. B.; Zhang, W.; Iacocca, E.; ...

    2016-03-02

    Magnetization dynamics in an artficial square spin-ice lattice made of Ni80Fe20 with magnetic field applied in the lattice plane is investigated by broadband ferromagnetic resonance spectroscopy. The experimentally observed dispersion shows a rich spectrum of modes corresponding to different magnetization states. These magnetization states are determined by exchange and dipolar interaction between individual islands, as is confirmed by a semianalytical model. In the low field regime below 400 Oe a hysteretic behavior in the mode spectrum is found. Micromagnetic simulations reveal that the origin of the observed spectra is due to the initialization of different magnetization states of individual nanomagnets.more » Our results indicate that it might be possible to determine the spin-ice state by resonance experiments and are a first step towards the understanding of artificial geometrically frustrated magnetic systems in the high-frequency regime.« less

  10. Dynamic response of an artificial square spin ice

    SciTech Connect

    Jungfleisch, M. B.; Zhang, W.; Iacocca, E.; Sklenar, J.; Ding, J.; Jiang, W.; Zhang, S.; Pearson, J. E.; Novosad, V.; Ketterson, J. B.; Heinonen, O.; Hoffmann, A.

    2016-03-02

    Magnetization dynamics in an artficial square spin-ice lattice made of Ni80Fe20 with magnetic field applied in the lattice plane is investigated by broadband ferromagnetic resonance spectroscopy. The experimentally observed dispersion shows a rich spectrum of modes corresponding to different magnetization states. These magnetization states are determined by exchange and dipolar interaction between individual islands, as is confirmed by a semianalytical model. In the low field regime below 400 Oe a hysteretic behavior in the mode spectrum is found. Micromagnetic simulations reveal that the origin of the observed spectra is due to the initialization of different magnetization states of individual nanomagnets. Our results indicate that it might be possible to determine the spin-ice state by resonance experiments and are a first step towards the understanding of artificial geometrically frustrated magnetic systems in the high-frequency regime.

  11. Evolution of Hydrogen Dynamics in Amorphous Ice with Density.

    PubMed

    Parmentier, A; Shephard, J J; Romanelli, G; Senesi, R; Salzmann, C G; Andreani, C

    2015-06-04

    The single-particle dynamics of hydrogen atoms in several of the amorphous ices are reported using a combination of deep inelastic neutron scattering (DINS) and inelastic neutron scattering (INS). The mean kinetic energies of the hydrogen nuclei are found to increase with increasing density, indicating the weakening of hydrogen bonds as well as a trend toward steeper and more harmonic hydrogen vibrational potential energy surfaces. DINS shows much more pronounced changes in the O-H stretching component of the mean kinetic energy going from low- to high-density amorphous ices than indicated by INS and Raman spectroscopy. This highlights the power of the DINS technique to retrieve accurate ground-state kinetic energies beyond the harmonic approximation. In a novel approach, we use information from DINS and INS to determine the anharmonicity constants of the O-H stretching modes. Furthermore, our experimental kinetic energies will serve as important benchmark values for path-integral Monte Carlo simulations.

  12. A robotic apparatus that dictates torque fields around joints without affecting inherent joint dynamics.

    PubMed

    Oytam, Yalchin; Lloyd, David; Reid, Campbell S; de Rugy, Aymar; Carson, Richard G

    2010-10-01

    This manuscript describes how motor behaviour researchers who are not at the same time expert roboticists may implement an experimental apparatus, which has the ability to dictate torque fields around a single joint on one limb or single joints on multiple limbs without otherwise interfering with the inherent dynamics of those joints. Such an apparatus expands the exploratory potential of the researcher wherever experimental distinction of factors may necessitate independent control of torque fields around multiple limbs, or the shaping of torque fields of a given joint independently of its plane of motion, or its directional phase within that plane. The apparatus utilizes torque motors. The challenge with torque motors is that they impose added inertia on limbs and thus attenuate joint dynamics. We eliminated this attenuation by establishing an accurate mathematical model of the robotic device using the Box-Jenkins method, and cancelling out its dynamics by employing the inverse of the model as a compensating controller. A direct measure of the remnant inertial torque as experienced by the hand during a 50 s period of wrist oscillations that increased gradually in frequency from 1.0 to 3.8 Hz confirmed that the removal of the inertial effect of the motor was effectively complete.

  13. Astronomical Ice: The Effects of Treating Ice as a Porous Media on the Dynamics and Evolution of Extraterrestrial Ice-Ocean Environments

    NASA Astrophysics Data System (ADS)

    Buffo, J.; Schmidt, B. E.

    2015-12-01

    With the prevalence of water and ice rich environments in the solar system, and likely the universe, becoming more apparent, understanding the evolutionary dynamics and physical processes of such locales is of great importance. Piqued interest arises from the understanding that the persistence of all known life depends on the presence of liquid water. As in situ investigation is currently infeasible, accurate numerical modeling is the best technique to demystify these environments. We will discuss an evolving model of ice-ocean interaction aimed at realistically describing the behavior of the ice-ocean interface by treating basal ice as a porous media, and its possible implications on the formation of astrobiological niches. Treating ice as a porous media drastically affects the thermodynamic properties it exhibits. Thus inclusion of this phenomenon is critical in accurately representing the dynamics and evolution of all ice-ocean environments. This model utilizes equations that describe the dynamics of sea ice when it is treated as a porous media (Hunke et. al. 2011), coupled with a basal melt and accretion model (Holland and Jenkins 1999). Combined, these two models produce the most accurate description of the processes occurring at the base of terrestrial sea ice and ice shelves, capable of resolving variations within the ice due to environmental pressures. While these models were designed for application to terrestrial environments, the physics occurring at any ice-water interface is identical, and these models can be used to represent the evolution of a variety of icy astronomical bodies. As terrestrial ice shelves provide a close analog to planetary ice-ocean environments, we truth test the models validity against observations of ice shelves. We apply this model to the ice-ocean interface of the icy Galilean moon Europa. We include profiles of temperature, salinity, solid fraction, and Darcy velocity, as well as temporally and spatially varying melt and

  14. Dynamic effects of linkage joints in electrostatic microengines

    SciTech Connect

    Allen, J.J.; Miller, S.L.; LaVigne, G.F.

    1998-05-01

    The electrostatic micro-engine is one of the major actuators used in MEMS applications. To ensure this MEMS actuator is operated in a fashion that will produce peak performance and long life, the system dynamics must be fully understood. One of the major trade-offs in the micro-engine design is the use of either pin or flexure joints. This paper will develop the equations of motion for flexure-jointed and pin-jointed surface micromachined microengines. An analytical mechanics approach will be used to derive the equations of motion and the appropriate equations of constraint. The effect of the flexure joints on the drive signals of the micro engine is experimentally shown to be significant during static tests.

  15. Greenland outlet glacier dynamics from Extreme Ice Survey (EIS) photogrammetry

    NASA Astrophysics Data System (ADS)

    Hawbecker, P.; Box, J. E.; Balog, J. D.; Ahn, Y.; Benson, R. J.

    2010-12-01

    Time Lapse cameras fill gaps in our observational capabilities: 1. By providing much higher temporal resolution than offered by conventional airborne or satellite remote sensing. 2. While GPS or auto-theodolite observations can provide higher time resolution data than from photogrammetry, survival of these instruments on the hazardous glacier surface is limited, plus, the maintenance of such systems can be more expensive than the maintenance of a terrestrial photogrammetry installation. 3. Imagery provide a high spatial density of observations across the glacier surface, higher than is realistically available from GPS or other in-situ observations. 4. time lapse cameras provide observational capabilities in Eulerian and Lagrangian frames while GPS or theodolite targets, going along for a ride on the glacier, provide only Lagrangian data. Photogrammetry techniques are applied to a year-plus of images from multiple west Greenland glaciers to determine the glacier front horizontal velocity variations at hourly to seasonal time scales. The presentation includes comparisons between glacier front velocities and: 1. surface melt rates inferred from surface air temperature and solar radiation observations; 2. major calving events identified from camera images; 3. surface and near-surface ocean temperature; 4. land-fast sea ice breakup; 5. tidal variations; 6. supra-glacial melt lake drainage events observed in daily optical satellite imagery; and 7.) GPS data. Extreme Ice Survey (EIS) time lapse camera overlooking the Petermann glacier, installed to image glacier dynamics and to capture the predicted ice "island" detachment.

  16. Cloud Susceptibilities to Ice Nuclei: Microphysical Effects and Dynamical Feedbacks

    NASA Astrophysics Data System (ADS)

    Paukert, Marco; Hoose, Corinna

    2015-04-01

    The impact of aerosols on cloud properties is currently not well established. This is largely attributed to the interdependencies of aerosols and cloud microphysical processes, among which primary ice formation contributes to considerable uncertainties. Although it is known that in a large range of thermodynamic conditions aerosol particles are required to initiate ice formation, identifying and characterizing the effect of specific ice nuclei is among current scientific efforts. Here we attempt to quantify the change of cloud properties with varying aerosol background concentrations. We adapt the concept of susceptibilities for mixed-phase and ice clouds, defining the susceptibility as the derivation of a macrophysical quantity with respect to ice nucleating aerosol concentrations. A focus of our study is the use of different model approaches in order to identify the distinct contributions of both cloud microphysics and cloud-dynamical feedbacks to the overall susceptibility. The classical method is the direct comparison of two independent model runs, where the whole range of microphysical and cloud-dynamical feedbacks contributes to different cloud properties in a perturbed simulation. Our alternative method relies on a single simulation which incorporates multiple executions of the microphysical scheme within the same time step, each "perturbed microphysics" scheme with varying aerosol concentrations and an additional set of cloud particle tracers. Since in the latter case the model dynamics are held constant and only microphysical feedbacks contribute to the properties of perturbed clouds, we can distinguish between the pure microphysical effect and the dynamical enhancement or suppression. For a persistent Arctic mixed-phase stratocumulus cloud layer which is expected to be particularly sensitive to feedback cycles, we show an enhancement of the cloud susceptibility to ice nucleating particles by dynamics of around 50%, but a decay of the enhancement with time

  17. A Newly Updated Database of Elevation-changes of the Greenand Ice Sheet to Study Surface Processes and Ice Dynamics

    NASA Astrophysics Data System (ADS)

    Schenk, A. F.; Csatho, B. M.; van den Broeke, M.; Kuipers Munneke, P.

    2015-12-01

    This paper reports about important upgrades of the Greenland Ice Sheet (GrIS) surface elevation and elevation-change database obtained with our Surface Elevation And Change detection (SERAC) software suite. We have developed SERAC to derive information from laser altimetry data, particularly time series of elevation changes and their partitioning into changes caused by ice dynamics. This allows direct investigation of ice dynamic processes that is much needed for improving the predictive power of ice sheet models. SERAC is different from most other change detection methods. It is based on detecting changes of surface patches, about 1 km by 1 km in size, rather than deriving elevation changes from individual laser points. The current database consists of ~100,000 time series with satellite laser altimetry data from ICESat, airborne laser observations obtained by NASA's Airborne Topographic Mapper (ATM) and the Land, Vegetation and Ice Sensor (LVIS). The upgrade is significant, because not only new observations from 2013 and 2014 have been added but also a number of improvements lead to a more comprehensive and consistent record of elevation-changes. First, we used the model that gives in addition to ice sheet also information about ice caps and glaciers (Rastner et al., 2012) for deciding if a laser point is on the ice sheet or ice cap. Then we added small gaps that exist in the ICESat GLA12 data set because the ice sheet mask is not wide enough. The new database is now more complete and will facilitate more accurate comparisons of mass balance studies obtained from the Gravity Recovery and Climate Experiment system (GRACE). For determining the part of a time series caused by ice dynamics we used the new firn compaction model and Surface Mass Balance (SMB) estimates from RACMO2.3. The new database spans the time period from 1993 to 2014. Adding new observations amounts to a spatial densification of the old record and at the same time extends the time domain by two

  18. Dynamic characteristics of a magnetorheological pin joint for civil structures

    NASA Astrophysics Data System (ADS)

    Li, Yancheng; Li, Jianchun

    2014-03-01

    Magnetorheological (MR) pin joint is a novel device in which its joint moment resistance can be controlled in real-time by altering the applied magnetic field. The smart pin joint is intended to be used as a controllable connector between the columns and beams of a civil structure to instantaneously shift the structural natural frequencies in order to avoid resonance and therefore to reduce unwanted vibrations and hence prevent structural damage. As an intrinsically nonlinear device, modelling of this MR fluid based device is a challenging task and makes the design of a suitable control algorithm a cumbersome situation. Aimed at its application in civil structure, the main purpose of this paper is to test and characterise the hysteretic behaviour of MR pin joint. A test scheme is designed to obtain the dynamic performance of MR pin joint in the dominant earthquake frequency range. Some unique phenomena different from those of MR damper are observed through the experimental testing. A computationally-efficient model is proposed by introducing a hyperbolic element to accurately reproduce its dynamic behaviour and to further facilitate the design of a suitable control algorithm. Comprehensive investigations on the model accuracy and dependences of the proposed model on loading condition (frequency and amplitude) and input current level are reported in the last section of this paper.

  19. ERS satellite microwave radar observations of Antarctic sea-ice dynamics

    NASA Technical Reports Server (NTRS)

    Drinkwater, Mark R.; Liu, Xiang

    1997-01-01

    ERS-1 and ERS-2 scatterometer and synthetic aperture radar (SAR) data are used to monitor and track large and small scale sea ice dynamics in the Southern Ocean, and in particular in the Weddell Sea, Antarctica. Sea ice formation in the Weddell Sea regulates vertical and horizontal thermohaline circulation and influences bottom water production rates. Significant seasonal to interannual variability is observed in the sea ice drift dynamics. Coupled model simulations reproduce this variability and indicate that there is significant interannual variability in Weddelll Sea ice formation, drifts and extent on the El Nino southern oscillation (ENSO) timescale, with a period of approximately eight years. Changes in ice dynamics on these timescales regulate the amount of sea ice divergence and polynya formation. Anomalies in the timing and duration of the opening of the Ronne ice shelf polynya system are closely related to the variability in outflow of Weddell Sea bottom water measured at Joinville Island.

  20. Dynamic Structure of Joint-Action Stimulus-Response Activity

    PubMed Central

    Malone, MaryLauren; Castillo, Ramon D.; Kloos, Heidi; Holden, John G.; Richardson, Michael J.

    2014-01-01

    The mere presence of a co-actor can influence an individual’s response behavior. For instance, a social Simon effect has been observed when two individuals perform a Go/No-Go response to one of two stimuli in the presence of each other, but not when they perform the same task alone. Such effects are argued to provide evidence that individuals co-represent the task goals and the to-be-performed actions of a co-actor. Motivated by the complex-systems approach, the present study was designed to investigate an alternative hypothesis — that such joint-action effects are due to a dynamical (time-evolving) interpersonal coupling that operates to perturb the behavior of socially situated actors. To investigate this possibility, participants performed a standard Go/No-Go Simon task in joint and individual conditions. The dynamic structure of recorded reaction times was examined using fractal statistics and instantaneous cross-correlation. Consistent with our hypothesis that participants responding in a shared space would become behaviorally coupled, the analyses revealed that reaction times in the joint condition displayed decreased fractal structure (indicative of interpersonal perturbation processes modulating ongoing participant behavior) compared to the individual condition, and were more correlated across a range of time-scales compared to the reaction times of pseudo-pair controls. Collectively, the findings imply that dynamic processes might underlie social stimulus-response compatibility effects and shape joint cognitive processes in general. PMID:24558467

  1. INSIGHTS INTO THE DYNAMIC RESPONSE OF TUNNELS IN JOINTED ROCKS

    SciTech Connect

    Heuze, F E; Morris, J P

    2005-02-17

    Tunnels in jointed rocks can be subjected to severe dynamic loads because of rock bursts, coal bumps, and large earthquakes. A series of 3-dimensional simulations was performed, based on discrete element analysis to gain insights into the parameters that influence the response of such tunnels. The simulations looked at the effect of joint set orientation, the effect of joint spacing, the effect of peak displacement for a given peak velocity, the effect of pulse peak velocity for a given displacement, the influence of using rigid versus deformable blocks in the analyses, and the effect of repeated loading. The results of this modeling were also compared to field evidence of dynamic tunnel failures. This comparison reinforced the notion that 3-dimensional discrete element analysis can capture very well the kinematics of structures in jointed rocks under dynamic loading. The paper concludes with a glimpse into the future. Results are shown for a 3-dimensional discrete element massively parallel simulation with 100 million contact elements, performed with the LLNL LDEC code.

  2. Modeling ice dynamic contributions to sea level rise from the Antarctic Peninsula

    NASA Astrophysics Data System (ADS)

    Schannwell, C.; Barrand, N. E.; Radić, V.

    2015-11-01

    The future ice dynamical contribution to sea level rise (SLR) from 199 ice shelf nourishing drainage basins of the Antarctic Peninsula Ice Sheet is simulated, using the British Antarctic Survey Antarctic Peninsula Ice Sheet Model. Simulations of the grounded ice sheet include response to ice shelf collapse, estimated by tracking thermal ice shelf viability limits in 14 Intergovernmental Panel on Climate Change global climate models ensemble temperature projections. Grounding line retreat in response to ice shelf collapse is parameterized with a new multivariate linear regression model utilizing a range of glaciological and geometric predictor variables. Multimodel means project SLR up to 9.4 mm sea level equivalent (SLE) by 2200, and up to 19 mm SLE by 2300. Rates of SLR from individual drainage basins throughout the peninsula are similar to 2100, yet diverge between 2100 and 2300 due to individual basin characteristics. Major contributors to SLR are the outlet glaciers feeding southern George VI Ice Shelf, accounting for >75% of total SLR in some model runs. Ice sheet thinning induced by ice-shelf removal is large (up to ˜500 m), especially in Palmer Land in the southern Antarctic Peninsula, and may propagate as far as 135 km inland. These results emphasize the importance of the ice dynamical contribution to future sea level of the APIS on decadal to centennial timescales.

  3. Earth Structure, Ice Mass Changes, and the Local Dynamic Geoid

    NASA Astrophysics Data System (ADS)

    Harig, C.; Simons, F. J.

    2014-12-01

    Spherical Slepian localization functions are a useful method for studying regional mass changes observed by satellite gravimetry. By projecting data onto a sparse basis set, the local field can be estimated more easily than with the full spherical harmonic basis. We have used this method previously to estimate the ice mass change in Greenland from GRACE data, and it can also be applied to other planetary problems such as global magnetic fields. Earth's static geoid, in contrast to the time-variable field, is in large part related to the internal density and rheological structure of the Earth. Past studies have used dynamic geoid kernels to relate this density structure and the internal deformation it induces to the surface geopotential at large scales. These now classical studies of the eighties and nineties were able to estimate the mantle's radial rheological profile, placing constraints on the ratio between upper and lower mantle viscosity. By combining these two methods, spherical Slepian localization and dynamic geoid kernels, we have created local dynamic geoid kernels which are sensitive only to density variations within an area of interest. With these kernels we can estimate the approximate local radial rheological structure that best explains the locally observed geoid on a regional basis. First-order differences of the regional mantle viscosity structure are accessible to this technique. In this contribution we present our latest, as yet unpublished results on the geographical and temporal pattern of ice mass changes in Antarctica over the past decade, and we introduce a new approach to extract regional information about the internal structure of the Earth from the static global gravity field. Both sets of results are linked in terms of the relevant physics, but also in being developed from the marriage of Slepian functions and geoid kernels. We make predictions on the utility of our approach to derive fully three-dimensional rheological Earth models, to

  4. High latitude changes in ice dynamics and their impact on polar marine ecosystems.

    PubMed

    Moline, Mark A; Karnovsky, Nina J; Brown, Zachary; Divoky, George J; Frazer, Thomas K; Jacoby, Charles A; Torres, Joseph J; Fraser, William R

    2008-01-01

    Polar regions have experienced significant warming in recent decades. Warming has been most pronounced across the Arctic Ocean Basin and along the Antarctic Peninsula, with significant decreases in the extent and seasonal duration of sea ice. Rapid retreat of glaciers and disintegration of ice sheets have also been documented. The rate of warming is increasing and is predicted to continue well into the current century, with continued impacts on ice dynamics. Climate-mediated changes in ice dynamics are a concern as ice serves as primary habitat for marine organisms central to the food webs of these regions. Changes in the timing and extent of sea ice impose temporal asynchronies and spatial separations between energy requirements and food availability for many higher trophic levels. These mismatches lead to decreased reproductive success, lower abundances, and changes in distribution. In addition to these direct impacts of ice loss, climate-induced changes also facilitate indirect effects through changes in hydrography, which include introduction of species from lower latitudes and altered assemblages of primary producers. Here, we review recent changes and trends in ice dynamics and the responses of marine ecosystems. Specifically, we provide examples of ice-dependent organisms and associated species from the Arctic and Antarctic to illustrate the impacts of the temporal and spatial changes in ice dynamics.

  5. The role of ice dynamics in shaping vegetation in flowing waters.

    PubMed

    Lind, Lovisa; Nilsson, Christer; Polvi, Lina E; Weber, Christine

    2014-11-01

    Ice dynamics is an important factor affecting vegetation in high-altitude and high-latitude streams and rivers. During the last few decades, knowledge about ice in streams and rivers has increased significantly and a respectable body of literature is now available. Here we review the literature on how ice dynamics influence riparian and aquatic vegetation. Traditionally, plant ecologists have focused their studies on the summer period, largely ignoring the fact that processes during winter also impact vegetation dynamics. For example, the freeze-up period in early winter may result in extensive formation of underwater ice that can restructure the channel, obstruct flow, and cause flooding and thus formation of more ice. In midwinter, slow-flowing reaches develop a surface-ice cover that accumulates snow, protecting habitats under the ice from formation of underwater ice but also reducing underwater light, thus suppressing photosynthesis. Towards the end of winter, ice breaks up and moves downstream. During this transport, ice floes can jam up and cause floods and major erosion. The magnitudes of the floods and their erosive power mainly depend on the size of the watercourse, also resulting in different degrees of disturbance to the vegetation. Vegetation responds both physically and physiologically to ice dynamics. Physical action involves the erosive force of moving ice and damage caused by ground frost, whereas physiological effects - mostly cell damage - happen as a result of plants freezing into the ice. On a community level, large magnitudes of ice dynamics seem to favour species richness, but can be detrimental for individual plants. Human impacts, such as flow regulation, channelisation, agriculturalisation and water pollution have modified ice dynamics; further changes are expected as a result of current and predicted future climate change. Human impacts and climate change can both favour and disfavour riverine vegetation dynamics. Restoration of streams

  6. Aerial photographs reveal late-20th-century dynamic ice loss in northwestern Greenland.

    PubMed

    Kjær, Kurt H; Khan, Shfaqat A; Korsgaard, Niels J; Wahr, John; Bamber, Jonathan L; Hurkmans, Ruud; van den Broeke, Michiel; Timm, Lars H; Kjeldsen, Kristian K; Bjørk, Anders A; Larsen, Nicolaj K; Jørgensen, Lars Tyge; Færch-Jensen, Anders; Willerslev, Eske

    2012-08-03

    Global warming is predicted to have a profound impact on the Greenland Ice Sheet and its contribution to global sea-level rise. Recent mass loss in the northwest of Greenland has been substantial. Using aerial photographs, we produced digital elevation models and extended the time record of recent observed marginal dynamic thinning back to the mid-1980s. We reveal two independent dynamic ice loss events on the northwestern Greenland Ice Sheet margin: from 1985 to 1993 and 2005 to 2010, which were separated by limited mass changes. Our results suggest that the ice mass changes in this sector were primarily caused by short-lived dynamic ice loss events rather than changes in the surface mass balance. This finding challenges predictions about the future response of the Greenland Ice Sheet to increasing global temperatures.

  7. The role of soils and soil heterogeneities in the dynamics and stability of Martian ground ice

    NASA Astrophysics Data System (ADS)

    Sizemore, Hanna Gail

    The dynamical state and equilibrium location of shallow ground ice on Mars have relevance to a variety of science questions, as well as future human and robotic exploration. I investigate the role of soils in the dynamical transport of ground ice and the role of soil heterogeneities in the equilibrium depth of the ice table. First, assuming ice to be in equilibrium with atmospheric water vapor, I develop a multi-dimensional model of ground-ice stability and use it to place quantitative constraints on the response of the ice table to meter-scale rocks, dust lenses, and albedo variations in the current climate. I find that rocks create localized areas of deep ice, producing depressions of a few to 60 cm over a horizontal range of 1-2 rock radii. Patches of dust produce locally shallow ice; however, the magnitude of this effect is small (1-4 cm). I employ these results to investigate the role played by heterogeneities in orbital estimates of ice table depth. I find that surface rocks can account for more than half of the discrepancy between ice table depths inferred from leakage neutron flux and those predicted by ice-stability simulations that utilize thermophysical observations. Turning to considerations of ground-ice dynamics, I present laboratory measurements of the structural properties most relevant to gas transport in five groups of Mars-analog soils. These measurements indicate that diffusive loss of ground ice on Mars can likely proceed up to four times faster than predicted by theoretical studies and that the pore volume in some Mars-analog soils is sufficiently large to explain high volumetric ice abundances inferred from Mars Odyssey Gamma Ray Spectrometer data as simple pore ice. The upcoming Mars Scout Mission Phoenix may provide links between the dynamical and equilibrium views of ground-ice. I combine simulations of ground-ice stability with statistical estimates of the abundance of rocks at the Phoenix landing site to predict the degree of ice table

  8. Mass Balance Changes and Ice Dynamics of Greenland and Antarctic Ice Sheets from Laser Altimetry

    NASA Astrophysics Data System (ADS)

    Babonis, G. S.; Csatho, B.; Schenk, T.

    2016-06-01

    During the past few decades the Greenland and Antarctic ice sheets have lost ice at accelerating rates, caused by increasing surface temperature. The melting of the two big ice sheets has a big impact on global sea level rise. If the ice sheets would melt down entirely, the sea level would rise more than 60 m. Even a much smaller rise would cause dramatic damage along coastal regions. In this paper we report about a major upgrade of surface elevation changes derived from laser altimetry data, acquired by NASA's Ice, Cloud and land Elevation Satellite mission (ICESat) and airborne laser campaigns, such as Airborne Topographic Mapper (ATM) and Land, Vegetation and Ice Sensor (LVIS). For detecting changes in ice sheet elevations we have developed the Surface Elevation Reconstruction And Change detection (SERAC) method. It computes elevation changes of small surface patches by keeping the surface shape constant and considering the absolute values as surface elevations. We report about important upgrades of earlier results, for example the inclusion of local ice caps and the temporal extension from 1993 to 2014 for the Greenland Ice Sheet and for a comprehensive reconstruction of ice thickness and mass changes for the Antarctic Ice Sheets.

  9. 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.

  10. Changes in ice dynamics and mass balance of the Antarctic ice sheet.

    PubMed

    Rignot, Eric

    2006-07-15

    The concept that the Antarctic ice sheet changes with eternal slowness has been challenged by recent observations from satellites. Pronounced regional warming in the Antarctic Peninsula triggered ice shelf collapse, which led to a 10-fold increase in glacier flow and rapid ice sheet retreat. This chain of events illustrated the vulnerability of ice shelves to climate warming and their buffering role on the mass balance of Antarctica. In West Antarctica, the Pine Island Bay sector is draining far more ice into the ocean than is stored upstream from snow accumulation. This sector could raise sea level by 1m and trigger widespread retreat of ice in West Antarctica. Pine Island Glacier accelerated 38% since 1975, and most of the speed up took place over the last decade. Its neighbour Thwaites Glacier is widening up and may double its width when its weakened eastern ice shelf breaks up. Widespread acceleration in this sector may be caused by glacier ungrounding from ice shelf melting by an ocean that has recently warmed by 0.3 degrees C. In contrast, glaciers buffered from oceanic change by large ice shelves have only small contributions to sea level. In East Antarctica, many glaciers are close to a state of mass balance, but sectors grounded well below sea level, such as Cook Ice Shelf, Ninnis/Mertz, Frost and Totten glaciers, are thinning and losing mass. Hence, East Antarctica is not immune to changes.

  11. Airborne Geophysics and Remote Sensing Applied to Study Greenland Ice Dynamics

    NASA Technical Reports Server (NTRS)

    Csatho, Beata M.

    2003-01-01

    Overview of project: we combined and jointly analysed geophysical, remote sensing and glaciological data for investigating the temporal changes in ice flow and the role of geologic control on glacial drainage. The project included two different studies, the investigation of recent changes of the Kangerlussuaq glacier and the study of geologic control of ice flow in NW Greenland, around the Humboldt, Petermann and Ryder glaciers.

  12. Time-lapse joint inversion of geophysical data with automatic joint constraints and dynamic attributes

    NASA Astrophysics Data System (ADS)

    Rittgers, J. B.; Revil, A.; Mooney, M. A.; Karaoulis, M.; Wodajo, L.; Hickey, C. J.

    2016-12-01

    Joint inversion and time-lapse inversion techniques of geophysical data are often implemented in an attempt to improve imaging of complex subsurface structures and dynamic processes by minimizing negative effects of random and uncorrelated spatial and temporal noise in the data. We focus on the structural cross-gradient (SCG) approach (enforcing recovered models to exhibit similar spatial structures) in combination with time-lapse inversion constraints applied to surface-based electrical resistivity and seismic traveltime refraction data. The combination of both techniques is justified by the underlying petrophysical models. We investigate the benefits and trade-offs of SCG and time-lapse constraints. Using a synthetic case study, we show that a combined joint time-lapse inversion approach provides an overall improvement in final recovered models. Additionally, we introduce a new approach to reweighting SCG constraints based on an iteratively updated normalized ratio of model sensitivity distributions at each time-step. We refer to the new technique as the Automatic Joint Constraints (AJC) approach. The relevance of the new joint time-lapse inversion process is demonstrated on the synthetic example. Then, these approaches are applied to real time-lapse monitoring field data collected during a quarter-scale earthen embankment induced-piping failure test. The use of time-lapse joint inversion is justified by the fact that a change of porosity drives concomitant changes in seismic velocities (through its effect on the bulk and shear moduli) and resistivities (through its influence upon the formation factor). Combined with the definition of attributes (i.e. specific characteristics) of the evolving target associated with piping, our approach allows localizing the position of the preferential flow path associated with internal erosion. This is not the case using other approaches.

  13. Seismic Observations on Greenland Ice Sheet By a Joint USA and Japanese Glisn Team (2011-2014)

    NASA Astrophysics Data System (ADS)

    Toyokuni, G.; Kanao, M.; Tono, Y.; Himeno, T.; Tsuboi, S.; Childs, D.; Dahl-Jensen, T.; Anderson, K. R.

    2014-12-01

    Global climate change is currently causing melting of the Greenland ice sheet. Recently, a new type of seismic event, referred to as a "glacial earthquake", has been recognized. Such earthquakes are generated by the movements of large masses of ice within the terminal regions of glacier, and represent a new approach for monitoring ice sheet dynamics. In 2009, the GreenLand Ice Sheet monitoring Network (GLISN) was initiated as international project to monitor changes in ice sheet by constructing a large broadband seismological network in and around Greenland. Japan is a partner country from when the GLISN project was launched, and has been sending an expedition team every year from 2011. In 2011, the Japanese GLISN team, together with the USA team, installed the dual seismic-GPS station ICESG-GLS2 in the middle of the Greenland ice cap. In 2012 and 2013, we performed maintenance at the ICESG-GLS2, DY2G-GLS1, and NUUK stations. In August 2014, we plan to participate in maintenance operations on three dual seismic-GPS stations on ice (ICESG-GLS2, DY2G-GLS1, and NEEM-GLS3), as well as two stations on bedrock at East coast (DBG and SOEG). This presentation will summarize our field activities for four years, and show results from preliminary analysis with the retrieved data. The Japanese GLISN team has been supported by JSPS KAKENHI 24403006.

  14. Nonlinear dynamic response of a simple ice-structure interaction model

    SciTech Connect

    Karr, D.G.; Troesch, A.W.; Wingate, W.C. . Dept. of Naval Architecture and Marine Engineering)

    1993-11-01

    The problem addressed in the continuous indentation of a ship or offshore structure into an ice sheet. The impacting ship or offshore structure is represented by a mass-spring-dashpot system having a constant velocity relative to the ice sheet. The dynamic response of this simple analogue model of ice-structure interaction is studied in considerable detail. The complicated, highly nonlinear dynamic response is due to intermittent ice breakage and intermittent contact of the structure with the ice. Periodic motions are found and the periodicity for a particular system is dependent upon initial conditions. For a representative system, a Poincare map is presented showing the fixed points. A description of some of the effects of random variations in system parameters is also presented. Some implications of these findings regarding structural design for ice interaction are discussed.

  15. Exposure age and ice-sheet model constraints on Pliocene East Antarctic ice sheet dynamics.

    PubMed

    Yamane, Masako; Yokoyama, Yusuke; Abe-Ouchi, Ayako; Obrochta, Stephen; Saito, Fuyuki; Moriwaki, Kiichi; Matsuzaki, Hiroyuki

    2015-04-24

    The Late Pliocene epoch is a potential analogue for future climate in a warming world. Here we reconstruct Plio-Pleistocene East Antarctic Ice Sheet (EAIS) variability using cosmogenic nuclide exposure ages and model simulations to better understand ice sheet behaviour under such warm conditions. New and previously published exposure ages indicate interior-thickening during the Pliocene. An ice sheet model with mid-Pliocene boundary conditions also results in interior thickening and suggests that both the Wilkes Subglacial and Aurora Basins largely melted, offsetting increased ice volume. Considering contributions from West Antarctica and Greenland, this is consistent with the most recent IPCC AR5 estimate, which indicates that the Pliocene sea level likely did not exceed +20 m on Milankovitch timescales. The inception of colder climate since ∼3 Myr has increased the sea ice cover and inhibited active moisture transport to Antarctica, resulting in reduced ice sheet thickness, at least in coastal areas.

  16. Exposure age and ice-sheet model constraints on Pliocene East Antarctic ice sheet dynamics

    PubMed Central

    Yamane, Masako; Yokoyama, Yusuke; Abe-Ouchi, Ayako; Obrochta, Stephen; Saito, Fuyuki; Moriwaki, Kiichi; Matsuzaki, Hiroyuki

    2015-01-01

    The Late Pliocene epoch is a potential analogue for future climate in a warming world. Here we reconstruct Plio-Pleistocene East Antarctic Ice Sheet (EAIS) variability using cosmogenic nuclide exposure ages and model simulations to better understand ice sheet behaviour under such warm conditions. New and previously published exposure ages indicate interior-thickening during the Pliocene. An ice sheet model with mid-Pliocene boundary conditions also results in interior thickening and suggests that both the Wilkes Subglacial and Aurora Basins largely melted, offsetting increased ice volume. Considering contributions from West Antarctica and Greenland, this is consistent with the most recent IPCC AR5 estimate, which indicates that the Pliocene sea level likely did not exceed +20 m on Milankovitch timescales. The inception of colder climate since ∼3 Myr has increased the sea ice cover and inhibited active moisture transport to Antarctica, resulting in reduced ice sheet thickness, at least in coastal areas. PMID:25908601

  17. Learning from the past: Antarctic Eemian ice sheet dynamics as an analogy for future warming.

    NASA Astrophysics Data System (ADS)

    Sutter, Johannes; Thoma, Malte; Grosfeld, Klaus; Gierz, Paul; Lohmann, Gerrit

    2015-04-01

    Facing considerable warming during this century the stability of the West Antarctic Ice Sheet is under increasing scrutiny. Recent observations suggest that the marine ice sheet instability of the WAIS has already started . We investigate the dynamic evolution of the Antarctic Ice Sheet during the last interglacial, forcing a state of the art 3D ice sheet model with Eemian boundary conditions. We elucidate the role of ocean warming and surface mass balance on the coupled ice sheet/shelf and grounding line dynamics. Special focus lies on an ice sheet modeling assessment of Antarctica's potential contribution to global sea level rise during the Eemian. The transient model runs are forced by time slice experiments of a fully coupled atmosphere-ocean global circulation model, as well as different sets of sea level and bedrock reconstructions. The model result show strong evidences for a severe ice-sheet retreat in West Antartica, leading to substantical contribution to global sea level from the Southern Hemisphere. Additionally we compare future warming scenarios of West Antarctic Ice Sheet dynamics to our paleo ice sheet modeling studies.

  18. Dynamics of landfast sea ice near Jangbogo Antarctic Research Station observed by SAR interferometry

    NASA Astrophysics Data System (ADS)

    Lee, H.; Han, H.

    2015-12-01

    Landfast sea ice is a type of sea ice adjacent to the coast and immobile for a certain period of time. It is important to analyze the temporal and spatial variation of landfast ice because it has significant influences on marine ecosystem and the safe operation of icebreaker vessels. However, it has been a difficult task for both remote sensing and in situ observation to discriminate landfast ice from other types of sea ice, such as pack ice, and also to understand the dynamics and internal strss-strain of fast ice. In this study, we identify landfast ice and its annual variation in Terra Nova Bay (74° 37' 4"S, 164° 13' 7"E), East Antarctica, where Jangbogo Antarctic Research Station has recently been constructed in 2014, by using Interferometric Synthetic Aperture Radar (InSAR) technology. We generated 38 interferograms having temporal baselines of 1-9 days out of 62 COSMO-SkyMed SAR images over Terra Nova Bay obtained from December 2010 to January 2012. Landfast ice began to melt in November 2011 when air temperature raised above freezing point but lasted more than two month to the end of the study period in January 2012. No meaningful relationship was found between sea ice extent and wind and current. Glacial strain (~67cm/day) is similar to tidal strain (~40 cm) so that they appear similar in one-day InSAR. As glacial stress is cumulative while tidal stress is oscillatory, InSAR images with weekly temporal baseline (7~9 days) revealed that a consistent motion of Campbell Glacier Tongue (CGT) is pushing the sea ice continuously to make interferometric fringes parallel to the glacier-sea ice contacts. Glacial interferometric fringe is parallel to the glacier-sea ice contact lines while tidal strain should be parallel to the coastlines defined by sea shore and glacier tongue. DDInSAR operation removed the consistent glacial strain leaving tidal strain alone so that the response of fast ice to tide can be used to deduce physical properties of sea ice in various

  19. Dynamic Nucleation of Ice Induced by a Single Stable Cavitation Bubble

    NASA Technical Reports Server (NTRS)

    Ohsaka, Kenichi; Trinh, Eugene H.

    1997-01-01

    Dynamic nucleation of ice induced by caviation bubble in undercooled water is observed using an acoustic levitation technique. The observation indicates that a high pressure pulse associated with a collapsing bubble is indeed responsible for the nucleation of a high pressure phase of ice.

  20. Ice-binding proteins that accumulate on different ice crystal planes produce distinct thermal hysteresis dynamics

    PubMed Central

    Drori, Ran; Celik, Yeliz; Davies, Peter L.; Braslavsky, Ido

    2014-01-01

    Ice-binding proteins that aid the survival of freeze-avoiding, cold-adapted organisms by inhibiting the growth of endogenous ice crystals are called antifreeze proteins (AFPs). The binding of AFPs to ice causes a separation between the melting point and the freezing point of the ice crystal (thermal hysteresis, TH). TH produced by hyperactive AFPs is an order of magnitude higher than that produced by a typical fish AFP. The basis for this difference in activity remains unclear. Here, we have compared the time dependence of TH activity for both hyperactive and moderately active AFPs using a custom-made nanolitre osmometer and a novel microfluidics system. We found that the TH activities of hyperactive AFPs were time-dependent, and that the TH activity of a moderate AFP was almost insensitive to time. Fluorescence microscopy measurement revealed that despite their higher TH activity, hyperactive AFPs from two insects (moth and beetle) took far longer to accumulate on the ice surface than did a moderately active fish AFP. An ice-binding protein from a bacterium that functions as an ice adhesin rather than as an antifreeze had intermediate TH properties. Nevertheless, the accumulation of this ice adhesion protein and the two hyperactive AFPs on the basal plane of ice is distinct and extensive, but not detectable for moderately active AFPs. Basal ice plane binding is the distinguishing feature of antifreeze hyperactivity, which is not strictly needed in fish that require only approximately 1°C of TH. Here, we found a correlation between the accumulation kinetics of the hyperactive AFP at the basal plane and the time sensitivity of the measured TH. PMID:25008081

  1. Ice-binding proteins that accumulate on different ice crystal planes produce distinct thermal hysteresis dynamics.

    PubMed

    Drori, Ran; Celik, Yeliz; Davies, Peter L; Braslavsky, Ido

    2014-09-06

    Ice-binding proteins that aid the survival of freeze-avoiding, cold-adapted organisms by inhibiting the growth of endogenous ice crystals are called antifreeze proteins (AFPs). The binding of AFPs to ice causes a separation between the melting point and the freezing point of the ice crystal (thermal hysteresis, TH). TH produced by hyperactive AFPs is an order of magnitude higher than that produced by a typical fish AFP. The basis for this difference in activity remains unclear. Here, we have compared the time dependence of TH activity for both hyperactive and moderately active AFPs using a custom-made nanolitre osmometer and a novel microfluidics system. We found that the TH activities of hyperactive AFPs were time-dependent, and that the TH activity of a moderate AFP was almost insensitive to time. Fluorescence microscopy measurement revealed that despite their higher TH activity, hyperactive AFPs from two insects (moth and beetle) took far longer to accumulate on the ice surface than did a moderately active fish AFP. An ice-binding protein from a bacterium that functions as an ice adhesin rather than as an antifreeze had intermediate TH properties. Nevertheless, the accumulation of this ice adhesion protein and the two hyperactive AFPs on the basal plane of ice is distinct and extensive, but not detectable for moderately active AFPs. Basal ice plane binding is the distinguishing feature of antifreeze hyperactivity, which is not strictly needed in fish that require only approximately 1°C of TH. Here, we found a correlation between the accumulation kinetics of the hyperactive AFP at the basal plane and the time sensitivity of the measured TH.

  2. Measured Two-Dimensional Ice-Wedge Polygon Thermal Dynamics

    NASA Astrophysics Data System (ADS)

    Cable, William; Romanovsky, Vladimir; Busey, Robert

    2016-04-01

    Ice-wedge polygons are perhaps the most dominant permafrost related features in the arctic landscape. The microtopography of these features, that includes rims, troughs, and high and low polygon centers, alters the local hydrology, as water tends to collect in the low areas. During winter, wind redistribution of snow leads to an increased snowpack depth in the low areas, while the slightly higher areas often have very thin snow cover, leading to differences across the landscape in vegetation communities and soil moisture between higher and lower areas. These differences in local surface conditions lead to spatial variability of the ground thermal regime in the different microtopographic areas and between different types of ice-wedge polygons. To study these features in depth, we established temperature transects across four different types of ice-wedge polygons near Barrow, Alaska. The transects were composed of five vertical array thermistor probes (VATP) beginning in the center of each polygon and extending through the trough to the rim of the adjacent polygon. Each VATP had 16 thermistors from the surface to a depth of 1.5 m. In addition to these 80 subsurface temperature measurement points per polygon, soil moisture, thermal conductivity, heat flux, and snow depth were all measured in multiple locations for each polygon. Above ground, a full suite of micrometeorological instrumentation was present at each polygon. Data from these sites has been collected continuously for the last three years. We found snow cover, timing and depth, and active layer soil moisture to be major controlling factors in the observed thermal regimes. In troughs and in the centers of low-center polygons, the combined effect of typically saturated soils and increased snow accumulation resulted in the highest mean annual ground temperatures (MAGT). Additionally, these areas were the last part of the polygon to refreeze during the winter. However, increased active layer thickness was not

  3. Modeling brine and nutrient dynamics in Antarctic sea ice: the case of dissolved silica

    NASA Astrophysics Data System (ADS)

    Vancoppenolle, M.; Goosse, H.; de Montety, A.; Fichefet, T.; Tremblay, B.; Tison, J.

    2009-12-01

    Sea ice ecosystems are characterized by micro-algae living in brine inclusions. The growth rate of ice algae depends on light and nutrient supply. Here, the interactions between nutrients and brine dynamics under the influence of algae are investigated using a one-dimensional model. The model includes snow and ice thermodynamics with brine physics and an idealized sea ice biological component, characterized by one nutrient, namely dissolved silica (DSi). In the model, DSi follows brine motion and is consumed by ice algae. Depending on physical ice characteristics, the brine flow is either advective, diffusive or turbulent. The vertical profiles of ice salinity and DSi concentration are solutions of advection-diffusion equations. The model is configured to simulate the typical thermodynamic regimes of first-year Antarctic pack ice. The simulated vertical profiles of salinity and DSi qualitatively reproduce observations. Analysis of results highlights the role of convection in the lowermost 5-10 cm of ice. Convection mixes saline, nutrient-poor brine with comparatively fresh, nutrient-rich seawater. This implies a rejection of salt to the ocean and a flux of DSi to the ice. In presence of growing algae, the simulated ocean-to-ice DSi flux increases by 0-115% compared to an abiotic situation. In turn, primary production and brine convection act in synergy to form a nutrient pump. The other important processes are the flooding of the surface by seawater and the percolation of meltwater. The former refills nutrients near the ice surface in spring. The latter, if present, tends to expell nutrients from the ice in summer. Sketch of salt (left) and nutrient (right) exchanges at the ice-ocean interface proposed in this paper.

  4. Tropical tropopause ice clouds: a dynamic approach to the mystery of low crystal numbers

    NASA Astrophysics Data System (ADS)

    Spichtinger, P.; Krämer, M.

    2013-10-01

    The occurrence of high, persistent ice supersaturation inside and outside cold cirrus in the tropical tropopause layer (TTL) remains an enigma that is intensely debated as the "ice supersaturation puzzle". However, it was recently confirmed that observed supersaturations are consistent with very low ice crystal concentrations, which is incompatible with the idea that homogeneous freezing is the major method of ice formation in the TTL. Thus, the tropical tropopause "ice supersaturation puzzle" has become an "ice nucleation puzzle". To explain the low ice crystal concentrations, a number of mainly heterogeneous freezing methods have been proposed. Here, we reproduce in situ measurements of frequencies of occurrence of ice crystal concentrations by extensive model simulations, driven by the special dynamic conditions in the TTL, namely the superposition of slow large-scale updraughts with high-frequency short waves. From the simulations, it follows that the full range of observed ice crystal concentrations can be explained when the model results are composed from scenarios with consecutive heterogeneous and homogeneous ice formation and scenarios with pure homogeneous ice formation occurring in very slow (< 1 cm s-1) and faster (> 1 cm s-1) large-scale updraughts, respectively. This statistical analysis shows that about 80% of TTL cirrus can be explained by "classical" homogeneous ice nucleation, while the remaining 20% stem from heterogeneous and homogeneous freezing occurring within the same environment. The mechanism limiting ice crystal production via homogeneous freezing in an environment full of gravity waves is the shortness of the gravity waves, which stalls freezing events before a higher ice crystal concentration can be formed.

  5. The influence of a model subglacial lake on ice dynamics and internal layering

    NASA Astrophysics Data System (ADS)

    Gudlaugsson, Eythor; Humbert, Angelika; Kleiner, Thomas; Kohler, Jack; Andreassen, Karin

    2016-04-01

    As ice flows over a subglacial lake, the drop in bed resistance leads to an increase in ice velocities and a draw down of isochrones and cold ice. The ice surface flattens as it adjusts to the lack of resisting forces at the base. The rapid transition in velocity induces changes in ice viscosity and releases deformation energy that can raise the temperature locally. Recent studies of Antarctic subglacial lakes indicate that many lakes experience very fast and possibly episodic drainage, during which the lake size is rapidly reduced as water flows out. Questions that arise are what effect this would have on internal layers within the ice and whether such past drainage events could be inferred from isochrone structures downstream. Here, we study the effect of a subglacial lake on ice dynamics as well as the influence that such short timescale drainage would have on the internal layers of the ice. To this end, we use a full Stokes, polythermal ice flow model. An enthalpy-gradient method is used to account for the evolution of temperature and water content within the ice. We find that a rapid transition between slow-moving ice outside the lake, and full sliding over the lake, can release considerable amounts of deformational energy, with the potential to form a temperate layer at depth in the transition zone. In addition, we provide an explanation for a characteristic surface feature commonly seen at the edges of subglacial lakes, a hummocky surface depression in the transition zone between little to full sliding. We also conclude that rapid changes in the horizontal extent of subglacial lakes and slippery patches, compared to the average ice column velocity, can create a traveling wave at depth within the isochrone structure that transfers downstream with the advection of ice, thus indicating the possibility of detecting past drainage events with ice penetrating radar.

  6. Unusual dynamic properties of water near the ice-binding plane of hyperactive antifreeze protein

    SciTech Connect

    Kuffel, Anna; Czapiewski, Dariusz; Zielkiewicz, Jan

    2015-10-07

    The dynamical properties of solvation water of hyperactive antifreeze protein from Choristoneura fumiferana (CfAFP) are analyzed and discussed in context of its antifreeze activity. The protein comprises of three well-defined planes and one of them binds to the surface of ice. The dynamical properties of solvation water around each of these planes were analyzed separately; the results are compared with the dynamical properties of solvation water of ice around its two crystallographic planes: basal and prism. Three main conclusions are inferred from our investigations. The first one is that the solvation shell of CfAFP does not seem to be particularly far-ranged, at least not beyond what is usually observed for proteins that do not interact with ice. Therefore, it does not appear to us that the antifreeze activity is enhanced by a long-ranged retardation of water mobility. Also the correlation between the collective mobility of water and the collective mobility of protein atoms highly resembles the one measured for the protein that does not interact with ice. Our second conclusion is that the dynamical properties of solvation water of CfAFP are non-uniform. The dynamics of solvation water of ice-binding plane is, in some respects, different from the dynamics of solvation water of the two remaining planes. The feature that distinguishes the dynamics of solvation water of the three planes is the activation energy of diffusion process. The third conclusion is that—from the three analyzed solvation shells of CfAFP—the dynamical properties of solvation water of the ice-binding plane resemble the most the properties of solvation water of ice; note, however, that these properties still clearly differ from the dynamic properties of solvation water of ice.

  7. Unusual dynamic properties of water near the ice-binding plane of hyperactive antifreeze protein

    NASA Astrophysics Data System (ADS)

    Kuffel, Anna; Czapiewski, Dariusz; Zielkiewicz, Jan

    2015-10-01

    The dynamical properties of solvation water of hyperactive antifreeze protein from Choristoneura fumiferana (CfAFP) are analyzed and discussed in context of its antifreeze activity. The protein comprises of three well-defined planes and one of them binds to the surface of ice. The dynamical properties of solvation water around each of these planes were analyzed separately; the results are compared with the dynamical properties of solvation water of ice around its two crystallographic planes: basal and prism. Three main conclusions are inferred from our investigations. The first one is that the solvation shell of CfAFP does not seem to be particularly far-ranged, at least not beyond what is usually observed for proteins that do not interact with ice. Therefore, it does not appear to us that the antifreeze activity is enhanced by a long-ranged retardation of water mobility. Also the correlation between the collective mobility of water and the collective mobility of protein atoms highly resembles the one measured for the protein that does not interact with ice. Our second conclusion is that the dynamical properties of solvation water of CfAFP are non-uniform. The dynamics of solvation water of ice-binding plane is, in some respects, different from the dynamics of solvation water of the two remaining planes. The feature that distinguishes the dynamics of solvation water of the three planes is the activation energy of diffusion process. The third conclusion is that—from the three analyzed solvation shells of CfAFP—the dynamical properties of solvation water of the ice-binding plane resemble the most the properties of solvation water of ice; note, however, that these properties still clearly differ from the dynamic properties of solvation water of ice.

  8. Deformation, Ecosystem Structure, and Dynamics of Ice (DESDynI)

    NASA Technical Reports Server (NTRS)

    Donnellan, Andrea; Rosen, Paul; Ranson, Jon; Zebker, Howard

    2008-01-01

    The National Research Council Earth Science Decadal Survey, Earth Science Applications from Space, recommends that DESDynI (Deformation, Ecosystem Structure, and Dynamics of Ice), an integrated L-band InSAR and multibeam Lidar mission, launch in the 2010- 2013 timeframe. The mission will measure surface deformation for solid Earth and cryosphere objectives and vegetation structure for understanding the carbon cycle. InSAR has been used to study surface deformation of the solid Earth and cryosphere and more recently vegetation structure for estimates of biomass and ecosystem function. Lidar directly measures topography and vegetation structure and is used to estimate biomass and detect changes in surface elevation. The goal of DESDynI is to take advantage of the spatial continuity of InSAR and the precision and directness of Lidar. There are several issues related to the design of the DESDynI mission, including combining the two instruments into a single platform, optimizing the coverage and orbit for the two techniques, and carrying out the science modeling to define and maximize the scientific output of the mission.

  9. Dynamic recrystallization during deformation of polycrystalline ice: insights from numerical simulations

    NASA Astrophysics Data System (ADS)

    Llorens, Maria-Gema; Griera, Albert; Steinbach, Florian; Bons, Paul D.; Gomez-Rivas, Enrique; Jansen, Daniela; Roessiger, Jens; Lebensohn, Ricardo A.; Weikusat, Ilka

    2017-02-01

    The flow of glaciers and polar ice sheets is controlled by the highly anisotropic rheology of ice crystals that have hexagonal symmetry (ice lh). To improve our knowledge of ice sheet dynamics, it is necessary to understand how dynamic recrystallization (DRX) controls ice microstructures and rheology at different boundary conditions that range from pure shear flattening at the top to simple shear near the base of the sheets. We present a series of two-dimensional numerical simulations that couple ice deformation with DRX of various intensities, paying special attention to the effect of boundary conditions. The simulations show how similar orientations of c-axis maxima with respect to the finite deformation direction develop regardless of the amount of DRX and applied boundary conditions. In pure shear this direction is parallel to the maximum compressional stress, while it rotates towards the shear direction in simple shear. This leads to strain hardening and increased activity of non-basal slip systems in pure shear and to strain softening in simple shear. Therefore, it is expected that ice is effectively weaker in the lower parts of the ice sheets than in the upper parts. Strain-rate localization occurs in all simulations, especially in simple shear cases. Recrystallization suppresses localization, which necessitates the activation of hard, non-basal slip systems. This article is part of the themed issue 'Microdynamics of ice'.

  10. Dynamic recrystallization during deformation of polycrystalline ice: insights from numerical simulations.

    PubMed

    Llorens, Maria-Gema; Griera, Albert; Steinbach, Florian; Bons, Paul D; Gomez-Rivas, Enrique; Jansen, Daniela; Roessiger, Jens; Lebensohn, Ricardo A; Weikusat, Ilka

    2017-02-13

    The flow of glaciers and polar ice sheets is controlled by the highly anisotropic rheology of ice crystals that have hexagonal symmetry (ice lh). To improve our knowledge of ice sheet dynamics, it is necessary to understand how dynamic recrystallization (DRX) controls ice microstructures and rheology at different boundary conditions that range from pure shear flattening at the top to simple shear near the base of the sheets. We present a series of two-dimensional numerical simulations that couple ice deformation with DRX of various intensities, paying special attention to the effect of boundary conditions. The simulations show how similar orientations of c-axis maxima with respect to the finite deformation direction develop regardless of the amount of DRX and applied boundary conditions. In pure shear this direction is parallel to the maximum compressional stress, while it rotates towards the shear direction in simple shear. This leads to strain hardening and increased activity of non-basal slip systems in pure shear and to strain softening in simple shear. Therefore, it is expected that ice is effectively weaker in the lower parts of the ice sheets than in the upper parts. Strain-rate localization occurs in all simulations, especially in simple shear cases. Recrystallization suppresses localization, which necessitates the activation of hard, non-basal slip systems.This article is part of the themed issue 'Microdynamics of ice'.

  11. Integrating terrestrial and marine archives of Late Wisconsinan ice stream dynamics in the Canadian Arctic Archipelago

    NASA Astrophysics Data System (ADS)

    Lakeman, Thomas; Blasco, Steve; MacLean, Brian; Bennett, Robbie; England, John; Hughes Clarke, John; Covill, Bob; Patton, Eric

    2014-05-01

    During Late Wisconsinan glaciation the northern Laurentide and Innuitian ice sheets converged over the Canadian Arctic Archipelago. This ice sheet complex included several major ice streams, which constituted important dynamical components. Discharging into the Beaufort Sea and Baffin Bay, these ice streams were a primary control on ice sheet mass balance and ice age sedimentation on adjacent continental margins, including the Arctic Ocean basin. This study presents a new compilation of multibeam echosounder data, sub-bottom profiler data, radiocarbon ages, and marine sediment cores acquired primarily during regional surveys with the CCGS Amundsen. These data characterize the nature and thickness of seafloor sediments in Parry Channel (and many of its connecting channels) and Amundsen Gulf. When combined with the results of terrestrial geomorphological mapping of the adjacent islands, this dataset constrains the maximum extent, chronology, and behaviour of former ice streams in M'Clure Strait, Viscount Melville Sound, Lancaster Sound, and Amundsen Gulf. Importantly, these data highlight complex patterns of past ice stream flow during regional deglaciation. These results contribute to a better understanding of the causal mechanisms that occasioned retreat of the terrestrial and marine sectors of the Laurentide and Innuitian ice sheets. As well, this study helps to quantify past iceberg fluxes to the Arctic Ocean, which has implications for assessing past climate, and the origin of ice-rafted sediment and deep iceberg scours in the Arctic Ocean basin.

  12. Investigating role of ice-ocean interaction on glacier dynamic: Results from numerical modeling applied to Petermann Glacier

    NASA Astrophysics Data System (ADS)

    Nick, F. M.; van der Veen, C. J.; Vieli, A.; Pattyn, F.; Hubbard, A.; Box, J. E.

    2010-12-01

    Calving of icebergs and bottom melting from ice shelves accounts for roughly half the ice transferred from the Greenland Ice Sheet into the surrounding ocean, and virtually all of the ice loss from the Antarctic Ice Sheet. Petermann Glacier (north Greenland) with its ~17 km wide and ~ 60 km long floating ice-shelf is experiencing high rates of bottom melting. The recent partial disintegration of its shelf (in August 2010) presents a natural experiment to investigate the dynamic response of the ice sheet to its shelf retreat. We apply a numerical ice flow model using a physically-based calving criterion based on crevasse depth to investigate the contribution of processes such as shelf disintegration, bottom melting, sea ice or sikkusak disintegration and surface run off to the mass balance of Petermann Glacier and assess its stability. Our modeling study provides insights into the role of ice-ocean interaction, and on response of Petermann Glacier to its recent massive ice loss.

  13. Holocene dynamics of the Arctic's largest ice shelf.

    PubMed

    Antoniades, Dermot; Francus, Pierre; Pienitz, Reinhard; St-Onge, Guillaume; Vincent, Warwick F

    2011-11-22

    Ice shelves in the Arctic lost more than 90% of their total surface area during the 20th century and are continuing to disintegrate rapidly. The significance of these changes, however, is obscured by the poorly constrained ontogeny of Arctic ice shelves. Here we use the sedimentary record behind the largest remaining ice shelf in the Arctic, the Ward Hunt Ice Shelf (Ellesmere Island, Canada), to establish a long-term context in which to evaluate recent ice-shelf deterioration. Multiproxy analysis of sediment cores revealed pronounced biological and geochemical changes in Disraeli Fiord in response to the formation of the Ward Hunt Ice Shelf and its fluctuations through time. Our results show that the ice shelf was absent during the early Holocene and formed 4,000 years ago in response to climate cooling. Paleoecological data then indicate that the Ward Hunt Ice Shelf remained stable for almost three millennia before a major fracturing event that occurred ∼1,400 years ago. After reformation ∼800 years ago, freshwater was a constant feature of Disraeli Fiord until the catastrophic drainage of its epishelf lake in the early 21st century.

  14. Holocene dynamics of the Arctic's largest ice shelf

    PubMed Central

    Antoniades, Dermot; Francus, Pierre; Pienitz, Reinhard; St-Onge, Guillaume; Vincent, Warwick F.

    2011-01-01

    Ice shelves in the Arctic lost more than 90% of their total surface area during the 20th century and are continuing to disintegrate rapidly. The significance of these changes, however, is obscured by the poorly constrained ontogeny of Arctic ice shelves. Here we use the sedimentary record behind the largest remaining ice shelf in the Arctic, the Ward Hunt Ice Shelf (Ellesmere Island, Canada), to establish a long-term context in which to evaluate recent ice-shelf deterioration. Multiproxy analysis of sediment cores revealed pronounced biological and geochemical changes in Disraeli Fiord in response to the formation of the Ward Hunt Ice Shelf and its fluctuations through time. Our results show that the ice shelf was absent during the early Holocene and formed 4,000 years ago in response to climate cooling. Paleoecological data then indicate that the Ward Hunt Ice Shelf remained stable for almost three millennia before a major fracturing event that occurred ∼1,400 years ago. After reformation ∼800 years ago, freshwater was a constant feature of Disraeli Fiord until the catastrophic drainage of its epishelf lake in the early 21st century. PMID:22025693

  15. Full Stokes or shallow ice approximation? Comparing the ice flow dynamics at the Shirase Drainage Basin, Antarctica

    NASA Astrophysics Data System (ADS)

    Seddik, H.; Greve, R.; Zwinger, T.; Sugiyama, S.

    2012-12-01

    Covering an area of 2 x 105 km2, the Shirase Drainage Basin is located in East Antarctica (37-50° E, 70-78° S). The basin is characterized by the convergence of the ice flow towards the Shirase glacier, one of the fastest flowing glacier in Antarctica. The Shirase glacier flows at a speed of 2.3 km a-1 at the grounding line (Rignot, 2002; Pattyn and Derauw, 2002; Nakamura and others, 2008) and drains about 10 Gt a-1 of ice through a narrow outlet into the Lützow-Holm Bay (Fujii, 1981). With nearly 90% of total ice discharge from the basin being calved by the glacier, the fast flowing nature of the Shirase glacier is important for the investigation of the ice sheet mass budget in this region. The dynamics of the Shirase glacier is investigated by means of the full Stokes equations and the shallow ice approximation. The model Elmer/Ice (http://elmerice.elmerfem.com) is applied to the Shirase Drainage Basin and employs the finite element method to solve the full Stokes equations, the temperature evolution equation and the evolution equation of the free surface. The shallow ice approximation is also implemented into Elmer/Ice so that both the full Stokes and the shallow ice approximation are computed on the same mesh. Data for the present geometry (surface and basal topographies with no shelf) are obtained from the Community Ice Sheet Model, based on the DEM of Bamber and others (2009) and Griggs and Bamber (2009), and on the BEDMAP1-Plus ice sheet basal topography. A mesh of the computational domain is created using an initial footprint which contains elements from 15 km to 500 m horizontal resolution. The footprint is vertically extruded to form a 3D mesh of 240720 elements with 21 equidistant, terrain-following layers. The approach taken in this study is to compare the response of the glacier to dynamical and climate forcings when separately the full Stokes and the shallow ice approximation are employed. The sensitivity experiments are modeled after the Sea

  16. Ice cliff dynamics in the Everest region of the Central Himalaya

    NASA Astrophysics Data System (ADS)

    Scott Watson, C.; Quincey, Duncan J.; Carrivick, Jonathan L.; Smith, Mark W.

    2017-02-01

    The importance of ice cliffs for glacier-scale ablation on debris-covered glaciers is now widely recognised. However, a paucity of data exists to describe the spatio-temporal distribution of ice cliffs. In this study we analysed the position and geometry of 8229 ice cliffs and 5582 supraglacial ponds on 14 glaciers in the Everest region between 2000 and 2015. We observed notable ice cliff and pond spatial coincidence. On average across our study glaciers, 77% of supraglacial pond area was associated with an adjacent ice cliff, and 49% of ice cliffs featured an adjacent supraglacial pond. The spatial density of ice cliffs was not directly related to glacier velocity, but did peak within zones of active ice. Furthermore, we found that ice cliff density was glacier-specific, temporally variable, and was positively correlated with surface lowering and decreasing debris thickness for individual glaciers. Ice cliffs predominantly had a north-facing (commonly north-westerly) aspect, which was independent of glacier flow direction, thereby signifying a strong solar radiation control on cliff evolution. Independent field observations indicated that cliff morphology was related to aspect, local debris thickness, and presence of a supraglacial pond, and highlighted the importance of surface runnel formation, which acts as a preferential pathway for meltwater and debris fluxes. Overall, by coupling remote sensing and in-situ observations it has been possible to capture local and glacier-scale ice cliff dynamics across 14 glaciers, which is necessary if explicit parameterisation of ice cliffs in dynamic glacier models is to be achieved.

  17. Dynamics of the last glacial maximum Antarctic ice-sheet and its response to ocean forcing.

    PubMed

    Golledge, Nicholas R; Fogwill, Christopher J; Mackintosh, Andrew N; Buckley, Kevin M

    2012-10-02

    Retreat of the Last Glacial Maximum (LGM) Antarctic ice sheet is thought to have been initiated by changes in ocean heat and eustatic sea level propagated from the Northern Hemisphere (NH) as northern ice sheets melted under rising atmospheric temperatures. The extent to which spatial variability in ice dynamics may have modulated the resultant pattern and timing of decay of the Antarctic ice sheet has so far received little attention, however, despite the growing recognition that dynamic effects account for a sizeable proportion of mass-balance changes observed in modern ice sheets. Here we use a 5-km resolution whole-continent numerical ice-sheet model to assess whether differences in the mechanisms governing ice sheet flow could account for discrepancies between geochronological studies in different parts of the continent. We first simulate the geometry and flow characteristics of an equilibrium LGM ice sheet, using pan-Antarctic terrestrial and marine geological data for constraint, then perturb the system with sea level and ocean heat flux increases to investigate ice-sheet vulnerability. Our results identify that fast-flowing glaciers in the eastern Weddell Sea, the Amundsen Sea, central Ross Sea, and in the Amery Trough respond most rapidly to ocean forcings, in agreement with empirical data. Most significantly, we find that although ocean warming and sea-level rise bring about mainly localized glacier acceleration, concomitant drawdown of ice from neighboring areas leads to widespread thinning of entire glacier catchments-a discovery that has important ramifications for the dynamic changes presently being observed in modern ice sheets.

  18. Heterogeneous Heat Flow and Groundwater Effects on East Antarctic Ice Sheet Dynamics

    NASA Astrophysics Data System (ADS)

    Gooch, B. T.; Soderlund, K. M.; Young, D. A.; Blankenship, D. D.

    2015-12-01

    We present the results numerical models describing the potential contributions groundwater and heterogeneous heat sources might have on ice dynamics. A two-phase, 1D hydrothermal model demonstrates the importance of groundwater flow in heat flux advection near the ice-bed interface. Typical, conservative vertical groundwater volume fluxes on the order of +/- 1-10 mm/yr can alter vertical heat flux by +/- 50-500 mW/m2 that could produce considerable volumes of meltwater depending on basin geometry and geothermal heat production. A 1D hydromechanical model demonstrates that during ice advance groundwater is mainly recharged into saturated sedimentary aquifers and during retreat groundwater discharges into the ice-bed interface, potentially contributing to subglacial water budgets on the order of 0.1-1 mm/yr during ice retreat. A map of most-likely elevated heat production provinces, estimated sedimentary basin depths, and radar-derived bed roughness are compared together to delineate areas of greatest potential to ice sheet instability in East Antarctica. Finally, a 2D numerical model of crustal fluid and heat flow typical to recently estimated sedimentary basins under the East Antarctic Ice Sheet is coupled to a 2.5D Full Stokes ice sheet model (with simple basal hydrology) to test for the sensitivity of hydrodynamic processes on ice sheet dynamics. Preliminary results show that the enhanced fluid flow can dramatically alter the basal heating of the ice and its temperature profile, as well as, the sliding rate, which heavily alter ice dynamics.

  19. Dynamics of the last glacial maximum Antarctic ice-sheet and its response to ocean forcing

    PubMed Central

    Golledge, Nicholas R.; Fogwill, Christopher J.; Mackintosh, Andrew N.; Buckley, Kevin M.

    2012-01-01

    Retreat of the Last Glacial Maximum (LGM) Antarctic ice sheet is thought to have been initiated by changes in ocean heat and eustatic sea level propagated from the Northern Hemisphere (NH) as northern ice sheets melted under rising atmospheric temperatures. The extent to which spatial variability in ice dynamics may have modulated the resultant pattern and timing of decay of the Antarctic ice sheet has so far received little attention, however, despite the growing recognition that dynamic effects account for a sizeable proportion of mass-balance changes observed in modern ice sheets. Here we use a 5-km resolution whole-continent numerical ice-sheet model to assess whether differences in the mechanisms governing ice sheet flow could account for discrepancies between geochronological studies in different parts of the continent. We first simulate the geometry and flow characteristics of an equilibrium LGM ice sheet, using pan-Antarctic terrestrial and marine geological data for constraint, then perturb the system with sea level and ocean heat flux increases to investigate ice-sheet vulnerability. Our results identify that fast-flowing glaciers in the eastern Weddell Sea, the Amundsen Sea, central Ross Sea, and in the Amery Trough respond most rapidly to ocean forcings, in agreement with empirical data. Most significantly, we find that although ocean warming and sea-level rise bring about mainly localized glacier acceleration, concomitant drawdown of ice from neighboring areas leads to widespread thinning of entire glacier catchments—a discovery that has important ramifications for the dynamic changes presently being observed in modern ice sheets. PMID:22988078

  20. Detection and Analysis of Complex Patterns of Ice Dynamics in Antarctica from ICESat Laser Altimetry

    NASA Astrophysics Data System (ADS)

    Babonis, Gregory Scott

    There remains much uncertainty in estimating the amount of Antarctic ice mass change, its dynamic component, and its spatial and temporal patterns. This work remedies the limitations of previous studies by generating the first detailed reconstruction of total and dynamic ice thickness and mass changes across Antarctica, from ICESat satellite altimetry observations in 2003-2009 using the Surface Elevation Reconstruction and Change Detection (SERAC) method. Ice sheet thickness changes are calculated with quantified error estimates for each time when ICESat flew over a ground-track crossover region, at approximately 110,000 locations across the Antarctic Ice Sheet. The time series are partitioned into changes due to surficial processes and ice dynamics. The new results markedly improve the spatial and temporal resolution of surface elevation, volume, and mass change rates for the AIS, and can be sampled at annual temporal resolutions. The results indicate a complex spatiotemporal pattern of dynamic mass loss in Antarctica, especially along individual outlet glaciers, and allow for the quantification of the annual contribution of Antarctic ice loss to sea level rise. Over 5000 individual locations exhibit either strong dynamic ice thickness change patterns, accounting for approximately 500 unique spatial clusters that identify regions likely influenced by subglacial hydrology. The spatial distribution and temporal behavior of these regions reveal the complexity and short-time scale variability in the subglacial hydrological system. From the 500 unique spatial clusters, over 370 represent newly identified, and not previously published, potential subglacial water bodies indicating an active subglacial hydrological system over a much larger region than previously observed. These numerous new observations of dynamic changes provide more than simply a larger set of data. Examination of both regional and local scale dynamic change patterns across Antarctica shows newly

  1. Tropical tropopause ice clouds: a dynamic approach to the mystery of low crystal numbers

    NASA Astrophysics Data System (ADS)

    Spichtinger, P.; Krämer, M.

    2012-10-01

    The occurrence of high, persistent ice supersaturation inside and outside cold cirrus in the tropical tropopause layer (TTL) remains an enigma that is intensely debated as the "ice supersaturation puzzle". However, it was recently confirmed that observed supersaturations are consistent with very low ice crystal concentrations, which is incompatible with the idea that homogeneous freezing is the major method of ice formation in the TTL. Thus, the tropical tropopause "ice supersaturation puzzle" has become an "ice nucleation puzzle". To explain the low ice crystal concentrations, a number of mainly heterogeneous freezing methods have been proposed. Here, we reproduce in situ measurements of frequencies of occurrence of ice crystal concentrations by extensive model simulations, driven by the special dynamic conditions in the TTL, namely the superposition of slow large-scale updraughts with high-frequency short waves. From the simulations, it follows that the full range of observed ice crystal concentrations can be explained when the model results of the scenarios are mixed for both heterogeneous/homogeneous and pure homogeneous ice formation occurring in very slow (<1 cm s-1) and faster (>1 cm s-1) large-scale updraughts. This statistical analysis shows that about 80% of TTL cirrus can be explained by "classical" homogeneous ice nucleation, while the remaining 20% stem from heterogeneous and homogeneous freezing occurring within the same environment. The mechanism limiting ice crystal production via homogeneous freezing in an environment full of gravity waves is the shortness of the gravity waves, which stalls freezing events before a higher ice crystal concentration can be formed.

  2. Bottom Fixed Platform Dynamics Models Assessing Surface Ice Interactions for Transitional Depth Structures in the Great Lakes: FAST8 – IceDyn

    SciTech Connect

    Karr, Dale G.; Yu, Bingbin; Sirnivas, Senu

    2015-04-01

    To create long-term solutions for offshore wind turbines in a variety of environmental conditions, CAE tools are needed to model the design-driving loads that interact with an offshore wind turbine system during operation. This report describes our efforts in augmenting existing CAE tools used for offshore wind turbine analysis with a new module that can provide simulation capabilities for ice loading on the system. This augmentation was accomplished by creating an ice-loading module coupled to FAST8, the CAE tool maintained by the NREL for simulating land-based and offshore wind turbine dynamics. The new module includes both static and dynamic ice loading that can be applied during a dynamic simulation of the response of an offshore wind turbine. The ice forces can be prescribed, or influenced by the structure’s compliant response, or by the dynamics of both the structure and the ice floe. The new module covers ice failure modes of spalling, buckling, crushing, splitting, and bending. The supporting structure of wind turbines can be modeled as a vertical or sloping form at the waterline. The Inward Battered Guide Structure (IBGS) foundation designed by Keystone Engineering for the Great Lakes was used to study the ice models coupled to FAST8. The IBGS foundation ice loading simulations in FAST8 were compared to the baseline simulation case without ice loading. The ice conditions reflecting those from Lake Huron at Port Huron and Lake Michigan at North Manitou were studied under near rated wind speed of 12 m/s for the NREL 5-MW reference turbine. Simulations were performed on ice loading models 1 through 4 and ice model 6 with their respective sub-models. The purpose of ice model 5 is to investigate ice loading on sloping structures such as ice-cones on a monopile and is not suitable for multi-membered jacketed structures like the IBGS foundation. The key response parameters from the simulations, shear forces and moments from the tower base and IBGS foundation

  3. Dynamic characteristics of vibration isolation platforms considering the joints of the struts

    NASA Astrophysics Data System (ADS)

    Zhang, Jingrui; Guo, Zixi; Zhang, Yao

    2016-09-01

    This paper discusses the dynamic characteristics of the impacts and corresponding frictions generated by the clearances of joints of vibration isolation platforms for control moment gyroscopes (CMGs) on spacecraft. A contact force model is applied using a nonlinear contact force model, and the frictions in the joints are considered in the dynamic analysis. First, the dynamic characteristics of a single isolation strut with spherical joints were studied, and joints with different initial clearance sizes were separately analyzed. Then, dynamic models of the vibration isolation platform for a CMG cluster with both perfect joints and joints with clearances were established. During the numeral simulation, joints with different elastic moduli were used to study the nonlinear characteristics. Finally, the distributions of the collision points, which can serve as a reference for the reliability and lifetime of a platform, were given.

  4. Dynamic similarity promotes interpersonal coordination in joint action.

    PubMed

    Słowiński, Piotr; Zhai, Chao; Alderisio, Francesco; Salesse, Robin; Gueugnon, Mathieu; Marin, Ludovic; Bardy, Benoit G; di Bernardo, Mario; Tsaneva-Atanasova, Krasimira

    2016-03-01

    Human movement has been studied for decades, and dynamic laws of motion that are common to all humans have been derived. Yet, every individual moves differently from everyone else (faster/slower, harder/smoother, etc.). We propose here an index of such variability, namely an individual motor signature (IMS) able to capture the subtle differences in the way each of us moves. We show that the IMS of a person is time-invariant and that it significantly differs from those of other individuals. This allows us to quantify the dynamic similarity, a measure of rapport between dynamics of different individuals' movements, and demonstrate that it facilitates coordination during interaction. We use our measure to confirm a key prediction of the theory of similarity that coordination between two individuals performing a joint-action task is higher if their motions share similar dynamic features. Furthermore, we use a virtual avatar driven by an interactive cognitive architecture based on feedback control theory to explore the effects of different kinematic features of the avatar motion on coordination with human players.

  5. Dynamic similarity promotes interpersonal coordination in joint action

    PubMed Central

    Słowiński, Piotr; Zhai, Chao; Alderisio, Francesco; Salesse, Robin; Gueugnon, Mathieu; Marin, Ludovic; Bardy, Benoit G.; di Bernardo, Mario; Tsaneva-Atanasova, Krasimira

    2016-01-01

    Human movement has been studied for decades, and dynamic laws of motion that are common to all humans have been derived. Yet, every individual moves differently from everyone else (faster/slower, harder/smoother, etc.). We propose here an index of such variability, namely an individual motor signature (IMS) able to capture the subtle differences in the way each of us moves. We show that the IMS of a person is time-invariant and that it significantly differs from those of other individuals. This allows us to quantify the dynamic similarity, a measure of rapport between dynamics of different individuals' movements, and demonstrate that it facilitates coordination during interaction. We use our measure to confirm a key prediction of the theory of similarity that coordination between two individuals performing a joint-action task is higher if their motions share similar dynamic features. Furthermore, we use a virtual avatar driven by an interactive cognitive architecture based on feedback control theory to explore the effects of different kinematic features of the avatar motion on coordination with human players. PMID:27009178

  6. Updated Position and Ice Velocity for the Arctic Ice Dynamics Joint Experiment. (AIDJEX) Manned Camps.

    DTIC Science & Technology

    1980-02-01

    FIGURES iv INTRODUCTION 1 DATA ACQUISITION 3 PREPROCESSING 5 KALMAN SMOOTHING 9 RESULTS 16 APPENDIX I Kalman Smoothing Equations 21 APPENDIX 2...measurements have been edited using Kalman smoothing techniques to give the best estimates of position and velocity. (The raw measurements themselves are...V(D C-4 Coj Li, U,) I U,) N >- g -4 UI 0 CDi - Ni I Nj c;0 4;C r- - - --r- - - - % r r r r r * * * . * * . . . . * . * . * * Kalman Smoothing In the

  7. Characterization of sea ice cover, motion and dynamics in Marguerite Bay, Antarctic Peninsula

    NASA Astrophysics Data System (ADS)

    Hyatt, Jason; Beardsley, Robert C.; Owens, W. Brechner

    2011-07-01

    As part of the U.S. GLOBEC Southern Ocean Program, data from two automatic weather stations (AWSs) on small islets and upward-looking acoustic Doppler current profilers (ADCPs) and an upward-looking sonar (ULS) on sub-surface moorings have been analyzed to produce time series of atmospheric forcing, sea ice thickness, sea ice and ocean velocities, and sea ice momentum balances within Marguerite Bay and at mid-shelf on the central west Antarctic Peninsula continental shelf for the austral winter-spring seasons of 2001 and 2002. Both years had roughly seven months of nearly complete sea ice cover, but ice onset was about two months earlier in 2002 than 2001 mostly due to extremely cold surface air temperatures in Marguerite Bay during May-June 2002. Sea ice draft was quite variable, but generally thickened with time, reaching ˜2-3 m by the end of September before thinning. In October, 2002, a polynya was observed at one site within Marguerite Bay that lasted for 4 days. The sea ice motion and dynamics in Marguerite Bay were analyzed when sea ice draft was greater than 2 m. Wind stress during these periods was predominantly southward and southeastward. Wind stress, sea ice, and near-surface water motion were partially correlated, with sea ice motion greater than water motion. Large wind stress and sea ice and water motions occurred during short energetic events of a few days or shorter; however, the rms wind stress, sea ice, and water velocities were small, about 0.3 N m -2, 8-16 cm s -1, and 5-7 cm s -1, respectively. Mean sea ice motion was southward, but quite small, of order 2 cm s -1, while mean near-surface water motion was not statistically different from zero. The dominant sea ice momentum balance was between wind and internal ice stresses on time scales of several days and longer, with water stress, Coriolis, and tilt terms playing secondary roles. The mean southward wind stress was balanced, within uncertainty, by the mean northward internal ice stress. The

  8. Molecular dynamics simulations of D2O ice photodesorption

    NASA Astrophysics Data System (ADS)

    Arasa, C.; Andersson, S.; Cuppen, H.; van Dishoeck, E. F.; Kroes, G. J.

    2011-05-01

    We present results of MD calculations performed to study the photodissociation of D2O in an amorphous ice at different ice temperatures in order to investigate isotope effects on the photodesorption processes. In dense interstellar clouds, small dust particles of micrometer silicates are covered by ice mantles, mainly consisting of H2O and also of CO, CO2. Previous MD calculations of H2O ice at Tice=10-90 K show that the photodesorption of H while OH remains trapped is the main outcome in the first three monolayers (MLs). On the other hand, the H and OH photofragments released recombine or are trapped at separate positions in the deeper MLs and can react with other species in the ice. Desorption and trapping probabilities have been calculated following photoexcitation of D2O amorphous ice at 10, 20, 60 and 90 K, and the main conclusions agree with previous calculations of H2O ice. But, the average D photodesorption probability is smaller than that of the H atom, whereas the average OD radical photodesorption probability is larger than that of OH, and the average D2O photodesorption probability is larger than that for H2O due to the D2O kick-out mechanism. The total (OD + D2O) yield has been compared with experiments and the total (OH + H2O) yield from previous simulations. We find better agreement when we compare experimental yields with calculated yields for D2O ice than when we compare with calculated yields for H2O ice.

  9. A dynamic early East Antarctic Ice Sheet suggested by ice-covered fjord landscapes.

    PubMed

    Young, Duncan A; Wright, Andrew P; Roberts, Jason L; Warner, Roland C; Young, Neal W; Greenbaum, Jamin S; Schroeder, Dustin M; Holt, John W; Sugden, David E; Blankenship, Donald D; van Ommen, Tas D; Siegert, Martin J

    2011-06-02

    The first Cenozoic ice sheets initiated in Antarctica from the Gamburtsev Subglacial Mountains and other highlands as a result of rapid global cooling ∼34 million years ago. In the subsequent 20 million years, at a time of declining atmospheric carbon dioxide concentrations and an evolving Antarctic circumpolar current, sedimentary sequence interpretation and numerical modelling suggest that cyclical periods of ice-sheet expansion to the continental margin, followed by retreat to the subglacial highlands, occurred up to thirty times. These fluctuations were paced by orbital changes and were a major influence on global sea levels. Ice-sheet models show that the nature of such oscillations is critically dependent on the pattern and extent of Antarctic topographic lowlands. Here we show that the basal topography of the Aurora Subglacial Basin of East Antarctica, at present overlain by 2-4.5 km of ice, is characterized by a series of well-defined topographic channels within a mountain block landscape. The identification of this fjord landscape, based on new data from ice-penetrating radar, provides an improved understanding of the topography of the Aurora Subglacial Basin and its surroundings, and reveals a complex surface sculpted by a succession of ice-sheet configurations substantially different from today's. At different stages during its fluctuations, the edge of the East Antarctic Ice Sheet lay pinned along the margins of the Aurora Subglacial Basin, the upland boundaries of which are currently above sea level and the deepest parts of which are more than 1 km below sea level. Although the timing of the channel incision remains uncertain, our results suggest that the fjord landscape was carved by at least two iceflow regimes of different scales and directions, each of which would have over-deepened existing topographic depressions, reversing valley floor slopes.

  10. Order and thermalized dynamics in Heisenberg-like square and Kagomé spin ices.

    PubMed

    Wysin, G M; Pereira, A R; Moura-Melo, W A; de Araujo, C I L

    2015-02-25

    Thermodynamic properties of a spin ice model on a Kagomé lattice are obtained from dynamic simulations and compared with properties in square lattice spin ice. The model assumes three-component Heisenberg-like dipoles of an array of planar magnetic islands situated on a Kagomé lattice. Ising variables are avoided. The island dipoles interact via long-range dipolar interactions and are restricted in their motion due to local shape anisotropies. We define various order parameters and obtain them and thermodynamic properties from the dynamics of the system via a Langevin equation, solved by the Heun algorithm. Generally, a slow cooling from high to low temperature does not lead to a particular state of order, even for a set of coupling parameters that gives well thermalized states and dynamics. At very low temperature, however, square ice is more likely to reach states near the ground state than Kagomé ice, for the same island coupling parameters.

  11. Pyroclastic density current dynamics and associated hazards at ice-covered volcanoes

    NASA Astrophysics Data System (ADS)

    Dufek, J.; Cowlyn, J.; Kennedy, B.; McAdams, J.

    2015-12-01

    Understanding the processes by which pyroclastic density currents (PDCs) are emplaced is crucial for volcanic hazard prediction and assessment. Snow and ice can facilitate PDC generation by lowering the coefficient of friction and by causing secondary hydrovolcanic explosions, promoting remobilisation of proximally deposited material. Where PDCs travel over snow or ice, the reduction in surface roughness and addition of steam and meltwater signficantly changes the flow dynamics, affecting PDC velocities and runout distances. Additionally, meltwater generated during transit and after the flow has come to rest presents an immediate secondary lahar hazard that can impact areas many tens of kilometers beyond the intial PDC. This, together with the fact that deposits emplaced on ice are rarely preserved means that PDCs over ice have been little studied despite the prevalence of summit ice at many tall stratovolcanoes. At Ruapehu volcano in the North Island of New Zealand, a monolithologic welded PDC deposit with unusually rounded clasts provides textural evidence for having been transported over glacial ice. Here, we present the results of high-resolution multiphase numerical PDC modeling coupled with experimentaly determined rates of water and steam production for the Ruapehu deposits in order to assess the effect of ice on the Ruapehu PDC. The results suggest that the presence of ice significantly modified the PDC dynamics, with implications for assessing the PDC and associated lahar hazards at Ruapehu and other glaciated volcanoes worldwide.

  12. The effect of salt on the melting of ice: A molecular dynamics simulation study.

    PubMed

    Kim, Jun Soo; Yethiraj, Arun

    2008-09-28

    The effect of added salt (NaCl) on the melting of ice is studied using molecular dynamics simulations. The equilibrium freezing point depression observed in the simulations is in good agreement with experimental data. The kinetic aspects of melting are investigated in terms of the exchange of water molecules between ice and the liquid phase. The ice/liquid equilibrium is a highly dynamic process with frequent exchange of water molecules between ice and the liquid phase. The balance is disturbed when ice melts and the melting proceeds in two stages; the inhibition of the association of water molecules to the ice surface at short times, followed by the increased dissociation of water molecules from the ice surface at longer times. We also find that Cl(-) ions penetrate more deeply into the interfacial region than Na(+) ions during melting. This study provides an understanding of the kinetic aspects of melting that could be useful in other processes such as the inhibition of ice growth by antifreeze proteins.

  13. Molecular-dynamics simulation of clustering processes in sea-ice floes.

    PubMed

    Herman, Agnieszka

    2011-11-01

    In seasonally ice-covered seas and along the margins of perennial ice pack, i.e., in regions with medium ice concentrations, the ice cover typically consists of separate floes interacting with each other by inelastic collisions. In this paper, hitherto unexplored analogies between this type of ice cover and two-dimensional granular gases are used to formulate a model of ice dynamics at the floe level. The model consists of (i) momentum equations for floe motion between collisions, formulated in the form of a Stokes-flow problem, with floe-size-dependent time constant and equilibrium velocity, and (ii) a hard-disk collision model. The numerical algorithm developed is suitable for simulating particle-laden flow of N disk-shaped floes with arbitrary size distributions. The model is applied to study clustering phenomena in sea ice with power-law floe-size distribution. In particular, the influence of the average ice concentration A on the formation and characteristics of clusters is analyzed in detail. The results show the existence of two regimes, at low and high ice concentrations, differing in terms of the exponents of the cluster-size distribution and of the size of the largest cluster.

  14. Numerical Investigation of the Dynamic Properties of Intermittent Jointed Rock Models Subjected to Cyclic Uniaxial Compression

    NASA Astrophysics Data System (ADS)

    Liu, Yi; Dai, Feng; Zhao, Tao; Xu, Nu-wen

    2017-01-01

    Intermittent jointed rocks, which exist in a myriad of engineering projects, are extraordinarily susceptible to cyclic loadings. Understanding the dynamic fatigue properties of jointed rocks is necessary for evaluating the stability of rock engineering structures. This study numerically investigated the influences of cyclic loading conditions (i.e., frequency, maximum stress and amplitude) and joint geometric configurations (i.e., dip angle, persistency and interspace) on the dynamic fatigue mechanisms of jointed rock models. A reduction model of stiffness and strength was first proposed, and then, sixteen cyclic uniaxial loading tests with distinct loading parameters and joint geometries were simulated. Our results indicate that the reduction model can effectively reproduce the hysteresis loops and the accumulative plastic deformation of jointed rocks in the cyclic process. Both the loading parameters and the joint geometries significantly affect the dynamic properties, including the irreversible strain, damage evolution, dynamic residual strength and fatigue life. Three failure modes of jointed rocks, which are principally controlled by joint geometries, occur in the simulations: splitting failure through the entire rock sample, sliding failure along joint planes and mixed failure, which are principally controlled by joint geometries. Furthermore, the progressive failure processes of the jointed rock samples are numerically observed, and the different loading stages can be distinguished by the relationship between the number of broken bonds and the axial stress.

  15. Synovial fluid dynamics with small disc perforation in temporomandibular joint.

    PubMed

    Xu, Y; Zhan, J; Zheng, Y; Han, Y; Zhang, Z; Xi, Y; Zhu, P

    2012-10-01

    The articular disc plays an important role as a stress absorber in joint movement, resulting in stress reduction and redistribution in the temporomandibular joint (TMJ). The flow of synovial fluid in the TMJ may follow a regular pattern during movement of the jaw. We hypothesised that the regular pattern is disrupted when the TMJ disc is perforated. By computed tomography arthrography, we studied the upper TMJ compartment in patients with small disc perforation during jaw opening-closing at positions from 0 to 3 cm. Finite element fluid dynamic modelling was accomplished to analyse the pattern of fluid flow and pressure distribution during the movements. The results showed that the fluid flow in the upper compartment generally formed an anticlockwise circulation but with local vortexes with the jaw opening up to 2 cm. However, when the jaw opening-closing reached 3 cm, an abnormal flow field and the fluid pressure change associated with the perforation may increase the risk of perforation expansion or rupture and is unfavourable for self-repair of the perforated disc.

  16. Dynamics of ice mass deformation: Linking processes to rheology, texture, and microstructure

    NASA Astrophysics Data System (ADS)

    Piazolo, Sandra; Wilson, Christopher J. L.; Luzin, Vladimir; Brouzet, Christophe; Peternell, Mark

    2013-10-01

    Prediction of glacier and polar ice sheet dynamics is a major challenge, especially in view of changing climate. The flow behavior of an ice mass is fundamentally linked to processes at the grain and subgrain scale. However, our understanding of ice rheology and microstructure evolution based on conventional deformation experiments, where samples are analyzed before and after deformation, remains incomplete. To close this gap, we combine deformation experiments with in situ neutron diffraction textural and grain analysis that allows continuous monitoring of the evolution of rheology, texture, and microstructure. We prepared ice samples from deuterium water, as hydrogen in water ice has a high incoherent neutron scattering rendering it unsuitable for neutron diffraction analysis. We report experimental results from deformation of initially randomly oriented polycrystalline ice at three different constant strain rates. Results show a dynamic system where steady-state rheology is not necessarily coupled to microstructural and textural stability. Textures change from a weak single central c axis maxima to a strong girdle distribution at 35° to the compression axis attributed to dominance of basal slip followed by basal combined with pyramidal slip. Dislocation-related hardening accompanies this switch and is followed by weakening due to new grain nucleation and grain boundary migration. With decreasing strain rate, grain boundary migration becomes increasingly dominant and texture more pronounced. Our observations highlight the link between the dynamics of processes competition and rheological and textural behavior. This link needs to be taken into account to improve ice mass deformation modeling critical for climate change predictions.

  17. Molecular dynamics simulations of CO2 formation in interstellar ices

    NASA Astrophysics Data System (ADS)

    Arasa, C.; Andersson, S.; van Dishoeck, E. F.; Kroes, G. J.

    2011-05-01

    In dense interstellar clouds where new stars and planets are formed, small dust particles of micrometer silicates are covered by ice mantles, mainly consisting of H2O and also of CO, CO2, CH4 and other molecules. A high flux of UV photons can produce several photodissociative events. Previous MD calculations of H2O ice at Tice=10-90 K show that the photodesorption of H while OH remains trapped is the main outcome following photoexcitation in the first three monolayers (MLs). On the other hand, the H and OH photofragments released following photoexcitation deeper in the ice recombine or are trapped at separate positions, and can then react with other species in the ice. We hope to present results of MD calculations performed to study the photoinduced reaction of OH with CO through photodissociation of H2O in an amorphous COad - H2O ice at 10 K. This reaction pathway is supposed to be a principle route to form CO2 in interstellar ices.

  18. Distributions of ice supersaturation and ice crystals from airborne observations in relation to upper tropospheric dynamical boundaries

    NASA Astrophysics Data System (ADS)

    Diao, Minghui; Jensen, Jorgen B.; Pan, Laura L.; Homeyer, Cameron R.; Honomichl, Shawn; Bresch, James F.; Bansemer, Aaron

    2015-05-01

    Ice supersaturation (ISS) is the prerequisite condition for cirrus cloud formation. To examine multiscale dynamics' influences on ISS formation, we analyze in situ aircraft observations (~200 m scale) over North America in coordinates relative to dynamical boundaries in the upper troposphere and lower stratosphere. Two case studies demonstrate that ISS formation is likely influenced by mesoscale uplifting, small-scale waves, and turbulence. A collective analysis of 15 flights in April-June 2008 shows that the top layers of ISS and ice crystal distributions are strongly associated with thermal tropopause height. In addition, the average occurrence frequencies of ISS and ice crystals on the anticyclonic side of the jet stream are ~1.5-2 times of those on the cyclonic side. By defining five cirrus evolution phases based on the spatial relationships between ice-supersaturated and in-cloud regions, we find that their peak occurrence frequencies are located at decreasing altitudes with respect to the thermal tropopause: (phase 1) clear-sky ISS around the tropopause, (phase 2) nucleation phase around 2 km below the tropopause, (phases 3 and 4) early and later growth phases around 6 km below the tropopause, and (phase 5) sedimentation/sublimation around 2-6 km below the tropopause. Consistent with this result, chemical tracer correlation analysis shows that the majority (~80%) of the earlier cirrus phases (clear-sky ISS and nucleation) occurs inside the chemical tropopause transition layer, while the later phases happen mostly below that layer. These results shed light on the role of dynamical environment in facilitating cirrus cloud formation and evolution.

  19. Geophysical constraints on the dynamics and retreat of the Barents Sea ice sheet as a paleobenchmark for models of marine ice sheet deglaciation

    NASA Astrophysics Data System (ADS)

    Patton, Henry; Andreassen, Karin; Bjarnadóttir, Lilja R.; Dowdeswell, Julian A.; Winsborrow, Monica C. M.; Noormets, Riko; Polyak, Leonid; Auriac, Amandine; Hubbard, Alun

    2015-12-01

    Our understanding of processes relating to the retreat of marine-based ice sheets, such as the West Antarctic Ice Sheet and tidewater-terminating glaciers in Greenland today, is still limited. In particular, the role of ice stream instabilities and oceanographic dynamics in driving their collapse are poorly constrained beyond observational timescales. Over numerous glaciations during the Quaternary, a marine-based ice sheet has waxed and waned over the Barents Sea continental shelf, characterized by a number of ice streams that extended to the shelf edge and subsequently collapsed during periods of climate and ocean warming. Increasing availability of offshore and onshore geophysical data over the last decade has significantly enhanced our knowledge of the pattern and timing of retreat of this Barents Sea ice sheet (BSIS), particularly so from its Late Weichselian maximum extent. We present a review of existing geophysical constraints that detail the dynamic evolution of the BSIS through the last glacial cycle, providing numerical modelers and geophysical workers with a benchmark data set with which to tune ice sheet reconstructions and explore ice sheet sensitivities and drivers of dynamic behavior. Although constraining data are generally spatially sporadic across the Barents and Kara Seas, behaviors such as ice sheet thinning, major ice divide migration, asynchronous and rapid flow switching, and ice stream collapses are all evident. Further investigation into the drivers and mechanisms of such dynamics within this unique paleo-analogue is seen as a key priority for advancing our understanding of marine-based ice sheet deglaciations, both in the deep past and in the short-term future.

  20. Modeling of joints for the dynamic analysis of truss structures

    NASA Technical Reports Server (NTRS)

    Belvin, W. Keith

    1987-01-01

    An experimentally-based method for determining the stiffness and damping of truss joints is described. The analytical models use springs and both viscous and friction dampers to simulate joint load-deflection behavior. A least-squares algorithm is developed to identify the stiffness and damping coefficients of the analytical joint models from test data. The effects of nonlinear joint stiffness such as joint dead band are also studied. Equations for predicting the sensitivity of beam deformations to changes in joint stiffness are derived and used to show the level of joint stiffness required for nearly rigid joint behavior. Finally, the global frequency sensitivity of a truss structure to random perturbations in joint stiffness is discussed.

  1. [Dynamic loads at knee joint of trans-tibial amputee on different terrains].

    PubMed

    Jia, Xiaohong; Zhang, Ming; Fan, Yubo; Wang, Rencheng

    2005-04-01

    Dynamic loads at knee joint of amputee are fundamental for rehabilitation of knee injury and prosthesis design. In this paper, a 3-D model for calculation of dynamic load at knee joint of trans-tibial amputee was developed. Gait analysis was done on three terrains including normal level walking, upstairs and downstairs. Dynamic loads at knee joint were calculated during one gait cycle. The results show that gait patterns and dynamic loads at knee joint were different among these three terrains. Although the general waveforms were about the same, the motion range of knee joint, ground reaction forces and loads at knee joint when walking upstairs or downstairs were larger than those in a normal level walking. The quantitative findings provide the theoretical basis of gait analysis and prosthesis design for trans-tibial amputee.

  2. Modelling the palaeo grounding-line retreat dynamics of the Uummannaq Ice Stream in Western Greenland.

    NASA Astrophysics Data System (ADS)

    Jamieson, Stewart; Vieli, Andreas; Roberts, Dave; Rea, Brice; Lane, Tim; Cofaigh, Colm Ó.

    2013-04-01

    We aim to understand what controlled the retreat pattern of the Uummannaq Ice Stream (UIS) during the last deglaciation. The ice stream was grounded close to the continental shelf edge at the Last Glacial Maximum, and retreated rapidly after 14.8 ka. Cosmogenic nuclide exposure dating on Ubekendt Island at the convergence zone of multiple feeder ice streams show that the ice surface thinned progressively and that the island became ice-free by ca. 12.4 ka. The ice stream then collapsed over the next 1-1.6 kyrs and the ice stream separated into a series of distinct inland arms. However, it is currently unclear what controlled the nonlinear retreat pattern identified in the Uummannaq system. We test the hypothesis that the geometry of the landscape strongly conditions the rate of retreat of the UIS. In order to do this, we constrain a numerical model of ice stream retreat using the marine geophysical data and measurements of sediment strength on the continental shelf. The model has the capability to dynamically and robustly simulate grounding line-retreat behaviour over millennial timescales. We simulate the retreat of the UIS grounding line into the northernmost Rinks system and conduct sensitivity tests to explore its response to a range of forcing patterns. The model is initialised at a steady-state LGM configuration and is subjected to a series of retreat perturbations forced by either rising sea-level, enhanced melting at the ice-ocean interface, or warming climate. We compare the simulated dynamic behaviour of the UIS against the terrestrial record of ice stream retreat to determine why retreat during the last deglaciation was nonlinear.

  3. Similitude of ice dynamics against scaling of geometry and physical parameters

    NASA Astrophysics Data System (ADS)

    Feldmann, Johannes; Levermann, Anders

    2016-08-01

    The concept of similitude is commonly employed in the fields of fluid dynamics and engineering but rarely used in cryospheric research. Here we apply this method to the problem of ice flow to examine the dynamic similitude of isothermal ice sheets in shallow-shelf approximation against the scaling of their geometry and physical parameters. Carrying out a dimensional analysis of the stress balance we obtain dimensionless numbers that characterize the flow. Requiring that these numbers remain the same under scaling we obtain conditions that relate the geometric scaling factors, the parameters for the ice softness, surface mass balance and basal friction as well as the ice-sheet intrinsic response time to each other. We demonstrate that these scaling laws are the same for both the (two-dimensional) flow-line case and the three-dimensional case. The theoretically predicted ice-sheet scaling behavior agrees with results from numerical simulations that we conduct in flow-line and three-dimensional conceptual setups. We further investigate analytically the implications of geometric scaling of ice sheets for their response time. With this study we provide a framework which, under several assumptions, allows for a fundamental comparison of the ice-dynamic behavior across different scales. It proves to be useful in the design of conceptual numerical model setups and could also be helpful for designing laboratory glacier experiments. The concept might also be applied to real-world systems, e.g., to examine the response times of glaciers, ice streams or ice sheets to climatic perturbations.

  4. Measurement and analysis of structural dynamics properties of robotic joint transmission system

    NASA Astrophysics Data System (ADS)

    Huang, Shiuh-Jer; Chen, Chin-Yih

    1993-02-01

    This study utilizes two techniques to identify the structural dynamic characteristics of each joint transmission system of an ITRI-U type robot. The driving system of each joint is modeled as a mass-spring-damper mechanism that has a second-order dynamic mathematical equation.

  5. Semi-brittle rheology and ice dynamics in DynEarthSol3D

    NASA Astrophysics Data System (ADS)

    Logan, Liz C.; Lavier, Luc L.; Choi, Eunseo; Tan, Eh; Catania, Ginny A.

    2017-01-01

    We present a semi-brittle rheology and explore its potential for simulating glacier and ice sheet deformation using a numerical model, DynEarthSol3D (DES), in simple, idealized experiments. DES is a finite-element solver for the dynamic and quasi-static simulation of continuous media. The experiments within demonstrate the potential for DES to simulate ice failure and deformation in dynamic regions of glaciers, especially at quickly changing boundaries like glacier termini in contact with the ocean. We explore the effect that different rheological assumptions have on the pattern of flow and failure. We find that the use of a semi-brittle constitutive law is a sufficient material condition to form the characteristic pattern of basal crevasse-aided pinch-and-swell geometry, which is observed globally in floating portions of ice and can often aid in eroding the ice sheet margins in direct contact with oceans.

  6. Skillful seasonal forecasts of Arctic sea ice retreat and advance dates in a dynamical forecast system

    NASA Astrophysics Data System (ADS)

    Sigmond, M.; Reader, M. C.; Flato, G. M.; Merryfield, W. J.; Tivy, A.

    2016-12-01

    The need for skillful seasonal forecasts of Arctic sea ice is rapidly increasing. Technology to perform such forecasts with coupled atmosphere-ocean-sea ice systems has only recently become available, with previous skill evaluations mainly limited to area-integrated quantities. Here we show, based on a large set of retrospective ensemble model forecasts, that a dynamical forecast system produces skillful seasonal forecasts of local sea ice retreat and advance dates - variables that are of great interest to a wide range of end users. Advance dates can generally be skillfully predicted at longer lead times ( 5 months on average) than retreat dates ( 3 months). The skill of retreat date forecasts mainly stems from persistence of initial sea ice anomalies, whereas advance date forecasts benefit from longer time scale and more predictable variability in ocean temperatures. These results suggest that further investments in the development of dynamical seasonal forecast systems may result in significant socioeconomic benefits.

  7. Experimental and theoretical investigation of the magnetization dynamics of an artificial square spin ice cluster

    NASA Astrophysics Data System (ADS)

    Pohlit, Merlin; Stockem, Irina; Porrati, Fabrizio; Huth, Michael; Schröder, Christian; Müller, Jens

    2016-10-01

    We study the magnetization dynamics of a spin ice cluster which is a building block of an artificial square spin ice fabricated by focused electron-beam-induced deposition both experimentally and theoretically. The spin ice cluster is composed of twelve interacting Co nanoislands grown directly on top of a high-resolution micro-Hall sensor. By employing micromagnetic simulations and a macrospin model, we calculate the magnetization and the experimentally investigated stray field emanating from a single nanoisland. The parameters determined from a comparison with the experimental hysteresis loop are used to derive an effective single-dipole macrospin model that allows us to investigate the dynamics of the spin ice cluster. Our model reproduces the experimentally observed non-deterministic sequences in the magnetization curves as well as the distinct temperature dependence of the hysteresis loop.

  8. Geological and meteorological controls on icing (aufeis) dynamics (1985 to 2014) in subarctic Canada

    NASA Astrophysics Data System (ADS)

    Morse, P. D.; Wolfe, S. A.

    2015-09-01

    Icings are widespread yet poorly understood winter hydrological phenomena that develop over the winter by freezing successive overflows of groundwater to the surface. Groundwater hydrology in arctic regions is constrained by geological setting and permafrost extent, and overflows are possibly driven by cold winters, winter warming intervals, high antecedent autumn rainfall, and low early winter snowfall. Consequently, icings are spatially recurrent but not necessarily annually nor to the same extent. We test the significance of identified meteorological forcing variables against a long-term data set of icing dynamics and distribution we developed for the Great Slave region around Yellowknife, Northwest Territories. Climate is regionally consistent, but variable geology and permafrost create hydrological conditions representative of much of the subarctic. We mapped 5500 icings in the study area (21,887 km2) with a semiautomated approach utilizing late spring Landsat archival images (1985 to 2014). Individual icing size, ranging 3 orders of magnitude (1.8 × 10-3 km2 to 4.1 km2), is related to return frequency. Infrequent ice (25% return frequency) accounts for 94% of the total icing area (86 km2). Winter warming intervals (≥5°C; typically over 1-3 days) and autumn rainfall (September and October) explain 28% of icing density interannual variation overall. Interannual icing variation and significant meteorological forcing variables differ among ecoregions where varied geological settings and permafrost conditions influence the hydrological regime. Future icings may develop less frequently due to decreasing winter warming intervals, but increasing autumn rainfall may increase icing density where Canadian Shield leads to strong threshold-mediated runoff generation processes.

  9. Drivers of inorganic carbon dynamics in first-year sea ice: A model study

    NASA Astrophysics Data System (ADS)

    Moreau, Sébastien; Vancoppenolle, Martin; Delille, Bruno; Tison, Jean-Louis; Zhou, Jiayun; Kotovich, Marie; Thomas, David; Geilfus, Nicolas-Xavier; Goosse, Hugues

    2015-04-01

    Sea ice is an active source or a sink for carbon dioxide (CO2), although to what extent is not clear. Here, we analyze CO2 dynamics within sea ice using a one-dimensional halo-thermodynamic sea ice model including gas physics and carbon biogeochemistry. The ice-ocean fluxes, and vertical transport, of total dissolved inorganic carbon (DIC) and total alkalinity (TA) are represented using fluid transport equations. Carbonate chemistry, the consumption and release of CO2 by primary production and respiration, the precipitation and dissolution of ikaite (CaCO3•6H2O) and ice-air CO2 fluxes, are also included. The model is evaluated using observations from a 6-month field study at Point Barrow, Alaska and an ice-tank experiment. At Barrow, results show that the DIC budget is mainly driven by physical processes, wheras brine-air CO2 fluxes, ikaite formation, and net primary production, are secondary factors. In terms of ice-atmosphere CO2 exchanges, sea ice is a net CO2 source and sink in winter and summer, respectively. The formulation of the ice-atmosphere CO2 flux impacts the simulated near-surface CO2 partial pressure (pCO2), but not the DIC budget. Because the simulated ice-atmosphere CO2 fluxes are limited by DIC stocks, and therefore < 2 mmol m-2 day-1, we argue that the observed much larger CO2 fluxes from eddy covariance retrievals cannot be explained by a sea ice direct source and must involve other processes or other sources of CO2. Finally, the simulations suggest that near surface TA/DIC ratios of ~2, sometimes used as an indicator of calcification, would rather suggest outgassing.

  10. Drivers of inorganic carbon dynamics in first-year sea ice: A model study

    NASA Astrophysics Data System (ADS)

    Moreau, Sébastien; Vancoppenolle, Martin; Delille, Bruno; Tison, Jean-Louis; Zhou, Jiayun; Kotovitch, Marie; Thomas, David N.; Geilfus, Nicolas-Xavier; Goosse, Hugues

    2015-01-01

    ice is an active source or a sink for carbon dioxide (CO2), although to what extent is not clear. Here, we analyze CO2 dynamics within sea ice using a one-dimensional halothermodynamic sea ice model including gas physics and carbon biogeochemistry. The ice-ocean fluxes, and vertical transport, of total dissolved inorganic carbon (DIC) and total alkalinity (TA) are represented using fluid transport equations. Carbonate chemistry, the consumption, and release of CO2 by primary production and respiration, the precipitation and dissolution of ikaite (CaCO3·6H2O) and ice-air CO2 fluxes, are also included. The model is evaluated using observations from a 6 month field study at Point Barrow, Alaska, and an ice-tank experiment. At Barrow, results show that the DIC budget is mainly driven by physical processes, wheras brine-air CO2 fluxes, ikaite formation, and net primary production, are secondary factors. In terms of ice-atmosphere CO2 exchanges, sea ice is a net CO2 source and sink in winter and summer, respectively. The formulation of the ice-atmosphere CO2 flux impacts the simulated near-surface CO2 partial pressure (pCO2), but not the DIC budget. Because the simulated ice-atmosphere CO2 fluxes are limited by DIC stocks, and therefore <2 mmol m-2 d-1, we argue that the observed much larger CO2 fluxes from eddy covariance retrievals cannot be explained by a sea ice direct source and must involve other processes or other sources of CO2. Finally, the simulations suggest that near-surface TA/DIC ratios of ˜2, sometimes used as an indicator of calcification, would rather suggest outgassing.

  11. A new experimental setup to investigate nucleation, dynamic growth and surface properties of single ice crystals

    NASA Astrophysics Data System (ADS)

    Voigtlaender, Jens; Bieligk, Henner; Niedermeier, Dennis; Clauss, Tina; Chou, Cédric; Ulanowski, Zbigniew; Stratmann, Frank

    2013-04-01

    The nucleation and growth of atmospheric ice particles is of importance for both, weather and climate. However, knowledge is still sparse, e.g. when considering the influences of ice particle surface properties on the radiative properties of clouds. Therefore, based on the experiences with our laminar flow tube chamber LACIS (Leipzig Aerosol Cloud Interaction Simulator, Stratmann et al., 2004), we developed a new device to characterize nucleation, dynamic growth and light scattering properties of a fixed single ice crystal in dependence on the prevailing thermodynamic conditions. Main part of the new setup is a thermodynamically controlled laminar flow tube with a diameter of 15 mm and a length of 1.0 m. Connected to the flow tube is a SID3-type (Small Ice Detector, Kaye et al., 2008) instrument called LISA (Leipzig Ice Scattering Apparatus), equipped with an additional optical microscope. For the investigations, a single ice nucleus (IN) with a dry size of 2-5 micrometer is attached to a thin glass fiber and positioned within the optical measuring volume of LISA. The fixed particle is exposed to the thermodynamically controlled air flow, exiting the flow tube. Two mass flow controllers adjusting a dry and a humidified gas flow are applied to control both, the temperature and the saturation ratio over a wide range. The thermodynamic conditions in the experiments were characterized using a) temperature and dew-point measurements, and b) computational fluid dynamics (CFD) calculations. Dependent on temperature and saturation ratio in the measuring volume, ice nucleation and ice crystal growth/shrinkage can occur. The optical microscope allows a time dependent visualization of the particle/ice crystal, and the LISA instrument is used to obtain 2-D light scattering patterns. Both devices together can be applied to investigate the influence of thermodynamic conditions on ice crystal growth, in particular its shape and surface properties. We successfully performed

  12. Dynamic influence of pinning points on marine ice-sheet stability: a numerical study in Dronning Maud Land, East Antarctica

    NASA Astrophysics Data System (ADS)

    Favier, Lionel; Pattyn, Frank; Berger, Sophie; Drews, Reinhard

    2016-11-01

    The East Antarctic ice sheet is likely more stable than its West Antarctic counterpart because its bed is largely lying above sea level. However, the ice sheet in Dronning Maud Land, East Antarctica, contains marine sectors that are in contact with the ocean through overdeepened marine basins interspersed by grounded ice promontories and ice rises, pinning and stabilising the ice shelves. In this paper, we use the ice-sheet model BISICLES to investigate the effect of sub-ice-shelf melting, using a series of scenarios compliant with current values, on the ice-dynamic stability of the outlet glaciers between the Lazarev and Roi Baudouin ice shelves over the next millennium. Overall, the sub-ice-shelf melting substantially impacts the sea-level contribution. Locally, we predict a short-term rapid grounding-line retreat of the overdeepened outlet glacier Hansenbreen, which further induces the transition of the bordering ice promontories into ice rises. Furthermore, our analysis demonstrated that the onset of the marine ice-sheet retreat and subsequent promontory transition into ice rise is controlled by small pinning points, mostly uncharted in pan-Antarctic datasets. Pinning points have a twofold impact on marine ice sheets. They decrease the ice discharge by buttressing effect, and they play a crucial role in initialising marine ice sheets through data assimilation, leading to errors in ice-shelf rheology when omitted. Our results show that unpinning increases the sea-level rise by 10 %, while omitting the same pinning point in data assimilation decreases it by 10 %, but the more striking effect is in the promontory transition time, advanced by two centuries for unpinning and delayed by almost half a millennium when the pinning point is missing in data assimilation. Pinning points exert a subtle influence on ice dynamics at the kilometre scale, which calls for a better knowledge of the Antarctic margins.

  13. Effect of joint damping and joint nonlinearity on the dynamics of space structures

    NASA Technical Reports Server (NTRS)

    Bowden, Mary; Dugundji, John

    1988-01-01

    Analyses of the effect of linear joint characteristics on the vibrations of a free-free, three-joint beam model show that increasing joint damping increases resonant frequencies and increases modal damping but only to the point where the joint gets 'locked up' by damping. This behavior is different from that predicted by modeling joint damping as proportional damping. Nonlinear analyses of the three-joint model with cubic springs at the joints show all the classical single DOF nonlinear response behavior at each resonance of the multiple DOF system: nondoubling of response for a doubling of forcing amplitude, multiple solutions, jump behavior, and resonant frequency shifts. These properties can be concisely quantified by characteristic backbone curves, which show the locus of resonant peaks for increasing forcing amplitude.

  14. Reconstructing the dynamics of the Greenland ice sheet during the last deglaciation

    NASA Astrophysics Data System (ADS)

    Keisling, Benjamin; DeConto, Robert

    2016-04-01

    Today, some outlet glaciers of the Greenland ice sheet (GrIS) are rapidly retreating and may mobilize large volumes of interior ice in the coming centuries. The last period that saw such dramatic, sustained retreat of the GrIS was the last deglaciation, when the ice sheet retreated from its Last Glacial Maximum (LGM) extent. Previous studies have used relative sea level observations to constrain changes in ice thickness and retreat timing during the deglaciation (e.g. Fleming and Lambert 2004, Simpson et al. 2009, Lecavalier et al. 2014). Here we build on these studies by isolating the drivers of ice-sheet retreat, and their spatial and temporal dynamics, during this period. Inclusion of ice-cliff failure and hydrofracturing parameterizations in our model has resulted in a better fit to paleodata for the Antarctic ice sheet, but this modeling approach has not been applied to the GrIS. Here we use a three-dimensional hybrid SSA/SIA ice-sheet model (Pollard et al. 2015) at 10km resolution over Greenland to simulate the last deglaciation. Boundary conditions for the last glacial maximum produce an LGM ice sheet with 3.81 meters sea level equivalent (m s.l.e.) of additional ice. The LGM ice sheet advances to the shelf-break in west, south, and east Greenland with an expansive ice shelf extending across Davis Strait. Applying modern atmospheric and oceanic forcing to the LGM ice sheet yields 1.25 and 1.09 m s.l.e. of melt, respectively, and 1.72 m s.l.e. for both. Ocean warming initially results in a higher rate and magnitude of retreat, but increased surface evaporation over open water results in additional accumulation that offsets losses in 10 kyr simulations. Here, we test the sensitivity of the magnitude of deglacial ice-sheet retreat to uncertainty in bedrock elevation and basal slding coefficients, the applied climate forcing, and the mass balance scheme (positive degree-day or energy balance). We also implement a deglacial climate forcing based on recently

  15. A Dynamic Antarctic Ice Sheet in the Miocene and Pliocene: Resolving a Classic Model-Data Paradox

    NASA Astrophysics Data System (ADS)

    Deconto, R. M.; Gasson, E.; Pollard, D.

    2015-12-01

    Proxy ice volume and sea-level indicators imply a highly dynamic Antarctic Ice Sheet in the Miocene and early-mid Pliocene, especially if the Northern Hemisphere is assumed to be ice-free. Until now, the presumed insensitivity of a fully developed Antarctic Ice Sheet to orbital forcing and a wide range of greenhouse gas concentrations has made Miocene and Pliocene ice volume variability difficult to reconcile. Here, we show how the inclusion of new ice-model physics, more highly resolved atmospheric models, and new ice-climate coupling techniques are reducing the strength of Antarctic Ice Sheet hysteresis, bringing data-model comparisons into better agreement. This is especially true in light of new atmospheric CO2 reconstructions hinting at concentrations higher than previous estimates. The global implications of a more dynamic Antarctic cryosphere in the Neogene will be discussed in light of its potential impact on the atmosphere and global ocean circulation.

  16. The role of the margins in ice stream dynamics

    NASA Technical Reports Server (NTRS)

    Echelmeyer, Keith; Harrison, William

    1993-01-01

    At first glance, it would appear that the bed of the active ice stream plays a much more important role in the overall force balance than do the margins, especially because the ratio of the half-width to depth for a typical ice stream is large (15:1 to 50:1). On the other hand, recent observations indicate that at least part of the ice stream is underlain by a layer of very weak till (shear strength about 2 kPa), and this weak basal layer would then imply that some or all of the resistive drag is transferred to the margins. In order to address this question, a detailed velocity profile near Upstream B Camp, which extends from the center of the ice stream, across the chaotic shear margin, and onto the Unicorn, which is part of the slow-moving ice sheet was measured. Comparison of this observed velocity profile with finite-element models of flow shows several interesting features. First, the shear stress at the margin is on the order of 130 kPa, while the mean value along the bed is about 15 kPa. Integration of these stresses along the boundaries indicates that the margins provide 40 to 50 percent, and the bed, 60 to 40 percent of the total resistive drag needed to balance the gravitational driving stress in this region. (The range of values represents calculations for different values of surface slope.) Second, the mean basal stress predicted by the models shows that the entire bed cannot be blanketed by the weak till observed beneath upstream B - instead there must be a distribution of weak till and 'sticky spots' (e.g., 85 percent till and 15 percent sticky spots of resistive stress equal to 100 kPa). If more of the bed were composed of weak till, then the modeled velocity would not match that observed. Third, the ice must exhibit an increasing enhancement factor as the margins are approached (E equals 10 in the chaotic zone), in keeping with laboratory measurements on ice under prolonged shear strain. Also, there is either a narrow zone of somewhat stiffer ice (E

  17. Mars together and FIRE and ICE: Report of the joint US/Russian technical working groups

    NASA Technical Reports Server (NTRS)

    1994-01-01

    The Cold War's end opened an opportunity for greater cooperation in planetary exploration for the United States and Russia. Two study groups were formed, Mars Together and FIRE and ICE. The Mars Together team developed a concept for a flight in 1998 that merged one U.S. Mars Surveyor 98 mission with the former Russian Mars 96 mission to further understanding of the Mars surface and atmosphere. The FIRE and ICE team developed concepts for a dual-spacecraft mission to the solar corona and for a mission to Pluto. The missions, scientific potential, and open issues are described.

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

    NASA Astrophysics Data System (ADS)

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

    2015-06-01

    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.

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

    PubMed

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

    2015-06-16

    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.

  20. 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

  1. Examination of upstream flow dynamics in response to the front retreat of ice shelves with different geometric configurations

    NASA Astrophysics Data System (ADS)

    Wang, S.; Liu, H.

    2015-12-01

    Ice shelves fringe ~75% of Antarctica's coastline, nourished by numerous terrestrial glacier systems. The ice-shelf disintegrations in recent decades and the observed thinning trends have revealed their susceptibility to the atmospheric and oceanic changes in the climate warming context. The buttressing effect of an ice shelf constrains the ice discharge of its upstream land ice, thus regulating the contribution to sea level of the terrestrial glaciers. The important role of ice shelves in stabilizing the upstream glacier flow dynamics is emphasized by the rapid accelerations and thinning of the tributary glaciers in response to the collapses of the northern Larsen Ice Shelf in Antarctic Peninsula. However, this buttressing effect is determined by the stress balance conditions of an ice shelf, which is further affected by the ice-shelf geometric configurations. The ice shelves confined by fjords, islands, promontories or seabed topographic highs exert greater buttressing effects than those less confined by the lateral or basal shear stresses. This research aims to assess the influences of different ice-shelf configurations on upstream flow dynamics in response to large ice-shelf retreat events. By using remotely sensed imagery acquired by multiple satellite missions, we derived the time series surface velocity records for the Larsen B glacier-ice shelf system in Antarctic Peninsula during 1995 - 2015 and for the Mertz glacier-ice shelf system in East Antarctica during 1997 - 2015, respectively. The former was well confined in the embayment, while the latter is unconfined by lateral margins. We compared the different temporal variation patterns in flow dynamics between these two sites before and after their large retreating events, i.e. the collapse event of Larsen B Ice Shelf in 2002 and the large calving event of Mertz Ice Shelf in 2010. The surface velocity profiles reveal the less sensitivity of upstream responses to the front retreat for the Mertz Ice Shelf.

  2. Applying High Resolution Imagery to Understand the Role of Dynamics in the Diminishing Arctic Sea Ice Cover

    DTIC Science & Technology

    2015-09-30

    ice to climate change and sea - level rise . IceBridge will also bridge the gap in observations between NASA’s ICESat satellite missions. Farrell and...Role of Dynamics in the Diminishing Arctic Sea Ice Cover” Dr. Sinead L. Farrell University of Maryland, ESSIC, 5825 University Research Court...characteristics, that describe the state of the sea ice pack during of the last decade. Assessment of the satellite imagery database will help to

  3. Early springtime dynamics of dimethylsulfoxide (DMSO) within East Antarctic sea ice

    NASA Astrophysics Data System (ADS)

    Brabant, F.; Carnat, G.; Tison, J.

    2009-12-01

    High resolution profiles of DMSO (dimethylsulfoxide) have been measured in a set of sea ice cores from eight stations sampled in the first-year early spring sea ice cover of East Antarctica (ARISE cruise, Sep.-Oct 2003, Australian sector of the Southern Ocean, 63-66° S; 109-118° E). Measurements have been performed following a precise enzymatic reduction method of DMSO originally developed for measuring DMSO in aqueous samples [1] and adapted to produce non-biased results while applied to measuring DMSO in sea ice samples. Sea ice DMSO concentrations measured in this study (6.7-1202 nM; average 73 nM) are higher and more variable than what has been previously measured in Arctic sea ice in the only study over sea ice DMSO concentration to date (1.35-102 nM; average 13.7 nM) [2]. DMSO concentrations are most of the time higher than dimethylsulfoxide (DMS) concentrations but far lower than dimethylsulfoniopropionate (DMSP) concentrations. A thorough comparison of DMSO data along with a full set of other physical (ice texture, ice temperature,…), biological (chlorophyll a, algal assemblage composition,…) and biogeochemical variables (brine salinity, DMS, DMSP,…) will be presented. Preliminary results of this study reveal that the composition of the algal assemblage (diatoms vs. dinoflagellates) and the thermodynamics of the sea ice cover (cold and not flooded stations vs. warm and flooded stations) were major factors controlling the DMSO dynamics in East Antarctic sea ice at that period of the year. [1] Hatton et al., 1994. Anal. Chem., 66, 4093-4096. [2] Lee et al., 2001. J. Phycol., 37, 488-499.

  4. A persistent and dynamic East Greenland Ice Sheet over the past 7.5 million years.

    PubMed

    Bierman, Paul R; Shakun, Jeremy D; Corbett, Lee B; Zimmerman, Susan R; Rood, Dylan H

    2016-12-07

    Climate models show that ice-sheet melt will dominate sea-level rise over the coming centuries, but our understanding of ice-sheet variations before the last interglacial 125,000 years ago remains fragmentary. This is because terrestrial deposits of ancient glacial and interglacial periods are overrun and eroded by more recent glacial advances, and are therefore usually rare, isolated and poorly dated. In contrast, material shed almost continuously from continents is preserved as marine sediment that can be analysed to infer the time-varying state of major ice sheets. Here we show that the East Greenland Ice Sheet existed over the past 7.5 million years, as indicated by beryllium and aluminium isotopes ((10)Be and (26)Al) in quartz sand removed by deep, ongoing glacial erosion on land and deposited offshore in the marine sedimentary record. During the early Pleistocene epoch, ice cover in East Greenland was dynamic; in contrast, East Greenland was mostly ice-covered during the mid-to-late Pleistocene. The isotope record we present is consistent with distinct signatures of changes in ice sheet behaviour coincident with major climate transitions. Although our data are continuous, they are from low-deposition-rate sites and sourced only from East Greenland. Consequently, the signal of extensive deglaciation during short, intense interglacials could be missed or blurred, and we cannot distinguish between a remnant ice sheet in the East Greenland highlands and a diminished continent-wide ice sheet. A clearer constraint on the behaviour of the ice sheet during past and, ultimately, future interglacial warmth could be produced by (10)Be and (26)Al records from a coring site with a higher deposition rate. Nonetheless, our analysis challenges the possibility of complete and extended deglaciation over the past several million years.

  5. A persistent and dynamic East Greenland Ice Sheet over the past 7.5 million years

    NASA Astrophysics Data System (ADS)

    Bierman, Paul R.; Shakun, Jeremy D.; Corbett, Lee B.; Zimmerman, Susan R.; Rood, Dylan H.

    2016-12-01

    Climate models show that ice-sheet melt will dominate sea-level rise over the coming centuries, but our understanding of ice-sheet variations before the last interglacial 125,000 years ago remains fragmentary. This is because terrestrial deposits of ancient glacial and interglacial periods are overrun and eroded by more recent glacial advances, and are therefore usually rare, isolated and poorly dated. In contrast, material shed almost continuously from continents is preserved as marine sediment that can be analysed to infer the time-varying state of major ice sheets. Here we show that the East Greenland Ice Sheet existed over the past 7.5 million years, as indicated by beryllium and aluminium isotopes (10Be and 26Al) in quartz sand removed by deep, ongoing glacial erosion on land and deposited offshore in the marine sedimentary record. During the early Pleistocene epoch, ice cover in East Greenland was dynamic; in contrast, East Greenland was mostly ice-covered during the mid-to-late Pleistocene. The isotope record we present is consistent with distinct signatures of changes in ice sheet behaviour coincident with major climate transitions. Although our data are continuous, they are from low-deposition-rate sites and sourced only from East Greenland. Consequently, the signal of extensive deglaciation during short, intense interglacials could be missed or blurred, and we cannot distinguish between a remnant ice sheet in the East Greenland highlands and a diminished continent-wide ice sheet. A clearer constraint on the behaviour of the ice sheet during past and, ultimately, future interglacial warmth could be produced by 10Be and 26Al records from a coring site with a higher deposition rate. Nonetheless, our analysis challenges the possibility of complete and extended deglaciation over the past several million years.

  6. Ice dynamics of Bowdoin tidewater glacier, Northwest Greenland, from borehole measurements and numerical modelling

    NASA Astrophysics Data System (ADS)

    Seguinot, Julien; Funk, Martin; Ryser, Claudia; Jouvet, Guillaume; Bauder, Andreas; Sugiyama, Shin

    2016-04-01

    The observed rapid retreat of ocean-terminating glaciers in southern Greenland in the last two decades has now propagated to the northwest. Hence, tidewater glaciers in this area, some of which have remain stable for decades, have started retreating rapidly through iceberg calving in recent years, thus allowing a monitoring and investigation of ice dynamical changes starting from the early stages of retreat. Here, we present an ice dynamical study from Bowdoin Glacier, a tidewater outlet glacier located at the northwestern margin of the Greenland Ice Sheet. The glacier surface experiences lowering at a rate of 1.5 m/a since 2007. A rapid calving front retreat of 260 m/a was also observed since 2008, while no significant changes occurred during the previous 20 years. From July 2014 to July 2015, we monitored, 2 km upstream from the calving front, subglacial water pressure changes in boreholes, internal ice deformation through tilt sensors at different depths, englacial ice temperature profiles from the glacier bed to the surface, and high resolution surface motion from GPS records. These measurement show that the glacier is temperate-based, yet internal deformation accounts for about 10 % of the annual surface motion. A seasonal increase in both deformation and sliding at the onset of the melt season is associated with a drop in water pressure in part of the subglacial system. These observations are used to calibrate the Parallel Ice Sheet Model (PISM) for numerical simulations of ice flow in the Bowdoin Glacier catchment, aiming for a better understanding of iceberg calving processes in relation to changes in internal and basal ice dynamics.

  7. Full-field predictions of ice dynamic recrystallisation under simple shear conditions

    NASA Astrophysics Data System (ADS)

    Llorens, Maria-Gema; Griera, Albert; Bons, Paul D.; Lebensohn, Ricardo A.; Evans, Lynn A.; Jansen, Daniela; Weikusat, Ilka

    2016-09-01

    Understanding the flow of ice on the microstructural scale is essential for improving our knowledge of large-scale ice dynamics, and thus our ability to predict future changes of ice sheets. Polar ice behaves anisotropically during flow, which can lead to strain localisation. In order to study how dynamic recrystallisation affects to strain localisation in deep levels of polar ice sheets, we present a series of numerical simulations of ice polycrystals deformed under simple-shear conditions. The models explicitly simulate the evolution of microstructures using a full-field approach, based on the coupling of a viscoplastic deformation code (VPFFT) with dynamic recrystallisation codes. The simulations provide new insights into the distribution of stress, strain rate and lattice orientation fields with progressive strain, up to a shear strain of three. Our simulations show how the recrystallisation processes have a strong influence on the resulting microstructure (grain size and shape), while the development of lattice preferred orientations (LPO) appears to be less affected. Activation of non-basal slip systems is enhanced by recrystallisation and induces a strain hardening behaviour up to the onset of strain localisation and strain weakening behaviour. Simulations demonstrate that the strong intrinsic anisotropy of ice crystals is transferred to the polycrystalline scale and results in the development of strain localisation bands than can be masked by grain boundary migration. Therefore, the finite-strain history is non-directly reflected by the final microstructure. Masked strain localisation can be recognised in ice cores, such as the EDML, from the presence of stepped boundaries, microshear and grains with zig-zag geometries.

  8. Modeling surface energy fluxes and thermal dynamics of a seasonally ice-covered hydroelectric reservoir.

    PubMed

    Wang, Weifeng; Roulet, Nigel T; Strachan, Ian B; Tremblay, Alain

    2016-04-15

    The thermal dynamics of human created northern reservoirs (e.g., water temperatures and ice cover dynamics) influence carbon processing and air-water gas exchange. Here, we developed a process-based one-dimensional model (Snow, Ice, WAater, and Sediment: SIWAS) to simulate a full year's surface energy fluxes and thermal dynamics for a moderately large (>500km(2)) boreal hydroelectric reservoir in northern Quebec, Canada. There is a lack of climate and weather data for most of the Canadian boreal so we designed SIWAS with a minimum of inputs and with a daily time step. The modeled surface energy fluxes were consistent with six years of observations from eddy covariance measurements taken in the middle of the reservoir. The simulated water temperature profiles agreed well with observations from over 100 sites across the reservoir. The model successfully captured the observed annual trend of ice cover timing, although the model overestimated the length of ice cover period (15days). Sensitivity analysis revealed that air temperature significantly affects the ice cover duration, water and sediment temperatures, but that dissolved organic carbon concentrations have little effect on the heat fluxes, and water and sediment temperatures. We conclude that the SIWAS model is capable of simulating surface energy fluxes and thermal dynamics for boreal reservoirs in regions where high temporal resolution climate data are not available. SIWAS is suitable for integration into biogeochemical models for simulating a reservoir's carbon cycle.

  9. Glacier velocities and dynamic ice discharge from the Queen Elizabeth Islands, Nunavut, Canada

    NASA Astrophysics Data System (ADS)

    Van Wychen, Wesley; Burgess, David O.; Gray, Laurence; Copland, Luke; Sharp, Martin; Dowdeswell, Julian A.; Benham, Toby J.

    2014-01-01

    Recent studies indicate an increase in glacier mass loss from the Canadian Arctic Archipelago as a result of warmer summer air temperatures. However, no complete assessment of dynamic ice discharge from this region exists. We present the first complete surface velocity mapping of all ice masses in the Queen Elizabeth Islands and show that these ice masses discharged ~2.6 ± 0.8 Gt a-1 of ice to the oceans in winter 2012. Approximately 50% of the dynamic discharge was channeled through non surge-type Trinity and Wykeham Glaciers alone. Dynamic discharge of the surge-type Mittie Glacier varied from 0.90 ± 0.09 Gt a-1 during its 2003 surge to 0.02 ± 0.02 Gt a-1 during quiescence in 2012, highlighting the importance of surge-type glaciers for interannual variability in regional mass loss. Queen Elizabeth Islands glaciers currently account for ~7.5% of reported dynamic discharge from Arctic ice masses outside Greenland.

  10. Generating Gaits for Biped Robots Using Multiple Dynamic Passivization of Joint Control

    NASA Astrophysics Data System (ADS)

    Ishida, Minoru; Kato, Shohei; Kanoh, Masayoshi; Itoh, Hidenori

    In the research field of bipedal locomotion, a central pattern generator (CPG) and passive dynamic walking (PDW) have attracted much attention. In this paper, we describe a motion control system for biped robots based on dynamic joint passivization. Our motion control system is based on a mixture of the CPG and PDW, that is, the multiple dynamic passivization of joint control (MDPJC). Our intention is to make the joint control of the swing leg temporarily passive in the swing leg phase. The important part is the passive phase time and the switch timings of the joint control. We optimize the switch timing parameters using simulated annealing with advanced adaptive neighborhood (SA/AAN). Experiments using the motion control system based on multiple dynamic passivization of joint control successfully generated energy efficient walking and enabled superior gaits.

  11. DYNAMIC BEHAVIOR OF CONCRETE GRAVITY DAM ON JOINTED ROCK FOUNDATION DURING LARGE-SCALE EARTHQUAKE

    NASA Astrophysics Data System (ADS)

    Kimata, Hiroyuki; Fujita, Yutaka; Horii, Hideyuki; Yazdani, Mahmoud

    Dynamic cracking analysis of concrete gravity dam has been carried out during large-scale earthquake, considering the progressive failure of jointed rock foundation. Firstly, in order to take into account the progressive failure of rock foundation, the constitutive law of jointed rock is assumed and its validity is evaluated by simulation analysis based on the past experimental model. Finally, dynamic cracking analysis of 100-m high dam model is performed, using the previously proposed approach with tangent stiffness-proportional damping to express the propagation behavior of crack and the constitutive law of jointed rock. The crack propagation behavior of dam body and the progressive failure of jointed rock foundation are investigated.

  12. Dynamic evaluation of a traction-drive joint for space telerobots

    NASA Technical Reports Server (NTRS)

    Desilva, Clarence W.; Hankins, Walter W., III

    1988-01-01

    Presented is an analysis and evaluation of a prototype traction-drive joint for robotic manipulators, developed under NASA sponsorship. A dynamic model is developed using the Lagrange formulation. Controllability, observability, dynamic stability, and response characteristics of the joint to test inputs are studied. A linear quadratic regulator (LQR) is implemented on the joint model to determine a basis for evaluating the performance of the traction-drive joint under servo control. An evaluation of the results and directions for future investigations are presented.

  13. Kinematic and dynamic analysis of an anatomically based knee joint.

    PubMed

    Lee, Kok-Meng; Guo, Jiajie

    2010-05-07

    This paper presents a knee-joint model to provide a better understanding on the interaction between natural joints and artificial mechanisms for design and control of rehabilitation exoskeletons. The anatomically based knee model relaxes several commonly made assumptions that approximate a human knee as engineering pin-joint in exoskeleton design. Based on published MRI data, we formulate the kinematics of a knee-joint and compare three mathematical approximations; one model bases on two sequential circles rolling a flat plane; and the other two are mathematically differentiable ellipses-based models with and without sliding at the contact. The ellipses-based model taking sliding contact into accounts shows that the rolling-sliding ratio of a knee-joint is not a constant but has an average value consistent with published measurements. This knee-joint kinematics leads to a physically more accurate contact-point trajectory than methods based on multiple circles or lines, and provides a basis to derive a knee-joint kinetic model upon which the effects of a planar exoskeleton mechanism on the internal joint forces and torque during flexion can be numerically investigated. Two different knee-joint kinetic models (pin-joint approximation and anatomically based model) are compared against a condition with no exoskeleton. The leg and exoskeleton form a closed kinematic chain that has a significant effect on the joint forces in the knee. Human knee is more tolerant than pin-joint in negotiating around a singularity but its internal forces increase with the exoskeleton mass-to-length ratio. An oversimplifying pin-joint approximation cannot capture the finite change in the knee forces due to the singularity effect.

  14. Ice-nucleating bacteria control the order and dynamics of interfacial water

    DOE PAGES

    Pandey, Ravindra; Usui, Kota; Livingstone, Ruth A.; ...

    2016-04-22

    Ice-nucleating organisms play important roles in the environment. With their ability to induce ice formation at temperatures just below the ice melting point, bacteria such as Pseudomonas syringae attack plants through frost damage using specialized ice-nucleating proteins. Besides the impact on agriculture and microbial ecology, airborne P. syringae can affect atmospheric glaciation processes, with consequences for cloud evolution, precipitation, and climate. Biogenic ice nucleation is also relevant for artificial snow production and for biomimetic materials for controlled interfacial freezing. We use interface-specific sum frequency generation (SFG) spectroscopy to show that hydrogen bonding at the water-bacteria contact imposes structural ordering onmore » the adjacent water network. Experimental SFG data and molecular dynamics simulations demonstrate that ice active sites within P. syringae feature unique hydrophilic-hydrophobic patterns to enhance ice nucleation. Finally, the freezing transition is further facilitated by the highly effective removal of latent heat from the nucleation site, as apparent from time-resolved SFG spectroscopy.« less

  15. Induced ice melting by the snow flea antifreeze protein from molecular dynamics simulations.

    PubMed

    Todde, Guido; Whitman, Christopher; Hovmöller, Sven; Laaksonen, Aatto

    2014-11-26

    Antifreeze proteins (AFP) allow different life forms, insects as well as fish and plants, to survive in subzero environments. AFPs prevent freezing of the physiological fluids. We have studied, through molecular dynamics simulations, the behavior of the small isoform of the AFP found in the snow flea (sfAFP), both in water and at the ice/water interface, of four different ice planes. In water at room temperature, the structure of the sfAFP is found to be slightly unstable. The loop between two polyproline II helices has large fluctuations as well as the C-terminus. Torsional angle analyses show a decrease of the polyproline II helix area in the Ramachandran plots. The protein structure instability, in any case, should not affect its antifreeze activity. At the ice/water interface the sfAFP triggers local melting of the ice surface. Bipyramidal, secondary prism, and prism ice planes melt in the presence of AFP at temperatures below the melting point of ice. Only the basal plane is found to be stable at the same temperatures, indicating an adsorption of the sfAFP on this ice plane as confirmed by experimental evidence.

  16. Ice-nucleating bacteria control the order and dynamics of interfacial water.

    PubMed

    Pandey, Ravindra; Usui, Kota; Livingstone, Ruth A; Fischer, Sean A; Pfaendtner, Jim; Backus, Ellen H G; Nagata, Yuki; Fröhlich-Nowoisky, Janine; Schmüser, Lars; Mauri, Sergio; Scheel, Jan F; Knopf, Daniel A; Pöschl, Ulrich; Bonn, Mischa; Weidner, Tobias

    2016-04-01

    Ice-nucleating organisms play important roles in the environment. With their ability to induce ice formation at temperatures just below the ice melting point, bacteria such as Pseudomonas syringae attack plants through frost damage using specialized ice-nucleating proteins. Besides the impact on agriculture and microbial ecology, airborne P. syringae can affect atmospheric glaciation processes, with consequences for cloud evolution, precipitation, and climate. Biogenic ice nucleation is also relevant for artificial snow production and for biomimetic materials for controlled interfacial freezing. We use interface-specific sum frequency generation (SFG) spectroscopy to show that hydrogen bonding at the water-bacteria contact imposes structural ordering on the adjacent water network. Experimental SFG data and molecular dynamics simulations demonstrate that ice-active sites within P. syringae feature unique hydrophilic-hydrophobic patterns to enhance ice nucleation. The freezing transition is further facilitated by the highly effective removal of latent heat from the nucleation site, as apparent from time-resolved SFG spectroscopy.

  17. Ice-nucleating bacteria control the order and dynamics of interfacial water

    PubMed Central

    Pandey, Ravindra; Usui, Kota; Livingstone, Ruth A.; Fischer, Sean A.; Pfaendtner, Jim; Backus, Ellen H. G.; Nagata, Yuki; Fröhlich-Nowoisky, Janine; Schmüser, Lars; Mauri, Sergio; Scheel, Jan F.; Knopf, Daniel A.; Pöschl, Ulrich; Bonn, Mischa; Weidner, Tobias

    2016-01-01

    Ice-nucleating organisms play important roles in the environment. With their ability to induce ice formation at temperatures just below the ice melting point, bacteria such as Pseudomonas syringae attack plants through frost damage using specialized ice-nucleating proteins. Besides the impact on agriculture and microbial ecology, airborne P. syringae can affect atmospheric glaciation processes, with consequences for cloud evolution, precipitation, and climate. Biogenic ice nucleation is also relevant for artificial snow production and for biomimetic materials for controlled interfacial freezing. We use interface-specific sum frequency generation (SFG) spectroscopy to show that hydrogen bonding at the water-bacteria contact imposes structural ordering on the adjacent water network. Experimental SFG data and molecular dynamics simulations demonstrate that ice-active sites within P. syringae feature unique hydrophilic-hydrophobic patterns to enhance ice nucleation. The freezing transition is further facilitated by the highly effective removal of latent heat from the nucleation site, as apparent from time-resolved SFG spectroscopy. PMID:27152346

  18. Ice-nucleating bacteria control the order and dynamics of interfacial water

    SciTech Connect

    Pandey, Ravindra; Usui, Kota; Livingstone, Ruth A.; Fischer, Sean A.; Pfaendtner, Jim; Backus, Ellen H. G.; Nagata, Yuki; Frohlich-Nowoisky, Janine; Schmuser, Lars; Mauri, Sergio; Scheel, Jan F.; Knopf, Daniel A.; Poschl, Ulrich; Bonn, Mischa; Weidner, Tobias

    2016-04-22

    Ice-nucleating organisms play important roles in the environment. With their ability to induce ice formation at temperatures just below the ice melting point, bacteria such as Pseudomonas syringae attack plants through frost damage using specialized ice-nucleating proteins. Besides the impact on agriculture and microbial ecology, airborne P. syringae can affect atmospheric glaciation processes, with consequences for cloud evolution, precipitation, and climate. Biogenic ice nucleation is also relevant for artificial snow production and for biomimetic materials for controlled interfacial freezing. We use interface-specific sum frequency generation (SFG) spectroscopy to show that hydrogen bonding at the water-bacteria contact imposes structural ordering on the adjacent water network. Experimental SFG data and molecular dynamics simulations demonstrate that ice active sites within P. syringae feature unique hydrophilic-hydrophobic patterns to enhance ice nucleation. Finally, the freezing transition is further facilitated by the highly effective removal of latent heat from the nucleation site, as apparent from time-resolved SFG spectroscopy.

  19. Diffusion of molecules in the bulk of a low density amorphous ice from molecular dynamics simulations.

    PubMed

    Ghesquière, P; Mineva, T; Talbi, D; Theulé, P; Noble, J A; Chiavassa, T

    2015-05-07

    The diffusion of molecules in interstellar ice is a fundamental phenomenon to take into account while studying the formation of complex molecules in this ice. This work presents a theoretical study on the diffusion of H2O, NH3, CO2, CO, and H2CO in the bulk of a low density amorphous (LDA) ice, while taking into account the physical conditions prevailing in space, i.e. temperatures below 150 K and extremely low pressure. This study was undertaken by means of molecular dynamics simulations. For CO2 for which no experimental data were available we conducted our own experiments. From our calculations we show that, at low temperatures, the diffusion of molecules in the bulk of a LDA ice is driven by the self-diffusion of water molecules in the ice. With this study we demonstrate that molecular dynamics allows the calculation of diffusion coefficients for small molecules in LDA ice that are convincingly comparable to experimentally measured diffusion coefficients. We also provide diffusion coefficients for a series of molecules of astrochemical interest.

  20. Computational analysis of dynamic recrystallization of ice aggregates during viscoplastic deformation

    NASA Astrophysics Data System (ADS)

    Llorens, Maria-Gema; Griera, Albert; Weikusat, Ilka; Bons, Paul; Lebensohn, Ricardo; Evans, Lynn; Piazolo, Sandra

    2015-04-01

    Ice is a common mineral at the Earth's surface. How much ice is stored in the Greenland and Antarctic ice sheets depends on its mechanical properties. Therefore properties of ice directly impact on human society through its role in controlling sea level. The bulk behaviour of large ice masses is the result of the behaviour of the ensemble of individual ice grains. This is strongly influenced by the viscoplastic anisotropy of these grains and their lattice orientation. Numerical modelling provides a better insight into the mechanics of ice from the micro to the ice sheet scale. We present numerical simulations that predict the microstructural evolution of an aggregate of pure ice grains at different strain rates. We simulate co-axial deformation and dynamic recrystallization up to large strain using a full-field approach. The crystal plasticity code (Lebensohn et al., 2009) is used to calculate the response of a polycrystalline aggregate that deforms by purely dislocation glide, applying a Fast Fourier Transform (FFT). This code is coupled with the ELLE microstructural modelling platform to include intracrystalline recovery, as well as grain boundary migration driven by the reduction of surface and strain energies. The results show a strong effect of recrystallization on the final microstructure, producing larger and more equiaxed grains, with smooth boundaries. This effect does not significantly modify the single-maximum pattern of c-axes that are distributed at a low angle to the shortening direction. However, in experiments with significant recrystallization the a-axes rotate towards the elongation axis at the same time as the c-axes rotate towards the compression axis. If slip systems on prismatic and/or pyramidal planes are active, it is thought that a-axes gradually concentrate with depth (Miyamoto, 2005). The bulk activity of the slip systems is different depending on the relative activity of deformation versus recrystallization: the non-basal slip systems

  1. Low field domain wall dynamics in artificial spin-ice basis structure

    SciTech Connect

    Kwon, J.; Goolaup, S.; Lim, G. J.; Kerk, I. S.; Lew, W. S.; Chang, C. H.; Roy, K.

    2015-10-28

    Artificial magnetic spin-ice nanostructures provide an ideal platform for the observation of magnetic monopoles. The formation of a magnetic monopole is governed by the motion of a magnetic charge carrier via the propagation of domain walls (DWs) in a lattice. To date, most experiments have been on the static visualization of DW propagation in the lattice. In this paper, we report on the low field dynamics of DW in a unit spin-ice structure measured by magnetoresistance changes. Our results show that reversible DW propagation can be initiated within the spin-ice basis. The initial magnetization configuration of the unit structure strongly influences the direction of DW motion in the branches. Single or multiple domain wall nucleation can be induced in the respective branches of the unit spin ice by the direction of the applied field.

  2. Overview of ICE Project: Integration of Computational Fluid Dynamics and Experiments

    NASA Technical Reports Server (NTRS)

    Stegeman, James D.; Blech, Richard A.; Babrauckas, Theresa L.; Jones, William H.

    2001-01-01

    Researchers at the NASA Glenn Research Center have developed a prototype integrated environment for interactively exploring, analyzing, and validating information from computational fluid dynamics (CFD) computations and experiments. The Integrated CFD and Experiments (ICE) project is a first attempt at providing a researcher with a common user interface for control, manipulation, analysis, and data storage for both experiments and simulation. ICE can be used as a live, on-tine system that displays and archives data as they are gathered; as a postprocessing system for dataset manipulation and analysis; and as a control interface or "steering mechanism" for simulation codes while visualizing the results. Although the full capabilities of ICE have not been completely demonstrated, this report documents the current system. Various applications of ICE are discussed: a low-speed compressor, a supersonic inlet, real-time data visualization, and a parallel-processing simulation code interface. A detailed data model for the compressor application is included in the appendix.

  3. Dynamics of the sputtering of water from ice films by collisions with energetic xenon atoms.

    PubMed

    Killelea, Daniel R; Gibson, K D; Yuan, Hanqiu; Becker, James S; Sibener, S J

    2012-04-14

    The flow of energy from the impact site of a heavy, translationally energetic xenon atom on an ice surface leads to several non-equilibrium events. The central focus of this paper is on the collision-induced desorption (sputtering) of water molecules into the gas-phase from the ice surface. Sputtering is strongly activated with respect to xenon translational energy, and a threshold for desorption was observed. To best understand these results, we discuss our findings in the context of other sputtering studies of molecular solids. The sputtering yield is quite small; differential measurements of the energy of xenon scattered from ice surfaces show that the ice efficiently accommodates the collisional energy. These results are important as they quantitatively elucidate the dynamics of such sputtering events, with implications for energetic non-equilibrium processes at interfaces.

  4. Injuries and disorders among young ice skaters: relationship with generalized joint laxity and tightness.

    PubMed

    Okamura, Shinobu; Wada, Naoki; Tazawa, Masayuki; Sohmiya, Makoto; Ibe, Yoko; Shimizu, Toru; Usuda, Shigeru; Shirakura, Kenji

    2014-01-01

    This study retrospectively investigated 192 teenage speed and figure skaters with prior injuries documented by an athletes' questionnaire, who underwent a physical examination to assess their muscle tightness and generalized joint laxity. In all athletes, the degree of muscle tightness and joint laxity were measured by a standardized physical examination. A descriptive report of the types of injuries showed a predominance of fractures, ligament injuries, enthesitis, and lower back pain. Approximately 5% of all skaters tested positive for tightness, while 25.8% of figure skaters and 15.2% of speed skaters had generalized ligamentous laxity. Statistical testing showed an association between ankle sprains and muscle tightness, and an association between knee enthesitis and muscle tightness in skating athletes. There was also an association between lower back pain and generalized joint laxity, which held true only for the male skaters.

  5. Injuries and disorders among young ice skaters: relationship with generalized joint laxity and tightness

    PubMed Central

    Okamura, Shinobu; Wada, Naoki; Tazawa, Masayuki; Sohmiya, Makoto; Ibe, Yoko; Shimizu, Toru; Usuda, Shigeru; Shirakura, Kenji

    2014-01-01

    This study retrospectively investigated 192 teenage speed and figure skaters with prior injuries documented by an athletes’ questionnaire, who underwent a physical examination to assess their muscle tightness and generalized joint laxity. In all athletes, the degree of muscle tightness and joint laxity were measured by a standardized physical examination. A descriptive report of the types of injuries showed a predominance of fractures, ligament injuries, enthesitis, and lower back pain. Approximately 5% of all skaters tested positive for tightness, while 25.8% of figure skaters and 15.2% of speed skaters had generalized ligamentous laxity. Statistical testing showed an association between ankle sprains and muscle tightness, and an association between knee enthesitis and muscle tightness in skating athletes. There was also an association between lower back pain and generalized joint laxity, which held true only for the male skaters. PMID:25177155

  6. Subglacial Volcanism in West-Antarctica - A Geologic and Ice Dynamical Perspective

    NASA Astrophysics Data System (ADS)

    Vogel, S. W.; Tulaczyk, S.; Carter, S.; Renne, P.; Turrin, B. D.; Joughin, I.

    2004-12-01

    Subglacial volcanic eruptions may increase the contribution of the West-Antarctic Ice-Sheet (WAIS) to global sea-level rise in the near-future by enhancing basal melt water production and ice flow lubrication. Geophysical data have led scientists to believe that the ice sheet may be located over an extensive, young volcanic province containing ~1 million cubic kilometers of basalts (Behrendt, 1964; Behrendt et. al., 1991; 1995; 1998). While not all scientists may recognize this theory of widespread subglacial volcanism, so far no scientific paper has challenged its existence. Here we present the first geologic constraints on the presence/absence of widespread Late Cenozoic subglacial volcanism beneath the WAIS and investigate the potential influence of an individual subglacial volcano (Blankenship et. al., 1993) on the flow dynamic of WAIS. Properties of subglacial sediments indicate limited presence of subglacial volcanic rocks. Moreover, the only two basaltic pebbles, recovered from the region, are of Mesozoic-Paleozoic age (~100 to ~500 million years). While these findings reduce the potential for widespread near-future increases in ice discharge from WAIS due to eruptions of subglacial volcanoes, they do not rule out the presence of individual hot spots associated with volcanic centers beneath the WAIS. Fuel for the existence of a proposed volcano (Mt. Casertz) on the Whitmore Mountain Ross Sea Transitional Crust (WRT; Blankenship et. al., 1993), in the southern part of the WAIS, comes from thermo-dynamical modeling in comparison with observed ice velocities. Ice velocities (Joughin et. al., 1999; 2002) downstream of Mt. Casertz indicate significant basal sliding, where thermo-dynamical models suggest that the ice sheet is frozen to its base. Routing of basal melt water, produced in the vicinity of Mt. Casertz, may lubricate the ice base in parts of the WRT, thus enabling basal sliding and enhancing the discharge of ice in this sector of the WAIS. The only

  7. Migration phenology and seasonal fidelity of an Arctic marine predator in relation to sea ice dynamics.

    PubMed

    Cherry, Seth G; Derocher, Andrew E; Thiemann, Gregory W; Lunn, Nicholas J

    2013-07-01

    Understanding how seasonal environmental conditions affect the timing and distribution of synchronized animal movement patterns is a central issue in animal ecology. Migration, a behavioural adaptation to seasonal environmental fluctuations, is a fundamental part of the life history of numerous species. However, global climate change can alter the spatiotemporal distribution of resources and thus affect the seasonal movement patterns of migratory animals. We examined sea ice dynamics relative to migration patterns and seasonal geographical fidelity of an Arctic marine predator, the polar bear (Ursus maritimus). Polar bear movement patterns were quantified using satellite-linked telemetry data collected from collars deployed between 1991-1997 and 2004-2009. We showed that specific sea ice characteristics can predict the timing of seasonal polar bear migration on and off terrestrial refugia. In addition, fidelity to specific onshore regions during the ice-free period was predicted by the spatial pattern of sea ice break-up but not by the timing of break-up. The timing of migration showed a trend towards earlier arrival of polar bears on shore and later departure from land, which has been driven by climate-induced declines in the availability of sea ice. Changes to the timing of migration have resulted in polar bears spending progressively longer periods of time on land without access to sea ice and their marine mammal prey. The links between increased atmospheric temperatures, sea ice dynamics, and the migratory behaviour of an ice-dependent species emphasizes the importance of quantifying and monitoring relationships between migratory wildlife and environmental cues that may be altered by climate change.

  8. Towards an annually-resolved record of Lateglacial Patagonian ice sheet dynamics using glaciolacustrine varves

    NASA Astrophysics Data System (ADS)

    Bendle, Jacob; Palmer, Adrain; Thorndycraft, Varyl

    2016-04-01

    Proglacial sedimentary archives, in particular, glaciolacustrine varve sequences, offer the potential for detailed reconstructions of past ice sheet dynamics. Specifically, glaciolacustrine varves (i) allow reconstructions of sediment (and thus meltwater) influx at annual and even sub-annual resolution; and (ii) provide a continuous, annually-resolved chronology to estimate rates of change and/or the duration of significant events in the deglaciation of a basin. In South America, glacial geologists have relied heavily on cosmogenic nuclide exposure dating to construct chronologies for palaeoglaciological activity. Whilst effective, the typical uncertainties associated with boulder dating methods (±10%) preclude the investigation of short-term (e.g. ≤ centennial-scale) glacier and/or climatic change(s), which are shown to be important at modern ice-margins. Moreover, moraine chronologies are fragmentary, and inherently biased towards episodes of positive glacier mass balance (i.e. moraine construction), and thus limit our understanding of ice sheet retreat dynamics. By contrast, long, continuous, high-resolution (i.e. varve) palaeolimnological records have the potential to significantly refine models of ice sheet deglaciation. In this talk, we present data from Valle Fenix Chico, in the Lago Buenos Aires (LBA) basin (-46.57°S -71.07°W), in which ice-contact Glacial Lake Buenos Aires formed as the LBA ice lobe of Patagonian ice sheet withdrew from its innermost LGM moraine (~17.2 ± 0.9 ka). Thick (>40m) sequences of laminated glaciolacustrine sediment were deposited in the palaeolake, and are now exposed in a sub-aerial canyon that was cut when the lake drained. We report on the detailed macro- and micro-facies of the LBA sediments. In particular, we: (1) develop a process model for the formation of silt and clay couplets, which suggests an annual (varve) origin; (2) present varve series for the initial phase (~1kyr) of LBA ice lobe deglaciation.

  9. The hierarchical structure of glacial climatic oscillations: Interactions between ice-sheet dynamics and climate

    SciTech Connect

    Paillard, D.

    1995-04-01

    Abrupt climatic oscillations around the North Atlantic have been identified recently in Greenland ice cores as well as in North Atlantic marine sediment cores. The good correlation between the {open_quote}Dansgaard Oeschger events{close_quote} in the ice and the {open_quote}Heinrich events{close_quote} in the ocean suggests climate, in the North Atlantic region, underwent several massive reorganizations in the last glacial period. A characteristic feature seems to be their hierarchical structure. Every 7 to 10-thousand years, when the temperature is close to its minimum, the ice-sheet undergoes a massive iceberg discharge. This Heinrich event is followed by an abrupt warming. then by other oscillations, each lasting between one and two thousand years. These secondary oscillations do not have a clear signature in marine sediments but constitute most of the{open_quote} Dansgaard-Oeschger events{close_quote} found in the ice. A simplified model coupling an ice-sheet and an ocean basin, to illustrate how the interactions between these two components can lead to such a hierarchical structure. The ice-sheet model exhibits internal oscillations composed of growing phases and basal ice melting phases that induce massive iceberg discharges. These fresh water inputs in the ocean stop for a moment the thermohaline circulation, enhancing the temperature contrast between low- and high-latitudes. Just after this event, the thermohaline circulation restarts and an abrupt warming of high-latitude regions is observed. For some parameter values, these warmer temperatures have some influence on the ice-sheet, inducing secondary oscillations similar to those found in paleoclimatic records. Although the mechanism presented here may be too grossly simplified. it nevertheless underlines the potential importance of the coupling between ice-sheet dynamics and oceanic thermohaline circulation on the structure of the climatic records during the last glacial period. 33 refs., 14 figs., 1 tab.

  10. Study of the dynamic behavior of a bolted joint under heavy loadings

    NASA Astrophysics Data System (ADS)

    Daouk, Sami; Louf, François; Cluzel, Christophe; Dorival, Olivier; Champaney, Laurent; Audebert, Sylvie

    2017-03-01

    In structural dynamics, the quantification of the quality and reliability of numerical models remains a relevant issue. While the behavior of structures such as beams and plates is generally understood, a large number of industrial structures are bolted assemblies of many components with connections that are not well understood. The main reason for this lack of understanding is that the dynamical behavior of the whole assembly depends critically upon joint conditions, especially under heavy loadings. For the purpose of improving our understanding and the development of pertinent models, a dynamic test bed, based on a bolted structure, is designed and modal testing is performed. The configuration of the bolted joint and the level of the loading are the relevant parameters, related to joint conditions, that are considered in this study. The results of the experimental campaign show the variation of the dissipation in a bolted joint and its apparent stiffness as a function of joint conditions.

  11. Effects of ice number concentration on dynamics of a shallow mixed-phase stratiform cloud

    SciTech Connect

    Ovchinnikov, Mikhail; Korolev, Alexei; Fan, Jiwen

    2011-09-17

    Previous modeling studies have shown a high sensitivity of simulated properties of mixed-phase clouds to ice number concentration, Ni, with many models losing their ability to maintain the liquid phase as Ni increases. Although models differ widely at what Ni the mixed-phase cloud becomes unstable, the transition from a mixed-phase to an ice only cloud in many cases occurs over a narrow range of ice concentration. To gain better understanding of this non-linear model behavior, in this study, we analyze simulations of a mixed-phase stratiform Artic cloud observed on 26 April 2008 during recent Indirect and Semi-Direct Aerosol Campaign (ISDAC). The BASE simulation, in which Ni is constrained to match the measured value, produces a long-lived cloud in a quasi steady state similar to that observed. The simulation without the ice (NO_ICE) produces a comparable but slightly thicker cloud because more moisture is kept in the mixed layer due to lack of precipitation. When Ni is quadrupled relative to BASE (HI_ICE), the cloud starts loosing liquid water almost immediately and the liquid water path is reduced by half in less than two hours. The changes in liquid water are accompanied by corresponding reduction in the radiative cooling of the layer and a slow down in the vertical mixing, confirming the important role of interactions among microphysics, radiation and dynamics in this type of clouds. Deviations of BASE and HI_ICE from NO_ICE are used to explore the linearity of the model response to variation in Ni. It is shown that at early stages, changes in liquid and ice water as well as in radiative cooling/heating rates are proportional to the Ni change, while changes in the vertical buoyancy flux are qualitatively different in HI_ICE compared to BASE. Thus, while the positive feedback between the liquid water path and radiative cooling of the cloud layer is essential for glaciation of the cloud at higher Ni, the non-linear (with respect to Ni) reduction in positive

  12. Sensitivity of Barnes Ice Cap, Baffin Island, Canada, to climate state and internal dynamics

    NASA Astrophysics Data System (ADS)

    Gilbert, A.; Flowers, G. E.; Miller, G. H.; Rabus, B. T.; Van Wychen, W.; Gardner, A. S.; Copland, L.

    2016-08-01

    Barnes Ice Cap is a remnant of the Laurentide Ice Sheet, which covered much of northern North America during the Last Glacial Maximum. Barnes reached a quasi-equilibrium state ~2000 years ago and has remained similar in size since then, with a small increase during the Little Ice Age. In this study, we combine historical observations (1960-1980) with more recent satellite and airborne data (1995-2010) to drive a mass balance model coupled to a transient thermomechanical model with an adaptive mesh geometry. The model is used to characterize the current state of the ice cap and to investigate its stability as a function of climate and its own internal dynamics. On millennial time scales we show that ice flow is influenced by adjustment of an unsteady shape, by gently sloping bedrock, and by contrasting viscosities between the Pleistocene and Holocene ice. On shorter time scales, Barnes is affected by surge activity. Sensitivity tests reveal that Barnes experienced climate conditions which enabled its stability 2000 to 3000 years ago but will disappear under current climate conditions in the next millennium.

  13. Maximum extent and dynamic behaviour of the last British-Irish Ice Sheet west of Ireland

    NASA Astrophysics Data System (ADS)

    Peters, Jared Lee; Benetti, Sara; Dunlop, Paul; Ó Cofaigh, Colm

    2015-11-01

    A complete reconstruction of the last British-Irish Ice Sheet (BIIS) is hindered by uncertainty surrounding its offshore extent and dynamic behaviour. This study addresses this problem by reconstructing the depositional history of four sediment cores taken from a series of sinuous glacigenic sediment ridges on the continental shelf west of Ireland. We present new geomorphic, sedimentary and micropaleontological data that record a maximum westward BIIS extent that was at least 80 km farther offshore from any previous estimates. The data suggests that a large ice shelf formed over parts of the shelf prior to retreat. This new data increases the areal extent of grounded BIIS ice by ∼6700 km2 from previous estimates, which represents a ∼3% increase in the Irish Sector of the ice sheet. Three new AMS radiocarbon dates demonstrate for the first time that the BIIS advanced to the shelf edge during last glaciation (Late Midlandian/Late Devensian), with ice advance onto the Porcupine Bank occurring after 24,720 ± 260 yr Cal. BP. Deglaciation was complete by 19,182 ± 155 yr Cal. BP, thus constraining BIIS occupation over the Porcupine Bank to less than 5500 years. Estimated retreat rates of marine-terminating ice across the shelf range from ∼70 to 180 myr-1.

  14. Strain localization and dynamic recrystallization in the ice-air aggregate: a numerical study

    NASA Astrophysics Data System (ADS)

    Steinbach, Florian; Bons, Paul D.; Griera, Albert; Jansen, Daniela; Llorens, Maria-Gema; Roessiger, Jens; Weikusat, Ilka

    2016-12-01

    We performed numerical simulations on the microdynamics of ice with air inclusions as a second phase. Our aim was to investigate the rheological effects of air inclusions and explain the onset of dynamic recrystallization in the permeable firn. The simulations employ a full-field theory crystal plasticity code coupled to codes simulating dynamic recrystallization processes and predict time-resolved microstructure evolution in terms of lattice orientations, strain distribution, grain sizes and grain-boundary network. Results show heterogeneous deformation throughout the simulations and indicate the importance of strain localization controlled by air inclusions. This strain localization gives rise to locally increased energies that drive dynamic recrystallization and induce heterogeneous microstructures that are coherent with natural firn microstructures from EPICA Dronning Maud Land ice coring site in Antarctica. We conclude that although overall strains and stresses in firn are low, strain localization associated with locally increased strain energies can explain the occurrence of dynamic recrystallization.

  15. Highly individualistic rates of plant phenological advance associated with arctic sea ice dynamics.

    PubMed

    Post, Eric; Kerby, Jeffrey; Pedersen, Christian; Steltzer, Heidi

    2016-12-01

    We analysed 12 years of species-specific emergence dates of plants at a Low-Arctic site near Kangerlussuaq, Greenland to investigate associations with sea ice dynamics, a potential contributor to local temperature variation in near-coastal tundra. Species displayed highly variable rates of phenological advance, from a maximum of -2.55 ± 0.17 and -2.93 ± 0.51 d yr(-1) among a graminoid and forb, respectively, to a minimum of -0.55 ± 0.19 d yr(-1) or no advance at all in the two deciduous shrub species. Monthly Arctic-wide sea ice extent was a significant predictor of emergence timing in 10 of 14 species. Despite variation in rates of advance among species, these rates were generally greatest in the earliest emerging species, for which monthly sea ice extent was also the primary predictor of emergence. Variation among species in rates of phenological advance reshuffled the phenological community, with deciduous shrubs leafing out progressively later relative to forbs and graminoids. Because early species advanced more rapidly than late species, and because rates of advance were greatest in species for which emergence phenology was associated with sea ice dynamics, accelerating sea ice decline may contribute to further divergence between early- and late-emerging species in this community.

  16. Polar bear population dynamics in the southern Beaufort Sea during a period of sea ice decline

    USGS Publications Warehouse

    Bromaghin, Jeffrey F.; McDonald, Trent L.; Stirling, Ian; Derocher, Andrew E.; Richardson, Evan S.; Regehr, Eric V.; Douglas, David C.; Durner, George M.; Atwood, Todd C.; Amstrup, Steven C.

    2015-01-01

    In the southern Beaufort Sea of the United States and Canada, prior investigations have linked declines in summer sea ice to reduced physical condition, growth, and survival of polar bears (Ursus maritimus). Combined with projections of population decline due to continued climate warming and the ensuing loss of sea ice habitat, those findings contributed to the 2008 decision to list the species as threatened under the U.S. Endangered Species Act. Here, we used mark–recapture models to investigate the population dynamics of polar bears in the southern Beaufort Sea from 2001 to 2010, years during which the spatial and temporal extent of summer sea ice generally declined. Low survival from 2004 through 2006 led to a 25–50% decline in abundance. We hypothesize that low survival during this period resulted from (1) unfavorable ice conditions that limited access to prey during multiple seasons; and possibly, (2) low prey abundance. For reasons that are not clear, survival of adults and cubs began to improve in 2007 and abundance was comparatively stable from 2008 to 2010, with ~900 bears in 2010 (90% CI 606–1212). However, survival of subadult bears declined throughout the entire period. Reduced spatial and temporal availability of sea ice is expected to increasingly force population dynamics of polar bears as the climate continues to warm. However, in the short term, our findings suggest that factors other than sea ice can influence survival. A refined understanding of the ecological mechanisms underlying polar bear population dynamics is necessary to improve projections of their future status and facilitate development of management strategies.

  17. Polar bear population dynamics in the southern Beaufort Sea during a period of sea ice decline.

    PubMed

    Bromaghin, Jeffrey F; Mcdonald, Trent L; Stirling, Ian; Derocher, Andrew E; Richardson, Evan S; Regehr, Eric V; Douglas, David C; Durner, George M; Atwood, Todd; Amstrup, Steven C

    2015-04-01

    In the southern Beaufort Sea of the United States and Canada, prior investigations have linked declines in summer sea ice to reduced physical condition, growth, and survival of polar bears (Ursus maritimus). Combined with projections of population decline due to continued climate warming and the ensuing loss of sea ice habitat, those findings contributed to the 2008 decision to list the species as threatened under the U.S. Endangered Species Act. Here, we used mark-recapture models to investigate the population dynamics of polar bears in the southern Beaufort Sea from 2001 to 2010, years during which the spatial and temporal extent of summer sea ice generally declined. Low survival from 2004 through 2006 led to a 25-50% decline in abundance. We hypothesize that low survival during this period resulted from (1) unfavorable ice conditions that limited access to prey during multiple seasons; and possibly, (2) low prey abundance. For reasons that are not clear, survival of adults and cubs began to improve in 2007 and abundance was comparatively stable from 2008 to 2010, with ~900 bears in 2010 (90% CI 606-1212). However, survival of subadult bears declined throughout the entire period. Reduced spatial and temporal availability of sea ice is expected to increasingly force population dynamics of polar bears as the climate continues to warm. However, in the short term, our findings suggest that factors other than sea ice can influence survival. A refined understanding of the ecological mechanisms underlying polar bear population dynamics is necessary to improve projections of their future status and facilitate development of management strategies.

  18. A statistical-dynamical approach to represent Greenland ocean-ice sheet interactions

    NASA Astrophysics Data System (ADS)

    Perrette, Mahé; Calov, Reinhard; Ganopolski, Andrey; Robinson, Alex

    2013-04-01

    An understanding of the dynamics of the Greenland ice sheet is fundamental, because of its potential to contribute strongly to future sea level rise. In recent years there has been a discussion about the role of the ocean in the Greenland ice sheet's present and future mass balance. The ocean interacts with the ice sheet's outlet glaciers via the water circulation in the fjords and considerably affects melting at the termini of the outlet glaciers. Processes related to this interaction are difficult to represent in Greenland-wide ice-sheet models because grid resolution of such models is typically 10 km, whereas large fjords are more commonly only 1 to 5 km wide. Local refinement techniques (e.g. finite elements with adaptive mesh) can be a way of addressing that problem but are still computationally expensive to run. Here we propose a simpler, statistical-dynamical approach suited for large ensemble simulations over 100- to 1000-year integration times, in the EMIC spirit: the fjord-outlet glacier system is restricted to its most fundamental dynamics, controlled by a handful of parameters describing the major characteristics of the system. The model has a generic structure, i.e., it is designed such that it applies to every Greenland outlet glacier. Some of its parameters are fixed by using the (little) available observational data - e.g. for Helheim, Kangerdlugssuaq and Jakobshavn Isbrae - other parameters may vary depending on location. It is not our aim to simulate every single small outlet glacier in its full accuracy; but we aim to represent, on average, important characteristics like ice discharge and general advance/retreat rate on a regional scale over major catchment areas. Aspects of the coupling strategy with the 3D ice-sheet model (SICOPOLIS) are discussed, e.g., critical issues such as the treatment of mass balance. Preliminary design and results will be presented.

  19. Correlation and prediction of dynamic human isolated joint strength from lean body mass

    NASA Technical Reports Server (NTRS)

    Pandya, Abhilash K.; Hasson, Scott M.; Aldridge, Ann M.; Maida, James C.; Woolford, Barbara J.

    1992-01-01

    A relationship between a person's lean body mass and the amount of maximum torque that can be produced with each isolated joint of the upper extremity was investigated. The maximum dynamic isolated joint torque (upper extremity) on 14 subjects was collected using a dynamometer multi-joint testing unit. These data were reduced to a table of coefficients of second degree polynomials, computed using a least squares regression method. All the coefficients were then organized into look-up tables, a compact and convenient storage/retrieval mechanism for the data set. Data from each joint, direction and velocity, were normalized with respect to that joint's average and merged into files (one for each curve for a particular joint). Regression was performed on each one of these files to derive a table of normalized population curve coefficients for each joint axis, direction, and velocity. In addition, a regression table which included all upper extremity joints was built which related average torque to lean body mass for an individual. These two tables are the basis of the regression model which allows the prediction of dynamic isolated joint torques from an individual's lean body mass.

  20. Studies on dynamic characteristics of the joint in the aero-engine rotor system

    NASA Astrophysics Data System (ADS)

    Shuguo, Liu; Yanhong, Ma; Dayi, Zhang; Jie, Hong

    2012-05-01

    The joint as a major part of the aero-engine rotating shafts directly influences its rotordynamics and state stability. This paper studies the dynamic effects of structure parameters and the external load on the stiffness and contact state of the rotor joints with nonlinear finite-element method and experiments. And a sensitivity analysis of critical speeds and vibration modes with respect to typical parameters (stiffness of the spline joints) is performed with finite difference methods, through two approaches, i.e. relative sensitivity analysis and absolute sensitivity analysis. The study results show that the stiffness and contact state of joints vary with external loads and geometry structures, and affect the rotor system operating. It is advisable to consider the influence of the position, structural parameter and external load of the rotor joints on aero-engine structure dynamics design.

  1. Submarine glacial landforms record Late Pleistocene ice-sheet dynamics, Inner Hebrides, Scotland

    NASA Astrophysics Data System (ADS)

    Dove, Dayton; Arosio, Riccardo; Finlayson, Andrew; Bradwell, Tom; Howe, John A.

    2015-09-01

    We use ∼7000 km2 of high-resolution swath bathymetry data to describe and map the submarine glacial geomorphology, and reconstruct Late Pleistocene ice sheet flow configurations and retreat dynamics within the Inner Hebrides, western Scotland. Frequently dominated by outcrops of structurally complex bedrock, the seabed also comprises numerous assemblages of well-preserved glacigenic landforms typical of grounded ice sheet flow and punctuated ice-margin retreat. The occurrence and character of the glacially streamlined landforms is controlled in part by the shallow geology and topography, however these factors alone cannot account for the location, orientation, and configuration of the observed landforms. We attribute the distribution of these elongate streamlined landforms to the onset zone of the former Hebrides Ice Stream (HIS) - part of a major ice stream system that drained 5-10% of the last British-Irish Ice Sheet (BIIS). We suggest this geomorphic signature represents the transition from slow 'sheet flow' to 'streaming flow' as ice accelerated out from an environment characterized by numerous bedrock obstacles (e.g. islands, headlands), towards the smooth, sediment dominated shelf. The majority of streamlined landforms associated with the HIS indicate ice sheet flow to the southwest, with regional-scale topography clearly playing a major role in governing the configuration of flow. During maximal glacial conditions (∼29-23 ka) we infer that the HIS merged with the North Channel-Malin Shelf Ice Stream to form a composite ice stream system that ultimately reached the continental shelf edge at the Barra-Donegal Trough-Mouth Fan. Taken collectively however, the pattern of landforms now preserved at seabed (e.g. convergent flow indicators, cross-cutting flow sets) is more indicative of a thinning ice mass, undergoing reorganization during overall ice sheet retreat (during latter stages of Late Weischselian glaciation). Suites of moraines overprinting the

  2. Nonlinear dynamic behavior of the human knee joint--Part I: Postmortem frequency domain analyses.

    PubMed

    Dortmans, L; Jans, H; Sauren, A; Huson, A

    1991-11-01

    Characteristics results of postmortem experiments on five knee-joint specimens are reported. The experiments were performed to investigate the applicability of a local linearization technique that would make it possible to describe the dynamic behavior of the joint in terms of transfer functions. The results indicate that the stiffness of the bracing wires, attached to muscle tendons to create a static equilibrium position, can be accounted for when determining the stiffness of the joint. Besides the static equilibrium configuration, the magnitude of the dynamic load and the type of dynamic load applied to the joint can be shown to have their influence. As the influence of the dynamic load is significant, it has to be concluded that in essence the knee joint has to be regarded as a nonlinear system, making application of a Local Linearization Technique questionable. However, when the magnitude of the dynamic load is included as an additional measurement parameter, an indication can be obtained about the behavior of the joint and the degree of nonlinearity.

  3. Oases on Snowball Earth: Confluence of Ice Dynamics Modeling and Geological Observations

    NASA Astrophysics Data System (ADS)

    Hoffman, P. F.; Maloof, A. C.; Halverson, G. P.; Schrag, D. P.

    2003-12-01

    Recent model experiments suggest that marine ice dynamics are important in the initiation and development of a snowball Earth. Ice-line advance is facilitated by the transport of latent heat and freshwater associated with Ekman forcing in the zone of westerlies (Lewis et al., 2002 this meeting) and with equatorward glacial flow of thick, multi-annual, marine ice (Goodman and Pierrehumbert, 2002 this meeting). After ice lines meet at the equator (snowball Earth), continued invasion by marine glaciers from higher latitudes maintains tropical marine ice >2.25 times thicker (<450 m) than static ice at thermal dynamic equilibrium (G & P, 2002). The dynamics imply that the tropical ocean will remain ice covered even after rising atmospheric pCO2 drives tropical sea surface temperatures to the melting point. However, landfast marine ice on low-latitude continental shelves and inland seas that are protected from invasion by marine and terrestrial glaciers will melt away, creating 'oases' on a snowball Earth. Snowball oases should occupy a small fraction (<5%) of the global surface area but they might significantly enhance water vapor transport and accumulation rates of adjacent terrestrial glaciers. Despite acidification by high pCO2, warming may cause critical oversaturation with respect to calcite or dolomite in snowball oases that are buffered by carbonate-rich bedrock and glacial debris (Fairchild, 1994). As snowball oases are small pools of water in contact with a pCO2-rich (>0.1 bar) atmosphere, the carbon isotopic composition of any carbonates they precipitate should evolve accordingly. Initially, oasis water may resemble evolved snowball seawater, which will be dominated by hydrothermal activity buffered by dissolution of sea-floor carbonate (Higgins and Schrag, G-cubed, 2003). Oasis water should evolve rapidly towards equilibrium with the atmospheric reservoir, whose isotopic composition is set by volcanic outgassing, not by the ocean. Oasis carbonate strata

  4. Ice-sheet dynamics through the Quaternary on the mid-Norwegian continental margin inferred from 3D seismic data.

    PubMed

    Montelli, A; Dowdeswell, J A; Ottesen, D; Johansen, S E

    2017-02-01

    Reconstructing the evolution of ice sheets is critical to our understanding of the global environmental system, but most detailed palaeo-glaciological reconstructions have hitherto focused on the very recent history of ice sheets. Here, we present a three-dimensional (3D) reconstruction of the changing nature of ice-sheet derived sedimentary architecture through the Quaternary Ice Age of almost 3 Ma. An extensive geophysical record documents a marine-terminating, calving Fennoscandian Ice Sheet (FIS) margin present periodically on the mid-Norwegian shelf since the beginning of the Quaternary. Spatial and temporal variability of the FIS is illustrated by the gradual development of fast-flowing ice streams and associated intensification of focused glacial erosion and sedimentation since that time. Buried subglacial landforms reveal a complex and dynamic ice sheet, with converging palaeo-ice streams and several flow-switching events that may reflect major changes in topography and basal thermal regime. Lack of major subglacial meltwater channels suggests a largely distributed drainage system beneath the marine-terminating part of the FIS. This palaeo-environmental examination of the FIS provides a useful framework for ice-sheet modelling and shows that fragmentary preservation of buried surfaces and variability of ice-sheet dynamics should be taken into account when reconstructing glacial history from spatially limited datasets.

  5. Overview of Ice-Sheet Mass Balance and Dynamics from ICESat Measurements

    NASA Technical Reports Server (NTRS)

    Zwally, H. Jay

    2010-01-01

    The primary purpose of the ICESat mission was to determine the present-day mass balance of the Greenland and Antarctic ice sheets, identify changes that may be occurring in the surface-mass flux and ice dynamics, and estimate their contributions to global sea-level rise. Although ICESat's three lasers were planned to make continuous measurements for 3 to 5 years, the mission was re-planned to operate in 33-day campaigns 2 to 3 times each year following failure of the first laser after 36 days. Seventeen campaigns were conducted with the last one in the Fall of 2009. Mass balance maps derived from measured ice-sheet elevation changes show that the mass loss from Greenland has increased significantly to about 170 Gt/yr for 2003 to 2007 from a state of near balance in the 1990's. Increased losses (189 Gt/yr) from melting and dynamic thinning are over seven times larger'than increased gains (25 gt/yr) from precipitation. Parts of the West Antarctic ice sheet and the Antarctic Peninsula are losing mass at an increasing rate, but other parts of West Antarctica and the East Antarctic ice sheet are gaining mass at an increasing rate. Increased losses of 35 Gt/yr in Pine Island, Thwaites-Smith, and Marie-Bryd.Coast are more than balanced by gains in base of Peninsula and ice stream C, D, & E systems. From the 1992-2002 to 2003-2007 period, the overall mass balance for Antarctica changed from a loss of about 60 Gt/yr to near balance or slightly positive.

  6. Dynamics of Social Interaction: Kinematic Analysis of a Joint Action

    PubMed Central

    Moreau, Quentin; Galvan, Lucie; Nazir, Tatjana A.; Paulignan, Yves

    2016-01-01

    Non-verbal social interaction between humans requires accurate understanding of the others’ actions. The cognitivist approach suggests that successful interaction depends on the creation of a shared representation of the task, where the pairing of perceptive and motor systems of partners allows inclusion of the other’s goal into the overarching representation. Activity of the Mirror Neurons System (MNS) is thought to be a crucial mechanism linking two individuals during a joint action through action observation. The construction of a shared representation of an interaction (i.e., joint action) depends upon sensorimotor cognitive processes that modulate the ability to adapt in time and space. We attempted to detect individuals’ behavioral/kinematic change resulting in a global amelioration of performance for both subjects when a common representation of the action is built using a repetitive joint action. We asked pairs of subjects to carry out a simple task where one puts a base in the middle of a table and the other places a parallelepiped fitting into the base, the crucial manipulation being that participants switched roles during the experiment. We aimed to show that a full comprehension of a joint action is not an automatic process. We found that, before switching the interactional role, the participant initially placing the base orientated it in a way that led to an uncomfortable action for participants placing the parallelepiped. However, after switching roles, the action’s kinematics by the participant who places the base changed in order to facilitate the action of the other. More precisely, our data shows significant modulation of the base angle in order to ease the completion of the joint action, highlighting the fact that a shared knowledge of the complete action facilitates the generation of a common representation. This evidence suggests the ability to establish an efficient shared representation of a joint action benefits from physically

  7. Dynamics of Social Interaction: Kinematic Analysis of a Joint Action.

    PubMed

    Moreau, Quentin; Galvan, Lucie; Nazir, Tatjana A; Paulignan, Yves

    2016-01-01

    Non-verbal social interaction between humans requires accurate understanding of the others' actions. The cognitivist approach suggests that successful interaction depends on the creation of a shared representation of the task, where the pairing of perceptive and motor systems of partners allows inclusion of the other's goal into the overarching representation. Activity of the Mirror Neurons System (MNS) is thought to be a crucial mechanism linking two individuals during a joint action through action observation. The construction of a shared representation of an interaction (i.e., joint action) depends upon sensorimotor cognitive processes that modulate the ability to adapt in time and space. We attempted to detect individuals' behavioral/kinematic change resulting in a global amelioration of performance for both subjects when a common representation of the action is built using a repetitive joint action. We asked pairs of subjects to carry out a simple task where one puts a base in the middle of a table and the other places a parallelepiped fitting into the base, the crucial manipulation being that participants switched roles during the experiment. We aimed to show that a full comprehension of a joint action is not an automatic process. We found that, before switching the interactional role, the participant initially placing the base orientated it in a way that led to an uncomfortable action for participants placing the parallelepiped. However, after switching roles, the action's kinematics by the participant who places the base changed in order to facilitate the action of the other. More precisely, our data shows significant modulation of the base angle in order to ease the completion of the joint action, highlighting the fact that a shared knowledge of the complete action facilitates the generation of a common representation. This evidence suggests the ability to establish an efficient shared representation of a joint action benefits from physically taking our

  8. Free oscillations in a climate model with ice-sheet dynamics

    NASA Technical Reports Server (NTRS)

    Kallen, E.; Crafoord, C.; Ghil, M.

    1979-01-01

    A study of stable periodic solutions to a simple nonlinear model of the ocean-atmosphere-ice system is presented. The model has two dependent variables: ocean-atmosphere temperature and latitudinal extent of the ice cover. No explicit dependence on latitude is considered in the model. Hence all variables depend only on time and the model consists of a coupled set of nonlinear ordinary differential equations. The globally averaged ocean-atmosphere temperature in the model is governed by the radiation balance. The reflectivity to incoming solar radiation, i.e., the planetary albedo, includes separate contributions from sea ice and from continental ice sheets. The major physical mechanisms active in the model are (1) albedo-temperature feedback, (2) continental ice-sheet dynamics and (3) precipitation-rate variations. The model has three-equilibrium solutions, two of which are linearly unstable, while one is linearly stable. For some choices of parameters, the stability picture changes and sustained, finite-amplitude oscillations obtain around the previously stable equilibrium solution. The physical interpretation of these oscillations points to the possibility of internal mechanisms playing a role in glaciation cycles.

  9. Carbon cycling dynamics in the seasonal sea-ice zone of East Antarctica

    NASA Astrophysics Data System (ADS)

    Roden, Nicholas P.; Tilbrook, Bronte; Trull, Thomas W.; Virtue, Patti; Williams, Guy D.

    2016-12-01

    The carbon cycle of the seasonally ice covered region of the southwest Indian Ocean sector of East Antarctica (30°-80°E, 60°-69°S) was investigated during austral summer (January-March 2006). Large variability in the drivers and timing of carbon cycling dynamics were observed and indicated that the study site was a weak net source of carbon dioxide (CO2) to the atmosphere of 0.8 ± 1.6 g C m-2 during the ice-free period, with narrow bands of CO2 uptake observed near the continental margin and north of the Southern Antarctic Circumpolar Current Front. Continuous surface measurements of dissolved oxygen and the fugacity of CO2 were combined with net community production estimates from oxygen/argon ratios to show that surface heat gain and photosynthesis were responsible for the majority of observed surface water variability. On seasonal timescales, winter sea-ice cover reduced the flux of CO2 to the atmosphere in the study area, followed by biologically driven drawdown of CO2 as the ice retreated in spring-summer highlighting the important role that sea-ice formation and retreat has on the biogeochemical cycling of the region.

  10. Biomechanical model for evaluation of pediatric upper extremity joint dynamics during wheelchair mobility.

    PubMed

    Schnorenberg, Alyssa J; Slavens, Brooke A; Wang, Mei; Vogel, Lawrence C; Smith, Peter A; Harris, Gerald F

    2014-01-03

    Pediatric manual wheelchair users (MWU) require high joint demands on their upper extremity (UE) during wheelchair mobility, leading them to be at risk of developing pain and pathology. Studies have examined UE biomechanics during wheelchair mobility in the adult population; however, current methods for evaluating UE joint dynamics of pediatric MWU are limited. An inverse dynamics model is proposed to characterize three-dimensional UE joint kinematics and kinetics during pediatric wheelchair mobility using a SmartWheel instrumented handrim system. The bilateral model comprises thorax, clavicle, scapula, upper arm, forearm, and hand segments and includes the sternoclavicular, acromioclavicular, glenohumeral, elbow and wrist joints. A single 17 year-old male with a C7 spinal cord injury (SCI) was evaluated while propelling his wheelchair across a 15-meter walkway. The subject exhibited wrist extension angles up to 60°, large elbow ranges of motion and peak glenohumeral joint forces up to 10% body weight. Statistically significant asymmetry of the wrist, elbow, glenohumeral and acromioclavicular joints was detected by the model. As demonstrated, the custom bilateral UE pediatric model may provide considerable quantitative insight into UE joint dynamics to improve wheelchair prescription, training, rehabilitation and long-term care of children with orthopedic disabilities. Further research is warranted to evaluate pediatric wheelchair mobility in a larger population of children with SCI to investigate correlations to pain, function and transitional changes to adulthood.

  11. Reconstruction of Wisconsinan-age ice dynamics and compositions of southern Ontario glacial diamictons, glaciofluvial/lacustrine, and deltaic sediment

    NASA Astrophysics Data System (ADS)

    Mahaney, W. C.; Hancock, R. G. V.; Milan, Alison; Pulleyblank, Coren; Costa, Pedro J. M.; Milner, M. W.

    2014-02-01

    Macrofabric analysis of till sections in south-central Ontario confirms that clast orientation yields information related to changing ice dynamics during the Wisconsinan glaciation. Test stations in six sections yield unimodal to multimodal macrofabrics that indicate ice flow direction, ranging from SE-NW vectors when ice was thin and flowing radially to variable NE-SW, NNE-SSW, and N-S vectors when ice thickened. Ice loci appear to range from the Lake Ontario basin and southern Quebec (thin ice), Labrador Ungava (thicker ice), and Hudson Bay (thickest ice). The north-south fabric may identify the intergrowth of Keewatin-Labrador ice, presumably the maximum ice thickness of the Last Glacial Maximum (LGM). The preliminary data support the theory that topography directed ice movement during preliminary and closing stages of glaciation in southern Ontario, while thick ice generated flow vectors largely unaffected by underlying topography; hence, leading to clast azimuthal variations reflecting changing ice loci with glacier growth. The fabrics analyzed suggest that inferring difference between ductile and brittle lodgement tills is possible as well as to identifying possible glacial tectonic action/overburden loading that disturbs the least friction-fit position of clasts in till. The changing dynamics within till sheets are supported, in part, by variations in glacial crushing seen in SEM imagery that depict a range of microtextures from full-scale fractures under brittle conditions to those indicating less viscous transport under ductile regimes. To some degree, changes in flow direction are further supported by geochemical variations that relate to bedrock/regolith up-glacier controlling Ca-dilution and variable concentrations of Rare Earth Elements (REEs).

  12. Impact of mesoscale dynamic and thermodynamic changes in sea ice on the development of low pressure systems in the Fram Strait

    NASA Astrophysics Data System (ADS)

    Bungert, U.; Schlünzen, K. H.; Ries, H.

    2009-09-01

    In polar regions the exchange of heat and momentum between the ocean and the atmosphere depends on the sea ice distribution. Sea ice acts as an insulating layer between the relatively warm ocean water and the mostly cold air. The sea ice concentration can change on time scales from several hours to a few days due to dynamic processes like ice drift or breaking of the ice sheet and thermodynamic processes like melting and freezing. The influence of these mesoscale changes of the ice distribution on the heat exchange at the surface and on atmospheric processes is investigated by numerical simulations for the Fram Strait region. The studies are performed with the model system METRAS/MESIM (Dierer et al., 2005). It consists of the mesoscale atmospheric model METRAS (Lüpkes and Schlünzen, 1996; Schlünzen, 1990) that is interactively coupled with the mesoscale sea ice model MESIM (Birnbaum, 1998). The sea ice model is able to simulate dynamic and thermodynamic processes in the ice jointly and separately. Therefore, it is possible to evaluate the influence of these processes on the ice concentration and the resulting impact on low pressure systems in detail. Two periods are simulated: The first one from 05 to 07 March 2002, and the second one from 12 to 15 March 2002. During the first phase, a trough was passing from East to West through the Fram Strait region. During the second phase, three cyclones were passing in series over Fram Strait (Brümmer et al., 2008). In March 2002, the field experiment FRAMZY 2002 took place in the region of Svalbard and Fram Strait including ship measurements, aircraft measurements and drift buoys (Brümmer et al., 2005). The model results are compared with these measurements and the influence of changes in the sea ice cover on the exchange of heat and momentum at the surface and on the development of the trough (first phase) and the "cyclone family" (second phase) are investigated. For this development dynamically caused changes of the

  13. A coupled dynamic-thermodynamic model of an ice-ocean system in the marginal ice zone

    NASA Technical Reports Server (NTRS)

    Hakkinen, Sirpa

    1987-01-01

    Thermodynamics are incorporated into a coupled ice-ocean model in order to investigate wind-driven ice-ocean processes in the marginal zone. Upswelling at the ice edge which is generated by the difference in the ice-air and air-water surface stresses is found to give rise to a strong entrainment by drawing the pycnocline closer to the surface. Entrainment is shown to be negligible outside the areas affected by the ice edge upswelling. If cooling at the top is included in the model, the heat and salt exchanges are further enhanced in the upswelling areas. It is noted that new ice formation occurs in the region not affected by ice edge upswelling, and it is suggested that the high-salinity mixed layer regions (with a scale of a few Rossby radii of deformation) will overturn due to cooling, possibly contributing to the formation of deep water.

  14. New insights into West Greenland ice sheet/stream dynamics during the last glacial cycle.

    NASA Astrophysics Data System (ADS)

    Roberts, David; Lane, Tim; Rea, Brice; Cofaigh, Colm O.; Jamieson, Stewart; Vieli, Andreas; Rodes, Angel

    2015-04-01

    output which indicates that non-linear retreat, grounding line stability and up-ice surface thinning is heavily influenced by both vertical and lateral constrictions in marine trough systems. While the offshore ice stream corridors are beginning to reveal their dynamic retreat history, knowledge of the inter-stream areas on the continental shelf remains very poor. The western, onshore sector of the GrIS has a much improved deglacial chronology derived from radiocarbon and new cosmogenic surface exposure dating undertaken in the last decade, but the deglacial history of wide swathes of the inner, mid and outer continental shelf remains completely unknown. The Hellefiske moraines on the West Greenland shelf were described in the late 1970's but little is known of ice sheet retreat behaviour across these areas. Understanding the deglacial signature of such regions is important if we are to use palaeo-reconstructions to understand ice sheet collapse/retreat mechanisms and to inform future model predictions.

  15. Dynamic coupling of magnetic fields, thermal emissions, and zonal flows in ice giant planets

    NASA Astrophysics Data System (ADS)

    Soderlund, Krista M.; Heimpel, M. H.; King, E. M.; Aurnou, J. M.

    2013-10-01

    Magnetic fields are ubiquitous in the solar system, yet their characteristics are as diverse as the planets themselves. These fields are thought to result from dynamo action driven by thermochemical convection in electrically conducting fluid regions. The multipolar dynamos of Uranus and Neptune provide a unique opportunity to test hypotheses for magnetic field generation. Since no sharp structural boundaries in the ice giants between the ionic ocean and overlying molecular envelope are expected, it is possible that these regions are linked dynamically. Thus, an understanding of the coupling between magnetic fields, heat flow, and atmospheric winds is crucial to determine what controls the strength, morphology, and evolution of giant planet dynamos. Here we present numerical simulations of turbulent convection in spherical shells to test the hypothesis that poorly organized turbulence will generate ice giant-like magnetic fields, thermal emissions, and zonal flows. We find that this style of convection leads to small-scale, fluctuating dynamo action that generates a multipolar magnetic field, Hadley-like circulation cells that promote equatorial upwellings to create low latitude peaks in internal heat flux, and homogenized absolute angular momentum that drives three-jet zonal flows. This qualitative agreement with observations suggests that the internal dynamics of ice giant planets may be characterized by three-dimensional convective turbulence with dynamic coupling between the dynamo region and electrically insulating envelope above playing an important role as well.

  16. Human joint motion estimation for electromyography (EMG)-based dynamic motion control.

    PubMed

    Zhang, Qin; Hosoda, Ryo; Venture, Gentiane

    2013-01-01

    This study aims to investigate a joint motion estimation method from Electromyography (EMG) signals during dynamic movement. In most EMG-based humanoid or prosthetics control systems, EMG features were directly or indirectly used to trigger intended motions. However, both physiological and nonphysiological factors can influence EMG characteristics during dynamic movements, resulting in subject-specific, non-stationary and crosstalk problems. Particularly, when motion velocity and/or joint torque are not constrained, joint motion estimation from EMG signals are more challenging. In this paper, we propose a joint motion estimation method based on muscle activation recorded from a pair of agonist and antagonist muscles of the joint. A linear state-space model with multi input single output is proposed to map the muscle activity to joint motion. An adaptive estimation method is proposed to train the model. The estimation performance is evaluated in performing a single elbow flexion-extension movement in two subjects. All the results in two subjects at two load levels indicate the feasibility and suitability of the proposed method in joint motion estimation. The estimation root-mean-square error is within 8.3% ∼ 10.6%, which is lower than that being reported in several previous studies. Moreover, this method is able to overcome subject-specific problem and compensate non-stationary EMG properties.

  17. Can xenon in water inhibit ice growth? Molecular dynamics of phase transitions in water-Xe system.

    PubMed

    Artyukhov, Vasilii I; Pulver, Alexander Yu; Peregudov, Alex; Artyuhov, Igor

    2014-07-21

    Motivated by recent experiments showing the promise of noble gases as cryoprotectants, we perform molecular dynamics modeling of phase transitions in water with xenon under cooling. We follow the structure and dynamics of xenon water solution as a function of temperature. Homogeneous nucleation of clathrate hydrate phase is observed and characterized. As the temperature is further reduced we observe hints of dissociation of clathrate due to stronger hydrophobic hydration, pointing towards a possible instability of clathrate at cryogenic temperatures and conversion to an amorphous phase comprised of "xenon + hydration shell" Xe·(H2O)21.5 clusters. Simulations of ice-xenon solution interface in equilibrium and during ice growth reveal the effects of xenon on the ice-liquid interface, where adsorbed xenon causes roughening of ice surface but does not preferentially form clathrate. These results provide evidence against the ice-blocker mechanism of xenon cryoprotection.

  18. Dynamics and reactivity of trapped electrons on supported ice crystallites.

    PubMed

    Stähler, Julia; Gahl, Cornelius; Wolf, Martin

    2012-01-17

    The solvation dynamics and reactivity of localized excess electrons in aqueous environments have attracted great attention in many areas of physics, chemistry, and biology. This manifold attraction results from the importance of water as a solvent in nature as well as from the key role of low-energy electrons in many chemical reactions. One prominent example is the electron-induced dissociation of chlorofluorocarbons (CFCs). Low-energy electrons are also critical in the radiation chemistry that occurs in nuclear reactors. Excess electrons in an aqueous environment are localized and stabilized by the local rearrangement of the surrounding water dipoles. Such solvated or hydrated electrons are known to play an important role in systems such as biochemical reactions and atmospheric chemistry. Despite numerous studies over many years, little is known about the microscopic details of these electron-induced chemical processes, and interest in the fundamental processes involved in the reactivity of trapped electrons continues. In this Account, we present a surface science study of the dynamics and reactivity of such localized low-energy electrons at D(2)O crystallites that are supported by a Ru(001) single crystal metal surface. This approach enables us to investigate the generation and relaxation dynamics as well as dissociative electron attachment (DEA) reaction of excess electrons under well-defined conditions. They are generated by photoexcitation in the metal template and transferred to trapping sites at the vacuum interface of crystalline D(2)O islands. In these traps, the electrons are effectively decoupled from the electronic states of the metal template, leading to extraordinarily long excited state lifetimes on the order of minutes. Using these long-lived, low-energy electrons, we study the DEA to CFCl(3) that is coadsorbed at very low concentrations (∼10(12) cm(-2)). Using rate equations and direct measurement of the change of surface dipole moment, we

  19. Sedimentation and particle dynamics in the seasonal ice zone of the Barents Sea

    NASA Astrophysics Data System (ADS)

    Maiti, Kanchan; Carroll, JoLynn; Benitez-Nelson, Claudia R.

    2010-01-01

    The Barents Sea seasonal ice zone (SIZ) is one of the most dynamic areas in the world ocean. This biologically productive area undergoes extreme intra- and inter-annual variabilities in sea ice and water mass transport properties. Here, we investigate seafloor burial processes in three regions of the SIZ with different ice-cover frequencies: predominantly open water (POW), marginally ice-covered (MIC), and predominantly ice-covered (PIC) with approximately 0, 10 and 50% sea ice cover, respectively, in 2002-2003. Down-core sediment profiles of the radionuclides 234Th, 210Pb, and 137Cs, along with sediment carbon, nitrogen and phosphorus concentrations are examined in two to three cores from each region. Sedimentation rates and velocities using 210Pb ex (excess 210Pb) profiles and assuming negligible mixing below a surface mixed layer are relatively uniform throughout the study area, averaging 558 ± 154 g m - 2 y - 1 and 1.1 ± 0.4 mm y - 1 ( n = 7). These sedimentation velocities are confirmed using 137Cs (1.0 ± 0.4 mm y - 1 , n = 7). 234Th ex (excess 234Th) derived bioturbation rates are positively correlated with number of benthic individuals per 0.5 m 2 ( R2 = 0.83) and exhibit a pattern of higher rates in the MIC (14.5 ± 2.1 cm - 2 y - 1) relative to both the POW (6.3 ± 2.2 cm - 2 y - 1) and PIC (5.3 ± 1.2 cm - 2 y - 1) ( p < 0.01). 234Th ex inventories are also significantly higher ( p = 0.026) within the MIC, while both 210Pb ex and 137Cs sediment inventories are more regionally uniform. Furthermore, organic carbon (C org) and total nitrogen (N tot) concentrations are relatively high in both the MIC and PIC compared to POW. For this limited data set, higher bioturbation rate coefficients and higher 234Th ex sediment inventories in the MIC relative to the other sampled regions, suggest that the MIC exhibits a greater predominance of marine versus terrestrial sediment sources that support enhanced scavenging and benthic biological activity. These results

  20. Dynamic Recrystallization in Ice : In-Situ Observation of the Strain Field during Grain Nucleation.

    NASA Astrophysics Data System (ADS)

    Chauve, T.; Montagnat, M.; Tommasi, A.; Vacher, P.

    2014-12-01

    Dynamic recrystallization (DRX) occurs in minerals, metals, ice and impact on large scale mechanisms as seismic anisotropy, mechanical properties inside the Earth mantle, material forming and anisotropic flow in polar ice sheet, for instance. In this frame, ice can be considered as a model material due to a strong viscoplastic anisotropy and deformation heterogeneities, which are precursors of the recrystallization. During creep deformation at high temperature, DRX occurs from 1% strain and involves grain nucleation and grain boundary migration. As DRX induces an evolution of microstructure and texture, it strongly affects the mechanical behavior, and it is expected to modify the strain field at the grain and/or the sample scale. Creep test (σ=0.5-0.8 MPa) were performed at high temperature (T/Tf 0,98) on granular polycrystalline ice (grains size 1mm) and columnar polycrystalline ice (microstructure 2D 1/2 in plane grain size 10mm) up to 18 % strain. Columnar ice provides interesting feature as it contains only one grain through the thickness and the columns are parallel. Post-deformation texture analysis with an Automatic Ice Texture Analyzer (AITA) and with EBSD (Geoscience Montpellier) were used to investigate DRX impact on texture and microstructure, at different scales. With increasing strain texture evolves to a strong concentrated girdle with a preferential orientation of c-axis close to 35° from the compression axis. During the experiment, local strain field is measured on the surface of the sample by Digital Image Correlation (DIC) with a spatial resolution between 0.2 and 0.5 mm, and a strain resolution between 0.2% to 1%. Grain size being large, we obtain a relatively good intra-granular resolution of the strain field. Thanks to the 2D configuration of the columnar ice samples, we can superimpose the strain field measured by DIC. We will present an overview of the impact of DRX on the texture and microstructure, from the 3D configuration down to a

  1. Dynamics of the Zemgale Lobe of the Scandinavian Ice Sheet reconstructed from the subglacial landform record

    NASA Astrophysics Data System (ADS)

    Lamsters, Kristaps; Zelčs, Vitālijs

    2015-04-01

    Deglacial ice dynamics were inferred from the distribution, morphometry and sedimentology of subglacial bedforms such as drumlins, mega-flutes, mega-scale glacial lineations (MSGL), ribbed moraines, from meltwater features such as subglacial channels and eskers, and ice-marginal landforms, which were identified and mapped from the topographical maps and digital elevation models. The Zemgale Lobe operated in the area of the Central Latvian and Lithuanian Lowlands, and it was characterized by the fast ice flow that was sustained by a combination of subglacial deformation and basal sliding. The mosaic ice-bed deformation model is favoured due to observed sediment structures indicating ice/bed coupling and decoupling episodes. The landform record indicates on two major reactivations of the Zemgale Lobe during the overall deglaciation of the Late Weichselian Scandinavian Ice Sheet and may imply surge-type behaviour. The coexistence of subglacial bedform assemblage and overlapping of their morphometry demonstrates subglacial bedform continuum. A significant number of prominent esker chains are distinguished proximally from the marginal ridges of the North Lithuanian deglacial phase with an average spacing of 10 - 15 km. Some of eskers are found within subglacial channels recording change in meltwater discharge. The cores of the many eskers consist of coarse deposits - gravels, cobbles and boulders indicating episodes of high-energy and hyper-concentrated flow conditions. Ribbed moraines are superimposed on streamlined subglacial features, thereby indicating a shift of subglacial conditions, which promoted the shutdown of the SE part of the Zemgale Lobe. The presence of ribbed moraines on the Zemgale Lobe bed proves that they are distributed not only at the central parts of ice sheets but also outside the core areas. The structure or ribbed moraines is glaciotectonically deformed, and comprises multiple units of diamicton and sorted sediments, which formed by repeated

  2. The dynamic crossover in dielectric relaxation behavior of ice I(h).

    PubMed

    Popov, Ivan; Puzenko, Alexander; Khamzin, Airat; Feldman, Yuri

    2015-01-14

    The main mechanism of the dielectric relaxation process of ordinary hexagonal ice (ice Ih) and its temperature dependence remains unclear. The most interesting and as yet unexplained feature of ice is the presence of the dynamical crossover in relaxation time behavior around Tc = 230 ± 3 K. Since there are no phase transitions in the ice at this temperature (first or second order), we cannot correlate the origin of this crossover with any structural change. Here we present a model according to which the temperature of the crossover is defined by the polarization mechanism. The dielectric relaxation driven by the diffusion of L-D orientational Bjerrum defects (at high temperature, T > Tc) is transformed into a dielectric relaxation dominated by the diffusion of intrinsic ionic H3O(+)/OH(-) defects (at low temperature, T < Tc). In the framework of the model, we propose an analytical equation for the complex dielectric permittivity that takes into account the contribution of both types of defects.

  3. Subglacial hydrology indicates a major shift in dynamics of the West Antarctic Ross Ice Streams within the next two centuries

    NASA Astrophysics Data System (ADS)

    Goeller, S.; Helm, V.; Thoma, M.; Grosfeld, K.

    2015-07-01

    The mass export of the West Antarctic Ice Sheet (WAIS) is dominated by fast flowing ice streams. Understanding their dynamics is a key to estimate the future integrity of the WAIS and its contributions to global sea level rise. This study focuses on the Ross Ice Streams (RIS) at the Siple Coast. In this sector, observations reveal a high variability of ice stream pathways and velocities which is assumed to be driven by subglacial hydrology. We compute subglacial water pathways for the present-day ice sheet and verify this assumption by finding high correlations between areas of enhanced basal water flow and the locations of the RIS. Moreover, we reveal that the ice flow velocities of the individual ice streams are correlated with the sizes of the water catchment areas draining underneath. The future development of the subglacial hydraulic environment is estimated by applying ice surface elevation change rates observed by ICESat and CryoSat-2 to the present-day ice sheet geometry and thus assessing prognostic basal pressure conditions. Our simulations consistently indicate that a major hydraulic tributary of the Kamb and Whillans Ice Stream (KIS and WIS) will be redirected underneath the Bindschadler Ice Stream (BIS) within the next two centuries. The water catchment area feeding underneath the BIS is estimated to grow by about 50 % while the lower part of the stagnated KIS becomes increasingly separated from its upper hydraulic tributaries. We conclude, that this might be a continuation of the subglacial hydraulic processes which caused the past stagnation of the KIS. The simulated hydraulic rerouting is also capable to explain the observed deceleration of the WIS and indicates a possible future acceleration of the BIS accompanied by an increased ice drainage of the corresponding ice sheet interior.

  4. A comparison between dynamic implicit and explicit finite element simulations of the native knee joint.

    PubMed

    Naghibi Beidokhti, Hamid; Janssen, Dennis; Khoshgoftar, Mehdi; Sprengers, Andre; Perdahcioglu, Emin Semih; Van den Boogaard, Ton; Verdonschot, Nico

    2016-10-01

    The finite element (FE) method has been widely used to investigate knee biomechanics. Time integration algorithms for dynamic problems in finite element analysis can be classified as either implicit or explicit. Although previously both static/dynamic implicit and dynamic explicit method have been used, a comparative study on the outcomes of both methods is of high interest for the knee modeling community. The aim of this study is to compare static, dynamic implicit and dynamic explicit solutions in analyses of the knee joint to assess the prediction of dynamic effects, potential convergence problems, the accuracy and stability of the calculations, the difference in computational time, and the influence of mass-scaling in the explicit formulation. The heel-strike phase of fast, normal and slow gait was simulated for two different body masses in a model of the native knee. Our results indicate that ignoring the dynamic effect can alter joint motion. Explicit analyses are suitable to simulate dynamic loading of the knee joint in high-speed simulations, as this method offers a substantial reduction of the computational time with a similar prediction of cartilage stresses and meniscus strains. Although mass-scaling can provide even more gain in computational time, it is not recommended for high-speed activities, in which inertial forces play a significant role.

  5. Inverse Dynamics Model for the Ankle Joint with Applications in Tibia Malleolus Fracture

    NASA Astrophysics Data System (ADS)

    Budescu, E.; Merticaru, E.; Chirazi, M.

    The paper presents a biomechanical model of the ankle joint, in order to determine the force and the torque of reaction into the articulation, through inverse dynamic analysis, in various stages of the gait. Thus, knowing the acceleration of the foot and the reaction force between foot and ground during the gait, determined by experimental measurement, there was calculated, for five different positions of the foot, the joint reaction forces, on the basis of dynamic balance equations. The values numerically determined were compared with the admissible forces appearing in the technical systems of osteosynthesis of tibia malleolus fracture, in order to emphasize the motion restrictions during bone healing.

  6. Ice-Sheet Dynamics and Millennial-Scale Climate Variability in the North Atlantic across the Middle Pleistocene Transition (Invited)

    NASA Astrophysics Data System (ADS)

    Hodell, D. A.; Nicholl, J.

    2013-12-01

    During the Middle Pleistocene Transition (MPT), the climate system evolved from a more linear response to insolation forcing in the '41-kyr world' to one that was decidedly non-linear in the '100-kyr world'. Smaller ice sheets in the early Pleistocene gave way to larger ice sheets in the late Pleistocene with an accompanying change in ice sheet dynamics. We studied Sites U1308 (49° 52.7'N, 24° 14.3'W; 3871 m) and U1304 (53° 3.4'N, 33° 31.8'W; 3024 m) in the North Atlantic to determine how ice sheet dynamics and millennial-scale climate variability evolved as glacial boundary conditions changed across the MPT. The frequency of ice-rafted detritus (IRD) in the North Atlantic was greater during glacial stages prior to 650 ka (MIS 16), reflecting more frequent crossing of an ice volume threshold when the climate system spent more time in the 'intermediate ice volume' window, resulting in persistent millennial scale variability. The rarity of Heinrich Events containing detrital carbonate and more frequent occurrence of IRD events prior to 650 ka may indicate the presence of 'low-slung, slippery ice sheets' that flowed more readily than their post-MPT counterparts (Bailey et al., 2010). Ice volume surpassed a critical threshold across the MPT that permitted ice sheets to survive boreal summer insolation maxima, thereby increasing ice volume and thickness, lengthening glacial cycles, and activating the dynamical processes responsible for Laurentide Ice Sheet instability in the region of Hudson Strait (i.e., Heinrich events). The excess ice volume during post-MPT glacial maxima provided a large, unstable reservoir of freshwater to be released to the North Atlantic during glacial terminations with the potential to perturb Atlantic Meridional Overtunring Circulation. We speculate that orbital- and millennial-scale variability co-evolved across the MPT and the interaction of processes on orbital and suborbital time scales gave rise to the changing patterns of glacial

  7. A quasi-liquid mediated continuum model of faceted ice dynamics

    NASA Astrophysics Data System (ADS)

    Neshyba, Steven; Adams, Jonathan; Reed, Kelsey; Rowe, Penny M.; Gladich, Ivan

    2016-12-01

    We present a quasi-liquid mediated continuum model for ice growth consisting of partial differential equations informed by molecular dynamics simulations. The main insight from molecular dynamics is the appearance of periodic variations in the equilibrium vapor pressure and quasi-liquid thickness of the ice/vapor interface. These variations are incorporated in the continuum model as subgrid scale microsurfaces. We show that persistent faceted ice growth in the presence of inhomogeneities in the ambient vapor field is due to a spontaneous narrowing of terraces at facet corners, which compensates for higher ambient water vapor density via feedback between surface supersaturation and quasi-liquid thickness. We argue that this emergent behavior has the mathematical structure of a stable limit cycle and characterize its robustness in terms of ranges of parameters that support it. Because the model is relevant in the high-surface-coverage regime, it serves as a useful complement to the Burton-Cabrera-Frank framework. Quantitative aspects and limitations of the model are also discussed.

  8. Nanocluster building blocks of artificial square spin ice: Stray-field studies of thermal dynamics

    SciTech Connect

    Pohlit, Merlin Porrati, Fabrizio; Huth, Michael; Müller, Jens

    2015-05-07

    We present measurements of the thermal dynamics of a Co-based single building block of an artificial square spin ice fabricated by focused electron-beam-induced deposition. We employ micro-Hall magnetometry, an ultra-sensitive tool to study the stray field emanating from magnetic nanostructures, as a new technique to access the dynamical properties during the magnetization reversal of the spin-ice nanocluster. The obtained hysteresis loop exhibits distinct steps, displaying a reduction of their “coercive field” with increasing temperature. Therefore, thermally unstable states could be repetitively prepared by relatively simple temperature and field protocols allowing one to investigate the statistics of their switching behavior within experimentally accessible timescales. For a selected switching event, we find a strong reduction of the so-prepared states' “survival time” with increasing temperature and magnetic field. Besides the possibility to control the lifetime of selected switching events at will, we find evidence for a more complex behavior caused by the special spin ice arrangement of the macrospins, i.e., that the magnetic reversal statistically follows distinct “paths” most likely driven by thermal perturbation.

  9. Dynamics of surface melting over Amery and Ross ice shelf in Antarctic using OSCAT data

    NASA Astrophysics Data System (ADS)

    Bothale, R. V.; Rao, P. V. N.; Dutt, C. B. S.; Dadhwal, V. K.

    2014-11-01

    Antarctic sea ice sheets play an important role in modulating the climate system. The present study investigates the dynamics of melt/freeze over Amery and Ross ice shelf located in Eastern and Southern part of continent using OSCAT, the microwave scatterometer data from OCEANSAT2. The study utilizes the sensitivity of backscatter coefficient values of scatterometer data to presence of liquid water in the snow caused due to melt conditions. The analysis carried out for four austral winters from 2010-2013 and five austral summer from 2009-2014 showed spatial and temporal variations in average backscatter coefficient over Amery and Ross shelf areas. A dynamic threshold based on the austral winter mean and standard deviation of HH polarization is considered for pixel by pixel analysis for the shelf area. There is significant spatio-temporal variability in melt extent, duration and melt index as observed in the analysis. Spatially, the melt over Amery shelf moves from South to North along coast and West towards inner shelf area. Maximum mean melt occurs on 9th January with January 1-15 fortnight accounting for 80 % of the melt. Extreme low melt conditions were observed during summer 2010-11 and 2011-12 indicating cold summer. Summer 2012-13 and 2013-14 were warm summer. Year 2014 experienced melt only in the month of January with entire shelf under melt conditions. Practically no melt was observed over Ross ice shelf.

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

    NASA Astrophysics Data System (ADS)

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

    2017-02-01

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

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

    PubMed

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

    2017-02-13

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

  12. Dynamics of Bound Monopoles in Artificial Spin Ice: How to Store Energy in Dirac Strings

    NASA Astrophysics Data System (ADS)

    Vedmedenko, E. Y.

    2016-02-01

    Dirac strings in spin ices are lines of reversed dipoles joining two quasiparticle excitations. These excitations behave as unbound emergent monopoles if the tension of Dirac strings vanishes. In this Letter, analytical and numerical analysis are used to study the dynamics of two-dimensional dipolar spin ices, artificially created analogs of bulk spin ice, in the regime of bound monopoles. It is shown that, in this regime, strings, rather than monopoles, are effective degrees of freedom explaining the finite-width band of Pauling states. A measurable prediction of path-time dependence of endpoints of a stretched and, then, released Dirac string is made and verified via simulations. It is shown that string dynamics is defined by the characteristic tension-to-mass ratio, which is determined by the fine structure constant and lattice dependent parameter. It is proposed to use string tension to achieve spontaneous magnetic currents. A concept of an energy storing device on the basis of this principle is proposed and illustrated by an experimental demonstration. A scheme of independent measurement at the nanoscale is proposed.

  13. Uneven onset and pace of ice-dynamical imbalance in the Amundsen Sea Embayment, West Antarctica

    NASA Astrophysics Data System (ADS)

    Konrad, Hannes; Gilbert, Lin; Cornford, Stephen L.; Payne, Antony; Hogg, Anna; Muir, Alan; Shepherd, Andrew

    2017-01-01

    We combine measurements acquired by five satellite altimeter missions to obtain an uninterrupted record of ice sheet elevation change over the Amundsen Sea Embayment, West Antarctica, since 1992. Using these data, we examine the onset of surface lowering arising through ice-dynamical imbalance, and the pace at which it has propagated inland, by tracking elevation changes along glacier flow lines. Surface lowering has spread slowest (<6 km/yr) along the Pope, Smith, and Kohler (PSK) Glaciers, due to their small extent. Pine Island Glacier (PIG) is characterized by a continuous inland spreading of surface lowering, notably fast at rates of 13 to 15 km/yr along tributaries draining the southeastern lobe, possibly due to basal conditions or tributary geometry. Surface lowering on Thwaites Glacier (THG) has been episodic and has spread inland fastest (10 to 12 km/yr) along its central flow lines. The current episodes of surface lowering started approximately 10 years before the first measurements on PSK, around 1990 on PIG, and around 2000 on THG. Ice-dynamical imbalance across the sector has therefore been uneven during the satellite record.

  14. Air-ice CO2 fluxes and pCO2 dynamics in the Arctic coastal area (Amundsen Gulf, Canada)

    NASA Astrophysics Data System (ADS)

    Geilfus, Nicolas-Xavier; Tison, Jean Louis; Carnat, Gauthier; Else, Brent; Borges, Alberto V.; Thomas, Helmuth; Shadwick, Elizabeth; Delille, Bruno

    2010-05-01

    Sea ice covers about 7% of the Earth surface at its maximum seasonal extent. For decades sea ice was assumed to be an impermeable and inert barrier for air - sea exchange of CO2 so that global climate models do not include CO2 exchange between the oceans and the atmosphere in the polar regions. However, uptake of atmospheric CO2 by sea ice cover was recently reported raising the need to further investigate pCO2 dynamics in the marine cryosphere realm and related air-ice CO2 fluxes. In addition, budget of CO2 fluxes are poorly constrained in high latitudes continental shelves [Borges et al., 2006]. We report measurements of air-ice CO2 fluxes above the Canadian continental shelf and compare them to previous measurements carried out in Antarctica. We carried out measurements of pCO2 within brines and bulk ice, and related air-ice CO2 fluxes (chamber method) in Antarctic first year pack ice ("Sea Ice Mass Balance in Antarctica -SIMBA" drifting station experiment September - October 2007) and in Arctic first year land fast ice ("Circumpolar Flaw Lead" - CFL, April - June 2008). These 2 experiments were carried out in contrasted sites. SIMBA was carried out on sea ice in early spring while CFL was carried out in from the middle of the winter to the late spring while sea ice was melting. Both in Arctic and Antarctic, no air-ice CO2 fluxes were detected when sea ice interface was below -10°C. Slightly above -10°C, fluxes toward the atmosphere were observed. In contrast, at -7°C fluxes from the atmosphere to the ice were significant. The pCO2 of the brine exhibits a same trend in both hemispheres with a strong decrease of the pCO2 anti-correlated with the increase of sea ice temperature. The pCO2 shifted from a large over-saturation at low temperature to a marked under-saturation at high temperature. These air-ice CO2 fluxes are partly controlled by the permeability of the air-ice interface, which depends of the temperature of this one. Moreover, air-ice CO2 fluxes are

  15. Geothermal Heat Flux: Linking Deep Earth's Interior and the Dynamics of Large-Scale Ice Sheets

    NASA Astrophysics Data System (ADS)

    Rogozhina, Irina; Vaughan, Alan

    2014-05-01

    Greenland results from the remanent effects of an Early Cenozoic passage of the lithosphere above the Iceland mantle plume that is implicated in strong thermochemical erosion of the lithosphere and significant long-term effects on the present-day subglacial heat flow pattern and thermodynamic state of the Greenland ice sheet. These observations and our modeling results (Petrunin et al., 2013) show that the present-day thermal state of Greenland and Antarctic lithosphere cannot be well understood without taking into account a long-term tectonic history of these regions. The goal of the IceGeoHeat project is to combine existing independent geophysical data and innovative modeling approaches to comprehensively study the evolution and present state of the lithosphere in Greenland and Antarctica, and assess the role of geothermal heat flux in shaping the present-day ice sheet dynamics. This requires multiple collaborations involving experts across a range of disciplines. The project builds on the IceGeoHeat initiative formed in April 2012 and now including researchers from ten countries in the main core (MC) with expertise in numerical modeling and data assessment in geodynamics, geology, geothermics, cryosphere and (paleo-)climate. Petrunin, A., Rogozhina, I., Vaughan, A. P. M., Kukkonen, I. T., Kaban, M., Koulakov, I., Thomas, M. (2013): Heat flux variations beneath central Greenland's ice due to anomalously thin lithosphere. - Nature Geoscience, 6, 746-750.

  16. Strain field evolution during creep on ice. Impact of dynamic recrystallization mechanisms.

    NASA Astrophysics Data System (ADS)

    Chauve, Thomas; Montagnat, Maurine; Barou, Fabrice; Hidas, Karoly; Tommasi, Andréa; Vacher, Pierre

    2015-04-01

    Discontinuous Dynamic Recrystallization (DDRX) occurs in minerals, metals, ice and impacts on texture and microstructure evolution during deformation. It therefore impacts on large scale mechanisms as seismic anisotropy, mechanical properties inside the Earth mantle, material forming and anisotropic flow in polar ice sheet, for instance. In this frame, ice can be considered as a model material due to a strong viscoplastic anisotropy inducing strong deformation heterogeneities, that are precursors of recrystallization. During creep deformation at high temperature in the laboratory, DDRX occurs from 1% strain and involves grain nucleation and grain boundary migration. As DDRX induces an evolution of microstructure and texture, it strongly affects the mechanical behavior (1,2), and it is expected to modify the strain field at the grain and/or the sample scale. Compressive creep test (σ=0.5-0.8 MPa) were performed at high temperature (T/Tf 0,98) on granular polycrystalline ice (grains size 1mm) and columnar polycrystalline ice (microstructure 2D 1/2 in plane grain size 10mm) up to 18 % strain. Columnar ice provides interesting feature as it contains only one grain through the thickness and the columns are parallel. Post-deformation texture analyses with an Automatic Ice Texture Analyzer (AITA) and with EBSD (CrystalProbe MEB of Geoscience Montpellier) were used to investigate DDRX mechanisms at high resolution, and deduce their impact on texture and microstructure, at different scales. During the experiment, local strain field is measured on the surface of the sample by Digital Image Correlation (DIC) (3) with a spatial resolution between 0.2 and 0.5 mm, and a strain resolution between 0.2% to 1%. Grain size being large, we obtain a relatively good intra-granular resolution of the strain field. Thanks to the 2D configuration of the columnar ice samples, we can superimpose the initial microstructure to the strain field measured by DIC. We will present an overview of

  17. A calving law for ice sheet models; Investigating the role of surface melt on dynamics of Greenland outlet glaciers

    NASA Astrophysics Data System (ADS)

    Nick, F. M.; van der Veen, C. J.; Vieli, A.

    2008-12-01

    alving of icebergs accounts for perhaps as much as half the ice transferred from the Greenland Ice Sheet into the surrounding ocean, and virtually all of the ice loss from the Antarctic Ice Sheet. We have formulated a calving model that can be readily incorporated into time-evolving numerical ice-flow models. Our model is based on downward penetration of water-filled surface crevasses and upward propagation of basal crevasses. A calving event occurs when the depth of the surface crevasse (which increases as melting progresses through the summer) reaches the height of the basal crevasse. Our numerical ice sheet model is able to reproduce observed seasonal changes of Greenland outlet glaciers, such as fluctuations in flow speed and terminus positions. We have applied the model to Helheim Glacier on the east coast, and Petermann Glacier in the northwest. Our model suggests that rapid retreat of the claving front is highly affected by the amplified calving rate due to increasing water level in surface crevasses during warmer summers. Our results show little response to seasonally enhanced basal lubrication from surface melt. This modeling study provides insights into the role of surface and basal hydrology to ice sheet dynamics and on how to incorporate calving in ice sheet models and therefore advances our ability to predict future ice sheet change.

  18. Last glacial ice-sheet dynamics and deglaciation on Svalbard inferred from fjord records

    NASA Astrophysics Data System (ADS)

    Forwick, Matthias; Baeten, Nicole J.; Bunin, Elizabeth; Hansen, Trude; Kempf, Philipp; Velle, Julie H.; Sverre Laberg, Jan

    2015-04-01

    Various glacigenic landforms and sedimentary processes identified in the Spitsbergen fjords provide valuable insights into the dynamics of the northwestern parts of the Svalbard Barents Sea Ice Sheet during the last glacial. Glacial linear features oriented parallel to most fjord axes are identified on swath-bathymetry and high-resolution sub-bottom profiler data. They provide evidence of locally fast-flowing grounded ice draining the northwestern parts of the Svalbard Barents Sea Ice Sheet to the shelf breaks off north and west Svalbard. Eskers overlying glacial lineations reveal the existence of englacial or sub-glacial drainage systems that developed after the termination of fast ice flow. Iceberg ploughmarks suggest that parts of the deglaciation occurred by iceberg calving. Multiple transverse ridges, e.g. grounding zone wedges and moraines, indicate that multiple halts and/or readvances interrupted the deglaciations of the fjords. This includes relatively small moraines, probably deposited during halts and/or readvances in consecutive winters, thus, allowing the calculation of annual retreat rates of the ice fronts in certain fjord areas. Their regular spacing may suggest that e.g. parts of Billefjorden, Smeerenburgfjorden and Woodfjorden were deglaciated at relatively constant rates of at least 140 m/year. However, the deglaciation of van Keulenfjorden accelerated from approx. 80 m/year to about 190 m/year. Lithological analyses allow the study of sub-glacial, glacier-proximal and glacier-distal sedimentary processes and environments, as well as the identification of influences from various sediment sources. They reveal, furthermore, that the deglaciations of multiple fjords terminated quasi-synchronously around 11,200 cal. years BP, but that significant local delays of up to several thousand years occurred.

  19. Northern Cordilleran Ice Sheet Dynamics in Coastal Alaska from MIS 3 to the Present: Initial Results

    NASA Astrophysics Data System (ADS)

    Penkrot, M. L.; Jaeger, J. M.; LeVay, L.; St-Onge, G.; Mix, A. C.; Bahlburg, H.; Davies-Walczak, M.; Gulick, S. P. S.

    2014-12-01

    Establishing the timing of northwestern Cordilleran ice sheet (NCIS) advance-retreat cycles in southern Alaska allows for investigation of global synchronicity in glacial-age climate forcing. Integrated Ocean Drilling Program Expedition 341 targeted the glacial dynamics of the NCIS in the coastal St. Elias range. Sediment cores from Site U1419 encompass times of global ice advance and retreat from MIS 3 to the present, based on a preliminary age model with 5-kya resolution developed using oxygen isotopes from benthic and planktonic foraminifera and stratigraphic correlation with a previously C-14 dated site survey core (Davies et al., 2011; doi:10.1029/2010PA002051). CT images of cores were used to identify sedimentary facies and relative ice sheet proximity. Six sedimentary facies were identified in the images; massive mud with and without lonestones, laminations with and without lonestones, massive and stratified diamict (>1 clast/cm). Elemental scanning XRF data were used to delineate possible downcore changes in sediment provenance using provenance-sensitive transition metals. Diamict and gravelly mud are the most common facies, indicative of persistent glacial input interpreted as marine-terminating glacial systems. Stratified diamicts are interpreted as periods of maximum ice extent (~18-20 ka), whereas massive mud (~14 ka-present) suggests terminus retreat. Intervals of laminated mud with and without lonestones are interpreted as periods of reduced ice cover, with the most recent (~14.5 kya) coinciding with the Bølling Interstade of northern Europe/Greenland (Davies et al., 2011). Downcore changes in Al-normalized metal XRF counts vary along with sedimentary lithoficies, suggesting changes in sediment provenance that may be related to the quantity of glacigenic sediment delivery to this location.

  20. Crystal structure and encapsulation dynamics of ice II-structured neon hydrate.

    PubMed

    Yu, Xiaohui; Zhu, Jinlong; Du, Shiyu; Xu, Hongwu; Vogel, Sven C; Han, Jiantao; Germann, Timothy C; Zhang, Jianzhong; Jin, Changqing; Francisco, Joseph S; Zhao, Yusheng

    2014-07-22

    Neon hydrate was synthesized and studied by in situ neutron diffraction at 480 MPa and temperatures ranging from 260 to 70 K. For the first time to our knowledge, we demonstrate that neon atoms can be enclathrated in water molecules to form ice II-structured hydrates. The guest Ne atoms occupy the centers of D2O channels and have substantial freedom of movement owing to the lack of direct bonding between guest molecules and host lattices. Molecular dynamics simulation confirms that the resolved structure where Ne dissolved in ice II is thermodynamically stable at 480 MPa and 260 K. The density distributions indicate that the vibration of Ne atoms is mainly in planes perpendicular to D2O channels, whereas their distributions along the channels are further constrained by interactions between adjacent Ne atoms.

  1. Reconstructing the retreat dynamics of the Bjørnøyrenna Ice Stream based on new 3D seismic data from the central Barents Sea

    NASA Astrophysics Data System (ADS)

    Piasecka, Emilia D.; Winsborrow, Monica C. M.; Andreassen, Karin; Stokes, Chris R.

    2016-11-01

    The stability of contemporary ice sheets is influenced by the discharge from ice streams - corridors of fast-flowing ice bounded by ice flowing an order of magnitude slower. Reconstructions of palaeo-ice stream dynamics contribute to our understanding of ice stream sensitivity to the ocean-climate system and can aid in the numerical modelling and prediction of future changes in contemporary ice sheets. Here we use 3D seismic data, covering 13,000 km2 in the central Bjørnøyrenna (Bear Island Trough), Barents Sea, to investigate the record of ice streaming preserved on the seafloor and on a buried palaeo-seafloor surface. The unusually broad coverage and high resolution of the dataset, as well as its location in the central area of the trough, enables improved reconstruction of dynamics of the former Bjørnøyrenna Ice Stream in terms of number of streaming events, their trajectory, and their relative age sequence during deglaciation. Our results reveal major changes in the configuration and flow dynamics of the ice stream, with up to 10 flow-switching events identified. For the first time, we also document ice streaming sourced from the eastern Barents Sea around the time of the LGM. This high degree of flow variability is suggested to have resulted from climate-driven changes in ice sheet geometry (and ice divide migration), and variations in topography that influenced calving at the ice stream terminus.

  2. The Roosevelt Island Climate Evolution (RICE) ice core: climate and ice dynamics of the Ross Sea, West Antarctica

    NASA Astrophysics Data System (ADS)

    Lee, J. E.; Brook, E.; Blunier, T.; Severinghaus, J. P.; Bertler, N. A. N.; Waddington, E. D.; Vallelonga, P. T.; Conway, H.; Dahl-Jensen, D.; Buizert, C.; Fudge, T. J.; Parrenin, F.

    2015-12-01

    Ice cores drilled in Antarctica have proven to be remarkable archives of past climate, but most have been recovered from the remote Antarctic interior. In contrast, little is known about the climate history of coastal ice domes despite their relevance to ocean-ice interaction and sea level rise. The Roosevelt Island Climate Evolution project (RICE) recovered a 763 m ice core in 2013 from Roosevelt Island, West Antarctica. Located at the edge of the Ross Ice Shelf and grounded below sea level, Roosevelt Island is sensitive to oceanic forcing and may provide new information about potential drivers of abrupt interhemispheric climate connections and its location is ideal for exploring the retreat of the West Antarctic Ice Sheet (WAIS) from its glacial maximum through the Ross Sea. Here we present a continuous chronology for the RICE Ice Core covering the last 40,000 years with additional evidence of ice dating to at least 80,000 years near the bottom of the core. Both the depth-age relationship and reconstructed profile of annual layer thicknesses can be used to infer changes in climate and the glacial history of the East Ross Sea Embayment. The most striking feature of the record occurred during the Antarctic Cold Reversal. At this time a combination of data including thin annual layers, abrupt lowering of δ15N of N2 and δ40Ar in trapped air, and strongly depleted δD of ice suggest either a pronounced change in cyclonic activity and regional storm tracks and/or adjustment in the configuration of the Ross Ice Sheet during this period of rapid climate change and sea level rise.

  3. Reconstruction of the Greenland ice sheet dynamics in a fully coupled Earth System Model

    NASA Astrophysics Data System (ADS)

    Rybak, Oleg; Volodin, Evgeny; Huybrechts, Philippe

    2016-04-01

    Earth system models (ESMs) are undoubtedly effective tools for studying climate dynamics. Incorporation of evolving ice sheets to ESMs is a challenging task because response times of the climate system and of ice sheets differ by several orders of magnitude. Besides, AO GCMs operate on spatial and temporal resolutions substantially differing from those of ice sheet models (ICMs). Therefore elaboration of an effective coupling methodology of an AO GCM and an ICM is the key problem of an ESM construction and utilization. Several downscaling strategies of varying complexity exist now of data exchange between modeled climate system and ice sheets. Application of a particular strategy depends on the research objectives. In our view, the optimum approach for model studying of significant environmental changes (e.g. glacial/interglacial transitions) when ice sheets undergo substantial evolution of geometry and volume would be an asynchronous coupling. The latter allows simulation in the interactive way of growth and decay of ice sheets in the changing climatic conditions. In the focus of the presentation, is the overview of coupling aspects of an AO GCM INMCM32 elaborated in the Institute of Numerical Mathematics (Moscow, Russia) to the Greenland ice sheet model (GrISM, Vrije Uninersiteit Brussel, Belgium). To provide interactive coupling of INMCM32 (spatial resolution 5°×4°, 21 vertical layers and temporal resolution 6 min. in the atmospheric block) and GrISM (spatial resolution 20×20 km, 51 vertical layers and 1 yr temporal resolution), we employ a special energy- and water balance model (EWBM-G), which serves as a buffer providing effective data exchange between INMCM32 and GrISM. EWBM-G operates in a rectangle domain including Greenland. Transfer of daily meanings of simulated climatic variables (air surface temperature and specific humidity) is provided on the lateral boundarias of the domain and inside the domain (sea level air pressure, wind speed and total

  4. Last glacial ice sheet dynamics and deglaciation on Svalbard inferred from fjord records (Invited)

    NASA Astrophysics Data System (ADS)

    Forwick, M.; Vorren, T. O.; Baeten, N. J.; Hansen, T.; Kempf, P.; Velle, J. H.; Laberg, J.

    2013-12-01

    Swath bathymetry, high-resolution sub-bottom profiles and sediment cores from fjords on north and west Svalbard document a variety of glacigenic landforms and sedimentary processes, providing valuable insights into the dynamics of the northwestern parts of the Svalbard Barents Sea Ice Sheet during the last glacial. Glacial linear features oriented parallel to most fjord axes are identified on swath-bathymetry and high-resolution sub-bottom profiler data. They provide evidence of locally fast-flowing grounded ice draining the northwestern parts of the Svalbard Barents Sea Ice Sheet to the shelf breaks off north and west Svalbard. Eskers overlying glacial lineations reveal the existence of englacial or sub-glacial drainage systems that developed after the termination of fast ice flow. Iceberg ploughmarks suggest that parts of the deglaciation occurred by iceberg calving. Multiple transverse ridges, e.g. grounding zone wedges and moraines, indicate that multiple halts and/or readvances interrupted the deglaciations of the fjords. This includes relatively small moraines, probably deposited during halts and/or readvances in consecutive winters, thus, allowing the calculation of annual retreat rates of the ice fronts in certain fjord areas. Their regular spacing may suggest that e.g. parts of Billefjorden, Smeerenburgfjorden and Woodfjorden were deglaciated at relatively constant rates of at least 140 m/year. However, the deglaciation of van Keulenfjorden accelerated from approx. 80 m/year to about 190 m/year. Lithological analyses allow the study of sub-glacial, glacier-proximal and glacier-distal sedimentary processes and environments, as well as the identification of influences from various sediment sources. They reveal, furthermore, that the deglaciations of multiple fjords terminated quasi-synchronously around 11,200 cal. years BP, but that significant local delays of up to several thousand years occurred. We present examples of the above mentioned landforms

  5. Intracardiac Echocardiography (ICE) Measurement of Dynamic Myocardial Stiffness with Shear Wave Velocimetry

    PubMed Central

    Hollender, Peter J.; Wolf, Patrick D.; Goswami, Robi; Trahey, Gregg E.

    2012-01-01

    Acoustic Radiation Force (ARF)-based methods have been demonstrated to be a viable tool for noninvasively estimating tissue elastic properties, and shear wave velocimetry has been used to quantitatively measure the stiffening and relaxation of myocardial tissue in open-chest experiments. Dynamic stiffness metrics may prove to be indicators for certain cardiac diseases, but a clinically-viable means of remotely generating and tracking transverse wave propagation in myocardium is needed. Intracardiac echocardiography (ICE) catheter-tip transducers are demonstrated here as a viable tool for making this measurement. ICE probes achieve favorable proximity to the myocardium, enabling the use of shear wave velocimetry from within the right ventricle throughout the cardiac cycle. This work describes the techniques used to overcome the challenges of using a small probe to perform ARF-driven shear wave velocimetry, and presents in vivo porcine data showing the effectiveness of this method in the interventricular septum. Acoustic Radiation Force (ARF)-based methods have been demonstrated to be a viable tool for noninvasively estimating tissue elastic properties, and shear wave velocimetry has been used to quantitatively measure the stiffening and relaxation of myocardial tissue in open-chest experiments. Dynamic stiffness metrics may prove to be indicators for certain cardiac diseases, but a clinically-viable means of remotely generating and tracking transverse wave propagation in myocardium is needed. Intracardiac echocardiography (ICE) catheter-tip transducers are demonstrated here as a viable tool for making this measurement. ICE probes achieve favorable proximity to the myocardium, enabling the use of shear wave velocimetry from within the right ventricle throughout the cardiac cycle. This work describes the techniques used to overcome the challenges of using a small probe to perform ARF-driven shear wave velocimetry, and presents in vivo porcine data showing the

  6. DRI Technical Program: Emerging Dynamics of the Marginal Ice Zone Ice, Ocean and Atmosphere Interactions in the Arctic Marginal Ice Zone. Year 3 Annual Report

    DTIC Science & Technology

    2014-09-30

    and Atmosphere Interactions in the Arctic Marginal...ice mass balance buoys (IMBs), wave buoys (WBs), and Automatic Weather Stations (AWS) in the region north of Alaska. The now deployed arrays have a... Arctic Marginal Ice Zone. Year 3 Annual Report 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) 5d. PROJECT NUMBER 5e

  7. Non-Linear Dynamics Tools for the Motion Analysis and Condition Monitoring of Robot Joints

    NASA Astrophysics Data System (ADS)

    Trendafilova, I.; van Brussel, H.

    2001-11-01

    Time series from non-damaged and three types of damaged robot joints are considered and analysed from the viewpoint of non-linear dynamics. The embedding spaces for the four types of signals are recovered. The application of surrogate data tests is used to prove the presence of non-linearities in the joints. The results suggest a rise in unstable behaviour due to the introduction of backlash in robot joints. The chaotic behaviour gets stronger with the increase of the backlash extent. This is confirmed by the increase of the embedding dimension as well as by the increase of the Lyapunov exponents and the correlation dimension with the backlash increase. A straightforward method for condition monitoring using non-linear dynamics characteristics, based on a classification procedure, is suggested.

  8. Dynamic optical imaging of vascular and metabolic reactivity in rheumatoid joints.

    PubMed

    Lasker, Joseph M; Fong, Christopher J; Ginat, Daniel T; Dwyer, Edward; Hielscher, Andreas H

    2007-01-01

    Dynamic optical imaging is increasingly applied to clinically relevant areas such as brain and cancer imaging. In this approach, some external stimulus is applied and changes in relevant physiological parameters (e.g., oxy- or deoxyhemoglobin concentrations) are determined. The advantage of this approach is that the prestimulus state can be used as a reference or baseline against which the changes can be calibrated. Here we present the first application of this method to the problem of characterizing joint diseases, especially effects of rheumatoid arthritis (RA) in the proximal interphalangeal finger joints. Using a dual-wavelength tomographic imaging system together with previously implemented model-based iterative image reconstruction schemes, we have performed initial dynamic imaging case studies on a limited number of healthy volunteers and patients diagnosed with RA. Focusing on three cases studies, we illustrated our major finds. These studies support our hypothesis that differences in the vascular reactivity exist between affected and unaffected joints.

  9. Comparative analysis of methods for estimating arm segment parameters and joint torques from inverse dynamics.

    PubMed

    Piovesan, Davide; Pierobon, Alberto; Dizio, Paul; Lackner, James R

    2011-03-01

    A common problem in the analyses of upper limb unfettered reaching movements is the estimation of joint torques using inverse dynamics. The inaccuracy in the estimation of joint torques can be caused by the inaccuracy in the acquisition of kinematic variables, body segment parameters (BSPs), and approximation in the biomechanical models. The effect of uncertainty in the estimation of body segment parameters can be especially important in the analysis of movements with high acceleration. A sensitivity analysis was performed to assess the relevance of different sources of inaccuracy in inverse dynamics analysis of a planar arm movement. Eight regression models and one water immersion method for the estimation of BSPs were used to quantify the influence of inertial models on the calculation of joint torques during numerical analysis of unfettered forward arm reaching movements. Thirteen subjects performed 72 forward planar reaches between two targets located on the horizontal plane and aligned with the median plane. Using a planar, double link model for the arm with a floating shoulder, we calculated the normalized joint torque peak and a normalized root mean square (rms) of torque at the shoulder and elbow joints. Statistical analyses quantified the influence of different BSP models on the kinetic variable variance for given uncertainty on the estimation of joint kinematics and biomechanical modeling errors. Our analysis revealed that the choice of BSP estimation method had a particular influence on the normalized rms of joint torques. Moreover, the normalization of kinetic variables to BSPs for a comparison among subjects showed that the interaction between the BSP estimation method and the subject specific somatotype and movement kinematics was a significant source of variance in the kinetic variables. The normalized joint torque peak and the normalized root mean square of joint torque represented valuable parameters to compare the effect of BSP estimation methods

  10. Structure, spectroscopy and dynamics of layered H2O and CO2 ices

    USGS Publications Warehouse

    ,; Plattner, Nuria; Meuwly, Markus

    2012-01-01

    Molecular dynamics simulations of structural, spectroscopic and dynamical properties of mixed water–carbon dioxide (H2O–CO2) ices are discussed over temperature ranges relevant to atmospheric and astrophysical conditions. The simulations employ multipolar force fields to represent electrostatic interactions which are essential for spectroscopic and dynamical investigations. It is found that at the water/CO2 interface the water surface acts as a template for the CO2 component. The rotational reorientation times in both bulk phases agree well with experimental observations. A pronounced temperature effect on the CO2 reorientation time is observed between 100 K and 200 K. At the interface, water reorientation times are nearly twice as long compared to water in the bulk. The spectroscopy of such ices is rich in the far-infrared region of the spectrum and can be related to translational and rotational modes. Furthermore, spectroscopic signatures mediated across the water/CO2 interface are found in this frequency range (around 440 cm−1). These results will be particularly important for new airborne experiments such as planned for SOFIA.

  11. Orbital Dynamics and Habitability II: Obliquity Forcing and Suppression of the Ice-Albedo Feedback

    NASA Astrophysics Data System (ADS)

    Barnes, Rory; Armstrong, J. C.; Domagal-Goldman, S. D.; Breiner, J.; Meadows, V. S.

    2012-05-01

    We explore the impact of obliquity variations on planetary habitability in hypothetical systems with high mutual inclination. We restrict our study to systems consisting of a solar-mass star, an Earth-mass planet at 1 AU, and 1 or 2 giant planets. We verify that these systems are stable for 100 million years with N-body simulations. We then calculate the obliquity variations induced by the orbital architecture on the Earth-mass planets. We find that in some cases the spin axes can precess through over 100 degrees per thousand years. Next, we run energy balance models (EBM) on the terrestrial planets to assess surface temperature and ice coverage on the planets' oceans. Finally, we explore differences in the outer edge of the habitable zone for planets with rapid obliquity variations compared to fixed obliquity. We run EBM simulations for a range of values for the semi-major axis and find that planets undergoing extreme axial perturbations may be habitable at larger distances than those with static obliquity. This extension arises because the obliquity variations suppress the build-up of ice sheets at the poles, reducing the effectiveness of the ice-albedo-temperature feedback. The dynamical evolution of planetary systems may be a crucial feature in the distribution of life in the galaxy.

  12. Impacts of marine instability across the East Antarctic Ice Sheet on Southern Ocean dynamics

    NASA Astrophysics Data System (ADS)

    Phipps, Steven J.; Fogwill, Christopher J.; Turney, Christian S. M.

    2016-09-01

    Recent observations and modelling studies have demonstrated the potential for rapid and substantial retreat of large sectors of the East Antarctic Ice Sheet (EAIS). This has major implications for ocean circulation and global sea level. Here we examine the effects of increasing meltwater from the Wilkes Basin, one of the major marine-based sectors of the EAIS, on Southern Ocean dynamics. Climate model simulations reveal that the meltwater flux rapidly stratifies surface waters, leading to a dramatic decrease in the rate of Antarctic Bottom Water (AABW) formation. The surface ocean cools but, critically, the Southern Ocean warms by more than 1 °C at depth. This warming is accompanied by a Southern Ocean-wide "domino effect", whereby the warming signal propagates westward with depth. Our results suggest that melting of one sector of the EAIS could result in accelerated warming across other sectors, including the Weddell Sea sector of the West Antarctic Ice Sheet. Thus, localised melting of the EAIS could potentially destabilise the wider Antarctic Ice Sheet.

  13. Outlines and Dynamics of Eurarctic Ice Caps in Anomalous Gravity Fields

    NASA Astrophysics Data System (ADS)

    Sharov, Aleksey; Nikolskiy, Dmitry

    2016-08-01

    The present investigation was aimed at studying spatial variability and directional dynamics of inland ice/snow fields in relation to lateral variations of surface gravity at the sub-regional scale of tens to hundreds of kilometres. The main goal was to evidence, both theoretically and empirically, the existence and significance of gravitational impacts and associated atmospheric effects on the status and fluctuations of Eurasia's northernmost insular ice caps using space- borne radar altimetry and interferometry data from the Earth Explorers and Sentinel missions in conjunction with GOCE satellite gradiometry, ground-based meteorological time series and glaciological observations. EO-based geodetic and cryospheric models describing the amount of solid precipitation, snow drift and accumulation, glacier elevation change and ice flow pattern were generated, homogenized and combined in the terrain-following reference frame. The models were then verified and applied to the diagnosis of glacioclimatic differences in arctic lowlands with strong gravity anomalies. It was ascertained that surface gravity gradients modulate the atmospheric circulation and stability thereby influencing the intensity of local precipitation and glacier growth and flow patterns in a cascade fashion.

  14. Temperature and magnetic-field driven dynamics in artificial magnetic square ice

    DOE PAGES

    Sophie A. Morley; Stein, Aaron; Rosamond, Mark C.; ...

    2015-08-09

    Artificial spin ices are often spoken of as being realisations of some of the celebrated vertex models of statistical mechanics, where the exact microstate of the system can be imaged using advanced magnetic microscopy methods. The fact that a stable image can be formed means that the system is in fact athermal and not undergoing the usual finite-temperature fluctuations of a statistical mechanical system. In this paper we report on the preparation of artificial spin ices with islands that are thermally fluctuating due to their very small size. The relaxation rate of these islands was determined using variable frequency focusedmore » magneto-optic Kerr measurements. We performed magnetic imaging of artificial spin ice under varied temperature and magnetic field using X-ray transmission microscopy which uses X-ray magnetic circular dichroism to generate magnetic contrast. Furthermore, we have developed an on-membrane heater in order to apply temperatures in excess of 700 K and have shown increased dynamics due to higher temperature. Due to the ‘photon-in, photon-out' method employed here, it is the first report where it is possible to image the microstates of an ASI system under the simultaneous application of temperature and magnetic field, enabling the determination of relaxation rates, coercivties, and the analysis of vertex population during reversal.« less

  15. Temperature and magnetic-field driven dynamics in artificial magnetic square ice

    SciTech Connect

    Sophie A. Morley; Stein, Aaron; Rosamond, Mark C.; Venero, Diego Alba; Hrabec, Ales; Shepley, Philippa M.; Im, Mi -Young; Fischer, Peter; Bryan, Matthew T.; Allwood, Dan A.; Steadman, Paul; Langridge, Sean; Marrows, Christopher H.

    2015-08-09

    Artificial spin ices are often spoken of as being realisations of some of the celebrated vertex models of statistical mechanics, where the exact microstate of the system can be imaged using advanced magnetic microscopy methods. The fact that a stable image can be formed means that the system is in fact athermal and not undergoing the usual finite-temperature fluctuations of a statistical mechanical system. In this paper we report on the preparation of artificial spin ices with islands that are thermally fluctuating due to their very small size. The relaxation rate of these islands was determined using variable frequency focused magneto-optic Kerr measurements. We performed magnetic imaging of artificial spin ice under varied temperature and magnetic field using X-ray transmission microscopy which uses X-ray magnetic circular dichroism to generate magnetic contrast. Furthermore, we have developed an on-membrane heater in order to apply temperatures in excess of 700 K and have shown increased dynamics due to higher temperature. Due to the ‘photon-in, photon-out' method employed here, it is the first report where it is possible to image the microstates of an ASI system under the simultaneous application of temperature and magnetic field, enabling the determination of relaxation rates, coercivties, and the analysis of vertex population during reversal.

  16. Defect Dynamics in Artificial Colloidal Ice: Real-Time Observation, Manipulation, and Logic Gate.

    PubMed

    Loehr, Johannes; Ortiz-Ambriz, Antonio; Tierno, Pietro

    2016-10-14

    We study the defect dynamics in a colloidal spin ice system realized by filling a square lattice of topographic double well islands with repulsively interacting magnetic colloids. We focus on the contraction of defects in the ground state, and contraction or expansion in a metastable biased state. Combining real-time experiments with simulations, we prove that these defects behave like emergent topological monopoles obeying a Coulomb law with an additional line tension. We further show how to realize a completely resettable "nor" gate, which provides guidelines for fabrication of nanoscale logic devices based on the motion of topological magnetic monopoles.

  17. Laser driven quasi-isentropic compression experiments (ICE) for dynamically loading materials at high strain rates

    SciTech Connect

    Smith, R; Eggert, J; Celliers, P; Jankowski, A; Lorenz, T; Moon, S; Edwards, M J; Collins, G

    2006-03-30

    We demonstrate the recently developed technique of laser driven isentropic compression (ICE) for dynamically compressing Al samples at high loading rates close to the room temperature isentrope and up to peak stresses above 100GPa. Upon analysis of the unloading profiles from a multi-stepped Al/LiF target a continuous path through Stress-Density space may be calculated. For materials with phase transformations ramp compression techniques reveals the location of equilibrium phase boundaries and provide information on the kinetics of the lattice re-ordering.

  18. Documentation for a Two-Level Dynamic Thermodynamic Sea Ice Model.

    DTIC Science & Technology

    1980-02-01

    DOCUMENTATION FOR A TWO-LEVEL DYNAMIC THERMODYNAMIC SEA ICE MO--ETCfU) UNCLASSIFIED CRREL-SR-80-8 NL La mIuIIIuuuhuumEllElllllEEEE EIIIIIIIIEI 3 6...ISTRUCTIONSREPORT DOCUMENTATION PAEBEFORE COMPLETIG FORM AREPORT NUMBER 2. GOVT ACCESSION NO. 3 . RECIPIENT’S CATALOG NUMBER LE (IM7711"W5. TYPE OF REPORT & PERIOD...AND ADDRESS ----- Office of Naval Research F Washington, D.C. 20360C/ National Aeronautics and Space Administration 3 Washington, D.C. 20546

  19. Self-organized complementary joint action: Behavioral dynamics of an interpersonal collision-avoidance task.

    PubMed

    Richardson, Michael J; Harrison, Steven J; Kallen, Rachel W; Walton, Ashley; Eiler, Brian A; Saltzman, Elliot; Schmidt, R C

    2015-06-01

    Understanding stable patterns of interpersonal movement coordination is essential to understanding successful social interaction and activity (i.e., joint action). Previous research investigating such coordination has primarily focused on the synchronization of simple rhythmic movements (e.g., finger/forearm oscillations or pendulum swinging). Very few studies, however, have explored the stable patterns of coordination that emerge during task-directed complementary coordination tasks. Thus, the aim of the current study was to investigate and model the behavioral dynamics of a complementary collision-avoidance task. Participant pairs performed a repetitive targeting task in which they moved computer stimuli back and forth between sets of target locations without colliding into each other. The results revealed that pairs quickly converged onto a stable, asymmetric pattern of movement coordination that reflected differential control across participants, with 1 participant adopting a more straight-line movement trajectory between targets, and the other participant adopting a more elliptical trajectory between targets. This asymmetric movement pattern was also characterized by a phase lag between participants and was essential to task success. Coupling directionality analysis and dynamical modeling revealed that this dynamic regime was due to participant-specific differences in the coupling functions that defined the task-dynamics of participant pairs. Collectively, the current findings provide evidence that the dynamical coordination processes previously identified to underlie simple motor synchronization can also support more complex, goal-directed, joint action behavior, and can participate the spontaneous emergence of complementary joint action roles.

  20. Chronology and dynamics of the Amundsen Gulf Ice Stream in Arctic Canada during the last glacial-interglacial transition

    NASA Astrophysics Data System (ADS)

    Lakeman, T. R.; MacLean, B.; Blasco, S.; Bennett, R.; Hughes Clarke, J. E.

    2012-04-01

    An extensive ice stream of the Laurentide ice sheet occupied Amundsen Gulf during the Last Glacial Maximum. The grounded ice stream extended northwestward to the margin of the inner shelf in the Beaufort Sea and to a depth of 450 metres. This glacier was one of the largest ice streams to emanate into the Arctic Ocean during the last glaciation and, as such, exerted a primary influence on the dynamics of the northwest Laurentide Ice Sheet. Ice stream retreat from its maximum position began prior to 13,000 cal yr BP. The pattern of extensive sole marks or glacial flutings on the seabed and on the adjacent mainland and islands confirms the direction of flow was from southeast to northwest. In the Gulf these features are imprinted primarily on subglacial sediment deposits. The bathymetry of the Gulf and known extent of the ice stream on land indicates the ice was at least 700 m thick. A series of moraines at the mouth of the Gulf mark temporary positions of the retreating ice stream margin. Early stages of ice retreat may have been associated with meltwater discharge under the ice stream as evidenced by current erosion associated with some sole marks or glacial flutings. Melting at the leading edge of the ice stream resulted in calving of icebergs and the generation of keel-scour marks in the seabed. Retreat of the ice stream was relatively rapid as indicated by thin and spatially discontinuous deglacial glaciomarine sediment in the Gulf. Furthermore, an expansive database of deglacial radiocarbon ages from eastern Banks Island, western Victoria Island, and the adjacent Arctic mainland, indicates that the ice stream had retreated fully from the Gulf by 12,500 cal yr BP. The lack of Holocene sediment draping the sole marks or flutings, and outcrops of exposed bedrock and glaciomarine sediment indicate very low sedimentation rates since ice retreat. The thin veneer of recent fine sediment that has been deposited discontinuously on the seabed in the Gulf indicates little

  1. Dynamics of the North American Ice Sheet Complex during its inception and build-up to the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Stokes, Chris R.; Tarasov, Lev; Dyke, Arthur S.

    2012-09-01

    The North American Ice Sheet Complex played a major role in global sea level fluctuations during the Late Quaternary but our knowledge of its dynamics is based mostly on its demise from the Last Glacial Maximum (LGM), a period characterised by non-linear behaviour in the form of punctuated ice margin recession, episodic ice streaming and major shifts in the location of ice divides. In comparison, knowledge of the pre-LGM ice complex is poorly constrained, largely because of the fragmentary nature of the evidence relating to ice sheet build-up. In this paper, we explore the inception and growth of ice (120-20 ka) using a glacial systems model which has been calibrated against a large and diverse set of data relating to the deglacial interval. We make use of calibration data prior to the LGM but its scarcity introduces greater uncertainty, which is partly alleviated by our large ensemble analysis. Results suggest that, following the last interglaciation (Oxygen Isotope Stage: OIS 5e), the ice complex initiated over the north-eastern Canadian Arctic and in the Cordillera within a few thousand years. It then underwent rapid growth to an OIS 5 maximum at ˜110 ka (5d) and covered ˜70% of the area occupied by the LGM ice cover (although only 30% by volume). An OIS 5 minimum is modelled at ˜80 ka (5a), before a second phase of rapid growth at the start of OIS 4, which culminated in a large ice complex at ˜65 ka (almost as large as at the LGM). Subsequent deglaciation was rapid (maximum modelled sea level contribution of >16 cm per century) and resulted in an OIS 3 minimum between ca 55-60 ka. Thereafter, the ice complex grew towards its LGM configuration, interrupted by several phases of successively less significant mass loss. Our results support and extend previous inferences based on geological evidence and reinforce the notion of a highly dynamic pre-LGM ice complex (e.g. with episodes of ±10 s m of eustatic sea level equivalent in <5 ka). Consistent with previous

  2. A Tale of Two Forcings: Present-Day Coupled Antarctic Ice-sheet/Southern Ocean dynamics using the POPSICLES model.

    NASA Astrophysics Data System (ADS)

    Martin, Daniel; Asay-Davis, Xylar; Cornford, Stephen; Price, Stephen; Ng, Esmond; Collins, William

    2015-04-01

    We present POPSICLES simulation results covering the full Antarctic Ice Sheet and the Southern Ocean spanning the period 1990 to 2010 resulting from two different choices of climate forcing: a 'normal-year' climatology and the CORE v. 2 interannual forcing data (Large and Yeager 2008). Simulations are performed at 0.1o (~5 km) ocean resolution and adaptive ice sheet resolution as fine as 500 m. We compare time-averaged melt rates below a number of major ice shelves with those reported by Rignot et al. (2013) as well as other recent studies. We also present seasonal variability and decadal melting trends from several Antarctic regions, along with the response of the ice shelves and consequent dynamics of the grounded ice sheet. POPSICLES couples the POP2x ocean model, a modified version of the Parallel Ocean Program (Smith and Gent, 2002), and the BISICLES ice-sheet model (Cornford et al., 2012). POP2x includes sub-ice-shelf circulation using partial top cells (Losch, 2008) and boundary layer physics following Holland and Jenkins (1999), Jenkins (2001), and Jenkins et al. (2010). Standalone POP2x output compares well with standard ice-ocean test cases (e.g., ISOMIP; Losch, 2008) and other continental-scale simulations and melt-rate observations (Kimura et al., 2013; Rignot et al., 2013). BISICLES makes use of adaptive mesh refinement and a 1st-order accurate momentum balance similar to the L1L2 model of Schoof and Hindmarsh (2009) to accurately model regions of dynamic complexity, such as ice streams, outlet glaciers, and grounding lines. Results of BISICLES simulations have compared favorably to comparable simulations with a Stokes momentum balance in both idealized tests (MISMIP-3d; Pattyn et al., 2013) and realistic configurations (Favier et al. 2014).

  3. Adaptive control for backward quadrupedal walking VI. metatarsophalangeal joint dynamics and motor patterns of digit muscles.

    PubMed

    Trank, T V; Smith, J L

    1996-02-01

    1. We compared the dynamics of the metatarsophalangeal (MTP) joint of the cat's hind paw and the motor patterns of two short and four long muscles of the digits for two walking forms, forward (FWD) and backward (BWD). Kinematic (angular displacements) data digitized from high-speed ciné film and electromyographic (EMG) data were synchronized and assessed for bouts of treadmill walking. Kinetic data (joint forces) were calculated from kinematic and anthropometric data with the use of inverse-dynamic calculations in which the MTP joint net torque was divided into gravitational, motion-dependent, ground contact (absent for swing), and muscle torque components. Swing-phase kinetics were calculated from treadmill steps and stance-phase kinetics from overground steps in which one hind paw contacted a miniature force platform embedded in the walkway. 2. The plantar angle at the intersection of the metatarsal and phalangeal segmental lines was used to measure MTP angular displacements. During swing for both walking forms, the MTP joint flexed (F) and then extended (E); however, the F-E transition occurred at the onset of FWD swing and at the end of BWD swing. For FWD walking, the MTP joint extended at a constant velocity during most of stance as the cat's weight rotated forward over the paw. During the unweighting phase at the end of stance, the MTP joint flexed rapidly before paw lift off. For BWD walking, the MTP joint extended briefly at stance onset (similar to a yield) and then flexed at a constant velocity as the cat's weight rotated backward over the paw. At the end of stance, the MTP joint extended and then flexed slightly as the paw was unweighted before paw lift off. 3. For both forms of walking, three of the six muscles tested were recruited just before paw contact and remained active for most (75-80%) of stance for both walking forms: plantaris (PLT), flexor hallucis longus (FHL), and flexor digitorum brevis (FDB). Their recruitment contributed to the flexor

  4. Energy relaxation of intermolecular motions in supercooled water and ice: A molecular dynamics study

    NASA Astrophysics Data System (ADS)

    Yagasaki, Takuma; Saito, Shinji

    2011-12-01

    We investigate the energy relaxation of intermolecular motions in liquid water at temperatures ranging from 220 K to 300 K and in ice at 220 K using molecular dynamics simulations. We employ the recently developed frequency resolved transient kinetic energy analysis, which provides detailed information on energy relaxation in condensed phases like two-color pump-probe spectroscopy. It is shown that the energy cascading in liquid water is characterized by four processes. The temperature dependences of the earlier three processes, the rotational-rotational, rotational-translational, and translational-translational energy transfers, are explained in terms of the density of states of the intermolecular motions. The last process is the slow energy transfer arising from the transitions between potential energy basins caused by the excitation of the low frequency translational motion. This process is absent in ice because the hydrogen bond network rearrangement, which accompanies the interbasin transitions in liquid water, cannot take place in the solid phase. We find that the last process in supercooled water is well approximated by a stretched exponential function. The stretching parameter, β, decreases from 1 to 0.72 with decreasing temperature. This result indicates that the dynamics of liquid water becomes heterogeneous at lower temperatures.

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

    NASA Astrophysics Data System (ADS)

    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.

  6. Gas Dynamic Spray Technology Demonstration Project Management. Joint Test Report

    NASA Technical Reports Server (NTRS)

    Lewis, Pattie

    2011-01-01

    The standard practice for protecting metallic substrates in atmospheric environments is the use of an applied coating system. Current coating systems used across AFSPC and NASA contain volatile organic compounds (VOCs) and hazardous air pollutants (HAPs). These coatings are sUbject to environmental regulations at the Federal and State levels that limit their usage. In addition, these coatings often cannot withstand the high temperatures and exhaust that may be experienced by Air Force Space Command (AFSPC) and NASA structures. In response to these concerns, AFSPC and NASA have approved the use of thermal spray coatings (TSCs). Thermal spray coatings are extremely durable and environmentally friendly coating alternatives, but utilize large cumbersome equipment for application that make the coatings difficult and time consuming to repair. Other concerns include difficulties coating complex geometries and the cost of equipment, training, and materials. Gas Dynamic Spray (GOS) technology (also known as Cold Spray) was evaluated as a smaller, more maneuverable repair method as well as for areas where thermal spray techniques are not as effective. The technology can result in reduced maintenance and thus reduced hazardous materials/wastes associated with current processes. Thermal spray and GOS coatings also have no VOCs and are environmentally preferable coatings. The primary objective of this effort was to demonstrate GDS technology as a repair method for TSCs. The aim was that successful completion of this project would result in approval of GDS technology as a repair method for TSCs at AFSPC and NASA installations to improve corrosion protection at critical systems, facilitate easier maintenance activity, extend maintenance cycles, eliminate flight hardware contamination, and reduce the amount of hazardous waste generated.

  7. Dynamical ice sheet model coupling with the GEOS-5 AGCM: A preliminary assessment

    NASA Astrophysics Data System (ADS)

    Cullather, R. I.; Zhao, B.; Nowicki, S.; Suarez, M. J.

    2013-12-01

    Dynamical ice sheet models (ISMs) have been developed to address well-known limitations in eustatic change prediction capabilities. Coupling ISMs to an atmospheric general circulation model (AGCM) is not straightforward, due in part to the extreme difference in spatial scales between the ISM mesh and AGCM grid. In given locations, ISM element edge lengths may be a few km or less, while the AGCM typically has grid spacings on the order of 10s to 100s of km. The Goddard Earth Observing System Model, version 5 (GEOS-5) is a finite-volume AGCM and employs a cube-sphere atmospheric grid (nominally 1° resolution) and a catchment-based land surface scheme that operates on sub-grid scale areas, or tiles, that describe surface characteristics. The land surface component communicates with the atmosphere on a semi-implicit time step via the exchange grid. In this study, coupling between the AGCM and the ISM is facilitated through sub-grid scale land surface tiles that are defined for each element of the ISM. The ISM used here is the Ice Sheet System Model (ISSM) from NASA Jet Propulsion Laboratory and Univ. California at Irvine, which has been adapted for the Greenland Ice Sheet using the 72,320-element Schlagel mesh and using a shallow ice approximation. In the AGCM, land surface tiles are uniquely characterized through a simple downscaling parameterization of surface temperature within each AGCM grid box using a defined lapse rate. On each land surface tile, GEOS-5 employs an advanced snow hydrology model for improved representation of the ice sheet surface mass balance. This preliminary assessment focuses on the differences in the AGCM surface mass balance and surface temperature fields resulting from the downscaling measures employed in the context of an exchange grid, semi-implicit coupling with the atmosphere, and the response of the ISM. Differences in AGCM computational performance with the addition of Greenland tiles is examined, and comparative advantages of

  8. Measurements of supraglacial lake drainage and surface streams over West Greenland and effects on ice dynamics

    NASA Astrophysics Data System (ADS)

    Tedesco, M.; Willis, I. C.; Alexander, P. M.; Banwell, A. F.

    2011-12-01

    manner, hence providing information on how ice sheet dynamics (at which distance and direction) are impacted by the drainage of surface lakes.

  9. A parameters optimization method for planar joint clearance model and its application for dynamics simulation of reciprocating compressor

    NASA Astrophysics Data System (ADS)

    Hai-yang, Zhao; Min-qiang, Xu; Jin-dong, Wang; Yong-bo, Li

    2015-05-01

    In order to improve the accuracy of dynamics response simulation for mechanism with joint clearance, a parameter optimization method for planar joint clearance contact force model was presented in this paper, and the optimized parameters were applied to the dynamics response simulation for mechanism with oversized joint clearance fault. By studying the effect of increased clearance on the parameters of joint clearance contact force model, the relation of model parameters between different clearances was concluded. Then the dynamic equation of a two-stage reciprocating compressor with four joint clearances was developed using Lagrange method, and a multi-body dynamic model built in ADAMS software was used to solve this equation. To obtain a simulated dynamic response much closer to that of experimental tests, the parameters of joint clearance model, instead of using the designed values, were optimized by genetic algorithms approach. Finally, the optimized parameters were applied to simulate the dynamics response of model with oversized joint clearance fault according to the concluded parameter relation. The dynamics response of experimental test verified the effectiveness of this application.

  10. Observation of ice-rule violation and monopole dynamics via edge nucleation of domain walls in artificial spin ice lattice

    NASA Astrophysics Data System (ADS)

    Krishnia, S.; Purnama, I.; Lew, W. S.

    2016-12-01

    In a patterned Co honeycomb spin ice structure, we show that violation in the ice-rule or magnetic monopoles, can be observed during a magnetization reversal process in 430 Oe≤H≤760 Oe magnetic field (H) range. The monopoles are shown to originate from the nucleation of domain walls at the edges, and they hop towards the other edge via the propagation of magnetic domain walls. The paths that the domain walls traveled or the Dirac strings, are shown to increase in length with magnetic fields increment and no random flipping of the bars are observed in the structure.

  11. Growth inhibition at the ice prismatic plane induced by a spruce budworm antifreeze protein: a molecular dynamics simulation study.

    PubMed

    Nada, H; Furukawa, Y

    2011-11-28

    A molecular dynamics simulation was conducted to investigate the growth kinetics at the ice prismatic interface to which a spruce budworm antifreeze protein was bound. Two initial binding conformations of the protein at the interface--one energetically stable and the other energetically unstable--were examined. For both binding conformations, the growth of ice was observed around the protein. A sharp decrease in the rate of ice growth was observed around the protein that initially had the energetically stable binding conformation. Simulation results suggest that the observed decrease in the ice growth rate was attributable to melting point depression caused by the Gibbs-Thomson effect. The protein that initially had the energetically unstable binding conformation markedly relaxed so as to stably bind to the prismatic plane interface of the grown ice; thereafter, a decrease in the ice growth rate was observed as well. However, the binding conformation that the protein approached during the relaxation was different from that of the protein that initially had the energetically stable binding conformation. Thus, the simulation indicates the existence of two binding conformations for inducing a decrease in the ice growth rate. The results are possibly related to the hyperactivity of a spruce budworm antifreeze protein in real systems.

  12. Comparison of selected polarizable and nonpolarizable water models in molecular dynamics simulations of ice I(h).

    PubMed

    Gladich, Ivan; Roeselová, Martina

    2012-08-28

    We present a molecular dynamics simulation study in which we determined the melting point of ice I(h) for the polarizable SWM4-NDP water model (Lamoureux et al., Chem. Phys. Lett., 2006, 418, 245-249) and compared the performance of several popular water force fields, both polarizable and nonpolarizable, in terms of melting temperature, stability and orientational structuring of ice. The simulations yield the melting temperature of SWM4-NDP ice as low as T(m) = 185 ± 10 K, despite the quadrupole moment of a SWM4-NDP water molecule being close to the experimental gas phase value. The results thus show that the dependence of T(m) on the molecular quadrupole, observed for the three- and four-site water models, is generally lost if polarization is explicitly included. The study also shows that adding polarizability to a planar three-charge water model increases orientational disorder in hexagonal ice. In addition, analysis of the tetrahedral order in bulk ice reveals a correlation between the pre-existing degree of orientational disorder in ice simulated using different polarizable and nonpolarizable models and the melting temperature of the models. Our findings thus suggest some new considerations regarding the role of polarization forces in a crystalline solid that may guide future development of reliable polarizable water models for ice.

  13. Joint Test Plan for Gas Dynamic Spray Technology Demonstration

    NASA Technical Reports Server (NTRS)

    Lewis, Pattie

    2008-01-01

    Air Force Space Command (AFSPC) and NASA have similar missions, facilities, and structures located in similar harsh environments. Both are responsible for a number of facilities/structures with metallic structural and non-structural components in highly and moderately corrosive environments. Regardless of the corrosivity of the environment, all metals require periodic maintenance activity to guard against the insidious effects of corrosion and thus ensure that structures meet or exceed design or performance life. The standard practice for protecting metallic substrates in atmospheric environments is the use of an applied coating system. Current coating systems used across AFSPC and NASA contain volatile organic compounds (VOCs) and hazardous air pollutants (HAPs). These coatings are subject to environmental regulations at the Federal and State levels that limit their usage. In addition, these coatings often cannot withstand the high temperatures and exhaust that may be experienced by AFSPC and NASA structures. In response to these concerns, AFSPC and NASA have approved the use of thermal spray coatings (TSCs). Thermal spray coatings are extremely durable and environmentally friendly coating alternatives, but utilize large cumbersome equipment for application that make the coatings difficult and time consuming to repair. Other concerns include difficulties coating complex geometries and the cost of equipment, training, and materials. Gas Dynamic Spray (GDS) technology (also known as Cold Spray) will be evaluated as a smaller, more maneuverable repair method as well as for areas where thermal spray techniques are not as effective. The technology can result in reduced maintenance and thus reduced hazardous materials/wastes associated with current processes. Thermal spray and GDS coatings also have no VOCs and are environmentally preferable coatings. To achieve a condition suitable for the application of a coating system, including GDS coatings, the substrate must

  14. Committed sea-level rise for the next century from Greenland ice sheet dynamics during the past decade.

    PubMed

    Price, Stephen F; Payne, Antony J; Howat, Ian M; Smith, Benjamin E

    2011-05-31

    We use a three-dimensional, higher-order ice flow model and a realistic initial condition to simulate dynamic perturbations to the Greenland ice sheet during the last decade and to assess their contribution to sea level by 2100. Starting from our initial condition, we apply a time series of observationally constrained dynamic perturbations at the marine termini of Greenland's three largest outlet glaciers, Jakobshavn Isbræ, Helheim Glacier, and Kangerdlugssuaq Glacier. The initial and long-term diffusive thinning within each glacier catchment is then integrated spatially and temporally to calculate a minimum sea-level contribution of approximately 1 ± 0.4 mm from these three glaciers by 2100. Based on scaling arguments, we extend our modeling to all of Greenland and estimate a minimum dynamic sea-level contribution of approximately 6 ± 2 mm by 2100. This estimate of committed sea-level rise is a minimum because it ignores mass loss due to future changes in ice sheet dynamics or surface mass balance. Importantly, > 75% of this value is from the long-term, diffusive response of the ice sheet, suggesting that the majority of sea-level rise from Greenland dynamics during the past decade is yet to come. Assuming similar and recurring forcing in future decades and a self-similar ice dynamical response, we estimate an upper bound of 45 mm of sea-level rise from Greenland dynamics by 2100. These estimates are constrained by recent observations of dynamic mass loss in Greenland and by realistic model behavior that accounts for both the long-term cumulative mass loss and its decay following episodic boundary forcing.

  15. Committed sea-level rise for the next century from Greenland ice sheet dynamics during the past decade

    PubMed Central

    Price, Stephen F.; Payne, Antony J.; Howat, Ian M.; Smith, Benjamin E.

    2011-01-01

    We use a three-dimensional, higher-order ice flow model and a realistic initial condition to simulate dynamic perturbations to the Greenland ice sheet during the last decade and to assess their contribution to sea level by 2100. Starting from our initial condition, we apply a time series of observationally constrained dynamic perturbations at the marine termini of Greenland’s three largest outlet glaciers, Jakobshavn Isbræ, Helheim Glacier, and Kangerdlugssuaq Glacier. The initial and long-term diffusive thinning within each glacier catchment is then integrated spatially and temporally to calculate a minimum sea-level contribution of approximately 1 ± 0.4 mm from these three glaciers by 2100. Based on scaling arguments, we extend our modeling to all of Greenland and estimate a minimum dynamic sea-level contribution of approximately 6 ± 2 mm by 2100. This estimate of committed sea-level rise is a minimum because it ignores mass loss due to future changes in ice sheet dynamics or surface mass balance. Importantly, > 75% of this value is from the long-term, diffusive response of the ice sheet, suggesting that the majority of sea-level rise from Greenland dynamics during the past decade is yet to come. Assuming similar and recurring forcing in future decades and a self-similar ice dynamical response, we estimate an upper bound of 45 mm of sea-level rise from Greenland dynamics by 2100. These estimates are constrained by recent observations of dynamic mass loss in Greenland and by realistic model behavior that accounts for both the long-term cumulative mass loss and its decay following episodic boundary forcing. PMID:21576500

  16. Antarctic ice-rafted detritus (IRD) in the South Atlantic: Indicators of iceshelf dynamics or ocean surface conditions?

    USGS Publications Warehouse

    Nielsen, Simon H.H.; Hodell, D.A.

    2007-01-01

    Ocean sediment core TN057-13PC4/ODP1094, from the Atlantic sector of the Southern Ocean, contains elevated lithogenic material in sections representing the last glacial period compared to the Holocene. This ice-rafted detritus is mainly comprised of volcanic glass and ash, but has a significant input of what was previously interpreted as quartz during peak intervals (Kanfoush et al., 2000, 2002). Our analysis of these clear mineral grains indicates that most are plagioclase, and that South Sandwich Islands is the predominant source, similar to that inferred for the volcanic glass (Nielsen et al., in review). In addition, quartz and feldspar with possible Antarctic origin occur in conjunction with postulated episodes of Antarctic deglaciation. We conclude that while sea ice was the dominant ice rafting agent in the Polar Frontal Zone of the South Atlantic during the last glacial period, the Holocene IRD variability may reflect Antarctic ice sheet dynamics.

  17. Dynamic magnetic resonance imaging of the temporomandibular joint using FLASH sequences.

    PubMed

    Conway, W F; Hayes, C W; Campbell, R L

    1988-11-01

    Magnetic resonance imaging (MRI) is a suitable modality for the visualization of the temporomandibular joint (TMJ) in both normal and pathologic conditions. Until recently, MRI had been unable to provide diagnostic dynamic images of the TMJ during opening. A series of 30 TMJ MRI examinations of 17 symptomatic patients and two normal volunteers (15 to 43 years old; 14 men and five women) was performed. Fast low angle shot (FLASH) sequences were used to provide a series of dynamic images of the TMJ in various phases of opening. In 30% of the joint examined, FLASH sequences contributed clinically significant information not available with standard T1-weighted sequences. These results suggest that FLASH images are particularly useful in distinguishing normal disc variants from pathologic conditions in which the disc is displaced anteriorly to a mild extent. The short imaging time of FLASH sequences decreases motion artifact in patients who have difficulty remaining still during the examination.

  18. Dynamical modeling of serial manipulators with flexible links and joints using the method of kinematic influence

    NASA Technical Reports Server (NTRS)

    Graves, Philip L.

    1989-01-01

    A method of formulating the dynamical equations of a flexible, serial manipulator is presented, using the Method of Kinematic Influence. The resulting equations account for rigid body motion, structural motion due to link and joint flexibilities, and the coupling between these two motions. Nonlinear inertial loads are included in the equations. A finite order mode summation method is used to model flexibilities. The structural data may be obtained from experimental, finite element, or analytical methods. Nonlinear flexibilities may be included in the model.

  19. Dynamic Coupling of Iron, Manganese, and Phosphorus Behavior in Water and Sediment of Shallow Ice-Covered Eutrophic Lakes.

    PubMed

    Schroth, Andrew W; Giles, Courtney D; Isles, Peter D F; Xu, Yaoyang; Perzan, Zachary; Druschel, Gregory K

    2015-08-18

    Decreasing duration and occurrence of northern hemisphere ice cover due to recent climate warming is well-documented; however, biogeochemical dynamics underneath the ice are poorly understood. We couple time-series analyses of water column and sediment water interface (SWI) geochemistry with hydrodynamic data to develop a holistic model of iron (Fe), manganese (Mn), and phosphorus (P) behavior underneath the ice of a shallow eutrophic freshwater bay. During periods of persistent subfreezing temperatures, a highly reactive pool of dissolved and colloidal Fe, Mn, and P develops over time in surface sediments and bottom waters due to reductive dissolution of Fe/Mn(oxy)hydroxides below the SWI. Redox dynamics are driven by benthic O2 consumption, limited air-water exchange of oxygen due to ice cover, and minimal circulation. During thaw events, the concentration, distribution and size partitioning of all species changes, with the highest concentrations of P and "truly dissolved" Fe near the water column surface, and a relatively well-mixed "truly dissolved" Mn and "colloidal" Fe profile due to the influx of geochemically distinct river water and increased circulation. The partitioning and flux of trace metals and phosphorus beneath the ice is dynamic, and heavily influenced by climate-dependent physical processes that vary in both time and space.

  20. The impact of dynamic topography change on Antarctic Ice Sheet stability during the Mid-Pliocene Warm Period

    NASA Astrophysics Data System (ADS)

    Austermann, J.; Pollard, D.; Mitrovica, J. X.; Moucha, R.; Forte, A. M.; Deconto, R. M.; Rowley, D. B.; Raymo, M. E.

    2015-12-01

    The mid-Pliocene warm period (MPWP; ~ 3Ma), characterized by globally elevated temperatures (2-3º C) and carbon dioxide levels of ~400ppm, is commonly used as a testing ground for investigating ice sheet stability in a slightly warmer world. The central, unanswered question in this regard is the extent of East Antarctic melting during the MPWP. Here we assess the potential role of dynamic topography on this issue. Model reconstructions of the evolution of the Antarctic ice sheet during the ice age require an estimate of bedrock elevation through time. Ice sheet models account for changes in bedrock elevation due to glacial isostatic adjustment (GIA), often using simplified models of the GIA process, but they generally do not consider other processes that may perturb subglacial topography. One such notable process is dynamic topography, i.e. the deflection of the solid surface of the Earth due to convective flow and buoyancy variations within the mantle and lithosphere. Paleo-shorelines of Pliocene age reflect the influence of dynamic topography, but the impact of these bedrock elevation changes on ice sheet stability in the Antarctic region is unknown. In this study we use viscous flow simulations of mantle dynamics to predict changes in dynamic topography and reconstruct bedrock elevations below the Antarctic Ice Sheet since the MPWP. We furthermore couple this reconstruction to a three-dimensional ice sheet model in order to explore the impact of dynamic topography on the extent of the Antarctic Ice Sheet during the Pliocene. Our modeling indicates that uplift occurred in the area of the Transantarctic Mountains and the adjacent Wilkes Basin. This predicted uplift, which is consistent with geological inferences of uplift in the Transantarctic Mountains, implies a significantly (~100-200 m) lower elevation of the Wilkes Basin in the Pliocene. This lower elevation leads to ~400 km of additional retreat of the grounding line in this region relative to simulations

  1. 4D rotational x-ray imaging of wrist joint dynamic motion

    SciTech Connect

    Carelsen, Bart; Bakker, Niels H.; Strackee, Simon D.; Boon, Sjirk N.; Maas, Mario; Sabczynski, Joerg; Grimbergen, Cornelis A.; Streekstra, Geert J.

    2005-09-15

    Current methods for imaging joint motion are limited to either two-dimensional (2D) video fluoroscopy, or to animated motions from a series of static three-dimensional (3D) images. 3D movement patterns can be detected from biplane fluoroscopy images matched with computed tomography images. This involves several x-ray modalities and sophisticated 2D to 3D matching for the complex wrist joint. We present a method for the acquisition of dynamic 3D images of a moving joint. In our method a 3D-rotational x-ray (3D-RX) system is used to image a cyclically moving joint. The cyclic motion is synchronized to the x-ray acquisition to yield multiple sets of projection images, which are reconstructed to a series of time resolved 3D images, i.e., four-dimensional rotational x ray (4D-RX). To investigate the obtained image quality parameters the full width at half maximum (FWHM) of the point spread function (PSF) via the edge spread function and the contrast to noise ratio between air and phantom were determined on reconstructions of a bullet and rod phantom, using 4D-RX as well as stationary 3D-RX images. The CNR in volume reconstructions based on 251 projection images in the static situation and on 41 and 34 projection images of a moving phantom were 6.9, 3.0, and 2.9, respectively. The average FWHM of the PSF of these same images was, respectively, 1.1, 1.7, and 2.2 mm orthogonal to the motion and parallel to direction of motion 0.6, 0.7, and 1.0 mm. The main deterioration of 4D-RX images compared to 3D-RX images is due to the low number of projection images used and not to the motion of the object. Using 41 projection images seems the best setting for the current system. Experiments on a postmortem wrist show the feasibility of the method for imaging 3D dynamic joint motion. We expect that 4D-RX will pave the way to improved assessment of joint disorders by detection of 3D dynamic motion patterns in joints.

  2. Microwave heating of water, ice, and saline solution: molecular dynamics study.

    PubMed

    Tanaka, Motohiko; Sato, Motoyasu

    2007-01-21

    In order to study the heating process of water by the microwaves of 2.5-20 GHz frequencies, the authors have performed molecular dynamics simulations by adopting a nonpolarizable water model that has fixed point charges on a rigid-body geometry. All runs are started from the equilibrated states derived from the I(c) ice with given density and temperature. In the presence of microwaves, the molecules of liquid water exhibit rotational motion whose average phase is delayed from the microwave electric field. Microwave energy is transferred to the kinetic and intermolecular energies of water, where one-third of the absorbed microwave energy is stored as the latter energy. The water in ice phase is scarcely heated by microwaves because of the tight hydrogen-bonded network of water molecules. Dilute salt water is significantly more heated than pure water because of the field-induced motion of salt ions, especially that of large-size ions, by the microwave electric field and energy transfer to water molecules by collisions.

  3. A Comprehensive Study of Hydrogen Adsorbing to Amorphous Water ice: Defining Adsorption in Classical Molecular Dynamics

    NASA Astrophysics Data System (ADS)

    Dupuy, John L.; Lewis, Steven P.; Stancil, P. C.

    2016-11-01

    Gas-grain and gas-phase reactions dominate the formation of molecules in the interstellar medium (ISM). Gas-grain reactions require a substrate (e.g., a dust or ice grain) on which the reaction is able to occur. The formation of molecular hydrogen (H2) in the ISM is the prototypical example of a gas-grain reaction. In these reactions, an atom of hydrogen will strike a surface, stick to it, and diffuse across it. When it encounters another adsorbed hydrogen atom, the two can react to form molecular hydrogen and then be ejected from the surface by the energy released in the reaction. We perform in-depth classical molecular dynamics simulations of hydrogen atoms interacting with an amorphous water-ice surface. This study focuses on the first step in the formation process; the sticking of the hydrogen atom to the substrate. We find that careful attention must be paid in dealing with the ambiguities in defining a sticking event. The technical definition of a sticking event will affect the computed sticking probabilities and coefficients. Here, using our new definition of a sticking event, we report sticking probabilities and sticking coefficients for nine different incident kinetic energies of hydrogen atoms [5-400 K] across seven different temperatures of dust grains [10-70 K]. We find that probabilities and coefficients vary both as a function of grain temperature and incident kinetic energy over the range of 0.99-0.22.

  4. Dynamic Postural-Stability Deficits After Cryotherapy to the Ankle Joint

    PubMed Central

    Fullam, Karl; Caulfield, Brian; Coughlan, Garrett F.; McGroarty, Mark; Delahunt, Eamonn

    2015-01-01

    Context  Decreased postural stability is a primary risk factor for lower limb musculoskeletal injuries. During athletic competitions, cryotherapy may be applied during short breaks in play or during half-time; however, its effects on postural stability remain unclear. Objective  To investigate the acute effects of a 15-minute ankle-joint cryotherapy application on dynamic postural stability. Design  Controlled laboratory study. Setting  University biomechanics laboratory. Patients or Other Participants  A total of 29 elite-level collegiate male field-sport athletes (age = 20.8 ± 1.12 years, height = 1.80 ± 0.06 m, mass = 81.89 ± 8.59 kg) participated. Intervention(s)  Participants were tested on the anterior (ANT), posterolateral (PL), and posteromedial (PM) reach directions of the Star Excursion Balance Test before and after a 15-minute ankle-joint cryotherapy application. Main Outcome Measure(s)  Normalized reach distances; sagittal-plane kinematics of the hip, knee, and ankle joints; and associated mean velocity of the center-of-pressure path during performance of the ANT, PL, and PM reach directions of the Star Excursion Balance Test. Results  We observed a decrease in reach-distance scores for the ANT, PL, and PM reach directions from precryotherapy to postcryotherapy (P < .05). No differences were observed in hip-, knee-, or ankle-joint sagittal-plane kinematics (P > .05). We noted a decrease in mean velocity of the center-of-pressure path from precryotherapy to postcryotherapy (P < .05) in all reach directions. Conclusions  Dynamic postural stability was adversely affected immediately after cryotherapy to the ankle joint. PMID:26285088

  5. Nonlinear structural joint model updating based on instantaneous characteristics of dynamic responses

    NASA Astrophysics Data System (ADS)

    Wang, Zuo-Cai; Xin, Yu; Ren, Wei-Xin

    2016-08-01

    This paper proposes a new nonlinear joint model updating method for shear type structures based on the instantaneous characteristics of the decomposed structural dynamic responses. To obtain an accurate representation of a nonlinear system's dynamics, the nonlinear joint model is described as the nonlinear spring element with bilinear stiffness. The instantaneous frequencies and amplitudes of the decomposed mono-component are first extracted by the analytical mode decomposition (AMD) method. Then, an objective function based on the residuals of the instantaneous frequencies and amplitudes between the experimental structure and the nonlinear model is created for the nonlinear joint model updating. The optimal values of the nonlinear joint model parameters are obtained by minimizing the objective function using the simulated annealing global optimization method. To validate the effectiveness of the proposed method, a single-story shear type structure subjected to earthquake and harmonic excitations is simulated as a numerical example. Then, a beam structure with multiple local nonlinear elements subjected to earthquake excitation is also simulated. The nonlinear beam structure is updated based on the global and local model using the proposed method. The results show that the proposed local nonlinear model updating method is more effective for structures with multiple local nonlinear elements. Finally, the proposed method is verified by the shake table test of a real high voltage switch structure. The accuracy of the proposed method is quantified both in numerical and experimental applications using the defined error indices. Both the numerical and experimental results have shown that the proposed method can effectively update the nonlinear joint model.

  6. Time-dependence of sea-ice concentration and multiyear ice fraction in the Arctic Basin

    USGS Publications Warehouse

    Gloersen, P.; Zwally, H.J.; Chang, A.T.C.; Hall, D.K.; Campbell, W.J.; Ramseier, R.O.

    1978-01-01

    The time variation of the sea-ice concentration and multiyear ice fraction within the pack ice in the Arctic Basin is examined, using microwave images of sea ice recently acquired by the Nimbus-5 spacecraft and the NASA CV-990 airborne laboratory. The images used for these studies were constructed from data acquired from the Electrically Scanned Microwave Radiometer (ESMR) which records radiation from earth and its atmosphere at a wavelength of 1.55 cm. Data are analyzed for four seasons during 1973-1975 to illustrate some basic differences in the properties of the sea ice during those times. Spacecraft data are compared with corresponding NASA CV-990 airborne laboratory data obtained over wide areas in the Arctic Basin during the Main Arctic Ice Dynamics Joint Experiment (1975) to illustrate the applicability of passive-microwave remote sensing for monitoring the time dependence of sea-ice concentration (divergence). These observations indicate significant variations in the sea-ice concentration in the spring, late fall and early winter. In addition, deep in the interior of the Arctic polar sea-ice pack, heretofore unobserved large areas, several hundred kilometers in extent, of sea-ice concentrations as low as 50% are indicated. ?? 1978 D. Reidel Publishing Company.

  7. Dynamical excitation of the tropical Pacific Ocean and ENSO variability by Little Ice Age cooling.

    PubMed

    Rustic, Gerald T; Koutavas, Athanasios; Marchitto, Thomas M; Linsley, Braddock K

    2015-12-18

    Tropical Pacific Ocean dynamics during the Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA) are poorly characterized due to a lack of evidence from the eastern equatorial Pacific. We reconstructed sea surface temperature, El Niño-Southern Oscillation (ENSO) activity, and the tropical Pacific zonal gradient for the past millennium from Galápagos ocean sediments. We document a mid-millennium shift (MMS) in ocean-atmosphere circulation around 1500-1650 CE, from a state with dampened ENSO and strong zonal gradient to one with amplified ENSO and weak gradient. The MMS coincided with the deepest LIA cooling and was probably caused by a southward shift of the intertropical convergence zone. The peak of the MCA (900-1150 CE) was a warm period in the eastern Pacific, contradicting the paradigm of a persistent La Niña pattern.

  8. Dynamical excitation of the tropical Pacific Ocean and ENSO variability by Little Ice Age cooling

    NASA Astrophysics Data System (ADS)

    Rustic, Gerald T.; Koutavas, Athanasios; Marchitto, Thomas M.; Linsley, Braddock K.

    2015-12-01

    Tropical Pacific Ocean dynamics during the Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA) are poorly characterized due to a lack of evidence from the eastern equatorial Pacific. We reconstructed sea surface temperature, El Niño-Southern Oscillation (ENSO) activity, and the tropical Pacific zonal gradient for the past millennium from Galápagos ocean sediments. We document a mid-millennium shift (MMS) in ocean-atmosphere circulation around 1500-1650 CE, from a state with dampened ENSO and strong zonal gradient to one with amplified ENSO and weak gradient. The MMS coincided with the deepest LIA cooling and was probably caused by a southward shift of the intertropical convergence zone. The peak of the MCA (900-1150 CE) was a warm period in the eastern Pacific, contradicting the paradigm of a persistent La Niña pattern.

  9. Isolation and characterisation of sericin antifreeze peptides and molecular dynamics modelling of their ice-binding interaction.

    PubMed

    Wu, Jinhong; Rong, Yuzhi; Wang, Zhengwu; Zhou, Yanfu; Wang, Shaoyun; Zhao, Bo

    2015-05-01

    This study aimed to isolate and characterise a novel sericin antifreeze peptide and investigate its ice-binding molecular mechanism. The thermal hysteresis activity of ice-binding sericin peptides (I-SP) was measured and their activity reached as high as 0.94 °C. A P4 fraction, with high hypothermia protective activity and inhibition activity of ice recrystallisation, was obtained from I-SP, and a purified sericin peptide, named SM-AFP, with the sequence of TTSPTNVSTT and a molecular weight of 1009.50 Da was then isolated from the P4 fraction. Treatment of Lactobacillus delbrueckii Subsp. bulgaricus LB340 LYO with 100 μg/ml synthetic SM-AFP led to 1.4-fold increased survival (p < 0.05). Finally, an SM-AFP/ice binding model was constructed and results of molecular dynamics simulation suggested that the binding of SM-AFP with ice and prevention of ice crystal growth could be attributed to hydrogen bond formation, hydrophobic interaction and non-bond interactions. Sericin peptides could be developed into beneficial cryoprotectants and used in frozen food processing.

  10. Changes in the Canada Basin: Results From Beaufort Gyre Observing Program/Joint Ocean Ice Studies Expeditions, 2003-2014.

    NASA Astrophysics Data System (ADS)

    Williams, W. J.; Proshutinsky, A. Y.; Krishfield, R. A.; Timmermans, M. L. E.; Yamamoto-Kawai, M.; Li, W.; Zimmermann, S.; Hutchings, J.; McLaughlin, F.; Carmack, E.

    2014-12-01

    Annual expeditions, that make use of ships, moorings and ice tethered platforms, have monitored oceanographic conditions in the Beaufort Gyre Region of the Canada Basin since 2003. These basin-wide surveys, together with available earlier data, show linkages between the physical, geo-chemical and ecosystem components during a period of rapid change, largely forced by increased multi-year ice melt and a prolonged anticyclonic phase of the Arctic Ocean circulation. The resulting Ekman convergence has led to a progressive accumulation of river and ice-melt-derived freshwater within the gyre, an increase in surface stratification and depression of the halocline. These changes in physical state have led to a decrease in aragonite saturation state, a deepening of the top of the nutricline and subsurface chlorophyll maximum and a shift in phytoplankton size spectra. Recent years have shown a slight relaxation of the Beaufort Gyre, in addition to large variation in ice cover, leading to informed speculation that the gyre may now be poised to release some of its accumulated freshwater as a salinity anomaly into the global system.

  11. Clastic injection dynamics during ice front oscillations: A case example from Sólheimajökull (Iceland)

    NASA Astrophysics Data System (ADS)

    Ravier, Edouard; Buoncristiani, Jean-François; Menzies, John; Guiraud, Michel; Portier, Eric

    2015-06-01

    Soft-sediment deformation structures are being increasingly used as a tool for reconstructing palaeoenvironments and porewater pressure conditions in glacial settings. However, the potential of hydrofractures and clastic injections in the reconstruction of ice dynamics remains poorly constrained. This paper presents the results of a detailed study of a clastic injection network outcropping in the Sólheimajökull forefield (South Iceland). Sedimentological descriptions are combined with microscopic to macroscopic analyses of clastic injection geometries, sediment-fills, and cross-cutting relationships. The 250 m long and 20 m high exposure observed along the east flank of the proglacial braid plain displays alternating glaciofluvial sediments and subglacial tills, illustrating oscillations of the ice margins. These sediments are cross-cut by a dense network of injection composed of dykes propagating upward or downward, sills, and stepped sills. These clastic injections result from processes of hydrofracturing and the sediment-fills in these hydrofractures are generally laminated with an increase of grain-size towards the centre of the injections. These fracture-fill characteristics suggest multiple injection phases within the hydrofractures and an increase of porewater pressure over time. Five main generations of clastic injections showing different senses of propagation and dip directions are determined and are interpreted as forming in different environments. Per descensum clastic dykes dipping down ice demonstrate subglacial hydrofracturing underneath flowing-ice, while sills and per ascensum clastic dykes form in submarginal to marginal environments due to the decrease of ice overburden pressure. The integration of these results with the sedimentological characteristics allows the Holocene ice front oscillations of the Sólheimajökull to be reconstructed. This study demonstrates the importance of hydrofracture systems and their sediment-fills in the

  12. [Validation of the Tekscan system for statistic and dynamic pressure measurements of the human femorotibial joint].

    PubMed

    Wirz, D; Becker, R; Li, S Feng; Friederich, N F; Müller, W

    2002-01-01

    In vitro dynamic pressure measurements in the healthy and pathologically altered knee joint help to improve our understanding of the loading pattern on femorotibial surfaces. The aim of the study was to evaluate a piezoresistive pressure measuring system. A human cadaveric knee was mounted in a material-testing machine (Bionix 858) using a specially designed knee-holding device. Axial loading of the knee, flexed at 20o, at 500 N, 1000N and 1500 N was then carried out. For the static investigations, the piezoresistive measuring system (Tekscan), was compared with the FUJI measuring system. In addition, dynamic measurements were also performed with the Tekscan System. With the exception of the lateral compartment at a load of 1500 N, no differences in maximum pressures were observed between the two systems. Nor were there any differences with regard to contact surfaces, either in the medial or lateral compartment (p > 0.05). However, the reproducibility of the data was significantly higher with the Tekscan System (p < 0.01). Dynamic pressure measurements obtained with the knee flexed 20 to 90o showed that the lateral contact area shifted from anterior to posterior, while the medial contact area remained virtually unchanged. The Tekscan System proved to be more reliable than the FUJI System, and permits simultaneous measurements in both compartments. The Tekscan System is suitable for dynamic measurement of the femorotibial joint, and permits measurements to be made under more physiological conditions.

  13. Tool use ability depends on understanding of functional dynamics and not specific joint contribution profiles

    PubMed Central

    Parry, Ross; Dietrich, Gilles; Bril, Blandine

    2014-01-01

    Researchers in cognitive neuroscience have become increasingly interested in how different aspects of tool use are integrated and represented by the brain. Comparatively less attention has been directed toward tool use actions themselves and how effective tool use behaviors are coordinated. In response, we take this opportunity to consider the mechanical principles of tool use actions and their relationship to motor learning. Using kinematic analysis, we examine both functional dynamics and joint contribution profiles of subjects with different levels of experience in a primordial percussive task. Our results show that the ability to successfully produce stone flakes using the Oldowan method did not correspond with any particular joint contribution profile. Rather, expertise in this tool use action was principally associated with the subject's ability to regulate the functional parameters that define the task itself. PMID:24795669

  14. Static and dynamic deflection studies of the SRM aft case-nozzle joint

    NASA Technical Reports Server (NTRS)

    Christian, David C.; Kos, Lawrence D.; Torres, Isaias

    1989-01-01

    The redesign of the joints on the solid rocket motor (SRM) has prompted the need for analyzing the behavior of the joints using several different types of analyses. The types of analyses performed include modal analysis, static analysis, transient response analysis, and base driving response analysis. The forces used in these analyses to drive the mathematical model include SRM internal chamber pressure, nozzle blowout and side forces, shuttle vehicle lift-off dynamics, SRM pressure transient rise curve, gimbal forces and moments, actuator gimbal loads, and vertical and radial bolt preloads. The math model represented the SRM from the aft base tangent point (1,823.95 in) all the way back to the nozzle, where a simplified, tuned nozzle model was attached. The new design used the radial bolts as an additional feature to reduce the gap opening at the aft dome/nozzle fixed housing interface.

  15. Imaging of hemodynamic effects in arthritic joints with dynamic optical tomography

    NASA Astrophysics Data System (ADS)

    Hielscher, Andreas H.; Lasker, Joseph M.; Fong, Christopher J.; Dwyer, Edward

    2007-07-01

    Optical probing of hemodynamics is often employed in areas such as brain, muscular, and breast-cancer imaging. In these studies an external stimulus is applied and changes in relevant physiological parameters, e.g. oxy or deoxyhemoglobin concentrations, are determined. In this work we present the first application of this method for characterizing joint diseases, especially effects of rheumatoid arthritis (RA) in the proximal-interphalangeal (PIP) finger joints. Using a dual-wavelength tomographic imaging system together with previously implemented model-based iterative image reconstruction schemes, we have performed dynamic imaging case studies on a limited number of healthy volunteers and patients diagnosed with RA. Inflating a sphygmomanometer cuff placed around the forearm we elicited a controlled vascular response. We observed pronounced differences between the hemodynamic effect occurring in healthy volunteers and patients affected by RA.

  16. Adaptive dynamic surface control of flexible-joint robots using self-recurrent wavelet neural networks.

    PubMed

    Yoo, Sung Jin; Park, Jin Bae; Choi, Yoon Ho

    2006-12-01

    A new method for the robust control of flexible-joint (FJ) robots with model uncertainties in both robot dynamics and actuator dynamics is proposed. The proposed control system is a combination of the adaptive dynamic surface control (DSC) technique and the self-recurrent wavelet neural network (SRWNN). The adaptive DSC technique provides the ability to overcome the "explosion of complexity" problem in backstepping controllers. The SRWNNs are used to observe the arbitrary model uncertainties of FJ robots, and all their weights are trained online. From the Lyapunov stability analysis, their adaptation laws are induced, and the uniformly ultimately boundedness of all signals in a closed-loop adaptive system is proved. Finally, simulation results for a three-link FJ robot are utilized to validate the good position tracking performance and robustness against payload uncertainties and external disturbances of the proposed control system.

  17. Dynamic spin correlations in 'stuffed' spin ice Ho(2+x)Ti(2-x)O(7-d)

    SciTech Connect

    Ehlers, Georg

    2008-02-01

    The magnetic correlations in 'stuffed' spin ice Ho{sub 2+x}Ti{sub 2-x}O{sub 7-{delta}} have been characterized using quasielastic neutron scattering. At temperatures above 1K , these correlations are short ranged in nature and dynamic on a picosecond to nanosecond time scale. As for the case of pure spin ice Ho{sub 2+x}Ti{sub 2-x}O{sub 7}, one can identify, above the freezing temperature, a quantum relaxation regime which is enhanced as it persists to even higher temperatures, T{approx}30-40K , than in the parent compound.

  18. Possible effects of anthropogenically-increased CO2 on the dynamics of climate - Implications for ice age cycles

    NASA Technical Reports Server (NTRS)

    Saltzman, Barry; Maasch, Kirk A.; Verbitsky, Mikhail YA.

    1993-01-01

    A dynamical model, developed to account for the observed major variations of global ice mass and atmospheric CO2 during the late Cenozoic, is used to provide a quantitative demonstration of the possibility that the anthropogenically-forced increase of atmospheric CO2, if maintained over a long period of time (perhaps by tectonic forcing), could displace the climatic system from an unstable regime of oscillating ice ages into a more stable regime representative of the pre-Pleistocene. This stable regime is characterized by orbitally-forced oscillations that are of much weaker amplitude than prevailed during the Pleistocene.

  19. An investigation of the dynamic relationship between navicular drop and first metatarsophalangeal joint dorsal excursion.

    PubMed

    Griffin, Nicole L; Miller, Charlotte; Schmitt, Daniel; D'Août, Kristiaan

    2013-06-01

    The modern human foot is a complex biomechanical structure that must act both as a shock absorber and as a propulsive strut during the stance phase of gait. Understanding the ways in which foot segments interact can illuminate the mechanics of foot function in healthy and pathological humans. It has been proposed that increased values of medial longitudinal arch deformation can limit metatarsophalangeal joint excursion via tension in the plantar aponeurosis. However, this model has not been tested directly in a dynamic setting. In this study, we tested the hypothesis that during the stance phase, subtalar pronation (stretching of the plantar aponeurosis and subsequent lowering of the medial longitudinal arch) will negatively affect the amount of first metatarsophalangeal joint excursion occurring at push-off. Vertical descent of the navicular (a proxy for subtalar pronation) and first metatarsophalangeal joint dorsal excursion were measured during steady locomotion over a flat substrate on a novel sample consisting of asymptomatic adult males and females, many of whom are habitually unshod. Least-squares regression analyses indicated that, contrary to the hypothesis, navicular drop did not explain a significant amount of variation in first metatarsophalangeal joint dorsal excursion. These results suggest that, in an asymptomatic subject, the plantar aponeurosis and the associated foot bones can function effectively within the normal range of subtalar pronation that takes place during walking gait. From a clinical standpoint, this study highlights the need for investigating the in vivo kinematic relationship between subtalar pronation and metatarsophalangeal joint dorsiflexion in symptomatic populations, and also the need to explore other factors that may affect the kinematics of asymptomatic feet.

  20. A feasibility study for experimentally determining dynamic force distribution in a lap joint.

    SciTech Connect

    Mayes, Randall Lee

    2013-11-01

    Developing constitutive models of the physics in mechanical joints is currently stymied by inability to measure forces and displacements within the joint. The current state of the art estimates whole joint stiffness and energy loss per cycle from external measured force input and one or two acceleration responses. To validate constitutive models beyond this state requires a measurement of the distributed forces and displacements at the joint interface. Unfortunately, introducing measurement devices at the interface completely disrupts the desired physics. A feasibility study is presented for a non-intrusive method of solving for the interface dynamic forces from an inverse problem using full field measured responses. The responses come from the viewable surface of a beam. The noise levels associated with digital image correlation and continuous scanning laser Doppler velocimetry are evaluated from typical beam experiments. Two inverse problems are simulated. One utilizes the extended Sum of Weighted Accelerations Technique (SWAT). The second is a new approach dubbed the method of truncated orthogonal forces. These methods are much more robust if the contact patch geometry is well identified. Various approaches to identifying the contact patch are investigated, including ion marker tracking, Prussian blue and ultrasonic measurements. A typical experiment is conceived for a beam which has a lap joint at one end with a single bolt connecting it to another identical beam. In a virtual test using the beam finite element analysis, it appears that the SWAT inverse method requires evaluation of too many coefficients to adequately identify the force distribution to be viable. However, the method of truncated orthogonal forces appears viable with current digital image correlation (and probably other) imaging techniques.

  1. Instantaneous Metabolic Cost of Walking: Joint-Space Dynamic Model with Subject-Specific Heat Rate

    PubMed Central

    Roberts, Dustyn; Hillstrom, Howard; Kim, Joo H.

    2016-01-01

    A subject-specific model of instantaneous cost of transport (ICOT) is introduced from the joint-space formulation of metabolic energy expenditure using the laws of thermodynamics and the principles of multibody system dynamics. Work and heat are formulated in generalized coordinates as functions of joint kinematic and dynamic variables. Generalized heat rates mapped from muscle energetics are estimated from experimental walking metabolic data for the whole body, including upper-body and bilateral data synchronization. Identified subject-specific energetic parameters—mass, height, (estimated) maximum oxygen uptake, and (estimated) maximum joint torques—are incorporated into the heat rate, as opposed to the traditional in vitro and subject-invariant muscle parameters. The total model metabolic energy expenditure values are within 5.7 ± 4.6% error of the measured values with strong (R2 > 0.90) inter- and intra-subject correlations. The model reliably predicts the characteristic convexity and magnitudes (0.326–0.348) of the experimental total COT (0.311–0.358) across different subjects and speeds. The ICOT as a function of time provides insights into gait energetic causes and effects (e.g., normalized comparison and sensitivity with respect to walking speed) and phase-specific COT, which are unavailable from conventional metabolic measurements or muscle models. Using the joint-space variables from commonly measured or simulated data, the models enable real-time and phase-specific evaluations of transient or non-periodic general tasks that use a range of (aerobic) energy pathway similar to that of steady-state walking. PMID:28030598

  2. Ikaite crystal distribution in Arctic winter sea ice and implications for CO2 system dynamics

    NASA Astrophysics Data System (ADS)

    Rysgaard, S.; Søgaard, D. H.; Cooper, M.; Pućko, M.; Lennert, K.; Papakyriakou, T. N.; Wang, F.; Geilfus, N. X.; Glud, R. N.; Ehn, J.; McGinnnis, D. F.; Attard, K.; Sievers, J.; Deming, J. W.; Barber, D.

    2012-12-01

    The precipitation of ikaite (CaCO3·6H2O) in polar sea ice is critical to the efficiency of the sea ice-driven carbon pump and potentially important to the global carbon cycle, yet the spatial and temporal occurrence of ikaite within the ice is poorly known. We report unique observations of ikaite in unmelted ice and vertical profiles of ikaite abundance and concentration in sea ice for the crucial season of winter. Ice was examined from two locations: a 1 m thick land-fast ice site and a 0.3 m thick polynya site, both in the Young Sound area (74° N, 20° W) of NE Greenland. Ikaite crystals, ranging in size from a few µm to 700 µm were observed to concentrate in the interstices between the ice platelets in both granular and columnar sea ice. In vertical sea-ice profiles from both locations, ikaite concentration determined from image analysis, decreased with depth from surfaceice values of 700-900 µmol kg-1 ice (~ 25 × 106 crystals kg-1) to bottom-layer values of 100-200 µmol kg-1 ice (1-7 × 106 kg-1), all of which are much higher (4-10 times) than those reported in the few previous studies. Direct measurements of total alkalinity (TA) in surface layers fell within the same range as ikaite concentration whereas TA concentrations in bottom layers were twice as high. This depth-related discrepancy suggests interior ice processes where ikaite crystals form in surface sea ice layers and partly dissolved in bottom layers. From these findings and model calculations we relate sea ice formation and melt to observed pCO2 conditions in polar surface waters, and hence, the air-sea CO2 flux.

  3. Comparison of elastic-viscous-plastic and viscous-plastic dynamics models using a high resolution Arctic sea ice model

    SciTech Connect

    Hunke, E.C.; Zhang, Y.

    1997-12-31

    A nonlinear viscous-plastic (VP) rheology proposed by Hibler (1979) has been demonstrated to be the most suitable of the rheologies commonly used for modeling sea ice dynamics. However, the presence of a huge range of effective viscosities hinders numerical implementations of this model, particularly on high resolution grids or when the ice model is coupled to an ocean or atmosphere model. Hunke and Dukowicz (1997) have modified the VP model by including elastic waves as a numerical regularization in the case of zero strain rate. This modification (EVP) allows an efficient, fully explicit discretization that adapts well to parallel architectures. The authors present a comparison of EVP and VP dynamics model results from two 5-year simulations of Arctic sea ice, obtained with a high resolution sea ice model. The purpose of the comparison is to determine how differently the two dynamics models behave, and to decide whether the elastic-viscous-plastic model is preferable for high resolution climate simulations, considering its high efficiency in parallel computation. Results from the first year of this experiment (1990) are discussed in detail in Hunke and Zhang (1997).

  4. Effect of a mutation on the structure and dynamics of an alpha-helical antifreeze protein in water and ice.

    PubMed

    Graether, Steffen P; Slupsky, Carolyn M; Sykes, Brian D

    2006-05-15

    One strategy of psychrophilic organisms to survive subzero temperature is to produce antifreeze protein (AFPs), which inhibit the growth of macromolecular ice. To better understand the binding mechanism, the structure and dynamics of several AFPs have been studied by nuclear magnetic resonance (NMR) and X-ray crystallography. The results have shown that different organisms can use diverse structures (alpha-helix, beta-helix, or different globular folds) to achieve the same function. A number of studies have focused on understanding the relationship between the alpha-helical structure of fish type I AFP and its function as an inhibitor of ice growth. The results have not explained whether the 90% activity loss caused by the conservative mutation of two threonines to serines (Thr13Ser/Thr24Ser) is attributable to a change in protein structure in solution or in ice. We examine here the structure and dynamics of the winter flounder type I AFP and the mutant Thr13Ser/Thr24Ser in both solution and solid states using a wide range of NMR approaches. Both proteins remain fully alpha-helical at all temperatures and in ice, demonstrating that the activity change must therefore not be attributable to changes in the protein fold or dynamics but differences in surface properties.

  5. Dynamic Wind-Tunnel Testing of a Sub-Scale Iced S-3B Viking

    NASA Technical Reports Server (NTRS)

    Lee, Sam; Barnhart, Billy; Ratvasky, Thomas P.

    2012-01-01

    The effect of ice accretion on a 1/12-scale complete aircraft model of S-3B Viking was studied in a rotary-balance wind tunnel. Two types of ice accretions were considered: ice protection system failure shape and runback shapes that form downstream of the thermal ice protection system. The results showed that the ice shapes altered the stall characteristics of the aircraft. The ice shapes also reduced the control surface effectiveness, but mostly near the stall angle of attack. There were some discrepancies with the data with the flaps deflected that were attributed to the low Reynolds number of the test. Rotational and forced-oscillation studies showed that the effects of ice were mostly in the longitudinal forces, and the effects on the lateral forces were relatively minor.

  6. Dynamic Wind-Tunnel Testing of a Sub-Scale Iced Business Jet

    NASA Technical Reports Server (NTRS)

    Lee, Sam; Barnhart, Billy P.; Ratvasky, Thomas P.; Dickes, Edward; Thacker, Michael

    2006-01-01

    The effect of ice accretion on a 1/12-scale complete aircraft model of a business jet was studied in a rotary-balance wind tunnel. Three types of ice accretions were considered: ice protection system failure shape, pre-activation roughness, and runback shapes that form downstream of the thermal ice protection system. The results were compared with those from a 1/12-scale semi-span wing of the same aircraft at similar Reynolds number. The data showed that the full aircraft and the semi-span wing models showed similar characteristics, especially post stall behavior under iced configuration. However, there were also some discrepancies, such as the magnitude in the reductions in the maximum lift coefficient. Most of the ice-induced effects were limited to longitudinal forces. Rotational and forced oscillation studies showed that the effects of ice on lateral forces were relatively minor.

  7. Confined water in hydrophobic nanopores: Dynamics of freezing into bilayer ice

    NASA Astrophysics Data System (ADS)

    Slovák, Jan; Koga, Kenichiro; Tanaka, Hideki; Zeng, Xiao C.

    1999-11-01

    Molecular dynamics simulations for a thin film of water confined to a slit nanopore are performed in order to investigate the dynamic process of crystallization of the system. The system upon freezing creates a bilayer ice crystal composed of two layers of hexagonal rings. We perform one simulation at T=257 K during which the system remains a supercooled liquid state, and another one at T=253 K during which the system freezes. Many patterns of molecular arrangement are found upon freezing, and an account is given of the origin of multiple peaks in the distributions of binding energy and pair interaction energy. A definition of the solidlike cluster is introduced in order to analyze the time evolution of the clusters' population and their shapes. A large variety of shapes including highly nonspherical ones can be detected during simulations. A steady population of clusters is found at T=257 K, whereas at T=253 K a post-critical nucleus of the solid phase emerges within a few nanoseconds and continues to grow until the system freezes completely.

  8. Future Antarctic Bed Topography and Its Implications for Ice Sheet Dynamics

    NASA Technical Reports Server (NTRS)

    Adhikari, Surendra; Ivins, Erik R.; Larour, Eric Y.; Seroussi, Helene L.; Morlighem, Mathieu; Nowicki, S.

    2014-01-01

    The Antarctic bedrock is evolving as the solid Earth responds to the past and ongoing evolution of the ice sheet. A recently improved ice loading history suggests that the Antarctic Ice Sheet (AIS) has generally been losing its mass since the Last Glacial Maximum. In a sustained warming climate, the AIS is predicted to retreat at a greater pace, primarily via melting beneath the ice shelves.We employ the glacial isostatic adjustment (GIA) capability of the Ice Sheet System Model (ISSM) to combine these past and future ice loadings and provide the new solid Earth computations for the AIS.We find that past loading is relatively less important than future loading for the evolution of the future bed topography. Our computations predict that the West Antarctic Ice Sheet (WAIS) may uplift by a few meters and a few tens of meters at years AD 2100 and 2500, respectively, and that the East Antarctic Ice Sheet is likely to remain unchanged or subside minimally except around the Amery Ice Shelf. The Amundsen Sea Sector in particular is predicted to rise at the greatest rate; one hundred years of ice evolution in this region, for example, predicts that the coastline of Pine Island Bay will approach roughly 45mmyr-1 in viscoelastic vertical motion. Of particular importance, we systematically demonstrate that the effect of a pervasive and large GIA uplift in the WAIS is generally associated with the flattening of reverse bed slope, reduction of local sea depth, and thus the extension of grounding line (GL) towards the continental shelf. Using the 3-D higher-order ice flow capability of ISSM, such a migration of GL is shown to inhibit the ice flow. This negative feedback between the ice sheet and the solid Earth may promote stability in marine portions of the ice sheet in the future.

  9. Hesperian polythermal glaciation in Isidis Planitia, Mars - Ice sheet dynamics and thermal regime inferred from numerical modeling

    NASA Astrophysics Data System (ADS)

    Souček, Ondřej; Bourgeois, Olivier; Pochat, Stéphane; Guidat, Thomas

    2015-04-01

    We test the hypothesis that the Thumbprint Terrain observed on the floor of Isidis Planitia, a giant impact crater located close to the martian equator, is a landform assemblage inherited from a glaciation during the Hesperian. For this purpose, we perform numerical simulations with a coupled thermo-mechanical model of ice sheet dynamics. We use surface temperatures and ice accumulation/ablation patterns predicted by a climatic Global Circulation Model, and values of the geothermal heat flux provided by a global model of planetary thermal evolution. We find that, with atmospheric physical properties similar to the current ones and under favorable orbital conditions, net ice accumulation in the northwestern part of Isidis Planitia leads within a few Ma to the development of a massive ice sheet, as much as 4.9 km in thickness, over the entire basin. The modeled ice sheet is polythermal: its center and its periphery are permanently frozen to the base, while the pressure melting point is reached episodically in an intermediate ring. Our simulations suggest that the propagation of thermo-mechanical melting waves in this ring is responsible for the formation of the Thumbprint Terrain, a probable martian equivalent of terrestrial ribbed moraines. They support the interpretation that sinuous ridges and linear valleys observed at the periphery of the basin are parts of a subglacial network of eskers and tunnel valleys that drained glacial meltwater outwards, across the cold-based outer part of the ice sheet. This work strengthens the hypothesis that massive glaciers covered large portions of the martian surface before the Amazonian and that basal melting below the wet-based portions of these ice sheets contributed significantly to the production and flow of liquid water in the ancient martian history.

  10. Tomography-based characterization of ice-air interface dynamics of temperature gradient snow metamorphism under advective conditions

    NASA Astrophysics Data System (ADS)

    Ebner, Pirmin Philipp; Andreoli, Christian; Schneebeli, Martin; Steinfeld, Aldo

    2015-12-01

    Snow at or close to the surface commonly undergoes temperature gradient metamorphism under advective flow, which alters its microstructure and physical properties. A functional understanding of this process is essential for many disciplines, from modeling the effects of snow on regional and global climate to assessing avalanche formation. Time-lapse X-ray microtomography was applied to investigate the structural dynamics of temperature gradient snow metamorphism exposed to an advective airflow in controlled laboratory conditions. Experiments specifically analyzed sublimation and deposition of water vapor on the ice structure. In addition, an analysis of the ice-air interface dynamics was carried out using a macroscopic equivalent model of heat and water vapor transport through a snow layer. The results indicate that sublimation of the ice matrix dominated for flow rates < 10-6 m3 s-1 while during increased mass flow rates the water vapor deposition supplied by the advective flow counteracted sublimation. A flow rate dependence of water vapor deposition at the ice interface was observed, asymptotically approaching an average estimated maximum deposition rate on the whole sample of 1.05 · 10-4 kg m-3 s-1. The growth of microsized whisker-like crystals on larger ice crystals was detected on microscope photographs, leading to an increase of the specific surface area and thus suggest a change of the physical and optical properties of the snow. The estimated values of the curvature effect of the ice crystals and the interface kinetic coefficient are in good agreement with previously published values.

  11. A digital-signal-processor-based optical tomographic system for dynamic imaging of joint diseases

    NASA Astrophysics Data System (ADS)

    Lasker, Joseph M.

    joint diseases, especially effects of rheumatoid arthritis (RA) in the proximal interphalangeal finger joints. Using a dual-wavelength tomographic imaging system and previously implemented reconstruction scheme, I have performed initial dynamic imaging case studies on healthy volunteers and patients diagnosed with RA. These studies support our hypothesis that differences in the vascular and metabolic reactivity exist between affected and unaffected joints and can be used for diagnostic purposes.

  12. Ikaite crystal distribution in winter sea ice and implications for CO2 system dynamics

    NASA Astrophysics Data System (ADS)

    Rysgaard, S.; Søgaard, D. H.; Cooper, M.; Pućko, M.; Lennert, K.; Papakyriakou, T. N.; Wang, F.; Geilfus, N. X.; Glud, R. N.; Ehn, J.; McGinnis, D. F.; Attard, K.; Sievers, J.; Deming, J. W.; Barber, D.

    2013-04-01

    The precipitation of ikaite (CaCO3 ⋅ 6H2O) in polar sea ice is critical to the efficiency of the sea ice-driven carbon pump and potentially important to the global carbon cycle, yet the spatial and temporal occurrence of ikaite within the ice is poorly known. We report unique observations of ikaite in unmelted ice and vertical profiles of ikaite abundance and concentration in sea ice for the crucial season of winter. Ice was examined from two locations: a 1 m thick land-fast ice site and a 0.3 m thick polynya site, both in the Young Sound area (74° N, 20° W) of NE Greenland. Ikaite crystals, ranging in size from a few μm to 700 μm, were observed to concentrate in the interstices between the ice platelets in both granular and columnar sea ice. In vertical sea ice profiles from both locations, ikaite concentration determined from image analysis, decreased with depth from surface-ice values of 700-900 μmol kg-1 ice (~25 × 106 crystals kg-1) to values of 100-200 μmol kg-1 ice (1-7 × 106 crystals kg-1) near the sea ice-water interface, all of which are much higher (4-10 times) than those reported in the few previous studies. Direct measurements of total alkalinity (TA) in surface layers fell within the same range as ikaite concentration, whereas TA concentrations in the lower half of the sea ice were twice as high. This depth-related discrepancy suggests interior ice processes where ikaite crystals form in surface sea ice layers and partly dissolve in layers below. Melting of sea ice and dissolution of observed concentrations of ikaite would result in meltwater with a pCO2 of <15 μatm. This value is far below atmospheric values of 390 μatm and surface water concentrations of 315 μatm. Hence, the meltwater increases the potential for seawater uptake of CO2.

  13. Measurement of Latent Heat of Melting of Thermal Storage Materials for Dynamic Type Ice Thermal Storage

    NASA Astrophysics Data System (ADS)

    Sawada, Hisashi; Okada, Masashi; Nakagawa, Shinji

    In order to measure the latent heat of melting of ice slurries with various solute concentrations, an adiabatic calorimeter was constructed. Ice slurries were made from each aqueous solution of ethanol, ethylene glycol and silane coupling agent. The latent heat of melting of ice made from tap water was measured with the present calorimeter and the uncertainty of the result was one percent. Ice slurries were made both by mixing ice particles made from water with each aqueous solution and by freezing each aqueous solution with stirring in a vessel. The latent heat of melting of these ice slurries was measured with various concentrations of solution. The latent heat of melting decreased as the solute concentration or the freezing point depression increased. The latent heat of ice slurries made from ethanol or ethylene glycol aqueous solution agreed with that of ice made from pure water known already. The latent heat of melting of ice slurries made from silane coupling agent aqueous solution got smaller than that of ice made from pure water as the freezing point depression increased.

  14. Modelled and measured dynamics of viruses in Arctic winter sea-ice brines.

    PubMed

    Wells, Llyd E; Deming, Jody W

    2006-06-01

    We describe a model based on diffusion theory and the temperature-dependent mechanism of brine concentration in sea ice to argue that, if viruses partition with bacteria into sea-ice brine inclusions, contact rates between the two can be higher in winter sea ice than in seawater, increasing the probability of infection and possible virus production. To examine this hypothesis, we determined viral and bacterial concentrations in select winter sea-ice horizons using epifluorescence microscopy. Viral concentrations ranged from 1.6 to 82 x 10(6) ml(-1) of brine volume of the ice, with highest values in brines from coldest (-24 to -31 degrees C) ice horizons. Calculated virus-bacteria contact rates in underlying -1 degrees C seawater were similar to those in brines of -11 degrees C ice but up to 600 times lower than those in ice brines at or below -24 degrees C. We then incubated native bacterial and viral assemblages from winter sea ice for 8 days in brine at a temperature (-12 degrees C) and salinity ( approximately 160 psu) near expected in situ values, monitoring their concentrations microscopically. While different cores yielded different results, consistent with known spatial heterogeneity in sea ice, these experiments provided unambiguous evidence for viral persistence and production, as well as for bacterial growth, in -12 degrees C brine.

  15. Dynamic Antarctic ice sheet during the early to mid-Miocene.

    PubMed

    Gasson, Edward; DeConto, Robert M; Pollard, David; Levy, Richard H

    2016-03-29

    Geological data indicate that there were major variations in Antarctic ice sheet volume and extent during the early to mid-Miocene. Simulating such large-scale changes is problematic because of a strong hysteresis effect, which results in stability once the ice sheets have reached continental size. A relatively narrow range of atmospheric CO2 concentrations indicated by proxy records exacerbates this problem. Here, we are able to simulate large-scale variability of the early to mid-Miocene Antarctic ice sheet because of three developments in our modeling approach. (i) We use a climate-ice sheet coupling method utilizing a high-resolution atmospheric component to account for ice sheet-climate feedbacks. (ii) The ice sheet model includes recently proposed mechanisms for retreat into deep subglacial basins caused by ice-cliff failure and ice-shelf hydrofracture. (iii) We account for changes in the oxygen isotopic composition of the ice sheet by using isotope-enabled climate and ice sheet models. We compare our modeling results with ice-proximal records emerging from a sedimentological drill core from the Ross Sea (Andrill-2A) that is presented in a companion article. The variability in Antarctic ice volume that we simulate is equivalent to a seawater oxygen isotope signal of 0.52-0.66‰, or a sea level equivalent change of 30-36 m, for a range of atmospheric CO2 between 280 and 500 ppm and a changing astronomical configuration. This result represents a substantial advance in resolving the long-standing model data conflict of Miocene Antarctic ice sheet and sea level variability.

  16. Origin and dynamic significance of longitudinal structures ("flow stripes") in the Antarctic Ice Sheet

    NASA Astrophysics Data System (ADS)

    Glasser, N. F.; Jennings, S. J. A.; Hambrey, M. J.; Hubbard, B.

    2015-04-01

    Longitudinal ice-surface structures in the Antarctic Ice Sheet can be traced continuously down-ice for distances of up to 1200 km. A map of the distribution of ~ 3600 of these features, compiled from satellite images, shows that they mirror the location of fast-flowing glaciers and ice streams that are dominated by basal sliding rates above tens of metres per annum and are strongly guided by subglacial topography. Longitudinal ice-surface structures dominate regions of converging flow, where ice flow is subject to non-coaxial strain and simple shear. They can be traced continuously through crevasse fields and through blue-ice areas, indicating that they represent the surface manifestation of a three-dimensional structure, interpreted as foliation. Flow lines are linear and undeformed for all major flow units described here in the Antarctic Ice Sheet except for the Kamb Ice Stream and the Institute and Möller Ice Stream areas, where areas of flow perturbation are evident. Parcels of ice along individual flow paths on the Lambert Glacier, Recovery Glacier, Byrd Glacier and Pine Island Glacier may reside in the glacier system for ~ 2500 to 18 500 years. Although it is unclear how long it takes for these features to form and decay, we infer that the major ice-flow configuration of the ice sheet may have remained largely unchanged for the last few hundred years, and possibly even longer. This conclusion has implications for our understanding of the long-term landscape evolution of Antarctica, including large-scale patterns of glacial erosion and deposition.

  17. Dynamic Antarctic ice sheet during the early to mid-Miocene

    NASA Astrophysics Data System (ADS)

    Gasson, Edward; DeConto, Robert M.; Pollard, David; Levy, Richard H.

    2016-03-01

    Geological data indicate that there were major variations in Antarctic ice sheet volume and extent during the early to mid-Miocene. Simulating such large-scale changes is problematic because of a strong hysteresis effect, which results in stability once the ice sheets have reached continental size. A relatively narrow range of atmospheric CO2 concentrations indicated by proxy records exacerbates this problem. Here, we are able to simulate large-scale variability of the early to mid-Miocene Antarctic ice sheet because of three developments in our modeling approach. (i) We use a climate-ice sheet coupling method utilizing a high-resolution atmospheric component to account for ice sheet-climate feedbacks. (ii) The ice sheet model includes recently proposed mechanisms for retreat into deep subglacial basins caused by ice-cliff failure and ice-shelf hydrofracture. (iii) We account for changes in the oxygen isotopic composition of the ice sheet by using isotope-enabled climate and ice sheet models. We compare our modeling results with ice-proximal records emerging from a sedimentological drill core from the Ross Sea (Andrill-2A) that is presented in a companion article. The variability in Antarctic ice volume that we simulate is equivalent to a seawater oxygen isotope signal of 0.52-0.66‰, or a sea level equivalent change of 30-36 m, for a range of atmospheric CO2 between 280 and 500 ppm and a changing astronomical configuration. This result represents a substantial advance in resolving the long-standing model data conflict of Miocene Antarctic ice sheet and sea level variability.

  18. Dynamic Antarctic ice sheet during the early to mid-Miocene

    PubMed Central

    DeConto, Robert M.; Pollard, David; Levy, Richard H.

    2016-01-01

    Geological data indicate that there were major variations in Antarctic ice sheet volume and extent during the early to mid-Miocene. Simulating such large-scale changes is problematic because of a strong hysteresis effect, which results in stability once the ice sheets have reached continental size. A relatively narrow range of atmospheric CO2 concentrations indicated by proxy records exacerbates this problem. Here, we are able to simulate large-scale variability of the early to mid-Miocene Antarctic ice sheet because of three developments in our modeling approach. (i) We use a climate–ice sheet coupling method utilizing a high-resolution atmospheric component to account for ice sheet–climate feedbacks. (ii) The ice sheet model includes recently proposed mechanisms for retreat into deep subglacial basins caused by ice-cliff failure and ice-shelf hydrofracture. (iii) We account for changes in the oxygen isotopic composition of the ice sheet by using isotope-enabled climate and ice sheet models. We compare our modeling results with ice-proximal records emerging from a sedimentological drill core from the Ross Sea (Andrill-2A) that is presented in a companion article. The variability in Antarctic ice volume that we simulate is equivalent to a seawater oxygen isotope signal of 0.52–0.66‰, or a sea level equivalent change of 30–36 m, for a range of atmospheric CO2 between 280 and 500 ppm and a changing astronomical configuration. This result represents a substantial advance in resolving the long-standing model data conflict of Miocene Antarctic ice sheet and sea level variability. PMID:26903645

  19. [Proposal for a dynamic study of the temporo-mandibular joint, using a computerized image analyzer].

    PubMed

    Tedde, G; Mazzanti, V; Devilla, L; Chessa, G

    1990-04-01

    With the aim to go deep into the knowledge of the morpho-functional anatomical characteristics of the temporo-mandibular joint in humans, a dynamic method of study by means of a computerized analyzer of images is suggested. The acquired advantages are the following: a) the accuracy of evaluation of the chosen morphometric parameters; b) the working speed, from which results: c) the possibility to increase adequately the number of cases and d) the possibility to easily investigate many parameters with a very high accuracy of the quantitative results. Both right and left temporo-mandibular joints of adult individuals aged from 18 to 53 have been studied utilizing lateral tomographies focused at 3.3 mm to the lateral surface of the condylar head. The evaluations were done both in the position of completely closed mouth and in extreme opening. From the barycentre of the condyle several straight lines were drawn according to the figure 2. The length of the segment a-b (distance of profiles of the condyle and mandibular fossa) were evaluated in all the lines counter-clockwise and the results submitted to a statistical analysis. The results furnish very good information on the normal or pathological anatomical characteristics, of the joint.

  20. A joint-space numerical model of metabolic energy expenditure for human multibody dynamic system.

    PubMed

    Kim, Joo H; Roberts, Dustyn

    2015-09-01

    Metabolic energy expenditure (MEE) is a critical performance measure of human motion. In this study, a general joint-space numerical model of MEE is derived by integrating the laws of thermodynamics and principles of multibody system dynamics, which can evaluate MEE without the limitations inherent in experimental measurements (phase delays, steady state and task restrictions, and limited range of motion) or muscle-space models (complexities and indeterminacies from excessive DOFs, contacts and wrapping interactions, and reliance on in vitro parameters). Muscle energetic components are mapped to the joint space, in which the MEE model is formulated. A constrained multi-objective optimization algorithm is established to estimate the model parameters from experimental walking data also used for initial validation. The joint-space parameters estimated directly from active subjects provide reliable MEE estimates with a mean absolute error of 3.6 ± 3.6% relative to validation values, which can be used to evaluate MEE for complex non-periodic tasks that may not be experimentally verifiable. This model also enables real-time calculations of instantaneous MEE rate as a function of time for transient evaluations. Although experimental measurements may not be completely replaced by model evaluations, predicted quantities can be used as strong complements to increase reliability of the results and yield unique insights for various applications.

  1. Greenland Ice Sheet nutrient export: Towards a reaction-transport model of fjord dynamics

    NASA Astrophysics Data System (ADS)

    Crosby, James; Arndt, Sandra; Wadham, Jemma; Bingham, Rory

    2015-04-01

    Glacial runoff has the potential to deliver large quantities of dissolved and particulate bioavailable nutrients to surrounding marine environments. The marine waters bordering the Greenland Ice Sheet (GrIS) host some of the most productive ecosystems in the world, and possess high socio-economic value from fisheries. Furthermore, the productivity of phytoplankton in the North Atlantic sequesters CO2 from the atmosphere with a potentially important effect on the global coastal ocean CO2 budget. Providing a link between glacier and coastal ocean, fjords are critical components of the marine coastal system in this region, acting as both transfer routes and sinks for glacial nutrient export. As such they have the potential to act as significant biogeochemical processors, yet are currently underexplored. We propose to close this knowledge gap by developing a coupled 2D physical-biogeochemical model of the Godthåbsfjord system to quantitatively assess the impact of nutrients exported from the GrIS on fjord primary productivity and biogeochemical dynamics. Here, we present the first results of the hydrodynamic model. Hydrodynamic circulation patterns and freshwater transit times are explored to provide a first understanding of the glacier-fjord-ocean continuum. The hydrodynamic model will be dynamically coupled to a biogeochemical model with the view to providing a comprehensive understanding of the fate of nutrients exported from the GrIS. This will be extended to address the future sensitivity of these coastal systems to a warming climate, knowledge of which is critical when assessing the role of these dynamic and unique environments.

  2. Real-time Non-contact Millimeter Wave Characterization of Water-Freezing and Ice-Melting Dynamics

    SciTech Connect

    Sundaram, S. K.; Woskov, Paul P.

    2008-11-12

    We applied millimeter wave radiometry for the first time to monitor water-freezing and ice-melting dynamics in real-time non-contact. The measurements were completed at a frequency of 137 GHz. Small amounts (about 2 mL) of freshwater or saltwater were frozen over a Peltier cooler and the freezing and melting sequence was recorded. Saltwater was prepared in the laboratory that contained 3.5% of table salt to simulate the ocean water. The dynamics of freezing-melting was observed by measuring the millimeter wave temperature as well as the changes in the ice or water surface reflectivity and position. This was repeated using large amounts of freshwater and saltwater (800 mL) mimicking glaciers. Millimeter wave surface level fluctuations indicated as the top surface melted, the light ice below floated up indicating lower surface temperature until the ice completely melted. Our results are useful for remote sensing and tracking temperature for potentially large-scale environmental applications, e.g., global warming.

  3. High-Resolution Dynamic Speech Imaging with Joint Low-Rank and Sparsity Constraints

    PubMed Central

    Fu, Maojing; Zhao, Bo; Carignan, Christopher; Shosted, Ryan K.; Perry, Jamie L.; Kuehn, David P.; Liang, Zhi-Pei; Sutton, Bradley P.

    2014-01-01

    Purpose To enable dynamic speech imaging with high spatiotemporal resolution and full-vocal-tract spatial coverage, leveraging recent advances in sparse sampling. Methods An imaging method is developed to enable high-speed dynamic speech imaging exploiting low-rank and sparsity of the dynamic images of articulatory motion during speech. The proposed method includes: a) a novel data acquisition strategy that collects navigators with high temporal frame rate, and b) an image reconstruction method that derives temporal subspaces from navigators and reconstructs high-resolution images from sparsely sampled data with joint low-rank and sparsity constraints. Results The proposed method has been systematically evaluated and validated through several dynamic speech experiments. A nominal imaging speed of 102 frames per second (fps) was achieved for a single-slice imaging protocol with a spatial resolution of 2.2 × 2.2 × 6.5 mm3. An eight-slice imaging protocol covering the entire vocal tract achieved a nominal imaging speed of 12.8 fps with the identical spatial resolution. The effectiveness of the proposed method and its practical utility was also demonstrated in a phonetic investigation. Conclusion High spatiotemporal resolution with full-vocal-tract spatial coverage can be achieved for dynamic speech imaging experiments with low-rank and sparsity constraints. PMID:24912452

  4. Coupling of dynamics and contact mechanics of artificial hip joints in a pendulum model.

    PubMed

    Liu, H; Ellison, P J; Xu, H; Jin, Z

    2010-01-01

    To date, fully coupled dynamics and contact mechanics analysis is still limited by expensive computational cost and long computing time and has not been addressed comprehensively, particularly in the hip joint. To understand the influence of different parameters on the biomechanics of the total hip replacement (THR) and improve its design, two numerical approaches were developed and implemented in finite element models to investigate the coupling between the dynamics response and the contact mechanics for three different THR configurations, metal-on-polyethylene (MOP), metal-on-metal (MOM), and ceramic-on-ceramic (COC). The dynamic force and the contact pressure distribution at the bearing surfaces from the two methods were predicted and compared. The influences of various parameters (motion angle, load applied in the pendulum, friction coefficient, geometry, and material properties) were subsequently investigated. From the comparisons, the decoupled method, based on the rigid-body dynamics and the quasi-static elastic contact mechanics, was adequate to predict the performance of the THRs efficiently. The load had the greatest influence on the dynamics/contact mechanics among other factors.

  5. Development and validation of a 3-D model to predict knee joint loading during dynamic movement.

    PubMed

    McLean, S G; Su, A; van den Bogert, A J

    2003-12-01

    The purpose of this study was to develop a subject-specific 3-D model of the lower extremity to predict neuromuscular control effects on 3-D knee joint loading during movements that can potentially cause injury to the anterior cruciate ligament (ACL) in the knee. The simulation consisted of a forward dynamic 3-D musculoskeletal model of the lower extremity, scaled to represent a specific subject. Inputs of the model were the initial position and velocity of the skeletal elements, and the muscle stimulation patterns. Outputs of the model were movement and ground reaction forces, as well as resultant 3-D forces and moments acting across the knee joint. An optimization method was established to find muscle stimulation patterns that best reproduced the subject's movement and ground reaction forces during a sidestepping task. The optimized model produced movements and forces that were generally within one standard deviation of the measured subject data. Resultant knee joint loading variables extracted from the optimized model were comparable to those reported in the literature. The ability of the model to successfully predict the subject's response to altered initial conditions was quantified and found acceptable for use of the model to investigate the effect of altered neuromuscular control on knee joint loading during sidestepping. Monte Carlo simulations (N = 100,000) using randomly perturbed initial kinematic conditions, based on the subject's variability, resulted in peak anterior force, valgus torque and internal torque values of 378 N, 94 Nm and 71 Nm, respectively, large enough to cause ACL rupture. We conclude that the procedures described in this paper were successful in creating valid simulations of normal movement, and in simulating injuries that are caused by perturbed neuromuscular control.

  6. In Vivo Dynamic Deformation of Articular Cartilage in Intact Joints Loaded by Controlled Muscular Contractions

    PubMed Central

    Abusara, Ziad; Von Kossel, Markus; Herzog, Walter

    2016-01-01

    When synovial joints are loaded, the articular cartilage and the cells residing in it deform. Cartilage deformation has been related to structural tissue damage, and cell deformation has been associated with cell signalling and corresponding anabolic and catabolic responses. Despite the acknowledged importance of cartilage and cell deformation, there are no dynamic data on these measures from joints of live animals using muscular load application. Research in this area has typically been done using confined and unconfined loading configurations and indentation testing. These loading conditions can be well controlled and allow for accurate measurements of cartilage and cell deformations, but they have little to do with the contact mechanics occurring in a joint where non-congruent cartilage surfaces with different material and functional properties are pressed against each other by muscular forces. The aim of this study was to measure in vivo, real time articular cartilage deformations for precisely controlled static and dynamic muscular loading conditions in the knees of mice. Fifty and 80% of the maximal knee extensor muscular force (equivalent to approximately 0.4N and 0.6N) produced average peak articular cartilage strains of 10.5±1.0% and 18.3±1.3% (Mean ± SD), respectively, during 8s contractions. A sequence of 15 repeat, isometric muscular contractions (0.5s on, 3.5s off) of 50% and 80% of maximal muscular force produced cartilage strains of 3.0±1.1% and 9.6±1.5% (Mean ± SD) on the femoral condyles of the mouse knee. Cartilage thickness recovery following mechanical compression was highly viscoelastic and took almost 50s following force removal in the static tests. PMID:26807930

  7. In Vivo Dynamic Deformation of Articular Cartilage in Intact Joints Loaded by Controlled Muscular Contractions.

    PubMed

    Abusara, Ziad; Von Kossel, Markus; Herzog, Walter

    2016-01-01

    When synovial joints are loaded, the articular cartilage and the cells residing in it deform. Cartilage deformation has been related to structural tissue damage, and cell deformation has been associated with cell signalling and corresponding anabolic and catabolic responses. Despite the acknowledged importance of cartilage and cell deformation, there are no dynamic data on these measures from joints of live animals using muscular load application. Research in this area has typically been done using confined and unconfined loading configurations and indentation testing. These loading conditions can be well controlled and allow for accurate measurements of cartilage and cell deformations, but they have little to do with the contact mechanics occurring in a joint where non-congruent cartilage surfaces with different material and functional properties are pressed against each other by muscular forces. The aim of this study was to measure in vivo, real time articular cartilage deformations for precisely controlled static and dynamic muscular loading conditions in the knees of mice. Fifty and 80% of the maximal knee extensor muscular force (equivalent to approximately 0.4N and 0.6N) produced average peak articular cartilage strains of 10.5±1.0% and 18.3±1.3% (Mean ± SD), respectively, during 8s contractions. A sequence of 15 repeat, isometric muscular contractions (0.5s on, 3.5s off) of 50% and 80% of maximal muscular force produced cartilage strains of 3.0±1.1% and 9.6±1.5% (Mean ± SD) on the femoral condyles of the mouse knee. Cartilage thickness recovery following mechanical compression was highly viscoelastic and took almost 50s following force removal in the static tests.

  8. Joint ARM/GCSS/SPARC TWP-ICE CRM Intercomparison Study: Description, Preliminary Results, and Invitation to Participate

    NASA Astrophysics Data System (ADS)

    Fridlind, A. M.; Ackerman, A. S.; Allen, G.; Beringer, J.; Comstock, J. M.; Field, P. R.; Gallagher, M.; Hacker, J. M.; Hume, T.; Jakob, C.; Liu, G.; Long, C. N.; Mather, J. H.; May, P. T.; McCoy, R. F.; McFarlane, S. A.; McFarquhar, G. M.; Minnis, P.; Petch, J. C.; Schumacher, C.; Turner, D. D.; Whiteway, J. A.; Williams, C. R.; Williams, P. I.; Xie, S.; Zhang, M.

    2008-12-01

    The 2006 Tropical Warm Pool - International Cloud Experiment (TWP-ICE) is 'the first field program in the tropics that attempted to describe the evolution of tropical convection, including the large-scale heat, moisture, and momentum budgets at 3-hourly time resolution, while at the same time obtaining detailed observations of cloud properties and the impact of the clouds on the environment' [May et al., 2008]. A cloud- resolving model (CRM) intercomparison based on TWP-ICE is now being undertaken by the Atmospheric Radiation Measurement (ARM), GEWEX Cloud Systems Study (GCSS), and Stratospheric Processes And their Role in Climate (SPARC) programs. We summarize the 16-day case study and the wealth of data being used to provide initial and boundary conditions, and evaluate some preliminary findings in the context of existing theories of moisture evolution in the tropical tropopause layer (TTL). Overall, simulated cloud fields evolve realistically by many measures. Budgets indicate that simulated convective flux convergence of water vapor is always positive or near zero at TTL elevations, except locally at lower levels during the driest suppressed monsoon conditions, while simulated water vapor deposition to hydrometeors always exceeds sublimation on average at all TTL elevations over 24-hour timescales. The next largest water vapor budget term is generally the nudging required to keep domain averages consistent with observations, which is at least partly attributable to large-scale forcing terms that cannot be derived from measurements. We discuss the primary uncertainties.

  9. Detection of dual-band infrared small target based on joint dynamic sparse representation

    NASA Astrophysics Data System (ADS)

    Zhou, Jinwei; Li, Jicheng; Shi, Zhiguang; Lu, Xiaowei; Ren, Dongwei

    2015-10-01

    Infrared small target detection is a crucial and yet still is a difficult issue in aeronautic and astronautic applications. Sparse representation is an important mathematic tool and has been used extensively in image processing in recent years. Joint sparse representation is applied in dual-band infrared dim target detection in this paper. Firstly, according to the characters of dim targets in dual-band infrared images, 2-dimension Gaussian intensity model was used to construct target dictionary, then the dictionary was classified into different sub-classes according to different positions of Gaussian function's center point in image block; The fact that dual-band small targets detection can use the same dictionary and the sparsity doesn't lie in atom-level but in sub-class level was utilized, hence the detection of targets in dual-band infrared images was converted to be a joint dynamic sparse representation problem. And the dynamic active sets were used to describe the sparse constraint of coefficients. Two modified sparsity concentration index (SCI) criteria was proposed to evaluate whether targets exist in the images. In experiments, it shows that the proposed algorithm can achieve better detecting performance and dual-band detection is much more robust to noise compared with single-band detection. Moreover, the proposed method can be expanded to multi-spectrum small target detection.

  10. Anchor ice, seabed freezing, and sediment dynamics in shallow arctic seas

    USGS Publications Warehouse

    Reimnitz, E.; Kempema, E.W.; Barnes, P.W.

    1987-01-01

    Diving investigations confirm previous circumstantial evidence of seafloor freezing and anchor ice accretion during freeze-up storms in the Alaskan Beaufort Sea. These related bottom types were found to be continuous from shore to 2 m depth and spotty to 4.5 m depth. The concretelike nature of frozen bottom, where present, should prohibit sediment transport by any conceivable wave or current regime during the freezing storm. But elsewhere, anchor ice lifts coarse material off the bottom and incorporates it into the ice canopy, thereby leading to significant ice rafting of shallow shelf sediment and likely sediment loss to the deep sea. -from Authors

  11. Observation of sea-ice dynamics using synthetic aperture radar images: Automated analysis

    NASA Technical Reports Server (NTRS)

    Vesecky, John F.; Samadani, Ramin; Smith, Martha P.; Daida, Jason M.; Bracewell, Ronald N.

    1988-01-01

    The European Space Agency's ERS-1 satellite, as well as others planned to follow, is expected to carry synthetic-aperture radars (SARs) over the polar regions beginning in 1989. A key component in utilization of these SAR data is an automated scheme for extracting the sea-ice velocity field from a time sequence of SAR images of the same geographical region. Two techniques for automated sea-ice tracking, image pyramid area correlation (hierarchical correlation) and feature tracking, are described. Each technique is applied to a pair of Seasat SAR sea-ice images. The results compare well with each other and with manually tracked estimates of the ice velocity. The advantages and disadvantages of these automated methods are pointed out. Using these ice velocity field estimates it is possible to construct one sea-ice image from the other member of the pair. Comparing the reconstructed image with the observed image, errors in the estimated velocity field can be recognized and a useful probable error display created automatically to accompany ice velocity estimates. It is suggested that this error display may be useful in segmenting the sea ice observed into regions that move as rigid plates of significant ice velocity shear and distortion.

  12. Spatial and Temporal Antarctic Ice Sheet Mass Trends, Glacio-Isostatic Adjustment, and Surface Processes from a Joint Inversion of Satellite Altimeter, Gravity, and GPS Data

    NASA Technical Reports Server (NTRS)

    Martin-Espanol, Alba; Zammit-Mangion, Andrew; Clarke, Peter J.; Flament, Thomas; Helm, Veit; King, Matt A.; Luthcke, Scott B.; Petrie, Elizabeth; Remy, Frederique; Schon, Nana; Wouters, Bert; Bamber, Jonathan L.

    2016-01-01

    We present spatiotemporal mass balance trends for the Antarctic Ice Sheet from a statistical inversion of satellite altimetry, gravimetry, and elastic-corrected GPS data for the period 2003-2013. Our method simultaneously determines annual trends in ice dynamics, surface mass balance anomalies, and a time-invariant solution for glacio-isostatic adjustment while remaining largely independent of forward models. We establish that over the period 2003-2013, Antarctica has been losing mass at a rateof -84 +/- 22 Gt per yr, with a sustained negative mean trend of dynamic imbalance of -111 +/- 13 Gt per yr. West Antarctica is the largest contributor with -112 +/- 10 Gt per yr, mainly triggered by high thinning rates of glaciers draining into the Amundsen Sea Embayment. The Antarctic Peninsula has experienced a dramatic increase in mass loss in the last decade, with a mean rate of -28 +/- 7 Gt per yr and significantly higher values for the most recent years following the destabilization of the Southern Antarctic Peninsula around 2010. The total mass loss is partly compensated by a significant mass gain of 56 +/- 18 Gt per yr in East Antarctica due to a positive trend of surface mass balance anomalies.

  13. Spatial and temporal Antarctic Ice Sheet mass trends, glacio-isostatic adjustment, and surface processes from a joint inversion of satellite altimeter, gravity, and GPS data.

    PubMed

    Martín-Español, Alba; Zammit-Mangion, Andrew; Clarke, Peter J; Flament, Thomas; Helm, Veit; King, Matt A; Luthcke, Scott B; Petrie, Elizabeth; Rémy, Frederique; Schön, Nana; Wouters, Bert; Bamber, Jonathan L

    2016-02-01

    We present spatiotemporal mass balance trends for the Antarctic Ice Sheet from a statistical inversion of satellite altimetry, gravimetry, and elastic-corrected GPS data for the period 2003-2013. Our method simultaneously determines annual trends in ice dynamics, surface mass balance anomalies, and a time-invariant solution for glacio-isostatic adjustment while remaining largely independent of forward models. We establish that over the period 2003-2013, Antarctica has been losing mass at a rate of -84 ± 22 Gt yr(-1), with a sustained negative mean trend of dynamic imbalance of -111 ± 13 Gt yr(-1). West Antarctica is the largest contributor with -112 ± 10 Gt yr(-1), mainly triggered by high thinning rates of glaciers draining into the Amundsen Sea Embayment. The Antarctic Peninsula has experienced a dramatic increase in mass loss in the last decade, with a mean rate of -28 ± 7 Gt yr(-1) and significantly higher values for the most recent years following the destabilization of the Southern Antarctic Peninsula around 2010. The total mass loss is partly compensated by a significant mass gain of 56 ± 18 Gt yr(-1) in East Antarctica due to a positive trend of surface mass balance anomalies.

  14. Spatial and temporal Antarctic Ice Sheet mass trends, glacio-isostatic adjustment, and surface processes from a joint inversion of satellite altimeter, gravity, and GPS data

    NASA Astrophysics Data System (ADS)

    Martín-Español, Alba; Zammit-Mangion, Andrew; Clarke, Peter J.; Flament, Thomas; Helm, Veit; King, Matt A.; Luthcke, Scott B.; Petrie, Elizabeth; Rémy, Frederique; Schön, Nana; Wouters, Bert; Bamber, Jonathan L.

    2016-02-01

    We present spatiotemporal mass balance trends for the Antarctic Ice Sheet from a statistical inversion of satellite altimetry, gravimetry, and elastic-corrected GPS data for the period 2003-2013. Our method simultaneously determines annual trends in ice dynamics, surface mass balance anomalies, and a time-invariant solution for glacio-isostatic adjustment while remaining largely independent of forward models. We establish that over the period 2003-2013, Antarctica has been losing mass at a rate of -84 ± 22 Gt yr-1, with a sustained negative mean trend of dynamic imbalance of -111 ± 13 Gt yr-1. West Antarctica is the largest contributor with -112 ± 10 Gt yr-1, mainly triggered by high thinning rates of glaciers draining into the Amundsen Sea Embayment. The Antarctic Peninsula has experienced a dramatic increase in mass loss in the last decade, with a mean rate of -28 ± 7 Gt yr-1 and significantly higher values for the most recent years following the destabilization of the Southern Antarctic Peninsula around 2010. The total mass loss is partly compensated by a significant mass gain of 56 ± 18 Gt yr-1 in East Antarctica due to a positive trend of surface mass balance anomalies.

  15. Subglacial conditions and Scandinavian Ice Sheet dynamics at the coarse-grained substratum of the fore-mountain area of southern Poland

    NASA Astrophysics Data System (ADS)

    Salamon, Tomasz

    2016-11-01

    The fore-mountain areas of southern Poland are locally composed of the coarse-grained sediments of alluvial fans, which created unusual conditions under the advancing Scandinavian Ice Sheet during the Elsterian glaciation. This highly permeable substratum potentially enabled rapid outflow of meltwater from the ice sheet base, thereby reducing the water pressure and strongly influencing the ice sheet dynamics. The subglacial conditions and the relationship between the ice sheet behaviour and its coarse-grained substratum were studied at the foreland of the western Carpathian Mountains. The sedimentological and structural analysis of the till and related sediments that were deposited above the alluvial gravel of the fore-mountain fans are presented. The study indicates that despite the high permeability of the coarse-grained substratum, it did not slow the ice sheet movement. Conversely, the ice sheet moved mainly due to basal slip and locally shallow deformations. This was a consequence of very high basal water pressure, which resulted largely from the presence of permafrost that restricted subglacial groundwater outflow. In addition, the ice sheet substratum was inclined opposite to the direction of its movement, increasing the pressure of the subglacial water. Numerous subhorizontal sandy laminae within the till indicate that the meltwater from the ice sheet base was drained by a water film along the ice/bed interface. The water escape structures within the till and subtill sediments indicate the occasional instability of the ice sheet hydrological system and suggest that the meltwater was periodically stored in the ice sheet base. Temporal changes occurring in the ice sheet hydrological system might indicate variations in the ice sheet behaviour; i.e. phases of relatively fast ice flow and phases of ice stagnation. The latter were probably correlated with the freezing of the ice margin to its base. The study shows how the coarse-grained substratum could

  16. Quaternary Ice-Age dynamics in the Colombian Andes: developing an understanding of our legacy.

    PubMed Central

    Hooghiemstra, Henry; Van der Hammen, Thomas

    2004-01-01

    Pollen records from lacustrine sediments of deep basins in the Colombian Andes provide records of vegetation history, the development of the floristic composition of biomes, and climate variation with increasing temporal resolution. Local differences in the altitudinal distribution of present-day vegetation belts in four Colombian Cordilleras are presented. Operating mechanisms during Quaternary Ice-Age cycles that stimulated speciation are discussed by considering endemism in the asteraceous genera Espeletia, Espeletiopsis and Coespeletia. The floristically diverse lower montane forest belt (1000-2300 m) was compressed by ca. 55% during the last glacial maximum (LGM) (20 ka), and occupied the slopes between 800 m and 1400 m during that period. Under low LGM atmospheric pCO2 values, C4-dominated vegetation, now occurring below 2200 m, expanded up to ca. 3500 m. Present-day C3-dominated paramo vegetation is therefore not an analogue for past C4-dominated vegetation (with abundant Sporobolus lasiophyllus). Quercus immigrated into Colombia 478 ka and formed an extensive zonal forest from 330 ka when former Podocarpus-dominated forest was replaced by zonal forest with Quercus and Weinmannia. During the last glacial cycle the ecological tolerance of Quercus may have increased. In the ecotone forests Quercus was rapidly and massively replaced by Polylepis between 45 and 30 ka illustrating complex forest dynamics in the tropical Andes. PMID:15101574

  17. A 3 Ga old polythermal ice sheet in Isidis Planitia, Mars: Dynamics and thermal regime inferred from numerical modeling

    NASA Astrophysics Data System (ADS)

    Souček, Ondřej; Bourgeois, Olivier; Pochat, Stéphane; Guidat, Thomas

    2015-09-01

    Isidis Planitia is a 1350 km wide impact crater located close to the martian equator. To test the hypothesis that the 2.8 to 3.4 Ga old Thumbprint Terrain preserved on the floor of this basin is a glacial landform assemblage, we perform a numerical simulation of glaciation with a thermo-mechanically coupled model of ice sheet dynamics. As model inputs, we use surface temperatures and ice accumulation patterns predicted by a General Circulation Model based on the present-day atmospheric characteristics, and values of the geothermal heat flux provided by a global model of planetary thermal evolution. We find that, under favorable orbital conditions, an ice sheet covering the entire basin can develop in 2 to 5 Ma, with a maximum thickness of 4.9 km. The modeled ice sheet is polythermal: it is permanently cold-based in the periphery and, due to a negative heat-flux anomaly, also in the center, while the pressure melting point is reached in an intermediate ring. Our simulation is consistent with the interpretation that the Thumbprint Terrain is a martian equivalent of terrestrial ribbed moraines and has formed below a wet-based ice sheet. It supports also the interpretation that sinuous ridges and linear valleys observed at the periphery of the basin are parts of a subglacial network of eskers and tunnel valleys that drained the glacial meltwater outwards, across the cold-based periphery of the ice sheet. This work strengthens the hypothesis that glaciers thick as much as several km may have existed on Mars several Ga ago and that glacial basal melting may have contributed to the production and flow of surface liquid water at that time, under an atmosphere no thicker than the present-day one.

  18. Hydrogen-bond vibrational and energetic dynamical properties in sI and sII clathrate hydrates and in ice Ih: Molecular dynamics insights

    NASA Astrophysics Data System (ADS)

    Chakraborty, Somendra Nath; English, Niall J.

    2015-10-01

    Equilibrium molecular dynamics (MD) simulations have been performed on cubic (sI and sII) polymorphs of methane hydrate, and hexagonal ice (ice Ih), to study the dynamical properties of hydrogen-bond vibrations and hydrogen-bond self-energy. It was found that hydrogen-bond energies are greatest in magnitude in sI hydrates, followed by sII, and their energies are least in magnitude in ice Ih. This is consistent with recent MD-based findings on thermal conductivities for these various materials [N. J. English and J. S. Tse, Phys. Rev. Lett. 103, 015901 (2009)], in which the lower thermal conductivity of sI methane hydrate was rationalised in terms of more strained hydrogen-bond arrangements. Further, modes for vibration and energy-transfer via hydrogen bonds in sI hydrate were found to occur at higher frequencies vis-à-vis ice Ih and sII hydrate in both the water-librational and OH⋯H regions because of the more strained nature of hydrogen bonds therein.

  19. Observational and Theoretical Foundation for the Dynamics in a High-resolution Sea Ice Model

    DTIC Science & Technology

    2016-06-07

    Ocean (SHEBA) field programs (Overland et al.,1998; Richter-Menge and Elder, 1998; Richter-Menge et al., 1998). These observations are derived from...The thickness distribution of the ice cover has a significant impact on heat and energy exchange between the atmosphere, ice, and ocean . 2) I am

  20. Effects of torque spring, CCL and latch mechanism on dynamic response of planar solar arrays with multiple clearance joints

    NASA Astrophysics Data System (ADS)

    Li, Yuanyuan; Wang, Zilu; Wang, Cong; Huang, Wenhu

    2017-03-01

    This paper numerically investigates the effects of torque spring, close cable loop (CCL) configuration and latch mechanism on the overall dynamic characteristics of a deployable solar arrays system considering joint clearance; and presents significant guidance for the key parameters design of these three mechanisms. A typical mechanism composed of a main-body with a yoke and two panels is used as a demonstration case to study the dynamic response of the deployable solar array system in the deployment process and post-latch phase. The normal contact force model and tangential friction model in clearance joint are established using nonlinear contact force model and modified Coulomb friction model, respectively. The numerical simulation results reveal that the joint clearances influence the dynamic characteristics of the deployable space solar arrays in different operation phases. Besides, parametric studies indicate some rules to design preload and stiffness coefficient of torque spring, equivalent stiffness coefficient of CCL mechanism and stiffness and damping coefficient of latch mechanism.

  1. Bacterial community dynamics and activity in relation to dissolved organic matter availability during sea-ice formation in a mesocosm experiment.

    PubMed

    Eronen-Rasimus, Eeva; Kaartokallio, Hermanni; Lyra, Christina; Autio, Riitta; Kuosa, Harri; Dieckmann, Gerhard S; Thomas, David N

    2014-02-01

    The structure of sea-ice bacterial communities is frequently different from that in seawater. Bacterial entrainment in sea ice has been studied with traditional microbiological, bacterial abundance, and bacterial production methods. However, the dynamics of the changes in bacterial communities during the transition from open water to frozen sea ice is largely unknown. Given previous evidence that the nutritional status of the parent water may affect bacterial communities during ice formation, bacterial succession was studied in under ice water and sea ice in two series of mesocosms: the first containing seawater from the North Sea and the second containing seawater enriched with algal-derived dissolved organic matter (DOM). The composition and dynamics of bacterial communities were investigated with terminal restriction fragment length polymorphism (T-RFLP), and cloning alongside bacterial production (thymidine and leucine uptake) and abundance measurements (measured by flow cytometry). Enriched and active sea-ice bacterial communities developed in ice formed in both unenriched and DOM-enriched seawater (0-6 days). γ-Proteobacteria dominated in the DOM-enriched samples, indicative of their capability for opportunistic growth in sea ice. The bacterial communities in the unenriched waters and ice consisted of the classes Flavobacteria, α- and γ-Proteobacteria, which are frequently found in natural sea ice in polar regions. Furthermore, the results indicate that seawater bacterial communities are able to adapt rapidly to sudden environmental changes when facing considerable physicochemical stress such as the changes in temperature, salinity, nutrient status, and organic matter supply during ice formation.

  2. Bacterial community dynamics and activity in relation to dissolved organic matter availability during sea-ice formation in a mesocosm experiment

    PubMed Central

    Eronen-Rasimus, Eeva; Kaartokallio, Hermanni; Lyra, Christina; Autio, Riitta; Kuosa, Harri; Dieckmann, Gerhard S; Thomas, David N

    2014-01-01

    The structure of sea-ice bacterial communities is frequently different from that in seawater. Bacterial entrainment in sea ice has been studied with traditional microbiological, bacterial abundance, and bacterial production methods. However, the dynamics of the changes in bacterial communities during the transition from open water to frozen sea ice is largely unknown. Given previous evidence that the nutritional status of the parent water may affect bacterial communities during ice formation, bacterial succession was studied in under ice water and sea ice in two series of mesocosms: the first containing seawater from the North Sea and the second containing seawater enriched with algal-derived dissolved organic matter (DOM). The composition and dynamics of bacterial communities were investigated with terminal restriction fragment length polymorphism (T-RFLP), and cloning alongside bacterial production (thymidine and leucine uptake) and abundance measurements (measured by flow cytometry). Enriched and active sea-ice bacterial communities developed in ice formed in both unenriched and DOM-enriched seawater (0–6 days). γ-Proteobacteria dominated in the DOM-enriched samples, indicative of their capability for opportunistic growth in sea ice. The bacterial communities in the unenriched waters and ice consisted of the classes Flavobacteria, α-and γ-Proteobacteria, which are frequently found in natural sea ice in polar regions. Furthermore, the results indicate that seawater bacterial communities are able to adapt rapidly to sudden environmental changes when facing considerable physicochemical stress such as the changes in temperature, salinity, nutrient status, and organic matter supply during ice formation. PMID:24443388

  3. Episodic speleothem deposition in Ireland during the late Quaternary; implications for Greenland ice core chronology and British-Irish Ice Sheet dynamics

    NASA Astrophysics Data System (ADS)

    McDermott, Frank; Fankhauser, Adelheid

    2016-04-01

    In shallow caves, episodes of speleothem deposition during the late Quaternary, constrained by U-series dates, provide unequivocal evidence for periods of climate amelioration (presence of liquid water, elevated soil pCO2). U-series data for speleothems from several cave systems in Ireland (Crag, Ballynamintra and Marble Arch) provide clear evidence for episodic speleothem deposition, ranging in age from Marine Isotope Stage (MIS) 7 to the Last Glacial Termination. Speleothem deposition and non-depositional phases within these caves are particularly sensitive to regional-scale climatic conditions, reflecting Ireland's mid-latitudinal, Atlantic margin location. Currently, the earliest dated speleothems from the region are sparsely preserved and thin MIS 7 and MIS 5 flowstones from Ballynamintra and Crag caves respectively. Relatively short-lived depositional phases also occurred at Crag cave during MIS4 and MIS3 and are coeval with the Greenland Interstadials (GI), supporting the recently modified GICC05 Greenland ice core chronology (Buizert et al., 2015), and new providing evidence for synchronous or nearly-synchronous climate amelioration in the N. hemisphere mid- and high-latitudes during the GI events. On the other hand, there is strong evidence that conditions at Crag cave site during stadials and the Heinrich stadials were not conducive to speleothem deposition. Episodes of non-deposition occur synchronously in several speleothems from Crag cave, providing independent constraints on the timing of Heinrich stadials HS-6 to HS-2. The new data also provide independent new insights into the behaviour of the British Irish Ice Sheet (BIIS) during MIS2. In this regard, the presence of a short depositional pulse at 23.35 ± 0.1 ka at Crag cave coincides precisely with the weak and short-lived GI2.2 event within MIS 2, suggesting a dynamic BIIS margin. Simple conductive thermal models for the propagation of surface air temperatures through the limestone karst

  4. Interlimb symmetry of dynamic knee joint stiffness and co-contraction is maintained in early stage knee osteoarthritis.

    PubMed

    Collins, A T; Richardson, R T; Higginson, J S

    2014-08-01

    Individuals with knee OA often exhibit greater co-contraction of antagonistic muscle groups surrounding the affected joint which may lead to increases in dynamic joint stiffness. These detrimental changes in the symptomatic limb may also exist in the contralateral limb, thus contributing to its risk of developing knee osteoarthritis. The purpose of this study is to investigate the interlimb symmetry of dynamic knee joint stiffness and muscular co-contraction in knee osteoarthritis. Muscular co-contraction and dynamic knee joint stiffness were assessed in 17 subjects with mild to moderate unilateral medial compartment knee osteoarthritis and 17 healthy control subjects while walking at a controlled speed (1.0m/s). Paired and independent t-tests determined whether significant differences exist between groups (p<0.05). There were no significant differences in dynamic joint stiffness or co-contraction between the OA symptomatic and OA contralateral group (p=0.247, p=0.874, respectively) or between the OA contralateral and healthy group (p=0.635, p=0.078, respectively). There was no significant difference in stiffness between the OA symptomatic and healthy group (p=0.600); however, there was a slight trend toward enhanced co-contraction in the symptomatic knees compared to the healthy group (p=0.051). Subjects with mild to moderate knee osteoarthritis maintain symmetric control strategies during gait.

  5. Massively parallel molecular-dynamics simulation of ice crystallisation and melting: the roles of system size, ensemble, and electrostatics.

    PubMed

    English, Niall J

    2014-12-21

    Ice crystallisation and melting was studied via massively parallel molecular dynamics under periodic boundary conditions, using approximately spherical ice nano-particles (both "isolated" and as a series of heterogeneous "seeds") of varying size, surrounded by liquid water and at a variety of temperatures. These studies were performed for a series of systems ranging in size from ∼1 × 10(6) to 8.6 × 10(6) molecules, in order to establish system-size effects upon the nano-clusters" crystallisation and dissociation kinetics. Both "traditional" four-site and "single-site" and water models were used, with and without formal point charges, dipoles, and electrostatics, respectively. Simulations were carried out in the microcanonical and isothermal-isobaric ensembles, to assess the influence of "artificial" thermo- and baro-statting, and important disparities were observed, which declined upon using larger systems. It was found that there was a dependence upon system size for both ice growth and dissociation, in that larger systems favoured slower growth and more rapid melting, given the lower extent of "communication" of ice nano-crystallites with their periodic replicae in neighbouring boxes. Although the single-site model exhibited less variation with system size vis-à-vis the multiple-site representation with explicit electrostatics, its crystallisation-dissociation kinetics was artificially fast.

  6. Massively parallel molecular-dynamics simulation of ice crystallisation and melting: The roles of system size, ensemble, and electrostatics

    NASA Astrophysics Data System (ADS)

    English, Niall J.

    2014-12-01

    Ice crystallisation and melting was studied via massively parallel molecular dynamics under periodic boundary conditions, using approximately spherical ice nano-particles (both "isolated" and as a series of heterogeneous "seeds") of varying size, surrounded by liquid water and at a variety of temperatures. These studies were performed for a series of systems ranging in size from ˜1 × 106 to 8.6 × 106 molecules, in order to establish system-size effects upon the nano-clusters" crystallisation and dissociation kinetics. Both "traditional" four-site and "single-site" and water models were used, with and without formal point charges, dipoles, and electrostatics, respectively. Simulations were carried out in the microcanonical and isothermal-isobaric ensembles, to assess the influence of "artificial" thermo- and baro-statting, and important disparities were observed, which declined upon using larger systems. It was found that there was a dependence upon system size for both ice growth and dissociation, in that larger systems favoured slower growth and more rapid melting, given the lower extent of "communication" of ice nano-crystallites with their periodic replicae in neighbouring boxes. Although the single-site model exhibited less variation with system size vis-à-vis the multiple-site representation with explicit electrostatics, its crystallisation-dissociation kinetics was artificially fast.

  7. Do climate mode flips control the dynamics of the Laurentide Ice Sheet

    SciTech Connect

    Lowell, T.V. . Dept. of Geology)

    1993-03-01

    Mode flips, major reorganizations of the earth's ocean-atmosphere system, are being debated as the cause of glacial terminations. If these do occur, one important implication is that ice sheets responded to, rather than drove, climate changes. Using the Laurentide Ice Sheet as an example, the author explores this implication and suggest that ice sheets acted in three fundamentally different modes. In the growth mode the LIS expanded under cold conditions, produced little meltwater and left little sediment. Equilibrium profiles were maintained during growth. During it's full extent mode, the ice sheet remained in a quasi-equilibrium state for several thousand years with minor marginal changes but produced little meltwater. In the decay mode, despite its rapid retreat, the ice sheet did most of its geomorphic work largely because of the abundant water produced from a rapid rise in ELA. Surface profiles would be low from the increased surface melting. This model explains the large volumes of meltwater that are necessary for deforming beds, surges, major subglacial erosion, and formation of proglacial lakes. If this hypothesis is correct it implies that the role of ice sheets in GCM models must be modified from driving to driven, and that anthropogenic warming may change the behavior of the Antarctic Ice Sheet by introducing a large ablation zone.

  8. Simulating a Dynamic Antarctic Ice Sheet in the Early to Middle Miocene

    NASA Astrophysics Data System (ADS)

    Gasson, E.; DeConto, R.; Pollard, D.; Levy, R. H.

    2015-12-01

    There are a variety of sources of geological data that suggest major variations in the volume and extent of the Antarctic ice sheet during the early to middle Miocene. Simulating such variability using coupled climate-ice sheet models is problematic due to a strong hysteresis effect caused by height-mass balance feedback and albedo feedback. This results in limited retreat of the ice sheet once it has reached the continental size, as likely occurred prior to the Miocene. Proxy records suggest a relatively narrow range of atmospheric CO2 during the early to middle Miocene, which exacerbates this problem. We use a new climate forcing which accounts for ice sheet-climate feedbacks through an asynchronous GCM-RCM coupling, which is able to better resolve the narrow Antarctic ablation zone in warm climate simulations. When combined with recently suggested mechanisms for retreat into subglacial basins due to ice shelf hydrofracture and ice cliff failure, we are able to simulate large-scale variability of the Antarctic ice sheet in the Miocene. This variability is equivalent to a seawater oxygen isotope signal of ~0.5 ‰, or a sea level equivalent change of ~35 m, for a range of atmospheric CO2 between 280 - 500 ppm.

  9. Characterizing interannual variability of glacier dynamics and dynamic discharge (1999-2015) for the ice masses of Ellesmere and Axel Heiberg Islands, Nunavut, Canada

    NASA Astrophysics Data System (ADS)

    Van Wychen, Wesley; Davis, Jamie; Burgess, David O.; Copland, Luke; Gray, Laurence; Sharp, Martin; Mortimer, Colleen

    2016-01-01

    Landsat 7 and RADARSAT-1/RADARSAT-2 satellite images are used to produce the most comprehensive record of glacier motion in the Canadian High Arctic to date and to characterize spatial and temporal variability in ice flow over the past ~15 years. This allows us to assess whether dynamically driven glacier change can be attributed to "surging" or "pulsing," or whether other mechanisms are involved. RADAR velocity mapping allows annual regional dynamic discharge (iceberg calving) to be calculated for 2000 and the period 2011-2015 (yielding a mean regional discharge of 2.21 ± 0.68 Gt a-1), and velocities derived from feature tracking of optical imagery allow for annual dynamic discharge to be calculated for select glaciers from 1999 to 2010. Since ~2011, several of the major tidewater-terminating glaciers within the region have decelerated and their dynamic discharge has decreased. Trinity and Wykeham Glaciers (Prince of Wales Icefield) represent a notable departure from this pattern as they have generally accelerated over the study period. The resulting increase in dynamic discharge from these glaciers entirely compensates (within error limits) for the decrease in discharge from the other tidewater glaciers across the study region. These two glaciers accounted for ~62% of total regional dynamic discharge in winter 2015 (compared to ~22% in 2000), demonstrating that total ice discharge from the Canadian High Arctic can be sensitive to variations in flow of just a few tidewater glaciers.

  10. Electromagnetic emission under uniaxial compression of ice: III. Dynamics and statistics of dislocation avalanches and cracks

    NASA Astrophysics Data System (ADS)

    Shibkov, A. A.; Kazakov, A. A.

    2009-03-01

    Statistical analysis of the plastic deformation steps and fracture of polycrystalline ice has been performed. It is established that an increase in deformation leads to gradual evolution of the statistics of amplitudes of mesoscopic deformation jumps from random (with a Poisson distribution of dislocation avalanche amplitudes) to “critical” (with a power-law distribution), which indicates occurrence of long-range correlations of the dislocation mesodynamics of deformed polycrystalline ice. The state of self-organized criticality at subcritical ice fracture has been revealed from the power-law statistics of the amplitudes of electric pulses and pauses between them, flicker-noise structure, and almost monofractal character of signals.

  11. Seasonal-to-Interannual Variability in Antarctic Sea-Ice Dynamics, and Its Impact on Surface Fluxes and Water Mass Production

    NASA Technical Reports Server (NTRS)

    Drinkwater, Mark R.

    1999-01-01

    Strong seasonal and interannual signals in Antarctic bottom-water outflow remain unexplained yet are highly correlated with anomalies in net sea-ice growth in coastal polynyas. The mechanisms responsible for driving salination and replenishment and rejuvenation of the dense shelf "source" waters likely also generate pulses of bottom water outflow. The objective of this research is to investigate time-scales of variability in the dynamics of sea-ice in the Southern Ocean in order to determine the primary sites for production of dense shelf waters. We are using a merged satellite/buoy sea-ice motion data set for the period 1978-present day to compute the dynamics of opening and closing of coastal polynyas over the continental shelf. The Ocean Circulation and Climate Advanced Model (OCCAM) ocean general circulation model with coupled sea-ice dynamics is presently forced using National Center for Environmental Prediction (NCEP) data to simulate fluxes and the salination impact of the ocean shelf regions. This work is relevant in the context of measuring the influence of polar sea-ice dynamics upon polar ocean characteristics, and thereby upon global thermohaline ocean circulation. Interannual variability in simulated net freezing rate in the Southern Weddell Sea is shown for the period 1986-1993. There is a pronounced maximum of ice production in 1988 and minimum in 1991 in response to anomalies in equatorward meridional wind velocity. This follows a similar approximate 8-year interannual cycle in Sea Surface Temperature (SST) and satellite-derived ice-edge anomalies reported elsewhere as the "Antarctic Circumpolar Wave." The amplitude of interannual fluctuations in annual net ice production are about 40% of the mean value, implying significant interannual variance in brine rejection and upper ocean heat loss. Southward anomalies in wind stress induce negative anomalies in open water production, which are observed in passive microwave satellite images. Thus, cycles of

  12. Use of Ground Imagery to Study Wood Raft and Ice Dynamics in Fluvial Systems: Potential and Challenges.

    NASA Astrophysics Data System (ADS)

    Benacchio, V.; Piegay, H.; Buffin-Belanger, T. K.; Vaudor, L.; Michel, K.

    2014-12-01

    Automatic cameras allow acquisition of large amounts of information at high resolution in both temporal and spatial dimensions, with a roughly close range. Recently, ground cameras have been used to study the morphological evolution of fluvial environments (e.g. bank erosion, bar mobility, braided pattern changes) or to quantify components of fluvial dynamics (e.g. flow velocity, wood transport or river ice development). As the amount of information increases, automation of the data processing becomes essential, but many challenges arise to improve features detection, taking into account light contrasts, shadow and reflection, or to calculate surfaces and volumes from image orthorectification. This study illustrates the high potential of ground cameras to observe and quantify rapid, stochastic or complex events in fluvial systems and the numerous challenges we have to face. In order to automatically monitor such key fluvial processes, two ground cameras were installed. The first one was placed on the Genissiat dam (Rhône River, France) focusing on the reservoir where pieces of wood are trapped, creating a large raft. The objective is to survey wood raft area over time as a surrogate of the basin wood production. The second camera was installed along the St Jean River (Gaspesia, Québec) focusing on a pool section. The objective here is to characterize the evolution of ice cover, in terms of growing rate and ice types. The snowy environment is particularly challenging because of brightness or fairly homogeneous radiometric conditions amongst ice types. In both cases, remote sensing technics, especially feature based classification are used. Radiometric and texture indexes are used to discriminate both wood and water and ice types.

  13. Dynamic Analysis of Overhead Power Lines after Ice-Shedding Using Finite Element Method

    NASA Astrophysics Data System (ADS)

    Murín, Justín; Hrabovský, Juraj; Gogola, Roman; Janíček, František

    2016-12-01

    In this paper, the analysis of ice-shedding from ACSR conductors to its swing up height and vibration using Finite Element Method (FEM) is presented. For the numerical simulations the effective material properties of the ACSR conductor are calculated using the homogenisation method. Numerical analysis concerning vibration of one and triple-bundle conductors with icing for a whole range or on their certain parts are performed. The impact of ice-shedding to the mechanical tension in the conductors at the points of attachment is investigated and evaluated. Identification of the impact of ice-shedding from the ACSR conductors on its mechanical state may contribute to increasing the safety and quality of an electrical transmission system.

  14. Joint application of non-invasive techniques to characterize the dynamic behaviuor of engineering structures

    NASA Astrophysics Data System (ADS)

    Gallipoli, M. R.; Perrone, A.; Stabile, T. A.; Ponzo, F. C.; Ditommaso, R.

    2012-04-01

    The systematic monitoring of strategic civil infrastructures such as bridges, large dams or high-rise buildings in order to ensure their structural stability is a strategic issue particularly in earthquake-prone regions. Nevertheless, in areas less exposed to seismic hazard, the monitoring is also an important tool for civil engineers, for instance if they have to deal with structures exposed to heavy operational demands for extended periods of time and whose structural integrity might be in question or at risk. A continuous monitoring of such structures allows the identification of their fundamental response characteristics and the changes of these over time, the latter representing indicators for potential structural degradation. The aim of this paper is the estimation of fundamental dynamic parameters of some civil infrastructures by the joint application of fast executable, non-invasive techniques such as the Ambient Noise Standard Spectral Ratio, and Ground-Based microwave Radar Interferometer techniques. The joint approach combine conventional, non-conventional and innovative techniques in order to set up a non destructive evaluation procedure allowing for a multi-sensing monitoring at a multi-scale and multi-depth levels (i.e. with different degrees of spatial resolution and different subsurface depths). In particular, techniques based on ambient vibration recordings have become a popular tool for characterizing the seismic response and state-of-health of strategic civil infrastructure. The primary advantage of these approaches lies in the fact that no transient earthquake signals or even active excitation of the structure under investigation are required. The microwave interferometry radar technology, it has proven to be a powerful remote sensing tool for vibration measurement of structures, such as bridge, heritage architectural structures, vibrating stay cables, and engineering structures. The main advantage of this radar technique is the possibility to

  15. Modeling the West Antarctic and Greenland ice sheets: New dynamic, thermodynamic, and isostatic insights

    NASA Astrophysics Data System (ADS)

    Parizek, Byron R.

    Numerical simulations indicate that the apparent long-term persistence and short-term variability of the Ross ice streams in West Antarctica are tied to regional thermal conditions and local basal lubrication. Modelling results suggest that the flux of latent heat in a throughgoing hydrologic system fed by melt beneath thick inland ice maintains the lubrication of the ice streams despite their tendency to freeze to the bed, and would allow additional thinning and grounding-line retreat. However, the efficiency of basal water distribution may be a constraint on the system. Because local thermal deficits promote basal freeze-on (especially on topographic highs), observed short-term variability is likely to persist. Furthermore, simulations indicate that the ice streams have experienced only small deglacial thickness changes and are thinning more rapidly than their beds are rising isostatically. Thickness changes of O (100)m are modelled at the modern grounding line through the last glacial cycle. Coupled ice and bedrock models indicate isostatic rebound is raising the ice sheet at the modern grounding line faster than the rising sea level is submerging it. While, in and of itself, this could potentially lead to a grounding-line re-advance, ice flow is modelled to respond to recent changes in temperature, accumulation rate, and basal processes more rapidly than it does to bedrock-elevation and/or sea-level fluctuations. Future projections of the Greenland ice sheet indicate a faster contribution to sea-level rise in a warming world than previously believed, based on numerical modelling using a parameterization of recent results showing surface-meltwater lubrication of Greenland ice flow (Zwally et al., 2002). Numerous simulations were conducted to test a wide range of parameter space linking surface melt with a new sliding law based on Zwally et al. data under different global warming scenarios. Comparisons to reconstructions generated with a traditional sliding

  16. Geological Influences on Bedrock Topography and East Antarctic Ice Sheet Dynamics in the Wilkes Subglacial Basin

    NASA Astrophysics Data System (ADS)

    Ferraccioli, F.; Armadillo, E.; Young, D. A.; Blankenship, D. D.; Jordan, T. A.; Balbi, P.; Bozzo, E.; Siegert, M. J.

    2014-12-01

    The Wilkes Subglacial Basin (WSB) extends for 1,400 km from George V Land into the interior of East Antarctica and hosts several major glaciers that drain a large sector of the East Antarctic Ice Sheet (EAIS). This region is of key significance for the long-term stability of the ice sheet in East Antarctica, as it lies well below sea level and its bedrock deepens inland, making it potentially prone to marine ice sheet instability, much like areas of the West Antarctic Ice Sheet (WAIS) that are presently experiencing significant mass loss. We present new enhanced potential field images of the WSB combined with existing radar imaging to study geological controls on bedrock topography and ice flow regimes in this key sector of the ice sheet. These images reveal mayor Precambrian and Paleozoic basement faults that exert tectonic controls both on the margins of the basin and its sub-basins. Several major sub-basins can be recognised: the Eastern Basin, the Central Basins and the Western Basins. Using ICECAP aerogeophysical data we show that these tectonically controlled interior basins connect to newly identified basins underlying the Cook Ice Shelf region. This connection implies that any ocean-induced changes at the margin of the EAIS could potentially propagate rapidly further into the interior. With the aid of simple magnetic and gravity models we show that the WSB does not presently include major post Jurassic sedimentary infill. Its bedrock geology is highly variable and includes Proterozoic basement, Neoproterozoic and Cambrian sediments, intruded by Cambrian arc rocks, and cover rocks formed by Beacon sediments intruded by Jurassic Ferrar sills. Enhanced ice flow in this part of the EAIS occurs therefore in a area of mixed and spatially variable bedrock geology. This contrasts with some regions of the WAIS where more extensive sedimentary basins may represent a geological template for the onset and maintenance of fast glacial flow.

  17. Dynamics of low velocity collisions of ice particle, coated with frost

    NASA Technical Reports Server (NTRS)

    Bridges, F.; Lin, D.; Boone, L.; Darknell, D.

    1991-01-01

    We continued our investigations of low velocity collisions of ice particles for velocities in range 10(exp -3) - 2 cm/s. The work focused on two effects: (1) the sticking forces for ice particles coated with CO2 frost, and (2) the completion of a 2-D pendulum system for glancing collisions. A new computer software was also developed to control and monitor the position of the 2-D pendulum.

  18. High-density amorphous ice: Molecular dynamics simulations of the glass transition at 0.3 GPa.

    PubMed

    Seidl, M; Loerting, T; Zifferer, G

    2009-09-21

    Based on several force fields (COMPASS, modified TIP3P and SPC/E) high-density amorphous ice is simulated by use of isothermal-isobaric molecular dynamics at a pressure of p approximately 0.3 GPa in the temperature range from 70 to 300 K. Starting at low temperature a large number of heating/cooling cycles are performed and several characteristic properties (density, total energy, and mobility) are traced as functions of temperature. While the first cycles are showing irreversible structural relaxation effects data points from further cycles are reproducible and give clear evidence for the existence of a glass-to-liquid transition. Although, the observed transition temperatures T(g) are dependent on the actual force field used and slightly dependent on the method adopted the results indicate that high-density amorphous ices may indeed be low-temperature structural proxies of ultraviscous high-density liquids.

  19. Altered dynamics of broad-leaved tree species in a Chinese subtropical montane mixed forest: the role of an anomalous extreme 2008 ice storm episode.

    PubMed

    Ge, Jielin; Xiong, Gaoming; Wang, Zhixian; Zhang, Mi; Zhao, Changming; Shen, Guozhen; Xu, Wenting; Xie, Zongqiang

    2015-04-01

    Extreme climatic events can trigger gradual or abrupt shifts in forest ecosystems via the reduction or elimination of foundation species. However, the impacts of these events on foundation species' demography and forest dynamics remain poorly understood. Here we quantified dynamics for both evergreen and deciduous broad-leaved species groups, utilizing a monitoring permanent plot in a subtropical montane mixed forest in central China from 2001 to 2010 with particular relevance to the anomalous 2008 ice storm episode. We found that both species groups showed limited floristic alterations over the study period. For each species group, size distribution of dead individuals approximated a roughly irregular and flat shape prior to the ice storm and resembled an inverse J-shaped distribution after the ice storm. Furthermore, patterns of mortality and recruitment displayed disequilibrium behaviors with mortality exceeding recruitment for both species groups following the ice storm. Deciduous broad-leaved species group accelerated overall diameter growth, but the ice storm reduced evergreen small-sized diameter growth. We concluded that evergreen broad-leaved species were more susceptible to ice storms than deciduous broad-leaved species, and ice storm events, which may become more frequent with climate change, might potentially threaten the perpetuity of evergreen-dominated broad-leaved forests in this subtropical region in the long term. These results underscore the importance of long-term monitoring that is indispensible to elucidate causal links between forest dynamics and climatic perturbations.

  20. Assessing the Influence of Tributary Glaciers on Ice Properties and Flow Dynamics

    NASA Astrophysics Data System (ADS)

    Quick, A. M.; Rupper, S.; McBride, J. H.; Ritter, S.; Tingey, D. G.; McKean, A.; Parks, E.

    2009-12-01

    Ice flow models designed to simulate glacier changes in response to changes in climatic forcing, past or present, must accurately predict glacier flow rates, which can only be determined if ice rheology is well constrained. In the commonly used flow-law models that assume strain rates are proportional to a power-law dependence on stress, the flow-law parameters are dependent upon numerous ice properties, some of which include temperature, impurities, liquid water fraction, crystal size and fabric. The aim of this study is to measure the ice properties between tributary glaciers within a single glacier system and assess the impact of the differences in these properties on the flow rates of the system as a whole. The preliminary study was done on the Gornergletscher, located in Valais, Switzerland. The Gornergletscher is the second largest glacier system in the European Alps, and results from the confluence of several tributary glaciers. Forty-three shallow ice cores (.30-3 m) were drilled in the ablation zone down-flow of the confluence of two of the tributary glaciers in the Gornergletscher system - fifteen ice cores on Grenzgletscher and twenty-eight on Zwillingsgletscher. Physical (density, grain size), chemical (stable isotopes, solutes, dust), and thermal (temperature) properties of ice were measured in all cores. Preliminary chemical analyses indicate statistically significant differences in the isotopic composition of the ice. In particular, there is a 20‰ difference in the mean δD between the two glaciers which can not be easily explained by isotopic lapse rates and elevation differences of the source regions. The isotopic difference may be evidence of flow pattern differences giving rise to differences in surface ice ages between the adjacent glaciers. In addition to the ice cores, a ground-penetrating radar survey using a 200-MHz bistatic antenna in continuous mode with a fixed transmitter-receiver offset was completed extending 1200 meters down

  1. Salt partitioning between water and high-pressure ices. Implication for the dynamics and habitability of icy moons and water-rich planetary bodies

    NASA Astrophysics Data System (ADS)

    Journaux, Baptiste; Daniel, Isabelle; Petitgirard, Sylvain; Cardon, Hervé; Perrillat, Jean-Philippe; Caracas, Razvan; Mezouar, Mohamed

    2017-04-01

    Water-rich planetary bodies including large icy moons and ocean exoplanets may host a deep liquid water ocean underlying a high-pressure icy mantle. The latter is often considered as a limitation to the habitability of the uppermost ocean because it would limit the availability of nutrients resulting from the hydrothermal alteration of the silicate mantle located beneath the deep ice layer. To assess the effects of salts on the physical properties of high-pressure ices and therefore the possible chemical exchanges and habitability inside H2O-rich planetary bodies, we measured partitioning coefficients and densities in the H2O-RbI system up to 450 K and 4 GPa; RbI standing as an experimentally amenable analog of NaCl in the H2O-salt solutions. We measured the partitioning coefficient of RbI between the aqueous fluid and ices VI and VII, using in-situ Synchrotron X-ray Fluorescence (XRF). With in-situ X-ray diffraction, we measured the unit-cell parameters and the densities of the high-pressure ice phases in equilibrium with the aqueous fluid, at pressures and temperatures relevant to the interior of planetary bodies. We conclude that RbI is strongly incompatible towards ice VI with a partitioning coefficient Kd(VI-L) = 5.0 (± 2.1) ṡ10-3 and moderately incompatible towards ice VII, Kd(VII-L) = 0.12 (± 0.05). RbI significantly increases the unit-cell volume of ice VI and VII by ca. 1%. This implies that RbI-poor ice VI is buoyant compared to H2O ice VI while RbI-enriched ice VII is denser than H2O ice VII. These new experimental results might profoundly impact the internal dynamics of water-rich planetary bodies. For instance, an icy mantle at moderate conditions of pressure and temperature will consist of buoyant ice VI with low concentration of salt, and would likely induce an upwelling current of solutes towards the above liquid ocean. In contrast, a deep and/or thick icy mantle of ice VII will be enriched in salt and hence would form a stable chemical boundary

  2. The use of pseudo-dynamic magnetic resonance imaging for evaluating the relationship between temporomandibular joint anterior disc displacement and joint pain.

    PubMed

    Lin, W-C; Lo, C-P; Chiang, I-C; Hsu, C-C; Hsu, W-L; Liu, D-W; Juan, Y-H; Liu, G-C

    2012-12-01

    The relationship between temporomandibular joint (TMJ) pain and the magnetic resonance imaging (MRI) finding of articular disc displacement is debated. The purpose of this study is to investigate the correlation between TMJ pain and anterior disc displacement (ADD) using pseudo-dynamic MRI. A retrospective review of MRI studies was carried out on 130 TMJs in 65 patients presenting unilateral TMJ pain. The contralateral asymptomatic joints served as the control group. Bilateral oblique sagittal and coronal MRIs as well as pseudo-dynamic studies in the oblique sagittal plane were obtained. The disc-condyle relationship was divided into three subtypes (normal disc position, ADD with reduction, and ADD without reduction), based on the pseudo-dynamic MRI findings. Fisher's exact test was used to determine whether the TMJ pain was linked to ADD. The results showed that TMJ pain was significantly related to ADD (with and without reduction) compared to the group with a normal disc position (P=.0001). A significant correlation was found between TMJ pain and the ADD subtype without reduction, as compared to the ADD subtype with reduction (P=.0156). These data suggest that a displaced disc, particularly in the subtype without reduction, is an important source of pain.

  3. Glacial landforms on German Bank, Scotian Shelf: evidence for Late Wisconsinan ice-sheet dynamics and implications for the formation of De Geer moraines

    USGS Publications Warehouse

    Todd, Brian J.; Valentine, Page C.; Longva, Oddvar; Shaw, John

    2007-01-01

    The extent and behaviour of the southeast margin of the Laurentide Ice Sheet in Atlantic Canada is of significance in the study of Late Wisconsinan ice sheet-ocean interactions. Multibeam sonar imagery of subglacial, ice-marginal and glaciomarine landforms on German Bank, Scotian Shelf, provides evidence of the pattern of glacial-dynamic events in the eastern Gulf of Maine. Northwest-southeast trending drumlins and megaflutes dominate northern German Bank. On southern German Bank, megaflutes of thin glacial deposits create a distinct northwest-southeast grain. Lobate regional moraines (>10km long) are concave to the northwest, up-ice direction and strike southwest-northeast, normal to the direction of ice flow. Ubiquitous, overlying De Geer moraines (

  4. Selection dynamics in joint matching to rate and magnitude of reinforcement.

    PubMed

    McDowell, J J; Popa, Andrei; Calvin, Nicholas T

    2012-09-01

    Virtual organisms animated by a selectionist theory of behavior dynamics worked on concurrent random interval schedules where both the rate and magnitude of reinforcement were varied. The selectionist theory consists of a set of simple rules of selection, recombination, and mutation that act on a population of potential behaviors by means of a genetic algorithm. An extension of the power function matching equation, which expresses behavior allocation as a joint function of exponentiated reinforcement rate and reinforcer magnitude ratios, was fitted to the virtual organisms' data, and over a range of moderate mutation rates was found to provide an excellent description of their behavior without residual trends. The mean exponents in this range of mutation rates were 0.83 for the reinforcement rate ratio and 0.68 for the reinforcer magnitude ratio, which are values that are comparable to those obtained in experiments with live organisms. These findings add to the evidence supporting the selectionist theory, which asserts that the world of behavior we observe and measure is created by evolutionary dynamics.

  5. Joint modeling of lithosphere and mantle dynamics: Evaluation of constraints from global tomography models

    NASA Astrophysics Data System (ADS)

    Wang, Xinguo; Holt, William E.; Ghosh, Attreyee

    2015-12-01

    With the advances in technology, seismological theory, and data acquisition, a number of high-resolution seismic tomography models have been published. However, discrepancies between tomography models often arise from different theoretical treatments of seismic wave propagation, different inversion strategies, and different data sets. Using a fixed velocity-to-density scaling and a fixed radial viscosity profile, we compute global mantle flow models associated with the different tomography models and test the impact of these for explaining surface geophysical observations (geoid, dynamic topography, stress, and strain rates). We use the joint modeling of lithosphere and mantle dynamics approach of Ghosh and Holt (2012) to compute the full lithosphere stresses, except that we use HC for the mantle circulation model, which accounts for the primary flow-coupling features associated with density-driven mantle flow. Our results show that the seismic tomography models of S40RTS and SAW642AN provide a better match with surface observables on a global scale than other models tested. Both of these tomography models have important similarities, including upwellings located in Pacific, Eastern Africa, Iceland, and mid-ocean ridges in the Atlantic and Indian Ocean and downwelling flows mainly located beneath the Andes, the Middle East, and central and Southeast Asia.

  6. Aeroelastic deployable wing simulation considering rotation hinge joint based on flexible multibody dynamics

    NASA Astrophysics Data System (ADS)

    Otsuka, Keisuke; Makihara, Kanjuro

    2016-05-01

    Morphing wings have been developed by several organizations for a variety of applications including the changing of flight ability while in the air and reducing the amount of space required to store an aircraft. One such example of morphing wings is the deployable wing that is expected to be used for Mars exploration. When designing wings, aeroelastic simulation is important to prevent the occurrence of destructive phenomena while the wing is in use. Flutter and divergence are typical issues to be addressed. However, it has been difficult to simulate the aeroelastic motion of deployable wings because of the significant differences between these deployable wings and conventional designs. The most apparent difference is the kinematic constraints of deployment, typically a hinge joint. These constraints lead not only to deformation but also to rigid body rotation. This research provides a novel method of overcoming the difficulties associated with handling these kinematic constraints. The proposed method utilizes flexible multibody dynamics and absolute nodal coordinate formulation to describe the dynamic motion of a deployable wing. This paper presents the simulation of the rigid body rotation around the kinematic constraints as induced by the aeroelasticity. The practicality of the proposed method is confirmed.

  7. SELECTION DYNAMICS IN JOINT MATCHING TO RATE AND MAGNITUDE OF REINFORCEMENT

    PubMed Central

    McDowell, J. J; Popa, Andrei; Calvin, Nicholas T

    2012-01-01

    Virtual organisms animated by a selectionist theory of behavior dynamics worked on concurrent random interval schedules where both the rate and magnitude of reinforcement were varied. The selectionist theory consists of a set of simple rules of selection, recombination, and mutation that act on a population of potential behaviors by means of a genetic algorithm. An extension of the power function matching equation, which expresses behavior allocation as a joint function of exponentiated reinforcement rate and reinforcer magnitude ratios, was fitted to the virtual organisms' data, and over a range of moderate mutation rates was found to provide an excellent description of their behavior without residual trends. The mean exponents in this range of mutation rates were 0.83 for the reinforcement rate ratio and 0.68 for the reinforcer magnitude ratio, which are values that are comparable to those obtained in experiments with live organisms. These findings add to the evidence supporting the selectionist theory, which asserts that the world of behavior we observe and measure is created by evolutionary dynamics. PMID:23008523

  8. Observed and Simulated Relationships Between Tropical Deep Convective Updraft Dynamics and Ice Microphysics

    NASA Astrophysics Data System (ADS)

    Varble, A.; Stanford, M.; Zipser, E. J.; Strapp, J. W.; Delanoë, J.; Korolev, A.; Leroy, D.; Potts, R.; Protat, A.; Schwarzenboeck, A.

    2015-12-01

    Relationships between tropical deep convective updraft cores and regions of high ice water content encountered by the Falcon-20 aircraft during the High Altitude Ice Crystals/High Ice Water Content (HAIC/HIWC) campaign in Darwin, Australia are analyzed and compared with high-resolution WRF simulation output. Most flight legs were performed at temperatures near -30°C and -40°C, where relationships between ice water content and vertical velocity are somewhat similar in observations and simulations, although observed ice water contents tend to be a bit higher for a given vertical velocity. This difference can be traced to substantial differences in ice and liquid properties in convective updraft cores at -10°C, where simulated updrafts tend to have far more graupel and liquid water than observed updrafts for a given vertical velocity, although total condensate contents are similar. This partly leads to the commonly observed reflectivity high bias in simulations, which overshadows observed and simulated large snow water contents that commonly exceed 2 g m-3 without reflectivities exceeding 25 dBZ. It appears that magnitudes of microphysical processes operating in mixed phase conditions between 0 and -10°C are quite different in observed and simulated updrafts of similar size and strength, and this difference may be common to most microphysics schemes. Mixed phase properties in convective updrafts end up impacting ice sedimentation and detrainment from convective cores, which go on to impact precipitation efficiency, distribution of rain rates, and likely the life cycle of the convective system. Possible reasons for differences in observed and simulated updrafts are explored.

  9. Numerical Modeling of Earthquake-Induced Landslide Using an Improved Discontinuous Deformation Analysis Considering Dynamic Friction Degradation of Joints

    NASA Astrophysics Data System (ADS)

    Huang, Da; Song, Yixiang; Cen, Duofeng; Fu, Guoyang

    2016-12-01

    Discontinuous deformation analysis (DDA) as an efficient technique has been extensively applied in the dynamic simulation of discontinuous rock mass. In the original DDA (ODDA), the Mohr-Coulomb failure criterion is employed as the judgment principle of failure between contact blocks, and the friction coefficient is assumed to be constant in the whole calculation process. However, it has been confirmed by a host of shear tests that the dynamic friction of rock joints degrades. Therefore, the friction coefficient should be gradually reduced during the numerical simulation of an earthquake-induced rockslide. In this paper, based on the experimental results of cyclic shear tests on limestone joints, exponential regression formulas are fitted for dynamic friction degradation, which is a function of the relative velocity, the amplitude of cyclic shear displacement and the number of its cycles between blocks with an edge-to-edge contact. Then, an improved DDA (IDDA) is developed by implementing the fitting regression formulas and a modified removing technique of joint cohesion, in which the cohesion is removed once the `sliding' or `open' state between blocks appears for the first time, into the ODDA. The IDDA is first validated by comparing with the theoretical solutions of the kinematic behaviors of a sliding block on an inclined plane under dynamic loading. Then, the program is applied to model the Donghekou landslide triggered by the 2008 Wenchuan earthquake in China. The simulation results demonstrate that the dynamic friction degradation of joints has great influences on the runout and velocity of sliding mass. Moreover, the friction coefficient possesses higher impact than the cohesion of joints on the kinematic behaviors of the sliding mass.

  10. Two linear regression models predicting cumulative dynamic L5/S1 joint moment during a range of lifting tasks based on static postures.

    PubMed

    Xu, Xu; Chang, Chien-Chi; Lu, Ming-Lun

    2012-01-01

    Previous studies have indicated that cumulative L5/S1 joint load is a potential risk factor for low back pain. The assessment of cumulative L5/S1 joint load during a field study is challenging due to the difficulty of continuously monitoring the dynamic joint load. This study proposes two regression models predicting cumulative dynamic L5/S1 joint moment based on the static L5/S1 joint moment of a lifting task at lift-off and set-down and the lift duration. Twelve men performed lifting tasks at varying lifting ranges and asymmetric angles in a laboratory environment. The cumulative L5/S1 joint moment was calculated from continuous dynamic L5/S1 moments as the reference for comparison. The static L5/S1 joint moments at lift-off and set-down were measured for the two regression models. The prediction error of the cumulative L5/S1 joint moment was 21 ± 14 Nm × s (12% of the measured cumulative L5/S1 joint moment) and 14 ± 9 Nm × s (8%) for the first and the second models, respectively. Practitioner Summary: The proposed regression models may provide a practical approach for predicting the cumulative dynamic L5/S1 joint loading of a lifting task for field studies since it requires only the lifting duration and the static moments at the lift-off and/or set-down instants of the lift.

  11. Effectively Communicating Information about Dynamically Changing Arctic Sea Ice to the Public through the Global Fiducials Program

    NASA Astrophysics Data System (ADS)

    Molnia, B. F.; Friesen, B.; Wilson, E.; Noble, S.

    2015-12-01

    On July 15, 2009, the National Academy of Sciences (NAS) released a report, Scientific Value of Arctic Sea Ice Imagery Derived Products, advocating public release of Arctic images derived from classified data. In the NAS press release that announced the release, report lead Stephanie Pfirman states "To prepare for a possibly ice-free Arctic and its subsequent effects on the environment, economy, and national security, it is critical to have accurate projections of changes over the next several decades." In the same release NAS President Ralph Cicerone states "We hope that these images are the first of many that could help scientists learn how the changing climate could impact the environment and our society." The same day, Secretary of the Interior Ken Salazar announced that the requested images had been released and were available to the public on a US Geological Survey Global Fiducials Program (GFP) Library website (http://gfl.usgs.gov). The website was developed by the USGS to provide public access to the images and to support environmental analysis of global climate-related science. In the statement describing the release titled, Information Derived from Classified Materials Will Aid Understanding of Changing Climate, Secretary Salazar states "We need the best data from all places if we are to meet the challenges that rising carbon emissions are creating. This information will be invaluable to scientists, researchers, and the public as we tackle climate change." Initially about 700 Arctic sea ice images were released. Six years later, the number exceeds 1,500. The GFP continues to facilitate the acquisition of new Arctic sea ice imagery from US National Imagery Systems. This example demonstrates how information about dynamically changing Arctic sea ice continues to be effectively communicated to the public by the GFP. In addition to Arctic sea ice imagery, the GFP has publicly released imagery time series of more than 125 other environmentally important

  12. Antarctic Ice Sheet dynamics in the Ross Sea during the Early to Middle Miocene

    NASA Astrophysics Data System (ADS)

    Levy, Richard; Harwood, David; Florindo, Fabio; DeConto, Robert; Golledge, Nicholas; Hoffmann, Stefan; Kuhn, Gerhard; McKay, Robert; Naish, Timothy; Pollard, David; Sangiorgi, Francesca; von Eynatten, Hilmar

    2015-04-01

    A 1138-meter sediment core (AND-2A) recovered from the Southern McMurdo Sound sector of the Ross Sea comprises a near-continuous record of Antarctic climate and ice sheet variability through the Early to early Middle Miocene (20.2 to 14.5 million years ago), including an interval of inferred sustained global warmth known as the Miocene Climatic Optimum (MCO). The record preserves 55 sedimentary sequences that reflect cycles of glacial advance and retreat. A new analysis of proxy environmental data from the AND-2A core, and synthesis with regional geological information, show that the early to middle Miocene Antarctic climate ranged from cold polar conditions, similar to Antarctica during the Holocene, to those that characterise modern sub-polar environments. Four disconformities that punctuate the sedimentary sequence coincide with regionally mapped seismic discontinuities and reflect transient expansion of marine-based ice across the Ross Sea. The timing of these major marine-based ice sheet advances correlates with shifts in highly-resolved deep sea isotope records and major drops in eustatic sea-level indicating the global nature of these events. In contrast, three distinct intervals in the core indicate that this high latitude site was periodically influenced by an ice sheet margin that had retreated beyond the coastline. These relatively large-scale changes in climate and ice sheet extent occurred under atmospheric carbon dioxide concentrations that generally varied between 300 to 500 ppm. Therefore, our reconstructions suggest that Antarctica's climate and ice sheets were sensitive to modest changes in greenhouse gas forcing and support previous studies, which indicate that marine-based portions of the WAIS and EAIS can retreat under climatic conditions that were similar to those projected for our future under current levels of atmospheric CO2.

  13. Community dynamics of bottom-ice algae in Dease Strait of the Canadian Arctic

    NASA Astrophysics Data System (ADS)

    Campbell, K.; Mundy, C. J.; Landy, J. C.; Delaforge, A.; Michel, C.; Rysgaard, S.

    2016-12-01

    Sea ice algae are a characteristic feature in ice-covered seas, contributing a significant fraction of the total primary production in many areas and providing a concentrated food source of high nutritional value to grazers in the spring. Algae respond to physical changes in the sea ice environment by modifying their cellular carbon, nitrogen and pigment content, and by adjusting their photophysiological characteristics. In this study we examined how the ratios of particulate organic carbon (POC) to nitrogen (PON), and POC to chlorophyll a (chl a), responded to the evolving snow-covered sea ice environment near Cambridge Bay, Nunavut, during spring 2014. We also estimated photosynthesis-irradiance (PI) curves using oxygen-optodes and evaluated the resulting time-series of PI parameters under thin and thick snow-covered sites. There were no significant differences in PI parameters between samples from different overlying snow depths, and only the maximum photosynthetic rates in the absence of photoinhibition (PsB) and photoacclimation (IS) parameters changed significantly over the spring bloom. Furthermore, we found that both these parameters increased over time in response to increasing percent transmission of photosynthetically active radiation (TPAR) through the ice, indicating that light was a limiting factor of photosynthesis and was an important driver of temporal (over the spring) rather than spatial (between snow depths) variability in photophysiological response. However, we note that spatial variability in primary production was evident. Higher TPAR over the spring and under thin snow affected the composition of algae over both time and space, causing greater POC:chl a estimates in late spring and under thin snow cover. Nitrogen limitation was pronounced in this study, likely reducing PsB and algal photosynthetic rates, and increasing POC:PON ratios to over six times the Redfield average. Our results highlight the influence of both light and nutrients on

  14. Strong isotope effects on melting dynamics and ice crystallisation processes in cryo vitrification solutions.

    PubMed

    Kirichek, Oleg; Soper, Alan; Dzyuba, Boris; Callear, Sam; Fuller, Barry

    2015-01-01

    The nucleation and growth of crystalline ice during cooling, and further crystallization processes during re-warming are considered to be key processes determining the success of low temperature storage of biological objects, as used in medical, agricultural and nature conservation applications. To avoid these problems a method, termed vitrification, is being developed to inhibit ice formation by use of high concentration of cryoprotectants and ultra-rapid cooling, but this is only successful across a limited number of biological objects and in small volume applications. This study explores physical processes of ice crystal formation in a model cryoprotective solution used previously in trials on vitrification of complex biological systems, to improve our understanding of the process and identify limiting biophysical factors. Here we present results of neutron scattering experiments which show that even if ice crystal formation has been suppressed during quench cooling, the water molecules, mobilised during warming, can crystallise as detectable ice. The crystallisation happens right after melting of the glass phase formed during quench cooling, whilst the sample is still transiting deep cryogenic temperatures. We also observe strong water isotope effects on ice crystallisation processes in the cryoprotectant mixture. In the neutron scattering experiment with a fully protiated water component, we observe ready crystallisation occurring just after the glass melting transition. On the contrary with a fully deuteriated water component, the process of crystallisation is either completely or substantially supressed. This behaviour might be explained by nuclear quantum effects in water. The strong isotope effect, observed here, may play an important role in development of new cryopreservation strategies.

  15. A painless and constraint-free method to estimate viscoelastic passive dynamics of limbs' joints to support diagnosis of neuromuscular diseases.

    PubMed

    Venture, Gentiane; Nakamura, Yoshihiko; Yamane, Katsu; Hirashima, Masaya

    2007-01-01

    Though seldom identified, the human joints dynamics is important in the fields of medical robotics and medical research. We present a general solution to estimate in-vivo and simultaneously the passive dynamics of the human limbs' joints. It is based on the use of the multi-body description of the human body and its kinematics and dynamics computations. The linear passive joint dynamics of the shoulders and the elbows: stiffness, viscosity and friction, is estimated simultaneously using the linear least squares method. Acquisition of movements is achieved with an optical motion capture studio on one examinee during the clinical diagnosis of neuromuscular diseases. Experimental results are given and discussed.

  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. Interactions Between Large Bedrock Features and Ice Sheet Dynamics Interpreted From Deep-Penetrating Radar Along the US-ITASE Traverse Routes

    NASA Astrophysics Data System (ADS)

    Welch, B. C.; Jacobel, R. W.; Christianson, K.; Cofell-Dwyer, K.

    2003-12-01

    Ice-penetrating radar studies depicting the structure of internal stratigraphy in ice sheets can be used to infer information about past ice dynamics and changes in ice flow over time. To date, most radar studies in the interior of major ice sheets have shown internal layers draped smoothly over bed topography with decreasing relief toward the surface. This result is one consequence of ice frozen to the bed and accumulation patterns that do not vary substantially in space or time. In contrast, areas that show significant deformation of internal layers are typically found in ice streams, where sliding can cause large strains. Deep-penetrating radar profiles from the 2001 and 2002 US-ITASE traverses show several areas in the interior of West Antarctica and the transition region between the East and West Antarctic Ice Sheets where internal stratigraphy is disrupted and discontinuous in the vicinity of large topographic bed features with relief >50% of regional ice thickness. Ice in these areas is presumably frozen to the bed. In some locations these disruptions in internal layers appear to result from surface wind scouring and redeposition. The influence of bed features on surface topography evidently causes local changes in snow accumulation and the interactions between wind and snow surface may facilitate the development of wind ablation regions. In another area near Byrd Surface Camp a significant bed feature, "Mt. Resnik," appears to be causing breaks in internal stratigraphy imaged in a grid of 4 radar profiles oriented across the flow direction and several kilometers downstream. We hypothesize that there is a ratio of mountain height to regional ice thickness where the ice above the mountain will effectively decouple from the surrounding ice flow and crevasses will develop. Such a scenario would cause a seam to form and disruption of internal layers that is similar to what we have observed. The fact that deeper layers in the same region are continuous implies

  18. Quantum Corrections to Classical Molecular Dynamics Simulations of Water and Ice.

    PubMed

    Waheed, Qaiser; Edholm, Olle

    2011-09-13

    Classical simulations of simple water models reproduce many properties of the liquid and ice but overestimate the heat capacity by about 65% at ordinary temperatures and much more for low temperature ice. This is due to the fact that the atomic vibrations are quantum mechanical. The application of harmonic quantum corrections to the molecular motion results in good heat capacities for the liquid and for ice at low temperatures but a successively growing positive deviation from experimental results for ice above 200 K that reaches 15% just below melting. We suggest that this deviation is due to the lack of quantum corrections to the anharmonic motions. For the liquid, the anharmonicities are even larger but also softer and thus in less need of quantum correction. Therefore, harmonic quantum corrections to the classically calculated liquid heat capacities result in agreement with the experimental values. The classical model underestimates the heat of melting by 15%, while the application of quantum corrections produces fair agreement. On the other hand, the heat of vaporization is overestimated by 10% in the harmonically corrected classical model.

  19. High-resolution sea ice dynamics modeling using the discrete element method

    NASA Astrophysics Data System (ADS)

    Song, A.; Morriss, B. F.; Deeb, E. J.; Richter-Menge, J.; Perovich, D. K.; Hopkins, M. A.

    2014-12-01

    One reason why coupled climate model simulations generally do not reproduce the observed increase in Antarctic sea ice extent may be that their internally generated climate variability does not sync with the observed phases of phenomena like the Pacific Decadal Oscillation (PDO) and ENSO. For example, it is unlikely for a free-running coupled model simulation to capture the shift of the PDO from its positive to negative phase during 1998, and the subsequent ~15 year duration of the negative PDO phase. In previously presented work based on atmospheric models forced by observed tropical SSTs and stratospheric ozone, we demonstrated that tropical variability is key to explaining the wind trends over the Southern Ocean during the past ~35 years, particularly in the Ross, Amundsen and Bellingshausen Seas, the regions of the largest trends in sea ice extent and ice season duration. Here, we extend this idea to coupled model simulations with the Community Earth System Model (CESM) in which the evolution of SST anomalies in the central and eastern tropical Pacific is constrained to match the observations. This ensemble of 10 "tropical pacemaker" simulations shows a more realistic evolution of Antarctic sea ice anomalies than does its unconstrained counterpart, the CESM Large Ensemble (both sets of runs include stratospheric ozone depletion and other time-dependent radiative forcings). In particular, the pacemaker runs show that increased sea ice in the eastern Ross Sea is associated with a deeper Amundsen Sea Low (ASL) and stronger westerlies over the south Pacific. These circulation patterns in turn are linked with the negative phase of the PDO, characterized by negative SST anomalies in the central and eastern Pacific. The timing of tropical decadal variability with respect to ozone depletion further suggests a strong role for tropical variability in the recent acceleration of the Antarctic sea ice trend, as ozone depletion stabilized by late 1990s, prior to the most

  20. A late glacial record of ice-sheet dynamics and melt supply recovered in the sediments of IODP Expedition 347 in the Baltic Sea

    NASA Astrophysics Data System (ADS)

    Passchier, Sandra; Jensen, Jørn Bo; Kenzler, Michael; Johnson, Sean; Andrén, Thomas; Barker Jørgensen, Bo

    2015-04-01

    Modern observations of increased surface ablation, meltwater routing to the bed, and increases in glacial speeds point to feedbacks between ice-sheet dynamics, melt supply, and subglacial discharge. Paleorecords have the potential to explore the decadal to centennial variability of these systems, but until recently such records were short and discontinuous in ice-proximal settings and underutilized for this specific purpose. The Integrated Ocean Drilling Program Expedition 347 in the Baltic Sea recovered annually laminated sediments that document the dynamics of the Scandinavian Ice Sheet. Hydraulic piston cores recovered from Sites M0060, M0063, M0064, and M0065 allow us to reconstruct a nearly complete record of ca. 6000 years in ice retreat history at annual to decadal resolution between ca. 17 and 11ka. The late glacial successions of these four IODP drillsites comprise of a till or proglacial fluvioglacial sediment overlain by variable thicknesses of well-laminated deglacial successions within several high-recovery holes. As the Scandinavian Ice Sheet retreated from the western Baltic Sea, and to the North, the ice-sheet's grounding line migrated across the four sites and deposited overlapping sections of high-resolution ice-proximal to ice-distal successions. Laser particle size results from Sites M0060 and M0063, and inspection of line-scan images, show shifts in sedimentary facies and lithologies that were not recognized during initial visual core description. For example, at Site M0060 in the Kattegat, ice-rafting fluxes in silty clays decrease upward and are negligible in the overlying varved succession. These characteristics are interpreted as ice retreat within a calving bay environment from ca. 17ka onward, followed by distal glacial marine deposition from sediment plumes governed by meltwater discharge. Moreover, at Site M0063 in the Baltic Sea, laser particle size distributions record an abrupt shift from interlaminated clayey silt to laminated clay

  1. Improved dynamic model of the human knee joint and its response to impact loading on the lower leg.

    PubMed

    Engin, A E; Tümer, S T

    1993-05-01

    Almost a decade ago, three-dimensional formulation for the dynamic modeling of an articulating human joint was introduced. Two-dimensional version of this formulation was subsequently applied to the knee joint. However, because of the iterative nature of the solution technique, this model cannot handle impact conditions. In this paper, alternative solution methods are introduced which enable investigation of the response of the human knee to impact loading on the lower leg via an anatomically based model. In addition, the classical impact theory is applied to the same model and a closed-form solution is obtained. The shortcomings of the classical impact theory as applied to the impact problem of the knee joint are delineated.

  2. Identification of the dynamic characteristics of a viscoelastic, nonlinear adhesive joint

    NASA Astrophysics Data System (ADS)

    Naraghi, T.; Nobari, A. S.

    2015-09-01

    In this paper, the nonlinear mechanical characteristics of an adhesive (Sikaflex-252) are identified over frequency range, using eigenvalues of nonlinear system and inverse eigen-sensitivity method and experimental data. Sikaflex-252 is selected as an adhesive which is mainly used as a joining medium (joint) in structural applications. In order to simulate the viscoelastic behaviour of the adhesive, the frequency dependent Young's modulus and damping coefficient are assumed in identification process leading to the updating process being repeated for different ranges of frequencies to identify stiffness and damping properties of the adhesive. Using the optimum equivalent linear frequency response function (OELF) concept, in order to realize the nonlinear nature of the adhesive, modal tests are performed under two different random excitation levels which illustrate the stiffness softening characteristic of adhesive which can have serious implications regarding dynamic stability of structures. Furthermore, based on the identified characteristics, the paper examines the possibility of tuning of the Standard Linear Solid model (SLS), in representing the adhesive viscoelastic behaviour. Results of this attempt proved that the S.L.S. model with tuned parameters significantly improves the fidelity of finite element (FE) model to experimental results.

  3. Trehalose solution viscosity at low temperatures measured by dynamic light scattering method: Trehalose depresses molecular transportation for ice crystal growth

    NASA Astrophysics Data System (ADS)

    Uchida, Tsutomu; Nagayama, Masafumi; Gohara, Kazutoshi

    2009-12-01

    The inhibitory effects of trehalose on ice crystal growth were discussed on the basis of the viscosity measurements of aqueous solutions via the dynamic light-scattering method. The temperature and concentration conditions of the solution were ranged between 268 and 343 K and up to 50 wt%, respectively, which were feasible for applying this novel technique and were useful in the indirect measurement of the macroscopic dynamic properties of the trehalose solutions. A comparison of the viscosity data with those reported in the literatures indicated the validity of this method for measuring the viscosity. The nonlinearity of the temperature and concentration dependences of the trehalose solutions suggested that two different hydrogen-bonding networks exist in the solutions within the investigated range. Dilute solutions of less than 10 wt% of trehalose exhibited properties very similar to those of pure water. Higher concentration solutions had large viscosities with large temperature and concentration dependences. This was caused by the decrease in the free water in the solution and the development of hydrogen-bonding networks with hydrated trehalose clusters. Sucrose and maltose solutions had the same properties, so this would be the dominant inhibitory process of disaccharides on ice crystal growth.

  4. Mobile Biplane X-Ray Imaging System for Measuring 3D Dynamic Joint Motion During Overground Gait.

    PubMed

    Guan, Shanyuanye; Gray, Hans A; Keynejad, Farzad; Pandy, Marcus G

    2016-01-01

    Most X-ray fluoroscopy systems are stationary and impose restrictions on the measurement of dynamic joint motion; for example, knee-joint kinematics during gait is usually measured with the subject ambulating on a treadmill. We developed a computer-controlled, mobile, biplane, X-ray fluoroscopy system to track human body movement for high-speed imaging of 3D joint motion during overground gait. A robotic gantry mechanism translates the two X-ray units alongside the subject, tracking and imaging the joint of interest as the subject moves. The main aim of the present study was to determine the accuracy with which the mobile imaging system measures 3D knee-joint kinematics during walking. In vitro experiments were performed to measure the relative positions of the tibia and femur in an intact human cadaver knee and of the tibial and femoral components of a total knee arthroplasty (TKA) implant during simulated overground gait. Accuracy was determined by calculating mean, standard deviation and root-mean-squared errors from differences between kinematic measurements obtained using volumetric models of the bones and TKA components and reference measurements obtained from metal beads embedded in the bones. Measurement accuracy was enhanced by the ability to track and image the joint concurrently. Maximum root-mean-squared errors were 0.33 mm and 0.65° for translations and rotations of the TKA knee and 0.78 mm and 0.77° for translations and rotations of the intact knee, which are comparable to results reported for treadmill walking using stationary biplane systems. System capability for in vivo joint motion measurement was also demonstrated for overground gait.

  5. Effect of progressive resistance exercise with neuromuscular joint facilitation on the dynamic balance performance of junior soccer players

    PubMed Central

    Wang, Hongzhao; Huo, Ming; Guan, Peipei; Onoda, Ko; Chen, Di; Huang, Qiuchen; Maruyama, Hitoshi

    2015-01-01

    [Purpose] The aim of this study was to investigate the change in dynamic balance performance of junior soccer players after progressive resistance treatment with neuromuscular joint facilitation (NJF). [Subjects] The subjects were 14 healthy males who were divided into two groups, namely the NJF and control groups. The NJF group consisted of 8 subjects, and the control group consisted of 6 subjects. [Methods] The participants in the NJF group received NJF progressive resistance treatment. Dynamic balance performance was measured before and after 3 weeks of exercise. [Results] Significant improvement in dynamic balance performance was observed both in the NJF and control groups. In the NJF group, dynamic balance performance was significantly increased compared with that in the control group. [Conclusion] The NJF intervention shortened movement time, which implies that NJF is effective for dynamic balance performance. PMID:26696714

  6. The Impact of Sea Ice Loss on Wave Dynamics and Coastal Erosion Along the Arctic Coast

    NASA Astrophysics Data System (ADS)

    Overeem, I.; Anderson, R. S.; Wobus, C. W.; Matell, N.; Urban, F. E.; Clow, G. D.; Stanton, T. P.

    2010-12-01

    The extent of Arctic sea ice has been shrinking rapidly over the past few decades, and attendant acceleration of erosion is now occurring along the Arctic coast. This both brings coastal infrastructure into harm’s way and promotes a complex response of the adjacent landscape to global change. We quantify the effects of declining sea ice extent on coastal erosion rates along a 75-km stretch of coastal permafrost bluffs adjacent to the Beaufort Sea, Alaska, where present-day erosion rates are among the highest in the world at ~14 m yr-1. Our own observations reinforce those of others, and suggest that the rate-limiting process is thermal erosion at the base of the several-meter tall bluffs. Here we focus on the interaction between the nearshore sea ice concentration, the location of the sea ice margin, and the fetch-limited, shallow water wave field, since these parameters ultimately control both sea surface temperatures and the height to which these waters can bathe the frozen bluffs. Thirty years of daily or bi-daily passive microwave data from Nimbus-7 SMMR and DMSP SSM/I satellites reveal that the nearshore open water season lengthened ~54 days over 1979-2009. The open water season, centered in August, expands more rapidly into the fall (September and October~0.92 day yr-1) than into the early summer (July~0.71 days yr-1). Average fetch, defined for our purposes as the distance from the sea ice margin to the coast over which the wind is blowing, increased by a factor 1.7 over the same time-span. Given these time series, we modeled daily nearshore wave heights during the open water season for each year, which we integrated to provide a quantitative metric for the annual exposure of the coastal bluffs to thermal erosion. This “annual wave exposure” increased by 250% during 1979-2009. In the same interval, coastal erosion rates reconstructed from satellite and aerial photo records show less acceleration. We attribute this to a disproportionate extension of the

  7. The Effects of Multiple-Joint Isokinetic Resistance Training on Maximal Isokinetic and Dynamic Muscle Strength and Local Muscular Endurance

    PubMed Central

    Ratamess, Nicholas A.; Beller, Noah A.; Gonzalez, Adam M.; Spatz, Gregory E.; Hoffman, Jay R.; Ross, Ryan E.; Faigenbaum, Avery D.; Kang, Jie

    2016-01-01

    The transfer of training effects of multiple-joint isokinetic resistance training to dynamic exercise performance remain poorly understood. Thus, the purpose of the present study was to investigate the magnitude of isokinetic and dynamic one repetition-maximum (1RM) strength and local muscular endurance increases after 6 weeks of multiple-joint isokinetic resistance training. Seventeen women were randomly assigned to either an isokinetic resistance training group (IRT) or a non-exercising control group (CTL). The IRT group underwent 6 weeks of training (2 days per week) consisting of 5 sets of 6-10 repetitions at 75-85% of subjects’ peak strength for the isokinetic chest press and seated row exercises at an average linear velocity of 0.15 m s-1 [3-sec concentric (CON) and 3-sec eccentric (ECC) phases]. Peak CON and ECC force during the chest press and row, 1RM bench press and bent-over row, and maximum number of modified push-ups were assessed pre and post training. A 2 x 2 analysis of variance with repeated measures and Tukey’s post hoc tests were used for data analysis. The results showed that 1RM bench press (from 38.6 ± 6.7 to 43.0 ± 5.9 kg), 1RM bent-over row (from 40.4 ± 7.7 to 45.5 ± 7.5 kg), and the maximal number of modified push-ups (from 39.5 ± 13.6 to 55.3 ± 13.1 repetitions) increased significantly only in the IRT group. Peak isokinetic CON and ECC force in the chest press and row significantly increased in the IRT group. No differences were shown in the CTL group for any measure. These data indicate 6 weeks of multiple-joint isokinetic resistance training increases dynamic muscle strength and local muscular endurance performance in addition to specific isokinetic strength gains in women. Key points Multiple-joint isokinetic resistance training increases dynamic maximal muscular strength, local muscular endurance, and maximal isokinetic strength in women. Multiple-joint isokinetic resistance training increased 1RM strength in the bench press

  8. The Effects of Multiple-Joint Isokinetic Resistance Training on Maximal Isokinetic and Dynamic Muscle Strength and Local Muscular Endurance.

    PubMed

    Ratamess, Nicholas A; Beller, Noah A; Gonzalez, Adam M; Spatz, Gregory E; Hoffman, Jay R; Ross, Ryan E; Faigenbaum, Avery D; Kang, Jie

    2016-03-01

    The transfer of training effects of multiple-joint isokinetic resistance training to dynamic exercise performance remain poorly understood. Thus, the purpose of the present study was to investigate the magnitude of isokinetic and dynamic one repetition-maximum (1RM) strength and local muscular endurance increases after 6 weeks of multiple-joint isokinetic resistance training. Seventeen women were randomly assigned to either an isokinetic resistance training group (IRT) or a non-exercising control group (CTL). The IRT group underwent 6 weeks of training (2 days per week) consisting of 5 sets of 6-10 repetitions at 75-85% of subjects' peak strength for the isokinetic chest press and seated row exercises at an average linear velocity of 0.15 m s(-1) [3-sec concentric (CON) and 3-sec eccentric (ECC) phases]. Peak CON and ECC force during the chest press and row, 1RM bench press and bent-over row, and maximum number of modified push-ups were assessed pre and post training. A 2 x 2 analysis of variance with repeated measures and Tukey's post hoc tests were used for data analysis. The results showed that 1RM bench press (from 38.6 ± 6.7 to 43.0 ± 5.9 kg), 1RM bent-over row (from 40.4 ± 7.7 to 45.5 ± 7.5 kg), and the maximal number of modified push-ups (from 39.5 ± 13.6 to 55.3 ± 13.1 repetitions) increased significantly only in the IRT group. Peak isokinetic CON and ECC force in the chest press and row significantly increased in the IRT group. No differences were shown in the CTL group for any measure. These data indicate 6 weeks of multiple-joint isokinetic resistance training increases dynamic muscle strength and local muscular endurance performance in addition to specific isokinetic strength gains in women. Key pointsMultiple-joint isokinetic resistance training increases dynamic maximal muscular strength, local muscular endurance, and maximal isokinetic strength in women.Multiple-joint isokinetic resistance training increased 1RM strength in the bench press (by

  9. Study of surface bonding imperfection effects on equivalent identified dynamic Young's and shear moduli using a modal based joint identification method

    NASA Astrophysics Data System (ADS)

    Meshki, M. M.; Nobari, A. S.; Nikbin, K.

    2015-02-01

    In this paper the effects of defects on the equivalent identified dynamic Young's and shear moduli of flexible structural adhesive joints have been investigated. Adhesive joints were subjected to initial surface bonding imperfection, in order to simulate the defects. Several debond patterns have been applied artificially on single-lap joint specimens and joint identification process has been performed for both bending and shear modes to see how surface bonding imperfection can affect equivalent identified dynamic Young's and shear moduli of the adhesive. Using a direct modal based method to identify mechanical characteristics of joints has been shown that degradation of the equivalent moduli of debonded joint is correlated to both frequency and mode shapes. The results reveal that debonding is easily detectable in bending modes whereas degradation in shear modes is also correlated to debonding orientation and mode shapes. Three identical specimens have been tested for each case to prove the consistency of the results.

  10. Low energy spin dynamics in the spin ice, Ho2Sn2O7

    SciTech Connect

    Ehlers, Georg; Huq, Ashfia; Diallo, Souleymane Omar; Adriano, Cris; Rule, K; Cornelius, A. L.; Fouquet, Peter; Pagliuso, P G; Gardner, Jason

    2012-01-01

    The magnetic properties of Ho{sub 2}Sn{sub 2}O{sub 7} have been investigated and compared to other spin ice compounds. Although the lattice has expanded by 3% relative to the better studied Ho{sub 2}Ti{sub 2}O{sub 7} spin ice, no significant changes were observed in the high temperature properties, T {approx}> 20 K. As the temperature is lowered and correlations develop, Ho{sub 2}Sn{sub 2}O{sub 7} enters its quantum phase at a slightly higher temperature than Ho{sub 2}Ti{sub 2}O{sub 7} and is more antiferromagnetic in character. Below 80 K a weak inelastic mode associated with the holmium nuclear spin system has been measured. The hyperfine field at the holmium nucleus was found to be {approx}700 T.

  11. Teleseismic Earthquake Signals Observed on an Ice Shelf

    NASA Astrophysics Data System (ADS)

    Baker, M. G.; Aster, R. C.; Anthony, R. E.; Wiens, D.; Nyblade, A.; Bromirski, P. D.; Stephen, R. A.; Gerstoft, P.

    2015-12-01

    The West Antarctic Rift System (WARS) is one of Earth's largest continental extension zones. Study of the WARS is complicated by the presence of the West Antarctic Ice Sheet, the Ross Ice Shelf, and the Ross Sea. Recent deployments of broadband seismographs in the POLENET project have allowed passive seismic techniques, such as receiver function analysis and surface wave dispersion, to be widely utilized to infer crustal and mantle velocity structure across much of the WARS and West Antarctica. However, a large sector of the WARS lies beneath the Ross Ice Shelf. In late 2014, 34 broadband seismographs were deployed atop the ice shelf to jointly study deep Earth structure and the dynamics of the ice shelf. Ice shelf conditions present strong challenges to broadband teleseismic imaging: 1) The presence of complicating signals in the microseism through long-period bands due to the influence of ocean gravity waves; 2) The strong velocity contrasts at the ice-water and water-sediment interfaces on either side of the water layer give rise to large amplitude reverberations; 3) The water layer screens S-waves or P-to-S phases originating from below the water layer. We present an initial analysis of the first teleseismic earthquake arrivals collected on the ice shelf at the end of the 2014 field season from a limited subset of these stations.

  12. Tectonomagmatic activity and ice dynamics in the Bransfield Strait back-arc basin, Antarctica

    NASA Astrophysics Data System (ADS)

    Dziak, Robert P.; Park, Minkyu; Lee, Won Sang; Matsumoto, Haru; Bohnenstiehl, Delwayne R.; Haxel, Joseph H.

    2010-01-01

    An array of moored hydrophones was used to monitor the spatiotemporal distribution of small- to moderate-sized earthquakes and ice-generated sounds within the Bransfield Strait, Antarctica. During a 2 year period, a total of 3900 earthquakes, 5925 icequakes and numerous ice tremor events were located throughout the region. The seismic activity included eight space-time earthquake clusters, positioned along the central neovolcanic rift zone of the young Bransfield back-arc basin. These sequences of small magnitude earthquakes, or swarms, suggest ongoing magmatic activity that becomes localized along isolated volcanic features and fissure-like ridges in the southwest portion of the basin. A total of 122 earthquakes were located along the South Shetland trench, indicating continued deformation and possibly ongoing subduction along this margin. The large number of icequakes observed show a temporal pattern related to seasonal freeze-thaw cycles and a spatial distribution consistent with channeling of sea ice along submarine canyons from glacier fronts. Several harmonic tremor episodes were sourced from a large (˜30 km2) iceberg that entered northeast portion of the basin. The spectral character of these signals suggests they were produced by either resonance of a small chamber of fluid within the iceberg, or more likely, due to periodicity of discrete stick-slip events caused by contact of the moving iceberg with the seafloor. These pressure waves appear to have been excited by abrasion of the iceberg along the seafloor as it passed Clarence and Elephant Islands.

  13. The build-up, configuration, and dynamical sensitivity of the Eurasian ice-sheet complex to Late Weichselian climatic and oceanic forcing

    NASA Astrophysics Data System (ADS)

    Patton, Henry; Hubbard, Alun; Andreassen, Karin; Winsborrow, Monica; Stroeven, Arjen P.

    2016-12-01

    The Eurasian ice-sheet complex (EISC) was the third largest ice mass during the Last Glacial Maximum (LGM), after the Antarctic and North American ice sheets. Despite its global significance, a comprehensive account of its evolution from independent nucleation centres to its maximum extent is conspicuously lacking. Here, a first-order, thermomechanical model, robustly constrained by empirical evidence, is used to investigate the dynamics of the EISC throughout its build-up to its maximum configuration. The ice flow model is coupled to a reference climate and applied at 10 km spatial resolution across a domain that includes the three main spreading centres of the Celtic, Fennoscandian and Barents Sea ice sheets. The model is forced with the NGRIP palaeo-isotope curve from 37 ka BP onwards and model skill is assessed against collated flowsets, marginal moraines, exposure ages and relative sea-level history. The evolution of the EISC to its LGM configuration was complex and asynchronous; the western, maritime margins of the Fennoscandian and Celtic ice sheets responded rapidly and advanced across their continental shelves by 29 ka BP, yet the maximum aerial extent (5.48 × 106 km2) and volume (7.18 × 106 km3) of the ice complex was attained some 6 ka later at c. 22.7 ka BP. This maximum stand was short-lived as the North Sea and Atlantic margins were already in retreat whilst eastern margins were still advancing up until c. 20 ka BP. High rates of basal erosion are modelled beneath ice streams and outlet glaciers draining the Celtic and Fennoscandian ice sheets with extensive preservation elsewhere due to frozen subglacial conditions, including much of the Barents and Kara seas. Here, and elsewhere across the Norwegian shelf and North Sea, high pressure subglacial conditions would have promoted localised gas hydrate formation.

  14. Ice interaction with offshore structures

    SciTech Connect

    Cammaert, A.B.; Muggeridge, D.B.

    1988-01-01

    Oil platforms and other offshore structures being built in the arctic regions must be able to withstand icebergs, ice islands, and pack ice. This reference explain the effect ice has on offshore structures and demonstrates design and construction methods that allow such structures to survive in harsh, ice-ridden environments. It analyzes the characteristics of sea ice as well as dynamic ice forces on structures. Techniques for ice modeling and field testing facilitate the design and construction of sturdy, offshore constructions. Computer programs included.

  15. Arctic Sea ice model sensitivities.

    SciTech Connect

    Peterson, Kara J.; Bochev, Pavel Blagoveston; Paskaleva, Biliana Stefanova

    2010-12-01

    Arctic sea ice is an important component of the global climate system and, due to feedback effects, the Arctic ice cover is changing rapidly. Predictive mathematical models are of paramount importance for accurate estimates of the future ice trajectory. However, the sea ice components of Global Climate Models (GCMs) vary significantly in their prediction of the future state of Arctic sea ice and have generally underestimated the rate of decline in minimum sea ice extent seen over the past thirty years. One of the contributing factors to this variability is the sensitivity of the sea ice state to internal model parameters. A new sea ice model that holds some promise for improving sea ice predictions incorporates an anisotropic elastic-decohesive rheology and dynamics solved using the material-point method (MPM), which combines Lagrangian particles for advection with a background grid for gradient computations. We evaluate the variability of this MPM sea ice code and compare it with the Los Alamos National Laboratory CICE code for a single year simulation of the Arctic basin using consistent ocean and atmospheric forcing. Sensitivities of ice volume, ice area, ice extent, root mean square (RMS) ice speed, central Arctic ice thickness,and central Arctic ice speed with respect to ten different dynamic and thermodynamic parameters are evaluated both individually and in combination using the Design Analysis Kit for Optimization and Terascale Applications (DAKOTA). We find similar responses for the two codes and some interesting seasonal variability in the strength of the parameters on the solution.

  16. Dynamics anomaly in high-density amorphous ice between 0.7 and 1.1 GPa

    NASA Astrophysics Data System (ADS)

    Handle, Philip H.; Loerting, Thomas

    2016-02-01

    We studied high-density amorphous ices between 0.004 and 1.6 GPa by isobaric in situ volumetry and by subsequent ex situ x-ray diffraction and differential scanning calorimetry at 1 bar. Our observations indicate two processes, namely, relaxation in the amorphous matrix and crystallization, taking place at well-separated time scales. For this reason, we are able to report rate constants of crystallization kX and glass-transition temperatures Tg in an unprecedented pressure range. Tg's agree within ±3 K with earlier work in the small pressure range where there is overlap. Both Tg and kX show a pressure anomaly between 0.7 and 1.1 GPa, namely, a kX minimum and a Tg maximum. This anomalous pressure dependence suggests a continuous phase transition from high- (HDA) to very-high-density amorphous ice (VHDA) and faster hydrogen bond dynamics in VHDA. We speculate this phenomenology can be rationalized by invoking the crossing of a Widom line between 0.7 and 1.1 GPa emanating from a low-lying HDA-VHDA critical point. Furthermore, we interpret the volumetric relaxation of the amorphous matrix to be accompanied by viscosity change to explain the findings such that the liquid state can be accessed prior to the crystallization temperature TX at <0.4 GPa and >0.8 GPa.

  17. GRACE Gravity Data Constrain Ancient Ice Geometries and Continental Dynamics over Laurentia

    NASA Technical Reports Server (NTRS)

    Tamisiea, M. E.; Mitrovica, J. X.; Davis, J. L.

    2007-01-01

    The free-air gravity trend over Canada, derived from the Gravity Recovery and Climate Experiment (GRACE) satellite mission, robustly isolates the gravity signal associated with glacial isostatic adjustment (GIA) from the longer-time scale mantle convection process. This trend proves that the ancient Laurentian ice complex was composed of two large domes to the west and east of Hudson Bay, in accord with one of two classes of earlier reconstructions. Moreover, GIA models that reconcile the peak rates contribute approximately 25 to approximately 45% to the observed static gravity field, which represents an important boundary condition on the buoyancy of the continental tectosphere.

  18. The validation of a human force model to predict dynamic forces resulting from multi-joint motions

    NASA Technical Reports Server (NTRS)

    Pandya, Abhilash K.; Maida, James C.; Aldridge, Ann M.; Hasson, Scott M.; Woolford, Barbara J.

    1992-01-01

    The development and validation is examined of a dynamic strength model for humans. This model is based on empirical data. The shoulder, elbow, and wrist joints were characterized in terms of maximum isolated torque, or position and velocity, in all rotational planes. This data was reduced by a least squares regression technique into a table of single variable second degree polynomial equations determining torque as a function of position and velocity. The isolated joint torque equations were then used to compute forces resulting from a composite motion, in this case, a ratchet wrench push and pull operation. A comparison of the predicted results of the model with the actual measured values for the composite motion indicates that forces derived from a composite motion of joints (ratcheting) can be predicted from isolated joint measures. Calculated T values comparing model versus measured values for 14 subjects were well within the statistically acceptable limits and regression analysis revealed coefficient of variation between actual and measured to be within 0.72 and 0.80.

  19. Ice flow dynamics forced by water pressure variations in subglacial granular beds

    NASA Astrophysics Data System (ADS)

    Damsgaard, Anders; Egholm, David L.; Beem, Lucas H.; Tulaczyk, Slawek; Larsen, Nicolaj K.; Piotrowski, Jan A.; Siegfried, Matthew R.

    2016-12-01

    Glaciers and ice streams can move by deforming underlying water-saturated sediments, and the nonlinear mechanics of these materials are often invoked as the main reason for initiation, persistence, and shutdown of fast-flowing ice streams. Existing models have failed to fully explain the internal mechanical processes driving transitions from stability to slip. We performed computational experiments that show how rearrangements of load-bearing force chains within the granular sediments drive the mechanical transitions. Cyclic variations in pore water pressure give rise to rate-dependent creeping motion at stress levels below the point of failure, while disruption of the force chain network induces fast rate-independent flow above it. This finding contrasts previous descriptions of subglacial sediment mechanics, which either assume rate dependence regardless of mechanical state or unconditional stability before the sediment yield point. Our new micromechanical computational approach is capable of reproducing important transitions between these two end-member models and can explain multimodal velocity patterns observed in glaciers, landslides, and slow-moving tremor zones.

  20. Community dynamics of nematodes after Larsen ice-shelf collapse in the eastern Antarctic Peninsula.

    PubMed

    Hauquier, Freija; Ballesteros-Redondo, Laura; Gutt, Julian; Vanreusel, Ann

    2016-01-01

    Free-living marine nematode communities of the Larsen B embayment at the eastern Antarctic Peninsula were investigated to provide insights on their response and colonization rate after large-scale ice-shelf collapse. This study compares published data on the post-collapse situation from 2007 with new material from 2011, focusing on two locations in the embayment that showed highly divergent communities in 2007 and that are characterized by a difference in timing of ice-shelf breakup. Data from 2007 exposed a more diverse community at outer station B.South, dominated by the genus Microlaimus. On the contrary, station B.West in the inner part of Larsen B was poor in both numbers of individuals and genera, with dominance of a single Halomonhystera species. Re-assessment of the situation in 2011 showed that communities at both stations diverged even more, due to a drastic increase in Halomonhystera at B.West compared to relatively little change at B.South. On a broader geographical scale, it seems that B.South gradually starts resembling other Antarctic shelf communities, although the absence of the genus Sabatieria and the high abundance of Microlaimus still set it apart nine years after the main Larsen B collapse. In contrast, thriving of Halomonhystera at B.West further separates its community from other Antarctic shelf areas.

  1. Climate Change Winners: Receding Ice Fields Facilitate Colony Expansion and Altered Dynamics in an Adélie Penguin Metapopulation

    PubMed Central

    LaRue, Michelle A.; Ainley, David G.; Swanson, Matt; Dugger, Katie M.; Lyver, Phil O′B.; Barton, Kerry; Ballard, Grant

    2013-01-01

    There will be winners and losers as climate change alters the habitats of polar organisms. For an Adélie penguin (Pygoscelis adeliae) colony on Beaufort Island (Beaufort), part of a cluster of colonies in the southern Ross Sea, we report a recent population increase in response to increased nesting habitat as glaciers have receded. Emigration rates of birds banded as chicks on Beaufort to colonies on nearby Ross Island decreased after 2005 as available habitat on Beaufort increased, leading to altered dynamics of the metapopulation. Using aerial photography beginning in 1958 and modern satellite imagery, we measured change in area of available nesting habitat and population size of the Beaufort colony. Population size varied with available habitat, and both increased rapidly since the 1990s. In accord with glacial retreat, summer temperatures at nearby McMurdo Station increased by ∼0.50°C per decade since the mid-1980s. Although the Ross Sea is likely to be the last ocean with an intact ecosystem, the recent retreat of ice fields at Beaufort that resulted in increased breeding habitat exemplifies a process that has been underway in the Ross Sea during the entire Holocene. Furthermore, our results are in line with predictions that major ice shelves and glaciers will retreat rapidly elsewhere in the Antarctic, potentially leading to increased breeding habitat for Adélie penguins. Results further indicated that satellite imagery may be used to estimate large changes in Adélie penguin populations, facilitating our understanding of metapopulation dynamics and environmental factors that influence regional populations. PMID:23573267

  2. Climate change winners: receding ice fields facilitate colony expansion and altered dynamics in an Adélie penguin metapopulation.

    PubMed

    LaRue, Michelle A; Ainley, David G; Swanson, Matt; Dugger, Katie M; Lyver, Phil O'B; Barton, Kerry; Ballard, Grant

    2013-01-01

    There will be winners and losers as climate change alters the habitats of polar organisms. For an Adélie penguin (Pygoscelis adeliae) colony on Beaufort Island (Beaufort), part of a cluster of colonies in the southern Ross Sea, we report a recent population increase in response to increased nesting habitat as glaciers have receded. Emigration rates of birds banded as chicks on Beaufort to colonies on nearby Ross Island decreased after 2005 as available habitat on Beaufort increased, leading to altered dynamics of the metapopulation. Using aerial photography beginning in 1958 and modern satellite imagery, we measured change in area of available nesting habitat and population size of the Beaufort colony. Population size varied with available habitat, and both increased rapidly since the 1990s. In accord with glacial retreat, summer temperatures at nearby McMurdo Station increased by ~0.50 °C per decade since the mid-1980s. Although the Ross Sea is likely to be the last ocean with an intact ecosystem, the recent retreat of ice fields at Beaufort that resulted in increased breeding habitat exemplifies a process that has been underway in the Ross Sea during the entire Holocene. Furthermore, our results are in line with predictions that major ice shelves and glaciers will retreat rapidly elsewhere in the Antarctic, potentially leading to increased breeding habitat for Adélie penguins. Results further indicated that satellite imagery may be used to estimate large changes in Adélie penguin populations, facilitating our understanding of metapopulation dynamics and environmental factors that influence regional populations.

  3. Climate change winners: receding ice fields facilitate colony expansion and altered dynamics in an Adélie penguin metapopulation

    USGS Publications Warehouse

    LaRue, Michelle A.; Ainley, David G.; Swanson, Matt; Dugger, Katie M.; Lyber, Phil O'B.; Barton, Kerry; Ballard, Grant

    2013-01-01

    There will be winners and losers as climate change alters the habitats of polar organisms. For an Adélie penguin (Pygoscelis adeliae) colony on Beaufort Island (Beaufort), part of a cluster of colonies in the southern Ross Sea, we report a recent population increase in response to increased nesting habitat as glaciers have receded. Emigration rates of birds banded as chicks on Beaufort to colonies on nearby Ross Island decreased after 2005 as available habitat on Beaufort increased, leading to altered dynamics of the metapopulation. Using aerial photography beginning in 1958 and modern satellite imagery, we measured change in area of available nesting habitat and population size of the Beaufort colony. Population size varied with available habitat, and both increased rapidly since the 1990s. In accord with glacial retreat, summer temperatures at nearby McMurdo Station increased by ~0.50°C per decade since the mid-1980s. Although the Ross Sea is likely to be the last ocean with an intact ecosystem, the recent retreat of ice fields at Beaufort that resulted in increased breeding habitat exemplifies a process that has been underway in the Ross Sea during the entire Holocene. Furthermore, our results are in line with predictions that major ice shelves and glaciers will retreat rapidly elsewhere in the Antarctic, potentially leading to increased breeding habitat for Adélie penguins. Results further indicated that satellite imagery may be used to estimate large changes in Adélie penguin populations, facilitating our understanding of metapopulation dynamics and environmental factors that influence regional populations.

  4. Sea surface height and dynamic topography of the ice-covered oceans from CryoSat-2: 2011-2014

    NASA Astrophysics Data System (ADS)

    Kwok, Ron; Morison, James

    2016-01-01

    We examine 4 years (2011-2014) of sea surface heights (SSH) from CryoSat-2 (CS-2) over the ice-covered Arctic and Southern Oceans. Results are from a procedure that identifies and determines the heights of sea surface returns. Along 25 km segments of satellite ground tracks, variability in the retrieved SSHs is between ˜2 and 3 cm (standard deviation) in the Arctic and is slightly higher (˜3 cm) in the summer and the Southern Ocean. Average sea surface tilts (along these 25 km segments) are 0.01 ± 3.8 cm/10 km in the Arctic, and slightly lower (0.01 ± 2.0 cm/10 km) in the Southern Ocean. Intra-seasonal variability of CS-2 dynamic ocean topography (DOT) in the ice-covered Arctic is nearly twice as high as that of the Southern Ocean. In the Arctic, we find a correlation of 0.92 between 3 years of DOT and dynamic heights (DH) from hydrographic stations. Further, correlation of 4 years of area-averaged CS-2 DOT near the North Pole with time-variable ocean-bottom pressure from a pressure gauge and from GRACE, yields coefficients of 0.83 and 0.77, with corresponding differences of <3 cm (RMS). These comparisons contrast the length scale of baroclinic and barotropic features and reveal the smaller amplitude barotropic signals in the Arctic Ocean. Broadly, the mean DOT from CS-2 for both poles compares well with those from the ICESat campaigns and the DOT2008A and DTU13MDT fields. Short length scale topographic variations, due to oceanographic signals and geoid residuals, are especially prominent in the Arctic Basin but less so in the Southern Ocean.

  5. Of Ice and Microbes

    NASA Astrophysics Data System (ADS)

    Deming, Jody

    2006-12-01

    Inuit hunters of the North have long recognized ice as the natural state of water from which life flows on Earth. Although unaware of the microscopic world, they chart changes in properties of ice and water that derive from a succession of microbial inhabitants. Scientific hunters of the West have largely overlooked all but the warmest of ices as dynamic scenes of microbial life, considering the frozen realm to archive life forms instead. Deeply frozen glacial ice on Earth does appear to preserve microbes effectively, but isn't the ocean beneath the geologically dynamic ice of Europa believed too salty? Aren't the subsurface ices of Mars expected to be rich in all manner of mineralogical impurities? Wherever salt and other mineral impurities are sufficiently abundant in Earth ice, the ice contains interior liquid water that can range from nano-layer films on grain surfaces (glacial ice) to a porous network of brine (Arctic winter sea ice down to 20°C). Other recent studies of saline ices have indicated a world of interacting life forms, with viruses infecting bacteria in brines at -12°C (the lowest temperature tested), the domains of Bacteria and Archaea undergoing succession in winter ices (down to -28°C), and evidence that cellular maintenance may go forward incrementally even below the eutectic of seawater (-55°C). Microbes are also known to alter the physical properties of their icy homes by producing exopolymers that further depress the freezing point, either directly or by entraining more salt into the ice. Even the most inhospitable of ices to human hunters may contain interior oases for microbes, in control to some degree of their own space. In considering the habitability of icy worlds beyond Earth, we'd do well to learn more about the evolutionary prowess of microbes in adapting to conditions beyond our warm-blooded imaginations.

  6. Ice Accretions and Full-Scale Iced Aerodynamic Performance Data for a Two-Dimensional NACA 23012 Airfoil

    NASA Technical Reports Server (NTRS)

    Addy, Harold E., Jr.; Broeren, Andy P.; Potapczuk, Mark G.; Lee, Sam; Guffond, Didier; Montreuil, Emmanuel; Moens, Frederic

    2016-01-01

    This report documents the data collected during the large wind tunnel campaigns conducted as part of the SUNSET project (StUdies oN Scaling EffecTs due to ice) also known as the Ice-Accretion Aerodynamics Simulation study: a joint effort by NASA, the Office National d'Etudes et Recherches Aérospatiales (ONERA), and the University of Illinois. These data form a benchmark database of full-scale ice accretions and corresponding ice-contaminated aerodynamic performance data for a two-dimensional (2D) NACA 23012 airfoil. The wider research effort also included an analysis of ice-contaminated aerodynamics that categorized ice accretions by aerodynamic effects and an investigation of subscale, low- Reynolds-number ice-contaminated aerodynamics for the NACA 23012 airfoil. The low-Reynolds-number investigation included an analysis of the geometric fidelity needed to reliably assess aerodynamic effects of airfoil icing using artificial ice shapes. Included herein are records of the ice accreted during campaigns in NASA Glenn Research Center's Icing Research Tunnel (IRT). Two different 2D NACA 23012 airfoil models were used during these campaigns; an 18-in. (45.7-cm) chord (subscale) model and a 72-in. (182.9-cm) chord (full-scale) model. The aircraft icing conditions used during these campaigns were selected from the Federal Aviation Administration's (FAA's) Code of Federal Regulations (CFR) Part 25 Appendix C icing envelopes. The records include the test conditions, photographs of the ice accreted, tracings of the ice, and ice depth measurements. Model coordinates and pressure tap locations are also presented. Also included herein are the data recorded during a wind tunnel campaign conducted in the F1 Subsonic Pressurized Wind Tunnel of ONERA. The F1 tunnel is a pressured, high- Reynolds-number facility that could accommodate the full-scale (72-in. (182.9-cm) chord) 2D NACA 23012 model. Molds were made of the ice accreted during selected test runs of the full-scale model

  7. Applying High Resolution Imagery to Understand the Role of Dynamics in the Diminishing Arctic Sea Ice Cover

    DTIC Science & Technology

    2014-09-30

    of sea ice, glaciers, and ice sheets. These observations are critical for predicting the response of Earth’s polar ice to climate change and sea...phone: (301) 683-3332 fax: (301) 683-3330 email: sineadf@umd.edu Award Number: N000141410599 Dr. Jennifer K. Hutchings Oregon State...the Arctic Ocean, and the processes that define it. OBJECTIVES Our goal is to assess changes in the characteristics of the Arctic sea ice pack

  8. Gender Dimorphic ACL Strain In Response to Combined Dynamic 3D Knee Joint Loading: Implications for ACL Injury Risk

    PubMed Central

    Mizuno, Kiyonori; Andrish, Jack T.; van den Bogert, Antonie J.; McLean, Scott G.

    2009-01-01

    While gender-based differences in knee joint anatomies/laxities are well documented, the potential for them to precipitate gender-dimorphic ACL loading and resultant injury risk has not been considered. To this end, we generated gender-specific models of ACL strain as a function of any six degrees of freedom (6DOF) knee joint load state via a combined cadaveric and analytical approach. Continuously varying joint forces and torques were applied to five male and five female cadaveric specimens and recorded along with synchronous knee flexion and ACL strain data. All data (~10,000 samples) were submitted to specimen-specific regression analyses, affording ACL strain predictions as a function of the combined 6 DOF knee loads. Following individual model verifications, generalized gender-specific models were generated and subjected to 6 DOF external load scenarios consistent with both a clinical examination and a dynamic sports maneuver. The ensuing model-based strain predictions were subsequently examined for gender-based discrepancies. Male and female specimen specific models predicted ACL strain within 0.51% ± 0.10% and 0.52% ± 0.07% of the measured data respectively, and explained more than 75% of the associated variance in each case. Predicted female ACL strains were also significantly larger than respective male values for both of simulated 6 DOF load scenarios. Outcomes suggest that the female ACL will rupture in response to comparatively smaller external load applications. Future work must address the underlying anatomical/laxity contributions to knee joint mechanical and resultant ACL loading, ultimately affording prevention strategies that may cater to individual joint vulnerabilities. PMID:19464897

  9. Upper extremity interaction with a helicopter side airbag: injury criteria for dynamic hyperextension of the female elbow joint.

    PubMed

    Duma, Stefan M; Hansen, Gail A; Kennedy, Eric A; Rath, Amber L; McNally, Craig; Kemper, Andrew R; Smith, Eric P; Brolinson, P Gunnar; Stitzel, Joel D; Davis, Martin B; Bass, Cameron R; Brozoski, Frederick T; McEntire, B Joseph; Alem, Nabih M; Crowley, John S

    2004-11-01

    This paper describes a three part analysis to characterize the interaction between the female upper extremity and a helicopter cockpit side airbag system and to develop dynamic hyperextension injury criteria for the female elbow joint. Part I involved a series of 10 experiments with an original Army Black Hawk helicopter side airbag. A 5(th) percentile female Hybrid III instrumented upper extremity was used to demonstrate side airbag upper extremity loading. Two out of the 10 tests resulted in high elbow bending moments of 128 Nm and 144 Nm. Part II included dynamic hyperextension tests on 24 female cadaver elbow joints. The energy source was a drop tower utilizing a three-point bending configuration to apply elbow bending moments matching the previously conducted side airbag tests. Post-test necropsy showed that 16 of the 24 elbow joint tests resulted in injuries. Injury severity ranged from minor cartilage damage to more moderate joint dislocations and severe transverse fractures of the distal humerus. Peak elbow bending moments ranged from 42.4 Nm to 146.3 Nm. Peak bending moment proved to be a significant indicator of any elbow injury (p = 0.02) as well as elbow joint dislocation (p = 0.01). Logistic regression analyses were used to develop single and multiple variate injury risk functions. Using peak moment data for the entire test population, a 50% risk of obtaining any elbow injury was found at 56 Nm while a 50% risk of sustaining an elbow joint dislocation was found at 93 Nm for the female population. These results indicate that the peak elbow bending moments achieved in Part I are associated with a greater than 90% risk for elbow injury. Subsequently, the airbag was re-designed in an effort to mitigate this as well as the other upper extremity injury risks. Part III assessed the redesigned side airbag module to ensure injury risks had been reduced prior to implementing the new system. To facilitate this, 12 redesigned side airbag deployments were conducted

  10. Antarctic ice dynamics and southern ocean surface hydrology during the last glacial maximum

    SciTech Connect

    Labeyrie, L.D.; Burckle, L.; Labracherie, M.; Pichon, J.J.; Ippolito, P.; Grojean, M.C.; Duplessy, J.C.

    1985-01-01

    Eight high sedimentation rate cores located between 61/sup 0/S and 43/sup 0/S in the Atlantic and Indian sectors of the Southern Ocean have been studied in detail for foraminifera and diatom /sup 18/O//sup 16/O ratios, and changes in radiolarian and diatom specific abundance. Comparison of these different parameters permits a detailed description of the surface water hydrology during the last glacial maximum. The authors demonstrate that from 25 kyr BP to 15 kyr BP a large number of icebergs formed around the Antarctic continent. Melting along the Polar Front decreased surface salinity by approximately 1.5 per thousand between 43/sup 0/S and 50/sup 0/S. They propose that an increase of snow accumulation at the Antarctic periphery and downdraw during maximum ice extension are primary causes for this major discharge of icebergs.

  11. Short time proton dynamics in bulk ice and in porous anode solid oxide fuel cell materials

    SciTech Connect

    Basoli, Francesco; Senesi, Roberto; Kolesnikov, Alexander I; Licoccia, Silvia

    2014-01-01

    Oxygen reduction and incorporation into solid electrolytes and the reverse reaction of oxygen evolution play a cru-cial role in Solid Oxide Fuel Cell (SOFC) applications. However a detailed un derstanding of the kinetics of the cor-responding reactions, i.e. on reaction mechanisms, rate limiting steps, reaction paths, electrocatalytic role of materials, is still missing. These include a thorough characterization of the binding potentials experienced by protons in the lattice. We report results of Inelastic Neutron Scattering (INS) measurements of the vibrational state of the protons in Ni- YSZ highly porous composites (75% to 90% ), a ceramic-metal material showing a high electrical conductivity and ther mal stability, which is known to be most effectively used as anodes for solid ox ide fuel cells. The results are compared with INS and Deep Inelastic Neutron Scattering (DINS) experiments on the proton binding states in bulk ice.

  12. Nature of the interior of Uranus based on studies of planetary ices at high dynamic pressure

    SciTech Connect

    Nellis, W.J.; Hamilton, D.C.; Holmes, N.C.; Radousky, H.B.; Ree, F.H.; Mitchell, A.C.; Nicol, M.

    1988-05-06

    Data from the Voyager II spacecraft showed that Uranus has a large magnetic field with geometry similar to an offset tilted dipole. To interpret the origin of the magnetic field, measurements were made of electrical conductivity and equation-of-state data of the planetary ices ammonia, methane, and synthetic Uranus at shock pressures and temperatures up to 75 gigapascals and 5000 K. These pressures and temperatures correspond to conditions at the depths at which the surface magnetic field is generated. Above 40 gigapascals the conductivities of synthetic Uranus, water, and ammonia plateau at about 20 (ohm-cm)/sup -1/, providing an upper limit for the electrical conductivity used in kinematic or dynamo calculations. The nature of materials at the extreme conditions in the interior is discussed. 29 references, 3 figures.

  13. Implications of 36Cl exposure ages from Skye, northwest Scotland for the timing of ice stream deglaciation and deglacial ice dynamics

    NASA Astrophysics Data System (ADS)

    Small, David; Rinterknecht, Vincent; Austin, William E. N.; Bates, Richard; Benn, Douglas I.; Scourse, James D.; Bourlès, Didier L.; Hibbert, Fiona D.

    2016-10-01

    Geochronological constraints on the deglaciation of former marine based ice streams provide information on the rates and modes by which marine based ice sheets have responded to external forcing factors such as climate change. This paper presents new 36Cl cosmic ray exp